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 = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
346 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
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;
368 // SearchStack::initKillers() initializes killers for a search stack entry
369 void SearchStack::initKillers() {
371 killers[0] = killers[1] = mateKiller = MOVE_NONE;
375 /// perft() is our utility to verify move generation is bug free. All the legal
376 /// moves up to given depth are generated and counted and the sum returned.
378 int perft(Position& pos, Depth depth)
383 MovePicker mp(pos, MOVE_NONE, depth, H);
385 // If we are at the last ply we don't need to do and undo
386 // the moves, just to count them.
387 if (depth <= OnePly) // Replace with '<' to test also qsearch
389 while (mp.get_next_move()) sum++;
393 // Loop through all legal moves
395 while ((move = mp.get_next_move()) != MOVE_NONE)
397 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
398 sum += perft(pos, depth - OnePly);
405 /// think() is the external interface to Stockfish's search, and is called when
406 /// the program receives the UCI 'go' command. It initializes various
407 /// search-related global variables, and calls root_search(). It returns false
408 /// when a quit command is received during the search.
410 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
411 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
413 // Initialize global search variables
414 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
415 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
417 TM.resetNodeCounters();
418 SearchStartTime = get_system_time();
419 ExactMaxTime = maxTime;
422 InfiniteSearch = infinite;
423 PonderSearch = ponder;
424 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
426 // Look for a book move, only during games, not tests
427 if (UseTimeManagement && get_option_value_bool("OwnBook"))
429 if (get_option_value_string("Book File") != OpeningBook.file_name())
430 OpeningBook.open(get_option_value_string("Book File"));
432 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
433 if (bookMove != MOVE_NONE)
436 wait_for_stop_or_ponderhit();
438 cout << "bestmove " << bookMove << endl;
443 // Read UCI option values
444 TT.set_size(get_option_value_int("Hash"));
445 if (button_was_pressed("Clear Hash"))
448 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
449 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
450 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
451 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
452 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
453 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
454 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
455 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
456 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
457 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
458 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
459 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
461 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
462 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
463 MultiPV = get_option_value_int("MultiPV");
464 Chess960 = get_option_value_bool("UCI_Chess960");
465 UseLogFile = get_option_value_bool("Use Search Log");
468 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
470 read_weights(pos.side_to_move());
472 // Set the number of active threads
473 int newActiveThreads = get_option_value_int("Threads");
474 if (newActiveThreads != TM.active_threads())
476 TM.set_active_threads(newActiveThreads);
477 init_eval(TM.active_threads());
480 // Wake up sleeping threads
481 TM.wake_sleeping_threads();
484 int myTime = time[pos.side_to_move()];
485 int myIncrement = increment[pos.side_to_move()];
486 if (UseTimeManagement)
488 if (!movesToGo) // Sudden death time control
492 MaxSearchTime = myTime / 30 + myIncrement;
493 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
495 else // Blitz game without increment
497 MaxSearchTime = myTime / 30;
498 AbsoluteMaxSearchTime = myTime / 8;
501 else // (x moves) / (y minutes)
505 MaxSearchTime = myTime / 2;
506 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
510 MaxSearchTime = myTime / Min(movesToGo, 20);
511 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
515 if (get_option_value_bool("Ponder"))
517 MaxSearchTime += MaxSearchTime / 4;
518 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
522 // Set best NodesBetweenPolls interval to avoid lagging under
523 // heavy time pressure.
525 NodesBetweenPolls = Min(MaxNodes, 30000);
526 else if (myTime && myTime < 1000)
527 NodesBetweenPolls = 1000;
528 else if (myTime && myTime < 5000)
529 NodesBetweenPolls = 5000;
531 NodesBetweenPolls = 30000;
533 // Write search information to log file
535 LogFile << "Searching: " << pos.to_fen() << endl
536 << "infinite: " << infinite
537 << " ponder: " << ponder
538 << " time: " << myTime
539 << " increment: " << myIncrement
540 << " moves to go: " << movesToGo << endl;
542 // We're ready to start thinking. Call the iterative deepening loop function
543 id_loop(pos, searchMoves);
548 TM.put_threads_to_sleep();
556 // id_loop() is the main iterative deepening loop. It calls root_search
557 // repeatedly with increasing depth until the allocated thinking time has
558 // been consumed, the user stops the search, or the maximum search depth is
561 Value id_loop(const Position& pos, Move searchMoves[]) {
563 Position p(pos, pos.thread());
564 SearchStack ss[PLY_MAX_PLUS_2];
565 Move pv[PLY_MAX_PLUS_2];
566 Move EasyMove = MOVE_NONE;
567 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
569 // Moves to search are verified, copied, scored and sorted
570 RootMoveList rml(p, searchMoves);
572 // Handle special case of searching on a mate/stale position
573 if (rml.move_count() == 0)
576 wait_for_stop_or_ponderhit();
578 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
581 // Print RootMoveList startup scoring to the standard output,
582 // so to output information also for iteration 1.
583 cout << "info depth " << 1
584 << "\ninfo depth " << 1
585 << " score " << value_to_uci(rml.get_move_score(0))
586 << " time " << current_search_time()
587 << " nodes " << TM.nodes_searched()
589 << " pv " << rml.get_move(0) << "\n";
594 init_ss_array(ss, PLY_MAX_PLUS_2);
595 pv[0] = pv[1] = MOVE_NONE;
596 ValueByIteration[1] = rml.get_move_score(0);
599 // Is one move significantly better than others after initial scoring ?
600 if ( rml.move_count() == 1
601 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
602 EasyMove = rml.get_move(0);
604 // Iterative deepening loop
605 while (Iteration < PLY_MAX)
607 // Initialize iteration
609 BestMoveChangesByIteration[Iteration] = 0;
611 cout << "info depth " << Iteration << endl;
613 // Calculate dynamic aspiration window based on previous iterations
614 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
616 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
617 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
619 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
620 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
622 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
623 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
626 // Search to the current depth, rml is updated and sorted, alpha and beta could change
627 value = root_search(p, ss, pv, rml, &alpha, &beta);
629 // Write PV to transposition table, in case the relevant entries have
630 // been overwritten during the search.
