/* polynomial multiplication */
void
mult_polys (int dst[], int p1[], int p2[])
{
int i, j;
int tmp1[MAXDEG*2];
for (i=0; i < (MAXDEG*2); i++) dst[i] = 0;
for (i = 0; i < MAXDEG; i++) {
for(j=MAXDEG; j<(MAXDEG*2); j++) tmp1[j]=0;
/* scale tmp1 by p1[i] */
for(j=0; j<MAXDEG; j++) tmp1[j]=gmult(p2[j], p1[i]);
/* and mult (shift) tmp1 right by i */
for (j = (MAXDEG*2)-1; j >= i; j--) tmp1[j] = tmp1[j-i];
for (j = 0; j < i; j++) tmp1[j] = 0;
/* add into partial product */
for(j=0; j < (MAXDEG*2); j++) dst[j] ^= tmp1[j];
}
}
BOOL CReedSolomon::Decode (unsigned char * szData, int iDataSize, unsigned char * szCorrectData, int *iCorrectDataSize) {
int sum;
int nz = 0;
int erasures[256];
int nerasures = 0;
int iRet;
for (int i = 0; i < MAX_LENGTH; i ++) {
m_synBytes [i] = 0;
}
for (int j = 0; j < m_iCorrectCodeSize; j ++) {
sum = 0;
for (int i = 0; i < iDataSize; i ++) {
sum = szData [i] ^ gmult (byExpToInt [j + 1], sum);
}
m_synBytes [j] = sum;
}
for (int i = 0; i < m_iCorrectCodeSize; i ++) {
if (m_synBytes [i] != 0) {
nz = 1;
}
}
if (nz == 0) {
memcpy (szCorrectData, szData, iDataSize);
*iCorrectDataSize = iDataSize - m_iCorrectCodeSize;
return TRUE;
}
iRet = correct_errors_erasures (szData, iDataSize, nerasures, erasures);
if (iRet == 0) {
return FALSE;
}
memcpy (szCorrectData, szData, iDataSize - m_iCorrectCodeSize);
*iCorrectDataSize = iDataSize - m_iCorrectCodeSize;
return TRUE;
}
void
mult_polys (unsigned short dst[], unsigned short p1[], unsigned short p2[])
{
int i, j;
int tmp1[MAXDEG*2];
for (i=0; i < (MAXDEG*2); i++) dst[i] = 0;
for (i = 0; i < MAXDEG; i++) {
for(j=MAXDEG; j<(MAXDEG*2); j++) tmp1[j]=0;
for(j=0; j<MAXDEG; j++) tmp1[j]=gmult(p2[j], p1[i]);
for (j = (MAXDEG*2)-1; j >= i; j--) tmp1[j] = tmp1[j-i];
for (j = 0; j < i; j++) tmp1[j] = 0;
for(j=0; j < (MAXDEG*2); j++) dst[j] ^= tmp1[j];
}
}
// Create a generator polynomial for an n byte RS code.
void init_genpoly_cache(int par)
{
int i;
unsigned char tp[256], tp1[256];
int tmp;
unsigned char *genpoly = genpoly_cache[par-1];
//multiply (x + a^n) for n = 1 to nbytes
zero_poly(tp1, par*2);
tp1[0] = 1;
for (i = 1; i <= par; i++)
{
zero_poly(tp, par*2);
tp[0] = gexp[i]; // set up x+a^n
tp[1] = 1;
mult_polys(genpoly, tp, tp1, par*2);
copy_poly(tp1, genpoly, par*2);
}
for(i=0; i<par/2; i++)
{
tmp = genpoly[i] ;
genpoly[i] = genpoly[par-1-i];
genpoly[par-1-i]=tmp;
}
for(i=0; i<256; i++)
{
for(int j=0; j<23; j++)
genpoly_23_mult_cache[i][j] = gmult(i, genpoly_cache[22][j]);
genpoly_23_mult_cache[i][23] = 0;
}
}
void CReedSolomon::scale_poly (int k, int poly []) {
for (int i = 0; i < MAX_LENGTH; i ++) {
poly [i] = gmult (k, poly [i]);
}
}
/*
* Multiplication of 4 byte words
* m(x) = x4+1
*/
void coef_mult(uint8_t *a, uint8_t *b, uint8_t *d) {
d[0] = gmult(a[0],b[0])^gmult(a[3],b[1])^gmult(a[2],b[2])^gmult(a[1],b[3]);
d[1] = gmult(a[1],b[0])^gmult(a[0],b[1])^gmult(a[3],b[2])^gmult(a[2],b[3]);
d[2] = gmult(a[2],b[0])^gmult(a[1],b[1])^gmult(a[0],b[2])^gmult(a[3],b[3]);
d[3] = gmult(a[3],b[0])^gmult(a[2],b[1])^gmult(a[1],b[2])^gmult(a[0],b[3]);
}
void scale_poly (int k, int poly[])
{
int i;
for (i = 0; i < MAXDEG; i++) poly[i] = gmult(k, poly[i]);
}
void scale_poly (int k, unsigned char *poly, int size)
{
int i;
for (i = 0; i < size; i++) poly[i] = gmult(k, poly[i]);
}