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/>.
40 #include "ucioption.h"
47 // Different node types, used as template parameter
48 enum NodeType { NonPV, PV };
50 // Set to true to force running with one thread. Used for debugging.
51 const bool FakeSplit = false;
53 // Lookup table to check if a Piece is a slider and its access function
54 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
55 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
57 // ThreadsManager class is used to handle all the threads related stuff like init,
58 // starting, parking and, the most important, launching a slave thread at a split
59 // point. All the access to shared thread data is done through this class.
61 class ThreadsManager {
62 /* As long as the single ThreadsManager object is defined as a global we don't
63 need to explicitly initialize to zero its data members because variables with
64 static storage duration are automatically set to zero before enter main()
70 int min_split_depth() const { return minimumSplitDepth; }
71 int active_threads() const { return activeThreads; }
72 void set_active_threads(int cnt) { activeThreads = cnt; }
74 void read_uci_options();
75 bool available_thread_exists(int master) const;
76 bool thread_is_available(int slave, int master) const;
77 bool cutoff_at_splitpoint(int threadID) const;
78 void wake_sleeping_thread(int threadID);
79 void idle_loop(int threadID, SplitPoint* sp);
82 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
83 Depth depth, Move threatMove, int moveCount, MovePicker* mp, bool pvNode);
86 Depth minimumSplitDepth;
87 int maxThreadsPerSplitPoint;
88 bool useSleepingThreads;
90 volatile bool allThreadsShouldExit;
91 Thread threads[MAX_THREADS];
92 Lock mpLock, sleepLock[MAX_THREADS];
93 WaitCondition sleepCond[MAX_THREADS];
97 // RootMove struct is used for moves at the root of the tree. For each root
98 // move, we store two scores, a node count, and a PV (really a refutation
99 // in the case of moves which fail low). Value pv_score is normally set at
100 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
101 // according to the order in which moves are returned by MovePicker.
106 RootMove(const RootMove& rm) { *this = rm; }
107 RootMove& operator=(const RootMove& rm);
109 // RootMove::operator<() is the comparison function used when
110 // sorting the moves. A move m1 is considered to be better
111 // than a move m2 if it has an higher pv_score, or if it has
112 // equal pv_score but m1 has the higher non_pv_score. In this way
113 // we are guaranteed that PV moves are always sorted as first.
114 bool operator<(const RootMove& m) const {
115 return pv_score != m.pv_score ? pv_score < m.pv_score
116 : non_pv_score < m.non_pv_score;
119 void extract_pv_from_tt(Position& pos);
120 void insert_pv_in_tt(Position& pos);
121 std::string pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvIdx);
126 Move pv[PLY_MAX_PLUS_2];
130 // RootMoveList struct is just a std::vector<> of RootMove objects,
131 // with an handful of methods above the standard ones.
133 struct RootMoveList : public std::vector<RootMove> {
135 typedef std::vector<RootMove> Base;
137 void init(Position& pos, Move searchMoves[]);
138 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
139 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
145 // Overload operator<<() to make it easier to print moves in a coordinate
146 // notation compatible with UCI protocol.
147 std::ostream& operator<<(std::ostream& os, Move m) {
149 bool chess960 = (os.iword(0) != 0); // See set960()
150 return os << move_to_uci(m, chess960);
154 // When formatting a move for std::cout we must know if we are in Chess960
155 // or not. To keep using the handy operator<<() on the move the trick is to
156 // embed this flag in the stream itself. Function-like named enum set960 is
157 // used as a custom manipulator and the stream internal general-purpose array,
158 // accessed through ios_base::iword(), is used to pass the flag to the move's
159 // operator<<() that will read it to properly format castling moves.
162 std::ostream& operator<< (std::ostream& os, const set960& f) {
164 os.iword(0) = int(f);
173 // Maximum depth for razoring
174 const Depth RazorDepth = 4 * ONE_PLY;
176 // Dynamic razoring margin based on depth
177 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
179 // Maximum depth for use of dynamic threat detection when null move fails low
180 const Depth ThreatDepth = 5 * ONE_PLY;
182 // Step 9. Internal iterative deepening
184 // Minimum depth for use of internal iterative deepening
185 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
187 // At Non-PV nodes we do an internal iterative deepening search
188 // when the static evaluation is bigger then beta - IIDMargin.
189 const Value IIDMargin = Value(0x100);
191 // Step 11. Decide the new search depth
193 // Extensions. Configurable UCI options
194 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
195 Depth CheckExtension[2], PawnPushTo7thExtension[2];
196 Depth PassedPawnExtension[2], PawnEndgameExtension[2];
198 // Minimum depth for use of singular extension
199 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
201 // Step 12. Futility pruning
203 // Futility margin for quiescence search
204 const Value FutilityMarginQS = Value(0x80);
206 // Futility lookup tables (initialized at startup) and their access functions
207 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
208 int FutilityMoveCountArray[32]; // [depth]
210 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
211 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
213 // Step 14. Reduced search
215 // Reduction lookup tables (initialized at startup) and their getter functions
216 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
218 template <NodeType PV>
219 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
221 // Easy move margin. An easy move candidate must be at least this much
222 // better than the second best move.
223 const Value EasyMoveMargin = Value(0x200);
226 /// Namespace variables
235 int MultiPV, UCIMultiPV;
237 // Time management variables
238 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
239 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
240 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
245 std::ofstream LogFile;
247 // Skill level adjustment
249 bool SkillLevelEnabled;
252 // Multi-threads manager
253 ThreadsManager ThreadsMgr;
255 // Node counters, used only by thread[0] but try to keep in different cache
256 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
257 bool SendSearchedNodes;
259 int NodesBetweenPolls = 30000;
267 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
269 template <NodeType PvNode, bool SpNode, bool Root>
270 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
272 template <NodeType PvNode>
273 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
275 template <NodeType PvNode>
276 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
278 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
279 : search<PvNode, false, false>(pos, ss, alpha, beta, depth, ply);
282 template <NodeType PvNode>
283 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
285 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
286 bool connected_moves(const Position& pos, Move m1, Move m2);
287 Value value_to_tt(Value v, int ply);
288 Value value_from_tt(Value v, int ply);
289 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
290 bool connected_threat(const Position& pos, Move m, Move threat);
291 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
292 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
293 void update_gains(const Position& pos, Move move, Value before, Value after);
294 void do_skill_level(Move* best, Move* ponder);
296 int current_search_time();
297 std::string value_to_uci(Value v);
298 std::string speed_to_uci(int64_t nodes);
299 void poll(const Position& pos);
300 void wait_for_stop_or_ponderhit();
302 #if !defined(_MSC_VER)
303 void* init_thread(void* threadID);
305 DWORD WINAPI init_thread(LPVOID threadID);
309 // MovePickerExt is an extended MovePicker used to choose at compile time
310 // the proper move source according to the type of node.
311 template<bool SpNode, bool Root> struct MovePickerExt;
313 // In Root nodes use RootMoveList as source. Score and sort the root moves
314 // before to search them.
315 template<> struct MovePickerExt<false, true> : public MovePicker {
317 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
318 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
320 Value score = VALUE_ZERO;
322 // Score root moves using standard ordering used in main search, the moves
323 // are scored according to the order in which they are returned by MovePicker.
324 // This is the second order score that is used to compare the moves when
325 // the first orders pv_score of both moves are equal.
