get human readable disk size in swift.

human_readables.swift

    /**
     * Get the human readable size String according to total bytes.
     */
    func uInt64ToHumanReadable(input: Int64, bBinary: Bool) -> String! {
        let unit:Int64 = bBinary ? 1024 : 1000;
        if input < unit { return String(describing: input)+" B"; }
        let exp:Int = Int(log(Double(input)) / log(Double(unit)));
        let units: String = (bBinary ? "KMGTPE": "kMGTPE");
        let startIndex = units.index(units.startIndex, offsetBy: exp-1);
        let endIndex = units.index(units.startIndex, offsetBy: exp-1);
        let str = units[startIndex...endIndex]+(bBinary ? "i": "");
        return String(format: "%.2f %@B",  Double(input) / pow(Double(unit), Double(exp)), str);
    }