2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
43 #include "ucioption.h"
49 //// Local definitions
55 enum NodeType { NonPV, PV };
57 // Set to true to force running with one thread.
58 // Used for debugging SMP code.
59 const bool FakeSplit = false;
61 // ThreadsManager class is used to handle all the threads related stuff in search,
62 // init, starting, parking and, the most important, launching a slave thread at a
63 // split point are what this class does. All the access to shared thread data is
64 // done through this class, so that we avoid using global variables instead.
66 class ThreadsManager {
67 /* As long as the single ThreadsManager object is defined as a global we don't
68 need to explicitly initialize to zero its data members because variables with
69 static storage duration are automatically set to zero before enter main()
75 int active_threads() const { return ActiveThreads; }
76 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
77 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
78 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
80 void resetNodeCounters();
81 void resetBetaCounters();
82 int64_t nodes_searched() const;
83 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
84 bool available_thread_exists(int master) const;
85 bool thread_is_available(int slave, int master) const;
86 bool thread_should_stop(int threadID) const;
87 void wake_sleeping_threads();
88 void put_threads_to_sleep();
89 void idle_loop(int threadID, SplitPoint* sp);
92 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
99 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
100 Thread threads[MAX_THREADS];
102 Lock MPLock, WaitLock;
104 #if !defined(_MSC_VER)
105 pthread_cond_t WaitCond;
107 HANDLE SitIdleEvent[MAX_THREADS];
113 // RootMove struct is used for moves at the root at the tree. For each
114 // root move, we store a score, a node count, and a PV (really a refutation
115 // in the case of moves which fail low).
119 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
121 // RootMove::operator<() is the comparison function used when
122 // sorting the moves. A move m1 is considered to be better
123 // than a move m2 if it has a higher score, or if the moves
124 // have equal score but m1 has the higher beta cut-off count.
125 bool operator<(const RootMove& m) const {
127 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
132 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
133 Move pv[PLY_MAX_PLUS_2];
137 // The RootMoveList class is essentially an array of RootMove objects, with
138 // a handful of methods for accessing the data in the individual moves.
143 RootMoveList(Position& pos, Move searchMoves[]);
145 int move_count() const { return count; }
146 Move get_move(int moveNum) const { return moves[moveNum].move; }
147 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
148 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
149 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
150 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
152 void set_move_nodes(int moveNum, int64_t nodes);
153 void set_beta_counters(int moveNum, int64_t our, int64_t their);
154 void set_move_pv(int moveNum, const Move pv[]);
156 void sort_multipv(int n);
159 static const int MaxRootMoves = 500;
160 RootMove moves[MaxRootMoves];
169 // Maximum depth for razoring
170 const Depth RazorDepth = 4 * OnePly;
172 // Dynamic razoring margin based on depth
173 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
175 // Step 8. Null move search with verification search
177 // Null move margin. A null move search will not be done if the static
178 // evaluation of the position is more than NullMoveMargin below beta.
179 const Value NullMoveMargin = Value(0x200);
181 // Maximum depth for use of dynamic threat detection when null move fails low
182 const Depth ThreatDepth = 5 * OnePly;
184 // Step 9. Internal iterative deepening
186 // Minimum depth for use of internal iterative deepening
187 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
189 // At Non-PV nodes we do an internal iterative deepening search
190 // when the static evaluation is bigger then beta - IIDMargin.
191 const Value IIDMargin = Value(0x100);
193 // Step 11. Decide the new search depth
195 // Extensions. Configurable UCI options
196 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
197 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
198 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
200 // Minimum depth for use of singular extension
201 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
203 // If the TT move is at least SingularExtensionMargin better then the
204 // remaining ones we will extend it.
205 const Value SingularExtensionMargin = Value(0x20);
207 // Step 12. Futility pruning
209 // Futility margin for quiescence search
210 const Value FutilityMarginQS = Value(0x80);
212 // Futility lookup tables (initialized at startup) and their getter functions
213 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
214 int FutilityMoveCountArray[32]; // [depth]
216 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
217 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
219 // Step 14. Reduced search
221 // Reduction lookup tables (initialized at startup) and their getter functions
222 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
224 template <NodeType PV>
225 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
227 // Common adjustments
229 // Search depth at iteration 1
230 const Depth InitialDepth = OnePly;
232 // Easy move margin. An easy move candidate must be at least this much
233 // better than the second best move.
234 const Value EasyMoveMargin = Value(0x200);
242 // Scores and number of times the best move changed for each iteration
243 Value ValueByIteration[PLY_MAX_PLUS_2];
244 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
246 // Search window management
252 // Time managment variables
253 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
254 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
255 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
256 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
260 std::ofstream LogFile;
262 // Multi-threads related variables
263 Depth MinimumSplitDepth;
264 int MaxThreadsPerSplitPoint;
267 // Node counters, used only by thread[0] but try to keep in different cache
268 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
270 int NodesBetweenPolls = 30000;
277 Value id_loop(const Position& pos, Move searchMoves[]);
278 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
280 template <NodeType PvNode>
281 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
283 template <NodeType PvNode>
284 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
286 template <NodeType PvNode>
287 void sp_search(SplitPoint* sp, int threadID);
289 template <NodeType PvNode>
290 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
292 bool connected_moves(const Position& pos, Move m1, Move m2);
293 bool value_is_mate(Value value);
294 Value value_to_tt(Value v, int ply);
295 Value value_from_tt(Value v, int ply);
296 bool move_is_killer(Move m, SearchStack* ss);
297 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
298 bool connected_threat(const Position& pos, Move m, Move threat);
299 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
300 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
301 void update_killers(Move m, SearchStack* ss);
302 void update_gains(const Position& pos, Move move, Value before, Value after);
304 int current_search_time();
305 std::string value_to_uci(Value v);
309 void wait_for_stop_or_ponderhit();
310 void init_ss_array(SearchStack* ss, int size);
311 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
313 #if !defined(_MSC_VER)
314 void *init_thread(void *threadID);
316 DWORD WINAPI init_thread(LPVOID threadID);
326 /// init_threads(), exit_threads() and nodes_searched() are helpers to
327 /// give accessibility to some TM methods from outside of current file.
329 void init_threads() { TM.init_threads(); }
330 void exit_threads() { TM.exit_threads(); }
331 int64_t nodes_searched() { return TM.nodes_searched(); }
334 /// init_search() is called during startup. It initializes various lookup tables
338 int d; // depth (OnePly == 2)
339 int hd; // half depth (OnePly == 1)
342 // Init reductions array
343 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
345 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
346 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
347 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
348 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
351 // Init futility margins array
352 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
353 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
355 // Init futility move count array
356 for (d = 0; d < 32; d++)
357 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
361 // SearchStack::init() initializes a search stack entry.
362 // Called at the beginning of search() when starting to examine a new node.
363 void SearchStack::init() {
365 currentMove = threatMove = bestMove = MOVE_NONE;
368 // SearchStack::initKillers() initializes killers for a search stack entry
369 void SearchStack::initKillers() {
371 mateKiller = MOVE_NONE;
372 for (int i = 0; i < KILLER_MAX; i++)
373 killers[i] = MOVE_NONE;
377 /// perft() is our utility to verify move generation is bug free. All the legal
378 /// moves up to given depth are generated and counted and the sum returned.
