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++, tte++)
113 if (!tte->key() || tte->key() == pos.get_key()) // empty or overwrite old
118 *tte = TTEntry(pos.get_key(), v, type, d, m, generation);
121 else if (i == 0) // replace would be a no-op in this common case
124 int c1 = (replace->generation() == generation ? 2 : 0);
125 int c2 = (tte->generation() == generation ? -2 : 0);
126 int c3 = (tte->depth() < replace->depth() ? 1 : 0);
128 if (c1 + c2 + c3 > 0)
131 *replace = TTEntry(pos.get_key(), v, type, d, m, generation);
136 /// TranspositionTable::retrieve looks up the current position in the
137 /// transposition table. Returns a pointer to the TTEntry or NULL
138 /// if position is not found.
140 const TTEntry* TranspositionTable::retrieve(const Position &pos) const {
142 TTEntry *tte = first_entry(pos);
144 for (int i = 0; i < 4; i++, tte++)
146 if (tte->key() == pos.get_key())
153 /// TranspositionTable::first_entry returns a pointer to the first
154 /// entry of a cluster given a position.
156 inline TTEntry* TranspositionTable::first_entry(const Position &pos) const {
158 return entries + (int(pos.get_key() & (size - 1)) << 2);
161 /// TranspositionTable::new_search() is called at the beginning of every new
162 /// search. It increments the "generation" variable, which is used to
163 /// distinguish transposition table entries from previous searches from
164 /// entries from the current search.
166 void TranspositionTable::new_search() {
173 /// TranspositionTable::insert_pv() is called at the end of a search
174 /// iteration, and inserts the PV back into the PV. This makes sure the
175 /// old PV moves are searched first, even if the old TT entries have been
178 void TranspositionTable::insert_pv(const Position &pos, Move pv[]) {
183 for (int i = 0; pv[i] != MOVE_NONE; i++)
185 store(p, VALUE_NONE, Depth(-127*OnePly), pv[i], VALUE_TYPE_NONE);
186 p.do_move(pv[i], st);
191 /// TranspositionTable::full() returns the permill of all transposition table
192 /// entries which have received at least one write during the current search.
193 /// It is used to display the "info hashfull ..." information in UCI.
195 int TranspositionTable::full() {
197 double N = double(size) * 4.0;
198 return int(1000 * (1 - exp(writes * log(1.0 - 1.0/N))));
207 TTEntry::TTEntry(Key k, Value v, ValueType t, Depth d, Move m,
209 key_ (k), data((m & 0x7FFFF) | (t << 20) | (generation << 23)),
210 value_(int16_t(v)), depth_(int16_t(d)) {}