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 min_split_depth() const { return minimumSplitDepth; }
81 int active_threads() const { return activeThreads; }
82 void set_active_threads(int cnt) { activeThreads = cnt; }
84 void read_uci_options();
85 bool available_thread_exists(int master) const;
86 bool thread_is_available(int slave, int master) const;
87 bool thread_should_stop(int threadID) const;
88 void wake_sleeping_thread(int threadID);
89 void idle_loop(int threadID, SplitPoint* sp);
92 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
96 Depth minimumSplitDepth;
97 int maxThreadsPerSplitPoint;
98 bool useSleepingThreads;
100 volatile bool allThreadsShouldExit;
101 Thread threads[MAX_THREADS];
102 Lock mpLock, sleepLock[MAX_THREADS];
103 WaitCondition sleepCond[MAX_THREADS];
107 // RootMove struct is used for moves at the root at the tree. For each
108 // root move, we store a score, a node count, and a PV (really a refutation
109 // in the case of moves which fail low).
113 RootMove() : mp_score(0), nodes(0) {}
115 // RootMove::operator<() is the comparison function used when
116 // sorting the moves. A move m1 is considered to be better
117 // than a move m2 if it has a higher score, or if the moves
118 // have equal score but m1 has the higher beta cut-off count.
119 bool operator<(const RootMove& m) const {
121 return score != m.score ? score < m.score : mp_score <= m.mp_score;
128 Move pv[PLY_MAX_PLUS_2];
132 // The RootMoveList class is essentially an array of RootMove objects, with
133 // a handful of methods for accessing the data in the individual moves.
138 RootMoveList(Position& pos, Move searchMoves[]);
140 Move move(int moveNum) const { return moves[moveNum].move; }
141 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
142 int move_count() const { return count; }
143 Value move_score(int moveNum) const { return moves[moveNum].score; }
144 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
145 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
146 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
148 void set_move_pv(int moveNum, const Move pv[]);
149 void score_moves(const Position& pos);
151 void sort_multipv(int n);
154 RootMove moves[MOVES_MAX];
159 // When formatting a move for std::cout we must know if we are in Chess960
160 // or not. To keep using the handy operator<<() on the move the trick is to
161 // embed this flag in the stream itself. Function-like named enum set960 is
162 // used as a custom manipulator and the stream internal general-purpose array,
163 // accessed through ios_base::iword(), is used to pass the flag to the move's
164 // operator<<() that will use it to properly format castling moves.
167 std::ostream& operator<< (std::ostream& os, const set960& m) {
169 os.iword(0) = int(m);
178 // Maximum depth for razoring
179 const Depth RazorDepth = 4 * ONE_PLY;
181 // Dynamic razoring margin based on depth
182 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
184 // Maximum depth for use of dynamic threat detection when null move fails low
185 const Depth ThreatDepth = 5 * ONE_PLY;
187 // Step 9. Internal iterative deepening
189 // Minimum depth for use of internal iterative deepening
190 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
192 // At Non-PV nodes we do an internal iterative deepening search
193 // when the static evaluation is bigger then beta - IIDMargin.
194 const Value IIDMargin = Value(0x100);
196 // Step 11. Decide the new search depth
198 // Extensions. Configurable UCI options
199 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
200 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
201 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
203 // Minimum depth for use of singular extension
204 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
206 // If the TT move is at least SingularExtensionMargin better then the
207 // remaining ones we will extend it.
208 const Value SingularExtensionMargin = Value(0x20);
210 // Step 12. Futility pruning
212 // Futility margin for quiescence search
213 const Value FutilityMarginQS = Value(0x80);
215 // Futility lookup tables (initialized at startup) and their getter functions
216 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
217 int FutilityMoveCountArray[32]; // [depth]
219 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
220 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
222 // Step 14. Reduced search
224 // Reduction lookup tables (initialized at startup) and their getter functions
225 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
227 template <NodeType PV>
228 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
230 // Common adjustments
232 // Search depth at iteration 1
233 const Depth InitialDepth = ONE_PLY;
235 // Easy move margin. An easy move candidate must be at least this much
236 // better than the second best move.
237 const Value EasyMoveMargin = Value(0x200);
240 /// Namespace variables
248 // Scores and number of times the best move changed for each iteration
249 Value ValueByIteration[PLY_MAX_PLUS_2];
250 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
252 // Search window management
258 // Time managment variables
259 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
260 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
261 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
266 std::ofstream LogFile;
268 // Multi-threads manager object
269 ThreadsManager ThreadsMgr;
271 // Node counters, used only by thread[0] but try to keep in different cache
272 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
274 int NodesBetweenPolls = 30000;
281 Value id_loop(Position& pos, Move searchMoves[]);
282 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
284 template <NodeType PvNode, bool SpNode>
285 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
287 template <NodeType PvNode>
288 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
290 template <NodeType PvNode>
291 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
293 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
294 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
297 template <NodeType PvNode>
298 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
300 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
301 bool connected_moves(const Position& pos, Move m1, Move m2);
302 bool value_is_mate(Value value);
303 Value value_to_tt(Value v, int ply);
304 Value value_from_tt(Value v, int ply);
305 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
306 bool connected_threat(const Position& pos, Move m, Move threat);
307 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
308 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
309 void update_killers(Move m, SearchStack* ss);
310 void update_gains(const Position& pos, Move move, Value before, Value after);
312 int current_search_time();
313 std::string value_to_uci(Value v);
314 int nps(const Position& pos);
315 void poll(const Position& pos);
317 void wait_for_stop_or_ponderhit();
318 void init_ss_array(SearchStack* ss, int size);
319 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
320 void insert_pv_in_tt(const Position& pos, Move pv[]);
321 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
323 #if !defined(_MSC_VER)
324 void* init_thread(void* threadID);
326 DWORD WINAPI init_thread(LPVOID threadID);
336 /// init_threads(), exit_threads() and nodes_searched() are helpers to
337 /// give accessibility to some TM methods from outside of current file.
339 void init_threads() { ThreadsMgr.init_threads(); }
340 void exit_threads() { ThreadsMgr.exit_threads(); }
343 /// init_search() is called during startup. It initializes various lookup tables
347 int d; // depth (ONE_PLY == 2)
348 int hd; // half depth (ONE_PLY == 1)
351 // Init reductions array
352 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
354 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
355 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
356 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
357 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
360 // Init futility margins array
361 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
362 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
364 // Init futility move count array
365 for (d = 0; d < 32; d++)
366 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
370 /// perft() is our utility to verify move generation is bug free. All the legal
371 /// moves up to given depth are generated and counted and the sum returned.
373 int perft(Position& pos, Depth depth)
375 MoveStack mlist[MOVES_MAX];
380 // Generate all legal moves
381 MoveStack* last = generate_moves(pos, mlist);
383 // If we are at the last ply we don't need to do and undo
384 // the moves, just to count them.
385 if (depth <= ONE_PLY)
386 return int(last - mlist);
388 // Loop through all legal moves
390 for (MoveStack* cur = mlist; cur != last; cur++)
393 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
394 sum += perft(pos, depth - ONE_PLY);
401 /// think() is the external interface to Stockfish's search, and is called when
402 /// the program receives the UCI 'go' command. It initializes various
403 /// search-related global variables, and calls root_search(). It returns false
404 /// when a quit command is received during the search.
