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, int depth, Value alpha, Value beta, int pvLine);
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 void init(Position& pos, Move searchMoves[]);
149 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
150 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], PawnPushTo7thExtension[2], PassedPawnExtension[2];
207 Depth 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 // Step 12. Futility pruning
214 // Futility margin for quiescence search
215 const Value FutilityMarginQS = Value(0x80);
217 // Futility lookup tables (initialized at startup) and their getter functions
218 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
219 int FutilityMoveCountArray[32]; // [depth]
221 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
222 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
224 // Step 14. Reduced search
226 // Reduction lookup tables (initialized at startup) and their getter functions
227 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
229 template <NodeType PV>
230 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
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
248 // Time management variables
249 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
250 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
251 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
256 std::ofstream LogFile;
258 // Multi-threads manager object
259 ThreadsManager ThreadsMgr;
261 // Node counters, used only by thread[0] but try to keep in different cache
262 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
263 bool SendSearchedNodes;
265 int NodesBetweenPolls = 30000;
272 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
274 template <NodeType PvNode, bool SpNode, bool Root>
275 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
277 template <NodeType PvNode>
278 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
280 template <NodeType PvNode>
281 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
283 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
284 : search<PvNode, false, false>(pos, ss, alpha, beta, depth, ply);
287 template <NodeType PvNode>
288 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool mateThreat, bool* dangerous);
290 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
291 bool connected_moves(const Position& pos, Move m1, Move m2);
292 bool value_is_mate(Value value);
293 Value value_to_tt(Value v, int ply);
294 Value value_from_tt(Value v, int ply);
295 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
296 bool connected_threat(const Position& pos, Move m, Move threat);
297 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
298 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
299 void update_killers(Move m, Move killers[]);
300 void update_gains(const Position& pos, Move move, Value before, Value after);
301 void qsearch_scoring(Position& pos, MoveStack* mlist, MoveStack* last);
303 int current_search_time();
304 std::string value_to_uci(Value v);
305 std::string speed_to_uci(int64_t nodes);
306 void poll(const Position& pos);
307 void wait_for_stop_or_ponderhit();
309 #if !defined(_MSC_VER)
310 void* init_thread(void* threadID);
312 DWORD WINAPI init_thread(LPVOID threadID);
316 // MovePickerExt is an extended MovePicker used to choose at compile time
317 // the proper move source according to the type of node.
318 template<bool SpNode, bool Root> struct MovePickerExt;
320 // In Root nodes use RootMoveList Rml as source. Score and sort the root moves
321 // before to search them.
322 template<> struct MovePickerExt<false, true> : public MovePicker {
324 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
325 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
327 Value score = VALUE_ZERO;
329 // Score root moves using the standard way used in main search, the moves
330 // are scored according to the order in which they are returned by MovePicker.
331 // This is the second order score that is used to compare the moves when
332 // the first order pv scores of both moves are equal.
333 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
334 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
335 if (rm->pv[0] == move)
337 rm->non_pv_score = score--;
345 Move get_next_move() {
352 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
355 RootMoveList::iterator rm;
359 // In SpNodes use split point's shared MovePicker object as move source
360 template<> struct MovePickerExt<true, false> : public MovePicker {
362 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
363 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b),
366 Move get_next_move() { return mp->get_next_move(); }
368 RootMoveList::iterator rm; // Dummy, needed to compile
372 // Default case, create and use a MovePicker object as source
373 template<> struct MovePickerExt<false, false> : public MovePicker {
375 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
376 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b) {}
378 RootMoveList::iterator rm; // Dummy, needed to compile
388 /// init_threads(), exit_threads() and nodes_searched() are helpers to
389 /// give accessibility to some TM methods from outside of current file.
391 void init_threads() { ThreadsMgr.init_threads(); }
392 void exit_threads() { ThreadsMgr.exit_threads(); }
395 /// init_search() is called during startup. It initializes various lookup tables
399 int d; // depth (ONE_PLY == 2)
400 int hd; // half depth (ONE_PLY == 1)
403 // Init reductions array
404 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
406 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
407 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
408 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
409 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
412 // Init futility margins array
413 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
414 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
416 // Init futility move count array
417 for (d = 0; d < 32; d++)
418 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
422 /// perft() is our utility to verify move generation is bug free. All the legal
423 /// moves up to given depth are generated and counted and the sum returned.
425 int64_t perft(Position& pos, Depth depth)
427 MoveStack mlist[MOVES_MAX];
432 // Generate all legal moves
433 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
435 // If we are at the last ply we don't need to do and undo
436 // the moves, just to count them.
437 if (depth <= ONE_PLY)
438 return int(last - mlist);
440 // Loop through all legal moves
442 for (MoveStack* cur = mlist; cur != last; cur++)
445 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
446 sum += perft(pos, depth - ONE_PLY);
453 /// think() is the external interface to Stockfish's search, and is called when
454 /// the program receives the UCI 'go' command. It initializes various
455 /// search-related global variables, and calls id_loop(). It returns false
456 /// when a quit command is received during the search.
458 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
459 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
461 // Initialize global search variables
462 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
464 SearchStartTime = get_system_time();
465 ExactMaxTime = maxTime;
468 InfiniteSearch = infinite;
470 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
472 // Look for a book move, only during games, not tests
473 if (UseTimeManagement && Options["OwnBook"].value<bool>())
475 if (Options["Book File"].value<std::string>() != OpeningBook.name())
476 OpeningBook.open(Options["Book File"].value<std::string>());
478 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
479 if (bookMove != MOVE_NONE)
482 wait_for_stop_or_ponderhit();
484 cout << "bestmove " << bookMove << endl;
489 // Read UCI option values
490 TT.set_size(Options["Hash"].value<int>());
491 if (Options["Clear Hash"].value<bool>())
493 Options["Clear Hash"].set_value("false");
497 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
498 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
499 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
500 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
501 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
502 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
503 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
504 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
505 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
506 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
507 MultiPV = Options["MultiPV"].value<int>();
508 UseLogFile = Options["Use Search Log"].value<bool>();
510 read_evaluation_uci_options(pos.side_to_move());
512 // Set the number of active threads
513 ThreadsMgr.read_uci_options();
514 init_eval(ThreadsMgr.active_threads());
516 // Wake up needed threads
517 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
518 ThreadsMgr.wake_sleeping_thread(i);
521 int myTime = time[pos.side_to_move()];
522 int myIncrement = increment[pos.side_to_move()];
523 if (UseTimeManagement)
524 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
526 // Set best NodesBetweenPolls interval to avoid lagging under
527 // heavy time pressure.
