2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
45 #include "ucioption.h"
51 //// Local definitions
57 enum NodeType { NonPV, PV };
59 // Set to true to force running with one thread.
60 // Used for debugging SMP code.
61 const bool FakeSplit = false;
63 // Fast lookup table of sliding pieces indexed by Piece
64 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
65 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
67 // ThreadsManager class is used to handle all the threads related stuff in search,
68 // init, starting, parking and, the most important, launching a slave thread at a
69 // split point are what this class does. All the access to shared thread data is
70 // done through this class, so that we avoid using global variables instead.
72 class ThreadsManager {
73 /* As long as the single ThreadsManager object is defined as a global we don't
74 need to explicitly initialize to zero its data members because variables with
75 static storage duration are automatically set to zero before enter main()
81 int min_split_depth() const { return minimumSplitDepth; }
82 int active_threads() const { return activeThreads; }
83 void set_active_threads(int cnt) { activeThreads = cnt; }
85 void read_uci_options();
86 bool available_thread_exists(int master) const;
87 bool thread_is_available(int slave, int master) const;
88 bool cutoff_at_splitpoint(int threadID) const;
89 void wake_sleeping_thread(int threadID);
90 void idle_loop(int threadID, SplitPoint* sp);
93 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
94 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
97 Depth minimumSplitDepth;
98 int maxThreadsPerSplitPoint;
99 bool useSleepingThreads;
101 volatile bool allThreadsShouldExit;
102 Thread threads[MAX_THREADS];
103 Lock mpLock, sleepLock[MAX_THREADS];
104 WaitCondition sleepCond[MAX_THREADS];
108 // RootMove struct is used for moves at the root at the tree. For each root
109 // move, we store two scores, a node count, and a PV (really a refutation
110 // in the case of moves which fail low). Value pv_score is normally set at
111 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
112 // according to the order in which moves are returned by MovePicker.
117 RootMove(const RootMove& rm) { *this = rm; }
118 RootMove& operator=(const RootMove& rm);
120 // RootMove::operator<() is the comparison function used when
121 // sorting the moves. A move m1 is considered to be better
122 // than a move m2 if it has an higher pv_score, or if it has
123 // equal pv_score but m1 has the higher non_pv_score. In this
124 // way we are guaranteed that PV moves are always sorted as first.
125 bool operator<(const RootMove& m) const {
126 return pv_score != m.pv_score ? pv_score < m.pv_score
127 : non_pv_score < m.non_pv_score;
130 void extract_pv_from_tt(Position& pos);
131 void insert_pv_in_tt(Position& pos);
132 std::string pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvLine);
137 Move pv[PLY_MAX_PLUS_2];
141 // RootMoveList struct is essentially a std::vector<> of RootMove objects,
142 // with an handful of methods above the standard ones.
144 struct RootMoveList : public std::vector<RootMove> {
146 typedef std::vector<RootMove> Base;
148 void init(Position& pos, Move searchMoves[]);
149 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
150 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
156 // When formatting a move for std::cout we must know if we are in Chess960
157 // or not. To keep using the handy operator<<() on the move the trick is to
158 // embed this flag in the stream itself. Function-like named enum set960 is
159 // used as a custom manipulator and the stream internal general-purpose array,
160 // accessed through ios_base::iword(), is used to pass the flag to the move's
161 // operator<<() that will use it to properly format castling moves.
164 std::ostream& operator<< (std::ostream& os, const set960& f) {
166 os.iword(0) = int(f);
171 // Overload operator << for moves to make it easier to print moves in
172 // coordinate notation compatible with UCI protocol.
173 std::ostream& operator<<(std::ostream& os, Move m) {
175 bool chess960 = (os.iword(0) != 0); // See set960()
176 return os << move_to_uci(m, chess960);
184 // Maximum depth for razoring
185 const Depth RazorDepth = 4 * ONE_PLY;
187 // Dynamic razoring margin based on depth
188 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
190 // Maximum depth for use of dynamic threat detection when null move fails low
191 const Depth ThreatDepth = 5 * ONE_PLY;
193 // Step 9. Internal iterative deepening
195 // Minimum depth for use of internal iterative deepening
196 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
198 // At Non-PV nodes we do an internal iterative deepening search
199 // when the static evaluation is bigger then beta - IIDMargin.
200 const Value IIDMargin = Value(0x100);
202 // Step 11. Decide the new search depth
204 // Extensions. Configurable UCI options
205 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
206 Depth CheckExtension[2], PawnPushTo7thExtension[2], PassedPawnExtension[2];
207 Depth PawnEndgameExtension[2], MateThreatExtension[2];
209 // Minimum depth for use of singular extension
210 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
212 // Step 12. Futility pruning
214 // Futility margin for quiescence search
215 const Value FutilityMarginQS = Value(0x80);
217 // Futility lookup tables (initialized at startup) and their getter functions
218 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
219 int FutilityMoveCountArray[32]; // [depth]
221 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
222 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
224 // Step 14. Reduced search
226 // Reduction lookup tables (initialized at startup) and their getter functions
227 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
229 template <NodeType PV>
230 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
232 // Easy move margin. An easy move candidate must be at least this much
233 // better than the second best move.
234 const Value EasyMoveMargin = Value(0x200);
237 /// Namespace variables
246 int MultiPV, UCIMultiPV;
248 // Time management variables
249 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
250 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
251 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
256 std::ofstream LogFile;
258 // Skill level adjustment
262 // Multi-threads manager object
263 ThreadsManager ThreadsMgr;
265 // Node counters, used only by thread[0] but try to keep in different cache
266 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
267 bool SendSearchedNodes;
269 int NodesBetweenPolls = 30000;
276 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
278 template <NodeType PvNode, bool SpNode, bool Root>
279 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
281 template <NodeType PvNode>
282 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
284 template <NodeType PvNode>
285 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
287 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
288 : search<PvNode, false, false>(pos, ss, alpha, beta, depth, ply);
291 template <NodeType PvNode>
292 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool mateThreat, bool* dangerous);
294 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
295 bool connected_moves(const Position& pos, Move m1, Move m2);
296 Value value_to_tt(Value v, int ply);
297 Value value_from_tt(Value v, int ply);
298 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
299 bool connected_threat(const Position& pos, Move m, Move threat);
300 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
301 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
302 void update_gains(const Position& pos, Move move, Value before, Value after);
304 int current_search_time();
305 std::string value_to_uci(Value v);
306 std::string speed_to_uci(int64_t nodes);
307 void poll(const Position& pos);
308 void wait_for_stop_or_ponderhit();
310 #if !defined(_MSC_VER)
311 void* init_thread(void* threadID);
313 DWORD WINAPI init_thread(LPVOID threadID);
317 // MovePickerExt is an extended MovePicker used to choose at compile time
318 // the proper move source according to the type of node.
319 template<bool SpNode, bool Root> struct MovePickerExt;
321 // In Root nodes use RootMoveList Rml as source. Score and sort the root moves
322 // before to search them.
323 template<> struct MovePickerExt<false, true> : public MovePicker {
325 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
326 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
328 Value score = VALUE_ZERO;
330 // Score root moves using the standard way used in main search, the moves
331 // are scored according to the order in which they are returned by MovePicker.
332 // This is the second order score that is used to compare the moves when
333 // the first order pv scores of both moves are equal.
