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/>.
43 #include "ucioption.h"
49 //// Local definitions
55 enum NodeType { NonPV, PV };
57 // Set to true to force running with one thread.
58 // Used for debugging SMP code.
59 const bool FakeSplit = false;
61 // ThreadsManager class is used to handle all the threads related stuff in search,
62 // init, starting, parking and, the most important, launching a slave thread at a
63 // split point are what this class does. All the access to shared thread data is
64 // done through this class, so that we avoid using global variables instead.
66 class ThreadsManager {
67 /* As long as the single ThreadsManager object is defined as a global we don't
68 need to explicitly initialize to zero its data members because variables with
69 static storage duration are automatically set to zero before enter main()
75 int active_threads() const { return ActiveThreads; }
76 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
77 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
78 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
80 void resetNodeCounters();
81 void resetBetaCounters();
82 int64_t nodes_searched() const;
83 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
84 bool available_thread_exists(int master) const;
85 bool thread_is_available(int slave, int master) const;
86 bool thread_should_stop(int threadID) const;
87 void wake_sleeping_threads();
88 void put_threads_to_sleep();
89 void idle_loop(int threadID, SplitPoint* sp);
92 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
99 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
100 Thread threads[MAX_THREADS];
102 Lock MPLock, WaitLock;
104 #if !defined(_MSC_VER)
105 pthread_cond_t WaitCond;
107 HANDLE SitIdleEvent[MAX_THREADS];
113 // RootMove struct is used for moves at the root at the tree. For each
114 // root move, we store a score, a node count, and a PV (really a refutation
115 // in the case of moves which fail low).
119 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
121 // RootMove::operator<() is the comparison function used when
122 // sorting the moves. A move m1 is considered to be better
123 // than a move m2 if it has a higher score, or if the moves
124 // have equal score but m1 has the higher beta cut-off count.
125 bool operator<(const RootMove& m) const {
127 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
132 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
133 Move pv[PLY_MAX_PLUS_2];
137 // The RootMoveList class is essentially an array of RootMove objects, with
138 // a handful of methods for accessing the data in the individual moves.
143 RootMoveList(Position& pos, Move searchMoves[]);
145 int move_count() const { return count; }
146 Move get_move(int moveNum) const { return moves[moveNum].move; }
147 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
148 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
149 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
150 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
152 void set_move_nodes(int moveNum, int64_t nodes);
153 void set_beta_counters(int moveNum, int64_t our, int64_t their);
154 void set_move_pv(int moveNum, const Move pv[]);
156 void sort_multipv(int n);
159 static const int MaxRootMoves = 500;
160 RootMove moves[MaxRootMoves];
169 // Maximum depth for razoring
170 const Depth RazorDepth = 4 * OnePly;
172 // Dynamic razoring margin based on depth
173 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
175 // Step 8. Null move search with verification search
177 // Null move margin. A null move search will not be done if the static
178 // evaluation of the position is more than NullMoveMargin below beta.
179 const Value NullMoveMargin = Value(0x200);
181 // Maximum depth for use of dynamic threat detection when null move fails low
182 const Depth ThreatDepth = 5 * OnePly;
184 // Step 9. Internal iterative deepening
186 // Minimum depth for use of internal iterative deepening
187 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
189 // At Non-PV nodes we do an internal iterative deepening search
190 // when the static evaluation is bigger then beta - IIDMargin.
191 const Value IIDMargin = Value(0x100);
193 // Step 11. Decide the new search depth
195 // Extensions. Configurable UCI options
196 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
197 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
198 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
200 // Minimum depth for use of singular extension
201 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
203 // If the TT move is at least SingularExtensionMargin better then the
204 // remaining ones we will extend it.
205 const Value SingularExtensionMargin = Value(0x20);
207 // Step 12. Futility pruning
209 // Futility margin for quiescence search
210 const Value FutilityMarginQS = Value(0x80);
212 // Futility lookup tables (initialized at startup) and their getter functions
213 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
214 int FutilityMoveCountArray[32]; // [depth]
216 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
217 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
219 // Step 14. Reduced search
221 // Reduction lookup tables (initialized at startup) and their getter functions
222 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
224 template <NodeType PV>
225 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
227 // Common adjustments
229 // Search depth at iteration 1
230 const Depth InitialDepth = OnePly;
232 // Easy move margin. An easy move candidate must be at least this much
233 // better than the second best move.
234 const Value EasyMoveMargin = Value(0x200);
242 // Scores and number of times the best move changed for each iteration
243 Value ValueByIteration[PLY_MAX_PLUS_2];
244 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
246 // Search window management
252 // Time managment variables
253 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
254 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
255 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
256 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
260 std::ofstream LogFile;
262 // Multi-threads related variables
263 Depth MinimumSplitDepth;
264 int MaxThreadsPerSplitPoint;
267 // Node counters, used only by thread[0] but try to keep in different cache
268 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
270 int NodesBetweenPolls = 30000;
277 Value id_loop(const Position& pos, Move searchMoves[]);
278 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
280 template <NodeType PvNode>
281 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
283 template <NodeType PvNode>
284 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
286 template <NodeType PvNode>
287 void sp_search(SplitPoint* sp, int threadID);
289 template <NodeType PvNode>
290 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
292 bool connected_moves(const Position& pos, Move m1, Move m2);
293 bool value_is_mate(Value value);
294 Value value_to_tt(Value v, int ply);
295 Value value_from_tt(Value v, int ply);
296 bool move_is_killer(Move m, SearchStack* ss);
297 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
298 bool connected_threat(const Position& pos, Move m, Move threat);
299 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
300 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
301 void update_killers(Move m, SearchStack* ss);
302 void update_gains(const Position& pos, Move move, Value before, Value after);
304 int current_search_time();
305 std::string value_to_uci(Value v);
309 void wait_for_stop_or_ponderhit();
310 void init_ss_array(SearchStack* ss, int size);
311 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
313 #if !defined(_MSC_VER)
314 void *init_thread(void *threadID);
316 DWORD WINAPI init_thread(LPVOID threadID);
326 /// init_threads(), exit_threads() and nodes_searched() are helpers to
327 /// give accessibility to some TM methods from outside of current file.
329 void init_threads() { TM.init_threads(); }
330 void exit_threads() { TM.exit_threads(); }
331 int64_t nodes_searched() { return TM.nodes_searched(); }
334 /// init_search() is called during startup. It initializes various lookup tables
338 int d; // depth (OnePly == 2)
339 int hd; // half depth (OnePly == 1)
342 // Init reductions array
343 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
345 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
346 double nonPVRed = log(double(hd)) * log(double(mc)) / 1.5;
347 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
348 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
351 // Init futility margins array
352 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
353 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
355 // Init futility move count array
356 for (d = 0; d < 32; d++)
357 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
361 // SearchStack::init() initializes a search stack entry.
362 // Called at the beginning of search() when starting to examine a new node.
363 void SearchStack::init() {
365 currentMove = threatMove = bestMove = MOVE_NONE;
366 reduction = Depth(0);
370 // SearchStack::initKillers() initializes killers for a search stack entry
371 void SearchStack::initKillers() {
373 mateKiller = MOVE_NONE;
374 for (int i = 0; i < KILLER_MAX; i++)
375 killers[i] = MOVE_NONE;
379 /// perft() is our utility to verify move generation is bug free. All the legal
380 /// moves up to given depth are generated and counted and the sum returned.
382 int perft(Position& pos, Depth depth)
387 MovePicker mp(pos, MOVE_NONE, depth, H);
389 // If we are at the last ply we don't need to do and undo
390 // the moves, just to count them.
391 if (depth <= OnePly) // Replace with '<' to test also qsearch
393 while (mp.get_next_move()) sum++;
397 // Loop through all legal moves
399 while ((move = mp.get_next_move()) != MOVE_NONE)
401 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
402 sum += perft(pos, depth - OnePly);
409 /// think() is the external interface to Stockfish's search, and is called when
410 /// the program receives the UCI 'go' command. It initializes various
411 /// search-related global variables, and calls root_search(). It returns false
412 /// when a quit command is received during the search.