406 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
407 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
409 // Initialize global search variables
410 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
412 SearchStartTime = get_system_time();
413 ExactMaxTime = maxTime;
416 InfiniteSearch = infinite;
417 PonderSearch = ponder;
418 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
420 // Look for a book move, only during games, not tests
421 if (UseTimeManagement && Options["OwnBook"].value<bool>())
423 if (Options["Book File"].value<std::string>() != OpeningBook.file_name())
424 OpeningBook.open(Options["Book File"].value<std::string>());
426 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
427 if (bookMove != MOVE_NONE)
430 wait_for_stop_or_ponderhit();
432 cout << "bestmove " << bookMove << endl;
437 // Read UCI option values
438 TT.set_size(Options["Hash"].value<int>());
439 if (Options["Clear Hash"].value<bool>())
441 Options["Clear Hash"].set_value("false");
445 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
446 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
447 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
448 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
449 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
450 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
451 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
452 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
453 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
454 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
455 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
456 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
457 MultiPV = Options["MultiPV"].value<int>();
458 UseLogFile = Options["Use Search Log"].value<bool>();
461 LogFile.open(Options["Search Log Filename"].value<std::string>().c_str(), std::ios::out | std::ios::app);
463 read_weights(pos.side_to_move());
465 // Set the number of active threads
466 ThreadsMgr.read_uci_options();
467 init_eval(ThreadsMgr.active_threads());
469 // Wake up needed threads
470 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
471 ThreadsMgr.wake_sleeping_thread(i);
474 int myTime = time[pos.side_to_move()];
475 int myIncrement = increment[pos.side_to_move()];
476 if (UseTimeManagement)
477 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
479 // Set best NodesBetweenPolls interval to avoid lagging under
480 // heavy time pressure.
482 NodesBetweenPolls = Min(MaxNodes, 30000);
483 else if (myTime && myTime < 1000)
484 NodesBetweenPolls = 1000;
485 else if (myTime && myTime < 5000)
486 NodesBetweenPolls = 5000;
488 NodesBetweenPolls = 30000;
490 // Write search information to log file
492 LogFile << "Searching: " << pos.to_fen() << endl
493 << "infinite: " << infinite
494 << " ponder: " << ponder
495 << " time: " << myTime
496 << " increment: " << myIncrement
497 << " moves to go: " << movesToGo << endl;
499 // We're ready to start thinking. Call the iterative deepening loop function
500 id_loop(pos, searchMoves);
505 // This makes all the threads to go to sleep
506 ThreadsMgr.set_active_threads(1);
514 // id_loop() is the main iterative deepening loop. It calls root_search
515 // repeatedly with increasing depth until the allocated thinking time has
516 // been consumed, the user stops the search, or the maximum search depth is
519 Value id_loop(Position& pos, Move searchMoves[]) {
521 SearchStack ss[PLY_MAX_PLUS_2];
522 Move pv[PLY_MAX_PLUS_2];
523 Move EasyMove = MOVE_NONE;
524 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
526 // Moves to search are verified, copied, scored and sorted
527 RootMoveList rml(pos, searchMoves);
529 // Handle special case of searching on a mate/stale position
530 if (rml.move_count() == 0)
533 wait_for_stop_or_ponderhit();
535 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
538 // Print RootMoveList startup scoring to the standard output,
539 // so to output information also for iteration 1.
540 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
541 << "info depth " << 1
542 << "\ninfo depth " << 1
543 << " score " << value_to_uci(rml.move_score(0))
544 << " time " << current_search_time()
545 << " nodes " << pos.nodes_searched()
546 << " nps " << nps(pos)
547 << " pv " << rml.move(0) << "\n";
552 init_ss_array(ss, PLY_MAX_PLUS_2);
553 pv[0] = pv[1] = MOVE_NONE;
554 ValueByIteration[1] = rml.move_score(0);
557 // Is one move significantly better than others after initial scoring ?
558 if ( rml.move_count() == 1
559 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
560 EasyMove = rml.move(0);
562 // Iterative deepening loop
563 while (Iteration < PLY_MAX)
565 // Initialize iteration
567 BestMoveChangesByIteration[Iteration] = 0;
569 cout << "info depth " << Iteration << endl;
571 // Calculate dynamic aspiration window based on previous iterations
572 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
574 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
575 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
577 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
578 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
580 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
581 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
584 // Search to the current depth, rml is updated and sorted, alpha and beta could change
585 value = root_search(pos, ss, pv, rml, &alpha, &beta);
587 // Write PV to transposition table, in case the relevant entries have
588 // been overwritten during the search.
589 insert_pv_in_tt(pos, pv);
592 break; // Value cannot be trusted. Break out immediately!
594 //Save info about search result
595 ValueByIteration[Iteration] = value;
597 // Drop the easy move if differs from the new best move
598 if (pv[0] != EasyMove)
599 EasyMove = MOVE_NONE;
601 if (UseTimeManagement)
604 bool stopSearch = false;
606 // Stop search early if there is only a single legal move,
607 // we search up to Iteration 6 anyway to get a proper score.
608 if (Iteration >= 6 && rml.move_count() == 1)
611 // Stop search early when the last two iterations returned a mate score
613 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
614 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
617 // Stop search early if one move seems to be much better than the others
620 && ( ( rml.move_nodes(0) > (pos.nodes_searched() * 85) / 100
621 && current_search_time() > TimeMgr.available_time() / 16)
622 ||( rml.move_nodes(0) > (pos.nodes_searched() * 98) / 100
623 && current_search_time() > TimeMgr.available_time() / 32)))
626 // Add some extra time if the best move has changed during the last two iterations
627 if (Iteration > 5 && Iteration <= 50)
628 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
629 BestMoveChangesByIteration[Iteration-1]);
631 // Stop search if most of MaxSearchTime is consumed at the end of the
632 // iteration. We probably don't have enough time to search the first
633 // move at the next iteration anyway.
634 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
640 StopOnPonderhit = true;
646 if (MaxDepth && Iteration >= MaxDepth)
650 // If we are pondering or in infinite search, we shouldn't print the
651 // best move before we are told to do so.
652 if (!AbortSearch && (PonderSearch || InfiniteSearch))
653 wait_for_stop_or_ponderhit();
655 // Print final search statistics
656 cout << "info nodes " << pos.nodes_searched()
657 << " nps " << nps(pos)
658 << " time " << current_search_time() << endl;
660 // Print the best move and the ponder move to the standard output
661 if (pv[0] == MOVE_NONE || MultiPV > 1)
667 assert(pv[0] != MOVE_NONE);
669 cout << "bestmove " << pv[0];
671 if (pv[1] != MOVE_NONE)
672 cout << " ponder " << pv[1];
679 dbg_print_mean(LogFile);
681 if (dbg_show_hit_rate)
682 dbg_print_hit_rate(LogFile);
684 LogFile << "\nNodes: " << pos.nodes_searched()
685 << "\nNodes/second: " << nps(pos)
686 << "\nBest move: " << move_to_san(pos, pv[0]);
689 pos.do_move(pv[0], st);
690 LogFile << "\nPonder move: "
691 << move_to_san(pos, pv[1]) // Works also with MOVE_NONE
694 return rml.move_score(0);
698 // root_search() is the function which searches the root node. It is
699 // similar to search_pv except that it uses a different move ordering
700 // scheme, prints some information to the standard output and handles
701 // the fail low/high loops.
703 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
709 Depth depth, ext, newDepth;
710 Value value, alpha, beta;
711 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
712 int researchCountFH, researchCountFL;
714 researchCountFH = researchCountFL = 0;
717 isCheck = pos.is_check();
718 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
720 // Step 1. Initialize node (polling is omitted at root)
721 ss->currentMove = ss->bestMove = MOVE_NONE;
723 // Step 2. Check for aborted search (omitted at root)
724 // Step 3. Mate distance pruning (omitted at root)
725 // Step 4. Transposition table lookup (omitted at root)
727 // Step 5. Evaluate the position statically
728 // At root we do this only to get reference value for child nodes
729 ss->evalMargin = VALUE_NONE;
730 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
732 // Step 6. Razoring (omitted at root)
733 // Step 7. Static null move pruning (omitted at root)
734 // Step 8. Null move search with verification search (omitted at root)
735 // Step 9. Internal iterative deepening (omitted at root)
737 // Step extra. Fail low loop
738 // We start with small aspiration window and in case of fail low, we research
739 // with bigger window until we are not failing low anymore.
