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);
151 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
152 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
156 // When formatting a move for std::cout we must know if we are in Chess960
157 // or not. To keep using the handy operator<<() on the move the trick is to
158 // embed this flag in the stream itself. Function-like named enum set960 is
159 // used as a custom manipulator and the stream internal general-purpose array,
160 // accessed through ios_base::iword(), is used to pass the flag to the move's
161 // operator<<() that will use it to properly format castling moves.
164 std::ostream& operator<< (std::ostream& os, const set960& m) {
166 os.iword(0) = int(m);
175 // Maximum depth for razoring
176 const Depth RazorDepth = 4 * ONE_PLY;
178 // Dynamic razoring margin based on depth
179 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
181 // Maximum depth for use of dynamic threat detection when null move fails low
182 const Depth ThreatDepth = 5 * ONE_PLY;
184 // Step 9. Internal iterative deepening
186 // Minimum depth for use of internal iterative deepening
187 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
189 // At Non-PV nodes we do an internal iterative deepening search
190 // when the static evaluation is bigger then beta - IIDMargin.
191 const Value IIDMargin = Value(0x100);
193 // Step 11. Decide the new search depth
195 // Extensions. Configurable UCI options
196 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
197 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
198 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
200 // Minimum depth for use of singular extension
201 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
203 // If the TT move is at least SingularExtensionMargin better then the
204 // remaining ones we will extend it.
205 const Value SingularExtensionMargin = Value(0x20);
207 // Step 12. Futility pruning
209 // Futility margin for quiescence search
210 const Value FutilityMarginQS = Value(0x80);
212 // Futility lookup tables (initialized at startup) and their getter functions
213 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
214 int FutilityMoveCountArray[32]; // [depth]
216 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
217 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
219 // Step 14. Reduced search
221 // Reduction lookup tables (initialized at startup) and their getter functions
222 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
224 template <NodeType PV>
225 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
227 // Common adjustments
229 // Search depth at iteration 1
230 const Depth InitialDepth = ONE_PLY;
232 // Easy move margin. An easy move candidate must be at least this much
233 // better than the second best move.
234 const Value EasyMoveMargin = Value(0x200);
237 /// Namespace variables
245 // Scores and number of times the best move changed for each iteration
246 Value ValueByIteration[PLY_MAX_PLUS_2];
247 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
249 // Search window management
255 // Time managment variables
256 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
257 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
258 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
263 std::ofstream LogFile;
265 // Multi-threads manager object
266 ThreadsManager ThreadsMgr;
268 // Node counters, used only by thread[0] but try to keep in different cache
269 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
271 int NodesBetweenPolls = 30000;
278 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
279 Value root_search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, RootMoveList& rml);
281 template <NodeType PvNode, bool SpNode>
282 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
284 template <NodeType PvNode>
285 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
287 template <NodeType PvNode>
288 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
290 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
291 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
294 template <NodeType PvNode>
295 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
297 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
298 bool connected_moves(const Position& pos, Move m1, Move m2);
299 bool value_is_mate(Value value);
300 Value value_to_tt(Value v, int ply);
301 Value value_from_tt(Value v, int ply);
302 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
303 bool connected_threat(const Position& pos, Move m, Move threat);
304 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
305 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
306 void update_killers(Move m, SearchStack* ss);
307 void update_gains(const Position& pos, Move move, Value before, Value after);
309 int current_search_time();
310 std::string value_to_uci(Value v);
311 int nps(const Position& pos);
312 void poll(const Position& pos);
314 void wait_for_stop_or_ponderhit();
315 void init_ss_array(SearchStack* ss, int size);
317 #if !defined(_MSC_VER)
318 void* init_thread(void* threadID);
320 DWORD WINAPI init_thread(LPVOID threadID);
330 /// init_threads(), exit_threads() and nodes_searched() are helpers to
331 /// give accessibility to some TM methods from outside of current file.
333 void init_threads() { ThreadsMgr.init_threads(); }
334 void exit_threads() { ThreadsMgr.exit_threads(); }
337 /// init_search() is called during startup. It initializes various lookup tables
341 int d; // depth (ONE_PLY == 2)
342 int hd; // half depth (ONE_PLY == 1)
345 // Init reductions array
346 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
348 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
349 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
350 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
351 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
354 // Init futility margins array
355 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
356 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
358 // Init futility move count array
359 for (d = 0; d < 32; d++)
360 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
364 /// perft() is our utility to verify move generation is bug free. All the legal
365 /// moves up to given depth are generated and counted and the sum returned.
367 int perft(Position& pos, Depth depth)
369 MoveStack mlist[MOVES_MAX];
374 // Generate all legal moves
375 MoveStack* last = generate_moves(pos, mlist);
377 // If we are at the last ply we don't need to do and undo
378 // the moves, just to count them.
379 if (depth <= ONE_PLY)
380 return int(last - mlist);
382 // Loop through all legal moves
384 for (MoveStack* cur = mlist; cur != last; cur++)
387 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
388 sum += perft(pos, depth - ONE_PLY);
395 /// think() is the external interface to Stockfish's search, and is called when
396 /// the program receives the UCI 'go' command. It initializes various
397 /// search-related global variables, and calls root_search(). It returns false
398 /// when a quit command is received during the search.
400 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
401 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
403 // Initialize global search variables
404 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
406 SearchStartTime = get_system_time();
407 ExactMaxTime = maxTime;
410 InfiniteSearch = infinite;
411 PonderSearch = ponder;
412 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
414 // Look for a book move, only during games, not tests
415 if (UseTimeManagement && Options["OwnBook"].value<bool>())
417 if (Options["Book File"].value<std::string>() != OpeningBook.file_name())
418 OpeningBook.open(Options["Book File"].value<std::string>());
420 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
421 if (bookMove != MOVE_NONE)
424 wait_for_stop_or_ponderhit();
426 cout << "bestmove " << bookMove << endl;
431 // Read UCI option values
432 TT.set_size(Options["Hash"].value<int>());
433 if (Options["Clear Hash"].value<bool>())
435 Options["Clear Hash"].set_value("false");
439 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
440 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
441 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
442 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
443 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
444 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
445 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
446 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
447 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
448 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
449 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
450 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
451 MultiPV = Options["MultiPV"].value<int>();
452 UseLogFile = Options["Use Search Log"].value<bool>();
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
519 // This makes all the threads to go to sleep
520 ThreadsMgr.set_active_threads(1);
522 // If we are pondering or in infinite search, we shouldn't print the
523 // best move before we are told to do so.
524 if (!AbortSearch && (PonderSearch || InfiniteSearch))
525 wait_for_stop_or_ponderhit();
527 // Could be both MOVE_NONE when searching on a stalemate position
528 cout << "bestmove " << bestMove << " ponder " << ponderMove << endl;
536 // id_loop() is the main iterative deepening loop. It calls root_search
537 // repeatedly with increasing depth until the allocated thinking time has
538 // been consumed, the user stops the search, or the maximum search depth is
541 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
543 SearchStack ss[PLY_MAX_PLUS_2];
545 Move EasyMove = MOVE_NONE;
546 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
548 // Moves to search are verified, scored and sorted
549 RootMoveList rml(pos, searchMoves);
551 // Handle special case of searching on a mate/stale position
554 Value s = (pos.is_check() ? -VALUE_MATE : VALUE_DRAW);
556 cout << "info depth " << 1
557 << " score " << value_to_uci(s) << endl;
565 init_ss_array(ss, PLY_MAX_PLUS_2);
566 ValueByIteration[1] = rml[0].pv_score;
569 // Send initial RootMoveList scoring (iteration 1)
570 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
571 << "info depth " << Iteration
572 << "\n" << rml[0].pv_info_to_uci(pos, alpha, beta) << endl;
574 // Is one move significantly better than others after initial scoring ?
