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;
997 else {} // Hack to fix icc's "statement is unreachable" warning
999 // Step 1. Initialize node and poll. Polling can abort search
1000 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
1001 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1003 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1009 // Step 2. Check for aborted search and immediate draw
1010 if ( AbortSearch || ThreadsMgr.thread_should_stop(threadID)
1011 || pos.is_draw() || ply >= PLY_MAX - 1)
1014 // Step 3. Mate distance pruning
1015 alpha = Max(value_mated_in(ply), alpha);
1016 beta = Min(value_mate_in(ply+1), beta);
1020 // Step 4. Transposition table lookup
1022 // We don't want the score of a partial search to overwrite a previous full search
1023 // TT value, so we use a different position key in case of an excluded move exists.
1024 excludedMove = ss->excludedMove;
1025 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1027 tte = TT.retrieve(posKey);
1028 ttMove = tte ? tte->move() : MOVE_NONE;
1030 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1031 // This is to avoid problems in the following areas:
1033 // * Repetition draw detection
1034 // * Fifty move rule detection
1035 // * Searching for a mate
1036 // * Printing of full PV line
1037 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1040 ss->bestMove = ttMove; // Can be MOVE_NONE
1041 return value_from_tt(tte->value(), ply);
1044 // Step 5. Evaluate the position statically and
1045 // update gain statistics of parent move.
1047 ss->eval = ss->evalMargin = VALUE_NONE;
1050 assert(tte->static_value() != VALUE_NONE);
1052 ss->eval = tte->static_value();
1053 ss->evalMargin = tte->static_value_margin();
1054 refinedValue = refine_eval(tte, ss->eval, ply);
1058 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1059 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1062 // Save gain for the parent non-capture move
1063 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1065 // Step 6. Razoring (is omitted in PV nodes)
1067 && depth < RazorDepth
1069 && refinedValue < beta - razor_margin(depth)
1070 && ttMove == MOVE_NONE
1071 && !value_is_mate(beta)
1072 && !pos.has_pawn_on_7th(pos.side_to_move()))
1074 Value rbeta = beta - razor_margin(depth);
1075 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1077 // Logically we should return (v + razor_margin(depth)), but
1078 // surprisingly this did slightly weaker in tests.
1082 // Step 7. Static null move pruning (is omitted in PV nodes)
1083 // We're betting that the opponent doesn't have a move that will reduce
1084 // the score by more than futility_margin(depth) if we do a null move.
1086 && !ss->skipNullMove
1087 && depth < RazorDepth
1089 && refinedValue >= beta + futility_margin(depth, 0)
1090 && !value_is_mate(beta)
1091 && pos.non_pawn_material(pos.side_to_move()))
1092 return refinedValue - futility_margin(depth, 0);
1094 // Step 8. Null move search with verification search (is omitted in PV nodes)
1096 && !ss->skipNullMove
1099 && refinedValue >= beta
1100 && !value_is_mate(beta)
1101 && pos.non_pawn_material(pos.side_to_move()))
1103 ss->currentMove = MOVE_NULL;
1105 // Null move dynamic reduction based on depth
1106 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1108 // Null move dynamic reduction based on value
1109 if (refinedValue - beta > PawnValueMidgame)
1112 pos.do_null_move(st);
1113 (ss+1)->skipNullMove = true;
1114 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1115 (ss+1)->skipNullMove = false;
1116 pos.undo_null_move();
1118 if (nullValue >= beta)
1120 // Do not return unproven mate scores
1121 if (nullValue >= value_mate_in(PLY_MAX))
1124 if (depth < 6 * ONE_PLY)
1127 // Do verification search at high depths
1128 ss->skipNullMove = true;
1129 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1130 ss->skipNullMove = false;
1137 // The null move failed low, which means that we may be faced with
1138 // some kind of threat. If the previous move was reduced, check if
1139 // the move that refuted the null move was somehow connected to the
1140 // move which was reduced. If a connection is found, return a fail
1141 // low score (which will cause the reduced move to fail high in the
1142 // parent node, which will trigger a re-search with full depth).
1143 if (nullValue == value_mated_in(ply + 2))
1146 threatMove = (ss+1)->bestMove;
1147 if ( depth < ThreatDepth
1148 && (ss-1)->reduction
1149 && threatMove != MOVE_NONE
1150 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1155 // Step 9. Internal iterative deepening
1156 if ( depth >= IIDDepth[PvNode]
1157 && ttMove == MOVE_NONE
1158 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1160 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1162 ss->skipNullMove = true;
1163 search<PvNode>(pos, ss, alpha, beta, d, ply);
1164 ss->skipNullMove = false;
1166 ttMove = ss->bestMove;
1167 tte = TT.retrieve(posKey);
1170 // Expensive mate threat detection (only for PV nodes)
1172 mateThreat = pos.has_mate_threat();
1174 split_point_start: // At split points actual search starts from here
1176 // Initialize a MovePicker object for the current position
1177 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1178 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1179 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1181 ss->bestMove = MOVE_NONE;
1182 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1183 futilityBase = ss->eval + ss->evalMargin;
1184 singularExtensionNode = !SpNode
1185 && depth >= SingularExtensionDepth[PvNode]
1188 && !excludedMove // Do not allow recursive singular extension search
1189 && (tte->type() & VALUE_TYPE_LOWER)
1190 && tte->depth() >= depth - 3 * ONE_PLY;
1193 lock_grab(&(sp->lock));
1194 bestValue = sp->bestValue;
1197 // Step 10. Loop through moves
1198 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1199 while ( bestValue < beta
1200 && (move = mp.get_next_move()) != MOVE_NONE
1201 && !ThreadsMgr.thread_should_stop(threadID))
1203 assert(move_is_ok(move));
1207 moveCount = ++sp->moveCount;
1208 lock_release(&(sp->lock));
1210 else if (move == excludedMove)
1213 movesSearched[moveCount++] = move;
1215 moveIsCheck = pos.move_is_check(move, ci);
1216 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1218 // Step 11. Decide the new search depth
1219 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1221 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1222 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1223 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1224 // lower then ttValue minus a margin then we extend ttMove.
