2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
45 #include "ucioption.h"
51 //// Local definitions
57 enum NodeType { NonPV, PV };
59 // Set to true to force running with one thread.
60 // Used for debugging SMP code.
61 const bool FakeSplit = false;
63 // Fast lookup table of sliding pieces indexed by Piece
64 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
65 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
67 // ThreadsManager class is used to handle all the threads related stuff in search,
68 // init, starting, parking and, the most important, launching a slave thread at a
69 // split point are what this class does. All the access to shared thread data is
70 // done through this class, so that we avoid using global variables instead.
72 class ThreadsManager {
73 /* As long as the single ThreadsManager object is defined as a global we don't
74 need to explicitly initialize to zero its data members because variables with
75 static storage duration are automatically set to zero before enter main()
81 int min_split_depth() const { return minimumSplitDepth; }
82 int active_threads() const { return activeThreads; }
83 void set_active_threads(int cnt) { activeThreads = cnt; }
85 void read_uci_options();
86 bool available_thread_exists(int master) const;
87 bool thread_is_available(int slave, int master) const;
88 bool cutoff_at_splitpoint(int threadID) const;
89 void wake_sleeping_thread(int threadID);
90 void idle_loop(int threadID, SplitPoint* sp);
93 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
94 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
97 Depth minimumSplitDepth;
98 int maxThreadsPerSplitPoint;
99 bool useSleepingThreads;
101 volatile bool allThreadsShouldExit;
102 Thread threads[MAX_THREADS];
103 Lock mpLock, sleepLock[MAX_THREADS];
104 WaitCondition sleepCond[MAX_THREADS];
108 // RootMove struct is used for moves at the root at the tree. For each root
109 // move, we store two scores, a node count, and a PV (really a refutation
110 // in the case of moves which fail low). Value pv_score is normally set at
111 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
112 // according to the order in which moves are returned by MovePicker.
117 RootMove(const RootMove& rm) { *this = rm; }
118 RootMove& operator=(const RootMove& rm);
120 // RootMove::operator<() is the comparison function used when
121 // sorting the moves. A move m1 is considered to be better
122 // than a move m2 if it has an higher pv_score, or if it has
123 // equal pv_score but m1 has the higher non_pv_score. In this
124 // way we are guaranteed that PV moves are always sorted as first.
125 bool operator<(const RootMove& m) const {
126 return pv_score != m.pv_score ? pv_score < m.pv_score
127 : non_pv_score < m.non_pv_score;
130 void extract_pv_from_tt(Position& pos);
131 void insert_pv_in_tt(Position& pos);
132 std::string pv_info_to_uci(Position& pos, Depth depth, Value alpha, Value beta, int pvLine = 0);
137 Move pv[PLY_MAX_PLUS_2];
141 // RootMoveList struct is essentially a std::vector<> of RootMove objects,
142 // with an handful of methods above the standard ones.
144 struct RootMoveList : public std::vector<RootMove> {
146 typedef std::vector<RootMove> Base;
148 RootMoveList(Position& pos, Move searchMoves[]);
149 void set_non_pv_scores(const Position& pos, Move ttm, SearchStack* ss);
151 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
152 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
158 // When formatting a move for std::cout we must know if we are in Chess960
159 // or not. To keep using the handy operator<<() on the move the trick is to
160 // embed this flag in the stream itself. Function-like named enum set960 is
161 // used as a custom manipulator and the stream internal general-purpose array,
162 // accessed through ios_base::iword(), is used to pass the flag to the move's
163 // operator<<() that will use it to properly format castling moves.
166 std::ostream& operator<< (std::ostream& os, const set960& f) {
168 os.iword(0) = int(f);
173 // Overload operator << for moves to make it easier to print moves in
174 // coordinate notation compatible with UCI protocol.
175 std::ostream& operator<<(std::ostream& os, Move m) {
177 bool chess960 = (os.iword(0) != 0); // See set960()
178 return os << move_to_uci(m, chess960);
186 // Maximum depth for razoring
187 const Depth RazorDepth = 4 * ONE_PLY;
189 // Dynamic razoring margin based on depth
190 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
192 // Maximum depth for use of dynamic threat detection when null move fails low
193 const Depth ThreatDepth = 5 * ONE_PLY;
195 // Step 9. Internal iterative deepening
197 // Minimum depth for use of internal iterative deepening
198 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
200 // At Non-PV nodes we do an internal iterative deepening search
201 // when the static evaluation is bigger then beta - IIDMargin.
202 const Value IIDMargin = Value(0x100);
204 // Step 11. Decide the new search depth
206 // Extensions. Configurable UCI options
207 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
208 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
209 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
211 // Minimum depth for use of singular extension
212 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
214 // If the TT move is at least SingularExtensionMargin better then the
215 // remaining ones we will extend it.
216 const Value SingularExtensionMargin = Value(0x20);
218 // Step 12. Futility pruning
220 // Futility margin for quiescence search
221 const Value FutilityMarginQS = Value(0x80);
223 // Futility lookup tables (initialized at startup) and their getter functions
224 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
225 int FutilityMoveCountArray[32]; // [depth]
227 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
228 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
230 // Step 14. Reduced search
232 // Reduction lookup tables (initialized at startup) and their getter functions
233 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
235 template <NodeType PV>
236 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
238 // Common adjustments
240 // Search depth at iteration 1
241 const Depth InitialDepth = ONE_PLY;
243 // Easy move margin. An easy move candidate must be at least this much
244 // better than the second best move.
245 const Value EasyMoveMargin = Value(0x200);
248 /// Namespace variables
253 // Pointer to root move list
259 // Time managment variables
260 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
261 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
262 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
267 std::ofstream LogFile;
269 // Multi-threads manager object
270 ThreadsManager ThreadsMgr;
272 // Node counters, used only by thread[0] but try to keep in different cache
273 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
274 bool SendSearchedNodes;
276 int NodesBetweenPolls = 30000;
283 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
285 template <NodeType PvNode, bool SpNode, bool Root>
286 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
288 template <NodeType PvNode>
289 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
291 template <NodeType PvNode>
292 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
294 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
295 : search<PvNode, false, false>(pos, ss, alpha, beta, depth, ply);
298 template <NodeType PvNode>
299 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
301 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
302 bool connected_moves(const Position& pos, Move m1, Move m2);
303 bool value_is_mate(Value value);
304 Value value_to_tt(Value v, int ply);
305 Value value_from_tt(Value v, int ply);
306 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
307 bool connected_threat(const Position& pos, Move m, Move threat);
308 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
309 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
310 void update_killers(Move m, Move killers[]);
311 void update_gains(const Position& pos, Move move, Value before, Value after);
313 int current_search_time();
314 std::string value_to_uci(Value v);
315 int nps(const Position& pos);
316 void poll(const Position& pos);
317 void wait_for_stop_or_ponderhit();
318 void init_ss_array(SearchStack* ss, int size);
320 #if !defined(_MSC_VER)
321 void* init_thread(void* threadID);
323 DWORD WINAPI init_thread(LPVOID threadID);
327 // A dispatcher to choose among different move sources according to the type of node
328 template<bool SpNode, bool Root> struct MovePickerExt;
330 // In Root nodes use RootMoveList Rml as source
331 template<> struct MovePickerExt<false, true> {
333 MovePickerExt(const Position&, Move, Depth, const History&, SearchStack*, Value)
334 : rm(Rml->begin()), firstCall(true) {}
336 Move get_next_move() {
343 return rm != Rml->end() ? rm->pv[0] : MOVE_NONE;
345 int number_of_evasions() const { return (int)Rml->size(); }
347 RootMoveList::iterator rm;
351 // In SpNodes use split point's shared MovePicker as move source
352 template<> struct MovePickerExt<true, false> {
354 MovePickerExt(const Position&, Move, Depth, const History&, SearchStack* ss, Value)
357 Move get_next_move() { return mp->get_next_move(); }
358 int number_of_evasions() const { return mp->number_of_evasions(); }
360 RootMoveList::iterator rm; // Dummy, never used
364 // Normal case, create and use a MovePicker object as source
365 template<> struct MovePickerExt<false, false> : public MovePicker {
367 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
368 SearchStack* ss, Value beta) : MovePicker(p, ttm, d, h, ss, beta) {}
370 RootMoveList::iterator rm; // Dummy, never used
380 /// init_threads(), exit_threads() and nodes_searched() are helpers to
381 /// give accessibility to some TM methods from outside of current file.
