Reintroduce futility pruning for captures

This is a reintroduction of an idea that was simplified away approximately 1 year ago.
There are some tweaks to it :
a) exclude promotions;
b) exclude Pv Nodes from it - Pv Nodes logic for captures is really different from non Pv nodes so it makes a lot of sense;
c) use a big grain of capture history - idea is taken from my recent patches in futility pruning.

passed STC
https://tests.stockfishchess.org/tests/view/61bd90f857a0d0f327c373b7
LLR: 2.96 (-2.94,2.94) <0.00,2.50>
Total: 86640 W: 22474 L: 22110 D: 42056
Ptnml(0-2): 268, 9732, 22963, 10082, 275

passed LTC
https://tests.stockfishchess.org/tests/view/61be094457a0d0f327c38aa3
LLR: 2.95 (-2.94,2.94) <0.50,3.00>
Total: 23240 W: 6079 L: 5838 D: 11323
Ptnml(0-2): 14, 2261, 6824, 2512, 9

https://github.com/official-stockfish/Stockfish/pull/3864

bench 4493723

diff --git a/src/search.cpp b/src/search.cpp
index 8a4db35185921776e4288e02e83c8744c2c35db7..d2ceee9fd1a15823bf6937e13873a3f626248bf3 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1037,6 +1037,16 @@ moves_loop: // When in check, search starts here
                   && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0)
                   continue;
 
+              // Futility pruning for captures
+              if (   !pos.empty(to_sq(move))
+                  && !givesCheck
+                  && !PvNode
+                  && lmrDepth < 6
+                  && !ss->inCheck
+                  && ss->staticEval + 342 + 238 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))] 
+                   + captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 8 < alpha)
+                  continue;
+
               // SEE based pruning
               if (!pos.see_ge(move, Value(-218) * depth)) // (~25 Elo)
                   continue;