334 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
335 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
336 if (rm->pv[0] == move)
338 rm->non_pv_score = score--;
346 Move get_next_move() {
353 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
356 RootMoveList::iterator rm;
360 // In SpNodes use split point's shared MovePicker object as move source
361 template<> struct MovePickerExt<true, false> : public MovePicker {
363 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
364 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b),
367 Move get_next_move() { return mp->get_next_move(); }
369 RootMoveList::iterator rm; // Dummy, needed to compile
373 // Default case, create and use a MovePicker object as source
374 template<> struct MovePickerExt<false, false> : public MovePicker {
376 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
377 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b) {}
379 RootMoveList::iterator rm; // Dummy, needed to compile
389 /// init_threads(), exit_threads() and nodes_searched() are helpers to
390 /// give accessibility to some TM methods from outside of current file.
392 void init_threads() { ThreadsMgr.init_threads(); }
393 void exit_threads() { ThreadsMgr.exit_threads(); }
396 /// init_search() is called during startup. It initializes various lookup tables
400 int d; // depth (ONE_PLY == 2)
401 int hd; // half depth (ONE_PLY == 1)
404 // Init reductions array
405 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
407 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
408 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
409 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
410 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
413 // Init futility margins array
414 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
415 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
417 // Init futility move count array
418 for (d = 0; d < 32; d++)
419 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
423 /// perft() is our utility to verify move generation is bug free. All the legal
424 /// moves up to given depth are generated and counted and the sum returned.
426 int64_t perft(Position& pos, Depth depth)
428 MoveStack mlist[MOVES_MAX];
433 // Generate all legal moves
434 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
436 // If we are at the last ply we don't need to do and undo
437 // the moves, just to count them.
438 if (depth <= ONE_PLY)
439 return int(last - mlist);
441 // Loop through all legal moves
443 for (MoveStack* cur = mlist; cur != last; cur++)
446 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
447 sum += perft(pos, depth - ONE_PLY);
454 /// think() is the external interface to Stockfish's search, and is called when
455 /// the program receives the UCI 'go' command. It initializes various
456 /// search-related global variables, and calls id_loop(). It returns false
457 /// when a quit command is received during the search.
459 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
460 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
462 // Initialize global search variables
463 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
465 SearchStartTime = get_system_time();
466 ExactMaxTime = maxTime;
469 InfiniteSearch = infinite;
471 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
473 // Look for a book move, only during games, not tests
474 if (UseTimeManagement && Options["OwnBook"].value<bool>())
476 if (Options["Book File"].value<std::string>() != OpeningBook.name())
477 OpeningBook.open(Options["Book File"].value<std::string>());
479 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
480 if (bookMove != MOVE_NONE)
483 wait_for_stop_or_ponderhit();
485 cout << "bestmove " << bookMove << endl;
490 // Read UCI option values
491 TT.set_size(Options["Hash"].value<int>());
492 if (Options["Clear Hash"].value<bool>())
494 Options["Clear Hash"].set_value("false");
498 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
499 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
500 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
501 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
502 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
503 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
504 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
505 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
506 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
507 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
508 UCIMultiPV = Options["MultiPV"].value<int>();
509 SkillLevel = Options["Skill level"].value<int>();
510 UseLogFile = Options["Use Search Log"].value<bool>();
512 read_evaluation_uci_options(pos.side_to_move());
514 // Do we have to play with skill handicap? In this case enable MultiPV that
515 // we will use behind the scenes to retrieve a set of possible moves.
516 MultiPV = (SkillLevel < 20 ? Max(UCIMultiPV, 4) : UCIMultiPV);
518 // Set the number of active threads
519 ThreadsMgr.read_uci_options();
520 init_eval(ThreadsMgr.active_threads());
522 // Wake up needed threads
523 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
524 ThreadsMgr.wake_sleeping_thread(i);
527 int myTime = time[pos.side_to_move()];
528 int myIncrement = increment[pos.side_to_move()];
529 if (UseTimeManagement)
530 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
532 // Set best NodesBetweenPolls interval to avoid lagging under
533 // heavy time pressure.
535 NodesBetweenPolls = Min(MaxNodes, 30000);
536 else if (myTime && myTime < 1000)
537 NodesBetweenPolls = 1000;
538 else if (myTime && myTime < 5000)
539 NodesBetweenPolls = 5000;
541 NodesBetweenPolls = 30000;
543 // Write search information to log file
546 std::string name = Options["Search Log Filename"].value<std::string>();
547 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
549 LogFile << "\nSearching: " << pos.to_fen()
550 << "\ninfinite: " << infinite
551 << " ponder: " << ponder
552 << " time: " << myTime
553 << " increment: " << myIncrement
554 << " moves to go: " << movesToGo
558 // We're ready to start thinking. Call the iterative deepening loop function
559 Move ponderMove = MOVE_NONE;
560 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
562 // Print final search statistics
563 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
567 int t = current_search_time();
569 LogFile << "Nodes: " << pos.nodes_searched()
570 << "\nNodes/second: " << (t > 0 ? int(pos.nodes_searched() * 1000 / t) : 0)
571 << "\nBest move: " << move_to_san(pos, bestMove);
574 pos.do_move(bestMove, st);
575 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
576 pos.undo_move(bestMove); // Return from think() with unchanged position
580 // This makes all the threads to go to sleep
581 ThreadsMgr.set_active_threads(1);
583 // If we are pondering or in infinite search, we shouldn't print the
584 // best move before we are told to do so.
585 if (!StopRequest && (Pondering || InfiniteSearch))
586 wait_for_stop_or_ponderhit();
588 // Could be MOVE_NONE when searching on a stalemate position
589 cout << "bestmove " << bestMove;
591 // UCI protol is not clear on allowing sending an empty ponder move, instead
592 // it is clear that ponder move is optional. So skip it if empty.
593 if (ponderMove != MOVE_NONE)
594 cout << " ponder " << ponderMove;
604 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
605 // with increasing depth until the allocated thinking time has been consumed,
606 // user stops the search, or the maximum search depth is reached.
608 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
610 SearchStack ss[PLY_MAX_PLUS_2];
611 Value bestValues[PLY_MAX_PLUS_2];
612 int bestMoveChanges[PLY_MAX_PLUS_2];
613 int depth, aspirationDelta;
614 Value value, alpha, beta;
615 Move bestMove, easyMove;
617 // Initialize stuff before a new search
618 memset(ss, 0, 4 * sizeof(SearchStack));
621 *ponderMove = bestMove = easyMove = MOVE_NONE;
622 depth = aspirationDelta = 0;
623 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
624 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
626 // Moves to search are verified and copied
627 Rml.init(pos, searchMoves);
629 // Handle special case of searching on a mate/stalemate position
632 cout << "info depth 0 score "
633 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
639 // Iterative deepening loop
640 while (++depth <= PLY_MAX && (!MaxDepth || depth <= MaxDepth) && !StopRequest)
642 Rml.bestMoveChanges = 0;
643 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
645 // Calculate dynamic aspiration window based on previous iterations
646 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
648 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
649 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
651 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
652 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
654 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
655 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
658 // Start with a small aspiration window and, in case of fail high/low,
659 // research with bigger window until not failing high/low anymore.
661 // Search starting from ss+1 to allow calling update_gains()
662 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY, 0);
664 // Write PV back to transposition table in case the relevant entries
665 // have been overwritten during the search.
666 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
667 Rml[i].insert_pv_in_tt(pos);
669 // Value cannot be trusted. Break out immediately!
673 assert(value >= alpha);
675 // In case of failing high/low increase aspiration window and research,
676 // otherwise exit the fail high/low loop.