576 || rml[0].pv_score > rml[1].pv_score + EasyMoveMargin)
577 EasyMove = rml[0].pv[0];
579 // Iterative deepening loop
580 while (Iteration < PLY_MAX)
582 // Initialize iteration
584 BestMoveChangesByIteration[Iteration] = 0;
586 cout << "info depth " << Iteration << endl;
588 // Calculate dynamic aspiration window based on previous iterations
589 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
591 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
592 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
594 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
595 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
597 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
598 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
601 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
603 // Search to the current depth, rml is updated and sorted
604 value = root_search(pos, ss, alpha, beta, depth, rml);
607 break; // Value cannot be trusted. Break out immediately!
609 //Save info about search result
610 ValueByIteration[Iteration] = value;
612 // Drop the easy move if differs from the new best move
613 if (rml[0].pv[0] != EasyMove)
614 EasyMove = MOVE_NONE;
616 if (UseTimeManagement)
619 bool stopSearch = false;
621 // Stop search early if there is only a single legal move,
622 // we search up to Iteration 6 anyway to get a proper score.
623 if (Iteration >= 6 && rml.size() == 1)
626 // Stop search early when the last two iterations returned a mate score
628 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
629 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
632 // Stop search early if one move seems to be much better than the others
634 && EasyMove == rml[0].pv[0]
635 && ( ( rml[0].nodes > (pos.nodes_searched() * 85) / 100
636 && current_search_time() > TimeMgr.available_time() / 16)
637 ||( rml[0].nodes > (pos.nodes_searched() * 98) / 100
638 && current_search_time() > TimeMgr.available_time() / 32)))
641 // Add some extra time if the best move has changed during the last two iterations
642 if (Iteration > 5 && Iteration <= 50)
643 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
644 BestMoveChangesByIteration[Iteration-1]);
646 // Stop search if most of MaxSearchTime is consumed at the end of the
647 // iteration. We probably don't have enough time to search the first
648 // move at the next iteration anyway.
649 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
655 StopOnPonderhit = true;
661 if (MaxDepth && Iteration >= MaxDepth)
665 *ponderMove = rml[0].pv[1];
670 // root_search() is the function which searches the root node. It is
671 // similar to search_pv except that it prints some information to the
672 // standard output and handles the fail low/high loops.
674 Value root_search(Position& pos, SearchStack* ss, Value alpha,
675 Value beta, Depth depth, RootMoveList& rml) {
681 Value value, oldAlpha;
682 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
683 int researchCountFH, researchCountFL;
685 researchCountFH = researchCountFL = 0;
687 isCheck = pos.is_check();
689 // Step 1. Initialize node (polling is omitted at root)
690 ss->currentMove = ss->bestMove = MOVE_NONE;
692 // Step 2. Check for aborted search (omitted at root)
693 // Step 3. Mate distance pruning (omitted at root)
694 // Step 4. Transposition table lookup (omitted at root)
696 // Step 5. Evaluate the position statically
697 // At root we do this only to get reference value for child nodes
698 ss->evalMargin = VALUE_NONE;
699 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
701 // Step 6. Razoring (omitted at root)
702 // Step 7. Static null move pruning (omitted at root)
703 // Step 8. Null move search with verification search (omitted at root)
704 // Step 9. Internal iterative deepening (omitted at root)
706 // Step extra. Fail low loop
707 // We start with small aspiration window and in case of fail low, we research
708 // with bigger window until we are not failing low anymore.
711 // Sort the moves before to (re)search
712 rml.set_non_pv_scores(pos);
715 // Step 10. Loop through all moves in the root move list
716 for (int i = 0; i < (int)rml.size() && !AbortSearch; i++)
718 // This is used by time management
719 FirstRootMove = (i == 0);
721 // Save the current node count before the move is searched
722 nodes = pos.nodes_searched();
724 // Pick the next root move, and print the move and the move number to
725 // the standard output.
726 move = ss->currentMove = rml[i].pv[0];
728 if (current_search_time() >= 1000)
729 cout << "info currmove " << move
730 << " currmovenumber " << i + 1 << endl;
732 moveIsCheck = pos.move_is_check(move);
733 captureOrPromotion = pos.move_is_capture_or_promotion(move);
735 // Step 11. Decide the new search depth
736 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
737 newDepth = depth + ext;
739 // Step 12. Futility pruning (omitted at root)
741 // Step extra. Fail high loop
742 // If move fails high, we research with bigger window until we are not failing
744 value = -VALUE_INFINITE;
748 // Step 13. Make the move
749 pos.do_move(move, st, ci, moveIsCheck);
751 // Step extra. pv search
752 // We do pv search for first moves (i < MultiPV)
753 // and for fail high research (value > alpha)
754 if (i < MultiPV || value > alpha)
756 // Aspiration window is disabled in multi-pv case
758 alpha = -VALUE_INFINITE;
760 // Full depth PV search, done on first move or after a fail high
761 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
765 // Step 14. Reduced search
766 // if the move fails high will be re-searched at full depth
767 bool doFullDepthSearch = true;
769 if ( depth >= 3 * ONE_PLY
771 && !captureOrPromotion
772 && !move_is_castle(move))
774 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
777 assert(newDepth-ss->reduction >= ONE_PLY);
779 // Reduced depth non-pv search using alpha as upperbound
780 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
781 doFullDepthSearch = (value > alpha);
783 ss->reduction = DEPTH_ZERO; // Restore original reduction
786 // Step 15. Full depth search
787 if (doFullDepthSearch)
789 // Full depth non-pv search using alpha as upperbound
790 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
792 // If we are above alpha then research at same depth but as PV
793 // to get a correct score or eventually a fail high above beta.
795 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
799 // Step 16. Undo move
802 // Can we exit fail high loop ?
803 if (AbortSearch || value < beta)
806 // We are failing high and going to do a research. It's important to update
807 // the score before research in case we run out of time while researching.
809 rml[i].pv_score = value;
810 rml[i].extract_pv_from_tt(pos);
812 // Inform GUI that PV has changed
813 cout << rml[i].pv_info_to_uci(pos, alpha, beta) << endl;
815 // Prepare for a research after a fail high, each time with a wider window
816 beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
819 } // End of fail high loop
821 // Finished searching the move. If AbortSearch is true, the search
822 // was aborted because the user interrupted the search or because we
823 // ran out of time. In this case, the return value of the search cannot
824 // be trusted, and we break out of the loop without updating the best
829 // Remember searched nodes counts for this move
830 rml[i].nodes += pos.nodes_searched() - nodes;
832 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
833 assert(value < beta);
835 // Step 17. Check for new best move
836 if (value <= alpha && i >= MultiPV)
837 rml[i].pv_score = -VALUE_INFINITE;
840 // PV move or new best move!
844 rml[i].pv_score = value;
845 rml[i].extract_pv_from_tt(pos);
847 // We record how often the best move has been changed in each
848 // iteration. This information is used for time managment: When
849 // the best move changes frequently, we allocate some more time.
