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, int master, bool pvNode);
99 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
100 Thread threads[MAX_THREADS];
101 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
103 Lock MPLock, WaitLock;
105 #if !defined(_MSC_VER)
106 pthread_cond_t WaitCond;
108 HANDLE SitIdleEvent[MAX_THREADS];
114 // RootMove struct is used for moves at the root at the tree. For each
115 // root move, we store a score, a node count, and a PV (really a refutation
116 // in the case of moves which fail low).
120 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
122 // RootMove::operator<() is the comparison function used when
123 // sorting the moves. A move m1 is considered to be better
124 // than a move m2 if it has a higher score, or if the moves
125 // have equal score but m1 has the higher beta cut-off count.
126 bool operator<(const RootMove& m) const {
128 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
133 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
134 Move pv[PLY_MAX_PLUS_2];
138 // The RootMoveList class is essentially an array of RootMove objects, with
139 // a handful of methods for accessing the data in the individual moves.
144 RootMoveList(Position& pos, Move searchMoves[]);
146 int move_count() const { return count; }
147 Move get_move(int moveNum) const { return moves[moveNum].move; }
148 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
149 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
150 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
151 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
153 void set_move_nodes(int moveNum, int64_t nodes);
154 void set_beta_counters(int moveNum, int64_t our, int64_t their);
155 void set_move_pv(int moveNum, const Move pv[]);
157 void sort_multipv(int n);
160 static const int MaxRootMoves = 500;
161 RootMove moves[MaxRootMoves];
170 // Maximum depth for razoring
171 const Depth RazorDepth = 4 * OnePly;
173 // Dynamic razoring margin based on depth
174 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
176 // Step 8. Null move search with verification search
178 // Null move margin. A null move search will not be done if the static
179 // evaluation of the position is more than NullMoveMargin below beta.
180 const Value NullMoveMargin = Value(0x200);
182 // Maximum depth for use of dynamic threat detection when null move fails low
183 const Depth ThreatDepth = 5 * OnePly;
185 // Step 9. Internal iterative deepening
187 // Minimum depth for use of internal iterative deepening
188 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
190 // At Non-PV nodes we do an internal iterative deepening search
191 // when the static evaluation is at most IIDMargin below beta.
192 const Value IIDMargin = Value(0x100);
194 // Step 11. Decide the new search depth
196 // Extensions. Configurable UCI options
197 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
198 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
199 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
201 // Minimum depth for use of singular extension
202 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
204 // If the TT move is at least SingularExtensionMargin better then the
205 // remaining ones we will extend it.
206 const Value SingularExtensionMargin = Value(0x20);
208 // Step 12. Futility pruning
210 // Futility margin for quiescence search
211 const Value FutilityMarginQS = Value(0x80);
213 // Futility lookup tables (initialized at startup) and their getter functions
214 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
215 int FutilityMoveCountArray[32]; // [depth]
217 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
218 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
220 // Step 14. Reduced search
222 // Reduction lookup tables (initialized at startup) and their getter functions
223 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
225 template <NodeType PV>
226 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
228 // Common adjustments
230 // Search depth at iteration 1
231 const Depth InitialDepth = OnePly;
233 // Easy move margin. An easy move candidate must be at least this much
234 // better than the second best move.
235 const Value EasyMoveMargin = Value(0x200);
237 // Last seconds noise filtering (LSN)
238 const bool UseLSNFiltering = true;
239 const int LSNTime = 4000; // In milliseconds
240 const Value LSNValue = value_from_centipawns(200);
241 bool loseOnTime = false;
249 // Scores and number of times the best move changed for each iteration
250 Value ValueByIteration[PLY_MAX_PLUS_2];
251 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
253 // Search window management
259 // Time managment variables
260 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
261 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
262 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
263 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
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);
287 template <NodeType PvNode>
288 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
290 template <NodeType PvNode>
291 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
293 template <NodeType PvNode>
294 void sp_search(SplitPoint* sp, int threadID);
296 template <NodeType PvNode>
297 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
299 void init_node(SearchStack ss[], int ply, int threadID);
300 void update_pv(SearchStack ss[], int ply);
301 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
302 bool connected_moves(const Position& pos, Move m1, Move m2);
303 bool value_is_mate(Value value);
304 bool move_is_killer(Move m, const SearchStack& ss);
305 bool ok_to_do_nullmove(const Position& pos);
306 bool ok_to_prune(const Position& pos, Move m, Move threat);
307 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
308 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
309 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
310 void update_killers(Move m, SearchStack& ss);
311 void update_gains(const Position& pos, Move move, Value before, Value after);
313 int current_search_time();
317 void wait_for_stop_or_ponderhit();
318 void init_ss_array(SearchStack ss[]);
319 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value);
321 #if !defined(_MSC_VER)
322 void *init_thread(void *threadID);
324 DWORD WINAPI init_thread(LPVOID threadID);
334 /// init_threads(), exit_threads() and nodes_searched() are helpers to
335 /// give accessibility to some TM methods from outside of current file.
337 void init_threads() { TM.init_threads(); }
338 void exit_threads() { TM.exit_threads(); }
339 int64_t nodes_searched() { return TM.nodes_searched(); }
342 /// perft() is our utility to verify move generation is bug free. All the legal
343 /// moves up to given depth are generated and counted and the sum returned.
345 int perft(Position& pos, Depth depth)
350 MovePicker mp(pos, MOVE_NONE, depth, H);
352 // If we are at the last ply we don't need to do and undo
353 // the moves, just to count them.
354 if (depth <= OnePly) // Replace with '<' to test also qsearch
356 while (mp.get_next_move()) sum++;
360 // Loop through all legal moves
362 while ((move = mp.get_next_move()) != MOVE_NONE)
364 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
365 sum += perft(pos, depth - OnePly);
372 /// think() is the external interface to Stockfish's search, and is called when
373 /// the program receives the UCI 'go' command. It initializes various
374 /// search-related global variables, and calls root_search(). It returns false
375 /// when a quit command is received during the search.
377 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
378 int time[], int increment[], int movesToGo, int maxDepth,
379 int maxNodes, int maxTime, Move searchMoves[]) {
381 // Initialize global search variables
382 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
383 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
385 TM.resetNodeCounters();
386 SearchStartTime = get_system_time();
387 ExactMaxTime = maxTime;
390 InfiniteSearch = infinite;
391 PonderSearch = ponder;
392 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
394 // Look for a book move, only during games, not tests
395 if (UseTimeManagement && get_option_value_bool("OwnBook"))
397 if (get_option_value_string("Book File") != OpeningBook.file_name())
398 OpeningBook.open(get_option_value_string("Book File"));
400 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
401 if (bookMove != MOVE_NONE)
404 wait_for_stop_or_ponderhit();
406 cout << "bestmove " << bookMove << endl;
411 // Reset loseOnTime flag at the beginning of a new game
412 if (button_was_pressed("New Game"))
415 // Read UCI option values
416 TT.set_size(get_option_value_int("Hash"));
417 if (button_was_pressed("Clear Hash"))
420 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
421 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
422 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
423 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
424 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
425 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
426 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
427 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
428 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
429 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
430 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
431 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
433 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
434 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
435 MultiPV = get_option_value_int("MultiPV");
436 Chess960 = get_option_value_bool("UCI_Chess960");
437 UseLogFile = get_option_value_bool("Use Search Log");
440 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
442 read_weights(pos.side_to_move());
444 // Set the number of active threads
445 int newActiveThreads = get_option_value_int("Threads");
446 if (newActiveThreads != TM.active_threads())
448 TM.set_active_threads(newActiveThreads);
449 init_eval(TM.active_threads());
452 // Wake up sleeping threads
453 TM.wake_sleeping_threads();
456 int myTime = time[side_to_move];
457 int myIncrement = increment[side_to_move];
458 if (UseTimeManagement)
460 if (!movesToGo) // Sudden death time control
464 MaxSearchTime = myTime / 30 + myIncrement;
465 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
467 else // Blitz game without increment
469 MaxSearchTime = myTime / 30;
470 AbsoluteMaxSearchTime = myTime / 8;
473 else // (x moves) / (y minutes)
477 MaxSearchTime = myTime / 2;
478 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
482 MaxSearchTime = myTime / Min(movesToGo, 20);
483 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
487 if (get_option_value_bool("Ponder"))
489 MaxSearchTime += MaxSearchTime / 4;
490 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
494 // Set best NodesBetweenPolls interval to avoid lagging under
495 // heavy time pressure.
