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 bigger then beta - IIDMargin.
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, 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->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->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->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->pv[0] == MOVE_NONE)
750 ss->pv[0] = rml.get_move(0);
751 ss->pv[1] = MOVE_NONE;
754 assert(ss->pv[0] != MOVE_NONE);
756 cout << "bestmove " << ss->pv[0];
758 if (ss->pv[1] != MOVE_NONE)
759 cout << " ponder " << ss->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->pv[0]);
776 p.do_move(ss->pv[0], st);
777 LogFile << "\nPonder move: "
778 << move_to_san(p, ss->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->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->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+1, -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->reduction = reduction<PV>(depth, i - MultiPV + 2);
896 // Reduced depth non-pv search using alpha as upperbound
897 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->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->reduction = Depth(0);
907 value = -search<NonPV>(pos, ss+1, -(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+1, -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->pv, PLY_MAX);
928 rml.set_move_pv(i, ss->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->pv, PLY_MAX);
968 rml.set_move_pv(i, ss->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->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->eval = tte->static_value();
1112 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1115 ss->eval = evaluate(pos, ei, threadID);
1117 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1118 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1121 // Step 6. Razoring (is omitted in PV nodes)
1123 && refinedValue < beta - razor_margin(depth)
1124 && ttMove == MOVE_NONE
1125 && (ss-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->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+1, -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->threatMove = (ss+1)->currentMove;
1202 if ( depth < ThreatDepth
1203 && (ss-1)->reduction
1204 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1209 // Step 9. Internal iterative deepening
1210 if ( depth >= IIDDepth[PvNode]
1211 && (ttMove == MOVE_NONE || (PvNode && tte->depth() <= depth - 4 * OnePly))
1212 && (PvNode || (!isCheck && ss->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->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, (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->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->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->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+1, -beta, -alpha, newDepth, ply+1, false, threadID);
1312 // Step 14. Reduced depth search
1313 // If the move fails high will be re-searched at full depth.
1314 bool doFullDepthSearch = true;
1316 if ( depth >= 3 * OnePly
1318 && !captureOrPromotion
1319 && !move_is_castle(move)
1320 && !move_is_killer(move, ss))
1322 ss->reduction = reduction<PvNode>(depth, moveCount);
1325 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1, true, threadID);
1326 doFullDepthSearch = (value > alpha);
1329 // The move failed high, but if reduction is very big we could
1330 // face a false positive, retry with a less aggressive reduction,
1331 // if the move fails high again then go with full depth search.
1332 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1334 ss->reduction = OnePly;
1335 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1, true, threadID);
1336 doFullDepthSearch = (value > alpha);
1340 // Step 15. Full depth search
1341 if (doFullDepthSearch)
1343 ss->reduction = Depth(0);
1344 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1, true, threadID);
1346 // Step extra. pv search (only in PV nodes)
1347 // Search only for possible new PV nodes, if instead value >= beta then
1348 // parent node fails low with value <= alpha and tries another move.
1349 if (PvNode && value > alpha && value < beta)
1350 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1, false, threadID);
1354 // Step 16. Undo move
1355 pos.undo_move(move);
1357 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1359 // Step 17. Check for new best move
1360 if (value > bestValue)
1365 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1370 if (value == value_mate_in(ply + 1))
1371 ss->mateKiller = move;
1375 // Step 18. Check for split
1376 if ( TM.active_threads() > 1
1378 && depth >= MinimumSplitDepth
1380 && TM.available_thread_exists(threadID)
1382 && !TM.thread_should_stop(threadID))
1383 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1384 mateThreat, &moveCount, &mp, threadID, PvNode);
1387 // Step 19. Check for mate and stalemate
1388 // All legal moves have been searched and if there are
1389 // no legal moves, it must be mate or stalemate.
1390 // If one move was excluded return fail low score.
1392 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1394 // Step 20. Update tables
1395 // If the search is not aborted, update the transposition table,
1396 // history counters, and killer moves.
1397 if (AbortSearch || TM.thread_should_stop(threadID))
1400 if (bestValue <= oldAlpha)
1401 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1403 else if (bestValue >= beta)
1405 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1407 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1408 if (!pos.move_is_capture_or_promotion(move))
1410 update_history(pos, move, depth, movesSearched, moveCount);
1411 update_killers(move, ss);
1415 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1417 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1423 // qsearch() is the quiescence search function, which is called by the main
1424 // search function when the remaining depth is zero (or, to be more precise,
1425 // less than OnePly).
1427 template <NodeType PvNode>
1428 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta,
1429 Depth depth, int ply, int threadID) {
1431 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1432 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1433 assert(PvNode || alpha == beta - 1);
1435 assert(ply >= 0 && ply < PLY_MAX);
1436 assert(threadID >= 0 && threadID < TM.active_threads());
1441 Value staticValue, bestValue, value, futilityBase, futilityValue;
1442 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1443 const TTEntry* tte = NULL;
1445 Value oldAlpha = alpha;
1447 // Initialize, and make an early exit in case of an aborted search,
1448 // an instant draw, maximum ply reached, etc.
