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
57 // ThreadsManager class is used to handle all the threads related stuff in search,
58 // init, starting, parking and, the most important, launching a slave thread at a
59 // split point are what this class does. All the access to shared thread data is
60 // done through this class, so that we avoid using global variables instead.
62 class ThreadsManager {
63 /* As long as the single ThreadsManager object is defined as a global we don't
64 need to explicitly initialize to zero its data members because variables with
65 static storage duration are automatically set to zero before enter main()
71 int active_threads() const { return ActiveThreads; }
72 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
73 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
74 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
76 void resetNodeCounters();
77 void resetBetaCounters();
78 int64_t nodes_searched() const;
79 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
80 bool available_thread_exists(int master) const;
81 bool thread_is_available(int slave, int master) const;
82 bool thread_should_stop(int threadID) const;
83 void wake_sleeping_threads();
84 void put_threads_to_sleep();
85 void idle_loop(int threadID, SplitPoint* waitSp);
86 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode);
90 friend void poll(SearchStack ss[], int ply);
93 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
94 Thread threads[MAX_THREADS];
95 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
97 Lock MPLock, WaitLock;
99 #if !defined(_MSC_VER)
100 pthread_cond_t WaitCond;
102 HANDLE SitIdleEvent[MAX_THREADS];
108 // RootMove struct is used for moves at the root at the tree. For each
109 // root move, we store a score, a node count, and a PV (really a refutation
110 // in the case of moves which fail low).
114 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
116 // RootMove::operator<() is the comparison function used when
117 // sorting the moves. A move m1 is considered to be better
118 // than a move m2 if it has a higher score, or if the moves
119 // have equal score but m1 has the higher node count.
120 bool operator<(const RootMove& m) const {
122 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
127 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
128 Move pv[PLY_MAX_PLUS_2];
132 // The RootMoveList class is essentially an array of RootMove objects, with
133 // a handful of methods for accessing the data in the individual moves.
138 RootMoveList(Position& pos, Move searchMoves[]);
140 int move_count() const { return count; }
141 Move get_move(int moveNum) const { return moves[moveNum].move; }
142 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
143 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
144 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
145 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
147 void set_move_nodes(int moveNum, int64_t nodes);
148 void set_beta_counters(int moveNum, int64_t our, int64_t their);
149 void set_move_pv(int moveNum, const Move pv[]);
151 void sort_multipv(int n);
154 static const int MaxRootMoves = 500;
155 RootMove moves[MaxRootMoves];
164 // Maximum depth for razoring
165 const Depth RazorDepth = 4 * OnePly;
167 // Dynamic razoring margin based on depth
168 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
170 // Step 8. Null move search with verification search
172 // Null move margin. A null move search will not be done if the static
173 // evaluation of the position is more than NullMoveMargin below beta.
174 const Value NullMoveMargin = Value(0x200);
176 // Maximum depth for use of dynamic threat detection when null move fails low
177 const Depth ThreatDepth = 5 * OnePly;
179 // Step 9. Internal iterative deepening
181 // Minimum depth for use of internal iterative deepening
182 const Depth IIDDepthAtPVNodes = 5 * OnePly;
183 const Depth IIDDepthAtNonPVNodes = 8 * OnePly;
185 // At Non-PV nodes we do an internal iterative deepening search
186 // when the static evaluation is at most IIDMargin below beta.
187 const Value IIDMargin = Value(0x100);
189 // Step 11. Decide the new search depth
191 // Extensions. Configurable UCI options
192 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
193 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
194 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
196 // Minimum depth for use of singular extension
197 const Depth SingularExtensionDepthAtPVNodes = 6 * OnePly;
198 const Depth SingularExtensionDepthAtNonPVNodes = 8 * OnePly;
200 // If the TT move is at least SingularExtensionMargin better then the
201 // remaining ones we will extend it.
202 const Value SingularExtensionMargin = Value(0x20);
204 // Step 12. Futility pruning
206 // Futility margin for quiescence search
207 const Value FutilityMarginQS = Value(0x80);
209 // Futility lookup tables (initialized at startup) and their getter functions
210 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
211 int FutilityMoveCountArray[32]; // [depth]
213 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
214 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
216 // Step 14. Reduced search
218 // Reduction lookup tables (initialized at startup) and their getter functions
219 int8_t PVReductionMatrix[8][64][64]; // [depth][moveNumber]
220 int8_t NonPVReductionMatrix[8][64][64]; // [depth][moveNumber]
222 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[0][Min(d / 2, 63)][Min(mn, 63)]; }
223 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[0][Min(d / 2, 63)][Min(mn, 63)]; }
225 // Common adjustments
227 // Search depth at iteration 1
228 const Depth InitialDepth = OnePly;
230 // Easy move margin. An easy move candidate must be at least this much
231 // better than the second best move.
232 const Value EasyMoveMargin = Value(0x200);
234 // Last seconds noise filtering (LSN)
235 const bool UseLSNFiltering = true;
236 const int LSNTime = 4000; // In milliseconds
237 const Value LSNValue = value_from_centipawns(200);
238 bool loseOnTime = false;
246 // Scores and number of times the best move changed for each iteration
247 Value ValueByIteration[PLY_MAX_PLUS_2];
248 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
250 // Search window management
256 // Time managment variables
257 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
258 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
259 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
260 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
262 // Show current line?
263 bool ShowCurrentLine;
267 std::ofstream LogFile;
269 // Multi-threads related variables
270 Depth MinimumSplitDepth;
271 int MaxThreadsPerSplitPoint;
274 // Node counters, used only by thread[0] but try to keep in different cache
275 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
277 int NodesBetweenPolls = 30000;
284 Value id_loop(const Position& pos, Move searchMoves[]);
285 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
286 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
287 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
288 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
289 void sp_search(SplitPoint* sp, int threadID);
290 void sp_search_pv(SplitPoint* sp, int threadID);
291 void init_node(SearchStack ss[], int ply, int threadID);
292 void update_pv(SearchStack ss[], int ply);
293 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
294 bool connected_moves(const Position& pos, Move m1, Move m2);
295 bool value_is_mate(Value value);
296 bool move_is_killer(Move m, const SearchStack& ss);
297 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
298 bool ok_to_do_nullmove(const Position& pos);
299 bool ok_to_prune(const Position& pos, Move m, Move threat);
300 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
301 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
302 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
303 void update_killers(Move m, SearchStack& ss);
304 void update_gains(const Position& pos, Move move, Value before, Value after);
306 int current_search_time();
308 void poll(SearchStack ss[], int ply);
310 void wait_for_stop_or_ponderhit();
311 void init_ss_array(SearchStack ss[]);
312 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value);
314 #if !defined(_MSC_VER)
315 void *init_thread(void *threadID);
317 DWORD WINAPI init_thread(LPVOID threadID);
327 /// init_threads(), exit_threads() and nodes_searched() are helpers to
328 /// give accessibility to some TM methods from outside of current file.
330 void init_threads() { TM.init_threads(); }
331 void exit_threads() { TM.exit_threads(); }
332 int64_t nodes_searched() { return TM.nodes_searched(); }
335 /// perft() is our utility to verify move generation is bug free. All the legal
336 /// moves up to given depth are generated and counted and the sum returned.
338 int perft(Position& pos, Depth depth)
343 MovePicker mp(pos, MOVE_NONE, depth, H);
345 // If we are at the last ply we don't need to do and undo
346 // the moves, just to count them.
347 if (depth <= OnePly) // Replace with '<' to test also qsearch
349 while (mp.get_next_move()) sum++;
353 // Loop through all legal moves
355 while ((move = mp.get_next_move()) != MOVE_NONE)
357 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
358 sum += perft(pos, depth - OnePly);
365 /// think() is the external interface to Stockfish's search, and is called when
366 /// the program receives the UCI 'go' command. It initializes various
367 /// search-related global variables, and calls root_search(). It returns false
368 /// when a quit command is received during the search.
370 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
371 int time[], int increment[], int movesToGo, int maxDepth,
372 int maxNodes, int maxTime, Move searchMoves[]) {
374 // Initialize global search variables
375 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
376 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
378 TM.resetNodeCounters();
379 SearchStartTime = get_system_time();
380 ExactMaxTime = maxTime;
383 InfiniteSearch = infinite;
384 PonderSearch = ponder;
385 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
387 // Look for a book move, only during games, not tests
388 if (UseTimeManagement && get_option_value_bool("OwnBook"))
390 if (get_option_value_string("Book File") != OpeningBook.file_name())
391 OpeningBook.open(get_option_value_string("Book File"));
393 Move bookMove = OpeningBook.get_move(pos);
394 if (bookMove != MOVE_NONE)
397 wait_for_stop_or_ponderhit();
399 cout << "bestmove " << bookMove << endl;
404 // Reset loseOnTime flag at the beginning of a new game
405 if (button_was_pressed("New Game"))
408 // Read UCI option values
409 TT.set_size(get_option_value_int("Hash"));
410 if (button_was_pressed("Clear Hash"))
413 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
414 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
415 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
416 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
417 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
418 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
419 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
420 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
421 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
422 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
423 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
424 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
426 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
427 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
428 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
429 MultiPV = get_option_value_int("MultiPV");
430 Chess960 = get_option_value_bool("UCI_Chess960");
431 UseLogFile = get_option_value_bool("Use Search Log");
434 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
436 read_weights(pos.side_to_move());
438 // Set the number of active threads
439 int newActiveThreads = get_option_value_int("Threads");
440 if (newActiveThreads != TM.active_threads())
442 TM.set_active_threads(newActiveThreads);
443 init_eval(TM.active_threads());
446 // Wake up sleeping threads
447 TM.wake_sleeping_threads();
450 int myTime = time[side_to_move];
451 int myIncrement = increment[side_to_move];
452 if (UseTimeManagement)
454 if (!movesToGo) // Sudden death time control
458 MaxSearchTime = myTime / 30 + myIncrement;
459 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
461 else // Blitz game without increment
463 MaxSearchTime = myTime / 30;
464 AbsoluteMaxSearchTime = myTime / 8;
467 else // (x moves) / (y minutes)
471 MaxSearchTime = myTime / 2;
472 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
476 MaxSearchTime = myTime / Min(movesToGo, 20);
477 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
481 if (get_option_value_bool("Ponder"))
483 MaxSearchTime += MaxSearchTime / 4;
484 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
488 // Set best NodesBetweenPolls interval to avoid lagging under
489 // heavy time pressure.
