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 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], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
207 Depth PassedPawnExtension[2], 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 // If the TT move is at least SingularExtensionMargin better then the
213 // remaining ones we will extend it.
214 const Value SingularExtensionMargin = Value(0x20);
216 // Step 12. Futility pruning
218 // Futility margin for quiescence search
219 const Value FutilityMarginQS = Value(0x80);
221 // Futility lookup tables (initialized at startup) and their getter functions
222 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
223 int FutilityMoveCountArray[32]; // [depth]
225 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
226 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
228 // Step 14. Reduced search
230 // Reduction lookup tables (initialized at startup) and their getter functions
231 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
233 template <NodeType PV>
234 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
236 // Common adjustments
238 // Search depth at iteration 1
239 const Depth InitialDepth = ONE_PLY;
241 // Easy move margin. An easy move candidate must be at least this much
242 // better than the second best move.
243 const Value EasyMoveMargin = Value(0x200);
246 /// Namespace variables
257 // Time managment variables
258 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
259 bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
260 bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
265 std::ofstream LogFile;
267 // Multi-threads manager object
268 ThreadsManager ThreadsMgr;
270 // Node counters, used only by thread[0] but try to keep in different cache
271 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
272 bool SendSearchedNodes;
274 int NodesBetweenPolls = 30000;
281 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
283 template <NodeType PvNode, bool SpNode, bool Root>
284 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
286 template <NodeType PvNode>
287 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
289 template <NodeType PvNode>
290 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
292 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
293 : search<PvNode, false, false>(pos, ss, alpha, beta, depth, ply);
296 template <NodeType PvNode>
297 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
299 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
300 bool connected_moves(const Position& pos, Move m1, Move m2);
301 bool value_is_mate(Value value);
302 Value value_to_tt(Value v, int ply);
303 Value value_from_tt(Value v, int ply);
304 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
305 bool connected_threat(const Position& pos, Move m, Move threat);
306 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
307 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
308 void update_killers(Move m, Move killers[]);
309 void update_gains(const Position& pos, Move move, Value before, Value after);
311 int current_search_time();
312 std::string value_to_uci(Value v);
313 int nps(const Position& pos);
314 void poll(const Position& pos);
315 void wait_for_stop_or_ponderhit();
317 #if !defined(_MSC_VER)
318 void* init_thread(void* threadID);
320 DWORD WINAPI init_thread(LPVOID threadID);
324 // MovePickerExt is an extended MovePicker used to choose at compile time
325 // the proper move source according to the type of node.
326 template<bool SpNode, bool Root> struct MovePickerExt;
328 // In Root nodes use RootMoveList Rml as source. Score and sort the root moves
329 // before to search them.
330 template<> struct MovePickerExt<false, true> : public MovePicker {
332 MovePickerExt(const Position& p, Move, Depth d, const History& h, SearchStack* ss, Value b)
333 : MovePicker(p, Rml[0].pv[0], d, h, ss, b), firstCall(true) {
335 Value score = VALUE_ZERO;
337 // Score root moves using the standard way used in main search, the moves
338 // are scored according to the order in which are returned by MovePicker.
339 // This is the second order score that is used to compare the moves when
340 // the first order pv scores of both moves are equal.
341 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
342 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
343 if (rm->pv[0] == move)
345 rm->non_pv_score = score--;
353 Move get_next_move() {
360 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
362 int number_of_evasions() const { return (int)Rml.size(); }
364 RootMoveList::iterator rm;
368 // In SpNodes use split point's shared MovePicker object as move source
369 template<> struct MovePickerExt<true, false> : public MovePicker {
371 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
372 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b),
375 Move get_next_move() { return mp->get_next_move(); }
377 RootMoveList::iterator rm; // Dummy, needed to compile
381 // Default case, create and use a MovePicker object as source
382 template<> struct MovePickerExt<false, false> : public MovePicker {
384 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
385 SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b) {}
387 RootMoveList::iterator rm; // Dummy, needed to compile
397 /// init_threads(), exit_threads() and nodes_searched() are helpers to
398 /// give accessibility to some TM methods from outside of current file.
400 void init_threads() { ThreadsMgr.init_threads(); }
401 void exit_threads() { ThreadsMgr.exit_threads(); }
404 /// init_search() is called during startup. It initializes various lookup tables
408 int d; // depth (ONE_PLY == 2)
409 int hd; // half depth (ONE_PLY == 1)
412 // Init reductions array
413 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
415 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
416 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
417 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
418 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
421 // Init futility margins array
422 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
423 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
425 // Init futility move count array
426 for (d = 0; d < 32; d++)
427 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
431 /// perft() is our utility to verify move generation is bug free. All the legal
432 /// moves up to given depth are generated and counted and the sum returned.
434 int64_t perft(Position& pos, Depth depth)
436 MoveStack mlist[MOVES_MAX];
441 // Generate all legal moves
442 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
444 // If we are at the last ply we don't need to do and undo
445 // the moves, just to count them.
446 if (depth <= ONE_PLY)
447 return int(last - mlist);
449 // Loop through all legal moves
451 for (MoveStack* cur = mlist; cur != last; cur++)
454 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
455 sum += perft(pos, depth - ONE_PLY);
462 /// think() is the external interface to Stockfish's search, and is called when
463 /// the program receives the UCI 'go' command. It initializes various
464 /// search-related global variables, and calls id_loop(). It returns false
465 /// when a quit command is received during the search.
467 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
468 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
470 // Initialize global search variables
471 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
473 SearchStartTime = get_system_time();
474 ExactMaxTime = maxTime;
477 InfiniteSearch = infinite;
479 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
481 // Look for a book move, only during games, not tests
482 if (UseTimeManagement && Options["OwnBook"].value<bool>())
484 if (Options["Book File"].value<std::string>() != OpeningBook.name())
485 OpeningBook.open(Options["Book File"].value<std::string>());
487 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
488 if (bookMove != MOVE_NONE)
491 wait_for_stop_or_ponderhit();
493 cout << "bestmove " << bookMove << endl;
498 // Read UCI option values
499 TT.set_size(Options["Hash"].value<int>());
500 if (Options["Clear Hash"].value<bool>())
502 Options["Clear Hash"].set_value("false");
506 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
507 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
508 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
509 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
510 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
511 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
512 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
513 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
514 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
515 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
516 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
517 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
518 MultiPV = Options["MultiPV"].value<int>();
519 UseLogFile = Options["Use Search Log"].value<bool>();
521 read_evaluation_uci_options(pos.side_to_move());
523 // Set the number of active threads
524 ThreadsMgr.read_uci_options();
525 init_eval(ThreadsMgr.active_threads());
527 // Wake up needed threads
528 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
529 ThreadsMgr.wake_sleeping_thread(i);
532 int myTime = time[pos.side_to_move()];
533 int myIncrement = increment[pos.side_to_move()];
534 if (UseTimeManagement)
535 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
537 // Set best NodesBetweenPolls interval to avoid lagging under
538 // heavy time pressure.
