From 627d2e9b141fef98cd2dc1d98e9cfff2e97fe665 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Lema=C5=84czyk?= <marek@lemanczyk.eu>
Date: Sun, 19 Oct 2025 22:49:38 +0200
Subject: [PATCH] Cache composite primality results in PartialFactor

---
 .../PrimeOrderCalculator.Cpu.cs               | 32 ++++++++++++--
 PerfectNumbers.Core/ThreadStaticPools.cs      | 42 +++++++++++++++++++
 2 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/PerfectNumbers.Core/PrimeOrderCalculator.Cpu.cs b/PerfectNumbers.Core/PrimeOrderCalculator.Cpu.cs
index 536eebd..835b80d 100644
--- a/PerfectNumbers.Core/PrimeOrderCalculator.Cpu.cs
+++ b/PerfectNumbers.Core/PrimeOrderCalculator.Cpu.cs
@@ -757,6 +757,27 @@ internal static partial class PrimeOrderCalculator
 		Stack<ulong>? compositeStack = null;
 		PartialFactorResult result;
 
+		Dictionary<ulong, bool>? localPrimalityCache = null;
+
+		bool EvaluatePrimality(ulong candidate)
+		{
+			Dictionary<ulong, bool>? cache = localPrimalityCache;
+			if (cache is not null && cache.TryGetValue(candidate, out bool cachedValue))
+			{
+				return cachedValue;
+			}
+
+			bool computed = GetOrComputePrimality(candidate);
+			if (!computed)
+			{
+				cache ??= ThreadStaticPools.RentUlongBoolDictionary(4);
+				cache[candidate] = false;
+				localPrimalityCache = cache;
+			}
+
+			return computed;
+		}
+
 		if (!gpuFactored)
 		{
 			// We don't need to worry about leftovers, because we always use indexes within the calculated counts
@@ -821,7 +842,7 @@ internal static partial class PrimeOrderCalculator
 					// 	continue;
 					// }
 
-					bool isPrime = GetOrComputePrimality(composite);
+					bool isPrime = EvaluatePrimality(composite);
 
 					if (isPrime)
 					{
@@ -868,7 +889,7 @@ internal static partial class PrimeOrderCalculator
 				continue;
 			}
 
-			bool isPrime = GetOrComputePrimality(composite);
+			bool isPrime = EvaluatePrimality(composite);
 
 			if (isPrime)
 			{
@@ -894,7 +915,7 @@ internal static partial class PrimeOrderCalculator
 		}
 		else
 		{
-			cofactorIsPrime = GetOrComputePrimality(cofactor);
+			cofactorIsPrime = EvaluatePrimality(cofactor);
 		}
 
 		ArrayPool<FactorEntry> pool = ThreadStaticPools.FactorEntryPool;
@@ -968,6 +989,11 @@ internal static partial class PrimeOrderCalculator
 		// ThreadStaticPools.UlongPool.Return(primeSlotsArray);
 		// ThreadStaticPools.IntPool.Return(exponentSlotsArray);
 
+		if (localPrimalityCache is not null)
+		{
+			ThreadStaticPools.ReturnUlongBoolDictionary(localPrimalityCache);
+		}
+
 		if (counts is not null)
 		{
 			ThreadStaticPools.ReturnUlongIntDictionary(counts);
diff --git a/PerfectNumbers.Core/ThreadStaticPools.cs b/PerfectNumbers.Core/ThreadStaticPools.cs
index 33a9de2..0a35395 100644
--- a/PerfectNumbers.Core/ThreadStaticPools.cs
+++ b/PerfectNumbers.Core/ThreadStaticPools.cs
@@ -278,6 +278,48 @@ namespace PerfectNumbers.Core
             pool.Add(dictionary);
         }
 
+        [ThreadStatic]
+        private static List<Dictionary<ulong, bool>>? _ulongBoolDictionaryPool;
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Dictionary<ulong, bool> RentUlongBoolDictionary(int capacityHint)
+        {
+            List<Dictionary<ulong, bool>>? pool = _ulongBoolDictionaryPool;
+            if (pool is not null && pool.Count > 0)
+            {
+                int lastIndex = pool.Count - 1;
+                Dictionary<ulong, bool> dictionary = pool[lastIndex];
+                pool.RemoveAt(lastIndex);
+                if (dictionary.Count > 0)
+                {
+                    dictionary.Clear();
+                }
+
+                if (dictionary.Count < capacityHint)
+                {
+                    dictionary.EnsureCapacity(capacityHint);
+                }
+
+                return dictionary;
+            }
+
+            return new Dictionary<ulong, bool>(capacityHint);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void ReturnUlongBoolDictionary(Dictionary<ulong, bool> dictionary)
+        {
+            List<Dictionary<ulong, bool>>? pool = _ulongBoolDictionaryPool;
+            if (pool is null)
+            {
+                pool = new List<Dictionary<ulong, bool>>(4);
+                _ulongBoolDictionaryPool = pool;
+            }
+
+            dictionary.Clear();
+            pool.Add(dictionary);
+        }
+
         [ThreadStatic]
         private static Dictionary<ulong, MersenneDivisorCycles.FactorCacheEntry>? _mersenneFactorCacheDictionary;