383 void init_threads() { ThreadsMgr.init_threads(); }
384 void exit_threads() { ThreadsMgr.exit_threads(); }
387 /// init_search() is called during startup. It initializes various lookup tables
391 int d; // depth (ONE_PLY == 2)
392 int hd; // half depth (ONE_PLY == 1)
395 // Init reductions array
396 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
398 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
399 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
400 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
401 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
404 // Init futility margins array
405 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
406 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
408 // Init futility move count array
409 for (d = 0; d < 32; d++)
410 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
414 /// perft() is our utility to verify move generation is bug free. All the legal
415 /// moves up to given depth are generated and counted and the sum returned.
417 int64_t perft(Position& pos, Depth depth)
419 MoveStack mlist[MOVES_MAX];
424 // Generate all legal moves
425 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
427 // If we are at the last ply we don't need to do and undo
428 // the moves, just to count them.
429 if (depth <= ONE_PLY)
430 return int(last - mlist);
432 // Loop through all legal moves
434 for (MoveStack* cur = mlist; cur != last; cur++)
437 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
438 sum += perft(pos, depth - ONE_PLY);
445 /// think() is the external interface to Stockfish's search, and is called when
446 /// the program receives the UCI 'go' command. It initializes various
447 /// search-related global variables, and calls id_loop(). It returns false
448 /// when a quit command is received during the search.
450 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
451 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
453 // Initialize global search variables
454 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
456 SearchStartTime = get_system_time();
457 ExactMaxTime = maxTime;
460 InfiniteSearch = infinite;
462 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
464 // Look for a book move, only during games, not tests
465 if (UseTimeManagement && Options["OwnBook"].value<bool>())
467 if (Options["Book File"].value<std::string>() != OpeningBook.name())
468 OpeningBook.open(Options["Book File"].value<std::string>());
470 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
471 if (bookMove != MOVE_NONE)
474 wait_for_stop_or_ponderhit();
476 cout << "bestmove " << bookMove << endl;
481 // Read UCI option values
482 TT.set_size(Options["Hash"].value<int>());
483 if (Options["Clear Hash"].value<bool>())
485 Options["Clear Hash"].set_value("false");
489 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
490 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
491 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
492 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
493 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
494 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
495 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
496 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
497 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
498 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
499 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
500 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
501 MultiPV = Options["MultiPV"].value<int>();
502 UseLogFile = Options["Use Search Log"].value<bool>();
504 read_evaluation_uci_options(pos.side_to_move());
506 // Set the number of active threads
507 ThreadsMgr.read_uci_options();
508 init_eval(ThreadsMgr.active_threads());
510 // Wake up needed threads
511 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
512 ThreadsMgr.wake_sleeping_thread(i);
515 int myTime = time[pos.side_to_move()];
516 int myIncrement = increment[pos.side_to_move()];
517 if (UseTimeManagement)
518 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
520 // Set best NodesBetweenPolls interval to avoid lagging under
521 // heavy 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 << "Searching: " << pos.to_fen()
538 << "\ninfinite: " << infinite
539 << " ponder: " << ponder
540 << " time: " << myTime
541 << " increment: " << myIncrement
542 << " moves to go: " << movesToGo << endl;
545 // We're ready to start thinking. Call the iterative deepening loop function
546 Move ponderMove = MOVE_NONE;
547 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
549 // Print final search statistics
550 cout << "info nodes " << pos.nodes_searched()
551 << " nps " << nps(pos)
552 << " time " << current_search_time() << endl;
556 LogFile << "\nNodes: " << pos.nodes_searched()
557 << "\nNodes/second: " << nps(pos)
558 << "\nBest move: " << move_to_san(pos, bestMove);
561 pos.do_move(bestMove, st);
562 LogFile << "\nPonder move: "
563 << move_to_san(pos, ponderMove) // Works also with MOVE_NONE
566 // Return from think() with unchanged position
567 pos.undo_move(bestMove);
572 // This makes all the threads to go to sleep
573 ThreadsMgr.set_active_threads(1);
575 // If we are pondering or in infinite search, we shouldn't print the
576 // best move before we are told to do so.
577 if (!StopRequest && (Pondering || InfiniteSearch))
578 wait_for_stop_or_ponderhit();
580 // Could be both MOVE_NONE when searching on a stalemate position
581 cout << "bestmove " << bestMove << " ponder " << ponderMove << endl;
589 // id_loop() is the main iterative deepening loop. It calls search()
590 // repeatedly with increasing depth until the allocated thinking time has
591 // been consumed, the user stops the search, or the maximum search depth is
594 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
596 SearchStack ss[PLY_MAX_PLUS_2];
599 Move EasyMove = MOVE_NONE;
600 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
601 int researchCountFL, researchCountFH;
604 int bestMoveChanges[PLY_MAX_PLUS_2];
605 Value values[PLY_MAX_PLUS_2];
606 int aspirationDelta = 0;
608 // Moves to search are verified, scored and sorted
609 RootMoveList rml(pos, searchMoves);
612 // Handle special case of searching on a mate/stale position
615 Value s = (pos.is_check() ? -VALUE_MATE : VALUE_DRAW);
617 cout << "info depth " << 1
618 << " score " << value_to_uci(s) << endl;
626 init_ss_array(ss, PLY_MAX_PLUS_2);
627 values[1] = rml[0].pv_score;
630 // Send initial RootMoveList scoring (iteration 1)
631 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
632 << "info depth " << iteration
633 << "\n" << rml[0].pv_info_to_uci(pos, ONE_PLY, alpha, beta) << endl;
635 // Is one move significantly better than others after initial scoring ?
637 || rml[0].pv_score > rml[1].pv_score + EasyMoveMargin)
638 EasyMove = rml[0].pv[0];
640 // Iterative deepening loop
641 while (iteration < PLY_MAX)
643 // Initialize iteration
645 Rml->bestMoveChanges = 0;
647 cout << "info depth " << iteration << endl;
649 // Calculate dynamic aspiration window based on previous iterations
650 if (MultiPV == 1 && iteration >= 6 && abs(values[iteration - 1]) < VALUE_KNOWN_WIN)
652 int prevDelta1 = values[iteration - 1] - values[iteration - 2];
653 int prevDelta2 = values[iteration - 2] - values[iteration - 3];
655 aspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
656 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
658 alpha = Max(values[iteration - 1] - aspirationDelta, -VALUE_INFINITE);
659 beta = Min(values[iteration - 1] + aspirationDelta, VALUE_INFINITE);
662 depth = (iteration - 2) * ONE_PLY + InitialDepth;
664 researchCountFL = researchCountFH = 0;
666 // We start with small aspiration window and in case of fail high/low, we
667 // research with bigger window until we are not failing high/low anymore.
670 // Sort the moves before to (re)search
671 rml.set_non_pv_scores(pos, rml[0].pv[0], ss);
674 // Search to the current depth
675 value = search<PV, false, true>(pos, ss, alpha, beta, depth, 0);
677 // Sort the moves and write PV lines to transposition table, in case
678 // the relevant entries have been overwritten during the search.
