/* hash - hashing table processing.

   Copyright (C) 1998-2004, 2006-2007, 2009-2023 Free Software Foundation, Inc.

   Written by Jim Meyering, 1992.

   This file is free software: you can redistribute it and/or modify

   it under the terms of the GNU Lesser General Public License as

   published by the Free Software Foundation; either version 2.1 of the

   License, or (at your option) any later version.

   This file is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License

   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

/* A generic hash table package.  */

/* Define USE_OBSTACK to 1 if you want the allocator to use obstacks instead

   of malloc.  If you change USE_OBSTACK, you have to recompile!  */

#include <config.h>

#include "hash.h"

#include "bitrotate.h"

#include "xalloc-oversized.h"

#include <stdint.h>

#include <stdio.h>

#include <stdlib.h>

#if USE_OBSTACK

# include "obstack.h"

# ifndef obstack_chunk_alloc

#  define obstack_chunk_alloc malloc

# endif

# ifndef obstack_chunk_free

#  define obstack_chunk_free free

# endif

#endif

struct hash_entry

  {

    void *data;

    struct hash_entry *next;

  };

struct hash_table

  {

    /* The array of buckets starts at BUCKET and extends to BUCKET_LIMIT-1,

       for a possibility of N_BUCKETS.  Among those, N_BUCKETS_USED buckets

       are not empty, there are N_ENTRIES active entries in the table.  */

    struct hash_entry *bucket;

    struct hash_entry const *bucket_limit;

    size_t n_buckets;

    size_t n_buckets_used;

    size_t n_entries;

    /* Tuning arguments, kept in a physically separate structure.  */

    const Hash_tuning *tuning;

    /* Three functions are given to 'hash_initialize', see the documentation

       block for this function.  In a word, HASHER randomizes a user entry

       into a number up from 0 up to some maximum minus 1; COMPARATOR returns

       true if two user entries compare equally; and DATA_FREER is the cleanup

       function for a user entry.  */

    Hash_hasher hasher;

    Hash_comparator comparator;

    Hash_data_freer data_freer;

    /* A linked list of freed struct hash_entry structs.  */

    struct hash_entry *free_entry_list;

#if USE_OBSTACK

    /* Whenever obstacks are used, it is possible to allocate all overflowed

       entries into a single stack, so they all can be freed in a single

       operation.  It is not clear if the speedup is worth the trouble.  */

    struct obstack entry_stack;

#endif

  };

/* A hash table contains many internal entries, each holding a pointer to

   some user-provided data (also called a user entry).  An entry indistinctly

   refers to both the internal entry and its associated user entry.  A user

   entry contents may be hashed by a randomization function (the hashing

   function, or just "hasher" for short) into a number (or "slot") between 0

   and the current table size.  At each slot position in the hash table,

   starts a linked chain of entries for which the user data all hash to this

   slot.  A bucket is the collection of all entries hashing to the same slot.

   A good "hasher" function will distribute entries rather evenly in buckets.

   In the ideal case, the length of each bucket is roughly the number of

   entries divided by the table size.  Finding the slot for a data is usually

   done in constant time by the "hasher", and the later finding of a precise

   entry is linear in time with the size of the bucket.  Consequently, a

   larger hash table size (that is, a larger number of buckets) is prone to

   yielding shorter chains, *given* the "hasher" function behaves properly.

   Long buckets slow down the lookup algorithm.  One might use big hash table

   sizes in hope to reduce the average length of buckets, but this might

   become inordinate, as unused slots in the hash table take some space.  The

   best bet is to make sure you are using a good "hasher" function (beware

   that those are not that easy to write! :-), and to use a table size

   larger than the actual number of entries.  */

/* If an insertion makes the ratio of nonempty buckets to table size larger

   than the growth threshold (a number between 0.0 and 1.0), then increase

   the table size by multiplying by the growth factor (a number greater than

   1.0).  The growth threshold defaults to 0.8, and the growth factor

   defaults to 1.414, meaning that the table will have doubled its size

   every second time 80% of the buckets get used.  */

#define DEFAULT_GROWTH_THRESHOLD 0.8f

#define DEFAULT_GROWTH_FACTOR 1.414f

/* If a deletion empties a bucket and causes the ratio of used buckets to

   table size to become smaller than the shrink threshold (a number between

   0.0 and 1.0), then shrink the table by multiplying by the shrink factor (a

   number greater than the shrink threshold but smaller than 1.0).  The shrink

   threshold and factor default to 0.0 and 1.0, meaning that the table never

   shrinks.  */

#define DEFAULT_SHRINK_THRESHOLD 0.0f

#define DEFAULT_SHRINK_FACTOR 1.0f

/* Use this to initialize or reset a TUNING structure to

   some sensible values. */

static const Hash_tuning default_tuning =

  {

    DEFAULT_SHRINK_THRESHOLD,

    DEFAULT_SHRINK_FACTOR,

    DEFAULT_GROWTH_THRESHOLD,

    DEFAULT_GROWTH_FACTOR,

    false

  };

