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(Position& pos, Value alpha, Value beta, int pvLine = 0);
137 Move pv[PLY_MAX_PLUS_2];
141 // RootMoveList struct is essentially a std::vector<> of RootMove objects,
142 // with an handful of methods above the standard ones.
144 struct RootMoveList : public std::vector<RootMove> {
146 typedef std::vector<RootMove> Base;
148 RootMoveList(Position& pos, Move searchMoves[]);
149 void set_non_pv_scores(const Position& pos, Move ttm, SearchStack* ss);
151 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
152 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
156 // When formatting a move for std::cout we must know if we are in Chess960
157 // or not. To keep using the handy operator<<() on the move the trick is to
158 // embed this flag in the stream itself. Function-like named enum set960 is
159 // used as a custom manipulator and the stream internal general-purpose array,
160 // accessed through ios_base::iword(), is used to pass the flag to the move's
161 // operator<<() that will use it to properly format castling moves.
164 std::ostream& operator<< (std::ostream& os, const set960& f) {
166 os.iword(0) = int(f);
171 // Overload operator << for moves to make it easier to print moves in
172 // coordinate notation compatible with UCI protocol.
173 std::ostream& operator<<(std::ostream& os, Move m) {
175 bool chess960 = (os.iword(0) != 0); // See set960()
176 return os << move_to_uci(m, chess960);
184 // Maximum depth for razoring
185 const Depth RazorDepth = 4 * ONE_PLY;
187 // Dynamic razoring margin based on depth
188 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
190 // Maximum depth for use of dynamic threat detection when null move fails low
191 const Depth ThreatDepth = 5 * ONE_PLY;
193 // Step 9. Internal iterative deepening
195 // Minimum depth for use of internal iterative deepening
196 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
198 // At Non-PV nodes we do an internal iterative deepening search
199 // when the static evaluation is bigger then beta - IIDMargin.
200 const Value IIDMargin = Value(0x100);
202 // Step 11. Decide the new search depth
204 // Extensions. Configurable UCI options
205 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
206 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
207 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
209 // Minimum depth for use of singular extension
210 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
212 // If the TT move is at least SingularExtensionMargin better then the
213 // remaining ones we will extend it.
214 const Value SingularExtensionMargin = Value(0x20);
216 // Step 12. Futility pruning
218 // Futility margin for quiescence search
219 const Value FutilityMarginQS = Value(0x80);
221 // Futility lookup tables (initialized at startup) and their getter functions
222 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
223 int FutilityMoveCountArray[32]; // [depth]
225 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
226 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
228 // Step 14. Reduced search
230 // Reduction lookup tables (initialized at startup) and their getter functions
231 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
233 template <NodeType PV>
234 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
236 // Common adjustments
238 // Search depth at iteration 1
239 const Depth InitialDepth = ONE_PLY;
241 // Easy move margin. An easy move candidate must be at least this much
242 // better than the second best move.
243 const Value EasyMoveMargin = Value(0x200);
246 /// Namespace variables
254 // Scores and number of times the best move changed for each iteration
255 Value ValueByIteration[PLY_MAX_PLUS_2];
256 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
258 // Search window management
264 // Time managment variables
265 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
266 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
267 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
272 std::ofstream LogFile;
274 // Multi-threads manager object
275 ThreadsManager ThreadsMgr;
277 // Node counters, used only by thread[0] but try to keep in different cache
278 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
279 bool SendSearchedNodes;
281 int NodesBetweenPolls = 30000;
288 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
289 Value root_search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, RootMoveList& rml);
291 template <NodeType PvNode, bool SpNode>
292 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
294 template <NodeType PvNode>
295 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
297 template <NodeType PvNode>
298 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
300 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
301 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
304 template <NodeType PvNode>
305 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
307 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
308 bool connected_moves(const Position& pos, Move m1, Move m2);
309 bool value_is_mate(Value value);
310 Value value_to_tt(Value v, int ply);
311 Value value_from_tt(Value v, int ply);
312 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
313 bool connected_threat(const Position& pos, Move m, Move threat);
314 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
315 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
316 void update_killers(Move m, Move killers[]);
317 void update_gains(const Position& pos, Move move, Value before, Value after);
319 int current_search_time();
320 std::string value_to_uci(Value v);
321 int nps(const Position& pos);
322 void poll(const Position& pos);
323 void wait_for_stop_or_ponderhit();
324 void init_ss_array(SearchStack* ss, int size);
326 #if !defined(_MSC_VER)
327 void* init_thread(void* threadID);
329 DWORD WINAPI init_thread(LPVOID threadID);
339 /// init_threads(), exit_threads() and nodes_searched() are helpers to
340 /// give accessibility to some TM methods from outside of current file.
342 void init_threads() { ThreadsMgr.init_threads(); }
343 void exit_threads() { ThreadsMgr.exit_threads(); }
346 /// init_search() is called during startup. It initializes various lookup tables
350 int d; // depth (ONE_PLY == 2)
351 int hd; // half depth (ONE_PLY == 1)
354 // Init reductions array
355 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
357 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
358 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
359 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
360 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
363 // Init futility margins array
364 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
365 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
367 // Init futility move count array
368 for (d = 0; d < 32; d++)
369 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
373 /// perft() is our utility to verify move generation is bug free. All the legal
374 /// moves up to given depth are generated and counted and the sum returned.
376 int64_t perft(Position& pos, Depth depth)
378 MoveStack mlist[MOVES_MAX];
383 // Generate all legal moves
384 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
386 // If we are at the last ply we don't need to do and undo
387 // the moves, just to count them.
388 if (depth <= ONE_PLY)
389 return int(last - mlist);
391 // Loop through all legal moves
393 for (MoveStack* cur = mlist; cur != last; cur++)
396 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
397 sum += perft(pos, depth - ONE_PLY);
404 /// think() is the external interface to Stockfish's search, and is called when
405 /// the program receives the UCI 'go' command. It initializes various
406 /// search-related global variables, and calls root_search(). It returns false
407 /// when a quit command is received during the search.
409 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
410 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
412 // Initialize global search variables
413 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
415 SearchStartTime = get_system_time();
416 ExactMaxTime = maxTime;
419 InfiniteSearch = infinite;
421 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
423 // Look for a book move, only during games, not tests
424 if (UseTimeManagement && Options["OwnBook"].value<bool>())
426 if (Options["Book File"].value<std::string>() != OpeningBook.name())
427 OpeningBook.open(Options["Book File"].value<std::string>());
429 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
430 if (bookMove != MOVE_NONE)
433 wait_for_stop_or_ponderhit();
435 cout << "bestmove " << bookMove << endl;
440 // Read UCI option values
441 TT.set_size(Options["Hash"].value<int>());
442 if (Options["Clear Hash"].value<bool>())
444 Options["Clear Hash"].set_value("false");
448 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
449 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
450 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
451 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
452 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
453 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
454 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
455 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
456 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
457 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
458 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
459 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
460 MultiPV = Options["MultiPV"].value<int>();
461 UseLogFile = Options["Use Search Log"].value<bool>();
463 read_evaluation_uci_options(pos.side_to_move());
465 // Set the number of active threads
466 ThreadsMgr.read_uci_options();
467 init_eval(ThreadsMgr.active_threads());
469 // Wake up needed threads
470 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
471 ThreadsMgr.wake_sleeping_thread(i);
474 int myTime = time[pos.side_to_move()];
475 int myIncrement = increment[pos.side_to_move()];
476 if (UseTimeManagement)
477 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
479 // Set best NodesBetweenPolls interval to avoid lagging under
480 // heavy time pressure.