1225 if ( singularExtensionNode
1226 && move == tte->move()
1229 Value ttValue = value_from_tt(tte->value(), ply);
1231 if (abs(ttValue) < VALUE_KNOWN_WIN)
1233 Value b = ttValue - SingularExtensionMargin;
1234 ss->excludedMove = move;
1235 ss->skipNullMove = true;
1236 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1237 ss->skipNullMove = false;
1238 ss->excludedMove = MOVE_NONE;
1239 ss->bestMove = MOVE_NONE;
1245 // Update current move (this must be done after singular extension search)
1246 ss->currentMove = move;
1247 newDepth = depth - ONE_PLY + ext;
1249 // Step 12. Futility pruning (is omitted in PV nodes)
1251 && !captureOrPromotion
1255 && !move_is_castle(move))
1257 // Move count based pruning
1258 if ( moveCount >= futility_move_count(depth)
1259 && !(threatMove && connected_threat(pos, move, threatMove))
1260 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1263 lock_grab(&(sp->lock));
1268 // Value based pruning
1269 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1270 // but fixing this made program slightly weaker.
1271 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1272 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1273 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1275 if (futilityValueScaled < beta)
1279 lock_grab(&(sp->lock));
1280 if (futilityValueScaled > sp->bestValue)
1281 sp->bestValue = bestValue = futilityValueScaled;
1283 else if (futilityValueScaled > bestValue)
1284 bestValue = futilityValueScaled;
1289 // Prune moves with negative SEE at low depths
1290 if ( predictedDepth < 2 * ONE_PLY
1291 && bestValue > value_mated_in(PLY_MAX)
1292 && pos.see_sign(move) < 0)
1295 lock_grab(&(sp->lock));
1301 // Step 13. Make the move
1302 pos.do_move(move, st, ci, moveIsCheck);
1304 // Step extra. pv search (only in PV nodes)
1305 // The first move in list is the expected PV
1306 if (PvNode && moveCount == 1)
1307 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1310 // Step 14. Reduced depth search
1311 // If the move fails high will be re-searched at full depth.
1312 bool doFullDepthSearch = true;
1314 if ( depth >= 3 * ONE_PLY
1315 && !captureOrPromotion
1317 && !move_is_castle(move)
1318 && ss->killers[0] != move
1319 && ss->killers[1] != move)
1321 ss->reduction = reduction<PvNode>(depth, moveCount);
1325 alpha = SpNode ? sp->alpha : alpha;
1326 Depth d = newDepth - ss->reduction;
1327 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1329 doFullDepthSearch = (value > alpha);
1332 // The move failed high, but if reduction is very big we could
1333 // face a false positive, retry with a less aggressive reduction,
1334 // if the move fails high again then go with full depth search.
1335 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1337 assert(newDepth - ONE_PLY >= ONE_PLY);
1339 ss->reduction = ONE_PLY;
1340 alpha = SpNode ? sp->alpha : alpha;
1341 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1342 doFullDepthSearch = (value > alpha);
1344 ss->reduction = DEPTH_ZERO; // Restore original reduction
1347 // Step 15. Full depth search
1348 if (doFullDepthSearch)
1350 alpha = SpNode ? sp->alpha : alpha;
1351 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1353 // Step extra. pv search (only in PV nodes)
1354 // Search only for possible new PV nodes, if instead value >= beta then
1355 // parent node fails low with value <= alpha and tries another move.
1356 if (PvNode && value > alpha && value < beta)
1357 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1361 // Step 16. Undo move
1362 pos.undo_move(move);
1364 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1366 // Step 17. Check for new best move
1369 lock_grab(&(sp->lock));
1370 bestValue = sp->bestValue;
1374 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1379 sp->bestValue = value;
1383 if (SpNode && (!PvNode || value >= beta))
1384 sp->stopRequest = true;
1386 if (PvNode && value < beta) // We want always alpha < beta
1393 if (value == value_mate_in(ply + 1))
1394 ss->mateKiller = move;
1396 ss->bestMove = move;
1399 sp->parentSstack->bestMove = move;
1403 // Step 18. Check for split
1405 && depth >= ThreadsMgr.min_split_depth()
1406 && ThreadsMgr.active_threads() > 1
1408 && ThreadsMgr.available_thread_exists(threadID)
1410 && !ThreadsMgr.thread_should_stop(threadID)
1412 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1413 threatMove, mateThreat, moveCount, &mp, PvNode);
1416 // Step 19. Check for mate and stalemate
1417 // All legal moves have been searched and if there are
1418 // no legal moves, it must be mate or stalemate.
