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
55 // Maximum number of allowed moves per position
56 const int MOVES_MAX = 256;
59 enum NodeType { NonPV, PV };
61 // Set to true to force running with one thread.
62 // Used for debugging SMP code.
63 const bool FakeSplit = false;
65 // ThreadsManager class is used to handle all the threads related stuff in search,
66 // init, starting, parking and, the most important, launching a slave thread at a
67 // split point are what this class does. All the access to shared thread data is
68 // done through this class, so that we avoid using global variables instead.
70 class ThreadsManager {
71 /* As long as the single ThreadsManager object is defined as a global we don't
72 need to explicitly initialize to zero its data members because variables with
73 static storage duration are automatically set to zero before enter main()
79 int active_threads() const { return ActiveThreads; }
80 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
81 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
83 void resetNodeCounters();
84 int64_t nodes_searched() const;
85 bool available_thread_exists(int master) const;
86 bool thread_is_available(int slave, int master) const;
87 bool thread_should_stop(int threadID) const;
88 void wake_sleeping_threads();
89 void put_threads_to_sleep();
90 void idle_loop(int threadID, SplitPoint* sp);
93 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
94 Depth depth, Move threatMove, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
100 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
101 Thread threads[MAX_THREADS];
103 Lock MPLock, WaitLock;
105 #if !defined(_MSC_VER)
106 pthread_cond_t WaitCond;
108 HANDLE SitIdleEvent[MAX_THREADS];
114 // RootMove struct is used for moves at the root at the tree. For each
115 // root move, we store a score, a node count, and a PV (really a refutation
116 // in the case of moves which fail low).
120 RootMove() : mp_score(0), nodes(0) {}
122 // RootMove::operator<() is the comparison function used when
123 // sorting the moves. A move m1 is considered to be better
124 // than a move m2 if it has a higher score, or if the moves
125 // have equal score but m1 has the higher beta cut-off count.
126 bool operator<(const RootMove& m) const {
128 return score != m.score ? score < m.score : mp_score <= m.mp_score;
135 Move pv[PLY_MAX_PLUS_2];
139 // The RootMoveList class is essentially an array of RootMove objects, with
140 // a handful of methods for accessing the data in the individual moves.
145 RootMoveList(Position& pos, Move searchMoves[]);
147 Move move(int moveNum) const { return moves[moveNum].move; }
148 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
149 int move_count() const { return count; }
150 Value move_score(int moveNum) const { return moves[moveNum].score; }
151 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
152 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
153 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
155 void set_move_pv(int moveNum, const Move pv[]);
156 void score_moves(const Position& pos);
158 void sort_multipv(int n);
161 RootMove moves[MOVES_MAX];
166 // When formatting a move for std::cout we must know if we are in Chess960
167 // or not. To keep using the handy operator<<() on the move the trick is to
168 // embed this flag in the stream itself. Function-like named enum set960 is
169 // used as a custom manipulator and the stream internal general-purpose array,
170 // accessed through ios_base::iword(), is used to pass the flag to the move's
171 // operator<<() that will use it to properly format castling moves.
174 std::ostream& operator<< (std::ostream& os, const set960& m) {
176 os.iword(0) = int(m);
185 // Maximum depth for razoring
186 const Depth RazorDepth = 4 * ONE_PLY;
188 // Dynamic razoring margin based on depth
189 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
191 // Maximum depth for use of dynamic threat detection when null move fails low
192 const Depth ThreatDepth = 5 * ONE_PLY;
194 // Step 9. Internal iterative deepening
196 // Minimum depth for use of internal iterative deepening
197 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
199 // At Non-PV nodes we do an internal iterative deepening search
200 // when the static evaluation is bigger then beta - IIDMargin.
201 const Value IIDMargin = Value(0x100);
203 // Step 11. Decide the new search depth
205 // Extensions. Configurable UCI options
206 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
207 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
208 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
210 // Minimum depth for use of singular extension
211 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
213 // If the TT move is at least SingularExtensionMargin better then the
214 // remaining ones we will extend it.
215 const Value SingularExtensionMargin = Value(0x20);
217 // Step 12. Futility pruning
219 // Futility margin for quiescence search
220 const Value FutilityMarginQS = Value(0x80);
222 // Futility lookup tables (initialized at startup) and their getter functions
223 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
224 int FutilityMoveCountArray[32]; // [depth]
226 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
227 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
229 // Step 14. Reduced search
231 // Reduction lookup tables (initialized at startup) and their getter functions
232 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
234 template <NodeType PV>
235 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
237 // Common adjustments
239 // Search depth at iteration 1
240 const Depth InitialDepth = ONE_PLY;
242 // Easy move margin. An easy move candidate must be at least this much
243 // better than the second best move.
244 const Value EasyMoveMargin = Value(0x200);
252 // Scores and number of times the best move changed for each iteration
253 Value ValueByIteration[PLY_MAX_PLUS_2];
254 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
256 // Search window management
262 // Time managment variables
263 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
264 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
265 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
270 std::ofstream LogFile;
272 // Multi-threads related variables
273 Depth MinimumSplitDepth;
274 int MaxThreadsPerSplitPoint;
275 ThreadsManager ThreadsMgr;
277 // Node counters, used only by thread[0] but try to keep in different cache
278 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
280 int NodesBetweenPolls = 30000;
287 Value id_loop(const Position& pos, Move searchMoves[]);
288 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
290 template <NodeType PvNode>
291 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
293 template <NodeType PvNode>
294 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
296 template <NodeType PvNode>
297 void sp_search(SplitPoint* sp, int threadID);
299 template <NodeType PvNode>
300 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
302 bool connected_moves(const Position& pos, Move m1, Move m2);
303 bool value_is_mate(Value value);
304 Value value_to_tt(Value v, int ply);
305 Value value_from_tt(Value v, int ply);
306 bool move_is_killer(Move m, SearchStack* ss);
307 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
308 bool connected_threat(const Position& pos, Move m, Move threat);
309 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
310 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
311 void update_killers(Move m, SearchStack* ss);
312 void update_gains(const Position& pos, Move move, Value before, Value after);
314 int current_search_time();
315 std::string value_to_uci(Value v);
319 void wait_for_stop_or_ponderhit();
320 void init_ss_array(SearchStack* ss, int size);
321 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
322 void insert_pv_in_tt(const Position& pos, Move pv[]);
323 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
325 #if !defined(_MSC_VER)
326 void *init_thread(void *threadID);
328 DWORD WINAPI init_thread(LPVOID threadID);
338 /// init_threads(), exit_threads() and nodes_searched() are helpers to
339 /// give accessibility to some TM methods from outside of current file.
341 void init_threads() { ThreadsMgr.init_threads(); }
342 void exit_threads() { ThreadsMgr.exit_threads(); }
343 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
346 /// init_search() is called during startup. It initializes various lookup tables
350 int d; // depth (ONE_PLY == 2)
351 int hd; // half depth (ONE_PLY == 1)
354 // Init reductions array
355 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
357 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
358 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
359 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
360 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
363 // Init futility margins array
364 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
365 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
367 // Init futility move count array
368 for (d = 0; d < 32; d++)
369 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
373 /// perft() is our utility to verify move generation is bug free. All the legal
374 /// moves up to given depth are generated and counted and the sum returned.
376 int perft(Position& pos, Depth depth)
378 MoveStack mlist[MOVES_MAX];
383 // Generate all legal moves
384 MoveStack* last = generate_moves(pos, mlist);
386 // If we are at the last ply we don't need to do and undo
387 // the moves, just to count them.
388 if (depth <= ONE_PLY)
389 return int(last - mlist);
391 // Loop through all legal moves
393 for (MoveStack* cur = mlist; cur != last; cur++)
396 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
397 sum += perft(pos, depth - ONE_PLY);
404 /// think() is the external interface to Stockfish's search, and is called when
405 /// the program receives the UCI 'go' command. It initializes various
406 /// search-related global variables, and calls root_search(). It returns false
407 /// when a quit command is received during the search.
