Refine by-divisor prime test time limits

EvenPerfectBitScanner/Program.cs

@@ -44,6 +44,7 @@ internal static class Program
     private static string? _resultsPrefix;
     private static readonly Optimized PrimeIterator = new();
     private static ulong _byDivisorStartPrime;
+    private static TimeSpan? _primeTestLimit;
 
     [ThreadStatic]
     private static bool _lastCompositeP;
@@ -181,6 +182,17 @@ internal static class Program
             {
                 mersenneOnGpu = !arg.AsSpan(arg.IndexOf('=') + 1).Equals("cpu", StringComparison.OrdinalIgnoreCase);
             }
+            else if (arg.StartsWith("--prime-test-limit=", StringComparison.OrdinalIgnoreCase))
+            {
+                ReadOnlySpan<char> value = arg.AsSpan(arg.IndexOf('=') + 1);
+                if (!TryParsePrimeTestLimit(value, out TimeSpan parsedLimitValue))
+                {
+                    Console.WriteLine("Failed to parse --prime-test-limit value.");
+                    return;
+                }
+
+                _primeTestLimit = parsedLimitValue;
+            }
             else if (arg.Equals("--workaround-mod", StringComparison.OrdinalIgnoreCase))
             {
                 useModuloWorkaround = true;
@@ -667,7 +679,7 @@ internal static class Program
 
         if (_useByDivisorMode)
         {
-            RunByDivisorMode(byDivisorCandidates, threadCount);
+            RunByDivisorMode(byDivisorCandidates, threadCount, _primeTestLimit);
             FlushBuffer();
             StringBuilderPool.Return(_outputBuilder!);
             return;
@@ -808,7 +820,7 @@ internal static class Program
         return candidates;
     }
 
-    private static void RunByDivisorMode(List<ulong> candidates, int threadCount)
+    private static void RunByDivisorMode(List<ulong> candidates, int threadCount, TimeSpan? primeTestLimit)
     {
         if (_byDivisorTester is null)
         {
@@ -825,7 +837,8 @@ internal static class Program
                 static () => _lastCompositeP = true,
                 static () => _lastCompositeP = false,
                 PrintResult,
-                threadCount);
+                threadCount,
+                primeTestLimit);
     }
 
     private static unsafe void LoadResultsFile(string resultsFileName, Action<ulong, bool, bool> lineProcessorAction)
@@ -892,6 +905,51 @@ internal static class Program
         }
     }
 
+    private static bool TryParsePrimeTestLimit(ReadOnlySpan<char> value, out TimeSpan result)
+    {
+        result = TimeSpan.Zero;
+        if (value.IsEmpty)
+        {
+            return false;
+        }
+
+        ReadOnlySpan<char> magnitudeSpan = value;
+        double magnitude;
+
+        if (value.Length >= 2 && value.EndsWith("ms", StringComparison.OrdinalIgnoreCase))
+        {
+            magnitudeSpan = value[..^2];
+            if (!double.TryParse(magnitudeSpan, NumberStyles.Float, CultureInfo.InvariantCulture, out magnitude))
+            {
+                return false;
+            }
+
+            result = TimeSpan.FromMilliseconds(magnitude);
+            return true;
+        }
+
+        char suffix = char.ToLowerInvariant(value[^1]);
+        if (suffix == 's' || suffix == 'm')
+        {
+            magnitudeSpan = value[..^1];
+            if (!double.TryParse(magnitudeSpan, NumberStyles.Float, CultureInfo.InvariantCulture, out magnitude))
+            {
+                return false;
+            }
+
+            result = suffix == 's' ? TimeSpan.FromSeconds(magnitude) : TimeSpan.FromMinutes(magnitude);
+            return true;
+        }
+
+        if (!double.TryParse(value, NumberStyles.Float, CultureInfo.InvariantCulture, out magnitude))
+        {
+            return false;
+        }
+
+        result = TimeSpan.FromMilliseconds(magnitude);
+        return true;
+    }
+
     private static void PrintHelp()
     {
         Console.WriteLine("Usage: EvenPerfectBitScanner [options]");
@@ -925,6 +983,7 @@ internal static class Program
         Console.WriteLine("  --divisor-cycles-batch=<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("  --prime-test-limit=<value>   Time limit for --mersenne=bydivisor prime checks (e.g. 5s, 500ms)");
         Console.WriteLine("  --use-order            test primality via q order");
         Console.WriteLine("  --workaround-mod       avoid '%' operator on the GPU");
         // mod-automaton removed