380 int perft(Position& pos, Depth depth)
385 MovePicker mp(pos, MOVE_NONE, depth, H);
387 // If we are at the last ply we don't need to do and undo
388 // the moves, just to count them.
389 if (depth <= OnePly) // Replace with '<' to test also qsearch
391 while (mp.get_next_move()) sum++;
395 // Loop through all legal moves
397 while ((move = mp.get_next_move()) != MOVE_NONE)
399 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
400 sum += perft(pos, depth - OnePly);
407 /// think() is the external interface to Stockfish's search, and is called when
408 /// the program receives the UCI 'go' command. It initializes various
409 /// search-related global variables, and calls root_search(). It returns false
410 /// when a quit command is received during the search.
412 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
413 int movesToGo, int maxDepth, 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[pos.side_to_move()];
487 int myIncrement = increment[pos.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_uci(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
772 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ei);
774 // Step 6. Razoring (omitted at root)
775 // Step 7. Static null move pruning (omitted at root)
776 // Step 8. Null move search with verification search (omitted at root)
777 // Step 9. Internal iterative deepening (omitted at root)
779 // Step extra. Fail low loop
780 // We start with small aspiration window and in case of fail low, we research
781 // with bigger window until we are not failing low anymore.
784 // Sort the moves before to (re)search
787 // Step 10. Loop through all moves in the root move list
788 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
790 // This is used by time management
791 FirstRootMove = (i == 0);
793 // Save the current node count before the move is searched
794 nodes = TM.nodes_searched();
796 // Reset beta cut-off counters
797 TM.resetBetaCounters();
799 // Pick the next root move, and print the move and the move number to
800 // the standard output.
801 move = ss->currentMove = rml.get_move(i);
803 if (current_search_time() >= 1000)
804 cout << "info currmove " << move
805 << " currmovenumber " << i + 1 << endl;
807 moveIsCheck = pos.move_is_check(move);
808 captureOrPromotion = pos.move_is_capture_or_promotion(move);
810 // Step 11. Decide the new search depth
811 depth = (Iteration - 2) * OnePly + InitialDepth;
812 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
813 newDepth = depth + ext;
815 // Step 12. Futility pruning (omitted at root)
817 // Step extra. Fail high loop
818 // If move fails high, we research with bigger window until we are not failing
820 value = - VALUE_INFINITE;
824 // Step 13. Make the move
825 pos.do_move(move, st, ci, moveIsCheck);
827 // Step extra. pv search
828 // We do pv search for first moves (i < MultiPV)
829 // and for fail high research (value > alpha)
830 if (i < MultiPV || value > alpha)
832 // Aspiration window is disabled in multi-pv case
834 alpha = -VALUE_INFINITE;
836 // Full depth PV search, done on first move or after a fail high
837 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
841 // Step 14. Reduced search
842 // if the move fails high will be re-searched at full depth
843 bool doFullDepthSearch = true;
845 if ( depth >= 3 * OnePly
847 && !captureOrPromotion
848 && !move_is_castle(move))
850 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
853 assert(newDepth-ss->reduction >= OnePly);
855 // Reduced depth non-pv search using alpha as upperbound
856 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
857 doFullDepthSearch = (value > alpha);
860 // The move failed high, but if reduction is very big we could
861 // face a false positive, retry with a less aggressive reduction,
862 // if the move fails high again then go with full depth search.
863 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
865 assert(newDepth - OnePly >= OnePly);
867 ss->reduction = OnePly;
868 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
869 doFullDepthSearch = (value > alpha);
871 ss->reduction = Depth(0); // Restore original reduction
874 // Step 15. Full depth search
875 if (doFullDepthSearch)
877 // Full depth non-pv search using alpha as upperbound
878 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
880 // If we are above alpha then research at same depth but as PV
881 // to get a correct score or eventually a fail high above beta.
883 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
887 // Step 16. Undo move
890 // Can we exit fail high loop ?
891 if (AbortSearch || value < beta)
894 // We are failing high and going to do a research. It's important to update
895 // the score before research in case we run out of time while researching.
896 rml.set_move_score(i, value);
898 TT.extract_pv(pos, move, pv, PLY_MAX);
899 rml.set_move_pv(i, pv);
901 // Print information to the standard output
902 print_pv_info(pos, pv, alpha, beta, value);
904 // Prepare for a research after a fail high, each time with a wider window
905 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
908 } // End of fail high loop
910 // Finished searching the move. If AbortSearch is true, the search
911 // was aborted because the user interrupted the search or because we
912 // ran out of time. In this case, the return value of the search cannot
913 // be trusted, and we break out of the loop without updating the best
918 // Remember beta-cutoff and searched nodes counts for this move. The
919 // info is used to sort the root moves for the next iteration.
921 TM.get_beta_counters(pos.side_to_move(), our, their);
922 rml.set_beta_counters(i, our, their);
923 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
925 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
926 assert(value < beta);
928 // Step 17. Check for new best move
929 if (value <= alpha && i >= MultiPV)
930 rml.set_move_score(i, -VALUE_INFINITE);
933 // PV move or new best move!
936 rml.set_move_score(i, value);
938 TT.extract_pv(pos, move, pv, PLY_MAX);
939 rml.set_move_pv(i, pv);
943 // We record how often the best move has been changed in each
944 // iteration. This information is used for time managment: When
945 // the best move changes frequently, we allocate some more time.
947 BestMoveChangesByIteration[Iteration]++;
949 // Print information to the standard output
950 print_pv_info(pos, pv, alpha, beta, value);
952 // Raise alpha to setup proper non-pv search upper bound
959 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
961 cout << "info multipv " << j + 1
962 << " score " << value_to_uci(rml.get_move_score(j))
963 << " depth " << (j <= i ? Iteration : Iteration - 1)
964 << " time " << current_search_time()
965 << " nodes " << TM.nodes_searched()
969 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
970 cout << rml.get_move_pv(j, k) << " ";
974 alpha = rml.get_move_score(Min(i, MultiPV - 1));
976 } // PV move or new best move
978 assert(alpha >= *alphaPtr);
980 AspirationFailLow = (alpha == *alphaPtr);
982 if (AspirationFailLow && StopOnPonderhit)
983 StopOnPonderhit = false;
986 // Can we exit fail low loop ?