1449 init_node(ss, ply, threadID);
1451 // After init_node() that calls poll()
1452 if (AbortSearch || TM.thread_should_stop(threadID))
1455 if (pos.is_draw() || ply >= PLY_MAX - 1)
1458 // Transposition table lookup. At PV nodes, we don't use the TT for
1459 // pruning, but only for move ordering.
1460 tte = TT.retrieve(pos.get_key());
1461 ttMove = (tte ? tte->move() : MOVE_NONE);
1463 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1465 ss->currentMove = ttMove; // Can be MOVE_NONE
1466 return value_from_tt(tte->value(), ply);
1469 isCheck = pos.is_check();
1471 // Evaluate the position statically
1473 staticValue = -VALUE_INFINITE;
1474 else if (tte && tte->static_value() != VALUE_NONE)
1476 staticValue = tte->static_value();
1477 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1480 staticValue = evaluate(pos, ei, threadID);
1484 ss->eval = staticValue;
1485 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1488 // Initialize "stand pat score", and return it immediately if it is
1490 bestValue = staticValue;
1492 if (bestValue >= beta)
1494 // Store the score to avoid a future costly evaluation() call
1495 if (!isCheck && !tte)
1496 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1501 if (bestValue > alpha)
1504 // If we are near beta then try to get a cutoff pushing checks a bit further
1505 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1507 // Initialize a MovePicker object for the current position, and prepare
1508 // to search the moves. Because the depth is <= 0 here, only captures,
1509 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1510 // and we are near beta) will be generated.
1511 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1513 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1514 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1516 // Loop through the moves until no moves remain or a beta cutoff occurs
1517 while ( alpha < beta
1518 && (move = mp.get_next_move()) != MOVE_NONE)
1520 assert(move_is_ok(move));
1522 moveIsCheck = pos.move_is_check(move, ci);
1524 // Update current move
1526 ss->currentMove = move;
1534 && !move_is_promotion(move)
1535 && !pos.move_is_passed_pawn_push(move))
1537 futilityValue = futilityBase
1538 + pos.endgame_value_of_piece_on(move_to(move))
1539 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1541 if (futilityValue < alpha)
1543 if (futilityValue > bestValue)
1544 bestValue = futilityValue;
1549 // Detect blocking evasions that are candidate to be pruned
1550 evasionPrunable = isCheck
1551 && bestValue > value_mated_in(PLY_MAX)
1552 && !pos.move_is_capture(move)
1553 && pos.type_of_piece_on(move_from(move)) != KING
1554 && !pos.can_castle(pos.side_to_move());
1556 // Don't search moves with negative SEE values
1558 && (!isCheck || evasionPrunable)
1560 && !move_is_promotion(move)
1561 && pos.see_sign(move) < 0)
1564 // Make and search the move
1565 pos.do_move(move, st, ci, moveIsCheck);
1566 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1, threadID);
1567 pos.undo_move(move);
1569 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1572 if (value > bestValue)
1583 // All legal moves have been searched. A special case: If we're in check
1584 // and no legal moves were found, it is checkmate.
1585 if (!moveCount && isCheck) // Mate!
1586 return value_mated_in(ply);
1588 // Update transposition table
1589 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1590 if (bestValue <= oldAlpha)
1592 // If bestValue isn't changed it means it is still the static evaluation
1593 // of the node, so keep this info to avoid a future evaluation() call.
1594 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1596 else if (bestValue >= beta)
1599 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1601 // Update killers only for good checking moves
1602 if (!pos.move_is_capture_or_promotion(move))
1603 update_killers(move, ss);
1606 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1608 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1614 // sp_search() is used to search from a split point. This function is called
1615 // by each thread working at the split point. It is similar to the normal
1616 // search() function, but simpler. Because we have already probed the hash
1617 // table, done a null move search, and searched the first move before
1618 // splitting, we don't have to repeat all this work in sp_search(). We
1619 // also don't need to store anything to the hash table here: This is taken
1620 // care of after we return from the split point.
