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 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
301 bool connected_moves(const Position& pos, Move m1, Move m2);
302 bool value_is_mate(Value value);
303 Value value_to_tt(Value v, int ply);
304 Value value_from_tt(Value v, int ply);
305 bool move_is_killer(Move m, SearchStack* ss);
306 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
307 bool connected_threat(const Position& pos, Move m, Move threat);
308 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
309 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
310 void update_killers(Move m, SearchStack* ss);
311 void update_gains(const Position& pos, Move move, Value before, Value after);
313 int current_search_time();
314 std::string value_to_uci(Value v);
318 void wait_for_stop_or_ponderhit();
319 void init_ss_array(SearchStack* ss, int size);
320 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
321 void insert_pv_in_tt(const Position& pos, Move pv[]);
322 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
324 #if !defined(_MSC_VER)
325 void *init_thread(void *threadID);
327 DWORD WINAPI init_thread(LPVOID threadID);
337 /// init_threads(), exit_threads() and nodes_searched() are helpers to
338 /// give accessibility to some TM methods from outside of current file.
340 void init_threads() { ThreadsMgr.init_threads(); }
341 void exit_threads() { ThreadsMgr.exit_threads(); }
342 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
345 /// init_search() is called during startup. It initializes various lookup tables
349 int d; // depth (ONE_PLY == 2)
350 int hd; // half depth (ONE_PLY == 1)
353 // Init reductions array
354 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
356 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
357 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
358 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
359 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
362 // Init futility margins array
363 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
364 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
366 // Init futility move count array
367 for (d = 0; d < 32; d++)
368 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
372 /// perft() is our utility to verify move generation is bug free. All the legal
373 /// moves up to given depth are generated and counted and the sum returned.
375 int perft(Position& pos, Depth depth)
377 MoveStack mlist[MOVES_MAX];
382 // Generate all legal moves
383 MoveStack* last = generate_moves(pos, mlist);
385 // If we are at the last ply we don't need to do and undo
386 // the moves, just to count them.
387 if (depth <= ONE_PLY)
388 return int(last - mlist);
390 // Loop through all legal moves
392 for (MoveStack* cur = mlist; cur != last; cur++)
395 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
396 sum += perft(pos, depth - ONE_PLY);
403 /// think() is the external interface to Stockfish's search, and is called when
404 /// the program receives the UCI 'go' command. It initializes various
405 /// search-related global variables, and calls root_search(). It returns false
406 /// when a quit command is received during the search.
408 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
409 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
411 // Initialize global search variables
412 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
414 ThreadsMgr.resetNodeCounters();
415 SearchStartTime = get_system_time();
416 ExactMaxTime = maxTime;
419 InfiniteSearch = infinite;
420 PonderSearch = ponder;
421 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
423 // Look for a book move, only during games, not tests
424 if (UseTimeManagement && get_option_value_bool("OwnBook"))
426 if (get_option_value_string("Book File") != OpeningBook.file_name())
427 OpeningBook.open(get_option_value_string("Book File"));
429 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
430 if (bookMove != MOVE_NONE)
433 wait_for_stop_or_ponderhit();
435 cout << "bestmove " << bookMove << endl;
440 // Read UCI option values
441 TT.set_size(get_option_value_int("Hash"));
442 if (button_was_pressed("Clear Hash"))
445 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
446 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
447 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
448 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
449 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
450 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
451 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
452 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
453 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
454 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
455 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
456 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
458 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
459 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
460 MultiPV = get_option_value_int("MultiPV");
461 UseLogFile = get_option_value_bool("Use Search Log");
464 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
466 read_weights(pos.side_to_move());
468 // Set the number of active threads
469 int newActiveThreads = get_option_value_int("Threads");
470 if (newActiveThreads != ThreadsMgr.active_threads())
472 ThreadsMgr.set_active_threads(newActiveThreads);
473 init_eval(ThreadsMgr.active_threads());
476 // Wake up sleeping threads
477 ThreadsMgr.wake_sleeping_threads();
480 int myTime = time[pos.side_to_move()];
481 int myIncrement = increment[pos.side_to_move()];
482 if (UseTimeManagement)
483 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
485 // Set best NodesBetweenPolls interval to avoid lagging under
486 // heavy time pressure.
488 NodesBetweenPolls = Min(MaxNodes, 30000);
489 else if (myTime && myTime < 1000)
490 NodesBetweenPolls = 1000;
491 else if (myTime && myTime < 5000)
492 NodesBetweenPolls = 5000;
494 NodesBetweenPolls = 30000;
496 // Write search information to log file
498 LogFile << "Searching: " << pos.to_fen() << endl
499 << "infinite: " << infinite
500 << " ponder: " << ponder
501 << " time: " << myTime
502 << " increment: " << myIncrement
503 << " moves to go: " << movesToGo << endl;
505 // We're ready to start thinking. Call the iterative deepening loop function
506 id_loop(pos, searchMoves);
511 ThreadsMgr.put_threads_to_sleep();
519 // id_loop() is the main iterative deepening loop. It calls root_search
520 // repeatedly with increasing depth until the allocated thinking time has
521 // been consumed, the user stops the search, or the maximum search depth is
524 Value id_loop(const Position& pos, Move searchMoves[]) {
526 Position p(pos, pos.thread());
527 SearchStack ss[PLY_MAX_PLUS_2];
528 Move pv[PLY_MAX_PLUS_2];
529 Move EasyMove = MOVE_NONE;
530 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
532 // Moves to search are verified, copied, scored and sorted
533 RootMoveList rml(p, searchMoves);
535 // Handle special case of searching on a mate/stale position
536 if (rml.move_count() == 0)
539 wait_for_stop_or_ponderhit();
541 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
544 // Print RootMoveList startup scoring to the standard output,
545 // so to output information also for iteration 1.
546 cout << set960(p.is_chess960()) // Is enough to set once at the beginning
547 << "info depth " << 1
548 << "\ninfo depth " << 1
549 << " score " << value_to_uci(rml.move_score(0))
550 << " time " << current_search_time()
551 << " nodes " << ThreadsMgr.nodes_searched()
553 << " pv " << rml.move(0) << "\n";
558 init_ss_array(ss, PLY_MAX_PLUS_2);
559 pv[0] = pv[1] = MOVE_NONE;
560 ValueByIteration[1] = rml.move_score(0);
563 // Is one move significantly better than others after initial scoring ?
