Пример #1
0
        public static int FindBestMove(SearchContext context, int depth, int ply, int alpha, int beta, bool allowNullMove, bool friendlyKingInCheck)
        {
            if (context.Statistics.Nodes >= context.MaxNodesCount)
            {
                context.AbortSearch = true;
                return(0);
            }

            if (context.AbortSearch)
            {
                return(0);
            }

            context.Statistics.Nodes++;

            if (context.BoardState.Pieces[context.BoardState.ColorToMove][Piece.King] == 0)
            {
                context.Statistics.Leafs++;
                return(-EvaluationConstants.Checkmate + ply);
            }

            if (context.BoardState.IsThreefoldRepetition())
            {
                context.Statistics.Leafs++;
                return(EvaluationConstants.ThreefoldRepetition);
            }

            if (context.BoardState.IsInsufficientMaterial())
            {
                if (!friendlyKingInCheck && !context.BoardState.IsKingChecked(ColorOperations.Invert(context.BoardState.ColorToMove)))
                {
                    context.Statistics.Leafs++;
                    return(EvaluationConstants.InsufficientMaterial);
                }
            }

            if (context.BoardState.IsFiftyMoveRuleDraw())
            {
                context.Statistics.Leafs++;

                if (context.BoardState.IsKingChecked(ColorOperations.Invert(context.BoardState.ColorToMove)))
                {
                    return(EvaluationConstants.Checkmate + ply);
                }

                return(EvaluationConstants.ThreefoldRepetition);
            }

            if (depth <= 0)
            {
                context.Statistics.Leafs++;
                return(QuiescenceSearch.FindBestMove(context, depth, ply, alpha, beta));
            }

            var originalAlpha = alpha;
            var pvNode        = beta - alpha > 1;

            var entry    = TranspositionTable.Get(context.BoardState.Hash);
            var hashMove = Move.Empty;

            if (entry.Flags != TranspositionTableEntryFlags.Invalid && entry.IsKeyValid(context.BoardState.Hash))
            {
#if DEBUG
                context.Statistics.TTHits++;
#endif
                if (entry.Flags != TranspositionTableEntryFlags.AlphaScore)
                {
                    var isMoveLegal = context.BoardState.IsMoveLegal(entry.BestMove);
                    if (isMoveLegal)
                    {
                        hashMove = entry.BestMove;
#if DEBUG
                        context.Statistics.TTValidMoves++;
#endif
                    }
#if DEBUG
                    else
                    {
                        context.Statistics.TTInvalidMoves++;
                    }
#endif
                }

                if (entry.Depth >= depth)
                {
                    switch (entry.Flags)
                    {
                    case TranspositionTableEntryFlags.AlphaScore:
                    {
                        if (entry.Score < beta)
                        {
                            beta = entry.Score;
                        }

                        break;
                    }

                    case TranspositionTableEntryFlags.ExactScore:
                    {
                        if (!pvNode)
                        {
                            entry.Score = (short)TranspositionTable.TTToRegularScore(entry.Score, ply);
                            return(entry.Score);
                        }

                        break;
                    }

                    case TranspositionTableEntryFlags.BetaScore:
                    {
                        if (entry.Score > alpha)
                        {
                            alpha = entry.Score;
                        }

                        break;
                    }
                    }

                    if (alpha >= beta)
                    {
                        context.Statistics.BetaCutoffs++;
                        return(entry.Score);
                    }
                }
            }
#if DEBUG
            else
            {
                context.Statistics.TTNonHits++;
            }
#endif

            if (NullWindowCanBeApplied(context.BoardState, depth, allowNullMove, pvNode, friendlyKingInCheck))
            {
                context.BoardState.MakeNullMove();
                var score = -FindBestMove(context, depth - 1 - SearchConstants.NullWindowDepthReduction, ply + 1, -beta, -beta + 1, false, false);
                context.BoardState.UndoNullMove();

                if (score >= beta)
                {
                    context.Statistics.BetaCutoffs++;
                    return(score);
                }
            }

            if (IIDCanBeApplied(depth, entry.Flags, hashMove))
            {
                FindBestMove(context, depth - 1 - SearchConstants.IIDDepthReduction, ply, alpha, beta, allowNullMove, friendlyKingInCheck);

                var iidEntry = TranspositionTable.Get(context.BoardState.Hash);
                if (iidEntry.IsKeyValid(context.BoardState.Hash))
                {
                    hashMove = iidEntry.BestMove;