414 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
415 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
417 // Initialize global search variables
418 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
419 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
421 TM.resetNodeCounters();
422 SearchStartTime = get_system_time();
423 ExactMaxTime = maxTime;
426 InfiniteSearch = infinite;
427 PonderSearch = ponder;
428 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
430 // Look for a book move, only during games, not tests
431 if (UseTimeManagement && get_option_value_bool("OwnBook"))
433 if (get_option_value_string("Book File") != OpeningBook.file_name())
434 OpeningBook.open(get_option_value_string("Book File"));
436 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
437 if (bookMove != MOVE_NONE)
440 wait_for_stop_or_ponderhit();
442 cout << "bestmove " << bookMove << endl;
447 // Read UCI option values
448 TT.set_size(get_option_value_int("Hash"));
449 if (button_was_pressed("Clear Hash"))
452 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
453 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
454 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
455 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
456 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
457 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
458 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
459 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
460 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
461 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
462 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
463 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
465 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
466 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
467 MultiPV = get_option_value_int("MultiPV");
468 Chess960 = get_option_value_bool("UCI_Chess960");
469 UseLogFile = get_option_value_bool("Use Search Log");
472 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
474 read_weights(pos.side_to_move());
476 // Set the number of active threads
477 int newActiveThreads = get_option_value_int("Threads");
478 if (newActiveThreads != TM.active_threads())
480 TM.set_active_threads(newActiveThreads);
481 init_eval(TM.active_threads());
484 // Wake up sleeping threads
485 TM.wake_sleeping_threads();
488 int myTime = time[pos.side_to_move()];
489 int myIncrement = increment[pos.side_to_move()];
490 if (UseTimeManagement)
492 if (!movesToGo) // Sudden death time control
496 MaxSearchTime = myTime / 30 + myIncrement;
497 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
499 else // Blitz game without increment
501 MaxSearchTime = myTime / 30;
502 AbsoluteMaxSearchTime = myTime / 8;
505 else // (x moves) / (y minutes)
509 MaxSearchTime = myTime / 2;
510 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
514 MaxSearchTime = myTime / Min(movesToGo, 20);
515 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
519 if (get_option_value_bool("Ponder"))
521 MaxSearchTime += MaxSearchTime / 4;
522 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
526 // Set best NodesBetweenPolls interval to avoid lagging under
527 // heavy time pressure.
529 NodesBetweenPolls = Min(MaxNodes, 30000);
530 else if (myTime && myTime < 1000)
531 NodesBetweenPolls = 1000;
532 else if (myTime && myTime < 5000)
533 NodesBetweenPolls = 5000;
535 NodesBetweenPolls = 30000;
537 // Write search information to log file
539 LogFile << "Searching: " << pos.to_fen() << endl
540 << "infinite: " << infinite
541 << " ponder: " << ponder
542 << " time: " << myTime
543 << " increment: " << myIncrement
544 << " moves to go: " << movesToGo << endl;
546 // We're ready to start thinking. Call the iterative deepening loop function
547 id_loop(pos, searchMoves);
552 TM.put_threads_to_sleep();
560 // id_loop() is the main iterative deepening loop. It calls root_search
561 // repeatedly with increasing depth until the allocated thinking time has
562 // been consumed, the user stops the search, or the maximum search depth is
565 Value id_loop(const Position& pos, Move searchMoves[]) {
567 Position p(pos, pos.thread());
568 SearchStack ss[PLY_MAX_PLUS_2];
569 Move pv[PLY_MAX_PLUS_2];
570 Move EasyMove = MOVE_NONE;
571 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
573 // Moves to search are verified, copied, scored and sorted
574 RootMoveList rml(p, searchMoves);
576 // Handle special case of searching on a mate/stale position
577 if (rml.move_count() == 0)
580 wait_for_stop_or_ponderhit();
582 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
585 // Print RootMoveList startup scoring to the standard output,
586 // so to output information also for iteration 1.
587 cout << "info depth " << 1
588 << "\ninfo depth " << 1
589 << " score " << value_to_uci(rml.get_move_score(0))
590 << " time " << current_search_time()
591 << " nodes " << TM.nodes_searched()
593 << " pv " << rml.get_move(0) << "\n";
598 init_ss_array(ss, PLY_MAX_PLUS_2);
599 pv[0] = pv[1] = MOVE_NONE;
600 ValueByIteration[1] = rml.get_move_score(0);
603 // Is one move significantly better than others after initial scoring ?
604 if ( rml.move_count() == 1
605 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
606 EasyMove = rml.get_move(0);
608 // Iterative deepening loop
609 while (Iteration < PLY_MAX)
611 // Initialize iteration
613 BestMoveChangesByIteration[Iteration] = 0;
615 cout << "info depth " << Iteration << endl;
617 // Calculate dynamic aspiration window based on previous iterations
618 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
620 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
621 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
623 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
624 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
626 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
627 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
630 // Search to the current depth, rml is updated and sorted, alpha and beta could change
631 value = root_search(p, ss, pv, rml, &alpha, &beta);
633 // Write PV to transposition table, in case the relevant entries have
634 // been overwritten during the search.
638 break; // Value cannot be trusted. Break out immediately!
640 //Save info about search result
641 ValueByIteration[Iteration] = value;
643 // Drop the easy move if differs from the new best move
644 if (pv[0] != EasyMove)
645 EasyMove = MOVE_NONE;
647 if (UseTimeManagement)
650 bool stopSearch = false;
652 // Stop search early if there is only a single legal move,
653 // we search up to Iteration 6 anyway to get a proper score.
654 if (Iteration >= 6 && rml.move_count() == 1)
657 // Stop search early when the last two iterations returned a mate score
659 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
660 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
663 // Stop search early if one move seems to be much better than the others
664 int64_t nodes = TM.nodes_searched();
667 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
668 && current_search_time() > MaxSearchTime / 16)
669 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
670 && current_search_time() > MaxSearchTime / 32)))
673 // Add some extra time if the best move has changed during the last two iterations
674 if (Iteration > 5 && Iteration <= 50)
675 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
676 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
678 // Stop search if most of MaxSearchTime is consumed at the end of the
679 // iteration. We probably don't have enough time to search the first
680 // move at the next iteration anyway.
681 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
687 StopOnPonderhit = true;
693 if (MaxDepth && Iteration >= MaxDepth)
697 // If we are pondering or in infinite search, we shouldn't print the
698 // best move before we are told to do so.
699 if (!AbortSearch && (PonderSearch || InfiniteSearch))
700 wait_for_stop_or_ponderhit();
702 // Print final search statistics
703 cout << "info nodes " << TM.nodes_searched()
705 << " time " << current_search_time() << endl;
707 // Print the best move and the ponder move to the standard output
708 if (pv[0] == MOVE_NONE)
710 pv[0] = rml.get_move(0);
714 assert(pv[0] != MOVE_NONE);
716 cout << "bestmove " << pv[0];
718 if (pv[1] != MOVE_NONE)
719 cout << " ponder " << pv[1];
726 dbg_print_mean(LogFile);
728 if (dbg_show_hit_rate)
729 dbg_print_hit_rate(LogFile);
731 LogFile << "\nNodes: " << TM.nodes_searched()
732 << "\nNodes/second: " << nps()
733 << "\nBest move: " << move_to_san(p, pv[0]);
736 p.do_move(pv[0], st);
737 LogFile << "\nPonder move: "
738 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
741 return rml.get_move_score(0);
745 // root_search() is the function which searches the root node. It is
746 // similar to search_pv except that it uses a different move ordering
747 // scheme, prints some information to the standard output and handles
748 // the fail low/high loops.