742 // Sort the moves before to (re)search
743 rml.score_moves(pos);
746 // Step 10. Loop through all moves in the root move list
747 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
749 // This is used by time management
750 FirstRootMove = (i == 0);
752 // Save the current node count before the move is searched
753 nodes = pos.nodes_searched();
755 // Pick the next root move, and print the move and the move number to
756 // the standard output.
757 move = ss->currentMove = rml.move(i);
759 if (current_search_time() >= 1000)
760 cout << "info currmove " << move
761 << " currmovenumber " << i + 1 << endl;
763 moveIsCheck = pos.move_is_check(move);
764 captureOrPromotion = pos.move_is_capture_or_promotion(move);
766 // Step 11. Decide the new search depth
767 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
768 newDepth = depth + ext;
770 // Step 12. Futility pruning (omitted at root)
772 // Step extra. Fail high loop
773 // If move fails high, we research with bigger window until we are not failing
775 value = - VALUE_INFINITE;
779 // Step 13. Make the move
780 pos.do_move(move, st, ci, moveIsCheck);
782 // Step extra. pv search
783 // We do pv search for first moves (i < MultiPV)
784 // and for fail high research (value > alpha)
785 if (i < MultiPV || value > alpha)
787 // Aspiration window is disabled in multi-pv case
789 alpha = -VALUE_INFINITE;
791 // Full depth PV search, done on first move or after a fail high
792 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
796 // Step 14. Reduced search
797 // if the move fails high will be re-searched at full depth
798 bool doFullDepthSearch = true;
800 if ( depth >= 3 * ONE_PLY
802 && !captureOrPromotion
803 && !move_is_castle(move))
805 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
808 assert(newDepth-ss->reduction >= ONE_PLY);
810 // Reduced depth non-pv search using alpha as upperbound
811 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
812 doFullDepthSearch = (value > alpha);
815 // The move failed high, but if reduction is very big we could
816 // face a false positive, retry with a less aggressive reduction,
817 // if the move fails high again then go with full depth search.
818 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
820 assert(newDepth - ONE_PLY >= ONE_PLY);
822 ss->reduction = ONE_PLY;
823 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
824 doFullDepthSearch = (value > alpha);
826 ss->reduction = DEPTH_ZERO; // Restore original reduction
829 // Step 15. Full depth search
830 if (doFullDepthSearch)
832 // Full depth non-pv search using alpha as upperbound
833 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
835 // If we are above alpha then research at same depth but as PV
836 // to get a correct score or eventually a fail high above beta.
838 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
842 // Step 16. Undo move
845 // Can we exit fail high loop ?
846 if (AbortSearch || value < beta)
849 // We are failing high and going to do a research. It's important to update
850 // the score before research in case we run out of time while researching.
851 rml.set_move_score(i, value);
853 extract_pv_from_tt(pos, move, pv);
854 rml.set_move_pv(i, pv);
856 // Print information to the standard output
857 print_pv_info(pos, pv, alpha, beta, value);
859 // Prepare for a research after a fail high, each time with a wider window
860 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
863 } // End of fail high loop
865 // Finished searching the move. If AbortSearch is true, the search
866 // was aborted because the user interrupted the search or because we
867 // ran out of time. In this case, the return value of the search cannot
868 // be trusted, and we break out of the loop without updating the best
873 // Remember searched nodes counts for this move
874 rml.add_move_nodes(i, pos.nodes_searched() - nodes);
876 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
877 assert(value < beta);
879 // Step 17. Check for new best move
880 if (value <= alpha && i >= MultiPV)
881 rml.set_move_score(i, -VALUE_INFINITE);
884 // PV move or new best move!
887 rml.set_move_score(i, value);
889 extract_pv_from_tt(pos, move, pv);
890 rml.set_move_pv(i, pv);
894 // We record how often the best move has been changed in each
895 // iteration. This information is used for time managment: When
896 // the best move changes frequently, we allocate some more time.
898 BestMoveChangesByIteration[Iteration]++;
900 // Print information to the standard output
901 print_pv_info(pos, pv, alpha, beta, value);
903 // Raise alpha to setup proper non-pv search upper bound
910 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
912 cout << "info multipv " << j + 1
913 << " score " << value_to_uci(rml.move_score(j))
914 << " depth " << (j <= i ? Iteration : Iteration - 1)
915 << " time " << current_search_time()
916 << " nodes " << pos.nodes_searched()
917 << " nps " << nps(pos)
920 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
921 cout << rml.move_pv(j, k) << " ";
925 alpha = rml.move_score(Min(i, MultiPV - 1));
927 } // PV move or new best move
929 assert(alpha >= *alphaPtr);
931 AspirationFailLow = (alpha == *alphaPtr);
933 if (AspirationFailLow && StopOnPonderhit)
934 StopOnPonderhit = false;
937 // Can we exit fail low loop ?
938 if (AbortSearch || !AspirationFailLow)
941 // Prepare for a research after a fail low, each time with a wider window
942 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
947 // Sort the moves before to return
954 // search<>() is the main search function for both PV and non-PV nodes and for
955 // normal and SplitPoint nodes. When called just after a split point the search
956 // is simpler because we have already probed the hash table, done a null move
957 // search, and searched the first move before splitting, we don't have to repeat
958 // all this work again. We also don't need to store anything to the hash table
959 // here: This is taken care of after we return from the split point.
961 template <NodeType PvNode, bool SpNode>
962 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
964 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
965 assert(beta > alpha && beta <= VALUE_INFINITE);
966 assert(PvNode || alpha == beta - 1);
967 assert(ply > 0 && ply < PLY_MAX);
968 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
970 Move movesSearched[MOVES_MAX];
974 Move ttMove, move, excludedMove, threatMove;
977 Value bestValue, value, oldAlpha;
978 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
979 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
980 bool mateThreat = false;
982 int threadID = pos.thread();
983 SplitPoint* sp = NULL;
984 refinedValue = bestValue = value = -VALUE_INFINITE;
986 isCheck = pos.is_check();
992 ttMove = excludedMove = MOVE_NONE;
993 threatMove = sp->threatMove;
994 mateThreat = sp->mateThreat;
995 goto split_point_start;
996 } else {} // Hack to fix icc's "statement is unreachable" warning
998 // Step 1. Initialize node and poll. Polling can abort search
999 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
1000 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1002 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1008 // Step 2. Check for aborted search and immediate draw
1009 if ( AbortSearch || ThreadsMgr.thread_should_stop(threadID)
1010 || pos.is_draw() || ply >= PLY_MAX - 1)
1013 // Step 3. Mate distance pruning
1014 alpha = Max(value_mated_in(ply), alpha);
1015 beta = Min(value_mate_in(ply+1), beta);
1019 // Step 4. Transposition table lookup
1021 // We don't want the score of a partial search to overwrite a previous full search
1022 // TT value, so we use a different position key in case of an excluded move exists.
1023 excludedMove = ss->excludedMove;
1024 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1026 tte = TT.retrieve(posKey);
1027 ttMove = tte ? tte->move() : MOVE_NONE;
1029 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1030 // This is to avoid problems in the following areas:
1032 // * Repetition draw detection
1033 // * Fifty move rule detection
1034 // * Searching for a mate
1035 // * Printing of full PV line
1036 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1039 ss->bestMove = ttMove; // Can be MOVE_NONE
1040 return value_from_tt(tte->value(), ply);
1043 // Step 5. Evaluate the position statically and
1044 // update gain statistics of parent move.
1046 ss->eval = ss->evalMargin = VALUE_NONE;
1049 assert(tte->static_value() != VALUE_NONE);
1051 ss->eval = tte->static_value();
1052 ss->evalMargin = tte->static_value_margin();
1053 refinedValue = refine_eval(tte, ss->eval, ply);
1057 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1058 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1061 // Save gain for the parent non-capture move
1062 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1064 // Step 6. Razoring (is omitted in PV nodes)
1066 && depth < RazorDepth
1068 && refinedValue < beta - razor_margin(depth)
1069 && ttMove == MOVE_NONE
1070 && !value_is_mate(beta)
1071 && !pos.has_pawn_on_7th(pos.side_to_move()))
1073 Value rbeta = beta - razor_margin(depth);
1074 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1076 // Logically we should return (v + razor_margin(depth)), but
1077 // surprisingly this did slightly weaker in tests.