#if DEBUG
                    context.Statistics.IIDHits++;
#endif
                }
            }

            Span <Move>  moves      = stackalloc Move[SearchConstants.MaxMovesCount];
            Span <short> moveValues = stackalloc short[SearchConstants.MaxMovesCount];
            var          bestMove   = Move.Empty;
            var          movesCount = 0;

            var loudMovesGenerated  = false;
            var quietMovesGenerated = false;

            if (hashMove == Move.Empty)
            {
                movesCount = context.BoardState.GetLoudMoves(moves, 0);
                MoveOrdering.AssignLoudValues(context.BoardState, moves, moveValues, movesCount, depth, bestMove);
                loudMovesGenerated = true;

                context.Statistics.LoudMovesGenerated++;

                if (movesCount == 0)
                {
                    movesCount = context.BoardState.GetQuietMoves(moves, 0);
                    MoveOrdering.AssignQuietValues(context.BoardState, moves, moveValues, 0, movesCount, depth);
                    quietMovesGenerated = true;

                    context.Statistics.QuietMovesGenerated++;
                }
            }
            else
            {
                moves[0]      = hashMove;
                moveValues[0] = MoveOrderingConstants.HashMove;
                movesCount    = 1;
            }

            var pvs = true;
            for (var moveIndex = 0; moveIndex < movesCount; moveIndex++)
            {
                MoveOrdering.SortNextBestMove(moves, moveValues, movesCount, moveIndex);

                if (loudMovesGenerated && moves[moveIndex] == hashMove)
                {
                    goto postLoopOperations;
                }

                if (loudMovesGenerated && !quietMovesGenerated && moveValues[moveIndex] < 100)
                {
                    var loudMovesCount = movesCount;

                    movesCount = context.BoardState.GetQuietMoves(moves, movesCount);
                    MoveOrdering.AssignQuietValues(context.BoardState, moves, moveValues, loudMovesCount, movesCount, depth);
                    MoveOrdering.SortNextBestMove(moves, moveValues, movesCount, moveIndex);
                    quietMovesGenerated = true;

                    context.Statistics.QuietMovesGenerated++;

                    if (moves[moveIndex] == hashMove)
                    {
                        goto postLoopOperations;
                    }
                }

                if (context.MoveRestrictions != null && ply == 0)
                {
                    if (!context.MoveRestrictions.Contains(moves[moveIndex]))
                    {
                        continue;
                    }
                }

                context.BoardState.MakeMove(moves[moveIndex]);

                var score            = 0;
                var enemyKingInCheck = context.BoardState.IsKingChecked(context.BoardState.ColorToMove);

                if (pvs)
                {
                    score = -FindBestMove(context, depth - 1, ply + 1, -beta, -alpha, allowNullMove, enemyKingInCheck);
                    pvs   = false;
                }
                else
                {
                    var reducedDepth = depth;

                    if (LMRCanBeApplied(depth, friendlyKingInCheck, enemyKingInCheck, moveIndex, moves))
                    {
                        reducedDepth = LMRGetReducedDepth(depth, pvNode);
                    }

                    score = -FindBestMove(context, reducedDepth - 1, ply + 1, -alpha - 1, -alpha, allowNullMove, enemyKingInCheck);
                    if (score > alpha)
                    {
                        score = -FindBestMove(context, depth - 1, ply + 1, -beta, -alpha, allowNullMove, enemyKingInCheck);
                    }
                }

                context.BoardState.UndoMove(moves[moveIndex]);

                if (score > alpha)
                {
                    alpha    = score;
                    bestMove = moves[moveIndex];

                    if (alpha >= beta)
                    {
                        if (moves[moveIndex].IsQuiet())
                        {
                            KillerHeuristic.AddKillerMove(moves[moveIndex], context.BoardState.ColorToMove, depth);
                            HistoryHeuristic.AddHistoryMove(context.BoardState.ColorToMove, moves[moveIndex].From, moves[moveIndex].To, depth);
                        }

