2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
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/>.
45 #include "ucioption.h"
51 //// Local definitions
57 enum NodeType { NonPV, PV };
59 // Set to true to force running with one thread.
60 // Used for debugging SMP code.
61 const bool FakeSplit = false;
63 // Fast lookup table of sliding pieces indexed by Piece
64 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
65 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
67 // ThreadsManager class is used to handle all the threads related stuff in search,
68 // init, starting, parking and, the most important, launching a slave thread at a
69 // split point are what this class does. All the access to shared thread data is
70 // done through this class, so that we avoid using global variables instead.
72 class ThreadsManager {
73 /* As long as the single ThreadsManager object is defined as a global we don't
74 need to explicitly initialize to zero its data members because variables with
75 static storage duration are automatically set to zero before enter main()
81 int min_split_depth() const { return minimumSplitDepth; }
82 int active_threads() const { return activeThreads; }
83 void set_active_threads(int cnt) { activeThreads = cnt; }
85 void read_uci_options();
86 bool available_thread_exists(int master) const;
87 bool thread_is_available(int slave, int master) const;
88 bool cutoff_at_splitpoint(int threadID) const;
89 void wake_sleeping_thread(int threadID);
90 void idle_loop(int threadID, SplitPoint* sp);
93 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
94 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
97 Depth minimumSplitDepth;
98 int maxThreadsPerSplitPoint;
99 bool useSleepingThreads;
101 volatile bool allThreadsShouldExit;
102 Thread threads[MAX_THREADS];
103 Lock mpLock, sleepLock[MAX_THREADS];
104 WaitCondition sleepCond[MAX_THREADS];
108 // RootMove struct is used for moves at the root at the tree. For each root
109 // move, we store two scores, a node count, and a PV (really a refutation
110 // in the case of moves which fail low). Value pv_score is normally set at
111 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
112 // according to the order in which moves are returned by MovePicker.
117 RootMove(const RootMove& rm) { *this = rm; }
118 RootMove& operator=(const RootMove& rm);
120 // RootMove::operator<() is the comparison function used when
121 // sorting the moves. A move m1 is considered to be better
122 // than a move m2 if it has an higher pv_score, or if it has
123 // equal pv_score but m1 has the higher non_pv_score. In this
124 // way we are guaranteed that PV moves are always sorted as first.
125 bool operator<(const RootMove& m) const {
126 return pv_score != m.pv_score ? pv_score < m.pv_score
127 : non_pv_score < m.non_pv_score;
130 void extract_pv_from_tt(Position& pos);
131 void insert_pv_in_tt(Position& pos);
132 std::string pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvLine);
137 Move pv[PLY_MAX_PLUS_2];
141 // RootMoveList struct is essentially a std::vector<> of RootMove objects,
142 // with an handful of methods above the standard ones.
144 struct RootMoveList : public std::vector<RootMove> {
146 typedef std::vector<RootMove> Base;
148 void init(Position& pos, Move searchMoves[]);
149 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
150 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
156 // When formatting a move for std::cout we must know if we are in Chess960
157 // or not. To keep using the handy operator<<() on the move the trick is to
158 // embed this flag in the stream itself. Function-like named enum set960 is
159 // used as a custom manipulator and the stream internal general-purpose array,
160 // accessed through ios_base::iword(), is used to pass the flag to the move's
161 // operator<<() that will use it to properly format castling moves.
164 std::ostream& operator<< (std::ostream& os, const set960& f) {
166 os.iword(0) = int(f);
171 // Overload operator << for moves to make it easier to print moves in
172 // coordinate notation compatible with UCI protocol.
173 std::ostream& operator<<(std::ostream& os, Move m) {
175 bool chess960 = (os.iword(0) != 0); // See set960()
176 return os << move_to_uci(m, chess960);
184 // Maximum depth for razoring
185 const Depth RazorDepth = 4 * ONE_PLY;
187 // Dynamic razoring margin based on depth
188 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
190 // Maximum depth for use of dynamic threat detection when null move fails low
191 const Depth ThreatDepth = 5 * ONE_PLY;
193 // Step 9. Internal iterative deepening
195 // Minimum depth for use of internal iterative deepening
196 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
198 // At Non-PV nodes we do an internal iterative deepening search
199 // when the static evaluation is bigger then beta - IIDMargin.
200 const Value IIDMargin = Value(0x100);
202 // Step 11. Decide the new search depth
204 // Extensions. Configurable UCI options
205 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
206 Depth CheckExtension[2], PawnPushTo7thExtension[2], PassedPawnExtension[2];
207 Depth PawnEndgameExtension[2], MateThreatExtension[2];
209 // Minimum depth for use of singular extension
210 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
212 // Step 12. Futility pruning
214 // Futility margin for quiescence search
215 const Value FutilityMarginQS = Value(0x80);
217 // Futility lookup tables (initialized at startup) and their getter functions
218 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
219 int FutilityMoveCountArray[32]; // [depth]
221 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
222 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
224 // Step 14. Reduced search
226 // Reduction lookup tables (initialized at startup) and their getter functions
227 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
229 template <NodeType PV>
230 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
232 // Easy move margin. An easy move candidate must be at least this much
233 // better than the second best move.
234 const Value EasyMoveMargin = Value(0x200);
237 /// Namespace variables
246 int MultiPV, UCIMultiPV;
248 // Time management variables
249 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
250 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
251 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
256 std::ofstream LogFile;
258 // Skill level adjustment
262 // Multi-threads manager object
263 ThreadsManager ThreadsMgr;
265 // Node counters, used only by thread[0] but try to keep in different cache
266 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
267 bool SendSearchedNodes;
269 int NodesBetweenPolls = 30000;
276 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
278 template <NodeType PvNode, bool SpNode, bool Root>
279 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
281 template <NodeType PvNode>
282 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
284 template <NodeType PvNode>
285 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
287 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
288 : search<PvNode, false, false>(pos, ss, alpha, beta, depth, ply);
291 template <NodeType PvNode>
292 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool mateThreat, bool* dangerous);
294 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
295 bool connected_moves(const Position& pos, Move m1, Move m2);
296 bool value_is_mate(Value value);
297 Value value_to_tt(Value v, int ply);
298 Value value_from_tt(Value v, int ply);
299 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
300 bool connected_threat(const Position& pos, Move m, Move threat);
301 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
302 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
303 void update_killers(Move m, Move killers[]);
304 void update_gains(const Position& pos, Move move, Value before, Value after);
306 int current_search_time();
307 std::string value_to_uci(Value v);
308 std::string speed_to_uci(int64_t nodes);
309 void poll(const Position& pos);
310 void wait_for_stop_or_ponderhit();
312 #if !defined(_MSC_VER)
313 void* init_thread(void* threadID);
315 DWORD WINAPI init_thread(LPVOID threadID);
319 // MovePickerExt is an extended MovePicker used to choose at compile time
320 // the proper move source according to the type of node.
321 template<bool SpNode, bool Root> struct MovePickerExt;
323 // In Root nodes use RootMoveList Rml as source. Score and sort the root moves
324 // before to search them.
325 template<> struct MovePickerExt<false, true> : public MovePicker {
327 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
328 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
330 Value score = VALUE_ZERO;
332 // Score root moves using the standard way used in main search, the moves
333 // are scored according to the order in which they are returned by MovePicker.
334 // This is the second order score that is used to compare the moves when
335 // the first order pv scores of both moves are equal.
