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(const Position& pos, Value alpha, Value beta);
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 RootMoveList(Position& pos, Move searchMoves[]);
149 void set_non_pv_scores(const Position& pos);
151 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
152 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& m) {
166 os.iword(0) = int(m);
175 // Maximum depth for razoring
176 const Depth RazorDepth = 4 * ONE_PLY;
178 // Dynamic razoring margin based on depth
179 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
181 // Maximum depth for use of dynamic threat detection when null move fails low
182 const Depth ThreatDepth = 5 * ONE_PLY;
184 // Step 9. Internal iterative deepening
186 // Minimum depth for use of internal iterative deepening
187 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
189 // At Non-PV nodes we do an internal iterative deepening search
190 // when the static evaluation is bigger then beta - IIDMargin.
191 const Value IIDMargin = Value(0x100);
193 // Step 11. Decide the new search depth
195 // Extensions. Configurable UCI options
196 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
197 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
198 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
200 // Minimum depth for use of singular extension
201 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
203 // If the TT move is at least SingularExtensionMargin better then the
204 // remaining ones we will extend it.
205 const Value SingularExtensionMargin = Value(0x20);
207 // Step 12. Futility pruning
209 // Futility margin for quiescence search
210 const Value FutilityMarginQS = Value(0x80);
212 // Futility lookup tables (initialized at startup) and their getter functions
213 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
214 int FutilityMoveCountArray[32]; // [depth]
216 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
217 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
219 // Step 14. Reduced search
221 // Reduction lookup tables (initialized at startup) and their getter functions
222 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
224 template <NodeType PV>
225 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
227 // Common adjustments
229 // Search depth at iteration 1
230 const Depth InitialDepth = ONE_PLY;
232 // Easy move margin. An easy move candidate must be at least this much
233 // better than the second best move.
234 const Value EasyMoveMargin = Value(0x200);
237 /// Namespace variables
245 // Scores and number of times the best move changed for each iteration
246 Value ValueByIteration[PLY_MAX_PLUS_2];
247 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
249 // Search window management
255 // Time managment variables
256 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
257 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
258 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
263 std::ofstream LogFile;
265 // Multi-threads manager object
266 ThreadsManager ThreadsMgr;
268 // Node counters, used only by thread[0] but try to keep in different cache
269 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
271 int NodesBetweenPolls = 30000;
278 Value id_loop(Position& pos, Move searchMoves[]);
279 Value root_search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, RootMoveList& rml);
281 template <NodeType PvNode, bool SpNode>
282 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
284 template <NodeType PvNode>
285 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
287 template <NodeType PvNode>
288 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
290 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
291 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
294 template <NodeType PvNode>
295 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
297 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
298 bool connected_moves(const Position& pos, Move m1, Move m2);
299 bool value_is_mate(Value value);
300 Value value_to_tt(Value v, int ply);
301 Value value_from_tt(Value v, int ply);
302 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
303 bool connected_threat(const Position& pos, Move m, Move threat);
304 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
305 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
306 void update_killers(Move m, SearchStack* ss);
307 void update_gains(const Position& pos, Move move, Value before, Value after);
309 int current_search_time();
310 std::string value_to_uci(Value v);
311 int nps(const Position& pos);
312 void poll(const Position& pos);
314 void wait_for_stop_or_ponderhit();
315 void init_ss_array(SearchStack* ss, int size);
317 #if !defined(_MSC_VER)
318 void* init_thread(void* threadID);
320 DWORD WINAPI init_thread(LPVOID threadID);
330 /// init_threads(), exit_threads() and nodes_searched() are helpers to
331 /// give accessibility to some TM methods from outside of current file.
333 void init_threads() { ThreadsMgr.init_threads(); }
334 void exit_threads() { ThreadsMgr.exit_threads(); }
337 /// init_search() is called during startup. It initializes various lookup tables
341 int d; // depth (ONE_PLY == 2)
342 int hd; // half depth (ONE_PLY == 1)
345 // Init reductions array
346 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
348 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
349 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
350 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
351 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
354 // Init futility margins array
355 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
356 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
358 // Init futility move count array
359 for (d = 0; d < 32; d++)
360 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
364 /// perft() is our utility to verify move generation is bug free. All the legal
365 /// moves up to given depth are generated and counted and the sum returned.
367 int perft(Position& pos, Depth depth)
369 MoveStack mlist[MOVES_MAX];
374 // Generate all legal moves
375 MoveStack* last = generate_moves(pos, mlist);
377 // If we are at the last ply we don't need to do and undo
378 // the moves, just to count them.
379 if (depth <= ONE_PLY)
380 return int(last - mlist);
382 // Loop through all legal moves
384 for (MoveStack* cur = mlist; cur != last; cur++)
387 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
388 sum += perft(pos, depth - ONE_PLY);
395 /// think() is the external interface to Stockfish's search, and is called when
396 /// the program receives the UCI 'go' command. It initializes various
397 /// search-related global variables, and calls root_search(). It returns false
398 /// when a quit command is received during the search.
400 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
401 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
403 // Initialize global search variables
404 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
406 SearchStartTime = get_system_time();
407 ExactMaxTime = maxTime;
410 InfiniteSearch = infinite;
411 PonderSearch = ponder;
412 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
414 // Look for a book move, only during games, not tests
415 if (UseTimeManagement && Options["OwnBook"].value<bool>())
417 if (Options["Book File"].value<std::string>() != OpeningBook.file_name())
418 OpeningBook.open(Options["Book File"].value<std::string>());
420 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
421 if (bookMove != MOVE_NONE)
424 wait_for_stop_or_ponderhit();
426 cout << "bestmove " << bookMove << endl;
431 // Read UCI option values
432 TT.set_size(Options["Hash"].value<int>());
433 if (Options["Clear Hash"].value<bool>())
435 Options["Clear Hash"].set_value("false");
439 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
440 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
441 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
442 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
443 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
444 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
445 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
446 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
447 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
448 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
449 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
450 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
451 MultiPV = Options["MultiPV"].value<int>();
452 UseLogFile = Options["Use Search Log"].value<bool>();
455 LogFile.open(Options["Search Log Filename"].value<std::string>().c_str(), std::ios::out | std::ios::app);
457 read_weights(pos.side_to_move());
459 // Set the number of active threads
460 ThreadsMgr.read_uci_options();
461 init_eval(ThreadsMgr.active_threads());
463 // Wake up needed threads
464 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
465 ThreadsMgr.wake_sleeping_thread(i);
468 int myTime = time[pos.side_to_move()];
469 int myIncrement = increment[pos.side_to_move()];
470 if (UseTimeManagement)
471 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
473 // Set best NodesBetweenPolls interval to avoid lagging under
474 // heavy time pressure.
