/// Power function, using Compass if enabled
/// @access private
/// @param {Number} $x - first value
/// @param {Number} $y - second value
/// @return {Number}
@function power($x, $y) {
  @if function-exists('pow') == true {
    @return pow($x, $y);
  }

  $ret: 1;

  @if $y > 0 {
    @for $i from 1 through $y {
        $ret: $ret * $x;
    }
  } @else {
    @for $i from $y to 0 {
        $ret: $ret / $x;
    }
  }

  @return $ret;
}