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), cumulativeNodes(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;
131 int64_t nodes, cumulativeNodes;
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 int move_count() const { return count; }
145 Move get_move(int moveNum) const { return moves[moveNum].move; }
146 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
147 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
148 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
149 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
150 void score_moves(const Position& pos);
152 void set_move_nodes(int moveNum, int64_t nodes);
153 void set_move_pv(int moveNum, const Move pv[]);
155 void sort_multipv(int n);
158 static const int MaxRootMoves = 500;
159 RootMove moves[MaxRootMoves];
164 // When formatting a move for std::cout we must know if we are in Chess960
165 // or not. To keep using the handy operator<<() on the move the trick is to
166 // embed this flag in the stream itself. Function-like named enum set960 is
167 // used as a custom manipulator and the stream internal general-purpose array,
168 // accessed through ios_base::iword(), is used to pass the flag to the move's
169 // operator<<() that will use it to properly format castling moves.
172 std::ostream& operator<< (std::ostream& os, const set960& m) {
174 os.iword(0) = int(m);
183 // Maximum depth for razoring
184 const Depth RazorDepth = 4 * ONE_PLY;
186 // Dynamic razoring margin based on depth
187 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
189 // Step 8. Null move search with verification search
191 // Null move margin. A null move search will not be done if the static
192 // evaluation of the position is more than NullMoveMargin below beta.
193 const Value NullMoveMargin = Value(0x200);
195 // Maximum depth for use of dynamic threat detection when null move fails low
196 const Depth ThreatDepth = 5 * ONE_PLY;
198 // Step 9. Internal iterative deepening
200 // Minimum depth for use of internal iterative deepening
201 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
203 // At Non-PV nodes we do an internal iterative deepening search
204 // when the static evaluation is bigger then beta - IIDMargin.
205 const Value IIDMargin = Value(0x100);
207 // Step 11. Decide the new search depth
209 // Extensions. Configurable UCI options
210 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
211 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
212 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
214 // Minimum depth for use of singular extension
215 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
217 // If the TT move is at least SingularExtensionMargin better then the
218 // remaining ones we will extend it.
219 const Value SingularExtensionMargin = Value(0x20);
221 // Step 12. Futility pruning
223 // Futility margin for quiescence search
224 const Value FutilityMarginQS = Value(0x80);
226 // Futility lookup tables (initialized at startup) and their getter functions
227 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
228 int FutilityMoveCountArray[32]; // [depth]
230 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
231 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
233 // Step 14. Reduced search
235 // Reduction lookup tables (initialized at startup) and their getter functions
236 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
238 template <NodeType PV>
239 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
241 // Common adjustments
243 // Search depth at iteration 1
244 const Depth InitialDepth = ONE_PLY;
246 // Easy move margin. An easy move candidate must be at least this much
247 // better than the second best move.
248 const Value EasyMoveMargin = Value(0x200);
256 // Scores and number of times the best move changed for each iteration
257 Value ValueByIteration[PLY_MAX_PLUS_2];
258 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
260 // Search window management
266 // Time managment variables
267 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
268 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
269 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
274 std::ofstream LogFile;
276 // Multi-threads related variables
277 Depth MinimumSplitDepth;
278 int MaxThreadsPerSplitPoint;
279 ThreadsManager ThreadsMgr;
281 // Node counters, used only by thread[0] but try to keep in different cache
282 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
284 int NodesBetweenPolls = 30000;
291 Value id_loop(const Position& pos, Move searchMoves[]);
292 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
294 template <NodeType PvNode>
295 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
297 template <NodeType PvNode>
298 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
300 template <NodeType PvNode>
301 void sp_search(SplitPoint* sp, int threadID);
303 template <NodeType PvNode>
304 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
306 bool connected_moves(const Position& pos, Move m1, Move m2);
307 bool value_is_mate(Value value);
308 Value value_to_tt(Value v, int ply);
309 Value value_from_tt(Value v, int ply);
310 bool move_is_killer(Move m, SearchStack* ss);
311 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
312 bool connected_threat(const Position& pos, Move m, Move threat);
313 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
314 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
315 void update_killers(Move m, SearchStack* ss);
316 void update_gains(const Position& pos, Move move, Value before, Value after);
318 int current_search_time();
319 std::string value_to_uci(Value v);
323 void wait_for_stop_or_ponderhit();
324 void init_ss_array(SearchStack* ss, int size);
325 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
326 void insert_pv_in_tt(const Position& pos, Move pv[]);
327 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
329 #if !defined(_MSC_VER)
330 void *init_thread(void *threadID);
332 DWORD WINAPI init_thread(LPVOID threadID);
342 /// init_threads(), exit_threads() and nodes_searched() are helpers to
343 /// give accessibility to some TM methods from outside of current file.
345 void init_threads() { ThreadsMgr.init_threads(); }
346 void exit_threads() { ThreadsMgr.exit_threads(); }
347 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
350 /// init_search() is called during startup. It initializes various lookup tables
354 int d; // depth (ONE_PLY == 2)
355 int hd; // half depth (ONE_PLY == 1)
358 // Init reductions array
359 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
361 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
362 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
363 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
364 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
367 // Init futility margins array
368 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
369 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
371 // Init futility move count array
372 for (d = 0; d < 32; d++)
373 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
377 /// perft() is our utility to verify move generation is bug free. All the legal
378 /// moves up to given depth are generated and counted and the sum returned.
380 int perft(Position& pos, Depth depth)
382 MoveStack mlist[256];
387 // Generate all legal moves
388 MoveStack* last = generate_moves(pos, mlist);
390 // If we are at the last ply we don't need to do and undo
391 // the moves, just to count them.
392 if (depth <= ONE_PLY)
393 return int(last - mlist);
395 // Loop through all legal moves
397 for (MoveStack* cur = mlist; cur != last; cur++)
400 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
401 sum += perft(pos, depth - ONE_PLY);
408 /// think() is the external interface to Stockfish's search, and is called when
409 /// the program receives the UCI 'go' command. It initializes various
410 /// search-related global variables, and calls root_search(). It returns false
411 /// when a quit command is received during the search.
413 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
414 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
416 // Initialize global search variables
417 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
419 ThreadsMgr.resetNodeCounters();
420 SearchStartTime = get_system_time();
421 ExactMaxTime = maxTime;
424 InfiniteSearch = infinite;
425 PonderSearch = ponder;
426 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
428 // Look for a book move, only during games, not tests
429 if (UseTimeManagement && get_option_value_bool("OwnBook"))
431 if (get_option_value_string("Book File") != OpeningBook.file_name())
432 OpeningBook.open(get_option_value_string("Book File"));
434 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
435 if (bookMove != MOVE_NONE)
438 wait_for_stop_or_ponderhit();
440 cout << "bestmove " << bookMove << endl;
445 // Read UCI option values
446 TT.set_size(get_option_value_int("Hash"));
447 if (button_was_pressed("Clear Hash"))
450 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
451 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
452 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
453 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
454 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
455 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
456 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
457 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
458 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
459 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
460 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
461 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
463 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
464 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
465 MultiPV = get_option_value_int("MultiPV");
466 UseLogFile = get_option_value_bool("Use Search Log");
469 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
471 read_weights(pos.side_to_move());
473 // Set the number of active threads
474 int newActiveThreads = get_option_value_int("Threads");
475 if (newActiveThreads != ThreadsMgr.active_threads())
477 ThreadsMgr.set_active_threads(newActiveThreads);
478 init_eval(ThreadsMgr.active_threads());
481 // Wake up sleeping threads
482 ThreadsMgr.wake_sleeping_threads();
485 int myTime = time[pos.side_to_move()];
486 int myIncrement = increment[pos.side_to_move()];
487 if (UseTimeManagement)
488 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
490 // Set best NodesBetweenPolls interval to avoid lagging under
491 // heavy time pressure.
