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, 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->evalMargin = VALUE_NONE;
740 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
742 // Step 6. Razoring (omitted at root)
743 // Step 7. Static null move pruning (omitted at root)
744 // Step 8. Null move search with verification search (omitted at root)
745 // Step 9. Internal iterative deepening (omitted at root)
747 // Step extra. Fail low loop
748 // We start with small aspiration window and in case of fail low, we research
749 // with bigger window until we are not failing low anymore.
752 // Sort the moves before to (re)search
753 rml.score_moves(pos);
756 // Step 10. Loop through all moves in the root move list
757 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
759 // This is used by time management
760 FirstRootMove = (i == 0);
762 // Save the current node count before the move is searched
763 nodes = ThreadsMgr.nodes_searched();
765 // Pick the next root move, and print the move and the move number to
766 // the standard output.
767 move = ss->currentMove = rml.move(i);
769 if (current_search_time() >= 1000)
770 cout << "info currmove " << move
771 << " currmovenumber " << i + 1 << endl;
773 moveIsCheck = pos.move_is_check(move);
774 captureOrPromotion = pos.move_is_capture_or_promotion(move);
776 // Step 11. Decide the new search depth
777 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
778 newDepth = depth + ext;
780 // Step 12. Futility pruning (omitted at root)
782 // Step extra. Fail high loop
783 // If move fails high, we research with bigger window until we are not failing
785 value = - VALUE_INFINITE;
789 // Step 13. Make the move
790 pos.do_move(move, st, ci, moveIsCheck);
792 // Step extra. pv search
793 // We do pv search for first moves (i < MultiPV)
794 // and for fail high research (value > alpha)
795 if (i < MultiPV || value > alpha)
797 // Aspiration window is disabled in multi-pv case
799 alpha = -VALUE_INFINITE;
801 // Full depth PV search, done on first move or after a fail high
802 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
806 // Step 14. Reduced search
807 // if the move fails high will be re-searched at full depth
808 bool doFullDepthSearch = true;
810 if ( depth >= 3 * ONE_PLY
812 && !captureOrPromotion
813 && !move_is_castle(move))
815 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
818 assert(newDepth-ss->reduction >= ONE_PLY);
820 // Reduced depth non-pv search using alpha as upperbound
821 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
822 doFullDepthSearch = (value > alpha);
825 // The move failed high, but if reduction is very big we could
826 // face a false positive, retry with a less aggressive reduction,
827 // if the move fails high again then go with full depth search.
828 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
830 assert(newDepth - ONE_PLY >= ONE_PLY);
832 ss->reduction = ONE_PLY;
833 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
834 doFullDepthSearch = (value > alpha);
836 ss->reduction = DEPTH_ZERO; // Restore original reduction
839 // Step 15. Full depth search
840 if (doFullDepthSearch)
842 // Full depth non-pv search using alpha as upperbound
843 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
845 // If we are above alpha then research at same depth but as PV
846 // to get a correct score or eventually a fail high above beta.
848 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
852 // Step 16. Undo move
855 // Can we exit fail high loop ?
856 if (AbortSearch || value < beta)
859 // We are failing high and going to do a research. It's important to update
860 // the score before research in case we run out of time while researching.
861 rml.set_move_score(i, value);
863 extract_pv_from_tt(pos, move, pv);
864 rml.set_move_pv(i, pv);
866 // Print information to the standard output
867 print_pv_info(pos, pv, alpha, beta, value);
869 // Prepare for a research after a fail high, each time with a wider window
870 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
873 } // End of fail high loop
875 // Finished searching the move. If AbortSearch is true, the search
876 // was aborted because the user interrupted the search or because we
877 // ran out of time. In this case, the return value of the search cannot
878 // be trusted, and we break out of the loop without updating the best
883 // Remember searched nodes counts for this move
884 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
886 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
887 assert(value < beta);
889 // Step 17. Check for new best move
890 if (value <= alpha && i >= MultiPV)
891 rml.set_move_score(i, -VALUE_INFINITE);
894 // PV move or new best move!
897 rml.set_move_score(i, value);
899 extract_pv_from_tt(pos, move, pv);
900 rml.set_move_pv(i, pv);
904 // We record how often the best move has been changed in each
905 // iteration. This information is used for time managment: When
906 // the best move changes frequently, we allocate some more time.
908 BestMoveChangesByIteration[Iteration]++;
910 // Print information to the standard output
911 print_pv_info(pos, pv, alpha, beta, value);
913 // Raise alpha to setup proper non-pv search upper bound
920 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
922 cout << "info multipv " << j + 1
923 << " score " << value_to_uci(rml.move_score(j))
924 << " depth " << (j <= i ? Iteration : Iteration - 1)
925 << " time " << current_search_time()
926 << " nodes " << ThreadsMgr.nodes_searched()
930 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
931 cout << rml.move_pv(j, k) << " ";
935 alpha = rml.move_score(Min(i, MultiPV - 1));
937 } // PV move or new best move
939 assert(alpha >= *alphaPtr);
941 AspirationFailLow = (alpha == *alphaPtr);
943 if (AspirationFailLow && StopOnPonderhit)
944 StopOnPonderhit = false;
947 // Can we exit fail low loop ?
