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, 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, 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 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);
643 // Is one move significantly better than others after initial scoring ?
644 if ( rml.move_count() == 1
645 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
646 EasyMove = rml.get_move(0);
648 // Iterative deepening loop
649 while (Iteration < PLY_MAX)
651 // Initialize iteration
653 BestMoveChangesByIteration[Iteration] = 0;
655 cout << "info depth " << Iteration << endl;
657 // Calculate dynamic aspiration window based on previous iterations
658 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
660 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
661 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
663 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
664 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
666 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
667 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
670 // Search to the current depth, rml is updated and sorted, alpha and beta could change
671 value = root_search(p, ss, rml, &alpha, &beta);
673 // Write PV to transposition table, in case the relevant entries have
674 // been overwritten during the search.
675 TT.insert_pv(p, ss->pv);
678 break; // Value cannot be trusted. Break out immediately!
680 //Save info about search result
681 ValueByIteration[Iteration] = value;
683 // Drop the easy move if differs from the new best move
684 if (ss->pv[0] != EasyMove)
685 EasyMove = MOVE_NONE;
687 if (UseTimeManagement)
690 bool stopSearch = false;
692 // Stop search early if there is only a single legal move,
693 // we search up to Iteration 6 anyway to get a proper score.
694 if (Iteration >= 6 && rml.move_count() == 1)
697 // Stop search early when the last two iterations returned a mate score
699 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
700 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
703 // Stop search early if one move seems to be much better than the others
704 int64_t nodes = TM.nodes_searched();
706 && EasyMove == ss->pv[0]
707 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
708 && current_search_time() > MaxSearchTime / 16)
709 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
710 && current_search_time() > MaxSearchTime / 32)))
713 // Add some extra time if the best move has changed during the last two iterations
714 if (Iteration > 5 && Iteration <= 50)
715 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
716 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
718 // Stop search if most of MaxSearchTime is consumed at the end of the
719 // iteration. We probably don't have enough time to search the first
720 // move at the next iteration anyway.
721 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
727 StopOnPonderhit = true;
733 if (MaxDepth && Iteration >= MaxDepth)
737 // If we are pondering or in infinite search, we shouldn't print the
738 // best move before we are told to do so.
739 if (!AbortSearch && (PonderSearch || InfiniteSearch))
740 wait_for_stop_or_ponderhit();
742 // Print final search statistics
743 cout << "info nodes " << TM.nodes_searched()
745 << " time " << current_search_time()
746 << " hashfull " << TT.full() << endl;
748 // Print the best move and the ponder move to the standard output
749 if (ss->pv[0] == MOVE_NONE)
751 ss->pv[0] = rml.get_move(0);
752 ss->pv[1] = MOVE_NONE;
755 assert(ss->pv[0] != MOVE_NONE);
757 cout << "bestmove " << ss->pv[0];
759 if (ss->pv[1] != MOVE_NONE)
760 cout << " ponder " << ss->pv[1];
767 dbg_print_mean(LogFile);
769 if (dbg_show_hit_rate)
770 dbg_print_hit_rate(LogFile);
772 LogFile << "\nNodes: " << TM.nodes_searched()
773 << "\nNodes/second: " << nps()
774 << "\nBest move: " << move_to_san(p, ss->pv[0]);
777 p.do_move(ss->pv[0], st);
778 LogFile << "\nPonder move: "
779 << move_to_san(p, ss->pv[1]) // Works also with MOVE_NONE
782 return rml.get_move_score(0);
786 // root_search() is the function which searches the root node. It is
787 // similar to search_pv except that it uses a different move ordering
788 // scheme, prints some information to the standard output and handles
789 // the fail low/high loops.
791 Value root_search(Position& pos, SearchStack* ss, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
798 Depth depth, ext, newDepth;
799 Value value, alpha, beta;
800 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
801 int researchCountFH, researchCountFL;
803 researchCountFH = researchCountFL = 0;
806 isCheck = pos.is_check();
808 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
809 // Step 2. Check for aborted search (omitted at root)
810 // Step 3. Mate distance pruning (omitted at root)
811 // Step 4. Transposition table lookup (omitted at root)
813 // Step 5. Evaluate the position statically
814 // At root we do this only to get reference value for child nodes
816 ss->eval = evaluate(pos, ei, 0);
818 // Step 6. Razoring (omitted at root)
819 // Step 7. Static null move pruning (omitted at root)
820 // Step 8. Null move search with verification search (omitted at root)
821 // Step 9. Internal iterative deepening (omitted at root)
823 // Step extra. Fail low loop
824 // We start with small aspiration window and in case of fail low, we research
825 // with bigger window until we are not failing low anymore.
828 // Sort the moves before to (re)search
831 // Step 10. Loop through all moves in the root move list
832 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
834 // This is used by time management
835 FirstRootMove = (i == 0);
837 // Save the current node count before the move is searched
838 nodes = TM.nodes_searched();
840 // Reset beta cut-off counters
841 TM.resetBetaCounters();
843 // Pick the next root move, and print the move and the move number to
844 // the standard output.
845 move = ss->currentMove = rml.get_move(i);
847 if (current_search_time() >= 1000)
848 cout << "info currmove " << move
849 << " currmovenumber " << i + 1 << endl;
851 moveIsCheck = pos.move_is_check(move);
852 captureOrPromotion = pos.move_is_capture_or_promotion(move);
854 // Step 11. Decide the new search depth
855 depth = (Iteration - 2) * OnePly + InitialDepth;
856 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
857 newDepth = depth + ext;
859 // Step 12. Futility pruning (omitted at root)
861 // Step extra. Fail high loop
862 // If move fails high, we research with bigger window until we are not failing
864 value = - VALUE_INFINITE;
868 // Step 13. Make the move
869 pos.do_move(move, st, ci, moveIsCheck);
871 // Step extra. pv search
872 // We do pv search for first moves (i < MultiPV)
873 // and for fail high research (value > alpha)
874 if (i < MultiPV || value > alpha)
876 // Aspiration window is disabled in multi-pv case
878 alpha = -VALUE_INFINITE;
880 // Full depth PV search, done on first move or after a fail high
881 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, 0);
885 // Step 14. Reduced search
886 // if the move fails high will be re-searched at full depth
887 bool doFullDepthSearch = true;
889 if ( depth >= 3 * OnePly
891 && !captureOrPromotion
892 && !move_is_castle(move))
894 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
897 // Reduced depth non-pv search using alpha as upperbound
898 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, true, 0);
899 doFullDepthSearch = (value > alpha);
903 // Step 15. Full depth search
904 if (doFullDepthSearch)
906 // Full depth non-pv search using alpha as upperbound
907 ss->reduction = Depth(0);
908 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, true, 0);
910 // If we are above alpha then research at same depth but as PV
911 // to get a correct score or eventually a fail high above beta.