476 NodesBetweenPolls = Min(MaxNodes, 30000);
477 else if (myTime && myTime < 1000)
478 NodesBetweenPolls = 1000;
479 else if (myTime && myTime < 5000)
480 NodesBetweenPolls = 5000;
482 NodesBetweenPolls = 30000;
484 // Write search information to log file
486 LogFile << "Searching: " << pos.to_fen() << endl
487 << "infinite: " << infinite
488 << " ponder: " << ponder
489 << " time: " << myTime
490 << " increment: " << myIncrement
491 << " moves to go: " << movesToGo << endl;
493 // We're ready to start thinking. Call the iterative deepening loop function
494 id_loop(pos, searchMoves);
499 // This makes all the threads to go to sleep
500 ThreadsMgr.set_active_threads(1);
508 // id_loop() is the main iterative deepening loop. It calls root_search
509 // repeatedly with increasing depth until the allocated thinking time has
510 // been consumed, the user stops the search, or the maximum search depth is
513 Value id_loop(Position& pos, Move searchMoves[]) {
515 SearchStack ss[PLY_MAX_PLUS_2];
517 Move EasyMove = MOVE_NONE;
518 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
520 // Moves to search are verified, scored and sorted
521 RootMoveList rml(pos, searchMoves);
523 // Handle special case of searching on a mate/stale position
527 wait_for_stop_or_ponderhit();
529 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
535 init_ss_array(ss, PLY_MAX_PLUS_2);
536 ValueByIteration[1] = rml[0].pv_score;
539 // Send initial RootMoveList scoring (iteration 1)
540 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
541 << "info depth " << Iteration
542 << "\n" << rml[0].pv_info_to_uci(pos, alpha, beta) << endl;
544 // Is one move significantly better than others after initial scoring ?
546 || rml[0].pv_score > rml[1].pv_score + EasyMoveMargin)
547 EasyMove = rml[0].pv[0];
549 // Iterative deepening loop
550 while (Iteration < PLY_MAX)
552 // Initialize iteration
554 BestMoveChangesByIteration[Iteration] = 0;
556 cout << "info depth " << Iteration << endl;
558 // Calculate dynamic aspiration window based on previous iterations
559 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
561 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
562 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
564 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
565 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
567 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
568 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
571 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
573 // Search to the current depth, rml is updated and sorted
574 value = root_search(pos, ss, alpha, beta, depth, rml);
577 break; // Value cannot be trusted. Break out immediately!
579 //Save info about search result
580 ValueByIteration[Iteration] = value;
582 // Drop the easy move if differs from the new best move
583 if (rml[0].pv[0] != EasyMove)
584 EasyMove = MOVE_NONE;
586 if (UseTimeManagement)
589 bool stopSearch = false;
591 // Stop search early if there is only a single legal move,
592 // we search up to Iteration 6 anyway to get a proper score.
593 if (Iteration >= 6 && rml.size() == 1)
596 // Stop search early when the last two iterations returned a mate score
598 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
599 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
602 // Stop search early if one move seems to be much better than the others
604 && EasyMove == rml[0].pv[0]
605 && ( ( rml[0].nodes > (pos.nodes_searched() * 85) / 100
606 && current_search_time() > TimeMgr.available_time() / 16)
607 ||( rml[0].nodes > (pos.nodes_searched() * 98) / 100
608 && current_search_time() > TimeMgr.available_time() / 32)))
611 // Add some extra time if the best move has changed during the last two iterations
612 if (Iteration > 5 && Iteration <= 50)
613 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
614 BestMoveChangesByIteration[Iteration-1]);
616 // Stop search if most of MaxSearchTime is consumed at the end of the
617 // iteration. We probably don't have enough time to search the first
618 // move at the next iteration anyway.
619 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
625 StopOnPonderhit = true;
631 if (MaxDepth && Iteration >= MaxDepth)
635 // If we are pondering or in infinite search, we shouldn't print the
636 // best move before we are told to do so.
637 if (!AbortSearch && (PonderSearch || InfiniteSearch))
638 wait_for_stop_or_ponderhit();
640 // Print final search statistics
641 cout << "info nodes " << pos.nodes_searched()
642 << " nps " << nps(pos)
643 << " time " << current_search_time() << endl;
645 // Print the best move and the ponder move to the standard output
646 cout << "bestmove " << rml[0].pv[0];
648 if (rml[0].pv[1] != MOVE_NONE)
649 cout << " ponder " << rml[0].pv[1];
656 dbg_print_mean(LogFile);
658 if (dbg_show_hit_rate)
659 dbg_print_hit_rate(LogFile);
661 LogFile << "\nNodes: " << pos.nodes_searched()
662 << "\nNodes/second: " << nps(pos)
663 << "\nBest move: " << move_to_san(pos, rml[0].pv[0]);
666 pos.do_move(rml[0].pv[0], st);
667 LogFile << "\nPonder move: "
668 << move_to_san(pos, rml[0].pv[1]) // Works also with MOVE_NONE
671 return rml[0].pv_score;
675 // root_search() is the function which searches the root node. It is
676 // similar to search_pv except that it prints some information to the
677 // standard output and handles the fail low/high loops.
679 Value root_search(Position& pos, SearchStack* ss, Value alpha,
680 Value beta, Depth depth, RootMoveList& rml) {
686 Value value, oldAlpha;
687 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
688 int researchCountFH, researchCountFL;
690 researchCountFH = researchCountFL = 0;
692 isCheck = pos.is_check();
694 // Step 1. Initialize node (polling is omitted at root)
695 ss->currentMove = ss->bestMove = MOVE_NONE;
697 // Step 2. Check for aborted search (omitted at root)
698 // Step 3. Mate distance pruning (omitted at root)
699 // Step 4. Transposition table lookup (omitted at root)
701 // Step 5. Evaluate the position statically
702 // At root we do this only to get reference value for child nodes
703 ss->evalMargin = VALUE_NONE;
704 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
706 // Step 6. Razoring (omitted at root)
707 // Step 7. Static null move pruning (omitted at root)
708 // Step 8. Null move search with verification search (omitted at root)
709 // Step 9. Internal iterative deepening (omitted at root)
711 // Step extra. Fail low loop
712 // We start with small aspiration window and in case of fail low, we research
713 // with bigger window until we are not failing low anymore.
716 // Sort the moves before to (re)search
717 rml.set_non_pv_scores(pos);
720 // Step 10. Loop through all moves in the root move list
721 for (int i = 0; i < (int)rml.size() && !AbortSearch; i++)
723 // This is used by time management
724 FirstRootMove = (i == 0);
726 // Save the current node count before the move is searched
727 nodes = pos.nodes_searched();
729 // Pick the next root move, and print the move and the move number to
730 // the standard output.
731 move = ss->currentMove = rml[i].pv[0];
733 if (current_search_time() >= 1000)
734 cout << "info currmove " << move
735 << " currmovenumber " << i + 1 << endl;
737 moveIsCheck = pos.move_is_check(move);
738 captureOrPromotion = pos.move_is_capture_or_promotion(move);
740 // Step 11. Decide the new search depth
741 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
742 newDepth = depth + ext;
744 // Step 12. Futility pruning (omitted at root)
746 // Step extra. Fail high loop
747 // If move fails high, we research with bigger window until we are not failing
749 value = -VALUE_INFINITE;
753 // Step 13. Make the move
754 pos.do_move(move, st, ci, moveIsCheck);
756 // Step extra. pv search
757 // We do pv search for first moves (i < MultiPV)
758 // and for fail high research (value > alpha)
759 if (i < MultiPV || value > alpha)
761 // Aspiration window is disabled in multi-pv case
763 alpha = -VALUE_INFINITE;
765 // Full depth PV search, done on first move or after a fail high
766 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
770 // Step 14. Reduced search
771 // if the move fails high will be re-searched at full depth
772 bool doFullDepthSearch = true;
774 if ( depth >= 3 * ONE_PLY
776 && !captureOrPromotion
777 && !move_is_castle(move))
779 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
782 assert(newDepth-ss->reduction >= ONE_PLY);
784 // Reduced depth non-pv search using alpha as upperbound
785 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
786 doFullDepthSearch = (value > alpha);
788 ss->reduction = DEPTH_ZERO; // Restore original reduction
791 // Step 15. Full depth search
792 if (doFullDepthSearch)
794 // Full depth non-pv search using alpha as upperbound
795 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
797 // If we are above alpha then research at same depth but as PV
798 // to get a correct score or eventually a fail high above beta.