680 for (int i = 0; i < Min(MultiPV, (int)rml.size()); i++)
681 rml[i].insert_pv_in_tt(pos);
683 bestMoveChanges[iteration] = Rml->bestMoveChanges;
688 assert(value >= alpha);
692 // Prepare for a research after a fail high, each time with a wider window
693 beta = Min(beta + aspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
696 else if (value <= alpha)
698 AspirationFailLow = true;
699 StopOnPonderhit = false;
701 // Prepare for a research after a fail low, each time with a wider window
702 alpha = Max(alpha - aspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
710 break; // Value cannot be trusted. Break out immediately!
712 //Save info about search result
713 values[iteration] = value;
715 // Drop the easy move if differs from the new best move
716 if (rml[0].pv[0] != EasyMove)
717 EasyMove = MOVE_NONE;
719 if (UseTimeManagement)
722 bool noMoreTime = false;
724 // Stop search early if there is only a single legal move,
725 // we search up to Iteration 6 anyway to get a proper score.
726 if (iteration >= 6 && rml.size() == 1)
729 // Stop search early when the last two iterations returned a mate score
731 && abs(values[iteration]) >= abs(VALUE_MATE) - 100
732 && abs(values[iteration-1]) >= abs(VALUE_MATE) - 100)
735 // Stop search early if one move seems to be much better than the others
737 && EasyMove == rml[0].pv[0]
738 && ( ( rml[0].nodes > (pos.nodes_searched() * 85) / 100
739 && current_search_time() > TimeMgr.available_time() / 16)
740 ||( rml[0].nodes > (pos.nodes_searched() * 98) / 100
741 && current_search_time() > TimeMgr.available_time() / 32)))
744 // Add some extra time if the best move has changed during the last two iterations
745 if (iteration > 5 && iteration <= 50)
746 TimeMgr.pv_instability(bestMoveChanges[iteration], bestMoveChanges[iteration-1]);
748 // Stop search if most of MaxSearchTime is consumed at the end of the
749 // iteration. We probably don't have enough time to search the first
750 // move at the next iteration anyway.
751 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
757 StopOnPonderhit = true;
763 if (MaxDepth && iteration >= MaxDepth)
767 *ponderMove = rml[0].pv[1];
772 // search<>() is the main search function for both PV and non-PV nodes and for
773 // normal and SplitPoint nodes. When called just after a split point the search
774 // is simpler because we have already probed the hash table, done a null move
775 // search, and searched the first move before splitting, we don't have to repeat
776 // all this work again. We also don't need to store anything to the hash table
777 // here: This is taken care of after we return from the split point.
779 template <NodeType PvNode, bool SpNode, bool Root>
780 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
782 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
783 assert(beta > alpha && beta <= VALUE_INFINITE);
784 assert(PvNode || alpha == beta - 1);
785 assert((Root || ply > 0) && ply < PLY_MAX);
786 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
788 Move movesSearched[MOVES_MAX];
793 Move ttMove, move, excludedMove, threatMove;
796 Value bestValue, value, oldAlpha;
797 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
798 bool isPvMove, isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
799 bool mateThreat = false;
801 int threadID = pos.thread();
802 SplitPoint* sp = NULL;
804 refinedValue = bestValue = value = -VALUE_INFINITE;
806 isCheck = pos.is_check();
812 ttMove = excludedMove = MOVE_NONE;
813 threatMove = sp->threatMove;
814 mateThreat = sp->mateThreat;
815 goto split_point_start;
817 else {} // Hack to fix icc's "statement is unreachable" warning
819 // Step 1. Initialize node and poll. Polling can abort search
820 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
821 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
825 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
831 // Step 2. Check for aborted search and immediate draw
833 || ThreadsMgr.cutoff_at_splitpoint(threadID)
835 || ply >= PLY_MAX - 1)
838 // Step 3. Mate distance pruning
839 alpha = Max(value_mated_in(ply), alpha);
840 beta = Min(value_mate_in(ply+1), beta);
845 // Step 4. Transposition table lookup
847 // We don't want the score of a partial search to overwrite a previous full search
848 // TT value, so we use a different position key in case of an excluded move exists.
849 excludedMove = ss->excludedMove;
850 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
852 tte = TT.retrieve(posKey);
853 ttMove = tte ? tte->move() : MOVE_NONE;
855 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
856 // This is to avoid problems in the following areas:
858 // * Repetition draw detection
859 // * Fifty move rule detection
860 // * Searching for a mate
861 // * Printing of full PV line
862 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
865 ss->bestMove = ttMove; // Can be MOVE_NONE
866 return value_from_tt(tte->value(), ply);
869 // Step 5. Evaluate the position statically and
870 // update gain statistics of parent move.
872 ss->eval = ss->evalMargin = VALUE_NONE;
875 assert(tte->static_value() != VALUE_NONE);
877 ss->eval = tte->static_value();
878 ss->evalMargin = tte->static_value_margin();
879 refinedValue = refine_eval(tte, ss->eval, ply);
883 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
884 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
887 // Save gain for the parent non-capture move
889 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
891 // Step 6. Razoring (is omitted in PV nodes)
893 && depth < RazorDepth
895 && refinedValue < beta - razor_margin(depth)
896 && ttMove == MOVE_NONE
897 && !value_is_mate(beta)
898 && !pos.has_pawn_on_7th(pos.side_to_move()))
900 Value rbeta = beta - razor_margin(depth);
901 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
903 // Logically we should return (v + razor_margin(depth)), but
904 // surprisingly this did slightly weaker in tests.
908 // Step 7. Static null move pruning (is omitted in PV nodes)
909 // We're betting that the opponent doesn't have a move that will reduce
910 // the score by more than futility_margin(depth) if we do a null move.
913 && depth < RazorDepth
915 && refinedValue >= beta + futility_margin(depth, 0)
916 && !value_is_mate(beta)
917 && pos.non_pawn_material(pos.side_to_move()))
918 return refinedValue - futility_margin(depth, 0);
920 // Step 8. Null move search with verification search (is omitted in PV nodes)
925 && refinedValue >= beta
926 && !value_is_mate(beta)
927 && pos.non_pawn_material(pos.side_to_move()))
929 ss->currentMove = MOVE_NULL;
931 // Null move dynamic reduction based on depth
932 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
934 // Null move dynamic reduction based on value
935 if (refinedValue - beta > PawnValueMidgame)
938 pos.do_null_move(st);
939 (ss+1)->skipNullMove = true;
940 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
941 (ss+1)->skipNullMove = false;
942 pos.undo_null_move();
944 if (nullValue >= beta)
946 // Do not return unproven mate scores
947 if (nullValue >= value_mate_in(PLY_MAX))
950 if (depth < 6 * ONE_PLY)
953 // Do verification search at high depths
954 ss->skipNullMove = true;
955 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
956 ss->skipNullMove = false;
963 // The null move failed low, which means that we may be faced with
964 // some kind of threat. If the previous move was reduced, check if
965 // the move that refuted the null move was somehow connected to the
966 // move which was reduced. If a connection is found, return a fail
967 // low score (which will cause the reduced move to fail high in the
968 // parent node, which will trigger a re-search with full depth).
