protected override ECPoint MultiplyPositive(ECPoint p, BigInteger k)
{
ECCurve c = p.Curve;
int size = FixedPointUtilities.GetCombSize(c);
if (k.BitLength > size)
{
/*
* TODO The comb works best when the scalars are less than the (possibly unknown) order.
* Still, if we want to handle larger scalars, we could allow customization of the comb
* size, or alternatively we could deal with the 'extra' bits either by running the comb
* multiple times as necessary, or by using an alternative multiplier as prelude.
*/
throw new InvalidOperationException("fixed-point comb doesn't support scalars larger than the curve order");
}
FixedPointPreCompInfo info = FixedPointUtilities.Precompute(p);
ECLookupTable lookupTable = info.LookupTable;
int width = info.Width;
int d = (size + width - 1) / width;
ECPoint R = c.Infinity;
int fullComb = d * width;
uint[] K = Nat.FromBigInteger(fullComb, k);
int top = fullComb - 1;
for (int i = 0; i < d; ++i)
{
int secretIndex = 0;
for (int j = top - i; j >= 0; j -= d)
{
secretIndex <<= 1;
secretIndex |= (int)Nat.GetBit(K, j);
}
ECPoint add = lookupTable.Lookup(secretIndex);
R = R.TwicePlus(add);
}
return(R.Add(info.Offset));
}
public override bool TestBitZero()
{
return(Nat.GetBit(x, 0) == 1);
}
public override bool TestBitZero()
{
return(Nat.GetBit(this.x, 0) == 1u);
}
public override bool TestBitZero() => (Nat.GetBit(this.x, 0) == 1);
