0627c58e7a
Fix a typo in comments. Signed-off-by: Andrew Kreimer <algonell@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
137 lines
3.4 KiB
C
137 lines
3.4 KiB
C
/*
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* crit-bit tree implementation, does no allocations internally
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* For more information on crit-bit trees: https://cr.yp.to/critbit.html
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* Based on Adam Langley's adaptation of Dan Bernstein's public domain code
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* git clone https://github.com/agl/critbit.git
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*/
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#include "git-compat-util.h"
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#include "cbtree.h"
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static struct cb_node *cb_node_of(const void *p)
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{
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return (struct cb_node *)((uintptr_t)p - 1);
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}
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/* locate the best match, does not do a final comparison */
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static struct cb_node *cb_internal_best_match(struct cb_node *p,
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const uint8_t *k, size_t klen)
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{
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while (1 & (uintptr_t)p) {
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struct cb_node *q = cb_node_of(p);
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uint8_t c = q->byte < klen ? k[q->byte] : 0;
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size_t direction = (1 + (q->otherbits | c)) >> 8;
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p = q->child[direction];
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}
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return p;
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}
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/* returns NULL if successful, existing cb_node if duplicate */
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struct cb_node *cb_insert(struct cb_tree *t, struct cb_node *node, size_t klen)
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{
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size_t newbyte, newotherbits;
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uint8_t c;
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int newdirection;
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struct cb_node **wherep, *p;
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assert(!((uintptr_t)node & 1)); /* allocations must be aligned */
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if (!t->root) { /* insert into empty tree */
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t->root = node;
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return NULL; /* success */
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}
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/* see if a node already exists */
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p = cb_internal_best_match(t->root, node->k, klen);
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/* find first differing byte */
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for (newbyte = 0; newbyte < klen; newbyte++) {
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if (p->k[newbyte] != node->k[newbyte])
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goto different_byte_found;
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}
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return p; /* element exists, let user deal with it */
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different_byte_found:
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newotherbits = p->k[newbyte] ^ node->k[newbyte];
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newotherbits |= newotherbits >> 1;
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newotherbits |= newotherbits >> 2;
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newotherbits |= newotherbits >> 4;
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newotherbits = (newotherbits & ~(newotherbits >> 1)) ^ 255;
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c = p->k[newbyte];
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newdirection = (1 + (newotherbits | c)) >> 8;
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node->byte = newbyte;
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node->otherbits = newotherbits;
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node->child[1 - newdirection] = node;
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/* find a place to insert it */
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wherep = &t->root;
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for (;;) {
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struct cb_node *q;
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size_t direction;
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p = *wherep;
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if (!(1 & (uintptr_t)p))
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break;
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q = cb_node_of(p);
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if (q->byte > newbyte)
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break;
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if (q->byte == newbyte && q->otherbits > newotherbits)
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break;
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c = q->byte < klen ? node->k[q->byte] : 0;
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direction = (1 + (q->otherbits | c)) >> 8;
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wherep = q->child + direction;
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}
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node->child[newdirection] = *wherep;
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*wherep = (struct cb_node *)(1 + (uintptr_t)node);
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return NULL; /* success */
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}
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struct cb_node *cb_lookup(struct cb_tree *t, const uint8_t *k, size_t klen)
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{
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struct cb_node *p = cb_internal_best_match(t->root, k, klen);
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return p && !memcmp(p->k, k, klen) ? p : NULL;
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}
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static enum cb_next cb_descend(struct cb_node *p, cb_iter fn, void *arg)
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{
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if (1 & (uintptr_t)p) {
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struct cb_node *q = cb_node_of(p);
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enum cb_next n = cb_descend(q->child[0], fn, arg);
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return n == CB_BREAK ? n : cb_descend(q->child[1], fn, arg);
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} else {
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return fn(p, arg);
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}
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}
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void cb_each(struct cb_tree *t, const uint8_t *kpfx, size_t klen,
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cb_iter fn, void *arg)
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{
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struct cb_node *p = t->root;
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struct cb_node *top = p;
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size_t i = 0;
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if (!p) return; /* empty tree */
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/* Walk tree, maintaining top pointer */
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while (1 & (uintptr_t)p) {
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struct cb_node *q = cb_node_of(p);
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uint8_t c = q->byte < klen ? kpfx[q->byte] : 0;
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size_t direction = (1 + (q->otherbits | c)) >> 8;
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p = q->child[direction];
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if (q->byte < klen)
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top = p;
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}
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for (i = 0; i < klen; i++) {
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if (p->k[i] != kpfx[i])
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return; /* "best" match failed */
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}
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cb_descend(top, fn, arg);
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}
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