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/*
* Copyright 2008, 2009 Free Software Foundation, Inc.
*
* This software is distributed under the terms of the GNU Public License.
* See the COPYING file in the main directory for details.
*
* This use of this software may be subject to additional restrictions.
* See the LEGAL file in the main directory for details.
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, either version 3 of the License, or
(at your option) any later version.
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 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/>.
*/
#ifndef FECVECTORS_H
#define FECVECTORS_H
#include "Vector.h"
#include <stdint.h>
class BitVector;
class SoftVector;
/** Shift-register (LFSR) generator. */
class Generator {
private:
uint64_t mCoeff; ///< polynomial coefficients. LSB is zero exponent.
uint64_t mState; ///< shift register state. LSB is most recent.
uint64_t mMask; ///< mask for reading state
unsigned mLen; ///< number of bits used in shift register
unsigned mLen_1; ///< mLen - 1
public:
Generator(uint64_t wCoeff, unsigned wLen)
:mCoeff(wCoeff),mState(0),
mMask((1ULL<<wLen)-1),
mLen(wLen),mLen_1(wLen-1)
{ assert(wLen<64); }
void clear() { mState=0; }
/**@name Accessors */
//@{
uint64_t state() const { return mState & mMask; }
unsigned size() const { return mLen; }
//@}
/**
Calculate one bit of a syndrome.
This is in the .h for inlining.
*/
void syndromeShift(unsigned inBit)
{
const unsigned fb = (mState>>(mLen_1)) & 0x01;
mState = (mState<<1) ^ (inBit & 0x01);
if (fb) mState ^= mCoeff;
}
/**
Update the generator state by one cycle.
This is in the .h for inlining.
*/
void encoderShift(unsigned inBit)
{
const unsigned fb = ((mState>>(mLen_1)) ^ inBit) & 0x01;
mState <<= 1;
if (fb) mState ^= mCoeff;
}
};
/** Parity (CRC-type) generator and checker based on a Generator. */
class Parity : public Generator {
protected:
unsigned mCodewordSize;
public:
Parity(uint64_t wCoefficients, unsigned wParitySize, unsigned wCodewordSize)
:Generator(wCoefficients, wParitySize),
mCodewordSize(wCodewordSize)
{ }
/** Compute the parity word and write it into the target segment. */
void writeParityWord(const BitVector& data, BitVector& parityWordTarget, bool invert=true);
/** Compute the syndrome of a received sequence. */
uint64_t syndrome(const BitVector& receivedCodeword);
};
/**
Class to represent convolutional coders/decoders of rate 1/2, memory length 4.
This is the "workhorse" coder for most GSM channels.
*/
class ViterbiR2O4 {
private:
/**name Lots of precomputed elements so the compiler can optimize like hell. */
//@{
/**@name Core values. */
//@{
static const unsigned mIRate = 2; ///< reciprocal of rate
static const unsigned mOrder = 4; ///< memory length of generators
//@}
/**@name Derived values. */
//@{
static const unsigned mIStates = 0x01 << mOrder; ///< number of states, number of survivors
static const uint32_t mSMask = mIStates-1; ///< survivor mask
static const uint32_t mCMask = (mSMask<<1) | 0x01; ///< candidate mask
static const uint32_t mOMask = (0x01<<mIRate)-1; ///< ouput mask, all iRate low bits set
static const unsigned mNumCands = mIStates*2; ///< number of candidates to generate during branching
static const unsigned mDeferral = 6*mOrder; ///< deferral to be used
//@}
//@}
/** Precomputed tables. */
//@{
uint32_t mCoeffs[mIRate]; ///< polynomial for each generator
uint32_t mStateTable[mIRate][2*mIStates]; ///< precomputed generator output tables
uint32_t mGeneratorTable[2*mIStates]; ///< precomputed coder output table
//@}
public:
/**
A candidate sequence in a Viterbi decoder.
The 32-bit state register can support a deferral of 6 with a 4th-order coder.
*/
typedef struct candStruct {
uint32_t iState; ///< encoder input associated with this candidate
uint32_t oState; ///< encoder output associated with this candidate
float cost; ///< cost (metric value), float to support soft inputs
} vCand;
/** Clear a structure. */
void clear(vCand& v)
{
v.iState=0;
v.oState=0;
v.cost=0;
}
private:
/**@name Survivors and candidates. */
//@{
vCand mSurvivors[mIStates]; ///< current survivor pool
vCand mCandidates[2*mIStates]; ///< current candidate pool
//@}
public:
unsigned iRate() const { return mIRate; }
uint32_t cMask() const { return mCMask; }
uint32_t stateTable(unsigned g, unsigned i) const { return mStateTable[g][i]; }
unsigned deferral() const { return mDeferral; }
ViterbiR2O4();
/** Set all cost metrics to zero. */
void initializeStates();
/**
Full cycle of the Viterbi algorithm: branch, metrics, prune, select.
@return reference to minimum-cost candidate.
*/
const vCand& step(uint32_t inSample, const float *probs, const float *iprobs);
private:
/** Branch survivors into new candidates. */
void branchCandidates();
/** Compute cost metrics for soft-inputs. */
void getSoftCostMetrics(uint32_t inSample, const float *probs, const float *iprobs);
/** Select survivors from the candidate set. */
void pruneCandidates();
/** Find the minimum cost survivor. */
const vCand& minCost() const;
/**
Precompute the state tables.
@param g Generator index 0..((1/rate)-1)
*/
void computeStateTables(unsigned g);
/**
Precompute the generator outputs.
mCoeffs must be defined first.
