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 bool move_is_killer(Move m, SearchStack* ss);
295 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
296 bool connected_threat(const Position& pos, Move m, Move threat);
297 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
298 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
299 void update_killers(Move m, SearchStack* ss);
300 void update_gains(const Position& pos, Move move, Value before, Value after);
302 int current_search_time();
306 void wait_for_stop_or_ponderhit();
307 void init_ss_array(SearchStack* ss, int size);
308 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
310 #if !defined(_MSC_VER)
311 void *init_thread(void *threadID);
313 DWORD WINAPI init_thread(LPVOID threadID);
323 /// init_threads(), exit_threads() and nodes_searched() are helpers to
324 /// give accessibility to some TM methods from outside of current file.
326 void init_threads() { TM.init_threads(); }
327 void exit_threads() { TM.exit_threads(); }
328 int64_t nodes_searched() { return TM.nodes_searched(); }
331 /// init_search() is called during startup. It initializes various lookup tables
335 int d; // depth (OnePly == 2)
336 int hd; // half depth (OnePly == 1)
339 // Init reductions array
340 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
342 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
343 double nonPVRed = log(double(hd)) * log(double(mc)) / 1.5;
344 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
345 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
348 // Init futility margins array
349 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
350 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
352 // Init futility move count array
353 for (d = 0; d < 32; d++)
354 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
358 // SearchStack::init() initializes a search stack entry.
359 // Called at the beginning of search() when starting to examine a new node.
360 void SearchStack::init() {
362 currentMove = threatMove = bestMove = MOVE_NONE;
363 reduction = Depth(0);
367 // SearchStack::initKillers() initializes killers for a search stack entry
368 void SearchStack::initKillers() {
370 mateKiller = MOVE_NONE;
371 for (int i = 0; i < KILLER_MAX; i++)
372 killers[i] = MOVE_NONE;
376 /// perft() is our utility to verify move generation is bug free. All the legal
377 /// moves up to given depth are generated and counted and the sum returned.
379 int perft(Position& pos, Depth depth)
384 MovePicker mp(pos, MOVE_NONE, depth, H);
386 // If we are at the last ply we don't need to do and undo
387 // the moves, just to count them.
388 if (depth <= OnePly) // Replace with '<' to test also qsearch
390 while (mp.get_next_move()) sum++;
394 // Loop through all legal moves
396 while ((move = mp.get_next_move()) != MOVE_NONE)
398 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
399 sum += perft(pos, depth - OnePly);
406 /// think() is the external interface to Stockfish's search, and is called when
407 /// the program receives the UCI 'go' command. It initializes various
408 /// search-related global variables, and calls root_search(). It returns false
409 /// when a quit command is received during the search.
411 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
412 int time[], int increment[], int movesToGo, int maxDepth,
413 int maxNodes, int maxTime, Move searchMoves[]) {
415 // Initialize global search variables
416 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
417 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
419 TM.resetNodeCounters();
420 SearchStartTime = get_system_time();
421 ExactMaxTime = maxTime;
424 InfiniteSearch = infinite;
425 PonderSearch = ponder;
426 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
428 // Look for a book move, only during games, not tests
429 if (UseTimeManagement && get_option_value_bool("OwnBook"))
431 if (get_option_value_string("Book File") != OpeningBook.file_name())
432 OpeningBook.open(get_option_value_string("Book File"));
434 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
435 if (bookMove != MOVE_NONE)
438 wait_for_stop_or_ponderhit();
440 cout << "bestmove " << bookMove << endl;
445 // Read UCI option values
446 TT.set_size(get_option_value_int("Hash"));
447 if (button_was_pressed("Clear Hash"))
450 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
451 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
452 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
453 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
454 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
455 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
456 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
457 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
458 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
459 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
460 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
461 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
463 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
464 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
465 MultiPV = get_option_value_int("MultiPV");
466 Chess960 = get_option_value_bool("UCI_Chess960");
467 UseLogFile = get_option_value_bool("Use Search Log");
470 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
472 read_weights(pos.side_to_move());
474 // Set the number of active threads
475 int newActiveThreads = get_option_value_int("Threads");
476 if (newActiveThreads != TM.active_threads())
478 TM.set_active_threads(newActiveThreads);
479 init_eval(TM.active_threads());
482 // Wake up sleeping threads
483 TM.wake_sleeping_threads();
486 int myTime = time[side_to_move];
487 int myIncrement = increment[side_to_move];
488 if (UseTimeManagement)
490 if (!movesToGo) // Sudden death time control
494 MaxSearchTime = myTime / 30 + myIncrement;
495 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
497 else // Blitz game without increment
499 MaxSearchTime = myTime / 30;
500 AbsoluteMaxSearchTime = myTime / 8;
503 else // (x moves) / (y minutes)
507 MaxSearchTime = myTime / 2;
508 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
512 MaxSearchTime = myTime / Min(movesToGo, 20);
513 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
517 if (get_option_value_bool("Ponder"))
519 MaxSearchTime += MaxSearchTime / 4;
520 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
524 // Set best NodesBetweenPolls interval to avoid lagging under
525 // heavy time pressure.
527 NodesBetweenPolls = Min(MaxNodes, 30000);
528 else if (myTime && myTime < 1000)
529 NodesBetweenPolls = 1000;
530 else if (myTime && myTime < 5000)
531 NodesBetweenPolls = 5000;
533 NodesBetweenPolls = 30000;
535 // Write search information to log file
537 LogFile << "Searching: " << pos.to_fen() << endl
538 << "infinite: " << infinite
539 << " ponder: " << ponder
540 << " time: " << myTime
541 << " increment: " << myIncrement
542 << " moves to go: " << movesToGo << endl;
544 // We're ready to start thinking. Call the iterative deepening loop function
545 id_loop(pos, searchMoves);
550 TM.put_threads_to_sleep();
558 // id_loop() is the main iterative deepening loop. It calls root_search
559 // repeatedly with increasing depth until the allocated thinking time has
560 // been consumed, the user stops the search, or the maximum search depth is
563 Value id_loop(const Position& pos, Move searchMoves[]) {
565 Position p(pos, pos.thread());
566 SearchStack ss[PLY_MAX_PLUS_2];
567 Move pv[PLY_MAX_PLUS_2];
568 Move EasyMove = MOVE_NONE;
569 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
571 // Moves to search are verified, copied, scored and sorted
572 RootMoveList rml(p, searchMoves);
574 // Handle special case of searching on a mate/stale position
575 if (rml.move_count() == 0)
578 wait_for_stop_or_ponderhit();
580 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
583 // Print RootMoveList startup scoring to the standard output,
584 // so to output information also for iteration 1.
585 cout << "info depth " << 1
586 << "\ninfo depth " << 1
587 << " score " << value_to_string(rml.get_move_score(0))
588 << " time " << current_search_time()
589 << " nodes " << TM.nodes_searched()
591 << " pv " << rml.get_move(0) << "\n";
596 init_ss_array(ss, PLY_MAX_PLUS_2);
597 pv[0] = pv[1] = MOVE_NONE;
598 ValueByIteration[1] = rml.get_move_score(0);
601 // Is one move significantly better than others after initial scoring ?
