private function toDecimal(string $bytes) : string
    {
        $result = '0';
        $power = '1';

        for ($i = \strlen($bytes) - 1; $i >= 0; $i--) {
            $index = \ord($bytes[$i]);

            if ($index !== 0) {
                $result = $this->add($result, ($index === 1)
                    ? $power
                    : $this->mul($power, (string) $index)
                );
            }

            if ($i !== 0) {
                $power = $this->mul($power, '256');
            }
        }

        return $result;
    }