That is with gcc -O2 (version 4.8) on an i7-4771 CPU With -O3 the speedup is even more: 7.2x on a Xeon E5-2690 (Sandy Bridge) with gcc 4.6.3 (same code genera

That is with gcc -O2 (version 4.8) on an i7-4771 CPU With -O3 the speedup is even more: 7.2x on a Xeon E5-2690 (Sandy Bridge) with gcc 4.6.3 (same code generated) it was "only" 3x