602 if ( rml.move_count() == 1
603 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
604 EasyMove = rml.get_move(0);
606 // Iterative deepening loop
607 while (Iteration < PLY_MAX)
609 // Initialize iteration
611 BestMoveChangesByIteration[Iteration] = 0;
613 cout << "info depth " << Iteration << endl;
615 // Calculate dynamic aspiration window based on previous iterations
616 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
618 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
619 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
621 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
622 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
624 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
625 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
628 // Search to the current depth, rml is updated and sorted, alpha and beta could change
629 value = root_search(p, ss, pv, rml, &alpha, &beta);
631 // Write PV to transposition table, in case the relevant entries have
632 // been overwritten during the search.
636 break; // Value cannot be trusted. Break out immediately!
638 //Save info about search result
639 ValueByIteration[Iteration] = value;
641 // Drop the easy move if differs from the new best move
642 if (pv[0] != EasyMove)
643 EasyMove = MOVE_NONE;
645 if (UseTimeManagement)
648 bool stopSearch = false;
650 // Stop search early if there is only a single legal move,
651 // we search up to Iteration 6 anyway to get a proper score.
652 if (Iteration >= 6 && rml.move_count() == 1)
655 // Stop search early when the last two iterations returned a mate score
657 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
658 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
661 // Stop search early if one move seems to be much better than the others
662 int64_t nodes = TM.nodes_searched();
665 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
666 && current_search_time() > MaxSearchTime / 16)
667 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
668 && current_search_time() > MaxSearchTime / 32)))
671 // Add some extra time if the best move has changed during the last two iterations
672 if (Iteration > 5 && Iteration <= 50)
673 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
674 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
676 // Stop search if most of MaxSearchTime is consumed at the end of the
677 // iteration. We probably don't have enough time to search the first
678 // move at the next iteration anyway.
679 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
685 StopOnPonderhit = true;
691 if (MaxDepth && Iteration >= MaxDepth)
695 // If we are pondering or in infinite search, we shouldn't print the
696 // best move before we are told to do so.
697 if (!AbortSearch && (PonderSearch || InfiniteSearch))
698 wait_for_stop_or_ponderhit();
700 // Print final search statistics
701 cout << "info nodes " << TM.nodes_searched()
703 << " time " << current_search_time() << endl;
705 // Print the best move and the ponder move to the standard output
706 if (pv[0] == MOVE_NONE)
708 pv[0] = rml.get_move(0);
712 assert(pv[0] != MOVE_NONE);
714 cout << "bestmove " << pv[0];
716 if (pv[1] != MOVE_NONE)
717 cout << " ponder " << pv[1];
724 dbg_print_mean(LogFile);
726 if (dbg_show_hit_rate)
727 dbg_print_hit_rate(LogFile);
729 LogFile << "\nNodes: " << TM.nodes_searched()
730 << "\nNodes/second: " << nps()
731 << "\nBest move: " << move_to_san(p, pv[0]);
734 p.do_move(pv[0], st);
735 LogFile << "\nPonder move: "
736 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
739 return rml.get_move_score(0);
743 // root_search() is the function which searches the root node. It is
744 // similar to search_pv except that it uses a different move ordering
745 // scheme, prints some information to the standard output and handles
746 // the fail low/high loops.
748 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
755 Depth depth, ext, newDepth;
756 Value value, alpha, beta;
757 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
758 int researchCountFH, researchCountFL;
760 researchCountFH = researchCountFL = 0;
763 isCheck = pos.is_check();
765 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
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
773 ss->eval = evaluate(pos, ei);
775 // Step 6. Razoring (omitted at root)
776 // Step 7. Static null move pruning (omitted at root)
777 // Step 8. Null move search with verification search (omitted at root)
778 // Step 9. Internal iterative deepening (omitted at root)
780 // Step extra. Fail low loop
781 // We start with small aspiration window and in case of fail low, we research
782 // with bigger window until we are not failing low anymore.
785 // Sort the moves before to (re)search
788 // Step 10. Loop through all moves in the root move list
789 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
791 // This is used by time management
792 FirstRootMove = (i == 0);
794 // Save the current node count before the move is searched
795 nodes = TM.nodes_searched();
797 // Reset beta cut-off counters
798 TM.resetBetaCounters();
800 // Pick the next root move, and print the move and the move number to
801 // the standard output.
802 move = ss->currentMove = rml.get_move(i);
804 if (current_search_time() >= 1000)
805 cout << "info currmove " << move
806 << " currmovenumber " << i + 1 << endl;
808 moveIsCheck = pos.move_is_check(move);
809 captureOrPromotion = pos.move_is_capture_or_promotion(move);
811 // Step 11. Decide the new search depth
812 depth = (Iteration - 2) * OnePly + InitialDepth;
813 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
814 newDepth = depth + ext;
816 // Step 12. Futility pruning (omitted at root)
818 // Step extra. Fail high loop
819 // If move fails high, we research with bigger window until we are not failing
821 value = - VALUE_INFINITE;
825 // Step 13. Make the move
826 pos.do_move(move, st, ci, moveIsCheck);
828 // Step extra. pv search
829 // We do pv search for first moves (i < MultiPV)
830 // and for fail high research (value > alpha)
831 if (i < MultiPV || value > alpha)
833 // Aspiration window is disabled in multi-pv case
835 alpha = -VALUE_INFINITE;
837 // Full depth PV search, done on first move or after a fail high
838 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
842 // Step 14. Reduced search
843 // if the move fails high will be re-searched at full depth
844 bool doFullDepthSearch = true;
846 if ( depth >= 3 * OnePly
848 && !captureOrPromotion
849 && !move_is_castle(move))
851 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
854 assert(newDepth-ss->reduction >= OnePly);
856 // Reduced depth non-pv search using alpha as upperbound
857 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
858 doFullDepthSearch = (value > alpha);
861 // The move failed high, but if reduction is very big we could
862 // face a false positive, retry with a less aggressive reduction,
863 // if the move fails high again then go with full depth search.
864 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
866 assert(newDepth - OnePly >= OnePly);
868 ss->reduction = OnePly;
869 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
870 doFullDepthSearch = (value > alpha);
872 ss->reduction = Depth(0); // Restore original reduction
875 // Step 15. Full depth search
876 if (doFullDepthSearch)
878 // Full depth non-pv search using alpha as upperbound
879 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
881 // If we are above alpha then research at same depth but as PV
882 // to get a correct score or eventually a fail high above beta.
884 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
888 // Step 16. Undo move
891 // Can we exit fail high loop ?
892 if (AbortSearch || value < beta)
895 // We are failing high and going to do a research. It's important to update
896 // the score before research in case we run out of time while researching.
897 rml.set_move_score(i, value);
899 TT.extract_pv(pos, move, pv, PLY_MAX);
900 rml.set_move_pv(i, pv);
902 // Print information to the standard output
903 print_pv_info(pos, pv, alpha, beta, value);
905 // Prepare for a research after a fail high, each time with a wider window
906 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
909 } // End of fail high loop
911 // Finished searching the move. If AbortSearch is true, the search
912 // was aborted because the user interrupted the search or because we
913 // ran out of time. In this case, the return value of the search cannot
914 // be trusted, and we break out of the loop without updating the best
919 // Remember beta-cutoff and searched nodes counts for this move. The
920 // info is used to sort the root moves for the next iteration.
