/// `<<` bitwise operator
/// @access public
/// @param {Number} $x - first value
/// @param {Number} $y - second value
/// @return {Number}
/// @require {function} power
/// @example scss
/// $value: bw-shift-left(42, 2);
/// // 168
@function bw-shift-left($x, $y) {
  @return $x * power(2, $y);
}