750 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
757 Depth depth, ext, newDepth;
758 Value value, alpha, beta;
759 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
760 int researchCountFH, researchCountFL;
762 researchCountFH = researchCountFL = 0;
765 isCheck = pos.is_check();
767 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
768 // Step 2. Check for aborted search (omitted at root)
769 // Step 3. Mate distance pruning (omitted at root)
770 // Step 4. Transposition table lookup (omitted at root)
772 // Step 5. Evaluate the position statically
773 // At root we do this only to get reference value for child nodes
775 ss->eval = evaluate(pos, ei);
777 // Step 6. Razoring (omitted at root)
778 // Step 7. Static null move pruning (omitted at root)
779 // Step 8. Null move search with verification search (omitted at root)
780 // Step 9. Internal iterative deepening (omitted at root)
782 // Step extra. Fail low loop
783 // We start with small aspiration window and in case of fail low, we research
784 // with bigger window until we are not failing low anymore.
787 // Sort the moves before to (re)search
790 // Step 10. Loop through all moves in the root move list
791 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
793 // This is used by time management
794 FirstRootMove = (i == 0);
796 // Save the current node count before the move is searched
797 nodes = TM.nodes_searched();
799 // Reset beta cut-off counters
800 TM.resetBetaCounters();
802 // Pick the next root move, and print the move and the move number to
803 // the standard output.
804 move = ss->currentMove = rml.get_move(i);
806 if (current_search_time() >= 1000)
807 cout << "info currmove " << move
808 << " currmovenumber " << i + 1 << endl;
810 moveIsCheck = pos.move_is_check(move);
811 captureOrPromotion = pos.move_is_capture_or_promotion(move);
813 // Step 11. Decide the new search depth
814 depth = (Iteration - 2) * OnePly + InitialDepth;
815 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
816 newDepth = depth + ext;
818 // Step 12. Futility pruning (omitted at root)
820 // Step extra. Fail high loop
821 // If move fails high, we research with bigger window until we are not failing
823 value = - VALUE_INFINITE;
827 // Step 13. Make the move
828 pos.do_move(move, st, ci, moveIsCheck);
830 // Step extra. pv search
831 // We do pv search for first moves (i < MultiPV)
832 // and for fail high research (value > alpha)
833 if (i < MultiPV || value > alpha)
835 // Aspiration window is disabled in multi-pv case
837 alpha = -VALUE_INFINITE;
839 // Full depth PV search, done on first move or after a fail high
840 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
844 // Step 14. Reduced search
845 // if the move fails high will be re-searched at full depth
846 bool doFullDepthSearch = true;
848 if ( depth >= 3 * OnePly
850 && !captureOrPromotion
851 && !move_is_castle(move))
853 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
856 assert(newDepth-ss->reduction >= OnePly);
858 // Reduced depth non-pv search using alpha as upperbound
859 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
860 doFullDepthSearch = (value > alpha);
863 // The move failed high, but if reduction is very big we could
864 // face a false positive, retry with a less aggressive reduction,
865 // if the move fails high again then go with full depth search.
866 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
868 assert(newDepth - OnePly >= OnePly);
870 ss->reduction = OnePly;
871 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
872 doFullDepthSearch = (value > alpha);
874 ss->reduction = Depth(0); // Restore original reduction
877 // Step 15. Full depth search
878 if (doFullDepthSearch)
880 // Full depth non-pv search using alpha as upperbound
881 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
883 // If we are above alpha then research at same depth but as PV
884 // to get a correct score or eventually a fail high above beta.
886 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
890 // Step 16. Undo move
893 // Can we exit fail high loop ?
894 if (AbortSearch || value < beta)
897 // We are failing high and going to do a research. It's important to update
898 // the score before research in case we run out of time while researching.
899 rml.set_move_score(i, value);
901 TT.extract_pv(pos, move, pv, PLY_MAX);
902 rml.set_move_pv(i, pv);
904 // Print information to the standard output
905 print_pv_info(pos, pv, alpha, beta, value);
907 // Prepare for a research after a fail high, each time with a wider window
908 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
911 } // End of fail high loop
913 // Finished searching the move. If AbortSearch is true, the search
914 // was aborted because the user interrupted the search or because we
915 // ran out of time. In this case, the return value of the search cannot
916 // be trusted, and we break out of the loop without updating the best
921 // Remember beta-cutoff and searched nodes counts for this move. The
922 // info is used to sort the root moves for the next iteration.
924 TM.get_beta_counters(pos.side_to_move(), our, their);
925 rml.set_beta_counters(i, our, their);
926 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
928 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
929 assert(value < beta);
931 // Step 17. Check for new best move
932 if (value <= alpha && i >= MultiPV)
933 rml.set_move_score(i, -VALUE_INFINITE);
936 // PV move or new best move!
939 rml.set_move_score(i, value);
941 TT.extract_pv(pos, move, pv, PLY_MAX);
942 rml.set_move_pv(i, pv);
946 // We record how often the best move has been changed in each
947 // iteration. This information is used for time managment: When
948 // the best move changes frequently, we allocate some more time.
950 BestMoveChangesByIteration[Iteration]++;
952 // Print information to the standard output
953 print_pv_info(pos, pv, alpha, beta, value);
955 // Raise alpha to setup proper non-pv search upper bound
962 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
964 cout << "info multipv " << j + 1
965 << " score " << value_to_uci(rml.get_move_score(j))
966 << " depth " << (j <= i ? Iteration : Iteration - 1)
967 << " time " << current_search_time()
968 << " nodes " << TM.nodes_searched()
972 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
973 cout << rml.get_move_pv(j, k) << " ";
977 alpha = rml.get_move_score(Min(i, MultiPV - 1));
979 } // PV move or new best move
981 assert(alpha >= *alphaPtr);
983 AspirationFailLow = (alpha == *alphaPtr);
985 if (AspirationFailLow && StopOnPonderhit)
986 StopOnPonderhit = false;
989 // Can we exit fail low loop ?
990 if (AbortSearch || !AspirationFailLow)
993 // Prepare for a research after a fail low, each time with a wider window
994 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
999 // Sort the moves before to return
1006 // search<>() is the main search function for both PV and non-PV nodes
1008 template <NodeType PvNode>
1009 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1011 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1012 assert(beta > alpha && beta <= VALUE_INFINITE);
1013 assert(PvNode || alpha == beta - 1);
1014 assert(ply > 0 && ply < PLY_MAX);
1015 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1017 Move movesSearched[256];
1022 Move ttMove, move, excludedMove;
1023 Depth ext, newDepth;
1024 Value bestValue, value, oldAlpha;
1025 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1026 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
1027 bool mateThreat = false;
1029 int threadID = pos.thread();
1030 refinedValue = bestValue = value = -VALUE_INFINITE;
1033 // Step 1. Initialize node and poll. Polling can abort search
1034 TM.incrementNodeCounter(threadID);
1036 (ss+2)->initKillers();
1038 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1044 // Step 2. Check for aborted search and immediate draw
1045 if (AbortSearch || TM.thread_should_stop(threadID))
1048 if (pos.is_draw() || ply >= PLY_MAX - 1)
1051 // Step 3. Mate distance pruning
1052 alpha = Max(value_mated_in(ply), alpha);
1053 beta = Min(value_mate_in(ply+1), beta);
1057 // Step 4. Transposition table lookup
1059 // We don't want the score of a partial search to overwrite a previous full search
1060 // TT value, so we use a different position key in case of an excluded move exists.
1061 excludedMove = ss->excludedMove;
1062 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1064 tte = TT.retrieve(posKey);
1065 ttMove = (tte ? tte->move() : MOVE_NONE);
1067 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1068 // This is to avoid problems in the following areas:
1070 // * Repetition draw detection
1071 // * Fifty move rule detection
1072 // * Searching for a mate
1073 // * Printing of full PV line
1075 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1077 // Refresh tte entry to avoid aging
1078 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1080 ss->currentMove = ttMove; // Can be MOVE_NONE
1081 return value_from_tt(tte->value(), ply);
1084 // Step 5. Evaluate the position statically
1085 // At PV nodes we do this only to update gain statistics
1086 isCheck = pos.is_check();
1089 if (tte && tte->static_value() != VALUE_NONE)
1091 ss->eval = tte->static_value();
1092 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1095 ss->eval = evaluate(pos, ei);
1097 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1098 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1101 // Step 6. Razoring (is omitted in PV nodes)
1103 && depth < RazorDepth
1105 && refinedValue < beta - razor_margin(depth)
1106 && ttMove == MOVE_NONE
1107 && (ss-1)->currentMove != MOVE_NULL
1108 && !value_is_mate(beta)
1109 && !pos.has_pawn_on_7th(pos.side_to_move()))
1111 // Pass ss->eval to qsearch() and avoid an evaluate call
1112 if (!tte || tte->static_value() == VALUE_NONE)
1113 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1115 Value rbeta = beta - razor_margin(depth);
1116 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1118 // Logically we should return (v + razor_margin(depth)), but
1119 // surprisingly this did slightly weaker in tests.
