/work/workdir/UnpackedTarball/harfbuzz/src/hb-ot-layout-gsubgpos.hh

Source
/*
 * Copyright © 2007,2008,2009,2010  Red Hat, Inc.
 * Copyright © 2010,2012  Google, Inc.
 *
 *  This is part of HarfBuzz, a text shaping library.
 *
 * Permission is hereby granted, without written agreement and without
 * license or royalty fees, to use, copy, modify, and distribute this
 * software and its documentation for any purpose, provided that the
 * above copyright notice and the following two paragraphs appear in
 * all copies of this software.
 *
 * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
 * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
 * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
 * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 *
 * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
 * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
 * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 *
 * Red Hat Author(s): Behdad Esfahbod
 * Google Author(s): Behdad Esfahbod
 */

#ifndef HB_OT_LAYOUT_GSUBGPOS_HH
#define HB_OT_LAYOUT_GSUBGPOS_HH

#include "hb.hh"
#include "hb-buffer.hh"
#include "hb-map.hh"
#include "hb-set.hh"
#include "hb-ot-map.hh"
#include "hb-ot-layout-common.hh"
#include "hb-ot-layout-gdef-table.hh"
#include "hb-depend-data.hh"


namespace OT {


struct hb_intersects_context_t :
       hb_dispatch_context_t<hb_intersects_context_t, bool>
{
  template <typename T>
  return_t dispatch (const T &obj) { return obj.intersects (this->glyphs); }
  static return_t default_return_value () { return false; }
  bool stop_sublookup_iteration (return_t r) const { return r; }

  const hb_set_t *glyphs;

  hb_intersects_context_t (const hb_set_t *glyphs_) :
                            glyphs (glyphs_) {}
};

struct hb_have_non_1to1_context_t :
       hb_dispatch_context_t<hb_have_non_1to1_context_t, bool>
{
  template <typename T>
  return_t dispatch (const T &obj) { return obj.may_have_non_1to1 (); }
  static return_t default_return_value () { return false; }
  bool stop_sublookup_iteration (return_t r) const { return r; }
};

struct hb_closure_context_t :
       hb_dispatch_context_t<hb_closure_context_t>
{
  typedef return_t (*recurse_func_t) (hb_closure_context_t *c, unsigned lookup_index, hb_set_t *covered_seq_indicies, unsigned seq_index, unsigned end_index);
  template <typename T>
  return_t dispatch (const T &obj) { obj.closure (this); return hb_empty_t (); }
  static return_t default_return_value () { return hb_empty_t (); }
  void recurse (unsigned lookup_index, hb_set_t *covered_seq_indicies, unsigned seq_index, unsigned end_index)
  {
    if (unlikely (nesting_level_left == 0 || !recurse_func))
      return;

    nesting_level_left--;
    recurse_func (this, lookup_index, covered_seq_indicies, seq_index, end_index);
    nesting_level_left++;
  }

  void reset_lookup_visit_count ()
  { lookup_count = 0; }

  bool lookup_limit_exceeded ()
  { return lookup_count > HB_MAX_LOOKUP_VISIT_COUNT; }

  bool should_visit_lookup (unsigned int lookup_index)
  {
    if (lookup_count++ > HB_MAX_LOOKUP_VISIT_COUNT)
      return false;

    if (is_lookup_done (lookup_index))
      return false;

    return true;
  }

  bool is_lookup_done (unsigned int lookup_index)
  {
    if (unlikely (done_lookups_glyph_count->in_error () ||
      done_lookups_glyph_set->in_error ()))
      return true;

    /* Have we visited this lookup with the current set of glyphs? */
    unsigned pop = glyphs->get_population ();
    if (unlikely (pop == HB_MAP_VALUE_INVALID)) // Avoid sentinel interference.
      pop--;
    if (done_lookups_glyph_count->get (lookup_index) != pop)
    {
      done_lookups_glyph_count->set (lookup_index, pop);

      if (!done_lookups_glyph_set->has (lookup_index))
      {
  if (unlikely (!done_lookups_glyph_set->set (lookup_index, hb::unique_ptr<hb_set_t> {hb_set_create ()})))
    return true;
      }

      done_lookups_glyph_set->get (lookup_index)->clear ();
    }

    hb_set_t *covered_glyph_set = done_lookups_glyph_set->get (lookup_index);
    if (unlikely (covered_glyph_set->in_error ()))
      return true;
    if (parent_active_glyphs ().is_subset (*covered_glyph_set))
      return true;

    covered_glyph_set->union_ (parent_active_glyphs ());
    return false;
  }

  const hb_set_t& previous_parent_active_glyphs () {
    if (active_glyphs_stack.length <= 1)
      return *glyphs;

    return active_glyphs_stack[active_glyphs_stack.length - 2];
  }

  const hb_set_t& parent_active_glyphs ()
  {
    if (!active_glyphs_stack)
      return *glyphs;

    return active_glyphs_stack.tail ();
  }

  hb_set_t* push_cur_active_glyphs ()
  {
    hb_set_t *s = active_glyphs_stack.push ();
    if (unlikely (active_glyphs_stack.in_error ()))
      return nullptr;
    return s;
  }

  bool pop_cur_done_glyphs ()
  {
    if (!active_glyphs_stack)
      return false;

    active_glyphs_stack.pop ();
    return true;
  }

  hb_face_t *face;
  hb_set_t *glyphs;
  hb_set_t output[1];
  hb_vector_t<hb_set_t> active_glyphs_stack;
  recurse_func_t recurse_func = nullptr;
  unsigned int nesting_level_left;

  hb_closure_context_t (hb_face_t *face_,
      hb_set_t *glyphs_,
      hb_map_t *done_lookups_glyph_count_,
      hb_hashmap_t<unsigned, hb::unique_ptr<hb_set_t>> *done_lookups_glyph_set_,
      unsigned int nesting_level_left_ = HB_MAX_NESTING_LEVEL) :
        face (face_),
        glyphs (glyphs_),
        nesting_level_left (nesting_level_left_),
        done_lookups_glyph_count (done_lookups_glyph_count_),
        done_lookups_glyph_set (done_lookups_glyph_set_)
  {}

  ~hb_closure_context_t () { flush (); }

  void set_recurse_func (recurse_func_t func) { recurse_func = func; }

  void flush ()
  {
    output->del_range (face->get_num_glyphs (), HB_SET_VALUE_INVALID);  /* Remove invalid glyphs. */
    glyphs->union_ (*output);
    output->clear ();
    active_glyphs_stack.pop ();
    active_glyphs_stack.reset ();
  }

  private:
  hb_map_t *done_lookups_glyph_count;
  hb_hashmap_t<unsigned, hb::unique_ptr<hb_set_t>> *done_lookups_glyph_set;
  unsigned int lookup_count = 0;
};



struct hb_closure_lookups_context_t :
       hb_dispatch_context_t<hb_closure_lookups_context_t>
{
  typedef return_t (*recurse_func_t) (hb_closure_lookups_context_t *c, unsigned lookup_index);
  template <typename T>
  return_t dispatch (const T &obj) { obj.closure_lookups (this); return hb_empty_t (); }
  static return_t default_return_value () { return hb_empty_t (); }
  void recurse (unsigned lookup_index)
  {
    if (unlikely (nesting_level_left == 0 || !recurse_func))
      return;

    /* Return if new lookup was recursed to before. */
    if (lookup_limit_exceeded ()
        || visited_lookups->in_error ()
        || visited_lookups->has (lookup_index))
      // Don't increment lookup count here, that will be done in the call to closure_lookups()
      // made by recurse_func.
      return;

    nesting_level_left--;
    recurse_func (this, lookup_index);
    nesting_level_left++;
  }

  void set_lookup_visited (unsigned lookup_index)
  { visited_lookups->add (lookup_index); }

  void set_lookup_inactive (unsigned lookup_index)
  { inactive_lookups->add (lookup_index); }

  bool lookup_limit_exceeded ()
  {
    bool ret = lookup_count > HB_MAX_LOOKUP_VISIT_COUNT;
    if (ret)
      DEBUG_MSG (SUBSET, nullptr, "lookup visit count limit exceeded in lookup closure!");
    return ret; }

  bool is_lookup_visited (unsigned lookup_index)
  {
    if (unlikely (lookup_count++ > HB_MAX_LOOKUP_VISIT_COUNT))
    {
      DEBUG_MSG (SUBSET, nullptr, "total visited lookup count %u exceeds max limit, lookup %u is dropped.",
                 lookup_count, lookup_index);
      return true;
    }

    if (unlikely (visited_lookups->in_error ()))
      return true;

    return visited_lookups->has (lookup_index);
  }

  hb_face_t *face;
  const hb_set_t *glyphs;
  recurse_func_t recurse_func;
  unsigned int nesting_level_left;

  hb_closure_lookups_context_t (hb_face_t *face_,
        const hb_set_t *glyphs_,
        hb_set_t *visited_lookups_,
        hb_set_t *inactive_lookups_,
        unsigned nesting_level_left_ = HB_MAX_NESTING_LEVEL) :
        face (face_),
        glyphs (glyphs_),
        recurse_func (nullptr),
        nesting_level_left (nesting_level_left_),
        visited_lookups (visited_lookups_),
        inactive_lookups (inactive_lookups_),
        lookup_count (0) {}

  void set_recurse_func (recurse_func_t func) { recurse_func = func; }

  private:
  hb_set_t *visited_lookups;
  hb_set_t *inactive_lookups;
  unsigned int lookup_count;
};

struct hb_would_apply_context_t :
       hb_dispatch_context_t<hb_would_apply_context_t, bool>
{
  template <typename T>
  return_t dispatch (const T &obj) { return obj.would_apply (this); }
  static return_t default_return_value () { return false; }
  bool stop_sublookup_iteration (return_t r) const { return r; }

  hb_face_t *face;
  const hb_codepoint_t *glyphs;
  unsigned int len;
  bool zero_context;

  hb_would_apply_context_t (hb_face_t *face_,
          const hb_codepoint_t *glyphs_,
          unsigned int len_,
          bool zero_context_) :
            face (face_),
            glyphs (glyphs_),
            len (len_),
            zero_context (zero_context_) {}
};

struct hb_collect_glyphs_context_t :
       hb_dispatch_context_t<hb_collect_glyphs_context_t>
{
  typedef return_t (*recurse_func_t) (hb_collect_glyphs_context_t *c, unsigned int lookup_index);
  template <typename T>
  return_t dispatch (const T &obj) { obj.collect_glyphs (this); return hb_empty_t (); }
  static return_t default_return_value () { return hb_empty_t (); }
  void recurse (unsigned int lookup_index)
  {
    if (unlikely (nesting_level_left == 0 || !recurse_func))
      return;

    /* Note that GPOS sets recurse_func to nullptr already, so it doesn't get
     * past the previous check.  For GSUB, we only want to collect the output
     * glyphs in the recursion.  If output is not requested, we can go home now.
     *
     * Note further, that the above is not exactly correct.  A recursed lookup
     * is allowed to match input that is not matched in the context, but that's
     * not how most fonts are built.  It's possible to relax that and recurse
     * with all sets here if it proves to be an issue.
     */

    if (output == hb_set_get_empty ())
      return;

    /* Return if new lookup was recursed to before. */
    if (recursed_lookups->has (lookup_index))
      return;

    hb_set_t *old_before = before;
    hb_set_t *old_input  = input;
    hb_set_t *old_after  = after;
    before = input = after = hb_set_get_empty ();

    nesting_level_left--;
    recurse_func (this, lookup_index);
    nesting_level_left++;

    before = old_before;
    input  = old_input;
    after  = old_after;

    recursed_lookups->add (lookup_index);
  }

  hb_face_t *face;
  hb_set_t *before;
  hb_set_t *input;
  hb_set_t *after;
  hb_set_t *output;
  recurse_func_t recurse_func;
  hb_set_t *recursed_lookups;
  unsigned int nesting_level_left;

  hb_collect_glyphs_context_t (hb_face_t *face_,
             hb_set_t  *glyphs_before, /* OUT.  May be NULL */
             hb_set_t  *glyphs_input,  /* OUT.  May be NULL */
             hb_set_t  *glyphs_after,  /* OUT.  May be NULL */
             hb_set_t  *glyphs_output, /* OUT.  May be NULL */
             unsigned int nesting_level_left_ = HB_MAX_NESTING_LEVEL) :
            face (face_),
            before (glyphs_before ? glyphs_before : hb_set_get_empty ()),
            input  (glyphs_input  ? glyphs_input  : hb_set_get_empty ()),
            after  (glyphs_after  ? glyphs_after  : hb_set_get_empty ()),
            output (glyphs_output ? glyphs_output : hb_set_get_empty ()),
            recurse_func (nullptr),
            recursed_lookups (hb_set_create ()),
            nesting_level_left (nesting_level_left_) {}
  ~hb_collect_glyphs_context_t () { hb_set_destroy (recursed_lookups); }

  void set_recurse_func (recurse_func_t func) { recurse_func = func; }
};

struct hb_depend_context_t :
       hb_dispatch_context_t<hb_depend_context_t>
{
  enum glyph_set_type_t
  {
    GLYPH_SET_CLASS,
    GLYPH_SET_COVERAGE,
    GLYPH_SET_SINGLE
  };

  static constexpr hb_codepoint_t SINGLE_GLYPH_ACTIVE_FLAG = 0x80000000u;

  struct glyph_set_cache_key_t
  {
    glyph_set_cache_key_t () = default;
    glyph_set_cache_key_t (const void *data_, unsigned value_, glyph_set_type_t type_)
      : data (data_), value (value_), type (type_) {}

    bool operator == (const glyph_set_cache_key_t &o) const
    { return data == o.data && value == o.value && type == o.type; }

    uint32_t hash () const
    {
      uint32_t current = hb_hash ((uintptr_t) data);
      current = current * 31 + hb_hash (value);
      return current * 31 + hb_hash ((unsigned) type);
    }

    const void *data = nullptr;
    unsigned value = 0;
    glyph_set_type_t type = GLYPH_SET_CLASS;
  };

  struct context_set_cache_key_t
  {
    context_set_cache_key_t () = default;
    context_set_cache_key_t (const void *rule_,
           const void *record_,
           const void *data_,
           hb_codepoint_t active_glyphs_,
           unsigned value_,
           unsigned format_)
      : rule (rule_), record (record_), data (data_), active_glyphs (active_glyphs_),
  value (value_), format (format_) {}

    bool operator == (const context_set_cache_key_t &o) const
    {
      return rule == o.rule &&
       record == o.record &&
       data == o.data &&
       active_glyphs == o.active_glyphs &&
       value == o.value &&
       format == o.format;
    }

    uint32_t hash () const
    {
      uint32_t current = hb_hash ((uintptr_t) rule);
      current = current * 31 + hb_hash ((uintptr_t) record);
      current = current * 31 + hb_hash ((uintptr_t) data);
      current = current * 31 + hb_hash (active_glyphs);
      current = current * 31 + hb_hash (value);
      return current * 31 + hb_hash (format);
    }

    const void *rule = nullptr;
    const void *record = nullptr;
    const void *data = nullptr;
    hb_codepoint_t active_glyphs = HB_CODEPOINT_INVALID;
    unsigned value = 0;
    unsigned format = 0;
  };

  struct recurse_key_t
  {
    recurse_key_t () = default;
    recurse_key_t (unsigned lookup_index_,
                   hb_codepoint_t active_glyphs_,
                   hb_codepoint_t recurse_path_,
                   hb_codepoint_t context_set_)
      : lookup_index (lookup_index_),
        active_glyphs (active_glyphs_),
        recurse_path (recurse_path_),
        context_set (context_set_) {}

    bool operator == (const recurse_key_t &o) const
    {
      return lookup_index == o.lookup_index &&
             active_glyphs == o.active_glyphs &&
             recurse_path == o.recurse_path &&
             context_set == o.context_set;
    }

    uint32_t hash () const
    {
      uint32_t current = 0x84222325;
      current = (current ^ hb_hash (lookup_index)) * 16777619;
      current = (current ^ hb_hash (active_glyphs)) * 16777619;
      current = (current ^ hb_hash (recurse_path)) * 16777619;
      current = (current ^ hb_hash (context_set)) * 16777619;
      return current;
    }

    unsigned lookup_index = 0;
    hb_codepoint_t active_glyphs = 0;
    hb_codepoint_t recurse_path = 0;
    hb_codepoint_t context_set = HB_CODEPOINT_INVALID;
  };

  typedef return_t (*recurse_func_t) (hb_depend_context_t *c, unsigned lookup_index, hb_bit_page_t *covered_seq_indices, unsigned seq_index, unsigned end_index);
  /* return_t is hb_empty_t — dispatch is purely for side-effects, like hb_closure_context_t. */
  template <typename T>
  return_t dispatch (const T &obj) { obj.depend (this); return hb_empty_t (); }
  static return_t default_return_value () { return hb_empty_t (); }

  void recurse (unsigned lookup_idx, hb_bit_page_t *covered_seq_indices, unsigned seq_index, unsigned end_index)
  {
    /* Cycle detection using call-stack semantics: block re-entry of a
     * lookup that is currently on the execution stack, but allow it again
     * once it has returned.
     *
     * A flat "visited" set would be wrong: the same lookup legitimately
     * appears more than once when a rule iterates over multiple sequence
     * positions — each such call is independent and must be processed.
     *
     * Cutting an in-progress cycle is safe because the active glyph set
     * can only stay the same or shrink as we recurse.  If we re-encounter
     * lookup L while it is still on the stack, L is already executing
     * with a context at least as broad, so any edges a re-entry would add
     * are a subset of what L is already in the process of registering.
     *
     * lookups_seen is pre-seeded with the top-level lookup index in
     * GSUB_accelerator_t::depend before the direct depend() call, so
     * that indirect cycles of the form A→B→A are also caught here. */
    if (lookups_seen.has (lookup_idx)) return;
    lookups_seen.add (lookup_idx);

    /* Intern the ordered recursion path instead of copying and interning the
     * lookups_seen set.  Path identity is more specific than set identity but
     * never merges states with different cycle-detection behavior. */
    hb_codepoint_t parent_path = recurse_path;
    uint64_t path_key = (uint64_t) parent_path << 32 | lookup_idx;
    hb_codepoint_t *path = nullptr;
    hb_codepoint_t path_index;
    if (!recurse_path_to_index.has (path_key, &path))
    {
      path_index = recurse_path_to_index.get_population () + 1;
      if (unlikely (!recurse_path_to_index.set (path_key, path_index)))
      {
  depend_data->fail ();
  lookups_seen.del (lookup_idx);
  return;
      }
    }
    else
      path_index = *path;
    recurse_path = path_index;
    recurse_func (this, lookup_idx, covered_seq_indices, seq_index, end_index);
    recurse_path = parent_path;
    lookups_seen.del (lookup_idx);
  }

  struct active_glyphs_frame_t
  {
    hb_set_t glyphs;
    hb_codepoint_t active_idx = HB_CODEPOINT_INVALID;
    bool use_root = false;
  };

  const hb_set_t& parent_active_glyphs ()
  {
    if (!active_glyphs_stack_depth)
      return *glyphs;

    const active_glyphs_frame_t &frame = active_glyphs_stack[active_glyphs_stack_depth - 1];
    return frame.use_root ? *glyphs : frame.glyphs;
  }

  hb_set_t* push_cur_active_glyphs (hb_codepoint_t active_idx = HB_CODEPOINT_INVALID)
  {
    if (active_glyphs_stack_depth == active_glyphs_stack.length &&
  unlikely (!active_glyphs_stack.push_or_fail ()))
      return nullptr;

    active_glyphs_frame_t &frame = active_glyphs_stack[active_glyphs_stack_depth++];
    frame.glyphs.clear ();
    frame.active_idx = active_idx;
    frame.use_root = false;
    return &frame.glyphs;
  }

  bool push_root_active_glyphs ()
  {
    if (active_glyphs_stack_depth == active_glyphs_stack.length &&
  unlikely (!active_glyphs_stack.push_or_fail ()))
      return false;

    active_glyphs_stack[active_glyphs_stack_depth++].use_root = true;
    return true;
  }

  bool pop_cur_done_glyphs ()
  {
    if (!active_glyphs_stack_depth)
      return false;

    active_glyphs_stack_depth--;
    return true;
  }

  bool get_parent_active_glyphs_index (hb_codepoint_t *active_idx)
  {
    if (!active_glyphs_stack_depth ||
  active_glyphs_stack[active_glyphs_stack_depth - 1].use_root)
    {
      *active_idx = HB_CODEPOINT_INVALID;
      return true;
    }

    active_glyphs_frame_t &frame = active_glyphs_stack[active_glyphs_stack_depth - 1];
    *active_idx = frame.active_idx;
    if (*active_idx != HB_CODEPOINT_INVALID)
      return true;

    hb_codepoint_t glyph;
    if (frame.glyphs.get_singleton (&glyph) &&
  likely (glyph < SINGLE_GLYPH_ACTIVE_FLAG))
      *active_idx = glyph | SINGLE_GLYPH_ACTIVE_FLAG;
    else if (!find_or_create_recurse_set (frame.glyphs, active_idx))
      return false;

    frame.active_idx = *active_idx;
    return true;
  }

  bool get_context_set_cache_key (const void *rule,
          const void *record,
          const void *data,
          unsigned value,
          unsigned format,
          context_set_cache_key_t *key)
  {
    hb_codepoint_t active_idx;
    if (!get_parent_active_glyphs_index (&active_idx))
      return false;
    *key = context_set_cache_key_t (rule, record, data, active_idx, value, format);
    return true;
  }

  bool get_recurse_key (unsigned lookup_idx, recurse_key_t *key)
  {
    /* The active glyphs and in-progress lookup set are part of the state.
     * Omitting the latter would make memoization incorrect for cyclic lookup
     * graphs whose available recursive paths depend on their ancestry.
     * Edge flags are not part of the state: they affect neither traversal nor
     * edge identity, so revisiting with different flags can only find edges
     * that the deduplication table already contains. */
    hb_codepoint_t active_idx;
    if (!get_parent_active_glyphs_index (&active_idx))
      return false;

    *key = recurse_key_t (lookup_idx,
                          active_idx,
                          recurse_path,
                          depend_data->current_context_set_index);
    return !completed_recursions.has (*key);
  }

  void finish_recurse (const recurse_key_t &key)
  { depend_data->check_success (completed_recursions.set (key, true)); }

  void reset_recurse_cache ()
  {
    completed_recursions.clear ();
    recurse_path_to_index.clear ();
    recurse_path = 0;
  }

  bool find_or_create_recurse_set (const hb_set_t &set, hb_codepoint_t *index)
  {
    hb_codepoint_t *existing = nullptr;
    if (recurse_set_to_index.has (&set, &existing))
    {
      *index = *existing;
      return true;
    }

    hb_set_t *copy = hb_object_create<hb_set_t> ();
    if (unlikely (!copy))
      return depend_data->fail ();
    copy->set (set);
    if (unlikely (copy->in_error ()))
    {
      hb_set_destroy (copy);
      return depend_data->fail ();
    }

    *index = recurse_sets.length;
    if (unlikely (*index & SINGLE_GLYPH_ACTIVE_FLAG))
    {
      hb_set_destroy (copy);
      return depend_data->fail ();
    }
    if (unlikely (!recurse_sets.push_or_fail (hb::unique_ptr<hb_set_t> {copy})))
      return depend_data->fail ();
    if (unlikely (!recurse_set_to_index.set (recurse_sets[*index].get (), *index)))
      return depend_data->fail ();
    return true;
  }

  const hb_set_t *find_or_create_glyph_set (const void *data,
                                             unsigned value,
                                             glyph_set_type_t type);
  hb_codepoint_t find_or_create_cached_context_set (const hb_set_t *set);

  struct depend_scratch_t
  {
    void clear ()
    {
      preliminary_context.clear ();
      position_scratch.clear ();
      pos_glyphs.clear ();
      position_context.clear ();
      disjunctive_indices.clear ();
      filtered_disjunctive_indices.clear ();
      backtrack_sets.clear ();
      lookahead_sets.clear ();
      input_position_glyphs.clear ();
      cached_context_sets.clear ();
      compact_workspace.clear ();
    }

    hb_set_t preliminary_context;
    hb_set_t position_scratch;
    hb_set_t pos_glyphs;
    hb_set_t position_context;
    hb_set_t disjunctive_indices;
    hb_set_t filtered_disjunctive_indices;
    hb_vector_t<const hb_set_t *> backtrack_sets;
    hb_vector_t<const hb_set_t *> lookahead_sets;
    hb_vector_t<const hb_set_t *> input_position_glyphs;
    hb_vector_t<hb_codepoint_t> cached_context_sets;
    hb_vector_t<unsigned> compact_workspace;
    depend_scratch_t *next = nullptr;
  };

  depend_scratch_t *acquire_depend_scratch ()
  {
    depend_scratch_t *scratch = depend_scratch_pool;
    if (scratch)
      depend_scratch_pool = scratch->next;
    else
    {
      scratch = (depend_scratch_t *) hb_malloc (sizeof (depend_scratch_t));
      if (unlikely (!scratch))
      {
        depend_data->fail ();
        return nullptr;
      }
      new (scratch) depend_scratch_t ();
    }

    scratch->next = nullptr;
    scratch->clear ();
    return scratch;
  }

  void release_depend_scratch (depend_scratch_t *scratch)
  {
    scratch->next = depend_scratch_pool;
    depend_scratch_pool = scratch;
  }

  hb_depend_data_builder_t *depend_data;
  hb_face_t *face;
  hb_set_t *glyphs;
  hb_vector_t<active_glyphs_frame_t> active_glyphs_stack;
  unsigned active_glyphs_stack_depth = 0;
  recurse_func_t recurse_func;
  hb_codepoint_t lookup_index = HB_CODEPOINT_INVALID;
  hb_bit_set_t lookups_seen;
  hb_vector_t<hb::unique_ptr<hb_set_t>> recurse_sets;
  hb_hashmap_t<const hb_set_t *, hb_codepoint_t> recurse_set_to_index;
  hb_hashmap_t<uint64_t, hb_codepoint_t> recurse_path_to_index;
  hb_codepoint_t recurse_path = 0;
  hb_hashmap_t<recurse_key_t, bool> completed_recursions;
  hb_vector_t<hb::unique_ptr<hb_set_t>> glyph_sets;
  hb_hashmap_t<glyph_set_cache_key_t, hb_codepoint_t> glyph_set_to_index;
  hb_hashmap_t<uintptr_t, hb_codepoint_t> cached_context_set_indices;
  hb_hashmap_t<context_set_cache_key_t, hb_codepoint_t> context_set_cache;
  depend_scratch_t *depend_scratch_pool = nullptr;

  hb_depend_context_t (hb_depend_data_builder_t *depend_data_,
                       hb_face_t *face_,
                       hb_set_t *glyphs_)
                      : depend_data (depend_data_),
                        face(face_),
                        glyphs (glyphs_),
                        recurse_func (nullptr) {}
  ~hb_depend_context_t ()
  {
    while (depend_scratch_pool)
    {
      depend_scratch_t *scratch = depend_scratch_pool;
      depend_scratch_pool = scratch->next;
      scratch->~depend_scratch_t ();
      hb_free (scratch);
    }
  }
  void set_recurse_func (recurse_func_t func) { recurse_func = func; }
};

template <typename set_t>
struct hb_collect_coverage_context_t :
       hb_dispatch_context_t<hb_collect_coverage_context_t<set_t>, const Coverage &>
{
  typedef const Coverage &return_t; // Stoopid that we have to dupe this here.
  template <typename T>
  return_t dispatch (const T &obj) { return obj.get_coverage (); }
  static return_t default_return_value () { return Null (Coverage); }
  bool stop_sublookup_iteration (return_t r) const
  {
    r.collect_coverage (set);
    return false;
  }

  hb_collect_coverage_context_t (set_t *set_) :
           set (set_) {}

  set_t *set;
};

struct matcher_t
{
  typedef bool (*match_func_t) (hb_glyph_info_t &info, unsigned value, const void *data);

  template <typename context_t>
  void init (const context_t *c, bool context_match = false)
  {
    set_match_func (nullptr, nullptr);
    lookup_props = c->lookup_props;
    /* Ignore ZWNJ if we are matching GPOS, or matching GSUB context and asked to. */
    ignore_zwnj = c->table_index == 1 || (context_match && c->auto_zwnj);
    /* Ignore ZWJ if we are matching context, or asked to. */
    ignore_zwj = context_match || c->auto_zwj;
    /* Ignore hidden glyphs (like CGJ) during GPOS. */
    ignore_hidden = c->table_index == 1;
    mask = context_match ? -1 : c->lookup_mask;
    /* Per syllable matching is only for GSUB. */
    per_syllable = c->table_index == 0 && c->per_syllable;
    syllable = 0;
  }

  void set_match_func (match_func_t match_func_,
           const void *match_data_)
  { match_func = match_func_; match_data = match_data_; }

  enum may_match_t {
    MATCH_NO,
    MATCH_YES,
    MATCH_MAYBE
  };