336 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
337 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
338 if (rm->pv[0] == move)
340 rm->non_pv_score = score--;
348 Move get_next_move() {
355 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
358 RootMoveList::iterator rm;
362 // In SpNodes use split point's shared MovePicker object as move source
363 template<> struct MovePickerExt<true, false> : public MovePicker {
365 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
366 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b),
369 Move get_next_move() { return mp->get_next_move(); }
371 RootMoveList::iterator rm; // Dummy, needed to compile
375 // Default case, create and use a MovePicker object as source
376 template<> struct MovePickerExt<false, false> : public MovePicker {
378 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
379 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b) {}
381 RootMoveList::iterator rm; // Dummy, needed to compile
391 /// init_threads(), exit_threads() and nodes_searched() are helpers to
392 /// give accessibility to some TM methods from outside of current file.
394 void init_threads() { ThreadsMgr.init_threads(); }
395 void exit_threads() { ThreadsMgr.exit_threads(); }
398 /// init_search() is called during startup. It initializes various lookup tables
402 int d; // depth (ONE_PLY == 2)
403 int hd; // half depth (ONE_PLY == 1)
406 // Init reductions array
407 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
409 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
410 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
411 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
412 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
415 // Init futility margins array
416 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
417 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
419 // Init futility move count array
420 for (d = 0; d < 32; d++)
421 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
425 /// perft() is our utility to verify move generation is bug free. All the legal
426 /// moves up to given depth are generated and counted and the sum returned.
428 int64_t perft(Position& pos, Depth depth)
430 MoveStack mlist[MOVES_MAX];
435 // Generate all legal moves
436 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
438 // If we are at the last ply we don't need to do and undo
439 // the moves, just to count them.
440 if (depth <= ONE_PLY)
441 return int(last - mlist);
443 // Loop through all legal moves
445 for (MoveStack* cur = mlist; cur != last; cur++)
448 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
449 sum += perft(pos, depth - ONE_PLY);
456 /// think() is the external interface to Stockfish's search, and is called when
457 /// the program receives the UCI 'go' command. It initializes various
458 /// search-related global variables, and calls id_loop(). It returns false
459 /// when a quit command is received during the search.
461 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
462 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
464 // Initialize global search variables
465 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
467 SearchStartTime = get_system_time();
468 ExactMaxTime = maxTime;
471 InfiniteSearch = infinite;
473 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
475 // Look for a book move, only during games, not tests
476 if (UseTimeManagement && Options["OwnBook"].value<bool>())
478 if (Options["Book File"].value<std::string>() != OpeningBook.name())
479 OpeningBook.open(Options["Book File"].value<std::string>());
481 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
482 if (bookMove != MOVE_NONE)
485 wait_for_stop_or_ponderhit();
487 cout << "bestmove " << bookMove << endl;
492 // Read UCI option values
493 TT.set_size(Options["Hash"].value<int>());
494 if (Options["Clear Hash"].value<bool>())
496 Options["Clear Hash"].set_value("false");
500 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
501 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
502 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
503 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
504 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
505 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
506 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
507 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
508 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
509 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
510 UCIMultiPV = Options["MultiPV"].value<int>();
511 SkillLevel = Options["Skill level"].value<int>();
512 UseLogFile = Options["Use Search Log"].value<bool>();
514 read_evaluation_uci_options(pos.side_to_move());
516 // Do we have to play with skill handicap? In this case enable MultiPV that
517 // we will use behind the scenes to retrieve a set of possible moves.
518 MultiPV = (SkillLevel < 10 ? Max(UCIMultiPV, 4) : UCIMultiPV);
520 // Set the number of active threads
521 ThreadsMgr.read_uci_options();
522 init_eval(ThreadsMgr.active_threads());
524 // Wake up needed threads
525 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
526 ThreadsMgr.wake_sleeping_thread(i);
529 int myTime = time[pos.side_to_move()];
530 int myIncrement = increment[pos.side_to_move()];
531 if (UseTimeManagement)
532 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
534 // Set best NodesBetweenPolls interval to avoid lagging under
535 // heavy time pressure.
537 NodesBetweenPolls = Min(MaxNodes, 30000);
538 else if (myTime && myTime < 1000)
539 NodesBetweenPolls = 1000;
540 else if (myTime && myTime < 5000)
541 NodesBetweenPolls = 5000;
543 NodesBetweenPolls = 30000;
545 // Write search information to log file
548 std::string name = Options["Search Log Filename"].value<std::string>();
549 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
551 LogFile << "\nSearching: " << pos.to_fen()
552 << "\ninfinite: " << infinite
553 << " ponder: " << ponder
554 << " time: " << myTime
555 << " increment: " << myIncrement
556 << " moves to go: " << movesToGo
560 // We're ready to start thinking. Call the iterative deepening loop function
561 Move ponderMove = MOVE_NONE;
562 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
564 // Print final search statistics
565 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
569 int t = current_search_time();
571 LogFile << "Nodes: " << pos.nodes_searched()
572 << "\nNodes/second: " << (t > 0 ? int(pos.nodes_searched() * 1000 / t) : 0)
573 << "\nBest move: " << move_to_san(pos, bestMove);
576 pos.do_move(bestMove, st);
577 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
578 pos.undo_move(bestMove); // Return from think() with unchanged position
582 // This makes all the threads to go to sleep
583 ThreadsMgr.set_active_threads(1);
585 // If we are pondering or in infinite search, we shouldn't print the
586 // best move before we are told to do so.
587 if (!StopRequest && (Pondering || InfiniteSearch))
588 wait_for_stop_or_ponderhit();
590 // Could be MOVE_NONE when searching on a stalemate position
591 cout << "bestmove " << bestMove;
593 // UCI protol is not clear on allowing sending an empty ponder move, instead
594 // it is clear that ponder move is optional. So skip it if empty.
595 if (ponderMove != MOVE_NONE)
596 cout << " ponder " << ponderMove;
606 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
607 // with increasing depth until the allocated thinking time has been consumed,
608 // user stops the search, or the maximum search depth is reached.
610 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
612 SearchStack ss[PLY_MAX_PLUS_2];
613 Value bestValues[PLY_MAX_PLUS_2];
614 int bestMoveChanges[PLY_MAX_PLUS_2];
615 int depth, aspirationDelta;
616 Value value, alpha, beta;
617 Move bestMove, easyMove;
619 // Initialize stuff before a new search
620 memset(ss, 0, 4 * sizeof(SearchStack));
623 *ponderMove = bestMove = easyMove = MOVE_NONE;
624 depth = aspirationDelta = 0;
625 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
626 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
628 // Moves to search are verified and copied
629 Rml.init(pos, searchMoves);
631 // Handle special case of searching on a mate/stalemate position
634 cout << "info depth 0 score "
635 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
641 // Iterative deepening loop
642 while (++depth <= PLY_MAX && (!MaxDepth || depth <= MaxDepth) && !StopRequest)
644 Rml.bestMoveChanges = 0;
645 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
647 // Calculate dynamic aspiration window based on previous iterations
648 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
650 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
651 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
653 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
654 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
656 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
657 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
660 // Start with a small aspiration window and, in case of fail high/low,
661 // research with bigger window until not failing high/low anymore.
663 // Search starting from ss+1 to allow calling update_gains()
664 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY, 0);
666 // Write PV back to transposition table in case the relevant entries
667 // have been overwritten during the search.
668 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
669 Rml[i].insert_pv_in_tt(pos);
671 // Value cannot be trusted. Break out immediately!
675 assert(value >= alpha);
677 // In case of failing high/low increase aspiration window and research,
678 // otherwise exit the fail high/low loop.