529 NodesBetweenPolls = Min(MaxNodes, 30000);
530 else if (myTime && myTime < 1000)
531 NodesBetweenPolls = 1000;
532 else if (myTime && myTime < 5000)
533 NodesBetweenPolls = 5000;
535 NodesBetweenPolls = 30000;
537 // Write search information to log file
540 std::string name = Options["Search Log Filename"].value<std::string>();
541 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
543 LogFile << "\nSearching: " << pos.to_fen()
544 << "\ninfinite: " << infinite
545 << " ponder: " << ponder
546 << " time: " << myTime
547 << " increment: " << myIncrement
548 << " moves to go: " << movesToGo
552 // We're ready to start thinking. Call the iterative deepening loop function
553 Move ponderMove = MOVE_NONE;
554 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
556 // Print final search statistics
557 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
561 int t = current_search_time();
563 LogFile << "Nodes: " << pos.nodes_searched()
564 << "\nNodes/second: " << (t > 0 ? int(pos.nodes_searched() * 1000 / t) : 0)
565 << "\nBest move: " << move_to_san(pos, bestMove);
568 pos.do_move(bestMove, st);
569 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
570 pos.undo_move(bestMove); // Return from think() with unchanged position
574 // This makes all the threads to go to sleep
575 ThreadsMgr.set_active_threads(1);
577 // If we are pondering or in infinite search, we shouldn't print the
578 // best move before we are told to do so.
579 if (!StopRequest && (Pondering || InfiniteSearch))
580 wait_for_stop_or_ponderhit();
582 // Could be both MOVE_NONE when searching on a stalemate position
583 cout << "bestmove " << bestMove << " ponder " << ponderMove << endl;
591 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
592 // with increasing depth until the allocated thinking time has been consumed,
593 // user stops the search, or the maximum search depth is reached.
595 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
597 SearchStack ss[PLY_MAX_PLUS_2];
598 Value bestValues[PLY_MAX_PLUS_2];
599 int bestMoveChanges[PLY_MAX_PLUS_2];
600 int depth, researchCountFL, researchCountFH, aspirationDelta;
601 Value value, alpha, beta;
602 Move bestMove, easyMove;
604 // Moves to search are verified, scored and sorted
605 Rml.init(pos, searchMoves);
607 // Initialize FIXME move before Rml.init()
610 memset(ss, 0, 4 * sizeof(SearchStack));
611 *ponderMove = bestMove = easyMove = MOVE_NONE;
612 depth = aspirationDelta = 0;
613 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
614 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
616 // Handle special case of searching on a mate/stalemate position
619 cout << "info depth 0 score "
620 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
626 // Is one move significantly better than others after initial scoring ?
628 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin)
629 easyMove = Rml[0].pv[0];
631 // Iterative deepening loop
632 while (++depth <= PLY_MAX && (!MaxDepth || depth <= MaxDepth) && !StopRequest)
634 Rml.bestMoveChanges = researchCountFL = researchCountFH = 0;
635 cout << "info depth " << depth << endl;
637 // Calculate dynamic aspiration window based on previous iterations
638 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
640 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
641 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
643 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
644 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
646 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
647 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
650 // Start with a small aspiration window and, in case of fail high/low,
651 // research with bigger window until not failing high/low anymore.
654 // Search starting from ss+1 to allow calling update_gains()
655 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY, 0);
657 // Send PV line to GUI and write to transposition table in case the
658 // relevant entries have been overwritten during the search.
659 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
661 Rml[i].insert_pv_in_tt(pos);
662 cout << set960(pos.is_chess960())
663 << Rml[i].pv_info_to_uci(pos, depth, alpha, beta, i) << endl;
666 // Value cannot be trusted. Break out immediately!
670 assert(value >= alpha);
672 // In case of failing high/low increase aspiration window and research,
673 // otherwise exit the fail high/low loop.
676 beta = Min(beta + aspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
679 else if (value <= alpha)
681 AspirationFailLow = true;
682 StopOnPonderhit = false;
684 alpha = Max(alpha - aspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
691 // Collect info about search result
692 bestMove = Rml[0].pv[0];
693 bestValues[depth] = value;
694 bestMoveChanges[depth] = Rml.bestMoveChanges;
697 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
699 // Drop the easy move if differs from the new best move
700 if (bestMove != easyMove)
701 easyMove = MOVE_NONE;
703 if (UseTimeManagement && !StopRequest)
706 bool noMoreTime = false;
708 // Stop search early when the last two iterations returned a mate score
710 && abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
711 && abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
714 // Stop search early if one move seems to be much better than the
715 // others or if there is only a single legal move. In this latter
716 // case we search up to Iteration 8 anyway to get a proper score.
718 && easyMove == bestMove
720 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
721 && current_search_time() > TimeMgr.available_time() / 16)
722 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
723 && current_search_time() > TimeMgr.available_time() / 32)))
726 // Add some extra time if the best move has changed during the last two iterations
727 if (depth > 4 && depth < 50)
728 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
730 // Stop search if most of MaxSearchTime is consumed at the end of the
731 // iteration. We probably don't have enough time to search the first
732 // move at the next iteration anyway.
733 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
739 StopOnPonderhit = true;
746 *ponderMove = Rml[0].pv[1];
751 // search<>() is the main search function for both PV and non-PV nodes and for
752 // normal and SplitPoint nodes. When called just after a split point the search
753 // is simpler because we have already probed the hash table, done a null move
754 // search, and searched the first move before splitting, we don't have to repeat
755 // all this work again. We also don't need to store anything to the hash table
756 // here: This is taken care of after we return from the split point.
758 template <NodeType PvNode, bool SpNode, bool Root>
759 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
761 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
762 assert(beta > alpha && beta <= VALUE_INFINITE);
763 assert(PvNode || alpha == beta - 1);
764 assert((Root || ply > 0) && ply < PLY_MAX);
765 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
767 Move movesSearched[MOVES_MAX];
772 Move ttMove, move, excludedMove, threatMove;
775 Value bestValue, value, oldAlpha;
776 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
777 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
778 bool mateThreat = false;
779 int moveCount = 0, playedMoveCount = 0;
780 int threadID = pos.thread();
781 SplitPoint* sp = NULL;
783 refinedValue = bestValue = value = -VALUE_INFINITE;
785 isCheck = pos.is_check();
791 ttMove = excludedMove = MOVE_NONE;
792 threatMove = sp->threatMove;
793 mateThreat = sp->mateThreat;
794 goto split_point_start;
799 // Step 1. Initialize node and poll. Polling can abort search
800 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
801 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
802 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
804 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
810 // Step 2. Check for aborted search and immediate draw
812 || ThreadsMgr.cutoff_at_splitpoint(threadID)
814 || ply >= PLY_MAX - 1) && !Root)
817 // Step 3. Mate distance pruning
818 alpha = Max(value_mated_in(ply), alpha);
819 beta = Min(value_mate_in(ply+1), beta);
823 // Step 4. Transposition table lookup
824 // We don't want the score of a partial search to overwrite a previous full search
825 // TT value, so we use a different position key in case of an excluded move.