1622 template <NodeType PvNode>
1623 void sp_search(SplitPoint* sp, int threadID) {
1625 assert(threadID >= 0 && threadID < TM.active_threads());
1626 assert(TM.active_threads() > 1);
1630 Depth ext, newDepth;
1632 Value futilityValueScaled; // NonPV specific
1633 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1635 value = -VALUE_INFINITE;
1637 Position pos(*sp->pos);
1639 SearchStack* ss = sp->sstack[threadID] + 1;
1640 isCheck = pos.is_check();
1642 // Step 10. Loop through moves
1643 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1644 lock_grab(&(sp->lock));
1646 while ( sp->bestValue < sp->beta
1647 && (move = sp->mp->get_next_move()) != MOVE_NONE
1648 && !TM.thread_should_stop(threadID))
1650 moveCount = ++sp->moveCount;
1651 lock_release(&(sp->lock));
1653 assert(move_is_ok(move));
1655 moveIsCheck = pos.move_is_check(move, ci);
1656 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1658 // Step 11. Decide the new search depth
1659 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1660 newDepth = sp->depth - OnePly + ext;
1662 // Update current move
1663 ss->currentMove = move;
1665 // Step 12. Futility pruning (is omitted in PV nodes)
1669 && !captureOrPromotion
1670 && !move_is_castle(move))
1672 // Move count based pruning
1673 if ( moveCount >= futility_move_count(sp->depth)
1674 && ok_to_prune(pos, move, ss->threatMove)
1675 && sp->bestValue > value_mated_in(PLY_MAX))
1677 lock_grab(&(sp->lock));
1681 // Value based pruning
1682 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1683 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1684 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1686 if (futilityValueScaled < sp->beta)
1688 lock_grab(&(sp->lock));
1690 if (futilityValueScaled > sp->bestValue)
1691 sp->bestValue = futilityValueScaled;
1696 // Step 13. Make the move
1697 pos.do_move(move, st, ci, moveIsCheck);
1699 // Step 14. Reduced search
1700 // If the move fails high will be re-searched at full depth.
1701 bool doFullDepthSearch = true;
1704 && !captureOrPromotion
1705 && !move_is_castle(move)
1706 && !move_is_killer(move, ss))
1708 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1711 Value localAlpha = sp->alpha;
1712 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1, true, threadID);
1713 doFullDepthSearch = (value > localAlpha);
1716 // The move failed high, but if reduction is very big we could
1717 // face a false positive, retry with a less aggressive reduction,
1718 // if the move fails high again then go with full depth search.
1719 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1721 ss->reduction = OnePly;
1722 Value localAlpha = sp->alpha;
1723 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1, true, threadID);
1724 doFullDepthSearch = (value > localAlpha);
1728 // Step 15. Full depth search
1729 if (doFullDepthSearch)
1731 ss->reduction = Depth(0);
1732 Value localAlpha = sp->alpha;
1733 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1, true, threadID);
1735 if (PvNode && value > localAlpha && value < sp->beta)
1736 value = -search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1, false, threadID);
1739 // Step 16. Undo move
1740 pos.undo_move(move);
1742 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1744 // Step 17. Check for new best move
1745 lock_grab(&(sp->lock));
1747 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1749 sp->bestValue = value;
1751 if (sp->bestValue > sp->alpha)
1753 if (!PvNode || value >= sp->beta)
1754 sp->stopRequest = true;
1756 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1759 sp_update_pv(sp->parentSstack, ss, sp->ply);
1764 /* Here we have the lock still grabbed */
1766 sp->slaves[threadID] = 0;
1768 lock_release(&(sp->lock));
1771 // init_node() is called at the beginning of all the search functions
1772 // (search() qsearch(), and so on) and initializes the
1773 // search stack object corresponding to the current node. Once every
1774 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1775 // for user input and checks whether it is time to stop the search.
1777 void init_node(SearchStack* ss, int ply, int threadID) {
1779 assert(ply >= 0 && ply < PLY_MAX);
1780 assert(threadID >= 0 && threadID < TM.active_threads());
1782 TM.incrementNodeCounter(threadID);
1787 if (NodesSincePoll >= NodesBetweenPolls)
1794 (ss + 2)->initKillers();
1797 // update_pv() is called whenever a search returns a value > alpha.
1798 // It updates the PV in the SearchStack object corresponding to the
1801 void update_pv(SearchStack* ss, int ply) {
1803 assert(ply >= 0 && ply < PLY_MAX);
1807 ss->pv[ply] = ss->currentMove;
1809 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1810 ss->pv[p] = (ss+1)->pv[p];
1812 ss->pv[p] = MOVE_NONE;
1816 // sp_update_pv() is a variant of update_pv for use at split points. The
1817 // difference between the two functions is that sp_update_pv also updates
1818 // the PV at the parent node.
1820 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply) {
1822 assert(ply >= 0 && ply < PLY_MAX);
1826 ss->pv[ply] = pss->pv[ply] = ss->currentMove;
1828 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1829 ss->pv[p] = pss->pv[p] = (ss+1)->pv[p];
1831 ss->pv[p] = pss->pv[p] = MOVE_NONE;
1835 // connected_moves() tests whether two moves are 'connected' in the sense
1836 // that the first move somehow made the second move possible (for instance
1837 // if the moving piece is the same in both moves). The first move is assumed
1838 // to be the move that was made to reach the current position, while the
1839 // second move is assumed to be a move from the current position.
