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/>.
40 #include "ucioption.h"
47 // Different node types, used as template parameter
48 enum NodeType { NonPV, PV };
50 // Set to true to force running with one thread. Used for debugging.
51 const bool FakeSplit = false;
53 // Lookup table to check if a Piece is a slider and its access function
54 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
55 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
57 // ThreadsManager class is used to handle all the threads related stuff like init,
58 // starting, parking and, the most important, launching a slave thread at a split
59 // point. All the access to shared thread data is done through this class.
61 class ThreadsManager {
62 /* As long as the single ThreadsManager object is defined as a global we don't
63 need to explicitly initialize to zero its data members because variables with
64 static storage duration are automatically set to zero before enter main()
67 Thread& operator[](int threadID) { return threads[threadID]; }
71 int min_split_depth() const { return minimumSplitDepth; }
72 int active_threads() const { return activeThreads; }
73 void set_active_threads(int cnt) { activeThreads = cnt; }
75 void read_uci_options();
76 bool available_thread_exists(int master) const;
77 bool thread_is_available(int slave, int master) const;
78 bool cutoff_at_splitpoint(int threadID) const;
79 void idle_loop(int threadID, SplitPoint* sp);
82 void split(Position& pos, SearchStack* ss, Value* alpha, const Value beta, Value* bestValue,
83 Depth depth, Move threatMove, int moveCount, MovePicker* mp, bool pvNode);
87 Depth minimumSplitDepth;
88 int maxThreadsPerSplitPoint;
89 bool useSleepingThreads;
91 volatile bool allThreadsShouldExit;
92 Thread threads[MAX_THREADS];
96 // RootMove struct is used for moves at the root of the tree. For each root
97 // move, we store two scores, a node count, and a PV (really a refutation
98 // in the case of moves which fail low). Value pv_score is normally set at
99 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
100 // according to the order in which moves are returned by MovePicker.
105 RootMove(const RootMove& rm) { *this = rm; }
106 RootMove& operator=(const RootMove& rm);
108 // RootMove::operator<() is the comparison function used when
109 // sorting the moves. A move m1 is considered to be better
110 // than a move m2 if it has an higher pv_score, or if it has
111 // equal pv_score but m1 has the higher non_pv_score. In this way
112 // we are guaranteed that PV moves are always sorted as first.
113 bool operator<(const RootMove& m) const {
114 return pv_score != m.pv_score ? pv_score < m.pv_score
115 : non_pv_score < m.non_pv_score;
118 void extract_pv_from_tt(Position& pos);
119 void insert_pv_in_tt(Position& pos);
120 std::string pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha, Value beta, int pvIdx);
125 Move pv[PLY_MAX_PLUS_2];
129 // RootMoveList struct is just a std::vector<> of RootMove objects,
130 // with an handful of methods above the standard ones.
132 struct RootMoveList : public std::vector<RootMove> {
134 typedef std::vector<RootMove> Base;
136 void init(Position& pos, Move searchMoves[]);
137 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
138 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
144 // Overload operator<<() to make it easier to print moves in a coordinate
145 // notation compatible with UCI protocol.
146 std::ostream& operator<<(std::ostream& os, Move m) {
148 bool chess960 = (os.iword(0) != 0); // See set960()
149 return os << move_to_uci(m, chess960);
153 // When formatting a move for std::cout we must know if we are in Chess960
154 // or not. To keep using the handy operator<<() on the move the trick is to
155 // embed this flag in the stream itself. Function-like named enum set960 is
156 // used as a custom manipulator and the stream internal general-purpose array,
157 // accessed through ios_base::iword(), is used to pass the flag to the move's
158 // operator<<() that will read it to properly format castling moves.
161 std::ostream& operator<< (std::ostream& os, const set960& f) {
163 os.iword(0) = int(f);
172 // Maximum depth for razoring
173 const Depth RazorDepth = 4 * ONE_PLY;
175 // Dynamic razoring margin based on depth
176 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
178 // Maximum depth for use of dynamic threat detection when null move fails low
179 const Depth ThreatDepth = 5 * ONE_PLY;
181 // Step 9. Internal iterative deepening
183 // Minimum depth for use of internal iterative deepening
184 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
186 // At Non-PV nodes we do an internal iterative deepening search
187 // when the static evaluation is bigger then beta - IIDMargin.
188 const Value IIDMargin = Value(0x100);
190 // Step 11. Decide the new search depth
192 // Extensions. Configurable UCI options
193 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
194 Depth CheckExtension[2], PawnPushTo7thExtension[2];
195 Depth PassedPawnExtension[2], PawnEndgameExtension[2];
197 // Minimum depth for use of singular extension
198 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
200 // Step 12. Futility pruning
202 // Futility margin for quiescence search
203 const Value FutilityMarginQS = Value(0x80);
205 // Futility lookup tables (initialized at startup) and their access functions
206 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
207 int FutilityMoveCountArray[32]; // [depth]
209 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
210 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
212 // Step 14. Reduced search
214 // Reduction lookup tables (initialized at startup) and their getter functions
215 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
217 template <NodeType PV>
218 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / ONE_PLY, 63)][Min(mn, 63)]; }
220 // Easy move margin. An easy move candidate must be at least this much
221 // better than the second best move.
222 const Value EasyMoveMargin = Value(0x200);
225 /// Namespace variables
234 int MultiPV, UCIMultiPV;
236 // Time management variables
237 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
238 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
239 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
244 std::ofstream LogFile;
246 // Skill level adjustment
248 bool SkillLevelEnabled;
251 // Multi-threads manager
252 ThreadsManager ThreadsMgr;
254 // Node counters, used only by thread[0] but try to keep in different cache
255 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
256 bool SendSearchedNodes;
258 int NodesBetweenPolls = 30000;
266 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
268 template <NodeType PvNode, bool SpNode, bool Root>
269 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
271 template <NodeType PvNode>
272 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
274 template <NodeType PvNode>
275 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
277 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO)
278 : search<PvNode, false, false>(pos, ss, alpha, beta, depth);
281 template <NodeType PvNode>
282 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
284 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
285 bool connected_moves(const Position& pos, Move m1, Move m2);
286 Value value_to_tt(Value v, int ply);
287 Value value_from_tt(Value v, int ply);
288 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
289 bool connected_threat(const Position& pos, Move m, Move threat);
290 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
291 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
292 void update_gains(const Position& pos, Move move, Value before, Value after);
293 void do_skill_level(Move* best, Move* ponder);
295 int current_search_time();
296 std::string value_to_uci(Value v);
297 std::string speed_to_uci(int64_t nodes);
298 void poll(const Position& pos);
299 void wait_for_stop_or_ponderhit();
301 #if !defined(_MSC_VER)
302 void* init_thread(void* threadID);
304 DWORD WINAPI init_thread(LPVOID threadID);
308 // MovePickerExt is an extended MovePicker used to choose at compile time
309 // the proper move source according to the type of node.
310 template<bool SpNode, bool Root> struct MovePickerExt;
312 // In Root nodes use RootMoveList as source. Score and sort the root moves
313 // before to search them.
314 template<> struct MovePickerExt<false, true> : public MovePicker {
316 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
317 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
319 Value score = VALUE_ZERO;
321 // Score root moves using standard ordering used in main search, the moves
322 // are scored according to the order in which they are returned by MovePicker.
323 // This is the second order score that is used to compare the moves when
324 // the first orders pv_score of both moves are equal.
