Subversion Repositories Games.Chess Giants

/*

  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) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, 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/>.

*/

#ifndef TT_H_INCLUDED

#define TT_H_INCLUDED

#include "misc.h"

#include "types.h"

/// TTEntry struct is the 10 bytes transposition table entry, defined as below:

///

/// key        16 bit

/// move       16 bit

/// value      16 bit

/// eval value 16 bit

/// generation  6 bit

/// bound type  2 bit

/// depth       8 bit

struct TTEntry {

  Move  move()  const { return (Move )move16; }

  Value value() const { return (Value)value16; }

  Value eval()  const { return (Value)eval16; }

  Depth depth() const { return (Depth)depth8; }

  Bound bound() const { return (Bound)(genBound8 & 0x3); }

  void save(Key k, Value v, Bound b, Depth d, Move m, Value ev, uint8_t g) {

    // Preserve any existing move for the same position

    if (m || (k >> 48) != key16)

        move16 = (uint16_t)m;

    // Don't overwrite more valuable entries

    if (  (k >> 48) != key16

        || d > depth8 - 4

     /* || g != (genBound8 & 0xFC) // Matching non-zero keys are already refreshed by probe() */

        || b == BOUND_EXACT)

    {

        key16     = (uint16_t)(k >> 48);

        value16   = (int16_t)v;

        eval16    = (int16_t)ev;

        genBound8 = (uint8_t)(g | b);

        depth8    = (int8_t)d;

    }

  }

private:

  friend class TranspositionTable;

  uint16_t key16;

  uint16_t move16;

  int16_t  value16;

  int16_t  eval16;

  uint8_t  genBound8;

  int8_t   depth8;

};

/// A TranspositionTable consists of a power of 2 number of clusters and each

/// cluster consists of ClusterSize number of TTEntry. Each non-empty entry

/// contains information of exactly one position. The size of a cluster should

/// divide the size of a cache line size, to ensure that clusters never cross

/// cache lines. This ensures best cache performance, as the cacheline is

/// prefetched, as soon as possible.

class TranspositionTable {

  static const int CacheLineSize = 64;

  static const int ClusterSize = 3;

  struct Cluster {

    TTEntry entry[ClusterSize];

    char padding[2]; // Align to a divisor of the cache line size

  };

  static_assert(CacheLineSize % sizeof(Cluster) == 0, "Cluster size incorrect");

public:

 ~TranspositionTable() { free(mem); }

  void new_search() { generation8 += 4; } // Lower 2 bits are used by Bound

  uint8_t generation() const { return generation8; }

  TTEntry* probe(const Key key, bool& found) const;

  int hashfull() const;

  void resize(size_t mbSize);

  void clear();

  // The lowest order bits of the key are used to get the index of the cluster

  TTEntry* first_entry(const Key key) const {

    return &table[(size_t)key & (clusterCount - 1)].entry[0];

  }

private:

  size_t clusterCount;

  Cluster* table;

  void* mem;

  uint8_t generation8; // Size must be not bigger than TTEntry::genBound8

};

extern TranspositionTable TT;

#endif // #ifndef TT_H_INCLUDED