Avoid more expensive legality check

[stockfish] / src / movepick.h

diff --git a/src/movepick.h b/src/movepick.h
index cdedc9b616f9f78c6a652626c0c0a5ba096ed71b..ea599cda1afbe10a04f8a2f9f77ffc4becc237b8 100644 (file)
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -1,8 +1,6 @@
 /*
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
-  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
-  Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
-  Copyright (C) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+  Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -86,7 +84,13 @@ enum StatsType { NoCaptures, Captures };
 /// unsuccessful during the current search, and is used for reduction and move
 /// ordering decisions. It uses 2 tables (one for each color) indexed by
 /// the move's from and to squares, see www.chessprogramming.org/Butterfly_Boards
-typedef Stats<int16_t, 10692, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyHistory;
+typedef Stats<int16_t, 13365, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyHistory;
+
+/// At higher depths LowPlyHistory records successful quiet moves near the root
+/// and quiet moves which are/were in the PV (ttPv). It is cleared with each new
+/// search and filled during iterative deepening.
+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
@@ -104,12 +108,12 @@ typedef Stats<int16_t, 29952, PIECE_NB, SQUARE_NB> PieceToHistory;
 typedef Stats<PieceToHistory, NOT_USED, PIECE_NB, SQUARE_NB> ContinuationHistory;
 
 
-/// MovePicker class is used to pick one pseudo legal move at a time from the
+/// MovePicker class is used to pick one pseudo-legal move at a time from the
 /// current position. The most important method is next_move(), which returns a
-/// new pseudo legal move each time it is called, until there are no moves left,
-/// when MOVE_NONE is returned. In order to improve the efficiency of the alpha
-/// beta algorithm, MovePicker attempts to return the moves which are most likely
-/// to get a cut-off first.
+/// new pseudo-legal move each time it is called, until there are no moves left,
+/// when MOVE_NONE is returned. In order to improve the efficiency of the
+/// alpha-beta algorithm, MovePicker attempts to return the moves which are most
+/// likely to get a cut-off first.
 class MovePicker {
 
   enum PickType { Next, Best };
@@ -123,10 +127,12 @@ public:
                                            const PieceToHistory**,
                                            Square);
   MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
+                                           const LowPlyHistory*,
                                            const CapturePieceToHistory*,
                                            const PieceToHistory**,
                                            Move,
-                                           Move*);
+                                           const Move*,
+                                           int);
   Move next_move(bool skipQuiets = false);
 
 private:
@@ -137,6 +143,7 @@ private:
 
   const Position& pos;
   const ButterflyHistory* mainHistory;
+  const LowPlyHistory* lowPlyHistory;
   const CapturePieceToHistory* captureHistory;
   const PieceToHistory** continuationHistory;
   Move ttMove;
@@ -145,6 +152,7 @@ private:
   Square recaptureSquare;
   Value threshold;
   Depth depth;
+  int ply;
   ExtMove moves[MAX_MOVES];
 };