1081 // Step 7. Static null move pruning (is omitted in PV nodes)
1082 // We're betting that the opponent doesn't have a move that will reduce
1083 // the score by more than futility_margin(depth) if we do a null move.
1085 && !ss->skipNullMove
1086 && depth < RazorDepth
1088 && refinedValue >= beta + futility_margin(depth, 0)
1089 && !value_is_mate(beta)
1090 && pos.non_pawn_material(pos.side_to_move()))
1091 return refinedValue - futility_margin(depth, 0);
1093 // Step 8. Null move search with verification search (is omitted in PV nodes)
1095 && !ss->skipNullMove
1098 && refinedValue >= beta
1099 && !value_is_mate(beta)
1100 && pos.non_pawn_material(pos.side_to_move()))
1102 ss->currentMove = MOVE_NULL;
1104 // Null move dynamic reduction based on depth
1105 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1107 // Null move dynamic reduction based on value
1108 if (refinedValue - beta > PawnValueMidgame)
1111 pos.do_null_move(st);
1112 (ss+1)->skipNullMove = true;
1113 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1114 (ss+1)->skipNullMove = false;
1115 pos.undo_null_move();
1117 if (nullValue >= beta)
1119 // Do not return unproven mate scores
1120 if (nullValue >= value_mate_in(PLY_MAX))
1123 if (depth < 6 * ONE_PLY)
1126 // Do verification search at high depths
1127 ss->skipNullMove = true;
1128 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1129 ss->skipNullMove = false;
1136 // The null move failed low, which means that we may be faced with
1137 // some kind of threat. If the previous move was reduced, check if
1138 // the move that refuted the null move was somehow connected to the
1139 // move which was reduced. If a connection is found, return a fail
1140 // low score (which will cause the reduced move to fail high in the
1141 // parent node, which will trigger a re-search with full depth).
1142 if (nullValue == value_mated_in(ply + 2))
1145 threatMove = (ss+1)->bestMove;
1146 if ( depth < ThreatDepth
1147 && (ss-1)->reduction
1148 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1153 // Step 9. Internal iterative deepening
1154 if ( depth >= IIDDepth[PvNode]
1155 && ttMove == MOVE_NONE
1156 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1158 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1160 ss->skipNullMove = true;
1161 search<PvNode>(pos, ss, alpha, beta, d, ply);
1162 ss->skipNullMove = false;
1164 ttMove = ss->bestMove;
1165 tte = TT.retrieve(posKey);
1168 // Expensive mate threat detection (only for PV nodes)
1170 mateThreat = pos.has_mate_threat();
1172 split_point_start: // At split points actual search starts from here
1174 // Initialize a MovePicker object for the current position
1175 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1176 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1177 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1179 ss->bestMove = MOVE_NONE;
1180 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1181 futilityBase = ss->eval + ss->evalMargin;
1182 singularExtensionNode = !SpNode
1183 && depth >= SingularExtensionDepth[PvNode]
1186 && !excludedMove // Do not allow recursive singular extension search
1187 && (tte->type() & VALUE_TYPE_LOWER)
1188 && tte->depth() >= depth - 3 * ONE_PLY;
1191 lock_grab(&(sp->lock));
1192 bestValue = sp->bestValue;
1195 // Step 10. Loop through moves
1196 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1197 while ( bestValue < beta
1198 && (move = mp.get_next_move()) != MOVE_NONE
1199 && !ThreadsMgr.thread_should_stop(threadID))
1201 assert(move_is_ok(move));
1205 moveCount = ++sp->moveCount;
1206 lock_release(&(sp->lock));
1208 else if (move == excludedMove)
1211 movesSearched[moveCount++] = move;
1213 moveIsCheck = pos.move_is_check(move, ci);
1214 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1216 // Step 11. Decide the new search depth
1217 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1219 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1220 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1221 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1222 // lower then ttValue minus a margin then we extend ttMove.
1223 if ( singularExtensionNode
1224 && move == tte->move()
1227 Value ttValue = value_from_tt(tte->value(), ply);
1229 if (abs(ttValue) < VALUE_KNOWN_WIN)
1231 Value b = ttValue - SingularExtensionMargin;
1232 ss->excludedMove = move;
1233 ss->skipNullMove = true;
1234 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1235 ss->skipNullMove = false;
1236 ss->excludedMove = MOVE_NONE;
1237 ss->bestMove = MOVE_NONE;
1243 // Update current move (this must be done after singular extension search)
1244 ss->currentMove = move;
1245 newDepth = depth - ONE_PLY + ext;
1247 // Step 12. Futility pruning (is omitted in PV nodes)
1249 && !captureOrPromotion
1253 && !move_is_castle(move))
1255 // Move count based pruning
1256 if ( moveCount >= futility_move_count(depth)
1257 && !(threatMove && connected_threat(pos, move, threatMove))
1258 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1261 lock_grab(&(sp->lock));
1266 // Value based pruning
1267 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1268 // but fixing this made program slightly weaker.
1269 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1270 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1271 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1273 if (futilityValueScaled < beta)
1277 lock_grab(&(sp->lock));
1278 if (futilityValueScaled > sp->bestValue)
1279 sp->bestValue = bestValue = futilityValueScaled;
1281 else if (futilityValueScaled > bestValue)
1282 bestValue = futilityValueScaled;
1287 // Prune neg. see moves at low depths
1288 if ( predictedDepth < 2 * ONE_PLY
1289 && bestValue > value_mated_in(PLY_MAX)
1290 && pos.see_sign(move) < 0)
1293 lock_grab(&(sp->lock));
1299 // Step 13. Make the move
1300 pos.do_move(move, st, ci, moveIsCheck);
1302 // Step extra. pv search (only in PV nodes)
1303 // The first move in list is the expected PV
1304 if (!SpNode && PvNode && moveCount == 1)
1305 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1308 // Step 14. Reduced depth search
1309 // If the move fails high will be re-searched at full depth.
1310 bool doFullDepthSearch = true;
1312 if ( depth >= 3 * ONE_PLY
1313 && !captureOrPromotion
1315 && !move_is_castle(move)
1316 && !(ss->killers[0] == move || ss->killers[1] == move))
1318 ss->reduction = reduction<PvNode>(depth, moveCount);
1321 alpha = SpNode ? sp->alpha : alpha;
1322 Depth d = newDepth - ss->reduction;
1323 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1325 doFullDepthSearch = (value > alpha);
1328 // The move failed high, but if reduction is very big we could
1329 // face a false positive, retry with a less aggressive reduction,
1330 // if the move fails high again then go with full depth search.
1331 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1333 assert(newDepth - ONE_PLY >= ONE_PLY);
1335 ss->reduction = ONE_PLY;
1336 alpha = SpNode ? sp->alpha : alpha;
1337 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1338 doFullDepthSearch = (value > alpha);
1340 ss->reduction = DEPTH_ZERO; // Restore original reduction
1343 // Step 15. Full depth search
1344 if (doFullDepthSearch)
1346 alpha = SpNode ? sp->alpha : alpha;
1347 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1349 // Step extra. pv search (only in PV nodes)
1350 // Search only for possible new PV nodes, if instead value >= beta then
1351 // parent node fails low with value <= alpha and tries another move.