681 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
682 aspirationDelta += aspirationDelta / 2;
684 else if (value <= alpha)
686 AspirationFailLow = true;
687 StopOnPonderhit = false;
689 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
690 aspirationDelta += aspirationDelta / 2;
695 } while (abs(value) < VALUE_KNOWN_WIN);
697 // Collect info about search result
698 bestMove = Rml[0].pv[0];
699 *ponderMove = Rml[0].pv[1];
700 bestValues[depth] = value;
701 bestMoveChanges[depth] = Rml.bestMoveChanges;
703 // Send PV line to GUI and to log file
704 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
705 cout << Rml[i].pv_info_to_uci(pos, depth, alpha, beta, i) << endl;
708 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
710 // Init easyMove after first iteration or drop if differs from the best move
711 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
713 else if (bestMove != easyMove)
714 easyMove = MOVE_NONE;
716 if (UseTimeManagement && !StopRequest)
719 bool noMoreTime = false;
721 // Stop search early when the last two iterations returned a mate score
723 && abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
724 && abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
727 // Stop search early if one move seems to be much better than the
728 // others or if there is only a single legal move. In this latter
729 // case we search up to Iteration 8 anyway to get a proper score.
731 && easyMove == bestMove
733 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
734 && current_search_time() > TimeMgr.available_time() / 16)
735 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
736 && current_search_time() > TimeMgr.available_time() / 32)))
739 // Add some extra time if the best move has changed during the last two iterations
740 if (depth > 4 && depth < 50)
741 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
743 // Stop search if most of MaxSearchTime is consumed at the end of the
744 // iteration. We probably don't have enough time to search the first
745 // move at the next iteration anyway.
746 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
752 StopOnPonderhit = true;
759 // When playing with strength handicap choose best move among the MultiPV
760 // set using a statistical rule dependent on SkillLevel.
765 // Rml list is already sorted by pv_score in descending order
767 int max_s = -VALUE_INFINITE;
768 int size = Min(MultiPV, (int)Rml.size());
769 int max = Rml[0].pv_score;
770 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
771 int wk = 128 - 8 * SkillLevel;
773 // PRNG sequence should be non deterministic
774 for (int i = abs(get_system_time() % 50); i > 0; i--)
777 // Choose best move. For each move's score we add two terms both dependent
778 // on wk, one deterministic and bigger for weaker moves, and one random,
779 // then we choose the move with the resulting highest score.
780 for (int i = 0; i < size; i++)
784 // Don't allow crazy blunders even at very low skills
785 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
788 // This is our magical formula
789 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
794 bestMove = Rml[i].pv[0];
795 *ponderMove = Rml[i].pv[1];
804 // search<>() is the main search function for both PV and non-PV nodes and for
805 // normal and SplitPoint nodes. When called just after a split point the search
806 // is simpler because we have already probed the hash table, done a null move
807 // search, and searched the first move before splitting, we don't have to repeat
808 // all this work again. We also don't need to store anything to the hash table
809 // here: This is taken care of after we return from the split point.
811 template <NodeType PvNode, bool SpNode, bool Root>
812 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
814 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
815 assert(beta > alpha && beta <= VALUE_INFINITE);
816 assert(PvNode || alpha == beta - 1);
817 assert((Root || ply > 0) && ply < PLY_MAX);
818 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
820 Move movesSearched[MOVES_MAX];
825 Move ttMove, move, excludedMove, threatMove;
828 Value bestValue, value, oldAlpha;
829 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
830 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
831 bool mateThreat = false;
832 int moveCount = 0, playedMoveCount = 0;
833 int threadID = pos.thread();
834 SplitPoint* sp = NULL;
836 refinedValue = bestValue = value = -VALUE_INFINITE;
838 isCheck = pos.is_check();
844 ttMove = excludedMove = MOVE_NONE;
845 threatMove = sp->threatMove;
846 mateThreat = sp->mateThreat;
847 goto split_point_start;
852 // Step 1. Initialize node and poll. Polling can abort search
853 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
854 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
855 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
857 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
863 // Step 2. Check for aborted search and immediate draw
865 || ThreadsMgr.cutoff_at_splitpoint(threadID)
867 || ply >= PLY_MAX - 1) && !Root)
870 // Step 3. Mate distance pruning
871 alpha = Max(value_mated_in(ply), alpha);
872 beta = Min(value_mate_in(ply+1), beta);
876 // Step 4. Transposition table lookup
877 // We don't want the score of a partial search to overwrite a previous full search
878 // TT value, so we use a different position key in case of an excluded move.
879 excludedMove = ss->excludedMove;
880 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
882 tte = TT.retrieve(posKey);
883 ttMove = tte ? tte->move() : MOVE_NONE;
885 // At PV nodes we check for exact scores, while at non-PV nodes we check for
886 // and return a fail high/low. Biggest advantage at probing at PV nodes is
887 // to have a smooth experience in analysis mode.
890 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
891 : ok_to_use_TT(tte, depth, beta, ply)))
894 ss->bestMove = ttMove; // Can be MOVE_NONE
895 return value_from_tt(tte->value(), ply);
898 // Step 5. Evaluate the position statically and
899 // update gain statistics of parent move.
901 ss->eval = ss->evalMargin = VALUE_NONE;
904 assert(tte->static_value() != VALUE_NONE);
906 ss->eval = tte->static_value();
907 ss->evalMargin = tte->static_value_margin();
908 refinedValue = refine_eval(tte, ss->eval, ply);
912 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
913 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
916 // Save gain for the parent non-capture move
917 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
919 // Step 6. Razoring (is omitted in PV nodes)
921 && depth < RazorDepth
923 && refinedValue < beta - razor_margin(depth)
924 && ttMove == MOVE_NONE
925 && !value_is_mate(beta)
926 && !pos.has_pawn_on_7th(pos.side_to_move()))
928 Value rbeta = beta - razor_margin(depth);
929 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
931 // Logically we should return (v + razor_margin(depth)), but
932 // surprisingly this did slightly weaker in tests.
936 // Step 7. Static null move pruning (is omitted in PV nodes)
937 // We're betting that the opponent doesn't have a move that will reduce
938 // the score by more than futility_margin(depth) if we do a null move.
941 && depth < RazorDepth
943 && refinedValue >= beta + futility_margin(depth, 0)
944 && !value_is_mate(beta)
945 && pos.non_pawn_material(pos.side_to_move()))
946 return refinedValue - futility_margin(depth, 0);
948 // Step 8. Null move search with verification search (is omitted in PV nodes)
953 && refinedValue >= beta
954 && !value_is_mate(beta)
955 && pos.non_pawn_material(pos.side_to_move()))
957 ss->currentMove = MOVE_NULL;
959 // Null move dynamic reduction based on depth
960 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
962 // Null move dynamic reduction based on value
963 if (refinedValue - beta > PawnValueMidgame)
966 pos.do_null_move(st);
967 (ss+1)->skipNullMove = true;
968 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
969 (ss+1)->skipNullMove = false;
970 pos.undo_null_move();
972 if (nullValue >= beta)
974 // Do not return unproven mate scores
975 if (nullValue >= value_mate_in(PLY_MAX))
978 if (depth < 6 * ONE_PLY)
981 // Do verification search at high depths
982 ss->skipNullMove = true;
983 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
984 ss->skipNullMove = false;
991 // The null move failed low, which means that we may be faced with
992 // some kind of threat. If the previous move was reduced, check if
993 // the move that refuted the null move was somehow connected to the
994 // move which was reduced. If a connection is found, return a fail
995 // low score (which will cause the reduced move to fail high in the
996 // parent node, which will trigger a re-search with full depth).
