compat/memmem.c

/*	$OpenBSD: memmem.c,v 1.4 2015/08/31 02:53:57 guenther Exp $ */
/*-
 * Copyright (c) 2005 Pascal Gloor <pascal.gloor@spale.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <string.h>

#include "compat.h"

/*
 * Find the first occurrence of the byte string s in byte string l.
 */

void *
memmem(const void *l, size_t l_len, const void *s, size_t s_len)
{
	const char *cur, *last;
	const char *cl = l;
	const char *cs = s;

	/* a zero length needle should just return the haystack */
	if (s_len == 0)
		return (void *)cl;

	/* "s" must be smaller or equal to "l" */
	if (l_len < s_len)
		return NULL;

	/* special case where s_len == 1 */
	if (s_len == 1)
		return memchr(l, *cs, l_len);

	/* the last position where its possible to find "s" in "l" */
	last = cl + l_len - s_len;

	for (cur = cl; cur <= last; cur++)
		if (cur[0] == cs[0] && memcmp(cur, cs, s_len) == 0)
			return (void *)cur;

	return NULL;
}