Increase reduction in case of stable best move

Vizvezdenec · vondele · commit a88a38c3a917 · 2020-12-14T07:52:02.000+01:00
The idea of this patch is pretty simple - we already do more reductions for non-PV and root nodes in case of stable best move for depth > 10. This patch makes us do so if root depth if > 10 instead, which is logical since best move changes (thus instability of it) is counted at root, so it makes a lot of sense to use depth of the root. passed STC https://tests.stockfishchess.org/tests/view/5fd643271ac16912018885c5 LLR: 2.94 (-2.94,2.94) {-0.25,1.25} Total: 13232 W: 1308 L: 1169 D: 10755 Ptnml(0-2): 39, 935, 4535, 1062, 45 passed LTC https://tests.stockfishchess.org/tests/view/5fd68db11ac16912018885f0 LLR: 2.96 (-2.94,2.94) {0.25,1.25} Total: 14024 W: 565 L: 463 D: 12996 Ptnml(0-2): 3, 423, 6062, 517, 7 closes official-stockfish/Stockfish#3263 Bench: 4050630
diff --git a/src/search.cpp b/src/search.cpp
@@ -1188,7 +1188,7 @@ namespace {
               r -= 2;
 
           // Increase reduction at root and non-PV nodes when the best move does not change frequently
-          if ((rootNode || !PvNode) && depth > 10 && thisThread->bestMoveChanges <= 2)
+          if ((rootNode || !PvNode) && thisThread->rootDepth > 10 && thisThread->bestMoveChanges <= 2)
               r++;
 
           // More reductions for late moves if position was not in previous PV
