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 + 1); }
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, SearchStack* ss);
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 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
687 int researchCountFH, researchCountFL;
689 researchCountFH = researchCountFL = 0;
691 isCheck = pos.is_check();
693 // Step 1. Initialize node (polling is omitted at root)
694 ss->currentMove = ss->bestMove = MOVE_NONE;
696 // Step 2. Check for aborted search (omitted at root)
697 // Step 3. Mate distance pruning (omitted at root)
698 // Step 4. Transposition table lookup (omitted at root)
700 // Step 5. Evaluate the position statically
701 // At root we do this only to get reference value for child nodes
702 ss->evalMargin = VALUE_NONE;
703 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
705 // Step 6. Razoring (omitted at root)
706 // Step 7. Static null move pruning (omitted at root)
707 // Step 8. Null move search with verification search (omitted at root)
708 // Step 9. Internal iterative deepening (omitted at root)
710 // Step extra. Fail low loop
711 // We start with small aspiration window and in case of fail low, we research
712 // with bigger window until we are not failing low anymore.
715 // Sort the moves before to (re)search
716 rml.set_non_pv_scores(pos, rml[0].pv[0], ss);
719 // Step 10. Loop through all moves in the root move list
720 for (int moveCount = 0; moveCount < (int)rml.size() && !StopRequest; moveCount++)
722 // This is used by time management
723 FirstRootMove = (moveCount == 0);
725 // Save the current node count before the move is searched
726 nodes = pos.nodes_searched();
728 // If it's time to send nodes info, do it here where we have the
729 // correct accumulated node counts searched by each thread.
730 if (SendSearchedNodes)
732 SendSearchedNodes = false;
733 cout << "info nodes " << nodes
734 << " nps " << nps(pos)
735 << " time " << current_search_time() << endl;
738 // Pick the next root move, and print the move and the move number to
739 // the standard output.
740 move = ss->currentMove = rml[moveCount].pv[0];
741 movesSearched[moveCount] = move;
743 if (current_search_time() >= 1000)
744 cout << "info currmove " << move
745 << " currmovenumber " << moveCount + 1 << endl;
747 moveIsCheck = pos.move_is_check(move);
748 captureOrPromotion = pos.move_is_capture_or_promotion(move);
750 // Step 11. Decide the new search depth
751 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
752 newDepth = depth + ext;
754 // Step 12. Futility pruning (omitted at root)
756 // Step extra. Fail high loop
757 // If move fails high, we research with bigger window until we are not failing
759 value = -VALUE_INFINITE;
763 // Step 13. Make the move
764 pos.do_move(move, st, ci, moveIsCheck);
766 // Step extra. pv search
767 // We do pv search for first moves (i < MultiPV)
768 // and for fail high research (value > alpha)
769 if (moveCount < MultiPV || value > alpha)
771 // Aspiration window is disabled in multi-pv case
773 alpha = -VALUE_INFINITE;
775 // Full depth PV search, done on first move or after a fail high
776 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
780 // Step 14. Reduced search
781 // if the move fails high will be re-searched at full depth
782 bool doFullDepthSearch = true;
784 if ( depth >= 3 * ONE_PLY
786 && !captureOrPromotion
787 && !move_is_castle(move))
789 ss->reduction = reduction<PV>(depth, moveCount - MultiPV + 2);
792 assert(newDepth-ss->reduction >= ONE_PLY);
794 // Reduced depth non-pv search using alpha as upperbound
795 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
796 doFullDepthSearch = (value > alpha);
798 ss->reduction = DEPTH_ZERO; // Restore original reduction
801 // Step 15. Full depth search
802 if (doFullDepthSearch)
804 // Full depth non-pv search using alpha as upperbound
805 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
807 // If we are above alpha then research at same depth but as PV
808 // to get a correct score or eventually a fail high above beta.
810 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
814 // Step 16. Undo move
817 // Can we exit fail high loop ?
818 if (StopRequest || value < beta)
821 // We are failing high and going to do a research. It's important to update
822 // the score before research in case we run out of time while researching.
824 rml[moveCount].pv_score = value;
825 rml[moveCount].extract_pv_from_tt(pos);
827 // Update killers and history only for non capture moves that fails high
828 if (!pos.move_is_capture_or_promotion(move))
830 update_history(pos, move, depth, movesSearched, moveCount + 1);
831 update_killers(move, ss);
834 // Inform GUI that PV has changed
835 cout << rml[moveCount].pv_info_to_uci(pos, alpha, beta) << endl;
837 // Prepare for a research after a fail high, each time with a wider window
838 beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
841 } // End of fail high loop
843 // Finished searching the move. If AbortSearch is true, the search
844 // was aborted because the user interrupted the search or because we
845 // ran out of time. In this case, the return value of the search cannot
846 // be trusted, and we break out of the loop without updating the best
851 // Remember searched nodes counts for this move
852 rml[moveCount].nodes += pos.nodes_searched() - nodes;
854 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
855 assert(value < beta);
857 // Step 17. Check for new best move
858 if (value <= alpha && moveCount >= MultiPV)
859 rml[moveCount].pv_score = -VALUE_INFINITE;
862 // PV move or new best move!
866 rml[moveCount].pv_score = value;
867 rml[moveCount].extract_pv_from_tt(pos);
869 // We record how often the best move has been changed in each
870 // iteration. This information is used for time managment: When
871 // the best move changes frequently, we allocate some more time.
872 if (MultiPV == 1 && moveCount > 0)
873 BestMoveChangesByIteration[Iteration]++;
875 // Inform GUI that PV has changed, in case of multi-pv UCI protocol
876 // requires we send all the PV lines properly sorted.