800 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
804 // Step 16. Undo move
807 // Can we exit fail high loop ?
808 if (AbortSearch || value < beta)
811 // We are failing high and going to do a research. It's important to update
812 // the score before research in case we run out of time while researching.
814 rml[i].pv_score = value;
815 rml[i].extract_pv_from_tt(pos);
817 // Inform GUI that PV has changed
818 cout << rml[i].pv_info_to_uci(pos, alpha, beta) << endl;
820 // Prepare for a research after a fail high, each time with a wider window
821 beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
824 } // End of fail high loop
826 // Finished searching the move. If AbortSearch is true, the search
827 // was aborted because the user interrupted the search or because we
828 // ran out of time. In this case, the return value of the search cannot
829 // be trusted, and we break out of the loop without updating the best
834 // Remember searched nodes counts for this move
835 rml[i].nodes += pos.nodes_searched() - nodes;
837 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
838 assert(value < beta);
840 // Step 17. Check for new best move
841 if (value <= alpha && i >= MultiPV)
842 rml[i].pv_score = -VALUE_INFINITE;
845 // PV move or new best move!
849 rml[i].pv_score = value;
850 rml[i].extract_pv_from_tt(pos);
854 // We record how often the best move has been changed in each
855 // iteration. This information is used for time managment: When
856 // the best move changes frequently, we allocate some more time.
858 BestMoveChangesByIteration[Iteration]++;
860 // Inform GUI that PV has changed
861 cout << rml[i].pv_info_to_uci(pos, alpha, beta) << endl;
863 // Raise alpha to setup proper non-pv search upper bound
870 for (int j = 0; j < Min(MultiPV, (int)rml.size()); j++)
872 cout << "info multipv " << j + 1
873 << " score " << value_to_uci(rml[j].pv_score)
874 << " depth " << (j <= i ? Iteration : Iteration - 1)
875 << " time " << current_search_time()
876 << " nodes " << pos.nodes_searched()
877 << " nps " << nps(pos)
880 for (int k = 0; rml[j].pv[k] != MOVE_NONE && k < PLY_MAX; k++)
881 cout << rml[j].pv[k] << " ";
885 alpha = rml[Min(i, MultiPV - 1)].pv_score;
887 } // PV move or new best move
889 assert(alpha >= oldAlpha);
891 AspirationFailLow = (alpha == oldAlpha);
893 if (AspirationFailLow && StopOnPonderhit)
894 StopOnPonderhit = false;
897 // Can we exit fail low loop ?
898 if (AbortSearch || !AspirationFailLow)
901 // Prepare for a research after a fail low, each time with a wider window
902 oldAlpha = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
907 // Sort the moves before to return
910 // Write PV lines to transposition table, in case the relevant entries
911 // have been overwritten during the search.
912 for (int i = 0; i < MultiPV; i++)
913 rml[i].insert_pv_in_tt(pos);
919 // search<>() is the main search function for both PV and non-PV nodes and for
920 // normal and SplitPoint nodes. When called just after a split point the search
921 // is simpler because we have already probed the hash table, done a null move
922 // search, and searched the first move before splitting, we don't have to repeat
923 // all this work again. We also don't need to store anything to the hash table
924 // here: This is taken care of after we return from the split point.
926 template <NodeType PvNode, bool SpNode>
927 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
929 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
930 assert(beta > alpha && beta <= VALUE_INFINITE);
931 assert(PvNode || alpha == beta - 1);
932 assert(ply > 0 && ply < PLY_MAX);
933 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
935 Move movesSearched[MOVES_MAX];
939 Move ttMove, move, excludedMove, threatMove;
942 Value bestValue, value, oldAlpha;
943 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
944 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
945 bool mateThreat = false;
947 int threadID = pos.thread();
948 SplitPoint* sp = NULL;
949 refinedValue = bestValue = value = -VALUE_INFINITE;
951 isCheck = pos.is_check();
957 ttMove = excludedMove = MOVE_NONE;
958 threatMove = sp->threatMove;
959 mateThreat = sp->mateThreat;
960 goto split_point_start;
962 else {} // Hack to fix icc's "statement is unreachable" warning
964 // Step 1. Initialize node and poll. Polling can abort search
965 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
966 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
968 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
974 // Step 2. Check for aborted search and immediate draw
976 || ThreadsMgr.cutoff_at_splitpoint(threadID)
978 || ply >= PLY_MAX - 1)
981 // Step 3. Mate distance pruning
982 alpha = Max(value_mated_in(ply), alpha);
983 beta = Min(value_mate_in(ply+1), beta);
987 // Step 4. Transposition table lookup
989 // We don't want the score of a partial search to overwrite a previous full search
990 // TT value, so we use a different position key in case of an excluded move exists.
991 excludedMove = ss->excludedMove;
992 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
994 tte = TT.retrieve(posKey);
995 ttMove = tte ? tte->move() : MOVE_NONE;
997 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
998 // This is to avoid problems in the following areas:
1000 // * Repetition draw detection
1001 // * Fifty move rule detection
1002 // * Searching for a mate
1003 // * Printing of full PV line
1004 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1007 ss->bestMove = ttMove; // Can be MOVE_NONE
1008 return value_from_tt(tte->value(), ply);
1011 // Step 5. Evaluate the position statically and
1012 // update gain statistics of parent move.
1014 ss->eval = ss->evalMargin = VALUE_NONE;
1017 assert(tte->static_value() != VALUE_NONE);
1019 ss->eval = tte->static_value();
1020 ss->evalMargin = tte->static_value_margin();
1021 refinedValue = refine_eval(tte, ss->eval, ply);
1025 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1026 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1029 // Save gain for the parent non-capture move
1030 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1032 // Step 6. Razoring (is omitted in PV nodes)
1034 && depth < RazorDepth
1036 && refinedValue < beta - razor_margin(depth)
1037 && ttMove == MOVE_NONE
1038 && !value_is_mate(beta)
1039 && !pos.has_pawn_on_7th(pos.side_to_move()))
1041 Value rbeta = beta - razor_margin(depth);
1042 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1044 // Logically we should return (v + razor_margin(depth)), but
1045 // surprisingly this did slightly weaker in tests.
1049 // Step 7. Static null move pruning (is omitted in PV nodes)
1050 // We're betting that the opponent doesn't have a move that will reduce
1051 // the score by more than futility_margin(depth) if we do a null move.
1053 && !ss->skipNullMove
1054 && depth < RazorDepth
1056 && refinedValue >= beta + futility_margin(depth, 0)
1057 && !value_is_mate(beta)
1058 && pos.non_pawn_material(pos.side_to_move()))
1059 return refinedValue - futility_margin(depth, 0);
1061 // Step 8. Null move search with verification search (is omitted in PV nodes)
1063 && !ss->skipNullMove
1066 && refinedValue >= beta
1067 && !value_is_mate(beta)
1068 && pos.non_pawn_material(pos.side_to_move()))
1070 ss->currentMove = MOVE_NULL;
1072 // Null move dynamic reduction based on depth
1073 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1075 // Null move dynamic reduction based on value
1076 if (refinedValue - beta > PawnValueMidgame)
1079 pos.do_null_move(st);
1080 (ss+1)->skipNullMove = true;
1081 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1082 (ss+1)->skipNullMove = false;
1083 pos.undo_null_move();
1085 if (nullValue >= beta)
1087 // Do not return unproven mate scores
1088 if (nullValue >= value_mate_in(PLY_MAX))
1091 if (depth < 6 * ONE_PLY)
1094 // Do verification search at high depths
1095 ss->skipNullMove = true;
1096 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1097 ss->skipNullMove = false;
1104 // The null move failed low, which means that we may be faced with
1105 // some kind of threat. If the previous move was reduced, check if
1106 // the move that refuted the null move was somehow connected to the
1107 // move which was reduced. If a connection is found, return a fail
1108 // low score (which will cause the reduced move to fail high in the
1109 // parent node, which will trigger a re-search with full depth).
