2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
43 #include "ucioption.h"
49 //// Local definitions
55 enum NodeType { NonPV, PV };
57 // Set to true to force running with one thread.
58 // Used for debugging SMP code.
59 const bool FakeSplit = false;
61 // ThreadsManager class is used to handle all the threads related stuff in search,
62 // init, starting, parking and, the most important, launching a slave thread at a
63 // split point are what this class does. All the access to shared thread data is
64 // done through this class, so that we avoid using global variables instead.
66 class ThreadsManager {
67 /* As long as the single ThreadsManager object is defined as a global we don't
68 need to explicitly initialize to zero its data members because variables with
69 static storage duration are automatically set to zero before enter main()
75 int active_threads() const { return ActiveThreads; }
76 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
77 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
78 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
80 void resetNodeCounters();
81 void resetBetaCounters();
82 int64_t nodes_searched() const;
83 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
84 bool available_thread_exists(int master) const;
85 bool thread_is_available(int slave, int master) const;
86 bool thread_should_stop(int threadID) const;
87 void wake_sleeping_threads();
88 void put_threads_to_sleep();
89 void idle_loop(int threadID, SplitPoint* sp);
92 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
99 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
100 Thread threads[MAX_THREADS];
102 Lock MPLock, WaitLock;
104 #if !defined(_MSC_VER)
105 pthread_cond_t WaitCond;
107 HANDLE SitIdleEvent[MAX_THREADS];
113 // RootMove struct is used for moves at the root at the tree. For each
114 // root move, we store a score, a node count, and a PV (really a refutation
115 // in the case of moves which fail low).
119 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
121 // RootMove::operator<() is the comparison function used when
122 // sorting the moves. A move m1 is considered to be better
123 // than a move m2 if it has a higher score, or if the moves
124 // have equal score but m1 has the higher beta cut-off count.
125 bool operator<(const RootMove& m) const {
127 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
132 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
133 Move pv[PLY_MAX_PLUS_2];
137 // The RootMoveList class is essentially an array of RootMove objects, with
138 // a handful of methods for accessing the data in the individual moves.
143 RootMoveList(Position& pos, Move searchMoves[]);
145 int move_count() const { return count; }
146 Move get_move(int moveNum) const { return moves[moveNum].move; }
147 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
148 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
149 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
150 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
152 void set_move_nodes(int moveNum, int64_t nodes);
153 void set_beta_counters(int moveNum, int64_t our, int64_t their);
154 void set_move_pv(int moveNum, const Move pv[]);
156 void sort_multipv(int n);
159 static const int MaxRootMoves = 500;
160 RootMove moves[MaxRootMoves];
169 // Maximum depth for razoring
170 const Depth RazorDepth = 4 * OnePly;
172 // Dynamic razoring margin based on depth
173 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
175 // Step 8. Null move search with verification search
177 // Null move margin. A null move search will not be done if the static
178 // evaluation of the position is more than NullMoveMargin below beta.
179 const Value NullMoveMargin = Value(0x200);
181 // Maximum depth for use of dynamic threat detection when null move fails low
182 const Depth ThreatDepth = 5 * OnePly;
184 // Step 9. Internal iterative deepening
186 // Minimum depth for use of internal iterative deepening
187 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
189 // At Non-PV nodes we do an internal iterative deepening search
190 // when the static evaluation is bigger then beta - IIDMargin.
191 const Value IIDMargin = Value(0x100);
193 // Step 11. Decide the new search depth
195 // Extensions. Configurable UCI options
196 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
197 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
198 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
200 // Minimum depth for use of singular extension
201 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
203 // If the TT move is at least SingularExtensionMargin better then the
204 // remaining ones we will extend it.
205 const Value SingularExtensionMargin = Value(0x20);
207 // Step 12. Futility pruning
209 // Futility margin for quiescence search
210 const Value FutilityMarginQS = Value(0x80);
212 // Futility lookup tables (initialized at startup) and their getter functions
213 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
214 int FutilityMoveCountArray[32]; // [depth]
216 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
217 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
219 // Step 14. Reduced search
221 // Reduction lookup tables (initialized at startup) and their getter functions
222 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
224 template <NodeType PV>
225 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
227 // Common adjustments
229 // Search depth at iteration 1
230 const Depth InitialDepth = OnePly;
232 // Easy move margin. An easy move candidate must be at least this much
233 // better than the second best move.
234 const Value EasyMoveMargin = Value(0x200);
242 // Scores and number of times the best move changed for each iteration
243 Value ValueByIteration[PLY_MAX_PLUS_2];
244 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
246 // Search window management
252 // Time managment variables
253 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
254 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
255 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
256 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
260 std::ofstream LogFile;
262 // Multi-threads related variables
263 Depth MinimumSplitDepth;
264 int MaxThreadsPerSplitPoint;
267 // Node counters, used only by thread[0] but try to keep in different cache
268 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
270 int NodesBetweenPolls = 30000;
277 Value id_loop(const Position& pos, Move searchMoves[]);
278 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
280 template <NodeType PvNode>
281 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
283 template <NodeType PvNode>
284 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
286 template <NodeType PvNode>
287 void sp_search(SplitPoint* sp, int threadID);
289 template <NodeType PvNode>
290 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
292 bool connected_moves(const Position& pos, Move m1, Move m2);
293 bool value_is_mate(Value value);
294 Value value_to_tt(Value v, int ply);
295 Value value_from_tt(Value v, int ply);
296 bool move_is_killer(Move m, SearchStack* ss);
297 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
298 bool connected_threat(const Position& pos, Move m, Move threat);
299 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
300 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
301 void update_killers(Move m, SearchStack* ss);
302 void update_gains(const Position& pos, Move move, Value before, Value after);
304 int current_search_time();
305 std::string value_to_uci(Value v);
309 void wait_for_stop_or_ponderhit();
310 void init_ss_array(SearchStack* ss, int size);
311 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
313 #if !defined(_MSC_VER)
314 void *init_thread(void *threadID);
316 DWORD WINAPI init_thread(LPVOID threadID);
326 /// init_threads(), exit_threads() and nodes_searched() are helpers to
327 /// give accessibility to some TM methods from outside of current file.
329 void init_threads() { TM.init_threads(); }
330 void exit_threads() { TM.exit_threads(); }
331 int64_t nodes_searched() { return TM.nodes_searched(); }
334 /// init_search() is called during startup. It initializes various lookup tables
338 int d; // depth (OnePly == 2)
339 int hd; // half depth (OnePly == 1)
342 // Init reductions array
343 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
345 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
346 double nonPVRed = log(double(hd)) * log(double(mc)) / 1.5;
347 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
348 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
351 // Init futility margins array
352 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
353 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
355 // Init futility move count array
356 for (d = 0; d < 32; d++)
357 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
361 // SearchStack::init() initializes a search stack entry.
362 // Called at the beginning of search() when starting to examine a new node.
363 void SearchStack::init() {
365 currentMove = threatMove = bestMove = MOVE_NONE;
366 reduction = Depth(0);
370 // SearchStack::initKillers() initializes killers for a search stack entry
371 void SearchStack::initKillers() {
373 mateKiller = MOVE_NONE;
374 for (int i = 0; i < KILLER_MAX; i++)
375 killers[i] = MOVE_NONE;
379 /// perft() is our utility to verify move generation is bug free. All the legal
380 /// moves up to given depth are generated and counted and the sum returned.
382 int perft(Position& pos, Depth depth)
387 MovePicker mp(pos, MOVE_NONE, depth, H);
389 // If we are at the last ply we don't need to do and undo
390 // the moves, just to count them.
391 if (depth <= OnePly) // Replace with '<' to test also qsearch
393 while (mp.get_next_move()) sum++;
397 // Loop through all legal moves
399 while ((move = mp.get_next_move()) != MOVE_NONE)
401 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
402 sum += perft(pos, depth - OnePly);
409 /// think() is the external interface to Stockfish's search, and is called when
410 /// the program receives the UCI 'go' command. It initializes various
411 /// search-related global variables, and calls root_search(). It returns false
412 /// when a quit command is received during the search.