913 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, 0);
917 // Step 16. Undo move
920 // Can we exit fail high loop ?
921 if (AbortSearch || value < beta)
924 // We are failing high and going to do a research. It's important to update
925 // the score before research in case we run out of time while researching.
926 rml.set_move_score(i, value);
928 TT.extract_pv(pos, ss->pv, PLY_MAX);
929 rml.set_move_pv(i, ss->pv);
931 // Print information to the standard output
932 print_pv_info(pos, ss, alpha, beta, value);
934 // Prepare for a research after a fail high, each time with a wider window
935 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
938 } // End of fail high loop
940 // Finished searching the move. If AbortSearch is true, the search
941 // was aborted because the user interrupted the search or because we
942 // ran out of time. In this case, the return value of the search cannot
943 // be trusted, and we break out of the loop without updating the best
948 // Remember beta-cutoff and searched nodes counts for this move. The
949 // info is used to sort the root moves for the next iteration.
951 TM.get_beta_counters(pos.side_to_move(), our, their);
952 rml.set_beta_counters(i, our, their);
953 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
955 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
956 assert(value < beta);
958 // Step 17. Check for new best move
959 if (value <= alpha && i >= MultiPV)
960 rml.set_move_score(i, -VALUE_INFINITE);
963 // PV move or new best move!
966 rml.set_move_score(i, value);
968 TT.extract_pv(pos, ss->pv, PLY_MAX);
969 rml.set_move_pv(i, ss->pv);
973 // We record how often the best move has been changed in each
974 // iteration. This information is used for time managment: When
975 // the best move changes frequently, we allocate some more time.
977 BestMoveChangesByIteration[Iteration]++;
979 // Print information to the standard output
980 print_pv_info(pos, ss, alpha, beta, value);
982 // Raise alpha to setup proper non-pv search upper bound
989 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
991 cout << "info multipv " << j + 1
992 << " score " << value_to_string(rml.get_move_score(j))
993 << " depth " << (j <= i ? Iteration : Iteration - 1)
994 << " time " << current_search_time()
995 << " nodes " << TM.nodes_searched()
999 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1000 cout << rml.get_move_pv(j, k) << " ";
1004 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1006 } // PV move or new best move
1008 assert(alpha >= *alphaPtr);
1010 AspirationFailLow = (alpha == *alphaPtr);
1012 if (AspirationFailLow && StopOnPonderhit)
1013 StopOnPonderhit = false;
1016 // Can we exit fail low loop ?
1017 if (AbortSearch || !AspirationFailLow)
1020 // Prepare for a research after a fail low, each time with a wider window
1021 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1026 // Sort the moves before to return
1033 // search<>() is the main search function for both PV and non-PV nodes
1035 template <NodeType PvNode>
1036 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth,
1037 bool allowNullmove, int threadID, Move excludedMove) {
1039 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1040 assert(beta > alpha && beta <= VALUE_INFINITE);
1041 assert(PvNode || alpha == beta - 1);
1042 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1043 assert(threadID >= 0 && threadID < TM.active_threads());
1045 Move movesSearched[256];
1050 Depth ext, newDepth;
1051 Value bestValue, value, oldAlpha;
1052 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1053 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1054 bool mateThreat = false;
1056 int ply = pos.ply();
1057 refinedValue = bestValue = value = -VALUE_INFINITE;
1061 return qsearch<PvNode>(pos, ss, alpha, beta, Depth(0), threadID);
1063 // Step 1. Initialize node and poll
1064 // Polling can abort search.
1065 init_node(ss, ply, threadID);
1067 // Step 2. Check for aborted search and immediate draw
1068 if (AbortSearch || TM.thread_should_stop(threadID))
1071 if (pos.is_draw() || ply >= PLY_MAX - 1)
1074 // Step 3. Mate distance pruning
1075 alpha = Max(value_mated_in(ply), alpha);
1076 beta = Min(value_mate_in(ply+1), beta);
1080 // Step 4. Transposition table lookup
1082 // We don't want the score of a partial search to overwrite a previous full search
1083 // TT value, so we use a different position key in case of an excluded move exists.
1084 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1086 tte = TT.retrieve(posKey);
1087 ttMove = (tte ? tte->move() : MOVE_NONE);
1089 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1090 // This is to avoid problems in the following areas:
1092 // * Repetition draw detection
1093 // * Fifty move rule detection
1094 // * Searching for a mate
1095 // * Printing of full PV line
1097 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1099 // Refresh tte entry to avoid aging
1100 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1102 ss->currentMove = ttMove; // Can be MOVE_NONE
1103 return value_from_tt(tte->value(), ply);
1106 // Step 5. Evaluate the position statically
1107 // At PV nodes we do this only to update gain statistics
1108 isCheck = pos.is_check();
1111 if (tte && tte->static_value() != VALUE_NONE)
1113 ss->eval = tte->static_value();
1114 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1117 ss->eval = evaluate(pos, ei, threadID);
1119 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1120 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1123 // Step 6. Razoring (is omitted in PV nodes)
1125 && refinedValue < beta - razor_margin(depth)
1126 && ttMove == MOVE_NONE
1127 && (ss-1)->currentMove != MOVE_NULL
1128 && depth < RazorDepth
1130 && !value_is_mate(beta)
1131 && !pos.has_pawn_on_7th(pos.side_to_move()))
1133 Value rbeta = beta - razor_margin(depth);
1134 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), threadID);
1136 // Logically we should return (v + razor_margin(depth)), but
1137 // surprisingly this did slightly weaker in tests.