1841 bool connected_moves(const Position& pos, Move m1, Move m2) {
1843 Square f1, t1, f2, t2;
1846 assert(move_is_ok(m1));
1847 assert(move_is_ok(m2));
1849 if (m2 == MOVE_NONE)
1852 // Case 1: The moving piece is the same in both moves
1858 // Case 2: The destination square for m2 was vacated by m1
1864 // Case 3: Moving through the vacated square
1865 if ( piece_is_slider(pos.piece_on(f2))
1866 && bit_is_set(squares_between(f2, t2), f1))
1869 // Case 4: The destination square for m2 is defended by the moving piece in m1
1870 p = pos.piece_on(t1);
1871 if (bit_is_set(pos.attacks_from(p, t1), t2))
1874 // Case 5: Discovered check, checking piece is the piece moved in m1
1875 if ( piece_is_slider(p)
1876 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1877 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1879 // discovered_check_candidates() works also if the Position's side to
1880 // move is the opposite of the checking piece.
1881 Color them = opposite_color(pos.side_to_move());
1882 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1884 if (bit_is_set(dcCandidates, f2))
1891 // value_is_mate() checks if the given value is a mate one
1892 // eventually compensated for the ply.
1894 bool value_is_mate(Value value) {
1896 assert(abs(value) <= VALUE_INFINITE);
1898 return value <= value_mated_in(PLY_MAX)
1899 || value >= value_mate_in(PLY_MAX);
1903 // move_is_killer() checks if the given move is among the
1904 // killer moves of that ply.
1906 bool move_is_killer(Move m, SearchStack* ss) {
1908 const Move* k = ss->killers;
1909 for (int i = 0; i < KILLER_MAX; i++, k++)
1917 // extension() decides whether a move should be searched with normal depth,
1918 // or with extended depth. Certain classes of moves (checking moves, in
1919 // particular) are searched with bigger depth than ordinary moves and in
1920 // any case are marked as 'dangerous'. Note that also if a move is not
1921 // extended, as example because the corresponding UCI option is set to zero,
1922 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1923 template <NodeType PvNode>
1924 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1925 bool singleEvasion, bool mateThreat, bool* dangerous) {
1927 assert(m != MOVE_NONE);
1929 Depth result = Depth(0);
1930 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1935 result += CheckExtension[PvNode];
1938 result += SingleEvasionExtension[PvNode];
1941 result += MateThreatExtension[PvNode];
1944 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1946 Color c = pos.side_to_move();
1947 if (relative_rank(c, move_to(m)) == RANK_7)
1949 result += PawnPushTo7thExtension[PvNode];
1952 if (pos.pawn_is_passed(c, move_to(m)))
1954 result += PassedPawnExtension[PvNode];
1959 if ( captureOrPromotion
1960 && pos.type_of_piece_on(move_to(m)) != PAWN
1961 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1962 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1963 && !move_is_promotion(m)
1966 result += PawnEndgameExtension[PvNode];
1971 && captureOrPromotion
1972 && pos.type_of_piece_on(move_to(m)) != PAWN
1973 && pos.see_sign(m) >= 0)
1979 return Min(result, OnePly);
1983 // ok_to_do_nullmove() looks at the current position and decides whether
1984 // doing a 'null move' should be allowed. In order to avoid zugzwang
1985 // problems, null moves are not allowed when the side to move has very
1986 // little material left. Currently, the test is a bit too simple: Null
1987 // moves are avoided only when the side to move has only pawns left.
1988 // It's probably a good idea to avoid null moves in at least some more
1989 // complicated endgames, e.g. KQ vs KR. FIXME
1991 bool ok_to_do_nullmove(const Position& pos) {
1993 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
1997 // ok_to_prune() tests whether it is safe to forward prune a move. Only
1998 // non-tactical moves late in the move list close to the leaves are
1999 // candidates for pruning.
2001 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2003 assert(move_is_ok(m));
2004 assert(threat == MOVE_NONE || move_is_ok(threat));
2005 assert(!pos.move_is_check(m));
2006 assert(!pos.move_is_capture_or_promotion(m));
2007 assert(!pos.move_is_passed_pawn_push(m));
2009 Square mfrom, mto, tfrom, tto;
2011 // Prune if there isn't any threat move
2012 if (threat == MOVE_NONE)
2015 mfrom = move_from(m);
2017 tfrom = move_from(threat);
2018 tto = move_to(threat);
2020 // Case 1: Don't prune moves which move the threatened piece
2024 // Case 2: If the threatened piece has value less than or equal to the
2025 // value of the threatening piece, don't prune move which defend it.
2026 if ( pos.move_is_capture(threat)
2027 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2028 || pos.type_of_piece_on(tfrom) == KING)
2029 && pos.move_attacks_square(m, tto))
2032 // Case 3: If the moving piece in the threatened move is a slider, don't
2033 // prune safe moves which block its ray.