564 if ( rml.move_count() == 1
565 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
566 EasyMove = rml.move(0);
568 // Iterative deepening loop
569 while (Iteration < PLY_MAX)
571 // Initialize iteration
573 BestMoveChangesByIteration[Iteration] = 0;
575 cout << "info depth " << Iteration << endl;
577 // Calculate dynamic aspiration window based on previous iterations
578 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
580 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
581 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
583 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
584 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
586 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
587 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
590 // Search to the current depth, rml is updated and sorted, alpha and beta could change
591 value = root_search(p, ss, pv, rml, &alpha, &beta);
593 // Write PV to transposition table, in case the relevant entries have
594 // been overwritten during the search.
595 insert_pv_in_tt(p, pv);
598 break; // Value cannot be trusted. Break out immediately!
600 //Save info about search result
601 ValueByIteration[Iteration] = value;
603 // Drop the easy move if differs from the new best move
604 if (pv[0] != EasyMove)
605 EasyMove = MOVE_NONE;
607 if (UseTimeManagement)
610 bool stopSearch = false;
612 // Stop search early if there is only a single legal move,
613 // we search up to Iteration 6 anyway to get a proper score.
614 if (Iteration >= 6 && rml.move_count() == 1)
617 // Stop search early when the last two iterations returned a mate score
619 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
620 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
623 // Stop search early if one move seems to be much better than the others
624 int64_t nodes = ThreadsMgr.nodes_searched();
627 && ( ( rml.move_nodes(0) > (nodes * 85) / 100
628 && current_search_time() > TimeMgr.available_time() / 16)
629 ||( rml.move_nodes(0) > (nodes * 98) / 100
630 && current_search_time() > TimeMgr.available_time() / 32)))
633 // Add some extra time if the best move has changed during the last two iterations
634 if (Iteration > 5 && Iteration <= 50)
635 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
636 BestMoveChangesByIteration[Iteration-1]);
638 // Stop search if most of MaxSearchTime is consumed at the end of the
639 // iteration. We probably don't have enough time to search the first
640 // move at the next iteration anyway.
641 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
647 StopOnPonderhit = true;
653 if (MaxDepth && Iteration >= MaxDepth)
657 // If we are pondering or in infinite search, we shouldn't print the
658 // best move before we are told to do so.
659 if (!AbortSearch && (PonderSearch || InfiniteSearch))
660 wait_for_stop_or_ponderhit();
662 // Print final search statistics
663 cout << "info nodes " << ThreadsMgr.nodes_searched()
665 << " time " << current_search_time() << endl;
667 // Print the best move and the ponder move to the standard output
668 if (pv[0] == MOVE_NONE)
674 assert(pv[0] != MOVE_NONE);
676 cout << "bestmove " << pv[0];
678 if (pv[1] != MOVE_NONE)
679 cout << " ponder " << pv[1];
686 dbg_print_mean(LogFile);
688 if (dbg_show_hit_rate)
689 dbg_print_hit_rate(LogFile);
691 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
692 << "\nNodes/second: " << nps()
693 << "\nBest move: " << move_to_san(p, pv[0]);
696 p.do_move(pv[0], st);
697 LogFile << "\nPonder move: "
698 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
701 return rml.move_score(0);
705 // root_search() is the function which searches the root node. It is
706 // similar to search_pv except that it uses a different move ordering
707 // scheme, prints some information to the standard output and handles
708 // the fail low/high loops.
710 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
716 Depth depth, ext, newDepth;
717 Value value, alpha, beta;
718 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
719 int researchCountFH, researchCountFL;
721 researchCountFH = researchCountFL = 0;
724 isCheck = pos.is_check();
725 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
727 // Step 1. Initialize node (polling is omitted at root)
728 ss->currentMove = ss->bestMove = MOVE_NONE;
730 // Step 2. Check for aborted search (omitted at root)
731 // Step 3. Mate distance pruning (omitted at root)
732 // Step 4. Transposition table lookup (omitted at root)
734 // Step 5. Evaluate the position statically
735 // At root we do this only to get reference value for child nodes
736 ss->evalMargin = VALUE_NONE;
737 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->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 and for
962 // normal and SplitPoint nodes. When called just after a split point the search
963 // is simpler because we have already probed the hash table, done a null move
964 // search, and searched the first move before splitting, we don't have to repeat
965 // all this work again. We also don't need to store anything to the hash table
966 // here: This is taken care of after we return from the split point.
968 template <NodeType PvNode, bool SplitPoint>
969 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
971 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
972 assert(beta > alpha && beta <= VALUE_INFINITE);
973 assert(PvNode || alpha == beta - 1);
974 assert(ply > 0 && ply < PLY_MAX);
975 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
977 Move movesSearched[MOVES_MAX];
981 Move ttMove, move, excludedMove, threatMove;
983 Value bestValue, value, oldAlpha;
984 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
985 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
986 bool mateThreat = false;
988 int threadID = pos.thread();
989 refinedValue = bestValue = value = -VALUE_INFINITE;
991 isCheck = pos.is_check();
996 ttMove = excludedMove = MOVE_NONE;
997 threatMove = ss->sp->threatMove;
998 mateThreat = ss->sp->mateThreat;
999 goto split_point_start;
1002 // Step 1. Initialize node and poll. Polling can abort search
1003 ThreadsMgr.incrementNodeCounter(threadID);
1004 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
1005 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
1007 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1013 // Step 2. Check for aborted search and immediate draw
1014 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1017 if (pos.is_draw() || ply >= PLY_MAX - 1)
1020 // Step 3. Mate distance pruning
1021 alpha = Max(value_mated_in(ply), alpha);
1022 beta = Min(value_mate_in(ply+1), beta);
1026 // Step 4. Transposition table lookup
1028 // We don't want the score of a partial search to overwrite a previous full search
1029 // TT value, so we use a different position key in case of an excluded move exists.
1030 excludedMove = ss->excludedMove;
1031 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1033 tte = TT.retrieve(posKey);
1034 ttMove = (tte ? tte->move() : MOVE_NONE);
1036 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1037 // This is to avoid problems in the following areas:
1039 // * Repetition draw detection
1040 // * Fifty move rule detection
1041 // * Searching for a mate
1042 // * Printing of full PV line
1044 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1046 // Refresh tte entry to avoid aging
1047 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1049 ss->bestMove = ttMove; // Can be MOVE_NONE
1050 return value_from_tt(tte->value(), ply);
1053 // Step 5. Evaluate the position statically and
1054 // update gain statistics of parent move.
