/**
* Multiplies a {@link org.bouncycastle.math.ec.F2mPoint F2mPoint}
* by an element <code>λ</code> of <code><b>Z</b>[τ]</code>
* using the <code>τ</code>-adic NAF (TNAF) method, given the TNAF
* of <code>λ</code>.
* @param p The F2mPoint to Multiply.
* @param u The the TNAF of <code>λ</code>..
* @return <code>λ * p</code>
*/
public static F2mPoint MultiplyFromTnaf(F2mPoint p, sbyte[] u)
{
F2mCurve curve = (F2mCurve)p.Curve;
F2mPoint q = (F2mPoint)curve.Infinity;
for (int i = u.Length - 1; i >= 0; i--)
{
q = Tau(q);
if (u[i] == 1)
{
q = (F2mPoint)q.AddSimple(p);
}
else if (u[i] == -1)
{
q = (F2mPoint)q.SubtractSimple(p);
}
}
return(q);
}
/**
* Multiplies a {@link org.bouncycastle.math.ec.F2mPoint F2mPoint}
* 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 F2mPoint to multiply.
* @param u The the WTNAF of <code>λ</code>..
* @return <code>λ * p</code>
*/
private static F2mPoint MultiplyFromWTnaf(F2mPoint p, sbyte[] u, PreCompInfo preCompInfo)
{
F2mCurve curve = (F2mCurve)p.Curve;
sbyte a = (sbyte)curve.A.ToBigInteger().IntValue;
F2mPoint[] pu;
if ((preCompInfo == null) || !(preCompInfo is WTauNafPreCompInfo))
{
pu = Tnaf.GetPreComp(p, a);
WTauNafPreCompInfo pre = new WTauNafPreCompInfo();
pre.PreComp = pu;
curve.SetPreCompInfo(p, PRECOMP_NAME, pre);
}
else
{
pu = ((WTauNafPreCompInfo)preCompInfo).PreComp;
}
// q = infinity
F2mPoint q = (F2mPoint)curve.Infinity;
for (int i = u.Length - 1; i >= 0; i--)
{
q = Tnaf.Tau(q);
sbyte ui = u[i];
if (ui != 0)
{
if (ui > 0)
{
q = q.AddSimple(pu[ui]);
}
else
{
// u[i] < 0
q = q.SubtractSimple(pu[-ui]);
}
}
}
return(q);
}
