Simplify LMR extension limit formula

aronpetko · vondele · commit 64e8e1b24736 · 2025-07-28T20:18:55.000+02:00
This patch simplifies the maximum depth formula that reductions in LMR can allow. Passed STC LLR: 2.93 (-2.94,2.94) <-1.75,0.25> Total: 35616 W: 9358 L: 9139 D: 17119 Ptnml(0-2): 101, 4051, 9278, 4284, 94 https://tests.stockfishchess.org/tests/view/688608cf966ed85face24882 Passed LTC LLR: 2.95 (-2.94,2.94) <-1.75,0.25> Total: 22284 W: 5833 L: 5613 D: 10838 Ptnml(0-2): 8, 2367, 6173, 2585, 9 https://tests.stockfishchess.org/tests/view/68860d7f966ed85face248d5 closes #6191 Bench: 2902492
diff --git a/src/search.cpp b/src/search.cpp
@@ -1219,9 +1219,7 @@ Value Search::Worker::search(
             // beyond the first move depth.
             // To prevent problems when the max value is less than the min value,
             // std::clamp has been replaced by a more robust implementation.
-            Depth d = std::max(1, std::min(newDepth - r / 1024,
-                                           newDepth + !allNode + (PvNode && !bestMove)))
-                    + PvNode;
+            Depth d = std::max(1, std::min(newDepth - r / 1024, newDepth + 1 + PvNode)) + PvNode;
 
             ss->reduction = newDepth - d;
             value         = -search<NonPV>(pos, ss + 1, -(alpha + 1), -alpha, d, true);
