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 connected_moves(const Position& pos, Move m1, Move m2);
301 bool value_is_mate(Value value);
302 Value value_to_tt(Value v, int ply);
303 Value value_from_tt(Value v, int ply);
304 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
305 bool connected_threat(const Position& pos, Move m, Move threat);
306 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
307 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
308 void update_killers(Move m, SearchStack* ss);
309 void update_gains(const Position& pos, Move move, Value before, Value after);
311 int current_search_time();
312 std::string value_to_uci(Value v);
313 int nps(const Position& pos);
314 void poll(const Position& pos);
316 void wait_for_stop_or_ponderhit();
317 void init_ss_array(SearchStack* ss, int size);
318 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
319 void insert_pv_in_tt(const Position& pos, Move pv[]);
320 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
322 #if !defined(_MSC_VER)
323 void* init_thread(void* threadID);
325 DWORD WINAPI init_thread(LPVOID threadID);
335 /// init_threads(), exit_threads() and nodes_searched() are helpers to
336 /// give accessibility to some TM methods from outside of current file.
338 void init_threads() { ThreadsMgr.init_threads(); }
339 void exit_threads() { ThreadsMgr.exit_threads(); }
342 /// init_search() is called during startup. It initializes various lookup tables
346 int d; // depth (ONE_PLY == 2)
347 int hd; // half depth (ONE_PLY == 1)
350 // Init reductions array
351 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
353 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
354 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
355 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
356 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
359 // Init futility margins array
360 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
361 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
363 // Init futility move count array
364 for (d = 0; d < 32; d++)
365 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
369 /// perft() is our utility to verify move generation is bug free. All the legal
370 /// moves up to given depth are generated and counted and the sum returned.
372 int perft(Position& pos, Depth depth)
374 MoveStack mlist[MOVES_MAX];
379 // Generate all legal moves
380 MoveStack* last = generate_moves(pos, mlist);
382 // If we are at the last ply we don't need to do and undo
383 // the moves, just to count them.
384 if (depth <= ONE_PLY)
385 return int(last - mlist);
387 // Loop through all legal moves
389 for (MoveStack* cur = mlist; cur != last; cur++)
392 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
393 sum += perft(pos, depth - ONE_PLY);
400 /// think() is the external interface to Stockfish's search, and is called when
401 /// the program receives the UCI 'go' command. It initializes various
402 /// search-related global variables, and calls root_search(). It returns false
403 /// when a quit command is received during the search.
405 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
406 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
408 // Initialize global search variables
409 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
411 SearchStartTime = get_system_time();
412 ExactMaxTime = maxTime;
415 InfiniteSearch = infinite;
416 PonderSearch = ponder;
417 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
419 // Look for a book move, only during games, not tests
420 if (UseTimeManagement && Options["OwnBook"].value<bool>())
422 if (Options["Book File"].value<std::string>() != OpeningBook.file_name())
423 OpeningBook.open(Options["Book File"].value<std::string>());
425 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
426 if (bookMove != MOVE_NONE)
429 wait_for_stop_or_ponderhit();
431 cout << "bestmove " << bookMove << endl;
436 // Read UCI option values
437 TT.set_size(Options["Hash"].value<int>());
438 if (Options["Clear Hash"].value<bool>())
440 Options["Clear Hash"].set_value("false");
444 CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
445 CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
446 SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
447 SingleEvasionExtension[0] = Options["Single Evasion Extension (non-PV nodes)"].value<Depth>();
448 PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
449 PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
450 PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
451 PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
452 PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
453 PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
454 MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
455 MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
456 MultiPV = Options["MultiPV"].value<int>();
457 UseLogFile = Options["Use Search Log"].value<bool>();
460 LogFile.open(Options["Search Log Filename"].value<std::string>().c_str(), std::ios::out | std::ios::app);
462 read_weights(pos.side_to_move());
464 // Set the number of active threads
465 ThreadsMgr.read_uci_options();
466 init_eval(ThreadsMgr.active_threads());
468 // Wake up needed threads
469 for (int i = 1; i < ThreadsMgr.active_threads(); i++)
470 ThreadsMgr.wake_sleeping_thread(i);
473 int myTime = time[pos.side_to_move()];
474 int myIncrement = increment[pos.side_to_move()];
475 if (UseTimeManagement)
476 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
478 // Set best NodesBetweenPolls interval to avoid lagging under
479 // heavy time pressure.
481 NodesBetweenPolls = Min(MaxNodes, 30000);
482 else if (myTime && myTime < 1000)
483 NodesBetweenPolls = 1000;
484 else if (myTime && myTime < 5000)
485 NodesBetweenPolls = 5000;
487 NodesBetweenPolls = 30000;
489 // Write search information to log file
491 LogFile << "Searching: " << pos.to_fen() << endl
492 << "infinite: " << infinite
493 << " ponder: " << ponder
494 << " time: " << myTime
495 << " increment: " << myIncrement
496 << " moves to go: " << movesToGo << endl;
498 // We're ready to start thinking. Call the iterative deepening loop function
499 id_loop(pos, searchMoves);
504 // This makes all the threads to go to sleep
505 ThreadsMgr.set_active_threads(1);
513 // id_loop() is the main iterative deepening loop. It calls root_search
514 // repeatedly with increasing depth until the allocated thinking time has
515 // been consumed, the user stops the search, or the maximum search depth is
518 Value id_loop(Position& pos, Move searchMoves[]) {
520 SearchStack ss[PLY_MAX_PLUS_2];
521 Move pv[PLY_MAX_PLUS_2];
522 Move EasyMove = MOVE_NONE;
523 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
525 // Moves to search are verified, copied, scored and sorted
526 RootMoveList rml(pos, searchMoves);
528 // Handle special case of searching on a mate/stale position
529 if (rml.move_count() == 0)
532 wait_for_stop_or_ponderhit();
534 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
537 // Print RootMoveList startup scoring to the standard output,
538 // so to output information also for iteration 1.
539 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
540 << "info depth " << 1
541 << "\ninfo depth " << 1
542 << " score " << value_to_uci(rml.move_score(0))
543 << " time " << current_search_time()
544 << " nodes " << pos.nodes_searched()
545 << " nps " << nps(pos)
546 << " pv " << rml.move(0) << "\n";
551 init_ss_array(ss, PLY_MAX_PLUS_2);
552 pv[0] = pv[1] = MOVE_NONE;
553 ValueByIteration[1] = rml.move_score(0);
556 // Is one move significantly better than others after initial scoring ?
557 if ( rml.move_count() == 1
558 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
559 EasyMove = rml.move(0);
561 // Iterative deepening loop
562 while (Iteration < PLY_MAX)
564 // Initialize iteration
566 BestMoveChangesByIteration[Iteration] = 0;
568 cout << "info depth " << Iteration << endl;
570 // Calculate dynamic aspiration window based on previous iterations
571 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
573 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
574 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
576 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
577 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
579 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
580 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
583 // Search to the current depth, rml is updated and sorted, alpha and beta could change
584 value = root_search(pos, ss, pv, rml, &alpha, &beta);
586 // Write PV to transposition table, in case the relevant entries have
587 // been overwritten during the search.
588 insert_pv_in_tt(pos, pv);
591 break; // Value cannot be trusted. Break out immediately!
593 //Save info about search result
594 ValueByIteration[Iteration] = value;
596 // Drop the easy move if differs from the new best move
597 if (pv[0] != EasyMove)
598 EasyMove = MOVE_NONE;
600 if (UseTimeManagement)
603 bool stopSearch = false;
605 // Stop search early if there is only a single legal move,
606 // we search up to Iteration 6 anyway to get a proper score.
