// Returns true if a check mate or stalemate is found
// Values of type of mate and side mated are stored in the three reference variables
internal static bool SearchForMate(ChessPieceColor movingSide,
Board examineBoard,
ref bool blackMate,
ref bool whiteMate,
ref bool staleMate)
{
var foundNonCheckBlack = false;
var foundNonCheckWhite = false;
for (byte x = 0; x < 64; x++)
{
var sqr = examineBoard.Squares[x];
//Make sure there is a piece on the square
if (sqr.Piece == null)
{
continue;
}
//Make sure the color is the same color as the one we are moving.
if (sqr.Piece.PieceColor != movingSide)
{
continue;
}
//For each valid move for this piece
foreach (var dst in sqr.Piece.ValidMoves)
{
//We make copies of the board and move so that we can move it without effecting the parent board
var board = examineBoard.FastCopy();
//Make move so we can examine it
Board.MovePiece(board, x, dst, ChessPieceType.Queen);
//We Generate Valid Moves for Board
PieceValidMoves.GenerateValidMoves(board);
if (board.BlackCheck == false)
{
foundNonCheckBlack = true;
}
else if (movingSide == ChessPieceColor.Black)
{
continue;
}
if (board.WhiteCheck == false)
{
foundNonCheckWhite = true;
}
else if (movingSide == ChessPieceColor.White)
{
}
}
}
if (foundNonCheckBlack == false)
{
if (examineBoard.BlackCheck)
{
blackMate = true;
return(true);
}
if (!examineBoard.WhiteMate && movingSide != ChessPieceColor.White)
{
staleMate = true;
return(true);
}
}
// ReSharper disable once InvertIf
if (foundNonCheckWhite == false)
{
if (examineBoard.WhiteCheck)
{
whiteMate = true;
return(true);
}
// ReSharper disable once InvertIf
if (!examineBoard.BlackMate && movingSide != ChessPieceColor.Black)
{
staleMate = true;
return(true);
}
}
return(false);
}
//Quiescence Search
private static int Quiescence(Board examineBoard, int alpha, int beta, ref int nodesSearched)
{
nodesSearched++;
//Evaluate Score
Evaluation.EvaluateBoardScore(examineBoard);
//Invert Score to support Negamax
examineBoard.Score = SideToMoveScore(examineBoard.Score, examineBoard.WhoseMove);
if (examineBoard.Score >= beta)
{
return(beta);
}
if (examineBoard.Score > alpha)
{
alpha = examineBoard.Score;
}
List <Position> positions;
if (examineBoard.WhiteCheck || examineBoard.BlackCheck)
{
positions = EvaluateMoves(examineBoard, 0);
}
else
{
positions = EvaluateMovesQ(examineBoard);
}
if (positions.Count == 0)
{
return(examineBoard.Score);
}
positions.Sort(Sort);
foreach (var move in positions)
{
if (StaticExchangeEvaluation(examineBoard.Squares[move.DstPosition]) >= 0)
{
continue;
}
//Make a copy
var board = examineBoard.FastCopy();
//Move Piece
Board.MovePiece(board, move.SrcPosition, move.DstPosition, ChessPieceType.Queen);
//We Generate Valid Moves for Board
PieceValidMoves.GenerateValidMoves(board);
if (board.BlackCheck)
{
if (examineBoard.WhoseMove == ChessPieceColor.Black)
{
continue;
}
}
if (board.WhiteCheck)
{
if (examineBoard.WhoseMove == ChessPieceColor.White)
{
continue;
}
}
var value = -Quiescence(board,
-beta,
-alpha,
ref nodesSearched);
if (value >= beta)
{
KillerMove[2, 0].SrcPosition = move.SrcPosition;
KillerMove[2, 0].DstPosition = move.DstPosition;
return(beta);
}
if (value > alpha)
{
alpha = value;
}
}
return(alpha);
}
// Final version
// ReSharper disable once IdentifierTypo
private static int AlphaBeta(Board examineBoard,
byte depth,
int alpha,
int beta,
ref int nodesSearched,
ref int nodesQuiessence,
ref List <Position> pvLine,
bool extended)
{
