1/* Copyright (C) 1991-2019 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <http://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#ifndef _LIBC
28# define __builtin_expect(expr, val) (expr)
29# define __memmem memmem
30#endif
31
32#define RETURN_TYPE void *
33#define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l))
34#define FASTSEARCH(S,C,N) (void*) memchr ((void *)(S), (C), (N))
35#include "str-two-way.h"
36
37#undef memmem
38
39/* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK
40 if NEEDLE_LEN is 0, otherwise NULL if NEEDLE is not found in
41 HAYSTACK. */
42void *
43__memmem (const void *haystack_start, size_t haystack_len,
44 const void *needle_start, size_t needle_len)
45{
46 /* Abstract memory is considered to be an array of 'unsigned char' values,
47 not an array of 'char' values. See ISO C 99 section 6.2.6.1. */
48 const unsigned char *haystack = (const unsigned char *) haystack_start;
49 const unsigned char *needle = (const unsigned char *) needle_start;
50
51 if (needle_len == 0)
52 /* The first occurrence of the empty string is deemed to occur at
53 the beginning of the string. */
54 return (void *) haystack;
55
56 /* Sanity check, otherwise the loop might search through the whole
57 memory. */
58 if (__glibc_unlikely (haystack_len < needle_len))
59 return NULL;
60
61 /* Use optimizations in memchr when possible, to reduce the search
62 size of haystack using a linear algorithm with a smaller
63 coefficient. However, avoid memchr for long needles, since we
64 can often achieve sublinear performance. */
65 if (needle_len < LONG_NEEDLE_THRESHOLD)
66 {
67 haystack = memchr (haystack, *needle, haystack_len);
68 if (!haystack || __builtin_expect (needle_len == 1, 0))
69 return (void *) haystack;
70 haystack_len -= haystack - (const unsigned char *) haystack_start;
71 if (haystack_len < needle_len)
72 return NULL;
73 /* Check whether we have a match. This improves performance since we
74 avoid the initialization overhead of the two-way algorithm. */
75 if (memcmp (haystack, needle, needle_len) == 0)
76 return (void *) haystack;
77 return two_way_short_needle (haystack, haystack_len, needle, needle_len);
78 }
79 else
80 return two_way_long_needle (haystack, haystack_len, needle, needle_len);
81}
82libc_hidden_def (__memmem)
83weak_alias (__memmem, memmem)
84libc_hidden_weak (memmem)
85
86#undef LONG_NEEDLE_THRESHOLD
87