Fixed-point-comb uses existing precomputation info if it's for the same _or greater_ width as requested release-1.8.0-beta.3

3 files changed, 24 insertions, 9 deletions

diff --git a/crypto/src/math/ec/multiplier/FixedPointCombMultiplier.cs b/crypto/src/math/ec/multiplier/FixedPointCombMultiplier.cs

index e3da3f7c2..a8ef5a77a 100644
--- a/crypto/src/math/ec/multiplier/FixedPointCombMultiplier.cs
+++ b/crypto/src/math/ec/multiplier/FixedPointCombMultiplier.cs
@@ -21,10 +21,11 @@ namespace Org.BouncyCastle.Math.EC.Multiplier
                 throw new InvalidOperationException("fixed-point comb doesn't support scalars larger than the curve order");
             }
 
-            int width = GetWidthForCombSize(size);
+            int minWidth = GetWidthForCombSize(size);
 
-            FixedPointPreCompInfo info = FixedPointUtilities.Precompute(p, width);
+            FixedPointPreCompInfo info = FixedPointUtilities.Precompute(p, minWidth);
             ECPoint[] lookupTable = info.PreComp;
+            int width = info.Width;
 
             int d = (size + width - 1) / width;
 
diff --git a/crypto/src/math/ec/multiplier/FixedPointPreCompInfo.cs b/crypto/src/math/ec/multiplier/FixedPointPreCompInfo.cs

index 306f40a11..56a6326a1 100644
--- a/crypto/src/math/ec/multiplier/FixedPointPreCompInfo.cs
+++ b/crypto/src/math/ec/multiplier/FixedPointPreCompInfo.cs
@@ -12,10 +12,23 @@
          */
         protected ECPoint[] m_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 m_width = -1;
+
         public virtual ECPoint[] PreComp
         {
             get { return m_preComp; }
             set { this.m_preComp = value; }
         }
+
+        public virtual int Width
+        {
+            get { return m_width; }
+            set { this.m_width = value; }
+        }
     }
 }
diff --git a/crypto/src/math/ec/multiplier/FixedPointUtilities.cs b/crypto/src/math/ec/multiplier/FixedPointUtilities.cs

index 194995e08..d927d010b 100644
--- a/crypto/src/math/ec/multiplier/FixedPointUtilities.cs
+++ b/crypto/src/math/ec/multiplier/FixedPointUtilities.cs
@@ -22,22 +22,22 @@ namespace Org.BouncyCastle.Math.EC.Multiplier
             return new FixedPointPreCompInfo();
         }
 
-        public static FixedPointPreCompInfo Precompute(ECPoint p, int width)
+        public static FixedPointPreCompInfo Precompute(ECPoint p, int minWidth)
         {
             ECCurve c = p.Curve;
 
-            int n = 1 << width;
+            int n = 1 << minWidth;
             FixedPointPreCompInfo info = GetFixedPointPreCompInfo(c.GetPreCompInfo(p, PRECOMP_NAME));
             ECPoint[] lookupTable = info.PreComp;
 
-            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 @@ namespace Org.BouncyCastle.Math.EC.Multiplier
                 lookupTable = new ECPoint[n];
                 lookupTable[0] = c.Infinity;
 
-                for (int bit = width - 1; bit >= 0; --bit)
+                for (int bit = minWidth - 1; bit >= 0; --bit)
                 {
                     ECPoint pow2 = pow2Table[bit];
 
@@ -61,6 +61,7 @@ namespace Org.BouncyCastle.Math.EC.Multiplier
                 c.NormalizeAll(lookupTable);
 
                 info.PreComp = lookupTable;
+                info.Width = minWidth;
 
                 c.SetPreCompInfo(p, PRECOMP_NAME, info);
             }