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 Marco Costalba
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/>.
38 TranspositionTable::TranspositionTable(unsigned mbSize) {
50 TranspositionTable::~TranspositionTable() {
56 /// TranspositionTable::set_size sets the size of the transposition table,
57 /// measured in megabytes.
59 void TranspositionTable::set_size(unsigned mbSize) {
61 assert(mbSize >= 4 && mbSize <= 1024);
63 unsigned newSize = 1024;
65 // We store a cluster of 4 TTEntry for each position and newSize is
66 // the maximum number of storable positions
67 for ( ; newSize * 4 * (sizeof(TTEntry)) <= (mbSize << 20); newSize *= 2);
73 entries = new TTEntry[size * 4];
76 std::cerr << "Failed to allocate " << mbSize
77 << " MB for transposition table."
86 /// TranspositionTable::clear overwrites the entire transposition table
87 /// with zeroes. It is called whenever the table is resized, or when the
88 /// user asks the program to clear the table (from the UCI interface).
89 /// Perhaps we should also clear it when the "ucinewgame" command is recieved?
91 void TranspositionTable::clear() {
93 memset(entries, 0, size * 4 * sizeof(TTEntry));
97 /// TranspositionTable::store writes a new entry containing a position,
98 /// a value, a value type, a search depth, and a best move to the
99 /// transposition table. The transposition table is organized in clusters
100 /// of four TTEntry objects, and when a new entry is written, it replaces
101 /// the least valuable of the four entries in a cluster. A TTEntry t1 is
102 /// considered to be more valuable than a TTEntry t2 if t1 is from the
103 /// current search and t2 is from a previous search, or if the depth of t1
104 /// is bigger than the depth of t2.
106 void TranspositionTable::store(const Position &pos, Value v, Depth d,
107 Move m, ValueType type) {
108 TTEntry *tte, *replace;
110 tte = replace = first_entry(pos);
111 for (int i = 0; i < 4; i++)
113 if (!(tte+i)->key()) // still empty
115 *(tte+i) = TTEntry(pos.get_key(), v, type, d, m, generation);
119 if ((tte+i)->key() == pos.get_key()) // overwrite old
124 *(tte+i) = TTEntry(pos.get_key(), v, type, d, m, generation);
127 if ( i == 0 // already is (replace == tte+i), common case
128 || replace->generation() < (tte+i)->generation())
131 if ( replace->generation() > (tte+i)->generation()
132 || (tte+i)->depth() < replace->depth())
135 *replace = TTEntry(pos.get_key(), v, type, d, m, generation);
140 /// TranspositionTable::retrieve looks up the current position in the
141 /// transposition table. Returns a pointer to the TTEntry or NULL
142 /// if position is not found.
144 const TTEntry* TranspositionTable::retrieve(const Position &pos) const {
146 TTEntry *tte = first_entry(pos);
148 for (int i = 0; i < 4; i++, tte++)
150 if (tte->key() == pos.get_key())
157 /// TranspositionTable::first_entry returns a pointer to the first
158 /// entry of a cluster given a position.
160 inline TTEntry* TranspositionTable::first_entry(const Position &pos) const {
162 return entries + (int(pos.get_key() & (size - 1)) << 2);
165 /// TranspositionTable::new_search() is called at the beginning of every new
166 /// search. It increments the "generation" variable, which is used to
167 /// distinguish transposition table entries from previous searches from
168 /// entries from the current search.
170 void TranspositionTable::new_search() {
177 /// TranspositionTable::insert_pv() is called at the end of a search
178 /// iteration, and inserts the PV back into the PV. This makes sure the
179 /// old PV moves are searched first, even if the old TT entries have been
182 void TranspositionTable::insert_pv(const Position &pos, Move pv[]) {
187 for (int i = 0; pv[i] != MOVE_NONE; i++)
189 store(p, VALUE_NONE, Depth(0), pv[i], VALUE_TYPE_NONE);
195 /// TranspositionTable::full() returns the permill of all transposition table
196 /// entries which have received at least one write during the current search.
197 /// It is used to display the "info hashfull ..." information in UCI.
199 int TranspositionTable::full() {
201 double N = double(size) * 4.0;
202 return int(1000 * (1 - exp(writes * log(1.0 - 1.0/N))));
211 TTEntry::TTEntry(Key k, Value v, ValueType t, Depth d, Move m,
213 key_ (k), data((m & 0x7FFFF) | (t << 20) | (generation << 23)),
214 value_(v), depth_(int16_t(d)) {}