997 if (nullValue == value_mated_in(ply + 2))
1000 threatMove = (ss+1)->bestMove;
1001 if ( depth < ThreatDepth
1002 && (ss-1)->reduction
1003 && threatMove != MOVE_NONE
1004 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1009 // Step 9. Internal iterative deepening
1010 if ( depth >= IIDDepth[PvNode]
1011 && ttMove == MOVE_NONE
1012 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1014 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1016 ss->skipNullMove = true;
1017 search<PvNode>(pos, ss, alpha, beta, d, ply);
1018 ss->skipNullMove = false;
1020 ttMove = ss->bestMove;
1021 tte = TT.retrieve(posKey);
1024 // Expensive mate threat detection (only for PV nodes)
1026 mateThreat = pos.has_mate_threat();
1028 split_point_start: // At split points actual search starts from here
1030 // Initialize a MovePicker object for the current position
1031 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1033 ss->bestMove = MOVE_NONE;
1034 futilityBase = ss->eval + ss->evalMargin;
1035 singularExtensionNode = !Root
1037 && depth >= SingularExtensionDepth[PvNode]
1040 && !excludedMove // Do not allow recursive singular extension search
1041 && (tte->type() & VALUE_TYPE_LOWER)
1042 && tte->depth() >= depth - 3 * ONE_PLY;
1045 lock_grab(&(sp->lock));
1046 bestValue = sp->bestValue;
1049 // Step 10. Loop through moves
1050 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1051 while ( bestValue < beta
1052 && (move = mp.get_next_move()) != MOVE_NONE
1053 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1055 assert(move_is_ok(move));
1059 moveCount = ++sp->moveCount;
1060 lock_release(&(sp->lock));
1062 else if (move == excludedMove)
1069 // This is used by time management
1070 FirstRootMove = (moveCount == 1);
1072 // Save the current node count before the move is searched
1073 nodes = pos.nodes_searched();
1075 // If it's time to send nodes info, do it here where we have the
1076 // correct accumulated node counts searched by each thread.
1077 if (SendSearchedNodes)
1079 SendSearchedNodes = false;
1080 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1083 if (current_search_time() >= 1000)
1084 cout << "info currmove " << move
1085 << " currmovenumber " << moveCount << endl;
1088 // At Root and at first iteration do a PV search on all the moves
1089 // to score root moves. Otherwise only the first one is the PV.
1090 isPvMove = (PvNode && moveCount <= (Root ? MultiPV + 1000 * (depth <= ONE_PLY) : 1));
1091 moveIsCheck = pos.move_is_check(move, ci);
1092 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1094 // Step 11. Decide the new search depth
1095 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, mateThreat, &dangerous);
1097 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1098 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1099 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1100 // lower than ttValue minus a margin then we extend ttMove.
1101 if ( singularExtensionNode
1102 && move == tte->move()
1105 Value ttValue = value_from_tt(tte->value(), ply);
1107 if (abs(ttValue) < VALUE_KNOWN_WIN)
1109 Value b = ttValue - int(depth);
1110 ss->excludedMove = move;
1111 ss->skipNullMove = true;
1112 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1113 ss->skipNullMove = false;
1114 ss->excludedMove = MOVE_NONE;
1115 ss->bestMove = MOVE_NONE;
1121 // Update current move (this must be done after singular extension search)
1122 ss->currentMove = move;
1123 newDepth = depth - ONE_PLY + ext;
1125 // Step 12. Futility pruning (is omitted in PV nodes)
1127 && !captureOrPromotion
1131 && !move_is_castle(move))
1133 // Move count based pruning
1134 if ( moveCount >= futility_move_count(depth)
1135 && !(threatMove && connected_threat(pos, move, threatMove))
1136 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1139 lock_grab(&(sp->lock));
1144 // Value based pruning
1145 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1146 // but fixing this made program slightly weaker.
1147 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1148 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1149 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1151 if (futilityValueScaled < beta)
1155 lock_grab(&(sp->lock));
1156 if (futilityValueScaled > sp->bestValue)
1157 sp->bestValue = bestValue = futilityValueScaled;
1159 else if (futilityValueScaled > bestValue)
1160 bestValue = futilityValueScaled;
1165 // Prune moves with negative SEE at low depths
1166 if ( predictedDepth < 2 * ONE_PLY
1167 && bestValue > value_mated_in(PLY_MAX)
1168 && pos.see_sign(move) < 0)
1171 lock_grab(&(sp->lock));
1177 // Step 13. Make the move
1178 pos.do_move(move, st, ci, moveIsCheck);
1180 if (!SpNode && !captureOrPromotion)
1181 movesSearched[playedMoveCount++] = move;
1183 // Step extra. pv search (only in PV nodes)
1184 // The first move in list is the expected PV
1187 // Aspiration window is disabled in multi-pv case
1188 if (Root && MultiPV > 1)
1189 alpha = -VALUE_INFINITE;
1191 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1195 // Step 14. Reduced depth search
1196 // If the move fails high will be re-searched at full depth.
1197 bool doFullDepthSearch = true;
1199 if ( depth >= 3 * ONE_PLY
1200 && !captureOrPromotion
1202 && !move_is_castle(move)
1203 && ss->killers[0] != move
1204 && ss->killers[1] != move)
1206 ss->reduction = reduction<PvNode>(depth, moveCount);
1209 alpha = SpNode ? sp->alpha : alpha;
1210 Depth d = newDepth - ss->reduction;
1211 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1213 doFullDepthSearch = (value > alpha);
1215 ss->reduction = DEPTH_ZERO; // Restore original reduction
1218 // Step 15. Full depth search
1219 if (doFullDepthSearch)
1221 alpha = SpNode ? sp->alpha : alpha;
1222 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1224 // Step extra. pv search (only in PV nodes)
1225 // Search only for possible new PV nodes, if instead value >= beta then
1226 // parent node fails low with value <= alpha and tries another move.
1227 if (PvNode && value > alpha && (Root || value < beta))
1228 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1232 // Step 16. Undo move
1233 pos.undo_move(move);
1235 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1237 // Step 17. Check for new best move
1240 lock_grab(&(sp->lock));
1241 bestValue = sp->bestValue;
1245 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1250 sp->bestValue = value;
1252 if (!Root && value > alpha)
1254 if (PvNode && value < beta) // We want always alpha < beta
1262 sp->betaCutoff = true;
1264 if (value == value_mate_in(ply + 1))
1265 ss->mateKiller = move;
1267 ss->bestMove = move;
1270 sp->ss->bestMove = move;
1276 // Finished searching the move. If StopRequest is true, the search
1277 // was aborted because the user interrupted the search or because we
1278 // ran out of time. In this case, the return value of the search cannot
1279 // be trusted, and we break out of the loop without updating the best
1284 // Remember searched nodes counts for this move
1285 mp.rm->nodes += pos.nodes_searched() - nodes;
1287 // PV move or new best move ?
1288 if (isPvMove || value > alpha)
1291 ss->bestMove = move;
1292 mp.rm->pv_score = value;
1293 mp.rm->extract_pv_from_tt(pos);
1295 // We record how often the best move has been changed in each
1296 // iteration. This information is used for time management: When
1297 // the best move changes frequently, we allocate some more time.
1298 if (!isPvMove && MultiPV == 1)
1299 Rml.bestMoveChanges++;
1301 Rml.sort_multipv(moveCount);
1303 // Update alpha. In multi-pv we don't use aspiration window, so
1304 // set alpha equal to minimum score among the PV lines.