634 break; // Value cannot be trusted. Break out immediately!
636 //Save info about search result
637 ValueByIteration[Iteration] = value;
639 // Drop the easy move if differs from the new best move
640 if (pv[0] != EasyMove)
641 EasyMove = MOVE_NONE;
643 if (UseTimeManagement)
646 bool stopSearch = false;
648 // Stop search early if there is only a single legal move,
649 // we search up to Iteration 6 anyway to get a proper score.
650 if (Iteration >= 6 && rml.move_count() == 1)
653 // Stop search early when the last two iterations returned a mate score
655 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
656 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
659 // Stop search early if one move seems to be much better than the others
660 int64_t nodes = TM.nodes_searched();
663 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
664 && current_search_time() > MaxSearchTime / 16)
665 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
666 && current_search_time() > MaxSearchTime / 32)))
669 // Add some extra time if the best move has changed during the last two iterations
670 if (Iteration > 5 && Iteration <= 50)
671 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
672 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
674 // Stop search if most of MaxSearchTime is consumed at the end of the
675 // iteration. We probably don't have enough time to search the first
676 // move at the next iteration anyway.
677 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
683 StopOnPonderhit = true;
689 if (MaxDepth && Iteration >= MaxDepth)
693 // If we are pondering or in infinite search, we shouldn't print the
694 // best move before we are told to do so.
695 if (!AbortSearch && (PonderSearch || InfiniteSearch))
696 wait_for_stop_or_ponderhit();
698 // Print final search statistics
699 cout << "info nodes " << TM.nodes_searched()
701 << " time " << current_search_time() << endl;
703 // Print the best move and the ponder move to the standard output
704 if (pv[0] == MOVE_NONE)
706 pv[0] = rml.get_move(0);
710 assert(pv[0] != MOVE_NONE);
712 cout << "bestmove " << pv[0];
714 if (pv[1] != MOVE_NONE)
715 cout << " ponder " << pv[1];
722 dbg_print_mean(LogFile);
724 if (dbg_show_hit_rate)
725 dbg_print_hit_rate(LogFile);
727 LogFile << "\nNodes: " << TM.nodes_searched()
728 << "\nNodes/second: " << nps()
729 << "\nBest move: " << move_to_san(p, pv[0]);
732 p.do_move(pv[0], st);
733 LogFile << "\nPonder move: "
734 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
737 return rml.get_move_score(0);
741 // root_search() is the function which searches the root node. It is
742 // similar to search_pv except that it uses a different move ordering
743 // scheme, prints some information to the standard output and handles
744 // the fail low/high loops.
746 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
753 Depth depth, ext, newDepth;
754 Value value, alpha, beta;
755 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
756 int researchCountFH, researchCountFL;
758 researchCountFH = researchCountFL = 0;
761 isCheck = pos.is_check();
763 // Step 1. Initialize node (polling is omitted at root)
766 // Step 2. Check for aborted search (omitted at root)
767 // Step 3. Mate distance pruning (omitted at root)
768 // Step 4. Transposition table lookup (omitted at root)
770 // Step 5. Evaluate the position statically
771 // At root we do this only to get reference value for child nodes
772 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ei);
774 // Step 6. Razoring (omitted at root)
775 // Step 7. Static null move pruning (omitted at root)
776 // Step 8. Null move search with verification search (omitted at root)
777 // Step 9. Internal iterative deepening (omitted at root)
779 // Step extra. Fail low loop
780 // We start with small aspiration window and in case of fail low, we research
781 // with bigger window until we are not failing low anymore.
784 // Sort the moves before to (re)search
787 // Step 10. Loop through all moves in the root move list
788 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
790 // This is used by time management
791 FirstRootMove = (i == 0);
793 // Save the current node count before the move is searched
794 nodes = TM.nodes_searched();
796 // Reset beta cut-off counters
797 TM.resetBetaCounters();
799 // Pick the next root move, and print the move and the move number to
800 // the standard output.
801 move = ss->currentMove = rml.get_move(i);
803 if (current_search_time() >= 1000)
804 cout << "info currmove " << move
805 << " currmovenumber " << i + 1 << endl;
807 moveIsCheck = pos.move_is_check(move);
808 captureOrPromotion = pos.move_is_capture_or_promotion(move);
810 // Step 11. Decide the new search depth
811 depth = (Iteration - 2) * OnePly + InitialDepth;
812 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
813 newDepth = depth + ext;
815 // Step 12. Futility pruning (omitted at root)
817 // Step extra. Fail high loop
818 // If move fails high, we research with bigger window until we are not failing
820 value = - VALUE_INFINITE;
824 // Step 13. Make the move
825 pos.do_move(move, st, ci, moveIsCheck);
827 // Step extra. pv search
828 // We do pv search for first moves (i < MultiPV)
829 // and for fail high research (value > alpha)
830 if (i < MultiPV || value > alpha)
832 // Aspiration window is disabled in multi-pv case
834 alpha = -VALUE_INFINITE;
836 // Full depth PV search, done on first move or after a fail high
837 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
841 // Step 14. Reduced search
842 // if the move fails high will be re-searched at full depth
843 bool doFullDepthSearch = true;
845 if ( depth >= 3 * OnePly
847 && !captureOrPromotion
848 && !move_is_castle(move))
850 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
853 assert(newDepth-ss->reduction >= OnePly);
855 // Reduced depth non-pv search using alpha as upperbound
856 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
857 doFullDepthSearch = (value > alpha);
860 // The move failed high, but if reduction is very big we could
861 // face a false positive, retry with a less aggressive reduction,
862 // if the move fails high again then go with full depth search.
863 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
865 assert(newDepth - OnePly >= OnePly);
867 ss->reduction = OnePly;
868 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
869 doFullDepthSearch = (value > alpha);
871 ss->reduction = Depth(0); // Restore original reduction
874 // Step 15. Full depth search
875 if (doFullDepthSearch)
877 // Full depth non-pv search using alpha as upperbound
878 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
880 // If we are above alpha then research at same depth but as PV
881 // to get a correct score or eventually a fail high above beta.