922 TM.get_beta_counters(pos.side_to_move(), our, their);
923 rml.set_beta_counters(i, our, their);
924 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
926 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
927 assert(value < beta);
929 // Step 17. Check for new best move
930 if (value <= alpha && i >= MultiPV)
931 rml.set_move_score(i, -VALUE_INFINITE);
934 // PV move or new best move!
937 rml.set_move_score(i, value);
939 TT.extract_pv(pos, move, pv, PLY_MAX);
940 rml.set_move_pv(i, pv);
944 // We record how often the best move has been changed in each
945 // iteration. This information is used for time managment: When
946 // the best move changes frequently, we allocate some more time.
948 BestMoveChangesByIteration[Iteration]++;
950 // Print information to the standard output
951 print_pv_info(pos, pv, alpha, beta, value);
953 // Raise alpha to setup proper non-pv search upper bound
960 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
962 cout << "info multipv " << j + 1
963 << " score " << value_to_string(rml.get_move_score(j))
964 << " depth " << (j <= i ? Iteration : Iteration - 1)
965 << " time " << current_search_time()
966 << " nodes " << TM.nodes_searched()
970 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
971 cout << rml.get_move_pv(j, k) << " ";
975 alpha = rml.get_move_score(Min(i, MultiPV - 1));
977 } // PV move or new best move
979 assert(alpha >= *alphaPtr);
981 AspirationFailLow = (alpha == *alphaPtr);
983 if (AspirationFailLow && StopOnPonderhit)
984 StopOnPonderhit = false;
987 // Can we exit fail low loop ?
988 if (AbortSearch || !AspirationFailLow)
991 // Prepare for a research after a fail low, each time with a wider window
992 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
997 // Sort the moves before to return
1004 // search<>() is the main search function for both PV and non-PV nodes
1006 template <NodeType PvNode>
1007 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1009 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1010 assert(beta > alpha && beta <= VALUE_INFINITE);
1011 assert(PvNode || alpha == beta - 1);
1012 assert(ply > 0 && ply < PLY_MAX);
1013 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1015 Move movesSearched[256];
1020 Move ttMove, move, excludedMove;
1021 Depth ext, newDepth;
1022 Value bestValue, value, oldAlpha;
1023 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1024 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
1025 bool mateThreat = false;
1027 int threadID = pos.thread();
1028 refinedValue = bestValue = value = -VALUE_INFINITE;
1031 // Step 1. Initialize node and poll. Polling can abort search
1032 TM.incrementNodeCounter(threadID);
1034 (ss+2)->initKillers();
1036 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1042 // Step 2. Check for aborted search and immediate draw
1043 if (AbortSearch || TM.thread_should_stop(threadID))
1046 if (pos.is_draw() || ply >= PLY_MAX - 1)
1049 // Step 3. Mate distance pruning
1050 alpha = Max(value_mated_in(ply), alpha);
1051 beta = Min(value_mate_in(ply+1), beta);
1055 // Step 4. Transposition table lookup
1057 // We don't want the score of a partial search to overwrite a previous full search
1058 // TT value, so we use a different position key in case of an excluded move exists.
1059 excludedMove = ss->excludedMove;
1060 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1062 tte = TT.retrieve(posKey);
1063 ttMove = (tte ? tte->move() : MOVE_NONE);
1065 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1066 // This is to avoid problems in the following areas:
1068 // * Repetition draw detection
1069 // * Fifty move rule detection
1070 // * Searching for a mate
1071 // * Printing of full PV line
1073 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1075 // Refresh tte entry to avoid aging
1076 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1078 ss->currentMove = ttMove; // Can be MOVE_NONE
1079 return value_from_tt(tte->value(), ply);
1082 // Step 5. Evaluate the position statically
1083 // At PV nodes we do this only to update gain statistics
1084 isCheck = pos.is_check();
1087 if (tte && tte->static_value() != VALUE_NONE)
1089 ss->eval = tte->static_value();
1090 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1093 ss->eval = evaluate(pos, ei);
1095 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1096 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1099 // Step 6. Razoring (is omitted in PV nodes)
1101 && depth < RazorDepth
1103 && refinedValue < beta - razor_margin(depth)
1104 && ttMove == MOVE_NONE
1105 && (ss-1)->currentMove != MOVE_NULL
1106 && !value_is_mate(beta)
1107 && !pos.has_pawn_on_7th(pos.side_to_move()))
1109 // Pass ss->eval to qsearch() and avoid an evaluate call
1110 if (!tte || tte->static_value() == VALUE_NONE)
1111 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1113 Value rbeta = beta - razor_margin(depth);
1114 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1116 // Logically we should return (v + razor_margin(depth)), but
1117 // surprisingly this did slightly weaker in tests.
1121 // Step 7. Static null move pruning (is omitted in PV nodes)
1122 // We're betting that the opponent doesn't have a move that will reduce
1123 // the score by more than futility_margin(depth) if we do a null move.
1125 && !ss->skipNullMove
1126 && depth < RazorDepth
1127 && refinedValue >= beta + futility_margin(depth, 0)
1129 && !value_is_mate(beta)
1130 && pos.non_pawn_material(pos.side_to_move()))
1131 return refinedValue - futility_margin(depth, 0);
1133 // Step 8. Null move search with verification search (is omitted in PV nodes)
1134 // When we jump directly to qsearch() we do a null move only if static value is
1135 // at least beta. Otherwise we do a null move if static value is not more than
1136 // NullMoveMargin under beta.
1138 && !ss->skipNullMove
1140 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1142 && !value_is_mate(beta)
1143 && pos.non_pawn_material(pos.side_to_move()))
1145 ss->currentMove = MOVE_NULL;
1147 // Null move dynamic reduction based on depth
1148 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1150 // Null move dynamic reduction based on value
1151 if (refinedValue - beta > PawnValueMidgame)
1154 pos.do_null_move(st);
1155 (ss+1)->skipNullMove = true;
1157 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1158 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1159 (ss+1)->skipNullMove = false;
1160 pos.undo_null_move();
1162 if (nullValue >= beta)
1164 // Do not return unproven mate scores
1165 if (nullValue >= value_mate_in(PLY_MAX))
1168 if (depth < 6 * OnePly)
1171 // Do verification search at high depths
1172 ss->skipNullMove = true;
1173 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1174 ss->skipNullMove = false;
1181 // The null move failed low, which means that we may be faced with
1182 // some kind of threat. If the previous move was reduced, check if
1183 // the move that refuted the null move was somehow connected to the
1184 // move which was reduced. If a connection is found, return a fail
1185 // low score (which will cause the reduced move to fail high in the
1186 // parent node, which will trigger a re-search with full depth).
