Divisor will now be saved to CSV file

EvenPerfectBitScanner.ResultsParser/Program.cs

@@ -19,7 +19,7 @@ internal static class Program
 				"/help"
 		};
 
-	private const string DefaultHeader = "p,searchedMersenne,detailedCheck,passedAllTests";
+private const string DefaultHeader = "p,divisor,searchedMersenne,detailedCheck,passedAllTests";
 
 	private static int Main(string[] args)
 	{

EvenPerfectBitScanner/CalculationResultHandler.cs

@@ -7,7 +7,7 @@ namespace EvenPerfectBitScanner;
 
 internal static class CalculationResultHandler
 {
-        private const string ResultsHeader = "p,searchedMersenne,detailedCheck,passedAllTests";
+        private const string ResultsHeader = "p,divisor,searchedMersenne,detailedCheck,passedAllTests";
         private const string PrimeFoundSuffix = " (FOUND VALID CANDIDATES)";
         internal const int DefaultWriteBatchSize = 100;
 
@@ -93,19 +93,19 @@ internal static class CalculationResultHandler
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal static void HandleResult(ulong currentP, bool searchedMersenne, bool detailedCheck, bool passedAllTests, bool lastWasComposite)
+        internal static void HandleResult(ulong currentP, ulong divisor, bool searchedMersenne, bool detailedCheck, bool passedAllTests, bool lastWasComposite)
         {
                 // Program flow ensures Initialize(...) and InitializeOutputBuffer() ran before this call. Do not add initialization guards here.
 
                 Span<byte> stackBuffer = stackalloc byte[128];
                 byte[]? rentedBuffer = null;
                 Span<byte> utf8Span = stackBuffer;
-                int byteCount = TryFormatResultLine(utf8Span, currentP, searchedMersenne, detailedCheck, passedAllTests);
+                int byteCount = TryFormatResultLine(utf8Span, currentP, divisor, searchedMersenne, detailedCheck, passedAllTests);
                 if (byteCount < 0)
                 {
                         rentedBuffer = ThreadStaticPools.BytePool.Rent(256);
                         utf8Span = rentedBuffer;
-                        byteCount = TryFormatResultLine(utf8Span, currentP, searchedMersenne, detailedCheck, passedAllTests);
+                        byteCount = TryFormatResultLine(utf8Span, currentP, divisor, searchedMersenne, detailedCheck, passedAllTests);
                         if (byteCount < 0)
                         {
                                 ThreadStaticPools.BytePool.Return(rentedBuffer);
@@ -229,7 +229,7 @@ internal static class CalculationResultHandler
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static int TryFormatResultLine(Span<byte> destination, ulong currentP, bool searchedMersenne, bool detailedCheck, bool passedAllTests)
+        private static int TryFormatResultLine(Span<byte> destination, ulong currentP, ulong divisor, bool searchedMersenne, bool detailedCheck, bool passedAllTests)
         {
                 int offset = 0;
 
@@ -246,6 +246,19 @@ internal static class CalculationResultHandler
 
                 destination[offset++] = (byte)',';
 
+                if (!Utf8Formatter.TryFormat(divisor, destination[offset..], out written))
+                {
+                        return -1;
+                }
+
+                offset += written;
+                if (offset >= destination.Length)
+                {
+                        return -1;
+                }
+
+                destination[offset++] = (byte)',';
+
                 if (!Utf8Formatter.TryFormat(searchedMersenne, destination[offset..], out written))
                 {
                         return -1;

EvenPerfectBitScanner/IO/CalculationResultsFile.cs

@@ -100,6 +100,7 @@ internal static class CalculationResultsFile
                 int first = 0;
                 int second = 0;
                 int third = 0;
+                int fourth = 0;
                 ulong parsedP = 0UL;
                 ReadOnlySpan<char> detailedSpan = default;
                 ReadOnlySpan<char> passedAllTestsSpan = default;
@@ -139,8 +140,15 @@ internal static class CalculationResultsFile
                                 continue;
                         }
 
-                        detailedSpan = span[..third];
-                        passedAllTestsSpan = span[(third + 1)..];
+                        span = span[(third + 1)..];
+                        fourth = span.IndexOf(',');
+                        if (fourth < 0)
+                        {
+                                continue;
+                        }
+
+                        detailedSpan = span[..fourth];
+                        passedAllTestsSpan = span[(fourth + 1)..];
 
