public function number(): string
    {
        $num = gmp_import($this->_flags, 1, GMP_MSW_FIRST | GMP_BIG_ENDIAN);
        $last_octet_bits = $this->_width % 8;
        $unused_bits = $last_octet_bits ? 8 - $last_octet_bits : 0;
        $num >>= $unused_bits;
        return gmp_strval($num, 10);
    }