1void *memmem(const void *haystack_start, size_t haystack_len, const void *needle_start, size_t needle_len)
2{
3
4    const unsigned char *haystack = (const unsigned char *) haystack_start;
5    const unsigned char *needle = (const unsigned char *) needle_start;
6    const unsigned char *h = NULL;
7    const unsigned char *n = NULL;
8    size_t x = needle_len;
9
10    /* The first occurrence of the empty string is deemed to occur at
11    the beginning of the string.  */
12    if (needle_len == 0)
13        return (void *) haystack_start;
14
15    /* Sanity check, otherwise the loop might search through the whole
16        memory.  */
17     if (haystack_len < needle_len)
18       return NULL;
19
20    for (; *haystack && haystack_len--; haystack++) {
21
22        x = needle_len;
23        n = needle;
24        h = haystack;
25
26        if (haystack_len < needle_len)
27            break;
28
29        if ((*haystack != *needle) || ( *haystack + needle_len != *needle + needle_len))
30            continue;
31
32        for (; x ; h++ , n++) {
33            x--;
34
35            if (*h != *n) 
36                break;
37
38           if (x == 0)
39            return (void *)haystack;
40        }
41    }
42
43    return NULL;
44}