1419 // If one move was excluded return fail low score.
1420 if (!SpNode && !moveCount)
1421 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1423 // Step 20. Update tables
1424 // If the search is not aborted, update the transposition table,
1425 // history counters, and killer moves.
1426 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1428 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1429 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1430 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1432 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1434 // Update killers and history only for non capture moves that fails high
1435 if ( bestValue >= beta
1436 && !pos.move_is_capture_or_promotion(move))
1438 update_history(pos, move, depth, movesSearched, moveCount);
1439 update_killers(move, ss);
1445 // Here we have the lock still grabbed
1446 sp->slaves[threadID] = 0;
1447 sp->nodes += pos.nodes_searched();
1448 lock_release(&(sp->lock));
1451 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1456 // qsearch() is the quiescence search function, which is called by the main
1457 // search function when the remaining depth is zero (or, to be more precise,
1458 // less than ONE_PLY).
1460 template <NodeType PvNode>
1461 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1463 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1464 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1465 assert(PvNode || alpha == beta - 1);
1467 assert(ply > 0 && ply < PLY_MAX);
1468 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1472 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1473 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1476 Value oldAlpha = alpha;
1478 ss->bestMove = ss->currentMove = MOVE_NONE;
1480 // Check for an instant draw or maximum ply reached
1481 if (pos.is_draw() || ply >= PLY_MAX - 1)
1484 // Decide whether or not to include checks, this fixes also the type of
1485 // TT entry depth that we are going to use. Note that in qsearch we use
1486 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1487 isCheck = pos.is_check();
1488 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1490 // Transposition table lookup. At PV nodes, we don't use the TT for
1491 // pruning, but only for move ordering.
1492 tte = TT.retrieve(pos.get_key());
1493 ttMove = (tte ? tte->move() : MOVE_NONE);
1495 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1497 ss->bestMove = ttMove; // Can be MOVE_NONE
1498 return value_from_tt(tte->value(), ply);
1501 // Evaluate the position statically
1504 bestValue = futilityBase = -VALUE_INFINITE;
1505 ss->eval = evalMargin = VALUE_NONE;
1506 enoughMaterial = false;
1512 assert(tte->static_value() != VALUE_NONE);
1514 evalMargin = tte->static_value_margin();
1515 ss->eval = bestValue = tte->static_value();
1518 ss->eval = bestValue = evaluate(pos, evalMargin);
1520 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1522 // Stand pat. Return immediately if static value is at least beta
1523 if (bestValue >= beta)
1526 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1531 if (PvNode && bestValue > alpha)
1534 // Futility pruning parameters, not needed when in check
1535 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1536 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1539 // Initialize a MovePicker object for the current position, and prepare
1540 // to search the moves. Because the depth is <= 0 here, only captures,
1541 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1543 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1546 // Loop through the moves until no moves remain or a beta cutoff occurs
1547 while ( alpha < beta
1548 && (move = mp.get_next_move()) != MOVE_NONE)
1550 assert(move_is_ok(move));
1552 moveIsCheck = pos.move_is_check(move, ci);
1560 && !move_is_promotion(move)
1561 && !pos.move_is_passed_pawn_push(move))
1563 futilityValue = futilityBase
1564 + pos.endgame_value_of_piece_on(move_to(move))
1565 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1567 if (futilityValue < alpha)
1569 if (futilityValue > bestValue)
1570 bestValue = futilityValue;
1575 // Detect non-capture evasions that are candidate to be pruned
1576 evasionPrunable = isCheck
1577 && bestValue > value_mated_in(PLY_MAX)
1578 && !pos.move_is_capture(move)
1579 && !pos.can_castle(pos.side_to_move());
1581 // Don't search moves with negative SEE values
1583 && (!isCheck || evasionPrunable)
1585 && !move_is_promotion(move)
1586 && pos.see_sign(move) < 0)
1589 // Don't search useless checks
1594 && !pos.move_is_capture_or_promotion(move)
1595 && ss->eval + PawnValueMidgame / 4 < beta
1596 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1598 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1599 bestValue = ss->eval + PawnValueMidgame / 4;
1604 // Update current move
1605 ss->currentMove = move;
1607 // Make and search the move
1608 pos.do_move(move, st, ci, moveIsCheck);
1609 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1610 pos.undo_move(move);
1612 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1615 if (value > bestValue)
1621 ss->bestMove = move;
1626 // All legal moves have been searched. A special case: If we're in check
1627 // and no legal moves were found, it is checkmate.