414 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
415 int time[], int increment[], int movesToGo, int maxDepth,
416 int maxNodes, int maxTime, Move searchMoves[]) {
418 // Initialize global search variables
419 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
420 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
422 TM.resetNodeCounters();
423 SearchStartTime = get_system_time();
424 ExactMaxTime = maxTime;
427 InfiniteSearch = infinite;
428 PonderSearch = ponder;
429 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
431 // Look for a book move, only during games, not tests
432 if (UseTimeManagement && get_option_value_bool("OwnBook"))
434 if (get_option_value_string("Book File") != OpeningBook.file_name())
435 OpeningBook.open(get_option_value_string("Book File"));
437 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
438 if (bookMove != MOVE_NONE)
441 wait_for_stop_or_ponderhit();
443 cout << "bestmove " << bookMove << endl;
448 // Read UCI option values
449 TT.set_size(get_option_value_int("Hash"));
450 if (button_was_pressed("Clear Hash"))
453 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
454 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
455 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
456 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
457 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
458 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
459 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
460 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
461 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
462 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
463 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
464 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
466 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
467 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
468 MultiPV = get_option_value_int("MultiPV");
469 Chess960 = get_option_value_bool("UCI_Chess960");
470 UseLogFile = get_option_value_bool("Use Search Log");
473 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
475 read_weights(pos.side_to_move());
477 // Set the number of active threads
478 int newActiveThreads = get_option_value_int("Threads");
479 if (newActiveThreads != TM.active_threads())
481 TM.set_active_threads(newActiveThreads);
482 init_eval(TM.active_threads());
485 // Wake up sleeping threads
486 TM.wake_sleeping_threads();
489 int myTime = time[side_to_move];
490 int myIncrement = increment[side_to_move];
491 if (UseTimeManagement)
493 if (!movesToGo) // Sudden death time control
497 MaxSearchTime = myTime / 30 + myIncrement;
498 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
500 else // Blitz game without increment
502 MaxSearchTime = myTime / 30;
503 AbsoluteMaxSearchTime = myTime / 8;
506 else // (x moves) / (y minutes)
510 MaxSearchTime = myTime / 2;
511 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
515 MaxSearchTime = myTime / Min(movesToGo, 20);
516 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
520 if (get_option_value_bool("Ponder"))
522 MaxSearchTime += MaxSearchTime / 4;
523 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
527 // Set best NodesBetweenPolls interval to avoid lagging under
528 // heavy time pressure.
530 NodesBetweenPolls = Min(MaxNodes, 30000);
531 else if (myTime && myTime < 1000)
532 NodesBetweenPolls = 1000;
533 else if (myTime && myTime < 5000)
534 NodesBetweenPolls = 5000;
536 NodesBetweenPolls = 30000;
538 // Write search information to log file
540 LogFile << "Searching: " << pos.to_fen() << endl
541 << "infinite: " << infinite
542 << " ponder: " << ponder
543 << " time: " << myTime
544 << " increment: " << myIncrement
545 << " moves to go: " << movesToGo << endl;
547 // We're ready to start thinking. Call the iterative deepening loop function
548 id_loop(pos, searchMoves);
553 TM.put_threads_to_sleep();
561 // id_loop() is the main iterative deepening loop. It calls root_search
562 // repeatedly with increasing depth until the allocated thinking time has
563 // been consumed, the user stops the search, or the maximum search depth is
566 Value id_loop(const Position& pos, Move searchMoves[]) {
568 Position p(pos, pos.thread());
569 SearchStack ss[PLY_MAX_PLUS_2];
570 Move pv[PLY_MAX_PLUS_2];
571 Move EasyMove = MOVE_NONE;
572 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
574 // Moves to search are verified, copied, scored and sorted
575 RootMoveList rml(p, searchMoves);
577 // Handle special case of searching on a mate/stale position
578 if (rml.move_count() == 0)
581 wait_for_stop_or_ponderhit();
583 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
586 // Print RootMoveList startup scoring to the standard output,
587 // so to output information also for iteration 1.
588 cout << "info depth " << 1
589 << "\ninfo depth " << 1
590 << " score " << value_to_uci(rml.get_move_score(0))
591 << " time " << current_search_time()
592 << " nodes " << TM.nodes_searched()
594 << " pv " << rml.get_move(0) << "\n";
599 init_ss_array(ss, PLY_MAX_PLUS_2);
600 pv[0] = pv[1] = MOVE_NONE;
601 ValueByIteration[1] = rml.get_move_score(0);
604 // Is one move significantly better than others after initial scoring ?
605 if ( rml.move_count() == 1
606 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
607 EasyMove = rml.get_move(0);
609 // Iterative deepening loop
610 while (Iteration < PLY_MAX)
612 // Initialize iteration
614 BestMoveChangesByIteration[Iteration] = 0;
616 cout << "info depth " << Iteration << endl;
618 // Calculate dynamic aspiration window based on previous iterations
619 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
621 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
622 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
624 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
625 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
627 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
628 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
631 // Search to the current depth, rml is updated and sorted, alpha and beta could change
632 value = root_search(p, ss, pv, rml, &alpha, &beta);
634 // Write PV to transposition table, in case the relevant entries have
635 // been overwritten during the search.
639 break; // Value cannot be trusted. Break out immediately!
641 //Save info about search result
642 ValueByIteration[Iteration] = value;
644 // Drop the easy move if differs from the new best move
645 if (pv[0] != EasyMove)
646 EasyMove = MOVE_NONE;
648 if (UseTimeManagement)
651 bool stopSearch = false;
653 // Stop search early if there is only a single legal move,
654 // we search up to Iteration 6 anyway to get a proper score.
655 if (Iteration >= 6 && rml.move_count() == 1)
658 // Stop search early when the last two iterations returned a mate score
660 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
661 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
664 // Stop search early if one move seems to be much better than the others
665 int64_t nodes = TM.nodes_searched();
668 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
669 && current_search_time() > MaxSearchTime / 16)
670 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
671 && current_search_time() > MaxSearchTime / 32)))
674 // Add some extra time if the best move has changed during the last two iterations
675 if (Iteration > 5 && Iteration <= 50)
676 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
677 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
679 // Stop search if most of MaxSearchTime is consumed at the end of the
680 // iteration. We probably don't have enough time to search the first
681 // move at the next iteration anyway.
682 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
688 StopOnPonderhit = true;
694 if (MaxDepth && Iteration >= MaxDepth)
698 // If we are pondering or in infinite search, we shouldn't print the
699 // best move before we are told to do so.
700 if (!AbortSearch && (PonderSearch || InfiniteSearch))
701 wait_for_stop_or_ponderhit();
703 // Print final search statistics
704 cout << "info nodes " << TM.nodes_searched()
706 << " time " << current_search_time() << endl;
708 // Print the best move and the ponder move to the standard output
709 if (pv[0] == MOVE_NONE)
711 pv[0] = rml.get_move(0);
715 assert(pv[0] != MOVE_NONE);
717 cout << "bestmove " << pv[0];
719 if (pv[1] != MOVE_NONE)
720 cout << " ponder " << pv[1];
727 dbg_print_mean(LogFile);
729 if (dbg_show_hit_rate)
730 dbg_print_hit_rate(LogFile);
732 LogFile << "\nNodes: " << TM.nodes_searched()
733 << "\nNodes/second: " << nps()
734 << "\nBest move: " << move_to_san(p, pv[0]);
737 p.do_move(pv[0], st);
738 LogFile << "\nPonder move: "
739 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
742 return rml.get_move_score(0);
746 // root_search() is the function which searches the root node. It is
747 // similar to search_pv except that it uses a different move ordering
748 // scheme, prints some information to the standard output and handles
749 // the fail low/high loops.
