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/>.
44 #include "ucioption.h"
50 //// Local definitions
56 enum NodeType { NonPV, PV };
58 // Set to true to force running with one thread.
59 // Used for debugging SMP code.
60 const bool FakeSplit = false;
62 // ThreadsManager class is used to handle all the threads related stuff in search,
63 // init, starting, parking and, the most important, launching a slave thread at a
64 // split point are what this class does. All the access to shared thread data is
65 // done through this class, so that we avoid using global variables instead.
67 class ThreadsManager {
68 /* As long as the single ThreadsManager object is defined as a global we don't
69 need to explicitly initialize to zero its data members because variables with
70 static storage duration are automatically set to zero before enter main()
76 int active_threads() const { return ActiveThreads; }
77 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
78 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
80 void resetNodeCounters();
81 int64_t nodes_searched() const;
82 bool available_thread_exists(int master) const;
83 bool thread_is_available(int slave, int master) const;
84 bool thread_should_stop(int threadID) const;
85 void wake_sleeping_threads();
86 void put_threads_to_sleep();
87 void idle_loop(int threadID, SplitPoint* sp);
90 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
91 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
97 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
98 Thread threads[MAX_THREADS];
100 Lock MPLock, WaitLock;
102 #if !defined(_MSC_VER)
103 pthread_cond_t WaitCond;
105 HANDLE SitIdleEvent[MAX_THREADS];
111 // RootMove struct is used for moves at the root at the tree. For each
112 // root move, we store a score, a node count, and a PV (really a refutation
113 // in the case of moves which fail low).
117 RootMove() : mp_score(0), nodes(0) {}
119 // RootMove::operator<() is the comparison function used when
120 // sorting the moves. A move m1 is considered to be better
121 // than a move m2 if it has a higher score, or if the moves
122 // have equal score but m1 has the higher beta cut-off count.
123 bool operator<(const RootMove& m) const {
125 return score != m.score ? score < m.score : mp_score <= m.mp_score;
132 Move pv[PLY_MAX_PLUS_2];
136 // The RootMoveList class is essentially an array of RootMove objects, with
137 // a handful of methods for accessing the data in the individual moves.
142 RootMoveList(Position& pos, Move searchMoves[]);
144 Move move(int moveNum) const { return moves[moveNum].move; }
145 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
146 int move_count() const { return count; }
147 Value move_score(int moveNum) const { return moves[moveNum].score; }
148 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
149 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
150 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
152 void set_move_pv(int moveNum, const Move pv[]);
153 void score_moves(const Position& pos);
155 void sort_multipv(int n);
158 RootMove moves[MOVES_MAX];
163 // When formatting a move for std::cout we must know if we are in Chess960
164 // or not. To keep using the handy operator<<() on the move the trick is to
165 // embed this flag in the stream itself. Function-like named enum set960 is
166 // used as a custom manipulator and the stream internal general-purpose array,
167 // accessed through ios_base::iword(), is used to pass the flag to the move's
168 // operator<<() that will use it to properly format castling moves.
171 std::ostream& operator<< (std::ostream& os, const set960& m) {
173 os.iword(0) = int(m);
182 // Maximum depth for razoring
183 const Depth RazorDepth = 4 * ONE_PLY;
185 // Dynamic razoring margin based on depth
186 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
188 // Maximum depth for use of dynamic threat detection when null move fails low
189 const Depth ThreatDepth = 5 * ONE_PLY;
191 // Step 9. Internal iterative deepening
193 // Minimum depth for use of internal iterative deepening
194 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
196 // At Non-PV nodes we do an internal iterative deepening search
197 // when the static evaluation is bigger then beta - IIDMargin.
198 const Value IIDMargin = Value(0x100);
200 // Step 11. Decide the new search depth
202 // Extensions. Configurable UCI options
203 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
204 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
205 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
207 // Minimum depth for use of singular extension
208 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
210 // If the TT move is at least SingularExtensionMargin better then the
211 // remaining ones we will extend it.
212 const Value SingularExtensionMargin = Value(0x20);
214 // Step 12. Futility pruning
216 // Futility margin for quiescence search
217 const Value FutilityMarginQS = Value(0x80);
219 // Futility lookup tables (initialized at startup) and their getter functions
220 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
221 int FutilityMoveCountArray[32]; // [depth]
223 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
224 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
226 // Step 14. Reduced search
228 // Reduction lookup tables (initialized at startup) and their getter functions
229 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
231 template <NodeType PV>
232 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
234 // Common adjustments
236 // Search depth at iteration 1
237 const Depth InitialDepth = ONE_PLY;
239 // Easy move margin. An easy move candidate must be at least this much
240 // better than the second best move.
241 const Value EasyMoveMargin = Value(0x200);
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, ExactMaxTime;
261 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
262 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
267 std::ofstream LogFile;
269 // Multi-threads related variables
270 Depth MinimumSplitDepth;
271 int MaxThreadsPerSplitPoint;
272 ThreadsManager ThreadsMgr;
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, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
287 template <NodeType PvNode, bool SplitPoint>
288 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
290 template <NodeType PvNode>
291 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
292 return search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
295 template <NodeType PvNode>
296 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
298 template <NodeType PvNode>
299 void do_sp_search(SplitPoint* sp, int threadID);
301 template <NodeType PvNode>
302 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
304 bool connected_moves(const Position& pos, Move m1, Move m2);
305 bool value_is_mate(Value value);
306 Value value_to_tt(Value v, int ply);
307 Value value_from_tt(Value v, int ply);
308 bool move_is_killer(Move m, SearchStack* ss);
309 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
310 bool connected_threat(const Position& pos, Move m, Move threat);
311 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
312 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
313 void update_killers(Move m, SearchStack* ss);
314 void update_gains(const Position& pos, Move move, Value before, Value after);
316 int current_search_time();
317 std::string value_to_uci(Value v);
321 void wait_for_stop_or_ponderhit();
322 void init_ss_array(SearchStack* ss, int size);
323 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
324 void insert_pv_in_tt(const Position& pos, Move pv[]);
325 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
327 #if !defined(_MSC_VER)
328 void *init_thread(void *threadID);
330 DWORD WINAPI init_thread(LPVOID threadID);
340 /// init_threads(), exit_threads() and nodes_searched() are helpers to
341 /// give accessibility to some TM methods from outside of current file.
343 void init_threads() { ThreadsMgr.init_threads(); }
344 void exit_threads() { ThreadsMgr.exit_threads(); }
345 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
348 /// init_search() is called during startup. It initializes various lookup tables
352 int d; // depth (ONE_PLY == 2)
353 int hd; // half depth (ONE_PLY == 1)
356 // Init reductions array
357 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
359 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
360 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
361 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
362 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
365 // Init futility margins array
366 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
367 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
369 // Init futility move count array
370 for (d = 0; d < 32; d++)
371 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
375 /// perft() is our utility to verify move generation is bug free. All the legal
376 /// moves up to given depth are generated and counted and the sum returned.
378 int perft(Position& pos, Depth depth)
380 MoveStack mlist[MOVES_MAX];
385 // Generate all legal moves
386 MoveStack* last = generate_moves(pos, mlist);
388 // If we are at the last ply we don't need to do and undo
389 // the moves, just to count them.
390 if (depth <= ONE_PLY)
391 return int(last - mlist);
393 // Loop through all legal moves
395 for (MoveStack* cur = mlist; cur != last; cur++)
398 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
399 sum += perft(pos, depth - ONE_PLY);
406 /// think() is the external interface to Stockfish's search, and is called when
407 /// the program receives the UCI 'go' command. It initializes various
408 /// search-related global variables, and calls root_search(). It returns false
409 /// when a quit command is received during the search.