/* Information and lookup.  */

size_t

hash_get_n_buckets (const Hash_table *table)

{

  return table->n_buckets;

}

size_t

hash_get_n_buckets_used (const Hash_table *table)

{

  return table->n_buckets_used;

}

size_t

hash_get_n_entries (const Hash_table *table)

{

  return table->n_entries;

}

size_t

hash_get_max_bucket_length (const Hash_table *table)

{

  struct hash_entry const *bucket;

  size_t max_bucket_length = 0;

  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)

    {

      if (bucket->data)

        {

          struct hash_entry const *cursor = bucket;

          size_t bucket_length = 1;

          while (cursor = cursor->next, cursor)

            bucket_length++;

          if (bucket_length > max_bucket_length)

            max_bucket_length = bucket_length;

        }

    }

  return max_bucket_length;

}

bool

hash_table_ok (const Hash_table *table)

{

  struct hash_entry const *bucket;

  size_t n_buckets_used = 0;

  size_t n_entries = 0;

  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)

    {

      if (bucket->data)

        {

          struct hash_entry const *cursor = bucket;

          /* Count bucket head.  */

          n_buckets_used++;

          n_entries++;

          /* Count bucket overflow.  */

          while (cursor = cursor->next, cursor)

            n_entries++;

        }

    }

  if (n_buckets_used == table->n_buckets_used && n_entries == table->n_entries)

    return true;

  return false;

}

void

hash_print_statistics (const Hash_table *table, FILE *stream)

{

  size_t n_entries = hash_get_n_entries (table);

  size_t n_buckets = hash_get_n_buckets (table);

  size_t n_buckets_used = hash_get_n_buckets_used (table);

  size_t max_bucket_length = hash_get_max_bucket_length (table);

  fprintf (stream, "# entries:         %lu\n", (unsigned long int) n_entries);

  fprintf (stream, "# buckets:         %lu\n", (unsigned long int) n_buckets);

  fprintf (stream, "# buckets used:    %lu (%.2f%%)\n",

           (unsigned long int) n_buckets_used,

           (100.0 * n_buckets_used) / n_buckets);

  fprintf (stream, "max bucket length: %lu\n",

           (unsigned long int) max_bucket_length);

}

/* Hash KEY and return a pointer to the selected bucket.

   If TABLE->hasher misbehaves, abort.  */

static struct hash_entry *

safe_hasher (const Hash_table *table, const void *key)

{

  size_t n = table->hasher (key, table->n_buckets);

  if (! (n < table->n_buckets))

    abort ();

  return table->bucket + n;

}

void *

hash_lookup (const Hash_table *table, const void *entry)

{

  struct hash_entry const *bucket = safe_hasher (table, entry);

  struct hash_entry const *cursor;

  if (bucket->data == NULL)

    return NULL;

  for (cursor = bucket; cursor; cursor = cursor->next)

    if (entry == cursor->data || table->comparator (entry, cursor->data))

      return cursor->data;

  return NULL;

}

/* Walking.  */

void *

hash_get_first (const Hash_table *table)

{

  struct hash_entry const *bucket;

  if (table->n_entries == 0)

    return NULL;

  for (bucket = table->bucket; ; bucket++)

    if (! (bucket < table->bucket_limit))

      abort ();

    else if (bucket->data)

      return bucket->data;

}

void *

hash_get_next (const Hash_table *table, const void *entry)

{

  struct hash_entry const *bucket = safe_hasher (table, entry);

  struct hash_entry const *cursor;

  /* Find next entry in the same bucket.  */

  cursor = bucket;

  do

    {

      if (cursor->data == entry && cursor->next)

        return cursor->next->data;

      cursor = cursor->next;

    }

  while (cursor != NULL);

  /* Find first entry in any subsequent bucket.  */

  while (++bucket < table->bucket_limit)

    if (bucket->data)

      return bucket->data;

  /* None found.  */

  return NULL;