1110 if (nullValue == value_mated_in(ply + 2))
1113 threatMove = (ss+1)->bestMove;
1114 if ( depth < ThreatDepth
1115 && (ss-1)->reduction
1116 && threatMove != MOVE_NONE
1117 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1122 // Step 9. Internal iterative deepening
1123 if ( depth >= IIDDepth[PvNode]
1124 && ttMove == MOVE_NONE
1125 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1127 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1129 ss->skipNullMove = true;
1130 search<PvNode>(pos, ss, alpha, beta, d, ply);
1131 ss->skipNullMove = false;
1133 ttMove = ss->bestMove;
1134 tte = TT.retrieve(posKey);
1137 // Expensive mate threat detection (only for PV nodes)
1139 mateThreat = pos.has_mate_threat();
1141 split_point_start: // At split points actual search starts from here
1143 // Initialize a MovePicker object for the current position
1144 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1145 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1146 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1148 ss->bestMove = MOVE_NONE;
1149 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1150 futilityBase = ss->eval + ss->evalMargin;
1151 singularExtensionNode = !SpNode
1152 && depth >= SingularExtensionDepth[PvNode]
1155 && !excludedMove // Do not allow recursive singular extension search
1156 && (tte->type() & VALUE_TYPE_LOWER)
1157 && tte->depth() >= depth - 3 * ONE_PLY;
1160 lock_grab(&(sp->lock));
1161 bestValue = sp->bestValue;
1164 // Step 10. Loop through moves
1165 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1166 while ( bestValue < beta
1167 && (move = mp.get_next_move()) != MOVE_NONE
1168 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1170 assert(move_is_ok(move));
1174 moveCount = ++sp->moveCount;
1175 lock_release(&(sp->lock));
1177 else if (move == excludedMove)
1180 movesSearched[moveCount++] = move;
1182 moveIsCheck = pos.move_is_check(move, ci);
1183 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1185 // Step 11. Decide the new search depth
1186 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1188 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1189 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1190 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1191 // lower then ttValue minus a margin then we extend ttMove.
1192 if ( singularExtensionNode
1193 && move == tte->move()
1196 Value ttValue = value_from_tt(tte->value(), ply);
1198 if (abs(ttValue) < VALUE_KNOWN_WIN)
1200 Value b = ttValue - SingularExtensionMargin;
1201 ss->excludedMove = move;
1202 ss->skipNullMove = true;
1203 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1204 ss->skipNullMove = false;
1205 ss->excludedMove = MOVE_NONE;
1206 ss->bestMove = MOVE_NONE;
1212 // Update current move (this must be done after singular extension search)
1213 ss->currentMove = move;
1214 newDepth = depth - ONE_PLY + ext;
1216 // Step 12. Futility pruning (is omitted in PV nodes)
1218 && !captureOrPromotion
1222 && !move_is_castle(move))
1224 // Move count based pruning
1225 if ( moveCount >= futility_move_count(depth)
1226 && !(threatMove && connected_threat(pos, move, threatMove))
1227 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1230 lock_grab(&(sp->lock));
1235 // Value based pruning
1236 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1237 // but fixing this made program slightly weaker.
1238 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1239 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1240 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1242 if (futilityValueScaled < beta)
1246 lock_grab(&(sp->lock));
1247 if (futilityValueScaled > sp->bestValue)
1248 sp->bestValue = bestValue = futilityValueScaled;
1250 else if (futilityValueScaled > bestValue)
1251 bestValue = futilityValueScaled;
1256 // Prune moves with negative SEE at low depths
1257 if ( predictedDepth < 2 * ONE_PLY
1258 && bestValue > value_mated_in(PLY_MAX)
1259 && pos.see_sign(move) < 0)
1262 lock_grab(&(sp->lock));
1268 // Step 13. Make the move
1269 pos.do_move(move, st, ci, moveIsCheck);
1271 // Step extra. pv search (only in PV nodes)
1272 // The first move in list is the expected PV
1273 if (PvNode && moveCount == 1)
1274 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1277 // Step 14. Reduced depth search
1278 // If the move fails high will be re-searched at full depth.
1279 bool doFullDepthSearch = true;
1281 if ( depth >= 3 * ONE_PLY
1282 && !captureOrPromotion
1284 && !move_is_castle(move)
1285 && ss->killers[0] != move
1286 && ss->killers[1] != move)
1288 ss->reduction = reduction<PvNode>(depth, moveCount);
1292 alpha = SpNode ? sp->alpha : alpha;
1293 Depth d = newDepth - ss->reduction;
1294 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1296 doFullDepthSearch = (value > alpha);
1298 ss->reduction = DEPTH_ZERO; // Restore original reduction
1301 // Step 15. Full depth search
1302 if (doFullDepthSearch)
1304 alpha = SpNode ? sp->alpha : alpha;
1305 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1307 // Step extra. pv search (only in PV nodes)
1308 // Search only for possible new PV nodes, if instead value >= beta then
1309 // parent node fails low with value <= alpha and tries another move.
1310 if (PvNode && value > alpha && value < beta)
1311 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1315 // Step 16. Undo move
1316 pos.undo_move(move);
1318 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1320 // Step 17. Check for new best move
1323 lock_grab(&(sp->lock));
1324 bestValue = sp->bestValue;
1328 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1333 sp->bestValue = value;
1337 if (PvNode && value < beta) // We want always alpha < beta
1345 sp->betaCutoff = true;
1347 if (value == value_mate_in(ply + 1))
1348 ss->mateKiller = move;
1350 ss->bestMove = move;
1353 sp->parentSstack->bestMove = move;
1357 // Step 18. Check for split
1359 && depth >= ThreadsMgr.min_split_depth()
1360 && ThreadsMgr.active_threads() > 1
1362 && ThreadsMgr.available_thread_exists(threadID)
1364 && !ThreadsMgr.cutoff_at_splitpoint(threadID)
1366 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1367 threatMove, mateThreat, moveCount, &mp, PvNode);
1370 // Step 19. Check for mate and stalemate
1371 // All legal moves have been searched and if there are
1372 // no legal moves, it must be mate or stalemate.
1373 // If one move was excluded return fail low score.
1374 if (!SpNode && !moveCount)
1375 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1377 // Step 20. Update tables
1378 // If the search is not aborted, update the transposition table,
1379 // history counters, and killer moves.
1380 if (!SpNode && !AbortSearch && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1382 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1383 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1384 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1386 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1388 // Update killers and history only for non capture moves that fails high
1389 if ( bestValue >= beta
1390 && !pos.move_is_capture_or_promotion(move))
1392 update_history(pos, move, depth, movesSearched, moveCount);
1393 update_killers(move, ss);
1399 // Here we have the lock still grabbed
1400 sp->slaves[threadID] = 0;
1401 sp->nodes += pos.nodes_searched();
1402 lock_release(&(sp->lock));
1405 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1410 // qsearch() is the quiescence search function, which is called by the main
1411 // search function when the remaining depth is zero (or, to be more precise,
1412 // less than ONE_PLY).