325 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
326 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
327 if (rm->pv[0] == move)
329 rm->non_pv_score = score--;
337 Move get_next_move() {
344 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
347 RootMoveList::iterator rm;
351 // In SpNodes use split point's shared MovePicker object as move source
352 template<> struct MovePickerExt<true, false> : public MovePicker {
354 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
355 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
357 Move get_next_move() { return mp->get_next_move(); }
359 RootMoveList::iterator rm; // Dummy, needed to compile
363 // Default case, create and use a MovePicker object as source
364 template<> struct MovePickerExt<false, false> : public MovePicker {
366 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
367 : MovePicker(p, ttm, d, h, ss, b) {}
369 RootMoveList::iterator rm; // Dummy, needed to compile
375 /// init_threads() is called during startup. It initializes various lookup tables
376 /// and creates and launches search threads.
378 void init_threads() {
380 int d; // depth (ONE_PLY == 2)
381 int hd; // half depth (ONE_PLY == 1)
384 // Init reductions array
385 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
387 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
388 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
389 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
390 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
393 // Init futility margins array
394 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
395 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
397 // Init futility move count array
398 for (d = 0; d < 32; d++)
399 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
401 // Create and startup threads
402 ThreadsMgr.init_threads();
406 /// exit_threads() is a trampoline to access ThreadsMgr from outside of current file
407 void exit_threads() { ThreadsMgr.exit_threads(); }
410 /// perft() is our utility to verify move generation. All the legal moves up to
411 /// given depth are generated and counted and the sum returned.
413 int64_t perft(Position& pos, Depth depth) {
415 MoveStack mlist[MOVES_MAX];
420 // Generate all legal moves
421 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
423 // If we are at the last ply we don't need to do and undo
424 // the moves, just to count them.
425 if (depth <= ONE_PLY)
426 return int(last - mlist);
428 // Loop through all legal moves
430 for (MoveStack* cur = mlist; cur != last; cur++)
433 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
434 sum += perft(pos, depth - ONE_PLY);
441 /// think() is the external interface to Stockfish's search, and is called when
442 /// the program receives the UCI 'go' command. It initializes various global
443 /// variables, and calls id_loop(). It returns false when a quit command is
444 /// received during the search.
446 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
447 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
449 // Initialize global search-related variables
450 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
452 SearchStartTime = get_system_time();
453 ExactMaxTime = maxTime;
456 InfiniteSearch = infinite;
458 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
460 // Look for a book move, only during games, not tests
461 if (UseTimeManagement && Options["OwnBook"].value<bool>())
463 if (Options["Book File"].value<std::string>() != OpeningBook.name())
464 OpeningBook.open(Options["Book File"].value<std::string>());
466 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
467 if (bookMove != MOVE_NONE)
470 wait_for_stop_or_ponderhit();
472 cout << "bestmove " << bookMove << endl;
478 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
479 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
480 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
481 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
482 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
483 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
484 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
485 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
486 UCIMultiPV = Options["MultiPV"].value<int>();
487 SkillLevel = Options["Skill level"].value<int>();
488 UseLogFile = Options["Use Search Log"].value<bool>();
490 read_evaluation_uci_options(pos.side_to_move());
492 if (Options["Clear Hash"].value<bool>())
494 Options["Clear Hash"].set_value("false");
497 TT.set_size(Options["Hash"].value<int>());
499 // Do we have to play with skill handicap? In this case enable MultiPV that
500 // we will use behind the scenes to retrieve a set of possible moves.
501 SkillLevelEnabled = (SkillLevel < 20);
502 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
504 // Set the number of active threads
505 ThreadsMgr.read_uci_options();
506 init_eval(ThreadsMgr.active_threads());
508 // Wake up needed threads and reset maxPly counter
509 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
511 ThreadsMgr[i].wake_up();
512 ThreadsMgr[i].maxPly = 0;
516 int myTime = time[pos.side_to_move()];
517 int myIncrement = increment[pos.side_to_move()];
518 if (UseTimeManagement)
519 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
521 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
523 NodesBetweenPolls = Min(MaxNodes, 30000);
524 else if (myTime && myTime < 1000)
525 NodesBetweenPolls = 1000;
526 else if (myTime && myTime < 5000)
527 NodesBetweenPolls = 5000;
529 NodesBetweenPolls = 30000;
531 // Write search information to log file
534 std::string name = Options["Search Log Filename"].value<std::string>();
535 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
537 LogFile << "\nSearching: " << pos.to_fen()
538 << "\ninfinite: " << infinite
539 << " ponder: " << ponder
540 << " time: " << myTime
541 << " increment: " << myIncrement
542 << " moves to go: " << movesToGo
546 // We're ready to start thinking. Call the iterative deepening loop function
547 Move ponderMove = MOVE_NONE;
548 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
550 // Print final search statistics
551 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
555 int t = current_search_time();
557 LogFile << "Nodes: " << pos.nodes_searched()
558 << "\nNodes/second: " << (t > 0 ? int(pos.nodes_searched() * 1000 / t) : 0)
559 << "\nBest move: " << move_to_san(pos, bestMove);
562 pos.do_move(bestMove, st);
563 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
564 pos.undo_move(bestMove); // Return from think() with unchanged position
568 // This makes all the threads to go to sleep
569 ThreadsMgr.set_active_threads(1);
571 // If we are pondering or in infinite search, we shouldn't print the
572 // best move before we are told to do so.
573 if (!StopRequest && (Pondering || InfiniteSearch))
574 wait_for_stop_or_ponderhit();
576 // Could be MOVE_NONE when searching on a stalemate position
577 cout << "bestmove " << bestMove;
579 // UCI protol is not clear on allowing sending an empty ponder move, instead
580 // it is clear that ponder move is optional. So skip it if empty.
581 if (ponderMove != MOVE_NONE)
582 cout << " ponder " << ponderMove;
592 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
593 // with increasing depth until the allocated thinking time has been consumed,
594 // user stops the search, or the maximum search depth is reached.
596 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
598 SearchStack ss[PLY_MAX_PLUS_2];
599 Value bestValues[PLY_MAX_PLUS_2];
600 int bestMoveChanges[PLY_MAX_PLUS_2];
601 int depth, selDepth, aspirationDelta;
602 Value value, alpha, beta;
603 Move bestMove, easyMove, skillBest, skillPonder;
605 // Initialize stuff before a new search
606 memset(ss, 0, 4 * sizeof(SearchStack));
609 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
610 depth = aspirationDelta = 0;
611 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
612 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
614 // Moves to search are verified and copied
615 Rml.init(pos, searchMoves);
617 // Handle special case of searching on a mate/stalemate position
620 cout << "info depth 0 score "
621 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
627 // Iterative deepening loop
628 while (++depth <= PLY_MAX && (!MaxDepth || depth <= MaxDepth) && !StopRequest)
630 Rml.bestMoveChanges = 0;
631 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
633 // Calculate dynamic aspiration window based on previous iterations
634 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
636 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
637 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
639 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
640 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
642 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
643 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
646 // Start with a small aspiration window and, in case of fail high/low,
647 // research with bigger window until not failing high/low anymore.
649 // Search starting from ss+1 to allow calling update_gains()
650 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY);
652 // Write PV back to transposition table in case the relevant entries
653 // have been overwritten during the search.
654 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
655 Rml[i].insert_pv_in_tt(pos);
657 // Value cannot be trusted. Break out immediately!
661 assert(value >= alpha);
663 // In case of failing high/low increase aspiration window and research,
664 // otherwise exit the fail high/low loop.
667 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
668 aspirationDelta += aspirationDelta / 2;
670 else if (value <= alpha)
672 AspirationFailLow = true;
673 StopOnPonderhit = false;
675 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
676 aspirationDelta += aspirationDelta / 2;
681 } while (abs(value) < VALUE_KNOWN_WIN);
683 // Collect info about search result
684 bestMove = Rml[0].pv[0];
685 *ponderMove = Rml[0].pv[1];
686 bestValues[depth] = value;
687 bestMoveChanges[depth] = Rml.bestMoveChanges;
689 // Do we need to pick now the best and the ponder moves ?
