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 cutoff_at_splitpoint(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
1011 || ThreadsMgr.cutoff_at_splitpoint(threadID)
1013 || ply >= PLY_MAX - 1)
1016 // Step 3. Mate distance pruning
1017 alpha = Max(value_mated_in(ply), alpha);
1018 beta = Min(value_mate_in(ply+1), beta);
1022 // Step 4. Transposition table lookup
1024 // We don't want the score of a partial search to overwrite a previous full search
1025 // TT value, so we use a different position key in case of an excluded move exists.
1026 excludedMove = ss->excludedMove;
1027 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1029 tte = TT.retrieve(posKey);
1030 ttMove = tte ? tte->move() : MOVE_NONE;
1032 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1033 // This is to avoid problems in the following areas:
1035 // * Repetition draw detection
1036 // * Fifty move rule detection
1037 // * Searching for a mate
1038 // * Printing of full PV line
1039 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1042 ss->bestMove = ttMove; // Can be MOVE_NONE
1043 return value_from_tt(tte->value(), ply);
1046 // Step 5. Evaluate the position statically and
1047 // update gain statistics of parent move.
1049 ss->eval = ss->evalMargin = VALUE_NONE;
1052 assert(tte->static_value() != VALUE_NONE);
1054 ss->eval = tte->static_value();
1055 ss->evalMargin = tte->static_value_margin();
1056 refinedValue = refine_eval(tte, ss->eval, ply);
1060 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1061 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1064 // Save gain for the parent non-capture move
1065 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1067 // Step 6. Razoring (is omitted in PV nodes)
1069 && depth < RazorDepth
1071 && refinedValue < beta - razor_margin(depth)
1072 && ttMove == MOVE_NONE
1073 && !value_is_mate(beta)
1074 && !pos.has_pawn_on_7th(pos.side_to_move()))
1076 Value rbeta = beta - razor_margin(depth);
1077 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1079 // Logically we should return (v + razor_margin(depth)), but
1080 // surprisingly this did slightly weaker in tests.
1084 // Step 7. Static null move pruning (is omitted in PV nodes)
1085 // We're betting that the opponent doesn't have a move that will reduce
1086 // the score by more than futility_margin(depth) if we do a null move.
1088 && !ss->skipNullMove
1089 && depth < RazorDepth
1091 && refinedValue >= beta + futility_margin(depth, 0)
1092 && !value_is_mate(beta)
1093 && pos.non_pawn_material(pos.side_to_move()))
1094 return refinedValue - futility_margin(depth, 0);
1096 // Step 8. Null move search with verification search (is omitted in PV nodes)
1098 && !ss->skipNullMove
1101 && refinedValue >= beta
1102 && !value_is_mate(beta)
1103 && pos.non_pawn_material(pos.side_to_move()))
1105 ss->currentMove = MOVE_NULL;
1107 // Null move dynamic reduction based on depth
1108 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1110 // Null move dynamic reduction based on value
1111 if (refinedValue - beta > PawnValueMidgame)
1114 pos.do_null_move(st);
1115 (ss+1)->skipNullMove = true;
1116 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1117 (ss+1)->skipNullMove = false;
1118 pos.undo_null_move();
1120 if (nullValue >= beta)
1122 // Do not return unproven mate scores
1123 if (nullValue >= value_mate_in(PLY_MAX))
1126 if (depth < 6 * ONE_PLY)
1129 // Do verification search at high depths
1130 ss->skipNullMove = true;
1131 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1132 ss->skipNullMove = false;
1139 // The null move failed low, which means that we may be faced with
1140 // some kind of threat. If the previous move was reduced, check if
1141 // the move that refuted the null move was somehow connected to the
1142 // move which was reduced. If a connection is found, return a fail
1143 // low score (which will cause the reduced move to fail high in the
1144 // parent node, which will trigger a re-search with full depth).
1145 if (nullValue == value_mated_in(ply + 2))
1148 threatMove = (ss+1)->bestMove;
1149 if ( depth < ThreatDepth
1150 && (ss-1)->reduction
1151 && threatMove != MOVE_NONE
1152 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1157 // Step 9. Internal iterative deepening
1158 if ( depth >= IIDDepth[PvNode]
1159 && ttMove == MOVE_NONE
1160 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1162 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1164 ss->skipNullMove = true;
1165 search<PvNode>(pos, ss, alpha, beta, d, ply);
1166 ss->skipNullMove = false;
1168 ttMove = ss->bestMove;
1169 tte = TT.retrieve(posKey);
1172 // Expensive mate threat detection (only for PV nodes)
1174 mateThreat = pos.has_mate_threat();
1176 split_point_start: // At split points actual search starts from here
1178 // Initialize a MovePicker object for the current position
1179 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1180 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1181 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1183 ss->bestMove = MOVE_NONE;
1184 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1185 futilityBase = ss->eval + ss->evalMargin;
1186 singularExtensionNode = !SpNode
1187 && depth >= SingularExtensionDepth[PvNode]
1190 && !excludedMove // Do not allow recursive singular extension search
1191 && (tte->type() & VALUE_TYPE_LOWER)
1192 && tte->depth() >= depth - 3 * ONE_PLY;
1195 lock_grab(&(sp->lock));
1196 bestValue = sp->bestValue;
1199 // Step 10. Loop through moves
1200 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1201 while ( bestValue < beta
1202 && (move = mp.get_next_move()) != MOVE_NONE
1203 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1205 assert(move_is_ok(move));
1209 moveCount = ++sp->moveCount;
1210 lock_release(&(sp->lock));
1212 else if (move == excludedMove)
1215 movesSearched[moveCount++] = move;
1217 moveIsCheck = pos.move_is_check(move, ci);
1218 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1220 // Step 11. Decide the new search depth
1221 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1223 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1224 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1225 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1226 // lower then ttValue minus a margin then we extend ttMove.
