Add HighestSetBit and LowestSetBit utilities

Source/Engine/Core/Utilities.h

@@ -91,12 +91,12 @@ namespace Utilities
     // Returns the amount of set bits in 32-bit integer.
     inline int32 CountBits(uint32 x)
     {
-        // [Reference: https://stackoverflow.com/questions/109023/how-to-count-the-number-of-set-bits-in-a-32-bit-integer]
 #ifdef __GNUC_
         return __builtin_popcount(x);
 #elif _MSC_VER && PLATFORM_SIMD_SSE4_2
         return __popcnt(x);
 #else
+        // [Reference: https://stackoverflow.com/questions/109023/how-to-count-the-number-of-set-bits-in-a-32-bit-integer]
         x = x - ((x >> 1) & 0x55555555);
         x = (x & 0x33333333) + ((x >> 2) & 0x33333333);
         x = (x + (x >> 4)) & 0x0F0F0F0F;
@@ -104,6 +104,52 @@ namespace Utilities
 #endif  
     }
 
+    // Returns the index of the highest set bit. Assumes input is non-zero.
+    inline uint32 HighestSetBit(uint32 x)
+    {
+#if _MSC_VER
+        unsigned long result;
+        _BitScanReverse(&result, x);
+        return result;
+#elif __clang__
+        return 31 - __builtin_clz(x);
+#else
+        // [Reference: http://graphics.stanford.edu/~seander/bithacks.html]
+        static const uint32 MultiplyDeBruijnBitPosition[32] =
+        {
+            0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
+            8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
+        };
+        v |= v >> 1;
+        v |= v >> 2;
+        v |= v >> 4;
+        v |= v >> 8;
+        v |= v >> 16;
+        return MultiplyDeBruijnBitPosition[(uint32)(v * 0x07C4ACDDU) >> 27];
+#endif
+    }
+
+    // Returns the index of the lowest set bit. Assumes input is non-zero.
+    inline uint32 LowestSetBit(uint32 v)
+    {
+#if _MSC_VER
+        unsigned long result;
+        _BitScanForward(&result, v);
+        return result;
+#elif __clang__
+        return __builtin_ctz(v);
+#else
+        // [Reference: http://graphics.stanford.edu/~seander/bithacks.html]
+        static const uint32 MultiplyDeBruijnBitPosition[32] =
+        {
+            0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
+            31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
+        };
+        int32 w = v;
+        return MultiplyDeBruijnBitPosition[(uint32)((w & -w) * 0x077CB531U) >> 27];
+#endif
+    }
+
     // Copy memory region but ignoring address sanatizer checks for memory regions.
     NO_SANITIZE_ADDRESS static void UnsafeMemoryCopy(void* dst, const void* src, uint64 size)
     {