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(const Position& pos, Value alpha, Value beta, int pvLine = 0);
137 Move pv[PLY_MAX_PLUS_2];
141 // RootMoveList struct is essentially a std::vector<> of RootMove objects,
142 // with an handful of methods above the standard ones.
144 struct RootMoveList : public std::vector<RootMove> {
146 typedef std::vector<RootMove> Base;
148 RootMoveList(Position& pos, Move searchMoves[]);
149 void set_non_pv_scores(const Position& pos);
151 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
152 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& m) {
166 os.iword(0) = int(m);
175 // Maximum depth for razoring
176 const Depth RazorDepth = 4 * ONE_PLY;
178 // Dynamic razoring margin based on depth
179 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
181 // Maximum depth for use of dynamic threat detection when null move fails low
182 const Depth ThreatDepth = 5 * ONE_PLY;
184 // Step 9. Internal iterative deepening
186 // Minimum depth for use of internal iterative deepening
187 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
189 // At Non-PV nodes we do an internal iterative deepening search
190 // when the static evaluation is bigger then beta - IIDMargin.
191 const Value IIDMargin = Value(0x100);
193 // Step 11. Decide the new search depth
195 // Extensions. Configurable UCI options
196 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
197 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
198 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
200 // Minimum depth for use of singular extension
201 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
203 // If the TT move is at least SingularExtensionMargin better then the
204 // remaining ones we will extend it.
205 const Value SingularExtensionMargin = Value(0x20);
207 // Step 12. Futility pruning
209 // Futility margin for quiescence search
210 const Value FutilityMarginQS = Value(0x80);
212 // Futility lookup tables (initialized at startup) and their getter functions
213 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
214 int FutilityMoveCountArray[32]; // [depth]
216 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
217 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
219 // Step 14. Reduced search
221 // Reduction lookup tables (initialized at startup) and their getter functions
222 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
224 template <NodeType PV>
225 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
227 // Common adjustments
229 // Search depth at iteration 1
230 const Depth InitialDepth = ONE_PLY;
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
245 // Scores and number of times the best move changed for each iteration
246 Value ValueByIteration[PLY_MAX_PLUS_2];
247 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
249 // Search window management
255 // Time managment variables
256 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
257 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
258 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
263 std::ofstream LogFile;
265 // Multi-threads manager object
266 ThreadsManager ThreadsMgr;
268 // Node counters, used only by thread[0] but try to keep in different cache
269 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
270 bool SendSearchedNodes;
272 int NodesBetweenPolls = 30000;
279 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
280 Value root_search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, RootMoveList& rml);
282 template <NodeType PvNode, bool SpNode>
283 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
285 template <NodeType PvNode>
286 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
288 template <NodeType PvNode>
289 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
291 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
292 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
295 template <NodeType PvNode>
296 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
298 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
299 bool connected_moves(const Position& pos, Move m1, Move m2);
300 bool value_is_mate(Value value);
301 Value value_to_tt(Value v, int ply);
302 Value value_from_tt(Value v, int ply);
303 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
304 bool connected_threat(const Position& pos, Move m, Move threat);
305 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
306 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
307 void update_killers(Move m, SearchStack* ss);
308 void update_gains(const Position& pos, Move move, Value before, Value after);
310 int current_search_time();
311 std::string value_to_uci(Value v);
312 int nps(const Position& pos);
313 void poll(const Position& pos);
315 void wait_for_stop_or_ponderhit();
316 void init_ss_array(SearchStack* ss, int size);
318 #if !defined(_MSC_VER)
319 void* init_thread(void* threadID);
321 DWORD WINAPI init_thread(LPVOID threadID);
331 /// init_threads(), exit_threads() and nodes_searched() are helpers to
332 /// give accessibility to some TM methods from outside of current file.
334 void init_threads() { ThreadsMgr.init_threads(); }
335 void exit_threads() { ThreadsMgr.exit_threads(); }
338 /// init_search() is called during startup. It initializes various lookup tables
342 int d; // depth (ONE_PLY == 2)
343 int hd; // half depth (ONE_PLY == 1)
346 // Init reductions array
347 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
349 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
350 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
351 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
352 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
355 // Init futility margins array
356 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
357 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
359 // Init futility move count array
360 for (d = 0; d < 32; d++)
361 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
365 /// perft() is our utility to verify move generation is bug free. All the legal
366 /// moves up to given depth are generated and counted and the sum returned.
368 int perft(Position& pos, Depth depth)
370 MoveStack mlist[MOVES_MAX];
375 // Generate all legal moves
376 MoveStack* last = generate_moves(pos, mlist);
378 // If we are at the last ply we don't need to do and undo
379 // the moves, just to count them.
380 if (depth <= ONE_PLY)
381 return int(last - mlist);
383 // Loop through all legal moves
385 for (MoveStack* cur = mlist; cur != last; cur++)
388 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
389 sum += perft(pos, depth - ONE_PLY);
396 /// think() is the external interface to Stockfish's search, and is called when
397 /// the program receives the UCI 'go' command. It initializes various
398 /// search-related global variables, and calls root_search(). It returns false
399 /// when a quit command is received during the search.
401 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
402 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
404 // Initialize global search variables
405 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = SendSearchedNodes = false;
407 SearchStartTime = get_system_time();
408 ExactMaxTime = maxTime;
411 InfiniteSearch = infinite;
412 PonderSearch = ponder;
413 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
415 // Look for a book move, only during games, not tests
416 if (UseTimeManagement && Options["OwnBook"].value<bool>())
418 if (Options["Book File"].value<std::string>() != OpeningBook.file_name())
419 OpeningBook.open(Options["Book File"].value<std::string>());
421 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
422 if (bookMove != MOVE_NONE)
425 wait_for_stop_or_ponderhit();
427 cout << "bestmove " << bookMove << endl;
432 // Read UCI option values
433 TT.set_size(Options["Hash"].value<int>());
434 if (Options["Clear Hash"].value<bool>())
436 Options["Clear Hash"].set_value("false");
440 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
441 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
442 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
443 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
444 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
445 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
446 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
447 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
448 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
449 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
450 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
451 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
452 MultiPV = Options["MultiPV"].value<int>();
453 UseLogFile = Options["Use Search Log"].value<bool>();
455 read_evaluation_uci_options(pos.side_to_move());
457 // Set the number of active threads
458 ThreadsMgr.read_uci_options();
459 init_eval(ThreadsMgr.active_threads());
461 // Wake up needed threads
462 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
463 ThreadsMgr.wake_sleeping_thread(i);
466 int myTime = time[pos.side_to_move()];
467 int myIncrement = increment[pos.side_to_move()];
468 if (UseTimeManagement)
469 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
471 // Set best NodesBetweenPolls interval to avoid lagging under
472 // heavy time pressure.
474 NodesBetweenPolls = Min(MaxNodes, 30000);
475 else if (myTime && myTime < 1000)
476 NodesBetweenPolls = 1000;
477 else if (myTime && myTime < 5000)
478 NodesBetweenPolls = 5000;
480 NodesBetweenPolls = 30000;
482 // Write search information to log file
485 std::string name = Options["Search Log Filename"].value<std::string>();
486 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
488 LogFile << "Searching: " << pos.to_fen()
489 << "\ninfinite: " << infinite
490 << " ponder: " << ponder
491 << " time: " << myTime
492 << " increment: " << myIncrement
493 << " moves to go: " << movesToGo << endl;
496 // We're ready to start thinking. Call the iterative deepening loop function
497 Move ponderMove = MOVE_NONE;
498 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
500 // Print final search statistics
501 cout << "info nodes " << pos.nodes_searched()
502 << " nps " << nps(pos)
503 << " time " << current_search_time() << endl;
507 LogFile << "\nNodes: " << pos.nodes_searched()
508 << "\nNodes/second: " << nps(pos)
509 << "\nBest move: " << move_to_san(pos, bestMove);
512 pos.do_move(bestMove, st);
513 LogFile << "\nPonder move: "
514 << move_to_san(pos, ponderMove) // Works also with MOVE_NONE
520 // This makes all the threads to go to sleep
521 ThreadsMgr.set_active_threads(1);
523 // If we are pondering or in infinite search, we shouldn't print the
524 // best move before we are told to do so.
