Android Question Byte question?

[wes58]

I receive data from BLE device which is in Hex Bytes (13 bytes of data).
When the received bytes are converted to hex string using ByteConverter: Dim notifyData As String = bc.HexFromBytes(data)
Displayed data look like this: 350100BF942C61B205CA18BA0B
But, when I display the value of each data byte as int using the following code:

            Dim notifyData As String = bc.HexFromBytes(data)
            Log(notifyData.Length & " " & notifyData)
            Dim j As Int = 0
            Dim s As String
            If data.Length = 13 Then
                Dim i As Int
                For i = 0 To data.Length-1
                    s = notifyData.SubString2(j, j+2)
                    j = j+2
                    Log(i & " " & data(i) & " " & s)
                Next
            End If

The log output is:

350100BF942C61B205CA18BA0B
0 53 35
1 1 01
2 0 00
3 -65 BF
4 -108 94
5 44 2C
6 97 61
7 -78 B2
8 5 05
9 -54 CA
10 24 18
11 -70 BA
12 11 0B

So in the log you can see that for example for byte 3 - for hex value of 0xBF the byte value is displayed as -65
The same happens for byte 4, 7, 9, 11

I can convert it to receive the correct value, by checking if it is negative value:

                    Dim k As Int
                    k = data(i)
                    If k < 0 Then
                        k = k + 256
                    End If

And then get: 256 + (- 65) = 191, which what 0xBF is.

The question is why? Why bytes values are treated as signed int?

 

[OliverA]

They are actually treated as signed bytes. All integers (of various bit sizes) are signed.

 

[wes58]

They are actually treated as signed bytes. All integers (of various bit sizes) are signed.

Yes, but integer is 4bytes and if I want to get an integer value from 1 byte (8 bits) I would expect to get 8 bits.
So the only way is to convert to a hexstring and then back to int. The conversion doesn't care about signed or not signed.
I guess that's a limitation of Java as well. In C you can define variable as "char" or "unsigned char", "int" or "unsigned int".

 

[OliverA]

Try

  k = Bit.And(data(i), 0xFF)

This should properly convert your byte to int as an unsigned byte

 

[wes58]

Try

  k = Bit.And(data(i), 0xFF)

This should properly convert your byte to int as an unsigned byte

Yes, thanks. This will do it