751 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
758 Depth depth, ext, newDepth;
759 Value value, alpha, beta;
760 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
761 int researchCountFH, researchCountFL;
763 researchCountFH = researchCountFL = 0;
766 isCheck = pos.is_check();
768 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
769 // Step 2. Check for aborted search (omitted at root)
770 // Step 3. Mate distance pruning (omitted at root)
771 // Step 4. Transposition table lookup (omitted at root)
773 // Step 5. Evaluate the position statically
774 // At root we do this only to get reference value for child nodes
776 ss->eval = evaluate(pos, ei);
778 // Step 6. Razoring (omitted at root)
779 // Step 7. Static null move pruning (omitted at root)
780 // Step 8. Null move search with verification search (omitted at root)
781 // Step 9. Internal iterative deepening (omitted at root)
783 // Step extra. Fail low loop
784 // We start with small aspiration window and in case of fail low, we research
785 // with bigger window until we are not failing low anymore.
788 // Sort the moves before to (re)search
791 // Step 10. Loop through all moves in the root move list
792 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
794 // This is used by time management
795 FirstRootMove = (i == 0);
797 // Save the current node count before the move is searched
798 nodes = TM.nodes_searched();
800 // Reset beta cut-off counters
801 TM.resetBetaCounters();
803 // Pick the next root move, and print the move and the move number to
804 // the standard output.
805 move = ss->currentMove = rml.get_move(i);
807 if (current_search_time() >= 1000)
808 cout << "info currmove " << move
809 << " currmovenumber " << i + 1 << endl;
811 moveIsCheck = pos.move_is_check(move);
812 captureOrPromotion = pos.move_is_capture_or_promotion(move);
814 // Step 11. Decide the new search depth
815 depth = (Iteration - 2) * OnePly + InitialDepth;
816 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
817 newDepth = depth + ext;
819 // Step 12. Futility pruning (omitted at root)
821 // Step extra. Fail high loop
822 // If move fails high, we research with bigger window until we are not failing
824 value = - VALUE_INFINITE;
828 // Step 13. Make the move
829 pos.do_move(move, st, ci, moveIsCheck);
831 // Step extra. pv search
832 // We do pv search for first moves (i < MultiPV)
833 // and for fail high research (value > alpha)
834 if (i < MultiPV || value > alpha)
836 // Aspiration window is disabled in multi-pv case
838 alpha = -VALUE_INFINITE;
840 // Full depth PV search, done on first move or after a fail high
841 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
845 // Step 14. Reduced search
846 // if the move fails high will be re-searched at full depth
847 bool doFullDepthSearch = true;
849 if ( depth >= 3 * OnePly
851 && !captureOrPromotion
852 && !move_is_castle(move))
854 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
857 assert(newDepth-ss->reduction >= OnePly);
859 // Reduced depth non-pv search using alpha as upperbound
860 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
861 doFullDepthSearch = (value > alpha);
864 // The move failed high, but if reduction is very big we could
865 // face a false positive, retry with a less aggressive reduction,
866 // if the move fails high again then go with full depth search.
867 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
869 assert(newDepth - OnePly >= OnePly);
871 ss->reduction = OnePly;
872 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
873 doFullDepthSearch = (value > alpha);
875 ss->reduction = Depth(0); // Restore original reduction
878 // Step 15. Full depth search
879 if (doFullDepthSearch)
881 // Full depth non-pv search using alpha as upperbound
882 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
884 // If we are above alpha then research at same depth but as PV
885 // to get a correct score or eventually a fail high above beta.
887 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
891 // Step 16. Undo move
894 // Can we exit fail high loop ?
895 if (AbortSearch || value < beta)
898 // We are failing high and going to do a research. It's important to update
899 // the score before research in case we run out of time while researching.
900 rml.set_move_score(i, value);
902 TT.extract_pv(pos, move, pv, PLY_MAX);
903 rml.set_move_pv(i, pv);
905 // Print information to the standard output
906 print_pv_info(pos, pv, alpha, beta, value);
908 // Prepare for a research after a fail high, each time with a wider window
909 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
912 } // End of fail high loop
914 // Finished searching the move. If AbortSearch is true, the search
915 // was aborted because the user interrupted the search or because we
916 // ran out of time. In this case, the return value of the search cannot
917 // be trusted, and we break out of the loop without updating the best
922 // Remember beta-cutoff and searched nodes counts for this move. The
923 // info is used to sort the root moves for the next iteration.
925 TM.get_beta_counters(pos.side_to_move(), our, their);
926 rml.set_beta_counters(i, our, their);
927 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
929 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
930 assert(value < beta);
932 // Step 17. Check for new best move
933 if (value <= alpha && i >= MultiPV)
934 rml.set_move_score(i, -VALUE_INFINITE);
937 // PV move or new best move!
940 rml.set_move_score(i, value);
942 TT.extract_pv(pos, move, pv, PLY_MAX);
943 rml.set_move_pv(i, pv);
947 // We record how often the best move has been changed in each
948 // iteration. This information is used for time managment: When
949 // the best move changes frequently, we allocate some more time.
951 BestMoveChangesByIteration[Iteration]++;
953 // Print information to the standard output
954 print_pv_info(pos, pv, alpha, beta, value);
956 // Raise alpha to setup proper non-pv search upper bound
963 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
965 cout << "info multipv " << j + 1
966 << " score " << value_to_uci(rml.get_move_score(j))
967 << " depth " << (j <= i ? Iteration : Iteration - 1)
968 << " time " << current_search_time()
969 << " nodes " << TM.nodes_searched()
973 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
974 cout << rml.get_move_pv(j, k) << " ";
978 alpha = rml.get_move_score(Min(i, MultiPV - 1));
980 } // PV move or new best move
982 assert(alpha >= *alphaPtr);
984 AspirationFailLow = (alpha == *alphaPtr);
986 if (AspirationFailLow && StopOnPonderhit)
987 StopOnPonderhit = false;
990 // Can we exit fail low loop ?
991 if (AbortSearch || !AspirationFailLow)
994 // Prepare for a research after a fail low, each time with a wider window
995 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1000 // Sort the moves before to return
1007 // search<>() is the main search function for both PV and non-PV nodes
1009 template <NodeType PvNode>
1010 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1012 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1013 assert(beta > alpha && beta <= VALUE_INFINITE);
1014 assert(PvNode || alpha == beta - 1);
1015 assert(ply > 0 && ply < PLY_MAX);
1016 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1018 Move movesSearched[256];
1023 Move ttMove, move, excludedMove;
1024 Depth ext, newDepth;
1025 Value bestValue, value, oldAlpha;
1026 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1027 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
1028 bool mateThreat = false;
1030 int threadID = pos.thread();
1031 refinedValue = bestValue = value = -VALUE_INFINITE;
1034 // Step 1. Initialize node and poll. Polling can abort search
1035 TM.incrementNodeCounter(threadID);
1037 (ss+2)->initKillers();
1039 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1045 // Step 2. Check for aborted search and immediate draw
1046 if (AbortSearch || TM.thread_should_stop(threadID))
1049 if (pos.is_draw() || ply >= PLY_MAX - 1)
1052 // Step 3. Mate distance pruning
1053 alpha = Max(value_mated_in(ply), alpha);
1054 beta = Min(value_mate_in(ply+1), beta);
1058 // Step 4. Transposition table lookup
1060 // We don't want the score of a partial search to overwrite a previous full search
1061 // TT value, so we use a different position key in case of an excluded move exists.
1062 excludedMove = ss->excludedMove;
1063 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1065 tte = TT.retrieve(posKey);
1066 ttMove = (tte ? tte->move() : MOVE_NONE);
1068 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1069 // This is to avoid problems in the following areas:
1071 // * Repetition draw detection
1072 // * Fifty move rule detection
1073 // * Searching for a mate
1074 // * Printing of full PV line
1076 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1078 // Refresh tte entry to avoid aging
1079 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1081 ss->currentMove = ttMove; // Can be MOVE_NONE
1082 return value_from_tt(tte->value(), ply);
1085 // Step 5. Evaluate the position statically
1086 // At PV nodes we do this only to update gain statistics
1087 isCheck = pos.is_check();
1090 if (tte && tte->static_value() != VALUE_NONE)
1092 ss->eval = tte->static_value();
1093 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1096 ss->eval = evaluate(pos, ei);
1098 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1099 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1102 // Step 6. Razoring (is omitted in PV nodes)
1104 && depth < RazorDepth
1106 && refinedValue < beta - razor_margin(depth)
1107 && ttMove == MOVE_NONE
1108 && (ss-1)->currentMove != MOVE_NULL
1109 && !value_is_mate(beta)
1110 && !pos.has_pawn_on_7th(pos.side_to_move()))
1112 // Pass ss->eval to qsearch() and avoid an evaluate call
1113 if (!tte || tte->static_value() == VALUE_NONE)
1114 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1116 Value rbeta = beta - razor_margin(depth);
1117 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1119 // Logically we should return (v + razor_margin(depth)), but
1120 // surprisingly this did slightly weaker in tests.