525 if (!AbortSearch && (PonderSearch || InfiniteSearch))
526 wait_for_stop_or_ponderhit();
528 // Could be both MOVE_NONE when searching on a stalemate position
529 cout << "bestmove " << bestMove << " ponder " << ponderMove << endl;
537 // id_loop() is the main iterative deepening loop. It calls root_search
538 // repeatedly with increasing depth until the allocated thinking time has
539 // been consumed, the user stops the search, or the maximum search depth is
542 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
544 SearchStack ss[PLY_MAX_PLUS_2];
546 Move EasyMove = MOVE_NONE;
547 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
549 // Moves to search are verified, scored and sorted
550 RootMoveList rml(pos, searchMoves);
552 // Handle special case of searching on a mate/stale position
555 Value s = (pos.is_check() ? -VALUE_MATE : VALUE_DRAW);
557 cout << "info depth " << 1
558 << " score " << value_to_uci(s) << endl;
566 init_ss_array(ss, PLY_MAX_PLUS_2);
567 ValueByIteration[1] = rml[0].pv_score;
570 // Send initial RootMoveList scoring (iteration 1)
571 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
572 << "info depth " << Iteration
573 << "\n" << rml[0].pv_info_to_uci(pos, alpha, beta) << endl;
575 // Is one move significantly better than others after initial scoring ?
577 || rml[0].pv_score > rml[1].pv_score + EasyMoveMargin)
578 EasyMove = rml[0].pv[0];
580 // Iterative deepening loop
581 while (Iteration < PLY_MAX)
583 // Initialize iteration
585 BestMoveChangesByIteration[Iteration] = 0;
587 cout << "info depth " << Iteration << endl;
589 // Calculate dynamic aspiration window based on previous iterations
590 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
592 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
593 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
595 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
596 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
598 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
599 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
602 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
604 // Search to the current depth, rml is updated and sorted
605 value = root_search(pos, ss, alpha, beta, depth, rml);
608 break; // Value cannot be trusted. Break out immediately!
610 //Save info about search result
611 ValueByIteration[Iteration] = value;
613 // Drop the easy move if differs from the new best move
614 if (rml[0].pv[0] != EasyMove)
615 EasyMove = MOVE_NONE;
617 if (UseTimeManagement)
620 bool stopSearch = false;
622 // Stop search early if there is only a single legal move,
623 // we search up to Iteration 6 anyway to get a proper score.
624 if (Iteration >= 6 && rml.size() == 1)
627 // Stop search early when the last two iterations returned a mate score
629 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
630 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
633 // Stop search early if one move seems to be much better than the others
635 && EasyMove == rml[0].pv[0]
636 && ( ( rml[0].nodes > (pos.nodes_searched() * 85) / 100
637 && current_search_time() > TimeMgr.available_time() / 16)
638 ||( rml[0].nodes > (pos.nodes_searched() * 98) / 100
639 && current_search_time() > TimeMgr.available_time() / 32)))
642 // Add some extra time if the best move has changed during the last two iterations
643 if (Iteration > 5 && Iteration <= 50)
644 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
645 BestMoveChangesByIteration[Iteration-1]);
647 // Stop search if most of MaxSearchTime is consumed at the end of the
648 // iteration. We probably don't have enough time to search the first
649 // move at the next iteration anyway.
650 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
656 StopOnPonderhit = true;
662 if (MaxDepth && Iteration >= MaxDepth)
666 *ponderMove = rml[0].pv[1];
671 // root_search() is the function which searches the root node. It is
672 // similar to search_pv except that it prints some information to the
673 // standard output and handles the fail low/high loops.
675 Value root_search(Position& pos, SearchStack* ss, Value alpha,
676 Value beta, Depth depth, RootMoveList& rml) {
682 Value value, oldAlpha;
683 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
684 int researchCountFH, researchCountFL;
686 researchCountFH = researchCountFL = 0;
688 isCheck = pos.is_check();
690 // Step 1. Initialize node (polling is omitted at root)
691 ss->currentMove = ss->bestMove = MOVE_NONE;
693 // Step 2. Check for aborted search (omitted at root)
694 // Step 3. Mate distance pruning (omitted at root)
695 // Step 4. Transposition table lookup (omitted at root)
697 // Step 5. Evaluate the position statically
698 // At root we do this only to get reference value for child nodes
699 ss->evalMargin = VALUE_NONE;
700 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
702 // Step 6. Razoring (omitted at root)
703 // Step 7. Static null move pruning (omitted at root)
704 // Step 8. Null move search with verification search (omitted at root)
705 // Step 9. Internal iterative deepening (omitted at root)
707 // Step extra. Fail low loop
708 // We start with small aspiration window and in case of fail low, we research
709 // with bigger window until we are not failing low anymore.
712 // Sort the moves before to (re)search
713 rml.set_non_pv_scores(pos);
716 // Step 10. Loop through all moves in the root move list
717 for (int i = 0; i < (int)rml.size() && !AbortSearch; i++)
719 // This is used by time management
720 FirstRootMove = (i == 0);
722 // Save the current node count before the move is searched
723 nodes = pos.nodes_searched();
725 // If it's time to send nodes info, do it here where we have the
726 // correct accumulated node counts searched by each thread.
727 if (SendSearchedNodes)
729 SendSearchedNodes = false;
730 cout << "info nodes " << nodes
731 << " nps " << nps(pos)
732 << " time " << current_search_time() << endl;
735 // Pick the next root move, and print the move and the move number to
736 // the standard output.
737 move = ss->currentMove = rml[i].pv[0];
739 if (current_search_time() >= 1000)
740 cout << "info currmove " << move
741 << " currmovenumber " << i + 1 << endl;
743 moveIsCheck = pos.move_is_check(move);
744 captureOrPromotion = pos.move_is_capture_or_promotion(move);
746 // Step 11. Decide the new search depth
747 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
748 newDepth = depth + ext;
750 // Step 12. Futility pruning (omitted at root)
752 // Step extra. Fail high loop
753 // If move fails high, we research with bigger window until we are not failing
755 value = -VALUE_INFINITE;
759 // Step 13. Make the move
760 pos.do_move(move, st, ci, moveIsCheck);
762 // Step extra. pv search
763 // We do pv search for first moves (i < MultiPV)
764 // and for fail high research (value > alpha)
765 if (i < MultiPV || value > alpha)
767 // Aspiration window is disabled in multi-pv case
769 alpha = -VALUE_INFINITE;
771 // Full depth PV search, done on first move or after a fail high
772 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
776 // Step 14. Reduced search
777 // if the move fails high will be re-searched at full depth
778 bool doFullDepthSearch = true;
780 if ( depth >= 3 * ONE_PLY
782 && !captureOrPromotion
783 && !move_is_castle(move))
785 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
788 assert(newDepth-ss->reduction >= ONE_PLY);
790 // Reduced depth non-pv search using alpha as upperbound
791 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
792 doFullDepthSearch = (value > alpha);
794 ss->reduction = DEPTH_ZERO; // Restore original reduction
797 // Step 15. Full depth search
798 if (doFullDepthSearch)
800 // Full depth non-pv search using alpha as upperbound
801 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
803 // If we are above alpha then research at same depth but as PV
804 // to get a correct score or eventually a fail high above beta.
