use Benchmark qw(:all);

sub recurse {
  #divide and conquer
  unshift @_, 1 if 2 != @_;
  my ($m, $n) = @_;

  if ($m < $n) {
    my $k = int($m/2 + $n/2);
    return recurse($m, $k) * recurse($k+1, $n);
  }
  else {
    return $m
  }
}

sub iterate {
   my $result = 1;
   $result *= $_ for 2..shift;
   return $result
}

cmpthese(10_000, {
        'recurse' => sub { recurse( 160) },
        'iterate' => sub { iterate( 160) },
    });

##</code><code>##

Benchmark: timing 10000 iterations of iterate, recurse...
   iterate:  2 wallclock secs ( 1.53 usr +  0.00 sys =  1.53 CPU) @ 6535.95/s (n=10000)
   recurse: 23 wallclock secs (22.82 usr +  0.00 sys = 22.82 CPU) @ 438.21/s (n=10000)
          Rate recurse iterate
recurse  438/s      --    -93%
iterate 6536/s   1392%      --