987 if (AbortSearch || !AspirationFailLow)
990 // Prepare for a research after a fail low, each time with a wider window
991 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
996 // Sort the moves before to return
1003 // search<>() is the main search function for both PV and non-PV nodes
1005 template <NodeType PvNode>
1006 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1008 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1009 assert(beta > alpha && beta <= VALUE_INFINITE);
1010 assert(PvNode || alpha == beta - 1);
1011 assert(ply > 0 && ply < PLY_MAX);
1012 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1014 Move movesSearched[256];
1019 Move ttMove, move, excludedMove;
1020 Depth ext, newDepth;
1021 Value bestValue, value, oldAlpha;
1022 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1023 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
1024 bool mateThreat = false;
1026 int threadID = pos.thread();
1027 refinedValue = bestValue = value = -VALUE_INFINITE;
1030 // Step 1. Initialize node and poll. Polling can abort search
1031 TM.incrementNodeCounter(threadID);
1033 (ss+2)->initKillers();
1035 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1041 // Step 2. Check for aborted search and immediate draw
1042 if (AbortSearch || TM.thread_should_stop(threadID))
1045 if (pos.is_draw() || ply >= PLY_MAX - 1)
1048 // Step 3. Mate distance pruning
1049 alpha = Max(value_mated_in(ply), alpha);
1050 beta = Min(value_mate_in(ply+1), beta);
1054 // Step 4. Transposition table lookup
1056 // We don't want the score of a partial search to overwrite a previous full search
1057 // TT value, so we use a different position key in case of an excluded move exists.
1058 excludedMove = ss->excludedMove;
1059 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1061 tte = TT.retrieve(posKey);
1062 ttMove = (tte ? tte->move() : MOVE_NONE);
1064 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1065 // This is to avoid problems in the following areas:
1067 // * Repetition draw detection
1068 // * Fifty move rule detection
1069 // * Searching for a mate
1070 // * Printing of full PV line
1072 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1074 // Refresh tte entry to avoid aging
1075 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1077 ss->currentMove = ttMove; // Can be MOVE_NONE
1078 return value_from_tt(tte->value(), ply);
1081 // Step 5. Evaluate the position statically
1082 // At PV nodes we do this only to update gain statistics
1083 isCheck = pos.is_check();
1086 if (tte && tte->static_value() != VALUE_NONE)
1088 ss->eval = tte->static_value();
1089 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1092 ss->eval = evaluate(pos, ei);
1094 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1095 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1098 ss->eval = VALUE_NONE;
1100 // Step 6. Razoring (is omitted in PV nodes)
1102 && depth < RazorDepth
1104 && refinedValue < beta - razor_margin(depth)
1105 && ttMove == MOVE_NONE
1106 && (ss-1)->currentMove != MOVE_NULL
1107 && !value_is_mate(beta)
1108 && !pos.has_pawn_on_7th(pos.side_to_move()))
1110 // Pass ss->eval to qsearch() and avoid an evaluate call
1111 if (!tte || tte->static_value() == VALUE_NONE)
1112 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1114 Value rbeta = beta - razor_margin(depth);
1115 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1117 // Logically we should return (v + razor_margin(depth)), but
1118 // surprisingly this did slightly weaker in tests.
1122 // Step 7. Static null move pruning (is omitted in PV nodes)
1123 // We're betting that the opponent doesn't have a move that will reduce
1124 // the score by more than futility_margin(depth) if we do a null move.
1126 && !ss->skipNullMove
1127 && depth < RazorDepth
1128 && refinedValue >= beta + futility_margin(depth, 0)
1130 && !value_is_mate(beta)
1131 && pos.non_pawn_material(pos.side_to_move()))
1132 return refinedValue - futility_margin(depth, 0);
1134 // Step 8. Null move search with verification search (is omitted in PV nodes)
1135 // When we jump directly to qsearch() we do a null move only if static value is
1136 // at least beta. Otherwise we do a null move if static value is not more than
1137 // NullMoveMargin under beta.
1139 && !ss->skipNullMove
1141 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1143 && !value_is_mate(beta)
1144 && pos.non_pawn_material(pos.side_to_move()))
1146 ss->currentMove = MOVE_NULL;
1148 // Null move dynamic reduction based on depth
1149 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1151 // Null move dynamic reduction based on value
1152 if (refinedValue - beta > PawnValueMidgame)
1155 pos.do_null_move(st);
1156 (ss+1)->skipNullMove = true;
1158 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1159 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1160 (ss+1)->skipNullMove = false;
1161 pos.undo_null_move();
1163 if (nullValue >= beta)
1165 // Do not return unproven mate scores
1166 if (nullValue >= value_mate_in(PLY_MAX))
1169 if (depth < 6 * OnePly)
1172 // Do verification search at high depths
1173 ss->skipNullMove = true;
1174 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1175 ss->skipNullMove = false;
1182 // The null move failed low, which means that we may be faced with
1183 // some kind of threat. If the previous move was reduced, check if
1184 // the move that refuted the null move was somehow connected to the
1185 // move which was reduced. If a connection is found, return a fail
1186 // low score (which will cause the reduced move to fail high in the
1187 // parent node, which will trigger a re-search with full depth).
1188 if (nullValue == value_mated_in(ply + 2))
1191 ss->threatMove = (ss+1)->currentMove;
1192 if ( depth < ThreatDepth
1193 && (ss-1)->reduction
1194 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1199 // Step 9. Internal iterative deepening
1200 if ( depth >= IIDDepth[PvNode]
1201 && ttMove == MOVE_NONE
1202 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1204 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1206 ss->skipNullMove = true;
1207 search<PvNode>(pos, ss, alpha, beta, d, ply);
1208 ss->skipNullMove = false;
1210 ttMove = ss->bestMove;
1211 tte = TT.retrieve(posKey);
1214 // Expensive mate threat detection (only for PV nodes)
1216 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1218 // Initialize a MovePicker object for the current position
1219 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1221 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1222 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1223 && tte && tte->move()
1224 && !excludedMove // Do not allow recursive singular extension search
1225 && is_lower_bound(tte->type())
1226 && tte->depth() >= depth - 3 * OnePly;
1228 // Step 10. Loop through moves
1229 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1230 while ( bestValue < beta
1231 && (move = mp.get_next_move()) != MOVE_NONE
1232 && !TM.thread_should_stop(threadID))
1234 assert(move_is_ok(move));
1236 if (move == excludedMove)
1239 moveIsCheck = pos.move_is_check(move, ci);
1240 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1242 // Step 11. Decide the new search depth
1243 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1245 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1246 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1247 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1248 // lower then ttValue minus a margin then we extend ttMove.
1249 if ( singularExtensionNode
1250 && move == tte->move()
1253 Value ttValue = value_from_tt(tte->value(), ply);
1255 if (abs(ttValue) < VALUE_KNOWN_WIN)
1257 Value b = ttValue - SingularExtensionMargin;
1258 ss->excludedMove = move;
1259 ss->skipNullMove = true;
1260 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1261 ss->skipNullMove = false;
1262 ss->excludedMove = MOVE_NONE;
1268 newDepth = depth - OnePly + ext;
1270 // Update current move (this must be done after singular extension search)
1271 movesSearched[moveCount++] = ss->currentMove = move;
1273 // Step 12. Futility pruning (is omitted in PV nodes)
1275 && !captureOrPromotion
1279 && !move_is_castle(move))
1281 // Move count based pruning
1282 if ( moveCount >= futility_move_count(depth)
1283 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1284 && bestValue > value_mated_in(PLY_MAX))
1287 // Value based pruning
1288 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1289 // but fixing this made program slightly weaker.