491 NodesBetweenPolls = Min(MaxNodes, 30000);
492 else if (myTime && myTime < 1000)
493 NodesBetweenPolls = 1000;
494 else if (myTime && myTime < 5000)
495 NodesBetweenPolls = 5000;
497 NodesBetweenPolls = 30000;
499 // Write search information to log file
501 LogFile << "Searching: " << pos.to_fen() << endl
502 << "infinite: " << infinite
503 << " ponder: " << ponder
504 << " time: " << myTime
505 << " increment: " << myIncrement
506 << " moves to go: " << movesToGo << endl;
508 // LSN filtering. Used only for developing purposes, disabled by default
512 // Step 2. If after last move we decided to lose on time, do it now!
513 while (SearchStartTime + myTime + 1000 > get_system_time())
517 // We're ready to start thinking. Call the iterative deepening loop function
518 Value v = id_loop(pos, searchMoves);
522 // Step 1. If this is sudden death game and our position is hopeless,
523 // decide to lose on time.
524 if ( !loseOnTime // If we already lost on time, go to step 3.
534 // Step 3. Now after stepping over the time limit, reset flag for next match.
542 TM.put_threads_to_sleep();
547 // init_reduction_tables()
549 void init_reduction_tables(int8_t pvTable[64][64], int8_t nonPvTable[64][64], int pvInhib, int nonPvInhib)
551 double pvBase = 1.001 - log(3.0) * log(16.0) / pvInhib;
552 double nonPvBase = 1.001 - log(3.0) * log(4.0) / nonPvInhib;
554 // Init reduction lookup tables
555 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
556 for (int j = 1; j < 64; j++) // j == moveNumber
558 double pvRed = pvBase + log(double(i)) * log(double(j)) / pvInhib;
559 double nonPVRed = nonPvBase + log(double(i)) * log(double(j)) / nonPvInhib;
561 pvTable[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
562 nonPvTable[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
566 // init_search() is called during startup. It initializes various lookup tables
570 for (int i = 0; i < 8; i++)
571 init_reduction_tables(PVReductionMatrix[i], NonPVReductionMatrix[i], 4.0 * pow(1.3, i), 2.0 * pow(1.3, i));
573 // Init futility margins array
574 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
575 for (int j = 0; j < 64; j++) // j == moveNumber
577 // FIXME: test using log instead of BSR
578 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j;
581 // Init futility move count array
582 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
583 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
587 // SearchStack::init() initializes a search stack. Used at the beginning of a
588 // new search from the root.
589 void SearchStack::init(int ply) {
591 pv[ply] = pv[ply + 1] = MOVE_NONE;
592 currentMove = threatMove = MOVE_NONE;
593 reduction = Depth(0);
597 void SearchStack::initKillers() {
599 mateKiller = MOVE_NONE;
600 for (int i = 0; i < KILLER_MAX; i++)
601 killers[i] = MOVE_NONE;
606 // id_loop() is the main iterative deepening loop. It calls root_search
607 // repeatedly with increasing depth until the allocated thinking time has
608 // been consumed, the user stops the search, or the maximum search depth is
611 Value id_loop(const Position& pos, Move searchMoves[]) {
614 SearchStack ss[PLY_MAX_PLUS_2];
615 Move EasyMove = MOVE_NONE;
616 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
618 // Moves to search are verified, copied, scored and sorted
619 RootMoveList rml(p, searchMoves);
621 // Handle special case of searching on a mate/stale position
622 if (rml.move_count() == 0)
625 wait_for_stop_or_ponderhit();
627 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
630 // Print RootMoveList startup scoring to the standard output,
631 // so to output information also for iteration 1.
632 cout << "info depth " << 1
633 << "\ninfo depth " << 1
634 << " score " << value_to_string(rml.get_move_score(0))
635 << " time " << current_search_time()
636 << " nodes " << TM.nodes_searched()
638 << " pv " << rml.get_move(0) << "\n";
644 ValueByIteration[1] = rml.get_move_score(0);
647 // Is one move significantly better than others after initial scoring ?
648 if ( rml.move_count() == 1
649 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
650 EasyMove = rml.get_move(0);
652 // Iterative deepening loop
653 while (Iteration < PLY_MAX)
655 // Initialize iteration
657 BestMoveChangesByIteration[Iteration] = 0;
659 cout << "info depth " << Iteration << endl;
661 // Calculate dynamic aspiration window based on previous iterations
662 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
664 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
665 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
667 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
668 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
670 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
671 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
674 // Search to the current depth, rml is updated and sorted, alpha and beta could change
675 value = root_search(p, ss, rml, &alpha, &beta);
677 // Write PV to transposition table, in case the relevant entries have
678 // been overwritten during the search.
679 TT.insert_pv(p, ss[0].pv);
682 break; // Value cannot be trusted. Break out immediately!
684 //Save info about search result
685 ValueByIteration[Iteration] = value;
687 // Drop the easy move if differs from the new best move
688 if (ss[0].pv[0] != EasyMove)
689 EasyMove = MOVE_NONE;
691 if (UseTimeManagement)
694 bool stopSearch = false;
696 // Stop search early if there is only a single legal move,
697 // we search up to Iteration 6 anyway to get a proper score.
698 if (Iteration >= 6 && rml.move_count() == 1)
701 // Stop search early when the last two iterations returned a mate score
703 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
704 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
707 // Stop search early if one move seems to be much better than the others
708 int64_t nodes = TM.nodes_searched();
710 && EasyMove == ss[0].pv[0]
711 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
712 && current_search_time() > MaxSearchTime / 16)
713 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
714 && current_search_time() > MaxSearchTime / 32)))
717 // Add some extra time if the best move has changed during the last two iterations
718 if (Iteration > 5 && Iteration <= 50)
719 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
720 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
722 // Stop search if most of MaxSearchTime is consumed at the end of the
723 // iteration. We probably don't have enough time to search the first
724 // move at the next iteration anyway.
725 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
731 StopOnPonderhit = true;
737 if (MaxDepth && Iteration >= MaxDepth)
741 // If we are pondering or in infinite search, we shouldn't print the
742 // best move before we are told to do so.
743 if (!AbortSearch && (PonderSearch || InfiniteSearch))
744 wait_for_stop_or_ponderhit();
746 // Print final search statistics
747 cout << "info nodes " << TM.nodes_searched()
749 << " time " << current_search_time()
750 << " hashfull " << TT.full() << endl;
752 // Print the best move and the ponder move to the standard output
753 if (ss[0].pv[0] == MOVE_NONE)
755 ss[0].pv[0] = rml.get_move(0);
756 ss[0].pv[1] = MOVE_NONE;
759 assert(ss[0].pv[0] != MOVE_NONE);
761 cout << "bestmove " << ss[0].pv[0];
763 if (ss[0].pv[1] != MOVE_NONE)
764 cout << " ponder " << ss[0].pv[1];
771 dbg_print_mean(LogFile);
773 if (dbg_show_hit_rate)
774 dbg_print_hit_rate(LogFile);
776 LogFile << "\nNodes: " << TM.nodes_searched()
777 << "\nNodes/second: " << nps()
778 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
781 p.do_move(ss[0].pv[0], st);
782 LogFile << "\nPonder move: "
783 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
786 return rml.get_move_score(0);
790 // root_search() is the function which searches the root node. It is
791 // similar to search_pv except that it uses a different move ordering
792 // scheme, prints some information to the standard output and handles
793 // the fail low/high loops.
