sub fp_equal {
  my ($x,$y,$precision) = @_;
  $precision ||= 0.000001;

  return 1 if (! defined($x) and ! defined($y) );
  return 0 if (! defined($x) or  ! defined($y) );
  return 1 if ($x == $y);     # for 0 == 0
  ($x,$y) = ($y,$x) if (!$y); # for $y == 0
  return ( abs ( 1 - $x/$y ) <= $precision ) ? 1 : 0;
}