948 if (AbortSearch || !AspirationFailLow)
951 // Prepare for a research after a fail low, each time with a wider window
952 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
957 // Sort the moves before to return
964 // search<>() is the main search function for both PV and non-PV nodes
966 template <NodeType PvNode, bool SplitPoint>
967 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
969 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
970 assert(beta > alpha && beta <= VALUE_INFINITE);
971 assert(PvNode || alpha == beta - 1);
972 assert(ply > 0 && ply < PLY_MAX);
973 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
975 Move movesSearched[MOVES_MAX];
979 Move ttMove, move, excludedMove, threatMove;
981 Value bestValue, value, oldAlpha;
982 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
983 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
984 bool mateThreat = false;
986 int threadID = pos.thread();
987 refinedValue = bestValue = value = -VALUE_INFINITE;
989 isCheck = pos.is_check();
994 ttMove = excludedMove = MOVE_NONE;
995 threatMove = ss->sp->threatMove;
996 mateThreat = ss->sp->mateThreat;
1000 // Step 1. Initialize node and poll. Polling can abort search
1001 ThreadsMgr.incrementNodeCounter(threadID);
1002 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
1003 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1005 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1011 // Step 2. Check for aborted search and immediate draw
1012 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1015 if (pos.is_draw() || ply >= PLY_MAX - 1)
1018 // Step 3. Mate distance pruning
1019 alpha = Max(value_mated_in(ply), alpha);
1020 beta = Min(value_mate_in(ply+1), beta);
1024 // Step 4. Transposition table lookup
1026 // We don't want the score of a partial search to overwrite a previous full search
1027 // TT value, so we use a different position key in case of an excluded move exists.
1028 excludedMove = ss->excludedMove;
1029 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1031 tte = TT.retrieve(posKey);
1032 ttMove = (tte ? tte->move() : MOVE_NONE);
1034 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1035 // This is to avoid problems in the following areas:
1037 // * Repetition draw detection
1038 // * Fifty move rule detection
1039 // * Searching for a mate
1040 // * Printing of full PV line
1042 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1044 // Refresh tte entry to avoid aging
1045 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1047 ss->bestMove = ttMove; // Can be MOVE_NONE
1048 return value_from_tt(tte->value(), ply);
1051 // Step 5. Evaluate the position statically and
1052 // update gain statistics of parent move.
1054 ss->eval = ss->evalMargin = VALUE_NONE;
1057 assert(tte->static_value() != VALUE_NONE);
1059 ss->eval = tte->static_value();
1060 ss->evalMargin = tte->static_value_margin();
1061 refinedValue = refine_eval(tte, ss->eval, ply);
1065 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1066 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1069 // Save gain for the parent non-capture move
1070 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1072 // Step 6. Razoring (is omitted in PV nodes)
1074 && depth < RazorDepth
1076 && refinedValue < beta - razor_margin(depth)
1077 && ttMove == MOVE_NONE
1078 && (ss-1)->currentMove != MOVE_NULL
1079 && !value_is_mate(beta)
1080 && !pos.has_pawn_on_7th(pos.side_to_move()))
1082 Value rbeta = beta - razor_margin(depth);
1083 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1085 // Logically we should return (v + razor_margin(depth)), but
1086 // surprisingly this did slightly weaker in tests.
1090 // Step 7. Static null move pruning (is omitted in PV nodes)
1091 // We're betting that the opponent doesn't have a move that will reduce
1092 // the score by more than futility_margin(depth) if we do a null move.
1094 && !ss->skipNullMove
1095 && depth < RazorDepth
1097 && refinedValue >= beta + futility_margin(depth, 0)
1098 && !value_is_mate(beta)
1099 && pos.non_pawn_material(pos.side_to_move()))
1100 return refinedValue - futility_margin(depth, 0);
1102 // Step 8. Null move search with verification search (is omitted in PV nodes)
1104 && !ss->skipNullMove
1107 && refinedValue >= beta
1108 && !value_is_mate(beta)
1109 && pos.non_pawn_material(pos.side_to_move()))
1111 ss->currentMove = MOVE_NULL;
1113 // Null move dynamic reduction based on depth
1114 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1116 // Null move dynamic reduction based on value
1117 if (refinedValue - beta > PawnValueMidgame)
1120 pos.do_null_move(st);
1121 (ss+1)->skipNullMove = true;
1123 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1124 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1125 (ss+1)->skipNullMove = false;
1126 pos.undo_null_move();
1128 if (nullValue >= beta)
1130 // Do not return unproven mate scores
1131 if (nullValue >= value_mate_in(PLY_MAX))
1134 if (depth < 6 * ONE_PLY)
1137 // Do verification search at high depths
1138 ss->skipNullMove = true;
1139 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1140 ss->skipNullMove = false;
1147 // The null move failed low, which means that we may be faced with
1148 // some kind of threat. If the previous move was reduced, check if
1149 // the move that refuted the null move was somehow connected to the
1150 // move which was reduced. If a connection is found, return a fail
1151 // low score (which will cause the reduced move to fail high in the
1152 // parent node, which will trigger a re-search with full depth).
1153 if (nullValue == value_mated_in(ply + 2))
1156 threatMove = (ss+1)->bestMove;
1157 if ( depth < ThreatDepth
1158 && (ss-1)->reduction
1159 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1164 // Step 9. Internal iterative deepening
1165 if ( depth >= IIDDepth[PvNode]
1166 && ttMove == MOVE_NONE
1167 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1169 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1171 ss->skipNullMove = true;
1172 search<PvNode>(pos, ss, alpha, beta, d, ply);
1173 ss->skipNullMove = false;
1175 ttMove = ss->bestMove;
1176 tte = TT.retrieve(posKey);
1179 // Expensive mate threat detection (only for PV nodes)
1181 mateThreat = pos.has_mate_threat();
1185 // Initialize a MovePicker object for the current position
1186 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1187 MovePicker mpBase = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1188 MovePicker& mp = SplitPoint ? *ss->sp->mp : mpBase;
1190 ss->bestMove = MOVE_NONE;
1191 singleEvasion = !SplitPoint && isCheck && mp.number_of_evasions() == 1;
1192 futilityBase = ss->eval + ss->evalMargin;
1193 singularExtensionNode = !SplitPoint
1194 && depth >= SingularExtensionDepth[PvNode]
1197 && !excludedMove // Do not allow recursive singular extension search
1198 && (tte->type() & VALUE_TYPE_LOWER)
1199 && tte->depth() >= depth - 3 * ONE_PLY;
1201 // Step 10. Loop through moves
1202 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1205 lock_grab(&(ss->sp->lock));
1206 bestValue = ss->sp->bestValue;
1209 while ( bestValue < beta
1210 && (move = mp.get_next_move()) != MOVE_NONE
1211 && !ThreadsMgr.thread_should_stop(threadID))
1215 moveCount = ++ss->sp->moveCount;
1216 lock_release(&(ss->sp->lock));
1219 assert(move_is_ok(move));
1221 if (move == excludedMove)
1224 moveIsCheck = pos.move_is_check(move, ci);
1225 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1227 // Step 11. Decide the new search depth
1228 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1230 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1231 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1232 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1233 // lower then ttValue minus a margin then we extend ttMove.
