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/>.
44 #include "ucioption.h"
50 //// Local definitions
56 enum NodeType { NonPV, PV };
58 // Set to true to force running with one thread.
59 // Used for debugging SMP code.
60 const bool FakeSplit = false;
62 // Fast lookup table of sliding pieces indexed by Piece
63 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
64 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
66 // ThreadsManager class is used to handle all the threads related stuff in search,
67 // init, starting, parking and, the most important, launching a slave thread at a
68 // split point are what this class does. All the access to shared thread data is
69 // done through this class, so that we avoid using global variables instead.
71 class ThreadsManager {
72 /* As long as the single ThreadsManager object is defined as a global we don't
73 need to explicitly initialize to zero its data members because variables with
74 static storage duration are automatically set to zero before enter main()
80 int active_threads() const { return ActiveThreads; }
81 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
83 bool available_thread_exists(int master) const;
84 bool thread_is_available(int slave, int master) const;
85 bool thread_should_stop(int threadID) const;
86 void wake_sleeping_thread(int threadID);
87 void idle_loop(int threadID, SplitPoint* sp);
90 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
91 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
95 volatile bool AllThreadsShouldExit;
96 Thread threads[MAX_THREADS];
97 Lock MPLock, WaitLock;
98 WaitCondition WaitCond[MAX_THREADS];
102 // RootMove struct is used for moves at the root at the tree. For each
103 // root move, we store a score, a node count, and a PV (really a refutation
104 // in the case of moves which fail low).
108 RootMove() : mp_score(0), nodes(0) {}
110 // RootMove::operator<() is the comparison function used when
111 // sorting the moves. A move m1 is considered to be better
112 // than a move m2 if it has a higher score, or if the moves
113 // have equal score but m1 has the higher beta cut-off count.
114 bool operator<(const RootMove& m) const {
116 return score != m.score ? score < m.score : mp_score <= m.mp_score;
123 Move pv[PLY_MAX_PLUS_2];
127 // The RootMoveList class is essentially an array of RootMove objects, with
128 // a handful of methods for accessing the data in the individual moves.
133 RootMoveList(Position& pos, Move searchMoves[]);
135 Move move(int moveNum) const { return moves[moveNum].move; }
136 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
137 int move_count() const { return count; }
138 Value move_score(int moveNum) const { return moves[moveNum].score; }
139 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
140 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
141 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
143 void set_move_pv(int moveNum, const Move pv[]);
144 void score_moves(const Position& pos);
146 void sort_multipv(int n);
149 RootMove moves[MOVES_MAX];
154 // When formatting a move for std::cout we must know if we are in Chess960
155 // or not. To keep using the handy operator<<() on the move the trick is to
156 // embed this flag in the stream itself. Function-like named enum set960 is
157 // used as a custom manipulator and the stream internal general-purpose array,
158 // accessed through ios_base::iword(), is used to pass the flag to the move's
159 // operator<<() that will use it to properly format castling moves.
162 std::ostream& operator<< (std::ostream& os, const set960& m) {
164 os.iword(0) = int(m);
173 // Maximum depth for razoring
174 const Depth RazorDepth = 4 * ONE_PLY;
176 // Dynamic razoring margin based on depth
177 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
179 // Maximum depth for use of dynamic threat detection when null move fails low
180 const Depth ThreatDepth = 5 * ONE_PLY;
182 // Step 9. Internal iterative deepening
184 // Minimum depth for use of internal iterative deepening
185 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
187 // At Non-PV nodes we do an internal iterative deepening search
188 // when the static evaluation is bigger then beta - IIDMargin.
189 const Value IIDMargin = Value(0x100);
191 // Step 11. Decide the new search depth
193 // Extensions. Configurable UCI options
194 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
195 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
196 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
198 // Minimum depth for use of singular extension
199 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
201 // If the TT move is at least SingularExtensionMargin better then the
202 // remaining ones we will extend it.
203 const Value SingularExtensionMargin = Value(0x20);
205 // Step 12. Futility pruning
207 // Futility margin for quiescence search
208 const Value FutilityMarginQS = Value(0x80);
210 // Futility lookup tables (initialized at startup) and their getter functions
211 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
212 int FutilityMoveCountArray[32]; // [depth]
214 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
215 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
217 // Step 14. Reduced search
219 // Reduction lookup tables (initialized at startup) and their getter functions
220 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
222 template <NodeType PV>
223 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
225 // Common adjustments
227 // Search depth at iteration 1
228 const Depth InitialDepth = ONE_PLY;
230 // Easy move margin. An easy move candidate must be at least this much
231 // better than the second best move.
232 const Value EasyMoveMargin = Value(0x200);
235 /// Namespace variables
243 // Scores and number of times the best move changed for each iteration
244 Value ValueByIteration[PLY_MAX_PLUS_2];
245 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
247 // Search window management
253 // Time managment variables
254 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
255 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
256 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
261 std::ofstream LogFile;
263 // Multi-threads related variables
264 Depth MinimumSplitDepth;
265 int MaxThreadsPerSplitPoint;
266 bool UseSleepingThreads;
267 ThreadsManager ThreadsMgr;
269 // Node counters, used only by thread[0] but try to keep in different cache
270 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
272 int NodesBetweenPolls = 30000;
279 Value id_loop(Position& pos, Move searchMoves[]);
280 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
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 connected_moves(const Position& pos, Move m1, Move m2);
299 bool value_is_mate(Value value);
300 Value value_to_tt(Value v, int ply);
301 Value value_from_tt(Value v, int ply);
302 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
303 bool connected_threat(const Position& pos, Move m, Move threat);
304 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
305 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
306 void update_killers(Move m, SearchStack* ss);
307 void update_gains(const Position& pos, Move move, Value before, Value after);
309 int current_search_time();
310 std::string value_to_uci(Value v);
311 int nps(const Position& pos);
312 void poll(const Position& pos);
314 void wait_for_stop_or_ponderhit();
315 void init_ss_array(SearchStack* ss, int size);
316 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
317 void insert_pv_in_tt(const Position& pos, Move pv[]);
318 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
320 #if !defined(_MSC_VER)
321 void* init_thread(void* threadID);
323 DWORD WINAPI init_thread(LPVOID threadID);
333 /// init_threads(), exit_threads() and nodes_searched() are helpers to
334 /// give accessibility to some TM methods from outside of current file.
336 void init_threads() { ThreadsMgr.init_threads(); }
337 void exit_threads() { ThreadsMgr.exit_threads(); }
340 /// init_search() is called during startup. It initializes various lookup tables
344 int d; // depth (ONE_PLY == 2)
345 int hd; // half depth (ONE_PLY == 1)
348 // Init reductions array
349 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
351 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
352 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
353 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
354 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
357 // Init futility margins array
358 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
359 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
361 // Init futility move count array
362 for (d = 0; d < 32; d++)
363 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
367 /// perft() is our utility to verify move generation is bug free. All the legal
368 /// moves up to given depth are generated and counted and the sum returned.
370 int perft(Position& pos, Depth depth)
372 MoveStack mlist[MOVES_MAX];
377 // Generate all legal moves
378 MoveStack* last = generate_moves(pos, mlist);
380 // If we are at the last ply we don't need to do and undo
381 // the moves, just to count them.
382 if (depth <= ONE_PLY)
383 return int(last - mlist);
385 // Loop through all legal moves
387 for (MoveStack* cur = mlist; cur != last; cur++)
390 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
391 sum += perft(pos, depth - ONE_PLY);
398 /// think() is the external interface to Stockfish's search, and is called when
399 /// the program receives the UCI 'go' command. It initializes various
400 /// search-related global variables, and calls root_search(). It returns false
401 /// when a quit command is received during the search.
