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/>.
32 // The main transposition table
33 TranspositionTable TT;
39 TranspositionTable::TranspositionTable() {
41 size = overwrites = 0;
46 TranspositionTable::~TranspositionTable() {
52 /// TranspositionTable::set_size sets the size of the transposition table,
53 /// measured in megabytes.
55 void TranspositionTable::set_size(size_t mbSize) {
57 size_t newSize = 1024;
59 // We store a cluster of ClusterSize number of TTEntry for each position
60 // and newSize is the maximum number of storable positions.
61 while ((2 * newSize) * sizeof(TTCluster) <= (mbSize << 20))
68 entries = new TTCluster[size];
71 std::cerr << "Failed to allocate " << mbSize
72 << " MB for transposition table." << std::endl;
73 Application::exit_with_failure();
79 /// TranspositionTable::clear overwrites the entire transposition table
80 /// with zeroes. It is called whenever the table is resized, or when the
81 /// user asks the program to clear the table (from the UCI interface).
82 /// Perhaps we should also clear it when the "ucinewgame" command is recieved?
84 void TranspositionTable::clear() {
86 memset(entries, 0, size * sizeof(TTCluster));
90 /// TranspositionTable::store writes a new entry containing a position,
91 /// a value, a value type, a search depth, and a best move to the
92 /// transposition table. Transposition table is organized in clusters of
93 /// four TTEntry objects, and when a new entry is written, it replaces
94 /// the least valuable of the four entries in a cluster. A TTEntry t1 is
95 /// considered to be more valuable than a TTEntry t2 if t1 is from the
96 /// current search and t2 is from a previous search, or if the depth of t1
97 /// is bigger than the depth of t2. A TTEntry of type VALUE_TYPE_EVAL
98 /// never replaces another entry for the same position.
100 void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d, Move m, Value statV, Value kingD) {
103 TTEntry *tte, *replace;
104 uint32_t posKey32 = posKey >> 32; // Use the high 32 bits as key
106 tte = replace = first_entry(posKey);
107 for (int i = 0; i < ClusterSize; i++, tte++)
109 if (!tte->key() || tte->key() == posKey32) // empty or overwrite old
111 // Preserve any exsisting ttMove
115 tte->save(posKey32, v, t, d, m, generation, statV, kingD);
119 if (i == 0) // replace would be a no-op in this common case
122 c1 = (replace->generation() == generation ? 2 : 0);
123 c2 = (tte->generation() == generation ? -2 : 0);
124 c3 = (tte->depth() < replace->depth() ? 1 : 0);
126 if (c1 + c2 + c3 > 0)
129 replace->save(posKey32, v, t, d, m, generation, statV, kingD);
134 /// TranspositionTable::retrieve looks up the current position in the
135 /// transposition table. Returns a pointer to the TTEntry or NULL
136 /// if position is not found.
138 TTEntry* TranspositionTable::retrieve(const Key posKey) const {
140 uint32_t posKey32 = posKey >> 32;
141 TTEntry* tte = first_entry(posKey);
143 for (int i = 0; i < ClusterSize; i++, tte++)
144 if (tte->key() == posKey32)
151 /// TranspositionTable::new_search() is called at the beginning of every new
152 /// search. It increments the "generation" variable, which is used to
153 /// distinguish transposition table entries from previous searches from
154 /// entries from the current search.
156 void TranspositionTable::new_search() {
163 /// TranspositionTable::insert_pv() is called at the end of a search
164 /// iteration, and inserts the PV back into the PV. This makes sure
165 /// the old PV moves are searched first, even if the old TT entries
166 /// have been overwritten.
168 void TranspositionTable::insert_pv(const Position& pos, Move pv[]) {
171 Position p(pos, pos.thread());
173 for (int i = 0; pv[i] != MOVE_NONE; i++)
175 TTEntry *tte = retrieve(p.get_key());
176 if (!tte || tte->move() != pv[i])
177 store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, Depth(-127*OnePly), pv[i], VALUE_NONE, VALUE_NONE);
178 p.do_move(pv[i], st);
183 /// TranspositionTable::extract_pv() extends a PV by adding moves from the
184 /// transposition table at the end. This should ensure that the PV is almost
185 /// always at least two plies long, which is important, because otherwise we
186 /// will often get single-move PVs when the search stops while failing high,
187 /// and a single-move PV means that we don't have a ponder move.
189 void TranspositionTable::extract_pv(const Position& pos, Move bestMove, Move pv[], const int PLY_MAX) {
193 Position p(pos, pos.thread());
196 assert(bestMove != MOVE_NONE);
199 p.do_move(pv[ply++], st);
201 // Extract moves from TT when possible. We try hard to always
202 // get a ponder move, that's the reason of ply < 2 conditions.
203 while ( (tte = retrieve(p.get_key())) != NULL
204 && tte->move() != MOVE_NONE
205 && (tte->type() == VALUE_TYPE_EXACT || ply < 2)
206 && move_is_legal(p, tte->move())
207 && (!p.is_draw() || ply < 2)
210 pv[ply] = tte->move();
211 p.do_move(pv[ply++], st);
217 /// TranspositionTable::full() returns the permill of all transposition table
218 /// entries which have received at least one overwrite during the current search.
219 /// It is used to display the "info hashfull ..." information in UCI.
221 int TranspositionTable::full() const {
223 double N = double(size) * ClusterSize;
224 return int(1000 * (1 - exp(overwrites * log(1.0 - 1.0/N))));