540 NodesBetweenPolls = Min(MaxNodes, 30000);
541 else if (myTime && myTime < 1000)
542 NodesBetweenPolls = 1000;
543 else if (myTime && myTime < 5000)
544 NodesBetweenPolls = 5000;
546 NodesBetweenPolls = 30000;
548 // Write search information to log file
551 std::string name = Options["Search Log Filename"].value<std::string>();
552 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
554 LogFile << "Searching: " << pos.to_fen()
555 << "\ninfinite: " << infinite
556 << " ponder: " << ponder
557 << " time: " << myTime
558 << " increment: " << myIncrement
559 << " moves to go: " << movesToGo << endl;
562 // We're ready to start thinking. Call the iterative deepening loop function
563 Move ponderMove = MOVE_NONE;
564 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
566 // Print final search statistics
567 cout << "info nodes " << pos.nodes_searched()
568 << " nps " << nps(pos)
569 << " time " << current_search_time() << endl;
573 LogFile << "\nNodes: " << pos.nodes_searched()
574 << "\nNodes/second: " << nps(pos)
575 << "\nBest move: " << move_to_san(pos, bestMove);
578 pos.do_move(bestMove, st);
579 LogFile << "\nPonder move: "
580 << move_to_san(pos, ponderMove) // Works also with MOVE_NONE
583 // Return from think() with unchanged position
584 pos.undo_move(bestMove);
589 // This makes all the threads to go to sleep
590 ThreadsMgr.set_active_threads(1);
592 // If we are pondering or in infinite search, we shouldn't print the
593 // best move before we are told to do so.
594 if (!StopRequest && (Pondering || InfiniteSearch))
595 wait_for_stop_or_ponderhit();
597 // Could be both MOVE_NONE when searching on a stalemate position
598 cout << "bestmove " << bestMove << " ponder " << ponderMove << endl;
606 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
607 // with increasing depth until the allocated thinking time has been consumed,
608 // user stops the search, or the maximum search depth is reached.
610 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
612 SearchStack ss[PLY_MAX_PLUS_2];
613 Value bestValues[PLY_MAX_PLUS_2];
614 int bestMoveChanges[PLY_MAX_PLUS_2];
615 int iteration, researchCountFL, researchCountFH, aspirationDelta;
616 Value value, alpha, beta;
618 Move bestMove, easyMove;
620 // Moves to search are verified, scored and sorted
621 Rml.init(pos, searchMoves);
623 // Initialize FIXME move before Rml.init()
626 memset(ss, 0, PLY_MAX_PLUS_2 * sizeof(SearchStack));
627 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
628 *ponderMove = bestMove = easyMove = MOVE_NONE;
631 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
633 // Handle special case of searching on a mate/stale position
636 cout << "info depth " << iteration << " score "
637 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
643 // Send initial scoring (iteration 1)
644 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
645 << "info depth " << iteration
646 << "\n" << Rml[0].pv_info_to_uci(pos, ONE_PLY, alpha, beta) << endl;
648 // Is one move significantly better than others after initial scoring ?
650 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin)
651 easyMove = Rml[0].pv[0];
653 // Iterative deepening loop
654 while (++iteration <= PLY_MAX && (!MaxDepth || iteration <= MaxDepth) && !StopRequest)
656 cout << "info depth " << iteration << endl;
658 Rml.bestMoveChanges = researchCountFL = researchCountFH = 0;
659 depth = (iteration - 2) * ONE_PLY + InitialDepth;
661 // Calculate dynamic aspiration window based on previous iterations
662 if (MultiPV == 1 && iteration >= 6 && abs(bestValues[iteration - 1]) < VALUE_KNOWN_WIN)
664 int prevDelta1 = bestValues[iteration - 1] - bestValues[iteration - 2];
665 int prevDelta2 = bestValues[iteration - 2] - bestValues[iteration - 3];
667 aspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
668 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
670 alpha = Max(bestValues[iteration - 1] - aspirationDelta, -VALUE_INFINITE);
671 beta = Min(bestValues[iteration - 1] + aspirationDelta, VALUE_INFINITE);
674 // Start with a small aspiration window and, in case of fail high/low,
675 // research with bigger window until not failing high/low anymore.
678 // Search starting from ss+1 to allow calling update_gains()
679 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth, 0);
681 // Write PV lines to transposition table, in case the relevant entries
682 // have been overwritten during the search.
683 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
684 Rml[i].insert_pv_in_tt(pos);
686 // Value cannot be trusted. Break out immediately!
690 assert(value >= alpha);
692 // In case of failing high/low increase aspiration window and research,
693 // otherwise exit the fail high/low loop.
696 beta = Min(beta + aspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
699 else if (value <= alpha)
701 AspirationFailLow = true;
702 StopOnPonderhit = false;
704 alpha = Max(alpha - aspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
711 // Collect info about search result
712 bestMove = Rml[0].pv[0];
713 bestValues[iteration] = value;
714 bestMoveChanges[iteration] = Rml.bestMoveChanges;
716 // Drop the easy move if differs from the new best move
717 if (bestMove != easyMove)
718 easyMove = MOVE_NONE;
720 if (UseTimeManagement && !StopRequest)
723 bool noMoreTime = false;
725 // Stop search early when the last two iterations returned a mate score
727 && abs(bestValues[iteration]) >= abs(VALUE_MATE) - 100
728 && abs(bestValues[iteration-1]) >= abs(VALUE_MATE) - 100)
731 // Stop search early if one move seems to be much better than the
732 // others or if there is only a single legal move. In this latter
733 // case we search up to Iteration 8 anyway to get a proper score.
735 && easyMove == bestMove
737 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
738 && current_search_time() > TimeMgr.available_time() / 16)
739 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
740 && current_search_time() > TimeMgr.available_time() / 32)))
743 // Add some extra time if the best move has changed during the last two iterations
744 if (iteration > 5 && iteration <= 50)
745 TimeMgr.pv_instability(bestMoveChanges[iteration], bestMoveChanges[iteration-1]);
747 // Stop search if most of MaxSearchTime is consumed at the end of the
748 // iteration. We probably don't have enough time to search the first
749 // move at the next iteration anyway.
750 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
756 StopOnPonderhit = true;
763 *ponderMove = Rml[0].pv[1];
768 // search<>() is the main search function for both PV and non-PV nodes and for
769 // normal and SplitPoint nodes. When called just after a split point the search
770 // is simpler because we have already probed the hash table, done a null move
771 // search, and searched the first move before splitting, we don't have to repeat
772 // all this work again. We also don't need to store anything to the hash table
773 // here: This is taken care of after we return from the split point.
775 template <NodeType PvNode, bool SpNode, bool Root>
776 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
778 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
779 assert(beta > alpha && beta <= VALUE_INFINITE);
780 assert(PvNode || alpha == beta - 1);
781 assert((Root || ply > 0) && ply < PLY_MAX);
782 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
784 Move movesSearched[MOVES_MAX];
789 Move ttMove, move, excludedMove, threatMove;
792 Value bestValue, value, oldAlpha;
793 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
794 bool isPvMove, isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
795 bool mateThreat = false;
797 int threadID = pos.thread();
798 SplitPoint* sp = NULL;
800 refinedValue = bestValue = value = -VALUE_INFINITE;
802 isCheck = pos.is_check();
808 ttMove = excludedMove = MOVE_NONE;
809 threatMove = sp->threatMove;
810 mateThreat = sp->mateThreat;
811 goto split_point_start;
816 // Step 1. Initialize node and poll. Polling can abort search
817 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
818 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
820 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
826 // Step 2. Check for aborted search and immediate draw
828 || ThreadsMgr.cutoff_at_splitpoint(threadID)
830 || ply >= PLY_MAX - 1) && !Root)
833 // Step 3. Mate distance pruning
834 alpha = Max(value_mated_in(ply), alpha);
835 beta = Min(value_mate_in(ply+1), beta);
839 // Step 4. Transposition table lookup
840 // We don't want the score of a partial search to overwrite a previous full search
841 // TT value, so we use a different position key in case of an excluded move exists.
