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 // ThreadsManager class is used to handle all the threads related stuff in search,
63 // init, starting, parking and, the most important, launching a slave thread at a
64 // split point are what this class does. All the access to shared thread data is
65 // done through this class, so that we avoid using global variables instead.
67 class ThreadsManager {
68 /* As long as the single ThreadsManager object is defined as a global we don't
69 need to explicitly initialize to zero its data members because variables with
70 static storage duration are automatically set to zero before enter main()
76 int active_threads() const { return ActiveThreads; }
77 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
78 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
80 void resetNodeCounters();
81 int64_t nodes_searched() const;
82 bool available_thread_exists(int master) const;
83 bool thread_is_available(int slave, int master) const;
84 bool thread_should_stop(int threadID) const;
85 void wake_sleeping_thread(int threadID);
86 void put_threads_to_sleep();
87 void idle_loop(int threadID, SplitPoint* sp);
90 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
91 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
97 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
98 Thread threads[MAX_THREADS];
100 Lock MPLock, WaitLock;
102 #if !defined(_MSC_VER)
103 pthread_cond_t WaitCond[MAX_THREADS];
105 HANDLE SitIdleEvent[MAX_THREADS];
111 // RootMove struct is used for moves at the root at the tree. For each
112 // root move, we store a score, a node count, and a PV (really a refutation
113 // in the case of moves which fail low).
117 RootMove() : mp_score(0), nodes(0) {}
119 // RootMove::operator<() is the comparison function used when
120 // sorting the moves. A move m1 is considered to be better
121 // than a move m2 if it has a higher score, or if the moves
122 // have equal score but m1 has the higher beta cut-off count.
123 bool operator<(const RootMove& m) const {
125 return score != m.score ? score < m.score : mp_score <= m.mp_score;
132 Move pv[PLY_MAX_PLUS_2];
136 // The RootMoveList class is essentially an array of RootMove objects, with
137 // a handful of methods for accessing the data in the individual moves.
142 RootMoveList(Position& pos, Move searchMoves[]);
144 Move move(int moveNum) const { return moves[moveNum].move; }
145 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
146 int move_count() const { return count; }
147 Value move_score(int moveNum) const { return moves[moveNum].score; }
148 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
149 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
150 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
152 void set_move_pv(int moveNum, const Move pv[]);
153 void score_moves(const Position& pos);
155 void sort_multipv(int n);
158 RootMove moves[MOVES_MAX];
163 // When formatting a move for std::cout we must know if we are in Chess960
164 // or not. To keep using the handy operator<<() on the move the trick is to
165 // embed this flag in the stream itself. Function-like named enum set960 is
166 // used as a custom manipulator and the stream internal general-purpose array,
167 // accessed through ios_base::iword(), is used to pass the flag to the move's
168 // operator<<() that will use it to properly format castling moves.
171 std::ostream& operator<< (std::ostream& os, const set960& m) {
173 os.iword(0) = int(m);
182 // Maximum depth for razoring
183 const Depth RazorDepth = 4 * ONE_PLY;
185 // Dynamic razoring margin based on depth
186 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
188 // Maximum depth for use of dynamic threat detection when null move fails low
189 const Depth ThreatDepth = 5 * ONE_PLY;
191 // Step 9. Internal iterative deepening
193 // Minimum depth for use of internal iterative deepening
194 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
196 // At Non-PV nodes we do an internal iterative deepening search
197 // when the static evaluation is bigger then beta - IIDMargin.
198 const Value IIDMargin = Value(0x100);
200 // Step 11. Decide the new search depth
202 // Extensions. Configurable UCI options
203 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
204 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
205 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
207 // Minimum depth for use of singular extension
208 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
210 // If the TT move is at least SingularExtensionMargin better then the
211 // remaining ones we will extend it.
212 const Value SingularExtensionMargin = Value(0x20);
214 // Step 12. Futility pruning
216 // Futility margin for quiescence search
217 const Value FutilityMarginQS = Value(0x80);
219 // Futility lookup tables (initialized at startup) and their getter functions
220 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
221 int FutilityMoveCountArray[32]; // [depth]
223 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
224 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
226 // Step 14. Reduced search
228 // Reduction lookup tables (initialized at startup) and their getter functions
229 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
231 template <NodeType PV>
232 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
234 // Common adjustments
236 // Search depth at iteration 1
237 const Depth InitialDepth = ONE_PLY;
239 // Easy move margin. An easy move candidate must be at least this much
240 // better than the second best move.
241 const Value EasyMoveMargin = Value(0x200);
249 // Scores and number of times the best move changed for each iteration
250 Value ValueByIteration[PLY_MAX_PLUS_2];
251 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
253 // Search window management
259 // Time managment variables
260 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
261 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
262 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
267 std::ofstream LogFile;
269 // Multi-threads related variables
270 Depth MinimumSplitDepth;
271 int MaxThreadsPerSplitPoint;
272 ThreadsManager ThreadsMgr;
274 // Node counters, used only by thread[0] but try to keep in different cache
275 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
277 int NodesBetweenPolls = 30000;
284 Value id_loop(const Position& pos, Move searchMoves[]);
285 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
287 template <NodeType PvNode, bool SpNode>
288 Value search(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) {
292 return search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
295 template <NodeType PvNode>
296 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
298 template <NodeType PvNode>
299 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
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);
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(); }
341 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
344 /// init_search() is called during startup. It initializes various lookup tables
348 int d; // depth (ONE_PLY == 2)
349 int hd; // half depth (ONE_PLY == 1)
352 // Init reductions array
353 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
355 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
356 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
357 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
358 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
361 // Init futility margins array
362 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
363 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
365 // Init futility move count array
366 for (d = 0; d < 32; d++)
367 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
371 /// perft() is our utility to verify move generation is bug free. All the legal
372 /// moves up to given depth are generated and counted and the sum returned.
374 int perft(Position& pos, Depth depth)
376 MoveStack mlist[MOVES_MAX];
381 // Generate all legal moves
382 MoveStack* last = generate_moves(pos, mlist);
384 // If we are at the last ply we don't need to do and undo
385 // the moves, just to count them.
386 if (depth <= ONE_PLY)
387 return int(last - mlist);
389 // Loop through all legal moves
391 for (MoveStack* cur = mlist; cur != last; cur++)
394 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
395 sum += perft(pos, depth - ONE_PLY);
402 /// think() is the external interface to Stockfish's search, and is called when
403 /// the program receives the UCI 'go' command. It initializes various
404 /// search-related global variables, and calls root_search(). It returns false
405 /// when a quit command is received during the search.
407 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
408 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
410 // Initialize global search variables
411 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
413 ThreadsMgr.resetNodeCounters();
414 SearchStartTime = get_system_time();
415 ExactMaxTime = maxTime;
418 InfiniteSearch = infinite;
419 PonderSearch = ponder;
420 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
422 // Look for a book move, only during games, not tests
423 if (UseTimeManagement && get_option_value_bool("OwnBook"))
425 if (get_option_value_string("Book File") != OpeningBook.file_name())
426 OpeningBook.open(get_option_value_string("Book File"));
428 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
429 if (bookMove != MOVE_NONE)
432 wait_for_stop_or_ponderhit();
434 cout << "bestmove " << bookMove << endl;
439 // Read UCI option values
440 TT.set_size(get_option_value_int("Hash"));
441 if (button_was_pressed("Clear Hash"))
444 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
445 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
446 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
447 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
448 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
449 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
450 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
451 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
452 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
453 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
454 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
455 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
457 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
458 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
459 MultiPV = get_option_value_int("MultiPV");
460 UseLogFile = get_option_value_bool("Use Search Log");
463 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
465 read_weights(pos.side_to_move());
467 // Set the number of active threads
468 int newActiveThreads = get_option_value_int("Threads");
469 if (newActiveThreads != ThreadsMgr.active_threads())
471 ThreadsMgr.set_active_threads(newActiveThreads);
472 init_eval(ThreadsMgr.active_threads());
475 // Wake up needed threads
476 for (int i = 1; i < newActiveThreads; i++)
477 ThreadsMgr.wake_sleeping_thread(i);
480 int myTime = time[pos.side_to_move()];
481 int myIncrement = increment[pos.side_to_move()];
482 if (UseTimeManagement)
483 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
485 // Set best NodesBetweenPolls interval to avoid lagging under
486 // heavy time pressure.
