2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2023 The Stockfish developers (see AUTHORS file)
5 Stockfish is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 Stockfish is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
34 TranspositionTable TT; // Our global transposition table
36 /// TTEntry::save() populates the TTEntry with a new node's data, possibly
37 /// overwriting an old position. Update is not atomic and can be racy.
39 void TTEntry::save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev) {
41 // Preserve any existing move for the same position
42 if (m || uint16_t(k) != key16)
45 // Overwrite less valuable entries (cheapest checks first)
47 || uint16_t(k) != key16
48 || d - DEPTH_OFFSET + 2 * pv > depth8 - 4)
50 assert(d > DEPTH_OFFSET);
51 assert(d < 256 + DEPTH_OFFSET);
54 depth8 = uint8_t(d - DEPTH_OFFSET);
55 genBound8 = uint8_t(TT.generation8 | uint8_t(pv) << 2 | b);
62 /// TranspositionTable::resize() sets the size of the transposition table,
63 /// measured in megabytes. Transposition table consists of a power of 2 number
64 /// of clusters and each cluster consists of ClusterSize number of TTEntry.
66 void TranspositionTable::resize(size_t mbSize) {
68 Threads.main()->wait_for_search_finished();
70 aligned_large_pages_free(table);
72 clusterCount = mbSize * 1024 * 1024 / sizeof(Cluster);
74 table = static_cast<Cluster*>(aligned_large_pages_alloc(clusterCount * sizeof(Cluster)));
77 std::cerr << "Failed to allocate " << mbSize
78 << "MB for transposition table." << std::endl;
86 /// TranspositionTable::clear() initializes the entire transposition table to zero,
87 // in a multi-threaded way.
89 void TranspositionTable::clear() {
91 std::vector<std::thread> threads;
93 for (size_t idx = 0; idx < size_t(Options["Threads"]); ++idx)
95 threads.emplace_back([this, idx]() {
97 // Thread binding gives faster search on systems with a first-touch policy
98 if (Options["Threads"] > 8)
99 WinProcGroup::bindThisThread(idx);
101 // Each thread will zero its part of the hash table
102 const size_t stride = size_t(clusterCount / Options["Threads"]),
103 start = size_t(stride * idx),
104 len = idx != size_t(Options["Threads"]) - 1 ?
105 stride : clusterCount - start;
107 std::memset(&table[start], 0, len * sizeof(Cluster));
111 for (std::thread& th : threads)
116 /// TranspositionTable::probe() looks up the current position in the transposition
117 /// table. It returns true and a pointer to the TTEntry if the position is found.
118 /// Otherwise, it returns false and a pointer to an empty or least valuable TTEntry
119 /// to be replaced later. The replace value of an entry is calculated as its depth
120 /// minus 8 times its relative age. TTEntry t1 is considered more valuable than
121 /// TTEntry t2 if its replace value is greater than that of t2.
123 TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
125 TTEntry* const tte = first_entry(key);
126 const uint16_t key16 = uint16_t(key); // Use the low 16 bits as key inside the cluster
128 for (int i = 0; i < ClusterSize; ++i)
129 if (tte[i].key16 == key16 || !tte[i].depth8)
131 tte[i].genBound8 = uint8_t(generation8 | (tte[i].genBound8 & (GENERATION_DELTA - 1))); // Refresh
133 return found = bool(tte[i].depth8), &tte[i];
136 // Find an entry to be replaced according to the replacement strategy
137 TTEntry* replace = tte;
138 for (int i = 1; i < ClusterSize; ++i)
139 // Due to our packed storage format for generation and its cyclic
140 // nature we add GENERATION_CYCLE (256 is the modulus, plus what
141 // is needed to keep the unrelated lowest n bits from affecting
142 // the result) to calculate the entry age correctly even after
143 // generation8 overflows into the next cycle.
144 if ( replace->depth8 - ((GENERATION_CYCLE + generation8 - replace->genBound8) & GENERATION_MASK)
145 > tte[i].depth8 - ((GENERATION_CYCLE + generation8 - tte[i].genBound8) & GENERATION_MASK))
148 return found = false, replace;
152 /// TranspositionTable::hashfull() returns an approximation of the hashtable
153 /// occupation during a search. The hash is x permill full, as per UCI protocol.
155 int TranspositionTable::hashfull() const {
158 for (int i = 0; i < 1000; ++i)
159 for (int j = 0; j < ClusterSize; ++j)
160 cnt += table[i].entry[j].depth8 && (table[i].entry[j].genBound8 & GENERATION_MASK) == generation8;
162 return cnt / ClusterSize;
165 } // namespace Stockfish