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117 lines
4.1 KiB
C++
117 lines
4.1 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
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Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
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Stockfish is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Stockfish is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <cstring> // For std::memset
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#include <iostream>
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#include "bitboard.h"
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#include "tt.h"
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TranspositionTable TT; // Our global transposition table
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/// TranspositionTable::resize() sets the size of the transposition table,
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/// measured in megabytes. Transposition table consists of a power of 2 number
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/// of clusters and each cluster consists of ClusterSize number of TTEntry.
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void TranspositionTable::resize(size_t mbSize) {
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size_t newClusterCount = size_t(1) << msb((mbSize * 1024 * 1024) / sizeof(Cluster));
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if (newClusterCount == clusterCount)
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return;
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clusterCount = newClusterCount;
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free(mem);
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mem = calloc(clusterCount * sizeof(Cluster) + CacheLineSize - 1, 1);
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if (!mem)
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{
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std::cerr << "Failed to allocate " << mbSize
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<< "MB for transposition table." << std::endl;
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exit(EXIT_FAILURE);
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}
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table = (Cluster*)((uintptr_t(mem) + CacheLineSize - 1) & ~(CacheLineSize - 1));
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}
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/// TranspositionTable::clear() overwrites the entire transposition table
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/// with zeros. It is called whenever the table is resized, or when the
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/// user asks the program to clear the table (from the UCI interface).
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void TranspositionTable::clear() {
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std::memset(table, 0, clusterCount * sizeof(Cluster));
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}
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/// TranspositionTable::probe() looks up the current position in the transposition
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/// table. It returns true and a pointer to the TTEntry if the position is found.
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/// Otherwise, it returns false and a pointer to an empty or least valuable TTEntry
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/// to be replaced later. The replace value of an entry is calculated as its depth
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/// minus 8 times its relative age. TTEntry t1 is considered more valuable than
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/// TTEntry t2 if its replace value is greater than that of t2.
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TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
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TTEntry* const tte = first_entry(key);
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const uint16_t key16 = key >> 48; // Use the high 16 bits as key inside the cluster
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for (int i = 0; i < ClusterSize; ++i)
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if (!tte[i].key16 || tte[i].key16 == key16)
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{
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if ((tte[i].genBound8 & 0xFC) != generation8 && tte[i].key16)
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tte[i].genBound8 = uint8_t(generation8 | tte[i].bound()); // Refresh
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return found = (bool)tte[i].key16, &tte[i];
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}
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// Find an entry to be replaced according to the replacement strategy
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TTEntry* replace = tte;
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for (int i = 1; i < ClusterSize; ++i)
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// Due to our packed storage format for generation and its cyclic
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// nature we add 259 (256 is the modulus plus 3 to keep the lowest
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// two bound bits from affecting the result) to calculate the entry
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// age correctly even after generation8 overflows into the next cycle.
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if ( replace->depth8 - ((259 + generation8 - replace->genBound8) & 0xFC) * 2 * ONE_PLY
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> tte[i].depth8 - ((259 + generation8 - tte[i].genBound8) & 0xFC) * 2 * ONE_PLY)
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replace = &tte[i];
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return found = false, replace;
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}
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/// Returns an approximation of the hashtable occupation during a search. The
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/// hash is x permill full, as per UCI protocol.
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int TranspositionTable::hashfull() const
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{
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int cnt = 0;
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for (int i = 0; i < 1000 / ClusterSize; i++)
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{
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const TTEntry* tte = &table[i].entry[0];
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for (int j = 0; j < ClusterSize; j++)
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if ((tte[j].genBound8 & 0xFC) == generation8)
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cnt++;
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}
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return cnt;
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}
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