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, int pvLine = 0);
137 Move pv[PLY_MAX_PLUS_2];
141 // RootMoveList struct is essentially a std::vector<> of RootMove objects,
142 // with an handful of methods above the standard ones.
144 struct RootMoveList : public std::vector<RootMove> {
146 typedef std::vector<RootMove> Base;
148 RootMoveList(Position& pos, Move searchMoves[]);
149 void set_non_pv_scores(const Position& pos, Move ttm, SearchStack* ss);
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, Pondering, StopOnPonderhit;
258 bool FirstRootMove, StopRequest, QuitRequest, 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.
270 bool SendSearchedNodes;
272 int NodesBetweenPolls = 30000;
279 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
280 Value root_search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, RootMoveList& rml);
282 template <NodeType PvNode, bool SpNode>
283 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
285 template <NodeType PvNode>
286 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
288 template <NodeType PvNode>
289 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
291 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
292 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
295 template <NodeType PvNode>
296 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
298 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
299 bool connected_moves(const Position& pos, Move m1, Move m2);
300 bool value_is_mate(Value value);
301 Value value_to_tt(Value v, int ply);
302 Value value_from_tt(Value v, int ply);
303 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
304 bool connected_threat(const Position& pos, Move m, Move threat);
305 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
306 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
307 void update_killers(Move m, Move killers[]);
308 void update_gains(const Position& pos, Move move, Value before, Value after);
310 int current_search_time();
311 std::string value_to_uci(Value v);
312 int nps(const Position& pos);
313 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 int64_t 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 = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
406 SearchStartTime = get_system_time();
407 ExactMaxTime = maxTime;
410 InfiniteSearch = infinite;
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>();
454 read_evaluation_uci_options(pos.side_to_move());
456 // Set the number of active threads
457 ThreadsMgr.read_uci_options();
458 init_eval(ThreadsMgr.active_threads());
460 // Wake up needed threads
461 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
462 ThreadsMgr.wake_sleeping_thread(i);
465 int myTime = time[pos.side_to_move()];
466 int myIncrement = increment[pos.side_to_move()];
467 if (UseTimeManagement)
468 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
470 // Set best NodesBetweenPolls interval to avoid lagging under
471 // heavy time pressure.
473 NodesBetweenPolls = Min(MaxNodes, 30000);
474 else if (myTime && myTime < 1000)
475 NodesBetweenPolls = 1000;
476 else if (myTime && myTime < 5000)
477 NodesBetweenPolls = 5000;
479 NodesBetweenPolls = 30000;
481 // Write search information to log file
484 std::string name = Options["Search Log Filename"].value<std::string>();
485 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
487 LogFile << "Searching: " << pos.to_fen()
488 << "\ninfinite: " << infinite
489 << " ponder: " << ponder
490 << " time: " << myTime
491 << " increment: " << myIncrement
492 << " moves to go: " << movesToGo << endl;
495 // We're ready to start thinking. Call the iterative deepening loop function
496 Move ponderMove = MOVE_NONE;
497 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
499 // Print final search statistics
500 cout << "info nodes " << pos.nodes_searched()
501 << " nps " << nps(pos)
502 << " time " << current_search_time() << endl;
506 LogFile << "\nNodes: " << pos.nodes_searched()
507 << "\nNodes/second: " << nps(pos)
508 << "\nBest move: " << move_to_san(pos, bestMove);
511 pos.do_move(bestMove, st);
512 LogFile << "\nPonder move: "
513 << move_to_san(pos, ponderMove) // Works also with MOVE_NONE
516 // Return from think() with unchanged position
517 pos.undo_move(bestMove);
522 // This makes all the threads to go to sleep
523 ThreadsMgr.set_active_threads(1);
525 // If we are pondering or in infinite search, we shouldn't print the
526 // best move before we are told to do so.
527 if (!StopRequest && (Pondering || InfiniteSearch))
528 wait_for_stop_or_ponderhit();
530 // Could be both MOVE_NONE when searching on a stalemate position
531 cout << "bestmove " << bestMove << " ponder " << ponderMove << endl;
539 // id_loop() is the main iterative deepening loop. It calls root_search
540 // repeatedly with increasing depth until the allocated thinking time has
541 // been consumed, the user stops the search, or the maximum search depth is
544 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
546 SearchStack ss[PLY_MAX_PLUS_2];
548 Move EasyMove = MOVE_NONE;
549 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
551 // Moves to search are verified, scored and sorted
552 RootMoveList rml(pos, searchMoves);
554 // Handle special case of searching on a mate/stale position
557 Value s = (pos.is_check() ? -VALUE_MATE : VALUE_DRAW);
559 cout << "info depth " << 1
560 << " score " << value_to_uci(s) << endl;
568 init_ss_array(ss, PLY_MAX_PLUS_2);
569 ValueByIteration[1] = rml[0].pv_score;
572 // Send initial RootMoveList scoring (iteration 1)
573 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
574 << "info depth " << Iteration
575 << "\n" << rml[0].pv_info_to_uci(pos, alpha, beta) << endl;
577 // Is one move significantly better than others after initial scoring ?
579 || rml[0].pv_score > rml[1].pv_score + EasyMoveMargin)
580 EasyMove = rml[0].pv[0];
582 // Iterative deepening loop
583 while (Iteration < PLY_MAX)
585 // Initialize iteration
587 BestMoveChangesByIteration[Iteration] = 0;
589 cout << "info depth " << Iteration << endl;
591 // Calculate dynamic aspiration window based on previous iterations
592 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
594 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
595 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
597 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
598 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
600 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
601 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
604 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
606 // Search to the current depth, rml is updated and sorted
607 value = root_search(pos, ss, alpha, beta, depth, rml);
610 break; // Value cannot be trusted. Break out immediately!
612 //Save info about search result
613 ValueByIteration[Iteration] = value;
615 // Drop the easy move if differs from the new best move
616 if (rml[0].pv[0] != EasyMove)
617 EasyMove = MOVE_NONE;
619 if (UseTimeManagement)
622 bool stopSearch = false;
624 // Stop search early if there is only a single legal move,
625 // we search up to Iteration 6 anyway to get a proper score.
626 if (Iteration >= 6 && rml.size() == 1)
629 // Stop search early when the last two iterations returned a mate score
631 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
632 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
635 // Stop search early if one move seems to be much better than the others
637 && EasyMove == rml[0].pv[0]
638 && ( ( rml[0].nodes > (pos.nodes_searched() * 85) / 100
639 && current_search_time() > TimeMgr.available_time() / 16)
640 ||( rml[0].nodes > (pos.nodes_searched() * 98) / 100
641 && current_search_time() > TimeMgr.available_time() / 32)))
644 // Add some extra time if the best move has changed during the last two iterations
645 if (Iteration > 5 && Iteration <= 50)
646 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
647 BestMoveChangesByIteration[Iteration-1]);
649 // Stop search if most of MaxSearchTime is consumed at the end of the
650 // iteration. We probably don't have enough time to search the first
651 // move at the next iteration anyway.