409 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
410 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
412 // Initialize global search variables
413 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
415 ThreadsMgr.resetNodeCounters();
416 SearchStartTime = get_system_time();
417 ExactMaxTime = maxTime;
420 InfiniteSearch = infinite;
421 PonderSearch = ponder;
422 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
424 // Look for a book move, only during games, not tests
425 if (UseTimeManagement && get_option_value_bool("OwnBook"))
427 if (get_option_value_string("Book File") != OpeningBook.file_name())
428 OpeningBook.open(get_option_value_string("Book File"));
430 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
431 if (bookMove != MOVE_NONE)
434 wait_for_stop_or_ponderhit();
436 cout << "bestmove " << bookMove << endl;
441 // Read UCI option values
442 TT.set_size(get_option_value_int("Hash"));
443 if (button_was_pressed("Clear Hash"))
446 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
447 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
448 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
449 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
450 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
451 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
452 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
453 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
454 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
455 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
456 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
457 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
459 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
460 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
461 MultiPV = get_option_value_int("MultiPV");
462 UseLogFile = get_option_value_bool("Use Search Log");
465 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
467 read_weights(pos.side_to_move());
469 // Set the number of active threads
470 int newActiveThreads = get_option_value_int("Threads");
471 if (newActiveThreads != ThreadsMgr.active_threads())
473 ThreadsMgr.set_active_threads(newActiveThreads);
474 init_eval(ThreadsMgr.active_threads());
477 // Wake up sleeping threads
478 ThreadsMgr.wake_sleeping_threads();
481 int myTime = time[pos.side_to_move()];
482 int myIncrement = increment[pos.side_to_move()];
483 if (UseTimeManagement)
484 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
486 // Set best NodesBetweenPolls interval to avoid lagging under
487 // heavy time pressure.
489 NodesBetweenPolls = Min(MaxNodes, 30000);
490 else if (myTime && myTime < 1000)
491 NodesBetweenPolls = 1000;
492 else if (myTime && myTime < 5000)
493 NodesBetweenPolls = 5000;
495 NodesBetweenPolls = 30000;
497 // Write search information to log file
499 LogFile << "Searching: " << pos.to_fen() << endl
500 << "infinite: " << infinite
501 << " ponder: " << ponder
502 << " time: " << myTime
503 << " increment: " << myIncrement
504 << " moves to go: " << movesToGo << endl;
506 // We're ready to start thinking. Call the iterative deepening loop function
507 id_loop(pos, searchMoves);
512 ThreadsMgr.put_threads_to_sleep();
520 // id_loop() is the main iterative deepening loop. It calls root_search
521 // repeatedly with increasing depth until the allocated thinking time has
522 // been consumed, the user stops the search, or the maximum search depth is
525 Value id_loop(const Position& pos, Move searchMoves[]) {
527 Position p(pos, pos.thread());
528 SearchStack ss[PLY_MAX_PLUS_2];
529 Move pv[PLY_MAX_PLUS_2];
530 Move EasyMove = MOVE_NONE;
531 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
533 // Moves to search are verified, copied, scored and sorted
534 RootMoveList rml(p, searchMoves);
536 // Handle special case of searching on a mate/stale position
537 if (rml.move_count() == 0)
540 wait_for_stop_or_ponderhit();
542 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
545 // Print RootMoveList startup scoring to the standard output,
546 // so to output information also for iteration 1.
547 cout << set960(p.is_chess960()) // Is enough to set once at the beginning
548 << "info depth " << 1
549 << "\ninfo depth " << 1
550 << " score " << value_to_uci(rml.move_score(0))
551 << " time " << current_search_time()
552 << " nodes " << ThreadsMgr.nodes_searched()
554 << " pv " << rml.move(0) << "\n";
559 init_ss_array(ss, PLY_MAX_PLUS_2);
560 pv[0] = pv[1] = MOVE_NONE;
561 ValueByIteration[1] = rml.move_score(0);
564 // Is one move significantly better than others after initial scoring ?
565 if ( rml.move_count() == 1
566 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
567 EasyMove = rml.move(0);
569 // Iterative deepening loop
570 while (Iteration < PLY_MAX)
572 // Initialize iteration
574 BestMoveChangesByIteration[Iteration] = 0;
576 cout << "info depth " << Iteration << endl;
578 // Calculate dynamic aspiration window based on previous iterations
579 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
581 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
582 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
584 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
585 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
587 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
588 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
591 // Search to the current depth, rml is updated and sorted, alpha and beta could change
592 value = root_search(p, ss, pv, rml, &alpha, &beta);
594 // Write PV to transposition table, in case the relevant entries have
595 // been overwritten during the search.
596 insert_pv_in_tt(p, pv);
599 break; // Value cannot be trusted. Break out immediately!
601 //Save info about search result
602 ValueByIteration[Iteration] = value;
604 // Drop the easy move if differs from the new best move
605 if (pv[0] != EasyMove)
606 EasyMove = MOVE_NONE;
608 if (UseTimeManagement)
611 bool stopSearch = false;
613 // Stop search early if there is only a single legal move,
614 // we search up to Iteration 6 anyway to get a proper score.
615 if (Iteration >= 6 && rml.move_count() == 1)
618 // Stop search early when the last two iterations returned a mate score
620 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
621 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
624 // Stop search early if one move seems to be much better than the others
625 int64_t nodes = ThreadsMgr.nodes_searched();
628 && ( ( rml.move_nodes(0) > (nodes * 85) / 100
629 && current_search_time() > TimeMgr.available_time() / 16)
630 ||( rml.move_nodes(0) > (nodes * 98) / 100
631 && current_search_time() > TimeMgr.available_time() / 32)))
634 // Add some extra time if the best move has changed during the last two iterations
635 if (Iteration > 5 && Iteration <= 50)
636 TimeMgr.pv_unstability(BestMoveChangesByIteration[Iteration],
637 BestMoveChangesByIteration[Iteration-1]);
639 // Stop search if most of MaxSearchTime is consumed at the end of the
640 // iteration. We probably don't have enough time to search the first
641 // move at the next iteration anyway.
642 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
648 StopOnPonderhit = true;
654 if (MaxDepth && Iteration >= MaxDepth)
658 // If we are pondering or in infinite search, we shouldn't print the
659 // best move before we are told to do so.
660 if (!AbortSearch && (PonderSearch || InfiniteSearch))
661 wait_for_stop_or_ponderhit();
663 // Print final search statistics
664 cout << "info nodes " << ThreadsMgr.nodes_searched()
666 << " time " << current_search_time() << endl;
668 // Print the best move and the ponder move to the standard output
669 if (pv[0] == MOVE_NONE)
675 assert(pv[0] != MOVE_NONE);
677 cout << "bestmove " << pv[0];
679 if (pv[1] != MOVE_NONE)
680 cout << " ponder " << pv[1];
687 dbg_print_mean(LogFile);
689 if (dbg_show_hit_rate)
690 dbg_print_hit_rate(LogFile);
692 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
693 << "\nNodes/second: " << nps()
694 << "\nBest move: " << move_to_san(p, pv[0]);
697 p.do_move(pv[0], st);
698 LogFile << "\nPonder move: "
699 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
702 return rml.move_score(0);
706 // root_search() is the function which searches the root node. It is
707 // similar to search_pv except that it uses a different move ordering
708 // scheme, prints some information to the standard output and handles
709 // the fail low/high loops.
711 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
717 Depth depth, ext, newDepth;
718 Value value, evalMargin, alpha, beta;
719 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
720 int researchCountFH, researchCountFL;
722 researchCountFH = researchCountFL = 0;
725 isCheck = pos.is_check();
726 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
728 // Step 1. Initialize node (polling is omitted at root)
729 ss->currentMove = ss->bestMove = MOVE_NONE;
731 // Step 2. Check for aborted search (omitted at root)
732 // Step 3. Mate distance pruning (omitted at root)
733 // Step 4. Transposition table lookup (omitted at root)
735 // Step 5. Evaluate the position statically
736 // At root we do this only to get reference value for child nodes
737 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, evalMargin);
739 // Step 6. Razoring (omitted at root)
740 // Step 7. Static null move pruning (omitted at root)
741 // Step 8. Null move search with verification search (omitted at root)
742 // Step 9. Internal iterative deepening (omitted at root)
744 // Step extra. Fail low loop
745 // We start with small aspiration window and in case of fail low, we research
746 // with bigger window until we are not failing low anymore.