607 if (Iteration >= 6 && rml.move_count() == 1)
610 // Stop search early when the last two iterations returned a mate score
612 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
613 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
616 // Stop search early if one move seems to be much better than the others
619 && ( ( rml.move_nodes(0) > (pos.nodes_searched() * 85) / 100
620 && current_search_time() > TimeMgr.available_time() / 16)
621 ||( rml.move_nodes(0) > (pos.nodes_searched() * 98) / 100
622 && current_search_time() > TimeMgr.available_time() / 32)))
625 // Add some extra time if the best move has changed during the last two iterations
626 if (Iteration > 5 && Iteration <= 50)
627 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
628 BestMoveChangesByIteration[Iteration-1]);
630 // Stop search if most of MaxSearchTime is consumed at the end of the
631 // iteration. We probably don't have enough time to search the first
632 // move at the next iteration anyway.
633 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
639 StopOnPonderhit = true;
645 if (MaxDepth && Iteration >= MaxDepth)
649 // If we are pondering or in infinite search, we shouldn't print the
650 // best move before we are told to do so.
651 if (!AbortSearch && (PonderSearch || InfiniteSearch))
652 wait_for_stop_or_ponderhit();
654 // Print final search statistics
655 cout << "info nodes " << pos.nodes_searched()
656 << " nps " << nps(pos)
657 << " time " << current_search_time() << endl;
659 // Print the best move and the ponder move to the standard output
660 if (pv[0] == MOVE_NONE || MultiPV > 1)
666 assert(pv[0] != MOVE_NONE);
668 cout << "bestmove " << pv[0];
670 if (pv[1] != MOVE_NONE)
671 cout << " ponder " << pv[1];
678 dbg_print_mean(LogFile);
680 if (dbg_show_hit_rate)
681 dbg_print_hit_rate(LogFile);
683 LogFile << "\nNodes: " << pos.nodes_searched()
684 << "\nNodes/second: " << nps(pos)
685 << "\nBest move: " << move_to_san(pos, pv[0]);
688 pos.do_move(pv[0], st);
689 LogFile << "\nPonder move: "
690 << move_to_san(pos, pv[1]) // Works also with MOVE_NONE
693 return rml.move_score(0);
697 // root_search() is the function which searches the root node. It is
698 // similar to search_pv except that it uses a different move ordering
699 // scheme, prints some information to the standard output and handles
700 // the fail low/high loops.
702 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
708 Depth depth, ext, newDepth;
709 Value value, alpha, beta;
710 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
711 int researchCountFH, researchCountFL;
713 researchCountFH = researchCountFL = 0;
716 isCheck = pos.is_check();
717 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
719 // Step 1. Initialize node (polling is omitted at root)
720 ss->currentMove = ss->bestMove = MOVE_NONE;
722 // Step 2. Check for aborted search (omitted at root)
723 // Step 3. Mate distance pruning (omitted at root)
724 // Step 4. Transposition table lookup (omitted at root)
726 // Step 5. Evaluate the position statically
727 // At root we do this only to get reference value for child nodes
728 ss->evalMargin = VALUE_NONE;
729 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
731 // Step 6. Razoring (omitted at root)
732 // Step 7. Static null move pruning (omitted at root)
733 // Step 8. Null move search with verification search (omitted at root)
734 // Step 9. Internal iterative deepening (omitted at root)
736 // Step extra. Fail low loop
737 // We start with small aspiration window and in case of fail low, we research
738 // with bigger window until we are not failing low anymore.
741 // Sort the moves before to (re)search
742 rml.score_moves(pos);
745 // Step 10. Loop through all moves in the root move list
746 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
748 // This is used by time management
749 FirstRootMove = (i == 0);
751 // Save the current node count before the move is searched
752 nodes = pos.nodes_searched();
754 // Pick the next root move, and print the move and the move number to
755 // the standard output.
756 move = ss->currentMove = rml.move(i);
758 if (current_search_time() >= 1000)
759 cout << "info currmove " << move
760 << " currmovenumber " << i + 1 << endl;
762 moveIsCheck = pos.move_is_check(move);
763 captureOrPromotion = pos.move_is_capture_or_promotion(move);
765 // Step 11. Decide the new search depth
766 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
767 newDepth = depth + ext;
769 // Step 12. Futility pruning (omitted at root)
771 // Step extra. Fail high loop
772 // If move fails high, we research with bigger window until we are not failing
774 value = - VALUE_INFINITE;
778 // Step 13. Make the move
779 pos.do_move(move, st, ci, moveIsCheck);
781 // Step extra. pv search
782 // We do pv search for first moves (i < MultiPV)
783 // and for fail high research (value > alpha)
784 if (i < MultiPV || value > alpha)
786 // Aspiration window is disabled in multi-pv case
788 alpha = -VALUE_INFINITE;
790 // Full depth PV search, done on first move or after a fail high
791 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
795 // Step 14. Reduced search
796 // if the move fails high will be re-searched at full depth
797 bool doFullDepthSearch = true;
799 if ( depth >= 3 * ONE_PLY
801 && !captureOrPromotion
802 && !move_is_castle(move))
804 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
807 assert(newDepth-ss->reduction >= ONE_PLY);
809 // Reduced depth non-pv search using alpha as upperbound
810 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
811 doFullDepthSearch = (value > alpha);
814 // The move failed high, but if reduction is very big we could
815 // face a false positive, retry with a less aggressive reduction,
816 // if the move fails high again then go with full depth search.
817 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
819 assert(newDepth - ONE_PLY >= ONE_PLY);
821 ss->reduction = ONE_PLY;
822 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
823 doFullDepthSearch = (value > alpha);
825 ss->reduction = DEPTH_ZERO; // Restore original reduction
828 // Step 15. Full depth search
829 if (doFullDepthSearch)
831 // Full depth non-pv search using alpha as upperbound
832 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
834 // If we are above alpha then research at same depth but as PV
835 // to get a correct score or eventually a fail high above beta.
837 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
841 // Step 16. Undo move
844 // Can we exit fail high loop ?
845 if (AbortSearch || value < beta)
848 // We are failing high and going to do a research. It's important to update
849 // the score before research in case we run out of time while researching.
850 rml.set_move_score(i, value);
852 extract_pv_from_tt(pos, move, pv);
853 rml.set_move_pv(i, pv);
855 // Print information to the standard output
856 print_pv_info(pos, pv, alpha, beta, value);
858 // Prepare for a research after a fail high, each time with a wider window
859 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
862 } // End of fail high loop
864 // Finished searching the move. If AbortSearch is true, the search
865 // was aborted because the user interrupted the search or because we
866 // ran out of time. In this case, the return value of the search cannot
867 // be trusted, and we break out of the loop without updating the best
872 // Remember searched nodes counts for this move
873 rml.add_move_nodes(i, pos.nodes_searched() - nodes);
875 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
876 assert(value < beta);
878 // Step 17. Check for new best move
879 if (value <= alpha && i >= MultiPV)
880 rml.set_move_score(i, -VALUE_INFINITE);
883 // PV move or new best move!
886 rml.set_move_score(i, value);
888 extract_pv_from_tt(pos, move, pv);
889 rml.set_move_pv(i, pv);
893 // We record how often the best move has been changed in each
894 // iteration. This information is used for time managment: When
895 // the best move changes frequently, we allocate some more time.