877 rml.sort_multipv(moveCount);
879 for (int j = 0; j < Min(MultiPV, (int)rml.size()); j++)
880 cout << rml[j].pv_info_to_uci(pos, alpha, beta, j) << endl;
882 // Update alpha. In multi-pv we don't use aspiration window
885 // Raise alpha to setup proper non-pv search upper bound
889 else // Set alpha equal to minimum score among the PV lines
890 alpha = rml[Min(moveCount, MultiPV - 1)].pv_score;
892 } // PV move or new best move
894 assert(alpha >= oldAlpha);
896 AspirationFailLow = (alpha == oldAlpha);
898 if (AspirationFailLow && StopOnPonderhit)
899 StopOnPonderhit = false;
903 // Can we exit fail low loop ?
904 if (StopRequest || !AspirationFailLow)
907 // Prepare for a research after a fail low, each time with a wider window
908 oldAlpha = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
913 // Sort the moves before to return
916 // Write PV lines to transposition table, in case the relevant entries
917 // have been overwritten during the search.
918 for (int i = 0; i < Min(MultiPV, (int)rml.size()); i++)
919 rml[i].insert_pv_in_tt(pos);
925 // search<>() is the main search function for both PV and non-PV nodes and for
926 // normal and SplitPoint nodes. When called just after a split point the search
927 // is simpler because we have already probed the hash table, done a null move
928 // search, and searched the first move before splitting, we don't have to repeat
929 // all this work again. We also don't need to store anything to the hash table
930 // here: This is taken care of after we return from the split point.
932 template <NodeType PvNode, bool SpNode>
933 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
935 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
936 assert(beta > alpha && beta <= VALUE_INFINITE);
937 assert(PvNode || alpha == beta - 1);
938 assert(ply > 0 && ply < PLY_MAX);
939 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
941 Move movesSearched[MOVES_MAX];
945 Move ttMove, move, excludedMove, threatMove;
948 Value bestValue, value, oldAlpha;
949 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
950 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
951 bool mateThreat = false;
953 int threadID = pos.thread();
954 SplitPoint* sp = NULL;
955 refinedValue = bestValue = value = -VALUE_INFINITE;
957 isCheck = pos.is_check();
963 ttMove = excludedMove = MOVE_NONE;
964 threatMove = sp->threatMove;
965 mateThreat = sp->mateThreat;
966 goto split_point_start;
968 else {} // Hack to fix icc's "statement is unreachable" warning
970 // Step 1. Initialize node and poll. Polling can abort search
971 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
972 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
974 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
980 // Step 2. Check for aborted search and immediate draw
982 || ThreadsMgr.cutoff_at_splitpoint(threadID)
984 || ply >= PLY_MAX - 1)
987 // Step 3. Mate distance pruning
988 alpha = Max(value_mated_in(ply), alpha);
989 beta = Min(value_mate_in(ply+1), beta);
993 // Step 4. Transposition table lookup
995 // We don't want the score of a partial search to overwrite a previous full search
996 // TT value, so we use a different position key in case of an excluded move exists.
997 excludedMove = ss->excludedMove;
998 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1000 tte = TT.retrieve(posKey);
1001 ttMove = tte ? tte->move() : MOVE_NONE;
1003 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1004 // This is to avoid problems in the following areas:
1006 // * Repetition draw detection
1007 // * Fifty move rule detection
1008 // * Searching for a mate
1009 // * Printing of full PV line
1010 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1013 ss->bestMove = ttMove; // Can be MOVE_NONE
1014 return value_from_tt(tte->value(), ply);
1017 // Step 5. Evaluate the position statically and
1018 // update gain statistics of parent move.
1020 ss->eval = ss->evalMargin = VALUE_NONE;
1023 assert(tte->static_value() != VALUE_NONE);
1025 ss->eval = tte->static_value();
1026 ss->evalMargin = tte->static_value_margin();
1027 refinedValue = refine_eval(tte, ss->eval, ply);
1031 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1032 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1035 // Save gain for the parent non-capture move
1036 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1038 // Step 6. Razoring (is omitted in PV nodes)
1040 && depth < RazorDepth
1042 && refinedValue < beta - razor_margin(depth)
1043 && ttMove == MOVE_NONE
1044 && !value_is_mate(beta)
1045 && !pos.has_pawn_on_7th(pos.side_to_move()))
1047 Value rbeta = beta - razor_margin(depth);
1048 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1050 // Logically we should return (v + razor_margin(depth)), but
1051 // surprisingly this did slightly weaker in tests.
1055 // Step 7. Static null move pruning (is omitted in PV nodes)
1056 // We're betting that the opponent doesn't have a move that will reduce
1057 // the score by more than futility_margin(depth) if we do a null move.
1059 && !ss->skipNullMove
1060 && depth < RazorDepth
1062 && refinedValue >= beta + futility_margin(depth, 0)
1063 && !value_is_mate(beta)
1064 && pos.non_pawn_material(pos.side_to_move()))
1065 return refinedValue - futility_margin(depth, 0);
1067 // Step 8. Null move search with verification search (is omitted in PV nodes)
1069 && !ss->skipNullMove
1072 && refinedValue >= beta
1073 && !value_is_mate(beta)
1074 && pos.non_pawn_material(pos.side_to_move()))
1076 ss->currentMove = MOVE_NULL;
1078 // Null move dynamic reduction based on depth
1079 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1081 // Null move dynamic reduction based on value
1082 if (refinedValue - beta > PawnValueMidgame)
1085 pos.do_null_move(st);
1086 (ss+1)->skipNullMove = true;
1087 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1088 (ss+1)->skipNullMove = false;
1089 pos.undo_null_move();
1091 if (nullValue >= beta)
1093 // Do not return unproven mate scores
1094 if (nullValue >= value_mate_in(PLY_MAX))
1097 if (depth < 6 * ONE_PLY)
1100 // Do verification search at high depths
1101 ss->skipNullMove = true;
1102 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1103 ss->skipNullMove = false;
1110 // The null move failed low, which means that we may be faced with
1111 // some kind of threat. If the previous move was reduced, check if
1112 // the move that refuted the null move was somehow connected to the
1113 // move which was reduced. If a connection is found, return a fail
1114 // low score (which will cause the reduced move to fail high in the
1115 // parent node, which will trigger a re-search with full depth).
