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) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
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.
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.
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/>.
21 #include <cstring> // For std::memset
30 TranspositionTable TT; // Our global transposition table
32 /// TTEntry::save saves a TTEntry
33 void TTEntry::save(Key k, Value v, Bound b, Depth d, Move m, Value ev) {
35 assert(d / ONE_PLY * ONE_PLY == d);
37 // Preserve any existing move for the same position
38 if (m || (k >> 48) != key16)
41 // Overwrite less valuable entries
42 if ( (k >> 48) != key16
43 || d / ONE_PLY > depth8 - 4
46 key16 = (uint16_t)(k >> 48);
49 genBound8 = (uint8_t)(TT.generation8 | b);
50 depth8 = (int8_t)(d / ONE_PLY);
55 /// TranspositionTable::resize() sets the size of the transposition table,
56 /// measured in megabytes. Transposition table consists of a power of 2 number
57 /// of clusters and each cluster consists of ClusterSize number of TTEntry.
59 void TranspositionTable::resize(size_t mbSize) {
61 clusterCount = mbSize * 1024 * 1024 / sizeof(Cluster);
64 mem = malloc(clusterCount * sizeof(Cluster) + CacheLineSize - 1);
68 std::cerr << "Failed to allocate " << mbSize
69 << "MB for transposition table." << std::endl;
73 table = (Cluster*)((uintptr_t(mem) + CacheLineSize - 1) & ~(CacheLineSize - 1));
78 /// TranspositionTable::clear() initializes the entire transposition table to zero,
79 // in a multi-threaded way.
81 void TranspositionTable::clear() {
83 std::vector<std::thread> threads;
85 for (size_t idx = 0; idx < Options["Threads"]; idx++)
87 threads.push_back(std::thread([this, idx]() {
89 // Thread binding gives faster search on systems with a first-touch policy
90 if (Options["Threads"] > 8)
91 WinProcGroup::bindThisThread(idx);
93 // Each thread will zero its part of the hash table
94 const size_t stride = clusterCount / Options["Threads"],
96 len = idx != Options["Threads"] - 1 ?
97 stride : clusterCount - start;
99 std::memset(&table[start], 0, len * sizeof(Cluster));
103 for (std::thread& th: threads)
107 /// TranspositionTable::probe() looks up the current position in the transposition
108 /// table. It returns true and a pointer to the TTEntry if the position is found.
109 /// Otherwise, it returns false and a pointer to an empty or least valuable TTEntry
110 /// to be replaced later. The replace value of an entry is calculated as its depth
111 /// minus 8 times its relative age. TTEntry t1 is considered more valuable than
112 /// TTEntry t2 if its replace value is greater than that of t2.
114 TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
116 TTEntry* const tte = first_entry(key);
117 const uint16_t key16 = key >> 48; // Use the high 16 bits as key inside the cluster
119 for (int i = 0; i < ClusterSize; ++i)
120 if (!tte[i].key16 || tte[i].key16 == key16)
122 tte[i].genBound8 = uint8_t(generation8 | tte[i].bound()); // Refresh
124 return found = (bool)tte[i].key16, &tte[i];
127 // Find an entry to be replaced according to the replacement strategy
128 TTEntry* replace = tte;
129 for (int i = 1; i < ClusterSize; ++i)
130 // Due to our packed storage format for generation and its cyclic
131 // nature we add 259 (256 is the modulus plus 3 to keep the lowest
132 // two bound bits from affecting the result) to calculate the entry
133 // age correctly even after generation8 overflows into the next cycle.
134 if ( replace->depth8 - ((259 + generation8 - replace->genBound8) & 0xFC) * 2
135 > tte[i].depth8 - ((259 + generation8 - tte[i].genBound8) & 0xFC) * 2)
138 return found = false, replace;
142 /// TranspositionTable::hashfull() returns an approximation of the hashtable
143 /// occupation during a search. The hash is x permill full, as per UCI protocol.
145 int TranspositionTable::hashfull() const {
148 for (int i = 0; i < 1000 / ClusterSize; i++)
150 const TTEntry* tte = &table[i].entry[0];
151 for (int j = 0; j < ClusterSize; j++)
152 if ((tte[j].genBound8 & 0xFC) == generation8)