#ifndef HB_OPTIMIZE_SIZE
  HB_ALWAYS_INLINE
#endif
  may_match_t may_match (hb_glyph_info_t &info,
       hb_codepoint_t glyph_data) const
  {
    if (!(info.mask & mask) ||
  (per_syllable && syllable && syllable != info.syllable ()))
      return MATCH_NO;

    if (match_func)
      return match_func (info, glyph_data, match_data) ? MATCH_YES : MATCH_NO;

    return MATCH_MAYBE;
  }

  enum may_skip_t {
    SKIP_NO,
    SKIP_YES,
    SKIP_MAYBE
  };

  template <typename context_t>
#ifndef HB_OPTIMIZE_SIZE
  HB_ALWAYS_INLINE
#endif
  may_skip_t may_skip (const context_t *c,
           const hb_glyph_info_t &info) const
  {
    if (!c->check_glyph_property (&info, lookup_props))
      return SKIP_YES;

    if (unlikely (_hb_glyph_info_is_default_ignorable (&info) &&
      (ignore_zwnj || !_hb_glyph_info_is_zwnj (&info)) &&
      (ignore_zwj || !_hb_glyph_info_is_zwj (&info)) &&
      (ignore_hidden || !_hb_glyph_info_is_hidden (&info))))
      return SKIP_MAYBE;

    return SKIP_NO;
  }

  public:
  unsigned int lookup_props = 0;
  hb_mask_t mask = -1;
  bool ignore_zwnj = false;
  bool ignore_zwj = false;
  bool ignore_hidden = false;
  bool per_syllable = false;
  uint8_t syllable = 0;
  match_func_t match_func = nullptr;
  const void *match_data = nullptr;
};

template <typename context_t>
struct skipping_iterator_t
{
  void init (context_t *c_, bool context_match = false)
  {
    c = c_;
    end = c->buffer->len;
    match_glyph_data16 = nullptr;
#ifndef HB_NO_BEYOND_64K
    match_glyph_data24 = nullptr;
#endif
    matcher.init (c, context_match);
  }
  void set_lookup_props (unsigned int lookup_props)
  {
    matcher.lookup_props = lookup_props;
  }
  void set_match_func (matcher_t::match_func_t match_func_,
           const void *match_data_)
  {
    matcher.set_match_func (match_func_, match_data_);
  }
  void set_glyph_data (const HBUINT16 glyph_data[])
  {
    match_glyph_data16 = glyph_data;
#ifndef HB_NO_BEYOND_64K
    match_glyph_data24 = nullptr;
#endif
  }
#ifndef HB_NO_BEYOND_64K
  void set_glyph_data (const HBUINT24 glyph_data[])
  {
    match_glyph_data16 = nullptr;
    match_glyph_data24 = glyph_data;
  }
#endif

#ifndef HB_OPTIMIZE_SIZE
  HB_ALWAYS_INLINE
#endif
  void reset (unsigned int start_index_)
  {
    // For GSUB forward iterator
    idx = start_index_;
    end = c->buffer->len;
    matcher.syllable = c->buffer->cur().syllable();
  }
  void reset_back (unsigned int start_index_, bool from_out_buffer = false)
  {
    // For GSUB backward iterator
    idx = start_index_;
    matcher.syllable = c->buffer->cur().syllable();
  }

#ifndef HB_OPTIMIZE_SIZE
  HB_ALWAYS_INLINE
#endif
  void reset_fast (unsigned int start_index_)
  {
    // Doesn't set end or syllable. Used by GPOS which doesn't care / change.
    idx = start_index_;
  }

#ifndef HB_OPTIMIZE_SIZE
  HB_ALWAYS_INLINE
#endif
  matcher_t::may_skip_t may_skip (const hb_glyph_info_t &info) const
  { return matcher.may_skip (c, info); }

  enum match_t {
    MATCH,
    NOT_MATCH,
    SKIP
  };

#ifndef HB_OPTIMIZE_SIZE
  HB_ALWAYS_INLINE
#endif
  match_t match (hb_glyph_info_t &info)
  {
    matcher_t::may_skip_t skip = matcher.may_skip (c, info);
    if (unlikely (skip == matcher_t::SKIP_YES))
      return SKIP;

    matcher_t::may_match_t match = matcher.may_match (info, get_glyph_data ());
    if (match == matcher_t::MATCH_YES ||
  (match == matcher_t::MATCH_MAYBE &&
   skip == matcher_t::SKIP_NO))
      return MATCH;

    if (skip == matcher_t::SKIP_NO)
      return NOT_MATCH;

    return SKIP;
  }

  bool next (unsigned *unsafe_to = nullptr)
  {
    auto *info = c->buffer->info;
    const signed stop = (signed) end - 1;
    while ((signed) idx < stop)
    {
      idx++;
      switch (match (info[idx]))
      {
  case MATCH:
  {
    advance_glyph_data ();
    return true;
  }
  case NOT_MATCH:
  {
    if (unsafe_to)
      *unsafe_to = idx + 1;
    return false;
  }
  case SKIP:
    continue;
      }
    }
    if (unsafe_to)
      *unsafe_to = end;
    return false;
  }
  bool prev (unsigned *unsafe_from = nullptr)
  {
    auto *out_info = c->buffer->out_info;
    const unsigned stop = 0;
    while (idx > stop)
    {
      idx--;
      switch (match (out_info[idx]))
      {
  case MATCH:
  {
    advance_glyph_data ();
    return true;
  }
  case NOT_MATCH:
  {
    if (unsafe_from)
      *unsafe_from = hb_max (1u, idx) - 1u;
    return false;
  }
  case SKIP:
    continue;
      }
    }
    if (unsafe_from)
      *unsafe_from = 0;
    return false;
  }

  HB_ALWAYS_INLINE
  hb_codepoint_t
  get_glyph_data ()
  {
    if (match_glyph_data16) return *match_glyph_data16;
#ifndef HB_NO_BEYOND_64K
    else
    if (match_glyph_data24) return *match_glyph_data24;
#endif
    return 0;
  }
  HB_ALWAYS_INLINE
  void
  advance_glyph_data ()
  {
    if (match_glyph_data16) match_glyph_data16++;
#ifndef HB_NO_BEYOND_64K
    else
    if (match_glyph_data24) match_glyph_data24++;
#endif
  }

  unsigned int idx;
  protected:
  context_t *c;
  matcher_t matcher;
  const HBUINT16 *match_glyph_data16;
#ifndef HB_NO_BEYOND_64K
  const HBUINT24 *match_glyph_data24;
#endif

  unsigned int end;
};

struct hb_ot_apply_context_t :
       hb_dispatch_context_t<hb_ot_apply_context_t, bool, HB_DEBUG_APPLY>
{
  const char *get_name () { return "APPLY"; }
  typedef return_t (*recurse_func_t) (hb_ot_apply_context_t *c, unsigned int lookup_index);

  template <typename T>
  static inline auto apply_ (const T &obj, hb_ot_apply_context_t *c, hb_priority<1>) HB_RETURN (return_t, obj.apply (c, nullptr) )
  template <typename T>
  static inline auto apply_ (const T &obj, hb_ot_apply_context_t *c, hb_priority<0>) HB_RETURN (return_t, obj.apply (c) )
  template <typename T>
  return_t dispatch (const T &obj) { return apply_(obj, this, hb_prioritize); }

  static return_t default_return_value () { return false; }
  bool stop_sublookup_iteration (return_t r) const { return r; }
  return_t recurse (unsigned int sub_lookup_index)
  {
    assert (recurse_func);
    if (unlikely (nesting_level_left == 0))
    {
      buffer->successful = false;
      return default_return_value ();
    }

    buffer->max_ops--;
    if (unlikely (buffer->max_ops < 0))
    {
      buffer->successful = false;
      return default_return_value ();
    }

    nesting_level_left--;
    bool ret = recurse_func (this, sub_lookup_index);
    nesting_level_left++;
    return ret;
  }

  skipping_iterator_t<hb_ot_apply_context_t> iter_input, iter_context;

  unsigned int table_index; /* GSUB/GPOS */
  hb_font_t *font;
  hb_face_t *face;
  hb_buffer_t *buffer;
  hb_sanitize_context_t sanitizer;
  recurse_func_t recurse_func = nullptr;
  const GDEF &gdef;
  const GDEF::accelerator_t &gdef_accel;
  const ItemVariationStore &var_store;
  hb_scalar_cache_t *var_store_cache;

  hb_direction_t direction;
  hb_mask_t lookup_mask = 1;
  unsigned int lookup_index = (unsigned) -1;
  unsigned int lookup_props = 0;
  unsigned int nesting_level_left = HB_MAX_NESTING_LEVEL;

  bool has_glyph_classes;
  bool auto_zwnj = true;
  bool auto_zwj = true;
  bool per_syllable = false;
  bool random = false;
  unsigned new_syllables = (unsigned) -1;

  signed last_base = -1; // GPOS uses
  unsigned last_base_until = 0; // GPOS uses

  hb_vector_t<uint32_t> match_positions;
  uint32_t stack_match_positions[8];
#ifndef HB_NO_BUFFER_MESSAGE
  hb_buffer_t::changed_func_t orig_changed_func = nullptr;
  void *orig_changed_data = nullptr;
#endif

  hb_ot_apply_context_t (unsigned int table_index_,
       hb_font_t *font_,
       hb_buffer_t *buffer_,
       hb_blob_t *table_blob_,
       hb_scalar_cache_t *var_store_cache_ = nullptr) :
      table_index (table_index_),
      font (font_), face (font->face), buffer (buffer_),
      sanitizer (table_blob_),
      gdef (
#ifndef HB_NO_OT_LAYOUT
            *face->table.GDEF->table
#else
            Null (GDEF)
#endif
           ),
      gdef_accel (
#ifndef HB_NO_OT_LAYOUT
            *face->table.GDEF
#else
            Null (GDEF::accelerator_t)
#endif
           ),
      var_store (gdef.get_var_store ()),
      var_store_cache (var_store_cache_),
      direction (buffer_->props.direction),
      has_glyph_classes (gdef.has_glyph_classes ())
  {
    init_iters ();
    match_positions.set_storage (stack_match_positions);

#ifndef HB_NO_BUFFER_MESSAGE
    if (buffer->messaging ())
    {
      assert (buffer->changed_func == nullptr ||
        buffer->changed_func == buffer_changed_trampoline);
      orig_changed_func = buffer->changed_func;
      orig_changed_data = buffer->changed_data;
      buffer->changed_func = buffer_changed_trampoline;
      buffer->changed_data = this;
    }
#endif
  }
  ~hb_ot_apply_context_t ()
  {
#ifndef HB_NO_BUFFER_MESSAGE
    if (buffer->messaging ())
    {
      assert (buffer->changed_func == buffer_changed_trampoline);
      assert (buffer->changed_data == this);
      buffer->changed_func = orig_changed_func;
      buffer->changed_data = orig_changed_data;
    }
#endif
  }

  void init_iters ()
  {
    iter_input.init (this, false);
    iter_context.init (this, true);
  }

  void set_lookup_mask (hb_mask_t mask, bool init = true) { lookup_mask = mask; last_base = -1; last_base_until = 0; if (init) init_iters (); }
  void set_auto_zwj (bool auto_zwj_, bool init = true) { auto_zwj = auto_zwj_; if (init) init_iters (); }
  void set_auto_zwnj (bool auto_zwnj_, bool init = true) { auto_zwnj = auto_zwnj_; if (init) init_iters (); }
  void set_per_syllable (bool per_syllable_, bool init = true) { per_syllable = per_syllable_; if (init) init_iters (); }
  void set_random (bool random_) { random = random_; }
  void set_recurse_func (recurse_func_t func) { recurse_func = func; }
  void set_lookup_index (unsigned int lookup_index_) { lookup_index = lookup_index_; }
  void set_lookup_props (unsigned int lookup_props_)
  {
    lookup_props = gdef_accel.sanitize_lookup_props (lookup_props_);
    init_iters ();
  }

  uint32_t random_number ()
  {
    /* http://www.cplusplus.com/reference/random/minstd_rand/ */
    buffer->random_state = buffer->random_state * 48271 % 2147483647;
    return buffer->random_state;
  }

  static void buffer_changed_trampoline (hb_buffer_t *buffer HB_UNUSED, void *user_data)
  {
    ((hb_ot_apply_context_t *) user_data)->buffer_changed ();
  }
  void buffer_changed ()
  {
    buffer->update_digest ();
    if (likely (has_glyph_classes))
      for (unsigned i = 0; i < buffer->len; i++)
  _set_glyph_class_props (buffer->info[i]);
  }

  HB_ALWAYS_INLINE
  HB_HOT
  bool match_properties_mark (const hb_glyph_info_t *info,
            unsigned int    glyph_props,
            unsigned int    match_props) const
  {
    /* If using mark filtering sets, the high short of
     * match_props has the set index.
     */
    if (match_props & LookupFlag::UseMarkFilteringSet)
    {
      unsigned set_index = match_props >> 16;
      return gdef_accel.mark_set_covers (set_index, info->codepoint);
    }

    /* The second byte of match_props has the meaning
     * "ignore marks of attachment type different than
     * the attachment type specified."
     */
    if (match_props & LookupFlag::MarkAttachmentType)
      return (match_props & LookupFlag::MarkAttachmentType) == (glyph_props & LookupFlag::MarkAttachmentType);

    return true;
  }

#ifndef HB_OPTIMIZE_SIZE
  HB_ALWAYS_INLINE
#endif
  bool check_glyph_property (const hb_glyph_info_t *info,
           unsigned match_props) const
  {
    unsigned int glyph_props = _hb_glyph_info_get_glyph_props (info);

    /* Not covered, if, for example, glyph class is ligature and
     * match_props includes LookupFlags::IgnoreLigatures
     */
    if (glyph_props & match_props & LookupFlag::IgnoreFlags)
      return false;

    if (glyph_props & HB_OT_LAYOUT_GLYPH_PROPS_MARK)
      return match_properties_mark (info, glyph_props, match_props);

    return true;
  }

  void _set_glyph_class (hb_codepoint_t glyph_index,
        unsigned int class_guess = 0,
        bool ligature = false,
        bool component = false)
  {
    buffer->digest.add (glyph_index);

    if (new_syllables != (unsigned) -1)
      buffer->cur().syllable() = new_syllables;

    unsigned int props = _hb_glyph_info_get_glyph_props (&buffer->cur());
    props |= HB_OT_LAYOUT_GLYPH_PROPS_SUBSTITUTED;
    if (ligature)
    {
      props |= HB_OT_LAYOUT_GLYPH_PROPS_LIGATED;
      /* In the only place that the MULTIPLIED bit is used, Uniscribe
       * seems to only care about the "last" transformation between
       * Ligature and Multiple substitutions.  Ie. if you ligate, expand,
       * and ligate again, it forgives the multiplication and acts as
       * if only ligation happened.  As such, clear MULTIPLIED bit.
       */
      props &= ~HB_OT_LAYOUT_GLYPH_PROPS_MULTIPLIED;
    }
    if (component)
      props |= HB_OT_LAYOUT_GLYPH_PROPS_MULTIPLIED;
    if (likely (has_glyph_classes))
    {
      _set_glyph_class_props (buffer->cur(), props, glyph_index);
    }
    else if (class_guess)
    {
      props &= HB_OT_LAYOUT_GLYPH_PROPS_PRESERVE;
      _hb_glyph_info_set_glyph_props (&buffer->cur(), props | class_guess);
    }
    else
      _hb_glyph_info_set_glyph_props (&buffer->cur(), props);
  }
  void _set_glyph_class_props (hb_glyph_info_t &info,
             unsigned int props,
             hb_codepoint_t glyph_index)
  {
    props &= HB_OT_LAYOUT_GLYPH_PROPS_PRESERVE;
    _hb_glyph_info_set_glyph_props (&info, props | gdef_accel.get_glyph_props (glyph_index));
  }
  void _set_glyph_class_props (hb_glyph_info_t &info)
  {
    _set_glyph_class_props (info,
          _hb_glyph_info_get_glyph_props (&info),
          info.codepoint);
  }

  void replace_glyph (hb_codepoint_t glyph_index)
  {
    _set_glyph_class (glyph_index);
    (void) buffer->replace_glyph (glyph_index);
  }
  void replace_glyph_inplace (hb_codepoint_t glyph_index)
  {
    _set_glyph_class (glyph_index);
    buffer->cur().codepoint = glyph_index;
  }
  void replace_glyph_with_ligature (hb_codepoint_t glyph_index,
            unsigned int class_guess)
  {
    _set_glyph_class (glyph_index, class_guess, true);
    (void) buffer->replace_glyph (glyph_index);
  }
  void output_glyph_for_component (hb_codepoint_t glyph_index,
           unsigned int class_guess)
  {
    _set_glyph_class (glyph_index, class_guess, false, true);
    (void) buffer->output_glyph (glyph_index);
  }
};

enum class hb_ot_subtable_cache_op_t
{
  ENTER,
  LEAVE,
};

struct hb_accelerate_subtables_context_t :
       hb_dispatch_context_t<hb_accelerate_subtables_context_t>
{
  template <typename T>
  static inline auto collect_second_glyphs_ (const T &obj,
               hb_set_digest_t *digest,
               hb_priority<1>) HB_RETURN (void, obj.collect_second_glyphs (digest) )
  template <typename T>
  static inline void collect_second_glyphs_ (const T &obj HB_UNUSED,
               hb_set_digest_t *digest,
               hb_priority<0>)
  { *digest = hb_set_digest_t::full (); }

  template <typename T>
  static inline auto apply_ (const T *obj, hb_ot_apply_context_t *c, void *external_cache, hb_priority<1>) HB_RETURN (bool, obj->apply (c, external_cache) )
  template <typename T>
  static inline auto apply_ (const T *obj, hb_ot_apply_context_t *c, void *external_cache, hb_priority<0>) HB_RETURN (bool, obj->apply (c) )
  template <typename T>
  static inline bool apply_to (const void *obj, hb_ot_apply_context_t *c, void *external_cache)
  {
    const T *typed_obj = (const T *) obj;
    return apply_ (typed_obj, c, external_cache, hb_prioritize);
  }

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
  template <typename T>
  static inline auto apply_cached_ (const T *obj, hb_ot_apply_context_t *c, void *external_cache, hb_priority<2>) HB_RETURN (bool, obj->apply_cached (c, external_cache) )
  template <typename T>
  static inline auto apply_cached_ (const T *obj, hb_ot_apply_context_t *c, void *external_cache, hb_priority<1>) HB_RETURN (bool, obj->apply (c, external_cache) )
  template <typename T>
  static inline auto apply_cached_ (const T *obj, hb_ot_apply_context_t *c, void *external_cache, hb_priority<0>) HB_RETURN (bool, obj->apply (c) )
  template <typename T>
  static inline bool apply_cached_to (const void *obj, hb_ot_apply_context_t *c, void *external_cache)
  {
    const T *typed_obj = (const T *) obj;
    return apply_cached_ (typed_obj, c, external_cache, hb_prioritize);
  }

  template <typename T>
  static inline auto cache_func_ (hb_ot_apply_context_t *c,
          hb_ot_subtable_cache_op_t op,
          hb_priority<1>) HB_RETURN (bool, T::cache_func (c, op) )
  template <typename T=void>
  static inline bool cache_func_ (hb_ot_apply_context_t *c,
          hb_ot_subtable_cache_op_t op HB_UNUSED,
          hb_priority<0>) { return false; }
  template <typename Type>
  static inline bool cache_func_to (hb_ot_apply_context_t *c,
            hb_ot_subtable_cache_op_t op)
  {
    return cache_func_<Type> (c, op, hb_prioritize);
  }
#endif

  typedef bool (*hb_apply_func_t) (const void *obj, hb_ot_apply_context_t *c, void *external_cache);
  typedef bool (*hb_cache_func_t) (hb_ot_apply_context_t *c, hb_ot_subtable_cache_op_t op);

  struct hb_applicable_t
  {
    friend struct hb_accelerate_subtables_context_t;
    friend struct hb_ot_layout_lookup_accelerator_t;

    template <typename T>
    void init (const T &obj_,
         hb_apply_func_t apply_func_
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
         , hb_apply_func_t apply_cached_func_
         , hb_cache_func_t cache_func_
         , void *external_cache_
#endif
    )
    {
      obj = &obj_;
      apply_func = apply_func_;
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
      apply_cached_func = apply_cached_func_;
      cache_func = cache_func_;
      external_cache = external_cache_;
#endif
      digest.init ();
      obj_.get_coverage ().collect_coverage (&digest);
    }

#ifdef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    bool apply (hb_ot_apply_context_t *c) const
    {
      return digest.may_have (c->buffer->cur().codepoint) && apply_func (obj, c, nullptr);
    }
    bool apply_no_digest (hb_ot_apply_context_t *c) const
    {
      return apply_func (obj, c, nullptr);
    }
#else
    bool apply (hb_ot_apply_context_t *c) const
    {
      return digest.may_have (c->buffer->cur().codepoint) && apply_func (obj, c, external_cache);
    }
    bool apply_cached (hb_ot_apply_context_t *c) const
    {
      return digest.may_have (c->buffer->cur().codepoint) &&  apply_cached_func (obj, c, external_cache);
    }
    bool apply_no_digest (hb_ot_apply_context_t *c) const
    {
      return apply_func (obj, c, external_cache);
    }
    bool apply_cached_no_digest (hb_ot_apply_context_t *c) const
    {
      return apply_cached_func (obj, c, external_cache);
    }

    bool cache_enter (hb_ot_apply_context_t *c) const
    {
      return cache_func (c, hb_ot_subtable_cache_op_t::ENTER);
    }
    void cache_leave (hb_ot_apply_context_t *c) const
    {
      cache_func (c, hb_ot_subtable_cache_op_t::LEAVE);
    }
#endif

    private:
    const void *obj;
    hb_apply_func_t apply_func;
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    hb_apply_func_t apply_cached_func;
    hb_cache_func_t cache_func;
    void *external_cache;
#endif
    hb_set_digest_t digest;
  };

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
  template <typename T>
  auto cache_cost (const T &obj, hb_priority<1>) HB_AUTO_RETURN ( obj.cache_cost () )
  template <typename T>
  auto cache_cost (const T &obj, hb_priority<0>) HB_AUTO_RETURN ( 0u )

  template <typename T>
  auto external_cache_create (const T &obj, hb_priority<1>) HB_AUTO_RETURN ( obj.external_cache_create () )
  template <typename T>
  auto external_cache_create (const T &obj, hb_priority<0>) HB_AUTO_RETURN ( nullptr )
#endif

  /* Dispatch interface. */
  template <typename T>
  return_t dispatch (const T &obj)
  {
    collect_second_glyphs_ (obj, &digest_second, hb_prioritize);

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    void *external_cache = nullptr;
    if (i < 8)
      external_cache = external_cache_create (obj, hb_prioritize);
#endif

    hb_applicable_t *entry = &array[i++];

    entry->init (obj,
     apply_to<T>
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
     , apply_cached_to<T>
     , cache_func_to<T>
     , external_cache
#endif
     );

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    /* Cache handling
     *
     * We allow one subtable from each lookup to use a cache. The assumption
     * being that multiple subtables of the same lookup cannot use a cache
     * because the resources they would use will collide.  As such, we ask
     * each subtable to tell us how much it costs (which a cache would avoid),
     * and we allocate the cache opportunity to the costliest subtable.
     */
    unsigned cost = cache_cost (obj, hb_prioritize);
    if (cost > subtable_cache_user_cost)
    {
      subtable_cache_user_idx = i - 1;
      subtable_cache_user_cost = cost;
    }
#endif

    return hb_empty_t ();
  }
  static return_t default_return_value () { return hb_empty_t (); }

  hb_accelerate_subtables_context_t (hb_applicable_t *array_) :
             array (array_) {}

  hb_applicable_t *array;
  unsigned i = 0;
  hb_set_digest_t digest_second;

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
  unsigned subtable_cache_user_idx = (unsigned) -1;
  unsigned subtable_cache_user_cost = 0;
#endif
};


typedef bool (*intersects_func_t) (const hb_set_t *glyphs, unsigned value, const void *data, void *cache);
typedef void (*intersected_glyphs_func_t) (const hb_set_t *glyphs, const void *data, unsigned value, hb_set_t *intersected_glyphs, void *cache);
typedef void (*collect_glyphs_func_t) (hb_set_t *glyphs, unsigned value, const void *data);
typedef bool (*match_func_t) (hb_glyph_info_t &info, unsigned value, const void *data);
typedef unsigned (*get_value_func_t) (hb_glyph_info_t &info, const void *data);

