1/*
2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
6
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
11
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
19*/
20
21#ifndef TT_H_INCLUDED
22#define TT_H_INCLUDED
23
24#include "misc.h"
25#include "types.h"
26
27/// TTEntry struct is the 10 bytes transposition table entry, defined as below:
28///
29/// key 16 bit
30/// move 16 bit
31/// value 16 bit
32/// eval value 16 bit
33/// generation 5 bit
34/// pv node 1 bit
35/// bound type 2 bit
36/// depth 8 bit
37
38struct TTEntry {
39
40 Move move() const { return (Move )move16; }
41 Value value() const { return (Value)value16; }
42 Value eval() const { return (Value)eval16; }
43 Depth depth() const { return (Depth)(depth8 * int(ONE_PLY)) + DEPTH_OFFSET; }
44 bool is_pv() const { return (bool)(genBound8 & 0x4); }
45 Bound bound() const { return (Bound)(genBound8 & 0x3); }
46 void save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev);
47
48private:
49 friend class TranspositionTable;
50
51 uint16_t key16;
52 uint16_t move16;
53 int16_t value16;
54 int16_t eval16;
55 uint8_t genBound8;
56 uint8_t depth8;
57};
58
59
60/// A TranspositionTable consists of a power of 2 number of clusters and each
61/// cluster consists of ClusterSize number of TTEntry. Each non-empty entry
62/// contains information of exactly one position. The size of a cluster should
63/// divide the size of a cache line size, to ensure that clusters never cross
64/// cache lines. This ensures best cache performance, as the cacheline is
65/// prefetched, as soon as possible.
66
67class TranspositionTable {
68
69 static constexpr int CacheLineSize = 64;
70 static constexpr int ClusterSize = 3;
71
72 struct Cluster {
73 TTEntry entry[ClusterSize];
74 char padding[2]; // Align to a divisor of the cache line size
75 };
76
77 static_assert(CacheLineSize % sizeof(Cluster) == 0, "Cluster size incorrect");
78
79public:
80 ~TranspositionTable() { free(mem); }
81 void new_search() { generation8 += 8; } // Lower 3 bits are used by PV flag and Bound
82 TTEntry* probe(const Key key, bool& found) const;
83 int hashfull() const;
84 void resize(size_t mbSize);
85 void clear();
86
87 // The 32 lowest order bits of the key are used to get the index of the cluster
88 TTEntry* first_entry(const Key key) const {
89 return &table[(uint32_t(key) * uint64_t(clusterCount)) >> 32].entry[0];
90 }
91
92private:
93 friend struct TTEntry;
94
95 size_t clusterCount;
96 Cluster* table;
97 void* mem;
98 uint8_t generation8; // Size must be not bigger than TTEntry::genBound8
99};
100
101extern TranspositionTable TT;
102
103#endif // #ifndef TT_H_INCLUDED
104