obd_iso15765/BleCanBoxCode/NRF51802/components/libraries/crc16/crc16.c

/* Copyright (c) 2013 Nordic Semiconductor. All Rights Reserved.
 *
 * The information contained herein is property of Nordic Semiconductor ASA.
 * Terms and conditions of usage are described in detail in NORDIC
 * SEMICONDUCTOR STANDARD SOFTWARE LICENSE AGREEMENT.
 *
 * Licensees are granted free, non-transferable use of the information. NO
 * WARRANTY of ANY KIND is provided. This heading must NOT be removed from
 * the file.
 *
 */

#include "crc16.h"

#include <stdlib.h>

uint16_t crc16_compute(uint8_t const * p_data, uint32_t size, uint16_t const * p_crc)
{
    uint16_t crc = (p_crc == NULL) ? 0xFFFF : *p_crc;

    for (uint32_t i = 0; i < size; i++)
    {
        crc  = (uint8_t)(crc >> 8) | (crc << 8);
        crc ^= p_data[i];
        crc ^= (uint8_t)(crc & 0xFF) >> 4;
        crc ^= (crc << 8) << 4;
        crc ^= ((crc & 0xFF) << 4) << 1;
    }

    return crc;
}