Refine futility pruning for parent nodes

This patch is a result of refining of tuning vondele did after
new net passed and some hand-made values adjustements - excluding
changes in other pruning heuristics and rounding value of history
divisor to the nearest power of 2.

With this patch futility pruning becomes more aggressive and
history influence on it is doubled again.

passed STC
https://tests.stockfishchess.org/tests/view/61a2c4c1a26505c2278c150d
LLR: 2.94 (-2.94,2.94) <0.00,2.50>
Total: 33848 W: 8841 L: 8574 D: 16433
Ptnml(0-2): 100, 3745, 8988, 3970, 121

passed LTC
https://tests.stockfishchess.org/tests/view/61a327ffa26505c2278c26d9
LLR: 2.94 (-2.94,2.94) <0.50,3.00>
Total: 22272 W: 5856 L: 5614 D: 10802
Ptnml(0-2): 12, 2230, 6412, 2468, 14

closes https://github.com/official-stockfish/Stockfish/pull/3814

bench 6302543

diff --git a/src/search.cpp b/src/search.cpp
index 8f9fa62c832150f7f5c02e3b38ee9354aee9399b..807d261472fc091b96f7aaf71ec46c784a1f810a 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1068,7 +1068,7 @@ moves_loop: // When in check, search starts here
               // Futility pruning: parent node (~5 Elo)
               if (   !ss->inCheck
                   && lmrDepth < 8
               // Futility pruning: parent node (~5 Elo)
               if (   !ss->inCheck
                   && lmrDepth < 8

-                  && ss->staticEval + 172 + 145 * lmrDepth + history / 128 <= alpha)
+                  && ss->staticEval + 142 + 139 * lmrDepth + history / 64 <= alpha)

                   continue;
 
               // Prune moves with negative SEE (~20 Elo)
                   continue;
 
               // Prune moves with negative SEE (~20 Elo)