1056 ss->eval = ss->evalMargin = VALUE_NONE;
1059 assert(tte->static_value() != VALUE_NONE);
1061 ss->eval = tte->static_value();
1062 ss->evalMargin = tte->static_value_margin();
1063 refinedValue = refine_eval(tte, ss->eval, ply);
1067 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1068 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1071 // Save gain for the parent non-capture move
1072 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1074 // Step 6. Razoring (is omitted in PV nodes)
1076 && depth < RazorDepth
1078 && refinedValue < beta - razor_margin(depth)
1079 && ttMove == MOVE_NONE
1080 && (ss-1)->currentMove != MOVE_NULL
1081 && !value_is_mate(beta)
1082 && !pos.has_pawn_on_7th(pos.side_to_move()))
1084 Value rbeta = beta - razor_margin(depth);
1085 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1087 // Logically we should return (v + razor_margin(depth)), but
1088 // surprisingly this did slightly weaker in tests.
1092 // Step 7. Static null move pruning (is omitted in PV nodes)
1093 // We're betting that the opponent doesn't have a move that will reduce
1094 // the score by more than futility_margin(depth) if we do a null move.
1096 && !ss->skipNullMove
1097 && depth < RazorDepth
1099 && refinedValue >= beta + futility_margin(depth, 0)
1100 && !value_is_mate(beta)
1101 && pos.non_pawn_material(pos.side_to_move()))
1102 return refinedValue - futility_margin(depth, 0);
1104 // Step 8. Null move search with verification search (is omitted in PV nodes)
1106 && !ss->skipNullMove
1109 && refinedValue >= beta
1110 && !value_is_mate(beta)
1111 && pos.non_pawn_material(pos.side_to_move()))
1113 ss->currentMove = MOVE_NULL;
1115 // Null move dynamic reduction based on depth
1116 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1118 // Null move dynamic reduction based on value
1119 if (refinedValue - beta > PawnValueMidgame)
1122 pos.do_null_move(st);
1123 (ss+1)->skipNullMove = true;
1125 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1126 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1127 (ss+1)->skipNullMove = false;
1128 pos.undo_null_move();
1130 if (nullValue >= beta)
1132 // Do not return unproven mate scores
1133 if (nullValue >= value_mate_in(PLY_MAX))
1136 if (depth < 6 * ONE_PLY)
1139 // Do verification search at high depths
1140 ss->skipNullMove = true;
1141 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1142 ss->skipNullMove = false;
1149 // The null move failed low, which means that we may be faced with
1150 // some kind of threat. If the previous move was reduced, check if
1151 // the move that refuted the null move was somehow connected to the
1152 // move which was reduced. If a connection is found, return a fail
1153 // low score (which will cause the reduced move to fail high in the
1154 // parent node, which will trigger a re-search with full depth).
1155 if (nullValue == value_mated_in(ply + 2))
1158 threatMove = (ss+1)->bestMove;
1159 if ( depth < ThreatDepth
1160 && (ss-1)->reduction
1161 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1166 // Step 9. Internal iterative deepening
1167 if ( depth >= IIDDepth[PvNode]
1168 && ttMove == MOVE_NONE
1169 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1171 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1173 ss->skipNullMove = true;
1174 search<PvNode>(pos, ss, alpha, beta, d, ply);
1175 ss->skipNullMove = false;
1177 ttMove = ss->bestMove;
1178 tte = TT.retrieve(posKey);
1181 // Expensive mate threat detection (only for PV nodes)
1183 mateThreat = pos.has_mate_threat();
1185 split_point_start: // At split points actual search starts from here
1187 // Initialize a MovePicker object for the current position
1188 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1189 MovePicker mpBase = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1190 MovePicker& mp = SplitPoint ? *ss->sp->mp : mpBase;
1192 ss->bestMove = MOVE_NONE;
1193 singleEvasion = !SplitPoint && isCheck && mp.number_of_evasions() == 1;
1194 futilityBase = ss->eval + ss->evalMargin;
1195 singularExtensionNode = !SplitPoint
1196 && depth >= SingularExtensionDepth[PvNode]
1199 && !excludedMove // Do not allow recursive singular extension search
1200 && (tte->type() & VALUE_TYPE_LOWER)
1201 && tte->depth() >= depth - 3 * ONE_PLY;
1203 // Step 10. Loop through moves
1204 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1207 lock_grab(&(ss->sp->lock));
1208 bestValue = ss->sp->bestValue;
1211 while ( bestValue < beta
1212 && (move = mp.get_next_move()) != MOVE_NONE
1213 && !ThreadsMgr.thread_should_stop(threadID))
1217 moveCount = ++ss->sp->moveCount;
1218 lock_release(&(ss->sp->lock));
1221 assert(move_is_ok(move));
1223 if (move == excludedMove)
1226 moveIsCheck = pos.move_is_check(move, ci);
1227 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1229 // Step 11. Decide the new search depth
1230 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1232 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1233 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1234 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1235 // lower then ttValue minus a margin then we extend ttMove.
1236 if ( singularExtensionNode
1237 && move == tte->move()
1240 Value ttValue = value_from_tt(tte->value(), ply);
1242 if (abs(ttValue) < VALUE_KNOWN_WIN)
1244 Value b = ttValue - SingularExtensionMargin;
1245 ss->excludedMove = move;
1246 ss->skipNullMove = true;
1247 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1248 ss->skipNullMove = false;
1249 ss->excludedMove = MOVE_NONE;
1250 ss->bestMove = MOVE_NONE;
1256 newDepth = depth - ONE_PLY + ext;
1258 // Update current move (this must be done after singular extension search)
1259 movesSearched[moveCount++] = ss->currentMove = move;
1261 // Step 12. Futility pruning (is omitted in PV nodes)
1263 && !captureOrPromotion
1267 && !move_is_castle(move))
1269 // Move count based pruning
1270 if ( moveCount >= futility_move_count(depth)
1271 && !(threatMove && connected_threat(pos, move, threatMove))
1272 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1275 lock_grab(&(ss->sp->lock));
1279 // Value based pruning
1280 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1281 // but fixing this made program slightly weaker.
1282 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1283 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1284 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1286 if (futilityValueScaled < beta)
1290 lock_grab(&(ss->sp->lock));
1291 if (futilityValueScaled > ss->sp->bestValue)
1292 ss->sp->bestValue = bestValue = futilityValueScaled;
1294 else if (futilityValueScaled > bestValue)
1295 bestValue = futilityValueScaled;
1300 // Step 13. Make the move
1301 pos.do_move(move, st, ci, moveIsCheck);
1303 // Step extra. pv search (only in PV nodes)
1304 // The first move in list is the expected PV
1305 if (!SplitPoint && PvNode && moveCount == 1)
1306 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1307 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1310 // Step 14. Reduced depth search
1311 // If the move fails high will be re-searched at full depth.
