442 lines
11 KiB
C++
442 lines
11 KiB
C++
/*
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* Copyright 2008, 2009 Free Software Foundation, Inc.
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*
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* This software is distributed under the terms of the GNU Affero Public License.
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* See the COPYING file in the main directory for details.
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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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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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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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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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#ifndef FECVECTORS_H
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#define FECVECTORS_H
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#include "Vector.h"
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#include <stdint.h>
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class BitVector;
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class SoftVector;
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/** Shift-register (LFSR) generator. */
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class Generator {
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private:
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uint64_t mCoeff; ///< polynomial coefficients. LSB is zero exponent.
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uint64_t mState; ///< shift register state. LSB is most recent.
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uint64_t mMask; ///< mask for reading state
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unsigned mLen; ///< number of bits used in shift register
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unsigned mLen_1; ///< mLen - 1
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public:
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Generator(uint64_t wCoeff, unsigned wLen)
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:mCoeff(wCoeff),mState(0),
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mMask((1ULL<<wLen)-1),
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mLen(wLen),mLen_1(wLen-1)
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{ assert(wLen<64); }
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void clear() { mState=0; }
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/**@name Accessors */
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//@{
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uint64_t state() const { return mState & mMask; }
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unsigned size() const { return mLen; }
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//@}
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/**
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Calculate one bit of a syndrome.
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This is in the .h for inlining.
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*/
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void syndromeShift(unsigned inBit)
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{
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const unsigned fb = (mState>>(mLen_1)) & 0x01;
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mState = (mState<<1) ^ (inBit & 0x01);
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if (fb) mState ^= mCoeff;
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}
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/**
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Update the generator state by one cycle.
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This is in the .h for inlining.
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*/
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void encoderShift(unsigned inBit)
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{
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const unsigned fb = ((mState>>(mLen_1)) ^ inBit) & 0x01;
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mState <<= 1;
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if (fb) mState ^= mCoeff;
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}
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};
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/** Parity (CRC-type) generator and checker based on a Generator. */
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class Parity : public Generator {
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protected:
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unsigned mCodewordSize;
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public:
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Parity(uint64_t wCoefficients, unsigned wParitySize, unsigned wCodewordSize)
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:Generator(wCoefficients, wParitySize),
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mCodewordSize(wCodewordSize)
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{ }
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/** Compute the parity word and write it into the target segment. */
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void writeParityWord(const BitVector& data, BitVector& parityWordTarget, bool invert=true);
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/** Compute the syndrome of a received sequence. */
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uint64_t syndrome(const BitVector& receivedCodeword);
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};
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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 {
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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; ///< 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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uint32_t mStateTable[mIRate][2*mIStates]; ///< precomputed generator output tables
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uint32_t mGeneratorTable[2*mIStates]; ///< precomputed coder output table
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//@}
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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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} vCand;
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/** Clear a structure. */
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void clear(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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}
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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& step(uint32_t inSample, const float *probs, const float *iprobs);
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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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};
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class BitVector : public Vector<char> {
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public:
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/**@name Constructors. */
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//@{
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/**@name Casts of Vector constructors. */
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//@{
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BitVector(char* wData, char* wStart, char* wEnd)
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:Vector<char>(wData,wStart,wEnd)
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{ }
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BitVector(size_t len=0):Vector<char>(len) {}
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BitVector(const Vector<char>& source):Vector<char>(source) {}
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BitVector(Vector<char>& source):Vector<char>(source) {}
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BitVector(const Vector<char>& source1, const Vector<char> source2):Vector<char>(source1,source2) {}
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//@}
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/** Construct from a string of "0" and "1". */
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BitVector(const char* valString);
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//@}
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/** Index a single bit. */
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bool bit(size_t index) const
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{
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// We put this code in .h for fast inlining.