#if DEBUG
                        if (moveIndex == 0)
                        {
                            context.Statistics.BetaCutoffsAtFirstMove++;
                        }
                        else
                        {
                            context.Statistics.BetaCutoffsNotAtFirstMove++;
                        }
#endif

                        context.Statistics.BetaCutoffs++;
                        break;
                    }
                }

postLoopOperations:
                if (!loudMovesGenerated)
                {
                    movesCount = context.BoardState.GetLoudMoves(moves, 0);
                    MoveOrdering.AssignLoudValues(context.BoardState, moves, moveValues, movesCount, depth, bestMove);
                    moveIndex          = -1;
                    loudMovesGenerated = true;

                    context.Statistics.LoudMovesGenerated++;

                    if (movesCount == 0)
                    {
                        movesCount = context.BoardState.GetQuietMoves(moves, 0);
                        MoveOrdering.AssignQuietValues(context.BoardState, moves, moveValues, 0, movesCount, depth);
                        quietMovesGenerated = true;

                        context.Statistics.QuietMovesGenerated++;
                    }
                }

                if (!quietMovesGenerated && moveIndex == movesCount - 1)
                {
                    var loudMovesCount = movesCount;

                    movesCount = context.BoardState.GetQuietMoves(moves, movesCount);
                    MoveOrdering.AssignQuietValues(context.BoardState, moves, moveValues, loudMovesCount, movesCount, depth);
                    quietMovesGenerated = true;

                    context.Statistics.QuietMovesGenerated++;
                }
            }

            // Don't save invalid scores to the transposition table
            if (context.AbortSearch)
            {
                return(0);
            }

            // Don't add invalid move (done after checkmate) to prevent strange behaviors
            if (alpha == -(-EvaluationConstants.Checkmate + ply + 1))
            {
                return(alpha);
            }

            // Return draw score or checkmate score as leafs
            if (alpha == -EvaluationConstants.Checkmate + ply + 2)
            {
                if (context.BoardState.IsKingChecked(context.BoardState.ColorToMove))
                {
                    return(alpha);
                }

                return(0);
            }

            if (entry.Age != context.TranspositionTableEntryAge || entry.Depth <= depth)
            {
                var valueToSave = alpha;
                var entryType   = alpha <= originalAlpha ? TranspositionTableEntryFlags.AlphaScore :
                                  alpha >= beta ? TranspositionTableEntryFlags.BetaScore :
                                  TranspositionTableEntryFlags.ExactScore;

                if (entryType == TranspositionTableEntryFlags.ExactScore)
                {
                    valueToSave = TranspositionTable.RegularToTTScore(alpha, ply);
                }

                TranspositionTable.Add(context.BoardState.Hash, new TranspositionTableEntry(
                                           context.BoardState.Hash,
                                           (short)valueToSave, bestMove,
                                           (byte)depth, entryType,
                                           (byte)context.TranspositionTableEntryAge)
                                       );

#if DEBUG
                if (entry.Flags != TranspositionTableEntryFlags.Invalid)
                {
                    context.Statistics.TTReplacements++;
                }

                context.Statistics.TTAddedEntries++;
#endif
            }

            return(alpha);
        }
Пример #2
0
        public static int FindBestMove(SearchContext context, int depth, int ply, int alpha, int beta, bool allowNullMove, bool friendlyKingInCheck, int extensionsCount)
        {
            if (context.Statistics.Nodes >= context.MaxNodesCount)
            {
                context.AbortSearch = true;
                return(0);
            }

            if (context.AbortSearch)
            {
                return(0);
            }

            context.Statistics.Nodes++;