883 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
887 // Step 16. Undo move
890 // Can we exit fail high loop ?
891 if (AbortSearch || value < beta)
894 // We are failing high and going to do a research. It's important to update
895 // the score before research in case we run out of time while researching.
896 rml.set_move_score(i, value);
898 TT.extract_pv(pos, move, pv, PLY_MAX);
899 rml.set_move_pv(i, pv);
901 // Print information to the standard output
902 print_pv_info(pos, pv, alpha, beta, value);
904 // Prepare for a research after a fail high, each time with a wider window
905 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
908 } // End of fail high loop
910 // Finished searching the move. If AbortSearch is true, the search
911 // was aborted because the user interrupted the search or because we
912 // ran out of time. In this case, the return value of the search cannot
913 // be trusted, and we break out of the loop without updating the best
918 // Remember beta-cutoff and searched nodes counts for this move. The
919 // info is used to sort the root moves for the next iteration.
921 TM.get_beta_counters(pos.side_to_move(), our, their);
922 rml.set_beta_counters(i, our, their);
923 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
925 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
926 assert(value < beta);
928 // Step 17. Check for new best move
929 if (value <= alpha && i >= MultiPV)
930 rml.set_move_score(i, -VALUE_INFINITE);
933 // PV move or new best move!
936 rml.set_move_score(i, value);
938 TT.extract_pv(pos, move, pv, PLY_MAX);
939 rml.set_move_pv(i, pv);
943 // We record how often the best move has been changed in each
944 // iteration. This information is used for time managment: When
945 // the best move changes frequently, we allocate some more time.
947 BestMoveChangesByIteration[Iteration]++;
949 // Print information to the standard output
950 print_pv_info(pos, pv, alpha, beta, value);
952 // Raise alpha to setup proper non-pv search upper bound
959 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
961 cout << "info multipv " << j + 1
962 << " score " << value_to_uci(rml.get_move_score(j))
963 << " depth " << (j <= i ? Iteration : Iteration - 1)
964 << " time " << current_search_time()
965 << " nodes " << TM.nodes_searched()
969 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
970 cout << rml.get_move_pv(j, k) << " ";
974 alpha = rml.get_move_score(Min(i, MultiPV - 1));
976 } // PV move or new best move
978 assert(alpha >= *alphaPtr);
980 AspirationFailLow = (alpha == *alphaPtr);
982 if (AspirationFailLow && StopOnPonderhit)
983 StopOnPonderhit = false;
986 // Can we exit fail low loop ?
987 if (AbortSearch || !AspirationFailLow)
990 // Prepare for a research after a fail low, each time with a wider window
991 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
996 // Sort the moves before to return
1003 // search<>() is the main search function for both PV and non-PV nodes
1005 template <NodeType PvNode>
1006 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1008 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1009 assert(beta > alpha && beta <= VALUE_INFINITE);
1010 assert(PvNode || alpha == beta - 1);
1011 assert(ply > 0 && ply < PLY_MAX);
1012 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1014 Move movesSearched[256];
1019 Move ttMove, move, excludedMove;
1020 Depth ext, newDepth;
1021 Value bestValue, value, oldAlpha;
1022 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1023 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
1024 bool mateThreat = false;
1026 int threadID = pos.thread();
1027 refinedValue = bestValue = value = -VALUE_INFINITE;
1030 // Step 1. Initialize node and poll. Polling can abort search
1031 TM.incrementNodeCounter(threadID);
1033 (ss+2)->initKillers();
1035 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1041 // Step 2. Check for aborted search and immediate draw
1042 if (AbortSearch || TM.thread_should_stop(threadID))
1045 if (pos.is_draw() || ply >= PLY_MAX - 1)
1048 // Step 3. Mate distance pruning
1049 alpha = Max(value_mated_in(ply), alpha);
1050 beta = Min(value_mate_in(ply+1), beta);
1054 // Step 4. Transposition table lookup
1056 // We don't want the score of a partial search to overwrite a previous full search
1057 // TT value, so we use a different position key in case of an excluded move exists.
1058 excludedMove = ss->excludedMove;
1059 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1061 tte = TT.retrieve(posKey);
1062 ttMove = (tte ? tte->move() : MOVE_NONE);
1064 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1065 // This is to avoid problems in the following areas:
1067 // * Repetition draw detection
1068 // * Fifty move rule detection
1069 // * Searching for a mate
1070 // * Printing of full PV line
1072 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1074 // Refresh tte entry to avoid aging
1075 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1077 ss->currentMove = ttMove; // Can be MOVE_NONE
1078 return value_from_tt(tte->value(), ply);
1081 // Step 5. Evaluate the position statically
1082 // At PV nodes we do this only to update gain statistics
1083 isCheck = pos.is_check();
1088 assert(tte->static_value() != VALUE_NONE);
1089 ss->eval = tte->static_value();
1090 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1094 ss->eval = evaluate(pos, ei);
1095 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1098 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1099 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1102 ss->eval = VALUE_NONE;
1104 // Step 6. Razoring (is omitted in PV nodes)
1106 && depth < RazorDepth
1108 && refinedValue < beta - razor_margin(depth)
1109 && ttMove == MOVE_NONE
1110 && (ss-1)->currentMove != MOVE_NULL
1111 && !value_is_mate(beta)
1112 && !pos.has_pawn_on_7th(pos.side_to_move()))
1114 Value rbeta = beta - razor_margin(depth);
1115 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1117 // Logically we should return (v + razor_margin(depth)), but
1118 // surprisingly this did slightly weaker in tests.
1122 // Step 7. Static null move pruning (is omitted in PV nodes)
1123 // We're betting that the opponent doesn't have a move that will reduce
1124 // the score by more than futility_margin(depth) if we do a null move.
1126 && !ss->skipNullMove
1127 && depth < RazorDepth
1128 && refinedValue >= beta + futility_margin(depth, 0)
1130 && !value_is_mate(beta)
1131 && pos.non_pawn_material(pos.side_to_move()))
1132 return refinedValue - futility_margin(depth, 0);
1134 // Step 8. Null move search with verification search (is omitted in PV nodes)
1135 // When we jump directly to qsearch() we do a null move only if static value is
1136 // at least beta. Otherwise we do a null move if static value is not more than
1137 // NullMoveMargin under beta.