1141 // Step 7. Static null move pruning (is omitted in PV nodes)
1142 // We're betting that the opponent doesn't have a move that will reduce
1143 // the score by more than futility_margin(depth) if we do a null move.
1146 && depth < RazorDepth
1148 && !value_is_mate(beta)
1149 && ok_to_do_nullmove(pos)
1150 && refinedValue >= beta + futility_margin(depth, 0))
1151 return refinedValue - futility_margin(depth, 0);
1153 // Step 8. Null move search with verification search (is omitted in PV nodes)
1154 // When we jump directly to qsearch() we do a null move only if static value is
1155 // at least beta. Otherwise we do a null move if static value is not more than
1156 // NullMoveMargin under beta.
1161 && !value_is_mate(beta)
1162 && ok_to_do_nullmove(pos)
1163 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1165 ss->currentMove = MOVE_NULL;
1167 // Null move dynamic reduction based on depth
1168 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1170 // Null move dynamic reduction based on value
1171 if (refinedValue - beta > PawnValueMidgame)
1174 pos.do_null_move(st);
1176 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, false, threadID);
1178 pos.undo_null_move();
1180 if (nullValue >= beta)
1182 // Do not return unproven mate scores
1183 if (nullValue >= value_mate_in(PLY_MAX))
1186 if (depth < 6 * OnePly)
1189 // Do zugzwang verification search
1190 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, false, threadID);
1194 // The null move failed low, which means that we may be faced with
1195 // some kind of threat. If the previous move was reduced, check if
1196 // the move that refuted the null move was somehow connected to the
1197 // move which was reduced. If a connection is found, return a fail
1198 // low score (which will cause the reduced move to fail high in the
1199 // parent node, which will trigger a re-search with full depth).
1200 if (nullValue == value_mated_in(ply + 2))
1203 ss->threatMove = (ss+1)->currentMove;
1204 if ( depth < ThreatDepth
1205 && (ss-1)->reduction
1206 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1211 // Step 9. Internal iterative deepening
1212 if ( depth >= IIDDepth[PvNode]
1213 && (ttMove == MOVE_NONE || (PvNode && tte->depth() <= depth - 4 * OnePly))
1214 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1216 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1217 search<PvNode>(pos, ss, alpha, beta, d, false, threadID);
1218 ttMove = ss->pv[ply];
1219 tte = TT.retrieve(posKey);
1222 // Expensive mate threat detection (only for PV nodes)
1224 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1226 // Initialize a MovePicker object for the current position
1227 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1230 // Step 10. Loop through moves
1231 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1232 while ( bestValue < beta
1233 && (move = mp.get_next_move()) != MOVE_NONE
1234 && !TM.thread_should_stop(threadID))
1236 assert(move_is_ok(move));
1238 if (move == excludedMove)
1241 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1242 moveIsCheck = pos.move_is_check(move, ci);
1243 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1245 // Step 11. Decide the new search depth
1246 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1248 // Singular extension search. We extend the TT move if its value is much better than
1249 // its siblings. To verify this we do a reduced search on all the other moves but the
1250 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1251 if ( depth >= SingularExtensionDepth[PvNode]
1253 && move == tte->move()
1254 && !excludedMove // Do not allow recursive singular extension search
1256 && is_lower_bound(tte->type())
1257 && tte->depth() >= depth - 3 * OnePly)
1259 Value ttValue = value_from_tt(tte->value(), ply);
1261 if (abs(ttValue) < VALUE_KNOWN_WIN)
1263 Value b = ttValue - SingularExtensionMargin;
1264 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, false, threadID, move);
1266 if (v < ttValue - SingularExtensionMargin)
1271 newDepth = depth - OnePly + ext;
1273 // Update current move (this must be done after singular extension search)
1274 movesSearched[moveCount++] = ss->currentMove = move;
1276 // Step 12. Futility pruning (is omitted in PV nodes)
1280 && !captureOrPromotion
1281 && !move_is_castle(move)
1284 // Move count based pruning
1285 if ( moveCount >= futility_move_count(depth)
1286 && ok_to_prune(pos, move, ss->threatMove)
1287 && bestValue > value_mated_in(PLY_MAX))
1290 // Value based pruning
1291 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1292 // but fixing this made program slightly weaker.
1293 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1294 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1295 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1297 if (futilityValueScaled < beta)
1299 if (futilityValueScaled > bestValue)
1300 bestValue = futilityValueScaled;
1305 // Step 13. Make the move
1306 pos.do_move(move, st, ci, moveIsCheck);
1308 // Step extra. pv search (only in PV nodes)
1309 // The first move in list is the expected PV
1310 if (PvNode && moveCount == 1)
1311 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, threadID);
1314 // Step 14. Reduced depth search
1315 // If the move fails high will be re-searched at full depth.
1316 bool doFullDepthSearch = true;
1318 if ( depth >= 3 * OnePly
1320 && !captureOrPromotion
1321 && !move_is_castle(move)
1322 && !move_is_killer(move, ss))
1324 ss->reduction = reduction<PvNode>(depth, moveCount);
1327 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, true, threadID);
1328 doFullDepthSearch = (value > alpha);
1331 // The move failed high, but if reduction is very big we could
1332 // face a false positive, retry with a less aggressive reduction,
1333 // if the move fails high again then go with full depth search.
1334 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1336 ss->reduction = OnePly;
1337 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, true, threadID);
1338 doFullDepthSearch = (value > alpha);
1342 // Step 15. Full depth search
1343 if (doFullDepthSearch)
1345 ss->reduction = Depth(0);
1346 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, true, threadID);
1348 // Step extra. pv search (only in PV nodes)
1349 // Search only for possible new PV nodes, if instead value >= beta then
1350 // parent node fails low with value <= alpha and tries another move.
1351 if (PvNode && value > alpha && value < beta)
1352 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, threadID);
1356 // Step 16. Undo move
1357 pos.undo_move(move);
1359 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1361 // Step 17. Check for new best move
1362 if (value > bestValue)
1367 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1372 if (value == value_mate_in(ply + 1))
1373 ss->mateKiller = move;
1377 // Step 18. Check for split
1378 if ( TM.active_threads() > 1
1380 && depth >= MinimumSplitDepth
1382 && TM.available_thread_exists(threadID)
1384 && !TM.thread_should_stop(threadID))
1385 TM.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1386 mateThreat, &moveCount, &mp, threadID, PvNode);
1389 // Step 19. Check for mate and stalemate
1390 // All legal moves have been searched and if there are
1391 // no legal moves, it must be mate or stalemate.
