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mstembera
3104cd72d5
https://tests.stockfishchess.org/tests/view/6757757686d5ee47d9541de9 LLR: 2.93 (-2.94,2.94) <-1.75,0.25> Total: 151200 W: 39396 L: 39306 D: 72498 Ptnml(0-2): 445, 16404, 41781, 16556, 414 Discussed in more detail here #5766 closes https://github.com/official-stockfish/Stockfish/pull/5773 No functional change
108 lines
3.6 KiB
C++
108 lines
3.6 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2025 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 <cstddef>
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#include <cstdint>
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#include <tuple>
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#include "memory.h"
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#include "types.h"
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namespace Stockfish {
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class ThreadPool;
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struct TTEntry;
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struct Cluster;
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// There is only one global hash table for the engine and all its threads. For chess in particular, we even allow racy
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// updates between threads to and from the TT, as taking the time to synchronize access would cost thinking time and
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// thus elo. As a hash table, collisions are possible and may cause chess playing issues (bizarre blunders, faulty mate
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// reports, etc). Fixing these also loses elo; however such risk decreases quickly with larger TT size.
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//
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// `probe` is the primary method: given a board position, we lookup its entry in the table, and return a tuple of:
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// 1) whether the entry already has this position
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// 2) a copy of the prior data (if any) (may be inconsistent due to read races)
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// 3) a writer object to this entry
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// The copied data and the writer are separated to maintain clear boundaries between local vs global objects.
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// A copy of the data already in the entry (possibly collided). `probe` may be racy, resulting in inconsistent data.
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struct TTData {
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Move move;
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Value value, eval;
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Depth depth;
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Bound bound;
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bool is_pv;
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TTData() = delete;
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TTData(Move m, Value v, Value ev, Depth d, Bound b, bool pv) :
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move(m),
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value(v),
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eval(ev),
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depth(d),
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bound(b),
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is_pv(pv) {};
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};
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// This is used to make racy writes to the global TT.
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struct TTWriter {
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public:
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void write(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev, uint8_t generation8);
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private:
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friend class TranspositionTable;
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TTEntry* entry;
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TTWriter(TTEntry* tte);
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};
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class TranspositionTable {
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public:
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~TranspositionTable() { aligned_large_pages_free(table); }
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void resize(size_t mbSize, ThreadPool& threads); // Set TT size
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void clear(ThreadPool& threads); // Re-initialize memory, multithreaded
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int hashfull(int maxAge = 0)
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const; // Approximate what fraction of entries (permille) have been written to during this root search
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void
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new_search(); // This must be called at the beginning of each root search to track entry aging
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uint8_t generation() const; // The current age, used when writing new data to the TT
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std::tuple<bool, TTData, TTWriter>
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probe(const Key key) const; // The main method, whose retvals separate local vs global objects
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TTEntry* first_entry(const Key key)
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const; // This is the hash function; its only external use is memory prefetching.
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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 = nullptr;
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uint8_t generation8 = 0; // Size must be not bigger than TTEntry::genBound8
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};
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} // namespace Stockfish
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#endif // #ifndef TT_H_INCLUDED
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