TinyFrame_CheckSum.hpp

/******************************************************************************
MIT License

TinyFramePlusPlus Library.
https://github.com/marcelnabeck/TinyFramePlusPlus

Copyright(c) 2017-2018 Ondřej Hruška
Copyright(c) 2022 Marcel Nabeck

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
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copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
******************************************************************************/

#ifndef TINYFRAME_CRC_HPP
#define TINYFRAME_CRC_HPP

#include "TinyFrame_Types.hpp"

namespace TinyFrame_n{

// Custom checksum functions

/**
 * Initialize a checksum
 *
 * @return initial checksum value
 */
template<CKSUM_t CKSUM_TYPE>
CKSUM<CKSUM_TYPE> CksumStart(void);

/**
 * Update a checksum with a byte
 *
 * @param cksum - previous checksum value
 * @param byte - byte to add
 * @return updated checksum value
 */
template<CKSUM_t CKSUM_TYPE>
CKSUM<CKSUM_TYPE> CksumAdd(CKSUM<CKSUM_TYPE> cksum, uint8_t byte);

/**
 * Finalize the checksum calculation
 *
 * @param cksum - previous checksum value
 * @return final checksum value
 */
template<CKSUM_t CKSUM_TYPE>
CKSUM<CKSUM_TYPE> CksumEnd(CKSUM<CKSUM_TYPE> cksum);

#define CKSUM_RESET(cksum)     do { (cksum) = CksumStart<CKSUM_TYPE>(); } while (0)
#define CKSUM_ADD(cksum, byte) do { (cksum) = CksumAdd<CKSUM_TYPE>((cksum), (byte)); } while (0)
#define CKSUM_FINALIZE(cksum)  do { (cksum) = CksumEnd<CKSUM_TYPE>((cksum)); } while (0)

static constexpr uint8_t bit_reflect_lut[16U] = {
    /* OUT,    IN */
    0b0000U, // 0b0000
    0b1000U, // 0b0001
    0b0100U, // 0b0010
    0b1100U, // 0b0011
    0b0010U, // 0b0100
    0b1010U, // 0b0101
    0b0110U, // 0b0110
    0b1110U, // 0b0111
    0b0001U, // 0b1000
    0b1001U, // 0b1001
    0b0101U, // 0b1010
    0b1101U, // 0b1011
    0b0011U, // 0b1100
    0b1011U, // 0b1101
    0b0111U, // 0b1110
    0b1111U, // 0b1111
};

static constexpr uint8_t reflect_bits(uint8_t byte)
{
    return (bit_reflect_lut[byte & 0b1111U] << 4U) | (bit_reflect_lut[byte >> 4U]);
}

static inline void reflect_bytes(uint8_t *p_start, size_t size, bool bit_reflect = false)
{
    uint8_t *p_end = p_start + (size - 1U);
    uint8_t temp = 0U;
    while (p_start <= p_end)
    {
        temp = *p_start;
        *p_start = bit_reflect ? reflect_bits(*p_end) : *p_end;
        *p_end = bit_reflect ? reflect_bits(temp) : temp;

        p_start += 1U;
        p_end -= 1U;
    }
}

/* Tableless CRC */
template <typename DATA_TYPE>
constexpr static DATA_TYPE TablelessCrc_Function(DATA_TYPE poly, DATA_TYPE inital_crc, uint8_t byte)
{

    /* extract relevant byte references */
    DATA_TYPE msbMask = static_cast<DATA_TYPE>(1U << ((sizeof(DATA_TYPE) * 8U) - 1U));

    /* init crc byte */
    inital_crc = inital_crc ^ (byte << ((sizeof(DATA_TYPE) - 1) * 8U));

    /* calculate byte CRC using XOR */
    for (uint8_t bitIndex = 0U; bitIndex < 8U; bitIndex++)
    {
        inital_crc = (inital_crc << 1U) ^ (((inital_crc & msbMask) != 0U) ? poly : 0U);
    }

    /* return modified crc */
    return inital_crc;
}

} // TinyFrame_n

#endif // TINYFRAME_CRC_HPP