482 NodesBetweenPolls = Min(MaxNodes, 30000);
483 else if (myTime && myTime < 1000)
484 NodesBetweenPolls = 1000;
485 else if (myTime && myTime < 5000)
486 NodesBetweenPolls = 5000;
488 NodesBetweenPolls = 30000;
490 // Write search information to log file
493 std::string name = Options["Search Log Filename"].value<std::string>();
494 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
496 LogFile << "Searching: " << pos.to_fen()
497 << "\ninfinite: " << infinite
498 << " ponder: " << ponder
499 << " time: " << myTime
500 << " increment: " << myIncrement
501 << " moves to go: " << movesToGo << endl;
504 // We're ready to start thinking. Call the iterative deepening loop function
505 Move ponderMove = MOVE_NONE;
506 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
508 // Print final search statistics
509 cout << "info nodes " << pos.nodes_searched()
510 << " nps " << nps(pos)
511 << " time " << current_search_time() << endl;
515 LogFile << "\nNodes: " << pos.nodes_searched()
516 << "\nNodes/second: " << nps(pos)
517 << "\nBest move: " << move_to_san(pos, bestMove);
520 pos.do_move(bestMove, st);
521 LogFile << "\nPonder move: "
522 << move_to_san(pos, ponderMove) // Works also with MOVE_NONE
525 // Return from think() with unchanged position
526 pos.undo_move(bestMove);
531 // This makes all the threads to go to sleep
532 ThreadsMgr.set_active_threads(1);
534 // If we are pondering or in infinite search, we shouldn't print the
535 // best move before we are told to do so.
536 if (!StopRequest && (Pondering || InfiniteSearch))
537 wait_for_stop_or_ponderhit();
539 // Could be both MOVE_NONE when searching on a stalemate position
540 cout << "bestmove " << bestMove << " ponder " << ponderMove << endl;
548 // id_loop() is the main iterative deepening loop. It calls root_search
549 // repeatedly with increasing depth until the allocated thinking time has
550 // been consumed, the user stops the search, or the maximum search depth is
553 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
555 SearchStack ss[PLY_MAX_PLUS_2];
557 Move EasyMove = MOVE_NONE;
558 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
559 int researchCountFL, researchCountFH;
561 // Moves to search are verified, scored and sorted
562 RootMoveList rml(pos, searchMoves);
564 // Handle special case of searching on a mate/stale position
567 Value s = (pos.is_check() ? -VALUE_MATE : VALUE_DRAW);
569 cout << "info depth " << 1
570 << " score " << value_to_uci(s) << endl;
578 init_ss_array(ss, PLY_MAX_PLUS_2);
579 ValueByIteration[1] = rml[0].pv_score;
582 // Send initial RootMoveList scoring (iteration 1)
583 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
584 << "info depth " << Iteration
585 << "\n" << rml[0].pv_info_to_uci(pos, alpha, beta) << endl;
587 // Is one move significantly better than others after initial scoring ?
589 || rml[0].pv_score > rml[1].pv_score + EasyMoveMargin)
590 EasyMove = rml[0].pv[0];
592 // Iterative deepening loop
593 while (Iteration < PLY_MAX)
595 // Initialize iteration
597 BestMoveChangesByIteration[Iteration] = 0;
599 cout << "info depth " << Iteration << endl;
601 // Calculate dynamic aspiration window based on previous iterations
602 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
604 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
605 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
607 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
608 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
610 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
611 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
614 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
616 researchCountFL = researchCountFH = 0;
618 // We start with small aspiration window and in case of fail high/low, we
619 // research with bigger window until we are not failing high/low anymore.
622 // Sort the moves before to (re)search
623 rml.set_non_pv_scores(pos, rml[0].pv[0], ss);
626 // Search to the current depth, rml is updated and sorted
627 value = root_search(pos, ss, alpha, beta, depth, rml);
632 assert(value >= alpha);
636 // Prepare for a research after a fail high, each time with a wider window
637 beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
640 else if (value <= alpha)
642 AspirationFailLow = true;
643 StopOnPonderhit = false;
645 // Prepare for a research after a fail low, each time with a wider window
646 alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
654 break; // Value cannot be trusted. Break out immediately!
656 //Save info about search result
657 ValueByIteration[Iteration] = value;
659 // Drop the easy move if differs from the new best move
660 if (rml[0].pv[0] != EasyMove)
661 EasyMove = MOVE_NONE;
663 if (UseTimeManagement)
666 bool stopSearch = false;
668 // Stop search early if there is only a single legal move,
669 // we search up to Iteration 6 anyway to get a proper score.
670 if (Iteration >= 6 && rml.size() == 1)
673 // Stop search early when the last two iterations returned a mate score
675 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
676 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
679 // Stop search early if one move seems to be much better than the others
681 && EasyMove == rml[0].pv[0]
682 && ( ( rml[0].nodes > (pos.nodes_searched() * 85) / 100
683 && current_search_time() > TimeMgr.available_time() / 16)
684 ||( rml[0].nodes > (pos.nodes_searched() * 98) / 100
685 && current_search_time() > TimeMgr.available_time() / 32)))
688 // Add some extra time if the best move has changed during the last two iterations
689 if (Iteration > 5 && Iteration <= 50)
690 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
691 BestMoveChangesByIteration[Iteration-1]);
693 // Stop search if most of MaxSearchTime is consumed at the end of the
694 // iteration. We probably don't have enough time to search the first
695 // move at the next iteration anyway.
696 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
702 StopOnPonderhit = true;
708 if (MaxDepth && Iteration >= MaxDepth)
712 *ponderMove = rml[0].pv[1];
717 // root_search() is the function which searches the root node. It is
718 // similar to search_pv except that it prints some information to the
719 // standard output and handles the fail low/high loops.
721 Value root_search(Position& pos, SearchStack* ss, Value alpha,
722 Value beta, Depth depth, RootMoveList& rml) {
724 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
725 assert(beta > alpha && beta <= VALUE_INFINITE);
726 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
728 Move movesSearched[MOVES_MAX];
734 Value value, oldAlpha;
735 bool isCheck, moveIsCheck, captureOrPromotion, dangerous, isPvMove;
738 value = -VALUE_INFINITE;
740 isCheck = pos.is_check();
742 // Step 1. Initialize node (polling is omitted at root)
743 ss->currentMove = ss->bestMove = MOVE_NONE;
744 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
746 // Step 2. Check for aborted search (omitted at root)
747 // Step 3. Mate distance pruning (omitted at root)
748 // Step 4. Transposition table lookup (omitted at root)
749 posKey = pos.get_key();
751 // Step 5. Evaluate the position statically
752 // At root we do this only to get reference value for child nodes
753 ss->evalMargin = VALUE_NONE;
754 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
756 // Step 6. Razoring (omitted at root)
757 // Step 7. Static null move pruning (omitted at root)
758 // Step 8. Null move search with verification search (omitted at root)
759 // Step 9. Internal iterative deepening (omitted at root)
763 RootMoveList::iterator rm = rml.begin();
765 // Step 10. Loop through moves
766 // Loop through all legal moves until no moves remain or a beta cutoff occurs
771 move = ss->currentMove = rm->pv[0];
772 movesSearched[moveCount++] = move;
773 isPvMove = (moveCount <= MultiPV);
775 // This is used by time management
776 FirstRootMove = (rm == rml.begin());
778 // Save the current node count before the move is searched
779 nodes = pos.nodes_searched();
781 // If it's time to send nodes info, do it here where we have the
782 // correct accumulated node counts searched by each thread.