1123 // Step 7. Static null move pruning (is omitted in PV nodes)
1124 // We're betting that the opponent doesn't have a move that will reduce
1125 // the score by more than futility_margin(depth) if we do a null move.
1127 && !ss->skipNullMove
1128 && depth < RazorDepth
1129 && refinedValue >= beta + futility_margin(depth, 0)
1131 && !value_is_mate(beta)
1132 && pos.non_pawn_material(pos.side_to_move()))
1133 return refinedValue - futility_margin(depth, 0);
1135 // Step 8. Null move search with verification search (is omitted in PV nodes)
1136 // When we jump directly to qsearch() we do a null move only if static value is
1137 // at least beta. Otherwise we do a null move if static value is not more than
1138 // NullMoveMargin under beta.
1140 && !ss->skipNullMove
1142 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1144 && !value_is_mate(beta)
1145 && pos.non_pawn_material(pos.side_to_move()))
1147 ss->currentMove = MOVE_NULL;
1149 // Null move dynamic reduction based on depth
1150 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1152 // Null move dynamic reduction based on value
1153 if (refinedValue - beta > PawnValueMidgame)
1156 pos.do_null_move(st);
1157 (ss+1)->skipNullMove = true;
1159 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1160 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1161 (ss+1)->skipNullMove = false;
1162 pos.undo_null_move();
1164 if (nullValue >= beta)
1166 // Do not return unproven mate scores
1167 if (nullValue >= value_mate_in(PLY_MAX))
1170 if (depth < 6 * OnePly)
1173 // Do verification search at high depths
1174 ss->skipNullMove = true;
1175 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1176 ss->skipNullMove = false;
1183 // The null move failed low, which means that we may be faced with
1184 // some kind of threat. If the previous move was reduced, check if
1185 // the move that refuted the null move was somehow connected to the
1186 // move which was reduced. If a connection is found, return a fail
1187 // low score (which will cause the reduced move to fail high in the
1188 // parent node, which will trigger a re-search with full depth).
1189 if (nullValue == value_mated_in(ply + 2))
1192 ss->threatMove = (ss+1)->currentMove;
1193 if ( depth < ThreatDepth
1194 && (ss-1)->reduction
1195 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1200 // Step 9. Internal iterative deepening
1201 if ( depth >= IIDDepth[PvNode]
1202 && ttMove == MOVE_NONE
1203 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1205 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1207 ss->skipNullMove = true;
1208 search<PvNode>(pos, ss, alpha, beta, d, ply);
1209 ss->skipNullMove = false;
1211 ttMove = ss->bestMove;
1212 tte = TT.retrieve(posKey);
1215 // Expensive mate threat detection (only for PV nodes)
1217 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1219 // Initialize a MovePicker object for the current position
1220 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1222 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1223 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1224 && tte && tte->move()
1225 && !excludedMove // Do not allow recursive singular extension search
1226 && is_lower_bound(tte->type())
1227 && tte->depth() >= depth - 3 * OnePly;
1229 // Step 10. Loop through moves
1230 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1231 while ( bestValue < beta
1232 && (move = mp.get_next_move()) != MOVE_NONE
1233 && !TM.thread_should_stop(threadID))
1235 assert(move_is_ok(move));
1237 if (move == excludedMove)
1240 moveIsCheck = pos.move_is_check(move, ci);
1241 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1243 // Step 11. Decide the new search depth
1244 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1246 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1247 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1248 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1249 // lower then ttValue minus a margin then we extend ttMove.
1250 if ( singularExtensionNode
1251 && move == tte->move()
1254 Value ttValue = value_from_tt(tte->value(), ply);
1256 if (abs(ttValue) < VALUE_KNOWN_WIN)
1258 Value b = ttValue - SingularExtensionMargin;
1259 ss->excludedMove = move;
1260 ss->skipNullMove = true;
1261 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1262 ss->skipNullMove = false;
1263 ss->excludedMove = MOVE_NONE;
1269 newDepth = depth - OnePly + ext;
1271 // Update current move (this must be done after singular extension search)
1272 movesSearched[moveCount++] = ss->currentMove = move;
1274 // Step 12. Futility pruning (is omitted in PV nodes)
1276 && !captureOrPromotion
1280 && !move_is_castle(move))
1282 // Move count based pruning
1283 if ( moveCount >= futility_move_count(depth)
1284 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1285 && bestValue > value_mated_in(PLY_MAX))
1288 // Value based pruning
1289 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1290 // but fixing this made program slightly weaker.
1291 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1292 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1293 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1295 if (futilityValueScaled < beta)
1297 if (futilityValueScaled > bestValue)
1298 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 (PvNode && moveCount == 1)
1309 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), 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 * OnePly
1318 && !captureOrPromotion
1320 && !move_is_castle(move)
1321 && !move_is_killer(move, ss))
1323 ss->reduction = reduction<PvNode>(depth, moveCount);
1326 Depth d = newDepth - ss->reduction;
1327 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1328 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1330 doFullDepthSearch = (value > alpha);
1333 // The move failed high, but if reduction is very big we could
1334 // face a false positive, retry with a less aggressive reduction,
1335 // if the move fails high again then go with full depth search.
1336 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1338 assert(newDepth - OnePly >= OnePly);
1340 ss->reduction = OnePly;
1341 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1342 doFullDepthSearch = (value > alpha);
1344 ss->reduction = Depth(0); // Restore original reduction
1347 // Step 15. Full depth search
1348 if (doFullDepthSearch)
1350 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1351 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1353 // Step extra. pv search (only in PV nodes)
1354 // Search only for possible new PV nodes, if instead value >= beta then
1355 // parent node fails low with value <= alpha and tries another move.
1356 if (PvNode && value > alpha && value < beta)
1357 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1358 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1362 // Step 16. Undo move
1363 pos.undo_move(move);
1365 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1367 // Step 17. Check for new best move
1368 if (value > bestValue)
1373 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1376 if (value == value_mate_in(ply + 1))
1377 ss->mateKiller = move;
1379 ss->bestMove = move;
1383 // Step 18. Check for split
1384 if ( depth >= MinimumSplitDepth
1385 && TM.active_threads() > 1
1387 && TM.available_thread_exists(threadID)
1389 && !TM.thread_should_stop(threadID)
1391 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1392 mateThreat, &moveCount, &mp, PvNode);
1395 // Step 19. Check for mate and stalemate
1396 // All legal moves have been searched and if there are
1397 // no legal moves, it must be mate or stalemate.
1398 // If one move was excluded return fail low score.
1400 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1402 // Step 20. Update tables
1403 // If the search is not aborted, update the transposition table,
1404 // history counters, and killer moves.
1405 if (AbortSearch || TM.thread_should_stop(threadID))
1408 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1409 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1410 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1412 // Update killers and history only for non capture moves that fails high
1413 if (bestValue >= beta)
1415 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1416 if (!pos.move_is_capture_or_promotion(move))
1418 update_history(pos, move, depth, movesSearched, moveCount);
1419 update_killers(move, ss);
1423 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1429 // qsearch() is the quiescence search function, which is called by the main
1430 // search function when the remaining depth is zero (or, to be more precise,
1431 // less than OnePly).
