CRC64.cpp

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// Copyright (C) 2016 Edouard Griffiths, F4EXB                                   //
//                                                                               //
// This program 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 as version 3 of the License, or                  //
// (at your option) any later version.                                           //
//                                                                               //
// This program 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 V3 for more details.                               //
//                                                                               //
// You should have received a copy of the GNU General Public License             //
// along with this program. If not, see <http://www.gnu.org/licenses/>.          //

#include "util/CRC64.h"

const uint64_t CRC64::m_poly = 0xC96C5795D7870F42ull;

CRC64::CRC64()
{
    build_crc_table();
}

CRC64::~CRC64()
{}

void CRC64::build_crc_table()
{
    for(int i = 0; i < 256; ++i)
    {
        uint64_t crc = i;

        for(unsigned int j = 0; j < 8; ++j)
        {
            if(crc & 1) // is current coefficient set?
            {
                crc >>= 1;   // yes, then assume it gets zero'd (by implied x^64 coefficient of dividend)
                crc ^= m_poly; // and add rest of the divisor
            }
            else // no? then move to next coefficient
            {
                crc >>= 1;
            }
        }

        m_crcTable[i] = crc;
    }
}

uint64_t CRC64::calculate_crc(uint8_t *stream, int length)
{
    uint64_t crc = 0;

    for (int i = 0 ; i < length; ++i)
    {
        uint8_t index = stream[i] ^ crc;
        uint64_t lookup = m_crcTable[index];

        crc >>= 8;
        crc ^= lookup;
    }

    return crc;
}