497 NodesBetweenPolls = Min(MaxNodes, 30000);
498 else if (myTime && myTime < 1000)
499 NodesBetweenPolls = 1000;
500 else if (myTime && myTime < 5000)
501 NodesBetweenPolls = 5000;
503 NodesBetweenPolls = 30000;
505 // Write search information to log file
507 LogFile << "Searching: " << pos.to_fen() << endl
508 << "infinite: " << infinite
509 << " ponder: " << ponder
510 << " time: " << myTime
511 << " increment: " << myIncrement
512 << " moves to go: " << movesToGo << endl;
514 // LSN filtering. Used only for developing purposes, disabled by default
518 // Step 2. If after last move we decided to lose on time, do it now!
519 while (SearchStartTime + myTime + 1000 > get_system_time())
523 // We're ready to start thinking. Call the iterative deepening loop function
524 Value v = id_loop(pos, searchMoves);
528 // Step 1. If this is sudden death game and our position is hopeless,
529 // decide to lose on time.
530 if ( !loseOnTime // If we already lost on time, go to step 3.
540 // Step 3. Now after stepping over the time limit, reset flag for next match.
548 TM.put_threads_to_sleep();
554 /// init_search() is called during startup. It initializes various lookup tables
558 // Init our reduction lookup tables
559 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
560 for (int j = 1; j < 64; j++) // j == moveNumber
562 double pvRed = log(double(i)) * log(double(j)) / 3.0;
563 double nonPVRed = log(double(i)) * log(double(j)) / 1.5;
564 ReductionMatrix[PV][i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
565 ReductionMatrix[NonPV][i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
568 // Init futility margins array
569 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
570 for (int j = 0; j < 64; j++) // j == moveNumber
572 // FIXME: test using log instead of BSR
573 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j + 45;
576 // Init futility move count array
577 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
578 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
582 // SearchStack::init() initializes a search stack. Used at the beginning of a
583 // new search from the root.
584 void SearchStack::init(int ply) {
586 pv[ply] = pv[ply + 1] = MOVE_NONE;
587 currentMove = threatMove = MOVE_NONE;
588 reduction = Depth(0);
592 void SearchStack::initKillers() {
594 mateKiller = MOVE_NONE;
595 for (int i = 0; i < KILLER_MAX; i++)
596 killers[i] = MOVE_NONE;
601 // id_loop() is the main iterative deepening loop. It calls root_search
602 // repeatedly with increasing depth until the allocated thinking time has
603 // been consumed, the user stops the search, or the maximum search depth is
606 Value id_loop(const Position& pos, Move searchMoves[]) {
609 SearchStack ss[PLY_MAX_PLUS_2];
610 Move EasyMove = MOVE_NONE;
611 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
613 // Moves to search are verified, copied, scored and sorted
614 RootMoveList rml(p, searchMoves);
616 // Handle special case of searching on a mate/stale position
617 if (rml.move_count() == 0)
620 wait_for_stop_or_ponderhit();
622 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
625 // Print RootMoveList startup scoring to the standard output,
626 // so to output information also for iteration 1.
627 cout << "info depth " << 1
628 << "\ninfo depth " << 1
629 << " score " << value_to_string(rml.get_move_score(0))
630 << " time " << current_search_time()
631 << " nodes " << TM.nodes_searched()
633 << " pv " << rml.get_move(0) << "\n";
639 ValueByIteration[1] = rml.get_move_score(0);
642 // Is one move significantly better than others after initial scoring ?
643 if ( rml.move_count() == 1
644 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
645 EasyMove = rml.get_move(0);
647 // Iterative deepening loop
648 while (Iteration < PLY_MAX)
650 // Initialize iteration
652 BestMoveChangesByIteration[Iteration] = 0;
654 cout << "info depth " << Iteration << endl;
656 // Calculate dynamic aspiration window based on previous iterations
657 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
659 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
660 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
662 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
663 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
665 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
666 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
669 // Search to the current depth, rml is updated and sorted, alpha and beta could change
670 value = root_search(p, ss, rml, &alpha, &beta);
672 // Write PV to transposition table, in case the relevant entries have
673 // been overwritten during the search.
674 TT.insert_pv(p, ss[0].pv);
677 break; // Value cannot be trusted. Break out immediately!
679 //Save info about search result
680 ValueByIteration[Iteration] = value;
682 // Drop the easy move if differs from the new best move
683 if (ss[0].pv[0] != EasyMove)
684 EasyMove = MOVE_NONE;
686 if (UseTimeManagement)
689 bool stopSearch = false;
691 // Stop search early if there is only a single legal move,
692 // we search up to Iteration 6 anyway to get a proper score.
693 if (Iteration >= 6 && rml.move_count() == 1)
696 // Stop search early when the last two iterations returned a mate score
698 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
699 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
702 // Stop search early if one move seems to be much better than the others
703 int64_t nodes = TM.nodes_searched();
705 && EasyMove == ss[0].pv[0]
706 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
707 && current_search_time() > MaxSearchTime / 16)
708 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
709 && current_search_time() > MaxSearchTime / 32)))
712 // Add some extra time if the best move has changed during the last two iterations
713 if (Iteration > 5 && Iteration <= 50)
714 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
715 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
717 // Stop search if most of MaxSearchTime is consumed at the end of the
718 // iteration. We probably don't have enough time to search the first
719 // move at the next iteration anyway.
720 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
726 StopOnPonderhit = true;
732 if (MaxDepth && Iteration >= MaxDepth)
736 // If we are pondering or in infinite search, we shouldn't print the
737 // best move before we are told to do so.
738 if (!AbortSearch && (PonderSearch || InfiniteSearch))
739 wait_for_stop_or_ponderhit();
741 // Print final search statistics
742 cout << "info nodes " << TM.nodes_searched()
744 << " time " << current_search_time()
745 << " hashfull " << TT.full() << endl;
747 // Print the best move and the ponder move to the standard output
748 if (ss[0].pv[0] == MOVE_NONE)
750 ss[0].pv[0] = rml.get_move(0);
751 ss[0].pv[1] = MOVE_NONE;
754 assert(ss[0].pv[0] != MOVE_NONE);
756 cout << "bestmove " << ss[0].pv[0];
758 if (ss[0].pv[1] != MOVE_NONE)
759 cout << " ponder " << ss[0].pv[1];
766 dbg_print_mean(LogFile);
768 if (dbg_show_hit_rate)
769 dbg_print_hit_rate(LogFile);
771 LogFile << "\nNodes: " << TM.nodes_searched()
772 << "\nNodes/second: " << nps()
773 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
776 p.do_move(ss[0].pv[0], st);
777 LogFile << "\nPonder move: "
778 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
781 return rml.get_move_score(0);
785 // root_search() is the function which searches the root node. It is
786 // similar to search_pv except that it uses a different move ordering
787 // scheme, prints some information to the standard output and handles
788 // the fail low/high loops.