1392 // If one move was excluded return fail low score.
1394 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1396 // Step 20. Update tables
1397 // If the search is not aborted, update the transposition table,
1398 // history counters, and killer moves.
1399 if (AbortSearch || TM.thread_should_stop(threadID))
1402 if (bestValue <= oldAlpha)
1403 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1405 else if (bestValue >= beta)
1407 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1409 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1410 if (!pos.move_is_capture_or_promotion(move))
1412 update_history(pos, move, depth, movesSearched, moveCount);
1413 update_killers(move, ss);
1417 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1419 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1425 // qsearch() is the quiescence search function, which is called by the main
1426 // search function when the remaining depth is zero (or, to be more precise,
1427 // less than OnePly).
1429 template <NodeType PvNode>
1430 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int threadID) {
1432 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1433 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1434 assert(PvNode || alpha == beta - 1);
1436 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1437 assert(threadID >= 0 && threadID < TM.active_threads());
1442 Value staticValue, bestValue, value, futilityBase, futilityValue;
1443 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1444 const TTEntry* tte = NULL;
1446 int ply = pos.ply();
1447 Value oldAlpha = alpha;
1449 // Initialize, and make an early exit in case of an aborted search,
1450 // an instant draw, maximum ply reached, etc.
1451 init_node(ss, ply, threadID);
1453 // After init_node() that calls poll()
1454 if (AbortSearch || TM.thread_should_stop(threadID))
1457 if (pos.is_draw() || ply >= PLY_MAX - 1)
1460 // Transposition table lookup. At PV nodes, we don't use the TT for
1461 // pruning, but only for move ordering.
1462 tte = TT.retrieve(pos.get_key());
1463 ttMove = (tte ? tte->move() : MOVE_NONE);
1465 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1467 ss->currentMove = ttMove; // Can be MOVE_NONE
1468 return value_from_tt(tte->value(), ply);
1471 isCheck = pos.is_check();
1473 // Evaluate the position statically
1475 staticValue = -VALUE_INFINITE;
1476 else if (tte && tte->static_value() != VALUE_NONE)
1478 staticValue = tte->static_value();
1479 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1482 staticValue = evaluate(pos, ei, threadID);
1486 ss->eval = staticValue;
1487 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1490 // Initialize "stand pat score", and return it immediately if it is
1492 bestValue = staticValue;
1494 if (bestValue >= beta)
1496 // Store the score to avoid a future costly evaluation() call
1497 if (!isCheck && !tte)
1498 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()]);
1503 if (bestValue > alpha)
1506 // If we are near beta then try to get a cutoff pushing checks a bit further
1507 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1509 // Initialize a MovePicker object for the current position, and prepare
1510 // to search the moves. Because the depth is <= 0 here, only captures,
1511 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1512 // and we are near beta) will be generated.
1513 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1515 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1516 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1518 // Loop through the moves until no moves remain or a beta cutoff occurs
1519 while ( alpha < beta
1520 && (move = mp.get_next_move()) != MOVE_NONE)
1522 assert(move_is_ok(move));
1524 moveIsCheck = pos.move_is_check(move, ci);
1526 // Update current move
1528 ss->currentMove = move;
1536 && !move_is_promotion(move)
1537 && !pos.move_is_passed_pawn_push(move))
1539 futilityValue = futilityBase
1540 + pos.endgame_value_of_piece_on(move_to(move))
1541 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1543 if (futilityValue < alpha)
1545 if (futilityValue > bestValue)
1546 bestValue = futilityValue;
1551 // Detect blocking evasions that are candidate to be pruned
1552 evasionPrunable = isCheck
1553 && bestValue > value_mated_in(PLY_MAX)
1554 && !pos.move_is_capture(move)
1555 && pos.type_of_piece_on(move_from(move)) != KING
1556 && !pos.can_castle(pos.side_to_move());
1558 // Don't search moves with negative SEE values
1560 && (!isCheck || evasionPrunable)
1562 && !move_is_promotion(move)
1563 && pos.see_sign(move) < 0)
1566 // Make and search the move
1567 pos.do_move(move, st, ci, moveIsCheck);
1568 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, threadID);
1569 pos.undo_move(move);
1571 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1574 if (value > bestValue)
1585 // All legal moves have been searched. A special case: If we're in check
1586 // and no legal moves were found, it is checkmate.
1587 if (!moveCount && isCheck) // Mate!
1588 return value_mated_in(ply);
1590 // Update transposition table
1591 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1592 if (bestValue <= oldAlpha)
1594 // If bestValue isn't changed it means it is still the static evaluation
1595 // of the node, so keep this info to avoid a future evaluation() call.
1596 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1598 else if (bestValue >= beta)
1601 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1603 // Update killers only for good checking moves
1604 if (!pos.move_is_capture_or_promotion(move))
1605 update_killers(move, ss);
1608 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()]);
1610 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1616 // sp_search() is used to search from a split point. This function is called
1617 // by each thread working at the split point. It is similar to the normal
1618 // search() function, but simpler. Because we have already probed the hash
1619 // table, done a null move search, and searched the first move before
1620 // splitting, we don't have to repeat all this work in sp_search(). We
1621 // also don't need to store anything to the hash table here: This is taken
1622 // care of after we return from the split point.
