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/>.
31 // The main transposition table
32 TranspositionTable TT;
38 TranspositionTable::TranspositionTable() {
45 TranspositionTable::~TranspositionTable() {
51 /// TranspositionTable::set_size sets the size of the transposition table,
52 /// measured in megabytes.
54 void TranspositionTable::set_size(size_t mbSize) {
56 size_t newSize = 1024;
58 // Transposition table consists of clusters and each cluster consists
59 // of ClusterSize number of TTEntries. Each non-empty entry contains
60 // information of exactly one position and newSize is the number of
61 // clusters we are going to allocate.
62 while (2ULL * newSize * sizeof(TTCluster) <= (mbSize << 20))
69 entries = new (std::nothrow) TTCluster[size];
72 std::cerr << "Failed to allocate " << mbSize
73 << " MB for transposition table." << std::endl;
81 /// TranspositionTable::clear overwrites the entire transposition table
82 /// with zeroes. It is called whenever the table is resized, or when the
83 /// user asks the program to clear the table (from the UCI interface).
84 /// Perhaps we should also clear it when the "ucinewgame" command is received?
86 void TranspositionTable::clear() {
88 memset(entries, 0, size * sizeof(TTCluster));
92 /// TranspositionTable::store writes a new entry containing position key and
93 /// valuable information of current position.
94 /// The Lowest order bits of position key are used to decide on which cluster
95 /// the position will be placed.
96 /// When a new entry is written and there are no empty entries available in cluster,
97 /// it replaces the least valuable of entries.
98 /// A TTEntry t1 is considered to be more valuable than a TTEntry t2 if t1 is from the
99 /// current search and t2 is from a previous search, or if the depth of t1
100 /// is bigger than the depth of t2.
102 void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d, Move m, Value statV, Value kingD) {
105 TTEntry *tte, *replace;
106 uint32_t posKey32 = posKey >> 32; // Use the high 32 bits as key
108 tte = replace = first_entry(posKey);
109 for (int i = 0; i < ClusterSize; i++, tte++)
111 if (!tte->key() || tte->key() == posKey32) // empty or overwrite old
113 // Preserve any existing ttMove
117 tte->save(posKey32, v, t, d, m, generation, statV, kingD);
121 if (i == 0) // Replacing first entry is default and already set before entering for-loop
124 c1 = (replace->generation() == generation ? 2 : 0);
125 c2 = (tte->generation() == generation ? -2 : 0);
126 c3 = (tte->depth() < replace->depth() ? 1 : 0);
128 if (c1 + c2 + c3 > 0)
131 replace->save(posKey32, v, t, d, m, generation, statV, kingD);
135 /// TranspositionTable::retrieve looks up the current position in the
136 /// transposition table. Returns a pointer to the TTEntry or NULL
137 /// if position is not found.
139 TTEntry* TranspositionTable::retrieve(const Key posKey) const {
141 uint32_t posKey32 = posKey >> 32;
142 TTEntry* tte = first_entry(posKey);
144 for (int i = 0; i < ClusterSize; i++, tte++)
145 if (tte->key() == posKey32)
152 /// TranspositionTable::new_search() is called at the beginning of every new
153 /// search. It increments the "generation" variable, which is used to
154 /// distinguish transposition table entries from previous searches from
155 /// entries from the current search.
157 void TranspositionTable::new_search() {