1139 && !ss->skipNullMove
1141 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1143 && !value_is_mate(beta)
1144 && pos.non_pawn_material(pos.side_to_move()))
1146 ss->currentMove = MOVE_NULL;
1148 // Null move dynamic reduction based on depth
1149 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1151 // Null move dynamic reduction based on value
1152 if (refinedValue - beta > PawnValueMidgame)
1155 pos.do_null_move(st);
1156 (ss+1)->skipNullMove = true;
1158 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1159 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1160 (ss+1)->skipNullMove = false;
1161 pos.undo_null_move();
1163 if (nullValue >= beta)
1165 // Do not return unproven mate scores
1166 if (nullValue >= value_mate_in(PLY_MAX))
1169 if (depth < 6 * OnePly)
1172 // Do verification search at high depths
1173 ss->skipNullMove = true;
1174 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1175 ss->skipNullMove = false;
1182 // The null move failed low, which means that we may be faced with
1183 // some kind of threat. If the previous move was reduced, check if
1184 // the move that refuted the null move was somehow connected to the
1185 // move which was reduced. If a connection is found, return a fail
1186 // low score (which will cause the reduced move to fail high in the
1187 // parent node, which will trigger a re-search with full depth).
1188 if (nullValue == value_mated_in(ply + 2))
1191 ss->threatMove = (ss+1)->currentMove;
1192 if ( depth < ThreatDepth
1193 && (ss-1)->reduction
1194 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1199 // Step 9. Internal iterative deepening
1200 if ( depth >= IIDDepth[PvNode]
1201 && ttMove == MOVE_NONE
1202 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1204 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1206 ss->skipNullMove = true;
1207 search<PvNode>(pos, ss, alpha, beta, d, ply);
1208 ss->skipNullMove = false;
1210 ttMove = ss->bestMove;
1211 tte = TT.retrieve(posKey);
1214 // Expensive mate threat detection (only for PV nodes)
1216 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1218 // Initialize a MovePicker object for the current position
1219 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1221 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1222 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1223 && tte && tte->move()
1224 && !excludedMove // Do not allow recursive singular extension search
1225 && is_lower_bound(tte->type())
1226 && tte->depth() >= depth - 3 * OnePly;
1228 // Step 10. Loop through moves
1229 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1230 while ( bestValue < beta
1231 && (move = mp.get_next_move()) != MOVE_NONE
1232 && !TM.thread_should_stop(threadID))
1234 assert(move_is_ok(move));
1236 if (move == excludedMove)
1239 moveIsCheck = pos.move_is_check(move, ci);
1240 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1242 // Step 11. Decide the new search depth
1243 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1245 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1246 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1247 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1248 // lower then ttValue minus a margin then we extend ttMove.
1249 if ( singularExtensionNode
1250 && move == tte->move()
1253 Value ttValue = value_from_tt(tte->value(), ply);
1255 if (abs(ttValue) < VALUE_KNOWN_WIN)
1257 Value b = ttValue - SingularExtensionMargin;
1258 ss->excludedMove = move;
1259 ss->skipNullMove = true;
1260 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1261 ss->skipNullMove = false;
1262 ss->excludedMove = MOVE_NONE;
1268 newDepth = depth - OnePly + ext;
1270 // Update current move (this must be done after singular extension search)
1271 movesSearched[moveCount++] = ss->currentMove = move;
1273 // Step 12. Futility pruning (is omitted in PV nodes)
1275 && !captureOrPromotion
1279 && !move_is_castle(move))
1281 // Move count based pruning
1282 if ( moveCount >= futility_move_count(depth)
1283 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1284 && bestValue > value_mated_in(PLY_MAX))
1287 // Value based pruning
1288 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1289 // but fixing this made program slightly weaker.
1290 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1291 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1292 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1294 if (futilityValueScaled < beta)
1296 if (futilityValueScaled > bestValue)
1297 bestValue = futilityValueScaled;
1302 // Step 13. Make the move
1303 pos.do_move(move, st, ci, moveIsCheck);
1305 // Step extra. pv search (only in PV nodes)
1306 // The first move in list is the expected PV
1307 if (PvNode && moveCount == 1)
1308 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1309 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1312 // Step 14. Reduced depth search
1313 // If the move fails high will be re-searched at full depth.
1314 bool doFullDepthSearch = true;
1316 if ( depth >= 3 * OnePly
1317 && !captureOrPromotion
1319 && !move_is_castle(move)
1320 && !move_is_killer(move, ss))
1322 ss->reduction = reduction<PvNode>(depth, moveCount);
1325 Depth d = newDepth - ss->reduction;
1326 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1327 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1329 doFullDepthSearch = (value > alpha);
1332 // The move failed high, but if reduction is very big we could
1333 // face a false positive, retry with a less aggressive reduction,
1334 // if the move fails high again then go with full depth search.
1335 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1337 assert(newDepth - OnePly >= OnePly);
1339 ss->reduction = OnePly;
1340 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1341 doFullDepthSearch = (value > alpha);
1343 ss->reduction = Depth(0); // Restore original reduction
1346 // Step 15. Full depth search
1347 if (doFullDepthSearch)
1349 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1350 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1352 // Step extra. pv search (only in PV nodes)
1353 // Search only for possible new PV nodes, if instead value >= beta then
1354 // parent node fails low with value <= alpha and tries another move.
1355 if (PvNode && value > alpha && value < beta)
1356 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1357 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1361 // Step 16. Undo move
1362 pos.undo_move(move);
1364 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1366 // Step 17. Check for new best move
1367 if (value > bestValue)
1372 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1375 if (value == value_mate_in(ply + 1))
1376 ss->mateKiller = move;
1378 ss->bestMove = move;
1382 // Step 18. Check for split
1383 if ( depth >= MinimumSplitDepth
1384 && TM.active_threads() > 1
1386 && TM.available_thread_exists(threadID)
1388 && !TM.thread_should_stop(threadID)
1390 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1391 mateThreat, &moveCount, &mp, PvNode);
1394 // Step 19. Check for mate and stalemate
1395 // All legal moves have been searched and if there are
1396 // no legal moves, it must be mate or stalemate.