1234 if ( singularExtensionNode
1235 && move == tte->move()
1238 Value ttValue = value_from_tt(tte->value(), ply);
1240 if (abs(ttValue) < VALUE_KNOWN_WIN)
1242 Value b = ttValue - SingularExtensionMargin;
1243 ss->excludedMove = move;
1244 ss->skipNullMove = true;
1245 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1246 ss->skipNullMove = false;
1247 ss->excludedMove = MOVE_NONE;
1248 ss->bestMove = MOVE_NONE;
1254 newDepth = depth - ONE_PLY + ext;
1256 // Update current move (this must be done after singular extension search)
1257 movesSearched[moveCount++] = ss->currentMove = move;
1259 // Step 12. Futility pruning (is omitted in PV nodes)
1261 && !captureOrPromotion
1265 && !move_is_castle(move))
1267 // Move count based pruning
1268 if ( moveCount >= futility_move_count(depth)
1269 && !(threatMove && connected_threat(pos, move, threatMove))
1270 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1273 lock_grab(&(ss->sp->lock));
1277 // Value based pruning
1278 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1279 // but fixing this made program slightly weaker.
1280 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1281 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1282 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1284 if (futilityValueScaled < beta)
1288 lock_grab(&(ss->sp->lock));
1289 if (futilityValueScaled > ss->sp->bestValue)
1290 ss->sp->bestValue = bestValue = futilityValueScaled;
1292 else if (futilityValueScaled > bestValue)
1293 bestValue = futilityValueScaled;
1298 // Step 13. Make the move
1299 pos.do_move(move, st, ci, moveIsCheck);
1301 // Step extra. pv search (only in PV nodes)
1302 // The first move in list is the expected PV
1303 if (!SplitPoint && PvNode && moveCount == 1)
1304 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1305 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1308 // Step 14. Reduced depth search
1309 // If the move fails high will be re-searched at full depth.
1310 bool doFullDepthSearch = true;
1312 if ( depth >= 3 * ONE_PLY
1313 && !captureOrPromotion
1315 && !move_is_castle(move)
1316 && !move_is_killer(move, ss))
1318 ss->reduction = reduction<PvNode>(depth, moveCount);
1321 alpha = SplitPoint ? ss->sp->alpha : alpha;
1322 Depth d = newDepth - ss->reduction;
1323 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1324 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1326 doFullDepthSearch = (value > alpha);
1329 // The move failed high, but if reduction is very big we could
1330 // face a false positive, retry with a less aggressive reduction,
1331 // if the move fails high again then go with full depth search.
1332 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1334 assert(newDepth - ONE_PLY >= ONE_PLY);
1336 ss->reduction = ONE_PLY;
1337 alpha = SplitPoint ? ss->sp->alpha : alpha;
1338 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1339 doFullDepthSearch = (value > alpha);
1341 ss->reduction = DEPTH_ZERO; // Restore original reduction
1344 // Step 15. Full depth search
1345 if (doFullDepthSearch)
1347 alpha = SplitPoint ? ss->sp->alpha : alpha;
1348 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1349 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1351 // Step extra. pv search (only in PV nodes)
1352 // Search only for possible new PV nodes, if instead value >= beta then
1353 // parent node fails low with value <= alpha and tries another move.
1354 if (PvNode && value > alpha && value < beta)
1355 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1356 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1360 // Step 16. Undo move
1361 pos.undo_move(move);
1363 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1365 // Step 17. Check for new best move
1368 lock_grab(&(ss->sp->lock));
1369 bestValue = ss->sp->bestValue;
1370 alpha = ss->sp->alpha;
1373 if (value > bestValue && !(SplitPoint && ThreadsMgr.thread_should_stop(threadID)))
1378 if (SplitPoint && (!PvNode || value >= beta))
1379 ss->sp->stopRequest = true;
1381 if (PvNode && value < beta) // We want always alpha < beta
1384 if (value == value_mate_in(ply + 1))
1385 ss->mateKiller = move;
1387 ss->bestMove = move;
1391 ss->sp->bestValue = bestValue;
1392 ss->sp->alpha = alpha;
1393 ss->sp->parentSstack->bestMove = ss->bestMove;
1397 // Step 18. Check for split
1399 && depth >= MinimumSplitDepth
1400 && ThreadsMgr.active_threads() > 1
1402 && ThreadsMgr.available_thread_exists(threadID)
1404 && !ThreadsMgr.thread_should_stop(threadID)
1406 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1407 threatMove, mateThreat, moveCount, &mp, PvNode);
1412 /* Here we have the lock still grabbed */
1413 ss->sp->slaves[threadID] = 0;
1414 lock_release(&(ss->sp->lock));
1418 // Step 19. Check for mate and stalemate
1419 // All legal moves have been searched and if there are
1420 // no legal moves, it must be mate or stalemate.
1421 // If one move was excluded return fail low score.
1423 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1425 // Step 20. Update tables
1426 // If the search is not aborted, update the transposition table,
1427 // history counters, and killer moves.
1428 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1431 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1432 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1433 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1435 // Update killers and history only for non capture moves that fails high
1436 if ( bestValue >= beta
1437 && !pos.move_is_capture_or_promotion(move))
1439 update_history(pos, move, depth, movesSearched, moveCount);
1440 update_killers(move, ss);
1443 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1449 // qsearch() is the quiescence search function, which is called by the main
1450 // search function when the remaining depth is zero (or, to be more precise,
1451 // less than ONE_PLY).