826 excludedMove = ss->excludedMove;
827 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
829 tte = TT.retrieve(posKey);
830 ttMove = tte ? tte->move() : MOVE_NONE;
832 // At PV nodes we check for exact scores, while at non-PV nodes we check for
833 // and return a fail high/low. Biggest advantage at probing at PV nodes is
834 // to have a smooth experience in analysis mode.
837 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
838 : ok_to_use_TT(tte, depth, beta, ply)))
841 ss->bestMove = ttMove; // Can be MOVE_NONE
842 return value_from_tt(tte->value(), ply);
845 // Step 5. Evaluate the position statically and
846 // update gain statistics of parent move.
848 ss->eval = ss->evalMargin = VALUE_NONE;
851 assert(tte->static_value() != VALUE_NONE);
853 ss->eval = tte->static_value();
854 ss->evalMargin = tte->static_value_margin();
855 refinedValue = refine_eval(tte, ss->eval, ply);
859 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
860 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
863 // Save gain for the parent non-capture move
864 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
866 // Step 6. Razoring (is omitted in PV nodes)
868 && depth < RazorDepth
870 && refinedValue < beta - razor_margin(depth)
871 && ttMove == MOVE_NONE
872 && !value_is_mate(beta)
873 && !pos.has_pawn_on_7th(pos.side_to_move()))
875 Value rbeta = beta - razor_margin(depth);
876 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
878 // Logically we should return (v + razor_margin(depth)), but
879 // surprisingly this did slightly weaker in tests.
883 // Step 7. Static null move pruning (is omitted in PV nodes)
884 // We're betting that the opponent doesn't have a move that will reduce
885 // the score by more than futility_margin(depth) if we do a null move.
888 && depth < RazorDepth
890 && refinedValue >= beta + futility_margin(depth, 0)
891 && !value_is_mate(beta)
892 && pos.non_pawn_material(pos.side_to_move()))
893 return refinedValue - futility_margin(depth, 0);
895 // Step 8. Null move search with verification search (is omitted in PV nodes)
900 && refinedValue >= beta
901 && !value_is_mate(beta)
902 && pos.non_pawn_material(pos.side_to_move()))
904 ss->currentMove = MOVE_NULL;
906 // Null move dynamic reduction based on depth
907 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
909 // Null move dynamic reduction based on value
910 if (refinedValue - beta > PawnValueMidgame)
913 pos.do_null_move(st);
914 (ss+1)->skipNullMove = true;
915 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
916 (ss+1)->skipNullMove = false;
917 pos.undo_null_move();
919 if (nullValue >= beta)
921 // Do not return unproven mate scores
922 if (nullValue >= value_mate_in(PLY_MAX))
925 if (depth < 6 * ONE_PLY)
928 // Do verification search at high depths
929 ss->skipNullMove = true;
930 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
931 ss->skipNullMove = false;
938 // The null move failed low, which means that we may be faced with
939 // some kind of threat. If the previous move was reduced, check if
940 // the move that refuted the null move was somehow connected to the
941 // move which was reduced. If a connection is found, return a fail
942 // low score (which will cause the reduced move to fail high in the
943 // parent node, which will trigger a re-search with full depth).
944 if (nullValue == value_mated_in(ply + 2))
947 threatMove = (ss+1)->bestMove;
948 if ( depth < ThreatDepth
950 && threatMove != MOVE_NONE
951 && connected_moves(pos, (ss-1)->currentMove, threatMove))
956 // Step 9. Internal iterative deepening
957 if ( depth >= IIDDepth[PvNode]
958 && ttMove == MOVE_NONE
959 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
961 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
963 ss->skipNullMove = true;
964 search<PvNode>(pos, ss, alpha, beta, d, ply);
965 ss->skipNullMove = false;
967 ttMove = ss->bestMove;
968 tte = TT.retrieve(posKey);
971 // Expensive mate threat detection (only for PV nodes)
973 mateThreat = pos.has_mate_threat();
975 split_point_start: // At split points actual search starts from here
977 // Initialize a MovePicker object for the current position
978 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
980 ss->bestMove = MOVE_NONE;
981 futilityBase = ss->eval + ss->evalMargin;
982 singularExtensionNode = !Root
984 && depth >= SingularExtensionDepth[PvNode]
987 && !excludedMove // Do not allow recursive singular extension search
988 && (tte->type() & VALUE_TYPE_LOWER)
989 && tte->depth() >= depth - 3 * ONE_PLY;
992 lock_grab(&(sp->lock));
993 bestValue = sp->bestValue;
996 // Step 10. Loop through moves
997 // Loop through all legal moves until no moves remain or a beta cutoff occurs
998 while ( bestValue < beta
999 && (move = mp.get_next_move()) != MOVE_NONE
1000 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1002 assert(move_is_ok(move));
1006 moveCount = ++sp->moveCount;
1007 lock_release(&(sp->lock));
1009 else if (move == excludedMove)
1016 // This is used by time management
1017 FirstRootMove = (moveCount == 1);
1019 // Save the current node count before the move is searched
1020 nodes = pos.nodes_searched();
1022 // If it's time to send nodes info, do it here where we have the
1023 // correct accumulated node counts searched by each thread.
1024 if (SendSearchedNodes)
1026 SendSearchedNodes = false;
1027 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1030 if (current_search_time() >= 1000)
1031 cout << "info currmove " << move
1032 << " currmovenumber " << moveCount << endl;
1035 isPvMove = (PvNode && moveCount <= (Root ? MultiPV : 1));
1036 moveIsCheck = pos.move_is_check(move, ci);
1037 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1039 // Step 11. Decide the new search depth
1040 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, mateThreat, &dangerous);
1042 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1043 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1044 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1045 // lower than ttValue minus a margin then we extend ttMove.
1046 if ( singularExtensionNode
1047 && move == tte->move()
1050 Value ttValue = value_from_tt(tte->value(), ply);
1052 if (abs(ttValue) < VALUE_KNOWN_WIN)
1054 Value b = ttValue - depth;
1055 ss->excludedMove = move;
1056 ss->skipNullMove = true;
1057 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1058 ss->skipNullMove = false;
1059 ss->excludedMove = MOVE_NONE;
1060 ss->bestMove = MOVE_NONE;
1066 // Update current move (this must be done after singular extension search)
1067 ss->currentMove = move;
1068 newDepth = depth - ONE_PLY + ext;
1070 // Step 12. Futility pruning (is omitted in PV nodes)
1072 && !captureOrPromotion
1076 && !move_is_castle(move))
1078 // Move count based pruning
1079 if ( moveCount >= futility_move_count(depth)
1080 && !(threatMove && connected_threat(pos, move, threatMove))
1081 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1084 lock_grab(&(sp->lock));
1089 // Value based pruning
1090 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1091 // but fixing this made program slightly weaker.
