///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2020 Jon Beniston, M7RCE                                        //
//                                                                               //
// 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 "crc.h"

// Reverse bit ordering
uint32_t crc::reverse(uint32_t val, int bits)
{
    uint32_t temp;
    int i;

    temp = 0;
    for (i = 0; i < bits; i++)
        temp |= ((val >> i) & 1) << (bits - 1 - i);
    return temp;
}

// Calculate CRC for specified number of bits
void crc::calculate(uint32_t data, int data_bits)
{
    uint32_t tmp;
    uint32_t mask;
    int bit, i;

    // Reverse data order.
    if (m_msb_first)
        data = reverse (data, data_bits);

    // Compute CRC.
    tmp = m_crc;
    for (i = 0; i < data_bits; i++) {
        bit = ((data >> i) & 1) ^ (tmp & 1);
        if (bit)
            tmp = (tmp >> 1) ^ m_polynomial_rev;
        else
            tmp = tmp >> 1;
    }
    m_crc = tmp;
}

// Calculate CRC for specified array
void crc::calculate(const uint8_t *data, int length)
{
    for(int i = 0; i < length; i++)
        calculate(data[i], 8);
}