850 if (MultiPV == 1 && i > 0)
851 BestMoveChangesByIteration[Iteration]++;
853 // Inform GUI that PV has changed, in case of multi-pv UCI protocol
854 // requires we send all the PV lines properly sorted.
857 for (int j = 0; j < Min(MultiPV, (int)rml.size()); j++)
858 cout << rml[j].pv_info_to_uci(pos, alpha, beta, j) << endl;
860 // Update alpha. In multi-pv we don't use aspiration window
863 // Raise alpha to setup proper non-pv search upper bound
867 else // Set alpha equal to minimum score among the PV lines
868 alpha = rml[Min(i, MultiPV - 1)].pv_score;
870 } // PV move or new best move
872 assert(alpha >= oldAlpha);
874 AspirationFailLow = (alpha == oldAlpha);
876 if (AspirationFailLow && StopOnPonderhit)
877 StopOnPonderhit = false;
881 // Can we exit fail low loop ?
882 if (AbortSearch || !AspirationFailLow)
885 // Prepare for a research after a fail low, each time with a wider window
886 oldAlpha = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
891 // Sort the moves before to return
894 // Write PV lines to transposition table, in case the relevant entries
895 // have been overwritten during the search.
896 for (int i = 0; i < MultiPV; i++)
897 rml[i].insert_pv_in_tt(pos);
903 // search<>() is the main search function for both PV and non-PV nodes and for
904 // normal and SplitPoint nodes. When called just after a split point the search
905 // is simpler because we have already probed the hash table, done a null move
906 // search, and searched the first move before splitting, we don't have to repeat
907 // all this work again. We also don't need to store anything to the hash table
908 // here: This is taken care of after we return from the split point.
910 template <NodeType PvNode, bool SpNode>
911 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
913 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
914 assert(beta > alpha && beta <= VALUE_INFINITE);
915 assert(PvNode || alpha == beta - 1);
916 assert(ply > 0 && ply < PLY_MAX);
917 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
919 Move movesSearched[MOVES_MAX];
923 Move ttMove, move, excludedMove, threatMove;
926 Value bestValue, value, oldAlpha;
927 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
928 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
929 bool mateThreat = false;
931 int threadID = pos.thread();
932 SplitPoint* sp = NULL;
933 refinedValue = bestValue = value = -VALUE_INFINITE;
935 isCheck = pos.is_check();
941 ttMove = excludedMove = MOVE_NONE;
942 threatMove = sp->threatMove;
943 mateThreat = sp->mateThreat;
944 goto split_point_start;
946 else {} // Hack to fix icc's "statement is unreachable" warning
948 // Step 1. Initialize node and poll. Polling can abort search
949 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
950 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
952 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
958 // Step 2. Check for aborted search and immediate draw
960 || ThreadsMgr.cutoff_at_splitpoint(threadID)
962 || ply >= PLY_MAX - 1)
965 // Step 3. Mate distance pruning
966 alpha = Max(value_mated_in(ply), alpha);
967 beta = Min(value_mate_in(ply+1), beta);
971 // Step 4. Transposition table lookup
973 // We don't want the score of a partial search to overwrite a previous full search
974 // TT value, so we use a different position key in case of an excluded move exists.
975 excludedMove = ss->excludedMove;
976 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
978 tte = TT.retrieve(posKey);
979 ttMove = tte ? tte->move() : MOVE_NONE;
981 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
982 // This is to avoid problems in the following areas:
984 // * Repetition draw detection
985 // * Fifty move rule detection
986 // * Searching for a mate
987 // * Printing of full PV line
988 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
991 ss->bestMove = ttMove; // Can be MOVE_NONE
992 return value_from_tt(tte->value(), ply);
995 // Step 5. Evaluate the position statically and
996 // update gain statistics of parent move.
998 ss->eval = ss->evalMargin = VALUE_NONE;
1001 assert(tte->static_value() != VALUE_NONE);
1003 ss->eval = tte->static_value();
1004 ss->evalMargin = tte->static_value_margin();
1005 refinedValue = refine_eval(tte, ss->eval, ply);
1009 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1010 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1013 // Save gain for the parent non-capture move
1014 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1016 // Step 6. Razoring (is omitted in PV nodes)
1018 && depth < RazorDepth
1020 && refinedValue < beta - razor_margin(depth)
1021 && ttMove == MOVE_NONE
1022 && !value_is_mate(beta)
1023 && !pos.has_pawn_on_7th(pos.side_to_move()))
1025 Value rbeta = beta - razor_margin(depth);
1026 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1028 // Logically we should return (v + razor_margin(depth)), but
1029 // surprisingly this did slightly weaker in tests.
1033 // Step 7. Static null move pruning (is omitted in PV nodes)
1034 // We're betting that the opponent doesn't have a move that will reduce
1035 // the score by more than futility_margin(depth) if we do a null move.
1037 && !ss->skipNullMove
1038 && depth < RazorDepth
1040 && refinedValue >= beta + futility_margin(depth, 0)
1041 && !value_is_mate(beta)
1042 && pos.non_pawn_material(pos.side_to_move()))
1043 return refinedValue - futility_margin(depth, 0);
1045 // Step 8. Null move search with verification search (is omitted in PV nodes)
1047 && !ss->skipNullMove
1050 && refinedValue >= beta
1051 && !value_is_mate(beta)
1052 && pos.non_pawn_material(pos.side_to_move()))
1054 ss->currentMove = MOVE_NULL;
1056 // Null move dynamic reduction based on depth
1057 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1059 // Null move dynamic reduction based on value
1060 if (refinedValue - beta > PawnValueMidgame)
1063 pos.do_null_move(st);
1064 (ss+1)->skipNullMove = true;
1065 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1066 (ss+1)->skipNullMove = false;
1067 pos.undo_null_move();
1069 if (nullValue >= beta)
1071 // Do not return unproven mate scores
1072 if (nullValue >= value_mate_in(PLY_MAX))
1075 if (depth < 6 * ONE_PLY)
1078 // Do verification search at high depths
1079 ss->skipNullMove = true;
1080 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1081 ss->skipNullMove = false;
1088 // The null move failed low, which means that we may be faced with
1089 // some kind of threat. If the previous move was reduced, check if
1090 // the move that refuted the null move was somehow connected to the
1091 // move which was reduced. If a connection is found, return a fail
1092 // low score (which will cause the reduced move to fail high in the
1093 // parent node, which will trigger a re-search with full depth).