1092 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1093 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1094 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1096 if (futilityValueScaled < beta)
1100 lock_grab(&(sp->lock));
1101 if (futilityValueScaled > sp->bestValue)
1102 sp->bestValue = bestValue = futilityValueScaled;
1104 else if (futilityValueScaled > bestValue)
1105 bestValue = futilityValueScaled;
1110 // Prune moves with negative SEE at low depths
1111 if ( predictedDepth < 2 * ONE_PLY
1112 && bestValue > value_mated_in(PLY_MAX)
1113 && pos.see_sign(move) < 0)
1116 lock_grab(&(sp->lock));
1122 // Step 13. Make the move
1123 pos.do_move(move, st, ci, moveIsCheck);
1125 if (!SpNode && !captureOrPromotion)
1126 movesSearched[playedMoveCount++] = move;
1128 // Step extra. pv search (only in PV nodes)
1129 // The first move in list is the expected PV
1132 // Aspiration window is disabled in multi-pv case
1133 if (Root && MultiPV > 1)
1134 alpha = -VALUE_INFINITE;
1136 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1140 // Step 14. Reduced depth search
1141 // If the move fails high will be re-searched at full depth.
1142 bool doFullDepthSearch = true;
1144 if ( depth >= 3 * ONE_PLY
1145 && !captureOrPromotion
1147 && !move_is_castle(move)
1148 && ss->killers[0] != move
1149 && ss->killers[1] != move)
1151 ss->reduction = reduction<PvNode>(depth, moveCount);
1154 alpha = SpNode ? sp->alpha : alpha;
1155 Depth d = newDepth - ss->reduction;
1156 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1158 doFullDepthSearch = (value > alpha);
1160 ss->reduction = DEPTH_ZERO; // Restore original reduction
1163 // Step 15. Full depth search
1164 if (doFullDepthSearch)
1166 alpha = SpNode ? sp->alpha : alpha;
1167 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1169 // Step extra. pv search (only in PV nodes)
1170 // Search only for possible new PV nodes, if instead value >= beta then
1171 // parent node fails low with value <= alpha and tries another move.
1172 if (PvNode && value > alpha && (Root || value < beta))
1173 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1177 // Step 16. Undo move
1178 pos.undo_move(move);
1180 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1182 // Step 17. Check for new best move
1185 lock_grab(&(sp->lock));
1186 bestValue = sp->bestValue;
1190 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1195 sp->bestValue = value;
1197 if (!Root && value > alpha)
1199 if (PvNode && value < beta) // We want always alpha < beta
1207 sp->betaCutoff = true;
1209 if (value == value_mate_in(ply + 1))
1210 ss->mateKiller = move;
1212 ss->bestMove = move;
1215 sp->ss->bestMove = move;
1221 // Finished searching the move. If StopRequest is true, the search
1222 // was aborted because the user interrupted the search or because we
1223 // ran out of time. In this case, the return value of the search cannot
1224 // be trusted, and we break out of the loop without updating the best
1229 // Remember searched nodes counts for this move
1230 mp.rm->nodes += pos.nodes_searched() - nodes;
1232 // PV move or new best move ?
1233 if (isPvMove || value > alpha)
1236 ss->bestMove = move;
1237 mp.rm->pv_score = value;
1238 mp.rm->extract_pv_from_tt(pos);
1240 // We record how often the best move has been changed in each
1241 // iteration. This information is used for time management: When
1242 // the best move changes frequently, we allocate some more time.
1243 if (!isPvMove && MultiPV == 1)
1244 Rml.bestMoveChanges++;
1246 Rml.sort_multipv(moveCount);
1248 // Update alpha. In multi-pv we don't use aspiration window, so
1249 // set alpha equal to minimum score among the PV lines.
1251 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1252 else if (value > alpha)
1256 mp.rm->pv_score = -VALUE_INFINITE;
1260 // Step 18. Check for split
1263 && depth >= ThreadsMgr.min_split_depth()
1264 && ThreadsMgr.active_threads() > 1
1266 && ThreadsMgr.available_thread_exists(threadID)
1268 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1269 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1270 threatMove, mateThreat, moveCount, &mp, PvNode);
1273 // Step 19. Check for mate and stalemate
1274 // All legal moves have been searched and if there are
1275 // no legal moves, it must be mate or stalemate.
1276 // If one move was excluded return fail low score.
1277 if (!SpNode && !moveCount)
1278 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1280 // Step 20. Update tables
1281 // If the search is not aborted, update the transposition table,
1282 // history counters, and killer moves.
1283 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1285 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1286 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1287 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1289 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1291 // Update killers and history only for non capture moves that fails high
1292 if ( bestValue >= beta
1293 && !pos.move_is_capture_or_promotion(move))
1295 update_history(pos, move, depth, movesSearched, playedMoveCount);
1296 update_killers(move, ss->killers);
1302 // Here we have the lock still grabbed
1303 sp->slaves[threadID] = 0;
1304 sp->nodes += pos.nodes_searched();
1305 lock_release(&(sp->lock));
1308 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1313 // qsearch() is the quiescence search function, which is called by the main
1314 // search function when the remaining depth is zero (or, to be more precise,
1315 // less than ONE_PLY).
1317 template <NodeType PvNode>
1318 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1320 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1321 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1322 assert(PvNode || alpha == beta - 1);
1324 assert(ply > 0 && ply < PLY_MAX);
1325 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1329 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1330 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1333 Value oldAlpha = alpha;
1335 ss->bestMove = ss->currentMove = MOVE_NONE;
1337 // Check for an instant draw or maximum ply reached
1338 if (pos.is_draw() || ply >= PLY_MAX - 1)
1341 // Decide whether or not to include checks, this fixes also the type of
1342 // TT entry depth that we are going to use. Note that in qsearch we use
1343 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1344 isCheck = pos.is_check();
1345 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1347 // Transposition table lookup. At PV nodes, we don't use the TT for
1348 // pruning, but only for move ordering.
