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254 lines
7.1 KiB
C++
254 lines
7.1 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2021 Edouard Griffiths, F4EXB //
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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 <algorithm>
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#include <bitset>
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#include "golay2312.h"
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const unsigned int Golay2312::m_B[11] = {
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0b101001001111,
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0b111101101000,
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0b011110110100,
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0b001111011010,
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0b000111101101,
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0b101010111001,
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0b111100010011,
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0b110111000110,
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0b011011100011,
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0b100100111110,
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0b010010011111,
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};
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const unsigned int Golay2312::m_I11[11] = {
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0b10000000000,
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0b01000000000,
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0b00100000000,
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0b00010000000,
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0b00001000000,
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0b00000100000,
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0b00000010000,
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0b00000001000,
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0b00000000100,
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0b00000000010,
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0b00000000001,
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};
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const unsigned int Golay2312::m_I12[12] = {
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0b100000000000,
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0b010000000000,
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0b001000000000,
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0b000100000000,
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0b000010000000,
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0b000001000000,
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0b000000100000,
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0b000000010000,
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0b000000001000,
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0b000000000100,
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0b000000000010,
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0b000000000001,
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};
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Golay2312::Golay2312()
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{
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initG();
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initH();
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buildCorrMatrix(m_corrPL, m_HPL);
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buildCorrMatrix(m_corrPF, m_HPF, true);
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}
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Golay2312::~Golay2312()
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{
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}
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void Golay2312::initG()
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{
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for (int r = 0; r < 23; r++)
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{
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// parity last
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if (r < 12) {
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m_GPL[r] = m_I12[r];
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} else {
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m_GPL[r] = m_B[r-12];
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}
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// parity first
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if (r < 11) {
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m_GPF[r] = m_B[r];
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} else {
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m_GPF[r] = m_I12[r-11];
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}
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}
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}
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void Golay2312::initH()
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{
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for (int r = 0; r < 11; r++)
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{
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m_HPL[r] = (m_B[r] << 11) + m_I11[r]; // parity last
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m_HPF[r] = (m_I11[r] << 12) + m_B[r]; // parity first
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}
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}
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void Golay2312::encodeParityLast(unsigned int msg, unsigned int *tx)
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{
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*tx = 0;
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for (int r = 0; r < 23; r++) {
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*tx += (std::bitset<32>(m_GPL[r] & msg).count() % 2) << (22-r);
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}
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}
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void Golay2312::encodeParityFirst(unsigned int msg, unsigned int *tx)
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{
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*tx = 0;
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for (int r = 0; r < 23; r++) {
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*tx += (std::bitset<32>(m_GPF[r] & msg).count() % 2) << (22-r);
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}
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}
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bool Golay2312::decodeParityLast(unsigned int *rx)
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{
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unsigned int s = syn(m_HPL, *rx);
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return lut(m_corrPL, s, rx);
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}
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bool Golay2312::decodeParityFirst(unsigned int *rx)
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{
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unsigned int s = syn(m_HPF, *rx);
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return lut(m_corrPF, s, rx);
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}
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unsigned int Golay2312::syn(unsigned int *H, unsigned int rx)
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{
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unsigned int s = 0;
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for (int r = 0; r < 11; r++) {
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s += (std::bitset<32>(H[r] & rx).count() % 2) << (10-r);
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}
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return s;
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}
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bool Golay2312::lut(unsigned char *corr, unsigned int syndrome, unsigned int *rx)
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{
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if (syndrome == 0) {
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return true;
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}
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int i = 0;
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for (; i < 3; i++)
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{
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if (corr[3*syndrome + i] == 0xFF) {
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break;
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} else {
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*rx ^= (1 << corr[3*syndrome + i]); // flip bit
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}
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}
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if (i == 0) {
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return false;
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}
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return true;
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}
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void Golay2312::buildCorrMatrix(unsigned char *corr, unsigned int *H, bool pf)
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{
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int shiftP = pf ? 12 : 0; // shift in position value for parity bits
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int shiftW = pf ? 0 : 11; // shift in position value for message word bits
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std::fill(corr, corr + 3*2048, 0xFF);
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int syndromeI;
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unsigned int cw;
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for (int i1 = 0; i1 < 12; i1++)
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{
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for (int i2 = i1+1; i2 < 12; i2++)
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{
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for (int i3 = i2+1; i3 < 12; i3++)
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{
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// 3 bit patterns (in message)
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cw = (1 << (i1+shiftW)) + (1 << (i2+shiftW)) + (1 << (i3+shiftW));
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syndromeI = syn(H, cw);
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corr[3*syndromeI + 0] = i1 + shiftW;
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corr[3*syndromeI + 1] = i2 + shiftW;
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corr[3*syndromeI + 2] = i3 + shiftW;
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}
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// 2 bit patterns (in message)
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cw = (1 << (i1+shiftW)) + (1 << (i2+shiftW));
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syndromeI = syn(H, cw);
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corr[3*syndromeI + 0] = i1 + shiftW;
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corr[3*syndromeI + 1] = i2 + shiftW;
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// 1 possible bit flip left in the parity part
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for (int ip = 0; ip < 11; ip++)
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{
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int syndromeIP = syndromeI ^ (1 << (10-ip));
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corr[3*syndromeIP + 0] = i1 + shiftW;
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corr[3*syndromeIP + 1] = i2 + shiftW;
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corr[3*syndromeIP + 2] = 10 - ip + shiftP;
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}
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}
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// single bit patterns (in message)
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cw = (1 << (i1+shiftW));
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syndromeI = syn(H, cw);
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corr[3*syndromeI + 0] = i1 + shiftW;
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for (int ip1 = 0; ip1 < 11; ip1++) // 1 more bit flip in parity
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{
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int syndromeIP1 = syndromeI ^ (1 << (10-ip1));
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corr[3*syndromeIP1 + 0] = i1 + shiftW;
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corr[3*syndromeIP1 + 1] = 10 - ip1 + shiftP;
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for (int ip2 = ip1+1; ip2 < 11; ip2++) // 1 more bit flip in parity
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{
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int syndromeIP2 = syndromeIP1 ^ (1 << (10-ip2));
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corr[3*syndromeIP2 + 0] = i1 + shiftW;
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corr[3*syndromeIP2 + 1] = 10 - ip1 + shiftP;
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corr[3*syndromeIP2 + 2] = 10 - ip2 + shiftP;
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}
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}
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}
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// no bit patterns (in message) -> all in parity
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for (int ip1 = 0; ip1 < 11; ip1++) // 1 bit flip in parity
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{
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int syndromeIP1 = (1 << (10-ip1));
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corr[3*syndromeIP1 + 0] = 10 - ip1 + shiftP;
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for (int ip2 = ip1+1; ip2 < 11; ip2++) // 1 more bit flip in parity
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{
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int syndromeIP2 = syndromeIP1 ^ (1 << (10-ip2));
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corr[3*syndromeIP2 + 0] = 10 - ip1 + shiftP;
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corr[3*syndromeIP2 + 1] = 10 - ip2 + shiftP;
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for (int ip3 = ip2+1; ip3 < 11; ip3++) // 1 more bit flip in parity
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{
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int syndromeIP3 = syndromeIP2 ^ (1 << (10-ip3));
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corr[3*syndromeIP3 + 0] = 10 - ip1 + shiftP;
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corr[3*syndromeIP3 + 1] = 10 - ip2 + shiftP;
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corr[3*syndromeIP3 + 2] = 10 - ip3 + shiftP;
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}
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}
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}
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}
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