2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
26 TranspositionTable TT; // Our global transposition table
28 TranspositionTable::TranspositionTable() {
30 size = generation = 0;
34 TranspositionTable::~TranspositionTable() {
40 /// TranspositionTable::set_size() sets the size of the transposition table,
41 /// measured in megabytes.
43 void TranspositionTable::set_size(size_t mbSize) {
45 size_t newSize = 1024;
47 // Transposition table consists of clusters and each cluster consists
48 // of ClusterSize number of TTEntries. Each non-empty entry contains
49 // information of exactly one position and newSize is the number of
50 // clusters we are going to allocate.
51 while (2ULL * newSize * sizeof(TTCluster) <= (mbSize << 20))
59 entries = new (std::nothrow) TTCluster[size];
62 std::cerr << "Failed to allocate " << mbSize
63 << " MB for transposition table." << std::endl;
70 /// TranspositionTable::clear() overwrites the entire transposition table
71 /// with zeroes. It is called whenever the table is resized, or when the
72 /// user asks the program to clear the table (from the UCI interface).
74 void TranspositionTable::clear() {
76 memset(entries, 0, size * sizeof(TTCluster));
80 /// TranspositionTable::store() writes a new entry containing position key and
81 /// valuable information of current position. The lowest order bits of position
82 /// key are used to decide on which cluster the position will be placed.
83 /// When a new entry is written and there are no empty entries available in cluster,
84 /// it replaces the least valuable of entries. A TTEntry t1 is considered to be
85 /// more valuable than a TTEntry t2 if t1 is from the current search and t2 is from
86 /// a previous search, or if the depth of t1 is bigger than the depth of t2.
88 void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d, Move m, Value statV, Value kingD) {
91 TTEntry *tte, *replace;
92 uint32_t posKey32 = posKey >> 32; // Use the high 32 bits as key inside the cluster
94 tte = replace = first_entry(posKey);
96 for (int i = 0; i < ClusterSize; i++, tte++)
98 if (!tte->key() || tte->key() == posKey32) // Empty or overwrite old
100 // Preserve any existing ttMove
104 tte->save(posKey32, v, t, d, m, generation, statV, kingD);
108 // Implement replace strategy
109 c1 = (replace->generation() == generation ? 2 : 0);
110 c2 = (tte->generation() == generation || tte->type() == VALUE_TYPE_EXACT ? -2 : 0);
111 c3 = (tte->depth() < replace->depth() ? 1 : 0);
113 if (c1 + c2 + c3 > 0)
116 replace->save(posKey32, v, t, d, m, generation, statV, kingD);
120 /// TranspositionTable::probe() looks up the current position in the
121 /// transposition table. Returns a pointer to the TTEntry or NULL if
122 /// position is not found.
124 TTEntry* TranspositionTable::probe(const Key posKey) const {
126 uint32_t posKey32 = posKey >> 32;
127 TTEntry* tte = first_entry(posKey);
129 for (int i = 0; i < ClusterSize; i++, tte++)
130 if (tte->key() == posKey32)
137 /// TranspositionTable::new_search() is called at the beginning of every new
138 /// search. It increments the "generation" variable, which is used to
139 /// distinguish transposition table entries from previous searches from
140 /// entries from the current search.
142 void TranspositionTable::new_search() {