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/* -*- c++ -*- */
/*
* Copyright 2002 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.
*/
#include <atsci_randomizer.h>
#include <assert.h>
unsigned char atsci_randomizer::s_output_map[1 << 14];
bool atsci_randomizer::s_output_map_initialized_p = false;
atsci_randomizer::atsci_randomizer ()
{
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
atsci_randomizer::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
atsci_randomizer::reset ()
{
d_state = PRELOAD_VALUE;
}
void
atsci_randomizer::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
atsci_randomizer::derandomize (atsc_mpeg_packet &out, const atsc_mpeg_packet_no_sync &in)
{
out.data[0] = MPEG_SYNC_BYTE; // add sync byte to beginning of packet
for (int i = 0; i < ATSC_MPEG_DATA_LENGTH; i++)
out.data[i + 1] = in.data[i] ^ output_and_clk ();
}
unsigned char
atsci_randomizer::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;
}
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