493 NodesBetweenPolls = Min(MaxNodes, 30000);
494 else if (myTime && myTime < 1000)
495 NodesBetweenPolls = 1000;
496 else if (myTime && myTime < 5000)
497 NodesBetweenPolls = 5000;
499 NodesBetweenPolls = 30000;
501 // Write search information to log file
503 LogFile << "Searching: " << pos.to_fen() << endl
504 << "infinite: " << infinite
505 << " ponder: " << ponder
506 << " time: " << myTime
507 << " increment: " << myIncrement
508 << " moves to go: " << movesToGo << endl;
510 // We're ready to start thinking. Call the iterative deepening loop function
511 id_loop(pos, searchMoves);
516 ThreadsMgr.put_threads_to_sleep();
524 // id_loop() is the main iterative deepening loop. It calls root_search
525 // repeatedly with increasing depth until the allocated thinking time has
526 // been consumed, the user stops the search, or the maximum search depth is
529 Value id_loop(const Position& pos, Move searchMoves[]) {
531 Position p(pos, pos.thread());
532 SearchStack ss[PLY_MAX_PLUS_2];
533 Move pv[PLY_MAX_PLUS_2];
534 Move EasyMove = MOVE_NONE;
535 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
537 // Moves to search are verified, copied, scored and sorted
538 RootMoveList rml(p, searchMoves);
540 // Handle special case of searching on a mate/stale position
541 if (rml.move_count() == 0)
544 wait_for_stop_or_ponderhit();
546 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
549 // Print RootMoveList startup scoring to the standard output,
550 // so to output information also for iteration 1.
551 cout << set960(p.is_chess960()) // Is enough to set once at the beginning
552 << "info depth " << 1
553 << "\ninfo depth " << 1
554 << " score " << value_to_uci(rml.get_move_score(0))
555 << " time " << current_search_time()
556 << " nodes " << ThreadsMgr.nodes_searched()
558 << " pv " << rml.get_move(0) << "\n";
563 init_ss_array(ss, PLY_MAX_PLUS_2);
564 pv[0] = pv[1] = MOVE_NONE;
565 ValueByIteration[1] = rml.get_move_score(0);
568 // Is one move significantly better than others after initial scoring ?
569 if ( rml.move_count() == 1
570 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
571 EasyMove = rml.get_move(0);
573 // Iterative deepening loop
574 while (Iteration < PLY_MAX)
576 // Initialize iteration
578 BestMoveChangesByIteration[Iteration] = 0;
580 cout << "info depth " << Iteration << endl;
582 // Calculate dynamic aspiration window based on previous iterations
583 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
585 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
586 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
588 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
589 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
591 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
592 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
595 // Search to the current depth, rml is updated and sorted, alpha and beta could change
596 value = root_search(p, ss, pv, rml, &alpha, &beta);
598 // Write PV to transposition table, in case the relevant entries have
599 // been overwritten during the search.
600 insert_pv_in_tt(p, pv);
603 break; // Value cannot be trusted. Break out immediately!
605 //Save info about search result
606 ValueByIteration[Iteration] = value;
608 // Drop the easy move if differs from the new best move
609 if (pv[0] != EasyMove)
610 EasyMove = MOVE_NONE;
612 if (UseTimeManagement)
615 bool stopSearch = false;
617 // Stop search early if there is only a single legal move,
618 // we search up to Iteration 6 anyway to get a proper score.
619 if (Iteration >= 6 && rml.move_count() == 1)
622 // Stop search early when the last two iterations returned a mate score
624 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
625 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
628 // Stop search early if one move seems to be much better than the others
629 int64_t nodes = ThreadsMgr.nodes_searched();
632 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
633 && current_search_time() > TimeMgr.available_time() / 16)
634 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
635 && current_search_time() > TimeMgr.available_time() / 32)))
638 // Add some extra time if the best move has changed during the last two iterations
639 if (Iteration > 5 && Iteration <= 50)
640 TimeMgr.pv_unstability(BestMoveChangesByIteration[Iteration],
641 BestMoveChangesByIteration[Iteration-1]);
643 // Stop search if most of MaxSearchTime is consumed at the end of the
644 // iteration. We probably don't have enough time to search the first
645 // move at the next iteration anyway.
646 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
652 StopOnPonderhit = true;
658 if (MaxDepth && Iteration >= MaxDepth)
662 // If we are pondering or in infinite search, we shouldn't print the
663 // best move before we are told to do so.
664 if (!AbortSearch && (PonderSearch || InfiniteSearch))
665 wait_for_stop_or_ponderhit();
667 // Print final search statistics
668 cout << "info nodes " << ThreadsMgr.nodes_searched()
670 << " time " << current_search_time() << endl;
672 // Print the best move and the ponder move to the standard output
673 if (pv[0] == MOVE_NONE)
675 pv[0] = rml.get_move(0);
679 assert(pv[0] != MOVE_NONE);
681 cout << "bestmove " << pv[0];
683 if (pv[1] != MOVE_NONE)
684 cout << " ponder " << pv[1];
691 dbg_print_mean(LogFile);
693 if (dbg_show_hit_rate)
694 dbg_print_hit_rate(LogFile);
696 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
697 << "\nNodes/second: " << nps()
698 << "\nBest move: " << move_to_san(p, pv[0]);
701 p.do_move(pv[0], st);
702 LogFile << "\nPonder move: "
703 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
706 return rml.get_move_score(0);
710 // root_search() is the function which searches the root node. It is
711 // similar to search_pv except that it uses a different move ordering
712 // scheme, prints some information to the standard output and handles
713 // the fail low/high loops.
715 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
722 Depth depth, ext, newDepth;
723 Value value, alpha, beta;
724 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
725 int researchCountFH, researchCountFL;
727 researchCountFH = researchCountFL = 0;
730 isCheck = pos.is_check();
731 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
733 // Step 1. Initialize node (polling is omitted at root)
734 ss->currentMove = ss->bestMove = MOVE_NONE;
736 // Step 2. Check for aborted search (omitted at root)
737 // Step 3. Mate distance pruning (omitted at root)
738 // Step 4. Transposition table lookup (omitted at root)
740 // Step 5. Evaluate the position statically
741 // At root we do this only to get reference value for child nodes
742 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, margins);
744 // Step 6. Razoring (omitted at root)
745 // Step 7. Static null move pruning (omitted at root)
746 // Step 8. Null move search with verification search (omitted at root)
747 // Step 9. Internal iterative deepening (omitted at root)
749 // Step extra. Fail low loop
750 // We start with small aspiration window and in case of fail low, we research
751 // with bigger window until we are not failing low anymore.