897 BestMoveChangesByIteration[Iteration]++;
899 // Print information to the standard output
900 print_pv_info(pos, pv, alpha, beta, value);
902 // Raise alpha to setup proper non-pv search upper bound
909 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
911 cout << "info multipv " << j + 1
912 << " score " << value_to_uci(rml.move_score(j))
913 << " depth " << (j <= i ? Iteration : Iteration - 1)
914 << " time " << current_search_time()
915 << " nodes " << pos.nodes_searched()
916 << " nps " << nps(pos)
919 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
920 cout << rml.move_pv(j, k) << " ";
924 alpha = rml.move_score(Min(i, MultiPV - 1));
926 } // PV move or new best move
928 assert(alpha >= *alphaPtr);
930 AspirationFailLow = (alpha == *alphaPtr);
932 if (AspirationFailLow && StopOnPonderhit)
933 StopOnPonderhit = false;
936 // Can we exit fail low loop ?
937 if (AbortSearch || !AspirationFailLow)
940 // Prepare for a research after a fail low, each time with a wider window
941 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
946 // Sort the moves before to return
953 // search<>() is the main search function for both PV and non-PV nodes and for
954 // normal and SplitPoint nodes. When called just after a split point the search
955 // is simpler because we have already probed the hash table, done a null move
956 // search, and searched the first move before splitting, we don't have to repeat
957 // all this work again. We also don't need to store anything to the hash table
958 // here: This is taken care of after we return from the split point.
960 template <NodeType PvNode, bool SpNode>
961 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
963 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
964 assert(beta > alpha && beta <= VALUE_INFINITE);
965 assert(PvNode || alpha == beta - 1);
966 assert(ply > 0 && ply < PLY_MAX);
967 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
969 Move movesSearched[MOVES_MAX];
973 Move ttMove, move, excludedMove, threatMove;
976 Value bestValue, value, oldAlpha;
977 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
978 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
979 bool mateThreat = false;
981 int threadID = pos.thread();
982 SplitPoint* sp = NULL;
983 refinedValue = bestValue = value = -VALUE_INFINITE;
985 isCheck = pos.is_check();
991 ttMove = excludedMove = MOVE_NONE;
992 threatMove = sp->threatMove;
993 mateThreat = sp->mateThreat;
994 goto split_point_start;
995 } else {} // Hack to fix icc's "statement is unreachable" warning
997 // Step 1. Initialize node and poll. Polling can abort search
998 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
999 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1001 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1007 // Step 2. Check for aborted search and immediate draw
1008 if ( AbortSearch || ThreadsMgr.thread_should_stop(threadID)
1009 || pos.is_draw() || ply >= PLY_MAX - 1)
1012 // Step 3. Mate distance pruning
1013 alpha = Max(value_mated_in(ply), alpha);
1014 beta = Min(value_mate_in(ply+1), beta);
1018 // Step 4. Transposition table lookup
1020 // We don't want the score of a partial search to overwrite a previous full search
1021 // TT value, so we use a different position key in case of an excluded move exists.
1022 excludedMove = ss->excludedMove;
1023 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1025 tte = TT.retrieve(posKey);
1026 ttMove = tte ? tte->move() : MOVE_NONE;
1028 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1029 // This is to avoid problems in the following areas:
1031 // * Repetition draw detection
1032 // * Fifty move rule detection
1033 // * Searching for a mate
1034 // * Printing of full PV line
1035 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1038 ss->bestMove = ttMove; // Can be MOVE_NONE
1039 return value_from_tt(tte->value(), ply);
1042 // Step 5. Evaluate the position statically and
1043 // update gain statistics of parent move.
1045 ss->eval = ss->evalMargin = VALUE_NONE;
1048 assert(tte->static_value() != VALUE_NONE);
1050 ss->eval = tte->static_value();
1051 ss->evalMargin = tte->static_value_margin();
1052 refinedValue = refine_eval(tte, ss->eval, ply);
1056 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1057 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1060 // Save gain for the parent non-capture move
1061 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1063 // Step 6. Razoring (is omitted in PV nodes)
1065 && depth < RazorDepth
1067 && refinedValue < beta - razor_margin(depth)
1068 && ttMove == MOVE_NONE
1069 && !value_is_mate(beta)
1070 && !pos.has_pawn_on_7th(pos.side_to_move()))
1072 Value rbeta = beta - razor_margin(depth);
1073 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1075 // Logically we should return (v + razor_margin(depth)), but
1076 // surprisingly this did slightly weaker in tests.
1080 // Step 7. Static null move pruning (is omitted in PV nodes)
1081 // We're betting that the opponent doesn't have a move that will reduce
1082 // the score by more than futility_margin(depth) if we do a null move.
1084 && !ss->skipNullMove
1085 && depth < RazorDepth
1087 && refinedValue >= beta + futility_margin(depth, 0)
1088 && !value_is_mate(beta)
1089 && pos.non_pawn_material(pos.side_to_move()))
1090 return refinedValue - futility_margin(depth, 0);
1092 // Step 8. Null move search with verification search (is omitted in PV nodes)
1094 && !ss->skipNullMove
1097 && refinedValue >= beta
1098 && !value_is_mate(beta)
1099 && pos.non_pawn_material(pos.side_to_move()))
1101 ss->currentMove = MOVE_NULL;
1103 // Null move dynamic reduction based on depth
1104 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1106 // Null move dynamic reduction based on value
1107 if (refinedValue - beta > PawnValueMidgame)
1110 pos.do_null_move(st);
1111 (ss+1)->skipNullMove = true;
1112 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1113 (ss+1)->skipNullMove = false;
1114 pos.undo_null_move();
1116 if (nullValue >= beta)
1118 // Do not return unproven mate scores
1119 if (nullValue >= value_mate_in(PLY_MAX))
1122 if (depth < 6 * ONE_PLY)
1125 // Do verification search at high depths
1126 ss->skipNullMove = true;
1127 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1128 ss->skipNullMove = false;
1135 // The null move failed low, which means that we may be faced with
1136 // some kind of threat. If the previous move was reduced, check if
1137 // the move that refuted the null move was somehow connected to the
1138 // move which was reduced. If a connection is found, return a fail
1139 // low score (which will cause the reduced move to fail high in the
1140 // parent node, which will trigger a re-search with full depth).
1141 if (nullValue == value_mated_in(ply + 2))
1144 threatMove = (ss+1)->bestMove;
1145 if ( depth < ThreatDepth
1146 && (ss-1)->reduction
1147 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1152 // Step 9. Internal iterative deepening
1153 if ( depth >= IIDDepth[PvNode]
1154 && ttMove == MOVE_NONE
1155 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1157 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1159 ss->skipNullMove = true;
1160 search<PvNode>(pos, ss, alpha, beta, d, ply);
1161 ss->skipNullMove = false;
1163 ttMove = ss->bestMove;
1164 tte = TT.retrieve(posKey);
1167 // Expensive mate threat detection (only for PV nodes)
1169 mateThreat = pos.has_mate_threat();
1171 split_point_start: // At split points actual search starts from here
1173 // Initialize a MovePicker object for the current position
1174 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1175 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1176 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1178 ss->bestMove = MOVE_NONE;
1179 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1180 futilityBase = ss->eval + ss->evalMargin;
1181 singularExtensionNode = !SpNode
1182 && depth >= SingularExtensionDepth[PvNode]
1185 && !excludedMove // Do not allow recursive singular extension search
1186 && (tte->type() & VALUE_TYPE_LOWER)
1187 && tte->depth() >= depth - 3 * ONE_PLY;
1190 lock_grab(&(sp->lock));
1191 bestValue = sp->bestValue;
1194 // Step 10. Loop through moves
1195 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1196 while ( bestValue < beta
1197 && (move = mp.get_next_move()) != MOVE_NONE
1198 && !ThreadsMgr.thread_should_stop(threadID))
1200 assert(move_is_ok(move));
1204 moveCount = ++sp->moveCount;
1205 lock_release(&(sp->lock));
1207 else if (move == excludedMove)
1210 movesSearched[moveCount++] = move;
1212 moveIsCheck = pos.move_is_check(move, ci);
1213 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1215 // Step 11. Decide the new search depth
1216 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1218 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1219 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1220 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1221 // lower then ttValue minus a margin then we extend ttMove.