842 excludedMove = ss->excludedMove;
843 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
845 tte = TT.retrieve(posKey);
846 ttMove = tte ? tte->move() : MOVE_NONE;
848 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
849 // This is to avoid problems in the following areas:
851 // * Repetition draw detection
852 // * Fifty move rule detection
853 // * Searching for a mate
854 // * Printing of full PV line
855 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
858 ss->bestMove = ttMove; // Can be MOVE_NONE
859 return value_from_tt(tte->value(), ply);
862 // Step 5. Evaluate the position statically and
863 // update gain statistics of parent move.
865 ss->eval = ss->evalMargin = VALUE_NONE;
868 assert(tte->static_value() != VALUE_NONE);
870 ss->eval = tte->static_value();
871 ss->evalMargin = tte->static_value_margin();
872 refinedValue = refine_eval(tte, ss->eval, ply);
876 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
877 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
880 // Save gain for the parent non-capture move
881 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
883 // Step 6. Razoring (is omitted in PV nodes)
885 && depth < RazorDepth
887 && refinedValue < beta - razor_margin(depth)
888 && ttMove == MOVE_NONE
889 && !value_is_mate(beta)
890 && !pos.has_pawn_on_7th(pos.side_to_move()))
892 Value rbeta = beta - razor_margin(depth);
893 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
895 // Logically we should return (v + razor_margin(depth)), but
896 // surprisingly this did slightly weaker in tests.
900 // Step 7. Static null move pruning (is omitted in PV nodes)
901 // We're betting that the opponent doesn't have a move that will reduce
902 // the score by more than futility_margin(depth) if we do a null move.
905 && depth < RazorDepth
907 && refinedValue >= beta + futility_margin(depth, 0)
908 && !value_is_mate(beta)
909 && pos.non_pawn_material(pos.side_to_move()))
910 return refinedValue - futility_margin(depth, 0);
912 // Step 8. Null move search with verification search (is omitted in PV nodes)
917 && refinedValue >= beta
918 && !value_is_mate(beta)
919 && pos.non_pawn_material(pos.side_to_move()))
921 ss->currentMove = MOVE_NULL;
923 // Null move dynamic reduction based on depth
924 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
926 // Null move dynamic reduction based on value
927 if (refinedValue - beta > PawnValueMidgame)
930 pos.do_null_move(st);
931 (ss+1)->skipNullMove = true;
932 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
933 (ss+1)->skipNullMove = false;
934 pos.undo_null_move();
936 if (nullValue >= beta)
938 // Do not return unproven mate scores
939 if (nullValue >= value_mate_in(PLY_MAX))
942 if (depth < 6 * ONE_PLY)
945 // Do verification search at high depths
946 ss->skipNullMove = true;
947 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
948 ss->skipNullMove = false;
955 // The null move failed low, which means that we may be faced with
956 // some kind of threat. If the previous move was reduced, check if
957 // the move that refuted the null move was somehow connected to the
958 // move which was reduced. If a connection is found, return a fail
959 // low score (which will cause the reduced move to fail high in the
960 // parent node, which will trigger a re-search with full depth).
961 if (nullValue == value_mated_in(ply + 2))
964 threatMove = (ss+1)->bestMove;
965 if ( depth < ThreatDepth
967 && threatMove != MOVE_NONE
968 && connected_moves(pos, (ss-1)->currentMove, threatMove))
973 // Step 9. Internal iterative deepening
974 if ( depth >= IIDDepth[PvNode]
975 && ttMove == MOVE_NONE
976 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
978 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
980 ss->skipNullMove = true;
981 search<PvNode>(pos, ss, alpha, beta, d, ply);
982 ss->skipNullMove = false;
984 ttMove = ss->bestMove;
985 tte = TT.retrieve(posKey);
988 // Expensive mate threat detection (only for PV nodes)
990 mateThreat = pos.has_mate_threat();
992 split_point_start: // At split points actual search starts from here
994 // Initialize a MovePicker object for the current position
995 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
997 ss->bestMove = MOVE_NONE;
998 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
999 futilityBase = ss->eval + ss->evalMargin;
1000 singularExtensionNode = !Root
1002 && depth >= SingularExtensionDepth[PvNode]
1005 && !excludedMove // Do not allow recursive singular extension search
1006 && (tte->type() & VALUE_TYPE_LOWER)
1007 && tte->depth() >= depth - 3 * ONE_PLY;
1010 lock_grab(&(sp->lock));
1011 bestValue = sp->bestValue;
1014 // Step 10. Loop through moves
1015 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1016 while ( bestValue < beta
1017 && (move = mp.get_next_move()) != MOVE_NONE
1018 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1020 assert(move_is_ok(move));
1024 moveCount = ++sp->moveCount;
1025 lock_release(&(sp->lock));
1027 else if (move == excludedMove)
1030 movesSearched[moveCount++] = move;
1034 // This is used by time management
1035 FirstRootMove = (moveCount == 1);
1037 // Save the current node count before the move is searched
1038 nodes = pos.nodes_searched();
1040 // If it's time to send nodes info, do it here where we have the
1041 // correct accumulated node counts searched by each thread.
1042 if (SendSearchedNodes)
1044 SendSearchedNodes = false;
1045 cout << "info nodes " << nodes
1046 << " nps " << nps(pos)
1047 << " time " << current_search_time() << endl;
1050 if (current_search_time() >= 1000)
1051 cout << "info currmove " << move
1052 << " currmovenumber " << moveCount << endl;
1055 isPvMove = (PvNode && moveCount <= (Root ? MultiPV : 1));
1056 moveIsCheck = pos.move_is_check(move, ci);
1057 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1059 // Step 11. Decide the new search depth
1060 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1062 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1063 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1064 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1065 // lower then ttValue minus a margin then we extend ttMove.
1066 if ( singularExtensionNode
1067 && move == tte->move()
1070 Value ttValue = value_from_tt(tte->value(), ply);
1072 if (abs(ttValue) < VALUE_KNOWN_WIN)
1074 Value b = ttValue - SingularExtensionMargin;
1075 ss->excludedMove = move;
1076 ss->skipNullMove = true;
1077 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1078 ss->skipNullMove = false;
1079 ss->excludedMove = MOVE_NONE;
1080 ss->bestMove = MOVE_NONE;
1086 // Update current move (this must be done after singular extension search)
1087 ss->currentMove = move;
1088 newDepth = depth - (!Root ? ONE_PLY : DEPTH_ZERO) + ext;
1090 // Step 12. Futility pruning (is omitted in PV nodes)
1092 && !captureOrPromotion
1096 && !move_is_castle(move))
1098 // Move count based pruning
1099 if ( moveCount >= futility_move_count(depth)
1100 && !(threatMove && connected_threat(pos, move, threatMove))
1101 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1104 lock_grab(&(sp->lock));
1109 // Value based pruning
1110 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1111 // but fixing this made program slightly weaker.
