memmem.c revision 330897 
1/*-
2 * SPDX-License-Identifier: MIT
3 *
4 * Copyright (c) 2005 Pascal Gloor <pascal.gloor@spale.com>
5 * Copyright (c) 2005-2014 Rich Felker, et al.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 * 3. The name of the author may not be used to endorse or promote
16 *    products derived from this software without specific prior written
17 *    permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 */
31
32#include <sys/cdefs.h>
33__FBSDID("$FreeBSD: stable/11/lib/libc/string/memmem.c 330897 2018-03-14 03:19:51Z eadler $");
34
35#include <string.h>
36
37/*
38 * Find the first occurrence of the byte string s in byte string l.
39 */
40
41void *
42memmem(const void *l, size_t l_len, const void *s, size_t s_len)
43{
44	register char *cur, *last;
45	const char *cl = (const char *)l;
46	const char *cs = (const char *)s;
47
48	/* empty "s" matches the beginning of "l" */
49	if (s_len == 0)
50		return (void *)cl;
51
52	/* "s" must be smaller or equal to "l" */
53	if (l_len < s_len)
54		return NULL;
55
56	/* special case where s_len == 1 */
57	if (s_len == 1)
58		return memchr(l, (int)*cs, l_len);
59
60	/* the last position where its possible to find "s" in "l" */
61	last = (char *)cl + l_len - s_len;
62
63	for (cur = (char *)cl; cur <= last; cur++)
64		if (cur[0] == cs[0] && memcmp(cur, cs, s_len) == 0)
65			return cur;
66
67	return NULL;
68}
69