How do I crack substr hash?

[epixoip]

here's my stab at creating a program to crack this type of hash. not exceptionally good since it doesn't use sse2 or anything, but it is multithreaded and should be quite a bit faster than the other two that atom and undeath provided. seems to reliably find a collision in under a minute on my box.

http://bindshell.nl/pub/md5substr_mt.c

Code:

epixoip@db:~$ ./md5substr cafebabe
Using 16 threads.
Elapsed: 38s  Progress: 3227859000/377149515625 (0.9%),  Speed: 84.9 M/s
cafebabe:t,gr>N

epixoip@db:~$ ./md5substr deadfa11
Using 16 threads.
Elapsed: 40s  Progress: 3397629000/377149515625 (0.9%),  Speed: 84.9 M/s
deadfa11:G,vzY;

epixoip@db:~$ ./md5substr deadbabe
Using 16 threads.
Elapsed: 32s  Progress: 2718719000/377149515625 (0.7%),  Speed: 85.0 M/s
deadbabe:=+y51e

epixoip@db:~$ ./md5substr ba5eba11
Using 16 threads.
Elapsed: 33s  Progress: 2803169000/377149515625 (0.7%),  Speed: 84.9 M/s
ba5eba11:),;~u`

epixoip@db:~$ ./md5substr aaaaaaaa
Using 16 threads.
Elapsed: 20s  Progress: 1698384000/377149515625 (0.5%),  Speed: 84.9 M/s
aaaaaaaa:8*pU]]