lib/crc/crc4_sw.c

/*
 * Copyright (c) 2023 Michal Morsisko
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr/sys/crc.h>

uint8_t crc4(const uint8_t *src, size_t len, uint8_t polynomial, uint8_t initial_value,
	  bool reversed)
{
	uint8_t crc = initial_value;
	size_t i, j, k;

	for (i = 0; i < len; i++) {
		for (j = 0; j < 2; j++) {
			crc ^= ((src[i] >> (4 * (1 - j))) & 0xf);

			for (k = 0; k < 4; k++) {
				if (reversed) {
					if (crc & 0x01) {
						crc = (crc >> 1) ^ polynomial;
					} else {
						crc >>= 1;
					}
				} else {
					if (crc & 0x8) {
						crc = (crc << 1) ^ polynomial;
					} else {
						crc <<= 1;
					}
				}
			}
		}
	}

	return crc & 0xF;
}

uint8_t crc4_ti(uint8_t seed, const uint8_t *src, size_t len)
{
	static const uint8_t lookup[8] = { 0x03, 0x65, 0xcf, 0xa9, 0xb8, 0xde, 0x74, 0x12 };
	uint8_t index;

	for (size_t i = 0; i < len; i++) {
		for (size_t j = 0U; j < 2U; j++) {
			index = seed ^ ((src[i] >> (4*(1-j))) & 0xf);
			seed = (lookup[index >> 1] >> (1 - (index & 1)) * 4) & 0xf;
		}
	}

	return seed;
}