411 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
412 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
414 // Initialize global search variables
415 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
417 ThreadsMgr.resetNodeCounters();
418 SearchStartTime = get_system_time();
419 ExactMaxTime = maxTime;
422 InfiniteSearch = infinite;
423 PonderSearch = ponder;
424 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
426 // Look for a book move, only during games, not tests
427 if (UseTimeManagement && get_option_value_bool("OwnBook"))
429 if (get_option_value_string("Book File") != OpeningBook.file_name())
430 OpeningBook.open(get_option_value_string("Book File"));
432 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
433 if (bookMove != MOVE_NONE)
436 wait_for_stop_or_ponderhit();
438 cout << "bestmove " << bookMove << endl;
443 // Read UCI option values
444 TT.set_size(get_option_value_int("Hash"));
445 if (button_was_pressed("Clear Hash"))
448 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
449 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
450 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
451 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
452 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
453 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
454 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
455 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
456 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
457 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
458 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
459 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
461 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
462 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
463 MultiPV = get_option_value_int("MultiPV");
464 UseLogFile = get_option_value_bool("Use Search Log");
467 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
469 read_weights(pos.side_to_move());
471 // Set the number of active threads
472 int newActiveThreads = get_option_value_int("Threads");
473 if (newActiveThreads != ThreadsMgr.active_threads())
475 ThreadsMgr.set_active_threads(newActiveThreads);
476 init_eval(ThreadsMgr.active_threads());
479 // Wake up sleeping threads
480 ThreadsMgr.wake_sleeping_threads();
483 int myTime = time[pos.side_to_move()];
484 int myIncrement = increment[pos.side_to_move()];
485 if (UseTimeManagement)
486 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
488 // Set best NodesBetweenPolls interval to avoid lagging under
489 // heavy time pressure.
491 NodesBetweenPolls = Min(MaxNodes, 30000);
492 else if (myTime && myTime < 1000)
493 NodesBetweenPolls = 1000;
494 else if (myTime && myTime < 5000)
495 NodesBetweenPolls = 5000;
497 NodesBetweenPolls = 30000;
499 // Write search information to log file
501 LogFile << "Searching: " << pos.to_fen() << endl
502 << "infinite: " << infinite
503 << " ponder: " << ponder
504 << " time: " << myTime
505 << " increment: " << myIncrement
506 << " moves to go: " << movesToGo << endl;
508 // We're ready to start thinking. Call the iterative deepening loop function
509 id_loop(pos, searchMoves);
514 ThreadsMgr.put_threads_to_sleep();
522 // id_loop() is the main iterative deepening loop. It calls root_search
523 // repeatedly with increasing depth until the allocated thinking time has
524 // been consumed, the user stops the search, or the maximum search depth is
527 Value id_loop(const Position& pos, Move searchMoves[]) {
529 Position p(pos, pos.thread());
530 SearchStack ss[PLY_MAX_PLUS_2];
531 Move pv[PLY_MAX_PLUS_2];
532 Move EasyMove = MOVE_NONE;
533 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
535 // Moves to search are verified, copied, scored and sorted
536 RootMoveList rml(p, searchMoves);
538 // Handle special case of searching on a mate/stale position
539 if (rml.move_count() == 0)
542 wait_for_stop_or_ponderhit();
544 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
547 // Print RootMoveList startup scoring to the standard output,
548 // so to output information also for iteration 1.
549 cout << set960(p.is_chess960()) // Is enough to set once at the beginning
550 << "info depth " << 1
551 << "\ninfo depth " << 1
552 << " score " << value_to_uci(rml.move_score(0))
553 << " time " << current_search_time()
554 << " nodes " << ThreadsMgr.nodes_searched()
556 << " pv " << rml.move(0) << "\n";
561 init_ss_array(ss, PLY_MAX_PLUS_2);
562 pv[0] = pv[1] = MOVE_NONE;
563 ValueByIteration[1] = rml.move_score(0);
566 // Is one move significantly better than others after initial scoring ?
567 if ( rml.move_count() == 1
568 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
569 EasyMove = rml.move(0);
571 // Iterative deepening loop
572 while (Iteration < PLY_MAX)
574 // Initialize iteration
576 BestMoveChangesByIteration[Iteration] = 0;
578 cout << "info depth " << Iteration << endl;
580 // Calculate dynamic aspiration window based on previous iterations
581 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
583 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
584 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
586 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
587 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
589 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
590 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
593 // Search to the current depth, rml is updated and sorted, alpha and beta could change
594 value = root_search(p, ss, pv, rml, &alpha, &beta);
596 // Write PV to transposition table, in case the relevant entries have
597 // been overwritten during the search.
598 insert_pv_in_tt(p, pv);
601 break; // Value cannot be trusted. Break out immediately!
603 //Save info about search result
604 ValueByIteration[Iteration] = value;
606 // Drop the easy move if differs from the new best move
607 if (pv[0] != EasyMove)
608 EasyMove = MOVE_NONE;
610 if (UseTimeManagement)
613 bool stopSearch = false;
615 // Stop search early if there is only a single legal move,
616 // we search up to Iteration 6 anyway to get a proper score.
617 if (Iteration >= 6 && rml.move_count() == 1)
620 // Stop search early when the last two iterations returned a mate score
622 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
623 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
626 // Stop search early if one move seems to be much better than the others
627 int64_t nodes = ThreadsMgr.nodes_searched();
630 && ( ( rml.move_nodes(0) > (nodes * 85) / 100
631 && current_search_time() > TimeMgr.available_time() / 16)
632 ||( rml.move_nodes(0) > (nodes * 98) / 100
633 && current_search_time() > TimeMgr.available_time() / 32)))
636 // Add some extra time if the best move has changed during the last two iterations
637 if (Iteration > 5 && Iteration <= 50)
638 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
639 BestMoveChangesByIteration[Iteration-1]);
641 // Stop search if most of MaxSearchTime is consumed at the end of the
642 // iteration. We probably don't have enough time to search the first
643 // move at the next iteration anyway.
644 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
650 StopOnPonderhit = true;
656 if (MaxDepth && Iteration >= MaxDepth)
660 // If we are pondering or in infinite search, we shouldn't print the
661 // best move before we are told to do so.
662 if (!AbortSearch && (PonderSearch || InfiniteSearch))
663 wait_for_stop_or_ponderhit();
665 // Print final search statistics
666 cout << "info nodes " << ThreadsMgr.nodes_searched()
668 << " time " << current_search_time() << endl;
670 // Print the best move and the ponder move to the standard output
671 if (pv[0] == MOVE_NONE)
677 assert(pv[0] != MOVE_NONE);
679 cout << "bestmove " << pv[0];
681 if (pv[1] != MOVE_NONE)
682 cout << " ponder " << pv[1];
689 dbg_print_mean(LogFile);
691 if (dbg_show_hit_rate)
692 dbg_print_hit_rate(LogFile);
694 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
695 << "\nNodes/second: " << nps()
696 << "\nBest move: " << move_to_san(p, pv[0]);
699 p.do_move(pv[0], st);
700 LogFile << "\nPonder move: "
701 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
704 return rml.move_score(0);
708 // root_search() is the function which searches the root node. It is
709 // similar to search_pv except that it uses a different move ordering
710 // scheme, prints some information to the standard output and handles
711 // the fail low/high loops.
713 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
719 Depth depth, ext, newDepth;
720 Value value, evalMargin, alpha, beta;
721 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
722 int researchCountFH, researchCountFL;
724 researchCountFH = researchCountFL = 0;
727 isCheck = pos.is_check();
728 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
730 // Step 1. Initialize node (polling is omitted at root)
731 ss->currentMove = ss->bestMove = MOVE_NONE;
733 // Step 2. Check for aborted search (omitted at root)
734 // Step 3. Mate distance pruning (omitted at root)
735 // Step 4. Transposition table lookup (omitted at root)
737 // Step 5. Evaluate the position statically
738 // At root we do this only to get reference value for child nodes
739 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, evalMargin);
741 // Step 6. Razoring (omitted at root)
742 // Step 7. Static null move pruning (omitted at root)
743 // Step 8. Null move search with verification search (omitted at root)
744 // Step 9. Internal iterative deepening (omitted at root)
746 // Step extra. Fail low loop
747 // We start with small aspiration window and in case of fail low, we research
748 // with bigger window until we are not failing low anymore.