652 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
658 StopOnPonderhit = true;
664 if (MaxDepth && Iteration >= MaxDepth)
668 *ponderMove = rml[0].pv[1];
673 // root_search() is the function which searches the root node. It is
674 // similar to search_pv except that it prints some information to the
675 // standard output and handles the fail low/high loops.
677 Value root_search(Position& pos, SearchStack* ss, Value alpha,
678 Value beta, Depth depth, RootMoveList& rml) {
680 Move movesSearched[MOVES_MAX];
685 Value value, oldAlpha;
686 RootMoveList::iterator rm;
687 bool isCheck, moveIsCheck, captureOrPromotion, dangerous, isPvMove;
688 int moveCount, 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, rml[0].pv[0], ss);
721 // Step 10. Loop through all moves in the root move list
722 for (rm = rml.begin(); rm != rml.end() && !StopRequest; ++rm)
724 // This is used by time management
725 FirstRootMove = (rm == rml.begin());
727 // Save the current node count before the move is searched
728 nodes = pos.nodes_searched();
730 // If it's time to send nodes info, do it here where we have the
731 // correct accumulated node counts searched by each thread.
732 if (SendSearchedNodes)
734 SendSearchedNodes = false;
735 cout << "info nodes " << nodes
736 << " nps " << nps(pos)
737 << " time " << current_search_time() << endl;
740 // Pick the next root move, and print the move and the move number to
741 // the standard output.
742 move = ss->currentMove = rm->pv[0];
743 movesSearched[moveCount++] = move;
744 isPvMove = (moveCount <= MultiPV);
746 if (current_search_time() >= 1000)
747 cout << "info currmove " << move
748 << " currmovenumber " << moveCount << endl;
750 moveIsCheck = pos.move_is_check(move);
751 captureOrPromotion = pos.move_is_capture_or_promotion(move);
753 // Step 11. Decide the new search depth
754 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
755 newDepth = depth + ext;
757 // Step 12. Futility pruning (omitted at root)
759 // Step extra. Fail high loop
760 // If move fails high, we research with bigger window until we are not failing
762 value = -VALUE_INFINITE;
766 // Step 13. Make the move
767 pos.do_move(move, st, ci, moveIsCheck);
769 // Step extra. pv search
770 // We do pv search for PV moves and when failing high
771 if (isPvMove || value > alpha)
773 // Aspiration window is disabled in multi-pv case
775 alpha = -VALUE_INFINITE;
777 // Full depth PV search, done on first move or after a fail high
778 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
782 // Step 14. Reduced search
783 // if the move fails high will be re-searched at full depth
784 bool doFullDepthSearch = true;
786 if ( depth >= 3 * ONE_PLY
788 && !captureOrPromotion
789 && !move_is_castle(move))
791 ss->reduction = reduction<PV>(depth, moveCount - MultiPV + 1);
794 assert(newDepth-ss->reduction >= ONE_PLY);
796 // Reduced depth non-pv search using alpha as upperbound
797 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
798 doFullDepthSearch = (value > alpha);
800 ss->reduction = DEPTH_ZERO; // Restore original reduction
803 // Step 15. Full depth search
804 if (doFullDepthSearch)
806 // Full depth non-pv search using alpha as upperbound
807 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
809 // If we are above alpha then research at same depth but as PV
810 // to get a correct score or eventually a fail high above beta.
812 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
816 // Step 16. Undo move
819 // Can we exit fail high loop ?
820 if (StopRequest || value < beta)
823 // We are failing high and going to do a research. It's important to update
824 // the score before research in case we run out of time while researching.
826 rm->pv_score = value;
827 rm->extract_pv_from_tt(pos);
829 // Update killers and history only for non capture moves that fails high
830 if (!pos.move_is_capture_or_promotion(move))
832 update_history(pos, move, depth, movesSearched, moveCount);
833 update_killers(move, ss->killers);
836 // Inform GUI that PV has changed
837 cout << rm->pv_info_to_uci(pos, alpha, beta) << endl;
839 // Prepare for a research after a fail high, each time with a wider window
840 beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
843 } // End of fail high loop
845 // Finished searching the move. If AbortSearch is true, the search
846 // was aborted because the user interrupted the search or because we
847 // ran out of time. In this case, the return value of the search cannot
848 // be trusted, and we break out of the loop without updating the best
853 // Remember searched nodes counts for this move
854 rm->nodes += pos.nodes_searched() - nodes;
856 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
857 assert(value < beta);
859 // Step 17. Check for new best move
860 if (!isPvMove && value <= alpha)
861 rm->pv_score = -VALUE_INFINITE;
864 // PV move or new best move!
868 rm->pv_score = value;
869 rm->extract_pv_from_tt(pos);
871 // We record how often the best move has been changed in each
872 // iteration. This information is used for time managment: When
873 // the best move changes frequently, we allocate some more time.
874 if (!isPvMove && MultiPV == 1)
875 BestMoveChangesByIteration[Iteration]++;
877 // Inform GUI that PV has changed, in case of multi-pv UCI protocol
878 // requires we send all the PV lines properly sorted.
879 rml.sort_multipv(moveCount);
881 for (int j = 0; j < Min(MultiPV, (int)rml.size()); j++)
882 cout << rml[j].pv_info_to_uci(pos, alpha, beta, j) << endl;
884 // Update alpha. In multi-pv we don't use aspiration window
887 // Raise alpha to setup proper non-pv search upper bound
891 else // Set alpha equal to minimum score among the PV lines
892 alpha = rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
894 } // PV move or new best move
896 assert(alpha >= oldAlpha);
898 AspirationFailLow = (alpha == oldAlpha);
900 if (AspirationFailLow && StopOnPonderhit)
901 StopOnPonderhit = false;
905 // Can we exit fail low loop ?
906 if (StopRequest || !AspirationFailLow)
909 // Prepare for a research after a fail low, each time with a wider window
910 oldAlpha = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
915 // Sort the moves before to return
918 // Write PV lines to transposition table, in case the relevant entries
919 // have been overwritten during the search.
920 for (int i = 0; i < Min(MultiPV, (int)rml.size()); i++)
921 rml[i].insert_pv_in_tt(pos);
927 // search<>() is the main search function for both PV and non-PV nodes and for
928 // normal and SplitPoint nodes. When called just after a split point the search
929 // is simpler because we have already probed the hash table, done a null move
930 // search, and searched the first move before splitting, we don't have to repeat
931 // all this work again. We also don't need to store anything to the hash table
932 // here: This is taken care of after we return from the split point.
