combinations of 4

[KF <dotslash () snosoft com>]

I am in the process of archiving power pc instructions that do not 
contain null... I have come to the decision that if I could generate a 
list of all possible unique 4 char combinations for a given list of 
alpha numeric chars then I could quickly sort the rest out in gdb...

My question is does anyone know how to programatically do this? Do i 
need to make use of bit shifting or something? I need only a program to 
print the list to the screen or something simple. Example output would 
be ...

AAAA
BBBBB
....
AAAB
AAAC
...
and so on but ONLY unique posibilities.

-KF