679 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
680 aspirationDelta += aspirationDelta / 2;
682 else if (value <= alpha)
684 AspirationFailLow = true;
685 StopOnPonderhit = false;
687 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
688 aspirationDelta += aspirationDelta / 2;
693 } while (abs(value) < VALUE_KNOWN_WIN);
695 // Collect info about search result
696 bestMove = Rml[0].pv[0];
697 *ponderMove = Rml[0].pv[1];
698 bestValues[depth] = value;
699 bestMoveChanges[depth] = Rml.bestMoveChanges;
701 // Send PV line to GUI and to log file
702 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
703 cout << Rml[i].pv_info_to_uci(pos, depth, alpha, beta, i) << endl;
706 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
708 // Init easyMove after first iteration or drop if differs from the best move
709 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
711 else if (bestMove != easyMove)
712 easyMove = MOVE_NONE;
714 if (UseTimeManagement && !StopRequest)
717 bool noMoreTime = false;
719 // Stop search early when the last two iterations returned a mate score
721 && abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
722 && abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
725 // Stop search early if one move seems to be much better than the
726 // others or if there is only a single legal move. In this latter
727 // case we search up to Iteration 8 anyway to get a proper score.
729 && easyMove == bestMove
731 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
732 && current_search_time() > TimeMgr.available_time() / 16)
733 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
734 && current_search_time() > TimeMgr.available_time() / 32)))
737 // Add some extra time if the best move has changed during the last two iterations
738 if (depth > 4 && depth < 50)
739 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
741 // Stop search if most of MaxSearchTime is consumed at the end of the
742 // iteration. We probably don't have enough time to search the first
743 // move at the next iteration anyway.
744 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
750 StopOnPonderhit = true;
757 // When playing with strength handicap choose best move among the MultiPV set
758 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
763 // Rml list is already sorted by pv_score in descending order
765 int max_s = -VALUE_INFINITE;
766 int size = Min(MultiPV, (int)Rml.size());
767 int max = Rml[0].pv_score;
768 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
769 int wk = 120 - 2 * SkillLevel;
771 // PRNG sequence should be non deterministic
772 for (int i = abs(get_system_time() % 50); i > 0; i--)
775 // Choose best move. For each move's score we add two terms both dependent
776 // on wk, one deterministic and bigger for weaker moves, and one random,
777 // then we choose the move with the resulting highest score.
778 for (int i = 0; i < size; i++)
782 // Don't allow crazy blunders even at very low skills
783 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
786 // This is our magical formula
787 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
792 bestMove = Rml[i].pv[0];
793 *ponderMove = Rml[i].pv[1];
802 // search<>() is the main search function for both PV and non-PV nodes and for
803 // normal and SplitPoint nodes. When called just after a split point the search
804 // is simpler because we have already probed the hash table, done a null move
805 // search, and searched the first move before splitting, we don't have to repeat
806 // all this work again. We also don't need to store anything to the hash table
807 // here: This is taken care of after we return from the split point.
809 template <NodeType PvNode, bool SpNode, bool Root>
810 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
812 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
813 assert(beta > alpha && beta <= VALUE_INFINITE);
814 assert(PvNode || alpha == beta - 1);
815 assert((Root || ply > 0) && ply < PLY_MAX);
816 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
818 Move movesSearched[MOVES_MAX];
823 Move ttMove, move, excludedMove, threatMove;
826 Value bestValue, value, oldAlpha;
827 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
828 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
829 bool mateThreat = false;
830 int moveCount = 0, playedMoveCount = 0;
831 int threadID = pos.thread();
832 SplitPoint* sp = NULL;
834 refinedValue = bestValue = value = -VALUE_INFINITE;
836 isCheck = pos.is_check();
842 ttMove = excludedMove = MOVE_NONE;
843 threatMove = sp->threatMove;
844 mateThreat = sp->mateThreat;
845 goto split_point_start;
850 // Step 1. Initialize node and poll. Polling can abort search
851 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
852 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
853 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
855 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
861 // Step 2. Check for aborted search and immediate draw
863 || ThreadsMgr.cutoff_at_splitpoint(threadID)
865 || ply >= PLY_MAX - 1) && !Root)
868 // Step 3. Mate distance pruning
869 alpha = Max(value_mated_in(ply), alpha);
870 beta = Min(value_mate_in(ply+1), beta);
874 // Step 4. Transposition table lookup
875 // We don't want the score of a partial search to overwrite a previous full search
876 // TT value, so we use a different position key in case of an excluded move.
877 excludedMove = ss->excludedMove;
878 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
880 tte = TT.retrieve(posKey);
881 ttMove = tte ? tte->move() : MOVE_NONE;
883 // At PV nodes we check for exact scores, while at non-PV nodes we check for
884 // and return a fail high/low. Biggest advantage at probing at PV nodes is
885 // to have a smooth experience in analysis mode.
888 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
889 : ok_to_use_TT(tte, depth, beta, ply)))
892 ss->bestMove = ttMove; // Can be MOVE_NONE
893 return value_from_tt(tte->value(), ply);
896 // Step 5. Evaluate the position statically and
897 // update gain statistics of parent move.
899 ss->eval = ss->evalMargin = VALUE_NONE;
902 assert(tte->static_value() != VALUE_NONE);
904 ss->eval = tte->static_value();
905 ss->evalMargin = tte->static_value_margin();
906 refinedValue = refine_eval(tte, ss->eval, ply);
910 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
911 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
914 // Save gain for the parent non-capture move
915 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
917 // Step 6. Razoring (is omitted in PV nodes)
919 && depth < RazorDepth
921 && refinedValue < beta - razor_margin(depth)
922 && ttMove == MOVE_NONE
923 && abs(beta) < VALUE_MATE_IN_PLY_MAX
924 && !pos.has_pawn_on_7th(pos.side_to_move()))
926 Value rbeta = beta - razor_margin(depth);
927 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
929 // Logically we should return (v + razor_margin(depth)), but
930 // surprisingly this did slightly weaker in tests.
934 // Step 7. Static null move pruning (is omitted in PV nodes)
935 // We're betting that the opponent doesn't have a move that will reduce
936 // the score by more than futility_margin(depth) if we do a null move.
939 && depth < RazorDepth
941 && refinedValue >= beta + futility_margin(depth, 0)
942 && abs(beta) < VALUE_MATE_IN_PLY_MAX
943 && pos.non_pawn_material(pos.side_to_move()))
944 return refinedValue - futility_margin(depth, 0);
946 // Step 8. Null move search with verification search (is omitted in PV nodes)
951 && refinedValue >= beta
952 && abs(beta) < VALUE_MATE_IN_PLY_MAX
953 && pos.non_pawn_material(pos.side_to_move()))
955 ss->currentMove = MOVE_NULL;
957 // Null move dynamic reduction based on depth
958 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
960 // Null move dynamic reduction based on value
961 if (refinedValue - beta > PawnValueMidgame)
964 pos.do_null_move(st);
965 (ss+1)->skipNullMove = true;
966 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
967 (ss+1)->skipNullMove = false;
968 pos.undo_null_move();
970 if (nullValue >= beta)
972 // Do not return unproven mate scores
973 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
976 if (depth < 6 * ONE_PLY)
979 // Do verification search at high depths
980 ss->skipNullMove = true;
981 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
982 ss->skipNullMove = false;
989 // The null move failed low, which means that we may be faced with
990 // some kind of threat. If the previous move was reduced, check if
991 // the move that refuted the null move was somehow connected to the
992 // move which was reduced. If a connection is found, return a fail
993 // low score (which will cause the reduced move to fail high in the
994 // parent node, which will trigger a re-search with full depth).
