| /* |
| The Hacker's Choice - http://www.thc.org |
| Part of THC's GSM SCANNER PROJECT |
| */ |
| |
| |
| #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"); |
| return 0; |
| } |
| |
| 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; |
| } |
| |
| |