// with hash functions from http://pastebin.com/nb51hyvd you could do substring matching like this: (pseudocode)

// features:
// ** no extra data storage, in fact needle can be freed immediately (if you trust the hash)
// ** only one loop through haystack, with each loop only consisting of 2 small hash operations

int InStr(String haystack, String needle) {
    int needleHash = Hash(needle);
    int hash = Hash(SubString(haystack, 0, needle.length));
    if (hash == needleHash)
        return 0;
    for(int i = 0, j = needle.length; j < haystack.length; i++, j++)
    {
        hash = Hash_Remove(hash, haystack[i]); // remove the first
        hash = Hash_Add(hash, haystack[j]);  // add the next
        if (hash == needleHash)
            return i + 1;
    }
    return -1;
}