1312 bool doFullDepthSearch = true;
1314 if ( depth >= 3 * ONE_PLY
1315 && !captureOrPromotion
1317 && !move_is_castle(move)
1318 && !move_is_killer(move, ss))
1320 ss->reduction = reduction<PvNode>(depth, moveCount);
1323 alpha = SplitPoint ? ss->sp->alpha : alpha;
1324 Depth d = newDepth - ss->reduction;
1325 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1326 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1328 doFullDepthSearch = (value > alpha);
1331 // The move failed high, but if reduction is very big we could
1332 // face a false positive, retry with a less aggressive reduction,
1333 // if the move fails high again then go with full depth search.
1334 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1336 assert(newDepth - ONE_PLY >= ONE_PLY);
1338 ss->reduction = ONE_PLY;
1339 alpha = SplitPoint ? ss->sp->alpha : alpha;
1340 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1341 doFullDepthSearch = (value > alpha);
1343 ss->reduction = DEPTH_ZERO; // Restore original reduction
1346 // Step 15. Full depth search
1347 if (doFullDepthSearch)
1349 alpha = SplitPoint ? ss->sp->alpha : alpha;
1350 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1351 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1353 // Step extra. pv search (only in PV nodes)
1354 // Search only for possible new PV nodes, if instead value >= beta then
1355 // parent node fails low with value <= alpha and tries another move.
1356 if (PvNode && value > alpha && value < beta)
1357 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1358 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1362 // Step 16. Undo move
1363 pos.undo_move(move);
1365 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1367 // Step 17. Check for new best move
1370 lock_grab(&(ss->sp->lock));
1371 bestValue = ss->sp->bestValue;
1372 alpha = ss->sp->alpha;
1375 if (value > bestValue && !(SplitPoint && ThreadsMgr.thread_should_stop(threadID)))
1380 if (SplitPoint && (!PvNode || value >= beta))
1381 ss->sp->stopRequest = true;
1383 if (PvNode && value < beta) // We want always alpha < beta
1386 if (value == value_mate_in(ply + 1))
1387 ss->mateKiller = move;
1389 ss->bestMove = move;
1393 ss->sp->bestValue = bestValue;
1394 ss->sp->alpha = alpha;
1395 ss->sp->parentSstack->bestMove = ss->bestMove;
1399 // Step 18. Check for split
1401 && depth >= MinimumSplitDepth
1402 && ThreadsMgr.active_threads() > 1
1404 && ThreadsMgr.available_thread_exists(threadID)
1406 && !ThreadsMgr.thread_should_stop(threadID)
1408 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1409 threatMove, mateThreat, moveCount, &mp, PvNode);
1414 /* Here we have the lock still grabbed */
1415 ss->sp->slaves[threadID] = 0;
1416 lock_release(&(ss->sp->lock));
1420 // Step 19. Check for mate and stalemate
1421 // All legal moves have been searched and if there are
1422 // no legal moves, it must be mate or stalemate.
1423 // If one move was excluded return fail low score.
1425 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1427 // Step 20. Update tables
1428 // If the search is not aborted, update the transposition table,
1429 // history counters, and killer moves.
1430 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1433 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1434 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1435 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1437 // Update killers and history only for non capture moves that fails high
1438 if ( bestValue >= beta
1439 && !pos.move_is_capture_or_promotion(move))
1441 update_history(pos, move, depth, movesSearched, moveCount);
1442 update_killers(move, ss);
1445 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1451 // qsearch() is the quiescence search function, which is called by the main
1452 // search function when the remaining depth is zero (or, to be more precise,
1453 // less than ONE_PLY).
1455 template <NodeType PvNode>
1456 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1458 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1459 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1460 assert(PvNode || alpha == beta - 1);
1462 assert(ply > 0 && ply < PLY_MAX);
1463 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1467 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1468 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1470 Value oldAlpha = alpha;
1472 ThreadsMgr.incrementNodeCounter(pos.thread());
1473 ss->bestMove = ss->currentMove = MOVE_NONE;
1475 // Check for an instant draw or maximum ply reached
1476 if (pos.is_draw() || ply >= PLY_MAX - 1)
1479 // Transposition table lookup. At PV nodes, we don't use the TT for
1480 // pruning, but only for move ordering.
1481 tte = TT.retrieve(pos.get_key());
1482 ttMove = (tte ? tte->move() : MOVE_NONE);
1484 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1486 ss->bestMove = ttMove; // Can be MOVE_NONE
1487 return value_from_tt(tte->value(), ply);
1490 isCheck = pos.is_check();
1492 // Evaluate the position statically
1495 bestValue = futilityBase = -VALUE_INFINITE;
1496 ss->eval = evalMargin = VALUE_NONE;
1497 deepChecks = enoughMaterial = false;
1503 assert(tte->static_value() != VALUE_NONE);
1505 evalMargin = tte->static_value_margin();
1506 ss->eval = bestValue = tte->static_value();
1509 ss->eval = bestValue = evaluate(pos, evalMargin);
1511 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1513 // Stand pat. Return immediately if static value is at least beta
1514 if (bestValue >= beta)
1517 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1522 if (PvNode && bestValue > alpha)
1525 // If we are near beta then try to get a cutoff pushing checks a bit further
1526 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1528 // Futility pruning parameters, not needed when in check
1529 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1530 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1533 // Initialize a MovePicker object for the current position, and prepare
1534 // to search the moves. Because the depth is <= 0 here, only captures,
1535 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1536 // and we are near beta) will be generated.
1537 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1540 // Loop through the moves until no moves remain or a beta cutoff occurs
1541 while ( alpha < beta
1542 && (move = mp.get_next_move()) != MOVE_NONE)
1544 assert(move_is_ok(move));
1546 moveIsCheck = pos.move_is_check(move, ci);
1554 && !move_is_promotion(move)
1555 && !pos.move_is_passed_pawn_push(move))
1557 futilityValue = futilityBase
1558 + pos.endgame_value_of_piece_on(move_to(move))
1559 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1561 if (futilityValue < alpha)
1563 if (futilityValue > bestValue)
1564 bestValue = futilityValue;
1569 // Detect non-capture evasions that are candidate to be pruned
1570 evasionPrunable = isCheck
1571 && bestValue > value_mated_in(PLY_MAX)
1572 && !pos.move_is_capture(move)
1573 && !pos.can_castle(pos.side_to_move());
1575 // Don't search moves with negative SEE values
1577 && (!isCheck || evasionPrunable)
1579 && !move_is_promotion(move)
1580 && pos.see_sign(move) < 0)
1583 // Update current move
1584 ss->currentMove = move;
1586 // Make and search the move
1587 pos.do_move(move, st, ci, moveIsCheck);
1588 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1589 pos.undo_move(move);
1591 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1594 if (value > bestValue)
1600 ss->bestMove = move;
1605 // All legal moves have been searched. A special case: If we're in check
1606 // and no legal moves were found, it is checkmate.