403 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
404 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
406 // Initialize global search variables
407 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
409 SearchStartTime = get_system_time();
410 ExactMaxTime = maxTime;
413 InfiniteSearch = infinite;
414 PonderSearch = ponder;
415 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
417 // Look for a book move, only during games, not tests
418 if (UseTimeManagement && Options["OwnBook"].value<bool>())
420 if (Options["Book File"].value<std::string>() != OpeningBook.file_name())
421 OpeningBook.open(Options["Book File"].value<std::string>());
423 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
424 if (bookMove != MOVE_NONE)
427 wait_for_stop_or_ponderhit();
429 cout << "bestmove " << bookMove << endl;
434 // Read UCI option values
435 TT.set_size(Options["Hash"].value<int>());
436 if (Options["Clear Hash"].value<bool>())
438 Options["Clear Hash"].set_value("false");
442 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
443 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
444 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
445 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
446 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
447 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
448 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
449 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
450 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
451 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
452 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
453 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
455 MinimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
456 MaxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
457 MultiPV = Options["MultiPV"].value<int>();
458 UseLogFile = Options["Use Search Log"].value<bool>();
459 UseSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
462 LogFile.open(Options["Search Log Filename"].value<std::string>().c_str(), std::ios::out | std::ios::app);
464 read_weights(pos.side_to_move());
466 // Set the number of active threads
467 int newActiveThreads = Options["Threads"].value<int>();
468 if (newActiveThreads != ThreadsMgr.active_threads())
470 ThreadsMgr.set_active_threads(newActiveThreads);
471 init_eval(newActiveThreads);
474 // Wake up needed threads
475 for (int i = 1; i < newActiveThreads; i++)
476 ThreadsMgr.wake_sleeping_thread(i);
479 int myTime = time[pos.side_to_move()];
480 int myIncrement = increment[pos.side_to_move()];
481 if (UseTimeManagement)
482 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
484 // Set best NodesBetweenPolls interval to avoid lagging under
485 // heavy time pressure.
487 NodesBetweenPolls = Min(MaxNodes, 30000);
488 else if (myTime && myTime < 1000)
489 NodesBetweenPolls = 1000;
490 else if (myTime && myTime < 5000)
491 NodesBetweenPolls = 5000;
493 NodesBetweenPolls = 30000;
495 // Write search information to log file
497 LogFile << "Searching: " << pos.to_fen() << endl
498 << "infinite: " << infinite
499 << " ponder: " << ponder
500 << " time: " << myTime
501 << " increment: " << myIncrement
502 << " moves to go: " << movesToGo << endl;
504 // We're ready to start thinking. Call the iterative deepening loop function
505 id_loop(pos, searchMoves);
510 // This makes all the threads to go to sleep
511 ThreadsMgr.set_active_threads(1);
519 // id_loop() is the main iterative deepening loop. It calls root_search
520 // repeatedly with increasing depth until the allocated thinking time has
521 // been consumed, the user stops the search, or the maximum search depth is
524 Value id_loop(Position& pos, Move searchMoves[]) {
526 SearchStack ss[PLY_MAX_PLUS_2];
527 Move pv[PLY_MAX_PLUS_2];
528 Move EasyMove = MOVE_NONE;
529 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
531 // Moves to search are verified, copied, scored and sorted
532 RootMoveList rml(pos, searchMoves);
534 // Handle special case of searching on a mate/stale position
535 if (rml.move_count() == 0)
538 wait_for_stop_or_ponderhit();
540 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
543 // Print RootMoveList startup scoring to the standard output,
544 // so to output information also for iteration 1.
545 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
546 << "info depth " << 1
547 << "\ninfo depth " << 1
548 << " score " << value_to_uci(rml.move_score(0))
549 << " time " << current_search_time()
550 << " nodes " << pos.nodes_searched()
551 << " nps " << nps(pos)
552 << " pv " << rml.move(0) << "\n";
557 init_ss_array(ss, PLY_MAX_PLUS_2);
558 pv[0] = pv[1] = MOVE_NONE;
559 ValueByIteration[1] = rml.move_score(0);
562 // Is one move significantly better than others after initial scoring ?
563 if ( rml.move_count() == 1
564 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
565 EasyMove = rml.move(0);
567 // Iterative deepening loop
568 while (Iteration < PLY_MAX)
570 // Initialize iteration
572 BestMoveChangesByIteration[Iteration] = 0;
574 cout << "info depth " << Iteration << endl;
576 // Calculate dynamic aspiration window based on previous iterations
577 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
579 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
580 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
582 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
583 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
585 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
586 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
589 // Search to the current depth, rml is updated and sorted, alpha and beta could change
590 value = root_search(pos, ss, pv, rml, &alpha, &beta);
592 // Write PV to transposition table, in case the relevant entries have
593 // been overwritten during the search.
594 insert_pv_in_tt(pos, pv);
597 break; // Value cannot be trusted. Break out immediately!
599 //Save info about search result
600 ValueByIteration[Iteration] = value;
602 // Drop the easy move if differs from the new best move
603 if (pv[0] != EasyMove)
604 EasyMove = MOVE_NONE;
606 if (UseTimeManagement)
609 bool stopSearch = false;
611 // Stop search early if there is only a single legal move,
612 // we search up to Iteration 6 anyway to get a proper score.
613 if (Iteration >= 6 && rml.move_count() == 1)
616 // Stop search early when the last two iterations returned a mate score
618 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
619 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
622 // Stop search early if one move seems to be much better than the others
625 && ( ( rml.move_nodes(0) > (pos.nodes_searched() * 85) / 100
626 && current_search_time() > TimeMgr.available_time() / 16)
627 ||( rml.move_nodes(0) > (pos.nodes_searched() * 98) / 100
628 && current_search_time() > TimeMgr.available_time() / 32)))
631 // Add some extra time if the best move has changed during the last two iterations
632 if (Iteration > 5 && Iteration <= 50)
633 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
634 BestMoveChangesByIteration[Iteration-1]);
636 // Stop search if most of MaxSearchTime is consumed at the end of the
637 // iteration. We probably don't have enough time to search the first
638 // move at the next iteration anyway.
639 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
645 StopOnPonderhit = true;
651 if (MaxDepth && Iteration >= MaxDepth)
655 // If we are pondering or in infinite search, we shouldn't print the
656 // best move before we are told to do so.
657 if (!AbortSearch && (PonderSearch || InfiniteSearch))
658 wait_for_stop_or_ponderhit();
660 // Print final search statistics
661 cout << "info nodes " << pos.nodes_searched()
662 << " nps " << nps(pos)
663 << " time " << current_search_time() << endl;
665 // Print the best move and the ponder move to the standard output
666 if (pv[0] == MOVE_NONE || MultiPV > 1)
672 assert(pv[0] != MOVE_NONE);
674 cout << "bestmove " << pv[0];
676 if (pv[1] != MOVE_NONE)
677 cout << " ponder " << pv[1];
684 dbg_print_mean(LogFile);
686 if (dbg_show_hit_rate)
687 dbg_print_hit_rate(LogFile);
689 LogFile << "\nNodes: " << pos.nodes_searched()
690 << "\nNodes/second: " << nps(pos)
691 << "\nBest move: " << move_to_san(pos, pv[0]);
694 pos.do_move(pv[0], st);
695 LogFile << "\nPonder move: "
696 << move_to_san(pos, pv[1]) // Works also with MOVE_NONE
699 return rml.move_score(0);
703 // root_search() is the function which searches the root node. It is
704 // similar to search_pv except that it uses a different move ordering
705 // scheme, prints some information to the standard output and handles
706 // the fail low/high loops.