                         if (Utf8CliParser.TryParseBoolean(detailedSpan, out detailed) && Utf8CliParser.TryParseBoolean(passedAllTestsSpan, out passedAllTests))
                         {

EvenPerfectBitScanner/Program.cs

@@ -422,7 +422,7 @@ internal static class Program
 						_byDivisorStartPrime,
 						static () => _lastCompositeP = true,
 						static () => _lastCompositeP = false,
-						static (candidate, searchedMersenne, detailedCheck, passedAllTests) => CalculationResultHandler.HandleResult(candidate, searchedMersenne, detailedCheck, passedAllTests, _lastCompositeP),
+						static (candidate, searchedMersenne, detailedCheck, passedAllTests, divisor) => CalculationResultHandler.HandleResult(candidate, divisor, searchedMersenne, detailedCheck, passedAllTests, _lastCompositeP),
 						threadCount,
 						byDivisorPrimeRange);
 						
@@ -483,7 +483,7 @@ internal static class Program
 							{
 								p = buffer[j];
 								passedAllTests = IsEvenPerfectCandidate(p, divisorCyclesSearchLimit, out searchedMersenne, out detailedCheck);
-								CalculationResultHandler.HandleResult(p, searchedMersenne, detailedCheck, passedAllTests, _lastCompositeP);
+								CalculationResultHandler.HandleResult(p, 0UL, searchedMersenne, detailedCheck, passedAllTests, _lastCompositeP);
 							}
 
 							continue;
@@ -506,7 +506,7 @@ internal static class Program
 							}
 
 							passedAllTests = IsEvenPerfectCandidate(p, divisorCyclesSearchLimit, out searchedMersenne, out detailedCheck);
-							CalculationResultHandler.HandleResult(p, searchedMersenne, detailedCheck, passedAllTests, _lastCompositeP);
+							CalculationResultHandler.HandleResult(p, 0UL, searchedMersenne, detailedCheck, passedAllTests, _lastCompositeP);
 
 							if (p == maxP)
 							{
@@ -649,7 +649,7 @@ internal static class Program
 		if (_cliArguments.UseByDivisor)
 		{
 			// Windowed pow2mod kernel handles by-divisor scans.
-			return _byDivisorTester!.IsPrime(p, out detailedCheck);
+			return _byDivisorTester!.IsPrime(p, out detailedCheck, out _);
 		}
 
 		detailedCheck = MersenneTesters.Value!.IsMersennePrime(p);

PerfectNumbers.Core.Tests/MersenneNumberDivisorByDivisorTesterTests.cs

@@ -11,7 +11,7 @@ public class MersenneNumberDivisorByDivisorTesterTests
     {
         var candidates = new List<ulong> { 5UL, 7UL, 11UL, 13UL };
         var tester = new FakeTester();
-        var results = new List<(ulong Prime, bool Searched, bool Detailed, bool Passed)>();
+        var results = new List<(ulong Prime, bool Searched, bool Detailed, bool Passed, ulong Divisor)>();
         int compositeMarks = 0;
         int clearedMarks = 0;
 
@@ -22,7 +22,7 @@ public class MersenneNumberDivisorByDivisorTesterTests
             startPrime: 0UL,
             markComposite: () => compositeMarks++,
             clearComposite: () => clearedMarks++,
-            printResult: (prime, searched, detailed, passed) => results.Add((prime, searched, detailed, passed)),
+            printResult: (prime, searched, detailed, passed, divisor) => results.Add((prime, searched, detailed, passed, divisor)),
             threadCount: 1,
             primesPerTask: 2);
 
@@ -32,10 +32,10 @@ public class MersenneNumberDivisorByDivisorTesterTests
         results.Should().Equal(
             new[]
             {
-                (5UL, true, true, true),
-                (7UL, true, true, false),
-                (11UL, true, true, false),
-                (13UL, true, true, true),
+                (5UL, true, true, true, 0UL),
+                (7UL, true, true, false, 7UL),
+                (11UL, true, true, false, 11UL),
+                (13UL, true, true, true, 0UL),
             });
     }
 