934 template <NodeType PvNode, bool SpNode>
935 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
937 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
938 assert(beta > alpha && beta <= VALUE_INFINITE);
939 assert(PvNode || alpha == beta - 1);
940 assert(ply > 0 && ply < PLY_MAX);
941 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
943 Move movesSearched[MOVES_MAX];
947 Move ttMove, move, excludedMove, threatMove;
950 Value bestValue, value, oldAlpha;
951 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
952 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
953 bool mateThreat = false;
955 int threadID = pos.thread();
956 SplitPoint* sp = NULL;
957 refinedValue = bestValue = value = -VALUE_INFINITE;
959 isCheck = pos.is_check();
965 ttMove = excludedMove = MOVE_NONE;
966 threatMove = sp->threatMove;
967 mateThreat = sp->mateThreat;
968 goto split_point_start;
970 else {} // Hack to fix icc's "statement is unreachable" warning
972 // Step 1. Initialize node and poll. Polling can abort search
973 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
974 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
976 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
982 // Step 2. Check for aborted search and immediate draw
984 || ThreadsMgr.cutoff_at_splitpoint(threadID)
986 || ply >= PLY_MAX - 1)
989 // Step 3. Mate distance pruning
990 alpha = Max(value_mated_in(ply), alpha);
991 beta = Min(value_mate_in(ply+1), beta);
995 // Step 4. Transposition table lookup
997 // We don't want the score of a partial search to overwrite a previous full search
998 // TT value, so we use a different position key in case of an excluded move exists.
999 excludedMove = ss->excludedMove;
1000 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1002 tte = TT.retrieve(posKey);
1003 ttMove = tte ? tte->move() : MOVE_NONE;
1005 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1006 // This is to avoid problems in the following areas:
1008 // * Repetition draw detection
1009 // * Fifty move rule detection
1010 // * Searching for a mate
1011 // * Printing of full PV line
1012 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1015 ss->bestMove = ttMove; // Can be MOVE_NONE
1016 return value_from_tt(tte->value(), ply);
1019 // Step 5. Evaluate the position statically and
1020 // update gain statistics of parent move.
1022 ss->eval = ss->evalMargin = VALUE_NONE;
1025 assert(tte->static_value() != VALUE_NONE);
1027 ss->eval = tte->static_value();
1028 ss->evalMargin = tte->static_value_margin();
1029 refinedValue = refine_eval(tte, ss->eval, ply);
1033 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1034 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1037 // Save gain for the parent non-capture move
1038 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1040 // Step 6. Razoring (is omitted in PV nodes)
1042 && depth < RazorDepth
1044 && refinedValue < beta - razor_margin(depth)
1045 && ttMove == MOVE_NONE
1046 && !value_is_mate(beta)
1047 && !pos.has_pawn_on_7th(pos.side_to_move()))
1049 Value rbeta = beta - razor_margin(depth);
1050 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1052 // Logically we should return (v + razor_margin(depth)), but
1053 // surprisingly this did slightly weaker in tests.
1057 // Step 7. Static null move pruning (is omitted in PV nodes)
1058 // We're betting that the opponent doesn't have a move that will reduce
1059 // the score by more than futility_margin(depth) if we do a null move.
1061 && !ss->skipNullMove
1062 && depth < RazorDepth
1064 && refinedValue >= beta + futility_margin(depth, 0)
1065 && !value_is_mate(beta)
1066 && pos.non_pawn_material(pos.side_to_move()))
1067 return refinedValue - futility_margin(depth, 0);
1069 // Step 8. Null move search with verification search (is omitted in PV nodes)
1071 && !ss->skipNullMove
1074 && refinedValue >= beta
1075 && !value_is_mate(beta)
1076 && pos.non_pawn_material(pos.side_to_move()))
1078 ss->currentMove = MOVE_NULL;
1080 // Null move dynamic reduction based on depth
1081 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1083 // Null move dynamic reduction based on value
1084 if (refinedValue - beta > PawnValueMidgame)
1087 pos.do_null_move(st);
1088 (ss+1)->skipNullMove = true;
1089 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1090 (ss+1)->skipNullMove = false;
1091 pos.undo_null_move();
1093 if (nullValue >= beta)
1095 // Do not return unproven mate scores
1096 if (nullValue >= value_mate_in(PLY_MAX))
1099 if (depth < 6 * ONE_PLY)
1102 // Do verification search at high depths
1103 ss->skipNullMove = true;
1104 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1105 ss->skipNullMove = false;
1112 // The null move failed low, which means that we may be faced with
1113 // some kind of threat. If the previous move was reduced, check if
1114 // the move that refuted the null move was somehow connected to the
1115 // move which was reduced. If a connection is found, return a fail
1116 // low score (which will cause the reduced move to fail high in the
1117 // parent node, which will trigger a re-search with full depth).
1118 if (nullValue == value_mated_in(ply + 2))
1121 threatMove = (ss+1)->bestMove;
1122 if ( depth < ThreatDepth
1123 && (ss-1)->reduction
1124 && threatMove != MOVE_NONE
1125 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1130 // Step 9. Internal iterative deepening
1131 if ( depth >= IIDDepth[PvNode]
1132 && ttMove == MOVE_NONE
1133 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1135 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1137 ss->skipNullMove = true;
1138 search<PvNode>(pos, ss, alpha, beta, d, ply);
1139 ss->skipNullMove = false;
1141 ttMove = ss->bestMove;
1142 tte = TT.retrieve(posKey);
1145 // Expensive mate threat detection (only for PV nodes)
1147 mateThreat = pos.has_mate_threat();
1149 split_point_start: // At split points actual search starts from here
1151 // Initialize a MovePicker object for the current position
1152 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1153 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1154 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1156 ss->bestMove = MOVE_NONE;
1157 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1158 futilityBase = ss->eval + ss->evalMargin;
1159 singularExtensionNode = !SpNode
1160 && depth >= SingularExtensionDepth[PvNode]
1163 && !excludedMove // Do not allow recursive singular extension search
1164 && (tte->type() & VALUE_TYPE_LOWER)
1165 && tte->depth() >= depth - 3 * ONE_PLY;
1168 lock_grab(&(sp->lock));
1169 bestValue = sp->bestValue;
1172 // Step 10. Loop through moves
1173 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1174 while ( bestValue < beta
1175 && (move = mp.get_next_move()) != MOVE_NONE
1176 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1178 assert(move_is_ok(move));
1182 moveCount = ++sp->moveCount;
1183 lock_release(&(sp->lock));
1185 else if (move == excludedMove)
1188 movesSearched[moveCount++] = move;
1190 moveIsCheck = pos.move_is_check(move, ci);
1191 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1193 // Step 11. Decide the new search depth
1194 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1196 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1197 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1198 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1199 // lower then ttValue minus a margin then we extend ttMove.
1200 if ( singularExtensionNode
1201 && move == tte->move()
1204 Value ttValue = value_from_tt(tte->value(), ply);
1206 if (abs(ttValue) < VALUE_KNOWN_WIN)
1208 Value b = ttValue - SingularExtensionMargin;
1209 ss->excludedMove = move;
1210 ss->skipNullMove = true;
1211 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1212 ss->skipNullMove = false;
1213 ss->excludedMove = MOVE_NONE;
1214 ss->bestMove = MOVE_NONE;
1220 // Update current move (this must be done after singular extension search)
1221 ss->currentMove = move;
1222 newDepth = depth - ONE_PLY + ext;
1224 // Step 12. Futility pruning (is omitted in PV nodes)
1226 && !captureOrPromotion
1230 && !move_is_castle(move))
1232 // Move count based pruning
1233 if ( moveCount >= futility_move_count(depth)
1234 && !(threatMove && connected_threat(pos, move, threatMove))
1235 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1238 lock_grab(&(sp->lock));
1243 // Value based pruning
1244 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1245 // but fixing this made program slightly weaker.
