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, Depth depth, Value alpha, Value beta, int pvLine = 0);
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], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
207 Depth PassedPawnExtension[2], 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 // If the TT move is at least SingularExtensionMargin better then the
213 // remaining ones we will extend it.
214 const Value SingularExtensionMargin = Value(0x20);
216 // Step 12. Futility pruning
218 // Futility margin for quiescence search
219 const Value FutilityMarginQS = Value(0x80);
221 // Futility lookup tables (initialized at startup) and their getter functions
222 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
223 int FutilityMoveCountArray[32]; // [depth]
225 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
226 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
228 // Step 14. Reduced search
230 // Reduction lookup tables (initialized at startup) and their getter functions
231 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
233 template <NodeType PV>
234 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
236 // Common adjustments
238 // Search depth at iteration 1
239 const Depth InitialDepth = ONE_PLY;
241 // Easy move margin. An easy move candidate must be at least this much
242 // better than the second best move.
243 const Value EasyMoveMargin = Value(0x200);
246 /// Namespace variables
251 // Pointer to root move list
257 // Time managment variables
258 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
259 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
260 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
265 std::ofstream LogFile;
267 // Multi-threads manager object
268 ThreadsManager ThreadsMgr;
270 // Node counters, used only by thread[0] but try to keep in different cache
271 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
272 bool SendSearchedNodes;
274 int NodesBetweenPolls = 30000;
281 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
283 template <NodeType PvNode, bool SpNode, bool Root>
284 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
286 template <NodeType PvNode>
287 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
289 template <NodeType PvNode>
290 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
292 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
293 : search<PvNode, false, false>(pos, ss, alpha, beta, depth, ply);
296 template <NodeType PvNode>
297 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
299 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
300 bool connected_moves(const Position& pos, Move m1, Move m2);
301 bool value_is_mate(Value value);
302 Value value_to_tt(Value v, int ply);
303 Value value_from_tt(Value v, int ply);
304 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
305 bool connected_threat(const Position& pos, Move m, Move threat);
306 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
307 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
308 void update_killers(Move m, Move killers[]);
309 void update_gains(const Position& pos, Move move, Value before, Value after);
311 int current_search_time();
312 std::string value_to_uci(Value v);
313 int nps(const Position& pos);
314 void poll(const Position& pos);
315 void wait_for_stop_or_ponderhit();
317 #if !defined(_MSC_VER)
318 void* init_thread(void* threadID);
320 DWORD WINAPI init_thread(LPVOID threadID);
324 // A dispatcher to choose among different move sources according to the type of node
325 template<bool SpNode, bool Root> struct MovePickerExt;
327 // In Root nodes use RootMoveList Rml as source. Score and sort the moves before to search them.
328 template<> struct MovePickerExt<false, true> : private MovePicker {
330 MovePickerExt(const Position& p, Move, Depth, const History& h, SearchStack* ss, Value beta)
331 : MovePicker(p, Rml[0].pv[0], ONE_PLY, h, ss, beta), firstCall(true) { // FIXME use depth
334 Value score = VALUE_ZERO;
336 // Score root moves using the standard way used in main search, the moves
337 // are scored according to the order in which are returned by MovePicker.
338 // This is the second order score that is used to compare the moves when
339 // the first order pv scores of both moves are equal.
340 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
341 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
342 if (rm->pv[0] == move)
344 rm->non_pv_score = score--;
352 Move get_next_move() {
359 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
361 int number_of_evasions() const { return (int)Rml.size(); }
363 RootMoveList::iterator rm;
367 // In SpNodes use split point's shared MovePicker as move source
368 template<> struct MovePickerExt<true, false> {
370 MovePickerExt(const Position&, Move, Depth, const History&, SearchStack* ss, Value)
373 Move get_next_move() { return mp->get_next_move(); }
374 int number_of_evasions() const { return mp->number_of_evasions(); }
376 RootMoveList::iterator rm; // Dummy, never used
380 // Normal case, create and use a MovePicker object as source
381 template<> struct MovePickerExt<false, false> : public MovePicker {
383 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
384 SearchStack* ss, Value beta) : MovePicker(p, ttm, d, h, ss, beta) {}
386 RootMoveList::iterator rm; // Dummy, never used
396 /// init_threads(), exit_threads() and nodes_searched() are helpers to
397 /// give accessibility to some TM methods from outside of current file.
399 void init_threads() { ThreadsMgr.init_threads(); }
400 void exit_threads() { ThreadsMgr.exit_threads(); }
403 /// init_search() is called during startup. It initializes various lookup tables
407 int d; // depth (ONE_PLY == 2)
408 int hd; // half depth (ONE_PLY == 1)
411 // Init reductions array
412 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
414 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
415 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
416 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
417 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
420 // Init futility margins array
421 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
422 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
424 // Init futility move count array
425 for (d = 0; d < 32; d++)
426 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
430 /// perft() is our utility to verify move generation is bug free. All the legal
431 /// moves up to given depth are generated and counted and the sum returned.
433 int64_t perft(Position& pos, Depth depth)
435 MoveStack mlist[MOVES_MAX];
440 // Generate all legal moves
441 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
443 // If we are at the last ply we don't need to do and undo
444 // the moves, just to count them.
445 if (depth <= ONE_PLY)
446 return int(last - mlist);
448 // Loop through all legal moves
450 for (MoveStack* cur = mlist; cur != last; cur++)
453 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
454 sum += perft(pos, depth - ONE_PLY);
461 /// think() is the external interface to Stockfish's search, and is called when
462 /// the program receives the UCI 'go' command. It initializes various
463 /// search-related global variables, and calls id_loop(). It returns false
464 /// when a quit command is received during the search.
466 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
467 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
469 // Initialize global search variables
470 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
472 SearchStartTime = get_system_time();
473 ExactMaxTime = maxTime;
476 InfiniteSearch = infinite;
478 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
480 // Look for a book move, only during games, not tests
481 if (UseTimeManagement && Options["OwnBook"].value<bool>())
483 if (Options["Book File"].value<std::string>() != OpeningBook.name())
484 OpeningBook.open(Options["Book File"].value<std::string>());
486 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
487 if (bookMove != MOVE_NONE)
490 wait_for_stop_or_ponderhit();
492 cout << "bestmove " << bookMove << endl;
497 // Read UCI option values
498 TT.set_size(Options["Hash"].value<int>());
499 if (Options["Clear Hash"].value<bool>())
501 Options["Clear Hash"].set_value("false");
505 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
506 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
507 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
508 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
509 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
510 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
511 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
512 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
513 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
514 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
515 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
516 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
517 MultiPV = Options["MultiPV"].value<int>();
518 UseLogFile = Options["Use Search Log"].value<bool>();
520 read_evaluation_uci_options(pos.side_to_move());
522 // Set the number of active threads
523 ThreadsMgr.read_uci_options();
524 init_eval(ThreadsMgr.active_threads());
526 // Wake up needed threads
527 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
528 ThreadsMgr.wake_sleeping_thread(i);
531 int myTime = time[pos.side_to_move()];
532 int myIncrement = increment[pos.side_to_move()];
533 if (UseTimeManagement)
534 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
536 // Set best NodesBetweenPolls interval to avoid lagging under
537 // heavy time pressure.
