Use fraction of history heuristics in futility pruning

This idea is somewhat of a respin of smth we had in futility pruning and that was simplified away - dependence of it not only on static evaluation of position but also on move history heuristics.
Instead of aborting it when they are high there we use fraction of their sum to adjust static eval pruning criteria.

passed STC
https://tests.stockfishchess.org/tests/view/619bd438c0a4ea18ba95a27d
LLR: 2.93 (-2.94,2.94) <0.00,2.50>
Total: 113704 W: 29284 L: 28870 D: 55550
Ptnml(0-2): 357, 12884, 30044, 13122, 445

passed LTC
https://tests.stockfishchess.org/tests/view/619cb8f0c0a4ea18ba95a334
LLR: 2.96 (-2.94,2.94) <0.50,3.00>
Total: 147136 W: 37307 L: 36770 D: 73059
Ptnml(0-2): 107, 15279, 42265, 15804, 113

closes https://github.com/official-stockfish/Stockfish/pull/3805

bench 6777918

diff --git a/src/search.cpp b/src/search.cpp
index 92ec9eca77dae75a800adf0f719c753288a233a4..12c89de457b187bc4898e3d9956a05a9d0b4bebb 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1054,17 +1054,19 @@ moves_loop: // When in check, search starts here
           }
           else
           {
+              int history =   (*contHist[0])[movedPiece][to_sq(move)]
+                            + (*contHist[1])[movedPiece][to_sq(move)]
+                            + (*contHist[3])[movedPiece][to_sq(move)];
+
               // Continuation history based pruning (~20 Elo)
-              if (lmrDepth < 5
-                  && (*contHist[0])[movedPiece][to_sq(move)]
-                  + (*contHist[1])[movedPiece][to_sq(move)]
-                  + (*contHist[3])[movedPiece][to_sq(move)] < -3000 * depth + 3000)
+              if (   lmrDepth < 5
+                  && history < -3000 * depth + 3000)
                   continue;
 
               // Futility pruning: parent node (~5 Elo)
               if (   !ss->inCheck
                   && lmrDepth < 8
-                  && ss->staticEval + 172 + 145 * lmrDepth <= alpha)
+                  && ss->staticEval + 172 + 145 * lmrDepth + history / 256 <= alpha)
                   continue;
 
               // Prune moves with negative SEE (~20 Elo)