1246 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1247 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1248 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1250 if (futilityValueScaled < beta)
1254 lock_grab(&(sp->lock));
1255 if (futilityValueScaled > sp->bestValue)
1256 sp->bestValue = bestValue = futilityValueScaled;
1258 else if (futilityValueScaled > bestValue)
1259 bestValue = futilityValueScaled;
1264 // Prune moves with negative SEE at low depths
1265 if ( predictedDepth < 2 * ONE_PLY
1266 && bestValue > value_mated_in(PLY_MAX)
1267 && pos.see_sign(move) < 0)
1270 lock_grab(&(sp->lock));
1276 // Step 13. Make the move
1277 pos.do_move(move, st, ci, moveIsCheck);
1279 // Step extra. pv search (only in PV nodes)
1280 // The first move in list is the expected PV
1281 if (PvNode && moveCount == 1)
1282 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1285 // Step 14. Reduced depth search
1286 // If the move fails high will be re-searched at full depth.
1287 bool doFullDepthSearch = true;
1289 if ( depth >= 3 * ONE_PLY
1290 && !captureOrPromotion
1292 && !move_is_castle(move)
1293 && ss->killers[0] != move
1294 && ss->killers[1] != move)
1296 ss->reduction = reduction<PvNode>(depth, moveCount);
1300 alpha = SpNode ? sp->alpha : alpha;
1301 Depth d = newDepth - ss->reduction;
1302 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1304 doFullDepthSearch = (value > alpha);
1306 ss->reduction = DEPTH_ZERO; // Restore original reduction
1309 // Step 15. Full depth search
1310 if (doFullDepthSearch)
1312 alpha = SpNode ? sp->alpha : alpha;
1313 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1315 // Step extra. pv search (only in PV nodes)
1316 // Search only for possible new PV nodes, if instead value >= beta then
1317 // parent node fails low with value <= alpha and tries another move.
1318 if (PvNode && value > alpha && value < beta)
1319 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1323 // Step 16. Undo move
1324 pos.undo_move(move);
1326 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1328 // Step 17. Check for new best move
1331 lock_grab(&(sp->lock));
1332 bestValue = sp->bestValue;
1336 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1341 sp->bestValue = value;
1345 if (PvNode && value < beta) // We want always alpha < beta
1353 sp->betaCutoff = true;
1355 if (value == value_mate_in(ply + 1))
1356 ss->mateKiller = move;
1358 ss->bestMove = move;
1361 sp->parentSstack->bestMove = move;
1365 // Step 18. Check for split
1367 && depth >= ThreadsMgr.min_split_depth()
1368 && ThreadsMgr.active_threads() > 1
1370 && ThreadsMgr.available_thread_exists(threadID)
1372 && !ThreadsMgr.cutoff_at_splitpoint(threadID)
1374 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1375 threatMove, mateThreat, moveCount, &mp, PvNode);
1378 // Step 19. Check for mate and stalemate
1379 // All legal moves have been searched and if there are
1380 // no legal moves, it must be mate or stalemate.
1381 // If one move was excluded return fail low score.
1382 if (!SpNode && !moveCount)
1383 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1385 // Step 20. Update tables
1386 // If the search is not aborted, update the transposition table,
1387 // history counters, and killer moves.
1388 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1390 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1391 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1392 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1394 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1396 // Update killers and history only for non capture moves that fails high
1397 if ( bestValue >= beta
1398 && !pos.move_is_capture_or_promotion(move))
1400 update_history(pos, move, depth, movesSearched, moveCount);
1401 update_killers(move, ss->killers);
1407 // Here we have the lock still grabbed
1408 sp->slaves[threadID] = 0;
1409 sp->nodes += pos.nodes_searched();
1410 lock_release(&(sp->lock));
1413 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1418 // qsearch() is the quiescence search function, which is called by the main
1419 // search function when the remaining depth is zero (or, to be more precise,
1420 // less than ONE_PLY).
1422 template <NodeType PvNode>
1423 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1425 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1426 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1427 assert(PvNode || alpha == beta - 1);
1429 assert(ply > 0 && ply < PLY_MAX);
1430 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1434 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1435 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1438 Value oldAlpha = alpha;
1440 ss->bestMove = ss->currentMove = MOVE_NONE;
1442 // Check for an instant draw or maximum ply reached
1443 if (pos.is_draw() || ply >= PLY_MAX - 1)
1446 // Decide whether or not to include checks, this fixes also the type of
1447 // TT entry depth that we are going to use. Note that in qsearch we use
1448 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1449 isCheck = pos.is_check();
1450 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1452 // Transposition table lookup. At PV nodes, we don't use the TT for
1453 // pruning, but only for move ordering.
1454 tte = TT.retrieve(pos.get_key());
1455 ttMove = (tte ? tte->move() : MOVE_NONE);
1457 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1459 ss->bestMove = ttMove; // Can be MOVE_NONE
1460 return value_from_tt(tte->value(), ply);
1463 // Evaluate the position statically
1466 bestValue = futilityBase = -VALUE_INFINITE;
1467 ss->eval = evalMargin = VALUE_NONE;
1468 enoughMaterial = false;
1474 assert(tte->static_value() != VALUE_NONE);
1476 evalMargin = tte->static_value_margin();
1477 ss->eval = bestValue = tte->static_value();
1480 ss->eval = bestValue = evaluate(pos, evalMargin);
1482 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1484 // Stand pat. Return immediately if static value is at least beta
1485 if (bestValue >= beta)
1488 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1493 if (PvNode && bestValue > alpha)
1496 // Futility pruning parameters, not needed when in check
1497 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1498 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1501 // Initialize a MovePicker object for the current position, and prepare
1502 // to search the moves. Because the depth is <= 0 here, only captures,
1503 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1505 MovePicker mp(pos, ttMove, depth, H);
1508 // Loop through the moves until no moves remain or a beta cutoff occurs
1509 while ( alpha < beta
1510 && (move = mp.get_next_move()) != MOVE_NONE)
1512 assert(move_is_ok(move));
1514 moveIsCheck = pos.move_is_check(move, ci);
1522 && !move_is_promotion(move)
1523 && !pos.move_is_passed_pawn_push(move))
1525 futilityValue = futilityBase
1526 + pos.endgame_value_of_piece_on(move_to(move))
1527 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1529 if (futilityValue < alpha)
1531 if (futilityValue > bestValue)
1532 bestValue = futilityValue;
1537 // Detect non-capture evasions that are candidate to be pruned
1538 evasionPrunable = isCheck
1539 && bestValue > value_mated_in(PLY_MAX)
1540 && !pos.move_is_capture(move)
1541 && !pos.can_castle(pos.side_to_move());
1543 // Don't search moves with negative SEE values
1545 && (!isCheck || evasionPrunable)
1547 && !move_is_promotion(move)
1548 && pos.see_sign(move) < 0)
1551 // Don't search useless checks
1556 && !pos.move_is_capture_or_promotion(move)
1557 && ss->eval + PawnValueMidgame / 4 < beta
1558 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1560 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1561 bestValue = ss->eval + PawnValueMidgame / 4;
1566 // Update current move
1567 ss->currentMove = move;
1569 // Make and search the move
1570 pos.do_move(move, st, ci, moveIsCheck);
1571 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1572 pos.undo_move(move);
1574 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1577 if (value > bestValue)
1583 ss->bestMove = move;
1588 // All legal moves have been searched. A special case: If we're in check
1589 // and no legal moves were found, it is checkmate.
