Add divisor-mode detailed check coverage for factors

EvenPerfectBitScanner.Tests/ProgramTests.cs

@@ -142,6 +142,95 @@ public class ProgramTests
         }
     }
 
+    [Fact]
+    public void Divisor_mode_sets_detailedCheck_when_divisor_is_found()
+    {
+        var useDivisorField = typeof(Program).GetField("_useDivisor", BindingFlags.NonPublic | BindingFlags.Static)!;
+        var divisorField = typeof(Program).GetField("_divisor", BindingFlags.NonPublic | BindingFlags.Static)!;
+        var testerField = typeof(Program).GetField("_divisorTester", BindingFlags.NonPublic | BindingFlags.Static)!;
+        var candidatesField = typeof(MersenneNumberDivisorGpuTester).GetField("_divisorCandidates", BindingFlags.NonPublic | BindingFlags.Static)!;
+        var primeField = typeof(Program).GetField("PrimeTesters", BindingFlags.NonPublic | BindingFlags.Static)!;
+        var residueField = typeof(Program).GetField("PResidue", BindingFlags.NonPublic | BindingFlags.Static)!;
+        var forceCpuProp = typeof(GpuContextPool).GetProperty("ForceCpu");
+
+        useDivisorField.SetValue(null, true);
+        divisorField.SetValue(null, UInt128.Zero);
+        testerField.SetValue(null, new MersenneNumberDivisorGpuTester());
+        primeField.SetValue(null, new ThreadLocal<PrimeTester>(() => new PrimeTester(), trackAllValues: true));
+        residueField.SetValue(null, new ThreadLocal<ModResidueTracker>(() => new ModResidueTracker(ResidueModel.Identity, 2UL, true), trackAllValues: true));
+        candidatesField.SetValue(null, new (ulong, uint)[] { (23UL, 11U) });
+        forceCpuProp!.SetValue(null, true);
+
+        try
+        {
+            Program.IsEvenPerfectCandidate(11UL, 32UL, out bool searched, out bool detailedCheck).Should().BeFalse();
+            searched.Should().BeTrue();
+            detailedCheck.Should().BeTrue();
+        }
+        finally
+        {
+            useDivisorField.SetValue(null, false);
+            testerField.SetValue(null, null);
+            candidatesField.SetValue(null, null);
+            primeField.SetValue(null, null);
+            residueField.SetValue(null, null);
+            forceCpuProp!.SetValue(null, false);
+        }
+    }
+
+    [Fact]
+    public void Residue_mode_sets_detailedCheck_based_on_exhaustion()
+    {
+        var useDivisorField = typeof(Program).GetField("_useDivisor", BindingFlags.NonPublic | BindingFlags.Static)!;
+        var residueModeField = typeof(Program).GetField("_useResidueMode", BindingFlags.NonPublic | BindingFlags.Static)!;
+        var mersenneField = typeof(Program).GetField("MersenneTesters", BindingFlags.NonPublic | BindingFlags.Static)!;
+        var primeField = typeof(Program).GetField("PrimeTesters", BindingFlags.NonPublic | BindingFlags.Static)!;
+        var residueField = typeof(Program).GetField("PResidue", BindingFlags.NonPublic | BindingFlags.Static)!;
+        var forceCpuProp = typeof(GpuContextPool).GetProperty("ForceCpu");
+
+        const ulong exponent = 7UL;
+
+        useDivisorField.SetValue(null, false);
+        residueModeField.SetValue(null, true);
+        primeField.SetValue(null, new ThreadLocal<PrimeTester>(() => new PrimeTester(), trackAllValues: true));
+        residueField.SetValue(null, new ThreadLocal<ModResidueTracker>(() => new ModResidueTracker(ResidueModel.Identity, exponent, true), trackAllValues: true));
+        forceCpuProp!.SetValue(null, true);
+
+        try
+        {
+            mersenneField.SetValue(null, new ThreadLocal<MersenneNumberTester>(() => new MersenneNumberTester(
+                    useGpuScan: false,
+                    useGpuOrder: false,
+                    useResidue: true,
+                    maxK: 0UL,
+                    residueDivisorSets: 0UL), trackAllValues: true));
+
+            Program.IsEvenPerfectCandidate(exponent, 0UL, out bool searched, out bool detailedCheck).Should().BeTrue();
+            searched.Should().BeTrue();
+            detailedCheck.Should().BeFalse();
+
+            mersenneField.SetValue(null, new ThreadLocal<MersenneNumberTester>(() => new MersenneNumberTester(
+                    useGpuScan: false,
+                    useGpuOrder: false,
+                    useResidue: true,
+                    maxK: 4UL,
+                    residueDivisorSets: 2UL), trackAllValues: true));
+
+            Program.IsEvenPerfectCandidate(exponent, 0UL, out searched, out detailedCheck).Should().BeTrue();
+            searched.Should().BeTrue();
+            detailedCheck.Should().BeTrue();
+        }
+        finally
+        {
+            mersenneField.SetValue(null, null);
+            primeField.SetValue(null, null);
+            residueField.SetValue(null, null);
+            residueModeField.SetValue(null, false);
+            forceCpuProp!.SetValue(null, false);
+            useDivisorField.SetValue(null, false);
+        }
+    }
+
     [Fact]
     public void Divisor_mode_accepts_large_search_limit()
     {
@@ -223,7 +312,7 @@ public class ProgramTests
         var forceCpuProp = typeof(GpuContextPool).GetProperty("ForceCpu");
 
