#!perl -w
use strict;
use Benchmark;

# Fibonnaci Number to calculate. 
use vars ('$n'); # Make it global, but appease strict.
$n = 30;

my $iter = 100_000;
timethese( $iter, {
    Binet => '&FibBinet($n)',
    Golf => '&FibGolf($n)',
#    Recursive => '&FibRecursive($n)',
});


sub FibRecursive
{
  my $index = shift;
  return 0 if 0 == $index;
  return 1 if 1 == $index;
  return FibRecursive( $index - 1 ) + FibRecursive( $index - 2 );
}

sub FibGolf
{
  my $index = shift;
  my $acc = 1;
  my $tmp;

  while( $index-- )
  {
    $acc-=$tmp+=$acc*=-1;
  }

  return $acc;
}

sub FibBinet
{
  my $index = shift;
  my $root5 = sqrt 5;

  return ( ( ( 1 + $root5 ) / 2 ) ** $index 
         - ( ( 1 - $root5 ) / 2 ) ** $index ) / $root5;
}