790 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
797 Depth depth, ext, newDepth;
798 Value value, alpha, beta;
799 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
800 int researchCountFH, researchCountFL;
802 researchCountFH = researchCountFL = 0;
805 isCheck = pos.is_check();
807 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
808 // Step 2. Check for aborted search (omitted at root)
809 // Step 3. Mate distance pruning (omitted at root)
810 // Step 4. Transposition table lookup (omitted at root)
812 // Step 5. Evaluate the position statically
813 // At root we do this only to get reference value for child nodes
815 ss[0].eval = evaluate(pos, ei, 0);
817 // Step 6. Razoring (omitted at root)
818 // Step 7. Static null move pruning (omitted at root)
819 // Step 8. Null move search with verification search (omitted at root)
820 // Step 9. Internal iterative deepening (omitted at root)
822 // Step extra. Fail low loop
823 // We start with small aspiration window and in case of fail low, we research
824 // with bigger window until we are not failing low anymore.
827 // Sort the moves before to (re)search
830 // Step 10. Loop through all moves in the root move list
831 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
833 // This is used by time management
834 FirstRootMove = (i == 0);
836 // Save the current node count before the move is searched
837 nodes = TM.nodes_searched();
839 // Reset beta cut-off counters
840 TM.resetBetaCounters();
842 // Pick the next root move, and print the move and the move number to
843 // the standard output.
844 move = ss[0].currentMove = rml.get_move(i);
846 if (current_search_time() >= 1000)
847 cout << "info currmove " << move
848 << " currmovenumber " << i + 1 << endl;
850 moveIsCheck = pos.move_is_check(move);
851 captureOrPromotion = pos.move_is_capture_or_promotion(move);
853 // Step 11. Decide the new search depth
854 depth = (Iteration - 2) * OnePly + InitialDepth;
855 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
856 newDepth = depth + ext;
858 // Step 12. Futility pruning (omitted at root)
860 // Step extra. Fail high loop
861 // If move fails high, we research with bigger window until we are not failing
863 value = - VALUE_INFINITE;
867 // Step 13. Make the move
868 pos.do_move(move, st, ci, moveIsCheck);
870 // Step extra. pv search
871 // We do pv search for first moves (i < MultiPV)
872 // and for fail high research (value > alpha)
873 if (i < MultiPV || value > alpha)
875 // Aspiration window is disabled in multi-pv case
877 alpha = -VALUE_INFINITE;
879 // Full depth PV search, done on first move or after a fail high
880 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
884 // Step 14. Reduced search
885 // if the move fails high will be re-searched at full depth
886 bool doFullDepthSearch = true;
888 if ( depth >= 3 * OnePly
890 && !captureOrPromotion
891 && !move_is_castle(move))
893 ss[0].reduction = reduction<PV>(depth, i - MultiPV + 2);
896 // Reduced depth non-pv search using alpha as upperbound
897 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[0].reduction, 1, true, 0);
898 doFullDepthSearch = (value > alpha);
902 // Step 15. Full depth search
903 if (doFullDepthSearch)
905 // Full depth non-pv search using alpha as upperbound
906 ss[0].reduction = Depth(0);
907 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, 1, true, 0);
909 // If we are above alpha then research at same depth but as PV
910 // to get a correct score or eventually a fail high above beta.
912 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
916 // Step 16. Undo move
919 // Can we exit fail high loop ?
920 if (AbortSearch || value < beta)
923 // We are failing high and going to do a research. It's important to update
924 // the score before research in case we run out of time while researching.
925 rml.set_move_score(i, value);
927 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
928 rml.set_move_pv(i, ss[0].pv);
930 // Print information to the standard output
931 print_pv_info(pos, ss, alpha, beta, value);
933 // Prepare for a research after a fail high, each time with a wider window
934 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
937 } // End of fail high loop
939 // Finished searching the move. If AbortSearch is true, the search
940 // was aborted because the user interrupted the search or because we
941 // ran out of time. In this case, the return value of the search cannot
942 // be trusted, and we break out of the loop without updating the best
947 // Remember beta-cutoff and searched nodes counts for this move. The
948 // info is used to sort the root moves for the next iteration.
950 TM.get_beta_counters(pos.side_to_move(), our, their);
951 rml.set_beta_counters(i, our, their);
952 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
954 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
955 assert(value < beta);
957 // Step 17. Check for new best move
958 if (value <= alpha && i >= MultiPV)
959 rml.set_move_score(i, -VALUE_INFINITE);
962 // PV move or new best move!
965 rml.set_move_score(i, value);
967 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
968 rml.set_move_pv(i, ss[0].pv);
972 // We record how often the best move has been changed in each
973 // iteration. This information is used for time managment: When
974 // the best move changes frequently, we allocate some more time.
976 BestMoveChangesByIteration[Iteration]++;
978 // Print information to the standard output
979 print_pv_info(pos, ss, alpha, beta, value);
981 // Raise alpha to setup proper non-pv search upper bound
988 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
990 cout << "info multipv " << j + 1
991 << " score " << value_to_string(rml.get_move_score(j))
992 << " depth " << (j <= i ? Iteration : Iteration - 1)
993 << " time " << current_search_time()
994 << " nodes " << TM.nodes_searched()
998 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
999 cout << rml.get_move_pv(j, k) << " ";
1003 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1005 } // PV move or new best move
1007 assert(alpha >= *alphaPtr);
1009 AspirationFailLow = (alpha == *alphaPtr);
1011 if (AspirationFailLow && StopOnPonderhit)
1012 StopOnPonderhit = false;
1015 // Can we exit fail low loop ?
1016 if (AbortSearch || !AspirationFailLow)
1019 // Prepare for a research after a fail low, each time with a wider window
1020 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1025 // Sort the moves before to return
1032 // search<>() is the main search function for both PV and non-PV nodes
1034 template <NodeType PvNode>
1035 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth,
1036 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1038 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1039 assert(beta > alpha && beta <= VALUE_INFINITE);
1040 assert(PvNode || alpha == beta - 1);
1041 assert(ply >= 0 && ply < PLY_MAX);
1042 assert(threadID >= 0 && threadID < TM.active_threads());
1044 Move movesSearched[256];
1049 Depth ext, newDepth;
1050 Value bestValue, value, oldAlpha;
1051 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1052 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1053 bool mateThreat = false;
1055 refinedValue = bestValue = value = -VALUE_INFINITE;
1059 return qsearch<PvNode>(pos, ss, alpha, beta, Depth(0), ply, threadID);
1061 // Step 1. Initialize node and poll
1062 // Polling can abort search.
1063 init_node(ss, ply, threadID);
1065 // Step 2. Check for aborted search and immediate draw
1066 if (AbortSearch || TM.thread_should_stop(threadID))
1069 if (pos.is_draw() || ply >= PLY_MAX - 1)
1072 // Step 3. Mate distance pruning
1073 alpha = Max(value_mated_in(ply), alpha);
1074 beta = Min(value_mate_in(ply+1), beta);
1078 // Step 4. Transposition table lookup
1080 // We don't want the score of a partial search to overwrite a previous full search
1081 // TT value, so we use a different position key in case of an excluded move exists.
1082 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1084 tte = TT.retrieve(posKey);
1085 ttMove = (tte ? tte->move() : MOVE_NONE);
1087 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1088 // This is to avoid problems in the following areas:
1090 // * Repetition draw detection
1091 // * Fifty move rule detection
1092 // * Searching for a mate
1093 // * Printing of full PV line
1095 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1097 // Refresh tte entry to avoid aging
1098 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1100 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1101 return value_from_tt(tte->value(), ply);
1104 // Step 5. Evaluate the position statically
1105 // At PV nodes we do this only to update gain statistics
1106 isCheck = pos.is_check();
1109 if (tte && tte->static_value() != VALUE_NONE)
1111 ss[ply].eval = tte->static_value();
1112 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1115 ss[ply].eval = evaluate(pos, ei, threadID);
1117 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1118 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1121 // Step 6. Razoring (is omitted in PV nodes)
1123 && refinedValue < beta - razor_margin(depth)
1124 && ttMove == MOVE_NONE
1125 && ss[ply - 1].currentMove != MOVE_NULL
1126 && depth < RazorDepth
1128 && !value_is_mate(beta)
1129 && !pos.has_pawn_on_7th(pos.side_to_move()))
1131 Value rbeta = beta - razor_margin(depth);
1132 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1134 // Logically we should return (v + razor_margin(depth)), but
1135 // surprisingly this did slightly weaker in tests.
