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);
86 Depth minimumSplitDepth;
87 int maxThreadsPerSplitPoint;
88 bool useSleepingThreads;
90 volatile bool allThreadsShouldExit;
91 Thread threads[MAX_THREADS];
95 // RootMove struct is used for moves at the root of the tree. For each root
96 // move, we store two scores, a node count, and a PV (really a refutation
97 // in the case of moves which fail low). Value pv_score is normally set at
98 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
99 // according to the order in which moves are returned by MovePicker.
104 RootMove(const RootMove& rm) { *this = rm; }
105 RootMove& operator=(const RootMove& rm);
107 // RootMove::operator<() is the comparison function used when
108 // sorting the moves. A move m1 is considered to be better
109 // than a move m2 if it has an higher pv_score, or if it has
110 // equal pv_score but m1 has the higher non_pv_score. In this way
111 // we are guaranteed that PV moves are always sorted as first.
112 bool operator<(const RootMove& m) const {
113 return pv_score != m.pv_score ? pv_score < m.pv_score
114 : non_pv_score < m.non_pv_score;
117 void extract_pv_from_tt(Position& pos);
118 void insert_pv_in_tt(Position& pos);
119 std::string pv_info_to_uci(Position& pos, int depth, int selDepth,
120 Value alpha, Value beta, int pvIdx);
124 Move pv[PLY_MAX_PLUS_2];
128 // RootMoveList struct is just a vector of RootMove objects,
129 // with an handful of methods above the standard ones.
131 struct RootMoveList : public std::vector<RootMove> {
133 typedef std::vector<RootMove> Base;
135 void init(Position& pos, Move searchMoves[]);
136 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
137 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
143 // Overload operator<<() to make it easier to print moves in a coordinate
144 // notation compatible with UCI protocol.
145 std::ostream& operator<<(std::ostream& os, Move m) {
147 bool chess960 = (os.iword(0) != 0); // See set960()
148 return os << move_to_uci(m, chess960);
152 // When formatting a move for std::cout we must know if we are in Chess960
153 // or not. To keep using the handy operator<<() on the move the trick is to
154 // embed this flag in the stream itself. Function-like named enum set960 is
155 // used as a custom manipulator and the stream internal general-purpose array,
156 // accessed through ios_base::iword(), is used to pass the flag to the move's
157 // operator<<() that will read it to properly format castling moves.
160 std::ostream& operator<< (std::ostream& os, const set960& f) {
162 os.iword(0) = int(f);
171 // Maximum depth for razoring
172 const Depth RazorDepth = 4 * ONE_PLY;
174 // Dynamic razoring margin based on depth
175 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
177 // Maximum depth for use of dynamic threat detection when null move fails low
178 const Depth ThreatDepth = 5 * ONE_PLY;
180 // Step 9. Internal iterative deepening
182 // Minimum depth for use of internal iterative deepening
183 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
185 // At Non-PV nodes we do an internal iterative deepening search
186 // when the static evaluation is bigger then beta - IIDMargin.
187 const Value IIDMargin = Value(0x100);
189 // Step 11. Decide the new search depth
191 // Extensions. Configurable UCI options. Array index 0 is used at
192 // non-PV nodes, index 1 at PV nodes.
193 Depth CheckExtension[2], PawnPushTo7thExtension[2];
194 Depth PassedPawnExtension[2], PawnEndgameExtension[2];
196 // Minimum depth for use of singular extension
197 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
199 // Step 12. Futility pruning
201 // Futility margin for quiescence search
202 const Value FutilityMarginQS = Value(0x80);
204 // Futility lookup tables (initialized at startup) and their access functions
205 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
206 int FutilityMoveCountArray[32]; // [depth]
208 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
209 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
211 // Step 14. Reduced search
213 // Reduction lookup tables (initialized at startup) and their access function
214 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
216 template <NodeType PV>
217 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / ONE_PLY, 63)][Min(mn, 63)]; }
219 // Easy move margin. An easy move candidate must be at least this much
220 // better than the second best move.
221 const Value EasyMoveMargin = Value(0x200);
224 /// Namespace variables
233 int MultiPV, UCIMultiPV;
235 // Time management variables
236 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
241 std::ofstream LogFile;
243 // Skill level adjustment
245 bool SkillLevelEnabled;
248 // Multi-threads manager
249 ThreadsManager ThreadsMgr;
251 // Node counters, used only by thread[0] but try to keep in different cache
252 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
253 bool SendSearchedNodes;
255 int NodesBetweenPolls = 30000;
263 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
265 template <NodeType PvNode, bool SpNode, bool Root>
266 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
268 template <NodeType PvNode>
269 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
271 template <NodeType PvNode>
272 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
274 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO)
275 : search<PvNode, false, false>(pos, ss, alpha, beta, depth);
278 template <NodeType PvNode>
279 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
281 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
282 bool connected_moves(const Position& pos, Move m1, Move m2);
283 Value value_to_tt(Value v, int ply);
284 Value value_from_tt(Value v, int ply);
285 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
286 bool connected_threat(const Position& pos, Move m, Move threat);
287 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
288 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
289 void update_gains(const Position& pos, Move move, Value before, Value after);
290 void do_skill_level(Move* best, Move* ponder);
292 int current_search_time(int set = 0);
293 std::string value_to_uci(Value v);
294 std::string speed_to_uci(int64_t nodes);
295 void poll(const Position& pos);
296 void wait_for_stop_or_ponderhit();
298 #if !defined(_MSC_VER)
299 void* init_thread(void* threadID);
301 DWORD WINAPI init_thread(LPVOID threadID);
305 // MovePickerExt is an extended MovePicker class used to choose at compile time
306 // the proper move source according to the type of node.
307 template<bool SpNode, bool Root> struct MovePickerExt;
309 // In Root nodes use RootMoveList as source. Score and sort the root moves
310 // before to search them.
311 template<> struct MovePickerExt<false, true> : public MovePicker {
313 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
314 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
316 Value score = VALUE_ZERO;
318 // Score root moves using standard ordering used in main search, the moves
319 // are scored according to the order in which they are returned by MovePicker.
320 // This is the second order score that is used to compare the moves when
321 // the first orders pv_score of both moves are equal.
322 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
323 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
324 if (rm->pv[0] == move)
326 rm->non_pv_score = score--;
334 Move get_next_move() {
341 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
344 RootMoveList::iterator rm;
348 // In SpNodes use split point's shared MovePicker object as move source
349 template<> struct MovePickerExt<true, false> : public MovePicker {
351 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
352 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
354 Move get_next_move() { return mp->get_next_move(); }
356 RootMoveList::iterator rm; // Dummy, needed to compile
360 // Default case, create and use a MovePicker object as source
361 template<> struct MovePickerExt<false, false> : public MovePicker {
363 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
364 : MovePicker(p, ttm, d, h, ss, b) {}
366 RootMoveList::iterator rm; // Dummy, needed to compile
372 /// init_threads() is called during startup. It initializes various lookup tables
373 /// and creates and launches search threads.
375 void init_threads() {
377 int d; // depth (ONE_PLY == 2)
378 int hd; // half depth (ONE_PLY == 1)
381 // Init reductions array
382 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
384 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
385 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
386 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
387 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
390 // Init futility margins array
391 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
392 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
394 // Init futility move count array
395 for (d = 0; d < 32; d++)
396 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
398 // Create and startup threads
399 ThreadsMgr.init_threads();
403 /// exit_threads() is a trampoline to access ThreadsMgr from outside of current file
404 void exit_threads() { ThreadsMgr.exit_threads(); }
407 /// perft() is our utility to verify move generation. All the legal moves up to
408 /// given depth are generated and counted and the sum returned.