539 NodesBetweenPolls = Min(MaxNodes, 30000);
540 else if (myTime && myTime < 1000)
541 NodesBetweenPolls = 1000;
542 else if (myTime && myTime < 5000)
543 NodesBetweenPolls = 5000;
545 NodesBetweenPolls = 30000;
547 // Write search information to log file
550 std::string name = Options["Search Log Filename"].value<std::string>();
551 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
553 LogFile << "Searching: " << pos.to_fen()
554 << "\ninfinite: " << infinite
555 << " ponder: " << ponder
556 << " time: " << myTime
557 << " increment: " << myIncrement
558 << " moves to go: " << movesToGo << endl;
561 // We're ready to start thinking. Call the iterative deepening loop function
562 Move ponderMove = MOVE_NONE;
563 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
565 // Print final search statistics
566 cout << "info nodes " << pos.nodes_searched()
567 << " nps " << nps(pos)
568 << " time " << current_search_time() << endl;
572 LogFile << "\nNodes: " << pos.nodes_searched()
573 << "\nNodes/second: " << nps(pos)
574 << "\nBest move: " << move_to_san(pos, bestMove);
577 pos.do_move(bestMove, st);
578 LogFile << "\nPonder move: "
579 << move_to_san(pos, ponderMove) // Works also with MOVE_NONE
582 // Return from think() with unchanged position
583 pos.undo_move(bestMove);
588 // This makes all the threads to go to sleep
589 ThreadsMgr.set_active_threads(1);
591 // If we are pondering or in infinite search, we shouldn't print the
592 // best move before we are told to do so.
593 if (!StopRequest && (Pondering || InfiniteSearch))
594 wait_for_stop_or_ponderhit();
596 // Could be both MOVE_NONE when searching on a stalemate position
597 cout << "bestmove " << bestMove << " ponder " << ponderMove << endl;
605 // id_loop() is the main iterative deepening loop. It calls search()
606 // repeatedly with increasing depth until the allocated thinking time has
607 // been consumed, the user stops the search, or the maximum search depth is
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 iteration, researchCountFL, researchCountFH, aspirationDelta;
616 Value value, alpha, beta;
620 // Moves to search are verified, scored and sorted
621 Rml.init(pos, searchMoves);
623 // Initialize FIXME move before Rml.init()
626 memset(ss, 0, PLY_MAX_PLUS_2 * sizeof(SearchStack));
627 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
628 EasyMove = MOVE_NONE;
632 // Handle special case of searching on a mate/stale position
635 cout << "info depth " << iteration << " score "
636 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
642 // Send initial scoring (iteration 1)
643 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
644 << "info depth " << iteration
645 << "\n" << Rml[0].pv_info_to_uci(pos, ONE_PLY, alpha, beta) << endl;
647 // Is one move significantly better than others after initial scoring ?
649 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin)
650 EasyMove = Rml[0].pv[0];
652 // Iterative deepening loop
653 while (++iteration <= PLY_MAX && (!MaxDepth || iteration <= MaxDepth) && !StopRequest)
655 cout << "info depth " << iteration << endl;
657 Rml.bestMoveChanges = researchCountFL = researchCountFH = 0;
658 depth = (iteration - 2) * ONE_PLY + InitialDepth;
660 // Calculate dynamic aspiration window based on previous iterations
661 if (MultiPV == 1 && iteration >= 6 && abs(bestValues[iteration - 1]) < VALUE_KNOWN_WIN)
663 int prevDelta1 = bestValues[iteration - 1] - bestValues[iteration - 2];
664 int prevDelta2 = bestValues[iteration - 2] - bestValues[iteration - 3];
666 aspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
667 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
669 alpha = Max(bestValues[iteration - 1] - aspirationDelta, -VALUE_INFINITE);
670 beta = Min(bestValues[iteration - 1] + aspirationDelta, VALUE_INFINITE);
673 // We start with small aspiration window and in case of fail high/low, we
674 // research with bigger window until we are not failing high/low anymore.
677 // Search to the current depth
678 value = search<PV, false, true>(pos, ss, alpha, beta, depth, 0);
680 // Sort root moves and write PV lines to transposition table, in case
681 // the relevant entries have been overwritten during the search.
683 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
684 Rml[i].insert_pv_in_tt(pos);
686 // Value cannot be trusted. Break out immediately!
688 break; // FIXME move to 'while' condition
690 assert(value >= alpha);
692 bestMoveChanges[iteration] = Rml.bestMoveChanges; // FIXME move outside fail high/low loop
694 // In case of failing high/low increase aspiration window and research,
695 // otherwise exit the fail high/low loop.
698 beta = Min(beta + aspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
701 else if (value <= alpha)
703 AspirationFailLow = true;
704 StopOnPonderhit = false;
706 alpha = Max(alpha - aspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
713 //Save info about search result
714 bestValues[iteration] = value;
716 // Drop the easy move if differs from the new best move
717 if (Rml[0].pv[0] != EasyMove)
718 EasyMove = MOVE_NONE;
720 if (UseTimeManagement && !StopRequest)
723 bool noMoreTime = false;
725 // Stop search early if there is only a single legal move,
726 // we search up to Iteration 6 anyway to get a proper score.
727 if (iteration >= 6 && Rml.size() == 1)
730 // Stop search early when the last two iterations returned a mate score
732 && abs(bestValues[iteration]) >= abs(VALUE_MATE) - 100
733 && abs(bestValues[iteration-1]) >= abs(VALUE_MATE) - 100)
736 // Stop search early if one move seems to be much better than the others
738 && EasyMove == Rml[0].pv[0]
739 && ( ( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
740 && current_search_time() > TimeMgr.available_time() / 16)
741 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
742 && current_search_time() > TimeMgr.available_time() / 32)))
745 // Add some extra time if the best move has changed during the last two iterations
746 if (iteration > 5 && iteration <= 50)
747 TimeMgr.pv_instability(bestMoveChanges[iteration], bestMoveChanges[iteration-1]);
749 // Stop search if most of MaxSearchTime is consumed at the end of the
750 // iteration. We probably don't have enough time to search the first
751 // move at the next iteration anyway.
752 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
758 StopOnPonderhit = true;
765 *ponderMove = Rml[0].pv[1];
770 // search<>() is the main search function for both PV and non-PV nodes and for
771 // normal and SplitPoint nodes. When called just after a split point the search
772 // is simpler because we have already probed the hash table, done a null move
773 // search, and searched the first move before splitting, we don't have to repeat
774 // all this work again. We also don't need to store anything to the hash table
775 // here: This is taken care of after we return from the split point.