326 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
327 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
328 if (rm->pv[0] == move)
330 rm->non_pv_score = score--;
338 Move get_next_move() {
345 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
348 RootMoveList::iterator rm;
352 // In SpNodes use split point's shared MovePicker object as move source
353 template<> struct MovePickerExt<true, false> : public MovePicker {
355 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
356 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
358 Move get_next_move() { return mp->get_next_move(); }
360 RootMoveList::iterator rm; // Dummy, needed to compile
364 // Default case, create and use a MovePicker object as source
365 template<> struct MovePickerExt<false, false> : public MovePicker {
367 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
368 : MovePicker(p, ttm, d, h, ss, b) {}
370 RootMoveList::iterator rm; // Dummy, needed to compile
376 /// init_threads() is called during startup. It initializes various lookup tables
377 /// and creates and launches search threads.
379 void init_threads() {
381 int d; // depth (ONE_PLY == 2)
382 int hd; // half depth (ONE_PLY == 1)
385 // Init reductions array
386 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
388 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
389 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
390 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
391 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
394 // Init futility margins array
395 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
396 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
398 // Init futility move count array
399 for (d = 0; d < 32; d++)
400 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
402 // Create and startup threads
403 ThreadsMgr.init_threads();
407 /// exit_threads() is a trampoline to access ThreadsMgr from outside of current file
408 void exit_threads() { ThreadsMgr.exit_threads(); }
411 /// perft() is our utility to verify move generation. All the legal moves up to
412 /// given depth are generated and counted and the sum returned.
414 int64_t perft(Position& pos, Depth depth) {
416 MoveStack mlist[MOVES_MAX];
421 // Generate all legal moves
422 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
424 // If we are at the last ply we don't need to do and undo
425 // the moves, just to count them.
426 if (depth <= ONE_PLY)
427 return int(last - mlist);
429 // Loop through all legal moves
431 for (MoveStack* cur = mlist; cur != last; cur++)
434 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
435 sum += perft(pos, depth - ONE_PLY);
442 /// think() is the external interface to Stockfish's search, and is called when
443 /// the program receives the UCI 'go' command. It initializes various global
444 /// variables, and calls id_loop(). It returns false when a quit command is
445 /// received during the search.
447 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
448 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
450 // Initialize global search-related variables
451 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
453 SearchStartTime = get_system_time();
454 ExactMaxTime = maxTime;
457 InfiniteSearch = infinite;
459 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
461 // Look for a book move, only during games, not tests
462 if (UseTimeManagement && Options["OwnBook"].value<bool>())
464 if (Options["Book File"].value<std::string>() != OpeningBook.name())
465 OpeningBook.open(Options["Book File"].value<std::string>());
467 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
468 if (bookMove != MOVE_NONE)
471 wait_for_stop_or_ponderhit();
473 cout << "bestmove " << bookMove << endl;
479 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
480 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
481 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
482 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
483 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
484 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
485 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
486 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
487 UCIMultiPV = Options["MultiPV"].value<int>();
488 SkillLevel = Options["Skill level"].value<int>();
489 UseLogFile = Options["Use Search Log"].value<bool>();
491 read_evaluation_uci_options(pos.side_to_move());
493 if (Options["Clear Hash"].value<bool>())
495 Options["Clear Hash"].set_value("false");
498 TT.set_size(Options["Hash"].value<int>());
500 // Do we have to play with skill handicap? In this case enable MultiPV that
501 // we will use behind the scenes to retrieve a set of possible moves.
502 SkillLevelEnabled = (SkillLevel < 20);
503 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
505 // Set the number of active threads
506 ThreadsMgr.read_uci_options();
507 init_eval(ThreadsMgr.active_threads());
509 // Wake up needed threads. Main thread, with threadID == 0, is always active
510 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
511 ThreadsMgr.wake_sleeping_thread(i);
514 int myTime = time[pos.side_to_move()];
515 int myIncrement = increment[pos.side_to_move()];
516 if (UseTimeManagement)
517 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
519 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
521 NodesBetweenPolls = Min(MaxNodes, 30000);
522 else if (myTime && myTime < 1000)
523 NodesBetweenPolls = 1000;
524 else if (myTime && myTime < 5000)
525 NodesBetweenPolls = 5000;
527 NodesBetweenPolls = 30000;
529 // Write search information to log file
532 std::string name = Options["Search Log Filename"].value<std::string>();
533 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
535 LogFile << "\nSearching: " << pos.to_fen()
536 << "\ninfinite: " << infinite
537 << " ponder: " << ponder
538 << " time: " << myTime
539 << " increment: " << myIncrement
540 << " moves to go: " << movesToGo
544 // We're ready to start thinking. Call the iterative deepening loop function
545 Move ponderMove = MOVE_NONE;
546 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
548 // Print final search statistics
549 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
553 int t = current_search_time();
555 LogFile << "Nodes: " << pos.nodes_searched()
556 << "\nNodes/second: " << (t > 0 ? int(pos.nodes_searched() * 1000 / t) : 0)
557 << "\nBest move: " << move_to_san(pos, bestMove);
560 pos.do_move(bestMove, st);
561 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
562 pos.undo_move(bestMove); // Return from think() with unchanged position
566 // This makes all the threads to go to sleep
567 ThreadsMgr.set_active_threads(1);
569 // If we are pondering or in infinite search, we shouldn't print the
570 // best move before we are told to do so.
571 if (!StopRequest && (Pondering || InfiniteSearch))
572 wait_for_stop_or_ponderhit();
574 // Could be MOVE_NONE when searching on a stalemate position
575 cout << "bestmove " << bestMove;
577 // UCI protol is not clear on allowing sending an empty ponder move, instead
578 // it is clear that ponder move is optional. So skip it if empty.
579 if (ponderMove != MOVE_NONE)
580 cout << " ponder " << ponderMove;
590 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
591 // with increasing depth until the allocated thinking time has been consumed,
592 // user stops the search, or the maximum search depth is reached.
594 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
596 SearchStack ss[PLY_MAX_PLUS_2];
597 Value bestValues[PLY_MAX_PLUS_2];
598 int bestMoveChanges[PLY_MAX_PLUS_2];
599 int depth, aspirationDelta, skillSamplingDepth;
600 Value value, alpha, beta;
601 Move bestMove, easyMove, skillBest, skillPonder;
603 // Initialize stuff before a new search
604 memset(ss, 0, 4 * sizeof(SearchStack));
607 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
608 depth = aspirationDelta = skillSamplingDepth = 0;
609 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
610 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
612 // Moves to search are verified and copied
613 Rml.init(pos, searchMoves);
615 // Handle special case of searching on a mate/stalemate position
618 cout << "info depth 0 score "
619 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
625 // Choose a random sampling depth according to SkillLevel so that at low
626 // skills there is an higher risk to pick up a blunder.
627 if (SkillLevelEnabled)
628 skillSamplingDepth = 4 + SkillLevel + (RK.rand<unsigned>() % 4);
630 // Iterative deepening loop
631 while (++depth <= PLY_MAX && (!MaxDepth || depth <= MaxDepth) && !StopRequest)
633 Rml.bestMoveChanges = 0;
634 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
636 // Calculate dynamic aspiration window based on previous iterations
637 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
639 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
640 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
642 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
643 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
645 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
646 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
649 // Start with a small aspiration window and, in case of fail high/low,
650 // research with bigger window until not failing high/low anymore.
652 // Search starting from ss+1 to allow calling update_gains()
653 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY, 0);
655 // Write PV back to transposition table in case the relevant entries
656 // have been overwritten during the search.
657 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
658 Rml[i].insert_pv_in_tt(pos);
660 // Value cannot be trusted. Break out immediately!
664 assert(value >= alpha);
666 // In case of failing high/low increase aspiration window and research,
667 // otherwise exit the fail high/low loop.