749 // Sort the moves before to (re)search
750 rml.score_moves(pos);
753 // Step 10. Loop through all moves in the root move list
754 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
756 // This is used by time management
757 FirstRootMove = (i == 0);
759 // Save the current node count before the move is searched
760 nodes = ThreadsMgr.nodes_searched();
762 // Pick the next root move, and print the move and the move number to
763 // the standard output.
764 move = ss->currentMove = rml.move(i);
766 if (current_search_time() >= 1000)
767 cout << "info currmove " << move
768 << " currmovenumber " << i + 1 << endl;
770 moveIsCheck = pos.move_is_check(move);
771 captureOrPromotion = pos.move_is_capture_or_promotion(move);
773 // Step 11. Decide the new search depth
774 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
775 newDepth = depth + ext;
777 // Step 12. Futility pruning (omitted at root)
779 // Step extra. Fail high loop
780 // If move fails high, we research with bigger window until we are not failing
782 value = - VALUE_INFINITE;
786 // Step 13. Make the move
787 pos.do_move(move, st, ci, moveIsCheck);
789 // Step extra. pv search
790 // We do pv search for first moves (i < MultiPV)
791 // and for fail high research (value > alpha)
792 if (i < MultiPV || value > alpha)
794 // Aspiration window is disabled in multi-pv case
796 alpha = -VALUE_INFINITE;
798 // Full depth PV search, done on first move or after a fail high
799 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
803 // Step 14. Reduced search
804 // if the move fails high will be re-searched at full depth
805 bool doFullDepthSearch = true;
807 if ( depth >= 3 * ONE_PLY
809 && !captureOrPromotion
810 && !move_is_castle(move))
812 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
815 assert(newDepth-ss->reduction >= ONE_PLY);
817 // Reduced depth non-pv search using alpha as upperbound
818 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
819 doFullDepthSearch = (value > alpha);
822 // The move failed high, but if reduction is very big we could
823 // face a false positive, retry with a less aggressive reduction,
824 // if the move fails high again then go with full depth search.
825 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
827 assert(newDepth - ONE_PLY >= ONE_PLY);
829 ss->reduction = ONE_PLY;
830 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
831 doFullDepthSearch = (value > alpha);
833 ss->reduction = DEPTH_ZERO; // Restore original reduction
836 // Step 15. Full depth search
837 if (doFullDepthSearch)
839 // Full depth non-pv search using alpha as upperbound
840 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
842 // If we are above alpha then research at same depth but as PV
843 // to get a correct score or eventually a fail high above beta.
845 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
849 // Step 16. Undo move
852 // Can we exit fail high loop ?
853 if (AbortSearch || value < beta)
856 // We are failing high and going to do a research. It's important to update
857 // the score before research in case we run out of time while researching.
858 rml.set_move_score(i, value);
860 extract_pv_from_tt(pos, move, pv);
861 rml.set_move_pv(i, pv);
863 // Print information to the standard output
864 print_pv_info(pos, pv, alpha, beta, value);
866 // Prepare for a research after a fail high, each time with a wider window
867 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
870 } // End of fail high loop
872 // Finished searching the move. If AbortSearch is true, the search
873 // was aborted because the user interrupted the search or because we
874 // ran out of time. In this case, the return value of the search cannot
875 // be trusted, and we break out of the loop without updating the best
880 // Remember searched nodes counts for this move
881 rml.add_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
883 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
884 assert(value < beta);
886 // Step 17. Check for new best move
887 if (value <= alpha && i >= MultiPV)
888 rml.set_move_score(i, -VALUE_INFINITE);
891 // PV move or new best move!
894 rml.set_move_score(i, value);
896 extract_pv_from_tt(pos, move, pv);
897 rml.set_move_pv(i, pv);
901 // We record how often the best move has been changed in each
902 // iteration. This information is used for time managment: When
903 // the best move changes frequently, we allocate some more time.
905 BestMoveChangesByIteration[Iteration]++;
907 // Print information to the standard output
908 print_pv_info(pos, pv, alpha, beta, value);
910 // Raise alpha to setup proper non-pv search upper bound
917 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
919 cout << "info multipv " << j + 1
920 << " score " << value_to_uci(rml.move_score(j))
921 << " depth " << (j <= i ? Iteration : Iteration - 1)
922 << " time " << current_search_time()
923 << " nodes " << ThreadsMgr.nodes_searched()
927 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
928 cout << rml.move_pv(j, k) << " ";
932 alpha = rml.move_score(Min(i, MultiPV - 1));
934 } // PV move or new best move
936 assert(alpha >= *alphaPtr);
938 AspirationFailLow = (alpha == *alphaPtr);
940 if (AspirationFailLow && StopOnPonderhit)
941 StopOnPonderhit = false;
944 // Can we exit fail low loop ?
945 if (AbortSearch || !AspirationFailLow)
948 // Prepare for a research after a fail low, each time with a wider window
949 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
954 // Sort the moves before to return
961 // search<>() is the main search function for both PV and non-PV nodes
963 template <NodeType PvNode>
964 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
966 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
967 assert(beta > alpha && beta <= VALUE_INFINITE);
968 assert(PvNode || alpha == beta - 1);
969 assert(ply > 0 && ply < PLY_MAX);
970 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
972 Move movesSearched[MOVES_MAX];
976 Move ttMove, move, excludedMove, threatMove;
978 Value bestValue, value, evalMargin, oldAlpha;
979 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
980 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
981 bool mateThreat = false;
983 int threadID = pos.thread();
984 refinedValue = bestValue = value = -VALUE_INFINITE;
987 // Step 1. Initialize node and poll. Polling can abort search
988 ThreadsMgr.incrementNodeCounter(threadID);
989 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
990 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
992 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
998 // Step 2. Check for aborted search and immediate draw
999 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1002 if (pos.is_draw() || ply >= PLY_MAX - 1)
1005 // Step 3. Mate distance pruning
1006 alpha = Max(value_mated_in(ply), alpha);
1007 beta = Min(value_mate_in(ply+1), beta);
1011 // Step 4. Transposition table lookup
1013 // We don't want the score of a partial search to overwrite a previous full search
1014 // TT value, so we use a different position key in case of an excluded move exists.
1015 excludedMove = ss->excludedMove;
1016 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1018 tte = TT.retrieve(posKey);
1019 ttMove = (tte ? tte->move() : MOVE_NONE);
1021 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1022 // This is to avoid problems in the following areas:
1024 // * Repetition draw detection
1025 // * Fifty move rule detection
1026 // * Searching for a mate
1027 // * Printing of full PV line
1029 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1031 // Refresh tte entry to avoid aging
1032 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1034 ss->bestMove = ttMove; // Can be MOVE_NONE
1035 return value_from_tt(tte->value(), ply);
1038 // Step 5. Evaluate the position statically and
1039 // update gain statistics of parent move.
1040 isCheck = pos.is_check();
1042 ss->eval = evalMargin = VALUE_NONE;
1045 assert(tte->static_value() != VALUE_NONE);
1047 ss->eval = tte->static_value();
1048 evalMargin = tte->static_value_margin();
1049 refinedValue = refine_eval(tte, ss->eval, ply);
1053 refinedValue = ss->eval = evaluate(pos, evalMargin);
1054 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1057 // Save gain for the parent non-capture move
1058 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1060 // Step 6. Razoring (is omitted in PV nodes)
1062 && depth < RazorDepth
1064 && refinedValue < beta - razor_margin(depth)
1065 && ttMove == MOVE_NONE
1066 && (ss-1)->currentMove != MOVE_NULL
1067 && !value_is_mate(beta)
1068 && !pos.has_pawn_on_7th(pos.side_to_move()))
1070 Value rbeta = beta - razor_margin(depth);
1071 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1073 // Logically we should return (v + razor_margin(depth)), but
1074 // surprisingly this did slightly weaker in tests.
1078 // Step 7. Static null move pruning (is omitted in PV nodes)
1079 // We're betting that the opponent doesn't have a move that will reduce
1080 // the score by more than futility_margin(depth) if we do a null move.