488 NodesBetweenPolls = Min(MaxNodes, 30000);
489 else if (myTime && myTime < 1000)
490 NodesBetweenPolls = 1000;
491 else if (myTime && myTime < 5000)
492 NodesBetweenPolls = 5000;
494 NodesBetweenPolls = 30000;
496 // Write search information to log file
498 LogFile << "Searching: " << pos.to_fen() << endl
499 << "infinite: " << infinite
500 << " ponder: " << ponder
501 << " time: " << myTime
502 << " increment: " << myIncrement
503 << " moves to go: " << movesToGo << endl;
505 // We're ready to start thinking. Call the iterative deepening loop function
506 id_loop(pos, searchMoves);
511 ThreadsMgr.put_threads_to_sleep();
519 // id_loop() is the main iterative deepening loop. It calls root_search
520 // repeatedly with increasing depth until the allocated thinking time has
521 // been consumed, the user stops the search, or the maximum search depth is
524 Value id_loop(const Position& pos, Move searchMoves[]) {
526 Position p(pos, pos.thread());
527 SearchStack ss[PLY_MAX_PLUS_2];
528 Move pv[PLY_MAX_PLUS_2];
529 Move EasyMove = MOVE_NONE;
530 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
532 // Moves to search are verified, copied, scored and sorted
533 RootMoveList rml(p, searchMoves);
535 // Handle special case of searching on a mate/stale position
536 if (rml.move_count() == 0)
539 wait_for_stop_or_ponderhit();
541 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
544 // Print RootMoveList startup scoring to the standard output,
545 // so to output information also for iteration 1.
546 cout << set960(p.is_chess960()) // Is enough to set once at the beginning
547 << "info depth " << 1
548 << "\ninfo depth " << 1
549 << " score " << value_to_uci(rml.move_score(0))
550 << " time " << current_search_time()
551 << " nodes " << ThreadsMgr.nodes_searched()
553 << " pv " << rml.move(0) << "\n";
558 init_ss_array(ss, PLY_MAX_PLUS_2);
559 pv[0] = pv[1] = MOVE_NONE;
560 ValueByIteration[1] = rml.move_score(0);
563 // Is one move significantly better than others after initial scoring ?
564 if ( rml.move_count() == 1
565 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
566 EasyMove = rml.move(0);
568 // Iterative deepening loop
569 while (Iteration < PLY_MAX)
571 // Initialize iteration
573 BestMoveChangesByIteration[Iteration] = 0;
575 cout << "info depth " << Iteration << endl;
577 // Calculate dynamic aspiration window based on previous iterations
578 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
580 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
581 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
583 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
584 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
586 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
587 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
590 // Search to the current depth, rml is updated and sorted, alpha and beta could change
591 value = root_search(p, ss, pv, rml, &alpha, &beta);
593 // Write PV to transposition table, in case the relevant entries have
594 // been overwritten during the search.
595 insert_pv_in_tt(p, pv);
598 break; // Value cannot be trusted. Break out immediately!
600 //Save info about search result
601 ValueByIteration[Iteration] = value;
603 // Drop the easy move if differs from the new best move
604 if (pv[0] != EasyMove)
605 EasyMove = MOVE_NONE;
607 if (UseTimeManagement)
610 bool stopSearch = false;
612 // Stop search early if there is only a single legal move,
613 // we search up to Iteration 6 anyway to get a proper score.
614 if (Iteration >= 6 && rml.move_count() == 1)
617 // Stop search early when the last two iterations returned a mate score
619 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
620 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
623 // Stop search early if one move seems to be much better than the others
624 int64_t nodes = ThreadsMgr.nodes_searched();
627 && ( ( rml.move_nodes(0) > (nodes * 85) / 100
628 && current_search_time() > TimeMgr.available_time() / 16)
629 ||( rml.move_nodes(0) > (nodes * 98) / 100
630 && current_search_time() > TimeMgr.available_time() / 32)))
633 // Add some extra time if the best move has changed during the last two iterations
634 if (Iteration > 5 && Iteration <= 50)
635 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
636 BestMoveChangesByIteration[Iteration-1]);
638 // Stop search if most of MaxSearchTime is consumed at the end of the
639 // iteration. We probably don't have enough time to search the first
640 // move at the next iteration anyway.
641 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
647 StopOnPonderhit = true;
653 if (MaxDepth && Iteration >= MaxDepth)
657 // If we are pondering or in infinite search, we shouldn't print the
658 // best move before we are told to do so.
659 if (!AbortSearch && (PonderSearch || InfiniteSearch))
660 wait_for_stop_or_ponderhit();
662 // Print final search statistics
663 cout << "info nodes " << ThreadsMgr.nodes_searched()
665 << " time " << current_search_time() << endl;
667 // Print the best move and the ponder move to the standard output
668 if (pv[0] == MOVE_NONE)
674 assert(pv[0] != MOVE_NONE);
676 cout << "bestmove " << pv[0];
678 if (pv[1] != MOVE_NONE)
679 cout << " ponder " << pv[1];
686 dbg_print_mean(LogFile);
688 if (dbg_show_hit_rate)
689 dbg_print_hit_rate(LogFile);
691 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
692 << "\nNodes/second: " << nps()
693 << "\nBest move: " << move_to_san(p, pv[0]);
696 p.do_move(pv[0], st);
697 LogFile << "\nPonder move: "
698 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
701 return rml.move_score(0);
705 // root_search() is the function which searches the root node. It is
706 // similar to search_pv except that it uses a different move ordering
707 // scheme, prints some information to the standard output and handles
708 // the fail low/high loops.
710 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
716 Depth depth, ext, newDepth;
717 Value value, alpha, beta;
718 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
719 int researchCountFH, researchCountFL;
721 researchCountFH = researchCountFL = 0;
724 isCheck = pos.is_check();
725 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
727 // Step 1. Initialize node (polling is omitted at root)
728 ss->currentMove = ss->bestMove = MOVE_NONE;
730 // Step 2. Check for aborted search (omitted at root)
731 // Step 3. Mate distance pruning (omitted at root)
732 // Step 4. Transposition table lookup (omitted at root)
734 // Step 5. Evaluate the position statically
735 // At root we do this only to get reference value for child nodes
736 ss->evalMargin = VALUE_NONE;
737 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
739 // Step 6. Razoring (omitted at root)
740 // Step 7. Static null move pruning (omitted at root)
741 // Step 8. Null move search with verification search (omitted at root)
742 // Step 9. Internal iterative deepening (omitted at root)
744 // Step extra. Fail low loop
745 // We start with small aspiration window and in case of fail low, we research
746 // with bigger window until we are not failing low anymore.
