From 75586d07b824cc94d62cafbc5b6626edf9bb5584 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Lema=C5=84czyk?= <marek@lemanczyk.eu>
Date: Sat, 4 Oct 2025 22:40:18 +0200
Subject: [PATCH] Relax ulong multiply-shift guards and refresh tests

---
 .../ULongExtensionsMultiplyShiftTests.cs      | 23 -----------------
 PerfectNumbers.Core/ULongExtensions.cs        | 25 -------------------
 todo.txt                                      |  2 ++
 3 files changed, 2 insertions(+), 48 deletions(-)

diff --git a/PerfectNumbers.Core.Tests/ULongExtensionsMultiplyShiftTests.cs b/PerfectNumbers.Core.Tests/ULongExtensionsMultiplyShiftTests.cs
index d755e1b..5267de5 100644
--- a/PerfectNumbers.Core.Tests/ULongExtensionsMultiplyShiftTests.cs
+++ b/PerfectNumbers.Core.Tests/ULongExtensionsMultiplyShiftTests.cs
@@ -39,29 +39,6 @@ public class ULongExtensionsMultiplyShiftTests
         result.Should().Be((ulong)expected);
     }
 
-    [Fact]
-    public void MultiplyShiftRightShiftFirst_returns_zero_when_shift_is_large()
-    {
-        ULongExtensions.MultiplyShiftRightShiftFirst(ulong.MaxValue, 123UL, 64).Should().Be(0UL);
-    }
 
-    [Theory]
-    [InlineData(0UL, ulong.MaxValue, -1)]
-    [InlineData(1UL, 1UL, -3)]
-    public void MultiplyShiftRight_throws_when_shift_is_negative(ulong value, ulong multiplier, int shift)
-    {
-        Action act = () => ULongExtensions.MultiplyShiftRight(value, multiplier, shift);
 
-        act.Should().Throw<ArgumentOutOfRangeException>();
-    }
-
-    [Theory]
-    [InlineData(0UL, ulong.MaxValue, -1)]
-    [InlineData(1UL, 1UL, -3)]
-    public void MultiplyShiftRightShiftFirst_throws_when_shift_is_negative(ulong value, ulong multiplier, int shift)
-    {
-        Action act = () => ULongExtensions.MultiplyShiftRightShiftFirst(value, multiplier, shift);
-
-        act.Should().Throw<ArgumentOutOfRangeException>();
-    }
 }
diff --git a/PerfectNumbers.Core/ULongExtensions.cs b/PerfectNumbers.Core/ULongExtensions.cs
index 58f2802..ab3b25a 100644
--- a/PerfectNumbers.Core/ULongExtensions.cs
+++ b/PerfectNumbers.Core/ULongExtensions.cs
@@ -59,22 +59,12 @@ public static class ULongExtensions
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static int GetBitLength(this ulong value)
     {
-        if (value == 0UL)
-        {
-            return 0;
-        }
-
         return 64 - BitOperations.LeadingZeroCount(value);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static ulong MultiplyShiftRight(ulong value, ulong multiplier, int shift)
     {
-        if (shift < 0)
-        {
-            throw new ArgumentOutOfRangeException(nameof(shift), "Shift must be non-negative.");
-        }
-
         UInt128 product = (UInt128)value * multiplier;
         return (ulong)(product >> shift);
     }
@@ -82,21 +72,6 @@ public static class ULongExtensions
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static ulong MultiplyShiftRightShiftFirst(ulong value, ulong multiplier, int shift)
     {
-        if (shift < 0)
-        {
-            throw new ArgumentOutOfRangeException(nameof(shift), "Shift must be non-negative.");
-        }
-
-        if (shift == 0)
-        {
-            return MultiplyShiftRight(value, multiplier, 0);
-        }
-
-        if (shift >= 64)
-        {
-            return 0UL;
-        }
-
         ulong high = value >> shift;
         ulong mask = (1UL << shift) - 1UL;
         ulong low = value & mask;
diff --git a/todo.txt b/todo.txt
index 19278dc..2ef5cb1 100644
--- a/todo.txt
+++ b/todo.txt
@@ -1 +1,3 @@
+- Inline the PrimeOrderGpuHeuristics capability checks at each call site and delete the temporary SupportsPrime/SupportsExponent helpers once the overflow gating is stable.
+- Swap PrimeOrderGpuHeuristics.Pow2ModCpu for the existing Pow2MontgomeryModWindowed helper and plan the same windowed ladder for the GPU kernel implementation.
 - 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.