Align divisor pooling with review feedback

PerfectNumbers.Core/Cpu/MersenneNumberDivisorByDivisorCpuTester.cs

@@ -112,7 +112,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
             Dictionary<ulong, MersenneDivisorCycles.FactorCacheEntry>? current = cache;
             if (current is null)
             {
-                current = ThreadStaticPools.TakeMersenneFactorCacheDictionary();
+                current = ThreadStaticPools.RentMersenneFactorCacheDictionary();
                 cache = current;
             }
 
@@ -149,11 +149,6 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
         // }
 
         UInt128 step = (UInt128)prime << 1;
-        if (step == UInt128.Zero)
-        {
-            processedAll = true;
-            return false;
-        }
 
         UInt128 limit = allowedMax;
         UInt128 divisor = step + UInt128.One;

PerfectNumbers.Core/MersenneDivisorCycles.cs

@@ -23,26 +23,6 @@ public class MersenneDivisorCycles
     {
     }
 
-    private static Dictionary<ulong, int> RentFactorCountDictionary()
-    {
-        return ThreadStaticPools.TakeFactorCountDictionary();
-    }
-
-    private static void ReturnFactorCountDictionary(Dictionary<ulong, int> dictionary)
-    {
-        ThreadStaticPools.ReturnFactorCountDictionary(dictionary);
-    }
-
-    private static Dictionary<ulong, int> RentFactorScratchDictionary()
-    {
-        return ThreadStaticPools.TakeFactorScratchDictionary();
-    }
-
-    private static void ReturnFactorScratchDictionary(Dictionary<ulong, int> dictionary)
-    {
-        ThreadStaticPools.ReturnFactorScratchDictionary(dictionary);
-    }
-
     public void LoadFrom(string path)
     {
         EnsureSmallBuffer();
@@ -317,10 +297,6 @@ public class MersenneDivisorCycles
         }
 
         ulong phi = divisor - 1UL;
-        if (phi == 0UL)
-        {
-            return false;
-        }
 
         int twoCount = BitOperations.TrailingZeroCount(phi);
         ulong reducedPhi = phi >> twoCount;
@@ -330,12 +306,8 @@ public class MersenneDivisorCycles
         }
 
         ulong k = reducedPhi / exponent;
-        if (k == 0UL)
-        {
-            return false;
-        }
 
-        Dictionary<ulong, int> factorCounts = RentFactorCountDictionary();
+        Dictionary<ulong, int> factorCounts = ThreadStaticPools.RentFactorCountDictionary();
 
         try
         {
@@ -354,7 +326,7 @@ public class MersenneDivisorCycles
         }
         finally
         {
-            ReturnFactorCountDictionary(factorCounts);
+            ThreadStaticPools.ReturnFactorCountDictionary(factorCounts);
         }
     }
 
@@ -397,7 +369,7 @@ public class MersenneDivisorCycles
             return true;
         }
 
-        Dictionary<ulong, int> scratch = RentFactorScratchDictionary();
+        Dictionary<ulong, int> scratch = ThreadStaticPools.RentFactorScratchDictionary();
 
         try
         {
@@ -430,18 +402,12 @@ public class MersenneDivisorCycles
         }
         finally
         {
-            ReturnFactorScratchDictionary(scratch);
+            ThreadStaticPools.ReturnFactorScratchDictionary(scratch);
         }
     }
 
     private static bool TryFactorIntoCountsInternal(ulong value, Dictionary<ulong, int> counts)
     {
-        // This guard terminates the recursion once Pollard-Rho factorization has reduced the input to 1.
-        if (value <= 1UL)
-        {
-            return true;
-        }
-
         ulong remaining = value;
         uint[] smallPrimes = PrimesGenerator.SmallPrimes;
         ulong[] smallPrimesSquared = PrimesGenerator.SmallPrimesPow2;
@@ -480,7 +446,18 @@ public class MersenneDivisorCycles
         }
 
         ulong quotient = remaining / factor;
-        return TryFactorIntoCountsInternal(factor, counts) && TryFactorIntoCountsInternal(quotient, counts);
+        if (factor > 1UL && !TryFactorIntoCountsInternal(factor, counts))
+        {
+            return false;
+        }
+
+        // Guard the recursive calls to terminate once Pollard-Rho reduces either branch to 1.
+        if (quotient > 1UL && !TryFactorIntoCountsInternal(quotient, counts))
+        {
+            return false;
+        }
+
+        return true;
     }
 
     private static void AddFactor(Dictionary<ulong, int> counts, ulong factor)

PerfectNumbers.Core/ThreadStaticPools.cs

@@ -47,7 +47,7 @@ namespace PerfectNumbers.Core
         private static Dictionary<ulong, MersenneDivisorCycles.FactorCacheEntry>? _mersenneFactorCacheDictionary;
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static Dictionary<ulong, MersenneDivisorCycles.FactorCacheEntry> TakeMersenneFactorCacheDictionary()
+        public static Dictionary<ulong, MersenneDivisorCycles.FactorCacheEntry> RentMersenneFactorCacheDictionary()
         {
             Dictionary<ulong, MersenneDivisorCycles.FactorCacheEntry>? cache = _mersenneFactorCacheDictionary;
             if (cache is null)
@@ -71,7 +71,7 @@ namespace PerfectNumbers.Core
         private static Dictionary<ulong, int>? _factorCountDictionary;
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static Dictionary<ulong, int> TakeFactorCountDictionary()
+        public static Dictionary<ulong, int> RentFactorCountDictionary()
         {
             Dictionary<ulong, int>? dictionary = _factorCountDictionary;
             if (dictionary is null)
@@ -95,7 +95,7 @@ namespace PerfectNumbers.Core
         private static Dictionary<ulong, int>? _factorScratchDictionary;
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static Dictionary<ulong, int> TakeFactorScratchDictionary()
+        public static Dictionary<ulong, int> RentFactorScratchDictionary()
         {
             Dictionary<ulong, int>? dictionary = _factorScratchDictionary;
             if (dictionary is null)