tt.h

/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
  Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad

  Stockfish 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.

  Stockfish 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(TT_H_INCLUDED)
#define TT_H_INCLUDED

////
//// Includes
////

#include "depth.h"
#include "move.h"
#include "value.h"


////
//// Types
////

/// The TTEntry class is the class of transposition table entries
///
/// A TTEntry needs 128 bits to be stored
///
/// bit  0-31: key
/// bit 32-63: data
/// bit 64-79: value
/// bit 80-95: depth
/// bit 96-111: static value
/// bit 112-127: margin of static value
///
/// the 32 bits of the data field are so defined
///
/// bit  0-16: move
/// bit 17-20: not used
/// bit 21-22: value type
/// bit 23-31: generation

class TTEntry {

public:
  void save(uint32_t k, Value v, ValueType t, Depth d, Move m, int g, Value statV, Value kd) {

      key32 = k;
      data = (m & 0x1FFFF) | (t << 21) | (g << 23);
      value16     = (int16_t)v;
      depth16     = (int16_t)d;
      staticValue = (int16_t)statV;
      staticValueMargin  = (int16_t)kd;
  }
  void set_generation(int g) { data = move() | (type() << 21) | (g << 23); }

  uint32_t key() const { return key32; }
  Depth depth() const { return Depth(depth16); }
  Move move() const { return Move(data & 0x1FFFF); }
  Value value() const { return Value(value16); }
  ValueType type() const { return ValueType((data >> 21) & 3); }
  int generation() const { return data >> 23; }
  Value static_value() const { return Value(staticValue); }
  Value static_value_margin() const { return Value(staticValueMargin); }

private:
  uint32_t key32;
  uint32_t data;
  int16_t value16;
  int16_t depth16;
  int16_t staticValue;
  int16_t staticValueMargin;
};


/// This is the number of TTEntry slots for each cluster
const int ClusterSize = 4;

/// TTCluster consists of ClusterSize number of TTEntries.
/// Size of TTCluster must not be bigger than a cache line size.
/// In case it is less, it should be padded to guarantee always aligned accesses.

struct TTCluster {
  TTEntry data[ClusterSize];
};


/// The transposition table class. This is basically just a huge array
/// containing TTCluster objects, and a few methods for writing new entries
/// and reading new ones.

class TranspositionTable {

  TranspositionTable(const TranspositionTable&);
  TranspositionTable& operator=(const TranspositionTable&);

public:
  TranspositionTable();
  ~TranspositionTable();
  void set_size(size_t mbSize);
  void clear();
  void store(const Key posKey, Value v, ValueType type, Depth d, Move m, Value statV, Value kingD);
  TTEntry* retrieve(const Key posKey) const;
  void new_search();
  TTEntry* first_entry(const Key posKey) const;
  void refresh(const TTEntry* tte) const;

private:
  size_t size;
  TTCluster* entries;
  uint8_t generation; // To properly compare, size must be smaller then TT stored value
};

extern TranspositionTable TT;


/// TranspositionTable::first_entry returns a pointer to the first
/// entry of a cluster given a position. The lowest order bits of the key
/// are used to get the index of the cluster.

inline TTEntry* TranspositionTable::first_entry(const Key posKey) const {

  return entries[((uint32_t)posKey) & (size - 1)].data;
}


/// TranspositionTable::refresh updates the 'generation' value of the TTEntry
/// to avoid aging. Normally called after a TT hit, before to return.

inline void TranspositionTable::refresh(const TTEntry* tte) const {

  const_cast<TTEntry*>(tte)->set_generation(generation);
}

#endif // !defined(TT_H_INCLUDED)