995 if (nullValue == value_mated_in(ply + 2))
998 threatMove = (ss+1)->bestMove;
999 if ( depth < ThreatDepth
1000 && (ss-1)->reduction
1001 && threatMove != MOVE_NONE
1002 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1007 // Step 9. Internal iterative deepening
1008 if ( depth >= IIDDepth[PvNode]
1009 && ttMove == MOVE_NONE
1010 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1012 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1014 ss->skipNullMove = true;
1015 search<PvNode>(pos, ss, alpha, beta, d, ply);
1016 ss->skipNullMove = false;
1018 ttMove = ss->bestMove;
1019 tte = TT.retrieve(posKey);
1022 // Expensive mate threat detection (only for PV nodes)
1024 mateThreat = pos.has_mate_threat();
1026 split_point_start: // At split points actual search starts from here
1028 // Initialize a MovePicker object for the current position
1029 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1031 ss->bestMove = MOVE_NONE;
1032 futilityBase = ss->eval + ss->evalMargin;
1033 singularExtensionNode = !Root
1035 && depth >= SingularExtensionDepth[PvNode]
1038 && !excludedMove // Do not allow recursive singular extension search
1039 && (tte->type() & VALUE_TYPE_LOWER)
1040 && tte->depth() >= depth - 3 * ONE_PLY;
1043 lock_grab(&(sp->lock));
1044 bestValue = sp->bestValue;
1047 // Step 10. Loop through moves
1048 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1049 while ( bestValue < beta
1050 && (move = mp.get_next_move()) != MOVE_NONE
1051 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1053 assert(move_is_ok(move));
1057 moveCount = ++sp->moveCount;
1058 lock_release(&(sp->lock));
1060 else if (move == excludedMove)
1067 // This is used by time management
1068 FirstRootMove = (moveCount == 1);
1070 // Save the current node count before the move is searched
1071 nodes = pos.nodes_searched();
1073 // If it's time to send nodes info, do it here where we have the
1074 // correct accumulated node counts searched by each thread.
1075 if (SendSearchedNodes)
1077 SendSearchedNodes = false;
1078 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1081 if (current_search_time() >= 1000)
1082 cout << "info currmove " << move
1083 << " currmovenumber " << moveCount << endl;
1086 // At Root and at first iteration do a PV search on all the moves
1087 // to score root moves. Otherwise only the first one is the PV.
1088 isPvMove = (PvNode && moveCount <= (Root ? MultiPV + 1000 * (depth <= ONE_PLY) : 1));
1089 moveIsCheck = pos.move_is_check(move, ci);
1090 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1092 // Step 11. Decide the new search depth
1093 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, mateThreat, &dangerous);
1095 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1096 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1097 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1098 // lower than ttValue minus a margin then we extend ttMove.
1099 if ( singularExtensionNode
1100 && move == tte->move()
1103 Value ttValue = value_from_tt(tte->value(), ply);
1105 if (abs(ttValue) < VALUE_KNOWN_WIN)
1107 Value b = ttValue - int(depth);
1108 ss->excludedMove = move;
1109 ss->skipNullMove = true;
1110 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1111 ss->skipNullMove = false;
1112 ss->excludedMove = MOVE_NONE;
1113 ss->bestMove = MOVE_NONE;
1119 // Update current move (this must be done after singular extension search)
1120 ss->currentMove = move;
1121 newDepth = depth - ONE_PLY + ext;
1123 // Step 12. Futility pruning (is omitted in PV nodes)
1125 && !captureOrPromotion
1129 && !move_is_castle(move))
1131 // Move count based pruning
1132 if ( moveCount >= futility_move_count(depth)
1133 && !(threatMove && connected_threat(pos, move, threatMove))
1134 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1137 lock_grab(&(sp->lock));
1142 // Value based pruning
1143 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1144 // but fixing this made program slightly weaker.
1145 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1146 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1147 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1149 if (futilityValueScaled < beta)
1153 lock_grab(&(sp->lock));
1154 if (futilityValueScaled > sp->bestValue)
1155 sp->bestValue = bestValue = futilityValueScaled;
1157 else if (futilityValueScaled > bestValue)
1158 bestValue = futilityValueScaled;
1163 // Prune moves with negative SEE at low depths
1164 if ( predictedDepth < 2 * ONE_PLY
1165 && bestValue > VALUE_MATED_IN_PLY_MAX
1166 && pos.see_sign(move) < 0)
1169 lock_grab(&(sp->lock));
1175 // Step 13. Make the move
1176 pos.do_move(move, st, ci, moveIsCheck);
1178 if (!SpNode && !captureOrPromotion)
1179 movesSearched[playedMoveCount++] = move;
1181 // Step extra. pv search (only in PV nodes)
1182 // The first move in list is the expected PV
1185 // Aspiration window is disabled in multi-pv case
1186 if (Root && MultiPV > 1)
1187 alpha = -VALUE_INFINITE;
1189 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1193 // Step 14. Reduced depth search
1194 // If the move fails high will be re-searched at full depth.
1195 bool doFullDepthSearch = true;
1197 if ( depth >= 3 * ONE_PLY
1198 && !captureOrPromotion
1200 && !move_is_castle(move)
1201 && ss->killers[0] != move
1202 && ss->killers[1] != move)
1204 ss->reduction = reduction<PvNode>(depth, moveCount);
1207 alpha = SpNode ? sp->alpha : alpha;
1208 Depth d = newDepth - ss->reduction;
1209 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1211 doFullDepthSearch = (value > alpha);
1213 ss->reduction = DEPTH_ZERO; // Restore original reduction
1216 // Step 15. Full depth search
1217 if (doFullDepthSearch)
1219 alpha = SpNode ? sp->alpha : alpha;
1220 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1222 // Step extra. pv search (only in PV nodes)
1223 // Search only for possible new PV nodes, if instead value >= beta then
1224 // parent node fails low with value <= alpha and tries another move.
1225 if (PvNode && value > alpha && (Root || value < beta))
1226 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1230 // Step 16. Undo move
1231 pos.undo_move(move);
1233 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1235 // Step 17. Check for new best move
1238 lock_grab(&(sp->lock));
1239 bestValue = sp->bestValue;
1243 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1248 sp->bestValue = value;
1250 if (!Root && value > alpha)
1252 if (PvNode && value < beta) // We want always alpha < beta
1260 sp->betaCutoff = true;
1262 if (value == value_mate_in(ply + 1))
1263 ss->mateKiller = move;
1265 ss->bestMove = move;
1268 sp->ss->bestMove = move;
1274 // Finished searching the move. If StopRequest is true, the search
1275 // was aborted because the user interrupted the search or because we
1276 // ran out of time. In this case, the return value of the search cannot
1277 // be trusted, and we break out of the loop without updating the best
1282 // Remember searched nodes counts for this move
1283 mp.rm->nodes += pos.nodes_searched() - nodes;
1285 // PV move or new best move ?
1286 if (isPvMove || value > alpha)
1289 ss->bestMove = move;
1290 mp.rm->pv_score = value;
1291 mp.rm->extract_pv_from_tt(pos);
1293 // We record how often the best move has been changed in each
1294 // iteration. This information is used for time management: When
1295 // the best move changes frequently, we allocate some more time.
