public static WNafPreCompInfo Precompute(ECPoint p, int width, bool includeNegated)
{
ECCurve c = p.Curve;
WNafPreCompInfo wnafPreCompInfo = GetWNafPreCompInfo(c.GetPreCompInfo(p));
ECPoint[] preComp = wnafPreCompInfo.PreComp;
if (preComp == null)
{
preComp = new ECPoint[] { p };
}
int preCompLen = preComp.Length;
int reqPreCompLen = 1 << System.Math.Max(0, width - 2);
if (preCompLen < reqPreCompLen)
{
ECPoint twiceP = wnafPreCompInfo.Twice;
if (twiceP == null)
{
twiceP = preComp[0].Twice().Normalize();
wnafPreCompInfo.Twice = twiceP;
}
preComp = ResizeTable(preComp, reqPreCompLen);
/*
* TODO Okeya/Sakurai paper has precomputation trick and "Montgomery's Trick" to speed this up.
* Also, co-Z arithmetic could avoid the subsequent normalization too.
*/
for (int i = preCompLen; i < reqPreCompLen; i++)
{
/*
* Compute the new ECPoints for the precomputation array. The values 1, 3, 5, ...,
* 2^(width-1)-1 times p are computed
*/
preComp[i] = twiceP.Add(preComp[i - 1]);
}
/*
* Having oft-used operands in affine form makes operations faster.
*/
c.NormalizeAll(preComp);
}
wnafPreCompInfo.PreComp = preComp;
if (includeNegated)
{
ECPoint[] preCompNeg = wnafPreCompInfo.PreCompNeg;
int pos;
if (preCompNeg == null)
{
pos = 0;
preCompNeg = new ECPoint[reqPreCompLen];
}
else
{
pos = preCompNeg.Length;
if (pos < reqPreCompLen)
{
preCompNeg = ResizeTable(preCompNeg, reqPreCompLen);
}
}
while (pos < reqPreCompLen)
{
preCompNeg[pos] = preComp[pos].Negate();
++pos;
}
wnafPreCompInfo.PreCompNeg = preCompNeg;
}
c.SetPreCompInfo(p, wnafPreCompInfo);
return(wnafPreCompInfo);
}