410 int64_t perft(Position& pos, Depth depth) {
412 MoveStack mlist[MOVES_MAX];
417 // Generate all legal moves
418 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
420 // If we are at the last ply we don't need to do and undo
421 // the moves, just to count them.
422 if (depth <= ONE_PLY)
423 return int(last - mlist);
425 // Loop through all legal moves
427 for (MoveStack* cur = mlist; cur != last; cur++)
430 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
431 sum += perft(pos, depth - ONE_PLY);
438 /// think() is the external interface to Stockfish's search, and is called when
439 /// the program receives the UCI 'go' command. It initializes various global
440 /// variables, and calls id_loop(). It returns false when a "quit" command is
441 /// received during the search.
443 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
445 // Initialize global search-related variables
446 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
448 current_search_time(get_system_time());
450 TimeMgr.init(Limits, pos.startpos_ply_counter());
452 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
454 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
455 else if (Limits.time && Limits.time < 1000)
456 NodesBetweenPolls = 1000;
457 else if (Limits.time && Limits.time < 5000)
458 NodesBetweenPolls = 5000;
460 NodesBetweenPolls = 30000;
462 // Look for a book move, only during games, not tests
463 if (Limits.useTimeManagement() && Options["OwnBook"].value<bool>())
465 if (Options["Book File"].value<std::string>() != OpeningBook.name())
466 OpeningBook.open(Options["Book File"].value<std::string>());
468 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
469 if (bookMove != MOVE_NONE)
472 wait_for_stop_or_ponderhit();
474 cout << "bestmove " << bookMove << endl;
480 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
481 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
482 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
483 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
484 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
485 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
486 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
487 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
488 UCIMultiPV = Options["MultiPV"].value<int>();
489 SkillLevel = Options["Skill level"].value<int>();
491 read_evaluation_uci_options(pos.side_to_move());
493 if (Options["Clear Hash"].value<bool>())
495 Options["Clear Hash"].set_value("false");
498 TT.set_size(Options["Hash"].value<int>());
500 // Do we have to play with skill handicap? In this case enable MultiPV that
501 // we will use behind the scenes to retrieve a set of possible moves.
502 SkillLevelEnabled = (SkillLevel < 20);
503 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
505 // Set the number of active threads
506 ThreadsMgr.read_uci_options();
507 init_eval(ThreadsMgr.active_threads());
509 // Wake up needed threads and reset maxPly counter
510 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
512 ThreadsMgr[i].wake_up();
513 ThreadsMgr[i].maxPly = 0;
516 // Write to log file and keep it open to be accessed during the search
517 if (Options["Use Search Log"].value<bool>())
519 std::string name = Options["Search Log Filename"].value<std::string>();
520 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
522 if (LogFile.is_open())
523 LogFile << "\nSearching: " << pos.to_fen()
524 << "\ninfinite: " << Limits.infinite
525 << " ponder: " << Limits.ponder
526 << " time: " << Limits.time
527 << " increment: " << Limits.increment
528 << " moves to go: " << Limits.movesToGo
532 // We're ready to start thinking. Call the iterative deepening loop function
533 Move ponderMove = MOVE_NONE;
534 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
536 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
538 // Write final search statistics and close log file
539 if (LogFile.is_open())
541 int t = current_search_time();
543 LogFile << "Nodes: " << pos.nodes_searched()
544 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
545 << "\nBest move: " << move_to_san(pos, bestMove);
548 pos.do_move(bestMove, st);
549 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
550 pos.undo_move(bestMove); // Return from think() with unchanged position
554 // This makes all the threads to go to sleep
555 ThreadsMgr.set_active_threads(1);
557 // If we are pondering or in infinite search, we shouldn't print the
558 // best move before we are told to do so.
559 if (!StopRequest && (Limits.ponder || Limits.infinite))
560 wait_for_stop_or_ponderhit();
562 // Could be MOVE_NONE when searching on a stalemate position
563 cout << "bestmove " << bestMove;
565 // UCI protol is not clear on allowing sending an empty ponder move, instead
566 // it is clear that ponder move is optional. So skip it if empty.
567 if (ponderMove != MOVE_NONE)
568 cout << " ponder " << ponderMove;
578 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
579 // with increasing depth until the allocated thinking time has been consumed,
580 // user stops the search, or the maximum search depth is reached.
582 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
584 SearchStack ss[PLY_MAX_PLUS_2];
585 Value bestValues[PLY_MAX_PLUS_2];
586 int bestMoveChanges[PLY_MAX_PLUS_2];
587 int depth, selDepth, aspirationDelta;
588 Value value, alpha, beta;
589 Move bestMove, easyMove, skillBest, skillPonder;
591 // Initialize stuff before a new search
592 memset(ss, 0, 4 * sizeof(SearchStack));
595 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
596 depth = aspirationDelta = 0;
597 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
598 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
600 // Moves to search are verified and copied
601 Rml.init(pos, searchMoves);
603 // Handle special case of searching on a mate/stalemate position
606 cout << "info depth 0 score "
607 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
613 // Iterative deepening loop
614 while (++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth) && !StopRequest)
616 Rml.bestMoveChanges = 0;
617 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
619 // Calculate dynamic aspiration window based on previous iterations
620 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
622 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
623 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
625 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
626 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
628 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
629 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
632 // Start with a small aspiration window and, in case of fail high/low,
633 // research with bigger window until not failing high/low anymore.
635 // Search starting from ss+1 to allow calling update_gains()
636 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY);
638 // Write PV back to transposition table in case the relevant entries
639 // have been overwritten during the search.
640 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
641 Rml[i].insert_pv_in_tt(pos);
643 // Value cannot be trusted. Break out immediately!
647 assert(value >= alpha);
649 // In case of failing high/low increase aspiration window and research,
650 // otherwise exit the fail high/low loop.
653 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
654 aspirationDelta += aspirationDelta / 2;
656 else if (value <= alpha)
658 AspirationFailLow = true;
659 StopOnPonderhit = false;
661 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
662 aspirationDelta += aspirationDelta / 2;
667 } while (abs(value) < VALUE_KNOWN_WIN);
669 // Collect info about search result
670 bestMove = Rml[0].pv[0];
671 *ponderMove = Rml[0].pv[1];
672 bestValues[depth] = value;
673 bestMoveChanges[depth] = Rml.bestMoveChanges;
675 // Do we need to pick now the best and the ponder moves ?
676 if (SkillLevelEnabled && depth == 1 + SkillLevel)
677 do_skill_level(&skillBest, &skillPonder);
679 // Retrieve max searched depth among threads
681 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
682 if (ThreadsMgr[i].maxPly > selDepth)
683 selDepth = ThreadsMgr[i].maxPly;
685 // Send PV line to GUI and to log file
686 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
687 cout << Rml[i].pv_info_to_uci(pos, depth, selDepth, alpha, beta, i) << endl;
689 if (LogFile.is_open())
690 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
692 // Init easyMove after first iteration or drop if differs from the best move
693 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
695 else if (bestMove != easyMove)
696 easyMove = MOVE_NONE;
698 if (Limits.useTimeManagement() && !StopRequest)
701 bool noMoreTime = false;
703 // Stop search early when the last two iterations returned a mate score
705 && abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
706 && abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
709 // Stop search early if one move seems to be much better than the
710 // others or if there is only a single legal move. In this latter
711 // case we search up to Iteration 8 anyway to get a proper score.