1453 template <NodeType PvNode>
1454 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1456 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1457 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1458 assert(PvNode || alpha == beta - 1);
1460 assert(ply > 0 && ply < PLY_MAX);
1461 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1465 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1466 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1468 Value oldAlpha = alpha;
1470 ThreadsMgr.incrementNodeCounter(pos.thread());
1471 ss->bestMove = ss->currentMove = MOVE_NONE;
1473 // Check for an instant draw or maximum ply reached
1474 if (pos.is_draw() || ply >= PLY_MAX - 1)
1477 // Transposition table lookup. At PV nodes, we don't use the TT for
1478 // pruning, but only for move ordering.
1479 tte = TT.retrieve(pos.get_key());
1480 ttMove = (tte ? tte->move() : MOVE_NONE);
1482 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1484 ss->bestMove = ttMove; // Can be MOVE_NONE
1485 return value_from_tt(tte->value(), ply);
1488 isCheck = pos.is_check();
1490 // Evaluate the position statically
1493 bestValue = futilityBase = -VALUE_INFINITE;
1494 ss->eval = evalMargin = VALUE_NONE;
1495 deepChecks = enoughMaterial = false;
1501 assert(tte->static_value() != VALUE_NONE);
1503 evalMargin = tte->static_value_margin();
1504 ss->eval = bestValue = tte->static_value();
1507 ss->eval = bestValue = evaluate(pos, evalMargin);
1509 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1511 // Stand pat. Return immediately if static value is at least beta
1512 if (bestValue >= beta)
1515 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1520 if (PvNode && bestValue > alpha)
1523 // If we are near beta then try to get a cutoff pushing checks a bit further
1524 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1526 // Futility pruning parameters, not needed when in check
1527 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1528 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1531 // Initialize a MovePicker object for the current position, and prepare
1532 // to search the moves. Because the depth is <= 0 here, only captures,
1533 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1534 // and we are near beta) will be generated.
1535 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1538 // Loop through the moves until no moves remain or a beta cutoff occurs
1539 while ( alpha < beta
1540 && (move = mp.get_next_move()) != MOVE_NONE)
1542 assert(move_is_ok(move));
1544 moveIsCheck = pos.move_is_check(move, ci);
1552 && !move_is_promotion(move)
1553 && !pos.move_is_passed_pawn_push(move))
1555 futilityValue = futilityBase
1556 + pos.endgame_value_of_piece_on(move_to(move))
1557 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1559 if (futilityValue < alpha)
1561 if (futilityValue > bestValue)
1562 bestValue = futilityValue;
1567 // Detect non-capture evasions that are candidate to be pruned
1568 evasionPrunable = isCheck
1569 && bestValue > value_mated_in(PLY_MAX)
1570 && !pos.move_is_capture(move)
1571 && !pos.can_castle(pos.side_to_move());
1573 // Don't search moves with negative SEE values
1575 && (!isCheck || evasionPrunable)
1577 && !move_is_promotion(move)
1578 && pos.see_sign(move) < 0)
1581 // Update current move
1582 ss->currentMove = move;
1584 // Make and search the move
1585 pos.do_move(move, st, ci, moveIsCheck);
1586 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1587 pos.undo_move(move);
1589 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1592 if (value > bestValue)
1598 ss->bestMove = move;
1603 // All legal moves have been searched. A special case: If we're in check
1604 // and no legal moves were found, it is checkmate.
1605 if (isCheck && bestValue == -VALUE_INFINITE)
1606 return value_mated_in(ply);
1608 // Update transposition table
1609 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1610 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1611 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1613 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1619 // sp_search() is used to search from a split point. This function is called
1620 // by each thread working at the split point. It is similar to the normal
1621 // search() function, but simpler. Because we have already probed the hash
1622 // table, done a null move search, and searched the first move before
1623 // splitting, we don't have to repeat all this work in sp_search(). We
1624 // also don't need to store anything to the hash table here: This is taken
1625 // care of after we return from the split point.
1627 template <NodeType PvNode>
1628 void do_sp_search(SplitPoint* sp, int threadID) {
1630 assert(threadID >= 0 && threadID < ThreadsMgr.active_threads());
1631 assert(ThreadsMgr.active_threads() > 1);
1633 Position pos(*sp->pos, threadID);
1634 SearchStack* ss = sp->sstack[threadID] + 1;
1637 search<PvNode, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->ply);
1641 // connected_moves() tests whether two moves are 'connected' in the sense
1642 // that the first move somehow made the second move possible (for instance
1643 // if the moving piece is the same in both moves). The first move is assumed
1644 // to be the move that was made to reach the current position, while the
1645 // second move is assumed to be a move from the current position.
1647 bool connected_moves(const Position& pos, Move m1, Move m2) {
1649 Square f1, t1, f2, t2;
1652 assert(move_is_ok(m1));
1653 assert(move_is_ok(m2));
1655 if (m2 == MOVE_NONE)
1658 // Case 1: The moving piece is the same in both moves
1664 // Case 2: The destination square for m2 was vacated by m1
1670 // Case 3: Moving through the vacated square
1671 if ( piece_is_slider(pos.piece_on(f2))
1672 && bit_is_set(squares_between(f2, t2), f1))
1675 // Case 4: The destination square for m2 is defended by the moving piece in m1
1676 p = pos.piece_on(t1);
1677 if (bit_is_set(pos.attacks_from(p, t1), t2))
1680 // Case 5: Discovered check, checking piece is the piece moved in m1
1681 if ( piece_is_slider(p)
1682 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1683 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1685 // discovered_check_candidates() works also if the Position's side to
1686 // move is the opposite of the checking piece.
1687 Color them = opposite_color(pos.side_to_move());
1688 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1690 if (bit_is_set(dcCandidates, f2))
1697 // value_is_mate() checks if the given value is a mate one eventually
1698 // compensated for the ply.
