#include "stdio.h"

// CRC8_SAE_J1850 
// - Polynomial: 0x1D
// - Start Val: 0xFF
// - Final Val: 0xFF
unsigned char Crc_CalculateCRC8(unsigned char *data, int length, unsigned char initVal)
{
    unsigned long crc;
    int i, bit;
	
    crc = initVal;
	
    for (i=0; i<length; i++)
	{
        crc ^= data[i];
		//printf("DATA[%i]: 0x%X\n", i, data[i]);
		
        for (bit=0 ; bit<8 ; bit++)
		{
            if ( (crc & 0x80)!=0 )
			{
                crc <<= 1;
                crc ^= 0x1D; // (Polynom)
            }
            else
			{
                crc <<= 1;
            }
        }
    }
	
	//printf("CRC = 0x%X\n", crc);
	crc &= 0xFF;
	crc ^= 0xFF; // -> needed | not needed?!
	printf("CRC = 0x%X\n", crc);
	//printf("CRC = 0x%X\n", crc);
	printf("----------\n");

	return crc;
}

// input data
unsigned char crcData1[] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }; // Counter = 0
unsigned char crcData2[] = { 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }; // Counter = 1

int main(int argc, char **argv)
{
	unsigned int dataID = 0x01234;
	unsigned char daID1  = dataID;
	unsigned char daID2  = (dataID>>8);
	unsigned char CRC = 0;
	
	printf("\nDataID is = 0x%X (0x%02X | 0x%02X)\n", dataID, daID1, daID2);
	
	CRC = Crc_CalculateCRC8(&daID1, 1, 0xFF);
	CRC = Crc_CalculateCRC8(&daID2, 1, CRC);
	CRC = Crc_CalculateCRC8(crcData1, 7, CRC);
	CRC ^= 0xFF;
	
	printf("Final CRC for data: 0x%02X\n", CRC);

	
    return 0;
}

import numpy as np
from numpy.linalg import norm
import scipy.signal 

a = np.random.random((20,20))
a /= norm(a)

b = np.random.random((20,20))
b /= norm(b)


c = scipy.signal.convolve2d(a, b, mode="same", boundary="wrap")

print(norm(a), norm(b), norm(c), norm(b)/norm(c))