1139 // Step 7. Static null move pruning (is omitted in PV nodes)
1140 // We're betting that the opponent doesn't have a move that will reduce
1141 // the score by more than futility_margin(depth) if we do a null move.
1144 && depth < RazorDepth
1146 && !value_is_mate(beta)
1147 && ok_to_do_nullmove(pos)
1148 && refinedValue >= beta + futility_margin(depth, 0))
1149 return refinedValue - futility_margin(depth, 0);
1151 // Step 8. Null move search with verification search (is omitted in PV nodes)
1152 // When we jump directly to qsearch() we do a null move only if static value is
1153 // at least beta. Otherwise we do a null move if static value is not more than
1154 // NullMoveMargin under beta.
1159 && !value_is_mate(beta)
1160 && ok_to_do_nullmove(pos)
1161 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1163 ss[ply].currentMove = MOVE_NULL;
1165 // Null move dynamic reduction based on depth
1166 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1168 // Null move dynamic reduction based on value
1169 if (refinedValue - beta > PawnValueMidgame)
1172 pos.do_null_move(st);
1174 nullValue = -search<NonPV>(pos, ss, -beta, -alpha, depth-R*OnePly, ply+1, false, threadID);
1176 pos.undo_null_move();
1178 if (nullValue >= beta)
1180 // Do not return unproven mate scores
1181 if (nullValue >= value_mate_in(PLY_MAX))
1184 if (depth < 6 * OnePly)
1187 // Do zugzwang verification search
1188 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply, false, threadID);
1192 // The null move failed low, which means that we may be faced with
1193 // some kind of threat. If the previous move was reduced, check if
1194 // the move that refuted the null move was somehow connected to the
1195 // move which was reduced. If a connection is found, return a fail
1196 // low score (which will cause the reduced move to fail high in the
1197 // parent node, which will trigger a re-search with full depth).
1198 if (nullValue == value_mated_in(ply + 2))
1201 ss[ply].threatMove = ss[ply + 1].currentMove;
1202 if ( depth < ThreatDepth
1203 && ss[ply - 1].reduction
1204 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1209 // Step 9. Internal iterative deepening
1210 if ( depth >= IIDDepth[PvNode]
1211 && ttMove == MOVE_NONE
1212 && (PvNode || (!isCheck && ss[ply].eval >= beta - IIDMargin)))
1214 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1215 search<PvNode>(pos, ss, alpha, beta, d, ply, false, threadID);
1216 ttMove = ss[ply].pv[ply];
1217 tte = TT.retrieve(posKey);
1220 // Expensive mate threat detection (only for PV nodes)
1222 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1224 // Initialize a MovePicker object for the current position
1225 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], (PvNode ? -VALUE_INFINITE : beta));
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 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1240 moveIsCheck = pos.move_is_check(move, ci);
1241 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1243 // Step 11. Decide the new search depth
1244 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1246 // Singular extension search. We extend the TT move if its value is much better than
1247 // its siblings. To verify this we do a reduced search on all the other moves but the
1248 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1249 if ( depth >= SingularExtensionDepth[PvNode]
1251 && move == tte->move()
1252 && !excludedMove // Do not allow recursive singular extension search
1254 && is_lower_bound(tte->type())
1255 && tte->depth() >= depth - 3 * OnePly)
1257 Value ttValue = value_from_tt(tte->value(), ply);
1259 if (abs(ttValue) < VALUE_KNOWN_WIN)
1261 Value b = ttValue - SingularExtensionMargin;
1262 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply, false, threadID, move);
1264 if (v < ttValue - SingularExtensionMargin)
1269 newDepth = depth - OnePly + ext;
1271 // Update current move (this must be done after singular extension search)
1272 movesSearched[moveCount++] = ss[ply].currentMove = move;
1274 // Step 12. Futility pruning (is omitted in PV nodes)
1278 && !captureOrPromotion
1279 && !move_is_castle(move)
1282 // Move count based pruning
1283 if ( moveCount >= futility_move_count(depth)
1284 && ok_to_prune(pos, move, ss[ply].threatMove)
1285 && bestValue > value_mated_in(PLY_MAX))
1288 // Value based pruning
1289 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1290 // but fixing this made program slightly weaker.
1291 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1292 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1293 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1295 if (futilityValueScaled < beta)
1297 if (futilityValueScaled > bestValue)
1298 bestValue = futilityValueScaled;
1303 // Step 13. Make the move
1304 pos.do_move(move, st, ci, moveIsCheck);
1306 // Step extra. pv search (only in PV nodes)
1307 // The first move in list is the expected PV
1308 if (PvNode && moveCount == 1)
1309 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1312 // Step 14. Reduced search
1313 // if the move fails high will be re-searched at full depth.
1314 bool doFullDepthSearch = true;
1316 if ( depth >= 3 * OnePly
1318 && !captureOrPromotion
1319 && !move_is_castle(move)
1320 && !move_is_killer(move, ss[ply]))
1322 ss[ply].reduction = reduction<PvNode>(depth, moveCount);
1323 if (ss[ply].reduction)
1325 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1326 doFullDepthSearch = (value > alpha);
1330 // Step 15. Full depth search
1331 if (doFullDepthSearch)
1333 ss[ply].reduction = Depth(0);
1334 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, ply+1, true, threadID);
1336 // Step extra. pv search (only in PV nodes)
1337 // Search only for possible new PV nodes, if instead value >= beta then
1338 // parent node fails low with value <= alpha and tries another move.
1339 if (PvNode && value > alpha && value < beta)
1340 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1344 // Step 16. Undo move
1345 pos.undo_move(move);
1347 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1349 // Step 17. Check for new best move
1350 if (value > bestValue)
1355 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1360 if (value == value_mate_in(ply + 1))
1361 ss[ply].mateKiller = move;
1365 // Step 18. Check for split
1366 if ( TM.active_threads() > 1
1368 && depth >= MinimumSplitDepth
1370 && TM.available_thread_exists(threadID)
1372 && !TM.thread_should_stop(threadID))
1373 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1374 mateThreat, &moveCount, &mp, threadID, PvNode);
1377 // Step 19. Check for mate and stalemate
1378 // All legal moves have been searched and if there are
1379 // no legal moves, it must be mate or stalemate.
1380 // If one move was excluded return fail low score.
1382 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1384 // Step 20. Update tables
1385 // If the search is not aborted, update the transposition table,
1386 // history counters, and killer moves.
1387 if (AbortSearch || TM.thread_should_stop(threadID))
1390 if (bestValue <= oldAlpha)
1391 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss[ply].eval, ei.kingDanger[pos.side_to_move()]);
1393 else if (bestValue >= beta)
1395 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1396 move = ss[ply].pv[ply];
1397 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss[ply].eval, ei.kingDanger[pos.side_to_move()]);
1398 if (!pos.move_is_capture_or_promotion(move))
1400 update_history(pos, move, depth, movesSearched, moveCount);
1401 update_killers(move, ss[ply]);
1405 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply], ss[ply].eval, ei.kingDanger[pos.side_to_move()]);
1407 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1413 // qsearch() is the quiescence search function, which is called by the main
1414 // search function when the remaining depth is zero (or, to be more precise,
1415 // less than OnePly).
1417 template <NodeType PvNode>
1418 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1419 Depth depth, int ply, int threadID) {
1421 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1422 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1423 assert(PvNode || alpha == beta - 1);
1425 assert(ply >= 0 && ply < PLY_MAX);
1426 assert(threadID >= 0 && threadID < TM.active_threads());
1431 Value staticValue, bestValue, value, futilityBase, futilityValue;
1432 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1433 const TTEntry* tte = NULL;
1435 Value oldAlpha = alpha;
1437 // Initialize, and make an early exit in case of an aborted search,
1438 // an instant draw, maximum ply reached, etc.