754 // Sort the moves before to (re)search
755 rml.score_moves(pos);
758 // Step 10. Loop through all moves in the root move list
759 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
761 // This is used by time management
762 FirstRootMove = (i == 0);
764 // Save the current node count before the move is searched
765 nodes = ThreadsMgr.nodes_searched();
767 // Pick the next root move, and print the move and the move number to
768 // the standard output.
769 move = ss->currentMove = rml.get_move(i);
771 if (current_search_time() >= 1000)
772 cout << "info currmove " << move
773 << " currmovenumber " << i + 1 << endl;
775 moveIsCheck = pos.move_is_check(move);
776 captureOrPromotion = pos.move_is_capture_or_promotion(move);
778 // Step 11. Decide the new search depth
779 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
780 newDepth = depth + ext;
782 // Step 12. Futility pruning (omitted at root)
784 // Step extra. Fail high loop
785 // If move fails high, we research with bigger window until we are not failing
787 value = - VALUE_INFINITE;
791 // Step 13. Make the move
792 pos.do_move(move, st, ci, moveIsCheck);
794 // Step extra. pv search
795 // We do pv search for first moves (i < MultiPV)
796 // and for fail high research (value > alpha)
797 if (i < MultiPV || value > alpha)
799 // Aspiration window is disabled in multi-pv case
801 alpha = -VALUE_INFINITE;
803 // Full depth PV search, done on first move or after a fail high
804 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
808 // Step 14. Reduced search
809 // if the move fails high will be re-searched at full depth
810 bool doFullDepthSearch = true;
812 if ( depth >= 3 * ONE_PLY
814 && !captureOrPromotion
815 && !move_is_castle(move))
817 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
820 assert(newDepth-ss->reduction >= ONE_PLY);
822 // Reduced depth non-pv search using alpha as upperbound
823 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
824 doFullDepthSearch = (value > alpha);
827 // The move failed high, but if reduction is very big we could
828 // face a false positive, retry with a less aggressive reduction,
829 // if the move fails high again then go with full depth search.
830 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
832 assert(newDepth - ONE_PLY >= ONE_PLY);
834 ss->reduction = ONE_PLY;
835 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
836 doFullDepthSearch = (value > alpha);
838 ss->reduction = DEPTH_ZERO; // Restore original reduction
841 // Step 15. Full depth search
842 if (doFullDepthSearch)
844 // Full depth non-pv search using alpha as upperbound
845 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
847 // If we are above alpha then research at same depth but as PV
848 // to get a correct score or eventually a fail high above beta.
850 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
854 // Step 16. Undo move
857 // Can we exit fail high loop ?
858 if (AbortSearch || value < beta)
861 // We are failing high and going to do a research. It's important to update
862 // the score before research in case we run out of time while researching.
863 rml.set_move_score(i, value);
865 extract_pv_from_tt(pos, move, pv);
866 rml.set_move_pv(i, pv);
868 // Print information to the standard output
869 print_pv_info(pos, pv, alpha, beta, value);
871 // Prepare for a research after a fail high, each time with a wider window
872 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
875 } // End of fail high loop
877 // Finished searching the move. If AbortSearch is true, the search
878 // was aborted because the user interrupted the search or because we
879 // ran out of time. In this case, the return value of the search cannot
880 // be trusted, and we break out of the loop without updating the best
885 // Remember searched nodes counts for this move
886 rml.set_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
888 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
889 assert(value < beta);
891 // Step 17. Check for new best move
892 if (value <= alpha && i >= MultiPV)
893 rml.set_move_score(i, -VALUE_INFINITE);
896 // PV move or new best move!
899 rml.set_move_score(i, value);
901 extract_pv_from_tt(pos, move, pv);
902 rml.set_move_pv(i, pv);
906 // We record how often the best move has been changed in each
907 // iteration. This information is used for time managment: When
908 // the best move changes frequently, we allocate some more time.
910 BestMoveChangesByIteration[Iteration]++;
912 // Print information to the standard output
913 print_pv_info(pos, pv, alpha, beta, value);
915 // Raise alpha to setup proper non-pv search upper bound
922 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
924 cout << "info multipv " << j + 1
925 << " score " << value_to_uci(rml.get_move_score(j))
926 << " depth " << (j <= i ? Iteration : Iteration - 1)
927 << " time " << current_search_time()
928 << " nodes " << ThreadsMgr.nodes_searched()
932 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
933 cout << rml.get_move_pv(j, k) << " ";
937 alpha = rml.get_move_score(Min(i, MultiPV - 1));
939 } // PV move or new best move
941 assert(alpha >= *alphaPtr);
943 AspirationFailLow = (alpha == *alphaPtr);
945 if (AspirationFailLow && StopOnPonderhit)
946 StopOnPonderhit = false;
949 // Can we exit fail low loop ?
950 if (AbortSearch || !AspirationFailLow)
953 // Prepare for a research after a fail low, each time with a wider window
954 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
959 // Sort the moves before to return
966 // search<>() is the main search function for both PV and non-PV nodes
968 template <NodeType PvNode>
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[256];
982 Move ttMove, move, excludedMove, threatMove;
984 Value bestValue, value, oldAlpha;
985 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
986 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
987 bool mateThreat = false;
989 int threadID = pos.thread();
990 refinedValue = bestValue = value = -VALUE_INFINITE;
993 // Step 1. Initialize node and poll. Polling can abort search
994 ThreadsMgr.incrementNodeCounter(threadID);
995 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
996 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
998 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1004 // Step 2. Check for aborted search and immediate draw
1005 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1008 if (pos.is_draw() || ply >= PLY_MAX - 1)
1011 // Step 3. Mate distance pruning
1012 alpha = Max(value_mated_in(ply), alpha);
1013 beta = Min(value_mate_in(ply+1), beta);
1017 // Step 4. Transposition table lookup
1019 // We don't want the score of a partial search to overwrite a previous full search
1020 // TT value, so we use a different position key in case of an excluded move exists.
1021 excludedMove = ss->excludedMove;
1022 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1024 tte = TT.retrieve(posKey);
1025 ttMove = (tte ? tte->move() : MOVE_NONE);
1027 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1028 // This is to avoid problems in the following areas:
1030 // * Repetition draw detection
1031 // * Fifty move rule detection
1032 // * Searching for a mate
1033 // * Printing of full PV line
1035 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1037 // Refresh tte entry to avoid aging
1038 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->static_value_margin());
1040 ss->bestMove = ttMove; // Can be MOVE_NONE
1041 return value_from_tt(tte->value(), ply);
1044 // Step 5. Evaluate the position statically and
1045 // update gain statistics of parent move.
