1 /* Copyright (C) 1991-1994, 1996-1998, 2000, 2004, 2007-2023 Free Software
2 Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 This file is free software: you can redistribute it and/or modify
6 it under the terms of the GNU Lesser General Public License as
7 published by the Free Software Foundation; either version 2.1 of the
8 License, or (at your option) any later version.
9
10 This file 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 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public License
16 along 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. */
34 void *
35 memmem (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