Skip previously excluded by-divisor candidates

EvenPerfectBitScanner/Program.cs

@@ -1,4 +1,5 @@
 using System.Buffers;
+using System.Collections.Generic;
 using System.Globalization;
 using System.Numerics;
 using System.Runtime.CompilerServices;
@@ -36,6 +37,7 @@ internal static class Program
         private static UInt128 _divisor;
         private static MersenneNumberDivisorGpuTester? _divisorTester;
         private static IMersenneNumberDivisorByDivisorTester? _byDivisorTester;
+        private static Dictionary<ulong, (bool DetailedCheck, bool PassedAllTests)>? _byDivisorPreviousResults;
         private static ulong? _orderWarmupLimitOverride;
 	private static unsafe delegate*<ulong, ref ulong, ulong> _transformP;
 	private static long _state;
@@ -588,6 +590,9 @@ internal static class Program
 		}
 
 
+                Dictionary<ulong, (bool DetailedCheck, bool PassedAllTests)>? previousResults = useByDivisor ? new Dictionary<ulong, (bool DetailedCheck, bool PassedAllTests)>() : null;
+                _byDivisorPreviousResults = previousResults;
+
                 if (File.Exists(ResultsFileName))
                 {
                         Console.WriteLine("Processing previous results...");
@@ -597,6 +602,11 @@ internal static class Program
                                 {
                                         _primeCount++;
                                 }
+
+                                if (previousResults is not null)
+                                {
+                                        previousResults[p] = (detailedCheck, passedAllTests);
+                                }
                         });
                 }
                 else
@@ -772,6 +782,8 @@ internal static class Program
                         bool searched = false;
                         bool detailed = false;
                         ulong allowedMax = 0UL;
+                        Dictionary<ulong, (bool DetailedCheck, bool PassedAllTests)>? previousResults = _byDivisorPreviousResults;
+                        int skippedByPreviousResults = 0;
 
                         _byDivisorPrecheckOnly = true;
                         ulong startPrime = _byDivisorStartPrime;
@@ -784,6 +796,12 @@ internal static class Program
                                         continue;
                                 }
 
+                                if (previousResults is not null && previousResults.TryGetValue(prime, out var previousResult) && !previousResult.PassedAllTests)
+                                {
+                                        skippedByPreviousResults++;
+                                        continue;
+                                }
+
                                 if (!IsEvenPerfectCandidate(prime, divisorCyclesSearchLimit, out searched, out detailed))
                                 {
                                         PrintResult(prime, searched, detailed, false);
@@ -811,6 +829,11 @@ internal static class Program
 
                         _byDivisorPrecheckOnly = false;
 
+                        if (skippedByPreviousResults > 0)
+                        {
+                                Console.WriteLine($"Skipped {skippedByPreviousResults.ToString(CultureInfo.InvariantCulture)} primes excluded by previous results.");
+                        }
+
                         if (states.Count == 0)
                         {
                                 if (applyStartPrime)