1116 if (nullValue == value_mated_in(ply + 2))
1119 threatMove = (ss+1)->bestMove;
1120 if ( depth < ThreatDepth
1121 && (ss-1)->reduction
1122 && threatMove != MOVE_NONE
1123 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1128 // Step 9. Internal iterative deepening
1129 if ( depth >= IIDDepth[PvNode]
1130 && ttMove == MOVE_NONE
1131 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1133 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1135 ss->skipNullMove = true;
1136 search<PvNode>(pos, ss, alpha, beta, d, ply);
1137 ss->skipNullMove = false;
1139 ttMove = ss->bestMove;
1140 tte = TT.retrieve(posKey);
1143 // Expensive mate threat detection (only for PV nodes)
1145 mateThreat = pos.has_mate_threat();
1147 split_point_start: // At split points actual search starts from here
1149 // Initialize a MovePicker object for the current position
1150 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1151 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1152 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1154 ss->bestMove = MOVE_NONE;
1155 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1156 futilityBase = ss->eval + ss->evalMargin;
1157 singularExtensionNode = !SpNode
1158 && depth >= SingularExtensionDepth[PvNode]
1161 && !excludedMove // Do not allow recursive singular extension search
1162 && (tte->type() & VALUE_TYPE_LOWER)
1163 && tte->depth() >= depth - 3 * ONE_PLY;
1166 lock_grab(&(sp->lock));
1167 bestValue = sp->bestValue;
1170 // Step 10. Loop through moves
1171 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1172 while ( bestValue < beta
1173 && (move = mp.get_next_move()) != MOVE_NONE
1174 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1176 assert(move_is_ok(move));
1180 moveCount = ++sp->moveCount;
1181 lock_release(&(sp->lock));
1183 else if (move == excludedMove)
1186 movesSearched[moveCount++] = move;
1188 moveIsCheck = pos.move_is_check(move, ci);
1189 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1191 // Step 11. Decide the new search depth
1192 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1194 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1195 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1196 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1197 // lower then ttValue minus a margin then we extend ttMove.
1198 if ( singularExtensionNode
1199 && move == tte->move()
1202 Value ttValue = value_from_tt(tte->value(), ply);
1204 if (abs(ttValue) < VALUE_KNOWN_WIN)
1206 Value b = ttValue - SingularExtensionMargin;
1207 ss->excludedMove = move;
1208 ss->skipNullMove = true;
1209 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1210 ss->skipNullMove = false;
1211 ss->excludedMove = MOVE_NONE;
1212 ss->bestMove = MOVE_NONE;
1218 // Update current move (this must be done after singular extension search)
1219 ss->currentMove = move;
1220 newDepth = depth - ONE_PLY + ext;
1222 // Step 12. Futility pruning (is omitted in PV nodes)
1224 && !captureOrPromotion
1228 && !move_is_castle(move))
1230 // Move count based pruning
1231 if ( moveCount >= futility_move_count(depth)
1232 && !(threatMove && connected_threat(pos, move, threatMove))
1233 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1236 lock_grab(&(sp->lock));
1241 // Value based pruning
1242 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1243 // but fixing this made program slightly weaker.
1244 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1245 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1246 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1248 if (futilityValueScaled < beta)
1252 lock_grab(&(sp->lock));
1253 if (futilityValueScaled > sp->bestValue)
1254 sp->bestValue = bestValue = futilityValueScaled;
1256 else if (futilityValueScaled > bestValue)
1257 bestValue = futilityValueScaled;
1262 // Prune moves with negative SEE at low depths
1263 if ( predictedDepth < 2 * ONE_PLY
1264 && bestValue > value_mated_in(PLY_MAX)
1265 && pos.see_sign(move) < 0)
1268 lock_grab(&(sp->lock));
1274 // Step 13. Make the move
1275 pos.do_move(move, st, ci, moveIsCheck);
1277 // Step extra. pv search (only in PV nodes)
1278 // The first move in list is the expected PV
1279 if (PvNode && moveCount == 1)
1280 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1283 // Step 14. Reduced depth search
1284 // If the move fails high will be re-searched at full depth.
1285 bool doFullDepthSearch = true;
1287 if ( depth >= 3 * ONE_PLY
1288 && !captureOrPromotion
1290 && !move_is_castle(move)
1291 && ss->killers[0] != move
1292 && ss->killers[1] != move)
1294 ss->reduction = reduction<PvNode>(depth, moveCount);
1298 alpha = SpNode ? sp->alpha : alpha;
1299 Depth d = newDepth - ss->reduction;
1300 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1302 doFullDepthSearch = (value > alpha);
1304 ss->reduction = DEPTH_ZERO; // Restore original reduction
1307 // Step 15. Full depth search
1308 if (doFullDepthSearch)
1310 alpha = SpNode ? sp->alpha : alpha;
1311 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1313 // Step extra. pv search (only in PV nodes)
1314 // Search only for possible new PV nodes, if instead value >= beta then
1315 // parent node fails low with value <= alpha and tries another move.
1316 if (PvNode && value > alpha && value < beta)
1317 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1321 // Step 16. Undo move
1322 pos.undo_move(move);
1324 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1326 // Step 17. Check for new best move
1329 lock_grab(&(sp->lock));
1330 bestValue = sp->bestValue;
1334 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1339 sp->bestValue = value;
1343 if (PvNode && value < beta) // We want always alpha < beta
1351 sp->betaCutoff = true;
1353 if (value == value_mate_in(ply + 1))
1354 ss->mateKiller = move;
1356 ss->bestMove = move;
1359 sp->parentSstack->bestMove = move;
1363 // Step 18. Check for split
1365 && depth >= ThreadsMgr.min_split_depth()
1366 && ThreadsMgr.active_threads() > 1
1368 && ThreadsMgr.available_thread_exists(threadID)
1370 && !ThreadsMgr.cutoff_at_splitpoint(threadID)
1372 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1373 threatMove, mateThreat, moveCount, &mp, PvNode);
1376 // Step 19. Check for mate and stalemate
1377 // All legal moves have been searched and if there are
1378 // no legal moves, it must be mate or stalemate.