708 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
714 Depth depth, ext, newDepth;
715 Value value, alpha, beta;
716 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
717 int researchCountFH, researchCountFL;
719 researchCountFH = researchCountFL = 0;
722 isCheck = pos.is_check();
723 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
725 // Step 1. Initialize node (polling is omitted at root)
726 ss->currentMove = ss->bestMove = MOVE_NONE;
728 // Step 2. Check for aborted search (omitted at root)
729 // Step 3. Mate distance pruning (omitted at root)
730 // Step 4. Transposition table lookup (omitted at root)
732 // Step 5. Evaluate the position statically
733 // At root we do this only to get reference value for child nodes
734 ss->evalMargin = VALUE_NONE;
735 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
737 // Step 6. Razoring (omitted at root)
738 // Step 7. Static null move pruning (omitted at root)
739 // Step 8. Null move search with verification search (omitted at root)
740 // Step 9. Internal iterative deepening (omitted at root)
742 // Step extra. Fail low loop
743 // We start with small aspiration window and in case of fail low, we research
744 // with bigger window until we are not failing low anymore.
747 // Sort the moves before to (re)search
748 rml.score_moves(pos);
751 // Step 10. Loop through all moves in the root move list
752 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
754 // This is used by time management
755 FirstRootMove = (i == 0);
757 // Save the current node count before the move is searched
758 nodes = pos.nodes_searched();
760 // Pick the next root move, and print the move and the move number to
761 // the standard output.
762 move = ss->currentMove = rml.move(i);
764 if (current_search_time() >= 1000)
765 cout << "info currmove " << move
766 << " currmovenumber " << i + 1 << endl;
768 moveIsCheck = pos.move_is_check(move);
769 captureOrPromotion = pos.move_is_capture_or_promotion(move);
771 // Step 11. Decide the new search depth
772 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
773 newDepth = depth + ext;
775 // Step 12. Futility pruning (omitted at root)
777 // Step extra. Fail high loop
778 // If move fails high, we research with bigger window until we are not failing
780 value = - VALUE_INFINITE;
784 // Step 13. Make the move
785 pos.do_move(move, st, ci, moveIsCheck);
787 // Step extra. pv search
788 // We do pv search for first moves (i < MultiPV)
789 // and for fail high research (value > alpha)
790 if (i < MultiPV || value > alpha)
792 // Aspiration window is disabled in multi-pv case
794 alpha = -VALUE_INFINITE;
796 // Full depth PV search, done on first move or after a fail high
797 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
801 // Step 14. Reduced search
802 // if the move fails high will be re-searched at full depth
803 bool doFullDepthSearch = true;
805 if ( depth >= 3 * ONE_PLY
807 && !captureOrPromotion
808 && !move_is_castle(move))
810 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
813 assert(newDepth-ss->reduction >= ONE_PLY);
815 // Reduced depth non-pv search using alpha as upperbound
816 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
817 doFullDepthSearch = (value > alpha);
820 // The move failed high, but if reduction is very big we could
821 // face a false positive, retry with a less aggressive reduction,
822 // if the move fails high again then go with full depth search.
823 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
825 assert(newDepth - ONE_PLY >= ONE_PLY);
827 ss->reduction = ONE_PLY;
828 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
829 doFullDepthSearch = (value > alpha);
831 ss->reduction = DEPTH_ZERO; // Restore original reduction
834 // Step 15. Full depth search
835 if (doFullDepthSearch)
837 // Full depth non-pv search using alpha as upperbound
838 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
840 // If we are above alpha then research at same depth but as PV
841 // to get a correct score or eventually a fail high above beta.
843 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
847 // Step 16. Undo move
850 // Can we exit fail high loop ?
851 if (AbortSearch || value < beta)
854 // We are failing high and going to do a research. It's important to update
855 // the score before research in case we run out of time while researching.
856 rml.set_move_score(i, value);
858 extract_pv_from_tt(pos, move, pv);
859 rml.set_move_pv(i, pv);
861 // Print information to the standard output
862 print_pv_info(pos, pv, alpha, beta, value);
864 // Prepare for a research after a fail high, each time with a wider window
865 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
868 } // End of fail high loop
870 // Finished searching the move. If AbortSearch is true, the search
871 // was aborted because the user interrupted the search or because we
872 // ran out of time. In this case, the return value of the search cannot
873 // be trusted, and we break out of the loop without updating the best
878 // Remember searched nodes counts for this move
879 rml.add_move_nodes(i, pos.nodes_searched() - nodes);
881 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
882 assert(value < beta);
884 // Step 17. Check for new best move
885 if (value <= alpha && i >= MultiPV)
886 rml.set_move_score(i, -VALUE_INFINITE);
889 // PV move or new best move!
892 rml.set_move_score(i, value);
894 extract_pv_from_tt(pos, move, pv);
895 rml.set_move_pv(i, pv);
899 // We record how often the best move has been changed in each
900 // iteration. This information is used for time managment: When
901 // the best move changes frequently, we allocate some more time.
903 BestMoveChangesByIteration[Iteration]++;
905 // Print information to the standard output
906 print_pv_info(pos, pv, alpha, beta, value);
908 // Raise alpha to setup proper non-pv search upper bound
915 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
917 cout << "info multipv " << j + 1
918 << " score " << value_to_uci(rml.move_score(j))
919 << " depth " << (j <= i ? Iteration : Iteration - 1)
920 << " time " << current_search_time()
921 << " nodes " << pos.nodes_searched()
922 << " nps " << nps(pos)
925 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
926 cout << rml.move_pv(j, k) << " ";
930 alpha = rml.move_score(Min(i, MultiPV - 1));
932 } // PV move or new best move
934 assert(alpha >= *alphaPtr);
936 AspirationFailLow = (alpha == *alphaPtr);
938 if (AspirationFailLow && StopOnPonderhit)
939 StopOnPonderhit = false;
942 // Can we exit fail low loop ?
943 if (AbortSearch || !AspirationFailLow)
946 // Prepare for a research after a fail low, each time with a wider window
947 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
952 // Sort the moves before to return
959 // search<>() is the main search function for both PV and non-PV nodes and for
960 // normal and SplitPoint nodes. When called just after a split point the search
961 // is simpler because we have already probed the hash table, done a null move
962 // search, and searched the first move before splitting, we don't have to repeat
963 // all this work again. We also don't need to store anything to the hash table
964 // here: This is taken care of after we return from the split point.
966 template <NodeType PvNode, bool SpNode>
967 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
969 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
970 assert(beta > alpha && beta <= VALUE_INFINITE);
971 assert(PvNode || alpha == beta - 1);
972 assert(ply > 0 && ply < PLY_MAX);
973 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
975 Move movesSearched[MOVES_MAX];
979 Move ttMove, move, excludedMove, threatMove;
982 Value bestValue, value, oldAlpha;
983 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
984 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
985 bool mateThreat = false;
987 int threadID = pos.thread();
988 SplitPoint* sp = NULL;
989 refinedValue = bestValue = value = -VALUE_INFINITE;
991 isCheck = pos.is_check();
997 ttMove = excludedMove = MOVE_NONE;
998 threatMove = sp->threatMove;
999 mateThreat = sp->mateThreat;
1000 goto split_point_start;
1001 } else {} // Hack to fix icc's "statement is unreachable" warning
1003 // Step 1. Initialize node and poll. Polling can abort search
1004 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
1005 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1007 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1013 // Step 2. Check for aborted search and immediate draw
1014 if ( AbortSearch || ThreadsMgr.thread_should_stop(threadID)
1015 || pos.is_draw() || ply >= PLY_MAX - 1)
1018 // Step 3. Mate distance pruning
1019 alpha = Max(value_mated_in(ply), alpha);
1020 beta = Min(value_mate_in(ply+1), beta);
1024 // Step 4. Transposition table lookup
1026 // We don't want the score of a partial search to overwrite a previous full search
1027 // TT value, so we use a different position key in case of an excluded move exists.
