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 and poll (omitted at root, init_ss_array() has already initialized root node)
764 // Step 2. Check for aborted search (omitted at root)
765 // Step 3. Mate distance pruning (omitted at root)
766 // Step 4. Transposition table lookup (omitted at root)
768 // Step 5. Evaluate the position statically
769 // At root we do this only to get reference value for child nodes
770 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ei);
772 // Step 6. Razoring (omitted at root)
773 // Step 7. Static null move pruning (omitted at root)
774 // Step 8. Null move search with verification search (omitted at root)
775 // Step 9. Internal iterative deepening (omitted at root)
777 // Step extra. Fail low loop
778 // We start with small aspiration window and in case of fail low, we research
779 // with bigger window until we are not failing low anymore.
782 // Sort the moves before to (re)search
785 // Step 10. Loop through all moves in the root move list
786 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
788 // This is used by time management
789 FirstRootMove = (i == 0);
791 // Save the current node count before the move is searched
792 nodes = TM.nodes_searched();
794 // Reset beta cut-off counters
795 TM.resetBetaCounters();
797 // Pick the next root move, and print the move and the move number to
798 // the standard output.
799 move = ss->currentMove = rml.get_move(i);
801 if (current_search_time() >= 1000)
802 cout << "info currmove " << move
803 << " currmovenumber " << i + 1 << endl;
805 moveIsCheck = pos.move_is_check(move);
806 captureOrPromotion = pos.move_is_capture_or_promotion(move);
808 // Step 11. Decide the new search depth
809 depth = (Iteration - 2) * OnePly + InitialDepth;
810 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
811 newDepth = depth + ext;
813 // Step 12. Futility pruning (omitted at root)
815 // Step extra. Fail high loop
816 // If move fails high, we research with bigger window until we are not failing
818 value = - VALUE_INFINITE;
822 // Step 13. Make the move
823 pos.do_move(move, st, ci, moveIsCheck);
825 // Step extra. pv search
826 // We do pv search for first moves (i < MultiPV)
827 // and for fail high research (value > alpha)
828 if (i < MultiPV || value > alpha)
830 // Aspiration window is disabled in multi-pv case
832 alpha = -VALUE_INFINITE;
834 // Full depth PV search, done on first move or after a fail high
835 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
839 // Step 14. Reduced search
840 // if the move fails high will be re-searched at full depth
841 bool doFullDepthSearch = true;
843 if ( depth >= 3 * OnePly
845 && !captureOrPromotion
846 && !move_is_castle(move))
848 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
851 assert(newDepth-ss->reduction >= OnePly);
853 // Reduced depth non-pv search using alpha as upperbound
854 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
855 doFullDepthSearch = (value > alpha);
858 // The move failed high, but if reduction is very big we could
859 // face a false positive, retry with a less aggressive reduction,
860 // if the move fails high again then go with full depth search.
861 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
863 assert(newDepth - OnePly >= OnePly);
865 ss->reduction = OnePly;
866 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
867 doFullDepthSearch = (value > alpha);
869 ss->reduction = Depth(0); // Restore original reduction
872 // Step 15. Full depth search
873 if (doFullDepthSearch)
875 // Full depth non-pv search using alpha as upperbound
876 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
878 // If we are above alpha then research at same depth but as PV
879 // to get a correct score or eventually a fail high above beta.
881 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
885 // Step 16. Undo move
888 // Can we exit fail high loop ?
889 if (AbortSearch || value < beta)
892 // We are failing high and going to do a research. It's important to update
893 // the score before research in case we run out of time while researching.
894 rml.set_move_score(i, value);
896 TT.extract_pv(pos, move, pv, PLY_MAX);
897 rml.set_move_pv(i, pv);
899 // Print information to the standard output
900 print_pv_info(pos, pv, alpha, beta, value);
902 // Prepare for a research after a fail high, each time with a wider window
903 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
906 } // End of fail high loop
908 // Finished searching the move. If AbortSearch is true, the search
909 // was aborted because the user interrupted the search or because we
910 // ran out of time. In this case, the return value of the search cannot
911 // be trusted, and we break out of the loop without updating the best
916 // Remember beta-cutoff and searched nodes counts for this move. The
917 // info is used to sort the root moves for the next iteration.
919 TM.get_beta_counters(pos.side_to_move(), our, their);
920 rml.set_beta_counters(i, our, their);
921 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
923 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
924 assert(value < beta);
926 // Step 17. Check for new best move
927 if (value <= alpha && i >= MultiPV)
928 rml.set_move_score(i, -VALUE_INFINITE);
931 // PV move or new best move!