806 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
810 // Step 16. Undo move
813 // Can we exit fail high loop ?
814 if (AbortSearch || value < beta)
817 // We are failing high and going to do a research. It's important to update
818 // the score before research in case we run out of time while researching.
820 rml[i].pv_score = value;
821 rml[i].extract_pv_from_tt(pos);
823 // Inform GUI that PV has changed
824 cout << rml[i].pv_info_to_uci(pos, alpha, beta) << endl;
826 // Prepare for a research after a fail high, each time with a wider window
827 beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
830 } // End of fail high loop
832 // Finished searching the move. If AbortSearch is true, the search
833 // was aborted because the user interrupted the search or because we
834 // ran out of time. In this case, the return value of the search cannot
835 // be trusted, and we break out of the loop without updating the best
840 // Remember searched nodes counts for this move
841 rml[i].nodes += pos.nodes_searched() - nodes;
843 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
844 assert(value < beta);
846 // Step 17. Check for new best move
847 if (value <= alpha && i >= MultiPV)
848 rml[i].pv_score = -VALUE_INFINITE;
851 // PV move or new best move!
855 rml[i].pv_score = value;
856 rml[i].extract_pv_from_tt(pos);
858 // We record how often the best move has been changed in each
859 // iteration. This information is used for time managment: When
860 // the best move changes frequently, we allocate some more time.
861 if (MultiPV == 1 && i > 0)
862 BestMoveChangesByIteration[Iteration]++;
864 // Inform GUI that PV has changed, in case of multi-pv UCI protocol
865 // requires we send all the PV lines properly sorted.
868 for (int j = 0; j < Min(MultiPV, (int)rml.size()); j++)
869 cout << rml[j].pv_info_to_uci(pos, alpha, beta, j) << endl;
871 // Update alpha. In multi-pv we don't use aspiration window
874 // Raise alpha to setup proper non-pv search upper bound
878 else // Set alpha equal to minimum score among the PV lines
879 alpha = rml[Min(i, MultiPV - 1)].pv_score;
881 } // PV move or new best move
883 assert(alpha >= oldAlpha);
885 AspirationFailLow = (alpha == oldAlpha);
887 if (AspirationFailLow && StopOnPonderhit)
888 StopOnPonderhit = false;
892 // Can we exit fail low loop ?
893 if (AbortSearch || !AspirationFailLow)
896 // Prepare for a research after a fail low, each time with a wider window
897 oldAlpha = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
902 // Sort the moves before to return
905 // Write PV lines to transposition table, in case the relevant entries
906 // have been overwritten during the search.
907 for (int i = 0; i < MultiPV; i++)
908 rml[i].insert_pv_in_tt(pos);
914 // search<>() is the main search function for both PV and non-PV nodes and for
915 // normal and SplitPoint nodes. When called just after a split point the search
916 // is simpler because we have already probed the hash table, done a null move
917 // search, and searched the first move before splitting, we don't have to repeat
918 // all this work again. We also don't need to store anything to the hash table
919 // here: This is taken care of after we return from the split point.
921 template <NodeType PvNode, bool SpNode>
922 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
924 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
925 assert(beta > alpha && beta <= VALUE_INFINITE);
926 assert(PvNode || alpha == beta - 1);
927 assert(ply > 0 && ply < PLY_MAX);
928 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
930 Move movesSearched[MOVES_MAX];
934 Move ttMove, move, excludedMove, threatMove;
937 Value bestValue, value, oldAlpha;
938 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
939 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
940 bool mateThreat = false;
942 int threadID = pos.thread();
943 SplitPoint* sp = NULL;
944 refinedValue = bestValue = value = -VALUE_INFINITE;
946 isCheck = pos.is_check();
952 ttMove = excludedMove = MOVE_NONE;
953 threatMove = sp->threatMove;
954 mateThreat = sp->mateThreat;
955 goto split_point_start;
957 else {} // Hack to fix icc's "statement is unreachable" warning
959 // Step 1. Initialize node and poll. Polling can abort search
960 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
961 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
963 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
969 // Step 2. Check for aborted search and immediate draw
971 || ThreadsMgr.cutoff_at_splitpoint(threadID)
973 || ply >= PLY_MAX - 1)
976 // Step 3. Mate distance pruning
977 alpha = Max(value_mated_in(ply), alpha);
978 beta = Min(value_mate_in(ply+1), beta);
982 // Step 4. Transposition table lookup
984 // We don't want the score of a partial search to overwrite a previous full search
985 // TT value, so we use a different position key in case of an excluded move exists.
986 excludedMove = ss->excludedMove;
987 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
989 tte = TT.retrieve(posKey);
990 ttMove = tte ? tte->move() : MOVE_NONE;
992 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
993 // This is to avoid problems in the following areas:
995 // * Repetition draw detection
996 // * Fifty move rule detection
997 // * Searching for a mate
998 // * Printing of full PV line
999 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1002 ss->bestMove = ttMove; // Can be MOVE_NONE
1003 return value_from_tt(tte->value(), ply);
1006 // Step 5. Evaluate the position statically and
1007 // update gain statistics of parent move.
1009 ss->eval = ss->evalMargin = VALUE_NONE;
1012 assert(tte->static_value() != VALUE_NONE);
1014 ss->eval = tte->static_value();
1015 ss->evalMargin = tte->static_value_margin();
1016 refinedValue = refine_eval(tte, ss->eval, ply);
1020 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1021 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1024 // Save gain for the parent non-capture move
1025 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1027 // Step 6. Razoring (is omitted in PV nodes)
1029 && depth < RazorDepth
1031 && refinedValue < beta - razor_margin(depth)
1032 && ttMove == MOVE_NONE
1033 && !value_is_mate(beta)
1034 && !pos.has_pawn_on_7th(pos.side_to_move()))
1036 Value rbeta = beta - razor_margin(depth);
1037 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1039 // Logically we should return (v + razor_margin(depth)), but
1040 // surprisingly this did slightly weaker in tests.
1044 // Step 7. Static null move pruning (is omitted in PV nodes)
1045 // We're betting that the opponent doesn't have a move that will reduce
1046 // the score by more than futility_margin(depth) if we do a null move.
1048 && !ss->skipNullMove
1049 && depth < RazorDepth
1051 && refinedValue >= beta + futility_margin(depth, 0)
1052 && !value_is_mate(beta)
1053 && pos.non_pawn_material(pos.side_to_move()))
1054 return refinedValue - futility_margin(depth, 0);
1056 // Step 8. Null move search with verification search (is omitted in PV nodes)
1058 && !ss->skipNullMove
1061 && refinedValue >= beta
1062 && !value_is_mate(beta)
1063 && pos.non_pawn_material(pos.side_to_move()))
1065 ss->currentMove = MOVE_NULL;
1067 // Null move dynamic reduction based on depth
1068 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1070 // Null move dynamic reduction based on value
1071 if (refinedValue - beta > PawnValueMidgame)
1074 pos.do_null_move(st);
1075 (ss+1)->skipNullMove = true;
1076 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1077 (ss+1)->skipNullMove = false;
1078 pos.undo_null_move();
1080 if (nullValue >= beta)
1082 // Do not return unproven mate scores
1083 if (nullValue >= value_mate_in(PLY_MAX))
1086 if (depth < 6 * ONE_PLY)
1089 // Do verification search at high depths
1090 ss->skipNullMove = true;
1091 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1092 ss->skipNullMove = false;
1099 // The null move failed low, which means that we may be faced with
1100 // some kind of threat. If the previous move was reduced, check if
1101 // the move that refuted the null move was somehow connected to the
1102 // move which was reduced. If a connection is found, return a fail
1103 // low score (which will cause the reduced move to fail high in the
1104 // parent node, which will trigger a re-search with full depth).