PerfectNumbers.Core.Tests/MersenneNumberDivisorByDivisorTesterTests.cs

@@ -26,7 +26,8 @@ public class MersenneNumberDivisorByDivisorTesterTests
             markComposite: () => compositeMarks++,
             clearComposite: () => clearedMarks++,
             printResult: (prime, searched, detailed, passed) => results.Add((prime, searched, detailed, passed)),
-            threadCount: 1);
+            threadCount: 1,
+            primeTestLimit: null);
 
         tester.ConfiguredMaxPrime.Should().Be(13UL);
         compositeMarks.Should().Be(2);
@@ -59,7 +60,7 @@ public class MersenneNumberDivisorByDivisorTesterTests
             return DivisorLimit;
         }
 
-        public bool IsPrime(ulong prime, out bool divisorsExhausted)
+        public bool IsPrime(ulong prime, out bool divisorsExhausted, TimeSpan? timeLimit = null)
         {
             divisorsExhausted = true;
             return prime % 7UL != 0UL && prime % 11UL != 0UL;

PerfectNumbers.Core.Tests/MersenneNumberDivisorCpuTesterTests.cs

@@ -7,78 +7,88 @@ namespace PerfectNumbers.Core.Tests;
 
 public class MersenneNumberDivisorCpuTesterTests
 {
-        [Fact]
-        [Trait("Category", "Fast")]
-        public void ByDivisor_tester_tracks_divisors_across_primes()
-        {
-                var tester = new MersenneNumberDivisorByDivisorCpuTester();
-                tester.ConfigureFromMaxPrime(11UL);
+    [Fact]
+    [Trait("Category", "Fast")]
+    public void ByDivisor_tester_tracks_divisors_across_primes()
+    {
+        var tester = new MersenneNumberDivisorByDivisorCpuTester();
+        tester.ConfigureFromMaxPrime(11UL);
 
-                tester.IsPrime(5UL, out bool divisorsExhausted).Should().BeTrue();
-                divisorsExhausted.Should().BeTrue();
+        tester.IsPrime(5UL, out bool divisorsExhausted).Should().BeTrue();
+        divisorsExhausted.Should().BeTrue();
 
-                tester.IsPrime(7UL, out divisorsExhausted).Should().BeTrue();
-                divisorsExhausted.Should().BeTrue();
+        tester.IsPrime(7UL, out divisorsExhausted).Should().BeTrue();
+        divisorsExhausted.Should().BeTrue();
 
-                tester.IsPrime(11UL, out divisorsExhausted).Should().BeFalse();
-                divisorsExhausted.Should().BeTrue();
-        }
+        tester.IsPrime(11UL, out divisorsExhausted).Should().BeFalse();
+        divisorsExhausted.Should().BeTrue();
+    }
 
-        [Fact]
-        [Trait("Category", "Fast")]
-        public void ByDivisor_session_checks_divisors_across_primes()
-        {
-                var tester = new MersenneNumberDivisorByDivisorCpuTester();
-                tester.ConfigureFromMaxPrime(13UL);
+    [Fact]
+    [Trait("Category", "Fast")]
+    public void ByDivisor_prime_test_limit_disables_divisor_exhaustion()
+    {
+        var tester = new MersenneNumberDivisorByDivisorCpuTester();
+        tester.ConfigureFromMaxPrime(11UL);
 
-                using var session = tester.CreateDivisorSession();
-                ulong[] primes = { 5UL, 7UL, 11UL, 13UL };
-                byte[] hits = new byte[primes.Length];
+        tester.IsPrime(5UL, out bool divisorsExhausted, TimeSpan.Zero).Should().BeTrue();
+        divisorsExhausted.Should().BeFalse();
+    }
 
-                ulong cycle23 = MersenneDivisorCycles.CalculateCycleLength(23UL, MontgomeryDivisorData.FromModulus(23UL));
-                session.CheckDivisor(23UL, MontgomeryDivisorData.FromModulus(23UL), cycle23, primes, hits);
-                hits.Should().ContainInOrder(new byte[] { 0, 0, 1, 0 });
+    [Fact]
+    [Trait("Category", "Fast")]
+    public void ByDivisor_session_checks_divisors_across_primes()
+    {
+        var tester = new MersenneNumberDivisorByDivisorCpuTester();
+        tester.ConfigureFromMaxPrime(13UL);
 