1352 if (PvNode && value > alpha && value < beta)
1353 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1357 // Step 16. Undo move
1358 pos.undo_move(move);
1360 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1362 // Step 17. Check for new best move
1365 lock_grab(&(sp->lock));
1366 bestValue = sp->bestValue;
1370 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1375 sp->bestValue = value;
1379 if (SpNode && (!PvNode || value >= beta))
1380 sp->stopRequest = true;
1382 if (PvNode && value < beta) // We want always alpha < beta
1389 if (value == value_mate_in(ply + 1))
1390 ss->mateKiller = move;
1392 ss->bestMove = move;
1395 sp->parentSstack->bestMove = move;
1399 // Step 18. Check for split
1401 && depth >= ThreadsMgr.min_split_depth()
1402 && ThreadsMgr.active_threads() > 1
1404 && ThreadsMgr.available_thread_exists(threadID)
1406 && !ThreadsMgr.thread_should_stop(threadID)
1408 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1409 threatMove, mateThreat, moveCount, &mp, PvNode);
1412 // Step 19. Check for mate and stalemate
1413 // All legal moves have been searched and if there are
1414 // no legal moves, it must be mate or stalemate.
1415 // If one move was excluded return fail low score.
1416 if (!SpNode && !moveCount)
1417 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1419 // Step 20. Update tables
1420 // If the search is not aborted, update the transposition table,
1421 // history counters, and killer moves.
1422 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1424 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1425 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1426 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1428 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1430 // Update killers and history only for non capture moves that fails high
1431 if ( bestValue >= beta
1432 && !pos.move_is_capture_or_promotion(move))
1434 update_history(pos, move, depth, movesSearched, moveCount);
1435 update_killers(move, ss);
1441 // Here we have the lock still grabbed
1442 sp->slaves[threadID] = 0;
1443 sp->nodes += pos.nodes_searched();
1444 lock_release(&(sp->lock));
1447 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1452 // qsearch() is the quiescence search function, which is called by the main
1453 // search function when the remaining depth is zero (or, to be more precise,
1454 // less than ONE_PLY).
1456 template <NodeType PvNode>
1457 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1459 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1460 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1461 assert(PvNode || alpha == beta - 1);
1463 assert(ply > 0 && ply < PLY_MAX);
1464 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1468 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1469 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1471 Value oldAlpha = alpha;
1473 ss->bestMove = ss->currentMove = MOVE_NONE;
1475 // Check for an instant draw or maximum ply reached
1476 if (pos.is_draw() || ply >= PLY_MAX - 1)
1479 // Decide whether or not to include checks
1480 isCheck = pos.is_check();
1483 if (isCheck || depth >= -ONE_PLY)
1486 d = DEPTH_ZERO - ONE_PLY;
1488 // Transposition table lookup. At PV nodes, we don't use the TT for
1489 // pruning, but only for move ordering.
1490 tte = TT.retrieve(pos.get_key());
1491 ttMove = (tte ? tte->move() : MOVE_NONE);
1493 if (!PvNode && tte && ok_to_use_TT(tte, d, beta, ply))
1495 ss->bestMove = ttMove; // Can be MOVE_NONE
1496 return value_from_tt(tte->value(), ply);
1499 // Evaluate the position statically
1502 bestValue = futilityBase = -VALUE_INFINITE;
1503 ss->eval = evalMargin = VALUE_NONE;
1504 enoughMaterial = false;
1510 assert(tte->static_value() != VALUE_NONE);
1512 evalMargin = tte->static_value_margin();
1513 ss->eval = bestValue = tte->static_value();
1516 ss->eval = bestValue = evaluate(pos, evalMargin);
1518 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1520 // Stand pat. Return immediately if static value is at least beta
1521 if (bestValue >= beta)
1524 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1529 if (PvNode && bestValue > alpha)
1532 // Futility pruning parameters, not needed when in check
1533 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1534 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1537 // Initialize a MovePicker object for the current position, and prepare
1538 // to search the moves. Because the depth is <= 0 here, only captures,
1539 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1540 // and we are near beta) will be generated.
1541 MovePicker mp = MovePicker(pos, ttMove, d, H);
1544 // Loop through the moves until no moves remain or a beta cutoff occurs
1545 while ( alpha < beta
1546 && (move = mp.get_next_move()) != MOVE_NONE)
1548 assert(move_is_ok(move));
1550 moveIsCheck = pos.move_is_check(move, ci);
1558 && !move_is_promotion(move)
1559 && !pos.move_is_passed_pawn_push(move))
1561 futilityValue = futilityBase
1562 + pos.endgame_value_of_piece_on(move_to(move))
1563 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1565 if (futilityValue < alpha)
1567 if (futilityValue > bestValue)
1568 bestValue = futilityValue;
1573 // Detect non-capture evasions that are candidate to be pruned
1574 evasionPrunable = isCheck
1575 && bestValue > value_mated_in(PLY_MAX)
1576 && !pos.move_is_capture(move)
1577 && !pos.can_castle(pos.side_to_move());
1579 // Don't search moves with negative SEE values
1581 && (!isCheck || evasionPrunable)
1583 && !move_is_promotion(move)
1584 && pos.see_sign(move) < 0)
1587 // Don't search useless checks
1592 && !pos.move_is_capture_or_promotion(move)
1593 && ss->eval + PawnValueMidgame / 4 < beta
1594 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1596 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1597 bestValue = ss->eval + PawnValueMidgame / 4;
1602 // Update current move
1603 ss->currentMove = move;
1605 // Make and search the move
1606 pos.do_move(move, st, ci, moveIsCheck);
1607 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1608 pos.undo_move(move);
1610 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1613 if (value > bestValue)
1619 ss->bestMove = move;
1624 // All legal moves have been searched. A special case: If we're in check
1625 // and no legal moves were found, it is checkmate.
1626 if (isCheck && bestValue == -VALUE_INFINITE)
1627 return value_mated_in(ply);
1629 // Update transposition table
1630 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1631 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1633 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1639 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1640 // bestValue is updated only when returning false because in that case move
1643 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1645 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1646 Square from, to, ksq, victimSq;
1649 Value futilityValue, bv = *bestValue;
1651 from = move_from(move);
1653 them = opposite_color(pos.side_to_move());
1654 ksq = pos.king_square(them);
1655 kingAtt = pos.attacks_from<KING>(ksq);
1656 pc = pos.piece_on(from);
1658 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1659 oldAtt = pos.attacks_from(pc, from, occ);
1660 newAtt = pos.attacks_from(pc, to, occ);
1662 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1663 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1665 if (!(b && (b & (b - 1))))
1668 // Rule 2. Queen contact check is very dangerous
1669 if ( type_of_piece(pc) == QUEEN
1670 && bit_is_set(kingAtt, to))
1673 // Rule 3. Creating new double threats with checks
1674 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1678 victimSq = pop_1st_bit(&b);
1679 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1681 // Note that here we generate illegal "double move"!
1682 if ( futilityValue >= beta
1683 && pos.see_sign(make_move(from, victimSq)) >= 0)
1686 if (futilityValue > bv)
1690 // Update bestValue only if check is not dangerous (because we will prune the move)
1696 // connected_moves() tests whether two moves are 'connected' in the sense
1697 // that the first move somehow made the second move possible (for instance
1698 // if the moving piece is the same in both moves). The first move is assumed
1699 // to be the move that was made to reach the current position, while the
1700 // second move is assumed to be a move from the current position.
1702 bool connected_moves(const Position& pos, Move m1, Move m2) {
1704 Square f1, t1, f2, t2;
1707 assert(move_is_ok(m1));
1708 assert(move_is_ok(m2));
1710 if (m2 == MOVE_NONE)
1713 // Case 1: The moving piece is the same in both moves
1719 // Case 2: The destination square for m2 was vacated by m1
1725 // Case 3: Moving through the vacated square
1726 if ( piece_is_slider(pos.piece_on(f2))
1727 && bit_is_set(squares_between(f2, t2), f1))
1730 // Case 4: The destination square for m2 is defended by the moving piece in m1
1731 p = pos.piece_on(t1);
1732 if (bit_is_set(pos.attacks_from(p, t1), t2))
1735 // Case 5: Discovered check, checking piece is the piece moved in m1
1736 if ( piece_is_slider(p)
1737 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1738 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1740 // discovered_check_candidates() works also if the Position's side to
1741 // move is the opposite of the checking piece.
