swift 转码关于gbk编码问题

Swift 我想把uint8数组转成字符串，是gbk编码的。请教下我应该怎么转

 func UTF8ToGB2312(str: String) -> (NSData?, UInt) {
    let enc = CFStringConvertEncodingToNSStringEncoding(UInt32(CFStringEncodings.GB_18030_2000.rawValue))

    var data = str.dataUsingEncoding(enc, allowLossyConversion: false)

    return (data, enc)
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let (data, enc) = UTF8ToGB2312("abcd1234")
        let gbkStr = NSString(data: data!, encoding: enc)!

        print("GBK string is: \(gbkStr)")
    }
}