1028 excludedMove = ss->excludedMove;
1029 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1031 tte = TT.retrieve(posKey);
1032 ttMove = tte ? tte->move() : MOVE_NONE;
1034 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1035 // This is to avoid problems in the following areas:
1037 // * Repetition draw detection
1038 // * Fifty move rule detection
1039 // * Searching for a mate
1040 // * Printing of full PV line
1041 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1044 ss->bestMove = ttMove; // Can be MOVE_NONE
1045 return value_from_tt(tte->value(), ply);
1048 // Step 5. Evaluate the position statically and
1049 // update gain statistics of parent move.
1051 ss->eval = ss->evalMargin = VALUE_NONE;
1054 assert(tte->static_value() != VALUE_NONE);
1056 ss->eval = tte->static_value();
1057 ss->evalMargin = tte->static_value_margin();
1058 refinedValue = refine_eval(tte, ss->eval, ply);
1062 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1063 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1066 // Save gain for the parent non-capture move
1067 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1069 // Step 6. Razoring (is omitted in PV nodes)
1071 && depth < RazorDepth
1073 && refinedValue < beta - razor_margin(depth)
1074 && ttMove == MOVE_NONE
1075 && !value_is_mate(beta)
1076 && !pos.has_pawn_on_7th(pos.side_to_move()))
1078 Value rbeta = beta - razor_margin(depth);
1079 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1081 // Logically we should return (v + razor_margin(depth)), but
1082 // surprisingly this did slightly weaker in tests.
1086 // Step 7. Static null move pruning (is omitted in PV nodes)
1087 // We're betting that the opponent doesn't have a move that will reduce
1088 // the score by more than futility_margin(depth) if we do a null move.
1090 && !ss->skipNullMove
1091 && depth < RazorDepth
1093 && refinedValue >= beta + futility_margin(depth, 0)
1094 && !value_is_mate(beta)
1095 && pos.non_pawn_material(pos.side_to_move()))
1096 return refinedValue - futility_margin(depth, 0);
1098 // Step 8. Null move search with verification search (is omitted in PV nodes)
1100 && !ss->skipNullMove
1103 && refinedValue >= beta
1104 && !value_is_mate(beta)
1105 && pos.non_pawn_material(pos.side_to_move()))
1107 ss->currentMove = MOVE_NULL;
1109 // Null move dynamic reduction based on depth
1110 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1112 // Null move dynamic reduction based on value
1113 if (refinedValue - beta > PawnValueMidgame)
1116 pos.do_null_move(st);
1117 (ss+1)->skipNullMove = true;
1118 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1119 (ss+1)->skipNullMove = false;
1120 pos.undo_null_move();
1122 if (nullValue >= beta)
1124 // Do not return unproven mate scores
1125 if (nullValue >= value_mate_in(PLY_MAX))
1128 if (depth < 6 * ONE_PLY)
1131 // Do verification search at high depths
1132 ss->skipNullMove = true;
1133 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1134 ss->skipNullMove = false;
1141 // The null move failed low, which means that we may be faced with
1142 // some kind of threat. If the previous move was reduced, check if
1143 // the move that refuted the null move was somehow connected to the
1144 // move which was reduced. If a connection is found, return a fail
1145 // low score (which will cause the reduced move to fail high in the
1146 // parent node, which will trigger a re-search with full depth).
1147 if (nullValue == value_mated_in(ply + 2))
1150 threatMove = (ss+1)->bestMove;
1151 if ( depth < ThreatDepth
1152 && (ss-1)->reduction
1153 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1158 // Step 9. Internal iterative deepening
1159 if ( depth >= IIDDepth[PvNode]
1160 && ttMove == MOVE_NONE
1161 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1163 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1165 ss->skipNullMove = true;
1166 search<PvNode>(pos, ss, alpha, beta, d, ply);
1167 ss->skipNullMove = false;
1169 ttMove = ss->bestMove;
1170 tte = TT.retrieve(posKey);
1173 // Expensive mate threat detection (only for PV nodes)
1175 mateThreat = pos.has_mate_threat();
1177 split_point_start: // At split points actual search starts from here
1179 // Initialize a MovePicker object for the current position
1180 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1181 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1182 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1184 ss->bestMove = MOVE_NONE;
1185 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1186 futilityBase = ss->eval + ss->evalMargin;
1187 singularExtensionNode = !SpNode
1188 && depth >= SingularExtensionDepth[PvNode]
1191 && !excludedMove // Do not allow recursive singular extension search
1192 && (tte->type() & VALUE_TYPE_LOWER)
1193 && tte->depth() >= depth - 3 * ONE_PLY;
1196 lock_grab(&(sp->lock));
1197 bestValue = sp->bestValue;
1200 // Step 10. Loop through moves
1201 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1202 while ( bestValue < beta
1203 && (move = mp.get_next_move()) != MOVE_NONE
1204 && !ThreadsMgr.thread_should_stop(threadID))
1206 assert(move_is_ok(move));
1210 moveCount = ++sp->moveCount;
1211 lock_release(&(sp->lock));
1213 else if (move == excludedMove)
1216 movesSearched[moveCount++] = move;
1218 moveIsCheck = pos.move_is_check(move, ci);
1219 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1221 // Step 11. Decide the new search depth
1222 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1224 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1225 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1226 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1227 // lower then ttValue minus a margin then we extend ttMove.
1228 if ( singularExtensionNode
1229 && move == tte->move()
1232 Value ttValue = value_from_tt(tte->value(), ply);
1234 if (abs(ttValue) < VALUE_KNOWN_WIN)
1236 Value b = ttValue - SingularExtensionMargin;
1237 ss->excludedMove = move;
1238 ss->skipNullMove = true;
1239 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1240 ss->skipNullMove = false;
1241 ss->excludedMove = MOVE_NONE;
1242 ss->bestMove = MOVE_NONE;
1248 // Update current move (this must be done after singular extension search)
1249 ss->currentMove = move;
1250 newDepth = depth - ONE_PLY + ext;
1252 // Step 12. Futility pruning (is omitted in PV nodes)
1254 && !captureOrPromotion
1258 && !move_is_castle(move))
1260 // Move count based pruning
1261 if ( moveCount >= futility_move_count(depth)
1262 && !(threatMove && connected_threat(pos, move, threatMove))
1263 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1266 lock_grab(&(sp->lock));
1271 // Value based pruning
1272 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1273 // but fixing this made program slightly weaker.
1274 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1275 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1276 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1278 if (futilityValueScaled < beta)
1282 lock_grab(&(sp->lock));
1283 if (futilityValueScaled > sp->bestValue)
1284 sp->bestValue = bestValue = futilityValueScaled;
1286 else if (futilityValueScaled > bestValue)
1287 bestValue = futilityValueScaled;
1292 // Prune neg. see moves at low depths
1293 if ( predictedDepth < 2 * ONE_PLY
1294 && bestValue > value_mated_in(PLY_MAX)
1295 && pos.see_sign(move) < 0)
1298 lock_grab(&(sp->lock));
1304 // Step 13. Make the move
1305 pos.do_move(move, st, ci, moveIsCheck);
1307 // Step extra. pv search (only in PV nodes)
1308 // The first move in list is the expected PV
1309 if (!SpNode && PvNode && moveCount == 1)
1310 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1313 // Step 14. Reduced depth search
1314 // If the move fails high will be re-searched at full depth.
1315 bool doFullDepthSearch = true;
1317 if ( depth >= 3 * ONE_PLY
1318 && !captureOrPromotion
1320 && !move_is_castle(move)
1321 && !(ss->killers[0] == move || ss->killers[1] == move))
1323 ss->reduction = reduction<PvNode>(depth, moveCount);
1326 alpha = SpNode ? sp->alpha : alpha;
1327 Depth d = newDepth - ss->reduction;
1328 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1330 doFullDepthSearch = (value > alpha);
1333 // The move failed high, but if reduction is very big we could
1334 // face a false positive, retry with a less aggressive reduction,
1335 // if the move fails high again then go with full depth search.
