CRC Calculation Of Byte Array in C#

Question

I am trying to port a piece of code that has been written in C language into C#. The purpose of the code is to calculate the CRC of an array of bytes. But so far I failed. My byte array looks something like this:

data = new byte[] { 0x01, 0x03, 0x00, 0x00, 0x00 };

And the C code I am trying to port to C# is as follows.

unsigned  int  crc_val(unsigned char* data_val, unsigned char data_len) 
{   
    int i;
    unsigned int crc_value=0ffff;
    while(data_len--)
    {
        crc_value^=*data_ val++;
        for(i=0;i<8;i++)
        {
            if(crc_value&0x0001)
                crc_value=(crc_value>> 1)^0xa001;
            else
                crc_value=crc_value>> 1;
        }
    }
    return (crc_value);
 }

Right now I have this:

private void GetCRC(byte[] message, ref byte[] CRC)
{
    ushort CRCFull = 0xFFFF;
    char CRCLSB;

    for (int i = 0; i < (message.Length) - 2; i++)
    {
        CRCFull = (ushort)(CRCFull ^ message[i]);

        for (int j = 0; j < 8; j++)
        {
            CRCLSB = (char)(CRCFull & 0x0001);
            CRCFull = (ushort)((CRCFull >> 1) & 0xFFFF);
            if (CRCLSB == 1)
                CRCFull = (ushort)(CRCFull ^ 0xA001);
        }
    }
    CRC[1] = (byte)((CRCFull >> 8) & 0xFF);
    CRC[0] = (byte)(CRCFull & 0xFF);
}

Please, please, please... Teach me how this code is written in C#, I am a quick learner and once I see the C# implementation of the above function, I shall pick it up from there and finish my application. I thank you for your attention and wish you all spend a fabulous day.

JonasH · Answer

Some tips:

unsigned char* -> byte[] or Span or IEnumerable
There is no need for a separate data_len parameter, just about all c# collections know their length, the only real exception would be raw pointers, but there is little need for those since the introduction of Span
0ffff -> looks like a typo, I assume 0xffff is intended

change your loop to a foreach, or for-loop i.e.

foreach(var b in data_val){ 
    crc_value^=b; 
    ...
}

bit operations should work the same way
You need to figure out what the length of the datatype is, unsigned int is minimum 16 bits, but may be 32 bit. In c# an uint is 32 bits, and ushort is 16 bit.
If you need to convert numbers to byte[] or vice versa, see BitConverter
C# has no implicit number to bool conversion, you need to do it explicitly, i.e. number != 0

CRC Calculation Of Byte Array in C#

1 Answers