Merge pull request #76 from mlemanczyk/codex/review-cache-cycle-generation-and-loading

Fix divisor cycle generation range partitioning

PerfectNumbers.Core.Tests/MersenneDivisorCyclesGenerateGpuTests.cs

@@ -49,4 +49,57 @@ public class MersenneDivisorCyclesGenerateGpuTests
             }
         }
     }
+
+    [Fact]
+    [Trait("Category", "Fast")]
+    public void Generate_produces_unique_cycles_for_expected_divisors()
+    {
+        string path = Path.GetTempFileName();
+        try
+        {
+            MersenneDivisorCycles.Generate(path, maxDivisor: 50UL, threads: 4);
+
+            var pairs = new List<(ulong divisor, ulong cycle)>();
+            using var stream = new FileStream(path, FileMode.Open, FileAccess.Read);
+            using var reader = new BinaryReader(stream);
+            while (stream.Position < stream.Length)
+            {
+                ulong divisor = reader.ReadUInt64();
+                ulong cycle = reader.ReadUInt64();
+                pairs.Add((divisor, cycle));
+            }
+
+            var expected = new List<ulong>();
+            for (ulong divisor = 3; divisor <= 50; divisor++)
+            {
+                if ((divisor & 1UL) == 0UL || divisor % 3UL == 0UL || divisor % 5UL == 0UL || divisor % 7UL == 0UL || divisor % 11UL == 0UL)
+                {
+                    continue;
+                }
+
+                expected.Add(divisor);
+            }
+
+            pairs.Should().HaveCount(expected.Count);
+
+            HashSet<ulong> uniqueDivisors = new();
+            foreach (var pair in pairs)
+            {
+                uniqueDivisors.Add(pair.divisor).Should().BeTrue();
+                pair.cycle.Should().Be(MersenneDivisorCycles.CalculateCycleLength(pair.divisor));
+            }
+
+            uniqueDivisors.Should().BeEquivalentTo(expected);
+
+            var (_, completeCount) = MersenneDivisorCycles.FindLast(path);
+            completeCount.Should().Be(expected.Count);
+        }
+        finally
+        {
+            if (File.Exists(path))
+            {
+                File.Delete(path);
+            }
+        }
+    }
 }

PerfectNumbers.Core/MersenneDivisorCycles.cs

@@ -153,8 +153,8 @@ public class MersenneDivisorCycles
         public static void Generate(string path, ulong maxDivisor, int threads = 16)
         {
                 // Binary-only generation of (divisor, cycle) pairs. CSV scaffolding removed.
-		ulong start, d = start = 2;
+                ulong start = 2;
-		ulong blockSize = maxDivisor / (ulong)threads + 1;
+                ulong blockSize = maxDivisor / (ulong)threads + 1UL;
                 Task[] tasks = new Task[threads];
                 using Stream outputStream = new FileStream(path, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.Read, BufferSize10M, useAsync: false);
                 // Start fresh to avoid mixing formats
@@ -163,48 +163,68 @@ public class MersenneDivisorCycles
                 using var writer = new BinaryWriter(outputStream, Encoding.UTF8, leaveOpen: false);
                 for (var taskIndex = 0; taskIndex < threads; taskIndex++)
                 {
-			Task t = Task.Factory.StartNew((taskIndex) =>
+                        ulong threadStart = start + (ulong)taskIndex * blockSize;
+                        if (threadStart > maxDivisor)
                         {
-				ulong cycle, d = start + (ulong)(int)taskIndex! * blockSize;
+                                tasks[taskIndex] = Task.CompletedTask;
-				(ulong d, ulong cycle)[] localCycles = ArrayPool<(ulong, ulong)>.Shared.Rent((int)(maxDivisor - d + 1UL));
-				int localCycleIndex = 0;
-				for (; d <= maxDivisor; d++)
-				{
-					if ((d & 1UL) == 0UL)
-					{
-						// skip even divisors
                                 continue;
                         }
 
-					cycle = CalculateCycleLength(d);
+                        ulong threadEnd = threadStart + blockSize - 1UL;
-
+                        if (threadEnd > maxDivisor)
-					localCycles[localCycleIndex++] = (d, cycle);
+                        {
+                                threadEnd = maxDivisor;
                         }
 
-				if (localCycleIndex > 0)
+                        ulong localStart = threadStart;
+                        ulong localEnd = threadEnd;
+                        tasks[taskIndex] = Task.Run(() =>
                         {
+                                ulong rangeLength = localEnd - localStart + 1UL;
+                                (ulong divisor, ulong cycle)[] localCycles = ArrayPool<(ulong, ulong)>.Shared.Rent(checked((int)rangeLength));
+                                int localCycleIndex = 0;
+
+                                try
+                                {
+                                        for (ulong divisor = localStart; divisor <= localEnd; divisor++)
+                                        {
+                                                if ((divisor & 1UL) == 0UL)
+                                                {
+                                                        continue;
+                                                }
+
+                                                if ((divisor % 3UL) == 0UL || (divisor % 5UL) == 0UL || (divisor % 7UL) == 0UL || (divisor % 11UL) == 0UL)
+                                                {
+                                                        continue;
+                                                }
+
+                                                ulong cycle = CalculateCycleLength(divisor);
+                                                localCycles[localCycleIndex++] = (divisor, cycle);
+                                        }
+
+                                        if (localCycleIndex == 0)
+                                        {
+                                                return;
+                                        }
+
                                         lock (writer)
                                         {
                                                 writer.BaseStream.Position = writer.BaseStream.Length;
                                                 for (int i = 0; i < localCycleIndex; i++)
                                                 {
-							(d, cycle) = localCycles[i];
+                                                        (ulong divisor, ulong cycle) = localCycles[i];
-							if ((d % 3UL) == 0UL || (d % 5UL) == 0UL || (d % 7UL) == 0UL || (d % 11UL) == 0UL)
+                                                        writer.Write(divisor);
-								continue;
-
-							writer.Write(d);
                                                         writer.Write(cycle);
                                                 }
 
                                                 writer.Flush();
                                         }
                                 }
-
+                                finally
+                                {
                                         ArrayPool<(ulong, ulong)>.Shared.Return(localCycles, clearArray: false);
-
+                                }
-			}, taskIndex);
+                        });
-
-			tasks[taskIndex] = t;
                 }
 
                 Task.WaitAll(tasks);