1336 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1338 assert(newDepth - ONE_PLY >= ONE_PLY);
1340 ss->reduction = ONE_PLY;
1341 alpha = SpNode ? sp->alpha : alpha;
1342 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1343 doFullDepthSearch = (value > alpha);
1345 ss->reduction = DEPTH_ZERO; // Restore original reduction
1348 // Step 15. Full depth search
1349 if (doFullDepthSearch)
1351 alpha = SpNode ? sp->alpha : alpha;
1352 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1354 // Step extra. pv search (only in PV nodes)
1355 // Search only for possible new PV nodes, if instead value >= beta then
1356 // parent node fails low with value <= alpha and tries another move.
1357 if (PvNode && value > alpha && value < beta)
1358 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1362 // Step 16. Undo move
1363 pos.undo_move(move);
1365 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1367 // Step 17. Check for new best move
1370 lock_grab(&(sp->lock));
1371 bestValue = sp->bestValue;
1375 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1380 sp->bestValue = value;
1384 if (SpNode && (!PvNode || value >= beta))
1385 sp->stopRequest = true;
1387 if (PvNode && value < beta) // We want always alpha < beta
1394 if (value == value_mate_in(ply + 1))
1395 ss->mateKiller = move;
1397 ss->bestMove = move;
1400 sp->parentSstack->bestMove = move;
1404 // Step 18. Check for split
1406 && depth >= MinimumSplitDepth
1407 && ThreadsMgr.active_threads() > 1
1409 && ThreadsMgr.available_thread_exists(threadID)
1411 && !ThreadsMgr.thread_should_stop(threadID)
1413 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1414 threatMove, mateThreat, moveCount, &mp, PvNode);
1417 // Step 19. Check for mate and stalemate
1418 // All legal moves have been searched and if there are
1419 // no legal moves, it must be mate or stalemate.
1420 // If one move was excluded return fail low score.
1421 if (!SpNode && !moveCount)
1422 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1424 // Step 20. Update tables
1425 // If the search is not aborted, update the transposition table,
1426 // history counters, and killer moves.
1427 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1429 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1430 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1431 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1433 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1435 // Update killers and history only for non capture moves that fails high
1436 if ( bestValue >= beta
1437 && !pos.move_is_capture_or_promotion(move))
1439 update_history(pos, move, depth, movesSearched, moveCount);
1440 update_killers(move, ss);
1446 // Here we have the lock still grabbed
1447 sp->slaves[threadID] = 0;
1448 sp->nodes += pos.nodes_searched();
1449 lock_release(&(sp->lock));
1452 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1458 // qsearch() is the quiescence search function, which is called by the main
1459 // search function when the remaining depth is zero (or, to be more precise,
1460 // less than ONE_PLY).
1462 template <NodeType PvNode>
1463 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1465 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1466 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1467 assert(PvNode || alpha == beta - 1);
1469 assert(ply > 0 && ply < PLY_MAX);
1470 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1474 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1475 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1477 Value oldAlpha = alpha;
1479 ss->bestMove = ss->currentMove = MOVE_NONE;
1481 // Check for an instant draw or maximum ply reached
1482 if (pos.is_draw() || ply >= PLY_MAX - 1)
1485 // Transposition table lookup. At PV nodes, we don't use the TT for
1486 // pruning, but only for move ordering.
1487 tte = TT.retrieve(pos.get_key());
1488 ttMove = (tte ? tte->move() : MOVE_NONE);
1490 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1492 ss->bestMove = ttMove; // Can be MOVE_NONE
1493 return value_from_tt(tte->value(), ply);
1496 isCheck = pos.is_check();
1498 // Evaluate the position statically
1501 bestValue = futilityBase = -VALUE_INFINITE;
1502 ss->eval = evalMargin = VALUE_NONE;
1503 deepChecks = enoughMaterial = false;
1509 assert(tte->static_value() != VALUE_NONE);
1511 evalMargin = tte->static_value_margin();
1512 ss->eval = bestValue = tte->static_value();
1515 ss->eval = bestValue = evaluate(pos, evalMargin);
1517 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1519 // Stand pat. Return immediately if static value is at least beta
1520 if (bestValue >= beta)
1523 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1528 if (PvNode && bestValue > alpha)
1531 // If we are near beta then try to get a cutoff pushing checks a bit further
1532 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1534 // Futility pruning parameters, not needed when in check
1535 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1536 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1539 // Initialize a MovePicker object for the current position, and prepare
1540 // to search the moves. Because the depth is <= 0 here, only captures,
1541 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1542 // and we are near beta) will be generated.
1543 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1546 // Loop through the moves until no moves remain or a beta cutoff occurs
1547 while ( alpha < beta
1548 && (move = mp.get_next_move()) != MOVE_NONE)
1550 assert(move_is_ok(move));
1552 moveIsCheck = pos.move_is_check(move, ci);
1560 && !move_is_promotion(move)
1561 && !pos.move_is_passed_pawn_push(move))
1563 futilityValue = futilityBase
1564 + pos.endgame_value_of_piece_on(move_to(move))
1565 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1567 if (futilityValue < alpha)
1569 if (futilityValue > bestValue)
1570 bestValue = futilityValue;
1575 // Detect non-capture evasions that are candidate to be pruned
1576 evasionPrunable = isCheck
1577 && bestValue > value_mated_in(PLY_MAX)
1578 && !pos.move_is_capture(move)
1579 && !pos.can_castle(pos.side_to_move());
1581 // Don't search moves with negative SEE values
1583 && (!isCheck || evasionPrunable)
1585 && !move_is_promotion(move)
1586 && pos.see_sign(move) < 0)
1589 // Update current move
1590 ss->currentMove = move;
1592 // Make and search the move
1593 pos.do_move(move, st, ci, moveIsCheck);
1594 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1595 pos.undo_move(move);
1597 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1600 if (value > bestValue)
1606 ss->bestMove = move;
1611 // All legal moves have been searched. A special case: If we're in check
1612 // and no legal moves were found, it is checkmate.
1613 if (isCheck && bestValue == -VALUE_INFINITE)
1614 return value_mated_in(ply);
1616 // Update transposition table
1617 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1618 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1619 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1621 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1627 // connected_moves() tests whether two moves are 'connected' in the sense
1628 // that the first move somehow made the second move possible (for instance
1629 // if the moving piece is the same in both moves). The first move is assumed
1630 // to be the move that was made to reach the current position, while the
1631 // second move is assumed to be a move from the current position.
1633 bool connected_moves(const Position& pos, Move m1, Move m2) {
1635 Square f1, t1, f2, t2;
1638 assert(move_is_ok(m1));
1639 assert(move_is_ok(m2));
1641 if (m2 == MOVE_NONE)
1644 // Case 1: The moving piece is the same in both moves
1650 // Case 2: The destination square for m2 was vacated by m1
1656 // Case 3: Moving through the vacated square
1657 if ( piece_is_slider(pos.piece_on(f2))
1658 && bit_is_set(squares_between(f2, t2), f1))
1661 // Case 4: The destination square for m2 is defended by the moving piece in m1
1662 p = pos.piece_on(t1);
1663 if (bit_is_set(pos.attacks_from(p, t1), t2))
1666 // Case 5: Discovered check, checking piece is the piece moved in m1
1667 if ( piece_is_slider(p)
1668 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1669 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1671 // discovered_check_candidates() works also if the Position's side to
1672 // move is the opposite of the checking piece.
1673 Color them = opposite_color(pos.side_to_move());
1674 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1676 if (bit_is_set(dcCandidates, f2))
1683 // value_is_mate() checks if the given value is a mate one eventually
1684 // compensated for the ply.