-                Array.Fill(hits, (byte)0);
-                ulong cycle31 = MersenneDivisorCycles.CalculateCycleLength(31UL, MontgomeryDivisorData.FromModulus(31UL));
-                session.CheckDivisor(31UL, MontgomeryDivisorData.FromModulus(31UL), cycle31, primes, hits);
-                hits.Should().ContainInOrder(new byte[] { 1, 0, 0, 0 });
-        }
+        using var session = tester.CreateDivisorSession();
+        ulong[] primes = { 5UL, 7UL, 11UL, 13UL };
+        byte[] hits = new byte[primes.Length];
 
-        [Fact]
-        [Trait("Category", "Fast")]
-        public void ByDivisor_session_marks_mersenne_numbers_divisible_by_seven_as_composite()
-        {
-                var tester = new MersenneNumberDivisorByDivisorCpuTester();
-                tester.ConfigureFromMaxPrime(43UL);
+        ulong cycle23 = MersenneDivisorCycles.CalculateCycleLength(23UL, MontgomeryDivisorData.FromModulus(23UL));
+        session.CheckDivisor(23UL, MontgomeryDivisorData.FromModulus(23UL), cycle23, primes, hits);
+        hits.Should().ContainInOrder(new byte[] { 0, 0, 1, 0 });
 
-                using var session = tester.CreateDivisorSession();
-                ulong[] exponents = { 6UL, 7UL, 9UL, 10UL, 12UL };
-                byte[] hits = new byte[exponents.Length];
+        Array.Fill(hits, (byte)0);
+        ulong cycle31 = MersenneDivisorCycles.CalculateCycleLength(31UL, MontgomeryDivisorData.FromModulus(31UL));
+        session.CheckDivisor(31UL, MontgomeryDivisorData.FromModulus(31UL), cycle31, primes, hits);
+        hits.Should().ContainInOrder(new byte[] { 1, 0, 0, 0 });
+    }
 
-                MontgomeryDivisorData divisorData = MontgomeryDivisorData.FromModulus(7UL);
-                ulong cycle = MersenneDivisorCycles.CalculateCycleLength(7UL, divisorData);
-                session.CheckDivisor(7UL, divisorData, cycle, exponents, hits);
+    [Fact]
+    [Trait("Category", "Fast")]
+    public void ByDivisor_session_marks_mersenne_numbers_divisible_by_seven_as_composite()
+    {
+        var tester = new MersenneNumberDivisorByDivisorCpuTester();
+        tester.ConfigureFromMaxPrime(43UL);
 
-                hits.Should().Equal(new byte[] { 1, 0, 1, 0, 1 });
-        }
+        using var session = tester.CreateDivisorSession();
+        ulong[] exponents = { 6UL, 7UL, 9UL, 10UL, 12UL };
+        byte[] hits = new byte[exponents.Length];
 
-        [Fact]
-        [Trait("Category", "Fast")]
-        public void ByDivisor_session_marks_mersenne_numbers_divisible_by_eleven_as_composite()
-        {
-                var tester = new MersenneNumberDivisorByDivisorCpuTester();
-                tester.ConfigureFromMaxPrime(61UL);
+        MontgomeryDivisorData divisorData = MontgomeryDivisorData.FromModulus(7UL);
+        ulong cycle = MersenneDivisorCycles.CalculateCycleLength(7UL, divisorData);
+        session.CheckDivisor(7UL, divisorData, cycle, exponents, hits);
 
-                using var session = tester.CreateDivisorSession();
-                ulong[] exponents = { 10UL, 11UL, 20UL, 21UL, 30UL };
-                byte[] hits = new byte[exponents.Length];
+        hits.Should().Equal(new byte[] { 1, 0, 1, 0, 1 });
+    }
 
-                MontgomeryDivisorData divisorData = MontgomeryDivisorData.FromModulus(11UL);
-                ulong cycle = MersenneDivisorCycles.CalculateCycleLength(11UL, divisorData);
-                session.CheckDivisor(11UL, divisorData, cycle, exponents, hits);
+    [Fact]
+    [Trait("Category", "Fast")]
+    public void ByDivisor_session_marks_mersenne_numbers_divisible_by_eleven_as_composite()
+    {
+        var tester = new MersenneNumberDivisorByDivisorCpuTester();
+        tester.ConfigureFromMaxPrime(61UL);
 