713 && easyMove == bestMove
715 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
716 && current_search_time() > TimeMgr.available_time() / 16)
717 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
718 && current_search_time() > TimeMgr.available_time() / 32)))
721 // Add some extra time if the best move has changed during the last two iterations
722 if (depth > 4 && depth < 50)
723 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
725 // Stop search if most of MaxSearchTime is consumed at the end of the
726 // iteration. We probably don't have enough time to search the first
727 // move at the next iteration anyway.
728 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
734 StopOnPonderhit = true;
741 // When using skills fake best and ponder moves with the sub-optimal ones
742 if (SkillLevelEnabled)
744 if (skillBest == MOVE_NONE) // Still unassigned ?
745 do_skill_level(&skillBest, &skillPonder);
747 bestMove = skillBest;
748 *ponderMove = skillPonder;
755 // search<>() is the main search function for both PV and non-PV nodes and for
756 // normal and SplitPoint nodes. When called just after a split point the search
757 // is simpler because we have already probed the hash table, done a null move
758 // search, and searched the first move before splitting, we don't have to repeat
759 // all this work again. We also don't need to store anything to the hash table
760 // here: This is taken care of after we return from the split point.
762 template <NodeType PvNode, bool SpNode, bool Root>
763 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
765 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
766 assert(beta > alpha && beta <= VALUE_INFINITE);
767 assert(PvNode || alpha == beta - 1);
768 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
770 Move movesSearched[MOVES_MAX];
775 Move ttMove, move, excludedMove, threatMove;
778 Value bestValue, value, oldAlpha;
779 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
780 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous, isBadCap;
781 int moveCount = 0, playedMoveCount = 0;
782 int threadID = pos.thread();
783 SplitPoint* sp = NULL;
785 refinedValue = bestValue = value = -VALUE_INFINITE;
787 isCheck = pos.is_check();
788 ss->ply = (ss-1)->ply + 1;
790 // Used to send selDepth info to GUI
791 if (PvNode && ThreadsMgr[threadID].maxPly < ss->ply)
792 ThreadsMgr[threadID].maxPly = ss->ply;
798 ttMove = excludedMove = MOVE_NONE;
799 threatMove = sp->threatMove;
800 goto split_point_start;
805 // Step 1. Initialize node and poll. Polling can abort search
806 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
807 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
808 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
810 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
816 // Step 2. Check for aborted search and immediate draw
818 || ThreadsMgr.cutoff_at_splitpoint(threadID)
820 || ss->ply > PLY_MAX) && !Root)
823 // Step 3. Mate distance pruning
824 alpha = Max(value_mated_in(ss->ply), alpha);
825 beta = Min(value_mate_in(ss->ply+1), beta);
829 // Step 4. Transposition table lookup
830 // We don't want the score of a partial search to overwrite a previous full search
831 // TT value, so we use a different position key in case of an excluded move.
832 excludedMove = ss->excludedMove;
833 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
835 tte = TT.retrieve(posKey);
836 ttMove = tte ? tte->move() : MOVE_NONE;
838 // At PV nodes we check for exact scores, while at non-PV nodes we check for
839 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
840 // smooth experience in analysis mode.
843 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
844 : ok_to_use_TT(tte, depth, beta, ss->ply)))
847 ss->bestMove = ttMove; // Can be MOVE_NONE
848 return value_from_tt(tte->value(), ss->ply);
851 // Step 5. Evaluate the position statically and update parent's gain statistics
853 ss->eval = ss->evalMargin = VALUE_NONE;
856 assert(tte->static_value() != VALUE_NONE);
858 ss->eval = tte->static_value();
859 ss->evalMargin = tte->static_value_margin();
860 refinedValue = refine_eval(tte, ss->eval, ss->ply);
864 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
865 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
868 // Save gain for the parent non-capture move
869 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
871 // Step 6. Razoring (is omitted in PV nodes)
873 && depth < RazorDepth
875 && refinedValue + razor_margin(depth) < beta
876 && ttMove == MOVE_NONE
877 && abs(beta) < VALUE_MATE_IN_PLY_MAX
878 && !pos.has_pawn_on_7th(pos.side_to_move()))
880 Value rbeta = beta - razor_margin(depth);
881 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
883 // Logically we should return (v + razor_margin(depth)), but
884 // surprisingly this did slightly weaker in tests.
888 // Step 7. Static null move pruning (is omitted in PV nodes)
889 // We're betting that the opponent doesn't have a move that will reduce
890 // the score by more than futility_margin(depth) if we do a null move.
893 && depth < RazorDepth
895 && refinedValue - futility_margin(depth, 0) >= beta
896 && abs(beta) < VALUE_MATE_IN_PLY_MAX
897 && pos.non_pawn_material(pos.side_to_move()))
898 return refinedValue - futility_margin(depth, 0);
900 // Step 8. Null move search with verification search (is omitted in PV nodes)
905 && refinedValue >= beta
906 && abs(beta) < VALUE_MATE_IN_PLY_MAX
907 && pos.non_pawn_material(pos.side_to_move()))
909 ss->currentMove = MOVE_NULL;
911 // Null move dynamic reduction based on depth
912 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
914 // Null move dynamic reduction based on value
915 if (refinedValue - PawnValueMidgame > beta)
918 pos.do_null_move(st);
919 (ss+1)->skipNullMove = true;
920 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
921 (ss+1)->skipNullMove = false;
922 pos.undo_null_move();
924 if (nullValue >= beta)
926 // Do not return unproven mate scores
927 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
930 if (depth < 6 * ONE_PLY)
933 // Do verification search at high depths
934 ss->skipNullMove = true;
935 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
936 ss->skipNullMove = false;
943 // The null move failed low, which means that we may be faced with
944 // some kind of threat. If the previous move was reduced, check if
945 // the move that refuted the null move was somehow connected to the
946 // move which was reduced. If a connection is found, return a fail
947 // low score (which will cause the reduced move to fail high in the
948 // parent node, which will trigger a re-search with full depth).
949 threatMove = (ss+1)->bestMove;
951 if ( depth < ThreatDepth
953 && threatMove != MOVE_NONE
954 && connected_moves(pos, (ss-1)->currentMove, threatMove))
959 // Step 9. Internal iterative deepening
960 if ( depth >= IIDDepth[PvNode]
961 && ttMove == MOVE_NONE
962 && (PvNode || (!isCheck && ss->eval + IIDMargin >= beta)))
964 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
966 ss->skipNullMove = true;
967 search<PvNode>(pos, ss, alpha, beta, d);
968 ss->skipNullMove = false;
970 ttMove = ss->bestMove;
971 tte = TT.retrieve(posKey);
974 split_point_start: // At split points actual search starts from here
976 // Initialize a MovePicker object for the current position
977 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
979 ss->bestMove = MOVE_NONE;
980 futilityBase = ss->eval + ss->evalMargin;
981 singularExtensionNode = !Root
983 && depth >= SingularExtensionDepth[PvNode]
986 && !excludedMove // Do not allow recursive singular extension search
987 && (tte->type() & VALUE_TYPE_LOWER)
988 && tte->depth() >= depth - 3 * ONE_PLY;
991 lock_grab(&(sp->lock));
992 bestValue = sp->bestValue;
995 // Step 10. Loop through moves
996 // Loop through all legal moves until no moves remain or a beta cutoff occurs
997 while ( bestValue < beta
998 && (move = mp.get_next_move()) != MOVE_NONE
999 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1001 assert(move_is_ok(move));
1005 moveCount = ++sp->moveCount;
1006 lock_release(&(sp->lock));
1008 else if (move == excludedMove)
1015 // This is used by time management
1016 FirstRootMove = (moveCount == 1);
1018 // Save the current node count before the move is searched
1019 nodes = pos.nodes_searched();
1021 // If it's time to send nodes info, do it here where we have the
1022 // correct accumulated node counts searched by each thread.
