mirror of
https://github.com/f4exb/sdrangel.git
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131 lines
4.1 KiB
C++
131 lines
4.1 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2020-2021 Jon Beniston, M7RCE <jon@beniston.com> //
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// //
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// This program is free software; you can redistribute it and/or modify //
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// it under the terms of the GNU General Public License as published by //
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// the Free Software Foundation as version 3 of the License, or //
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// (at your option) any later version. //
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// //
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// This program is distributed in the hope that it will be useful, //
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// but WITHOUT ANY WARRANTY; without even the implied warranty of //
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
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// GNU General Public License V3 for more details. //
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// //
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// You should have received a copy of the GNU General Public License //
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// along with this program. If not, see <http://www.gnu.org/licenses/>. //
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///////////////////////////////////////////////////////////////////////////////////
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#include "lfsr.h"
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#include "popcount.h"
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// Shift LFSR one bit
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int LFSR::shift()
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{
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int bit;
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bit = (popcount(m_sr & m_polynomial) & 1) ^ 1;
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m_sr = (m_sr << 1) | bit;
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return bit;
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}
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// Scramble a single bit
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int LFSR::scramble(int bit_in)
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{
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int bit_out;
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bit_out = (popcount(m_sr & m_polynomial) & 1) ^ bit_in;
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m_sr = (m_sr << 1) | bit_out;
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return bit_out;
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}
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// Scramble data using LFSR - LSB first
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void LFSR::scramble(uint8_t *data, int length)
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{
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uint8_t byte_in, byte_out;
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int bit_in, bit_out;
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for(int i = 0; i < length; i++)
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{
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byte_in = data[i];
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byte_out = 0;
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for (int j = 0; j < 8; j++)
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{
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bit_in = (byte_in >> j) & 1;
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bit_out = (popcount(m_sr & m_polynomial) & 1) ^ bit_in;
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m_sr = (m_sr << 1) | bit_out;
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byte_out = byte_out | (bit_out << j);
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}
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data[i] = byte_out;
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}
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}
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// Descramble data using LFSR - LSB first
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void LFSR::descramble(uint8_t *data, int length)
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{
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uint8_t byte_in, byte_out;
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int bit_in, bit_out;
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for(int i = 0; i < length; i++)
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{
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byte_in = data[i];
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byte_out = 0;
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for (int j = 0; j < 8; j++)
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{
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bit_in = (byte_in >> j) & 1;
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bit_out = (popcount(m_sr & m_polynomial) & 1) ^ bit_in;
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m_sr = (m_sr << 1) | bit_in;
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byte_out = byte_out | (bit_out << j);
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}
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data[i] = byte_out;
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}
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}
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// XOR data with rand_bits of LFSR - LSB first
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void LFSR::randomize(uint8_t *data, int length)
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{
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uint8_t byte_in, byte_out;
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int bit_in, bit_out, bit;
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for(int i = 0; i < length; i++)
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{
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byte_in = data[i];
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byte_out = 0;
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for (int j = 0; j < 8; j++)
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{
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// XOR input bit with specified bit from SR
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bit_in = (byte_in >> j) & 1;
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//bit_out = ((m_sr >> m_rand_bit) & 1) ^ bit_in;
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bit_out = (popcount(m_sr & m_rand_bits) & 1) ^ bit_in;
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byte_out = byte_out | (bit_out << j);
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// Update LFSR
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bit = popcount(m_sr & m_polynomial) & 1;
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m_sr = (m_sr << 1) | bit;
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}
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data[i] = byte_out;
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}
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}
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// XOR data with rand_bits of LFSR - MSB first
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void LFSR::randomizeMSB(const uint8_t *dataIn, uint8_t *dataOut, int length)
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{
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uint8_t byte_in, byte_out;
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int bit_in, bit_out, bit;
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for(int i = 0; i < length; i++)
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{
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byte_in = dataIn[i];
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byte_out = 0;
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for (int j = 7; j >= 0; j--)
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{
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// XOR input bit with selected bits from SR
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bit_in = (byte_in >> j) & 1;
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bit_out = (popcount(m_sr & m_rand_bits) & 1) ^ bit_in;
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byte_out = byte_out | (bit_out << j);
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// Update LFSR
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bit = popcount(m_sr & m_polynomial) & 1;
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m_sr = (m_sr << 1) | bit;
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}
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dataOut[i] = byte_out;
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}
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}
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