-                hits.Should().Equal(new byte[] { 1, 0, 1, 0, 1 });
-        }
+        using var session = tester.CreateDivisorSession();
+        ulong[] exponents = { 10UL, 11UL, 20UL, 21UL, 30UL };
+        byte[] hits = new byte[exponents.Length];
+
+        MontgomeryDivisorData divisorData = MontgomeryDivisorData.FromModulus(11UL);
+        ulong cycle = MersenneDivisorCycles.CalculateCycleLength(11UL, divisorData);
+        session.CheckDivisor(11UL, divisorData, cycle, exponents, hits);
+
+        hits.Should().Equal(new byte[] { 1, 0, 1, 0, 1 });
+    }
 }
-

PerfectNumbers.Core.Tests/MersenneNumberDivisorGpuTesterTests.cs

@@ -86,6 +86,17 @@ public class MersenneNumberDivisorGpuTesterTests
         exhausted.Should().BeTrue();
     }
 
+    [Fact]
+    [Trait("Category", "Fast")]
+    public void ByDivisor_gpu_prime_test_limit_stops_scan_immediately()
+    {
+        var tester = new MersenneNumberDivisorByDivisorGpuTester();
+        tester.ConfigureFromMaxPrime(43UL);
+
+        tester.IsPrime(31UL, out bool divisorsExhausted, TimeSpan.Zero).Should().BeTrue();
+        divisorsExhausted.Should().BeFalse();
+    }
+
     [Fact]
     [Trait("Category", "Fast")]
     public void ByDivisor_tester_requires_configuration()

PerfectNumbers.Core/Cpu/MersenneNumberDivisorByDivisorCpuTester.cs

@@ -61,7 +61,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
         }
     }
 
-    public bool IsPrime(ulong prime, out bool divisorsExhausted)
+    public bool IsPrime(ulong prime, out bool divisorsExhausted, TimeSpan? timeLimit = null)
     {
         ulong allowedMax;
         lock (_sync)
@@ -89,7 +89,8 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
             allowedMax,
             out lastProcessed,
             out processedAll,
-            out processedCount);
+            out processedCount,
+            timeLimit);
 
         if (processedCount > 0UL)
         {
@@ -163,12 +164,22 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
         ulong allowedMax,
         out ulong lastProcessed,
         out bool processedAll,
-        out ulong processedCount)
+        out ulong processedCount,
+        TimeSpan? timeLimit)
     {
         lastProcessed = 0UL;
         processedCount = 0UL;
         processedAll = false;
 
+        PrimeTestTimeLimit limitGuard;
+        if (!PrimeTestTimeLimit.TryCreate(timeLimit, out limitGuard))
+        {
+            return false;
+        }
+
+        bool enforceLimit = limitGuard.IsActive;
+        ulong iterationCounter = 0UL;
+
         if (allowedMax < 3UL)
         {
             return false;
@@ -216,6 +227,13 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 
         while (divisor <= limit)
         {
+            if (enforceLimit && (iterationCounter == 0UL || (iterationCounter & 63UL) == 0UL) && limitGuard.HasExpired())
+            {
+                processedAll = false;
+                return false;
+            }
+
+            iterationCounter++;
             ulong candidate = (ulong)divisor;
             processedCount++;
             lastProcessed = candidate;

PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs

@@ -71,7 +71,7 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
         }
     }
 
-    public bool IsPrime(ulong prime, out bool divisorsExhausted)
+    public bool IsPrime(ulong prime, out bool divisorsExhausted, TimeSpan? timeLimit = null)
     {
         ulong allowedMax;
         int batchCapacity;
@@ -108,6 +108,7 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
             composite = CheckDivisors(
             prime,
             allowedMax,
+            timeLimit,
             accelerator,
             kernel,
             resources.DivisorsBuffer,
@@ -175,6 +176,7 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
     private static bool CheckDivisors(
         ulong prime,
         ulong allowedMax,
+        TimeSpan? timeLimit,
         Accelerator accelerator,
         Action<Index1D, ArrayView<MontgomeryDivisorData>, ArrayView<ulong>, ArrayView<byte>> kernel,
         MemoryBuffer1D<MontgomeryDivisorData, Stride1D.Dense> divisorsBuffer,
@@ -202,6 +204,15 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
         bool processedAll = false;
         processedCount = 0UL;
         lastProcessed = 0UL;
+        coveredRange = false;
+
+        PrimeTestTimeLimit limitGuard;
+        if (!PrimeTestTimeLimit.TryCreate(timeLimit, out limitGuard))
+        {
+            return false;
+        }
+
+        bool enforceLimit = limitGuard.IsActive;
 