783 if (SendSearchedNodes)
785 SendSearchedNodes = false;
786 cout << "info nodes " << nodes
787 << " nps " << nps(pos)
788 << " time " << current_search_time() << endl;
791 if (current_search_time() >= 1000)
792 cout << "info currmove " << move
793 << " currmovenumber " << moveCount << endl;
795 moveIsCheck = pos.move_is_check(move);
796 captureOrPromotion = pos.move_is_capture_or_promotion(move);
798 // Step 11. Decide the new search depth
799 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
800 newDepth = depth + ext;
802 // Step 12. Futility pruning (omitted at root)
803 // Step 13. Make the move
804 pos.do_move(move, st, ci, moveIsCheck);
806 // Step extra. pv search
807 // We do pv search for PV moves
810 // Aspiration window is disabled in multi-pv case
812 alpha = -VALUE_INFINITE;
814 // Full depth PV search, done on first move or after a fail high
815 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
819 // Step 14. Reduced search
820 // if the move fails high will be re-searched at full depth
821 bool doFullDepthSearch = true;
823 if ( depth >= 3 * ONE_PLY
824 && !captureOrPromotion
826 && !move_is_castle(move)
827 && ss->killers[0] != move
828 && ss->killers[1] != move)
830 ss->reduction = reduction<PV>(depth, moveCount - MultiPV + 1);
834 Depth d = newDepth - ss->reduction;
835 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, 1);
837 doFullDepthSearch = (value > alpha);
839 ss->reduction = DEPTH_ZERO; // Restore original reduction
842 // Step 15. Full depth search
843 if (doFullDepthSearch)
845 // Full depth non-pv search using alpha as upperbound
846 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
848 // If we are above alpha then research at same depth but as PV
849 // to get a correct score or eventually a fail high above beta.
851 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
855 // Step 16. Undo move
858 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
860 // Finished searching the move. If StopRequest is true, the search
861 // was aborted because the user interrupted the search or because we
862 // ran out of time. In this case, the return value of the search cannot
863 // be trusted, and we break out of the loop without updating the best
868 // Remember searched nodes counts for this move
869 rm->nodes += pos.nodes_searched() - nodes;
871 // Step 17. Check for new best move
872 if (!isPvMove && value <= alpha)
873 rm->pv_score = -VALUE_INFINITE;
876 // PV move or new best move!
880 rm->pv_score = value;
881 rm->extract_pv_from_tt(pos);
883 // We record how often the best move has been changed in each
884 // iteration. This information is used for time managment: When
885 // the best move changes frequently, we allocate some more time.
886 if (!isPvMove && MultiPV == 1)
887 BestMoveChangesByIteration[Iteration]++;
889 // Inform GUI that PV has changed, in case of multi-pv UCI protocol
890 // requires we send all the PV lines properly sorted.
891 rml.sort_multipv(moveCount);
893 for (int j = 0; j < Min(MultiPV, (int)rml.size()); j++)
894 cout << rml[j].pv_info_to_uci(pos, alpha, beta, j) << endl;
896 // Update alpha. In multi-pv we don't use aspiration window
899 // Raise alpha to setup proper non-pv search upper bound
903 else // Set alpha equal to minimum score among the PV lines
904 alpha = rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
906 } // PV move or new best move
913 // Step 20. Update tables
914 // If the search is not aborted, update the transposition table,
915 // history counters, and killer moves.
918 move = alpha <= oldAlpha ? MOVE_NONE : ss->bestMove;
919 vt = alpha <= oldAlpha ? VALUE_TYPE_UPPER
920 : alpha >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
922 TT.store(posKey, value_to_tt(alpha, 0), vt, depth, move, ss->eval, ss->evalMargin);
924 // Update killers and history only for non capture moves that fails high
926 && !pos.move_is_capture_or_promotion(move))
928 update_history(pos, move, depth, movesSearched, moveCount);
929 update_killers(move, ss->killers);
933 // Sort the moves before to return
936 // Write PV lines to transposition table, in case the relevant entries
937 // have been overwritten during the search.
938 for (int i = 0; i < Min(MultiPV, (int)rml.size()); i++)
939 rml[i].insert_pv_in_tt(pos);
941 assert(alpha > -VALUE_INFINITE && alpha < VALUE_INFINITE);
947 // search<>() is the main search function for both PV and non-PV nodes and for
948 // normal and SplitPoint nodes. When called just after a split point the search
949 // is simpler because we have already probed the hash table, done a null move
950 // search, and searched the first move before splitting, we don't have to repeat
951 // all this work again. We also don't need to store anything to the hash table
952 // here: This is taken care of after we return from the split point.
954 template <NodeType PvNode, bool SpNode>
955 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
957 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
958 assert(beta > alpha && beta <= VALUE_INFINITE);
959 assert(PvNode || alpha == beta - 1);
960 assert(ply > 0 && ply < PLY_MAX);
961 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
963 Move movesSearched[MOVES_MAX];
967 Move ttMove, move, excludedMove, threatMove;
970 Value bestValue, value, oldAlpha;
971 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
972 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
973 bool mateThreat = false;
975 int threadID = pos.thread();
976 SplitPoint* sp = NULL;
977 refinedValue = bestValue = value = -VALUE_INFINITE;
979 isCheck = pos.is_check();
985 ttMove = excludedMove = MOVE_NONE;
986 threatMove = sp->threatMove;
987 mateThreat = sp->mateThreat;
988 goto split_point_start;
990 else {} // Hack to fix icc's "statement is unreachable" warning
992 // Step 1. Initialize node and poll. Polling can abort search
993 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
994 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
996 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1002 // Step 2. Check for aborted search and immediate draw
1004 || ThreadsMgr.cutoff_at_splitpoint(threadID)
1006 || ply >= PLY_MAX - 1)
1009 // Step 3. Mate distance pruning
1010 alpha = Max(value_mated_in(ply), alpha);
1011 beta = Min(value_mate_in(ply+1), beta);
1015 // Step 4. Transposition table lookup
1017 // We don't want the score of a partial search to overwrite a previous full search
1018 // TT value, so we use a different position key in case of an excluded move exists.
1019 excludedMove = ss->excludedMove;
1020 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1022 tte = TT.retrieve(posKey);
1023 ttMove = tte ? tte->move() : MOVE_NONE;
1025 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1026 // This is to avoid problems in the following areas:
1028 // * Repetition draw detection
1029 // * Fifty move rule detection
1030 // * Searching for a mate
1031 // * Printing of full PV line
1032 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1035 ss->bestMove = ttMove; // Can be MOVE_NONE
1036 return value_from_tt(tte->value(), ply);
1039 // Step 5. Evaluate the position statically and
1040 // update gain statistics of parent move.
1042 ss->eval = ss->evalMargin = VALUE_NONE;
1045 assert(tte->static_value() != VALUE_NONE);
1047 ss->eval = tte->static_value();
1048 ss->evalMargin = tte->static_value_margin();
1049 refinedValue = refine_eval(tte, ss->eval, ply);
1053 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1054 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1057 // Save gain for the parent non-capture move
1058 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1060 // Step 6. Razoring (is omitted in PV nodes)
1062 && depth < RazorDepth
1064 && refinedValue < beta - razor_margin(depth)
1065 && ttMove == MOVE_NONE
1066 && !value_is_mate(beta)
1067 && !pos.has_pawn_on_7th(pos.side_to_move()))
1069 Value rbeta = beta - razor_margin(depth);
1070 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1072 // Logically we should return (v + razor_margin(depth)), but
1073 // surprisingly this did slightly weaker in tests.
1077 // Step 7. Static null move pruning (is omitted in PV nodes)
1078 // We're betting that the opponent doesn't have a move that will reduce
1079 // the score by more than futility_margin(depth) if we do a null move.