1222 if ( singularExtensionNode
1223 && move == tte->move()
1226 Value ttValue = value_from_tt(tte->value(), ply);
1228 if (abs(ttValue) < VALUE_KNOWN_WIN)
1230 Value b = ttValue - SingularExtensionMargin;
1231 ss->excludedMove = move;
1232 ss->skipNullMove = true;
1233 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1234 ss->skipNullMove = false;
1235 ss->excludedMove = MOVE_NONE;
1236 ss->bestMove = MOVE_NONE;
1242 // Update current move (this must be done after singular extension search)
1243 ss->currentMove = move;
1244 newDepth = depth - ONE_PLY + ext;
1246 // Step 12. Futility pruning (is omitted in PV nodes)
1248 && !captureOrPromotion
1252 && !move_is_castle(move))
1254 // Move count based pruning
1255 if ( moveCount >= futility_move_count(depth)
1256 && !(threatMove && connected_threat(pos, move, threatMove))
1257 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1260 lock_grab(&(sp->lock));
1265 // Value based pruning
1266 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1267 // but fixing this made program slightly weaker.
1268 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1269 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1270 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1272 if (futilityValueScaled < beta)
1276 lock_grab(&(sp->lock));
1277 if (futilityValueScaled > sp->bestValue)
1278 sp->bestValue = bestValue = futilityValueScaled;
1280 else if (futilityValueScaled > bestValue)
1281 bestValue = futilityValueScaled;
1286 // Prune neg. see moves at low depths
1287 if ( predictedDepth < 2 * ONE_PLY
1288 && bestValue > value_mated_in(PLY_MAX)
1289 && pos.see_sign(move) < 0)
1292 lock_grab(&(sp->lock));
1298 // Step 13. Make the move
1299 pos.do_move(move, st, ci, moveIsCheck);
1301 // Step extra. pv search (only in PV nodes)
1302 // The first move in list is the expected PV
1303 if (!SpNode && PvNode && moveCount == 1)
1304 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1307 // Step 14. Reduced depth search
1308 // If the move fails high will be re-searched at full depth.
1309 bool doFullDepthSearch = true;
1311 if ( depth >= 3 * ONE_PLY
1312 && !captureOrPromotion
1314 && !move_is_castle(move)
1315 && !(ss->killers[0] == move || ss->killers[1] == move))
1317 ss->reduction = reduction<PvNode>(depth, moveCount);
1320 alpha = SpNode ? sp->alpha : alpha;
1321 Depth d = newDepth - ss->reduction;
1322 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1324 doFullDepthSearch = (value > alpha);
1327 // The move failed high, but if reduction is very big we could
1328 // face a false positive, retry with a less aggressive reduction,
1329 // if the move fails high again then go with full depth search.
1330 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1332 assert(newDepth - ONE_PLY >= ONE_PLY);
1334 ss->reduction = ONE_PLY;
1335 alpha = SpNode ? sp->alpha : alpha;
1336 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1337 doFullDepthSearch = (value > alpha);
1339 ss->reduction = DEPTH_ZERO; // Restore original reduction
1342 // Step 15. Full depth search
1343 if (doFullDepthSearch)
1345 alpha = SpNode ? sp->alpha : alpha;
1346 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1348 // Step extra. pv search (only in PV nodes)
1349 // Search only for possible new PV nodes, if instead value >= beta then
1350 // parent node fails low with value <= alpha and tries another move.
1351 if (PvNode && value > alpha && value < beta)
1352 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1356 // Step 16. Undo move
1357 pos.undo_move(move);
1359 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1361 // Step 17. Check for new best move
1364 lock_grab(&(sp->lock));
1365 bestValue = sp->bestValue;
1369 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1374 sp->bestValue = value;
1378 if (SpNode && (!PvNode || value >= beta))
1379 sp->stopRequest = true;
1381 if (PvNode && value < beta) // We want always alpha < beta
1388 if (value == value_mate_in(ply + 1))
1389 ss->mateKiller = move;
1391 ss->bestMove = move;
1394 sp->parentSstack->bestMove = move;
1398 // Step 18. Check for split
1400 && depth >= ThreadsMgr.min_split_depth()
1401 && ThreadsMgr.active_threads() > 1
1403 && ThreadsMgr.available_thread_exists(threadID)
1405 && !ThreadsMgr.thread_should_stop(threadID)
1407 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1408 threatMove, mateThreat, moveCount, &mp, PvNode);
1411 // Step 19. Check for mate and stalemate
1412 // All legal moves have been searched and if there are
1413 // no legal moves, it must be mate or stalemate.
1414 // If one move was excluded return fail low score.
1415 if (!SpNode && !moveCount)
1416 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1418 // Step 20. Update tables
1419 // If the search is not aborted, update the transposition table,
1420 // history counters, and killer moves.
1421 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1423 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1424 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1425 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1427 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1429 // Update killers and history only for non capture moves that fails high
1430 if ( bestValue >= beta
1431 && !pos.move_is_capture_or_promotion(move))
1433 update_history(pos, move, depth, movesSearched, moveCount);
1434 update_killers(move, ss);
1440 // Here we have the lock still grabbed
1441 sp->slaves[threadID] = 0;
1442 sp->nodes += pos.nodes_searched();
1443 lock_release(&(sp->lock));
1446 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1451 Bitboard attacks(const Piece P, const Square sq, const Bitboard occ)
1461 return StepAttackBB[P][sq];
1464 return bishop_attacks_bb(sq, occ);
1467 return rook_attacks_bb(sq, occ);
1470 return bishop_attacks_bb(sq, occ) | rook_attacks_bb(sq, occ);
1477 bool check_is_useless(Position &pos, Move move, Value eval, Value futilityBase, Value beta, Value *bValue)
1479 Value bestValue = *bValue;
1481 /// Rule 1. Using checks to reposition pieces when close to beta
1482 if (eval + PawnValueMidgame / 4 < beta)
1484 if (eval + PawnValueMidgame / 4 > bestValue)
1485 bestValue = eval + PawnValueMidgame / 4;
1490 Square from = move_from(move);
1491 Square to = move_to(move);
1492 Color oppColor = opposite_color(pos.side_to_move());
1493 Square oppKing = pos.king_square(oppColor);
1495 Bitboard occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL <<oppKing);
1496 Bitboard oppOcc = pos.pieces_of_color(oppColor) & ~(1ULL <<oppKing);
1497 Bitboard oldAtt = attacks(pos.piece_on(from), from, occ);
1498 Bitboard newAtt = attacks(pos.piece_on(from), to, occ);
1500 // Rule 2. Checks which give opponent's king at most one escape square are dangerous
1501 Bitboard escapeBB = attacks(WK, oppKing, 0) & ~oppOcc & ~newAtt & ~(1ULL << to);
1506 if (!(escapeBB & (escapeBB - 1)))
1509 /// Rule 3. Queen contact check is very dangerous
1510 if ( pos.type_of_piece_on(from) == QUEEN
1511 && bit_is_set(attacks(WK, oppKing, 0), to))
1514 /// Rule 4. Creating new double threats with checks
1515 Bitboard newVictims = oppOcc & ~oldAtt & newAtt;
1519 Square victimSq = pop_1st_bit(&newVictims);
1521 Value futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1523 // Note that here we generate illegal "double move"!
