org.bouncycastle.math.ec.FixedPointUtil Maven / Gradle / Ivy
package org.bouncycastle.math.ec;
import java.math.BigInteger;
public class FixedPointUtil
{
public static final String PRECOMP_NAME = "bc_fixed_point";
public static int getCombSize(ECCurve c)
{
BigInteger order = c.getOrder();
return order == null ? c.getFieldSize() + 1 : order.bitLength();
}
public static FixedPointPreCompInfo getFixedPointPreCompInfo(PreCompInfo preCompInfo)
{
if ((preCompInfo != null) && (preCompInfo instanceof FixedPointPreCompInfo))
{
return (FixedPointPreCompInfo)preCompInfo;
}
return new FixedPointPreCompInfo();
}
public static FixedPointPreCompInfo precompute(ECPoint p, int minWidth)
{
ECCurve c = p.getCurve();
int n = 1 << minWidth;
FixedPointPreCompInfo info = getFixedPointPreCompInfo(c.getPreCompInfo(p, PRECOMP_NAME));
ECPoint[] lookupTable = info.getPreComp();
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.getInfinity();
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.setPreComp(lookupTable);
info.setWidth(minWidth);
c.setPreCompInfo(p, PRECOMP_NAME, info);
}
return info;
}
}