934 rml.set_move_score(i, value);
936 TT.extract_pv(pos, move, pv, PLY_MAX);
937 rml.set_move_pv(i, pv);
941 // We record how often the best move has been changed in each
942 // iteration. This information is used for time managment: When
943 // the best move changes frequently, we allocate some more time.
945 BestMoveChangesByIteration[Iteration]++;
947 // Print information to the standard output
948 print_pv_info(pos, pv, alpha, beta, value);
950 // Raise alpha to setup proper non-pv search upper bound
957 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
959 cout << "info multipv " << j + 1
960 << " score " << value_to_uci(rml.get_move_score(j))
961 << " depth " << (j <= i ? Iteration : Iteration - 1)
962 << " time " << current_search_time()
963 << " nodes " << TM.nodes_searched()
967 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
968 cout << rml.get_move_pv(j, k) << " ";
972 alpha = rml.get_move_score(Min(i, MultiPV - 1));
974 } // PV move or new best move
976 assert(alpha >= *alphaPtr);
978 AspirationFailLow = (alpha == *alphaPtr);
980 if (AspirationFailLow && StopOnPonderhit)
981 StopOnPonderhit = false;
984 // Can we exit fail low loop ?
985 if (AbortSearch || !AspirationFailLow)
988 // Prepare for a research after a fail low, each time with a wider window
989 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
994 // Sort the moves before to return
1001 // search<>() is the main search function for both PV and non-PV nodes
1003 template <NodeType PvNode>
1004 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1006 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1007 assert(beta > alpha && beta <= VALUE_INFINITE);
1008 assert(PvNode || alpha == beta - 1);
1009 assert(ply > 0 && ply < PLY_MAX);
1010 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1012 Move movesSearched[256];
1017 Move ttMove, move, excludedMove;
1018 Depth ext, newDepth;
1019 Value bestValue, value, oldAlpha;
1020 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1021 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
1022 bool mateThreat = false;
1024 int threadID = pos.thread();
1025 refinedValue = bestValue = value = -VALUE_INFINITE;
1028 // Step 1. Initialize node and poll. Polling can abort search
1029 TM.incrementNodeCounter(threadID);
1031 (ss+2)->initKillers();
1033 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1039 // Step 2. Check for aborted search and immediate draw
1040 if (AbortSearch || TM.thread_should_stop(threadID))
1043 if (pos.is_draw() || ply >= PLY_MAX - 1)
1046 // Step 3. Mate distance pruning
1047 alpha = Max(value_mated_in(ply), alpha);
1048 beta = Min(value_mate_in(ply+1), beta);
1052 // Step 4. Transposition table lookup
1054 // We don't want the score of a partial search to overwrite a previous full search
1055 // TT value, so we use a different position key in case of an excluded move exists.
1056 excludedMove = ss->excludedMove;
1057 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1059 tte = TT.retrieve(posKey);
1060 ttMove = (tte ? tte->move() : MOVE_NONE);
1062 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1063 // This is to avoid problems in the following areas:
1065 // * Repetition draw detection
1066 // * Fifty move rule detection
1067 // * Searching for a mate
1068 // * Printing of full PV line
1070 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1072 // Refresh tte entry to avoid aging
1073 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1075 ss->currentMove = ttMove; // Can be MOVE_NONE
1076 return value_from_tt(tte->value(), ply);
1079 // Step 5. Evaluate the position statically
1080 // At PV nodes we do this only to update gain statistics
1081 isCheck = pos.is_check();
1084 if (tte && tte->static_value() != VALUE_NONE)
1086 ss->eval = tte->static_value();
1087 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1090 ss->eval = evaluate(pos, ei);
1092 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1093 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1096 ss->eval = VALUE_NONE;
1098 // Step 6. Razoring (is omitted in PV nodes)
1100 && depth < RazorDepth
1102 && refinedValue < beta - razor_margin(depth)
1103 && ttMove == MOVE_NONE
1104 && (ss-1)->currentMove != MOVE_NULL
1105 && !value_is_mate(beta)
1106 && !pos.has_pawn_on_7th(pos.side_to_move()))
1108 // Pass ss->eval to qsearch() and avoid an evaluate call
1109 if (!tte || tte->static_value() == VALUE_NONE)
1110 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1112 Value rbeta = beta - razor_margin(depth);
1113 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1115 // Logically we should return (v + razor_margin(depth)), but
1116 // surprisingly this did slightly weaker in tests.