670 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
671 aspirationDelta += aspirationDelta / 2;
673 else if (value <= alpha)
675 AspirationFailLow = true;
676 StopOnPonderhit = false;
678 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
679 aspirationDelta += aspirationDelta / 2;
684 } while (abs(value) < VALUE_KNOWN_WIN);
686 // Collect info about search result
687 bestMove = Rml[0].pv[0];
688 *ponderMove = Rml[0].pv[1];
689 bestValues[depth] = value;
690 bestMoveChanges[depth] = Rml.bestMoveChanges;
692 // Do we need to pick now the best and the ponder moves ?
693 if (SkillLevelEnabled && depth == skillSamplingDepth)
694 do_skill_level(&skillBest, &skillPonder);
696 // Send PV line to GUI and to log file
697 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
698 cout << Rml[i].pv_info_to_uci(pos, depth, alpha, beta, i) << endl;
701 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
703 // Init easyMove after first iteration or drop if differs from the best move
704 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
706 else if (bestMove != easyMove)
707 easyMove = MOVE_NONE;
709 if (UseTimeManagement && !StopRequest)
712 bool noMoreTime = false;
714 // Stop search early when the last two iterations returned a mate score
716 && abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
717 && abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
720 // Stop search early if one move seems to be much better than the
721 // others or if there is only a single legal move. In this latter
722 // case we search up to Iteration 8 anyway to get a proper score.
724 && easyMove == bestMove
726 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
727 && current_search_time() > TimeMgr.available_time() / 16)
728 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
729 && current_search_time() > TimeMgr.available_time() / 32)))
732 // Add some extra time if the best move has changed during the last two iterations
733 if (depth > 4 && depth < 50)
734 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
736 // Stop search if most of MaxSearchTime is consumed at the end of the
737 // iteration. We probably don't have enough time to search the first
738 // move at the next iteration anyway.
739 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
745 StopOnPonderhit = true;
752 // When using skills fake best and ponder moves with the sub-optimal ones
753 if (SkillLevelEnabled)
755 if (skillBest == MOVE_NONE) // Still unassigned ?
756 do_skill_level(&skillBest, &skillPonder);
758 bestMove = skillBest;
759 *ponderMove = skillPonder;
766 // search<>() is the main search function for both PV and non-PV nodes and for
767 // normal and SplitPoint nodes. When called just after a split point the search
768 // is simpler because we have already probed the hash table, done a null move
769 // search, and searched the first move before splitting, we don't have to repeat
770 // all this work again. We also don't need to store anything to the hash table
771 // here: This is taken care of after we return from the split point.
773 template <NodeType PvNode, bool SpNode, bool Root>
774 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
776 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
777 assert(beta > alpha && beta <= VALUE_INFINITE);
778 assert(PvNode || alpha == beta - 1);
779 assert((Root || ply > 0) && ply < PLY_MAX);
780 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
782 Move movesSearched[MOVES_MAX];
787 Move ttMove, move, excludedMove, threatMove;
790 Value bestValue, value, oldAlpha;
791 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
792 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous, isBadCap;
793 int moveCount = 0, playedMoveCount = 0;
794 int threadID = pos.thread();
795 SplitPoint* sp = NULL;
797 refinedValue = bestValue = value = -VALUE_INFINITE;
799 isCheck = pos.is_check();
805 ttMove = excludedMove = MOVE_NONE;
806 threatMove = sp->threatMove;
807 goto split_point_start;
812 // Step 1. Initialize node and poll. Polling can abort search
813 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
814 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
815 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
817 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
823 // Step 2. Check for aborted search and immediate draw
825 || ThreadsMgr.cutoff_at_splitpoint(threadID)
827 || ply >= PLY_MAX - 1) && !Root)
830 // Step 3. Mate distance pruning
831 alpha = Max(value_mated_in(ply), alpha);
832 beta = Min(value_mate_in(ply+1), beta);
836 // Step 4. Transposition table lookup
837 // We don't want the score of a partial search to overwrite a previous full search
838 // TT value, so we use a different position key in case of an excluded move.
839 excludedMove = ss->excludedMove;
840 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
842 tte = TT.retrieve(posKey);
843 ttMove = tte ? tte->move() : MOVE_NONE;
845 // At PV nodes we check for exact scores, while at non-PV nodes we check for
846 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
847 // smooth experience in analysis mode.
850 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
851 : ok_to_use_TT(tte, depth, beta, ply)))
854 ss->bestMove = ttMove; // Can be MOVE_NONE
855 return value_from_tt(tte->value(), ply);
858 // Step 5. Evaluate the position statically and update parent's gain statistics
860 ss->eval = ss->evalMargin = VALUE_NONE;
863 assert(tte->static_value() != VALUE_NONE);
865 ss->eval = tte->static_value();
866 ss->evalMargin = tte->static_value_margin();
867 refinedValue = refine_eval(tte, ss->eval, ply);
871 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
872 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
875 // Save gain for the parent non-capture move
876 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
878 // Step 6. Razoring (is omitted in PV nodes)
880 && depth < RazorDepth
882 && refinedValue + razor_margin(depth) < beta
883 && ttMove == MOVE_NONE
884 && abs(beta) < VALUE_MATE_IN_PLY_MAX
885 && !pos.has_pawn_on_7th(pos.side_to_move()))
887 Value rbeta = beta - razor_margin(depth);
888 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
890 // Logically we should return (v + razor_margin(depth)), but
891 // surprisingly this did slightly weaker in tests.
895 // Step 7. Static null move pruning (is omitted in PV nodes)
896 // We're betting that the opponent doesn't have a move that will reduce
897 // the score by more than futility_margin(depth) if we do a null move.
900 && depth < RazorDepth
902 && refinedValue - futility_margin(depth, 0) >= beta
903 && abs(beta) < VALUE_MATE_IN_PLY_MAX
904 && pos.non_pawn_material(pos.side_to_move()))
905 return refinedValue - futility_margin(depth, 0);
907 // Step 8. Null move search with verification search (is omitted in PV nodes)
912 && refinedValue >= beta
913 && abs(beta) < VALUE_MATE_IN_PLY_MAX
914 && pos.non_pawn_material(pos.side_to_move()))
916 ss->currentMove = MOVE_NULL;
918 // Null move dynamic reduction based on depth
919 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
921 // Null move dynamic reduction based on value
922 if (refinedValue - PawnValueMidgame > beta)
925 pos.do_null_move(st);
926 (ss+1)->skipNullMove = true;
927 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
928 (ss+1)->skipNullMove = false;
929 pos.undo_null_move();
931 if (nullValue >= beta)
933 // Do not return unproven mate scores
934 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
937 if (depth < 6 * ONE_PLY)
940 // Do verification search at high depths
941 ss->skipNullMove = true;
942 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
943 ss->skipNullMove = false;
950 // The null move failed low, which means that we may be faced with
951 // some kind of threat. If the previous move was reduced, check if
952 // the move that refuted the null move was somehow connected to the
953 // move which was reduced. If a connection is found, return a fail
954 // low score (which will cause the reduced move to fail high in the
955 // parent node, which will trigger a re-search with full depth).