1046 isCheck = pos.is_check();
1048 ss->eval = VALUE_NONE;
1051 assert(tte->static_value() != VALUE_NONE);
1053 ss->eval = tte->static_value();
1054 margins[pos.side_to_move()] = tte->static_value_margin();
1055 refinedValue = refine_eval(tte, ss->eval, ply);
1059 refinedValue = ss->eval = evaluate(pos, margins);
1060 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, margins[pos.side_to_move()]);
1063 // Save gain for the parent non-capture move
1064 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1066 // Step 6. Razoring (is omitted in PV nodes)
1068 && depth < RazorDepth
1070 && refinedValue < beta - razor_margin(depth)
1071 && ttMove == MOVE_NONE
1072 && (ss-1)->currentMove != MOVE_NULL
1073 && !value_is_mate(beta)
1074 && !pos.has_pawn_on_7th(pos.side_to_move()))
1076 Value rbeta = beta - razor_margin(depth);
1077 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1079 // Logically we should return (v + razor_margin(depth)), but
1080 // surprisingly this did slightly weaker in tests.
1084 // Step 7. Static null move pruning (is omitted in PV nodes)
1085 // We're betting that the opponent doesn't have a move that will reduce
1086 // the score by more than futility_margin(depth) if we do a null move.
1088 && !ss->skipNullMove
1089 && depth < RazorDepth
1091 && refinedValue >= beta + futility_margin(depth, 0)
1092 && !value_is_mate(beta)
1093 && pos.non_pawn_material(pos.side_to_move()))
1094 return refinedValue - futility_margin(depth, 0);
1096 // Step 8. Null move search with verification search (is omitted in PV nodes)
1097 // When we jump directly to qsearch() we do a null move only if static value is
1098 // at least beta. Otherwise we do a null move if static value is not more than
1099 // NullMoveMargin under beta.
1101 && !ss->skipNullMove
1104 && refinedValue >= beta - (depth >= 4 * ONE_PLY ? NullMoveMargin : 0)
1105 && !value_is_mate(beta)
1106 && pos.non_pawn_material(pos.side_to_move()))
1108 ss->currentMove = MOVE_NULL;
1110 // Null move dynamic reduction based on depth
1111 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1113 // Null move dynamic reduction based on value
1114 if (refinedValue - beta > PawnValueMidgame)
1117 pos.do_null_move(st);
1118 (ss+1)->skipNullMove = true;
1120 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1121 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1122 (ss+1)->skipNullMove = false;
1123 pos.undo_null_move();
1125 if (nullValue >= beta)
1127 // Do not return unproven mate scores
1128 if (nullValue >= value_mate_in(PLY_MAX))
1131 if (depth < 6 * ONE_PLY)
1134 // Do verification search at high depths
1135 ss->skipNullMove = true;
1136 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1137 ss->skipNullMove = false;
1144 // The null move failed low, which means that we may be faced with
1145 // some kind of threat. If the previous move was reduced, check if
1146 // the move that refuted the null move was somehow connected to the
1147 // move which was reduced. If a connection is found, return a fail
1148 // low score (which will cause the reduced move to fail high in the
1149 // parent node, which will trigger a re-search with full depth).
1150 if (nullValue == value_mated_in(ply + 2))
1153 threatMove = (ss+1)->bestMove;
1154 if ( depth < ThreatDepth
1155 && (ss-1)->reduction
1156 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1161 // Step 9. Internal iterative deepening
1162 if ( depth >= IIDDepth[PvNode]
1163 && ttMove == MOVE_NONE
1164 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1166 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1168 ss->skipNullMove = true;
1169 search<PvNode>(pos, ss, alpha, beta, d, ply);
1170 ss->skipNullMove = false;
1172 ttMove = ss->bestMove;
1173 tte = TT.retrieve(posKey);
1176 // Expensive mate threat detection (only for PV nodes)
1178 mateThreat = pos.has_mate_threat();
1180 // Initialize a MovePicker object for the current position
1181 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1183 ss->bestMove = MOVE_NONE;
1184 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1185 futilityBase = ss->eval + margins[pos.side_to_move()];
1186 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1189 && !excludedMove // Do not allow recursive singular extension search
1190 && (tte->type() & VALUE_TYPE_LOWER)
1191 && tte->depth() >= depth - 3 * ONE_PLY;
1193 // Step 10. Loop through moves
1194 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1195 while ( bestValue < beta
1196 && (move = mp.get_next_move()) != MOVE_NONE
1197 && !ThreadsMgr.thread_should_stop(threadID))
1199 assert(move_is_ok(move));
1201 if (move == excludedMove)
1204 moveIsCheck = pos.move_is_check(move, ci);
1205 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1207 // Step 11. Decide the new search depth
1208 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1210 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1211 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1212 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1213 // lower then ttValue minus a margin then we extend ttMove.
1214 if ( singularExtensionNode
1215 && move == tte->move()
1218 Value ttValue = value_from_tt(tte->value(), ply);
1220 if (abs(ttValue) < VALUE_KNOWN_WIN)
1222 Value b = ttValue - SingularExtensionMargin;
1223 ss->excludedMove = move;
1224 ss->skipNullMove = true;
1225 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1226 ss->skipNullMove = false;
1227 ss->excludedMove = MOVE_NONE;
1228 ss->bestMove = MOVE_NONE;
1234 newDepth = depth - ONE_PLY + ext;
1236 // Update current move (this must be done after singular extension search)
1237 movesSearched[moveCount++] = ss->currentMove = move;
1239 // Step 12. Futility pruning (is omitted in PV nodes)
1241 && !captureOrPromotion
1245 && !move_is_castle(move))
1247 // Move count based pruning
1248 if ( moveCount >= futility_move_count(depth)
1249 && !(threatMove && connected_threat(pos, move, threatMove))
1250 && bestValue > value_mated_in(PLY_MAX))
1253 // Value based pruning
1254 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1255 // but fixing this made program slightly weaker.
1256 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1257 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1258 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1260 if (futilityValueScaled < beta)
1262 if (futilityValueScaled > bestValue)
1263 bestValue = futilityValueScaled;
1268 // Step 13. Make the move
1269 pos.do_move(move, st, ci, moveIsCheck);
1271 // Step extra. pv search (only in PV nodes)
1272 // The first move in list is the expected PV
1273 if (PvNode && moveCount == 1)
1274 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1275 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1278 // Step 14. Reduced depth search
1279 // If the move fails high will be re-searched at full depth.
1280 bool doFullDepthSearch = true;
1282 if ( depth >= 3 * ONE_PLY
1283 && !captureOrPromotion
1285 && !move_is_castle(move)
1286 && !move_is_killer(move, ss))
1288 ss->reduction = reduction<PvNode>(depth, moveCount);
1291 Depth d = newDepth - ss->reduction;
1292 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1293 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1295 doFullDepthSearch = (value > alpha);
1298 // The move failed high, but if reduction is very big we could
1299 // face a false positive, retry with a less aggressive reduction,
1300 // if the move fails high again then go with full depth search.