1227 if ( singularExtensionNode
1228 && move == tte->move()
1231 Value ttValue = value_from_tt(tte->value(), ply);
1233 if (abs(ttValue) < VALUE_KNOWN_WIN)
1235 Value b = ttValue - SingularExtensionMargin;
1236 ss->excludedMove = move;
1237 ss->skipNullMove = true;
1238 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1239 ss->skipNullMove = false;
1240 ss->excludedMove = MOVE_NONE;
1241 ss->bestMove = MOVE_NONE;
1247 // Update current move (this must be done after singular extension search)
1248 ss->currentMove = move;
1249 newDepth = depth - ONE_PLY + ext;
1251 // Step 12. Futility pruning (is omitted in PV nodes)
1253 && !captureOrPromotion
1257 && !move_is_castle(move))
1259 // Move count based pruning
1260 if ( moveCount >= futility_move_count(depth)
1261 && !(threatMove && connected_threat(pos, move, threatMove))
1262 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1265 lock_grab(&(sp->lock));
1270 // Value based pruning
1271 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1272 // but fixing this made program slightly weaker.
1273 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1274 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1275 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1277 if (futilityValueScaled < beta)
1281 lock_grab(&(sp->lock));
1282 if (futilityValueScaled > sp->bestValue)
1283 sp->bestValue = bestValue = futilityValueScaled;
1285 else if (futilityValueScaled > bestValue)
1286 bestValue = futilityValueScaled;
1291 // Prune moves with negative SEE at low depths
1292 if ( predictedDepth < 2 * ONE_PLY
1293 && bestValue > value_mated_in(PLY_MAX)
1294 && pos.see_sign(move) < 0)
1297 lock_grab(&(sp->lock));
1303 // Step 13. Make the move
1304 pos.do_move(move, st, ci, moveIsCheck);
1306 // Step extra. pv search (only in PV nodes)
1307 // The first move in list is the expected PV
1308 if (PvNode && moveCount == 1)
1309 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1312 // Step 14. Reduced depth search
1313 // If the move fails high will be re-searched at full depth.
1314 bool doFullDepthSearch = true;
1316 if ( depth >= 3 * ONE_PLY
1317 && !captureOrPromotion
1319 && !move_is_castle(move)
1320 && ss->killers[0] != move
1321 && ss->killers[1] != move)
1323 ss->reduction = reduction<PvNode>(depth, moveCount);
1327 alpha = SpNode ? sp->alpha : alpha;
1328 Depth d = newDepth - ss->reduction;
1329 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1331 doFullDepthSearch = (value > alpha);
1334 // The move failed high, but if reduction is very big we could
1335 // face a false positive, retry with a less aggressive reduction,
1336 // if the move fails high again then go with full depth search.
1337 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1339 assert(newDepth - ONE_PLY >= ONE_PLY);
1341 ss->reduction = ONE_PLY;
1342 alpha = SpNode ? sp->alpha : alpha;
1343 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1344 doFullDepthSearch = (value > alpha);
1346 ss->reduction = DEPTH_ZERO; // Restore original reduction
1349 // Step 15. Full depth search
1350 if (doFullDepthSearch)
1352 alpha = SpNode ? sp->alpha : alpha;
1353 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1355 // Step extra. pv search (only in PV nodes)
1356 // Search only for possible new PV nodes, if instead value >= beta then
1357 // parent node fails low with value <= alpha and tries another move.
1358 if (PvNode && value > alpha && value < beta)
1359 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1363 // Step 16. Undo move
1364 pos.undo_move(move);
1366 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1368 // Step 17. Check for new best move
1371 lock_grab(&(sp->lock));
1372 bestValue = sp->bestValue;
1376 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1381 sp->bestValue = value;
1385 if (PvNode && value < beta) // We want always alpha < beta
1393 sp->betaCutoff = true;
1395 if (value == value_mate_in(ply + 1))
1396 ss->mateKiller = move;
1398 ss->bestMove = move;
1401 sp->parentSstack->bestMove = move;
1405 // Step 18. Check for split
1407 && depth >= ThreadsMgr.min_split_depth()
1408 && ThreadsMgr.active_threads() > 1
1410 && ThreadsMgr.available_thread_exists(threadID)
1412 && !ThreadsMgr.cutoff_at_splitpoint(threadID)
1414 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1415 threatMove, mateThreat, moveCount, &mp, PvNode);
1418 // Step 19. Check for mate and stalemate
1419 // All legal moves have been searched and if there are
1420 // no legal moves, it must be mate or stalemate.
