public function sqrt(int $scale) : BigDecimal
    {
        if ($scale < 0) {
            throw new \InvalidArgumentException('Scale cannot be negative.');
        }

        if ($this->value === '0') {
            return new BigDecimal('0', $scale);
        }

        if ($this->value[0] === '-') {
            throw new NegativeNumberException('Cannot calculate the square root of a negative number.');
        }

        $value = $this->value;
        $addDigits = 2 * $scale - $this->scale;

        if ($addDigits > 0) {
            // add zeros
            $value .= \str_repeat('0', $addDigits);
        } elseif ($addDigits < 0) {
            // trim digits
            if (-$addDigits >= \strlen($this->value)) {
                // requesting a scale too low, will always yield a zero result
                return new BigDecimal('0', $scale);
            }

            $value = \substr($value, 0, $addDigits);
        }

        $value = Calculator::get()->sqrt($value);

        return new BigDecimal($value, $scale);
    }