1187 if (nullValue == value_mated_in(ply + 2))
1190 ss->threatMove = (ss+1)->currentMove;
1191 if ( depth < ThreatDepth
1192 && (ss-1)->reduction
1193 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1198 // Step 9. Internal iterative deepening
1199 if ( depth >= IIDDepth[PvNode]
1200 && ttMove == MOVE_NONE
1201 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1203 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1205 ss->skipNullMove = true;
1206 search<PvNode>(pos, ss, alpha, beta, d, ply);
1207 ss->skipNullMove = false;
1209 ttMove = ss->bestMove;
1210 tte = TT.retrieve(posKey);
1213 // Expensive mate threat detection (only for PV nodes)
1215 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1217 // Initialize a MovePicker object for the current position
1218 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1220 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1221 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1222 && tte && tte->move()
1223 && !excludedMove // Do not allow recursive singular extension search
1224 && is_lower_bound(tte->type())
1225 && tte->depth() >= depth - 3 * OnePly;
1227 // Step 10. Loop through moves
1228 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1229 while ( bestValue < beta
1230 && (move = mp.get_next_move()) != MOVE_NONE
1231 && !TM.thread_should_stop(threadID))
1233 assert(move_is_ok(move));
1235 if (move == excludedMove)
1238 moveIsCheck = pos.move_is_check(move, ci);
1239 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1241 // Step 11. Decide the new search depth
1242 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1244 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1245 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1246 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1247 // lower then ttValue minus a margin then we extend ttMove.
1248 if ( singularExtensionNode
1249 && move == tte->move()
1252 Value ttValue = value_from_tt(tte->value(), ply);
1254 if (abs(ttValue) < VALUE_KNOWN_WIN)
1256 Value b = ttValue - SingularExtensionMargin;
1257 ss->excludedMove = move;
1258 ss->skipNullMove = true;
1259 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1260 ss->skipNullMove = false;
1261 ss->excludedMove = MOVE_NONE;
1267 newDepth = depth - OnePly + ext;
1269 // Update current move (this must be done after singular extension search)
1270 movesSearched[moveCount++] = ss->currentMove = move;
1272 // Step 12. Futility pruning (is omitted in PV nodes)
1274 && !captureOrPromotion
1278 && !move_is_castle(move))
1280 // Move count based pruning
1281 if ( moveCount >= futility_move_count(depth)
1282 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1283 && bestValue > value_mated_in(PLY_MAX))
1286 // Value based pruning
1287 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1288 // but fixing this made program slightly weaker.
1289 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1290 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1291 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1293 if (futilityValueScaled < beta)
1295 if (futilityValueScaled > bestValue)
1296 bestValue = futilityValueScaled;
1301 // Step 13. Make the move
1302 pos.do_move(move, st, ci, moveIsCheck);
1304 // Step extra. pv search (only in PV nodes)
1305 // The first move in list is the expected PV
1306 if (PvNode && moveCount == 1)
1307 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1308 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1311 // Step 14. Reduced depth search
1312 // If the move fails high will be re-searched at full depth.
1313 bool doFullDepthSearch = true;
1315 if ( depth >= 3 * OnePly
1316 && !captureOrPromotion
1318 && !move_is_castle(move)
1319 && !move_is_killer(move, ss))
1321 ss->reduction = reduction<PvNode>(depth, moveCount);
1324 Depth d = newDepth - ss->reduction;
1325 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1326 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1328 doFullDepthSearch = (value > alpha);
1331 // The move failed high, but if reduction is very big we could
1332 // face a false positive, retry with a less aggressive reduction,
1333 // if the move fails high again then go with full depth search.
1334 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1336 assert(newDepth - OnePly >= OnePly);
1338 ss->reduction = OnePly;
1339 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1340 doFullDepthSearch = (value > alpha);
1342 ss->reduction = Depth(0); // Restore original reduction
1345 // Step 15. Full depth search
1346 if (doFullDepthSearch)
1348 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1349 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1351 // Step extra. pv search (only in PV nodes)
1352 // Search only for possible new PV nodes, if instead value >= beta then
1353 // parent node fails low with value <= alpha and tries another move.
1354 if (PvNode && value > alpha && value < beta)
1355 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1356 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1360 // Step 16. Undo move
1361 pos.undo_move(move);
1363 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1365 // Step 17. Check for new best move
1366 if (value > bestValue)
1371 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1374 if (value == value_mate_in(ply + 1))
1375 ss->mateKiller = move;
1377 ss->bestMove = move;
1381 // Step 18. Check for split
1382 if ( depth >= MinimumSplitDepth
1383 && TM.active_threads() > 1
1385 && TM.available_thread_exists(threadID)
1387 && !TM.thread_should_stop(threadID)
1389 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1390 mateThreat, &moveCount, &mp, PvNode);
1393 // Step 19. Check for mate and stalemate
1394 // All legal moves have been searched and if there are
1395 // no legal moves, it must be mate or stalemate.
1396 // If one move was excluded return fail low score.
1398 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1400 // Step 20. Update tables
1401 // If the search is not aborted, update the transposition table,
1402 // history counters, and killer moves.
1403 if (AbortSearch || TM.thread_should_stop(threadID))
1406 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1407 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1408 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1410 // Update killers and history only for non capture moves that fails high
1411 if (bestValue >= beta)
1413 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1414 if (!pos.move_is_capture_or_promotion(move))
1416 update_history(pos, move, depth, movesSearched, moveCount);
1417 update_killers(move, ss);
1421 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1427 // qsearch() is the quiescence search function, which is called by the main
1428 // search function when the remaining depth is zero (or, to be more precise,
1429 // less than OnePly).
1431 template <NodeType PvNode>
1432 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1434 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1435 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1436 assert(PvNode || alpha == beta - 1);
1438 assert(ply > 0 && ply < PLY_MAX);
1439 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1444 Value bestValue, value, futilityValue, futilityBase;
1445 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1447 Value oldAlpha = alpha;
1449 TM.incrementNodeCounter(pos.thread());
1450 ss->bestMove = ss->currentMove = MOVE_NONE;
1451 ss->eval = VALUE_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 deepChecks = enoughMaterial = false;
1478 if (tte && tte->static_value() != VALUE_NONE)
1480 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1481 bestValue = tte->static_value();
1484 bestValue = evaluate(pos, ei);
1486 ss->eval = bestValue;
1487 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1489 // Stand pat. Return immediately if static value is at least beta
1490 if (bestValue >= beta)
1493 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()]);
1498 if (PvNode && bestValue > alpha)
1501 // If we are near beta then try to get a cutoff pushing checks a bit further
1502 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1504 // Futility pruning parameters, not needed when in check
1505 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1506 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1509 // Initialize a MovePicker object for the current position, and prepare
1510 // to search the moves. Because the depth is <= 0 here, only captures,
1511 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1512 // and we are near beta) will be generated.
1513 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1516 // Loop through the moves until no moves remain or a beta cutoff occurs
1517 while ( alpha < beta
1518 && (move = mp.get_next_move()) != MOVE_NONE)
1520 assert(move_is_ok(move));
1522 moveIsCheck = pos.move_is_check(move, ci);
1530 && !move_is_promotion(move)
1531 && !pos.move_is_passed_pawn_push(move))
1533 futilityValue = futilityBase
1534 + pos.endgame_value_of_piece_on(move_to(move))
1535 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1537 if (futilityValue < alpha)
1539 if (futilityValue > bestValue)
1540 bestValue = futilityValue;
1545 // Detect blocking evasions that are candidate to be pruned
1546 evasionPrunable = isCheck
1547 && bestValue > value_mated_in(PLY_MAX)
1548 && !pos.move_is_capture(move)
1549 && pos.type_of_piece_on(move_from(move)) != KING
1550 && !pos.can_castle(pos.side_to_move());
1552 // Don't search moves with negative SEE values
1554 && (!isCheck || evasionPrunable)
1556 && !move_is_promotion(move)
1557 && pos.see_sign(move) < 0)
1560 // Update current move
1561 ss->currentMove = move;
1563 // Make and search the move
1564 pos.do_move(move, st, ci, moveIsCheck);
1565 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1566 pos.undo_move(move);
1568 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1571 if (value > bestValue)
1577 ss->bestMove = move;
1582 // All legal moves have been searched. A special case: If we're in check
1583 // and no legal moves were found, it is checkmate.