/* One word per RuleSet, summarizing the classes accepted at the first
 * input position after the current glyph.  Collisions only cause extra work. */
struct hb_ot_layout_ruleset_digest_t
{
  void init () { mask = 0; }
  void set_full () { mask = (uint64_t) -1; }
  void add (unsigned value) { mask |= (uint64_t) 1 << (value & 63); }
  bool may_have (unsigned value) const { return mask & ((uint64_t) 1 << (value & 63)); }

  uint64_t mask;
};

struct ContextClosureFuncs
{
  intersects_func_t intersects;
  intersected_glyphs_func_t intersected_glyphs;
};
struct ContextCollectGlyphsFuncs
{
  collect_glyphs_func_t collect;
};
struct ContextApplyFuncs
{
  match_func_t match;
};
struct ChainContextApplyFuncs
{
  match_func_t match[3];
};


static inline bool intersects_glyph (const hb_set_t *glyphs, unsigned value, const void *data HB_UNUSED, void *cache HB_UNUSED)
{
  return glyphs->has (value);
}
static inline bool intersects_class (const hb_set_t *glyphs, unsigned value, const void *data, void *cache)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
  hb_map_t *map = (hb_map_t *) cache;

  hb_codepoint_t *cached_v;
  if (map->has (value, &cached_v))
    return *cached_v;

  bool v = class_def.intersects_class (glyphs, value);
  map->set (value, v);

  return v;
}
static inline bool intersects_coverage (const hb_set_t *glyphs, unsigned value, const void *data, void *cache HB_UNUSED)
{
  Offset16To<Coverage> coverage;
  coverage = value;
  return (data+coverage).intersects (glyphs);
}


static inline void intersected_glyph (const hb_set_t *glyphs HB_UNUSED, const void *data, unsigned value, hb_set_t *intersected_glyphs, HB_UNUSED void *cache)
{
  unsigned g = reinterpret_cast<const HBUINT16 *>(data)[value];
  intersected_glyphs->add (g);
}

using intersected_class_cache_t = hb_hashmap_t<unsigned, hb_set_t>;

static inline void intersected_class_glyphs (const hb_set_t *glyphs, const void *data, unsigned value, hb_set_t *intersected_glyphs, void *cache)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);

  intersected_class_cache_t *map = (intersected_class_cache_t *) cache;

  hb_set_t *cached_v;
  if (map->has (value, &cached_v))
  {
    intersected_glyphs->union_ (*cached_v);
    return;
  }

  hb_set_t v;
  class_def.intersected_class_glyphs (glyphs, value, &v);

  intersected_glyphs->union_ (v);

  map->set (value, std::move (v));
}

static inline void intersected_coverage_glyphs (const hb_set_t *glyphs, const void *data, unsigned value, hb_set_t *intersected_glyphs, HB_UNUSED void *cache)
{
  Offset16To<Coverage> coverage;
  coverage = value;
  (data+coverage).intersect_set (*glyphs, *intersected_glyphs);
}


template <typename HBUINT>
static inline bool array_is_subset_of (const hb_set_t *glyphs,
               unsigned int count,
               const HBUINT values[],
               intersects_func_t intersects_func,
               const void *intersects_data,
               void *cache)
{
  for (const auto &_ : + hb_iter (values, count))
    if (!intersects_func (glyphs, _, intersects_data, cache)) return false;
  return true;
}


static inline void collect_glyph (hb_set_t *glyphs, unsigned value, const void *data HB_UNUSED)
{
  glyphs->add (value);
}
static inline void collect_class (hb_set_t *glyphs, unsigned value, const void *data)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
  class_def.collect_class (glyphs, value);
}
static inline void collect_coverage (hb_set_t *glyphs, unsigned value, const void *data)
{
  Offset16To<Coverage> coverage;
  coverage = value;
  (data+coverage).collect_coverage (glyphs);
}

inline const hb_set_t *
hb_depend_context_t::find_or_create_glyph_set (const void *data,
                                                unsigned value,
                                                glyph_set_type_t type)
{
  /* Class definitions and coverages are immutable for the lifetime of the
   * context, so their expanded glyph sets can be shared across traversals. */
  glyph_set_cache_key_t key (data, value, type);
  hb_codepoint_t *existing = nullptr;
  if (glyph_set_to_index.has (key, &existing))
    return glyph_sets[*existing].get ();

  hb_set_t *set = hb_object_create<hb_set_t> ();
  if (unlikely (!set))
  {
    depend_data->fail ();
    return nullptr;
  }

  if (type == GLYPH_SET_COVERAGE)
    collect_coverage (set, value, data);
  else if (type == GLYPH_SET_CLASS)
    collect_class (set, value, data);
  else
    set->add (value);
  if (unlikely (set->in_error ()))
  {
    hb_set_destroy (set);
    depend_data->fail ();
    return nullptr;
  }

  hb_codepoint_t index = glyph_sets.length;
  if (unlikely (!glyph_sets.push_or_fail (hb::unique_ptr<hb_set_t> {set})))
  {
    depend_data->fail ();
    return nullptr;
  }
  if (unlikely (!glyph_set_to_index.set (key, index)))
  {
    depend_data->fail ();
    return nullptr;
  }
  return glyph_sets[index].get ();
}

inline hb_codepoint_t
hb_depend_context_t::find_or_create_cached_context_set (const hb_set_t *set)
{
  uintptr_t key = (uintptr_t) set;
  hb_codepoint_t *existing = nullptr;
  if (cached_context_set_indices.has (key, &existing))
    return *existing;

  hb_codepoint_t index = depend_data->find_or_create_context_set (*set);
  if (unlikely (index == HB_CODEPOINT_INVALID))
    return HB_CODEPOINT_INVALID;
  if (unlikely (!cached_context_set_indices.set (key, index)))
    return depend_data->fail_invalid ();
  return index;
}

template <typename HBUINT>
static inline void collect_array (hb_collect_glyphs_context_t *c HB_UNUSED,
          hb_set_t *glyphs,
          unsigned int count,
          const HBUINT values[],
          collect_glyphs_func_t collect_func,
          const void *collect_data)
{
  return
  + hb_iter (values, count)
  | hb_apply ([&] (const HBUINT &_) { collect_func (glyphs, _, collect_data); })
  ;
}


static inline bool match_always (hb_glyph_info_t &info HB_UNUSED, unsigned value HB_UNUSED, const void *data HB_UNUSED)
{
  return true;
}
static inline bool match_glyph (hb_glyph_info_t &info, unsigned value, const void *data HB_UNUSED)
{
  return info.codepoint == value;
}
static inline bool match_class (hb_glyph_info_t &info, unsigned value, const void *data)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
  return class_def.get_class (info.codepoint) == value;
}
static inline unsigned get_class_value (hb_glyph_info_t &info, const void *data)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *> (data);
  return class_def.get_class (info.codepoint);
}
struct match_class_cache_data_t
{
  const ClassDef *class_def;
  hb_ot_layout_mapping_cache_t *cache;
};
static inline bool match_class_cache (hb_glyph_info_t &info, unsigned value, const void *data)
{
  const auto &cache_data = *reinterpret_cast<const match_class_cache_data_t *> (data);
  return cache_data.class_def->get_class (info.codepoint, cache_data.cache) == value;
}
static inline unsigned get_class_cache_value (hb_glyph_info_t &info, const void *data)
{
  const auto &cache_data = *reinterpret_cast<const match_class_cache_data_t *> (data);
  return cache_data.class_def->get_class (info.codepoint, cache_data.cache);
}
static inline unsigned get_class_cached (const ClassDef &class_def, hb_glyph_info_t &info)
{
  unsigned klass = info.syllable();
  if (klass < 255)
    return klass;
  klass = class_def.get_class (info.codepoint);
  if (likely (klass < 255))
    info.syllable() = klass;
  return klass;
}
static inline bool match_class_cached (hb_glyph_info_t &info, unsigned value, const void *data)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
  return get_class_cached (class_def, info) == value;
}
static inline unsigned get_class_cached_value (hb_glyph_info_t &info, const void *data)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *> (data);
  return get_class_cached (class_def, info);
}
static inline unsigned get_class_cached1 (const ClassDef &class_def, hb_glyph_info_t &info)
{
  unsigned klass = info.syllable() & 0x0F;
  if (klass < 15)
    return klass;
  klass = class_def.get_class (info.codepoint);
  if (likely (klass < 15))
    info.syllable() = (info.syllable() & 0xF0) | klass;
  return klass;
}
static inline bool match_class_cached1 (hb_glyph_info_t &info, unsigned value, const void *data)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
  return get_class_cached1 (class_def, info) == value;
}
static inline unsigned get_class_cached2 (const ClassDef &class_def, hb_glyph_info_t &info)
{
  unsigned klass = (info.syllable() & 0xF0) >> 4;
  if (klass < 15)
    return klass;
  klass = class_def.get_class (info.codepoint);
  if (likely (klass < 15))
    info.syllable() = (info.syllable() & 0x0F) | (klass << 4);
  return klass;
}
static inline bool match_class_cached2 (hb_glyph_info_t &info, unsigned value, const void *data)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
  return get_class_cached2 (class_def, info) == value;
}
static inline unsigned get_class_cached2_value (hb_glyph_info_t &info, const void *data)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *> (data);
  return get_class_cached2 (class_def, info);
}
static inline bool match_coverage (hb_glyph_info_t &info, unsigned value, const void *data)
{
  Offset16To<Coverage> coverage;
  coverage = value;
  return (data+coverage).get_coverage (info.codepoint) != NOT_COVERED;
}

template <typename HBUINT>
static inline bool would_match_input (hb_would_apply_context_t *c,
              unsigned int count, /* Including the first glyph (not matched) */
              const HBUINT input[], /* Array of input values--start with second glyph */
              match_func_t match_func,
              const void *match_data)
{
  if (count != c->len)
    return false;

  for (unsigned int i = 1; i < count; i++)
  {
    hb_glyph_info_t info;
    info.codepoint = c->glyphs[i];
    if (likely (!match_func (info, input[i - 1], match_data)))
      return false;
  }

  return true;
}
template <typename HBUINT>
#ifndef HB_OPTIMIZE_SIZE
HB_ALWAYS_INLINE
#endif
static bool match_input (hb_ot_apply_context_t *c,
       unsigned int count, /* Including the first glyph (not matched) */
       const HBUINT input[], /* Array of input values--start with second glyph */
       match_func_t match_func,
       const void *match_data,
       unsigned int *end_position,
       unsigned int *p_total_component_count = nullptr)
{
  TRACE_APPLY (nullptr);

  hb_buffer_t *buffer = c->buffer;

  if (count == 1)
  {
    *end_position = buffer->idx + 1;
    c->match_positions[0] = buffer->idx;
    if (p_total_component_count)
      *p_total_component_count = _hb_glyph_info_get_lig_num_comps (&buffer->cur());
    return_trace (true);
  }

  if (unlikely (count > HB_MAX_CONTEXT_LENGTH)) return_trace (false);

  auto &skippy_iter = c->iter_input;
  skippy_iter.reset (buffer->idx);
  skippy_iter.set_match_func (match_func, match_data);
  skippy_iter.set_glyph_data (input);

  /*
   * This is perhaps the trickiest part of OpenType...  Remarks:
   *
   * - If all components of the ligature were marks, we call this a mark ligature.
   *
   * - If there is no GDEF, and the ligature is NOT a mark ligature, we categorize
   *   it as a ligature glyph.
   *
   * - Ligatures cannot be formed across glyphs attached to different components
   *   of previous ligatures.  Eg. the sequence is LAM,SHADDA,LAM,FATHA,HEH, and
   *   LAM,LAM,HEH form a ligature, leaving SHADDA,FATHA next to eachother.
   *   However, it would be wrong to ligate that SHADDA,FATHA sequence.
   *   There are a couple of exceptions to this:
   *
   *   o If a ligature tries ligating with marks that belong to it itself, go ahead,
   *     assuming that the font designer knows what they are doing (otherwise it can
   *     break Indic stuff when a matra wants to ligate with a conjunct,
   *
   *   o If two marks want to ligate and they belong to different components of the
   *     same ligature glyph, and said ligature glyph is to be ignored according to
   *     mark-filtering rules, then allow.
   *     https://github.com/harfbuzz/harfbuzz/issues/545
   */

  unsigned int total_component_count = 0;

  unsigned int first_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
  unsigned int first_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());

  enum {
    LIGBASE_NOT_CHECKED,
    LIGBASE_MAY_NOT_SKIP,
    LIGBASE_MAY_SKIP
  } ligbase = LIGBASE_NOT_CHECKED;

  for (unsigned int i = 1; i < count; i++)
  {
    unsigned unsafe_to;
    if (!skippy_iter.next (&unsafe_to))
    {
      *end_position = unsafe_to;
      return_trace (false);
    }

    if (unlikely (i + 1 > c->match_positions.length &&
      !c->match_positions.resize_dirty  (i + 1)))
      return_trace (false);
    c->match_positions.arrayZ[i] = skippy_iter.idx;

    unsigned int this_lig_id = _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx]);
    unsigned int this_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]);

    if (first_lig_id && first_lig_comp)
    {
      /* If first component was attached to a previous ligature component,
       * all subsequent components should be attached to the same ligature
       * component, otherwise we shouldn't ligate them... */
      if (first_lig_id != this_lig_id || first_lig_comp != this_lig_comp)
      {
  /* ...unless, we are attached to a base ligature and that base
   * ligature is ignorable. */
  if (ligbase == LIGBASE_NOT_CHECKED)
  {
    bool found = false;
    const auto *out = buffer->out_info;
    unsigned int j = buffer->out_len;
    while (j && _hb_glyph_info_get_lig_id (&out[j - 1]) == first_lig_id)
    {
      if (_hb_glyph_info_get_lig_comp (&out[j - 1]) == 0)
      {
        j--;
        found = true;
        break;
      }
      j--;
    }

    if (found && skippy_iter.may_skip (out[j]) == matcher_t::SKIP_YES)
      ligbase = LIGBASE_MAY_SKIP;
    else
      ligbase = LIGBASE_MAY_NOT_SKIP;
  }

  if (ligbase == LIGBASE_MAY_NOT_SKIP)
    return_trace (false);
      }
    }
    else
    {
      /* If first component was NOT attached to a previous ligature component,
       * all subsequent components should also NOT be attached to any ligature
       * component, unless they are attached to the first component itself! */
      if (this_lig_id && this_lig_comp && (this_lig_id != first_lig_id))
  return_trace (false);
    }

    total_component_count += _hb_glyph_info_get_lig_num_comps_in_ligation (&buffer->info[skippy_iter.idx]);
  }

  *end_position = skippy_iter.idx + 1;

  if (p_total_component_count)
  {
    total_component_count += _hb_glyph_info_get_lig_num_comps (&buffer->cur());
    *p_total_component_count = total_component_count;
  }

  c->match_positions.arrayZ[0] = buffer->idx;

  return_trace (true);
}
static inline bool ligate_input (hb_ot_apply_context_t *c,
         unsigned int count, /* Including the first glyph */
         unsigned int match_end,
         hb_codepoint_t lig_glyph,
         unsigned int total_component_count)
{
  TRACE_APPLY (nullptr);

  hb_buffer_t *buffer = c->buffer;

  buffer->merge_clusters (buffer->idx, match_end);

  /* - If a base and one or more marks ligate, consider that as a base, NOT
   *   ligature, such that all following marks can still attach to it.
   *   https://github.com/harfbuzz/harfbuzz/issues/1109
   *
   * - If all components of the ligature were marks, we call this a mark ligature.
   *   If it *is* a mark ligature, we don't allocate a new ligature id, and leave
   *   the ligature to keep its old ligature id.  This will allow it to attach to
   *   a base ligature in GPOS.  Eg. if the sequence is: LAM,LAM,SHADDA,FATHA,HEH,
   *   and LAM,LAM,HEH for a ligature, they will leave SHADDA and FATHA with a
   *   ligature id and component value of 2.  Then if SHADDA,FATHA form a ligature
   *   later, we don't want them to lose their ligature id/component, otherwise
   *   GPOS will fail to correctly position the mark ligature on top of the
   *   LAM,LAM,HEH ligature.  See:
   *     https://bugzilla.gnome.org/show_bug.cgi?id=676343
   *
   * - If a ligature is formed of components that some of which are also ligatures
   *   themselves, and those ligature components had marks attached to *their*
   *   components, we have to attach the marks to the new ligature component
   *   positions!  Now *that*'s tricky!  And these marks may be following the
   *   last component of the whole sequence, so we should loop forward looking
   *   for them and update them.
   *
   *   Eg. the sequence is LAM,LAM,SHADDA,FATHA,HEH, and the font first forms a
   *   'calt' ligature of LAM,HEH, leaving the SHADDA and FATHA with a ligature
   *   id and component == 1.  Now, during 'liga', the LAM and the LAM-HEH ligature
   *   form a LAM-LAM-HEH ligature.  We need to reassign the SHADDA and FATHA to
   *   the new ligature with a component value of 2.
   *
   *   This in fact happened to a font...  See:
   *   https://bugzilla.gnome.org/show_bug.cgi?id=437633
   */

  bool is_base_ligature = _hb_glyph_info_is_base_glyph (&buffer->info[c->match_positions.arrayZ[0]]);
  bool is_mark_ligature = _hb_glyph_info_is_mark (&buffer->info[c->match_positions.arrayZ[0]]);
  for (unsigned int i = 1; i < count; i++)
    if (!_hb_glyph_info_is_mark (&buffer->info[c->match_positions.arrayZ[i]]))
    {
      is_base_ligature = false;
      is_mark_ligature = false;
      break;
    }
  bool is_ligature = !is_base_ligature && !is_mark_ligature;

  unsigned int klass = is_ligature ? HB_OT_LAYOUT_GLYPH_PROPS_LIGATURE : 0;
  unsigned int lig_id = is_ligature ? _hb_allocate_lig_id (buffer) : 0;
  unsigned int last_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
  unsigned int last_num_components = _hb_glyph_info_get_lig_num_comps (&buffer->cur());
  unsigned int components_so_far = last_num_components;

  if (is_ligature)
  {
    _hb_glyph_info_set_lig_props_for_ligature (&buffer->cur(), lig_id, total_component_count);
    if (_hb_glyph_info_get_general_category (&buffer->cur()) == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)
    {
      _hb_glyph_info_set_general_category (&buffer->cur(), HB_UNICODE_GENERAL_CATEGORY_OTHER_LETTER);
    }
  }
  c->replace_glyph_with_ligature (lig_glyph, klass);

  for (unsigned int i = 1; i < count; i++)
  {
    while (buffer->idx < c->match_positions.arrayZ[i] && buffer->successful)
    {
      if (is_ligature)
      {
  unsigned int this_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());
  if (this_comp == 0)
    this_comp = last_num_components;
  assert (components_so_far >= last_num_components);
  unsigned int new_lig_comp = components_so_far - last_num_components +
            hb_min (this_comp, last_num_components);
    _hb_glyph_info_set_lig_props_for_mark (&buffer->cur(), lig_id, new_lig_comp);
      }
      (void) buffer->next_glyph ();
    }

    last_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
    last_num_components = _hb_glyph_info_get_lig_num_comps_in_ligation (&buffer->cur());
    components_so_far += last_num_components;

    /* Skip the base glyph */
    buffer->idx++;
  }

  if (!is_mark_ligature && last_lig_id)
  {
    /* Re-adjust components for any marks following. */
    for (unsigned i = buffer->idx; i < buffer->len; ++i)
    {
      if (last_lig_id != _hb_glyph_info_get_lig_id (&buffer->info[i])) break;

      unsigned this_comp = _hb_glyph_info_get_lig_comp (&buffer->info[i]);
      if (!this_comp) break;

      assert (components_so_far >= last_num_components);
      unsigned new_lig_comp = components_so_far - last_num_components +
            hb_min (this_comp, last_num_components);
      _hb_glyph_info_set_lig_props_for_mark (&buffer->info[i], lig_id, new_lig_comp);
    }
  }
  return_trace (true);
}

template <typename HBUINT>
#ifndef HB_OPTIMIZE_SIZE
HB_ALWAYS_INLINE
#endif
static bool match_backtrack (hb_ot_apply_context_t *c,
           unsigned int count,
           const HBUINT backtrack[],
           match_func_t match_func,
           const void *match_data,
           unsigned int *match_start)
{
  TRACE_APPLY (nullptr);

  if (!count)
  {
    *match_start = c->buffer->backtrack_len ();
    return_trace (true);
  }

  auto &skippy_iter = c->iter_context;
  skippy_iter.reset_back (c->buffer->backtrack_len ());
  skippy_iter.set_match_func (match_func, match_data);
  skippy_iter.set_glyph_data (backtrack);

  for (unsigned int i = 0; i < count; i++)
  {
    unsigned unsafe_from;
    if (!skippy_iter.prev (&unsafe_from))
    {
      *match_start = unsafe_from;
      return_trace (false);
    }
  }

  *match_start = skippy_iter.idx;
  return_trace (true);
}

template <typename HBUINT>
#ifndef HB_OPTIMIZE_SIZE
HB_ALWAYS_INLINE
#endif
static bool match_lookahead (hb_ot_apply_context_t *c,
           unsigned int count,
           const HBUINT lookahead[],
           match_func_t match_func,
           const void *match_data,
           unsigned int start_index,
           unsigned int *end_index)
{
  TRACE_APPLY (nullptr);

  if (!count)
  {
    *end_index = start_index;
    return_trace (true);
  }

  auto &skippy_iter = c->iter_context;
  assert (start_index >= 1);
  skippy_iter.reset (start_index - 1);
  skippy_iter.set_match_func (match_func, match_data);
  skippy_iter.set_glyph_data (lookahead);

  for (unsigned int i = 0; i < count; i++)
  {
    unsigned unsafe_to;
    if (!skippy_iter.next (&unsafe_to))
    {
      *end_index = unsafe_to;
      return_trace (false);
    }
  }

  *end_index = skippy_iter.idx + 1;
  return_trace (true);
}



struct LookupRecord
{
  bool serialize (hb_serialize_context_t *c,
      const hb_map_t         *lookup_map) const
  {
    TRACE_SERIALIZE (this);
    auto *out = c->embed (*this);
    if (unlikely (!out)) return_trace (false);

    return_trace (c->check_assign (out->lookupListIndex, lookup_map->get (lookupListIndex), HB_SERIALIZE_ERROR_INT_OVERFLOW));
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this));
  }

  HBUINT16  sequenceIndex;    /* Index into current glyph
           * sequence--first glyph = 0 */
  HBUINT16  lookupListIndex;  /* Lookup to apply to that
           * position--zero--based */
  public:
  DEFINE_SIZE_STATIC (4);
};

static unsigned serialize_lookuprecord_array (hb_serialize_context_t *c,
                const hb_array_t<const LookupRecord> lookupRecords,
                const hb_map_t *lookup_map)
{
  unsigned count = 0;
  for (const LookupRecord& r : lookupRecords)
  {
    if (!lookup_map->has (r.lookupListIndex))
      continue;

    if (!r.serialize (c, lookup_map))
      return 0;

    count++;
  }
  return count;
}

enum ContextFormat { SimpleContext = 1, ClassBasedContext = 2, CoverageBasedContext = 3 };

static inline const hb_set_t *
depend_position_glyphs (hb_depend_context_t *c,
      ContextFormat context_format,
      const void *data,
      unsigned value,
      bool filter_class_by_parent,
      hb_set_t *scratch,
      hb_vector_t<unsigned> *compact_workspace = nullptr)
{
  switch (context_format)
  {
    case ContextFormat::SimpleContext:
      return c->find_or_create_glyph_set (nullptr, value,
                                           hb_depend_context_t::GLYPH_SET_SINGLE);
    case ContextFormat::ClassBasedContext:
    {
      const hb_set_t *class_set = c->find_or_create_glyph_set (
        data, value, hb_depend_context_t::GLYPH_SET_CLASS);
      if (unlikely (!class_set))
  return nullptr;
      if (!filter_class_by_parent)
  return class_set;
      scratch->set (*class_set);
      scratch->intersect (c->parent_active_glyphs (), compact_workspace);
      break;
    }
    case ContextFormat::CoverageBasedContext:
      return c->find_or_create_glyph_set (
        data, value, hb_depend_context_t::GLYPH_SET_COVERAGE);
  }

  if (unlikely (scratch->in_error ()))
  {
    c->depend_data->fail ();
    return nullptr;
  }
  return scratch;
}

template <typename HBUINT>
static void context_closure_recurse_lookups (hb_closure_context_t *c,
               unsigned inputCount, const HBUINT input[],
               unsigned lookupCount,
               const LookupRecord lookupRecord[] /* Array of LookupRecords--in design order */,
               unsigned value,
               ContextFormat context_format,
               const void *data,
               intersected_glyphs_func_t intersected_glyphs_func,
               void *cache)
{
  hb_set_t covered_seq_indicies;
  hb_set_t pos_glyphs;
  for (unsigned int i = 0; i < lookupCount; i++)
  {
    unsigned seqIndex = lookupRecord[i].sequenceIndex;
    if (seqIndex >= inputCount) continue;

    bool has_pos_glyphs = false;

    if (!covered_seq_indicies.has (seqIndex))
    {
      has_pos_glyphs = true;
      pos_glyphs.clear ();
      if (seqIndex == 0)
      {
        switch (context_format) {
        case ContextFormat::SimpleContext:
          pos_glyphs.add (value);
          break;
        case ContextFormat::ClassBasedContext:
          intersected_glyphs_func (&c->parent_active_glyphs (), data, value, &pos_glyphs, cache);
          break;
        case ContextFormat::CoverageBasedContext:
          pos_glyphs.set (c->parent_active_glyphs ());
          break;
        }
      }
      else
      {
        const void *input_data = input;
        unsigned input_value = seqIndex - 1;
        if (context_format != ContextFormat::SimpleContext)
        {
          input_data = data;
          input_value = input[seqIndex - 1];
        }

        intersected_glyphs_func (c->glyphs, input_data, input_value, &pos_glyphs, cache);
      }
    }

    covered_seq_indicies.add (seqIndex);
    hb_set_t *cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs))
      return;
    if (has_pos_glyphs) {
      *cur_active_glyphs = std::move (pos_glyphs);
    } else {
      *cur_active_glyphs = *c->glyphs;
    }

    unsigned endIndex = inputCount;
    if (context_format == ContextFormat::CoverageBasedContext)
      endIndex += 1;

    c->recurse (lookupRecord[i].lookupListIndex, &covered_seq_indicies, seqIndex, endIndex);

    c->pop_cur_done_glyphs ();
  }
}

static bool
context_depend_sets_are_cached (hb_depend_context_t *c,
        unsigned input_count,
        unsigned lookup_count,
        const LookupRecord lookup_records[],
        const void *rule,
        unsigned value,
        ContextFormat context_format,
        const void *data,
        hb_vector_t<hb_codepoint_t> *cached_context_sets)
{
  hb_codepoint_t active_idx = HB_CODEPOINT_INVALID;
  bool have_active_idx = false;
  for (unsigned i = 0; i < lookup_count; i++)
  {
    if (lookup_records[i].sequenceIndex >= input_count)
      continue;

    if (!have_active_idx)
    {
      if (unlikely (!c->get_parent_active_glyphs_index (&active_idx)))
  return false;
      have_active_idx = true;
    }

    hb_depend_context_t::context_set_cache_key_t key (
      rule, &lookup_records[i], data, active_idx, value, context_format);
    hb_codepoint_t *cached_context_set = nullptr;
    if (!c->context_set_cache.has (key, &cached_context_set))
      return false;
    if (unlikely (!cached_context_sets->push_or_fail (*cached_context_set)))
      return c->depend_data->fail ();
  }
  /* A rule with no valid records has no cache entries, and its preparation
   * can still allocate dependency sets in an observable order. */
  return have_active_idx;
}

template <typename HBUINT>
static void context_depend_recurse_lookups (hb_depend_context_t *c,
               unsigned inputCount, const HBUINT input[],
               unsigned lookupCount,
               const LookupRecord lookupRecord[] /* Array of LookupRecords--in design order */,
               const void *rule,
               unsigned value,
               ContextFormat context_format,
               const void *data,
               intersected_glyphs_func_t intersected_glyphs_func,
               void *cache,
               const hb_set_t &preliminary_context,
               const hb_vector_t<const hb_set_t *> *input_position_glyphs,
               const hb_vector_t<hb_codepoint_t> *cached_context_sets,
               hb_depend_context_t::depend_scratch_t *scratch)
{
  /* For depend graph extraction, we filter active glyphs by InputCoverage constraints
   * (same as closure), but we do NOT do sequential accumulation of outputs.
   *
   * - Position filtering (InputCoverage): Required. The contextual rule can only match
   *   glyphs in its InputCoverage. Edges for other glyphs are spurious.
   * - Sequential accumulation: Not done. We want ALL possible edges, so we don't
   *   limit later lookups based on outputs from earlier lookups in the same rule. */