690 if (SkillLevelEnabled && depth == 1 + SkillLevel)
691 do_skill_level(&skillBest, &skillPonder);
693 // Retrieve max searched depth among threads
695 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
696 if (ThreadsMgr[i].maxPly > selDepth)
697 selDepth = ThreadsMgr[i].maxPly;
699 // Send PV line to GUI and to log file
700 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
701 cout << Rml[i].pv_info_to_uci(pos, depth, selDepth, alpha, beta, i) << endl;
704 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
706 // Init easyMove after first iteration or drop if differs from the best move
707 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
709 else if (bestMove != easyMove)
710 easyMove = MOVE_NONE;
712 if (UseTimeManagement && !StopRequest)
715 bool noMoreTime = false;
717 // Stop search early when the last two iterations returned a mate score
719 && abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
720 && abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
723 // Stop search early if one move seems to be much better than the
724 // others or if there is only a single legal move. In this latter
725 // case we search up to Iteration 8 anyway to get a proper score.
727 && easyMove == bestMove
729 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
730 && current_search_time() > TimeMgr.available_time() / 16)
731 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
732 && current_search_time() > TimeMgr.available_time() / 32)))
735 // Add some extra time if the best move has changed during the last two iterations
736 if (depth > 4 && depth < 50)
737 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
739 // Stop search if most of MaxSearchTime is consumed at the end of the
740 // iteration. We probably don't have enough time to search the first
741 // move at the next iteration anyway.
742 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
748 StopOnPonderhit = true;
755 // When using skills fake best and ponder moves with the sub-optimal ones
756 if (SkillLevelEnabled)
758 if (skillBest == MOVE_NONE) // Still unassigned ?
759 do_skill_level(&skillBest, &skillPonder);
761 bestMove = skillBest;
762 *ponderMove = skillPonder;
769 // search<>() is the main search function for both PV and non-PV nodes and for
770 // normal and SplitPoint nodes. When called just after a split point the search
771 // is simpler because we have already probed the hash table, done a null move
772 // search, and searched the first move before splitting, we don't have to repeat
773 // all this work again. We also don't need to store anything to the hash table
774 // here: This is taken care of after we return from the split point.
776 template <NodeType PvNode, bool SpNode, bool Root>
777 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
779 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
780 assert(beta > alpha && beta <= VALUE_INFINITE);
781 assert(PvNode || alpha == beta - 1);
782 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
784 Move movesSearched[MOVES_MAX];
789 Move ttMove, move, excludedMove, threatMove;
792 Value bestValue, value, oldAlpha;
793 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
794 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous, isBadCap;
795 int moveCount = 0, playedMoveCount = 0;
796 int threadID = pos.thread();
797 SplitPoint* sp = NULL;
799 refinedValue = bestValue = value = -VALUE_INFINITE;
801 isCheck = pos.is_check();
802 ss->ply = (ss-1)->ply + 1;
804 // Used to send selDepth info to GUI
805 if (PvNode && ThreadsMgr[threadID].maxPly < ss->ply)
806 ThreadsMgr[threadID].maxPly = ss->ply;
812 ttMove = excludedMove = MOVE_NONE;
813 threatMove = sp->threatMove;
814 goto split_point_start;
819 // Step 1. Initialize node and poll. Polling can abort search
820 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
821 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
822 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
824 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
830 // Step 2. Check for aborted search and immediate draw
832 || ThreadsMgr.cutoff_at_splitpoint(threadID)
834 || ss->ply > PLY_MAX) && !Root)
837 // Step 3. Mate distance pruning
838 alpha = Max(value_mated_in(ss->ply), alpha);
839 beta = Min(value_mate_in(ss->ply+1), beta);
843 // Step 4. Transposition table lookup
844 // We don't want the score of a partial search to overwrite a previous full search
845 // TT value, so we use a different position key in case of an excluded move.
846 excludedMove = ss->excludedMove;
847 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
849 tte = TT.retrieve(posKey);
850 ttMove = tte ? tte->move() : MOVE_NONE;
852 // At PV nodes we check for exact scores, while at non-PV nodes we check for
853 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
854 // smooth experience in analysis mode.
857 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
858 : ok_to_use_TT(tte, depth, beta, ss->ply)))
861 ss->bestMove = ttMove; // Can be MOVE_NONE
862 return value_from_tt(tte->value(), ss->ply);
865 // Step 5. Evaluate the position statically and update parent's gain statistics
867 ss->eval = ss->evalMargin = VALUE_NONE;
870 assert(tte->static_value() != VALUE_NONE);
872 ss->eval = tte->static_value();
873 ss->evalMargin = tte->static_value_margin();
874 refinedValue = refine_eval(tte, ss->eval, ss->ply);
878 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
879 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
882 // Save gain for the parent non-capture move
883 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
885 // Step 6. Razoring (is omitted in PV nodes)
887 && depth < RazorDepth
889 && refinedValue + razor_margin(depth) < beta
890 && ttMove == MOVE_NONE
891 && abs(beta) < VALUE_MATE_IN_PLY_MAX
892 && !pos.has_pawn_on_7th(pos.side_to_move()))
894 Value rbeta = beta - razor_margin(depth);
895 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
897 // Logically we should return (v + razor_margin(depth)), but
898 // surprisingly this did slightly weaker in tests.
902 // Step 7. Static null move pruning (is omitted in PV nodes)
903 // We're betting that the opponent doesn't have a move that will reduce
904 // the score by more than futility_margin(depth) if we do a null move.
907 && depth < RazorDepth
909 && refinedValue - futility_margin(depth, 0) >= beta
910 && abs(beta) < VALUE_MATE_IN_PLY_MAX
911 && pos.non_pawn_material(pos.side_to_move()))
912 return refinedValue - futility_margin(depth, 0);
914 // Step 8. Null move search with verification search (is omitted in PV nodes)
919 && refinedValue >= beta
920 && abs(beta) < VALUE_MATE_IN_PLY_MAX
921 && pos.non_pawn_material(pos.side_to_move()))
923 ss->currentMove = MOVE_NULL;
925 // Null move dynamic reduction based on depth
926 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
928 // Null move dynamic reduction based on value
929 if (refinedValue - PawnValueMidgame > beta)
932 pos.do_null_move(st);
933 (ss+1)->skipNullMove = true;
934 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
935 (ss+1)->skipNullMove = false;
936 pos.undo_null_move();
938 if (nullValue >= beta)
940 // Do not return unproven mate scores
941 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
944 if (depth < 6 * ONE_PLY)
947 // Do verification search at high depths
948 ss->skipNullMove = true;
949 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
950 ss->skipNullMove = false;
957 // The null move failed low, which means that we may be faced with
958 // some kind of threat. If the previous move was reduced, check if
959 // the move that refuted the null move was somehow connected to the
960 // move which was reduced. If a connection is found, return a fail
961 // low score (which will cause the reduced move to fail high in the
962 // parent node, which will trigger a re-search with full depth).