1301 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1303 assert(newDepth - ONE_PLY >= ONE_PLY);
1305 ss->reduction = ONE_PLY;
1306 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1307 doFullDepthSearch = (value > alpha);
1309 ss->reduction = DEPTH_ZERO; // Restore original reduction
1312 // Step 15. Full depth search
1313 if (doFullDepthSearch)
1315 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO, ply+1)
1316 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1318 // Step extra. pv search (only in PV nodes)
1319 // Search only for possible new PV nodes, if instead value >= beta then
1320 // parent node fails low with value <= alpha and tries another move.
1321 if (PvNode && value > alpha && value < beta)
1322 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO, ply+1)
1323 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1327 // Step 16. Undo move
1328 pos.undo_move(move);
1330 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1332 // Step 17. Check for new best move
1333 if (value > bestValue)
1338 if (PvNode && value < beta) // We want always alpha < beta
1341 if (value == value_mate_in(ply + 1))
1342 ss->mateKiller = move;
1344 ss->bestMove = move;
1348 // Step 18. Check for split
1349 if ( depth >= MinimumSplitDepth
1350 && ThreadsMgr.active_threads() > 1
1352 && ThreadsMgr.available_thread_exists(threadID)
1354 && !ThreadsMgr.thread_should_stop(threadID)
1356 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1357 threatMove, mateThreat, &moveCount, &mp, PvNode);
1360 // Step 19. Check for mate and stalemate
1361 // All legal moves have been searched and if there are
1362 // no legal moves, it must be mate or stalemate.
1363 // If one move was excluded return fail low score.
1365 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1367 // Step 20. Update tables
1368 // If the search is not aborted, update the transposition table,
1369 // history counters, and killer moves.
1370 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1373 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1374 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1375 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, margins[pos.side_to_move()]);
1377 // Update killers and history only for non capture moves that fails high
1378 if ( bestValue >= beta
1379 && !pos.move_is_capture_or_promotion(move))
1381 update_history(pos, move, depth, movesSearched, moveCount);
1382 update_killers(move, ss);
1385 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1391 // qsearch() is the quiescence search function, which is called by the main
1392 // search function when the remaining depth is zero (or, to be more precise,
1393 // less than ONE_PLY).
1395 template <NodeType PvNode>
1396 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1398 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1399 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1400 assert(PvNode || alpha == beta - 1);
1402 assert(ply > 0 && ply < PLY_MAX);
1403 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1408 Value bestValue, value, futilityValue, futilityBase;
1409 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1411 Value oldAlpha = alpha;
1413 ThreadsMgr.incrementNodeCounter(pos.thread());
1414 ss->bestMove = ss->currentMove = MOVE_NONE;
1416 // Check for an instant draw or maximum ply reached
1417 if (pos.is_draw() || ply >= PLY_MAX - 1)
1420 // Transposition table lookup. At PV nodes, we don't use the TT for
1421 // pruning, but only for move ordering.
1422 tte = TT.retrieve(pos.get_key());
1423 ttMove = (tte ? tte->move() : MOVE_NONE);
1425 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1427 ss->bestMove = ttMove; // Can be MOVE_NONE
1428 return value_from_tt(tte->value(), ply);
1431 isCheck = pos.is_check();
1433 // Evaluate the position statically
1436 bestValue = futilityBase = -VALUE_INFINITE;
1437 ss->eval = VALUE_NONE;
1438 deepChecks = enoughMaterial = false;
1444 assert(tte->static_value() != VALUE_NONE);
1446 margins[pos.side_to_move()] = tte->static_value_margin();
1447 bestValue = tte->static_value();
1450 bestValue = evaluate(pos, margins);
1452 ss->eval = bestValue;
1453 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1455 // Stand pat. Return immediately if static value is at least beta
1456 if (bestValue >= beta)
1459 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, margins[pos.side_to_move()]);
1464 if (PvNode && bestValue > alpha)
1467 // If we are near beta then try to get a cutoff pushing checks a bit further
1468 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1470 // Futility pruning parameters, not needed when in check
1471 futilityBase = bestValue + FutilityMarginQS + margins[pos.side_to_move()];
1472 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1475 // Initialize a MovePicker object for the current position, and prepare
1476 // to search the moves. Because the depth is <= 0 here, only captures,
1477 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1478 // and we are near beta) will be generated.
1479 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1482 // Loop through the moves until no moves remain or a beta cutoff occurs
1483 while ( alpha < beta
1484 && (move = mp.get_next_move()) != MOVE_NONE)
1486 assert(move_is_ok(move));
1488 moveIsCheck = pos.move_is_check(move, ci);
1496 && !move_is_promotion(move)
1497 && !pos.move_is_passed_pawn_push(move))
1499 futilityValue = futilityBase
1500 + pos.endgame_value_of_piece_on(move_to(move))
1501 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1503 if (futilityValue < alpha)
1505 if (futilityValue > bestValue)
1506 bestValue = futilityValue;
1511 // Detect blocking evasions that are candidate to be pruned
1512 evasionPrunable = isCheck
1513 && bestValue > value_mated_in(PLY_MAX)
1514 && !pos.move_is_capture(move)
1515 && pos.type_of_piece_on(move_from(move)) != KING
1516 && !pos.can_castle(pos.side_to_move());
1518 // Don't search moves with negative SEE values
1520 && (!isCheck || evasionPrunable)
1522 && !move_is_promotion(move)
1523 && pos.see_sign(move) < 0)
1526 // Update current move
1527 ss->currentMove = move;
1529 // Make and search the move
1530 pos.do_move(move, st, ci, moveIsCheck);
1531 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1532 pos.undo_move(move);
1534 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1537 if (value > bestValue)
1543 ss->bestMove = move;
1548 // All legal moves have been searched. A special case: If we're in check
1549 // and no legal moves were found, it is checkmate.
1550 if (isCheck && bestValue == -VALUE_INFINITE)
1551 return value_mated_in(ply);
1553 // Update transposition table
1554 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1555 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1556 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, margins[pos.side_to_move()]);
1558 // Update killers only for checking moves that fails high
1559 if ( bestValue >= beta
1560 && !pos.move_is_capture_or_promotion(ss->bestMove))
1561 update_killers(ss->bestMove, ss);
1563 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1569 // sp_search() is used to search from a split point. This function is called
1570 // by each thread working at the split point. It is similar to the normal
1571 // search() function, but simpler. Because we have already probed the hash
1572 // table, done a null move search, and searched the first move before
1573 // splitting, we don't have to repeat all this work in sp_search(). We
1574 // also don't need to store anything to the hash table here: This is taken
1575 // care of after we return from the split point.