1296 if (!isPvMove && MultiPV == 1)
1297 Rml.bestMoveChanges++;
1299 Rml.sort_multipv(moveCount);
1301 // Update alpha. In multi-pv we don't use aspiration window, so
1302 // set alpha equal to minimum score among the PV lines.
1304 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1305 else if (value > alpha)
1309 mp.rm->pv_score = -VALUE_INFINITE;
1313 // Step 18. Check for split
1316 && depth >= ThreadsMgr.min_split_depth()
1317 && ThreadsMgr.active_threads() > 1
1319 && ThreadsMgr.available_thread_exists(threadID)
1321 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1322 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1323 threatMove, mateThreat, moveCount, &mp, PvNode);
1326 // Step 19. Check for mate and stalemate
1327 // All legal moves have been searched and if there are
1328 // no legal moves, it must be mate or stalemate.
1329 // If one move was excluded return fail low score.
1330 if (!SpNode && !moveCount)
1331 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1333 // Step 20. Update tables
1334 // If the search is not aborted, update the transposition table,
1335 // history counters, and killer moves.
1336 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1338 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1339 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1340 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1342 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1344 // Update killers and history only for non capture moves that fails high
1345 if ( bestValue >= beta
1346 && !pos.move_is_capture_or_promotion(move))
1348 if (move != ss->killers[0])
1350 ss->killers[1] = ss->killers[0];
1351 ss->killers[0] = move;
1353 update_history(pos, move, depth, movesSearched, playedMoveCount);
1359 // Here we have the lock still grabbed
1360 sp->slaves[threadID] = 0;
1361 sp->nodes += pos.nodes_searched();
1362 lock_release(&(sp->lock));
1365 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1370 // qsearch() is the quiescence search function, which is called by the main
1371 // search function when the remaining depth is zero (or, to be more precise,
1372 // less than ONE_PLY).
1374 template <NodeType PvNode>
1375 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1377 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1378 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1379 assert(PvNode || alpha == beta - 1);
1381 assert(ply > 0 && ply < PLY_MAX);
1382 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1386 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1387 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1390 Value oldAlpha = alpha;
1392 ss->bestMove = ss->currentMove = MOVE_NONE;
1394 // Check for an instant draw or maximum ply reached
1395 if (pos.is_draw() || ply >= PLY_MAX - 1)
1398 // Decide whether or not to include checks, this fixes also the type of
1399 // TT entry depth that we are going to use. Note that in qsearch we use
1400 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1401 isCheck = pos.is_check();
1402 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1404 // Transposition table lookup. At PV nodes, we don't use the TT for
1405 // pruning, but only for move ordering.
1406 tte = TT.retrieve(pos.get_key());
1407 ttMove = (tte ? tte->move() : MOVE_NONE);
1409 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1411 ss->bestMove = ttMove; // Can be MOVE_NONE
1412 return value_from_tt(tte->value(), ply);
1415 // Evaluate the position statically
1418 bestValue = futilityBase = -VALUE_INFINITE;
1419 ss->eval = evalMargin = VALUE_NONE;
1420 enoughMaterial = false;
1426 assert(tte->static_value() != VALUE_NONE);
1428 evalMargin = tte->static_value_margin();
1429 ss->eval = bestValue = tte->static_value();
1432 ss->eval = bestValue = evaluate(pos, evalMargin);
1434 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1436 // Stand pat. Return immediately if static value is at least beta
1437 if (bestValue >= beta)
1440 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1445 if (PvNode && bestValue > alpha)
1448 // Futility pruning parameters, not needed when in check
1449 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1450 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1453 // Initialize a MovePicker object for the current position, and prepare
1454 // to search the moves. Because the depth is <= 0 here, only captures,
1455 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1457 MovePicker mp(pos, ttMove, depth, H);
1460 // Loop through the moves until no moves remain or a beta cutoff occurs
1461 while ( alpha < beta
1462 && (move = mp.get_next_move()) != MOVE_NONE)
1464 assert(move_is_ok(move));
1466 moveIsCheck = pos.move_is_check(move, ci);
1474 && !move_is_promotion(move)
1475 && !pos.move_is_passed_pawn_push(move))
1477 futilityValue = futilityBase
1478 + pos.endgame_value_of_piece_on(move_to(move))
1479 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1481 if (futilityValue < alpha)
1483 if (futilityValue > bestValue)
1484 bestValue = futilityValue;
1488 // Prune moves with negative or equal SEE
1489 if ( futilityBase < beta
1490 && depth < DEPTH_ZERO
1491 && pos.see(move) <= 0)
1495 // Detect non-capture evasions that are candidate to be pruned
1496 evasionPrunable = isCheck
1497 && bestValue > VALUE_MATED_IN_PLY_MAX
1498 && !pos.move_is_capture(move)
1499 && !pos.can_castle(pos.side_to_move());
1501 // Don't search moves with negative SEE values
1503 && (!isCheck || evasionPrunable)
1505 && !move_is_promotion(move)
1506 && pos.see_sign(move) < 0)
1509 // Don't search useless checks
1514 && !pos.move_is_capture_or_promotion(move)
1515 && ss->eval + PawnValueMidgame / 4 < beta
1516 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1518 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1519 bestValue = ss->eval + PawnValueMidgame / 4;
1524 // Update current move
1525 ss->currentMove = move;
1527 // Make and search the move
1528 pos.do_move(move, st, ci, moveIsCheck);
1529 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1530 pos.undo_move(move);
1532 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1535 if (value > bestValue)
1541 ss->bestMove = move;
1546 // All legal moves have been searched. A special case: If we're in check
1547 // and no legal moves were found, it is checkmate.
1548 if (isCheck && bestValue == -VALUE_INFINITE)
1549 return value_mated_in(ply);
1551 // Update transposition table
1552 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1553 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1555 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1561 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1562 // bestValue is updated only when returning false because in that case move
1565 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1567 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1568 Square from, to, ksq, victimSq;
1571 Value futilityValue, bv = *bestValue;
1573 from = move_from(move);
1575 them = opposite_color(pos.side_to_move());
1576 ksq = pos.king_square(them);
1577 kingAtt = pos.attacks_from<KING>(ksq);
1578 pc = pos.piece_on(from);
1580 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1581 oldAtt = pos.attacks_from(pc, from, occ);
1582 newAtt = pos.attacks_from(pc, to, occ);
1584 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1585 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1587 if (!(b && (b & (b - 1))))
1590 // Rule 2. Queen contact check is very dangerous
1591 if ( type_of_piece(pc) == QUEEN
1592 && bit_is_set(kingAtt, to))
1595 // Rule 3. Creating new double threats with checks
1596 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1600 victimSq = pop_1st_bit(&b);
1601 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1603 // Note that here we generate illegal "double move"!
1604 if ( futilityValue >= beta
1605 && pos.see_sign(make_move(from, victimSq)) >= 0)
1608 if (futilityValue > bv)
1612 // Update bestValue only if check is not dangerous (because we will prune the move)
1618 // connected_moves() tests whether two moves are 'connected' in the sense
1619 // that the first move somehow made the second move possible (for instance
1620 // if the moving piece is the same in both moves). The first move is assumed
1621 // to be the move that was made to reach the current position, while the
1622 // second move is assumed to be a move from the current position.