1105 if (nullValue == value_mated_in(ply + 2))
1108 threatMove = (ss+1)->bestMove;
1109 if ( depth < ThreatDepth
1110 && (ss-1)->reduction
1111 && threatMove != MOVE_NONE
1112 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1117 // Step 9. Internal iterative deepening
1118 if ( depth >= IIDDepth[PvNode]
1119 && ttMove == MOVE_NONE
1120 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1122 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1124 ss->skipNullMove = true;
1125 search<PvNode>(pos, ss, alpha, beta, d, ply);
1126 ss->skipNullMove = false;
1128 ttMove = ss->bestMove;
1129 tte = TT.retrieve(posKey);
1132 // Expensive mate threat detection (only for PV nodes)
1134 mateThreat = pos.has_mate_threat();
1136 split_point_start: // At split points actual search starts from here
1138 // Initialize a MovePicker object for the current position
1139 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1140 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1141 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1143 ss->bestMove = MOVE_NONE;
1144 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1145 futilityBase = ss->eval + ss->evalMargin;
1146 singularExtensionNode = !SpNode
1147 && depth >= SingularExtensionDepth[PvNode]
1150 && !excludedMove // Do not allow recursive singular extension search
1151 && (tte->type() & VALUE_TYPE_LOWER)
1152 && tte->depth() >= depth - 3 * ONE_PLY;
1155 lock_grab(&(sp->lock));
1156 bestValue = sp->bestValue;
1159 // Step 10. Loop through moves
1160 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1161 while ( bestValue < beta
1162 && (move = mp.get_next_move()) != MOVE_NONE
1163 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1165 assert(move_is_ok(move));
1169 moveCount = ++sp->moveCount;
1170 lock_release(&(sp->lock));
1172 else if (move == excludedMove)
1175 movesSearched[moveCount++] = move;
1177 moveIsCheck = pos.move_is_check(move, ci);
1178 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1180 // Step 11. Decide the new search depth
1181 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1183 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1184 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1185 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1186 // lower then ttValue minus a margin then we extend ttMove.
1187 if ( singularExtensionNode
1188 && move == tte->move()
1191 Value ttValue = value_from_tt(tte->value(), ply);
1193 if (abs(ttValue) < VALUE_KNOWN_WIN)
1195 Value b = ttValue - SingularExtensionMargin;
1196 ss->excludedMove = move;
1197 ss->skipNullMove = true;
1198 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1199 ss->skipNullMove = false;
1200 ss->excludedMove = MOVE_NONE;
1201 ss->bestMove = MOVE_NONE;
1207 // Update current move (this must be done after singular extension search)
1208 ss->currentMove = move;
1209 newDepth = depth - ONE_PLY + ext;
1211 // Step 12. Futility pruning (is omitted in PV nodes)
1213 && !captureOrPromotion
1217 && !move_is_castle(move))
1219 // Move count based pruning
1220 if ( moveCount >= futility_move_count(depth)
1221 && !(threatMove && connected_threat(pos, move, threatMove))
1222 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1225 lock_grab(&(sp->lock));
1230 // Value based pruning
1231 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1232 // but fixing this made program slightly weaker.
1233 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1234 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1235 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1237 if (futilityValueScaled < beta)
1241 lock_grab(&(sp->lock));
1242 if (futilityValueScaled > sp->bestValue)
1243 sp->bestValue = bestValue = futilityValueScaled;
1245 else if (futilityValueScaled > bestValue)
1246 bestValue = futilityValueScaled;
1251 // Prune moves with negative SEE at low depths
1252 if ( predictedDepth < 2 * ONE_PLY
1253 && bestValue > value_mated_in(PLY_MAX)
1254 && pos.see_sign(move) < 0)
1257 lock_grab(&(sp->lock));
1263 // Step 13. Make the move
1264 pos.do_move(move, st, ci, moveIsCheck);
1266 // Step extra. pv search (only in PV nodes)
1267 // The first move in list is the expected PV
1268 if (PvNode && moveCount == 1)
1269 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1272 // Step 14. Reduced depth search
1273 // If the move fails high will be re-searched at full depth.
1274 bool doFullDepthSearch = true;
1276 if ( depth >= 3 * ONE_PLY
1277 && !captureOrPromotion
1279 && !move_is_castle(move)
1280 && ss->killers[0] != move
1281 && ss->killers[1] != move)
1283 ss->reduction = reduction<PvNode>(depth, moveCount);
1287 alpha = SpNode ? sp->alpha : alpha;
1288 Depth d = newDepth - ss->reduction;
1289 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1291 doFullDepthSearch = (value > alpha);
1293 ss->reduction = DEPTH_ZERO; // Restore original reduction
1296 // Step 15. Full depth search
1297 if (doFullDepthSearch)
1299 alpha = SpNode ? sp->alpha : alpha;
1300 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1302 // Step extra. pv search (only in PV nodes)
1303 // Search only for possible new PV nodes, if instead value >= beta then
1304 // parent node fails low with value <= alpha and tries another move.
1305 if (PvNode && value > alpha && value < beta)
1306 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1310 // Step 16. Undo move
1311 pos.undo_move(move);
1313 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1315 // Step 17. Check for new best move
1318 lock_grab(&(sp->lock));
1319 bestValue = sp->bestValue;
1323 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1328 sp->bestValue = value;
1332 if (PvNode && value < beta) // We want always alpha < beta
1340 sp->betaCutoff = true;
1342 if (value == value_mate_in(ply + 1))
1343 ss->mateKiller = move;
1345 ss->bestMove = move;
1348 sp->parentSstack->bestMove = move;
1352 // Step 18. Check for split
1354 && depth >= ThreadsMgr.min_split_depth()
1355 && ThreadsMgr.active_threads() > 1
1357 && ThreadsMgr.available_thread_exists(threadID)
1359 && !ThreadsMgr.cutoff_at_splitpoint(threadID)
1361 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1362 threatMove, mateThreat, moveCount, &mp, PvNode);
1365 // Step 19. Check for mate and stalemate
1366 // All legal moves have been searched and if there are
1367 // no legal moves, it must be mate or stalemate.
1368 // If one move was excluded return fail low score.
1369 if (!SpNode && !moveCount)
1370 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1372 // Step 20. Update tables
1373 // If the search is not aborted, update the transposition table,
1374 // history counters, and killer moves.
1375 if (!SpNode && !AbortSearch && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1377 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1378 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1379 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1381 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1383 // Update killers and history only for non capture moves that fails high
1384 if ( bestValue >= beta
1385 && !pos.move_is_capture_or_promotion(move))
1387 update_history(pos, move, depth, movesSearched, moveCount);
1388 update_killers(move, ss);
1394 // Here we have the lock still grabbed
1395 sp->slaves[threadID] = 0;
1396 sp->nodes += pos.nodes_searched();
1397 lock_release(&(sp->lock));
1400 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1405 // qsearch() is the quiescence search function, which is called by the main
1406 // search function when the remaining depth is zero (or, to be more precise,
1407 // less than ONE_PLY).
