The PARI system is a package which is capable of doing formal computations on
recursive types at high speed.

It is possible to use PARI in two different ways:

1) as a library, which can be called from any upper-level language
application (for instance written in C, C++, Pascal or Fortran);

2) as a sophisticated programmable calculator, named GP, which contains 
most of the standard control instructions of a standard language
like C.

WWW: http://www.parigp-home.de/