}

size_t

hash_get_entries (const Hash_table *table, void **buffer,

                  size_t buffer_size)

{

  size_t counter = 0;

  struct hash_entry const *bucket;

  struct hash_entry const *cursor;

  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)

    {

      if (bucket->data)

        {

          for (cursor = bucket; cursor; cursor = cursor->next)

            {

              if (counter >= buffer_size)

                return counter;

              buffer[counter++] = cursor->data;

            }

        }

    }

  return counter;

}

size_t

hash_do_for_each (const Hash_table *table, Hash_processor processor,

                  void *processor_data)

{

  size_t counter = 0;

  struct hash_entry const *bucket;

  struct hash_entry const *cursor;

  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)

    {

      if (bucket->data)

        {

          for (cursor = bucket; cursor; cursor = cursor->next)

            {

              if (! processor (cursor->data, processor_data))

                return counter;

              counter++;

            }

        }

    }

  return counter;

}

/* Allocation and clean-up.  */

#if USE_DIFF_HASH

/* About hashings, Paul Eggert writes to me (FP), on 1994-01-01: "Please see

   B. J. McKenzie, R. Harries & T. Bell, Selecting a hashing algorithm,

   Software--practice & experience 20, 2 (Feb 1990), 209-224.  Good hash

   algorithms tend to be domain-specific, so what's good for [diffutils'] io.c

   may not be good for your application."  */

size_t

hash_string (const char *string, size_t n_buckets)

{

# define HASH_ONE_CHAR(Value, Byte) \

  ((Byte) + rotl_sz (Value, 7))

  size_t value = 0;

  unsigned char ch;

  for (; (ch = *string); string++)

    value = HASH_ONE_CHAR (value, ch);

  return value % n_buckets;

# undef HASH_ONE_CHAR

}

#else /* not USE_DIFF_HASH */

/* This one comes from 'recode', and performs a bit better than the above as

   per a few experiments.  It is inspired from a hashing routine found in the

   very old Cyber 'snoop', itself written in typical Greg Mansfield style.

   (By the way, what happened to this excellent man?  Is he still alive?)  */

size_t

hash_string (const char *string, size_t n_buckets)

{

  size_t value = 0;

  unsigned char ch;

  for (; (ch = *string); string++)

    value = (value * 31 + ch) % n_buckets;

  return value;

}

#endif /* not USE_DIFF_HASH */

/* Return true if CANDIDATE is a prime number.  CANDIDATE should be an odd

   number at least equal to 11.  */

static bool _GL_ATTRIBUTE_CONST

is_prime (size_t candidate)

{

  size_t divisor = 3;

  size_t square = divisor * divisor;

  while (square < candidate && (candidate % divisor))

    {

      divisor++;

      square += 4 * divisor;

      divisor++;

    }

  return (candidate % divisor ? true : false);

}

/* Round a given CANDIDATE number up to the nearest prime, and return that

   prime.  Primes lower than 10 are merely skipped.  */

static size_t _GL_ATTRIBUTE_CONST

next_prime (size_t candidate)

{

  /* Skip small primes.  */

  if (candidate < 10)

    candidate = 10;

  /* Make it definitely odd.  */

  candidate |= 1;

  while (SIZE_MAX != candidate && !is_prime (candidate))

    candidate += 2;

  return candidate;

}

void

hash_reset_tuning (Hash_tuning *tuning)

{

  *tuning = default_tuning;

}

/* If the user passes a NULL hasher, we hash the raw pointer.  */

static size_t

raw_hasher (const void *data, size_t n)

{

  /* When hashing unique pointers, it is often the case that they were

     generated by malloc and thus have the property that the low-order

     bits are 0.  As this tends to give poorer performance with small

     tables, we rotate the pointer value before performing division,

     in an attempt to improve hash quality.  */

  size_t val = rotr_sz ((size_t) data, 3);

  return val % n;

}

/* If the user passes a NULL comparator, we use pointer comparison.  */

static bool

raw_comparator (const void *a, const void *b)

{

  return a == b;

}

/* For the given hash TABLE, check the user supplied tuning structure for

   reasonable values, and return true if there is no gross error with it.