1409 template <NodeType PvNode>
1410 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1412 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1413 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1414 assert(PvNode || alpha == beta - 1);
1416 assert(ply > 0 && ply < PLY_MAX);
1417 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1421 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1422 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1425 Value oldAlpha = alpha;
1427 ss->bestMove = ss->currentMove = MOVE_NONE;
1429 // Check for an instant draw or maximum ply reached
1430 if (pos.is_draw() || ply >= PLY_MAX - 1)
1433 // Decide whether or not to include checks, this fixes also the type of
1434 // TT entry depth that we are going to use. Note that in qsearch we use
1435 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1436 isCheck = pos.is_check();
1437 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1439 // Transposition table lookup. At PV nodes, we don't use the TT for
1440 // pruning, but only for move ordering.
1441 tte = TT.retrieve(pos.get_key());
1442 ttMove = (tte ? tte->move() : MOVE_NONE);
1444 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1446 ss->bestMove = ttMove; // Can be MOVE_NONE
1447 return value_from_tt(tte->value(), ply);
1450 // Evaluate the position statically
1453 bestValue = futilityBase = -VALUE_INFINITE;
1454 ss->eval = evalMargin = VALUE_NONE;
1455 enoughMaterial = false;
1461 assert(tte->static_value() != VALUE_NONE);
1463 evalMargin = tte->static_value_margin();
1464 ss->eval = bestValue = tte->static_value();
1467 ss->eval = bestValue = evaluate(pos, evalMargin);
1469 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1471 // Stand pat. Return immediately if static value is at least beta
1472 if (bestValue >= beta)
1475 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1480 if (PvNode && bestValue > alpha)
1483 // Futility pruning parameters, not needed when in check
1484 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1485 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1488 // Initialize a MovePicker object for the current position, and prepare
1489 // to search the moves. Because the depth is <= 0 here, only captures,
1490 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1492 MovePicker mp(pos, ttMove, depth, H);
1495 // Loop through the moves until no moves remain or a beta cutoff occurs
1496 while ( alpha < beta
1497 && (move = mp.get_next_move()) != MOVE_NONE)
1499 assert(move_is_ok(move));
1501 moveIsCheck = pos.move_is_check(move, ci);
1509 && !move_is_promotion(move)
1510 && !pos.move_is_passed_pawn_push(move))
1512 futilityValue = futilityBase
1513 + pos.endgame_value_of_piece_on(move_to(move))
1514 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1516 if (futilityValue < alpha)
1518 if (futilityValue > bestValue)
1519 bestValue = futilityValue;
1524 // Detect non-capture evasions that are candidate to be pruned
1525 evasionPrunable = isCheck
1526 && bestValue > value_mated_in(PLY_MAX)
1527 && !pos.move_is_capture(move)
1528 && !pos.can_castle(pos.side_to_move());
1530 // Don't search moves with negative SEE values
1532 && (!isCheck || evasionPrunable)
1534 && !move_is_promotion(move)
1535 && pos.see_sign(move) < 0)
1538 // Don't search useless checks
1543 && !pos.move_is_capture_or_promotion(move)
1544 && ss->eval + PawnValueMidgame / 4 < beta
1545 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1547 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1548 bestValue = ss->eval + PawnValueMidgame / 4;
1553 // Update current move
1554 ss->currentMove = move;
1556 // Make and search the move
1557 pos.do_move(move, st, ci, moveIsCheck);
1558 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1559 pos.undo_move(move);
1561 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1564 if (value > bestValue)
1570 ss->bestMove = move;
1575 // All legal moves have been searched. A special case: If we're in check
1576 // and no legal moves were found, it is checkmate.
1577 if (isCheck && bestValue == -VALUE_INFINITE)
1578 return value_mated_in(ply);
1580 // Update transposition table
1581 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1582 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1584 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1590 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1591 // bestValue is updated only when returning false because in that case move
1594 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1596 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1597 Square from, to, ksq, victimSq;
1600 Value futilityValue, bv = *bestValue;
1602 from = move_from(move);
1604 them = opposite_color(pos.side_to_move());
1605 ksq = pos.king_square(them);
1606 kingAtt = pos.attacks_from<KING>(ksq);
1607 pc = pos.piece_on(from);
1609 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1610 oldAtt = pos.attacks_from(pc, from, occ);
1611 newAtt = pos.attacks_from(pc, to, occ);
1613 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1614 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1616 if (!(b && (b & (b - 1))))
1619 // Rule 2. Queen contact check is very dangerous
1620 if ( type_of_piece(pc) == QUEEN
1621 && bit_is_set(kingAtt, to))
1624 // Rule 3. Creating new double threats with checks
1625 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1629 victimSq = pop_1st_bit(&b);
1630 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1632 // Note that here we generate illegal "double move"!
1633 if ( futilityValue >= beta
1634 && pos.see_sign(make_move(from, victimSq)) >= 0)
1637 if (futilityValue > bv)
1641 // Update bestValue only if check is not dangerous (because we will prune the move)
1647 // connected_moves() tests whether two moves are 'connected' in the sense
1648 // that the first move somehow made the second move possible (for instance
1649 // if the moving piece is the same in both moves). The first move is assumed
1650 // to be the move that was made to reach the current position, while the
1651 // second move is assumed to be a move from the current position.
1653 bool connected_moves(const Position& pos, Move m1, Move m2) {
1655 Square f1, t1, f2, t2;
1658 assert(m1 && move_is_ok(m1));
1659 assert(m2 && move_is_ok(m2));
1661 // Case 1: The moving piece is the same in both moves
1667 // Case 2: The destination square for m2 was vacated by m1
1673 // Case 3: Moving through the vacated square
1674 if ( piece_is_slider(pos.piece_on(f2))
1675 && bit_is_set(squares_between(f2, t2), f1))
1678 // Case 4: The destination square for m2 is defended by the moving piece in m1
1679 p = pos.piece_on(t1);
1680 if (bit_is_set(pos.attacks_from(p, t1), t2))
1683 // Case 5: Discovered check, checking piece is the piece moved in m1
1684 if ( piece_is_slider(p)
1685 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1686 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1688 // discovered_check_candidates() works also if the Position's side to
1689 // move is the opposite of the checking piece.
1690 Color them = opposite_color(pos.side_to_move());
1691 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1693 if (bit_is_set(dcCandidates, f2))
1700 // value_is_mate() checks if the given value is a mate one eventually
1701 // compensated for the ply.
1703 bool value_is_mate(Value value) {
1705 assert(abs(value) <= VALUE_INFINITE);
1707 return value <= value_mated_in(PLY_MAX)
1708 || value >= value_mate_in(PLY_MAX);
1712 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1713 // "plies to mate from the current ply". Non-mate scores are unchanged.
1714 // The function is called before storing a value to the transposition table.
1716 Value value_to_tt(Value v, int ply) {
1718 if (v >= value_mate_in(PLY_MAX))
1721 if (v <= value_mated_in(PLY_MAX))
1728 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1729 // the transposition table to a mate score corrected for the current ply.