1023 if (SendSearchedNodes)
1025 SendSearchedNodes = false;
1026 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1029 if (current_search_time() > 2000)
1030 cout << "info currmove " << move
1031 << " currmovenumber " << moveCount << endl;
1034 // At Root and at first iteration do a PV search on all the moves to score root moves
1035 isPvMove = (PvNode && moveCount <= (Root ? depth <= ONE_PLY ? 1000 : 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, &dangerous);
1042 // Singular extension search. If all moves but one fail low on a search of
1043 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1044 // is singular and should be extended. To verify this we do a reduced search
1045 // on all the other moves but the ttMove, if result is lower than ttValue minus
1046 // a margin then we extend ttMove.
1047 if ( singularExtensionNode
1048 && move == tte->move()
1051 Value ttValue = value_from_tt(tte->value(), ss->ply);
1053 if (abs(ttValue) < VALUE_KNOWN_WIN)
1055 Value rBeta = ttValue - int(depth);
1056 ss->excludedMove = move;
1057 ss->skipNullMove = true;
1058 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1059 ss->skipNullMove = false;
1060 ss->excludedMove = MOVE_NONE;
1061 ss->bestMove = MOVE_NONE;
1067 // Update current move (this must be done after singular extension search)
1068 ss->currentMove = move;
1069 newDepth = depth - ONE_PLY + ext;
1071 // Step 12. Futility pruning (is omitted in PV nodes)
1073 && !captureOrPromotion
1077 && !move_is_castle(move))
1079 // Move count based pruning
1080 if ( moveCount >= futility_move_count(depth)
1081 && (!threatMove || !connected_threat(pos, move, threatMove))
1082 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1085 lock_grab(&(sp->lock));
1090 // Value based pruning
1091 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1092 // but fixing this made program slightly weaker.
1093 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1094 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1095 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1097 if (futilityValueScaled < beta)
1101 lock_grab(&(sp->lock));
1102 if (futilityValueScaled > sp->bestValue)
1103 sp->bestValue = bestValue = futilityValueScaled;
1105 else if (futilityValueScaled > bestValue)
1106 bestValue = futilityValueScaled;
1111 // Prune moves with negative SEE at low depths
1112 if ( predictedDepth < 2 * ONE_PLY
1113 && bestValue > VALUE_MATED_IN_PLY_MAX
1114 && pos.see_sign(move) < 0)
1117 lock_grab(&(sp->lock));
1123 // Bad capture detection. Will be used by prob-cut search
1124 isBadCap = depth >= 3 * ONE_PLY
1125 && depth < 8 * ONE_PLY
1126 && captureOrPromotion
1129 && !move_is_promotion(move)
1130 && abs(alpha) < VALUE_MATE_IN_PLY_MAX
1131 && pos.see_sign(move) < 0;
1133 // Step 13. Make the move
1134 pos.do_move(move, st, ci, moveIsCheck);
1136 if (!SpNode && !captureOrPromotion)
1137 movesSearched[playedMoveCount++] = move;
1139 // Step extra. pv search (only in PV nodes)
1140 // The first move in list is the expected PV
1143 // Aspiration window is disabled in multi-pv case
1144 if (Root && MultiPV > 1)
1145 alpha = -VALUE_INFINITE;
1147 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1151 // Step 14. Reduced depth search
1152 // If the move fails high will be re-searched at full depth.
1153 bool doFullDepthSearch = true;
1154 alpha = SpNode ? sp->alpha : alpha;
1156 if ( depth >= 3 * ONE_PLY
1157 && !captureOrPromotion
1159 && !move_is_castle(move)
1160 && ss->killers[0] != move
1161 && ss->killers[1] != move)
1163 ss->reduction = reduction<PvNode>(depth, moveCount);
1166 alpha = SpNode ? sp->alpha : alpha;
1167 Depth d = newDepth - ss->reduction;
1168 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1170 doFullDepthSearch = (value > alpha);
1172 ss->reduction = DEPTH_ZERO; // Restore original reduction
1175 // Probcut search for bad captures. If a reduced search returns a value
1176 // very below beta then we can (almost) safely prune the bad capture.
1179 ss->reduction = 3 * ONE_PLY;
1180 Value rAlpha = alpha - 300;
1181 Depth d = newDepth - ss->reduction;
1182 value = -search<NonPV>(pos, ss+1, -(rAlpha+1), -rAlpha, d);
1183 doFullDepthSearch = (value > rAlpha);
1184 ss->reduction = DEPTH_ZERO; // Restore original reduction
1187 // Step 15. Full depth search
1188 if (doFullDepthSearch)
1190 alpha = SpNode ? sp->alpha : alpha;
1191 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1193 // Step extra. pv search (only in PV nodes)
1194 // Search only for possible new PV nodes, if instead value >= beta then
1195 // parent node fails low with value <= alpha and tries another move.
1196 if (PvNode && value > alpha && (Root || value < beta))
1197 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1201 // Step 16. Undo move
1202 pos.undo_move(move);
1204 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1206 // Step 17. Check for new best move
1209 lock_grab(&(sp->lock));
1210 bestValue = sp->bestValue;
1214 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1219 sp->bestValue = value;
1221 if (!Root && value > alpha)
1223 if (PvNode && value < beta) // We want always alpha < beta
1231 sp->betaCutoff = true;
1233 if (value == value_mate_in(ss->ply + 1))
1234 ss->mateKiller = move;
1236 ss->bestMove = move;
1239 sp->ss->bestMove = move;
1245 // Finished searching the move. If StopRequest is true, the search
1246 // was aborted because the user interrupted the search or because we
1247 // ran out of time. In this case, the return value of the search cannot
1248 // be trusted, and we break out of the loop without updating the best
1253 // Remember searched nodes counts for this move
1254 mp.rm->nodes += pos.nodes_searched() - nodes;
1256 // PV move or new best move ?
1257 if (isPvMove || value > alpha)
1260 ss->bestMove = move;
1261 mp.rm->pv_score = value;
1262 mp.rm->extract_pv_from_tt(pos);
1264 // We record how often the best move has been changed in each
1265 // iteration. This information is used for time management: When
1266 // the best move changes frequently, we allocate some more time.
1267 if (!isPvMove && MultiPV == 1)
1268 Rml.bestMoveChanges++;
1270 Rml.sort_multipv(moveCount);
1272 // Update alpha. In multi-pv we don't use aspiration window, so
1273 // set alpha equal to minimum score among the PV lines.
1275 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1276 else if (value > alpha)
1280 mp.rm->pv_score = -VALUE_INFINITE;
1284 // Step 18. Check for split
1287 && depth >= ThreadsMgr.min_split_depth()
1288 && ThreadsMgr.active_threads() > 1
1290 && ThreadsMgr.available_thread_exists(threadID)
1292 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1293 ThreadsMgr.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1294 threatMove, moveCount, &mp, PvNode);
1297 // Step 19. Check for mate and stalemate
1298 // All legal moves have been searched and if there are
1299 // no legal moves, it must be mate or stalemate.
1300 // If one move was excluded return fail low score.