1433 template <NodeType PvNode>
1434 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1436 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1437 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1438 assert(PvNode || alpha == beta - 1);
1440 assert(ply > 0 && ply < PLY_MAX);
1441 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1446 Value bestValue, value, futilityValue, futilityBase;
1447 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1449 Value oldAlpha = alpha;
1451 TM.incrementNodeCounter(pos.thread());
1452 ss->bestMove = ss->currentMove = MOVE_NONE;
1453 ss->eval = VALUE_NONE;
1455 // Check for an instant draw or maximum ply reached
1456 if (pos.is_draw() || ply >= PLY_MAX - 1)
1459 // Transposition table lookup. At PV nodes, we don't use the TT for
1460 // pruning, but only for move ordering.
1461 tte = TT.retrieve(pos.get_key());
1462 ttMove = (tte ? tte->move() : MOVE_NONE);
1464 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1466 ss->currentMove = ttMove; // Can be MOVE_NONE
1467 return value_from_tt(tte->value(), ply);
1470 isCheck = pos.is_check();
1472 // Evaluate the position statically
1475 bestValue = futilityBase = -VALUE_INFINITE;
1476 deepChecks = enoughMaterial = false;
1480 if (tte && tte->static_value() != VALUE_NONE)
1482 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1483 bestValue = tte->static_value();
1486 bestValue = evaluate(pos, ei);
1488 ss->eval = bestValue;
1489 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1491 // Stand pat. Return immediately if static value is at least beta
1492 if (bestValue >= beta)
1495 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1500 if (PvNode && bestValue > alpha)
1503 // If we are near beta then try to get a cutoff pushing checks a bit further
1504 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1506 // Futility pruning parameters, not needed when in check
1507 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1508 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1511 // Initialize a MovePicker object for the current position, and prepare
1512 // to search the moves. Because the depth is <= 0 here, only captures,
1513 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1514 // and we are near beta) will be generated.
1515 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1518 // Loop through the moves until no moves remain or a beta cutoff occurs
1519 while ( alpha < beta
1520 && (move = mp.get_next_move()) != MOVE_NONE)
1522 assert(move_is_ok(move));
1524 moveIsCheck = pos.move_is_check(move, ci);
1532 && !move_is_promotion(move)
1533 && !pos.move_is_passed_pawn_push(move))
1535 futilityValue = futilityBase
1536 + pos.endgame_value_of_piece_on(move_to(move))
1537 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1539 if (futilityValue < alpha)
1541 if (futilityValue > bestValue)
1542 bestValue = futilityValue;
1547 // Detect blocking evasions that are candidate to be pruned
1548 evasionPrunable = isCheck
1549 && bestValue > value_mated_in(PLY_MAX)
1550 && !pos.move_is_capture(move)
1551 && pos.type_of_piece_on(move_from(move)) != KING
1552 && !pos.can_castle(pos.side_to_move());
1554 // Don't search moves with negative SEE values
1556 && (!isCheck || evasionPrunable)
1558 && !move_is_promotion(move)
1559 && pos.see_sign(move) < 0)
1562 // Update current move
1563 ss->currentMove = move;
1565 // Make and search the move
1566 pos.do_move(move, st, ci, moveIsCheck);
1567 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1568 pos.undo_move(move);
1570 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1573 if (value > bestValue)
1579 ss->bestMove = move;
1584 // All legal moves have been searched. A special case: If we're in check
1585 // and no legal moves were found, it is checkmate.
1586 if (isCheck && bestValue == -VALUE_INFINITE)
1587 return value_mated_in(ply);
1589 // Update transposition table
1590 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1591 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1592 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1594 // Update killers only for checking moves that fails high
1595 if ( bestValue >= beta
1596 && !pos.move_is_capture_or_promotion(ss->bestMove))
1597 update_killers(ss->bestMove, ss);
1599 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1605 // sp_search() is used to search from a split point. This function is called
1606 // by each thread working at the split point. It is similar to the normal
1607 // search() function, but simpler. Because we have already probed the hash
1608 // table, done a null move search, and searched the first move before
1609 // splitting, we don't have to repeat all this work in sp_search(). We
1610 // also don't need to store anything to the hash table here: This is taken
1611 // care of after we return from the split point.
1613 template <NodeType PvNode>
1614 void sp_search(SplitPoint* sp, int threadID) {
1616 assert(threadID >= 0 && threadID < TM.active_threads());
1617 assert(TM.active_threads() > 1);
1621 Depth ext, newDepth;
1623 Value futilityValueScaled; // NonPV specific
1624 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1626 value = -VALUE_INFINITE;
1628 Position pos(*sp->pos, threadID);
1630 SearchStack* ss = sp->sstack[threadID] + 1;
1631 isCheck = pos.is_check();
1633 // Step 10. Loop through moves
1634 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1635 lock_grab(&(sp->lock));
1637 while ( sp->bestValue < sp->beta
1638 && (move = sp->mp->get_next_move()) != MOVE_NONE
1639 && !TM.thread_should_stop(threadID))
1641 moveCount = ++sp->moveCount;
1642 lock_release(&(sp->lock));
1644 assert(move_is_ok(move));
1646 moveIsCheck = pos.move_is_check(move, ci);
1647 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1649 // Step 11. Decide the new search depth
1650 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1651 newDepth = sp->depth - OnePly + ext;
1653 // Update current move
1654 ss->currentMove = move;
1656 // Step 12. Futility pruning (is omitted in PV nodes)
1658 && !captureOrPromotion
1661 && !move_is_castle(move))
1663 // Move count based pruning
1664 if ( moveCount >= futility_move_count(sp->depth)
1665 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1666 && sp->bestValue > value_mated_in(PLY_MAX))
1668 lock_grab(&(sp->lock));
1672 // Value based pruning
1673 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1674 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1675 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1677 if (futilityValueScaled < sp->beta)
1679 lock_grab(&(sp->lock));
1681 if (futilityValueScaled > sp->bestValue)
1682 sp->bestValue = futilityValueScaled;
1687 // Step 13. Make the move
1688 pos.do_move(move, st, ci, moveIsCheck);
1690 // Step 14. Reduced search
1691 // If the move fails high will be re-searched at full depth.
1692 bool doFullDepthSearch = true;
1694 if ( !captureOrPromotion
1696 && !move_is_castle(move)
1697 && !move_is_killer(move, ss))
1699 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1702 Value localAlpha = sp->alpha;
1703 Depth d = newDepth - ss->reduction;
1704 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1705 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1707 doFullDepthSearch = (value > localAlpha);
1710 // The move failed high, but if reduction is very big we could
1711 // face a false positive, retry with a less aggressive reduction,
1712 // if the move fails high again then go with full depth search.
1713 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1715 assert(newDepth - OnePly >= OnePly);
1717 ss->reduction = OnePly;
1718 Value localAlpha = sp->alpha;
1719 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1720 doFullDepthSearch = (value > localAlpha);
1722 ss->reduction = Depth(0); // Restore original reduction
1725 // Step 15. Full depth search
1726 if (doFullDepthSearch)
1728 Value localAlpha = sp->alpha;
1729 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1730 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1732 // Step extra. pv search (only in PV nodes)
1733 // Search only for possible new PV nodes, if instead value >= beta then
1734 // parent node fails low with value <= alpha and tries another move.
1735 if (PvNode && value > localAlpha && value < sp->beta)
1736 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1737 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1740 // Step 16. Undo move
1741 pos.undo_move(move);
1743 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1745 // Step 17. Check for new best move
1746 lock_grab(&(sp->lock));
1748 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1750 sp->bestValue = value;
1752 if (sp->bestValue > sp->alpha)
1754 if (!PvNode || value >= sp->beta)
1755 sp->stopRequest = true;
1757 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1760 sp->parentSstack->bestMove = ss->bestMove = move;
1765 /* Here we have the lock still grabbed */
1767 sp->slaves[threadID] = 0;
1769 lock_release(&(sp->lock));
1773 // connected_moves() tests whether two moves are 'connected' in the sense
1774 // that the first move somehow made the second move possible (for instance
1775 // if the moving piece is the same in both moves). The first move is assumed
1776 // to be the move that was made to reach the current position, while the
1777 // second move is assumed to be a move from the current position.
