From: Stefan Geschwentner <locutus2@users.noreply.github.com>
Date: Tue, 27 Feb 2018 17:18:07 +0000 (+0100)
Subject: Stat score initialization: children
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=1463881153a20690871086208eaf76f20041effb

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 394f228f..a5b07d2f 100644
--- 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();