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/*

* 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 comparison */

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);

}