777 template <NodeType PvNode, bool SpNode, bool Root>
778 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
780 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
781 assert(beta > alpha && beta <= VALUE_INFINITE);
782 assert(PvNode || alpha == beta - 1);
783 assert((Root || ply > 0) && ply < PLY_MAX);
784 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
786 Move movesSearched[MOVES_MAX];
791 Move ttMove, move, excludedMove, threatMove;
794 Value bestValue, value, oldAlpha;
795 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
796 bool isPvMove, isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
797 bool mateThreat = false;
799 int threadID = pos.thread();
800 SplitPoint* sp = NULL;
802 refinedValue = bestValue = value = -VALUE_INFINITE;
804 isCheck = pos.is_check();
810 ttMove = excludedMove = MOVE_NONE;
811 threatMove = sp->threatMove;
812 mateThreat = sp->mateThreat;
813 goto split_point_start;
818 // Step 1. Initialize node and poll. Polling can abort search
819 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
820 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
822 if (!Root) // FIXME remove
824 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
830 // Step 2. Check for aborted search and immediate draw
832 || ThreadsMgr.cutoff_at_splitpoint(threadID)
834 || ply >= PLY_MAX - 1)
837 // Step 3. Mate distance pruning
838 alpha = Max(value_mated_in(ply), alpha);
839 beta = Min(value_mate_in(ply+1), beta);
844 // Step 4. Transposition table lookup
846 // We don't want the score of a partial search to overwrite a previous full search
847 // TT value, so we use a different position key in case of an excluded move exists.
848 excludedMove = ss->excludedMove;
849 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
851 tte = TT.retrieve(posKey);
852 ttMove = tte ? tte->move() : MOVE_NONE;
854 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
855 // This is to avoid problems in the following areas:
857 // * Repetition draw detection
858 // * Fifty move rule detection
859 // * Searching for a mate
860 // * Printing of full PV line
861 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
864 ss->bestMove = ttMove; // Can be MOVE_NONE
865 return value_from_tt(tte->value(), ply);
868 // Step 5. Evaluate the position statically and
869 // update gain statistics of parent move.
871 ss->eval = ss->evalMargin = VALUE_NONE;
874 assert(tte->static_value() != VALUE_NONE);
876 ss->eval = tte->static_value();
877 ss->evalMargin = tte->static_value_margin();
878 refinedValue = refine_eval(tte, ss->eval, ply);
882 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
883 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
886 // Save gain for the parent non-capture move
888 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
890 // Step 6. Razoring (is omitted in PV nodes)
892 && depth < RazorDepth
894 && refinedValue < beta - razor_margin(depth)
895 && ttMove == MOVE_NONE
896 && !value_is_mate(beta)
897 && !pos.has_pawn_on_7th(pos.side_to_move()))
899 Value rbeta = beta - razor_margin(depth);
900 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
902 // Logically we should return (v + razor_margin(depth)), but
903 // surprisingly this did slightly weaker in tests.
907 // Step 7. Static null move pruning (is omitted in PV nodes)
908 // We're betting that the opponent doesn't have a move that will reduce
909 // the score by more than futility_margin(depth) if we do a null move.
912 && depth < RazorDepth
914 && refinedValue >= beta + futility_margin(depth, 0)
915 && !value_is_mate(beta)
916 && pos.non_pawn_material(pos.side_to_move()))
917 return refinedValue - futility_margin(depth, 0);
919 // Step 8. Null move search with verification search (is omitted in PV nodes)
924 && refinedValue >= beta
925 && !value_is_mate(beta)
926 && pos.non_pawn_material(pos.side_to_move()))
928 ss->currentMove = MOVE_NULL;
930 // Null move dynamic reduction based on depth
931 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
933 // Null move dynamic reduction based on value
934 if (refinedValue - beta > PawnValueMidgame)
937 pos.do_null_move(st);
938 (ss+1)->skipNullMove = true;
939 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
940 (ss+1)->skipNullMove = false;
941 pos.undo_null_move();
943 if (nullValue >= beta)
945 // Do not return unproven mate scores
946 if (nullValue >= value_mate_in(PLY_MAX))
949 if (depth < 6 * ONE_PLY)
952 // Do verification search at high depths
953 ss->skipNullMove = true;
954 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
955 ss->skipNullMove = false;
962 // The null move failed low, which means that we may be faced with
963 // some kind of threat. If the previous move was reduced, check if
964 // the move that refuted the null move was somehow connected to the
965 // move which was reduced. If a connection is found, return a fail
966 // low score (which will cause the reduced move to fail high in the
967 // parent node, which will trigger a re-search with full depth).
968 if (nullValue == value_mated_in(ply + 2))
971 threatMove = (ss+1)->bestMove;
972 if ( depth < ThreatDepth
974 && threatMove != MOVE_NONE
975 && connected_moves(pos, (ss-1)->currentMove, threatMove))
980 // Step 9. Internal iterative deepening
982 && depth >= IIDDepth[PvNode]
983 && ttMove == MOVE_NONE
984 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
986 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
988 ss->skipNullMove = true;
989 search<PvNode>(pos, ss, alpha, beta, d, ply);
990 ss->skipNullMove = false;
992 ttMove = ss->bestMove;
993 tte = TT.retrieve(posKey);
996 // Expensive mate threat detection (only for PV nodes)
997 if (PvNode && !Root) // FIXME
998 mateThreat = pos.has_mate_threat();
1000 split_point_start: // At split points actual search starts from here
1002 // Initialize a MovePicker object for the current position
1003 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1005 ss->bestMove = MOVE_NONE;
1006 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1007 futilityBase = ss->eval + ss->evalMargin;
1008 singularExtensionNode = !Root
1010 && depth >= SingularExtensionDepth[PvNode]
1013 && !excludedMove // Do not allow recursive singular extension search
1014 && (tte->type() & VALUE_TYPE_LOWER)
1015 && tte->depth() >= depth - 3 * ONE_PLY;
1018 lock_grab(&(sp->lock));
1019 bestValue = sp->bestValue;
1022 // Step 10. Loop through moves
1023 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1024 while ( bestValue < beta
1025 && (move = mp.get_next_move()) != MOVE_NONE
1026 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1028 assert(move_is_ok(move));
1032 moveCount = ++sp->moveCount;
1033 lock_release(&(sp->lock));
1035 else if (move == excludedMove)
1038 movesSearched[moveCount++] = move;
1042 // This is used by time management
1043 FirstRootMove = (moveCount == 1);
1045 // Save the current node count before the move is searched
1046 nodes = pos.nodes_searched();
1048 // If it's time to send nodes info, do it here where we have the
1049 // correct accumulated node counts searched by each thread.
1050 if (SendSearchedNodes)
1052 SendSearchedNodes = false;
1053 cout << "info nodes " << nodes
1054 << " nps " << nps(pos)
1055 << " time " << current_search_time() << endl;
1058 if (current_search_time() >= 1000)
1059 cout << "info currmove " << move
1060 << " currmovenumber " << moveCount << endl;
1063 isPvMove = (PvNode && moveCount <= (Root ? MultiPV : 1));
1064 moveIsCheck = pos.move_is_check(move, ci);
1065 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1067 // Step 11. Decide the new search depth
1068 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1070 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1071 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1072 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1073 // lower then ttValue minus a margin then we extend ttMove.
