Clarification regarding CRC16 calculation-CodePudding

I am trying to calculate CRC for the first time. I have read a few pages that explain what is crc and how to calculate. Mainly this :

Could someone help me understand what is wrong here? Thanks in advance.

CodePudding user response：

You are missing a bit shift in the calculation. Change:

        ACC = buf[byte];

to:

        ACC = (unsigned)buf[byte] << 8;

Compare with this C# example code from Sunshine's Understanding and implementing CRC (Cyclic Redundancy Check) calculation:

public static ushort Compute_CRC16_Simple(byte[] bytes)
{
    const ushort generator = 0x1021; /* divisor is 16bit */
    ushort crc = 0; /* CRC value is 16bit */

    foreach (byte b in bytes)
    {
        crc ^= (ushort(b << 8); /* move byte into MSB of 16bit CRC */

        for (int i = 0; i < 8; i  )
        {
            if ((crc & 0x8000) != 0) /* test for MSB = bit 15 */
            {
                crc = (ushort((crc << 1) ^ generator);
            }
            else
            {
                crc <<= 1;
            }
        }
    }

    return crc;
}

It uses a different initial value to your function, but note the line that XORs the byte into the MSB of the 16-bit CRC:

        crc ^= (ushort(b << 8); /* move byte into MSB of 16bit CRC */