1379 // If one move was excluded return fail low score.
1380 if (!SpNode && !moveCount)
1381 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1383 // Step 20. Update tables
1384 // If the search is not aborted, update the transposition table,
1385 // history counters, and killer moves.
1386 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1388 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1389 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1390 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1392 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1394 // Update killers and history only for non capture moves that fails high
1395 if ( bestValue >= beta
1396 && !pos.move_is_capture_or_promotion(move))
1398 update_history(pos, move, depth, movesSearched, moveCount);
1399 update_killers(move, ss);
1405 // Here we have the lock still grabbed
1406 sp->slaves[threadID] = 0;
1407 sp->nodes += pos.nodes_searched();
1408 lock_release(&(sp->lock));
1411 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1416 // qsearch() is the quiescence search function, which is called by the main
1417 // search function when the remaining depth is zero (or, to be more precise,
1418 // less than ONE_PLY).
1420 template <NodeType PvNode>
1421 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1423 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1424 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1425 assert(PvNode || alpha == beta - 1);
1427 assert(ply > 0 && ply < PLY_MAX);
1428 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1432 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1433 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1436 Value oldAlpha = alpha;
1438 ss->bestMove = ss->currentMove = MOVE_NONE;
1440 // Check for an instant draw or maximum ply reached
1441 if (pos.is_draw() || ply >= PLY_MAX - 1)
1444 // Decide whether or not to include checks, this fixes also the type of
1445 // TT entry depth that we are going to use. Note that in qsearch we use
1446 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1447 isCheck = pos.is_check();
1448 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1450 // Transposition table lookup. At PV nodes, we don't use the TT for
1451 // pruning, but only for move ordering.
1452 tte = TT.retrieve(pos.get_key());
1453 ttMove = (tte ? tte->move() : MOVE_NONE);
1455 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1457 ss->bestMove = ttMove; // Can be MOVE_NONE
1458 return value_from_tt(tte->value(), ply);
1461 // Evaluate the position statically
1464 bestValue = futilityBase = -VALUE_INFINITE;
1465 ss->eval = evalMargin = VALUE_NONE;
1466 enoughMaterial = false;
1472 assert(tte->static_value() != VALUE_NONE);
1474 evalMargin = tte->static_value_margin();
1475 ss->eval = bestValue = tte->static_value();
1478 ss->eval = bestValue = evaluate(pos, evalMargin);
1480 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1482 // Stand pat. Return immediately if static value is at least beta
1483 if (bestValue >= beta)
1486 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1491 if (PvNode && bestValue > alpha)
1494 // Futility pruning parameters, not needed when in check
1495 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1496 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1499 // Initialize a MovePicker object for the current position, and prepare
1500 // to search the moves. Because the depth is <= 0 here, only captures,
1501 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1503 MovePicker mp(pos, ttMove, depth, H);
1506 // Loop through the moves until no moves remain or a beta cutoff occurs
1507 while ( alpha < beta
1508 && (move = mp.get_next_move()) != MOVE_NONE)
1510 assert(move_is_ok(move));
1512 moveIsCheck = pos.move_is_check(move, ci);
1520 && !move_is_promotion(move)
1521 && !pos.move_is_passed_pawn_push(move))
1523 futilityValue = futilityBase
1524 + pos.endgame_value_of_piece_on(move_to(move))
1525 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1527 if (futilityValue < alpha)
1529 if (futilityValue > bestValue)
1530 bestValue = futilityValue;
1535 // Detect non-capture evasions that are candidate to be pruned
1536 evasionPrunable = isCheck
1537 && bestValue > value_mated_in(PLY_MAX)
1538 && !pos.move_is_capture(move)
1539 && !pos.can_castle(pos.side_to_move());
1541 // Don't search moves with negative SEE values
1543 && (!isCheck || evasionPrunable)
1545 && !move_is_promotion(move)
1546 && pos.see_sign(move) < 0)
1549 // Don't search useless checks
1554 && !pos.move_is_capture_or_promotion(move)
1555 && ss->eval + PawnValueMidgame / 4 < beta
1556 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1558 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1559 bestValue = ss->eval + PawnValueMidgame / 4;
1564 // Update current move
1565 ss->currentMove = move;
1567 // Make and search the move
1568 pos.do_move(move, st, ci, moveIsCheck);
1569 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1570 pos.undo_move(move);
1572 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1575 if (value > bestValue)
1581 ss->bestMove = move;
1586 // All legal moves have been searched. A special case: If we're in check
1587 // and no legal moves were found, it is checkmate.
1588 if (isCheck && bestValue == -VALUE_INFINITE)
1589 return value_mated_in(ply);
1591 // Update transposition table
1592 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1593 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1595 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1601 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1602 // bestValue is updated only when returning false because in that case move
1605 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1607 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1608 Square from, to, ksq, victimSq;
1611 Value futilityValue, bv = *bestValue;
1613 from = move_from(move);
1615 them = opposite_color(pos.side_to_move());
1616 ksq = pos.king_square(them);
1617 kingAtt = pos.attacks_from<KING>(ksq);
1618 pc = pos.piece_on(from);
1620 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1621 oldAtt = pos.attacks_from(pc, from, occ);
1622 newAtt = pos.attacks_from(pc, to, occ);
1624 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1625 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1627 if (!(b && (b & (b - 1))))
1630 // Rule 2. Queen contact check is very dangerous
1631 if ( type_of_piece(pc) == QUEEN
1632 && bit_is_set(kingAtt, to))
1635 // Rule 3. Creating new double threats with checks
1636 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1640 victimSq = pop_1st_bit(&b);
1641 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1643 // Note that here we generate illegal "double move"!
1644 if ( futilityValue >= beta
1645 && pos.see_sign(make_move(from, victimSq)) >= 0)
1648 if (futilityValue > bv)
1652 // Update bestValue only if check is not dangerous (because we will prune the move)
1658 // connected_moves() tests whether two moves are 'connected' in the sense
1659 // that the first move somehow made the second move possible (for instance
1660 // if the moving piece is the same in both moves). The first move is assumed
1661 // to be the move that was made to reach the current position, while the
1662 // second move is assumed to be a move from the current position.
