parallel-calculations.p6

sub prime-factors ( Int $n where * > 0 ) {
    return $n if $n.is-prime;
    return [] if $n == 1;
    my $factor = find-factor( $n );
    sort flat prime-factors( $factor ), prime-factors( $n div $factor );
}

sub find-factor ( Int $n, $constant = 1 ) {
    my $x      = 2;
    my $rho    = 1;
    my $factor = 1;
    while $factor == 1 {
        $rho *= 2;
        my $fixed = $x;
        for ^$rho {
            $x = ( $x * $x + $constant ) % $n;
            $factor = ( $x - $fixed ) gcd $n;
            last if 1 < $factor;
        }
    }
    $factor = find-factor( $n, $constant + 1 ) if $n == $factor;
    $factor;
}

my @nums = (1_000_000 .. 100_000_000).pick: 100000;
 
my \factories = @nums.race(:batch(4)).map: *.&prime-factors.cache;

my $gmf = ([max] factories»[0] »=>« @nums).value;

say $gmf;