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/* -*- 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_ */
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