1700 bool value_is_mate(Value value) {
1702 assert(abs(value) <= VALUE_INFINITE);
1704 return value <= value_mated_in(PLY_MAX)
1705 || value >= value_mate_in(PLY_MAX);
1709 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1710 // "plies to mate from the current ply". Non-mate scores are unchanged.
1711 // The function is called before storing a value to the transposition table.
1713 Value value_to_tt(Value v, int ply) {
1715 if (v >= value_mate_in(PLY_MAX))
1718 if (v <= value_mated_in(PLY_MAX))
1725 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1726 // the transposition table to a mate score corrected for the current ply.
1728 Value value_from_tt(Value v, int ply) {
1730 if (v >= value_mate_in(PLY_MAX))
1733 if (v <= value_mated_in(PLY_MAX))
1740 // move_is_killer() checks if the given move is among the killer moves
1742 bool move_is_killer(Move m, SearchStack* ss) {
1744 if (ss->killers[0] == m || ss->killers[1] == m)
1751 // extension() decides whether a move should be searched with normal depth,
1752 // or with extended depth. Certain classes of moves (checking moves, in
1753 // particular) are searched with bigger depth than ordinary moves and in
1754 // any case are marked as 'dangerous'. Note that also if a move is not
1755 // extended, as example because the corresponding UCI option is set to zero,
1756 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1757 template <NodeType PvNode>
1758 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1759 bool singleEvasion, bool mateThreat, bool* dangerous) {
1761 assert(m != MOVE_NONE);
1763 Depth result = DEPTH_ZERO;
1764 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1768 if (moveIsCheck && pos.see_sign(m) >= 0)
1769 result += CheckExtension[PvNode];
1772 result += SingleEvasionExtension[PvNode];
1775 result += MateThreatExtension[PvNode];
1778 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1780 Color c = pos.side_to_move();
1781 if (relative_rank(c, move_to(m)) == RANK_7)
1783 result += PawnPushTo7thExtension[PvNode];
1786 if (pos.pawn_is_passed(c, move_to(m)))
1788 result += PassedPawnExtension[PvNode];
1793 if ( captureOrPromotion
1794 && pos.type_of_piece_on(move_to(m)) != PAWN
1795 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1796 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1797 && !move_is_promotion(m)
1800 result += PawnEndgameExtension[PvNode];
1805 && captureOrPromotion
1806 && pos.type_of_piece_on(move_to(m)) != PAWN
1807 && pos.see_sign(m) >= 0)
1809 result += ONE_PLY / 2;
1813 return Min(result, ONE_PLY);
1817 // connected_threat() tests whether it is safe to forward prune a move or if
1818 // is somehow coonected to the threat move returned by null search.
1820 bool connected_threat(const Position& pos, Move m, Move threat) {
1822 assert(move_is_ok(m));
1823 assert(threat && move_is_ok(threat));
1824 assert(!pos.move_is_check(m));
1825 assert(!pos.move_is_capture_or_promotion(m));
1826 assert(!pos.move_is_passed_pawn_push(m));
1828 Square mfrom, mto, tfrom, tto;
1830 mfrom = move_from(m);
1832 tfrom = move_from(threat);
1833 tto = move_to(threat);
1835 // Case 1: Don't prune moves which move the threatened piece
1839 // Case 2: If the threatened piece has value less than or equal to the
1840 // value of the threatening piece, don't prune move which defend it.
1841 if ( pos.move_is_capture(threat)
1842 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1843 || pos.type_of_piece_on(tfrom) == KING)
1844 && pos.move_attacks_square(m, tto))
1847 // Case 3: If the moving piece in the threatened move is a slider, don't
1848 // prune safe moves which block its ray.
1849 if ( piece_is_slider(pos.piece_on(tfrom))
1850 && bit_is_set(squares_between(tfrom, tto), mto)
1851 && pos.see_sign(m) >= 0)
1858 // ok_to_use_TT() returns true if a transposition table score
1859 // can be used at a given point in search.
1861 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1863 Value v = value_from_tt(tte->value(), ply);
1865 return ( tte->depth() >= depth
1866 || v >= Max(value_mate_in(PLY_MAX), beta)
1867 || v < Min(value_mated_in(PLY_MAX), beta))
1869 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1870 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1874 // refine_eval() returns the transposition table score if
1875 // possible otherwise falls back on static position evaluation.
1877 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1881 Value v = value_from_tt(tte->value(), ply);
1883 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1884 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1891 // update_history() registers a good move that produced a beta-cutoff
1892 // in history and marks as failures all the other moves of that ply.
1894 void update_history(const Position& pos, Move move, Depth depth,
1895 Move movesSearched[], int moveCount) {
1899 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1901 for (int i = 0; i < moveCount - 1; i++)
1903 m = movesSearched[i];
1907 if (!pos.move_is_capture_or_promotion(m))
1908 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1913 // update_killers() add a good move that produced a beta-cutoff
1914 // among the killer moves of that ply.
1916 void update_killers(Move m, SearchStack* ss) {
1918 if (m == ss->killers[0])
1921 ss->killers[1] = ss->killers[0];
1926 // update_gains() updates the gains table of a non-capture move given
1927 // the static position evaluation before and after the move.
1929 void update_gains(const Position& pos, Move m, Value before, Value after) {
1932 && before != VALUE_NONE
1933 && after != VALUE_NONE
1934 && pos.captured_piece_type() == PIECE_TYPE_NONE
1935 && !move_is_special(m))
1936 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1940 // current_search_time() returns the number of milliseconds which have passed
1941 // since the beginning of the current search.
1943 int current_search_time() {
1945 return get_system_time() - SearchStartTime;
1949 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1951 std::string value_to_uci(Value v) {
1953 std::stringstream s;
1955 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1956 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1958 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1963 // nps() computes the current nodes/second count.