956 threatMove = (ss+1)->bestMove;
958 if ( depth < ThreatDepth
960 && threatMove != MOVE_NONE
961 && connected_moves(pos, (ss-1)->currentMove, threatMove))
966 // Step 9. Internal iterative deepening
967 if ( depth >= IIDDepth[PvNode]
968 && ttMove == MOVE_NONE
969 && (PvNode || (!isCheck && ss->eval + IIDMargin >= beta)))
971 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
973 ss->skipNullMove = true;
974 search<PvNode>(pos, ss, alpha, beta, d, ply);
975 ss->skipNullMove = false;
977 ttMove = ss->bestMove;
978 tte = TT.retrieve(posKey);
981 split_point_start: // At split points actual search starts from here
983 // Initialize a MovePicker object for the current position
984 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
986 ss->bestMove = MOVE_NONE;
987 futilityBase = ss->eval + ss->evalMargin;
988 singularExtensionNode = !Root
990 && depth >= SingularExtensionDepth[PvNode]
993 && !excludedMove // Do not allow recursive singular extension search
994 && (tte->type() & VALUE_TYPE_LOWER)
995 && tte->depth() >= depth - 3 * ONE_PLY;
998 lock_grab(&(sp->lock));
999 bestValue = sp->bestValue;
1002 // Step 10. Loop through moves
1003 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1004 while ( bestValue < beta
1005 && (move = mp.get_next_move()) != MOVE_NONE
1006 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1008 assert(move_is_ok(move));
1012 moveCount = ++sp->moveCount;
1013 lock_release(&(sp->lock));
1015 else if (move == excludedMove)
1022 // This is used by time management
1023 FirstRootMove = (moveCount == 1);
1025 // Save the current node count before the move is searched
1026 nodes = pos.nodes_searched();
1028 // If it's time to send nodes info, do it here where we have the
1029 // correct accumulated node counts searched by each thread.
1030 if (SendSearchedNodes)
1032 SendSearchedNodes = false;
1033 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1036 if (current_search_time() > 2000)
1037 cout << "info currmove " << move
1038 << " currmovenumber " << moveCount << endl;
1041 // At Root and at first iteration do a PV search on all the moves to score root moves
1042 isPvMove = (PvNode && moveCount <= (Root ? depth <= ONE_PLY ? 1000 : MultiPV : 1));
1043 moveIsCheck = pos.move_is_check(move, ci);
1044 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1046 // Step 11. Decide the new search depth
1047 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, &dangerous);
1049 // Singular extension search. If all moves but one fail low on a search of
1050 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1051 // is singular and should be extended. To verify this we do a reduced search
1052 // on all the other moves but the ttMove, if result is lower than ttValue minus
1053 // a margin then we extend ttMove.
1054 if ( singularExtensionNode
1055 && move == tte->move()
1058 Value ttValue = value_from_tt(tte->value(), ply);
1060 if (abs(ttValue) < VALUE_KNOWN_WIN)
1062 Value rBeta = ttValue - int(depth);
1063 ss->excludedMove = move;
1064 ss->skipNullMove = true;
1065 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, ply);
1066 ss->skipNullMove = false;
1067 ss->excludedMove = MOVE_NONE;
1068 ss->bestMove = MOVE_NONE;
1074 // Update current move (this must be done after singular extension search)
1075 ss->currentMove = move;
1076 newDepth = depth - ONE_PLY + ext;
1078 // Step 12. Futility pruning (is omitted in PV nodes)
1080 && !captureOrPromotion
1084 && !move_is_castle(move))
1086 // Move count based pruning
1087 if ( moveCount >= futility_move_count(depth)
1088 && (!threatMove || !connected_threat(pos, move, threatMove))
1089 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1092 lock_grab(&(sp->lock));
1097 // Value based pruning
1098 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1099 // but fixing this made program slightly weaker.
1100 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1101 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1102 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1104 if (futilityValueScaled < beta)
1108 lock_grab(&(sp->lock));
1109 if (futilityValueScaled > sp->bestValue)
1110 sp->bestValue = bestValue = futilityValueScaled;
1112 else if (futilityValueScaled > bestValue)
1113 bestValue = futilityValueScaled;
1118 // Prune moves with negative SEE at low depths
1119 if ( predictedDepth < 2 * ONE_PLY
1120 && bestValue > VALUE_MATED_IN_PLY_MAX
1121 && pos.see_sign(move) < 0)
1124 lock_grab(&(sp->lock));
1130 // Bad capture detection. Will be used by prob-cut search
1131 isBadCap = depth >= 3 * ONE_PLY
1132 && depth < 8 * ONE_PLY
1133 && captureOrPromotion
1136 && !move_is_promotion(move)
1137 && abs(alpha) < VALUE_MATE_IN_PLY_MAX
1138 && pos.see_sign(move) < 0;
1140 // Step 13. Make the move
1141 pos.do_move(move, st, ci, moveIsCheck);
1143 if (!SpNode && !captureOrPromotion)
1144 movesSearched[playedMoveCount++] = move;
1146 // Step extra. pv search (only in PV nodes)
1147 // The first move in list is the expected PV
1150 // Aspiration window is disabled in multi-pv case
1151 if (Root && MultiPV > 1)
1152 alpha = -VALUE_INFINITE;
1154 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1158 // Step 14. Reduced depth search
1159 // If the move fails high will be re-searched at full depth.
1160 bool doFullDepthSearch = true;
1161 alpha = SpNode ? sp->alpha : alpha;
1163 if ( depth >= 3 * ONE_PLY
1164 && !captureOrPromotion
1166 && !move_is_castle(move)
1167 && ss->killers[0] != move
1168 && ss->killers[1] != move)
1170 ss->reduction = reduction<PvNode>(depth, moveCount);
1173 alpha = SpNode ? sp->alpha : alpha;
1174 Depth d = newDepth - ss->reduction;
1175 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1177 doFullDepthSearch = (value > alpha);
1179 ss->reduction = DEPTH_ZERO; // Restore original reduction
1182 // Probcut search for bad captures. If a reduced search returns a value
1183 // very below beta then we can (almost) safely prune the bad capture.
1186 ss->reduction = 3 * ONE_PLY;
1187 Value rAlpha = alpha - 300;
1188 Depth d = newDepth - ss->reduction;
1189 value = -search<NonPV>(pos, ss+1, -(rAlpha+1), -rAlpha, d, ply+1);
1190 doFullDepthSearch = (value > rAlpha);
1191 ss->reduction = DEPTH_ZERO; // Restore original reduction
1194 // Step 15. Full depth search
1195 if (doFullDepthSearch)
1197 alpha = SpNode ? sp->alpha : alpha;
1198 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1200 // Step extra. pv search (only in PV nodes)
1201 // Search only for possible new PV nodes, if instead value >= beta then
1202 // parent node fails low with value <= alpha and tries another move.
1203 if (PvNode && value > alpha && (Root || value < beta))
1204 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1208 // Step 16. Undo move
1209 pos.undo_move(move);
1211 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1213 // Step 17. Check for new best move
1216 lock_grab(&(sp->lock));
1217 bestValue = sp->bestValue;
1221 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1226 sp->bestValue = value;
1228 if (!Root && value > alpha)
1230 if (PvNode && value < beta) // We want always alpha < beta
1238 sp->betaCutoff = true;
1240 if (value == value_mate_in(ply + 1))
1241 ss->mateKiller = move;
1243 ss->bestMove = move;
1246 sp->ss->bestMove = move;
1252 // Finished searching the move. If StopRequest is true, the search
1253 // was aborted because the user interrupted the search or because we
1254 // ran out of time. In this case, the return value of the search cannot
1255 // be trusted, and we break out of the loop without updating the best
1260 // Remember searched nodes counts for this move
1261 mp.rm->nodes += pos.nodes_searched() - nodes;
1263 // PV move or new best move ?
1264 if (isPvMove || value > alpha)
1267 ss->bestMove = move;
1268 mp.rm->pv_score = value;
1269 mp.rm->extract_pv_from_tt(pos);
1271 // We record how often the best move has been changed in each
1272 // iteration. This information is used for time management: When
1273 // the best move changes frequently, we allocate some more time.
1274 if (!isPvMove && MultiPV == 1)
1275 Rml.bestMoveChanges++;
1277 Rml.sort_multipv(moveCount);
1279 // Update alpha. In multi-pv we don't use aspiration window, so
1280 // set alpha equal to minimum score among the PV lines.