1414 template <NodeType PvNode>
1415 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1417 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1418 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1419 assert(PvNode || alpha == beta - 1);
1421 assert(ply > 0 && ply < PLY_MAX);
1422 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1426 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1427 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1430 Value oldAlpha = alpha;
1432 ss->bestMove = ss->currentMove = MOVE_NONE;
1434 // Check for an instant draw or maximum ply reached
1435 if (pos.is_draw() || ply >= PLY_MAX - 1)
1438 // Decide whether or not to include checks, this fixes also the type of
1439 // TT entry depth that we are going to use. Note that in qsearch we use
1440 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1441 isCheck = pos.is_check();
1442 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1444 // Transposition table lookup. At PV nodes, we don't use the TT for
1445 // pruning, but only for move ordering.
1446 tte = TT.retrieve(pos.get_key());
1447 ttMove = (tte ? tte->move() : MOVE_NONE);
1449 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1451 ss->bestMove = ttMove; // Can be MOVE_NONE
1452 return value_from_tt(tte->value(), ply);
1455 // Evaluate the position statically
1458 bestValue = futilityBase = -VALUE_INFINITE;
1459 ss->eval = evalMargin = VALUE_NONE;
1460 enoughMaterial = false;
1466 assert(tte->static_value() != VALUE_NONE);
1468 evalMargin = tte->static_value_margin();
1469 ss->eval = bestValue = tte->static_value();
1472 ss->eval = bestValue = evaluate(pos, evalMargin);
1474 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1476 // Stand pat. Return immediately if static value is at least beta
1477 if (bestValue >= beta)
1480 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1485 if (PvNode && bestValue > alpha)
1488 // Futility pruning parameters, not needed when in check
1489 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1490 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1493 // Initialize a MovePicker object for the current position, and prepare
1494 // to search the moves. Because the depth is <= 0 here, only captures,
1495 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1497 MovePicker mp(pos, ttMove, depth, H);
1500 // Loop through the moves until no moves remain or a beta cutoff occurs
1501 while ( alpha < beta
1502 && (move = mp.get_next_move()) != MOVE_NONE)
1504 assert(move_is_ok(move));
1506 moveIsCheck = pos.move_is_check(move, ci);
1514 && !move_is_promotion(move)
1515 && !pos.move_is_passed_pawn_push(move))
1517 futilityValue = futilityBase
1518 + pos.endgame_value_of_piece_on(move_to(move))
1519 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1521 if (futilityValue < alpha)
1523 if (futilityValue > bestValue)
1524 bestValue = futilityValue;
1529 // Detect non-capture evasions that are candidate to be pruned
1530 evasionPrunable = isCheck
1531 && bestValue > value_mated_in(PLY_MAX)
1532 && !pos.move_is_capture(move)
1533 && !pos.can_castle(pos.side_to_move());
1535 // Don't search moves with negative SEE values
1537 && (!isCheck || evasionPrunable)
1539 && !move_is_promotion(move)
1540 && pos.see_sign(move) < 0)
1543 // Don't search useless checks
1548 && !pos.move_is_capture_or_promotion(move)
1549 && ss->eval + PawnValueMidgame / 4 < beta
1550 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1552 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1553 bestValue = ss->eval + PawnValueMidgame / 4;
1558 // Update current move
1559 ss->currentMove = move;
1561 // Make and search the move
1562 pos.do_move(move, st, ci, moveIsCheck);
1563 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1564 pos.undo_move(move);
1566 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1569 if (value > bestValue)
1575 ss->bestMove = move;
1580 // All legal moves have been searched. A special case: If we're in check
1581 // and no legal moves were found, it is checkmate.
1582 if (isCheck && bestValue == -VALUE_INFINITE)
1583 return value_mated_in(ply);
1585 // Update transposition table
1586 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1587 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1589 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1595 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1596 // bestValue is updated only when returning false because in that case move
1599 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1601 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1602 Square from, to, ksq, victimSq;
1605 Value futilityValue, bv = *bestValue;
1607 from = move_from(move);
1609 them = opposite_color(pos.side_to_move());
1610 ksq = pos.king_square(them);
1611 kingAtt = pos.attacks_from<KING>(ksq);
1612 pc = pos.piece_on(from);
1614 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1615 oldAtt = pos.attacks_from(pc, from, occ);
1616 newAtt = pos.attacks_from(pc, to, occ);
1618 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1619 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1621 if (!(b && (b & (b - 1))))
1624 // Rule 2. Queen contact check is very dangerous
1625 if ( type_of_piece(pc) == QUEEN
1626 && bit_is_set(kingAtt, to))
1629 // Rule 3. Creating new double threats with checks
1630 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1634 victimSq = pop_1st_bit(&b);
1635 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1637 // Note that here we generate illegal "double move"!
1638 if ( futilityValue >= beta
1639 && pos.see_sign(make_move(from, victimSq)) >= 0)
1642 if (futilityValue > bv)
1646 // Update bestValue only if check is not dangerous (because we will prune the move)
1652 // connected_moves() tests whether two moves are 'connected' in the sense
1653 // that the first move somehow made the second move possible (for instance
1654 // if the moving piece is the same in both moves). The first move is assumed
1655 // to be the move that was made to reach the current position, while the
1656 // second move is assumed to be a move from the current position.
1658 bool connected_moves(const Position& pos, Move m1, Move m2) {
1660 Square f1, t1, f2, t2;
1663 assert(m1 && move_is_ok(m1));
1664 assert(m2 && move_is_ok(m2));
1666 // Case 1: The moving piece is the same in both moves
1672 // Case 2: The destination square for m2 was vacated by m1
1678 // Case 3: Moving through the vacated square
1679 if ( piece_is_slider(pos.piece_on(f2))
1680 && bit_is_set(squares_between(f2, t2), f1))
1683 // Case 4: The destination square for m2 is defended by the moving piece in m1
1684 p = pos.piece_on(t1);
1685 if (bit_is_set(pos.attacks_from(p, t1), t2))
1688 // Case 5: Discovered check, checking piece is the piece moved in m1
1689 if ( piece_is_slider(p)
1690 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1691 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1693 // discovered_check_candidates() works also if the Position's side to
1694 // move is the opposite of the checking piece.
1695 Color them = opposite_color(pos.side_to_move());
1696 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1698 if (bit_is_set(dcCandidates, f2))
1705 // value_is_mate() checks if the given value is a mate one eventually
1706 // compensated for the ply.
1708 bool value_is_mate(Value value) {
1710 assert(abs(value) <= VALUE_INFINITE);
1712 return value <= value_mated_in(PLY_MAX)
1713 || value >= value_mate_in(PLY_MAX);
1717 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1718 // "plies to mate from the current ply". Non-mate scores are unchanged.
1719 // The function is called before storing a value to the transposition table.
1721 Value value_to_tt(Value v, int ply) {
1723 if (v >= value_mate_in(PLY_MAX))
1726 if (v <= value_mated_in(PLY_MAX))
1733 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1734 // the transposition table to a mate score corrected for the current ply.