1524 if (futilityValue >= beta && pos.see_sign(make_move(from, victimSq)) >= 0)
1527 if (futilityValue > bestValue)
1528 bestValue = futilityValue;
1531 *bValue = bestValue;
1535 // qsearch() is the quiescence search function, which is called by the main
1536 // search function when the remaining depth is zero (or, to be more precise,
1537 // less than ONE_PLY).
1539 template <NodeType PvNode>
1540 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1542 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1543 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1544 assert(PvNode || alpha == beta - 1);
1546 assert(ply > 0 && ply < PLY_MAX);
1547 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1551 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1552 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1554 Value oldAlpha = alpha;
1556 ss->bestMove = ss->currentMove = MOVE_NONE;
1558 // Check for an instant draw or maximum ply reached
1559 if (pos.is_draw() || ply >= PLY_MAX - 1)
1562 // Decide whether or not to include checks
1563 isCheck = pos.is_check();
1566 if (isCheck || depth >= -ONE_PLY)
1569 d = DEPTH_ZERO - ONE_PLY;
1571 // Transposition table lookup. At PV nodes, we don't use the TT for
1572 // pruning, but only for move ordering.
1573 tte = TT.retrieve(pos.get_key());
1574 ttMove = (tte ? tte->move() : MOVE_NONE);
1576 if (!PvNode && tte && ok_to_use_TT(tte, d, beta, ply))
1578 ss->bestMove = ttMove; // Can be MOVE_NONE
1579 return value_from_tt(tte->value(), ply);
1582 // Evaluate the position statically
1585 bestValue = futilityBase = -VALUE_INFINITE;
1586 ss->eval = evalMargin = VALUE_NONE;
1587 enoughMaterial = false;
1593 assert(tte->static_value() != VALUE_NONE);
1595 evalMargin = tte->static_value_margin();
1596 ss->eval = bestValue = tte->static_value();
1599 ss->eval = bestValue = evaluate(pos, evalMargin);
1601 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1603 // Stand pat. Return immediately if static value is at least beta
1604 if (bestValue >= beta)
1607 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1612 if (PvNode && bestValue > alpha)
1615 // Futility pruning parameters, not needed when in check
1616 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1617 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1620 // Initialize a MovePicker object for the current position, and prepare
1621 // to search the moves. Because the depth is <= 0 here, only captures,
1622 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1623 // and we are near beta) will be generated.
1624 MovePicker mp = MovePicker(pos, ttMove, d, H);
1627 // Loop through the moves until no moves remain or a beta cutoff occurs
1628 while ( alpha < beta
1629 && (move = mp.get_next_move()) != MOVE_NONE)
1631 assert(move_is_ok(move));
1633 moveIsCheck = pos.move_is_check(move, ci);
1641 && !move_is_promotion(move)
1642 && !pos.move_is_passed_pawn_push(move))
1644 futilityValue = futilityBase
1645 + pos.endgame_value_of_piece_on(move_to(move))
1646 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1648 if (futilityValue < alpha)
1650 if (futilityValue > bestValue)
1651 bestValue = futilityValue;
1656 // Detect non-capture evasions that are candidate to be pruned
1657 evasionPrunable = isCheck
1658 && bestValue > value_mated_in(PLY_MAX)
1659 && !pos.move_is_capture(move)
1660 && !pos.can_castle(pos.side_to_move());
1662 // Don't search moves with negative SEE values
1664 && (!isCheck || evasionPrunable)
1666 && !move_is_promotion(move)
1667 && pos.see_sign(move) < 0)
1670 // Don't search useless checks
1674 && !move_is_promotion(move)
1675 && !pos.move_is_capture(move)
1677 && check_is_useless(pos, move, ss->eval, futilityBase, beta, &bestValue))
1680 // Update current move
1681 ss->currentMove = move;
1683 // Make and search the move
1684 pos.do_move(move, st, ci, moveIsCheck);
1685 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1686 pos.undo_move(move);
1688 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1691 if (value > bestValue)
1697 ss->bestMove = move;
1702 // All legal moves have been searched. A special case: If we're in check
1703 // and no legal moves were found, it is checkmate.
1704 if (isCheck && bestValue == -VALUE_INFINITE)
1705 return value_mated_in(ply);
1707 // Update transposition table
1708 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1709 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1711 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1717 // connected_moves() tests whether two moves are 'connected' in the sense
1718 // that the first move somehow made the second move possible (for instance
1719 // if the moving piece is the same in both moves). The first move is assumed
1720 // to be the move that was made to reach the current position, while the
1721 // second move is assumed to be a move from the current position.
1723 bool connected_moves(const Position& pos, Move m1, Move m2) {
1725 Square f1, t1, f2, t2;
1728 assert(move_is_ok(m1));
1729 assert(move_is_ok(m2));
1731 if (m2 == MOVE_NONE)
1734 // Case 1: The moving piece is the same in both moves
1740 // Case 2: The destination square for m2 was vacated by m1
1746 // Case 3: Moving through the vacated square
1747 if ( piece_is_slider(pos.piece_on(f2))
1748 && bit_is_set(squares_between(f2, t2), f1))
1751 // Case 4: The destination square for m2 is defended by the moving piece in m1
1752 p = pos.piece_on(t1);
1753 if (bit_is_set(pos.attacks_from(p, t1), t2))
1756 // Case 5: Discovered check, checking piece is the piece moved in m1
1757 if ( piece_is_slider(p)
1758 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1759 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1761 // discovered_check_candidates() works also if the Position's side to
1762 // move is the opposite of the checking piece.
1763 Color them = opposite_color(pos.side_to_move());
1764 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1766 if (bit_is_set(dcCandidates, f2))
1773 // value_is_mate() checks if the given value is a mate one eventually
1774 // compensated for the ply.
1776 bool value_is_mate(Value value) {
1778 assert(abs(value) <= VALUE_INFINITE);
1780 return value <= value_mated_in(PLY_MAX)
1781 || value >= value_mate_in(PLY_MAX);
1785 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1786 // "plies to mate from the current ply". Non-mate scores are unchanged.
1787 // The function is called before storing a value to the transposition table.
1789 Value value_to_tt(Value v, int ply) {
1791 if (v >= value_mate_in(PLY_MAX))
1794 if (v <= value_mated_in(PLY_MAX))
1801 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1802 // the transposition table to a mate score corrected for the current ply.