1439 init_node(ss, ply, threadID);
1441 // After init_node() that calls poll()
1442 if (AbortSearch || TM.thread_should_stop(threadID))
1445 if (pos.is_draw() || ply >= PLY_MAX - 1)
1448 // Transposition table lookup. At PV nodes, we don't use the TT for
1449 // pruning, but only for move ordering.
1450 tte = TT.retrieve(pos.get_key());
1451 ttMove = (tte ? tte->move() : MOVE_NONE);
1453 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1455 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1456 return value_from_tt(tte->value(), ply);
1459 isCheck = pos.is_check();
1461 // Evaluate the position statically
1463 staticValue = -VALUE_INFINITE;
1464 else if (tte && tte->static_value() != VALUE_NONE)
1466 staticValue = tte->static_value();
1467 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1470 staticValue = evaluate(pos, ei, threadID);
1474 ss[ply].eval = staticValue;
1475 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1478 // Initialize "stand pat score", and return it immediately if it is
1480 bestValue = staticValue;
1482 if (bestValue >= beta)
1484 // Store the score to avoid a future costly evaluation() call
1485 if (!isCheck && !tte)
1486 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, Depth(-127*OnePly), MOVE_NONE, ss[ply].eval, ei.kingDanger[pos.side_to_move()]);
1491 if (bestValue > alpha)
1494 // If we are near beta then try to get a cutoff pushing checks a bit further
1495 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1497 // Initialize a MovePicker object for the current position, and prepare
1498 // to search the moves. Because the depth is <= 0 here, only captures,
1499 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1500 // and we are near beta) will be generated.
1501 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1503 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1504 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1506 // Loop through the moves until no moves remain or a beta cutoff occurs
1507 while ( alpha < beta
1508 && (move = mp.get_next_move()) != MOVE_NONE)
1510 assert(move_is_ok(move));
1512 moveIsCheck = pos.move_is_check(move, ci);
1514 // Update current move
1516 ss[ply].currentMove = move;
1524 && !move_is_promotion(move)
1525 && !pos.move_is_passed_pawn_push(move))
1527 futilityValue = futilityBase
1528 + pos.endgame_value_of_piece_on(move_to(move))
1529 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1531 if (futilityValue < alpha)
1533 if (futilityValue > bestValue)
1534 bestValue = futilityValue;
1539 // Detect blocking evasions that are candidate to be pruned
1540 evasionPrunable = isCheck
1541 && bestValue > value_mated_in(PLY_MAX)
1542 && !pos.move_is_capture(move)
1543 && pos.type_of_piece_on(move_from(move)) != KING
1544 && !pos.can_castle(pos.side_to_move());
1546 // Don't search moves with negative SEE values
1548 && (!isCheck || evasionPrunable)
1550 && !move_is_promotion(move)
1551 && pos.see_sign(move) < 0)
1554 // Make and search the move
1555 pos.do_move(move, st, ci, moveIsCheck);
1556 value = -qsearch<PvNode>(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1557 pos.undo_move(move);
1559 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1562 if (value > bestValue)
1573 // All legal moves have been searched. A special case: If we're in check
1574 // and no legal moves were found, it is checkmate.
1575 if (!moveCount && isCheck) // Mate!
1576 return value_mated_in(ply);
1578 // Update transposition table
1579 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1580 if (bestValue <= oldAlpha)
1582 // If bestValue isn't changed it means it is still the static evaluation
1583 // of the node, so keep this info to avoid a future evaluation() call.
1584 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss[ply].eval, ei.kingDanger[pos.side_to_move()]);
1586 else if (bestValue >= beta)
1588 move = ss[ply].pv[ply];
1589 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss[ply].eval, ei.kingDanger[pos.side_to_move()]);
1591 // Update killers only for good checking moves
1592 if (!pos.move_is_capture_or_promotion(move))
1593 update_killers(move, ss[ply]);
1596 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply], ss[ply].eval, ei.kingDanger[pos.side_to_move()]);
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);
1629 SearchStack* ss = sp->sstack[threadID];
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[sp->ply].currentMove = move;
1655 // Step 12. Futility pruning (is omitted in PV nodes)
1659 && !captureOrPromotion
1660 && !move_is_castle(move))
1662 // Move count based pruning
1663 if ( moveCount >= futility_move_count(sp->depth)
1664 && ok_to_prune(pos, move, ss[sp->ply].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[sp->ply].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;
1694 && !captureOrPromotion
1695 && !move_is_castle(move)
1696 && !move_is_killer(move, ss[sp->ply]))
1698 ss[sp->ply].reduction = reduction<PvNode>(sp->depth, moveCount);
1699 if (ss[sp->ply].reduction)
1701 Value localAlpha = sp->alpha;
1702 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1703 doFullDepthSearch = (value > localAlpha);
1707 // Step 15. Full depth search
1708 if (doFullDepthSearch)
1710 ss[sp->ply].reduction = Depth(0);
1711 Value localAlpha = sp->alpha;
1712 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1, true, threadID);
1714 if (PvNode && value > localAlpha && value < sp->beta)
1715 value = -search<PV>(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, false, threadID);
1718 // Step 16. Undo move
1719 pos.undo_move(move);
1721 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1723 // Step 17. Check for new best move
1724 lock_grab(&(sp->lock));
1726 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1728 sp->bestValue = value;
1730 if (sp->bestValue > sp->alpha)
1732 if (!PvNode || value >= sp->beta)
1733 sp->stopRequest = true;
1735 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1738 sp_update_pv(sp->parentSstack, ss, sp->ply);
1743 /* Here we have the lock still grabbed */
1745 sp->slaves[threadID] = 0;
1747 lock_release(&(sp->lock));
1750 // init_node() is called at the beginning of all the search functions
1751 // (search() qsearch(), and so on) and initializes the
1752 // search stack object corresponding to the current node. Once every
1753 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1754 // for user input and checks whether it is time to stop the search.
1756 void init_node(SearchStack ss[], int ply, int threadID) {
1758 assert(ply >= 0 && ply < PLY_MAX);
1759 assert(threadID >= 0 && threadID < TM.active_threads());
1761 TM.incrementNodeCounter(threadID);
1766 if (NodesSincePoll >= NodesBetweenPolls)
1773 ss[ply + 2].initKillers();
1776 // update_pv() is called whenever a search returns a value > alpha.
1777 // It updates the PV in the SearchStack object corresponding to the
1780 void update_pv(SearchStack ss[], int ply) {
1782 assert(ply >= 0 && ply < PLY_MAX);
1786 ss[ply].pv[ply] = ss[ply].currentMove;
1788 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1789 ss[ply].pv[p] = ss[ply + 1].pv[p];
1791 ss[ply].pv[p] = MOVE_NONE;
1795 // sp_update_pv() is a variant of update_pv for use at split points. The
1796 // difference between the two functions is that sp_update_pv also updates
1797 // the PV at the parent node.
1799 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
1801 assert(ply >= 0 && ply < PLY_MAX);
1805 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
1807 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1808 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
1810 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
1814 // connected_moves() tests whether two moves are 'connected' in the sense
1815 // that the first move somehow made the second move possible (for instance
1816 // if the moving piece is the same in both moves). The first move is assumed
1817 // to be the move that was made to reach the current position, while the
1818 // second move is assumed to be a move from the current position.
1820 bool connected_moves(const Position& pos, Move m1, Move m2) {
1822 Square f1, t1, f2, t2;
1825 assert(move_is_ok(m1));
1826 assert(move_is_ok(m2));
1828 if (m2 == MOVE_NONE)
1831 // Case 1: The moving piece is the same in both moves
1837 // Case 2: The destination square for m2 was vacated by m1
1843 // Case 3: Moving through the vacated square
1844 if ( piece_is_slider(pos.piece_on(f2))
1845 && bit_is_set(squares_between(f2, t2), f1))
1848 // Case 4: The destination square for m2 is defended by the moving piece in m1
1849 p = pos.piece_on(t1);
1850 if (bit_is_set(pos.attacks_from(p, t1), t2))
1853 // Case 5: Discovered check, checking piece is the piece moved in m1
1854 if ( piece_is_slider(p)
1855 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1856 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1858 // discovered_check_candidates() works also if the Position's side to
1859 // move is the opposite of the checking piece.