1736 Value value_from_tt(Value v, int ply) {
1738 if (v >= value_mate_in(PLY_MAX))
1741 if (v <= value_mated_in(PLY_MAX))
1748 // extension() decides whether a move should be searched with normal depth,
1749 // or with extended depth. Certain classes of moves (checking moves, in
1750 // particular) are searched with bigger depth than ordinary moves and in
1751 // any case are marked as 'dangerous'. Note that also if a move is not
1752 // extended, as example because the corresponding UCI option is set to zero,
1753 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1754 template <NodeType PvNode>
1755 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1756 bool singleEvasion, bool mateThreat, bool* dangerous) {
1758 assert(m != MOVE_NONE);
1760 Depth result = DEPTH_ZERO;
1761 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1765 if (moveIsCheck && pos.see_sign(m) >= 0)
1766 result += CheckExtension[PvNode];
1769 result += SingleEvasionExtension[PvNode];
1772 result += MateThreatExtension[PvNode];
1775 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1777 Color c = pos.side_to_move();
1778 if (relative_rank(c, move_to(m)) == RANK_7)
1780 result += PawnPushTo7thExtension[PvNode];
1783 if (pos.pawn_is_passed(c, move_to(m)))
1785 result += PassedPawnExtension[PvNode];
1790 if ( captureOrPromotion
1791 && pos.type_of_piece_on(move_to(m)) != PAWN
1792 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1793 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1794 && !move_is_promotion(m)
1797 result += PawnEndgameExtension[PvNode];
1802 && captureOrPromotion
1803 && pos.type_of_piece_on(move_to(m)) != PAWN
1804 && pos.see_sign(m) >= 0)
1806 result += ONE_PLY / 2;
1810 return Min(result, ONE_PLY);
1814 // connected_threat() tests whether it is safe to forward prune a move or if
1815 // is somehow coonected to the threat move returned by null search.
1817 bool connected_threat(const Position& pos, Move m, Move threat) {
1819 assert(move_is_ok(m));
1820 assert(threat && move_is_ok(threat));
1821 assert(!pos.move_is_check(m));
1822 assert(!pos.move_is_capture_or_promotion(m));
1823 assert(!pos.move_is_passed_pawn_push(m));
1825 Square mfrom, mto, tfrom, tto;
1827 mfrom = move_from(m);
1829 tfrom = move_from(threat);
1830 tto = move_to(threat);
1832 // Case 1: Don't prune moves which move the threatened piece
1836 // Case 2: If the threatened piece has value less than or equal to the
1837 // value of the threatening piece, don't prune move which defend it.
1838 if ( pos.move_is_capture(threat)
1839 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1840 || pos.type_of_piece_on(tfrom) == KING)
1841 && pos.move_attacks_square(m, tto))
1844 // Case 3: If the moving piece in the threatened move is a slider, don't
1845 // prune safe moves which block its ray.
1846 if ( piece_is_slider(pos.piece_on(tfrom))
1847 && bit_is_set(squares_between(tfrom, tto), mto)
1848 && pos.see_sign(m) >= 0)
1855 // ok_to_use_TT() returns true if a transposition table score
1856 // can be used at a given point in search.
1858 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1860 Value v = value_from_tt(tte->value(), ply);
1862 return ( tte->depth() >= depth
1863 || v >= Max(value_mate_in(PLY_MAX), beta)
1864 || v < Min(value_mated_in(PLY_MAX), beta))
1866 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1867 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1871 // refine_eval() returns the transposition table score if
1872 // possible otherwise falls back on static position evaluation.
1874 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1878 Value v = value_from_tt(tte->value(), ply);
1880 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1881 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1888 // update_history() registers a good move that produced a beta-cutoff
1889 // in history and marks as failures all the other moves of that ply.
1891 void update_history(const Position& pos, Move move, Depth depth,
1892 Move movesSearched[], int moveCount) {
1895 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1897 for (int i = 0; i < moveCount - 1; i++)
1899 m = movesSearched[i];
1903 if (!pos.move_is_capture_or_promotion(m))
1904 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1909 // update_killers() add a good move that produced a beta-cutoff
1910 // among the killer moves of that ply.
1912 void update_killers(Move m, SearchStack* ss) {
1914 if (m == ss->killers[0])
1917 ss->killers[1] = ss->killers[0];
1922 // update_gains() updates the gains table of a non-capture move given
1923 // the static position evaluation before and after the move.
1925 void update_gains(const Position& pos, Move m, Value before, Value after) {
1928 && before != VALUE_NONE
1929 && after != VALUE_NONE
1930 && pos.captured_piece_type() == PIECE_TYPE_NONE
1931 && !move_is_special(m))
1932 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1936 // current_search_time() returns the number of milliseconds which have passed
1937 // since the beginning of the current search.
1939 int current_search_time() {
1941 return get_system_time() - SearchStartTime;
1945 // value_to_uci() converts a value to a string suitable for use with the UCI
1946 // protocol specifications:
1948 // cp <x> The score from the engine's point of view in centipawns.
1949 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1950 // use negative values for y.
1952 std::string value_to_uci(Value v) {
1954 std::stringstream s;
1956 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1957 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1959 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1964 // nps() computes the current nodes/second count.
1966 int nps(const Position& pos) {
1968 int t = current_search_time();
1969 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1973 // poll() performs two different functions: It polls for user input, and it
1974 // looks at the time consumed so far and decides if it's time to abort the
1977 void poll(const Position& pos) {
1979 static int lastInfoTime;
1980 int t = current_search_time();
1983 if (data_available())
1985 // We are line oriented, don't read single chars
1986 std::string command;
1988 if (!std::getline(std::cin, command))
1991 if (command == "quit")
1994 PonderSearch = false;
1998 else if (command == "stop")
2001 PonderSearch = false;
2003 else if (command == "ponderhit")
2007 // Print search information
2011 else if (lastInfoTime > t)
2012 // HACK: Must be a new search where we searched less than
2013 // NodesBetweenPolls nodes during the first second of search.
2016 else if (t - lastInfoTime >= 1000)
2023 if (dbg_show_hit_rate)
2024 dbg_print_hit_rate();
2026 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
2027 << " time " << t << endl;
2030 // Should we stop the search?
2034 bool stillAtFirstMove = FirstRootMove
2035 && !AspirationFailLow
2036 && t > TimeMgr.available_time();
2038 bool noMoreTime = t > TimeMgr.maximum_time()
2039 || stillAtFirstMove;
2041 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2042 || (ExactMaxTime && t >= ExactMaxTime)
2043 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2048 // ponderhit() is called when the program is pondering (i.e. thinking while
2049 // it's the opponent's turn to move) in order to let the engine know that
2050 // it correctly predicted the opponent's move.
2054 int t = current_search_time();
2055 PonderSearch = false;
2057 bool stillAtFirstMove = FirstRootMove
2058 && !AspirationFailLow
2059 && t > TimeMgr.available_time();
2061 bool noMoreTime = t > TimeMgr.maximum_time()
2062 || stillAtFirstMove;
2064 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2069 // init_ss_array() does a fast reset of the first entries of a SearchStack
2070 // array and of all the excludedMove and skipNullMove entries.
2072 void init_ss_array(SearchStack* ss, int size) {
2074 for (int i = 0; i < size; i++, ss++)
2076 ss->excludedMove = MOVE_NONE;
2077 ss->skipNullMove = false;
2078 ss->reduction = DEPTH_ZERO;
2082 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2087 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2088 // while the program is pondering. The point is to work around a wrinkle in
2089 // the UCI protocol: When pondering, the engine is not allowed to give a
2090 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2091 // We simply wait here until one of these commands is sent, and return,
2092 // after which the bestmove and pondermove will be printed (in id_loop()).
2094 void wait_for_stop_or_ponderhit() {
2096 std::string command;
2100 if (!std::getline(std::cin, command))
2103 if (command == "quit")
2108 else if (command == "ponderhit" || command == "stop")
2114 // init_thread() is the function which is called when a new thread is
2115 // launched. It simply calls the idle_loop() function with the supplied
2116 // threadID. There are two versions of this function; one for POSIX
2117 // threads and one for Windows threads.