1301 if (!SpNode && !moveCount)
1302 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1304 // Step 20. Update tables
1305 // If the search is not aborted, update the transposition table,
1306 // history counters, and killer moves.
1307 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1309 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1310 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1311 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1313 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1315 // Update killers and history only for non capture moves that fails high
1316 if ( bestValue >= beta
1317 && !pos.move_is_capture_or_promotion(move))
1319 if (move != ss->killers[0])
1321 ss->killers[1] = ss->killers[0];
1322 ss->killers[0] = move;
1324 update_history(pos, move, depth, movesSearched, playedMoveCount);
1330 // Here we have the lock still grabbed
1331 sp->slaves[threadID] = 0;
1332 sp->nodes += pos.nodes_searched();
1333 lock_release(&(sp->lock));
1336 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1341 // qsearch() is the quiescence search function, which is called by the main
1342 // search function when the remaining depth is zero (or, to be more precise,
1343 // less than ONE_PLY).
1345 template <NodeType PvNode>
1346 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1348 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1349 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1350 assert(PvNode || alpha == beta - 1);
1352 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1356 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1357 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1360 Value oldAlpha = alpha;
1362 ss->bestMove = ss->currentMove = MOVE_NONE;
1363 ss->ply = (ss-1)->ply + 1;
1365 // Check for an instant draw or maximum ply reached
1366 if (ss->ply > PLY_MAX || pos.is_draw())
1369 // Decide whether or not to include checks, this fixes also the type of
1370 // TT entry depth that we are going to use. Note that in qsearch we use
1371 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1372 isCheck = pos.is_check();
1373 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1375 // Transposition table lookup. At PV nodes, we don't use the TT for
1376 // pruning, but only for move ordering.
1377 tte = TT.retrieve(pos.get_key());
1378 ttMove = (tte ? tte->move() : MOVE_NONE);
1380 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1382 ss->bestMove = ttMove; // Can be MOVE_NONE
1383 return value_from_tt(tte->value(), ss->ply);
1386 // Evaluate the position statically
1389 bestValue = futilityBase = -VALUE_INFINITE;
1390 ss->eval = evalMargin = VALUE_NONE;
1391 enoughMaterial = false;
1397 assert(tte->static_value() != VALUE_NONE);
1399 evalMargin = tte->static_value_margin();
1400 ss->eval = bestValue = tte->static_value();
1403 ss->eval = bestValue = evaluate(pos, evalMargin);
1405 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1407 // Stand pat. Return immediately if static value is at least beta
1408 if (bestValue >= beta)
1411 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1416 if (PvNode && bestValue > alpha)
1419 // Futility pruning parameters, not needed when in check
1420 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1421 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1424 // Initialize a MovePicker object for the current position, and prepare
1425 // to search the moves. Because the depth is <= 0 here, only captures,
1426 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1428 MovePicker mp(pos, ttMove, depth, H);
1431 // Loop through the moves until no moves remain or a beta cutoff occurs
1432 while ( alpha < beta
1433 && (move = mp.get_next_move()) != MOVE_NONE)
1435 assert(move_is_ok(move));
1437 moveIsCheck = pos.move_is_check(move, ci);
1445 && !move_is_promotion(move)
1446 && !pos.move_is_passed_pawn_push(move))
1448 futilityValue = futilityBase
1449 + pos.endgame_value_of_piece_on(move_to(move))
1450 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1452 if (futilityValue < alpha)
1454 if (futilityValue > bestValue)
1455 bestValue = futilityValue;
1459 // Prune moves with negative or equal SEE
1460 if ( futilityBase < beta
1461 && depth < DEPTH_ZERO
1462 && pos.see(move) <= 0)
1466 // Detect non-capture evasions that are candidate to be pruned
1467 evasionPrunable = isCheck
1468 && bestValue > VALUE_MATED_IN_PLY_MAX
1469 && !pos.move_is_capture(move)
1470 && !pos.can_castle(pos.side_to_move());
1472 // Don't search moves with negative SEE values
1474 && (!isCheck || evasionPrunable)
1476 && !move_is_promotion(move)
1477 && pos.see_sign(move) < 0)
1480 // Don't search useless checks
1485 && !pos.move_is_capture_or_promotion(move)
1486 && ss->eval + PawnValueMidgame / 4 < beta
1487 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1489 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1490 bestValue = ss->eval + PawnValueMidgame / 4;
1495 // Update current move
1496 ss->currentMove = move;
1498 // Make and search the move
1499 pos.do_move(move, st, ci, moveIsCheck);
1500 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1501 pos.undo_move(move);
1503 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1506 if (value > bestValue)
1512 ss->bestMove = move;
1517 // All legal moves have been searched. A special case: If we're in check
1518 // and no legal moves were found, it is checkmate.
1519 if (isCheck && bestValue == -VALUE_INFINITE)
1520 return value_mated_in(ss->ply);
1522 // Update transposition table
1523 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1524 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1526 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1532 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1533 // bestValue is updated only when returning false because in that case move
1536 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1538 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1539 Square from, to, ksq, victimSq;
1542 Value futilityValue, bv = *bestValue;
1544 from = move_from(move);
1546 them = opposite_color(pos.side_to_move());
1547 ksq = pos.king_square(them);
1548 kingAtt = pos.attacks_from<KING>(ksq);
1549 pc = pos.piece_on(from);
1551 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1552 oldAtt = pos.attacks_from(pc, from, occ);
1553 newAtt = pos.attacks_from(pc, to, occ);
1555 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1556 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1558 if (!(b && (b & (b - 1))))
1561 // Rule 2. Queen contact check is very dangerous
1562 if ( type_of_piece(pc) == QUEEN
1563 && bit_is_set(kingAtt, to))
1566 // Rule 3. Creating new double threats with checks
1567 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1571 victimSq = pop_1st_bit(&b);
1572 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1574 // Note that here we generate illegal "double move"!
1575 if ( futilityValue >= beta
1576 && pos.see_sign(make_move(from, victimSq)) >= 0)
1579 if (futilityValue > bv)
1583 // Update bestValue only if check is not dangerous (because we will prune the move)
1589 // connected_moves() tests whether two moves are 'connected' in the sense
1590 // that the first move somehow made the second move possible (for instance
1591 // if the moving piece is the same in both moves). The first move is assumed
1592 // to be the move that was made to reach the current position, while the
1593 // second move is assumed to be a move from the current position.
1595 bool connected_moves(const Position& pos, Move m1, Move m2) {
1597 Square f1, t1, f2, t2;
1600 assert(m1 && move_is_ok(m1));
1601 assert(m2 && move_is_ok(m2));
1603 // Case 1: The moving piece is the same in both moves
1609 // Case 2: The destination square for m2 was vacated by m1
1615 // Case 3: Moving through the vacated square
1616 if ( piece_is_slider(pos.piece_on(f2))
1617 && bit_is_set(squares_between(f2, t2), f1))
1620 // Case 4: The destination square for m2 is defended by the moving piece in m1
1621 p = pos.piece_on(t1);
1622 if (bit_is_set(pos.attacks_from(p, t1), t2))
1625 // Case 5: Discovered check, checking piece is the piece moved in m1
1626 if ( piece_is_slider(p)
1627 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1628 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1630 // discovered_check_candidates() works also if the Position's side to
1631 // move is the opposite of the checking piece.
1632 Color them = opposite_color(pos.side_to_move());
1633 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1635 if (bit_is_set(dcCandidates, f2))
1642 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1643 // "plies to mate from the current ply". Non-mate scores are unchanged.
