powm_gmp

Compute $base ** $exp mod $mod without building the full power.

Synopsis

my $base = Math::GMP->new(157);
my $exp  = Math::GMP->new(100);
my $mod  = Math::GMP->new(5013);
my $r    = $base->powm_gmp($exp, $mod);   # 157**100 mod 5013

The workhorse of RSA-style modular exponentiation: fast enough for thousand-bit exponents, and never materialises the intermediate $base ** $exp. Behaviour is undefined when $mod is 0.