void evaluate_error(unsigned int *error_magnitudes,
unsigned int *error_locator_poly_derivative,
unsigned int *error_evaluator_poly,
unsigned int *locators,
int length_of_locators){
int i = 0, j = 0, k = 0;
unsigned int poly_evaluation = 0;
unsigned int power = 1;
unsigned int inverse_locator = 0 ;
int temp = 0;// temp is the power of locator[i], also the error location,
//ranges from 1 to N
for(i = 0; i < length_of_locators; i++){
inverse_locator = galois_inverse(locators[i], w);
//nominator computing
poly_evaluation = 0;
for(j = N - 1; j >= K - 1; j--){//?
power = 1;
for(k = 0; k < N - 1 - j; k++)
power = galois_single_multiply(power, inverse_locator, w);
poly_evaluation ^= galois_single_multiply(power, error_evaluator_poly[j], w);
// printf("test %d \n", poly_evaluation);
}
error_magnitudes[i] = galois_single_multiply(poly_evaluation, locators[i], w);
//denominator computing
poly_evaluation = 0;
for(j = (N - K)/2; j >= 0; j--){
power = 1;
for(k = 0; k < (N - K)/2 - j; k++)
power = galois_single_multiply(power, inverse_locator, w);
poly_evaluation ^= galois_single_multiply(power, error_locator_poly_derivative[j], w);
}
// error magnitudes computing
error_magnitudes[i] = galois_single_divide(error_magnitudes[i], poly_evaluation, w);
//if decode GRS, then we will have to divide error_magnitudes by parity
//check matrix's corresponding column multipliers, otherwise we have to
//comment this function or set multipliers vector to all ones.
temp = galois_log(locators[i], w);
error_magnitudes[i] = galois_single_divide(error_magnitudes[i],
multiplier[temp], w);
}
printf("The error magnitudes are:\n");
for(i = 0; i < length_of_locators; i ++){
printf("%d ", error_magnitudes[i]);
}
printf("\n");
}
main(int argc, char **argv)
{
unsigned int x, w;
if (argc != 3) {
fprintf(stderr, "usage: gf_log x w - returns the discrete log if x in GF(2^w)\n");
exit(1);
}
sscanf(argv[1], "%u", &x);
w = atoi(argv[2]);
if (w < 1 || w > 32) { fprintf(stderr, "Bad w\n"); exit(1); }
if (x == 0 || (w < 32 && x >= (1 << w))) { fprintf(stderr, "x must be in [1,%d]\n", (1 << w)-1); exit(1); }
printf("%u\n", galois_log(x, w));
exit(0);
}
void rsdecode(unsigned int *locators, unsigned int *received_codeword){
unsigned int syndrome[N - K] = {0};
unsigned int error_locator_poly[(N - K)/2 + 1] = {0};
unsigned int error_locator_poly_derivative[(N - K)/2 + 1] = {0};
unsigned int error_evaluator_poly[N] = {0};
unsigned int error_magnitudes[ERROR_NUM] = {0};
int i = 0;
int error_location = 0;
compute_syndrome(syndrome, received_codeword);
get_error_locate_poly(locators, ERROR_NUM, error_locator_poly);
get_evaluator_poly(syndrome, error_locator_poly, error_evaluator_poly);
get_formal_derivation(error_locator_poly, error_locator_poly_derivative, (N - K)/2 + 1);
evaluate_error(error_magnitudes, error_locator_poly_derivative, error_evaluator_poly, locators,ERROR_NUM);
//add the error magnitudes to received codeword
for(i = 0; i < ERROR_NUM; i++){
error_location = galois_log(locators[i], w);
received_codeword[error_location] ^= error_magnitudes[i];
}
}
/*
* Class: eu_vandertil_jerasure_jni_Galois
* Method: galois_log
* Signature: (II)I
*/
JNIEXPORT jint JNICALL Java_eu_vandertil_jerasure_jni_Galois_galois_1log
(JNIEnv *env, jclass clazz, jint value, jint w)
{
return galois_log(value, w);
}