1282 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1283 else if (value > alpha)
1287 mp.rm->pv_score = -VALUE_INFINITE;
1291 // Step 18. Check for split
1294 && depth >= ThreadsMgr.min_split_depth()
1295 && ThreadsMgr.active_threads() > 1
1297 && ThreadsMgr.available_thread_exists(threadID)
1299 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1300 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1301 threatMove, moveCount, &mp, PvNode);
1304 // Step 19. Check for mate and stalemate
1305 // All legal moves have been searched and if there are
1306 // no legal moves, it must be mate or stalemate.
1307 // If one move was excluded return fail low score.
1308 if (!SpNode && !moveCount)
1309 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1311 // Step 20. Update tables
1312 // If the search is not aborted, update the transposition table,
1313 // history counters, and killer moves.
1314 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1316 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1317 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1318 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1320 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1322 // Update killers and history only for non capture moves that fails high
1323 if ( bestValue >= beta
1324 && !pos.move_is_capture_or_promotion(move))
1326 if (move != ss->killers[0])
1328 ss->killers[1] = ss->killers[0];
1329 ss->killers[0] = move;
1331 update_history(pos, move, depth, movesSearched, playedMoveCount);
1337 // Here we have the lock still grabbed
1338 sp->slaves[threadID] = 0;
1339 sp->nodes += pos.nodes_searched();
1340 lock_release(&(sp->lock));
1343 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1348 // qsearch() is the quiescence search function, which is called by the main
1349 // search function when the remaining depth is zero (or, to be more precise,
1350 // less than ONE_PLY).
1352 template <NodeType PvNode>
1353 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1355 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1356 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1357 assert(PvNode || alpha == beta - 1);
1359 assert(ply > 0 && ply < PLY_MAX);
1360 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1364 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1365 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1368 Value oldAlpha = alpha;
1370 ss->bestMove = ss->currentMove = MOVE_NONE;
1372 // Check for an instant draw or maximum ply reached
1373 if (pos.is_draw() || ply >= PLY_MAX - 1)
1376 // Decide whether or not to include checks, this fixes also the type of
1377 // TT entry depth that we are going to use. Note that in qsearch we use
1378 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1379 isCheck = pos.is_check();
1380 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1382 // Transposition table lookup. At PV nodes, we don't use the TT for
1383 // pruning, but only for move ordering.
1384 tte = TT.retrieve(pos.get_key());
1385 ttMove = (tte ? tte->move() : MOVE_NONE);
1387 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1389 ss->bestMove = ttMove; // Can be MOVE_NONE
1390 return value_from_tt(tte->value(), ply);
1393 // Evaluate the position statically
1396 bestValue = futilityBase = -VALUE_INFINITE;
1397 ss->eval = evalMargin = VALUE_NONE;
1398 enoughMaterial = false;
1404 assert(tte->static_value() != VALUE_NONE);
1406 evalMargin = tte->static_value_margin();
1407 ss->eval = bestValue = tte->static_value();
1410 ss->eval = bestValue = evaluate(pos, evalMargin);
1412 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1414 // Stand pat. Return immediately if static value is at least beta
1415 if (bestValue >= beta)
1418 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1423 if (PvNode && bestValue > alpha)
1426 // Futility pruning parameters, not needed when in check
1427 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1428 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1431 // Initialize a MovePicker object for the current position, and prepare
1432 // to search the moves. Because the depth is <= 0 here, only captures,
1433 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1435 MovePicker mp(pos, ttMove, depth, H);
1438 // Loop through the moves until no moves remain or a beta cutoff occurs
1439 while ( alpha < beta
1440 && (move = mp.get_next_move()) != MOVE_NONE)
1442 assert(move_is_ok(move));
1444 moveIsCheck = pos.move_is_check(move, ci);
1452 && !move_is_promotion(move)
1453 && !pos.move_is_passed_pawn_push(move))
1455 futilityValue = futilityBase
1456 + pos.endgame_value_of_piece_on(move_to(move))
1457 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1459 if (futilityValue < alpha)
1461 if (futilityValue > bestValue)
1462 bestValue = futilityValue;
1466 // Prune moves with negative or equal SEE
1467 if ( futilityBase < beta
1468 && depth < DEPTH_ZERO
1469 && pos.see(move) <= 0)
1473 // Detect non-capture evasions that are candidate to be pruned
1474 evasionPrunable = isCheck
1475 && bestValue > VALUE_MATED_IN_PLY_MAX
1476 && !pos.move_is_capture(move)
1477 && !pos.can_castle(pos.side_to_move());
1479 // Don't search moves with negative SEE values
1481 && (!isCheck || evasionPrunable)
1483 && !move_is_promotion(move)
1484 && pos.see_sign(move) < 0)
1487 // Don't search useless checks
1492 && !pos.move_is_capture_or_promotion(move)
1493 && ss->eval + PawnValueMidgame / 4 < beta
1494 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1496 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1497 bestValue = ss->eval + PawnValueMidgame / 4;
1502 // Update current move
1503 ss->currentMove = move;
1505 // Make and search the move
1506 pos.do_move(move, st, ci, moveIsCheck);
1507 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1508 pos.undo_move(move);
1510 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1513 if (value > bestValue)
1519 ss->bestMove = move;
1524 // All legal moves have been searched. A special case: If we're in check
1525 // and no legal moves were found, it is checkmate.
1526 if (isCheck && bestValue == -VALUE_INFINITE)
1527 return value_mated_in(ply);
1529 // Update transposition table
1530 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1531 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1533 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1539 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1540 // bestValue is updated only when returning false because in that case move
1543 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1545 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1546 Square from, to, ksq, victimSq;
1549 Value futilityValue, bv = *bestValue;
1551 from = move_from(move);
1553 them = opposite_color(pos.side_to_move());
1554 ksq = pos.king_square(them);
1555 kingAtt = pos.attacks_from<KING>(ksq);
1556 pc = pos.piece_on(from);
1558 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1559 oldAtt = pos.attacks_from(pc, from, occ);
1560 newAtt = pos.attacks_from(pc, to, occ);
1562 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1563 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1565 if (!(b && (b & (b - 1))))
1568 // Rule 2. Queen contact check is very dangerous
1569 if ( type_of_piece(pc) == QUEEN
1570 && bit_is_set(kingAtt, to))
1573 // Rule 3. Creating new double threats with checks
1574 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1578 victimSq = pop_1st_bit(&b);
1579 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1581 // Note that here we generate illegal "double move"!
1582 if ( futilityValue >= beta
1583 && pos.see_sign(make_move(from, victimSq)) >= 0)
1586 if (futilityValue > bv)
1590 // Update bestValue only if check is not dangerous (because we will prune the move)
1596 // connected_moves() tests whether two moves are 'connected' in the sense
1597 // that the first move somehow made the second move possible (for instance
1598 // if the moving piece is the same in both moves). The first move is assumed
1599 // to be the move that was made to reach the current position, while the
1600 // second move is assumed to be a move from the current position.
1602 bool connected_moves(const Position& pos, Move m1, Move m2) {
1604 Square f1, t1, f2, t2;
1607 assert(m1 && move_is_ok(m1));
1608 assert(m2 && move_is_ok(m2));
1610 // Case 1: The moving piece is the same in both moves
1616 // Case 2: The destination square for m2 was vacated by m1
1622 // Case 3: Moving through the vacated square
1623 if ( piece_is_slider(pos.piece_on(f2))
1624 && bit_is_set(squares_between(f2, t2), f1))
1627 // Case 4: The destination square for m2 is defended by the moving piece in m1
1628 p = pos.piece_on(t1);
1629 if (bit_is_set(pos.attacks_from(p, t1), t2))
1632 // Case 5: Discovered check, checking piece is the piece moved in m1
1633 if ( piece_is_slider(p)
1634 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1635 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1637 // discovered_check_candidates() works also if the Position's side to
1638 // move is the opposite of the checking piece.
