use Benchmark qw(:all);
use  Math::BigInt;

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, $n);
  }
  else {
     return new Math::BigInt->new($m);
  }
}

sub iterate {
   my $result = Math::BigInt->new(1);
   $result *= $_ for 2..shift;
   return $result
}

sub direct {
   my $result =  Math::BigInt->new(shift);
   return $result->bfac();
}

cmpthese(1000, {
        'recurse' => sub { recurse( 100) },
        'iterate' => sub { iterate( 100) },
        'direct' =>  sub { direct(  100) },
    });