How to store a chess position in 26 bytes using bit-level magic

Re:How to store a chess position in 26 bytes using bit-level... by arnsholt on Friday January 09, 2026 @03:06PM (#46558603)

Lichess uses a scheme which is probably more efficient on average, described on revoof's blog[0]. Basically, it's a variable length scheme where the first 64 bits encode square occupancies, followed by piece codes (including castling, side to move, and ep with some trickery), followed by half-move clocks if necessary.

0: https://lichess.org/@/revoof/blog/adapting-nnue-pytorchs-bin...

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Re:How to store a chess position in 26 bytes using bit-level... by bonzini on Friday January 09, 2026 @05:52PM (#46560555)

It also can encode chess960 positions. With the article's encoding, uncastled rooks can only be decoded if their starting position is known, which it isn't in chess960.

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Re:How to store a chess position in 26 bytes using bit-level... by datsci_est_2015 on Saturday January 10, 2026 @09:52AM (#46566176)

It’s mathematically dissatisfying, but often the most optimal storage (or algorithm) solutions involve clever heuristics that are dynamically applied.

Some systems just have to be observed in order for solutions to be optimally designed around how they actually behave, rather than how they theoretically behave.

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