1/* Copyright (C) 1991-1994, 1996-1998, 2000, 2004, 2007-2020 Free Software 2 Foundation, Inc. 3 This file is part of the GNU C Library. 4 5 This program is free software; you can redistribute it and/or modify 6 it under the terms of the GNU General Public License as published by 7 the Free Software Foundation; either version 3, or (at your option) 8 any later version. 9 10 This program is distributed in the hope that it will be useful, 11 but WITHOUT ANY WARRANTY; without even the implied warranty of 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13 GNU General Public License for more details. 14 15 You should have received a copy of the GNU General Public License along 16 with this program; if not, see <https://www.gnu.org/licenses/>. */ 17 18/* This particular implementation was written by Eric Blake, 2008. */ 19 20#ifndef _LIBC 21# include <config.h> 22#endif 23 24/* Specification of memmem. */ 25#include <string.h> 26 27#define RETURN_TYPE void * 28#define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l)) 29#include "str-two-way.h" 30 31/* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK 32 if NEEDLE_LEN is 0, otherwise NULL if NEEDLE is not found in 33 HAYSTACK. */ 34void * 35memmem (const void *haystack_start, size_t haystack_len, 36 const void *needle_start, size_t needle_len) 37{ 38 /* Abstract memory is considered to be an array of 'unsigned char' values, 39 not an array of 'char' values. See ISO C 99 section 6.2.6.1. */ 40 const unsigned char *haystack = (const unsigned char *) haystack_start; 41 const unsigned char *needle = (const unsigned char *) needle_start; 42 43 if (needle_len == 0) 44 /* The first occurrence of the empty string is deemed to occur at 45 the beginning of the string. */ 46 return (void *) haystack; 47 48 /* Sanity check, otherwise the loop might search through the whole 49 memory. */ 50 if (__builtin_expect (haystack_len < needle_len, 0)) 51 return NULL; 52 53 /* Use optimizations in memchr when possible, to reduce the search 54 size of haystack using a linear algorithm with a smaller 55 coefficient. However, avoid memchr for long needles, since we 56 can often achieve sublinear performance. */ 57 if (needle_len < LONG_NEEDLE_THRESHOLD) 58 { 59 haystack = memchr (haystack, *needle, haystack_len); 60 if (!haystack || __builtin_expect (needle_len == 1, 0)) 61 return (void *) haystack; 62 haystack_len -= haystack - (const unsigned char *) haystack_start; 63 if (haystack_len < needle_len) 64 return NULL; 65 return two_way_short_needle (haystack, haystack_len, needle, needle_len); 66 } 67 else 68 return two_way_long_needle (haystack, haystack_len, needle, needle_len); 69} 70 71#undef LONG_NEEDLE_THRESHOLD 72