crc8_demo_101.c

// =============================================================
// title      : crc8_demo_101.c
// edit       : 2022-01-15
// editor     : Neil Rieck (Waterloo, Ontario, Canada)
// Linux build: gcc crc8_demo_101.c -o crc8_demo_101 -std=gnu99
// Linux run  : ./crc8_demo_101
// notes      : while performing crc calculations in real-time
// is possible, it is too compute intensive to be desireable. So
// this routine employs a precomputed table of starting values.
// See crc8_demo_100.c to see how this table was generated.
// =============================================================
#include <stdio.h>
#include <string.h>
//
typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
//
//	see: crc8_demo_100.c to see how this table was generated
//
static const uint8_t crc_table[] = {
 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
};
//
//	this stub came from stackoverflow
//
uint8_t CRC8(uint8_t *p, uint8_t len)
{
    uint16_t i;
    uint16_t crc = 0x0;

    while (len--) {
	// printf("debug: 0x%02hx\n", len, crc_table[*p]);
        i = (crc ^ *p++) & 0xFF;
        crc = (crc_table[i] ^ (crc << 8)) & 0xFF;
    }
    return crc & 0xFF;	// ensure we only return 8-bits
}
//
//	main hack
//
int main(){
    uint8_t buffer[255];
    uint8_t crc;
    //
    buffer[0] = 0x00;
    crc = CRC8(buffer, 1);
    printf("data: 0x%02hx", buffer[0]);
    printf(" len: %d", 1);
    printf(" crc: 0x%02hx\n", crc);
    //
    buffer[0] = 0x01;
    crc = CRC8(buffer, 1);
    printf("data: 0x%02hx", buffer[0]);
    printf(" len: %d", 1);
    printf(" crc: 0x%02hx\n", crc);
    //
    sprintf(buffer,"A");
    crc = CRC8(buffer, strlen(buffer));
    printf("data: %s", buffer);
    printf(" len: %d", strlen(buffer));
    printf(" crc: 0x%02hx\n", crc);
    //
    sprintf(buffer,"this is a test");
    crc = CRC8(buffer, strlen(buffer));
    printf("data: %s", buffer);
    printf(" len: %d", strlen(buffer));
    printf(" crc: 0x%02hx\n", crc);
    //
    return 0;
 }

Output

$ ./crc8_demo_101
data: 0x00 len: 1 crc: 0x00
data: 0x01 len: 1 crc: 0x07
data: A len: 1 crc: 0xc0
data: this is a test len: 14 crc: 0x84
$

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Neil Rieck
Waterloo, Ontario, Canada.