1349 tte = TT.retrieve(pos.get_key());
1350 ttMove = (tte ? tte->move() : MOVE_NONE);
1352 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1354 ss->bestMove = ttMove; // Can be MOVE_NONE
1355 return value_from_tt(tte->value(), ply);
1358 // Evaluate the position statically
1361 bestValue = futilityBase = -VALUE_INFINITE;
1362 ss->eval = evalMargin = VALUE_NONE;
1363 enoughMaterial = false;
1369 assert(tte->static_value() != VALUE_NONE);
1371 evalMargin = tte->static_value_margin();
1372 ss->eval = bestValue = tte->static_value();
1375 ss->eval = bestValue = evaluate(pos, evalMargin);
1377 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1379 // Stand pat. Return immediately if static value is at least beta
1380 if (bestValue >= beta)
1383 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1388 if (PvNode && bestValue > alpha)
1391 // Futility pruning parameters, not needed when in check
1392 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1393 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1396 // Initialize a MovePicker object for the current position, and prepare
1397 // to search the moves. Because the depth is <= 0 here, only captures,
1398 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1400 MovePicker mp(pos, ttMove, depth, H);
1403 // Loop through the moves until no moves remain or a beta cutoff occurs
1404 while ( alpha < beta
1405 && (move = mp.get_next_move()) != MOVE_NONE)
1407 assert(move_is_ok(move));
1409 moveIsCheck = pos.move_is_check(move, ci);
1417 && !move_is_promotion(move)
1418 && !pos.move_is_passed_pawn_push(move))
1420 futilityValue = futilityBase
1421 + pos.endgame_value_of_piece_on(move_to(move))
1422 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1424 if (futilityValue < alpha)
1426 if (futilityValue > bestValue)
1427 bestValue = futilityValue;
1431 // Prune moves with negative or equal SEE
1432 if ( futilityBase < beta
1433 && depth < DEPTH_ZERO
1434 && bestValue > value_mated_in(PLY_MAX)
1435 && pos.see(move) <= 0)
1439 // Detect non-capture evasions that are candidate to be pruned
1440 evasionPrunable = isCheck
1441 && bestValue > value_mated_in(PLY_MAX)
1442 && !pos.move_is_capture(move)
1443 && !pos.can_castle(pos.side_to_move());
1445 // Don't search moves with negative SEE values
1447 && (!isCheck || evasionPrunable)
1449 && !move_is_promotion(move)
1450 && pos.see_sign(move) < 0)
1453 // Don't search useless checks
1458 && !pos.move_is_capture_or_promotion(move)
1459 && ss->eval + PawnValueMidgame / 4 < beta
1460 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1462 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1463 bestValue = ss->eval + PawnValueMidgame / 4;
1468 // Update current move
1469 ss->currentMove = move;
1471 // Make and search the move
1472 pos.do_move(move, st, ci, moveIsCheck);
1473 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1474 pos.undo_move(move);
1476 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1479 if (value > bestValue)
1485 ss->bestMove = move;
1490 // All legal moves have been searched. A special case: If we're in check
1491 // and no legal moves were found, it is checkmate.
1492 if (isCheck && bestValue == -VALUE_INFINITE)
1493 return value_mated_in(ply);
1495 // Update transposition table
1496 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1497 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1499 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1505 // qsearch_scoring() scores each move of a list using a qsearch() evaluation,
1506 // it is used in RootMoveList to get an initial scoring.
1507 void qsearch_scoring(Position& pos, MoveStack* mlist, MoveStack* last) {
1509 SearchStack ss[PLY_MAX_PLUS_2];
1512 memset(ss, 0, 4 * sizeof(SearchStack));
1513 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
1515 for (MoveStack* cur = mlist; cur != last; cur++)
1517 ss[0].currentMove = cur->move;
1518 pos.do_move(cur->move, st);
1519 cur->score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
1520 pos.undo_move(cur->move);
1525 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1526 // bestValue is updated only when returning false because in that case move
1529 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1531 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1532 Square from, to, ksq, victimSq;
1535 Value futilityValue, bv = *bestValue;
1537 from = move_from(move);
1539 them = opposite_color(pos.side_to_move());
1540 ksq = pos.king_square(them);
1541 kingAtt = pos.attacks_from<KING>(ksq);
1542 pc = pos.piece_on(from);
1544 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1545 oldAtt = pos.attacks_from(pc, from, occ);
1546 newAtt = pos.attacks_from(pc, to, occ);
1548 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1549 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1551 if (!(b && (b & (b - 1))))
1554 // Rule 2. Queen contact check is very dangerous
1555 if ( type_of_piece(pc) == QUEEN
1556 && bit_is_set(kingAtt, to))
1559 // Rule 3. Creating new double threats with checks
1560 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1564 victimSq = pop_1st_bit(&b);
1565 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1567 // Note that here we generate illegal "double move"!
1568 if ( futilityValue >= beta
1569 && pos.see_sign(make_move(from, victimSq)) >= 0)
1572 if (futilityValue > bv)
1576 // Update bestValue only if check is not dangerous (because we will prune the move)
1582 // connected_moves() tests whether two moves are 'connected' in the sense
1583 // that the first move somehow made the second move possible (for instance
1584 // if the moving piece is the same in both moves). The first move is assumed
1585 // to be the move that was made to reach the current position, while the
1586 // second move is assumed to be a move from the current position.
1588 bool connected_moves(const Position& pos, Move m1, Move m2) {
1590 Square f1, t1, f2, t2;
1593 assert(m1 && move_is_ok(m1));
1594 assert(m2 && move_is_ok(m2));
1596 // Case 1: The moving piece is the same in both moves
1602 // Case 2: The destination square for m2 was vacated by m1
1608 // Case 3: Moving through the vacated square
1609 if ( piece_is_slider(pos.piece_on(f2))
1610 && bit_is_set(squares_between(f2, t2), f1))
1613 // Case 4: The destination square for m2 is defended by the moving piece in m1
1614 p = pos.piece_on(t1);
1615 if (bit_is_set(pos.attacks_from(p, t1), t2))
1618 // Case 5: Discovered check, checking piece is the piece moved in m1
1619 if ( piece_is_slider(p)
1620 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1621 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1623 // discovered_check_candidates() works also if the Position's side to
1624 // move is the opposite of the checking piece.
1625 Color them = opposite_color(pos.side_to_move());
1626 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1628 if (bit_is_set(dcCandidates, f2))
1635 // value_is_mate() checks if the given value is a mate one eventually
1636 // compensated for the ply.
1638 bool value_is_mate(Value value) {
1640 assert(abs(value) <= VALUE_INFINITE);
1642 return value <= value_mated_in(PLY_MAX)
1643 || value >= value_mate_in(PLY_MAX);
1647 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1648 // "plies to mate from the current ply". Non-mate scores are unchanged.
1649 // The function is called before storing a value to the transposition table.
1651 Value value_to_tt(Value v, int ply) {
1653 if (v >= value_mate_in(PLY_MAX))
1656 if (v <= value_mated_in(PLY_MAX))
1663 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1664 // the transposition table to a mate score corrected for the current ply.
1666 Value value_from_tt(Value v, int ply) {
1668 if (v >= value_mate_in(PLY_MAX))
1671 if (v <= value_mated_in(PLY_MAX))
1678 // extension() decides whether a move should be searched with normal depth,
1679 // or with extended depth. Certain classes of moves (checking moves, in
1680 // particular) are searched with bigger depth than ordinary moves and in
1681 // any case are marked as 'dangerous'. Note that also if a move is not
1682 // extended, as example because the corresponding UCI option is set to zero,
1683 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1684 template <NodeType PvNode>
1685 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1686 bool moveIsCheck, bool mateThreat, bool* dangerous) {
1688 assert(m != MOVE_NONE);
1690 Depth result = DEPTH_ZERO;
1691 *dangerous = moveIsCheck | mateThreat;
1695 if (moveIsCheck && pos.see_sign(m) >= 0)
1696 result += CheckExtension[PvNode];
1699 result += MateThreatExtension[PvNode];
1702 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1704 Color c = pos.side_to_move();
1705 if (relative_rank(c, move_to(m)) == RANK_7)
1707 result += PawnPushTo7thExtension[PvNode];
1710 if (pos.pawn_is_passed(c, move_to(m)))
1712 result += PassedPawnExtension[PvNode];
1717 if ( captureOrPromotion
1718 && pos.type_of_piece_on(move_to(m)) != PAWN
1719 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1720 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1721 && !move_is_promotion(m)
1724 result += PawnEndgameExtension[PvNode];
1729 && captureOrPromotion
1730 && pos.type_of_piece_on(move_to(m)) != PAWN
1731 && pos.see_sign(m) >= 0)
1733 result += ONE_PLY / 2;
1737 return Min(result, ONE_PLY);
1741 // connected_threat() tests whether it is safe to forward prune a move or if
1742 // is somehow connected to the threat move returned by null search.