  /* Sequence positions are tracked in one allocation-free bit page below.
   * A rule longer than HB_MAX_CONTEXT_LENGTH never applies during shaping
   * (the apply path rejects it), so skip it here instead of running past
   * the fixed page in add_range(). */
  if (unlikely (inputCount > HB_MAX_CONTEXT_LENGTH))
    return;

  hb_bit_page_t covered_seq_indices;
  hb_set_t &pos_glyphs = scratch->pos_glyphs;
  hb_set_t &position_context = scratch->position_context;
  hb_set_t &disjunctive_indices = scratch->disjunctive_indices;
  hb_set_t &filtered_disjunctive_indices = scratch->filtered_disjunctive_indices;
  unsigned cached_context_index = 0;
  for (unsigned int i = 0; i < lookupCount; i++)
  {
    unsigned seqIndex = lookupRecord[i].sequenceIndex;
    if (seqIndex >= inputCount)
      continue;

    hb_depend_context_t::context_set_cache_key_t context_cache_key;
    if (unlikely (!c->get_context_set_cache_key (rule, &lookupRecord[i], data, value,
             context_format, &context_cache_key)))
      return;

    hb_codepoint_t context_set_idx;
    hb_codepoint_t *cached_context_set_idx;
    if (cached_context_sets)
      context_set_idx = (*cached_context_sets)[cached_context_index++];
    else if (c->context_set_cache.has (context_cache_key, &cached_context_set_idx))
      context_set_idx = *cached_context_set_idx;
    else
    {
      if (unlikely (!input_position_glyphs))
      {
  c->depend_data->fail ();
  return;
      }

      /* Build position-specific context_set for this lookup. */
      position_context.clear ();  // Will hold direct glyphs
      disjunctive_indices.clear ();  // Will hold encoded set references
      filtered_disjunctive_indices.clear ();

      /* Process preliminary_context in one pass. */
      hb_codepoint_t elem = HB_SET_VALUE_INVALID;
      while (preliminary_context.next (&elem)) {
  if (!(elem & HB_DEPEND_CONTEXT_SET_FLAG)) {
    /* Direct glyph */
    position_context.add (elem);
  } else {
    /* Encoded set reference - defer processing until we have all direct requirements */
    disjunctive_indices.add (elem);
  }
      }

      /* Add singleton glyphs from OTHER input positions. */
      for (unsigned j = 0; j < input_position_glyphs->length; j++) {
  if (j != seqIndex && (*input_position_glyphs)[j]->get_population () == 1) {
    position_context.add ((*input_position_glyphs)[j]->get_min ());
  }
      }

      /* Now position_context has all direct requirements.
       * Process deferred encoded sets and filter them. */
      elem = HB_SET_VALUE_INVALID;
      while (disjunctive_indices.next (&elem)) {
  hb_codepoint_t set_idx = elem & 0x7FFFFFFF;
  const hb_set_t *original_set = c->depend_data->get_set_from_index (set_idx);
  if (unlikely (!original_set)) continue;

  /* Dependency context sets are never inverted. */
  if (!original_set->intersects (position_context)) {
    /* No overlap with position_context - add full requirement */
    filtered_disjunctive_indices.add (elem);
  }
  /* Otherwise: position_context intersects with original_set.
   * Since disjunctive requirements need only ONE glyph from the set,
   * and position_context already has a glyph from this set, the
   * requirement is satisfied - no need to add anything. */
      }

      /* Process non-singleton input positions. */
      for (unsigned j = 0; j < input_position_glyphs->length; j++) {
  if (j != seqIndex && (*input_position_glyphs)[j]->get_population () > 1) {
    /* Input-position sets are also never inverted. */
    if (!(*input_position_glyphs)[j]->intersects (position_context)) {
      /* No overlap with position_context - add full requirement */
      bool cached_set = context_format == ContextFormat::CoverageBasedContext ||
            (context_format == ContextFormat::ClassBasedContext && j != 0);
      hb_codepoint_t idx = cached_set
        ? c->find_or_create_cached_context_set ((*input_position_glyphs)[j])
        : c->depend_data->find_or_create_context_set (*(*input_position_glyphs)[j]);
      if (unlikely (idx == HB_CODEPOINT_INVALID))
        return;
      filtered_disjunctive_indices.add (HB_DEPEND_CONTEXT_SET_FLAG | idx);
    }
    /* Otherwise: position_context intersects, requirement satisfied */
  }
      }

      /* Combine direct + disjunctive. */
      position_context.union_ (filtered_disjunctive_indices);
      if (unlikely (position_context.in_error () ||
        filtered_disjunctive_indices.in_error ()))
      {
  c->depend_data->fail ();
  return;
      }

      context_set_idx = position_context.is_empty ()
  ? HB_CODEPOINT_INVALID
  : c->depend_data->find_or_create_context_set (position_context);
      if (unlikely (!position_context.is_empty () &&
        context_set_idx == HB_CODEPOINT_INVALID))
  return;

      if (unlikely (!c->context_set_cache.set (context_cache_key, context_set_idx)))
      {
  c->depend_data->fail ();
  return;
      }
    }

    /* Save outer context to restore after this lookup. When a contextual lookup
     * calls another contextual lookup, we want each lookup in this rule to see
     * the same outer context, not context from a sibling lookup. */
    hb_codepoint_t saved_context_set_index = c->depend_data->current_context_set_index;
    hb_subset_depend_edge_flags_t saved_edge_flags = c->depend_data->current_edge_flags;

    /* Detect nested contextual: if we already have a context set, we're inside
     * an outer contextual rule that called this one. The outer context will be
     * lost, so edges created here may over-approximate. */
    bool nested_contextual = (saved_context_set_index != HB_CODEPOINT_INVALID);

    /* Set for this position's edges */
    c->depend_data->current_context_set_index = context_set_idx;

    /* Mark edges from multi-position rules (inputCount > 1) as potentially
     * over-approximate. Depend extraction records edges based on what glyphs
     * COULD be at each position per the static input coverage/class. But during
     * closure computation, lookups within the rule are applied sequentially:
     * lookups at earlier positions may transform later positions, and multiple
     * lookups at the same position may interact (one produces a glyph, another
     * immediately consumes it as an "intermediate"). So a glyph matching the
     * coverage might not persist at that position when closure traverses. */
    c->depend_data->current_edge_flags = HB_SUBSET_DEPEND_EDGE_FLAG_NONE;
    if (inputCount > 1) {
      c->depend_data->current_edge_flags |= HB_SUBSET_DEPEND_EDGE_FLAG_FROM_CONTEXT_POSITION;
    }
    if (nested_contextual) {
      c->depend_data->current_edge_flags |= HB_SUBSET_DEPEND_EDGE_FLAG_FROM_NESTED_CONTEXT;
    }

    bool has_pos_glyphs = false;

    if (!covered_seq_indices.has (seqIndex))
    {
      has_pos_glyphs = true;
      pos_glyphs.clear ();
      if (seqIndex == 0)
      {
        switch (context_format) {
        case ContextFormat::SimpleContext:
          pos_glyphs.add (value);
          break;
        case ContextFormat::ClassBasedContext:
          intersected_glyphs_func (&c->parent_active_glyphs (), data, value, &pos_glyphs, cache);
          break;
        case ContextFormat::CoverageBasedContext:
          pos_glyphs.set (c->parent_active_glyphs ());
          break;
        }
      }
      else
      {
        const void *input_data = input;
        unsigned input_value = seqIndex - 1;
        if (context_format != ContextFormat::SimpleContext)
        {
          input_data = data;
          input_value = input[seqIndex - 1];
        }

        intersected_glyphs_func (c->glyphs, input_data, input_value, &pos_glyphs, cache);
      }
    }

    covered_seq_indices.add (seqIndex);
    if (has_pos_glyphs)
    {
      hb_codepoint_t active_idx = HB_CODEPOINT_INVALID;
      if (context_format == ContextFormat::SimpleContext)
      {
  hb_codepoint_t glyph = seqIndex ? pos_glyphs.get_min () : value;
  if (likely (glyph < hb_depend_context_t::SINGLE_GLYPH_ACTIVE_FLAG))
    active_idx = glyph | hb_depend_context_t::SINGLE_GLYPH_ACTIVE_FLAG;
      }
      hb_set_t *cur_active_glyphs = c->push_cur_active_glyphs (active_idx);
      if (unlikely (!cur_active_glyphs))
      {
  c->depend_data->current_context_set_index = saved_context_set_index;
  c->depend_data->current_edge_flags = saved_edge_flags;
  return;
      }
      *cur_active_glyphs = std::move (pos_glyphs);
    }
    else if (unlikely (!c->push_root_active_glyphs ()))
    {
      c->depend_data->current_context_set_index = saved_context_set_index;
      c->depend_data->current_edge_flags = saved_edge_flags;
      return;
    }

    unsigned endIndex = inputCount;
    if (context_format == ContextFormat::CoverageBasedContext)
      endIndex += 1;

    c->recurse (lookupRecord[i].lookupListIndex, &covered_seq_indices, seqIndex, endIndex);
    c->pop_cur_done_glyphs ();

    /* Restore outer context after this lookup, so subsequent lookups in this
     * rule see the original context rather than this lookup's context. */
    c->depend_data->current_context_set_index = saved_context_set_index;
    c->depend_data->current_edge_flags = saved_edge_flags;
  }
}

template <typename context_t>
static inline void recurse_lookups (context_t *c,
                                    unsigned int lookupCount,
                                    const LookupRecord lookupRecord[] /* Array of LookupRecords--in design order */)
{
  for (unsigned int i = 0; i < lookupCount; i++)
    c->recurse (lookupRecord[i].lookupListIndex);
}

static inline void apply_lookup (hb_ot_apply_context_t *c,
         unsigned int count, /* Including the first glyph */
         unsigned int lookupCount,
         const LookupRecord lookupRecord[], /* Array of LookupRecords--in design order */
         unsigned int match_end)
{
  hb_buffer_t *buffer = c->buffer;
  int end;

  /* All positions are distance from beginning of *output* buffer.
   * Adjust. */
  {
    unsigned int bl = buffer->backtrack_len ();
    end = bl + match_end - buffer->idx;

    int delta = bl - buffer->idx;
    /* Convert positions to new indexing. */
    for (unsigned int j = 0; j < count; j++)
      c->match_positions.arrayZ[j] += delta;
  }

  for (unsigned int i = 0; i < lookupCount && buffer->successful; i++)
  {
    unsigned int idx = lookupRecord[i].sequenceIndex;
    if (idx >= count)
      continue;

    unsigned int orig_len = buffer->backtrack_len () + buffer->lookahead_len ();

    /* This can happen if earlier recursed lookups deleted many entries. */
    if (unlikely (c->match_positions.arrayZ[idx] >= orig_len))
      continue;

    if (unlikely (!buffer->move_to (c->match_positions.arrayZ[idx])))
      break;

    if (unlikely (buffer->max_ops <= 0))
      break;

    if (HB_BUFFER_MESSAGE_MORE && c->buffer->messaging ())
    {
      if (buffer->have_output)
        c->buffer->sync_so_far ();
      c->buffer->message (c->font,
        "start recursing to lookup %u at %u",
        (unsigned) lookupRecord[i].lookupListIndex,
        buffer->idx);
    }

    bool ret = c->recurse (lookupRecord[i].lookupListIndex);

    if (HB_BUFFER_MESSAGE_MORE && c->buffer->messaging ())
    {
      if (buffer->have_output)
        c->buffer->sync_so_far ();
      c->buffer->message (c->font,
        "end recursing to lookup %u",
        (unsigned) lookupRecord[i].lookupListIndex);
    }

    if (!ret)
      continue;

    unsigned int new_len = buffer->backtrack_len () + buffer->lookahead_len ();
    int delta = new_len - orig_len;

    if (!delta)
      continue;

    /* Recursed lookup changed buffer len.  Adjust.
     *
     * TODO:
     *
     * Right now, if buffer length increased by n, we assume n new glyphs
     * were added right after the current position, and if buffer length
     * was decreased by n, we assume n match positions after the current
     * one where removed.  The former (buffer length increased) case is
     * fine, but the decrease case can be improved in at least two ways,
     * both of which are significant:
     *
     *   - If recursed-to lookup is MultipleSubst and buffer length
     *     decreased, then it's current match position that was deleted,
     *     NOT the one after it.
     *
     *   - If buffer length was decreased by n, it does not necessarily
     *     mean that n match positions where removed, as there recursed-to
     *     lookup might had a different LookupFlag.  Here's a constructed
     *     case of that:
     *     https://github.com/harfbuzz/harfbuzz/discussions/3538
     *
     * It should be possible to construct tests for both of these cases.
     */

    end += delta;
    if (end < int (c->match_positions.arrayZ[idx]))
    {
      /* End might end up being smaller than match_positions.arrayZ[idx] if the recursed
       * lookup ended up removing many items.
       * Just never rewind end beyond start of current position, since that is
       * not possible in the recursed lookup.  Also adjust delta as such.
       *
       * https://bugs.chromium.org/p/chromium/issues/detail?id=659496
       * https://github.com/harfbuzz/harfbuzz/issues/1611
       */
      delta += c->match_positions.arrayZ[idx] - end;
      end = c->match_positions.arrayZ[idx];
    }

    unsigned int next = idx + 1; /* next now is the position after the recursed lookup. */

    if (delta > 0)
    {
      if (unlikely (delta + count > HB_MAX_CONTEXT_LENGTH))
  break;
      if (unlikely (count + delta > c->match_positions.length &&
        !c->match_positions.resize_dirty  (count + delta)))
        return;
    }
    else
    {
      /* NOTE: delta is non-positive. */
      delta = hb_max (delta, (int) next - (int) count);
      next -= delta;
    }

    /* Shift! */
    memmove (c->match_positions + next + delta, c->match_positions + next,
       (count - next) * sizeof (c->match_positions.arrayZ[0]));
    next += delta;
    count += delta;

    /* Fill in new entries. */
    for (unsigned int j = idx + 1; j < next; j++)
      c->match_positions.arrayZ[j] = c->match_positions.arrayZ[j - 1] + 1;

    /* And fixup the rest. */
    for (; next < count; next++)
      c->match_positions.arrayZ[next] += delta;
  }

  assert (end >= 0);
  (void) buffer->move_to (end);
}



/* Contextual lookups */

struct ContextClosureLookupContext
{
  ContextClosureFuncs funcs;
  ContextFormat context_format;
  const void *intersects_data;
  void *intersects_cache;
  void *intersected_glyphs_cache;
};

typedef ContextClosureLookupContext ContextDependLookupContext;

struct ContextCollectGlyphsLookupContext
{
  ContextCollectGlyphsFuncs funcs;
  const void *collect_data;
};

struct ContextApplyLookupContext
{
  ContextApplyFuncs funcs;
  const void *match_data;
  get_value_func_t get_value;
};

template <typename HBUINT>
static inline bool context_intersects (const hb_set_t *glyphs,
               unsigned int inputCount, /* Including the first glyph (not matched) */
               const HBUINT input[], /* Array of input values--start with second glyph */
               ContextClosureLookupContext &lookup_context)
{
  return array_is_subset_of (glyphs,
           inputCount ? inputCount - 1 : 0, input,
           lookup_context.funcs.intersects,
           lookup_context.intersects_data,
           lookup_context.intersects_cache);
}

template <typename HBUINT>
static inline void context_closure_lookup (hb_closure_context_t *c,
             unsigned int inputCount, /* Including the first glyph (not matched) */
             const HBUINT input[], /* Array of input values--start with second glyph */
             unsigned int lookupCount,
             const LookupRecord lookupRecord[],
             unsigned value, /* Index of first glyph in Coverage or Class value in ClassDef table */
             ContextClosureLookupContext &lookup_context)
{
  if (context_intersects (c->glyphs,
        inputCount, input,
        lookup_context))
    context_closure_recurse_lookups (c,
             inputCount, input,
             lookupCount, lookupRecord,
             value,
             lookup_context.context_format,
             lookup_context.intersects_data,
             lookup_context.funcs.intersected_glyphs,
             lookup_context.intersected_glyphs_cache);
}

template <typename HBUINT>
static inline void context_depend_lookup (hb_depend_context_t *c,
            unsigned int inputCount, /* Including the first glyph (not matched) */
            const HBUINT input[], /* Array of input values--start with second glyph */
            unsigned int lookupCount,
            const LookupRecord lookupRecord[],
            const void *rule,
            unsigned value, /* Index of first glyph in Coverage or Class value in ClassDef table */
            ContextDependLookupContext &lookup_context)
{
  if (!context_intersects (c->glyphs,
         inputCount, input,
         lookup_context))
    return;

  hb_depend_context_t::depend_scratch_t *scratch = c->acquire_depend_scratch ();
  if (unlikely (!scratch))
    return;
  HB_SCOPE_GUARD (c->release_depend_scratch (scratch));

  bool context_sets_cached = context_depend_sets_are_cached (
    c, inputCount, lookupCount, lookupRecord, rule, value,
    lookup_context.context_format, lookup_context.intersects_data,
    &scratch->cached_context_sets);
  if (unlikely (!c->depend_data->successful))
    return;

  /* Build preliminary_context (empty for ContextSubst - no backtrack/lookahead) */
  hb_set_t &preliminary_context = scratch->preliminary_context;

  /* Build glyph sets for ALL input positions */
  hb_set_t &position_scratch = scratch->position_scratch;
  hb_vector_t<const hb_set_t *> &input_position_glyphs = scratch->input_position_glyphs;

  /* Cached labels no longer need the expanded input-position sets. */
  if (!context_sets_cached)
  {
    /* Position 0 (Coverage glyph) — must be in both the class AND the
     * coverage, so intersect with parent_active_glyphs (= coverage ∩ glyphs
     * set by the ContextFormat2/3 caller). */
    const hb_set_t *pos0_glyphs = depend_position_glyphs (
      c, lookup_context.context_format, lookup_context.intersects_data, value,
      true, &position_scratch, &scratch->compact_workspace);
    if (unlikely (!pos0_glyphs ||
      !input_position_glyphs.push_or_fail (pos0_glyphs)))
    {
      c->depend_data->fail ();
      return;
    }

    /* Positions 1+ (Input array) */
    for (unsigned i = 0; i + 1 < inputCount; i++)
    {
      const hb_set_t *pos_glyphs = depend_position_glyphs (
  c, lookup_context.context_format, lookup_context.intersects_data,
  input[i], false, &position_scratch);
      if (unlikely (!pos_glyphs ||
        !input_position_glyphs.push_or_fail (pos_glyphs)))
      {
  c->depend_data->fail ();
  return;
      }
    }
  }

  context_depend_recurse_lookups (c,
          inputCount, input,
          lookupCount, lookupRecord,
          rule,
          value,
          lookup_context.context_format,
          lookup_context.intersects_data,
          lookup_context.funcs.intersected_glyphs,
          lookup_context.intersected_glyphs_cache,
          preliminary_context,
          context_sets_cached ? nullptr : &input_position_glyphs,
          context_sets_cached ? &scratch->cached_context_sets : nullptr,
          scratch);
}

template <typename HBUINT>
static inline void context_collect_glyphs_lookup (hb_collect_glyphs_context_t *c,
              unsigned int inputCount, /* Including the first glyph (not matched) */
              const HBUINT input[], /* Array of input values--start with second glyph */
              unsigned int lookupCount,
              const LookupRecord lookupRecord[],
              ContextCollectGlyphsLookupContext &lookup_context)
{
  collect_array (c, c->input,
     inputCount ? inputCount - 1 : 0, input,
     lookup_context.funcs.collect, lookup_context.collect_data);
  recurse_lookups (c,
       lookupCount, lookupRecord);
}

template <typename HBUINT>
static inline bool context_would_apply_lookup (hb_would_apply_context_t *c,
                 unsigned int inputCount, /* Including the first glyph (not matched) */
                 const HBUINT input[], /* Array of input values--start with second glyph */
                 unsigned int lookupCount HB_UNUSED,
                 const LookupRecord lookupRecord[] HB_UNUSED,
                 const ContextApplyLookupContext &lookup_context)
{
  return would_match_input (c,
          inputCount, input,
          lookup_context.funcs.match, lookup_context.match_data);
}

template <typename HBUINT>
static inline bool context_apply_lookup (hb_ot_apply_context_t *c,
           unsigned int inputCount, /* Including the first glyph (not matched) */
           const HBUINT input[], /* Array of input values--start with second glyph */
           unsigned int lookupCount,
           const LookupRecord lookupRecord[],
           const ContextApplyLookupContext &lookup_context)
{
  if (unlikely (inputCount > HB_MAX_CONTEXT_LENGTH)) return false;

  unsigned match_end = 0;
  bool ret = false;
  if (match_input (c,
       inputCount, input,
       lookup_context.funcs.match, lookup_context.match_data,
       &match_end))
  {
    c->buffer->unsafe_to_break (c->buffer->idx, match_end);
    apply_lookup (c,
      inputCount,
      lookupCount, lookupRecord,
      match_end);
    ret = true;
  }
  else
  {
    c->buffer->unsafe_to_concat (c->buffer->idx, match_end);
    ret = false;
  }

  return ret;
}

static inline bool context_cache_func (hb_ot_apply_context_t *c, hb_ot_subtable_cache_op_t op)
{
  switch (op)
  {
    case hb_ot_subtable_cache_op_t::ENTER:
    {
      if (!HB_BUFFER_TRY_ALLOCATE_VAR (c->buffer, syllable))
  return false;
      auto &info = c->buffer->info;
      unsigned count = c->buffer->len;
      for (unsigned i = 0; i < count; i++)
  info[i].syllable() = 255;
      c->new_syllables = 255;
      return true;
    }
    case hb_ot_subtable_cache_op_t::LEAVE:
    {
      c->new_syllables = (unsigned) -1;
      HB_BUFFER_DEALLOCATE_VAR (c->buffer, syllable);
      break;
    }
  }
  return false;
}

template <typename Types>
struct Rule
{
  template <typename T>
  friend struct RuleSet;

  bool intersects (const hb_set_t *glyphs, ContextClosureLookupContext &lookup_context) const
  {
    return context_intersects (glyphs,
             inputCount, inputZ.arrayZ,
             lookup_context);
  }

  void depend (hb_depend_context_t *c, unsigned value, ContextDependLookupContext &lookup_context) const
  {
    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
             (inputZ.as_array ((inputCount ? inputCount - 1 : 0)));
    context_depend_lookup (c,
         inputCount, inputZ.arrayZ,
         lookupCount, lookupRecord.arrayZ,
         this,
         value, lookup_context);
  }

  void closure (hb_closure_context_t *c, unsigned value, ContextClosureLookupContext &lookup_context) const
  {
    if (unlikely (c->lookup_limit_exceeded ())) return;

    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
             (inputZ.as_array ((inputCount ? inputCount - 1 : 0)));
    context_closure_lookup (c,
          inputCount, inputZ.arrayZ,
          lookupCount, lookupRecord.arrayZ,
          value, lookup_context);
  }

  void closure_lookups (hb_closure_lookups_context_t *c,
                        ContextClosureLookupContext &lookup_context) const
  {
    if (unlikely (c->lookup_limit_exceeded ())) return;
    if (!intersects (c->glyphs, lookup_context)) return;

    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
             (inputZ.as_array (inputCount ? inputCount - 1 : 0));
    recurse_lookups (c, lookupCount, lookupRecord.arrayZ);
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c,
           ContextCollectGlyphsLookupContext &lookup_context) const
  {
    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
             (inputZ.as_array (inputCount ? inputCount - 1 : 0));
    context_collect_glyphs_lookup (c,
           inputCount, inputZ.arrayZ,
           lookupCount, lookupRecord.arrayZ,
           lookup_context);
  }

  void collect_second_glyphs (hb_set_digest_t *digest,
            const ClassDef *class_def = nullptr) const
  {
    if (inputCount <= 1)
    {
      *digest = hb_set_digest_t::full ();
      return;
    }

    unsigned second = inputZ.arrayZ[0];
    if (!class_def)
      digest->add (second);
    else if (!second)
      *digest = hb_set_digest_t::full ();
    else
      class_def->collect_class (digest, second);
  }

  bool would_apply (hb_would_apply_context_t *c,
        const ContextApplyLookupContext &lookup_context) const
  {
    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
             (inputZ.as_array (inputCount ? inputCount - 1 : 0));
    return context_would_apply_lookup (c,
               inputCount, inputZ.arrayZ,
               lookupCount, lookupRecord.arrayZ,
               lookup_context);
  }

  bool apply (hb_ot_apply_context_t *c,
        const ContextApplyLookupContext &lookup_context) const
  {
    TRACE_APPLY (this);
    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
             (inputZ.as_array (inputCount ? inputCount - 1 : 0));
    return_trace (context_apply_lookup (c, inputCount, inputZ.arrayZ, lookupCount, lookupRecord.arrayZ, lookup_context));
  }

  bool serialize (hb_serialize_context_t *c,
      const hb_map_t *input_mapping, /* old->new glyphid or class mapping */
      const hb_map_t *lookup_map) const
  {
    TRACE_SERIALIZE (this);
    auto *out = c->start_embed (this);
    if (unlikely (!c->extend_min (out))) return_trace (false);

    out->inputCount = inputCount;
    const auto input = inputZ.as_array (inputCount - 1);
    for (const auto org : input)
    {
      HBUINT16 d;
      d = input_mapping->get (org);
      c->copy (d);
    }

