MulAdd optimized

EvenPerfectBitScanner.Benchmarks/MutableUInt128MultiplyAddBenchmarks.cs

@@ -27,34 +27,41 @@ public class MutableUInt128MultiplyAddBenchmarks
         return ((UInt128)high << 64) | low;
     }
 
-    /// <summary>
-    /// Baseline MultiplyAdd implementation that chains Multiply and Add; measured 4.59 ns with mixed operands,
-    /// 4.68 ns when both limbs and inputs are near their maxima, and 4.49 ns with tiny operands.
-    /// </summary>
-    /// <remarks>
-    /// Observed means: MixedOperands 4.593 ns, NearMaxOperands 4.681 ns, TinyOperands 4.487 ns.
-    /// </remarks>
-    [Benchmark(Baseline = true)]
-    public UInt128 MultiplyAddChained()
-    {
-        MutableUInt128 value = new(Input.InitialValue);
-        value.MultiplyAdd(Input.Multiplier, Input.Addend);
-        return value.ToUInt128();
-    }
+	private static void MultiplyAdd(ref MutableUInt128 source, ulong multiplier, ulong addend)
+	{
+		source.Mul(multiplier);
+		source.Add(addend);
+	}
+
+	/// <summary>
+	/// Baseline MultiplyAdd implementation that chains Multiply and Add; measured 3.370 ns with mixed operands,
+	/// 3.361 ns when both limbs and inputs are near their maxima, and 3.368 ns with tiny operands.
+	/// </summary>
+	/// <remarks>
+	/// Observed means: MixedOperands 3.370 ns, NearMaxOperands 3.361 ns, TinyOperands 3.368 ns.
+	/// </remarks>
+	[Benchmark(Baseline = true)]
+	public MutableUInt128 MultiplyAddChained()
+	{
+		MutableUInt128 value = new(Input.InitialValue);
+		MultiplyAdd(ref value, Input.Multiplier, Input.Addend);
+		return value;
+	}
 
     /// <summary>
-    /// Fully inlined MultiplyAdd implementation that kept all arithmetic inside the method; landed at 4.11 ns on mixed operands,
-    /// 4.25 ns on near-max inputs, and 4.27 ns on tiny operands.
+    /// Fully inlined MultiplyAdd implementation that kept all arithmetic inside the method; landed at 3.175 ns on mixed operands,
+    /// 3.177 ns on near-max inputs, and 3.178 ns on tiny operands.
     /// </summary>
     /// <remarks>
-    /// Observed means: MixedOperands 4.109 ns, NearMaxOperands 4.253 ns, TinyOperands 4.271 ns.
+    /// Observed means: MixedOperands 3.175 ns, NearMaxOperands 3.177 ns, TinyOperands 3.178 ns.
+	/// Status: Implemented
     /// </remarks>
     [Benchmark]
-    public UInt128 MultiplyAddFullyInlined()
+    public MutableUInt128 MultiplyAddFullyInlined()
     {
         MutableUInt128 value = new(Input.InitialValue);
-        value.MultiplyAddInline(Input.Multiplier, Input.Addend);
-        return value.ToUInt128();
+        value.MulAdd(Input.Multiplier, Input.Addend);
+        return value;
     }
 
     public readonly record struct MultiplyAddInput(UInt128 InitialValue, ulong Multiplier, ulong Addend, string Name)