         useDivisorField.SetValue(null, false);
-        mersenneField.SetValue(null, new ThreadLocal<MersenneNumberTester>(() => new MersenneNumberTester(useIncremental: true, useResidue: true, maxK: 1_000UL), trackAllValues: true));
+        mersenneField.SetValue(null, new ThreadLocal<MersenneNumberTester>(() => new MersenneNumberTester(useIncremental: true, useResidue: true, maxK: 1_000UL, residueDivisorSets: 1UL), trackAllValues: true));
         primeField.SetValue(null, new ThreadLocal<PrimeTester>(() => new PrimeTester(), trackAllValues: true));
         residueField.SetValue(null, new ThreadLocal<ModResidueTracker>(() => new ModResidueTracker(ResidueModel.Identity, 2UL, true), trackAllValues: true));
         forceCpuProp!.SetValue(null, false);
@@ -232,7 +321,7 @@ public class ProgramTests
         {
             Program.IsEvenPerfectCandidate(29UL, 0UL, out bool searched, out bool detailed).Should().BeFalse();
             searched.Should().BeTrue();
-            detailed.Should().BeFalse();
+            detailed.Should().BeTrue();
 
             Program.IsEvenPerfectCandidate(31UL, 0UL, out searched, out detailed).Should().BeTrue();
             searched.Should().BeTrue();

EvenPerfectBitScanner/Program.cs

@@ -447,7 +447,8 @@ internal static class Program
                                                                         useGpuScan: mersenneOnGpu,
                                                                         useGpuOrder: orderOnGpu,
                                                                         useResidue: useResidue,
-									maxK: residueKMax);
+                                                                        maxK: residueKMax,
+                                                                        residueDivisorSets: divisorCyclesSearchLimit);
 				if (!useLucas)
 				{
 					tester.WarmUpOrders(currentP, _orderWarmupLimitOverride ?? 5_000_000UL);
@@ -731,7 +732,7 @@ internal static class Program
 		Console.WriteLine("  --divisor-cycles-device=cpu|gpu  device for cycles generation (default gpu)");
 		Console.WriteLine("  --divisor-cycles-batch-size=<value> batch size for cycles generation (default 512)");
 		Console.WriteLine("  --divisor-cycles-continue  continue divisor cycles generation");
-		Console.WriteLine("  --divisor-cycles-limit=<value> cycle search iterations when --mersenne=divisor");
+            Console.WriteLine("  --divisor-cycles-limit=<value> cycle search iterations when --mersenne=divisor or residue");
 
 		Console.WriteLine("  --use-order            test primality via q order");
 		Console.WriteLine("  --workaround-mod       avoid '%' operator on the GPU");
@@ -1083,8 +1084,9 @@ internal static class Program
                         return _divisorTester!.IsPrime(p, _divisor, divisorCyclesSearchLimit, out detailedCheck);
                 }
 
-		detailedCheck = MersenneTesters.Value!.IsMersennePrime(p);
+                bool mersennePrime = MersenneTesters.Value!.IsMersennePrime(p, out bool residueExhausted);
-		return detailedCheck;
+                detailedCheck = residueExhausted;
+                return mersennePrime;
         }
 
 	// Use ModResidueTracker with a small set of primes to pre-filter composite p.