1686 bool value_is_mate(Value value) {
1688 assert(abs(value) <= VALUE_INFINITE);
1690 return value <= value_mated_in(PLY_MAX)
1691 || value >= value_mate_in(PLY_MAX);
1695 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1696 // "plies to mate from the current ply". Non-mate scores are unchanged.
1697 // The function is called before storing a value to the transposition table.
1699 Value value_to_tt(Value v, int ply) {
1701 if (v >= value_mate_in(PLY_MAX))
1704 if (v <= value_mated_in(PLY_MAX))
1711 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1712 // the transposition table to a mate score corrected for the current ply.
1714 Value value_from_tt(Value v, int ply) {
1716 if (v >= value_mate_in(PLY_MAX))
1719 if (v <= value_mated_in(PLY_MAX))
1726 // extension() decides whether a move should be searched with normal depth,
1727 // or with extended depth. Certain classes of moves (checking moves, in
1728 // particular) are searched with bigger depth than ordinary moves and in
1729 // any case are marked as 'dangerous'. Note that also if a move is not
1730 // extended, as example because the corresponding UCI option is set to zero,
1731 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1732 template <NodeType PvNode>
1733 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1734 bool singleEvasion, bool mateThreat, bool* dangerous) {
1736 assert(m != MOVE_NONE);
1738 Depth result = DEPTH_ZERO;
1739 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1743 if (moveIsCheck && pos.see_sign(m) >= 0)
1744 result += CheckExtension[PvNode];
1747 result += SingleEvasionExtension[PvNode];
1750 result += MateThreatExtension[PvNode];
1753 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1755 Color c = pos.side_to_move();
1756 if (relative_rank(c, move_to(m)) == RANK_7)
1758 result += PawnPushTo7thExtension[PvNode];
1761 if (pos.pawn_is_passed(c, move_to(m)))
1763 result += PassedPawnExtension[PvNode];
1768 if ( captureOrPromotion
1769 && pos.type_of_piece_on(move_to(m)) != PAWN
1770 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1771 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1772 && !move_is_promotion(m)
1775 result += PawnEndgameExtension[PvNode];
1780 && captureOrPromotion
1781 && pos.type_of_piece_on(move_to(m)) != PAWN
1782 && pos.see_sign(m) >= 0)
1784 result += ONE_PLY / 2;
1788 return Min(result, ONE_PLY);
1792 // connected_threat() tests whether it is safe to forward prune a move or if
1793 // is somehow coonected to the threat move returned by null search.
1795 bool connected_threat(const Position& pos, Move m, Move threat) {
1797 assert(move_is_ok(m));
1798 assert(threat && move_is_ok(threat));
1799 assert(!pos.move_is_check(m));
1800 assert(!pos.move_is_capture_or_promotion(m));
1801 assert(!pos.move_is_passed_pawn_push(m));
1803 Square mfrom, mto, tfrom, tto;
1805 mfrom = move_from(m);
1807 tfrom = move_from(threat);
1808 tto = move_to(threat);
1810 // Case 1: Don't prune moves which move the threatened piece
1814 // Case 2: If the threatened piece has value less than or equal to the
1815 // value of the threatening piece, don't prune move which defend it.
1816 if ( pos.move_is_capture(threat)
1817 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1818 || pos.type_of_piece_on(tfrom) == KING)
1819 && pos.move_attacks_square(m, tto))
1822 // Case 3: If the moving piece in the threatened move is a slider, don't
1823 // prune safe moves which block its ray.
1824 if ( piece_is_slider(pos.piece_on(tfrom))
1825 && bit_is_set(squares_between(tfrom, tto), mto)
1826 && pos.see_sign(m) >= 0)
1833 // ok_to_use_TT() returns true if a transposition table score
1834 // can be used at a given point in search.
1836 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1838 Value v = value_from_tt(tte->value(), ply);
1840 return ( tte->depth() >= depth
1841 || v >= Max(value_mate_in(PLY_MAX), beta)
1842 || v < Min(value_mated_in(PLY_MAX), beta))
1844 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1845 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1849 // refine_eval() returns the transposition table score if
1850 // possible otherwise falls back on static position evaluation.
1852 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1856 Value v = value_from_tt(tte->value(), ply);
1858 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1859 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1866 // update_history() registers a good move that produced a beta-cutoff
1867 // in history and marks as failures all the other moves of that ply.
1869 void update_history(const Position& pos, Move move, Depth depth,
1870 Move movesSearched[], int moveCount) {
1873 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1875 for (int i = 0; i < moveCount - 1; i++)
1877 m = movesSearched[i];
1881 if (!pos.move_is_capture_or_promotion(m))
1882 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1887 // update_killers() add a good move that produced a beta-cutoff
1888 // among the killer moves of that ply.
1890 void update_killers(Move m, SearchStack* ss) {
1892 if (m == ss->killers[0])
1895 ss->killers[1] = ss->killers[0];
1900 // update_gains() updates the gains table of a non-capture move given
1901 // the static position evaluation before and after the move.
1903 void update_gains(const Position& pos, Move m, Value before, Value after) {
1906 && before != VALUE_NONE
1907 && after != VALUE_NONE
1908 && pos.captured_piece_type() == PIECE_TYPE_NONE
1909 && !move_is_special(m))
1910 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1914 // current_search_time() returns the number of milliseconds which have passed
1915 // since the beginning of the current search.
1917 int current_search_time() {
1919 return get_system_time() - SearchStartTime;
1923 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1925 std::string value_to_uci(Value v) {
1927 std::stringstream s;
1929 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1930 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1932 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1937 // nps() computes the current nodes/second count.
1939 int nps(const Position& pos) {
1941 int t = current_search_time();
1942 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1946 // poll() performs two different functions: It polls for user input, and it
1947 // looks at the time consumed so far and decides if it's time to abort the
1950 void poll(const Position& pos) {
1952 static int lastInfoTime;
1953 int t = current_search_time();
1956 if (data_available())
1958 // We are line oriented, don't read single chars
1959 std::string command;
1961 if (!std::getline(std::cin, command))
1964 if (command == "quit")
1967 PonderSearch = false;
1971 else if (command == "stop")
1974 PonderSearch = false;
1976 else if (command == "ponderhit")
1980 // Print search information
1984 else if (lastInfoTime > t)
1985 // HACK: Must be a new search where we searched less than
1986 // NodesBetweenPolls nodes during the first second of search.
1989 else if (t - lastInfoTime >= 1000)
1996 if (dbg_show_hit_rate)
1997 dbg_print_hit_rate();
1999 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
2000 << " time " << t << endl;
2003 // Should we stop the search?
2007 bool stillAtFirstMove = FirstRootMove
2008 && !AspirationFailLow
2009 && t > TimeMgr.available_time();
2011 bool noMoreTime = t > TimeMgr.maximum_time()
2012 || stillAtFirstMove;
2014 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2015 || (ExactMaxTime && t >= ExactMaxTime)
2016 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2021 // ponderhit() is called when the program is pondering (i.e. thinking while
2022 // it's the opponent's turn to move) in order to let the engine know that
2023 // it correctly predicted the opponent's move.
2027 int t = current_search_time();
2028 PonderSearch = false;
2030 bool stillAtFirstMove = FirstRootMove
2031 && !AspirationFailLow
2032 && t > TimeMgr.available_time();
2034 bool noMoreTime = t > TimeMgr.maximum_time()
2035 || stillAtFirstMove;
2037 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2042 // init_ss_array() does a fast reset of the first entries of a SearchStack
2043 // array and of all the excludedMove and skipNullMove entries.