1306 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1307 else if (value > alpha)
1311 mp.rm->pv_score = -VALUE_INFINITE;
1315 // Step 18. Check for split
1318 && depth >= ThreadsMgr.min_split_depth()
1319 && ThreadsMgr.active_threads() > 1
1321 && ThreadsMgr.available_thread_exists(threadID)
1323 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1324 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1325 threatMove, mateThreat, moveCount, &mp, PvNode);
1328 // Step 19. Check for mate and stalemate
1329 // All legal moves have been searched and if there are
1330 // no legal moves, it must be mate or stalemate.
1331 // If one move was excluded return fail low score.
1332 if (!SpNode && !moveCount)
1333 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1335 // Step 20. Update tables
1336 // If the search is not aborted, update the transposition table,
1337 // history counters, and killer moves.
1338 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1340 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1341 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1342 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1344 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1346 // Update killers and history only for non capture moves that fails high
1347 if ( bestValue >= beta
1348 && !pos.move_is_capture_or_promotion(move))
1350 update_history(pos, move, depth, movesSearched, playedMoveCount);
1351 update_killers(move, ss->killers);
1357 // Here we have the lock still grabbed
1358 sp->slaves[threadID] = 0;
1359 sp->nodes += pos.nodes_searched();
1360 lock_release(&(sp->lock));
1363 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1368 // qsearch() is the quiescence search function, which is called by the main
1369 // search function when the remaining depth is zero (or, to be more precise,
1370 // less than ONE_PLY).
1372 template <NodeType PvNode>
1373 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1375 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1376 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1377 assert(PvNode || alpha == beta - 1);
1379 assert(ply > 0 && ply < PLY_MAX);
1380 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1384 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1385 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1388 Value oldAlpha = alpha;
1390 ss->bestMove = ss->currentMove = MOVE_NONE;
1392 // Check for an instant draw or maximum ply reached
1393 if (pos.is_draw() || ply >= PLY_MAX - 1)
1396 // Decide whether or not to include checks, this fixes also the type of
1397 // TT entry depth that we are going to use. Note that in qsearch we use
1398 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1399 isCheck = pos.is_check();
1400 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1402 // Transposition table lookup. At PV nodes, we don't use the TT for
1403 // pruning, but only for move ordering.
1404 tte = TT.retrieve(pos.get_key());
1405 ttMove = (tte ? tte->move() : MOVE_NONE);
1407 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1409 ss->bestMove = ttMove; // Can be MOVE_NONE
1410 return value_from_tt(tte->value(), ply);
1413 // Evaluate the position statically
1416 bestValue = futilityBase = -VALUE_INFINITE;
1417 ss->eval = evalMargin = VALUE_NONE;
1418 enoughMaterial = false;
1424 assert(tte->static_value() != VALUE_NONE);
1426 evalMargin = tte->static_value_margin();
1427 ss->eval = bestValue = tte->static_value();
1430 ss->eval = bestValue = evaluate(pos, evalMargin);
1432 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1434 // Stand pat. Return immediately if static value is at least beta
1435 if (bestValue >= beta)
1438 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1443 if (PvNode && bestValue > alpha)
1446 // Futility pruning parameters, not needed when in check
1447 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1448 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1451 // Initialize a MovePicker object for the current position, and prepare
1452 // to search the moves. Because the depth is <= 0 here, only captures,
1453 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1455 MovePicker mp(pos, ttMove, depth, H);
1458 // Loop through the moves until no moves remain or a beta cutoff occurs
1459 while ( alpha < beta
1460 && (move = mp.get_next_move()) != MOVE_NONE)
1462 assert(move_is_ok(move));
1464 moveIsCheck = pos.move_is_check(move, ci);
1472 && !move_is_promotion(move)
1473 && !pos.move_is_passed_pawn_push(move))
1475 futilityValue = futilityBase
1476 + pos.endgame_value_of_piece_on(move_to(move))
1477 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1479 if (futilityValue < alpha)
1481 if (futilityValue > bestValue)
1482 bestValue = futilityValue;
1486 // Prune moves with negative or equal SEE
1487 if ( futilityBase < beta
1488 && depth < DEPTH_ZERO
1489 && pos.see(move) <= 0)
1493 // Detect non-capture evasions that are candidate to be pruned
1494 evasionPrunable = isCheck
1495 && bestValue > value_mated_in(PLY_MAX)
1496 && !pos.move_is_capture(move)
1497 && !pos.can_castle(pos.side_to_move());
1499 // Don't search moves with negative SEE values
1501 && (!isCheck || evasionPrunable)
1503 && !move_is_promotion(move)
1504 && pos.see_sign(move) < 0)
1507 // Don't search useless checks
1512 && !pos.move_is_capture_or_promotion(move)
1513 && ss->eval + PawnValueMidgame / 4 < beta
1514 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1516 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1517 bestValue = ss->eval + PawnValueMidgame / 4;
1522 // Update current move
1523 ss->currentMove = move;
1525 // Make and search the move
1526 pos.do_move(move, st, ci, moveIsCheck);
1527 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1528 pos.undo_move(move);
1530 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1533 if (value > bestValue)
1539 ss->bestMove = move;
1544 // All legal moves have been searched. A special case: If we're in check
1545 // and no legal moves were found, it is checkmate.
1546 if (isCheck && bestValue == -VALUE_INFINITE)
1547 return value_mated_in(ply);
1549 // Update transposition table
1550 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1551 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1553 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1559 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1560 // bestValue is updated only when returning false because in that case move
1563 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1565 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1566 Square from, to, ksq, victimSq;
1569 Value futilityValue, bv = *bestValue;
1571 from = move_from(move);
1573 them = opposite_color(pos.side_to_move());
1574 ksq = pos.king_square(them);
1575 kingAtt = pos.attacks_from<KING>(ksq);
1576 pc = pos.piece_on(from);
1578 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1579 oldAtt = pos.attacks_from(pc, from, occ);
1580 newAtt = pos.attacks_from(pc, to, occ);
1582 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1583 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1585 if (!(b && (b & (b - 1))))
1588 // Rule 2. Queen contact check is very dangerous
1589 if ( type_of_piece(pc) == QUEEN
1590 && bit_is_set(kingAtt, to))
1593 // Rule 3. Creating new double threats with checks
1594 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1598 victimSq = pop_1st_bit(&b);
1599 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1601 // Note that here we generate illegal "double move"!
1602 if ( futilityValue >= beta
1603 && pos.see_sign(make_move(from, victimSq)) >= 0)
1606 if (futilityValue > bv)
1610 // Update bestValue only if check is not dangerous (because we will prune the move)
1616 // connected_moves() tests whether two moves are 'connected' in the sense
1617 // that the first move somehow made the second move possible (for instance
1618 // if the moving piece is the same in both moves). The first move is assumed
1619 // to be the move that was made to reach the current position, while the
1620 // second move is assumed to be a move from the current position.
1622 bool connected_moves(const Position& pos, Move m1, Move m2) {
1624 Square f1, t1, f2, t2;
1627 assert(m1 && move_is_ok(m1));
1628 assert(m2 && move_is_ok(m2));
1630 // Case 1: The moving piece is the same in both moves
1636 // Case 2: The destination square for m2 was vacated by m1
1642 // Case 3: Moving through the vacated square
1643 if ( piece_is_slider(pos.piece_on(f2))
1644 && bit_is_set(squares_between(f2, t2), f1))
1647 // Case 4: The destination square for m2 is defended by the moving piece in m1
1648 p = pos.piece_on(t1);
1649 if (bit_is_set(pos.attacks_from(p, t1), t2))
1652 // Case 5: Discovered check, checking piece is the piece moved in m1
1653 if ( piece_is_slider(p)
1654 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1655 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1657 // discovered_check_candidates() works also if the Position's side to
1658 // move is the opposite of the checking piece.