PerfectNumbers.Core.Tests/MersenneNumberResidueCpuTesterTests.cs

@@ -24,8 +24,18 @@ public class MersenneNumberResidueCpuTesterTests
     private static void RunCase(MersenneNumberResidueCpuTester tester, ulong exponent, ulong maxK, bool expectedPrime)
     {
         bool isPrime = true;
-        tester.Scan(exponent, (UInt128)exponent << 1, LastDigitIsSeven(exponent), (UInt128)maxK, ref isPrime);
+        bool exhausted = false;
+        tester.Scan(
+                exponent,
+                (UInt128)exponent << 1,
+                LastDigitIsSeven(exponent),
+                (UInt128)maxK,
+                1UL,
+                (UInt128)maxK,
+                ref isPrime,
+                ref exhausted);
         isPrime.Should().Be(expectedPrime);
+        exhausted.Should().BeTrue();
     }
 }
 

PerfectNumbers.Core.Tests/MersenneNumberResidueGpuTesterTests.cs

@@ -27,8 +27,18 @@ public class MersenneNumberResidueGpuTesterTests
     private static void RunCase(MersenneNumberResidueGpuTester tester, ulong exponent, ulong maxK, bool expectedPrime)
     {
         bool isPrime = true;
-        tester.Scan(exponent, (UInt128)exponent << 1, LastDigitIsSeven(exponent), (UInt128)maxK, ref isPrime);
+        bool exhausted = false;
+        tester.Scan(
+                exponent,
+                (UInt128)exponent << 1,
+                LastDigitIsSeven(exponent),
+                (UInt128)maxK,
+                1UL,
+                (UInt128)maxK,
+                ref isPrime,
+                ref exhausted);
         isPrime.Should().Be(expectedPrime);
+        exhausted.Should().BeTrue();
     }
 }
 

PerfectNumbers.Core/Cpu/MersenneNumberResidueCpuTester.cs

@@ -5,8 +5,21 @@ public class MersenneNumberResidueCpuTester
 	private ModResidueTracker? _mersenneResidueTracker;
 
 	// CPU residue variant using tracker + unrolled residue updates (no method calls in the loop).
-	public void Scan(ulong exponent, UInt128 twoP, bool lastIsSeven, UInt128 maxK, ref bool isPrime)
+    public void Scan(
+            ulong exponent,
+            UInt128 twoP,
+            bool lastIsSeven,
+            UInt128 perSetLimit,
+            ulong setCount,
+            UInt128 overallLimit,
+            ref bool isPrime,
+            ref bool divisorsExhausted)
     {
+            if (setCount == 0UL || perSetLimit == UInt128.Zero || overallLimit == UInt128.Zero)
+            {
+                    return;
+            }
+
                 // Initialize/update Mersenne residue tracker and start a merge walk for ascending q divisors
 
                 _mersenneResidueTracker ??= new(ResidueModel.Mersenne);
@@ -14,12 +27,6 @@ public class MersenneNumberResidueCpuTester
                 // and avoid per-q powmods when possible when scanning lanes.
                 _mersenneResidueTracker.BeginMerge(exponent);
 
-		// Start at k = 1: q0 = 2*p*1 + 1
-		UInt128 k = UInt128.One;
-		UInt128 q = twoP + UInt128.One;
-		// Current residues
-		q.Mod10_8_5_3(out ulong r10, out ulong r8, out ulong r5, out ulong r3);
-		// Step residues for q += 2*p
                 ulong step10 = (ulong)(twoP % 10UL) % 10UL;
                 ulong step8 = (ulong)(twoP % 8UL);
                 ulong step3 = (ulong)(twoP % 3UL);
@@ -43,18 +50,39 @@ public class MersenneNumberResidueCpuTester
 
                 bool localIsPrime, isDivider;
 