1397 // If one move was excluded return fail low score.
1399 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1401 // Step 20. Update tables
1402 // If the search is not aborted, update the transposition table,
1403 // history counters, and killer moves.
1404 if (AbortSearch || TM.thread_should_stop(threadID))
1407 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1408 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1409 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1411 // Update killers and history only for non capture moves that fails high
1412 if (bestValue >= beta)
1414 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1415 if (!pos.move_is_capture_or_promotion(move))
1417 update_history(pos, move, depth, movesSearched, moveCount);
1418 update_killers(move, ss);
1422 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1428 // qsearch() is the quiescence search function, which is called by the main
1429 // search function when the remaining depth is zero (or, to be more precise,
1430 // less than OnePly).
1432 template <NodeType PvNode>
1433 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1435 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1436 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1437 assert(PvNode || alpha == beta - 1);
1439 assert(ply > 0 && ply < PLY_MAX);
1440 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1445 Value bestValue, value, futilityValue, futilityBase;
1446 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1448 Value oldAlpha = alpha;
1450 TM.incrementNodeCounter(pos.thread());
1451 ss->bestMove = ss->currentMove = MOVE_NONE;
1453 // Check for an instant draw or maximum ply reached
1454 if (pos.is_draw() || ply >= PLY_MAX - 1)
1457 // Transposition table lookup. At PV nodes, we don't use the TT for
1458 // pruning, but only for move ordering.
1459 tte = TT.retrieve(pos.get_key());
1460 ttMove = (tte ? tte->move() : MOVE_NONE);
1462 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1464 ss->currentMove = ttMove; // Can be MOVE_NONE
1465 return value_from_tt(tte->value(), ply);
1468 isCheck = pos.is_check();
1470 // Evaluate the position statically
1473 bestValue = futilityBase = -VALUE_INFINITE;
1474 ss->eval = VALUE_NONE;
1475 deepChecks = enoughMaterial = false;
1481 assert(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_NONE, 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 if (ss->killers[0] == m || ss->killers[1] == m)
1883 // extension() decides whether a move should be searched with normal depth,
1884 // or with extended depth. Certain classes of moves (checking moves, in
1885 // particular) are searched with bigger depth than ordinary moves and in
1886 // any case are marked as 'dangerous'. Note that also if a move is not
1887 // extended, as example because the corresponding UCI option is set to zero,
1888 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1889 template <NodeType PvNode>
1890 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1891 bool singleEvasion, bool mateThreat, bool* dangerous) {
1893 assert(m != MOVE_NONE);
1895 Depth result = Depth(0);
1896 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1900 if (moveIsCheck && pos.see_sign(m) >= 0)
1901 result += CheckExtension[PvNode];
1904 result += SingleEvasionExtension[PvNode];
1907 result += MateThreatExtension[PvNode];
1910 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1912 Color c = pos.side_to_move();
1913 if (relative_rank(c, move_to(m)) == RANK_7)
1915 result += PawnPushTo7thExtension[PvNode];
1918 if (pos.pawn_is_passed(c, move_to(m)))
1920 result += PassedPawnExtension[PvNode];
1925 if ( captureOrPromotion
1926 && pos.type_of_piece_on(move_to(m)) != PAWN
1927 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1928 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1929 && !move_is_promotion(m)
1932 result += PawnEndgameExtension[PvNode];
1937 && captureOrPromotion
1938 && pos.type_of_piece_on(move_to(m)) != PAWN
1939 && pos.see_sign(m) >= 0)
1945 return Min(result, OnePly);
1949 // connected_threat() tests whether it is safe to forward prune a move or if
1950 // is somehow coonected to the threat move returned by null search.
1952 bool connected_threat(const Position& pos, Move m, Move threat) {
1954 assert(move_is_ok(m));
1955 assert(threat && move_is_ok(threat));
1956 assert(!pos.move_is_check(m));
1957 assert(!pos.move_is_capture_or_promotion(m));
1958 assert(!pos.move_is_passed_pawn_push(m));
1960 Square mfrom, mto, tfrom, tto;
1962 mfrom = move_from(m);
1964 tfrom = move_from(threat);
1965 tto = move_to(threat);
1967 // Case 1: Don't prune moves which move the threatened piece
1971 // Case 2: If the threatened piece has value less than or equal to the
1972 // value of the threatening piece, don't prune move which defend it.
1973 if ( pos.move_is_capture(threat)
1974 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1975 || pos.type_of_piece_on(tfrom) == KING)
1976 && pos.move_attacks_square(m, tto))
1979 // Case 3: If the moving piece in the threatened move is a slider, don't
1980 // prune safe moves which block its ray.
1981 if ( piece_is_slider(pos.piece_on(tfrom))
1982 && bit_is_set(squares_between(tfrom, tto), mto)
1983 && pos.see_sign(m) >= 0)
1990 // ok_to_use_TT() returns true if a transposition table score
1991 // can be used at a given point in search.
1993 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1995 Value v = value_from_tt(tte->value(), ply);
1997 return ( tte->depth() >= depth
1998 || v >= Max(value_mate_in(PLY_MAX), beta)
1999 || v < Min(value_mated_in(PLY_MAX), beta))
2001 && ( (is_lower_bound(tte->type()) && v >= beta)
2002 || (is_upper_bound(tte->type()) && v < beta));
2006 // refine_eval() returns the transposition table score if
2007 // possible otherwise falls back on static position evaluation.
2009 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2014 Value v = value_from_tt(tte->value(), ply);
2016 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2017 || (is_upper_bound(tte->type()) && v < defaultEval))
2024 // update_history() registers a good move that produced a beta-cutoff
2025 // in history and marks as failures all the other moves of that ply.
2027 void update_history(const Position& pos, Move move, Depth depth,
2028 Move movesSearched[], int moveCount) {
2032 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2034 for (int i = 0; i < moveCount - 1; i++)
2036 m = movesSearched[i];
2040 if (!pos.move_is_capture_or_promotion(m))
2041 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2046 // update_killers() add a good move that produced a beta-cutoff
2047 // among the killer moves of that ply.