1082 && !ss->skipNullMove
1083 && depth < RazorDepth
1085 && refinedValue >= beta + futility_margin(depth, 0)
1086 && !value_is_mate(beta)
1087 && pos.non_pawn_material(pos.side_to_move()))
1088 return refinedValue - futility_margin(depth, 0);
1090 // Step 8. Null move search with verification search (is omitted in PV nodes)
1092 && !ss->skipNullMove
1095 && refinedValue >= beta
1096 && !value_is_mate(beta)
1097 && pos.non_pawn_material(pos.side_to_move()))
1099 ss->currentMove = MOVE_NULL;
1101 // Null move dynamic reduction based on depth
1102 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1104 // Null move dynamic reduction based on value
1105 if (refinedValue - beta > PawnValueMidgame)
1108 pos.do_null_move(st);
1109 (ss+1)->skipNullMove = true;
1111 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1112 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1113 (ss+1)->skipNullMove = false;
1114 pos.undo_null_move();
1116 if (nullValue >= beta)
1118 // Do not return unproven mate scores
1119 if (nullValue >= value_mate_in(PLY_MAX))
1122 if (depth < 6 * ONE_PLY)
1125 // Do verification search at high depths
1126 ss->skipNullMove = true;
1127 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1128 ss->skipNullMove = false;
1135 // The null move failed low, which means that we may be faced with
1136 // some kind of threat. If the previous move was reduced, check if
1137 // the move that refuted the null move was somehow connected to the
1138 // move which was reduced. If a connection is found, return a fail
1139 // low score (which will cause the reduced move to fail high in the
1140 // parent node, which will trigger a re-search with full depth).
1141 if (nullValue == value_mated_in(ply + 2))
1144 threatMove = (ss+1)->bestMove;
1145 if ( depth < ThreatDepth
1146 && (ss-1)->reduction
1147 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1152 // Step 9. Internal iterative deepening
1153 if ( depth >= IIDDepth[PvNode]
1154 && ttMove == MOVE_NONE
1155 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1157 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1159 ss->skipNullMove = true;
1160 search<PvNode>(pos, ss, alpha, beta, d, ply);
1161 ss->skipNullMove = false;
1163 ttMove = ss->bestMove;
1164 tte = TT.retrieve(posKey);
1167 // Expensive mate threat detection (only for PV nodes)
1169 mateThreat = pos.has_mate_threat();
1171 // Initialize a MovePicker object for the current position
1172 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1174 ss->bestMove = MOVE_NONE;
1175 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1176 futilityBase = ss->eval + evalMargin;
1177 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1180 && !excludedMove // Do not allow recursive singular extension search
1181 && (tte->type() & VALUE_TYPE_LOWER)
1182 && tte->depth() >= depth - 3 * ONE_PLY;
1184 // Step 10. Loop through moves
1185 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1186 while ( bestValue < beta
1187 && (move = mp.get_next_move()) != MOVE_NONE
1188 && !ThreadsMgr.thread_should_stop(threadID))
1190 assert(move_is_ok(move));
1192 if (move == excludedMove)
1195 moveIsCheck = pos.move_is_check(move, ci);
1196 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1198 // Step 11. Decide the new search depth
1199 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1201 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1202 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1203 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1204 // lower then ttValue minus a margin then we extend ttMove.
1205 if ( singularExtensionNode
1206 && move == tte->move()
1209 Value ttValue = value_from_tt(tte->value(), ply);
1211 if (abs(ttValue) < VALUE_KNOWN_WIN)
1213 Value b = ttValue - SingularExtensionMargin;
1214 ss->excludedMove = move;
1215 ss->skipNullMove = true;
1216 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1217 ss->skipNullMove = false;
1218 ss->excludedMove = MOVE_NONE;
1219 ss->bestMove = MOVE_NONE;
1225 newDepth = depth - ONE_PLY + ext;
1227 // Update current move (this must be done after singular extension search)
1228 movesSearched[moveCount++] = ss->currentMove = move;
1230 // Step 12. Futility pruning (is omitted in PV nodes)
1232 && !captureOrPromotion
1236 && !move_is_castle(move))
1238 // Move count based pruning
1239 if ( moveCount >= futility_move_count(depth)
1240 && !(threatMove && connected_threat(pos, move, threatMove))
1241 && bestValue > value_mated_in(PLY_MAX))
1244 // Value based pruning
1245 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1246 // but fixing this made program slightly weaker.
1247 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1248 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1249 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1251 if (futilityValueScaled < beta)
1253 if (futilityValueScaled > bestValue)
1254 bestValue = futilityValueScaled;
1259 // Step 13. Make the move
1260 pos.do_move(move, st, ci, moveIsCheck);
1262 // Step extra. pv search (only in PV nodes)
1263 // The first move in list is the expected PV
1264 if (PvNode && moveCount == 1)
1265 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1266 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1269 // Step 14. Reduced depth search
1270 // If the move fails high will be re-searched at full depth.
1271 bool doFullDepthSearch = true;
1273 if ( depth >= 3 * ONE_PLY
1274 && !captureOrPromotion
1276 && !move_is_castle(move)
1277 && !move_is_killer(move, ss))
1279 ss->reduction = reduction<PvNode>(depth, moveCount);
1282 Depth d = newDepth - ss->reduction;
1283 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1284 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1286 doFullDepthSearch = (value > alpha);
1289 // The move failed high, but if reduction is very big we could
1290 // face a false positive, retry with a less aggressive reduction,
1291 // if the move fails high again then go with full depth search.
1292 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1294 assert(newDepth - ONE_PLY >= ONE_PLY);
1296 ss->reduction = ONE_PLY;
1297 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1298 doFullDepthSearch = (value > alpha);
1300 ss->reduction = DEPTH_ZERO; // Restore original reduction
1303 // Step 15. Full depth search
1304 if (doFullDepthSearch)
1306 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1307 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1309 // Step extra. pv search (only in PV nodes)
1310 // Search only for possible new PV nodes, if instead value >= beta then
1311 // parent node fails low with value <= alpha and tries another move.
1312 if (PvNode && value > alpha && value < beta)
1313 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1314 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1318 // Step 16. Undo move
1319 pos.undo_move(move);
1321 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1323 // Step 17. Check for new best move
1324 if (value > bestValue)
1329 if (PvNode && value < beta) // We want always alpha < beta
1332 if (value == value_mate_in(ply + 1))
1333 ss->mateKiller = move;
1335 ss->bestMove = move;
1339 // Step 18. Check for split
1340 if ( depth >= MinimumSplitDepth
1341 && ThreadsMgr.active_threads() > 1
1343 && ThreadsMgr.available_thread_exists(threadID)
1345 && !ThreadsMgr.thread_should_stop(threadID)
1347 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1348 threatMove, mateThreat, &moveCount, &mp, PvNode);
1351 // Step 19. Check for mate and stalemate
1352 // All legal moves have been searched and if there are
1353 // no legal moves, it must be mate or stalemate.
1354 // If one move was excluded return fail low score.
1356 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1358 // Step 20. Update tables
1359 // If the search is not aborted, update the transposition table,
1360 // history counters, and killer moves.
1361 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1364 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1365 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1366 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, evalMargin);
1368 // Update killers and history only for non capture moves that fails high
1369 if ( bestValue >= beta
1370 && !pos.move_is_capture_or_promotion(move))
1372 update_history(pos, move, depth, movesSearched, moveCount);
1373 update_killers(move, ss);
1376 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1382 // qsearch() is the quiescence search function, which is called by the main
1383 // search function when the remaining depth is zero (or, to be more precise,
1384 // less than ONE_PLY).
1386 template <NodeType PvNode>
1387 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1389 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1390 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1391 assert(PvNode || alpha == beta - 1);
1393 assert(ply > 0 && ply < PLY_MAX);
1394 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1398 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1399 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1401 Value oldAlpha = alpha;
1403 ThreadsMgr.incrementNodeCounter(pos.thread());
1404 ss->bestMove = ss->currentMove = MOVE_NONE;
1406 // Check for an instant draw or maximum ply reached
1407 if (pos.is_draw() || ply >= PLY_MAX - 1)
1410 // Transposition table lookup. At PV nodes, we don't use the TT for
1411 // pruning, but only for move ordering.
