openssl passwd crypt algorithm and salting function

I have been playing around with the command:

$openssl passwd -crypt -salt

And I really need to see the actual code for which the crypt algorithm and the function for salting the user's input password prior to it's encryption.

Where or how do I view documentation relating to these codes and the code themselves?

Also I was wondering if there is a package that I can modify these definitions so I can discover how all the different flavours of spam are made