| private static ResizeTable ( ECPoint a, int length ) : ECPoint[] | ||
| a | ECPoint | |
| length | int | |
| return | ECPoint[] | |
public static WNafPreCompInfo Precompute(ECPoint p, int width, bool includeNegated)
{
ECCurve curve = p.Curve;
WNafPreCompInfo wNafPreCompInfo = WNafUtilities.GetWNafPreCompInfo(curve.GetPreCompInfo(p, WNafUtilities.PRECOMP_NAME));
int num = 0;
int num2 = 1 << Math.Max(0, width - 2);
ECPoint[] array = wNafPreCompInfo.PreComp;
if (array == null)
{
array = WNafUtilities.EMPTY_POINTS;
}
else
{
num = array.Length;
}
if (num < num2)
{
array = WNafUtilities.ResizeTable(array, num2);
if (num2 == 1)
{
array[0] = p.Normalize();
}
else
{
int i = num;
if (i == 0)
{
array[0] = p;
i = 1;
}
ECFieldElement eCFieldElement = null;
if (num2 == 2)
{
array[1] = p.ThreeTimes();
}
else
{
ECPoint eCPoint = wNafPreCompInfo.Twice;
ECPoint eCPoint2 = array[i - 1];
if (eCPoint == null)
{
eCPoint = array[0].Twice();
wNafPreCompInfo.Twice = eCPoint;
if (ECAlgorithms.IsFpCurve(curve) && curve.FieldSize >= 64)
{
switch (curve.CoordinateSystem)
{
case 2:
case 3:
case 4:
{
eCFieldElement = eCPoint.GetZCoord(0);
eCPoint = curve.CreatePoint(eCPoint.XCoord.ToBigInteger(), eCPoint.YCoord.ToBigInteger());
ECFieldElement eCFieldElement2 = eCFieldElement.Square();
ECFieldElement scale = eCFieldElement2.Multiply(eCFieldElement);
eCPoint2 = eCPoint2.ScaleX(eCFieldElement2).ScaleY(scale);
if (num == 0)
{
array[0] = eCPoint2;
}
break;
}
}
}
}
while (i < num2)
{
eCPoint2 = (array[i++] = eCPoint2.Add(eCPoint));
}
}
curve.NormalizeAll(array, num, num2 - num, eCFieldElement);
}
}
wNafPreCompInfo.PreComp = array;
if (includeNegated)
{
ECPoint[] array2 = wNafPreCompInfo.PreCompNeg;
int j;
if (array2 == null)
{
j = 0;
array2 = new ECPoint[num2];
}
else
{
j = array2.Length;
if (j < num2)
{
array2 = WNafUtilities.ResizeTable(array2, num2);
}
}
while (j < num2)
{
array2[j] = array[j].Negate();
j++;
}
wNafPreCompInfo.PreCompNeg = array2;
}
curve.SetPreCompInfo(p, WNafUtilities.PRECOMP_NAME, wNafPreCompInfo);
return(wNafPreCompInfo);
}
public PreCompInfo Precompute(PreCompInfo existing)
{
WNafPreCompInfo existingWNaf = existing as WNafPreCompInfo;
int reqPreCompLen = 1 << System.Math.Max(0, m_width - 2);
if (CheckExisting(existingWNaf, reqPreCompLen, m_includeNegated))
{
return(existingWNaf);
}
ECCurve c = m_p.Curve;
ECPoint[] preComp = null, preCompNeg = null;
ECPoint twiceP = null;
if (existingWNaf != null)
{
preComp = existingWNaf.PreComp;
preCompNeg = existingWNaf.PreCompNeg;
twiceP = existingWNaf.Twice;
}
int iniPreCompLen = 0;
if (preComp == null)
{
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 (isoTwiceP == null)
{
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 (preCompNeg == null)
{
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;
}
}
WNafPreCompInfo result = new WNafPreCompInfo();
result.PreComp = preComp;
result.PreCompNeg = preCompNeg;
result.Twice = twiceP;
return(result);
}