    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
             (inputZ.as_array ((inputCount ? inputCount - 1 : 0)));

    unsigned count = serialize_lookuprecord_array (c, lookupRecord.as_array (lookupCount), lookup_map);
    return_trace (c->check_assign (out->lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
  }

  bool subset (hb_subset_context_t *c,
         const hb_map_t *lookup_map,
         const hb_map_t *klass_map = nullptr) const
  {
    TRACE_SUBSET (this);
    if (unlikely (!inputCount)) return_trace (false);
    const auto input = inputZ.as_array (inputCount - 1);

    const hb_map_t *mapping = klass_map == nullptr ? c->plan->glyph_map : klass_map;
    if (!hb_all (input, mapping)) return_trace (false);
    return_trace (serialize (c->serializer, mapping, lookup_map));
  }

  public:
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this) &&
      hb_barrier () &&
      c->check_range (inputZ.arrayZ,
          inputZ.item_size * (inputCount ? inputCount - 1 : 0) +
          LookupRecord::static_size * lookupCount));
  }

  protected:
  HBUINT16  inputCount;   /* Total number of glyphs in input
           * glyph sequence--includes the first
           * glyph */
  HBUINT16  lookupCount;    /* Number of LookupRecords */
  UnsizedArrayOf<typename Types::HBUINT>
    inputZ;     /* Array of match inputs--start with
           * second glyph */
/*UnsizedArrayOf<LookupRecord>
    lookupRecordX;*/  /* Array of LookupRecords--in
           * design order */
  public:
  DEFINE_SIZE_ARRAY (4, inputZ);
};

template <typename Types>
struct RuleSet
{
  using Rule = OT::Rule<Types>;

  bool intersects (const hb_set_t *glyphs,
       ContextClosureLookupContext &lookup_context) const
  {
    return
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_map ([&] (const Rule &_) { return _.intersects (glyphs, lookup_context); })
    | hb_any
    ;
  }

  void collect_first_input_classes (hb_ot_layout_ruleset_digest_t *digest) const
  {
    digest->init ();
    for (unsigned i = 0; i < rule.len; i++)
    {
      const Rule &r = this+rule.arrayZ[i];
      if (r.inputCount <= 1)
      {
  digest->set_full ();
  return;
      }
      digest->add (r.inputZ.arrayZ[0]);
    }
  }

  void depend (hb_depend_context_t *c, unsigned value, ContextDependLookupContext &lookup_context) const
  {
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const Rule &_) { _.depend (c, value, lookup_context); })
    ;
  }

  void closure (hb_closure_context_t *c, unsigned value,
    ContextClosureLookupContext &lookup_context) const
  {
    if (unlikely (c->lookup_limit_exceeded ())) return;

    return
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const Rule &_) { _.closure (c, value, lookup_context); })
    ;
  }

  void closure_lookups (hb_closure_lookups_context_t *c,
                        ContextClosureLookupContext &lookup_context) const
  {
    if (unlikely (c->lookup_limit_exceeded ())) return;
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const Rule &_) { _.closure_lookups (c, lookup_context); })
    ;
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c,
           ContextCollectGlyphsLookupContext &lookup_context) const
  {
    return
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const Rule &_) { _.collect_glyphs (c, lookup_context); })
    ;
  }

  void collect_second_glyphs (hb_set_digest_t *digest,
            const ClassDef *class_def = nullptr) const
  {
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_apply ([=] (const Rule &_) { _.collect_second_glyphs (digest, class_def); })
    ;
  }

  bool would_apply (hb_would_apply_context_t *c,
        const ContextApplyLookupContext &lookup_context) const
  {
    return
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_map ([&] (const Rule &_) { return _.would_apply (c, lookup_context); })
    | hb_any
    ;
  }

  bool apply (hb_ot_apply_context_t *c,
        const ContextApplyLookupContext &lookup_context,
        const hb_ot_layout_ruleset_digest_t *digest = nullptr) const
  {
    TRACE_APPLY (this);

    unsigned num_rules = rule.len;

#ifndef HB_NO_OT_RULESETS_FAST_PATH
    if (HB_OPTIMIZE_SIZE_VAL || num_rules <= 4)
#endif
    {
    slow:
      return_trace (
      + hb_iter (rule)
      | hb_map (hb_add (this))
      | hb_map ([&] (const Rule &_) { return _.apply (c, lookup_context); })
      | hb_any
      )
      ;
    }

    /* This version is optimized for speed by matching the first & second
     * components of the rule here, instead of calling into the matching code.
     *
     * Replicated from LigatureSet::apply(). */

    /* We use the iter_context instead of iter_input, to avoid skipping
     * default-ignorables and such.
     *
     * Related: https://github.com/harfbuzz/harfbuzz/issues/4813
     */
    auto &skippy_iter = c->iter_context;
    skippy_iter.reset (c->buffer->idx);
    skippy_iter.set_match_func (match_always, nullptr);
    skippy_iter.set_glyph_data ((HBUINT16 *) nullptr);
    unsigned unsafe_to = (unsigned) -1, unsafe_to1, unsafe_to2 = 0;
    hb_glyph_info_t *first = nullptr, *second = nullptr;
    bool matched = skippy_iter.next (&unsafe_to1);
    if (likely (matched))
    {
      if (skippy_iter.may_skip (c->buffer->info[skippy_iter.idx]))
      {
  /* Can't use the fast path if eg. the next char is a default-ignorable
   * or other skippable. */
        goto slow;
      }

      first = &c->buffer->info[skippy_iter.idx];
      unsafe_to1 = skippy_iter.idx + 1;

      if (digest && lookup_context.get_value &&
    !digest->may_have (lookup_context.get_value (*first, lookup_context.match_data)))
  {
    c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to1);
    return_trace (false);
  }
    }
    else
    {
      bool unsafe_to_concat = false;
      bool ret =
      + hb_iter (rule)
      | hb_map (hb_add (this))
      | hb_filter ([&] (const Rule &_)
       {
         if (_.inputCount <= 1) return true;
         unsafe_to_concat = true;
         return false;
       })
      | hb_map ([&] (const Rule &_) { return _.apply (c, lookup_context); })
      | hb_any
      ;
      if (unsafe_to_concat)
  c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to1);
      return_trace (ret);
    }
    matched = skippy_iter.next ();
    if (likely (matched))
    {
      if (skippy_iter.may_skip (c->buffer->info[skippy_iter.idx]))
      {
  /* Can't use the fast path if eg. the next char is a default-ignorable
   * or other skippable. */
        goto slow;
      }

      second = &c->buffer->info[skippy_iter.idx];
      unsafe_to2 = skippy_iter.idx + 1;
    }

    auto match_input = lookup_context.funcs.match;
    auto *input_data = lookup_context.match_data;
    for (unsigned int i = 0; i < num_rules; i++)
    {
      const auto &r = this+rule.arrayZ[i];

      const auto &input = r.inputZ;

      if (r.inputCount <= 1 ||
    (!match_input ||
     match_input (*first, input.arrayZ[0], input_data)))
      {
        if (!second ||
      (r.inputCount <= 2 ||
       (!match_input ||
        match_input (*second, input.arrayZ[1], input_data)))
     )
  {
    if (r.apply (c, lookup_context))
    {
      if (unsafe_to != (unsigned) -1)
        c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to);
      return_trace (true);
    }
  }
  else
    unsafe_to = unsafe_to2;
      }
      else
      {
  if (unsafe_to == (unsigned) -1)
    unsafe_to = unsafe_to1;

  // Skip ahead to next possible first glyph match.
  for (; i + 1 < num_rules; i++)
  {
    const auto &r2 = this+rule.arrayZ[i + 1];
    const auto &input2 = r2.inputZ;
    if (r2.inputCount <= 1 || input2.arrayZ[0] != input.arrayZ[0])
      break;
  }
      }
    }
    if (likely (unsafe_to != (unsigned) -1))
      c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to);

    return_trace (false);
  }

  bool subset (hb_subset_context_t *c,
         const hb_map_t *lookup_map,
         const hb_map_t *klass_map = nullptr) const
  {
    TRACE_SUBSET (this);

    auto snap = c->serializer->snapshot ();
    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);

    for (const Offset16To<Rule>& _ : rule)
    {
      if (!_) continue;
      auto o_snap = c->serializer->snapshot ();
      auto *o = out->rule.serialize_append (c->serializer);
      if (unlikely (!o)) continue;

      if (!o->serialize_subset (c, _, this, lookup_map, klass_map))
      {
  out->rule.pop ();
  c->serializer->revert (o_snap);
      }
    }

    bool ret = bool (out->rule);
    if (!ret) c->serializer->revert (snap);

    return_trace (ret);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (rule.sanitize (c, this));
  }

  protected:
  Array16OfOffset16To<Rule>
    rule;     /* Array of Rule tables
           * ordered by preference */
  public:
  DEFINE_SIZE_ARRAY (2, rule);
};


template <typename Types>
struct ContextFormat1_4
{
  using RuleSet = OT::RuleSet<Types>;

  bool intersects (const hb_set_t *glyphs) const
  {
    struct ContextClosureLookupContext lookup_context = {
      {intersects_glyph, intersected_glyph},
      ContextFormat::SimpleContext,
      nullptr
    };

    return
    + hb_zip (this+coverage, ruleSet)
    | hb_filter (*glyphs, hb_first)
    | hb_map (hb_second)
    | hb_map (hb_add (this))
    | hb_map ([&] (const RuleSet &_) { return _.intersects (glyphs, lookup_context); })
    | hb_any
    ;
  }

  bool may_have_non_1to1 () const
  { return true; }

  void depend (hb_depend_context_t *c) const
  {
    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs)) return;
    get_coverage ().intersect_set (*c->glyphs, *cur_active_glyphs);

    ContextDependLookupContext lookup_context = {
      {intersects_glyph, intersected_glyph},
      ContextFormat::SimpleContext,
      nullptr,
      nullptr,  /* intersects_cache */
      nullptr   /* intersected_glyphs_cache */
    };

    + hb_zip (this+coverage, hb_range ((unsigned) ruleSet.len))
    | hb_filter ([&] (hb_codepoint_t _) {
      return c->parent_active_glyphs ().has (_);
    }, hb_first)
    | hb_map ([&](const hb_pair_t<hb_codepoint_t, unsigned> _) { return hb_pair_t<unsigned, const RuleSet&> (_.first, this+ruleSet[_.second]); })
    | hb_apply ([&] (const hb_pair_t<unsigned, const RuleSet&>& _) { _.second.depend (c, _.first, lookup_context); })
    ;

    c->pop_cur_done_glyphs ();
  }

  void closure (hb_closure_context_t *c) const
  {
    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs)) return;
    get_coverage ().intersect_set (c->previous_parent_active_glyphs (), *cur_active_glyphs);

    struct ContextClosureLookupContext lookup_context = {
      {intersects_glyph, intersected_glyph},
      ContextFormat::SimpleContext,
      nullptr
    };

    + hb_zip (this+coverage, hb_range ((unsigned) ruleSet.len))
    | hb_filter ([&] (hb_codepoint_t _) {
      return c->previous_parent_active_glyphs ().has (_);
    }, hb_first)
    | hb_map ([&](const hb_pair_t<hb_codepoint_t, unsigned> _) { return hb_pair_t<unsigned, const RuleSet&> (_.first, this+ruleSet[_.second]); })
    | hb_apply ([&] (const hb_pair_t<unsigned, const RuleSet&>& _) { _.second.closure (c, _.first, lookup_context); })
    ;

    c->pop_cur_done_glyphs ();
  }

  void closure_lookups (hb_closure_lookups_context_t *c) const
  {
    struct ContextClosureLookupContext lookup_context = {
      {intersects_glyph, nullptr},
      ContextFormat::SimpleContext,
      nullptr
    };

    + hb_zip (this+coverage, ruleSet)
    | hb_filter (*c->glyphs, hb_first)
    | hb_map (hb_second)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const RuleSet &_) { _.closure_lookups (c, lookup_context); })
    ;
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    (this+coverage).collect_coverage (c->input);

    struct ContextCollectGlyphsLookupContext lookup_context = {
      {collect_glyph},
      nullptr
    };

    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const RuleSet &_) { _.collect_glyphs (c, lookup_context); })
    ;
  }

  void collect_second_glyphs (hb_set_digest_t *digest) const
  {
    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_apply ([digest] (const RuleSet &_) { _.collect_second_glyphs (digest); })
    ;
  }

  bool would_apply (hb_would_apply_context_t *c) const
  {
    const RuleSet &rule_set = this+ruleSet[(this+coverage).get_coverage (c->glyphs[0])];
    struct ContextApplyLookupContext lookup_context = {
      {match_glyph},
      nullptr
    };
    return rule_set.would_apply (c, lookup_context);
  }

  const Coverage &get_coverage () const { return this+coverage; }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
    if (likely (index == NOT_COVERED))
      return_trace (false);

    const RuleSet &rule_set = this+ruleSet[index];
    struct ContextApplyLookupContext lookup_context = {
      {match_glyph},
      nullptr
    };
    return_trace (rule_set.apply (c, lookup_context));
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
    const hb_map_t &glyph_map = *c->plan->glyph_map;

    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
    out->format = format;

    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;
    hb_sorted_vector_t<hb_codepoint_t> new_coverage;
    + hb_zip (this+coverage, ruleSet)
    | hb_filter (glyphset, hb_first)
    | hb_filter (subset_offset_array (c, out->ruleSet, this, lookup_map), hb_second)
    | hb_map (hb_first)
    | hb_map (glyph_map)
    | hb_sink (new_coverage)
    ;

    out->coverage.serialize_serialize (c->serializer, new_coverage.iter ());
    return_trace (bool (new_coverage));
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (coverage.sanitize (c, this) && ruleSet.sanitize (c, this));
  }

  protected:
  HBUINT16  format;     /* Format identifier--format = 1 */
  typename Types::template OffsetTo<Coverage>
    coverage;   /* Offset to Coverage table--from
           * beginning of table */
  Array16Of<typename Types::template OffsetTo<RuleSet>>
    ruleSet;    /* Array of RuleSet tables
           * ordered by Coverage Index */
  public:
  DEFINE_SIZE_ARRAY (2 + 2 * Types::size, ruleSet);
};


template <typename Types>
struct ContextFormat2_5
{
  using RuleSet = OT::RuleSet<SmallTypes>;

  bool intersects (const hb_set_t *glyphs) const
  {
    if (!(this+coverage).intersects (glyphs))
      return false;

    const ClassDef &class_def = this+classDef;

    hb_map_t cache;
    struct ContextClosureLookupContext lookup_context = {
      {intersects_class, nullptr},
      ContextFormat::ClassBasedContext,
      &class_def,
      &cache
    };

    hb_set_t retained_coverage_glyphs;
    (this+coverage).intersect_set (*glyphs, retained_coverage_glyphs);

    hb_set_t coverage_glyph_classes;
    class_def.intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);


    return
    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_enumerate
    | hb_map ([&] (const hb_pair_t<unsigned, const RuleSet &> p)
        { return class_def.intersects_class (glyphs, p.first) &&
           coverage_glyph_classes.has (p.first) &&
           p.second.intersects (glyphs, lookup_context); })
    | hb_any
    ;
  }

  bool may_have_non_1to1 () const
  { return true; }

  void depend (hb_depend_context_t *c) const
  {
    if (!(this+coverage).intersects (c->glyphs))
      return;

    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs)) return;
    get_coverage ().intersect_set (*c->glyphs, *cur_active_glyphs);

    const ClassDef &class_def = this+classDef;

    hb_map_t cache;
    intersected_class_cache_t intersected_cache;
    ContextDependLookupContext lookup_context = {
      {intersects_class, intersected_class_glyphs},
      ContextFormat::ClassBasedContext,
      &class_def,
      &cache,
      &intersected_cache
    };

    + hb_enumerate (ruleSet)
    | hb_filter ([&] (unsigned _)
    { return class_def.intersects_class (&c->parent_active_glyphs (), _); },
     hb_first)
    | hb_apply ([&] (const hb_pair_t<unsigned, const typename Types::template OffsetTo<RuleSet>&> _)
                {
                  const RuleSet& rule_set = this+_.second;
                  rule_set.depend (c, _.first, lookup_context);
                })
    ;

    c->pop_cur_done_glyphs ();
  }

  void closure (hb_closure_context_t *c) const
  {
    if (!(this+coverage).intersects (c->glyphs))
      return;

    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs)) return;
    get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
           *cur_active_glyphs);

    const ClassDef &class_def = this+classDef;

    hb_map_t cache;
    intersected_class_cache_t intersected_cache;
    struct ContextClosureLookupContext lookup_context = {
      {intersects_class, intersected_class_glyphs},
      ContextFormat::ClassBasedContext,
      &class_def,
      &cache,
      &intersected_cache
    };

    + hb_enumerate (ruleSet)
    | hb_filter ([&] (unsigned _)
    { return class_def.intersects_class (&c->parent_active_glyphs (), _); },
     hb_first)
    | hb_apply ([&] (const hb_pair_t<unsigned, const typename Types::template OffsetTo<RuleSet>&> _)
                {
                  const RuleSet& rule_set = this+_.second;
                  rule_set.closure (c, _.first, lookup_context);
                })
    ;

    c->pop_cur_done_glyphs ();
  }

  void closure_lookups (hb_closure_lookups_context_t *c) const
  {
    if (!(this+coverage).intersects (c->glyphs))
      return;

    const ClassDef &class_def = this+classDef;

    hb_map_t cache;
    struct ContextClosureLookupContext lookup_context = {
      {intersects_class, nullptr},
      ContextFormat::ClassBasedContext,
      &class_def,
      &cache
    };

    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_enumerate
    | hb_filter ([&] (const hb_pair_t<unsigned, const RuleSet &> p)
    { return class_def.intersects_class (c->glyphs, p.first); })
    | hb_map (hb_second)
    | hb_apply ([&] (const RuleSet & _)
    { _.closure_lookups (c, lookup_context); });
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    (this+coverage).collect_coverage (c->input);

    const ClassDef &class_def = this+classDef;
    struct ContextCollectGlyphsLookupContext lookup_context = {
      {collect_class},
      &class_def
    };

    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const RuleSet &_) { _.collect_glyphs (c, lookup_context); })
    ;
  }

  void collect_second_glyphs (hb_set_digest_t *digest) const
  {
    const ClassDef &class_def = this+classDef;
    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_apply ([=, &class_def] (const RuleSet &_) { _.collect_second_glyphs (digest, &class_def); })
    ;
  }

  bool would_apply (hb_would_apply_context_t *c) const
  {
    const ClassDef &class_def = this+classDef;
    unsigned int index = class_def.get_class (c->glyphs[0]);
    const RuleSet &rule_set = this+ruleSet[index];
    struct ContextApplyLookupContext lookup_context = {
      {match_class},
      &class_def
    };
    return rule_set.would_apply (c, lookup_context);
  }

  const Coverage &get_coverage () const { return this+coverage; }

  unsigned cache_cost () const
  {
    return (this+classDef).cost ();
  }
  static bool cache_func (hb_ot_apply_context_t *c, hb_ot_subtable_cache_op_t op)
  {
    return context_cache_func (c, op);
  }

  struct external_cache_t
  {
    hb_ot_layout_binary_cache_t coverage;
    hb_ot_layout_ruleset_digest_t rule_sets[HB_VAR_ARRAY];
  };
  void *external_cache_create () const
  {
    unsigned count = ruleSet.len;
    unsigned size = sizeof (external_cache_t) -
        HB_VAR_ARRAY * sizeof (hb_ot_layout_ruleset_digest_t) +
        count * sizeof (hb_ot_layout_ruleset_digest_t);
    external_cache_t *cache = (external_cache_t *) hb_malloc (size);
    if (likely (cache))
    {
      cache->coverage.clear ();
      for (unsigned i = 0; i < count; i++)
  (this+ruleSet[i]).collect_first_input_classes (&cache->rule_sets[i]);
    }
    return cache;
  }
  bool apply_cached (hb_ot_apply_context_t *c, void *external_cache) const { return _apply (c, true, external_cache); }
  bool apply (hb_ot_apply_context_t *c, void *external_cache) const { return _apply (c, false, external_cache); }
  bool _apply (hb_ot_apply_context_t *c, bool cached, void *external_cache) const
  {
    TRACE_APPLY (this);
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    external_cache_t *cache = (external_cache_t *) external_cache;
    unsigned int index = (this+coverage).get_coverage_binary (c->buffer->cur().codepoint, cache ? &cache->coverage : nullptr);
#else
    unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
#endif
    if (index == NOT_COVERED) return_trace (false);

    const ClassDef &class_def = this+classDef;

    struct ContextApplyLookupContext lookup_context = {
      {cached ? match_class_cached : match_class},
      &class_def,
      cached ? get_class_cached_value : get_class_value
    };

    index = cached ? get_class_cached (class_def, c->buffer->cur()) : class_def.get_class (c->buffer->cur().codepoint);
    const RuleSet &rule_set = this+ruleSet[index];
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    const hb_ot_layout_ruleset_digest_t *digest = cache && index < ruleSet.len ? &cache->rule_sets[index] : nullptr;
#else
    const hb_ot_layout_ruleset_digest_t *digest = nullptr;
#endif
    return_trace (rule_set.apply (c, lookup_context, digest));
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
    out->format = format;
    if (unlikely (!out->coverage.serialize_subset (c, coverage, this)))
      return_trace (false);

    hb_map_t klass_map;
    out->classDef.serialize_subset (c, classDef, this, &klass_map);

    const hb_set_t* glyphset = c->plan->glyphset_gsub ();
    hb_set_t retained_coverage_glyphs;
    (this+coverage).intersect_set (*glyphset, retained_coverage_glyphs);

    hb_set_t coverage_glyph_classes;
    (this+classDef).intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);

    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;
    bool ret = true;
    int non_zero_index = -1, index = 0;
    auto snapshot = c->serializer->snapshot();
    for (const auto& _ : + hb_enumerate (ruleSet)
       | hb_filter (klass_map, hb_first))
    {
      auto *o = out->ruleSet.serialize_append (c->serializer);
      if (unlikely (!o))
      {
  ret = false;
  break;
      }

      if (coverage_glyph_classes.has (_.first) &&
    o->serialize_subset (c, _.second, this, lookup_map, &klass_map)) {
  non_zero_index = index;
        snapshot = c->serializer->snapshot();
      }

      index++;
    }

    if (!ret || non_zero_index == -1) return_trace (false);

    //prune empty trailing ruleSets
    --index;
    while (index > non_zero_index)
    {
      out->ruleSet.pop ();
      index--;
    }
    c->serializer->revert (snapshot);

    return_trace (bool (out->ruleSet));
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (coverage.sanitize (c, this) && classDef.sanitize (c, this) && ruleSet.sanitize (c, this));
  }

  protected:
  HBUINT16  format;     /* Format identifier--format = 2 */
  typename Types::template OffsetTo<Coverage>
    coverage;   /* Offset to Coverage table--from
           * beginning of table */
  typename Types::template OffsetTo<ClassDef>
    classDef;   /* Offset to glyph ClassDef table--from
           * beginning of table */
  Array16Of<typename Types::template OffsetTo<RuleSet>>
    ruleSet;    /* Array of RuleSet tables
           * ordered by class */
  public:
  DEFINE_SIZE_ARRAY (4 + 2 * Types::size, ruleSet);
};


struct ContextFormat3
{
  using RuleSet = OT::RuleSet<SmallTypes>;

  bool intersects (const hb_set_t *glyphs) const
  {
    if (!(this+coverageZ[0]).intersects (glyphs))
      return false;

    struct ContextClosureLookupContext lookup_context = {
      {intersects_coverage, nullptr},
      ContextFormat::CoverageBasedContext,
      this
    };
    return context_intersects (glyphs,
             glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
             lookup_context);
  }

  bool may_have_non_1to1 () const
  { return true; }

  void depend (hb_depend_context_t *c) const
  {
    if (!(this+coverageZ[0]).intersects (c->glyphs))
      return;

    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs)) return;
    get_coverage ().intersect_set (*c->glyphs, *cur_active_glyphs);

    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
    ContextDependLookupContext lookup_context = {
      {intersects_coverage, intersected_coverage_glyphs},
      ContextFormat::CoverageBasedContext,
      this,
      nullptr,  /* intersects_cache */
      nullptr   /* intersected_glyphs_cache */
    };
    context_depend_lookup (c,
         glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
         lookupCount, lookupRecord,
         this,
         coverageZ[0], lookup_context);

    c->pop_cur_done_glyphs ();
  }

  void closure (hb_closure_context_t *c) const
  {
    if (!(this+coverageZ[0]).intersects (c->glyphs))
      return;

    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs)) return;
    get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
           *cur_active_glyphs);

    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
    struct ContextClosureLookupContext lookup_context = {
      {intersects_coverage, intersected_coverage_glyphs},
      ContextFormat::CoverageBasedContext,
      this
    };
    context_closure_lookup (c,
          glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
          lookupCount, lookupRecord,
          0, lookup_context);

    c->pop_cur_done_glyphs ();
  }

  void closure_lookups (hb_closure_lookups_context_t *c) const
  {
    if (!intersects (c->glyphs))
      return;
    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
    recurse_lookups (c, lookupCount, lookupRecord);
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    (this+coverageZ[0]).collect_coverage (c->input);

    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
    struct ContextCollectGlyphsLookupContext lookup_context = {
      {collect_coverage},
      this
    };

    context_collect_glyphs_lookup (c,
           glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
           lookupCount, lookupRecord,
           lookup_context);
  }

  void collect_second_glyphs (hb_set_digest_t *digest) const
  {
    if (glyphCount <= 1)
      *digest = hb_set_digest_t::full ();
    else
      (this+coverageZ[1]).collect_coverage (digest);
  }

  bool would_apply (hb_would_apply_context_t *c) const
  {
    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
    struct ContextApplyLookupContext lookup_context = {
      {match_coverage},
      this
    };
    return context_would_apply_lookup (c,
               glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
               lookupCount, lookupRecord,
               lookup_context);
  }

  const Coverage &get_coverage () const { return this+coverageZ[0]; }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    unsigned int index = (this+coverageZ[0]).get_coverage (c->buffer->cur().codepoint);
    if (index == NOT_COVERED) return_trace (false);