1639 Color them = opposite_color(pos.side_to_move());
1640 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1642 if (bit_is_set(dcCandidates, f2))
1649 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1650 // "plies to mate from the current ply". Non-mate scores are unchanged.
1651 // The function is called before storing a value to the transposition table.
1653 Value value_to_tt(Value v, int ply) {
1655 if (v >= VALUE_MATE_IN_PLY_MAX)
1658 if (v <= VALUE_MATED_IN_PLY_MAX)
1665 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1666 // the transposition table to a mate score corrected for the current ply.
1668 Value value_from_tt(Value v, int ply) {
1670 if (v >= VALUE_MATE_IN_PLY_MAX)
1673 if (v <= VALUE_MATED_IN_PLY_MAX)
1680 // extension() decides whether a move should be searched with normal depth,
1681 // or with extended depth. Certain classes of moves (checking moves, in
1682 // particular) are searched with bigger depth than ordinary moves and in
1683 // any case are marked as 'dangerous'. Note that also if a move is not
1684 // extended, as example because the corresponding UCI option is set to zero,
1685 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1686 template <NodeType PvNode>
1687 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1688 bool moveIsCheck, bool* dangerous) {
1690 assert(m != MOVE_NONE);
1692 Depth result = DEPTH_ZERO;
1693 *dangerous = moveIsCheck;
1695 if (moveIsCheck && pos.see_sign(m) >= 0)
1696 result += CheckExtension[PvNode];
1698 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1700 Color c = pos.side_to_move();
1701 if (relative_rank(c, move_to(m)) == RANK_7)
1703 result += PawnPushTo7thExtension[PvNode];
1706 if (pos.pawn_is_passed(c, move_to(m)))
1708 result += PassedPawnExtension[PvNode];
1713 if ( captureOrPromotion
1714 && pos.type_of_piece_on(move_to(m)) != PAWN
1715 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1716 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1717 && !move_is_promotion(m)
1720 result += PawnEndgameExtension[PvNode];
1724 return Min(result, ONE_PLY);
1728 // connected_threat() tests whether it is safe to forward prune a move or if
1729 // is somehow connected to the threat move returned by null search.
1731 bool connected_threat(const Position& pos, Move m, Move threat) {
1733 assert(move_is_ok(m));
1734 assert(threat && move_is_ok(threat));
1735 assert(!pos.move_is_check(m));
1736 assert(!pos.move_is_capture_or_promotion(m));
1737 assert(!pos.move_is_passed_pawn_push(m));
1739 Square mfrom, mto, tfrom, tto;
1741 mfrom = move_from(m);
1743 tfrom = move_from(threat);
1744 tto = move_to(threat);
1746 // Case 1: Don't prune moves which move the threatened piece
1750 // Case 2: If the threatened piece has value less than or equal to the
1751 // value of the threatening piece, don't prune moves which defend it.
1752 if ( pos.move_is_capture(threat)
1753 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1754 || pos.type_of_piece_on(tfrom) == KING)
1755 && pos.move_attacks_square(m, tto))
1758 // Case 3: If the moving piece in the threatened move is a slider, don't
1759 // prune safe moves which block its ray.
1760 if ( piece_is_slider(pos.piece_on(tfrom))
1761 && bit_is_set(squares_between(tfrom, tto), mto)
1762 && pos.see_sign(m) >= 0)
1769 // ok_to_use_TT() returns true if a transposition table score
1770 // can be used at a given point in search.
1772 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1774 Value v = value_from_tt(tte->value(), ply);
1776 return ( tte->depth() >= depth
1777 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1778 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1780 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1781 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1785 // refine_eval() returns the transposition table score if
1786 // possible otherwise falls back on static position evaluation.
1788 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1792 Value v = value_from_tt(tte->value(), ply);
1794 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1795 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1802 // update_history() registers a good move that produced a beta-cutoff
1803 // in history and marks as failures all the other moves of that ply.
1805 void update_history(const Position& pos, Move move, Depth depth,
1806 Move movesSearched[], int moveCount) {
1808 Value bonus = Value(int(depth) * int(depth));
1810 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1812 for (int i = 0; i < moveCount - 1; i++)
1814 m = movesSearched[i];
1818 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1823 // update_gains() updates the gains table of a non-capture move given
1824 // the static position evaluation before and after the move.
1826 void update_gains(const Position& pos, Move m, Value before, Value after) {
1829 && before != VALUE_NONE
1830 && after != VALUE_NONE
1831 && pos.captured_piece_type() == PIECE_TYPE_NONE
1832 && !move_is_special(m))
1833 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1837 // current_search_time() returns the number of milliseconds which have passed
1838 // since the beginning of the current search.
1840 int current_search_time() {
1842 return get_system_time() - SearchStartTime;
1846 // value_to_uci() converts a value to a string suitable for use with the UCI
1847 // protocol specifications:
1849 // cp <x> The score from the engine's point of view in centipawns.
1850 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1851 // use negative values for y.
1853 std::string value_to_uci(Value v) {
1855 std::stringstream s;
1857 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1858 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1860 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1866 // speed_to_uci() returns a string with time stats of current search suitable
1867 // to be sent to UCI gui.
1869 std::string speed_to_uci(int64_t nodes) {
1871 std::stringstream s;
1872 int t = current_search_time();
1874 s << " nodes " << nodes
1875 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1882 // poll() performs two different functions: It polls for user input, and it
1883 // looks at the time consumed so far and decides if it's time to abort the
1886 void poll(const Position& pos) {
1888 static int lastInfoTime;
1889 int t = current_search_time();
1892 if (input_available())
1894 // We are line oriented, don't read single chars
1895 std::string command;
1897 if (!std::getline(std::cin, command) || command == "quit")
1899 // Quit the program as soon as possible
1901 QuitRequest = StopRequest = true;
1904 else if (command == "stop")
1906 // Stop calculating as soon as possible, but still send the "bestmove"
1907 // and possibly the "ponder" token when finishing the search.
1911 else if (command == "ponderhit")
1913 // The opponent has played the expected move. GUI sends "ponderhit" if
1914 // we were told to ponder on the same move the opponent has played. We
1915 // should continue searching but switching from pondering to normal search.
1918 if (StopOnPonderhit)
1923 // Print search information
1927 else if (lastInfoTime > t)
1928 // HACK: Must be a new search where we searched less than
1929 // NodesBetweenPolls nodes during the first second of search.
1932 else if (t - lastInfoTime >= 1000)
1939 if (dbg_show_hit_rate)
1940 dbg_print_hit_rate();
1942 // Send info on searched nodes as soon as we return to root
1943 SendSearchedNodes = true;
1946 // Should we stop the search?
1950 bool stillAtFirstMove = FirstRootMove
1951 && !AspirationFailLow
1952 && t > TimeMgr.available_time();
1954 bool noMoreTime = t > TimeMgr.maximum_time()
1955 || stillAtFirstMove;
1957 if ( (UseTimeManagement && noMoreTime)
1958 || (ExactMaxTime && t >= ExactMaxTime)
1959 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
1964 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1965 // while the program is pondering. The point is to work around a wrinkle in
1966 // the UCI protocol: When pondering, the engine is not allowed to give a
1967 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1968 // We simply wait here until one of these commands is sent, and return,
1969 // after which the bestmove and pondermove will be printed.