1744 bool connected_threat(const Position& pos, Move m, Move threat) {
1746 assert(move_is_ok(m));
1747 assert(threat && move_is_ok(threat));
1748 assert(!pos.move_is_check(m));
1749 assert(!pos.move_is_capture_or_promotion(m));
1750 assert(!pos.move_is_passed_pawn_push(m));
1752 Square mfrom, mto, tfrom, tto;
1754 mfrom = move_from(m);
1756 tfrom = move_from(threat);
1757 tto = move_to(threat);
1759 // Case 1: Don't prune moves which move the threatened piece
1763 // Case 2: If the threatened piece has value less than or equal to the
1764 // value of the threatening piece, don't prune moves which defend it.
1765 if ( pos.move_is_capture(threat)
1766 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1767 || pos.type_of_piece_on(tfrom) == KING)
1768 && pos.move_attacks_square(m, tto))
1771 // Case 3: If the moving piece in the threatened move is a slider, don't
1772 // prune safe moves which block its ray.
1773 if ( piece_is_slider(pos.piece_on(tfrom))
1774 && bit_is_set(squares_between(tfrom, tto), mto)
1775 && pos.see_sign(m) >= 0)
1782 // ok_to_use_TT() returns true if a transposition table score
1783 // can be used at a given point in search.
1785 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1787 Value v = value_from_tt(tte->value(), ply);
1789 return ( tte->depth() >= depth
1790 || v >= Max(value_mate_in(PLY_MAX), beta)
1791 || v < Min(value_mated_in(PLY_MAX), beta))
1793 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1794 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1798 // refine_eval() returns the transposition table score if
1799 // possible otherwise falls back on static position evaluation.
1801 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1805 Value v = value_from_tt(tte->value(), ply);
1807 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1808 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1815 // update_history() registers a good move that produced a beta-cutoff
1816 // in history and marks as failures all the other moves of that ply.
1818 void update_history(const Position& pos, Move move, Depth depth,
1819 Move movesSearched[], int moveCount) {
1821 Value bonus = Value(int(depth) * int(depth));
1823 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1825 for (int i = 0; i < moveCount - 1; i++)
1827 m = movesSearched[i];
1831 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1836 // update_killers() add a good move that produced a beta-cutoff
1837 // among the killer moves of that ply.
1839 void update_killers(Move m, Move killers[]) {
1841 if (m != killers[0])
1843 killers[1] = killers[0];
1849 // update_gains() updates the gains table of a non-capture move given
1850 // the static position evaluation before and after the move.
1852 void update_gains(const Position& pos, Move m, Value before, Value after) {
1855 && before != VALUE_NONE
1856 && after != VALUE_NONE
1857 && pos.captured_piece_type() == PIECE_TYPE_NONE
1858 && !move_is_special(m))
1859 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1862 // current_search_time() returns the number of milliseconds which have passed
1863 // since the beginning of the current search.
1865 int current_search_time() {
1867 return get_system_time() - SearchStartTime;
1871 // value_to_uci() converts a value to a string suitable for use with the UCI
1872 // protocol specifications:
1874 // cp <x> The score from the engine's point of view in centipawns.
1875 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1876 // use negative values for y.
1878 std::string value_to_uci(Value v) {
1880 std::stringstream s;
1882 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1883 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1885 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2);
1891 // speed_to_uci() returns a string with time stats of current search suitable
1892 // to be sent to UCI gui.
1894 std::string speed_to_uci(int64_t nodes) {
1896 std::stringstream s;
1897 int t = current_search_time();
1899 s << " nodes " << nodes
1900 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1907 // poll() performs two different functions: It polls for user input, and it
1908 // looks at the time consumed so far and decides if it's time to abort the
1911 void poll(const Position& pos) {
1913 static int lastInfoTime;
1914 int t = current_search_time();
1917 if (input_available())
1919 // We are line oriented, don't read single chars
1920 std::string command;
1922 if (!std::getline(std::cin, command))
1925 if (command == "quit")
1927 // Quit the program as soon as possible
1929 QuitRequest = StopRequest = true;
1932 else if (command == "stop")
1934 // Stop calculating as soon as possible, but still send the "bestmove"
1935 // and possibly the "ponder" token when finishing the search.
1939 else if (command == "ponderhit")
1941 // The opponent has played the expected move. GUI sends "ponderhit" if
1942 // we were told to ponder on the same move the opponent has played. We
1943 // should continue searching but switching from pondering to normal search.
1946 if (StopOnPonderhit)
1951 // Print search information
1955 else if (lastInfoTime > t)
1956 // HACK: Must be a new search where we searched less than
1957 // NodesBetweenPolls nodes during the first second of search.
1960 else if (t - lastInfoTime >= 1000)
1967 if (dbg_show_hit_rate)
1968 dbg_print_hit_rate();
1970 // Send info on searched nodes as soon as we return to root
1971 SendSearchedNodes = true;
1974 // Should we stop the search?
1978 bool stillAtFirstMove = FirstRootMove
1979 && !AspirationFailLow
1980 && t > TimeMgr.available_time();
1982 bool noMoreTime = t > TimeMgr.maximum_time()
1983 || stillAtFirstMove;
1985 if ( (UseTimeManagement && noMoreTime)
1986 || (ExactMaxTime && t >= ExactMaxTime)
1987 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
1992 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1993 // while the program is pondering. The point is to work around a wrinkle in
1994 // the UCI protocol: When pondering, the engine is not allowed to give a
1995 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1996 // We simply wait here until one of these commands is sent, and return,
1997 // after which the bestmove and pondermove will be printed.
1999 void wait_for_stop_or_ponderhit() {
2001 std::string command;
2005 // Wait for a command from stdin
2006 if (!std::getline(std::cin, command))
2009 if (command == "quit")
2014 else if (command == "ponderhit" || command == "stop")
2020 // init_thread() is the function which is called when a new thread is
2021 // launched. It simply calls the idle_loop() function with the supplied
2022 // threadID. There are two versions of this function; one for POSIX
2023 // threads and one for Windows threads.
