flipperzero-firmware/lib/ST25RFAL002/source/rfal_crc.c

/******************************************************************************
  * \attention
  *
  * <h2><center>&copy; COPYRIGHT 2020 STMicroelectronics</center></h2>
  *
  * Licensed under ST MYLIBERTY SOFTWARE LICENSE AGREEMENT (the "License");
  * You may not use this file except in compliance with the License.
  * You may obtain a copy of the License at:
  *
  *        www.st.com/myliberty
  *
  * Unless required by applicable law or agreed to in writing, software 
  * distributed under the License is distributed on an "AS IS" BASIS, 
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied,
  * AND SPECIFICALLY DISCLAIMING THE IMPLIED WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  *
******************************************************************************/

/*
 *      PROJECT:   ST25R391x firmware
 *      Revision:
 *      LANGUAGE:  ISO C99
 */

/*! \file rfal_crc.c
 *
 *  \author Oliver Regenfelder
 *
 *  \brief CRC calculation implementation
 *
 */

/*
******************************************************************************
* INCLUDES
******************************************************************************
*/
#include "rfal_crc.h"

/*
******************************************************************************
* LOCAL FUNCTION PROTOTYPES
******************************************************************************
*/
static uint16_t rfalCrcUpdateCcitt(uint16_t crcSeed, uint8_t dataByte);

/*
******************************************************************************
* GLOBAL FUNCTIONS
******************************************************************************
*/
uint16_t rfalCrcCalculateCcitt(uint16_t preloadValue, const uint8_t* buf, uint16_t length) {
    uint16_t crc = preloadValue;
    uint16_t index;

    for(index = 0; index < length; index++) {
        crc = rfalCrcUpdateCcitt(crc, buf[index]);
    }

    return crc;
}

/*
******************************************************************************
* LOCAL FUNCTIONS
******************************************************************************
*/
static uint16_t rfalCrcUpdateCcitt(uint16_t crcSeed, uint8_t dataByte) {
    uint16_t crc = crcSeed;
    uint8_t dat = dataByte;

    dat ^= (uint8_t)(crc & 0xFFU);
    dat ^= (dat << 4);

    crc = (crc >> 8) ^ (((uint16_t)dat) << 8) ^ (((uint16_t)dat) << 3) ^ (((uint16_t)dat) >> 4);

    return crc;
}