749 // Sort the moves before to (re)search
750 rml.score_moves(pos);
753 // Step 10. Loop through all moves in the root move list
754 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
756 // This is used by time management
757 FirstRootMove = (i == 0);
759 // Save the current node count before the move is searched
760 nodes = ThreadsMgr.nodes_searched();
762 // Pick the next root move, and print the move and the move number to
763 // the standard output.
764 move = ss->currentMove = rml.move(i);
766 if (current_search_time() >= 1000)
767 cout << "info currmove " << move
768 << " currmovenumber " << i + 1 << endl;
770 moveIsCheck = pos.move_is_check(move);
771 captureOrPromotion = pos.move_is_capture_or_promotion(move);
773 // Step 11. Decide the new search depth
774 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
775 newDepth = depth + ext;
777 // Step 12. Futility pruning (omitted at root)
779 // Step extra. Fail high loop
780 // If move fails high, we research with bigger window until we are not failing
782 value = - VALUE_INFINITE;
786 // Step 13. Make the move
787 pos.do_move(move, st, ci, moveIsCheck);
789 // Step extra. pv search
790 // We do pv search for first moves (i < MultiPV)
791 // and for fail high research (value > alpha)
792 if (i < MultiPV || value > alpha)
794 // Aspiration window is disabled in multi-pv case
796 alpha = -VALUE_INFINITE;
798 // Full depth PV search, done on first move or after a fail high
799 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
803 // Step 14. Reduced search
804 // if the move fails high will be re-searched at full depth
805 bool doFullDepthSearch = true;
807 if ( depth >= 3 * ONE_PLY
809 && !captureOrPromotion
810 && !move_is_castle(move))
812 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
815 assert(newDepth-ss->reduction >= ONE_PLY);
817 // Reduced depth non-pv search using alpha as upperbound
818 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
819 doFullDepthSearch = (value > alpha);
822 // The move failed high, but if reduction is very big we could
823 // face a false positive, retry with a less aggressive reduction,
824 // if the move fails high again then go with full depth search.
825 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
827 assert(newDepth - ONE_PLY >= ONE_PLY);
829 ss->reduction = ONE_PLY;
830 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
831 doFullDepthSearch = (value > alpha);
833 ss->reduction = DEPTH_ZERO; // Restore original reduction
836 // Step 15. Full depth search
837 if (doFullDepthSearch)
839 // Full depth non-pv search using alpha as upperbound
840 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
842 // If we are above alpha then research at same depth but as PV
843 // to get a correct score or eventually a fail high above beta.
845 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
849 // Step 16. Undo move
852 // Can we exit fail high loop ?
853 if (AbortSearch || value < beta)
856 // We are failing high and going to do a research. It's important to update
857 // the score before research in case we run out of time while researching.
858 rml.set_move_score(i, value);
860 extract_pv_from_tt(pos, move, pv);
861 rml.set_move_pv(i, pv);
863 // Print information to the standard output
864 print_pv_info(pos, pv, alpha, beta, value);
866 // Prepare for a research after a fail high, each time with a wider window
867 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
870 } // End of fail high loop
872 // Finished searching the move. If AbortSearch is true, the search
873 // was aborted because the user interrupted the search or because we
874 // ran out of time. In this case, the return value of the search cannot
875 // be trusted, and we break out of the loop without updating the best
880 // Remember searched nodes counts for this move
881 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
883 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
884 assert(value < beta);
886 // Step 17. Check for new best move
887 if (value <= alpha && i >= MultiPV)
888 rml.set_move_score(i, -VALUE_INFINITE);
891 // PV move or new best move!
894 rml.set_move_score(i, value);
896 extract_pv_from_tt(pos, move, pv);
897 rml.set_move_pv(i, pv);
901 // We record how often the best move has been changed in each
902 // iteration. This information is used for time managment: When
903 // the best move changes frequently, we allocate some more time.
905 BestMoveChangesByIteration[Iteration]++;
907 // Print information to the standard output
908 print_pv_info(pos, pv, alpha, beta, value);
910 // Raise alpha to setup proper non-pv search upper bound
917 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
919 cout << "info multipv " << j + 1
920 << " score " << value_to_uci(rml.move_score(j))
921 << " depth " << (j <= i ? Iteration : Iteration - 1)
922 << " time " << current_search_time()
923 << " nodes " << ThreadsMgr.nodes_searched()
927 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
928 cout << rml.move_pv(j, k) << " ";
932 alpha = rml.move_score(Min(i, MultiPV - 1));
934 } // PV move or new best move
936 assert(alpha >= *alphaPtr);
938 AspirationFailLow = (alpha == *alphaPtr);
940 if (AspirationFailLow && StopOnPonderhit)
941 StopOnPonderhit = false;
944 // Can we exit fail low loop ?
945 if (AbortSearch || !AspirationFailLow)
948 // Prepare for a research after a fail low, each time with a wider window
949 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
954 // Sort the moves before to return
961 // search<>() is the main search function for both PV and non-PV nodes and for
962 // normal and SplitPoint nodes. When called just after a split point the search
963 // is simpler because we have already probed the hash table, done a null move
964 // search, and searched the first move before splitting, we don't have to repeat
965 // all this work again. We also don't need to store anything to the hash table
966 // here: This is taken care of after we return from the split point.
968 template <NodeType PvNode, bool SpNode>
969 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
971 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
972 assert(beta > alpha && beta <= VALUE_INFINITE);
973 assert(PvNode || alpha == beta - 1);
974 assert(ply > 0 && ply < PLY_MAX);
975 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
977 Move movesSearched[MOVES_MAX];
981 Move ttMove, move, excludedMove, threatMove;
983 Value bestValue, value, oldAlpha;
984 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
985 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
986 bool mateThreat = false;
988 int threadID = pos.thread();
989 SplitPoint* sp = NULL;
990 refinedValue = bestValue = value = -VALUE_INFINITE;
992 isCheck = pos.is_check();
998 ttMove = excludedMove = MOVE_NONE;
999 threatMove = sp->threatMove;
1000 mateThreat = sp->mateThreat;
1001 goto split_point_start;
1004 // Step 1. Initialize node and poll. Polling can abort search
1005 ThreadsMgr.incrementNodeCounter(threadID);
1006 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
1007 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1009 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1015 // Step 2. Check for aborted search and immediate draw
1016 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1019 if (pos.is_draw() || ply >= PLY_MAX - 1)
1022 // Step 3. Mate distance pruning
1023 alpha = Max(value_mated_in(ply), alpha);
1024 beta = Min(value_mate_in(ply+1), beta);
1028 // Step 4. Transposition table lookup
1030 // We don't want the score of a partial search to overwrite a previous full search
1031 // TT value, so we use a different position key in case of an excluded move exists.
1032 excludedMove = ss->excludedMove;
1033 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1035 tte = TT.retrieve(posKey);
1036 ttMove = (tte ? tte->move() : MOVE_NONE);
1038 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1039 // This is to avoid problems in the following areas:
1041 // * Repetition draw detection
1042 // * Fifty move rule detection
1043 // * Searching for a mate
1044 // * Printing of full PV line
1046 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1048 // Refresh tte entry to avoid aging
1049 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1051 ss->bestMove = ttMove; // Can be MOVE_NONE
1052 return value_from_tt(tte->value(), ply);
1055 // Step 5. Evaluate the position statically and
1056 // update gain statistics of parent move.
