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 // Populates the TTEntry with a new node's data, possibly
37 // overwriting an old position. The update is not atomic and can be racy.
38 void TTEntry::save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev) {
40 // Preserve any existing move for the same position
41 if (m || uint16_t(k) != key16)
44 // Overwrite less valuable entries (cheapest checks first)
45 if (b == BOUND_EXACT || uint16_t(k) != key16 || d - DEPTH_OFFSET + 2 * pv > depth8 - 4)
47 assert(d > DEPTH_OFFSET);
48 assert(d < 256 + DEPTH_OFFSET);
51 depth8 = uint8_t(d - DEPTH_OFFSET);
52 genBound8 = uint8_t(TT.generation8 | uint8_t(pv) << 2 | b);
59 // Sets the size of the transposition table,
60 // measured in megabytes. Transposition table consists of a power of 2 number
61 // of clusters and each cluster consists of ClusterSize number of TTEntry.
62 void TranspositionTable::resize(size_t mbSize) {
64 Threads.main()->wait_for_search_finished();
66 aligned_large_pages_free(table);
68 clusterCount = mbSize * 1024 * 1024 / sizeof(Cluster);
70 table = static_cast<Cluster*>(aligned_large_pages_alloc(clusterCount * sizeof(Cluster)));
73 std::cerr << "Failed to allocate " << mbSize << "MB for transposition table." << std::endl;
81 // Initializes the entire transposition table to zero,
82 // in a multi-threaded way.
83 void TranspositionTable::clear() {
85 std::vector<std::thread> threads;
87 for (size_t idx = 0; idx < size_t(Options["Threads"]); ++idx)
89 threads.emplace_back([this, idx]() {
90 // Thread binding gives faster search on systems with a first-touch policy
91 if (Options["Threads"] > 8)
92 WinProcGroup::bindThisThread(idx);
94 // Each thread will zero its part of the hash table
95 const size_t stride = size_t(clusterCount / Options["Threads"]),
96 start = size_t(stride * idx),
98 idx != size_t(Options["Threads"]) - 1 ? stride : clusterCount - start;
100 std::memset(&table[start], 0, len * sizeof(Cluster));
104 for (std::thread& th : threads)
109 // Looks up the current position in the transposition
110 // table. It returns true and a pointer to the TTEntry if the position is found.
111 // Otherwise, it returns false and a pointer to an empty or least valuable TTEntry
112 // to be replaced later. The replace value of an entry is calculated as its depth
113 // minus 8 times its relative age. TTEntry t1 is considered more valuable than
114 // TTEntry t2 if its replace value is greater than that of t2.
115 TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
117 TTEntry* const tte = first_entry(key);
118 const uint16_t key16 = uint16_t(key); // Use the low 16 bits as key inside the cluster
120 for (int i = 0; i < ClusterSize; ++i)
121 if (tte[i].key16 == key16 || !tte[i].depth8)
124 uint8_t(generation8 | (tte[i].genBound8 & (GENERATION_DELTA - 1))); // Refresh
126 return found = bool(tte[i].depth8), &tte[i];
129 // Find an entry to be replaced according to the replacement strategy
130 TTEntry* replace = tte;
131 for (int i = 1; i < ClusterSize; ++i)
132 // Due to our packed storage format for generation and its cyclic
133 // nature we add GENERATION_CYCLE (256 is the modulus, plus what
134 // is needed to keep the unrelated lowest n bits from affecting
135 // the result) to calculate the entry age correctly even after
136 // generation8 overflows into the next cycle.
138 - ((GENERATION_CYCLE + generation8 - replace->genBound8) & GENERATION_MASK)
140 - ((GENERATION_CYCLE + generation8 - tte[i].genBound8) & GENERATION_MASK))
143 return found = false, replace;
147 // Returns an approximation of the hashtable
148 // occupation during a search. The hash is x permill full, as per UCI protocol.
150 int TranspositionTable::hashfull() const {
153 for (int i = 0; i < 1000; ++i)
154 for (int j = 0; j < ClusterSize; ++j)
155 cnt += table[i].entry[j].depth8
156 && (table[i].entry[j].genBound8 & GENERATION_MASK) == generation8;
158 return cnt / ClusterSize;
161 } // namespace Stockfish