Pixel4u/checkers-endgame-tablebase

Checkers endgame tablebase (4 pieces and fewer, solved exactly)

Every American checkers (English draughts) position with four pieces or fewer, solved exactly: 6,408,836 positions with win/loss/draw and the exact distance to the end in plies. One byte per position, 1.82 MB gzipped.

• 2,675,270 won · 2,004,797 lost · 1,728,769 drawn
• Longest forced win: 109 plies (55 moves), two men against two men
• Includes a dependency-free Python reader and the full byte/index spec, so a reader in any language is an afternoon's work

Why you can trust it

Built forwards rather than by retrograde analysis: the successor graph comes from the same move generator that validates live games, then gets walked in reverse. No separate reverse-move generator exists to be subtly wrong.

Verified four independent ways: the index is proved a bijection; local consistency was checked exhaustively across all 6.4M entries; a second reader, written from the format spec rather than translated from the original code, agrees on slot numbers and not merely on verdicts; and known textbook endings come out right (king vs king drawn, two kings vs one won in 11 moves, three vs one in 7).

One invariant needs no reference: wins take an odd number of plies and losses an even number. All 2,675,270 win distances in the file are odd.

Files

• endgame4.bin.gz – the tablebase, one byte per position
• checkers_endgame.py – reference reader in Python, no dependencies
• cases.json – known test positions with expected results, for checking your own reader

Citation

CC BY 4.0. Archived with a DOI: https://doi.org/10.5281/zenodo.23002849

Browser-playable version: https://checkersarena.io/checkers-endgame/

Source and reader on GitHub: https://github.com/Pixel4youcorp/checkers-endgame-tablebase