Fix for old HarmonyX not having MonoMod backports.

ModTek/Features/Logging/FormattingHelpers.cs

@@ -1,4 +1,3 @@
-using System.Numerics;
 using System.Runtime.CompilerServices;
 
 namespace ModTek.Features.Logging;
@@ -22,7 +21,7 @@ internal static unsafe void WriteDigits(byte* positionPtr, long value, int digit
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     internal static int CountDigits(uint value)
     {
-        var tableValue = s_countDigitsTable[(uint)BitOperations.Log2(value)];
+        var tableValue = s_countDigitsTable[Log2(value)];
         return (int)((value + tableValue) >> 32);
     }
     // Algorithm based on https://lemire.me/blog/2021/06/03/computing-the-number-of-digits-of-an-integer-even-faster.
@@ -61,4 +60,41 @@ internal static int CountDigits(uint value)
         42949672960,
         42949672960,
     ];
+
+    // following from MonoMod.Backports
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static int Log2(uint value)
+    {
+        // The 0->0 contract is fulfilled by setting the LSB to 1.
+        // Log(1) is 0, and setting the LSB for values > 1 does not change the log2 result.
+        value |= 1;
+
+        // Fallback contract is 0->0
+        return Log2SoftwareFallback(value);
+    }
+    private static unsafe int Log2SoftwareFallback(uint value)
+    {
+        // No AggressiveInlining due to large method size
+        // Has conventional contract 0->0 (Log(0) is undefined)
+
+        // Fill trailing zeros with ones, eg 00010010 becomes 00011111
+        value |= value >> 01;
+        value |= value >> 02;
+        value |= value >> 04;
+        value |= value >> 08;
+        value |= value >> 16;
+
+        var offset = (value * 0x07C4ACDDu) >> 27;
+        fixed (byte* ptr = s_log2DeBruijn)
+        {
+            return ptr[offset];
+        }
+    }
+    private static readonly byte[] s_log2DeBruijn =
+    [
+        00, 09, 01, 10, 13, 21, 02, 29,
+        11, 14, 16, 18, 22, 25, 03, 30,
+        08, 12, 20, 28, 15, 17, 24, 07,
+        19, 27, 23, 06, 26, 05, 04, 31
+    ];
 }