[hbelusca] 64680: [FAST486] Use a more performant CountLeadingZeros64 version from Timo (tested by Thomas), and disable the MSVC-specific one until you find a version that works, and is supported f...

Author: hbelusca
Date: Sat Oct 11 18:35:23 2014
New Revision: 64680

URL: http://svn.reactos.org/svn/reactos?rev=64680&view=rev
Log:
[FAST486]
Use a more performant CountLeadingZeros64 version from Timo (tested by Thomas), and disable the MSVC-specific one until you find a version that works, and is supported for any CPU.

Modified:
    trunk/reactos/lib/fast486/common.inl

Modified: trunk/reactos/lib/fast486/common.inl
URL: http://svn.reactos.org/svn/reactos/trunk/reactos/lib/fast486/common.inl?rev=...
==============================================================================
--- trunk/reactos/lib/fast486/common.inl	[iso-8859-1] (original)
+++ trunk/reactos/lib/fast486/common.inl	[iso-8859-1] Sat Oct 11 18:35:23 2014
@@ -26,24 +26,27 @@

#if defined (__GNUC__)
     #define CountLeadingZeros64(x) __builtin_clzll(x)
+
+#if 0
 #elif (_MSC_VER >= 1500) && defined(_WIN64)
     #define CountLeadingZeros64(x) __lzcnt64(x)
 #elif (_MSC_VER >= 1500)
     #define CountLeadingZeros64(x) ((x) > 0xFFFFFFFFULL) ? __lzcnt((x) >> 32) \
                                                          : (__lzcnt(x) + 32)
+#endif
+
 #else
-    static FORCEINLINE
-    ULONG CountLeadingZeros64(ULONGLONG Value)
+    FORCEINLINE
+    ULONG
+    CountLeadingZeros64(ULONGLONG Value)
     {
         ULONG Count = 0;
-        ULONGLONG Mask = 1ULL << 63;
-
-        while (!(Value & Mask) && Mask)
+        Value = ~Value;
+        while ((LONGLONG)Value < 0)
         {
             Count++;
-            Mask >>= 1;
-        }
-
+            Value <<= 1;
+        }
         return Count;
     }
 #endif