2034 if ( piece_is_slider(pos.piece_on(tfrom))
2035 && bit_is_set(squares_between(tfrom, tto), mto)
2036 && pos.see_sign(m) >= 0)
2043 // ok_to_use_TT() returns true if a transposition table score
2044 // can be used at a given point in search.
2046 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2048 Value v = value_from_tt(tte->value(), ply);
2050 return ( tte->depth() >= depth
2051 || v >= Max(value_mate_in(PLY_MAX), beta)
2052 || v < Min(value_mated_in(PLY_MAX), beta))
2054 && ( (is_lower_bound(tte->type()) && v >= beta)
2055 || (is_upper_bound(tte->type()) && v < beta));
2059 // refine_eval() returns the transposition table score if
2060 // possible otherwise falls back on static position evaluation.
2062 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2067 Value v = value_from_tt(tte->value(), ply);
2069 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2070 || (is_upper_bound(tte->type()) && v < defaultEval))
2077 // update_history() registers a good move that produced a beta-cutoff
2078 // in history and marks as failures all the other moves of that ply.
2080 void update_history(const Position& pos, Move move, Depth depth,
2081 Move movesSearched[], int moveCount) {
2085 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2087 for (int i = 0; i < moveCount - 1; i++)
2089 m = movesSearched[i];
2093 if (!pos.move_is_capture_or_promotion(m))
2094 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2099 // update_killers() add a good move that produced a beta-cutoff
2100 // among the killer moves of that ply.
2102 void update_killers(Move m, SearchStack* ss) {
2104 if (m == ss->killers[0])
2107 for (int i = KILLER_MAX - 1; i > 0; i--)
2108 ss->killers[i] = ss->killers[i - 1];
2114 // update_gains() updates the gains table of a non-capture move given
2115 // the static position evaluation before and after the move.
2117 void update_gains(const Position& pos, Move m, Value before, Value after) {
2120 && before != VALUE_NONE
2121 && after != VALUE_NONE
2122 && pos.captured_piece() == NO_PIECE_TYPE
2123 && !move_is_castle(m)
2124 && !move_is_promotion(m))
2125 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2129 // current_search_time() returns the number of milliseconds which have passed
2130 // since the beginning of the current search.
2132 int current_search_time() {
2134 return get_system_time() - SearchStartTime;
2138 // nps() computes the current nodes/second count.
2142 int t = current_search_time();
2143 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2147 // poll() performs two different functions: It polls for user input, and it
2148 // looks at the time consumed so far and decides if it's time to abort the
2153 static int lastInfoTime;
2154 int t = current_search_time();
2159 // We are line oriented, don't read single chars
2160 std::string command;
2162 if (!std::getline(std::cin, command))
2165 if (command == "quit")
2168 PonderSearch = false;
2172 else if (command == "stop")
2175 PonderSearch = false;
2177 else if (command == "ponderhit")
2181 // Print search information
2185 else if (lastInfoTime > t)
2186 // HACK: Must be a new search where we searched less than
2187 // NodesBetweenPolls nodes during the first second of search.
2190 else if (t - lastInfoTime >= 1000)
2197 if (dbg_show_hit_rate)
2198 dbg_print_hit_rate();
2200 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2201 << " time " << t << " hashfull " << TT.full() << endl;
2204 // Should we stop the search?
2208 bool stillAtFirstMove = FirstRootMove
2209 && !AspirationFailLow
2210 && t > MaxSearchTime + ExtraSearchTime;
2212 bool noMoreTime = t > AbsoluteMaxSearchTime
2213 || stillAtFirstMove;
2215 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2216 || (ExactMaxTime && t >= ExactMaxTime)
2217 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2222 // ponderhit() is called when the program is pondering (i.e. thinking while
2223 // it's the opponent's turn to move) in order to let the engine know that
2224 // it correctly predicted the opponent's move.
2228 int t = current_search_time();
2229 PonderSearch = false;
2231 bool stillAtFirstMove = FirstRootMove
2232 && !AspirationFailLow
2233 && t > MaxSearchTime + ExtraSearchTime;
2235 bool noMoreTime = t > AbsoluteMaxSearchTime
2236 || stillAtFirstMove;
2238 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2243 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2245 void init_ss_array(SearchStack* ss) {
2247 for (int i = 0; i < 3; i++, ss++)
2255 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2256 // while the program is pondering. The point is to work around a wrinkle in
2257 // the UCI protocol: When pondering, the engine is not allowed to give a
2258 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2259 // We simply wait here until one of these commands is sent, and return,
2260 // after which the bestmove and pondermove will be printed (in id_loop()).
2262 void wait_for_stop_or_ponderhit() {
2264 std::string command;
2268 if (!std::getline(std::cin, command))
2271 if (command == "quit")
2276 else if (command == "ponderhit" || command == "stop")
2282 // print_pv_info() prints to standard output and eventually to log file information on
2283 // the current PV line. It is called at each iteration or after a new pv is found.