795 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
802 Depth depth, ext, newDepth;
803 Value value, alpha, beta;
804 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
805 int researchCountFH, researchCountFL;
807 researchCountFH = researchCountFL = 0;
810 isCheck = pos.is_check();
812 // Step 1. Initialize node and poll (omitted at root, but I can see no good reason for this, FIXME)
813 // Step 2. Check for aborted search (omitted at root, because we do not initialize root node)
814 // Step 3. Mate distance pruning (omitted at root)
815 // Step 4. Transposition table lookup (omitted at root)
817 // Step 5. Evaluate the position statically
818 // At root we do this only to get reference value for child nodes
820 ss[0].eval = evaluate(pos, ei, 0);
822 ss[0].eval = VALUE_NONE; // HACK because we do not initialize root node
824 // Step 6. Razoring (omitted at root)
825 // Step 7. Static null move pruning (omitted at root)
826 // Step 8. Null move search with verification search (omitted at root)
827 // Step 9. Internal iterative deepening (omitted at root)
829 // Step extra. Fail low loop
830 // We start with small aspiration window and in case of fail low, we research
831 // with bigger window until we are not failing low anymore.
834 // Sort the moves before to (re)search
837 // Step 10. Loop through all moves in the root move list
838 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
840 // This is used by time management
841 FirstRootMove = (i == 0);
843 // Save the current node count before the move is searched
844 nodes = TM.nodes_searched();
846 // Reset beta cut-off counters
847 TM.resetBetaCounters();
849 // Pick the next root move, and print the move and the move number to
850 // the standard output.
851 move = ss[0].currentMove = rml.get_move(i);
853 if (current_search_time() >= 1000)
854 cout << "info currmove " << move
855 << " currmovenumber " << i + 1 << endl;
857 moveIsCheck = pos.move_is_check(move);
858 captureOrPromotion = pos.move_is_capture_or_promotion(move);
860 // Step 11. Decide the new search depth
861 depth = (Iteration - 2) * OnePly + InitialDepth;
862 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
863 newDepth = depth + ext;
865 // Step 12. Futility pruning (omitted at root)
867 // Step extra. Fail high loop
868 // If move fails high, we research with bigger window until we are not failing
870 value = - VALUE_INFINITE;
874 // Step 13. Make the move
875 pos.do_move(move, st, ci, moveIsCheck);
877 // Step extra. pv search
878 // We do pv search for first moves (i < MultiPV)
879 // and for fail high research (value > alpha)
880 if (i < MultiPV || value > alpha)
882 // Aspiration window is disabled in multi-pv case
884 alpha = -VALUE_INFINITE;
886 // Full depth PV search, done on first move or after a fail high
887 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
891 // Step 14. Reduced search
892 // if the move fails high will be re-searched at full depth
893 bool doFullDepthSearch = true;
895 if ( depth >= 3 * OnePly
897 && !captureOrPromotion
898 && !move_is_castle(move))
900 ss[0].reduction = pv_reduction(depth, i - MultiPV + 2);
903 // Reduced depth non-pv search using alpha as upperbound
904 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
905 doFullDepthSearch = (value > alpha);
909 // Step 15. Full depth search
910 if (doFullDepthSearch)
912 // Full depth non-pv search using alpha as upperbound
913 ss[0].reduction = Depth(0);
914 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
916 // If we are above alpha then research at same depth but as PV
917 // to get a correct score or eventually a fail high above beta.
919 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
923 // Step 16. Undo move
926 // Can we exit fail high loop ?
927 if (AbortSearch || value < beta)
930 // We are failing high and going to do a research. It's important to update
931 // the score before research in case we run out of time while researching.
932 rml.set_move_score(i, value);
934 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
935 rml.set_move_pv(i, ss[0].pv);
937 // Print information to the standard output
938 print_pv_info(pos, ss, alpha, beta, value);
940 // Prepare for a research after a fail high, each time with a wider window
941 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
944 } // End of fail high loop
946 // Finished searching the move. If AbortSearch is true, the search
947 // was aborted because the user interrupted the search or because we
948 // ran out of time. In this case, the return value of the search cannot
949 // be trusted, and we break out of the loop without updating the best
954 // Remember beta-cutoff and searched nodes counts for this move. The
955 // info is used to sort the root moves for the next iteration.
957 TM.get_beta_counters(pos.side_to_move(), our, their);
958 rml.set_beta_counters(i, our, their);
959 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
961 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
962 assert(value < beta);
964 // Step 17. Check for new best move
965 if (value <= alpha && i >= MultiPV)
966 rml.set_move_score(i, -VALUE_INFINITE);
969 // PV move or new best move!
972 rml.set_move_score(i, value);
974 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
975 rml.set_move_pv(i, ss[0].pv);
979 // We record how often the best move has been changed in each
980 // iteration. This information is used for time managment: When
981 // the best move changes frequently, we allocate some more time.
983 BestMoveChangesByIteration[Iteration]++;
985 // Print information to the standard output
986 print_pv_info(pos, ss, alpha, beta, value);
988 // Raise alpha to setup proper non-pv search upper bound
995 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
997 cout << "info multipv " << j + 1
998 << " score " << value_to_string(rml.get_move_score(j))
999 << " depth " << (j <= i ? Iteration : Iteration - 1)
1000 << " time " << current_search_time()
1001 << " nodes " << TM.nodes_searched()
1005 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1006 cout << rml.get_move_pv(j, k) << " ";
1010 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1012 } // PV move or new best move
1014 assert(alpha >= *alphaPtr);
1016 AspirationFailLow = (alpha == *alphaPtr);
1018 if (AspirationFailLow && StopOnPonderhit)
1019 StopOnPonderhit = false;
1022 // Can we exit fail low loop ?
1023 if (AbortSearch || !AspirationFailLow)
1026 // Prepare for a research after a fail low, each time with a wider window
1027 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1032 // Sort the moves before to return
1039 // search_pv() is the main search function for PV nodes.
1041 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1042 Depth depth, int ply, int threadID) {
1044 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1045 assert(beta > alpha && beta <= VALUE_INFINITE);
1046 assert(ply >= 0 && ply < PLY_MAX);
1047 assert(threadID >= 0 && threadID < TM.active_threads());
1049 Move movesSearched[256];
1054 Depth ext, newDepth;
1055 Value bestValue, value, oldAlpha;
1056 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1057 bool mateThreat = false;
1059 bestValue = value = -VALUE_INFINITE;
1062 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1064 // Step 1. Initialize node and poll
1065 // Polling can abort search.
1066 init_node(ss, ply, threadID);
1068 // Step 2. Check for aborted search and immediate draw
1069 if (AbortSearch || TM.thread_should_stop(threadID))
1072 if (pos.is_draw() || ply >= PLY_MAX - 1)
1075 // Step 3. Mate distance pruning
1077 alpha = Max(value_mated_in(ply), alpha);
1078 beta = Min(value_mate_in(ply+1), beta);
1082 // Step 4. Transposition table lookup
1083 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1084 // This is to avoid problems in the following areas:
1086 // * Repetition draw detection
1087 // * Fifty move rule detection
1088 // * Searching for a mate
1089 // * Printing of full PV line
1090 tte = TT.retrieve(pos.get_key());
1091 ttMove = (tte ? tte->move() : MOVE_NONE);
1093 // Step 5. Evaluate the position statically
1094 // At PV nodes we do this only to update gain statistics
1095 isCheck = pos.is_check();
1098 ss[ply].eval = evaluate(pos, ei, threadID);
1099 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1102 // Step 6. Razoring (is omitted in PV nodes)
1103 // Step 7. Static null move pruning (is omitted in PV nodes)
1104 // Step 8. Null move search with verification search (is omitted in PV nodes)
1106 // Step 9. Internal iterative deepening
1107 if ( depth >= IIDDepthAtPVNodes
1108 && ttMove == MOVE_NONE)
1110 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1111 ttMove = ss[ply].pv[ply];
1112 tte = TT.retrieve(pos.get_key());
1115 // Step 10. Loop through moves
1116 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1118 // Initialize a MovePicker object for the current position
1119 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1120 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1123 while ( alpha < beta
1124 && (move = mp.get_next_move()) != MOVE_NONE
1125 && !TM.thread_should_stop(threadID))
1127 assert(move_is_ok(move));
1129 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1130 moveIsCheck = pos.move_is_check(move, ci);
1131 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1133 // Step 11. Decide the new search depth
1134 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1136 // Singular extension search. We extend the TT move if its value is much better than
1137 // its siblings. To verify this we do a reduced search on all the other moves but the
1138 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1139 if ( depth >= SingularExtensionDepthAtPVNodes
1141 && move == tte->move()
1143 && is_lower_bound(tte->type())
1144 && tte->depth() >= depth - 3 * OnePly)
1146 Value ttValue = value_from_tt(tte->value(), ply);
1148 if (abs(ttValue) < VALUE_KNOWN_WIN)
1150 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1152 if (excValue < ttValue - SingularExtensionMargin)
1157 newDepth = depth - OnePly + ext;
1159 // Update current move (this must be done after singular extension search)
1160 movesSearched[moveCount++] = ss[ply].currentMove = move;
1162 // Step 12. Futility pruning (is omitted in PV nodes)
1164 // Step 13. Make the move
1165 pos.do_move(move, st, ci, moveIsCheck);
1167 // Step extra. pv search (only in PV nodes)
1168 // The first move in list is the expected PV
1170 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1173 // Step 14. Reduced search
1174 // if the move fails high will be re-searched at full depth.