1120 // Step 7. Static null move pruning (is omitted in PV nodes)
1121 // We're betting that the opponent doesn't have a move that will reduce
1122 // the score by more than futility_margin(depth) if we do a null move.
1124 && !ss->skipNullMove
1125 && depth < RazorDepth
1126 && refinedValue >= beta + futility_margin(depth, 0)
1128 && !value_is_mate(beta)
1129 && pos.non_pawn_material(pos.side_to_move()))
1130 return refinedValue - futility_margin(depth, 0);
1132 // Step 8. Null move search with verification search (is omitted in PV nodes)
1133 // When we jump directly to qsearch() we do a null move only if static value is
1134 // at least beta. Otherwise we do a null move if static value is not more than
1135 // NullMoveMargin under beta.
1137 && !ss->skipNullMove
1139 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1141 && !value_is_mate(beta)
1142 && pos.non_pawn_material(pos.side_to_move()))
1144 ss->currentMove = MOVE_NULL;
1146 // Null move dynamic reduction based on depth
1147 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1149 // Null move dynamic reduction based on value
1150 if (refinedValue - beta > PawnValueMidgame)
1153 pos.do_null_move(st);
1154 (ss+1)->skipNullMove = true;
1156 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1157 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1158 (ss+1)->skipNullMove = false;
1159 pos.undo_null_move();
1161 if (nullValue >= beta)
1163 // Do not return unproven mate scores
1164 if (nullValue >= value_mate_in(PLY_MAX))
1167 if (depth < 6 * OnePly)
1170 // Do verification search at high depths
1171 ss->skipNullMove = true;
1172 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1173 ss->skipNullMove = false;
1180 // The null move failed low, which means that we may be faced with
1181 // some kind of threat. If the previous move was reduced, check if
1182 // the move that refuted the null move was somehow connected to the
1183 // move which was reduced. If a connection is found, return a fail
1184 // low score (which will cause the reduced move to fail high in the
1185 // parent node, which will trigger a re-search with full depth).
1186 if (nullValue == value_mated_in(ply + 2))
1189 ss->threatMove = (ss+1)->currentMove;
1190 if ( depth < ThreatDepth
1191 && (ss-1)->reduction
1192 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1197 // Step 9. Internal iterative deepening
1198 if ( depth >= IIDDepth[PvNode]
1199 && ttMove == MOVE_NONE
1200 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1202 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1204 ss->skipNullMove = true;
1205 search<PvNode>(pos, ss, alpha, beta, d, ply);
1206 ss->skipNullMove = false;
1208 ttMove = ss->bestMove;
1209 tte = TT.retrieve(posKey);
1212 // Expensive mate threat detection (only for PV nodes)
1214 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1216 // Initialize a MovePicker object for the current position
1217 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1219 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1220 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1221 && tte && tte->move()
1222 && !excludedMove // Do not allow recursive singular extension search
1223 && is_lower_bound(tte->type())
1224 && tte->depth() >= depth - 3 * OnePly;
1226 // Step 10. Loop through moves
1227 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1228 while ( bestValue < beta
1229 && (move = mp.get_next_move()) != MOVE_NONE
1230 && !TM.thread_should_stop(threadID))
1232 assert(move_is_ok(move));
1234 if (move == excludedMove)
1237 moveIsCheck = pos.move_is_check(move, ci);
1238 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1240 // Step 11. Decide the new search depth
1241 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1243 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1244 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1245 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1246 // lower then ttValue minus a margin then we extend ttMove.
1247 if ( singularExtensionNode
1248 && move == tte->move()
1251 Value ttValue = value_from_tt(tte->value(), ply);
1253 if (abs(ttValue) < VALUE_KNOWN_WIN)
1255 Value b = ttValue - SingularExtensionMargin;
1256 ss->excludedMove = move;
1257 ss->skipNullMove = true;
1258 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1259 ss->skipNullMove = false;
1260 ss->excludedMove = MOVE_NONE;
1266 newDepth = depth - OnePly + ext;
1268 // Update current move (this must be done after singular extension search)
1269 movesSearched[moveCount++] = ss->currentMove = move;
1271 // Step 12. Futility pruning (is omitted in PV nodes)
1273 && !captureOrPromotion
1277 && !move_is_castle(move))
1279 // Move count based pruning
1280 if ( moveCount >= futility_move_count(depth)
1281 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1282 && bestValue > value_mated_in(PLY_MAX))
1285 // Value based pruning
1286 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1287 // but fixing this made program slightly weaker.