   Otherwise, definitively reset the TUNING field to some acceptable default

   in the hash table (that is, the user loses the right of further modifying

   tuning arguments), and return false.  */

static bool

check_tuning (Hash_table *table)

{

  const Hash_tuning *tuning = table->tuning;

  float epsilon;

  if (tuning == &default_tuning)

    return true;

  /* Be a bit stricter than mathematics would require, so that

     rounding errors in size calculations do not cause allocations to

     fail to grow or shrink as they should.  The smallest allocation

     is 11 (due to next_prime's algorithm), so an epsilon of 0.1

     should be good enough.  */

  epsilon = 0.1f;

  if (epsilon < tuning->growth_threshold

      && tuning->growth_threshold < 1 - epsilon

      && 1 + epsilon < tuning->growth_factor

      && 0 <= tuning->shrink_threshold

      && tuning->shrink_threshold + epsilon < tuning->shrink_factor

      && tuning->shrink_factor <= 1

      && tuning->shrink_threshold + epsilon < tuning->growth_threshold)

    return true;

  table->tuning = &default_tuning;

  return false;

}

/* Compute the size of the bucket array for the given CANDIDATE and

   TUNING, or return 0 if there is no possible way to allocate that

   many entries.  */

static size_t _GL_ATTRIBUTE_PURE

compute_bucket_size (size_t candidate, const Hash_tuning *tuning)

{

  if (!tuning->is_n_buckets)

    {

      float new_candidate = candidate / tuning->growth_threshold;

      if ((float) SIZE_MAX <= new_candidate)

        return 0;

      candidate = new_candidate;

    }

  candidate = next_prime (candidate);

  if (xalloc_oversized (candidate, sizeof (struct hash_entry *)))

    return 0;

  return candidate;

}

Hash_table *

hash_initialize (size_t candidate, const Hash_tuning *tuning,

                 Hash_hasher hasher, Hash_comparator comparator,

                 Hash_data_freer data_freer)

{

  Hash_table *table;

  if (hasher == NULL)

    hasher = raw_hasher;

  if (comparator == NULL)

    comparator = raw_comparator;

  table = malloc (sizeof *table);

  if (table == NULL)

    return NULL;

  if (!tuning)

    tuning = &default_tuning;

  table->tuning = tuning;

  if (!check_tuning (table))

    {

      /* Fail if the tuning options are invalid.  This is the only occasion

         when the user gets some feedback about it.  Once the table is created,

         if the user provides invalid tuning options, we silently revert to

         using the defaults, and ignore further request to change the tuning

         options.  */

      goto fail;

    }

  table->n_buckets = compute_bucket_size (candidate, tuning);

  if (!table->n_buckets)

    goto fail;

  table->bucket = calloc (table->n_buckets, sizeof *table->bucket);

  if (table->bucket == NULL)

    goto fail;

  table->bucket_limit = table->bucket + table->n_buckets;

  table->n_buckets_used = 0;

  table->n_entries = 0;

  table->hasher = hasher;

  table->comparator = comparator;

  table->data_freer = data_freer;

  table->free_entry_list = NULL;

#if USE_OBSTACK

  obstack_init (&table->entry_stack);

#endif

  return table;

 fail:

  free (table);

  return NULL;

}

void

hash_clear (Hash_table *table)

{

  struct hash_entry *bucket;

  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)

    {

      if (bucket->data)

        {

          struct hash_entry *cursor;

          struct hash_entry *next;

          /* Free the bucket overflow.  */

          for (cursor = bucket->next; cursor; cursor = next)

            {

              if (table->data_freer)

                table->data_freer (cursor->data);

              cursor->data = NULL;

              next = cursor->next;

              /* Relinking is done one entry at a time, as it is to be expected

                 that overflows are either rare or short.  */

              cursor->next = table->free_entry_list;

              table->free_entry_list = cursor;

            }

          /* Free the bucket head.  */

          if (table->data_freer)

            table->data_freer (bucket->data);

          bucket->data = NULL;

          bucket->next = NULL;

        }

    }

  table->n_buckets_used = 0;

  table->n_entries = 0;

}

void

hash_free (Hash_table *table)

{

  struct hash_entry *bucket;

  struct hash_entry *cursor;

  struct hash_entry *next;

  /* Call the user data_freer function.  */

  if (table->data_freer && table->n_entries)

    {

      for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)

        {

          if (bucket->data)

            {

              for (cursor = bucket; cursor; cursor = cursor->next)

                table->data_freer (cursor->data);

            }

        }

    }

#if USE_OBSTACK

  obstack_free (&table->entry_stack, NULL);

#else

  /* Free all bucket overflowed entries.  */

  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)

    {

      for (cursor = bucket->next; cursor; cursor = next)

        {

          next = cursor->next;

          free (cursor);