1074 if ( singularExtensionNode
1075 && move == tte->move()
1078 Value ttValue = value_from_tt(tte->value(), ply);
1080 if (abs(ttValue) < VALUE_KNOWN_WIN)
1082 Value b = ttValue - SingularExtensionMargin;
1083 ss->excludedMove = move;
1084 ss->skipNullMove = true;
1085 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1086 ss->skipNullMove = false;
1087 ss->excludedMove = MOVE_NONE;
1088 ss->bestMove = MOVE_NONE;
1094 // Update current move (this must be done after singular extension search)
1095 ss->currentMove = move;
1096 newDepth = depth - (!Root ? ONE_PLY : DEPTH_ZERO) + ext;
1098 // Step 12. Futility pruning (is omitted in PV nodes)
1100 && !captureOrPromotion
1104 && !move_is_castle(move))
1106 // Move count based pruning
1107 if ( moveCount >= futility_move_count(depth)
1108 && !(threatMove && connected_threat(pos, move, threatMove))
1109 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1112 lock_grab(&(sp->lock));
1117 // Value based pruning
1118 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1119 // but fixing this made program slightly weaker.
1120 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1121 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1122 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1124 if (futilityValueScaled < beta)
1128 lock_grab(&(sp->lock));
1129 if (futilityValueScaled > sp->bestValue)
1130 sp->bestValue = bestValue = futilityValueScaled;
1132 else if (futilityValueScaled > bestValue)
1133 bestValue = futilityValueScaled;
1138 // Prune moves with negative SEE at low depths
1139 if ( predictedDepth < 2 * ONE_PLY
1140 && bestValue > value_mated_in(PLY_MAX)
1141 && pos.see_sign(move) < 0)
1144 lock_grab(&(sp->lock));
1150 // Step 13. Make the move
1151 pos.do_move(move, st, ci, moveIsCheck);
1153 // Step extra. pv search (only in PV nodes)
1154 // The first move in list is the expected PV
1157 // Aspiration window is disabled in multi-pv case
1158 if (Root && MultiPV > 1)
1159 alpha = -VALUE_INFINITE;
1161 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1165 // Step 14. Reduced depth search
1166 // If the move fails high will be re-searched at full depth.
1167 bool doFullDepthSearch = true;
1169 if ( depth >= 3 * ONE_PLY
1170 && !captureOrPromotion
1172 && !move_is_castle(move)
1173 && ss->killers[0] != move
1174 && ss->killers[1] != move)
1176 ss->reduction = Root ? reduction<PvNode>(depth, moveCount - MultiPV + 1)
1177 : reduction<PvNode>(depth, moveCount);
1180 alpha = SpNode ? sp->alpha : alpha;
1181 Depth d = newDepth - ss->reduction;
1182 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1184 doFullDepthSearch = (value > alpha);
1186 ss->reduction = DEPTH_ZERO; // Restore original reduction
1189 // Step 15. Full depth search
1190 if (doFullDepthSearch)
1192 alpha = SpNode ? sp->alpha : alpha;
1193 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1195 // Step extra. pv search (only in PV nodes)
1196 // Search only for possible new PV nodes, if instead value >= beta then
1197 // parent node fails low with value <= alpha and tries another move.
1198 if (PvNode && value > alpha && (Root || value < beta))
1199 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1203 // Step 16. Undo move
1204 pos.undo_move(move);
1206 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1208 // Step 17. Check for new best move
1211 lock_grab(&(sp->lock));
1212 bestValue = sp->bestValue;
1216 if (!Root && value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1221 sp->bestValue = value;
1225 if (PvNode && value < beta) // We want always alpha < beta
1233 sp->betaCutoff = true;
1235 if (value == value_mate_in(ply + 1))
1236 ss->mateKiller = move;
1238 ss->bestMove = move;
1241 sp->parentSstack->bestMove = move;
1247 // To avoid to exit with bestValue == -VALUE_INFINITE
1248 if (value > bestValue)
1251 // Finished searching the move. If StopRequest is true, the search
1252 // was aborted because the user interrupted the search or because we
1253 // ran out of time. In this case, the return value of the search cannot
1254 // be trusted, and we break out of the loop without updating the best
1259 // Remember searched nodes counts for this move
1260 mp.rm->nodes += pos.nodes_searched() - nodes;
1262 // Step 17. Check for new best move
1263 if (!isPvMove && value <= alpha)
1264 mp.rm->pv_score = -VALUE_INFINITE;
1267 // PV move or new best move!
1270 ss->bestMove = move;
1271 mp.rm->pv_score = value;
1272 mp.rm->extract_pv_from_tt(pos);
1274 // We record how often the best move has been changed in each
1275 // iteration. This information is used for time managment: When
1276 // the best move changes frequently, we allocate some more time.
1277 if (!isPvMove && MultiPV == 1)
1278 Rml.bestMoveChanges++;
1280 // Inform GUI that PV has changed, in case of multi-pv UCI protocol
1281 // requires we send all the PV lines properly sorted.
1282 Rml.sort_multipv(moveCount);
1284 for (int j = 0; j < Min(MultiPV, (int)Rml.size()); j++)
1285 cout << Rml[j].pv_info_to_uci(pos, depth, alpha, beta, j) << endl;
1287 // Update alpha. In multi-pv we don't use aspiration window, so
1288 // set alpha equal to minimum score among the PV lines.
1290 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1291 else if (value > alpha)
1294 } // PV move or new best move
1297 // Step 18. Check for split
1300 && depth >= ThreadsMgr.min_split_depth()
1301 && ThreadsMgr.active_threads() > 1
1303 && ThreadsMgr.available_thread_exists(threadID)
1305 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1306 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1307 threatMove, mateThreat, moveCount, (MovePicker*)&mp, PvNode);
1310 // Step 19. Check for mate and stalemate
1311 // All legal moves have been searched and if there are
1312 // no legal moves, it must be mate or stalemate.
1313 // If one move was excluded return fail low score.
1314 if (!SpNode && !moveCount)
1315 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1317 // Step 20. Update tables
1318 // If the search is not aborted, update the transposition table,
1319 // history counters, and killer moves.
1320 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1322 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1323 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1324 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1326 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1328 // Update killers and history only for non capture moves that fails high
1329 if ( bestValue >= beta
1330 && !pos.move_is_capture_or_promotion(move))
1332 update_history(pos, move, depth, movesSearched, moveCount);
1333 update_killers(move, ss->killers);
1339 // Here we have the lock still grabbed
1340 sp->slaves[threadID] = 0;
1341 sp->nodes += pos.nodes_searched();
1342 lock_release(&(sp->lock));
1345 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1350 // qsearch() is the quiescence search function, which is called by the main
1351 // search function when the remaining depth is zero (or, to be more precise,
1352 // less than ONE_PLY).
1354 template <NodeType PvNode>
1355 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1357 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1358 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1359 assert(PvNode || alpha == beta - 1);
1361 assert(ply > 0 && ply < PLY_MAX);
1362 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1366 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1367 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1370 Value oldAlpha = alpha;
1372 ss->bestMove = ss->currentMove = MOVE_NONE;
1374 // Check for an instant draw or maximum ply reached
1375 if (pos.is_draw() || ply >= PLY_MAX - 1)
1378 // Decide whether or not to include checks, this fixes also the type of
1379 // TT entry depth that we are going to use. Note that in qsearch we use
1380 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1381 isCheck = pos.is_check();
1382 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1384 // Transposition table lookup. At PV nodes, we don't use the TT for
1385 // pruning, but only for move ordering.
