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

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::GMP $m;
  }
}

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

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

cmpthese(10, {
        'recurse' => sub { recurse( 25_000) },
        'iterate' => sub { iterate( 25_000) },
        'direct' =>  sub { direct(  25_000) },
    });