1112 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1113 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1114 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1116 if (futilityValueScaled < beta)
1120 lock_grab(&(sp->lock));
1121 if (futilityValueScaled > sp->bestValue)
1122 sp->bestValue = bestValue = futilityValueScaled;
1124 else if (futilityValueScaled > bestValue)
1125 bestValue = futilityValueScaled;
1130 // Prune moves with negative SEE at low depths
1131 if ( predictedDepth < 2 * ONE_PLY
1132 && bestValue > value_mated_in(PLY_MAX)
1133 && pos.see_sign(move) < 0)
1136 lock_grab(&(sp->lock));
1142 // Step 13. Make the move
1143 pos.do_move(move, st, ci, moveIsCheck);
1145 // Step extra. pv search (only in PV nodes)
1146 // The first move in list is the expected PV
1149 // Aspiration window is disabled in multi-pv case
1150 if (Root && MultiPV > 1)
1151 alpha = -VALUE_INFINITE;
1153 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1157 // Step 14. Reduced depth search
1158 // If the move fails high will be re-searched at full depth.
1159 bool doFullDepthSearch = true;
1161 if ( depth >= 3 * ONE_PLY
1162 && !captureOrPromotion
1164 && !move_is_castle(move)
1165 && ss->killers[0] != move
1166 && ss->killers[1] != move)
1168 ss->reduction = Root ? reduction<PvNode>(depth, moveCount - MultiPV + 1)
1169 : reduction<PvNode>(depth, moveCount);
1172 alpha = SpNode ? sp->alpha : alpha;
1173 Depth d = newDepth - ss->reduction;
1174 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1176 doFullDepthSearch = (value > alpha);
1178 ss->reduction = DEPTH_ZERO; // Restore original reduction
1181 // Step 15. Full depth search
1182 if (doFullDepthSearch)
1184 alpha = SpNode ? sp->alpha : alpha;
1185 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1187 // Step extra. pv search (only in PV nodes)
1188 // Search only for possible new PV nodes, if instead value >= beta then
1189 // parent node fails low with value <= alpha and tries another move.
1190 if (PvNode && value > alpha && (Root || value < beta))
1191 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1195 // Step 16. Undo move
1196 pos.undo_move(move);
1198 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1200 // Step 17. Check for new best move
1203 lock_grab(&(sp->lock));
1204 bestValue = sp->bestValue;
1208 if (!Root && value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1213 sp->bestValue = value;
1217 if (PvNode && value < beta) // We want always alpha < beta
1225 sp->betaCutoff = true;
1227 if (value == value_mate_in(ply + 1))
1228 ss->mateKiller = move;
1230 ss->bestMove = move;
1233 sp->parentSstack->bestMove = move;
1239 // To avoid to exit with bestValue == -VALUE_INFINITE
1240 if (value > bestValue)
1243 // Finished searching the move. If StopRequest is true, the search
1244 // was aborted because the user interrupted the search or because we
1245 // ran out of time. In this case, the return value of the search cannot
1246 // be trusted, and we break out of the loop without updating the best
1251 // Remember searched nodes counts for this move
1252 mp.rm->nodes += pos.nodes_searched() - nodes;
1254 // Step 17. Check for new best move
1255 if (!isPvMove && value <= alpha)
1256 mp.rm->pv_score = -VALUE_INFINITE;
1259 // PV move or new best move!
1262 ss->bestMove = move;
1263 mp.rm->pv_score = value;
1264 mp.rm->extract_pv_from_tt(pos);
1266 // We record how often the best move has been changed in each
1267 // iteration. This information is used for time managment: When
1268 // the best move changes frequently, we allocate some more time.
1269 if (!isPvMove && MultiPV == 1)
1270 Rml.bestMoveChanges++;
1272 // Inform GUI that PV has changed, in case of multi-pv UCI protocol
1273 // requires we send all the PV lines properly sorted.
1274 Rml.sort_multipv(moveCount);
1276 for (int j = 0; j < Min(MultiPV, (int)Rml.size()); j++)
1277 cout << Rml[j].pv_info_to_uci(pos, depth, alpha, beta, j) << endl;
1279 // Update alpha. In multi-pv we don't use aspiration window, so
1280 // set alpha equal to minimum score among the PV lines.
1282 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1283 else if (value > alpha)
1286 } // PV move or new best move
1289 // Step 18. Check for split
1292 && depth >= ThreadsMgr.min_split_depth()
1293 && ThreadsMgr.active_threads() > 1
1295 && ThreadsMgr.available_thread_exists(threadID)
1297 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1298 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1299 threatMove, mateThreat, moveCount, &mp, PvNode);
1302 // Step 19. Check for mate and stalemate
1303 // All legal moves have been searched and if there are
1304 // no legal moves, it must be mate or stalemate.
1305 // If one move was excluded return fail low score.
1306 if (!SpNode && !moveCount)
1307 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1309 // Step 20. Update tables
1310 // If the search is not aborted, update the transposition table,
1311 // history counters, and killer moves.
1312 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1314 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1315 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1316 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1318 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1320 // Update killers and history only for non capture moves that fails high
1321 if ( bestValue >= beta
1322 && !pos.move_is_capture_or_promotion(move))
1324 update_history(pos, move, depth, movesSearched, moveCount);
1325 update_killers(move, ss->killers);
1331 // Here we have the lock still grabbed
1332 sp->slaves[threadID] = 0;
1333 sp->nodes += pos.nodes_searched();
1334 lock_release(&(sp->lock));
1337 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1342 // qsearch() is the quiescence search function, which is called by the main
1343 // search function when the remaining depth is zero (or, to be more precise,
1344 // less than ONE_PLY).
1346 template <NodeType PvNode>
1347 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1349 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1350 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1351 assert(PvNode || alpha == beta - 1);
1353 assert(ply > 0 && ply < PLY_MAX);
1354 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1358 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1359 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1362 Value oldAlpha = alpha;
1364 ss->bestMove = ss->currentMove = MOVE_NONE;
1366 // Check for an instant draw or maximum ply reached
1367 if (pos.is_draw() || ply >= PLY_MAX - 1)
1370 // Decide whether or not to include checks, this fixes also the type of
1371 // TT entry depth that we are going to use. Note that in qsearch we use
1372 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1373 isCheck = pos.is_check();
1374 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1376 // Transposition table lookup. At PV nodes, we don't use the TT for
1377 // pruning, but only for move ordering.