969 if (nullValue == value_mated_in(ply + 2))
972 threatMove = (ss+1)->bestMove;
973 if ( depth < ThreatDepth
975 && threatMove != MOVE_NONE
976 && connected_moves(pos, (ss-1)->currentMove, threatMove))
981 // Step 9. Internal iterative deepening
983 && depth >= IIDDepth[PvNode]
984 && ttMove == MOVE_NONE
985 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
987 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
989 ss->skipNullMove = true;
990 search<PvNode>(pos, ss, alpha, beta, d, ply);
991 ss->skipNullMove = false;
993 ttMove = ss->bestMove;
994 tte = TT.retrieve(posKey);
997 // Expensive mate threat detection (only for PV nodes)
998 if (PvNode && !Root) // FIXME
999 mateThreat = pos.has_mate_threat();
1001 split_point_start: // At split points actual search starts from here
1003 // Initialize a MovePicker object for the current position
1004 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1006 ss->bestMove = MOVE_NONE;
1007 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1008 futilityBase = ss->eval + ss->evalMargin;
1009 singularExtensionNode = !Root
1011 && depth >= SingularExtensionDepth[PvNode]
1014 && !excludedMove // Do not allow recursive singular extension search
1015 && (tte->type() & VALUE_TYPE_LOWER)
1016 && tte->depth() >= depth - 3 * ONE_PLY;
1022 lock_grab(&(sp->lock));
1023 bestValue = sp->bestValue;
1026 // Step 10. Loop through moves
1027 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1028 while ( bestValue < beta
1029 && (move = mp.get_next_move()) != MOVE_NONE
1030 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1032 assert(move_is_ok(move));
1036 moveCount = ++sp->moveCount;
1037 lock_release(&(sp->lock));
1039 else if (move == excludedMove)
1042 movesSearched[moveCount++] = move;
1046 // This is used by time management
1047 FirstRootMove = (moveCount == 1);
1049 // Save the current node count before the move is searched
1050 nodes = pos.nodes_searched();
1052 // If it's time to send nodes info, do it here where we have the
1053 // correct accumulated node counts searched by each thread.
1054 if (SendSearchedNodes)
1056 SendSearchedNodes = false;
1057 cout << "info nodes " << nodes
1058 << " nps " << nps(pos)
1059 << " time " << current_search_time() << endl;
1062 if (current_search_time() >= 1000)
1063 cout << "info currmove " << move
1064 << " currmovenumber " << moveCount << endl;
1067 isPvMove = (PvNode && moveCount <= (Root ? MultiPV : 1));
1068 moveIsCheck = pos.move_is_check(move, ci);
1069 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1071 // Step 11. Decide the new search depth
1072 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1074 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1075 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1076 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1077 // lower then ttValue minus a margin then we extend ttMove.
1078 if ( singularExtensionNode
1079 && move == tte->move()
1082 Value ttValue = value_from_tt(tte->value(), ply);
1084 if (abs(ttValue) < VALUE_KNOWN_WIN)
1086 Value b = ttValue - SingularExtensionMargin;
1087 ss->excludedMove = move;
1088 ss->skipNullMove = true;
1089 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1090 ss->skipNullMove = false;
1091 ss->excludedMove = MOVE_NONE;
1092 ss->bestMove = MOVE_NONE;
1098 // Update current move (this must be done after singular extension search)
1099 ss->currentMove = move;
1100 newDepth = depth - (!Root ? ONE_PLY : DEPTH_ZERO) + ext;
1102 // Step 12. Futility pruning (is omitted in PV nodes)
1104 && !captureOrPromotion
1108 && !move_is_castle(move))
1110 // Move count based pruning
1111 if ( moveCount >= futility_move_count(depth)
1112 && !(threatMove && connected_threat(pos, move, threatMove))
1113 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1116 lock_grab(&(sp->lock));
1121 // Value based pruning
1122 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1123 // but fixing this made program slightly weaker.
1124 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1125 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1126 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1128 if (futilityValueScaled < beta)
1132 lock_grab(&(sp->lock));
1133 if (futilityValueScaled > sp->bestValue)
1134 sp->bestValue = bestValue = futilityValueScaled;
1136 else if (futilityValueScaled > bestValue)
1137 bestValue = futilityValueScaled;
1142 // Prune moves with negative SEE at low depths
1143 if ( predictedDepth < 2 * ONE_PLY
1144 && bestValue > value_mated_in(PLY_MAX)
1145 && pos.see_sign(move) < 0)
1148 lock_grab(&(sp->lock));
1154 // Step 13. Make the move
1155 pos.do_move(move, st, ci, moveIsCheck);
1157 // Step extra. pv search (only in PV nodes)
1158 // The first move in list is the expected PV
1161 // Aspiration window is disabled in multi-pv case
1162 if (Root && MultiPV > 1)
1163 alpha = -VALUE_INFINITE;
1165 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1169 // Step 14. Reduced depth search
1170 // If the move fails high will be re-searched at full depth.
1171 bool doFullDepthSearch = true;
1173 if ( depth >= 3 * ONE_PLY
1174 && !captureOrPromotion
1176 && !move_is_castle(move)
1177 && ss->killers[0] != move
1178 && ss->killers[1] != move)
1180 ss->reduction = Root ? reduction<PvNode>(depth, moveCount - MultiPV + 1)
1181 : reduction<PvNode>(depth, moveCount);
1184 alpha = SpNode ? sp->alpha : alpha;
1185 Depth d = newDepth - ss->reduction;
1186 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1188 doFullDepthSearch = (value > alpha);
1190 ss->reduction = DEPTH_ZERO; // Restore original reduction
1193 // Step 15. Full depth search
1194 if (doFullDepthSearch)
1196 alpha = SpNode ? sp->alpha : alpha;
1197 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1199 // Step extra. pv search (only in PV nodes)
1200 // Search only for possible new PV nodes, if instead value >= beta then
1201 // parent node fails low with value <= alpha and tries another move.
1202 if (PvNode && value > alpha && (Root || value < beta))
1203 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1207 // Step 16. Undo move
1208 pos.undo_move(move);
1210 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1212 // Step 17. Check for new best move
1215 lock_grab(&(sp->lock));
1216 bestValue = sp->bestValue;
1220 if (!Root && value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1225 sp->bestValue = value;
1229 if (PvNode && value < beta) // We want always alpha < beta
1237 sp->betaCutoff = true;
1239 if (value == value_mate_in(ply + 1))
1240 ss->mateKiller = move;
1242 ss->bestMove = move;
1245 sp->parentSstack->bestMove = move;
1251 // Finished searching the move. If StopRequest is true, the search
1252 // was aborted because the user interrupted the search or because we
1253 // ran out of time. In this case, the return value of the search cannot
1254 // be trusted, and we break out of the loop without updating the best
1259 // Remember searched nodes counts for this move
1260 mp.rm->nodes += pos.nodes_searched() - nodes;
1262 // Step 17. Check for new best move
1263 if (!isPvMove && value <= alpha)
1264 mp.rm->pv_score = -VALUE_INFINITE;
1267 // PV move or new best move!
1270 ss->bestMove = move;
1271 mp.rm->pv_score = value;
1272 mp.rm->extract_pv_from_tt(pos);
1274 // We record how often the best move has been changed in each
1275 // iteration. This information is used for time managment: When
1276 // the best move changes frequently, we allocate some more time.
1277 if (!isPvMove && MultiPV == 1)
1278 Rml->bestMoveChanges++;
1280 // Inform GUI that PV has changed, in case of multi-pv UCI protocol
1281 // requires we send all the PV lines properly sorted.
1282 Rml->sort_multipv(moveCount);
1284 for (int j = 0; j < Min(MultiPV, (int)Rml->size()); j++)
1285 cout << (*Rml)[j].pv_info_to_uci(pos, depth, alpha, beta, j) << endl;
1287 // Update alpha. In multi-pv we don't use aspiration window
1290 // Raise alpha to setup proper non-pv search upper bound
1292 alpha = bestValue = value;
1294 else // Set alpha equal to minimum score among the PV lines
1295 alpha = bestValue = (*Rml)[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1297 } // PV move or new best move
1300 // Step 18. Check for split
1303 && depth >= ThreadsMgr.min_split_depth()
1304 && ThreadsMgr.active_threads() > 1
1306 && ThreadsMgr.available_thread_exists(threadID)
1308 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1309 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1310 threatMove, mateThreat, moveCount, (MovePicker*)&mp, PvNode);
1313 // Step 19. Check for mate and stalemate
1314 // All legal moves have been searched and if there are
1315 // no legal moves, it must be mate or stalemate.
1316 // If one move was excluded return fail low score.
1317 if (!SpNode && !moveCount)
1318 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1320 // Step 20. Update tables
1321 // If the search is not aborted, update the transposition table,
1322 // history counters, and killer moves.
