crc8_demo_100.c

// =============================================================
// title      : crc8_demo_100.c
// edit       : 2022-01-15
// editor     : Neil Rieck (Waterloo, Ontario, Canada)
// Linux build: gcc crc8_demo_100.c -o crc8_demo_100 -std=gnu99
// Linux run  : ./crc8_demo_100
// notes      : while performing crc calculations in real-time
// is possible, it is too compute intensive to be desirable. So
// a routine like this can be used to precompute starting values
// to be stored in a init table (see: crc8_demo_101.c to see how
// this might work)
// =============================================================

#include <stddef.h>
#include <stdint.h>
#include <stdio.h>

unsigned char table[256] = {0};

void crc_table_create(unsigned char *pdata, unsigned char factor)
{
    unsigned char temp;
    for (int i = 0; i < 256; i++)
    {
        pdata[i] = i;
    }
    for (int i = 0; i < 256; i++)
    {
        for (int j = 7; j >= 0; j--)
        {
            temp = pdata[i] & 0x80;	// take the MSB bit
            if (temp)			// if the MSB bit is 1
            {
                pdata[i] = pdata[i] << 1;
                pdata[i] ^= factor;
            }
            else
            {
                pdata[i] = pdata[i] << 1;
            }
        }
        // printf("table[%i]= 0x%02x", i, table[i]);
        // getchar();
    }
}


int main(void)
{
    int i, j = 0;
    uint8_t poly = 0x07;     // X8 + X2 + X1 + 1 (100000111B the MSB bit is mute, so it turn to 0x07)
    crc_table_create(table, poly);
    for (i = 0; i < 256; i++)
    {
        if (i % 12 == 0) {
            printf("\n");
        }
        printf("0x%02x, ", table[i]);
    }
    printf("\n");
    return 1;
}

Output

$ ./crc8_demo_100

0x00, 0x07, 0x0e, 0x09, 0x1c, 0x1b, 0x12, 0x15, 0x38, 0x3f, 0x36, 0x31, 
0x24, 0x23, 0x2a, 0x2d, 0x70, 0x77, 0x7e, 0x79, 0x6c, 0x6b, 0x62, 0x65, 
0x48, 0x4f, 0x46, 0x41, 0x54, 0x53, 0x5a, 0x5d, 0xe0, 0xe7, 0xee, 0xe9, 
0xfc, 0xfb, 0xf2, 0xf5, 0xd8, 0xdf, 0xd6, 0xd1, 0xc4, 0xc3, 0xca, 0xcd, 
0x90, 0x97, 0x9e, 0x99, 0x8c, 0x8b, 0x82, 0x85, 0xa8, 0xaf, 0xa6, 0xa1, 
0xb4, 0xb3, 0xba, 0xbd, 0xc7, 0xc0, 0xc9, 0xce, 0xdb, 0xdc, 0xd5, 0xd2, 
0xff, 0xf8, 0xf1, 0xf6, 0xe3, 0xe4, 0xed, 0xea, 0xb7, 0xb0, 0xb9, 0xbe, 
0xab, 0xac, 0xa5, 0xa2, 0x8f, 0x88, 0x81, 0x86, 0x93, 0x94, 0x9d, 0x9a, 
0x27, 0x20, 0x29, 0x2e, 0x3b, 0x3c, 0x35, 0x32, 0x1f, 0x18, 0x11, 0x16, 
0x03, 0x04, 0x0d, 0x0a, 0x57, 0x50, 0x59, 0x5e, 0x4b, 0x4c, 0x45, 0x42, 
0x6f, 0x68, 0x61, 0x66, 0x73, 0x74, 0x7d, 0x7a, 0x89, 0x8e, 0x87, 0x80, 
0x95, 0x92, 0x9b, 0x9c, 0xb1, 0xb6, 0xbf, 0xb8, 0xad, 0xaa, 0xa3, 0xa4, 
0xf9, 0xfe, 0xf7, 0xf0, 0xe5, 0xe2, 0xeb, 0xec, 0xc1, 0xc6, 0xcf, 0xc8, 
0xdd, 0xda, 0xd3, 0xd4, 0x69, 0x6e, 0x67, 0x60, 0x75, 0x72, 0x7b, 0x7c, 
0x51, 0x56, 0x5f, 0x58, 0x4d, 0x4a, 0x43, 0x44, 0x19, 0x1e, 0x17, 0x10, 
0x05, 0x02, 0x0b, 0x0c, 0x21, 0x26, 0x2f, 0x28, 0x3d, 0x3a, 0x33, 0x34, 
0x4e, 0x49, 0x40, 0x47, 0x52, 0x55, 0x5c, 0x5b, 0x76, 0x71, 0x78, 0x7f, 
0x6a, 0x6d, 0x64, 0x63, 0x3e, 0x39, 0x30, 0x37, 0x22, 0x25, 0x2c, 0x2b, 
0x06, 0x01, 0x08, 0x0f, 0x1a, 0x1d, 0x14, 0x13, 0xae, 0xa9, 0xa0, 0xa7, 
0xb2, 0xb5, 0xbc, 0xbb, 0x96, 0x91, 0x98, 0x9f, 0x8a, 0x8d, 0x84, 0x83, 
0xde, 0xd9, 0xd0, 0xd7, 0xc2, 0xc5, 0xcc, 0xcb, 0xe6, 0xe1, 0xe8, 0xef, 
0xfa, 0xfd, 0xf4, 0xf3, 
$

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Neil Rieck
Waterloo, Ontario, Canada.