1378 tte = TT.retrieve(pos.get_key());
1379 ttMove = (tte ? tte->move() : MOVE_NONE);
1381 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1383 ss->bestMove = ttMove; // Can be MOVE_NONE
1384 return value_from_tt(tte->value(), ply);
1387 // Evaluate the position statically
1390 bestValue = futilityBase = -VALUE_INFINITE;
1391 ss->eval = evalMargin = VALUE_NONE;
1392 enoughMaterial = false;
1398 assert(tte->static_value() != VALUE_NONE);
1400 evalMargin = tte->static_value_margin();
1401 ss->eval = bestValue = tte->static_value();
1404 ss->eval = bestValue = evaluate(pos, evalMargin);
1406 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1408 // Stand pat. Return immediately if static value is at least beta
1409 if (bestValue >= beta)
1412 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1417 if (PvNode && bestValue > alpha)
1420 // Futility pruning parameters, not needed when in check
1421 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1422 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1425 // Initialize a MovePicker object for the current position, and prepare
1426 // to search the moves. Because the depth is <= 0 here, only captures,
1427 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1429 MovePicker mp(pos, ttMove, depth, H);
1432 // Loop through the moves until no moves remain or a beta cutoff occurs
1433 while ( alpha < beta
1434 && (move = mp.get_next_move()) != MOVE_NONE)
1436 assert(move_is_ok(move));
1438 moveIsCheck = pos.move_is_check(move, ci);
1446 && !move_is_promotion(move)
1447 && !pos.move_is_passed_pawn_push(move))
1449 futilityValue = futilityBase
1450 + pos.endgame_value_of_piece_on(move_to(move))
1451 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1453 if (futilityValue < alpha)
1455 if (futilityValue > bestValue)
1456 bestValue = futilityValue;
1461 // Detect non-capture evasions that are candidate to be pruned
1462 evasionPrunable = isCheck
1463 && bestValue > value_mated_in(PLY_MAX)
1464 && !pos.move_is_capture(move)
1465 && !pos.can_castle(pos.side_to_move());
1467 // Don't search moves with negative SEE values
1469 && (!isCheck || evasionPrunable)
1471 && !move_is_promotion(move)
1472 && pos.see_sign(move) < 0)
1475 // Don't search useless checks
1480 && !pos.move_is_capture_or_promotion(move)
1481 && ss->eval + PawnValueMidgame / 4 < beta
1482 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1484 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1485 bestValue = ss->eval + PawnValueMidgame / 4;
1490 // Update current move
1491 ss->currentMove = move;
1493 // Make and search the move
1494 pos.do_move(move, st, ci, moveIsCheck);
1495 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1496 pos.undo_move(move);
1498 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1501 if (value > bestValue)
1507 ss->bestMove = move;
1512 // All legal moves have been searched. A special case: If we're in check
1513 // and no legal moves were found, it is checkmate.
1514 if (isCheck && bestValue == -VALUE_INFINITE)
1515 return value_mated_in(ply);
1517 // Update transposition table
1518 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1519 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1521 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1527 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1528 // bestValue is updated only when returning false because in that case move
1531 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1533 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1534 Square from, to, ksq, victimSq;
1537 Value futilityValue, bv = *bestValue;
1539 from = move_from(move);
1541 them = opposite_color(pos.side_to_move());
1542 ksq = pos.king_square(them);
1543 kingAtt = pos.attacks_from<KING>(ksq);
1544 pc = pos.piece_on(from);
1546 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1547 oldAtt = pos.attacks_from(pc, from, occ);
1548 newAtt = pos.attacks_from(pc, to, occ);
1550 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1551 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1553 if (!(b && (b & (b - 1))))
1556 // Rule 2. Queen contact check is very dangerous
1557 if ( type_of_piece(pc) == QUEEN
1558 && bit_is_set(kingAtt, to))
1561 // Rule 3. Creating new double threats with checks
1562 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1566 victimSq = pop_1st_bit(&b);
1567 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1569 // Note that here we generate illegal "double move"!
1570 if ( futilityValue >= beta
1571 && pos.see_sign(make_move(from, victimSq)) >= 0)
1574 if (futilityValue > bv)
1578 // Update bestValue only if check is not dangerous (because we will prune the move)
1584 // connected_moves() tests whether two moves are 'connected' in the sense
1585 // that the first move somehow made the second move possible (for instance
1586 // if the moving piece is the same in both moves). The first move is assumed
1587 // to be the move that was made to reach the current position, while the
1588 // second move is assumed to be a move from the current position.
1590 bool connected_moves(const Position& pos, Move m1, Move m2) {
1592 Square f1, t1, f2, t2;
1595 assert(m1 && move_is_ok(m1));
1596 assert(m2 && move_is_ok(m2));
1598 // Case 1: The moving piece is the same in both moves
1604 // Case 2: The destination square for m2 was vacated by m1
1610 // Case 3: Moving through the vacated square
1611 if ( piece_is_slider(pos.piece_on(f2))
1612 && bit_is_set(squares_between(f2, t2), f1))
1615 // Case 4: The destination square for m2 is defended by the moving piece in m1
1616 p = pos.piece_on(t1);
1617 if (bit_is_set(pos.attacks_from(p, t1), t2))
1620 // Case 5: Discovered check, checking piece is the piece moved in m1
1621 if ( piece_is_slider(p)
1622 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1623 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1625 // discovered_check_candidates() works also if the Position's side to
1626 // move is the opposite of the checking piece.
1627 Color them = opposite_color(pos.side_to_move());
1628 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1630 if (bit_is_set(dcCandidates, f2))
1637 // value_is_mate() checks if the given value is a mate one eventually
1638 // compensated for the ply.
1640 bool value_is_mate(Value value) {
1642 assert(abs(value) <= VALUE_INFINITE);
1644 return value <= value_mated_in(PLY_MAX)
1645 || value >= value_mate_in(PLY_MAX);
1649 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1650 // "plies to mate from the current ply". Non-mate scores are unchanged.
1651 // The function is called before storing a value to the transposition table.
1653 Value value_to_tt(Value v, int ply) {
1655 if (v >= value_mate_in(PLY_MAX))
1658 if (v <= value_mated_in(PLY_MAX))
1665 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1666 // the transposition table to a mate score corrected for the current ply.
1668 Value value_from_tt(Value v, int ply) {
1670 if (v >= value_mate_in(PLY_MAX))
1673 if (v <= value_mated_in(PLY_MAX))
1680 // extension() decides whether a move should be searched with normal depth,
1681 // or with extended depth. Certain classes of moves (checking moves, in
1682 // particular) are searched with bigger depth than ordinary moves and in
1683 // any case are marked as 'dangerous'. Note that also if a move is not
1684 // extended, as example because the corresponding UCI option is set to zero,
1685 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1686 template <NodeType PvNode>
1687 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1688 bool singleEvasion, bool mateThreat, bool* dangerous) {
1690 assert(m != MOVE_NONE);
1692 Depth result = DEPTH_ZERO;
1693 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1697 if (moveIsCheck && pos.see_sign(m) >= 0)
1698 result += CheckExtension[PvNode];
1701 result += SingleEvasionExtension[PvNode];
1704 result += MateThreatExtension[PvNode];
1707 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1709 Color c = pos.side_to_move();
1710 if (relative_rank(c, move_to(m)) == RANK_7)
1712 result += PawnPushTo7thExtension[PvNode];
1715 if (pos.pawn_is_passed(c, move_to(m)))
1717 result += PassedPawnExtension[PvNode];
1722 if ( captureOrPromotion
1723 && pos.type_of_piece_on(move_to(m)) != PAWN
1724 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1725 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1726 && !move_is_promotion(m)
1729 result += PawnEndgameExtension[PvNode];
1734 && captureOrPromotion
1735 && pos.type_of_piece_on(move_to(m)) != PAWN
1736 && pos.see_sign(m) >= 0)
1738 result += ONE_PLY / 2;
1742 return Min(result, ONE_PLY);
1746 // connected_threat() tests whether it is safe to forward prune a move or if
1747 // is somehow coonected to the threat move returned by null search.