2285 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2287 cout << "info depth " << Iteration
2288 << " score " << value_to_string(value)
2289 << ((value >= beta) ? " lowerbound" :
2290 ((value <= alpha)? " upperbound" : ""))
2291 << " time " << current_search_time()
2292 << " nodes " << TM.nodes_searched()
2296 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2297 cout << ss->pv[j] << " ";
2303 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2304 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2306 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2307 TM.nodes_searched(), value, type, ss->pv) << endl;
2312 // init_thread() is the function which is called when a new thread is
2313 // launched. It simply calls the idle_loop() function with the supplied
2314 // threadID. There are two versions of this function; one for POSIX
2315 // threads and one for Windows threads.
2317 #if !defined(_MSC_VER)
2319 void* init_thread(void *threadID) {
2321 TM.idle_loop(*(int*)threadID, NULL);
2327 DWORD WINAPI init_thread(LPVOID threadID) {
2329 TM.idle_loop(*(int*)threadID, NULL);
2336 /// The ThreadsManager class
2338 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2339 // get_beta_counters() are getters/setters for the per thread
2340 // counters used to sort the moves at root.
2342 void ThreadsManager::resetNodeCounters() {
2344 for (int i = 0; i < MAX_THREADS; i++)
2345 threads[i].nodes = 0ULL;
2348 void ThreadsManager::resetBetaCounters() {
2350 for (int i = 0; i < MAX_THREADS; i++)
2351 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2354 int64_t ThreadsManager::nodes_searched() const {
2356 int64_t result = 0ULL;
2357 for (int i = 0; i < ActiveThreads; i++)
2358 result += threads[i].nodes;
2363 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2366 for (int i = 0; i < MAX_THREADS; i++)
2368 our += threads[i].betaCutOffs[us];
2369 their += threads[i].betaCutOffs[opposite_color(us)];
2374 // idle_loop() is where the threads are parked when they have no work to do.
2375 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2376 // object for which the current thread is the master.
2378 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2380 assert(threadID >= 0 && threadID < MAX_THREADS);
2384 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2385 // master should exit as last one.
2386 if (AllThreadsShouldExit)
2389 threads[threadID].state = THREAD_TERMINATED;
2393 // If we are not thinking, wait for a condition to be signaled
2394 // instead of wasting CPU time polling for work.
2395 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2398 assert(threadID != 0);
2399 threads[threadID].state = THREAD_SLEEPING;
2401 #if !defined(_MSC_VER)
2402 lock_grab(&WaitLock);
2403 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2404 pthread_cond_wait(&WaitCond, &WaitLock);
2405 lock_release(&WaitLock);
2407 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2411 // If thread has just woken up, mark it as available
2412 if (threads[threadID].state == THREAD_SLEEPING)
2413 threads[threadID].state = THREAD_AVAILABLE;
2415 // If this thread has been assigned work, launch a search
2416 if (threads[threadID].state == THREAD_WORKISWAITING)
2418 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2420 threads[threadID].state = THREAD_SEARCHING;
2422 if (threads[threadID].splitPoint->pvNode)
2423 sp_search<PV>(threads[threadID].splitPoint, threadID);
2425 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2427 assert(threads[threadID].state == THREAD_SEARCHING);
2429 threads[threadID].state = THREAD_AVAILABLE;
2432 // If this thread is the master of a split point and all slaves have
2433 // finished their work at this split point, return from the idle loop.
2435 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2437 if (i == ActiveThreads)
2439 // Because sp->slaves[] is reset under lock protection,
2440 // be sure sp->lock has been released before to return.
2441 lock_grab(&(sp->lock));
2442 lock_release(&(sp->lock));
2444 assert(threads[threadID].state == THREAD_AVAILABLE);
2446 threads[threadID].state = THREAD_SEARCHING;
2453 // init_threads() is called during startup. It launches all helper threads,
2454 // and initializes the split point stack and the global locks and condition
2457 void ThreadsManager::init_threads() {
2462 #if !defined(_MSC_VER)
2463 pthread_t pthread[1];
2466 // Initialize global locks
2467 lock_init(&MPLock, NULL);
2468 lock_init(&WaitLock, NULL);
2470 #if !defined(_MSC_VER)
2471 pthread_cond_init(&WaitCond, NULL);
2473 for (i = 0; i < MAX_THREADS; i++)
2474 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2477 // Initialize SplitPointStack locks
2478 for (i = 0; i < MAX_THREADS; i++)
2479 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2481 SplitPointStack[i][j].parent = NULL;
2482 lock_init(&(SplitPointStack[i][j].lock), NULL);
2485 // Will be set just before program exits to properly end the threads
2486 AllThreadsShouldExit = false;
2488 // Threads will be put to sleep as soon as created
2489 AllThreadsShouldSleep = true;
2491 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2493 threads[0].state = THREAD_SEARCHING;
2494 for (i = 1; i < MAX_THREADS; i++)
2495 threads[i].state = THREAD_AVAILABLE;
2497 // Launch the helper threads
2498 for (i = 1; i < MAX_THREADS; i++)
2501 #if !defined(_MSC_VER)
2502 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2504 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2509 cout << "Failed to create thread number " << i << endl;
2510 Application::exit_with_failure();
2513 // Wait until the thread has finished launching and is gone to sleep
2514 while (threads[i].state != THREAD_SLEEPING) {}
2519 // exit_threads() is called when the program exits. It makes all the
2520 // helper threads exit cleanly.