1058 ss->eval = ss->evalMargin = VALUE_NONE;
1061 assert(tte->static_value() != VALUE_NONE);
1063 ss->eval = tte->static_value();
1064 ss->evalMargin = tte->static_value_margin();
1065 refinedValue = refine_eval(tte, ss->eval, ply);
1069 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1070 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1073 // Save gain for the parent non-capture move
1074 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1076 // Step 6. Razoring (is omitted in PV nodes)
1078 && depth < RazorDepth
1080 && refinedValue < beta - razor_margin(depth)
1081 && ttMove == MOVE_NONE
1082 && (ss-1)->currentMove != MOVE_NULL
1083 && !value_is_mate(beta)
1084 && !pos.has_pawn_on_7th(pos.side_to_move()))
1086 Value rbeta = beta - razor_margin(depth);
1087 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1089 // Logically we should return (v + razor_margin(depth)), but
1090 // surprisingly this did slightly weaker in tests.
1094 // Step 7. Static null move pruning (is omitted in PV nodes)
1095 // We're betting that the opponent doesn't have a move that will reduce
1096 // the score by more than futility_margin(depth) if we do a null move.
1098 && !ss->skipNullMove
1099 && depth < RazorDepth
1101 && refinedValue >= beta + futility_margin(depth, 0)
1102 && !value_is_mate(beta)
1103 && pos.non_pawn_material(pos.side_to_move()))
1104 return refinedValue - futility_margin(depth, 0);
1106 // Step 8. Null move search with verification search (is omitted in PV nodes)
1108 && !ss->skipNullMove
1111 && refinedValue >= beta
1112 && !value_is_mate(beta)
1113 && pos.non_pawn_material(pos.side_to_move()))
1115 ss->currentMove = MOVE_NULL;
1117 // Null move dynamic reduction based on depth
1118 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1120 // Null move dynamic reduction based on value
1121 if (refinedValue - beta > PawnValueMidgame)
1124 pos.do_null_move(st);
1125 (ss+1)->skipNullMove = true;
1127 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1128 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1129 (ss+1)->skipNullMove = false;
1130 pos.undo_null_move();
1132 if (nullValue >= beta)
1134 // Do not return unproven mate scores
1135 if (nullValue >= value_mate_in(PLY_MAX))
1138 if (depth < 6 * ONE_PLY)
1141 // Do verification search at high depths
1142 ss->skipNullMove = true;
1143 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1144 ss->skipNullMove = false;
1151 // The null move failed low, which means that we may be faced with
1152 // some kind of threat. If the previous move was reduced, check if
1153 // the move that refuted the null move was somehow connected to the
1154 // move which was reduced. If a connection is found, return a fail
1155 // low score (which will cause the reduced move to fail high in the
1156 // parent node, which will trigger a re-search with full depth).
1157 if (nullValue == value_mated_in(ply + 2))
1160 threatMove = (ss+1)->bestMove;
1161 if ( depth < ThreatDepth
1162 && (ss-1)->reduction
1163 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1168 // Step 9. Internal iterative deepening
1169 if ( depth >= IIDDepth[PvNode]
1170 && ttMove == MOVE_NONE
1171 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1173 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1175 ss->skipNullMove = true;
1176 search<PvNode>(pos, ss, alpha, beta, d, ply);
1177 ss->skipNullMove = false;
1179 ttMove = ss->bestMove;
1180 tte = TT.retrieve(posKey);
1183 // Expensive mate threat detection (only for PV nodes)
1185 mateThreat = pos.has_mate_threat();
1187 split_point_start: // At split points actual search starts from here
1189 // Initialize a MovePicker object for the current position
1190 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1191 MovePicker mpBase = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1192 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1194 ss->bestMove = MOVE_NONE;
1195 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1196 futilityBase = ss->eval + ss->evalMargin;
1197 singularExtensionNode = !SpNode
1198 && depth >= SingularExtensionDepth[PvNode]
1201 && !excludedMove // Do not allow recursive singular extension search
1202 && (tte->type() & VALUE_TYPE_LOWER)
1203 && tte->depth() >= depth - 3 * ONE_PLY;
1206 lock_grab(&(sp->lock));
1207 bestValue = sp->bestValue;
1210 // Step 10. Loop through moves
1211 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1212 while ( bestValue < beta
1213 && (move = mp.get_next_move()) != MOVE_NONE
1214 && !ThreadsMgr.thread_should_stop(threadID))
1218 moveCount = ++sp->moveCount;
1219 lock_release(&(sp->lock));
1222 assert(move_is_ok(move));
1224 if (move == excludedMove)
1227 moveIsCheck = pos.move_is_check(move, ci);
1228 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1230 // Step 11. Decide the new search depth
1231 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1233 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1234 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1235 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1236 // lower then ttValue minus a margin then we extend ttMove.
1237 if ( singularExtensionNode
1238 && move == tte->move()
1241 Value ttValue = value_from_tt(tte->value(), ply);
1243 if (abs(ttValue) < VALUE_KNOWN_WIN)
1245 Value b = ttValue - SingularExtensionMargin;
1246 ss->excludedMove = move;
1247 ss->skipNullMove = true;
1248 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1249 ss->skipNullMove = false;
1250 ss->excludedMove = MOVE_NONE;
1251 ss->bestMove = MOVE_NONE;
1257 newDepth = depth - ONE_PLY + ext;
1259 // Update current move (this must be done after singular extension search)
1260 movesSearched[moveCount++] = ss->currentMove = move;
1262 // Step 12. Futility pruning (is omitted in PV nodes)
1264 && !captureOrPromotion
1268 && !move_is_castle(move))
1270 // Move count based pruning
1271 if ( moveCount >= futility_move_count(depth)
1272 && !(threatMove && connected_threat(pos, move, threatMove))
1273 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1276 lock_grab(&(sp->lock));
1281 // Value based pruning
1282 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1283 // but fixing this made program slightly weaker.
1284 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1285 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1286 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1288 if (futilityValueScaled < beta)
1292 lock_grab(&(sp->lock));
1293 if (futilityValueScaled > sp->bestValue)
1294 sp->bestValue = bestValue = futilityValueScaled;
1296 else if (futilityValueScaled > bestValue)
1297 bestValue = futilityValueScaled;
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 (!SpNode && PvNode && moveCount == 1)
1309 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1310 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1313 // Step 14. Reduced depth search
1314 // If the move fails high will be re-searched at full depth.
1315 bool doFullDepthSearch = true;
1317 if ( depth >= 3 * ONE_PLY
1318 && !captureOrPromotion
1320 && !move_is_castle(move)
1321 && !(ss->killers[0] == move || ss->killers[1] == move))
1323 ss->reduction = reduction<PvNode>(depth, moveCount);
1326 alpha = SpNode ? sp->alpha : alpha;
1327 Depth d = newDepth - ss->reduction;
1328 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1329 : - 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 = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1354 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1356 // Step extra. pv search (only in PV nodes)
1357 // Search only for possible new PV nodes, if instead value >= beta then
1358 // parent node fails low with value <= alpha and tries another move.