1577 template <NodeType PvNode>
1578 void sp_search(SplitPoint* sp, int threadID) {
1580 assert(threadID >= 0 && threadID < ThreadsMgr.active_threads());
1581 assert(ThreadsMgr.active_threads() > 1);
1585 Depth ext, newDepth;
1587 Value futilityValueScaled; // NonPV specific
1588 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1590 value = -VALUE_INFINITE;
1592 Position pos(*sp->pos, threadID);
1594 SearchStack* ss = sp->sstack[threadID] + 1;
1595 isCheck = pos.is_check();
1597 // Step 10. Loop through moves
1598 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1599 lock_grab(&(sp->lock));
1601 while ( sp->bestValue < sp->beta
1602 && (move = sp->mp->get_next_move()) != MOVE_NONE
1603 && !ThreadsMgr.thread_should_stop(threadID))
1605 moveCount = ++sp->moveCount;
1606 lock_release(&(sp->lock));
1608 assert(move_is_ok(move));
1610 moveIsCheck = pos.move_is_check(move, ci);
1611 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1613 // Step 11. Decide the new search depth
1614 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1615 newDepth = sp->depth - ONE_PLY + ext;
1617 // Update current move
1618 ss->currentMove = move;
1620 // Step 12. Futility pruning (is omitted in PV nodes)
1622 && !captureOrPromotion
1625 && !move_is_castle(move))
1627 // Move count based pruning
1628 if ( moveCount >= futility_move_count(sp->depth)
1629 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1630 && sp->bestValue > value_mated_in(PLY_MAX))
1632 lock_grab(&(sp->lock));
1636 // Value based pruning
1637 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1638 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1639 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1641 if (futilityValueScaled < sp->beta)
1643 lock_grab(&(sp->lock));
1645 if (futilityValueScaled > sp->bestValue)
1646 sp->bestValue = futilityValueScaled;
1651 // Step 13. Make the move
1652 pos.do_move(move, st, ci, moveIsCheck);
1654 // Step 14. Reduced search
1655 // If the move fails high will be re-searched at full depth.
1656 bool doFullDepthSearch = true;
1658 if ( !captureOrPromotion
1660 && !move_is_castle(move)
1661 && !move_is_killer(move, ss))
1663 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1666 Value localAlpha = sp->alpha;
1667 Depth d = newDepth - ss->reduction;
1668 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, sp->ply+1)
1669 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1671 doFullDepthSearch = (value > localAlpha);
1674 // The move failed high, but if reduction is very big we could
1675 // face a false positive, retry with a less aggressive reduction,
1676 // if the move fails high again then go with full depth search.
1677 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1679 assert(newDepth - ONE_PLY >= ONE_PLY);
1681 ss->reduction = ONE_PLY;
1682 Value localAlpha = sp->alpha;
1683 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1684 doFullDepthSearch = (value > localAlpha);
1686 ss->reduction = DEPTH_ZERO; // Restore original reduction
1689 // Step 15. Full depth search
1690 if (doFullDepthSearch)
1692 Value localAlpha = sp->alpha;
1693 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, DEPTH_ZERO, sp->ply+1)
1694 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1696 // Step extra. pv search (only in PV nodes)
1697 // Search only for possible new PV nodes, if instead value >= beta then
1698 // parent node fails low with value <= alpha and tries another move.
1699 if (PvNode && value > localAlpha && value < sp->beta)
1700 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, DEPTH_ZERO, sp->ply+1)
1701 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1704 // Step 16. Undo move
1705 pos.undo_move(move);
1707 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1709 // Step 17. Check for new best move
1710 lock_grab(&(sp->lock));
1712 if (value > sp->bestValue && !ThreadsMgr.thread_should_stop(threadID))
1714 sp->bestValue = value;
1716 if (sp->bestValue > sp->alpha)
1718 if (!PvNode || value >= sp->beta)
1719 sp->stopRequest = true;
1721 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1724 sp->parentSstack->bestMove = ss->bestMove = move;
1729 /* Here we have the lock still grabbed */
1731 sp->slaves[threadID] = 0;
1733 lock_release(&(sp->lock));
1737 // connected_moves() tests whether two moves are 'connected' in the sense
1738 // that the first move somehow made the second move possible (for instance
1739 // if the moving piece is the same in both moves). The first move is assumed
1740 // to be the move that was made to reach the current position, while the
1741 // second move is assumed to be a move from the current position.
1743 bool connected_moves(const Position& pos, Move m1, Move m2) {
1745 Square f1, t1, f2, t2;
1748 assert(move_is_ok(m1));
1749 assert(move_is_ok(m2));
1751 if (m2 == MOVE_NONE)
1754 // Case 1: The moving piece is the same in both moves
1760 // Case 2: The destination square for m2 was vacated by m1
1766 // Case 3: Moving through the vacated square
1767 if ( piece_is_slider(pos.piece_on(f2))
1768 && bit_is_set(squares_between(f2, t2), f1))
1771 // Case 4: The destination square for m2 is defended by the moving piece in m1
1772 p = pos.piece_on(t1);
1773 if (bit_is_set(pos.attacks_from(p, t1), t2))
1776 // Case 5: Discovered check, checking piece is the piece moved in m1
1777 if ( piece_is_slider(p)
1778 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1779 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1781 // discovered_check_candidates() works also if the Position's side to
1782 // move is the opposite of the checking piece.
1783 Color them = opposite_color(pos.side_to_move());
1784 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1786 if (bit_is_set(dcCandidates, f2))
1793 // value_is_mate() checks if the given value is a mate one eventually
1794 // compensated for the ply.
1796 bool value_is_mate(Value value) {
1798 assert(abs(value) <= VALUE_INFINITE);
1800 return value <= value_mated_in(PLY_MAX)
1801 || value >= value_mate_in(PLY_MAX);
1805 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1806 // "plies to mate from the current ply". Non-mate scores are unchanged.
1807 // The function is called before storing a value to the transposition table.
1809 Value value_to_tt(Value v, int ply) {
1811 if (v >= value_mate_in(PLY_MAX))
1814 if (v <= value_mated_in(PLY_MAX))
1821 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1822 // the transposition table to a mate score corrected for the current ply.
1824 Value value_from_tt(Value v, int ply) {
1826 if (v >= value_mate_in(PLY_MAX))
1829 if (v <= value_mated_in(PLY_MAX))
1836 // move_is_killer() checks if the given move is among the killer moves
1838 bool move_is_killer(Move m, SearchStack* ss) {
1840 if (ss->killers[0] == m || ss->killers[1] == m)
1847 // extension() decides whether a move should be searched with normal depth,
1848 // or with extended depth. Certain classes of moves (checking moves, in
1849 // particular) are searched with bigger depth than ordinary moves and in
1850 // any case are marked as 'dangerous'. Note that also if a move is not
1851 // extended, as example because the corresponding UCI option is set to zero,
1852 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1853 template <NodeType PvNode>
1854 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1855 bool singleEvasion, bool mateThreat, bool* dangerous) {
1857 assert(m != MOVE_NONE);
1859 Depth result = DEPTH_ZERO;
1860 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1864 if (moveIsCheck && pos.see_sign(m) >= 0)
1865 result += CheckExtension[PvNode];
1868 result += SingleEvasionExtension[PvNode];
1871 result += MateThreatExtension[PvNode];
1874 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1876 Color c = pos.side_to_move();
1877 if (relative_rank(c, move_to(m)) == RANK_7)
1879 result += PawnPushTo7thExtension[PvNode];
1882 if (pos.pawn_is_passed(c, move_to(m)))
1884 result += PassedPawnExtension[PvNode];
1889 if ( captureOrPromotion
1890 && pos.type_of_piece_on(move_to(m)) != PAWN
1891 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1892 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1893 && !move_is_promotion(m)
1896 result += PawnEndgameExtension[PvNode];
1901 && captureOrPromotion
1902 && pos.type_of_piece_on(move_to(m)) != PAWN
1903 && pos.see_sign(m) >= 0)
1905 result += ONE_PLY / 2;
1909 return Min(result, ONE_PLY);
1913 // connected_threat() tests whether it is safe to forward prune a move or if
1914 // is somehow coonected to the threat move returned by null search.
