/* -*- c++ -*- */

/*

 * Copyright 2004 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_GR_SIMPLE_CORRELATOR_H

#define INCLUDED_GR_SIMPLE_CORRELATOR_H

#include <gr_block.h>

#include <assert.h>

//#define        DEBUG_SIMPLE_CORRELATOR

class gr_simple_correlator;

typedef boost::shared_ptr<gr_simple_correlator> gr_simple_correlator_sptr;

gr_simple_correlator_sptr gr_make_simple_correlator (int payload_bytesize);

/*!

 * \brief inverse of gr_simple_framer (more or less)

 * \ingroup sync_blk

 */

class gr_simple_correlator : public gr_block

{

  static const int OVERSAMPLE = 8;

  enum state_t { ST_LOOKING, ST_UNDER_THRESHOLD, ST_LOCKED };

  int                   d_payload_bytesize;

  state_t         d_state;

  unsigned int         d_osi;                                // over sample index [0,OVERSAMPLE-1]

  unsigned int         d_transition_osi;                // first index where Hamming dist < thresh

  unsigned int         d_center_osi;                        // center of bit

  unsigned long long int d_shift_reg[OVERSAMPLE];

  int                 d_bblen;                        // length of bitbuf

  unsigned char        *d_bitbuf;                        // demodulated bits

  int                 d_bbi;                                // bitbuf index

  static const int AVG_PERIOD = 512;                // must be power of 2 (for freq offset correction)

  int        d_avbi;

  float        d_avgbuf[AVG_PERIOD];

  float d_avg;

  float d_accum;

#ifdef DEBUG_SIMPLE_CORRELATOR

  FILE                *d_debug_fp;                        // binary log file

#endif

  friend gr_simple_correlator_sptr gr_make_simple_correlator (int payload_bytesize);

  gr_simple_correlator (int payload_bytesize);

  inline int slice (float x)

  {

    return x >= d_avg ? 1 : 0;

  }

  void update_avg(float x);

  void enter_locked ();

  void enter_under_threshold ();

  void enter_looking ();

  static int add_index (int a, int b)

  {

    int t = a + b;

    if (t >= OVERSAMPLE)

      t -= OVERSAMPLE;

    assert (t >= 0 && t < OVERSAMPLE);

    return t;

  }

  static int sub_index (int a, int b)

  {

    int t = a - b;

    if (t < 0)

      t += OVERSAMPLE;

    assert (t >= 0 && t < OVERSAMPLE);

    return t;

  }

 public:

  ~gr_simple_correlator ();

  int general_work (int noutput_items,

                    gr_vector_int &ninput_items,

                    gr_vector_const_void_star &input_items,

                    gr_vector_void_star &output_items);

};

#endif /* INCLUDED_GR_SIMPLE_CORRELATOR_H */