1323 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1325 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1326 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1327 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1329 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1331 // Update killers and history only for non capture moves that fails high
1332 if ( bestValue >= beta
1333 && !pos.move_is_capture_or_promotion(move))
1335 update_history(pos, move, depth, movesSearched, moveCount);
1336 update_killers(move, ss->killers);
1342 // Here we have the lock still grabbed
1343 sp->slaves[threadID] = 0;
1344 sp->nodes += pos.nodes_searched();
1345 lock_release(&(sp->lock));
1348 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1353 // qsearch() is the quiescence search function, which is called by the main
1354 // search function when the remaining depth is zero (or, to be more precise,
1355 // less than ONE_PLY).
1357 template <NodeType PvNode>
1358 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1360 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1361 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1362 assert(PvNode || alpha == beta - 1);
1364 assert(ply > 0 && ply < PLY_MAX);
1365 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1369 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1370 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1373 Value oldAlpha = alpha;
1375 ss->bestMove = ss->currentMove = MOVE_NONE;
1377 // Check for an instant draw or maximum ply reached
1378 if (pos.is_draw() || ply >= PLY_MAX - 1)
1381 // Decide whether or not to include checks, this fixes also the type of
1382 // TT entry depth that we are going to use. Note that in qsearch we use
1383 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1384 isCheck = pos.is_check();
1385 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1387 // Transposition table lookup. At PV nodes, we don't use the TT for
1388 // pruning, but only for move ordering.
1389 tte = TT.retrieve(pos.get_key());
1390 ttMove = (tte ? tte->move() : MOVE_NONE);
1392 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1394 ss->bestMove = ttMove; // Can be MOVE_NONE
1395 return value_from_tt(tte->value(), ply);
1398 // Evaluate the position statically
1401 bestValue = futilityBase = -VALUE_INFINITE;
1402 ss->eval = evalMargin = VALUE_NONE;
1403 enoughMaterial = false;
1409 assert(tte->static_value() != VALUE_NONE);
1411 evalMargin = tte->static_value_margin();
1412 ss->eval = bestValue = tte->static_value();
1415 ss->eval = bestValue = evaluate(pos, evalMargin);
1417 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1419 // Stand pat. Return immediately if static value is at least beta
1420 if (bestValue >= beta)
1423 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1428 if (PvNode && bestValue > alpha)
1431 // Futility pruning parameters, not needed when in check
1432 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1433 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1436 // Initialize a MovePicker object for the current position, and prepare
1437 // to search the moves. Because the depth is <= 0 here, only captures,
1438 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1440 MovePicker mp(pos, ttMove, depth, H);
1443 // Loop through the moves until no moves remain or a beta cutoff occurs
1444 while ( alpha < beta
1445 && (move = mp.get_next_move()) != MOVE_NONE)
1447 assert(move_is_ok(move));
1449 moveIsCheck = pos.move_is_check(move, ci);
1457 && !move_is_promotion(move)
1458 && !pos.move_is_passed_pawn_push(move))
1460 futilityValue = futilityBase
1461 + pos.endgame_value_of_piece_on(move_to(move))
1462 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1464 if (futilityValue < alpha)
1466 if (futilityValue > bestValue)
1467 bestValue = futilityValue;
1472 // Detect non-capture evasions that are candidate to be pruned
1473 evasionPrunable = isCheck
1474 && bestValue > value_mated_in(PLY_MAX)
1475 && !pos.move_is_capture(move)
1476 && !pos.can_castle(pos.side_to_move());
1478 // Don't search moves with negative SEE values
1480 && (!isCheck || evasionPrunable)
1482 && !move_is_promotion(move)
1483 && pos.see_sign(move) < 0)
1486 // Don't search useless checks
1491 && !pos.move_is_capture_or_promotion(move)
1492 && ss->eval + PawnValueMidgame / 4 < beta
1493 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1495 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1496 bestValue = ss->eval + PawnValueMidgame / 4;
1501 // Update current move
1502 ss->currentMove = move;
1504 // Make and search the move
1505 pos.do_move(move, st, ci, moveIsCheck);
1506 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1507 pos.undo_move(move);
1509 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1512 if (value > bestValue)
1518 ss->bestMove = move;
1523 // All legal moves have been searched. A special case: If we're in check
1524 // and no legal moves were found, it is checkmate.
1525 if (isCheck && bestValue == -VALUE_INFINITE)
1526 return value_mated_in(ply);
1528 // Update transposition table
1529 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1530 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1532 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1538 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1539 // bestValue is updated only when returning false because in that case move
1542 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1544 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1545 Square from, to, ksq, victimSq;
1548 Value futilityValue, bv = *bestValue;
1550 from = move_from(move);
1552 them = opposite_color(pos.side_to_move());
1553 ksq = pos.king_square(them);
1554 kingAtt = pos.attacks_from<KING>(ksq);
1555 pc = pos.piece_on(from);
1557 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1558 oldAtt = pos.attacks_from(pc, from, occ);
1559 newAtt = pos.attacks_from(pc, to, occ);
1561 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1562 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1564 if (!(b && (b & (b - 1))))
1567 // Rule 2. Queen contact check is very dangerous
1568 if ( type_of_piece(pc) == QUEEN
1569 && bit_is_set(kingAtt, to))
1572 // Rule 3. Creating new double threats with checks
1573 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1577 victimSq = pop_1st_bit(&b);
1578 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1580 // Note that here we generate illegal "double move"!
1581 if ( futilityValue >= beta
1582 && pos.see_sign(make_move(from, victimSq)) >= 0)
1585 if (futilityValue > bv)
1589 // Update bestValue only if check is not dangerous (because we will prune the move)
1595 // connected_moves() tests whether two moves are 'connected' in the sense
1596 // that the first move somehow made the second move possible (for instance
1597 // if the moving piece is the same in both moves). The first move is assumed
1598 // to be the move that was made to reach the current position, while the
1599 // second move is assumed to be a move from the current position.
1601 bool connected_moves(const Position& pos, Move m1, Move m2) {
1603 Square f1, t1, f2, t2;
1606 assert(m1 && move_is_ok(m1));
1607 assert(m2 && move_is_ok(m2));
1609 // Case 1: The moving piece is the same in both moves
1615 // Case 2: The destination square for m2 was vacated by m1
1621 // Case 3: Moving through the vacated square
1622 if ( piece_is_slider(pos.piece_on(f2))
1623 && bit_is_set(squares_between(f2, t2), f1))
1626 // Case 4: The destination square for m2 is defended by the moving piece in m1
1627 p = pos.piece_on(t1);
1628 if (bit_is_set(pos.attacks_from(p, t1), t2))
1631 // Case 5: Discovered check, checking piece is the piece moved in m1
1632 if ( piece_is_slider(p)
1633 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1634 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1636 // discovered_check_candidates() works also if the Position's side to
1637 // move is the opposite of the checking piece.
1638 Color them = opposite_color(pos.side_to_move());
1639 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1641 if (bit_is_set(dcCandidates, f2))
1648 // value_is_mate() checks if the given value is a mate one eventually
1649 // compensated for the ply.
1651 bool value_is_mate(Value value) {
1653 assert(abs(value) <= VALUE_INFINITE);
1655 return value <= value_mated_in(PLY_MAX)
1656 || value >= value_mate_in(PLY_MAX);
1660 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1661 // "plies to mate from the current ply". Non-mate scores are unchanged.
1662 // The function is called before storing a value to the transposition table.
1664 Value value_to_tt(Value v, int ply) {
1666 if (v >= value_mate_in(PLY_MAX))
1669 if (v <= value_mated_in(PLY_MAX))
1676 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1677 // the transposition table to a mate score corrected for the current ply.
