Negative extension for ttMove that is less than alpha and value

in the context of singular extensions

Passed STC:
https://tests.stockfishchess.org/tests/view/626047e8b03f22647441ade0
LLR: 2.97 (-2.94,2.94) <0.00,2.50>
Total: 50296 W: 13410 L: 13108 D: 23778
Ptnml(0-2): 196, 5548, 13370, 5826, 208

Passed LTC:
https://tests.stockfishchess.org/tests/view/6260a513b03f22647441b970
LLR: 2.96 (-2.94,2.94) <0.50,3.00>
Total: 83896 W: 22433 L: 22054 D: 39409
Ptnml(0-2): 49, 8273, 24938, 8626, 62

closes https://github.com/official-stockfish/Stockfish/pull/3995

bench: 7729968

diff --git a/src/search.cpp b/src/search.cpp
index 167209a315b065d8885723663fb39641fd91bff5..ff6bf335d06d695bd17abda8567b7981c8d9e79a 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1098,6 +1098,10 @@ moves_loop: // When in check, search starts here
               // If the eval of ttMove is greater than beta, we reduce it (negative extension)
               else if (ttValue >= beta)
                   extension = -2;
+
+              // If the eval of ttMove is less than alpha and value, we reduce it (negative extension)
+              else if (ttValue <= alpha && ttValue <= value)
+                  extension = -1;
           }
 
           // Check extensions (~1 Elo)