1659 Color them = opposite_color(pos.side_to_move());
1660 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1662 if (bit_is_set(dcCandidates, f2))
1669 // value_is_mate() checks if the given value is a mate one eventually
1670 // compensated for the ply.
1672 bool value_is_mate(Value value) {
1674 assert(abs(value) <= VALUE_INFINITE);
1676 return value <= value_mated_in(PLY_MAX)
1677 || value >= value_mate_in(PLY_MAX);
1681 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1682 // "plies to mate from the current ply". Non-mate scores are unchanged.
1683 // The function is called before storing a value to the transposition table.
1685 Value value_to_tt(Value v, int ply) {
1687 if (v >= value_mate_in(PLY_MAX))
1690 if (v <= value_mated_in(PLY_MAX))
1697 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1698 // the transposition table to a mate score corrected for the current ply.
1700 Value value_from_tt(Value v, int ply) {
1702 if (v >= value_mate_in(PLY_MAX))
1705 if (v <= value_mated_in(PLY_MAX))
1712 // extension() decides whether a move should be searched with normal depth,
1713 // or with extended depth. Certain classes of moves (checking moves, in
1714 // particular) are searched with bigger depth than ordinary moves and in
1715 // any case are marked as 'dangerous'. Note that also if a move is not
1716 // extended, as example because the corresponding UCI option is set to zero,
1717 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1718 template <NodeType PvNode>
1719 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1720 bool moveIsCheck, bool mateThreat, bool* dangerous) {
1722 assert(m != MOVE_NONE);
1724 Depth result = DEPTH_ZERO;
1725 *dangerous = moveIsCheck | mateThreat;
1729 if (moveIsCheck && pos.see_sign(m) >= 0)
1730 result += CheckExtension[PvNode];
1733 result += MateThreatExtension[PvNode];
1736 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1738 Color c = pos.side_to_move();
1739 if (relative_rank(c, move_to(m)) == RANK_7)
1741 result += PawnPushTo7thExtension[PvNode];
1744 if (pos.pawn_is_passed(c, move_to(m)))
1746 result += PassedPawnExtension[PvNode];
1751 if ( captureOrPromotion
1752 && pos.type_of_piece_on(move_to(m)) != PAWN
1753 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1754 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1755 && !move_is_promotion(m)
1758 result += PawnEndgameExtension[PvNode];
1763 && captureOrPromotion
1764 && pos.type_of_piece_on(move_to(m)) != PAWN
1765 && pos.see_sign(m) >= 0)
1767 result += ONE_PLY / 2;
1771 return Min(result, ONE_PLY);
1775 // connected_threat() tests whether it is safe to forward prune a move or if
1776 // is somehow connected to the threat move returned by null search.
1778 bool connected_threat(const Position& pos, Move m, Move threat) {
1780 assert(move_is_ok(m));
1781 assert(threat && move_is_ok(threat));
1782 assert(!pos.move_is_check(m));
1783 assert(!pos.move_is_capture_or_promotion(m));
1784 assert(!pos.move_is_passed_pawn_push(m));
1786 Square mfrom, mto, tfrom, tto;
1788 mfrom = move_from(m);
1790 tfrom = move_from(threat);
1791 tto = move_to(threat);
1793 // Case 1: Don't prune moves which move the threatened piece
1797 // Case 2: If the threatened piece has value less than or equal to the
1798 // value of the threatening piece, don't prune moves which defend it.
1799 if ( pos.move_is_capture(threat)
1800 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1801 || pos.type_of_piece_on(tfrom) == KING)
1802 && pos.move_attacks_square(m, tto))
1805 // Case 3: If the moving piece in the threatened move is a slider, don't
1806 // prune safe moves which block its ray.
1807 if ( piece_is_slider(pos.piece_on(tfrom))
1808 && bit_is_set(squares_between(tfrom, tto), mto)
1809 && pos.see_sign(m) >= 0)
1816 // ok_to_use_TT() returns true if a transposition table score
1817 // can be used at a given point in search.
1819 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1821 Value v = value_from_tt(tte->value(), ply);
1823 return ( tte->depth() >= depth
1824 || v >= Max(value_mate_in(PLY_MAX), beta)
1825 || v < Min(value_mated_in(PLY_MAX), beta))
1827 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1828 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1832 // refine_eval() returns the transposition table score if
1833 // possible otherwise falls back on static position evaluation.
1835 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1839 Value v = value_from_tt(tte->value(), ply);
1841 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1842 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1849 // update_history() registers a good move that produced a beta-cutoff
1850 // in history and marks as failures all the other moves of that ply.
1852 void update_history(const Position& pos, Move move, Depth depth,
1853 Move movesSearched[], int moveCount) {
1855 Value bonus = Value(int(depth) * int(depth));
1857 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1859 for (int i = 0; i < moveCount - 1; i++)
1861 m = movesSearched[i];
1865 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1870 // update_killers() add a good move that produced a beta-cutoff
1871 // among the killer moves of that ply.
1873 void update_killers(Move m, Move killers[]) {
1875 if (m != killers[0])
1877 killers[1] = killers[0];
1883 // update_gains() updates the gains table of a non-capture move given
1884 // the static position evaluation before and after the move.
1886 void update_gains(const Position& pos, Move m, Value before, Value after) {
1889 && before != VALUE_NONE
1890 && after != VALUE_NONE
1891 && pos.captured_piece_type() == PIECE_TYPE_NONE
1892 && !move_is_special(m))
1893 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1896 // current_search_time() returns the number of milliseconds which have passed
1897 // since the beginning of the current search.
1899 int current_search_time() {
1901 return get_system_time() - SearchStartTime;
1905 // value_to_uci() converts a value to a string suitable for use with the UCI
1906 // protocol specifications:
1908 // cp <x> The score from the engine's point of view in centipawns.
1909 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1910 // use negative values for y.
1912 std::string value_to_uci(Value v) {
1914 std::stringstream s;
1916 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1917 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1919 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2);
1925 // speed_to_uci() returns a string with time stats of current search suitable
1926 // to be sent to UCI gui.
1928 std::string speed_to_uci(int64_t nodes) {
1930 std::stringstream s;
1931 int t = current_search_time();
1933 s << " nodes " << nodes
1934 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1941 // poll() performs two different functions: It polls for user input, and it
1942 // looks at the time consumed so far and decides if it's time to abort the
1945 void poll(const Position& pos) {
1947 static int lastInfoTime;
1948 int t = current_search_time();
1951 if (input_available())
1953 // We are line oriented, don't read single chars
1954 std::string command;
1956 if (!std::getline(std::cin, command))
1959 if (command == "quit")
1961 // Quit the program as soon as possible
1963 QuitRequest = StopRequest = true;
1966 else if (command == "stop")
1968 // Stop calculating as soon as possible, but still send the "bestmove"
1969 // and possibly the "ponder" token when finishing the search.
1973 else if (command == "ponderhit")
1975 // The opponent has played the expected move. GUI sends "ponderhit" if
1976 // we were told to ponder on the same move the opponent has played. We
1977 // should continue searching but switching from pondering to normal search.
1980 if (StopOnPonderhit)
1985 // Print search information
1989 else if (lastInfoTime > t)
1990 // HACK: Must be a new search where we searched less than
1991 // NodesBetweenPolls nodes during the first second of search.
1994 else if (t - lastInfoTime >= 1000)
2001 if (dbg_show_hit_rate)
2002 dbg_print_hit_rate();
2004 // Send info on searched nodes as soon as we return to root
2005 SendSearchedNodes = true;
2008 // Should we stop the search?