1584 if (isCheck && bestValue == -VALUE_INFINITE)
1585 return value_mated_in(ply);
1587 // Update transposition table
1588 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1589 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1590 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1592 // Update killers only for checking moves that fails high
1593 if ( bestValue >= beta
1594 && !pos.move_is_capture_or_promotion(ss->bestMove))
1595 update_killers(ss->bestMove, ss);
1597 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1603 // sp_search() is used to search from a split point. This function is called
1604 // by each thread working at the split point. It is similar to the normal
1605 // search() function, but simpler. Because we have already probed the hash
1606 // table, done a null move search, and searched the first move before
1607 // splitting, we don't have to repeat all this work in sp_search(). We
1608 // also don't need to store anything to the hash table here: This is taken
1609 // care of after we return from the split point.
1611 template <NodeType PvNode>
1612 void sp_search(SplitPoint* sp, int threadID) {
1614 assert(threadID >= 0 && threadID < TM.active_threads());
1615 assert(TM.active_threads() > 1);
1619 Depth ext, newDepth;
1621 Value futilityValueScaled; // NonPV specific
1622 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1624 value = -VALUE_INFINITE;
1626 Position pos(*sp->pos, threadID);
1628 SearchStack* ss = sp->sstack[threadID] + 1;
1629 isCheck = pos.is_check();
1631 // Step 10. Loop through moves
1632 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1633 lock_grab(&(sp->lock));
1635 while ( sp->bestValue < sp->beta
1636 && (move = sp->mp->get_next_move()) != MOVE_NONE
1637 && !TM.thread_should_stop(threadID))
1639 moveCount = ++sp->moveCount;
1640 lock_release(&(sp->lock));
1642 assert(move_is_ok(move));
1644 moveIsCheck = pos.move_is_check(move, ci);
1645 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1647 // Step 11. Decide the new search depth
1648 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1649 newDepth = sp->depth - OnePly + ext;
1651 // Update current move
1652 ss->currentMove = move;
1654 // Step 12. Futility pruning (is omitted in PV nodes)
1656 && !captureOrPromotion
1659 && !move_is_castle(move))
1661 // Move count based pruning
1662 if ( moveCount >= futility_move_count(sp->depth)
1663 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1664 && sp->bestValue > value_mated_in(PLY_MAX))
1666 lock_grab(&(sp->lock));
1670 // Value based pruning
1671 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1672 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1673 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1675 if (futilityValueScaled < sp->beta)
1677 lock_grab(&(sp->lock));
1679 if (futilityValueScaled > sp->bestValue)
1680 sp->bestValue = futilityValueScaled;
1685 // Step 13. Make the move
1686 pos.do_move(move, st, ci, moveIsCheck);
1688 // Step 14. Reduced search
1689 // If the move fails high will be re-searched at full depth.
1690 bool doFullDepthSearch = true;
1692 if ( !captureOrPromotion
1694 && !move_is_castle(move)
1695 && !move_is_killer(move, ss))
1697 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1700 Value localAlpha = sp->alpha;
1701 Depth d = newDepth - ss->reduction;
1702 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1703 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1705 doFullDepthSearch = (value > localAlpha);
1708 // The move failed high, but if reduction is very big we could
1709 // face a false positive, retry with a less aggressive reduction,
1710 // if the move fails high again then go with full depth search.
1711 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1713 assert(newDepth - OnePly >= OnePly);
1715 ss->reduction = OnePly;
1716 Value localAlpha = sp->alpha;
1717 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1718 doFullDepthSearch = (value > localAlpha);
1720 ss->reduction = Depth(0); // Restore original reduction
1723 // Step 15. Full depth search
1724 if (doFullDepthSearch)
1726 Value localAlpha = sp->alpha;
1727 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1728 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1730 // Step extra. pv search (only in PV nodes)
1731 // Search only for possible new PV nodes, if instead value >= beta then
1732 // parent node fails low with value <= alpha and tries another move.
1733 if (PvNode && value > localAlpha && value < sp->beta)
1734 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1735 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1738 // Step 16. Undo move
1739 pos.undo_move(move);
1741 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1743 // Step 17. Check for new best move
1744 lock_grab(&(sp->lock));
1746 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1748 sp->bestValue = value;
1750 if (sp->bestValue > sp->alpha)
1752 if (!PvNode || value >= sp->beta)
1753 sp->stopRequest = true;
1755 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1758 sp->parentSstack->bestMove = ss->bestMove = move;
1763 /* Here we have the lock still grabbed */
1765 sp->slaves[threadID] = 0;
1767 lock_release(&(sp->lock));
1771 // connected_moves() tests whether two moves are 'connected' in the sense
1772 // that the first move somehow made the second move possible (for instance
1773 // if the moving piece is the same in both moves). The first move is assumed
1774 // to be the move that was made to reach the current position, while the
1775 // second move is assumed to be a move from the current position.
1777 bool connected_moves(const Position& pos, Move m1, Move m2) {
1779 Square f1, t1, f2, t2;
1782 assert(move_is_ok(m1));
1783 assert(move_is_ok(m2));
1785 if (m2 == MOVE_NONE)
1788 // Case 1: The moving piece is the same in both moves
1794 // Case 2: The destination square for m2 was vacated by m1
1800 // Case 3: Moving through the vacated square
1801 if ( piece_is_slider(pos.piece_on(f2))
1802 && bit_is_set(squares_between(f2, t2), f1))
1805 // Case 4: The destination square for m2 is defended by the moving piece in m1
1806 p = pos.piece_on(t1);
1807 if (bit_is_set(pos.attacks_from(p, t1), t2))
1810 // Case 5: Discovered check, checking piece is the piece moved in m1
1811 if ( piece_is_slider(p)
1812 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1813 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1815 // discovered_check_candidates() works also if the Position's side to
1816 // move is the opposite of the checking piece.
1817 Color them = opposite_color(pos.side_to_move());
1818 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1820 if (bit_is_set(dcCandidates, f2))
1827 // value_is_mate() checks if the given value is a mate one
1828 // eventually compensated for the ply.
1830 bool value_is_mate(Value value) {
1832 assert(abs(value) <= VALUE_INFINITE);
1834 return value <= value_mated_in(PLY_MAX)
1835 || value >= value_mate_in(PLY_MAX);
1839 // move_is_killer() checks if the given move is among the
1840 // killer moves of that ply.