1094 if (nullValue == value_mated_in(ply + 2))
1097 threatMove = (ss+1)->bestMove;
1098 if ( depth < ThreatDepth
1099 && (ss-1)->reduction
1100 && threatMove != MOVE_NONE
1101 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1106 // Step 9. Internal iterative deepening
1107 if ( depth >= IIDDepth[PvNode]
1108 && ttMove == MOVE_NONE
1109 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1111 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1113 ss->skipNullMove = true;
1114 search<PvNode>(pos, ss, alpha, beta, d, ply);
1115 ss->skipNullMove = false;
1117 ttMove = ss->bestMove;
1118 tte = TT.retrieve(posKey);
1121 // Expensive mate threat detection (only for PV nodes)
1123 mateThreat = pos.has_mate_threat();
1125 split_point_start: // At split points actual search starts from here
1127 // Initialize a MovePicker object for the current position
1128 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1129 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1130 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1132 ss->bestMove = MOVE_NONE;
1133 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1134 futilityBase = ss->eval + ss->evalMargin;
1135 singularExtensionNode = !SpNode
1136 && depth >= SingularExtensionDepth[PvNode]
1139 && !excludedMove // Do not allow recursive singular extension search
1140 && (tte->type() & VALUE_TYPE_LOWER)
1141 && tte->depth() >= depth - 3 * ONE_PLY;
1144 lock_grab(&(sp->lock));
1145 bestValue = sp->bestValue;
1148 // Step 10. Loop through moves
1149 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1150 while ( bestValue < beta
1151 && (move = mp.get_next_move()) != MOVE_NONE
1152 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1154 assert(move_is_ok(move));
1158 moveCount = ++sp->moveCount;
1159 lock_release(&(sp->lock));
1161 else if (move == excludedMove)
1164 movesSearched[moveCount++] = move;
1166 moveIsCheck = pos.move_is_check(move, ci);
1167 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1169 // Step 11. Decide the new search depth
1170 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1172 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1173 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1174 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1175 // lower then ttValue minus a margin then we extend ttMove.
1176 if ( singularExtensionNode
1177 && move == tte->move()
1180 Value ttValue = value_from_tt(tte->value(), ply);
1182 if (abs(ttValue) < VALUE_KNOWN_WIN)
1184 Value b = ttValue - SingularExtensionMargin;
1185 ss->excludedMove = move;
1186 ss->skipNullMove = true;
1187 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1188 ss->skipNullMove = false;
1189 ss->excludedMove = MOVE_NONE;
1190 ss->bestMove = MOVE_NONE;
1196 // Update current move (this must be done after singular extension search)
1197 ss->currentMove = move;
1198 newDepth = depth - ONE_PLY + ext;
1200 // Step 12. Futility pruning (is omitted in PV nodes)
1202 && !captureOrPromotion
1206 && !move_is_castle(move))
1208 // Move count based pruning
1209 if ( moveCount >= futility_move_count(depth)
1210 && !(threatMove && connected_threat(pos, move, threatMove))
1211 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1214 lock_grab(&(sp->lock));
1219 // Value based pruning
1220 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1221 // but fixing this made program slightly weaker.
1222 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1223 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1224 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1226 if (futilityValueScaled < beta)
1230 lock_grab(&(sp->lock));
1231 if (futilityValueScaled > sp->bestValue)
1232 sp->bestValue = bestValue = futilityValueScaled;
1234 else if (futilityValueScaled > bestValue)
1235 bestValue = futilityValueScaled;
1240 // Prune moves with negative SEE at low depths
1241 if ( predictedDepth < 2 * ONE_PLY
1242 && bestValue > value_mated_in(PLY_MAX)
1243 && pos.see_sign(move) < 0)
1246 lock_grab(&(sp->lock));
1252 // Step 13. Make the move
1253 pos.do_move(move, st, ci, moveIsCheck);
1255 // Step extra. pv search (only in PV nodes)
1256 // The first move in list is the expected PV
1257 if (PvNode && moveCount == 1)
1258 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1261 // Step 14. Reduced depth search
1262 // If the move fails high will be re-searched at full depth.
1263 bool doFullDepthSearch = true;
1265 if ( depth >= 3 * ONE_PLY
1266 && !captureOrPromotion
1268 && !move_is_castle(move)
1269 && ss->killers[0] != move
1270 && ss->killers[1] != move)
1272 ss->reduction = reduction<PvNode>(depth, moveCount);
1276 alpha = SpNode ? sp->alpha : alpha;
1277 Depth d = newDepth - ss->reduction;
1278 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1280 doFullDepthSearch = (value > alpha);
1282 ss->reduction = DEPTH_ZERO; // Restore original reduction
1285 // Step 15. Full depth search
1286 if (doFullDepthSearch)
1288 alpha = SpNode ? sp->alpha : alpha;
1289 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1291 // Step extra. pv search (only in PV nodes)
1292 // Search only for possible new PV nodes, if instead value >= beta then
1293 // parent node fails low with value <= alpha and tries another move.
1294 if (PvNode && value > alpha && value < beta)
1295 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1299 // Step 16. Undo move
1300 pos.undo_move(move);
1302 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1304 // Step 17. Check for new best move
1307 lock_grab(&(sp->lock));
1308 bestValue = sp->bestValue;
1312 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1317 sp->bestValue = value;
1321 if (PvNode && value < beta) // We want always alpha < beta
1329 sp->betaCutoff = true;
1331 if (value == value_mate_in(ply + 1))
1332 ss->mateKiller = move;
1334 ss->bestMove = move;
1337 sp->parentSstack->bestMove = move;
1341 // Step 18. Check for split
1343 && depth >= ThreadsMgr.min_split_depth()
1344 && ThreadsMgr.active_threads() > 1
1346 && ThreadsMgr.available_thread_exists(threadID)
1348 && !ThreadsMgr.cutoff_at_splitpoint(threadID)
1350 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1351 threatMove, mateThreat, moveCount, &mp, PvNode);
1354 // Step 19. Check for mate and stalemate
1355 // All legal moves have been searched and if there are
1356 // no legal moves, it must be mate or stalemate.
1357 // If one move was excluded return fail low score.
1358 if (!SpNode && !moveCount)
1359 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1361 // Step 20. Update tables
1362 // If the search is not aborted, update the transposition table,
1363 // history counters, and killer moves.
1364 if (!SpNode && !AbortSearch && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1366 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1367 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1368 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1370 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1372 // Update killers and history only for non capture moves that fails high
1373 if ( bestValue >= beta
1374 && !pos.move_is_capture_or_promotion(move))
1376 update_history(pos, move, depth, movesSearched, moveCount);
1377 update_killers(move, ss);
1383 // Here we have the lock still grabbed
1384 sp->slaves[threadID] = 0;
1385 sp->nodes += pos.nodes_searched();
1386 lock_release(&(sp->lock));
1389 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1394 // qsearch() is the quiescence search function, which is called by the main
1395 // search function when the remaining depth is zero (or, to be more precise,
1396 // less than ONE_PLY).
1398 template <NodeType PvNode>
1399 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1401 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1402 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1403 assert(PvNode || alpha == beta - 1);
1405 assert(ply > 0 && ply < PLY_MAX);
1406 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1410 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1411 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1414 Value oldAlpha = alpha;
1416 ss->bestMove = ss->currentMove = MOVE_NONE;
1418 // Check for an instant draw or maximum ply reached
1419 if (pos.is_draw() || ply >= PLY_MAX - 1)
1422 // Decide whether or not to include checks, this fixes also the type of
1423 // TT entry depth that we are going to use. Note that in qsearch we use
1424 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1425 isCheck = pos.is_check();
1426 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1428 // Transposition table lookup. At PV nodes, we don't use the TT for
1429 // pruning, but only for move ordering.
