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Home * Board Representation

Paul Klee - Überschach, 1937 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.

Contents

Piece Centric
Square Centric
Hybrid Solutions
Move Generation
Make and Unmake
See Also
Publications
Forum Posts
1. 1999
2. 2000 ...
3. 2010 ...
External Links
References

Piece Centric

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.

Square Centric

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.

Mailbox

0x88

Hybrid Solutions

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.

Move Generation

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.