Initial import of Glaurung 2.1

src/history.h

@@ -0,0 +1,76 @@
+/*
+  Glaurung, a UCI chess playing engine.
+  Copyright (C) 2004-2008 Tord Romstad
+
+  Glaurung is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+  
+  Glaurung is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+  
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+
+#if !defined(HISTORY_H_INCLUDED)
+#define HISTORY_H_INCLUDED
+
+////
+//// Includes
+////
+
+#include "depth.h"
+#include "move.h"
+#include "piece.h"
+
+
+////
+//// Types
+////
+
+/// The History class stores statistics about how often different moves have
+/// been successful or unsuccessful during the current search.  These
+/// statistics are used for reduction and move ordering decisions.
+
+class History {
+
+public:
+  History();
+  void clear();
+  void success(Piece p, Move m, Depth d);
+  void failure(Piece p, Move m);
+  int move_ordering_score(Piece p, Move m) const;
+  bool ok_to_prune(Piece p, Move m, Depth d) const;
+
+private:
+  int history[16][64];  // [piece][square]
+  int successCount[16][64];
+  int failureCount[16][64];
+};
+
+
+////
+//// Constants and variables
+////
+
+/// HistoryMax controls how often the history counters will be scaled down:
+/// When the history score for a move gets bigger than HistoryMax, all
+/// entries in the table are divided by 2.  It is difficult to guess what
+/// the ideal value of this constant is.  Scaling down the scores often has
+/// the effect that parts of the search tree which have been searched
+/// recently have a bigger importance for move ordering than the moves which
+/// have been searched a long time ago.
+///
+/// Note that HistoryMax should probably be changed whenever the constant
+/// OnePly in depth.h is changed.  This is somewhat annoying.  Perhaps it
+/// would be better to scale down the history table at regular intervals?
+
+const int HistoryMax = 50000;
+
+
+#endif // !defined(HISTORY_H_INCLUDED)