1590 if (isCheck && bestValue == -VALUE_INFINITE)
1591 return value_mated_in(ply);
1593 // Update transposition table
1594 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1595 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1597 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1603 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1604 // bestValue is updated only when returning false because in that case move
1607 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1609 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1610 Square from, to, ksq, victimSq;
1613 Value futilityValue, bv = *bestValue;
1615 from = move_from(move);
1617 them = opposite_color(pos.side_to_move());
1618 ksq = pos.king_square(them);
1619 kingAtt = pos.attacks_from<KING>(ksq);
1620 pc = pos.piece_on(from);
1622 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1623 oldAtt = pos.attacks_from(pc, from, occ);
1624 newAtt = pos.attacks_from(pc, to, occ);
1626 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1627 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1629 if (!(b && (b & (b - 1))))
1632 // Rule 2. Queen contact check is very dangerous
1633 if ( type_of_piece(pc) == QUEEN
1634 && bit_is_set(kingAtt, to))
1637 // Rule 3. Creating new double threats with checks
1638 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1642 victimSq = pop_1st_bit(&b);
1643 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1645 // Note that here we generate illegal "double move"!
1646 if ( futilityValue >= beta
1647 && pos.see_sign(make_move(from, victimSq)) >= 0)
1650 if (futilityValue > bv)
1654 // Update bestValue only if check is not dangerous (because we will prune the move)
1660 // connected_moves() tests whether two moves are 'connected' in the sense
1661 // that the first move somehow made the second move possible (for instance
1662 // if the moving piece is the same in both moves). The first move is assumed
1663 // to be the move that was made to reach the current position, while the
1664 // second move is assumed to be a move from the current position.
1666 bool connected_moves(const Position& pos, Move m1, Move m2) {
1668 Square f1, t1, f2, t2;
1671 assert(m1 && move_is_ok(m1));
1672 assert(m2 && move_is_ok(m2));
1674 // Case 1: The moving piece is the same in both moves
1680 // Case 2: The destination square for m2 was vacated by m1
1686 // Case 3: Moving through the vacated square
1687 if ( piece_is_slider(pos.piece_on(f2))
1688 && bit_is_set(squares_between(f2, t2), f1))
1691 // Case 4: The destination square for m2 is defended by the moving piece in m1
1692 p = pos.piece_on(t1);
1693 if (bit_is_set(pos.attacks_from(p, t1), t2))
1696 // Case 5: Discovered check, checking piece is the piece moved in m1
1697 if ( piece_is_slider(p)
1698 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1699 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1701 // discovered_check_candidates() works also if the Position's side to
1702 // move is the opposite of the checking piece.
1703 Color them = opposite_color(pos.side_to_move());
1704 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1706 if (bit_is_set(dcCandidates, f2))
1713 // value_is_mate() checks if the given value is a mate one eventually
1714 // compensated for the ply.
1716 bool value_is_mate(Value value) {
1718 assert(abs(value) <= VALUE_INFINITE);
1720 return value <= value_mated_in(PLY_MAX)
1721 || value >= value_mate_in(PLY_MAX);
1725 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1726 // "plies to mate from the current ply". Non-mate scores are unchanged.
1727 // The function is called before storing a value to the transposition table.
1729 Value value_to_tt(Value v, int ply) {
1731 if (v >= value_mate_in(PLY_MAX))
1734 if (v <= value_mated_in(PLY_MAX))
1741 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1742 // the transposition table to a mate score corrected for the current ply.
1744 Value value_from_tt(Value v, int ply) {
1746 if (v >= value_mate_in(PLY_MAX))
1749 if (v <= value_mated_in(PLY_MAX))
1756 // extension() decides whether a move should be searched with normal depth,
1757 // or with extended depth. Certain classes of moves (checking moves, in
1758 // particular) are searched with bigger depth than ordinary moves and in
1759 // any case are marked as 'dangerous'. Note that also if a move is not
1760 // extended, as example because the corresponding UCI option is set to zero,
1761 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1762 template <NodeType PvNode>
1763 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1764 bool singleEvasion, bool mateThreat, bool* dangerous) {
1766 assert(m != MOVE_NONE);
1768 Depth result = DEPTH_ZERO;
1769 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1773 if (moveIsCheck && pos.see_sign(m) >= 0)
1774 result += CheckExtension[PvNode];
1777 result += SingleEvasionExtension[PvNode];
1780 result += MateThreatExtension[PvNode];
1783 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1785 Color c = pos.side_to_move();
1786 if (relative_rank(c, move_to(m)) == RANK_7)
1788 result += PawnPushTo7thExtension[PvNode];
1791 if (pos.pawn_is_passed(c, move_to(m)))
1793 result += PassedPawnExtension[PvNode];
1798 if ( captureOrPromotion
1799 && pos.type_of_piece_on(move_to(m)) != PAWN
1800 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1801 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1802 && !move_is_promotion(m)
1805 result += PawnEndgameExtension[PvNode];
1810 && captureOrPromotion
1811 && pos.type_of_piece_on(move_to(m)) != PAWN
1812 && pos.see_sign(m) >= 0)
1814 result += ONE_PLY / 2;
1818 return Min(result, ONE_PLY);
1822 // connected_threat() tests whether it is safe to forward prune a move or if
1823 // is somehow coonected to the threat move returned by null search.
1825 bool connected_threat(const Position& pos, Move m, Move threat) {
1827 assert(move_is_ok(m));
1828 assert(threat && move_is_ok(threat));
1829 assert(!pos.move_is_check(m));
1830 assert(!pos.move_is_capture_or_promotion(m));
1831 assert(!pos.move_is_passed_pawn_push(m));
1833 Square mfrom, mto, tfrom, tto;
1835 mfrom = move_from(m);
1837 tfrom = move_from(threat);
1838 tto = move_to(threat);
1840 // Case 1: Don't prune moves which move the threatened piece
1844 // Case 2: If the threatened piece has value less than or equal to the
1845 // value of the threatening piece, don't prune move which defend it.