1175 bool doFullDepthSearch = true;
1177 if ( depth >= 3 * OnePly
1179 && !captureOrPromotion
1180 && !move_is_castle(move)
1181 && !move_is_killer(move, ss[ply]))
1183 ss[ply].reduction = pv_reduction(depth, moveCount);
1184 if (ss[ply].reduction)
1186 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1187 doFullDepthSearch = (value > alpha);
1191 // Step 15. Full depth search
1192 if (doFullDepthSearch)
1194 ss[ply].reduction = Depth(0);
1195 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1197 // Step extra. pv search (only in PV nodes)
1198 if (value > alpha && value < beta)
1199 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1203 // Step 16. Undo move
1204 pos.undo_move(move);
1206 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1208 // Step 17. Check for new best move
1209 if (value > bestValue)
1216 if (value == value_mate_in(ply + 1))
1217 ss[ply].mateKiller = move;
1221 // Step 18. Check for split
1222 if ( TM.active_threads() > 1
1224 && depth >= MinimumSplitDepth
1226 && TM.available_thread_exists(threadID)
1228 && !TM.thread_should_stop(threadID)
1229 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1230 depth, mateThreat, &moveCount, &mp, threadID, true))
1234 // Step 19. Check for mate and stalemate
1235 // All legal moves have been searched and if there were
1236 // no legal moves, it must be mate or stalemate.
1238 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1240 // Step 20. Update tables
1241 // If the search is not aborted, update the transposition table,
1242 // history counters, and killer moves.
1243 if (AbortSearch || TM.thread_should_stop(threadID))
1246 if (bestValue <= oldAlpha)
1247 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1249 else if (bestValue >= beta)
1251 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1252 move = ss[ply].pv[ply];
1253 if (!pos.move_is_capture_or_promotion(move))
1255 update_history(pos, move, depth, movesSearched, moveCount);
1256 update_killers(move, ss[ply]);
1258 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1261 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1267 // search() is the search function for zero-width nodes.
1269 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1270 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1272 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1273 assert(ply >= 0 && ply < PLY_MAX);
1274 assert(threadID >= 0 && threadID < TM.active_threads());
1276 Move movesSearched[256];
1281 Depth ext, newDepth;
1282 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1283 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1284 bool mateThreat = false;
1286 refinedValue = bestValue = value = -VALUE_INFINITE;
1289 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1291 // Step 1. Initialize node and poll
1292 // Polling can abort search.
1293 init_node(ss, ply, threadID);
1295 // Step 2. Check for aborted search and immediate draw
1296 if (AbortSearch || TM.thread_should_stop(threadID))
1299 if (pos.is_draw() || ply >= PLY_MAX - 1)
1302 // Step 3. Mate distance pruning
1303 if (value_mated_in(ply) >= beta)
1306 if (value_mate_in(ply + 1) < beta)
1309 // Step 4. Transposition table lookup
1311 // We don't want the score of a partial search to overwrite a previous full search
1312 // TT value, so we use a different position key in case of an excluded move exists.
1313 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1315 tte = TT.retrieve(posKey);
1316 ttMove = (tte ? tte->move() : MOVE_NONE);
1318 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1320 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1321 return value_from_tt(tte->value(), ply);
1324 // Step 5. Evaluate the position statically
1325 isCheck = pos.is_check();
1329 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1330 ss[ply].eval = value_from_tt(tte->value(), ply);
1332 ss[ply].eval = evaluate(pos, ei, threadID);
1334 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1335 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1339 if ( !value_is_mate(beta)
1341 && depth < RazorDepth
1342 && refinedValue < beta - razor_margin(depth)
1343 && ss[ply - 1].currentMove != MOVE_NULL
1344 && ttMove == MOVE_NONE
1345 && !pos.has_pawn_on_7th(pos.side_to_move()))
1347 Value rbeta = beta - razor_margin(depth);
1348 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1350 // Logically we should return (v + razor_margin(depth)), but
1351 // surprisingly this did slightly weaker in tests.
1355 // Step 7. Static null move pruning
1356 // We're betting that the opponent doesn't have a move that will reduce
1357 // the score by more than fuility_margin(depth) if we do a null move.
1360 && depth < RazorDepth
1361 && refinedValue - futility_margin(depth, 0) >= beta)
1362 return refinedValue - futility_margin(depth, 0);
1364 // Step 8. Null move search with verification search
1365 // When we jump directly to qsearch() we do a null move only if static value is
1366 // at least beta. Otherwise we do a null move if static value is not more than
1367 // NullMoveMargin under beta.
1371 && !value_is_mate(beta)
1372 && ok_to_do_nullmove(pos)
1373 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1375 ss[ply].currentMove = MOVE_NULL;
1377 pos.do_null_move(st);
1379 // Null move dynamic reduction based on depth
1380 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1382 // Null move dynamic reduction based on value
1383 if (refinedValue - beta > PawnValueMidgame)
1386 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1388 pos.undo_null_move();
1390 if (nullValue >= beta)
1392 // Do not return unproven mate scores
1393 if (nullValue >= value_mate_in(PLY_MAX))
1396 if (depth < 6 * OnePly)
1399 // Do zugzwang verification search
1400 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1404 // The null move failed low, which means that we may be faced with
1405 // some kind of threat. If the previous move was reduced, check if
1406 // the move that refuted the null move was somehow connected to the
1407 // move which was reduced. If a connection is found, return a fail
1408 // low score (which will cause the reduced move to fail high in the
1409 // parent node, which will trigger a re-search with full depth).
1410 if (nullValue == value_mated_in(ply + 2))
1413 ss[ply].threatMove = ss[ply + 1].currentMove;
1414 if ( depth < ThreatDepth
1415 && ss[ply - 1].reduction
1416 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1421 // Step 9. Internal iterative deepening
1422 if ( depth >= IIDDepthAtNonPVNodes
1423 && ttMove == MOVE_NONE
1425 && ss[ply].eval >= beta - IIDMargin)
1427 search(pos, ss, beta, depth/2, ply, false, threadID);
1428 ttMove = ss[ply].pv[ply];
1429 tte = TT.retrieve(posKey);
1432 // Step 10. Loop through moves
1433 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1435 // Initialize a MovePicker object for the current position
1436 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1439 while ( bestValue < beta
1440 && (move = mp.get_next_move()) != MOVE_NONE
1441 && !TM.thread_should_stop(threadID))
1443 assert(move_is_ok(move));
1445 if (move == excludedMove)
1448 moveIsCheck = pos.move_is_check(move, ci);
1449 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1450 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1452 // Step 11. Decide the new search depth
1453 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1455 // Singular extension search. We extend the TT move if its value is much better than
1456 // its siblings. To verify this we do a reduced search on all the other moves but the
1457 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1458 if ( depth >= SingularExtensionDepthAtNonPVNodes
1460 && move == tte->move()
1461 && !excludedMove // Do not allow recursive single-reply search
1463 && is_lower_bound(tte->type())
1464 && tte->depth() >= depth - 3 * OnePly)
1466 Value ttValue = value_from_tt(tte->value(), ply);
1468 if (abs(ttValue) < VALUE_KNOWN_WIN)
1470 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1472 if (excValue < ttValue - SingularExtensionMargin)
1477 newDepth = depth - OnePly + ext;
1479 // Update current move (this must be done after singular extension search)
1480 movesSearched[moveCount++] = ss[ply].currentMove = move;
1482 // Step 12. Futility pruning
1485 && !captureOrPromotion
1486 && !move_is_castle(move)
1489 // Move count based pruning
1490 if ( moveCount >= futility_move_count(depth)
1491 && ok_to_prune(pos, move, ss[ply].threatMove)
1492 && bestValue > value_mated_in(PLY_MAX))
1495 // Value based pruning
1496 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1497 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1498 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1500 if (futilityValueScaled < beta)
1502 if (futilityValueScaled > bestValue)
1503 bestValue = futilityValueScaled;
1508 // Step 13. Make the move
1509 pos.do_move(move, st, ci, moveIsCheck);
1511 // Step 14. Reduced search
1512 // if the move fails high will be re-searched at full depth.
1513 bool doFullDepthSearch = true;
1515 if ( depth >= 3*OnePly
1517 && !captureOrPromotion
1518 && !move_is_castle(move)
1519 && !move_is_killer(move, ss[ply]))
1521 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1522 if (ss[ply].reduction)
1524 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1525 doFullDepthSearch = (value >= beta);
1529 // Step 15. Full depth search
1530 if (doFullDepthSearch)
1532 ss[ply].reduction = Depth(0);
1533 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1536 // Step 16. Undo move
1537 pos.undo_move(move);
1539 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1541 // Step 17. Check for new best move
1542 if (value > bestValue)
1548 if (value == value_mate_in(ply + 1))
1549 ss[ply].mateKiller = move;
1552 // Step 18. Check for split
1553 if ( TM.active_threads() > 1
1555 && depth >= MinimumSplitDepth
1557 && TM.available_thread_exists(threadID)
1559 && !TM.thread_should_stop(threadID)
1560 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1561 depth, mateThreat, &moveCount, &mp, threadID, false))
1565 // Step 19. Check for mate and stalemate
1566 // All legal moves have been searched and if there were
1567 // no legal moves, it must be mate or stalemate.
1568 // If one move was excluded return fail low.
1570 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1572 // Step 20. Update tables
1573 // If the search is not aborted, update the transposition table,
1574 // history counters, and killer moves.