@@ -57,10 +57,23 @@ public class MersenneNumberDivisorByDivisorTesterTests
             return DivisorLimit;
         }
 
-        public bool IsPrime(ulong prime, out bool divisorsExhausted)
+        public bool IsPrime(ulong prime, out bool divisorsExhausted, out ulong divisor)
         {
             divisorsExhausted = true;
-            return prime % 7UL != 0UL && prime % 11UL != 0UL;
+            if (prime % 7UL == 0UL)
+            {
+                divisor = 7UL;
+                return false;
+            }
+
+            if (prime % 11UL == 0UL)
+            {
+                divisor = 11UL;
+                return false;
+            }
+
+            divisor = 0UL;
+            return true;
         }
 
         public IMersenneNumberDivisorByDivisorTester.IDivisorScanSession CreateDivisorSession()

PerfectNumbers.Core.Tests/MersenneNumberDivisorCpuTesterTests.cs

@@ -13,14 +13,17 @@ public class MersenneNumberDivisorCpuTesterTests
                 var tester = new MersenneNumberDivisorByDivisorCpuTester();
                 tester.ConfigureFromMaxPrime(11UL);
 
-                tester.IsPrime(5UL, out bool divisorsExhausted).Should().BeTrue();
+                tester.IsPrime(5UL, out bool divisorsExhausted, out ulong divisor).Should().BeTrue();
                 divisorsExhausted.Should().BeTrue();
+                divisor.Should().Be(0UL);
 
-                tester.IsPrime(7UL, out divisorsExhausted).Should().BeTrue();
+                tester.IsPrime(7UL, out divisorsExhausted, out divisor).Should().BeTrue();
                 divisorsExhausted.Should().BeTrue();
+                divisor.Should().Be(0UL);
 
-                tester.IsPrime(11UL, out divisorsExhausted).Should().BeFalse();
+                tester.IsPrime(11UL, out divisorsExhausted, out divisor).Should().BeFalse();
                 divisorsExhausted.Should().BeTrue();
+                divisor.Should().BeGreaterThan(0UL);
         }
 
         [Fact]

PerfectNumbers.Core.Tests/MersenneNumberDivisorGpuTesterTests.cs

@@ -73,14 +73,17 @@ public class MersenneNumberDivisorGpuTesterTests
         var tester = new MersenneNumberDivisorByDivisorGpuTester();
         tester.ConfigureFromMaxPrime(43UL);
 
-        tester.IsPrime(31UL, out bool exhausted).Should().BeTrue();
+        tester.IsPrime(31UL, out bool exhausted, out ulong divisor).Should().BeTrue();
         exhausted.Should().BeTrue();
+        divisor.Should().Be(0UL);
 
-        tester.IsPrime(37UL, out exhausted).Should().BeFalse();
+        tester.IsPrime(37UL, out exhausted, out divisor).Should().BeFalse();
         exhausted.Should().BeTrue();
+        divisor.Should().BeGreaterThan(0UL);
 
-        tester.IsPrime(43UL, out exhausted).Should().BeFalse();
+        tester.IsPrime(43UL, out exhausted, out divisor).Should().BeFalse();
         exhausted.Should().BeTrue();
+        divisor.Should().BeGreaterThan(0UL);
     }
 
     [Fact]
@@ -105,12 +108,15 @@ public class MersenneNumberDivisorGpuTesterTests
         var tester = new MersenneNumberDivisorByDivisorGpuTester();
         tester.ConfigureFromMaxPrime(41UL);
 
-        tester.IsPrime(31UL, out _).Should().BeTrue();
-        tester.IsPrime(37UL, out bool exhausted).Should().BeFalse();
+        tester.IsPrime(31UL, out _, out ulong divisor).Should().BeTrue();
+        divisor.Should().Be(0UL);
+        tester.IsPrime(37UL, out bool exhausted, out divisor).Should().BeFalse();
         exhausted.Should().BeTrue();
+        divisor.Should().BeGreaterThan(0UL);
 
-        tester.IsPrime(41UL, out bool divisorsExhausted).Should().BeFalse();
+        tester.IsPrime(41UL, out bool divisorsExhausted, out divisor).Should().BeFalse();
         divisorsExhausted.Should().BeTrue();
+        divisor.Should().BeGreaterThan(0UL);
     }
 