1421 // If one move was excluded return fail low score.
1422 if (!SpNode && !moveCount)
1423 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1425 // Step 20. Update tables
1426 // If the search is not aborted, update the transposition table,
1427 // history counters, and killer moves.
1428 if (!SpNode && !AbortSearch && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1430 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1431 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1432 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1434 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1436 // Update killers and history only for non capture moves that fails high
1437 if ( bestValue >= beta
1438 && !pos.move_is_capture_or_promotion(move))
1440 update_history(pos, move, depth, movesSearched, moveCount);
1441 update_killers(move, ss);
1447 // Here we have the lock still grabbed
1448 sp->slaves[threadID] = 0;
1449 sp->nodes += pos.nodes_searched();
1450 lock_release(&(sp->lock));
1453 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1458 // qsearch() is the quiescence search function, which is called by the main
1459 // search function when the remaining depth is zero (or, to be more precise,
1460 // less than ONE_PLY).
1462 template <NodeType PvNode>
1463 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1465 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1466 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1467 assert(PvNode || alpha == beta - 1);
1469 assert(ply > 0 && ply < PLY_MAX);
1470 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1474 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1475 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1478 Value oldAlpha = alpha;
1480 ss->bestMove = ss->currentMove = MOVE_NONE;
1482 // Check for an instant draw or maximum ply reached
1483 if (pos.is_draw() || ply >= PLY_MAX - 1)
1486 // Decide whether or not to include checks, this fixes also the type of
1487 // TT entry depth that we are going to use. Note that in qsearch we use
1488 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1489 isCheck = pos.is_check();
1490 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1492 // Transposition table lookup. At PV nodes, we don't use the TT for
1493 // pruning, but only for move ordering.
1494 tte = TT.retrieve(pos.get_key());
1495 ttMove = (tte ? tte->move() : MOVE_NONE);
1497 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
1499 ss->bestMove = ttMove; // Can be MOVE_NONE
1500 return value_from_tt(tte->value(), ply);
1503 // Evaluate the position statically
1506 bestValue = futilityBase = -VALUE_INFINITE;
1507 ss->eval = evalMargin = VALUE_NONE;
1508 enoughMaterial = false;
1514 assert(tte->static_value() != VALUE_NONE);
1516 evalMargin = tte->static_value_margin();
1517 ss->eval = bestValue = tte->static_value();
1520 ss->eval = bestValue = evaluate(pos, evalMargin);
1522 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1524 // Stand pat. Return immediately if static value is at least beta
1525 if (bestValue >= beta)
1528 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1533 if (PvNode && bestValue > alpha)
1536 // Futility pruning parameters, not needed when in check
1537 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1538 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1541 // Initialize a MovePicker object for the current position, and prepare
1542 // to search the moves. Because the depth is <= 0 here, only captures,
1543 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1545 MovePicker mp(pos, ttMove, depth, H);
1548 // Loop through the moves until no moves remain or a beta cutoff occurs
1549 while ( alpha < beta
1550 && (move = mp.get_next_move()) != MOVE_NONE)
1552 assert(move_is_ok(move));
1554 moveIsCheck = pos.move_is_check(move, ci);
1562 && !move_is_promotion(move)
1563 && !pos.move_is_passed_pawn_push(move))
1565 futilityValue = futilityBase
1566 + pos.endgame_value_of_piece_on(move_to(move))
1567 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1569 if (futilityValue < alpha)
1571 if (futilityValue > bestValue)
1572 bestValue = futilityValue;
1577 // Detect non-capture evasions that are candidate to be pruned
1578 evasionPrunable = isCheck
1579 && bestValue > value_mated_in(PLY_MAX)
1580 && !pos.move_is_capture(move)
1581 && !pos.can_castle(pos.side_to_move());
1583 // Don't search moves with negative SEE values
1585 && (!isCheck || evasionPrunable)
1587 && !move_is_promotion(move)
1588 && pos.see_sign(move) < 0)
1591 // Don't search useless checks
1596 && !pos.move_is_capture_or_promotion(move)
1597 && ss->eval + PawnValueMidgame / 4 < beta
1598 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1600 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1601 bestValue = ss->eval + PawnValueMidgame / 4;
1606 // Update current move
1607 ss->currentMove = move;
1609 // Make and search the move
1610 pos.do_move(move, st, ci, moveIsCheck);
1611 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1612 pos.undo_move(move);
1614 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1617 if (value > bestValue)
1623 ss->bestMove = move;
1628 // All legal moves have been searched. A special case: If we're in check
1629 // and no legal moves were found, it is checkmate.