1860 Color them = opposite_color(pos.side_to_move());
1861 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1863 if (bit_is_set(dcCandidates, f2))
1870 // value_is_mate() checks if the given value is a mate one
1871 // eventually compensated for the ply.
1873 bool value_is_mate(Value value) {
1875 assert(abs(value) <= VALUE_INFINITE);
1877 return value <= value_mated_in(PLY_MAX)
1878 || value >= value_mate_in(PLY_MAX);
1882 // move_is_killer() checks if the given move is among the
1883 // killer moves of that ply.
1885 bool move_is_killer(Move m, const SearchStack& ss) {
1887 const Move* k = ss.killers;
1888 for (int i = 0; i < KILLER_MAX; i++, k++)
1896 // extension() decides whether a move should be searched with normal depth,
1897 // or with extended depth. Certain classes of moves (checking moves, in
1898 // particular) are searched with bigger depth than ordinary moves and in
1899 // any case are marked as 'dangerous'. Note that also if a move is not
1900 // extended, as example because the corresponding UCI option is set to zero,
1901 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1902 template <NodeType PvNode>
1903 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1904 bool singleEvasion, bool mateThreat, bool* dangerous) {
1906 assert(m != MOVE_NONE);
1908 Depth result = Depth(0);
1909 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1914 result += CheckExtension[PvNode];
1917 result += SingleEvasionExtension[PvNode];
1920 result += MateThreatExtension[PvNode];
1923 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1925 Color c = pos.side_to_move();
1926 if (relative_rank(c, move_to(m)) == RANK_7)
1928 result += PawnPushTo7thExtension[PvNode];
1931 if (pos.pawn_is_passed(c, move_to(m)))
1933 result += PassedPawnExtension[PvNode];
1938 if ( captureOrPromotion
1939 && pos.type_of_piece_on(move_to(m)) != PAWN
1940 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1941 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1942 && !move_is_promotion(m)
1945 result += PawnEndgameExtension[PvNode];
1950 && captureOrPromotion
1951 && pos.type_of_piece_on(move_to(m)) != PAWN
1952 && pos.see_sign(m) >= 0)
1958 return Min(result, OnePly);
1962 // ok_to_do_nullmove() looks at the current position and decides whether
1963 // doing a 'null move' should be allowed. In order to avoid zugzwang
1964 // problems, null moves are not allowed when the side to move has very
1965 // little material left. Currently, the test is a bit too simple: Null
1966 // moves are avoided only when the side to move has only pawns left.
1967 // It's probably a good idea to avoid null moves in at least some more
1968 // complicated endgames, e.g. KQ vs KR. FIXME
1970 bool ok_to_do_nullmove(const Position& pos) {
1972 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
1976 // ok_to_prune() tests whether it is safe to forward prune a move. Only
1977 // non-tactical moves late in the move list close to the leaves are
1978 // candidates for pruning.
1980 bool ok_to_prune(const Position& pos, Move m, Move threat) {
1982 assert(move_is_ok(m));
1983 assert(threat == MOVE_NONE || move_is_ok(threat));
1984 assert(!pos.move_is_check(m));
1985 assert(!pos.move_is_capture_or_promotion(m));
1986 assert(!pos.move_is_passed_pawn_push(m));
1988 Square mfrom, mto, tfrom, tto;
1990 // Prune if there isn't any threat move
1991 if (threat == MOVE_NONE)
1994 mfrom = move_from(m);
1996 tfrom = move_from(threat);
1997 tto = move_to(threat);
1999 // Case 1: Don't prune moves which move the threatened piece
2003 // Case 2: If the threatened piece has value less than or equal to the
2004 // value of the threatening piece, don't prune move which defend it.
2005 if ( pos.move_is_capture(threat)
2006 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2007 || pos.type_of_piece_on(tfrom) == KING)
2008 && pos.move_attacks_square(m, tto))
2011 // Case 3: If the moving piece in the threatened move is a slider, don't
2012 // prune safe moves which block its ray.
2013 if ( piece_is_slider(pos.piece_on(tfrom))
2014 && bit_is_set(squares_between(tfrom, tto), mto)
2015 && pos.see_sign(m) >= 0)
2022 // ok_to_use_TT() returns true if a transposition table score
2023 // can be used at a given point in search.
2025 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2027 Value v = value_from_tt(tte->value(), ply);
2029 return ( tte->depth() >= depth
2030 || v >= Max(value_mate_in(PLY_MAX), beta)
2031 || v < Min(value_mated_in(PLY_MAX), beta))
2033 && ( (is_lower_bound(tte->type()) && v >= beta)
2034 || (is_upper_bound(tte->type()) && v < beta));
2038 // refine_eval() returns the transposition table score if
2039 // possible otherwise falls back on static position evaluation.
2041 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2046 Value v = value_from_tt(tte->value(), ply);
2048 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2049 || (is_upper_bound(tte->type()) && v < defaultEval))
2056 // update_history() registers a good move that produced a beta-cutoff
2057 // in history and marks as failures all the other moves of that ply.
2059 void update_history(const Position& pos, Move move, Depth depth,
2060 Move movesSearched[], int moveCount) {
2064 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2066 for (int i = 0; i < moveCount - 1; i++)
2068 m = movesSearched[i];
2072 if (!pos.move_is_capture_or_promotion(m))
2073 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2078 // update_killers() add a good move that produced a beta-cutoff
2079 // among the killer moves of that ply.
2081 void update_killers(Move m, SearchStack& ss) {
2083 if (m == ss.killers[0])
2086 for (int i = KILLER_MAX - 1; i > 0; i--)
2087 ss.killers[i] = ss.killers[i - 1];
2093 // update_gains() updates the gains table of a non-capture move given
2094 // the static position evaluation before and after the move.
2096 void update_gains(const Position& pos, Move m, Value before, Value after) {
2099 && before != VALUE_NONE
2100 && after != VALUE_NONE
2101 && pos.captured_piece() == NO_PIECE_TYPE
2102 && !move_is_castle(m)
2103 && !move_is_promotion(m))
2104 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2108 // current_search_time() returns the number of milliseconds which have passed
2109 // since the beginning of the current search.
2111 int current_search_time() {
2113 return get_system_time() - SearchStartTime;
2117 // nps() computes the current nodes/second count.
2121 int t = current_search_time();
2122 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2126 // poll() performs two different functions: It polls for user input, and it
2127 // looks at the time consumed so far and decides if it's time to abort the
2132 static int lastInfoTime;
2133 int t = current_search_time();
2138 // We are line oriented, don't read single chars
2139 std::string command;
2141 if (!std::getline(std::cin, command))
2144 if (command == "quit")
2147 PonderSearch = false;
2151 else if (command == "stop")
2154 PonderSearch = false;
2156 else if (command == "ponderhit")
2160 // Print search information
2164 else if (lastInfoTime > t)
2165 // HACK: Must be a new search where we searched less than
2166 // NodesBetweenPolls nodes during the first second of search.
2169 else if (t - lastInfoTime >= 1000)
2176 if (dbg_show_hit_rate)
2177 dbg_print_hit_rate();
2179 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2180 << " time " << t << " hashfull " << TT.full() << endl;
2183 // Should we stop the search?
2187 bool stillAtFirstMove = FirstRootMove
2188 && !AspirationFailLow
2189 && t > MaxSearchTime + ExtraSearchTime;
2191 bool noMoreTime = t > AbsoluteMaxSearchTime
2192 || stillAtFirstMove;
2194 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2195 || (ExactMaxTime && t >= ExactMaxTime)
2196 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2201 // ponderhit() is called when the program is pondering (i.e. thinking while
2202 // it's the opponent's turn to move) in order to let the engine know that
2203 // it correctly predicted the opponent's move.