 
@@ -124,8 +130,16 @@ public class MersenneNumberDivisorGpuTesterTests
         var tester = new MersenneNumberDivisorByDivisorGpuTester();
         tester.ConfigureFromMaxPrime(exponent);
 
-        tester.IsPrime(exponent, out bool exhausted).Should().Be(expectedPrime);
+        tester.IsPrime(exponent, out bool exhausted, out ulong divisor).Should().Be(expectedPrime);
         exhausted.Should().BeTrue();
+        if (expectedPrime)
+        {
+            divisor.Should().Be(0UL);
+        }
+        else
+        {
+            divisor.Should().BeGreaterThan(0UL);
+        }
     }
     [Fact]
     [Trait("Category", "Fast")]
@@ -138,8 +152,9 @@ public class MersenneNumberDivisorGpuTesterTests
 
         tester.ConfigureFromMaxPrime(43UL);
 
-        tester.IsPrime(41UL, out bool divisorsExhausted).Should().BeFalse();
+        tester.IsPrime(41UL, out bool divisorsExhausted, out ulong divisor).Should().BeFalse();
         divisorsExhausted.Should().BeTrue();
+        divisor.Should().BeGreaterThan(0UL);
     }
 
     [Fact]
@@ -309,8 +324,9 @@ public class MersenneNumberDivisorGpuTesterTests
                 .GetField("_divisorLimit", BindingFlags.NonPublic | BindingFlags.Instance)!
                 .SetValue(tester, 200UL);
 
-            tester.IsPrime(19UL, out bool divisorsExhausted).Should().BeTrue();
+            tester.IsPrime(19UL, out bool divisorsExhausted, out ulong divisor).Should().BeTrue();
             divisorsExhausted.Should().BeTrue();
+            divisor.Should().Be(0UL);
         }
         finally
         {

PerfectNumbers.Core/Cpu/MersenneNumberDivisorByDivisorCpuTester.cs

@@ -42,7 +42,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 	[MethodImpl(MethodImplOptions.AggressiveInlining)]
 	public ulong GetAllowedMaxDivisor(ulong prime) => ComputeAllowedMaxDivisor(prime, _divisorLimit);
 
-	public bool IsPrime(ulong prime, out bool divisorsExhausted)
+	public bool IsPrime(ulong prime, out bool divisorsExhausted, out ulong divisor)
 	{
 		ulong allowedMax = ComputeAllowedMaxDivisor(prime, _divisorLimit);
 
@@ -60,7 +60,8 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 		bool composite = CheckDivisors(
 			prime,
 			allowedMax,
-			out processedAll);
+			out processedAll,
+			out divisor);
 
 		if (composite)
 		{
@@ -69,6 +70,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 		}
 
 		divisorsExhausted = processedAll || composite;
+		divisor = 0UL;
 		return true;
 	}
 
@@ -96,8 +98,10 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 	private bool CheckDivisors(
 		ulong prime,
 		ulong allowedMax,
-		out bool processedAll)
+		out bool processedAll,
+		out ulong foundDivisor)
 	{
+		foundDivisor = 0UL;
 		// The EvenPerfectBitScanner feeds primes >= 138,000,000 here, so allowedMax >= 3 in production runs.
 		// Keeping the guard commented out documents the reasoning for benchmarks and tests.
 		// if (allowedMax < 3UL)
@@ -123,6 +127,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 		if (divisor.CompareTo(limit) > 0)
 		{
 			processedAll = true;
+			foundDivisor = 0UL;
 			return false;
 		}
 
@@ -182,7 +187,8 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 				remainder3,
 				remainder7,
 				remainder11,
-				out processedAll);
+				out processedAll,
+				out foundDivisor);
 		}
 
 		ulong divisorHigh = divisor.High;
@@ -240,6 +246,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 				{
 					// A cycle equal to the tested exponent (which is prime in this path) guarantees that the candidate divides
 					// the corresponding Mersenne number because the order of 2 modulo the divisor is exactly p.
+					foundDivisor = candidate;
 					processedAll = true;
 					PrimeOrderCalculatorAccelerator.Return(gpu);
 					return true;
@@ -261,6 +268,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 
 		PrimeOrderCalculatorAccelerator.Return(gpu);
 		processedAll = true;
+		foundDivisor = 0UL;
 		return false;
 	}
 