1607 if (isCheck && bestValue == -VALUE_INFINITE)
1608 return value_mated_in(ply);
1610 // Update transposition table
1611 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1612 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1613 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1615 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1621 // connected_moves() tests whether two moves are 'connected' in the sense
1622 // that the first move somehow made the second move possible (for instance
1623 // if the moving piece is the same in both moves). The first move is assumed
1624 // to be the move that was made to reach the current position, while the
1625 // second move is assumed to be a move from the current position.
1627 bool connected_moves(const Position& pos, Move m1, Move m2) {
1629 Square f1, t1, f2, t2;
1632 assert(move_is_ok(m1));
1633 assert(move_is_ok(m2));
1635 if (m2 == MOVE_NONE)
1638 // Case 1: The moving piece is the same in both moves
1644 // Case 2: The destination square for m2 was vacated by m1
1650 // Case 3: Moving through the vacated square
1651 if ( piece_is_slider(pos.piece_on(f2))
1652 && bit_is_set(squares_between(f2, t2), f1))
1655 // Case 4: The destination square for m2 is defended by the moving piece in m1
1656 p = pos.piece_on(t1);
1657 if (bit_is_set(pos.attacks_from(p, t1), t2))
1660 // Case 5: Discovered check, checking piece is the piece moved in m1
1661 if ( piece_is_slider(p)
1662 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1663 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1665 // discovered_check_candidates() works also if the Position's side to
1666 // move is the opposite of the checking piece.
1667 Color them = opposite_color(pos.side_to_move());
1668 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1670 if (bit_is_set(dcCandidates, f2))
1677 // value_is_mate() checks if the given value is a mate one eventually
1678 // compensated for the ply.
1680 bool value_is_mate(Value value) {
1682 assert(abs(value) <= VALUE_INFINITE);
1684 return value <= value_mated_in(PLY_MAX)
1685 || value >= value_mate_in(PLY_MAX);
1689 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1690 // "plies to mate from the current ply". Non-mate scores are unchanged.
1691 // The function is called before storing a value to the transposition table.
1693 Value value_to_tt(Value v, int ply) {
1695 if (v >= value_mate_in(PLY_MAX))
1698 if (v <= value_mated_in(PLY_MAX))
1705 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1706 // the transposition table to a mate score corrected for the current ply.
1708 Value value_from_tt(Value v, int ply) {
1710 if (v >= value_mate_in(PLY_MAX))
1713 if (v <= value_mated_in(PLY_MAX))
1720 // move_is_killer() checks if the given move is among the killer moves
1722 bool move_is_killer(Move m, SearchStack* ss) {
1724 if (ss->killers[0] == m || ss->killers[1] == m)
1731 // extension() decides whether a move should be searched with normal depth,
1732 // or with extended depth. Certain classes of moves (checking moves, in
1733 // particular) are searched with bigger depth than ordinary moves and in
1734 // any case are marked as 'dangerous'. Note that also if a move is not
1735 // extended, as example because the corresponding UCI option is set to zero,
1736 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1737 template <NodeType PvNode>
1738 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1739 bool singleEvasion, bool mateThreat, bool* dangerous) {
1741 assert(m != MOVE_NONE);
1743 Depth result = DEPTH_ZERO;
1744 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1748 if (moveIsCheck && pos.see_sign(m) >= 0)
1749 result += CheckExtension[PvNode];
1752 result += SingleEvasionExtension[PvNode];
1755 result += MateThreatExtension[PvNode];
1758 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1760 Color c = pos.side_to_move();
1761 if (relative_rank(c, move_to(m)) == RANK_7)
1763 result += PawnPushTo7thExtension[PvNode];
1766 if (pos.pawn_is_passed(c, move_to(m)))
1768 result += PassedPawnExtension[PvNode];
1773 if ( captureOrPromotion
1774 && pos.type_of_piece_on(move_to(m)) != PAWN
1775 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1776 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1777 && !move_is_promotion(m)
1780 result += PawnEndgameExtension[PvNode];
1785 && captureOrPromotion
1786 && pos.type_of_piece_on(move_to(m)) != PAWN
1787 && pos.see_sign(m) >= 0)
1789 result += ONE_PLY / 2;
1793 return Min(result, ONE_PLY);
1797 // connected_threat() tests whether it is safe to forward prune a move or if
1798 // is somehow coonected to the threat move returned by null search.
1800 bool connected_threat(const Position& pos, Move m, Move threat) {
1802 assert(move_is_ok(m));
1803 assert(threat && move_is_ok(threat));
1804 assert(!pos.move_is_check(m));
1805 assert(!pos.move_is_capture_or_promotion(m));
1806 assert(!pos.move_is_passed_pawn_push(m));
1808 Square mfrom, mto, tfrom, tto;
1810 mfrom = move_from(m);
1812 tfrom = move_from(threat);
1813 tto = move_to(threat);
1815 // Case 1: Don't prune moves which move the threatened piece
1819 // Case 2: If the threatened piece has value less than or equal to the
1820 // value of the threatening piece, don't prune move which defend it.
1821 if ( pos.move_is_capture(threat)
1822 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1823 || pos.type_of_piece_on(tfrom) == KING)
1824 && pos.move_attacks_square(m, tto))
1827 // Case 3: If the moving piece in the threatened move is a slider, don't
1828 // prune safe moves which block its ray.
1829 if ( piece_is_slider(pos.piece_on(tfrom))
1830 && bit_is_set(squares_between(tfrom, tto), mto)
1831 && pos.see_sign(m) >= 0)
1838 // ok_to_use_TT() returns true if a transposition table score
1839 // can be used at a given point in search.
1841 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1843 Value v = value_from_tt(tte->value(), ply);
1845 return ( tte->depth() >= depth
1846 || v >= Max(value_mate_in(PLY_MAX), beta)
1847 || v < Min(value_mated_in(PLY_MAX), beta))
1849 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1850 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1854 // refine_eval() returns the transposition table score if
1855 // possible otherwise falls back on static position evaluation.
