SensirionCrc.cpp

/*
 * Copyright (c) 2022, Sensirion AG
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 *
 * * Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
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 * * Neither the name of Sensirion AG nor the names of its
 *   contributors may be used to endorse or promote products derived from
 *   this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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 */

#include "SensirionCrc.h"

uint8_t generateCRCGeneric(const uint8_t* data, size_t count, uint8_t init,
                           uint8_t polynomial) {
    uint8_t crc = init;

    /* calculates 8-Bit checksum with given polynomial */
    for (size_t current_byte = 0; current_byte < count; ++current_byte) {
        crc ^= (data[current_byte]);
        for (uint8_t crc_bit = 8; crc_bit > 0; --crc_bit) {
            if (crc & 0x80)
                crc = (crc << 1) ^ polynomial;
            else
                crc = (crc << 1);
        }
    }
    return crc;
}

uint8_t generateCRC31_ff(const uint8_t* data, size_t count) {
    return generateCRCGeneric(data, count, 0xff, 0x31);
}

uint8_t generateCRC31_00(const uint8_t* data, size_t count) {
    return generateCRCGeneric(data, count, 0x00, 0x31);
}

uint8_t generateCRC(const uint8_t* data, size_t count, CrcPolynomial type) {
    if (CRC31_00 == type) {
        return generateCRC31_00(data, count);
    }
    return generateCRC31_ff(data, count);
}