RosettaCodeData/Task/Modular-exponentiation/Perl/modular-exponentiation.pl

use bigint;

sub expmod {
    my($a, $b, $n) = @_;
    my $c = 1;
    do {
        ($c *= $a) %= $n if $b % 2;
        ($a *= $a) %= $n;
    } while ($b = int $b/2);
    $c;
}

my $a = 2988348162058574136915891421498819466320163312926952423791023078876139;
my $b = 2351399303373464486466122544523690094744975233415544072992656881240319;
my $m = 10 ** 40;

print expmod($a, $b, $m), "\n";
print $a->bmodpow($b, $m), "\n";