How to store a chess position in 26 bytes using bit-level magic (2022)
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Re: How to store a chess position in 26 bytes using bit-level magic (2022)
#2oh fuck. I feel like this is going to become an interview question.
Re: How to store a chess position in 26 bytes using bit-level magic (2022)
#3A chess position, not a game (still very interesting though!)
Re: How to store a chess position in 26 bytes using bit-level magic (2022)
#4Original title is:
> Compressing chess positions for fun and profit
Which unlike that here is correct: you can store a board, the positions, in 26B; not an arbitrary length game!
Re: How to store a chess position in 26 bytes using bit-level magic (2022)
#5Meanwhile the non-comp-sci dev in me is like, "why not just store every position in a simple JSON so everyone can read it and everything can parse it". Yeah, it might be half a kB, but you don't have to run through mental gymnastics just to render the pieces...
Re: How to store a chess position in 26 bytes using bit-level magic (2022)
#6Original title is: > Compressing chess positions for fun and profit Which unlike that here is correct: you can store a board , the positions, in 26B; not an arbitrary length game!
Most games could possibly be encoded in less than 26 bytes. There are not that many legal moves each time and if you sort them by probability it may not require many bits to describe which one the players chose.
Re: How to store a chess position in 26 bytes using bit-level magic (2022)
#7It's as long as my comment
Re: How to store a chess position in 26 bytes using bit-level magic (2022)
#8When I was building my multiplayer Sudoku app, I had fun experimenting with how small I could pack a sudoku grid into a URL. I came up with a scheme combining bit packing with the knowledge of how the grid works. So as you move through the grid, based on the knowledge of what's been placed where and the remaining digits you have a fewer options.
Was fun, I was playing code golf with myself. Sadly seem to have lost the code and I didn't use it in the end.
It would probably have been possible to go smaller than I got it by combining it with a sudoku solver, so stop packing positions once it's solvable. But life moved on.
Re: How to store a chess position in 26 bytes using bit-level magic (2022)
#9A chess position , not a game (still very interesting though!)
Storing the game would give you the position though
Re: How to store a chess position in 26 bytes using bit-level magic (2022)
#10Storing a chess position in 26 bytes.
Storing a game is also interesting. The number of legal moves varies depending on the position. You could try to define a variable length encoding by giving more likely moves a shorter encoding, but the ordering would need to be deterministic so it could be decoded (running Stockfish for a second isn't).