1630 if (isCheck && bestValue == -VALUE_INFINITE)
1631 return value_mated_in(ply);
1633 // Update transposition table
1634 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1635 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1637 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1643 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1644 // bestValue is updated only when returning false because in that case move
1647 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1649 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1650 Square from, to, ksq, victimSq;
1653 Value futilityValue, bv = *bestValue;
1655 from = move_from(move);
1657 them = opposite_color(pos.side_to_move());
1658 ksq = pos.king_square(them);
1659 kingAtt = pos.attacks_from<KING>(ksq);
1660 pc = pos.piece_on(from);
1662 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1663 oldAtt = pos.attacks_from(pc, from, occ);
1664 newAtt = pos.attacks_from(pc, to, occ);
1666 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1667 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1669 if (!(b && (b & (b - 1))))
1672 // Rule 2. Queen contact check is very dangerous
1673 if ( type_of_piece(pc) == QUEEN
1674 && bit_is_set(kingAtt, to))
1677 // Rule 3. Creating new double threats with checks
1678 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1682 victimSq = pop_1st_bit(&b);
1683 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1685 // Note that here we generate illegal "double move"!
1686 if ( futilityValue >= beta
1687 && pos.see_sign(make_move(from, victimSq)) >= 0)
1690 if (futilityValue > bv)
1694 // Update bestValue only if check is not dangerous (because we will prune the move)
1700 // connected_moves() tests whether two moves are 'connected' in the sense
1701 // that the first move somehow made the second move possible (for instance
1702 // if the moving piece is the same in both moves). The first move is assumed
1703 // to be the move that was made to reach the current position, while the
1704 // second move is assumed to be a move from the current position.
1706 bool connected_moves(const Position& pos, Move m1, Move m2) {
1708 Square f1, t1, f2, t2;
1711 assert(m1 && move_is_ok(m1));
1712 assert(m2 && move_is_ok(m2));
1714 // Case 1: The moving piece is the same in both moves
1720 // Case 2: The destination square for m2 was vacated by m1
1726 // Case 3: Moving through the vacated square
1727 if ( piece_is_slider(pos.piece_on(f2))
1728 && bit_is_set(squares_between(f2, t2), f1))
1731 // Case 4: The destination square for m2 is defended by the moving piece in m1
1732 p = pos.piece_on(t1);
1733 if (bit_is_set(pos.attacks_from(p, t1), t2))
1736 // Case 5: Discovered check, checking piece is the piece moved in m1
1737 if ( piece_is_slider(p)
1738 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1739 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1741 // discovered_check_candidates() works also if the Position's side to
1742 // move is the opposite of the checking piece.
1743 Color them = opposite_color(pos.side_to_move());
1744 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1746 if (bit_is_set(dcCandidates, f2))
1753 // value_is_mate() checks if the given value is a mate one eventually
1754 // compensated for the ply.
1756 bool value_is_mate(Value value) {
1758 assert(abs(value) <= VALUE_INFINITE);
1760 return value <= value_mated_in(PLY_MAX)
1761 || value >= value_mate_in(PLY_MAX);
1765 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1766 // "plies to mate from the current ply". Non-mate scores are unchanged.
1767 // The function is called before storing a value to the transposition table.
1769 Value value_to_tt(Value v, int ply) {
1771 if (v >= value_mate_in(PLY_MAX))
1774 if (v <= value_mated_in(PLY_MAX))
1781 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1782 // the transposition table to a mate score corrected for the current ply.
1784 Value value_from_tt(Value v, int ply) {
1786 if (v >= value_mate_in(PLY_MAX))
1789 if (v <= value_mated_in(PLY_MAX))
1796 // extension() decides whether a move should be searched with normal depth,
1797 // or with extended depth. Certain classes of moves (checking moves, in
1798 // particular) are searched with bigger depth than ordinary moves and in
1799 // any case are marked as 'dangerous'. Note that also if a move is not
1800 // extended, as example because the corresponding UCI option is set to zero,
1801 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1802 template <NodeType PvNode>
1803 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1804 bool singleEvasion, bool mateThreat, bool* dangerous) {
1806 assert(m != MOVE_NONE);
1808 Depth result = DEPTH_ZERO;
1809 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1813 if (moveIsCheck && pos.see_sign(m) >= 0)
1814 result += CheckExtension[PvNode];
1817 result += SingleEvasionExtension[PvNode];
1820 result += MateThreatExtension[PvNode];
1823 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1825 Color c = pos.side_to_move();
1826 if (relative_rank(c, move_to(m)) == RANK_7)
1828 result += PawnPushTo7thExtension[PvNode];
1831 if (pos.pawn_is_passed(c, move_to(m)))
1833 result += PassedPawnExtension[PvNode];
1838 if ( captureOrPromotion
1839 && pos.type_of_piece_on(move_to(m)) != PAWN
1840 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1841 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1842 && !move_is_promotion(m)
1845 result += PawnEndgameExtension[PvNode];
1850 && captureOrPromotion
1851 && pos.type_of_piece_on(move_to(m)) != PAWN
1852 && pos.see_sign(m) >= 0)
1854 result += ONE_PLY / 2;
1858 return Min(result, ONE_PLY);
1862 // connected_threat() tests whether it is safe to forward prune a move or if
1863 // is somehow coonected to the threat move returned by null search.
1865 bool connected_threat(const Position& pos, Move m, Move threat) {
1867 assert(move_is_ok(m));
1868 assert(threat && move_is_ok(threat));
1869 assert(!pos.move_is_check(m));
1870 assert(!pos.move_is_capture_or_promotion(m));
1871 assert(!pos.move_is_passed_pawn_push(m));
1873 Square mfrom, mto, tfrom, tto;
1875 mfrom = move_from(m);
1877 tfrom = move_from(threat);
1878 tto = move_to(threat);
1880 // Case 1: Don't prune moves which move the threatened piece
1884 // Case 2: If the threatened piece has value less than or equal to the
1885 // value of the threatening piece, don't prune move which defend it.