1967 int t = current_search_time();
1968 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
1972 // poll() performs two different functions: It polls for user input, and it
1973 // looks at the time consumed so far and decides if it's time to abort the
1978 static int lastInfoTime;
1979 int t = current_search_time();
1984 // We are line oriented, don't read single chars
1985 std::string command;
1987 if (!std::getline(std::cin, command))
1990 if (command == "quit")
1993 PonderSearch = false;
1997 else if (command == "stop")
2000 PonderSearch = false;
2002 else if (command == "ponderhit")
2006 // Print search information
2010 else if (lastInfoTime > t)
2011 // HACK: Must be a new search where we searched less than
2012 // NodesBetweenPolls nodes during the first second of search.
2015 else if (t - lastInfoTime >= 1000)
2022 if (dbg_show_hit_rate)
2023 dbg_print_hit_rate();
2025 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
2026 << " time " << t << endl;
2029 // Should we stop the search?
2033 bool stillAtFirstMove = FirstRootMove
2034 && !AspirationFailLow
2035 && t > TimeMgr.available_time();
2037 bool noMoreTime = t > TimeMgr.maximum_time()
2038 || stillAtFirstMove;
2040 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2041 || (ExactMaxTime && t >= ExactMaxTime)
2042 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2047 // ponderhit() is called when the program is pondering (i.e. thinking while
2048 // it's the opponent's turn to move) in order to let the engine know that
2049 // it correctly predicted the opponent's move.
2053 int t = current_search_time();
2054 PonderSearch = false;
2056 bool stillAtFirstMove = FirstRootMove
2057 && !AspirationFailLow
2058 && t > TimeMgr.available_time();
2060 bool noMoreTime = t > TimeMgr.maximum_time()
2061 || stillAtFirstMove;
2063 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2068 // init_ss_array() does a fast reset of the first entries of a SearchStack
2069 // array and of all the excludedMove and skipNullMove entries.
2071 void init_ss_array(SearchStack* ss, int size) {
2073 for (int i = 0; i < size; i++, ss++)
2075 ss->excludedMove = MOVE_NONE;
2076 ss->skipNullMove = false;
2077 ss->reduction = DEPTH_ZERO;
2081 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2086 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2087 // while the program is pondering. The point is to work around a wrinkle in
2088 // the UCI protocol: When pondering, the engine is not allowed to give a
2089 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2090 // We simply wait here until one of these commands is sent, and return,
2091 // after which the bestmove and pondermove will be printed (in id_loop()).
2093 void wait_for_stop_or_ponderhit() {
2095 std::string command;
2099 if (!std::getline(std::cin, command))
2102 if (command == "quit")
2107 else if (command == "ponderhit" || command == "stop")
2113 // print_pv_info() prints to standard output and eventually to log file information on
2114 // the current PV line. It is called at each iteration or after a new pv is found.
2116 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2118 cout << "info depth " << Iteration
2119 << " score " << value_to_uci(value)
2120 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2121 << " time " << current_search_time()
2122 << " nodes " << ThreadsMgr.nodes_searched()
2126 for (Move* m = pv; *m != MOVE_NONE; m++)
2133 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2134 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2136 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2137 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2142 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2143 // the PV back into the TT. This makes sure the old PV moves are searched
2144 // first, even if the old TT entries have been overwritten.
2146 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2150 Position p(pos, pos.thread());
2151 Value v, m = VALUE_NONE;
2153 for (int i = 0; pv[i] != MOVE_NONE; i++)
2155 tte = TT.retrieve(p.get_key());
2156 if (!tte || tte->move() != pv[i])
2158 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2159 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2161 p.do_move(pv[i], st);
2166 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2167 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2168 // allow to always have a ponder move even when we fail high at root and also a
2169 // long PV to print that is important for position analysis.
2171 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2175 Position p(pos, pos.thread());
2178 assert(bestMove != MOVE_NONE);
2181 p.do_move(pv[ply++], st);
2183 while ( (tte = TT.retrieve(p.get_key())) != NULL
2184 && tte->move() != MOVE_NONE
2185 && move_is_legal(p, tte->move())
2187 && (!p.is_draw() || ply < 2))
2189 pv[ply] = tte->move();
2190 p.do_move(pv[ply++], st);
2192 pv[ply] = MOVE_NONE;
2196 // init_thread() is the function which is called when a new thread is
2197 // launched. It simply calls the idle_loop() function with the supplied
2198 // threadID. There are two versions of this function; one for POSIX
2199 // threads and one for Windows threads.
2201 #if !defined(_MSC_VER)
2203 void* init_thread(void *threadID) {
2205 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2211 DWORD WINAPI init_thread(LPVOID threadID) {
2213 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2220 /// The ThreadsManager class
2222 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2223 // get_beta_counters() are getters/setters for the per thread
2224 // counters used to sort the moves at root.
2226 void ThreadsManager::resetNodeCounters() {
2228 for (int i = 0; i < MAX_THREADS; i++)
2229 threads[i].nodes = 0ULL;
2232 int64_t ThreadsManager::nodes_searched() const {
2234 int64_t result = 0ULL;
2235 for (int i = 0; i < ActiveThreads; i++)
2236 result += threads[i].nodes;
2242 // idle_loop() is where the threads are parked when they have no work to do.
2243 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2244 // object for which the current thread is the master.
2246 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2248 assert(threadID >= 0 && threadID < MAX_THREADS);
2252 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2253 // master should exit as last one.
2254 if (AllThreadsShouldExit)
2257 threads[threadID].state = THREAD_TERMINATED;
2261 // If we are not thinking, wait for a condition to be signaled
2262 // instead of wasting CPU time polling for work.