1916 bool connected_threat(const Position& pos, Move m, Move threat) {
1918 assert(move_is_ok(m));
1919 assert(threat && move_is_ok(threat));
1920 assert(!pos.move_is_check(m));
1921 assert(!pos.move_is_capture_or_promotion(m));
1922 assert(!pos.move_is_passed_pawn_push(m));
1924 Square mfrom, mto, tfrom, tto;
1926 mfrom = move_from(m);
1928 tfrom = move_from(threat);
1929 tto = move_to(threat);
1931 // Case 1: Don't prune moves which move the threatened piece
1935 // Case 2: If the threatened piece has value less than or equal to the
1936 // value of the threatening piece, don't prune move which defend it.
1937 if ( pos.move_is_capture(threat)
1938 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1939 || pos.type_of_piece_on(tfrom) == KING)
1940 && pos.move_attacks_square(m, tto))
1943 // Case 3: If the moving piece in the threatened move is a slider, don't
1944 // prune safe moves which block its ray.
1945 if ( piece_is_slider(pos.piece_on(tfrom))
1946 && bit_is_set(squares_between(tfrom, tto), mto)
1947 && pos.see_sign(m) >= 0)
1954 // ok_to_use_TT() returns true if a transposition table score
1955 // can be used at a given point in search.
1957 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1959 Value v = value_from_tt(tte->value(), ply);
1961 return ( tte->depth() >= depth
1962 || v >= Max(value_mate_in(PLY_MAX), beta)
1963 || v < Min(value_mated_in(PLY_MAX), beta))
1965 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1966 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1970 // refine_eval() returns the transposition table score if
1971 // possible otherwise falls back on static position evaluation.
1973 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1977 Value v = value_from_tt(tte->value(), ply);
1979 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1980 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1987 // update_history() registers a good move that produced a beta-cutoff
1988 // in history and marks as failures all the other moves of that ply.
1990 void update_history(const Position& pos, Move move, Depth depth,
1991 Move movesSearched[], int moveCount) {
1995 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1997 for (int i = 0; i < moveCount - 1; i++)
1999 m = movesSearched[i];
2003 if (!pos.move_is_capture_or_promotion(m))
2004 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2009 // update_killers() add a good move that produced a beta-cutoff
2010 // among the killer moves of that ply.
2012 void update_killers(Move m, SearchStack* ss) {
2014 if (m == ss->killers[0])
2017 ss->killers[1] = ss->killers[0];
2022 // update_gains() updates the gains table of a non-capture move given
2023 // the static position evaluation before and after the move.
2025 void update_gains(const Position& pos, Move m, Value before, Value after) {
2028 && before != VALUE_NONE
2029 && after != VALUE_NONE
2030 && pos.captured_piece_type() == PIECE_TYPE_NONE
2031 && !move_is_special(m))
2032 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2036 // current_search_time() returns the number of milliseconds which have passed
2037 // since the beginning of the current search.
2039 int current_search_time() {
2041 return get_system_time() - SearchStartTime;
2045 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2047 std::string value_to_uci(Value v) {
2049 std::stringstream s;
2051 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
2052 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2054 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2059 // nps() computes the current nodes/second count.
2063 int t = current_search_time();
2064 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
2068 // poll() performs two different functions: It polls for user input, and it
2069 // looks at the time consumed so far and decides if it's time to abort the
2074 static int lastInfoTime;
2075 int t = current_search_time();
2080 // We are line oriented, don't read single chars
2081 std::string command;
2083 if (!std::getline(std::cin, command))
2086 if (command == "quit")
2089 PonderSearch = false;
2093 else if (command == "stop")
2096 PonderSearch = false;
2098 else if (command == "ponderhit")
2102 // Print search information
2106 else if (lastInfoTime > t)
2107 // HACK: Must be a new search where we searched less than
2108 // NodesBetweenPolls nodes during the first second of search.
2111 else if (t - lastInfoTime >= 1000)
2118 if (dbg_show_hit_rate)
2119 dbg_print_hit_rate();
2121 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
2122 << " time " << t << endl;
2125 // Should we stop the search?
2129 bool stillAtFirstMove = FirstRootMove
2130 && !AspirationFailLow
2131 && t > TimeMgr.available_time();
2133 bool noMoreTime = t > TimeMgr.maximum_time()
2134 || stillAtFirstMove;
2136 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2137 || (ExactMaxTime && t >= ExactMaxTime)
2138 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2143 // ponderhit() is called when the program is pondering (i.e. thinking while
2144 // it's the opponent's turn to move) in order to let the engine know that
2145 // it correctly predicted the opponent's move.
2149 int t = current_search_time();
2150 PonderSearch = false;
2152 bool stillAtFirstMove = FirstRootMove
2153 && !AspirationFailLow
2154 && t > TimeMgr.available_time();
2156 bool noMoreTime = t > TimeMgr.maximum_time()
2157 || stillAtFirstMove;
2159 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2164 // init_ss_array() does a fast reset of the first entries of a SearchStack
2165 // array and of all the excludedMove and skipNullMove entries.
2167 void init_ss_array(SearchStack* ss, int size) {
2169 for (int i = 0; i < size; i++, ss++)
2171 ss->excludedMove = MOVE_NONE;
2172 ss->skipNullMove = false;
2173 ss->reduction = DEPTH_ZERO;
2176 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2181 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2182 // while the program is pondering. The point is to work around a wrinkle in
2183 // the UCI protocol: When pondering, the engine is not allowed to give a
2184 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2185 // We simply wait here until one of these commands is sent, and return,
2186 // after which the bestmove and pondermove will be printed (in id_loop()).
2188 void wait_for_stop_or_ponderhit() {
2190 std::string command;
2194 if (!std::getline(std::cin, command))
2197 if (command == "quit")
2202 else if (command == "ponderhit" || command == "stop")
2208 // print_pv_info() prints to standard output and eventually to log file information on
2209 // the current PV line. It is called at each iteration or after a new pv is found.