            if (context.BoardState.Pieces[context.BoardState.ColorToMove][Piece.King] == 0)
            {
                context.Statistics.Leafs++;
                return(SearchConstants.NoKingValue);
            }

            if (context.BoardState.IsKingChecked(ColorOperations.Invert(context.BoardState.ColorToMove)))
            {
                context.Statistics.Leafs++;
                return(-SearchConstants.NoKingValue);
            }

            if (context.BoardState.IsThreefoldRepetition())
            {
                context.Statistics.Leafs++;
                return(EvaluationConstants.ThreefoldRepetition);
            }

            if (context.BoardState.IsInsufficientMaterial())
            {
                var enemyColor = ColorOperations.Invert(context.BoardState.ColorToMove);
                if (!friendlyKingInCheck && !context.BoardState.IsKingChecked(enemyColor))
                {
                    context.Statistics.Leafs++;
                    return(EvaluationConstants.InsufficientMaterial);
                }
            }

            if (context.BoardState.IsFiftyMoveRuleDraw())
            {
                context.Statistics.Leafs++;
                return(EvaluationConstants.ThreefoldRepetition);
            }

            if (depth <= 0)
            {
                context.Statistics.Leafs++;
                return(QuiescenceSearch.FindBestMove(context, depth, ply, alpha, beta));
            }

            var originalAlpha = alpha;
            var pvNode        = beta - alpha > 1;

            var entry    = TranspositionTable.Get(context.BoardState.Hash);
            var hashMove = Move.Empty;
            var bestMove = Move.Empty;

            if (entry.Flags != TranspositionTableEntryFlags.Invalid && entry.IsKeyValid(context.BoardState.Hash))
            {
#if DEBUG
                context.Statistics.TTHits++;
#endif
                if (entry.Flags != TranspositionTableEntryFlags.AlphaScore)
                {
                    var isMoveLegal = context.BoardState.IsMoveLegal(entry.BestMove);
                    if (isMoveLegal)
                    {
                        hashMove = entry.BestMove;
                        bestMove = entry.BestMove;
#if DEBUG
                        context.Statistics.TTValidMoves++;
#endif
                    }
#if DEBUG
                    else
                    {
                        context.Statistics.TTInvalidMoves++;
                    }
#endif
                }

                if (entry.Depth >= depth)
                {
                    entry.Score = (short)TranspositionTable.TTToRegularScore(entry.Score, ply);
                    switch (entry.Flags)
                    {
                    case TranspositionTableEntryFlags.AlphaScore:
                    {
                        if (entry.Score < beta)
                        {
                            beta = entry.Score;
                        }

                        break;
                    }

                    case TranspositionTableEntryFlags.ExactScore:
                    {
                        if (!pvNode || IterativeDeepening.IsScoreNearCheckmate(entry.Score))
                        {
                            return(entry.Score);
                        }

                        break;
                    }

                    case TranspositionTableEntryFlags.BetaScore:
                    {
                        if (entry.Score > alpha)
                        {
                            alpha = entry.Score;
                        }

                        break;
                    }
                    }

                    if (alpha >= beta)
                    {
                        context.Statistics.BetaCutoffs++;
                        return(entry.Score);
                    }
                }
            }
#if DEBUG
            else
            {
                entry = TranspositionTableEntry.Empty;
                context.Statistics.TTNonHits++;
            }
#endif

            if (RazoringCanBeApplied(depth, context.Statistics.Depth, friendlyKingInCheck, pvNode, alpha))
            {
                var fastEvaluation = Evaluation.FastEvaluate(context.BoardState, context.Statistics.EvaluationStatistics);
                var margin         = SearchConstants.RazoringMargin + (depth - SearchConstants.RazoringMinDepth) * SearchConstants.RazoringMarginMultiplier;
                var futileAlpha    = alpha - margin;