1624 template <NodeType PvNode>
1625 void sp_search(SplitPoint* sp, int threadID) {
1627 assert(threadID >= 0 && threadID < TM.active_threads());
1628 assert(TM.active_threads() > 1);
1632 Depth ext, newDepth;
1634 Value futilityValueScaled; // NonPV specific
1635 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1637 value = -VALUE_INFINITE;
1639 Position pos(*sp->pos);
1641 int ply = pos.ply();
1642 SearchStack* ss = sp->sstack[threadID] + 1;
1643 isCheck = pos.is_check();
1645 // Step 10. Loop through moves
1646 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1647 lock_grab(&(sp->lock));
1649 while ( sp->bestValue < sp->beta
1650 && (move = sp->mp->get_next_move()) != MOVE_NONE
1651 && !TM.thread_should_stop(threadID))
1653 moveCount = ++sp->moveCount;
1654 lock_release(&(sp->lock));
1656 assert(move_is_ok(move));
1658 moveIsCheck = pos.move_is_check(move, ci);
1659 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1661 // Step 11. Decide the new search depth
1662 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1663 newDepth = sp->depth - OnePly + ext;
1665 // Update current move
1666 ss->currentMove = move;
1668 // Step 12. Futility pruning (is omitted in PV nodes)
1672 && !captureOrPromotion
1673 && !move_is_castle(move))
1675 // Move count based pruning
1676 if ( moveCount >= futility_move_count(sp->depth)
1677 && ok_to_prune(pos, move, ss->threatMove)
1678 && sp->bestValue > value_mated_in(PLY_MAX))
1680 lock_grab(&(sp->lock));
1684 // Value based pruning
1685 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1686 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1687 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1689 if (futilityValueScaled < sp->beta)
1691 lock_grab(&(sp->lock));
1693 if (futilityValueScaled > sp->bestValue)
1694 sp->bestValue = futilityValueScaled;
1699 // Step 13. Make the move
1700 pos.do_move(move, st, ci, moveIsCheck);
1702 // Step 14. Reduced search
1703 // If the move fails high will be re-searched at full depth.
1704 bool doFullDepthSearch = true;
1707 && !captureOrPromotion
1708 && !move_is_castle(move)
1709 && !move_is_killer(move, ss))
1711 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1714 Value localAlpha = sp->alpha;
1715 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, true, threadID);
1716 doFullDepthSearch = (value > localAlpha);
1719 // The move failed high, but if reduction is very big we could
1720 // face a false positive, retry with a less aggressive reduction,
1721 // if the move fails high again then go with full depth search.
1722 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1724 ss->reduction = OnePly;
1725 Value localAlpha = sp->alpha;
1726 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, true, threadID);
1727 doFullDepthSearch = (value > localAlpha);
1731 // Step 15. Full depth search
1732 if (doFullDepthSearch)
1734 ss->reduction = Depth(0);
1735 Value localAlpha = sp->alpha;
1736 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, true, threadID);
1738 if (PvNode && value > localAlpha && value < sp->beta)
1739 value = -search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, false, threadID);
1742 // Step 16. Undo move
1743 pos.undo_move(move);
1745 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1747 // Step 17. Check for new best move
1748 lock_grab(&(sp->lock));
1750 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1752 sp->bestValue = value;
1754 if (sp->bestValue > sp->alpha)
1756 if (!PvNode || value >= sp->beta)
1757 sp->stopRequest = true;
1759 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1762 sp_update_pv(sp->parentSstack, ss, ply);
1767 /* Here we have the lock still grabbed */
1769 sp->slaves[threadID] = 0;
1771 lock_release(&(sp->lock));
1774 // init_node() is called at the beginning of all the search functions
1775 // (search() qsearch(), and so on) and initializes the
1776 // search stack object corresponding to the current node. Once every
1777 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1778 // for user input and checks whether it is time to stop the search.
1780 void init_node(SearchStack* ss, int ply, int threadID) {
1782 assert(ply >= 0 && ply < PLY_MAX);
1783 assert(threadID >= 0 && threadID < TM.active_threads());
1785 TM.incrementNodeCounter(threadID);
1790 if (NodesSincePoll >= NodesBetweenPolls)
1797 (ss + 2)->initKillers();
1800 // update_pv() is called whenever a search returns a value > alpha.
1801 // It updates the PV in the SearchStack object corresponding to the
1804 void update_pv(SearchStack* ss, int ply) {
1806 assert(ply >= 0 && ply < PLY_MAX);
1810 ss->pv[ply] = ss->currentMove;
1812 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1813 ss->pv[p] = (ss+1)->pv[p];
1815 ss->pv[p] = MOVE_NONE;
1819 // sp_update_pv() is a variant of update_pv for use at split points. The
1820 // difference between the two functions is that sp_update_pv also updates
1821 // the PV at the parent node.
1823 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply) {
1825 assert(ply >= 0 && ply < PLY_MAX);
1829 ss->pv[ply] = pss->pv[ply] = ss->currentMove;
1831 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1832 ss->pv[p] = pss->pv[p] = (ss+1)->pv[p];
1834 ss->pv[p] = pss->pv[p] = MOVE_NONE;
1838 // connected_moves() tests whether two moves are 'connected' in the sense
1839 // that the first move somehow made the second move possible (for instance
1840 // if the moving piece is the same in both moves). The first move is assumed
1841 // to be the move that was made to reach the current position, while the
1842 // second move is assumed to be a move from the current position.
1844 bool connected_moves(const Position& pos, Move m1, Move m2) {
1846 Square f1, t1, f2, t2;
1849 assert(move_is_ok(m1));
1850 assert(move_is_ok(m2));
1852 if (m2 == MOVE_NONE)
1855 // Case 1: The moving piece is the same in both moves
1861 // Case 2: The destination square for m2 was vacated by m1
1867 // Case 3: Moving through the vacated square
1868 if ( piece_is_slider(pos.piece_on(f2))
1869 && bit_is_set(squares_between(f2, t2), f1))
1872 // Case 4: The destination square for m2 is defended by the moving piece in m1
1873 p = pos.piece_on(t1);
1874 if (bit_is_set(pos.attacks_from(p, t1), t2))
1877 // Case 5: Discovered check, checking piece is the piece moved in m1
1878 if ( piece_is_slider(p)
1879 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1880 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1882 // discovered_check_candidates() works also if the Position's side to
1883 // move is the opposite of the checking piece.
1884 Color them = opposite_color(pos.side_to_move());
1885 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1887 if (bit_is_set(dcCandidates, f2))
1894 // value_is_mate() checks if the given value is a mate one
1895 // eventually compensated for the ply.
1897 bool value_is_mate(Value value) {
1899 assert(abs(value) <= VALUE_INFINITE);
1901 return value <= value_mated_in(PLY_MAX)
1902 || value >= value_mate_in(PLY_MAX);
1906 // move_is_killer() checks if the given move is among the
1907 // killer moves of that ply.
