Home * Board Representation
A chess program needs an internal board representation to maintain chess positions for its search, evaluation and game-play. Beside modelizing the chessboard with its piece-placement, some additional information is required to fully specify a chess position, such as side to move, castling rights, possible en passant target square and the number of reversible moves to keep track on the fifty-move rule.
To begin with, we further elaborate on the pure data structures to represent the board and its piece-placement. There are piece centric and square centric representations as well as hybrid solutions.
A piece centric representation keeps lists, arrays or sets of all pieces still on the board - with the associated information which square they occupy. A popular piece centric representative is the set-wise bitboard-approach. One 64-bit word for each piece type, where one-bits associate their occupancy.
The square centric representation implements the inverse association - is a square empty or is it occupied by a particular piece? The most popular square centric representations, mailbox or it's 0x88-enhancements - are basically arrays of direct piece-codes including the empty square and probably out of board codes. Hybrid solutions may further refer piece-list entries.
While different algorithms and tasks inside a chess program might prefer one of these associations, it is quite common to use redundant board representations with elements of both. Bitboard approaches often keep a 8x8 board to determine a piece by square, while square centric board array approaches typically keep piece-lists and/or piece-sets to avoid scanning the board for move generation purposes.
With a board representation, one big consideration is the generation of moves. This is essential to the game playing aspect of a chess program, and it must be completely correct. Writing a good move generator is often the first basic step of creating a chess program.
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- Re: How do you represent chess boards in your chess programms by Sven Reichard, CCC, September 29, 1999
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- Fruit's Board Representation? by Steve Maughan, Winboard Programming Forum, April 27, 2005
- Board representation : 0x88 or 10x12 ? by Philippe, Winboard Forum, March 02, 2006
- Board Types in '08 by Joshua Shriver, CCC, June 28, 2008
- I'm Puzzled - Storing Piece Info & Magic Move Gen... by Steve Maughan, CCC, March 27, 2013
- Table-less bitboards (bitrays?) by Harm Geert Muller, CCC, June 18, 2013
- Best Board Representation for 32bit CPUs by net, Winboard Forum, July 14, 2013
- Some questions from a beginner by Tim Hagen, CCC, March 30, 2016
- CCR board representation by Maksim Korzh, CCC, November 25, 2018 » Array of Nibbles
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- Chess Board Representations by Paul Verhelst
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- Representation of Chess Game - Computer Architecture and Languages Laboratory, University of Maribor