                if (fastEvaluation < futileAlpha)
                {
                    var result = QuiescenceSearch.FindBestMove(context, depth, ply, futileAlpha, futileAlpha + 1);
                    if (result <= futileAlpha)
                    {
#if DEBUG
                        context.Statistics.Razorings++;
#endif
                        return(futileAlpha);
                    }
#if DEBUG
                    else
                    {
                        context.Statistics.RazoringsRejected++;
                    }
#endif
                }
            }

            if (StaticNullMoveCanBeApplied(depth, context.Statistics.Depth, friendlyKingInCheck, pvNode, beta))
            {
                var fastEvaluation = Evaluation.FastEvaluate(context.BoardState, context.Statistics.EvaluationStatistics);
                var margin         = SearchConstants.StaticNullMoveMargin + (depth - 1) * SearchConstants.StaticNullMoveMarginMultiplier;
                var score          = fastEvaluation - margin;

                if (score >= beta)
                {
#if DEBUG
                    context.Statistics.StaticNullMovePrunes++;
#endif

                    return(score);
                }
            }

            if (NullMoveCanBeApplied(context.BoardState, depth, allowNullMove, pvNode, friendlyKingInCheck))
            {
                context.BoardState.MakeNullMove();
                var score = -FindBestMove(context, depth - 1 - NullMoveGetReduction(depth), ply + 1, -beta, -beta + 1, false, false, extensionsCount);
                context.BoardState.UndoNullMove();

                if (score >= beta)
                {
#if DEBUG
                    context.Statistics.NullMovePrunes++;
#endif

                    return(score);
                }
            }

            if (IIDCanBeApplied(depth, entry.Flags, hashMove))
            {
                FindBestMove(context, depth - 1 - SearchConstants.IIDDepthReduction, ply, alpha, beta, allowNullMove, friendlyKingInCheck, extensionsCount);

                var iidEntry = TranspositionTable.Get(context.BoardState.Hash);
                if (iidEntry.IsKeyValid(context.BoardState.Hash))
                {
                    hashMove = iidEntry.BestMove;

#if DEBUG
                    context.Statistics.IIDHits++;
#endif
                }
            }

            var futilityPruningCanBeApplied = false;
            var futilityPruningEvaluation   = 0;
            var futilityPruningMargin       = 0;

            if (FutilityPruningCanBeApplied(depth, context.Statistics.Depth, friendlyKingInCheck, pvNode, alpha))
            {
                futilityPruningCanBeApplied = true;
                futilityPruningEvaluation   = Evaluation.FastEvaluate(context.BoardState, context.Statistics.EvaluationStatistics);
                futilityPruningMargin       = SearchConstants.FutilityPruningMargin + (depth - 1) * SearchConstants.FutilityPruningMarginMultiplier;
            }

            Span <Move>  moves      = stackalloc Move[SearchConstants.MaxMovesCount];
            Span <short> moveValues = stackalloc short[SearchConstants.MaxMovesCount];
            var          movesCount = 0;

            var loudMovesGenerated  = false;
            var quietMovesGenerated = false;

            var evasionMask = ulong.MaxValue;
            if (friendlyKingInCheck && !context.BoardState.IsKingChecked(ColorOperations.Invert(context.BoardState.ColorToMove)))
            {
                var kingField      = context.BoardState.Pieces[context.BoardState.ColorToMove][Piece.King];
                var kingFieldIndex = BitOperations.BitScan(kingField);

                evasionMask = KnightMovesGenerator.GetMoves(kingFieldIndex) |
                              QueenMovesGenerator.GetMoves(context.BoardState.OccupancySummary, kingFieldIndex);
            }

            if (hashMove == Move.Empty)
            {
                movesCount = context.BoardState.GetLoudMoves(moves, 0, evasionMask);
                MoveOrdering.AssignLoudValues(context.BoardState, moves, moveValues, movesCount, depth, Move.Empty);
                loudMovesGenerated = true;

#if DEBUG
                context.Statistics.LoudMovesGenerated++;
#endif

                if (movesCount == 0)
                {
                    movesCount = context.BoardState.GetQuietMoves(moves, 0, evasionMask);
                    MoveOrdering.AssignQuietValues(context.BoardState, moves, moveValues, 0, movesCount, ply);
                    quietMovesGenerated = true;