nodesSearched++;
if (examineBoard.HalfMoveClock >= 100 || examineBoard.RepeatedMove >= 3)
{
return(0);
}
//End Main Search with Quiescence
if (depth == 0)
{
if (!extended && examineBoard.BlackCheck || examineBoard.WhiteCheck)
{
depth++;
extended = true;
}
else
{
//Perform a Quiessence Search
return(Quiescence(examineBoard,
alpha,
beta,
ref nodesQuiessence));
}
}
var positions = EvaluateMoves(examineBoard, depth);
if (examineBoard.WhiteCheck || examineBoard.BlackCheck || positions.Count == 0)
{
if (SearchForMate(examineBoard.WhoseMove, examineBoard, ref examineBoard.BlackMate,
ref examineBoard.WhiteMate, ref examineBoard.StaleMate))
{
if (examineBoard.BlackMate)
{
if (examineBoard.WhoseMove == ChessPieceColor.Black)
{
return(-32767 - depth);
}
return(32767 + depth);
}
// ReSharper disable once InvertIf
if (examineBoard.WhiteMate)
{
if (examineBoard.WhoseMove == ChessPieceColor.Black)
{
return(32767 + depth);
}
return(-32767 - depth);
}
//If Not Mate then StaleMate
return(0);
}
}
positions.Sort(Sort);
foreach (var move in positions)
{
var pvChild = new List <Position>();
//Make a copy
var board = examineBoard.FastCopy();
//Move Piece
Board.MovePiece(board, move.SrcPosition, move.DstPosition, ChessPieceType.Queen);
//We Generate Valid Moves for Board
PieceValidMoves.GenerateValidMoves(board);
if (board.BlackCheck)
{
if (examineBoard.WhoseMove == ChessPieceColor.Black)
{
continue;
}
}
if (board.WhiteCheck)
{
if (examineBoard.WhoseMove == ChessPieceColor.White)
{
continue;
}
}
var value = -AlphaBeta(board,
(byte)(depth - 1),
-beta,
-alpha,
ref nodesSearched,
ref nodesQuiessence,
ref pvChild,
extended);
if (value >= beta)
{
KillerMove[kIndex, depth].SrcPosition = move.SrcPosition;
KillerMove[kIndex, depth].DstPosition = move.DstPosition;
kIndex = (kIndex + 1) % 2;
return(beta);
}
// ReSharper disable once InvertIf
if (value > alpha)
{
//This nodes is PV-node
//That nodes have a score that ends up being inside the window
//Between the lower bound Alpha and the upper bound Beta.
var pvPos = new Position
{
SrcPosition = board.LastMove.MovingPiecePrimary.SrcPosition,
DstPosition = board.LastMove.MovingPiecePrimary.DstPosition,
Move = board.LastMove.ToString()
};
//All Siblings of a PV-node are expected Cut-nodes
pvChild.Insert(0, pvPos);
pvLine = pvChild;
alpha = value;
}
}
return(alpha);
}
// Not used anymore
// ReSharper disable once UnusedMember.Local
private static int AlphaBeta(Board examineBoard, byte depth, int alpha, int beta, ref int nodesSearched)
{
nodesSearched++;
if (examineBoard.HalfMoveClock >= 100 || examineBoard.RepeatedMove >= 3)
{
return(0);
}
if (depth == 0)
{
//Evaluate Score
Evaluation.EvaluateBoardScore(examineBoard);
//Invert Score to support Negamax
return(SideToMoveScore(examineBoard.Score, examineBoard.WhoseMove));
}
var positions = EvaluateMoves(examineBoard, depth);
if (examineBoard.WhiteCheck || examineBoard.BlackCheck || positions.Count == 0)
{
if (SearchForMate(examineBoard.WhoseMove, examineBoard, ref examineBoard.BlackMate,
ref examineBoard.WhiteMate, ref examineBoard.StaleMate))
{
if (examineBoard.BlackMate)
{
if (examineBoard.WhoseMove == ChessPieceColor.Black)
{
return(-32767 - depth);
}
return(32767 + depth);
}
// ReSharper disable once InvertIf
if (examineBoard.WhiteMate)
{
if (examineBoard.WhoseMove == ChessPieceColor.Black)
{
return(32767 + depth);
}
return(-32767 - depth);
}
//If Not Mate then StaleMate
return(0);
}
}
positions.Sort(Sort);