-		maxK++;
-
                 ModResidueTracker tracker = _mersenneResidueTracker!;
-		while (k < maxK && (localIsPrime = Volatile.Read(ref isPrime)))
+                UInt128 limitInclusive = overallLimit + UInt128.One;
+                for (ulong setIndex = 0; setIndex < setCount && Volatile.Read(ref isPrime); setIndex++)
                 {
-			remaining = maxK - k;
+                        UInt128 setOffset = perSetLimit * (UInt128)setIndex;
+                        UInt128 k = setOffset + UInt128.One;
+                        if (k >= limitInclusive)
+                        {
+                                break;
+                        }
+
+                        UInt128 setLimitExclusive = setOffset + perSetLimit + UInt128.One;
+                        if (setLimitExclusive > limitInclusive)
+                        {
+                                setLimitExclusive = limitInclusive;
+                        }
+
+                        UInt128 q = twoP * k + UInt128.One;
+                        q.Mod10_8_5_3(out ulong r10, out ulong r8, out ulong r5, out ulong r3);
+
+                        while (k < setLimitExclusive && (localIsPrime = Volatile.Read(ref isPrime)))
+                        {
+                                remaining = setLimitExclusive - k;
                                 if (remaining == UInt128.Zero)
                                 {
                                         break;
                                 }
 
                                 lanes = remaining > 4UL ? 4 : (int)remaining;
+                                if (lanes <= 0)
+                                {
+                                        break;
+                                }
 
                                 // Compute lane residues incrementally (avoid multiplications, minimize reductions)
                                 // r10
@@ -85,7 +113,6 @@ public class MersenneNumberResidueCpuTester
                                 if (lanes >= 1 &&
                                         (((allowMask >> (int)r10_0) & 1) != 0 && (r8_0 == 1UL || r8_0 == 7UL) && r3_0 != 0UL && r5_0 != 0UL))
                                 {
-				// cycle-based quick check for small q
                                         if (localIsPrime && tracker.MergeOrAppend(exponent, q, out isDivider) && isDivider &&
                                                 (q <= ulong.MaxValue ? ((ulong)q).IsPrimeCandidate() : q.IsPrimeCandidate()))
                                         {
@@ -135,10 +162,12 @@ public class MersenneNumberResidueCpuTester
                                 if (!localIsPrime)
                                 {
                                         Volatile.Write(ref isPrime, false);
+                                        divisorsExhausted = true;
                                         return;
                                 }
                                 else if (!Volatile.Read(ref isPrime))
                                 {
+                                        divisorsExhausted = true;
                                         return;
                                 }
 
@@ -162,8 +191,9 @@ public class MersenneNumberResidueCpuTester
                                         r3 += step3; if (r3 >= 3UL) r3 -= 3UL;
                                         r5 += step5; if (r5 >= 10UL) r5 -= 10UL; if (r5 >= 5UL) r5 -= 5UL;
                 }
-		}
 
-		return;
+                divisorsExhausted = true;
+    }
+}
         }
 }

PerfectNumbers.Core/Gpu/MersenneNumberResidueGpuTester.cs

@@ -12,15 +12,27 @@ public class MersenneNumberResidueGpuTester(bool useGpuOrder)
 	// via GpuKernelPool to avoid host round-trips.
 
         // GPU residue variant: check 2^p % q == 1 for q = 2*p*k + 1.
-	public void Scan(ulong exponent, UInt128 twoP, bool lastIsSeven, UInt128 maxK, ref bool isPrime)
+    public void Scan(
+            ulong exponent,
+            UInt128 twoP,
+            bool lastIsSeven,
+            UInt128 perSetLimit,
+            ulong setCount,
+            UInt128 overallLimit,
+            ref bool isPrime,
+            ref bool divisorsExhausted)
     {
+            if (setCount == 0UL || perSetLimit == UInt128.Zero || overallLimit == UInt128.Zero)
+            {
+                    return;
+            }
+
                 var gpuLease = GpuKernelPool.GetKernel(_useGpuOrder);
                 var accelerator = gpuLease.Accelerator;
                 // Ensure device has small cycles and primes tables for in-kernel lookup
                 var smallCyclesView = GpuKernelPool.EnsureSmallCyclesOnDevice(accelerator);
                 ResiduePrimeViews primeViews = GpuKernelPool.EnsureSmallPrimesOnDevice(accelerator);
                 int batchSize = GpuConstants.ScanBatchSize;
-                UInt128 kStart = 1UL;
                 byte last = lastIsSeven ? (byte)1 : (byte)0;
                 var kernel = gpuLease.Pow2ModKernel;
                 ulong step10 = ((exponent % 10UL) << 1) % 10UL;
@@ -31,27 +43,38 @@ public class MersenneNumberResidueGpuTester(bool useGpuOrder)
 