1842 bool move_is_killer(Move m, SearchStack* ss) {
1844 const Move* k = ss->killers;
1845 for (int i = 0; i < KILLER_MAX; i++, k++)
1853 // extension() decides whether a move should be searched with normal depth,
1854 // or with extended depth. Certain classes of moves (checking moves, in
1855 // particular) are searched with bigger depth than ordinary moves and in
1856 // any case are marked as 'dangerous'. Note that also if a move is not
1857 // extended, as example because the corresponding UCI option is set to zero,
1858 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1859 template <NodeType PvNode>
1860 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1861 bool singleEvasion, bool mateThreat, bool* dangerous) {
1863 assert(m != MOVE_NONE);
1865 Depth result = Depth(0);
1866 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1870 if (moveIsCheck && pos.see_sign(m) >= 0)
1871 result += CheckExtension[PvNode];
1874 result += SingleEvasionExtension[PvNode];
1877 result += MateThreatExtension[PvNode];
1880 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1882 Color c = pos.side_to_move();
1883 if (relative_rank(c, move_to(m)) == RANK_7)
1885 result += PawnPushTo7thExtension[PvNode];
1888 if (pos.pawn_is_passed(c, move_to(m)))
1890 result += PassedPawnExtension[PvNode];
1895 if ( captureOrPromotion
1896 && pos.type_of_piece_on(move_to(m)) != PAWN
1897 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1898 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1899 && !move_is_promotion(m)
1902 result += PawnEndgameExtension[PvNode];
1907 && captureOrPromotion
1908 && pos.type_of_piece_on(move_to(m)) != PAWN
1909 && pos.see_sign(m) >= 0)
1915 return Min(result, OnePly);
1919 // connected_threat() tests whether it is safe to forward prune a move or if
1920 // is somehow coonected to the threat move returned by null search.
1922 bool connected_threat(const Position& pos, Move m, Move threat) {
1924 assert(move_is_ok(m));
1925 assert(threat && move_is_ok(threat));
1926 assert(!pos.move_is_check(m));
1927 assert(!pos.move_is_capture_or_promotion(m));
1928 assert(!pos.move_is_passed_pawn_push(m));
1930 Square mfrom, mto, tfrom, tto;
1932 mfrom = move_from(m);
1934 tfrom = move_from(threat);
1935 tto = move_to(threat);
1937 // Case 1: Don't prune moves which move the threatened piece
1941 // Case 2: If the threatened piece has value less than or equal to the
1942 // value of the threatening piece, don't prune move which defend it.
1943 if ( pos.move_is_capture(threat)
1944 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1945 || pos.type_of_piece_on(tfrom) == KING)
1946 && pos.move_attacks_square(m, tto))
1949 // Case 3: If the moving piece in the threatened move is a slider, don't
1950 // prune safe moves which block its ray.
1951 if ( piece_is_slider(pos.piece_on(tfrom))
1952 && bit_is_set(squares_between(tfrom, tto), mto)
1953 && pos.see_sign(m) >= 0)
1960 // ok_to_use_TT() returns true if a transposition table score
1961 // can be used at a given point in search.
1963 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1965 Value v = value_from_tt(tte->value(), ply);
1967 return ( tte->depth() >= depth
1968 || v >= Max(value_mate_in(PLY_MAX), beta)
1969 || v < Min(value_mated_in(PLY_MAX), beta))
1971 && ( (is_lower_bound(tte->type()) && v >= beta)
1972 || (is_upper_bound(tte->type()) && v < beta));
1976 // refine_eval() returns the transposition table score if
1977 // possible otherwise falls back on static position evaluation.
1979 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1984 Value v = value_from_tt(tte->value(), ply);
1986 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
1987 || (is_upper_bound(tte->type()) && v < defaultEval))
1994 // update_history() registers a good move that produced a beta-cutoff
1995 // in history and marks as failures all the other moves of that ply.
1997 void update_history(const Position& pos, Move move, Depth depth,
1998 Move movesSearched[], int moveCount) {
2002 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2004 for (int i = 0; i < moveCount - 1; i++)
2006 m = movesSearched[i];
2010 if (!pos.move_is_capture_or_promotion(m))
2011 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2016 // update_killers() add a good move that produced a beta-cutoff
2017 // among the killer moves of that ply.
2019 void update_killers(Move m, SearchStack* ss) {
2021 if (m == ss->killers[0])
2024 for (int i = KILLER_MAX - 1; i > 0; i--)
2025 ss->killers[i] = ss->killers[i - 1];
2031 // update_gains() updates the gains table of a non-capture move given
2032 // the static position evaluation before and after the move.
2034 void update_gains(const Position& pos, Move m, Value before, Value after) {
2037 && before != VALUE_NONE
2038 && after != VALUE_NONE
2039 && pos.captured_piece() == NO_PIECE_TYPE
2040 && !move_is_castle(m)
2041 && !move_is_promotion(m))
2042 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2046 // current_search_time() returns the number of milliseconds which have passed
2047 // since the beginning of the current search.
2049 int current_search_time() {
2051 return get_system_time() - SearchStartTime;
2055 // nps() computes the current nodes/second count.
2059 int t = current_search_time();
2060 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2064 // poll() performs two different functions: It polls for user input, and it
2065 // looks at the time consumed so far and decides if it's time to abort the
2070 static int lastInfoTime;
2071 int t = current_search_time();
2076 // We are line oriented, don't read single chars
2077 std::string command;
2079 if (!std::getline(std::cin, command))
2082 if (command == "quit")
2085 PonderSearch = false;
2089 else if (command == "stop")
2092 PonderSearch = false;
2094 else if (command == "ponderhit")
2098 // Print search information
2102 else if (lastInfoTime > t)
2103 // HACK: Must be a new search where we searched less than
2104 // NodesBetweenPolls nodes during the first second of search.
2107 else if (t - lastInfoTime >= 1000)
2114 if (dbg_show_hit_rate)
2115 dbg_print_hit_rate();
2117 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2118 << " time " << t << endl;
2121 // Should we stop the search?
2125 bool stillAtFirstMove = FirstRootMove
2126 && !AspirationFailLow
2127 && t > MaxSearchTime + ExtraSearchTime;
2129 bool noMoreTime = t > AbsoluteMaxSearchTime
2130 || stillAtFirstMove;
2132 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2133 || (ExactMaxTime && t >= ExactMaxTime)
2134 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2139 // ponderhit() is called when the program is pondering (i.e. thinking while
2140 // it's the opponent's turn to move) in order to let the engine know that
2141 // it correctly predicted the opponent's move.
2145 int t = current_search_time();
2146 PonderSearch = false;
2148 bool stillAtFirstMove = FirstRootMove
2149 && !AspirationFailLow
2150 && t > MaxSearchTime + ExtraSearchTime;
2152 bool noMoreTime = t > AbsoluteMaxSearchTime
2153 || stillAtFirstMove;
2155 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2160 // init_ss_array() does a fast reset of the first entries of a SearchStack
2161 // array and of all the excludedMove and skipNullMove entries.
2163 void init_ss_array(SearchStack* ss, int size) {
2165 for (int i = 0; i < size; i++, ss++)
2167 ss->excludedMove = MOVE_NONE;
2168 ss->skipNullMove = false;
2179 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2180 // while the program is pondering. The point is to work around a wrinkle in
2181 // the UCI protocol: When pondering, the engine is not allowed to give a
2182 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2183 // We simply wait here until one of these commands is sent, and return,
2184 // after which the bestmove and pondermove will be printed (in id_loop()).
