ESP32

/*
 *   This file is part of DroneBridge: https://github.com/DroneBridge/ESP32
 *
 *   Copyright 2017 Wolfgang Christl
 *
 *   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.
 *
 */

#include "db_crc.h"

/**
 * This function is part of Cleanflight & iNAV.
 *
 * Cleanflight is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Cleanflight is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Cleanflight.  If not, see <http://www.gnu.org/licenses/>.
 */
uint8_t crc8_dvb_s2(uint8_t crc, unsigned char a)
{
    crc ^= a;
    for (int ii = 0; ii < 8; ++ii) {
        if (crc & 0x80) {
            crc = (crc << 1) ^ 0xD5;
        } else {
            crc = crc << 1;
        }
    }
    return crc;
}

/**
 * Does the same as crc8_dvb_s2 just way more efficient (CPU) but with a little bit more RAM usage
 * @param crc The current crc value
 * @param a The next byte
 * @return The new crc value
 */
uint8_t crc8_dvb_s2_table(uint8_t crc, unsigned char a)
{
    return (uint8_t) (crc_dvb_s2_table[(crc ^ a)] & 0xff);
}