2049 void update_killers(Move m, SearchStack* ss) {
2051 if (m == ss->killers[0])
2054 ss->killers[1] = ss->killers[0];
2059 // update_gains() updates the gains table of a non-capture move given
2060 // the static position evaluation before and after the move.
2062 void update_gains(const Position& pos, Move m, Value before, Value after) {
2065 && before != VALUE_NONE
2066 && after != VALUE_NONE
2067 && pos.captured_piece() == NO_PIECE_TYPE
2068 && !move_is_castle(m)
2069 && !move_is_promotion(m))
2070 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2074 // current_search_time() returns the number of milliseconds which have passed
2075 // since the beginning of the current search.
2077 int current_search_time() {
2079 return get_system_time() - SearchStartTime;
2083 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2085 std::string value_to_uci(Value v) {
2087 std::stringstream s;
2089 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2090 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2092 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2097 // nps() computes the current nodes/second count.
2101 int t = current_search_time();
2102 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2106 // poll() performs two different functions: It polls for user input, and it
2107 // looks at the time consumed so far and decides if it's time to abort the
2112 static int lastInfoTime;
2113 int t = current_search_time();
2118 // We are line oriented, don't read single chars
2119 std::string command;
2121 if (!std::getline(std::cin, command))
2124 if (command == "quit")
2127 PonderSearch = false;
2131 else if (command == "stop")
2134 PonderSearch = false;
2136 else if (command == "ponderhit")
2140 // Print search information
2144 else if (lastInfoTime > t)
2145 // HACK: Must be a new search where we searched less than
2146 // NodesBetweenPolls nodes during the first second of search.
2149 else if (t - lastInfoTime >= 1000)
2156 if (dbg_show_hit_rate)
2157 dbg_print_hit_rate();
2159 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2160 << " time " << t << endl;
2163 // Should we stop the search?
2167 bool stillAtFirstMove = FirstRootMove
2168 && !AspirationFailLow
2169 && t > MaxSearchTime + ExtraSearchTime;
2171 bool noMoreTime = t > AbsoluteMaxSearchTime
2172 || stillAtFirstMove;
2174 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2175 || (ExactMaxTime && t >= ExactMaxTime)
2176 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2181 // ponderhit() is called when the program is pondering (i.e. thinking while
2182 // it's the opponent's turn to move) in order to let the engine know that
2183 // it correctly predicted the opponent's move.
2187 int t = current_search_time();
2188 PonderSearch = false;
2190 bool stillAtFirstMove = FirstRootMove
2191 && !AspirationFailLow
2192 && t > MaxSearchTime + ExtraSearchTime;
2194 bool noMoreTime = t > AbsoluteMaxSearchTime
2195 || stillAtFirstMove;
2197 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2202 // init_ss_array() does a fast reset of the first entries of a SearchStack
2203 // array and of all the excludedMove and skipNullMove entries.
2205 void init_ss_array(SearchStack* ss, int size) {
2207 for (int i = 0; i < size; i++, ss++)
2209 ss->excludedMove = MOVE_NONE;
2210 ss->skipNullMove = false;
2211 ss->reduction = Depth(0);
2219 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2220 // while the program is pondering. The point is to work around a wrinkle in
2221 // the UCI protocol: When pondering, the engine is not allowed to give a
2222 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2223 // We simply wait here until one of these commands is sent, and return,
2224 // after which the bestmove and pondermove will be printed (in id_loop()).
2226 void wait_for_stop_or_ponderhit() {
2228 std::string command;
2232 if (!std::getline(std::cin, command))
2235 if (command == "quit")
2240 else if (command == "ponderhit" || command == "stop")
2246 // print_pv_info() prints to standard output and eventually to log file information on
2247 // the current PV line. It is called at each iteration or after a new pv is found.
2249 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2251 cout << "info depth " << Iteration
2252 << " score " << value_to_uci(value)
2253 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2254 << " time " << current_search_time()
2255 << " nodes " << TM.nodes_searched()
2259 for (Move* m = pv; *m != MOVE_NONE; m++)
2266 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2267 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2269 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2270 TM.nodes_searched(), value, t, pv) << endl;
2275 // init_thread() is the function which is called when a new thread is
2276 // launched. It simply calls the idle_loop() function with the supplied
2277 // threadID. There are two versions of this function; one for POSIX
2278 // threads and one for Windows threads.
2280 #if !defined(_MSC_VER)
2282 void* init_thread(void *threadID) {
2284 TM.idle_loop(*(int*)threadID, NULL);
2290 DWORD WINAPI init_thread(LPVOID threadID) {
2292 TM.idle_loop(*(int*)threadID, NULL);
2299 /// The ThreadsManager class
2301 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2302 // get_beta_counters() are getters/setters for the per thread
2303 // counters used to sort the moves at root.
2305 void ThreadsManager::resetNodeCounters() {
2307 for (int i = 0; i < MAX_THREADS; i++)
2308 threads[i].nodes = 0ULL;
2311 void ThreadsManager::resetBetaCounters() {
2313 for (int i = 0; i < MAX_THREADS; i++)
2314 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2317 int64_t ThreadsManager::nodes_searched() const {
2319 int64_t result = 0ULL;
2320 for (int i = 0; i < ActiveThreads; i++)
2321 result += threads[i].nodes;
2326 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2329 for (int i = 0; i < MAX_THREADS; i++)
2331 our += threads[i].betaCutOffs[us];
2332 their += threads[i].betaCutOffs[opposite_color(us)];
2337 // idle_loop() is where the threads are parked when they have no work to do.
2338 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2339 // object for which the current thread is the master.
2341 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2343 assert(threadID >= 0 && threadID < MAX_THREADS);
2347 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2348 // master should exit as last one.
2349 if (AllThreadsShouldExit)
2352 threads[threadID].state = THREAD_TERMINATED;
2356 // If we are not thinking, wait for a condition to be signaled
2357 // instead of wasting CPU time polling for work.