1909 bool move_is_killer(Move m, SearchStack* ss) {
1911 const Move* k = ss->killers;
1912 for (int i = 0; i < KILLER_MAX; i++, k++)
1920 // extension() decides whether a move should be searched with normal depth,
1921 // or with extended depth. Certain classes of moves (checking moves, in
1922 // particular) are searched with bigger depth than ordinary moves and in
1923 // any case are marked as 'dangerous'. Note that also if a move is not
1924 // extended, as example because the corresponding UCI option is set to zero,
1925 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1926 template <NodeType PvNode>
1927 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1928 bool singleEvasion, bool mateThreat, bool* dangerous) {
1930 assert(m != MOVE_NONE);
1932 Depth result = Depth(0);
1933 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1938 result += CheckExtension[PvNode];
1941 result += SingleEvasionExtension[PvNode];
1944 result += MateThreatExtension[PvNode];
1947 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1949 Color c = pos.side_to_move();
1950 if (relative_rank(c, move_to(m)) == RANK_7)
1952 result += PawnPushTo7thExtension[PvNode];
1955 if (pos.pawn_is_passed(c, move_to(m)))
1957 result += PassedPawnExtension[PvNode];
1962 if ( captureOrPromotion
1963 && pos.type_of_piece_on(move_to(m)) != PAWN
1964 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1965 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1966 && !move_is_promotion(m)
1969 result += PawnEndgameExtension[PvNode];
1974 && captureOrPromotion
1975 && pos.type_of_piece_on(move_to(m)) != PAWN
1976 && pos.see_sign(m) >= 0)
1982 return Min(result, OnePly);
1986 // ok_to_do_nullmove() looks at the current position and decides whether
1987 // doing a 'null move' should be allowed. In order to avoid zugzwang
1988 // problems, null moves are not allowed when the side to move has very
1989 // little material left. Currently, the test is a bit too simple: Null
1990 // moves are avoided only when the side to move has only pawns left.
1991 // It's probably a good idea to avoid null moves in at least some more
1992 // complicated endgames, e.g. KQ vs KR. FIXME
1994 bool ok_to_do_nullmove(const Position& pos) {
1996 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2000 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2001 // non-tactical moves late in the move list close to the leaves are
2002 // candidates for pruning.
2004 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2006 assert(move_is_ok(m));
2007 assert(threat == MOVE_NONE || move_is_ok(threat));
2008 assert(!pos.move_is_check(m));
2009 assert(!pos.move_is_capture_or_promotion(m));
2010 assert(!pos.move_is_passed_pawn_push(m));
2012 Square mfrom, mto, tfrom, tto;
2014 // Prune if there isn't any threat move
2015 if (threat == MOVE_NONE)
2018 mfrom = move_from(m);
2020 tfrom = move_from(threat);
2021 tto = move_to(threat);
2023 // Case 1: Don't prune moves which move the threatened piece
2027 // Case 2: If the threatened piece has value less than or equal to the
2028 // value of the threatening piece, don't prune move which defend it.
2029 if ( pos.move_is_capture(threat)
2030 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2031 || pos.type_of_piece_on(tfrom) == KING)
2032 && pos.move_attacks_square(m, tto))
2035 // Case 3: If the moving piece in the threatened move is a slider, don't
2036 // prune safe moves which block its ray.
2037 if ( piece_is_slider(pos.piece_on(tfrom))
2038 && bit_is_set(squares_between(tfrom, tto), mto)
2039 && pos.see_sign(m) >= 0)
2046 // ok_to_use_TT() returns true if a transposition table score
2047 // can be used at a given point in search.
2049 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2051 Value v = value_from_tt(tte->value(), ply);
2053 return ( tte->depth() >= depth
2054 || v >= Max(value_mate_in(PLY_MAX), beta)
2055 || v < Min(value_mated_in(PLY_MAX), beta))
2057 && ( (is_lower_bound(tte->type()) && v >= beta)
2058 || (is_upper_bound(tte->type()) && v < beta));
2062 // refine_eval() returns the transposition table score if
2063 // possible otherwise falls back on static position evaluation.
2065 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2070 Value v = value_from_tt(tte->value(), ply);
2072 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2073 || (is_upper_bound(tte->type()) && v < defaultEval))
2080 // update_history() registers a good move that produced a beta-cutoff
2081 // in history and marks as failures all the other moves of that ply.
2083 void update_history(const Position& pos, Move move, Depth depth,
2084 Move movesSearched[], int moveCount) {
2088 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2090 for (int i = 0; i < moveCount - 1; i++)
2092 m = movesSearched[i];
2096 if (!pos.move_is_capture_or_promotion(m))
2097 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2102 // update_killers() add a good move that produced a beta-cutoff
2103 // among the killer moves of that ply.
2105 void update_killers(Move m, SearchStack* ss) {
2107 if (m == ss->killers[0])
2110 for (int i = KILLER_MAX - 1; i > 0; i--)
2111 ss->killers[i] = ss->killers[i - 1];
2117 // update_gains() updates the gains table of a non-capture move given
2118 // the static position evaluation before and after the move.
2120 void update_gains(const Position& pos, Move m, Value before, Value after) {
2123 && before != VALUE_NONE
2124 && after != VALUE_NONE
2125 && pos.captured_piece() == NO_PIECE_TYPE
2126 && !move_is_castle(m)
2127 && !move_is_promotion(m))
2128 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2132 // current_search_time() returns the number of milliseconds which have passed
2133 // since the beginning of the current search.
2135 int current_search_time() {
2137 return get_system_time() - SearchStartTime;
2141 // nps() computes the current nodes/second count.
2145 int t = current_search_time();
2146 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2150 // poll() performs two different functions: It polls for user input, and it
2151 // looks at the time consumed so far and decides if it's time to abort the
2156 static int lastInfoTime;
2157 int t = current_search_time();
2162 // We are line oriented, don't read single chars
2163 std::string command;
2165 if (!std::getline(std::cin, command))
2168 if (command == "quit")
2171 PonderSearch = false;
2175 else if (command == "stop")
2178 PonderSearch = false;
2180 else if (command == "ponderhit")
2184 // Print search information
2188 else if (lastInfoTime > t)
2189 // HACK: Must be a new search where we searched less than
2190 // NodesBetweenPolls nodes during the first second of search.
