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 : https://www.fatalerrors.org/a/implementation-of-crc-checksum-c-crc16-as-an-example.html
I have a code that calculates CRC16
uint16_t CalCrc(uint16_t crc_initial, uint8_t* buf,uint16_t len,uint16_t POLY)
{
unsigned int byte;
unsigned char k;
unsigned short ACC,TOPBIT;
unsigned short remainder = crc_initial;
TOPBIT = 0x8000;
for (byte = 0; byte < len; ++byte)
{
ACC = buf[byte];
remainder ^= ACC;
printf("new remainder = %u \n",remainder);
for (k = 8; k > 0; --k)
{
if (remainder & TOPBIT)
{
remainder = remainder << 1;
remainder = remainder ^ POLY;
}
else
{
remainder = (remainder << 1);
}
}
}
remainder = remainder^0x0000;
printf("result remainder = %02X \n",remainder);
return remainder;
}
and I call it my main.c:
uint8_t crc_buf[5] = {0x05,0x03,0x04,0x08,0x04};
CalCrc(0xffff,crc_buf,5,0x1021);
The result is:
result remainder = BDD5
As you can see from my function call, I pass 0xffff as initial crc value and 0x1021 as polynomial.
I am trying to confirm if my calculation is correct with some online crc calculators such as: http://www.sunshine2k.de/coding/javascript/crc/crc_js.html https://crccalc.com/
According to the initial and polynomial values that I use, the result should be:
Could someone help me understand what is wrong here? Thanks in advance.
