1 /*
2 * Copyright (c) 2023 Michal Morsisko
3 *
4 * SPDX-License-Identifier: Apache-2.0
5 */
6
7 #include <zephyr/sys/crc.h>
8
crc4(const uint8_t * src,size_t len,uint8_t polynomial,uint8_t initial_value,bool reversed)9 uint8_t crc4(const uint8_t *src, size_t len, uint8_t polynomial, uint8_t initial_value,
10 bool reversed)
11 {
12 uint8_t crc = initial_value;
13 size_t i, j, k;
14
15 for (i = 0; i < len; i++) {
16 for (j = 0; j < 2; j++) {
17 crc ^= ((src[i] >> (4 * (1 - j))) & 0xf);
18
19 for (k = 0; k < 4; k++) {
20 if (reversed) {
21 if (crc & 0x01) {
22 crc = (crc >> 1) ^ polynomial;
23 } else {
24 crc >>= 1;
25 }
26 } else {
27 if (crc & 0x8) {
28 crc = (crc << 1) ^ polynomial;
29 } else {
30 crc <<= 1;
31 }
32 }
33 }
34 }
35 }
36
37 return crc & 0xF;
38 }
39
crc4_ti(uint8_t seed,const uint8_t * src,size_t len)40 uint8_t crc4_ti(uint8_t seed, const uint8_t *src, size_t len)
41 {
42 static const uint8_t lookup[8] = { 0x03, 0x65, 0xcf, 0xa9, 0xb8, 0xde, 0x74, 0x12 };
43 uint8_t index;
44
45 for (size_t i = 0; i < len; i++) {
46 for (size_t j = 0U; j < 2U; j++) {
47 index = seed ^ ((src[i] >> (4*(1-j))) & 0xf);
48 seed = (lookup[index >> 1] >> (1 - (index & 1)) * 4) & 0xf;
49 }
50 }
51
52 return seed;
53 }
54