1081 && !ss->skipNullMove
1082 && depth < RazorDepth
1084 && refinedValue >= beta + futility_margin(depth, 0)
1085 && !value_is_mate(beta)
1086 && pos.non_pawn_material(pos.side_to_move()))
1087 return refinedValue - futility_margin(depth, 0);
1089 // Step 8. Null move search with verification search (is omitted in PV nodes)
1091 && !ss->skipNullMove
1094 && refinedValue >= beta
1095 && !value_is_mate(beta)
1096 && pos.non_pawn_material(pos.side_to_move()))
1098 ss->currentMove = MOVE_NULL;
1100 // Null move dynamic reduction based on depth
1101 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1103 // Null move dynamic reduction based on value
1104 if (refinedValue - beta > PawnValueMidgame)
1107 pos.do_null_move(st);
1108 (ss+1)->skipNullMove = true;
1109 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1110 (ss+1)->skipNullMove = false;
1111 pos.undo_null_move();
1113 if (nullValue >= beta)
1115 // Do not return unproven mate scores
1116 if (nullValue >= value_mate_in(PLY_MAX))
1119 if (depth < 6 * ONE_PLY)
1122 // Do verification search at high depths
1123 ss->skipNullMove = true;
1124 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1125 ss->skipNullMove = false;
1132 // The null move failed low, which means that we may be faced with
1133 // some kind of threat. If the previous move was reduced, check if
1134 // the move that refuted the null move was somehow connected to the
1135 // move which was reduced. If a connection is found, return a fail
1136 // low score (which will cause the reduced move to fail high in the
1137 // parent node, which will trigger a re-search with full depth).
1138 if (nullValue == value_mated_in(ply + 2))
1141 threatMove = (ss+1)->bestMove;
1142 if ( depth < ThreatDepth
1143 && (ss-1)->reduction
1144 && threatMove != MOVE_NONE
1145 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1150 // Step 9. Internal iterative deepening
1151 if ( depth >= IIDDepth[PvNode]
1152 && ttMove == MOVE_NONE
1153 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1155 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1157 ss->skipNullMove = true;
1158 search<PvNode>(pos, ss, alpha, beta, d, ply);
1159 ss->skipNullMove = false;
1161 ttMove = ss->bestMove;
1162 tte = TT.retrieve(posKey);
1165 // Expensive mate threat detection (only for PV nodes)
1167 mateThreat = pos.has_mate_threat();
1169 split_point_start: // At split points actual search starts from here
1171 // Initialize a MovePicker object for the current position
1172 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1173 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1174 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1176 ss->bestMove = MOVE_NONE;
1177 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1178 futilityBase = ss->eval + ss->evalMargin;
1179 singularExtensionNode = !SpNode
1180 && depth >= SingularExtensionDepth[PvNode]
1183 && !excludedMove // Do not allow recursive singular extension search
1184 && (tte->type() & VALUE_TYPE_LOWER)
1185 && tte->depth() >= depth - 3 * ONE_PLY;
1188 lock_grab(&(sp->lock));
1189 bestValue = sp->bestValue;
1192 // Step 10. Loop through moves
1193 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1194 while ( bestValue < beta
1195 && (move = mp.get_next_move()) != MOVE_NONE
1196 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1198 assert(move_is_ok(move));
1202 moveCount = ++sp->moveCount;
1203 lock_release(&(sp->lock));
1205 else if (move == excludedMove)
1208 movesSearched[moveCount++] = move;
1210 moveIsCheck = pos.move_is_check(move, ci);
1211 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1213 // Step 11. Decide the new search depth
1214 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1216 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1217 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1218 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1219 // lower then ttValue minus a margin then we extend ttMove.
1220 if ( singularExtensionNode
1221 && move == tte->move()
1224 Value ttValue = value_from_tt(tte->value(), ply);
1226 if (abs(ttValue) < VALUE_KNOWN_WIN)
1228 Value b = ttValue - SingularExtensionMargin;
1229 ss->excludedMove = move;
1230 ss->skipNullMove = true;
1231 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1232 ss->skipNullMove = false;
1233 ss->excludedMove = MOVE_NONE;
1234 ss->bestMove = MOVE_NONE;
1240 // Update current move (this must be done after singular extension search)
1241 ss->currentMove = move;
1242 newDepth = depth - ONE_PLY + ext;
1244 // Step 12. Futility pruning (is omitted in PV nodes)
1246 && !captureOrPromotion
1250 && !move_is_castle(move))
1252 // Move count based pruning
1253 if ( moveCount >= futility_move_count(depth)
1254 && !(threatMove && connected_threat(pos, move, threatMove))
1255 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1258 lock_grab(&(sp->lock));
1263 // Value based pruning
1264 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1265 // but fixing this made program slightly weaker.
1266 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1267 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1268 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1270 if (futilityValueScaled < beta)
1274 lock_grab(&(sp->lock));
1275 if (futilityValueScaled > sp->bestValue)
1276 sp->bestValue = bestValue = futilityValueScaled;
1278 else if (futilityValueScaled > bestValue)
1279 bestValue = futilityValueScaled;
1284 // Prune moves with negative SEE at low depths
1285 if ( predictedDepth < 2 * ONE_PLY
1286 && bestValue > value_mated_in(PLY_MAX)
1287 && pos.see_sign(move) < 0)
1290 lock_grab(&(sp->lock));
1296 // Step 13. Make the move
1297 pos.do_move(move, st, ci, moveIsCheck);
1299 // Step extra. pv search (only in PV nodes)
1300 // The first move in list is the expected PV
1301 if (PvNode && moveCount == 1)
1302 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1305 // Step 14. Reduced depth search
1306 // If the move fails high will be re-searched at full depth.
1307 bool doFullDepthSearch = true;
1309 if ( depth >= 3 * ONE_PLY
1310 && !captureOrPromotion
1312 && !move_is_castle(move)
1313 && ss->killers[0] != move
1314 && ss->killers[1] != move)
1316 ss->reduction = reduction<PvNode>(depth, moveCount);
1320 alpha = SpNode ? sp->alpha : alpha;
1321 Depth d = newDepth - ss->reduction;
1322 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1324 doFullDepthSearch = (value > alpha);
1326 ss->reduction = DEPTH_ZERO; // Restore original reduction
1329 // Step 15. Full depth search
1330 if (doFullDepthSearch)
1332 alpha = SpNode ? sp->alpha : alpha;
1333 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1335 // Step extra. pv search (only in PV nodes)
1336 // Search only for possible new PV nodes, if instead value >= beta then
1337 // parent node fails low with value <= alpha and tries another move.
1338 if (PvNode && value > alpha && value < beta)
1339 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1343 // Step 16. Undo move
1344 pos.undo_move(move);
1346 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1348 // Step 17. Check for new best move
1351 lock_grab(&(sp->lock));
1352 bestValue = sp->bestValue;
1356 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1361 sp->bestValue = value;
1365 if (PvNode && value < beta) // We want always alpha < beta
1373 sp->betaCutoff = true;
1375 if (value == value_mate_in(ply + 1))
1376 ss->mateKiller = move;
1378 ss->bestMove = move;
1381 sp->parentSstack->bestMove = move;
1385 // Step 18. Check for split
1387 && depth >= ThreadsMgr.min_split_depth()
1388 && ThreadsMgr.active_threads() > 1
1390 && ThreadsMgr.available_thread_exists(threadID)
1392 && !ThreadsMgr.cutoff_at_splitpoint(threadID)
1394 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1395 threatMove, mateThreat, moveCount, &mp, PvNode);
1398 // Step 19. Check for mate and stalemate
1399 // All legal moves have been searched and if there are
1400 // no legal moves, it must be mate or stalemate.
1401 // If one move was excluded return fail low score.
1402 if (!SpNode && !moveCount)
1403 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1405 // Step 20. Update tables
1406 // If the search is not aborted, update the transposition table,
1407 // history counters, and killer moves.