1644 // The function is called before storing a value to the transposition table.
1646 Value value_to_tt(Value v, int ply) {
1648 if (v >= VALUE_MATE_IN_PLY_MAX)
1651 if (v <= VALUE_MATED_IN_PLY_MAX)
1658 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1659 // the transposition table to a mate score corrected for the current ply.
1661 Value value_from_tt(Value v, int ply) {
1663 if (v >= VALUE_MATE_IN_PLY_MAX)
1666 if (v <= VALUE_MATED_IN_PLY_MAX)
1673 // extension() decides whether a move should be searched with normal depth,
1674 // or with extended depth. Certain classes of moves (checking moves, in
1675 // particular) are searched with bigger depth than ordinary moves and in
1676 // any case are marked as 'dangerous'. Note that also if a move is not
1677 // extended, as example because the corresponding UCI option is set to zero,
1678 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1679 template <NodeType PvNode>
1680 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1681 bool moveIsCheck, bool* dangerous) {
1683 assert(m != MOVE_NONE);
1685 Depth result = DEPTH_ZERO;
1686 *dangerous = moveIsCheck;
1688 if (moveIsCheck && pos.see_sign(m) >= 0)
1689 result += CheckExtension[PvNode];
1691 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1693 Color c = pos.side_to_move();
1694 if (relative_rank(c, move_to(m)) == RANK_7)
1696 result += PawnPushTo7thExtension[PvNode];
1699 if (pos.pawn_is_passed(c, move_to(m)))
1701 result += PassedPawnExtension[PvNode];
1706 if ( captureOrPromotion
1707 && pos.type_of_piece_on(move_to(m)) != PAWN
1708 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1709 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1710 && !move_is_special(m))
1712 result += PawnEndgameExtension[PvNode];
1716 return Min(result, ONE_PLY);
1720 // connected_threat() tests whether it is safe to forward prune a move or if
1721 // is somehow connected to the threat move returned by null search.
1723 bool connected_threat(const Position& pos, Move m, Move threat) {
1725 assert(move_is_ok(m));
1726 assert(threat && move_is_ok(threat));
1727 assert(!pos.move_is_check(m));
1728 assert(!pos.move_is_capture_or_promotion(m));
1729 assert(!pos.move_is_passed_pawn_push(m));
1731 Square mfrom, mto, tfrom, tto;
1733 mfrom = move_from(m);
1735 tfrom = move_from(threat);
1736 tto = move_to(threat);
1738 // Case 1: Don't prune moves which move the threatened piece
1742 // Case 2: If the threatened piece has value less than or equal to the
1743 // value of the threatening piece, don't prune moves which defend it.
1744 if ( pos.move_is_capture(threat)
1745 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1746 || pos.type_of_piece_on(tfrom) == KING)
1747 && pos.move_attacks_square(m, tto))
1750 // Case 3: If the moving piece in the threatened move is a slider, don't
1751 // prune safe moves which block its ray.
1752 if ( piece_is_slider(pos.piece_on(tfrom))
1753 && bit_is_set(squares_between(tfrom, tto), mto)
1754 && pos.see_sign(m) >= 0)
1761 // ok_to_use_TT() returns true if a transposition table score
1762 // can be used at a given point in search.
1764 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1766 Value v = value_from_tt(tte->value(), ply);
1768 return ( tte->depth() >= depth
1769 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1770 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1772 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1773 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1777 // refine_eval() returns the transposition table score if
1778 // possible otherwise falls back on static position evaluation.
1780 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1784 Value v = value_from_tt(tte->value(), ply);
1786 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1787 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1794 // update_history() registers a good move that produced a beta-cutoff
1795 // in history and marks as failures all the other moves of that ply.
1797 void update_history(const Position& pos, Move move, Depth depth,
1798 Move movesSearched[], int moveCount) {
1800 Value bonus = Value(int(depth) * int(depth));
1802 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1804 for (int i = 0; i < moveCount - 1; i++)
1806 m = movesSearched[i];
1810 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1815 // update_gains() updates the gains table of a non-capture move given
1816 // the static position evaluation before and after the move.
1818 void update_gains(const Position& pos, Move m, Value before, Value after) {
1821 && before != VALUE_NONE
1822 && after != VALUE_NONE
1823 && pos.captured_piece_type() == PIECE_TYPE_NONE
1824 && !move_is_special(m))
1825 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1829 // current_search_time() returns the number of milliseconds which have passed
1830 // since the beginning of the current search.
1832 int current_search_time(int set) {
1834 static int searchStartTime;
1837 searchStartTime = set;
1839 return get_system_time() - searchStartTime;
1843 // value_to_uci() converts a value to a string suitable for use with the UCI
1844 // protocol specifications:
1846 // cp <x> The score from the engine's point of view in centipawns.
1847 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1848 // use negative values for y.
1850 std::string value_to_uci(Value v) {
1852 std::stringstream s;
1854 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1855 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1857 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1863 // speed_to_uci() returns a string with time stats of current search suitable
1864 // to be sent to UCI gui.
1866 std::string speed_to_uci(int64_t nodes) {
1868 std::stringstream s;
1869 int t = current_search_time();
1871 s << " nodes " << nodes
1872 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1879 // poll() performs two different functions: It polls for user input, and it
1880 // looks at the time consumed so far and decides if it's time to abort the
1883 void poll(const Position& pos) {
1885 static int lastInfoTime;
1886 int t = current_search_time();
1889 if (input_available())
1891 // We are line oriented, don't read single chars
1892 std::string command;
1894 if (!std::getline(std::cin, command) || command == "quit")
1896 // Quit the program as soon as possible
1897 Limits.ponder = false;
1898 QuitRequest = StopRequest = true;
1901 else if (command == "stop")
1903 // Stop calculating as soon as possible, but still send the "bestmove"
1904 // and possibly the "ponder" token when finishing the search.
1905 Limits.ponder = false;
1908 else if (command == "ponderhit")
1910 // The opponent has played the expected move. GUI sends "ponderhit" if
1911 // we were told to ponder on the same move the opponent has played. We
1912 // should continue searching but switching from pondering to normal search.
1913 Limits.ponder = false;
1915 if (StopOnPonderhit)
1920 // Print search information
1924 else if (lastInfoTime > t)
1925 // HACK: Must be a new search where we searched less than
1926 // NodesBetweenPolls nodes during the first second of search.
1929 else if (t - lastInfoTime >= 1000)
1934 dbg_print_hit_rate();
1936 // Send info on searched nodes as soon as we return to root
1937 SendSearchedNodes = true;
1940 // Should we stop the search?
1944 bool stillAtFirstMove = FirstRootMove
1945 && !AspirationFailLow
1946 && t > TimeMgr.available_time();
1948 bool noMoreTime = t > TimeMgr.maximum_time()
1949 || stillAtFirstMove;
1951 if ( (Limits.useTimeManagement() && noMoreTime)
1952 || (Limits.maxTime && t >= Limits.maxTime)
1953 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1958 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1959 // while the program is pondering. The point is to work around a wrinkle in
1960 // the UCI protocol: When pondering, the engine is not allowed to give a
1961 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1962 // We simply wait here until one of these commands is sent, and return,
1963 // after which the bestmove and pondermove will be printed.
