Less reduction for later threads.

locutus2 · vondele · commit 39c077f15a88 · 2025-08-24T20:07:50.000+02:00
Give "(thread id mod 8) * 64" less reductions (up to nearly a half ply). Passed SMP STC: LLR: 2.95 (-2.94,2.94) <0.00,2.00> Total: 413176 W: 106496 L: 105666 D: 201014 Ptnml(0-2): 504, 46732, 111266, 47602, 484 https://tests.stockfishchess.org/tests/view/68a24aeeb6fb3300203bbdc4 Passed SMP LTC: LLR: 2.95 (-2.94,2.94) <0.50,2.50> Total: 60420 W: 15622 L: 15268 D: 29530 Ptnml(0-2): 11, 6106, 17632, 6440, 21 https://tests.stockfishchess.org/tests/view/68a2c2ffb6fb3300203bc516 closes #6249 No functional change
diff --git a/src/search.cpp b/src/search.cpp
@@ -1177,6 +1177,7 @@ Value Search::Worker::search(
         // These reduction adjustments have no proven non-linear scaling
 
         r += 671;  // Base reduction offset to compensate for other tweaks
+        r -= (threadIdx % 8) * 64;
         r -= moveCount * 66;
         r -= std::abs(correctionValue) / 30450;
 
