Product::getSum

public function getSum($placeholder)
{
	if($placeholder === 'DISCOUNT_TOTAL')
	{
		$placeholder = 'DISCOUNT_SUM';
	}
	else
	{
		$placeholder = str_replace('_SUM', '', $placeholder);
	}
	$value = $this->data[$placeholder];
	if($value instanceof Value)
	{
		$value = $value->getValue();
	}

	return $value * $this->data['QUANTITY'];
}