#if DEBUG
                    context.Statistics.QuietMovesGenerated++;
#endif
                }
            }
            else
            {
                moves[0]      = hashMove;
                moveValues[0] = MoveOrderingConstants.HashMove;
                movesCount    = 1;
            }

            var pvs            = true;
            var bestScore      = 0;
            var allMovesPruned = true;

            for (var moveIndex = 0; moveIndex < movesCount; moveIndex++)
            {
                if (LMPCanBeApplied(context, depth, friendlyKingInCheck, quietMovesGenerated, moveIndex, movesCount, pvNode))
                {
                    break;
                }

                MoveOrdering.SortNextBestMove(moves, moveValues, movesCount, moveIndex);

                if (loudMovesGenerated && moves[moveIndex] == hashMove)
                {
                    goto postLoopOperations;
                }

                if (loudMovesGenerated && !quietMovesGenerated && moveValues[moveIndex] < 100)
                {
                    var loudMovesCount = movesCount;

                    movesCount = context.BoardState.GetQuietMoves(moves, movesCount, evasionMask);
                    MoveOrdering.AssignQuietValues(context.BoardState, moves, moveValues, loudMovesCount, movesCount, ply);
                    MoveOrdering.SortNextBestMove(moves, moveValues, movesCount, moveIndex);
                    quietMovesGenerated = true;

#if DEBUG
                    context.Statistics.QuietMovesGenerated++;
#endif

                    if (moves[moveIndex] == hashMove)
                    {
                        goto postLoopOperations;
                    }
                }

                if (context.MoveRestrictions != null && ply == 0)
                {
                    if (!context.MoveRestrictions.Contains(moves[moveIndex]))
                    {
                        goto postLoopOperations;
                    }
                }

                context.BoardState.MakeMove(moves[moveIndex]);

                var enemyKingInCheck = context.BoardState.IsKingChecked(context.BoardState.ColorToMove);
                var extension        = GetExtensions(depth, extensionsCount, enemyKingInCheck);

#if DEBUG
                context.Statistics.Extensions += extension;
#endif

                if (futilityPruningCanBeApplied && FutilityPruningCanBeAppliedForMove(context, moves[moveIndex], enemyKingInCheck, pvs))
                {
                    var gain = FutilityPruningGetGain(context, moves[moveIndex]);
                    if (futilityPruningEvaluation + futilityPruningMargin + gain <= alpha)
                    {
#if DEBUG
                        context.Statistics.FutilityPrunes++;
#endif

                        context.BoardState.UndoMove(moves[moveIndex]);
                        goto postLoopOperations;
                    }
                }

                allMovesPruned = false;

                if (pvs)
                {
                    bestScore = -FindBestMove(context, depth - 1 + extension, ply + 1, -beta, -alpha, allowNullMove, enemyKingInCheck, extensionsCount + extension);
                    pvs       = false;
                }
                else
                {
                    var lmrReduction = 0;
                    if (LMRCanBeApplied(context, depth, friendlyKingInCheck, enemyKingInCheck, moveIndex, moves, moveValues))
                    {
                        lmrReduction = LMRGetReduction(pvNode, moveIndex);
                    }

                    var score = -FindBestMove(context, depth - lmrReduction - 1 + extension, ply + 1, -alpha - 1, -alpha, allowNullMove, enemyKingInCheck, extensionsCount + extension);
                    if (score > alpha)
                    {
                        if (pvNode)
                        {
                            score = -FindBestMove(context, depth - 1 + extension, ply + 1, -beta, -alpha, allowNullMove, enemyKingInCheck, extensionsCount + extension);
                        }
                        else
                        {
                            if (lmrReduction != 0)
                            {
                                score = -FindBestMove(context, depth - 1 + extension, ply + 1, -beta, -alpha, allowNullMove, enemyKingInCheck, extensionsCount + extension);
                            }
                        }
                    }

                    if (score > bestScore)
                    {
                        bestScore = score;
                    }
                }