1886 if ( pos.move_is_capture(threat)
1887 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1888 || pos.type_of_piece_on(tfrom) == KING)
1889 && pos.move_attacks_square(m, tto))
1892 // Case 3: If the moving piece in the threatened move is a slider, don't
1893 // prune safe moves which block its ray.
1894 if ( piece_is_slider(pos.piece_on(tfrom))
1895 && bit_is_set(squares_between(tfrom, tto), mto)
1896 && pos.see_sign(m) >= 0)
1903 // ok_to_use_TT() returns true if a transposition table score
1904 // can be used at a given point in search.
1906 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1908 Value v = value_from_tt(tte->value(), ply);
1910 return ( tte->depth() >= depth
1911 || v >= Max(value_mate_in(PLY_MAX), beta)
1912 || v < Min(value_mated_in(PLY_MAX), beta))
1914 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1915 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1919 // refine_eval() returns the transposition table score if
1920 // possible otherwise falls back on static position evaluation.
1922 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1926 Value v = value_from_tt(tte->value(), ply);
1928 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1929 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1936 // update_history() registers a good move that produced a beta-cutoff
1937 // in history and marks as failures all the other moves of that ply.
1939 void update_history(const Position& pos, Move move, Depth depth,
1940 Move movesSearched[], int moveCount) {
1943 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1945 for (int i = 0; i < moveCount - 1; i++)
1947 m = movesSearched[i];
1951 if (!pos.move_is_capture_or_promotion(m))
1952 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1957 // update_killers() add a good move that produced a beta-cutoff
1958 // among the killer moves of that ply.
1960 void update_killers(Move m, SearchStack* ss) {
1962 if (m == ss->killers[0])
1965 ss->killers[1] = ss->killers[0];
1970 // update_gains() updates the gains table of a non-capture move given
1971 // the static position evaluation before and after the move.
1973 void update_gains(const Position& pos, Move m, Value before, Value after) {
1976 && before != VALUE_NONE
1977 && after != VALUE_NONE
1978 && pos.captured_piece_type() == PIECE_TYPE_NONE
1979 && !move_is_special(m))
1980 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1984 // current_search_time() returns the number of milliseconds which have passed
1985 // since the beginning of the current search.
1987 int current_search_time() {
1989 return get_system_time() - SearchStartTime;
1993 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1995 std::string value_to_uci(Value v) {
1997 std::stringstream s;
1999 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
2000 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2002 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2007 // nps() computes the current nodes/second count.
2009 int nps(const Position& pos) {
2011 int t = current_search_time();
2012 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
2016 // poll() performs two different functions: It polls for user input, and it
2017 // looks at the time consumed so far and decides if it's time to abort the
2020 void poll(const Position& pos) {
2022 static int lastInfoTime;
2023 int t = current_search_time();
2026 if (data_available())
2028 // We are line oriented, don't read single chars
2029 std::string command;
2031 if (!std::getline(std::cin, command))
2034 if (command == "quit")
2037 PonderSearch = false;
2041 else if (command == "stop")
2044 PonderSearch = false;
2046 else if (command == "ponderhit")
2050 // Print search information
2054 else if (lastInfoTime > t)
2055 // HACK: Must be a new search where we searched less than
2056 // NodesBetweenPolls nodes during the first second of search.
2059 else if (t - lastInfoTime >= 1000)
2066 if (dbg_show_hit_rate)
2067 dbg_print_hit_rate();
2069 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
2070 << " time " << t << endl;
2073 // Should we stop the search?
2077 bool stillAtFirstMove = FirstRootMove
2078 && !AspirationFailLow
2079 && t > TimeMgr.available_time();
2081 bool noMoreTime = t > TimeMgr.maximum_time()
2082 || stillAtFirstMove;
2084 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2085 || (ExactMaxTime && t >= ExactMaxTime)
2086 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
2091 // ponderhit() is called when the program is pondering (i.e. thinking while
2092 // it's the opponent's turn to move) in order to let the engine know that
2093 // it correctly predicted the opponent's move.
2097 int t = current_search_time();
2098 PonderSearch = false;
2100 bool stillAtFirstMove = FirstRootMove
2101 && !AspirationFailLow
2102 && t > TimeMgr.available_time();
2104 bool noMoreTime = t > TimeMgr.maximum_time()
2105 || stillAtFirstMove;
2107 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2112 // init_ss_array() does a fast reset of the first entries of a SearchStack
2113 // array and of all the excludedMove and skipNullMove entries.
2115 void init_ss_array(SearchStack* ss, int size) {
2117 for (int i = 0; i < size; i++, ss++)
2119 ss->excludedMove = MOVE_NONE;
2120 ss->skipNullMove = false;
2121 ss->reduction = DEPTH_ZERO;
2125 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2130 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2131 // while the program is pondering. The point is to work around a wrinkle in
2132 // the UCI protocol: When pondering, the engine is not allowed to give a
2133 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2134 // We simply wait here until one of these commands is sent, and return,
2135 // after which the bestmove and pondermove will be printed (in id_loop()).