751 // Sort the moves before to (re)search
752 rml.score_moves(pos);
755 // Step 10. Loop through all moves in the root move list
756 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
758 // This is used by time management
759 FirstRootMove = (i == 0);
761 // Save the current node count before the move is searched
762 nodes = ThreadsMgr.nodes_searched();
764 // Pick the next root move, and print the move and the move number to
765 // the standard output.
766 move = ss->currentMove = rml.move(i);
768 if (current_search_time() >= 1000)
769 cout << "info currmove " << move
770 << " currmovenumber " << i + 1 << endl;
772 moveIsCheck = pos.move_is_check(move);
773 captureOrPromotion = pos.move_is_capture_or_promotion(move);
775 // Step 11. Decide the new search depth
776 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
777 newDepth = depth + ext;
779 // Step 12. Futility pruning (omitted at root)
781 // Step extra. Fail high loop
782 // If move fails high, we research with bigger window until we are not failing
784 value = - VALUE_INFINITE;
788 // Step 13. Make the move
789 pos.do_move(move, st, ci, moveIsCheck);
791 // Step extra. pv search
792 // We do pv search for first moves (i < MultiPV)
793 // and for fail high research (value > alpha)
794 if (i < MultiPV || value > alpha)
796 // Aspiration window is disabled in multi-pv case
798 alpha = -VALUE_INFINITE;
800 // Full depth PV search, done on first move or after a fail high
801 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
805 // Step 14. Reduced search
806 // if the move fails high will be re-searched at full depth
807 bool doFullDepthSearch = true;
809 if ( depth >= 3 * ONE_PLY
811 && !captureOrPromotion
812 && !move_is_castle(move))
814 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
817 assert(newDepth-ss->reduction >= ONE_PLY);
819 // Reduced depth non-pv search using alpha as upperbound
820 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
821 doFullDepthSearch = (value > alpha);
824 // The move failed high, but if reduction is very big we could
825 // face a false positive, retry with a less aggressive reduction,
826 // if the move fails high again then go with full depth search.
827 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
829 assert(newDepth - ONE_PLY >= ONE_PLY);
831 ss->reduction = ONE_PLY;
832 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
833 doFullDepthSearch = (value > alpha);
835 ss->reduction = DEPTH_ZERO; // Restore original reduction
838 // Step 15. Full depth search
839 if (doFullDepthSearch)
841 // Full depth non-pv search using alpha as upperbound
842 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
844 // If we are above alpha then research at same depth but as PV
845 // to get a correct score or eventually a fail high above beta.
847 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
851 // Step 16. Undo move
854 // Can we exit fail high loop ?
855 if (AbortSearch || value < beta)
858 // We are failing high and going to do a research. It's important to update
859 // the score before research in case we run out of time while researching.
860 rml.set_move_score(i, value);
862 extract_pv_from_tt(pos, move, pv);
863 rml.set_move_pv(i, pv);
865 // Print information to the standard output
866 print_pv_info(pos, pv, alpha, beta, value);
868 // Prepare for a research after a fail high, each time with a wider window
869 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
872 } // End of fail high loop
874 // Finished searching the move. If AbortSearch is true, the search
875 // was aborted because the user interrupted the search or because we
876 // ran out of time. In this case, the return value of the search cannot
877 // be trusted, and we break out of the loop without updating the best
882 // Remember searched nodes counts for this move
883 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
885 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
886 assert(value < beta);
888 // Step 17. Check for new best move
889 if (value <= alpha && i >= MultiPV)
890 rml.set_move_score(i, -VALUE_INFINITE);
893 // PV move or new best move!
896 rml.set_move_score(i, value);
898 extract_pv_from_tt(pos, move, pv);
899 rml.set_move_pv(i, pv);
903 // We record how often the best move has been changed in each
904 // iteration. This information is used for time managment: When
905 // the best move changes frequently, we allocate some more time.
907 BestMoveChangesByIteration[Iteration]++;
909 // Print information to the standard output
910 print_pv_info(pos, pv, alpha, beta, value);
912 // Raise alpha to setup proper non-pv search upper bound
919 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
921 cout << "info multipv " << j + 1
922 << " score " << value_to_uci(rml.move_score(j))
923 << " depth " << (j <= i ? Iteration : Iteration - 1)
924 << " time " << current_search_time()
925 << " nodes " << ThreadsMgr.nodes_searched()
929 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
930 cout << rml.move_pv(j, k) << " ";
934 alpha = rml.move_score(Min(i, MultiPV - 1));
936 } // PV move or new best move
938 assert(alpha >= *alphaPtr);
940 AspirationFailLow = (alpha == *alphaPtr);
942 if (AspirationFailLow && StopOnPonderhit)
943 StopOnPonderhit = false;
946 // Can we exit fail low loop ?
947 if (AbortSearch || !AspirationFailLow)
950 // Prepare for a research after a fail low, each time with a wider window
951 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
956 // Sort the moves before to return
963 // search<>() is the main search function for both PV and non-PV nodes
965 template <NodeType PvNode, bool SplitPoint>
966 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
968 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
969 assert(beta > alpha && beta <= VALUE_INFINITE);
970 assert(PvNode || alpha == beta - 1);
971 assert(ply > 0 && ply < PLY_MAX);
972 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
974 Move movesSearched[MOVES_MAX];
978 Move ttMove, move, excludedMove, threatMove;
980 Value bestValue, value, evalMargin, oldAlpha;
981 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
982 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
983 bool mateThreat = false;
985 int threadID = pos.thread();
986 refinedValue = bestValue = value = -VALUE_INFINITE;
988 isCheck = pos.is_check();
993 ttMove = excludedMove = MOVE_NONE;
994 threatMove = ss->sp->threatMove;
995 mateThreat = ss->sp->mateThreat;
999 // Step 1. Initialize node and poll. Polling can abort search
1000 ThreadsMgr.incrementNodeCounter(threadID);
1001 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
1002 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1004 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1010 // Step 2. Check for aborted search and immediate draw
1011 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1014 if (pos.is_draw() || ply >= PLY_MAX - 1)
1017 // Step 3. Mate distance pruning
1018 alpha = Max(value_mated_in(ply), alpha);
1019 beta = Min(value_mate_in(ply+1), beta);
1023 // Step 4. Transposition table lookup
1025 // We don't want the score of a partial search to overwrite a previous full search
1026 // TT value, so we use a different position key in case of an excluded move exists.
1027 excludedMove = ss->excludedMove;
1028 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1030 tte = TT.retrieve(posKey);
1031 ttMove = (tte ? tte->move() : MOVE_NONE);
1033 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1034 // This is to avoid problems in the following areas:
1036 // * Repetition draw detection
1037 // * Fifty move rule detection
1038 // * Searching for a mate
1039 // * Printing of full PV line
1041 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1043 // Refresh tte entry to avoid aging
1044 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1046 ss->bestMove = ttMove; // Can be MOVE_NONE
1047 return value_from_tt(tte->value(), ply);
1050 // Step 5. Evaluate the position statically and
1051 // update gain statistics of parent move.
1053 ss->eval = evalMargin = VALUE_NONE;
1056 assert(tte->static_value() != VALUE_NONE);
1058 ss->eval = tte->static_value();
1059 evalMargin = tte->static_value_margin();
1060 refinedValue = refine_eval(tte, ss->eval, ply);
1064 refinedValue = ss->eval = evaluate(pos, evalMargin);
1065 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1068 // Save gain for the parent non-capture move
1069 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1071 // Step 6. Razoring (is omitted in PV nodes)
1073 && depth < RazorDepth
1075 && refinedValue < beta - razor_margin(depth)
1076 && ttMove == MOVE_NONE
1077 && (ss-1)->currentMove != MOVE_NULL
1078 && !value_is_mate(beta)
1079 && !pos.has_pawn_on_7th(pos.side_to_move()))
1081 Value rbeta = beta - razor_margin(depth);
1082 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1084 // Logically we should return (v + razor_margin(depth)), but
1085 // surprisingly this did slightly weaker in tests.
