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) 2015-2016 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
27 TranspositionTable TT; // Our global transposition table
30 /// TranspositionTable::resize() sets the size of the transposition table,
31 /// measured in megabytes. Transposition table consists of a power of 2 number
32 /// of clusters and each cluster consists of ClusterSize number of TTEntry.
34 void TranspositionTable::resize(size_t mbSize) {
36 size_t newClusterCount = size_t(1) << msb((mbSize * 1024 * 1024) / sizeof(Cluster));
38 if (newClusterCount == clusterCount)
41 clusterCount = newClusterCount;
44 mem = calloc(clusterCount * sizeof(Cluster) + CacheLineSize - 1, 1);
48 std::cerr << "Failed to allocate " << mbSize
49 << "MB for transposition table." << std::endl;
53 table = (Cluster*)((uintptr_t(mem) + CacheLineSize - 1) & ~(CacheLineSize - 1));
57 /// TranspositionTable::clear() overwrites the entire transposition table
58 /// with zeros. It is called whenever the table is resized, or when the
59 /// user asks the program to clear the table (from the UCI interface).
61 void TranspositionTable::clear() {
63 std::memset(table, 0, clusterCount * sizeof(Cluster));
67 /// TranspositionTable::probe() looks up the current position in the transposition
68 /// table. It returns true and a pointer to the TTEntry if the position is found.
69 /// Otherwise, it returns false and a pointer to an empty or least valuable TTEntry
70 /// to be replaced later. The replace value of an entry is calculated as its depth
71 /// minus 8 times its relative age. TTEntry t1 is considered more valuable than
72 /// TTEntry t2 if its replace value is greater than that of t2.
74 TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
76 TTEntry* const tte = first_entry(key);
77 const uint16_t key16 = key >> 48; // Use the high 16 bits as key inside the cluster
79 for (int i = 0; i < ClusterSize; ++i)
80 if (!tte[i].key16 || tte[i].key16 == key16)
82 if ((tte[i].genBound8 & 0xFC) != generation8 && tte[i].key16)
83 tte[i].genBound8 = uint8_t(generation8 | tte[i].bound()); // Refresh
85 return found = (bool)tte[i].key16, &tte[i];
88 // Find an entry to be replaced according to the replacement strategy
89 TTEntry* replace = tte;
90 for (int i = 1; i < ClusterSize; ++i)
91 // Due to our packed storage format for generation and its cyclic
92 // nature we add 259 (256 is the modulus plus 3 to keep the lowest
93 // two bound bits from affecting the result) to calculate the entry
94 // age correctly even after generation8 overflows into the next cycle.
95 if ( replace->depth8 - ((259 + generation8 - replace->genBound8) & 0xFC) * 2
96 > tte[i].depth8 - ((259 + generation8 - tte[i].genBound8) & 0xFC) * 2)
99 return found = false, replace;
103 /// TranspositionTable::hashfull() returns an approximation of the hashtable
104 /// occupation during a search. The hash is x permill full, as per UCI protocol.
106 int TranspositionTable::hashfull() const {
109 for (int i = 0; i < 1000 / ClusterSize; i++)
111 const TTEntry* tte = &table[i].entry[0];
112 for (int j = 0; j < ClusterSize; j++)
113 if ((tte[j].genBound8 & 0xFC) == generation8)