1359 if (PvNode && value > alpha && value < beta)
1360 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1361 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1365 // Step 16. Undo move
1366 pos.undo_move(move);
1368 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1370 // Step 17. Check for new best move
1373 lock_grab(&(sp->lock));
1374 bestValue = sp->bestValue;
1378 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1383 if (SpNode && (!PvNode || value >= beta))
1384 sp->stopRequest = true;
1386 if (PvNode && value < beta) // We want always alpha < beta
1389 if (value == value_mate_in(ply + 1))
1390 ss->mateKiller = move;
1392 ss->bestMove = move;
1396 sp->bestValue = bestValue;
1398 sp->parentSstack->bestMove = ss->bestMove;
1402 // Step 18. Check for split
1404 && depth >= MinimumSplitDepth
1405 && ThreadsMgr.active_threads() > 1
1407 && ThreadsMgr.available_thread_exists(threadID)
1409 && !ThreadsMgr.thread_should_stop(threadID)
1411 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1412 threatMove, mateThreat, moveCount, &mp, PvNode);
1417 /* Here we have the lock still grabbed */
1418 sp->slaves[threadID] = 0;
1419 lock_release(&(sp->lock));
1423 // Step 19. Check for mate and stalemate
1424 // All legal moves have been searched and if there are
1425 // no legal moves, it must be mate or stalemate.
1426 // If one move was excluded return fail low score.
1428 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1430 // Step 20. Update tables
1431 // If the search is not aborted, update the transposition table,
1432 // history counters, and killer moves.
1433 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1436 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1437 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1438 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1440 // Update killers and history only for non capture moves that fails high
1441 if ( bestValue >= beta
1442 && !pos.move_is_capture_or_promotion(move))
1444 update_history(pos, move, depth, movesSearched, moveCount);
1445 update_killers(move, ss);
1448 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1454 // qsearch() is the quiescence search function, which is called by the main
1455 // search function when the remaining depth is zero (or, to be more precise,
1456 // less than ONE_PLY).
1458 template <NodeType PvNode>
1459 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1461 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1462 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1463 assert(PvNode || alpha == beta - 1);
1465 assert(ply > 0 && ply < PLY_MAX);
1466 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1470 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1471 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1473 Value oldAlpha = alpha;
1475 ThreadsMgr.incrementNodeCounter(pos.thread());
1476 ss->bestMove = ss->currentMove = MOVE_NONE;
1478 // Check for an instant draw or maximum ply reached
1479 if (pos.is_draw() || ply >= PLY_MAX - 1)
1482 // Transposition table lookup. At PV nodes, we don't use the TT for
1483 // pruning, but only for move ordering.
1484 tte = TT.retrieve(pos.get_key());
1485 ttMove = (tte ? tte->move() : MOVE_NONE);
1487 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1489 ss->bestMove = ttMove; // Can be MOVE_NONE
1490 return value_from_tt(tte->value(), ply);
1493 isCheck = pos.is_check();
1495 // Evaluate the position statically
1498 bestValue = futilityBase = -VALUE_INFINITE;
1499 ss->eval = evalMargin = VALUE_NONE;
1500 deepChecks = enoughMaterial = false;
1506 assert(tte->static_value() != VALUE_NONE);
1508 evalMargin = tte->static_value_margin();
1509 ss->eval = bestValue = tte->static_value();
1512 ss->eval = bestValue = evaluate(pos, evalMargin);
1514 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1516 // Stand pat. Return immediately if static value is at least beta
1517 if (bestValue >= beta)
1520 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1525 if (PvNode && bestValue > alpha)
1528 // If we are near beta then try to get a cutoff pushing checks a bit further
1529 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1531 // Futility pruning parameters, not needed when in check
1532 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1533 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1536 // Initialize a MovePicker object for the current position, and prepare
1537 // to search the moves. Because the depth is <= 0 here, only captures,
1538 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1539 // and we are near beta) will be generated.
1540 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1543 // Loop through the moves until no moves remain or a beta cutoff occurs
1544 while ( alpha < beta
1545 && (move = mp.get_next_move()) != MOVE_NONE)
1547 assert(move_is_ok(move));
1549 moveIsCheck = pos.move_is_check(move, ci);
1557 && !move_is_promotion(move)
1558 && !pos.move_is_passed_pawn_push(move))
1560 futilityValue = futilityBase
1561 + pos.endgame_value_of_piece_on(move_to(move))
1562 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1564 if (futilityValue < alpha)
1566 if (futilityValue > bestValue)
1567 bestValue = futilityValue;
1572 // Detect non-capture evasions that are candidate to be pruned
1573 evasionPrunable = isCheck
1574 && bestValue > value_mated_in(PLY_MAX)
1575 && !pos.move_is_capture(move)
1576 && !pos.can_castle(pos.side_to_move());
1578 // Don't search moves with negative SEE values
1580 && (!isCheck || evasionPrunable)
1582 && !move_is_promotion(move)
1583 && pos.see_sign(move) < 0)
1586 // Update current move
1587 ss->currentMove = move;
1589 // Make and search the move
1590 pos.do_move(move, st, ci, moveIsCheck);
1591 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1592 pos.undo_move(move);
1594 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1597 if (value > bestValue)
1603 ss->bestMove = move;
1608 // All legal moves have been searched. A special case: If we're in check
1609 // and no legal moves were found, it is checkmate.
1610 if (isCheck && bestValue == -VALUE_INFINITE)
1611 return value_mated_in(ply);
1613 // Update transposition table
1614 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1615 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1616 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1618 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1624 // connected_moves() tests whether two moves are 'connected' in the sense
1625 // that the first move somehow made the second move possible (for instance
1626 // if the moving piece is the same in both moves). The first move is assumed
1627 // to be the move that was made to reach the current position, while the
1628 // second move is assumed to be a move from the current position.
1630 bool connected_moves(const Position& pos, Move m1, Move m2) {
1632 Square f1, t1, f2, t2;
1635 assert(move_is_ok(m1));
1636 assert(move_is_ok(m2));
1638 if (m2 == MOVE_NONE)
1641 // Case 1: The moving piece is the same in both moves
1647 // Case 2: The destination square for m2 was vacated by m1
1653 // Case 3: Moving through the vacated square
1654 if ( piece_is_slider(pos.piece_on(f2))
1655 && bit_is_set(squares_between(f2, t2), f1))
1658 // Case 4: The destination square for m2 is defended by the moving piece in m1
1659 p = pos.piece_on(t1);
1660 if (bit_is_set(pos.attacks_from(p, t1), t2))
1663 // Case 5: Discovered check, checking piece is the piece moved in m1
1664 if ( piece_is_slider(p)
1665 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1666 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1668 // discovered_check_candidates() works also if the Position's side to
1669 // move is the opposite of the checking piece.
1670 Color them = opposite_color(pos.side_to_move());
1671 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1673 if (bit_is_set(dcCandidates, f2))
1680 // value_is_mate() checks if the given value is a mate one eventually
1681 // compensated for the ply.
1683 bool value_is_mate(Value value) {
1685 assert(abs(value) <= VALUE_INFINITE);
1687 return value <= value_mated_in(PLY_MAX)
1688 || value >= value_mate_in(PLY_MAX);
1692 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1693 // "plies to mate from the current ply". Non-mate scores are unchanged.
1694 // The function is called before storing a value to the transposition table.
1696 Value value_to_tt(Value v, int ply) {
1698 if (v >= value_mate_in(PLY_MAX))
1701 if (v <= value_mated_in(PLY_MAX))
1708 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1709 // the transposition table to a mate score corrected for the current ply.
