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/*
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;
}
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