private static GroupElementP4 Select(int pos, sbyte b)
{
GroupElementP4 t;
GroupElementP4 minust;
var bnegative = Negative(b);
var babs = (byte)(b - ((-bnegative & b) << 1));
t = new GroupElementP4
{
YplusX = FieldElementOperations.Set1(),
YminusX = FieldElementOperations.Set1(),
XY2D = FieldElementOperations.Set0()
};
var table = LookupTables.Base[pos];
Cmov(ref t, ref table[0], Equal(babs, 1));
Cmov(ref t, ref table[1], Equal(babs, 2));
Cmov(ref t, ref table[2], Equal(babs, 3));
Cmov(ref t, ref table[3], Equal(babs, 4));
Cmov(ref t, ref table[4], Equal(babs, 5));
Cmov(ref t, ref table[5], Equal(babs, 6));
Cmov(ref t, ref table[6], Equal(babs, 7));
Cmov(ref t, ref table[7], Equal(babs, 8));
minust.YplusX = t.YminusX;
minust.YminusX = t.YplusX;
minust.XY2D = FieldElementOperations.Negate(ref t.XY2D);
Cmov(ref t, ref minust, bnegative);
return(t);
}