2025 #if !defined(_MSC_VER)
2027 void* init_thread(void* threadID) {
2029 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2035 DWORD WINAPI init_thread(LPVOID threadID) {
2037 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2044 /// The ThreadsManager class
2047 // read_uci_options() updates number of active threads and other internal
2048 // parameters according to the UCI options values. It is called before
2049 // to start a new search.
2051 void ThreadsManager::read_uci_options() {
2053 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2054 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2055 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2056 activeThreads = Options["Threads"].value<int>();
2060 // idle_loop() is where the threads are parked when they have no work to do.
2061 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2062 // object for which the current thread is the master.
2064 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2066 assert(threadID >= 0 && threadID < MAX_THREADS);
2069 bool allFinished = false;
2073 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2074 // master should exit as last one.
2075 if (allThreadsShouldExit)
2078 threads[threadID].state = THREAD_TERMINATED;
2082 // If we are not thinking, wait for a condition to be signaled
2083 // instead of wasting CPU time polling for work.
2084 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2085 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2087 assert(!sp || useSleepingThreads);
2088 assert(threadID != 0 || useSleepingThreads);
2090 if (threads[threadID].state == THREAD_INITIALIZING)
2091 threads[threadID].state = THREAD_AVAILABLE;
2093 // Grab the lock to avoid races with wake_sleeping_thread()
2094 lock_grab(&sleepLock[threadID]);
2096 // If we are master and all slaves have finished do not go to sleep
2097 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2098 allFinished = (i == activeThreads);
2100 if (allFinished || allThreadsShouldExit)
2102 lock_release(&sleepLock[threadID]);
2106 // Do sleep here after retesting sleep conditions
2107 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2108 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2110 lock_release(&sleepLock[threadID]);
2113 // If this thread has been assigned work, launch a search
2114 if (threads[threadID].state == THREAD_WORKISWAITING)
2116 assert(!allThreadsShouldExit);
2118 threads[threadID].state = THREAD_SEARCHING;
2120 // Copy SplitPoint position and search stack and call search()
2121 // with SplitPoint template parameter set to true.
2122 SearchStack ss[PLY_MAX_PLUS_2];
2123 SplitPoint* tsp = threads[threadID].splitPoint;
2124 Position pos(*tsp->pos, threadID);
2126 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2130 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2132 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2134 assert(threads[threadID].state == THREAD_SEARCHING);
2136 threads[threadID].state = THREAD_AVAILABLE;
2138 // Wake up master thread so to allow it to return from the idle loop in
2139 // case we are the last slave of the split point.
2140 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2141 wake_sleeping_thread(tsp->master);
2144 // If this thread is the master of a split point and all slaves have
2145 // finished their work at this split point, return from the idle loop.
2146 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2147 allFinished = (i == activeThreads);
2151 // Because sp->slaves[] is reset under lock protection,
2152 // be sure sp->lock has been released before to return.
2153 lock_grab(&(sp->lock));
2154 lock_release(&(sp->lock));
2156 // In helpful master concept a master can help only a sub-tree, and
2157 // because here is all finished is not possible master is booked.
2158 assert(threads[threadID].state == THREAD_AVAILABLE);
2160 threads[threadID].state = THREAD_SEARCHING;
2167 // init_threads() is called during startup. It launches all helper threads,
2168 // and initializes the split point stack and the global locks and condition
2171 void ThreadsManager::init_threads() {
2173 int i, arg[MAX_THREADS];
2176 // Initialize global locks
2179 for (i = 0; i < MAX_THREADS; i++)
2181 lock_init(&sleepLock[i]);
2182 cond_init(&sleepCond[i]);
2185 // Initialize splitPoints[] locks
2186 for (i = 0; i < MAX_THREADS; i++)
2187 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2188 lock_init(&(threads[i].splitPoints[j].lock));
2190 // Will be set just before program exits to properly end the threads
2191 allThreadsShouldExit = false;
2193 // Threads will be put all threads to sleep as soon as created
2196 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2197 threads[0].state = THREAD_SEARCHING;
2198 for (i = 1; i < MAX_THREADS; i++)
2199 threads[i].state = THREAD_INITIALIZING;
2201 // Launch the helper threads
2202 for (i = 1; i < MAX_THREADS; i++)
2206 #if !defined(_MSC_VER)
2207 pthread_t pthread[1];
2208 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2209 pthread_detach(pthread[0]);
2211 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2215 cout << "Failed to create thread number " << i << endl;
2219 // Wait until the thread has finished launching and is gone to sleep
2220 while (threads[i].state == THREAD_INITIALIZING) {}
2225 // exit_threads() is called when the program exits. It makes all the
2226 // helper threads exit cleanly.
2228 void ThreadsManager::exit_threads() {
2230 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2232 // Wake up all the threads and waits for termination
2233 for (int i = 1; i < MAX_THREADS; i++)
2235 wake_sleeping_thread(i);
2236 while (threads[i].state != THREAD_TERMINATED) {}
2239 // Now we can safely destroy the locks
2240 for (int i = 0; i < MAX_THREADS; i++)
2241 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2242 lock_destroy(&(threads[i].splitPoints[j].lock));
2244 lock_destroy(&mpLock);
2246 // Now we can safely destroy the wait conditions
2247 for (int i = 0; i < MAX_THREADS; i++)
2249 lock_destroy(&sleepLock[i]);
2250 cond_destroy(&sleepCond[i]);
2255 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2256 // the thread's currently active split point, or in some ancestor of
2257 // the current split point.
2259 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2261 assert(threadID >= 0 && threadID < activeThreads);
2263 SplitPoint* sp = threads[threadID].splitPoint;
2265 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2270 // thread_is_available() checks whether the thread with threadID "slave" is
2271 // available to help the thread with threadID "master" at a split point. An
2272 // obvious requirement is that "slave" must be idle. With more than two
2273 // threads, this is not by itself sufficient: If "slave" is the master of
2274 // some active split point, it is only available as a slave to the other
2275 // threads which are busy searching the split point at the top of "slave"'s
2276 // split point stack (the "helpful master concept" in YBWC terminology).
2278 bool ThreadsManager::thread_is_available(int slave, int master) const {
2280 assert(slave >= 0 && slave < activeThreads);
2281 assert(master >= 0 && master < activeThreads);
2282 assert(activeThreads > 1);
2284 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2287 // Make a local copy to be sure doesn't change under our feet
2288 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2290 // No active split points means that the thread is available as
2291 // a slave for any other thread.
2292 if (localActiveSplitPoints == 0 || activeThreads == 2)
2295 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2296 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2297 // could have been set to 0 by another thread leading to an out of bound access.
2298 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2305 // available_thread_exists() tries to find an idle thread which is available as
2306 // a slave for the thread with threadID "master".