2358 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2361 assert(threadID != 0);
2362 threads[threadID].state = THREAD_SLEEPING;
2364 #if !defined(_MSC_VER)
2365 lock_grab(&WaitLock);
2366 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2367 pthread_cond_wait(&WaitCond, &WaitLock);
2368 lock_release(&WaitLock);
2370 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2374 // If thread has just woken up, mark it as available
2375 if (threads[threadID].state == THREAD_SLEEPING)
2376 threads[threadID].state = THREAD_AVAILABLE;
2378 // If this thread has been assigned work, launch a search
2379 if (threads[threadID].state == THREAD_WORKISWAITING)
2381 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2383 threads[threadID].state = THREAD_SEARCHING;
2385 if (threads[threadID].splitPoint->pvNode)
2386 sp_search<PV>(threads[threadID].splitPoint, threadID);
2388 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2390 assert(threads[threadID].state == THREAD_SEARCHING);
2392 threads[threadID].state = THREAD_AVAILABLE;
2395 // If this thread is the master of a split point and all slaves have
2396 // finished their work at this split point, return from the idle loop.
2398 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2400 if (i == ActiveThreads)
2402 // Because sp->slaves[] is reset under lock protection,
2403 // be sure sp->lock has been released before to return.
2404 lock_grab(&(sp->lock));
2405 lock_release(&(sp->lock));
2407 assert(threads[threadID].state == THREAD_AVAILABLE);
2409 threads[threadID].state = THREAD_SEARCHING;
2416 // init_threads() is called during startup. It launches all helper threads,
2417 // and initializes the split point stack and the global locks and condition
2420 void ThreadsManager::init_threads() {
2425 #if !defined(_MSC_VER)
2426 pthread_t pthread[1];
2429 // Initialize global locks
2430 lock_init(&MPLock, NULL);
2431 lock_init(&WaitLock, NULL);
2433 #if !defined(_MSC_VER)
2434 pthread_cond_init(&WaitCond, NULL);
2436 for (i = 0; i < MAX_THREADS; i++)
2437 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2440 // Initialize splitPoints[] locks
2441 for (i = 0; i < MAX_THREADS; i++)
2442 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2443 lock_init(&(threads[i].splitPoints[j].lock), NULL);
2445 // Will be set just before program exits to properly end the threads
2446 AllThreadsShouldExit = false;
2448 // Threads will be put to sleep as soon as created
2449 AllThreadsShouldSleep = true;
2451 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2453 threads[0].state = THREAD_SEARCHING;
2454 for (i = 1; i < MAX_THREADS; i++)
2455 threads[i].state = THREAD_AVAILABLE;
2457 // Launch the helper threads
2458 for (i = 1; i < MAX_THREADS; i++)
2461 #if !defined(_MSC_VER)
2462 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2464 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2469 cout << "Failed to create thread number " << i << endl;
2470 Application::exit_with_failure();
2473 // Wait until the thread has finished launching and is gone to sleep
2474 while (threads[i].state != THREAD_SLEEPING) {}
2479 // exit_threads() is called when the program exits. It makes all the
2480 // helper threads exit cleanly.
2482 void ThreadsManager::exit_threads() {
2484 ActiveThreads = MAX_THREADS; // HACK
2485 AllThreadsShouldSleep = true; // HACK
2486 wake_sleeping_threads();
2488 // This makes the threads to exit idle_loop()
2489 AllThreadsShouldExit = true;
2491 // Wait for thread termination
2492 for (int i = 1; i < MAX_THREADS; i++)
2493 while (threads[i].state != THREAD_TERMINATED) {}
2495 // Now we can safely destroy the locks
2496 for (int i = 0; i < MAX_THREADS; i++)
2497 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2498 lock_destroy(&(threads[i].splitPoints[j].lock));
2500 lock_destroy(&WaitLock);
2501 lock_destroy(&MPLock);
2505 // thread_should_stop() checks whether the thread should stop its search.
2506 // This can happen if a beta cutoff has occurred in the thread's currently
2507 // active split point, or in some ancestor of the current split point.
2509 bool ThreadsManager::thread_should_stop(int threadID) const {
2511 assert(threadID >= 0 && threadID < ActiveThreads);
2515 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2520 // thread_is_available() checks whether the thread with threadID "slave" is
2521 // available to help the thread with threadID "master" at a split point. An
2522 // obvious requirement is that "slave" must be idle. With more than two
2523 // threads, this is not by itself sufficient: If "slave" is the master of
2524 // some active split point, it is only available as a slave to the other
2525 // threads which are busy searching the split point at the top of "slave"'s
2526 // split point stack (the "helpful master concept" in YBWC terminology).
2528 bool ThreadsManager::thread_is_available(int slave, int master) const {
2530 assert(slave >= 0 && slave < ActiveThreads);
2531 assert(master >= 0 && master < ActiveThreads);
2532 assert(ActiveThreads > 1);
2534 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2537 // Make a local copy to be sure doesn't change under our feet
2538 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2540 if (localActiveSplitPoints == 0)
2541 // No active split points means that the thread is available as
2542 // a slave for any other thread.
2545 if (ActiveThreads == 2)
2548 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2549 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2550 // could have been set to 0 by another thread leading to an out of bound access.
2551 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2558 // available_thread_exists() tries to find an idle thread which is available as
2559 // a slave for the thread with threadID "master".
2561 bool ThreadsManager::available_thread_exists(int master) const {
2563 assert(master >= 0 && master < ActiveThreads);
2564 assert(ActiveThreads > 1);
2566 for (int i = 0; i < ActiveThreads; i++)
2567 if (thread_is_available(i, master))
2574 // split() does the actual work of distributing the work at a node between
2575 // several available threads. If it does not succeed in splitting the
2576 // node (because no idle threads are available, or because we have no unused
2577 // split point objects), the function immediately returns. If splitting is
2578 // possible, a SplitPoint object is initialized with all the data that must be
2579 // copied to the helper threads and we tell our helper threads that they have
2580 // been assigned work. This will cause them to instantly leave their idle loops
2581 // and call sp_search(). When all threads have returned from sp_search() then
2584 template <bool Fake>
2585 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2586 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2587 int* moveCount, MovePicker* mp, bool pvNode) {
2589 assert(ply > 0 && ply < PLY_MAX);
2590 assert(*bestValue >= -VALUE_INFINITE);
2591 assert(*bestValue <= *alpha);
2592 assert(*alpha < beta);
2593 assert(beta <= VALUE_INFINITE);
2594 assert(depth > Depth(0));
2595 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2596 assert(ActiveThreads > 1);
2598 int i, master = p.thread();
2599 Thread& masterThread = threads[master];
2603 // If no other thread is available to help us, or if we have too many
2604 // active split points, don't split.
