STk bignums are implemented with the GNU mp APIs. This library provides a
VERY EFFICIENT implementation of multiple precision numbers. This library
is placed under the GNU GENERAL PUBLIC LICENSE. However, to avoid to fall
under the restrictive GPL terms you can use the FGMP package (FGMP is a
public domain implementation of a subset of the GNU gmp library with the
same API, written by Mark Henderson <firstname.lastname@example.org>). This package
has the advantage to be FREE, and disadventage to be SLOW.
So, if your concern is speed, and if the GPL is not a problem for you,
use the Gnu package.