int
correct_errors_erasures (unsigned char codeword[],
int csize,
int nerasures,
int erasures[])
{
int r, i, j, err;
/* If you want to take advantage of erasure correction, be sure to
set NErasures and ErasureLocs[] with the locations of erasures.
*/
NErasures = nerasures;
for (i = 0; i < NErasures; i++) ErasureLocs[i] = erasures[i];
Modified_Berlekamp_Massey();
Find_Roots();
if ((NErrors <= NPAR) && NErrors > 0) {
/* first check for illegal error locs */
for (r = 0; r < NErrors; r++) {
if (ErrorLocs[r] >= csize) {
if (RS_DEBUG) fprintf(stderr, "Error loc i=%d outside of codeword length %d\n", i, csize);
return(0);
}
}
for (r = 0; r < NErrors; r++) {
int num, denom;
i = ErrorLocs[r];
/* evaluate Omega at alpha^(-i) */
num = 0;
for (j = 0; j < MAXDEG; j++)
num ^= gmult(Omega[j], gexp[((255-i)*j)%255]);
/* evaluate Lambda' (derivative) at alpha^(-i) ; all odd powers disappear */
denom = 0;
for (j = 1; j < MAXDEG; j += 2) {
denom ^= gmult(Lambda[j], gexp[((255-i)*(j-1)) % 255]);
}
err = gmult(num, ginv(denom));
if (RS_DEBUG) fprintf(stderr, "Error magnitude %#x at loc %d\n", err, csize-i);
codeword[csize-i-1] ^= err;
}
return(1);
}
else {
if (RS_DEBUG && NErrors) fprintf(stderr, "Uncorrectable codeword\n");
return(0);
}
}
int CReedSolomon::correct_errors_erasures (unsigned char codeword [], int csize, int nerasures, int erasures []) {
int i, err;
m_NErasures = nerasures;
for (i = 0; i < m_NErasures; i ++) {
m_ErasureLocs [i] = erasures [i];
}
Modified_Berlekamp_Massey ();
Find_Roots ();
if ((m_NErrors <= m_iCorrectCodeSize) && m_NErrors > 0) {
/* first check for illegal error locs */
for (int r = 0; r < m_NErrors; r ++) {
if (m_ErrorLocs [r] >= csize) {
return(0);
}
}
for (int r = 0; r < m_NErrors; r ++) {
int num, denom;
i = m_ErrorLocs [r];
/* evaluate m_Omega at alpha^(-i) */
num = 0;
for (int j = 0; j < MAX_LENGTH; j ++) {
num ^= gmult (m_Omega [j], byExpToInt [((255 - i) * j) % 255]);
}
/* evaluate m_Lambda' (derivative) at alpha^(-i) ; all odd powers disappear */
denom = 0;
for (int j = 1; j < MAX_LENGTH; j += 2) {
denom ^= gmult (m_Lambda [j], byExpToInt [((255 - i) * (j - 1)) % 255]);
}
err = gmult (num, ginv (denom));
codeword [csize - i - 1] ^= err;
}
return 1;
} else {
return 0;
}
}
