503 lines
18 KiB
Nim
503 lines
18 KiB
Nim
# Copyright 2024 Mattia Giambirtone & All Contributors
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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## Implementation of a simple chessboard
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import std/strformat
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import std/strutils
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import pieces
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import magics
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import moves
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import rays
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import bitboards
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import position
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export pieces, position, bitboards, moves, magics, rays
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type
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Chessboard* = ref object
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## A chessboard
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# The actual board where pieces live
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grid*: array[64, Piece]
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# The current position
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position*: Position
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# List of all previously reached positions
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positions*: seq[Position]
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# A bunch of simple utility functions and forward declarations
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proc toFEN*(self: Chessboard): string
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proc updateChecksAndPins*(self: Chessboard)
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proc newChessboard: Chessboard =
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## Returns a new, empty chessboard
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new(result)
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for i in 0..63:
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result.grid[i] = nullPiece()
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result.position = Position(enPassantSquare: nullSquare(), sideToMove: White)
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# Indexing operations
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func `[]`*(self: array[64, Piece], square: Square): Piece {.inline.} = self[square.int8]
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func `[]=`*(self: var array[64, Piece], square: Square, piece: Piece) {.inline.} = self[square.int8] = piece
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func getBitboard*(self: Chessboard, kind: PieceKind, color: PieceColor): Bitboard {.inline.} =
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## Returns the positional bitboard for the given piece kind and color
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return self.position.getBitboard(kind, color)
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func getBitboard*(self: Chessboard, piece: Piece): Bitboard {.inline.} =
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## Returns the positional bitboard for the given piece type
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return self.getBitboard(piece.kind, piece.color)
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proc newChessboardFromFEN*(fen: string): Chessboard =
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## Initializes a chessboard with the
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## position encoded by the given FEN string
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result = newChessboard()
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var
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# Current square in the grid
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row: int8 = 0
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column: int8 = 0
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# Current section in the FEN string
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section = 0
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# Current index into the FEN string
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index = 0
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# Temporary variable to store a piece
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piece: Piece
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# See https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation
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while index <= fen.high():
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var c = fen[index]
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if c == ' ':
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# Next section
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inc(section)
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inc(index)
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continue
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case section:
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of 0:
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# Piece placement data
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case c.toLowerAscii():
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# Piece
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of 'r', 'n', 'b', 'q', 'k', 'p':
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let square = makeSquare(row, column)
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piece = c.fromChar()
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result.position.pieces[piece.color][piece.kind][].setBit(square)
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result.grid[square] = piece
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inc(column)
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of '/':
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# Next row
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inc(row)
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column = 0
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of '0'..'9':
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# Skip x columns
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let x = int(uint8(c) - uint8('0'))
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if x > 8:
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raise newException(ValueError, &"invalid FEN: invalid column skip size ({x} > 8)")
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column += int8(x)
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else:
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raise newException(ValueError, &"invalid FEN: unknown piece identifier '{c}'")
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of 1:
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# Active color
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case c:
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of 'w':
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result.position.sideToMove = White
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of 'b':
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result.position.sideToMove = Black
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else:
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raise newException(ValueError, &"invalid FEN: invalid active color identifier '{c}'")
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of 2:
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# Castling availability
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case c:
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# TODO
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of '-':
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discard
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of 'K':
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result.position.castlingAvailability.white.king = true
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of 'Q':
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result.position.castlingAvailability.white.queen = true
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of 'k':
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result.position.castlingAvailability.black.king = true
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of 'q':
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result.position.castlingAvailability.black.queen = true
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else:
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raise newException(ValueError, &"invalid FEN: unknown symbol '{c}' found in castlingRights availability section")
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of 3:
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# En passant target square
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case c:
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of '-':
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# Field is already uninitialized to the correct state
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discard
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else:
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result.position.enPassantSquare = fen[index..index+1].toSquare()
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# Square metadata is 2 bytes long
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inc(index)
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of 4:
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# Halfmove clock
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var s = ""
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while not fen[index].isSpaceAscii():
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s.add(fen[index])
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inc(index)
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# Backtrack so the space is seen by the
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# next iteration of the loop
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dec(index)
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result.position.halfMoveClock = parseInt(s).int8
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of 5:
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# Fullmove number
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var s = ""
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while index <= fen.high():
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s.add(fen[index])
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inc(index)
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result.position.fullMoveCount = parseInt(s).int8
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else:
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raise newException(ValueError, "invalid FEN: too many fields in FEN string")
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inc(index)
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result.updateChecksAndPins()
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proc newDefaultChessboard*: Chessboard {.inline.} =
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## Initializes a chessboard with the
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## starting position
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return newChessboardFromFEN("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1")
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func countPieces*(self: Chessboard, kind: PieceKind, color: PieceColor): int {.inline.} =
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## Returns the number of pieces with
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## the given color and type in the
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## current position
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return self.position.pieces[color][kind][].countSquares()
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func countPieces*(self: Chessboard, piece: Piece): int {.inline.} =
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## Returns the number of pieces on the board that
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## are of the same type and color as the given piece
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return self.countPieces(piece.kind, piece.color)
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func getPiece*(self: Chessboard, square: Square): Piece {.inline.} =
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## Gets the piece at the given square
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return self.grid[square]
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func getPiece*(self: Chessboard, square: string): Piece {.inline.} =
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## Gets the piece on the given square
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## in algebraic notation
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return self.getPiece(square.toSquare())
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func getOccupancyFor*(self: Chessboard, color: PieceColor): Bitboard =
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## Get the occupancy bitboard for every piece of the given color
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result = Bitboard(0)
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for b in self.position.pieces[color][]:
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result = result or b
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func getOccupancy*(self: Chessboard): Bitboard {.inline.} =
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## Get the occupancy bitboard for every piece on
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## the chessboard
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result = self.getOccupancyFor(Black) or self.getOccupancyFor(White)
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func getPawnAttacks*(self: Chessboard, square: Square, attacker: PieceColor): Bitboard {.inline.} =
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## Returns the locations of the pawns attacking the given square
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let
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sq = square.toBitboard()
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pawns = self.getBitboard(Pawn, attacker)
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bottomLeft = sq.backwardLeftRelativeTo(attacker)
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bottomRight = sq.backwardRightRelativeTo(attacker)
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return pawns and (bottomLeft or bottomRight)
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func getKingAttacks*(self: Chessboard, square: Square, attacker: PieceColor): Bitboard {.inline.} =
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## Returns the location of the king if it is attacking the given square
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result = Bitboard(0)
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let
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king = self.getBitboard(King, attacker)
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if (getKingAttacks(square) and king) != 0:
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result = result or king
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func getKnightAttacks*(self: Chessboard, square: Square, attacker: PieceColor): Bitboard =
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## Returns the locations of the knights attacking the given square
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let
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knights = self.getBitboard(Knight, attacker)
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result = Bitboard(0)
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for knight in knights:
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let knightBB = knight.toBitboard()
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if (getKnightAttacks(knight) and knightBB) != 0:
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result = result or knightBB
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proc getSlidingAttacks*(self: Chessboard, square: Square, attacker: PieceColor): Bitboard =
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## Returns the locations of the sliding pieces attacking the given square
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let
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queens = self.getBitboard(Queen, attacker)
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rooks = self.getBitboard(Rook, attacker) or queens
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bishops = self.getBitboard(Bishop, attacker) or queens
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occupancy = self.getOccupancy()
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squareBB = square.toBitboard()
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result = Bitboard(0)
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for rook in rooks:
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let
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blockers = occupancy and Rook.getRelevantBlockers(rook)
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moves = getRookMoves(rook, blockers)
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# Attack set intersects our chosen square
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if (moves and squareBB) != 0:
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result = result or rook.toBitboard()