2522 void ThreadsManager::exit_threads() {
2524 ActiveThreads = MAX_THREADS; // HACK
2525 AllThreadsShouldSleep = true; // HACK
2526 wake_sleeping_threads();
2528 // This makes the threads to exit idle_loop()
2529 AllThreadsShouldExit = true;
2531 // Wait for thread termination
2532 for (int i = 1; i < MAX_THREADS; i++)
2533 while (threads[i].state != THREAD_TERMINATED);
2535 // Now we can safely destroy the locks
2536 for (int i = 0; i < MAX_THREADS; i++)
2537 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2538 lock_destroy(&(SplitPointStack[i][j].lock));
2540 lock_destroy(&WaitLock);
2541 lock_destroy(&MPLock);
2545 // thread_should_stop() checks whether the thread should stop its search.
2546 // This can happen if a beta cutoff has occurred in the thread's currently
2547 // active split point, or in some ancestor of the current split point.
2549 bool ThreadsManager::thread_should_stop(int threadID) const {
2551 assert(threadID >= 0 && threadID < ActiveThreads);
2555 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2560 // thread_is_available() checks whether the thread with threadID "slave" is
2561 // available to help the thread with threadID "master" at a split point. An
2562 // obvious requirement is that "slave" must be idle. With more than two
2563 // threads, this is not by itself sufficient: If "slave" is the master of
2564 // some active split point, it is only available as a slave to the other
2565 // threads which are busy searching the split point at the top of "slave"'s
2566 // split point stack (the "helpful master concept" in YBWC terminology).
2568 bool ThreadsManager::thread_is_available(int slave, int master) const {
2570 assert(slave >= 0 && slave < ActiveThreads);
2571 assert(master >= 0 && master < ActiveThreads);
2572 assert(ActiveThreads > 1);
2574 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2577 // Make a local copy to be sure doesn't change under our feet
2578 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2580 if (localActiveSplitPoints == 0)
2581 // No active split points means that the thread is available as
2582 // a slave for any other thread.
2585 if (ActiveThreads == 2)
2588 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2589 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2590 // could have been set to 0 by another thread leading to an out of bound access.
2591 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2598 // available_thread_exists() tries to find an idle thread which is available as
2599 // a slave for the thread with threadID "master".
2601 bool ThreadsManager::available_thread_exists(int master) const {
2603 assert(master >= 0 && master < ActiveThreads);
2604 assert(ActiveThreads > 1);
2606 for (int i = 0; i < ActiveThreads; i++)
2607 if (thread_is_available(i, master))
2614 // split() does the actual work of distributing the work at a node between
2615 // several available threads. If it does not succeed in splitting the
2616 // node (because no idle threads are available, or because we have no unused
2617 // split point objects), the function immediately returns. If splitting is
2618 // possible, a SplitPoint object is initialized with all the data that must be
2619 // copied to the helper threads and we tell our helper threads that they have
2620 // been assigned work. This will cause them to instantly leave their idle loops
2621 // and call sp_search(). When all threads have returned from sp_search() then
2624 template <bool Fake>
2625 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2626 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2627 int* moveCount, MovePicker* mp, int master, bool pvNode) {
2629 assert(ply > 0 && ply < PLY_MAX);
2630 assert(*bestValue >= -VALUE_INFINITE);
2631 assert(*bestValue <= *alpha);
2632 assert(*alpha < beta);
2633 assert(beta <= VALUE_INFINITE);
2634 assert(depth > Depth(0));
2635 assert(master >= 0 && master < ActiveThreads);
2636 assert(ActiveThreads > 1);
2640 // If no other thread is available to help us, or if we have too many
2641 // active split points, don't split.