foreach (var move in positions)
{
//Make a copy
var board = examineBoard.FastCopy();
//Move Piece
Board.MovePiece(board, move.SrcPosition, move.DstPosition, ChessPieceType.Queen);
//We Generate Valid Moves for Board
PieceValidMoves.GenerateValidMoves(board);
if (board.BlackCheck)
{
if (examineBoard.WhoseMove == ChessPieceColor.Black)
{
continue;
}
}
if (board.WhiteCheck)
{
if (examineBoard.WhoseMove == ChessPieceColor.White)
{
continue;
}
}
var value = -AlphaBeta(board,
(byte)(depth - 1),
-beta,
-alpha,
ref nodesSearched);
if (value >= beta)
{
return(beta);
}
if (value > alpha)
{
alpha = value;
}
}
return(alpha);
}
// Not used anymore
// ReSharper disable once UnusedMember.Local
private static int MinMax(Board examineBoard, byte depth)
{
if (depth == 0)
{
//Evaluate Score
Evaluation.EvaluateBoardScore(examineBoard);
//Invert Score to support Negamax
return(SideToMoveScore(examineBoard.Score, examineBoard.WhoseMove));
}
var positions = EvaluateMoves(examineBoard, depth);
if (examineBoard.WhiteCheck || examineBoard.BlackCheck || positions.Count == 0)
{
if (SearchForMate(examineBoard.WhoseMove, examineBoard, ref examineBoard.BlackMate,
ref examineBoard.WhiteMate, ref examineBoard.StaleMate))
{
if (examineBoard.BlackMate)
{
if (examineBoard.WhoseMove == ChessPieceColor.Black)
{
return(-32767 - depth);
}
return(32767 + depth);
}
// ReSharper disable once InvertIf
if (examineBoard.WhiteMate)
{
if (examineBoard.WhoseMove == ChessPieceColor.Black)
{
return(32767 + depth);
}
return(-32767 - depth);
}
//If Not Mate then StaleMate
return(0);
}
}
var bestScore = -32767;
foreach (var move in positions)
{
//Make a copy
var board = examineBoard.FastCopy();
//Move Piece
Board.MovePiece(board, move.SrcPosition, move.DstPosition, ChessPieceType.Queen);
//We Generate Valid Moves for Board
PieceValidMoves.GenerateValidMoves(board);
if (board.BlackCheck)
{
if (examineBoard.WhoseMove == ChessPieceColor.Black)
{
continue;
}
}
if (board.WhiteCheck)
{
if (examineBoard.WhoseMove == ChessPieceColor.White)
{
continue;
}
}
var value = -MinMax(board, (byte)(depth - 1));
if (value > bestScore)
{
bestScore = value;
}
}
return(bestScore);
}
private static ResultBoards GetSortValidMoves(Board examineBoard)
{
var sortValidMoves = new ResultBoards {
Positions = new List <Board>(30)
};
piecesRemaining = 0;
for (byte x = 0; x < 64; x++)
{
var sqr = examineBoard.Squares[x];
//Make sure there is a piece on the square
if (sqr.Piece == null)
{
continue;
}
piecesRemaining++;
//Make sure the color is the same color as the one we are moving.
if (sqr.Piece.PieceColor != examineBoard.WhoseMove)
{
continue;
}
//For each valid move for this piece
foreach (var dst in sqr.Piece.ValidMoves)
{
//We make copies of the board and move so that we can move it without effecting the parent board
var board = examineBoard.FastCopy();
//Make move so we can examine it
Board.MovePiece(board, x, dst, ChessPieceType.Queen);
//We Generate Valid Moves for Board
PieceValidMoves.GenerateValidMoves(board);
//Invalid Move
if (board.WhiteCheck && examineBoard.WhoseMove == ChessPieceColor.White)
{
continue;
}
//Invalid Move
if (board.BlackCheck && examineBoard.WhoseMove == ChessPieceColor.Black)
{
continue;
}
//We calculate the board score
Evaluation.EvaluateBoardScore(board);
//Invert Score to support Negamax
board.Score = SideToMoveScore(board.Score, board.WhoseMove);
sortValidMoves.Positions.Add(board);
}
}
sortValidMoves.Positions.Sort(Sort);
return(sortValidMoves);
}