1804 Value value_from_tt(Value v, int ply) {
1806 if (v >= value_mate_in(PLY_MAX))
1809 if (v <= value_mated_in(PLY_MAX))
1816 // extension() decides whether a move should be searched with normal depth,
1817 // or with extended depth. Certain classes of moves (checking moves, in
1818 // particular) are searched with bigger depth than ordinary moves and in
1819 // any case are marked as 'dangerous'. Note that also if a move is not
1820 // extended, as example because the corresponding UCI option is set to zero,
1821 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1822 template <NodeType PvNode>
1823 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1824 bool singleEvasion, bool mateThreat, bool* dangerous) {
1826 assert(m != MOVE_NONE);
1828 Depth result = DEPTH_ZERO;
1829 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1833 if (moveIsCheck && pos.see_sign(m) >= 0)
1834 result += CheckExtension[PvNode];
1837 result += SingleEvasionExtension[PvNode];
1840 result += MateThreatExtension[PvNode];
1843 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1845 Color c = pos.side_to_move();
1846 if (relative_rank(c, move_to(m)) == RANK_7)
1848 result += PawnPushTo7thExtension[PvNode];
1851 if (pos.pawn_is_passed(c, move_to(m)))
1853 result += PassedPawnExtension[PvNode];
1858 if ( captureOrPromotion
1859 && pos.type_of_piece_on(move_to(m)) != PAWN
1860 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1861 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1862 && !move_is_promotion(m)
1865 result += PawnEndgameExtension[PvNode];
1870 && captureOrPromotion
1871 && pos.type_of_piece_on(move_to(m)) != PAWN
1872 && pos.see_sign(m) >= 0)
1874 result += ONE_PLY / 2;
1878 return Min(result, ONE_PLY);
1882 // connected_threat() tests whether it is safe to forward prune a move or if
1883 // is somehow coonected to the threat move returned by null search.
1885 bool connected_threat(const Position& pos, Move m, Move threat) {
1887 assert(move_is_ok(m));
1888 assert(threat && move_is_ok(threat));
1889 assert(!pos.move_is_check(m));
1890 assert(!pos.move_is_capture_or_promotion(m));
1891 assert(!pos.move_is_passed_pawn_push(m));
1893 Square mfrom, mto, tfrom, tto;
1895 mfrom = move_from(m);
1897 tfrom = move_from(threat);
1898 tto = move_to(threat);
1900 // Case 1: Don't prune moves which move the threatened piece
1904 // Case 2: If the threatened piece has value less than or equal to the
1905 // value of the threatening piece, don't prune move which defend it.
1906 if ( pos.move_is_capture(threat)
1907 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1908 || pos.type_of_piece_on(tfrom) == KING)
1909 && pos.move_attacks_square(m, tto))
1912 // Case 3: If the moving piece in the threatened move is a slider, don't
1913 // prune safe moves which block its ray.
1914 if ( piece_is_slider(pos.piece_on(tfrom))
1915 && bit_is_set(squares_between(tfrom, tto), mto)
1916 && pos.see_sign(m) >= 0)
1923 // ok_to_use_TT() returns true if a transposition table score
1924 // can be used at a given point in search.
1926 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1928 Value v = value_from_tt(tte->value(), ply);
1930 return ( tte->depth() >= depth
1931 || v >= Max(value_mate_in(PLY_MAX), beta)
1932 || v < Min(value_mated_in(PLY_MAX), beta))
1934 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1935 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1939 // refine_eval() returns the transposition table score if
1940 // possible otherwise falls back on static position evaluation.
1942 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1946 Value v = value_from_tt(tte->value(), ply);
1948 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1949 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1956 // update_history() registers a good move that produced a beta-cutoff
1957 // in history and marks as failures all the other moves of that ply.
1959 void update_history(const Position& pos, Move move, Depth depth,
1960 Move movesSearched[], int moveCount) {
1963 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1965 for (int i = 0; i < moveCount - 1; i++)
1967 m = movesSearched[i];
1971 if (!pos.move_is_capture_or_promotion(m))
1972 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1977 // update_killers() add a good move that produced a beta-cutoff
1978 // among the killer moves of that ply.
1980 void update_killers(Move m, SearchStack* ss) {
1982 if (m == ss->killers[0])
1985 ss->killers[1] = ss->killers[0];
1990 // update_gains() updates the gains table of a non-capture move given
1991 // the static position evaluation before and after the move.
1993 void update_gains(const Position& pos, Move m, Value before, Value after) {
1996 && before != VALUE_NONE
1997 && after != VALUE_NONE
1998 && pos.captured_piece_type() == PIECE_TYPE_NONE
1999 && !move_is_special(m))
2000 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2004 // current_search_time() returns the number of milliseconds which have passed
2005 // since the beginning of the current search.
2007 int current_search_time() {
2009 return get_system_time() - SearchStartTime;
2013 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2015 std::string value_to_uci(Value v) {
2017 std::stringstream s;
2019 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
2020 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2022 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2027 // nps() computes the current nodes/second count.
2029 int nps(const Position& pos) {
2031 int t = current_search_time();
2032 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
2036 // poll() performs two different functions: It polls for user input, and it
2037 // looks at the time consumed so far and decides if it's time to abort the
2040 void poll(const Position& pos) {
2042 static int lastInfoTime;
2043 int t = current_search_time();
2046 if (data_available())
2048 // We are line oriented, don't read single chars
2049 std::string command;
2051 if (!std::getline(std::cin, command))
2054 if (command == "quit")
2057 PonderSearch = false;
2061 else if (command == "stop")
2064 PonderSearch = false;
2066 else if (command == "ponderhit")
2070 // Print search information
2074 else if (lastInfoTime > t)
2075 // HACK: Must be a new search where we searched less than
2076 // NodesBetweenPolls nodes during the first second of search.
2079 else if (t - lastInfoTime >= 1000)
2086 if (dbg_show_hit_rate)
2087 dbg_print_hit_rate();
2089 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
2090 << " time " << t << endl;
2093 // Should we stop the search?
2097 bool stillAtFirstMove = FirstRootMove
2098 && !AspirationFailLow
2099 && t > TimeMgr.available_time();
2101 bool noMoreTime = t > TimeMgr.maximum_time()
2102 || stillAtFirstMove;
2104 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2105 || (ExactMaxTime && t >= ExactMaxTime)
2106 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2111 // ponderhit() is called when the program is pondering (i.e. thinking while
2112 // it's the opponent's turn to move) in order to let the engine know that
2113 // it correctly predicted the opponent's move.
2117 int t = current_search_time();
2118 PonderSearch = false;
2120 bool stillAtFirstMove = FirstRootMove
2121 && !AspirationFailLow
2122 && t > TimeMgr.available_time();
2124 bool noMoreTime = t > TimeMgr.maximum_time()
2125 || stillAtFirstMove;
2127 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2132 // init_ss_array() does a fast reset of the first entries of a SearchStack
2133 // array and of all the excludedMove and skipNullMove entries.
2135 void init_ss_array(SearchStack* ss, int size) {
2137 for (int i = 0; i < size; i++, ss++)
2139 ss->excludedMove = MOVE_NONE;
2140 ss->skipNullMove = false;
2141 ss->reduction = DEPTH_ZERO;
2145 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2150 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2151 // while the program is pondering. The point is to work around a wrinkle in
2152 // the UCI protocol: When pondering, the engine is not allowed to give a
2153 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2154 // We simply wait here until one of these commands is sent, and return,
2155 // after which the bestmove and pondermove will be printed (in id_loop()).
2157 void wait_for_stop_or_ponderhit() {
2159 std::string command;
2163 if (!std::getline(std::cin, command))
2166 if (command == "quit")
2171 else if (command == "ponderhit" || command == "stop")
2177 // print_pv_info() prints to standard output and eventually to log file information on
2178 // the current PV line. It is called at each iteration or after a new pv is found.
