Adjust singular extension search depth

Vizvezdenec · vondele · commit 6ecab03dee15 · 2020-03-20T21:07:37.000+01:00
This patch applies a different singular extension search logic in case the position is ttPv && !PvNode. It changes the depth of this search, higher for this types of nodes, and lower for other nodes. passed STC http://tests.stockfishchess.org/tests/view/5e72bbaae42a5c3b3ca2e75e LLR: 2.94 (-2.94,2.94) {-0.50,1.50} Total: 12692 W: 2608 L: 2389 D: 7695 Ptnml(0-2): 238, 1414, 2839, 1601, 254 passed LTC http://tests.stockfishchess.org/tests/view/5e731c07e42a5c3b3ca2e770 LLR: 2.96 (-2.94,2.94) {0.25,1.75} Total: 145716 W: 19218 L: 18626 D: 107872 Ptnml(0-2): 1100, 13605, 42899, 14111, 1143 closes #2590 Bench: 5398277
diff --git a/src/search.cpp b/src/search.cpp
@@ -1055,9 +1055,9 @@ namespace {
           &&  pos.legal(move))
       {
           Value singularBeta = ttValue - (((ttPv && !PvNode) + 4) * depth) / 2;
-          Depth halfDepth = depth / 2;
+          Depth singularDepth = (depth - 1 + 3 * (ttPv && !PvNode)) / 2;
           ss->excludedMove = move;
-          value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, halfDepth, cutNode);
+          value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
           ss->excludedMove = MOVE_NONE;
 
           if (value < singularBeta)