1124 // Step 7. Static null move pruning (is omitted in PV nodes)
1125 // We're betting that the opponent doesn't have a move that will reduce
1126 // the score by more than futility_margin(depth) if we do a null move.
1128 && !ss->skipNullMove
1129 && depth < RazorDepth
1130 && refinedValue >= beta + futility_margin(depth, 0)
1132 && !value_is_mate(beta)
1133 && pos.non_pawn_material(pos.side_to_move()))
1134 return refinedValue - futility_margin(depth, 0);
1136 // Step 8. Null move search with verification search (is omitted in PV nodes)
1137 // When we jump directly to qsearch() we do a null move only if static value is
1138 // at least beta. Otherwise we do a null move if static value is not more than
1139 // NullMoveMargin under beta.
1141 && !ss->skipNullMove
1143 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1145 && !value_is_mate(beta)
1146 && pos.non_pawn_material(pos.side_to_move()))
1148 ss->currentMove = MOVE_NULL;
1150 // Null move dynamic reduction based on depth
1151 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1153 // Null move dynamic reduction based on value
1154 if (refinedValue - beta > PawnValueMidgame)
1157 pos.do_null_move(st);
1158 (ss+1)->skipNullMove = true;
1160 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1161 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1162 (ss+1)->skipNullMove = false;
1163 pos.undo_null_move();
1165 if (nullValue >= beta)
1167 // Do not return unproven mate scores
1168 if (nullValue >= value_mate_in(PLY_MAX))
1171 if (depth < 6 * OnePly)
1174 // Do verification search at high depths
1175 ss->skipNullMove = true;
1176 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1177 ss->skipNullMove = false;
1184 // The null move failed low, which means that we may be faced with
1185 // some kind of threat. If the previous move was reduced, check if
1186 // the move that refuted the null move was somehow connected to the
1187 // move which was reduced. If a connection is found, return a fail
1188 // low score (which will cause the reduced move to fail high in the
1189 // parent node, which will trigger a re-search with full depth).
1190 if (nullValue == value_mated_in(ply + 2))
1193 ss->threatMove = (ss+1)->currentMove;
1194 if ( depth < ThreatDepth
1195 && (ss-1)->reduction
1196 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1201 // Step 9. Internal iterative deepening
1202 if ( depth >= IIDDepth[PvNode]
1203 && ttMove == MOVE_NONE
1204 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1206 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1208 ss->skipNullMove = true;
1209 search<PvNode>(pos, ss, alpha, beta, d, ply);
1210 ss->skipNullMove = false;
1212 ttMove = ss->bestMove;
1213 tte = TT.retrieve(posKey);
1216 // Expensive mate threat detection (only for PV nodes)
1218 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1220 // Initialize a MovePicker object for the current position
1221 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1223 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1224 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1225 && tte && tte->move()
1226 && !excludedMove // Do not allow recursive singular extension search
1227 && is_lower_bound(tte->type())
1228 && tte->depth() >= depth - 3 * OnePly;
1230 // Step 10. Loop through moves
1231 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1232 while ( bestValue < beta
1233 && (move = mp.get_next_move()) != MOVE_NONE
1234 && !TM.thread_should_stop(threadID))
1236 assert(move_is_ok(move));
1238 if (move == excludedMove)
1241 moveIsCheck = pos.move_is_check(move, ci);
1242 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1244 // Step 11. Decide the new search depth
1245 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1247 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1248 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1249 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1250 // lower then ttValue minus a margin then we extend ttMove.
1251 if ( singularExtensionNode
1252 && move == tte->move()
1255 Value ttValue = value_from_tt(tte->value(), ply);
1257 if (abs(ttValue) < VALUE_KNOWN_WIN)
1259 Value b = ttValue - SingularExtensionMargin;
1260 ss->excludedMove = move;
1261 ss->skipNullMove = true;
1262 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1263 ss->skipNullMove = false;
1264 ss->excludedMove = MOVE_NONE;
1270 newDepth = depth - OnePly + ext;
1272 // Update current move (this must be done after singular extension search)
1273 movesSearched[moveCount++] = ss->currentMove = move;
1275 // Step 12. Futility pruning (is omitted in PV nodes)
1277 && !captureOrPromotion
1281 && !move_is_castle(move))
1283 // Move count based pruning
1284 if ( moveCount >= futility_move_count(depth)
1285 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1286 && bestValue > value_mated_in(PLY_MAX))
1289 // Value based pruning
1290 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1291 // but fixing this made program slightly weaker.
1292 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1293 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1294 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1296 if (futilityValueScaled < beta)
1298 if (futilityValueScaled > bestValue)
1299 bestValue = futilityValueScaled;
1304 // Step 13. Make the move
1305 pos.do_move(move, st, ci, moveIsCheck);
1307 // Step extra. pv search (only in PV nodes)
1308 // The first move in list is the expected PV
1309 if (PvNode && moveCount == 1)
1310 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1311 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1314 // Step 14. Reduced depth search
1315 // If the move fails high will be re-searched at full depth.
1316 bool doFullDepthSearch = true;
1318 if ( depth >= 3 * OnePly
1319 && !captureOrPromotion
1321 && !move_is_castle(move)
1322 && !move_is_killer(move, ss))
1324 ss->reduction = reduction<PvNode>(depth, moveCount);
1327 Depth d = newDepth - ss->reduction;
1328 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1329 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1331 doFullDepthSearch = (value > alpha);
1334 // The move failed high, but if reduction is very big we could
1335 // face a false positive, retry with a less aggressive reduction,
1336 // if the move fails high again then go with full depth search.
1337 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1339 assert(newDepth - OnePly >= OnePly);
1341 ss->reduction = OnePly;
1342 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1343 doFullDepthSearch = (value > alpha);
1345 ss->reduction = Depth(0); // Restore original reduction
1348 // Step 15. Full depth search
1349 if (doFullDepthSearch)
1351 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1352 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1354 // Step extra. pv search (only in PV nodes)
1355 // Search only for possible new PV nodes, if instead value >= beta then
1356 // parent node fails low with value <= alpha and tries another move.
1357 if (PvNode && value > alpha && value < beta)
1358 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1359 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1363 // Step 16. Undo move
1364 pos.undo_move(move);
1366 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1368 // Step 17. Check for new best move
1369 if (value > bestValue)
1374 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1377 if (value == value_mate_in(ply + 1))
1378 ss->mateKiller = move;
1380 ss->bestMove = move;
1384 // Step 18. Check for split
1385 if ( depth >= MinimumSplitDepth
1386 && TM.active_threads() > 1
1388 && TM.available_thread_exists(threadID)
1390 && !TM.thread_should_stop(threadID)
1392 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1393 mateThreat, &moveCount, &mp, PvNode);
1396 // Step 19. Check for mate and stalemate
1397 // All legal moves have been searched and if there are
1398 // no legal moves, it must be mate or stalemate.
1399 // If one move was excluded return fail low score.
1401 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1403 // Step 20. Update tables
1404 // If the search is not aborted, update the transposition table,
1405 // history counters, and killer moves.
1406 if (AbortSearch || TM.thread_should_stop(threadID))
1409 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1410 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1411 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1413 // Update killers and history only for non capture moves that fails high
1414 if (bestValue >= beta)
1416 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1417 if (!pos.move_is_capture_or_promotion(move))
1419 update_history(pos, move, depth, movesSearched, moveCount);
1420 update_killers(move, ss);
1424 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1430 // qsearch() is the quiescence search function, which is called by the main
1431 // search function when the remaining depth is zero (or, to be more precise,
1432 // less than OnePly).