963 threatMove = (ss+1)->bestMove;
965 if ( depth < ThreatDepth
967 && threatMove != MOVE_NONE
968 && connected_moves(pos, (ss-1)->currentMove, threatMove))
973 // Step 9. Internal iterative deepening
974 if ( depth >= IIDDepth[PvNode]
975 && ttMove == MOVE_NONE
976 && (PvNode || (!isCheck && ss->eval + IIDMargin >= beta)))
978 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
980 ss->skipNullMove = true;
981 search<PvNode>(pos, ss, alpha, beta, d);
982 ss->skipNullMove = false;
984 ttMove = ss->bestMove;
985 tte = TT.retrieve(posKey);
988 split_point_start: // At split points actual search starts from here
990 // Initialize a MovePicker object for the current position
991 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
993 ss->bestMove = MOVE_NONE;
994 futilityBase = ss->eval + ss->evalMargin;
995 singularExtensionNode = !Root
997 && depth >= SingularExtensionDepth[PvNode]
1000 && !excludedMove // Do not allow recursive singular extension search
1001 && (tte->type() & VALUE_TYPE_LOWER)
1002 && tte->depth() >= depth - 3 * ONE_PLY;
1005 lock_grab(&(sp->lock));
1006 bestValue = sp->bestValue;
1009 // Step 10. Loop through moves
1010 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1011 while ( bestValue < beta
1012 && (move = mp.get_next_move()) != MOVE_NONE
1013 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1015 assert(move_is_ok(move));
1019 moveCount = ++sp->moveCount;
1020 lock_release(&(sp->lock));
1022 else if (move == excludedMove)
1029 // This is used by time management
1030 FirstRootMove = (moveCount == 1);
1032 // Save the current node count before the move is searched
1033 nodes = pos.nodes_searched();
1035 // If it's time to send nodes info, do it here where we have the
1036 // correct accumulated node counts searched by each thread.
1037 if (SendSearchedNodes)
1039 SendSearchedNodes = false;
1040 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1043 if (current_search_time() > 2000)
1044 cout << "info currmove " << move
1045 << " currmovenumber " << moveCount << endl;
1048 // At Root and at first iteration do a PV search on all the moves to score root moves
1049 isPvMove = (PvNode && moveCount <= (Root ? depth <= ONE_PLY ? 1000 : MultiPV : 1));
1050 moveIsCheck = pos.move_is_check(move, ci);
1051 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1053 // Step 11. Decide the new search depth
1054 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, &dangerous);
1056 // Singular extension search. If all moves but one fail low on a search of
1057 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1058 // is singular and should be extended. To verify this we do a reduced search
1059 // on all the other moves but the ttMove, if result is lower than ttValue minus
1060 // a margin then we extend ttMove.
1061 if ( singularExtensionNode
1062 && move == tte->move()
1065 Value ttValue = value_from_tt(tte->value(), ss->ply);
1067 if (abs(ttValue) < VALUE_KNOWN_WIN)
1069 Value rBeta = ttValue - int(depth);
1070 ss->excludedMove = move;
1071 ss->skipNullMove = true;
1072 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1073 ss->skipNullMove = false;
1074 ss->excludedMove = MOVE_NONE;
1075 ss->bestMove = MOVE_NONE;
1081 // Update current move (this must be done after singular extension search)
1082 ss->currentMove = move;
1083 newDepth = depth - ONE_PLY + ext;
1085 // Step 12. Futility pruning (is omitted in PV nodes)
1087 && !captureOrPromotion
1091 && !move_is_castle(move))
1093 // Move count based pruning
1094 if ( moveCount >= futility_move_count(depth)
1095 && (!threatMove || !connected_threat(pos, move, threatMove))
1096 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1099 lock_grab(&(sp->lock));
1104 // Value based pruning
1105 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1106 // but fixing this made program slightly weaker.
1107 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1108 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1109 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1111 if (futilityValueScaled < beta)
1115 lock_grab(&(sp->lock));
1116 if (futilityValueScaled > sp->bestValue)
1117 sp->bestValue = bestValue = futilityValueScaled;
1119 else if (futilityValueScaled > bestValue)
1120 bestValue = futilityValueScaled;
1125 // Prune moves with negative SEE at low depths
1126 if ( predictedDepth < 2 * ONE_PLY
1127 && bestValue > VALUE_MATED_IN_PLY_MAX
1128 && pos.see_sign(move) < 0)
1131 lock_grab(&(sp->lock));
1137 // Bad capture detection. Will be used by prob-cut search
1138 isBadCap = depth >= 3 * ONE_PLY
1139 && depth < 8 * ONE_PLY
1140 && captureOrPromotion
1143 && !move_is_promotion(move)
1144 && abs(alpha) < VALUE_MATE_IN_PLY_MAX
1145 && pos.see_sign(move) < 0;
1147 // Step 13. Make the move
1148 pos.do_move(move, st, ci, moveIsCheck);
1150 if (!SpNode && !captureOrPromotion)
1151 movesSearched[playedMoveCount++] = move;
1153 // Step extra. pv search (only in PV nodes)
1154 // The first move in list is the expected PV
1157 // Aspiration window is disabled in multi-pv case
1158 if (Root && MultiPV > 1)
1159 alpha = -VALUE_INFINITE;
1161 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1165 // Step 14. Reduced depth search
1166 // If the move fails high will be re-searched at full depth.
1167 bool doFullDepthSearch = true;
1168 alpha = SpNode ? sp->alpha : alpha;
1170 if ( depth >= 3 * ONE_PLY
1171 && !captureOrPromotion
1173 && !move_is_castle(move)
1174 && ss->killers[0] != move
1175 && ss->killers[1] != move)
1177 ss->reduction = reduction<PvNode>(depth, moveCount);
1180 alpha = SpNode ? sp->alpha : alpha;
1181 Depth d = newDepth - ss->reduction;
1182 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1184 doFullDepthSearch = (value > alpha);
1186 ss->reduction = DEPTH_ZERO; // Restore original reduction
1189 // Probcut search for bad captures. If a reduced search returns a value
1190 // very below beta then we can (almost) safely prune the bad capture.
1193 ss->reduction = 3 * ONE_PLY;
1194 Value rAlpha = alpha - 300;
1195 Depth d = newDepth - ss->reduction;
1196 value = -search<NonPV>(pos, ss+1, -(rAlpha+1), -rAlpha, d);
1197 doFullDepthSearch = (value > rAlpha);
1198 ss->reduction = DEPTH_ZERO; // Restore original reduction
1201 // Step 15. Full depth search
1202 if (doFullDepthSearch)
1204 alpha = SpNode ? sp->alpha : alpha;
1205 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1207 // Step extra. pv search (only in PV nodes)
1208 // Search only for possible new PV nodes, if instead value >= beta then
1209 // parent node fails low with value <= alpha and tries another move.
1210 if (PvNode && value > alpha && (Root || value < beta))
1211 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1215 // Step 16. Undo move
1216 pos.undo_move(move);
1218 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1220 // Step 17. Check for new best move
1223 lock_grab(&(sp->lock));
1224 bestValue = sp->bestValue;
1228 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1233 sp->bestValue = value;
1235 if (!Root && value > alpha)
1237 if (PvNode && value < beta) // We want always alpha < beta
1245 sp->betaCutoff = true;
1247 if (value == value_mate_in(ss->ply + 1))
1248 ss->mateKiller = move;
1250 ss->bestMove = move;
1253 sp->ss->bestMove = move;
1259 // Finished searching the move. If StopRequest is true, the search
1260 // was aborted because the user interrupted the search or because we
1261 // ran out of time. In this case, the return value of the search cannot
1262 // be trusted, and we break out of the loop without updating the best
1267 // Remember searched nodes counts for this move
1268 mp.rm->nodes += pos.nodes_searched() - nodes;
1270 // PV move or new best move ?
1271 if (isPvMove || value > alpha)
1274 ss->bestMove = move;
1275 mp.rm->pv_score = value;
1276 mp.rm->extract_pv_from_tt(pos);
1278 // We record how often the best move has been changed in each
1279 // iteration. This information is used for time management: When
1280 // the best move changes frequently, we allocate some more time.
