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+/*
+ * Copyright 2008, 2009, 2014 Free Software Foundation, Inc.
+ * Copyright 2014 Range Networks, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * This use of this software may be subject to additional restrictions.
+ * See the LEGAL file in the main directory for details.
+ */
+
+#ifndef _VITERBIR204_H_
+#define _VITERBIR204_H_ 1
+
+#include "Viterbi.h"
+
+
+/**
+	Class to represent convolutional coders/decoders of rate 1/2, memory length 4.
+	This is the "workhorse" coder for most GSM channels.
+*/
+class ViterbiR2O4 : public ViterbiBase {
+
+	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;	///< (16) 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
+		// (pat) There are 16 states, each of which has two possible output states.
+		// These are stored in these two tables in consecutive locations.
+		uint32_t mStateTable[mIRate][2*mIStates];	///< precomputed generator output tables
+		// mGeneratorTable is the encoder output state for a given input state and encoder input bit.
+		uint32_t mGeneratorTable[2*mIStates];		///< precomputed coder output table
+		//@}
+		int mBitErrorCnt;
+	
+	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
+			int bitErrorCnt;	///< number of bit errors in the encoded vector being decoded.
+		} vCand;
+
+		/** Clear a structure. */
+		void vitClear(vCand& v)
+		{
+			v.iState=0;
+			v.oState=0;
+			v.cost=0;
+			v.bitErrorCnt = 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* vstep(uint32_t inSample, const float *probs, const float *iprobs, bool isNotTailBits);
+
+	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();
+
+	public:
+		void encode(const BitVector &in, BitVector& target) const;
+		void decode(const SoftVector &in, BitVector& target);
+		int getBEC() { return mBitErrorCnt; }
+};
+#endif