use strict;
use warnings 'all';

sub factorial_r {
    my ($n) = @_;
    
    return $n if ($n < 2);
    return $n * factorial_r($n-1);
}

sub factorial_i {
    my ($n) = @_;
    
    my $i = $n - 1;
    $n *= ($n - $i--) while $i > 1;
    return $n;
}

sub factorial_r_extra {
    my ($n) = @_;
    my $x = "blah" x 100;
    return $n if ($n < 2);
    return $n * factorial_r_extra($n-1);
}

sub factorial_i_extra {
    my ($n) = @_;
    my $x = "blah" x 100;
    my $i = $n - 1;
    $n *= ($n - $i--) while $i > 1;
    return $n;
}

use Benchmark qw(timethese);
timethese(100000, {
    first  => sub { factorial_r(50) },
    second => sub { factorial_i(50) },
});