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