1628 if (isCheck && bestValue == -VALUE_INFINITE)
1629 return value_mated_in(ply);
1631 // Update transposition table
1632 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1633 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1635 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1641 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1642 // bestValue is updated only when returning false because in that case move
1645 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1647 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1648 Square from, to, ksq, victimSq;
1651 Value futilityValue, bv = *bestValue;
1653 from = move_from(move);
1655 them = opposite_color(pos.side_to_move());
1656 ksq = pos.king_square(them);
1657 kingAtt = pos.attacks_from<KING>(ksq);
1658 pc = pos.piece_on(from);
1660 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1661 oldAtt = pos.attacks_from(pc, from, occ);
1662 newAtt = pos.attacks_from(pc, to, occ);
1664 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1665 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1667 if (!(b && (b & (b - 1))))
1670 // Rule 2. Queen contact check is very dangerous
1671 if ( type_of_piece(pc) == QUEEN
1672 && bit_is_set(kingAtt, to))
1675 // Rule 3. Creating new double threats with checks
1676 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1680 victimSq = pop_1st_bit(&b);
1681 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1683 // Note that here we generate illegal "double move"!
1684 if ( futilityValue >= beta
1685 && pos.see_sign(make_move(from, victimSq)) >= 0)
1688 if (futilityValue > bv)
1692 // Update bestValue only if check is not dangerous (because we will prune the move)
1698 // connected_moves() tests whether two moves are 'connected' in the sense
1699 // that the first move somehow made the second move possible (for instance
1700 // if the moving piece is the same in both moves). The first move is assumed
1701 // to be the move that was made to reach the current position, while the
1702 // second move is assumed to be a move from the current position.
1704 bool connected_moves(const Position& pos, Move m1, Move m2) {
1706 Square f1, t1, f2, t2;
1709 assert(m1 && move_is_ok(m1));
1710 assert(m2 && move_is_ok(m2));
1712 // Case 1: The moving piece is the same in both moves
1718 // Case 2: The destination square for m2 was vacated by m1
1724 // Case 3: Moving through the vacated square
1725 if ( piece_is_slider(pos.piece_on(f2))
1726 && bit_is_set(squares_between(f2, t2), f1))
1729 // Case 4: The destination square for m2 is defended by the moving piece in m1
1730 p = pos.piece_on(t1);
1731 if (bit_is_set(pos.attacks_from(p, t1), t2))
1734 // Case 5: Discovered check, checking piece is the piece moved in m1
1735 if ( piece_is_slider(p)
1736 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1737 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1739 // discovered_check_candidates() works also if the Position's side to
1740 // move is the opposite of the checking piece.
1741 Color them = opposite_color(pos.side_to_move());
1742 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1744 if (bit_is_set(dcCandidates, f2))
1751 // value_is_mate() checks if the given value is a mate one eventually
1752 // compensated for the ply.
1754 bool value_is_mate(Value value) {
1756 assert(abs(value) <= VALUE_INFINITE);
1758 return value <= value_mated_in(PLY_MAX)
1759 || value >= value_mate_in(PLY_MAX);
1763 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1764 // "plies to mate from the current ply". Non-mate scores are unchanged.
1765 // The function is called before storing a value to the transposition table.
1767 Value value_to_tt(Value v, int ply) {
1769 if (v >= value_mate_in(PLY_MAX))
1772 if (v <= value_mated_in(PLY_MAX))
1779 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1780 // the transposition table to a mate score corrected for the current ply.
1782 Value value_from_tt(Value v, int ply) {
1784 if (v >= value_mate_in(PLY_MAX))
1787 if (v <= value_mated_in(PLY_MAX))
1794 // extension() decides whether a move should be searched with normal depth,
1795 // or with extended depth. Certain classes of moves (checking moves, in
1796 // particular) are searched with bigger depth than ordinary moves and in
1797 // any case are marked as 'dangerous'. Note that also if a move is not
1798 // extended, as example because the corresponding UCI option is set to zero,
1799 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1800 template <NodeType PvNode>
1801 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1802 bool singleEvasion, bool mateThreat, bool* dangerous) {
1804 assert(m != MOVE_NONE);
1806 Depth result = DEPTH_ZERO;
1807 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1811 if (moveIsCheck && pos.see_sign(m) >= 0)
1812 result += CheckExtension[PvNode];
1815 result += SingleEvasionExtension[PvNode];
1818 result += MateThreatExtension[PvNode];
1821 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1823 Color c = pos.side_to_move();
1824 if (relative_rank(c, move_to(m)) == RANK_7)
1826 result += PawnPushTo7thExtension[PvNode];
1829 if (pos.pawn_is_passed(c, move_to(m)))
1831 result += PassedPawnExtension[PvNode];
1836 if ( captureOrPromotion
1837 && pos.type_of_piece_on(move_to(m)) != PAWN
1838 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1839 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1840 && !move_is_promotion(m)
1843 result += PawnEndgameExtension[PvNode];
1848 && captureOrPromotion
1849 && pos.type_of_piece_on(move_to(m)) != PAWN
1850 && pos.see_sign(m) >= 0)
1852 result += ONE_PLY / 2;
1856 return Min(result, ONE_PLY);
1860 // connected_threat() tests whether it is safe to forward prune a move or if
1861 // is somehow coonected to the threat move returned by null search.