1779 bool connected_moves(const Position& pos, Move m1, Move m2) {
1781 Square f1, t1, f2, t2;
1784 assert(move_is_ok(m1));
1785 assert(move_is_ok(m2));
1787 if (m2 == MOVE_NONE)
1790 // Case 1: The moving piece is the same in both moves
1796 // Case 2: The destination square for m2 was vacated by m1
1802 // Case 3: Moving through the vacated square
1803 if ( piece_is_slider(pos.piece_on(f2))
1804 && bit_is_set(squares_between(f2, t2), f1))
1807 // Case 4: The destination square for m2 is defended by the moving piece in m1
1808 p = pos.piece_on(t1);
1809 if (bit_is_set(pos.attacks_from(p, t1), t2))
1812 // Case 5: Discovered check, checking piece is the piece moved in m1
1813 if ( piece_is_slider(p)
1814 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1815 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1817 // discovered_check_candidates() works also if the Position's side to
1818 // move is the opposite of the checking piece.
1819 Color them = opposite_color(pos.side_to_move());
1820 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1822 if (bit_is_set(dcCandidates, f2))
1829 // value_is_mate() checks if the given value is a mate one eventually
1830 // compensated for the ply.
1832 bool value_is_mate(Value value) {
1834 assert(abs(value) <= VALUE_INFINITE);
1836 return value <= value_mated_in(PLY_MAX)
1837 || value >= value_mate_in(PLY_MAX);
1841 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1842 // "plies to mate from the current ply". Non-mate scores are unchanged.
1843 // The function is called before storing a value to the transposition table.
1845 Value value_to_tt(Value v, int ply) {
1847 if (v >= value_mate_in(PLY_MAX))
1850 if (v <= value_mated_in(PLY_MAX))
1857 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1858 // the transposition table to a mate score corrected for the current ply.
1860 Value value_from_tt(Value v, int ply) {
1862 if (v >= value_mate_in(PLY_MAX))
1865 if (v <= value_mated_in(PLY_MAX))
1872 // move_is_killer() checks if the given move is among the killer moves
1874 bool move_is_killer(Move m, SearchStack* ss) {
1876 const Move* k = ss->killers;
1877 for (int i = 0; i < KILLER_MAX; i++, k++)
1885 // extension() decides whether a move should be searched with normal depth,
1886 // or with extended depth. Certain classes of moves (checking moves, in
1887 // particular) are searched with bigger depth than ordinary moves and in
1888 // any case are marked as 'dangerous'. Note that also if a move is not
1889 // extended, as example because the corresponding UCI option is set to zero,
1890 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1891 template <NodeType PvNode>
1892 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1893 bool singleEvasion, bool mateThreat, bool* dangerous) {
1895 assert(m != MOVE_NONE);
1897 Depth result = Depth(0);
1898 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1902 if (moveIsCheck && pos.see_sign(m) >= 0)
1903 result += CheckExtension[PvNode];
1906 result += SingleEvasionExtension[PvNode];
1909 result += MateThreatExtension[PvNode];
1912 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1914 Color c = pos.side_to_move();
1915 if (relative_rank(c, move_to(m)) == RANK_7)
1917 result += PawnPushTo7thExtension[PvNode];
1920 if (pos.pawn_is_passed(c, move_to(m)))
1922 result += PassedPawnExtension[PvNode];
1927 if ( captureOrPromotion
1928 && pos.type_of_piece_on(move_to(m)) != PAWN
1929 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1930 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1931 && !move_is_promotion(m)
1934 result += PawnEndgameExtension[PvNode];
1939 && captureOrPromotion
1940 && pos.type_of_piece_on(move_to(m)) != PAWN
1941 && pos.see_sign(m) >= 0)
1947 return Min(result, OnePly);
1951 // connected_threat() tests whether it is safe to forward prune a move or if
1952 // is somehow coonected to the threat move returned by null search.
1954 bool connected_threat(const Position& pos, Move m, Move threat) {
1956 assert(move_is_ok(m));
1957 assert(threat && move_is_ok(threat));
1958 assert(!pos.move_is_check(m));
1959 assert(!pos.move_is_capture_or_promotion(m));
1960 assert(!pos.move_is_passed_pawn_push(m));
1962 Square mfrom, mto, tfrom, tto;
1964 mfrom = move_from(m);
1966 tfrom = move_from(threat);
1967 tto = move_to(threat);
1969 // Case 1: Don't prune moves which move the threatened piece
1973 // Case 2: If the threatened piece has value less than or equal to the
1974 // value of the threatening piece, don't prune move which defend it.
1975 if ( pos.move_is_capture(threat)
1976 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1977 || pos.type_of_piece_on(tfrom) == KING)
1978 && pos.move_attacks_square(m, tto))
1981 // Case 3: If the moving piece in the threatened move is a slider, don't
1982 // prune safe moves which block its ray.
1983 if ( piece_is_slider(pos.piece_on(tfrom))
1984 && bit_is_set(squares_between(tfrom, tto), mto)
1985 && pos.see_sign(m) >= 0)
1992 // ok_to_use_TT() returns true if a transposition table score
1993 // can be used at a given point in search.
1995 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1997 Value v = value_from_tt(tte->value(), ply);
1999 return ( tte->depth() >= depth
2000 || v >= Max(value_mate_in(PLY_MAX), beta)
2001 || v < Min(value_mated_in(PLY_MAX), beta))
2003 && ( (is_lower_bound(tte->type()) && v >= beta)
2004 || (is_upper_bound(tte->type()) && v < beta));
2008 // refine_eval() returns the transposition table score if
2009 // possible otherwise falls back on static position evaluation.
2011 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2016 Value v = value_from_tt(tte->value(), ply);
2018 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2019 || (is_upper_bound(tte->type()) && v < defaultEval))
2026 // update_history() registers a good move that produced a beta-cutoff
2027 // in history and marks as failures all the other moves of that ply.
2029 void update_history(const Position& pos, Move move, Depth depth,
2030 Move movesSearched[], int moveCount) {
2034 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2036 for (int i = 0; i < moveCount - 1; i++)
2038 m = movesSearched[i];
2042 if (!pos.move_is_capture_or_promotion(m))
2043 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2048 // update_killers() add a good move that produced a beta-cutoff
2049 // among the killer moves of that ply.
2051 void update_killers(Move m, SearchStack* ss) {
2053 if (m == ss->killers[0])
2056 for (int i = KILLER_MAX - 1; i > 0; i--)
2057 ss->killers[i] = ss->killers[i - 1];
2063 // update_gains() updates the gains table of a non-capture move given
2064 // the static position evaluation before and after the move.
2066 void update_gains(const Position& pos, Move m, Value before, Value after) {
2069 && before != VALUE_NONE
2070 && after != VALUE_NONE
2071 && pos.captured_piece() == NO_PIECE_TYPE
2072 && !move_is_castle(m)
2073 && !move_is_promotion(m))
2074 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2078 // current_search_time() returns the number of milliseconds which have passed
2079 // since the beginning of the current search.
2081 int current_search_time() {
2083 return get_system_time() - SearchStartTime;
2087 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2089 std::string value_to_uci(Value v) {
2091 std::stringstream s;
2093 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2094 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2096 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2101 // nps() computes the current nodes/second count.
2105 int t = current_search_time();
2106 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2110 // poll() performs two different functions: It polls for user input, and it
2111 // looks at the time consumed so far and decides if it's time to abort the
2116 static int lastInfoTime;
2117 int t = current_search_time();
2122 // We are line oriented, don't read single chars
2123 std::string command;
2125 if (!std::getline(std::cin, command))
2128 if (command == "quit")
2131 PonderSearch = false;
2135 else if (command == "stop")
2138 PonderSearch = false;
2140 else if (command == "ponderhit")
2144 // Print search information
2148 else if (lastInfoTime > t)
2149 // HACK: Must be a new search where we searched less than
2150 // NodesBetweenPolls nodes during the first second of search.
2153 else if (t - lastInfoTime >= 1000)
2160 if (dbg_show_hit_rate)
2161 dbg_print_hit_rate();
2163 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2164 << " time " << t << endl;
2167 // Should we stop the search?