2180 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2182 cout << "info depth " << Iteration
2183 << " score " << value_to_uci(value)
2184 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2185 << " time " << current_search_time()
2186 << " nodes " << pos.nodes_searched()
2187 << " nps " << nps(pos)
2190 for (Move* m = pv; *m != MOVE_NONE; m++)
2197 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2198 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2200 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2205 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2206 // the PV back into the TT. This makes sure the old PV moves are searched
2207 // first, even if the old TT entries have been overwritten.
2209 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2213 Position p(pos, pos.thread());
2214 Value v, m = VALUE_NONE;
2216 for (int i = 0; pv[i] != MOVE_NONE; i++)
2218 tte = TT.retrieve(p.get_key());
2219 if (!tte || tte->move() != pv[i])
2221 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2222 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2224 p.do_move(pv[i], st);
2229 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2230 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2231 // allow to always have a ponder move even when we fail high at root and also a
2232 // long PV to print that is important for position analysis.
2234 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2238 Position p(pos, pos.thread());
2241 assert(bestMove != MOVE_NONE);
2244 p.do_move(pv[ply++], st);
2246 while ( (tte = TT.retrieve(p.get_key())) != NULL
2247 && tte->move() != MOVE_NONE
2248 && move_is_legal(p, tte->move())
2250 && (!p.is_draw() || ply < 2))
2252 pv[ply] = tte->move();
2253 p.do_move(pv[ply++], st);
2255 pv[ply] = MOVE_NONE;
2259 // init_thread() is the function which is called when a new thread is
2260 // launched. It simply calls the idle_loop() function with the supplied
2261 // threadID. There are two versions of this function; one for POSIX
2262 // threads and one for Windows threads.
2264 #if !defined(_MSC_VER)
2266 void* init_thread(void* threadID) {
2268 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2274 DWORD WINAPI init_thread(LPVOID threadID) {
2276 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2283 /// The ThreadsManager class
2286 // read_uci_options() updates number of active threads and other internal
2287 // parameters according to the UCI options values. It is called before
2288 // to start a new search.
2290 void ThreadsManager::read_uci_options() {
2292 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2293 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2294 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2295 activeThreads = Options["Threads"].value<int>();
2299 // idle_loop() is where the threads are parked when they have no work to do.
2300 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2301 // object for which the current thread is the master.
2303 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2305 assert(threadID >= 0 && threadID < MAX_THREADS);
2308 bool allFinished = false;
2312 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2313 // master should exit as last one.
2314 if (allThreadsShouldExit)
2317 threads[threadID].state = THREAD_TERMINATED;
2321 // If we are not thinking, wait for a condition to be signaled
2322 // instead of wasting CPU time polling for work.
2323 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2324 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2326 assert(!sp || useSleepingThreads);
2327 assert(threadID != 0 || useSleepingThreads);
2329 if (threads[threadID].state == THREAD_INITIALIZING)
2330 threads[threadID].state = THREAD_AVAILABLE;
2332 // Grab the lock to avoid races with wake_sleeping_thread()
2333 lock_grab(&sleepLock[threadID]);
2335 // If we are master and all slaves have finished do not go to sleep
2336 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2337 allFinished = (i == activeThreads);
2339 if (allFinished || allThreadsShouldExit)
2341 lock_release(&sleepLock[threadID]);
2345 // Do sleep here after retesting sleep conditions
2346 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2347 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2349 lock_release(&sleepLock[threadID]);
2352 // If this thread has been assigned work, launch a search
2353 if (threads[threadID].state == THREAD_WORKISWAITING)
2355 assert(!allThreadsShouldExit);
2357 threads[threadID].state = THREAD_SEARCHING;
2359 // Here we call search() with SplitPoint template parameter set to true
2360 SplitPoint* tsp = threads[threadID].splitPoint;
2361 Position pos(*tsp->pos, threadID);
2362 SearchStack* ss = tsp->sstack[threadID] + 1;
2366 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2368 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2370 assert(threads[threadID].state == THREAD_SEARCHING);
2372 threads[threadID].state = THREAD_AVAILABLE;
2374 // Wake up master thread so to allow it to return from the idle loop in
2375 // case we are the last slave of the split point.
2376 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2377 wake_sleeping_thread(tsp->master);
2380 // If this thread is the master of a split point and all slaves have
2381 // finished their work at this split point, return from the idle loop.
2382 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2383 allFinished = (i == activeThreads);
2387 // Because sp->slaves[] is reset under lock protection,
2388 // be sure sp->lock has been released before to return.
2389 lock_grab(&(sp->lock));
2390 lock_release(&(sp->lock));
2392 // In helpful master concept a master can help only a sub-tree, and
2393 // because here is all finished is not possible master is booked.
2394 assert(threads[threadID].state == THREAD_AVAILABLE);
2396 threads[threadID].state = THREAD_SEARCHING;
2403 // init_threads() is called during startup. It launches all helper threads,
2404 // and initializes the split point stack and the global locks and condition
2407 void ThreadsManager::init_threads() {
2409 int i, arg[MAX_THREADS];
2412 // Initialize global locks
2415 for (i = 0; i < MAX_THREADS; i++)
2417 lock_init(&sleepLock[i]);
2418 cond_init(&sleepCond[i]);
2421 // Initialize splitPoints[] locks
2422 for (i = 0; i < MAX_THREADS; i++)
2423 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2424 lock_init(&(threads[i].splitPoints[j].lock));
2426 // Will be set just before program exits to properly end the threads
2427 allThreadsShouldExit = false;
2429 // Threads will be put all threads to sleep as soon as created
2432 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2433 threads[0].state = THREAD_SEARCHING;
2434 for (i = 1; i < MAX_THREADS; i++)
2435 threads[i].state = THREAD_INITIALIZING;
2437 // Launch the helper threads
2438 for (i = 1; i < MAX_THREADS; i++)
2442 #if !defined(_MSC_VER)
2443 pthread_t pthread[1];
2444 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2445 pthread_detach(pthread[0]);
2447 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2451 cout << "Failed to create thread number " << i << endl;
2455 // Wait until the thread has finished launching and is gone to sleep
2456 while (threads[i].state == THREAD_INITIALIZING) {}
2461 // exit_threads() is called when the program exits. It makes all the
2462 // helper threads exit cleanly.
2464 void ThreadsManager::exit_threads() {
2466 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2468 // Wake up all the threads and waits for termination
2469 for (int i = 1; i < MAX_THREADS; i++)
2471 wake_sleeping_thread(i);
2472 while (threads[i].state != THREAD_TERMINATED) {}
2475 // Now we can safely destroy the locks
2476 for (int i = 0; i < MAX_THREADS; i++)
2477 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2478 lock_destroy(&(threads[i].splitPoints[j].lock));
2480 lock_destroy(&mpLock);
2482 // Now we can safely destroy the wait conditions
2483 for (int i = 0; i < MAX_THREADS; i++)
2485 lock_destroy(&sleepLock[i]);
2486 cond_destroy(&sleepCond[i]);
2491 // thread_should_stop() checks whether the thread should stop its search.
2492 // This can happen if a beta cutoff has occurred in the thread's currently
2493 // active split point, or in some ancestor of the current split point.
