Stat score initialization: grandchildren

This is the sequel of the previous patch, we now let the parent node initialize
stat score to zero once for all grandchildren.

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

Tests results against the previous patch:

STC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 23676 W: 5417 L: 5157 D: 13102
http://tests.stockfishchess.org/tests/view/5a9423a90ebc590297cc8a46

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 35485 W: 6168 L: 5898 D: 23419
http://tests.stockfishchess.org/tests/view/5a9435550ebc590297cc8a54

Bench: 5643520

diff --git a/src/search.cpp b/src/search.cpp
index a5b07d2f18c30185d2da0192076dd612578a0480..3874852b1bbcac48a34ea38812b79b047a283d5d 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -517,13 +517,6 @@ namespace {
     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();
@@ -560,6 +553,13 @@ namespace {
     (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
     Square prevSq = to_sq((ss-1)->currentMove);
 
+    // Initialize statScore to zero for the grandchildren of the current position.
+    // So statScore is shared between all grandchildren and only the first grandchild
+    // starts with statScore = 0. Later grandchildren start with the last calculated
+    // statScore of the previous grandchild. This influences the reduction rules in
+    // LMR which are based on the statScore of parent position.
+    (ss+2)->statScore = 0;
+
     // Step 4. Transposition table lookup. We don't want the score of a partial
     // search to overwrite a previous full search TT value, so we use a different
     // position key in case of an excluded move.