public PreCompInfo Precompute(PreCompInfo existing)
{
WNafPreCompInfo existingWNaf = existing as WNafPreCompInfo;
int width = m_fromWNaf.Width;
int reqPreCompLen = m_fromWNaf.PreComp.Length;
if (CheckExisting(existingWNaf, width, reqPreCompLen, m_includeNegated))
{
existingWNaf.DecrementPromotionCountdown();
return(existingWNaf);
}
/*
* TODO Ideally this method would support incremental calculation, but given the
* existing use-cases it would be of little-to-no benefit.
*/
WNafPreCompInfo result = new WNafPreCompInfo();
result.PromotionCountdown = m_fromWNaf.PromotionCountdown;
ECPoint twiceFrom = m_fromWNaf.Twice;
if (null != twiceFrom)
{
ECPoint twice = m_pointMap.Map(twiceFrom);
result.Twice = twice;
}
ECPoint[] preCompFrom = m_fromWNaf.PreComp;
ECPoint[] preComp = new ECPoint[preCompFrom.Length];
for (int i = 0; i < preCompFrom.Length; ++i)
{
preComp[i] = m_pointMap.Map(preCompFrom[i]);
}
result.PreComp = preComp;
result.Width = width;
if (m_includeNegated)
{
ECPoint[] preCompNeg = new ECPoint[preComp.Length];
for (int i = 0; i < preCompNeg.Length; ++i)
{
preCompNeg[i] = preComp[i].Negate();
}
result.PreCompNeg = preCompNeg;
}
return(result);
}
public PreCompInfo Precompute(PreCompInfo existing)
{
WNafPreCompInfo existingWNaf = existing as WNafPreCompInfo;
int width = System.Math.Max(2, System.Math.Min(MAX_WIDTH, m_minWidth));
int reqPreCompLen = 1 << (width - 2);
if (CheckExisting(existingWNaf, width, reqPreCompLen, m_includeNegated))
{
existingWNaf.DecrementPromotionCountdown();
return(existingWNaf);
}
WNafPreCompInfo result = new WNafPreCompInfo();
ECCurve c = m_p.Curve;
ECPoint[] preComp = null, preCompNeg = null;
ECPoint twiceP = null;
if (null != existingWNaf)
{
int promotionCountdown = existingWNaf.DecrementPromotionCountdown();
result.PromotionCountdown = promotionCountdown;
int confWidth = existingWNaf.ConfWidth;
result.ConfWidth = confWidth;
preComp = existingWNaf.PreComp;
preCompNeg = existingWNaf.PreCompNeg;
twiceP = existingWNaf.Twice;
}
width = System.Math.Min(MAX_WIDTH, System.Math.Max(result.ConfWidth, width));
reqPreCompLen = 1 << (width - 2);
int iniPreCompLen = 0;
if (null == preComp)
{
preComp = EMPTY_POINTS;
}
else
{
iniPreCompLen = preComp.Length;
}
if (iniPreCompLen < reqPreCompLen)
{
preComp = WNafUtilities.ResizeTable(preComp, reqPreCompLen);
if (reqPreCompLen == 1)
{
preComp[0] = m_p.Normalize();
}
else
{
int curPreCompLen = iniPreCompLen;
if (curPreCompLen == 0)
{
preComp[0] = m_p;
curPreCompLen = 1;
}
ECFieldElement iso = null;
if (reqPreCompLen == 2)
{
preComp[1] = m_p.ThreeTimes();
}
else
{
ECPoint isoTwiceP = twiceP, last = preComp[curPreCompLen - 1];
if (null == isoTwiceP)
{
isoTwiceP = preComp[0].Twice();
twiceP = isoTwiceP;
/*
* For Fp curves with Jacobian projective coordinates, use a (quasi-)isomorphism
* where 'twiceP' is "affine", so that the subsequent additions are cheaper. This
* also requires scaling the initial point's X, Y coordinates, and reversing the
* isomorphism as part of the subsequent normalization.
*
* NOTE: The correctness of this optimization depends on:
* 1) additions do not use the curve's A, B coefficients.
* 2) no special cases (i.e. Q +/- Q) when calculating 1P, 3P, 5P, ...
*/
if (!twiceP.IsInfinity && ECAlgorithms.IsFpCurve(c) && c.FieldSize >= 64)
{
switch (c.CoordinateSystem)
{
case ECCurve.COORD_JACOBIAN:
case ECCurve.COORD_JACOBIAN_CHUDNOVSKY:
case ECCurve.COORD_JACOBIAN_MODIFIED:
{
iso = twiceP.GetZCoord(0);
isoTwiceP = c.CreatePoint(twiceP.XCoord.ToBigInteger(),
twiceP.YCoord.ToBigInteger());
ECFieldElement iso2 = iso.Square(), iso3 = iso2.Multiply(iso);
last = last.ScaleX(iso2).ScaleY(iso3);
if (iniPreCompLen == 0)
{
preComp[0] = last;
}
break;
}
}
}
}
while (curPreCompLen < reqPreCompLen)
{
/*
* Compute the new ECPoints for the precomputation array. The values 1, 3,
* 5, ..., 2^(width-1)-1 times p are computed
*/
preComp[curPreCompLen++] = last = last.Add(isoTwiceP);
}
}
/*
* Having oft-used operands in affine form makes operations faster.
*/
c.NormalizeAll(preComp, iniPreCompLen, reqPreCompLen - iniPreCompLen, iso);
}
}
if (m_includeNegated)
{
int pos;
if (null == preCompNeg)
{
pos = 0;
preCompNeg = new ECPoint[reqPreCompLen];
}
else
{
pos = preCompNeg.Length;
if (pos < reqPreCompLen)
{
preCompNeg = WNafUtilities.ResizeTable(preCompNeg, reqPreCompLen);
}
}
while (pos < reqPreCompLen)
{
preCompNeg[pos] = preComp[pos].Negate();
++pos;
}
}
result.PreComp = preComp;
result.PreCompNeg = preCompNeg;
result.Twice = twiceP;
result.Width = width;
return(result);
}