1664 bool connected_moves(const Position& pos, Move m1, Move m2) {
1666 Square f1, t1, f2, t2;
1669 assert(m1 && move_is_ok(m1));
1670 assert(m2 && move_is_ok(m2));
1672 // Case 1: The moving piece is the same in both moves
1678 // Case 2: The destination square for m2 was vacated by m1
1684 // Case 3: Moving through the vacated square
1685 if ( piece_is_slider(pos.piece_on(f2))
1686 && bit_is_set(squares_between(f2, t2), f1))
1689 // Case 4: The destination square for m2 is defended by the moving piece in m1
1690 p = pos.piece_on(t1);
1691 if (bit_is_set(pos.attacks_from(p, t1), t2))
1694 // Case 5: Discovered check, checking piece is the piece moved in m1
1695 if ( piece_is_slider(p)
1696 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1697 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1699 // discovered_check_candidates() works also if the Position's side to
1700 // move is the opposite of the checking piece.
1701 Color them = opposite_color(pos.side_to_move());
1702 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1704 if (bit_is_set(dcCandidates, f2))
1711 // value_is_mate() checks if the given value is a mate one eventually
1712 // compensated for the ply.
1714 bool value_is_mate(Value value) {
1716 assert(abs(value) <= VALUE_INFINITE);
1718 return value <= value_mated_in(PLY_MAX)
1719 || value >= value_mate_in(PLY_MAX);
1723 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1724 // "plies to mate from the current ply". Non-mate scores are unchanged.
1725 // The function is called before storing a value to the transposition table.
1727 Value value_to_tt(Value v, int ply) {
1729 if (v >= value_mate_in(PLY_MAX))
1732 if (v <= value_mated_in(PLY_MAX))
1739 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1740 // the transposition table to a mate score corrected for the current ply.
1742 Value value_from_tt(Value v, int ply) {
1744 if (v >= value_mate_in(PLY_MAX))
1747 if (v <= value_mated_in(PLY_MAX))
1754 // extension() decides whether a move should be searched with normal depth,
1755 // or with extended depth. Certain classes of moves (checking moves, in
1756 // particular) are searched with bigger depth than ordinary moves and in
1757 // any case are marked as 'dangerous'. Note that also if a move is not
1758 // extended, as example because the corresponding UCI option is set to zero,
1759 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1760 template <NodeType PvNode>
1761 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1762 bool singleEvasion, bool mateThreat, bool* dangerous) {
1764 assert(m != MOVE_NONE);
1766 Depth result = DEPTH_ZERO;
1767 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1771 if (moveIsCheck && pos.see_sign(m) >= 0)
1772 result += CheckExtension[PvNode];
1775 result += SingleEvasionExtension[PvNode];
1778 result += MateThreatExtension[PvNode];
1781 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1783 Color c = pos.side_to_move();
1784 if (relative_rank(c, move_to(m)) == RANK_7)
1786 result += PawnPushTo7thExtension[PvNode];
1789 if (pos.pawn_is_passed(c, move_to(m)))
1791 result += PassedPawnExtension[PvNode];
1796 if ( captureOrPromotion
1797 && pos.type_of_piece_on(move_to(m)) != PAWN
1798 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1799 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1800 && !move_is_promotion(m)
1803 result += PawnEndgameExtension[PvNode];
1808 && captureOrPromotion
1809 && pos.type_of_piece_on(move_to(m)) != PAWN
1810 && pos.see_sign(m) >= 0)
1812 result += ONE_PLY / 2;
1816 return Min(result, ONE_PLY);
1820 // connected_threat() tests whether it is safe to forward prune a move or if
1821 // is somehow coonected to the threat move returned by null search.
1823 bool connected_threat(const Position& pos, Move m, Move threat) {
1825 assert(move_is_ok(m));
1826 assert(threat && move_is_ok(threat));
1827 assert(!pos.move_is_check(m));
1828 assert(!pos.move_is_capture_or_promotion(m));
1829 assert(!pos.move_is_passed_pawn_push(m));
1831 Square mfrom, mto, tfrom, tto;
1833 mfrom = move_from(m);
1835 tfrom = move_from(threat);
1836 tto = move_to(threat);
1838 // Case 1: Don't prune moves which move the threatened piece
1842 // Case 2: If the threatened piece has value less than or equal to the
1843 // value of the threatening piece, don't prune move which defend it.
1844 if ( pos.move_is_capture(threat)
1845 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1846 || pos.type_of_piece_on(tfrom) == KING)
1847 && pos.move_attacks_square(m, tto))
1850 // Case 3: If the moving piece in the threatened move is a slider, don't
1851 // prune safe moves which block its ray.
1852 if ( piece_is_slider(pos.piece_on(tfrom))
1853 && bit_is_set(squares_between(tfrom, tto), mto)
1854 && pos.see_sign(m) >= 0)
1861 // ok_to_use_TT() returns true if a transposition table score
1862 // can be used at a given point in search.
1864 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1866 Value v = value_from_tt(tte->value(), ply);
1868 return ( tte->depth() >= depth
1869 || v >= Max(value_mate_in(PLY_MAX), beta)
1870 || v < Min(value_mated_in(PLY_MAX), beta))
1872 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1873 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1877 // refine_eval() returns the transposition table score if
1878 // possible otherwise falls back on static position evaluation.
1880 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1884 Value v = value_from_tt(tte->value(), ply);
1886 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1887 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1894 // update_history() registers a good move that produced a beta-cutoff
1895 // in history and marks as failures all the other moves of that ply.
1897 void update_history(const Position& pos, Move move, Depth depth,
1898 Move movesSearched[], int moveCount) {
1901 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1903 for (int i = 0; i < moveCount - 1; i++)
1905 m = movesSearched[i];
1909 if (!pos.move_is_capture_or_promotion(m))
1910 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1915 // update_killers() add a good move that produced a beta-cutoff
1916 // among the killer moves of that ply.