1089 // Step 7. Static null move pruning (is omitted in PV nodes)
1090 // We're betting that the opponent doesn't have a move that will reduce
1091 // the score by more than futility_margin(depth) if we do a null move.
1093 && !ss->skipNullMove
1094 && depth < RazorDepth
1096 && refinedValue >= beta + futility_margin(depth, 0)
1097 && !value_is_mate(beta)
1098 && pos.non_pawn_material(pos.side_to_move()))
1099 return refinedValue - futility_margin(depth, 0);
1101 // Step 8. Null move search with verification search (is omitted in PV nodes)
1103 && !ss->skipNullMove
1106 && refinedValue >= beta
1107 && !value_is_mate(beta)
1108 && pos.non_pawn_material(pos.side_to_move()))
1110 ss->currentMove = MOVE_NULL;
1112 // Null move dynamic reduction based on depth
1113 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1115 // Null move dynamic reduction based on value
1116 if (refinedValue - beta > PawnValueMidgame)
1119 pos.do_null_move(st);
1120 (ss+1)->skipNullMove = true;
1122 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1123 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1124 (ss+1)->skipNullMove = false;
1125 pos.undo_null_move();
1127 if (nullValue >= beta)
1129 // Do not return unproven mate scores
1130 if (nullValue >= value_mate_in(PLY_MAX))
1133 if (depth < 6 * ONE_PLY)
1136 // Do verification search at high depths
1137 ss->skipNullMove = true;
1138 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1139 ss->skipNullMove = false;
1146 // The null move failed low, which means that we may be faced with
1147 // some kind of threat. If the previous move was reduced, check if
1148 // the move that refuted the null move was somehow connected to the
1149 // move which was reduced. If a connection is found, return a fail
1150 // low score (which will cause the reduced move to fail high in the
1151 // parent node, which will trigger a re-search with full depth).
1152 if (nullValue == value_mated_in(ply + 2))
1155 threatMove = (ss+1)->bestMove;
1156 if ( depth < ThreatDepth
1157 && (ss-1)->reduction
1158 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1163 // Step 9. Internal iterative deepening
1164 if ( depth >= IIDDepth[PvNode]
1165 && ttMove == MOVE_NONE
1166 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1168 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1170 ss->skipNullMove = true;
1171 search<PvNode>(pos, ss, alpha, beta, d, ply);
1172 ss->skipNullMove = false;
1174 ttMove = ss->bestMove;
1175 tte = TT.retrieve(posKey);
1178 // Expensive mate threat detection (only for PV nodes)
1180 mateThreat = pos.has_mate_threat();
1184 // Initialize a MovePicker object for the current position
1185 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1186 MovePicker mpBase = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1187 MovePicker& mp = SplitPoint ? *ss->sp->mp : mpBase;
1189 ss->bestMove = MOVE_NONE;
1190 singleEvasion = SplitPoint ? false : isCheck && mp.number_of_evasions() == 1;
1191 futilityBase = SplitPoint ? ss->eval : ss->eval + evalMargin;
1192 singularExtensionNode = !SplitPoint
1193 && depth >= SingularExtensionDepth[PvNode]
1196 && !excludedMove // Do not allow recursive singular extension search
1197 && (tte->type() & VALUE_TYPE_LOWER)
1198 && tte->depth() >= depth - 3 * ONE_PLY;
1200 // Step 10. Loop through moves
1201 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1204 lock_grab(&(ss->sp->lock));
1205 bestValue = ss->sp->bestValue;
1208 while ( bestValue < beta
1209 && (move = mp.get_next_move()) != MOVE_NONE
1210 && !ThreadsMgr.thread_should_stop(threadID))
1214 moveCount = ++ss->sp->moveCount;
1215 lock_release(&(ss->sp->lock));
1218 assert(move_is_ok(move));
1220 if (move == excludedMove)
1223 moveIsCheck = pos.move_is_check(move, ci);
1224 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1226 // Step 11. Decide the new search depth
1227 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1229 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1230 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1231 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1232 // lower then ttValue minus a margin then we extend ttMove.
1233 if ( singularExtensionNode
1234 && move == tte->move()
1237 Value ttValue = value_from_tt(tte->value(), ply);
1239 if (abs(ttValue) < VALUE_KNOWN_WIN)
1241 Value b = ttValue - SingularExtensionMargin;
1242 ss->excludedMove = move;
1243 ss->skipNullMove = true;
1244 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1245 ss->skipNullMove = false;
1246 ss->excludedMove = MOVE_NONE;
1247 ss->bestMove = MOVE_NONE;
1253 newDepth = depth - ONE_PLY + ext;
1255 // Update current move (this must be done after singular extension search)
1256 movesSearched[moveCount++] = ss->currentMove = move;
1258 // Step 12. Futility pruning (is omitted in PV nodes)
1260 && !captureOrPromotion
1264 && !move_is_castle(move))
1266 // Move count based pruning
1267 if ( moveCount >= futility_move_count(depth)
1268 && !(threatMove && connected_threat(pos, move, threatMove))
1269 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1272 lock_grab(&(ss->sp->lock));
1276 // Value based pruning
1277 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1278 // but fixing this made program slightly weaker.
1279 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1280 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1281 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1283 if (futilityValueScaled < beta)
1287 lock_grab(&(ss->sp->lock));
1288 if (futilityValueScaled > ss->sp->bestValue)
1289 ss->sp->bestValue = bestValue = futilityValueScaled;
1291 else if (futilityValueScaled > bestValue)
1292 bestValue = futilityValueScaled;
1297 // Step 13. Make the move
1298 pos.do_move(move, st, ci, moveIsCheck);
1300 // Step extra. pv search (only in PV nodes)
1301 // The first move in list is the expected PV
1302 if (!SplitPoint && PvNode && moveCount == 1)
1303 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1304 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1307 // Step 14. Reduced depth search
1308 // If the move fails high will be re-searched at full depth.
1309 bool doFullDepthSearch = true;
1311 if ( depth >= 3 * ONE_PLY
1312 && !captureOrPromotion
1314 && !move_is_castle(move)
1315 && !move_is_killer(move, ss))
1317 ss->reduction = reduction<PvNode>(depth, moveCount);
1320 alpha = SplitPoint ? ss->sp->alpha : alpha;
1321 Depth d = newDepth - ss->reduction;
1322 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1323 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1325 doFullDepthSearch = (value > alpha);
1328 // The move failed high, but if reduction is very big we could
1329 // face a false positive, retry with a less aggressive reduction,
1330 // if the move fails high again then go with full depth search.
1331 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1333 assert(newDepth - ONE_PLY >= ONE_PLY);
1335 ss->reduction = ONE_PLY;
1336 alpha = SplitPoint ? ss->sp->alpha : alpha;
1337 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1338 doFullDepthSearch = (value > alpha);
1340 ss->reduction = DEPTH_ZERO; // Restore original reduction
1343 // Step 15. Full depth search
1344 if (doFullDepthSearch)
1346 alpha = SplitPoint ? ss->sp->alpha : alpha;
1347 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1348 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1350 // Step extra. pv search (only in PV nodes)
1351 // Search only for possible new PV nodes, if instead value >= beta then
1352 // parent node fails low with value <= alpha and tries another move.
