public static function big2dec(string $alpha): string
    {
	    static::checkExtensionOrFail();

        if (strlen($alpha) <= 0) {
            throw new Exception('Got empty string in big2dec, can not proceed');
        }

        $alphabet = array_flip(static::NUMBERS);
        $mod = (string)count($alphabet);

        $x = '0';
        for ($i = 0, $j = strlen($alpha) - 1; $i < strlen($alpha); $i++, $j--) {
            $char = substr($alpha, $j, 1);
            $val = $alphabet[$char];

            $x = bcadd($x, bcmul((string)$val, bcpow($mod, (string)$i)));
        }

        return $x;
    }