1711 Value value_from_tt(Value v, int ply) {
1713 if (v >= value_mate_in(PLY_MAX))
1716 if (v <= value_mated_in(PLY_MAX))
1723 // extension() decides whether a move should be searched with normal depth,
1724 // or with extended depth. Certain classes of moves (checking moves, in
1725 // particular) are searched with bigger depth than ordinary moves and in
1726 // any case are marked as 'dangerous'. Note that also if a move is not
1727 // extended, as example because the corresponding UCI option is set to zero,
1728 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1729 template <NodeType PvNode>
1730 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1731 bool singleEvasion, bool mateThreat, bool* dangerous) {
1733 assert(m != MOVE_NONE);
1735 Depth result = DEPTH_ZERO;
1736 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1740 if (moveIsCheck && pos.see_sign(m) >= 0)
1741 result += CheckExtension[PvNode];
1744 result += SingleEvasionExtension[PvNode];
1747 result += MateThreatExtension[PvNode];
1750 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1752 Color c = pos.side_to_move();
1753 if (relative_rank(c, move_to(m)) == RANK_7)
1755 result += PawnPushTo7thExtension[PvNode];
1758 if (pos.pawn_is_passed(c, move_to(m)))
1760 result += PassedPawnExtension[PvNode];
1765 if ( captureOrPromotion
1766 && pos.type_of_piece_on(move_to(m)) != PAWN
1767 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1768 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1769 && !move_is_promotion(m)
1772 result += PawnEndgameExtension[PvNode];
1777 && captureOrPromotion
1778 && pos.type_of_piece_on(move_to(m)) != PAWN
1779 && pos.see_sign(m) >= 0)
1781 result += ONE_PLY / 2;
1785 return Min(result, ONE_PLY);
1789 // connected_threat() tests whether it is safe to forward prune a move or if
1790 // is somehow coonected to the threat move returned by null search.
1792 bool connected_threat(const Position& pos, Move m, Move threat) {
1794 assert(move_is_ok(m));
1795 assert(threat && move_is_ok(threat));
1796 assert(!pos.move_is_check(m));
1797 assert(!pos.move_is_capture_or_promotion(m));
1798 assert(!pos.move_is_passed_pawn_push(m));
1800 Square mfrom, mto, tfrom, tto;
1802 mfrom = move_from(m);
1804 tfrom = move_from(threat);
1805 tto = move_to(threat);
1807 // Case 1: Don't prune moves which move the threatened piece
1811 // Case 2: If the threatened piece has value less than or equal to the
1812 // value of the threatening piece, don't prune move which defend it.
1813 if ( pos.move_is_capture(threat)
1814 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1815 || pos.type_of_piece_on(tfrom) == KING)
1816 && pos.move_attacks_square(m, tto))
1819 // Case 3: If the moving piece in the threatened move is a slider, don't
1820 // prune safe moves which block its ray.
1821 if ( piece_is_slider(pos.piece_on(tfrom))
1822 && bit_is_set(squares_between(tfrom, tto), mto)
1823 && pos.see_sign(m) >= 0)
1830 // ok_to_use_TT() returns true if a transposition table score
1831 // can be used at a given point in search.
1833 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1835 Value v = value_from_tt(tte->value(), ply);
1837 return ( tte->depth() >= depth
1838 || v >= Max(value_mate_in(PLY_MAX), beta)
1839 || v < Min(value_mated_in(PLY_MAX), beta))
1841 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1842 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1846 // refine_eval() returns the transposition table score if
1847 // possible otherwise falls back on static position evaluation.
1849 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1853 Value v = value_from_tt(tte->value(), ply);
1855 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1856 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1863 // update_history() registers a good move that produced a beta-cutoff
1864 // in history and marks as failures all the other moves of that ply.
1866 void update_history(const Position& pos, Move move, Depth depth,
1867 Move movesSearched[], int moveCount) {
1870 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1872 for (int i = 0; i < moveCount - 1; i++)
1874 m = movesSearched[i];
1878 if (!pos.move_is_capture_or_promotion(m))
1879 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1884 // update_killers() add a good move that produced a beta-cutoff
1885 // among the killer moves of that ply.
1887 void update_killers(Move m, SearchStack* ss) {
1889 if (m == ss->killers[0])
1892 ss->killers[1] = ss->killers[0];
1897 // update_gains() updates the gains table of a non-capture move given
1898 // the static position evaluation before and after the move.
1900 void update_gains(const Position& pos, Move m, Value before, Value after) {
1903 && before != VALUE_NONE
1904 && after != VALUE_NONE
1905 && pos.captured_piece_type() == PIECE_TYPE_NONE
1906 && !move_is_special(m))
1907 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1911 // current_search_time() returns the number of milliseconds which have passed
1912 // since the beginning of the current search.
1914 int current_search_time() {
1916 return get_system_time() - SearchStartTime;
1920 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1922 std::string value_to_uci(Value v) {
1924 std::stringstream s;
1926 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1927 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1929 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1934 // nps() computes the current nodes/second count.
1938 int t = current_search_time();
1939 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
1943 // poll() performs two different functions: It polls for user input, and it
1944 // looks at the time consumed so far and decides if it's time to abort the
1949 static int lastInfoTime;
1950 int t = current_search_time();
1955 // We are line oriented, don't read single chars
1956 std::string command;
1958 if (!std::getline(std::cin, command))
1961 if (command == "quit")
1964 PonderSearch = false;
1968 else if (command == "stop")
1971 PonderSearch = false;
1973 else if (command == "ponderhit")
1977 // Print search information
1981 else if (lastInfoTime > t)
1982 // HACK: Must be a new search where we searched less than
1983 // NodesBetweenPolls nodes during the first second of search.
1986 else if (t - lastInfoTime >= 1000)
1993 if (dbg_show_hit_rate)
1994 dbg_print_hit_rate();
1996 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
1997 << " time " << t << endl;
2000 // Should we stop the search?
2004 bool stillAtFirstMove = FirstRootMove
2005 && !AspirationFailLow
2006 && t > TimeMgr.available_time();
2008 bool noMoreTime = t > TimeMgr.maximum_time()
2009 || stillAtFirstMove;
2011 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2012 || (ExactMaxTime && t >= ExactMaxTime)
2013 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2018 // ponderhit() is called when the program is pondering (i.e. thinking while
2019 // it's the opponent's turn to move) in order to let the engine know that
2020 // it correctly predicted the opponent's move.
2024 int t = current_search_time();
2025 PonderSearch = false;
2027 bool stillAtFirstMove = FirstRootMove
2028 && !AspirationFailLow
2029 && t > TimeMgr.available_time();
2031 bool noMoreTime = t > TimeMgr.maximum_time()
2032 || stillAtFirstMove;
2034 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2039 // init_ss_array() does a fast reset of the first entries of a SearchStack
2040 // array and of all the excludedMove and skipNullMove entries.
2042 void init_ss_array(SearchStack* ss, int size) {
2044 for (int i = 0; i < size; i++, ss++)
2046 ss->excludedMove = MOVE_NONE;
2047 ss->skipNullMove = false;
2048 ss->reduction = DEPTH_ZERO;
2052 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2057 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2058 // while the program is pondering. The point is to work around a wrinkle in
2059 // the UCI protocol: When pondering, the engine is not allowed to give a
2060 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2061 // We simply wait here until one of these commands is sent, and return,
2062 // after which the bestmove and pondermove will be printed (in id_loop()).
2064 void wait_for_stop_or_ponderhit() {
2066 std::string command;
2070 if (!std::getline(std::cin, command))
2073 if (command == "quit")
2078 else if (command == "ponderhit" || command == "stop")
2084 // print_pv_info() prints to standard output and eventually to log file information on
2085 // the current PV line. It is called at each iteration or after a new pv is found.
