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============================== My email: jotes@go2.pl



Grail 2.0.1 - new version chess engine

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Grail - UCI chess engine
Author: Jørgen Hanssen

After working on it for a while, I feel my hobby chess engine is finally ready for v1.0.0. Not cutting edge, but plays a solid game.

Grail uses modern search techniques and evaluates positions using a simple NNUE trained on 500 million positions from self-play.

Development continues in my spare time, and I plan to release updates with several missing features and improvements like threading, tablebase support, and pondering. But don't worry! Grail supports all standard UCI time controls and analysis modes, so it works seamlessly with your favorite GUI for matches and analysis.

Grail 2.0.1 what's new?

Highlights

  • Another round of datagen and training of the NNUE.
  • Various bug/correctness fixes and performance improvements.

Search Improvements

  • Added continuation correction.
  • Tuned correction history weights.
  • Razoring now uses the TT/search eval instead of the static eval.
  • Use the TT/search eval instead of the static eval on the search stack.
  • Skip null-move pruning when the static eval is below beta.
  • Reduce quiet moves when the TT move is a capture.

Bug Fixes / Correctness

  • Fixed an issue where futility pruning could prune the PV move at low depth (occasionally produced a wrong mate score).
  • QS was storing the corrected eval in the TT. Now stores the raw static eval to avoid double-correction.
  • No longer demote the PV move to a Cut node in the LMR re-search.
  • Null-move pruning now returns the null score instead of beta.
  • No longer store partial results from an aborted search in the TT.
  • Preserve the existing TT move when an overwrite carries no move of its own.
  • Fixed an i16 overflow in the score-drop check.

Misc

  • General cleanup and dependency updates.

Elo gain over 2.0.0 (1 thread without endgame tablebases)

STC  (10+0.1):  +30.86 ± 4.21 Elo  (10k games)
LTC  (60+0.6):  +34.28 ± 6.97 Elo (3k games)
VLTC (180+1.8): +33.11 ± 11.56 Elo (1k games)

Downloads

  • x86-64-v4: Modern CPUs with AVX-512 (2017+)
  • x86-64-v3: CPUs with AVX2 (2013+)
  • arm64: Apple Silicon



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