Introduce movecount pruning for qsearch()

If in quiescence search, we assume that me can prune late moves when:

a) the move ordering count of the move is : moveCount > abs(depth) + 2
b) we are not in check
c) the late move does not give check
d) the late move is not an advanced pawn push

Modification of an original idea by @VoyagerOne.

STC
https://tests.stockfishchess.org/tests/view/5f40581787a5c3c63d8f535f
LLR: 2.96 (-2.94,2.94) {-0.25,1.25}
Total: 132848 W: 14999 L: 14661 D: 103188
Ptnml(0-2): 684, 11242, 42309, 11430, 759

LTC
https://tests.stockfishchess.org/tests/view/5f4226da87a5c3c63d8f5412
LLR: 2.98 (-2.94,2.94) {0.25,1.25}
Total: 12008 W: 678 L: 551 D: 10779
Ptnml(0-2): 8, 485, 4899, 596, 16

closes https://github.com/official-stockfish/Stockfish/pull/3053

Bench: 3749974

diff --git a/src/movepick.h b/src/movepick.h
index 97ea5bec75f2c434585bf57ce47746aba9a6d60d..4c0ad55172d15101466b53babba99c2b9ea90f08 100644 (file)
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -93,7 +93,7 @@ constexpr int MAX_LPH = 4;
 typedef Stats<int16_t, 10692, MAX_LPH, int(SQUARE_NB) * int(SQUARE_NB)> LowPlyHistory;
 
 /// CounterMoveHistory stores counter moves indexed by [piece][to] of the previous
-/// move, see www.chessprogramming.org/Countermove_Heuristic 
+/// move, see www.chessprogramming.org/Countermove_Heuristic
 typedef Stats<Move, NOT_USED, PIECE_NB, SQUARE_NB> CounterMoveHistory;
 
 /// CapturePieceToHistory is addressed by a move's [piece][to][captured piece type]

diff --git a/src/search.cpp b/src/search.cpp
index 82d8bb9dfa96d97cf25022c760202360d0a685b0..266e2db30d0f2516abeb078a894cce3e16136d39 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1531,6 +1531,10 @@ moves_loop: // When in check, search starts from here
       {
           assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
 
+          // moveCount pruning
+          if (moveCount > abs(depth) + 2)
+              continue;
+
           futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
 
           if (futilityValue <= alpha)
@@ -1547,7 +1551,7 @@ moves_loop: // When in check, search starts from here
       }
 
       // Do not search moves with negative SEE values
-      if (  !ss->inCheck && !pos.see_ge(move))
+      if (!ss->inCheck && !pos.see_ge(move))
           continue;
 
       // Speculative prefetch as early as possible