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f7b3f0e842
Fix the issue where a TT entry with key16==0 would always be reported
as a miss. Instead, we'll use depth8 to detect whether the TT entry is
occupied. In order to do that, we'll change DEPTH_OFFSET to -7
(depth8==0) to distinguish between an unoccupied entry and the
otherwise lowest possible depth, i.e., DEPTH_NONE (depth8==1).
To prevent a performance regression, we'll reorder the TT entry fields
by the access order of TranspositionTable::probe(). Memory in general
works fastest when accessed in sequential order. We'll also match the
store order in TTEntry::save() with the entry field order, and
re-order the 'if-or' expressions in TTEntry::save() from the cheapest
to the most expensive.
Finally, as we now have a proper TT entry occupancy test, we'll fix a
minor corner case with hashfull reporting. To reproduce:
- Use a big hash
- Either:
a. Start 31 very quick searches (this wraparounds generation to 0); or
b. Force generation of the first search to 0.
- go depth infinite
Before the fix, hashfull would incorrectly report nearly full hash
immediately after the search start, since
TranspositionTable::hashfull() used to consider only the entry
generation and not whether the entry was actually occupied.
STC:
LLR: 2.95 (-2.94,2.94) {-0.25,1.25}
Total: 36848 W: 4091 L: 3898 D: 28859
Ptnml(0-2): 158, 2996, 11972, 3091, 207
https://tests.stockfishchess.org/tests/view/5f3f98d5dc02a01a0c2881f7
LTC:
LLR: 2.95 (-2.94,2.94) {0.25,1.25}
Total: 32280 W: 1828 L: 1653 D: 28799
Ptnml(0-2): 34, 1428, 13051, 1583, 44
https://tests.stockfishchess.org/tests/view/5f3fe77a87a5c3c63d8f5332
closes https://github.com/official-stockfish/Stockfish/pull/3048
Bench: 3760677
99 lines
2.8 KiB
C++
99 lines
2.8 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2020 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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public:
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~TranspositionTable() { aligned_ttmem_free(mem); }
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void new_search() { generation8 += 8; } // Lower 3 bits are used by PV flag and Bound
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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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void* mem;
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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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