Further improve history updates

Now even double history updates if a search failed low at an expected PV or CUT node.

STC:
LLR: 2.93 (-2.94,2.94) <-0.50,2.50>
Total: 30736 W: 7891 L: 7674 D: 15171
Ptnml(0-2): 90, 3477, 8017, 3694, 90
https://tests.stockfishchess.org/tests/view/61364ae30cd98ab40c0c9da5

LTC:
LLR: 2.94 (-2.94,2.94) <0.50,3.50>
Total: 73600 W: 18684 L: 18326 D: 36590
Ptnml(0-2): 41, 7734, 20899, 8078, 48
https://tests.stockfishchess.org/tests/view/6136940f0cd98ab40c0c9df3

closes https://github.com/official-stockfish/Stockfish/pull/3694

Bench: 6030657

diff --git a/src/search.cpp b/src/search.cpp
index 6affa5107b0cfe6544c60ac4ab66b128be0c7d73..ed5dd6c2c7ad5aab3e39b26cb038833c3a6b58d2 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1325,7 +1325,7 @@ moves_loop: // When in check, search starts here
     // Bonus for prior countermove that caused the fail low
     else if (   (depth >= 3 || PvNode)
              && !priorCapture)
-        update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth + (PvNode || cutNode)));
+        update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + (PvNode || cutNode)));
 
     if (PvNode)
         bestValue = std::min(bestValue, maxValue);