private function getDosTime($timestamp = 0) {
        $timestamp = (int)$timestamp;
        $oldTZ = @date_default_timezone_get();
        date_default_timezone_set('UTC');
        $date = ($timestamp == 0 ? getdate() : getdate($timestamp));
        date_default_timezone_set($oldTZ);
        if ($date["year"] >= 1980) {
            return pack("V", (($date["mday"] + ($date["mon"] << 5) + (($date["year"]-1980) << 9)) << 16) |
                             (($date["seconds"] >> 1) + ($date["minutes"] << 5) + ($date["hours"] << 11)));
        }
        return "\x00\x00\x00\x00";
    }