ECC: Binary field perf. opt.

1 files changed, 17 insertions, 0 deletions

diff --git a/crypto/src/math/raw/Interleave.cs b/crypto/src/math/raw/Interleave.cs
index 591ba3f15..49d3768d7 100644
--- a/crypto/src/math/raw/Interleave.cs
+++ b/crypto/src/math/raw/Interleave.cs
@@ -93,6 +93,23 @@ namespace Org.BouncyCastle.Math.Raw
             z[zOff + 1] = (x >> 1) & M64;
         }
 
+        internal static void Expand64To128(ulong[] xs, int xsOff, int xsLen, ulong[] zs, int zsOff)
+        {
+            for (int i = 0; i < xsLen; ++i)
+            {
+                // "shuffle" low half to even bits and high half to odd bits
+                ulong x = xs[xsOff + i], t;
+                t = (x ^ (x >> 16)) & 0x00000000FFFF0000UL; x ^= (t ^ (t << 16));
+                t = (x ^ (x >>  8)) & 0x0000FF000000FF00UL; x ^= (t ^ (t <<  8));
+                t = (x ^ (x >>  4)) & 0x00F000F000F000F0UL; x ^= (t ^ (t <<  4));
+                t = (x ^ (x >>  2)) & 0x0C0C0C0C0C0C0C0CUL; x ^= (t ^ (t <<  2));
+                t = (x ^ (x >>  1)) & 0x2222222222222222UL; x ^= (t ^ (t <<  1));
+
+                zs[zsOff++] = (x     ) & M64;
+                zs[zsOff++] = (x >> 1) & M64;
+            }
+        }
+
         internal static void Expand64To128Rev(ulong x, ulong[] z, int zOff)
         {
             // "shuffle" low half to even bits and high half to odd bits