Add three-A-one-B schedule to combined tester

PerfectNumbers.Core.Tests/HeuristicCombinedPrimeTesterTests.cs

@@ -0,0 +1,93 @@
+using System;
+using System.Collections.Generic;
+using PerfectNumbers.Core;
+using FluentAssertions;
+using Xunit;
+
+namespace PerfectNumbers.Core.Tests;
+
+public class HeuristicCombinedPrimeTesterTests
+{
+    [Theory]
+    [Trait("Category", "Fast")]
+    [InlineData((byte)1)]
+    [InlineData((byte)7)]
+    [InlineData((byte)9)]
+    public void Enumerator_uses_three_a_one_b_schedule_by_default(byte lastDigit)
+    {
+        Span<HeuristicCombinedPrimeTester.HeuristicGroupBSequenceState> groupBState =
+            stackalloc HeuristicCombinedPrimeTester.HeuristicGroupBSequenceState[4];
+
+        var enumerator = HeuristicCombinedPrimeTester.CreateHeuristicDivisorEnumerator(500, lastDigit, groupBState);
+        var results = new List<HeuristicCombinedPrimeTester.HeuristicDivisorCandidate>(32);
+
+        while (results.Count < 20 && enumerator.TryGetNext(out var candidate))
+        {
+            results.Add(candidate);
+        }
+
+        results.Count.Should().BeGreaterThanOrEqualTo(16);
+        results[0].Value.Should().Be(3UL);
+        results[0].Group.Should().Be(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupAConstant);
+        results[1].Value.Should().Be(7UL);
+        results[1].Group.Should().Be(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupAConstant);
+        results[2].Value.Should().Be(11UL);
+        results[2].Group.Should().Be(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupAConstant);
+        results[3].Value.Should().Be(13UL);
+        results[3].Group.Should().Be(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupAConstant);
+
+        int index = 4;
+        const int segmentsToCheck = 3;
+
+        for (int segment = 0; segment < segmentsToCheck; segment++)
+        {
+            for (int i = 0; i < 3; i++)
+            {
+                HeuristicCombinedPrimeTester.HeuristicDivisorCandidate groupACandidate = results[index++];
+                groupACandidate.Value.Should().BeGreaterThan(13UL);
+                (groupACandidate.Value % 10UL).Should().Be(3UL);
+                groupACandidate.Group.Should().NotBe(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupB);
+            }
+
+            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_one_b_pattern_interleaves_three_group_a_values_before_group_b(byte lastDigit)
+    {
+        ReadOnlySpan<uint> combined = HeuristicCombinedPrimeTester.GetCombinedDivisors(
+            lastDigit,
+            HeuristicCombinedPrimeTester.CombinedDivisorPattern.ThreeAOneB);
+
+        combined.Length.Should().BeGreaterThan(24);
+        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);
+            }
+
+            uint groupBValue = combined[index++];
+            groupBValue.Should().BeGreaterThan(13U);
+            (groupBValue % 10U).Should().NotBe(3U);
+        }
+    }
+}