1434 template <NodeType PvNode>
1435 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1437 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1438 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1439 assert(PvNode || alpha == beta - 1);
1441 assert(ply > 0 && ply < PLY_MAX);
1442 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1447 Value bestValue, value, futilityValue, futilityBase;
1448 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1450 Value oldAlpha = alpha;
1452 TM.incrementNodeCounter(pos.thread());
1453 ss->bestMove = ss->currentMove = MOVE_NONE;
1454 ss->eval = VALUE_NONE;
1456 // Check for an instant draw or maximum ply reached
1457 if (pos.is_draw() || ply >= PLY_MAX - 1)
1460 // Transposition table lookup. At PV nodes, we don't use the TT for
1461 // pruning, but only for move ordering.
1462 tte = TT.retrieve(pos.get_key());
1463 ttMove = (tte ? tte->move() : MOVE_NONE);
1465 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1467 ss->currentMove = ttMove; // Can be MOVE_NONE
1468 return value_from_tt(tte->value(), ply);
1471 isCheck = pos.is_check();
1473 // Evaluate the position statically
1476 bestValue = futilityBase = -VALUE_INFINITE;
1477 deepChecks = enoughMaterial = false;
1481 if (tte && tte->static_value() != VALUE_NONE)
1483 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1484 bestValue = tte->static_value();
1487 bestValue = evaluate(pos, ei);
1489 ss->eval = bestValue;
1490 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1492 // Stand pat. Return immediately if static value is at least beta
1493 if (bestValue >= beta)
1496 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()]);
1501 if (PvNode && bestValue > alpha)
1504 // If we are near beta then try to get a cutoff pushing checks a bit further
1505 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1507 // Futility pruning parameters, not needed when in check
1508 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1509 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1512 // Initialize a MovePicker object for the current position, and prepare
1513 // to search the moves. Because the depth is <= 0 here, only captures,
1514 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1515 // and we are near beta) will be generated.
1516 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1519 // Loop through the moves until no moves remain or a beta cutoff occurs
1520 while ( alpha < beta
1521 && (move = mp.get_next_move()) != MOVE_NONE)
1523 assert(move_is_ok(move));
1525 moveIsCheck = pos.move_is_check(move, ci);
1533 && !move_is_promotion(move)
1534 && !pos.move_is_passed_pawn_push(move))
1536 futilityValue = futilityBase
1537 + pos.endgame_value_of_piece_on(move_to(move))
1538 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1540 if (futilityValue < alpha)
1542 if (futilityValue > bestValue)
1543 bestValue = futilityValue;
1548 // Detect blocking evasions that are candidate to be pruned
1549 evasionPrunable = isCheck
1550 && bestValue > value_mated_in(PLY_MAX)
1551 && !pos.move_is_capture(move)
1552 && pos.type_of_piece_on(move_from(move)) != KING
1553 && !pos.can_castle(pos.side_to_move());
1555 // Don't search moves with negative SEE values
1557 && (!isCheck || evasionPrunable)
1559 && !move_is_promotion(move)
1560 && pos.see_sign(move) < 0)
1563 // Update current move
1564 ss->currentMove = move;
1566 // Make and search the move
1567 pos.do_move(move, st, ci, moveIsCheck);
1568 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1569 pos.undo_move(move);
1571 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1574 if (value > bestValue)
1580 ss->bestMove = move;
1585 // All legal moves have been searched. A special case: If we're in check
1586 // and no legal moves were found, it is checkmate.
1587 if (isCheck && bestValue == -VALUE_INFINITE)
1588 return value_mated_in(ply);
1590 // Update transposition table
1591 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1592 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1593 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1595 // Update killers only for checking moves that fails high
1596 if ( bestValue >= beta
1597 && !pos.move_is_capture_or_promotion(ss->bestMove))
1598 update_killers(ss->bestMove, ss);
1600 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1606 // sp_search() is used to search from a split point. This function is called
1607 // by each thread working at the split point. It is similar to the normal
1608 // search() function, but simpler. Because we have already probed the hash
1609 // table, done a null move search, and searched the first move before
1610 // splitting, we don't have to repeat all this work in sp_search(). We
1611 // also don't need to store anything to the hash table here: This is taken
1612 // care of after we return from the split point.
1614 template <NodeType PvNode>
1615 void sp_search(SplitPoint* sp, int threadID) {
1617 assert(threadID >= 0 && threadID < TM.active_threads());
1618 assert(TM.active_threads() > 1);
1622 Depth ext, newDepth;
1624 Value futilityValueScaled; // NonPV specific
1625 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1627 value = -VALUE_INFINITE;
1629 Position pos(*sp->pos, threadID);
1631 SearchStack* ss = sp->sstack[threadID] + 1;
1632 isCheck = pos.is_check();
1634 // Step 10. Loop through moves
1635 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1636 lock_grab(&(sp->lock));
1638 while ( sp->bestValue < sp->beta
1639 && (move = sp->mp->get_next_move()) != MOVE_NONE
1640 && !TM.thread_should_stop(threadID))
1642 moveCount = ++sp->moveCount;
1643 lock_release(&(sp->lock));
1645 assert(move_is_ok(move));
1647 moveIsCheck = pos.move_is_check(move, ci);
1648 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1650 // Step 11. Decide the new search depth
1651 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1652 newDepth = sp->depth - OnePly + ext;
1654 // Update current move
1655 ss->currentMove = move;
1657 // Step 12. Futility pruning (is omitted in PV nodes)
1659 && !captureOrPromotion
1662 && !move_is_castle(move))
1664 // Move count based pruning
1665 if ( moveCount >= futility_move_count(sp->depth)
1666 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1667 && sp->bestValue > value_mated_in(PLY_MAX))
1669 lock_grab(&(sp->lock));
1673 // Value based pruning
1674 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1675 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1676 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1678 if (futilityValueScaled < sp->beta)
1680 lock_grab(&(sp->lock));
1682 if (futilityValueScaled > sp->bestValue)
1683 sp->bestValue = futilityValueScaled;
1688 // Step 13. Make the move
1689 pos.do_move(move, st, ci, moveIsCheck);
1691 // Step 14. Reduced search
1692 // If the move fails high will be re-searched at full depth.
1693 bool doFullDepthSearch = true;
1695 if ( !captureOrPromotion
1697 && !move_is_castle(move)
1698 && !move_is_killer(move, ss))
1700 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1703 Value localAlpha = sp->alpha;
1704 Depth d = newDepth - ss->reduction;
1705 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1706 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1708 doFullDepthSearch = (value > localAlpha);
1711 // The move failed high, but if reduction is very big we could
1712 // face a false positive, retry with a less aggressive reduction,
1713 // if the move fails high again then go with full depth search.
1714 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1716 assert(newDepth - OnePly >= OnePly);
1718 ss->reduction = OnePly;
1719 Value localAlpha = sp->alpha;
1720 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1721 doFullDepthSearch = (value > localAlpha);
1723 ss->reduction = Depth(0); // Restore original reduction
1726 // Step 15. Full depth search
1727 if (doFullDepthSearch)
1729 Value localAlpha = sp->alpha;
1730 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1731 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1733 // Step extra. pv search (only in PV nodes)
1734 // Search only for possible new PV nodes, if instead value >= beta then
1735 // parent node fails low with value <= alpha and tries another move.
1736 if (PvNode && value > localAlpha && value < sp->beta)
1737 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1738 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1741 // Step 16. Undo move
1742 pos.undo_move(move);
1744 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1746 // Step 17. Check for new best move
1747 lock_grab(&(sp->lock));
1749 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1751 sp->bestValue = value;
1753 if (sp->bestValue > sp->alpha)
1755 if (!PvNode || value >= sp->beta)
1756 sp->stopRequest = true;
1758 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1761 sp->parentSstack->bestMove = ss->bestMove = move;
1766 /* Here we have the lock still grabbed */
1768 sp->slaves[threadID] = 0;
1770 lock_release(&(sp->lock));
1774 // connected_moves() tests whether two moves are 'connected' in the sense
1775 // that the first move somehow made the second move possible (for instance
1776 // if the moving piece is the same in both moves). The first move is assumed
1777 // to be the move that was made to reach the current position, while the
1778 // second move is assumed to be a move from the current position.