1430 tte = TT.retrieve(pos.get_key());
1431 ttMove = (tte ? tte->move() : MOVE_NONE);
1433 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1435 ss->bestMove = ttMove; // Can be MOVE_NONE
1436 return value_from_tt(tte->value(), ply);
1439 // Evaluate the position statically
1442 bestValue = futilityBase = -VALUE_INFINITE;
1443 ss->eval = evalMargin = VALUE_NONE;
1444 enoughMaterial = false;
1450 assert(tte->static_value() != VALUE_NONE);
1452 evalMargin = tte->static_value_margin();
1453 ss->eval = bestValue = tte->static_value();
1456 ss->eval = bestValue = evaluate(pos, evalMargin);
1458 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1460 // Stand pat. Return immediately if static value is at least beta
1461 if (bestValue >= beta)
1464 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1469 if (PvNode && bestValue > alpha)
1472 // Futility pruning parameters, not needed when in check
1473 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1474 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1477 // Initialize a MovePicker object for the current position, and prepare
1478 // to search the moves. Because the depth is <= 0 here, only captures,
1479 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1481 MovePicker mp(pos, ttMove, depth, H);
1484 // Loop through the moves until no moves remain or a beta cutoff occurs
1485 while ( alpha < beta
1486 && (move = mp.get_next_move()) != MOVE_NONE)
1488 assert(move_is_ok(move));
1490 moveIsCheck = pos.move_is_check(move, ci);
1498 && !move_is_promotion(move)
1499 && !pos.move_is_passed_pawn_push(move))
1501 futilityValue = futilityBase
1502 + pos.endgame_value_of_piece_on(move_to(move))
1503 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1505 if (futilityValue < alpha)
1507 if (futilityValue > bestValue)
1508 bestValue = futilityValue;
1513 // Detect non-capture evasions that are candidate to be pruned
1514 evasionPrunable = isCheck
1515 && bestValue > value_mated_in(PLY_MAX)
1516 && !pos.move_is_capture(move)
1517 && !pos.can_castle(pos.side_to_move());
1519 // Don't search moves with negative SEE values
1521 && (!isCheck || evasionPrunable)
1523 && !move_is_promotion(move)
1524 && pos.see_sign(move) < 0)
1527 // Don't search useless checks
1532 && !pos.move_is_capture_or_promotion(move)
1533 && ss->eval + PawnValueMidgame / 4 < beta
1534 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1536 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1537 bestValue = ss->eval + PawnValueMidgame / 4;
1542 // Update current move
1543 ss->currentMove = move;
1545 // Make and search the move
1546 pos.do_move(move, st, ci, moveIsCheck);
1547 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1548 pos.undo_move(move);
1550 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1553 if (value > bestValue)
1559 ss->bestMove = move;
1564 // All legal moves have been searched. A special case: If we're in check
1565 // and no legal moves were found, it is checkmate.
1566 if (isCheck && bestValue == -VALUE_INFINITE)
1567 return value_mated_in(ply);
1569 // Update transposition table
1570 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1571 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1573 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1579 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1580 // bestValue is updated only when returning false because in that case move
1583 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1585 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1586 Square from, to, ksq, victimSq;
1589 Value futilityValue, bv = *bestValue;
1591 from = move_from(move);
1593 them = opposite_color(pos.side_to_move());
1594 ksq = pos.king_square(them);
1595 kingAtt = pos.attacks_from<KING>(ksq);
1596 pc = pos.piece_on(from);
1598 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1599 oldAtt = pos.attacks_from(pc, from, occ);
1600 newAtt = pos.attacks_from(pc, to, occ);
1602 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1603 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1605 if (!(b && (b & (b - 1))))
1608 // Rule 2. Queen contact check is very dangerous
1609 if ( type_of_piece(pc) == QUEEN
1610 && bit_is_set(kingAtt, to))
1613 // Rule 3. Creating new double threats with checks
1614 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1618 victimSq = pop_1st_bit(&b);
1619 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1621 // Note that here we generate illegal "double move"!
1622 if ( futilityValue >= beta
1623 && pos.see_sign(make_move(from, victimSq)) >= 0)
1626 if (futilityValue > bv)
1630 // Update bestValue only if check is not dangerous (because we will prune the move)
1636 // connected_moves() tests whether two moves are 'connected' in the sense
1637 // that the first move somehow made the second move possible (for instance
1638 // if the moving piece is the same in both moves). The first move is assumed
1639 // to be the move that was made to reach the current position, while the
1640 // second move is assumed to be a move from the current position.
1642 bool connected_moves(const Position& pos, Move m1, Move m2) {
1644 Square f1, t1, f2, t2;
1647 assert(m1 && move_is_ok(m1));
1648 assert(m2 && move_is_ok(m2));
1650 // Case 1: The moving piece is the same in both moves
1656 // Case 2: The destination square for m2 was vacated by m1
1662 // Case 3: Moving through the vacated square
1663 if ( piece_is_slider(pos.piece_on(f2))
1664 && bit_is_set(squares_between(f2, t2), f1))
1667 // Case 4: The destination square for m2 is defended by the moving piece in m1
1668 p = pos.piece_on(t1);
1669 if (bit_is_set(pos.attacks_from(p, t1), t2))
1672 // Case 5: Discovered check, checking piece is the piece moved in m1
1673 if ( piece_is_slider(p)
1674 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1675 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1677 // discovered_check_candidates() works also if the Position's side to
1678 // move is the opposite of the checking piece.
1679 Color them = opposite_color(pos.side_to_move());
1680 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1682 if (bit_is_set(dcCandidates, f2))
1689 // value_is_mate() checks if the given value is a mate one eventually
1690 // compensated for the ply.
1692 bool value_is_mate(Value value) {
1694 assert(abs(value) <= VALUE_INFINITE);
1696 return value <= value_mated_in(PLY_MAX)
1697 || value >= value_mate_in(PLY_MAX);
1701 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1702 // "plies to mate from the current ply". Non-mate scores are unchanged.
1703 // The function is called before storing a value to the transposition table.
1705 Value value_to_tt(Value v, int ply) {
1707 if (v >= value_mate_in(PLY_MAX))
1710 if (v <= value_mated_in(PLY_MAX))
1717 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1718 // the transposition table to a mate score corrected for the current ply.
1720 Value value_from_tt(Value v, int ply) {
1722 if (v >= value_mate_in(PLY_MAX))
1725 if (v <= value_mated_in(PLY_MAX))
1732 // extension() decides whether a move should be searched with normal depth,
1733 // or with extended depth. Certain classes of moves (checking moves, in
1734 // particular) are searched with bigger depth than ordinary moves and in
1735 // any case are marked as 'dangerous'. Note that also if a move is not
1736 // extended, as example because the corresponding UCI option is set to zero,
1737 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1738 template <NodeType PvNode>
1739 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1740 bool singleEvasion, bool mateThreat, bool* dangerous) {
1742 assert(m != MOVE_NONE);
1744 Depth result = DEPTH_ZERO;
1745 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1749 if (moveIsCheck && pos.see_sign(m) >= 0)
1750 result += CheckExtension[PvNode];
1753 result += SingleEvasionExtension[PvNode];
1756 result += MateThreatExtension[PvNode];
1759 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1761 Color c = pos.side_to_move();
1762 if (relative_rank(c, move_to(m)) == RANK_7)
1764 result += PawnPushTo7thExtension[PvNode];
1767 if (pos.pawn_is_passed(c, move_to(m)))
1769 result += PassedPawnExtension[PvNode];
1774 if ( captureOrPromotion
1775 && pos.type_of_piece_on(move_to(m)) != PAWN
1776 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1777 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1778 && !move_is_promotion(m)
1781 result += PawnEndgameExtension[PvNode];
1786 && captureOrPromotion
1787 && pos.type_of_piece_on(move_to(m)) != PAWN
1788 && pos.see_sign(m) >= 0)
1790 result += ONE_PLY / 2;
1794 return Min(result, ONE_PLY);
1798 // connected_threat() tests whether it is safe to forward prune a move or if
1799 // is somehow coonected to the threat move returned by null search.
