Remove aspiration windows

src/Lynx/Search/IDDFS.cs

@@ -104,56 +104,7 @@ public SearchResult IDDFS(int maxDepth, int softLimitTimeBound)
                 _absoluteSearchCancellationTokenSource.Token.ThrowIfCancellationRequested();
                 _searchCancellationTokenSource.Token.ThrowIfCancellationRequested();
 
-                if (depth < Configuration.EngineSettings.AspirationWindow_MinDepth
-                    || lastSearchResult?.Score is null)
-                {
-                    bestScore = NegaMax(depth: depth, ply: 0, alpha, beta);
-                }
-                else
-                {
-                    // 🔍 Aspiration windows - search using a window around an expected score (the previous search one)
-                    // If the resulting score doesn't fall inside of the window, it is widened it until it does
-                    var window = Configuration.EngineSettings.AspirationWindow_Base;
-
-                    // A temporary reduction is used for fail highs, because the verification for those 'too good' lines
-                    // are expected to happen at lower depths
-                    int failHighReduction = 0;
-
-                    alpha = Math.Max(EvaluationConstants.MinEval, lastSearchResult.Score - window);
-                    beta = Math.Min(EvaluationConstants.MaxEval, lastSearchResult.Score + window);
-
-                    _logger.Debug("Aspiration windows depth {Depth}: [{Alpha}, {Beta}] for previous search score {Score}, nodes {Nodes}",
-                        depth, alpha, beta, lastSearchResult.Score, _nodes);
-                    Debug.Assert(lastSearchResult.Mate == 0 && lastSearchResult.Score > EvaluationConstants.NegativeCheckmateDetectionLimit && lastSearchResult.Score < EvaluationConstants.PositiveCheckmateDetectionLimit);
-
-                    while (true)
-                    {
-                        _logger.Debug("Aspiration windows depth {Depth}: [{Alpha}, {Beta}] for score {Score}, nodes {Nodes}",
-                            depth, alpha, beta, bestScore, _nodes);
-
-                        bestScore = NegaMax(depth: depth - failHighReduction, ply: 0, alpha, beta);
-
-                        // 13, 19, 28, 42, 63, 94, 141, 211, 316, 474, 711, 1066, 1599, 2398, 3597, 5395, 8092, 12138, 18207, 27310, |EvaluationConstants.MaxEval|, 40965
-                        window += window >> 1;   // window / 2
-
-                        // Depth change: https://github.com/lynx-chess/Lynx/pull/440
-                        if (alpha >= bestScore)     // Fail low
-                        {
-                            alpha = Math.Max(bestScore - window, EvaluationConstants.MinEval);
-                            beta = (alpha + beta) >> 1;  // (alpha + beta) / 2
-                            failHighReduction = 0;
-                        }
-                        else if (beta <= bestScore)     // Fail high
-                        {
-                            beta = Math.Min(bestScore + window, EvaluationConstants.MaxEval);
-                            ++failHighReduction;
-                        }
-                        else
-                        {
-                            break;
-                        }
-                    }
-                }
+                bestScore = NegaMax(depth: depth, ply: 0, alpha, beta);
 
                 //PrintPvTable(depth: depth);
                 ValidatePVTable();