1408 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1410 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1411 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1412 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1414 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1416 // Update killers and history only for non capture moves that fails high
1417 if ( bestValue >= beta
1418 && !pos.move_is_capture_or_promotion(move))
1420 update_history(pos, move, depth, movesSearched, moveCount);
1421 update_killers(move, ss->killers);
1427 // Here we have the lock still grabbed
1428 sp->slaves[threadID] = 0;
1429 sp->nodes += pos.nodes_searched();
1430 lock_release(&(sp->lock));
1433 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1438 // qsearch() is the quiescence search function, which is called by the main
1439 // search function when the remaining depth is zero (or, to be more precise,
1440 // less than ONE_PLY).
1442 template <NodeType PvNode>
1443 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1445 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1446 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1447 assert(PvNode || alpha == beta - 1);
1449 assert(ply > 0 && ply < PLY_MAX);
1450 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1454 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1455 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1458 Value oldAlpha = alpha;
1460 ss->bestMove = ss->currentMove = MOVE_NONE;
1462 // Check for an instant draw or maximum ply reached
1463 if (pos.is_draw() || ply >= PLY_MAX - 1)
1466 // Decide whether or not to include checks, this fixes also the type of
1467 // TT entry depth that we are going to use. Note that in qsearch we use
1468 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1469 isCheck = pos.is_check();
1470 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1472 // Transposition table lookup. At PV nodes, we don't use the TT for
1473 // pruning, but only for move ordering.
1474 tte = TT.retrieve(pos.get_key());
1475 ttMove = (tte ? tte->move() : MOVE_NONE);
1477 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1479 ss->bestMove = ttMove; // Can be MOVE_NONE
1480 return value_from_tt(tte->value(), ply);
1483 // Evaluate the position statically
1486 bestValue = futilityBase = -VALUE_INFINITE;
1487 ss->eval = evalMargin = VALUE_NONE;
1488 enoughMaterial = false;
1494 assert(tte->static_value() != VALUE_NONE);
1496 evalMargin = tte->static_value_margin();
1497 ss->eval = bestValue = tte->static_value();
1500 ss->eval = bestValue = evaluate(pos, evalMargin);
1502 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1504 // Stand pat. Return immediately if static value is at least beta
1505 if (bestValue >= beta)
1508 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1513 if (PvNode && bestValue > alpha)
1516 // Futility pruning parameters, not needed when in check
1517 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1518 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1521 // Initialize a MovePicker object for the current position, and prepare
1522 // to search the moves. Because the depth is <= 0 here, only captures,
1523 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1525 MovePicker mp(pos, ttMove, depth, H);
1528 // Loop through the moves until no moves remain or a beta cutoff occurs
1529 while ( alpha < beta
1530 && (move = mp.get_next_move()) != MOVE_NONE)
1532 assert(move_is_ok(move));
1534 moveIsCheck = pos.move_is_check(move, ci);
1542 && !move_is_promotion(move)
1543 && !pos.move_is_passed_pawn_push(move))
1545 futilityValue = futilityBase
1546 + pos.endgame_value_of_piece_on(move_to(move))
1547 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1549 if (futilityValue < alpha)
1551 if (futilityValue > bestValue)
1552 bestValue = futilityValue;
1557 // Detect non-capture evasions that are candidate to be pruned
1558 evasionPrunable = isCheck
1559 && bestValue > value_mated_in(PLY_MAX)
1560 && !pos.move_is_capture(move)
1561 && !pos.can_castle(pos.side_to_move());
1563 // Don't search moves with negative SEE values
1565 && (!isCheck || evasionPrunable)
1567 && !move_is_promotion(move)
1568 && pos.see_sign(move) < 0)
1571 // Don't search useless checks
1576 && !pos.move_is_capture_or_promotion(move)
1577 && ss->eval + PawnValueMidgame / 4 < beta
1578 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1580 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1581 bestValue = ss->eval + PawnValueMidgame / 4;
1586 // Update current move
1587 ss->currentMove = move;
1589 // Make and search the move
1590 pos.do_move(move, st, ci, moveIsCheck);
1591 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1592 pos.undo_move(move);
1594 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1597 if (value > bestValue)
1603 ss->bestMove = move;
1608 // All legal moves have been searched. A special case: If we're in check
1609 // and no legal moves were found, it is checkmate.
1610 if (isCheck && bestValue == -VALUE_INFINITE)
1611 return value_mated_in(ply);
1613 // Update transposition table
1614 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1615 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1617 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1623 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1624 // bestValue is updated only when returning false because in that case move
1627 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1629 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1630 Square from, to, ksq, victimSq;
1633 Value futilityValue, bv = *bestValue;
1635 from = move_from(move);
1637 them = opposite_color(pos.side_to_move());
1638 ksq = pos.king_square(them);
1639 kingAtt = pos.attacks_from<KING>(ksq);
1640 pc = pos.piece_on(from);
1642 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1643 oldAtt = pos.attacks_from(pc, from, occ);
1644 newAtt = pos.attacks_from(pc, to, occ);
1646 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1647 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1649 if (!(b && (b & (b - 1))))
1652 // Rule 2. Queen contact check is very dangerous
1653 if ( type_of_piece(pc) == QUEEN
1654 && bit_is_set(kingAtt, to))
1657 // Rule 3. Creating new double threats with checks
1658 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1662 victimSq = pop_1st_bit(&b);
1663 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1665 // Note that here we generate illegal "double move"!
1666 if ( futilityValue >= beta
1667 && pos.see_sign(make_move(from, victimSq)) >= 0)
1670 if (futilityValue > bv)
1674 // Update bestValue only if check is not dangerous (because we will prune the move)
1680 // connected_moves() tests whether two moves are 'connected' in the sense
1681 // that the first move somehow made the second move possible (for instance
1682 // if the moving piece is the same in both moves). The first move is assumed
1683 // to be the move that was made to reach the current position, while the
1684 // second move is assumed to be a move from the current position.
1686 bool connected_moves(const Position& pos, Move m1, Move m2) {
1688 Square f1, t1, f2, t2;
1691 assert(m1 && move_is_ok(m1));
1692 assert(m2 && move_is_ok(m2));
1694 // Case 1: The moving piece is the same in both moves
1700 // Case 2: The destination square for m2 was vacated by m1
1706 // Case 3: Moving through the vacated square
1707 if ( piece_is_slider(pos.piece_on(f2))
1708 && bit_is_set(squares_between(f2, t2), f1))
1711 // Case 4: The destination square for m2 is defended by the moving piece in m1
1712 p = pos.piece_on(t1);
1713 if (bit_is_set(pos.attacks_from(p, t1), t2))
1716 // Case 5: Discovered check, checking piece is the piece moved in m1
1717 if ( piece_is_slider(p)
1718 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1719 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1721 // discovered_check_candidates() works also if the Position's side to
1722 // move is the opposite of the checking piece.
1723 Color them = opposite_color(pos.side_to_move());
1724 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1726 if (bit_is_set(dcCandidates, f2))
1733 // value_is_mate() checks if the given value is a mate one eventually
1734 // compensated for the ply.
1736 bool value_is_mate(Value value) {
1738 assert(abs(value) <= VALUE_INFINITE);
1740 return value <= value_mated_in(PLY_MAX)
1741 || value >= value_mate_in(PLY_MAX);
1745 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1746 // "plies to mate from the current ply". Non-mate scores are unchanged.
1747 // The function is called before storing a value to the transposition table.
1749 Value value_to_tt(Value v, int ply) {
1751 if (v >= value_mate_in(PLY_MAX))
1754 if (v <= value_mated_in(PLY_MAX))
1761 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1762 // the transposition table to a mate score corrected for the current ply.
