B4J Question CRC -CCITT vb.net function conversion to b4j

[Michael Sergio]

Hi.
I would like some help with the conversion from this function from vb.net :

    Public Function ComputeCRC(val As Byte()) As Byte()

        Dim crc As Long
        Dim q As Long
        Dim c As Byte
        crc = 0
        For i As Integer = 0 To val.Length - 1
            c = val(i)
            q = (crc Xor c) And &HF
            crc = (crc >> 4) Xor (q * &H1081)
            q = (crc Xor (c >> 4)) And &HF
            crc = (crc >> 4) Xor (q * &H1081)
        Next
        Return New Byte() {CByte(crc And &HFF), CByte(crc >> 8)}

    End Function

I need this to calculate the checksum for my data that i`m sending to the SerialPort.
I tried making a conversion, but I don`t know even how to begin.
Any help would be appreciated.
Thank you.

 

[Cableguy]

All I can help with is by telling you that all bitwise operations are accessible using the Byte keyword

 

[Erel]

It is better to post an example of input and the expected output so we can test it.

Try this:

Sub ComputeCRC (val() As Byte) As Byte()
   Dim crc As Long
   Dim q As Long
   Dim c As Byte
   For i = 0 To val.Length - 1
     c = val(i)
     q = Bit.And(Bit.Xor(crc, c), 0xF)
     crc = Bit.Xor(Bit.ShiftRight(crc, 4), q * 0x1081)
     q = Bit.And(Bit.Xor(crc, Bit.ShiftRight(c, 4)), 0xF)
     crc = Bit.Xor(Bit.ShiftRight(crc, 4), q * 0x1081)
   Next
   Return Array As Byte(Bit.And(crc, 0xFF), Bit.ShiftRight(crc, 8))
End Sub

You can use ByteConverter.HexFromBytes to see the bytes arrays values.

 

[Michael Sergio]

It is better to post an example of input and the expected output so we can test it.

Try this:

Sub ComputeCRC (val() As Byte) As Byte()
   Dim crc As Long
   Dim q As Long
   Dim c As Byte
   For i = 0 To val.Length - 1
     c = val(i)
     q = Bit.And(Bit.Xor(crc, c), 0xF)
     crc = Bit.Xor(Bit.ShiftRight(crc, 4), q * 0x1081)
     q = Bit.And(Bit.Xor(crc, Bit.ShiftRight(c, 4)), 0xF)
     crc = Bit.Xor(Bit.ShiftRight(crc, 4), q * 0x1081)
   Next
   Return Array As Byte(Bit.And(crc, 0xFF), Bit.ShiftRight(crc, 8))
End Sub

You can use ByteConverter.HexFromBytes to see the bytes arrays values.

Yes, this is perfect , it is EXACTLY what i need.

Dim FstLine As String="FC0511" 
    Dim Secline As String= bc.HexFromBytes(ComputeCRC(bc.HexToBytes(FstLine)))
    Log(FstLine & Secline)

The result that I expected was : "FC05112756" , and the conversion is working, i have the same result in B4j.

Thank you very much for your help and for this awesome IDE .I`m still learning, but i made some basic programs that i use on my Raspberry Pi , including the usage of the GPIO`s.
Best wishes.

 

[sales]

It is better to post an example of input and the expected output so we can test it.

Try this:

Sub ComputeCRC (val() As Byte) As Byte()
   Dim crc As Long
   Dim q As Long
   Dim c As Byte
   For i = 0 To val.Length - 1
     c = val(i)
     q = Bit.And(Bit.Xor(crc, c), 0xF)
     crc = Bit.Xor(Bit.ShiftRight(crc, 4), q * 0x1081)
     q = Bit.And(Bit.Xor(crc, Bit.ShiftRight(c, 4)), 0xF)
     crc = Bit.Xor(Bit.ShiftRight(crc, 4), q * 0x1081)
   Next
   Return Array As Byte(Bit.And(crc, 0xFF), Bit.ShiftRight(crc, 8))
End Sub

You can use ByteConverter.HexFromBytes to see the bytes arrays values.

that code will generate CRC-CCITT (Kermit) from: FC0511 CRC: 2756

then i need to get CRC-CCITT (XModem) from: FC0511 expected CRC: 6BD6

https://www.lammertbies.nl/comm/info/crc-calculation.html

which code should be modified?

many thanks