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Show HN: Sameshi – a ~1200 Elo chess engine that fits within 2KB (github.com)

230 points by datavorous_ ↗ HN
I made a chess engine today, and made it fit within 2KB. I used a variant of MinMax called Negamax, with alpha beta pruning. For the board representation I have used a 120-cell "mailbox". I managed to squeeze in checkmate/stalemate in there, after trimming out some edge cases.

I am a great fan of demoscene (computer art subculture) since middle school, and hence it was a ritual i had to perform.

For estimating the Elo, I measured 240 automated games against Stockfish Elo levels (1320 to 1600) under fixed depth-5 and some constrained rules, using equal color distribution.

Then converted pooled win/draw/loss scores to Elo through some standard logistic formula with binomial 95% confidence interval.

27 comments

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chvid
Cool that you could keep it under 2k but it would nice to have a readable version of the source code.

Do you work with it like this or do you have some sort of script you apply to get it down to a single line, single letter variable names?

GeertB
How did you handle games where Stockfish would castle or promote?
lekevicius
Do you think it would be possible to achieve 1:1 ELO:bytes? Even smaller, but can be less smart.
haute_cuisine
This is amazing! Thanks for sharing. What would be the elo gain for 4KB engine?

P.S. I assume 1200 elo in chess com scale (not lichess / fide elo) and bullet chess variant?

falsaberN1
Oh my god the source is so tiny! It's really hard to parse because of it being minified but I love it to bits.
burstw0w
Good job! I love how you obfuscated your code, really in a spirit of FOSS!
jll29
Cool project. You could also use the front-end of GNU chess to save some lines, and implement only a back-end.

Bug report:

    a b c d e f g h
  8 r n b q k b n r 8
  7 . . p p p p p p 7
  6 . p . . . . . . 6
  5 p . . . . . . . 5
  4 P . . P P . . . 4
  3 . . . . . . . . 3
  2 . P P . . P P P 2
  1 R N B Q K B N R 1
    a b c d e f g h
  move: b2b3
  ai: b6b4
The pawn is not permitted to move two fields after it has already beeen moved once before: b6b4 isn't a valid move after b7b6. (First moving two fields, and then one would have been okay, in contrast.)
dfc
How many games did you have to throw away because stockfish wanted to castle? Or did you force stockfish to not castle? Castling seems like such a frequent move it is hard to draw any conclusions about the strength of an engine that does not support it.
oh_my_goodness
If you ever spent much time at a chess club, you've seen why 2kB is a really disturbing number.
sireat
This is very cool and having stalemate is nice, however how much space would it take to implement the full ruleset?

As you write: not implemented: castling, en passant, promotion, repetition, 50-move rule - those are all required to call the game being played modern chess.

I could see an argument for skipping repetition and 50-move rule for tiny engines, but you do need castling, en pessant and promotion for pretty much any serious play.

https://en.wikipedia.org/wiki/Video_Chess fit in 4k and supported fuller ruleset in 1980 did it not?

So I would ask what is the smallest fully UCI (https://www.chessprogramming.org/UCI) compliant engine available currently?

This would be a fun goal to beat - make something tiny that supports full ruleset.

PS my first chess computer in early 1980s was this: https://www.ismenio.com/chess_fidelity_cc3.html - it also supported castling, en pessant, not sure about 50 move rule.

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thomasmg
Cool! I just recently implemented a chess engine in ~400 (readable) lines, with all rules, first in Java and then ported to my own programming language "Bau" [1]. This is including a terminal UI. I'll measure the ELO, but I was never able to beat it :-) The castling moves are specially tricky to implement I think. I enjoyed the challenge as well.

[1] https://github.com/thomasmueller/bau-lang/blob/main/src/test...

dxxvi
I wonder how big 1300, 1400, ..., 2200 Elo chess engines are.
kachapopopow
need to start measuring these things in the size of compiled functions so we can stop looking at oneliners (maybe wasm since it has an easy to read text representation)
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galkk
This is not chess, but something that allows to move chess pieces.

> Not implemented: castling, en passant, promotion, repetition, 50-move rule.