2137 void wait_for_stop_or_ponderhit() {
2139 std::string command;
2143 if (!std::getline(std::cin, command))
2146 if (command == "quit")
2151 else if (command == "ponderhit" || command == "stop")
2157 // print_pv_info() prints to standard output and eventually to log file information on
2158 // the current PV line. It is called at each iteration or after a new pv is found.
2160 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2162 cout << "info depth " << Iteration
2163 << " score " << value_to_uci(value)
2164 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2165 << " time " << current_search_time()
2166 << " nodes " << pos.nodes_searched()
2167 << " nps " << nps(pos)
2170 for (Move* m = pv; *m != MOVE_NONE; m++)
2177 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2178 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2180 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2185 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2186 // the PV back into the TT. This makes sure the old PV moves are searched
2187 // first, even if the old TT entries have been overwritten.
2189 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2193 Position p(pos, pos.thread());
2194 Value v, m = VALUE_NONE;
2196 for (int i = 0; pv[i] != MOVE_NONE; i++)
2198 tte = TT.retrieve(p.get_key());
2199 if (!tte || tte->move() != pv[i])
2201 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2202 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2204 p.do_move(pv[i], st);
2209 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2210 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2211 // allow to always have a ponder move even when we fail high at root and also a
2212 // long PV to print that is important for position analysis.
2214 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2218 Position p(pos, pos.thread());
2221 assert(bestMove != MOVE_NONE);
2224 p.do_move(pv[ply++], st);
2226 while ( (tte = TT.retrieve(p.get_key())) != NULL
2227 && tte->move() != MOVE_NONE
2228 && move_is_legal(p, tte->move())
2230 && (!p.is_draw() || ply < 2))
2232 pv[ply] = tte->move();
2233 p.do_move(pv[ply++], st);
2235 pv[ply] = MOVE_NONE;
2239 // init_thread() is the function which is called when a new thread is
2240 // launched. It simply calls the idle_loop() function with the supplied
2241 // threadID. There are two versions of this function; one for POSIX
2242 // threads and one for Windows threads.
2244 #if !defined(_MSC_VER)
2246 void* init_thread(void* threadID) {
2248 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2254 DWORD WINAPI init_thread(LPVOID threadID) {
2256 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2263 /// The ThreadsManager class
2266 // read_uci_options() updates number of active threads and other internal
2267 // parameters according to the UCI options values. It is called before
2268 // to start a new search.
2270 void ThreadsManager::read_uci_options() {
2272 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
2273 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
2274 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
2275 activeThreads = Options["Threads"].value<int>();
2279 // idle_loop() is where the threads are parked when they have no work to do.
2280 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2281 // object for which the current thread is the master.
2283 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2285 assert(threadID >= 0 && threadID < MAX_THREADS);
2288 bool allFinished = false;
2292 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2293 // master should exit as last one.
2294 if (allThreadsShouldExit)
2297 threads[threadID].state = THREAD_TERMINATED;
2301 // If we are not thinking, wait for a condition to be signaled
2302 // instead of wasting CPU time polling for work.
2303 while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
2304 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2306 assert(!sp || useSleepingThreads);
2307 assert(threadID != 0 || useSleepingThreads);
2309 if (threads[threadID].state == THREAD_INITIALIZING)
2310 threads[threadID].state = THREAD_AVAILABLE;
2312 // Grab the lock to avoid races with wake_sleeping_thread()
2313 lock_grab(&sleepLock[threadID]);
2315 // If we are master and all slaves have finished do not go to sleep
2316 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2317 allFinished = (i == activeThreads);
2319 if (allFinished || allThreadsShouldExit)
2321 lock_release(&sleepLock[threadID]);
2325 // Do sleep here after retesting sleep conditions
2326 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2327 cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
2329 lock_release(&sleepLock[threadID]);
2332 // If this thread has been assigned work, launch a search
2333 if (threads[threadID].state == THREAD_WORKISWAITING)
2335 assert(!allThreadsShouldExit);
2337 threads[threadID].state = THREAD_SEARCHING;
2339 // Here we call search() with SplitPoint template parameter set to true
2340 SplitPoint* tsp = threads[threadID].splitPoint;
2341 Position pos(*tsp->pos, threadID);
2342 SearchStack* ss = tsp->sstack[threadID] + 1;
2346 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2348 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2350 assert(threads[threadID].state == THREAD_SEARCHING);
2352 threads[threadID].state = THREAD_AVAILABLE;
2354 // Wake up master thread so to allow it to return from the idle loop in
2355 // case we are the last slave of the split point.
2356 if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
2357 wake_sleeping_thread(tsp->master);
2360 // If this thread is the master of a split point and all slaves have
2361 // finished their work at this split point, return from the idle loop.
2362 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2363 allFinished = (i == activeThreads);
2367 // Because sp->slaves[] is reset under lock protection,
2368 // be sure sp->lock has been released before to return.
2369 lock_grab(&(sp->lock));
2370 lock_release(&(sp->lock));
2372 // In helpful master concept a master can help only a sub-tree, and
2373 // because here is all finished is not possible master is booked.