2171 bool stillAtFirstMove = FirstRootMove
2172 && !AspirationFailLow
2173 && t > MaxSearchTime + ExtraSearchTime;
2175 bool noMoreTime = t > AbsoluteMaxSearchTime
2176 || stillAtFirstMove;
2178 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2179 || (ExactMaxTime && t >= ExactMaxTime)
2180 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2185 // ponderhit() is called when the program is pondering (i.e. thinking while
2186 // it's the opponent's turn to move) in order to let the engine know that
2187 // it correctly predicted the opponent's move.
2191 int t = current_search_time();
2192 PonderSearch = false;
2194 bool stillAtFirstMove = FirstRootMove
2195 && !AspirationFailLow
2196 && t > MaxSearchTime + ExtraSearchTime;
2198 bool noMoreTime = t > AbsoluteMaxSearchTime
2199 || stillAtFirstMove;
2201 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2206 // init_ss_array() does a fast reset of the first entries of a SearchStack
2207 // array and of all the excludedMove and skipNullMove entries.
2209 void init_ss_array(SearchStack* ss, int size) {
2211 for (int i = 0; i < size; i++, ss++)
2213 ss->excludedMove = MOVE_NONE;
2214 ss->skipNullMove = false;
2225 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2226 // while the program is pondering. The point is to work around a wrinkle in
2227 // the UCI protocol: When pondering, the engine is not allowed to give a
2228 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2229 // We simply wait here until one of these commands is sent, and return,
2230 // after which the bestmove and pondermove will be printed (in id_loop()).
2232 void wait_for_stop_or_ponderhit() {
2234 std::string command;
2238 if (!std::getline(std::cin, command))
2241 if (command == "quit")
2246 else if (command == "ponderhit" || command == "stop")
2252 // print_pv_info() prints to standard output and eventually to log file information on
2253 // the current PV line. It is called at each iteration or after a new pv is found.
2255 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2257 cout << "info depth " << Iteration
2258 << " score " << value_to_uci(value)
2259 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2260 << " time " << current_search_time()
2261 << " nodes " << TM.nodes_searched()
2265 for (Move* m = pv; *m != MOVE_NONE; m++)
2272 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2273 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2275 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2276 TM.nodes_searched(), value, t, pv) << endl;
2281 // init_thread() is the function which is called when a new thread is
2282 // launched. It simply calls the idle_loop() function with the supplied
2283 // threadID. There are two versions of this function; one for POSIX
2284 // threads and one for Windows threads.
2286 #if !defined(_MSC_VER)
2288 void* init_thread(void *threadID) {
2290 TM.idle_loop(*(int*)threadID, NULL);
2296 DWORD WINAPI init_thread(LPVOID threadID) {
2298 TM.idle_loop(*(int*)threadID, NULL);
2305 /// The ThreadsManager class
2307 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2308 // get_beta_counters() are getters/setters for the per thread
2309 // counters used to sort the moves at root.
2311 void ThreadsManager::resetNodeCounters() {
2313 for (int i = 0; i < MAX_THREADS; i++)
2314 threads[i].nodes = 0ULL;
2317 void ThreadsManager::resetBetaCounters() {
2319 for (int i = 0; i < MAX_THREADS; i++)
2320 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2323 int64_t ThreadsManager::nodes_searched() const {
2325 int64_t result = 0ULL;
2326 for (int i = 0; i < ActiveThreads; i++)
2327 result += threads[i].nodes;
2332 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2335 for (int i = 0; i < MAX_THREADS; i++)
2337 our += threads[i].betaCutOffs[us];
2338 their += threads[i].betaCutOffs[opposite_color(us)];
2343 // idle_loop() is where the threads are parked when they have no work to do.
2344 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2345 // object for which the current thread is the master.
2347 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2349 assert(threadID >= 0 && threadID < MAX_THREADS);
2353 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2354 // master should exit as last one.
2355 if (AllThreadsShouldExit)
2358 threads[threadID].state = THREAD_TERMINATED;
2362 // If we are not thinking, wait for a condition to be signaled
2363 // instead of wasting CPU time polling for work.
2364 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2367 assert(threadID != 0);
2368 threads[threadID].state = THREAD_SLEEPING;
2370 #if !defined(_MSC_VER)
2371 lock_grab(&WaitLock);
2372 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2373 pthread_cond_wait(&WaitCond, &WaitLock);
2374 lock_release(&WaitLock);
2376 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2380 // If thread has just woken up, mark it as available
2381 if (threads[threadID].state == THREAD_SLEEPING)
2382 threads[threadID].state = THREAD_AVAILABLE;
2384 // If this thread has been assigned work, launch a search
2385 if (threads[threadID].state == THREAD_WORKISWAITING)
2387 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2389 threads[threadID].state = THREAD_SEARCHING;
2391 if (threads[threadID].splitPoint->pvNode)
2392 sp_search<PV>(threads[threadID].splitPoint, threadID);
2394 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2396 assert(threads[threadID].state == THREAD_SEARCHING);
2398 threads[threadID].state = THREAD_AVAILABLE;
2401 // If this thread is the master of a split point and all slaves have
2402 // finished their work at this split point, return from the idle loop.
2404 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2406 if (i == ActiveThreads)
2408 // Because sp->slaves[] is reset under lock protection,
2409 // be sure sp->lock has been released before to return.
2410 lock_grab(&(sp->lock));
2411 lock_release(&(sp->lock));
2413 assert(threads[threadID].state == THREAD_AVAILABLE);
2415 threads[threadID].state = THREAD_SEARCHING;
2422 // init_threads() is called during startup. It launches all helper threads,
2423 // and initializes the split point stack and the global locks and condition
2426 void ThreadsManager::init_threads() {
2431 #if !defined(_MSC_VER)
2432 pthread_t pthread[1];
2435 // Initialize global locks
2436 lock_init(&MPLock, NULL);
2437 lock_init(&WaitLock, NULL);
2439 #if !defined(_MSC_VER)
2440 pthread_cond_init(&WaitCond, NULL);
2442 for (i = 0; i < MAX_THREADS; i++)
2443 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2446 // Initialize splitPoints[] locks
2447 for (i = 0; i < MAX_THREADS; i++)
2448 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2449 lock_init(&(threads[i].splitPoints[j].lock), NULL);
2451 // Will be set just before program exits to properly end the threads
2452 AllThreadsShouldExit = false;
2454 // Threads will be put to sleep as soon as created
2455 AllThreadsShouldSleep = true;
2457 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2459 threads[0].state = THREAD_SEARCHING;
2460 for (i = 1; i < MAX_THREADS; i++)
2461 threads[i].state = THREAD_AVAILABLE;
2463 // Launch the helper threads
2464 for (i = 1; i < MAX_THREADS; i++)
2467 #if !defined(_MSC_VER)
2468 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2470 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2475 cout << "Failed to create thread number " << i << endl;
2476 Application::exit_with_failure();
2479 // Wait until the thread has finished launching and is gone to sleep
2480 while (threads[i].state != THREAD_SLEEPING) {}
2485 // exit_threads() is called when the program exits. It makes all the
2486 // helper threads exit cleanly.
2488 void ThreadsManager::exit_threads() {
2490 ActiveThreads = MAX_THREADS; // HACK
2491 AllThreadsShouldSleep = true; // HACK
2492 wake_sleeping_threads();
2494 // This makes the threads to exit idle_loop()
2495 AllThreadsShouldExit = true;
2497 // Wait for thread termination
2498 for (int i = 1; i < MAX_THREADS; i++)
2499 while (threads[i].state != THREAD_TERMINATED) {}
2501 // Now we can safely destroy the locks
2502 for (int i = 0; i < MAX_THREADS; i++)
2503 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2504 lock_destroy(&(threads[i].splitPoints[j].lock));
2506 lock_destroy(&WaitLock);
2507 lock_destroy(&MPLock);
2511 // thread_should_stop() checks whether the thread should stop its search.
2512 // This can happen if a beta cutoff has occurred in the thread's currently
2513 // active split point, or in some ancestor of the current split point.