1353 if (PvNode && value > alpha && value < beta)
1354 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1355 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1359 // Step 16. Undo move
1360 pos.undo_move(move);
1362 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1364 // Step 17. Check for new best move
1367 lock_grab(&(ss->sp->lock));
1368 bestValue = ss->sp->bestValue;
1369 alpha = ss->sp->alpha;
1372 if (value > bestValue && !(SplitPoint && ThreadsMgr.thread_should_stop(threadID)))
1377 if (SplitPoint && (!PvNode || value >= beta))
1378 ss->sp->stopRequest = true;
1380 if (PvNode && value < beta) // We want always alpha < beta
1383 if (value == value_mate_in(ply + 1))
1384 ss->mateKiller = move;
1386 ss->bestMove = move;
1390 ss->sp->bestValue = bestValue;
1391 ss->sp->alpha = alpha;
1392 ss->sp->parentSstack->bestMove = ss->bestMove;
1396 // Step 18. Check for split
1398 && depth >= MinimumSplitDepth
1399 && ThreadsMgr.active_threads() > 1
1401 && ThreadsMgr.available_thread_exists(threadID)
1403 && !ThreadsMgr.thread_should_stop(threadID)
1405 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1406 threatMove, mateThreat, moveCount, &mp, PvNode);
1411 /* Here we have the lock still grabbed */
1412 ss->sp->slaves[threadID] = 0;
1413 lock_release(&(ss->sp->lock));
1417 // Step 19. Check for mate and stalemate
1418 // All legal moves have been searched and if there are
1419 // no legal moves, it must be mate or stalemate.
1420 // If one move was excluded return fail low score.
1422 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1424 // Step 20. Update tables
1425 // If the search is not aborted, update the transposition table,
1426 // history counters, and killer moves.
1427 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1430 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1431 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1432 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, evalMargin);
1434 // Update killers and history only for non capture moves that fails high
1435 if ( bestValue >= beta
1436 && !pos.move_is_capture_or_promotion(move))
1438 update_history(pos, move, depth, movesSearched, moveCount);
1439 update_killers(move, ss);
1442 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1448 // qsearch() is the quiescence search function, which is called by the main
1449 // search function when the remaining depth is zero (or, to be more precise,
1450 // less than ONE_PLY).
1452 template <NodeType PvNode>
1453 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1455 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1456 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1457 assert(PvNode || alpha == beta - 1);
1459 assert(ply > 0 && ply < PLY_MAX);
1460 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1464 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1465 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1467 Value oldAlpha = alpha;
1469 ThreadsMgr.incrementNodeCounter(pos.thread());
1470 ss->bestMove = ss->currentMove = MOVE_NONE;
1472 // Check for an instant draw or maximum ply reached
1473 if (pos.is_draw() || ply >= PLY_MAX - 1)
1476 // Transposition table lookup. At PV nodes, we don't use the TT for
1477 // pruning, but only for move ordering.
1478 tte = TT.retrieve(pos.get_key());
1479 ttMove = (tte ? tte->move() : MOVE_NONE);
1481 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1483 ss->bestMove = ttMove; // Can be MOVE_NONE
1484 return value_from_tt(tte->value(), ply);
1487 isCheck = pos.is_check();
1489 // Evaluate the position statically
1492 bestValue = futilityBase = -VALUE_INFINITE;
1493 ss->eval = evalMargin = VALUE_NONE;
1494 deepChecks = enoughMaterial = false;
1500 assert(tte->static_value() != VALUE_NONE);
1502 evalMargin = tte->static_value_margin();
1503 ss->eval = bestValue = tte->static_value();
1506 ss->eval = bestValue = evaluate(pos, evalMargin);
1508 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1510 // Stand pat. Return immediately if static value is at least beta
1511 if (bestValue >= beta)
1514 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1519 if (PvNode && bestValue > alpha)
1522 // If we are near beta then try to get a cutoff pushing checks a bit further
1523 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1525 // Futility pruning parameters, not needed when in check
1526 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1527 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1530 // Initialize a MovePicker object for the current position, and prepare
1531 // to search the moves. Because the depth is <= 0 here, only captures,
1532 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1533 // and we are near beta) will be generated.
1534 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1537 // Loop through the moves until no moves remain or a beta cutoff occurs
1538 while ( alpha < beta
1539 && (move = mp.get_next_move()) != MOVE_NONE)
1541 assert(move_is_ok(move));
1543 moveIsCheck = pos.move_is_check(move, ci);
1551 && !move_is_promotion(move)
1552 && !pos.move_is_passed_pawn_push(move))
1554 futilityValue = futilityBase
1555 + pos.endgame_value_of_piece_on(move_to(move))
1556 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1558 if (futilityValue < alpha)
1560 if (futilityValue > bestValue)
1561 bestValue = futilityValue;
1566 // Detect non-capture evasions that are candidate to be pruned
1567 evasionPrunable = isCheck
1568 && bestValue > value_mated_in(PLY_MAX)
1569 && !pos.move_is_capture(move)
1570 && !pos.can_castle(pos.side_to_move());
1572 // Don't search moves with negative SEE values
1574 && (!isCheck || evasionPrunable)
1576 && !move_is_promotion(move)
1577 && pos.see_sign(move) < 0)
1580 // Update current move
1581 ss->currentMove = move;
1583 // Make and search the move
1584 pos.do_move(move, st, ci, moveIsCheck);
1585 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1586 pos.undo_move(move);
1588 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1591 if (value > bestValue)
1597 ss->bestMove = move;
1602 // All legal moves have been searched. A special case: If we're in check
1603 // and no legal moves were found, it is checkmate.
1604 if (isCheck && bestValue == -VALUE_INFINITE)
1605 return value_mated_in(ply);
1607 // Update transposition table
1608 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1609 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1610 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1612 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1618 // sp_search() is used to search from a split point. This function is called
1619 // by each thread working at the split point. It is similar to the normal
1620 // search() function, but simpler. Because we have already probed the hash
1621 // table, done a null move search, and searched the first move before
1622 // splitting, we don't have to repeat all this work in sp_search(). We
1623 // also don't need to store anything to the hash table here: This is taken
1624 // care of after we return from the split point.
1626 template <NodeType PvNode>
1627 void do_sp_search(SplitPoint* sp, int threadID) {
1629 assert(threadID >= 0 && threadID < ThreadsMgr.active_threads());
1630 assert(ThreadsMgr.active_threads() > 1);
1632 Position pos(*sp->pos, threadID);
1633 SearchStack* ss = sp->sstack[threadID] + 1;
1636 search<PvNode, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->ply);
1640 // connected_moves() tests whether two moves are 'connected' in the sense
1641 // that the first move somehow made the second move possible (for instance
1642 // if the moving piece is the same in both moves). The first move is assumed
1643 // to be the move that was made to reach the current position, while the
1644 // second move is assumed to be a move from the current position.
1646 bool connected_moves(const Position& pos, Move m1, Move m2) {
1648 Square f1, t1, f2, t2;
1651 assert(move_is_ok(m1));
1652 assert(move_is_ok(m2));
1654 if (m2 == MOVE_NONE)
1657 // Case 1: The moving piece is the same in both moves
1663 // Case 2: The destination square for m2 was vacated by m1
1669 // Case 3: Moving through the vacated square
1670 if ( piece_is_slider(pos.piece_on(f2))
1671 && bit_is_set(squares_between(f2, t2), f1))
1674 // Case 4: The destination square for m2 is defended by the moving piece in m1
1675 p = pos.piece_on(t1);
1676 if (bit_is_set(pos.attacks_from(p, t1), t2))
1679 // Case 5: Discovered check, checking piece is the piece moved in m1
1680 if ( piece_is_slider(p)
1681 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1682 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1684 // discovered_check_candidates() works also if the Position's side to
1685 // move is the opposite of the checking piece.
1686 Color them = opposite_color(pos.side_to_move());
1687 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1689 if (bit_is_set(dcCandidates, f2))
1696 // value_is_mate() checks if the given value is a mate one eventually
1697 // compensated for the ply.