    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
    struct ContextApplyLookupContext lookup_context = {
      {match_coverage},
      this
    };
    return_trace (context_apply_lookup (c, glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1), lookupCount, lookupRecord, lookup_context));
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    auto *out = c->serializer->start_embed (this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);

    out->format = format;
    out->glyphCount = glyphCount;

    auto coverages = coverageZ.as_array (glyphCount);

    for (const Offset16To<Coverage>& offset : coverages)
    {
      /* TODO(subset) This looks like should not be necessary to write this way. */
      auto *o = c->serializer->allocate_size<Offset16To<Coverage>> (Offset16To<Coverage>::static_size);
      if (unlikely (!o)) return_trace (false);
      if (!o->serialize_subset (c, offset, this)) return_trace (false);
    }

    const auto& lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>> (coverageZ.as_array (glyphCount));
    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;


    unsigned count = serialize_lookuprecord_array (c->serializer, lookupRecord.as_array (lookupCount), lookup_map);
    return_trace (c->serializer->check_assign (out->lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    if (unlikely (!c->check_struct (this))) return_trace (false);
    hb_barrier ();
    unsigned int count = glyphCount;
    if (unlikely (!count)) return_trace (false); /* We want to access coverageZ[0] freely. */
    if (unlikely (!c->check_array (coverageZ.arrayZ, count))) return_trace (false);
    for (unsigned int i = 0; i < count; i++)
      if (unlikely (!coverageZ[i].sanitize (c, this))) return_trace (false);
    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
    return_trace (likely (c->check_array (lookupRecord, lookupCount)));
  }

  protected:
  HBUINT16  format;     /* Format identifier--format = 3 */
  HBUINT16  glyphCount;   /* Number of glyphs in the input glyph
           * sequence */
  HBUINT16  lookupCount;    /* Number of LookupRecords */
  UnsizedArrayOf<Offset16To<Coverage>>
    coverageZ;    /* Array of offsets to Coverage
           * table in glyph sequence order */
/*UnsizedArrayOf<LookupRecord>
    lookupRecordX;*/  /* Array of LookupRecords--in
           * design order */
  public:
  DEFINE_SIZE_ARRAY (6, coverageZ);
};

struct Context
{
  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  {
    if (unlikely (!c->may_dispatch (this, &u.format.v))) return c->no_dispatch_return_value ();
    TRACE_DISPATCH (this, u.format.v);
    switch (u.format.v) {
    case 1: hb_barrier (); return_trace (c->dispatch (u.format1, std::forward<Ts> (ds)...));
    case 2: hb_barrier (); return_trace (c->dispatch (u.format2, std::forward<Ts> (ds)...));
    case 3: hb_barrier (); return_trace (c->dispatch (u.format3, std::forward<Ts> (ds)...));
#ifndef HB_NO_BEYOND_64K
    case 4: hb_barrier (); return_trace (c->dispatch (u.format4, std::forward<Ts> (ds)...));
    case 5: hb_barrier (); return_trace (c->dispatch (u.format5, std::forward<Ts> (ds)...));
#endif
    default:return_trace (c->default_return_value ());
    }
  }

  protected:
  union {
  struct { HBUINT16 v; }  format;   /* Format identifier */
  ContextFormat1_4<SmallTypes>  format1;
  ContextFormat2_5<SmallTypes>  format2;
  ContextFormat3    format3;
#ifndef HB_NO_BEYOND_64K
  ContextFormat1_4<MediumTypes> format4;
  ContextFormat2_5<MediumTypes> format5;
#endif
  } u;
};


/* Chaining Contextual lookups */

struct ChainContextClosureLookupContext
{
  ContextClosureFuncs funcs;
  ContextFormat context_format;
  const void *intersects_data[3];
  void *intersects_cache[3];
  void *intersected_glyphs_cache;
};

typedef ChainContextClosureLookupContext ChainContextDependLookupContext;

struct ChainContextCollectGlyphsLookupContext
{
  ContextCollectGlyphsFuncs funcs;
  const void *collect_data[3];
};

struct ChainContextApplyLookupContext
{
  ChainContextApplyFuncs funcs;
  const void *match_data[3];
  get_value_func_t get_input_value;
};

template <typename HBUINT>
static inline bool chain_context_intersects (const hb_set_t *glyphs,
               unsigned int backtrackCount,
               const HBUINT backtrack[],
               unsigned int inputCount, /* Including the first glyph (not matched) */
               const HBUINT input[], /* Array of input values--start with second glyph */
               unsigned int lookaheadCount,
               const HBUINT lookahead[],
               ChainContextClosureLookupContext &lookup_context)
{
  bool bt_ok = array_is_subset_of (glyphs,
           backtrackCount, backtrack,
           lookup_context.funcs.intersects,
           lookup_context.intersects_data[0],
           lookup_context.intersects_cache[0]);
  bool in_ok = array_is_subset_of (glyphs,
           inputCount ? inputCount - 1 : 0, input,
           lookup_context.funcs.intersects,
           lookup_context.intersects_data[1],
           lookup_context.intersects_cache[1]);
  bool la_ok = array_is_subset_of (glyphs,
           lookaheadCount, lookahead,
           lookup_context.funcs.intersects,
           lookup_context.intersects_data[2],
           lookup_context.intersects_cache[2]);

  return bt_ok && in_ok && la_ok;
}

template <typename HBUINT>
static inline void chain_context_closure_lookup (hb_closure_context_t *c,
             unsigned int backtrackCount,
             const HBUINT backtrack[],
             unsigned int inputCount, /* Including the first glyph (not matched) */
             const HBUINT input[], /* Array of input values--start with second glyph */
             unsigned int lookaheadCount,
             const HBUINT lookahead[],
             unsigned int lookupCount,
             const LookupRecord lookupRecord[],
             unsigned value,
             ChainContextClosureLookupContext &lookup_context)
{
  if (chain_context_intersects (c->glyphs,
        backtrackCount, backtrack,
        inputCount, input,
        lookaheadCount, lookahead,
        lookup_context))
    context_closure_recurse_lookups (c,
         inputCount, input,
         lookupCount, lookupRecord,
         value,
         lookup_context.context_format,
         lookup_context.intersects_data[1],
         lookup_context.funcs.intersected_glyphs,
         lookup_context.intersected_glyphs_cache);
}

template <typename HBUINT>
static inline void chain_context_depend_lookup (hb_depend_context_t *c,
            unsigned int backtrackCount,
            const HBUINT backtrack[],
            unsigned int inputCount, /* Including the first glyph (not matched) */
            const HBUINT input[], /* Array of input values--start with second glyph */
            unsigned int lookaheadCount,
            const HBUINT lookahead[],
            unsigned int lookupCount,
            const LookupRecord lookupRecord[],
            const void *rule,
            unsigned value,
            ChainContextDependLookupContext &lookup_context)
{
  if (!chain_context_intersects (c->glyphs,
         backtrackCount, backtrack,
         inputCount, input,
         lookaheadCount, lookahead,
         lookup_context))
    return;

  hb_depend_context_t::depend_scratch_t *scratch = c->acquire_depend_scratch ();
  if (unlikely (!scratch))
    return;
  HB_SCOPE_GUARD (c->release_depend_scratch (scratch));

  bool context_sets_cached = context_depend_sets_are_cached (
    c, inputCount, lookupCount, lookupRecord, rule, value,
    lookup_context.context_format, lookup_context.intersects_data[1],
    &scratch->cached_context_sets);
  if (unlikely (!c->depend_data->successful))
    return;
  if (context_sets_cached)
  {
    context_depend_recurse_lookups (c,
            inputCount, input,
            lookupCount, lookupRecord,
            rule,
            value,
            lookup_context.context_format,
            lookup_context.intersects_data[1],
            lookup_context.funcs.intersected_glyphs,
            lookup_context.intersected_glyphs_cache,
            scratch->preliminary_context,
            nullptr,
            &scratch->cached_context_sets,
            scratch);
    return;
  }

  /* Cache misses and rules without valid records still perform the original
   * dependency-set interning in its observable order. */
  hb_set_t &position_scratch = scratch->position_scratch;
  hb_vector_t<const hb_set_t *> &backtrack_sets = scratch->backtrack_sets;
  hb_vector_t<const hb_set_t *> &lookahead_sets = scratch->lookahead_sets;

  /* Extract backtrack glyphs */
  for (unsigned i = 0; i < backtrackCount; i++)
  {
    const hb_set_t *pos_glyphs = depend_position_glyphs (
      c, lookup_context.context_format, lookup_context.intersects_data[0],
      backtrack[i], false, &position_scratch);
    if (unlikely (!pos_glyphs))
      return;
    if (!pos_glyphs->is_empty ())
    {
      if (unlikely (!backtrack_sets.push_or_fail (pos_glyphs)))
      {
        c->depend_data->fail ();
        return;
      }
    }
  }

  /* Extract lookahead glyphs */
  for (unsigned i = 0; i < lookaheadCount; i++)
  {
    const hb_set_t *pos_glyphs = depend_position_glyphs (
      c, lookup_context.context_format, lookup_context.intersects_data[2],
      lookahead[i], false, &position_scratch);
    if (unlikely (!pos_glyphs))
      return;
    if (!pos_glyphs->is_empty ())
    {
      if (unlikely (!lookahead_sets.push_or_fail (pos_glyphs)))
      {
        c->depend_data->fail ();
        return;
      }
    }
  }

  /* Build preliminary_context with backtrack + lookahead encoded */
  hb_set_t &preliminary_context = scratch->preliminary_context;
  for (const hb_set_t *back_set : backtrack_sets)
  {
    if (back_set->get_population () == 1) {
      preliminary_context.add (back_set->get_min ());  // Direct glyph
    } else if (back_set->get_population () > 1) {
      hb_codepoint_t set_idx = lookup_context.context_format == ContextFormat::SimpleContext
        ? c->depend_data->find_or_create_context_set (*back_set)
        : c->find_or_create_cached_context_set (back_set);
      if (unlikely (set_idx == HB_CODEPOINT_INVALID))
        return;
      preliminary_context.add (HB_DEPEND_CONTEXT_SET_FLAG | set_idx);  // Encoded set reference
    }
  }
  for (const hb_set_t *look_set : lookahead_sets)
  {
    if (look_set->get_population () == 1) {
      preliminary_context.add (look_set->get_min ());  // Direct glyph
    } else if (look_set->get_population () > 1) {
      hb_codepoint_t set_idx = lookup_context.context_format == ContextFormat::SimpleContext
        ? c->depend_data->find_or_create_context_set (*look_set)
        : c->find_or_create_cached_context_set (look_set);
      if (unlikely (set_idx == HB_CODEPOINT_INVALID))
        return;
      preliminary_context.add (HB_DEPEND_CONTEXT_SET_FLAG | set_idx);  // Encoded set reference
    }
  }
  if (unlikely (preliminary_context.in_error ()))
  {
    c->depend_data->fail ();
    return;
  }

  /* Build glyph sets for ALL input positions */
  hb_vector_t<const hb_set_t *> &input_position_glyphs = scratch->input_position_glyphs;

  if (!context_sets_cached)
  {
    /* Position 0 (first input coverage/class/glyph) — must be in both the
     * class AND the coverage, so intersect with parent_active_glyphs. */
    const hb_set_t *pos0_glyphs = depend_position_glyphs (
      c, lookup_context.context_format, lookup_context.intersects_data[1], value,
      true, &position_scratch, &scratch->compact_workspace);
    if (unlikely (!pos0_glyphs ||
      !input_position_glyphs.push_or_fail (pos0_glyphs)))
    {
      c->depend_data->fail ();
      return;
    }

    /* Positions 1+ (Input array) */
    for (unsigned i = 0; i + 1 < inputCount; i++)
    {
      const hb_set_t *pos_glyphs = depend_position_glyphs (
  c, lookup_context.context_format, lookup_context.intersects_data[1],
  input[i], false, &position_scratch);
      if (unlikely (!pos_glyphs ||
        !input_position_glyphs.push_or_fail (pos_glyphs)))
      {
  c->depend_data->fail ();
  return;
      }
    }
  }

  context_depend_recurse_lookups (c,
          inputCount, input,
          lookupCount, lookupRecord,
          rule,
          value,
          lookup_context.context_format,
          lookup_context.intersects_data[1],
          lookup_context.funcs.intersected_glyphs,
          lookup_context.intersected_glyphs_cache,
          preliminary_context,
          context_sets_cached ? nullptr : &input_position_glyphs,
          context_sets_cached ? &scratch->cached_context_sets : nullptr,
          scratch);
}

template <typename HBUINT>
static inline void chain_context_collect_glyphs_lookup (hb_collect_glyphs_context_t *c,
              unsigned int backtrackCount,
              const HBUINT backtrack[],
              unsigned int inputCount, /* Including the first glyph (not matched) */
              const HBUINT input[], /* Array of input values--start with second glyph */
              unsigned int lookaheadCount,
              const HBUINT lookahead[],
              unsigned int lookupCount,
              const LookupRecord lookupRecord[],
              ChainContextCollectGlyphsLookupContext &lookup_context)
{
  collect_array (c, c->before,
     backtrackCount, backtrack,
     lookup_context.funcs.collect, lookup_context.collect_data[0]);
  collect_array (c, c->input,
     inputCount ? inputCount - 1 : 0, input,
     lookup_context.funcs.collect, lookup_context.collect_data[1]);
  collect_array (c, c->after,
     lookaheadCount, lookahead,
     lookup_context.funcs.collect, lookup_context.collect_data[2]);
  recurse_lookups (c,
       lookupCount, lookupRecord);
}

template <typename HBUINT>
static inline bool chain_context_would_apply_lookup (hb_would_apply_context_t *c,
                 unsigned int backtrackCount,
                 const HBUINT backtrack[] HB_UNUSED,
                 unsigned int inputCount, /* Including the first glyph (not matched) */
                 const HBUINT input[], /* Array of input values--start with second glyph */
                 unsigned int lookaheadCount,
                 const HBUINT lookahead[] HB_UNUSED,
                 unsigned int lookupCount HB_UNUSED,
                 const LookupRecord lookupRecord[] HB_UNUSED,
                 const ChainContextApplyLookupContext &lookup_context)
{
  return (c->zero_context ? !backtrackCount && !lookaheadCount : true)
      && would_match_input (c,
          inputCount, input,
          lookup_context.funcs.match[1], lookup_context.match_data[1]);
}

template <typename HBUINT>
static inline bool chain_context_apply_lookup (hb_ot_apply_context_t *c,
                 unsigned int backtrackCount,
                 const HBUINT backtrack[],
                 unsigned int inputCount, /* Including the first glyph (not matched) */
                 const HBUINT input[], /* Array of input values--start with second glyph */
                 unsigned int lookaheadCount,
                 const HBUINT lookahead[],
                 unsigned int lookupCount,
                 const LookupRecord lookupRecord[],
                 const ChainContextApplyLookupContext &lookup_context)
{
  if (unlikely (inputCount > HB_MAX_CONTEXT_LENGTH)) return false;

  unsigned start_index = c->buffer->out_len;
  unsigned end_index = c->buffer->idx;
  unsigned match_end = 0;
  bool ret = true;
  if (!(match_input (c,
         inputCount, input,
         lookup_context.funcs.match[1], lookup_context.match_data[1],
         &match_end) && (end_index = match_end)
       && match_lookahead (c,
         lookaheadCount, lookahead,
         lookup_context.funcs.match[2], lookup_context.match_data[2],
         match_end, &end_index)))
  {
    c->buffer->unsafe_to_concat (c->buffer->idx, end_index);
    return false;
  }

  if (!match_backtrack (c,
      backtrackCount, backtrack,
      lookup_context.funcs.match[0], lookup_context.match_data[0],
      &start_index))
  {
    c->buffer->unsafe_to_concat_from_outbuffer (start_index, end_index);
    return false;
  }

  c->buffer->unsafe_to_break_from_outbuffer (start_index, end_index);
  apply_lookup (c,
    inputCount,
    lookupCount, lookupRecord,
    match_end);

  return ret;
}

template <typename Types>
struct ChainRule
{
  template <typename T>
  friend struct ChainRuleSet;

  bool intersects (const hb_set_t *glyphs, ChainContextClosureLookupContext &lookup_context) const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    return chain_context_intersects (glyphs,
             backtrack.len, backtrack.arrayZ,
             input.lenP1, input.arrayZ,
             lookahead.len, lookahead.arrayZ,
             lookup_context);
  }

  void depend (hb_depend_context_t *c, unsigned value, ChainContextDependLookupContext &lookup_context) const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    chain_context_depend_lookup (c,
         backtrack.len, backtrack.arrayZ,
         input.lenP1, input.arrayZ,
         lookahead.len, lookahead.arrayZ,
         lookup.len, lookup.arrayZ,
         this,
         value,
         lookup_context);
  }

  void closure (hb_closure_context_t *c, unsigned value,
    ChainContextClosureLookupContext &lookup_context) const
  {
    if (unlikely (c->lookup_limit_exceeded ())) return;

    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    chain_context_closure_lookup (c,
          backtrack.len, backtrack.arrayZ,
          input.lenP1, input.arrayZ,
          lookahead.len, lookahead.arrayZ,
          lookup.len, lookup.arrayZ,
          value,
          lookup_context);
  }

  void closure_lookups (hb_closure_lookups_context_t *c,
                        ChainContextClosureLookupContext &lookup_context) const
  {
    if (unlikely (c->lookup_limit_exceeded ())) return;
    if (!intersects (c->glyphs, lookup_context)) return;

    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    recurse_lookups (c, lookup.len, lookup.arrayZ);
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c,
           ChainContextCollectGlyphsLookupContext &lookup_context) const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    chain_context_collect_glyphs_lookup (c,
           backtrack.len, backtrack.arrayZ,
           input.lenP1, input.arrayZ,
           lookahead.len, lookahead.arrayZ,
           lookup.len, lookup.arrayZ,
           lookup_context);
  }

  void collect_second_glyphs (hb_set_digest_t *digest,
            const ClassDef *input_class_def = nullptr,
            const ClassDef *lookahead_class_def = nullptr) const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);

    unsigned second;
    const ClassDef *class_def;
    if (input.lenP1 > 1)
    {
      second = input.arrayZ[0];
      class_def = input_class_def;
    }
    else if (lookahead.len)
    {
      second = lookahead.arrayZ[0];
      class_def = lookahead_class_def;
    }
    else
    {
      *digest = hb_set_digest_t::full ();
      return;
    }

    if (!class_def)
      digest->add (second);
    else if (!second)
      *digest = hb_set_digest_t::full ();
    else
      class_def->collect_class (digest, second);
  }

  bool would_apply (hb_would_apply_context_t *c,
        const ChainContextApplyLookupContext &lookup_context) const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    return chain_context_would_apply_lookup (c,
               backtrack.len, backtrack.arrayZ,
               input.lenP1, input.arrayZ,
               lookahead.len, lookahead.arrayZ, lookup.len,
               lookup.arrayZ, lookup_context);
  }

  bool apply (hb_ot_apply_context_t *c,
        const ChainContextApplyLookupContext &lookup_context) const
  {
    TRACE_APPLY (this);
    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    return_trace (chain_context_apply_lookup (c,
                backtrack.len, backtrack.arrayZ,
                input.lenP1, input.arrayZ,
                lookahead.len, lookahead.arrayZ, lookup.len,
                lookup.arrayZ, lookup_context));
  }

  template<typename Iterator,
     hb_requires (hb_is_iterator (Iterator))>
  void serialize_array (hb_serialize_context_t *c,
      HBUINT16 len,
      Iterator it) const
  {
    c->copy (len);
    for (const auto g : it)
      c->copy ((HBUINT16) g);
  }

  bool serialize (hb_serialize_context_t *c,
      const hb_map_t *lookup_map,
      const hb_map_t *backtrack_map,
      const hb_map_t *input_map = nullptr,
      const hb_map_t *lookahead_map = nullptr) const
  {
    TRACE_SERIALIZE (this);

    const hb_map_t *mapping = backtrack_map;
    serialize_array (c, backtrack.len, + backtrack.iter ()
               | hb_map (mapping));

    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    if (input_map) mapping = input_map;
    serialize_array (c, input.lenP1, + input.iter ()
             | hb_map (mapping));

    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    if (lookahead_map) mapping = lookahead_map;
    serialize_array (c, lookahead.len, + lookahead.iter ()
               | hb_map (mapping));

    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);

    HBUINT16* lookupCount = c->embed (&(lookup.len));
    if (!lookupCount) return_trace (false);

    unsigned count = serialize_lookuprecord_array (c, lookup.as_array (), lookup_map);
    return_trace (c->check_assign (*lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
  }

  bool subset (hb_subset_context_t *c,
         const hb_map_t *lookup_map,
         const hb_map_t *backtrack_map = nullptr,
         const hb_map_t *input_map = nullptr,
         const hb_map_t *lookahead_map = nullptr) const
  {
    TRACE_SUBSET (this);

    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);

    if (!backtrack_map)
    {
      const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
      if (!hb_all (backtrack, glyphset) ||
    !hb_all (input, glyphset) ||
    !hb_all (lookahead, glyphset))
  return_trace (false);

      serialize (c->serializer, lookup_map, c->plan->glyph_map);
    }
    else
    {
      if (!hb_all (backtrack, backtrack_map) ||
    !hb_all (input, input_map) ||
    !hb_all (lookahead, lookahead_map))
  return_trace (false);

      serialize (c->serializer, lookup_map, backtrack_map, input_map, lookahead_map);
    }

    return_trace (true);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    /* Hyper-optimized sanitized because this is really hot. */
    if (unlikely (!backtrack.len.sanitize (c))) return_trace (false);
    hb_barrier ();
    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    if (unlikely (!input.lenP1.sanitize (c))) return_trace (false);
    hb_barrier ();
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    if (unlikely (!lookahead.len.sanitize (c))) return_trace (false);
    hb_barrier ();
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    return_trace (likely (lookup.sanitize (c)));
  }

  protected:
  Array16Of<typename Types::HBUINT>
    backtrack;    /* Array of backtracking values
           * (to be matched before the input
           * sequence) */
  HeadlessArray16Of<typename Types::HBUINT>
    inputX;     /* Array of input values (start with
           * second glyph) */
  Array16Of<typename Types::HBUINT>
    lookaheadX;   /* Array of lookahead values's (to be
           * matched after the input sequence) */
  Array16Of<LookupRecord>
    lookupX;    /* Array of LookupRecords--in
           * design order) */
  public:
  DEFINE_SIZE_MIN (8);
};

template <typename Types>
struct ChainRuleSet
{
  using ChainRule = OT::ChainRule<Types>;

  bool intersects (const hb_set_t *glyphs, ChainContextClosureLookupContext &lookup_context) const
  {
    return
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_map ([&] (const ChainRule &_) { return _.intersects (glyphs, lookup_context); })
    | hb_any
    ;
  }

  void collect_first_input_classes (hb_ot_layout_ruleset_digest_t *digest) const
  {
    digest->init ();
    for (unsigned i = 0; i < rule.len; i++)
    {
      const ChainRule &r = this+rule.arrayZ[i];
      const auto &input = StructAfter<decltype (r.inputX)> (r.backtrack);
      if (input.lenP1 <= 1)
      {
  digest->set_full ();
  return;
      }
      digest->add (input.arrayZ[0]);
    }
  }
  void depend (hb_depend_context_t *c, unsigned value, ChainContextDependLookupContext &lookup_context) const
  {
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const ChainRule &_) { _.depend (c, value, lookup_context); })
    ;
  }
  void closure (hb_closure_context_t *c, unsigned value, ChainContextClosureLookupContext &lookup_context) const
  {
    if (unlikely (c->lookup_limit_exceeded ())) return;

    return
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const ChainRule &_) { _.closure (c, value, lookup_context); })
    ;
  }

  void closure_lookups (hb_closure_lookups_context_t *c,
                        ChainContextClosureLookupContext &lookup_context) const
  {
    if (unlikely (c->lookup_limit_exceeded ())) return;

    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const ChainRule &_) { _.closure_lookups (c, lookup_context); })
    ;
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c, ChainContextCollectGlyphsLookupContext &lookup_context) const
  {
    return
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const ChainRule &_) { _.collect_glyphs (c, lookup_context); })
    ;
  }

  void collect_second_glyphs (hb_set_digest_t *digest,
            const ClassDef *input_class_def = nullptr,
            const ClassDef *lookahead_class_def = nullptr) const
  {
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_apply ([=] (const ChainRule &_)
    { _.collect_second_glyphs (digest, input_class_def, lookahead_class_def); })
    ;
  }

  bool would_apply (hb_would_apply_context_t *c,
        const ChainContextApplyLookupContext &lookup_context) const
  {
    return
    + hb_iter (rule)
    | hb_map (hb_add (this))
    | hb_map ([&] (const ChainRule &_) { return _.would_apply (c, lookup_context); })
    | hb_any
    ;
  }

  bool apply (hb_ot_apply_context_t *c,
        const ChainContextApplyLookupContext &lookup_context,
        const hb_ot_layout_ruleset_digest_t *digest = nullptr) const
  {
    TRACE_APPLY (this);

    unsigned num_rules = rule.len;

#ifndef HB_NO_OT_RULESETS_FAST_PATH
    if (HB_OPTIMIZE_SIZE_VAL || num_rules <= 4)
#endif
    {
    slow:
      return_trace (
      + hb_iter (rule)
      | hb_map (hb_add (this))
      | hb_map ([&] (const ChainRule &_) { return _.apply (c, lookup_context); })
      | hb_any
      )
      ;
    }

    /* This version is optimized for speed by matching the first & second
     * components of the rule here, instead of calling into the matching code.
     *
     * Replicated from LigatureSet::apply(). */