2045 void init_ss_array(SearchStack* ss, int size) {
2047 for (int i = 0; i < size; i++, ss++)
2049 ss->excludedMove = MOVE_NONE;
2050 ss->skipNullMove = false;
2051 ss->reduction = DEPTH_ZERO;
2055 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2060 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2061 // while the program is pondering. The point is to work around a wrinkle in
2062 // the UCI protocol: When pondering, the engine is not allowed to give a
2063 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2064 // We simply wait here until one of these commands is sent, and return,
2065 // after which the bestmove and pondermove will be printed (in id_loop()).
2067 void wait_for_stop_or_ponderhit() {
2069 std::string command;
2073 if (!std::getline(std::cin, command))
2076 if (command == "quit")
2081 else if (command == "ponderhit" || command == "stop")
2087 // print_pv_info() prints to standard output and eventually to log file information on
2088 // the current PV line. It is called at each iteration or after a new pv is found.
2090 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2092 cout << "info depth " << Iteration
2093 << " score " << value_to_uci(value)
2094 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2095 << " time " << current_search_time()
2096 << " nodes " << pos.nodes_searched()
2097 << " nps " << nps(pos)
2100 for (Move* m = pv; *m != MOVE_NONE; m++)
2107 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2108 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2110 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2115 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2116 // the PV back into the TT. This makes sure the old PV moves are searched
2117 // first, even if the old TT entries have been overwritten.
2119 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2123 Position p(pos, pos.thread());
2124 Value v, m = VALUE_NONE;
2126 for (int i = 0; pv[i] != MOVE_NONE; i++)
2128 tte = TT.retrieve(p.get_key());
2129 if (!tte || tte->move() != pv[i])
2131 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2132 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2134 p.do_move(pv[i], st);
2139 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2140 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2141 // allow to always have a ponder move even when we fail high at root and also a
2142 // long PV to print that is important for position analysis.
2144 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2148 Position p(pos, pos.thread());
2151 assert(bestMove != MOVE_NONE);
2154 p.do_move(pv[ply++], st);
2156 while ( (tte = TT.retrieve(p.get_key())) != NULL
2157 && tte->move() != MOVE_NONE
2158 && move_is_legal(p, tte->move())
2160 && (!p.is_draw() || ply < 2))
2162 pv[ply] = tte->move();
2163 p.do_move(pv[ply++], st);
2165 pv[ply] = MOVE_NONE;
2169 // init_thread() is the function which is called when a new thread is
2170 // launched. It simply calls the idle_loop() function with the supplied
2171 // threadID. There are two versions of this function; one for POSIX
2172 // threads and one for Windows threads.
2174 #if !defined(_MSC_VER)
2176 void* init_thread(void* threadID) {
2178 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2184 DWORD WINAPI init_thread(LPVOID threadID) {
2186 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2193 /// The ThreadsManager class
2196 // idle_loop() is where the threads are parked when they have no work to do.
2197 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2198 // object for which the current thread is the master.
2200 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2202 assert(threadID >= 0 && threadID < MAX_THREADS);
2205 bool allFinished = false;
2209 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2210 // master should exit as last one.
2211 if (AllThreadsShouldExit)
2214 threads[threadID].state = THREAD_TERMINATED;
2218 // If we are not thinking, wait for a condition to be signaled
2219 // instead of wasting CPU time polling for work.
2220 while ( threadID >= ActiveThreads || threads[threadID].state == THREAD_INITIALIZING
2221 || (UseSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2223 assert(!sp || UseSleepingThreads);
2224 assert(threadID != 0 || UseSleepingThreads);
2226 if (threads[threadID].state == THREAD_INITIALIZING)
2227 threads[threadID].state = THREAD_AVAILABLE;
2229 // Grab the lock to avoid races with wake_sleeping_thread()
2230 lock_grab(&WaitLock);
2232 // If we are master and all slaves have finished do not go to sleep
2233 for (i = 0; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2234 allFinished = (i == ActiveThreads);
2236 if (allFinished || AllThreadsShouldExit)
2238 lock_release(&WaitLock);
2242 // Do sleep here after retesting sleep conditions
2243 if (threadID >= ActiveThreads || threads[threadID].state == THREAD_AVAILABLE)
2244 cond_wait(&WaitCond[threadID], &WaitLock);
2246 lock_release(&WaitLock);
2249 // If this thread has been assigned work, launch a search
2250 if (threads[threadID].state == THREAD_WORKISWAITING)
2252 assert(!AllThreadsShouldExit);
2254 threads[threadID].state = THREAD_SEARCHING;
2256 // Here we call search() with SplitPoint template parameter set to true
2257 SplitPoint* tsp = threads[threadID].splitPoint;
2258 Position pos(*tsp->pos, threadID);
2259 SearchStack* ss = tsp->sstack[threadID] + 1;
2263 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2265 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2267 assert(threads[threadID].state == THREAD_SEARCHING);
2269 threads[threadID].state = THREAD_AVAILABLE;
2271 // Wake up master thread so to allow it to return from the idle loop in
2272 // case we are the last slave of the split point.
2273 if (UseSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2274 wake_sleeping_thread(tsp->master);
2277 // If this thread is the master of a split point and all slaves have
2278 // finished their work at this split point, return from the idle loop.
2279 for (i = 0; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2280 allFinished = (i == ActiveThreads);
2284 // Because sp->slaves[] is reset under lock protection,
2285 // be sure sp->lock has been released before to return.
2286 lock_grab(&(sp->lock));
2287 lock_release(&(sp->lock));
2289 // In helpful master concept a master can help only a sub-tree, and
2290 // because here is all finished is not possible master is booked.
2291 assert(threads[threadID].state == THREAD_AVAILABLE);
2293 threads[threadID].state = THREAD_SEARCHING;
2300 // init_threads() is called during startup. It launches all helper threads,
2301 // and initializes the split point stack and the global locks and condition
2304 void ThreadsManager::init_threads() {
2306 int i, arg[MAX_THREADS];
2309 // Initialize global locks
2311 lock_init(&WaitLock);
2313 for (i = 0; i < MAX_THREADS; i++)
2314 cond_init(&WaitCond[i]);
2316 // Initialize splitPoints[] locks
2317 for (i = 0; i < MAX_THREADS; i++)
2318 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2319 lock_init(&(threads[i].splitPoints[j].lock));
2321 // Will be set just before program exits to properly end the threads
2322 AllThreadsShouldExit = false;
2324 // Threads will be put all threads to sleep as soon as created
2327 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2328 threads[0].state = THREAD_SEARCHING;
2329 for (i = 1; i < MAX_THREADS; i++)
2330 threads[i].state = THREAD_INITIALIZING;
2332 // Launch the helper threads
2333 for (i = 1; i < MAX_THREADS; i++)
2337 #if !defined(_MSC_VER)
2338 pthread_t pthread[1];
2339 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2340 pthread_detach(pthread[0]);
2342 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2346 cout << "Failed to create thread number " << i << endl;
2350 // Wait until the thread has finished launching and is gone to sleep
2351 while (threads[i].state == THREAD_INITIALIZING) {}
2356 // exit_threads() is called when the program exits. It makes all the
2357 // helper threads exit cleanly.
2359 void ThreadsManager::exit_threads() {
2361 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2363 // Wake up all the threads and waits for termination
2364 for (int i = 1; i < MAX_THREADS; i++)
2366 wake_sleeping_thread(i);
2367 while (threads[i].state != THREAD_TERMINATED) {}
2370 // Now we can safely destroy the locks
2371 for (int i = 0; i < MAX_THREADS; i++)
2372 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2373 lock_destroy(&(threads[i].splitPoints[j].lock));
2375 lock_destroy(&WaitLock);
2376 lock_destroy(&MPLock);
2378 // Now we can safely destroy the wait conditions
2379 for (int i = 0; i < MAX_THREADS; i++)
2380 cond_destroy(&WaitCond[i]);
2384 // thread_should_stop() checks whether the thread should stop its search.
