Skip full depth search in LMR depending on depth

dynamically adjust newDepth, and skip full depth search if newDepth doesn't exceed the previous search depth.
This affects the used newDepth for future searches, and influences the stat bonus for the move.

Passed STC:
https://tests.stockfishchess.org/tests/view/63795500aa34433735bc1cfe
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 112776 W: 30082 L: 29663 D: 53031
Ptnml(0-2): 352, 12453, 30423, 12744, 416

Passed LTC:
https://tests.stockfishchess.org/tests/view/6379ea39aa34433735bc2f9b
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 83576 W: 22559 L: 22169 D: 38848
Ptnml(0-2): 38, 8011, 25303, 8395, 41

closes https://github.com/official-stockfish/Stockfish/pull/4240

Bench: 4390318

diff --git a/src/search.cpp b/src/search.cpp
index fa87f1c3f0f3a4aced851f4ef795d08c8f5a568d..5cef5c40c235e719b5ad3bdb7ed7abc664e6da88 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1188,7 +1188,11 @@ moves_loop: // When in check, search starts here
               // was good enough search deeper, if it was bad enough search shallower
               const bool doDeeperSearch = value > (alpha + 64 + 11 * (newDepth - d));
               const bool doShallowerSearch = value < bestValue + newDepth;
-              value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth + doDeeperSearch - doShallowerSearch, !cutNode);
+
+              newDepth += doDeeperSearch - doShallowerSearch;
+
+              if (newDepth > d)
+                  value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
 
               int bonus = value > alpha ?  stat_bonus(newDepth)
                                         : -stat_bonus(newDepth);