1386 tte = TT.retrieve(pos.get_key());
1387 ttMove = (tte ? tte->move() : MOVE_NONE);
1389 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1391 ss->bestMove = ttMove; // Can be MOVE_NONE
1392 return value_from_tt(tte->value(), ply);
1395 // Evaluate the position statically
1398 bestValue = futilityBase = -VALUE_INFINITE;
1399 ss->eval = evalMargin = VALUE_NONE;
1400 enoughMaterial = false;
1406 assert(tte->static_value() != VALUE_NONE);
1408 evalMargin = tte->static_value_margin();
1409 ss->eval = bestValue = tte->static_value();
1412 ss->eval = bestValue = evaluate(pos, evalMargin);
1414 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1416 // Stand pat. Return immediately if static value is at least beta
1417 if (bestValue >= beta)
1420 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1425 if (PvNode && bestValue > alpha)
1428 // Futility pruning parameters, not needed when in check
1429 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1430 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1433 // Initialize a MovePicker object for the current position, and prepare
1434 // to search the moves. Because the depth is <= 0 here, only captures,
1435 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1437 MovePicker mp(pos, ttMove, depth, H);
1440 // Loop through the moves until no moves remain or a beta cutoff occurs
1441 while ( alpha < beta
1442 && (move = mp.get_next_move()) != MOVE_NONE)
1444 assert(move_is_ok(move));
1446 moveIsCheck = pos.move_is_check(move, ci);
1454 && !move_is_promotion(move)
1455 && !pos.move_is_passed_pawn_push(move))
1457 futilityValue = futilityBase
1458 + pos.endgame_value_of_piece_on(move_to(move))
1459 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1461 if (futilityValue < alpha)
1463 if (futilityValue > bestValue)
1464 bestValue = futilityValue;
1469 // Detect non-capture evasions that are candidate to be pruned
1470 evasionPrunable = isCheck
1471 && bestValue > value_mated_in(PLY_MAX)
1472 && !pos.move_is_capture(move)
1473 && !pos.can_castle(pos.side_to_move());
1475 // Don't search moves with negative SEE values
1477 && (!isCheck || evasionPrunable)
1479 && !move_is_promotion(move)
1480 && pos.see_sign(move) < 0)
1483 // Don't search useless checks
1488 && !pos.move_is_capture_or_promotion(move)
1489 && ss->eval + PawnValueMidgame / 4 < beta
1490 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1492 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1493 bestValue = ss->eval + PawnValueMidgame / 4;
1498 // Update current move
1499 ss->currentMove = move;
1501 // Make and search the move
1502 pos.do_move(move, st, ci, moveIsCheck);
1503 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1504 pos.undo_move(move);
1506 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1509 if (value > bestValue)
1515 ss->bestMove = move;
1520 // All legal moves have been searched. A special case: If we're in check
1521 // and no legal moves were found, it is checkmate.
1522 if (isCheck && bestValue == -VALUE_INFINITE)
1523 return value_mated_in(ply);
1525 // Update transposition table
1526 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1527 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1529 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1535 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1536 // bestValue is updated only when returning false because in that case move
1539 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1541 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1542 Square from, to, ksq, victimSq;
1545 Value futilityValue, bv = *bestValue;
1547 from = move_from(move);
1549 them = opposite_color(pos.side_to_move());
1550 ksq = pos.king_square(them);
1551 kingAtt = pos.attacks_from<KING>(ksq);
1552 pc = pos.piece_on(from);
1554 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1555 oldAtt = pos.attacks_from(pc, from, occ);
1556 newAtt = pos.attacks_from(pc, to, occ);
1558 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1559 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1561 if (!(b && (b & (b - 1))))
1564 // Rule 2. Queen contact check is very dangerous
1565 if ( type_of_piece(pc) == QUEEN
1566 && bit_is_set(kingAtt, to))
1569 // Rule 3. Creating new double threats with checks
1570 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1574 victimSq = pop_1st_bit(&b);
1575 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1577 // Note that here we generate illegal "double move"!
1578 if ( futilityValue >= beta
1579 && pos.see_sign(make_move(from, victimSq)) >= 0)
1582 if (futilityValue > bv)
1586 // Update bestValue only if check is not dangerous (because we will prune the move)
1592 // connected_moves() tests whether two moves are 'connected' in the sense
1593 // that the first move somehow made the second move possible (for instance
1594 // if the moving piece is the same in both moves). The first move is assumed
1595 // to be the move that was made to reach the current position, while the
1596 // second move is assumed to be a move from the current position.
1598 bool connected_moves(const Position& pos, Move m1, Move m2) {
1600 Square f1, t1, f2, t2;
1603 assert(m1 && move_is_ok(m1));
1604 assert(m2 && move_is_ok(m2));
1606 // Case 1: The moving piece is the same in both moves
1612 // Case 2: The destination square for m2 was vacated by m1
1618 // Case 3: Moving through the vacated square
1619 if ( piece_is_slider(pos.piece_on(f2))
1620 && bit_is_set(squares_between(f2, t2), f1))
1623 // Case 4: The destination square for m2 is defended by the moving piece in m1
1624 p = pos.piece_on(t1);
1625 if (bit_is_set(pos.attacks_from(p, t1), t2))
1628 // Case 5: Discovered check, checking piece is the piece moved in m1
1629 if ( piece_is_slider(p)
1630 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1631 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1633 // discovered_check_candidates() works also if the Position's side to
1634 // move is the opposite of the checking piece.
1635 Color them = opposite_color(pos.side_to_move());
1636 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1638 if (bit_is_set(dcCandidates, f2))
1645 // value_is_mate() checks if the given value is a mate one eventually
1646 // compensated for the ply.
1648 bool value_is_mate(Value value) {
1650 assert(abs(value) <= VALUE_INFINITE);
1652 return value <= value_mated_in(PLY_MAX)
1653 || value >= value_mate_in(PLY_MAX);
1657 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1658 // "plies to mate from the current ply". Non-mate scores are unchanged.
1659 // The function is called before storing a value to the transposition table.
1661 Value value_to_tt(Value v, int ply) {
1663 if (v >= value_mate_in(PLY_MAX))
1666 if (v <= value_mated_in(PLY_MAX))
1673 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1674 // the transposition table to a mate score corrected for the current ply.
1676 Value value_from_tt(Value v, int ply) {
1678 if (v >= value_mate_in(PLY_MAX))
1681 if (v <= value_mated_in(PLY_MAX))
1688 // extension() decides whether a move should be searched with normal depth,
1689 // or with extended depth. Certain classes of moves (checking moves, in
1690 // particular) are searched with bigger depth than ordinary moves and in
1691 // any case are marked as 'dangerous'. Note that also if a move is not
1692 // extended, as example because the corresponding UCI option is set to zero,
1693 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1694 template <NodeType PvNode>
1695 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1696 bool singleEvasion, bool mateThreat, bool* dangerous) {
1698 assert(m != MOVE_NONE);
1700 Depth result = DEPTH_ZERO;
1701 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1705 if (moveIsCheck && pos.see_sign(m) >= 0)
1706 result += CheckExtension[PvNode];
1709 result += SingleEvasionExtension[PvNode];
1712 result += MateThreatExtension[PvNode];
1715 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1717 Color c = pos.side_to_move();
1718 if (relative_rank(c, move_to(m)) == RANK_7)
1720 result += PawnPushTo7thExtension[PvNode];
1723 if (pos.pawn_is_passed(c, move_to(m)))
1725 result += PassedPawnExtension[PvNode];
1730 if ( captureOrPromotion
1731 && pos.type_of_piece_on(move_to(m)) != PAWN
1732 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1733 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1734 && !move_is_promotion(m)
1737 result += PawnEndgameExtension[PvNode];
1742 && captureOrPromotion
1743 && pos.type_of_piece_on(move_to(m)) != PAWN
1744 && pos.see_sign(m) >= 0)
1746 result += ONE_PLY / 2;
1750 return Min(result, ONE_PLY);
1754 // connected_threat() tests whether it is safe to forward prune a move or if
1755 // is somehow coonected to the threat move returned by null search.
