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///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2016 Edouard Griffiths, F4EXB. //
// //
// 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 "viterbi.h"
namespace DSDcc
{
const unsigned int Viterbi::Poly23[] = { 0x7, 0x6 };
const unsigned int Viterbi::Poly23a[] = { 0x7, 0x5 };
const unsigned int Viterbi::Poly24[] = { 0xf, 0xb };
const unsigned int Viterbi::Poly25[] = { 0x17, 0x19 };
const unsigned int Viterbi::Poly25a[] = { 0x13, 0x1b };
const unsigned int Viterbi::Poly25y[] = { 0x13, 0x1d };
const unsigned char Viterbi::Partab[] = {
0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0,
};
// calculated with:
//int NumberOfSetBits(int i)
//{
// // Java: use >>> instead of >>
// // C or C++: use uint32_t
// i = i - ((i >> 1) & 0x55555555);
// i = (i & 0x33333333) + ((i >> 2) & 0x33333333);
// return (((i + (i >> 4)) & 0x0F0F0F0F) * 0x01010101) >> 24;
//}
const unsigned char Viterbi::NbOnes[] = {
0, 1, 1, 2, 1, 2, 2, 3,
1, 2, 2, 3, 2, 3, 3, 4,
1, 2, 2, 3, 2, 3, 3, 4,
2, 3, 3, 4, 3, 4, 4, 5,
1, 2, 2, 3, 2, 3, 3, 4,
2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5,
3, 4, 4, 5, 4, 5, 5, 6,
1, 2, 2, 3, 2, 3, 3, 4,
2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5,
3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5,
3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6,
4, 5, 5, 6, 5, 6, 6, 7,
1, 2, 2, 3, 2, 3, 3, 4,
2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5,
3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5,
3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6,
4, 5, 5, 6, 5, 6, 6, 7,
2, 3, 3, 4, 3, 4, 4, 5,
3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6,
4, 5, 5, 6, 5, 6, 6, 7,
3, 4, 4, 5, 4, 5, 5, 6,
4, 5, 5, 6, 5, 6, 6, 7,
4, 5, 5, 6, 5, 6, 6, 7,
5, 6, 6, 7, 6, 7, 7, 8,
};
const uint32_t Viterbi::m_maxMetric = 0xFFFE0000; // Account for any possible accumulation of branch metrics
Viterbi::Viterbi(int k, int n, const unsigned int *polys, bool msbFirst) :
m_k(k),
m_n(n),
m_polys(polys),
m_msbFirst(msbFirst),
m_nbSymbolsMax(0),
m_nbBitsMax(0)
{
m_branchCodes = new unsigned char[(1<<m_k)];
m_predA = new unsigned char[1<<(m_k-1)];
m_predB = new unsigned char[1<<(m_k-1)];
m_pathMetrics = 0;
m_traceback = 0;
m_symbols = 0;
initCodes();
initTreillis();
}
Viterbi::~Viterbi()
{
if (m_symbols) {
delete[] m_symbols;
}
if (m_pathMetrics) {
delete[] m_pathMetrics;
}
if (m_traceback) {
delete[] m_traceback;
}
delete[] m_predB;
delete[] m_predA;
delete[] m_branchCodes;
}
void Viterbi::initCodes()
{
unsigned char symbol;
unsigned char dataBit;
for (int i = 0; i < (1<<(m_k-1)); i++)
{
dataBit = 0;
encodeToSymbols(&symbol, &dataBit, 1, i<<1);
m_branchCodes[2*i] = symbol;
dataBit = 1;
encodeToSymbols(&symbol, &dataBit, 1, i<<1);
m_branchCodes[2*i+1] = symbol;
}
}
void Viterbi::initTreillis()
{
for (int s = 0; s < 1<<(m_k-2); s++)
{
m_predA[s] = (s<<1);
m_predB[s] = (s<<1) + 1;
m_predA[s+(1<<(m_k-2))] = (s<<1);
m_predB[s+(1<<(m_k-2))] = (s<<1) + 1;
}
}
void Viterbi::encodeToSymbols(
unsigned char *symbols,
const unsigned char *dataBits,
unsigned int nbBits,
unsigned int startstate)
{
unsigned int encstate = startstate;
for (unsigned int i = 0; i < nbBits; i++)
{
encstate = (encstate >> 1) | (dataBits[i] << (m_k-1));
*symbols = 0;
for (int j = 0; j < m_n; j++)
{
*symbols += parity(encstate & m_polys[j]) << (m_msbFirst ? (m_n - 1) - j : j);
}
symbols++;
}
}
void Viterbi::encodeToBits(
unsigned char *codedBits,
const unsigned char *dataBits,
unsigned int nbBits,
