The optimization is achieved by following techniques:
> hashing of needle.
> hashing avoids scanning of duplicate entries in needle across the string.
> initializing the hash table with Vector instructions (VSX) by quadword access.
> unrolling when scanning for character in string across hash table.
Joseph Myers
Vidya Ranganathan
Allan McRae
Paul Eggert
Ulrich Drepper
Jakub Jelinek