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sdrangel/sdrbase/util/lfsr.cpp
2020-09-24 08:36:13 +02:00

107 lines
3.4 KiB
C++

///////////////////////////////////////////////////////////////////////////////////
// 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 "lfsr.h"
#include "popcount.h"
// Shift LFSR one bit
int LFSR::shift()
{
int bit;
bit = (popcount(m_sr & m_polynomial) & 1) ^ 1;
m_sr = (m_sr << 1) | bit;
return bit;
}
// Scramble a single bit
int LFSR::scramble(int bit_in)
{
int bit_out;
bit_out = (popcount(m_sr & m_polynomial) & 1) ^ bit_in;
m_sr = (m_sr << 1) | bit_out;
return bit_out;
}
#include <stdio.h>
// Scramble data using LFSR - LSB first
void LFSR::scramble(uint8_t *data, int length)
{
uint8_t byte_in, byte_out;
int bit_in, bit_out;
for(int i = 0; i < length; i++)
{
byte_in = data[i];
byte_out = 0;
for (int j = 0; j < 8; j++)
{
bit_in = (byte_in >> j) & 1;
bit_out = (popcount(m_sr & m_polynomial) & 1) ^ bit_in;
m_sr = (m_sr << 1) | bit_out;
byte_out = byte_out | (bit_out << j);
}
data[i] = byte_out;
}
}
// Descramble data using LFSR - LSB first
void LFSR::descramble(uint8_t *data, int length)
{
uint8_t byte_in, byte_out;
int bit_in, bit_out;
for(int i = 0; i < length; i++)
{
byte_in = data[i];
byte_out = 0;
for (int j = 0; j < 8; j++)
{
bit_in = (byte_in >> j) & 1;
bit_out = (popcount(m_sr & m_polynomial) & 1) ^ bit_in;
m_sr = (m_sr << 1) | bit_in;
byte_out = byte_out | (bit_out << j);
}
data[i] = byte_out;
}
}
// XOR data with rand_bit of LFSR - LSB first
void LFSR::randomize(uint8_t *data, int length)
{
uint8_t byte_in, byte_out;
int bit_in, bit_out, bit;
for(int i = 0; i < length; i++)
{
byte_in = data[i];
byte_out = 0;
for (int j = 0; j < 8; j++)
{
// XOR input bit with specified bit from SR
bit_in = (byte_in >> j) & 1;
bit_out = ((m_sr >> m_rand_bit) & 1) ^ bit_in;
byte_out = byte_out | (bit_out << j);
// Update LFSR
bit = popcount(m_sr & m_polynomial) & 1;
m_sr = (m_sr << 1) | bit;
}
data[i] = byte_out;
}
}