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| /* | |
| Stockfish, a UCI chess playing engine derived from Glaurung 2.1 | |
| Copyright (C) 2004-2008 Tord Romstad (Glaurung author) | |
| Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad | |
| Stockfish is free software: you can redistribute it and/or modify | |
| it under the terms of the GNU General Public License as published by | |
| the Free Software Foundation, either version 3 of the License, or | |
| (at your option) any later version. | |
| Stockfish is distributed in the hope that it will be useful, | |
| but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
| GNU General Public License for more details. | |
| You should have received a copy of the GNU General Public License | |
| along with this program. If not, see <http://www.gnu.org/licenses/>. | |
| */ | |
| TranspositionTable TT; // Our global transposition table | |
| /// TranspositionTable::set_size() sets the size of the transposition table, | |
| /// measured in megabytes. Transposition table consists of a power of 2 number | |
| /// of clusters and each cluster consists of ClusterSize number of TTEntry. | |
| void TranspositionTable::set_size(size_t mbSize) { | |
| assert(msb((mbSize << 20) / sizeof(TTEntry)) < 32); | |
| uint32_t size = ClusterSize << msb((mbSize << 20) / sizeof(TTEntry[ClusterSize])); | |
| if (hashMask == size - ClusterSize) | |
| return; | |
| hashMask = size - ClusterSize; | |
| free(mem); | |
| mem = calloc(size * sizeof(TTEntry) + CACHE_LINE_SIZE - 1, 1); | |
| if (!mem) | |
| { | |
| std::cerr << "Failed to allocate " << mbSize | |
| << "MB for transposition table." << std::endl; | |
| exit(EXIT_FAILURE); | |
| } | |
| table = (TTEntry*)((uintptr_t(mem) + CACHE_LINE_SIZE - 1) & ~(CACHE_LINE_SIZE - 1)); | |
| } | |
| /// TranspositionTable::clear() overwrites the entire transposition table | |
| /// with zeroes. It is called whenever the table is resized, or when the | |
| /// user asks the program to clear the table (from the UCI interface). | |
| void TranspositionTable::clear() { | |
| std::memset(table, 0, (hashMask + ClusterSize) * sizeof(TTEntry)); | |
| } | |
| /// TranspositionTable::probe() looks up the current position in the | |
| /// transposition table. Returns a pointer to the TTEntry or NULL if | |
| /// position is not found. | |
| const TTEntry* TranspositionTable::probe(const Key key) const { | |
| const TTEntry* tte = first_entry(key); | |
| uint32_t key32 = key >> 32; | |
| for (unsigned i = 0; i < ClusterSize; i++, tte++) | |
| if (tte->key() == key32) | |
| return tte; | |
| return NULL; | |
| } | |
| /// TranspositionTable::store() writes a new entry containing position key and | |
| /// valuable information of current position. The lowest order bits of position | |
| /// key are used to decide on which cluster the position will be placed. | |
| /// When a new entry is written and there are no empty entries available in cluster, | |
| /// it replaces the least valuable of entries. A TTEntry t1 is considered to be | |
| /// more valuable than a TTEntry t2 if t1 is from the current search and t2 is from | |
| /// a previous search, or if the depth of t1 is bigger than the depth of t2. | |
| void TranspositionTable::store(const Key key, Value v, Bound b, Depth d, Move m, Value statV, Value evalM) { | |
| int c1, c2, c3; | |
| TTEntry *tte, *replace; | |
| uint32_t key32 = key >> 32; // Use the high 32 bits as key inside the cluster | |
| tte = replace = first_entry(key); | |
| for (unsigned i = 0; i < ClusterSize; i++, tte++) | |
| { | |
| if (!tte->key() || tte->key() == key32) // Empty or overwrite old | |
| { | |
| if (!m) | |
| m = tte->move(); // Preserve any existing ttMove | |
| replace = tte; | |
| break; | |
| } | |
| // Implement replace strategy | |
| c1 = (replace->generation() == generation ? 2 : 0); | |
| c2 = (tte->generation() == generation || tte->bound() == BOUND_EXACT ? -2 : 0); | |
| c3 = (tte->depth() < replace->depth() ? 1 : 0); | |
| if (c1 + c2 + c3 > 0) | |
| replace = tte; | |
| } | |
| replace->save(key32, v, b, d, m, generation, statV, evalM); | |
| } | |