1749 bool connected_threat(const Position& pos, Move m, Move threat) {
1751 assert(move_is_ok(m));
1752 assert(threat && move_is_ok(threat));
1753 assert(!pos.move_is_check(m));
1754 assert(!pos.move_is_capture_or_promotion(m));
1755 assert(!pos.move_is_passed_pawn_push(m));
1757 Square mfrom, mto, tfrom, tto;
1759 mfrom = move_from(m);
1761 tfrom = move_from(threat);
1762 tto = move_to(threat);
1764 // Case 1: Don't prune moves which move the threatened piece
1768 // Case 2: If the threatened piece has value less than or equal to the
1769 // value of the threatening piece, don't prune move which defend it.
1770 if ( pos.move_is_capture(threat)
1771 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1772 || pos.type_of_piece_on(tfrom) == KING)
1773 && pos.move_attacks_square(m, tto))
1776 // Case 3: If the moving piece in the threatened move is a slider, don't
1777 // prune safe moves which block its ray.
1778 if ( piece_is_slider(pos.piece_on(tfrom))
1779 && bit_is_set(squares_between(tfrom, tto), mto)
1780 && pos.see_sign(m) >= 0)
1787 // ok_to_use_TT() returns true if a transposition table score
1788 // can be used at a given point in search.
1790 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1792 Value v = value_from_tt(tte->value(), ply);
1794 return ( tte->depth() >= depth
1795 || v >= Max(value_mate_in(PLY_MAX), beta)
1796 || v < Min(value_mated_in(PLY_MAX), beta))
1798 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1799 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1803 // refine_eval() returns the transposition table score if
1804 // possible otherwise falls back on static position evaluation.
1806 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1810 Value v = value_from_tt(tte->value(), ply);
1812 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1813 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1820 // update_history() registers a good move that produced a beta-cutoff
1821 // in history and marks as failures all the other moves of that ply.
1823 void update_history(const Position& pos, Move move, Depth depth,
1824 Move movesSearched[], int moveCount) {
1826 Value bonus = Value(int(depth) * int(depth));
1828 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1830 for (int i = 0; i < moveCount - 1; i++)
1832 m = movesSearched[i];
1836 if (!pos.move_is_capture_or_promotion(m))
1837 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1842 // update_killers() add a good move that produced a beta-cutoff
1843 // among the killer moves of that ply.
1845 void update_killers(Move m, Move killers[]) {
1847 if (m == killers[0])
1850 killers[1] = killers[0];
1855 // update_gains() updates the gains table of a non-capture move given
1856 // the static position evaluation before and after the move.
1858 void update_gains(const Position& pos, Move m, Value before, Value after) {
1861 && before != VALUE_NONE
1862 && after != VALUE_NONE
1863 && pos.captured_piece_type() == PIECE_TYPE_NONE
1864 && !move_is_special(m))
1865 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1869 // value_to_uci() converts a value to a string suitable for use with the UCI
1870 // protocol specifications:
1872 // cp <x> The score from the engine's point of view in centipawns.
1873 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1874 // use negative values for y.
1876 std::string value_to_uci(Value v) {
1878 std::stringstream s;
1880 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1881 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1883 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1889 // current_search_time() returns the number of milliseconds which have passed
1890 // since the beginning of the current search.
1892 int current_search_time() {
1894 return get_system_time() - SearchStartTime;
1898 // nps() computes the current nodes/second count
1900 int nps(const Position& pos) {
1902 int t = current_search_time();
1903 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1907 // poll() performs two different functions: It polls for user input, and it
1908 // looks at the time consumed so far and decides if it's time to abort the
1911 void poll(const Position& pos) {
1913 static int lastInfoTime;
1914 int t = current_search_time();
1917 if (input_available())
1919 // We are line oriented, don't read single chars
1920 std::string command;
1922 if (!std::getline(std::cin, command))
1925 if (command == "quit")
1927 // Quit the program as soon as possible
1929 QuitRequest = StopRequest = true;
1932 else if (command == "stop")
1934 // Stop calculating as soon as possible, but still send the "bestmove"
1935 // and possibly the "ponder" token when finishing the search.
1939 else if (command == "ponderhit")
1941 // The opponent has played the expected move. GUI sends "ponderhit" if
1942 // we were told to ponder on the same move the opponent has played. We
1943 // should continue searching but switching from pondering to normal search.
1946 if (StopOnPonderhit)
1951 // Print search information
1955 else if (lastInfoTime > t)
1956 // HACK: Must be a new search where we searched less than
1957 // NodesBetweenPolls nodes during the first second of search.
1960 else if (t - lastInfoTime >= 1000)
1967 if (dbg_show_hit_rate)
1968 dbg_print_hit_rate();
1970 // Send info on searched nodes as soon as we return to root
1971 SendSearchedNodes = true;
1974 // Should we stop the search?
1978 bool stillAtFirstMove = FirstRootMove
1979 && !AspirationFailLow
1980 && t > TimeMgr.available_time();
1982 bool noMoreTime = t > TimeMgr.maximum_time()
1983 || stillAtFirstMove;
1985 if ( (UseTimeManagement && noMoreTime)
1986 || (ExactMaxTime && t >= ExactMaxTime)
1987 || (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
1992 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1993 // while the program is pondering. The point is to work around a wrinkle in
1994 // the UCI protocol: When pondering, the engine is not allowed to give a
1995 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1996 // We simply wait here until one of these commands is sent, and return,
1997 // after which the bestmove and pondermove will be printed.
1999 void wait_for_stop_or_ponderhit() {
2001 std::string command;
2005 // Wait for a command from stdin
2006 if (!std::getline(std::cin, command))
2009 if (command == "quit")
2014 else if (command == "ponderhit" || command == "stop")
2020 // init_thread() is the function which is called when a new thread is
2021 // launched. It simply calls the idle_loop() function with the supplied
2022 // threadID. There are two versions of this function; one for POSIX
2023 // threads and one for Windows threads.
2025 #if !defined(_MSC_VER)
2027 void* init_thread(void* threadID) {
2029 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2035 DWORD WINAPI init_thread(LPVOID threadID) {
2037 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2044 /// The ThreadsManager class
2047 // read_uci_options() updates number of active threads and other internal
2048 // parameters according to the UCI options values. It is called before
2049 // to start a new search.
2051 void ThreadsManager::read_uci_options() {
2053 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2054 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2055 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2056 activeThreads = Options["Threads"].value<int>();
2060 // idle_loop() is where the threads are parked when they have no work to do.