2012 bool stillAtFirstMove = FirstRootMove
2013 && !AspirationFailLow
2014 && t > TimeMgr.available_time();
2016 bool noMoreTime = t > TimeMgr.maximum_time()
2017 || stillAtFirstMove;
2019 if ( (UseTimeManagement && noMoreTime)
2020 || (ExactMaxTime && t >= ExactMaxTime)
2021 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
2026 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2027 // while the program is pondering. The point is to work around a wrinkle in
2028 // the UCI protocol: When pondering, the engine is not allowed to give a
2029 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2030 // We simply wait here until one of these commands is sent, and return,
2031 // after which the bestmove and pondermove will be printed.
2033 void wait_for_stop_or_ponderhit() {
2035 std::string command;
2039 // Wait for a command from stdin
2040 if (!std::getline(std::cin, command))
2043 if (command == "quit")
2048 else if (command == "ponderhit" || command == "stop")
2054 // init_thread() is the function which is called when a new thread is
2055 // launched. It simply calls the idle_loop() function with the supplied
2056 // threadID. There are two versions of this function; one for POSIX
2057 // threads and one for Windows threads.
2059 #if !defined(_MSC_VER)
2061 void* init_thread(void* threadID) {
2063 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2069 DWORD WINAPI init_thread(LPVOID threadID) {
2071 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2078 /// The ThreadsManager class
2081 // read_uci_options() updates number of active threads and other internal
2082 // parameters according to the UCI options values. It is called before
2083 // to start a new search.
2085 void ThreadsManager::read_uci_options() {
2087 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2088 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2089 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2090 activeThreads = Options["Threads"].value<int>();
2094 // idle_loop() is where the threads are parked when they have no work to do.
2095 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2096 // object for which the current thread is the master.
2098 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2100 assert(threadID >= 0 && threadID < MAX_THREADS);
2103 bool allFinished = false;
2107 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2108 // master should exit as last one.
2109 if (allThreadsShouldExit)
2112 threads[threadID].state = THREAD_TERMINATED;
2116 // If we are not thinking, wait for a condition to be signaled
2117 // instead of wasting CPU time polling for work.
2118 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2119 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2121 assert(!sp || useSleepingThreads);
2122 assert(threadID != 0 || useSleepingThreads);
2124 if (threads[threadID].state == THREAD_INITIALIZING)
2125 threads[threadID].state = THREAD_AVAILABLE;
2127 // Grab the lock to avoid races with wake_sleeping_thread()
2128 lock_grab(&sleepLock[threadID]);
2130 // If we are master and all slaves have finished do not go to sleep
2131 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2132 allFinished = (i == activeThreads);
2134 if (allFinished || allThreadsShouldExit)
2136 lock_release(&sleepLock[threadID]);
2140 // Do sleep here after retesting sleep conditions
2141 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2142 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2144 lock_release(&sleepLock[threadID]);
2147 // If this thread has been assigned work, launch a search
2148 if (threads[threadID].state == THREAD_WORKISWAITING)
2150 assert(!allThreadsShouldExit);
2152 threads[threadID].state = THREAD_SEARCHING;
2154 // Copy SplitPoint position and search stack and call search()
2155 // with SplitPoint template parameter set to true.
2156 SearchStack ss[PLY_MAX_PLUS_2];
2157 SplitPoint* tsp = threads[threadID].splitPoint;
2158 Position pos(*tsp->pos, threadID);
2160 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2164 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2166 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2168 assert(threads[threadID].state == THREAD_SEARCHING);
2170 threads[threadID].state = THREAD_AVAILABLE;
2172 // Wake up master thread so to allow it to return from the idle loop in
2173 // case we are the last slave of the split point.
2174 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2175 wake_sleeping_thread(tsp->master);
2178 // If this thread is the master of a split point and all slaves have
2179 // finished their work at this split point, return from the idle loop.
2180 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2181 allFinished = (i == activeThreads);
2185 // Because sp->slaves[] is reset under lock protection,
2186 // be sure sp->lock has been released before to return.
2187 lock_grab(&(sp->lock));
2188 lock_release(&(sp->lock));
2190 // In helpful master concept a master can help only a sub-tree, and
2191 // because here is all finished is not possible master is booked.
2192 assert(threads[threadID].state == THREAD_AVAILABLE);
2194 threads[threadID].state = THREAD_SEARCHING;
2201 // init_threads() is called during startup. It launches all helper threads,
2202 // and initializes the split point stack and the global locks and condition
2205 void ThreadsManager::init_threads() {
2207 int i, arg[MAX_THREADS];
2210 // Initialize global locks
2213 for (i = 0; i < MAX_THREADS; i++)
2215 lock_init(&sleepLock[i]);
2216 cond_init(&sleepCond[i]);
2219 // Initialize splitPoints[] locks
2220 for (i = 0; i < MAX_THREADS; i++)
2221 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2222 lock_init(&(threads[i].splitPoints[j].lock));
2224 // Will be set just before program exits to properly end the threads
2225 allThreadsShouldExit = false;
2227 // Threads will be put all threads to sleep as soon as created
2230 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2231 threads[0].state = THREAD_SEARCHING;
2232 for (i = 1; i < MAX_THREADS; i++)
2233 threads[i].state = THREAD_INITIALIZING;
2235 // Launch the helper threads
2236 for (i = 1; i < MAX_THREADS; i++)
2240 #if !defined(_MSC_VER)
2241 pthread_t pthread[1];
2242 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2243 pthread_detach(pthread[0]);
2245 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2249 cout << "Failed to create thread number " << i << endl;
2253 // Wait until the thread has finished launching and is gone to sleep
2254 while (threads[i].state == THREAD_INITIALIZING) {}
2259 // exit_threads() is called when the program exits. It makes all the
2260 // helper threads exit cleanly.
2262 void ThreadsManager::exit_threads() {
2264 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2266 // Wake up all the threads and waits for termination
2267 for (int i = 1; i < MAX_THREADS; i++)
2269 wake_sleeping_thread(i);
2270 while (threads[i].state != THREAD_TERMINATED) {}
2273 // Now we can safely destroy the locks
2274 for (int i = 0; i < MAX_THREADS; i++)
2275 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2276 lock_destroy(&(threads[i].splitPoints[j].lock));
2278 lock_destroy(&mpLock);
2280 // Now we can safely destroy the wait conditions
2281 for (int i = 0; i < MAX_THREADS; i++)
2283 lock_destroy(&sleepLock[i]);
2284 cond_destroy(&sleepCond[i]);
2289 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2290 // the thread's currently active split point, or in some ancestor of
2291 // the current split point.
2293 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2295 assert(threadID >= 0 && threadID < activeThreads);
2297 SplitPoint* sp = threads[threadID].splitPoint;
2299 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2304 // thread_is_available() checks whether the thread with threadID "slave" is
2305 // available to help the thread with threadID "master" at a split point. An
2306 // obvious requirement is that "slave" must be idle. With more than two
2307 // threads, this is not by itself sufficient: If "slave" is the master of
2308 // some active split point, it is only available as a slave to the other
2309 // threads which are busy searching the split point at the top of "slave"'s
2310 // split point stack (the "helpful master concept" in YBWC terminology).
2312 bool ThreadsManager::thread_is_available(int slave, int master) const {
2314 assert(slave >= 0 && slave < activeThreads);
2315 assert(master >= 0 && master < activeThreads);
2316 assert(activeThreads > 1);
2318 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2321 // Make a local copy to be sure doesn't change under our feet
2322 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2324 // No active split points means that the thread is available as
2325 // a slave for any other thread.
