Tweak of SEE pruning condition

passed STC
http://tests.stockfishchess.org/tests/view/5d386bda0ebc5925cf0ef49a
LLR: 2.95 (-2.94,2.94) [0.50,4.50]
Total: 56874 W: 12820 L: 12373 D: 31681

passed LTC
http://tests.stockfishchess.org/tests/view/5d38873a0ebc5925cf0ef86e
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 43512 W: 7547 L: 7247 D: 28718

Additional thanks to @locutus2 , @miguel-l and @xoto10 for fruitful discussion.
There may be some more elo there since this tweak was the first one and numbers
are more or less arbitrary.

Closes https://github.com/official-stockfish/Stockfish/pull/2256

Bench 3935523

diff --git a/src/search.cpp b/src/search.cpp
index 222be393be5c915834429b5302cfd5de164bf4fd..09df1ac2697989e9736ddf4c983c08d7407ce765 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1041,7 +1041,7 @@ moves_loop: // When in check, search starts from here
                   continue;
 
               // Prune moves with negative SEE (~10 Elo)
                   continue;
 
               // Prune moves with negative SEE (~10 Elo)

-              if (!pos.see_ge(move, Value(-29 * lmrDepth * lmrDepth)))
+              if (!pos.see_ge(move, Value(-(31 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))

                   continue;
           }
           else if (  (!givesCheck || !extension)
                   continue;
           }
           else if (  (!givesCheck || !extension)