1757 bool connected_threat(const Position& pos, Move m, Move threat) {
1759 assert(move_is_ok(m));
1760 assert(threat && move_is_ok(threat));
1761 assert(!pos.move_is_check(m));
1762 assert(!pos.move_is_capture_or_promotion(m));
1763 assert(!pos.move_is_passed_pawn_push(m));
1765 Square mfrom, mto, tfrom, tto;
1767 mfrom = move_from(m);
1769 tfrom = move_from(threat);
1770 tto = move_to(threat);
1772 // Case 1: Don't prune moves which move the threatened piece
1776 // Case 2: If the threatened piece has value less than or equal to the
1777 // value of the threatening piece, don't prune move which defend it.
1778 if ( pos.move_is_capture(threat)
1779 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1780 || pos.type_of_piece_on(tfrom) == KING)
1781 && pos.move_attacks_square(m, tto))
1784 // Case 3: If the moving piece in the threatened move is a slider, don't
1785 // prune safe moves which block its ray.
1786 if ( piece_is_slider(pos.piece_on(tfrom))
1787 && bit_is_set(squares_between(tfrom, tto), mto)
1788 && pos.see_sign(m) >= 0)
1795 // ok_to_use_TT() returns true if a transposition table score
1796 // can be used at a given point in search.
1798 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1800 Value v = value_from_tt(tte->value(), ply);
1802 return ( tte->depth() >= depth
1803 || v >= Max(value_mate_in(PLY_MAX), beta)
1804 || v < Min(value_mated_in(PLY_MAX), beta))
1806 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1807 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1811 // refine_eval() returns the transposition table score if
1812 // possible otherwise falls back on static position evaluation.
1814 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1818 Value v = value_from_tt(tte->value(), ply);
1820 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1821 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1828 // update_history() registers a good move that produced a beta-cutoff
1829 // in history and marks as failures all the other moves of that ply.
1831 void update_history(const Position& pos, Move move, Depth depth,
1832 Move movesSearched[], int moveCount) {
1834 Value bonus = Value(int(depth) * int(depth));
1836 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1838 for (int i = 0; i < moveCount - 1; i++)
1840 m = movesSearched[i];
1844 if (!pos.move_is_capture_or_promotion(m))
1845 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1850 // update_killers() add a good move that produced a beta-cutoff
1851 // among the killer moves of that ply.
1853 void update_killers(Move m, Move killers[]) {
1855 if (m == killers[0])
1858 killers[1] = killers[0];
1863 // update_gains() updates the gains table of a non-capture move given
1864 // the static position evaluation before and after the move.
1866 void update_gains(const Position& pos, Move m, Value before, Value after) {
1869 && before != VALUE_NONE
1870 && after != VALUE_NONE
1871 && pos.captured_piece_type() == PIECE_TYPE_NONE
1872 && !move_is_special(m))
1873 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1877 // value_to_uci() converts a value to a string suitable for use with the UCI
1878 // protocol specifications:
1880 // cp <x> The score from the engine's point of view in centipawns.
1881 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1882 // use negative values for y.
1884 std::string value_to_uci(Value v) {
1886 std::stringstream s;
1888 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1889 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1891 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1897 // current_search_time() returns the number of milliseconds which have passed
1898 // since the beginning of the current search.
1900 int current_search_time() {
1902 return get_system_time() - SearchStartTime;
1906 // nps() computes the current nodes/second count
1908 int nps(const Position& pos) {
1910 int t = current_search_time();
1911 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1915 // poll() performs two different functions: It polls for user input, and it
1916 // looks at the time consumed so far and decides if it's time to abort the
1919 void poll(const Position& pos) {
1921 static int lastInfoTime;
1922 int t = current_search_time();
1925 if (input_available())
1927 // We are line oriented, don't read single chars
1928 std::string command;
1930 if (!std::getline(std::cin, command))
1933 if (command == "quit")
1935 // Quit the program as soon as possible
1937 QuitRequest = StopRequest = true;
1940 else if (command == "stop")
1942 // Stop calculating as soon as possible, but still send the "bestmove"
1943 // and possibly the "ponder" token when finishing the search.
1947 else if (command == "ponderhit")
1949 // The opponent has played the expected move. GUI sends "ponderhit" if
1950 // we were told to ponder on the same move the opponent has played. We
1951 // should continue searching but switching from pondering to normal search.
1954 if (StopOnPonderhit)
1959 // Print search information
1963 else if (lastInfoTime > t)
1964 // HACK: Must be a new search where we searched less than
1965 // NodesBetweenPolls nodes during the first second of search.
1968 else if (t - lastInfoTime >= 1000)
1975 if (dbg_show_hit_rate)
1976 dbg_print_hit_rate();
1978 // Send info on searched nodes as soon as we return to root
1979 SendSearchedNodes = true;
1982 // Should we stop the search?
1986 bool stillAtFirstMove = FirstRootMove
1987 && !AspirationFailLow
1988 && t > TimeMgr.available_time();
1990 bool noMoreTime = t > TimeMgr.maximum_time()
1991 || stillAtFirstMove;
1993 if ( (UseTimeManagement && noMoreTime)
1994 || (ExactMaxTime && t >= ExactMaxTime)
1995 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
2000 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2001 // while the program is pondering. The point is to work around a wrinkle in
2002 // the UCI protocol: When pondering, the engine is not allowed to give a
2003 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2004 // We simply wait here until one of these commands is sent, and return,
2005 // after which the bestmove and pondermove will be printed.
2007 void wait_for_stop_or_ponderhit() {
2009 std::string command;
2013 // Wait for a command from stdin
2014 if (!std::getline(std::cin, command))
2017 if (command == "quit")
2022 else if (command == "ponderhit" || command == "stop")
2028 // init_thread() is the function which is called when a new thread is
2029 // launched. It simply calls the idle_loop() function with the supplied
2030 // threadID. There are two versions of this function; one for POSIX
2031 // threads and one for Windows threads.
2033 #if !defined(_MSC_VER)
2035 void* init_thread(void* threadID) {
2037 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2043 DWORD WINAPI init_thread(LPVOID threadID) {
2045 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2052 /// The ThreadsManager class
2055 // read_uci_options() updates number of active threads and other internal
2056 // parameters according to the UCI options values. It is called before
2057 // to start a new search.
2059 void ThreadsManager::read_uci_options() {
2061 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2062 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2063 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2064 activeThreads = Options["Threads"].value<int>();
2068 // idle_loop() is where the threads are parked when they have no work to do.