                 var orderBuffer = accelerator.Allocate1D<ulong>(batchSize);
                 ulong[] orderArray = ArrayPool<ulong>.Shared.Rent(batchSize);
-                UInt128 remaining;
+                UInt128 batchSize128 = (UInt128)batchSize;
-                int currentSize;
+                UInt128 limitInclusive = overallLimit + UInt128.One;
-                int i;
-                UInt128 batchSize128 = (UInt128)batchSize, q;
                 Span<ulong> orders = orderArray.AsSpan(0, batchSize);
                 try
                 {
-                        while (kStart < maxK && Volatile.Read(ref isPrime))
+                        for (ulong setIndex = 0; setIndex < setCount && Volatile.Read(ref isPrime); setIndex++)
                         {
-                                remaining = maxK - kStart;
+                                UInt128 setOffset = perSetLimit * (UInt128)setIndex;
-				if (remaining > batchSize128)
+                                UInt128 setStart = setOffset + UInt128.One;
+                                if (setStart >= limitInclusive)
                                 {
-					currentSize = batchSize;
+                                        break;
-				}
-				else
-				{
-					currentSize = (int)remaining;
-					orders = orderArray.AsSpan(0, currentSize);
                                 }
 
-                                q = twoP * kStart + UInt128.One;
+                                UInt128 setLimitExclusive = setOffset + perSetLimit + UInt128.One;
+                                if (setLimitExclusive > limitInclusive)
+                                {
+                                        setLimitExclusive = limitInclusive;
+                                }
+
+                                UInt128 kStart = setStart;
+                                while (kStart < setLimitExclusive && Volatile.Read(ref isPrime))
+                                {
+                                        UInt128 remaining = setLimitExclusive - kStart;
+                                        int currentSize = remaining > batchSize128 ? batchSize : (int)remaining;
+                                        if (currentSize <= 0)
+                                        {
+                                                break;
+                                        }
+                                        orders = orderArray.AsSpan(0, currentSize);
+
+                                        UInt128 q = twoP * kStart + UInt128.One;
                                         q.Mod10_8_5_3(out ulong q0m10, out ulong q0m8, out ulong q0m5, out ulong q0m3);
                                         var ra = new ResidueAutomatonArgs(q0m10, step10, q0m8, step8, q0m3, step3, q0m5, step5);
 
@@ -65,7 +88,7 @@ public class MersenneNumberResidueGpuTester(bool useGpuOrder)
                                                 break;
                                         }
 
-                                for (i = 0; i < currentSize; i++)
+                                        for (int i = 0; i < currentSize; i++)
                                         {
                                                 if (orders[i] != 0UL)
                                                 {
@@ -77,11 +100,14 @@ public class MersenneNumberResidueGpuTester(bool useGpuOrder)
                                         kStart += batchSize128;
                                 }
                         }
+                }
                 finally
                 {
                         ArrayPool<ulong>.Shared.Return(orderArray);
                         orderBuffer.Dispose();
                         gpuLease.Dispose();
                 }
+
+                divisorsExhausted = true;
     }
 }

PerfectNumbers.Core/MersenneNumberTester.cs

@@ -25,11 +25,13 @@ public sealed class MersenneNumberTester(
     bool useGpuScan = true,
     bool useGpuOrder = true,
         bool useResidue = true,
-    ulong maxK = 5_000_000UL)
+    ulong maxK = 5_000_000UL,
+        ulong residueDivisorSets = PerfectNumberConstants.ExtraDivisorCycleSearchLimit)
 {
     private readonly bool _useResidue = useResidue;
     private readonly bool _useIncremental = useIncremental && !useResidue;
         private readonly ulong _maxK = maxK;
+        private readonly ulong _residueDivisorSetCount = residueDivisorSets;
         private readonly GpuKernelType _kernelType = kernelType;
     private readonly bool _useModuloWorkaround = useModuloWorkaround;
     private readonly bool _useGpuLucas = useGpuLucas;
@@ -48,6 +50,23 @@ public sealed class MersenneNumberTester(
         // TODO: Ensure Program passes useResidue correctly and that residue-vs-incremental-vs-LL selection respects CLI flags.
         // Also consider injecting a shared cycles cache (MersenneDivisorCycles.Shared) to both CPU and GPU testers.
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static UInt128 DivideRoundUp(UInt128 value, UInt128 divisor)
+        {
+                if (divisor == UInt128.Zero)
+                {
+                        return UInt128.Zero;
+                }
+
+                UInt128 result = value / divisor;
+                if (result * divisor == value)
+                {
+                        return result;
+                }
+
+                return result + UInt128.One;
+        }
+
     public void WarmUpOrders(ulong exponent, ulong limit = 5_000_000UL)
 	{
 		bool cacheEnabled = useOrderCache;
@@ -191,23 +210,30 @@ public sealed class MersenneNumberTester(
                 ArrayPool<UInt128>.Shared.Return(qs);
 	}
 