2263 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2266 assert(threadID != 0);
2267 threads[threadID].state = THREAD_SLEEPING;
2269 #if !defined(_MSC_VER)
2270 lock_grab(&WaitLock);
2271 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2272 pthread_cond_wait(&WaitCond, &WaitLock);
2273 lock_release(&WaitLock);
2275 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2279 // If thread has just woken up, mark it as available
2280 if (threads[threadID].state == THREAD_SLEEPING)
2281 threads[threadID].state = THREAD_AVAILABLE;
2283 // If this thread has been assigned work, launch a search
2284 if (threads[threadID].state == THREAD_WORKISWAITING)
2286 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2288 threads[threadID].state = THREAD_SEARCHING;
2290 if (threads[threadID].splitPoint->pvNode)
2291 do_sp_search<PV>(threads[threadID].splitPoint, threadID);
2293 do_sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2295 assert(threads[threadID].state == THREAD_SEARCHING);
2297 threads[threadID].state = THREAD_AVAILABLE;
2300 // If this thread is the master of a split point and all slaves have
2301 // finished their work at this split point, return from the idle loop.
2303 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2305 if (i == ActiveThreads)
2307 // Because sp->slaves[] is reset under lock protection,
2308 // be sure sp->lock has been released before to return.
2309 lock_grab(&(sp->lock));
2310 lock_release(&(sp->lock));
2312 // In helpful master concept a master can help only a sub-tree, and
2313 // because here is all finished is not possible master is booked.
2314 assert(threads[threadID].state == THREAD_AVAILABLE);
2316 threads[threadID].state = THREAD_SEARCHING;
2323 // init_threads() is called during startup. It launches all helper threads,
2324 // and initializes the split point stack and the global locks and condition
2327 void ThreadsManager::init_threads() {
2332 #if !defined(_MSC_VER)
2333 pthread_t pthread[1];
2336 // Initialize global locks
2338 lock_init(&WaitLock);
2340 #if !defined(_MSC_VER)
2341 pthread_cond_init(&WaitCond, NULL);
2343 for (i = 0; i < MAX_THREADS; i++)
2344 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2347 // Initialize splitPoints[] locks
2348 for (i = 0; i < MAX_THREADS; i++)
2349 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2350 lock_init(&(threads[i].splitPoints[j].lock));
2352 // Will be set just before program exits to properly end the threads
2353 AllThreadsShouldExit = false;
2355 // Threads will be put to sleep as soon as created
2356 AllThreadsShouldSleep = true;
2358 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2360 threads[0].state = THREAD_SEARCHING;
2361 for (i = 1; i < MAX_THREADS; i++)
2362 threads[i].state = THREAD_AVAILABLE;
2364 // Launch the helper threads
2365 for (i = 1; i < MAX_THREADS; i++)
2368 #if !defined(_MSC_VER)
2369 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2371 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2376 cout << "Failed to create thread number " << i << endl;
2377 Application::exit_with_failure();
2380 // Wait until the thread has finished launching and is gone to sleep
2381 while (threads[i].state != THREAD_SLEEPING) {}
2386 // exit_threads() is called when the program exits. It makes all the
2387 // helper threads exit cleanly.
2389 void ThreadsManager::exit_threads() {
2391 ActiveThreads = MAX_THREADS; // Wake up all the threads
2392 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2393 AllThreadsShouldSleep = true; // Avoid an assert in wake_sleeping_threads()
2394 wake_sleeping_threads();
2396 // Wait for thread termination
2397 for (int i = 1; i < MAX_THREADS; i++)
2398 while (threads[i].state != THREAD_TERMINATED) {}
2400 // Now we can safely destroy the locks
2401 for (int i = 0; i < MAX_THREADS; i++)
2402 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2403 lock_destroy(&(threads[i].splitPoints[j].lock));
2405 lock_destroy(&WaitLock);
2406 lock_destroy(&MPLock);
2410 // thread_should_stop() checks whether the thread should stop its search.
2411 // This can happen if a beta cutoff has occurred in the thread's currently
2412 // active split point, or in some ancestor of the current split point.
2414 bool ThreadsManager::thread_should_stop(int threadID) const {
2416 assert(threadID >= 0 && threadID < ActiveThreads);
2418 SplitPoint* sp = threads[threadID].splitPoint;
2420 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2425 // thread_is_available() checks whether the thread with threadID "slave" is
2426 // available to help the thread with threadID "master" at a split point. An
2427 // obvious requirement is that "slave" must be idle. With more than two
2428 // threads, this is not by itself sufficient: If "slave" is the master of
2429 // some active split point, it is only available as a slave to the other
2430 // threads which are busy searching the split point at the top of "slave"'s
2431 // split point stack (the "helpful master concept" in YBWC terminology).
2433 bool ThreadsManager::thread_is_available(int slave, int master) const {
2435 assert(slave >= 0 && slave < ActiveThreads);
2436 assert(master >= 0 && master < ActiveThreads);
2437 assert(ActiveThreads > 1);
2439 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2442 // Make a local copy to be sure doesn't change under our feet
2443 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2445 // No active split points means that the thread is available as
2446 // a slave for any other thread.
2447 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2450 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2451 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2452 // could have been set to 0 by another thread leading to an out of bound access.
2453 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2460 // available_thread_exists() tries to find an idle thread which is available as
2461 // a slave for the thread with threadID "master".
2463 bool ThreadsManager::available_thread_exists(int master) const {
2465 assert(master >= 0 && master < ActiveThreads);
2466 assert(ActiveThreads > 1);
2468 for (int i = 0; i < ActiveThreads; i++)
2469 if (thread_is_available(i, master))
2476 // split() does the actual work of distributing the work at a node between
2477 // several available threads. If it does not succeed in splitting the
2478 // node (because no idle threads are available, or because we have no unused
2479 // split point objects), the function immediately returns. If splitting is
2480 // possible, a SplitPoint object is initialized with all the data that must be
2481 // copied to the helper threads and we tell our helper threads that they have
2482 // been assigned work. This will cause them to instantly leave their idle loops
2483 // and call sp_search(). When all threads have returned from sp_search() then
2486 template <bool Fake>
2487 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2488 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2489 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2491 assert(ply > 0 && ply < PLY_MAX);
2492 assert(*bestValue >= -VALUE_INFINITE);
2493 assert(*bestValue <= *alpha);
2494 assert(*alpha < beta);
2495 assert(beta <= VALUE_INFINITE);
2496 assert(depth > DEPTH_ZERO);
2497 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2498 assert(ActiveThreads > 1);
2500 int i, master = p.thread();
2501 Thread& masterThread = threads[master];
2505 // If no other thread is available to help us, or if we have too many
2506 // active split points, don't split.