1780 bool connected_moves(const Position& pos, Move m1, Move m2) {
1782 Square f1, t1, f2, t2;
1785 assert(move_is_ok(m1));
1786 assert(move_is_ok(m2));
1788 if (m2 == MOVE_NONE)
1791 // Case 1: The moving piece is the same in both moves
1797 // Case 2: The destination square for m2 was vacated by m1
1803 // Case 3: Moving through the vacated square
1804 if ( piece_is_slider(pos.piece_on(f2))
1805 && bit_is_set(squares_between(f2, t2), f1))
1808 // Case 4: The destination square for m2 is defended by the moving piece in m1
1809 p = pos.piece_on(t1);
1810 if (bit_is_set(pos.attacks_from(p, t1), t2))
1813 // Case 5: Discovered check, checking piece is the piece moved in m1
1814 if ( piece_is_slider(p)
1815 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1816 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1818 // discovered_check_candidates() works also if the Position's side to
1819 // move is the opposite of the checking piece.
1820 Color them = opposite_color(pos.side_to_move());
1821 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1823 if (bit_is_set(dcCandidates, f2))
1830 // value_is_mate() checks if the given value is a mate one eventually
1831 // compensated for the ply.
1833 bool value_is_mate(Value value) {
1835 assert(abs(value) <= VALUE_INFINITE);
1837 return value <= value_mated_in(PLY_MAX)
1838 || value >= value_mate_in(PLY_MAX);
1842 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1843 // "plies to mate from the current ply". Non-mate scores are unchanged.
1844 // The function is called before storing a value to the transposition table.
1846 Value value_to_tt(Value v, int ply) {
1848 if (v >= value_mate_in(PLY_MAX))
1851 if (v <= value_mated_in(PLY_MAX))
1858 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1859 // the transposition table to a mate score corrected for the current ply.
1861 Value value_from_tt(Value v, int ply) {
1863 if (v >= value_mate_in(PLY_MAX))
1866 if (v <= value_mated_in(PLY_MAX))
1873 // move_is_killer() checks if the given move is among the killer moves
1875 bool move_is_killer(Move m, SearchStack* ss) {
1877 const Move* k = ss->killers;
1878 for (int i = 0; i < KILLER_MAX; i++, k++)
1886 // extension() decides whether a move should be searched with normal depth,
1887 // or with extended depth. Certain classes of moves (checking moves, in
1888 // particular) are searched with bigger depth than ordinary moves and in
1889 // any case are marked as 'dangerous'. Note that also if a move is not
1890 // extended, as example because the corresponding UCI option is set to zero,
1891 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1892 template <NodeType PvNode>
1893 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1894 bool singleEvasion, bool mateThreat, bool* dangerous) {
1896 assert(m != MOVE_NONE);
1898 Depth result = Depth(0);
1899 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1903 if (moveIsCheck && pos.see_sign(m) >= 0)
1904 result += CheckExtension[PvNode];
1907 result += SingleEvasionExtension[PvNode];
1910 result += MateThreatExtension[PvNode];
1913 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1915 Color c = pos.side_to_move();
1916 if (relative_rank(c, move_to(m)) == RANK_7)
1918 result += PawnPushTo7thExtension[PvNode];
1921 if (pos.pawn_is_passed(c, move_to(m)))
1923 result += PassedPawnExtension[PvNode];
1928 if ( captureOrPromotion
1929 && pos.type_of_piece_on(move_to(m)) != PAWN
1930 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1931 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1932 && !move_is_promotion(m)
1935 result += PawnEndgameExtension[PvNode];
1940 && captureOrPromotion
1941 && pos.type_of_piece_on(move_to(m)) != PAWN
1942 && pos.see_sign(m) >= 0)
1948 return Min(result, OnePly);
1952 // connected_threat() tests whether it is safe to forward prune a move or if
1953 // is somehow coonected to the threat move returned by null search.
1955 bool connected_threat(const Position& pos, Move m, Move threat) {
1957 assert(move_is_ok(m));
1958 assert(threat && move_is_ok(threat));
1959 assert(!pos.move_is_check(m));
1960 assert(!pos.move_is_capture_or_promotion(m));
1961 assert(!pos.move_is_passed_pawn_push(m));
1963 Square mfrom, mto, tfrom, tto;
1965 mfrom = move_from(m);
1967 tfrom = move_from(threat);
1968 tto = move_to(threat);
1970 // Case 1: Don't prune moves which move the threatened piece
1974 // Case 2: If the threatened piece has value less than or equal to the
1975 // value of the threatening piece, don't prune move which defend it.
1976 if ( pos.move_is_capture(threat)
1977 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1978 || pos.type_of_piece_on(tfrom) == KING)
1979 && pos.move_attacks_square(m, tto))
1982 // Case 3: If the moving piece in the threatened move is a slider, don't
1983 // prune safe moves which block its ray.
1984 if ( piece_is_slider(pos.piece_on(tfrom))
1985 && bit_is_set(squares_between(tfrom, tto), mto)
1986 && pos.see_sign(m) >= 0)
1993 // ok_to_use_TT() returns true if a transposition table score
1994 // can be used at a given point in search.
1996 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1998 Value v = value_from_tt(tte->value(), ply);
2000 return ( tte->depth() >= depth
2001 || v >= Max(value_mate_in(PLY_MAX), beta)
2002 || v < Min(value_mated_in(PLY_MAX), beta))
2004 && ( (is_lower_bound(tte->type()) && v >= beta)
2005 || (is_upper_bound(tte->type()) && v < beta));
2009 // refine_eval() returns the transposition table score if
2010 // possible otherwise falls back on static position evaluation.
2012 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2017 Value v = value_from_tt(tte->value(), ply);
2019 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2020 || (is_upper_bound(tte->type()) && v < defaultEval))
2027 // update_history() registers a good move that produced a beta-cutoff
2028 // in history and marks as failures all the other moves of that ply.
2030 void update_history(const Position& pos, Move move, Depth depth,
2031 Move movesSearched[], int moveCount) {
2035 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2037 for (int i = 0; i < moveCount - 1; i++)
2039 m = movesSearched[i];
2043 if (!pos.move_is_capture_or_promotion(m))
2044 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2049 // update_killers() add a good move that produced a beta-cutoff
2050 // among the killer moves of that ply.
2052 void update_killers(Move m, SearchStack* ss) {
2054 if (m == ss->killers[0])
2057 for (int i = KILLER_MAX - 1; i > 0; i--)
2058 ss->killers[i] = ss->killers[i - 1];
2064 // update_gains() updates the gains table of a non-capture move given
2065 // the static position evaluation before and after the move.
2067 void update_gains(const Position& pos, Move m, Value before, Value after) {
2070 && before != VALUE_NONE
2071 && after != VALUE_NONE
2072 && pos.captured_piece() == NO_PIECE_TYPE
2073 && !move_is_castle(m)
2074 && !move_is_promotion(m))
2075 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2079 // current_search_time() returns the number of milliseconds which have passed
2080 // since the beginning of the current search.
2082 int current_search_time() {
2084 return get_system_time() - SearchStartTime;
2088 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2090 std::string value_to_uci(Value v) {
2092 std::stringstream s;
2094 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2095 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2097 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2102 // nps() computes the current nodes/second count.
2106 int t = current_search_time();
2107 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2111 // poll() performs two different functions: It polls for user input, and it
2112 // looks at the time consumed so far and decides if it's time to abort the
2117 static int lastInfoTime;
2118 int t = current_search_time();
2123 // We are line oriented, don't read single chars
2124 std::string command;
2126 if (!std::getline(std::cin, command))
2129 if (command == "quit")
2132 PonderSearch = false;
2136 else if (command == "stop")
2139 PonderSearch = false;
2141 else if (command == "ponderhit")
2145 // Print search information
2149 else if (lastInfoTime > t)
2150 // HACK: Must be a new search where we searched less than
2151 // NodesBetweenPolls nodes during the first second of search.