        }

    }

  /* Also reclaim the internal list of previously freed entries.  */

  for (cursor = table->free_entry_list; cursor; cursor = next)

    {

      next = cursor->next;

      free (cursor);

    }

#endif

  /* Free the remainder of the hash table structure.  */

  free (table->bucket);

  free (table);

}

/* Insertion and deletion.  */

/* Get a new hash entry for a bucket overflow, possibly by recycling a

   previously freed one.  If this is not possible, allocate a new one.  */

static struct hash_entry *

allocate_entry (Hash_table *table)

{

  struct hash_entry *new;

  if (table->free_entry_list)

    {

      new = table->free_entry_list;

      table->free_entry_list = new->next;

    }

  else

    {

#if USE_OBSTACK

      new = obstack_alloc (&table->entry_stack, sizeof *new);

#else

      new = malloc (sizeof *new);

#endif

    }

  return new;

}

/* Free a hash entry which was part of some bucket overflow,

   saving it for later recycling.  */

static void

free_entry (Hash_table *table, struct hash_entry *entry)

{

  entry->data = NULL;

  entry->next = table->free_entry_list;

  table->free_entry_list = entry;

}

/* This private function is used to help with insertion and deletion.  When

   ENTRY matches an entry in the table, return a pointer to the corresponding

   user data and set *BUCKET_HEAD to the head of the selected bucket.

   Otherwise, return NULL.  When DELETE is true and ENTRY matches an entry in

   the table, unlink the matching entry.  */

static void *

hash_find_entry (Hash_table *table, const void *entry,

                 struct hash_entry **bucket_head, bool delete)

{

  struct hash_entry *bucket = safe_hasher (table, entry);

  struct hash_entry *cursor;

  *bucket_head = bucket;

  /* Test for empty bucket.  */

  if (bucket->data == NULL)

    return NULL;

  /* See if the entry is the first in the bucket.  */

  if (entry == bucket->data || table->comparator (entry, bucket->data))

    {

      void *data = bucket->data;

      if (delete)

        {

          if (bucket->next)

            {

              struct hash_entry *next = bucket->next;

              /* Bump the first overflow entry into the bucket head, then save

                 the previous first overflow entry for later recycling.  */

              *bucket = *next;

              free_entry (table, next);

            }

          else

            {

              bucket->data = NULL;

            }

        }

      return data;

    }

  /* Scan the bucket overflow.  */

  for (cursor = bucket; cursor->next; cursor = cursor->next)

    {

      if (entry == cursor->next->data

          || table->comparator (entry, cursor->next->data))

        {

          void *data = cursor->next->data;

          if (delete)

            {

              struct hash_entry *next = cursor->next;

              /* Unlink the entry to delete, then save the freed entry for later

                 recycling.  */

              cursor->next = next->next;

              free_entry (table, next);

            }

          return data;

        }

    }

  /* No entry found.  */

  return NULL;

}

/* Internal helper, to move entries from SRC to DST.  Both tables must

   share the same free entry list.  If SAFE, only move overflow

   entries, saving bucket heads for later, so that no allocations will

   occur.  Return false if the free entry list is exhausted and an

   allocation fails.  */

static bool

transfer_entries (Hash_table *dst, Hash_table *src, bool safe)

{

  struct hash_entry *bucket;

  struct hash_entry *cursor;

  struct hash_entry *next;

  for (bucket = src->bucket; bucket < src->bucket_limit; bucket++)

    if (bucket->data)

      {

        void *data;

        struct hash_entry *new_bucket;

        /* Within each bucket, transfer overflow entries first and

           then the bucket head, to minimize memory pressure.  After

           all, the only time we might allocate is when moving the

           bucket head, but moving overflow entries first may create

           free entries that can be recycled by the time we finally

           get to the bucket head.  */

        for (cursor = bucket->next; cursor; cursor = next)

          {

            data = cursor->data;

            new_bucket = safe_hasher (dst, data);

            next = cursor->next;

            if (new_bucket->data)

              {

                /* Merely relink an existing entry, when moving from a

                   bucket overflow into a bucket overflow.  */

                cursor->next = new_bucket->next;

                new_bucket->next = cursor;

              }

            else

              {

                /* Free an existing entry, when moving from a bucket

                   overflow into a bucket header.  */

                new_bucket->data = data;

                dst->n_buckets_used++;

                free_entry (dst, cursor);

              }

          }

        /* Now move the bucket head.  Be sure that if we fail due to

           allocation failure that the src table is in a consistent

           state.  */

        data = bucket->data;

        bucket->next = NULL;

        if (safe)

          continue;

        new_bucket = safe_hasher (dst, data);

        if (new_bucket->data)