                context.BoardState.UndoMove(moves[moveIndex]);

                if (bestScore > alpha)
                {
                    alpha    = bestScore;
                    bestMove = moves[moveIndex];

                    if (alpha >= beta)
                    {
                        if (moves[moveIndex].IsQuiet())
                        {
                            KillerHeuristic.AddKillerMove(moves[moveIndex], context.BoardState.ColorToMove, ply);
                            HistoryHeuristic.AddHistoryMove(context.BoardState.ColorToMove, context.BoardState.PieceTable[moves[moveIndex].From], moves[moveIndex].To, depth);
                        }

#if DEBUG
                        if (moveIndex == 0)
                        {
                            context.Statistics.BetaCutoffsAtFirstMove++;
                        }
                        else
                        {
                            context.Statistics.BetaCutoffsNotAtFirstMove++;
                        }
#endif

                        context.Statistics.BetaCutoffs++;
                        break;
                    }
                }

postLoopOperations:
                if (!loudMovesGenerated)
                {
                    movesCount = context.BoardState.GetLoudMoves(moves, 0, evasionMask);
                    MoveOrdering.AssignLoudValues(context.BoardState, moves, moveValues, movesCount, depth, hashMove);
                    moveIndex          = -1;
                    loudMovesGenerated = true;

#if DEBUG
                    context.Statistics.LoudMovesGenerated++;
#endif

                    if (movesCount == 0)
                    {
                        movesCount = context.BoardState.GetQuietMoves(moves, 0, evasionMask);
                        MoveOrdering.AssignQuietValues(context.BoardState, moves, moveValues, 0, movesCount, ply);
                        quietMovesGenerated = true;

#if DEBUG
                        context.Statistics.QuietMovesGenerated++;
#endif
                    }
                }

                if (!quietMovesGenerated && moveIndex == movesCount - 1)
                {
                    var loudMovesCount = movesCount;

                    movesCount = context.BoardState.GetQuietMoves(moves, movesCount, evasionMask);
                    MoveOrdering.AssignQuietValues(context.BoardState, moves, moveValues, loudMovesCount, movesCount, ply);
                    quietMovesGenerated = true;

#if DEBUG
                    context.Statistics.QuietMovesGenerated++;
#endif
                }
            }

            // Don't save invalid scores to the transposition table
            if (context.AbortSearch)
            {
                return(0);
            }

            if (allMovesPruned)
            {
                return(alpha);
            }

            // Don't add invalid move (done after checkmate) to prevent strange behaviors
            if (bestScore == -SearchConstants.NoKingValue)
            {
                return(bestScore);
            }

            // Return draw score or checkmate score as leafs
            if (bestScore == SearchConstants.NoKingValue)
            {
                if (friendlyKingInCheck)
                {
                    return(-EvaluationConstants.Checkmate + ply);
                }

                return(0);
            }

            if (entry.Flags == TranspositionTableEntryFlags.Invalid || alpha != originalAlpha)
            {
                if (entry.Age != context.TranspositionTableEntryAge || entry.Depth <= depth)
                {
                    var valueToSave = alpha;
                    var entryType   = alpha <= originalAlpha ? TranspositionTableEntryFlags.AlphaScore :
                                      alpha >= beta ? TranspositionTableEntryFlags.BetaScore :
                                      TranspositionTableEntryFlags.ExactScore;

                    valueToSave = TranspositionTable.RegularToTTScore(alpha, ply);

                    TranspositionTable.Add(context.BoardState.Hash, new TranspositionTableEntry(
                                               context.BoardState.Hash,
                                               (short)valueToSave, bestMove,
                                               (byte)depth, entryType,
                                               (byte)context.TranspositionTableEntryAge)
                                           );

#if DEBUG
                    if (entry.Flags != TranspositionTableEntryFlags.Invalid)
                    {
                        context.Statistics.TTReplacements++;
                    }

                    context.Statistics.TTAddedEntries++;
#endif
                }
            }

            return(bestScore);
        }