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/* -*- c++ -*- */
/*
* Copyright 2004,2010 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.
*/
//
// This is a (partial) rewrite of the GNU radio code, for use
// within the DAB/DAB+ sdr-j receiver software
// all rights are acknowledged.
//
#include "firecode-checker.h"
#include <cstring>
// g(x)=(x^11+1)(x^5+x^3+x^2+x+1)=1+x+x^2+x^3+x^5+x^11+x^12+x^13+x^14+x^16
const uint8_t firecode_checker::g[16] = {1, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0};
firecode_checker::firecode_checker(void)
{
// prepare the table
uint8_t regs[16];
int16_t i, j;
uint16_t itab[8];
for (i = 0; i < 8; i++) {
memset(regs, 0, 16);
regs[8 + i] = 1;
itab[i] = run8(regs);
}
for (i = 0; i < 256; i++) {
tab[i] = 0;
for (j = 0; j < 8; j++) {
if (i & (1 << j))
tab[i] = tab[i] ^ itab[j];
}
}
}
firecode_checker::~firecode_checker(void)
{
}
uint16_t firecode_checker::run8(uint8_t regs[])
{
int16_t i, j;
uint16_t z;
uint16_t v = 0;
for (i = 0; i < 8; i++) {
z = regs[15];
for (j = 15; j > 0; j--)
regs[j] = regs[j - 1] ^ (z & g[j]);
regs[0] = z;
}
for (i = 15; i >= 0; i--)
v = (v << 1) | regs[i];
return v;
}
bool firecode_checker::check(const uint8_t *x)
{
int16_t i;
uint16_t state = (x[2] << 8) | x[3];
uint16_t istate;
for (i = 4; i < 11; i++) {
istate = tab[state >> 8];
state = ((istate & 0x00ff) ^ x[i]) |
((istate ^ state << 8) & 0xff00);
}
for (i = 0; i < 2; i++) {
istate = tab[state >> 8];
state = ((istate & 0x00ff) ^ x[i]) |
((istate ^ state << 8) & 0xff00);
}
return state == 0;
}
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