1679 Value value_from_tt(Value v, int ply) {
1681 if (v >= value_mate_in(PLY_MAX))
1684 if (v <= value_mated_in(PLY_MAX))
1691 // extension() decides whether a move should be searched with normal depth,
1692 // or with extended depth. Certain classes of moves (checking moves, in
1693 // particular) are searched with bigger depth than ordinary moves and in
1694 // any case are marked as 'dangerous'. Note that also if a move is not
1695 // extended, as example because the corresponding UCI option is set to zero,
1696 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1697 template <NodeType PvNode>
1698 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1699 bool singleEvasion, bool mateThreat, bool* dangerous) {
1701 assert(m != MOVE_NONE);
1703 Depth result = DEPTH_ZERO;
1704 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1708 if (moveIsCheck && pos.see_sign(m) >= 0)
1709 result += CheckExtension[PvNode];
1712 result += SingleEvasionExtension[PvNode];
1715 result += MateThreatExtension[PvNode];
1718 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1720 Color c = pos.side_to_move();
1721 if (relative_rank(c, move_to(m)) == RANK_7)
1723 result += PawnPushTo7thExtension[PvNode];
1726 if (pos.pawn_is_passed(c, move_to(m)))
1728 result += PassedPawnExtension[PvNode];
1733 if ( captureOrPromotion
1734 && pos.type_of_piece_on(move_to(m)) != PAWN
1735 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1736 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1737 && !move_is_promotion(m)
1740 result += PawnEndgameExtension[PvNode];
1745 && captureOrPromotion
1746 && pos.type_of_piece_on(move_to(m)) != PAWN
1747 && pos.see_sign(m) >= 0)
1749 result += ONE_PLY / 2;
1753 return Min(result, ONE_PLY);
1757 // connected_threat() tests whether it is safe to forward prune a move or if
1758 // is somehow coonected to the threat move returned by null search.
1760 bool connected_threat(const Position& pos, Move m, Move threat) {
1762 assert(move_is_ok(m));
1763 assert(threat && move_is_ok(threat));
1764 assert(!pos.move_is_check(m));
1765 assert(!pos.move_is_capture_or_promotion(m));
1766 assert(!pos.move_is_passed_pawn_push(m));
1768 Square mfrom, mto, tfrom, tto;
1770 mfrom = move_from(m);
1772 tfrom = move_from(threat);
1773 tto = move_to(threat);
1775 // Case 1: Don't prune moves which move the threatened piece
1779 // Case 2: If the threatened piece has value less than or equal to the
1780 // value of the threatening piece, don't prune move which defend it.
1781 if ( pos.move_is_capture(threat)
1782 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1783 || pos.type_of_piece_on(tfrom) == KING)
1784 && pos.move_attacks_square(m, tto))
1787 // Case 3: If the moving piece in the threatened move is a slider, don't
1788 // prune safe moves which block its ray.
1789 if ( piece_is_slider(pos.piece_on(tfrom))
1790 && bit_is_set(squares_between(tfrom, tto), mto)
1791 && pos.see_sign(m) >= 0)
1798 // ok_to_use_TT() returns true if a transposition table score
1799 // can be used at a given point in search.
1801 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1803 Value v = value_from_tt(tte->value(), ply);
1805 return ( tte->depth() >= depth
1806 || v >= Max(value_mate_in(PLY_MAX), beta)
1807 || v < Min(value_mated_in(PLY_MAX), beta))
1809 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1810 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1814 // refine_eval() returns the transposition table score if
1815 // possible otherwise falls back on static position evaluation.
1817 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1821 Value v = value_from_tt(tte->value(), ply);
1823 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1824 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1831 // update_history() registers a good move that produced a beta-cutoff
1832 // in history and marks as failures all the other moves of that ply.
1834 void update_history(const Position& pos, Move move, Depth depth,
1835 Move movesSearched[], int moveCount) {
1837 Value bonus = Value(int(depth) * int(depth));
1839 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1841 for (int i = 0; i < moveCount - 1; i++)
1843 m = movesSearched[i];
1847 if (!pos.move_is_capture_or_promotion(m))
1848 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1853 // update_killers() add a good move that produced a beta-cutoff
1854 // among the killer moves of that ply.
1856 void update_killers(Move m, Move killers[]) {
1858 if (m == killers[0])
1861 killers[1] = killers[0];
1866 // update_gains() updates the gains table of a non-capture move given
1867 // the static position evaluation before and after the move.
1869 void update_gains(const Position& pos, Move m, Value before, Value after) {
1872 && before != VALUE_NONE
1873 && after != VALUE_NONE
1874 && pos.captured_piece_type() == PIECE_TYPE_NONE
1875 && !move_is_special(m))
1876 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1880 // init_ss_array() does a fast reset of the first entries of a SearchStack
1881 // array and of all the excludedMove and skipNullMove entries.
1883 void init_ss_array(SearchStack* ss, int size) {
1885 for (int i = 0; i < size; i++, ss++)
1887 ss->excludedMove = MOVE_NONE;
1888 ss->skipNullMove = false;
1889 ss->reduction = DEPTH_ZERO;
1893 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
1898 // value_to_uci() converts a value to a string suitable for use with the UCI
1899 // protocol specifications:
1901 // cp <x> The score from the engine's point of view in centipawns.
1902 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1903 // use negative values for y.
1905 std::string value_to_uci(Value v) {
1907 std::stringstream s;
1909 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1910 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1912 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1918 // current_search_time() returns the number of milliseconds which have passed
1919 // since the beginning of the current search.
1921 int current_search_time() {
1923 return get_system_time() - SearchStartTime;
1927 // nps() computes the current nodes/second count
1929 int nps(const Position& pos) {
1931 int t = current_search_time();
1932 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1936 // poll() performs two different functions: It polls for user input, and it
1937 // looks at the time consumed so far and decides if it's time to abort the
1940 void poll(const Position& pos) {
1942 static int lastInfoTime;
1943 int t = current_search_time();
1946 if (input_available())
1948 // We are line oriented, don't read single chars
1949 std::string command;
1951 if (!std::getline(std::cin, command))
1954 if (command == "quit")
1956 // Quit the program as soon as possible
1958 QuitRequest = StopRequest = true;
1961 else if (command == "stop")
1963 // Stop calculating as soon as possible, but still send the "bestmove"
1964 // and possibly the "ponder" token when finishing the search.
1968 else if (command == "ponderhit")
1970 // The opponent has played the expected move. GUI sends "ponderhit" if
1971 // we were told to ponder on the same move the opponent has played. We
1972 // should continue searching but switching from pondering to normal search.
1975 if (StopOnPonderhit)
1980 // Print search information
1984 else if (lastInfoTime > t)
1985 // HACK: Must be a new search where we searched less than
1986 // NodesBetweenPolls nodes during the first second of search.
1989 else if (t - lastInfoTime >= 1000)
1996 if (dbg_show_hit_rate)
1997 dbg_print_hit_rate();
1999 // Send info on searched nodes as soon as we return to root
2000 SendSearchedNodes = true;
2003 // Should we stop the search?
2007 bool stillAtFirstMove = FirstRootMove
2008 && !AspirationFailLow
2009 && t > TimeMgr.available_time();
2011 bool noMoreTime = t > TimeMgr.maximum_time()
2012 || stillAtFirstMove;
2014 if ( (UseTimeManagement && noMoreTime)
2015 || (ExactMaxTime && t >= ExactMaxTime)
2016 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
2021 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2022 // while the program is pondering. The point is to work around a wrinkle in
2023 // the UCI protocol: When pondering, the engine is not allowed to give a
2024 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2025 // We simply wait here until one of these commands is sent, and return,
2026 // after which the bestmove and pondermove will be printed.
2028 void wait_for_stop_or_ponderhit() {
2030 std::string command;
2034 // Wait for a command from stdin
2035 if (!std::getline(std::cin, command))
2038 if (command == "quit")
2043 else if (command == "ponderhit" || command == "stop")
2049 // init_thread() is the function which is called when a new thread is
2050 // launched. It simply calls the idle_loop() function with the supplied
2051 // threadID. There are two versions of this function; one for POSIX
2052 // threads and one for Windows threads.
