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Assets/BestHTTP/SecureProtocol/math/ec/multiplier/FixedPointCombMultiplier.cs

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+#if !BESTHTTP_DISABLE_ALTERNATE_SSL && (!UNITY_WEBGL || UNITY_EDITOR)
+
+using System;
+
+namespace Org.BouncyCastle.Math.EC.Multiplier
+{
+    public class FixedPointCombMultiplier
+        : AbstractECMultiplier
+    {
+        protected override ECPoint MultiplyPositive(ECPoint p, BigInteger k)
+        {
+            ECCurve c = p.Curve;
+            int size = FixedPointUtilities.GetCombSize(c);
+
+            if (k.BitLength > size)
+            {
+                /*
+                 * TODO The comb works best when the scalars are less than the (possibly unknown) order.
+                 * Still, if we want to handle larger scalars, we could allow customization of the comb
+                 * size, or alternatively we could deal with the 'extra' bits either by running the comb
+                 * multiple times as necessary, or by using an alternative multiplier as prelude.
+                 */
+                throw new InvalidOperationException("fixed-point comb doesn't support scalars larger than the curve order");
+            }
+
+            int minWidth = GetWidthForCombSize(size);
+
+            FixedPointPreCompInfo info = FixedPointUtilities.Precompute(p, minWidth);
+            ECPoint[] lookupTable = info.PreComp;
+            int width = info.Width;
+
+            int d = (size + width - 1) / width;
+
+            ECPoint R = c.Infinity;
+
+            int top = d * width - 1;
+            for (int i = 0; i < d; ++i)
+            {
+                int index = 0;
+
+                for (int j = top - i; j >= 0; j -= d)
+                {
+                    index <<= 1;
+                    if (k.TestBit(j))
+                    {
+                        index |= 1;
+                    }
+                }
+
+                R = R.TwicePlus(lookupTable[index]);
+            }
+
+            return R;
+        }
+
+        protected virtual int GetWidthForCombSize(int combSize)
+        {
+            return combSize > 257 ? 6 : 5;
+        }
+    }
+}
+
+#endif