1290 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1291 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1292 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1294 if (futilityValueScaled < beta)
1296 if (futilityValueScaled > bestValue)
1297 bestValue = futilityValueScaled;
1302 // Step 13. Make the move
1303 pos.do_move(move, st, ci, moveIsCheck);
1305 // Step extra. pv search (only in PV nodes)
1306 // The first move in list is the expected PV
1307 if (PvNode && moveCount == 1)
1308 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1309 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1312 // Step 14. Reduced depth search
1313 // If the move fails high will be re-searched at full depth.
1314 bool doFullDepthSearch = true;
1316 if ( depth >= 3 * OnePly
1317 && !captureOrPromotion
1319 && !move_is_castle(move)
1320 && !move_is_killer(move, ss))
1322 ss->reduction = reduction<PvNode>(depth, moveCount);
1325 Depth d = newDepth - ss->reduction;
1326 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1327 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1329 doFullDepthSearch = (value > alpha);
1332 // The move failed high, but if reduction is very big we could
1333 // face a false positive, retry with a less aggressive reduction,
1334 // if the move fails high again then go with full depth search.
1335 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1337 assert(newDepth - OnePly >= OnePly);
1339 ss->reduction = OnePly;
1340 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1341 doFullDepthSearch = (value > alpha);
1343 ss->reduction = Depth(0); // Restore original reduction
1346 // Step 15. Full depth search
1347 if (doFullDepthSearch)
1349 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1350 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1352 // Step extra. pv search (only in PV nodes)
1353 // Search only for possible new PV nodes, if instead value >= beta then
1354 // parent node fails low with value <= alpha and tries another move.
1355 if (PvNode && value > alpha && value < beta)
1356 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1357 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1361 // Step 16. Undo move
1362 pos.undo_move(move);
1364 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1366 // Step 17. Check for new best move
1367 if (value > bestValue)
1372 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1375 if (value == value_mate_in(ply + 1))
1376 ss->mateKiller = move;
1378 ss->bestMove = move;
1382 // Step 18. Check for split
1383 if ( depth >= MinimumSplitDepth
1384 && TM.active_threads() > 1
1386 && TM.available_thread_exists(threadID)
1388 && !TM.thread_should_stop(threadID)
1390 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1391 mateThreat, &moveCount, &mp, PvNode);
1394 // Step 19. Check for mate and stalemate
1395 // All legal moves have been searched and if there are
1396 // no legal moves, it must be mate or stalemate.
1397 // If one move was excluded return fail low score.
1399 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1401 // Step 20. Update tables
1402 // If the search is not aborted, update the transposition table,
1403 // history counters, and killer moves.
1404 if (AbortSearch || TM.thread_should_stop(threadID))
1407 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1408 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1409 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1411 // Update killers and history only for non capture moves that fails high
1412 if (bestValue >= beta)
1414 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1415 if (!pos.move_is_capture_or_promotion(move))
1417 update_history(pos, move, depth, movesSearched, moveCount);
1418 update_killers(move, ss);
1422 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1428 // qsearch() is the quiescence search function, which is called by the main
1429 // search function when the remaining depth is zero (or, to be more precise,
1430 // less than OnePly).
1432 template <NodeType PvNode>
1433 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1435 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1436 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1437 assert(PvNode || alpha == beta - 1);
1439 assert(ply > 0 && ply < PLY_MAX);
1440 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1445 Value bestValue, value, futilityValue, futilityBase;
1446 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1448 Value oldAlpha = alpha;
1450 TM.incrementNodeCounter(pos.thread());
1451 ss->bestMove = ss->currentMove = MOVE_NONE;
1453 // Check for an instant draw or maximum ply reached
1454 if (pos.is_draw() || ply >= PLY_MAX - 1)
1457 // Transposition table lookup. At PV nodes, we don't use the TT for
1458 // pruning, but only for move ordering.
1459 tte = TT.retrieve(pos.get_key());
1460 ttMove = (tte ? tte->move() : MOVE_NONE);
1462 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1464 ss->currentMove = ttMove; // Can be MOVE_NONE
1465 return value_from_tt(tte->value(), ply);
1468 isCheck = pos.is_check();
1470 // Evaluate the position statically
1473 bestValue = futilityBase = -VALUE_INFINITE;
1474 ss->eval = VALUE_NONE;
1475 deepChecks = enoughMaterial = false;
1479 if (tte && tte->static_value() != VALUE_NONE)
1481 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1482 bestValue = tte->static_value();
1485 bestValue = evaluate(pos, ei);
1487 ss->eval = bestValue;
1488 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1490 // Stand pat. Return immediately if static value is at least beta
1491 if (bestValue >= beta)
1494 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()]);
1499 if (PvNode && bestValue > alpha)
1502 // If we are near beta then try to get a cutoff pushing checks a bit further
1503 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1505 // Futility pruning parameters, not needed when in check
1506 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1507 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1510 // Initialize a MovePicker object for the current position, and prepare
1511 // to search the moves. Because the depth is <= 0 here, only captures,
1512 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1513 // and we are near beta) will be generated.
1514 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1517 // Loop through the moves until no moves remain or a beta cutoff occurs
1518 while ( alpha < beta
1519 && (move = mp.get_next_move()) != MOVE_NONE)
1521 assert(move_is_ok(move));
1523 moveIsCheck = pos.move_is_check(move, ci);
1531 && !move_is_promotion(move)
1532 && !pos.move_is_passed_pawn_push(move))
1534 futilityValue = futilityBase
1535 + pos.endgame_value_of_piece_on(move_to(move))
1536 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1538 if (futilityValue < alpha)
1540 if (futilityValue > bestValue)
1541 bestValue = futilityValue;
1546 // Detect blocking evasions that are candidate to be pruned
1547 evasionPrunable = isCheck
1548 && bestValue > value_mated_in(PLY_MAX)
1549 && !pos.move_is_capture(move)
1550 && pos.type_of_piece_on(move_from(move)) != KING
1551 && !pos.can_castle(pos.side_to_move());
1553 // Don't search moves with negative SEE values
1555 && (!isCheck || evasionPrunable)
1557 && !move_is_promotion(move)
1558 && pos.see_sign(move) < 0)
1561 // Update current move
1562 ss->currentMove = move;
1564 // Make and search the move
1565 pos.do_move(move, st, ci, moveIsCheck);
1566 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1567 pos.undo_move(move);
1569 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1572 if (value > bestValue)
1578 ss->bestMove = move;
1583 // All legal moves have been searched. A special case: If we're in check
1584 // and no legal moves were found, it is checkmate.
1585 if (isCheck && bestValue == -VALUE_INFINITE)
1586 return value_mated_in(ply);
1588 // Update transposition table
1589 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1590 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1591 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1593 // Update killers only for checking moves that fails high
1594 if ( bestValue >= beta
1595 && !pos.move_is_capture_or_promotion(ss->bestMove))
1596 update_killers(ss->bestMove, ss);
1598 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1604 // sp_search() is used to search from a split point. This function is called
1605 // by each thread working at the split point. It is similar to the normal
1606 // search() function, but simpler. Because we have already probed the hash
1607 // table, done a null move search, and searched the first move before
1608 // splitting, we don't have to repeat all this work in sp_search(). We
1609 // also don't need to store anything to the hash table here: This is taken
1610 // care of after we return from the split point.