1731 Value value_from_tt(Value v, int ply) {
1733 if (v >= value_mate_in(PLY_MAX))
1736 if (v <= value_mated_in(PLY_MAX))
1743 // extension() decides whether a move should be searched with normal depth,
1744 // or with extended depth. Certain classes of moves (checking moves, in
1745 // particular) are searched with bigger depth than ordinary moves and in
1746 // any case are marked as 'dangerous'. Note that also if a move is not
1747 // extended, as example because the corresponding UCI option is set to zero,
1748 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1749 template <NodeType PvNode>
1750 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1751 bool singleEvasion, bool mateThreat, bool* dangerous) {
1753 assert(m != MOVE_NONE);
1755 Depth result = DEPTH_ZERO;
1756 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1760 if (moveIsCheck && pos.see_sign(m) >= 0)
1761 result += CheckExtension[PvNode];
1764 result += SingleEvasionExtension[PvNode];
1767 result += MateThreatExtension[PvNode];
1770 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1772 Color c = pos.side_to_move();
1773 if (relative_rank(c, move_to(m)) == RANK_7)
1775 result += PawnPushTo7thExtension[PvNode];
1778 if (pos.pawn_is_passed(c, move_to(m)))
1780 result += PassedPawnExtension[PvNode];
1785 if ( captureOrPromotion
1786 && pos.type_of_piece_on(move_to(m)) != PAWN
1787 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1788 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1789 && !move_is_promotion(m)
1792 result += PawnEndgameExtension[PvNode];
1797 && captureOrPromotion
1798 && pos.type_of_piece_on(move_to(m)) != PAWN
1799 && pos.see_sign(m) >= 0)
1801 result += ONE_PLY / 2;
1805 return Min(result, ONE_PLY);
1809 // connected_threat() tests whether it is safe to forward prune a move or if
1810 // is somehow coonected to the threat move returned by null search.
1812 bool connected_threat(const Position& pos, Move m, Move threat) {
1814 assert(move_is_ok(m));
1815 assert(threat && move_is_ok(threat));
1816 assert(!pos.move_is_check(m));
1817 assert(!pos.move_is_capture_or_promotion(m));
1818 assert(!pos.move_is_passed_pawn_push(m));
1820 Square mfrom, mto, tfrom, tto;
1822 mfrom = move_from(m);
1824 tfrom = move_from(threat);
1825 tto = move_to(threat);
1827 // Case 1: Don't prune moves which move the threatened piece
1831 // Case 2: If the threatened piece has value less than or equal to the
1832 // value of the threatening piece, don't prune move which defend it.
1833 if ( pos.move_is_capture(threat)
1834 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1835 || pos.type_of_piece_on(tfrom) == KING)
1836 && pos.move_attacks_square(m, tto))
1839 // Case 3: If the moving piece in the threatened move is a slider, don't
1840 // prune safe moves which block its ray.
1841 if ( piece_is_slider(pos.piece_on(tfrom))
1842 && bit_is_set(squares_between(tfrom, tto), mto)
1843 && pos.see_sign(m) >= 0)
1850 // ok_to_use_TT() returns true if a transposition table score
1851 // can be used at a given point in search.
1853 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1855 Value v = value_from_tt(tte->value(), ply);
1857 return ( tte->depth() >= depth
1858 || v >= Max(value_mate_in(PLY_MAX), beta)
1859 || v < Min(value_mated_in(PLY_MAX), beta))
1861 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1862 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1866 // refine_eval() returns the transposition table score if
1867 // possible otherwise falls back on static position evaluation.
1869 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1873 Value v = value_from_tt(tte->value(), ply);
1875 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1876 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1883 // update_history() registers a good move that produced a beta-cutoff
1884 // in history and marks as failures all the other moves of that ply.
1886 void update_history(const Position& pos, Move move, Depth depth,
1887 Move movesSearched[], int moveCount) {
1890 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1892 for (int i = 0; i < moveCount - 1; i++)
1894 m = movesSearched[i];
1898 if (!pos.move_is_capture_or_promotion(m))
1899 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1904 // update_killers() add a good move that produced a beta-cutoff
1905 // among the killer moves of that ply.
1907 void update_killers(Move m, SearchStack* ss) {
1909 if (m == ss->killers[0])
1912 ss->killers[1] = ss->killers[0];
1917 // update_gains() updates the gains table of a non-capture move given
1918 // the static position evaluation before and after the move.
1920 void update_gains(const Position& pos, Move m, Value before, Value after) {
1923 && before != VALUE_NONE
1924 && after != VALUE_NONE
1925 && pos.captured_piece_type() == PIECE_TYPE_NONE
1926 && !move_is_special(m))
1927 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1931 // current_search_time() returns the number of milliseconds which have passed
1932 // since the beginning of the current search.
1934 int current_search_time() {
1936 return get_system_time() - SearchStartTime;
1940 // value_to_uci() converts a value to a string suitable for use with the UCI
1941 // protocol specifications:
1943 // cp <x> The score from the engine's point of view in centipawns.
1944 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1945 // use negative values for y.
1947 std::string value_to_uci(Value v) {
1949 std::stringstream s;
1951 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1952 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1954 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1959 // nps() computes the current nodes/second count.
1961 int nps(const Position& pos) {
1963 int t = current_search_time();
1964 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1968 // poll() performs two different functions: It polls for user input, and it
1969 // looks at the time consumed so far and decides if it's time to abort the
1972 void poll(const Position& pos) {
1974 static int lastInfoTime;
1975 int t = current_search_time();
1978 if (data_available())
1980 // We are line oriented, don't read single chars
1981 std::string command;
1983 if (!std::getline(std::cin, command))
1986 if (command == "quit")
1989 PonderSearch = false;
1993 else if (command == "stop")
1996 PonderSearch = false;
1998 else if (command == "ponderhit")
2002 // Print search information
2006 else if (lastInfoTime > t)
2007 // HACK: Must be a new search where we searched less than
2008 // NodesBetweenPolls nodes during the first second of search.
2011 else if (t - lastInfoTime >= 1000)
2018 if (dbg_show_hit_rate)
2019 dbg_print_hit_rate();
2021 // Send info on searched nodes as soon as we return to root
2022 SendSearchedNodes = true;
2025 // Should we stop the search?
2029 bool stillAtFirstMove = FirstRootMove
2030 && !AspirationFailLow
2031 && t > TimeMgr.available_time();
2033 bool noMoreTime = t > TimeMgr.maximum_time()
2034 || stillAtFirstMove;
2036 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2037 || (ExactMaxTime && t >= ExactMaxTime)
2038 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2043 // ponderhit() is called when the program is pondering (i.e. thinking while
2044 // it's the opponent's turn to move) in order to let the engine know that
2045 // it correctly predicted the opponent's move.
2049 int t = current_search_time();
2050 PonderSearch = false;
2052 bool stillAtFirstMove = FirstRootMove
2053 && !AspirationFailLow
2054 && t > TimeMgr.available_time();
2056 bool noMoreTime = t > TimeMgr.maximum_time()
2057 || stillAtFirstMove;
2059 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2064 // init_ss_array() does a fast reset of the first entries of a SearchStack
2065 // array and of all the excludedMove and skipNullMove entries.
2067 void init_ss_array(SearchStack* ss, int size) {
2069 for (int i = 0; i < size; i++, ss++)
2071 ss->excludedMove = MOVE_NONE;
2072 ss->skipNullMove = false;
2073 ss->reduction = DEPTH_ZERO;
2077 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2082 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2083 // while the program is pondering. The point is to work around a wrinkle in
2084 // the UCI protocol: When pondering, the engine is not allowed to give a
2085 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2086 // We simply wait here until one of these commands is sent, and return,
2087 // after which the bestmove and pondermove will be printed (in id_loop()).
2089 void wait_for_stop_or_ponderhit() {
2091 std::string command;
2095 if (!std::getline(std::cin, command))
2098 if (command == "quit")
2103 else if (command == "ponderhit" || command == "stop")
2109 // init_thread() is the function which is called when a new thread is
2110 // launched. It simply calls the idle_loop() function with the supplied
2111 // threadID. There are two versions of this function; one for POSIX
2112 // threads and one for Windows threads.
2114 #if !defined(_MSC_VER)
2116 void* init_thread(void* threadID) {
2118 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2124 DWORD WINAPI init_thread(LPVOID threadID) {
2126 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2133 /// The ThreadsManager class
2136 // read_uci_options() updates number of active threads and other internal
2137 // parameters according to the UCI options values. It is called before
2138 // to start a new search.
