use warnings;
use strict;
use Benchmark;
use Test::More tests => 4;
 
my $_fact3;
$_fact3 = sub {
    my ($result, $counter, $max) = @_;
    return $result if $counter > $max;
    @_ = (($result * $counter), ($counter + 1), $max);
    goto $_fact3;
};
 
my $number = shift or die "No number supplied";
 
validate_factorial_routines($number);
 
print "Timing factorial of $number\n";
 
timethese(100_000, {
    'recursion 1' => sub { fact0($number) },
    'recursion 2' => sub { fact1($number) },
    'typeglob'    => sub { fact2($number) },
    'lexical'     => sub { fact3($number) },
});
 
sub validate_factorial_routines {
    my $num = shift;
    my @result = (fact0($num), fact1($num), fact2($num), fact3($num));
    is(fact0(5), 120, 'fact0 should return the correct amount');
    is(fact1(5), 120, 'fact1 should return the correct amount');
    is(fact2(5), 120, 'fact2 should return the correct amount');
    is(fact3(5), 120, 'fact3 should return the correct amount');
}
 
sub fact0 {
    my ($num) = @_;
    return _fact0(1,1,$num);
}

sub _fact0 {
    my ($result, $counter, $max) = @_;
    return $result if $counter > $max;
    return _fact1(($result * $counter), ($counter + 1), $max);
}

sub fact1 {
    @_ = ( 1, 1, $_[0] );
    return &_fact1;
}
 
sub _fact1 {
    my ($result, $counter, $max) = @_;
    return $result if $counter > $max;
    @_ = (($result * $counter), ($counter + 1), $max);
    return &_fact1;
}
 
sub fact2 {
    my ($num) = @_;
    @_ = (1, 1, $num);
    goto &_fact2;
}
 
sub _fact2 {
    my ($result, $counter, $max) = @_;
    return $result if $counter > $max;
    @_ = (($result * $counter), ($counter + 1), $max);
    goto &_fact2;
}
 
sub fact3 {
    my ($num) = @_;
    @_ = (1, 1, $num);
    goto $_fact3;
}

__output__

1..4
ok 1 - fact0 should return the correct amount
ok 2 - fact1 should return the correct amount
ok 3 - fact2 should return the correct amount
ok 4 - fact3 should return the correct amount
Timing factorial of 5
Benchmark: timing 100000 iterations of lexical, recursion 1, recursion 2, typeglob...
   lexical: 17 wallclock secs (16.19 usr +  0.02 sys = 16.20 CPU) @ 6171.70/s (n=100000)
recursion 1:  4 wallclock secs ( 3.74 usr +  0.00 sys =  3.74 CPU) @ 26773.76/s (n=100000)
recursion 2: 14 wallclock secs (13.41 usr +  0.00 sys = 13.41 CPU) @ 7459.35/s (n=100000)
  typeglob: 17 wallclock secs (17.61 usr +  0.00 sys = 17.61 CPU) @ 5678.91/s (n=100000)