public function mul(Decimal $b, int $scale = null): Decimal
    {
        self::paramsValidation($b, $scale);

        if ($b->isZero()) {
            return DecimalConstants::Zero();
        }

        return self::fromString(
            \bcmul($this->value, $b->value, $this->scale + $b->scale),
            $scale
        );
    }