public static function fromArbitraryBase(string $number, string $alphabet) : BigInteger
    {
        if ($number === '') {
            throw new NumberFormatException('The number cannot be empty.');
        }

        $base = \strlen($alphabet);

        if ($base < 2) {
            throw new \InvalidArgumentException('The alphabet must contain at least 2 chars.');
        }

        $pattern = '/[^' . \preg_quote($alphabet, '/') . ']/';

        if (\preg_match($pattern, $number, $matches) === 1) {
            throw NumberFormatException::charNotInAlphabet($matches[0]);
        }

        $number = Calculator::get()->fromArbitraryBase($number, $alphabet, $base);

        return new BigInteger($number);
    }