int gpmi_verify_hamming_13_8(void *data, u8 *parity, size_t size)
{
int i;
u8 *pdata = data;
int bit_to_flip;
u8 np, syndrome;
int errors = 0;
for (i = 0; i < size; i ++, pdata++) {
np = calculate_parity(*pdata);
syndrome = np ^ parity[i];
if (syndrome == 0) /* cool */ {
continue;
}
if (even_number_of_1s(syndrome))
return -i; /* can't recover */
bit_to_flip = lookup_single_error(syndrome);
if (bit_to_flip < 0)
return -i; /* can't fix the error */
if (bit_to_flip < 8) {
*pdata ^= (1 << bit_to_flip);
errors++;
}
}
return errors;
}
void gpmi_encode_hamming_13_8(void *source_block, size_t src_size,
void *source_ecc, size_t ecc_size)
{
int i;
u8 *src = source_block;
u8 *ecc = source_ecc;
for (i = 0; i < src_size && i < ecc_size; i++)
ecc[i] = calculate_parity(src[i]);
}
int *bad_parity(char* string) {
int i=0, j=0, len=strlen(string);
int *bad_parity = (int *)malloc(sizeof(int));
char *check = (char*)malloc(len*sizeof(char));
bad_parity[0] = bad_parity[1] = -1;
strncpy(check, string, len);
calculate_parity(check);
//printf("[•] parity_ck '%s' (len:%d)\n",check,(int)strlen(check));
// compare all parity bits
for(i=0; i<len; i++) {
if (power_of_2(i+1) && string[i] != check[i]) {
int *tmp = (int *)realloc(bad_parity, j+1*sizeof(int));
if (tmp) {bad_parity = tmp;}
bad_parity[j] = i;
bad_parity[j+1] = -1;
j++;
}
}
free(check);
return bad_parity;
}
int main (int argc, char *argv[], char *arge[]) {
if (argc < 2) {
print_usage();
return 0;
}
// check if argv[1] is a binary string
if (!check_binary(argv[1])) {
fprintf(stderr, "%s is not a binary string\n", argv[1]);
return -1;
}
// init rand()
srand(time(NULL));
// copy the argv[1] message
// calculate final message length
// so we don't need to realloc it everytime
int len = strlen(argv[1]);
int parity_len = 2;
for (int i = 0; i<=len; i++) {
//printf("t:%d - %s\n",t,power_of_2(t+1) ? "YES" : "NO");
parity_len++;
if (power_of_2(parity_len)) {
parity_len++;
}
}
printf("F2^%d -> F2^%d\n",len, parity_len-1);
char *message = (char*)malloc(parity_len*sizeof(char));
strncpy(message, argv[1], len+1);
// print the raw binary message
printf("[•] encoding '%s' (len:%d)\n",message,len);
// then add spaces for parity bits
// and calculate them
add_parity_space(message);
calculate_parity(message);
printf("[•] sent '%s' (len:%d)\n",message,(int)strlen(message));
// copy the message and alter one bit
char *bad = (char*)malloc(strlen(message)*sizeof(char));
strncpy(bad, message, strlen(message));
alter_a_bit(bad);
// print altered message
printf("[•] recieve '%s' (len:%d)\n",bad,(int)strlen(bad));
// check parity to correct the altered message
int *bad_bits = bad_parity(bad);
int i = 0, sum=0;
printf("[?] corrupted parity bits :");
while (bad_bits[i] != -1) {
sum+=bad_bits[i]+1;
printf(" %d",bad_bits[i]+1);
i++;
}
printf("\n");
printf("[?] fixed data bit at index %d\n",sum);
free(bad_bits);
// correct if necessary
if (sum>0) {
bad[sum-1] = (bad[sum-1] == '0') ? '1' : '0';
printf("[•] corrected '%s' (len:%d)\n",bad,(int)strlen(bad));
}else {
printf("[•] already_ok '%s' (len:%d)\n",bad,(int)strlen(bad));
}
// remove the parity bits
remove_parity_space(bad);
printf("[•] decoding '%s' (len:%d)\n",bad,(int)strlen(bad));
// compare with original message
printf("[•] %s\n",strncmp(argv[1],bad,len) == 0 ? "message successfully decoded" : "failed to decode message");
//printf(" in: '%s'\n",argv[1]);
//printf("out: '%s'\n",bad);
// free memory space
free(message);
free(bad);
return 0;
}