2119 #if !defined(_MSC_VER)
2121 void* init_thread(void* threadID) {
2123 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2129 DWORD WINAPI init_thread(LPVOID threadID) {
2131 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2138 /// The ThreadsManager class
2141 // read_uci_options() updates number of active threads and other internal
2142 // parameters according to the UCI options values. It is called before
2143 // to start a new search.
2145 void ThreadsManager::read_uci_options() {
2147 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2148 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2149 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2150 activeThreads = Options["Threads"].value<int>();
2154 // idle_loop() is where the threads are parked when they have no work to do.
2155 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2156 // object for which the current thread is the master.
2158 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2160 assert(threadID >= 0 && threadID < MAX_THREADS);
2163 bool allFinished = false;
2167 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2168 // master should exit as last one.
2169 if (allThreadsShouldExit)
2172 threads[threadID].state = THREAD_TERMINATED;
2176 // If we are not thinking, wait for a condition to be signaled
2177 // instead of wasting CPU time polling for work.
2178 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2179 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2181 assert(!sp || useSleepingThreads);
2182 assert(threadID != 0 || useSleepingThreads);
2184 if (threads[threadID].state == THREAD_INITIALIZING)
2185 threads[threadID].state = THREAD_AVAILABLE;
2187 // Grab the lock to avoid races with wake_sleeping_thread()
2188 lock_grab(&sleepLock[threadID]);
2190 // If we are master and all slaves have finished do not go to sleep
2191 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2192 allFinished = (i == activeThreads);
2194 if (allFinished || allThreadsShouldExit)
2196 lock_release(&sleepLock[threadID]);
2200 // Do sleep here after retesting sleep conditions
2201 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2202 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2204 lock_release(&sleepLock[threadID]);
2207 // If this thread has been assigned work, launch a search
2208 if (threads[threadID].state == THREAD_WORKISWAITING)
2210 assert(!allThreadsShouldExit);
2212 threads[threadID].state = THREAD_SEARCHING;
2214 // Here we call search() with SplitPoint template parameter set to true
2215 SplitPoint* tsp = threads[threadID].splitPoint;
2216 Position pos(*tsp->pos, threadID);
2217 SearchStack* ss = tsp->sstack[threadID] + 1;
2221 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2223 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2225 assert(threads[threadID].state == THREAD_SEARCHING);
2227 threads[threadID].state = THREAD_AVAILABLE;
2229 // Wake up master thread so to allow it to return from the idle loop in
2230 // case we are the last slave of the split point.
2231 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2232 wake_sleeping_thread(tsp->master);
2235 // If this thread is the master of a split point and all slaves have
2236 // finished their work at this split point, return from the idle loop.
2237 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2238 allFinished = (i == activeThreads);
2242 // Because sp->slaves[] is reset under lock protection,
2243 // be sure sp->lock has been released before to return.
2244 lock_grab(&(sp->lock));
2245 lock_release(&(sp->lock));
2247 // In helpful master concept a master can help only a sub-tree, and
2248 // because here is all finished is not possible master is booked.
2249 assert(threads[threadID].state == THREAD_AVAILABLE);
2251 threads[threadID].state = THREAD_SEARCHING;
2258 // init_threads() is called during startup. It launches all helper threads,
2259 // and initializes the split point stack and the global locks and condition
2262 void ThreadsManager::init_threads() {
2264 int i, arg[MAX_THREADS];
2267 // Initialize global locks
2270 for (i = 0; i < MAX_THREADS; i++)
2272 lock_init(&sleepLock[i]);
2273 cond_init(&sleepCond[i]);
2276 // Initialize splitPoints[] locks
2277 for (i = 0; i < MAX_THREADS; i++)
2278 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2279 lock_init(&(threads[i].splitPoints[j].lock));
2281 // Will be set just before program exits to properly end the threads
2282 allThreadsShouldExit = false;
2284 // Threads will be put all threads to sleep as soon as created
2287 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2288 threads[0].state = THREAD_SEARCHING;
2289 for (i = 1; i < MAX_THREADS; i++)
2290 threads[i].state = THREAD_INITIALIZING;
2292 // Launch the helper threads
2293 for (i = 1; i < MAX_THREADS; i++)
2297 #if !defined(_MSC_VER)
2298 pthread_t pthread[1];
2299 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2300 pthread_detach(pthread[0]);
2302 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2306 cout << "Failed to create thread number " << i << endl;
2310 // Wait until the thread has finished launching and is gone to sleep
2311 while (threads[i].state == THREAD_INITIALIZING) {}
2316 // exit_threads() is called when the program exits. It makes all the
2317 // helper threads exit cleanly.
2319 void ThreadsManager::exit_threads() {
2321 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2323 // Wake up all the threads and waits for termination
2324 for (int i = 1; i < MAX_THREADS; i++)
2326 wake_sleeping_thread(i);
2327 while (threads[i].state != THREAD_TERMINATED) {}
2330 // Now we can safely destroy the locks
2331 for (int i = 0; i < MAX_THREADS; i++)
2332 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2333 lock_destroy(&(threads[i].splitPoints[j].lock));
2335 lock_destroy(&mpLock);
2337 // Now we can safely destroy the wait conditions
2338 for (int i = 0; i < MAX_THREADS; i++)
2340 lock_destroy(&sleepLock[i]);
2341 cond_destroy(&sleepCond[i]);
2346 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2347 // the thread's currently active split point, or in some ancestor of
2348 // the current split point.
2350 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2352 assert(threadID >= 0 && threadID < activeThreads);
2354 SplitPoint* sp = threads[threadID].splitPoint;
2356 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2361 // thread_is_available() checks whether the thread with threadID "slave" is
2362 // available to help the thread with threadID "master" at a split point. An
2363 // obvious requirement is that "slave" must be idle. With more than two
2364 // threads, this is not by itself sufficient: If "slave" is the master of
2365 // some active split point, it is only available as a slave to the other
2366 // threads which are busy searching the split point at the top of "slave"'s
2367 // split point stack (the "helpful master concept" in YBWC terminology).
2369 bool ThreadsManager::thread_is_available(int slave, int master) const {
2371 assert(slave >= 0 && slave < activeThreads);
2372 assert(master >= 0 && master < activeThreads);
2373 assert(activeThreads > 1);
2375 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2378 // Make a local copy to be sure doesn't change under our feet
2379 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2381 // No active split points means that the thread is available as
2382 // a slave for any other thread.
2383 if (localActiveSplitPoints == 0 || activeThreads == 2)
2386 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2387 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2388 // could have been set to 0 by another thread leading to an out of bound access.
2389 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2396 // available_thread_exists() tries to find an idle thread which is available as
2397 // a slave for the thread with threadID "master".
2399 bool ThreadsManager::available_thread_exists(int master) const {
2401 assert(master >= 0 && master < activeThreads);
2402 assert(activeThreads > 1);
2404 for (int i = 0; i < activeThreads; i++)
2405 if (thread_is_available(i, master))
2412 // split() does the actual work of distributing the work at a node between
2413 // several available threads. If it does not succeed in splitting the
2414 // node (because no idle threads are available, or because we have no unused
2415 // split point objects), the function immediately returns. If splitting is
2416 // possible, a SplitPoint object is initialized with all the data that must be
2417 // copied to the helper threads and we tell our helper threads that they have
2418 // been assigned work. This will cause them to instantly leave their idle loops and
2419 // call search().When all threads have returned from search() then split() returns.