2308 bool ThreadsManager::available_thread_exists(int master) const {
2310 assert(master >= 0 && master < activeThreads);
2311 assert(activeThreads > 1);
2313 for (int i = 0; i < activeThreads; i++)
2314 if (thread_is_available(i, master))
2321 // split() does the actual work of distributing the work at a node between
2322 // several available threads. If it does not succeed in splitting the
2323 // node (because no idle threads are available, or because we have no unused
2324 // split point objects), the function immediately returns. If splitting is
2325 // possible, a SplitPoint object is initialized with all the data that must be
2326 // copied to the helper threads and we tell our helper threads that they have
2327 // been assigned work. This will cause them to instantly leave their idle loops and
2328 // call search().When all threads have returned from search() then split() returns.
2330 template <bool Fake>
2331 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2332 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2333 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2334 assert(pos.is_ok());
2335 assert(ply > 0 && ply < PLY_MAX);
2336 assert(*bestValue >= -VALUE_INFINITE);
2337 assert(*bestValue <= *alpha);
2338 assert(*alpha < beta);
2339 assert(beta <= VALUE_INFINITE);
2340 assert(depth > DEPTH_ZERO);
2341 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2342 assert(activeThreads > 1);
2344 int i, master = pos.thread();
2345 Thread& masterThread = threads[master];
2349 // If no other thread is available to help us, or if we have too many
2350 // active split points, don't split.
2351 if ( !available_thread_exists(master)
2352 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2354 lock_release(&mpLock);
2358 // Pick the next available split point object from the split point stack
2359 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2361 // Initialize the split point object
2362 splitPoint.parent = masterThread.splitPoint;
2363 splitPoint.master = master;
2364 splitPoint.betaCutoff = false;
2365 splitPoint.ply = ply;
2366 splitPoint.depth = depth;
2367 splitPoint.threatMove = threatMove;
2368 splitPoint.mateThreat = mateThreat;
2369 splitPoint.alpha = *alpha;
2370 splitPoint.beta = beta;
2371 splitPoint.pvNode = pvNode;
2372 splitPoint.bestValue = *bestValue;
2374 splitPoint.moveCount = moveCount;
2375 splitPoint.pos = &pos;
2376 splitPoint.nodes = 0;
2378 for (i = 0; i < activeThreads; i++)
2379 splitPoint.slaves[i] = 0;
2381 masterThread.splitPoint = &splitPoint;
2383 // If we are here it means we are not available
2384 assert(masterThread.state != THREAD_AVAILABLE);
2386 int workersCnt = 1; // At least the master is included
2388 // Allocate available threads setting state to THREAD_BOOKED
2389 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2390 if (thread_is_available(i, master))
2392 threads[i].state = THREAD_BOOKED;
2393 threads[i].splitPoint = &splitPoint;
2394 splitPoint.slaves[i] = 1;
2398 assert(Fake || workersCnt > 1);
2400 // We can release the lock because slave threads are already booked and master is not available
2401 lock_release(&mpLock);
2403 // Tell the threads that they have work to do. This will make them leave
2405 for (i = 0; i < activeThreads; i++)
2406 if (i == master || splitPoint.slaves[i])
2408 assert(i == master || threads[i].state == THREAD_BOOKED);
2410 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2412 if (useSleepingThreads && i != master)
2413 wake_sleeping_thread(i);
2416 // Everything is set up. The master thread enters the idle loop, from
2417 // which it will instantly launch a search, because its state is
2418 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2419 // idle loop, which means that the main thread will return from the idle
2420 // loop when all threads have finished their work at this split point.
2421 idle_loop(master, &splitPoint);
2423 // We have returned from the idle loop, which means that all threads are
2424 // finished. Update alpha and bestValue, and return.
2427 *alpha = splitPoint.alpha;
2428 *bestValue = splitPoint.bestValue;
2429 masterThread.activeSplitPoints--;
2430 masterThread.splitPoint = splitPoint.parent;
2431 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2433 lock_release(&mpLock);
2437 // wake_sleeping_thread() wakes up the thread with the given threadID
2438 // when it is time to start a new search.
2440 void ThreadsManager::wake_sleeping_thread(int threadID) {
2442 lock_grab(&sleepLock[threadID]);
2443 cond_signal(&sleepCond[threadID]);
2444 lock_release(&sleepLock[threadID]);
2448 /// RootMove and RootMoveList method's definitions
2450 RootMove::RootMove() {
2453 pv_score = non_pv_score = -VALUE_INFINITE;
2457 RootMove& RootMove::operator=(const RootMove& rm) {
2459 const Move* src = rm.pv;
2462 // Avoid a costly full rm.pv[] copy
2463 do *dst++ = *src; while (*src++ != MOVE_NONE);
2466 pv_score = rm.pv_score;
2467 non_pv_score = rm.non_pv_score;
2471 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2472 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2473 // allow to always have a ponder move even when we fail high at root and also a
2474 // long PV to print that is important for position analysis.
2476 void RootMove::extract_pv_from_tt(Position& pos) {
2478 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2482 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2484 pos.do_move(pv[0], *st++);
2486 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2487 && tte->move() != MOVE_NONE
2488 && move_is_legal(pos, tte->move())
2490 && (!pos.is_draw() || ply < 2))
2492 pv[ply] = tte->move();
2493 pos.do_move(pv[ply++], *st++);
2495 pv[ply] = MOVE_NONE;
2497 do pos.undo_move(pv[--ply]); while (ply);
2500 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2501 // the PV back into the TT. This makes sure the old PV moves are searched
2502 // first, even if the old TT entries have been overwritten.
2504 void RootMove::insert_pv_in_tt(Position& pos) {
2506 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2509 Value v, m = VALUE_NONE;
2512 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2516 tte = TT.retrieve(k);
2518 // Don't overwrite existing correct entries
2519 if (!tte || tte->move() != pv[ply])
2521 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2522 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2524 pos.do_move(pv[ply], *st++);
2526 } while (pv[++ply] != MOVE_NONE);
2528 do pos.undo_move(pv[--ply]); while (ply);
2531 // pv_info_to_uci() returns a string with information on the current PV line
2532 // formatted according to UCI specification. It is called at each iteration
2533 // or after a new pv is found.
2535 std::string RootMove::pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvLine) {
2537 std::stringstream s, l;
2540 while (*m != MOVE_NONE)
2543 s << "info depth " << depth
2544 << " seldepth " << int(m - pv)
2545 << " multipv " << pvLine + 1
2546 << " score " << value_to_uci(pv_score)
2547 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2548 << speed_to_uci(pos.nodes_searched())
2549 << " pv " << l.str();
2555 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2557 MoveStack mlist[MOVES_MAX];
2561 bestMoveChanges = 0;
2563 // Generate all legal moves and score them
2564 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2565 qsearch_scoring(pos, mlist, last);
2567 // Add each move to the RootMoveList's vector
2568 for (MoveStack* cur = mlist; cur != last; cur++)
2570 // If we have a searchMoves[] list then verify cur->move
2571 // is in the list before to add it.
2572 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2574 if (searchMoves[0] && *sm != cur->move)
2578 rm.pv[0] = cur->move;
2579 rm.pv[1] = MOVE_NONE;
2580 rm.pv_score = Value(cur->score);