2054 #if !defined(_MSC_VER)
2056 void* init_thread(void* threadID) {
2058 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2064 DWORD WINAPI init_thread(LPVOID threadID) {
2066 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2073 /// The ThreadsManager class
2076 // read_uci_options() updates number of active threads and other internal
2077 // parameters according to the UCI options values. It is called before
2078 // to start a new search.
2080 void ThreadsManager::read_uci_options() {
2082 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2083 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2084 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2085 activeThreads = Options["Threads"].value<int>();
2089 // idle_loop() is where the threads are parked when they have no work to do.
2090 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2091 // object for which the current thread is the master.
2093 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2095 assert(threadID >= 0 && threadID < MAX_THREADS);
2098 bool allFinished = false;
2102 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2103 // master should exit as last one.
2104 if (allThreadsShouldExit)
2107 threads[threadID].state = THREAD_TERMINATED;
2111 // If we are not thinking, wait for a condition to be signaled
2112 // instead of wasting CPU time polling for work.
2113 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2114 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2116 assert(!sp || useSleepingThreads);
2117 assert(threadID != 0 || useSleepingThreads);
2119 if (threads[threadID].state == THREAD_INITIALIZING)
2120 threads[threadID].state = THREAD_AVAILABLE;
2122 // Grab the lock to avoid races with wake_sleeping_thread()
2123 lock_grab(&sleepLock[threadID]);
2125 // If we are master and all slaves have finished do not go to sleep
2126 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2127 allFinished = (i == activeThreads);
2129 if (allFinished || allThreadsShouldExit)
2131 lock_release(&sleepLock[threadID]);
2135 // Do sleep here after retesting sleep conditions
2136 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2137 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2139 lock_release(&sleepLock[threadID]);
2142 // If this thread has been assigned work, launch a search
2143 if (threads[threadID].state == THREAD_WORKISWAITING)
2145 assert(!allThreadsShouldExit);
2147 threads[threadID].state = THREAD_SEARCHING;
2149 // Here we call search() with SplitPoint template parameter set to true
2150 SplitPoint* tsp = threads[threadID].splitPoint;
2151 Position pos(*tsp->pos, threadID);
2152 SearchStack* ss = tsp->sstack[threadID] + 1;
2156 search<PV, true, false>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2158 search<NonPV, true, false>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2160 assert(threads[threadID].state == THREAD_SEARCHING);
2162 threads[threadID].state = THREAD_AVAILABLE;
2164 // Wake up master thread so to allow it to return from the idle loop in
2165 // case we are the last slave of the split point.
2166 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2167 wake_sleeping_thread(tsp->master);
2170 // If this thread is the master of a split point and all slaves have
2171 // finished their work at this split point, return from the idle loop.
2172 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2173 allFinished = (i == activeThreads);
2177 // Because sp->slaves[] is reset under lock protection,
2178 // be sure sp->lock has been released before to return.
2179 lock_grab(&(sp->lock));
2180 lock_release(&(sp->lock));
2182 // In helpful master concept a master can help only a sub-tree, and
2183 // because here is all finished is not possible master is booked.
2184 assert(threads[threadID].state == THREAD_AVAILABLE);
2186 threads[threadID].state = THREAD_SEARCHING;
2193 // init_threads() is called during startup. It launches all helper threads,
2194 // and initializes the split point stack and the global locks and condition
2197 void ThreadsManager::init_threads() {
2199 int i, arg[MAX_THREADS];
2202 // Initialize global locks
2205 for (i = 0; i < MAX_THREADS; i++)
2207 lock_init(&sleepLock[i]);
2208 cond_init(&sleepCond[i]);
2211 // Initialize splitPoints[] locks
2212 for (i = 0; i < MAX_THREADS; i++)
2213 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2214 lock_init(&(threads[i].splitPoints[j].lock));
2216 // Will be set just before program exits to properly end the threads
2217 allThreadsShouldExit = false;
2219 // Threads will be put all threads to sleep as soon as created
2222 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2223 threads[0].state = THREAD_SEARCHING;
2224 for (i = 1; i < MAX_THREADS; i++)
2225 threads[i].state = THREAD_INITIALIZING;
2227 // Launch the helper threads
2228 for (i = 1; i < MAX_THREADS; i++)
2232 #if !defined(_MSC_VER)
2233 pthread_t pthread[1];
2234 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2235 pthread_detach(pthread[0]);
2237 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2241 cout << "Failed to create thread number " << i << endl;
2245 // Wait until the thread has finished launching and is gone to sleep
2246 while (threads[i].state == THREAD_INITIALIZING) {}
2251 // exit_threads() is called when the program exits. It makes all the
2252 // helper threads exit cleanly.
2254 void ThreadsManager::exit_threads() {
2256 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2258 // Wake up all the threads and waits for termination
2259 for (int i = 1; i < MAX_THREADS; i++)
2261 wake_sleeping_thread(i);
2262 while (threads[i].state != THREAD_TERMINATED) {}
2265 // Now we can safely destroy the locks
2266 for (int i = 0; i < MAX_THREADS; i++)
2267 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2268 lock_destroy(&(threads[i].splitPoints[j].lock));
2270 lock_destroy(&mpLock);
2272 // Now we can safely destroy the wait conditions
2273 for (int i = 0; i < MAX_THREADS; i++)
2275 lock_destroy(&sleepLock[i]);
2276 cond_destroy(&sleepCond[i]);
2281 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2282 // the thread's currently active split point, or in some ancestor of
2283 // the current split point.
2285 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2287 assert(threadID >= 0 && threadID < activeThreads);
2289 SplitPoint* sp = threads[threadID].splitPoint;
2291 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2296 // thread_is_available() checks whether the thread with threadID "slave" is
2297 // available to help the thread with threadID "master" at a split point. An
2298 // obvious requirement is that "slave" must be idle. With more than two
2299 // threads, this is not by itself sufficient: If "slave" is the master of
2300 // some active split point, it is only available as a slave to the other
2301 // threads which are busy searching the split point at the top of "slave"'s
2302 // split point stack (the "helpful master concept" in YBWC terminology).
2304 bool ThreadsManager::thread_is_available(int slave, int master) const {
2306 assert(slave >= 0 && slave < activeThreads);
2307 assert(master >= 0 && master < activeThreads);
2308 assert(activeThreads > 1);
2310 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2313 // Make a local copy to be sure doesn't change under our feet
2314 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2316 // No active split points means that the thread is available as
2317 // a slave for any other thread.
2318 if (localActiveSplitPoints == 0 || activeThreads == 2)
2321 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2322 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2323 // could have been set to 0 by another thread leading to an out of bound access.
2324 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2331 // available_thread_exists() tries to find an idle thread which is available as
2332 // a slave for the thread with threadID "master".
2334 bool ThreadsManager::available_thread_exists(int master) const {
2336 assert(master >= 0 && master < activeThreads);
2337 assert(activeThreads > 1);
2339 for (int i = 0; i < activeThreads; i++)
2340 if (thread_is_available(i, master))
2347 // split() does the actual work of distributing the work at a node between
2348 // several available threads. If it does not succeed in splitting the
2349 // node (because no idle threads are available, or because we have no unused
2350 // split point objects), the function immediately returns. If splitting is
2351 // possible, a SplitPoint object is initialized with all the data that must be
2352 // copied to the helper threads and we tell our helper threads that they have
2353 // been assigned work. This will cause them to instantly leave their idle loops and
2354 // call search().When all threads have returned from search() then split() returns.