2186 void wait_for_stop_or_ponderhit() {
2188 std::string command;
2192 if (!std::getline(std::cin, command))
2195 if (command == "quit")
2200 else if (command == "ponderhit" || command == "stop")
2206 // print_pv_info() prints to standard output and eventually to log file information on
2207 // the current PV line. It is called at each iteration or after a new pv is found.
2209 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2211 cout << "info depth " << Iteration
2212 << " score " << value_to_string(value)
2213 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2214 << " time " << current_search_time()
2215 << " nodes " << TM.nodes_searched()
2219 for (Move* m = pv; *m != MOVE_NONE; m++)
2226 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2227 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2229 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2230 TM.nodes_searched(), value, t, pv) << endl;
2235 // init_thread() is the function which is called when a new thread is
2236 // launched. It simply calls the idle_loop() function with the supplied
2237 // threadID. There are two versions of this function; one for POSIX
2238 // threads and one for Windows threads.
2240 #if !defined(_MSC_VER)
2242 void* init_thread(void *threadID) {
2244 TM.idle_loop(*(int*)threadID, NULL);
2250 DWORD WINAPI init_thread(LPVOID threadID) {
2252 TM.idle_loop(*(int*)threadID, NULL);
2259 /// The ThreadsManager class
2261 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2262 // get_beta_counters() are getters/setters for the per thread
2263 // counters used to sort the moves at root.
2265 void ThreadsManager::resetNodeCounters() {
2267 for (int i = 0; i < MAX_THREADS; i++)
2268 threads[i].nodes = 0ULL;
2271 void ThreadsManager::resetBetaCounters() {
2273 for (int i = 0; i < MAX_THREADS; i++)
2274 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2277 int64_t ThreadsManager::nodes_searched() const {
2279 int64_t result = 0ULL;
2280 for (int i = 0; i < ActiveThreads; i++)
2281 result += threads[i].nodes;
2286 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2289 for (int i = 0; i < MAX_THREADS; i++)
2291 our += threads[i].betaCutOffs[us];
2292 their += threads[i].betaCutOffs[opposite_color(us)];
2297 // idle_loop() is where the threads are parked when they have no work to do.
2298 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2299 // object for which the current thread is the master.
2301 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2303 assert(threadID >= 0 && threadID < MAX_THREADS);
2307 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2308 // master should exit as last one.
2309 if (AllThreadsShouldExit)
2312 threads[threadID].state = THREAD_TERMINATED;
2316 // If we are not thinking, wait for a condition to be signaled
2317 // instead of wasting CPU time polling for work.
2318 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2321 assert(threadID != 0);
2322 threads[threadID].state = THREAD_SLEEPING;
2324 #if !defined(_MSC_VER)
2325 lock_grab(&WaitLock);
2326 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2327 pthread_cond_wait(&WaitCond, &WaitLock);
2328 lock_release(&WaitLock);
2330 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2334 // If thread has just woken up, mark it as available
2335 if (threads[threadID].state == THREAD_SLEEPING)
2336 threads[threadID].state = THREAD_AVAILABLE;
2338 // If this thread has been assigned work, launch a search
2339 if (threads[threadID].state == THREAD_WORKISWAITING)
2341 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2343 threads[threadID].state = THREAD_SEARCHING;
2345 if (threads[threadID].splitPoint->pvNode)
2346 sp_search<PV>(threads[threadID].splitPoint, threadID);
2348 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2350 assert(threads[threadID].state == THREAD_SEARCHING);
2352 threads[threadID].state = THREAD_AVAILABLE;
2355 // If this thread is the master of a split point and all slaves have
2356 // finished their work at this split point, return from the idle loop.
2358 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2360 if (i == ActiveThreads)
2362 // Because sp->slaves[] is reset under lock protection,
2363 // be sure sp->lock has been released before to return.
2364 lock_grab(&(sp->lock));
2365 lock_release(&(sp->lock));
2367 assert(threads[threadID].state == THREAD_AVAILABLE);
2369 threads[threadID].state = THREAD_SEARCHING;
2376 // init_threads() is called during startup. It launches all helper threads,
2377 // and initializes the split point stack and the global locks and condition
2380 void ThreadsManager::init_threads() {
2385 #if !defined(_MSC_VER)
2386 pthread_t pthread[1];
2389 // Initialize global locks
2390 lock_init(&MPLock, NULL);
2391 lock_init(&WaitLock, NULL);
2393 #if !defined(_MSC_VER)
2394 pthread_cond_init(&WaitCond, NULL);
2396 for (i = 0; i < MAX_THREADS; i++)
2397 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2400 // Initialize splitPoints[] locks
2401 for (i = 0; i < MAX_THREADS; i++)
2402 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2403 lock_init(&(threads[i].splitPoints[j].lock), NULL);
2405 // Will be set just before program exits to properly end the threads
2406 AllThreadsShouldExit = false;
2408 // Threads will be put to sleep as soon as created
2409 AllThreadsShouldSleep = true;
2411 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2413 threads[0].state = THREAD_SEARCHING;
2414 for (i = 1; i < MAX_THREADS; i++)
2415 threads[i].state = THREAD_AVAILABLE;
2417 // Launch the helper threads
2418 for (i = 1; i < MAX_THREADS; i++)
2421 #if !defined(_MSC_VER)
2422 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2424 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2429 cout << "Failed to create thread number " << i << endl;
2430 Application::exit_with_failure();
2433 // Wait until the thread has finished launching and is gone to sleep
2434 while (threads[i].state != THREAD_SLEEPING) {}
2439 // exit_threads() is called when the program exits. It makes all the
2440 // helper threads exit cleanly.
2442 void ThreadsManager::exit_threads() {
2444 ActiveThreads = MAX_THREADS; // HACK
2445 AllThreadsShouldSleep = true; // HACK
2446 wake_sleeping_threads();
2448 // This makes the threads to exit idle_loop()
2449 AllThreadsShouldExit = true;
2451 // Wait for thread termination
2452 for (int i = 1; i < MAX_THREADS; i++)
2453 while (threads[i].state != THREAD_TERMINATED) {}
2455 // Now we can safely destroy the locks
2456 for (int i = 0; i < MAX_THREADS; i++)
2457 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2458 lock_destroy(&(threads[i].splitPoints[j].lock));
2460 lock_destroy(&WaitLock);
2461 lock_destroy(&MPLock);
2465 // thread_should_stop() checks whether the thread should stop its search.
2466 // This can happen if a beta cutoff has occurred in the thread's currently
2467 // active split point, or in some ancestor of the current split point.
2469 bool ThreadsManager::thread_should_stop(int threadID) const {
2471 assert(threadID >= 0 && threadID < ActiveThreads);
2475 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2480 // thread_is_available() checks whether the thread with threadID "slave" is
2481 // available to help the thread with threadID "master" at a split point. An
2482 // obvious requirement is that "slave" must be idle. With more than two
2483 // threads, this is not by itself sufficient: If "slave" is the master of
2484 // some active split point, it is only available as a slave to the other
2485 // threads which are busy searching the split point at the top of "slave"'s
2486 // split point stack (the "helpful master concept" in YBWC terminology).