1281 if (!isPvMove && MultiPV == 1)
1282 Rml.bestMoveChanges++;
1284 Rml.sort_multipv(moveCount);
1286 // Update alpha. In multi-pv we don't use aspiration window, so
1287 // set alpha equal to minimum score among the PV lines.
1289 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1290 else if (value > alpha)
1294 mp.rm->pv_score = -VALUE_INFINITE;
1298 // Step 18. Check for split
1301 && depth >= ThreadsMgr.min_split_depth()
1302 && ThreadsMgr.active_threads() > 1
1304 && ThreadsMgr.available_thread_exists(threadID)
1306 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1307 ThreadsMgr.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1308 threatMove, moveCount, &mp, PvNode);
1311 // Step 19. Check for mate and stalemate
1312 // All legal moves have been searched and if there are
1313 // no legal moves, it must be mate or stalemate.
1314 // If one move was excluded return fail low score.
1315 if (!SpNode && !moveCount)
1316 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1318 // Step 20. Update tables
1319 // If the search is not aborted, update the transposition table,
1320 // history counters, and killer moves.
1321 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1323 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1324 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1325 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1327 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1329 // Update killers and history only for non capture moves that fails high
1330 if ( bestValue >= beta
1331 && !pos.move_is_capture_or_promotion(move))
1333 if (move != ss->killers[0])
1335 ss->killers[1] = ss->killers[0];
1336 ss->killers[0] = move;
1338 update_history(pos, move, depth, movesSearched, playedMoveCount);
1344 // Here we have the lock still grabbed
1345 sp->slaves[threadID] = 0;
1346 sp->nodes += pos.nodes_searched();
1347 lock_release(&(sp->lock));
1350 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1355 // qsearch() is the quiescence search function, which is called by the main
1356 // search function when the remaining depth is zero (or, to be more precise,
1357 // less than ONE_PLY).
1359 template <NodeType PvNode>
1360 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1362 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1363 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1364 assert(PvNode || alpha == beta - 1);
1366 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1370 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1371 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1374 Value oldAlpha = alpha;
1376 ss->bestMove = ss->currentMove = MOVE_NONE;
1377 ss->ply = (ss-1)->ply + 1;
1379 // Check for an instant draw or maximum ply reached
1380 if (ss->ply > PLY_MAX || pos.is_draw())
1383 // Decide whether or not to include checks, this fixes also the type of
1384 // TT entry depth that we are going to use. Note that in qsearch we use
1385 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1386 isCheck = pos.is_check();
1387 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1389 // Transposition table lookup. At PV nodes, we don't use the TT for
1390 // pruning, but only for move ordering.
1391 tte = TT.retrieve(pos.get_key());
1392 ttMove = (tte ? tte->move() : MOVE_NONE);
1394 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1396 ss->bestMove = ttMove; // Can be MOVE_NONE
1397 return value_from_tt(tte->value(), ss->ply);
1400 // Evaluate the position statically
1403 bestValue = futilityBase = -VALUE_INFINITE;
1404 ss->eval = evalMargin = VALUE_NONE;
1405 enoughMaterial = false;
1411 assert(tte->static_value() != VALUE_NONE);
1413 evalMargin = tte->static_value_margin();
1414 ss->eval = bestValue = tte->static_value();
1417 ss->eval = bestValue = evaluate(pos, evalMargin);
1419 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1421 // Stand pat. Return immediately if static value is at least beta
1422 if (bestValue >= beta)
1425 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1430 if (PvNode && bestValue > alpha)
1433 // Futility pruning parameters, not needed when in check
1434 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1435 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1438 // Initialize a MovePicker object for the current position, and prepare
1439 // to search the moves. Because the depth is <= 0 here, only captures,
1440 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1442 MovePicker mp(pos, ttMove, depth, H);
1445 // Loop through the moves until no moves remain or a beta cutoff occurs
1446 while ( alpha < beta
1447 && (move = mp.get_next_move()) != MOVE_NONE)
1449 assert(move_is_ok(move));
1451 moveIsCheck = pos.move_is_check(move, ci);
1459 && !move_is_promotion(move)
1460 && !pos.move_is_passed_pawn_push(move))
1462 futilityValue = futilityBase
1463 + pos.endgame_value_of_piece_on(move_to(move))
1464 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1466 if (futilityValue < alpha)
1468 if (futilityValue > bestValue)
1469 bestValue = futilityValue;
1473 // Prune moves with negative or equal SEE
1474 if ( futilityBase < beta
1475 && depth < DEPTH_ZERO
1476 && pos.see(move) <= 0)
1480 // Detect non-capture evasions that are candidate to be pruned
1481 evasionPrunable = isCheck
1482 && bestValue > VALUE_MATED_IN_PLY_MAX
1483 && !pos.move_is_capture(move)
1484 && !pos.can_castle(pos.side_to_move());
1486 // Don't search moves with negative SEE values
1488 && (!isCheck || evasionPrunable)
1490 && !move_is_promotion(move)
1491 && pos.see_sign(move) < 0)
1494 // Don't search useless checks
1499 && !pos.move_is_capture_or_promotion(move)
1500 && ss->eval + PawnValueMidgame / 4 < beta
1501 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1503 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1504 bestValue = ss->eval + PawnValueMidgame / 4;
1509 // Update current move
1510 ss->currentMove = move;
1512 // Make and search the move
1513 pos.do_move(move, st, ci, moveIsCheck);
1514 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1515 pos.undo_move(move);
1517 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1520 if (value > bestValue)
1526 ss->bestMove = move;
1531 // All legal moves have been searched. A special case: If we're in check
1532 // and no legal moves were found, it is checkmate.
1533 if (isCheck && bestValue == -VALUE_INFINITE)
1534 return value_mated_in(ss->ply);
1536 // Update transposition table
1537 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1538 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1540 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1546 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1547 // bestValue is updated only when returning false because in that case move
1550 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1552 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1553 Square from, to, ksq, victimSq;
1556 Value futilityValue, bv = *bestValue;
1558 from = move_from(move);
1560 them = opposite_color(pos.side_to_move());
1561 ksq = pos.king_square(them);
1562 kingAtt = pos.attacks_from<KING>(ksq);
1563 pc = pos.piece_on(from);
1565 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1566 oldAtt = pos.attacks_from(pc, from, occ);
1567 newAtt = pos.attacks_from(pc, to, occ);
1569 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1570 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1572 if (!(b && (b & (b - 1))))
1575 // Rule 2. Queen contact check is very dangerous
1576 if ( type_of_piece(pc) == QUEEN
1577 && bit_is_set(kingAtt, to))
1580 // Rule 3. Creating new double threats with checks
1581 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1585 victimSq = pop_1st_bit(&b);
1586 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1588 // Note that here we generate illegal "double move"!
1589 if ( futilityValue >= beta
1590 && pos.see_sign(make_move(from, victimSq)) >= 0)
1593 if (futilityValue > bv)
1597 // Update bestValue only if check is not dangerous (because we will prune the move)
1603 // connected_moves() tests whether two moves are 'connected' in the sense
1604 // that the first move somehow made the second move possible (for instance
1605 // if the moving piece is the same in both moves). The first move is assumed
1606 // to be the move that was made to reach the current position, while the
1607 // second move is assumed to be a move from the current position.
