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

/*

 * Copyright 2001 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 _ATSC_RANDOMIZER_H_

#define _ATSC_RANDOMIZER_H_

#include <atsc_types.h>

/*! 

 * \brief ATSC data "whitener"

 *

 * The data randomizer described in ATSC standard A/53B.  

 * See figure D4 on page 54.

 */

class atsci_randomizer {

  friend class qa_atsci_randomizer;

 public:

  atsci_randomizer();

  /*! \brief reset randomizer LFSR

   *

   * must be called during the Data Segment Sync interval prior to the

   * first data segment.  I.e., the LFSR is reset prior to the first

   * field of each VSB data frame.

   */

  void reset ();

  //! randomize (whiten) mpeg packet and remove leading MPEG-2 sync byte

  void randomize (atsc_mpeg_packet_no_sync &out, const atsc_mpeg_packet &in);

  //! derandomize (de-whiten) mpeg packet and add leading MPEG-2 sync byte

  void derandomize (atsc_mpeg_packet &out, const atsc_mpeg_packet_no_sync &in);

  unsigned int state() const { return d_state; }

 private:

  static void initialize_output_map ();

  static unsigned char slow_output_map (int st);

  static unsigned char fast_output_map (int st){

    return s_output_map[(st & 0xb23c) >> 2]; // Magic const with 8 bits set improves cache 

                                             // utilization.  The bits correspond to the taps

                                             // used in output calculation.  Others may be 

                                             // safely ignored.

  }

  //! return current output value

  unsigned char output (){

    return fast_output_map (d_state);

  }

  //! clock LFSR; advance to next state.

  void clk (){

    if (d_state & 0x1)

      d_state = ((d_state ^ MASK) >> 1) | 0x8000;

    else

      d_state = d_state >> 1;

  }

  //! return current output value and advance to next state

  unsigned char output_and_clk (){

    unsigned char r = output ();

    clk ();

    return r;

  }

  unsigned int                    d_state;

  static const unsigned int PRELOAD_VALUE = 0x018f; /* 0xf180 bit reversed */

  static const unsigned int MASK = 0xa638;

  static unsigned char             s_output_map[1 << 14];

  static bool                     s_output_map_initialized_p;

};

#endif /* _ATSC_RANDOMIZER_H_ */