108 lines
3.4 KiB
C++
108 lines
3.4 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
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Stockfish is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Stockfish is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef TT_H_INCLUDED
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#define TT_H_INCLUDED
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#include "misc.h"
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#include "types.h"
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namespace Stockfish {
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/// TTEntry struct is the 10 bytes transposition table entry, defined as below:
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///
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/// key 16 bit
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/// depth 8 bit
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/// generation 5 bit
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/// pv node 1 bit
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/// bound type 2 bit
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/// move 16 bit
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/// value 16 bit
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/// eval value 16 bit
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struct TTEntry {
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Move move() const { return (Move )move16; }
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Value value() const { return (Value)value16; }
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Value eval() const { return (Value)eval16; }
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Depth depth() const { return (Depth)depth8 + DEPTH_OFFSET; }
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bool is_pv() const { return (bool)(genBound8 & 0x4); }
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Bound bound() const { return (Bound)(genBound8 & 0x3); }
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void save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev);
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private:
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friend class TranspositionTable;
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uint16_t key16;
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uint8_t depth8;
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uint8_t genBound8;
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uint16_t move16;
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int16_t value16;
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int16_t eval16;
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};
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/// A TranspositionTable is an array of Cluster, of size clusterCount. Each
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/// cluster consists of ClusterSize number of TTEntry. Each non-empty TTEntry
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/// contains information on exactly one position. The size of a Cluster should
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/// divide the size of a cache line for best performance, as the cacheline is
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/// prefetched when possible.
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class TranspositionTable {
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static constexpr int ClusterSize = 3;
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struct Cluster {
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TTEntry entry[ClusterSize];
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char padding[2]; // Pad to 32 bytes
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};
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static_assert(sizeof(Cluster) == 32, "Unexpected Cluster size");
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// Constants used to refresh the hash table periodically
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static constexpr unsigned GENERATION_BITS = 3; // nb of bits reserved for other things
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static constexpr int GENERATION_DELTA = (1 << GENERATION_BITS); // increment for generation field
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static constexpr int GENERATION_CYCLE = 255 + (1 << GENERATION_BITS); // cycle length
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static constexpr int GENERATION_MASK = (0xFF << GENERATION_BITS) & 0xFF; // mask to pull out generation number
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public:
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~TranspositionTable() { aligned_large_pages_free(table); }
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void new_search() { generation8 += GENERATION_DELTA; } // Lower bits are used for other things
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TTEntry* probe(const Key key, bool& found) const;
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int hashfull() const;
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void resize(size_t mbSize);
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void clear();
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TTEntry* first_entry(const Key key) const {
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return &table[mul_hi64(key, clusterCount)].entry[0];
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}
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private:
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friend struct TTEntry;
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size_t clusterCount;
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Cluster* table;
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uint8_t generation8; // Size must be not bigger than TTEntry::genBound8
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};
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extern TranspositionTable TT;
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} // namespace Stockfish
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#endif // #ifndef TT_H_INCLUDED
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