1764 Value value_from_tt(Value v, int ply) {
1766 if (v >= value_mate_in(PLY_MAX))
1769 if (v <= value_mated_in(PLY_MAX))
1776 // extension() decides whether a move should be searched with normal depth,
1777 // or with extended depth. Certain classes of moves (checking moves, in
1778 // particular) are searched with bigger depth than ordinary moves and in
1779 // any case are marked as 'dangerous'. Note that also if a move is not
1780 // extended, as example because the corresponding UCI option is set to zero,
1781 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1782 template <NodeType PvNode>
1783 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1784 bool singleEvasion, bool mateThreat, bool* dangerous) {
1786 assert(m != MOVE_NONE);
1788 Depth result = DEPTH_ZERO;
1789 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1793 if (moveIsCheck && pos.see_sign(m) >= 0)
1794 result += CheckExtension[PvNode];
1797 result += SingleEvasionExtension[PvNode];
1800 result += MateThreatExtension[PvNode];
1803 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1805 Color c = pos.side_to_move();
1806 if (relative_rank(c, move_to(m)) == RANK_7)
1808 result += PawnPushTo7thExtension[PvNode];
1811 if (pos.pawn_is_passed(c, move_to(m)))
1813 result += PassedPawnExtension[PvNode];
1818 if ( captureOrPromotion
1819 && pos.type_of_piece_on(move_to(m)) != PAWN
1820 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1821 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1822 && !move_is_promotion(m)
1825 result += PawnEndgameExtension[PvNode];
1830 && captureOrPromotion
1831 && pos.type_of_piece_on(move_to(m)) != PAWN
1832 && pos.see_sign(m) >= 0)
1834 result += ONE_PLY / 2;
1838 return Min(result, ONE_PLY);
1842 // connected_threat() tests whether it is safe to forward prune a move or if
1843 // is somehow coonected to the threat move returned by null search.
1845 bool connected_threat(const Position& pos, Move m, Move threat) {
1847 assert(move_is_ok(m));
1848 assert(threat && move_is_ok(threat));
1849 assert(!pos.move_is_check(m));
1850 assert(!pos.move_is_capture_or_promotion(m));
1851 assert(!pos.move_is_passed_pawn_push(m));
1853 Square mfrom, mto, tfrom, tto;
1855 mfrom = move_from(m);
1857 tfrom = move_from(threat);
1858 tto = move_to(threat);
1860 // Case 1: Don't prune moves which move the threatened piece
1864 // Case 2: If the threatened piece has value less than or equal to the
1865 // value of the threatening piece, don't prune move which defend it.
1866 if ( pos.move_is_capture(threat)
1867 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1868 || pos.type_of_piece_on(tfrom) == KING)
1869 && pos.move_attacks_square(m, tto))
1872 // Case 3: If the moving piece in the threatened move is a slider, don't
1873 // prune safe moves which block its ray.
1874 if ( piece_is_slider(pos.piece_on(tfrom))
1875 && bit_is_set(squares_between(tfrom, tto), mto)
1876 && pos.see_sign(m) >= 0)
1883 // ok_to_use_TT() returns true if a transposition table score
1884 // can be used at a given point in search.
1886 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1888 Value v = value_from_tt(tte->value(), ply);
1890 return ( tte->depth() >= depth
1891 || v >= Max(value_mate_in(PLY_MAX), beta)
1892 || v < Min(value_mated_in(PLY_MAX), beta))
1894 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1895 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1899 // refine_eval() returns the transposition table score if
1900 // possible otherwise falls back on static position evaluation.
1902 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1906 Value v = value_from_tt(tte->value(), ply);
1908 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1909 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1916 // update_history() registers a good move that produced a beta-cutoff
1917 // in history and marks as failures all the other moves of that ply.
1919 void update_history(const Position& pos, Move move, Depth depth,
1920 Move movesSearched[], int moveCount) {
1922 Value bonus = Value(int(depth) * int(depth));
1924 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1926 for (int i = 0; i < moveCount - 1; i++)
1928 m = movesSearched[i];
1932 if (!pos.move_is_capture_or_promotion(m))
1933 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1938 // update_killers() add a good move that produced a beta-cutoff
1939 // among the killer moves of that ply.
1941 void update_killers(Move m, Move killers[]) {
1943 if (m == killers[0])
1946 killers[1] = killers[0];
1951 // update_gains() updates the gains table of a non-capture move given
1952 // the static position evaluation before and after the move.
1954 void update_gains(const Position& pos, Move m, Value before, Value after) {
1957 && before != VALUE_NONE
1958 && after != VALUE_NONE
1959 && pos.captured_piece_type() == PIECE_TYPE_NONE
1960 && !move_is_special(m))
1961 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1965 // init_ss_array() does a fast reset of the first entries of a SearchStack
1966 // array and of all the excludedMove and skipNullMove entries.
1968 void init_ss_array(SearchStack* ss, int size) {
1970 for (int i = 0; i < size; i++, ss++)
1972 ss->excludedMove = MOVE_NONE;
1973 ss->skipNullMove = false;
1974 ss->reduction = DEPTH_ZERO;
1978 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
1983 // value_to_uci() converts a value to a string suitable for use with the UCI
1984 // protocol specifications:
1986 // cp <x> The score from the engine's point of view in centipawns.
1987 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1988 // use negative values for y.
1990 std::string value_to_uci(Value v) {
1992 std::stringstream s;
1994 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1995 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1997 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2003 // current_search_time() returns the number of milliseconds which have passed
2004 // since the beginning of the current search.
2006 int current_search_time() {
2008 return get_system_time() - SearchStartTime;
2012 // nps() computes the current nodes/second count
2014 int nps(const Position& pos) {
2016 int t = current_search_time();
2017 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
2021 // poll() performs two different functions: It polls for user input, and it
2022 // looks at the time consumed so far and decides if it's time to abort the
2025 void poll(const Position& pos) {
2027 static int lastInfoTime;
2028 int t = current_search_time();
2031 if (input_available())
2033 // We are line oriented, don't read single chars
2034 std::string command;
2036 if (!std::getline(std::cin, command))
2039 if (command == "quit")
2041 // Quit the program as soon as possible
2043 QuitRequest = StopRequest = true;
2046 else if (command == "stop")
2048 // Stop calculating as soon as possible, but still send the "bestmove"
2049 // and possibly the "ponder" token when finishing the search.
2053 else if (command == "ponderhit")
2055 // The opponent has played the expected move. GUI sends "ponderhit" if
2056 // we were told to ponder on the same move the opponent has played. We
2057 // should continue searching but switching from pondering to normal search.
2060 if (StopOnPonderhit)
2065 // Print search information
2069 else if (lastInfoTime > t)
2070 // HACK: Must be a new search where we searched less than
2071 // NodesBetweenPolls nodes during the first second of search.
2074 else if (t - lastInfoTime >= 1000)
2081 if (dbg_show_hit_rate)
2082 dbg_print_hit_rate();
2084 // Send info on searched nodes as soon as we return to root
2085 SendSearchedNodes = true;
2088 // Should we stop the search?
2092 bool stillAtFirstMove = FirstRootMove
2093 && !AspirationFailLow
2094 && t > TimeMgr.available_time();
2096 bool noMoreTime = t > TimeMgr.maximum_time()
2097 || stillAtFirstMove;
2099 if ( (UseTimeManagement && noMoreTime)
2100 || (ExactMaxTime && t >= ExactMaxTime)
2101 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
2106 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2107 // while the program is pondering. The point is to work around a wrinkle in
2108 // the UCI protocol: When pondering, the engine is not allowed to give a
2109 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2110 // We simply wait here until one of these commands is sent, and return,
2111 // after which the bestmove and pondermove will be printed.
2113 void wait_for_stop_or_ponderhit() {
2115 std::string command;
2119 // Wait for a command from stdin
2120 if (!std::getline(std::cin, command))
2123 if (command == "quit")
2128 else if (command == "ponderhit" || command == "stop")
2134 // init_thread() is the function which is called when a new thread is
2135 // launched. It simply calls the idle_loop() function with the supplied
2136 // threadID. There are two versions of this function; one for POSIX
2137 // threads and one for Windows threads.