1575 if (AbortSearch || TM.thread_should_stop(threadID))
1578 if (bestValue < beta)
1579 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1582 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1583 move = ss[ply].pv[ply];
1584 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1585 if (!pos.move_is_capture_or_promotion(move))
1587 update_history(pos, move, depth, movesSearched, moveCount);
1588 update_killers(move, ss[ply]);
1593 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1599 // qsearch() is the quiescence search function, which is called by the main
1600 // search function when the remaining depth is zero (or, to be more precise,
1601 // less than OnePly).
1603 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1604 Depth depth, int ply, int threadID) {
1606 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1607 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1609 assert(ply >= 0 && ply < PLY_MAX);
1610 assert(threadID >= 0 && threadID < TM.active_threads());
1615 Value staticValue, bestValue, value, futilityBase, futilityValue;
1616 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1617 const TTEntry* tte = NULL;
1619 bool pvNode = (beta - alpha != 1);
1620 Value oldAlpha = alpha;
1622 // Initialize, and make an early exit in case of an aborted search,
1623 // an instant draw, maximum ply reached, etc.
1624 init_node(ss, ply, threadID);
1626 // After init_node() that calls poll()
1627 if (AbortSearch || TM.thread_should_stop(threadID))
1630 if (pos.is_draw() || ply >= PLY_MAX - 1)
1633 // Transposition table lookup. At PV nodes, we don't use the TT for
1634 // pruning, but only for move ordering.
1635 tte = TT.retrieve(pos.get_key());
1636 ttMove = (tte ? tte->move() : MOVE_NONE);
1638 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1640 assert(tte->type() != VALUE_TYPE_EVAL);
1642 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1643 return value_from_tt(tte->value(), ply);
1646 isCheck = pos.is_check();
1648 // Evaluate the position statically
1650 staticValue = -VALUE_INFINITE;
1651 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1652 staticValue = value_from_tt(tte->value(), ply);
1654 staticValue = evaluate(pos, ei, threadID);
1658 ss[ply].eval = staticValue;
1659 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1662 // Initialize "stand pat score", and return it immediately if it is
1664 bestValue = staticValue;
1666 if (bestValue >= beta)
1668 // Store the score to avoid a future costly evaluation() call
1669 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1670 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1675 if (bestValue > alpha)
1678 // If we are near beta then try to get a cutoff pushing checks a bit further
1679 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1681 // Initialize a MovePicker object for the current position, and prepare
1682 // to search the moves. Because the depth is <= 0 here, only captures,
1683 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1684 // and we are near beta) will be generated.
1685 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1687 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1688 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1690 // Loop through the moves until no moves remain or a beta cutoff
1692 while ( alpha < beta
1693 && (move = mp.get_next_move()) != MOVE_NONE)
1695 assert(move_is_ok(move));
1697 moveIsCheck = pos.move_is_check(move, ci);
1699 // Update current move
1701 ss[ply].currentMove = move;
1709 && !move_is_promotion(move)
1710 && !pos.move_is_passed_pawn_push(move))
1712 futilityValue = futilityBase
1713 + pos.endgame_value_of_piece_on(move_to(move))
1714 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1716 if (futilityValue < alpha)
1718 if (futilityValue > bestValue)
1719 bestValue = futilityValue;
1724 // Detect blocking evasions that are candidate to be pruned
1725 evasionPrunable = isCheck
1726 && bestValue != -VALUE_INFINITE
1727 && !pos.move_is_capture(move)
1728 && pos.type_of_piece_on(move_from(move)) != KING
1729 && !pos.can_castle(pos.side_to_move());
1731 // Don't search moves with negative SEE values
1732 if ( (!isCheck || evasionPrunable)
1735 && !move_is_promotion(move)
1736 && pos.see_sign(move) < 0)
1739 // Make and search the move
1740 pos.do_move(move, st, ci, moveIsCheck);
1741 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1742 pos.undo_move(move);
1744 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1747 if (value > bestValue)
1758 // All legal moves have been searched. A special case: If we're in check
1759 // and no legal moves were found, it is checkmate.
1760 if (!moveCount && pos.is_check()) // Mate!
1761 return value_mated_in(ply);
1763 // Update transposition table
1764 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1765 if (bestValue <= oldAlpha)
1767 // If bestValue isn't changed it means it is still the static evaluation
1768 // of the node, so keep this info to avoid a future evaluation() call.
1769 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1770 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1772 else if (bestValue >= beta)
1774 move = ss[ply].pv[ply];
1775 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1777 // Update killers only for good checking moves
1778 if (!pos.move_is_capture_or_promotion(move))
1779 update_killers(move, ss[ply]);
1782 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1784 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1790 // sp_search() is used to search from a split point. This function is called
1791 // by each thread working at the split point. It is similar to the normal
1792 // search() function, but simpler. Because we have already probed the hash
1793 // table, done a null move search, and searched the first move before
1794 // splitting, we don't have to repeat all this work in sp_search(). We
1795 // also don't need to store anything to the hash table here: This is taken
1796 // care of after we return from the split point.
1798 void sp_search(SplitPoint* sp, int threadID) {
1800 assert(threadID >= 0 && threadID < TM.active_threads());
1801 assert(TM.active_threads() > 1);
1805 Depth ext, newDepth;
1806 Value value, futilityValueScaled;
1807 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1809 value = -VALUE_INFINITE;
1811 Position pos(*sp->pos);
1813 SearchStack* ss = sp->sstack[threadID];
1814 isCheck = pos.is_check();
1816 // Step 10. Loop through moves
1817 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1818 lock_grab(&(sp->lock));
1820 while ( sp->bestValue < sp->beta
1821 && !TM.thread_should_stop(threadID)
1822 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1824 moveCount = ++sp->moves;
1825 lock_release(&(sp->lock));
1827 assert(move_is_ok(move));
1829 moveIsCheck = pos.move_is_check(move, ci);
1830 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1832 // Step 11. Decide the new search depth
1833 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1834 newDepth = sp->depth - OnePly + ext;
1836 // Update current move
1837 ss[sp->ply].currentMove = move;
1839 // Step 12. Futility pruning
1842 && !captureOrPromotion
1843 && !move_is_castle(move))
1845 // Move count based pruning
1846 if ( moveCount >= futility_move_count(sp->depth)
1847 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1848 && sp->bestValue > value_mated_in(PLY_MAX))
1850 lock_grab(&(sp->lock));
1854 // Value based pruning
1855 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1856 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1857 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1859 if (futilityValueScaled < sp->beta)
1861 lock_grab(&(sp->lock));
1863 if (futilityValueScaled > sp->bestValue)
1864 sp->bestValue = futilityValueScaled;
1869 // Step 13. Make the move
1870 pos.do_move(move, st, ci, moveIsCheck);
1872 // Step 14. Reduced search
1873 // if the move fails high will be re-searched at full depth.
1874 bool doFullDepthSearch = true;
1877 && !captureOrPromotion
1878 && !move_is_castle(move)
1879 && !move_is_killer(move, ss[sp->ply]))
1881 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1882 if (ss[sp->ply].reduction)
1884 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1885 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1889 // Step 15. Full depth search
1890 if (doFullDepthSearch)
1892 ss[sp->ply].reduction = Depth(0);
1893 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1896 // Step 16. Undo move
1897 pos.undo_move(move);
1899 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1901 // Step 17. Check for new best move
1902 lock_grab(&(sp->lock));
1904 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1906 sp->bestValue = value;
1907 if (sp->bestValue >= sp->beta)
1909 sp->stopRequest = true;
1910 sp_update_pv(sp->parentSstack, ss, sp->ply);
1915 /* Here we have the lock still grabbed */
1917 sp->slaves[threadID] = 0;
1920 lock_release(&(sp->lock));
1924 // sp_search_pv() is used to search from a PV split point. This function
1925 // is called by each thread working at the split point. It is similar to
1926 // the normal search_pv() function, but simpler. Because we have already
1927 // probed the hash table and searched the first move before splitting, we
1928 // don't have to repeat all this work in sp_search_pv(). We also don't
1929 // need to store anything to the hash table here: This is taken care of
1930 // after we return from the split point.
1932 void sp_search_pv(SplitPoint* sp, int threadID) {
1934 assert(threadID >= 0 && threadID < TM.active_threads());
1935 assert(TM.active_threads() > 1);
1939 Depth ext, newDepth;
1941 bool moveIsCheck, captureOrPromotion, dangerous;
1943 value = -VALUE_INFINITE;
1945 Position pos(*sp->pos);
1947 SearchStack* ss = sp->sstack[threadID];
1949 // Step 10. Loop through moves
1950 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1951 lock_grab(&(sp->lock));
1953 while ( sp->alpha < sp->beta
1954 && !TM.thread_should_stop(threadID)
1955 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1957 moveCount = ++sp->moves;
1958 lock_release(&(sp->lock));
1960 assert(move_is_ok(move));
1962 moveIsCheck = pos.move_is_check(move, ci);
1963 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1965 // Step 11. Decide the new search depth
1966 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1967 newDepth = sp->depth - OnePly + ext;
1969 // Update current move
1970 ss[sp->ply].currentMove = move;
1972 // Step 12. Futility pruning (is omitted in PV nodes)
1974 // Step 13. Make the move
1975 pos.do_move(move, st, ci, moveIsCheck);
1977 // Step 14. Reduced search
1978 // if the move fails high will be re-searched at full depth.