2207 int t = current_search_time();
2208 PonderSearch = false;
2210 bool stillAtFirstMove = FirstRootMove
2211 && !AspirationFailLow
2212 && t > MaxSearchTime + ExtraSearchTime;
2214 bool noMoreTime = t > AbsoluteMaxSearchTime
2215 || stillAtFirstMove;
2217 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2222 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2224 void init_ss_array(SearchStack ss[]) {
2226 for (int i = 0; i < 3; i++)
2229 ss[i].initKillers();
2234 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2235 // while the program is pondering. The point is to work around a wrinkle in
2236 // the UCI protocol: When pondering, the engine is not allowed to give a
2237 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2238 // We simply wait here until one of these commands is sent, and return,
2239 // after which the bestmove and pondermove will be printed (in id_loop()).
2241 void wait_for_stop_or_ponderhit() {
2243 std::string command;
2247 if (!std::getline(std::cin, command))
2250 if (command == "quit")
2255 else if (command == "ponderhit" || command == "stop")
2261 // print_pv_info() prints to standard output and eventually to log file information on
2262 // the current PV line. It is called at each iteration or after a new pv is found.
2264 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2266 cout << "info depth " << Iteration
2267 << " score " << value_to_string(value)
2268 << ((value >= beta) ? " lowerbound" :
2269 ((value <= alpha)? " upperbound" : ""))
2270 << " time " << current_search_time()
2271 << " nodes " << TM.nodes_searched()
2275 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2276 cout << ss[0].pv[j] << " ";
2282 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2283 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2285 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2286 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2291 // init_thread() is the function which is called when a new thread is
2292 // launched. It simply calls the idle_loop() function with the supplied
2293 // threadID. There are two versions of this function; one for POSIX
2294 // threads and one for Windows threads.
2296 #if !defined(_MSC_VER)
2298 void* init_thread(void *threadID) {
2300 TM.idle_loop(*(int*)threadID, NULL);
2306 DWORD WINAPI init_thread(LPVOID threadID) {
2308 TM.idle_loop(*(int*)threadID, NULL);
2315 /// The ThreadsManager class
2317 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2318 // get_beta_counters() are getters/setters for the per thread
2319 // counters used to sort the moves at root.
2321 void ThreadsManager::resetNodeCounters() {
2323 for (int i = 0; i < MAX_THREADS; i++)
2324 threads[i].nodes = 0ULL;
2327 void ThreadsManager::resetBetaCounters() {
2329 for (int i = 0; i < MAX_THREADS; i++)
2330 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2333 int64_t ThreadsManager::nodes_searched() const {
2335 int64_t result = 0ULL;
2336 for (int i = 0; i < ActiveThreads; i++)
2337 result += threads[i].nodes;
2342 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2345 for (int i = 0; i < MAX_THREADS; i++)
2347 our += threads[i].betaCutOffs[us];
2348 their += threads[i].betaCutOffs[opposite_color(us)];
2353 // idle_loop() is where the threads are parked when they have no work to do.
2354 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2355 // object for which the current thread is the master.
2357 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2359 assert(threadID >= 0 && threadID < MAX_THREADS);
2363 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2364 // master should exit as last one.
2365 if (AllThreadsShouldExit)
2368 threads[threadID].state = THREAD_TERMINATED;
2372 // If we are not thinking, wait for a condition to be signaled
2373 // instead of wasting CPU time polling for work.
2374 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2377 assert(threadID != 0);
2378 threads[threadID].state = THREAD_SLEEPING;
2380 #if !defined(_MSC_VER)
2381 lock_grab(&WaitLock);
2382 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2383 pthread_cond_wait(&WaitCond, &WaitLock);
2384 lock_release(&WaitLock);
2386 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2390 // If thread has just woken up, mark it as available
2391 if (threads[threadID].state == THREAD_SLEEPING)
2392 threads[threadID].state = THREAD_AVAILABLE;
2394 // If this thread has been assigned work, launch a search
2395 if (threads[threadID].state == THREAD_WORKISWAITING)
2397 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2399 threads[threadID].state = THREAD_SEARCHING;
2401 if (threads[threadID].splitPoint->pvNode)
2402 sp_search<PV>(threads[threadID].splitPoint, threadID);
2404 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2406 assert(threads[threadID].state == THREAD_SEARCHING);
2408 threads[threadID].state = THREAD_AVAILABLE;
2411 // If this thread is the master of a split point and all slaves have
2412 // finished their work at this split point, return from the idle loop.
2414 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2416 if (i == ActiveThreads)
2418 // Because sp->slaves[] is reset under lock protection,
2419 // be sure sp->lock has been released before to return.
2420 lock_grab(&(sp->lock));
2421 lock_release(&(sp->lock));
2423 assert(threads[threadID].state == THREAD_AVAILABLE);
2425 threads[threadID].state = THREAD_SEARCHING;
2432 // init_threads() is called during startup. It launches all helper threads,
2433 // and initializes the split point stack and the global locks and condition
2436 void ThreadsManager::init_threads() {
2441 #if !defined(_MSC_VER)
2442 pthread_t pthread[1];
2445 // Initialize global locks
2446 lock_init(&MPLock, NULL);
2447 lock_init(&WaitLock, NULL);
2449 #if !defined(_MSC_VER)
2450 pthread_cond_init(&WaitCond, NULL);
2452 for (i = 0; i < MAX_THREADS; i++)
2453 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2456 // Initialize SplitPointStack locks
2457 for (i = 0; i < MAX_THREADS; i++)
2458 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2460 SplitPointStack[i][j].parent = NULL;
2461 lock_init(&(SplitPointStack[i][j].lock), NULL);
2464 // Will be set just before program exits to properly end the threads
2465 AllThreadsShouldExit = false;
2467 // Threads will be put to sleep as soon as created
2468 AllThreadsShouldSleep = true;
2470 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2472 threads[0].state = THREAD_SEARCHING;
2473 for (i = 1; i < MAX_THREADS; i++)
2474 threads[i].state = THREAD_AVAILABLE;
2476 // Launch the helper threads
2477 for (i = 1; i < MAX_THREADS; i++)
2480 #if !defined(_MSC_VER)
2481 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2483 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2488 cout << "Failed to create thread number " << i << endl;
2489 Application::exit_with_failure();
2492 // Wait until the thread has finished launching and is gone to sleep
2493 while (threads[i].state != THREAD_SLEEPING) {}
2498 // exit_threads() is called when the program exits. It makes all the
2499 // helper threads exit cleanly.
2501 void ThreadsManager::exit_threads() {
2503 ActiveThreads = MAX_THREADS; // HACK
2504 AllThreadsShouldSleep = true; // HACK
2505 wake_sleeping_threads();
2507 // This makes the threads to exit idle_loop()
2508 AllThreadsShouldExit = true;
2510 // Wait for thread termination
2511 for (int i = 1; i < MAX_THREADS; i++)
2512 while (threads[i].state != THREAD_TERMINATED);
2514 // Now we can safely destroy the locks
2515 for (int i = 0; i < MAX_THREADS; i++)
2516 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2517 lock_destroy(&(SplitPointStack[i][j].lock));
2519 lock_destroy(&WaitLock);
2520 lock_destroy(&MPLock);
2524 // thread_should_stop() checks whether the thread should stop its search.
2525 // This can happen if a beta cutoff has occurred in the thread's currently
2526 // active split point, or in some ancestor of the current split point.