1288 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1289 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1290 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1292 if (futilityValueScaled < beta)
1294 if (futilityValueScaled > bestValue)
1295 bestValue = futilityValueScaled;
1300 // Step 13. Make the move
1301 pos.do_move(move, st, ci, moveIsCheck);
1303 // Step extra. pv search (only in PV nodes)
1304 // The first move in list is the expected PV
1305 if (PvNode && moveCount == 1)
1306 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1307 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1310 // Step 14. Reduced depth search
1311 // If the move fails high will be re-searched at full depth.
1312 bool doFullDepthSearch = true;
1314 if ( depth >= 3 * OnePly
1315 && !captureOrPromotion
1317 && !move_is_castle(move)
1318 && !move_is_killer(move, ss))
1320 ss->reduction = reduction<PvNode>(depth, moveCount);
1323 Depth d = newDepth - ss->reduction;
1324 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1325 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1327 doFullDepthSearch = (value > alpha);
1330 // The move failed high, but if reduction is very big we could
1331 // face a false positive, retry with a less aggressive reduction,
1332 // if the move fails high again then go with full depth search.
1333 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1335 assert(newDepth - OnePly >= OnePly);
1337 ss->reduction = OnePly;
1338 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1339 doFullDepthSearch = (value > alpha);
1341 ss->reduction = Depth(0); // Restore original reduction
1344 // Step 15. Full depth search
1345 if (doFullDepthSearch)
1347 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1348 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1350 // Step extra. pv search (only in PV nodes)
1351 // Search only for possible new PV nodes, if instead value >= beta then
1352 // parent node fails low with value <= alpha and tries another move.
1353 if (PvNode && value > alpha && value < beta)
1354 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1355 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1359 // Step 16. Undo move
1360 pos.undo_move(move);
1362 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1364 // Step 17. Check for new best move
1365 if (value > bestValue)
1370 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1373 if (value == value_mate_in(ply + 1))
1374 ss->mateKiller = move;
1376 ss->bestMove = move;
1380 // Step 18. Check for split
1381 if ( depth >= MinimumSplitDepth
1382 && TM.active_threads() > 1
1384 && TM.available_thread_exists(threadID)
1386 && !TM.thread_should_stop(threadID)
1388 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1389 mateThreat, &moveCount, &mp, PvNode);
1392 // Step 19. Check for mate and stalemate
1393 // All legal moves have been searched and if there are
1394 // no legal moves, it must be mate or stalemate.
1395 // If one move was excluded return fail low score.
1397 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1399 // Step 20. Update tables
1400 // If the search is not aborted, update the transposition table,
1401 // history counters, and killer moves.
1402 if (AbortSearch || TM.thread_should_stop(threadID))
1405 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1406 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1407 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1409 // Update killers and history only for non capture moves that fails high
1410 if (bestValue >= beta)
1412 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1413 if (!pos.move_is_capture_or_promotion(move))
1415 update_history(pos, move, depth, movesSearched, moveCount);
1416 update_killers(move, ss);
1420 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1426 // qsearch() is the quiescence search function, which is called by the main
1427 // search function when the remaining depth is zero (or, to be more precise,
1428 // less than OnePly).
1430 template <NodeType PvNode>
1431 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1433 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1434 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1435 assert(PvNode || alpha == beta - 1);
1437 assert(ply > 0 && ply < PLY_MAX);
1438 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1443 Value bestValue, value, futilityValue, futilityBase;
1444 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1446 Value oldAlpha = alpha;
1448 TM.incrementNodeCounter(pos.thread());
1449 ss->bestMove = ss->currentMove = MOVE_NONE;
1451 // Check for an instant draw or maximum ply reached
1452 if (pos.is_draw() || ply >= PLY_MAX - 1)
1455 // Transposition table lookup. At PV nodes, we don't use the TT for
1456 // pruning, but only for move ordering.
1457 tte = TT.retrieve(pos.get_key());
1458 ttMove = (tte ? tte->move() : MOVE_NONE);
1460 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1462 ss->currentMove = ttMove; // Can be MOVE_NONE
1463 return value_from_tt(tte->value(), ply);
1466 isCheck = pos.is_check();
1468 // Evaluate the position statically
1471 bestValue = futilityBase = -VALUE_INFINITE;
1472 ss->eval = VALUE_NONE;
1473 deepChecks = enoughMaterial = false;
1477 if (tte && tte->static_value() != VALUE_NONE)
1479 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1480 bestValue = tte->static_value();
1483 bestValue = evaluate(pos, ei);
1485 ss->eval = bestValue;
1486 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1488 // Stand pat. Return immediately if static value is at least beta
1489 if (bestValue >= beta)
1492 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()]);
1497 if (PvNode && bestValue > alpha)
1500 // If we are near beta then try to get a cutoff pushing checks a bit further
1501 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1503 // Futility pruning parameters, not needed when in check
1504 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1505 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1508 // Initialize a MovePicker object for the current position, and prepare
1509 // to search the moves. Because the depth is <= 0 here, only captures,
1510 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1511 // and we are near beta) will be generated.