1801 bool connected_threat(const Position& pos, Move m, Move threat) {
1803 assert(move_is_ok(m));
1804 assert(threat && move_is_ok(threat));
1805 assert(!pos.move_is_check(m));
1806 assert(!pos.move_is_capture_or_promotion(m));
1807 assert(!pos.move_is_passed_pawn_push(m));
1809 Square mfrom, mto, tfrom, tto;
1811 mfrom = move_from(m);
1813 tfrom = move_from(threat);
1814 tto = move_to(threat);
1816 // Case 1: Don't prune moves which move the threatened piece
1820 // Case 2: If the threatened piece has value less than or equal to the
1821 // value of the threatening piece, don't prune move which defend it.
1822 if ( pos.move_is_capture(threat)
1823 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1824 || pos.type_of_piece_on(tfrom) == KING)
1825 && pos.move_attacks_square(m, tto))
1828 // Case 3: If the moving piece in the threatened move is a slider, don't
1829 // prune safe moves which block its ray.
1830 if ( piece_is_slider(pos.piece_on(tfrom))
1831 && bit_is_set(squares_between(tfrom, tto), mto)
1832 && pos.see_sign(m) >= 0)
1839 // ok_to_use_TT() returns true if a transposition table score
1840 // can be used at a given point in search.
1842 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1844 Value v = value_from_tt(tte->value(), ply);
1846 return ( tte->depth() >= depth
1847 || v >= Max(value_mate_in(PLY_MAX), beta)
1848 || v < Min(value_mated_in(PLY_MAX), beta))
1850 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1851 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1855 // refine_eval() returns the transposition table score if
1856 // possible otherwise falls back on static position evaluation.
1858 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1862 Value v = value_from_tt(tte->value(), ply);
1864 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1865 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1872 // update_history() registers a good move that produced a beta-cutoff
1873 // in history and marks as failures all the other moves of that ply.
1875 void update_history(const Position& pos, Move move, Depth depth,
1876 Move movesSearched[], int moveCount) {
1879 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1881 for (int i = 0; i < moveCount - 1; i++)
1883 m = movesSearched[i];
1887 if (!pos.move_is_capture_or_promotion(m))
1888 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1893 // update_killers() add a good move that produced a beta-cutoff
1894 // among the killer moves of that ply.
1896 void update_killers(Move m, SearchStack* ss) {
1898 if (m == ss->killers[0])
1901 ss->killers[1] = ss->killers[0];
1906 // update_gains() updates the gains table of a non-capture move given
1907 // the static position evaluation before and after the move.
1909 void update_gains(const Position& pos, Move m, Value before, Value after) {
1912 && before != VALUE_NONE
1913 && after != VALUE_NONE
1914 && pos.captured_piece_type() == PIECE_TYPE_NONE
1915 && !move_is_special(m))
1916 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1920 // current_search_time() returns the number of milliseconds which have passed
1921 // since the beginning of the current search.
1923 int current_search_time() {
1925 return get_system_time() - SearchStartTime;
1929 // value_to_uci() converts a value to a string suitable for use with the UCI
1930 // protocol specifications:
1932 // cp <x> The score from the engine's point of view in centipawns.
1933 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1934 // use negative values for y.
1936 std::string value_to_uci(Value v) {
1938 std::stringstream s;
1940 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1941 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1943 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1948 // nps() computes the current nodes/second count.
1950 int nps(const Position& pos) {
1952 int t = current_search_time();
1953 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1957 // poll() performs two different functions: It polls for user input, and it
1958 // looks at the time consumed so far and decides if it's time to abort the
1961 void poll(const Position& pos) {
1963 static int lastInfoTime;
1964 int t = current_search_time();
1967 if (data_available())
1969 // We are line oriented, don't read single chars
1970 std::string command;
1972 if (!std::getline(std::cin, command))
1975 if (command == "quit")
1978 PonderSearch = false;
1982 else if (command == "stop")
1985 PonderSearch = false;
1987 else if (command == "ponderhit")
1991 // Print search information
1995 else if (lastInfoTime > t)
1996 // HACK: Must be a new search where we searched less than
1997 // NodesBetweenPolls nodes during the first second of search.
2000 else if (t - lastInfoTime >= 1000)
2007 if (dbg_show_hit_rate)
2008 dbg_print_hit_rate();
2010 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
2011 << " time " << t << endl;
2014 // Should we stop the search?
2018 bool stillAtFirstMove = FirstRootMove
2019 && !AspirationFailLow
2020 && t > TimeMgr.available_time();
2022 bool noMoreTime = t > TimeMgr.maximum_time()
2023 || stillAtFirstMove;
2025 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2026 || (ExactMaxTime && t >= ExactMaxTime)
2027 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2032 // ponderhit() is called when the program is pondering (i.e. thinking while
2033 // it's the opponent's turn to move) in order to let the engine know that
2034 // it correctly predicted the opponent's move.
2038 int t = current_search_time();
2039 PonderSearch = false;
2041 bool stillAtFirstMove = FirstRootMove
2042 && !AspirationFailLow
2043 && t > TimeMgr.available_time();
2045 bool noMoreTime = t > TimeMgr.maximum_time()
2046 || stillAtFirstMove;
2048 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2053 // init_ss_array() does a fast reset of the first entries of a SearchStack
2054 // array and of all the excludedMove and skipNullMove entries.
2056 void init_ss_array(SearchStack* ss, int size) {
2058 for (int i = 0; i < size; i++, ss++)
2060 ss->excludedMove = MOVE_NONE;
2061 ss->skipNullMove = false;
2062 ss->reduction = DEPTH_ZERO;
2066 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2071 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2072 // while the program is pondering. The point is to work around a wrinkle in
2073 // the UCI protocol: When pondering, the engine is not allowed to give a
2074 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2075 // We simply wait here until one of these commands is sent, and return,
2076 // after which the bestmove and pondermove will be printed (in id_loop()).
2078 void wait_for_stop_or_ponderhit() {
2080 std::string command;
2084 if (!std::getline(std::cin, command))
2087 if (command == "quit")
2092 else if (command == "ponderhit" || command == "stop")
2098 // init_thread() is the function which is called when a new thread is
2099 // launched. It simply calls the idle_loop() function with the supplied
2100 // threadID. There are two versions of this function; one for POSIX
2101 // threads and one for Windows threads.
2103 #if !defined(_MSC_VER)
2105 void* init_thread(void* threadID) {
2107 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2113 DWORD WINAPI init_thread(LPVOID threadID) {
2115 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2122 /// The ThreadsManager class
2125 // read_uci_options() updates number of active threads and other internal
2126 // parameters according to the UCI options values. It is called before
2127 // to start a new search.
2129 void ThreadsManager::read_uci_options() {
2131 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2132 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2133 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2134 activeThreads = Options["Threads"].value<int>();
2138 // idle_loop() is where the threads are parked when they have no work to do.
2139 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2140 // object for which the current thread is the master.
2142 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2144 assert(threadID >= 0 && threadID < MAX_THREADS);
2147 bool allFinished = false;
2151 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2152 // master should exit as last one.