1609 bool connected_moves(const Position& pos, Move m1, Move m2) {
1611 Square f1, t1, f2, t2;
1614 assert(m1 && move_is_ok(m1));
1615 assert(m2 && move_is_ok(m2));
1617 // Case 1: The moving piece is the same in both moves
1623 // Case 2: The destination square for m2 was vacated by m1
1629 // Case 3: Moving through the vacated square
1630 if ( piece_is_slider(pos.piece_on(f2))
1631 && bit_is_set(squares_between(f2, t2), f1))
1634 // Case 4: The destination square for m2 is defended by the moving piece in m1
1635 p = pos.piece_on(t1);
1636 if (bit_is_set(pos.attacks_from(p, t1), t2))
1639 // Case 5: Discovered check, checking piece is the piece moved in m1
1640 if ( piece_is_slider(p)
1641 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1642 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1644 // discovered_check_candidates() works also if the Position's side to
1645 // move is the opposite of the checking piece.
1646 Color them = opposite_color(pos.side_to_move());
1647 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1649 if (bit_is_set(dcCandidates, f2))
1656 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1657 // "plies to mate from the current ply". Non-mate scores are unchanged.
1658 // The function is called before storing a value to the transposition table.
1660 Value value_to_tt(Value v, int ply) {
1662 if (v >= VALUE_MATE_IN_PLY_MAX)
1665 if (v <= VALUE_MATED_IN_PLY_MAX)
1672 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1673 // the transposition table to a mate score corrected for the current ply.
1675 Value value_from_tt(Value v, int ply) {
1677 if (v >= VALUE_MATE_IN_PLY_MAX)
1680 if (v <= VALUE_MATED_IN_PLY_MAX)
1687 // extension() decides whether a move should be searched with normal depth,
1688 // or with extended depth. Certain classes of moves (checking moves, in
1689 // particular) are searched with bigger depth than ordinary moves and in
1690 // any case are marked as 'dangerous'. Note that also if a move is not
1691 // extended, as example because the corresponding UCI option is set to zero,
1692 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1693 template <NodeType PvNode>
1694 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1695 bool moveIsCheck, bool* dangerous) {
1697 assert(m != MOVE_NONE);
1699 Depth result = DEPTH_ZERO;
1700 *dangerous = moveIsCheck;
1702 if (moveIsCheck && pos.see_sign(m) >= 0)
1703 result += CheckExtension[PvNode];
1705 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1707 Color c = pos.side_to_move();
1708 if (relative_rank(c, move_to(m)) == RANK_7)
1710 result += PawnPushTo7thExtension[PvNode];
1713 if (pos.pawn_is_passed(c, move_to(m)))
1715 result += PassedPawnExtension[PvNode];
1720 if ( captureOrPromotion
1721 && pos.type_of_piece_on(move_to(m)) != PAWN
1722 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1723 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1724 && !move_is_promotion(m)
1727 result += PawnEndgameExtension[PvNode];
1731 return Min(result, ONE_PLY);
1735 // connected_threat() tests whether it is safe to forward prune a move or if
1736 // is somehow connected to the threat move returned by null search.
1738 bool connected_threat(const Position& pos, Move m, Move threat) {
1740 assert(move_is_ok(m));
1741 assert(threat && move_is_ok(threat));
1742 assert(!pos.move_is_check(m));
1743 assert(!pos.move_is_capture_or_promotion(m));
1744 assert(!pos.move_is_passed_pawn_push(m));
1746 Square mfrom, mto, tfrom, tto;
1748 mfrom = move_from(m);
1750 tfrom = move_from(threat);
1751 tto = move_to(threat);
1753 // Case 1: Don't prune moves which move the threatened piece
1757 // Case 2: If the threatened piece has value less than or equal to the
1758 // value of the threatening piece, don't prune moves which defend it.
1759 if ( pos.move_is_capture(threat)
1760 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1761 || pos.type_of_piece_on(tfrom) == KING)
1762 && pos.move_attacks_square(m, tto))
1765 // Case 3: If the moving piece in the threatened move is a slider, don't
1766 // prune safe moves which block its ray.
1767 if ( piece_is_slider(pos.piece_on(tfrom))
1768 && bit_is_set(squares_between(tfrom, tto), mto)
1769 && pos.see_sign(m) >= 0)
1776 // ok_to_use_TT() returns true if a transposition table score
1777 // can be used at a given point in search.
1779 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1781 Value v = value_from_tt(tte->value(), ply);
1783 return ( tte->depth() >= depth
1784 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1785 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1787 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1788 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1792 // refine_eval() returns the transposition table score if
1793 // possible otherwise falls back on static position evaluation.
1795 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1799 Value v = value_from_tt(tte->value(), ply);
1801 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1802 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1809 // update_history() registers a good move that produced a beta-cutoff
1810 // in history and marks as failures all the other moves of that ply.
1812 void update_history(const Position& pos, Move move, Depth depth,
1813 Move movesSearched[], int moveCount) {
1815 Value bonus = Value(int(depth) * int(depth));
1817 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1819 for (int i = 0; i < moveCount - 1; i++)
1821 m = movesSearched[i];
1825 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1830 // update_gains() updates the gains table of a non-capture move given
1831 // the static position evaluation before and after the move.
1833 void update_gains(const Position& pos, Move m, Value before, Value after) {
1836 && before != VALUE_NONE
1837 && after != VALUE_NONE
1838 && pos.captured_piece_type() == PIECE_TYPE_NONE
1839 && !move_is_special(m))
1840 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1844 // current_search_time() returns the number of milliseconds which have passed
1845 // since the beginning of the current search.
1847 int current_search_time() {
1849 return get_system_time() - SearchStartTime;
1853 // value_to_uci() converts a value to a string suitable for use with the UCI
1854 // protocol specifications:
1856 // cp <x> The score from the engine's point of view in centipawns.
1857 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1858 // use negative values for y.
1860 std::string value_to_uci(Value v) {
1862 std::stringstream s;
1864 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1865 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1867 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1873 // speed_to_uci() returns a string with time stats of current search suitable
1874 // to be sent to UCI gui.
1876 std::string speed_to_uci(int64_t nodes) {
1878 std::stringstream s;
1879 int t = current_search_time();
1881 s << " nodes " << nodes
1882 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1889 // poll() performs two different functions: It polls for user input, and it
1890 // looks at the time consumed so far and decides if it's time to abort the
1893 void poll(const Position& pos) {
1895 static int lastInfoTime;
1896 int t = current_search_time();
1899 if (input_available())
1901 // We are line oriented, don't read single chars
1902 std::string command;
1904 if (!std::getline(std::cin, command) || command == "quit")
1906 // Quit the program as soon as possible
1908 QuitRequest = StopRequest = true;
1911 else if (command == "stop")
1913 // Stop calculating as soon as possible, but still send the "bestmove"
1914 // and possibly the "ponder" token when finishing the search.
1918 else if (command == "ponderhit")
1920 // The opponent has played the expected move. GUI sends "ponderhit" if
1921 // we were told to ponder on the same move the opponent has played. We
1922 // should continue searching but switching from pondering to normal search.
1925 if (StopOnPonderhit)
1930 // Print search information
1934 else if (lastInfoTime > t)
1935 // HACK: Must be a new search where we searched less than
1936 // NodesBetweenPolls nodes during the first second of search.
1939 else if (t - lastInfoTime >= 1000)
1944 dbg_print_hit_rate();
1946 // Send info on searched nodes as soon as we return to root
1947 SendSearchedNodes = true;
1950 // Should we stop the search?
1954 bool stillAtFirstMove = FirstRootMove
1955 && !AspirationFailLow
1956 && t > TimeMgr.available_time();
1958 bool noMoreTime = t > TimeMgr.maximum_time()
1959 || stillAtFirstMove;
1961 if ( (UseTimeManagement && noMoreTime)
1962 || (ExactMaxTime && t >= ExactMaxTime)
1963 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
1968 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1969 // while the program is pondering. The point is to work around a wrinkle in
1970 // the UCI protocol: When pondering, the engine is not allowed to give a
1971 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1972 // We simply wait here until one of these commands is sent, and return,
1973 // after which the bestmove and pondermove will be printed.