1857 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1861 Value v = value_from_tt(tte->value(), ply);
1863 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1864 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1871 // update_history() registers a good move that produced a beta-cutoff
1872 // in history and marks as failures all the other moves of that ply.
1874 void update_history(const Position& pos, Move move, Depth depth,
1875 Move movesSearched[], int moveCount) {
1879 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1881 for (int i = 0; i < moveCount - 1; i++)
1883 m = movesSearched[i];
1887 if (!pos.move_is_capture_or_promotion(m))
1888 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1893 // update_killers() add a good move that produced a beta-cutoff
1894 // among the killer moves of that ply.
1896 void update_killers(Move m, SearchStack* ss) {
1898 if (m == ss->killers[0])
1901 ss->killers[1] = ss->killers[0];
1906 // update_gains() updates the gains table of a non-capture move given
1907 // the static position evaluation before and after the move.
1909 void update_gains(const Position& pos, Move m, Value before, Value after) {
1912 && before != VALUE_NONE
1913 && after != VALUE_NONE
1914 && pos.captured_piece_type() == PIECE_TYPE_NONE
1915 && !move_is_special(m))
1916 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1920 // current_search_time() returns the number of milliseconds which have passed
1921 // since the beginning of the current search.
1923 int current_search_time() {
1925 return get_system_time() - SearchStartTime;
1929 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1931 std::string value_to_uci(Value v) {
1933 std::stringstream s;
1935 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1936 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1938 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1943 // nps() computes the current nodes/second count.
1947 int t = current_search_time();
1948 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
1952 // poll() performs two different functions: It polls for user input, and it
1953 // looks at the time consumed so far and decides if it's time to abort the
1958 static int lastInfoTime;
1959 int t = current_search_time();
1964 // We are line oriented, don't read single chars
1965 std::string command;
1967 if (!std::getline(std::cin, command))
1970 if (command == "quit")
1973 PonderSearch = false;
1977 else if (command == "stop")
1980 PonderSearch = false;
1982 else if (command == "ponderhit")
1986 // Print search information
1990 else if (lastInfoTime > t)
1991 // HACK: Must be a new search where we searched less than
1992 // NodesBetweenPolls nodes during the first second of search.
1995 else if (t - lastInfoTime >= 1000)
2002 if (dbg_show_hit_rate)
2003 dbg_print_hit_rate();
2005 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
2006 << " time " << t << endl;
2009 // Should we stop the search?
2013 bool stillAtFirstMove = FirstRootMove
2014 && !AspirationFailLow
2015 && t > TimeMgr.available_time();
2017 bool noMoreTime = t > TimeMgr.maximum_time()
2018 || stillAtFirstMove;
2020 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2021 || (ExactMaxTime && t >= ExactMaxTime)
2022 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2027 // ponderhit() is called when the program is pondering (i.e. thinking while
2028 // it's the opponent's turn to move) in order to let the engine know that
2029 // it correctly predicted the opponent's move.
2033 int t = current_search_time();
2034 PonderSearch = false;
2036 bool stillAtFirstMove = FirstRootMove
2037 && !AspirationFailLow
2038 && t > TimeMgr.available_time();
2040 bool noMoreTime = t > TimeMgr.maximum_time()
2041 || stillAtFirstMove;
2043 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2048 // init_ss_array() does a fast reset of the first entries of a SearchStack
2049 // array and of all the excludedMove and skipNullMove entries.
2051 void init_ss_array(SearchStack* ss, int size) {
2053 for (int i = 0; i < size; i++, ss++)
2055 ss->excludedMove = MOVE_NONE;
2056 ss->skipNullMove = false;
2057 ss->reduction = DEPTH_ZERO;
2061 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2066 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2067 // while the program is pondering. The point is to work around a wrinkle in
2068 // the UCI protocol: When pondering, the engine is not allowed to give a
2069 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2070 // We simply wait here until one of these commands is sent, and return,
2071 // after which the bestmove and pondermove will be printed (in id_loop()).
2073 void wait_for_stop_or_ponderhit() {
2075 std::string command;
2079 if (!std::getline(std::cin, command))
2082 if (command == "quit")
2087 else if (command == "ponderhit" || command == "stop")
2093 // print_pv_info() prints to standard output and eventually to log file information on
2094 // the current PV line. It is called at each iteration or after a new pv is found.
2096 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2098 cout << "info depth " << Iteration
2099 << " score " << value_to_uci(value)
2100 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2101 << " time " << current_search_time()
2102 << " nodes " << ThreadsMgr.nodes_searched()
2106 for (Move* m = pv; *m != MOVE_NONE; m++)
2113 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2114 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2116 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2117 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2122 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2123 // the PV back into the TT. This makes sure the old PV moves are searched
2124 // first, even if the old TT entries have been overwritten.
2126 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2130 Position p(pos, pos.thread());
2131 Value v, m = VALUE_NONE;
2133 for (int i = 0; pv[i] != MOVE_NONE; i++)
2135 tte = TT.retrieve(p.get_key());
2136 if (!tte || tte->move() != pv[i])
2138 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2139 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2141 p.do_move(pv[i], st);
2146 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2147 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2148 // allow to always have a ponder move even when we fail high at root and also a
2149 // long PV to print that is important for position analysis.
2151 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2155 Position p(pos, pos.thread());
2158 assert(bestMove != MOVE_NONE);
2161 p.do_move(pv[ply++], st);
2163 while ( (tte = TT.retrieve(p.get_key())) != NULL
2164 && tte->move() != MOVE_NONE
2165 && move_is_legal(p, tte->move())
2167 && (!p.is_draw() || ply < 2))
2169 pv[ply] = tte->move();
2170 p.do_move(pv[ply++], st);
2172 pv[ply] = MOVE_NONE;
2176 // init_thread() is the function which is called when a new thread is
2177 // launched. It simply calls the idle_loop() function with the supplied
2178 // threadID. There are two versions of this function; one for POSIX
2179 // threads and one for Windows threads.
2181 #if !defined(_MSC_VER)
2183 void* init_thread(void *threadID) {
2185 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2191 DWORD WINAPI init_thread(LPVOID threadID) {
2193 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2200 /// The ThreadsManager class
2202 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2203 // get_beta_counters() are getters/setters for the per thread
2204 // counters used to sort the moves at root.