2495 bool ThreadsManager::thread_should_stop(int threadID) const {
2497 assert(threadID >= 0 && threadID < activeThreads);
2499 SplitPoint* sp = threads[threadID].splitPoint;
2501 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2506 // thread_is_available() checks whether the thread with threadID "slave" is
2507 // available to help the thread with threadID "master" at a split point. An
2508 // obvious requirement is that "slave" must be idle. With more than two
2509 // threads, this is not by itself sufficient: If "slave" is the master of
2510 // some active split point, it is only available as a slave to the other
2511 // threads which are busy searching the split point at the top of "slave"'s
2512 // split point stack (the "helpful master concept" in YBWC terminology).
2514 bool ThreadsManager::thread_is_available(int slave, int master) const {
2516 assert(slave >= 0 && slave < activeThreads);
2517 assert(master >= 0 && master < activeThreads);
2518 assert(activeThreads > 1);
2520 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2523 // Make a local copy to be sure doesn't change under our feet
2524 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2526 // No active split points means that the thread is available as
2527 // a slave for any other thread.
2528 if (localActiveSplitPoints == 0 || activeThreads == 2)
2531 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2532 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2533 // could have been set to 0 by another thread leading to an out of bound access.
2534 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2541 // available_thread_exists() tries to find an idle thread which is available as
2542 // a slave for the thread with threadID "master".
2544 bool ThreadsManager::available_thread_exists(int master) const {
2546 assert(master >= 0 && master < activeThreads);
2547 assert(activeThreads > 1);
2549 for (int i = 0; i < activeThreads; i++)
2550 if (thread_is_available(i, master))
2557 // split() does the actual work of distributing the work at a node between
2558 // several available threads. If it does not succeed in splitting the
2559 // node (because no idle threads are available, or because we have no unused
2560 // split point objects), the function immediately returns. If splitting is
2561 // possible, a SplitPoint object is initialized with all the data that must be
2562 // copied to the helper threads and we tell our helper threads that they have
2563 // been assigned work. This will cause them to instantly leave their idle loops and
2564 // call search().When all threads have returned from search() then split() returns.
2566 template <bool Fake>
2567 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2568 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2569 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2570 assert(pos.is_ok());
2571 assert(ply > 0 && ply < PLY_MAX);
2572 assert(*bestValue >= -VALUE_INFINITE);
2573 assert(*bestValue <= *alpha);
2574 assert(*alpha < beta);
2575 assert(beta <= VALUE_INFINITE);
2576 assert(depth > DEPTH_ZERO);
2577 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2578 assert(activeThreads > 1);
2580 int i, master = pos.thread();
2581 Thread& masterThread = threads[master];
2585 // If no other thread is available to help us, or if we have too many
2586 // active split points, don't split.
2587 if ( !available_thread_exists(master)
2588 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2590 lock_release(&mpLock);
2594 // Pick the next available split point object from the split point stack
2595 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2597 // Initialize the split point object
2598 splitPoint.parent = masterThread.splitPoint;
2599 splitPoint.master = master;
2600 splitPoint.stopRequest = false;
2601 splitPoint.ply = ply;
2602 splitPoint.depth = depth;
2603 splitPoint.threatMove = threatMove;
2604 splitPoint.mateThreat = mateThreat;
2605 splitPoint.alpha = *alpha;
2606 splitPoint.beta = beta;
2607 splitPoint.pvNode = pvNode;
2608 splitPoint.bestValue = *bestValue;
2610 splitPoint.moveCount = moveCount;
2611 splitPoint.pos = &pos;
2612 splitPoint.nodes = 0;
2613 splitPoint.parentSstack = ss;
2614 for (i = 0; i < activeThreads; i++)
2615 splitPoint.slaves[i] = 0;
2617 masterThread.splitPoint = &splitPoint;
2619 // If we are here it means we are not available
2620 assert(masterThread.state != THREAD_AVAILABLE);
2622 int workersCnt = 1; // At least the master is included
2624 // Allocate available threads setting state to THREAD_BOOKED
2625 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2626 if (thread_is_available(i, master))
2628 threads[i].state = THREAD_BOOKED;
2629 threads[i].splitPoint = &splitPoint;
2630 splitPoint.slaves[i] = 1;
2634 assert(Fake || workersCnt > 1);
2636 // We can release the lock because slave threads are already booked and master is not available
2637 lock_release(&mpLock);
2639 // Tell the threads that they have work to do. This will make them leave
2640 // their idle loop. But before copy search stack tail for each thread.
2641 for (i = 0; i < activeThreads; i++)
2642 if (i == master || splitPoint.slaves[i])
2644 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2646 assert(i == master || threads[i].state == THREAD_BOOKED);
2648 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2650 if (useSleepingThreads && i != master)
2651 wake_sleeping_thread(i);
2654 // Everything is set up. The master thread enters the idle loop, from
2655 // which it will instantly launch a search, because its state is
2656 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2657 // idle loop, which means that the main thread will return from the idle
2658 // loop when all threads have finished their work at this split point.
2659 idle_loop(master, &splitPoint);
2661 // We have returned from the idle loop, which means that all threads are
2662 // finished. Update alpha and bestValue, and return.
2665 *alpha = splitPoint.alpha;
2666 *bestValue = splitPoint.bestValue;
2667 masterThread.activeSplitPoints--;
2668 masterThread.splitPoint = splitPoint.parent;
2669 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2671 lock_release(&mpLock);
2675 // wake_sleeping_thread() wakes up the thread with the given threadID
2676 // when it is time to start a new search.
2678 void ThreadsManager::wake_sleeping_thread(int threadID) {
2680 lock_grab(&sleepLock[threadID]);
2681 cond_signal(&sleepCond[threadID]);
2682 lock_release(&sleepLock[threadID]);
2686 /// The RootMoveList class
2688 // RootMoveList c'tor
2690 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2692 SearchStack ss[PLY_MAX_PLUS_2];
2693 MoveStack mlist[MOVES_MAX];
2695 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2697 // Initialize search stack
2698 init_ss_array(ss, PLY_MAX_PLUS_2);
2699 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2702 // Generate all legal moves
2703 MoveStack* last = generate_moves(pos, mlist);
2705 // Add each move to the moves[] array
2706 for (MoveStack* cur = mlist; cur != last; cur++)
2708 bool includeMove = includeAllMoves;
2710 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2711 includeMove = (searchMoves[k] == cur->move);
2716 // Find a quick score for the move
2717 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2718 moves[count].pv[1] = MOVE_NONE;
2719 pos.do_move(cur->move, st);
2720 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2721 pos.undo_move(cur->move);
2727 // Score root moves using the standard way used in main search, the moves
2728 // are scored according to the order in which are returned by MovePicker.
2730 void RootMoveList::score_moves(const Position& pos)
2734 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2736 while ((move = mp.get_next_move()) != MOVE_NONE)
2737 for (int i = 0; i < count; i++)
2738 if (moves[i].move == move)
2740 moves[i].mp_score = score--;
2745 // RootMoveList simple methods definitions
2747 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2751 for (j = 0; pv[j] != MOVE_NONE; j++)
2752 moves[moveNum].pv[j] = pv[j];
2754 moves[moveNum].pv[j] = MOVE_NONE;
2758 // RootMoveList::sort() sorts the root move list at the beginning of a new
2761 void RootMoveList::sort() {
2763 sort_multipv(count - 1); // Sort all items
2767 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2768 // list by their scores and depths. It is used to order the different PVs
2769 // correctly in MultiPV mode.
2771 void RootMoveList::sort_multipv(int n) {
2775 for (i = 1; i <= n; i++)
2777 RootMove rm = moves[i];
2778 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2779 moves[j] = moves[j - 1];