Remove unsafe code from Log2SoftwareFallback

Author: stephentoub

src/libraries/System.Private.CoreLib/src/System/Numerics/BitOperations.cs

@@ -389,12 +389,8 @@ private static int Log2SoftwareFallback(uint value)
             value |= value >> 08;
             value |= value >> 16;
 
-            // uint.MaxValue >> 27 is always in range [0 - 31] so we use Unsafe.AddByteOffset to avoid bounds check
-            return Unsafe.AddByteOffset(
-                // Using deBruijn sequence, k=2, n=5 (2^5=32) : 0b_0000_0111_1100_0100_1010_1100_1101_1101u
-                ref MemoryMarshal.GetReference(Log2DeBruijn),
-                // uint|long -> IntPtr cast on 32-bit platforms does expensive overflow checks not needed here
-                (IntPtr)(int)((value * 0x07C4ACDDu) >> 27));
+            // Using deBruijn sequence, k=2, n=5 (2^5=32) : 0b_0000_0111_1100_0100_1010_1100_1101_1101u
+            return Log2DeBruijn[(int)((value * 0x07C4ACDDu) >> 27)];
         }
 
         /// <summary>Returns the integer (ceiling) log of the specified value, base 2.</summary>