2488 bool ThreadsManager::thread_is_available(int slave, int master) const {
2490 assert(slave >= 0 && slave < ActiveThreads);
2491 assert(master >= 0 && master < ActiveThreads);
2492 assert(ActiveThreads > 1);
2494 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2497 // Make a local copy to be sure doesn't change under our feet
2498 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2500 if (localActiveSplitPoints == 0)
2501 // No active split points means that the thread is available as
2502 // a slave for any other thread.
2505 if (ActiveThreads == 2)
2508 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2509 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2510 // could have been set to 0 by another thread leading to an out of bound access.
2511 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2518 // available_thread_exists() tries to find an idle thread which is available as
2519 // a slave for the thread with threadID "master".
2521 bool ThreadsManager::available_thread_exists(int master) const {
2523 assert(master >= 0 && master < ActiveThreads);
2524 assert(ActiveThreads > 1);
2526 for (int i = 0; i < ActiveThreads; i++)
2527 if (thread_is_available(i, master))
2534 // split() does the actual work of distributing the work at a node between
2535 // several available threads. If it does not succeed in splitting the
2536 // node (because no idle threads are available, or because we have no unused
2537 // split point objects), the function immediately returns. If splitting is
2538 // possible, a SplitPoint object is initialized with all the data that must be
2539 // copied to the helper threads and we tell our helper threads that they have
2540 // been assigned work. This will cause them to instantly leave their idle loops
2541 // and call sp_search(). When all threads have returned from sp_search() then
2544 template <bool Fake>
2545 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2546 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2547 int* moveCount, MovePicker* mp, bool pvNode) {
2549 assert(ply > 0 && ply < PLY_MAX);
2550 assert(*bestValue >= -VALUE_INFINITE);
2551 assert(*bestValue <= *alpha);
2552 assert(*alpha < beta);
2553 assert(beta <= VALUE_INFINITE);
2554 assert(depth > Depth(0));
2555 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2556 assert(ActiveThreads > 1);
2558 int i, master = p.thread();
2559 Thread& masterThread = threads[master];
2563 // If no other thread is available to help us, or if we have too many
2564 // active split points, don't split.
2565 if ( !available_thread_exists(master)
2566 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2568 lock_release(&MPLock);
2572 // Pick the next available split point object from the split point stack
2573 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2575 // Initialize the split point object
2576 splitPoint.parent = masterThread.splitPoint;
2577 splitPoint.stopRequest = false;
2578 splitPoint.ply = ply;
2579 splitPoint.depth = depth;
2580 splitPoint.mateThreat = mateThreat;
2581 splitPoint.alpha = *alpha;
2582 splitPoint.beta = beta;
2583 splitPoint.pvNode = pvNode;
2584 splitPoint.bestValue = *bestValue;
2586 splitPoint.moveCount = *moveCount;
2587 splitPoint.pos = &p;
2588 splitPoint.parentSstack = ss;
2589 for (i = 0; i < ActiveThreads; i++)
2590 splitPoint.slaves[i] = 0;
2592 masterThread.splitPoint = &splitPoint;
2594 // If we are here it means we are not available
2595 assert(masterThread.state != THREAD_AVAILABLE);
2597 int workersCnt = 1; // At least the master is included
2599 // Allocate available threads setting state to THREAD_BOOKED
2600 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2601 if (thread_is_available(i, master))
2603 threads[i].state = THREAD_BOOKED;
2604 threads[i].splitPoint = &splitPoint;
2605 splitPoint.slaves[i] = 1;
2609 assert(Fake || workersCnt > 1);
2611 // We can release the lock because slave threads are already booked and master is not available
2612 lock_release(&MPLock);
2614 // Tell the threads that they have work to do. This will make them leave
2615 // their idle loop. But before copy search stack tail for each thread.
2616 for (i = 0; i < ActiveThreads; i++)
2617 if (i == master || splitPoint.slaves[i])
2619 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2621 assert(i == master || threads[i].state == THREAD_BOOKED);
2623 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2626 // Everything is set up. The master thread enters the idle loop, from
2627 // which it will instantly launch a search, because its state is
2628 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2629 // idle loop, which means that the main thread will return from the idle
2630 // loop when all threads have finished their work at this split point.
2631 idle_loop(master, &splitPoint);
2633 // We have returned from the idle loop, which means that all threads are
2634 // finished. Update alpha and bestValue, and return.
2637 *alpha = splitPoint.alpha;
2638 *bestValue = splitPoint.bestValue;
2639 masterThread.activeSplitPoints--;
2640 masterThread.splitPoint = splitPoint.parent;
2642 lock_release(&MPLock);
2646 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2647 // to start a new search from the root.
2649 void ThreadsManager::wake_sleeping_threads() {
2651 assert(AllThreadsShouldSleep);
2652 assert(ActiveThreads > 0);
2654 AllThreadsShouldSleep = false;
2656 if (ActiveThreads == 1)
2659 #if !defined(_MSC_VER)
2660 pthread_mutex_lock(&WaitLock);
2661 pthread_cond_broadcast(&WaitCond);
2662 pthread_mutex_unlock(&WaitLock);
2664 for (int i = 1; i < MAX_THREADS; i++)
2665 SetEvent(SitIdleEvent[i]);
2671 // put_threads_to_sleep() makes all the threads go to sleep just before
2672 // to leave think(), at the end of the search. Threads should have already
2673 // finished the job and should be idle.
2675 void ThreadsManager::put_threads_to_sleep() {
2677 assert(!AllThreadsShouldSleep);
2679 // This makes the threads to go to sleep
2680 AllThreadsShouldSleep = true;
2683 /// The RootMoveList class
2685 // RootMoveList c'tor
2687 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2689 SearchStack ss[PLY_MAX_PLUS_2];
2690 MoveStack mlist[MaxRootMoves];
2692 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2694 // Generate all legal moves
2695 MoveStack* last = generate_moves(pos, mlist);
2697 // Add each move to the moves[] array
2698 for (MoveStack* cur = mlist; cur != last; cur++)
2700 bool includeMove = includeAllMoves;
2702 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2703 includeMove = (searchMoves[k] == cur->move);
2708 // Find a quick score for the move
2709 init_ss_array(ss, PLY_MAX_PLUS_2);
2710 pos.do_move(cur->move, st);
2711 moves[count].move = cur->move;
2712 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2713 moves[count].pv[0] = cur->move;
2714 moves[count].pv[1] = MOVE_NONE;
2715 pos.undo_move(cur->move);
2722 // RootMoveList simple methods definitions
2724 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2726 moves[moveNum].nodes = nodes;
2727 moves[moveNum].cumulativeNodes += nodes;
2730 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2732 moves[moveNum].ourBeta = our;
2733 moves[moveNum].theirBeta = their;
2736 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2740 for (j = 0; pv[j] != MOVE_NONE; j++)
2741 moves[moveNum].pv[j] = pv[j];
2743 moves[moveNum].pv[j] = MOVE_NONE;
2747 // RootMoveList::sort() sorts the root move list at the beginning of a new
2750 void RootMoveList::sort() {
2752 sort_multipv(count - 1); // Sort all items
2756 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2757 // list by their scores and depths. It is used to order the different PVs
2758 // correctly in MultiPV mode.
2760 void RootMoveList::sort_multipv(int n) {
2764 for (i = 1; i <= n; i++)
2766 RootMove rm = moves[i];
2767 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2768 moves[j] = moves[j - 1];