1863 bool connected_threat(const Position& pos, Move m, Move threat) {
1865 assert(move_is_ok(m));
1866 assert(threat && move_is_ok(threat));
1867 assert(!pos.move_is_check(m));
1868 assert(!pos.move_is_capture_or_promotion(m));
1869 assert(!pos.move_is_passed_pawn_push(m));
1871 Square mfrom, mto, tfrom, tto;
1873 mfrom = move_from(m);
1875 tfrom = move_from(threat);
1876 tto = move_to(threat);
1878 // Case 1: Don't prune moves which move the threatened piece
1882 // Case 2: If the threatened piece has value less than or equal to the
1883 // value of the threatening piece, don't prune move which defend it.
1884 if ( pos.move_is_capture(threat)
1885 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1886 || pos.type_of_piece_on(tfrom) == KING)
1887 && pos.move_attacks_square(m, tto))
1890 // Case 3: If the moving piece in the threatened move is a slider, don't
1891 // prune safe moves which block its ray.
1892 if ( piece_is_slider(pos.piece_on(tfrom))
1893 && bit_is_set(squares_between(tfrom, tto), mto)
1894 && pos.see_sign(m) >= 0)
1901 // ok_to_use_TT() returns true if a transposition table score
1902 // can be used at a given point in search.
1904 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1906 Value v = value_from_tt(tte->value(), ply);
1908 return ( tte->depth() >= depth
1909 || v >= Max(value_mate_in(PLY_MAX), beta)
1910 || v < Min(value_mated_in(PLY_MAX), beta))
1912 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1913 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1917 // refine_eval() returns the transposition table score if
1918 // possible otherwise falls back on static position evaluation.
1920 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1924 Value v = value_from_tt(tte->value(), ply);
1926 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1927 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1934 // update_history() registers a good move that produced a beta-cutoff
1935 // in history and marks as failures all the other moves of that ply.
1937 void update_history(const Position& pos, Move move, Depth depth,
1938 Move movesSearched[], int moveCount) {
1941 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1943 for (int i = 0; i < moveCount - 1; i++)
1945 m = movesSearched[i];
1949 if (!pos.move_is_capture_or_promotion(m))
1950 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1955 // update_killers() add a good move that produced a beta-cutoff
1956 // among the killer moves of that ply.
1958 void update_killers(Move m, SearchStack* ss) {
1960 if (m == ss->killers[0])
1963 ss->killers[1] = ss->killers[0];
1968 // update_gains() updates the gains table of a non-capture move given
1969 // the static position evaluation before and after the move.
1971 void update_gains(const Position& pos, Move m, Value before, Value after) {
1974 && before != VALUE_NONE
1975 && after != VALUE_NONE
1976 && pos.captured_piece_type() == PIECE_TYPE_NONE
1977 && !move_is_special(m))
1978 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1982 // current_search_time() returns the number of milliseconds which have passed
1983 // since the beginning of the current search.
1985 int current_search_time() {
1987 return get_system_time() - SearchStartTime;
1991 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1993 std::string value_to_uci(Value v) {
1995 std::stringstream s;
1997 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1998 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2000 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2005 // nps() computes the current nodes/second count.
2007 int nps(const Position& pos) {
2009 int t = current_search_time();
2010 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
2014 // poll() performs two different functions: It polls for user input, and it
2015 // looks at the time consumed so far and decides if it's time to abort the
2018 void poll(const Position& pos) {
2020 static int lastInfoTime;
2021 int t = current_search_time();
2024 if (data_available())
2026 // We are line oriented, don't read single chars
2027 std::string command;
2029 if (!std::getline(std::cin, command))
2032 if (command == "quit")
2035 PonderSearch = false;
2039 else if (command == "stop")
2042 PonderSearch = false;
2044 else if (command == "ponderhit")
2048 // Print search information
2052 else if (lastInfoTime > t)
2053 // HACK: Must be a new search where we searched less than
2054 // NodesBetweenPolls nodes during the first second of search.
2057 else if (t - lastInfoTime >= 1000)
2064 if (dbg_show_hit_rate)
2065 dbg_print_hit_rate();
2067 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
2068 << " time " << t << endl;
2071 // Should we stop the search?
2075 bool stillAtFirstMove = FirstRootMove
2076 && !AspirationFailLow
2077 && t > TimeMgr.available_time();
2079 bool noMoreTime = t > TimeMgr.maximum_time()
2080 || stillAtFirstMove;
2082 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2083 || (ExactMaxTime && t >= ExactMaxTime)
2084 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2089 // ponderhit() is called when the program is pondering (i.e. thinking while
2090 // it's the opponent's turn to move) in order to let the engine know that
2091 // it correctly predicted the opponent's move.
2095 int t = current_search_time();
2096 PonderSearch = false;
2098 bool stillAtFirstMove = FirstRootMove
2099 && !AspirationFailLow
2100 && t > TimeMgr.available_time();
2102 bool noMoreTime = t > TimeMgr.maximum_time()
2103 || stillAtFirstMove;
2105 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2110 // init_ss_array() does a fast reset of the first entries of a SearchStack
2111 // array and of all the excludedMove and skipNullMove entries.
2113 void init_ss_array(SearchStack* ss, int size) {
2115 for (int i = 0; i < size; i++, ss++)
2117 ss->excludedMove = MOVE_NONE;
2118 ss->skipNullMove = false;
2119 ss->reduction = DEPTH_ZERO;
2123 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2128 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2129 // while the program is pondering. The point is to work around a wrinkle in
2130 // the UCI protocol: When pondering, the engine is not allowed to give a
2131 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2132 // We simply wait here until one of these commands is sent, and return,
2133 // after which the bestmove and pondermove will be printed (in id_loop()).