1512 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1515 // Loop through the moves until no moves remain or a beta cutoff occurs
1516 while ( alpha < beta
1517 && (move = mp.get_next_move()) != MOVE_NONE)
1519 assert(move_is_ok(move));
1521 moveIsCheck = pos.move_is_check(move, ci);
1529 && !move_is_promotion(move)
1530 && !pos.move_is_passed_pawn_push(move))
1532 futilityValue = futilityBase
1533 + pos.endgame_value_of_piece_on(move_to(move))
1534 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1536 if (futilityValue < alpha)
1538 if (futilityValue > bestValue)
1539 bestValue = futilityValue;
1544 // Detect blocking evasions that are candidate to be pruned
1545 evasionPrunable = isCheck
1546 && bestValue > value_mated_in(PLY_MAX)
1547 && !pos.move_is_capture(move)
1548 && pos.type_of_piece_on(move_from(move)) != KING
1549 && !pos.can_castle(pos.side_to_move());
1551 // Don't search moves with negative SEE values
1553 && (!isCheck || evasionPrunable)
1555 && !move_is_promotion(move)
1556 && pos.see_sign(move) < 0)
1559 // Update current move
1560 ss->currentMove = move;
1562 // Make and search the move
1563 pos.do_move(move, st, ci, moveIsCheck);
1564 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1565 pos.undo_move(move);
1567 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1570 if (value > bestValue)
1576 ss->bestMove = move;
1581 // All legal moves have been searched. A special case: If we're in check
1582 // and no legal moves were found, it is checkmate.
1583 if (isCheck && bestValue == -VALUE_INFINITE)
1584 return value_mated_in(ply);
1586 // Update transposition table
1587 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1588 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1589 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1591 // Update killers only for checking moves that fails high
1592 if ( bestValue >= beta
1593 && !pos.move_is_capture_or_promotion(ss->bestMove))
1594 update_killers(ss->bestMove, ss);
1596 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1602 // sp_search() is used to search from a split point. This function is called
1603 // by each thread working at the split point. It is similar to the normal
1604 // search() function, but simpler. Because we have already probed the hash
1605 // table, done a null move search, and searched the first move before
1606 // splitting, we don't have to repeat all this work in sp_search(). We
1607 // also don't need to store anything to the hash table here: This is taken
1608 // care of after we return from the split point.
1610 template <NodeType PvNode>
1611 void sp_search(SplitPoint* sp, int threadID) {
1613 assert(threadID >= 0 && threadID < TM.active_threads());
1614 assert(TM.active_threads() > 1);
1618 Depth ext, newDepth;
1620 Value futilityValueScaled; // NonPV specific
1621 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1623 value = -VALUE_INFINITE;
1625 Position pos(*sp->pos, threadID);
1627 SearchStack* ss = sp->sstack[threadID] + 1;
1628 isCheck = pos.is_check();
1630 // Step 10. Loop through moves
1631 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1632 lock_grab(&(sp->lock));
1634 while ( sp->bestValue < sp->beta
1635 && (move = sp->mp->get_next_move()) != MOVE_NONE
1636 && !TM.thread_should_stop(threadID))
1638 moveCount = ++sp->moveCount;
1639 lock_release(&(sp->lock));
1641 assert(move_is_ok(move));
1643 moveIsCheck = pos.move_is_check(move, ci);
1644 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1646 // Step 11. Decide the new search depth
1647 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1648 newDepth = sp->depth - OnePly + ext;
1650 // Update current move
1651 ss->currentMove = move;
1653 // Step 12. Futility pruning (is omitted in PV nodes)
1655 && !captureOrPromotion
1658 && !move_is_castle(move))
1660 // Move count based pruning
1661 if ( moveCount >= futility_move_count(sp->depth)
1662 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1663 && sp->bestValue > value_mated_in(PLY_MAX))
1665 lock_grab(&(sp->lock));
1669 // Value based pruning
1670 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1671 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1672 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1674 if (futilityValueScaled < sp->beta)
1676 lock_grab(&(sp->lock));
1678 if (futilityValueScaled > sp->bestValue)
1679 sp->bestValue = futilityValueScaled;
1684 // Step 13. Make the move
1685 pos.do_move(move, st, ci, moveIsCheck);
1687 // Step 14. Reduced search
1688 // If the move fails high will be re-searched at full depth.