2087 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2089 cout << "info depth " << Iteration
2090 << " score " << value_to_uci(value)
2091 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2092 << " time " << current_search_time()
2093 << " nodes " << ThreadsMgr.nodes_searched()
2097 for (Move* m = pv; *m != MOVE_NONE; m++)
2104 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2105 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2107 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2108 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2113 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2114 // the PV back into the TT. This makes sure the old PV moves are searched
2115 // first, even if the old TT entries have been overwritten.
2117 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2121 Position p(pos, pos.thread());
2122 Value v, m = VALUE_NONE;
2124 for (int i = 0; pv[i] != MOVE_NONE; i++)
2126 tte = TT.retrieve(p.get_key());
2127 if (!tte || tte->move() != pv[i])
2129 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2130 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2132 p.do_move(pv[i], st);
2137 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2138 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2139 // allow to always have a ponder move even when we fail high at root and also a
2140 // long PV to print that is important for position analysis.
2142 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2146 Position p(pos, pos.thread());
2149 assert(bestMove != MOVE_NONE);
2152 p.do_move(pv[ply++], st);
2154 while ( (tte = TT.retrieve(p.get_key())) != NULL
2155 && tte->move() != MOVE_NONE
2156 && move_is_legal(p, tte->move())
2158 && (!p.is_draw() || ply < 2))
2160 pv[ply] = tte->move();
2161 p.do_move(pv[ply++], st);
2163 pv[ply] = MOVE_NONE;
2167 // init_thread() is the function which is called when a new thread is
2168 // launched. It simply calls the idle_loop() function with the supplied
2169 // threadID. There are two versions of this function; one for POSIX
2170 // threads and one for Windows threads.
2172 #if !defined(_MSC_VER)
2174 void* init_thread(void *threadID) {
2176 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2182 DWORD WINAPI init_thread(LPVOID threadID) {
2184 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2191 /// The ThreadsManager class
2193 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2194 // get_beta_counters() are getters/setters for the per thread
2195 // counters used to sort the moves at root.
2197 void ThreadsManager::resetNodeCounters() {
2199 for (int i = 0; i < MAX_THREADS; i++)
2200 threads[i].nodes = 0ULL;
2203 int64_t ThreadsManager::nodes_searched() const {
2205 int64_t result = 0ULL;
2206 for (int i = 0; i < ActiveThreads; i++)
2207 result += threads[i].nodes;
2213 // idle_loop() is where the threads are parked when they have no work to do.
2214 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2215 // object for which the current thread is the master.
2217 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2219 assert(threadID >= 0 && threadID < MAX_THREADS);
2223 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2224 // master should exit as last one.
2225 if (AllThreadsShouldExit)
2228 threads[threadID].state = THREAD_TERMINATED;
2232 // If we are not thinking, wait for a condition to be signaled
2233 // instead of wasting CPU time polling for work.
2234 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2237 assert(threadID != 0);
2238 threads[threadID].state = THREAD_SLEEPING;
2240 #if !defined(_MSC_VER)
2241 lock_grab(&WaitLock);
2242 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2243 pthread_cond_wait(&WaitCond[threadID], &WaitLock);
2244 lock_release(&WaitLock);
2246 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2250 // If thread has just woken up, mark it as available
2251 if (threads[threadID].state == THREAD_SLEEPING)
2252 threads[threadID].state = THREAD_AVAILABLE;
2254 // If this thread has been assigned work, launch a search
2255 if (threads[threadID].state == THREAD_WORKISWAITING)
2257 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2259 threads[threadID].state = THREAD_SEARCHING;
2261 // Here we call search() with SplitPoint template parameter set to true
2262 SplitPoint* tsp = threads[threadID].splitPoint;
2263 Position pos(*tsp->pos, threadID);
2264 SearchStack* ss = tsp->sstack[threadID] + 1;
2268 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2270 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2272 assert(threads[threadID].state == THREAD_SEARCHING);
2274 threads[threadID].state = THREAD_AVAILABLE;
2277 // If this thread is the master of a split point and all slaves have
2278 // finished their work at this split point, return from the idle loop.
2280 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2282 if (i == ActiveThreads)
2284 // Because sp->slaves[] is reset under lock protection,
2285 // be sure sp->lock has been released before to return.
2286 lock_grab(&(sp->lock));
2287 lock_release(&(sp->lock));
2289 // In helpful master concept a master can help only a sub-tree, and
2290 // because here is all finished is not possible master is booked.
2291 assert(threads[threadID].state == THREAD_AVAILABLE);
2293 threads[threadID].state = THREAD_SEARCHING;
2300 // init_threads() is called during startup. It launches all helper threads,
2301 // and initializes the split point stack and the global locks and condition
2304 void ThreadsManager::init_threads() {
2309 #if !defined(_MSC_VER)
2310 pthread_t pthread[1];
2313 // Initialize global locks
2315 lock_init(&WaitLock);
2317 for (i = 0; i < MAX_THREADS; i++)
2318 #if !defined(_MSC_VER)
2319 pthread_cond_init(&WaitCond[i], NULL);
2321 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2324 // Initialize splitPoints[] locks
2325 for (i = 0; i < MAX_THREADS; i++)
2326 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2327 lock_init(&(threads[i].splitPoints[j].lock));
2329 // Will be set just before program exits to properly end the threads
2330 AllThreadsShouldExit = false;
2332 // Threads will be put to sleep as soon as created
2333 AllThreadsShouldSleep = true;
2335 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2337 threads[0].state = THREAD_SEARCHING;
2338 for (i = 1; i < MAX_THREADS; i++)
2339 threads[i].state = THREAD_AVAILABLE;
2341 // Launch the helper threads
2342 for (i = 1; i < MAX_THREADS; i++)
2345 #if !defined(_MSC_VER)
2346 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2348 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2353 cout << "Failed to create thread number " << i << endl;
2354 Application::exit_with_failure();
2357 // Wait until the thread has finished launching and is gone to sleep
2358 while (threads[i].state != THREAD_SLEEPING) {}
2363 // exit_threads() is called when the program exits. It makes all the
2364 // helper threads exit cleanly.
2366 void ThreadsManager::exit_threads() {
2368 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2369 ActiveThreads = MAX_THREADS; // Avoid any woken up thread comes back to sleep
2371 // Wake up all the threads and waits for termination
2372 for (int i = 1; i < MAX_THREADS; i++)
2374 wake_sleeping_thread(i);
2375 while (threads[i].state != THREAD_TERMINATED) {}
2378 // Now we can safely destroy the locks
2379 for (int i = 0; i < MAX_THREADS; i++)
2380 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2381 lock_destroy(&(threads[i].splitPoints[j].lock));
2383 lock_destroy(&WaitLock);
2384 lock_destroy(&MPLock);
2388 // thread_should_stop() checks whether the thread should stop its search.
2389 // This can happen if a beta cutoff has occurred in the thread's currently
2390 // active split point, or in some ancestor of the current split point.
2392 bool ThreadsManager::thread_should_stop(int threadID) const {
2394 assert(threadID >= 0 && threadID < ActiveThreads);
2396 SplitPoint* sp = threads[threadID].splitPoint;
2398 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2403 // thread_is_available() checks whether the thread with threadID "slave" is
2404 // available to help the thread with threadID "master" at a split point. An
2405 // obvious requirement is that "slave" must be idle. With more than two
2406 // threads, this is not by itself sufficient: If "slave" is the master of
2407 // some active split point, it is only available as a slave to the other
2408 // threads which are busy searching the split point at the top of "slave"'s
2409 // split point stack (the "helpful master concept" in YBWC terminology).
