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Justine Tunney 2020-06-15 07:18:57 -07:00
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libc/alg/critbit0_delete.c Normal file
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney │
│ │
│ This program is free software; you can redistribute it and/or modify │
│ it under the terms of the GNU General Public License as published by │
│ the Free Software Foundation; version 2 of the License. │
│ │
│ This program 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 │
│ General Public License for more details. │
│ │
│ You should have received a copy of the GNU General Public License │
│ along with this program; if not, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/alg/alg.h"
#include "libc/alg/internal.h"
#include "libc/mem/mem.h"
#include "libc/str/str.h"
/**
* Removes 𝑢 from 𝑡.
* @param t tree
* @param u NUL-terminated string
* @return true if 𝑡 was mutated
* @note h/t djb and agl
*/
bool critbit0_delete(struct critbit0 *t, const char *u) {
const unsigned char *ubytes = (void *)u;
const size_t ulen = strlen(u);
unsigned char *p = t->root;
void **wherep = &t->root;
void **whereq = 0;
struct CritbitNode *q = 0;
int direction = 0;
if (!p) return false;
while (1 & (intptr_t)p) {
whereq = wherep;
q = (void *)(p - 1);
unsigned char c = 0;
if (q->byte < ulen) c = ubytes[q->byte];
direction = (1 + (q->otherbits | c)) >> 8;
wherep = q->child + direction;
p = *wherep;
}
if (0 != strcmp(u, (const char *)p)) return false;
free(p), p = NULL;
if (!whereq) {
t->root = NULL;
t->count = 0;
return true;
}
*whereq = q->child[1 - direction];
free(q), q = NULL;
t->count--;
return true;
}