1 files changed, 71 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/math/ec/FixedPointUtil.java b/core/src/main/java/org/spongycastle/math/ec/FixedPointUtil.java
new file mode 100644
index 00000000..aa96ebcb
--- /dev/null
+++ b/core/src/main/java/org/spongycastle/math/ec/FixedPointUtil.java
@@ -0,0 +1,71 @@
+package org.spongycastle.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;
+    }
+}