          {

            /* Allocate or recycle an entry, when moving from a bucket

               header into a bucket overflow.  */

            struct hash_entry *new_entry = allocate_entry (dst);

            if (new_entry == NULL)

              return false;

            new_entry->data = data;

            new_entry->next = new_bucket->next;

            new_bucket->next = new_entry;

          }

        else

          {

            /* Move from one bucket header to another.  */

            new_bucket->data = data;

            dst->n_buckets_used++;

          }

        bucket->data = NULL;

        src->n_buckets_used--;

      }

  return true;

}

bool

hash_rehash (Hash_table *table, size_t candidate)

{

  Hash_table storage;

  Hash_table *new_table;

  size_t new_size = compute_bucket_size (candidate, table->tuning);

  if (!new_size)

    return false;

  if (new_size == table->n_buckets)

    return true;

  new_table = &storage;

  new_table->bucket = calloc (new_size, sizeof *new_table->bucket);

  if (new_table->bucket == NULL)

    return false;

  new_table->n_buckets = new_size;

  new_table->bucket_limit = new_table->bucket + new_size;

  new_table->n_buckets_used = 0;

  new_table->n_entries = 0;

  new_table->tuning = table->tuning;

  new_table->hasher = table->hasher;

  new_table->comparator = table->comparator;

  new_table->data_freer = table->data_freer;

  /* In order for the transfer to successfully complete, we need

     additional overflow entries when distinct buckets in the old

     table collide into a common bucket in the new table.  The worst

     case possible is a hasher that gives a good spread with the old

     size, but returns a constant with the new size; if we were to

     guarantee table->n_buckets_used-1 free entries in advance, then

     the transfer would be guaranteed to not allocate memory.

     However, for large tables, a guarantee of no further allocation

     introduces a lot of extra memory pressure, all for an unlikely

     corner case (most rehashes reduce, rather than increase, the

     number of overflow entries needed).  So, we instead ensure that

     the transfer process can be reversed if we hit a memory

     allocation failure mid-transfer.  */

  /* Merely reuse the extra old space into the new table.  */

#if USE_OBSTACK

  new_table->entry_stack = table->entry_stack;

#endif

  new_table->free_entry_list = table->free_entry_list;

  if (transfer_entries (new_table, table, false))

    {

      /* Entries transferred successfully; tie up the loose ends.  */

      free (table->bucket);

      table->bucket = new_table->bucket;

      table->bucket_limit = new_table->bucket_limit;

      table->n_buckets = new_table->n_buckets;

      table->n_buckets_used = new_table->n_buckets_used;

      table->free_entry_list = new_table->free_entry_list;

      /* table->n_entries and table->entry_stack already hold their value.  */

      return true;

    }

  /* We've allocated new_table->bucket (and possibly some entries),

     exhausted the free list, and moved some but not all entries into

     new_table.  We must undo the partial move before returning

     failure.  The only way to get into this situation is if new_table

     uses fewer buckets than the old table, so we will reclaim some

     free entries as overflows in the new table are put back into

     distinct buckets in the old table.

     There are some pathological cases where a single pass through the

     table requires more intermediate overflow entries than using two

     passes.  Two passes give worse cache performance and takes

     longer, but at this point, we're already out of memory, so slow

     and safe is better than failure.  */

  table->free_entry_list = new_table->free_entry_list;

  if (! (transfer_entries (table, new_table, true)

         && transfer_entries (table, new_table, false)))

    abort ();

  /* table->n_entries already holds its value.  */

  free (new_table->bucket);

  return false;

}

int

hash_insert_if_absent (Hash_table *table, void const *entry,

                       void const **matched_ent)

{

  void *data;

  struct hash_entry *bucket;

  /* The caller cannot insert a NULL entry, since hash_lookup returns NULL

     to indicate "not found", and hash_find_entry uses "bucket->data == NULL"

     to indicate an empty bucket.  */

  if (! entry)

    abort ();

  /* If there's a matching entry already in the table, return that.  */

  if ((data = hash_find_entry (table, entry, &bucket, false)) != NULL)

    {

      if (matched_ent)

        *matched_ent = data;

      return 0;

    }

  /* If the growth threshold of the buckets in use has been reached, increase

     the table size and rehash.  There's no point in checking the number of

     entries:  if the hashing function is ill-conditioned, rehashing is not

     likely to improve it.  */