2154 else if (t - lastInfoTime >= 1000)
2161 if (dbg_show_hit_rate)
2162 dbg_print_hit_rate();
2164 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2165 << " time " << t << endl;
2168 // Should we stop the search?
2172 bool stillAtFirstMove = FirstRootMove
2173 && !AspirationFailLow
2174 && t > MaxSearchTime + ExtraSearchTime;
2176 bool noMoreTime = t > AbsoluteMaxSearchTime
2177 || stillAtFirstMove;
2179 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2180 || (ExactMaxTime && t >= ExactMaxTime)
2181 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2186 // ponderhit() is called when the program is pondering (i.e. thinking while
2187 // it's the opponent's turn to move) in order to let the engine know that
2188 // it correctly predicted the opponent's move.
2192 int t = current_search_time();
2193 PonderSearch = false;
2195 bool stillAtFirstMove = FirstRootMove
2196 && !AspirationFailLow
2197 && t > MaxSearchTime + ExtraSearchTime;
2199 bool noMoreTime = t > AbsoluteMaxSearchTime
2200 || stillAtFirstMove;
2202 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2207 // init_ss_array() does a fast reset of the first entries of a SearchStack
2208 // array and of all the excludedMove and skipNullMove entries.
2210 void init_ss_array(SearchStack* ss, int size) {
2212 for (int i = 0; i < size; i++, ss++)
2214 ss->excludedMove = MOVE_NONE;
2215 ss->skipNullMove = false;
2226 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2227 // while the program is pondering. The point is to work around a wrinkle in
2228 // the UCI protocol: When pondering, the engine is not allowed to give a
2229 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2230 // We simply wait here until one of these commands is sent, and return,
2231 // after which the bestmove and pondermove will be printed (in id_loop()).
2233 void wait_for_stop_or_ponderhit() {
2235 std::string command;
2239 if (!std::getline(std::cin, command))
2242 if (command == "quit")
2247 else if (command == "ponderhit" || command == "stop")
2253 // print_pv_info() prints to standard output and eventually to log file information on
2254 // the current PV line. It is called at each iteration or after a new pv is found.
2256 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2258 cout << "info depth " << Iteration
2259 << " score " << value_to_uci(value)
2260 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2261 << " time " << current_search_time()
2262 << " nodes " << TM.nodes_searched()
2266 for (Move* m = pv; *m != MOVE_NONE; m++)
2273 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2274 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2276 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2277 TM.nodes_searched(), value, t, pv) << endl;
2282 // init_thread() is the function which is called when a new thread is
2283 // launched. It simply calls the idle_loop() function with the supplied
2284 // threadID. There are two versions of this function; one for POSIX
2285 // threads and one for Windows threads.
2287 #if !defined(_MSC_VER)
2289 void* init_thread(void *threadID) {
2291 TM.idle_loop(*(int*)threadID, NULL);
2297 DWORD WINAPI init_thread(LPVOID threadID) {
2299 TM.idle_loop(*(int*)threadID, NULL);
2306 /// The ThreadsManager class
2308 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2309 // get_beta_counters() are getters/setters for the per thread
2310 // counters used to sort the moves at root.
2312 void ThreadsManager::resetNodeCounters() {
2314 for (int i = 0; i < MAX_THREADS; i++)
2315 threads[i].nodes = 0ULL;
2318 void ThreadsManager::resetBetaCounters() {
2320 for (int i = 0; i < MAX_THREADS; i++)
2321 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2324 int64_t ThreadsManager::nodes_searched() const {
2326 int64_t result = 0ULL;
2327 for (int i = 0; i < ActiveThreads; i++)
2328 result += threads[i].nodes;
2333 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2336 for (int i = 0; i < MAX_THREADS; i++)
2338 our += threads[i].betaCutOffs[us];
2339 their += threads[i].betaCutOffs[opposite_color(us)];
2344 // idle_loop() is where the threads are parked when they have no work to do.
2345 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2346 // object for which the current thread is the master.
2348 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2350 assert(threadID >= 0 && threadID < MAX_THREADS);
2354 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2355 // master should exit as last one.
2356 if (AllThreadsShouldExit)
2359 threads[threadID].state = THREAD_TERMINATED;
2363 // If we are not thinking, wait for a condition to be signaled
2364 // instead of wasting CPU time polling for work.
2365 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2368 assert(threadID != 0);
2369 threads[threadID].state = THREAD_SLEEPING;
2371 #if !defined(_MSC_VER)
2372 lock_grab(&WaitLock);
2373 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2374 pthread_cond_wait(&WaitCond, &WaitLock);
2375 lock_release(&WaitLock);
2377 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2381 // If thread has just woken up, mark it as available
2382 if (threads[threadID].state == THREAD_SLEEPING)
2383 threads[threadID].state = THREAD_AVAILABLE;
2385 // If this thread has been assigned work, launch a search
2386 if (threads[threadID].state == THREAD_WORKISWAITING)
2388 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2390 threads[threadID].state = THREAD_SEARCHING;
2392 if (threads[threadID].splitPoint->pvNode)
2393 sp_search<PV>(threads[threadID].splitPoint, threadID);
2395 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2397 assert(threads[threadID].state == THREAD_SEARCHING);
2399 threads[threadID].state = THREAD_AVAILABLE;
2402 // If this thread is the master of a split point and all slaves have
2403 // finished their work at this split point, return from the idle loop.
2405 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2407 if (i == ActiveThreads)
2409 // Because sp->slaves[] is reset under lock protection,
2410 // be sure sp->lock has been released before to return.
2411 lock_grab(&(sp->lock));
2412 lock_release(&(sp->lock));
2414 assert(threads[threadID].state == THREAD_AVAILABLE);
2416 threads[threadID].state = THREAD_SEARCHING;
2423 // init_threads() is called during startup. It launches all helper threads,
2424 // and initializes the split point stack and the global locks and condition
2427 void ThreadsManager::init_threads() {
2432 #if !defined(_MSC_VER)
2433 pthread_t pthread[1];
2436 // Initialize global locks
2437 lock_init(&MPLock, NULL);
2438 lock_init(&WaitLock, NULL);
2440 #if !defined(_MSC_VER)
2441 pthread_cond_init(&WaitCond, NULL);
2443 for (i = 0; i < MAX_THREADS; i++)
2444 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2447 // Initialize splitPoints[] locks
2448 for (i = 0; i < MAX_THREADS; i++)
2449 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2450 lock_init(&(threads[i].splitPoints[j].lock), NULL);
2452 // Will be set just before program exits to properly end the threads
2453 AllThreadsShouldExit = false;
2455 // Threads will be put to sleep as soon as created
2456 AllThreadsShouldSleep = true;
2458 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2460 threads[0].state = THREAD_SEARCHING;
2461 for (i = 1; i < MAX_THREADS; i++)
2462 threads[i].state = THREAD_AVAILABLE;
2464 // Launch the helper threads
2465 for (i = 1; i < MAX_THREADS; i++)
2468 #if !defined(_MSC_VER)
2469 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2471 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2476 cout << "Failed to create thread number " << i << endl;
2477 Application::exit_with_failure();
2480 // Wait until the thread has finished launching and is gone to sleep
2481 while (threads[i].state != THREAD_SLEEPING) {}
2486 // exit_threads() is called when the program exits. It makes all the
2487 // helper threads exit cleanly.
2489 void ThreadsManager::exit_threads() {
2491 ActiveThreads = MAX_THREADS; // HACK
2492 AllThreadsShouldSleep = true; // HACK
2493 wake_sleeping_threads();
2495 // This makes the threads to exit idle_loop()
2496 AllThreadsShouldExit = true;
2498 // Wait for thread termination
2499 for (int i = 1; i < MAX_THREADS; i++)
2500 while (threads[i].state != THREAD_TERMINATED) {}
2502 // Now we can safely destroy the locks
2503 for (int i = 0; i < MAX_THREADS; i++)
2504 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2505 lock_destroy(&(threads[i].splitPoints[j].lock));
2507 lock_destroy(&WaitLock);
2508 lock_destroy(&MPLock);
2512 // thread_should_stop() checks whether the thread should stop its search.
