/*
 * Calculation of CRC 16 CCITT polynomial, x^16 + x^12 + x^5 + 1.
 *
 * @file        crc16-ccitt.c
 * @ingroup     crc16-ccitt
 * @author      Janez Paternoster
 * @copyright   2012 - 2020 Janez Paternoster
 *
 * This file is part of CANopenNode, an opensource CANopen Stack.
 * Project home page is <https://github.com/CANopenNode/CANopenNode>.
 * For more information on CANopen see <http://www.can-cia.org/>.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * 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.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef CO_USE_OWN_CRC16

#include "crc16-ccitt.h"


/*
 * CRC table calculated by the following algorithm:
 *
 * void crc16_ccitt_table_init(void){
 *     unsigned short i, j;
 *     for(i=0; i<256; i++){
 *         unsigned short crc = 0;
 *         unsigned short c = i << 8;
 *         for(j=0; j<8; j++){
 *             if((crc ^ c) & 0x8000) crc = (crc << 1) ^ 0x1021;
 *             else                   crc = crc << 1;
 *             c = c << 1;
 *         }
 *         crc16_ccitt_table[i] = crc;
 *     }
 * }
 */
static const unsigned short crc16_ccitt_table[256] = {
    0x0000U, 0x1021U, 0x2042U, 0x3063U, 0x4084U, 0x50A5U, 0x60C6U, 0x70E7U,
    0x8108U, 0x9129U, 0xA14AU, 0xB16BU, 0xC18CU, 0xD1ADU, 0xE1CEU, 0xF1EFU,
    0x1231U, 0x0210U, 0x3273U, 0x2252U, 0x52B5U, 0x4294U, 0x72F7U, 0x62D6U,
    0x9339U, 0x8318U, 0xB37BU, 0xA35AU, 0xD3BDU, 0xC39CU, 0xF3FFU, 0xE3DEU,
    0x2462U, 0x3443U, 0x0420U, 0x1401U, 0x64E6U, 0x74C7U, 0x44A4U, 0x5485U,
    0xA56AU, 0xB54BU, 0x8528U, 0x9509U, 0xE5EEU, 0xF5CFU, 0xC5ACU, 0xD58DU,
    0x3653U, 0x2672U, 0x1611U, 0x0630U, 0x76D7U, 0x66F6U, 0x5695U, 0x46B4U,
    0xB75BU, 0xA77AU, 0x9719U, 0x8738U, 0xF7DFU, 0xE7FEU, 0xD79DU, 0xC7BCU,
    0x48C4U, 0x58E5U, 0x6886U, 0x78A7U, 0x0840U, 0x1861U, 0x2802U, 0x3823U,
    0xC9CCU, 0xD9EDU, 0xE98EU, 0xF9AFU, 0x8948U, 0x9969U, 0xA90AU, 0xB92BU,
    0x5AF5U, 0x4AD4U, 0x7AB7U, 0x6A96U, 0x1A71U, 0x0A50U, 0x3A33U, 0x2A12U,
    0xDBFDU, 0xCBDCU, 0xFBBFU, 0xEB9EU, 0x9B79U, 0x8B58U, 0xBB3BU, 0xAB1AU,
    0x6CA6U, 0x7C87U, 0x4CE4U, 0x5CC5U, 0x2C22U, 0x3C03U, 0x0C60U, 0x1C41U,
    0xEDAEU, 0xFD8FU, 0xCDECU, 0xDDCDU, 0xAD2AU, 0xBD0BU, 0x8D68U, 0x9D49U,
    0x7E97U, 0x6EB6U, 0x5ED5U, 0x4EF4U, 0x3E13U, 0x2E32U, 0x1E51U, 0x0E70U,
    0xFF9FU, 0xEFBEU, 0xDFDDU, 0xCFFCU, 0xBF1BU, 0xAF3AU, 0x9F59U, 0x8F78U,
    0x9188U, 0x81A9U, 0xB1CAU, 0xA1EBU, 0xD10CU, 0xC12DU, 0xF14EU, 0xE16FU,
    0x1080U, 0x00A1U, 0x30C2U, 0x20E3U, 0x5004U, 0x4025U, 0x7046U, 0x6067U,
    0x83B9U, 0x9398U, 0xA3FBU, 0xB3DAU, 0xC33DU, 0xD31CU, 0xE37FU, 0xF35EU,
    0x02B1U, 0x1290U, 0x22F3U, 0x32D2U, 0x4235U, 0x5214U, 0x6277U, 0x7256U,
    0xB5EAU, 0xA5CBU, 0x95A8U, 0x8589U, 0xF56EU, 0xE54FU, 0xD52CU, 0xC50DU,
    0x34E2U, 0x24C3U, 0x14A0U, 0x0481U, 0x7466U, 0x6447U, 0x5424U, 0x4405U,
    0xA7DBU, 0xB7FAU, 0x8799U, 0x97B8U, 0xE75FU, 0xF77EU, 0xC71DU, 0xD73CU,
    0x26D3U, 0x36F2U, 0x0691U, 0x16B0U, 0x6657U, 0x7676U, 0x4615U, 0x5634U,
    0xD94CU, 0xC96DU, 0xF90EU, 0xE92FU, 0x99C8U, 0x89E9U, 0xB98AU, 0xA9ABU,
    0x5844U, 0x4865U, 0x7806U, 0x6827U, 0x18C0U, 0x08E1U, 0x3882U, 0x28A3U,
    0xCB7DU, 0xDB5CU, 0xEB3FU, 0xFB1EU, 0x8BF9U, 0x9BD8U, 0xABBBU, 0xBB9AU,
    0x4A75U, 0x5A54U, 0x6A37U, 0x7A16U, 0x0AF1U, 0x1AD0U, 0x2AB3U, 0x3A92U,
    0xFD2EU, 0xED0FU, 0xDD6CU, 0xCD4DU, 0xBDAAU, 0xAD8BU, 0x9DE8U, 0x8DC9U,
    0x7C26U, 0x6C07U, 0x5C64U, 0x4C45U, 0x3CA2U, 0x2C83U, 0x1CE0U, 0x0CC1U,
    0xEF1FU, 0xFF3EU, 0xCF5DU, 0xDF7CU, 0xAF9BU, 0xBFBAU, 0x8FD9U, 0x9FF8U,
    0x6E17U, 0x7E36U, 0x4E55U, 0x5E74U, 0x2E93U, 0x3EB2U, 0x0ED1U, 0x1EF0U
};


/******************************************************************************/
unsigned short crc16_ccitt(
        const unsigned char     block[],
        unsigned int            blockLength,
        unsigned short          crc)
{
    unsigned int i;

    for(i=0U; i<blockLength; i++){
        unsigned short tmp = (crc >> 8) ^ (unsigned short) block[i];
        crc = ((unsigned short)(crc << 8U)) ^ crc16_ccitt_table[tmp];
    }
    return crc;
}

#endif /* CO_USE_OWN_CRC16 */