/*
 * crc.c
 *
 *  Created on: Jun 9, 2021
 *      Author: user
 */

#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;
}