1699 bool value_is_mate(Value value) {
1701 assert(abs(value) <= VALUE_INFINITE);
1703 return value <= value_mated_in(PLY_MAX)
1704 || value >= value_mate_in(PLY_MAX);
1708 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1709 // "plies to mate from the current ply". Non-mate scores are unchanged.
1710 // The function is called before storing a value to the transposition table.
1712 Value value_to_tt(Value v, int ply) {
1714 if (v >= value_mate_in(PLY_MAX))
1717 if (v <= value_mated_in(PLY_MAX))
1724 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1725 // the transposition table to a mate score corrected for the current ply.
1727 Value value_from_tt(Value v, int ply) {
1729 if (v >= value_mate_in(PLY_MAX))
1732 if (v <= value_mated_in(PLY_MAX))
1739 // move_is_killer() checks if the given move is among the killer moves
1741 bool move_is_killer(Move m, SearchStack* ss) {
1743 if (ss->killers[0] == m || ss->killers[1] == m)
1750 // extension() decides whether a move should be searched with normal depth,
1751 // or with extended depth. Certain classes of moves (checking moves, in
1752 // particular) are searched with bigger depth than ordinary moves and in
1753 // any case are marked as 'dangerous'. Note that also if a move is not
1754 // extended, as example because the corresponding UCI option is set to zero,
1755 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1756 template <NodeType PvNode>
1757 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1758 bool singleEvasion, bool mateThreat, bool* dangerous) {
1760 assert(m != MOVE_NONE);
1762 Depth result = DEPTH_ZERO;
1763 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1767 if (moveIsCheck && pos.see_sign(m) >= 0)
1768 result += CheckExtension[PvNode];
1771 result += SingleEvasionExtension[PvNode];
1774 result += MateThreatExtension[PvNode];
1777 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1779 Color c = pos.side_to_move();
1780 if (relative_rank(c, move_to(m)) == RANK_7)
1782 result += PawnPushTo7thExtension[PvNode];
1785 if (pos.pawn_is_passed(c, move_to(m)))
1787 result += PassedPawnExtension[PvNode];
1792 if ( captureOrPromotion
1793 && pos.type_of_piece_on(move_to(m)) != PAWN
1794 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1795 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1796 && !move_is_promotion(m)
1799 result += PawnEndgameExtension[PvNode];
1804 && captureOrPromotion
1805 && pos.type_of_piece_on(move_to(m)) != PAWN
1806 && pos.see_sign(m) >= 0)
1808 result += ONE_PLY / 2;
1812 return Min(result, ONE_PLY);
1816 // connected_threat() tests whether it is safe to forward prune a move or if
1817 // is somehow coonected to the threat move returned by null search.
1819 bool connected_threat(const Position& pos, Move m, Move threat) {
1821 assert(move_is_ok(m));
1822 assert(threat && move_is_ok(threat));
1823 assert(!pos.move_is_check(m));
1824 assert(!pos.move_is_capture_or_promotion(m));
1825 assert(!pos.move_is_passed_pawn_push(m));
1827 Square mfrom, mto, tfrom, tto;
1829 mfrom = move_from(m);
1831 tfrom = move_from(threat);
1832 tto = move_to(threat);
1834 // Case 1: Don't prune moves which move the threatened piece
1838 // Case 2: If the threatened piece has value less than or equal to the
1839 // value of the threatening piece, don't prune move which defend it.
1840 if ( pos.move_is_capture(threat)
1841 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1842 || pos.type_of_piece_on(tfrom) == KING)
1843 && pos.move_attacks_square(m, tto))
1846 // Case 3: If the moving piece in the threatened move is a slider, don't
1847 // prune safe moves which block its ray.
1848 if ( piece_is_slider(pos.piece_on(tfrom))
1849 && bit_is_set(squares_between(tfrom, tto), mto)
1850 && pos.see_sign(m) >= 0)
1857 // ok_to_use_TT() returns true if a transposition table score
1858 // can be used at a given point in search.
1860 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1862 Value v = value_from_tt(tte->value(), ply);
1864 return ( tte->depth() >= depth
1865 || v >= Max(value_mate_in(PLY_MAX), beta)
1866 || v < Min(value_mated_in(PLY_MAX), beta))
1868 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1869 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1873 // refine_eval() returns the transposition table score if
1874 // possible otherwise falls back on static position evaluation.
1876 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1880 Value v = value_from_tt(tte->value(), ply);
1882 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1883 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1890 // update_history() registers a good move that produced a beta-cutoff
1891 // in history and marks as failures all the other moves of that ply.
1893 void update_history(const Position& pos, Move move, Depth depth,
1894 Move movesSearched[], int moveCount) {
1898 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1900 for (int i = 0; i < moveCount - 1; i++)
1902 m = movesSearched[i];
1906 if (!pos.move_is_capture_or_promotion(m))
1907 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1912 // update_killers() add a good move that produced a beta-cutoff
1913 // among the killer moves of that ply.
1915 void update_killers(Move m, SearchStack* ss) {
1917 if (m == ss->killers[0])
1920 ss->killers[1] = ss->killers[0];
1925 // update_gains() updates the gains table of a non-capture move given
1926 // the static position evaluation before and after the move.
1928 void update_gains(const Position& pos, Move m, Value before, Value after) {
1931 && before != VALUE_NONE
1932 && after != VALUE_NONE
1933 && pos.captured_piece_type() == PIECE_TYPE_NONE
1934 && !move_is_special(m))
1935 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1939 // current_search_time() returns the number of milliseconds which have passed
1940 // since the beginning of the current search.
1942 int current_search_time() {
1944 return get_system_time() - SearchStartTime;
1948 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1950 std::string value_to_uci(Value v) {
1952 std::stringstream s;
1954 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1955 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1957 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1962 // nps() computes the current nodes/second count.
1966 int t = current_search_time();
1967 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
1971 // poll() performs two different functions: It polls for user input, and it
1972 // looks at the time consumed so far and decides if it's time to abort the
1977 static int lastInfoTime;
1978 int t = current_search_time();
1983 // We are line oriented, don't read single chars
1984 std::string command;
1986 if (!std::getline(std::cin, command))
1989 if (command == "quit")
1992 PonderSearch = false;
1996 else if (command == "stop")
1999 PonderSearch = false;
2001 else if (command == "ponderhit")
2005 // Print search information
2009 else if (lastInfoTime > t)
2010 // HACK: Must be a new search where we searched less than
2011 // NodesBetweenPolls nodes during the first second of search.
2014 else if (t - lastInfoTime >= 1000)
2021 if (dbg_show_hit_rate)
2022 dbg_print_hit_rate();
2024 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
2025 << " time " << t << endl;
2028 // Should we stop the search?
2032 bool stillAtFirstMove = FirstRootMove
2033 && !AspirationFailLow
2034 && t > TimeMgr.available_time();
2036 bool noMoreTime = t > TimeMgr.maximum_time()
2037 || stillAtFirstMove;
2039 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2040 || (ExactMaxTime && t >= ExactMaxTime)
2041 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2046 // ponderhit() is called when the program is pondering (i.e. thinking while
2047 // it's the opponent's turn to move) in order to let the engine know that
2048 // it correctly predicted the opponent's move.
2052 int t = current_search_time();
2053 PonderSearch = false;
2055 bool stillAtFirstMove = FirstRootMove
2056 && !AspirationFailLow
2057 && t > TimeMgr.available_time();
2059 bool noMoreTime = t > TimeMgr.maximum_time()
2060 || stillAtFirstMove;
2062 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2067 // init_ss_array() does a fast reset of the first entries of a SearchStack
2068 // array and of all the excludedMove and skipNullMove entries.
