void RSCoder::Encode(unsigned char *Data,int DataSize,unsigned char *DestData)
{
int ShiftReg[MAXPAR+1];
Clean(ShiftReg,ParSize+1);
for (int I=0;I<DataSize;I++)
{
int D=Data[I]^ShiftReg[ParSize-1];
for (int J=ParSize-1;J>0;J--)
ShiftReg[J]=ShiftReg[J-1]^gfMult(GXPol[J],D);
ShiftReg[0]=gfMult(GXPol[0],D);
}
for (int I=0;I<ParSize;I++)
DestData[I]=ShiftReg[ParSize-I-1];
}
void RSCoder::Encode(byte *Data,int DataSize,byte *DestData)
{
int ShiftReg[MAXPAR+1]; // Linear Feedback Shift Register.
Clean(ShiftReg,ParSize+1);
for (int I=0;I<DataSize;I++)
{
int D=Data[I]^ShiftReg[ParSize-1];
// Use g(x) to define feedback taps.
for (int J=ParSize-1;J>0;J--)
ShiftReg[J]=ShiftReg[J-1]^gfMult(GXPol[J],D);
ShiftReg[0]=gfMult(GXPol[0],D);
}
for (int I=0;I<ParSize;I++)
DestData[I]=ShiftReg[ParSize-I-1];
}
// Multiply polynomial 'p1' to 'p2' and store the result in 'r'.
void RSCoder::pnMult(int *p1,int *p2,int *r)
{
Clean(r,ParSize);
for (int I=0;I<ParSize;I++)
if (p1[I]!=0)
for(int J=0;J<ParSize-I;J++)
r[I+J]^=gfMult(p1[I],p2[J]);
}
/* return a u32 containing the result of multiplying the RS Code matrix
by the sd matrix
*/
u32 RSMatrixMultiply(BYTE sd[8])
{
int j, k;
BYTE t;
BYTE result[4];
for (j = 0; j < 4; j++)
{
t = 0;
for (k = 0; k < 8; k++)
{
/*printf("t=%X %X\n", t, gfMult(RS[j][k], sd[k], RS_MOD));*/
t ^= gfMult(RS[j][k], sd[k], RS_MOD);
}
result[3-j] = t;
}
return BYTEARRAY_TO_U32(result);
}
bool RSCoder::Decode(byte *Data,int DataSize,int *EraLoc,int EraSize)
{
int SynData[MAXPOL]; // Syndrome data.
bool AllZeroes=true;
for (int I=0;I<ParSize;I++)
{
int Sum=0;
for (int J=0;J<DataSize;J++)
Sum=Data[J]^gfMult(gfExp[I+1],Sum);
if ((SynData[I]=Sum)!=0)
AllZeroes=false;
}
// If all syndrome numbers are zero, message does not have errors.
if (AllZeroes)
return(true);
if (!FirstBlockDone) // Do things which we need to do once for all data.
{
FirstBlockDone=true;
// Calculate the error locator polynomial.
Clean(ELPol,ParSize+1);
ELPol[0]=1;
for (int EraPos=0;EraPos<EraSize;EraPos++)
for (int I=ParSize,M=gfExp[DataSize-EraLoc[EraPos]-1];I>0;I--)
ELPol[I]^=gfMult(M,ELPol[I-1]);
ErrCount=0;
// Find roots of error locator polynomial.
for (int Root=MAXPAR-DataSize;Root<MAXPAR+1;Root++)
{
int Sum=0;
for (int B=0;B<ParSize+1;B++)
Sum^=gfMult(gfExp[(B*Root)%MAXPAR],ELPol[B]);
if (Sum==0) // Root found.
{
ErrorLocs[ErrCount]=MAXPAR-Root; // Location of error.
// Calculate the denominator for every error location.
Dnm[ErrCount]=0;
for (int I=1;I<ParSize+1;I+=2)
Dnm[ErrCount]^= gfMult(ELPol[I],gfExp[Root*(I-1)%MAXPAR]);
ErrCount++;
}
}
}
int EEPol[MAXPOL]; // Error Evaluator Polynomial.
pnMult(ELPol,SynData,EEPol);
// If errors are present and their number is correctable.
if ((ErrCount<=ParSize) && ErrCount>0)
for (int I=0;I<ErrCount;I++)
{
int Loc=ErrorLocs[I],DLoc=MAXPAR-Loc,N=0;
for (int J=0;J<ParSize;J++)
N^=gfMult(EEPol[J],gfExp[DLoc*J%MAXPAR]);
int DataPos=DataSize-Loc-1;
// Perform bounds check and correct the data error.
if (DataPos>=0 && DataPos<DataSize)
Data[DataPos]^=gfMult(N,gfExp[MAXPAR-gfLog[Dnm[I]]]);
}
return(ErrCount<=ParSize); // Return true if success.
}
bool RSCoder::Decode(unsigned char *Data,int DataSize,int *EraLoc,int EraSize)
{
int SynData[MAXPOL];
bool AllZeroes=true;
for (int I=0;I<ParSize;I++)
{
int Sum=Data[0],J=1,Exp=gfExp[I+1];
for (;J+8<=DataSize;J+=8)
{
Sum=Data[J]^gfMult(Exp,Sum);
Sum=Data[J+1]^gfMult(Exp,Sum);
Sum=Data[J+2]^gfMult(Exp,Sum);
Sum=Data[J+3]^gfMult(Exp,Sum);
Sum=Data[J+4]^gfMult(Exp,Sum);
Sum=Data[J+5]^gfMult(Exp,Sum);
Sum=Data[J+6]^gfMult(Exp,Sum);
Sum=Data[J+7]^gfMult(Exp,Sum);
}
for (;J<DataSize;J++)
Sum=Data[J]^gfMult(Exp,Sum);
if ((SynData[I]=Sum)!=0)
AllZeroes=false;
}
if (AllZeroes)
return(true);
if (!FirstBlockDone)
{
FirstBlockDone=true;
Clean(PolB,ParSize+1);
PolB[0]=1;
for (int EraPos=0;EraPos<EraSize;EraPos++)
for (int I=ParSize,M=gfExp[DataSize-EraLoc[EraPos]-1];I>0;I--)
PolB[I]^=gfMult(M,PolB[I-1]);
ErrCount=0;
for (int Root=MAXPAR-DataSize;Root<MAXPAR+1;Root++)
{
int Sum=0;
for (int B=0;B<ParSize+1;B++)
Sum^=gfMult(gfExp[(B*Root)%MAXPAR],PolB[B]);
if (Sum==0)
{
Dn[ErrCount]=0;
for (int I=1;I<ParSize+1;I+=2)
Dn[ErrCount]^= gfMult(PolB[I],gfExp[Root*(I-1)%MAXPAR]);
ErrorLocs[ErrCount++]=MAXPAR-Root;
}
}
}
int PolD[MAXPOL];
pnMult(PolB,SynData,PolD);
if ((ErrCount<=ParSize) && ErrCount>0)
for (int I=0;I<ErrCount;I++)
{
int Loc=ErrorLocs[I],DLoc=MAXPAR-Loc,N=0;
for (int J=0;J<ParSize;J++)
N^=gfMult(PolD[J],gfExp[DLoc*J%MAXPAR]);
int DataPos=DataSize-Loc-1;
if (DataPos>=0 && DataPos<DataSize)
Data[DataPos]^=gfMult(N,gfExp[MAXPAR-gfLog[Dn[I]]]);
}
return(ErrCount<=ParSize);
}
