CRC32.h

/*
 Copyright 2016 Djones A. Boni

 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 CRC32_H_
#define CRC32_H_

#include <stdint.h>
#include <avr/pgmspace.h>

struct CRC32 {
    typedef uint32_t CRC_t;
    static const int8_t size        = 4;
    static const CRC_t CRC_INIT     = 0xFFFFFFFFUL;
    static const CRC_t CRC_FINALXOR = 0xFFFFFFFFUL;
    static const CRC_t CRC_GOOD     = 0xDEBB20E3UL;

    PROGMEM static const CRC_t CRC_TAB[256U];

    void init() { crc = CRC_INIT; }
    void update(uint8_t data) {
        /* crc = (crc >> 8U) ^ CRC_TAB[(crc ^ data) & 0xFFU]; */
        crc = (crc >> 8U) ^ pgm_read_dword(&CRC_TAB[(crc ^ data) & 0xFFU]);
    }

    bool good() { return crc == CRC_GOOD; }

    void final() { crc ^= CRC_FINALXOR; }
    uint8_t operator[](int8_t pos) {
        switch(pos) {
            case 0:  return crc;
            case 1:  return crc >> 8U;
            case 2:  return crc >> 16U;
            default: return crc >> 24U;
        }
    }

    CRC_t crc;
};

#endif /* CRC32_H_ */