diff options
Diffstat (limited to 'gsm-receiver/src/lib/decoder/fire_crc.c')
| -rw-r--r-- | gsm-receiver/src/lib/decoder/fire_crc.c | 179 |
1 files changed, 179 insertions, 0 deletions
diff --git a/gsm-receiver/src/lib/decoder/fire_crc.c b/gsm-receiver/src/lib/decoder/fire_crc.c new file mode 100644 index 0000000..7cdfc0b --- /dev/null +++ b/gsm-receiver/src/lib/decoder/fire_crc.c @@ -0,0 +1,179 @@ +//TODO: this file shouldn't be part of the GSM Receiver +/* -*- 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 <stdio.h> +#include <string.h> + +#define REM(x, y) (x) % (y) + +static int FC_syndrome_shift(FC_CTX *ctx, unsigned int bit); + +static int +outit(int *data, int len) +{ + int i; + + for (i = 0; i < len; i++) + printf("%d ", data[i]); + printf("\n"); +} + +int +FC_init(FC_CTX *ctx, unsigned int crc_size, unsigned int data_size) +{ + ctx->crc_size = crc_size; + ctx->data_size = data_size; + ctx->syn_start = 0; + + return 0; +} + +int +FC_check_crc(FC_CTX *ctx, unsigned char *input_bits, unsigned char *control_data) +{ + int j,error_count = 0, error_index = 0, success_flag = 0, syn_index = 0; + unsigned int i; + + ctx->syn_start = 0; + // reset the syndrome register + memset(ctx->syndrome_reg, 0, sizeof ctx->syndrome_reg); + + // shift in the data bits + for (i=0; i < ctx->data_size; i++) { + error_count = FC_syndrome_shift(ctx, input_bits[i]); + control_data[i] = input_bits[i]; + } + + // shift in the crc bits + for (i=0; i < ctx->crc_size; i++) { + error_count = FC_syndrome_shift(ctx, 1-input_bits[i+ctx->data_size]); + } + + // Find position of error burst + if (error_count == 0) { + error_index = 0; + } + else { + error_index = 1; + error_count = FC_syndrome_shift(ctx, 0); + error_index += 1; + while (error_index < (ctx->data_size + ctx->crc_size) ) { + error_count = FC_syndrome_shift(ctx, 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] ^ + ctx->syndrome_reg[REM(ctx->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] ^ + ctx->syndrome_reg[REM(ctx->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; +} + +static int +FC_syndrome_shift(FC_CTX *ctx, unsigned int bit) +{ + int error_count = 0; + unsigned int i; + + if (ctx->syn_start == 0) + ctx->syn_start = 39; + else ctx->syn_start -= 1; + + int temp_syndrome_reg[sizeof ctx->syndrome_reg]; + + memcpy(temp_syndrome_reg, ctx->syndrome_reg, sizeof temp_syndrome_reg); + + temp_syndrome_reg[REM(ctx->syn_start+3,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+3,40)] ^ + ctx->syndrome_reg[ctx->syn_start]; + temp_syndrome_reg[REM(ctx->syn_start+17,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+17,40)] ^ + ctx->syndrome_reg[ctx->syn_start]; + temp_syndrome_reg[REM(ctx->syn_start+23,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+23,40)] ^ + ctx->syndrome_reg[ctx->syn_start]; + temp_syndrome_reg[REM(ctx->syn_start+26,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+26,40)] ^ + ctx->syndrome_reg[ctx->syn_start]; + + temp_syndrome_reg[REM(ctx->syn_start+4,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+4,40)] ^ bit; + temp_syndrome_reg[REM(ctx->syn_start+6,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+6,40)] ^ bit; + temp_syndrome_reg[REM(ctx->syn_start+10,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+10,40)] ^ bit; + temp_syndrome_reg[REM(ctx->syn_start+16,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+16,40)] ^ bit; + temp_syndrome_reg[REM(ctx->syn_start+27,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+27,40)] ^ bit; + temp_syndrome_reg[REM(ctx->syn_start+29,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+29,40)] ^ bit; + temp_syndrome_reg[REM(ctx->syn_start+33,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+33,40)] ^ bit; + temp_syndrome_reg[REM(ctx->syn_start+39,40)] = + ctx->syndrome_reg[REM(ctx->syn_start+39,40)] ^ bit; + + temp_syndrome_reg[ctx->syn_start] = ctx->syndrome_reg[ctx->syn_start] ^ bit; + + memcpy(ctx->syndrome_reg, temp_syndrome_reg, sizeof ctx->syndrome_reg); + + for (i = 0; i < 28; i++) { + error_count = error_count + ctx->syndrome_reg[REM(ctx->syn_start+i,40)]; + } + return error_count; +} + + |