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for bishop in bishops:
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let
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blockers = occupancy and Bishop.getRelevantBlockers(bishop)
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moves = getBishopMoves(bishop, blockers)
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if (moves and squareBB) != 0:
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result = result or bishop.toBitboard()
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proc getAttacksTo*(self: Chessboard, square: Square, attacker: PieceColor): Bitboard =
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## Computes the attack bitboard for the given square from
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## the given side
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result = Bitboard(0)
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result = result or self.getPawnAttacks(square, attacker)
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result = result or self.getKingAttacks(square, attacker)
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result = result or self.getKnightAttacks(square, attacker)
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result = result or self.getSlidingAttacks(square, attacker)
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proc isOccupancyAttacked*(self: Chessboard, square: Square, occupancy: Bitboard): bool =
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## Returns whether the given square would be attacked by the
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## enemy side if the board had the given occupancy. This function
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## is necessary mostly to make sure sliding attacks can check the
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## king properly: due to how we generate our attack bitboards, if
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## the king moved backwards along a ray from a slider we would not
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## consider it to be in check (because the ray stops at the first
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## blocker). In order to fix that, in generateKingMoves() we use this
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## function and pass in the board's occupancy without the moving king so
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## that we can pick the correct magic bitboard and ray. Also, since this
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## function doesn't need to generate all the attacks to know whether a
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## given square is unsafe, it can short circuit at the first attack and
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## exit early, unlike getAttacksTo
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let
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sideToMove = self.position.sideToMove
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nonSideToMove = sideToMove.opposite()
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knights = self.getBitboard(Knight, nonSideToMove)
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# Let's do the cheap ones first (the ones which are precomputed)
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if (getKnightAttacks(square) and knights) != 0:
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return true
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let king = self.getBitboard(King, nonSideToMove)
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if (getKingAttacks(square) and king) != 0:
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return true
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let
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queens = self.getBitboard(Queen, nonSideToMove)
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bishops = self.getBitboard(Bishop, nonSideToMove) or queens
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if (getBishopMoves(square, occupancy) and bishops) != 0:
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return true
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let rooks = self.getBitboard(Rook, nonSideToMove) or queens
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if (getRookMoves(square, occupancy) and rooks) != 0:
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return true
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# TODO: Precompute pawn moves as well?
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let pawns = self.getBitboard(Pawn, nonSideToMove)
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if (self.getPawnAttacks(square, nonSideToMove) and pawns) != 0:
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return true
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proc updateChecksAndPins*(self: Chessboard) =
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## Updates internal metadata about checks and
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## pinned pieces
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# *Ahem*, stolen from https://github.com/Ciekce/voidstar/blob/424ac4624011271c4d1dbd743602c23f6dbda1de/src/position.rs
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# Can you tell I'm a *great* coder?
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let
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sideToMove = self.position.sideToMove
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nonSideToMove = sideToMove.opposite()
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friendlyKing = self.getBitboard(King, sideToMove).toSquare()
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friendlyPieces = self.getOccupancyFor(sideToMove)
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enemyPieces = self.getOccupancyFor(nonSideToMove)
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# Update checks
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self.position.checkers = self.getAttacksTo(friendlyKing, nonSideToMove)
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# Update pins
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self.position.diagonalPins = Bitboard(0)
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self.position.orthogonalPins = Bitboard(0)
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let
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diagonalAttackers = self.getBitboard(Queen, nonSideToMove) or self.getBitboard(Bishop, nonSideToMove)
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orthogonalAttackers = self.getBitboard(Queen, nonSideToMove) or self.getBitboard(Rook, nonSideToMove)
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canPinDiagonally = diagonalAttackers and getBishopMoves(friendlyKing, enemyPieces)
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canPinOrthogonally = orthogonalAttackers and getRookMoves(friendlyKing, enemyPieces)
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for piece in canPinDiagonally:
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let pinningRay = getRayBetween(friendlyKing, piece) or piece.toBitboard()
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# Is the pinning ray obstructed by any of our friendly pieces? If so, the
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# piece is pinned
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if (pinningRay and friendlyPieces).countSquares() == 1:
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self.position.diagonalPins = self.position.diagonalPins or pinningRay
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for piece in canPinOrthogonally:
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let pinningRay = getRayBetween(friendlyKing, piece) or piece.toBitboard()
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if (pinningRay and friendlyPieces).countSquares() == 1:
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self.position.orthogonalPins = self.position.orthogonalPins or pinningRay
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func inCheck*(self: Chessboard): bool {.inline.} =
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## Returns if the current side to move is in check
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return self.position.checkers != 0
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proc canCastle*(self: Chessboard, side: PieceColor): tuple[king, queen: bool] =
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## Returns if the current side to move can castle
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return (false, false) # TODO
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proc update*(self: Chessboard) =
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## Updates the internal grid representation
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## according to the positional data stored