2356 template <bool Fake>
2357 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2358 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2359 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2360 assert(pos.is_ok());
2361 assert(ply > 0 && ply < PLY_MAX);
2362 assert(*bestValue >= -VALUE_INFINITE);
2363 assert(*bestValue <= *alpha);
2364 assert(*alpha < beta);
2365 assert(beta <= VALUE_INFINITE);
2366 assert(depth > DEPTH_ZERO);
2367 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2368 assert(activeThreads > 1);
2370 int i, master = pos.thread();
2371 Thread& masterThread = threads[master];
2375 // If no other thread is available to help us, or if we have too many
2376 // active split points, don't split.
2377 if ( !available_thread_exists(master)
2378 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2380 lock_release(&mpLock);
2384 // Pick the next available split point object from the split point stack
2385 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2387 // Initialize the split point object
2388 splitPoint.parent = masterThread.splitPoint;
2389 splitPoint.master = master;
2390 splitPoint.betaCutoff = false;
2391 splitPoint.ply = ply;
2392 splitPoint.depth = depth;
2393 splitPoint.threatMove = threatMove;
2394 splitPoint.mateThreat = mateThreat;
2395 splitPoint.alpha = *alpha;
2396 splitPoint.beta = beta;
2397 splitPoint.pvNode = pvNode;
2398 splitPoint.bestValue = *bestValue;
2400 splitPoint.moveCount = moveCount;
2401 splitPoint.pos = &pos;
2402 splitPoint.nodes = 0;
2403 splitPoint.parentSstack = ss;
2404 for (i = 0; i < activeThreads; i++)
2405 splitPoint.slaves[i] = 0;
2407 masterThread.splitPoint = &splitPoint;
2409 // If we are here it means we are not available
2410 assert(masterThread.state != THREAD_AVAILABLE);
2412 int workersCnt = 1; // At least the master is included
2414 // Allocate available threads setting state to THREAD_BOOKED
2415 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2416 if (thread_is_available(i, master))
2418 threads[i].state = THREAD_BOOKED;
2419 threads[i].splitPoint = &splitPoint;
2420 splitPoint.slaves[i] = 1;
2424 assert(Fake || workersCnt > 1);
2426 // We can release the lock because slave threads are already booked and master is not available
2427 lock_release(&mpLock);
2429 // Tell the threads that they have work to do. This will make them leave
2430 // their idle loop. But before copy search stack tail for each thread.
2431 for (i = 0; i < activeThreads; i++)
2432 if (i == master || splitPoint.slaves[i])
2434 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2436 assert(i == master || threads[i].state == THREAD_BOOKED);
2438 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2440 if (useSleepingThreads && i != master)
2441 wake_sleeping_thread(i);
2444 // Everything is set up. The master thread enters the idle loop, from
2445 // which it will instantly launch a search, because its state is
2446 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2447 // idle loop, which means that the main thread will return from the idle
2448 // loop when all threads have finished their work at this split point.
2449 idle_loop(master, &splitPoint);
2451 // We have returned from the idle loop, which means that all threads are
2452 // finished. Update alpha and bestValue, and return.
2455 *alpha = splitPoint.alpha;
2456 *bestValue = splitPoint.bestValue;
2457 masterThread.activeSplitPoints--;
2458 masterThread.splitPoint = splitPoint.parent;
2459 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2461 lock_release(&mpLock);
2465 // wake_sleeping_thread() wakes up the thread with the given threadID
2466 // when it is time to start a new search.
2468 void ThreadsManager::wake_sleeping_thread(int threadID) {
2470 lock_grab(&sleepLock[threadID]);
2471 cond_signal(&sleepCond[threadID]);
2472 lock_release(&sleepLock[threadID]);
2476 /// RootMove and RootMoveList method's definitions
2478 RootMove::RootMove() {
2481 pv_score = non_pv_score = -VALUE_INFINITE;
2485 RootMove& RootMove::operator=(const RootMove& rm) {
2487 const Move* src = rm.pv;
2490 // Avoid a costly full rm.pv[] copy
2491 do *dst++ = *src; while (*src++ != MOVE_NONE);
2494 pv_score = rm.pv_score;
2495 non_pv_score = rm.non_pv_score;
2499 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2500 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2501 // allow to always have a ponder move even when we fail high at root and also a
2502 // long PV to print that is important for position analysis.
2504 void RootMove::extract_pv_from_tt(Position& pos) {
2506 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2510 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2512 pos.do_move(pv[0], *st++);
2514 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2515 && tte->move() != MOVE_NONE
2516 && move_is_legal(pos, tte->move())
2518 && (!pos.is_draw() || ply < 2))
2520 pv[ply] = tte->move();
2521 pos.do_move(pv[ply++], *st++);
2523 pv[ply] = MOVE_NONE;
2525 do pos.undo_move(pv[--ply]); while (ply);
2528 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2529 // the PV back into the TT. This makes sure the old PV moves are searched
2530 // first, even if the old TT entries have been overwritten.
2532 void RootMove::insert_pv_in_tt(Position& pos) {
2534 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2537 Value v, m = VALUE_NONE;
2540 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2544 tte = TT.retrieve(k);
2546 // Don't overwrite exsisting correct entries
2547 if (!tte || tte->move() != pv[ply])
2549 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2550 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2552 pos.do_move(pv[ply], *st++);
2554 } while (pv[++ply] != MOVE_NONE);
2556 do pos.undo_move(pv[--ply]); while (ply);
2559 // pv_info_to_uci() returns a string with information on the current PV line
2560 // formatted according to UCI specification and eventually writes the info
2561 // to a log file. It is called at each iteration or after a new pv is found.
2563 std::string RootMove::pv_info_to_uci(Position& pos, Depth depth, Value alpha, Value beta, int pvLine) {
2565 std::stringstream s, l;
2568 while (*m != MOVE_NONE)
2571 s << "info depth " << depth / ONE_PLY
2572 << " seldepth " << int(m - pv)
2573 << " multipv " << pvLine + 1
2574 << " score " << value_to_uci(pv_score)
2575 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2576 << " time " << current_search_time()
2577 << " nodes " << pos.nodes_searched()
2578 << " nps " << nps(pos)
2579 << " pv " << l.str();
2581 if (UseLogFile && pvLine == 0)
2583 ValueType t = pv_score >= beta ? VALUE_TYPE_LOWER :
2584 pv_score <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2586 LogFile << pretty_pv(pos, current_search_time(), depth, pv_score, t, pv) << endl;
2592 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2594 SearchStack ss[PLY_MAX_PLUS_2];
2595 MoveStack mlist[MOVES_MAX];
2599 // Initialize search stack
2600 init_ss_array(ss, PLY_MAX_PLUS_2);
2601 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2602 bestMoveChanges = 0;
2604 // Generate all legal moves
2605 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2607 // Add each move to the RootMoveList's vector
2608 for (MoveStack* cur = mlist; cur != last; cur++)
2610 // If we have a searchMoves[] list then verify cur->move
2611 // is in the list before to add it.
2612 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2614 if (searchMoves[0] && *sm != cur->move)
2617 // Find a quick score for the move and add to the list
2618 pos.do_move(cur->move, st);
2621 rm.pv[0] = ss[0].currentMove = cur->move;
2622 rm.pv[1] = MOVE_NONE;
2623 rm.pv_score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2626 pos.undo_move(cur->move);
2631 // Score root moves using the standard way used in main search, the moves
2632 // are scored according to the order in which are returned by MovePicker.
2633 // This is the second order score that is used to compare the moves when
2634 // the first order pv scores of both moves are equal.
2636 void RootMoveList::set_non_pv_scores(const Position& pos, Move ttm, SearchStack* ss)
2639 Value score = VALUE_ZERO;
2640 MovePicker mp(pos, ttm, ONE_PLY, H, ss);
2642 while ((move = mp.get_next_move()) != MOVE_NONE)
2643 for (Base::iterator it = begin(); it != end(); ++it)
2644 if (it->pv[0] == move)
2646 it->non_pv_score = score--;