1979 bool doFullDepthSearch = true;
1982 && !captureOrPromotion
1983 && !move_is_castle(move)
1984 && !move_is_killer(move, ss[sp->ply]))
1986 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1987 if (ss[sp->ply].reduction)
1989 Value localAlpha = sp->alpha;
1990 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1991 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1995 // Step 15. Full depth search
1996 if (doFullDepthSearch)
1998 Value localAlpha = sp->alpha;
1999 ss[sp->ply].reduction = Depth(0);
2000 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
2002 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
2004 // If another thread has failed high then sp->alpha has been increased
2005 // to be higher or equal then beta, if so, avoid to start a PV search.
2006 localAlpha = sp->alpha;
2007 if (localAlpha < sp->beta)
2008 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2012 // Step 16. Undo move
2013 pos.undo_move(move);
2015 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2017 // Step 17. Check for new best move
2018 lock_grab(&(sp->lock));
2020 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
2022 sp->bestValue = value;
2023 if (value > sp->alpha)
2025 // Ask threads to stop before to modify sp->alpha
2026 if (value >= sp->beta)
2027 sp->stopRequest = true;
2031 sp_update_pv(sp->parentSstack, ss, sp->ply);
2032 if (value == value_mate_in(sp->ply + 1))
2033 ss[sp->ply].mateKiller = move;
2038 /* Here we have the lock still grabbed */
2040 sp->slaves[threadID] = 0;
2043 lock_release(&(sp->lock));
2047 // init_node() is called at the beginning of all the search functions
2048 // (search(), search_pv(), qsearch(), and so on) and initializes the
2049 // search stack object corresponding to the current node. Once every
2050 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2051 // for user input and checks whether it is time to stop the search.
2053 void init_node(SearchStack ss[], int ply, int threadID) {
2055 assert(ply >= 0 && ply < PLY_MAX);
2056 assert(threadID >= 0 && threadID < TM.active_threads());
2058 TM.incrementNodeCounter(threadID);
2063 if (NodesSincePoll >= NodesBetweenPolls)
2070 ss[ply + 2].initKillers();
2074 // update_pv() is called whenever a search returns a value > alpha.
2075 // It updates the PV in the SearchStack object corresponding to the
2078 void update_pv(SearchStack ss[], int ply) {
2080 assert(ply >= 0 && ply < PLY_MAX);
2084 ss[ply].pv[ply] = ss[ply].currentMove;
2086 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2087 ss[ply].pv[p] = ss[ply + 1].pv[p];
2089 ss[ply].pv[p] = MOVE_NONE;
2093 // sp_update_pv() is a variant of update_pv for use at split points. The
2094 // difference between the two functions is that sp_update_pv also updates
2095 // the PV at the parent node.
2097 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2099 assert(ply >= 0 && ply < PLY_MAX);
2103 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2105 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2106 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2108 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2112 // connected_moves() tests whether two moves are 'connected' in the sense
2113 // that the first move somehow made the second move possible (for instance
2114 // if the moving piece is the same in both moves). The first move is assumed
2115 // to be the move that was made to reach the current position, while the
2116 // second move is assumed to be a move from the current position.
2118 bool connected_moves(const Position& pos, Move m1, Move m2) {
2120 Square f1, t1, f2, t2;
2123 assert(move_is_ok(m1));
2124 assert(move_is_ok(m2));
2126 if (m2 == MOVE_NONE)
2129 // Case 1: The moving piece is the same in both moves
2135 // Case 2: The destination square for m2 was vacated by m1
2141 // Case 3: Moving through the vacated square
2142 if ( piece_is_slider(pos.piece_on(f2))
2143 && bit_is_set(squares_between(f2, t2), f1))
2146 // Case 4: The destination square for m2 is defended by the moving piece in m1
2147 p = pos.piece_on(t1);
2148 if (bit_is_set(pos.attacks_from(p, t1), t2))
2151 // Case 5: Discovered check, checking piece is the piece moved in m1
2152 if ( piece_is_slider(p)
2153 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2154 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2156 // discovered_check_candidates() works also if the Position's side to
2157 // move is the opposite of the checking piece.
2158 Color them = opposite_color(pos.side_to_move());
2159 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2161 if (bit_is_set(dcCandidates, f2))
2168 // value_is_mate() checks if the given value is a mate one
2169 // eventually compensated for the ply.
2171 bool value_is_mate(Value value) {
2173 assert(abs(value) <= VALUE_INFINITE);
2175 return value <= value_mated_in(PLY_MAX)
2176 || value >= value_mate_in(PLY_MAX);
2180 // move_is_killer() checks if the given move is among the
2181 // killer moves of that ply.
2183 bool move_is_killer(Move m, const SearchStack& ss) {
2185 const Move* k = ss.killers;
2186 for (int i = 0; i < KILLER_MAX; i++, k++)
2194 // extension() decides whether a move should be searched with normal depth,
2195 // or with extended depth. Certain classes of moves (checking moves, in
2196 // particular) are searched with bigger depth than ordinary moves and in
2197 // any case are marked as 'dangerous'. Note that also if a move is not
2198 // extended, as example because the corresponding UCI option is set to zero,
2199 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2201 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2202 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2204 assert(m != MOVE_NONE);
2206 Depth result = Depth(0);
2207 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2212 result += CheckExtension[pvNode];
2215 result += SingleEvasionExtension[pvNode];
2218 result += MateThreatExtension[pvNode];
2221 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2223 Color c = pos.side_to_move();
2224 if (relative_rank(c, move_to(m)) == RANK_7)
2226 result += PawnPushTo7thExtension[pvNode];
2229 if (pos.pawn_is_passed(c, move_to(m)))
2231 result += PassedPawnExtension[pvNode];
2236 if ( captureOrPromotion
2237 && pos.type_of_piece_on(move_to(m)) != PAWN
2238 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2239 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2240 && !move_is_promotion(m)
2243 result += PawnEndgameExtension[pvNode];
2248 && captureOrPromotion
2249 && pos.type_of_piece_on(move_to(m)) != PAWN
2250 && pos.see_sign(m) >= 0)
2256 return Min(result, OnePly);
2260 // ok_to_do_nullmove() looks at the current position and decides whether
2261 // doing a 'null move' should be allowed. In order to avoid zugzwang
2262 // problems, null moves are not allowed when the side to move has very
2263 // little material left. Currently, the test is a bit too simple: Null
2264 // moves are avoided only when the side to move has only pawns left.
2265 // It's probably a good idea to avoid null moves in at least some more
2266 // complicated endgames, e.g. KQ vs KR. FIXME
2268 bool ok_to_do_nullmove(const Position& pos) {
2270 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2274 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2275 // non-tactical moves late in the move list close to the leaves are
2276 // candidates for pruning.
2278 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2280 assert(move_is_ok(m));
2281 assert(threat == MOVE_NONE || move_is_ok(threat));
2282 assert(!pos.move_is_check(m));
2283 assert(!pos.move_is_capture_or_promotion(m));
2284 assert(!pos.move_is_passed_pawn_push(m));
2286 Square mfrom, mto, tfrom, tto;
2288 // Prune if there isn't any threat move
2289 if (threat == MOVE_NONE)
2292 mfrom = move_from(m);
2294 tfrom = move_from(threat);
2295 tto = move_to(threat);
2297 // Case 1: Don't prune moves which move the threatened piece
2301 // Case 2: If the threatened piece has value less than or equal to the
2302 // value of the threatening piece, don't prune move which defend it.
2303 if ( pos.move_is_capture(threat)
2304 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2305 || pos.type_of_piece_on(tfrom) == KING)
2306 && pos.move_attacks_square(m, tto))
2309 // Case 3: If the moving piece in the threatened move is a slider, don't
2310 // prune safe moves which block its ray.
2311 if ( piece_is_slider(pos.piece_on(tfrom))
2312 && bit_is_set(squares_between(tfrom, tto), mto)
2313 && pos.see_sign(m) >= 0)
2320 // ok_to_use_TT() returns true if a transposition table score
2321 // can be used at a given point in search.
2323 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2325 Value v = value_from_tt(tte->value(), ply);
2327 return ( tte->depth() >= depth
2328 || v >= Max(value_mate_in(PLY_MAX), beta)
2329 || v < Min(value_mated_in(PLY_MAX), beta))
2331 && ( (is_lower_bound(tte->type()) && v >= beta)
2332 || (is_upper_bound(tte->type()) && v < beta));
2336 // refine_eval() returns the transposition table score if
2337 // possible otherwise falls back on static position evaluation.
2339 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2344 Value v = value_from_tt(tte->value(), ply);
2346 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2347 || (is_upper_bound(tte->type()) && v < defaultEval))
2354 // update_history() registers a good move that produced a beta-cutoff
2355 // in history and marks as failures all the other moves of that ply.
2357 void update_history(const Position& pos, Move move, Depth depth,
2358 Move movesSearched[], int moveCount) {
2362 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2364 for (int i = 0; i < moveCount - 1; i++)
2366 m = movesSearched[i];
2370 if (!pos.move_is_capture_or_promotion(m))
2371 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2376 // update_killers() add a good move that produced a beta-cutoff
2377 // among the killer moves of that ply.
