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
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
20 #include <cstring> // For std::memset
26 TranspositionTable TT; // Our global transposition table
29 /// TranspositionTable::resize() sets the size of the transposition table,
30 /// measured in megabytes. Transposition table consists of a power of 2 number
31 /// of clusters and each cluster consists of ClusterSize number of TTEntry.
33 void TranspositionTable::resize(size_t mbSize) {
35 size_t newClusterCount = size_t(1) << msb((mbSize * 1024 * 1024) / sizeof(Cluster));
37 if (newClusterCount == clusterCount)
40 clusterCount = newClusterCount;
43 mem = calloc(clusterCount * sizeof(Cluster) + CacheLineSize - 1, 1);
47 std::cerr << "Failed to allocate " << mbSize
48 << "MB for transposition table." << std::endl;
52 table = (Cluster*)((uintptr_t(mem) + CacheLineSize - 1) & ~(CacheLineSize - 1));
56 /// TranspositionTable::clear() overwrites the entire transposition table
57 /// with zeros. It is called whenever the table is resized, or when the
58 /// user asks the program to clear the table (from the UCI interface).
60 void TranspositionTable::clear() {
62 std::memset(table, 0, clusterCount * sizeof(Cluster));
66 /// TranspositionTable::probe() looks up the current position in the transposition
67 /// table. It returns true and a pointer to the TTEntry if the position is found.
68 /// Otherwise, it returns false and a pointer to an empty or least valuable TTEntry
69 /// to be replaced later. The replace value of an entry is calculated as its depth
70 /// minus 8 times its relative age. TTEntry t1 is considered more valuable than
71 /// TTEntry t2 if its replace value is greater than that of t2.
73 TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
75 TTEntry* const tte = first_entry(key);
76 const uint16_t key16 = key >> 48; // Use the high 16 bits as key inside the cluster
78 for (int i = 0; i < ClusterSize; ++i)
79 if (!tte[i].key16 || tte[i].key16 == key16)
82 tte[i].genBound8 = uint8_t(generation8 | tte[i].bound()); // Refresh
84 return found = (bool)tte[i].key16, &tte[i];
87 // Find an entry to be replaced according to the replacement strategy
88 TTEntry* replace = tte;
89 for (int i = 1; i < ClusterSize; ++i)
90 // Due to our packed storage format for generation and its cyclic
91 // nature we add 259 (256 is the modulus plus 3 to keep the lowest
92 // two bound bits from affecting the result) to calculate the entry
93 // age correctly even after generation8 overflows into the next cycle.
94 if ( replace->depth8 - ((259 + generation8 - replace->genBound8) & 0xFC) * 2 * ONE_PLY
95 > tte[i].depth8 - ((259 + generation8 - tte[i].genBound8) & 0xFC) * 2 * ONE_PLY)
98 return found = false, replace;
102 /// Returns an approximation of the hashtable occupation during a search. The
103 /// hash is x permill full, as per UCI protocol.
105 int TranspositionTable::hashfull() const
108 for (int i = 0; i < 1000 / ClusterSize; i++)
110 const TTEntry* tte = &table[i].entry[0];
111 for (int j = 0; j < ClusterSize; j++)
112 if ((tte[j].genBound8 & 0xFC) == generation8)