BadFish/src/tt.h

/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2024 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
  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 <cstddef>
#include <cstdint>

#include "misc.h"
#include "types.h"

namespace Stockfish {

// TTEntry struct is the 10 bytes transposition table entry, defined as below:
//
// key        16 bit
// depth       8 bit
// generation  5 bit
// pv node     1 bit
// bound type  2 bit
// move       16 bit
// value      16 bit
// eval value 16 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 + DEPTH_OFFSET); }
    bool  is_pv() const { return bool(genBound8 & 0x4); }
    Bound bound() const { return Bound(genBound8 & 0x3); }
    void  save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev, uint8_t generation8);

   private:
    friend class TranspositionTable;

    uint16_t key16;
    uint8_t  depth8;
    uint8_t  genBound8;
    Move     move16;
    int16_t  value16;
    int16_t  eval16;
};


// A TranspositionTable is an array of Cluster, of size clusterCount. Each
// cluster consists of ClusterSize number of TTEntry. Each non-empty TTEntry
// contains information on exactly one position. The size of a Cluster should
// divide the size of a cache line for best performance, as the cacheline is
// prefetched when possible.
class TranspositionTable {

    static constexpr int ClusterSize = 3;

    struct Cluster {
        TTEntry entry[ClusterSize];
        char    padding[2];  // Pad to 32 bytes
    };

    static_assert(sizeof(Cluster) == 32, "Unexpected Cluster size");

    // Constants used to refresh the hash table periodically
    static constexpr unsigned GENERATION_BITS = 3;  // nb of bits reserved for other things
    static constexpr int      GENERATION_DELTA =
      (1 << GENERATION_BITS);  // increment for generation field
    static constexpr int GENERATION_CYCLE = 255 + (1 << GENERATION_BITS);  // cycle length
    static constexpr int GENERATION_MASK =
      (0xFF << GENERATION_BITS) & 0xFF;  // mask to pull out generation number

   public:
    ~TranspositionTable() { aligned_large_pages_free(table); }
    void new_search() { generation8 += GENERATION_DELTA; }  // Lower bits are used for other things
    TTEntry* probe(const Key key, bool& found) const;
    int      hashfull() const;
    void     resize(size_t mbSize, int threadCount);
    void     clear(size_t threadCount);

    TTEntry* first_entry(const Key key) const {
        return &table[mul_hi64(key, clusterCount)].entry[0];
    }

    uint8_t generation() const { return generation8; }

   private:
    friend struct TTEntry;

    size_t   clusterCount;
    Cluster* table       = nullptr;
    uint8_t  generation8 = 0;  // Size must be not bigger than TTEntry::genBound8
};

}  // namespace Stockfish

#endif  // #ifndef TT_H_INCLUDED