1612 template <NodeType PvNode>
1613 void sp_search(SplitPoint* sp, int threadID) {
1615 assert(threadID >= 0 && threadID < TM.active_threads());
1616 assert(TM.active_threads() > 1);
1620 Depth ext, newDepth;
1622 Value futilityValueScaled; // NonPV specific
1623 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1625 value = -VALUE_INFINITE;
1627 Position pos(*sp->pos, threadID);
1629 SearchStack* ss = sp->sstack[threadID] + 1;
1630 isCheck = pos.is_check();
1632 // Step 10. Loop through moves
1633 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1634 lock_grab(&(sp->lock));
1636 while ( sp->bestValue < sp->beta
1637 && (move = sp->mp->get_next_move()) != MOVE_NONE
1638 && !TM.thread_should_stop(threadID))
1640 moveCount = ++sp->moveCount;
1641 lock_release(&(sp->lock));
1643 assert(move_is_ok(move));
1645 moveIsCheck = pos.move_is_check(move, ci);
1646 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1648 // Step 11. Decide the new search depth
1649 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1650 newDepth = sp->depth - OnePly + ext;
1652 // Update current move
1653 ss->currentMove = move;
1655 // Step 12. Futility pruning (is omitted in PV nodes)
1657 && !captureOrPromotion
1660 && !move_is_castle(move))
1662 // Move count based pruning
1663 if ( moveCount >= futility_move_count(sp->depth)
1664 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1665 && sp->bestValue > value_mated_in(PLY_MAX))
1667 lock_grab(&(sp->lock));
1671 // Value based pruning
1672 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1673 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1674 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1676 if (futilityValueScaled < sp->beta)
1678 lock_grab(&(sp->lock));
1680 if (futilityValueScaled > sp->bestValue)
1681 sp->bestValue = futilityValueScaled;
1686 // Step 13. Make the move
1687 pos.do_move(move, st, ci, moveIsCheck);
1689 // Step 14. Reduced search
1690 // If the move fails high will be re-searched at full depth.
1691 bool doFullDepthSearch = true;
1693 if ( !captureOrPromotion
1695 && !move_is_castle(move)
1696 && !move_is_killer(move, ss))
1698 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1701 Value localAlpha = sp->alpha;
1702 Depth d = newDepth - ss->reduction;
1703 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1704 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1706 doFullDepthSearch = (value > localAlpha);
1709 // The move failed high, but if reduction is very big we could
1710 // face a false positive, retry with a less aggressive reduction,
1711 // if the move fails high again then go with full depth search.
1712 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1714 assert(newDepth - OnePly >= OnePly);
1716 ss->reduction = OnePly;
1717 Value localAlpha = sp->alpha;
1718 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1719 doFullDepthSearch = (value > localAlpha);
1721 ss->reduction = Depth(0); // Restore original reduction
1724 // Step 15. Full depth search
1725 if (doFullDepthSearch)
1727 Value localAlpha = sp->alpha;
1728 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1729 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1731 // Step extra. pv search (only in PV nodes)
1732 // Search only for possible new PV nodes, if instead value >= beta then
1733 // parent node fails low with value <= alpha and tries another move.
1734 if (PvNode && value > localAlpha && value < sp->beta)
1735 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1736 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1739 // Step 16. Undo move
1740 pos.undo_move(move);
1742 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1744 // Step 17. Check for new best move
1745 lock_grab(&(sp->lock));
1747 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1749 sp->bestValue = value;
1751 if (sp->bestValue > sp->alpha)
1753 if (!PvNode || value >= sp->beta)
1754 sp->stopRequest = true;
1756 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1759 sp->parentSstack->bestMove = ss->bestMove = move;
1764 /* Here we have the lock still grabbed */
1766 sp->slaves[threadID] = 0;
1768 lock_release(&(sp->lock));
1772 // connected_moves() tests whether two moves are 'connected' in the sense
1773 // that the first move somehow made the second move possible (for instance
1774 // if the moving piece is the same in both moves). The first move is assumed
1775 // to be the move that was made to reach the current position, while the
1776 // second move is assumed to be a move from the current position.
1778 bool connected_moves(const Position& pos, Move m1, Move m2) {
1780 Square f1, t1, f2, t2;
1783 assert(move_is_ok(m1));
1784 assert(move_is_ok(m2));
1786 if (m2 == MOVE_NONE)
1789 // Case 1: The moving piece is the same in both moves
1795 // Case 2: The destination square for m2 was vacated by m1
1801 // Case 3: Moving through the vacated square
1802 if ( piece_is_slider(pos.piece_on(f2))
1803 && bit_is_set(squares_between(f2, t2), f1))
1806 // Case 4: The destination square for m2 is defended by the moving piece in m1
1807 p = pos.piece_on(t1);
1808 if (bit_is_set(pos.attacks_from(p, t1), t2))
1811 // Case 5: Discovered check, checking piece is the piece moved in m1
1812 if ( piece_is_slider(p)
1813 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1814 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1816 // discovered_check_candidates() works also if the Position's side to
1817 // move is the opposite of the checking piece.
1818 Color them = opposite_color(pos.side_to_move());
1819 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1821 if (bit_is_set(dcCandidates, f2))
1828 // value_is_mate() checks if the given value is a mate one eventually
1829 // compensated for the ply.
1831 bool value_is_mate(Value value) {
1833 assert(abs(value) <= VALUE_INFINITE);
1835 return value <= value_mated_in(PLY_MAX)
1836 || value >= value_mate_in(PLY_MAX);
1840 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1841 // "plies to mate from the current ply". Non-mate scores are unchanged.
1842 // The function is called before storing a value to the transposition table.
1844 Value value_to_tt(Value v, int ply) {
1846 if (v >= value_mate_in(PLY_MAX))
1849 if (v <= value_mated_in(PLY_MAX))
1856 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1857 // the transposition table to a mate score corrected for the current ply.
1859 Value value_from_tt(Value v, int ply) {
1861 if (v >= value_mate_in(PLY_MAX))
1864 if (v <= value_mated_in(PLY_MAX))
1871 // move_is_killer() checks if the given move is among the killer moves
1873 bool move_is_killer(Move m, SearchStack* ss) {
1875 const Move* k = ss->killers;
1876 for (int i = 0; i < KILLER_MAX; i++, k++)
1884 // extension() decides whether a move should be searched with normal depth,
1885 // or with extended depth. Certain classes of moves (checking moves, in
1886 // particular) are searched with bigger depth than ordinary moves and in
1887 // any case are marked as 'dangerous'. Note that also if a move is not
1888 // extended, as example because the corresponding UCI option is set to zero,
1889 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1890 template <NodeType PvNode>
1891 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1892 bool singleEvasion, bool mateThreat, bool* dangerous) {
1894 assert(m != MOVE_NONE);
1896 Depth result = Depth(0);
1897 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1901 if (moveIsCheck && pos.see_sign(m) >= 0)
1902 result += CheckExtension[PvNode];
1905 result += SingleEvasionExtension[PvNode];
1908 result += MateThreatExtension[PvNode];
1911 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1913 Color c = pos.side_to_move();
1914 if (relative_rank(c, move_to(m)) == RANK_7)
1916 result += PawnPushTo7thExtension[PvNode];
1919 if (pos.pawn_is_passed(c, move_to(m)))
1921 result += PassedPawnExtension[PvNode];
1926 if ( captureOrPromotion
1927 && pos.type_of_piece_on(move_to(m)) != PAWN
1928 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1929 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1930 && !move_is_promotion(m)
1933 result += PawnEndgameExtension[PvNode];
1938 && captureOrPromotion
1939 && pos.type_of_piece_on(move_to(m)) != PAWN
1940 && pos.see_sign(m) >= 0)
1946 return Min(result, OnePly);
1950 // connected_threat() tests whether it is safe to forward prune a move or if
1951 // is somehow coonected to the threat move returned by null search.