2139 #if !defined(_MSC_VER)
2141 void* init_thread(void* threadID) {
2143 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2149 DWORD WINAPI init_thread(LPVOID threadID) {
2151 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2158 /// The ThreadsManager class
2161 // read_uci_options() updates number of active threads and other internal
2162 // parameters according to the UCI options values. It is called before
2163 // to start a new search.
2165 void ThreadsManager::read_uci_options() {
2167 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2168 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2169 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2170 activeThreads = Options["Threads"].value<int>();
2174 // idle_loop() is where the threads are parked when they have no work to do.
2175 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2176 // object for which the current thread is the master.
2178 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2180 assert(threadID >= 0 && threadID < MAX_THREADS);
2183 bool allFinished = false;
2187 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2188 // master should exit as last one.
2189 if (allThreadsShouldExit)
2192 threads[threadID].state = THREAD_TERMINATED;
2196 // If we are not thinking, wait for a condition to be signaled
2197 // instead of wasting CPU time polling for work.
2198 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2199 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2201 assert(!sp || useSleepingThreads);
2202 assert(threadID != 0 || useSleepingThreads);
2204 if (threads[threadID].state == THREAD_INITIALIZING)
2205 threads[threadID].state = THREAD_AVAILABLE;
2207 // Grab the lock to avoid races with wake_sleeping_thread()
2208 lock_grab(&sleepLock[threadID]);
2210 // If we are master and all slaves have finished do not go to sleep
2211 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2212 allFinished = (i == activeThreads);
2214 if (allFinished || allThreadsShouldExit)
2216 lock_release(&sleepLock[threadID]);
2220 // Do sleep here after retesting sleep conditions
2221 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2222 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2224 lock_release(&sleepLock[threadID]);
2227 // If this thread has been assigned work, launch a search
2228 if (threads[threadID].state == THREAD_WORKISWAITING)
2230 assert(!allThreadsShouldExit);
2232 threads[threadID].state = THREAD_SEARCHING;
2234 // Here we call search() with SplitPoint template parameter set to true
2235 SplitPoint* tsp = threads[threadID].splitPoint;
2236 Position pos(*tsp->pos, threadID);
2237 SearchStack* ss = tsp->sstack[threadID] + 1;
2241 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2243 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2245 assert(threads[threadID].state == THREAD_SEARCHING);
2247 threads[threadID].state = THREAD_AVAILABLE;
2249 // Wake up master thread so to allow it to return from the idle loop in
2250 // case we are the last slave of the split point.
2251 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2252 wake_sleeping_thread(tsp->master);
2255 // If this thread is the master of a split point and all slaves have
2256 // finished their work at this split point, return from the idle loop.
2257 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2258 allFinished = (i == activeThreads);
2262 // Because sp->slaves[] is reset under lock protection,
2263 // be sure sp->lock has been released before to return.
2264 lock_grab(&(sp->lock));
2265 lock_release(&(sp->lock));
2267 // In helpful master concept a master can help only a sub-tree, and
2268 // because here is all finished is not possible master is booked.
2269 assert(threads[threadID].state == THREAD_AVAILABLE);
2271 threads[threadID].state = THREAD_SEARCHING;
2278 // init_threads() is called during startup. It launches all helper threads,
2279 // and initializes the split point stack and the global locks and condition
2282 void ThreadsManager::init_threads() {
2284 int i, arg[MAX_THREADS];
2287 // Initialize global locks
2290 for (i = 0; i < MAX_THREADS; i++)
2292 lock_init(&sleepLock[i]);
2293 cond_init(&sleepCond[i]);
2296 // Initialize splitPoints[] locks
2297 for (i = 0; i < MAX_THREADS; i++)
2298 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2299 lock_init(&(threads[i].splitPoints[j].lock));
2301 // Will be set just before program exits to properly end the threads
2302 allThreadsShouldExit = false;
2304 // Threads will be put all threads to sleep as soon as created
2307 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2308 threads[0].state = THREAD_SEARCHING;
2309 for (i = 1; i < MAX_THREADS; i++)
2310 threads[i].state = THREAD_INITIALIZING;
2312 // Launch the helper threads
2313 for (i = 1; i < MAX_THREADS; i++)
2317 #if !defined(_MSC_VER)
2318 pthread_t pthread[1];
2319 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2320 pthread_detach(pthread[0]);
2322 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2326 cout << "Failed to create thread number " << i << endl;
2330 // Wait until the thread has finished launching and is gone to sleep
2331 while (threads[i].state == THREAD_INITIALIZING) {}
2336 // exit_threads() is called when the program exits. It makes all the
2337 // helper threads exit cleanly.
2339 void ThreadsManager::exit_threads() {
2341 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2343 // Wake up all the threads and waits for termination
2344 for (int i = 1; i < MAX_THREADS; i++)
2346 wake_sleeping_thread(i);
2347 while (threads[i].state != THREAD_TERMINATED) {}
2350 // Now we can safely destroy the locks
2351 for (int i = 0; i < MAX_THREADS; i++)
2352 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2353 lock_destroy(&(threads[i].splitPoints[j].lock));
2355 lock_destroy(&mpLock);
2357 // Now we can safely destroy the wait conditions
2358 for (int i = 0; i < MAX_THREADS; i++)
2360 lock_destroy(&sleepLock[i]);
2361 cond_destroy(&sleepCond[i]);
2366 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2367 // the thread's currently active split point, or in some ancestor of
2368 // the current split point.
2370 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2372 assert(threadID >= 0 && threadID < activeThreads);
2374 SplitPoint* sp = threads[threadID].splitPoint;
2376 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2381 // thread_is_available() checks whether the thread with threadID "slave" is
2382 // available to help the thread with threadID "master" at a split point. An
2383 // obvious requirement is that "slave" must be idle. With more than two
2384 // threads, this is not by itself sufficient: If "slave" is the master of
2385 // some active split point, it is only available as a slave to the other
2386 // threads which are busy searching the split point at the top of "slave"'s
2387 // split point stack (the "helpful master concept" in YBWC terminology).
2389 bool ThreadsManager::thread_is_available(int slave, int master) const {
2391 assert(slave >= 0 && slave < activeThreads);
2392 assert(master >= 0 && master < activeThreads);
2393 assert(activeThreads > 1);
2395 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2398 // Make a local copy to be sure doesn't change under our feet
2399 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2401 // No active split points means that the thread is available as
2402 // a slave for any other thread.
2403 if (localActiveSplitPoints == 0 || activeThreads == 2)
2406 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2407 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2408 // could have been set to 0 by another thread leading to an out of bound access.
2409 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2416 // available_thread_exists() tries to find an idle thread which is available as
2417 // a slave for the thread with threadID "master".
2419 bool ThreadsManager::available_thread_exists(int master) const {
2421 assert(master >= 0 && master < activeThreads);
2422 assert(activeThreads > 1);
2424 for (int i = 0; i < activeThreads; i++)
2425 if (thread_is_available(i, master))
2432 // split() does the actual work of distributing the work at a node between
2433 // several available threads. If it does not succeed in splitting the
2434 // node (because no idle threads are available, or because we have no unused
2435 // split point objects), the function immediately returns. If splitting is
2436 // possible, a SplitPoint object is initialized with all the data that must be
2437 // copied to the helper threads and we tell our helper threads that they have
2438 // been assigned work. This will cause them to instantly leave their idle loops and
2439 // call search().When all threads have returned from search() then split() returns.
