Stat score initialization: children

Let the parent node initialize stat score to zero once for all siblings.

Initialize statScore to zero for the children of the current position.
So statScore is shared between sibling positions and only the first sibling
starts with statScore = 0. Later siblings start with the last calculated
statScore of the previous sibling. This influences the reduction rules in
in LMR which are based on the statScore of parent position.

STC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 22683 W: 5202 L: 4946 D: 12535
http://tests.stockfishchess.org/tests/view/5a93315f0ebc590297cc894f

LTC:
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 48548 W: 8346 L: 8035 D: 32167
http://tests.stockfishchess.org/tests/view/5a933ba90ebc590297cc8962

Bench: 5833683

diff --git a/src/search.cpp b/src/search.cpp
index 394f228fb4f59956914ab3d014b199934d245716..a5b07d2f18c30185d2da0192076dd612578a0480 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -514,10 +514,16 @@ namespace {
     Thread* thisThread = pos.this_thread();
     inCheck = pos.checkers();
     moveCount = captureCount = quietCount = ss->moveCount = 0;
-    ss->statScore = 0;
     bestValue = -VALUE_INFINITE;
     maxValue = VALUE_INFINITE;
 
+    // Initialize statScore to zero for the childs of the current position.
+    // So statScore is shared between sibling positions and only the first sibling
+    // starts with statScore = 0. Later siblings start with the last calculated
+    // statScore of the previous sibling. This influences in LMR the reduction rules
+    // which based on the statScore of parent position.
+    (ss+1)->statScore = 0;
+
     // Check for the available remaining time
     if (thisThread == Threads.main())
         static_cast<MainThread*>(thisThread)->check_time();