-    public bool IsMersennePrime(ulong exponent)
+    public bool IsMersennePrime(ulong exponent) => IsMersennePrime(exponent, out _);
+
+    public bool IsMersennePrime(ulong exponent, out bool divisorsExhausted)
     {
+        divisorsExhausted = false;
+
         // Safe early rejections using known orders for tiny primes:
         // 7 | M_p iff 3 | p. Avoid rejecting p == 3 where M_3 == 7 is prime.
         if ((exponent % 3UL) == 0UL && exponent != 3UL)
         {
+            divisorsExhausted = true;
             return false;
         }
 
         if ((exponent & 3UL) == 1UL && exponent.SharesFactorWithExponentMinusOne())
         {
+            divisorsExhausted = true;
             return false;
         }
 
         // Skip even exponents: for even p > 2, M_p is composite; here p is large.
         if ((exponent & 1UL) == 0UL)
         {
+            divisorsExhausted = true;
             return false;
         }
 
@@ -225,16 +251,60 @@ public sealed class MersenneNumberTester(
                 maxK = _maxK;
             }
 
+            if (_maxK == 0UL || _residueDivisorSetCount == 0UL)
+            {
+                return prePrime;
+            }
+
+            UInt128 totalLimit = (UInt128)_maxK;
+            if (totalLimit > maxK)
+            {
+                totalLimit = maxK;
+            }
+
+            if (totalLimit == UInt128.Zero)
+            {
+                return true;
+            }
+
+            ulong requestedSets = _residueDivisorSetCount;
+            if (requestedSets == 0UL)
+            {
+                requestedSets = 1UL;
+            }
+
+            UInt128 perSetLimit = DivideRoundUp(totalLimit, (UInt128)requestedSets);
+            if (perSetLimit == UInt128.Zero)
+            {
+                perSetLimit = UInt128.One;
+            }
+
+            UInt128 setsNeeded = DivideRoundUp(totalLimit, perSetLimit);
+            ulong effectiveSets = requestedSets;
+            if (setsNeeded < (UInt128)effectiveSets)
+            {
+                effectiveSets = (ulong)setsNeeded;
+            }
+
+            bool scanCompleted = false;
+
             if (_useGpuScan)
             {
-                _residueGpuTester!.Scan(exponent, twoP, lastIsSeven, maxK, ref prePrime);
+                _residueGpuTester!.Scan(exponent, twoP, lastIsSeven, perSetLimit, effectiveSets, totalLimit, ref prePrime, ref scanCompleted);
             }
             else
             {
-                _residueCpuTester!.Scan(exponent, twoP, lastIsSeven, maxK, ref prePrime);
+                _residueCpuTester!.Scan(exponent, twoP, lastIsSeven, perSetLimit, effectiveSets, totalLimit, ref prePrime, ref scanCompleted);
             }
 
-            return prePrime;
+            if (!prePrime)
+            {
+                divisorsExhausted = true;
+                return false;
+            }
+
+            divisorsExhausted = scanCompleted;
+            return true;
         }
 
 		if (!_useIncremental)
@@ -255,12 +325,15 @@ public sealed class MersenneNumberTester(
 
                         if (!prePrime)
                         {
+                                divisorsExhausted = true;
                                 return false;
                         }
 
-			return _useGpuLucas
+                        bool lucasPrime = _useGpuLucas
                                 ? _lucasLehmerGpuTester.IsPrime(exponent, runOnGpu: true)
                                 : _lucasLehmerCpuTester.IsPrime(exponent);
+                        divisorsExhausted = true;
+                        return lucasPrime;
                 }
 
         bool isPrime = true;
@@ -288,6 +361,7 @@ public sealed class MersenneNumberTester(
             }
         }
 
+        divisorsExhausted = true;
         return isPrime;
     }