2528 bool ThreadsManager::thread_should_stop(int threadID) const {
2530 assert(threadID >= 0 && threadID < ActiveThreads);
2534 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2539 // thread_is_available() checks whether the thread with threadID "slave" is
2540 // available to help the thread with threadID "master" at a split point. An
2541 // obvious requirement is that "slave" must be idle. With more than two
2542 // threads, this is not by itself sufficient: If "slave" is the master of
2543 // some active split point, it is only available as a slave to the other
2544 // threads which are busy searching the split point at the top of "slave"'s
2545 // split point stack (the "helpful master concept" in YBWC terminology).
2547 bool ThreadsManager::thread_is_available(int slave, int master) const {
2549 assert(slave >= 0 && slave < ActiveThreads);
2550 assert(master >= 0 && master < ActiveThreads);
2551 assert(ActiveThreads > 1);
2553 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2556 // Make a local copy to be sure doesn't change under our feet
2557 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2559 if (localActiveSplitPoints == 0)
2560 // No active split points means that the thread is available as
2561 // a slave for any other thread.
2564 if (ActiveThreads == 2)
2567 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2568 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2569 // could have been set to 0 by another thread leading to an out of bound access.
2570 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2577 // available_thread_exists() tries to find an idle thread which is available as
2578 // a slave for the thread with threadID "master".
2580 bool ThreadsManager::available_thread_exists(int master) const {
2582 assert(master >= 0 && master < ActiveThreads);
2583 assert(ActiveThreads > 1);
2585 for (int i = 0; i < ActiveThreads; i++)
2586 if (thread_is_available(i, master))
2593 // split() does the actual work of distributing the work at a node between
2594 // several available threads. If it does not succeed in splitting the
2595 // node (because no idle threads are available, or because we have no unused
2596 // split point objects), the function immediately returns. If splitting is
2597 // possible, a SplitPoint object is initialized with all the data that must be
2598 // copied to the helper threads and we tell our helper threads that they have
2599 // been assigned work. This will cause them to instantly leave their idle loops
2600 // and call sp_search(). When all threads have returned from sp_search() then
2603 template <bool Fake>
2604 void ThreadsManager::split(const Position& p, SearchStack* sstck, int ply, Value* alpha,
2605 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2606 int* moveCount, MovePicker* mp, int master, bool pvNode) {
2608 assert(sstck != NULL);
2609 assert(ply >= 0 && ply < PLY_MAX);
2610 assert(*bestValue >= -VALUE_INFINITE);
2611 assert(*bestValue <= *alpha);
2612 assert(*alpha < beta);
2613 assert(beta <= VALUE_INFINITE);
2614 assert(depth > Depth(0));
2615 assert(master >= 0 && master < ActiveThreads);
2616 assert(ActiveThreads > 1);
2620 // If no other thread is available to help us, or if we have too many
2621 // active split points, don't split.
2622 if ( !available_thread_exists(master)
2623 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2625 lock_release(&MPLock);
2629 // Pick the next available split point object from the split point stack
2630 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2632 // Initialize the split point object
2633 splitPoint->parent = threads[master].splitPoint;
2634 splitPoint->stopRequest = false;
2635 splitPoint->ply = ply;
2636 splitPoint->depth = depth;
2637 splitPoint->mateThreat = mateThreat;
2638 splitPoint->alpha = *alpha;
2639 splitPoint->beta = beta;
2640 splitPoint->pvNode = pvNode;
2641 splitPoint->bestValue = *bestValue;
2642 splitPoint->mp = mp;
2643 splitPoint->moveCount = *moveCount;
2644 splitPoint->pos = &p;
2645 splitPoint->parentSstack = sstck;
2646 for (int i = 0; i < ActiveThreads; i++)
2647 splitPoint->slaves[i] = 0;
2649 threads[master].splitPoint = splitPoint;
2650 threads[master].activeSplitPoints++;
2652 // If we are here it means we are not available
2653 assert(threads[master].state != THREAD_AVAILABLE);
2655 int workersCnt = 1; // At least the master is included
2657 // Allocate available threads setting state to THREAD_BOOKED
2658 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2659 if (thread_is_available(i, master))
2661 threads[i].state = THREAD_BOOKED;
2662 threads[i].splitPoint = splitPoint;
2663 splitPoint->slaves[i] = 1;
2667 assert(Fake || workersCnt > 1);
2669 // We can release the lock because slave threads are already booked and master is not available
2670 lock_release(&MPLock);
2672 // Tell the threads that they have work to do. This will make them leave
2673 // their idle loop. But before copy search stack tail for each thread.
2674 for (int i = 0; i < ActiveThreads; i++)
2675 if (i == master || splitPoint->slaves[i])
2677 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2679 assert(i == master || threads[i].state == THREAD_BOOKED);
2681 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2684 // Everything is set up. The master thread enters the idle loop, from
2685 // which it will instantly launch a search, because its state is
2686 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2687 // idle loop, which means that the main thread will return from the idle
2688 // loop when all threads have finished their work at this split point.
2689 idle_loop(master, splitPoint);
2691 // We have returned from the idle loop, which means that all threads are
2692 // finished. Update alpha and bestValue, and return.
2695 *alpha = splitPoint->alpha;
2696 *bestValue = splitPoint->bestValue;
2697 threads[master].activeSplitPoints--;
2698 threads[master].splitPoint = splitPoint->parent;
2700 lock_release(&MPLock);
2704 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2705 // to start a new search from the root.
2707 void ThreadsManager::wake_sleeping_threads() {
2709 assert(AllThreadsShouldSleep);
2710 assert(ActiveThreads > 0);
2712 AllThreadsShouldSleep = false;
2714 if (ActiveThreads == 1)
2717 #if !defined(_MSC_VER)
2718 pthread_mutex_lock(&WaitLock);
2719 pthread_cond_broadcast(&WaitCond);
2720 pthread_mutex_unlock(&WaitLock);
2722 for (int i = 1; i < MAX_THREADS; i++)
2723 SetEvent(SitIdleEvent[i]);
2729 // put_threads_to_sleep() makes all the threads go to sleep just before
2730 // to leave think(), at the end of the search. Threads should have already
2731 // finished the job and should be idle.
2733 void ThreadsManager::put_threads_to_sleep() {
2735 assert(!AllThreadsShouldSleep);
2737 // This makes the threads to go to sleep
2738 AllThreadsShouldSleep = true;
2741 /// The RootMoveList class
2743 // RootMoveList c'tor
2745 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2747 SearchStack ss[PLY_MAX_PLUS_2];
2748 MoveStack mlist[MaxRootMoves];
2750 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2752 // Generate all legal moves
2753 MoveStack* last = generate_moves(pos, mlist);
2755 // Add each move to the moves[] array
2756 for (MoveStack* cur = mlist; cur != last; cur++)
2758 bool includeMove = includeAllMoves;
2760 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2761 includeMove = (searchMoves[k] == cur->move);
2766 // Find a quick score for the move
2768 pos.do_move(cur->move, st);
2769 moves[count].move = cur->move;
2770 moves[count].score = -qsearch<PV>(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2771 moves[count].pv[0] = cur->move;
2772 moves[count].pv[1] = MOVE_NONE;
2773 pos.undo_move(cur->move);
2780 // RootMoveList simple methods definitions
2782 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2784 moves[moveNum].nodes = nodes;
2785 moves[moveNum].cumulativeNodes += nodes;
2788 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2790 moves[moveNum].ourBeta = our;
2791 moves[moveNum].theirBeta = their;
2794 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2798 for (j = 0; pv[j] != MOVE_NONE; j++)
2799 moves[moveNum].pv[j] = pv[j];
2801 moves[moveNum].pv[j] = MOVE_NONE;
2805 // RootMoveList::sort() sorts the root move list at the beginning of a new
2808 void RootMoveList::sort() {
2810 sort_multipv(count - 1); // Sort all items
2814 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2815 // list by their scores and depths. It is used to order the different PVs
2816 // correctly in MultiPV mode.
2818 void RootMoveList::sort_multipv(int n) {
2822 for (i = 1; i <= n; i++)
2824 RootMove rm = moves[i];
2825 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2826 moves[j] = moves[j - 1];