2135 void wait_for_stop_or_ponderhit() {
2137 std::string command;
2141 if (!std::getline(std::cin, command))
2144 if (command == "quit")
2149 else if (command == "ponderhit" || command == "stop")
2155 // print_pv_info() prints to standard output and eventually to log file information on
2156 // the current PV line. It is called at each iteration or after a new pv is found.
2158 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2160 cout << "info depth " << Iteration
2161 << " score " << value_to_uci(value)
2162 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2163 << " time " << current_search_time()
2164 << " nodes " << pos.nodes_searched()
2165 << " nps " << nps(pos)
2168 for (Move* m = pv; *m != MOVE_NONE; m++)
2175 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2176 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2178 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2183 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2184 // the PV back into the TT. This makes sure the old PV moves are searched
2185 // first, even if the old TT entries have been overwritten.
2187 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2191 Position p(pos, pos.thread());
2192 Value v, m = VALUE_NONE;
2194 for (int i = 0; pv[i] != MOVE_NONE; i++)
2196 tte = TT.retrieve(p.get_key());
2197 if (!tte || tte->move() != pv[i])
2199 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2200 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2202 p.do_move(pv[i], st);
2207 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2208 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2209 // allow to always have a ponder move even when we fail high at root and also a
2210 // long PV to print that is important for position analysis.
2212 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2216 Position p(pos, pos.thread());
2219 assert(bestMove != MOVE_NONE);
2222 p.do_move(pv[ply++], st);
2224 while ( (tte = TT.retrieve(p.get_key())) != NULL
2225 && tte->move() != MOVE_NONE
2226 && move_is_legal(p, tte->move())
2228 && (!p.is_draw() || ply < 2))
2230 pv[ply] = tte->move();
2231 p.do_move(pv[ply++], st);
2233 pv[ply] = MOVE_NONE;
2237 // init_thread() is the function which is called when a new thread is
2238 // launched. It simply calls the idle_loop() function with the supplied
2239 // threadID. There are two versions of this function; one for POSIX
2240 // threads and one for Windows threads.
2242 #if !defined(_MSC_VER)
2244 void* init_thread(void* threadID) {
2246 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2252 DWORD WINAPI init_thread(LPVOID threadID) {
2254 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2261 /// The ThreadsManager class
2264 // read_uci_options() updates number of active threads and other internal
2265 // parameters according to the UCI options values. It is called before
2266 // to start a new search.
2268 void ThreadsManager::read_uci_options() {
2270 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2271 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2272 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2273 activeThreads = Options["Threads"].value<int>();
2277 // idle_loop() is where the threads are parked when they have no work to do.
2278 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2279 // object for which the current thread is the master.
2281 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2283 assert(threadID >= 0 && threadID < MAX_THREADS);
2286 bool allFinished = false;
2290 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2291 // master should exit as last one.
2292 if (allThreadsShouldExit)
2295 threads[threadID].state = THREAD_TERMINATED;
2299 // If we are not thinking, wait for a condition to be signaled
2300 // instead of wasting CPU time polling for work.
2301 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2302 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2304 assert(!sp || useSleepingThreads);
2305 assert(threadID != 0 || useSleepingThreads);
2307 if (threads[threadID].state == THREAD_INITIALIZING)
2308 threads[threadID].state = THREAD_AVAILABLE;
2310 // Grab the lock to avoid races with wake_sleeping_thread()
2311 lock_grab(&sleepLock[threadID]);
2313 // If we are master and all slaves have finished do not go to sleep
2314 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2315 allFinished = (i == activeThreads);
2317 if (allFinished || allThreadsShouldExit)
2319 lock_release(&sleepLock[threadID]);
2323 // Do sleep here after retesting sleep conditions
2324 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2325 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2327 lock_release(&sleepLock[threadID]);
2330 // If this thread has been assigned work, launch a search
2331 if (threads[threadID].state == THREAD_WORKISWAITING)
2333 assert(!allThreadsShouldExit);
2335 threads[threadID].state = THREAD_SEARCHING;
2337 // Here we call search() with SplitPoint template parameter set to true
2338 SplitPoint* tsp = threads[threadID].splitPoint;
2339 Position pos(*tsp->pos, threadID);
2340 SearchStack* ss = tsp->sstack[threadID] + 1;
2344 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2346 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2348 assert(threads[threadID].state == THREAD_SEARCHING);
2350 threads[threadID].state = THREAD_AVAILABLE;
2352 // Wake up master thread so to allow it to return from the idle loop in
2353 // case we are the last slave of the split point.
2354 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2355 wake_sleeping_thread(tsp->master);
2358 // If this thread is the master of a split point and all slaves have
2359 // finished their work at this split point, return from the idle loop.
2360 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2361 allFinished = (i == activeThreads);
2365 // Because sp->slaves[] is reset under lock protection,
2366 // be sure sp->lock has been released before to return.
2367 lock_grab(&(sp->lock));
2368 lock_release(&(sp->lock));
2370 // In helpful master concept a master can help only a sub-tree, and
2371 // because here is all finished is not possible master is booked.
