polar_decoder_common.h

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/* -*- c++ -*- */
/*
 * Copyright 2015 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * GNU Radio 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, or (at your option)
 * any later version.
 *
 * GNU Radio 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 GNU Radio; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */


#ifndef INCLUDED_FEC_POLAR_DECODER_COMMON_H
#define INCLUDED_FEC_POLAR_DECODER_COMMON_H

#include <gnuradio/fec/api.h>
#include <gnuradio/fec/generic_decoder.h>
#include <gnuradio/fec/polar_common.h>

#ifndef BOOST_CONSTEXPR_OR_CONST
#define BOOST_CONSTEXPR_OR_CONST const
#endif

namespace gr {
  namespace fec {
    namespace code {

      /*!
       * \brief Class holds common methods and attributes for different
       * decoder implementations
       */
      class FEC_API polar_decoder_common : public generic_decoder, public polar_common
      {
      public:
        /*!
         *
         * \param block_size codeword size. MUST be a power of 2.
         * \param num_info_bits represents the number of information bits
         *        in a block. Also called frame_size. <= block_size
         * \param frozen_bit_positions is an integer vector which defines
         *        the position of all frozen bits in a block.  Its size
         *        MUST be equal to block_size - num_info_bits.  Also it
         *        must be sorted and every position must only occur once.
         * \param frozen_bit_values holds an unpacked byte for every
         *        frozen bit position. It defines if a frozen bit is
         *        fixed to '0' or '1'. Defaults to all ZERO.
         */
        polar_decoder_common(int block_size, int num_info_bits,
                             std::vector<int> frozen_bit_positions,
                             std::vector<char> frozen_bit_values);
        ~polar_decoder_common();

        // FECAPI
        double rate(){return (1.0 * get_output_size() / get_input_size());};
        int get_input_size(){return block_size();};
        int get_output_size(){return num_info_bits();};
        bool set_frame_size(unsigned int frame_size){return false;};

      private:
        static BOOST_CONSTEXPR_OR_CONST float D_LLR_FACTOR = -2.19722458f;
        unsigned int d_frozen_bit_counter;

      protected:
        // calculate LLRs for stage
        float llr_odd(const float la, const float lb) const;
        float llr_even(const float la, const float lb, const unsigned char f) const;
        unsigned char llr_bit_decision(const float llr) const {return (llr < 0.0f) ? 1 : 0;};

        // control retrieval of frozen bits.
        const bool is_frozen_bit(const int u_num) const;
        const unsigned char next_frozen_bit();

        // preparation for decoding
        void initialize_decoder(unsigned char* u, float* llrs, const float* input);

        // basic algorithm methods
        void butterfly(float* llrs, unsigned char* u, const int stage, const int u_num, const int row);
        void butterfly_volk(float* llrs, unsigned char* u, const int stage, const int u_num, const int row);
        void butterfly_generic(float* llrs, unsigned char* u, const int stage, const int u_num, const int row);
        void even_u_values(unsigned char* u_even, const unsigned char* u, const int u_num);
        void odd_xor_even_values(unsigned char* u_xor, const unsigned char* u, const int u_num);
        void extract_info_bits(unsigned char* output, const unsigned char* input) const;

        // helper functions.
        void print_pretty_llr_vector(const float* llr_vec) const;

      };

    } // namespace code
  } // namespace fec
} // namespace gr

#endif /* INCLUDED_FEC_POLAR_DECODER_COMMON_H */