2140 void ThreadsManager::read_uci_options() {
2142 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2143 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2144 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2145 activeThreads = Options["Threads"].value<int>();
2149 // idle_loop() is where the threads are parked when they have no work to do.
2150 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2151 // object for which the current thread is the master.
2153 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2155 assert(threadID >= 0 && threadID < MAX_THREADS);
2158 bool allFinished = false;
2162 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2163 // master should exit as last one.
2164 if (allThreadsShouldExit)
2167 threads[threadID].state = THREAD_TERMINATED;
2171 // If we are not thinking, wait for a condition to be signaled
2172 // instead of wasting CPU time polling for work.
2173 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2174 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2176 assert(!sp || useSleepingThreads);
2177 assert(threadID != 0 || useSleepingThreads);
2179 if (threads[threadID].state == THREAD_INITIALIZING)
2180 threads[threadID].state = THREAD_AVAILABLE;
2182 // Grab the lock to avoid races with wake_sleeping_thread()
2183 lock_grab(&sleepLock[threadID]);
2185 // If we are master and all slaves have finished do not go to sleep
2186 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2187 allFinished = (i == activeThreads);
2189 if (allFinished || allThreadsShouldExit)
2191 lock_release(&sleepLock[threadID]);
2195 // Do sleep here after retesting sleep conditions
2196 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2197 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2199 lock_release(&sleepLock[threadID]);
2202 // If this thread has been assigned work, launch a search
2203 if (threads[threadID].state == THREAD_WORKISWAITING)
2205 assert(!allThreadsShouldExit);
2207 threads[threadID].state = THREAD_SEARCHING;
2209 // Here we call search() with SplitPoint template parameter set to true
2210 SplitPoint* tsp = threads[threadID].splitPoint;
2211 Position pos(*tsp->pos, threadID);
2212 SearchStack* ss = tsp->sstack[threadID] + 1;
2216 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2218 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2220 assert(threads[threadID].state == THREAD_SEARCHING);
2222 threads[threadID].state = THREAD_AVAILABLE;
2224 // Wake up master thread so to allow it to return from the idle loop in
2225 // case we are the last slave of the split point.
2226 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2227 wake_sleeping_thread(tsp->master);
2230 // If this thread is the master of a split point and all slaves have
2231 // finished their work at this split point, return from the idle loop.
2232 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2233 allFinished = (i == activeThreads);
2237 // Because sp->slaves[] is reset under lock protection,
2238 // be sure sp->lock has been released before to return.
2239 lock_grab(&(sp->lock));
2240 lock_release(&(sp->lock));
2242 // In helpful master concept a master can help only a sub-tree, and
2243 // because here is all finished is not possible master is booked.
2244 assert(threads[threadID].state == THREAD_AVAILABLE);
2246 threads[threadID].state = THREAD_SEARCHING;
2253 // init_threads() is called during startup. It launches all helper threads,
2254 // and initializes the split point stack and the global locks and condition
2257 void ThreadsManager::init_threads() {
2259 int i, arg[MAX_THREADS];
2262 // Initialize global locks
2265 for (i = 0; i < MAX_THREADS; i++)
2267 lock_init(&sleepLock[i]);
2268 cond_init(&sleepCond[i]);
2271 // Initialize splitPoints[] locks
2272 for (i = 0; i < MAX_THREADS; i++)
2273 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2274 lock_init(&(threads[i].splitPoints[j].lock));
2276 // Will be set just before program exits to properly end the threads
2277 allThreadsShouldExit = false;
2279 // Threads will be put all threads to sleep as soon as created
2282 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2283 threads[0].state = THREAD_SEARCHING;
2284 for (i = 1; i < MAX_THREADS; i++)
2285 threads[i].state = THREAD_INITIALIZING;
2287 // Launch the helper threads
2288 for (i = 1; i < MAX_THREADS; i++)
2292 #if !defined(_MSC_VER)
2293 pthread_t pthread[1];
2294 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2295 pthread_detach(pthread[0]);
2297 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2301 cout << "Failed to create thread number " << i << endl;
2305 // Wait until the thread has finished launching and is gone to sleep
2306 while (threads[i].state == THREAD_INITIALIZING) {}
2311 // exit_threads() is called when the program exits. It makes all the
2312 // helper threads exit cleanly.
2314 void ThreadsManager::exit_threads() {
2316 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2318 // Wake up all the threads and waits for termination
2319 for (int i = 1; i < MAX_THREADS; i++)
2321 wake_sleeping_thread(i);
2322 while (threads[i].state != THREAD_TERMINATED) {}
2325 // Now we can safely destroy the locks
2326 for (int i = 0; i < MAX_THREADS; i++)
2327 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2328 lock_destroy(&(threads[i].splitPoints[j].lock));
2330 lock_destroy(&mpLock);
2332 // Now we can safely destroy the wait conditions
2333 for (int i = 0; i < MAX_THREADS; i++)
2335 lock_destroy(&sleepLock[i]);
2336 cond_destroy(&sleepCond[i]);
2341 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2342 // the thread's currently active split point, or in some ancestor of
2343 // the current split point.
2345 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2347 assert(threadID >= 0 && threadID < activeThreads);
2349 SplitPoint* sp = threads[threadID].splitPoint;
2351 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2356 // thread_is_available() checks whether the thread with threadID "slave" is
2357 // available to help the thread with threadID "master" at a split point. An
2358 // obvious requirement is that "slave" must be idle. With more than two
2359 // threads, this is not by itself sufficient: If "slave" is the master of
2360 // some active split point, it is only available as a slave to the other
2361 // threads which are busy searching the split point at the top of "slave"'s
2362 // split point stack (the "helpful master concept" in YBWC terminology).
2364 bool ThreadsManager::thread_is_available(int slave, int master) const {
2366 assert(slave >= 0 && slave < activeThreads);
2367 assert(master >= 0 && master < activeThreads);
2368 assert(activeThreads > 1);
2370 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2373 // Make a local copy to be sure doesn't change under our feet
2374 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2376 // No active split points means that the thread is available as
2377 // a slave for any other thread.
2378 if (localActiveSplitPoints == 0 || activeThreads == 2)
2381 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2382 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2383 // could have been set to 0 by another thread leading to an out of bound access.
2384 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2391 // available_thread_exists() tries to find an idle thread which is available as
2392 // a slave for the thread with threadID "master".
2394 bool ThreadsManager::available_thread_exists(int master) const {
2396 assert(master >= 0 && master < activeThreads);
2397 assert(activeThreads > 1);
2399 for (int i = 0; i < activeThreads; i++)
2400 if (thread_is_available(i, master))
2407 // split() does the actual work of distributing the work at a node between
2408 // several available threads. If it does not succeed in splitting the
2409 // node (because no idle threads are available, or because we have no unused
2410 // split point objects), the function immediately returns. If splitting is
2411 // possible, a SplitPoint object is initialized with all the data that must be
2412 // copied to the helper threads and we tell our helper threads that they have
2413 // been assigned work. This will cause them to instantly leave their idle loops and
2414 // call search().When all threads have returned from search() then split() returns.
2416 template <bool Fake>
2417 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2418 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2419 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2420 assert(pos.is_ok());
2421 assert(ply > 0 && ply < PLY_MAX);
2422 assert(*bestValue >= -VALUE_INFINITE);
2423 assert(*bestValue <= *alpha);
2424 assert(*alpha < beta);
2425 assert(beta <= VALUE_INFINITE);
2426 assert(depth > DEPTH_ZERO);
2427 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2428 assert(activeThreads > 1);
2430 int i, master = pos.thread();
2431 Thread& masterThread = threads[master];
2435 // If no other thread is available to help us, or if we have too many
2436 // active split points, don't split.