1953 bool connected_threat(const Position& pos, Move m, Move threat) {
1955 assert(move_is_ok(m));
1956 assert(threat && move_is_ok(threat));
1957 assert(!pos.move_is_check(m));
1958 assert(!pos.move_is_capture_or_promotion(m));
1959 assert(!pos.move_is_passed_pawn_push(m));
1961 Square mfrom, mto, tfrom, tto;
1963 mfrom = move_from(m);
1965 tfrom = move_from(threat);
1966 tto = move_to(threat);
1968 // Case 1: Don't prune moves which move the threatened piece
1972 // Case 2: If the threatened piece has value less than or equal to the
1973 // value of the threatening piece, don't prune move which defend it.
1974 if ( pos.move_is_capture(threat)
1975 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1976 || pos.type_of_piece_on(tfrom) == KING)
1977 && pos.move_attacks_square(m, tto))
1980 // Case 3: If the moving piece in the threatened move is a slider, don't
1981 // prune safe moves which block its ray.
1982 if ( piece_is_slider(pos.piece_on(tfrom))
1983 && bit_is_set(squares_between(tfrom, tto), mto)
1984 && pos.see_sign(m) >= 0)
1991 // ok_to_use_TT() returns true if a transposition table score
1992 // can be used at a given point in search.
1994 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1996 Value v = value_from_tt(tte->value(), ply);
1998 return ( tte->depth() >= depth
1999 || v >= Max(value_mate_in(PLY_MAX), beta)
2000 || v < Min(value_mated_in(PLY_MAX), beta))
2002 && ( (is_lower_bound(tte->type()) && v >= beta)
2003 || (is_upper_bound(tte->type()) && v < beta));
2007 // refine_eval() returns the transposition table score if
2008 // possible otherwise falls back on static position evaluation.
2010 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2015 Value v = value_from_tt(tte->value(), ply);
2017 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2018 || (is_upper_bound(tte->type()) && v < defaultEval))
2025 // update_history() registers a good move that produced a beta-cutoff
2026 // in history and marks as failures all the other moves of that ply.
2028 void update_history(const Position& pos, Move move, Depth depth,
2029 Move movesSearched[], int moveCount) {
2033 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2035 for (int i = 0; i < moveCount - 1; i++)
2037 m = movesSearched[i];
2041 if (!pos.move_is_capture_or_promotion(m))
2042 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2047 // update_killers() add a good move that produced a beta-cutoff
2048 // among the killer moves of that ply.
2050 void update_killers(Move m, SearchStack* ss) {
2052 if (m == ss->killers[0])
2055 for (int i = KILLER_MAX - 1; i > 0; i--)
2056 ss->killers[i] = ss->killers[i - 1];
2062 // update_gains() updates the gains table of a non-capture move given
2063 // the static position evaluation before and after the move.
2065 void update_gains(const Position& pos, Move m, Value before, Value after) {
2068 && before != VALUE_NONE
2069 && after != VALUE_NONE
2070 && pos.captured_piece() == NO_PIECE_TYPE
2071 && !move_is_castle(m)
2072 && !move_is_promotion(m))
2073 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2077 // current_search_time() returns the number of milliseconds which have passed
2078 // since the beginning of the current search.
2080 int current_search_time() {
2082 return get_system_time() - SearchStartTime;
2086 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2088 std::string value_to_uci(Value v) {
2090 std::stringstream s;
2092 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2093 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2095 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2100 // nps() computes the current nodes/second count.
2104 int t = current_search_time();
2105 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2109 // poll() performs two different functions: It polls for user input, and it
2110 // looks at the time consumed so far and decides if it's time to abort the
2115 static int lastInfoTime;
2116 int t = current_search_time();
2121 // We are line oriented, don't read single chars
2122 std::string command;
2124 if (!std::getline(std::cin, command))
2127 if (command == "quit")
2130 PonderSearch = false;
2134 else if (command == "stop")
2137 PonderSearch = false;
2139 else if (command == "ponderhit")
2143 // Print search information
2147 else if (lastInfoTime > t)
2148 // HACK: Must be a new search where we searched less than
2149 // NodesBetweenPolls nodes during the first second of search.
2152 else if (t - lastInfoTime >= 1000)
2159 if (dbg_show_hit_rate)
2160 dbg_print_hit_rate();
2162 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2163 << " time " << t << endl;
2166 // Should we stop the search?
2170 bool stillAtFirstMove = FirstRootMove
2171 && !AspirationFailLow
2172 && t > MaxSearchTime + ExtraSearchTime;
2174 bool noMoreTime = t > AbsoluteMaxSearchTime
2175 || stillAtFirstMove;
2177 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2178 || (ExactMaxTime && t >= ExactMaxTime)
2179 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2184 // ponderhit() is called when the program is pondering (i.e. thinking while
2185 // it's the opponent's turn to move) in order to let the engine know that
2186 // it correctly predicted the opponent's move.
2190 int t = current_search_time();
2191 PonderSearch = false;
2193 bool stillAtFirstMove = FirstRootMove
2194 && !AspirationFailLow
2195 && t > MaxSearchTime + ExtraSearchTime;
2197 bool noMoreTime = t > AbsoluteMaxSearchTime
2198 || stillAtFirstMove;
2200 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2205 // init_ss_array() does a fast reset of the first entries of a SearchStack
2206 // array and of all the excludedMove and skipNullMove entries.
2208 void init_ss_array(SearchStack* ss, int size) {
2210 for (int i = 0; i < size; i++, ss++)
2212 ss->excludedMove = MOVE_NONE;
2213 ss->skipNullMove = false;
2214 ss->reduction = Depth(0);
2225 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2226 // while the program is pondering. The point is to work around a wrinkle in
2227 // the UCI protocol: When pondering, the engine is not allowed to give a
2228 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2229 // We simply wait here until one of these commands is sent, and return,
2230 // after which the bestmove and pondermove will be printed (in id_loop()).
2232 void wait_for_stop_or_ponderhit() {
2234 std::string command;
2238 if (!std::getline(std::cin, command))
2241 if (command == "quit")
2246 else if (command == "ponderhit" || command == "stop")
2252 // print_pv_info() prints to standard output and eventually to log file information on
2253 // the current PV line. It is called at each iteration or after a new pv is found.