1965 void wait_for_stop_or_ponderhit() {
1967 std::string command;
1969 // Wait for a command from stdin
1970 while ( std::getline(std::cin, command)
1971 && command != "ponderhit" && command != "stop" && command != "quit") {};
1973 if (command != "ponderhit" && command != "stop")
1974 QuitRequest = true; // Must be "quit" or getline() returned false
1978 // init_thread() is the function which is called when a new thread is
1979 // launched. It simply calls the idle_loop() function with the supplied
1980 // threadID. There are two versions of this function; one for POSIX
1981 // threads and one for Windows threads.
1983 #if !defined(_MSC_VER)
1985 void* init_thread(void* threadID) {
1987 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
1993 DWORD WINAPI init_thread(LPVOID threadID) {
1995 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2002 /// The ThreadsManager class
2005 // read_uci_options() updates number of active threads and other internal
2006 // parameters according to the UCI options values. It is called before
2007 // to start a new search.
2009 void ThreadsManager::read_uci_options() {
2011 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2012 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2013 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2014 activeThreads = Options["Threads"].value<int>();
2018 // idle_loop() is where the threads are parked when they have no work to do.
2019 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2020 // object for which the current thread is the master.
2022 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2024 assert(threadID >= 0 && threadID < MAX_THREADS);
2031 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2032 // master should exit as last one.
2033 if (allThreadsShouldExit)
2036 threads[threadID].state = THREAD_TERMINATED;
2040 // If we are not thinking, wait for a condition to be signaled
2041 // instead of wasting CPU time polling for work.
2042 while ( threadID >= activeThreads
2043 || threads[threadID].state == THREAD_INITIALIZING
2044 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2046 assert(!sp || useSleepingThreads);
2047 assert(threadID != 0 || useSleepingThreads);
2049 if (threads[threadID].state == THREAD_INITIALIZING)
2050 threads[threadID].state = THREAD_AVAILABLE;
2052 // Grab the lock to avoid races with Thread::wake_up()
2053 lock_grab(&threads[threadID].sleepLock);
2055 // If we are master and all slaves have finished do not go to sleep
2056 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2057 allFinished = (i == activeThreads);
2059 if (allFinished || allThreadsShouldExit)
2061 lock_release(&threads[threadID].sleepLock);
2065 // Do sleep here after retesting sleep conditions
2066 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2067 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2069 lock_release(&threads[threadID].sleepLock);
2072 // If this thread has been assigned work, launch a search
2073 if (threads[threadID].state == THREAD_WORKISWAITING)
2075 assert(!allThreadsShouldExit);
2077 threads[threadID].state = THREAD_SEARCHING;
2079 // Copy split point position and search stack and call search()
2080 // with SplitPoint template parameter set to true.
2081 SearchStack ss[PLY_MAX_PLUS_2];
2082 SplitPoint* tsp = threads[threadID].splitPoint;
2083 Position pos(*tsp->pos, threadID);
2085 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2089 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2091 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2093 assert(threads[threadID].state == THREAD_SEARCHING);
2095 threads[threadID].state = THREAD_AVAILABLE;
2097 // Wake up master thread so to allow it to return from the idle loop in
2098 // case we are the last slave of the split point.
2099 if ( useSleepingThreads
2100 && threadID != tsp->master
2101 && threads[tsp->master].state == THREAD_AVAILABLE)
2102 threads[tsp->master].wake_up();
2105 // If this thread is the master of a split point and all slaves have
2106 // finished their work at this split point, return from the idle loop.
2107 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2108 allFinished = (i == activeThreads);
2112 // Because sp->slaves[] is reset under lock protection,
2113 // be sure sp->lock has been released before to return.
2114 lock_grab(&(sp->lock));
2115 lock_release(&(sp->lock));
2117 // In helpful master concept a master can help only a sub-tree, and
2118 // because here is all finished is not possible master is booked.
2119 assert(threads[threadID].state == THREAD_AVAILABLE);
2121 threads[threadID].state = THREAD_SEARCHING;
2128 // init_threads() is called during startup. Initializes locks and condition
2129 // variables and launches all threads sending them immediately to sleep.
2131 void ThreadsManager::init_threads() {
2133 int i, arg[MAX_THREADS];
2136 // This flag is needed to properly end the threads when program exits
2137 allThreadsShouldExit = false;
2139 // Threads will sent to sleep as soon as created, only main thread is kept alive
2144 for (i = 0; i < MAX_THREADS; i++)
2146 // Initialize thread and split point locks
2147 lock_init(&threads[i].sleepLock);
2148 cond_init(&threads[i].sleepCond);
2150 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2151 lock_init(&(threads[i].splitPoints[j].lock));
2153 // All threads but first should be set to THREAD_INITIALIZING
2154 threads[i].state = (i == 0 ? THREAD_SEARCHING : THREAD_INITIALIZING);
2157 // Create and startup the threads
2158 for (i = 1; i < MAX_THREADS; i++)
2162 #if !defined(_MSC_VER)
2163 pthread_t pthread[1];
2164 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2165 pthread_detach(pthread[0]);
2167 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2171 cout << "Failed to create thread number " << i << endl;
2175 // Wait until the thread has finished launching and is gone to sleep
2176 while (threads[i].state == THREAD_INITIALIZING) {}
2181 // exit_threads() is called when the program exits. It makes all the
2182 // helper threads exit cleanly.
2184 void ThreadsManager::exit_threads() {
2186 // Force the woken up threads to exit idle_loop() and hence terminate
2187 allThreadsShouldExit = true;
2189 for (int i = 0; i < MAX_THREADS; i++)
2191 // Wake up all the threads and waits for termination
2194 threads[i].wake_up();
2195 while (threads[i].state != THREAD_TERMINATED) {}
2198 // Now we can safely destroy the locks and wait conditions
2199 lock_destroy(&threads[i].sleepLock);
2200 cond_destroy(&threads[i].sleepCond);
2202 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2203 lock_destroy(&(threads[i].splitPoints[j].lock));
2206 lock_destroy(&mpLock);
2210 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2211 // the thread's currently active split point, or in some ancestor of
2212 // the current split point.
2214 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2216 assert(threadID >= 0 && threadID < activeThreads);
2218 SplitPoint* sp = threads[threadID].splitPoint;
2220 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2225 // thread_is_available() checks whether the thread with threadID "slave" is
2226 // available to help the thread with threadID "master" at a split point. An
2227 // obvious requirement is that "slave" must be idle. With more than two
2228 // threads, this is not by itself sufficient: If "slave" is the master of
2229 // some active split point, it is only available as a slave to the other
2230 // threads which are busy searching the split point at the top of "slave"'s
2231 // split point stack (the "helpful master concept" in YBWC terminology).
2233 bool ThreadsManager::thread_is_available(int slave, int master) const {
2235 assert(slave >= 0 && slave < activeThreads);
2236 assert(master >= 0 && master < activeThreads);
2237 assert(activeThreads > 1);
2239 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2242 // Make a local copy to be sure doesn't change under our feet
2243 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2245 // No active split points means that the thread is available as
2246 // a slave for any other thread.
2247 if (localActiveSplitPoints == 0 || activeThreads == 2)
2250 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2251 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2252 // could have been set to 0 by another thread leading to an out of bound access.
2253 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2260 // available_thread_exists() tries to find an idle thread which is available as
2261 // a slave for the thread with threadID "master".
