libzahl - big integer library

http://git.suckless.org/libzahl/tree/
The rationale for its creation can be found on the README file.
What do you think?

I can't believe it!
suigin-sama used a bashism.
Oh no!
[[ ... ]] is not defined by POSIX.

He's also using echo "$var". No good.
Read the beginning of this document.
http://www.etalabs.net/sh_tricks.html