2379 void update_killers(Move m, SearchStack& ss) {
2381 if (m == ss.killers[0])
2384 for (int i = KILLER_MAX - 1; i > 0; i--)
2385 ss.killers[i] = ss.killers[i - 1];
2391 // update_gains() updates the gains table of a non-capture move given
2392 // the static position evaluation before and after the move.
2394 void update_gains(const Position& pos, Move m, Value before, Value after) {
2397 && before != VALUE_NONE
2398 && after != VALUE_NONE
2399 && pos.captured_piece() == NO_PIECE_TYPE
2400 && !move_is_castle(m)
2401 && !move_is_promotion(m))
2402 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2406 // current_search_time() returns the number of milliseconds which have passed
2407 // since the beginning of the current search.
2409 int current_search_time() {
2411 return get_system_time() - SearchStartTime;
2415 // nps() computes the current nodes/second count.
2419 int t = current_search_time();
2420 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2424 // poll() performs two different functions: It polls for user input, and it
2425 // looks at the time consumed so far and decides if it's time to abort the
2428 void poll(SearchStack ss[], int ply) {
2430 static int lastInfoTime;
2431 int t = current_search_time();
2436 // We are line oriented, don't read single chars
2437 std::string command;
2439 if (!std::getline(std::cin, command))
2442 if (command == "quit")
2445 PonderSearch = false;
2449 else if (command == "stop")
2452 PonderSearch = false;
2454 else if (command == "ponderhit")
2458 // Print search information
2462 else if (lastInfoTime > t)
2463 // HACK: Must be a new search where we searched less than
2464 // NodesBetweenPolls nodes during the first second of search.
2467 else if (t - lastInfoTime >= 1000)
2474 if (dbg_show_hit_rate)
2475 dbg_print_hit_rate();
2477 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2478 << " time " << t << " hashfull " << TT.full() << endl;
2480 // We only support current line printing in single thread mode
2481 if (ShowCurrentLine && TM.active_threads() == 1)
2483 cout << "info currline";
2484 for (int p = 0; p < ply; p++)
2485 cout << " " << ss[p].currentMove;
2491 // Should we stop the search?
2495 bool stillAtFirstMove = FirstRootMove
2496 && !AspirationFailLow
2497 && t > MaxSearchTime + ExtraSearchTime;
2499 bool noMoreTime = t > AbsoluteMaxSearchTime
2500 || stillAtFirstMove;
2502 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2503 || (ExactMaxTime && t >= ExactMaxTime)
2504 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2509 // ponderhit() is called when the program is pondering (i.e. thinking while
2510 // it's the opponent's turn to move) in order to let the engine know that
2511 // it correctly predicted the opponent's move.
2515 int t = current_search_time();
2516 PonderSearch = false;
2518 bool stillAtFirstMove = FirstRootMove
2519 && !AspirationFailLow
2520 && t > MaxSearchTime + ExtraSearchTime;
2522 bool noMoreTime = t > AbsoluteMaxSearchTime
2523 || stillAtFirstMove;
2525 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2530 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2532 void init_ss_array(SearchStack ss[]) {
2534 for (int i = 0; i < 3; i++)
2537 ss[i].initKillers();
2542 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2543 // while the program is pondering. The point is to work around a wrinkle in
2544 // the UCI protocol: When pondering, the engine is not allowed to give a
2545 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2546 // We simply wait here until one of these commands is sent, and return,
2547 // after which the bestmove and pondermove will be printed (in id_loop()).
2549 void wait_for_stop_or_ponderhit() {
2551 std::string command;
2555 if (!std::getline(std::cin, command))
2558 if (command == "quit")
2563 else if (command == "ponderhit" || command == "stop")
2569 // print_pv_info() prints to standard output and eventually to log file information on
2570 // the current PV line. It is called at each iteration or after a new pv is found.
2572 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2574 cout << "info depth " << Iteration
2575 << " score " << value_to_string(value)
2576 << ((value >= beta) ? " lowerbound" :
2577 ((value <= alpha)? " upperbound" : ""))
2578 << " time " << current_search_time()
2579 << " nodes " << TM.nodes_searched()
2583 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2584 cout << ss[0].pv[j] << " ";
2590 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2591 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2593 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2594 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2599 // init_thread() is the function which is called when a new thread is
2600 // launched. It simply calls the idle_loop() function with the supplied
2601 // threadID. There are two versions of this function; one for POSIX
2602 // threads and one for Windows threads.
2604 #if !defined(_MSC_VER)
2606 void* init_thread(void *threadID) {
2608 TM.idle_loop(*(int*)threadID, NULL);
2614 DWORD WINAPI init_thread(LPVOID threadID) {
2616 TM.idle_loop(*(int*)threadID, NULL);
2623 /// The ThreadsManager class
2625 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2626 // get_beta_counters() are getters/setters for the per thread
2627 // counters used to sort the moves at root.
2629 void ThreadsManager::resetNodeCounters() {
2631 for (int i = 0; i < MAX_THREADS; i++)
2632 threads[i].nodes = 0ULL;
2635 void ThreadsManager::resetBetaCounters() {
2637 for (int i = 0; i < MAX_THREADS; i++)
2638 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2641 int64_t ThreadsManager::nodes_searched() const {
2643 int64_t result = 0ULL;
2644 for (int i = 0; i < ActiveThreads; i++)
2645 result += threads[i].nodes;
2650 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2653 for (int i = 0; i < MAX_THREADS; i++)
2655 our += threads[i].betaCutOffs[us];
2656 their += threads[i].betaCutOffs[opposite_color(us)];
2661 // idle_loop() is where the threads are parked when they have no work to do.
2662 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2663 // object for which the current thread is the master.
2665 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2667 assert(threadID >= 0 && threadID < MAX_THREADS);
2671 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2672 // master should exit as last one.
2673 if (AllThreadsShouldExit)
2676 threads[threadID].state = THREAD_TERMINATED;
2680 // If we are not thinking, wait for a condition to be signaled
2681 // instead of wasting CPU time polling for work.
2682 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2685 assert(threadID != 0);
2686 threads[threadID].state = THREAD_SLEEPING;
2688 #if !defined(_MSC_VER)
2689 lock_grab(&WaitLock);
2690 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2691 pthread_cond_wait(&WaitCond, &WaitLock);
2692 lock_release(&WaitLock);
2694 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2698 // If thread has just woken up, mark it as available
2699 if (threads[threadID].state == THREAD_SLEEPING)
2700 threads[threadID].state = THREAD_AVAILABLE;
2702 // If this thread has been assigned work, launch a search
2703 if (threads[threadID].state == THREAD_WORKISWAITING)
2705 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2707 threads[threadID].state = THREAD_SEARCHING;
2709 if (threads[threadID].splitPoint->pvNode)
2710 sp_search_pv(threads[threadID].splitPoint, threadID);
2712 sp_search(threads[threadID].splitPoint, threadID);
2714 assert(threads[threadID].state == THREAD_SEARCHING);
2716 threads[threadID].state = THREAD_AVAILABLE;
2719 // If this thread is the master of a split point and all threads have
2720 // finished their work at this split point, return from the idle loop.
2721 if (waitSp != NULL && waitSp->cpus == 0)
2723 assert(threads[threadID].state == THREAD_AVAILABLE);
2725 threads[threadID].state = THREAD_SEARCHING;
2732 // init_threads() is called during startup. It launches all helper threads,
2733 // and initializes the split point stack and the global locks and condition
2736 void ThreadsManager::init_threads() {
2741 #if !defined(_MSC_VER)
2742 pthread_t pthread[1];
2745 // Initialize global locks
2746 lock_init(&MPLock, NULL);
2747 lock_init(&WaitLock, NULL);
2749 #if !defined(_MSC_VER)
2750 pthread_cond_init(&WaitCond, NULL);
2752 for (i = 0; i < MAX_THREADS; i++)
2753 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2756 // Initialize SplitPointStack locks
2757 for (i = 0; i < MAX_THREADS; i++)
2758 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2760 SplitPointStack[i][j].parent = NULL;
2761 lock_init(&(SplitPointStack[i][j].lock), NULL);
2764 // Will be set just before program exits to properly end the threads
2765 AllThreadsShouldExit = false;
2767 // Threads will be put to sleep as soon as created
2768 AllThreadsShouldSleep = true;
2770 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2772 threads[0].state = THREAD_SEARCHING;
2773 for (i = 1; i < MAX_THREADS; i++)
2774 threads[i].state = THREAD_AVAILABLE;
2776 // Launch the helper threads
2777 for (i = 1; i < MAX_THREADS; i++)
2780 #if !defined(_MSC_VER)
2781 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2783 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2788 cout << "Failed to create thread number " << i << endl;
2789 Application::exit_with_failure();
2792 // Wait until the thread has finished launching and is gone to sleep
2793 while (threads[i].state != THREAD_SLEEPING);
2798 // exit_threads() is called when the program exits. It makes all the
2799 // helper threads exit cleanly.
