public static function unpack($string)
    {
        if (strlen($string) !== 8) {
            throw new StorageException("The string is not 64 bit long.");
        }
        $unpack = unpack("d", $string);
        if (!is_array($unpack) || !array_key_exists(1, $unpack)) {
            throw new StorageException("Could not unpack string.");
        }
        return $unpack[1];
    }