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
33 /// TranspositionTable::resize() sets the size of the transposition table,
34 /// measured in megabytes. Transposition table consists of a power of 2 number
35 /// of clusters and each cluster consists of ClusterSize number of TTEntry.
37 void TranspositionTable::resize(size_t mbSize) {
39 clusterCount = mbSize * 1024 * 1024 / sizeof(Cluster);
42 mem = malloc(clusterCount * sizeof(Cluster) + CacheLineSize - 1);
46 std::cerr << "Failed to allocate " << mbSize
47 << "MB for transposition table." << std::endl;
51 table = (Cluster*)((uintptr_t(mem) + CacheLineSize - 1) & ~(CacheLineSize - 1));
56 /// TranspositionTable::clear() initializes the entire transposition table to zero,
57 // in a multi-threaded way.
59 void TranspositionTable::clear() {
61 std::vector<std::thread> threads;
63 for (size_t idx = 0; idx < Options["Threads"]; idx++)
65 threads.push_back(std::thread([this, idx]() {
67 // Thread binding gives faster search on systems with a first-touch policy
68 if (Options["Threads"] >= 8)
69 WinProcGroup::bindThisThread(idx);
71 // Each thread will zero its part of the hash table
72 const size_t stride = clusterCount / Options["Threads"],
74 len = idx != Options["Threads"] - 1 ?
75 stride : clusterCount - start;
77 std::memset(&table[start], 0, len * sizeof(Cluster));
81 for (std::thread& th: threads)
85 /// TranspositionTable::probe() looks up the current position in the transposition
86 /// table. It returns true and a pointer to the TTEntry if the position is found.
87 /// Otherwise, it returns false and a pointer to an empty or least valuable TTEntry
88 /// to be replaced later. The replace value of an entry is calculated as its depth
89 /// minus 8 times its relative age. TTEntry t1 is considered more valuable than
90 /// TTEntry t2 if its replace value is greater than that of t2.
92 TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
94 TTEntry* const tte = first_entry(key);
95 const uint16_t key16 = key >> 48; // Use the high 16 bits as key inside the cluster
97 for (int i = 0; i < ClusterSize; ++i)
98 if (!tte[i].key16 || tte[i].key16 == key16)
100 if ((tte[i].genBound8 & 0xFC) != generation8 && tte[i].key16)
101 tte[i].genBound8 = uint8_t(generation8 | tte[i].bound()); // Refresh
103 return found = (bool)tte[i].key16, &tte[i];
106 // Find an entry to be replaced according to the replacement strategy
107 TTEntry* replace = tte;
108 for (int i = 1; i < ClusterSize; ++i)
109 // Due to our packed storage format for generation and its cyclic
110 // nature we add 259 (256 is the modulus plus 3 to keep the lowest
111 // two bound bits from affecting the result) to calculate the entry
112 // age correctly even after generation8 overflows into the next cycle.
113 if ( replace->depth8 - ((259 + generation8 - replace->genBound8) & 0xFC) * 2
114 > tte[i].depth8 - ((259 + generation8 - tte[i].genBound8) & 0xFC) * 2)
117 return found = false, replace;
121 /// TranspositionTable::hashfull() returns an approximation of the hashtable
122 /// occupation during a search. The hash is x permill full, as per UCI protocol.
124 int TranspositionTable::hashfull() const {
127 for (int i = 0; i < 1000 / ClusterSize; i++)
129 const TTEntry* tte = &table[i].entry[0];
130 for (int j = 0; j < ClusterSize; j++)
131 if ((tte[j].genBound8 & 0xFC) == generation8)