2255 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2257 cout << "info depth " << Iteration
2258 << " score " << value_to_uci(value)
2259 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2260 << " time " << current_search_time()
2261 << " nodes " << TM.nodes_searched()
2265 for (Move* m = pv; *m != MOVE_NONE; m++)
2272 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2273 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2275 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2276 TM.nodes_searched(), value, t, pv) << endl;
2281 // init_thread() is the function which is called when a new thread is
2282 // launched. It simply calls the idle_loop() function with the supplied
2283 // threadID. There are two versions of this function; one for POSIX
2284 // threads and one for Windows threads.
2286 #if !defined(_MSC_VER)
2288 void* init_thread(void *threadID) {
2290 TM.idle_loop(*(int*)threadID, NULL);
2296 DWORD WINAPI init_thread(LPVOID threadID) {
2298 TM.idle_loop(*(int*)threadID, NULL);
2305 /// The ThreadsManager class
2307 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2308 // get_beta_counters() are getters/setters for the per thread
2309 // counters used to sort the moves at root.
2311 void ThreadsManager::resetNodeCounters() {
2313 for (int i = 0; i < MAX_THREADS; i++)
2314 threads[i].nodes = 0ULL;
2317 void ThreadsManager::resetBetaCounters() {
2319 for (int i = 0; i < MAX_THREADS; i++)
2320 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2323 int64_t ThreadsManager::nodes_searched() const {
2325 int64_t result = 0ULL;
2326 for (int i = 0; i < ActiveThreads; i++)
2327 result += threads[i].nodes;
2332 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2335 for (int i = 0; i < MAX_THREADS; i++)
2337 our += threads[i].betaCutOffs[us];
2338 their += threads[i].betaCutOffs[opposite_color(us)];
2343 // idle_loop() is where the threads are parked when they have no work to do.
2344 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2345 // object for which the current thread is the master.
2347 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2349 assert(threadID >= 0 && threadID < MAX_THREADS);
2353 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2354 // master should exit as last one.
2355 if (AllThreadsShouldExit)
2358 threads[threadID].state = THREAD_TERMINATED;
2362 // If we are not thinking, wait for a condition to be signaled
2363 // instead of wasting CPU time polling for work.
2364 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2367 assert(threadID != 0);
2368 threads[threadID].state = THREAD_SLEEPING;
2370 #if !defined(_MSC_VER)
2371 lock_grab(&WaitLock);
2372 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2373 pthread_cond_wait(&WaitCond, &WaitLock);
2374 lock_release(&WaitLock);
2376 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2380 // If thread has just woken up, mark it as available
2381 if (threads[threadID].state == THREAD_SLEEPING)
2382 threads[threadID].state = THREAD_AVAILABLE;
2384 // If this thread has been assigned work, launch a search
2385 if (threads[threadID].state == THREAD_WORKISWAITING)
2387 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2389 threads[threadID].state = THREAD_SEARCHING;
2391 if (threads[threadID].splitPoint->pvNode)
2392 sp_search<PV>(threads[threadID].splitPoint, threadID);
2394 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2396 assert(threads[threadID].state == THREAD_SEARCHING);
2398 threads[threadID].state = THREAD_AVAILABLE;
2401 // If this thread is the master of a split point and all slaves have
2402 // finished their work at this split point, return from the idle loop.
2404 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2406 if (i == ActiveThreads)
2408 // Because sp->slaves[] is reset under lock protection,
2409 // be sure sp->lock has been released before to return.
2410 lock_grab(&(sp->lock));
2411 lock_release(&(sp->lock));
2413 assert(threads[threadID].state == THREAD_AVAILABLE);
2415 threads[threadID].state = THREAD_SEARCHING;
2422 // init_threads() is called during startup. It launches all helper threads,
2423 // and initializes the split point stack and the global locks and condition
2426 void ThreadsManager::init_threads() {
2431 #if !defined(_MSC_VER)
2432 pthread_t pthread[1];
2435 // Initialize global locks
2436 lock_init(&MPLock, NULL);
2437 lock_init(&WaitLock, NULL);
2439 #if !defined(_MSC_VER)
2440 pthread_cond_init(&WaitCond, NULL);
2442 for (i = 0; i < MAX_THREADS; i++)
2443 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2446 // Initialize splitPoints[] locks
2447 for (i = 0; i < MAX_THREADS; i++)
2448 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2449 lock_init(&(threads[i].splitPoints[j].lock), NULL);
2451 // Will be set just before program exits to properly end the threads
2452 AllThreadsShouldExit = false;
2454 // Threads will be put to sleep as soon as created
2455 AllThreadsShouldSleep = true;
2457 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2459 threads[0].state = THREAD_SEARCHING;
2460 for (i = 1; i < MAX_THREADS; i++)
2461 threads[i].state = THREAD_AVAILABLE;
2463 // Launch the helper threads
2464 for (i = 1; i < MAX_THREADS; i++)
2467 #if !defined(_MSC_VER)
2468 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2470 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2475 cout << "Failed to create thread number " << i << endl;
2476 Application::exit_with_failure();
2479 // Wait until the thread has finished launching and is gone to sleep
2480 while (threads[i].state != THREAD_SLEEPING) {}
2485 // exit_threads() is called when the program exits. It makes all the
2486 // helper threads exit cleanly.
2488 void ThreadsManager::exit_threads() {
2490 ActiveThreads = MAX_THREADS; // HACK
2491 AllThreadsShouldSleep = true; // HACK
2492 wake_sleeping_threads();
2494 // This makes the threads to exit idle_loop()
2495 AllThreadsShouldExit = true;
2497 // Wait for thread termination
2498 for (int i = 1; i < MAX_THREADS; i++)
2499 while (threads[i].state != THREAD_TERMINATED) {}
2501 // Now we can safely destroy the locks
2502 for (int i = 0; i < MAX_THREADS; i++)
2503 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2504 lock_destroy(&(threads[i].splitPoints[j].lock));
2506 lock_destroy(&WaitLock);
2507 lock_destroy(&MPLock);
2511 // thread_should_stop() checks whether the thread should stop its search.
2512 // This can happen if a beta cutoff has occurred in the thread's currently
2513 // active split point, or in some ancestor of the current split point.
2515 bool ThreadsManager::thread_should_stop(int threadID) const {
2517 assert(threadID >= 0 && threadID < ActiveThreads);
2521 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2526 // thread_is_available() checks whether the thread with threadID "slave" is
2527 // available to help the thread with threadID "master" at a split point. An
2528 // obvious requirement is that "slave" must be idle. With more than two
2529 // threads, this is not by itself sufficient: If "slave" is the master of
2530 // some active split point, it is only available as a slave to the other
2531 // threads which are busy searching the split point at the top of "slave"'s
2532 // split point stack (the "helpful master concept" in YBWC terminology).
2534 bool ThreadsManager::thread_is_available(int slave, int master) const {
2536 assert(slave >= 0 && slave < ActiveThreads);
2537 assert(master >= 0 && master < ActiveThreads);
2538 assert(ActiveThreads > 1);
2540 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2543 // Make a local copy to be sure doesn't change under our feet
2544 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2546 if (localActiveSplitPoints == 0)
2547 // No active split points means that the thread is available as
2548 // a slave for any other thread.