2061 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2062 // object for which the current thread is the master.
2064 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2066 assert(threadID >= 0 && threadID < MAX_THREADS);
2069 bool allFinished = false;
2073 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2074 // master should exit as last one.
2075 if (allThreadsShouldExit)
2078 threads[threadID].state = THREAD_TERMINATED;
2082 // If we are not thinking, wait for a condition to be signaled
2083 // instead of wasting CPU time polling for work.
2084 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2085 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2087 assert(!sp || useSleepingThreads);
2088 assert(threadID != 0 || useSleepingThreads);
2090 if (threads[threadID].state == THREAD_INITIALIZING)
2091 threads[threadID].state = THREAD_AVAILABLE;
2093 // Grab the lock to avoid races with wake_sleeping_thread()
2094 lock_grab(&sleepLock[threadID]);
2096 // If we are master and all slaves have finished do not go to sleep
2097 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2098 allFinished = (i == activeThreads);
2100 if (allFinished || allThreadsShouldExit)
2102 lock_release(&sleepLock[threadID]);
2106 // Do sleep here after retesting sleep conditions
2107 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2108 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2110 lock_release(&sleepLock[threadID]);
2113 // If this thread has been assigned work, launch a search
2114 if (threads[threadID].state == THREAD_WORKISWAITING)
2116 assert(!allThreadsShouldExit);
2118 threads[threadID].state = THREAD_SEARCHING;
2120 // Here we call search() with SplitPoint template parameter set to true
2121 SplitPoint* tsp = threads[threadID].splitPoint;
2122 Position pos(*tsp->pos, threadID);
2123 SearchStack* ss = tsp->sstack[threadID] + 1;
2127 search<PV, true, false>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2129 search<NonPV, true, false>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2131 assert(threads[threadID].state == THREAD_SEARCHING);
2133 threads[threadID].state = THREAD_AVAILABLE;
2135 // Wake up master thread so to allow it to return from the idle loop in
2136 // case we are the last slave of the split point.
2137 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2138 wake_sleeping_thread(tsp->master);
2141 // If this thread is the master of a split point and all slaves have
2142 // finished their work at this split point, return from the idle loop.
2143 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2144 allFinished = (i == activeThreads);
2148 // Because sp->slaves[] is reset under lock protection,
2149 // be sure sp->lock has been released before to return.
2150 lock_grab(&(sp->lock));
2151 lock_release(&(sp->lock));
2153 // In helpful master concept a master can help only a sub-tree, and
2154 // because here is all finished is not possible master is booked.
2155 assert(threads[threadID].state == THREAD_AVAILABLE);
2157 threads[threadID].state = THREAD_SEARCHING;
2164 // init_threads() is called during startup. It launches all helper threads,
2165 // and initializes the split point stack and the global locks and condition
2168 void ThreadsManager::init_threads() {
2170 int i, arg[MAX_THREADS];
2173 // Initialize global locks
2176 for (i = 0; i < MAX_THREADS; i++)
2178 lock_init(&sleepLock[i]);
2179 cond_init(&sleepCond[i]);
2182 // Initialize splitPoints[] locks
2183 for (i = 0; i < MAX_THREADS; i++)
2184 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2185 lock_init(&(threads[i].splitPoints[j].lock));
2187 // Will be set just before program exits to properly end the threads
2188 allThreadsShouldExit = false;
2190 // Threads will be put all threads to sleep as soon as created
2193 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2194 threads[0].state = THREAD_SEARCHING;
2195 for (i = 1; i < MAX_THREADS; i++)
2196 threads[i].state = THREAD_INITIALIZING;
2198 // Launch the helper threads
2199 for (i = 1; i < MAX_THREADS; i++)
2203 #if !defined(_MSC_VER)
2204 pthread_t pthread[1];
2205 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2206 pthread_detach(pthread[0]);
2208 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2212 cout << "Failed to create thread number " << i << endl;
2216 // Wait until the thread has finished launching and is gone to sleep
2217 while (threads[i].state == THREAD_INITIALIZING) {}
2222 // exit_threads() is called when the program exits. It makes all the
2223 // helper threads exit cleanly.
2225 void ThreadsManager::exit_threads() {
2227 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2229 // Wake up all the threads and waits for termination
2230 for (int i = 1; i < MAX_THREADS; i++)
2232 wake_sleeping_thread(i);
2233 while (threads[i].state != THREAD_TERMINATED) {}
2236 // Now we can safely destroy the locks
2237 for (int i = 0; i < MAX_THREADS; i++)
2238 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2239 lock_destroy(&(threads[i].splitPoints[j].lock));
2241 lock_destroy(&mpLock);
2243 // Now we can safely destroy the wait conditions
2244 for (int i = 0; i < MAX_THREADS; i++)
2246 lock_destroy(&sleepLock[i]);
2247 cond_destroy(&sleepCond[i]);
2252 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2253 // the thread's currently active split point, or in some ancestor of
2254 // the current split point.
2256 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2258 assert(threadID >= 0 && threadID < activeThreads);
2260 SplitPoint* sp = threads[threadID].splitPoint;
2262 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2267 // thread_is_available() checks whether the thread with threadID "slave" is
2268 // available to help the thread with threadID "master" at a split point. An
2269 // obvious requirement is that "slave" must be idle. With more than two
2270 // threads, this is not by itself sufficient: If "slave" is the master of
2271 // some active split point, it is only available as a slave to the other
2272 // threads which are busy searching the split point at the top of "slave"'s
2273 // split point stack (the "helpful master concept" in YBWC terminology).
2275 bool ThreadsManager::thread_is_available(int slave, int master) const {
2277 assert(slave >= 0 && slave < activeThreads);
2278 assert(master >= 0 && master < activeThreads);
2279 assert(activeThreads > 1);
2281 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2284 // Make a local copy to be sure doesn't change under our feet
2285 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2287 // No active split points means that the thread is available as
2288 // a slave for any other thread.
2289 if (localActiveSplitPoints == 0 || activeThreads == 2)
2292 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2293 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2294 // could have been set to 0 by another thread leading to an out of bound access.
2295 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2302 // available_thread_exists() tries to find an idle thread which is available as
2303 // a slave for the thread with threadID "master".
2305 bool ThreadsManager::available_thread_exists(int master) const {
2307 assert(master >= 0 && master < activeThreads);
2308 assert(activeThreads > 1);
2310 for (int i = 0; i < activeThreads; i++)
2311 if (thread_is_available(i, master))
2318 // split() does the actual work of distributing the work at a node between
2319 // several available threads. If it does not succeed in splitting the
2320 // node (because no idle threads are available, or because we have no unused
2321 // split point objects), the function immediately returns. If splitting is
2322 // possible, a SplitPoint object is initialized with all the data that must be
2323 // copied to the helper threads and we tell our helper threads that they have
2324 // been assigned work. This will cause them to instantly leave their idle loops and
2325 // call search().When all threads have returned from search() then split() returns.
