Add three-A-two-B combined divisor schedule

PerfectNumbers.Core.Tests/HeuristicCombinedPrimeTesterTests.cs

@@ -13,7 +13,7 @@ public class HeuristicCombinedPrimeTesterTests
     [InlineData((byte)1)]
     [InlineData((byte)7)]
     [InlineData((byte)9)]
-    public void Enumerator_uses_three_a_one_b_schedule_by_default(byte lastDigit)
+    public void Enumerator_uses_three_a_two_b_schedule_by_default(byte lastDigit)
     {
         Span<HeuristicCombinedPrimeTester.HeuristicGroupBSequenceState> groupBState =
             stackalloc HeuristicCombinedPrimeTester.HeuristicGroupBSequenceState[4];
@@ -49,12 +49,53 @@ public class HeuristicCombinedPrimeTesterTests
                 groupACandidate.Group.Should().NotBe(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupB);
             }
 
+            for (int i = 0; i < 2; i++)
+            {
                 HeuristicCombinedPrimeTester.HeuristicDivisorCandidate groupBCandidate = results[index++];
                 groupBCandidate.Value.Should().BeGreaterThan(13UL);
                 (groupBCandidate.Value % 10UL).Should().NotBe(3UL);
                 groupBCandidate.Group.Should().Be(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupB);
             }
         }
+    }
+
+    [Theory]
+    [Trait("Category", "Fast")]
+    [InlineData((byte)1)]
+    [InlineData((byte)7)]
+    [InlineData((byte)9)]
+    public void Three_a_two_b_pattern_interleaves_three_group_a_values_before_two_group_b_values(byte lastDigit)
+    {
+        ReadOnlySpan<uint> combined = HeuristicCombinedPrimeTester.GetCombinedDivisors(
+            lastDigit,
+            HeuristicCombinedPrimeTester.CombinedDivisorPattern.ThreeATwoB);
+
+        combined.Length.Should().BeGreaterThan(28);
+        combined[0].Should().Be(3U);
+        combined[1].Should().Be(7U);
+        combined[2].Should().Be(11U);
+        combined[3].Should().Be(13U);
+
+        int index = 4;
+        const int segmentsToCheck = 4;
+
+        for (int segment = 0; segment < segmentsToCheck; segment++)
+        {
+            for (int i = 0; i < 3; i++)
+            {
+                uint groupAValue = combined[index++];
+                groupAValue.Should().BeGreaterThan(13U);
+                (groupAValue % 10U).Should().Be(3U);
+            }
+
+            for (int i = 0; i < 2; i++)
+            {
+                uint groupBValue = combined[index++];
+                groupBValue.Should().BeGreaterThan(13U);
+                (groupBValue % 10U).Should().NotBe(3U);
+            }
+        }
+    }
 
     [Theory]
     [Trait("Category", "Fast")]

PerfectNumbers.Core/HeuristicCombinedPrimeTester.cs

@@ -39,6 +39,11 @@ public sealed class HeuristicCombinedPrimeTester
     private static readonly Lazy<uint[]> CombinedDivisorsEnding7ThreeAOneB = new(() => BuildCombinedDivisors(7, CombinedDivisorPattern.ThreeAOneB), LazyThreadSafetyMode.ExecutionAndPublication);
     private static readonly Lazy<uint[]> CombinedDivisorsEnding9ThreeAOneB = new(() => BuildCombinedDivisors(9, CombinedDivisorPattern.ThreeAOneB), LazyThreadSafetyMode.ExecutionAndPublication);
 