2374 assert(threads[threadID].state == THREAD_AVAILABLE);
2376 threads[threadID].state = THREAD_SEARCHING;
2383 // init_threads() is called during startup. It launches all helper threads,
2384 // and initializes the split point stack and the global locks and condition
2387 void ThreadsManager::init_threads() {
2389 int i, arg[MAX_THREADS];
2392 // Initialize global locks
2395 for (i = 0; i < MAX_THREADS; i++)
2397 lock_init(&sleepLock[i]);
2398 cond_init(&sleepCond[i]);
2401 // Initialize splitPoints[] locks
2402 for (i = 0; i < MAX_THREADS; i++)
2403 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2404 lock_init(&(threads[i].splitPoints[j].lock));
2406 // Will be set just before program exits to properly end the threads
2407 allThreadsShouldExit = false;
2409 // Threads will be put all threads to sleep as soon as created
2412 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2413 threads[0].state = THREAD_SEARCHING;
2414 for (i = 1; i < MAX_THREADS; i++)
2415 threads[i].state = THREAD_INITIALIZING;
2417 // Launch the helper threads
2418 for (i = 1; i < MAX_THREADS; i++)
2422 #if !defined(_MSC_VER)
2423 pthread_t pthread[1];
2424 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
2425 pthread_detach(pthread[0]);
2427 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
2431 cout << "Failed to create thread number " << i << endl;
2435 // Wait until the thread has finished launching and is gone to sleep
2436 while (threads[i].state == THREAD_INITIALIZING) {}
2441 // exit_threads() is called when the program exits. It makes all the
2442 // helper threads exit cleanly.
2444 void ThreadsManager::exit_threads() {
2446 allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2448 // Wake up all the threads and waits for termination
2449 for (int i = 1; i < MAX_THREADS; i++)
2451 wake_sleeping_thread(i);
2452 while (threads[i].state != THREAD_TERMINATED) {}
2455 // Now we can safely destroy the locks
2456 for (int i = 0; i < MAX_THREADS; i++)
2457 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2458 lock_destroy(&(threads[i].splitPoints[j].lock));
2460 lock_destroy(&mpLock);
2462 // Now we can safely destroy the wait conditions
2463 for (int i = 0; i < MAX_THREADS; i++)
2465 lock_destroy(&sleepLock[i]);
2466 cond_destroy(&sleepCond[i]);
2471 // cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
2472 // the thread's currently active split point, or in some ancestor of
2473 // the current split point.
2475 bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
2477 assert(threadID >= 0 && threadID < activeThreads);
2479 SplitPoint* sp = threads[threadID].splitPoint;
2481 for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
2486 // thread_is_available() checks whether the thread with threadID "slave" is
2487 // available to help the thread with threadID "master" at a split point. An
2488 // obvious requirement is that "slave" must be idle. With more than two
2489 // threads, this is not by itself sufficient: If "slave" is the master of
2490 // some active split point, it is only available as a slave to the other
2491 // threads which are busy searching the split point at the top of "slave"'s
2492 // split point stack (the "helpful master concept" in YBWC terminology).
2494 bool ThreadsManager::thread_is_available(int slave, int master) const {
2496 assert(slave >= 0 && slave < activeThreads);
2497 assert(master >= 0 && master < activeThreads);
2498 assert(activeThreads > 1);
2500 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2503 // Make a local copy to be sure doesn't change under our feet
2504 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2506 // No active split points means that the thread is available as
2507 // a slave for any other thread.
2508 if (localActiveSplitPoints == 0 || activeThreads == 2)
2511 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2512 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2513 // could have been set to 0 by another thread leading to an out of bound access.
2514 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2521 // available_thread_exists() tries to find an idle thread which is available as
2522 // a slave for the thread with threadID "master".
2524 bool ThreadsManager::available_thread_exists(int master) const {
2526 assert(master >= 0 && master < activeThreads);
2527 assert(activeThreads > 1);
2529 for (int i = 0; i < activeThreads; i++)
2530 if (thread_is_available(i, master))
2537 // split() does the actual work of distributing the work at a node between
2538 // several available threads. If it does not succeed in splitting the
2539 // node (because no idle threads are available, or because we have no unused
2540 // split point objects), the function immediately returns. If splitting is
2541 // possible, a SplitPoint object is initialized with all the data that must be
2542 // copied to the helper threads and we tell our helper threads that they have
2543 // been assigned work. This will cause them to instantly leave their idle loops and
2544 // call search().When all threads have returned from search() then split() returns.
2546 template <bool Fake>
2547 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2548 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2549 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2550 assert(pos.is_ok());
2551 assert(ply > 0 && ply < PLY_MAX);
2552 assert(*bestValue >= -VALUE_INFINITE);
2553 assert(*bestValue <= *alpha);
2554 assert(*alpha < beta);
2555 assert(beta <= VALUE_INFINITE);
2556 assert(depth > DEPTH_ZERO);
2557 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
2558 assert(activeThreads > 1);
2560 int i, master = pos.thread();
2561 Thread& masterThread = threads[master];
2565 // If no other thread is available to help us, or if we have too many
2566 // active split points, don't split.