2421 template <bool Fake>
2422 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2423 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2424 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2425 assert(pos.is_ok());
2426 assert(ply > 0 && ply < PLY_MAX);
2427 assert(*bestValue >= -VALUE_INFINITE);
2428 assert(*bestValue <= *alpha);
2429 assert(*alpha < beta);
2430 assert(beta <= VALUE_INFINITE);
2431 assert(depth > DEPTH_ZERO);
2432 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2433 assert(activeThreads > 1);
2435 int i, master = pos.thread();
2436 Thread& masterThread = threads[master];
2440 // If no other thread is available to help us, or if we have too many
2441 // active split points, don't split.
2442 if ( !available_thread_exists(master)
2443 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2445 lock_release(&mpLock);
2449 // Pick the next available split point object from the split point stack
2450 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2452 // Initialize the split point object
2453 splitPoint.parent = masterThread.splitPoint;
2454 splitPoint.master = master;
2455 splitPoint.betaCutoff = false;
2456 splitPoint.ply = ply;
2457 splitPoint.depth = depth;
2458 splitPoint.threatMove = threatMove;
2459 splitPoint.mateThreat = mateThreat;
2460 splitPoint.alpha = *alpha;
2461 splitPoint.beta = beta;
2462 splitPoint.pvNode = pvNode;
2463 splitPoint.bestValue = *bestValue;
2465 splitPoint.moveCount = moveCount;
2466 splitPoint.pos = &pos;
2467 splitPoint.nodes = 0;
2468 splitPoint.parentSstack = ss;
2469 for (i = 0; i < activeThreads; i++)
2470 splitPoint.slaves[i] = 0;
2472 masterThread.splitPoint = &splitPoint;
2474 // If we are here it means we are not available
2475 assert(masterThread.state != THREAD_AVAILABLE);
2477 int workersCnt = 1; // At least the master is included
2479 // Allocate available threads setting state to THREAD_BOOKED
2480 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2481 if (thread_is_available(i, master))
2483 threads[i].state = THREAD_BOOKED;
2484 threads[i].splitPoint = &splitPoint;
2485 splitPoint.slaves[i] = 1;
2489 assert(Fake || workersCnt > 1);
2491 // We can release the lock because slave threads are already booked and master is not available
2492 lock_release(&mpLock);
2494 // Tell the threads that they have work to do. This will make them leave
2495 // their idle loop. But before copy search stack tail for each thread.
2496 for (i = 0; i < activeThreads; i++)
2497 if (i == master || splitPoint.slaves[i])
2499 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2501 assert(i == master || threads[i].state == THREAD_BOOKED);
2503 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2505 if (useSleepingThreads && i != master)
2506 wake_sleeping_thread(i);
2509 // Everything is set up. The master thread enters the idle loop, from
2510 // which it will instantly launch a search, because its state is
2511 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2512 // idle loop, which means that the main thread will return from the idle
2513 // loop when all threads have finished their work at this split point.
2514 idle_loop(master, &splitPoint);
2516 // We have returned from the idle loop, which means that all threads are
2517 // finished. Update alpha and bestValue, and return.
2520 *alpha = splitPoint.alpha;
2521 *bestValue = splitPoint.bestValue;
2522 masterThread.activeSplitPoints--;
2523 masterThread.splitPoint = splitPoint.parent;
2524 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2526 lock_release(&mpLock);
2530 // wake_sleeping_thread() wakes up the thread with the given threadID
2531 // when it is time to start a new search.
2533 void ThreadsManager::wake_sleeping_thread(int threadID) {
2535 lock_grab(&sleepLock[threadID]);
2536 cond_signal(&sleepCond[threadID]);
2537 lock_release(&sleepLock[threadID]);
2541 /// RootMove and RootMoveList method's definitions
2543 RootMove::RootMove() {
2546 pv_score = non_pv_score = -VALUE_INFINITE;
2550 RootMove& RootMove::operator=(const RootMove& rm) {
2552 const Move* src = rm.pv;
2555 // Avoid a costly full rm.pv[] copy
2556 do *dst++ = *src; while (*src++ != MOVE_NONE);
2559 pv_score = rm.pv_score;
2560 non_pv_score = rm.non_pv_score;
2564 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2565 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2566 // allow to always have a ponder move even when we fail high at root and also a
2567 // long PV to print that is important for position analysis.
2569 void RootMove::extract_pv_from_tt(Position& pos) {
2571 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2575 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2577 pos.do_move(pv[0], *st++);
2579 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2580 && tte->move() != MOVE_NONE
2581 && move_is_legal(pos, tte->move())
2583 && (!pos.is_draw() || ply < 2))
2585 pv[ply] = tte->move();
2586 pos.do_move(pv[ply++], *st++);
2588 pv[ply] = MOVE_NONE;
2590 do pos.undo_move(pv[--ply]); while (ply);
2593 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2594 // the PV back into the TT. This makes sure the old PV moves are searched
2595 // first, even if the old TT entries have been overwritten.
2597 void RootMove::insert_pv_in_tt(Position& pos) {
2599 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2602 Value v, m = VALUE_NONE;
2605 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2609 tte = TT.retrieve(k);
2611 // Don't overwrite exsisting correct entries
2612 if (!tte || tte->move() != pv[ply])
2614 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2615 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2617 pos.do_move(pv[ply], *st++);
2619 } while (pv[++ply] != MOVE_NONE);
2621 do pos.undo_move(pv[--ply]); while (ply);
2624 // pv_info_to_uci() returns a string with information on the current PV line
2625 // formatted according to UCI specification and eventually writes the info
2626 // to a log file. It is called at each iteration or after a new pv is found.
2628 std::string RootMove::pv_info_to_uci(const Position& pos, Value alpha, Value beta) {
2630 std::stringstream s;
2632 s << "info depth " << Iteration
2633 << " score " << value_to_uci(pv_score)
2634 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2635 << " time " << current_search_time()
2636 << " nodes " << pos.nodes_searched()
2637 << " nps " << nps(pos)
2640 for (Move* m = pv; *m != MOVE_NONE; m++)
2645 ValueType t = pv_score >= beta ? VALUE_TYPE_LOWER :
2646 pv_score <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2648 LogFile << pretty_pv(pos, current_search_time(), Iteration, pv_score, t, pv) << endl;
2654 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2656 SearchStack ss[PLY_MAX_PLUS_2];
2657 MoveStack mlist[MOVES_MAX];
2661 // Initialize search stack
2662 init_ss_array(ss, PLY_MAX_PLUS_2);
2663 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2665 // Generate all legal moves
2666 MoveStack* last = generate_moves(pos, mlist);
2668 // Add each move to the RootMoveList's vector
2669 for (MoveStack* cur = mlist; cur != last; cur++)
2671 // If we have a searchMoves[] list then verify cur->move
2672 // is in the list before to add it.
2673 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2675 if (searchMoves[0] && *sm != cur->move)
2678 // Find a quick score for the move and add to the list
2679 pos.do_move(cur->move, st);
2682 rm.pv[0] = ss[0].currentMove = cur->move;
2683 rm.pv[1] = MOVE_NONE;
2684 rm.pv_score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2687 pos.undo_move(cur->move);
2692 // Score root moves using the standard way used in main search, the moves
2693 // are scored according to the order in which are returned by MovePicker.
2694 // This is the second order score that is used to compare the moves when
2695 // the first order pv scores of both moves are equal.
2697 void RootMoveList::set_non_pv_scores(const Position& pos)
2700 Value score = VALUE_ZERO;
2701 MovePicker mp(pos, MOVE_NONE, ONE_PLY, H);
2703 while ((move = mp.get_next_move()) != MOVE_NONE)
2704 for (Base::iterator it = begin(); it != end(); ++it)
2705 if (it->pv[0] == move)
2707 it->non_pv_score = score--;