Fixed-point-comb uses existing precomputation info if it's for the same

_or greater_ width as requested

3 files changed, 29 insertions, 10 deletions

diff --git a/core/src/main/java/org/bouncycastle/math/ec/FixedPointCombMultiplier.java b/core/src/main/java/org/bouncycastle/math/ec/FixedPointCombMultiplier.java
index d2cc2e3b..9fe00b9b 100644
--- a/core/src/main/java/org/bouncycastle/math/ec/FixedPointCombMultiplier.java
+++ b/core/src/main/java/org/bouncycastle/math/ec/FixedPointCombMultiplier.java
@@ -20,10 +20,11 @@ public class FixedPointCombMultiplier extends AbstractECMultiplier
             throw new IllegalStateException("fixed-point comb doesn't support scalars larger than the curve order");
         }
 
-        int width = getWidthForCombSize(size);
+        int minWidth = getWidthForCombSize(size);
 
-        FixedPointPreCompInfo info = FixedPointUtil.precompute(p, width);
+        FixedPointPreCompInfo info = FixedPointUtil.precompute(p, minWidth);
         ECPoint[] lookupTable = info.getPreComp();
+        int width = info.getWidth();
 
         int d = (size + width - 1) / width;
 
diff --git a/core/src/main/java/org/bouncycastle/math/ec/FixedPointPreCompInfo.java b/core/src/main/java/org/bouncycastle/math/ec/FixedPointPreCompInfo.java
index 7cfb7f47..b7569aae 100644
--- a/core/src/main/java/org/bouncycastle/math/ec/FixedPointPreCompInfo.java
+++ b/core/src/main/java/org/bouncycastle/math/ec/FixedPointPreCompInfo.java
@@ -11,6 +11,13 @@ public class FixedPointPreCompInfo implements PreCompInfo
      */
     protected ECPoint[] preComp = null;
 
+    /**
+     * The width used for the precomputation. If a larger width precomputation
+     * is already available this may be larger than was requested, so calling
+     * code should refer to the actual width.
+     */
+    protected int width = -1;
+
     public ECPoint[] getPreComp()
     {
         return preComp;
@@ -20,4 +27,14 @@ public class FixedPointPreCompInfo implements PreCompInfo
     {
         this.preComp = preComp;
     }
+
+    public int getWidth()
+    {
+        return width;
+    }
+
+    public void setWidth(int width)
+    {
+        this.width = width;
+    }
 }
diff --git a/core/src/main/java/org/bouncycastle/math/ec/FixedPointUtil.java b/core/src/main/java/org/bouncycastle/math/ec/FixedPointUtil.java
index aba9143f..e4fbb8d0 100644
--- a/core/src/main/java/org/bouncycastle/math/ec/FixedPointUtil.java
+++ b/core/src/main/java/org/bouncycastle/math/ec/FixedPointUtil.java
@@ -22,22 +22,22 @@ public class FixedPointUtil
         return new FixedPointPreCompInfo();
     }
 
-    public static FixedPointPreCompInfo precompute(ECPoint p, int width)
+    public static FixedPointPreCompInfo precompute(ECPoint p, int minWidth)
     {
         ECCurve c = p.getCurve();
 
-        int n = 1 << width;
+        int n = 1 << minWidth;
         FixedPointPreCompInfo info = getFixedPointPreCompInfo(c.getPreCompInfo(p, PRECOMP_NAME));
         ECPoint[] lookupTable = info.getPreComp();
 
-        if (lookupTable == null || lookupTable.length != n)
+        if (lookupTable == null || lookupTable.length < n)
         {
             int bits = getCombSize(c);
-            int d = (bits + width - 1) / width;
+            int d = (bits + minWidth - 1) / minWidth;
 
-            ECPoint[] pow2Table = new ECPoint[width];
+            ECPoint[] pow2Table = new ECPoint[minWidth];
             pow2Table[0] = p;
-            for (int i = 1; i < width; ++i)
+            for (int i = 1; i < minWidth; ++i)
             {
                 pow2Table[i] = pow2Table[i - 1].timesPow2(d);
             }
@@ -47,7 +47,7 @@ public class FixedPointUtil
             lookupTable = new ECPoint[n];
             lookupTable[0] = c.getInfinity();
     
-            for (int bit = width - 1; bit >= 0; --bit)
+            for (int bit = minWidth - 1; bit >= 0; --bit)
             {
                 ECPoint pow2 = pow2Table[bit];
 
@@ -57,10 +57,11 @@ public class FixedPointUtil
                     lookupTable[i] = lookupTable[i - step].add(pow2);
                 }
             }
-    
+
             c.normalizeAll(lookupTable);
 
             info.setPreComp(lookupTable);
+            info.setWidth(minWidth);
 
             c.setPreCompInfo(p, PRECOMP_NAME, info);
         }