mirror of
https://github.com/sockspls/badfish
synced 2025-05-01 09:13:08 +00:00
ca7d4e9ac7
Simplification that eliminates ONE_PLY, based on a suggestion in the forum that support for fractional plies has never been used, and @mcostalba's openness to the idea of eliminating it. We lose a little bit of type safety by making Depth an integer, but in return we simplify the code in search.cpp quite significantly. No functional change ------------------------------------------ The argument favoring eliminating ONE_PLY: * The term “ONE_PLY” comes up in a lot of forum posts (474 to date) https://groups.google.com/forum/?fromgroups=#!searchin/fishcooking/ONE_PLY%7Csort:relevance * There is occasionally a commit that breaks invariance of the code with respect to ONE_PLY https://groups.google.com/forum/?fromgroups=#!searchin/fishcooking/ONE_PLY%7Csort:date/fishcooking/ZIPdYj6k0fk/KdNGcPWeBgAJ * To prevent such commits, there is a Travis CI hack that doubles ONE_PLY and rechecks bench * Sustaining ONE_PLY has, alas, not resulted in any improvements to the engine, despite many individuals testing many experiments over 5 years. The strongest argument in favor of preserving ONE_PLY comes from @locutus: “If we use par example ONE_PLY=256 the parameter space is increases by the factor 256. So it seems very unlikely that the optimal setting is in the subspace of ONE_PLY=1.” There is a strong theoretical impediment to fractional depth systems: the transposition table uses depth to determine when a stored result is good enough to supply an answer for a current search. If you have fractional depths, then different pathways to the position can be at fractionally different depths. In the end, there are three separate times when a proposal to remove ONE_PLY was defeated by the suggestion to “give it a few more months.” So… it seems like time to remove this distraction from the community. See the pull request here: https://github.com/official-stockfish/Stockfish/pull/2289
103 lines
3.2 KiB
C++
103 lines
3.2 KiB
C++
/*
|
|
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
|
|
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
|
|
Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
|
|
Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, 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/>.
|
|
*/
|
|
|
|
#ifndef TT_H_INCLUDED
|
|
#define TT_H_INCLUDED
|
|
|
|
#include "misc.h"
|
|
#include "types.h"
|
|
|
|
/// TTEntry struct is the 10 bytes transposition table entry, defined as below:
|
|
///
|
|
/// key 16 bit
|
|
/// move 16 bit
|
|
/// value 16 bit
|
|
/// eval value 16 bit
|
|
/// generation 5 bit
|
|
/// pv node 1 bit
|
|
/// bound type 2 bit
|
|
/// depth 8 bit
|
|
|
|
struct TTEntry {
|
|
|
|
Move move() const { return (Move )move16; }
|
|
Value value() const { return (Value)value16; }
|
|
Value eval() const { return (Value)eval16; }
|
|
Depth depth() const { return (Depth)depth8 + DEPTH_OFFSET; }
|
|
bool is_pv() const { return (bool)(genBound8 & 0x4); }
|
|
Bound bound() const { return (Bound)(genBound8 & 0x3); }
|
|
void save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev);
|
|
|
|
private:
|
|
friend class TranspositionTable;
|
|
|
|
uint16_t key16;
|
|
uint16_t move16;
|
|
int16_t value16;
|
|
int16_t eval16;
|
|
uint8_t genBound8;
|
|
uint8_t depth8;
|
|
};
|
|
|
|
|
|
/// A TranspositionTable consists of a power of 2 number of clusters and each
|
|
/// cluster consists of ClusterSize number of TTEntry. Each non-empty entry
|
|
/// contains information of exactly one position. The size of a cluster should
|
|
/// divide the size of a cache line size, to ensure that clusters never cross
|
|
/// cache lines. This ensures best cache performance, as the cacheline is
|
|
/// prefetched, as soon as possible.
|
|
|
|
class TranspositionTable {
|
|
|
|
static constexpr int CacheLineSize = 64;
|
|
static constexpr int ClusterSize = 3;
|
|
|
|
struct Cluster {
|
|
TTEntry entry[ClusterSize];
|
|
char padding[2]; // Align to a divisor of the cache line size
|
|
};
|
|
|
|
static_assert(CacheLineSize % sizeof(Cluster) == 0, "Cluster size incorrect");
|
|
|
|
public:
|
|
~TranspositionTable() { free(mem); }
|
|
void new_search() { generation8 += 8; } // Lower 3 bits are used by PV flag and Bound
|
|
TTEntry* probe(const Key key, bool& found) const;
|
|
int hashfull() const;
|
|
void resize(size_t mbSize);
|
|
void clear();
|
|
|
|
// The 32 lowest order bits of the key are used to get the index of the cluster
|
|
TTEntry* first_entry(const Key key) const {
|
|
return &table[(uint32_t(key) * uint64_t(clusterCount)) >> 32].entry[0];
|
|
}
|
|
|
|
private:
|
|
friend struct TTEntry;
|
|
|
|
size_t clusterCount;
|
|
Cluster* table;
|
|
void* mem;
|
|
uint8_t generation8; // Size must be not bigger than TTEntry::genBound8
|
|
};
|
|
|
|
extern TranspositionTable TT;
|
|
|
|
#endif // #ifndef TT_H_INCLUDED
|