2206 void ThreadsManager::resetNodeCounters() {
2208 for (int i = 0; i < MAX_THREADS; i++)
2209 threads[i].nodes = 0ULL;
2212 int64_t ThreadsManager::nodes_searched() const {
2214 int64_t result = 0ULL;
2215 for (int i = 0; i < ActiveThreads; i++)
2216 result += threads[i].nodes;
2222 // idle_loop() is where the threads are parked when they have no work to do.
2223 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2224 // object for which the current thread is the master.
2226 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2228 assert(threadID >= 0 && threadID < MAX_THREADS);
2232 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2233 // master should exit as last one.
2234 if (AllThreadsShouldExit)
2237 threads[threadID].state = THREAD_TERMINATED;
2241 // If we are not thinking, wait for a condition to be signaled
2242 // instead of wasting CPU time polling for work.
2243 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2246 assert(threadID != 0);
2247 threads[threadID].state = THREAD_SLEEPING;
2249 #if !defined(_MSC_VER)
2250 lock_grab(&WaitLock);
2251 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2252 pthread_cond_wait(&WaitCond, &WaitLock);
2253 lock_release(&WaitLock);
2255 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2259 // If thread has just woken up, mark it as available
2260 if (threads[threadID].state == THREAD_SLEEPING)
2261 threads[threadID].state = THREAD_AVAILABLE;
2263 // If this thread has been assigned work, launch a search
2264 if (threads[threadID].state == THREAD_WORKISWAITING)
2266 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2268 threads[threadID].state = THREAD_SEARCHING;
2270 // Here we call search() with SplitPoint template parameter set to true
2271 SplitPoint* sp = threads[threadID].splitPoint;
2272 Position pos(*sp->pos, threadID);
2273 SearchStack* ss = sp->sstack[threadID] + 1;
2277 search<PV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->ply);
2279 search<NonPV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->ply);
2281 assert(threads[threadID].state == THREAD_SEARCHING);
2283 threads[threadID].state = THREAD_AVAILABLE;
2286 // If this thread is the master of a split point and all slaves have
2287 // finished their work at this split point, return from the idle loop.
2289 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2291 if (i == ActiveThreads)
2293 // Because sp->slaves[] is reset under lock protection,
2294 // be sure sp->lock has been released before to return.
2295 lock_grab(&(sp->lock));
2296 lock_release(&(sp->lock));
2298 // In helpful master concept a master can help only a sub-tree, and
2299 // because here is all finished is not possible master is booked.
2300 assert(threads[threadID].state == THREAD_AVAILABLE);
2302 threads[threadID].state = THREAD_SEARCHING;
2309 // init_threads() is called during startup. It launches all helper threads,
2310 // and initializes the split point stack and the global locks and condition
2313 void ThreadsManager::init_threads() {
2318 #if !defined(_MSC_VER)
2319 pthread_t pthread[1];
2322 // Initialize global locks
2324 lock_init(&WaitLock);
2326 #if !defined(_MSC_VER)
2327 pthread_cond_init(&WaitCond, NULL);
2329 for (i = 0; i < MAX_THREADS; i++)
2330 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2333 // Initialize splitPoints[] locks
2334 for (i = 0; i < MAX_THREADS; i++)
2335 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2336 lock_init(&(threads[i].splitPoints[j].lock));
2338 // Will be set just before program exits to properly end the threads
2339 AllThreadsShouldExit = false;
2341 // Threads will be put to sleep as soon as created
2342 AllThreadsShouldSleep = true;
2344 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2346 threads[0].state = THREAD_SEARCHING;
2347 for (i = 1; i < MAX_THREADS; i++)
2348 threads[i].state = THREAD_AVAILABLE;
2350 // Launch the helper threads
2351 for (i = 1; i < MAX_THREADS; i++)
2354 #if !defined(_MSC_VER)
2355 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2357 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2362 cout << "Failed to create thread number " << i << endl;
2363 Application::exit_with_failure();
2366 // Wait until the thread has finished launching and is gone to sleep
2367 while (threads[i].state != THREAD_SLEEPING) {}
2372 // exit_threads() is called when the program exits. It makes all the
2373 // helper threads exit cleanly.
2375 void ThreadsManager::exit_threads() {
2377 ActiveThreads = MAX_THREADS; // Wake up all the threads
2378 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2379 AllThreadsShouldSleep = true; // Avoid an assert in wake_sleeping_threads()
2380 wake_sleeping_threads();
2382 // Wait for thread termination
2383 for (int i = 1; i < MAX_THREADS; i++)
2384 while (threads[i].state != THREAD_TERMINATED) {}
2386 // Now we can safely destroy the locks
2387 for (int i = 0; i < MAX_THREADS; i++)
2388 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2389 lock_destroy(&(threads[i].splitPoints[j].lock));
2391 lock_destroy(&WaitLock);
2392 lock_destroy(&MPLock);
2396 // thread_should_stop() checks whether the thread should stop its search.
2397 // This can happen if a beta cutoff has occurred in the thread's currently
2398 // active split point, or in some ancestor of the current split point.
2400 bool ThreadsManager::thread_should_stop(int threadID) const {
2402 assert(threadID >= 0 && threadID < ActiveThreads);
2404 SplitPoint* sp = threads[threadID].splitPoint;
2406 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2411 // thread_is_available() checks whether the thread with threadID "slave" is
2412 // available to help the thread with threadID "master" at a split point. An
2413 // obvious requirement is that "slave" must be idle. With more than two
2414 // threads, this is not by itself sufficient: If "slave" is the master of
2415 // some active split point, it is only available as a slave to the other
2416 // threads which are busy searching the split point at the top of "slave"'s
2417 // split point stack (the "helpful master concept" in YBWC terminology).
2419 bool ThreadsManager::thread_is_available(int slave, int master) const {
2421 assert(slave >= 0 && slave < ActiveThreads);
2422 assert(master >= 0 && master < ActiveThreads);
2423 assert(ActiveThreads > 1);
2425 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2428 // Make a local copy to be sure doesn't change under our feet
2429 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2431 // No active split points means that the thread is available as
2432 // a slave for any other thread.
2433 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2436 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2437 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2438 // could have been set to 0 by another thread leading to an out of bound access.
2439 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2446 // available_thread_exists() tries to find an idle thread which is available as
2447 // a slave for the thread with threadID "master".