1846 if ( pos.move_is_capture(threat)
1847 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1848 || pos.type_of_piece_on(tfrom) == KING)
1849 && pos.move_attacks_square(m, tto))
1852 // Case 3: If the moving piece in the threatened move is a slider, don't
1853 // prune safe moves which block its ray.
1854 if ( piece_is_slider(pos.piece_on(tfrom))
1855 && bit_is_set(squares_between(tfrom, tto), mto)
1856 && pos.see_sign(m) >= 0)
1863 // ok_to_use_TT() returns true if a transposition table score
1864 // can be used at a given point in search.
1866 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1868 Value v = value_from_tt(tte->value(), ply);
1870 return ( tte->depth() >= depth
1871 || v >= Max(value_mate_in(PLY_MAX), beta)
1872 || v < Min(value_mated_in(PLY_MAX), beta))
1874 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1875 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1879 // refine_eval() returns the transposition table score if
1880 // possible otherwise falls back on static position evaluation.
1882 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1886 Value v = value_from_tt(tte->value(), ply);
1888 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1889 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1896 // update_history() registers a good move that produced a beta-cutoff
1897 // in history and marks as failures all the other moves of that ply.
1899 void update_history(const Position& pos, Move move, Depth depth,
1900 Move movesSearched[], int moveCount) {
1903 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1905 for (int i = 0; i < moveCount - 1; i++)
1907 m = movesSearched[i];
1911 if (!pos.move_is_capture_or_promotion(m))
1912 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1917 // update_killers() add a good move that produced a beta-cutoff
1918 // among the killer moves of that ply.
1920 void update_killers(Move m, Move killers[]) {
1922 if (m == killers[0])
1925 killers[1] = killers[0];
1930 // update_gains() updates the gains table of a non-capture move given
1931 // the static position evaluation before and after the move.
1933 void update_gains(const Position& pos, Move m, Value before, Value after) {
1936 && before != VALUE_NONE
1937 && after != VALUE_NONE
1938 && pos.captured_piece_type() == PIECE_TYPE_NONE
1939 && !move_is_special(m))
1940 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1944 // init_ss_array() does a fast reset of the first entries of a SearchStack
1945 // array and of all the excludedMove and skipNullMove entries.
1947 void init_ss_array(SearchStack* ss, int size) {
1949 for (int i = 0; i < size; i++, ss++)
1951 ss->excludedMove = MOVE_NONE;
1952 ss->skipNullMove = false;
1953 ss->reduction = DEPTH_ZERO;
1957 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
1962 // value_to_uci() converts a value to a string suitable for use with the UCI
1963 // protocol specifications:
1965 // cp <x> The score from the engine's point of view in centipawns.
1966 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1967 // use negative values for y.
1969 std::string value_to_uci(Value v) {
1971 std::stringstream s;
1973 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1974 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1976 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1982 // current_search_time() returns the number of milliseconds which have passed
1983 // since the beginning of the current search.
1985 int current_search_time() {
1987 return get_system_time() - SearchStartTime;
1991 // nps() computes the current nodes/second count
1993 int nps(const Position& pos) {
1995 int t = current_search_time();
1996 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
2000 // poll() performs two different functions: It polls for user input, and it
2001 // looks at the time consumed so far and decides if it's time to abort the
2004 void poll(const Position& pos) {
2006 static int lastInfoTime;
2007 int t = current_search_time();
2010 if (data_available())
2012 // We are line oriented, don't read single chars
2013 std::string command;
2015 if (!std::getline(std::cin, command))
2018 if (command == "quit")
2020 // Quit the program as soon as possible
2022 QuitRequest = StopRequest = true;
2025 else if (command == "stop")
2027 // Stop calculating as soon as possible, but still send the "bestmove"
2028 // and possibly the "ponder" token when finishing the search.
2032 else if (command == "ponderhit")
2034 // The opponent has played the expected move. GUI sends "ponderhit" if
2035 // we were told to ponder on the same move the opponent has played. We
2036 // should continue searching but switching from pondering to normal search.
2039 if (StopOnPonderhit)
2044 // Print search information
2048 else if (lastInfoTime > t)
2049 // HACK: Must be a new search where we searched less than
2050 // NodesBetweenPolls nodes during the first second of search.
2053 else if (t - lastInfoTime >= 1000)
2060 if (dbg_show_hit_rate)
2061 dbg_print_hit_rate();
2063 // Send info on searched nodes as soon as we return to root
2064 SendSearchedNodes = true;
2067 // Should we stop the search?
2071 bool stillAtFirstMove = FirstRootMove
2072 && !AspirationFailLow
2073 && t > TimeMgr.available_time();
2075 bool noMoreTime = t > TimeMgr.maximum_time()
2076 || stillAtFirstMove;
2078 if ( (UseTimeManagement && noMoreTime)
2079 || (ExactMaxTime && t >= ExactMaxTime)
2080 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
2085 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2086 // while the program is pondering. The point is to work around a wrinkle in
2087 // the UCI protocol: When pondering, the engine is not allowed to give a
2088 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2089 // We simply wait here until one of these commands is sent, and return,
2090 // after which the bestmove and pondermove will be printed.
2092 void wait_for_stop_or_ponderhit() {
2094 std::string command;
2098 // Wait for a command from stdin
2099 if (!std::getline(std::cin, command))
2102 if (command == "quit")
2107 else if (command == "ponderhit" || command == "stop")
2113 // init_thread() is the function which is called when a new thread is
2114 // launched. It simply calls the idle_loop() function with the supplied
2115 // threadID. There are two versions of this function; one for POSIX
2116 // threads and one for Windows threads.
2118 #if !defined(_MSC_VER)
2120 void* init_thread(void* threadID) {
2122 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2128 DWORD WINAPI init_thread(LPVOID threadID) {
2130 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2137 /// The ThreadsManager class
2140 // read_uci_options() updates number of active threads and other internal
2141 // parameters according to the UCI options values. It is called before
2142 // to start a new search.
2144 void ThreadsManager::read_uci_options() {
2146 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2147 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2148 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2149 activeThreads = Options["Threads"].value<int>();
2153 // idle_loop() is where the threads are parked when they have no work to do.
2154 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2155 // object for which the current thread is the master.
2157 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2159 assert(threadID >= 0 && threadID < MAX_THREADS);
2162 bool allFinished = false;
2166 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2167 // master should exit as last one.
2168 if (allThreadsShouldExit)
2171 threads[threadID].state = THREAD_TERMINATED;
2175 // If we are not thinking, wait for a condition to be signaled
2176 // instead of wasting CPU time polling for work.