@@ -280,9 +288,11 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 		byte remainder3,
 		byte remainder7,
 		byte remainder11,
-		out bool processedAll)
+		out bool processedAll,
+		out ulong foundDivisor)
 	{
 		processedAll = false;
+		foundDivisor = 0UL;
 
 		bool canAdvance = step <= limit;
 		var gpu = PrimeOrderCalculatorAccelerator.Rent(1);
@@ -314,6 +324,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 
 					if (divisorCycle == prime)
 					{
+						foundDivisor = divisor;
 						processedAll = true;
 						PrimeOrderCalculatorAccelerator.Return(gpu);
 						return true;
@@ -327,12 +338,14 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 			}
 
 			processedAll = true;
+			foundDivisor = 0UL;
 			return false;
 		}
 
 		if (divisor > limit)
 		{
 			processedAll = true;
+			foundDivisor = 0UL;
 			return false;
 		}
 
@@ -365,6 +378,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 
 				if (divisorCycle == prime)
 				{
+					foundDivisor = divisor;
 					processedAll = true;
 					PrimeOrderCalculatorAccelerator.Return(gpu);
 					return true;
@@ -380,6 +394,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
 			if (remainingIterations == 0UL)
 			{
 				processedAll = true;
+				foundDivisor = 0UL;
 				return false;
 			}
 

PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs

@@ -70,7 +70,7 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
 
 	private static readonly Accelerator[] _accelerators = AcceleratorPool.Shared.Accelerators;
 
-	public bool IsPrime(ulong prime, out bool divisorsExhausted)
+	public bool IsPrime(ulong prime, out bool divisorsExhausted, out ulong divisor)
 	{
 		ulong allowedMax;
 		int batchCapacity;
@@ -147,10 +147,12 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
 		if (composite)
 		{
 			divisorsExhausted = true;
+			divisor = lastProcessed;
 			return false;
 		}
 
 		divisorsExhausted = coveredRange;
+		divisor = 0UL;
 		return true;
 	}
 
@@ -933,4 +935,4 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
 	}
 
 	IMersenneNumberDivisorByDivisorTester.IDivisorScanSession IMersenneNumberDivisorByDivisorTester.CreateDivisorSession() => CreateDivisorSession();
-}
+}

PerfectNumbers.Core/IMersenneNumberDivisorByDivisorTester.cs

@@ -10,7 +10,7 @@ public interface IMersenneNumberDivisorByDivisorTester
 
     ulong GetAllowedMaxDivisor(ulong prime);
 
-    bool IsPrime(ulong prime, out bool divisorsExhausted);
+    bool IsPrime(ulong prime, out bool divisorsExhausted, out ulong divisor);
 
     IDivisorScanSession CreateDivisorSession();
 

PerfectNumbers.Core/MersenneNumberDivisorByDivisorTester.cs

@@ -14,7 +14,7 @@ public static class MersenneNumberDivisorByDivisorTester
 			ulong startPrime,
 			Action markComposite,
 			Action clearComposite,
-			Action<ulong, bool, bool, bool> printResult,
+			Action<ulong, bool, bool, bool, ulong> printResult,
 			int threadCount,
 			int primesPerTask)
 	{
@@ -242,18 +242,18 @@ public static class MersenneNumberDivisorByDivisorTester
 		void ProcessPrime(ulong prime)
 		{
 			Console.WriteLine($"Processing {prime}");
-			bool isPrime = tester.IsPrime(prime, out bool divisorsExhausted);
+			bool isPrime = tester.IsPrime(prime, out bool divisorsExhausted, out ulong divisor);
 
 			if (!isPrime)
 			{
 				markComposite();
-				printResult(prime, true, true, false);
+				printResult(prime, true, true, false, divisor);
 				Console.WriteLine($"Finished processing {prime}");
 				return;
 			}
 
 			clearComposite();
-			printResult(prime, true, divisorsExhausted, true);
+			printResult(prime, true, divisorsExhausted, true, divisor);
 			Console.WriteLine($"Finished processing {prime}");
 		}