1742 Color them = opposite_color(pos.side_to_move());
1743 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1745 if (bit_is_set(dcCandidates, f2))
1752 // value_is_mate() checks if the given value is a mate one eventually
1753 // compensated for the ply.
1755 bool value_is_mate(Value value) {
1757 assert(abs(value) <= VALUE_INFINITE);
1759 return value <= value_mated_in(PLY_MAX)
1760 || value >= value_mate_in(PLY_MAX);
1764 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1765 // "plies to mate from the current ply". Non-mate scores are unchanged.
1766 // The function is called before storing a value to the transposition table.
1768 Value value_to_tt(Value v, int ply) {
1770 if (v >= value_mate_in(PLY_MAX))
1773 if (v <= value_mated_in(PLY_MAX))
1780 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1781 // the transposition table to a mate score corrected for the current ply.
1783 Value value_from_tt(Value v, int ply) {
1785 if (v >= value_mate_in(PLY_MAX))
1788 if (v <= value_mated_in(PLY_MAX))
1795 // extension() decides whether a move should be searched with normal depth,
1796 // or with extended depth. Certain classes of moves (checking moves, in
1797 // particular) are searched with bigger depth than ordinary moves and in
1798 // any case are marked as 'dangerous'. Note that also if a move is not
1799 // extended, as example because the corresponding UCI option is set to zero,
1800 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1801 template <NodeType PvNode>
1802 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1803 bool singleEvasion, bool mateThreat, bool* dangerous) {
1805 assert(m != MOVE_NONE);
1807 Depth result = DEPTH_ZERO;
1808 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1812 if (moveIsCheck && pos.see_sign(m) >= 0)
1813 result += CheckExtension[PvNode];
1816 result += SingleEvasionExtension[PvNode];
1819 result += MateThreatExtension[PvNode];
1822 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1824 Color c = pos.side_to_move();
1825 if (relative_rank(c, move_to(m)) == RANK_7)
1827 result += PawnPushTo7thExtension[PvNode];
1830 if (pos.pawn_is_passed(c, move_to(m)))
1832 result += PassedPawnExtension[PvNode];
1837 if ( captureOrPromotion
1838 && pos.type_of_piece_on(move_to(m)) != PAWN
1839 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1840 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1841 && !move_is_promotion(m)
1844 result += PawnEndgameExtension[PvNode];
1849 && captureOrPromotion
1850 && pos.type_of_piece_on(move_to(m)) != PAWN
1851 && pos.see_sign(m) >= 0)
1853 result += ONE_PLY / 2;
1857 return Min(result, ONE_PLY);
1861 // connected_threat() tests whether it is safe to forward prune a move or if
1862 // is somehow coonected to the threat move returned by null search.
1864 bool connected_threat(const Position& pos, Move m, Move threat) {
1866 assert(move_is_ok(m));
1867 assert(threat && move_is_ok(threat));
1868 assert(!pos.move_is_check(m));
1869 assert(!pos.move_is_capture_or_promotion(m));
1870 assert(!pos.move_is_passed_pawn_push(m));
1872 Square mfrom, mto, tfrom, tto;
1874 mfrom = move_from(m);
1876 tfrom = move_from(threat);
1877 tto = move_to(threat);
1879 // Case 1: Don't prune moves which move the threatened piece
1883 // Case 2: If the threatened piece has value less than or equal to the
1884 // value of the threatening piece, don't prune move which defend it.
1885 if ( pos.move_is_capture(threat)
1886 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1887 || pos.type_of_piece_on(tfrom) == KING)
1888 && pos.move_attacks_square(m, tto))
1891 // Case 3: If the moving piece in the threatened move is a slider, don't
1892 // prune safe moves which block its ray.
1893 if ( piece_is_slider(pos.piece_on(tfrom))
1894 && bit_is_set(squares_between(tfrom, tto), mto)
1895 && pos.see_sign(m) >= 0)
1902 // ok_to_use_TT() returns true if a transposition table score
1903 // can be used at a given point in search.
1905 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1907 Value v = value_from_tt(tte->value(), ply);
1909 return ( tte->depth() >= depth
1910 || v >= Max(value_mate_in(PLY_MAX), beta)
1911 || v < Min(value_mated_in(PLY_MAX), beta))
1913 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1914 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1918 // refine_eval() returns the transposition table score if
1919 // possible otherwise falls back on static position evaluation.
1921 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1925 Value v = value_from_tt(tte->value(), ply);
1927 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1928 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1935 // update_history() registers a good move that produced a beta-cutoff
1936 // in history and marks as failures all the other moves of that ply.
1938 void update_history(const Position& pos, Move move, Depth depth,
1939 Move movesSearched[], int moveCount) {
1942 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1944 for (int i = 0; i < moveCount - 1; i++)
1946 m = movesSearched[i];
1950 if (!pos.move_is_capture_or_promotion(m))
1951 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1956 // update_killers() add a good move that produced a beta-cutoff
1957 // among the killer moves of that ply.
1959 void update_killers(Move m, SearchStack* ss) {
1961 if (m == ss->killers[0])
1964 ss->killers[1] = ss->killers[0];
1969 // update_gains() updates the gains table of a non-capture move given
1970 // the static position evaluation before and after the move.
1972 void update_gains(const Position& pos, Move m, Value before, Value after) {
1975 && before != VALUE_NONE
1976 && after != VALUE_NONE
1977 && pos.captured_piece_type() == PIECE_TYPE_NONE
1978 && !move_is_special(m))
1979 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1983 // current_search_time() returns the number of milliseconds which have passed
1984 // since the beginning of the current search.
1986 int current_search_time() {
1988 return get_system_time() - SearchStartTime;
1992 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1994 std::string value_to_uci(Value v) {
1996 std::stringstream s;
1998 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1999 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2001 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2006 // nps() computes the current nodes/second count.
2008 int nps(const Position& pos) {
2010 int t = current_search_time();
2011 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
2015 // poll() performs two different functions: It polls for user input, and it
2016 // looks at the time consumed so far and decides if it's time to abort the
2019 void poll(const Position& pos) {
2021 static int lastInfoTime;
2022 int t = current_search_time();
2025 if (data_available())
2027 // We are line oriented, don't read single chars
2028 std::string command;
2030 if (!std::getline(std::cin, command))
2033 if (command == "quit")
2036 PonderSearch = false;
2040 else if (command == "stop")
2043 PonderSearch = false;
2045 else if (command == "ponderhit")
2049 // Print search information
2053 else if (lastInfoTime > t)
2054 // HACK: Must be a new search where we searched less than
2055 // NodesBetweenPolls nodes during the first second of search.
2058 else if (t - lastInfoTime >= 1000)
2065 if (dbg_show_hit_rate)
2066 dbg_print_hit_rate();
2068 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
2069 << " time " << t << endl;
2072 // Should we stop the search?
2076 bool stillAtFirstMove = FirstRootMove
2077 && !AspirationFailLow
2078 && t > TimeMgr.available_time();
2080 bool noMoreTime = t > TimeMgr.maximum_time()
2081 || stillAtFirstMove;
2083 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2084 || (ExactMaxTime && t >= ExactMaxTime)
2085 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2090 // ponderhit() is called when the program is pondering (i.e. thinking while
2091 // it's the opponent's turn to move) in order to let the engine know that
2092 // it correctly predicted the opponent's move.
2096 int t = current_search_time();
2097 PonderSearch = false;
2099 bool stillAtFirstMove = FirstRootMove
2100 && !AspirationFailLow
2101 && t > TimeMgr.available_time();
2103 bool noMoreTime = t > TimeMgr.maximum_time()
2104 || stillAtFirstMove;
2106 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2111 // init_ss_array() does a fast reset of the first entries of a SearchStack
2112 // array and of all the excludedMove and skipNullMove entries.
