optimized rabin-miller prime test (Rakudo)

rabin-miller.pl

my Bool multi sub is_prime(PrimeCandidate $n, Int $k) {
    my Int $d = $n - 1;
    my Int $s = 0;

    while $d %% 2 {
        $d div= 2;
        $s++;
    }

    for (2 ..^ $n).pick($k) -> $a {
        my $x = nqp::expmod_I(nqp::p6decont($a), nqp::p6decont($d), nqp::p6decont($n), Int);
#        my $x = modexp($a, $d, $n);
        next if $x == 1 or $x == $n - 1;


        my int $max = nqp::unbox_i($s);

        loop ( my int $i = 0; $i < $max; $i = $i + 1) {
            $x = nqp::expmod_I(nqp::p6decont($x), 2, nqp::p6decont($n), Int);
            return False if $x == 1;
            last if $x == $n - 1;
        }
        return False if $x !== $n - 1;
    }

    return True;
}