2449 bool ThreadsManager::available_thread_exists(int master) const {
2451 assert(master >= 0 && master < ActiveThreads);
2452 assert(ActiveThreads > 1);
2454 for (int i = 0; i < ActiveThreads; i++)
2455 if (thread_is_available(i, master))
2462 // split() does the actual work of distributing the work at a node between
2463 // several available threads. If it does not succeed in splitting the
2464 // node (because no idle threads are available, or because we have no unused
2465 // split point objects), the function immediately returns. If splitting is
2466 // possible, a SplitPoint object is initialized with all the data that must be
2467 // copied to the helper threads and we tell our helper threads that they have
2468 // been assigned work. This will cause them to instantly leave their idle loops
2469 // and call sp_search(). When all threads have returned from sp_search() then
2472 template <bool Fake>
2473 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2474 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2475 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2477 assert(ply > 0 && ply < PLY_MAX);
2478 assert(*bestValue >= -VALUE_INFINITE);
2479 assert(*bestValue <= *alpha);
2480 assert(*alpha < beta);
2481 assert(beta <= VALUE_INFINITE);
2482 assert(depth > DEPTH_ZERO);
2483 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2484 assert(ActiveThreads > 1);
2486 int i, master = p.thread();
2487 Thread& masterThread = threads[master];
2491 // If no other thread is available to help us, or if we have too many
2492 // active split points, don't split.
2493 if ( !available_thread_exists(master)
2494 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2496 lock_release(&MPLock);
2500 // Pick the next available split point object from the split point stack
2501 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2503 // Initialize the split point object
2504 splitPoint.parent = masterThread.splitPoint;
2505 splitPoint.stopRequest = false;
2506 splitPoint.ply = ply;
2507 splitPoint.depth = depth;
2508 splitPoint.threatMove = threatMove;
2509 splitPoint.mateThreat = mateThreat;
2510 splitPoint.alpha = *alpha;
2511 splitPoint.beta = beta;
2512 splitPoint.pvNode = pvNode;
2513 splitPoint.bestValue = *bestValue;
2515 splitPoint.moveCount = moveCount;
2516 splitPoint.pos = &p;
2517 splitPoint.parentSstack = ss;
2518 for (i = 0; i < ActiveThreads; i++)
2519 splitPoint.slaves[i] = 0;
2521 masterThread.splitPoint = &splitPoint;
2523 // If we are here it means we are not available
2524 assert(masterThread.state != THREAD_AVAILABLE);
2526 int workersCnt = 1; // At least the master is included
2528 // Allocate available threads setting state to THREAD_BOOKED
2529 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2530 if (thread_is_available(i, master))
2532 threads[i].state = THREAD_BOOKED;
2533 threads[i].splitPoint = &splitPoint;
2534 splitPoint.slaves[i] = 1;
2538 assert(Fake || workersCnt > 1);
2540 // We can release the lock because slave threads are already booked and master is not available
2541 lock_release(&MPLock);
2543 // Tell the threads that they have work to do. This will make them leave
2544 // their idle loop. But before copy search stack tail for each thread.
2545 for (i = 0; i < ActiveThreads; i++)
2546 if (i == master || splitPoint.slaves[i])
2548 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2550 assert(i == master || threads[i].state == THREAD_BOOKED);
2552 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2555 // Everything is set up. The master thread enters the idle loop, from
2556 // which it will instantly launch a search, because its state is
2557 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2558 // idle loop, which means that the main thread will return from the idle
2559 // loop when all threads have finished their work at this split point.
2560 idle_loop(master, &splitPoint);
2562 // We have returned from the idle loop, which means that all threads are
2563 // finished. Update alpha and bestValue, and return.
2566 *alpha = splitPoint.alpha;
2567 *bestValue = splitPoint.bestValue;
2568 masterThread.activeSplitPoints--;
2569 masterThread.splitPoint = splitPoint.parent;
2571 lock_release(&MPLock);
2575 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2576 // to start a new search from the root.
2578 void ThreadsManager::wake_sleeping_threads() {
2580 assert(AllThreadsShouldSleep);
2581 assert(ActiveThreads > 0);
2583 AllThreadsShouldSleep = false;
2585 if (ActiveThreads == 1)
2588 #if !defined(_MSC_VER)
2589 pthread_mutex_lock(&WaitLock);
2590 pthread_cond_broadcast(&WaitCond);
2591 pthread_mutex_unlock(&WaitLock);
2593 for (int i = 1; i < MAX_THREADS; i++)
2594 SetEvent(SitIdleEvent[i]);
2600 // put_threads_to_sleep() makes all the threads go to sleep just before
2601 // to leave think(), at the end of the search. Threads should have already
2602 // finished the job and should be idle.
2604 void ThreadsManager::put_threads_to_sleep() {
2606 assert(!AllThreadsShouldSleep);
2608 // This makes the threads to go to sleep
2609 AllThreadsShouldSleep = true;
2612 /// The RootMoveList class
2614 // RootMoveList c'tor
2616 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2618 SearchStack ss[PLY_MAX_PLUS_2];
2619 MoveStack mlist[MOVES_MAX];
2621 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2623 // Initialize search stack
2624 init_ss_array(ss, PLY_MAX_PLUS_2);
2625 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2628 // Generate all legal moves
2629 MoveStack* last = generate_moves(pos, mlist);
2631 // Add each move to the moves[] array
2632 for (MoveStack* cur = mlist; cur != last; cur++)
2634 bool includeMove = includeAllMoves;
2636 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2637 includeMove = (searchMoves[k] == cur->move);
2642 // Find a quick score for the move
2643 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2644 moves[count].pv[1] = MOVE_NONE;
2645 pos.do_move(cur->move, st);
2646 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2647 pos.undo_move(cur->move);
2653 // Score root moves using the standard way used in main search, the moves
2654 // are scored according to the order in which are returned by MovePicker.
2656 void RootMoveList::score_moves(const Position& pos)
2660 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2662 while ((move = mp.get_next_move()) != MOVE_NONE)
2663 for (int i = 0; i < count; i++)
2664 if (moves[i].move == move)
2666 moves[i].mp_score = score--;
2671 // RootMoveList simple methods definitions
2673 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2677 for (j = 0; pv[j] != MOVE_NONE; j++)
2678 moves[moveNum].pv[j] = pv[j];
2680 moves[moveNum].pv[j] = MOVE_NONE;
2684 // RootMoveList::sort() sorts the root move list at the beginning of a new
2687 void RootMoveList::sort() {
2689 sort_multipv(count - 1); // Sort all items
2693 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2694 // list by their scores and depths. It is used to order the different PVs
2695 // correctly in MultiPV mode.
2697 void RootMoveList::sort_multipv(int n) {
2701 for (i = 1; i <= n; i++)
2703 RootMove rm = moves[i];
2704 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2705 moves[j] = moves[j - 1];