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/* -*- c++ -*- */
/*
* Copyright 2014 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* SPDX-License-Identifier: GPL-3.0-or-later
*
*/
#ifndef INCLUDED_ATSC_RANDOMIZE_H
#define INCLUDED_ATSC_RANDOMIZE_H
#include "atsc_types.h"
#include <stdint.h>
namespace gr {
namespace dtv {
class atsc_randomize
{
public:
atsc_randomize();
/*! \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(uint8_t* out, const uint8_t* 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 constexpr unsigned int PRELOAD_VALUE = 0x018f; /* 0xf180 bit reversed */
static constexpr unsigned int MASK = 0xa638;
static unsigned char s_output_map[1 << 14];
static bool s_output_map_initialized_p;
};
} /* namespace dtv */
} /* namespace gr */
#endif /* INCLUDED_ATSC_RANDOMIZE_H */
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