2177 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2178 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2180 assert(!sp || useSleepingThreads);
2181 assert(threadID != 0 || useSleepingThreads);
2183 if (threads[threadID].state == THREAD_INITIALIZING)
2184 threads[threadID].state = THREAD_AVAILABLE;
2186 // Grab the lock to avoid races with wake_sleeping_thread()
2187 lock_grab(&sleepLock[threadID]);
2189 // If we are master and all slaves have finished do not go to sleep
2190 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2191 allFinished = (i == activeThreads);
2193 if (allFinished || allThreadsShouldExit)
2195 lock_release(&sleepLock[threadID]);
2199 // Do sleep here after retesting sleep conditions
2200 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2201 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2203 lock_release(&sleepLock[threadID]);
2206 // If this thread has been assigned work, launch a search
2207 if (threads[threadID].state == THREAD_WORKISWAITING)
2209 assert(!allThreadsShouldExit);
2211 threads[threadID].state = THREAD_SEARCHING;
2213 // Here we call search() with SplitPoint template parameter set to true
2214 SplitPoint* tsp = threads[threadID].splitPoint;
2215 Position pos(*tsp->pos, threadID);
2216 SearchStack* ss = tsp->sstack[threadID] + 1;
2220 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2222 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2224 assert(threads[threadID].state == THREAD_SEARCHING);
2226 threads[threadID].state = THREAD_AVAILABLE;
2228 // Wake up master thread so to allow it to return from the idle loop in
2229 // case we are the last slave of the split point.
2230 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2231 wake_sleeping_thread(tsp->master);
2234 // If this thread is the master of a split point and all slaves have
2235 // finished their work at this split point, return from the idle loop.
2236 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2237 allFinished = (i == activeThreads);
2241 // Because sp->slaves[] is reset under lock protection,
2242 // be sure sp->lock has been released before to return.
2243 lock_grab(&(sp->lock));
2244 lock_release(&(sp->lock));
2246 // In helpful master concept a master can help only a sub-tree, and
2247 // because here is all finished is not possible master is booked.
2248 assert(threads[threadID].state == THREAD_AVAILABLE);
2250 threads[threadID].state = THREAD_SEARCHING;
2257 // init_threads() is called during startup. It launches all helper threads,
2258 // and initializes the split point stack and the global locks and condition
2261 void ThreadsManager::init_threads() {
2263 int i, arg[MAX_THREADS];
2266 // Initialize global locks
2269 for (i = 0; i < MAX_THREADS; i++)
2271 lock_init(&sleepLock[i]);
2272 cond_init(&sleepCond[i]);
2275 // Initialize splitPoints[] locks
2276 for (i = 0; i < MAX_THREADS; i++)
2277 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2278 lock_init(&(threads[i].splitPoints[j].lock));
2280 // Will be set just before program exits to properly end the threads
2281 allThreadsShouldExit = false;
2283 // Threads will be put all threads to sleep as soon as created
2286 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2287 threads[0].state = THREAD_SEARCHING;
2288 for (i = 1; i < MAX_THREADS; i++)
2289 threads[i].state = THREAD_INITIALIZING;
2291 // Launch the helper threads
2292 for (i = 1; i < MAX_THREADS; i++)
2296 #if !defined(_MSC_VER)
2297 pthread_t pthread[1];
2298 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2299 pthread_detach(pthread[0]);
2301 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2305 cout << "Failed to create thread number " << i << endl;
2309 // Wait until the thread has finished launching and is gone to sleep
2310 while (threads[i].state == THREAD_INITIALIZING) {}
2315 // exit_threads() is called when the program exits. It makes all the
2316 // helper threads exit cleanly.
2318 void ThreadsManager::exit_threads() {
2320 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2322 // Wake up all the threads and waits for termination
2323 for (int i = 1; i < MAX_THREADS; i++)
2325 wake_sleeping_thread(i);
2326 while (threads[i].state != THREAD_TERMINATED) {}
2329 // Now we can safely destroy the locks
2330 for (int i = 0; i < MAX_THREADS; i++)
2331 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2332 lock_destroy(&(threads[i].splitPoints[j].lock));
2334 lock_destroy(&mpLock);
2336 // Now we can safely destroy the wait conditions
2337 for (int i = 0; i < MAX_THREADS; i++)
2339 lock_destroy(&sleepLock[i]);
2340 cond_destroy(&sleepCond[i]);
2345 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2346 // the thread's currently active split point, or in some ancestor of
2347 // the current split point.
2349 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2351 assert(threadID >= 0 && threadID < activeThreads);
2353 SplitPoint* sp = threads[threadID].splitPoint;
2355 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2360 // thread_is_available() checks whether the thread with threadID "slave" is
2361 // available to help the thread with threadID "master" at a split point. An
2362 // obvious requirement is that "slave" must be idle. With more than two
2363 // threads, this is not by itself sufficient: If "slave" is the master of
2364 // some active split point, it is only available as a slave to the other
2365 // threads which are busy searching the split point at the top of "slave"'s
2366 // split point stack (the "helpful master concept" in YBWC terminology).
2368 bool ThreadsManager::thread_is_available(int slave, int master) const {
2370 assert(slave >= 0 && slave < activeThreads);
2371 assert(master >= 0 && master < activeThreads);
2372 assert(activeThreads > 1);
2374 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2377 // Make a local copy to be sure doesn't change under our feet
2378 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2380 // No active split points means that the thread is available as
2381 // a slave for any other thread.
2382 if (localActiveSplitPoints == 0 || activeThreads == 2)
2385 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2386 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2387 // could have been set to 0 by another thread leading to an out of bound access.
2388 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2395 // available_thread_exists() tries to find an idle thread which is available as
2396 // a slave for the thread with threadID "master".
2398 bool ThreadsManager::available_thread_exists(int master) const {
2400 assert(master >= 0 && master < activeThreads);
2401 assert(activeThreads > 1);
2403 for (int i = 0; i < activeThreads; i++)
2404 if (thread_is_available(i, master))
2411 // split() does the actual work of distributing the work at a node between
2412 // several available threads. If it does not succeed in splitting the
2413 // node (because no idle threads are available, or because we have no unused
2414 // split point objects), the function immediately returns. If splitting is
2415 // possible, a SplitPoint object is initialized with all the data that must be
2416 // copied to the helper threads and we tell our helper threads that they have
2417 // been assigned work. This will cause them to instantly leave their idle loops and
2418 // call search().When all threads have returned from search() then split() returns.
2420 template <bool Fake>
2421 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2422 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2423 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2424 assert(pos.is_ok());
2425 assert(ply > 0 && ply < PLY_MAX);
2426 assert(*bestValue >= -VALUE_INFINITE);
2427 assert(*bestValue <= *alpha);
2428 assert(*alpha < beta);
2429 assert(beta <= VALUE_INFINITE);
2430 assert(depth > DEPTH_ZERO);
2431 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2432 assert(activeThreads > 1);
2434 int i, master = pos.thread();
2435 Thread& masterThread = threads[master];
2439 // If no other thread is available to help us, or if we have too many
2440 // active split points, don't split.
