piotr | faacc72 | 2014-07-20 23:48:32 +0200 | [diff] [blame] | 1 | /* -*- c++ -*- */ |
| 2 | /* |
| 3 | * Copyright 2005 Free Software Foundation, Inc. |
| 4 | * |
| 5 | * This file is part of GNU Radio |
| 6 | * |
| 7 | * GNU Radio is free software; you can redistribute it and/or modify |
| 8 | * it under the terms of the GNU General Public License as published by |
| 9 | * the Free Software Foundation; either version 2, or (at your option) |
| 10 | * any later version. |
| 11 | * |
| 12 | * GNU Radio is distributed in the hope that it will be useful, |
| 13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 15 | * GNU General Public License for more details. |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License |
| 18 | * along with GNU Radio; see the file COPYING. If not, write to |
| 19 | * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, |
| 20 | * Boston, MA 02111-1307, USA. |
| 21 | */ |
| 22 | |
| 23 | #include "fire_crc.h" |
| 24 | #include <stdio.h> |
| 25 | #include <string.h> |
| 26 | |
| 27 | #define REM(x, y) (x) % (y) |
| 28 | |
| 29 | static int FC_syndrome_shift(FC_CTX *ctx, unsigned int bit); |
| 30 | |
| 31 | static int |
| 32 | outit(int *data, int len) |
| 33 | { |
| 34 | int i; |
| 35 | |
| 36 | for (i = 0; i < len; i++) |
| 37 | printf("%d ", data[i]); |
| 38 | printf("\n"); |
| 39 | } |
| 40 | |
| 41 | int |
| 42 | FC_init(FC_CTX *ctx, unsigned int crc_size, unsigned int data_size) |
| 43 | { |
| 44 | ctx->crc_size = crc_size; |
| 45 | ctx->data_size = data_size; |
| 46 | ctx->syn_start = 0; |
| 47 | |
| 48 | return 0; |
| 49 | } |
| 50 | |
| 51 | int |
| 52 | FC_check_crc(FC_CTX *ctx, unsigned char *input_bits, unsigned char *control_data) |
| 53 | { |
| 54 | int j,error_count = 0, error_index = 0, success_flag = 0, syn_index = 0; |
| 55 | unsigned int i; |
| 56 | |
| 57 | ctx->syn_start = 0; |
| 58 | // reset the syndrome register |
| 59 | memset(ctx->syndrome_reg, 0, sizeof ctx->syndrome_reg); |
| 60 | |
| 61 | // shift in the data bits |
| 62 | for (i=0; i < ctx->data_size; i++) { |
| 63 | error_count = FC_syndrome_shift(ctx, input_bits[i]); |
| 64 | control_data[i] = input_bits[i]; |
| 65 | } |
| 66 | |
| 67 | // shift in the crc bits |
| 68 | for (i=0; i < ctx->crc_size; i++) { |
| 69 | error_count = FC_syndrome_shift(ctx, 1-input_bits[i+ctx->data_size]); |
| 70 | } |
| 71 | |
| 72 | // Find position of error burst |
| 73 | if (error_count == 0) { |
| 74 | error_index = 0; |
| 75 | } |
| 76 | else { |
| 77 | error_index = 1; |
| 78 | error_count = FC_syndrome_shift(ctx, 0); |
| 79 | error_index += 1; |
| 80 | while (error_index < (ctx->data_size + ctx->crc_size) ) { |
| 81 | error_count = FC_syndrome_shift(ctx, 0); |
| 82 | error_index += 1; |
| 83 | if ( error_count == 0 ) break; |
| 84 | } |
| 85 | } |
| 86 | |
| 87 | // Test for correctable errors |
| 88 | //printf("error_index %d\n",error_index); |
| 89 | if (error_index == 224) success_flag = 0; |
| 90 | else { |
| 91 | |
| 92 | // correct index depending on the position of the error |
| 93 | if (error_index == 0) syn_index = error_index; |
| 94 | else syn_index = error_index - 1; |
| 95 | |
| 96 | // error burst lies within data bits |
| 97 | if (error_index < 184) { |