1412 tte = TT.retrieve(pos.get_key());
1413 ttMove = (tte ? tte->move() : MOVE_NONE);
1415 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1417 ss->bestMove = ttMove; // Can be MOVE_NONE
1418 return value_from_tt(tte->value(), ply);
1421 isCheck = pos.is_check();
1423 // Evaluate the position statically
1426 bestValue = futilityBase = -VALUE_INFINITE;
1427 ss->eval = evalMargin = VALUE_NONE;
1428 deepChecks = enoughMaterial = false;
1434 assert(tte->static_value() != VALUE_NONE);
1436 evalMargin = tte->static_value_margin();
1437 ss->eval = bestValue = tte->static_value();
1440 ss->eval = bestValue = evaluate(pos, evalMargin);
1442 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1444 // Stand pat. Return immediately if static value is at least beta
1445 if (bestValue >= beta)
1448 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1453 if (PvNode && bestValue > alpha)
1456 // If we are near beta then try to get a cutoff pushing checks a bit further
1457 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1459 // Futility pruning parameters, not needed when in check
1460 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1461 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1464 // Initialize a MovePicker object for the current position, and prepare
1465 // to search the moves. Because the depth is <= 0 here, only captures,
1466 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1467 // and we are near beta) will be generated.
1468 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1471 // Loop through the moves until no moves remain or a beta cutoff occurs
1472 while ( alpha < beta
1473 && (move = mp.get_next_move()) != MOVE_NONE)
1475 assert(move_is_ok(move));
1477 moveIsCheck = pos.move_is_check(move, ci);
1485 && !move_is_promotion(move)
1486 && !pos.move_is_passed_pawn_push(move))
1488 futilityValue = futilityBase
1489 + pos.endgame_value_of_piece_on(move_to(move))
1490 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1492 if (futilityValue < alpha)
1494 if (futilityValue > bestValue)
1495 bestValue = futilityValue;
1500 // Detect non-capture evasions that are candidate to be pruned
1501 evasionPrunable = isCheck
1502 && bestValue > value_mated_in(PLY_MAX)
1503 && !pos.move_is_capture(move)
1504 && !pos.can_castle(pos.side_to_move());
1506 // Don't search moves with negative SEE values
1508 && (!isCheck || evasionPrunable)
1510 && !move_is_promotion(move)
1511 && pos.see_sign(move) < 0)
1514 // Update current move
1515 ss->currentMove = move;
1517 // Make and search the move
1518 pos.do_move(move, st, ci, moveIsCheck);
1519 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1520 pos.undo_move(move);
1522 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1525 if (value > bestValue)
1531 ss->bestMove = move;
1536 // All legal moves have been searched. A special case: If we're in check
1537 // and no legal moves were found, it is checkmate.
1538 if (isCheck && bestValue == -VALUE_INFINITE)
1539 return value_mated_in(ply);
1541 // Update transposition table
1542 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1543 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1544 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1546 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1552 // sp_search() is used to search from a split point. This function is called
1553 // by each thread working at the split point. It is similar to the normal
1554 // search() function, but simpler. Because we have already probed the hash
1555 // table, done a null move search, and searched the first move before
1556 // splitting, we don't have to repeat all this work in sp_search(). We
1557 // also don't need to store anything to the hash table here: This is taken
1558 // care of after we return from the split point.
1560 template <NodeType PvNode>
1561 void sp_search(SplitPoint* sp, int threadID) {
1563 assert(threadID >= 0 && threadID < ThreadsMgr.active_threads());
1564 assert(ThreadsMgr.active_threads() > 1);
1568 Depth ext, newDepth;
1570 Value futilityValueScaled; // NonPV specific
1571 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1573 value = -VALUE_INFINITE;
1575 Position pos(*sp->pos, threadID);
1577 SearchStack* ss = sp->sstack[threadID] + 1;
1578 isCheck = pos.is_check();
1580 // Step 10. Loop through moves
1581 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1582 lock_grab(&(sp->lock));
1584 while ( sp->bestValue < sp->beta
1585 && (move = sp->mp->get_next_move()) != MOVE_NONE
1586 && !ThreadsMgr.thread_should_stop(threadID))
1588 moveCount = ++sp->moveCount;
1589 lock_release(&(sp->lock));
1591 assert(move_is_ok(move));
1593 moveIsCheck = pos.move_is_check(move, ci);
1594 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1596 // Step 11. Decide the new search depth
1597 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1598 newDepth = sp->depth - ONE_PLY + ext;
1600 // Update current move
1601 ss->currentMove = move;
1603 // Step 12. Futility pruning (is omitted in PV nodes)
1605 && !captureOrPromotion
1608 && !move_is_castle(move))
1610 // Move count based pruning
1611 if ( moveCount >= futility_move_count(sp->depth)
1612 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1613 && sp->bestValue > value_mated_in(PLY_MAX))
1615 lock_grab(&(sp->lock));
1619 // Value based pruning
1620 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1621 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1622 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1624 if (futilityValueScaled < sp->beta)
1626 lock_grab(&(sp->lock));
1628 if (futilityValueScaled > sp->bestValue)
1629 sp->bestValue = futilityValueScaled;
1634 // Step 13. Make the move
1635 pos.do_move(move, st, ci, moveIsCheck);
1637 // Step 14. Reduced search
1638 // If the move fails high will be re-searched at full depth.
1639 bool doFullDepthSearch = true;
1641 if ( !captureOrPromotion
1643 && !move_is_castle(move)
1644 && !move_is_killer(move, ss))
1646 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1649 Value localAlpha = sp->alpha;
1650 Depth d = newDepth - ss->reduction;
1651 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, sp->ply+1)
1652 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1654 doFullDepthSearch = (value > localAlpha);
1657 // The move failed high, but if reduction is very big we could
1658 // face a false positive, retry with a less aggressive reduction,
1659 // if the move fails high again then go with full depth search.
1660 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1662 assert(newDepth - ONE_PLY >= ONE_PLY);
1664 ss->reduction = ONE_PLY;
1665 Value localAlpha = sp->alpha;
1666 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1667 doFullDepthSearch = (value > localAlpha);
1669 ss->reduction = DEPTH_ZERO; // Restore original reduction
1672 // Step 15. Full depth search
1673 if (doFullDepthSearch)
1675 Value localAlpha = sp->alpha;
1676 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, sp->ply+1)
1677 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1679 // Step extra. pv search (only in PV nodes)
1680 // Search only for possible new PV nodes, if instead value >= beta then
1681 // parent node fails low with value <= alpha and tries another move.
1682 if (PvNode && value > localAlpha && value < sp->beta)
1683 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, DEPTH_ZERO, sp->ply+1)
1684 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1687 // Step 16. Undo move
1688 pos.undo_move(move);
1690 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1692 // Step 17. Check for new best move
1693 lock_grab(&(sp->lock));
1695 if (value > sp->bestValue && !ThreadsMgr.thread_should_stop(threadID))
1697 sp->bestValue = value;
1699 if (sp->bestValue > sp->alpha)
1701 if (!PvNode || value >= sp->beta)
1702 sp->stopRequest = true;
1704 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1707 sp->parentSstack->bestMove = ss->bestMove = move;
1712 /* Here we have the lock still grabbed */
1714 sp->slaves[threadID] = 0;
1716 lock_release(&(sp->lock));
1720 // connected_moves() tests whether two moves are 'connected' in the sense
1721 // that the first move somehow made the second move possible (for instance
1722 // if the moving piece is the same in both moves). The first move is assumed
1723 // to be the move that was made to reach the current position, while the
1724 // second move is assumed to be a move from the current position.
