in reply to MD5 compatibility in PHP
Also run them on the empty string "" just to be sure.
It used to be that such functions would use the underlying system libraries, but now languages tend to use their own library functions. Nonetheless if it says 'MD5' I'd guess there's a high chance they will be the same function. There's probably a standard somewhere.
Update: My thinking, which may not be clear to casual bystanders, is that if two functions both claiming to be MD5 hashing functions return the same values for the null value and any other representative value then they are probably the same function. I keep thinking that I want the kernel (or nullspace) and a basis but that's not going to work because the functions are many-to-one. Wait four months till I finish my crypto course and then I'll be able to tell you :D