mirror of
https://github.com/opelly27/Stockfish.git
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mattginsberg
573f0e364f
This patch removes some magic numbers in TT bit management and introduce proper constants in the code, to improve documentation and ease further modifications. No function change
104 lines
3.3 KiB
C++
104 lines
3.3 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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/// 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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#endif // #ifndef TT_H_INCLUDED
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