         Span<MontgomeryDivisorData> divisorDataSpan;
         Span<ulong> divisorSpan;
@@ -277,6 +288,12 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
         {
             while (currentK <= maxK)
             {
+                if (enforceLimit && limitGuard.HasExpired())
+                {
+                    processedAll = false;
+                    return false;
+                }
+
                 int chunkCount = Math.Min(chunkCapacity, batchCapacity);
                 ulong remainingK = maxK - currentK + 1UL;
                 if ((ulong)chunkCount > remainingK)

PerfectNumbers.Core/IMersenneNumberDivisorByDivisorTester.cs

@@ -12,7 +12,7 @@ public interface IMersenneNumberDivisorByDivisorTester
 
     ulong GetAllowedMaxDivisor(ulong prime);
 
-    bool IsPrime(ulong prime, out bool divisorsExhausted);
+    bool IsPrime(ulong prime, out bool divisorsExhausted, TimeSpan? timeLimit = null);
 
     IDivisorScanSession CreateDivisorSession();
 

PerfectNumbers.Core/MersenneNumberDivisorByDivisorTester.cs

@@ -18,7 +18,8 @@ public static class MersenneNumberDivisorByDivisorTester
             Action markComposite,
             Action clearComposite,
             Action<ulong, bool, bool, bool> printResult,
-            int threadCount)
+            int threadCount,
+            TimeSpan? primeTestLimit)
     {
         if (candidates.Count == 0)
         {
@@ -243,7 +244,7 @@ public static class MersenneNumberDivisorByDivisorTester
 
         void ProcessPrime(ulong prime)
         {
-            bool isPrime = tester.IsPrime(prime, out bool divisorsExhausted);
+            bool isPrime = tester.IsPrime(prime, out bool divisorsExhausted, primeTestLimit);
 
             if (!isPrime)
             {

PerfectNumbers.Core/PrimeTestTimeLimit.cs

@@ -0,0 +1,72 @@
+using System;
+using System.Diagnostics;
+
+namespace PerfectNumbers.Core;
+
+internal readonly struct PrimeTestTimeLimit
+{
+    private readonly long _deadlineTimestamp;
+
+    private PrimeTestTimeLimit(bool isActive, long deadlineTimestamp)
+    {
+        IsActive = isActive;
+        _deadlineTimestamp = deadlineTimestamp;
+    }
+
+    internal bool IsActive { get; }
+
+    internal static bool TryCreate(TimeSpan? timeLimit, out PrimeTestTimeLimit limit)
+    {
+        if (!timeLimit.HasValue)
+        {
+            limit = new PrimeTestTimeLimit(isActive: false, deadlineTimestamp: long.MaxValue);
+            return true;
+        }
+
+        TimeSpan limitValue = timeLimit.GetValueOrDefault();
+        if (limitValue <= TimeSpan.Zero)
+        {
+            limit = new PrimeTestTimeLimit(isActive: true, deadlineTimestamp: long.MinValue);
+            return false;
+        }
+
+        double seconds = limitValue.TotalSeconds;
+        if (double.IsInfinity(seconds))
+        {
+            limit = new PrimeTestTimeLimit(isActive: true, deadlineTimestamp: long.MaxValue);
+            return true;
+        }
+
+        double scaled = seconds * Stopwatch.Frequency;
+        long limitTicks = scaled >= long.MaxValue ? long.MaxValue : (long)scaled;
+        long startTimestamp = Stopwatch.GetTimestamp();
+        long deadline = startTimestamp <= long.MaxValue - limitTicks ? startTimestamp + limitTicks : long.MaxValue;
+        if (deadline < startTimestamp)
+        {
+            deadline = long.MaxValue;
+        }
+
+        limit = new PrimeTestTimeLimit(isActive: true, deadlineTimestamp: deadline);
+        return true;
+    }
+
+    internal bool HasExpired()
+    {
+        if (!IsActive)
+        {
+            return false;
+        }
+
+        if (_deadlineTimestamp == long.MaxValue)
+        {
+            return false;
+        }
+
+        if (_deadlineTimestamp == long.MinValue)
+        {
+            return true;
+        }
+
+        return Stopwatch.GetTimestamp() >= _deadlineTimestamp;
+    }
+}