2070 void init_ss_array(SearchStack* ss, int size) {
2072 for (int i = 0; i < size; i++, ss++)
2074 ss->excludedMove = MOVE_NONE;
2075 ss->skipNullMove = false;
2076 ss->reduction = DEPTH_ZERO;
2080 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2085 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2086 // while the program is pondering. The point is to work around a wrinkle in
2087 // the UCI protocol: When pondering, the engine is not allowed to give a
2088 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2089 // We simply wait here until one of these commands is sent, and return,
2090 // after which the bestmove and pondermove will be printed (in id_loop()).
2092 void wait_for_stop_or_ponderhit() {
2094 std::string command;
2098 if (!std::getline(std::cin, command))
2101 if (command == "quit")
2106 else if (command == "ponderhit" || command == "stop")
2112 // print_pv_info() prints to standard output and eventually to log file information on
2113 // the current PV line. It is called at each iteration or after a new pv is found.
2115 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2117 cout << "info depth " << Iteration
2118 << " score " << value_to_uci(value)
2119 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2120 << " time " << current_search_time()
2121 << " nodes " << ThreadsMgr.nodes_searched()
2125 for (Move* m = pv; *m != MOVE_NONE; m++)
2132 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2133 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2135 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2136 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2141 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2142 // the PV back into the TT. This makes sure the old PV moves are searched
2143 // first, even if the old TT entries have been overwritten.
2145 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2149 Position p(pos, pos.thread());
2150 Value v, m = VALUE_NONE;
2152 for (int i = 0; pv[i] != MOVE_NONE; i++)
2154 tte = TT.retrieve(p.get_key());
2155 if (!tte || tte->move() != pv[i])
2157 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2158 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2160 p.do_move(pv[i], st);
2165 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2166 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2167 // allow to always have a ponder move even when we fail high at root and also a
2168 // long PV to print that is important for position analysis.
2170 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2174 Position p(pos, pos.thread());
2177 assert(bestMove != MOVE_NONE);
2180 p.do_move(pv[ply++], st);
2182 while ( (tte = TT.retrieve(p.get_key())) != NULL
2183 && tte->move() != MOVE_NONE
2184 && move_is_legal(p, tte->move())
2186 && (!p.is_draw() || ply < 2))
2188 pv[ply] = tte->move();
2189 p.do_move(pv[ply++], st);
2191 pv[ply] = MOVE_NONE;
2195 // init_thread() is the function which is called when a new thread is
2196 // launched. It simply calls the idle_loop() function with the supplied
2197 // threadID. There are two versions of this function; one for POSIX
2198 // threads and one for Windows threads.
2200 #if !defined(_MSC_VER)
2202 void* init_thread(void *threadID) {
2204 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2210 DWORD WINAPI init_thread(LPVOID threadID) {
2212 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2219 /// The ThreadsManager class
2221 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2222 // get_beta_counters() are getters/setters for the per thread
2223 // counters used to sort the moves at root.
2225 void ThreadsManager::resetNodeCounters() {
2227 for (int i = 0; i < MAX_THREADS; i++)
2228 threads[i].nodes = 0ULL;
2231 int64_t ThreadsManager::nodes_searched() const {
2233 int64_t result = 0ULL;
2234 for (int i = 0; i < ActiveThreads; i++)
2235 result += threads[i].nodes;
2241 // idle_loop() is where the threads are parked when they have no work to do.
2242 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2243 // object for which the current thread is the master.
2245 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2247 assert(threadID >= 0 && threadID < MAX_THREADS);
2251 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2252 // master should exit as last one.
2253 if (AllThreadsShouldExit)
2256 threads[threadID].state = THREAD_TERMINATED;
2260 // If we are not thinking, wait for a condition to be signaled
2261 // instead of wasting CPU time polling for work.
2262 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2265 assert(threadID != 0);
2266 threads[threadID].state = THREAD_SLEEPING;
2268 #if !defined(_MSC_VER)
2269 lock_grab(&WaitLock);
2270 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2271 pthread_cond_wait(&WaitCond, &WaitLock);
2272 lock_release(&WaitLock);
2274 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2278 // If thread has just woken up, mark it as available
2279 if (threads[threadID].state == THREAD_SLEEPING)
2280 threads[threadID].state = THREAD_AVAILABLE;
2282 // If this thread has been assigned work, launch a search
2283 if (threads[threadID].state == THREAD_WORKISWAITING)
2285 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2287 threads[threadID].state = THREAD_SEARCHING;
2289 if (threads[threadID].splitPoint->pvNode)
2290 do_sp_search<PV>(threads[threadID].splitPoint, threadID);
2292 do_sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2294 assert(threads[threadID].state == THREAD_SEARCHING);
2296 threads[threadID].state = THREAD_AVAILABLE;
2299 // If this thread is the master of a split point and all slaves have
2300 // finished their work at this split point, return from the idle loop.
2302 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2304 if (i == ActiveThreads)
2306 // Because sp->slaves[] is reset under lock protection,
2307 // be sure sp->lock has been released before to return.
2308 lock_grab(&(sp->lock));
2309 lock_release(&(sp->lock));
2311 // In helpful master concept a master can help only a sub-tree, and
2312 // because here is all finished is not possible master is booked.
2313 assert(threads[threadID].state == THREAD_AVAILABLE);
2315 threads[threadID].state = THREAD_SEARCHING;
2322 // init_threads() is called during startup. It launches all helper threads,
2323 // and initializes the split point stack and the global locks and condition
2326 void ThreadsManager::init_threads() {
2331 #if !defined(_MSC_VER)
2332 pthread_t pthread[1];
2335 // Initialize global locks
2337 lock_init(&WaitLock);
2339 #if !defined(_MSC_VER)
2340 pthread_cond_init(&WaitCond, NULL);
2342 for (i = 0; i < MAX_THREADS; i++)
2343 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2346 // Initialize splitPoints[] locks
2347 for (i = 0; i < MAX_THREADS; i++)
2348 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2349 lock_init(&(threads[i].splitPoints[j].lock));
2351 // Will be set just before program exits to properly end the threads
2352 AllThreadsShouldExit = false;
2354 // Threads will be put to sleep as soon as created
2355 AllThreadsShouldSleep = true;
2357 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2359 threads[0].state = THREAD_SEARCHING;
2360 for (i = 1; i < MAX_THREADS; i++)
2361 threads[i].state = THREAD_AVAILABLE;
2363 // Launch the helper threads
2364 for (i = 1; i < MAX_THREADS; i++)
2367 #if !defined(_MSC_VER)
2368 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2370 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2375 cout << "Failed to create thread number " << i << endl;
2376 Application::exit_with_failure();
2379 // Wait until the thread has finished launching and is gone to sleep
2380 while (threads[i].state != THREAD_SLEEPING) {}
2385 // exit_threads() is called when the program exits. It makes all the
2386 // helper threads exit cleanly.
2388 void ThreadsManager::exit_threads() {
2390 ActiveThreads = MAX_THREADS; // Wake up all the threads
2391 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2392 AllThreadsShouldSleep = true; // Avoid an assert in wake_sleeping_threads()
2393 wake_sleeping_threads();
2395 // Wait for thread termination
2396 for (int i = 1; i < MAX_THREADS; i++)
2397 while (threads[i].state != THREAD_TERMINATED) {}
2399 // Now we can safely destroy the locks
2400 for (int i = 0; i < MAX_THREADS; i++)
2401 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2402 lock_destroy(&(threads[i].splitPoints[j].lock));
2404 lock_destroy(&WaitLock);
2405 lock_destroy(&MPLock);
2409 // thread_should_stop() checks whether the thread should stop its search.
2410 // This can happen if a beta cutoff has occurred in the thread's currently
2411 // active split point, or in some ancestor of the current split point.
