public PreCompInfo Precompute(PreCompInfo existing)
{
if (existing is WTauNafPreCompInfo)
{
return(existing);
}
WTauNafPreCompInfo result = new WTauNafPreCompInfo();
result.PreComp = Tnaf.GetPreComp(m_p, m_a);
return(result);
}
/**
* Multiplies a {@link org.bouncycastle.math.ec.AbstractF2mPoint AbstractF2mPoint}
* by an element <code>λ</code> of <code><b>Z</b>[τ]</code>
* using the window <code>τ</code>-adic NAF (TNAF) method, given the
* WTNAF of <code>λ</code>.
* @param p The AbstractF2mPoint to multiply.
* @param u The the WTNAF of <code>λ</code>..
* @return <code>λ * p</code>
*/
private static AbstractF2mPoint MultiplyFromWTnaf(AbstractF2mPoint p, sbyte[] u)
{
AbstractF2mCurve curve = (AbstractF2mCurve)p.Curve;
sbyte a = (sbyte)curve.A.ToBigInteger().IntValue;
WTauNafCallback callback = new WTauNafCallback(p, a);
WTauNafPreCompInfo preCompInfo = (WTauNafPreCompInfo)curve.Precompute(p, PRECOMP_NAME, callback);
AbstractF2mPoint[] pu = preCompInfo.PreComp;
// TODO Include negations in precomp (optionally) and use from here
AbstractF2mPoint[] puNeg = new AbstractF2mPoint[pu.Length];
for (int i = 0; i < pu.Length; ++i)
{
puNeg[i] = (AbstractF2mPoint)pu[i].Negate();
}
// q = infinity
AbstractF2mPoint q = (AbstractF2mPoint)p.Curve.Infinity;
int tauCount = 0;
for (int i = u.Length - 1; i >= 0; i--)
{
++tauCount;
int ui = u[i];
if (ui != 0)
{
q = q.TauPow(tauCount);
tauCount = 0;
ECPoint x = ui > 0 ? pu[ui >> 1] : puNeg[(-ui) >> 1];
q = (AbstractF2mPoint)q.Add(x);
}
}
if (tauCount > 0)
{
q = q.TauPow(tauCount);
}
return(q);
}