1975 void wait_for_stop_or_ponderhit() {
1977 std::string command;
1979 // Wait for a command from stdin
1980 while ( std::getline(std::cin, command)
1981 && command != "ponderhit" && command != "stop" && command != "quit") {};
1983 if (command != "ponderhit" && command != "stop")
1984 QuitRequest = true; // Must be "quit" or getline() returned false
1988 // init_thread() is the function which is called when a new thread is
1989 // launched. It simply calls the idle_loop() function with the supplied
1990 // threadID. There are two versions of this function; one for POSIX
1991 // threads and one for Windows threads.
1993 #if !defined(_MSC_VER)
1995 void* init_thread(void* threadID) {
1997 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2003 DWORD WINAPI init_thread(LPVOID threadID) {
2005 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2012 /// The ThreadsManager class
2015 // read_uci_options() updates number of active threads and other internal
2016 // parameters according to the UCI options values. It is called before
2017 // to start a new search.
2019 void ThreadsManager::read_uci_options() {
2021 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2022 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2023 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2024 activeThreads = Options["Threads"].value<int>();
2028 // idle_loop() is where the threads are parked when they have no work to do.
2029 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2030 // object for which the current thread is the master.
2032 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2034 assert(threadID >= 0 && threadID < MAX_THREADS);
2037 bool allFinished = false;
2041 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2042 // master should exit as last one.
2043 if (allThreadsShouldExit)
2046 threads[threadID].state = THREAD_TERMINATED;
2050 // If we are not thinking, wait for a condition to be signaled
2051 // instead of wasting CPU time polling for work.
2052 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2053 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2055 assert(!sp || useSleepingThreads);
2056 assert(threadID != 0 || useSleepingThreads);
2058 if (threads[threadID].state == THREAD_INITIALIZING)
2059 threads[threadID].state = THREAD_AVAILABLE;
2061 // Grab the lock to avoid races with wake_sleeping_thread()
2062 lock_grab(&threads[threadID].sleepLock);
2064 // If we are master and all slaves have finished do not go to sleep
2065 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2066 allFinished = (i == activeThreads);
2068 if (allFinished || allThreadsShouldExit)
2070 lock_release(&threads[threadID].sleepLock);
2074 // Do sleep here after retesting sleep conditions
2075 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2076 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2078 lock_release(&threads[threadID].sleepLock);
2081 // If this thread has been assigned work, launch a search
2082 if (threads[threadID].state == THREAD_WORKISWAITING)
2084 assert(!allThreadsShouldExit);
2086 threads[threadID].state = THREAD_SEARCHING;
2088 // Copy SplitPoint position and search stack and call search()
2089 // with SplitPoint template parameter set to true.
2090 SearchStack ss[PLY_MAX_PLUS_2];
2091 SplitPoint* tsp = threads[threadID].splitPoint;
2092 Position pos(*tsp->pos, threadID);
2094 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2098 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2100 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2102 assert(threads[threadID].state == THREAD_SEARCHING);
2104 threads[threadID].state = THREAD_AVAILABLE;
2106 // Wake up master thread so to allow it to return from the idle loop in
2107 // case we are the last slave of the split point.
2108 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2109 threads[tsp->master].wake_up();
2112 // If this thread is the master of a split point and all slaves have
2113 // finished their work at this split point, return from the idle loop.
2114 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2115 allFinished = (i == activeThreads);
2119 // Because sp->slaves[] is reset under lock protection,
2120 // be sure sp->lock has been released before to return.
2121 lock_grab(&(sp->lock));
2122 lock_release(&(sp->lock));
2124 // In helpful master concept a master can help only a sub-tree, and
2125 // because here is all finished is not possible master is booked.
2126 assert(threads[threadID].state == THREAD_AVAILABLE);
2128 threads[threadID].state = THREAD_SEARCHING;
2135 // init_threads() is called during startup. It launches all helper threads,
2136 // and initializes the split point stack and the global locks and condition
2139 void ThreadsManager::init_threads() {
2141 int i, arg[MAX_THREADS];
2144 // Initialize global locks
2147 for (i = 0; i < MAX_THREADS; i++)
2149 lock_init(&threads[i].sleepLock);
2150 cond_init(&threads[i].sleepCond);
2153 // Initialize splitPoints[] locks
2154 for (i = 0; i < MAX_THREADS; i++)
2155 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2156 lock_init(&(threads[i].splitPoints[j].lock));
2158 // Will be set just before program exits to properly end the threads
2159 allThreadsShouldExit = false;
2161 // Threads will be put all threads to sleep as soon as created
2164 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2165 threads[0].state = THREAD_SEARCHING;
2166 for (i = 1; i < MAX_THREADS; i++)
2167 threads[i].state = THREAD_INITIALIZING;
2169 // Launch the helper threads
2170 for (i = 1; i < MAX_THREADS; i++)
2174 #if !defined(_MSC_VER)
2175 pthread_t pthread[1];
2176 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2177 pthread_detach(pthread[0]);
2179 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2183 cout << "Failed to create thread number " << i << endl;
2187 // Wait until the thread has finished launching and is gone to sleep
2188 while (threads[i].state == THREAD_INITIALIZING) {}
2193 // exit_threads() is called when the program exits. It makes all the
2194 // helper threads exit cleanly.
2196 void ThreadsManager::exit_threads() {
2198 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2200 // Wake up all the threads and waits for termination
2201 for (int i = 1; i < MAX_THREADS; i++)
2203 threads[i].wake_up();
2204 while (threads[i].state != THREAD_TERMINATED) {}
2207 // Now we can safely destroy the locks
2208 for (int i = 0; i < MAX_THREADS; i++)
2209 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2210 lock_destroy(&(threads[i].splitPoints[j].lock));
2212 lock_destroy(&mpLock);
2214 // Now we can safely destroy the wait conditions
2215 for (int i = 0; i < MAX_THREADS; i++)
2217 lock_destroy(&threads[i].sleepLock);
2218 cond_destroy(&threads[i].sleepCond);
2223 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2224 // the thread's currently active split point, or in some ancestor of
2225 // the current split point.
2227 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2229 assert(threadID >= 0 && threadID < activeThreads);
2231 SplitPoint* sp = threads[threadID].splitPoint;
2233 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2238 // thread_is_available() checks whether the thread with threadID "slave" is
2239 // available to help the thread with threadID "master" at a split point. An
2240 // obvious requirement is that "slave" must be idle. With more than two
2241 // threads, this is not by itself sufficient: If "slave" is the master of
2242 // some active split point, it is only available as a slave to the other
2243 // threads which are busy searching the split point at the top of "slave"'s
2244 // split point stack (the "helpful master concept" in YBWC terminology).
2246 bool ThreadsManager::thread_is_available(int slave, int master) const {
2248 assert(slave >= 0 && slave < activeThreads);
2249 assert(master >= 0 && master < activeThreads);
2250 assert(activeThreads > 1);
2252 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2255 // Make a local copy to be sure doesn't change under our feet
2256 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2258 // No active split points means that the thread is available as
2259 // a slave for any other thread.
2260 if (localActiveSplitPoints == 0 || activeThreads == 2)
2263 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2264 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2265 // could have been set to 0 by another thread leading to an out of bound access.
2266 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2273 // available_thread_exists() tries to find an idle thread which is available as
2274 // a slave for the thread with threadID "master".
