Tweak cutnode reduction

locutus2 · noobpwnftw · commit e857d3d59075 · 2020-08-15T22:58:18.000+08:00
Less reduction for second move at non-check CUT node with depth <= 10. STC: LLR: 2.94 (-2.94,2.94) {-0.50,1.50} Total: 38680 W: 7490 L: 7245 D: 23945 Ptnml(0-2): 643, 4441, 8967, 4606, 683 https://tests.stockfishchess.org/tests/view/5f21e1782f7e63962b99f451 LTC: LLR: 2.95 (-2.94,2.94) {0.25,1.75} Total: 71976 W: 9003 L: 8636 D: 54337 Ptnml(0-2): 440, 6414, 21972, 6663, 499 https://tests.stockfishchess.org/tests/view/5f2245762f7e63962b99f4bd closes official-stockfish#2868 Bench: 4746616
diff --git a/src/search.cpp b/src/search.cpp
@@ -1185,6 +1185,13 @@ namespace {
       {
           Depth r = reduction(improving, depth, moveCount);
 
+          // Decrease reduction at non-check cut nodes for second move at low depths
+          if (   cutNode
+              && depth <= 10
+              && moveCount <= 2
+              && !ss->inCheck)
+              r--;
+
           // Decrease reduction if the ttHit running average is large
           if (thisThread->ttHitAverage > 473 * TtHitAverageResolution * TtHitAverageWindow / 1024)
               r--;