*/
void computeGeneratorTable();
};
class BitVector : public Vector<char> {
public:
/**@name Constructors. */
//@{
/**@name Casts of Vector constructors. */
//@{
BitVector(char* wData, char* wStart, char* wEnd)
:Vector<char>(wData,wStart,wEnd)
{ }
BitVector(size_t len=0):Vector<char>(len) {}
BitVector(const Vector<char>& source):Vector<char>(source) {}
BitVector(Vector<char>& source):Vector<char>(source) {}
BitVector(const Vector<char>& source1, const Vector<char> source2):Vector<char>(source1,source2) {}
//@}
/** Construct from a string of "0" and "1". */
BitVector(const char* valString);
//@}
/** Index a single bit. */
bool bit(size_t index) const
{
// We put this code in .h for fast inlining.
const char *dp = mStart+index;
assert(dp<mEnd);
return (*dp) & 0x01;
}
/**@name Casts and overrides of Vector operators. */
//@{
BitVector segment(size_t start, size_t span)
{
char* wStart = mStart + start;
char* wEnd = wStart + span;
assert(wEnd<=mEnd);
return BitVector(NULL,wStart,wEnd);
}
BitVector alias()
{ return segment(0,size()); }
const BitVector segment(size_t start, size_t span) const
{ return (BitVector)(Vector<char>::segment(start,span)); }
BitVector head(size_t span) { return segment(0,span); }
const BitVector head(size_t span) const { return segment(0,span); }
BitVector tail(size_t start) { return segment(start,size()-start); }
const BitVector tail(size_t start) const { return segment(start,size()-start); }
//@}
void zero() { fill(0); }
/**@name FEC operations. */
//@{
/** Calculate the syndrome of the vector with the given Generator. */
uint64_t syndrome(Generator& gen) const;
/** Calculate the parity word for the vector with the given Generator. */
uint64_t parity(Generator& gen) const;
/** Encode the signal with the GSM rate 1/2 convolutional encoder. */
void encode(const ViterbiR2O4& encoder, BitVector& target);
//@}
/** Invert 0<->1. */
void invert();
/**@name Byte-wise operations. */
//@{
/** Reverse an 8-bit vector. */
void reverse8();
/** Reverse groups of 8 within the vector (byte reversal). */
void LSB8MSB();
//@}
/**@name Serialization and deserialization. */
//@{
uint64_t peekField(size_t readIndex, unsigned length) const;
uint64_t peekFieldReversed(size_t readIndex, unsigned length) const;
uint64_t readField(size_t& readIndex, unsigned length) const;
uint64_t readFieldReversed(size_t& readIndex, unsigned length) const;
void fillField(size_t writeIndex, uint64_t value, unsigned length);
void fillFieldReversed(size_t writeIndex, uint64_t value, unsigned length);
void writeField(size_t& writeIndex, uint64_t value, unsigned length);
void writeFieldReversed(size_t& writeIndex, uint64_t value, unsigned length);
//@}
/** Sum of bits. */
unsigned sum() const;
/** Reorder bits, dest[i] = this[map[i]]. */
void map(const unsigned *map, size_t mapSize, BitVector& dest) const;
/** Reorder bits, dest[map[i]] = this[i]. */
void unmap(const unsigned *map, size_t mapSize, BitVector& dest) const;
/** Pack into a char array. */
void pack(unsigned char*) const;
/** Unopack from a char array. */
void unpack(const unsigned char*);
/** Make a hexdump string. */
void hex(std::ostream&) const;
};
std::ostream& operator<<(std::ostream&, const BitVector&);
/**
The SoftVector class is used to represent a soft-decision signal.
Values 0..1 represent probabilities that a bit is "true".
*/
class SoftVector: public Vector<float> {
public:
/** Build a SoftVector of a given length. */
SoftVector(size_t wSize=0):Vector<float>(wSize) {}
/** Construct a SoftVector from a C string of "0", "1", and "X". */
SoftVector(const char* valString);
/** Construct a SoftVector from a BitVector. */
SoftVector(const BitVector& source);
/**
Wrap a SoftVector around a block of floats.
The block will be delete[]ed upon desctuction.
*/
SoftVector(float *wData, unsigned length)
:Vector<float>(wData,length)
{}
SoftVector(float* wData, float* wStart, float* wEnd)
:Vector<float>(wData,wStart,wEnd)
{ }
/**
Casting from a Vector<float>.
Note that this is NOT pass-by-reference.
*/
SoftVector(Vector<float> source)
:Vector<float>(source)
{}
/**@name Casts and overrides of Vector operators. */
//@{
SoftVector segment(size_t start, size_t span)
{
float* wStart = mStart + start;
float* wEnd = wStart + span;
assert(wEnd<=mEnd);
return SoftVector(NULL,wStart,wEnd);
}
SoftVector alias()
{ return segment(0,size()); }
const SoftVector segment(size_t start, size_t span) const
{ return (SoftVector)(Vector<float>::segment(start,span)); }
SoftVector head(size_t span) { return segment(0,span); }
const SoftVector head(size_t span) const { return segment(0,span); }
SoftVector tail(size_t start) { return segment(start,size()-start); }
const SoftVector tail(size_t start) const { return segment(start,size()-start); }
//@}
/** Decode soft symbols with the GSM rate-1/2 Viterbi decoder. */
void decode(ViterbiR2O4 &decoder, BitVector& target) const;
/** Fill with "unknown" values. */
void unknown() { fill(0.5F); }
/** Return a hard bit value from a given index by slicing. */
bool bit(size_t index) const
{
const float *dp = mStart+index;
assert(dp<mEnd);
return (*dp)>0.5F;
}
/** Slice the whole signal into bits. */
BitVector sliced() const;
};
std::ostream& operator<<(std::ostream&, const SoftVector&);
#endif
// vim: ts=4 sw=4