Endgame bitbase

A bit is a unit of information that can hold only 0 or 1. An endgame bitbase assigns one or a few bits to every position in a limited family of endings. Because the outcomes are precomputed, a program can look them up without searching every continuation again.

The most compact form uses one bit per position, such as 1 for win and 0 for not-win. Two bits can distinguish more states, such as win, draw, loss, or invalid position. Because each bit takes very little space, millions of outcomes can fit in relatively little memory.

That compactness has a cost. A bitbase often answers which outcome belongs to a position but may not store the best move or a distance to the goal. A chess engine can generate legal moves, look up the resulting positions, and reconstruct a choice that preserves the outcome.

It should not be confused with a bitboard. A bitboard represents a set of squares inside one position; a bitbase organizes many complete positions and stores an outcome for each. It is also not necessarily a rich tablebase, meaning a precomputed collection of endings that additionally contains metrics such as DTM or DTZ.