1918 void update_killers(Move m, SearchStack* ss) {
1920 if (m == ss->killers[0])
1923 ss->killers[1] = ss->killers[0];
1928 // update_gains() updates the gains table of a non-capture move given
1929 // the static position evaluation before and after the move.
1931 void update_gains(const Position& pos, Move m, Value before, Value after) {
1934 && before != VALUE_NONE
1935 && after != VALUE_NONE
1936 && pos.captured_piece_type() == PIECE_TYPE_NONE
1937 && !move_is_special(m))
1938 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1942 // init_ss_array() does a fast reset of the first entries of a SearchStack
1943 // array and of all the excludedMove and skipNullMove entries.
1945 void init_ss_array(SearchStack* ss, int size) {
1947 for (int i = 0; i < size; i++, ss++)
1949 ss->excludedMove = MOVE_NONE;
1950 ss->skipNullMove = false;
1951 ss->reduction = DEPTH_ZERO;
1955 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
1960 // value_to_uci() converts a value to a string suitable for use with the UCI
1961 // protocol specifications:
1963 // cp <x> The score from the engine's point of view in centipawns.
1964 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1965 // use negative values for y.
1967 std::string value_to_uci(Value v) {
1969 std::stringstream s;
1971 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1972 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1974 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1980 // current_search_time() returns the number of milliseconds which have passed
1981 // since the beginning of the current search.
1983 int current_search_time() {
1985 return get_system_time() - SearchStartTime;
1989 // nps() computes the current nodes/second count
1991 int nps(const Position& pos) {
1993 int t = current_search_time();
1994 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1998 // poll() performs two different functions: It polls for user input, and it
1999 // looks at the time consumed so far and decides if it's time to abort the
2002 void poll(const Position& pos) {
2004 static int lastInfoTime;
2005 int t = current_search_time();
2008 if (data_available())
2010 // We are line oriented, don't read single chars
2011 std::string command;
2013 if (!std::getline(std::cin, command))
2016 if (command == "quit")
2018 // Quit the program as soon as possible
2020 QuitRequest = StopRequest = true;
2023 else if (command == "stop")
2025 // Stop calculating as soon as possible, but still send the "bestmove"
2026 // and possibly the "ponder" token when finishing the search.
2030 else if (command == "ponderhit")
2032 // The opponent has played the expected move. GUI sends "ponderhit" if
2033 // we were told to ponder on the same move the opponent has played. We
2034 // should continue searching but switching from pondering to normal search.
2037 if (StopOnPonderhit)
2042 // Print search information
2046 else if (lastInfoTime > t)
2047 // HACK: Must be a new search where we searched less than
2048 // NodesBetweenPolls nodes during the first second of search.
2051 else if (t - lastInfoTime >= 1000)
2058 if (dbg_show_hit_rate)
2059 dbg_print_hit_rate();
2061 // Send info on searched nodes as soon as we return to root
2062 SendSearchedNodes = true;
2065 // Should we stop the search?
2069 bool stillAtFirstMove = FirstRootMove
2070 && !AspirationFailLow
2071 && t > TimeMgr.available_time();
2073 bool noMoreTime = t > TimeMgr.maximum_time()
2074 || stillAtFirstMove;
2076 if ( (UseTimeManagement && noMoreTime)
2077 || (ExactMaxTime && t >= ExactMaxTime)
2078 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
2083 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2084 // while the program is pondering. The point is to work around a wrinkle in
2085 // the UCI protocol: When pondering, the engine is not allowed to give a
2086 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2087 // We simply wait here until one of these commands is sent, and return,
2088 // after which the bestmove and pondermove will be printed.
2090 void wait_for_stop_or_ponderhit() {
2092 std::string command;
2096 // Wait for a command from stdin
2097 if (!std::getline(std::cin, command))
2100 if (command == "quit")
2105 else if (command == "ponderhit" || command == "stop")
2111 // init_thread() is the function which is called when a new thread is
2112 // launched. It simply calls the idle_loop() function with the supplied
2113 // threadID. There are two versions of this function; one for POSIX
2114 // threads and one for Windows threads.
2116 #if !defined(_MSC_VER)
2118 void* init_thread(void* threadID) {
2120 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2126 DWORD WINAPI init_thread(LPVOID threadID) {
2128 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2135 /// The ThreadsManager class
2138 // read_uci_options() updates number of active threads and other internal
2139 // parameters according to the UCI options values. It is called before
2140 // to start a new search.
2142 void ThreadsManager::read_uci_options() {
2144 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2145 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2146 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2147 activeThreads = Options["Threads"].value<int>();
2151 // idle_loop() is where the threads are parked when they have no work to do.
2152 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2153 // object for which the current thread is the master.
2155 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2157 assert(threadID >= 0 && threadID < MAX_THREADS);
2160 bool allFinished = false;
2164 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2165 // master should exit as last one.
2166 if (allThreadsShouldExit)
2169 threads[threadID].state = THREAD_TERMINATED;
2173 // If we are not thinking, wait for a condition to be signaled
2174 // instead of wasting CPU time polling for work.
2175 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2176 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2178 assert(!sp || useSleepingThreads);
2179 assert(threadID != 0 || useSleepingThreads);
2181 if (threads[threadID].state == THREAD_INITIALIZING)
2182 threads[threadID].state = THREAD_AVAILABLE;
2184 // Grab the lock to avoid races with wake_sleeping_thread()
2185 lock_grab(&sleepLock[threadID]);
2187 // If we are master and all slaves have finished do not go to sleep
2188 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2189 allFinished = (i == activeThreads);
2191 if (allFinished || allThreadsShouldExit)
2193 lock_release(&sleepLock[threadID]);
2197 // Do sleep here after retesting sleep conditions
2198 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2199 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2201 lock_release(&sleepLock[threadID]);
2204 // If this thread has been assigned work, launch a search
2205 if (threads[threadID].state == THREAD_WORKISWAITING)
2207 assert(!allThreadsShouldExit);
2209 threads[threadID].state = THREAD_SEARCHING;
2211 // Here we call search() with SplitPoint template parameter set to true
2212 SplitPoint* tsp = threads[threadID].splitPoint;
2213 Position pos(*tsp->pos, threadID);
2214 SearchStack* ss = tsp->sstack[threadID] + 1;
2218 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2220 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2222 assert(threads[threadID].state == THREAD_SEARCHING);
2224 threads[threadID].state = THREAD_AVAILABLE;
2226 // Wake up master thread so to allow it to return from the idle loop in
2227 // case we are the last slave of the split point.