2372 assert(threads[threadID].state == THREAD_AVAILABLE);
2374 threads[threadID].state = THREAD_SEARCHING;
2381 // init_threads() is called during startup. It launches all helper threads,
2382 // and initializes the split point stack and the global locks and condition
2385 void ThreadsManager::init_threads() {
2387 int i, arg[MAX_THREADS];
2390 // Initialize global locks
2393 for (i = 0; i < MAX_THREADS; i++)
2395 lock_init(&sleepLock[i]);
2396 cond_init(&sleepCond[i]);
2399 // Initialize splitPoints[] locks
2400 for (i = 0; i < MAX_THREADS; i++)
2401 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2402 lock_init(&(threads[i].splitPoints[j].lock));
2404 // Will be set just before program exits to properly end the threads
2405 allThreadsShouldExit = false;
2407 // Threads will be put all threads to sleep as soon as created
2410 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2411 threads[0].state = THREAD_SEARCHING;
2412 for (i = 1; i < MAX_THREADS; i++)
2413 threads[i].state = THREAD_INITIALIZING;
2415 // Launch the helper threads
2416 for (i = 1; i < MAX_THREADS; i++)
2420 #if !defined(_MSC_VER)
2421 pthread_t pthread[1];
2422 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2423 pthread_detach(pthread[0]);
2425 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2429 cout << "Failed to create thread number " << i << endl;
2433 // Wait until the thread has finished launching and is gone to sleep
2434 while (threads[i].state == THREAD_INITIALIZING) {}
2439 // exit_threads() is called when the program exits. It makes all the
2440 // helper threads exit cleanly.
2442 void ThreadsManager::exit_threads() {
2444 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2446 // Wake up all the threads and waits for termination
2447 for (int i = 1; i < MAX_THREADS; i++)
2449 wake_sleeping_thread(i);
2450 while (threads[i].state != THREAD_TERMINATED) {}
2453 // Now we can safely destroy the locks
2454 for (int i = 0; i < MAX_THREADS; i++)
2455 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2456 lock_destroy(&(threads[i].splitPoints[j].lock));
2458 lock_destroy(&mpLock);
2460 // Now we can safely destroy the wait conditions
2461 for (int i = 0; i < MAX_THREADS; i++)
2463 lock_destroy(&sleepLock[i]);
2464 cond_destroy(&sleepCond[i]);
2469 // thread_should_stop() checks whether the thread should stop its search.
2470 // This can happen if a beta cutoff has occurred in the thread's currently
2471 // active split point, or in some ancestor of the current split point.
2473 bool ThreadsManager::thread_should_stop(int threadID) const {
2475 assert(threadID >= 0 && threadID < activeThreads);
2477 SplitPoint* sp = threads[threadID].splitPoint;
2479 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2484 // thread_is_available() checks whether the thread with threadID "slave" is
2485 // available to help the thread with threadID "master" at a split point. An
2486 // obvious requirement is that "slave" must be idle. With more than two
2487 // threads, this is not by itself sufficient: If "slave" is the master of
2488 // some active split point, it is only available as a slave to the other
2489 // threads which are busy searching the split point at the top of "slave"'s
2490 // split point stack (the "helpful master concept" in YBWC terminology).
2492 bool ThreadsManager::thread_is_available(int slave, int master) const {
2494 assert(slave >= 0 && slave < activeThreads);
2495 assert(master >= 0 && master < activeThreads);
2496 assert(activeThreads > 1);
2498 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2501 // Make a local copy to be sure doesn't change under our feet
2502 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2504 // No active split points means that the thread is available as
2505 // a slave for any other thread.
2506 if (localActiveSplitPoints == 0 || activeThreads == 2)
2509 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2510 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2511 // could have been set to 0 by another thread leading to an out of bound access.
2512 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2519 // available_thread_exists() tries to find an idle thread which is available as
2520 // a slave for the thread with threadID "master".
2522 bool ThreadsManager::available_thread_exists(int master) const {
2524 assert(master >= 0 && master < activeThreads);
2525 assert(activeThreads > 1);
2527 for (int i = 0; i < activeThreads; i++)
2528 if (thread_is_available(i, master))
2535 // split() does the actual work of distributing the work at a node between
2536 // several available threads. If it does not succeed in splitting the
2537 // node (because no idle threads are available, or because we have no unused
2538 // split point objects), the function immediately returns. If splitting is
2539 // possible, a SplitPoint object is initialized with all the data that must be
2540 // copied to the helper threads and we tell our helper threads that they have
2541 // been assigned work. This will cause them to instantly leave their idle loops and
2542 // call search().When all threads have returned from search() then split() returns.
2544 template <bool Fake>
2545 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2546 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2547 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2548 assert(pos.is_ok());
2549 assert(ply > 0 && ply < PLY_MAX);
2550 assert(*bestValue >= -VALUE_INFINITE);
2551 assert(*bestValue <= *alpha);
2552 assert(*alpha < beta);
2553 assert(beta <= VALUE_INFINITE);
2554 assert(depth > DEPTH_ZERO);
2555 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2556 assert(activeThreads > 1);
2558 int i, master = pos.thread();
2559 Thread& masterThread = threads[master];
2563 // If no other thread is available to help us, or if we have too many
2564 // active split points, don't split.