2193 else if (t - lastInfoTime >= 1000)
2200 if (dbg_show_hit_rate)
2201 dbg_print_hit_rate();
2203 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2204 << " time " << t << " hashfull " << TT.full() << endl;
2207 // Should we stop the search?
2211 bool stillAtFirstMove = FirstRootMove
2212 && !AspirationFailLow
2213 && t > MaxSearchTime + ExtraSearchTime;
2215 bool noMoreTime = t > AbsoluteMaxSearchTime
2216 || stillAtFirstMove;
2218 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2219 || (ExactMaxTime && t >= ExactMaxTime)
2220 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2225 // ponderhit() is called when the program is pondering (i.e. thinking while
2226 // it's the opponent's turn to move) in order to let the engine know that
2227 // it correctly predicted the opponent's move.
2231 int t = current_search_time();
2232 PonderSearch = false;
2234 bool stillAtFirstMove = FirstRootMove
2235 && !AspirationFailLow
2236 && t > MaxSearchTime + ExtraSearchTime;
2238 bool noMoreTime = t > AbsoluteMaxSearchTime
2239 || stillAtFirstMove;
2241 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2246 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2248 void init_ss_array(SearchStack* ss) {
2250 for (int i = 0; i < 3; i++, ss++)
2258 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2259 // while the program is pondering. The point is to work around a wrinkle in
2260 // the UCI protocol: When pondering, the engine is not allowed to give a
2261 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2262 // We simply wait here until one of these commands is sent, and return,
2263 // after which the bestmove and pondermove will be printed (in id_loop()).
2265 void wait_for_stop_or_ponderhit() {
2267 std::string command;
2271 if (!std::getline(std::cin, command))
2274 if (command == "quit")
2279 else if (command == "ponderhit" || command == "stop")
2285 // print_pv_info() prints to standard output and eventually to log file information on
2286 // the current PV line. It is called at each iteration or after a new pv is found.
2288 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2290 cout << "info depth " << Iteration
2291 << " score " << value_to_string(value)
2292 << ((value >= beta) ? " lowerbound" :
2293 ((value <= alpha)? " upperbound" : ""))
2294 << " time " << current_search_time()
2295 << " nodes " << TM.nodes_searched()
2299 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2300 cout << ss->pv[j] << " ";
2306 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2307 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2309 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2310 TM.nodes_searched(), value, type, ss->pv) << endl;
2315 // init_thread() is the function which is called when a new thread is
2316 // launched. It simply calls the idle_loop() function with the supplied
2317 // threadID. There are two versions of this function; one for POSIX
2318 // threads and one for Windows threads.
2320 #if !defined(_MSC_VER)
2322 void* init_thread(void *threadID) {
2324 TM.idle_loop(*(int*)threadID, NULL);
2330 DWORD WINAPI init_thread(LPVOID threadID) {
2332 TM.idle_loop(*(int*)threadID, NULL);
2339 /// The ThreadsManager class
2341 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2342 // get_beta_counters() are getters/setters for the per thread
2343 // counters used to sort the moves at root.
2345 void ThreadsManager::resetNodeCounters() {
2347 for (int i = 0; i < MAX_THREADS; i++)
2348 threads[i].nodes = 0ULL;
2351 void ThreadsManager::resetBetaCounters() {
2353 for (int i = 0; i < MAX_THREADS; i++)
2354 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2357 int64_t ThreadsManager::nodes_searched() const {
2359 int64_t result = 0ULL;
2360 for (int i = 0; i < ActiveThreads; i++)
2361 result += threads[i].nodes;
2366 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2369 for (int i = 0; i < MAX_THREADS; i++)
2371 our += threads[i].betaCutOffs[us];
2372 their += threads[i].betaCutOffs[opposite_color(us)];
2377 // idle_loop() is where the threads are parked when they have no work to do.
2378 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2379 // object for which the current thread is the master.
2381 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2383 assert(threadID >= 0 && threadID < MAX_THREADS);
2387 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2388 // master should exit as last one.
2389 if (AllThreadsShouldExit)
2392 threads[threadID].state = THREAD_TERMINATED;
2396 // If we are not thinking, wait for a condition to be signaled
2397 // instead of wasting CPU time polling for work.
2398 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2401 assert(threadID != 0);
2402 threads[threadID].state = THREAD_SLEEPING;
2404 #if !defined(_MSC_VER)
2405 lock_grab(&WaitLock);
2406 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2407 pthread_cond_wait(&WaitCond, &WaitLock);
2408 lock_release(&WaitLock);
2410 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2414 // If thread has just woken up, mark it as available
2415 if (threads[threadID].state == THREAD_SLEEPING)
2416 threads[threadID].state = THREAD_AVAILABLE;
2418 // If this thread has been assigned work, launch a search
2419 if (threads[threadID].state == THREAD_WORKISWAITING)
2421 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2423 threads[threadID].state = THREAD_SEARCHING;
2425 if (threads[threadID].splitPoint->pvNode)
2426 sp_search<PV>(threads[threadID].splitPoint, threadID);
2428 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2430 assert(threads[threadID].state == THREAD_SEARCHING);
2432 threads[threadID].state = THREAD_AVAILABLE;
2435 // If this thread is the master of a split point and all slaves have
2436 // finished their work at this split point, return from the idle loop.
2438 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2440 if (i == ActiveThreads)
2442 // Because sp->slaves[] is reset under lock protection,
2443 // be sure sp->lock has been released before to return.
