国际象棋编程(没有AI)——走法验证

对于给定的棋盘位置，大多数国际象棋引擎仅从生成伪合法移动开始。所谓伪合法，我的意思是即使它:

• 让国王在检查
• 移动国王到检查
• 被攻击的广场上的城堡

这样做的原因是性能。由于beta修剪，许多移动实际上不会被搜索，您可以通过避免对移动有效性进行全面检查来节省时间。

对于被搜索的每一个移动，您需要检查它是否真的有效。这通常是通过将国王的颜色和方块(以及国王旁边的方块)传递给 isattack 方法来完成的。如果这个方法返回true，你知道这个移动是无效的，因此你不应该在你的搜索中包含它。

这是我自己的c#象棋引擎中的 isattack 方法。请记住，我的引擎是基于魔法位板的，所以代码不能直接适用于您所链接的象棋初学者工具包。除非您熟悉魔法位板，否则翻译不会是微不足道的。

// IsAttacked is primarily used as a move legality test to see if a set of 
// one or more squares is under attack from the side to move.
// It returns true as soon as an attack is detected, otherwise returns false.
// It can be used for check detection, castling legality, or simply to 
// detect whether a specific square is attacked.
internal bool IsAttacked(Board board, UInt64 targetSquares, bool whiteAttacking)
{
    UInt64 slidingAttackers; Int32 targetSquare;
    UInt64 remainingTargetSquares = targetSquares;
    // Test for attacks by WHITE on any of the target squares.
    if (whiteAttacking) 
    {
        // For the remaining target squares...
        while (remainingTargetSquares != 0)
        {
            // Find the next square in the list.
            targetSquare = BitOperations.BitScanForward(remainingTargetSquares);
            // Is this square attacked by a pawn, knight, or king?
            if ((board.WhitePawns & Constants.BLACK_PAWN_ATTACKS[targetSquare]) != 0) return true;
            if ((board.WhiteKnights & Constants.KNIGHT_ATTACKS[targetSquare]) != 0) return true;
            if ((board.WhiteKing & Constants.KING_ATTACKS[targetSquare]) != 0) return true;
            // Is this square attacked by a queen or rook along a file or rank?
            slidingAttackers = board.WhiteQueens | board.WhiteRooks;
            if (slidingAttackers != 0)
            {
                if (this.RankMoves(board.OccupiedSquares, slidingAttackers, targetSquare) != 0) return true;
                if (this.FileMoves(board.OccupiedSquares, slidingAttackers, targetSquare) != 0) return true;
            }
            // Is this square attacked by a queen or bishop along a diagonal?
            slidingAttackers = board.WhiteQueens | board.WhiteBishops;
            if (slidingAttackers != 0)
            {
                if (this.DiagonalA8H1Moves(board.OccupiedSquares, slidingAttackers, targetSquare) != 0) return true;
                if (this.DiagonalA1H8Moves(board.OccupiedSquares, slidingAttackers, targetSquare) != 0) return true;
            }
            // This square isn't attacked - remove and move on to next target square.
            remainingTargetSquares ^= Constants.BITSET[targetSquare];
        }
    }
    // Test for attacks by BLACK on any of the target squares.
    else
    {
        // For the remaining target squares...
        while (remainingTargetSquares != 0)
        {
            // Find the next square in the list.
            targetSquare = BitOperations.BitScanForward(remainingTargetSquares);
            // Is this square attacked by a pawn, knight, or king?
            if ((board.BlackPawns & Constants.WHITE_PAWN_ATTACKS[targetSquare]) != 0) return true;
            if ((board.BlackKnights & Constants.KNIGHT_ATTACKS[targetSquare]) != 0) return true;
            if ((board.BlackKing & Constants.KING_ATTACKS[targetSquare]) != 0) return true;
            // Is this square attacked by a queen or rook along a file or rank?
            slidingAttackers = board.BlackQueens | board.BlackRooks;
            if (slidingAttackers != 0)
            {
                if (this.RankMoves(board.OccupiedSquares, slidingAttackers, targetSquare) != 0) return true;
                if (this.FileMoves(board.OccupiedSquares, slidingAttackers, targetSquare) != 0) return true;
            }
            // Is this square attacked by a queen or bishop along a diagonal?
            slidingAttackers = board.BlackQueens | board.BlackBishops;
            if (slidingAttackers != 0)
            {
                if (this.DiagonalA8H1Moves(board.OccupiedSquares, slidingAttackers, targetSquare) != 0) return true;
                if (this.DiagonalA1H8Moves(board.OccupiedSquares, slidingAttackers, targetSquare) != 0) return true;
            }
            // This square isn't attacked - remove and move on to next target square.
            remainingTargetSquares ^= Constants.BITSET[targetSquare];
        }
    }
    // None of the target squares are attacked.
    return false;
}

下面是生成白棋伪合法易位的代码片段:

// If White can still castle kingside...
if ((board.WhiteCastlingStatus & Board.EnumCastlingStatus.CanCastleOO) != 0)
{
    // And the White kingside castling squares (F1/G1) aren't occupied...
    if ((Constants.MASK_FG[Constants.WHITE_MOVE] & board.OccupiedSquares) == 0)
    {
        board.MoveBuffer[moveIndex++] = Constants.WHITE_CASTLING_OO;
    }
}
// If White can still castle queenside...
if ((board.WhiteCastlingStatus & Board.EnumCastlingStatus.CanCastleOOO) != 0)
{
    // And the White queenside castling squares (D1/C1/B1) aren't occupied...
    if ((Constants.MASK_BD[Constants.WHITE_MOVE] & board.OccupiedSquares) == 0)
    {
        board.MoveBuffer[moveIndex++] = Constants.WHITE_CASTLING_OOO;
    }
}

下面是检查伪合法易位是否合法的代码:

// Checks whether the King is moving from or into check.
// Checks whether the King is moving across attacked squares.
internal bool IsCastlingMoveLegal(Board board, Move move)
{
    if (move.IsCastlingOO)
    {
        if (move.IsWhiteMove)
        {
            // Are any of the White kingside castling squares (E1/F1/G1) attacked?
            return !this.IsAttacked(board, Constants.MASK_EG[Constants.WHITE_MOVE], false);
        }
        else
        {
            // Are any of the Black kingside castling squares (E8/F8/G8) attacked?
            return !this.IsAttacked(board, Constants.MASK_EG[Constants.BLACK_MOVE], true);
        }
    }
    else if (move.IsCastlingOOO)
    {
        if (move.IsWhiteMove)
        {
            // Are any of the White queenside castling squares (E1/D1/C1) attacked?
            return !this.IsAttacked(board, Constants.MASK_CE[Constants.WHITE_MOVE], false);
        }
        else
        {
            // Are any of the Black queenside castling squares (E8/D8/C8) attacked?
            return !this.IsAttacked(board, Constants.MASK_CE[Constants.BLACK_MOVE], true);
        }
    }
    // Not a castling move!
    else
    {
        Debug.Assert(false, "Not a castling move!");
        return true;
    }
}

我的象棋程序有一个方法来检查一个字段是否受到威胁。当计算国王的移动时，它检查国王可能移动到的每个领域，如果该领域受到威胁。