    /* We use the iter_context instead of iter_input, to avoid skipping
     * default-ignorables and such.
     *
     * Related: https://github.com/harfbuzz/harfbuzz/issues/4813
     */
    auto &skippy_iter = c->iter_context;
    skippy_iter.reset (c->buffer->idx);
    skippy_iter.set_match_func (match_always, nullptr);
    skippy_iter.set_glyph_data ((HBUINT16 *) nullptr);
    unsigned unsafe_to = (unsigned) -1, unsafe_to1, unsafe_to2 = 0;
    hb_glyph_info_t *first = nullptr, *second = nullptr;
    bool matched = skippy_iter.next (&unsafe_to1);
    if (likely (matched))
    {
      if (skippy_iter.may_skip (c->buffer->info[skippy_iter.idx]))
      {
  /* Can't use the fast path if eg. the next char is a default-ignorable
   * or other skippable. */
        goto slow;
      }

      first = &c->buffer->info[skippy_iter.idx];
      unsafe_to1 = skippy_iter.idx + 1;

      if (digest && lookup_context.get_input_value &&
    !digest->may_have (lookup_context.get_input_value (*first, lookup_context.match_data[1])))
  {
    c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to1);
    return_trace (false);
  }
    }
    else
    {
      bool unsafe_to_concat = false;
      bool ret =
      + hb_iter (rule)
      | hb_map (hb_add (this))
      | hb_filter ([&] (const ChainRule &_)
       {
         const auto &input = StructAfter<decltype (_.inputX)> (_.backtrack);
         const auto &lookahead = StructAfter<decltype (_.lookaheadX)> (input);
         if (input.lenP1 <= 1 && lookahead.len == 0) return true;
         unsafe_to_concat = true;
         return false;
       })
      | hb_map ([&] (const ChainRule &_) { return _.apply (c, lookup_context); })
      | hb_any
      ;
      if (unsafe_to_concat)
  c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to1);
      return_trace (ret);
    }
    matched = skippy_iter.next ();
    if (likely (matched))
    {
      if (skippy_iter.may_skip (c->buffer->info[skippy_iter.idx]))
      {
  /* Can't use the fast path if eg. the next char is a default-ignorable
   * or other skippable. */
        goto slow;
      }

      second = &c->buffer->info[skippy_iter.idx];
      unsafe_to2 = skippy_iter.idx + 1;
    }

    auto match_input = lookup_context.funcs.match[1];
    auto match_lookahead = lookup_context.funcs.match[2];
    auto *input_data = lookup_context.match_data[1];
    auto *lookahead_data = lookup_context.match_data[2];
    for (unsigned int i = 0; i < num_rules; i++)
    {
      const auto &r = this+rule.arrayZ[i];

      const auto &input = StructAfter<decltype (r.inputX)> (r.backtrack);
      const auto &lookahead = StructAfter<decltype (r.lookaheadX)> (input);

      unsigned lenP1 = input.lenP1;
      if (lenP1 > 1 ?
     (!match_input ||
      match_input (*first, input.arrayZ[0], input_data))
    :
     (!lookahead.len || !match_lookahead ||
      match_lookahead (*first, lookahead.arrayZ[0], lookahead_data)))
      {
  lenP1 = hb_max (lenP1, 1u);
        if (!second ||
      (lenP1 > 2 ?
       (!match_input ||
        match_input (*second, input.arrayZ[1], input_data))
       :
       (lookahead.len <= 2 - lenP1 || !match_lookahead ||
        match_lookahead (*second, lookahead.arrayZ[2 - lenP1], lookahead_data))))
  {
    if (r.apply (c, lookup_context))
    {
      if (unsafe_to != (unsigned) -1)
        c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to);
      return_trace (true);
    }
  }
  else
    unsafe_to = unsafe_to2;
      }
      else
      {
  if (unsafe_to == (unsigned) -1)
    unsafe_to = unsafe_to1;

  if (lenP1 > 1)
  {
    // Skip ahead to next possible first glyph match.
    for (; i + 1 < num_rules; i++)
    {
      const auto &r2 = this+rule.arrayZ[i + 1];
      const auto &input2 = StructAfter<decltype (r2.inputX)> (r2.backtrack);
      if (input2.lenP1 <= 1 || input2.arrayZ[0] != input.arrayZ[0])
        break;
    }
  }
      }
    }
    if (likely (unsafe_to != (unsigned) -1))
      c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to);

    return_trace (false);
  }

  bool subset (hb_subset_context_t *c,
         const hb_map_t *lookup_map,
         const hb_map_t *backtrack_klass_map = nullptr,
         const hb_map_t *input_klass_map = nullptr,
         const hb_map_t *lookahead_klass_map = nullptr) const
  {
    TRACE_SUBSET (this);

    auto snap = c->serializer->snapshot ();
    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);

    for (const Offset16To<ChainRule>& _ : rule)
    {
      if (!_) continue;
      auto o_snap = c->serializer->snapshot ();
      auto *o = out->rule.serialize_append (c->serializer);
      if (unlikely (!o)) continue;

      if (!o->serialize_subset (c, _, this,
        lookup_map,
        backtrack_klass_map,
        input_klass_map,
        lookahead_klass_map))
      {
  out->rule.pop ();
  c->serializer->revert (o_snap);
      }
    }

    bool ret = bool (out->rule);
    if (!ret) c->serializer->revert (snap);

    return_trace (ret);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (rule.sanitize (c, this));
  }

  protected:
  Array16OfOffset16To<ChainRule>
    rule;     /* Array of ChainRule tables
           * ordered by preference */
  public:
  DEFINE_SIZE_ARRAY (2, rule);
};

template <typename Types>
struct ChainContextFormat1_4
{
  using ChainRuleSet = OT::ChainRuleSet<Types>;

  bool intersects (const hb_set_t *glyphs) const
  {
    struct ChainContextClosureLookupContext lookup_context = {
      {intersects_glyph, intersected_glyph},
      ContextFormat::SimpleContext,
      {nullptr, nullptr, nullptr}
    };

    return
    + hb_zip (this+coverage, ruleSet)
    | hb_filter (*glyphs, hb_first)
    | hb_map (hb_second)
    | hb_map (hb_add (this))
    | hb_map ([&] (const ChainRuleSet &_) { return _.intersects (glyphs, lookup_context); })
    | hb_any
    ;
  }

  bool may_have_non_1to1 () const
  { return true; }

  void depend (hb_depend_context_t *c) const
  {
    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs)) return;
    get_coverage ().intersect_set (*c->glyphs, *cur_active_glyphs);

    ChainContextDependLookupContext lookup_context = {
      {intersects_glyph, intersected_glyph},
      ContextFormat::SimpleContext,
      {nullptr, nullptr, nullptr},
      {nullptr, nullptr, nullptr},  /* intersects_cache */
      nullptr                        /* intersected_glyphs_cache */
    };

    + hb_zip (this+coverage, hb_range ((unsigned) ruleSet.len))
    | hb_filter ([&] (hb_codepoint_t _) {
      return c->parent_active_glyphs ().has (_);
    }, hb_first)
    | hb_map ([&](const hb_pair_t<hb_codepoint_t, unsigned> _) { return hb_pair_t<unsigned, const ChainRuleSet&> (_.first, this+ruleSet[_.second]); })
    | hb_apply ([&] (const hb_pair_t<unsigned, const ChainRuleSet&>& _) { _.second.depend (c, _.first, lookup_context); })
    ;

    c->pop_cur_done_glyphs ();
  }

  void closure (hb_closure_context_t *c) const
  {
    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs)) return;
    get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
           *cur_active_glyphs);

    struct ChainContextClosureLookupContext lookup_context = {
      {intersects_glyph, intersected_glyph},
      ContextFormat::SimpleContext,
      {nullptr, nullptr, nullptr}
    };

    + hb_zip (this+coverage, hb_range ((unsigned) ruleSet.len))
    | hb_filter ([&] (hb_codepoint_t _) {
      return c->previous_parent_active_glyphs ().has (_);
    }, hb_first)
    | hb_map ([&](const hb_pair_t<hb_codepoint_t, unsigned> _) { return hb_pair_t<unsigned, const ChainRuleSet&> (_.first, this+ruleSet[_.second]); })
    | hb_apply ([&] (const hb_pair_t<unsigned, const ChainRuleSet&>& _) { _.second.closure (c, _.first, lookup_context); })
    ;

    c->pop_cur_done_glyphs ();
  }

  void closure_lookups (hb_closure_lookups_context_t *c) const
  {
    struct ChainContextClosureLookupContext lookup_context = {
      {intersects_glyph, nullptr},
      ContextFormat::SimpleContext,
      {nullptr, nullptr, nullptr}
    };

    + hb_zip (this+coverage, ruleSet)
    | hb_filter (*c->glyphs, hb_first)
    | hb_map (hb_second)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const ChainRuleSet &_) { _.closure_lookups (c, lookup_context); })
    ;
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    (this+coverage).collect_coverage (c->input);

    struct ChainContextCollectGlyphsLookupContext lookup_context = {
      {collect_glyph},
      {nullptr, nullptr, nullptr}
    };

    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const ChainRuleSet &_) { _.collect_glyphs (c, lookup_context); })
    ;
  }

  void collect_second_glyphs (hb_set_digest_t *digest) const
  {
    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_apply ([digest] (const ChainRuleSet &_) { _.collect_second_glyphs (digest); })
    ;
  }

  bool would_apply (hb_would_apply_context_t *c) const
  {
    const ChainRuleSet &rule_set = this+ruleSet[(this+coverage).get_coverage (c->glyphs[0])];
    struct ChainContextApplyLookupContext lookup_context = {
      {{match_glyph, match_glyph, match_glyph}},
      {nullptr, nullptr, nullptr}
    };
    return rule_set.would_apply (c, lookup_context);
  }

  const Coverage &get_coverage () const { return this+coverage; }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
    if (index == NOT_COVERED) return_trace (false);

    const ChainRuleSet &rule_set = this+ruleSet[index];
    struct ChainContextApplyLookupContext lookup_context = {
      {{match_glyph, match_glyph, match_glyph}},
      {nullptr, nullptr, nullptr}
    };
    return_trace (rule_set.apply (c, lookup_context));
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
    const hb_map_t &glyph_map = *c->plan->glyph_map;

    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
    out->format = format;

    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;
    hb_sorted_vector_t<hb_codepoint_t> new_coverage;
    + hb_zip (this+coverage, ruleSet)
    | hb_filter (glyphset, hb_first)
    | hb_filter (subset_offset_array (c, out->ruleSet, this, lookup_map), hb_second)
    | hb_map (hb_first)
    | hb_map (glyph_map)
    | hb_sink (new_coverage)
    ;

    out->coverage.serialize_serialize (c->serializer, new_coverage.iter ());
    return_trace (bool (new_coverage));
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (coverage.sanitize (c, this) && ruleSet.sanitize (c, this));
  }

  protected:
  HBUINT16  format;     /* Format identifier--format = 1 */
  typename Types::template OffsetTo<Coverage>
    coverage;   /* Offset to Coverage table--from
           * beginning of table */
  Array16Of<typename Types::template OffsetTo<ChainRuleSet>>
    ruleSet;    /* Array of ChainRuleSet tables
           * ordered by Coverage Index */
  public:
  DEFINE_SIZE_ARRAY (2 + 2 * Types::size, ruleSet);
};

template <typename Types>
struct ChainContextFormat2_5
{
  using ChainRuleSet = OT::ChainRuleSet<SmallTypes>;

  bool intersects (const hb_set_t *glyphs) const
  {
    if (!(this+coverage).intersects (glyphs))
      return false;

    const ClassDef &backtrack_class_def = this+backtrackClassDef;
    const ClassDef &input_class_def = this+inputClassDef;
    const ClassDef &lookahead_class_def = this+lookaheadClassDef;

    hb_map_t caches[3] = {};
    struct ChainContextClosureLookupContext lookup_context = {
      {intersects_class, nullptr},
      ContextFormat::ClassBasedContext,
      {&backtrack_class_def,
       &input_class_def,
       &lookahead_class_def},
      {&caches[0], &caches[1], &caches[2]}
    };

    hb_set_t retained_coverage_glyphs;
    (this+coverage).intersect_set (*glyphs, retained_coverage_glyphs);

    hb_set_t coverage_glyph_classes;
    input_class_def.intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);

    return
    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_enumerate
    | hb_map ([&] (const hb_pair_t<unsigned, const ChainRuleSet &> p)
        { return input_class_def.intersects_class (glyphs, p.first) &&
           coverage_glyph_classes.has (p.first) &&
           p.second.intersects (glyphs, lookup_context); })
    | hb_any
    ;
  }

  bool may_have_non_1to1 () const
  { return true; }

  void depend (hb_depend_context_t *c) const
  {
    if (!(this+coverage).intersects (c->glyphs))
      return;

    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs)) return;
    get_coverage ().intersect_set (*c->glyphs, *cur_active_glyphs);

    const ClassDef &backtrack_class_def = this+backtrackClassDef;
    const ClassDef &input_class_def = this+inputClassDef;
    const ClassDef &lookahead_class_def = this+lookaheadClassDef;

    hb_map_t caches[3] = {};
    intersected_class_cache_t intersected_cache;
    ChainContextDependLookupContext lookup_context = {
      {intersects_class, intersected_class_glyphs},
      ContextFormat::ClassBasedContext,
      {&backtrack_class_def,
       &input_class_def,
       &lookahead_class_def},
      {&caches[0], &caches[1], &caches[2]},
      &intersected_cache
    };

    + hb_enumerate (ruleSet)
    | hb_filter ([&] (unsigned _)
    { return input_class_def.intersects_class (&c->parent_active_glyphs (), _); },
     hb_first)
    | hb_apply ([&] (const hb_pair_t<unsigned, const typename Types::template OffsetTo<ChainRuleSet>&> _)
                {
                  const ChainRuleSet& chainrule_set = this+_.second;
                  chainrule_set.depend (c, _.first, lookup_context);
                })
    ;

    c->pop_cur_done_glyphs ();
  }

  void closure (hb_closure_context_t *c) const
  {
    if (!(this+coverage).intersects (c->glyphs))
      return;

    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs)) return;
    get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
           *cur_active_glyphs);

    const ClassDef &backtrack_class_def = this+backtrackClassDef;
    const ClassDef &input_class_def = this+inputClassDef;
    const ClassDef &lookahead_class_def = this+lookaheadClassDef;

    hb_map_t caches[3] = {};
    intersected_class_cache_t intersected_cache;
    struct ChainContextClosureLookupContext lookup_context = {
      {intersects_class, intersected_class_glyphs},
      ContextFormat::ClassBasedContext,
      {&backtrack_class_def,
       &input_class_def,
       &lookahead_class_def},
      {&caches[0], &caches[1], &caches[2]},
      &intersected_cache
    };

    + hb_enumerate (ruleSet)
    | hb_filter ([&] (unsigned _)
    { return input_class_def.intersects_class (&c->parent_active_glyphs (), _); },
     hb_first)
    | hb_apply ([&] (const hb_pair_t<unsigned, const typename Types::template OffsetTo<ChainRuleSet>&> _)
                {
                  const ChainRuleSet& chainrule_set = this+_.second;
                  chainrule_set.closure (c, _.first, lookup_context);
                })
    ;

    c->pop_cur_done_glyphs ();
  }

  void closure_lookups (hb_closure_lookups_context_t *c) const
  {
    if (!(this+coverage).intersects (c->glyphs))
      return;

    const ClassDef &backtrack_class_def = this+backtrackClassDef;
    const ClassDef &input_class_def = this+inputClassDef;
    const ClassDef &lookahead_class_def = this+lookaheadClassDef;

    hb_map_t caches[3] = {};
    struct ChainContextClosureLookupContext lookup_context = {
      {intersects_class, nullptr},
      ContextFormat::ClassBasedContext,
      {&backtrack_class_def,
       &input_class_def,
       &lookahead_class_def},
      {&caches[0], &caches[1], &caches[2]}
    };

    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_enumerate
    | hb_filter([&] (unsigned klass)
    { return input_class_def.intersects_class (c->glyphs, klass); }, hb_first)
    | hb_map (hb_second)
    | hb_apply ([&] (const ChainRuleSet &_)
    { _.closure_lookups (c, lookup_context); })
    ;
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    (this+coverage).collect_coverage (c->input);

    const ClassDef &backtrack_class_def = this+backtrackClassDef;
    const ClassDef &input_class_def = this+inputClassDef;
    const ClassDef &lookahead_class_def = this+lookaheadClassDef;

    struct ChainContextCollectGlyphsLookupContext lookup_context = {
      {collect_class},
      {&backtrack_class_def,
       &input_class_def,
       &lookahead_class_def}
    };

    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_apply ([&] (const ChainRuleSet &_) { _.collect_glyphs (c, lookup_context); })
    ;
  }

  void collect_second_glyphs (hb_set_digest_t *digest) const
  {
    const ClassDef &input_class_def = this+inputClassDef;
    const ClassDef &lookahead_class_def = this+lookaheadClassDef;
    + hb_iter (ruleSet)
    | hb_map (hb_add (this))
    | hb_apply ([digest, &input_class_def, &lookahead_class_def] (const ChainRuleSet &_)
    { _.collect_second_glyphs (digest, &input_class_def, &lookahead_class_def); })
    ;
  }

  bool would_apply (hb_would_apply_context_t *c) const
  {
    const ClassDef &backtrack_class_def = this+backtrackClassDef;
    const ClassDef &input_class_def = this+inputClassDef;
    const ClassDef &lookahead_class_def = this+lookaheadClassDef;

    unsigned int index = input_class_def.get_class (c->glyphs[0]);
    const ChainRuleSet &rule_set = this+ruleSet[index];
    struct ChainContextApplyLookupContext lookup_context = {
      {{match_class, match_class, match_class}},
      {&backtrack_class_def,
       &input_class_def,
       &lookahead_class_def}
    };
    return rule_set.would_apply (c, lookup_context);
  }

  const Coverage &get_coverage () const { return this+coverage; }

  unsigned cache_cost () const
  {
    return (this+inputClassDef).cost () + (this+lookaheadClassDef).cost ();
  }
  static bool cache_func (hb_ot_apply_context_t *c, hb_ot_subtable_cache_op_t op)
  {
    return context_cache_func (c, op);
  }

  struct external_cache_t
  {
    hb_ot_layout_binary_cache_t coverage;
    hb_ot_layout_mapping_cache_t input_class;
    hb_ot_layout_mapping_cache_t lookahead_class;
    hb_ot_layout_ruleset_digest_t rule_sets[HB_VAR_ARRAY];
  };
  void *external_cache_create () const
  {
    unsigned count = ruleSet.len;
    unsigned size = sizeof (external_cache_t) -
        HB_VAR_ARRAY * sizeof (hb_ot_layout_ruleset_digest_t) +
        count * sizeof (hb_ot_layout_ruleset_digest_t);
    external_cache_t *cache = (external_cache_t *) hb_malloc (size);
    if (likely (cache))
    {
      cache->coverage.clear ();
      cache->input_class.clear ();
      cache->lookahead_class.clear ();
      for (unsigned i = 0; i < count; i++)
  (this+ruleSet[i]).collect_first_input_classes (&cache->rule_sets[i]);
    }
    return cache;
  }
  bool apply_cached (hb_ot_apply_context_t *c, void *external_cache) const { return _apply (c, true, external_cache); }
  bool apply (hb_ot_apply_context_t *c, void *external_cache) const { return _apply (c, false, external_cache); }
  bool _apply (hb_ot_apply_context_t *c, bool cached, void *external_cache) const
  {
    TRACE_APPLY (this);
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    external_cache_t *cache = (external_cache_t *) external_cache;
    unsigned int index = (this+coverage).get_coverage_binary (c->buffer->cur().codepoint, cache ? &cache->coverage : nullptr);
#else
    unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
#endif
    if (index == NOT_COVERED) return_trace (false);

    const ClassDef &backtrack_class_def = this+backtrackClassDef;
    const ClassDef &input_class_def = this+inputClassDef;
    const ClassDef &lookahead_class_def = this+lookaheadClassDef;

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    match_class_cache_data_t input_cache_data = {
      &input_class_def,
      cache ? &cache->input_class : nullptr
    };
    match_class_cache_data_t lookahead_cache_data = {
      &lookahead_class_def,
      cache ? &cache->lookahead_class : nullptr
    };
    const void *input_match_data = cached
      ? static_cast<const void *> (&input_class_def)
      : static_cast<const void *> (&input_cache_data);
    const void *lookahead_match_data = cached
      ? static_cast<const void *> (&lookahead_class_def)
      : static_cast<const void *> (&lookahead_cache_data);
    bool backtrack_uses_lookahead_cache =
      !cached && &backtrack_class_def == &lookahead_class_def;
    const void *backtrack_match_data = backtrack_uses_lookahead_cache
      ? static_cast<const void *> (&lookahead_cache_data)
      : static_cast<const void *> (&backtrack_class_def);
#endif

    /* match_class_caches1 is slightly faster. Use it for lookahead,
     * which is typically longer. */
    struct ChainContextApplyLookupContext lookup_context = {
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
      {{cached && &backtrack_class_def == &lookahead_class_def ? match_class_cached1 :
        backtrack_uses_lookahead_cache ? match_class_cache : match_class,
        cached ? match_class_cached2 : match_class_cache,
        cached ? match_class_cached1 : match_class_cache}},
      {backtrack_match_data,
       input_match_data,
       lookahead_match_data},
      cached ? get_class_cached2_value : get_class_cache_value
#else
      {{cached && &backtrack_class_def == &lookahead_class_def ? match_class_cached1 : match_class,
        cached ? match_class_cached2 : match_class,
        cached ? match_class_cached1 : match_class}},
      {&backtrack_class_def,
       &input_class_def,
       &lookahead_class_def},
      cached ? get_class_cached2_value : get_class_value
#endif
    };

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    index = cached
         ? get_class_cached2 (input_class_def, c->buffer->cur())
         : input_class_def.get_class (c->buffer->cur().codepoint, input_cache_data.cache);
#else
    index = cached
         ? get_class_cached2 (input_class_def, c->buffer->cur())
          : input_class_def.get_class (c->buffer->cur().codepoint);
#endif
    const ChainRuleSet &rule_set = this+ruleSet[index];
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    const hb_ot_layout_ruleset_digest_t *digest = cache && index < ruleSet.len ? &cache->rule_sets[index] : nullptr;
#else
    const hb_ot_layout_ruleset_digest_t *digest = nullptr;
#endif
    return_trace (rule_set.apply (c, lookup_context, digest));
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
    out->format = format;
    out->coverage.serialize_subset (c, coverage, this);

    hb_map_t backtrack_klass_map;
    hb_map_t input_klass_map;
    hb_map_t lookahead_klass_map;

    out->backtrackClassDef.serialize_subset (c, backtrackClassDef, this, &backtrack_klass_map);
    // TODO: subset inputClassDef based on glyphs survived in Coverage subsetting
    out->inputClassDef.serialize_subset (c, inputClassDef, this, &input_klass_map);
    out->lookaheadClassDef.serialize_subset (c, lookaheadClassDef, this, &lookahead_klass_map);

    if (unlikely (!c->serializer->propagate_error (backtrack_klass_map,
               input_klass_map,
               lookahead_klass_map)))
      return_trace (false);

    const hb_set_t* glyphset = c->plan->glyphset_gsub ();
    hb_set_t retained_coverage_glyphs;
    (this+coverage).intersect_set (*glyphset, retained_coverage_glyphs);

    hb_set_t coverage_glyph_classes;
    (this+inputClassDef).intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);

    int non_zero_index = -1, index = 0;
    bool ret = true;
    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;
    auto last_non_zero = c->serializer->snapshot ();
    for (const auto& _ : + hb_enumerate (ruleSet)
       | hb_filter (input_klass_map, hb_first))
    {
      auto *o = out->ruleSet.serialize_append (c->serializer);
      if (unlikely (!o))
      {
  ret = false;
  break;
      }
      if (coverage_glyph_classes.has (_.first) &&
          o->serialize_subset (c, _.second, this,
             lookup_map,
             &backtrack_klass_map,
             &input_klass_map,
             &lookahead_klass_map))
      {
        last_non_zero = c->serializer->snapshot ();
  non_zero_index = index;
      }

      index++;
    }

    if (!ret || non_zero_index == -1) return_trace (false);

    // prune empty trailing ruleSets
    if (index > non_zero_index) {
      c->serializer->revert (last_non_zero);
      out->ruleSet.len = non_zero_index + 1;
    }

    return_trace (bool (out->ruleSet));
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (coverage.sanitize (c, this) &&
      backtrackClassDef.sanitize (c, this) &&
      inputClassDef.sanitize (c, this) &&
      lookaheadClassDef.sanitize (c, this) &&
      ruleSet.sanitize (c, this));
  }

  protected:
  HBUINT16  format;     /* Format identifier--format = 2 */
  typename Types::template OffsetTo<Coverage>
    coverage;   /* Offset to Coverage table--from
           * beginning of table */
  typename Types::template OffsetTo<ClassDef>
    backtrackClassDef;  /* Offset to glyph ClassDef table
           * containing backtrack sequence
           * data--from beginning of table */
  typename Types::template OffsetTo<ClassDef>
    inputClassDef;    /* Offset to glyph ClassDef
           * table containing input sequence
           * data--from beginning of table */
  typename Types::template OffsetTo<ClassDef>
    lookaheadClassDef;  /* Offset to glyph ClassDef table
           * containing lookahead sequence
           * data--from beginning of table */
  Array16Of<typename Types::template OffsetTo<ChainRuleSet>>
    ruleSet;    /* Array of ChainRuleSet tables
           * ordered by class */
  public:
  DEFINE_SIZE_ARRAY (4 + 4 * Types::size, ruleSet);
};

struct ChainContextFormat3
{
  using RuleSet = OT::RuleSet<SmallTypes>;

  bool intersects (const hb_set_t *glyphs) const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);

    if (!(this+input[0]).intersects (glyphs))
      return false;

    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    struct ChainContextClosureLookupContext lookup_context = {
      {intersects_coverage, nullptr},
      ContextFormat::CoverageBasedContext,
      {this, this, this}
    };
    return chain_context_intersects (glyphs,
             backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
             input.len, (const HBUINT16 *) input.arrayZ + 1,
             lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
             lookup_context);
  }

  bool may_have_non_1to1 () const
  { return true; }

  void depend (hb_depend_context_t *c) const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);

    if (!(this+input[0]).intersects (c->glyphs))
      return;

    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs))
      return;
    get_coverage ().intersect_set (*c->glyphs, *cur_active_glyphs);

    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    ChainContextDependLookupContext lookup_context = {
      {intersects_coverage, intersected_coverage_glyphs},
      ContextFormat::CoverageBasedContext,
      {this, this, this},
      {nullptr, nullptr, nullptr},  /* intersects_cache */
      nullptr                        /* intersected_glyphs_cache */
    };
    chain_context_depend_lookup (c,
         backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
         input.len, (const HBUINT16 *) input.arrayZ + 1,
         lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
         lookup.len, lookup.arrayZ,
         this,
         input[0], lookup_context);

    c->pop_cur_done_glyphs ();
  }

  void closure (hb_closure_context_t *c) const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);

    if (!(this+input[0]).intersects (c->glyphs))
      return;

    hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
    if (unlikely (!cur_active_glyphs))
      return;
    get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
           *cur_active_glyphs);

    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    struct ChainContextClosureLookupContext lookup_context = {
      {intersects_coverage, intersected_coverage_glyphs},
      ContextFormat::CoverageBasedContext,
      {this, this, this}
    };
    chain_context_closure_lookup (c,
          backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
          input.len, (const HBUINT16 *) input.arrayZ + 1,
          lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
          lookup.len, lookup.arrayZ,
          0, lookup_context);

    c->pop_cur_done_glyphs ();
  }

  void closure_lookups (hb_closure_lookups_context_t *c) const
  {
    if (!intersects (c->glyphs))
      return;

    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    recurse_lookups (c, lookup.len, lookup.arrayZ);
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);

    (this+input[0]).collect_coverage (c->input);