2565 if ( !available_thread_exists(master)
2566 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2568 lock_release(&mpLock);
2572 // Pick the next available split point object from the split point stack
2573 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2575 // Initialize the split point object
2576 splitPoint.parent = masterThread.splitPoint;
2577 splitPoint.master = master;
2578 splitPoint.stopRequest = false;
2579 splitPoint.ply = ply;
2580 splitPoint.depth = depth;
2581 splitPoint.threatMove = threatMove;
2582 splitPoint.mateThreat = mateThreat;
2583 splitPoint.alpha = *alpha;
2584 splitPoint.beta = beta;
2585 splitPoint.pvNode = pvNode;
2586 splitPoint.bestValue = *bestValue;
2588 splitPoint.moveCount = moveCount;
2589 splitPoint.pos = &pos;
2590 splitPoint.nodes = 0;
2591 splitPoint.parentSstack = ss;
2592 for (i = 0; i < activeThreads; i++)
2593 splitPoint.slaves[i] = 0;
2595 masterThread.splitPoint = &splitPoint;
2597 // If we are here it means we are not available
2598 assert(masterThread.state != THREAD_AVAILABLE);
2600 int workersCnt = 1; // At least the master is included
2602 // Allocate available threads setting state to THREAD_BOOKED
2603 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2604 if (thread_is_available(i, master))
2606 threads[i].state = THREAD_BOOKED;
2607 threads[i].splitPoint = &splitPoint;
2608 splitPoint.slaves[i] = 1;
2612 assert(Fake || workersCnt > 1);
2614 // We can release the lock because slave threads are already booked and master is not available
2615 lock_release(&mpLock);
2617 // Tell the threads that they have work to do. This will make them leave
2618 // their idle loop. But before copy search stack tail for each thread.
2619 for (i = 0; i < activeThreads; i++)
2620 if (i == master || splitPoint.slaves[i])
2622 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2624 assert(i == master || threads[i].state == THREAD_BOOKED);
2626 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2628 if (useSleepingThreads && i != master)
2629 wake_sleeping_thread(i);
2632 // Everything is set up. The master thread enters the idle loop, from
2633 // which it will instantly launch a search, because its state is
2634 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2635 // idle loop, which means that the main thread will return from the idle
2636 // loop when all threads have finished their work at this split point.
2637 idle_loop(master, &splitPoint);
2639 // We have returned from the idle loop, which means that all threads are
2640 // finished. Update alpha and bestValue, and return.
2643 *alpha = splitPoint.alpha;
2644 *bestValue = splitPoint.bestValue;
2645 masterThread.activeSplitPoints--;
2646 masterThread.splitPoint = splitPoint.parent;
2647 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2649 lock_release(&mpLock);
2653 // wake_sleeping_thread() wakes up the thread with the given threadID
2654 // when it is time to start a new search.
2656 void ThreadsManager::wake_sleeping_thread(int threadID) {
2658 lock_grab(&sleepLock[threadID]);
2659 cond_signal(&sleepCond[threadID]);
2660 lock_release(&sleepLock[threadID]);
2664 /// The RootMoveList class
2666 // RootMoveList c'tor
2668 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2670 SearchStack ss[PLY_MAX_PLUS_2];
2671 MoveStack mlist[MOVES_MAX];
2673 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2675 // Initialize search stack
2676 init_ss_array(ss, PLY_MAX_PLUS_2);
2677 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2680 // Generate all legal moves
2681 MoveStack* last = generate_moves(pos, mlist);
2683 // Add each move to the moves[] array
2684 for (MoveStack* cur = mlist; cur != last; cur++)
2686 bool includeMove = includeAllMoves;
2688 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2689 includeMove = (searchMoves[k] == cur->move);
2694 // Find a quick score for the move
2695 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2696 moves[count].pv[1] = MOVE_NONE;
2697 pos.do_move(cur->move, st);
2698 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2699 pos.undo_move(cur->move);
2705 // Score root moves using the standard way used in main search, the moves
2706 // are scored according to the order in which are returned by MovePicker.
2708 void RootMoveList::score_moves(const Position& pos)
2712 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2714 while ((move = mp.get_next_move()) != MOVE_NONE)
2715 for (int i = 0; i < count; i++)
2716 if (moves[i].move == move)
2718 moves[i].mp_score = score--;
2723 // RootMoveList simple methods definitions
2725 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2729 for (j = 0; pv[j] != MOVE_NONE; j++)
2730 moves[moveNum].pv[j] = pv[j];
2732 moves[moveNum].pv[j] = MOVE_NONE;
2736 // RootMoveList::sort() sorts the root move list at the beginning of a new
2739 void RootMoveList::sort() {
2741 sort_multipv(count - 1); // Sort all items
2745 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2746 // list by their scores and depths. It is used to order the different PVs
2747 // correctly in MultiPV mode.
2749 void RootMoveList::sort_multipv(int n) {
2753 for (i = 1; i <= n; i++)
2755 RootMove rm = moves[i];
2756 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2757 moves[j] = moves[j - 1];