2551 if (ActiveThreads == 2)
2554 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2555 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2556 // could have been set to 0 by another thread leading to an out of bound access.
2557 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2564 // available_thread_exists() tries to find an idle thread which is available as
2565 // a slave for the thread with threadID "master".
2567 bool ThreadsManager::available_thread_exists(int master) const {
2569 assert(master >= 0 && master < ActiveThreads);
2570 assert(ActiveThreads > 1);
2572 for (int i = 0; i < ActiveThreads; i++)
2573 if (thread_is_available(i, master))
2580 // split() does the actual work of distributing the work at a node between
2581 // several available threads. If it does not succeed in splitting the
2582 // node (because no idle threads are available, or because we have no unused
2583 // split point objects), the function immediately returns. If splitting is
2584 // possible, a SplitPoint object is initialized with all the data that must be
2585 // copied to the helper threads and we tell our helper threads that they have
2586 // been assigned work. This will cause them to instantly leave their idle loops
2587 // and call sp_search(). When all threads have returned from sp_search() then
2590 template <bool Fake>
2591 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2592 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2593 int* moveCount, MovePicker* mp, bool pvNode) {
2595 assert(ply > 0 && ply < PLY_MAX);
2596 assert(*bestValue >= -VALUE_INFINITE);
2597 assert(*bestValue <= *alpha);
2598 assert(*alpha < beta);
2599 assert(beta <= VALUE_INFINITE);
2600 assert(depth > Depth(0));
2601 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2602 assert(ActiveThreads > 1);
2604 int i, master = p.thread();
2605 Thread& masterThread = threads[master];
2609 // If no other thread is available to help us, or if we have too many
2610 // active split points, don't split.
2611 if ( !available_thread_exists(master)
2612 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2614 lock_release(&MPLock);
2618 // Pick the next available split point object from the split point stack
2619 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2621 // Initialize the split point object
2622 splitPoint.parent = masterThread.splitPoint;
2623 splitPoint.stopRequest = false;
2624 splitPoint.ply = ply;
2625 splitPoint.depth = depth;
2626 splitPoint.mateThreat = mateThreat;
2627 splitPoint.alpha = *alpha;
2628 splitPoint.beta = beta;
2629 splitPoint.pvNode = pvNode;
2630 splitPoint.bestValue = *bestValue;
2632 splitPoint.moveCount = *moveCount;
2633 splitPoint.pos = &p;
2634 splitPoint.parentSstack = ss;
2635 for (i = 0; i < ActiveThreads; i++)
2636 splitPoint.slaves[i] = 0;
2638 masterThread.splitPoint = &splitPoint;
2640 // If we are here it means we are not available
2641 assert(masterThread.state != THREAD_AVAILABLE);
2643 int workersCnt = 1; // At least the master is included
2645 // Allocate available threads setting state to THREAD_BOOKED
2646 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2647 if (thread_is_available(i, master))
2649 threads[i].state = THREAD_BOOKED;
2650 threads[i].splitPoint = &splitPoint;
2651 splitPoint.slaves[i] = 1;
2655 assert(Fake || workersCnt > 1);
2657 // We can release the lock because slave threads are already booked and master is not available
2658 lock_release(&MPLock);
2660 // Tell the threads that they have work to do. This will make them leave
2661 // their idle loop. But before copy search stack tail for each thread.
2662 for (i = 0; i < ActiveThreads; i++)
2663 if (i == master || splitPoint.slaves[i])
2665 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2667 assert(i == master || threads[i].state == THREAD_BOOKED);
2669 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2672 // Everything is set up. The master thread enters the idle loop, from
2673 // which it will instantly launch a search, because its state is
2674 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2675 // idle loop, which means that the main thread will return from the idle
2676 // loop when all threads have finished their work at this split point.
2677 idle_loop(master, &splitPoint);
2679 // We have returned from the idle loop, which means that all threads are
2680 // finished. Update alpha and bestValue, and return.
2683 *alpha = splitPoint.alpha;
2684 *bestValue = splitPoint.bestValue;
2685 masterThread.activeSplitPoints--;
2686 masterThread.splitPoint = splitPoint.parent;
2688 lock_release(&MPLock);
2692 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2693 // to start a new search from the root.
2695 void ThreadsManager::wake_sleeping_threads() {
2697 assert(AllThreadsShouldSleep);
2698 assert(ActiveThreads > 0);
2700 AllThreadsShouldSleep = false;
2702 if (ActiveThreads == 1)
2705 #if !defined(_MSC_VER)
2706 pthread_mutex_lock(&WaitLock);
2707 pthread_cond_broadcast(&WaitCond);
2708 pthread_mutex_unlock(&WaitLock);
2710 for (int i = 1; i < MAX_THREADS; i++)
2711 SetEvent(SitIdleEvent[i]);
2717 // put_threads_to_sleep() makes all the threads go to sleep just before
2718 // to leave think(), at the end of the search. Threads should have already
2719 // finished the job and should be idle.
2721 void ThreadsManager::put_threads_to_sleep() {
2723 assert(!AllThreadsShouldSleep);
2725 // This makes the threads to go to sleep
2726 AllThreadsShouldSleep = true;
2729 /// The RootMoveList class
2731 // RootMoveList c'tor
2733 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2735 SearchStack ss[PLY_MAX_PLUS_2];
2736 MoveStack mlist[MaxRootMoves];
2738 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2740 // Generate all legal moves
2741 MoveStack* last = generate_moves(pos, mlist);
2743 // Add each move to the moves[] array
2744 for (MoveStack* cur = mlist; cur != last; cur++)
2746 bool includeMove = includeAllMoves;
2748 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2749 includeMove = (searchMoves[k] == cur->move);
2754 // Find a quick score for the move
2755 init_ss_array(ss, PLY_MAX_PLUS_2);
2756 ss[0].eval = VALUE_NONE;
2757 ss[0].currentMove = cur->move;
2758 pos.do_move(cur->move, st);
2759 moves[count].move = cur->move;
2760 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2761 moves[count].pv[0] = cur->move;
2762 moves[count].pv[1] = MOVE_NONE;
2763 pos.undo_move(cur->move);
2770 // RootMoveList simple methods definitions
2772 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2774 moves[moveNum].nodes = nodes;
2775 moves[moveNum].cumulativeNodes += nodes;
2778 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2780 moves[moveNum].ourBeta = our;
2781 moves[moveNum].theirBeta = their;
2784 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2788 for (j = 0; pv[j] != MOVE_NONE; j++)
2789 moves[moveNum].pv[j] = pv[j];
2791 moves[moveNum].pv[j] = MOVE_NONE;
2795 // RootMoveList::sort() sorts the root move list at the beginning of a new
2798 void RootMoveList::sort() {
2800 sort_multipv(count - 1); // Sort all items
2804 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2805 // list by their scores and depths. It is used to order the different PVs
2806 // correctly in MultiPV mode.
2808 void RootMoveList::sort_multipv(int n) {
2812 for (i = 1; i <= n; i++)
2814 RootMove rm = moves[i];
2815 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2816 moves[j] = moves[j - 1];