1726 bool connected_moves(const Position& pos, Move m1, Move m2) {
1728 Square f1, t1, f2, t2;
1731 assert(move_is_ok(m1));
1732 assert(move_is_ok(m2));
1734 if (m2 == MOVE_NONE)
1737 // Case 1: The moving piece is the same in both moves
1743 // Case 2: The destination square for m2 was vacated by m1
1749 // Case 3: Moving through the vacated square
1750 if ( piece_is_slider(pos.piece_on(f2))
1751 && bit_is_set(squares_between(f2, t2), f1))
1754 // Case 4: The destination square for m2 is defended by the moving piece in m1
1755 p = pos.piece_on(t1);
1756 if (bit_is_set(pos.attacks_from(p, t1), t2))
1759 // Case 5: Discovered check, checking piece is the piece moved in m1
1760 if ( piece_is_slider(p)
1761 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1762 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1764 // discovered_check_candidates() works also if the Position's side to
1765 // move is the opposite of the checking piece.
1766 Color them = opposite_color(pos.side_to_move());
1767 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1769 if (bit_is_set(dcCandidates, f2))
1776 // value_is_mate() checks if the given value is a mate one eventually
1777 // compensated for the ply.
1779 bool value_is_mate(Value value) {
1781 assert(abs(value) <= VALUE_INFINITE);
1783 return value <= value_mated_in(PLY_MAX)
1784 || value >= value_mate_in(PLY_MAX);
1788 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1789 // "plies to mate from the current ply". Non-mate scores are unchanged.
1790 // The function is called before storing a value to the transposition table.
1792 Value value_to_tt(Value v, int ply) {
1794 if (v >= value_mate_in(PLY_MAX))
1797 if (v <= value_mated_in(PLY_MAX))
1804 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1805 // the transposition table to a mate score corrected for the current ply.
1807 Value value_from_tt(Value v, int ply) {
1809 if (v >= value_mate_in(PLY_MAX))
1812 if (v <= value_mated_in(PLY_MAX))
1819 // move_is_killer() checks if the given move is among the killer moves
1821 bool move_is_killer(Move m, SearchStack* ss) {
1823 if (ss->killers[0] == m || ss->killers[1] == m)
1830 // extension() decides whether a move should be searched with normal depth,
1831 // or with extended depth. Certain classes of moves (checking moves, in
1832 // particular) are searched with bigger depth than ordinary moves and in
1833 // any case are marked as 'dangerous'. Note that also if a move is not
1834 // extended, as example because the corresponding UCI option is set to zero,
1835 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1836 template <NodeType PvNode>
1837 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1838 bool singleEvasion, bool mateThreat, bool* dangerous) {
1840 assert(m != MOVE_NONE);
1842 Depth result = DEPTH_ZERO;
1843 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1847 if (moveIsCheck && pos.see_sign(m) >= 0)
1848 result += CheckExtension[PvNode];
1851 result += SingleEvasionExtension[PvNode];
1854 result += MateThreatExtension[PvNode];
1857 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1859 Color c = pos.side_to_move();
1860 if (relative_rank(c, move_to(m)) == RANK_7)
1862 result += PawnPushTo7thExtension[PvNode];
1865 if (pos.pawn_is_passed(c, move_to(m)))
1867 result += PassedPawnExtension[PvNode];
1872 if ( captureOrPromotion
1873 && pos.type_of_piece_on(move_to(m)) != PAWN
1874 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1875 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1876 && !move_is_promotion(m)
1879 result += PawnEndgameExtension[PvNode];
1884 && captureOrPromotion
1885 && pos.type_of_piece_on(move_to(m)) != PAWN
1886 && pos.see_sign(m) >= 0)
1888 result += ONE_PLY / 2;
1892 return Min(result, ONE_PLY);
1896 // connected_threat() tests whether it is safe to forward prune a move or if
1897 // is somehow coonected to the threat move returned by null search.
1899 bool connected_threat(const Position& pos, Move m, Move threat) {
1901 assert(move_is_ok(m));
1902 assert(threat && move_is_ok(threat));
1903 assert(!pos.move_is_check(m));
1904 assert(!pos.move_is_capture_or_promotion(m));
1905 assert(!pos.move_is_passed_pawn_push(m));
1907 Square mfrom, mto, tfrom, tto;
1909 mfrom = move_from(m);
1911 tfrom = move_from(threat);
1912 tto = move_to(threat);
1914 // Case 1: Don't prune moves which move the threatened piece
1918 // Case 2: If the threatened piece has value less than or equal to the
1919 // value of the threatening piece, don't prune move which defend it.
1920 if ( pos.move_is_capture(threat)
1921 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1922 || pos.type_of_piece_on(tfrom) == KING)
1923 && pos.move_attacks_square(m, tto))
1926 // Case 3: If the moving piece in the threatened move is a slider, don't
1927 // prune safe moves which block its ray.
1928 if ( piece_is_slider(pos.piece_on(tfrom))
1929 && bit_is_set(squares_between(tfrom, tto), mto)
1930 && pos.see_sign(m) >= 0)
1937 // ok_to_use_TT() returns true if a transposition table score
1938 // can be used at a given point in search.
1940 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1942 Value v = value_from_tt(tte->value(), ply);
1944 return ( tte->depth() >= depth
1945 || v >= Max(value_mate_in(PLY_MAX), beta)
1946 || v < Min(value_mated_in(PLY_MAX), beta))
1948 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1949 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1953 // refine_eval() returns the transposition table score if
1954 // possible otherwise falls back on static position evaluation.
1956 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1960 Value v = value_from_tt(tte->value(), ply);
1962 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1963 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1970 // update_history() registers a good move that produced a beta-cutoff
1971 // in history and marks as failures all the other moves of that ply.
1973 void update_history(const Position& pos, Move move, Depth depth,
1974 Move movesSearched[], int moveCount) {
1978 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1980 for (int i = 0; i < moveCount - 1; i++)
1982 m = movesSearched[i];
1986 if (!pos.move_is_capture_or_promotion(m))
1987 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1992 // update_killers() add a good move that produced a beta-cutoff
1993 // among the killer moves of that ply.
1995 void update_killers(Move m, SearchStack* ss) {
1997 if (m == ss->killers[0])
2000 ss->killers[1] = ss->killers[0];
2005 // update_gains() updates the gains table of a non-capture move given
2006 // the static position evaluation before and after the move.
2008 void update_gains(const Position& pos, Move m, Value before, Value after) {
2011 && before != VALUE_NONE
2012 && after != VALUE_NONE
2013 && pos.captured_piece_type() == PIECE_TYPE_NONE
2014 && !move_is_special(m))
2015 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2019 // current_search_time() returns the number of milliseconds which have passed
2020 // since the beginning of the current search.
2022 int current_search_time() {
2024 return get_system_time() - SearchStartTime;
2028 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2030 std::string value_to_uci(Value v) {
2032 std::stringstream s;
2034 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
2035 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2037 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2042 // nps() computes the current nodes/second count.
2046 int t = current_search_time();
2047 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
2051 // poll() performs two different functions: It polls for user input, and it
2052 // looks at the time consumed so far and decides if it's time to abort the
2057 static int lastInfoTime;
2058 int t = current_search_time();
2063 // We are line oriented, don't read single chars
2064 std::string command;
2066 if (!std::getline(std::cin, command))
2069 if (command == "quit")
2072 PonderSearch = false;
2076 else if (command == "stop")
2079 PonderSearch = false;
2081 else if (command == "ponderhit")
2085 // Print search information
2089 else if (lastInfoTime > t)
2090 // HACK: Must be a new search where we searched less than
2091 // NodesBetweenPolls nodes during the first second of search.
2094 else if (t - lastInfoTime >= 1000)
2101 if (dbg_show_hit_rate)
2102 dbg_print_hit_rate();
2104 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
2105 << " time " << t << endl;
2108 // Should we stop the search?
2112 bool stillAtFirstMove = FirstRootMove
2113 && !AspirationFailLow
2114 && t > TimeMgr.available_time();
2116 bool noMoreTime = t > TimeMgr.maximum_time()
2117 || stillAtFirstMove;
2119 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2120 || (ExactMaxTime && t >= ExactMaxTime)
2121 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2126 // ponderhit() is called when the program is pondering (i.e. thinking while
2127 // it's the opponent's turn to move) in order to let the engine know that
2128 // it correctly predicted the opponent's move.
