Method gfInit

Libraries/unrar/rs16.cpp:33–53

Initialize logarithms and exponents Galois field tables.

// Initialize logarithms and exponents Galois field tables.
void RSCoder16::gfInit()
{
  gfExp=new uint[4*gfSize+1];
  gfLog=new uint[gfSize+1];

  for (uint L=0,E=1;L<gfSize;L++)
  {
    gfLog[E]=L;
    gfExp[L]=E;
    gfExp[L+gfSize]=E;  // Duplicate the table to avoid gfExp overflow check.
    E<<=1;
    if (E>gfSize)
      E^=0x1100B; // Irreducible field-generator polynomial.
  }

  // log(0)+log(x) must be outside of usual log table, so we can set it
  // to 0 and avoid check for 0 in multiplication parameters.
  gfLog[0]= 2*gfSize;
  for (uint I=2*gfSize;I<=4*gfSize;I++) // Results for log(0)+log(x).
    gfExp[I]=0;
}


uint RSCoder16::gfAdd(uint a,uint b) // Addition in Galois field.