/*
* The memmem() function finds the start of the first occurrence of the
* substring 'needle' of length 'nlen' in the memory area 'haystack' of
* length 'hlen'.
*
* The return value is a pointer to the beginning of the sub-string, or
* NULL if the substring is not found.
*/
char* memmem(char* haystack, size_t hlen, char* needle, size_t nlen)
{
    int needle_first;
    char *p = haystack;
    size_t plen = hlen;

    if (!nlen)
        return NULL;

    needle_first = *(unsigned char *)needle;

    while (plen >= nlen && (p = memchr(p, needle_first, plen - nlen + 1)) != NULL)
    {
        if (!memcmp(p, needle, nlen))
            return (char*)p;

        p++;
        plen = hlen - (p - haystack);
    }

    return NULL;
}