2327 template <bool Fake>
2328 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2329 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2330 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2331 assert(pos.is_ok());
2332 assert(ply > 0 && ply < PLY_MAX);
2333 assert(*bestValue >= -VALUE_INFINITE);
2334 assert(*bestValue <= *alpha);
2335 assert(*alpha < beta);
2336 assert(beta <= VALUE_INFINITE);
2337 assert(depth > DEPTH_ZERO);
2338 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2339 assert(activeThreads > 1);
2341 int i, master = pos.thread();
2342 Thread& masterThread = threads[master];
2346 // If no other thread is available to help us, or if we have too many
2347 // active split points, don't split.
2348 if ( !available_thread_exists(master)
2349 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2351 lock_release(&mpLock);
2355 // Pick the next available split point object from the split point stack
2356 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2358 // Initialize the split point object
2359 splitPoint.parent = masterThread.splitPoint;
2360 splitPoint.master = master;
2361 splitPoint.betaCutoff = false;
2362 splitPoint.ply = ply;
2363 splitPoint.depth = depth;
2364 splitPoint.threatMove = threatMove;
2365 splitPoint.mateThreat = mateThreat;
2366 splitPoint.alpha = *alpha;
2367 splitPoint.beta = beta;
2368 splitPoint.pvNode = pvNode;
2369 splitPoint.bestValue = *bestValue;
2371 splitPoint.moveCount = moveCount;
2372 splitPoint.pos = &pos;
2373 splitPoint.nodes = 0;
2374 splitPoint.parentSstack = ss;
2375 for (i = 0; i < activeThreads; i++)
2376 splitPoint.slaves[i] = 0;
2378 masterThread.splitPoint = &splitPoint;
2380 // If we are here it means we are not available
2381 assert(masterThread.state != THREAD_AVAILABLE);
2383 int workersCnt = 1; // At least the master is included
2385 // Allocate available threads setting state to THREAD_BOOKED
2386 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2387 if (thread_is_available(i, master))
2389 threads[i].state = THREAD_BOOKED;
2390 threads[i].splitPoint = &splitPoint;
2391 splitPoint.slaves[i] = 1;
2395 assert(Fake || workersCnt > 1);
2397 // We can release the lock because slave threads are already booked and master is not available
2398 lock_release(&mpLock);
2400 // Tell the threads that they have work to do. This will make them leave
2401 // their idle loop. But before copy search stack tail for each thread.
2402 for (i = 0; i < activeThreads; i++)
2403 if (i == master || splitPoint.slaves[i])
2405 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2407 assert(i == master || threads[i].state == THREAD_BOOKED);
2409 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2411 if (useSleepingThreads && i != master)
2412 wake_sleeping_thread(i);
2415 // Everything is set up. The master thread enters the idle loop, from
2416 // which it will instantly launch a search, because its state is
2417 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2418 // idle loop, which means that the main thread will return from the idle
2419 // loop when all threads have finished their work at this split point.
2420 idle_loop(master, &splitPoint);
2422 // We have returned from the idle loop, which means that all threads are
2423 // finished. Update alpha and bestValue, and return.
2426 *alpha = splitPoint.alpha;
2427 *bestValue = splitPoint.bestValue;
2428 masterThread.activeSplitPoints--;
2429 masterThread.splitPoint = splitPoint.parent;
2430 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2432 lock_release(&mpLock);
2436 // wake_sleeping_thread() wakes up the thread with the given threadID
2437 // when it is time to start a new search.
2439 void ThreadsManager::wake_sleeping_thread(int threadID) {
2441 lock_grab(&sleepLock[threadID]);
2442 cond_signal(&sleepCond[threadID]);
2443 lock_release(&sleepLock[threadID]);
2447 /// RootMove and RootMoveList method's definitions
2449 RootMove::RootMove() {
2452 pv_score = non_pv_score = -VALUE_INFINITE;
2456 RootMove& RootMove::operator=(const RootMove& rm) {
2458 const Move* src = rm.pv;
2461 // Avoid a costly full rm.pv[] copy
2462 do *dst++ = *src; while (*src++ != MOVE_NONE);
2465 pv_score = rm.pv_score;
2466 non_pv_score = rm.non_pv_score;
2470 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2471 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2472 // allow to always have a ponder move even when we fail high at root and also a
2473 // long PV to print that is important for position analysis.
2475 void RootMove::extract_pv_from_tt(Position& pos) {
2477 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2481 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2483 pos.do_move(pv[0], *st++);
2485 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2486 && tte->move() != MOVE_NONE
2487 && move_is_legal(pos, tte->move())
2489 && (!pos.is_draw() || ply < 2))
2491 pv[ply] = tte->move();
2492 pos.do_move(pv[ply++], *st++);
2494 pv[ply] = MOVE_NONE;
2496 do pos.undo_move(pv[--ply]); while (ply);
2499 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2500 // the PV back into the TT. This makes sure the old PV moves are searched
2501 // first, even if the old TT entries have been overwritten.
2503 void RootMove::insert_pv_in_tt(Position& pos) {
2505 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2508 Value v, m = VALUE_NONE;
2511 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2515 tte = TT.retrieve(k);
2517 // Don't overwrite exsisting correct entries
2518 if (!tte || tte->move() != pv[ply])
2520 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2521 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2523 pos.do_move(pv[ply], *st++);
2525 } while (pv[++ply] != MOVE_NONE);
2527 do pos.undo_move(pv[--ply]); while (ply);
2530 // pv_info_to_uci() returns a string with information on the current PV line
2531 // formatted according to UCI specification and eventually writes the info
2532 // to a log file. It is called at each iteration or after a new pv is found.
2534 std::string RootMove::pv_info_to_uci(Position& pos, Depth depth, Value alpha, Value beta, int pvLine) {
2536 std::stringstream s, l;
2539 while (*m != MOVE_NONE)
2542 s << "info depth " << depth / ONE_PLY
2543 << " seldepth " << int(m - pv)
2544 << " multipv " << pvLine + 1
2545 << " score " << value_to_uci(pv_score)
2546 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2547 << " time " << current_search_time()
2548 << " nodes " << pos.nodes_searched()
2549 << " nps " << nps(pos)
2550 << " pv " << l.str();
2552 if (UseLogFile && pvLine == 0)
2554 ValueType t = pv_score >= beta ? VALUE_TYPE_LOWER :
2555 pv_score <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2557 LogFile << pretty_pv(pos, current_search_time(), depth / ONE_PLY, pv_score, t, pv) << endl;
2563 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2565 SearchStack ss[PLY_MAX_PLUS_2];
2566 MoveStack mlist[MOVES_MAX];
2570 // Initialize search stack
2571 memset(ss, 0, PLY_MAX_PLUS_2 * sizeof(SearchStack));
2572 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2573 bestMoveChanges = 0;
2576 // Generate all legal moves
2577 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
2579 // Add each move to the RootMoveList's vector
2580 for (MoveStack* cur = mlist; cur != last; cur++)
2582 // If we have a searchMoves[] list then verify cur->move
2583 // is in the list before to add it.
2584 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2586 if (searchMoves[0] && *sm != cur->move)
2589 // Find a quick score for the move and add to the list
2590 pos.do_move(cur->move, st);
2593 rm.pv[0] = ss[0].currentMove = cur->move;
2594 rm.pv[1] = MOVE_NONE;
2595 rm.pv_score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2598 pos.undo_move(cur->move);