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## in the chessboard
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for i in 0..63:
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self.grid[i] = nullPiece()
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for sq in self.position.pieces[White][Pawn][]:
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self.grid[sq] = Piece(color: White, kind: Pawn)
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for sq in self.position.pieces[Black][Pawn][]:
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self.grid[sq] = Piece(color: Black, kind: Pawn)
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for sq in self.position.pieces[White][Bishop][]:
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self.grid[sq] = Piece(color: White, kind: Bishop)
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for sq in self.position.pieces[Black][Bishop][]:
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self.grid[sq] = Piece(color: Black, kind: Bishop)
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for sq in self.position.pieces[White][Knight][]:
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self.grid[sq] = Piece(color: White, kind: Knight)
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for sq in self.position.pieces[Black][Knight][]:
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self.grid[sq] = Piece(color: Black, kind: Knight)
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for sq in self.position.pieces[White][Rook][]:
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self.grid[sq] = Piece(color: White, kind: Rook)
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for sq in self.position.pieces[Black][Rook][]:
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self.grid[sq] = Piece(color: Black, kind: Rook)
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for sq in self.position.pieces[White][Queen][]:
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self.grid[sq] = Piece(color: White, kind: Queen)
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for sq in self.position.pieces[Black][Queen][]:
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self.grid[sq] = Piece(color: Black, kind: Queen)
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for sq in self.position.pieces[White][King][]:
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self.grid[sq] = Piece(color: White, kind: King)
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for sq in self.position.pieces[Black][King][]:
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self.grid[sq] = Piece(color: Black, kind: King)
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proc `$`*(self: Chessboard): string =
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result &= "- - - - - - - -"
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var file = 8
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for i in 0..7:
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result &= "\n"
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for j in 0..7:
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let piece = self.grid[makeSquare(i, j)]
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if piece.kind == Empty:
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result &= "x "
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continue
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result &= &"{piece.toChar()} "
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result &= &"{file}"
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dec(file)
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result &= "\n- - - - - - - -"
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result &= "\na b c d e f g h"
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proc pretty*(self: Chessboard): string =
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## Returns a colored version of the
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## board for easier visualization
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var file = 8
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for i in 0..7:
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if i > 0:
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result &= "\n"
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for j in 0..7:
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# Equivalent to (i + j) mod 2
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# (I'm just evil)
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if ((i + j) and 1) == 0:
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result &= "\x1b[39;44;1m"
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else:
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result &= "\x1b[39;40;1m"
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let piece = self.grid[makeSquare(i, j)]
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if piece.kind == Empty:
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result &= " \x1b[0m"
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else:
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result &= &"{piece.toPretty()} \x1b[0m"
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result &= &" \x1b[33;1m{file}\x1b[0m"
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dec(file)
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result &= "\n\x1b[31;1ma b c d e f g h"
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result &= "\x1b[0m"
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proc toFEN*(self: Chessboard): string =
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## Returns a FEN string of the current
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## position in the chessboard
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var skip: int
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# Piece placement data
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for i in 0..7:
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skip = 0
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for j in 0..7:
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let piece = self.grid[makeSquare(i, j)]
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if piece.kind == Empty:
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inc(skip)
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elif skip > 0:
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result &= &"{skip}{piece.toChar()}"
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skip = 0
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else:
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result &= piece.toChar()
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if skip > 0:
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result &= $skip
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if i < 7:
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result &= "/"
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result &= " "
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# Active color
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result &= (if self.position.sideToMove == White: "w" else: "b")
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result &= " "
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# Castling availability
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let castleWhite = self.position.castlingAvailability.white
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let castleBlack = self.position.castlingAvailability.black
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if not (castleBlack.king or castleBlack.queen or castleWhite.king or castleWhite.queen):
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result &= "-"
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else:
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if castleWhite.king:
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result &= "K"
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if castleWhite.queen:
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result &= "Q"
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if castleBlack.king:
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result &= "k"
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if castleBlack.queen:
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result &= "q"
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result &= " "
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# En passant target
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if self.position.enPassantSquare == nullSquare():
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|
result &= "-"
|
|
else:
|
|
result &= self.position.enPassantSquare.toAlgebraic()
|
|
result &= " "
|
|
# Halfmove clock
|
|
result &= $self.position.halfMoveClock
|
|
result &= " "
|
|
# Fullmove number
|
|
result &= $self.position.fullMoveCount
|