memmem.c

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/*-
 * 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>

/*
 * 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 register char *cur, *last;
    const char* cl = (const char*)l;
    const char* cs = (const char*)s;

    /* we need something to compare */
    if(l_len == 0 || s_len == 0)
    {
        return NULL;
    }

    /* "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, (int)*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*)(uintptr_t)cur;
        }
    }

    return NULL;
}