Another Delphi to Java porting issue

Question

I'm porting an old application written in Delphi to Java. I'm having some trouble with this function, that calculates the CRC of a transmitted message. Here's the original code: ``` if(ReceivedMessage[slot].Message[1] = $FD) and (ReceivedMessage[slot].MessageLength in [1..16]) and (ReceivedMessage[slot].Message[counter] = $FF) then begin index := 2; ReceivedMessage[slot].DataReady := TRUE; for counter := 1 to ReceivedMessage[slot].MessageLength do begin Inc(index); if ReceivedMessage[slot].Message[index] < $F8 then ReceivedMessage[slot].Data[counter] := ReceivedMessage[slot].Message[index] else if ReceivedMessage[slot].Message[index] = $F8 then begin Inc(index); ReceivedMessage[slot].Data[counter] := ReceivedMessage[slot].Message[index] or $F0; end else ReceivedMessage[slot].DataReady := FALSE; // Invalid data end; if ReceivedMessage[slot].DataReady = TRUE then begin Inc(index); if ReceivedMessage[slot].Message[index] < $F8 then ReceivedMessage[slot].CRC := ReceivedMessage[slot].Messa…

Accepted Answer

Remember:

Java byte is signed. So:

```
byte test = (byte)255;
System.out.println(test);
```

will output: `-1`

and

```
    byte test = (byte)255;
    System.out.println(test == 255);
```

will print `false`, but

```
    byte test = (byte)255;
    System.out.println((test & 255) == 255);
```

will do what I think you want to achieve (in this case prints `true`).

To get unsigned (byte) values use `(array[index] & 255)`.

You will have to do the masking with 0xff everywhere, otherwise you will get sign extended integers for byte values larger than 127.

For compares you can also always do a cast to `byte` (e.g. `if(test == (byte)255)`) but I think one should stick to a single conversion, so I would recommend going with the `& 0xff` masking.

Another Delphi to Java porting issue

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