2801 void ThreadsManager::exit_threads() {
2803 ActiveThreads = MAX_THREADS; // HACK
2804 AllThreadsShouldSleep = true; // HACK
2805 wake_sleeping_threads();
2807 // This makes the threads to exit idle_loop()
2808 AllThreadsShouldExit = true;
2810 // Wait for thread termination
2811 for (int i = 1; i < MAX_THREADS; i++)
2812 while (threads[i].state != THREAD_TERMINATED);
2814 // Now we can safely destroy the locks
2815 for (int i = 0; i < MAX_THREADS; i++)
2816 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2817 lock_destroy(&(SplitPointStack[i][j].lock));
2819 lock_destroy(&WaitLock);
2820 lock_destroy(&MPLock);
2824 // thread_should_stop() checks whether the thread should stop its search.
2825 // This can happen if a beta cutoff has occurred in the thread's currently
2826 // active split point, or in some ancestor of the current split point.
2828 bool ThreadsManager::thread_should_stop(int threadID) const {
2830 assert(threadID >= 0 && threadID < ActiveThreads);
2834 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2839 // thread_is_available() checks whether the thread with threadID "slave" is
2840 // available to help the thread with threadID "master" at a split point. An
2841 // obvious requirement is that "slave" must be idle. With more than two
2842 // threads, this is not by itself sufficient: If "slave" is the master of
2843 // some active split point, it is only available as a slave to the other
2844 // threads which are busy searching the split point at the top of "slave"'s
2845 // split point stack (the "helpful master concept" in YBWC terminology).
2847 bool ThreadsManager::thread_is_available(int slave, int master) const {
2849 assert(slave >= 0 && slave < ActiveThreads);
2850 assert(master >= 0 && master < ActiveThreads);
2851 assert(ActiveThreads > 1);
2853 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2856 // Make a local copy to be sure doesn't change under our feet
2857 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2859 if (localActiveSplitPoints == 0)
2860 // No active split points means that the thread is available as
2861 // a slave for any other thread.
2864 if (ActiveThreads == 2)
2867 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2868 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2869 // could have been set to 0 by another thread leading to an out of bound access.
2870 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2877 // available_thread_exists() tries to find an idle thread which is available as
2878 // a slave for the thread with threadID "master".
2880 bool ThreadsManager::available_thread_exists(int master) const {
2882 assert(master >= 0 && master < ActiveThreads);
2883 assert(ActiveThreads > 1);
2885 for (int i = 0; i < ActiveThreads; i++)
2886 if (thread_is_available(i, master))
2893 // split() does the actual work of distributing the work at a node between
2894 // several threads at PV nodes. If it does not succeed in splitting the
2895 // node (because no idle threads are available, or because we have no unused
2896 // split point objects), the function immediately returns false. If
2897 // splitting is possible, a SplitPoint object is initialized with all the
2898 // data that must be copied to the helper threads (the current position and
2899 // search stack, alpha, beta, the search depth, etc.), and we tell our
2900 // helper threads that they have been assigned work. This will cause them
2901 // to instantly leave their idle loops and call sp_search_pv(). When all
2902 // threads have returned from sp_search_pv (or, equivalently, when
2903 // splitPoint->cpus becomes 0), split() returns true.
2905 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2906 Value* alpha, const Value beta, Value* bestValue,
2907 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2910 assert(sstck != NULL);
2911 assert(ply >= 0 && ply < PLY_MAX);
2912 assert(*bestValue >= -VALUE_INFINITE);
2913 assert( ( pvNode && *bestValue <= *alpha)
2914 || (!pvNode && *bestValue < beta ));
2915 assert(!pvNode || *alpha < beta);
2916 assert(beta <= VALUE_INFINITE);
2917 assert(depth > Depth(0));
2918 assert(master >= 0 && master < ActiveThreads);
2919 assert(ActiveThreads > 1);
2921 SplitPoint* splitPoint;
2925 // If no other thread is available to help us, or if we have too many
2926 // active split points, don't split.
2927 if ( !available_thread_exists(master)
2928 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2930 lock_release(&MPLock);
2934 // Pick the next available split point object from the split point stack
2935 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2937 // Initialize the split point object
2938 splitPoint->parent = threads[master].splitPoint;
2939 splitPoint->stopRequest = false;
2940 splitPoint->ply = ply;
2941 splitPoint->depth = depth;
2942 splitPoint->mateThreat = mateThreat;
2943 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2944 splitPoint->beta = beta;
2945 splitPoint->pvNode = pvNode;
2946 splitPoint->bestValue = *bestValue;
2947 splitPoint->master = master;
2948 splitPoint->mp = mp;
2949 splitPoint->moves = *moves;
2950 splitPoint->cpus = 1;
2951 splitPoint->pos = &p;
2952 splitPoint->parentSstack = sstck;
2953 for (int i = 0; i < ActiveThreads; i++)
2954 splitPoint->slaves[i] = 0;
2956 threads[master].splitPoint = splitPoint;
2957 threads[master].activeSplitPoints++;
2959 // If we are here it means we are not available
2960 assert(threads[master].state != THREAD_AVAILABLE);
2962 // Allocate available threads setting state to THREAD_BOOKED
2963 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2964 if (thread_is_available(i, master))
2966 threads[i].state = THREAD_BOOKED;
2967 threads[i].splitPoint = splitPoint;
2968 splitPoint->slaves[i] = 1;
2972 assert(splitPoint->cpus > 1);
2974 // We can release the lock because slave threads are already booked and master is not available
2975 lock_release(&MPLock);
2977 // Tell the threads that they have work to do. This will make them leave
2978 // their idle loop. But before copy search stack tail for each thread.
2979 for (int i = 0; i < ActiveThreads; i++)
2980 if (i == master || splitPoint->slaves[i])
2982 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2984 assert(i == master || threads[i].state == THREAD_BOOKED);
2986 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2989 // Everything is set up. The master thread enters the idle loop, from
2990 // which it will instantly launch a search, because its state is
2991 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2992 // idle loop, which means that the main thread will return from the idle
2993 // loop when all threads have finished their work at this split point
2994 // (i.e. when splitPoint->cpus == 0).
2995 idle_loop(master, splitPoint);
2997 // We have returned from the idle loop, which means that all threads are
2998 // finished. Update alpha, beta and bestValue, and return.
3002 *alpha = splitPoint->alpha;
3004 *bestValue = splitPoint->bestValue;
3005 threads[master].activeSplitPoints--;
3006 threads[master].splitPoint = splitPoint->parent;
3008 lock_release(&MPLock);
3013 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3014 // to start a new search from the root.
3016 void ThreadsManager::wake_sleeping_threads() {
3018 assert(AllThreadsShouldSleep);
3019 assert(ActiveThreads > 0);
3021 AllThreadsShouldSleep = false;
3023 if (ActiveThreads == 1)
3026 #if !defined(_MSC_VER)
3027 pthread_mutex_lock(&WaitLock);
3028 pthread_cond_broadcast(&WaitCond);
3029 pthread_mutex_unlock(&WaitLock);
3031 for (int i = 1; i < MAX_THREADS; i++)
3032 SetEvent(SitIdleEvent[i]);
3038 // put_threads_to_sleep() makes all the threads go to sleep just before
3039 // to leave think(), at the end of the search. Threads should have already
3040 // finished the job and should be idle.
3042 void ThreadsManager::put_threads_to_sleep() {
3044 assert(!AllThreadsShouldSleep);
3046 // This makes the threads to go to sleep
3047 AllThreadsShouldSleep = true;
3050 /// The RootMoveList class
3052 // RootMoveList c'tor
3054 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3056 SearchStack ss[PLY_MAX_PLUS_2];
3057 MoveStack mlist[MaxRootMoves];
3059 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3061 // Generate all legal moves
3062 MoveStack* last = generate_moves(pos, mlist);
3064 // Add each move to the moves[] array
3065 for (MoveStack* cur = mlist; cur != last; cur++)
3067 bool includeMove = includeAllMoves;
3069 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3070 includeMove = (searchMoves[k] == cur->move);
3075 // Find a quick score for the move
3077 pos.do_move(cur->move, st);
3078 moves[count].move = cur->move;
3079 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3080 moves[count].pv[0] = cur->move;
3081 moves[count].pv[1] = MOVE_NONE;
3082 pos.undo_move(cur->move);
3089 // RootMoveList simple methods definitions
3091 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3093 moves[moveNum].nodes = nodes;
3094 moves[moveNum].cumulativeNodes += nodes;
3097 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3099 moves[moveNum].ourBeta = our;
3100 moves[moveNum].theirBeta = their;
3103 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3107 for (j = 0; pv[j] != MOVE_NONE; j++)
3108 moves[moveNum].pv[j] = pv[j];
3110 moves[moveNum].pv[j] = MOVE_NONE;
3114 // RootMoveList::sort() sorts the root move list at the beginning of a new
3117 void RootMoveList::sort() {
3119 sort_multipv(count - 1); // Sort all items
3123 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3124 // list by their scores and depths. It is used to order the different PVs
3125 // correctly in MultiPV mode.
3127 void RootMoveList::sort_multipv(int n) {
3131 for (i = 1; i <= n; i++)
3133 RootMove rm = moves[i];
3134 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3135 moves[j] = moves[j - 1];