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Further Simplify Stalemate Detection

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Passed Non-regression STC:
LLR: 2.98 (-2.94,2.94) <-1.75,0.25>
Total: 191520 W: 49633 L: 49582 D: 92305
Ptnml(0-2): 557, 20676, 53260, 20693, 574
https://tests.stockfishchess.org/tests/view/68ab570075da51a345a5abe1

Passed Non-regression LTC:
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 212934 W: 54643 L: 54618 D: 103673
Ptnml(0-2): 117, 22417, 61364, 22462, 107
https://tests.stockfishchess.org/tests/view/68ab84e975da51a345a5ac6b

10k Stalemate:
Elo: 0.35 ± 1.2 (95%) LOS: 71.6%
Total: 10000 W: 4602 L: 4592 D: 806
Ptnml(0-2): 0, 148, 4694, 158, 0
nElo: 1.99 ± 6.8 (95%) PairsRatio: 1.07
https://tests.stockfishchess.org/tests/view/68abeb8175da51a345a5af82

closes https://github.com/official-stockfish/Stockfish/pull/6268

Bench: 2420973
This commit is contained in:
Shawn Xu
2025-08-30 15:12:06 +02:00
committed by Joost VandeVondele
parent 7d213afd37
commit 3f18352396
2 changed files with 2 additions and 5 deletions
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src/search.cpp
+1 -4
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@@ -1053,10 +1053,7 @@ moves_loop: // When in check, search starts here
if (!pos.see_ge(move, -margin))
{
bool mayStalemateTrap =
depth > 2 && alpha < 0 && pos.non_pawn_material(us) == PieceValue[movedPiece]
&& PieceValue[movedPiece] >= RookValue
// it can't be stalemate if we moved a piece adjacent to the king
&& !(attacks_bb<KING>(pos.square<KING>(us)) & move.from_sq());
depth > 2 && alpha < 0 && pos.non_pawn_material(us) == PieceValue[movedPiece];
// avoid pruning sacrifices of our last piece for stalemate
if (!mayStalemateTrap)