2276 bool ThreadsManager::available_thread_exists(int master) const {
2278 assert(master >= 0 && master < activeThreads);
2279 assert(activeThreads > 1);
2281 for (int i = 0; i < activeThreads; i++)
2282 if (thread_is_available(i, master))
2289 // split() does the actual work of distributing the work at a node between
2290 // several available threads. If it does not succeed in splitting the
2291 // node (because no idle threads are available, or because we have no unused
2292 // split point objects), the function immediately returns. If splitting is
2293 // possible, a SplitPoint object is initialized with all the data that must be
2294 // copied to the helper threads and we tell our helper threads that they have
2295 // been assigned work. This will cause them to instantly leave their idle loops and
2296 // call search().When all threads have returned from search() then split() returns.
2298 template <bool Fake>
2299 void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const Value beta,
2300 Value* bestValue, Depth depth, Move threatMove,
2301 int moveCount, MovePicker* mp, bool pvNode) {
2302 assert(pos.is_ok());
2303 assert(*bestValue >= -VALUE_INFINITE);
2304 assert(*bestValue <= *alpha);
2305 assert(*alpha < beta);
2306 assert(beta <= VALUE_INFINITE);
2307 assert(depth > DEPTH_ZERO);
2308 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2309 assert(activeThreads > 1);
2311 int i, master = pos.thread();
2312 Thread& masterThread = threads[master];
2316 // If no other thread is available to help us, or if we have too many
2317 // active split points, don't split.
2318 if ( !available_thread_exists(master)
2319 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2321 lock_release(&mpLock);
2325 // Pick the next available split point object from the split point stack
2326 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2328 // Initialize the split point object
2329 splitPoint.parent = masterThread.splitPoint;
2330 splitPoint.master = master;
2331 splitPoint.betaCutoff = false;
2332 splitPoint.depth = depth;
2333 splitPoint.threatMove = threatMove;
2334 splitPoint.alpha = *alpha;
2335 splitPoint.beta = beta;
2336 splitPoint.pvNode = pvNode;
2337 splitPoint.bestValue = *bestValue;
2339 splitPoint.moveCount = moveCount;
2340 splitPoint.pos = &pos;
2341 splitPoint.nodes = 0;
2343 for (i = 0; i < activeThreads; i++)
2344 splitPoint.slaves[i] = 0;
2346 masterThread.splitPoint = &splitPoint;
2348 // If we are here it means we are not available
2349 assert(masterThread.state != THREAD_AVAILABLE);
2351 int workersCnt = 1; // At least the master is included
2353 // Allocate available threads setting state to THREAD_BOOKED
2354 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2355 if (thread_is_available(i, master))
2357 threads[i].state = THREAD_BOOKED;
2358 threads[i].splitPoint = &splitPoint;
2359 splitPoint.slaves[i] = 1;
2363 assert(Fake || workersCnt > 1);
2365 // We can release the lock because slave threads are already booked and master is not available
2366 lock_release(&mpLock);
2368 // Tell the threads that they have work to do. This will make them leave
2370 for (i = 0; i < activeThreads; i++)
2371 if (i == master || splitPoint.slaves[i])
2373 assert(i == master || threads[i].state == THREAD_BOOKED);
2375 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2377 if (useSleepingThreads && i != master)
2378 threads[i].wake_up();
2381 // Everything is set up. The master thread enters the idle loop, from
2382 // which it will instantly launch a search, because its state is
2383 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2384 // idle loop, which means that the main thread will return from the idle
2385 // loop when all threads have finished their work at this split point.
2386 idle_loop(master, &splitPoint);
2388 // We have returned from the idle loop, which means that all threads are
2389 // finished. Update alpha and bestValue, and return.
2392 *alpha = splitPoint.alpha;
2393 *bestValue = splitPoint.bestValue;
2394 masterThread.activeSplitPoints--;
2395 masterThread.splitPoint = splitPoint.parent;
2396 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2398 lock_release(&mpLock);
2402 /// RootMove and RootMoveList method's definitions
2404 RootMove::RootMove() {
2407 pv_score = non_pv_score = -VALUE_INFINITE;
2411 RootMove& RootMove::operator=(const RootMove& rm) {
2413 const Move* src = rm.pv;
2416 // Avoid a costly full rm.pv[] copy
2417 do *dst++ = *src; while (*src++ != MOVE_NONE);
2420 pv_score = rm.pv_score;
2421 non_pv_score = rm.non_pv_score;
2425 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2426 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2427 // allow to always have a ponder move even when we fail high at root and also a
2428 // long PV to print that is important for position analysis.
2430 void RootMove::extract_pv_from_tt(Position& pos) {
2432 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2436 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2438 pos.do_move(pv[0], *st++);
2440 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2441 && tte->move() != MOVE_NONE
2442 && pos.move_is_legal(tte->move())
2444 && (!pos.is_draw() || ply < 2))
2446 pv[ply] = tte->move();
2447 pos.do_move(pv[ply++], *st++);
2449 pv[ply] = MOVE_NONE;
2451 do pos.undo_move(pv[--ply]); while (ply);
2454 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2455 // the PV back into the TT. This makes sure the old PV moves are searched
2456 // first, even if the old TT entries have been overwritten.
2458 void RootMove::insert_pv_in_tt(Position& pos) {
2460 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2463 Value v, m = VALUE_NONE;
2466 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2470 tte = TT.retrieve(k);
2472 // Don't overwrite existing correct entries
2473 if (!tte || tte->move() != pv[ply])
2475 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2476 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2478 pos.do_move(pv[ply], *st++);
2480 } while (pv[++ply] != MOVE_NONE);
2482 do pos.undo_move(pv[--ply]); while (ply);
2485 // pv_info_to_uci() returns a string with information on the current PV line
2486 // formatted according to UCI specification.
2488 std::string RootMove::pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha,
2489 Value beta, int pvIdx) {
2490 std::stringstream s;
2492 s << "info depth " << depth
2493 << " seldepth " << selDepth
2494 << " multipv " << pvIdx + 1
2495 << " score " << value_to_uci(pv_score)
2496 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2497 << speed_to_uci(pos.nodes_searched())
2500 for (Move* m = pv; *m != MOVE_NONE; m++)
2507 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2509 MoveStack mlist[MOVES_MAX];
2513 bestMoveChanges = 0;
2515 // Generate all legal moves and add them to RootMoveList
2516 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2517 for (MoveStack* cur = mlist; cur != last; cur++)
2519 // If we have a searchMoves[] list then verify cur->move
2520 // is in the list before to add it.
2521 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2523 if (searchMoves[0] && *sm != cur->move)
2527 rm.pv[0] = cur->move;
2528 rm.pv[1] = MOVE_NONE;
2529 rm.pv_score = -VALUE_INFINITE;
2535 // When playing with strength handicap choose best move among the MultiPV set
2536 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2537 void do_skill_level(Move* best, Move* ponder) {
2539 assert(MultiPV > 1);
2541 // Rml list is already sorted by pv_score in descending order
2543 int max_s = -VALUE_INFINITE;
2544 int size = Min(MultiPV, (int)Rml.size());
2545 int max = Rml[0].pv_score;
2546 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
2547 int wk = 120 - 2 * SkillLevel;
2549 // PRNG sequence should be non deterministic
2550 for (int i = abs(get_system_time() % 50); i > 0; i--)
2551 RK.rand<unsigned>();
2553 // Choose best move. For each move's score we add two terms both dependent
2554 // on wk, one deterministic and bigger for weaker moves, and one random,
2555 // then we choose the move with the resulting highest score.
2556 for (int i = 0; i < size; i++)
2558 s = Rml[i].pv_score;
2560 // Don't allow crazy blunders even at very low skills
2561 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
2564 // This is our magical formula
2565 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
2570 *best = Rml[i].pv[0];
2571 *ponder = Rml[i].pv[1];