1689 bool doFullDepthSearch = true;
1691 if ( !captureOrPromotion
1693 && !move_is_castle(move)
1694 && !move_is_killer(move, ss))
1696 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1699 Value localAlpha = sp->alpha;
1700 Depth d = newDepth - ss->reduction;
1701 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1702 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1704 doFullDepthSearch = (value > localAlpha);
1707 // The move failed high, but if reduction is very big we could
1708 // face a false positive, retry with a less aggressive reduction,
1709 // if the move fails high again then go with full depth search.
1710 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1712 assert(newDepth - OnePly >= OnePly);
1714 ss->reduction = OnePly;
1715 Value localAlpha = sp->alpha;
1716 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1717 doFullDepthSearch = (value > localAlpha);
1719 ss->reduction = Depth(0); // Restore original reduction
1722 // Step 15. Full depth search
1723 if (doFullDepthSearch)
1725 Value localAlpha = sp->alpha;
1726 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1727 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1729 // Step extra. pv search (only in PV nodes)
1730 // Search only for possible new PV nodes, if instead value >= beta then
1731 // parent node fails low with value <= alpha and tries another move.
1732 if (PvNode && value > localAlpha && value < sp->beta)
1733 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1734 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1737 // Step 16. Undo move
1738 pos.undo_move(move);
1740 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1742 // Step 17. Check for new best move
1743 lock_grab(&(sp->lock));
1745 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1747 sp->bestValue = value;
1749 if (sp->bestValue > sp->alpha)
1751 if (!PvNode || value >= sp->beta)
1752 sp->stopRequest = true;
1754 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1757 sp->parentSstack->bestMove = ss->bestMove = move;
1762 /* Here we have the lock still grabbed */
1764 sp->slaves[threadID] = 0;
1766 lock_release(&(sp->lock));
1770 // connected_moves() tests whether two moves are 'connected' in the sense
1771 // that the first move somehow made the second move possible (for instance
1772 // if the moving piece is the same in both moves). The first move is assumed
1773 // to be the move that was made to reach the current position, while the
1774 // second move is assumed to be a move from the current position.
1776 bool connected_moves(const Position& pos, Move m1, Move m2) {
1778 Square f1, t1, f2, t2;
1781 assert(move_is_ok(m1));
1782 assert(move_is_ok(m2));
1784 if (m2 == MOVE_NONE)
1787 // Case 1: The moving piece is the same in both moves
1793 // Case 2: The destination square for m2 was vacated by m1
1799 // Case 3: Moving through the vacated square
1800 if ( piece_is_slider(pos.piece_on(f2))
1801 && bit_is_set(squares_between(f2, t2), f1))
1804 // Case 4: The destination square for m2 is defended by the moving piece in m1
1805 p = pos.piece_on(t1);
1806 if (bit_is_set(pos.attacks_from(p, t1), t2))
1809 // Case 5: Discovered check, checking piece is the piece moved in m1
1810 if ( piece_is_slider(p)
1811 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1812 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1814 // discovered_check_candidates() works also if the Position's side to
1815 // move is the opposite of the checking piece.
1816 Color them = opposite_color(pos.side_to_move());
1817 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1819 if (bit_is_set(dcCandidates, f2))
1826 // value_is_mate() checks if the given value is a mate one eventually
1827 // compensated for the ply.
1829 bool value_is_mate(Value value) {
1831 assert(abs(value) <= VALUE_INFINITE);
1833 return value <= value_mated_in(PLY_MAX)
1834 || value >= value_mate_in(PLY_MAX);
1838 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1839 // "plies to mate from the current ply". Non-mate scores are unchanged.
1840 // The function is called before storing a value to the transposition table.
1842 Value value_to_tt(Value v, int ply) {
1844 if (v >= value_mate_in(PLY_MAX))
1847 if (v <= value_mated_in(PLY_MAX))
1854 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1855 // the transposition table to a mate score corrected for the current ply.