2069 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2070 // object for which the current thread is the master.
2072 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2074 assert(threadID >= 0 && threadID < MAX_THREADS);
2077 bool allFinished = false;
2081 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2082 // master should exit as last one.
2083 if (allThreadsShouldExit)
2086 threads[threadID].state = THREAD_TERMINATED;
2090 // If we are not thinking, wait for a condition to be signaled
2091 // instead of wasting CPU time polling for work.
2092 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2093 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2095 assert(!sp || useSleepingThreads);
2096 assert(threadID != 0 || useSleepingThreads);
2098 if (threads[threadID].state == THREAD_INITIALIZING)
2099 threads[threadID].state = THREAD_AVAILABLE;
2101 // Grab the lock to avoid races with wake_sleeping_thread()
2102 lock_grab(&sleepLock[threadID]);
2104 // If we are master and all slaves have finished do not go to sleep
2105 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2106 allFinished = (i == activeThreads);
2108 if (allFinished || allThreadsShouldExit)
2110 lock_release(&sleepLock[threadID]);
2114 // Do sleep here after retesting sleep conditions
2115 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2116 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2118 lock_release(&sleepLock[threadID]);
2121 // If this thread has been assigned work, launch a search
2122 if (threads[threadID].state == THREAD_WORKISWAITING)
2124 assert(!allThreadsShouldExit);
2126 threads[threadID].state = THREAD_SEARCHING;
2128 // Here we call search() with SplitPoint template parameter set to true
2129 SplitPoint* tsp = threads[threadID].splitPoint;
2130 Position pos(*tsp->pos, threadID);
2131 SearchStack* ss = tsp->sstack[threadID] + 1;
2135 search<PV, true, false>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2137 search<NonPV, true, false>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2139 assert(threads[threadID].state == THREAD_SEARCHING);
2141 threads[threadID].state = THREAD_AVAILABLE;
2143 // Wake up master thread so to allow it to return from the idle loop in
2144 // case we are the last slave of the split point.
2145 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2146 wake_sleeping_thread(tsp->master);
2149 // If this thread is the master of a split point and all slaves have
2150 // finished their work at this split point, return from the idle loop.
2151 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2152 allFinished = (i == activeThreads);
2156 // Because sp->slaves[] is reset under lock protection,
2157 // be sure sp->lock has been released before to return.
2158 lock_grab(&(sp->lock));
2159 lock_release(&(sp->lock));
2161 // In helpful master concept a master can help only a sub-tree, and
2162 // because here is all finished is not possible master is booked.
2163 assert(threads[threadID].state == THREAD_AVAILABLE);
2165 threads[threadID].state = THREAD_SEARCHING;
2172 // init_threads() is called during startup. It launches all helper threads,
2173 // and initializes the split point stack and the global locks and condition
2176 void ThreadsManager::init_threads() {
2178 int i, arg[MAX_THREADS];
2181 // Initialize global locks
2184 for (i = 0; i < MAX_THREADS; i++)
2186 lock_init(&sleepLock[i]);
2187 cond_init(&sleepCond[i]);
2190 // Initialize splitPoints[] locks
2191 for (i = 0; i < MAX_THREADS; i++)
2192 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2193 lock_init(&(threads[i].splitPoints[j].lock));
2195 // Will be set just before program exits to properly end the threads
2196 allThreadsShouldExit = false;
2198 // Threads will be put all threads to sleep as soon as created
2201 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2202 threads[0].state = THREAD_SEARCHING;
2203 for (i = 1; i < MAX_THREADS; i++)
2204 threads[i].state = THREAD_INITIALIZING;
2206 // Launch the helper threads
2207 for (i = 1; i < MAX_THREADS; i++)
2211 #if !defined(_MSC_VER)
2212 pthread_t pthread[1];
2213 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2214 pthread_detach(pthread[0]);
2216 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2220 cout << "Failed to create thread number " << i << endl;
2224 // Wait until the thread has finished launching and is gone to sleep
2225 while (threads[i].state == THREAD_INITIALIZING) {}
2230 // exit_threads() is called when the program exits. It makes all the
2231 // helper threads exit cleanly.
2233 void ThreadsManager::exit_threads() {
2235 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2237 // Wake up all the threads and waits for termination
2238 for (int i = 1; i < MAX_THREADS; i++)
2240 wake_sleeping_thread(i);
2241 while (threads[i].state != THREAD_TERMINATED) {}
2244 // Now we can safely destroy the locks
2245 for (int i = 0; i < MAX_THREADS; i++)
2246 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2247 lock_destroy(&(threads[i].splitPoints[j].lock));
2249 lock_destroy(&mpLock);
2251 // Now we can safely destroy the wait conditions
2252 for (int i = 0; i < MAX_THREADS; i++)
2254 lock_destroy(&sleepLock[i]);
2255 cond_destroy(&sleepCond[i]);
2260 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2261 // the thread's currently active split point, or in some ancestor of
2262 // the current split point.
2264 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2266 assert(threadID >= 0 && threadID < activeThreads);
2268 SplitPoint* sp = threads[threadID].splitPoint;
2270 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2275 // thread_is_available() checks whether the thread with threadID "slave" is
2276 // available to help the thread with threadID "master" at a split point. An
2277 // obvious requirement is that "slave" must be idle. With more than two
2278 // threads, this is not by itself sufficient: If "slave" is the master of
2279 // some active split point, it is only available as a slave to the other
2280 // threads which are busy searching the split point at the top of "slave"'s
2281 // split point stack (the "helpful master concept" in YBWC terminology).
2283 bool ThreadsManager::thread_is_available(int slave, int master) const {
2285 assert(slave >= 0 && slave < activeThreads);
2286 assert(master >= 0 && master < activeThreads);
2287 assert(activeThreads > 1);
2289 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2292 // Make a local copy to be sure doesn't change under our feet
2293 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2295 // No active split points means that the thread is available as
2296 // a slave for any other thread.
2297 if (localActiveSplitPoints == 0 || activeThreads == 2)
2300 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2301 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2302 // could have been set to 0 by another thread leading to an out of bound access.
2303 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2310 // available_thread_exists() tries to find an idle thread which is available as
2311 // a slave for the thread with threadID "master".
2313 bool ThreadsManager::available_thread_exists(int master) const {
2315 assert(master >= 0 && master < activeThreads);
2316 assert(activeThreads > 1);
2318 for (int i = 0; i < activeThreads; i++)
2319 if (thread_is_available(i, master))
2326 // split() does the actual work of distributing the work at a node between
2327 // several available threads. If it does not succeed in splitting the
2328 // node (because no idle threads are available, or because we have no unused
2329 // split point objects), the function immediately returns. If splitting is
2330 // possible, a SplitPoint object is initialized with all the data that must be
2331 // copied to the helper threads and we tell our helper threads that they have
2332 // been assigned work. This will cause them to instantly leave their idle loops and
2333 // call search().When all threads have returned from search() then split() returns.
