/*
 * File:        crc8.c
 * Description: Simple CRC8 library
 * Author:      Jan Mrna
 * Date:        2022-06-09
 *
 *
 * Copyright (c) 2024 Veles Labs s.r.o.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 */

#include "crc8.h"

/* TODO add polynomial and init value to make this function
 * generic */

/* Stolen from Sensirion SCD4x datasheet, section 3.11 */
uint8_t crc8_calculate(const uint8_t *data, uint16_t count)
{
	uint16_t current_byte;
	uint8_t crc = CRC8_INIT;
	uint8_t crc_bit;
	/* calculates 8-Bit checksum with given polynomial */
	for (current_byte = 0; current_byte < count; ++current_byte) {
		crc ^= (data[current_byte]);
		for(crc_bit = 8; crc_bit > 0; --crc_bit) {
			if (crc & 0x80) {
				crc =(crc << 1) ^ CRC8_POLYNOMIAL;
			} else {
				crc = (crc << 1);
			}
		}
	}
	return crc;
}