2228 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2229 wake_sleeping_thread(tsp->master);
2232 // If this thread is the master of a split point and all slaves have
2233 // finished their work at this split point, return from the idle loop.
2234 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2235 allFinished = (i == activeThreads);
2239 // Because sp->slaves[] is reset under lock protection,
2240 // be sure sp->lock has been released before to return.
2241 lock_grab(&(sp->lock));
2242 lock_release(&(sp->lock));
2244 // In helpful master concept a master can help only a sub-tree, and
2245 // because here is all finished is not possible master is booked.
2246 assert(threads[threadID].state == THREAD_AVAILABLE);
2248 threads[threadID].state = THREAD_SEARCHING;
2255 // init_threads() is called during startup. It launches all helper threads,
2256 // and initializes the split point stack and the global locks and condition
2259 void ThreadsManager::init_threads() {
2261 int i, arg[MAX_THREADS];
2264 // Initialize global locks
2267 for (i = 0; i < MAX_THREADS; i++)
2269 lock_init(&sleepLock[i]);
2270 cond_init(&sleepCond[i]);
2273 // Initialize splitPoints[] locks
2274 for (i = 0; i < MAX_THREADS; i++)
2275 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2276 lock_init(&(threads[i].splitPoints[j].lock));
2278 // Will be set just before program exits to properly end the threads
2279 allThreadsShouldExit = false;
2281 // Threads will be put all threads to sleep as soon as created
2284 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2285 threads[0].state = THREAD_SEARCHING;
2286 for (i = 1; i < MAX_THREADS; i++)
2287 threads[i].state = THREAD_INITIALIZING;
2289 // Launch the helper threads
2290 for (i = 1; i < MAX_THREADS; i++)
2294 #if !defined(_MSC_VER)
2295 pthread_t pthread[1];
2296 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2297 pthread_detach(pthread[0]);
2299 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2303 cout << "Failed to create thread number " << i << endl;
2307 // Wait until the thread has finished launching and is gone to sleep
2308 while (threads[i].state == THREAD_INITIALIZING) {}
2313 // exit_threads() is called when the program exits. It makes all the
2314 // helper threads exit cleanly.
2316 void ThreadsManager::exit_threads() {
2318 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2320 // Wake up all the threads and waits for termination
2321 for (int i = 1; i < MAX_THREADS; i++)
2323 wake_sleeping_thread(i);
2324 while (threads[i].state != THREAD_TERMINATED) {}
2327 // Now we can safely destroy the locks
2328 for (int i = 0; i < MAX_THREADS; i++)
2329 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2330 lock_destroy(&(threads[i].splitPoints[j].lock));
2332 lock_destroy(&mpLock);
2334 // Now we can safely destroy the wait conditions
2335 for (int i = 0; i < MAX_THREADS; i++)
2337 lock_destroy(&sleepLock[i]);
2338 cond_destroy(&sleepCond[i]);
2343 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2344 // the thread's currently active split point, or in some ancestor of
2345 // the current split point.
2347 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2349 assert(threadID >= 0 && threadID < activeThreads);
2351 SplitPoint* sp = threads[threadID].splitPoint;
2353 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2358 // thread_is_available() checks whether the thread with threadID "slave" is
2359 // available to help the thread with threadID "master" at a split point. An
2360 // obvious requirement is that "slave" must be idle. With more than two
2361 // threads, this is not by itself sufficient: If "slave" is the master of
2362 // some active split point, it is only available as a slave to the other
2363 // threads which are busy searching the split point at the top of "slave"'s
2364 // split point stack (the "helpful master concept" in YBWC terminology).
2366 bool ThreadsManager::thread_is_available(int slave, int master) const {
2368 assert(slave >= 0 && slave < activeThreads);
2369 assert(master >= 0 && master < activeThreads);
2370 assert(activeThreads > 1);
2372 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2375 // Make a local copy to be sure doesn't change under our feet
2376 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2378 // No active split points means that the thread is available as
2379 // a slave for any other thread.
2380 if (localActiveSplitPoints == 0 || activeThreads == 2)
2383 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2384 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2385 // could have been set to 0 by another thread leading to an out of bound access.
2386 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2393 // available_thread_exists() tries to find an idle thread which is available as
2394 // a slave for the thread with threadID "master".
2396 bool ThreadsManager::available_thread_exists(int master) const {
2398 assert(master >= 0 && master < activeThreads);
2399 assert(activeThreads > 1);
2401 for (int i = 0; i < activeThreads; i++)
2402 if (thread_is_available(i, master))
2409 // split() does the actual work of distributing the work at a node between
2410 // several available threads. If it does not succeed in splitting the
2411 // node (because no idle threads are available, or because we have no unused
2412 // split point objects), the function immediately returns. If splitting is
2413 // possible, a SplitPoint object is initialized with all the data that must be
2414 // copied to the helper threads and we tell our helper threads that they have
2415 // been assigned work. This will cause them to instantly leave their idle loops and
2416 // call search().When all threads have returned from search() then split() returns.
2418 template <bool Fake>
2419 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2420 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2421 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2422 assert(pos.is_ok());
2423 assert(ply > 0 && ply < PLY_MAX);
2424 assert(*bestValue >= -VALUE_INFINITE);
2425 assert(*bestValue <= *alpha);
2426 assert(*alpha < beta);
2427 assert(beta <= VALUE_INFINITE);
2428 assert(depth > DEPTH_ZERO);
2429 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2430 assert(activeThreads > 1);
2432 int i, master = pos.thread();
2433 Thread& masterThread = threads[master];
2437 // If no other thread is available to help us, or if we have too many
2438 // active split points, don't split.