2132 int t = current_search_time();
2133 PonderSearch = false;
2135 bool stillAtFirstMove = FirstRootMove
2136 && !AspirationFailLow
2137 && t > TimeMgr.available_time();
2139 bool noMoreTime = t > TimeMgr.maximum_time()
2140 || stillAtFirstMove;
2142 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2147 // init_ss_array() does a fast reset of the first entries of a SearchStack
2148 // array and of all the excludedMove and skipNullMove entries.
2150 void init_ss_array(SearchStack* ss, int size) {
2152 for (int i = 0; i < size; i++, ss++)
2154 ss->excludedMove = MOVE_NONE;
2155 ss->skipNullMove = false;
2156 ss->reduction = DEPTH_ZERO;
2159 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2164 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2165 // while the program is pondering. The point is to work around a wrinkle in
2166 // the UCI protocol: When pondering, the engine is not allowed to give a
2167 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2168 // We simply wait here until one of these commands is sent, and return,
2169 // after which the bestmove and pondermove will be printed (in id_loop()).
2171 void wait_for_stop_or_ponderhit() {
2173 std::string command;
2177 if (!std::getline(std::cin, command))
2180 if (command == "quit")
2185 else if (command == "ponderhit" || command == "stop")
2191 // print_pv_info() prints to standard output and eventually to log file information on
2192 // the current PV line. It is called at each iteration or after a new pv is found.
2194 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2196 cout << "info depth " << Iteration
2197 << " score " << value_to_uci(value)
2198 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2199 << " time " << current_search_time()
2200 << " nodes " << ThreadsMgr.nodes_searched()
2204 for (Move* m = pv; *m != MOVE_NONE; m++)
2211 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2212 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2214 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2215 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2220 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2221 // the PV back into the TT. This makes sure the old PV moves are searched
2222 // first, even if the old TT entries have been overwritten.
2224 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2228 Position p(pos, pos.thread());
2229 Value v, m = VALUE_NONE;
2231 for (int i = 0; pv[i] != MOVE_NONE; i++)
2233 tte = TT.retrieve(p.get_key());
2234 if (!tte || tte->move() != pv[i])
2236 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2237 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2239 p.do_move(pv[i], st);
2244 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2245 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2246 // allow to always have a ponder move even when we fail high at root and also a
2247 // long PV to print that is important for position analysis.
2249 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2253 Position p(pos, pos.thread());
2256 assert(bestMove != MOVE_NONE);
2259 p.do_move(pv[ply++], st);
2261 while ( (tte = TT.retrieve(p.get_key())) != NULL
2262 && tte->move() != MOVE_NONE
2263 && move_is_legal(p, tte->move())
2265 && (!p.is_draw() || ply < 2))
2267 pv[ply] = tte->move();
2268 p.do_move(pv[ply++], st);
2270 pv[ply] = MOVE_NONE;
2274 // init_thread() is the function which is called when a new thread is
2275 // launched. It simply calls the idle_loop() function with the supplied
2276 // threadID. There are two versions of this function; one for POSIX
2277 // threads and one for Windows threads.
2279 #if !defined(_MSC_VER)
2281 void* init_thread(void *threadID) {
2283 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2289 DWORD WINAPI init_thread(LPVOID threadID) {
2291 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2298 /// The ThreadsManager class
2300 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2301 // get_beta_counters() are getters/setters for the per thread
2302 // counters used to sort the moves at root.
2304 void ThreadsManager::resetNodeCounters() {
2306 for (int i = 0; i < MAX_THREADS; i++)
2307 threads[i].nodes = 0ULL;
2310 int64_t ThreadsManager::nodes_searched() const {
2312 int64_t result = 0ULL;
2313 for (int i = 0; i < ActiveThreads; i++)
2314 result += threads[i].nodes;
2320 // idle_loop() is where the threads are parked when they have no work to do.
2321 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2322 // object for which the current thread is the master.
2324 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2326 assert(threadID >= 0 && threadID < MAX_THREADS);
2330 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2331 // master should exit as last one.
2332 if (AllThreadsShouldExit)
2335 threads[threadID].state = THREAD_TERMINATED;
2339 // If we are not thinking, wait for a condition to be signaled
2340 // instead of wasting CPU time polling for work.
2341 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2344 assert(threadID != 0);
2345 threads[threadID].state = THREAD_SLEEPING;
2347 #if !defined(_MSC_VER)
2348 lock_grab(&WaitLock);
2349 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2350 pthread_cond_wait(&WaitCond, &WaitLock);
2351 lock_release(&WaitLock);
2353 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2357 // If thread has just woken up, mark it as available
2358 if (threads[threadID].state == THREAD_SLEEPING)
2359 threads[threadID].state = THREAD_AVAILABLE;
2361 // If this thread has been assigned work, launch a search
2362 if (threads[threadID].state == THREAD_WORKISWAITING)
2364 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2366 threads[threadID].state = THREAD_SEARCHING;
2368 if (threads[threadID].splitPoint->pvNode)
2369 sp_search<PV>(threads[threadID].splitPoint, threadID);
2371 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2373 assert(threads[threadID].state == THREAD_SEARCHING);
2375 threads[threadID].state = THREAD_AVAILABLE;
2378 // If this thread is the master of a split point and all slaves have
2379 // finished their work at this split point, return from the idle loop.
2381 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2383 if (i == ActiveThreads)
2385 // Because sp->slaves[] is reset under lock protection,
2386 // be sure sp->lock has been released before to return.
2387 lock_grab(&(sp->lock));
2388 lock_release(&(sp->lock));
2390 assert(threads[threadID].state == THREAD_AVAILABLE);
2392 threads[threadID].state = THREAD_SEARCHING;
2399 // init_threads() is called during startup. It launches all helper threads,
2400 // and initializes the split point stack and the global locks and condition
2403 void ThreadsManager::init_threads() {
2408 #if !defined(_MSC_VER)
2409 pthread_t pthread[1];
2412 // Initialize global locks
2414 lock_init(&WaitLock);
2416 #if !defined(_MSC_VER)
2417 pthread_cond_init(&WaitCond, NULL);
2419 for (i = 0; i < MAX_THREADS; i++)
2420 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2423 // Initialize splitPoints[] locks
2424 for (i = 0; i < MAX_THREADS; i++)
2425 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2426 lock_init(&(threads[i].splitPoints[j].lock));
2428 // Will be set just before program exits to properly end the threads
2429 AllThreadsShouldExit = false;
2431 // Threads will be put to sleep as soon as created
2432 AllThreadsShouldSleep = true;
2434 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2436 threads[0].state = THREAD_SEARCHING;
2437 for (i = 1; i < MAX_THREADS; i++)
2438 threads[i].state = THREAD_AVAILABLE;
2440 // Launch the helper threads
2441 for (i = 1; i < MAX_THREADS; i++)
2444 #if !defined(_MSC_VER)
2445 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2447 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2452 cout << "Failed to create thread number " << i << endl;
2453 Application::exit_with_failure();
2456 // Wait until the thread has finished launching and is gone to sleep
2457 while (threads[i].state != THREAD_SLEEPING) {}
2462 // exit_threads() is called when the program exits. It makes all the
2463 // helper threads exit cleanly.
2465 void ThreadsManager::exit_threads() {
2467 ActiveThreads = MAX_THREADS; // HACK
2468 AllThreadsShouldSleep = true; // HACK
2469 wake_sleeping_threads();
2471 // This makes the threads to exit idle_loop()
2472 AllThreadsShouldExit = true;
2474 // Wait for thread termination
2475 for (int i = 1; i < MAX_THREADS; i++)
2476 while (threads[i].state != THREAD_TERMINATED) {}
2478 // Now we can safely destroy the locks
2479 for (int i = 0; i < MAX_THREADS; i++)
2480 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2481 lock_destroy(&(threads[i].splitPoints[j].lock));
2483 lock_destroy(&WaitLock);
2484 lock_destroy(&MPLock);
2488 // thread_should_stop() checks whether the thread should stop its search.
2489 // This can happen if a beta cutoff has occurred in the thread's currently
2490 // active split point, or in some ancestor of the current split point.