2114 void init_ss_array(SearchStack* ss, int size) {
2116 for (int i = 0; i < size; i++, ss++)
2118 ss->excludedMove = MOVE_NONE;
2119 ss->skipNullMove = false;
2120 ss->reduction = DEPTH_ZERO;
2124 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2129 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2130 // while the program is pondering. The point is to work around a wrinkle in
2131 // the UCI protocol: When pondering, the engine is not allowed to give a
2132 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2133 // We simply wait here until one of these commands is sent, and return,
2134 // after which the bestmove and pondermove will be printed (in id_loop()).
2136 void wait_for_stop_or_ponderhit() {
2138 std::string command;
2142 if (!std::getline(std::cin, command))
2145 if (command == "quit")
2150 else if (command == "ponderhit" || command == "stop")
2156 // print_pv_info() prints to standard output and eventually to log file information on
2157 // the current PV line. It is called at each iteration or after a new pv is found.
2159 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2161 cout << "info depth " << Iteration
2162 << " score " << value_to_uci(value)
2163 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2164 << " time " << current_search_time()
2165 << " nodes " << pos.nodes_searched()
2166 << " nps " << nps(pos)
2169 for (Move* m = pv; *m != MOVE_NONE; m++)
2176 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2177 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2179 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2184 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2185 // the PV back into the TT. This makes sure the old PV moves are searched
2186 // first, even if the old TT entries have been overwritten.
2188 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2192 Position p(pos, pos.thread());
2193 Value v, m = VALUE_NONE;
2195 for (int i = 0; pv[i] != MOVE_NONE; i++)
2197 tte = TT.retrieve(p.get_key());
2198 if (!tte || tte->move() != pv[i])
2200 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2201 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2203 p.do_move(pv[i], st);
2208 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2209 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2210 // allow to always have a ponder move even when we fail high at root and also a
2211 // long PV to print that is important for position analysis.
2213 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2217 Position p(pos, pos.thread());
2220 assert(bestMove != MOVE_NONE);
2223 p.do_move(pv[ply++], st);
2225 while ( (tte = TT.retrieve(p.get_key())) != NULL
2226 && tte->move() != MOVE_NONE
2227 && move_is_legal(p, tte->move())
2229 && (!p.is_draw() || ply < 2))
2231 pv[ply] = tte->move();
2232 p.do_move(pv[ply++], st);
2234 pv[ply] = MOVE_NONE;
2238 // init_thread() is the function which is called when a new thread is
2239 // launched. It simply calls the idle_loop() function with the supplied
2240 // threadID. There are two versions of this function; one for POSIX
2241 // threads and one for Windows threads.
2243 #if !defined(_MSC_VER)
2245 void* init_thread(void* threadID) {
2247 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2253 DWORD WINAPI init_thread(LPVOID threadID) {
2255 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2262 /// The ThreadsManager class
2265 // read_uci_options() updates number of active threads and other internal
2266 // parameters according to the UCI options values. It is called before
2267 // to start a new search.
2269 void ThreadsManager::read_uci_options() {
2271 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2272 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2273 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2274 activeThreads = Options["Threads"].value<int>();
2278 // idle_loop() is where the threads are parked when they have no work to do.
2279 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2280 // object for which the current thread is the master.
2282 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2284 assert(threadID >= 0 && threadID < MAX_THREADS);
2287 bool allFinished = false;
2291 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2292 // master should exit as last one.
2293 if (allThreadsShouldExit)
2296 threads[threadID].state = THREAD_TERMINATED;
2300 // If we are not thinking, wait for a condition to be signaled
2301 // instead of wasting CPU time polling for work.
2302 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2303 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2305 assert(!sp || useSleepingThreads);
2306 assert(threadID != 0 || useSleepingThreads);
2308 if (threads[threadID].state == THREAD_INITIALIZING)
2309 threads[threadID].state = THREAD_AVAILABLE;
2311 // Grab the lock to avoid races with wake_sleeping_thread()
2312 lock_grab(&sleepLock[threadID]);
2314 // If we are master and all slaves have finished do not go to sleep
2315 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2316 allFinished = (i == activeThreads);
2318 if (allFinished || allThreadsShouldExit)
2320 lock_release(&sleepLock[threadID]);
2324 // Do sleep here after retesting sleep conditions
2325 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2326 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2328 lock_release(&sleepLock[threadID]);
2331 // If this thread has been assigned work, launch a search
2332 if (threads[threadID].state == THREAD_WORKISWAITING)
2334 assert(!allThreadsShouldExit);
2336 threads[threadID].state = THREAD_SEARCHING;
2338 // Here we call search() with SplitPoint template parameter set to true
2339 SplitPoint* tsp = threads[threadID].splitPoint;
2340 Position pos(*tsp->pos, threadID);
2341 SearchStack* ss = tsp->sstack[threadID] + 1;
2345 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2347 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2349 assert(threads[threadID].state == THREAD_SEARCHING);
2351 threads[threadID].state = THREAD_AVAILABLE;
2353 // Wake up master thread so to allow it to return from the idle loop in
2354 // case we are the last slave of the split point.
2355 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2356 wake_sleeping_thread(tsp->master);
2359 // If this thread is the master of a split point and all slaves have
2360 // finished their work at this split point, return from the idle loop.
2361 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2362 allFinished = (i == activeThreads);
2366 // Because sp->slaves[] is reset under lock protection,
2367 // be sure sp->lock has been released before to return.
2368 lock_grab(&(sp->lock));
2369 lock_release(&(sp->lock));
2371 // In helpful master concept a master can help only a sub-tree, and
2372 // because here is all finished is not possible master is booked.
2373 assert(threads[threadID].state == THREAD_AVAILABLE);
2375 threads[threadID].state = THREAD_SEARCHING;
2382 // init_threads() is called during startup. It launches all helper threads,
2383 // and initializes the split point stack and the global locks and condition
2386 void ThreadsManager::init_threads() {
2388 int i, arg[MAX_THREADS];
2391 // Initialize global locks
2394 for (i = 0; i < MAX_THREADS; i++)
2396 lock_init(&sleepLock[i]);
2397 cond_init(&sleepCond[i]);
2400 // Initialize splitPoints[] locks
2401 for (i = 0; i < MAX_THREADS; i++)
2402 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2403 lock_init(&(threads[i].splitPoints[j].lock));
2405 // Will be set just before program exits to properly end the threads
2406 allThreadsShouldExit = false;
2408 // Threads will be put all threads to sleep as soon as created
2411 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2412 threads[0].state = THREAD_SEARCHING;
2413 for (i = 1; i < MAX_THREADS; i++)
2414 threads[i].state = THREAD_INITIALIZING;
2416 // Launch the helper threads
2417 for (i = 1; i < MAX_THREADS; i++)
2421 #if !defined(_MSC_VER)
2422 pthread_t pthread[1];
2423 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2424 pthread_detach(pthread[0]);
2426 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2430 cout << "Failed to create thread number " << i << endl;
2434 // Wait until the thread has finished launching and is gone to sleep
2435 while (threads[i].state == THREAD_INITIALIZING) {}
2440 // exit_threads() is called when the program exits. It makes all the
2441 // helper threads exit cleanly.
2443 void ThreadsManager::exit_threads() {
2445 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2447 // Wake up all the threads and waits for termination
2448 for (int i = 1; i < MAX_THREADS; i++)
2450 wake_sleeping_thread(i);
2451 while (threads[i].state != THREAD_TERMINATED) {}
2454 // Now we can safely destroy the locks
2455 for (int i = 0; i < MAX_THREADS; i++)
2456 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2457 lock_destroy(&(threads[i].splitPoints[j].lock));
2459 lock_destroy(&mpLock);
2461 // Now we can safely destroy the wait conditions
2462 for (int i = 0; i < MAX_THREADS; i++)
2464 lock_destroy(&sleepLock[i]);
2465 cond_destroy(&sleepCond[i]);
2470 // thread_should_stop() checks whether the thread should stop its search.