unsigned int startstate)
{
unsigned int encstate = startstate;
for (unsigned int i = 0; i < nbBits; i++)
{
encstate = (encstate >> 1) | (dataBits[i] << (m_k-1));
for (int j = 0; j < m_n; j++)
{
*codedBits = parity(encstate & m_polys[j]);
codedBits++;
}
}
}
void Viterbi::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 Viterbi::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[(1<<(m_k-1)) * nbSymbols];
m_pathMetrics = new uint32_t[(1<<(m_k-1))*2]; // only one step back in memory
m_nbSymbolsMax = nbSymbols;
}
// initial path metrics state
memset(m_pathMetrics, m_maxMetric, sizeof(uint32_t) * (1<<(m_k-1)));
m_pathMetrics[startstate] = 0;
unsigned int minPathIndex;
unsigned int minMetric;
for (unsigned int is = 0; is < nbSymbols; is++)
{
minMetric = m_maxMetric;
// std::cerr << "S[" << is << "]=" << (int) symbols[is] << std::endl;
// compute branch metrics
for (int ib = 0; ib < 1<<(m_k-1); ib++)
{
unsigned char bit = ib < 1<<(m_k-2) ? 0 : 1;
// path A
unsigned char predA = m_predA[ib];
unsigned int predPMIxA = (is%2)*(1<<(m_k-1)) + predA;
unsigned char codeA = m_branchCodes[(predA<<1)+bit];
unsigned char bmA = NbOnes[codeA ^ symbols[is]]; // branch metric
unsigned int pmA = m_pathMetrics[predPMIxA] + bmA; // add branch metric to path metric
// path B
unsigned char predB = m_predB[ib];
unsigned int predPMIxB = (is%2)*(1<<(m_k-1)) + predB;
unsigned char codeB = m_branchCodes[(predB<<1)+bit];
unsigned char bmB = NbOnes[codeB ^ symbols[is]]; // branch metric
unsigned int pmB = m_pathMetrics[predPMIxB] + bmB; // add branch metric to path metric
// decisions, decisions ...
// std::cerr << " Branch:"
// << " " << ib
// << " bit: " << (int) bit
// << " predA: " << (int) predA
// << " pm[" << (int) predA << ":" << is*(1<<(m_k-1)) << "]: " << m_pathMetrics[predPMIxA]
// << " codeA: " << (int) codeA
// << " bmA: " << (int) bmA
// << " pmA: " << pmA
// << " | predB: " << (int) predB
// << " pm[" << (int) predB << ":" << is*(1<<(m_k-1)) << "]: " << m_pathMetrics[predPMIxB]
// << " codeB: " << (int) codeB
// << " bmB: " << (int) bmB
// << " pmB: " << pmB << std::endl;
bool a_b; // true: A, false: B
if (pmA == pmB) // path metrics are even
{
if (bmA == bmB)
{
a_b = true; // arbitrary
}
else
{
a_b = bmA < bmB;
}
}
else
{
a_b = pmA < pmB;
}
if (a_b) // A selected
{
m_pathMetrics[ib + ((is+1)%2)*(1<<(m_k-1))] = pmA;
m_traceback[ib + is*(1<<(m_k-1))] = predA; // Pack predecessor branch # and bit value
if (pmA < minMetric)
{
minMetric = pmA;
minPathIndex = ib;
}
// std::cerr << " Select A:"
// << " pm: " << pmA
// << " bit: " << (int) bit
// << " m_traceback[" << ib + is*(1<<(m_k-1)) << "]: " << (int) predA
// << std::endl;
}
else
{
m_pathMetrics[ib + ((is+1)%2)*(1<<(m_k-1))] = pmB;
m_traceback[ib + is*(1<<(m_k-1))] = predB; // Pack predecessor branch # and bit value
if (pmB < minMetric)
{
minMetric = pmB;
minPathIndex = ib;
}
// std::cerr << " Select B:"
// << " pm: " << pmB
// << " bit: " << (int) bit
// << " m_traceback[" << ib + is*(1<<(m_k-1)) << "]: " << (int) predB
// << std::endl;
} // path decision
} // branches
} // symbols
// trace back
int bIx = minPathIndex = 0;
for (int is = nbSymbols-1; is >= 0; is--)
{
// std::cerr << "is: " << is
// << " bIx: " << (int) bIx
// << " bit: " << bIx < 1<<(m_k-2) ? 0 : 1;
// << " pred: " << (int) m_traceback[bIx + is*(1<<(m_k-1))]
// << std::endl;
dataBits[is] = bIx < 1<<(m_k-2) ? 0U : 1U;
bIx = m_traceback[bIx + is*(1<<(m_k-1))];
}
}
} // namespace DSDcc
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