How does 15 character limitation help in a speed up?

[epixoip]

NeonFlash, here's an illustration of how much this optimization is good for.

Using the example code above, optimized for length 8:

Code:

epixoip@ike:$ ./md5substr_len8 babeface
Using 4 threads, 12x XOP
Elapsed: 17s  Progress: 1935998064/377149515625 (0.5%),  Speed: 117.33 M/s virt, 113.88 M/s real
babeface:>2HX2l

Same code, modified for a full single block (not optimizing out the ADDs):

Code:

epixoip@ike:$ ./md5substr_len55 babeface
Using 4 threads, 12x XOP
Elapsed: 29s  Progress: 2015997984/404567235136 (0.5%),  Speed: 74.67 M/s virt, 71.11 M/s real
babeface:>2HX2l

So by optimizing out the ADDs we gained 40%. And mind you this is on a low-end CPU (FX-4100.)