diff --git a/ArcFormats/ArcCommon.cs b/ArcFormats/ArcCommon.cs
index 12a0f818..6c6fba08 100644
--- a/ArcFormats/ArcCommon.cs
+++ b/ArcFormats/ArcCommon.cs
@@ -405,6 +405,30 @@ namespace GameRes.Formats
         }
     }
 
+    public static class MMX
+    {
+        public static ulong PAddW (ulong x, ulong y)
+        {
+            ulong mask = 0xffff;
+            ulong r = ((x & mask) + (y & mask)) & mask;
+            mask <<= 16;
+            r |= ((x & mask) + (y & mask)) & mask;
+            mask <<= 16;
+            r |= ((x & mask) + (y & mask)) & mask;
+            mask <<= 16;
+            r |= ((x & mask) + (y & mask)) & mask;
+            return r;
+        }
+
+        public static ulong PAddD (ulong x, ulong y)
+        {
+            ulong mask = 0xffffffff;
+            ulong r = ((x & mask) + (y & mask)) & mask;
+            mask <<= 32;
+            return r | ((x & mask) + (y & mask)) & mask;
+        }
+    }
+
     public static class Dump
     {
         public static string DirectoryName = Environment.GetFolderPath (Environment.SpecialFolder.UserProfile);
diff --git a/ArcFormats/ArcNEKO.cs b/ArcFormats/ArcNEKO.cs
index d9bc1ebf..4df32b19 100644
--- a/ArcFormats/ArcNEKO.cs
+++ b/ArcFormats/ArcNEKO.cs
@@ -201,7 +201,7 @@ namespace GameRes.Formats.Neko
                     while (first != last)
                     {
                         ulong v = *first ^ key;
-                        key = _m_paddw (key, v);
+                        key = MMX.PAddW (key, v);
                         *first++ = v;
                     }
                     return key;
@@ -209,19 +209,6 @@ namespace GameRes.Formats.Neko
             }
         }
 
-        static ulong _m_paddw (ulong x, ulong y)
-        {
-            ulong mask = 0xffff;
-            ulong r = ((x & mask) + (y & mask)) & mask;
-            mask <<= 16;
-            r |= ((x & mask) + (y & mask)) & mask;
-            mask <<= 16;
-            r |= ((x & mask) + (y & mask)) & mask;
-            mask <<= 16;
-            r |= ((x & mask) + (y & mask)) & mask;
-            return r;
-        }
-
         static byte[] ReadBlock (ArcView.Frame view, uint id, long offset, out int length)
         {
             uint hash = view.ReadUInt32 (offset);