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chess: Moved replaced with CastleRights
Moved was a 10x12 1-d array, that stored bools. It was only used for checking if a pawn moved (especially important for the double move of the pawns) and if the other pieces moved (important for checking if the player can castle or not). The pawn moves are now checked by the starting position (pawns on the second rank cant be already moved). The castle rights of a game are expressed as CastleRights, a tuple with 4 bools. This saves basically 116 boolean values.
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TiynGER
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@ -8,8 +8,6 @@ type
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White = 1
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Board* = array[0..119, int] ## \
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## `Board` saves the position of the chess pieces.
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Moved* = array[0..119, bool] ## \
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## `Moved` saves the position of squares a piece moved on or from.
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CastleRights = tuple
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## `CastleRights` contains the rights to castling for each player.
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wk: bool # `wk` describes White kingside castle
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@ -19,11 +17,11 @@ type
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Game* = object
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## `Game` stores all important information of a chess game.
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board*: Board
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moved: Moved
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toMove*: Color
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previousBoard: seq[Board]
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previousCastleRights: seq[CastleRights]
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fiftyMoveCounter: int
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castleRights: CastleRights
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Move* = object
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## `Move` stores all important information for a move.
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start: int
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@ -246,16 +244,11 @@ proc initBoard(board: array[0..63, int]): Board =
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Block, Block, Block, Block, Block, Block, Block, Block, Block, Block]
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return board
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proc initMoved(): Moved =
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## Create and return a board of pieces moved.
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var moved: Moved
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return moved
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proc initGame*(): Game =
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## Create and return a Game object.
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let game = Game(board: initBoard(), moved: initMoved(),
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let game = Game(board: initBoard(),
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to_move: Color.White, previousBoard: @[], previousCastleRights: @[],
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fiftyMoveCounter: 0)
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fiftyMoveCounter: 0, castleRights: (true, true, true, true))
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return game
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proc initGame*(board: array[0..63, int], color: Color): Game =
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@ -263,14 +256,26 @@ proc initGame*(board: array[0..63, int], color: Color): Game =
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## `board` describes the pieces, `color` the color that is about to move.
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let board = initBoard(board)
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let compare = initBoard()
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var moved = initMoved()
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var same_piece: bool
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var wk = false
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var wq = false
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var bk = false
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var bq = false
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if (board[fieldToInd("e1")] == compare[fieldToInd("e1")]):
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if (board[fieldToInd("a1")] == compare[fieldToInd("a1")]):
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wq = true
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if (board[fieldToInd("h1")] == compare[fieldToInd("h1")]):
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wk = true
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if (board[fieldToInd("e8")] == compare[fieldToInd("e8")]):
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if (board[fieldToInd("a8")] == compare[fieldToInd("a8")]):
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bq = true
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if (board[fieldToInd("h8")] == compare[fieldToInd("h8")]):
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bk = true
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for ind in board.low..board.high:
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same_piece = (board[ind] != compare[ind])
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moved[ind] = same_piece
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let game = Game(board: board, moved: moved,
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let game = Game(board: board,
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to_move: color, previousBoard: @[], previousCastleRights: @[],
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fiftyMoveCounter: 0)
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fiftyMoveCounter: 0, castleRights: (wk, wq, bk, bq))
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return game
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proc echoBoard*(game: Game, color: Color) =
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@ -296,14 +301,6 @@ proc echoBoard*(game: Game, color: Color) =
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echo line_str
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echo "a b c d e f g h"
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proc genCastleRights(moved: Moved): CastleRights =
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## Generate and return rights to castle from given `moved`
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let wk = not moved[fieldToInd("e1")] and not moved[fieldToInd("h1")]
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let wq = not moved[fieldToInd("e1")] and not moved[fieldToInd("a1")]
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let bk = not moved[fieldToInd("e8")] and not moved[fieldToInd("h8")]
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let bq = not moved[fieldToInd("e8")] and not moved[fieldToInd("a8")]
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return (wk, wq, bk, bq)
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proc genPawnAttackDests(game: Game, field: int, color: Color): seq[int] =
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## Generate possible attack destinations for a pawn with specific `color`
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## located at index `field` of `game`.
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@ -337,9 +334,13 @@ proc genPawnDoubleDests(game: Game, field: int, color: Color): seq[int] =
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if (not dest in game.board.low..game.board.high):
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continue
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target = game.board[dest]
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if (game.moved[field] or (target != 0) or (
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if ((target != 0) or (
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game.board[dest+(S*ord(color))] != 0)):
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continue
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if (color == Color.White and not (field in fieldToInd("h2")..fieldToInd("a2"))):
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continue
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if (color == Color.Black and not (field in fieldToInd("h7")..fieldToInd("a7"))):
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continue
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res.add(dest)
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return res
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@ -538,8 +539,22 @@ proc uncheckedMove(game: var Game, start: int, dest: int): bool {.discardable.}
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let piece = game.board[start]
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game.board[start] = 0
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game.board[dest] = piece
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game.moved[start] = true
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game.moved[dest] = true
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if (start == fieldToInd("e1") or start == fieldToInd("a1")):
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game.castleRights.wq = false
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if (start == fieldToInd("e1") or start == fieldToInd("h1")):
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game.castleRights.wk = false
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if (start == fieldToInd("e8") or start == fieldToInd("a8")):
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game.castleRights.bq = false
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if (start == fieldToInd("e8") or start == fieldToInd("h8")):
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game.castleRights.bk = false
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if (dest == fieldToInd("e1") or dest == fieldToInd("a1")):
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game.castleRights.wq = false
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if (dest == fieldToInd("e1") or dest == fieldToInd("h1")):
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game.castleRights.wk = false
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if (dest == fieldToInd("e8") or dest == fieldToInd("a8")):
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game.castleRights.bq = false
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if (dest == fieldToInd("e8") or dest == fieldToInd("h8")):
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game.castleRights.bk = false
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return true
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proc moveLeadsToCheck(game: Game, start: int, dest: int,
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@ -681,15 +696,24 @@ proc castling(game: var Game, kstart: int, dest_kingside: bool,
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var kdest = kstart
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var rstart: int
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var rdest: int
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var rights = false
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if (dest_kingside):
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kdest = kstart + (E+E)
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rstart = kstart + (E+E+E)
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rdest = rstart + (W+W)
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if (color == Color.White):
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rights = game.castleRights.wk
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else:
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rights = game.castleRights.bk
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else:
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rstart = kstart + (W+W+W+W)
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rdest = rstart + (E+E+E)
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kdest = kstart + (W+W)
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if not game.moved[kstart] and not game.moved[rstart]:
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if (color == Color.White):
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rights = game.castleRights.bq
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else:
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rights = game.castleRights.bq
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if (rights):
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var check = false
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if (dest_kingside):
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check = check or game.isAttacked(kstart, color)
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@ -756,7 +780,7 @@ proc checkedMove*(game: var Game, move: Move): bool {.discardable.} =
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var prevBoard = game.previousBoard
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var prevCastle = game.previousCastleRights
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game.previousBoard.add(game.board)
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game.previousCastleRights.add(game.moved.genCastleRights())
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game.previousCastleRights.add(game.castleRights)
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game.fiftyMoveCounter = game.fiftyMoveCounter + 1
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if fiftyMoveRuleReset:
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game.fiftyMoveCounter = 0
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