use strict;
use Benchmark qw/ cmpthese /;

cmpthese(
    10000,
    {
        regular => sub{ regrecurse($_) for ( map{10*$_} (1..10) ) },
        goto    => sub{ gotorecurse($_) for ( map{10*$_} (1..10) ) },
        iterative => sub{ iterative($_) for ( map{ 10* $_ } (1..10) ) }
    },
);

sub iterative
{
    my $n = shift;
    my $m = 1;
    for(1..$n) {
        $m *= $_;
    }
    return $m;
}

sub regrecurse
{
    my $n = shift;
    _reghelp(1, $n);
}

sub _reghelp
{
    my($n, $m) = @_;
    if($m <= 1) {
        return $n;
    }
    return _reghelp($n * $m, $m - 1);
}

sub gotorecurse
{
    my $n = shift;
    @_ = (1, $n);
    goto &_gotohelp;
}

sub _gotohelp
{
    if($_[1] <= 1) {
        return $_[0];
    }
    $_[0] *= $_[1];
    $_[1]--;

    goto &_gotohelp;
}