2444 lock_grab(&(sp->lock));
2445 lock_release(&(sp->lock));
2447 assert(threads[threadID].state == THREAD_AVAILABLE);
2449 threads[threadID].state = THREAD_SEARCHING;
2456 // init_threads() is called during startup. It launches all helper threads,
2457 // and initializes the split point stack and the global locks and condition
2460 void ThreadsManager::init_threads() {
2465 #if !defined(_MSC_VER)
2466 pthread_t pthread[1];
2469 // Initialize global locks
2470 lock_init(&MPLock, NULL);
2471 lock_init(&WaitLock, NULL);
2473 #if !defined(_MSC_VER)
2474 pthread_cond_init(&WaitCond, NULL);
2476 for (i = 0; i < MAX_THREADS; i++)
2477 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2480 // Initialize SplitPointStack locks
2481 for (i = 0; i < MAX_THREADS; i++)
2482 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2483 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, Value* alpha, const Value beta,
2626 Value* bestValue, Depth depth, bool mateThreat, int* moveCount,
2627 MovePicker* mp, int master, bool pvNode) {
2629 assert(*bestValue >= -VALUE_INFINITE);
2630 assert(*bestValue <= *alpha);
2631 assert(*alpha < beta);
2632 assert(beta <= VALUE_INFINITE);
2633 assert(depth > Depth(0));
2634 assert(master >= 0 && master < ActiveThreads);
2635 assert(ActiveThreads > 1);
2639 // If no other thread is available to help us, or if we have too many
2640 // active split points, don't split.
2641 if ( !available_thread_exists(master)
2642 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2644 lock_release(&MPLock);
2648 // Pick the next available split point object from the split point stack
2649 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2651 // Initialize the split point object
2652 splitPoint->parent = threads[master].splitPoint;
2653 splitPoint->stopRequest = false;
2654 splitPoint->depth = depth;
2655 splitPoint->mateThreat = mateThreat;
2656 splitPoint->alpha = *alpha;
2657 splitPoint->beta = beta;
2658 splitPoint->pvNode = pvNode;
2659 splitPoint->bestValue = *bestValue;
2660 splitPoint->mp = mp;
2661 splitPoint->moveCount = *moveCount;
2662 splitPoint->pos = &p;
2663 splitPoint->parentSstack = ss;
2664 for (int i = 0; i < ActiveThreads; i++)
2665 splitPoint->slaves[i] = 0;
2667 threads[master].splitPoint = splitPoint;
2668 threads[master].activeSplitPoints++;
2670 // If we are here it means we are not available
2671 assert(threads[master].state != THREAD_AVAILABLE);
2673 int workersCnt = 1; // At least the master is included
2675 // Allocate available threads setting state to THREAD_BOOKED
2676 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2677 if (thread_is_available(i, master))
2679 threads[i].state = THREAD_BOOKED;
2680 threads[i].splitPoint = splitPoint;
2681 splitPoint->slaves[i] = 1;
2685 assert(Fake || workersCnt > 1);
2687 // We can release the lock because slave threads are already booked and master is not available
2688 lock_release(&MPLock);
2690 // Tell the threads that they have work to do. This will make them leave
2691 // their idle loop. But before copy search stack tail for each thread.
2692 for (int i = 0; i < ActiveThreads; i++)
2693 if (i == master || splitPoint->slaves[i])
2695 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2697 assert(i == master || threads[i].state == THREAD_BOOKED);
2699 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2702 // Everything is set up. The master thread enters the idle loop, from
2703 // which it will instantly launch a search, because its state is
2704 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2705 // idle loop, which means that the main thread will return from the idle
2706 // loop when all threads have finished their work at this split point.
2707 idle_loop(master, splitPoint);
2709 // We have returned from the idle loop, which means that all threads are
2710 // finished. Update alpha and bestValue, and return.
2713 *alpha = splitPoint->alpha;
2714 *bestValue = splitPoint->bestValue;
2715 threads[master].activeSplitPoints--;
2716 threads[master].splitPoint = splitPoint->parent;
2718 lock_release(&MPLock);
2722 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2723 // to start a new search from the root.
2725 void ThreadsManager::wake_sleeping_threads() {
2727 assert(AllThreadsShouldSleep);
2728 assert(ActiveThreads > 0);
2730 AllThreadsShouldSleep = false;
2732 if (ActiveThreads == 1)
2735 #if !defined(_MSC_VER)
2736 pthread_mutex_lock(&WaitLock);
2737 pthread_cond_broadcast(&WaitCond);
2738 pthread_mutex_unlock(&WaitLock);
2740 for (int i = 1; i < MAX_THREADS; i++)
2741 SetEvent(SitIdleEvent[i]);
2747 // put_threads_to_sleep() makes all the threads go to sleep just before
2748 // to leave think(), at the end of the search. Threads should have already
2749 // finished the job and should be idle.
2751 void ThreadsManager::put_threads_to_sleep() {
2753 assert(!AllThreadsShouldSleep);
2755 // This makes the threads to go to sleep
2756 AllThreadsShouldSleep = true;
2759 /// The RootMoveList class
2761 // RootMoveList c'tor
2763 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2765 SearchStack ss[PLY_MAX_PLUS_2];
2766 MoveStack mlist[MaxRootMoves];
2768 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2770 // Generate all legal moves
2771 MoveStack* last = generate_moves(pos, mlist);
2773 // Add each move to the moves[] array
2774 for (MoveStack* cur = mlist; cur != last; cur++)
2776 bool includeMove = includeAllMoves;
2778 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2779 includeMove = (searchMoves[k] == cur->move);
2784 // Find a quick score for the move
2786 pos.do_move(cur->move, st);
2787 moves[count].move = cur->move;
2788 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 0);
2789 moves[count].pv[0] = cur->move;
2790 moves[count].pv[1] = MOVE_NONE;
2791 pos.undo_move(cur->move);
2798 // RootMoveList simple methods definitions
2800 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2802 moves[moveNum].nodes = nodes;
2803 moves[moveNum].cumulativeNodes += nodes;
2806 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2808 moves[moveNum].ourBeta = our;
2809 moves[moveNum].theirBeta = their;
2812 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2816 for (j = 0; pv[j] != MOVE_NONE; j++)
2817 moves[moveNum].pv[j] = pv[j];
2819 moves[moveNum].pv[j] = MOVE_NONE;
2823 // RootMoveList::sort() sorts the root move list at the beginning of a new
2826 void RootMoveList::sort() {
2828 sort_multipv(count - 1); // Sort all items
2832 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2833 // list by their scores and depths. It is used to order the different PVs
2834 // correctly in MultiPV mode.
2836 void RootMoveList::sort_multipv(int n) {
2840 for (i = 1; i <= n; i++)
2842 RootMove rm = moves[i];
2843 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2844 moves[j] = moves[j - 1];