1971 void wait_for_stop_or_ponderhit() {
1973 std::string command;
1975 // Wait for a command from stdin
1976 while ( std::getline(std::cin, command)
1977 && command != "ponderhit" && command != "stop" && command != "quit") {};
1979 if (command != "ponderhit" && command != "stop")
1980 QuitRequest = true; // Must be "quit" or getline() returned false
1984 // init_thread() is the function which is called when a new thread is
1985 // launched. It simply calls the idle_loop() function with the supplied
1986 // threadID. There are two versions of this function; one for POSIX
1987 // threads and one for Windows threads.
1989 #if !defined(_MSC_VER)
1991 void* init_thread(void* threadID) {
1993 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
1999 DWORD WINAPI init_thread(LPVOID threadID) {
2001 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2008 /// The ThreadsManager class
2011 // read_uci_options() updates number of active threads and other internal
2012 // parameters according to the UCI options values. It is called before
2013 // to start a new search.
2015 void ThreadsManager::read_uci_options() {
2017 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2018 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2019 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2020 activeThreads = Options["Threads"].value<int>();
2024 // idle_loop() is where the threads are parked when they have no work to do.
2025 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2026 // object for which the current thread is the master.
2028 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2030 assert(threadID >= 0 && threadID < MAX_THREADS);
2033 bool allFinished = false;
2037 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2038 // master should exit as last one.
2039 if (allThreadsShouldExit)
2042 threads[threadID].state = THREAD_TERMINATED;
2046 // If we are not thinking, wait for a condition to be signaled
2047 // instead of wasting CPU time polling for work.
2048 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2049 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2051 assert(!sp || useSleepingThreads);
2052 assert(threadID != 0 || useSleepingThreads);
2054 if (threads[threadID].state == THREAD_INITIALIZING)
2055 threads[threadID].state = THREAD_AVAILABLE;
2057 // Grab the lock to avoid races with wake_sleeping_thread()
2058 lock_grab(&sleepLock[threadID]);
2060 // If we are master and all slaves have finished do not go to sleep
2061 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2062 allFinished = (i == activeThreads);
2064 if (allFinished || allThreadsShouldExit)
2066 lock_release(&sleepLock[threadID]);
2070 // Do sleep here after retesting sleep conditions
2071 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2072 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2074 lock_release(&sleepLock[threadID]);
2077 // If this thread has been assigned work, launch a search
2078 if (threads[threadID].state == THREAD_WORKISWAITING)
2080 assert(!allThreadsShouldExit);
2082 threads[threadID].state = THREAD_SEARCHING;
2084 // Copy SplitPoint position and search stack and call search()
2085 // with SplitPoint template parameter set to true.
2086 SearchStack ss[PLY_MAX_PLUS_2];
2087 SplitPoint* tsp = threads[threadID].splitPoint;
2088 Position pos(*tsp->pos, threadID);
2090 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2094 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2096 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2098 assert(threads[threadID].state == THREAD_SEARCHING);
2100 threads[threadID].state = THREAD_AVAILABLE;
2102 // Wake up master thread so to allow it to return from the idle loop in
2103 // case we are the last slave of the split point.
2104 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2105 wake_sleeping_thread(tsp->master);
2108 // If this thread is the master of a split point and all slaves have
2109 // finished their work at this split point, return from the idle loop.
2110 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2111 allFinished = (i == activeThreads);
2115 // Because sp->slaves[] is reset under lock protection,
2116 // be sure sp->lock has been released before to return.
2117 lock_grab(&(sp->lock));
2118 lock_release(&(sp->lock));
2120 // In helpful master concept a master can help only a sub-tree, and
2121 // because here is all finished is not possible master is booked.
2122 assert(threads[threadID].state == THREAD_AVAILABLE);
2124 threads[threadID].state = THREAD_SEARCHING;
2131 // init_threads() is called during startup. It launches all helper threads,
2132 // and initializes the split point stack and the global locks and condition
2135 void ThreadsManager::init_threads() {
2137 int i, arg[MAX_THREADS];
2140 // Initialize global locks
2143 for (i = 0; i < MAX_THREADS; i++)
2145 lock_init(&sleepLock[i]);
2146 cond_init(&sleepCond[i]);
2149 // Initialize splitPoints[] locks
2150 for (i = 0; i < MAX_THREADS; i++)
2151 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2152 lock_init(&(threads[i].splitPoints[j].lock));
2154 // Will be set just before program exits to properly end the threads
2155 allThreadsShouldExit = false;
2157 // Threads will be put all threads to sleep as soon as created
2160 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2161 threads[0].state = THREAD_SEARCHING;
2162 for (i = 1; i < MAX_THREADS; i++)
2163 threads[i].state = THREAD_INITIALIZING;
2165 // Launch the helper threads
2166 for (i = 1; i < MAX_THREADS; i++)
2170 #if !defined(_MSC_VER)
2171 pthread_t pthread[1];
2172 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2173 pthread_detach(pthread[0]);
2175 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2179 cout << "Failed to create thread number " << i << endl;
2183 // Wait until the thread has finished launching and is gone to sleep
2184 while (threads[i].state == THREAD_INITIALIZING) {}
2189 // exit_threads() is called when the program exits. It makes all the
2190 // helper threads exit cleanly.
2192 void ThreadsManager::exit_threads() {
2194 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2196 // Wake up all the threads and waits for termination
2197 for (int i = 1; i < MAX_THREADS; i++)
2199 wake_sleeping_thread(i);
2200 while (threads[i].state != THREAD_TERMINATED) {}
2203 // Now we can safely destroy the locks
2204 for (int i = 0; i < MAX_THREADS; i++)
2205 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2206 lock_destroy(&(threads[i].splitPoints[j].lock));
2208 lock_destroy(&mpLock);
2210 // Now we can safely destroy the wait conditions
2211 for (int i = 0; i < MAX_THREADS; i++)
2213 lock_destroy(&sleepLock[i]);
2214 cond_destroy(&sleepCond[i]);
2219 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2220 // the thread's currently active split point, or in some ancestor of
2221 // the current split point.
2223 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2225 assert(threadID >= 0 && threadID < activeThreads);
2227 SplitPoint* sp = threads[threadID].splitPoint;
2229 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2234 // thread_is_available() checks whether the thread with threadID "slave" is
2235 // available to help the thread with threadID "master" at a split point. An
2236 // obvious requirement is that "slave" must be idle. With more than two
2237 // threads, this is not by itself sufficient: If "slave" is the master of
2238 // some active split point, it is only available as a slave to the other
2239 // threads which are busy searching the split point at the top of "slave"'s
2240 // split point stack (the "helpful master concept" in YBWC terminology).
2242 bool ThreadsManager::thread_is_available(int slave, int master) const {
2244 assert(slave >= 0 && slave < activeThreads);
2245 assert(master >= 0 && master < activeThreads);
2246 assert(activeThreads > 1);
2248 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2251 // Make a local copy to be sure doesn't change under our feet
2252 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2254 // No active split points means that the thread is available as
2255 // a slave for any other thread.
2256 if (localActiveSplitPoints == 0 || activeThreads == 2)
2259 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2260 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2261 // could have been set to 0 by another thread leading to an out of bound access.
2262 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2269 // available_thread_exists() tries to find an idle thread which is available as
2270 // a slave for the thread with threadID "master".
2272 bool ThreadsManager::available_thread_exists(int master) const {
2274 assert(master >= 0 && master < activeThreads);
2275 assert(activeThreads > 1);
2277 for (int i = 0; i < activeThreads; i++)
2278 if (thread_is_available(i, master))
2285 // split() does the actual work of distributing the work at a node between
2286 // several available threads. If it does not succeed in splitting the
2287 // node (because no idle threads are available, or because we have no unused
2288 // split point objects), the function immediately returns. If splitting is
2289 // possible, a SplitPoint object is initialized with all the data that must be
2290 // copied to the helper threads and we tell our helper threads that they have
2291 // been assigned work. This will cause them to instantly leave their idle loops and
2292 // call search().When all threads have returned from search() then split() returns.