2642 if ( !available_thread_exists(master)
2643 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2645 lock_release(&MPLock);
2649 // Pick the next available split point object from the split point stack
2650 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2652 // Initialize the split point object
2653 splitPoint->parent = threads[master].splitPoint;
2654 splitPoint->stopRequest = false;
2655 splitPoint->ply = ply;
2656 splitPoint->depth = depth;
2657 splitPoint->mateThreat = mateThreat;
2658 splitPoint->alpha = *alpha;
2659 splitPoint->beta = beta;
2660 splitPoint->pvNode = pvNode;
2661 splitPoint->bestValue = *bestValue;
2662 splitPoint->mp = mp;
2663 splitPoint->moveCount = *moveCount;
2664 splitPoint->pos = &p;
2665 splitPoint->parentSstack = ss;
2666 for (int i = 0; i < ActiveThreads; i++)
2667 splitPoint->slaves[i] = 0;
2669 threads[master].splitPoint = splitPoint;
2670 threads[master].activeSplitPoints++;
2672 // If we are here it means we are not available
2673 assert(threads[master].state != THREAD_AVAILABLE);
2675 int workersCnt = 1; // At least the master is included
2677 // Allocate available threads setting state to THREAD_BOOKED
2678 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2679 if (thread_is_available(i, master))
2681 threads[i].state = THREAD_BOOKED;
2682 threads[i].splitPoint = splitPoint;
2683 splitPoint->slaves[i] = 1;
2687 assert(Fake || workersCnt > 1);
2689 // We can release the lock because slave threads are already booked and master is not available
2690 lock_release(&MPLock);
2692 // Tell the threads that they have work to do. This will make them leave
2693 // their idle loop. But before copy search stack tail for each thread.
2694 for (int i = 0; i < ActiveThreads; i++)
2695 if (i == master || splitPoint->slaves[i])
2697 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2699 assert(i == master || threads[i].state == THREAD_BOOKED);
2701 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2704 // Everything is set up. The master thread enters the idle loop, from
2705 // which it will instantly launch a search, because its state is
2706 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2707 // idle loop, which means that the main thread will return from the idle
2708 // loop when all threads have finished their work at this split point.
2709 idle_loop(master, splitPoint);
2711 // We have returned from the idle loop, which means that all threads are
2712 // finished. Update alpha and bestValue, and return.
2715 *alpha = splitPoint->alpha;
2716 *bestValue = splitPoint->bestValue;
2717 threads[master].activeSplitPoints--;
2718 threads[master].splitPoint = splitPoint->parent;
2720 lock_release(&MPLock);
2724 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2725 // to start a new search from the root.
2727 void ThreadsManager::wake_sleeping_threads() {
2729 assert(AllThreadsShouldSleep);
2730 assert(ActiveThreads > 0);
2732 AllThreadsShouldSleep = false;
2734 if (ActiveThreads == 1)
2737 #if !defined(_MSC_VER)
2738 pthread_mutex_lock(&WaitLock);
2739 pthread_cond_broadcast(&WaitCond);
2740 pthread_mutex_unlock(&WaitLock);
2742 for (int i = 1; i < MAX_THREADS; i++)
2743 SetEvent(SitIdleEvent[i]);
2749 // put_threads_to_sleep() makes all the threads go to sleep just before
2750 // to leave think(), at the end of the search. Threads should have already
2751 // finished the job and should be idle.
2753 void ThreadsManager::put_threads_to_sleep() {
2755 assert(!AllThreadsShouldSleep);
2757 // This makes the threads to go to sleep
2758 AllThreadsShouldSleep = true;
2761 /// The RootMoveList class
2763 // RootMoveList c'tor
2765 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2767 SearchStack ss[PLY_MAX_PLUS_2];
2768 MoveStack mlist[MaxRootMoves];
2770 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2772 // Generate all legal moves
2773 MoveStack* last = generate_moves(pos, mlist);
2775 // Add each move to the moves[] array
2776 for (MoveStack* cur = mlist; cur != last; cur++)
2778 bool includeMove = includeAllMoves;
2780 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2781 includeMove = (searchMoves[k] == cur->move);
2786 // Find a quick score for the move
2788 pos.do_move(cur->move, st);
2789 moves[count].move = cur->move;
2790 moves[count].score = -qsearch<PV>(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2791 moves[count].pv[0] = cur->move;
2792 moves[count].pv[1] = MOVE_NONE;
2793 pos.undo_move(cur->move);
2800 // RootMoveList simple methods definitions
2802 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2804 moves[moveNum].nodes = nodes;
2805 moves[moveNum].cumulativeNodes += nodes;
2808 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2810 moves[moveNum].ourBeta = our;
2811 moves[moveNum].theirBeta = their;
2814 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2818 for (j = 0; pv[j] != MOVE_NONE; j++)
2819 moves[moveNum].pv[j] = pv[j];
2821 moves[moveNum].pv[j] = MOVE_NONE;
2825 // RootMoveList::sort() sorts the root move list at the beginning of a new
2828 void RootMoveList::sort() {
2830 sort_multipv(count - 1); // Sort all items
2834 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2835 // list by their scores and depths. It is used to order the different PVs
2836 // correctly in MultiPV mode.
2838 void RootMoveList::sort_multipv(int n) {
2842 for (i = 1; i <= n; i++)
2844 RootMove rm = moves[i];
2845 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2846 moves[j] = moves[j - 1];