2413 bool ThreadsManager::thread_should_stop(int threadID) const {
2415 assert(threadID >= 0 && threadID < ActiveThreads);
2417 SplitPoint* sp = threads[threadID].splitPoint;
2419 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2424 // thread_is_available() checks whether the thread with threadID "slave" is
2425 // available to help the thread with threadID "master" at a split point. An
2426 // obvious requirement is that "slave" must be idle. With more than two
2427 // threads, this is not by itself sufficient: If "slave" is the master of
2428 // some active split point, it is only available as a slave to the other
2429 // threads which are busy searching the split point at the top of "slave"'s
2430 // split point stack (the "helpful master concept" in YBWC terminology).
2432 bool ThreadsManager::thread_is_available(int slave, int master) const {
2434 assert(slave >= 0 && slave < ActiveThreads);
2435 assert(master >= 0 && master < ActiveThreads);
2436 assert(ActiveThreads > 1);
2438 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2441 // Make a local copy to be sure doesn't change under our feet
2442 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2444 // No active split points means that the thread is available as
2445 // a slave for any other thread.
2446 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2449 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2450 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2451 // could have been set to 0 by another thread leading to an out of bound access.
2452 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2459 // available_thread_exists() tries to find an idle thread which is available as
2460 // a slave for the thread with threadID "master".
2462 bool ThreadsManager::available_thread_exists(int master) const {
2464 assert(master >= 0 && master < ActiveThreads);
2465 assert(ActiveThreads > 1);
2467 for (int i = 0; i < ActiveThreads; i++)
2468 if (thread_is_available(i, master))
2475 // split() does the actual work of distributing the work at a node between
2476 // several available threads. If it does not succeed in splitting the
2477 // node (because no idle threads are available, or because we have no unused
2478 // split point objects), the function immediately returns. If splitting is
2479 // possible, a SplitPoint object is initialized with all the data that must be
2480 // copied to the helper threads and we tell our helper threads that they have
2481 // been assigned work. This will cause them to instantly leave their idle loops
2482 // and call sp_search(). When all threads have returned from sp_search() then
2485 template <bool Fake>
2486 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2487 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2488 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2490 assert(ply > 0 && ply < PLY_MAX);
2491 assert(*bestValue >= -VALUE_INFINITE);
2492 assert(*bestValue <= *alpha);
2493 assert(*alpha < beta);
2494 assert(beta <= VALUE_INFINITE);
2495 assert(depth > DEPTH_ZERO);
2496 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2497 assert(ActiveThreads > 1);
2499 int i, master = p.thread();
2500 Thread& masterThread = threads[master];
2504 // If no other thread is available to help us, or if we have too many
2505 // active split points, don't split.
2506 if ( !available_thread_exists(master)
2507 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2509 lock_release(&MPLock);
2513 // Pick the next available split point object from the split point stack
2514 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2516 // Initialize the split point object
2517 splitPoint.parent = masterThread.splitPoint;
2518 splitPoint.stopRequest = false;
2519 splitPoint.ply = ply;
2520 splitPoint.depth = depth;
2521 splitPoint.threatMove = threatMove;
2522 splitPoint.mateThreat = mateThreat;
2523 splitPoint.alpha = *alpha;
2524 splitPoint.beta = beta;
2525 splitPoint.pvNode = pvNode;
2526 splitPoint.bestValue = *bestValue;
2528 splitPoint.moveCount = moveCount;
2529 splitPoint.pos = &p;
2530 splitPoint.parentSstack = ss;
2531 for (i = 0; i < ActiveThreads; i++)
2532 splitPoint.slaves[i] = 0;
2534 masterThread.splitPoint = &splitPoint;
2536 // If we are here it means we are not available
2537 assert(masterThread.state != THREAD_AVAILABLE);
2539 int workersCnt = 1; // At least the master is included
2541 // Allocate available threads setting state to THREAD_BOOKED
2542 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2543 if (thread_is_available(i, master))
2545 threads[i].state = THREAD_BOOKED;
2546 threads[i].splitPoint = &splitPoint;
2547 splitPoint.slaves[i] = 1;
2551 assert(Fake || workersCnt > 1);
2553 // We can release the lock because slave threads are already booked and master is not available
2554 lock_release(&MPLock);
2556 // Tell the threads that they have work to do. This will make them leave
2557 // their idle loop. But before copy search stack tail for each thread.
2558 for (i = 0; i < ActiveThreads; i++)
2559 if (i == master || splitPoint.slaves[i])
2561 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2563 assert(i == master || threads[i].state == THREAD_BOOKED);
2565 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2568 // Everything is set up. The master thread enters the idle loop, from
2569 // which it will instantly launch a search, because its state is
2570 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2571 // idle loop, which means that the main thread will return from the idle
2572 // loop when all threads have finished their work at this split point.
2573 idle_loop(master, &splitPoint);
2575 // We have returned from the idle loop, which means that all threads are
2576 // finished. Update alpha and bestValue, and return.
2579 *alpha = splitPoint.alpha;
2580 *bestValue = splitPoint.bestValue;
2581 masterThread.activeSplitPoints--;
2582 masterThread.splitPoint = splitPoint.parent;
2584 lock_release(&MPLock);
2588 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2589 // to start a new search from the root.
2591 void ThreadsManager::wake_sleeping_threads() {
2593 assert(AllThreadsShouldSleep);
2594 assert(ActiveThreads > 0);
2596 AllThreadsShouldSleep = false;
2598 if (ActiveThreads == 1)
2601 #if !defined(_MSC_VER)
2602 pthread_mutex_lock(&WaitLock);
2603 pthread_cond_broadcast(&WaitCond);
2604 pthread_mutex_unlock(&WaitLock);
2606 for (int i = 1; i < MAX_THREADS; i++)
2607 SetEvent(SitIdleEvent[i]);
2613 // put_threads_to_sleep() makes all the threads go to sleep just before
2614 // to leave think(), at the end of the search. Threads should have already
2615 // finished the job and should be idle.
2617 void ThreadsManager::put_threads_to_sleep() {
2619 assert(!AllThreadsShouldSleep);
2621 // This makes the threads to go to sleep
2622 AllThreadsShouldSleep = true;
2625 /// The RootMoveList class
2627 // RootMoveList c'tor
2629 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2631 SearchStack ss[PLY_MAX_PLUS_2];
2632 MoveStack mlist[MOVES_MAX];
2634 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2636 // Initialize search stack
2637 init_ss_array(ss, PLY_MAX_PLUS_2);
2638 ss[0].eval = VALUE_NONE;
2641 // Generate all legal moves
2642 MoveStack* last = generate_moves(pos, mlist);
2644 // Add each move to the moves[] array
2645 for (MoveStack* cur = mlist; cur != last; cur++)
2647 bool includeMove = includeAllMoves;
2649 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2650 includeMove = (searchMoves[k] == cur->move);
2655 // Find a quick score for the move
2656 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2657 moves[count].pv[1] = MOVE_NONE;
2658 pos.do_move(cur->move, st);
2659 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2660 pos.undo_move(cur->move);
2666 // Score root moves using the standard way used in main search, the moves
2667 // are scored according to the order in which are returned by MovePicker.
2669 void RootMoveList::score_moves(const Position& pos)
2673 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2675 while ((move = mp.get_next_move()) != MOVE_NONE)
2676 for (int i = 0; i < count; i++)
2677 if (moves[i].move == move)
2679 moves[i].mp_score = score--;
2684 // RootMoveList simple methods definitions
2686 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2690 for (j = 0; pv[j] != MOVE_NONE; j++)
2691 moves[moveNum].pv[j] = pv[j];
2693 moves[moveNum].pv[j] = MOVE_NONE;
2697 // RootMoveList::sort() sorts the root move list at the beginning of a new
2700 void RootMoveList::sort() {
2702 sort_multipv(count - 1); // Sort all items
2706 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2707 // list by their scores and depths. It is used to order the different PVs
2708 // correctly in MultiPV mode.
2710 void RootMoveList::sort_multipv(int n) {
2714 for (i = 1; i <= n; i++)
2716 RootMove rm = moves[i];
2717 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2718 moves[j] = moves[j - 1];