TODO moved to the code to concentrate on mirroring heuristic cycle algorithm on GPU

PerfectNumbers.Core/UInt128Extensions.cs

@@ -67,6 +67,7 @@ public static class UInt128Extensions
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static UInt128 Pow2MontgomeryModWindowed(this UInt128 exponent, UInt128 modulus)
     {
+        // TODO: Prototype a UInt128-native Pow2MontgomeryModWindowed path that matches the GPU implementation once a faster modular multiplication helper is available, so we can revisit removing the GPU struct dependency without regressing benchmarks.
         if (modulus == UInt128.One)
         {
             return UInt128.Zero;
@@ -139,10 +140,7 @@ public static class UInt128Extensions
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private static bool ShouldUseSingleBit(UInt128 exponent)
+    private static bool ShouldUseSingleBit(UInt128 exponent) => (exponent >> 64) == UInt128.Zero && (ulong)exponent <= Pow2WindowFallbackThreshold;
-    {
-        return (exponent >> 64) == UInt128.Zero && (ulong)exponent <= Pow2WindowFallbackThreshold;
-    }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private static int GetWindowSize(int bitLength)

todo.txt

@@ -1,3 +1,2 @@
-- Prototype a UInt128-native Pow2MontgomeryModWindowed path that matches the GPU implementation once a faster modular multiplication helper is available, so we can revisit removing the GPU struct dependency without regressing benchmarks.
 - Mirror the complete CPU heuristic cycle algorithm on the GPU path so both implementations stay aligned.
 - Extend the GPU numeric type probe to cover proposed custom types such as GpuUInt256 and GpuUInt512 once their definitions are available so we can plan the wide-order heuristics on the device.