2326 if (localActiveSplitPoints == 0 || activeThreads == 2)
2329 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2330 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2331 // could have been set to 0 by another thread leading to an out of bound access.
2332 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2339 // available_thread_exists() tries to find an idle thread which is available as
2340 // a slave for the thread with threadID "master".
2342 bool ThreadsManager::available_thread_exists(int master) const {
2344 assert(master >= 0 && master < activeThreads);
2345 assert(activeThreads > 1);
2347 for (int i = 0; i < activeThreads; i++)
2348 if (thread_is_available(i, master))
2355 // split() does the actual work of distributing the work at a node between
2356 // several available threads. If it does not succeed in splitting the
2357 // node (because no idle threads are available, or because we have no unused
2358 // split point objects), the function immediately returns. If splitting is
2359 // possible, a SplitPoint object is initialized with all the data that must be
2360 // copied to the helper threads and we tell our helper threads that they have
2361 // been assigned work. This will cause them to instantly leave their idle loops and
2362 // call search().When all threads have returned from search() then split() returns.
2364 template <bool Fake>
2365 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2366 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2367 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2368 assert(pos.is_ok());
2369 assert(ply > 0 && ply < PLY_MAX);
2370 assert(*bestValue >= -VALUE_INFINITE);
2371 assert(*bestValue <= *alpha);
2372 assert(*alpha < beta);
2373 assert(beta <= VALUE_INFINITE);
2374 assert(depth > DEPTH_ZERO);
2375 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2376 assert(activeThreads > 1);
2378 int i, master = pos.thread();
2379 Thread& masterThread = threads[master];
2383 // If no other thread is available to help us, or if we have too many
2384 // active split points, don't split.
2385 if ( !available_thread_exists(master)
2386 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2388 lock_release(&mpLock);
2392 // Pick the next available split point object from the split point stack
2393 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2395 // Initialize the split point object
2396 splitPoint.parent = masterThread.splitPoint;
2397 splitPoint.master = master;
2398 splitPoint.betaCutoff = false;
2399 splitPoint.ply = ply;
2400 splitPoint.depth = depth;
2401 splitPoint.threatMove = threatMove;
2402 splitPoint.mateThreat = mateThreat;
2403 splitPoint.alpha = *alpha;
2404 splitPoint.beta = beta;
2405 splitPoint.pvNode = pvNode;
2406 splitPoint.bestValue = *bestValue;
2408 splitPoint.moveCount = moveCount;
2409 splitPoint.pos = &pos;
2410 splitPoint.nodes = 0;
2412 for (i = 0; i < activeThreads; i++)
2413 splitPoint.slaves[i] = 0;
2415 masterThread.splitPoint = &splitPoint;
2417 // If we are here it means we are not available
2418 assert(masterThread.state != THREAD_AVAILABLE);
2420 int workersCnt = 1; // At least the master is included
2422 // Allocate available threads setting state to THREAD_BOOKED
2423 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2424 if (thread_is_available(i, master))
2426 threads[i].state = THREAD_BOOKED;
2427 threads[i].splitPoint = &splitPoint;
2428 splitPoint.slaves[i] = 1;
2432 assert(Fake || workersCnt > 1);
2434 // We can release the lock because slave threads are already booked and master is not available
2435 lock_release(&mpLock);
2437 // Tell the threads that they have work to do. This will make them leave
2439 for (i = 0; i < activeThreads; i++)
2440 if (i == master || splitPoint.slaves[i])
2442 assert(i == master || threads[i].state == THREAD_BOOKED);
2444 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2446 if (useSleepingThreads && i != master)
2447 wake_sleeping_thread(i);
2450 // Everything is set up. The master thread enters the idle loop, from
2451 // which it will instantly launch a search, because its state is
2452 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2453 // idle loop, which means that the main thread will return from the idle
2454 // loop when all threads have finished their work at this split point.
2455 idle_loop(master, &splitPoint);
2457 // We have returned from the idle loop, which means that all threads are
2458 // finished. Update alpha and bestValue, and return.
2461 *alpha = splitPoint.alpha;
2462 *bestValue = splitPoint.bestValue;
2463 masterThread.activeSplitPoints--;
2464 masterThread.splitPoint = splitPoint.parent;
2465 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2467 lock_release(&mpLock);
2471 // wake_sleeping_thread() wakes up the thread with the given threadID
2472 // when it is time to start a new search.
2474 void ThreadsManager::wake_sleeping_thread(int threadID) {
2476 lock_grab(&sleepLock[threadID]);
2477 cond_signal(&sleepCond[threadID]);
2478 lock_release(&sleepLock[threadID]);
2482 /// RootMove and RootMoveList method's definitions
2484 RootMove::RootMove() {
2487 pv_score = non_pv_score = -VALUE_INFINITE;
2491 RootMove& RootMove::operator=(const RootMove& rm) {
2493 const Move* src = rm.pv;
2496 // Avoid a costly full rm.pv[] copy
2497 do *dst++ = *src; while (*src++ != MOVE_NONE);
2500 pv_score = rm.pv_score;
2501 non_pv_score = rm.non_pv_score;
2505 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2506 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2507 // allow to always have a ponder move even when we fail high at root and also a
2508 // long PV to print that is important for position analysis.
2510 void RootMove::extract_pv_from_tt(Position& pos) {
2512 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2516 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2518 pos.do_move(pv[0], *st++);
2520 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2521 && tte->move() != MOVE_NONE
2522 && move_is_legal(pos, tte->move())
2524 && (!pos.is_draw() || ply < 2))
2526 pv[ply] = tte->move();
2527 pos.do_move(pv[ply++], *st++);
2529 pv[ply] = MOVE_NONE;
2531 do pos.undo_move(pv[--ply]); while (ply);
2534 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2535 // the PV back into the TT. This makes sure the old PV moves are searched
2536 // first, even if the old TT entries have been overwritten.
2538 void RootMove::insert_pv_in_tt(Position& pos) {
2540 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2543 Value v, m = VALUE_NONE;
2546 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2550 tte = TT.retrieve(k);
2552 // Don't overwrite existing correct entries
2553 if (!tte || tte->move() != pv[ply])
2555 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2556 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2558 pos.do_move(pv[ply], *st++);
2560 } while (pv[++ply] != MOVE_NONE);
2562 do pos.undo_move(pv[--ply]); while (ply);
2565 // pv_info_to_uci() returns a string with information on the current PV line
2566 // formatted according to UCI specification. It is called at each iteration
2567 // or after a new pv is found.
2569 std::string RootMove::pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvLine) {
2571 std::stringstream s, l;
2574 while (*m != MOVE_NONE)
2577 s << "info depth " << depth
2578 << " seldepth " << int(m - pv)
2579 << " multipv " << pvLine + 1
2580 << " score " << value_to_uci(pv_score)
2581 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2582 << speed_to_uci(pos.nodes_searched())
2583 << " pv " << l.str();
2589 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2591 MoveStack mlist[MOVES_MAX];
2595 bestMoveChanges = 0;
2597 // Generate all legal moves and add them to RootMoveList
2598 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2599 for (MoveStack* cur = mlist; cur != last; cur++)
2601 // If we have a searchMoves[] list then verify cur->move
2602 // is in the list before to add it.
2603 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2605 if (searchMoves[0] && *sm != cur->move)
2609 rm.pv[0] = cur->move;
2610 rm.pv[1] = MOVE_NONE;
2611 rm.pv_score = -VALUE_INFINITE;