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/* -*- c++ -*- */
/*
* Copyright 2005 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 2, 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., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
#include "fire_crc.h"
#include <math.h>
#include <iostream>
fire_crc::fire_crc (unsigned int crc_size, unsigned int data_size)
: d_crc_size(crc_size),
d_data_size(data_size),
d_syn_start(0),
d_syndrome_reg()
{
// Initialise syndrome
}
fire_crc::~fire_crc()
{
}
int
fire_crc::rem(const int x, const int y)
{
return (x % y);
}
int
fire_crc::check_crc(const unsigned char *input_bits,
unsigned char *control_data)
{
int j,error_count = 0, error_index = 0, success_flag = 0, syn_index = 0;
d_syn_start = 0;
// reset the syndrome register
d_syndrome_reg.clear();
d_syndrome_reg.insert(d_syndrome_reg.begin(),40,0);
// shift in the data bits
for (unsigned int i=0; i < d_data_size; i++) {
error_count = syndrome_shift(input_bits[i]);
control_data[i] = input_bits[i];
}
// shift in the crc bits
for (unsigned int i=0; i < d_crc_size; i++) {
error_count = syndrome_shift(1-input_bits[i+d_data_size]);
}
// Find position of error burst
if (error_count == 0) {
error_index = 0;
}
else {
error_index = 1;
error_count = syndrome_shift(0);
error_index += 1;
while (error_index < (d_data_size + d_crc_size) ) {
error_count = syndrome_shift(0);
error_index += 1;
if ( error_count == 0 ) break;
}
}
// Test for correctable errors
//printf("error_index %d\n",error_index);
if (error_index == 224) success_flag = 0;
else {
// correct index depending on the position of the error
if (error_index == 0) syn_index = error_index;
else syn_index = error_index - 1;
// error burst lies within data bits
if (error_index < 184) {
//printf("error < bit 184,%d\n",error_index);
j = error_index;
while ( j < (error_index+12) ) {
if (j < 184) {
control_data[j] = control_data[j] ^
d_syndrome_reg[rem(d_syn_start+39-j+syn_index,40)];
}
else break;
j = j + 1;
}
}
else if ( error_index > 212 ) {
//printf("error > bit 212,%d\n",error_index);
j = 0;
while ( j < (error_index - 212) ) {
control_data[j] = control_data[j] ^
d_syndrome_reg[rem(d_syn_start+39-j-224+syn_index,40)];
j = j + 1;
}
}
// for 183 < error_index < 213 error in parity alone so ignore
success_flag = 1;
}
return success_flag;
}
int
fire_crc::syndrome_shift(unsigned int bit)
{
int error_count = 0;
if (d_syn_start == 0) d_syn_start = 39;
else d_syn_start -= 1;
std::vector<int> temp_syndrome_reg = d_syndrome_reg;
temp_syndrome_reg[rem(d_syn_start+3,40)] =
d_syndrome_reg[rem(d_syn_start+3,40)] ^
d_syndrome_reg[d_syn_start];
temp_syndrome_reg[rem(d_syn_start+17,40)] =
d_syndrome_reg[rem(d_syn_start+17,40)] ^
d_syndrome_reg[d_syn_start];
temp_syndrome_reg[rem(d_syn_start+23,40)] =
d_syndrome_reg[rem(d_syn_start+23,40)] ^
d_syndrome_reg[d_syn_start];
temp_syndrome_reg[rem(d_syn_start+26,40)] =
d_syndrome_reg[rem(d_syn_start+26,40)] ^
d_syndrome_reg[d_syn_start];
temp_syndrome_reg[rem(d_syn_start+4,40)] =
d_syndrome_reg[rem(d_syn_start+4,40)] ^ bit;
temp_syndrome_reg[rem(d_syn_start+6,40)] =
d_syndrome_reg[rem(d_syn_start+6,40)] ^ bit;
temp_syndrome_reg[rem(d_syn_start+10,40)] =
d_syndrome_reg[rem(d_syn_start+10,40)] ^ bit;
temp_syndrome_reg[rem(d_syn_start+16,40)] =
d_syndrome_reg[rem(d_syn_start+16,40)] ^ bit;
temp_syndrome_reg[rem(d_syn_start+27,40)] =
d_syndrome_reg[rem(d_syn_start+27,40)] ^ bit;
temp_syndrome_reg[rem(d_syn_start+29,40)] =
d_syndrome_reg[rem(d_syn_start+29,40)] ^ bit;
temp_syndrome_reg[rem(d_syn_start+33,40)] =
d_syndrome_reg[rem(d_syn_start+33,40)] ^ bit;
temp_syndrome_reg[rem(d_syn_start+39,40)] =
d_syndrome_reg[rem(d_syn_start+39,40)] ^ bit;
temp_syndrome_reg[d_syn_start] = d_syndrome_reg[d_syn_start] ^ bit;
d_syndrome_reg = temp_syndrome_reg;
for (unsigned int i = 0; i < 28; i++) {
error_count = error_count + d_syndrome_reg[rem(d_syn_start+i,40)];
}
return error_count;
}
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