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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
*
*/
#include "atsc_randomize.h"
namespace gr {
namespace dtv {
unsigned char atsc_randomize::s_output_map[1 << 14];
bool atsc_randomize::s_output_map_initialized_p = false;
atsc_randomize::atsc_randomize()
{
d_state = PRELOAD_VALUE;
if (!s_output_map_initialized_p)
initialize_output_map();
}
/*!
* \brief Generate the table used in the fast_output_map function.
*
* The table has 16K byte entries, but because of how is is used, only
* 256 entries end up being resident in the cache. This seems
* like a good use of memory. We can get away with a 16K table
* because the low two bits of the state do not affect the output
* function. By shifting right those two bits we shrink the table,
* and also get better cache line utilization.
*/
void atsc_randomize::initialize_output_map()
{
s_output_map_initialized_p = true;
for (int i = 0; i < (1 << 14); i++)
s_output_map[i] = slow_output_map(i << 2);
}
void atsc_randomize::reset() { d_state = PRELOAD_VALUE; }
void atsc_randomize::randomize(atsc_mpeg_packet_no_sync& out, const atsc_mpeg_packet& in)
{
assert(in.data[0] == MPEG_SYNC_BYTE); // confirm it's there, then drop
for (int i = 0; i < ATSC_MPEG_DATA_LENGTH; i++)
out.data[i] = in.data[i + 1] ^ output_and_clk();
}
void atsc_randomize::derandomize(uint8_t* out, const uint8_t* in)
{
out[0] = MPEG_SYNC_BYTE; // add sync byte to beginning of packet
for (int i = 0; i < ATSC_MPEG_DATA_LENGTH; i++)
out[i + 1] = in[i] ^ output_and_clk();
}
unsigned char atsc_randomize::slow_output_map(int st)
{
int output = 0;
if (st & 0x8000)
output |= 0x01;
if (st & 0x2000)
output |= 0x02;
if (st & 0x1000)
output |= 0x04;
if (st & 0x0200)
output |= 0x08;
if (st & 0x0020)
output |= 0x10;
if (st & 0x0010)
output |= 0x20;
if (st & 0x0008)
output |= 0x40;
if (st & 0x0004)
output |= 0x80;
return output;
}
} /* namespace dtv */
} /* namespace gr */
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