+    private static readonly Lazy<uint[]> CombinedDivisorsEnding1ThreeATwoB = new(() => BuildCombinedDivisors(1, CombinedDivisorPattern.ThreeATwoB), LazyThreadSafetyMode.ExecutionAndPublication);
+    private static readonly Lazy<uint[]> CombinedDivisorsEnding3ThreeATwoB = new(() => BuildCombinedDivisors(3, CombinedDivisorPattern.ThreeATwoB), LazyThreadSafetyMode.ExecutionAndPublication);
+    private static readonly Lazy<uint[]> CombinedDivisorsEnding7ThreeATwoB = new(() => BuildCombinedDivisors(7, CombinedDivisorPattern.ThreeATwoB), LazyThreadSafetyMode.ExecutionAndPublication);
+    private static readonly Lazy<uint[]> CombinedDivisorsEnding9ThreeATwoB = new(() => BuildCombinedDivisors(9, CombinedDivisorPattern.ThreeATwoB), LazyThreadSafetyMode.ExecutionAndPublication);
+
     private static readonly ulong[] HeuristicSmallCycleSnapshot = MersenneDivisorCycles.Shared.ExportSmallCyclesSnapshot();
 
     internal enum CombinedDivisorPattern : byte
@@ -46,6 +51,7 @@ public sealed class HeuristicCombinedPrimeTester
         TwoAOneB = 0,
         OneAOneB = 1,
         ThreeAOneB = 2,
+        ThreeATwoB = 3,
     }
 
     internal enum HeuristicDivisorGroup : byte
@@ -404,7 +410,7 @@ Cleanup:
 
     private static ReadOnlySpan<uint> GetCombinedDivisors(byte nMod10)
     {
-        return GetCombinedDivisors(nMod10, CombinedDivisorPattern.ThreeAOneB);
+        return GetCombinedDivisors(nMod10, CombinedDivisorPattern.ThreeATwoB);
     }
 
     internal static ReadOnlySpan<uint> GetCombinedDivisors(byte nMod10, CombinedDivisorPattern pattern)
@@ -435,6 +441,14 @@ Cleanup:
                 9 => CombinedDivisorsEnding9ThreeAOneB.Value,
                 _ => ReadOnlySpan<uint>.Empty,
             },
+            CombinedDivisorPattern.ThreeATwoB => nMod10 switch
+            {
+                1 => CombinedDivisorsEnding1ThreeATwoB.Value,
+                3 => CombinedDivisorsEnding3ThreeATwoB.Value,
+                7 => CombinedDivisorsEnding7ThreeATwoB.Value,
+                9 => CombinedDivisorsEnding9ThreeATwoB.Value,
+                _ => ReadOnlySpan<uint>.Empty,
+            },
             _ => ReadOnlySpan<uint>.Empty,
         };
     }
@@ -454,13 +468,31 @@ Cleanup:
         }
 
         int groupBIndex = GetGroupBStartIndex(groupB);
-        int groupAInterleaveCount = pattern switch
+        int groupAInterleaveCount;
+        int groupBInterleaveCount;
+        switch (pattern)
         {
-            CombinedDivisorPattern.OneAOneB => 1,
+            case CombinedDivisorPattern.OneAOneB:
-            CombinedDivisorPattern.TwoAOneB => 2,
+                groupAInterleaveCount = 1;
-            CombinedDivisorPattern.ThreeAOneB => 3,
+                groupBInterleaveCount = 1;
-            _ => 2,
+                break;
-        };
+            case CombinedDivisorPattern.TwoAOneB:
+                groupAInterleaveCount = 2;
+                groupBInterleaveCount = 1;
+                break;
+            case CombinedDivisorPattern.ThreeAOneB:
+                groupAInterleaveCount = 3;
+                groupBInterleaveCount = 1;
+                break;
+            case CombinedDivisorPattern.ThreeATwoB:
+                groupAInterleaveCount = 3;
+                groupBInterleaveCount = 2;
+                break;
+            default:
+                groupAInterleaveCount = 2;
+                groupBInterleaveCount = 1;
+                break;
+        }
 
         while (groupAIndex < groupA.Length || groupBIndex < groupB.Length)
         {
@@ -472,10 +504,12 @@ Cleanup:
                 addedA++;
             }
 
-            if (groupBIndex < groupB.Length)
+            int addedB = 0;
+            while (addedB < groupBInterleaveCount && groupBIndex < groupB.Length)
             {
                 combined.Add(groupB[groupBIndex]);
                 groupBIndex++;
+                addedB++;
             }
         }