    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);

    struct ChainContextCollectGlyphsLookupContext lookup_context = {
      {collect_coverage},
      {this, this, this}
    };
    chain_context_collect_glyphs_lookup (c,
           backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
           input.len, (const HBUINT16 *) input.arrayZ + 1,
           lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
           lookup.len, lookup.arrayZ,
           lookup_context);
  }

  void collect_second_glyphs (hb_set_digest_t *digest) const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    if (input.len > 1)
      (this+input[1]).collect_coverage (digest);
    else if (lookahead.len)
      (this+lookahead[0]).collect_coverage (digest);
    else
      *digest = hb_set_digest_t::full ();
  }

  bool would_apply (hb_would_apply_context_t *c) const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    struct ChainContextApplyLookupContext lookup_context = {
      {{match_coverage, match_coverage, match_coverage}},
      {this, this, this}
    };
    return chain_context_would_apply_lookup (c,
               backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
               input.len, (const HBUINT16 *) input.arrayZ + 1,
               lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
               lookup.len, lookup.arrayZ, lookup_context);
  }

  const Coverage &get_coverage () const
  {
    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    return this+input[0];
  }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    const auto &input = StructAfter<decltype (inputX)> (backtrack);

    unsigned int index = (this+input[0]).get_coverage (c->buffer->cur().codepoint);
    if (index == NOT_COVERED) return_trace (false);

    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    struct ChainContextApplyLookupContext lookup_context = {
      {{match_coverage, match_coverage, match_coverage}},
      {this, this, this}
    };
    return_trace (chain_context_apply_lookup (c,
                backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
                input.len, (const HBUINT16 *) input.arrayZ + 1,
                lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
                lookup.len, lookup.arrayZ, lookup_context));
  }

  template<typename Iterator,
     hb_requires (hb_is_iterator (Iterator))>
  bool serialize_coverage_offsets (hb_subset_context_t *c, Iterator it, const void* base) const
  {
    TRACE_SERIALIZE (this);
    auto *out = c->serializer->start_embed<Array16OfOffset16To<Coverage>> ();

    if (unlikely (!c->serializer->allocate_size<HBUINT16> (HBUINT16::static_size)))
      return_trace (false);

    for (auto& offset : it) {
      auto *o = out->serialize_append (c->serializer);
      if (unlikely (!o) || !o->serialize_subset (c, offset, base))
        return_trace (false);
    }

    return_trace (true);
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);

    if (unlikely (!c->serializer->embed (this->format))) return_trace (false);

    if (!serialize_coverage_offsets (c, backtrack.iter (), this))
      return_trace (false);

    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    if (!serialize_coverage_offsets (c, input.iter (), this))
      return_trace (false);

    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    if (!serialize_coverage_offsets (c, lookahead.iter (), this))
      return_trace (false);

    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;

    HBUINT16 *lookupCount = c->serializer->copy<HBUINT16> (lookup.len);
    if (!lookupCount) return_trace (false);

    unsigned count = serialize_lookuprecord_array (c->serializer, lookup.as_array (), lookup_map);
    return_trace (c->serializer->check_assign (*lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    if (unlikely (!backtrack.sanitize (c, this))) return_trace (false);
    hb_barrier ();
    const auto &input = StructAfter<decltype (inputX)> (backtrack);
    if (unlikely (!input.sanitize (c, this))) return_trace (false);
    hb_barrier ();
    if (unlikely (!input.len)) return_trace (false); /* To be consistent with Context. */
    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
    if (unlikely (!lookahead.sanitize (c, this))) return_trace (false);
    hb_barrier ();
    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
    return_trace (likely (lookup.sanitize (c)));
  }

  protected:
  HBUINT16  format;     /* Format identifier--format = 3 */
  Array16OfOffset16To<Coverage>
    backtrack;    /* Array of coverage tables
           * in backtracking sequence, in  glyph
           * sequence order */
  Array16OfOffset16To<Coverage>
    inputX    ; /* Array of coverage
           * tables in input sequence, in glyph
           * sequence order */
  Array16OfOffset16To<Coverage>
    lookaheadX;   /* Array of coverage tables
           * in lookahead sequence, in glyph
           * sequence order */
  Array16Of<LookupRecord>
    lookupX;    /* Array of LookupRecords--in
           * design order) */
  public:
  DEFINE_SIZE_MIN (10);
};

struct ChainContext
{
  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  {
    if (unlikely (!c->may_dispatch (this, &u.format.v))) return c->no_dispatch_return_value ();
    TRACE_DISPATCH (this, u.format.v);
    switch (u.format.v) {
    case 1: hb_barrier (); return_trace (c->dispatch (u.format1, std::forward<Ts> (ds)...));
    case 2: hb_barrier (); return_trace (c->dispatch (u.format2, std::forward<Ts> (ds)...));
    case 3: hb_barrier (); return_trace (c->dispatch (u.format3, std::forward<Ts> (ds)...));
#ifndef HB_NO_BEYOND_64K
    case 4: hb_barrier (); return_trace (c->dispatch (u.format4, std::forward<Ts> (ds)...));
    case 5: hb_barrier (); return_trace (c->dispatch (u.format5, std::forward<Ts> (ds)...));
#endif
    default:return_trace (c->default_return_value ());
    }
  }

  protected:
  union {
  struct { HBUINT16 v; }    format; /* Format identifier */
  ChainContextFormat1_4<SmallTypes> format1;
  ChainContextFormat2_5<SmallTypes> format2;
  ChainContextFormat3     format3;
#ifndef HB_NO_BEYOND_64K
  ChainContextFormat1_4<MediumTypes>  format4;
  ChainContextFormat2_5<MediumTypes>  format5;
#endif
  } u;
};


template <typename T>
struct ExtensionFormat1
{
  unsigned int get_type () const { return extensionLookupType; }

  template <typename X>
  const X& get_subtable () const
  { return this + reinterpret_cast<const Offset32To<typename T::SubTable> &> (extensionOffset); }

  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  {
    if (unlikely (!c->may_dispatch (this, this))) return c->no_dispatch_return_value ();
    TRACE_DISPATCH (this, format);
    return_trace (get_subtable<typename T::SubTable> ().dispatch (c, get_type (), std::forward<Ts> (ds)...));
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  { dispatch (c); }

  /* This is called from may_dispatch() above with hb_sanitize_context_t. */
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this) &&
      hb_barrier () &&
      extensionLookupType != T::SubTable::Extension);
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);

    auto *out = c->serializer->start_embed (this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);

    out->format = format;
    out->extensionLookupType = extensionLookupType;

    const auto& src_offset =
        reinterpret_cast<const Offset32To<typename T::SubTable> &> (extensionOffset);
    auto& dest_offset =
        reinterpret_cast<Offset32To<typename T::SubTable> &> (out->extensionOffset);

    return_trace (dest_offset.serialize_subset (c, src_offset, this, get_type ()));
  }

  protected:
  HBUINT16  format;     /* Format identifier. Set to 1. */
  HBUINT16  extensionLookupType;  /* Lookup type of subtable referenced
           * by ExtensionOffset (i.e. the
           * extension subtable). */
  Offset32  extensionOffset;  /* Offset to the extension subtable,
           * of lookup type subtable. */
  public:
  DEFINE_SIZE_STATIC (8);
};

template <typename T>
struct Extension
{
  unsigned int get_type () const
  {
    switch (u.format.v) {
    case 1: hb_barrier (); return u.format1.get_type ();
    default:return 0;
    }
  }
  template <typename X>
  const X& get_subtable () const
  {
    switch (u.format.v) {
    case 1: hb_barrier (); return u.format1.template get_subtable<typename T::SubTable> ();
    default:return Null (typename T::SubTable);
    }
  }

  // Specialization of dispatch for subset. dispatch() normally just
  // dispatches to the sub table this points too, but for subset
  // we need to run subset on this subtable too.
  template <typename ...Ts>
  typename hb_subset_context_t::return_t dispatch (hb_subset_context_t *c, Ts&&... ds) const
  {
    switch (u.format.v) {
    case 1: hb_barrier (); return u.format1.subset (c);
    default: return c->default_return_value ();
    }
  }

  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  {
    if (unlikely (!c->may_dispatch (this, &u.format.v))) return c->no_dispatch_return_value ();
    TRACE_DISPATCH (this, u.format.v);
    switch (u.format.v) {
    case 1: hb_barrier (); return_trace (u.format1.dispatch (c, std::forward<Ts> (ds)...));
    default:return_trace (c->default_return_value ());
    }
  }

  protected:
  union {
  struct { HBUINT16 v; }  format;   /* Format identifier */
  ExtensionFormat1<T> format1;
  } u;
};


/*
 * GSUB/GPOS Common
 */

struct hb_ot_layout_lookup_accelerator_t
{
  template <typename TLookup>
  static hb_ot_layout_lookup_accelerator_t *create (const TLookup &lookup)
  {
    unsigned count = lookup.get_subtable_count ();

    unsigned size = sizeof (hb_ot_layout_lookup_accelerator_t) -
        HB_VAR_ARRAY * sizeof (hb_accelerate_subtables_context_t::hb_applicable_t) +
        count * sizeof (hb_accelerate_subtables_context_t::hb_applicable_t);

    /* The following is a calloc because when we are collecting subtables,
     * some of them might be invalid and hence not collect; as a result,
     * we might not fill in all the count entries of the subtables array.
     * Zeroing it allows the set digest to gatekeep it without having to
     * initialize it further. */
    auto *thiz = (hb_ot_layout_lookup_accelerator_t *) hb_calloc (1, size);
    if (unlikely (!thiz))
      return nullptr;

    hb_accelerate_subtables_context_t c_accelerate_subtables (thiz->subtables);
    lookup.dispatch (&c_accelerate_subtables);

    /* Invalid subtables do not collect and leave zeroed tail entries
     * (see the calloc note above); trim them so the apply paths never
     * see a null apply func. */
    while (count && !thiz->subtables[count - 1].apply_func)
      count--;

    thiz->digest.init ();
    for (auto& subtable : hb_iter (thiz->subtables, count))
      thiz->digest.union_ (subtable.digest);
    thiz->digest_second = c_accelerate_subtables.digest_second;

    thiz->count = count;

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    thiz->subtable_cache_user_idx = c_accelerate_subtables.subtable_cache_user_idx;

    for (unsigned i = 0; i < count; i++)
      if (i != thiz->subtable_cache_user_idx)
       thiz->subtables[i].apply_cached_func = thiz->subtables[i].apply_func;
#endif

    return thiz;
  }

  void fini ()
  {
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    for (unsigned i = 0; i < count; i++)
      hb_free (subtables[i].external_cache);
#endif
  }

  bool may_have (hb_codepoint_t g) const
  { return digest.may_have (g); }

#ifndef HB_OPTIMIZE_SIZE
  HB_ALWAYS_INLINE
#endif
  bool apply (hb_ot_apply_context_t *c, bool use_cache) const
  {
    if (count == 1)
    {
      /* The accelerator digest is the union of the subtable digests, so
       * for a single subtable it equals that subtable's digest, which the
       * caller has already tested; skip the redundant retest. Zeroed
       * invalid entries were trimmed at create time, so the subtable is
       * always valid here. */
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
      if (use_cache)
  return subtables[0].apply_cached_no_digest (c);
#endif
      return subtables[0].apply_no_digest (c);
    }
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    if (use_cache)
    {
      return
      + hb_iter (hb_iter (subtables, count))
      | hb_map ([&c] (const hb_accelerate_subtables_context_t::hb_applicable_t &_) { return _.apply_cached (c); })
      | hb_any
      ;
    }
    else
#endif
    {
      return
      + hb_iter (hb_iter (subtables, count))
      | hb_map ([&c] (const hb_accelerate_subtables_context_t::hb_applicable_t &_) { return _.apply (c); })
      | hb_any
      ;
    }
    return false;
  }

  bool cache_enter (hb_ot_apply_context_t *c) const
  {
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    return subtable_cache_user_idx != (unsigned) -1 &&
     subtables[subtable_cache_user_idx].cache_enter (c);
#else
    return false;
#endif
  }
  void cache_leave (hb_ot_apply_context_t *c) const
  {
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
    subtables[subtable_cache_user_idx].cache_leave (c);
#endif
  }


  hb_set_digest_t digest;
  hb_set_digest_t digest_second;
  private:
  unsigned count = 0; /* Number of subtables in the array. */
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
  unsigned subtable_cache_user_idx = (unsigned) -1;
#endif
  hb_accelerate_subtables_context_t::hb_applicable_t subtables[HB_VAR_ARRAY];
};

template <typename Types>
struct GSUBGPOSVersion1_2
{
  friend struct GSUBGPOS;

  protected:
  FixedVersion<>version;  /* Version of the GSUB/GPOS table--initially set
         * to 0x00010000u */
  typename Types:: template OffsetTo<ScriptList>
    scriptList; /* ScriptList table */
  typename Types::template OffsetTo<FeatureList>
    featureList;  /* FeatureList table */
  typename Types::template OffsetTo<LookupList<Types>>
    lookupList; /* LookupList table */
  Offset32To<FeatureVariations>
    featureVars;  /* Offset to Feature Variations
           table--from beginning of table
         * (may be NULL).  Introduced
         * in version 0x00010001. */
  public:
  DEFINE_SIZE_MIN (4 + 3 * Types::size);

  size_t get_size () const
  {
    return min_size +
     (version.to_int () >= 0x00010001u ? featureVars.static_size : 0);
  }

  const typename Types::template OffsetTo<LookupList<Types>>* get_lookup_list_offset () const
  {
    return &lookupList;
  }

  template <typename TLookup>
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    typedef List16OfOffsetTo<TLookup, typename Types::HBUINT> TLookupList;
    if (unlikely (!(scriptList.sanitize (c, this) &&
        featureList.sanitize (c, this) &&
        reinterpret_cast<const typename Types::template OffsetTo<TLookupList> &> (lookupList).sanitize (c, this))))
      return_trace (false);

#ifndef HB_NO_VAR
    if (unlikely (!(version.to_int () < 0x00010001u || featureVars.sanitize (c, this))))
      return_trace (false);
#endif

    return_trace (true);
  }

  template <typename TLookup>
  bool subset (hb_subset_layout_context_t *c) const
  {
    TRACE_SUBSET (this);

    auto *out = c->subset_context->serializer->start_embed (this);
    if (unlikely (!c->subset_context->serializer->extend_min (out))) return_trace (false);

    out->version = version;

    typedef LookupOffsetList<TLookup, typename Types::HBUINT> TLookupList;
    reinterpret_cast<typename Types::template OffsetTo<TLookupList> &> (out->lookupList)
  .serialize_subset (c->subset_context,
         reinterpret_cast<const typename Types::template OffsetTo<TLookupList> &> (lookupList),
         this,
         c);

    reinterpret_cast<typename Types::template OffsetTo<RecordListOfFeature> &> (out->featureList)
  .serialize_subset (c->subset_context,
         reinterpret_cast<const typename Types::template OffsetTo<RecordListOfFeature> &> (featureList),
         this,
         c);

    out->scriptList.serialize_subset (c->subset_context,
              scriptList,
              this,
              c);

#ifndef HB_NO_VAR
    if (version.to_int () >= 0x00010001u)
    {
      auto snapshot = c->subset_context->serializer->snapshot ();
      if (!c->subset_context->serializer->extend_min (&out->featureVars))
        return_trace (false);

      // if all axes are pinned all feature vars are dropped.
      bool ret = !c->subset_context->plan->all_axes_pinned
                 && out->featureVars.serialize_subset (c->subset_context, featureVars, this, c);
      if (!ret && version.major == 1)
      {
        c->subset_context->serializer->revert (snapshot);
  out->version.major = 1;
  out->version.minor = 0;
      }
    }
#endif

    return_trace (true);
  }
};

struct GSUBGPOS
{
  size_t get_size () const
  {
    switch (u.version.major) {
    case 1: hb_barrier (); return u.version1.get_size ();
#ifndef HB_NO_BEYOND_64K
    case 2: hb_barrier (); return u.version2.get_size ();
#endif
    default: return u.version.static_size;
    }
  }

  template <typename TLookup>
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    if (unlikely (!u.version.sanitize (c))) return_trace (false);
    hb_barrier ();
    switch (u.version.major) {
    case 1: hb_barrier (); return_trace (u.version1.sanitize<TLookup> (c));
#ifndef HB_NO_BEYOND_64K
    case 2: hb_barrier (); return_trace (u.version2.sanitize<TLookup> (c));
#endif
    default: return_trace (true);
    }
  }

  template <typename TLookup>
  bool subset (hb_subset_layout_context_t *c) const
  {
    switch (u.version.major) {
    case 1: hb_barrier (); return u.version1.subset<TLookup> (c);
#ifndef HB_NO_BEYOND_64K
    case 2: hb_barrier (); return u.version2.subset<TLookup> (c);
#endif
    default: return false;
    }
  }

  const ScriptList &get_script_list () const
  {
    switch (u.version.major) {
    case 1: hb_barrier (); return this+u.version1.scriptList;
#ifndef HB_NO_BEYOND_64K
    case 2: hb_barrier (); return this+u.version2.scriptList;
#endif
    default: return Null (ScriptList);
    }
  }
  const FeatureList &get_feature_list () const
  {
    switch (u.version.major) {
    case 1: hb_barrier (); return this+u.version1.featureList;
#ifndef HB_NO_BEYOND_64K
    case 2: hb_barrier (); return this+u.version2.featureList;
#endif
    default: return Null (FeatureList);
    }
  }
  unsigned int get_lookup_count () const
  {
    switch (u.version.major) {
    case 1: hb_barrier (); return (this+u.version1.lookupList).len;
#ifndef HB_NO_BEYOND_64K
    case 2: hb_barrier (); return (this+u.version2.lookupList).len;
#endif
    default: return 0;
    }
  }
  const Lookup& get_lookup (unsigned int i) const
  {
    switch (u.version.major) {
    case 1: hb_barrier (); return (this+u.version1.lookupList)[i];
#ifndef HB_NO_BEYOND_64K
    case 2: hb_barrier (); return (this+u.version2.lookupList)[i];
#endif
    default: return Null (Lookup);
    }
  }
  const FeatureVariations &get_feature_variations () const
  {
    switch (u.version.major) {
    case 1: hb_barrier (); return (u.version.to_int () >= 0x00010001u && hb_barrier () ? this+u.version1.featureVars : Null (FeatureVariations));
#ifndef HB_NO_BEYOND_64K
    case 2: hb_barrier (); return this+u.version2.featureVars;
#endif
    default: return Null (FeatureVariations);
    }
  }

  bool has_data () const { return u.version.to_int (); }
  unsigned int get_script_count () const
  { return get_script_list ().len; }
  const Tag& get_script_tag (unsigned int i) const
  { return get_script_list ().get_tag (i); }
  unsigned int get_script_tags (unsigned int start_offset,
        unsigned int *script_count /* IN/OUT */,
        hb_tag_t     *script_tags /* OUT */) const
  { return get_script_list ().get_tags (start_offset, script_count, script_tags); }
  const Script& get_script (unsigned int i) const
  { return get_script_list ()[i]; }
  bool find_script_index (hb_tag_t tag, unsigned int *index) const
  { return get_script_list ().find_index (tag, index); }

  unsigned int get_feature_count () const
  { return get_feature_list ().len; }
  hb_tag_t get_feature_tag (unsigned int i) const
  { return i == Index::NOT_FOUND_INDEX ? HB_TAG_NONE : get_feature_list ().get_tag (i); }
  unsigned int get_feature_tags (unsigned int start_offset,
         unsigned int *feature_count /* IN/OUT */,
         hb_tag_t     *feature_tags /* OUT */) const
  { return get_feature_list ().get_tags (start_offset, feature_count, feature_tags); }
  const Feature& get_feature (unsigned int i) const
  { return get_feature_list ()[i]; }
  bool find_feature_index (hb_tag_t tag, unsigned int *index) const
  { return get_feature_list ().find_index (tag, index); }

  bool find_variations_index (const int *coords, unsigned int num_coords,
            unsigned int *index,
            ItemVarStoreInstancer *instancer) const
  {
#ifdef HB_NO_VAR
    *index = FeatureVariations::NOT_FOUND_INDEX;
    return false;
#endif
    return get_feature_variations ().find_index (coords, num_coords, index, instancer);
  }
  const Feature& get_feature_variation (unsigned int feature_index,
          unsigned int variations_index) const
  {
#ifndef HB_NO_VAR
    if (FeatureVariations::NOT_FOUND_INDEX != variations_index &&
  u.version.to_int () >= 0x00010001u)
    {
      const Feature *feature = get_feature_variations ().find_substitute (variations_index,
                    feature_index);
      if (feature)
  return *feature;
    }
#endif
    return get_feature (feature_index);
  }

  void feature_variation_collect_lookups (const hb_set_t *feature_indexes,
            const hb_hashmap_t<unsigned, hb::shared_ptr<hb_set_t>> *feature_record_cond_idx_map,
            hb_set_t       *lookup_indexes /* OUT */) const
  {
#ifndef HB_NO_VAR
    get_feature_variations ().collect_lookups (feature_indexes, feature_record_cond_idx_map, lookup_indexes);
#endif
  }

#ifndef HB_NO_VAR
  void collect_feature_substitutes_with_variations (hb_collect_feature_substitutes_with_var_context_t *c) const
  { get_feature_variations ().collect_feature_substitutes_with_variations (c); }
#endif

  template <typename TLookup>
  void closure_lookups (hb_face_t      *face,
      const hb_set_t *glyphs,
      hb_set_t       *lookup_indexes /* IN/OUT */) const
  {
    hb_set_t visited_lookups, inactive_lookups;
    hb_closure_lookups_context_t c (face, glyphs, &visited_lookups, &inactive_lookups);

    c.set_recurse_func (TLookup::template dispatch_recurse_func<hb_closure_lookups_context_t>);

    for (unsigned lookup_index : *lookup_indexes)
      reinterpret_cast<const TLookup &> (get_lookup (lookup_index)).closure_lookups (&c, lookup_index);

    hb_set_union (lookup_indexes, &visited_lookups);
    hb_set_subtract (lookup_indexes, &inactive_lookups);
  }

  void prune_langsys (const hb_map_t *duplicate_feature_map,
                      const hb_set_t *layout_scripts,
                      hb_hashmap_t<unsigned, hb::unique_ptr<hb_set_t>> *script_langsys_map,
                      hb_set_t       *new_feature_indexes /* OUT */) const
  {
    hb_prune_langsys_context_t c (this, script_langsys_map, duplicate_feature_map, new_feature_indexes);

    unsigned count = get_script_count ();
    for (unsigned script_index = 0; script_index < count; script_index++)
    {
      const Tag& tag = get_script_tag (script_index);
      if (!layout_scripts->has (tag)) continue;
      const Script& s = get_script (script_index);
      s.prune_langsys (&c, script_index);
    }
  }

  void prune_features (const hb_map_t *lookup_indices, /* IN */
           const hb_hashmap_t<unsigned, hb::shared_ptr<hb_set_t>> *feature_record_cond_idx_map, /* IN */
           const hb_hashmap_t<unsigned, const Feature*> *feature_substitutes_map, /* IN */
           hb_set_t       *feature_indices /* IN/OUT */) const
  {
#ifndef HB_NO_VAR
    // This is the set of feature indices which have alternate versions defined
    // if the FeatureVariation's table and the alternate version(s) intersect the
    // set of lookup indices.
    hb_set_t alternate_feature_indices;
    get_feature_variations ().closure_features (lookup_indices, feature_record_cond_idx_map, &alternate_feature_indices);
    if (unlikely (alternate_feature_indices.in_error()))
    {
      feature_indices->err ();
      return;
    }
#endif

    for (unsigned i : hb_iter (feature_indices))
    {
      hb_tag_t tag =  get_feature_tag (i);
      if (tag == HB_TAG ('p', 'r', 'e', 'f'))
        // Note: Never ever drop feature 'pref', even if it's empty.
        // HarfBuzz chooses shaper for Khmer based on presence of this
        // feature. See thread at:
  // http://lists.freedesktop.org/archives/harfbuzz/2012-November/002660.html
        continue;


      const Feature *f = &(get_feature (i));
      const Feature** p = nullptr;
      if (feature_substitutes_map->has (i, &p))
        f = *p;

      if (!f->featureParams.is_null () &&
          tag == HB_TAG ('s', 'i', 'z', 'e'))
        continue;

      if (!f->intersects_lookup_indexes (lookup_indices)
#ifndef HB_NO_VAR
          && !alternate_feature_indices.has (i)
#endif
    )
  feature_indices->del (i);
    }
  }

  void collect_name_ids (const hb_map_t *feature_index_map,
                         hb_set_t *nameids_to_retain /* OUT */) const
  {
    unsigned count = get_feature_count ();
    for (unsigned i = 0 ; i < count; i++)
    {
      if (!feature_index_map->has (i)) continue;
      hb_tag_t tag = get_feature_tag (i);
      get_feature (i).collect_name_ids (tag, nameids_to_retain);
    }
  }

  template <typename T>
  struct accelerator_t
  {
    accelerator_t (hb_face_t *face)
    {
      hb_sanitize_context_t sc;
      sc.lazy_some_gpos = true;
      this->table = sc.reference_table<T> (face);

      if (unlikely (this->table->is_blocklisted (this->table.get_blob (), face)))
      {
  hb_blob_destroy (this->table.get_blob ());
  this->table = hb_blob_get_empty ();
      }

      this->lookup_count = table->get_lookup_count ();

      this->accels = (hb_atomic_t<hb_ot_layout_lookup_accelerator_t *> *) hb_calloc (this->lookup_count, sizeof (*accels));
      if (unlikely (!this->accels))
      {
  this->lookup_count = 0;
  this->table.destroy ();
  this->table = hb_blob_get_empty ();
      }
    }
    ~accelerator_t ()
    {
      for (unsigned int i = 0; i < this->lookup_count; i++)
      {
  auto *accel = this->accels[i].get_relaxed ();
  if (accel)
    accel->fini ();
  hb_free (accel);
      }
      hb_free (this->accels);
      this->table.destroy ();
    }

    hb_blob_t *get_blob () const { return table.get_blob (); }

    hb_ot_layout_lookup_accelerator_t *get_accel (unsigned lookup_index) const
    {
      if (unlikely (lookup_index >= lookup_count)) return nullptr;

    retry:
      auto *accel = accels[lookup_index].get_acquire ();
      if (unlikely (!accel))
      {
  accel = hb_ot_layout_lookup_accelerator_t::create (table->get_lookup (lookup_index));
  if (unlikely (!accel))
    return nullptr;

  if (unlikely (!accels[lookup_index].cmpexch (nullptr, accel)))
  {
    accel->fini ();
    hb_free (accel);
    goto retry;
  }
      }

      return accel;
    }

    hb_blob_ptr_t<T> table;
    unsigned int lookup_count;
    hb_atomic_t<hb_ot_layout_lookup_accelerator_t *> *accels;
  };

  protected:
  union {
  FixedVersion<>      version;  /* Version identifier */
  GSUBGPOSVersion1_2<SmallTypes>  version1;
#ifndef HB_NO_BEYOND_64K
  GSUBGPOSVersion1_2<MediumTypes> version2;
#endif
  } u;
  public:
  DEFINE_SIZE_MIN (4);
};


} /* namespace OT */


#endif /* HB_OT_LAYOUT_GSUBGPOS_HH */

Coverage Report

Created: 2026-09-28 10:59