The GNU MP library (GMP) provides routines for arbitrary precision integer and floating point arithmetic, and is distributed under the terms of the GNU Lesser General Public License (LGPL), version 3, and also under the GNU General Public License (GPL), version 2. It is available at
ftp://ftp.gnu.org/gnu/gmp/ and
http://gmplib.org/. To see whether your copy of Macaulay2 is linked with it (or with MPIR), examine the variable
version.