2492 bool ThreadsManager::thread_should_stop(int threadID) const {
2494 assert(threadID >= 0 && threadID < ActiveThreads);
2498 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2503 // thread_is_available() checks whether the thread with threadID "slave" is
2504 // available to help the thread with threadID "master" at a split point. An
2505 // obvious requirement is that "slave" must be idle. With more than two
2506 // threads, this is not by itself sufficient: If "slave" is the master of
2507 // some active split point, it is only available as a slave to the other
2508 // threads which are busy searching the split point at the top of "slave"'s
2509 // split point stack (the "helpful master concept" in YBWC terminology).
2511 bool ThreadsManager::thread_is_available(int slave, int master) const {
2513 assert(slave >= 0 && slave < ActiveThreads);
2514 assert(master >= 0 && master < ActiveThreads);
2515 assert(ActiveThreads > 1);
2517 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2520 // Make a local copy to be sure doesn't change under our feet
2521 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2523 if (localActiveSplitPoints == 0)
2524 // No active split points means that the thread is available as
2525 // a slave for any other thread.
2528 if (ActiveThreads == 2)
2531 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2532 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2533 // could have been set to 0 by another thread leading to an out of bound access.
2534 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2541 // available_thread_exists() tries to find an idle thread which is available as
2542 // a slave for the thread with threadID "master".
2544 bool ThreadsManager::available_thread_exists(int master) const {
2546 assert(master >= 0 && master < ActiveThreads);
2547 assert(ActiveThreads > 1);
2549 for (int i = 0; i < ActiveThreads; i++)
2550 if (thread_is_available(i, master))
2557 // split() does the actual work of distributing the work at a node between
2558 // several available threads. If it does not succeed in splitting the
2559 // node (because no idle threads are available, or because we have no unused
2560 // split point objects), the function immediately returns. If splitting is
2561 // possible, a SplitPoint object is initialized with all the data that must be
2562 // copied to the helper threads and we tell our helper threads that they have
2563 // been assigned work. This will cause them to instantly leave their idle loops
2564 // and call sp_search(). When all threads have returned from sp_search() then
2567 template <bool Fake>
2568 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2569 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2570 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2572 assert(ply > 0 && ply < PLY_MAX);
2573 assert(*bestValue >= -VALUE_INFINITE);
2574 assert(*bestValue <= *alpha);
2575 assert(*alpha < beta);
2576 assert(beta <= VALUE_INFINITE);
2577 assert(depth > DEPTH_ZERO);
2578 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2579 assert(ActiveThreads > 1);
2581 int i, master = p.thread();
2582 Thread& masterThread = threads[master];
2586 // If no other thread is available to help us, or if we have too many
2587 // active split points, don't split.
2588 if ( !available_thread_exists(master)
2589 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2591 lock_release(&MPLock);
2595 // Pick the next available split point object from the split point stack
2596 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2598 // Initialize the split point object
2599 splitPoint.parent = masterThread.splitPoint;
2600 splitPoint.stopRequest = false;
2601 splitPoint.ply = ply;
2602 splitPoint.depth = depth;
2603 splitPoint.threatMove = threatMove;
2604 splitPoint.mateThreat = mateThreat;
2605 splitPoint.alpha = *alpha;
2606 splitPoint.beta = beta;
2607 splitPoint.pvNode = pvNode;
2608 splitPoint.bestValue = *bestValue;
2610 splitPoint.moveCount = *moveCount;
2611 splitPoint.pos = &p;
2612 splitPoint.parentSstack = ss;
2613 for (i = 0; i < ActiveThreads; i++)
2614 splitPoint.slaves[i] = 0;
2616 masterThread.splitPoint = &splitPoint;
2618 // If we are here it means we are not available
2619 assert(masterThread.state != THREAD_AVAILABLE);
2621 int workersCnt = 1; // At least the master is included
2623 // Allocate available threads setting state to THREAD_BOOKED
2624 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2625 if (thread_is_available(i, master))
2627 threads[i].state = THREAD_BOOKED;
2628 threads[i].splitPoint = &splitPoint;
2629 splitPoint.slaves[i] = 1;
2633 assert(Fake || workersCnt > 1);
2635 // We can release the lock because slave threads are already booked and master is not available
2636 lock_release(&MPLock);
2638 // Tell the threads that they have work to do. This will make them leave
2639 // their idle loop. But before copy search stack tail for each thread.
2640 for (i = 0; i < ActiveThreads; i++)
2641 if (i == master || splitPoint.slaves[i])
2643 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2645 assert(i == master || threads[i].state == THREAD_BOOKED);
2647 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2650 // Everything is set up. The master thread enters the idle loop, from
2651 // which it will instantly launch a search, because its state is
2652 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2653 // idle loop, which means that the main thread will return from the idle
2654 // loop when all threads have finished their work at this split point.
2655 idle_loop(master, &splitPoint);
2657 // We have returned from the idle loop, which means that all threads are
2658 // finished. Update alpha and bestValue, and return.
2661 *alpha = splitPoint.alpha;
2662 *bestValue = splitPoint.bestValue;
2663 masterThread.activeSplitPoints--;
2664 masterThread.splitPoint = splitPoint.parent;
2666 lock_release(&MPLock);
2670 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2671 // to start a new search from the root.
2673 void ThreadsManager::wake_sleeping_threads() {
2675 assert(AllThreadsShouldSleep);
2676 assert(ActiveThreads > 0);
2678 AllThreadsShouldSleep = false;
2680 if (ActiveThreads == 1)
2683 #if !defined(_MSC_VER)
2684 pthread_mutex_lock(&WaitLock);
2685 pthread_cond_broadcast(&WaitCond);
2686 pthread_mutex_unlock(&WaitLock);
2688 for (int i = 1; i < MAX_THREADS; i++)
2689 SetEvent(SitIdleEvent[i]);
2695 // put_threads_to_sleep() makes all the threads go to sleep just before
2696 // to leave think(), at the end of the search. Threads should have already
2697 // finished the job and should be idle.
2699 void ThreadsManager::put_threads_to_sleep() {
2701 assert(!AllThreadsShouldSleep);
2703 // This makes the threads to go to sleep
2704 AllThreadsShouldSleep = true;
2707 /// The RootMoveList class
2709 // RootMoveList c'tor
2711 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2713 SearchStack ss[PLY_MAX_PLUS_2];
2714 MoveStack mlist[MOVES_MAX];
2716 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2718 // Initialize search stack
2719 init_ss_array(ss, PLY_MAX_PLUS_2);
2720 ss[0].eval = VALUE_NONE;
2723 // Generate all legal moves
2724 MoveStack* last = generate_moves(pos, mlist);
2726 // Add each move to the moves[] array
2727 for (MoveStack* cur = mlist; cur != last; cur++)
2729 bool includeMove = includeAllMoves;
2731 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2732 includeMove = (searchMoves[k] == cur->move);
2737 // Find a quick score for the move
2738 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2739 moves[count].pv[1] = MOVE_NONE;
2740 pos.do_move(cur->move, st);
2741 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2742 pos.undo_move(cur->move);
2748 // Score root moves using the standard way used in main search, the moves
2749 // are scored according to the order in which are returned by MovePicker.
2751 void RootMoveList::score_moves(const Position& pos)
2755 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2757 while ((move = mp.get_next_move()) != MOVE_NONE)
2758 for (int i = 0; i < count; i++)
2759 if (moves[i].move == move)
2761 moves[i].mp_score = score--;
2766 // RootMoveList simple methods definitions
2768 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2772 for (j = 0; pv[j] != MOVE_NONE; j++)
2773 moves[moveNum].pv[j] = pv[j];
2775 moves[moveNum].pv[j] = MOVE_NONE;
2779 // RootMoveList::sort() sorts the root move list at the beginning of a new
2782 void RootMoveList::sort() {
2784 sort_multipv(count - 1); // Sort all items
2788 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2789 // list by their scores and depths. It is used to order the different PVs
2790 // correctly in MultiPV mode.
2792 void RootMoveList::sort_multipv(int n) {
2796 for (i = 1; i <= n; i++)
2798 RootMove rm = moves[i];
2799 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2800 moves[j] = moves[j - 1];