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const char *dp = mStart+index;
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assert(dp<mEnd);
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return (*dp) & 0x01;
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}
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/**@name Casts and overrides of Vector operators. */
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//@{
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BitVector segment(size_t start, size_t span)
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{
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char* wStart = mStart + start;
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char* wEnd = wStart + span;
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assert(wEnd<=mEnd);
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return BitVector(NULL,wStart,wEnd);
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}
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BitVector alias()
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{ return segment(0,size()); }
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const BitVector segment(size_t start, size_t span) const
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{ return (BitVector)(Vector<char>::segment(start,span)); }
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BitVector head(size_t span) { return segment(0,span); }
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const BitVector head(size_t span) const { return segment(0,span); }
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BitVector tail(size_t start) { return segment(start,size()-start); }
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const BitVector tail(size_t start) const { return segment(start,size()-start); }
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//@}
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void zero() { fill(0); }
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/**@name FEC operations. */
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//@{
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/** Calculate the syndrome of the vector with the given Generator. */
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uint64_t syndrome(Generator& gen) const;
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/** Calculate the parity word for the vector with the given Generator. */
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uint64_t parity(Generator& gen) const;
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/** Encode the signal with the GSM rate 1/2 convolutional encoder. */
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void encode(const ViterbiR2O4& encoder, BitVector& target);
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//@}
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/** Invert 0<->1. */
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void invert();
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/**@name Byte-wise operations. */
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//@{
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/** Reverse an 8-bit vector. */
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void reverse8();
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/** Reverse groups of 8 within the vector (byte reversal). */
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void LSB8MSB();
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//@}
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/**@name Serialization and deserialization. */
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//@{
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uint64_t peekField(size_t readIndex, unsigned length) const;
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uint64_t peekFieldReversed(size_t readIndex, unsigned length) const;
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uint64_t readField(size_t& readIndex, unsigned length) const;
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uint64_t readFieldReversed(size_t& readIndex, unsigned length) const;
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void fillField(size_t writeIndex, uint64_t value, unsigned length);
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void fillFieldReversed(size_t writeIndex, uint64_t value, unsigned length);
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void writeField(size_t& writeIndex, uint64_t value, unsigned length);
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void writeFieldReversed(size_t& writeIndex, uint64_t value, unsigned length);
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//@}
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/** Sum of bits. */
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unsigned sum() const;
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/** Reorder bits, dest[i] = this[map[i]]. */
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void map(const unsigned *map, size_t mapSize, BitVector& dest) const;
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/** Reorder bits, dest[map[i]] = this[i]. */
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void unmap(const unsigned *map, size_t mapSize, BitVector& dest) const;
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/** Pack into a char array. */
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void pack(unsigned char*) const;
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/** Unpack from a char array. */
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void unpack(const unsigned char*);
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/** Make a hexdump string. */
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void hex(std::ostream&) const;
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/** Unpack from a hexdump string.
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* @returns true on success, false on error. */
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bool unhex(const char*);
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};
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std::ostream& operator<<(std::ostream&, const BitVector&);
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/**
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The SoftVector class is used to represent a soft-decision signal.
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Values 0..1 represent probabilities that a bit is "true".
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*/
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class SoftVector: public Vector<float> {
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public:
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/** Build a SoftVector of a given length. */
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SoftVector(size_t wSize=0):Vector<float>(wSize) {}
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/** Construct a SoftVector from a C string of "0", "1", and "X". */
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SoftVector(const char* valString);
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/** Construct a SoftVector from a BitVector. */
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SoftVector(const BitVector& source);
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/**
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Wrap a SoftVector around a block of floats.
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The block will be delete[]ed upon desctuction.
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*/
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SoftVector(float *wData, unsigned length)
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:Vector<float>(wData,length)
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{}
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SoftVector(float* wData, float* wStart, float* wEnd)
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:Vector<float>(wData,wStart,wEnd)
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{ }
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/**
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Casting from a Vector<float>.
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Note that this is NOT pass-by-reference.
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*/
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SoftVector(Vector<float> source)
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:Vector<float>(source)
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{}
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/**@name Casts and overrides of Vector operators. */
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//@{
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SoftVector segment(size_t start, size_t span)
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{
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float* wStart = mStart + start;
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float* wEnd = wStart + span;
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assert(wEnd<=mEnd);
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return SoftVector(NULL,wStart,wEnd);
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}
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SoftVector alias()
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{ return segment(0,size()); }
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const SoftVector segment(size_t start, size_t span) const
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{ return (SoftVector)(Vector<float>::segment(start,span)); }
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SoftVector head(size_t span) { return segment(0,span); }
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const SoftVector head(size_t span) const { return segment(0,span); }
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SoftVector tail(size_t start) { return segment(start,size()-start); }
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const SoftVector tail(size_t start) const { return segment(start,size()-start); }
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//@}
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/** Decode soft symbols with the GSM rate-1/2 Viterbi decoder. */
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void decode(ViterbiR2O4 &decoder, BitVector& target) const;
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/** Fill with "unknown" values. */
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void unknown() { fill(0.5F); }
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/** Return a hard bit value from a given index by slicing. */
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bool bit(size_t index) const
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{
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const float *dp = mStart+index;
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assert(dp<mEnd);
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return (*dp)>0.5F;
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}
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/** Slice the whole signal into bits. */
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BitVector sliced() const;
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};
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std::ostream& operator<<(std::ostream&, const SoftVector&);
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#endif
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// vim: ts=4 sw=4
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