generic_decoder.h

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/* -*- c++ -*- */
/*
 * Copyright 2013-2014 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_GENERIC_DECODER_H
#define INCLUDED_FEC_GENERIC_DECODER_H

#include <gnuradio/fec/api.h>
#include <gnuradio/logger.h>
#include <boost/format.hpp>
#include <boost/shared_ptr.hpp>

namespace gr {
namespace fec {

/*!
 * \brief Parent class for FECAPI objects.
 *
 * \ingroup error_coding_blk
 *
 * \details
 *
 * Parent of a decoder variable class for FECAPI that will fit
 * into the gr::fec::decoder block to handle FEC decoding. This
 * class provides the basic information required to fit into the
 * FECAPI structure. It provides information about input and
 * output data types, potential data conversions, and a few other
 * parameters useful to establish the decoder's behavior.
 *
 * We create objects from FECAPI-derived classes to go into the
 * actual GNU Radio decoder block. Each object contains its own
 * state and so there should be a one-to-one mapping of an FECAPI
 * object and a GR decoder block. Sharing these objects is not
 * guaranteed to be thread-safe.
 *
 * This is a pure virtual class and must be derived from by a
 * child class.
 *
 * \sa gr::fec::code::cc_decoder
 * \sa gr::fec::code::ccsds_decoder
 */
class FEC_API generic_decoder
{
protected:
    gr::logger_ptr d_logger;

public:
    friend class decoder;
    virtual void generic_work(void* inbuffer, void* outbuffer) = 0;
    static int base_unique_id;
    int my_id;
    int unique_id();
    std::string d_name;
    std::string alias() { return (boost::format("%s%d") % d_name % unique_id()).str(); }

public:
    typedef boost::shared_ptr<generic_decoder> sptr;

    generic_decoder(void){};
    generic_decoder(std::string name);
    virtual ~generic_decoder();

    /*!
     * Returns the rate of the code. For every r input bits, there
     * is 1 output bit, so the rate is 1/r. Used for setting things
     * like the encoder block's relative rate.
     *
     * This function MUST be reimplemented by the child class.
     */
    virtual double rate() = 0;

    /*!
     * Returns the input size in items that the decoder object uses
     * to decode a full frame. Often, this number is the number of
     * bits per frame if the input format is unpacked. If the block
     * expects packed bytes, then this value should be the number of
     * bytes (number of bits / 8) per input frame.
     *
     * The child class MUST implement this function.
     */
    virtual int get_input_size() = 0;

    /*!
     * Returns the output size in items that the decoder object
     * produces after decoding a full frame. Often, this number is
     * the number of bits in the outputted frame if the input format
     * is unpacked. If the block produces packed bytes, then this
     * value should be the number of bytes (number of bits / 8) per
     * frame produced. This value is generally something like
     * get_input_size()/R for a 1/R rate code.
     *
     * The child class MUST implement this function.
     */
    virtual int get_output_size() = 0;

    /*!
     * Sets up history for the decoder when the decoder is required
     * to look ahead in the data stream in order to finish
     * its processing.
     *
     * The child class MAY implement this function. If not
     * reimplemented, it returns 0.
     */
    virtual int get_history();

    /*!
     * Some decoders require the input items to float around a
     * particular soft value. We can set that floating value by
     * setting this value to return some non-zero number.
     *
     * The fec.extended_decoder block will use this to create an
     * add_const_ff block before the decoder block to adjust all
     * input samples appropriately.
     *
     * The child class MAY implement this function. If not
     * reimplemented, it returns 0.
     */
    virtual float get_shift();

    /*!
     * Sets the size of an input item, as in the size of a char or
     * float item.
     *
     * The child class SHOULD implement this function. If not
     * reimplemented, it returns sizeof(float) as the decoders
     * typically expect floating point input types.
     */
    virtual int get_input_item_size();

    /*!
     * Sets the size of an output item, as in the size of a char or
     * float item.
     *
     * The child class SHOULD implement this function. If not
     * reimplemented, it returns sizeof(char) as the decoders
     * typically expect to produce bits or bytes.
     */
    virtual int get_output_item_size();

    /*!
     * Set up a conversion type required to setup the data properly
     * for this decoder. The decoder itself will not implement the
     * conversion and expects an external wrapper (e.g.,
     * fec.extended_decoder) to read this value and "do the right
     * thing" to format the data.
     *
     * The default behavior is 'none', which means no conversion is
     * required. Whatever the get_input_item_size() value returns,
     * the input is expected to conform directly to this.
     *
     * This may also return 'uchar', which indicates that the
     * wrapper should convert the standard float samples to unsigned
     * characters, either hard sliced or 8-bit soft symbols. See
     * gr::fec::code::cc_decoder as an example decoder that uses
     * this conversion format.
     *
     * If 'packed_bits', the block expects the inputs to be packed
     * hard bits. Each input item is a unsigned char where each of
     * the 8-bits is a hard bit value.
     *
     * The child class SHOULD implement this function. If not
     * reimplemented, it returns "none".
     */
    virtual const char* get_input_conversion();

    /*!
     * Set up a conversion type required to understand the output
     * style of this decoder. Generally, follow-on processing
     * expects unpacked bits, so we specify the conversion type here
     * to indicate what the wrapper (e.g., fec.extended_decoder)
     * should do to convert the output samples from the decoder into
     * unpacked bits.
     *
     * The default behavior is 'none', which means no conversion is
     * required. This should mean that the output data is produced
     * from this decoder as unpacked bit.
     *
     * If 'unpack', the block produces packed bytes that should be
     * unpacked by the wrapper. See gr::fec::code::ccsds_decoder as
     * an example of a decoder that produces packed bytes.
     *
     * The child class SHOULD implement this function. If not
     * reimplemented, it returns "none".
     */
    virtual const char* get_output_conversion();

    /*!
     * Updates the size of a decoded frame.
     *
     * The child class MUST implement this function and interpret
     * how the \p frame_size information affects the block's
     * behavior. It should also provide bounds checks.
     */
    virtual bool set_frame_size(unsigned int frame_size) = 0;


    /*!
     * Get repetitions to decode.
     *
     * The child class should implement this function and return the
     * number of iterations required to decode.
     */
    virtual float get_iterations() { return -1; }
};

/*! see generic_decoder::get_output_size() */
FEC_API int get_decoder_output_size(generic_decoder::sptr my_decoder);

/*! see generic_decoder::get_input_size() */
FEC_API int get_decoder_input_size(generic_decoder::sptr my_decoder);

/*! see generic_decoder::get_shift() */
FEC_API float get_shift(generic_decoder::sptr my_decoder);

/*! see generic_decoder::get_history() */
FEC_API int get_history(generic_decoder::sptr my_decoder);

/*! see generic_decoder::get_input_item_size() */
FEC_API int get_decoder_input_item_size(generic_decoder::sptr my_decoder);

/*! see generic_decoder::get_output_item_size() */
FEC_API int get_decoder_output_item_size(generic_decoder::sptr my_decoder);

/*! see generic_decoder::get_input_conversion() */
FEC_API const char* get_decoder_input_conversion(generic_decoder::sptr my_decoder);

/*! see generic_decoder::get_output_conversion() */
FEC_API const char* get_decoder_output_conversion(generic_decoder::sptr my_decoder);

} /* namespace fec */
} /* namespace gr */

#endif /* INCLUDED_FEC_GENRIC_DECODER_H */