Assign negative stat bonuses for quiet moves at Pv nodes

This patch assigns negative stat bonuses for quiet moves
at pv nodes which are searched at depth greater than
this node assumes, so are extended.

Passed STC:
https://tests.stockfishchess.org/tests/view/6426198bdb43ab2ba6f9cfa2
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 548944 W: 147287 L: 146254 D: 255403
Ptnml(0-2): 1662, 59772, 150671, 60605, 1762

Passed LTC:
https://tests.stockfishchess.org/tests/view/642be4f177ff3301150d892d
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 93352 W: 25400 L: 24994 D: 42958
Ptnml(0-2): 44, 8817, 28547, 9225, 43

closes https://github.com/official-stockfish/Stockfish/pull/4495

bench 5044536

diff --git a/src/search.cpp b/src/search.cpp
index 749de792dd63c6589b5d8924a7d914991d622fb5..aa1a3e8c17fec2a39407c3753e95338e9cd5d443 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -290,7 +290,7 @@ void Thread::search() {
 
   bestValue = delta = alpha = -VALUE_INFINITE;
   beta = VALUE_INFINITE;
-  optimism[us] = optimism[~us] = VALUE_ZERO;
+  optimism[WHITE] = optimism[BLACK] = VALUE_ZERO;
 
   if (mainThread)
   {
@@ -1257,6 +1257,9 @@ moves_loop: // When in check, search starts here
           (ss+1)->pv[0] = MOVE_NONE;
 
           value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
+
+          if (moveCount > 1 && newDepth >= depth && !capture)
+              update_continuation_histories(ss, movedPiece, to_sq(move), -stat_bonus(newDepth));
       }
 
       // Step 19. Undo move