1624 bool connected_moves(const Position& pos, Move m1, Move m2) {
1626 Square f1, t1, f2, t2;
1629 assert(m1 && move_is_ok(m1));
1630 assert(m2 && move_is_ok(m2));
1632 // Case 1: The moving piece is the same in both moves
1638 // Case 2: The destination square for m2 was vacated by m1
1644 // Case 3: Moving through the vacated square
1645 if ( piece_is_slider(pos.piece_on(f2))
1646 && bit_is_set(squares_between(f2, t2), f1))
1649 // Case 4: The destination square for m2 is defended by the moving piece in m1
1650 p = pos.piece_on(t1);
1651 if (bit_is_set(pos.attacks_from(p, t1), t2))
1654 // Case 5: Discovered check, checking piece is the piece moved in m1
1655 if ( piece_is_slider(p)
1656 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1657 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1659 // discovered_check_candidates() works also if the Position's side to
1660 // move is the opposite of the checking piece.
1661 Color them = opposite_color(pos.side_to_move());
1662 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1664 if (bit_is_set(dcCandidates, f2))
1671 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1672 // "plies to mate from the current ply". Non-mate scores are unchanged.
1673 // The function is called before storing a value to the transposition table.
1675 Value value_to_tt(Value v, int ply) {
1677 if (v >= VALUE_MATE_IN_PLY_MAX)
1680 if (v <= VALUE_MATED_IN_PLY_MAX)
1687 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1688 // the transposition table to a mate score corrected for the current ply.
1690 Value value_from_tt(Value v, int ply) {
1692 if (v >= VALUE_MATE_IN_PLY_MAX)
1695 if (v <= VALUE_MATED_IN_PLY_MAX)
1702 // extension() decides whether a move should be searched with normal depth,
1703 // or with extended depth. Certain classes of moves (checking moves, in
1704 // particular) are searched with bigger depth than ordinary moves and in
1705 // any case are marked as 'dangerous'. Note that also if a move is not
1706 // extended, as example because the corresponding UCI option is set to zero,
1707 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1708 template <NodeType PvNode>
1709 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1710 bool moveIsCheck, bool mateThreat, bool* dangerous) {
1712 assert(m != MOVE_NONE);
1714 Depth result = DEPTH_ZERO;
1715 *dangerous = moveIsCheck | mateThreat;
1719 if (moveIsCheck && pos.see_sign(m) >= 0)
1720 result += CheckExtension[PvNode];
1723 result += MateThreatExtension[PvNode];
1726 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1728 Color c = pos.side_to_move();
1729 if (relative_rank(c, move_to(m)) == RANK_7)
1731 result += PawnPushTo7thExtension[PvNode];
1734 if (pos.pawn_is_passed(c, move_to(m)))
1736 result += PassedPawnExtension[PvNode];
1741 if ( captureOrPromotion
1742 && pos.type_of_piece_on(move_to(m)) != PAWN
1743 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1744 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1745 && !move_is_promotion(m)
1748 result += PawnEndgameExtension[PvNode];
1752 return Min(result, ONE_PLY);
1756 // connected_threat() tests whether it is safe to forward prune a move or if
1757 // is somehow connected to the threat move returned by null search.
1759 bool connected_threat(const Position& pos, Move m, Move threat) {
1761 assert(move_is_ok(m));
1762 assert(threat && move_is_ok(threat));
1763 assert(!pos.move_is_check(m));
1764 assert(!pos.move_is_capture_or_promotion(m));
1765 assert(!pos.move_is_passed_pawn_push(m));
1767 Square mfrom, mto, tfrom, tto;
1769 mfrom = move_from(m);
1771 tfrom = move_from(threat);
1772 tto = move_to(threat);
1774 // Case 1: Don't prune moves which move the threatened piece
1778 // Case 2: If the threatened piece has value less than or equal to the
1779 // value of the threatening piece, don't prune moves which defend it.
1780 if ( pos.move_is_capture(threat)
1781 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1782 || pos.type_of_piece_on(tfrom) == KING)
1783 && pos.move_attacks_square(m, tto))
1786 // Case 3: If the moving piece in the threatened move is a slider, don't
1787 // prune safe moves which block its ray.
1788 if ( piece_is_slider(pos.piece_on(tfrom))
1789 && bit_is_set(squares_between(tfrom, tto), mto)
1790 && pos.see_sign(m) >= 0)
1797 // ok_to_use_TT() returns true if a transposition table score
1798 // can be used at a given point in search.
1800 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1802 Value v = value_from_tt(tte->value(), ply);
1804 return ( tte->depth() >= depth
1805 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1806 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1808 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1809 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1813 // refine_eval() returns the transposition table score if
1814 // possible otherwise falls back on static position evaluation.
1816 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1820 Value v = value_from_tt(tte->value(), ply);
1822 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1823 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1830 // update_history() registers a good move that produced a beta-cutoff
1831 // in history and marks as failures all the other moves of that ply.
1833 void update_history(const Position& pos, Move move, Depth depth,
1834 Move movesSearched[], int moveCount) {
1836 Value bonus = Value(int(depth) * int(depth));
1838 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1840 for (int i = 0; i < moveCount - 1; i++)
1842 m = movesSearched[i];
1846 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1851 // update_gains() updates the gains table of a non-capture move given
1852 // the static position evaluation before and after the move.
1854 void update_gains(const Position& pos, Move m, Value before, Value after) {
1857 && before != VALUE_NONE
1858 && after != VALUE_NONE
1859 && pos.captured_piece_type() == PIECE_TYPE_NONE
1860 && !move_is_special(m))
1861 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1865 // current_search_time() returns the number of milliseconds which have passed
1866 // since the beginning of the current search.
1868 int current_search_time() {
1870 return get_system_time() - SearchStartTime;
1874 // value_to_uci() converts a value to a string suitable for use with the UCI
1875 // protocol specifications:
1877 // cp <x> The score from the engine's point of view in centipawns.
1878 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1879 // use negative values for y.
1881 std::string value_to_uci(Value v) {
1883 std::stringstream s;
1885 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1886 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1888 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1894 // speed_to_uci() returns a string with time stats of current search suitable
1895 // to be sent to UCI gui.
1897 std::string speed_to_uci(int64_t nodes) {
1899 std::stringstream s;
1900 int t = current_search_time();
1902 s << " nodes " << nodes
1903 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1910 // poll() performs two different functions: It polls for user input, and it
1911 // looks at the time consumed so far and decides if it's time to abort the
1914 void poll(const Position& pos) {
1916 static int lastInfoTime;
1917 int t = current_search_time();
1920 if (input_available())
1922 // We are line oriented, don't read single chars
1923 std::string command;
1925 if (!std::getline(std::cin, command) || command == "quit")
1927 // Quit the program as soon as possible
1929 QuitRequest = StopRequest = true;
1932 else if (command == "stop")
1934 // Stop calculating as soon as possible, but still send the "bestmove"
1935 // and possibly the "ponder" token when finishing the search.
1939 else if (command == "ponderhit")
1941 // The opponent has played the expected move. GUI sends "ponderhit" if
1942 // we were told to ponder on the same move the opponent has played. We
1943 // should continue searching but switching from pondering to normal search.
1946 if (StopOnPonderhit)
1951 // Print search information
1955 else if (lastInfoTime > t)
1956 // HACK: Must be a new search where we searched less than
1957 // NodesBetweenPolls nodes during the first second of search.
1960 else if (t - lastInfoTime >= 1000)
1967 if (dbg_show_hit_rate)
1968 dbg_print_hit_rate();
1970 // Send info on searched nodes as soon as we return to root
1971 SendSearchedNodes = true;
1974 // Should we stop the search?
