From cd69c08fb43fd5e63823d351eeeeca8a4402486f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Lema=C5=84czyk?= <marek@lemanczyk.eu>
Date: Sat, 11 Oct 2025 20:50:13 +0200
Subject: [PATCH] Remove Montgomery divisor cache

---
 ...MersenneNumberDivisorByDivisorCpuTester.cs | 28 +++++++++++++++++--
 ...MersenneNumberDivisorByDivisorGpuTester.cs |  1 -
 PerfectNumbers.Core/MontgomeryDivisorData.cs  | 28 -------------------
 3 files changed, 26 insertions(+), 31 deletions(-)

diff --git a/PerfectNumbers.Core/Cpu/MersenneNumberDivisorByDivisorCpuTester.cs b/PerfectNumbers.Core/Cpu/MersenneNumberDivisorByDivisorCpuTester.cs
index f5862af..d4d74cd 100644
--- a/PerfectNumbers.Core/Cpu/MersenneNumberDivisorByDivisorCpuTester.cs
+++ b/PerfectNumbers.Core/Cpu/MersenneNumberDivisorByDivisorCpuTester.cs
@@ -192,6 +192,10 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
         Dictionary<ulong, MersenneDivisorCycles.FactorCacheEntry>? factorCache = null;
         DivisorCycleCache cycleCache = DivisorCycleCache.Shared;
 
+        ulong cachedModulus = 0UL;
+        MontgomeryDivisorData cachedDivisorData = default;
+        bool hasCachedDivisorData = false;
+
         byte step10 = (byte)(step % 10UL);
         byte step8 = (byte)(step % 8UL);
         byte step5 = (byte)(step % 5UL);
@@ -222,7 +226,14 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 
             if (admissible && (remainder8 == 1 || remainder8 == 7) && remainder3 != 0 && remainder5 != 0 && remainder7 != 0 && remainder11 != 0)
             {
-                MontgomeryDivisorData divisorData = MontgomeryDivisorDataCache.Get(candidate);
+                if (!hasCachedDivisorData || cachedModulus != candidate)
+                {
+                    cachedDivisorData = MontgomeryDivisorData.FromModulus(candidate);
+                    cachedModulus = candidate;
+                    hasCachedDivisorData = true;
+                }
+
+                MontgomeryDivisorData divisorData = cachedDivisorData;
                 ulong divisorCycle;
 
                 if (candidate <= PerfectNumberConstants.MaxQForDivisorCycles)
@@ -340,6 +351,9 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
     {
         private readonly MersenneNumberDivisorByDivisorCpuTester _owner;
         private bool _disposed;
+        private bool _hasCachedDivisorData;
+        private ulong _cachedDivisor;
+        private MontgomeryDivisorData _cachedDivisorData;
 
         internal DivisorScanSession(MersenneNumberDivisorByDivisorCpuTester owner)
         {
@@ -349,6 +363,9 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
         internal void Reset()
         {
             _disposed = false;
+            _hasCachedDivisorData = false;
+            _cachedDivisor = 0UL;
+            _cachedDivisorData = default;
         }
 
         public void CheckDivisor(ulong divisor, in MontgomeryDivisorData divisorData, ulong divisorCycle, ReadOnlySpan<ulong> primes, Span<byte> hits)
@@ -367,7 +384,14 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
             MontgomeryDivisorData cachedData = divisorData;
             if (cachedData.Modulus != divisor)
             {
-                cachedData = MontgomeryDivisorDataCache.Get(divisor);
+                if (!_hasCachedDivisorData || _cachedDivisor != divisor)
+                {
+                    _cachedDivisorData = MontgomeryDivisorData.FromModulus(divisor);
+                    _cachedDivisor = divisor;
+                    _hasCachedDivisorData = true;
+                }
+
+                cachedData = _cachedDivisorData;
             }
 
             if (divisorCycle == 0UL)
diff --git a/PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs b/PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs
index 2220711..a67ce8f 100644
--- a/PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs
+++ b/PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs
@@ -7,7 +7,6 @@ using System.Numerics;
 using ILGPU;
 using ILGPU.Runtime;
 using MontgomeryDivisorData = PerfectNumbers.Core.MontgomeryDivisorData;
-using MontgomeryDivisorDataCache = PerfectNumbers.Core.MontgomeryDivisorDataCache;
 using CycleRemainderStepper = PerfectNumbers.Core.CycleRemainderStepper;
 
 namespace PerfectNumbers.Core.Gpu;
diff --git a/PerfectNumbers.Core/MontgomeryDivisorData.cs b/PerfectNumbers.Core/MontgomeryDivisorData.cs
index 348471b..187e921 100644
--- a/PerfectNumbers.Core/MontgomeryDivisorData.cs
+++ b/PerfectNumbers.Core/MontgomeryDivisorData.cs
@@ -45,32 +45,4 @@ public readonly struct MontgomeryDivisorData(ulong modulus, ulong nPrime, ulong
             montgomeryTwo,
             montgomeryTwoSquared);
     }
-
-}
-
-internal static class MontgomeryDivisorDataCache
-{
-    [ThreadStatic]
-    private static bool s_hasCachedValue;
-
-    [ThreadStatic]
-    private static ulong s_cachedModulus;
-
-    [ThreadStatic]
-    private static MontgomeryDivisorData s_cachedData;
-
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static MontgomeryDivisorData Get(ulong modulus)
-    {
-        if (s_hasCachedValue && s_cachedModulus == modulus)
-        {
-            return s_cachedData;
-        }
-
-        MontgomeryDivisorData computed = MontgomeryDivisorData.FromModulus(modulus);
-        s_cachedModulus = modulus;
-        s_cachedData = computed;
-        s_hasCachedValue = true;
-        return computed;
-    }
 }