2567 if ( !available_thread_exists(master)
2568 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2570 lock_release(&mpLock);
2574 // Pick the next available split point object from the split point stack
2575 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2577 // Initialize the split point object
2578 splitPoint.parent = masterThread.splitPoint;
2579 splitPoint.master = master;
2580 splitPoint.betaCutoff = false;
2581 splitPoint.ply = ply;
2582 splitPoint.depth = depth;
2583 splitPoint.threatMove = threatMove;
2584 splitPoint.mateThreat = mateThreat;
2585 splitPoint.alpha = *alpha;
2586 splitPoint.beta = beta;
2587 splitPoint.pvNode = pvNode;
2588 splitPoint.bestValue = *bestValue;
2590 splitPoint.moveCount = moveCount;
2591 splitPoint.pos = &pos;
2592 splitPoint.nodes = 0;
2593 splitPoint.parentSstack = ss;
2594 for (i = 0; i < activeThreads; i++)
2595 splitPoint.slaves[i] = 0;
2597 masterThread.splitPoint = &splitPoint;
2599 // If we are here it means we are not available
2600 assert(masterThread.state != THREAD_AVAILABLE);
2602 int workersCnt = 1; // At least the master is included
2604 // Allocate available threads setting state to THREAD_BOOKED
2605 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
2606 if (thread_is_available(i, master))
2608 threads[i].state = THREAD_BOOKED;
2609 threads[i].splitPoint = &splitPoint;
2610 splitPoint.slaves[i] = 1;
2614 assert(Fake || workersCnt > 1);
2616 // We can release the lock because slave threads are already booked and master is not available
2617 lock_release(&mpLock);
2619 // Tell the threads that they have work to do. This will make them leave
2620 // their idle loop. But before copy search stack tail for each thread.
2621 for (i = 0; i < activeThreads; i++)
2622 if (i == master || splitPoint.slaves[i])
2624 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2626 assert(i == master || threads[i].state == THREAD_BOOKED);
2628 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2630 if (useSleepingThreads && i != master)
2631 wake_sleeping_thread(i);
2634 // Everything is set up. The master thread enters the idle loop, from
2635 // which it will instantly launch a search, because its state is
2636 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2637 // idle loop, which means that the main thread will return from the idle
2638 // loop when all threads have finished their work at this split point.
2639 idle_loop(master, &splitPoint);
2641 // We have returned from the idle loop, which means that all threads are
2642 // finished. Update alpha and bestValue, and return.
2645 *alpha = splitPoint.alpha;
2646 *bestValue = splitPoint.bestValue;
2647 masterThread.activeSplitPoints--;
2648 masterThread.splitPoint = splitPoint.parent;
2649 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2651 lock_release(&mpLock);
2655 // wake_sleeping_thread() wakes up the thread with the given threadID
2656 // when it is time to start a new search.
2658 void ThreadsManager::wake_sleeping_thread(int threadID) {
2660 lock_grab(&sleepLock[threadID]);
2661 cond_signal(&sleepCond[threadID]);
2662 lock_release(&sleepLock[threadID]);
2666 /// The RootMoveList class
2668 // RootMoveList c'tor
2670 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2672 SearchStack ss[PLY_MAX_PLUS_2];
2673 MoveStack mlist[MOVES_MAX];
2675 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2677 // Initialize search stack
2678 init_ss_array(ss, PLY_MAX_PLUS_2);
2679 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2682 // Generate all legal moves
2683 MoveStack* last = generate_moves(pos, mlist);
2685 // Add each move to the moves[] array
2686 for (MoveStack* cur = mlist; cur != last; cur++)
2688 bool includeMove = includeAllMoves;
2690 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2691 includeMove = (searchMoves[k] == cur->move);
2696 // Find a quick score for the move
2697 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2698 moves[count].pv[1] = MOVE_NONE;
2699 pos.do_move(cur->move, st);
2700 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2701 pos.undo_move(cur->move);
2707 // Score root moves using the standard way used in main search, the moves
2708 // are scored according to the order in which are returned by MovePicker.
2710 void RootMoveList::score_moves(const Position& pos)
2714 MovePicker mp(pos, MOVE_NONE, ONE_PLY, H);
2716 while ((move = mp.get_next_move()) != MOVE_NONE)
2717 for (int i = 0; i < count; i++)
2718 if (moves[i].move == move)
2720 moves[i].mp_score = score--;
2725 // RootMoveList simple methods definitions
2727 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2731 for (j = 0; pv[j] != MOVE_NONE; j++)
2732 moves[moveNum].pv[j] = pv[j];
2734 moves[moveNum].pv[j] = MOVE_NONE;
2738 // RootMoveList::sort() sorts the root move list at the beginning of a new
2741 void RootMoveList::sort() {
2743 sort_multipv(count - 1); // Sort all items
2747 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2748 // list by their scores and depths. It is used to order the different PVs
2749 // correctly in MultiPV mode.
2751 void RootMoveList::sort_multipv(int n) {
2755 for (i = 1; i <= n; i++)
2757 RootMove rm = moves[i];
2758 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2759 moves[j] = moves[j - 1];