| 98 | //printf("error < bit 184,%d\n",error_index); |
| 99 | j = error_index; |
| 100 | while ( j < (error_index+12) ) { |
| 101 | if (j < 184) { |
| 102 | control_data[j] = control_data[j] ^ |
| 103 | ctx->syndrome_reg[REM(ctx->syn_start+39-j+syn_index,40)]; |
| 104 | } |
| 105 | else break; |
| 106 | j = j + 1; |
| 107 | } |
| 108 | } |
| 109 | else if ( error_index > 212 ) { |
| 110 | //printf("error > bit 212,%d\n",error_index); |
| 111 | j = 0; |
| 112 | while ( j < (error_index - 212) ) { |
| 113 | control_data[j] = control_data[j] ^ |
| 114 | ctx->syndrome_reg[REM(ctx->syn_start+39-j-224+syn_index,40)]; |
| 115 | j = j + 1; |
| 116 | } |
| 117 | } |
| 118 | // for 183 < error_index < 213 error in parity alone so ignore |
| 119 | success_flag = 1; |
| 120 | } |
| 121 | return success_flag; |
| 122 | } |
| 123 | |
| 124 | static int |
| 125 | FC_syndrome_shift(FC_CTX *ctx, unsigned int bit) |
| 126 | { |
| 127 | int error_count = 0; |
| 128 | unsigned int i; |
| 129 | |
| 130 | if (ctx->syn_start == 0) |
| 131 | ctx->syn_start = 39; |
| 132 | else ctx->syn_start -= 1; |
| 133 | |
| 134 | int temp_syndrome_reg[sizeof ctx->syndrome_reg]; |
| 135 | |
| 136 | memcpy(temp_syndrome_reg, ctx->syndrome_reg, sizeof temp_syndrome_reg); |
| 137 | |
| 138 | temp_syndrome_reg[REM(ctx->syn_start+3,40)] = |
| 139 | ctx->syndrome_reg[REM(ctx->syn_start+3,40)] ^ |
| 140 | ctx->syndrome_reg[ctx->syn_start]; |
| 141 | temp_syndrome_reg[REM(ctx->syn_start+17,40)] = |
| 142 | ctx->syndrome_reg[REM(ctx->syn_start+17,40)] ^ |
| 143 | ctx->syndrome_reg[ctx->syn_start]; |
| 144 | temp_syndrome_reg[REM(ctx->syn_start+23,40)] = |
| 145 | ctx->syndrome_reg[REM(ctx->syn_start+23,40)] ^ |
| 146 | ctx->syndrome_reg[ctx->syn_start]; |
| 147 | temp_syndrome_reg[REM(ctx->syn_start+26,40)] = |
| 148 | ctx->syndrome_reg[REM(ctx->syn_start+26,40)] ^ |
| 149 | ctx->syndrome_reg[ctx->syn_start]; |
| 150 | |
| 151 | temp_syndrome_reg[REM(ctx->syn_start+4,40)] = |
| 152 | ctx->syndrome_reg[REM(ctx->syn_start+4,40)] ^ bit; |
| 153 | temp_syndrome_reg[REM(ctx->syn_start+6,40)] = |
| 154 | ctx->syndrome_reg[REM(ctx->syn_start+6,40)] ^ bit; |
| 155 | temp_syndrome_reg[REM(ctx->syn_start+10,40)] = |
| 156 | ctx->syndrome_reg[REM(ctx->syn_start+10,40)] ^ bit; |
| 157 | temp_syndrome_reg[REM(ctx->syn_start+16,40)] = |
| 158 | ctx->syndrome_reg[REM(ctx->syn_start+16,40)] ^ bit; |
| 159 | temp_syndrome_reg[REM(ctx->syn_start+27,40)] = |
| 160 | ctx->syndrome_reg[REM(ctx->syn_start+27,40)] ^ bit; |
| 161 | temp_syndrome_reg[REM(ctx->syn_start+29,40)] = |
| 162 | ctx->syndrome_reg[REM(ctx->syn_start+29,40)] ^ bit; |
| 163 | temp_syndrome_reg[REM(ctx->syn_start+33,40)] = |
| 164 | ctx->syndrome_reg[REM(ctx->syn_start+33,40)] ^ bit; |
| 165 | temp_syndrome_reg[REM(ctx->syn_start+39,40)] = |
| 166 | ctx->syndrome_reg[REM(ctx->syn_start+39,40)] ^ bit; |
| 167 | |
| 168 | temp_syndrome_reg[ctx->syn_start] = ctx->syndrome_reg[ctx->syn_start] ^ bit; |
| 169 | |
| 170 | memcpy(ctx->syndrome_reg, temp_syndrome_reg, sizeof ctx->syndrome_reg); |
| 171 | |
| 172 | for (i = 0; i < 28; i++) { |
| 173 | error_count = error_count + ctx->syndrome_reg[REM(ctx->syn_start+i,40)]; |
| 174 | } |
| 175 | return error_count; |
| 176 | } |
| 177 | |
| 178 | |