1978 bool stillAtFirstMove = FirstRootMove
1979 && !AspirationFailLow
1980 && t > TimeMgr.available_time();
1982 bool noMoreTime = t > TimeMgr.maximum_time()
1983 || stillAtFirstMove;
1985 if ( (UseTimeManagement && noMoreTime)
1986 || (ExactMaxTime && t >= ExactMaxTime)
1987 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
1992 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1993 // while the program is pondering. The point is to work around a wrinkle in
1994 // the UCI protocol: When pondering, the engine is not allowed to give a
1995 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1996 // We simply wait here until one of these commands is sent, and return,
1997 // after which the bestmove and pondermove will be printed.
1999 void wait_for_stop_or_ponderhit() {
2001 std::string command;
2003 // Wait for a command from stdin
2004 while ( std::getline(std::cin, command)
2005 && command != "ponderhit" && command != "stop" && command != "quit") {};
2007 if (command != "ponderhit" && command != "stop")
2008 QuitRequest = true; // Must be "quit" or getline() returned false
2012 // init_thread() is the function which is called when a new thread is
2013 // launched. It simply calls the idle_loop() function with the supplied
2014 // threadID. There are two versions of this function; one for POSIX
2015 // threads and one for Windows threads.
2017 #if !defined(_MSC_VER)
2019 void* init_thread(void* threadID) {
2021 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2027 DWORD WINAPI init_thread(LPVOID threadID) {
2029 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2036 /// The ThreadsManager class
2039 // read_uci_options() updates number of active threads and other internal
2040 // parameters according to the UCI options values. It is called before
2041 // to start a new search.
2043 void ThreadsManager::read_uci_options() {
2045 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2046 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2047 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2048 activeThreads = Options["Threads"].value<int>();
2052 // idle_loop() is where the threads are parked when they have no work to do.
2053 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2054 // object for which the current thread is the master.
2056 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2058 assert(threadID >= 0 && threadID < MAX_THREADS);
2061 bool allFinished = false;
2065 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2066 // master should exit as last one.
2067 if (allThreadsShouldExit)
2070 threads[threadID].state = THREAD_TERMINATED;
2074 // If we are not thinking, wait for a condition to be signaled
2075 // instead of wasting CPU time polling for work.
2076 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2077 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2079 assert(!sp || useSleepingThreads);
2080 assert(threadID != 0 || useSleepingThreads);
2082 if (threads[threadID].state == THREAD_INITIALIZING)
2083 threads[threadID].state = THREAD_AVAILABLE;
2085 // Grab the lock to avoid races with wake_sleeping_thread()
2086 lock_grab(&sleepLock[threadID]);
2088 // If we are master and all slaves have finished do not go to sleep
2089 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2090 allFinished = (i == activeThreads);
2092 if (allFinished || allThreadsShouldExit)
2094 lock_release(&sleepLock[threadID]);
2098 // Do sleep here after retesting sleep conditions
2099 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2100 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2102 lock_release(&sleepLock[threadID]);
2105 // If this thread has been assigned work, launch a search
2106 if (threads[threadID].state == THREAD_WORKISWAITING)
2108 assert(!allThreadsShouldExit);
2110 threads[threadID].state = THREAD_SEARCHING;
2112 // Copy SplitPoint position and search stack and call search()
2113 // with SplitPoint template parameter set to true.
2114 SearchStack ss[PLY_MAX_PLUS_2];
2115 SplitPoint* tsp = threads[threadID].splitPoint;
2116 Position pos(*tsp->pos, threadID);
2118 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2122 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2124 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2126 assert(threads[threadID].state == THREAD_SEARCHING);
2128 threads[threadID].state = THREAD_AVAILABLE;
2130 // Wake up master thread so to allow it to return from the idle loop in
2131 // case we are the last slave of the split point.
2132 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2133 wake_sleeping_thread(tsp->master);
2136 // If this thread is the master of a split point and all slaves have
2137 // finished their work at this split point, return from the idle loop.
2138 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2139 allFinished = (i == activeThreads);
2143 // Because sp->slaves[] is reset under lock protection,
2144 // be sure sp->lock has been released before to return.
2145 lock_grab(&(sp->lock));
2146 lock_release(&(sp->lock));
2148 // In helpful master concept a master can help only a sub-tree, and
2149 // because here is all finished is not possible master is booked.
2150 assert(threads[threadID].state == THREAD_AVAILABLE);
2152 threads[threadID].state = THREAD_SEARCHING;
2159 // init_threads() is called during startup. It launches all helper threads,
2160 // and initializes the split point stack and the global locks and condition
2163 void ThreadsManager::init_threads() {
2165 int i, arg[MAX_THREADS];
2168 // Initialize global locks
2171 for (i = 0; i < MAX_THREADS; i++)
2173 lock_init(&sleepLock[i]);
2174 cond_init(&sleepCond[i]);
2177 // Initialize splitPoints[] locks
2178 for (i = 0; i < MAX_THREADS; i++)
2179 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2180 lock_init(&(threads[i].splitPoints[j].lock));
2182 // Will be set just before program exits to properly end the threads
2183 allThreadsShouldExit = false;
2185 // Threads will be put all threads to sleep as soon as created
2188 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2189 threads[0].state = THREAD_SEARCHING;
2190 for (i = 1; i < MAX_THREADS; i++)
2191 threads[i].state = THREAD_INITIALIZING;
2193 // Launch the helper threads
2194 for (i = 1; i < MAX_THREADS; i++)
2198 #if !defined(_MSC_VER)
2199 pthread_t pthread[1];
2200 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2201 pthread_detach(pthread[0]);
2203 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2207 cout << "Failed to create thread number " << i << endl;
2211 // Wait until the thread has finished launching and is gone to sleep
2212 while (threads[i].state == THREAD_INITIALIZING) {}
2217 // exit_threads() is called when the program exits. It makes all the
2218 // helper threads exit cleanly.
2220 void ThreadsManager::exit_threads() {
2222 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2224 // Wake up all the threads and waits for termination
2225 for (int i = 1; i < MAX_THREADS; i++)
2227 wake_sleeping_thread(i);
2228 while (threads[i].state != THREAD_TERMINATED) {}
2231 // Now we can safely destroy the locks
2232 for (int i = 0; i < MAX_THREADS; i++)
2233 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2234 lock_destroy(&(threads[i].splitPoints[j].lock));
2236 lock_destroy(&mpLock);
2238 // Now we can safely destroy the wait conditions
2239 for (int i = 0; i < MAX_THREADS; i++)
2241 lock_destroy(&sleepLock[i]);
2242 cond_destroy(&sleepCond[i]);
2247 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2248 // the thread's currently active split point, or in some ancestor of
2249 // the current split point.
2251 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2253 assert(threadID >= 0 && threadID < activeThreads);
2255 SplitPoint* sp = threads[threadID].splitPoint;
2257 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2262 // thread_is_available() checks whether the thread with threadID "slave" is
2263 // available to help the thread with threadID "master" at a split point. An
2264 // obvious requirement is that "slave" must be idle. With more than two
2265 // threads, this is not by itself sufficient: If "slave" is the master of
2266 // some active split point, it is only available as a slave to the other
2267 // threads which are busy searching the split point at the top of "slave"'s
2268 // split point stack (the "helpful master concept" in YBWC terminology).
2270 bool ThreadsManager::thread_is_available(int slave, int master) const {
2272 assert(slave >= 0 && slave < activeThreads);
2273 assert(master >= 0 && master < activeThreads);
2274 assert(activeThreads > 1);
2276 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2279 // Make a local copy to be sure doesn't change under our feet
2280 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2282 // No active split points means that the thread is available as
2283 // a slave for any other thread.
