180 lines
5.9 KiB
C
180 lines
5.9 KiB
C
//TODO: this file shouldn't be part of the GSM Receiver
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/* -*- c++ -*- */
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/*
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* Copyright 2005 Free Software Foundation, Inc.
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*
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* This file is part of GNU Radio
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*
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* GNU Radio is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* GNU Radio is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GNU Radio; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 02111-1307, USA.
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*/
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#include "fire_crc.h"
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#include <stdio.h>
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#include <string.h>
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#define REM(x, y) (x) % (y)
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static int FC_syndrome_shift(FC_CTX *ctx, unsigned int bit);
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static int
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outit(int *data, int len)
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{
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int i;
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for (i = 0; i < len; i++)
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printf("%d ", data[i]);
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printf("\n");
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}
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int
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FC_init(FC_CTX *ctx, unsigned int crc_size, unsigned int data_size)
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{
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ctx->crc_size = crc_size;
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ctx->data_size = data_size;
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ctx->syn_start = 0;
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return 0;
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}
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int
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FC_check_crc(FC_CTX *ctx, unsigned char *input_bits, unsigned char *control_data)
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{
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int j,error_count = 0, error_index = 0, success_flag = 0, syn_index = 0;
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unsigned int i;
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ctx->syn_start = 0;
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// reset the syndrome register
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memset(ctx->syndrome_reg, 0, sizeof ctx->syndrome_reg);
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// shift in the data bits
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for (i=0; i < ctx->data_size; i++) {
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error_count = FC_syndrome_shift(ctx, input_bits[i]);
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control_data[i] = input_bits[i];
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}
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// shift in the crc bits
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for (i=0; i < ctx->crc_size; i++) {
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error_count = FC_syndrome_shift(ctx, 1-input_bits[i+ctx->data_size]);
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}
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// Find position of error burst
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if (error_count == 0) {
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error_index = 0;
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}
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else {
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error_index = 1;
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error_count = FC_syndrome_shift(ctx, 0);
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error_index += 1;
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while (error_index < (ctx->data_size + ctx->crc_size) ) {
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error_count = FC_syndrome_shift(ctx, 0);
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error_index += 1;
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if ( error_count == 0 ) break;
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}
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}
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// Test for correctable errors
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//printf("error_index %d\n",error_index);
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if (error_index == 224) success_flag = 0;
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else {
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// correct index depending on the position of the error
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if (error_index == 0) syn_index = error_index;
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else syn_index = error_index - 1;
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// error burst lies within data bits
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if (error_index < 184) {
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//printf("error < bit 184,%d\n",error_index);
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j = error_index;
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while ( j < (error_index+12) ) {
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if (j < 184) {
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control_data[j] = control_data[j] ^
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ctx->syndrome_reg[REM(ctx->syn_start+39-j+syn_index,40)];
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}
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else break;
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j = j + 1;
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}
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}
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else if ( error_index > 212 ) {
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//printf("error > bit 212,%d\n",error_index);
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j = 0;
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while ( j < (error_index - 212) ) {
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control_data[j] = control_data[j] ^
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ctx->syndrome_reg[REM(ctx->syn_start+39-j-224+syn_index,40)];
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j = j + 1;
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}
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}
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// for 183 < error_index < 213 error in parity alone so ignore
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success_flag = 1;
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}
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return success_flag;
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}
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static int
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FC_syndrome_shift(FC_CTX *ctx, unsigned int bit)
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{
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int error_count = 0;
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unsigned int i;
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if (ctx->syn_start == 0)
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ctx->syn_start = 39;
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else ctx->syn_start -= 1;
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int temp_syndrome_reg[sizeof ctx->syndrome_reg];
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memcpy(temp_syndrome_reg, ctx->syndrome_reg, sizeof temp_syndrome_reg);
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temp_syndrome_reg[REM(ctx->syn_start+3,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+3,40)] ^
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ctx->syndrome_reg[ctx->syn_start];
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temp_syndrome_reg[REM(ctx->syn_start+17,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+17,40)] ^
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ctx->syndrome_reg[ctx->syn_start];
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temp_syndrome_reg[REM(ctx->syn_start+23,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+23,40)] ^
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ctx->syndrome_reg[ctx->syn_start];
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temp_syndrome_reg[REM(ctx->syn_start+26,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+26,40)] ^
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ctx->syndrome_reg[ctx->syn_start];
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temp_syndrome_reg[REM(ctx->syn_start+4,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+4,40)] ^ bit;
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temp_syndrome_reg[REM(ctx->syn_start+6,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+6,40)] ^ bit;
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temp_syndrome_reg[REM(ctx->syn_start+10,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+10,40)] ^ bit;
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temp_syndrome_reg[REM(ctx->syn_start+16,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+16,40)] ^ bit;
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temp_syndrome_reg[REM(ctx->syn_start+27,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+27,40)] ^ bit;
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temp_syndrome_reg[REM(ctx->syn_start+29,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+29,40)] ^ bit;
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temp_syndrome_reg[REM(ctx->syn_start+33,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+33,40)] ^ bit;
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temp_syndrome_reg[REM(ctx->syn_start+39,40)] =
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ctx->syndrome_reg[REM(ctx->syn_start+39,40)] ^ bit;
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temp_syndrome_reg[ctx->syn_start] = ctx->syndrome_reg[ctx->syn_start] ^ bit;
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memcpy(ctx->syndrome_reg, temp_syndrome_reg, sizeof ctx->syndrome_reg);
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for (i = 0; i < 28; i++) {
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error_count = error_count + ctx->syndrome_reg[REM(ctx->syn_start+i,40)];
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}
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return error_count;
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}
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