2441 template <bool Fake>
2442 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2443 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2444 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2445 assert(pos.is_ok());
2446 assert(ply > 0 && ply < PLY_MAX);
2447 assert(*bestValue >= -VALUE_INFINITE);
2448 assert(*bestValue <= *alpha);
2449 assert(*alpha < beta);
2450 assert(beta <= VALUE_INFINITE);
2451 assert(depth > DEPTH_ZERO);
2452 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2453 assert(activeThreads > 1);
2455 int i, master = pos.thread();
2456 Thread& masterThread = threads[master];
2460 // If no other thread is available to help us, or if we have too many
2461 // active split points, don't split.
2462 if ( !available_thread_exists(master)
2463 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2465 lock_release(&mpLock);
2469 // Pick the next available split point object from the split point stack
2470 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2472 // Initialize the split point object
2473 splitPoint.parent = masterThread.splitPoint;
2474 splitPoint.master = master;
2475 splitPoint.betaCutoff = false;
2476 splitPoint.ply = ply;
2477 splitPoint.depth = depth;
2478 splitPoint.threatMove = threatMove;
2479 splitPoint.mateThreat = mateThreat;
2480 splitPoint.alpha = *alpha;
2481 splitPoint.beta = beta;
2482 splitPoint.pvNode = pvNode;
2483 splitPoint.bestValue = *bestValue;
2485 splitPoint.moveCount = moveCount;
2486 splitPoint.pos = &pos;
2487 splitPoint.nodes = 0;
2488 splitPoint.parentSstack = ss;
2489 for (i = 0; i < activeThreads; i++)
2490 splitPoint.slaves[i] = 0;
2492 masterThread.splitPoint = &splitPoint;
2494 // If we are here it means we are not available
2495 assert(masterThread.state != THREAD_AVAILABLE);
2497 int workersCnt = 1; // At least the master is included
2499 // Allocate available threads setting state to THREAD_BOOKED
2500 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2501 if (thread_is_available(i, master))
2503 threads[i].state = THREAD_BOOKED;
2504 threads[i].splitPoint = &splitPoint;
2505 splitPoint.slaves[i] = 1;
2509 assert(Fake || workersCnt > 1);
2511 // We can release the lock because slave threads are already booked and master is not available
2512 lock_release(&mpLock);
2514 // Tell the threads that they have work to do. This will make them leave
2515 // their idle loop. But before copy search stack tail for each thread.
2516 for (i = 0; i < activeThreads; i++)
2517 if (i == master || splitPoint.slaves[i])
2519 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2521 assert(i == master || threads[i].state == THREAD_BOOKED);
2523 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2525 if (useSleepingThreads && i != master)
2526 wake_sleeping_thread(i);
2529 // Everything is set up. The master thread enters the idle loop, from
2530 // which it will instantly launch a search, because its state is
2531 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2532 // idle loop, which means that the main thread will return from the idle
2533 // loop when all threads have finished their work at this split point.
2534 idle_loop(master, &splitPoint);
2536 // We have returned from the idle loop, which means that all threads are
2537 // finished. Update alpha and bestValue, and return.
2540 *alpha = splitPoint.alpha;
2541 *bestValue = splitPoint.bestValue;
2542 masterThread.activeSplitPoints--;
2543 masterThread.splitPoint = splitPoint.parent;
2544 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2546 lock_release(&mpLock);
2550 // wake_sleeping_thread() wakes up the thread with the given threadID
2551 // when it is time to start a new search.
2553 void ThreadsManager::wake_sleeping_thread(int threadID) {
2555 lock_grab(&sleepLock[threadID]);
2556 cond_signal(&sleepCond[threadID]);
2557 lock_release(&sleepLock[threadID]);
2561 /// RootMove and RootMoveList method's definitions
2563 RootMove::RootMove() {
2566 pv_score = non_pv_score = -VALUE_INFINITE;
2570 RootMove& RootMove::operator=(const RootMove& rm) {
2572 const Move* src = rm.pv;
2575 // Avoid a costly full rm.pv[] copy
2576 do *dst++ = *src; while (*src++ != MOVE_NONE);
2579 pv_score = rm.pv_score;
2580 non_pv_score = rm.non_pv_score;
2584 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2585 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2586 // allow to always have a ponder move even when we fail high at root and also a
2587 // long PV to print that is important for position analysis.
2589 void RootMove::extract_pv_from_tt(Position& pos) {
2591 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2595 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2597 pos.do_move(pv[0], *st++);
2599 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2600 && tte->move() != MOVE_NONE
2601 && move_is_legal(pos, tte->move())
2603 && (!pos.is_draw() || ply < 2))
2605 pv[ply] = tte->move();
2606 pos.do_move(pv[ply++], *st++);
2608 pv[ply] = MOVE_NONE;
2610 do pos.undo_move(pv[--ply]); while (ply);
2613 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2614 // the PV back into the TT. This makes sure the old PV moves are searched
2615 // first, even if the old TT entries have been overwritten.
2617 void RootMove::insert_pv_in_tt(Position& pos) {
2619 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2622 Value v, m = VALUE_NONE;
2625 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2629 tte = TT.retrieve(k);
2631 // Don't overwrite exsisting correct entries
2632 if (!tte || tte->move() != pv[ply])
2634 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2635 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2637 pos.do_move(pv[ply], *st++);
2639 } while (pv[++ply] != MOVE_NONE);
2641 do pos.undo_move(pv[--ply]); while (ply);
2644 // pv_info_to_uci() returns a string with information on the current PV line
2645 // formatted according to UCI specification and eventually writes the info
2646 // to a log file. It is called at each iteration or after a new pv is found.
2648 std::string RootMove::pv_info_to_uci(Position& pos, Value alpha, Value beta, int pvLine) {
2650 std::stringstream s, l;
2653 while (*m != MOVE_NONE)
2656 s << "info depth " << Iteration // FIXME
2657 << " seldepth " << int(m - pv)
2658 << " multipv " << pvLine + 1
2659 << " score " << value_to_uci(pv_score)
2660 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2661 << " time " << current_search_time()
2662 << " nodes " << pos.nodes_searched()
2663 << " nps " << nps(pos)
2664 << " pv " << l.str();
2666 if (UseLogFile && pvLine == 0)
2668 ValueType t = pv_score >= beta ? VALUE_TYPE_LOWER :
2669 pv_score <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2671 LogFile << pretty_pv(pos, current_search_time(), Iteration, pv_score, t, pv) << endl;
2677 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2679 SearchStack ss[PLY_MAX_PLUS_2];
2680 MoveStack mlist[MOVES_MAX];
2684 // Initialize search stack
2685 init_ss_array(ss, PLY_MAX_PLUS_2);
2686 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2688 // Generate all legal moves
2689 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2691 // Add each move to the RootMoveList's vector
2692 for (MoveStack* cur = mlist; cur != last; cur++)
2694 // If we have a searchMoves[] list then verify cur->move
2695 // is in the list before to add it.
2696 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2698 if (searchMoves[0] && *sm != cur->move)
2701 // Find a quick score for the move and add to the list
2702 pos.do_move(cur->move, st);
2705 rm.pv[0] = ss[0].currentMove = cur->move;
2706 rm.pv[1] = MOVE_NONE;
2707 rm.pv_score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2710 pos.undo_move(cur->move);
2715 // Score root moves using the standard way used in main search, the moves
2716 // are scored according to the order in which are returned by MovePicker.
2717 // This is the second order score that is used to compare the moves when
2718 // the first order pv scores of both moves are equal.
2720 void RootMoveList::set_non_pv_scores(const Position& pos, Move ttm, SearchStack* ss)
2723 Value score = VALUE_ZERO;
2724 MovePicker mp(pos, ttm, ONE_PLY, H, ss);
2726 while ((move = mp.get_next_move()) != MOVE_NONE)
2727 for (Base::iterator it = begin(); it != end(); ++it)
2728 if (it->pv[0] == move)
2730 it->non_pv_score = score--;