[fpc-pascal] Calculating CRC16?

[Bo Berglund]

On Tue, 25 Oct 2022 08:30:19 +0200, Bo Berglund via fpc-pascal
<fpc-pascal at lists.freepascal.org> wrote:

>I am working on a handler for IoT data from an electricity meter which
>communicates via TTL serial at 115200 baud. It only sends data in packets of
>less than 1 kbytes every 5-10 seconds.
>
>In order to validate the data I need to check the CRC16 checksum at the end and
>here is where I don't find a good way to do it...
>The application will run on Linux so I checked for operating support but found
>only sksum, which apparently does not do CRC16.
>
>Is there some package or code available somewhere which can calculate the CRC16
>value over a byte array of some 1000 bytes?
>
>In a description of the protocol after showing the data structure it adds this:
>
>crc16 = libscrc.ibm(example_data).to_bytes(2, 'big').hex() >> '7945'
>
>Googling libscrc brings me to Python code on GitHub, which I am not really able
>to use, never programmed Python...
>https://github.com/hex-in/libscrc
>
>Anyone able to help with FPC implementation?

I have found a c++ function that purportedly does CRC16:

unsigned int CRC16(unsigned int crc, unsigned char *buf, int len)
{
	for (int pos = 0; pos < len; pos++)
    {
		crc ^= (unsigned int)buf[pos];    // * XOR byte into least sig. byte of
crc
                                          // * Loop over each bit
        for (int i = 8; i != 0; i--)
        {
            // * If the LSB is set
            if ((crc & 0x0001) != 0)
            {
                // * Shift right and XOR 0xA001
                crc >>= 1;
				crc ^= 0xA001;
			}
            // * Else LSB is not set
            else
                // * Just shift right
                crc >>= 1;
		}
	}
	return crc;
}

Can someone please decode this into pascal?


-- 
Bo Berglund
Developer in Sweden