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Calculating the CRC8 with program (non-table approach) on C looks like:
/***************************************************/
unsigned char CRC8( unsigned char crc, unsigned char data )
/***************************************************/
// 8 bits CRC calculation. Initial value of the CRC register is 0
// polynomial X^8 + X^5 + X^4 + 1
// crc is a 8 bit number - contains the current CRC
// data is an 8 bit number
{
unsigned char i; // counter
unsigned char feed_back;
for (i = 8; i !=0; i--)
{
feed_back = (crc ^ data) & 0x01; // get the backfeed
data >>= 1; // shift data
crc >>= 1; // shift CRC register
if (feed_back)
{
crc ^= 0x8C; // if feedback == 1
}
}
return crc;
}
Calculating the CRC8 with program (table approach) on C looks like:
const unsigned char CRC_table[256] = {
0, 94, 188, 226, 97, 63, 221, 131, 194, 156, 126, 32, 163, 253, 31, 65,
157, 195, 33, 127, 252, 162, 64, 30, 95, 1, 227, 189, 62, 96, 130, 220,
35, 125, 159, 193, 66, 28, 254, 160, 225, 191, 93, 3, 128, 222, 60, 98,
190, 224, 2, 92, 223, 129, 99, 61, 124, 34, 192, 158, 29, 67, 161, 255,
70, 24, 250, 164, 39, 121, 155, 197, 132, 218, 56, 102, 229, 187, 89, 7,
219, 133, 103, 57, 186, 228, 6, 88, 25, 71, 165, 251, 120, 38, 196, 154,
101, 59, 217, 135, 4, 90, 184, 230, 167, 249, 27, 69, 198, 152, 122, 36,
248, 166, 68, 26, 153, 199, 37, 123, 58, 100, 134, 216, 91, 5, 231, 185,
140, 210, 48, 110, 237, 179, 81, 15, 78, 16, 242, 172, 47, 113, 147, 205,
17, 79, 173, 243, 112, 46, 204, 146, 211, 141, 111, 49, 178, 236, 14, 80,
175, 241, 19, 77, 206, 144, 114, 44, 109, 51, 209, 143, 12, 82, 176, 238,
50, 108, 142, 208, 83, 13, 239, 177, 240, 174, 76, 18, 145, 207, 45, 115,
202, 148, 118, 40, 171, 245, 23, 73, 8, 86, 180, 234, 105, 55, 213, 139,
87, 9, 235, 181, 54, 104, 138, 212, 149, 203, 41, 119, 244, 170, 72, 22,
233, 183, 85, 11, 136, 214, 52, 106, 43, 117, 151, 201, 74, 20, 246, 168,
116, 42, 200, 150, 21, 75, 169, 247, 182, 232, 10, 84, 215, 137, 107, 53 };
/***************************************************/
unsigned char CRC8( unsigned char crc, unsigned char data )
/***************************************************/
// 8 bits CRC calculation. Initial value of the CRC register is 0
// polynomial X^8 + X^5 + X^4 + 1
// crc is an 8 bit number - contains the current CRC
// data is an 8 bit number
{
crc = CRC_table[ crc ^ data]; // calculates the new CRC
return crc;
}
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