1857 Value value_from_tt(Value v, int ply) {
1859 if (v >= value_mate_in(PLY_MAX))
1862 if (v <= value_mated_in(PLY_MAX))
1869 // move_is_killer() checks if the given move is among the killer moves
1871 bool move_is_killer(Move m, SearchStack* ss) {
1873 if (ss->killers[0] == m || ss->killers[1] == m)
1880 // extension() decides whether a move should be searched with normal depth,
1881 // or with extended depth. Certain classes of moves (checking moves, in
1882 // particular) are searched with bigger depth than ordinary moves and in
1883 // any case are marked as 'dangerous'. Note that also if a move is not
1884 // extended, as example because the corresponding UCI option is set to zero,
1885 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1886 template <NodeType PvNode>
1887 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1888 bool singleEvasion, bool mateThreat, bool* dangerous) {
1890 assert(m != MOVE_NONE);
1892 Depth result = Depth(0);
1893 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1897 if (moveIsCheck && pos.see_sign(m) >= 0)
1898 result += CheckExtension[PvNode];
1901 result += SingleEvasionExtension[PvNode];
1904 result += MateThreatExtension[PvNode];
1907 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1909 Color c = pos.side_to_move();
1910 if (relative_rank(c, move_to(m)) == RANK_7)
1912 result += PawnPushTo7thExtension[PvNode];
1915 if (pos.pawn_is_passed(c, move_to(m)))
1917 result += PassedPawnExtension[PvNode];
1922 if ( captureOrPromotion
1923 && pos.type_of_piece_on(move_to(m)) != PAWN
1924 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1925 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1926 && !move_is_promotion(m)
1929 result += PawnEndgameExtension[PvNode];
1934 && captureOrPromotion
1935 && pos.type_of_piece_on(move_to(m)) != PAWN
1936 && pos.see_sign(m) >= 0)
1942 return Min(result, OnePly);
1946 // connected_threat() tests whether it is safe to forward prune a move or if
1947 // is somehow coonected to the threat move returned by null search.
1949 bool connected_threat(const Position& pos, Move m, Move threat) {
1951 assert(move_is_ok(m));
1952 assert(threat && move_is_ok(threat));
1953 assert(!pos.move_is_check(m));
1954 assert(!pos.move_is_capture_or_promotion(m));
1955 assert(!pos.move_is_passed_pawn_push(m));
1957 Square mfrom, mto, tfrom, tto;
1959 mfrom = move_from(m);
1961 tfrom = move_from(threat);
1962 tto = move_to(threat);
1964 // Case 1: Don't prune moves which move the threatened piece
1968 // Case 2: If the threatened piece has value less than or equal to the
1969 // value of the threatening piece, don't prune move which defend it.
1970 if ( pos.move_is_capture(threat)
1971 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1972 || pos.type_of_piece_on(tfrom) == KING)
1973 && pos.move_attacks_square(m, tto))
1976 // Case 3: If the moving piece in the threatened move is a slider, don't
1977 // prune safe moves which block its ray.
1978 if ( piece_is_slider(pos.piece_on(tfrom))
1979 && bit_is_set(squares_between(tfrom, tto), mto)
1980 && pos.see_sign(m) >= 0)
1987 // ok_to_use_TT() returns true if a transposition table score
1988 // can be used at a given point in search.
1990 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1992 Value v = value_from_tt(tte->value(), ply);
1994 return ( tte->depth() >= depth
1995 || v >= Max(value_mate_in(PLY_MAX), beta)
1996 || v < Min(value_mated_in(PLY_MAX), beta))
1998 && ( (is_lower_bound(tte->type()) && v >= beta)
1999 || (is_upper_bound(tte->type()) && v < beta));
2003 // refine_eval() returns the transposition table score if
2004 // possible otherwise falls back on static position evaluation.
2006 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2011 Value v = value_from_tt(tte->value(), ply);
2013 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2014 || (is_upper_bound(tte->type()) && v < defaultEval))
2021 // update_history() registers a good move that produced a beta-cutoff
2022 // in history and marks as failures all the other moves of that ply.
2024 void update_history(const Position& pos, Move move, Depth depth,
2025 Move movesSearched[], int moveCount) {
2029 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2031 for (int i = 0; i < moveCount - 1; i++)
2033 m = movesSearched[i];
2037 if (!pos.move_is_capture_or_promotion(m))
2038 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2043 // update_killers() add a good move that produced a beta-cutoff
2044 // among the killer moves of that ply.
2046 void update_killers(Move m, SearchStack* ss) {
2048 if (m == ss->killers[0])
2051 ss->killers[1] = ss->killers[0];
2056 // update_gains() updates the gains table of a non-capture move given
2057 // the static position evaluation before and after the move.
