In order to allow for multiple big integer libraries, Math::BigInt was rewritten to use library modules for core math routines. Any module which follows the same API as this can be used instead by using the following:

use Math::BigInt lib => 'libname';

'libname' is either the long name ('Math::BigInt::Pari'), or only the short version like 'Pari'. To use this library:

use Math::BigInt lib => 'FastCalc';

Note that from Math::BigInt v1.76 onwards, FastCalc will be loaded automatically, if possible.