2441 if ( !available_thread_exists(master)
2442 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2444 lock_release(&mpLock);
2448 // Pick the next available split point object from the split point stack
2449 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2451 // Initialize the split point object
2452 splitPoint.parent = masterThread.splitPoint;
2453 splitPoint.master = master;
2454 splitPoint.betaCutoff = false;
2455 splitPoint.ply = ply;
2456 splitPoint.depth = depth;
2457 splitPoint.threatMove = threatMove;
2458 splitPoint.mateThreat = mateThreat;
2459 splitPoint.alpha = *alpha;
2460 splitPoint.beta = beta;
2461 splitPoint.pvNode = pvNode;
2462 splitPoint.bestValue = *bestValue;
2464 splitPoint.moveCount = moveCount;
2465 splitPoint.pos = &pos;
2466 splitPoint.nodes = 0;
2467 splitPoint.parentSstack = ss;
2468 for (i = 0; i < activeThreads; i++)
2469 splitPoint.slaves[i] = 0;
2471 masterThread.splitPoint = &splitPoint;
2473 // If we are here it means we are not available
2474 assert(masterThread.state != THREAD_AVAILABLE);
2476 int workersCnt = 1; // At least the master is included
2478 // Allocate available threads setting state to THREAD_BOOKED
2479 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2480 if (thread_is_available(i, master))
2482 threads[i].state = THREAD_BOOKED;
2483 threads[i].splitPoint = &splitPoint;
2484 splitPoint.slaves[i] = 1;
2488 assert(Fake || workersCnt > 1);
2490 // We can release the lock because slave threads are already booked and master is not available
2491 lock_release(&mpLock);
2493 // Tell the threads that they have work to do. This will make them leave
2494 // their idle loop. But before copy search stack tail for each thread.
2495 for (i = 0; i < activeThreads; i++)
2496 if (i == master || splitPoint.slaves[i])
2498 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2500 assert(i == master || threads[i].state == THREAD_BOOKED);
2502 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2504 if (useSleepingThreads && i != master)
2505 wake_sleeping_thread(i);
2508 // Everything is set up. The master thread enters the idle loop, from
2509 // which it will instantly launch a search, because its state is
2510 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2511 // idle loop, which means that the main thread will return from the idle
2512 // loop when all threads have finished their work at this split point.
2513 idle_loop(master, &splitPoint);
2515 // We have returned from the idle loop, which means that all threads are
2516 // finished. Update alpha and bestValue, and return.
2519 *alpha = splitPoint.alpha;
2520 *bestValue = splitPoint.bestValue;
2521 masterThread.activeSplitPoints--;
2522 masterThread.splitPoint = splitPoint.parent;
2523 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2525 lock_release(&mpLock);
2529 // wake_sleeping_thread() wakes up the thread with the given threadID
2530 // when it is time to start a new search.
2532 void ThreadsManager::wake_sleeping_thread(int threadID) {
2534 lock_grab(&sleepLock[threadID]);
2535 cond_signal(&sleepCond[threadID]);
2536 lock_release(&sleepLock[threadID]);
2540 /// RootMove and RootMoveList method's definitions
2542 RootMove::RootMove() {
2545 pv_score = non_pv_score = -VALUE_INFINITE;
2549 RootMove& RootMove::operator=(const RootMove& rm) {
2551 const Move* src = rm.pv;
2554 // Avoid a costly full rm.pv[] copy
2555 do *dst++ = *src; while (*src++ != MOVE_NONE);
2558 pv_score = rm.pv_score;
2559 non_pv_score = rm.non_pv_score;
2563 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2564 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2565 // allow to always have a ponder move even when we fail high at root and also a
2566 // long PV to print that is important for position analysis.
2568 void RootMove::extract_pv_from_tt(Position& pos) {
2570 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2574 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2576 pos.do_move(pv[0], *st++);
2578 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2579 && tte->move() != MOVE_NONE
2580 && move_is_legal(pos, tte->move())
2582 && (!pos.is_draw() || ply < 2))
2584 pv[ply] = tte->move();
2585 pos.do_move(pv[ply++], *st++);
2587 pv[ply] = MOVE_NONE;
2589 do pos.undo_move(pv[--ply]); while (ply);
2592 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2593 // the PV back into the TT. This makes sure the old PV moves are searched
2594 // first, even if the old TT entries have been overwritten.
2596 void RootMove::insert_pv_in_tt(Position& pos) {
2598 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2601 Value v, m = VALUE_NONE;
2604 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2608 tte = TT.retrieve(k);
2610 // Don't overwrite exsisting correct entries
2611 if (!tte || tte->move() != pv[ply])
2613 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2614 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2616 pos.do_move(pv[ply], *st++);
2618 } while (pv[++ply] != MOVE_NONE);
2620 do pos.undo_move(pv[--ply]); while (ply);
2623 // pv_info_to_uci() returns a string with information on the current PV line
2624 // formatted according to UCI specification and eventually writes the info
2625 // to a log file. It is called at each iteration or after a new pv is found.
2627 std::string RootMove::pv_info_to_uci(const Position& pos, Value alpha, Value beta, int pvLine) {
2629 std::stringstream s, l;
2632 while (*m != MOVE_NONE)
2635 s << "info depth " << Iteration // FIXME
2636 << " seldepth " << int(m - pv)
2637 << " multipv " << pvLine + 1
2638 << " score " << value_to_uci(pv_score)
2639 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2640 << " time " << current_search_time()
2641 << " nodes " << pos.nodes_searched()
2642 << " nps " << nps(pos)
2643 << " pv " << l.str();
2645 if (UseLogFile && pvLine == 0)
2647 ValueType t = pv_score >= beta ? VALUE_TYPE_LOWER :
2648 pv_score <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2650 LogFile << pretty_pv(pos, current_search_time(), Iteration, pv_score, t, pv) << endl;
2656 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2658 SearchStack ss[PLY_MAX_PLUS_2];
2659 MoveStack mlist[MOVES_MAX];
2663 // Initialize search stack
2664 init_ss_array(ss, PLY_MAX_PLUS_2);
2665 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2667 // Generate all legal moves
2668 MoveStack* last = generate_moves(pos, mlist);
2670 // Add each move to the RootMoveList's vector
2671 for (MoveStack* cur = mlist; cur != last; cur++)
2673 // If we have a searchMoves[] list then verify cur->move
2674 // is in the list before to add it.
2675 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2677 if (searchMoves[0] && *sm != cur->move)
2680 // Find a quick score for the move and add to the list
2681 pos.do_move(cur->move, st);
2684 rm.pv[0] = ss[0].currentMove = cur->move;
2685 rm.pv[1] = MOVE_NONE;
2686 rm.pv_score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2689 pos.undo_move(cur->move);
2694 // Score root moves using the standard way used in main search, the moves
2695 // are scored according to the order in which are returned by MovePicker.
2696 // This is the second order score that is used to compare the moves when
2697 // the first order pv scores of both moves are equal.
2699 void RootMoveList::set_non_pv_scores(const Position& pos, Move ttm, SearchStack* ss)
2702 Value score = VALUE_ZERO;
2703 MovePicker mp(pos, ttm, ONE_PLY, H, ss);
2705 while ((move = mp.get_next_move()) != MOVE_NONE)
2706 for (Base::iterator it = begin(); it != end(); ++it)
2707 if (it->pv[0] == move)
2709 it->non_pv_score = score--;