2437 if ( !available_thread_exists(master)
2438 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2440 lock_release(&mpLock);
2444 // Pick the next available split point object from the split point stack
2445 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2447 // Initialize the split point object
2448 splitPoint.parent = masterThread.splitPoint;
2449 splitPoint.master = master;
2450 splitPoint.betaCutoff = false;
2451 splitPoint.ply = ply;
2452 splitPoint.depth = depth;
2453 splitPoint.threatMove = threatMove;
2454 splitPoint.mateThreat = mateThreat;
2455 splitPoint.alpha = *alpha;
2456 splitPoint.beta = beta;
2457 splitPoint.pvNode = pvNode;
2458 splitPoint.bestValue = *bestValue;
2460 splitPoint.moveCount = moveCount;
2461 splitPoint.pos = &pos;
2462 splitPoint.nodes = 0;
2463 splitPoint.parentSstack = ss;
2464 for (i = 0; i < activeThreads; i++)
2465 splitPoint.slaves[i] = 0;
2467 masterThread.splitPoint = &splitPoint;
2469 // If we are here it means we are not available
2470 assert(masterThread.state != THREAD_AVAILABLE);
2472 int workersCnt = 1; // At least the master is included
2474 // Allocate available threads setting state to THREAD_BOOKED
2475 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2476 if (thread_is_available(i, master))
2478 threads[i].state = THREAD_BOOKED;
2479 threads[i].splitPoint = &splitPoint;
2480 splitPoint.slaves[i] = 1;
2484 assert(Fake || workersCnt > 1);
2486 // We can release the lock because slave threads are already booked and master is not available
2487 lock_release(&mpLock);
2489 // Tell the threads that they have work to do. This will make them leave
2490 // their idle loop. But before copy search stack tail for each thread.
2491 for (i = 0; i < activeThreads; i++)
2492 if (i == master || splitPoint.slaves[i])
2494 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2496 assert(i == master || threads[i].state == THREAD_BOOKED);
2498 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2500 if (useSleepingThreads && i != master)
2501 wake_sleeping_thread(i);
2504 // Everything is set up. The master thread enters the idle loop, from
2505 // which it will instantly launch a search, because its state is
2506 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2507 // idle loop, which means that the main thread will return from the idle
2508 // loop when all threads have finished their work at this split point.
2509 idle_loop(master, &splitPoint);
2511 // We have returned from the idle loop, which means that all threads are
2512 // finished. Update alpha and bestValue, and return.
2515 *alpha = splitPoint.alpha;
2516 *bestValue = splitPoint.bestValue;
2517 masterThread.activeSplitPoints--;
2518 masterThread.splitPoint = splitPoint.parent;
2519 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2521 lock_release(&mpLock);
2525 // wake_sleeping_thread() wakes up the thread with the given threadID
2526 // when it is time to start a new search.
2528 void ThreadsManager::wake_sleeping_thread(int threadID) {
2530 lock_grab(&sleepLock[threadID]);
2531 cond_signal(&sleepCond[threadID]);
2532 lock_release(&sleepLock[threadID]);
2536 /// RootMove and RootMoveList method's definitions
2538 RootMove::RootMove() {
2541 pv_score = non_pv_score = -VALUE_INFINITE;
2545 RootMove& RootMove::operator=(const RootMove& rm) {
2547 const Move* src = rm.pv;
2550 // Avoid a costly full rm.pv[] copy
2551 do *dst++ = *src; while (*src++ != MOVE_NONE);
2554 pv_score = rm.pv_score;
2555 non_pv_score = rm.non_pv_score;
2559 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2560 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2561 // allow to always have a ponder move even when we fail high at root and also a
2562 // long PV to print that is important for position analysis.
2564 void RootMove::extract_pv_from_tt(Position& pos) {
2566 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2570 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2572 pos.do_move(pv[0], *st++);
2574 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2575 && tte->move() != MOVE_NONE
2576 && move_is_legal(pos, tte->move())
2578 && (!pos.is_draw() || ply < 2))
2580 pv[ply] = tte->move();
2581 pos.do_move(pv[ply++], *st++);
2583 pv[ply] = MOVE_NONE;
2585 do pos.undo_move(pv[--ply]); while (ply);
2588 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2589 // the PV back into the TT. This makes sure the old PV moves are searched
2590 // first, even if the old TT entries have been overwritten.
2592 void RootMove::insert_pv_in_tt(Position& pos) {
2594 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2597 Value v, m = VALUE_NONE;
2600 assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
2604 tte = TT.retrieve(k);
2606 // Don't overwrite exsisting correct entries
2607 if (!tte || tte->move() != pv[ply])
2609 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2610 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2612 pos.do_move(pv[ply], *st++);
2614 } while (pv[++ply] != MOVE_NONE);
2616 do pos.undo_move(pv[--ply]); while (ply);
2619 // pv_info_to_uci() returns a string with information on the current PV line
2620 // formatted according to UCI specification and eventually writes the info
2621 // to a log file. It is called at each iteration or after a new pv is found.
2623 std::string RootMove::pv_info_to_uci(const Position& pos, Value alpha, Value beta, int pvLine) {
2625 std::stringstream s, l;
2628 while (*m != MOVE_NONE)
2631 s << "info depth " << Iteration // FIXME
2632 << " seldepth " << int(m - pv)
2633 << " multipv " << pvLine + 1
2634 << " score " << value_to_uci(pv_score)
2635 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2636 << " time " << current_search_time()
2637 << " nodes " << pos.nodes_searched()
2638 << " nps " << nps(pos)
2639 << " pv " << l.str();
2641 if (UseLogFile && pvLine == 0)
2643 ValueType t = pv_score >= beta ? VALUE_TYPE_LOWER :
2644 pv_score <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2646 LogFile << pretty_pv(pos, current_search_time(), Iteration, pv_score, t, pv) << endl;
2652 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2654 SearchStack ss[PLY_MAX_PLUS_2];
2655 MoveStack mlist[MOVES_MAX];
2659 // Initialize search stack
2660 init_ss_array(ss, PLY_MAX_PLUS_2);
2661 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2663 // Generate all legal moves
2664 MoveStack* last = generate_moves(pos, mlist);
2666 // Add each move to the RootMoveList's vector
2667 for (MoveStack* cur = mlist; cur != last; cur++)
2669 // If we have a searchMoves[] list then verify cur->move
2670 // is in the list before to add it.
2671 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2673 if (searchMoves[0] && *sm != cur->move)
2676 // Find a quick score for the move and add to the list
2677 pos.do_move(cur->move, st);
2680 rm.pv[0] = ss[0].currentMove = cur->move;
2681 rm.pv[1] = MOVE_NONE;
2682 rm.pv_score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2685 pos.undo_move(cur->move);
2690 // Score root moves using the standard way used in main search, the moves
2691 // are scored according to the order in which are returned by MovePicker.
2692 // This is the second order score that is used to compare the moves when
2693 // the first order pv scores of both moves are equal.
2695 void RootMoveList::set_non_pv_scores(const Position& pos)
2698 Value score = VALUE_ZERO;
2699 MovePicker mp(pos, MOVE_NONE, ONE_PLY, H);
2701 while ((move = mp.get_next_move()) != MOVE_NONE)
2702 for (Base::iterator it = begin(); it != end(); ++it)
2703 if (it->pv[0] == move)
2705 it->non_pv_score = score--;