2411 bool ThreadsManager::thread_is_available(int slave, int master) const {
2413 assert(slave >= 0 && slave < ActiveThreads);
2414 assert(master >= 0 && master < ActiveThreads);
2415 assert(ActiveThreads > 1);
2417 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2420 // Make a local copy to be sure doesn't change under our feet
2421 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2423 // No active split points means that the thread is available as
2424 // a slave for any other thread.
2425 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2428 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2429 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2430 // could have been set to 0 by another thread leading to an out of bound access.
2431 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2438 // available_thread_exists() tries to find an idle thread which is available as
2439 // a slave for the thread with threadID "master".
2441 bool ThreadsManager::available_thread_exists(int master) const {
2443 assert(master >= 0 && master < ActiveThreads);
2444 assert(ActiveThreads > 1);
2446 for (int i = 0; i < ActiveThreads; i++)
2447 if (thread_is_available(i, master))
2454 // split() does the actual work of distributing the work at a node between
2455 // several available threads. If it does not succeed in splitting the
2456 // node (because no idle threads are available, or because we have no unused
2457 // split point objects), the function immediately returns. If splitting is
2458 // possible, a SplitPoint object is initialized with all the data that must be
2459 // copied to the helper threads and we tell our helper threads that they have
2460 // been assigned work. This will cause them to instantly leave their idle loops
2461 // and call sp_search(). When all threads have returned from sp_search() then
2464 template <bool Fake>
2465 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2466 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2467 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2469 assert(ply > 0 && ply < PLY_MAX);
2470 assert(*bestValue >= -VALUE_INFINITE);
2471 assert(*bestValue <= *alpha);
2472 assert(*alpha < beta);
2473 assert(beta <= VALUE_INFINITE);
2474 assert(depth > DEPTH_ZERO);
2475 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2476 assert(ActiveThreads > 1);
2478 int i, master = p.thread();
2479 Thread& masterThread = threads[master];
2483 // If no other thread is available to help us, or if we have too many
2484 // active split points, don't split.
2485 if ( !available_thread_exists(master)
2486 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2488 lock_release(&MPLock);
2492 // Pick the next available split point object from the split point stack
2493 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2495 // Initialize the split point object
2496 splitPoint.parent = masterThread.splitPoint;
2497 splitPoint.stopRequest = false;
2498 splitPoint.ply = ply;
2499 splitPoint.depth = depth;
2500 splitPoint.threatMove = threatMove;
2501 splitPoint.mateThreat = mateThreat;
2502 splitPoint.alpha = *alpha;
2503 splitPoint.beta = beta;
2504 splitPoint.pvNode = pvNode;
2505 splitPoint.bestValue = *bestValue;
2507 splitPoint.moveCount = moveCount;
2508 splitPoint.pos = &p;
2509 splitPoint.parentSstack = ss;
2510 for (i = 0; i < ActiveThreads; i++)
2511 splitPoint.slaves[i] = 0;
2513 masterThread.splitPoint = &splitPoint;
2515 // If we are here it means we are not available
2516 assert(masterThread.state != THREAD_AVAILABLE);
2518 int workersCnt = 1; // At least the master is included
2520 // Allocate available threads setting state to THREAD_BOOKED
2521 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2522 if (thread_is_available(i, master))
2524 threads[i].state = THREAD_BOOKED;
2525 threads[i].splitPoint = &splitPoint;
2526 splitPoint.slaves[i] = 1;
2530 assert(Fake || workersCnt > 1);
2532 // We can release the lock because slave threads are already booked and master is not available
2533 lock_release(&MPLock);
2535 // Tell the threads that they have work to do. This will make them leave
2536 // their idle loop. But before copy search stack tail for each thread.
2537 for (i = 0; i < ActiveThreads; i++)
2538 if (i == master || splitPoint.slaves[i])
2540 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2542 assert(i == master || threads[i].state == THREAD_BOOKED);
2544 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2547 // Everything is set up. The master thread enters the idle loop, from
2548 // which it will instantly launch a search, because its state is
2549 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2550 // idle loop, which means that the main thread will return from the idle
2551 // loop when all threads have finished their work at this split point.
2552 idle_loop(master, &splitPoint);
2554 // We have returned from the idle loop, which means that all threads are
2555 // finished. Update alpha and bestValue, and return.
2558 *alpha = splitPoint.alpha;
2559 *bestValue = splitPoint.bestValue;
2560 masterThread.activeSplitPoints--;
2561 masterThread.splitPoint = splitPoint.parent;
2563 lock_release(&MPLock);
2567 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2568 // to start a new search from the root.
2570 void ThreadsManager::wake_sleeping_thread(int threadID) {
2572 assert(threadID > 0);
2573 assert(threads[threadID].state == THREAD_SLEEPING);
2575 AllThreadsShouldSleep = false; // Avoid the woken up thread comes back to sleep
2577 #if !defined(_MSC_VER)
2578 pthread_mutex_lock(&WaitLock);
2579 pthread_cond_signal(&WaitCond[threadID]);
2580 pthread_mutex_unlock(&WaitLock);
2582 SetEvent(SitIdleEvent[threadID]);
2587 // put_threads_to_sleep() makes all the threads go to sleep just before
2588 // to leave think(), at the end of the search. Threads should have already
2589 // finished the job and should be idle.
2591 void ThreadsManager::put_threads_to_sleep() {
2593 assert(!AllThreadsShouldSleep || ActiveThreads == 1);
2595 // This makes the threads to go to sleep
2596 AllThreadsShouldSleep = true;
2599 /// The RootMoveList class
2601 // RootMoveList c'tor
2603 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2605 SearchStack ss[PLY_MAX_PLUS_2];
2606 MoveStack mlist[MOVES_MAX];
2608 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2610 // Initialize search stack
2611 init_ss_array(ss, PLY_MAX_PLUS_2);
2612 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2615 // Generate all legal moves
2616 MoveStack* last = generate_moves(pos, mlist);
2618 // Add each move to the moves[] array
2619 for (MoveStack* cur = mlist; cur != last; cur++)
2621 bool includeMove = includeAllMoves;
2623 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2624 includeMove = (searchMoves[k] == cur->move);
2629 // Find a quick score for the move
2630 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2631 moves[count].pv[1] = MOVE_NONE;
2632 pos.do_move(cur->move, st);
2633 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2634 pos.undo_move(cur->move);
2640 // Score root moves using the standard way used in main search, the moves
2641 // are scored according to the order in which are returned by MovePicker.
2643 void RootMoveList::score_moves(const Position& pos)
2647 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2649 while ((move = mp.get_next_move()) != MOVE_NONE)
2650 for (int i = 0; i < count; i++)
2651 if (moves[i].move == move)
2653 moves[i].mp_score = score--;
2658 // RootMoveList simple methods definitions
2660 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2664 for (j = 0; pv[j] != MOVE_NONE; j++)
2665 moves[moveNum].pv[j] = pv[j];
2667 moves[moveNum].pv[j] = MOVE_NONE;
2671 // RootMoveList::sort() sorts the root move list at the beginning of a new
2674 void RootMoveList::sort() {
2676 sort_multipv(count - 1); // Sort all items
2680 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2681 // list by their scores and depths. It is used to order the different PVs
2682 // correctly in MultiPV mode.
2684 void RootMoveList::sort_multipv(int n) {
2688 for (i = 1; i <= n; i++)
2690 RootMove rm = moves[i];
2691 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2692 moves[j] = moves[j - 1];