2153 if (allThreadsShouldExit)
2156 threads[threadID].state = THREAD_TERMINATED;
2160 // If we are not thinking, wait for a condition to be signaled
2161 // instead of wasting CPU time polling for work.
2162 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2163 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2165 assert(!sp || useSleepingThreads);
2166 assert(threadID != 0 || useSleepingThreads);
2168 if (threads[threadID].state == THREAD_INITIALIZING)
2169 threads[threadID].state = THREAD_AVAILABLE;
2171 // Grab the lock to avoid races with wake_sleeping_thread()
2172 lock_grab(&sleepLock[threadID]);
2174 // If we are master and all slaves have finished do not go to sleep
2175 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2176 allFinished = (i == activeThreads);
2178 if (allFinished || allThreadsShouldExit)
2180 lock_release(&sleepLock[threadID]);
2184 // Do sleep here after retesting sleep conditions
2185 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2186 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2188 lock_release(&sleepLock[threadID]);
2191 // If this thread has been assigned work, launch a search
2192 if (threads[threadID].state == THREAD_WORKISWAITING)
2194 assert(!allThreadsShouldExit);
2196 threads[threadID].state = THREAD_SEARCHING;
2198 // Here we call search() with SplitPoint template parameter set to true
2199 SplitPoint* tsp = threads[threadID].splitPoint;
2200 Position pos(*tsp->pos, threadID);
2201 SearchStack* ss = tsp->sstack[threadID] + 1;
2205 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2207 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2209 assert(threads[threadID].state == THREAD_SEARCHING);
2211 threads[threadID].state = THREAD_AVAILABLE;
2213 // Wake up master thread so to allow it to return from the idle loop in
2214 // case we are the last slave of the split point.
2215 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2216 wake_sleeping_thread(tsp->master);
2219 // If this thread is the master of a split point and all slaves have
2220 // finished their work at this split point, return from the idle loop.
2221 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2222 allFinished = (i == activeThreads);
2226 // Because sp->slaves[] is reset under lock protection,
2227 // be sure sp->lock has been released before to return.
2228 lock_grab(&(sp->lock));
2229 lock_release(&(sp->lock));
2231 // In helpful master concept a master can help only a sub-tree, and
2232 // because here is all finished is not possible master is booked.
2233 assert(threads[threadID].state == THREAD_AVAILABLE);
2235 threads[threadID].state = THREAD_SEARCHING;
2242 // init_threads() is called during startup. It launches all helper threads,
2243 // and initializes the split point stack and the global locks and condition
2246 void ThreadsManager::init_threads() {
2248 int i, arg[MAX_THREADS];
2251 // Initialize global locks
2254 for (i = 0; i < MAX_THREADS; i++)
2256 lock_init(&sleepLock[i]);
2257 cond_init(&sleepCond[i]);
2260 // Initialize splitPoints[] locks
2261 for (i = 0; i < MAX_THREADS; i++)
2262 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2263 lock_init(&(threads[i].splitPoints[j].lock));
2265 // Will be set just before program exits to properly end the threads
2266 allThreadsShouldExit = false;
2268 // Threads will be put all threads to sleep as soon as created
2271 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2272 threads[0].state = THREAD_SEARCHING;
2273 for (i = 1; i < MAX_THREADS; i++)
2274 threads[i].state = THREAD_INITIALIZING;
2276 // Launch the helper threads
2277 for (i = 1; i < MAX_THREADS; i++)
2281 #if !defined(_MSC_VER)
2282 pthread_t pthread[1];
2283 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2284 pthread_detach(pthread[0]);
2286 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2290 cout << "Failed to create thread number " << i << endl;
2294 // Wait until the thread has finished launching and is gone to sleep
2295 while (threads[i].state == THREAD_INITIALIZING) {}
2300 // exit_threads() is called when the program exits. It makes all the
2301 // helper threads exit cleanly.
2303 void ThreadsManager::exit_threads() {
2305 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2307 // Wake up all the threads and waits for termination
2308 for (int i = 1; i < MAX_THREADS; i++)
2310 wake_sleeping_thread(i);
2311 while (threads[i].state != THREAD_TERMINATED) {}
2314 // Now we can safely destroy the locks
2315 for (int i = 0; i < MAX_THREADS; i++)
2316 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2317 lock_destroy(&(threads[i].splitPoints[j].lock));
2319 lock_destroy(&mpLock);
2321 // Now we can safely destroy the wait conditions
2322 for (int i = 0; i < MAX_THREADS; i++)
2324 lock_destroy(&sleepLock[i]);
2325 cond_destroy(&sleepCond[i]);
2330 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2331 // the thread's currently active split point, or in some ancestor of
2332 // the current split point.
2334 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2336 assert(threadID >= 0 && threadID < activeThreads);
2338 SplitPoint* sp = threads[threadID].splitPoint;
2340 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2345 // thread_is_available() checks whether the thread with threadID "slave" is
2346 // available to help the thread with threadID "master" at a split point. An
2347 // obvious requirement is that "slave" must be idle. With more than two
2348 // threads, this is not by itself sufficient: If "slave" is the master of
2349 // some active split point, it is only available as a slave to the other
2350 // threads which are busy searching the split point at the top of "slave"'s
2351 // split point stack (the "helpful master concept" in YBWC terminology).
2353 bool ThreadsManager::thread_is_available(int slave, int master) const {
2355 assert(slave >= 0 && slave < activeThreads);
2356 assert(master >= 0 && master < activeThreads);
2357 assert(activeThreads > 1);
2359 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2362 // Make a local copy to be sure doesn't change under our feet
2363 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2365 // No active split points means that the thread is available as
2366 // a slave for any other thread.
2367 if (localActiveSplitPoints == 0 || activeThreads == 2)
2370 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2371 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2372 // could have been set to 0 by another thread leading to an out of bound access.
2373 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2380 // available_thread_exists() tries to find an idle thread which is available as
2381 // a slave for the thread with threadID "master".
2383 bool ThreadsManager::available_thread_exists(int master) const {
2385 assert(master >= 0 && master < activeThreads);
2386 assert(activeThreads > 1);
2388 for (int i = 0; i < activeThreads; i++)
2389 if (thread_is_available(i, master))
2396 // split() does the actual work of distributing the work at a node between
2397 // several available threads. If it does not succeed in splitting the
2398 // node (because no idle threads are available, or because we have no unused
2399 // split point objects), the function immediately returns. If splitting is
2400 // possible, a SplitPoint object is initialized with all the data that must be
2401 // copied to the helper threads and we tell our helper threads that they have
2402 // been assigned work. This will cause them to instantly leave their idle loops and
2403 // call search().When all threads have returned from search() then split() returns.
2405 template <bool Fake>
2406 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2407 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2408 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2409 assert(pos.is_ok());
2410 assert(ply > 0 && ply < PLY_MAX);
2411 assert(*bestValue >= -VALUE_INFINITE);
2412 assert(*bestValue <= *alpha);
2413 assert(*alpha < beta);
2414 assert(beta <= VALUE_INFINITE);
2415 assert(depth > DEPTH_ZERO);
2416 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2417 assert(activeThreads > 1);
2419 int i, master = pos.thread();
2420 Thread& masterThread = threads[master];
2424 // If no other thread is available to help us, or if we have too many
2425 // active split points, don't split.