2059 void update_gains(const Position& pos, Move m, Value before, Value after) {
2062 && before != VALUE_NONE
2063 && after != VALUE_NONE
2064 && pos.captured_piece() == NO_PIECE_TYPE
2065 && !move_is_castle(m)
2066 && !move_is_promotion(m))
2067 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2071 // current_search_time() returns the number of milliseconds which have passed
2072 // since the beginning of the current search.
2074 int current_search_time() {
2076 return get_system_time() - SearchStartTime;
2080 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2082 std::string value_to_uci(Value v) {
2084 std::stringstream s;
2086 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2087 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2089 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2094 // nps() computes the current nodes/second count.
2098 int t = current_search_time();
2099 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2103 // poll() performs two different functions: It polls for user input, and it
2104 // looks at the time consumed so far and decides if it's time to abort the
2109 static int lastInfoTime;
2110 int t = current_search_time();
2115 // We are line oriented, don't read single chars
2116 std::string command;
2118 if (!std::getline(std::cin, command))
2121 if (command == "quit")
2124 PonderSearch = false;
2128 else if (command == "stop")
2131 PonderSearch = false;
2133 else if (command == "ponderhit")
2137 // Print search information
2141 else if (lastInfoTime > t)
2142 // HACK: Must be a new search where we searched less than
2143 // NodesBetweenPolls nodes during the first second of search.
2146 else if (t - lastInfoTime >= 1000)
2153 if (dbg_show_hit_rate)
2154 dbg_print_hit_rate();
2156 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2157 << " time " << t << endl;
2160 // Should we stop the search?
2164 bool stillAtFirstMove = FirstRootMove
2165 && !AspirationFailLow
2166 && t > MaxSearchTime + ExtraSearchTime;
2168 bool noMoreTime = t > AbsoluteMaxSearchTime
2169 || stillAtFirstMove;
2171 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2172 || (ExactMaxTime && t >= ExactMaxTime)
2173 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2178 // ponderhit() is called when the program is pondering (i.e. thinking while
2179 // it's the opponent's turn to move) in order to let the engine know that
2180 // it correctly predicted the opponent's move.
2184 int t = current_search_time();
2185 PonderSearch = false;
2187 bool stillAtFirstMove = FirstRootMove
2188 && !AspirationFailLow
2189 && t > MaxSearchTime + ExtraSearchTime;
2191 bool noMoreTime = t > AbsoluteMaxSearchTime
2192 || stillAtFirstMove;
2194 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2199 // init_ss_array() does a fast reset of the first entries of a SearchStack
2200 // array and of all the excludedMove and skipNullMove entries.
2202 void init_ss_array(SearchStack* ss, int size) {
2204 for (int i = 0; i < size; i++, ss++)
2206 ss->excludedMove = MOVE_NONE;
2207 ss->skipNullMove = false;
2208 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 // Generate all legal moves
2735 MoveStack* last = generate_moves(pos, mlist);
2737 // Add each move to the moves[] array
2738 for (MoveStack* cur = mlist; cur != last; cur++)
2740 bool includeMove = includeAllMoves;
2742 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2743 includeMove = (searchMoves[k] == cur->move);
2748 // Find a quick score for the move
2749 init_ss_array(ss, PLY_MAX_PLUS_2);
2750 ss[0].eval = VALUE_NONE;
2751 ss[0].currentMove = cur->move;
2752 pos.do_move(cur->move, st);
2753 moves[count].move = cur->move;
2754 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2755 moves[count].pv[0] = cur->move;
2756 moves[count].pv[1] = MOVE_NONE;
2757 pos.undo_move(cur->move);
2764 // RootMoveList simple methods definitions
2766 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2768 moves[moveNum].nodes = nodes;
2769 moves[moveNum].cumulativeNodes += nodes;
2772 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2774 moves[moveNum].ourBeta = our;
2775 moves[moveNum].theirBeta = their;
2778 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2782 for (j = 0; pv[j] != MOVE_NONE; j++)
2783 moves[moveNum].pv[j] = pv[j];
2785 moves[moveNum].pv[j] = MOVE_NONE;
2789 // RootMoveList::sort() sorts the root move list at the beginning of a new
2792 void RootMoveList::sort() {
2794 sort_multipv(count - 1); // Sort all items
2798 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2799 // list by their scores and depths. It is used to order the different PVs
2800 // correctly in MultiPV mode.
2802 void RootMoveList::sort_multipv(int n) {
2806 for (i = 1; i <= n; i++)
2808 RootMove rm = moves[i];
2809 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2810 moves[j] = moves[j - 1];