GMP/Description
From ScientificComputing
The GNU Multiple Precision Arithmetic Library (GMP) is a free library for arbitrary-precision arithmetic, operating on signed integers, rational numbers, and floating point numbers. GMP has a rich set of functions, and the functions have a regular interface. The basic interface is for C but wrappers exist for other languages including Ada, C++, C#, OCaml, Perl, PHP, Python, Ruby and R.