CODEWITHSUNDEEP
c#crc
user9964422
user9964422

Reputation: 119

c# generating a crc8 byte method with a byte array input

Right now I have the following code to generate a CRC-16 (Modbus). I am rather new to the idea of CRC, and I need to make a CRC-8. Can this code be modified to generated a CRC-8? I have the for loop starting at int = 1; and ending at i<tembByteList.Count - 1; because I am ignoring the first and last byte. 

public List<byte> crc16(List<byte> tempByteList)
    {
        ushort reg_crc = 0xFFFF;
        for(int i = 1; i<tempByteList.Count - 1; i++)
        {
            reg_crc ^= tempByteList[i];
            for(int j = 0; j < 8; j++)
            {
                if((reg_crc & 0x01) == 1)
                {
                    reg_crc = (ushort)((reg_crc >> 1) ^ 0xA001);
                }
                else
                {
                    reg_crc = (ushort)(reg_crc >> 1);
                }
            }
        }
        tempByteList.Insert(tempByteList.Count - 1, (byte)((reg_crc >> 8) & 0xFF));
        tempByteList.Insert(tempByteList.Count - 1, (byte)(reg_crc & 0xFF));
        return tempByteList;
    }

Upvotes: 0

Views: 1532

Answers (1)

Mark Adler
Mark Adler

Reputation: 112209

Sure. Just replace 0xa001 with 0xe5, and the initialization with zero (ushort reg_crc = 0;). That will generate the Bluetooth CRC-8. Using 0x8c will generate the Maxim CRC-8. And of course you'll only need to insert one byte into your message at the end.

If you would prefer a CRC that initializes with all ones, which would be sensitive to an initial string of zeros in the message, then you can use the ROHC CRC-8, which would use 0xe0 for the polynomial, and you would initialize reg_crc to 0xff.

By the way, the if statement could be replaced by a a ternary operator, which I consider to be more readable:

    reg_crc = (reg_crc & 1) != 0 ? (reg_crc >> 1) ^ POLY : reg_crc >> 1;

Upvotes: 1

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