- /* $OpenBSD: memmem.c,v 1.5 2020/04/16 12:39:28 claudio Exp $ */
-
- /*
- * Copyright (c) 2005-2020 Rich Felker, et al.
- *
- * Permission is hereby granted, free of charge, to any person obtaining
- * a copy of this software and associated documentation files (the
- * "Software"), to deal in the Software without restriction, including
- * without limitation the rights to use, copy, modify, merge, publish,
- * distribute, sublicense, and/or sell copies of the Software, and to
- * permit persons to whom the Software is furnished to do so, subject to
- * the following conditions:
- *
- * The above copyright notice and this permission notice shall be
- * included in all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
- * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
- * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
- * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
- * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
- * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
- * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- */
-
- #include <string.h>
- #include <stdint.h>
-
- static char *
- twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
- {
- uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
- for (h+=2, k-=2; k; k--, hw = hw<<8 | *h++)
- if (hw == nw) return (char *)h-2;
- return hw == nw ? (char *)h-2 : 0;
- }
-
- static char *
- threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
- {
- uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
- uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
- for (h+=3, k-=3; k; k--, hw = (hw|*h++)<<8)
- if (hw == nw) return (char *)h-3;
- return hw == nw ? (char *)h-3 : 0;
- }
-
- static char *
- fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
- {
- uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
- uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
- for (h+=4, k-=4; k; k--, hw = hw<<8 | *h++)
- if (hw == nw) return (char *)h-4;
- return hw == nw ? (char *)h-4 : 0;
- }
-
- #define MAX(a,b) ((a)>(b)?(a):(b))
- #define MIN(a,b) ((a)<(b)?(a):(b))
-
- #define BITOP(a,b,op) \
- ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
-
- /*
- * Maxime Crochemore and Dominique Perrin, Two-way string-matching,
- * Journal of the ACM, 38(3):651-675, July 1991.
- */
- static char *
- twoway_memmem(const unsigned char *h, const unsigned char *z,
- const unsigned char *n, size_t l)
- {
- size_t i, ip, jp, k, p, ms, p0, mem, mem0;
- size_t byteset[32 / sizeof(size_t)] = { 0 };
- size_t shift[256];
-
- /* Computing length of needle and fill shift table */
- for (i=0; i<l; i++)
- BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
-
- /* Compute maximal suffix */
- ip = -1; jp = 0; k = p = 1;
- while (jp+k<l) {
- if (n[ip+k] == n[jp+k]) {
- if (k == p) {
- jp += p;
- k = 1;
- } else k++;
- } else if (n[ip+k] > n[jp+k]) {
- jp += k;
- k = 1;
- p = jp - ip;
- } else {
- ip = jp++;
- k = p = 1;
- }
- }
- ms = ip;
- p0 = p;
-
- /* And with the opposite comparison */
- ip = -1; jp = 0; k = p = 1;
- while (jp+k<l) {
- if (n[ip+k] == n[jp+k]) {
- if (k == p) {
- jp += p;
- k = 1;
- } else k++;
- } else if (n[ip+k] < n[jp+k]) {
- jp += k;
- k = 1;
- p = jp - ip;
- } else {
- ip = jp++;
- k = p = 1;
- }
- }
- if (ip+1 > ms+1) ms = ip;
- else p = p0;
-
- /* Periodic needle? */
- if (memcmp(n, n+p, ms+1)) {
- mem0 = 0;
- p = MAX(ms, l-ms-1) + 1;
- } else mem0 = l-p;
- mem = 0;
-
- /* Search loop */
- for (;;) {
- /* If remainder of haystack is shorter than needle, done */
- if (z-h < l) return 0;
-
- /* Check last byte first; advance by shift on mismatch */
- if (BITOP(byteset, h[l-1], &)) {
- k = l-shift[h[l-1]];
- if (k) {
- if (k < mem) k = mem;
- h += k;
- mem = 0;
- continue;
- }
- } else {
- h += l;
- mem = 0;
- continue;
- }
-
- /* Compare right half */
- for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++);
- if (k < l) {
- h += k-ms;
- mem = 0;
- continue;
- }
- /* Compare left half */
- for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
- if (k <= mem) return (char *)h;
- h += p;
- mem = mem0;
- }
- }
-
- void *
- memmem(const void *h0, size_t k, const void *n0, size_t l)
- {
- const unsigned char *h = h0, *n = n0;
-
- /* Return immediately on empty needle */
- if (!l) return (void *)h;
-
- /* Return immediately when needle is longer than haystack */
- if (k<l) return 0;
-
- /* Use faster algorithms for short needles */
- h = memchr(h0, *n, k);
- if (!h || l==1) return (void *)h;
- k -= h - (const unsigned char *)h0;
- if (k<l) return 0;
- if (l==2) return twobyte_memmem(h, k, n);
- if (l==3) return threebyte_memmem(h, k, n);
- if (l==4) return fourbyte_memmem(h, k, n);
-
- return twoway_memmem(h, h+k, n, l);
- }
- DEF_WEAK(memmem);
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