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
  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)

//// 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 {

  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;

  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)