2513 // This can happen if a beta cutoff has occurred in the thread's currently
2514 // active split point, or in some ancestor of the current split point.
2516 bool ThreadsManager::thread_should_stop(int threadID) const {
2518 assert(threadID >= 0 && threadID < ActiveThreads);
2522 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2527 // thread_is_available() checks whether the thread with threadID "slave" is
2528 // available to help the thread with threadID "master" at a split point. An
2529 // obvious requirement is that "slave" must be idle. With more than two
2530 // threads, this is not by itself sufficient: If "slave" is the master of
2531 // some active split point, it is only available as a slave to the other
2532 // threads which are busy searching the split point at the top of "slave"'s
2533 // split point stack (the "helpful master concept" in YBWC terminology).
2535 bool ThreadsManager::thread_is_available(int slave, int master) const {
2537 assert(slave >= 0 && slave < ActiveThreads);
2538 assert(master >= 0 && master < ActiveThreads);
2539 assert(ActiveThreads > 1);
2541 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2544 // Make a local copy to be sure doesn't change under our feet
2545 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2547 if (localActiveSplitPoints == 0)
2548 // No active split points means that the thread is available as
2549 // a slave for any other thread.
2552 if (ActiveThreads == 2)
2555 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2556 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2557 // could have been set to 0 by another thread leading to an out of bound access.
2558 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2565 // available_thread_exists() tries to find an idle thread which is available as
2566 // a slave for the thread with threadID "master".
2568 bool ThreadsManager::available_thread_exists(int master) const {
2570 assert(master >= 0 && master < ActiveThreads);
2571 assert(ActiveThreads > 1);
2573 for (int i = 0; i < ActiveThreads; i++)
2574 if (thread_is_available(i, master))
2581 // split() does the actual work of distributing the work at a node between
2582 // several available threads. If it does not succeed in splitting the
2583 // node (because no idle threads are available, or because we have no unused
2584 // split point objects), the function immediately returns. If splitting is
2585 // possible, a SplitPoint object is initialized with all the data that must be
2586 // copied to the helper threads and we tell our helper threads that they have
2587 // been assigned work. This will cause them to instantly leave their idle loops
2588 // and call sp_search(). When all threads have returned from sp_search() then
2591 template <bool Fake>
2592 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2593 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2594 int* moveCount, MovePicker* mp, bool pvNode) {
2596 assert(ply > 0 && ply < PLY_MAX);
2597 assert(*bestValue >= -VALUE_INFINITE);
2598 assert(*bestValue <= *alpha);
2599 assert(*alpha < beta);
2600 assert(beta <= VALUE_INFINITE);
2601 assert(depth > Depth(0));
2602 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2603 assert(ActiveThreads > 1);
2605 int i, master = p.thread();
2606 Thread& masterThread = threads[master];
2610 // If no other thread is available to help us, or if we have too many
2611 // active split points, don't split.
2612 if ( !available_thread_exists(master)
2613 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2615 lock_release(&MPLock);
2619 // Pick the next available split point object from the split point stack
2620 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2622 // Initialize the split point object
2623 splitPoint.parent = masterThread.splitPoint;
2624 splitPoint.stopRequest = false;
2625 splitPoint.ply = ply;
2626 splitPoint.depth = depth;
2627 splitPoint.mateThreat = mateThreat;
2628 splitPoint.alpha = *alpha;
2629 splitPoint.beta = beta;
2630 splitPoint.pvNode = pvNode;
2631 splitPoint.bestValue = *bestValue;
2633 splitPoint.moveCount = *moveCount;
2634 splitPoint.pos = &p;
2635 splitPoint.parentSstack = ss;
2636 for (i = 0; i < ActiveThreads; i++)
2637 splitPoint.slaves[i] = 0;
2639 masterThread.splitPoint = &splitPoint;
2641 // If we are here it means we are not available
2642 assert(masterThread.state != THREAD_AVAILABLE);
2644 int workersCnt = 1; // At least the master is included
2646 // Allocate available threads setting state to THREAD_BOOKED
2647 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2648 if (thread_is_available(i, master))
2650 threads[i].state = THREAD_BOOKED;
2651 threads[i].splitPoint = &splitPoint;
2652 splitPoint.slaves[i] = 1;
2656 assert(Fake || workersCnt > 1);
2658 // We can release the lock because slave threads are already booked and master is not available
2659 lock_release(&MPLock);
2661 // Tell the threads that they have work to do. This will make them leave
2662 // their idle loop. But before copy search stack tail for each thread.
2663 for (i = 0; i < ActiveThreads; i++)
2664 if (i == master || splitPoint.slaves[i])
2666 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2668 assert(i == master || threads[i].state == THREAD_BOOKED);
2670 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2673 // Everything is set up. The master thread enters the idle loop, from
2674 // which it will instantly launch a search, because its state is
2675 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2676 // idle loop, which means that the main thread will return from the idle
2677 // loop when all threads have finished their work at this split point.
2678 idle_loop(master, &splitPoint);
2680 // We have returned from the idle loop, which means that all threads are
2681 // finished. Update alpha and bestValue, and return.
2684 *alpha = splitPoint.alpha;
2685 *bestValue = splitPoint.bestValue;
2686 masterThread.activeSplitPoints--;
2687 masterThread.splitPoint = splitPoint.parent;
2689 lock_release(&MPLock);
2693 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2694 // to start a new search from the root.
2696 void ThreadsManager::wake_sleeping_threads() {
2698 assert(AllThreadsShouldSleep);
2699 assert(ActiveThreads > 0);
2701 AllThreadsShouldSleep = false;
2703 if (ActiveThreads == 1)
2706 #if !defined(_MSC_VER)
2707 pthread_mutex_lock(&WaitLock);
2708 pthread_cond_broadcast(&WaitCond);
2709 pthread_mutex_unlock(&WaitLock);
2711 for (int i = 1; i < MAX_THREADS; i++)
2712 SetEvent(SitIdleEvent[i]);
2718 // put_threads_to_sleep() makes all the threads go to sleep just before
2719 // to leave think(), at the end of the search. Threads should have already
2720 // finished the job and should be idle.
2722 void ThreadsManager::put_threads_to_sleep() {
2724 assert(!AllThreadsShouldSleep);
2726 // This makes the threads to go to sleep
2727 AllThreadsShouldSleep = true;
2730 /// The RootMoveList class
2732 // RootMoveList c'tor
2734 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2736 SearchStack ss[PLY_MAX_PLUS_2];
2737 MoveStack mlist[MaxRootMoves];
2739 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2741 // Generate all legal moves
2742 MoveStack* last = generate_moves(pos, mlist);
2744 // Add each move to the moves[] array
2745 for (MoveStack* cur = mlist; cur != last; cur++)
2747 bool includeMove = includeAllMoves;
2749 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2750 includeMove = (searchMoves[k] == cur->move);
2755 // Find a quick score for the move
2756 init_ss_array(ss, PLY_MAX_PLUS_2);
2757 pos.do_move(cur->move, st);
2758 moves[count].move = cur->move;
2759 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2760 moves[count].pv[0] = cur->move;
2761 moves[count].pv[1] = MOVE_NONE;
2762 pos.undo_move(cur->move);
2769 // RootMoveList simple methods definitions
2771 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2773 moves[moveNum].nodes = nodes;
2774 moves[moveNum].cumulativeNodes += nodes;
2777 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2779 moves[moveNum].ourBeta = our;
2780 moves[moveNum].theirBeta = their;
2783 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2787 for (j = 0; pv[j] != MOVE_NONE; j++)
2788 moves[moveNum].pv[j] = pv[j];
2790 moves[moveNum].pv[j] = MOVE_NONE;
2794 // RootMoveList::sort() sorts the root move list at the beginning of a new
2797 void RootMoveList::sort() {
2799 sort_multipv(count - 1); // Sort all items
2803 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2804 // list by their scores and depths. It is used to order the different PVs
2805 // correctly in MultiPV mode.
2807 void RootMoveList::sort_multipv(int n) {
2811 for (i = 1; i <= n; i++)
2813 RootMove rm = moves[i];
2814 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2815 moves[j] = moves[j - 1];