2439 if ( !available_thread_exists(master)
2440 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2442 lock_release(&mpLock);
2446 // Pick the next available split point object from the split point stack
2447 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2449 // Initialize the split point object
2450 splitPoint.parent = masterThread.splitPoint;
2451 splitPoint.master = master;
2452 splitPoint.betaCutoff = false;
2453 splitPoint.ply = ply;
2454 splitPoint.depth = depth;
2455 splitPoint.threatMove = threatMove;
2456 splitPoint.mateThreat = mateThreat;
2457 splitPoint.alpha = *alpha;
2458 splitPoint.beta = beta;
2459 splitPoint.pvNode = pvNode;
2460 splitPoint.bestValue = *bestValue;
2462 splitPoint.moveCount = moveCount;
2463 splitPoint.pos = &pos;
2464 splitPoint.nodes = 0;
2465 splitPoint.parentSstack = ss;
2466 for (i = 0; i < activeThreads; i++)
2467 splitPoint.slaves[i] = 0;
2469 masterThread.splitPoint = &splitPoint;
2471 // If we are here it means we are not available
2472 assert(masterThread.state != THREAD_AVAILABLE);
2474 int workersCnt = 1; // At least the master is included
2476 // Allocate available threads setting state to THREAD_BOOKED
2477 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2478 if (thread_is_available(i, master))
2480 threads[i].state = THREAD_BOOKED;
2481 threads[i].splitPoint = &splitPoint;
2482 splitPoint.slaves[i] = 1;
2486 assert(Fake || workersCnt > 1);
2488 // We can release the lock because slave threads are already booked and master is not available
2489 lock_release(&mpLock);
2491 // Tell the threads that they have work to do. This will make them leave
2492 // their idle loop. But before copy search stack tail for each thread.
2493 for (i = 0; i < activeThreads; i++)
2494 if (i == master || splitPoint.slaves[i])
2496 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2498 assert(i == master || threads[i].state == THREAD_BOOKED);
2500 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2502 if (useSleepingThreads && i != master)
2503 wake_sleeping_thread(i);
2506 // Everything is set up. The master thread enters the idle loop, from
2507 // which it will instantly launch a search, because its state is
2508 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2509 // idle loop, which means that the main thread will return from the idle
2510 // loop when all threads have finished their work at this split point.
2511 idle_loop(master, &splitPoint);
2513 // We have returned from the idle loop, which means that all threads are
2514 // finished. Update alpha and bestValue, and return.
2517 *alpha = splitPoint.alpha;
2518 *bestValue = splitPoint.bestValue;
2519 masterThread.activeSplitPoints--;
2520 masterThread.splitPoint = splitPoint.parent;
2521 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2523 lock_release(&mpLock);
2527 // wake_sleeping_thread() wakes up the thread with the given threadID
2528 // when it is time to start a new search.
2530 void ThreadsManager::wake_sleeping_thread(int threadID) {
2532 lock_grab(&sleepLock[threadID]);
2533 cond_signal(&sleepCond[threadID]);
2534 lock_release(&sleepLock[threadID]);
2538 /// RootMove and RootMoveList method's definitions
2540 RootMove::RootMove() {
2543 pv_score = non_pv_score = -VALUE_INFINITE;
2547 RootMove& RootMove::operator=(const RootMove& rm) {
2549 const Move* src = rm.pv;
2552 // Avoid a costly full rm.pv[] copy
2553 do *dst++ = *src; while (*src++ != MOVE_NONE);
2556 pv_score = rm.pv_score;
2557 non_pv_score = rm.non_pv_score;
2561 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2562 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2563 // allow to always have a ponder move even when we fail high at root and also a
2564 // long PV to print that is important for position analysis.
2566 void RootMove::extract_pv_from_tt(Position& pos) {
2568 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2572 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2574 pos.do_move(pv[0], *st++);
2576 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2577 && tte->move() != MOVE_NONE
2578 && move_is_legal(pos, tte->move())
2580 && (!pos.is_draw() || ply < 2))
2582 pv[ply] = tte->move();
2583 pos.do_move(pv[ply++], *st++);
2585 pv[ply] = MOVE_NONE;
2587 do pos.undo_move(pv[--ply]); while (ply);
2590 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2591 // the PV back into the TT. This makes sure the old PV moves are searched
2592 // first, even if the old TT entries have been overwritten.
2594 void RootMove::insert_pv_in_tt(Position& pos) {
2596 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2599 Value v, m = VALUE_NONE;
2602 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2606 tte = TT.retrieve(k);
2608 // Don't overwrite exsisting correct entries
2609 if (!tte || tte->move() != pv[ply])
2611 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2612 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2614 pos.do_move(pv[ply], *st++);
2616 } while (pv[++ply] != MOVE_NONE);
2618 do pos.undo_move(pv[--ply]); while (ply);
2621 // pv_info_to_uci() returns a string with information on the current PV line
2622 // formatted according to UCI specification and eventually writes the info
2623 // to a log file. It is called at each iteration or after a new pv is found.
2625 std::string RootMove::pv_info_to_uci(const Position& pos, Value alpha, Value beta, int pvLine) {
2627 std::stringstream s, l;
2630 while (*m != MOVE_NONE)
2633 s << "info depth " << Iteration // FIXME
2634 << " seldepth " << int(m - pv)
2635 << " multipv " << pvLine + 1
2636 << " score " << value_to_uci(pv_score)
2637 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2638 << " time " << current_search_time()
2639 << " nodes " << pos.nodes_searched()
2640 << " nps " << nps(pos)
2641 << " pv " << l.str();
2643 if (UseLogFile && pvLine == 0)
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, Move ttm, SearchStack* ss)
2700 Value score = VALUE_ZERO;
2701 MovePicker mp(pos, ttm, ONE_PLY, H, ss);
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--;