| /* GENERATED SOURCE. DO NOT MODIFY. */ |
| package com.android.internal.org.bouncycastle.math.ec; |
| |
| import java.math.BigInteger; |
| |
| /** |
| * @hide This class is not part of the Android public SDK API |
| */ |
| 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) |
| { |
| return (preCompInfo instanceof FixedPointPreCompInfo) ? (FixedPointPreCompInfo)preCompInfo : null; |
| } |
| |
| public static FixedPointPreCompInfo precompute(final ECPoint p) |
| { |
| final ECCurve c = p.getCurve(); |
| |
| return (FixedPointPreCompInfo)c.precompute(p, PRECOMP_NAME, new PreCompCallback() |
| { |
| public PreCompInfo precompute(PreCompInfo existing) |
| { |
| FixedPointPreCompInfo existingFP = (existing instanceof FixedPointPreCompInfo) ? (FixedPointPreCompInfo)existing : null; |
| |
| int bits = getCombSize(c); |
| int minWidth = bits > 250 ? 6 : 5; |
| int n = 1 << minWidth; |
| |
| if (checkExisting(existingFP, n)) |
| { |
| return existingFP; |
| } |
| |
| int d = (bits + minWidth - 1) / minWidth; |
| |
| ECPoint[] pow2Table = new ECPoint[minWidth + 1]; |
| pow2Table[0] = p; |
| for (int i = 1; i < minWidth; ++i) |
| { |
| pow2Table[i] = pow2Table[i - 1].timesPow2(d); |
| } |
| |
| // This will be the 'offset' value |
| pow2Table[minWidth] = pow2Table[0].subtract(pow2Table[1]); |
| |
| c.normalizeAll(pow2Table); |
| |
| ECPoint[] lookupTable = new ECPoint[n]; |
| lookupTable[0] = pow2Table[0]; |
| |
| 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); |
| |
| FixedPointPreCompInfo result = new FixedPointPreCompInfo(); |
| result.setLookupTable(c.createCacheSafeLookupTable(lookupTable, 0, lookupTable.length)); |
| result.setOffset(pow2Table[minWidth]); |
| result.setWidth(minWidth); |
| return result; |
| } |
| |
| private boolean checkExisting(FixedPointPreCompInfo existingFP, int n) |
| { |
| return existingFP != null && checkTable(existingFP.getLookupTable(), n); |
| } |
| |
| private boolean checkTable(ECLookupTable table, int n) |
| { |
| return table != null && table.getSize() >= n; |
| } |
| }); |
| } |
| } |