2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2020 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/>.
19 #include <cstring> // For std::memset
29 TranspositionTable TT; // Our global transposition table
31 /// TTEntry::save() populates the TTEntry with a new node's data, possibly
32 /// overwriting an old position. Update is not atomic and can be racy.
34 void TTEntry::save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev) {
36 // Preserve any existing move for the same position
37 if (m || (uint16_t)k != key16)
40 // Overwrite less valuable entries
41 if ((uint16_t)k != key16
42 || d - DEPTH_OFFSET > depth8 - 4
45 assert(d >= DEPTH_OFFSET);
50 genBound8 = (uint8_t)(TT.generation8 | uint8_t(pv) << 2 | b);
51 depth8 = (uint8_t)(d - DEPTH_OFFSET);
56 /// TranspositionTable::resize() sets the size of the transposition table,
57 /// measured in megabytes. Transposition table consists of a power of 2 number
58 /// of clusters and each cluster consists of ClusterSize number of TTEntry.
60 void TranspositionTable::resize(size_t mbSize) {
62 Threads.main()->wait_for_search_finished();
64 aligned_ttmem_free(mem);
66 clusterCount = mbSize * 1024 * 1024 / sizeof(Cluster);
67 table = static_cast<Cluster*>(aligned_ttmem_alloc(clusterCount * sizeof(Cluster), mem));
70 std::cerr << "Failed to allocate " << mbSize
71 << "MB for transposition table." << std::endl;
79 /// TranspositionTable::clear() initializes the entire transposition table to zero,
80 // in a multi-threaded way.
82 void TranspositionTable::clear() {
84 std::vector<std::thread> threads;
86 for (size_t idx = 0; idx < Options["Threads"]; ++idx)
88 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),
97 len = idx != Options["Threads"] - 1 ?
98 stride : clusterCount - start;
100 std::memset(&table[start], 0, len * sizeof(Cluster));
104 for (std::thread& th : threads)
109 /// TranspositionTable::probe() 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.
116 TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
118 TTEntry* const tte = first_entry(key);
119 const uint16_t key16 = (uint16_t)key; // Use the low 16 bits as key inside the cluster
121 for (int i = 0; i < ClusterSize; ++i)
122 if (!tte[i].key16 || tte[i].key16 == key16)
124 tte[i].genBound8 = uint8_t(generation8 | (tte[i].genBound8 & 0x7)); // Refresh
126 return found = (bool)tte[i].key16, &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 263 (256 is the modulus plus 7 to keep the unrelated
134 // lowest three bits from affecting the result) to calculate the entry
135 // age correctly even after generation8 overflows into the next cycle.
136 if ( replace->depth8 - ((263 + generation8 - replace->genBound8) & 0xF8)
137 > tte[i].depth8 - ((263 + generation8 - tte[i].genBound8) & 0xF8))
140 return found = false, replace;
144 /// TranspositionTable::hashfull() returns an approximation of the hashtable
145 /// occupation during a search. The hash is x permill full, as per UCI protocol.
147 int TranspositionTable::hashfull() const {
150 for (int i = 0; i < 1000; ++i)
151 for (int j = 0; j < ClusterSize; ++j)
152 cnt += (table[i].entry[j].genBound8 & 0xF8) == generation8;
154 return cnt / ClusterSize;