146 lines
4.6 KiB
C++
146 lines
4.6 KiB
C++
/*
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* Copyright 2008, 2009, 2014 Free Software Foundation, Inc.
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* Copyright 2014 Range Networks, Inc.
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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 Affero General Public License as published by
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* the Free Software Foundation, either 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 Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero 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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* This use of this software may be subject to additional restrictions.
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* See the LEGAL file in the main directory for details.
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*/
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#ifndef _VITERBIR204_H_
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#define _VITERBIR204_H_ 1
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#include "Viterbi.h"
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/**
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Class to represent convolutional coders/decoders of rate 1/2, memory length 4.
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This is the "workhorse" coder for most GSM channels.
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*/
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class ViterbiR2O4 : public ViterbiBase {
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private:
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/**name Lots of precomputed elements so the compiler can optimize like hell. */
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//@{
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/**@name Core values. */
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//@{
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static const unsigned mIRate = 2; ///< reciprocal of rate
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static const unsigned mOrder = 4; ///< memory length of generators
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//@}
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/**@name Derived values. */
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//@{
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static const unsigned mIStates = 0x01 << mOrder; ///< (16) number of states, number of survivors
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static const uint32_t mSMask = mIStates-1; ///< survivor mask
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static const uint32_t mCMask = (mSMask<<1) | 0x01; ///< candidate mask
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static const uint32_t mOMask = (0x01<<mIRate)-1; ///< ouput mask, all iRate low bits set
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static const unsigned mNumCands = mIStates*2; ///< number of candidates to generate during branching
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static const unsigned mDeferral = 6*mOrder; ///< deferral to be used
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//@}
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//@}
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/** Precomputed tables. */
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//@{
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uint32_t mCoeffs[mIRate]; ///< polynomial for each generator
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// (pat) There are 16 states, each of which has two possible output states.
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// These are stored in these two tables in consecutive locations.
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uint32_t mStateTable[mIRate][2*mIStates]; ///< precomputed generator output tables
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// mGeneratorTable is the encoder output state for a given input state and encoder input bit.
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uint32_t mGeneratorTable[2*mIStates]; ///< precomputed coder output table
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//@}
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int mBitErrorCnt;
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public:
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/**
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A candidate sequence in a Viterbi decoder.
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The 32-bit state register can support a deferral of 6 with a 4th-order coder.
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*/
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typedef struct candStruct {
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uint32_t iState; ///< encoder input associated with this candidate
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uint32_t oState; ///< encoder output associated with this candidate
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float cost; ///< cost (metric value), float to support soft inputs
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int bitErrorCnt; ///< number of bit errors in the encoded vector being decoded.
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} vCand;
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/** Clear a structure. */
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void vitClear(vCand& v)
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{
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v.iState=0;
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v.oState=0;
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v.cost=0;
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v.bitErrorCnt = 0;
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}
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private:
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/**@name Survivors and candidates. */
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//@{
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vCand mSurvivors[mIStates]; ///< current survivor pool
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vCand mCandidates[2*mIStates]; ///< current candidate pool
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//@}
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public:
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unsigned iRate() const { return mIRate; }
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uint32_t cMask() const { return mCMask; }
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uint32_t stateTable(unsigned g, unsigned i) const { return mStateTable[g][i]; }
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unsigned deferral() const { return mDeferral; }
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ViterbiR2O4();
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/** Set all cost metrics to zero. */
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void initializeStates();
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/**
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Full cycle of the Viterbi algorithm: branch, metrics, prune, select.
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@return reference to minimum-cost candidate.
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*/
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const vCand* vstep(uint32_t inSample, const float *probs, const float *iprobs, bool isNotTailBits);
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private:
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/** Branch survivors into new candidates. */
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void branchCandidates();
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/** Compute cost metrics for soft-inputs. */
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void getSoftCostMetrics(uint32_t inSample, const float *probs, const float *iprobs);
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/** Select survivors from the candidate set. */
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void pruneCandidates();
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/** Find the minimum cost survivor. */
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const vCand& minCost() const;
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/**
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Precompute the state tables.
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@param g Generator index 0..((1/rate)-1)
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*/
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void computeStateTables(unsigned g);
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/**
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Precompute the generator outputs.
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mCoeffs must be defined first.
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*/
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void computeGeneratorTable();
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public:
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void encode(const BitVector &in, BitVector& target) const;
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void decode(const SoftVector &in, BitVector& target);
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int getBEC() { return mBitErrorCnt; }
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};
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#endif
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