FixedPointUtilities.cs
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using System;
namespace Org.BouncyCastle.Math.EC.Multiplier
{
public class FixedPointUtilities
{
public static readonly string PRECOMP_NAME = "bc_fixed_point";
public static int GetCombSize(ECCurve c)
{
BigInteger order = c.Order;
return order == null ? c.FieldSize + 1 : order.BitLength;
}
public static FixedPointPreCompInfo GetFixedPointPreCompInfo(PreCompInfo preCompInfo)
{
if ((preCompInfo != null) && (preCompInfo is FixedPointPreCompInfo))
{
return (FixedPointPreCompInfo)preCompInfo;
}
return new FixedPointPreCompInfo();
}
public static FixedPointPreCompInfo Precompute(ECPoint p, int minWidth)
{
ECCurve c = p.Curve;
int n = 1 << minWidth;
FixedPointPreCompInfo info = GetFixedPointPreCompInfo(c.GetPreCompInfo(p, PRECOMP_NAME));
ECPoint[] lookupTable = info.PreComp;
if (lookupTable == null || lookupTable.Length < n)
{
int bits = GetCombSize(c);
int d = (bits + minWidth - 1) / minWidth;
ECPoint[] pow2Table = new ECPoint[minWidth];
pow2Table[0] = p;
for (int i = 1; i < minWidth; ++i)
{
pow2Table[i] = pow2Table[i - 1].TimesPow2(d);
}
c.NormalizeAll(pow2Table);
lookupTable = new ECPoint[n];
lookupTable[0] = c.Infinity;
for (int bit = minWidth - 1; bit >= 0; --bit)
{
ECPoint pow2 = pow2Table[bit];
int step = 1 << bit;
for (int i = step; i < n; i += (step << 1))
{
lookupTable[i] = lookupTable[i - step].Add(pow2);
}
}
c.NormalizeAll(lookupTable);
info.PreComp = lookupTable;
info.Width = minWidth;
c.SetPreCompInfo(p, PRECOMP_NAME, info);
}
return info;
}
}
}