2471 // This can happen if a beta cutoff has occurred in the thread's currently
2472 // active split point, or in some ancestor of the current split point.
2474 bool ThreadsManager::thread_should_stop(int threadID) const {
2476 assert(threadID >= 0 && threadID < activeThreads);
2478 SplitPoint* sp = threads[threadID].splitPoint;
2480 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2485 // thread_is_available() checks whether the thread with threadID "slave" is
2486 // available to help the thread with threadID "master" at a split point. An
2487 // obvious requirement is that "slave" must be idle. With more than two
2488 // threads, this is not by itself sufficient: If "slave" is the master of
2489 // some active split point, it is only available as a slave to the other
2490 // threads which are busy searching the split point at the top of "slave"'s
2491 // split point stack (the "helpful master concept" in YBWC terminology).
2493 bool ThreadsManager::thread_is_available(int slave, int master) const {
2495 assert(slave >= 0 && slave < activeThreads);
2496 assert(master >= 0 && master < activeThreads);
2497 assert(activeThreads > 1);
2499 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2502 // Make a local copy to be sure doesn't change under our feet
2503 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2505 // No active split points means that the thread is available as
2506 // a slave for any other thread.
2507 if (localActiveSplitPoints == 0 || activeThreads == 2)
2510 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2511 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2512 // could have been set to 0 by another thread leading to an out of bound access.
2513 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2520 // available_thread_exists() tries to find an idle thread which is available as
2521 // a slave for the thread with threadID "master".
2523 bool ThreadsManager::available_thread_exists(int master) const {
2525 assert(master >= 0 && master < activeThreads);
2526 assert(activeThreads > 1);
2528 for (int i = 0; i < activeThreads; i++)
2529 if (thread_is_available(i, master))
2536 // split() does the actual work of distributing the work at a node between
2537 // several available threads. If it does not succeed in splitting the
2538 // node (because no idle threads are available, or because we have no unused
2539 // split point objects), the function immediately returns. If splitting is
2540 // possible, a SplitPoint object is initialized with all the data that must be
2541 // copied to the helper threads and we tell our helper threads that they have
2542 // been assigned work. This will cause them to instantly leave their idle loops and
2543 // call search().When all threads have returned from search() then split() returns.
2545 template <bool Fake>
2546 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2547 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2548 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2549 assert(pos.is_ok());
2550 assert(ply > 0 && ply < PLY_MAX);
2551 assert(*bestValue >= -VALUE_INFINITE);
2552 assert(*bestValue <= *alpha);
2553 assert(*alpha < beta);
2554 assert(beta <= VALUE_INFINITE);
2555 assert(depth > DEPTH_ZERO);
2556 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2557 assert(activeThreads > 1);
2559 int i, master = pos.thread();
2560 Thread& masterThread = threads[master];
2564 // If no other thread is available to help us, or if we have too many
2565 // active split points, don't split.
2566 if ( !available_thread_exists(master)
2567 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2569 lock_release(&mpLock);
2573 // Pick the next available split point object from the split point stack
2574 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2576 // Initialize the split point object
2577 splitPoint.parent = masterThread.splitPoint;
2578 splitPoint.master = master;
2579 splitPoint.stopRequest = false;
2580 splitPoint.ply = ply;
2581 splitPoint.depth = depth;
2582 splitPoint.threatMove = threatMove;
2583 splitPoint.mateThreat = mateThreat;
2584 splitPoint.alpha = *alpha;
2585 splitPoint.beta = beta;
2586 splitPoint.pvNode = pvNode;
2587 splitPoint.bestValue = *bestValue;
2589 splitPoint.moveCount = moveCount;
2590 splitPoint.pos = &pos;
2591 splitPoint.nodes = 0;
2592 splitPoint.parentSstack = ss;
2593 for (i = 0; i < activeThreads; i++)
2594 splitPoint.slaves[i] = 0;
2596 masterThread.splitPoint = &splitPoint;
2598 // If we are here it means we are not available
2599 assert(masterThread.state != THREAD_AVAILABLE);
2601 int workersCnt = 1; // At least the master is included
2603 // Allocate available threads setting state to THREAD_BOOKED
2604 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2605 if (thread_is_available(i, master))
2607 threads[i].state = THREAD_BOOKED;
2608 threads[i].splitPoint = &splitPoint;
2609 splitPoint.slaves[i] = 1;
2613 assert(Fake || workersCnt > 1);
2615 // We can release the lock because slave threads are already booked and master is not available
2616 lock_release(&mpLock);
2618 // Tell the threads that they have work to do. This will make them leave
2619 // their idle loop. But before copy search stack tail for each thread.
2620 for (i = 0; i < activeThreads; i++)
2621 if (i == master || splitPoint.slaves[i])
2623 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2625 assert(i == master || threads[i].state == THREAD_BOOKED);
2627 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2629 if (useSleepingThreads && i != master)
2630 wake_sleeping_thread(i);
2633 // Everything is set up. The master thread enters the idle loop, from
2634 // which it will instantly launch a search, because its state is
2635 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2636 // idle loop, which means that the main thread will return from the idle
2637 // loop when all threads have finished their work at this split point.
2638 idle_loop(master, &splitPoint);
2640 // We have returned from the idle loop, which means that all threads are
2641 // finished. Update alpha and bestValue, and return.
2644 *alpha = splitPoint.alpha;
2645 *bestValue = splitPoint.bestValue;
2646 masterThread.activeSplitPoints--;
2647 masterThread.splitPoint = splitPoint.parent;
2648 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2650 lock_release(&mpLock);
2654 // wake_sleeping_thread() wakes up the thread with the given threadID
2655 // when it is time to start a new search.
2657 void ThreadsManager::wake_sleeping_thread(int threadID) {
2659 lock_grab(&sleepLock[threadID]);
2660 cond_signal(&sleepCond[threadID]);
2661 lock_release(&sleepLock[threadID]);
2665 /// The RootMoveList class
2667 // RootMoveList c'tor
2669 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2671 SearchStack ss[PLY_MAX_PLUS_2];
2672 MoveStack mlist[MOVES_MAX];
2674 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2676 // Initialize search stack
2677 init_ss_array(ss, PLY_MAX_PLUS_2);
2678 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2681 // Generate all legal moves
2682 MoveStack* last = generate_moves(pos, mlist);
2684 // Add each move to the moves[] array
2685 for (MoveStack* cur = mlist; cur != last; cur++)
2687 bool includeMove = includeAllMoves;
2689 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2690 includeMove = (searchMoves[k] == cur->move);
2695 // Find a quick score for the move
2696 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2697 moves[count].pv[1] = MOVE_NONE;
2698 pos.do_move(cur->move, st);
2699 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2700 pos.undo_move(cur->move);
2706 // Score root moves using the standard way used in main search, the moves
2707 // are scored according to the order in which are returned by MovePicker.
2709 void RootMoveList::score_moves(const Position& pos)
2713 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2715 while ((move = mp.get_next_move()) != MOVE_NONE)
2716 for (int i = 0; i < count; i++)
2717 if (moves[i].move == move)
2719 moves[i].mp_score = score--;
2724 // RootMoveList simple methods definitions
2726 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2730 for (j = 0; pv[j] != MOVE_NONE; j++)
2731 moves[moveNum].pv[j] = pv[j];
2733 moves[moveNum].pv[j] = MOVE_NONE;
2737 // RootMoveList::sort() sorts the root move list at the beginning of a new
2740 void RootMoveList::sort() {
2742 sort_multipv(count - 1); // Sort all items
2746 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2747 // list by their scores and depths. It is used to order the different PVs
2748 // correctly in MultiPV mode.
2750 void RootMoveList::sort_multipv(int n) {
2754 for (i = 1; i <= n; i++)
2756 RootMove rm = moves[i];
2757 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2758 moves[j] = moves[j - 1];