2605 if ( !available_thread_exists(master)
2606 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2608 lock_release(&MPLock);
2612 // Pick the next available split point object from the split point stack
2613 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2615 // Initialize the split point object
2616 splitPoint.parent = masterThread.splitPoint;
2617 splitPoint.stopRequest = false;
2618 splitPoint.ply = ply;
2619 splitPoint.depth = depth;
2620 splitPoint.mateThreat = mateThreat;
2621 splitPoint.alpha = *alpha;
2622 splitPoint.beta = beta;
2623 splitPoint.pvNode = pvNode;
2624 splitPoint.bestValue = *bestValue;
2626 splitPoint.moveCount = *moveCount;
2627 splitPoint.pos = &p;
2628 splitPoint.parentSstack = ss;
2629 for (i = 0; i < ActiveThreads; i++)
2630 splitPoint.slaves[i] = 0;
2632 masterThread.splitPoint = &splitPoint;
2634 // If we are here it means we are not available
2635 assert(masterThread.state != THREAD_AVAILABLE);
2637 int workersCnt = 1; // At least the master is included
2639 // Allocate available threads setting state to THREAD_BOOKED
2640 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2641 if (thread_is_available(i, master))
2643 threads[i].state = THREAD_BOOKED;
2644 threads[i].splitPoint = &splitPoint;
2645 splitPoint.slaves[i] = 1;
2649 assert(Fake || workersCnt > 1);
2651 // We can release the lock because slave threads are already booked and master is not available
2652 lock_release(&MPLock);
2654 // Tell the threads that they have work to do. This will make them leave
2655 // their idle loop. But before copy search stack tail for each thread.
2656 for (i = 0; i < ActiveThreads; i++)
2657 if (i == master || splitPoint.slaves[i])
2659 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2661 assert(i == master || threads[i].state == THREAD_BOOKED);
2663 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2666 // Everything is set up. The master thread enters the idle loop, from
2667 // which it will instantly launch a search, because its state is
2668 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2669 // idle loop, which means that the main thread will return from the idle
2670 // loop when all threads have finished their work at this split point.
2671 idle_loop(master, &splitPoint);
2673 // We have returned from the idle loop, which means that all threads are
2674 // finished. Update alpha and bestValue, and return.
2677 *alpha = splitPoint.alpha;
2678 *bestValue = splitPoint.bestValue;
2679 masterThread.activeSplitPoints--;
2680 masterThread.splitPoint = splitPoint.parent;
2682 lock_release(&MPLock);
2686 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2687 // to start a new search from the root.
2689 void ThreadsManager::wake_sleeping_threads() {
2691 assert(AllThreadsShouldSleep);
2692 assert(ActiveThreads > 0);
2694 AllThreadsShouldSleep = false;
2696 if (ActiveThreads == 1)
2699 #if !defined(_MSC_VER)
2700 pthread_mutex_lock(&WaitLock);
2701 pthread_cond_broadcast(&WaitCond);
2702 pthread_mutex_unlock(&WaitLock);
2704 for (int i = 1; i < MAX_THREADS; i++)
2705 SetEvent(SitIdleEvent[i]);
2711 // put_threads_to_sleep() makes all the threads go to sleep just before
2712 // to leave think(), at the end of the search. Threads should have already
2713 // finished the job and should be idle.
2715 void ThreadsManager::put_threads_to_sleep() {
2717 assert(!AllThreadsShouldSleep);
2719 // This makes the threads to go to sleep
2720 AllThreadsShouldSleep = true;
2723 /// The RootMoveList class
2725 // RootMoveList c'tor
2727 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2729 SearchStack ss[PLY_MAX_PLUS_2];
2730 MoveStack mlist[MaxRootMoves];
2732 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2734 // Initialize search stack
2735 init_ss_array(ss, PLY_MAX_PLUS_2);
2737 ss[0].eval = VALUE_NONE;
2739 // Generate all legal moves
2740 MoveStack* last = generate_moves(pos, mlist);
2742 // Add each move to the moves[] array
2743 for (MoveStack* cur = mlist; cur != last; cur++)
2745 bool includeMove = includeAllMoves;
2747 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2748 includeMove = (searchMoves[k] == cur->move);
2753 // Find a quick score for the move
2754 pos.do_move(cur->move, st);
2755 ss[0].currentMove = cur->move;
2756 moves[count].move = cur->move;
2757 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2758 moves[count].pv[0] = cur->move;
2759 moves[count].pv[1] = MOVE_NONE;
2760 pos.undo_move(cur->move);
2767 // RootMoveList simple methods definitions
2769 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2771 moves[moveNum].nodes = nodes;
2772 moves[moveNum].cumulativeNodes += nodes;
2775 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2777 moves[moveNum].ourBeta = our;
2778 moves[moveNum].theirBeta = their;
2781 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2785 for (j = 0; pv[j] != MOVE_NONE; j++)
2786 moves[moveNum].pv[j] = pv[j];
2788 moves[moveNum].pv[j] = MOVE_NONE;
2792 // RootMoveList::sort() sorts the root move list at the beginning of a new
2795 void RootMoveList::sort() {
2797 sort_multipv(count - 1); // Sort all items
2801 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2802 // list by their scores and depths. It is used to order the different PVs
2803 // correctly in MultiPV mode.
2805 void RootMoveList::sort_multipv(int n) {
2809 for (i = 1; i <= n; i++)
2811 RootMove rm = moves[i];
2812 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2813 moves[j] = moves[j - 1];