2284 if (localActiveSplitPoints == 0 || activeThreads == 2)
2287 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2288 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2289 // could have been set to 0 by another thread leading to an out of bound access.
2290 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2297 // available_thread_exists() tries to find an idle thread which is available as
2298 // a slave for the thread with threadID "master".
2300 bool ThreadsManager::available_thread_exists(int master) const {
2302 assert(master >= 0 && master < activeThreads);
2303 assert(activeThreads > 1);
2305 for (int i = 0; i < activeThreads; i++)
2306 if (thread_is_available(i, master))
2313 // split() does the actual work of distributing the work at a node between
2314 // several available threads. If it does not succeed in splitting the
2315 // node (because no idle threads are available, or because we have no unused
2316 // split point objects), the function immediately returns. If splitting is
2317 // possible, a SplitPoint object is initialized with all the data that must be
2318 // copied to the helper threads and we tell our helper threads that they have
2319 // been assigned work. This will cause them to instantly leave their idle loops and
2320 // call search().When all threads have returned from search() then split() returns.
2322 template <bool Fake>
2323 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2324 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2325 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2326 assert(pos.is_ok());
2327 assert(ply > 0 && ply < PLY_MAX);
2328 assert(*bestValue >= -VALUE_INFINITE);
2329 assert(*bestValue <= *alpha);
2330 assert(*alpha < beta);
2331 assert(beta <= VALUE_INFINITE);
2332 assert(depth > DEPTH_ZERO);
2333 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2334 assert(activeThreads > 1);
2336 int i, master = pos.thread();
2337 Thread& masterThread = threads[master];
2341 // If no other thread is available to help us, or if we have too many
2342 // active split points, don't split.
2343 if ( !available_thread_exists(master)
2344 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2346 lock_release(&mpLock);
2350 // Pick the next available split point object from the split point stack
2351 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2353 // Initialize the split point object
2354 splitPoint.parent = masterThread.splitPoint;
2355 splitPoint.master = master;
2356 splitPoint.betaCutoff = false;
2357 splitPoint.ply = ply;
2358 splitPoint.depth = depth;
2359 splitPoint.threatMove = threatMove;
2360 splitPoint.mateThreat = mateThreat;
2361 splitPoint.alpha = *alpha;
2362 splitPoint.beta = beta;
2363 splitPoint.pvNode = pvNode;
2364 splitPoint.bestValue = *bestValue;
2366 splitPoint.moveCount = moveCount;
2367 splitPoint.pos = &pos;
2368 splitPoint.nodes = 0;
2370 for (i = 0; i < activeThreads; i++)
2371 splitPoint.slaves[i] = 0;
2373 masterThread.splitPoint = &splitPoint;
2375 // If we are here it means we are not available
2376 assert(masterThread.state != THREAD_AVAILABLE);
2378 int workersCnt = 1; // At least the master is included
2380 // Allocate available threads setting state to THREAD_BOOKED
2381 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2382 if (thread_is_available(i, master))
2384 threads[i].state = THREAD_BOOKED;
2385 threads[i].splitPoint = &splitPoint;
2386 splitPoint.slaves[i] = 1;
2390 assert(Fake || workersCnt > 1);
2392 // We can release the lock because slave threads are already booked and master is not available
2393 lock_release(&mpLock);
2395 // Tell the threads that they have work to do. This will make them leave
2397 for (i = 0; i < activeThreads; i++)
2398 if (i == master || splitPoint.slaves[i])
2400 assert(i == master || threads[i].state == THREAD_BOOKED);
2402 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2404 if (useSleepingThreads && i != master)
2405 wake_sleeping_thread(i);
2408 // Everything is set up. The master thread enters the idle loop, from
2409 // which it will instantly launch a search, because its state is
2410 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2411 // idle loop, which means that the main thread will return from the idle
2412 // loop when all threads have finished their work at this split point.
2413 idle_loop(master, &splitPoint);
2415 // We have returned from the idle loop, which means that all threads are
2416 // finished. Update alpha and bestValue, and return.
2419 *alpha = splitPoint.alpha;
2420 *bestValue = splitPoint.bestValue;
2421 masterThread.activeSplitPoints--;
2422 masterThread.splitPoint = splitPoint.parent;
2423 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2425 lock_release(&mpLock);
2429 // wake_sleeping_thread() wakes up the thread with the given threadID
2430 // when it is time to start a new search.
2432 void ThreadsManager::wake_sleeping_thread(int threadID) {
2434 lock_grab(&sleepLock[threadID]);
2435 cond_signal(&sleepCond[threadID]);
2436 lock_release(&sleepLock[threadID]);
2440 /// RootMove and RootMoveList method's definitions
2442 RootMove::RootMove() {
2445 pv_score = non_pv_score = -VALUE_INFINITE;
2449 RootMove& RootMove::operator=(const RootMove& rm) {
2451 const Move* src = rm.pv;
2454 // Avoid a costly full rm.pv[] copy
2455 do *dst++ = *src; while (*src++ != MOVE_NONE);
2458 pv_score = rm.pv_score;
2459 non_pv_score = rm.non_pv_score;
2463 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2464 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2465 // allow to always have a ponder move even when we fail high at root and also a
2466 // long PV to print that is important for position analysis.
2468 void RootMove::extract_pv_from_tt(Position& pos) {
2470 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2474 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2476 pos.do_move(pv[0], *st++);
2478 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2479 && tte->move() != MOVE_NONE
2480 && move_is_legal(pos, tte->move())
2482 && (!pos.is_draw() || ply < 2))
2484 pv[ply] = tte->move();
2485 pos.do_move(pv[ply++], *st++);
2487 pv[ply] = MOVE_NONE;
2489 do pos.undo_move(pv[--ply]); while (ply);
2492 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2493 // the PV back into the TT. This makes sure the old PV moves are searched
2494 // first, even if the old TT entries have been overwritten.
2496 void RootMove::insert_pv_in_tt(Position& pos) {
2498 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2501 Value v, m = VALUE_NONE;
2504 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2508 tte = TT.retrieve(k);
2510 // Don't overwrite existing correct entries
2511 if (!tte || tte->move() != pv[ply])
2513 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2514 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2516 pos.do_move(pv[ply], *st++);
2518 } while (pv[++ply] != MOVE_NONE);
2520 do pos.undo_move(pv[--ply]); while (ply);
2523 // pv_info_to_uci() returns a string with information on the current PV line
2524 // formatted according to UCI specification. It is called at each iteration
2525 // or after a new pv is found.
2527 std::string RootMove::pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvLine) {
2529 std::stringstream s, l;
2532 while (*m != MOVE_NONE)
2535 s << "info depth " << depth
2536 << " seldepth " << int(m - pv)
2537 << " multipv " << pvLine + 1
2538 << " score " << value_to_uci(pv_score)
2539 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2540 << speed_to_uci(pos.nodes_searched())
2541 << " pv " << l.str();
2547 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2549 MoveStack mlist[MOVES_MAX];
2553 bestMoveChanges = 0;
2555 // Generate all legal moves and add them to RootMoveList
2556 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2557 for (MoveStack* cur = mlist; cur != last; cur++)
2559 // If we have a searchMoves[] list then verify cur->move
2560 // is in the list before to add it.
2561 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2563 if (searchMoves[0] && *sm != cur->move)
2567 rm.pv[0] = cur->move;
2568 rm.pv[1] = MOVE_NONE;
2569 rm.pv_score = -VALUE_INFINITE;