Initial BitTree implementation added.

PerfectNumbers.Core.Tests/BitTreeSolverTests.cs

@@ -0,0 +1,43 @@
+using System.Numerics;
+using FluentAssertions;
+using PerfectNumbers.Core.Cpu;
+using Xunit;
+
+namespace PerfectNumbers.Core.Tests;
+
+public class BitTreeSolverTests
+{
+    [Fact]
+    public void BitTree_FindsKnownDivisor()
+    {
+        // 2^11-1 = 2047 = 23 * 89, so k=1 yields divisor 23.
+        var tester = new MersenneNumberDivisorByDivisorCpuTesterWithForBitTreeDivisorSetForCpuOrder
+        {
+            DivisorLimit = new BigInteger(1000),
+            MinK = BigInteger.One,
+        };
+
+        bool isPrime = tester.IsPrime(11, out bool exhausted, out BigInteger divisor);
+
+        isPrime.Should().BeFalse();
+        exhausted.Should().BeTrue();
+        divisor.Should().Be(23);
+    }
+
+    [Fact]
+    public void BitTree_ReportsPrimeWhenNoDivisorFound()
+    {
+        // 2^5-1 = 31 is prime.
+        var tester = new MersenneNumberDivisorByDivisorCpuTesterWithForBitTreeDivisorSetForCpuOrder
+        {
+            DivisorLimit = new BigInteger(10_000),
+            MinK = BigInteger.One,
+        };
+
+        bool isPrime = tester.IsPrime(5, out bool exhausted, out BigInteger divisor);
+
+        isPrime.Should().BeTrue();
+        exhausted.Should().BeTrue();
+        divisor.Should().Be(BigInteger.Zero);
+    }
+}