2385 // This can happen if a beta cutoff has occurred in the thread's currently
2386 // active split point, or in some ancestor of the current split point.
2388 bool ThreadsManager::thread_should_stop(int threadID) const {
2390 assert(threadID >= 0 && threadID < ActiveThreads);
2392 SplitPoint* sp = threads[threadID].splitPoint;
2394 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2399 // thread_is_available() checks whether the thread with threadID "slave" is
2400 // available to help the thread with threadID "master" at a split point. An
2401 // obvious requirement is that "slave" must be idle. With more than two
2402 // threads, this is not by itself sufficient: If "slave" is the master of
2403 // some active split point, it is only available as a slave to the other
2404 // threads which are busy searching the split point at the top of "slave"'s
2405 // split point stack (the "helpful master concept" in YBWC terminology).
2407 bool ThreadsManager::thread_is_available(int slave, int master) const {
2409 assert(slave >= 0 && slave < ActiveThreads);
2410 assert(master >= 0 && master < ActiveThreads);
2411 assert(ActiveThreads > 1);
2413 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2416 // Make a local copy to be sure doesn't change under our feet
2417 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2419 // No active split points means that the thread is available as
2420 // a slave for any other thread.
2421 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2424 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2425 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2426 // could have been set to 0 by another thread leading to an out of bound access.
2427 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2434 // available_thread_exists() tries to find an idle thread which is available as
2435 // a slave for the thread with threadID "master".
2437 bool ThreadsManager::available_thread_exists(int master) const {
2439 assert(master >= 0 && master < ActiveThreads);
2440 assert(ActiveThreads > 1);
2442 for (int i = 0; i < ActiveThreads; i++)
2443 if (thread_is_available(i, master))
2450 // split() does the actual work of distributing the work at a node between
2451 // several available threads. If it does not succeed in splitting the
2452 // node (because no idle threads are available, or because we have no unused
2453 // split point objects), the function immediately returns. If splitting is
2454 // possible, a SplitPoint object is initialized with all the data that must be
2455 // copied to the helper threads and we tell our helper threads that they have
2456 // been assigned work. This will cause them to instantly leave their idle loops and
2457 // call search().When all threads have returned from search() then split() returns.
2459 template <bool Fake>
2460 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2461 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2462 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2463 assert(pos.is_ok());
2464 assert(ply > 0 && ply < PLY_MAX);
2465 assert(*bestValue >= -VALUE_INFINITE);
2466 assert(*bestValue <= *alpha);
2467 assert(*alpha < beta);
2468 assert(beta <= VALUE_INFINITE);
2469 assert(depth > DEPTH_ZERO);
2470 assert(pos.thread() >= 0 && pos.thread() < ActiveThreads);
2471 assert(ActiveThreads > 1);
2473 int i, master = pos.thread();
2474 Thread& masterThread = threads[master];
2478 // If no other thread is available to help us, or if we have too many
2479 // active split points, don't split.
2480 if ( !available_thread_exists(master)
2481 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2483 lock_release(&MPLock);
2487 // Pick the next available split point object from the split point stack
2488 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2490 // Initialize the split point object
2491 splitPoint.parent = masterThread.splitPoint;
2492 splitPoint.master = master;
2493 splitPoint.stopRequest = false;
2494 splitPoint.ply = ply;
2495 splitPoint.depth = depth;
2496 splitPoint.threatMove = threatMove;
2497 splitPoint.mateThreat = mateThreat;
2498 splitPoint.alpha = *alpha;
2499 splitPoint.beta = beta;
2500 splitPoint.pvNode = pvNode;
2501 splitPoint.bestValue = *bestValue;
2503 splitPoint.moveCount = moveCount;
2504 splitPoint.pos = &pos;
2505 splitPoint.nodes = 0;
2506 splitPoint.parentSstack = ss;
2507 for (i = 0; i < ActiveThreads; i++)
2508 splitPoint.slaves[i] = 0;
2510 masterThread.splitPoint = &splitPoint;
2512 // If we are here it means we are not available
2513 assert(masterThread.state != THREAD_AVAILABLE);
2515 int workersCnt = 1; // At least the master is included
2517 // Allocate available threads setting state to THREAD_BOOKED
2518 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2519 if (thread_is_available(i, master))
2521 threads[i].state = THREAD_BOOKED;
2522 threads[i].splitPoint = &splitPoint;
2523 splitPoint.slaves[i] = 1;
2527 assert(Fake || workersCnt > 1);
2529 // We can release the lock because slave threads are already booked and master is not available
2530 lock_release(&MPLock);
2532 // Tell the threads that they have work to do. This will make them leave
2533 // their idle loop. But before copy search stack tail for each thread.
2534 for (i = 0; i < ActiveThreads; i++)
2535 if (i == master || splitPoint.slaves[i])
2537 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2539 assert(i == master || threads[i].state == THREAD_BOOKED);
2541 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2543 if (UseSleepingThreads && i != master)
2544 wake_sleeping_thread(i);
2547 // Everything is set up. The master thread enters the idle loop, from
2548 // which it will instantly launch a search, because its state is
2549 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2550 // idle loop, which means that the main thread will return from the idle
2551 // loop when all threads have finished their work at this split point.
2552 idle_loop(master, &splitPoint);
2554 // We have returned from the idle loop, which means that all threads are
2555 // finished. Update alpha and bestValue, and return.
2558 *alpha = splitPoint.alpha;
2559 *bestValue = splitPoint.bestValue;
2560 masterThread.activeSplitPoints--;
2561 masterThread.splitPoint = splitPoint.parent;
2562 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2564 lock_release(&MPLock);
2568 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2569 // to start a new search from the root.
2571 void ThreadsManager::wake_sleeping_thread(int threadID) {
2573 lock_grab(&WaitLock);
2574 cond_signal(&WaitCond[threadID]);
2575 lock_release(&WaitLock);
2579 /// The RootMoveList class
2581 // RootMoveList c'tor
2583 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2585 SearchStack ss[PLY_MAX_PLUS_2];
2586 MoveStack mlist[MOVES_MAX];
2588 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2590 // Initialize search stack
2591 init_ss_array(ss, PLY_MAX_PLUS_2);
2592 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2595 // Generate all legal moves
2596 MoveStack* last = generate_moves(pos, mlist);
2598 // Add each move to the moves[] array
2599 for (MoveStack* cur = mlist; cur != last; cur++)
2601 bool includeMove = includeAllMoves;
2603 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2604 includeMove = (searchMoves[k] == cur->move);
2609 // Find a quick score for the move
2610 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2611 moves[count].pv[1] = MOVE_NONE;
2612 pos.do_move(cur->move, st);
2613 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2614 pos.undo_move(cur->move);
2620 // Score root moves using the standard way used in main search, the moves
2621 // are scored according to the order in which are returned by MovePicker.
2623 void RootMoveList::score_moves(const Position& pos)
2627 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2629 while ((move = mp.get_next_move()) != MOVE_NONE)
2630 for (int i = 0; i < count; i++)
2631 if (moves[i].move == move)
2633 moves[i].mp_score = score--;
2638 // RootMoveList simple methods definitions
2640 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2644 for (j = 0; pv[j] != MOVE_NONE; j++)
2645 moves[moveNum].pv[j] = pv[j];
2647 moves[moveNum].pv[j] = MOVE_NONE;
2651 // RootMoveList::sort() sorts the root move list at the beginning of a new
2654 void RootMoveList::sort() {
2656 sort_multipv(count - 1); // Sort all items
2660 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2661 // list by their scores and depths. It is used to order the different PVs
2662 // correctly in MultiPV mode.
2664 void RootMoveList::sort_multipv(int n) {
2668 for (i = 1; i <= n; i++)
2670 RootMove rm = moves[i];
2671 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2672 moves[j] = moves[j - 1];