2294 template <bool Fake>
2295 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2296 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2297 int moveCount, MovePicker* mp, bool pvNode) {
2298 assert(pos.is_ok());
2299 assert(ply > 0 && ply < PLY_MAX);
2300 assert(*bestValue >= -VALUE_INFINITE);
2301 assert(*bestValue <= *alpha);
2302 assert(*alpha < beta);
2303 assert(beta <= VALUE_INFINITE);
2304 assert(depth > DEPTH_ZERO);
2305 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2306 assert(activeThreads > 1);
2308 int i, master = pos.thread();
2309 Thread& masterThread = threads[master];
2313 // If no other thread is available to help us, or if we have too many
2314 // active split points, don't split.
2315 if ( !available_thread_exists(master)
2316 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2318 lock_release(&mpLock);
2322 // Pick the next available split point object from the split point stack
2323 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2325 // Initialize the split point object
2326 splitPoint.parent = masterThread.splitPoint;
2327 splitPoint.master = master;
2328 splitPoint.betaCutoff = false;
2329 splitPoint.ply = ply;
2330 splitPoint.depth = depth;
2331 splitPoint.threatMove = threatMove;
2332 splitPoint.alpha = *alpha;
2333 splitPoint.beta = beta;
2334 splitPoint.pvNode = pvNode;
2335 splitPoint.bestValue = *bestValue;
2337 splitPoint.moveCount = moveCount;
2338 splitPoint.pos = &pos;
2339 splitPoint.nodes = 0;
2341 for (i = 0; i < activeThreads; i++)
2342 splitPoint.slaves[i] = 0;
2344 masterThread.splitPoint = &splitPoint;
2346 // If we are here it means we are not available
2347 assert(masterThread.state != THREAD_AVAILABLE);
2349 int workersCnt = 1; // At least the master is included
2351 // Allocate available threads setting state to THREAD_BOOKED
2352 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2353 if (thread_is_available(i, master))
2355 threads[i].state = THREAD_BOOKED;
2356 threads[i].splitPoint = &splitPoint;
2357 splitPoint.slaves[i] = 1;
2361 assert(Fake || workersCnt > 1);
2363 // We can release the lock because slave threads are already booked and master is not available
2364 lock_release(&mpLock);
2366 // Tell the threads that they have work to do. This will make them leave
2368 for (i = 0; i < activeThreads; i++)
2369 if (i == master || splitPoint.slaves[i])
2371 assert(i == master || threads[i].state == THREAD_BOOKED);
2373 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2375 if (useSleepingThreads && i != master)
2376 wake_sleeping_thread(i);
2379 // Everything is set up. The master thread enters the idle loop, from
2380 // which it will instantly launch a search, because its state is
2381 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2382 // idle loop, which means that the main thread will return from the idle
2383 // loop when all threads have finished their work at this split point.
2384 idle_loop(master, &splitPoint);
2386 // We have returned from the idle loop, which means that all threads are
2387 // finished. Update alpha and bestValue, and return.
2390 *alpha = splitPoint.alpha;
2391 *bestValue = splitPoint.bestValue;
2392 masterThread.activeSplitPoints--;
2393 masterThread.splitPoint = splitPoint.parent;
2394 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2396 lock_release(&mpLock);
2400 // wake_sleeping_thread() wakes up the thread with the given threadID
2401 // when it is time to start a new search.
2403 void ThreadsManager::wake_sleeping_thread(int threadID) {
2405 lock_grab(&sleepLock[threadID]);
2406 cond_signal(&sleepCond[threadID]);
2407 lock_release(&sleepLock[threadID]);
2411 /// RootMove and RootMoveList method's definitions
2413 RootMove::RootMove() {
2416 pv_score = non_pv_score = -VALUE_INFINITE;
2420 RootMove& RootMove::operator=(const RootMove& rm) {
2422 const Move* src = rm.pv;
2425 // Avoid a costly full rm.pv[] copy
2426 do *dst++ = *src; while (*src++ != MOVE_NONE);
2429 pv_score = rm.pv_score;
2430 non_pv_score = rm.non_pv_score;
2434 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2435 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2436 // allow to always have a ponder move even when we fail high at root and also a
2437 // long PV to print that is important for position analysis.
2439 void RootMove::extract_pv_from_tt(Position& pos) {
2441 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2445 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2447 pos.do_move(pv[0], *st++);
2449 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2450 && tte->move() != MOVE_NONE
2451 && pos.move_is_legal(tte->move())
2453 && (!pos.is_draw() || ply < 2))
2455 pv[ply] = tte->move();
2456 pos.do_move(pv[ply++], *st++);
2458 pv[ply] = MOVE_NONE;
2460 do pos.undo_move(pv[--ply]); while (ply);
2463 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2464 // the PV back into the TT. This makes sure the old PV moves are searched
2465 // first, even if the old TT entries have been overwritten.
2467 void RootMove::insert_pv_in_tt(Position& pos) {
2469 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2472 Value v, m = VALUE_NONE;
2475 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2479 tte = TT.retrieve(k);
2481 // Don't overwrite existing correct entries
2482 if (!tte || tte->move() != pv[ply])
2484 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2485 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2487 pos.do_move(pv[ply], *st++);
2489 } while (pv[++ply] != MOVE_NONE);
2491 do pos.undo_move(pv[--ply]); while (ply);
2494 // pv_info_to_uci() returns a string with information on the current PV line
2495 // formatted according to UCI specification.
2497 std::string RootMove::pv_info_to_uci(Position& pos, int depth, Value alpha,
2498 Value beta, int pvIdx) {
2499 std::stringstream s, l;
2502 while (*m != MOVE_NONE)
2505 s << "info depth " << depth
2506 << " seldepth " << int(m - pv)
2507 << " multipv " << pvIdx + 1
2508 << " score " << value_to_uci(pv_score)
2509 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2510 << speed_to_uci(pos.nodes_searched())
2511 << " pv " << l.str();
2517 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2519 MoveStack mlist[MOVES_MAX];
2523 bestMoveChanges = 0;
2525 // Generate all legal moves and add them to RootMoveList
2526 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2527 for (MoveStack* cur = mlist; cur != last; cur++)
2529 // If we have a searchMoves[] list then verify cur->move
2530 // is in the list before to add it.
2531 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2533 if (searchMoves[0] && *sm != cur->move)
2537 rm.pv[0] = cur->move;
2538 rm.pv[1] = MOVE_NONE;
2539 rm.pv_score = -VALUE_INFINITE;
2545 // When playing with strength handicap choose best move among the MultiPV set
2546 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2547 void do_skill_level(Move* best, Move* ponder) {
2549 assert(MultiPV > 1);
2551 // Rml list is already sorted by pv_score in descending order
2553 int max_s = -VALUE_INFINITE;
2554 int size = Min(MultiPV, (int)Rml.size());
2555 int max = Rml[0].pv_score;
2556 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
2557 int wk = 120 - 2 * SkillLevel;
2559 // PRNG sequence should be non deterministic
2560 for (int i = abs(get_system_time() % 50); i > 0; i--)
2561 RK.rand<unsigned>();
2563 // Choose best move. For each move's score we add two terms both dependent
2564 // on wk, one deterministic and bigger for weaker moves, and one random,
2565 // then we choose the move with the resulting highest score.
2566 for (int i = 0; i < size; i++)
2568 s = Rml[i].pv_score;
2570 // Don't allow crazy blunders even at very low skills
2571 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
2574 // This is our magical formula
2575 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
2580 *best = Rml[i].pv[0];
2581 *ponder = Rml[i].pv[1];