2507 if ( !available_thread_exists(master)
2508 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2510 lock_release(&MPLock);
2514 // Pick the next available split point object from the split point stack
2515 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2517 // Initialize the split point object
2518 splitPoint.parent = masterThread.splitPoint;
2519 splitPoint.stopRequest = false;
2520 splitPoint.ply = ply;
2521 splitPoint.depth = depth;
2522 splitPoint.threatMove = threatMove;
2523 splitPoint.mateThreat = mateThreat;
2524 splitPoint.alpha = *alpha;
2525 splitPoint.beta = beta;
2526 splitPoint.pvNode = pvNode;
2527 splitPoint.bestValue = *bestValue;
2529 splitPoint.moveCount = moveCount;
2530 splitPoint.pos = &p;
2531 splitPoint.parentSstack = ss;
2532 for (i = 0; i < ActiveThreads; i++)
2533 splitPoint.slaves[i] = 0;
2535 masterThread.splitPoint = &splitPoint;
2537 // If we are here it means we are not available
2538 assert(masterThread.state != THREAD_AVAILABLE);
2540 int workersCnt = 1; // At least the master is included
2542 // Allocate available threads setting state to THREAD_BOOKED
2543 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2544 if (thread_is_available(i, master))
2546 threads[i].state = THREAD_BOOKED;
2547 threads[i].splitPoint = &splitPoint;
2548 splitPoint.slaves[i] = 1;
2552 assert(Fake || workersCnt > 1);
2554 // We can release the lock because slave threads are already booked and master is not available
2555 lock_release(&MPLock);
2557 // Tell the threads that they have work to do. This will make them leave
2558 // their idle loop. But before copy search stack tail for each thread.
2559 for (i = 0; i < ActiveThreads; i++)
2560 if (i == master || splitPoint.slaves[i])
2562 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2564 assert(i == master || threads[i].state == THREAD_BOOKED);
2566 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2569 // Everything is set up. The master thread enters the idle loop, from
2570 // which it will instantly launch a search, because its state is
2571 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2572 // idle loop, which means that the main thread will return from the idle
2573 // loop when all threads have finished their work at this split point.
2574 idle_loop(master, &splitPoint);
2576 // We have returned from the idle loop, which means that all threads are
2577 // finished. Update alpha and bestValue, and return.
2580 *alpha = splitPoint.alpha;
2581 *bestValue = splitPoint.bestValue;
2582 masterThread.activeSplitPoints--;
2583 masterThread.splitPoint = splitPoint.parent;
2585 lock_release(&MPLock);
2589 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2590 // to start a new search from the root.
2592 void ThreadsManager::wake_sleeping_threads() {
2594 assert(AllThreadsShouldSleep);
2595 assert(ActiveThreads > 0);
2597 AllThreadsShouldSleep = false;
2599 if (ActiveThreads == 1)
2602 #if !defined(_MSC_VER)
2603 pthread_mutex_lock(&WaitLock);
2604 pthread_cond_broadcast(&WaitCond);
2605 pthread_mutex_unlock(&WaitLock);
2607 for (int i = 1; i < MAX_THREADS; i++)
2608 SetEvent(SitIdleEvent[i]);
2614 // put_threads_to_sleep() makes all the threads go to sleep just before
2615 // to leave think(), at the end of the search. Threads should have already
2616 // finished the job and should be idle.
2618 void ThreadsManager::put_threads_to_sleep() {
2620 assert(!AllThreadsShouldSleep);
2622 // This makes the threads to go to sleep
2623 AllThreadsShouldSleep = true;
2626 /// The RootMoveList class
2628 // RootMoveList c'tor
2630 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2632 SearchStack ss[PLY_MAX_PLUS_2];
2633 MoveStack mlist[MOVES_MAX];
2635 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2637 // Initialize search stack
2638 init_ss_array(ss, PLY_MAX_PLUS_2);
2639 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2642 // Generate all legal moves
2643 MoveStack* last = generate_moves(pos, mlist);
2645 // Add each move to the moves[] array
2646 for (MoveStack* cur = mlist; cur != last; cur++)
2648 bool includeMove = includeAllMoves;
2650 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2651 includeMove = (searchMoves[k] == cur->move);
2656 // Find a quick score for the move
2657 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2658 moves[count].pv[1] = MOVE_NONE;
2659 pos.do_move(cur->move, st);
2660 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2661 pos.undo_move(cur->move);
2667 // Score root moves using the standard way used in main search, the moves
2668 // are scored according to the order in which are returned by MovePicker.
2670 void RootMoveList::score_moves(const Position& pos)
2674 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2676 while ((move = mp.get_next_move()) != MOVE_NONE)
2677 for (int i = 0; i < count; i++)
2678 if (moves[i].move == move)
2680 moves[i].mp_score = score--;
2685 // RootMoveList simple methods definitions
2687 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2691 for (j = 0; pv[j] != MOVE_NONE; j++)
2692 moves[moveNum].pv[j] = pv[j];
2694 moves[moveNum].pv[j] = MOVE_NONE;
2698 // RootMoveList::sort() sorts the root move list at the beginning of a new
2701 void RootMoveList::sort() {
2703 sort_multipv(count - 1); // Sort all items
2707 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2708 // list by their scores and depths. It is used to order the different PVs
2709 // correctly in MultiPV mode.
2711 void RootMoveList::sort_multipv(int n) {
2715 for (i = 1; i <= n; i++)
2717 RootMove rm = moves[i];
2718 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2719 moves[j] = moves[j - 1];