2426 if ( !available_thread_exists(master)
2427 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2429 lock_release(&mpLock);
2433 // Pick the next available split point object from the split point stack
2434 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2436 // Initialize the split point object
2437 splitPoint.parent = masterThread.splitPoint;
2438 splitPoint.master = master;
2439 splitPoint.betaCutoff = false;
2440 splitPoint.ply = ply;
2441 splitPoint.depth = depth;
2442 splitPoint.threatMove = threatMove;
2443 splitPoint.mateThreat = mateThreat;
2444 splitPoint.alpha = *alpha;
2445 splitPoint.beta = beta;
2446 splitPoint.pvNode = pvNode;
2447 splitPoint.bestValue = *bestValue;
2449 splitPoint.moveCount = moveCount;
2450 splitPoint.pos = &pos;
2451 splitPoint.nodes = 0;
2452 splitPoint.parentSstack = ss;
2453 for (i = 0; i < activeThreads; i++)
2454 splitPoint.slaves[i] = 0;
2456 masterThread.splitPoint = &splitPoint;
2458 // If we are here it means we are not available
2459 assert(masterThread.state != THREAD_AVAILABLE);
2461 int workersCnt = 1; // At least the master is included
2463 // Allocate available threads setting state to THREAD_BOOKED
2464 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2465 if (thread_is_available(i, master))
2467 threads[i].state = THREAD_BOOKED;
2468 threads[i].splitPoint = &splitPoint;
2469 splitPoint.slaves[i] = 1;
2473 assert(Fake || workersCnt > 1);
2475 // We can release the lock because slave threads are already booked and master is not available
2476 lock_release(&mpLock);
2478 // Tell the threads that they have work to do. This will make them leave
2479 // their idle loop. But before copy search stack tail for each thread.
2480 for (i = 0; i < activeThreads; i++)
2481 if (i == master || splitPoint.slaves[i])
2483 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2485 assert(i == master || threads[i].state == THREAD_BOOKED);
2487 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2489 if (useSleepingThreads && i != master)
2490 wake_sleeping_thread(i);
2493 // Everything is set up. The master thread enters the idle loop, from
2494 // which it will instantly launch a search, because its state is
2495 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2496 // idle loop, which means that the main thread will return from the idle
2497 // loop when all threads have finished their work at this split point.
2498 idle_loop(master, &splitPoint);
2500 // We have returned from the idle loop, which means that all threads are
2501 // finished. Update alpha and bestValue, and return.
2504 *alpha = splitPoint.alpha;
2505 *bestValue = splitPoint.bestValue;
2506 masterThread.activeSplitPoints--;
2507 masterThread.splitPoint = splitPoint.parent;
2508 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2510 lock_release(&mpLock);
2514 // wake_sleeping_thread() wakes up the thread with the given threadID
2515 // when it is time to start a new search.
2517 void ThreadsManager::wake_sleeping_thread(int threadID) {
2519 lock_grab(&sleepLock[threadID]);
2520 cond_signal(&sleepCond[threadID]);
2521 lock_release(&sleepLock[threadID]);
2525 /// RootMove and RootMoveList method's definitions
2527 RootMove::RootMove() {
2530 pv_score = non_pv_score = -VALUE_INFINITE;
2534 RootMove& RootMove::operator=(const RootMove& rm) {
2536 const Move* src = rm.pv;
2539 // Avoid a costly full rm.pv[] copy
2540 do *dst++ = *src; while (*src++ != MOVE_NONE);
2543 pv_score = rm.pv_score;
2544 non_pv_score = rm.non_pv_score;
2548 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2549 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2550 // allow to always have a ponder move even when we fail high at root and also a
2551 // long PV to print that is important for position analysis.
2553 void RootMove::extract_pv_from_tt(Position& pos) {
2555 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2559 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2561 pos.do_move(pv[0], *st++);
2563 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2564 && tte->move() != MOVE_NONE
2565 && move_is_legal(pos, tte->move())
2567 && (!pos.is_draw() || ply < 2))
2569 pv[ply] = tte->move();
2570 pos.do_move(pv[ply++], *st++);
2572 pv[ply] = MOVE_NONE;
2574 do pos.undo_move(pv[--ply]); while (ply);
2577 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2578 // the PV back into the TT. This makes sure the old PV moves are searched
2579 // first, even if the old TT entries have been overwritten.
2581 void RootMove::insert_pv_in_tt(Position& pos) {
2583 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2586 Value v, m = VALUE_NONE;
2589 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2593 tte = TT.retrieve(k);
2595 // Don't overwrite exsisting correct entries
2596 if (!tte || tte->move() != pv[ply])
2598 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2599 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2601 pos.do_move(pv[ply], *st++);
2603 } while (pv[++ply] != MOVE_NONE);
2605 do pos.undo_move(pv[--ply]); while (ply);
2608 // pv_info_to_uci() returns a string with information on the current PV line
2609 // formatted according to UCI specification and eventually writes the info
2610 // to a log file. It is called at each iteration or after a new pv is found.
2612 std::string RootMove::pv_info_to_uci(const Position& pos, Value alpha, Value beta, int pvLine) {
2614 std::stringstream s, l;
2617 while (*m != MOVE_NONE)
2620 s << "info depth " << Iteration // FIXME
2621 << " seldepth " << int(m - pv)
2622 << " multipv " << pvLine + 1
2623 << " score " << value_to_uci(pv_score)
2624 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2625 << " time " << current_search_time()
2626 << " nodes " << pos.nodes_searched()
2627 << " nps " << nps(pos)
2628 << " pv " << l.str();
2630 if (UseLogFile && pvLine == 0)
2632 ValueType t = pv_score >= beta ? VALUE_TYPE_LOWER :
2633 pv_score <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2635 LogFile << pretty_pv(pos, current_search_time(), Iteration, pv_score, t, pv) << endl;
2641 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2643 SearchStack ss[PLY_MAX_PLUS_2];
2644 MoveStack mlist[MOVES_MAX];
2648 // Initialize search stack
2649 init_ss_array(ss, PLY_MAX_PLUS_2);
2650 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2652 // Generate all legal moves
2653 MoveStack* last = generate_moves(pos, mlist);
2655 // Add each move to the RootMoveList's vector
2656 for (MoveStack* cur = mlist; cur != last; cur++)
2658 // If we have a searchMoves[] list then verify cur->move
2659 // is in the list before to add it.
2660 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2662 if (searchMoves[0] && *sm != cur->move)
2665 // Find a quick score for the move and add to the list
2666 pos.do_move(cur->move, st);
2669 rm.pv[0] = ss[0].currentMove = cur->move;
2670 rm.pv[1] = MOVE_NONE;
2671 rm.pv_score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2674 pos.undo_move(cur->move);
2679 // Score root moves using the standard way used in main search, the moves
2680 // are scored according to the order in which are returned by MovePicker.
2681 // This is the second order score that is used to compare the moves when
2682 // the first order pv scores of both moves are equal.
2684 void RootMoveList::set_non_pv_scores(const Position& pos)
2687 Value score = VALUE_ZERO;
2688 MovePicker mp(pos, MOVE_NONE, ONE_PLY, H);
2690 while ((move = mp.get_next_move()) != MOVE_NONE)
2691 for (Base::iterator it = begin(); it != end(); ++it)
2692 if (it->pv[0] == move)
2694 it->non_pv_score = score--;