simplify stalemate further

xu-shawn · vondele · commit 75ac6c7a061a · 2025-09-02T20:39:02.000+02:00
Non-regression STC: LLR: 2.93 (-2.94,2.94) <-1.75,0.25> Total: 155200 W: 40650 L: 40562 D: 73988 Ptnml(0-2): 533, 17588, 41258, 17700, 521 https://tests.stockfishchess.org/tests/view/68abe11375da51a345a5adec Non-regression LTC: LLR: 2.94 (-2.94,2.94) <-1.75,0.25> Total: 82824 W: 21442 L: 21287 D: 40095 Ptnml(0-2): 51, 8738, 23675, 8901, 47 https://tests.stockfishchess.org/tests/view/68b205606217b8721dca9c8e 10k Stalemate: Elo: 1.46 ± 1.2 (95%) LOS: 99.0% Total: 10000 W: 4640 L: 4598 D: 762 Ptnml(0-2): 0, 140, 4678, 182, 0 https://tests.stockfishchess.org/tests/view/68b2059b6217b8721dca9c90 closes #6283 Bench: 2431727
diff --git a/src/search.cpp b/src/search.cpp
@@ -1049,16 +1049,11 @@ Value Search::Worker::search(
                 }
 
                 // SEE based pruning for captures and checks
+                // Avoid pruning sacrifices of our last piece for stalemate
                 int margin = std::max(157 * depth + captHist / 29, 0);
-                if (!pos.see_ge(move, -margin))
-                {
-                    bool mayStalemateTrap =
-                      depth > 2 && alpha < 0 && pos.non_pawn_material(us) == PieceValue[movedPiece];
-
-                    // avoid pruning sacrifices of our last piece for stalemate
-                    if (!mayStalemateTrap)
-                        continue;
-                }
+                if ((alpha >= VALUE_DRAW || pos.non_pawn_material(us) != PieceValue[movedPiece])
+                    && !pos.see_ge(move, -margin))
+                    continue;
             }
             else
             {