2335 template <bool Fake>
2336 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2337 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2338 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2339 assert(pos.is_ok());
2340 assert(ply > 0 && ply < PLY_MAX);
2341 assert(*bestValue >= -VALUE_INFINITE);
2342 assert(*bestValue <= *alpha);
2343 assert(*alpha < beta);
2344 assert(beta <= VALUE_INFINITE);
2345 assert(depth > DEPTH_ZERO);
2346 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2347 assert(activeThreads > 1);
2349 int i, master = pos.thread();
2350 Thread& masterThread = threads[master];
2354 // If no other thread is available to help us, or if we have too many
2355 // active split points, don't split.
2356 if ( !available_thread_exists(master)
2357 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2359 lock_release(&mpLock);
2363 // Pick the next available split point object from the split point stack
2364 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2366 // Initialize the split point object
2367 splitPoint.parent = masterThread.splitPoint;
2368 splitPoint.master = master;
2369 splitPoint.betaCutoff = false;
2370 splitPoint.ply = ply;
2371 splitPoint.depth = depth;
2372 splitPoint.threatMove = threatMove;
2373 splitPoint.mateThreat = mateThreat;
2374 splitPoint.alpha = *alpha;
2375 splitPoint.beta = beta;
2376 splitPoint.pvNode = pvNode;
2377 splitPoint.bestValue = *bestValue;
2379 splitPoint.moveCount = moveCount;
2380 splitPoint.pos = &pos;
2381 splitPoint.nodes = 0;
2382 splitPoint.parentSstack = ss;
2383 for (i = 0; i < activeThreads; i++)
2384 splitPoint.slaves[i] = 0;
2386 masterThread.splitPoint = &splitPoint;
2388 // If we are here it means we are not available
2389 assert(masterThread.state != THREAD_AVAILABLE);
2391 int workersCnt = 1; // At least the master is included
2393 // Allocate available threads setting state to THREAD_BOOKED
2394 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2395 if (thread_is_available(i, master))
2397 threads[i].state = THREAD_BOOKED;
2398 threads[i].splitPoint = &splitPoint;
2399 splitPoint.slaves[i] = 1;
2403 assert(Fake || workersCnt > 1);
2405 // We can release the lock because slave threads are already booked and master is not available
2406 lock_release(&mpLock);
2408 // Tell the threads that they have work to do. This will make them leave
2409 // their idle loop. But before copy search stack tail for each thread.
2410 for (i = 0; i < activeThreads; i++)
2411 if (i == master || splitPoint.slaves[i])
2413 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2415 assert(i == master || threads[i].state == THREAD_BOOKED);
2417 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2419 if (useSleepingThreads && i != master)
2420 wake_sleeping_thread(i);
2423 // Everything is set up. The master thread enters the idle loop, from
2424 // which it will instantly launch a search, because its state is
2425 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2426 // idle loop, which means that the main thread will return from the idle
2427 // loop when all threads have finished their work at this split point.
2428 idle_loop(master, &splitPoint);
2430 // We have returned from the idle loop, which means that all threads are
2431 // finished. Update alpha and bestValue, and return.
2434 *alpha = splitPoint.alpha;
2435 *bestValue = splitPoint.bestValue;
2436 masterThread.activeSplitPoints--;
2437 masterThread.splitPoint = splitPoint.parent;
2438 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2440 lock_release(&mpLock);
2444 // wake_sleeping_thread() wakes up the thread with the given threadID
2445 // when it is time to start a new search.
2447 void ThreadsManager::wake_sleeping_thread(int threadID) {
2449 lock_grab(&sleepLock[threadID]);
2450 cond_signal(&sleepCond[threadID]);
2451 lock_release(&sleepLock[threadID]);
2455 /// RootMove and RootMoveList method's definitions
2457 RootMove::RootMove() {
2460 pv_score = non_pv_score = -VALUE_INFINITE;
2464 RootMove& RootMove::operator=(const RootMove& rm) {
2466 const Move* src = rm.pv;
2469 // Avoid a costly full rm.pv[] copy
2470 do *dst++ = *src; while (*src++ != MOVE_NONE);
2473 pv_score = rm.pv_score;
2474 non_pv_score = rm.non_pv_score;
2478 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2479 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2480 // allow to always have a ponder move even when we fail high at root and also a
2481 // long PV to print that is important for position analysis.
2483 void RootMove::extract_pv_from_tt(Position& pos) {
2485 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2489 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2491 pos.do_move(pv[0], *st++);
2493 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2494 && tte->move() != MOVE_NONE
2495 && move_is_legal(pos, tte->move())
2497 && (!pos.is_draw() || ply < 2))
2499 pv[ply] = tte->move();
2500 pos.do_move(pv[ply++], *st++);
2502 pv[ply] = MOVE_NONE;
2504 do pos.undo_move(pv[--ply]); while (ply);
2507 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2508 // the PV back into the TT. This makes sure the old PV moves are searched
2509 // first, even if the old TT entries have been overwritten.
2511 void RootMove::insert_pv_in_tt(Position& pos) {
2513 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2516 Value v, m = VALUE_NONE;
2519 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2523 tte = TT.retrieve(k);
2525 // Don't overwrite exsisting correct entries
2526 if (!tte || tte->move() != pv[ply])
2528 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2529 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2531 pos.do_move(pv[ply], *st++);
2533 } while (pv[++ply] != MOVE_NONE);
2535 do pos.undo_move(pv[--ply]); while (ply);
2538 // pv_info_to_uci() returns a string with information on the current PV line
2539 // formatted according to UCI specification and eventually writes the info
2540 // to a log file. It is called at each iteration or after a new pv is found.
2542 std::string RootMove::pv_info_to_uci(Position& pos, Depth depth, Value alpha, Value beta, int pvLine) {
2544 std::stringstream s, l;
2547 while (*m != MOVE_NONE)
2550 s << "info depth " << depth / ONE_PLY
2551 << " seldepth " << int(m - pv)
2552 << " multipv " << pvLine + 1
2553 << " score " << value_to_uci(pv_score)
2554 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2555 << " time " << current_search_time()
2556 << " nodes " << pos.nodes_searched()
2557 << " nps " << nps(pos)
2558 << " pv " << l.str();
2560 if (UseLogFile && pvLine == 0)
2562 ValueType t = pv_score >= beta ? VALUE_TYPE_LOWER :
2563 pv_score <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2565 LogFile << pretty_pv(pos, current_search_time(), depth / ONE_PLY, pv_score, t, pv) << endl;
2571 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2573 SearchStack ss[PLY_MAX_PLUS_2];
2574 MoveStack mlist[MOVES_MAX];
2578 // Initialize search stack
2579 memset(ss, 0, PLY_MAX_PLUS_2 * sizeof(SearchStack));
2580 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2581 bestMoveChanges = 0;
2584 // Generate all legal moves
2585 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2587 // Add each move to the RootMoveList's vector
2588 for (MoveStack* cur = mlist; cur != last; cur++)
2590 // If we have a searchMoves[] list then verify cur->move
2591 // is in the list before to add it.
2592 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2594 if (searchMoves[0] && *sm != cur->move)
2597 // Find a quick score for the move and add to the list
2598 pos.do_move(cur->move, st);
2601 rm.pv[0] = ss[0].currentMove = cur->move;
2602 rm.pv[1] = MOVE_NONE;
2603 rm.pv_score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2606 pos.undo_move(cur->move);