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viterbi3.cpp
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viterbi3.cpp
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///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2016 Edouard Griffiths, F4EXB. //
// //
// Class specialized for K=3 decoding //
// //
// 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 //
// //
// 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 <iostream>
#include <string.h>
#include <limits.h>
#include "viterbi3.h"
namespace DSDcc
{
Viterbi3::Viterbi3(int n, const unsigned int *polys, bool msbFirst) :
Viterbi(3, n, polys, msbFirst)
{
}
Viterbi3::~Viterbi3()
{
}
void Viterbi3::decodeFromBits(
unsigned char *dataBits, //!< Decoded output data bits
const unsigned char *bits, //!< Input bits
unsigned int nbBits, //!< Number of input bits
unsigned int startstate) //!< Encoder starting state
{
if (nbBits > m_nbBitsMax)
{
if (m_symbols) {
delete[] m_symbols;
}
m_symbols = new unsigned char[nbBits/m_n];
m_nbBitsMax = nbBits;
}
for (unsigned int i = 0; i < nbBits; i += m_n)
{
m_symbols[i/m_n] = bits[i];
for (int j = m_n-1; j > 0; j--)
{
m_symbols[i/m_n] += bits[i+j] << j;
}
}
decodeFromSymbols(dataBits, m_symbols, nbBits/m_n, startstate);
}
void Viterbi3::decodeFromSymbols(
unsigned char *dataBits, //!< Decoded output data bits
const unsigned char *symbols, //!< Input symbols
unsigned int nbSymbols, //!< Number of input symbols
unsigned int startstate) //!< Encoder starting state
{
if (nbSymbols > m_nbSymbolsMax)
{
if (m_traceback) {
delete[] m_traceback;
}
if (m_pathMetrics) {
delete[] m_pathMetrics;
}
m_traceback = new unsigned char[4 * nbSymbols];
m_pathMetrics = new uint32_t[4];
m_nbSymbolsMax = nbSymbols;
}
// initial path metrics state
memset(m_pathMetrics, Viterbi::m_maxMetric, sizeof(uint32_t) * (1<<(m_k-1)));
m_pathMetrics[startstate] = 0;
for (unsigned int is = 0; is < nbSymbols; is++)
{
// std::cerr << "Viterbi3::decodeFromSymbols: S[" << is << "]=" << (int) symbols[is] << std::endl;
// compute metrics
doMetrics(
is,
m_branchCodes,
symbols[is],
m_traceback,
&m_traceback[nbSymbols],
&m_traceback[2*nbSymbols],
&m_traceback[3*nbSymbols],
m_pathMetrics
);
} // symbols
// trace back
uint32_t minPathMetric = m_pathMetrics[0];
unsigned int minPathIndex = 0;
for (int i = 1; i < 4; i++)
{
if (m_pathMetrics[i] < minPathMetric)
{
minPathMetric = m_pathMetrics[i];
minPathIndex = i;
}
}
// std::cerr << "Viterbi3::decodeFromSymbols: last path node: " << minPathIndex << std::endl;
traceBack(
nbSymbols,
minPathIndex,
dataBits,
m_traceback,
&m_traceback[nbSymbols],
&m_traceback[2*nbSymbols],
&m_traceback[3*nbSymbols]
);
}
void Viterbi3::doMetrics(
int n,
unsigned char *branchCodes,
unsigned char symbol,
unsigned char *m_pathMemory0,
unsigned char *m_pathMemory1,
unsigned char *m_pathMemory2,
unsigned char *m_pathMemory3,
uint32_t *m_pathMetric
)
{
uint32_t tempMetric[4];
uint32_t metric[8];
uint32_t m1;
uint32_t m2;
// Treillis edges:
// State Received
metric[0] = NbOnes[branchCodes[0] ^ symbol]; // 00 0
metric[1] = NbOnes[branchCodes[1] ^ symbol]; // 00 1
metric[2] = NbOnes[branchCodes[2] ^ symbol]; // 01 0
metric[3] = NbOnes[branchCodes[3] ^ symbol]; // 01 1
metric[4] = NbOnes[branchCodes[4] ^ symbol]; // 10 0
metric[5] = NbOnes[branchCodes[5] ^ symbol]; // 10 1
metric[6] = NbOnes[branchCodes[6] ^ symbol]; // 11 0
metric[7] = NbOnes[branchCodes[7] ^ symbol]; // 11 1
// This hardcodes the Treillis structure:
// Pres. state = S0, Prev. state = S0 & S1
m1 = metric[0] + m_pathMetric[0];
m2 = metric[2] + m_pathMetric[1];
if (m1 < m2)
{
m_pathMemory0[n] = 0; // upper path (S0)
tempMetric[0] = m1;
}
else
{
m_pathMemory0[n] = 1; // lower path (S1)
tempMetric[0] = m2;
}; // end else - if
// Pres. state = S1, Prev. state = S2 & S3
m1 = metric[4] + m_pathMetric[2];
m2 = metric[6] + m_pathMetric[3];
if (m1 < m2)
{
m_pathMemory1[n] = 2; // upper path (S2)
tempMetric[1] = m1;
}
else
{
m_pathMemory1[n] = 3; // lower path (S3)
tempMetric[1] = m2;
}; // end else - if
// Pres. state = S2, Prev. state = S0 & S1
m1 = metric[1] + m_pathMetric[0];
m2 = metric[3] + m_pathMetric[1];
if (m1 < m2)
{
m_pathMemory2[n] = 0; // upper path (S0)
tempMetric[2] = m1;
}
else
{
m_pathMemory2[n] = 1; // lower path (S1)
tempMetric[2] = m2;
}
// Pres. state = S3, Prev. state = S2 & S3
m1 = metric[5] + m_pathMetric[2];
m2 = metric[7] + m_pathMetric[3];
if (m1 < m2)
{
m_pathMemory3[n] = 2; // upper path (S2)
tempMetric[3] = m1;
}
else
{
m_pathMemory3[n] = 3; // lower path (S3)
tempMetric[3] = m2;
}; // end else - if
// Store new path metrics
m_pathMetric[0] = tempMetric[0];
m_pathMetric[1] = tempMetric[1];
m_pathMetric[2] = tempMetric[2];
m_pathMetric[3] = tempMetric[3];
} // end function ViterbiDecode
void Viterbi3::traceBack (
int nbSymbols,
unsigned int startState,
unsigned char *out,
unsigned char *m_pathMemory0,
unsigned char *m_pathMemory1,
unsigned char *m_pathMemory2,
unsigned char *m_pathMemory3
)
{
unsigned int state = startState;
for (int loop = nbSymbols - 1; loop >= 0; loop--)
{
// TODO: store directly the integer state value in path memory
switch (state)
{
case 0: // if state S0, Prev. state = S0 | S1
state = m_pathMemory0[loop];
out[loop] = 0;
break;
case 1: // if state S1, Prev. state = S2 | S3
state = m_pathMemory1[loop];
out[loop] = 0;
break;
case 2: // if state S2, Prev. state = S0 | S1
state = m_pathMemory2[loop];
out[loop] = 1;
break;
case 3: // if state S3, Prev. state = S2 | S3
state = m_pathMemory3[loop];
out[loop] = 1;
break;
}; // end switch
}; // end for
}
}