Chess Engine Board Representation

Basics

The board representation is simply how the board is represented. This is split into two main types

Piece Centric

This representation answers the following question: for a given piece, what square is it at?

Chess Engine Bitboards are the preferred choice.

Piecelists and Piecesets are alternative implementations using a list or set to hold the pieces

• piecelists: array or list with 32 pieces, holding their square information
• piecesets: uses bits in 32 bit word to point to index in piecelist

References

• https://www.chessprogramming.org/Piece-Lists
• https://www.chessprogramming.org/Piece-Sets

Square Centric

This representations answers the following question: for a given square, what piece is on it?

Mailbox is main way to do this, and simply means a memory location holds some information about the square. The main way is to simply use a large array

• 8x8 board: Chess Engine 8x8
• 10x12 board: the extra rows and columns serve as sentinels to notify when a piece goes off the board as the result of an attack
• vector attacks: encodes into a table how a piece may move using vectors
• 0x88 (16x8 board): uses the upper bit to determine out of board pieces, compliments vector attacks

References:

• https://www.chessprogramming.org/10x12_Board
• https://www.chessprogramming.org/Vector_Attacks
• https://www.chessprogramming.org/0x88

Hybrid

While an engine can focus on one representation, it will also use the other representation as well. For example

• bitboard-based might also use 8x8 board
• 8x8 might also use piece-lists