2515 bool ThreadsManager::thread_should_stop(int threadID) const {
2517 assert(threadID >= 0 && threadID < ActiveThreads);
2521 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2526 // thread_is_available() checks whether the thread with threadID "slave" is
2527 // available to help the thread with threadID "master" at a split point. An
2528 // obvious requirement is that "slave" must be idle. With more than two
2529 // threads, this is not by itself sufficient: If "slave" is the master of
2530 // some active split point, it is only available as a slave to the other
2531 // threads which are busy searching the split point at the top of "slave"'s
2532 // split point stack (the "helpful master concept" in YBWC terminology).
2534 bool ThreadsManager::thread_is_available(int slave, int master) const {
2536 assert(slave >= 0 && slave < ActiveThreads);
2537 assert(master >= 0 && master < ActiveThreads);
2538 assert(ActiveThreads > 1);
2540 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2543 // Make a local copy to be sure doesn't change under our feet
2544 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2546 if (localActiveSplitPoints == 0)
2547 // No active split points means that the thread is available as
2548 // a slave for any other thread.
2551 if (ActiveThreads == 2)
2554 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2555 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2556 // could have been set to 0 by another thread leading to an out of bound access.
2557 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2564 // available_thread_exists() tries to find an idle thread which is available as
2565 // a slave for the thread with threadID "master".
2567 bool ThreadsManager::available_thread_exists(int master) const {
2569 assert(master >= 0 && master < ActiveThreads);
2570 assert(ActiveThreads > 1);
2572 for (int i = 0; i < ActiveThreads; i++)
2573 if (thread_is_available(i, master))
2580 // split() does the actual work of distributing the work at a node between
2581 // several available threads. If it does not succeed in splitting the
2582 // node (because no idle threads are available, or because we have no unused
2583 // split point objects), the function immediately returns. If splitting is
2584 // possible, a SplitPoint object is initialized with all the data that must be
2585 // copied to the helper threads and we tell our helper threads that they have
2586 // been assigned work. This will cause them to instantly leave their idle loops
2587 // and call sp_search(). When all threads have returned from sp_search() then
2590 template <bool Fake>
2591 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2592 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2593 int* moveCount, MovePicker* mp, bool pvNode) {
2595 assert(ply > 0 && ply < PLY_MAX);
2596 assert(*bestValue >= -VALUE_INFINITE);
2597 assert(*bestValue <= *alpha);
2598 assert(*alpha < beta);
2599 assert(beta <= VALUE_INFINITE);
2600 assert(depth > Depth(0));
2601 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2602 assert(ActiveThreads > 1);
2604 int i, master = p.thread();
2605 Thread& masterThread = threads[master];
2609 // If no other thread is available to help us, or if we have too many
2610 // active split points, don't split.
2611 if ( !available_thread_exists(master)
2612 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2614 lock_release(&MPLock);
2618 // Pick the next available split point object from the split point stack
2619 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2621 // Initialize the split point object
2622 splitPoint.parent = masterThread.splitPoint;
2623 splitPoint.stopRequest = false;
2624 splitPoint.ply = ply;
2625 splitPoint.depth = depth;
2626 splitPoint.mateThreat = mateThreat;
2627 splitPoint.alpha = *alpha;
2628 splitPoint.beta = beta;
2629 splitPoint.pvNode = pvNode;
2630 splitPoint.bestValue = *bestValue;
2632 splitPoint.moveCount = *moveCount;
2633 splitPoint.pos = &p;
2634 splitPoint.parentSstack = ss;
2635 for (i = 0; i < ActiveThreads; i++)
2636 splitPoint.slaves[i] = 0;
2638 masterThread.splitPoint = &splitPoint;
2640 // If we are here it means we are not available
2641 assert(masterThread.state != THREAD_AVAILABLE);
2643 int workersCnt = 1; // At least the master is included
2645 // Allocate available threads setting state to THREAD_BOOKED
2646 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2647 if (thread_is_available(i, master))
2649 threads[i].state = THREAD_BOOKED;
2650 threads[i].splitPoint = &splitPoint;
2651 splitPoint.slaves[i] = 1;
2655 assert(Fake || workersCnt > 1);
2657 // We can release the lock because slave threads are already booked and master is not available
2658 lock_release(&MPLock);
2660 // Tell the threads that they have work to do. This will make them leave
2661 // their idle loop. But before copy search stack tail for each thread.
2662 for (i = 0; i < ActiveThreads; i++)
2663 if (i == master || splitPoint.slaves[i])
2665 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2667 assert(i == master || threads[i].state == THREAD_BOOKED);
2669 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2672 // Everything is set up. The master thread enters the idle loop, from
2673 // which it will instantly launch a search, because its state is
2674 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2675 // idle loop, which means that the main thread will return from the idle
2676 // loop when all threads have finished their work at this split point.
2677 idle_loop(master, &splitPoint);
2679 // We have returned from the idle loop, which means that all threads are
2680 // finished. Update alpha and bestValue, and return.
2683 *alpha = splitPoint.alpha;
2684 *bestValue = splitPoint.bestValue;
2685 masterThread.activeSplitPoints--;
2686 masterThread.splitPoint = splitPoint.parent;
2688 lock_release(&MPLock);
2692 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2693 // to start a new search from the root.
2695 void ThreadsManager::wake_sleeping_threads() {
2697 assert(AllThreadsShouldSleep);
2698 assert(ActiveThreads > 0);
2700 AllThreadsShouldSleep = false;
2702 if (ActiveThreads == 1)
2705 #if !defined(_MSC_VER)
2706 pthread_mutex_lock(&WaitLock);
2707 pthread_cond_broadcast(&WaitCond);
2708 pthread_mutex_unlock(&WaitLock);
2710 for (int i = 1; i < MAX_THREADS; i++)
2711 SetEvent(SitIdleEvent[i]);
2717 // put_threads_to_sleep() makes all the threads go to sleep just before
2718 // to leave think(), at the end of the search. Threads should have already
2719 // finished the job and should be idle.
2721 void ThreadsManager::put_threads_to_sleep() {
2723 assert(!AllThreadsShouldSleep);
2725 // This makes the threads to go to sleep
2726 AllThreadsShouldSleep = true;
2729 /// The RootMoveList class
2731 // RootMoveList c'tor
2733 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2735 SearchStack ss[PLY_MAX_PLUS_2];
2736 MoveStack mlist[MaxRootMoves];
2738 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2740 // Generate all legal moves
2741 MoveStack* last = generate_moves(pos, mlist);
2743 // Add each move to the moves[] array
2744 for (MoveStack* cur = mlist; cur != last; cur++)
2746 bool includeMove = includeAllMoves;
2748 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2749 includeMove = (searchMoves[k] == cur->move);
2754 // Find a quick score for the move
2755 init_ss_array(ss, PLY_MAX_PLUS_2);
2756 pos.do_move(cur->move, st);
2757 moves[count].move = cur->move;
2758 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2759 moves[count].pv[0] = cur->move;
2760 moves[count].pv[1] = MOVE_NONE;
2761 pos.undo_move(cur->move);
2768 // RootMoveList simple methods definitions
2770 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2772 moves[moveNum].nodes = nodes;
2773 moves[moveNum].cumulativeNodes += nodes;
2776 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2778 moves[moveNum].ourBeta = our;
2779 moves[moveNum].theirBeta = their;
2782 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2786 for (j = 0; pv[j] != MOVE_NONE; j++)
2787 moves[moveNum].pv[j] = pv[j];
2789 moves[moveNum].pv[j] = MOVE_NONE;
2793 // RootMoveList::sort() sorts the root move list at the beginning of a new
2796 void RootMoveList::sort() {
2798 sort_multipv(count - 1); // Sort all items
2802 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2803 // list by their scores and depths. It is used to order the different PVs
2804 // correctly in MultiPV mode.
2806 void RootMoveList::sort_multipv(int n) {
2810 for (i = 1; i <= n; i++)
2812 RootMove rm = moves[i];
2813 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2814 moves[j] = moves[j - 1];