protected function encodeFilename($original)
    {
        $cp437 = $this->utf8ToCp($original);
        if ($cp437 === $original) {
            return array($original, '');
        }

        $extra = pack(
            'vvCV',
            0x7075, // tag
            strlen($original) + 5, // length of file + version + crc
            1, // version
            crc32($original) // crc
        );
        $extra .= $original;

        return array($cp437, $extra);
    }