2263 bool ThreadsManager::available_thread_exists(int master) const {
2265 assert(master >= 0 && master < activeThreads);
2266 assert(activeThreads > 1);
2268 for (int i = 0; i < activeThreads; i++)
2269 if (thread_is_available(i, master))
2276 // split() does the actual work of distributing the work at a node between
2277 // several available threads. If it does not succeed in splitting the
2278 // node (because no idle threads are available, or because we have no unused
2279 // split point objects), the function immediately returns. If splitting is
2280 // possible, a SplitPoint object is initialized with all the data that must be
2281 // copied to the helper threads and we tell our helper threads that they have
2282 // been assigned work. This will cause them to instantly leave their idle loops and
2283 // call search().When all threads have returned from search() then split() returns.
2285 template <bool Fake>
2286 void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const Value beta,
2287 Value* bestValue, Depth depth, Move threatMove,
2288 int moveCount, MovePicker* mp, bool pvNode) {
2289 assert(pos.is_ok());
2290 assert(*bestValue >= -VALUE_INFINITE);
2291 assert(*bestValue <= *alpha);
2292 assert(*alpha < beta);
2293 assert(beta <= VALUE_INFINITE);
2294 assert(depth > DEPTH_ZERO);
2295 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2296 assert(activeThreads > 1);
2298 int i, master = pos.thread();
2299 Thread& masterThread = threads[master];
2303 // If no other thread is available to help us, or if we have too many
2304 // active split points, don't split.
2305 if ( !available_thread_exists(master)
2306 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2308 lock_release(&mpLock);
2312 // Pick the next available split point object from the split point stack
2313 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2315 // Initialize the split point object
2316 splitPoint.parent = masterThread.splitPoint;
2317 splitPoint.master = master;
2318 splitPoint.betaCutoff = false;
2319 splitPoint.depth = depth;
2320 splitPoint.threatMove = threatMove;
2321 splitPoint.alpha = *alpha;
2322 splitPoint.beta = beta;
2323 splitPoint.pvNode = pvNode;
2324 splitPoint.bestValue = *bestValue;
2326 splitPoint.moveCount = moveCount;
2327 splitPoint.pos = &pos;
2328 splitPoint.nodes = 0;
2330 for (i = 0; i < activeThreads; i++)
2331 splitPoint.slaves[i] = 0;
2333 masterThread.splitPoint = &splitPoint;
2335 // If we are here it means we are not available
2336 assert(masterThread.state != THREAD_AVAILABLE);
2338 int workersCnt = 1; // At least the master is included
2340 // Allocate available threads setting state to THREAD_BOOKED
2341 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2342 if (thread_is_available(i, master))
2344 threads[i].state = THREAD_BOOKED;
2345 threads[i].splitPoint = &splitPoint;
2346 splitPoint.slaves[i] = 1;
2350 assert(Fake || workersCnt > 1);
2352 // We can release the lock because slave threads are already booked and master is not available
2353 lock_release(&mpLock);
2355 // Tell the threads that they have work to do. This will make them leave
2357 for (i = 0; i < activeThreads; i++)
2358 if (i == master || splitPoint.slaves[i])
2360 assert(i == master || threads[i].state == THREAD_BOOKED);
2362 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2364 if (useSleepingThreads && i != master)
2365 threads[i].wake_up();
2368 // Everything is set up. The master thread enters the idle loop, from
2369 // which it will instantly launch a search, because its state is
2370 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2371 // idle loop, which means that the main thread will return from the idle
2372 // loop when all threads have finished their work at this split point.
2373 idle_loop(master, &splitPoint);
2375 // We have returned from the idle loop, which means that all threads are
2376 // finished. Update alpha and bestValue, and return.
2379 *alpha = splitPoint.alpha;
2380 *bestValue = splitPoint.bestValue;
2381 masterThread.activeSplitPoints--;
2382 masterThread.splitPoint = splitPoint.parent;
2383 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2385 lock_release(&mpLock);
2389 /// RootMove and RootMoveList method's definitions
2391 RootMove::RootMove() {
2394 pv_score = non_pv_score = -VALUE_INFINITE;
2398 RootMove& RootMove::operator=(const RootMove& rm) {
2400 const Move* src = rm.pv;
2403 // Avoid a costly full rm.pv[] copy
2404 do *dst++ = *src; while (*src++ != MOVE_NONE);
2407 pv_score = rm.pv_score;
2408 non_pv_score = rm.non_pv_score;
2412 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2413 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2414 // allow to always have a ponder move even when we fail high at root and also a
2415 // long PV to print that is important for position analysis.
2417 void RootMove::extract_pv_from_tt(Position& pos) {
2419 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2423 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2425 pos.do_move(pv[0], *st++);
2427 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2428 && tte->move() != MOVE_NONE
2429 && pos.move_is_legal(tte->move())
2431 && (!pos.is_draw() || ply < 2))
2433 pv[ply] = tte->move();
2434 pos.do_move(pv[ply++], *st++);
2436 pv[ply] = MOVE_NONE;
2438 do pos.undo_move(pv[--ply]); while (ply);
2441 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2442 // the PV back into the TT. This makes sure the old PV moves are searched
2443 // first, even if the old TT entries have been overwritten.
2445 void RootMove::insert_pv_in_tt(Position& pos) {
2447 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2450 Value v, m = VALUE_NONE;
2453 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2457 tte = TT.retrieve(k);
2459 // Don't overwrite existing correct entries
2460 if (!tte || tte->move() != pv[ply])
2462 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2463 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2465 pos.do_move(pv[ply], *st++);
2467 } while (pv[++ply] != MOVE_NONE);
2469 do pos.undo_move(pv[--ply]); while (ply);
2472 // pv_info_to_uci() returns a string with information on the current PV line
2473 // formatted according to UCI specification.
2475 std::string RootMove::pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha,
2476 Value beta, int pvIdx) {
2477 std::stringstream s;
2479 s << "info depth " << depth
2480 << " seldepth " << selDepth
2481 << " multipv " << pvIdx + 1
2482 << " score " << value_to_uci(pv_score)
2483 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2484 << speed_to_uci(pos.nodes_searched())
2487 for (Move* m = pv; *m != MOVE_NONE; m++)
2494 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2496 MoveStack mlist[MOVES_MAX];
2500 bestMoveChanges = 0;
2502 // Generate all legal moves and add them to RootMoveList
2503 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2504 for (MoveStack* cur = mlist; cur != last; cur++)
2506 // If we have a searchMoves[] list then verify cur->move
2507 // is in the list before to add it.
2508 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2510 if (searchMoves[0] && *sm != cur->move)
2514 rm.pv[0] = cur->move;
2515 rm.pv[1] = MOVE_NONE;
2516 rm.pv_score = -VALUE_INFINITE;
2522 // When playing with strength handicap choose best move among the MultiPV set
2523 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2524 void do_skill_level(Move* best, Move* ponder) {
2526 assert(MultiPV > 1);
2528 // Rml list is already sorted by pv_score in descending order
2530 int max_s = -VALUE_INFINITE;
2531 int size = Min(MultiPV, (int)Rml.size());
2532 int max = Rml[0].pv_score;
2533 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
2534 int wk = 120 - 2 * SkillLevel;
2536 // PRNG sequence should be non deterministic
2537 for (int i = abs(get_system_time() % 50); i > 0; i--)
2538 RK.rand<unsigned>();
2540 // Choose best move. For each move's score we add two terms both dependent
2541 // on wk, one deterministic and bigger for weaker moves, and one random,
2542 // then we choose the move with the resulting highest score.
2543 for (int i = 0; i < size; i++)
2545 s = Rml[i].pv_score;
2547 // Don't allow crazy blunders even at very low skills
2548 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
2551 // This is our magical formula
2552 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
2557 *best = Rml[i].pv[0];
2558 *ponder = Rml[i].pv[1];