/*

 * crit-bit tree implementation, does no allocations internally

 * For more information on crit-bit trees: https://cr.yp.to/critbit.html

 * Based on Adam Langley's adaptation of Dan Bernstein's public domain code

 * git clone https://github.com/agl/critbit.git

 */

#include "git-compat-util.h"

#include "cbtree.h"

static struct cb_node *cb_node_of(const void *p)

{

  return (struct cb_node *)((uintptr_t)p - 1);

}

/* locate the best match, does not do a final comparision */

static struct cb_node *cb_internal_best_match(struct cb_node *p,

          const uint8_t *k, size_t klen)

{

  while (1 & (uintptr_t)p) {

    struct cb_node *q = cb_node_of(p);

    uint8_t c = q->byte < klen ? k[q->byte] : 0;

    size_t direction = (1 + (q->otherbits | c)) >> 8;

    p = q->child[direction];

  }

  return p;

}

/* returns NULL if successful, existing cb_node if duplicate */

struct cb_node *cb_insert(struct cb_tree *t, struct cb_node *node, size_t klen)

{

  size_t newbyte, newotherbits;

  uint8_t c;

  int newdirection;

  struct cb_node **wherep, *p;

  assert(!((uintptr_t)node & 1)); /* allocations must be aligned */

  if (!t->root) {   /* insert into empty tree */

    t->root = node;

    return NULL;  /* success */

  }

  /* see if a node already exists */

  p = cb_internal_best_match(t->root, node->k, klen);

  /* find first differing byte */

  for (newbyte = 0; newbyte < klen; newbyte++) {

    if (p->k[newbyte] != node->k[newbyte])

      goto different_byte_found;

  }

  return p;  /* element exists, let user deal with it */

different_byte_found:

  newotherbits = p->k[newbyte] ^ node->k[newbyte];

  newotherbits |= newotherbits >> 1;

  newotherbits |= newotherbits >> 2;

  newotherbits |= newotherbits >> 4;

  newotherbits = (newotherbits & ~(newotherbits >> 1)) ^ 255;

  c = p->k[newbyte];

  newdirection = (1 + (newotherbits | c)) >> 8;

  node->byte = newbyte;

  node->otherbits = newotherbits;

  node->child[1 - newdirection] = node;

  /* find a place to insert it */

  wherep = &t->root;

  for (;;) {

    struct cb_node *q;

    size_t direction;

    p = *wherep;

    if (!(1 & (uintptr_t)p))

      break;

    q = cb_node_of(p);

    if (q->byte > newbyte)

      break;

    if (q->byte == newbyte && q->otherbits > newotherbits)

      break;

    c = q->byte < klen ? node->k[q->byte] : 0;

    direction = (1 + (q->otherbits | c)) >> 8;

    wherep = q->child + direction;

  }

  node->child[newdirection] = *wherep;

  *wherep = (struct cb_node *)(1 + (uintptr_t)node);

  return NULL; /* success */

}

struct cb_node *cb_lookup(struct cb_tree *t, const uint8_t *k, size_t klen)

{

  struct cb_node *p = cb_internal_best_match(t->root, k, klen);

  return p && !memcmp(p->k, k, klen) ? p : NULL;

}

static enum cb_next cb_descend(struct cb_node *p, cb_iter fn, void *arg)

{

  if (1 & (uintptr_t)p) {

    struct cb_node *q = cb_node_of(p);

    enum cb_next n = cb_descend(q->child[0], fn, arg);

    return n == CB_BREAK ? n : cb_descend(q->child[1], fn, arg);

  } else {

    return fn(p, arg);

  }

}

void cb_each(struct cb_tree *t, const uint8_t *kpfx, size_t klen,

      cb_iter fn, void *arg)

{

  struct cb_node *p = t->root;

  struct cb_node *top = p;

  size_t i = 0;

  if (!p) return; /* empty tree */

  /* Walk tree, maintaining top pointer */

  while (1 & (uintptr_t)p) {

    struct cb_node *q = cb_node_of(p);

    uint8_t c = q->byte < klen ? kpfx[q->byte] : 0;

    size_t direction = (1 + (q->otherbits | c)) >> 8;

    p = q->child[direction];

    if (q->byte < klen)

      top = p;

  }

  for (i = 0; i < klen; i++) {

    if (p->k[i] != kpfx[i])

      return; /* "best" match failed */

  }

  cb_descend(top, fn, arg);

}