2211 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2213 cout << "info depth " << Iteration
2214 << " score " << value_to_uci(value)
2215 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2216 << " time " << current_search_time()
2217 << " nodes " << ThreadsMgr.nodes_searched()
2221 for (Move* m = pv; *m != MOVE_NONE; m++)
2228 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2229 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2231 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2232 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2237 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2238 // the PV back into the TT. This makes sure the old PV moves are searched
2239 // first, even if the old TT entries have been overwritten.
2241 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2245 Position p(pos, pos.thread());
2249 for (int i = 0; pv[i] != MOVE_NONE; i++)
2251 tte = TT.retrieve(p.get_key());
2252 if (!tte || tte->move() != pv[i])
2254 v = (p.is_check() ? VALUE_NONE : evaluate(p, margins));
2255 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, margins[pos.side_to_move()]);
2257 p.do_move(pv[i], st);
2262 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2263 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2264 // allow to always have a ponder move even when we fail high at root and also a
2265 // long PV to print that is important for position analysis.
2267 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2271 Position p(pos, pos.thread());
2274 assert(bestMove != MOVE_NONE);
2277 p.do_move(pv[ply++], st);
2279 while ( (tte = TT.retrieve(p.get_key())) != NULL
2280 && tte->move() != MOVE_NONE
2281 && move_is_legal(p, tte->move())
2283 && (!p.is_draw() || ply < 2))
2285 pv[ply] = tte->move();
2286 p.do_move(pv[ply++], st);
2288 pv[ply] = MOVE_NONE;
2292 // init_thread() is the function which is called when a new thread is
2293 // launched. It simply calls the idle_loop() function with the supplied
2294 // threadID. There are two versions of this function; one for POSIX
2295 // threads and one for Windows threads.
2297 #if !defined(_MSC_VER)
2299 void* init_thread(void *threadID) {
2301 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2307 DWORD WINAPI init_thread(LPVOID threadID) {
2309 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2316 /// The ThreadsManager class
2318 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2319 // get_beta_counters() are getters/setters for the per thread
2320 // counters used to sort the moves at root.
2322 void ThreadsManager::resetNodeCounters() {
2324 for (int i = 0; i < MAX_THREADS; i++)
2325 threads[i].nodes = 0ULL;
2328 int64_t ThreadsManager::nodes_searched() const {
2330 int64_t result = 0ULL;
2331 for (int i = 0; i < ActiveThreads; i++)
2332 result += threads[i].nodes;
2338 // idle_loop() is where the threads are parked when they have no work to do.
2339 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2340 // object for which the current thread is the master.
2342 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2344 assert(threadID >= 0 && threadID < MAX_THREADS);
2348 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2349 // master should exit as last one.
2350 if (AllThreadsShouldExit)
2353 threads[threadID].state = THREAD_TERMINATED;
2357 // If we are not thinking, wait for a condition to be signaled
2358 // instead of wasting CPU time polling for work.
2359 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2362 assert(threadID != 0);
2363 threads[threadID].state = THREAD_SLEEPING;
2365 #if !defined(_MSC_VER)
2366 lock_grab(&WaitLock);
2367 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2368 pthread_cond_wait(&WaitCond, &WaitLock);
2369 lock_release(&WaitLock);
2371 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2375 // If thread has just woken up, mark it as available
2376 if (threads[threadID].state == THREAD_SLEEPING)
2377 threads[threadID].state = THREAD_AVAILABLE;
2379 // If this thread has been assigned work, launch a search
2380 if (threads[threadID].state == THREAD_WORKISWAITING)
2382 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2384 threads[threadID].state = THREAD_SEARCHING;
2386 if (threads[threadID].splitPoint->pvNode)
2387 sp_search<PV>(threads[threadID].splitPoint, threadID);
2389 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2391 assert(threads[threadID].state == THREAD_SEARCHING);
2393 threads[threadID].state = THREAD_AVAILABLE;
2396 // If this thread is the master of a split point and all slaves have
2397 // finished their work at this split point, return from the idle loop.
2399 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2401 if (i == ActiveThreads)
2403 // Because sp->slaves[] is reset under lock protection,
2404 // be sure sp->lock has been released before to return.
2405 lock_grab(&(sp->lock));
2406 lock_release(&(sp->lock));
2408 assert(threads[threadID].state == THREAD_AVAILABLE);
2410 threads[threadID].state = THREAD_SEARCHING;
2417 // init_threads() is called during startup. It launches all helper threads,
2418 // and initializes the split point stack and the global locks and condition
2421 void ThreadsManager::init_threads() {
2426 #if !defined(_MSC_VER)
2427 pthread_t pthread[1];
2430 // Initialize global locks
2432 lock_init(&WaitLock);
2434 #if !defined(_MSC_VER)
2435 pthread_cond_init(&WaitCond, NULL);
2437 for (i = 0; i < MAX_THREADS; i++)
2438 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2441 // Initialize splitPoints[] locks
2442 for (i = 0; i < MAX_THREADS; i++)
2443 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2444 lock_init(&(threads[i].splitPoints[j].lock));
2446 // Will be set just before program exits to properly end the threads
2447 AllThreadsShouldExit = false;
2449 // Threads will be put to sleep as soon as created
2450 AllThreadsShouldSleep = true;
2452 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2454 threads[0].state = THREAD_SEARCHING;
2455 for (i = 1; i < MAX_THREADS; i++)
2456 threads[i].state = THREAD_AVAILABLE;
2458 // Launch the helper threads
2459 for (i = 1; i < MAX_THREADS; i++)
2462 #if !defined(_MSC_VER)
2463 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2465 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2470 cout << "Failed to create thread number " << i << endl;
2471 Application::exit_with_failure();
2474 // Wait until the thread has finished launching and is gone to sleep
2475 while (threads[i].state != THREAD_SLEEPING) {}
2480 // exit_threads() is called when the program exits. It makes all the
2481 // helper threads exit cleanly.
2483 void ThreadsManager::exit_threads() {
2485 ActiveThreads = MAX_THREADS; // HACK
2486 AllThreadsShouldSleep = true; // HACK
2487 wake_sleeping_threads();
2489 // This makes the threads to exit idle_loop()
2490 AllThreadsShouldExit = true;
2492 // Wait for thread termination
2493 for (int i = 1; i < MAX_THREADS; i++)
2494 while (threads[i].state != THREAD_TERMINATED) {}
2496 // Now we can safely destroy the locks
2497 for (int i = 0; i < MAX_THREADS; i++)
2498 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2499 lock_destroy(&(threads[i].splitPoints[j].lock));
2501 lock_destroy(&WaitLock);
2502 lock_destroy(&MPLock);
2506 // thread_should_stop() checks whether the thread should stop its search.
2507 // This can happen if a beta cutoff has occurred in the thread's currently
2508 // active split point, or in some ancestor of the current split point.
2510 bool ThreadsManager::thread_should_stop(int threadID) const {
2512 assert(threadID >= 0 && threadID < ActiveThreads);
2516 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2521 // thread_is_available() checks whether the thread with threadID "slave" is
2522 // available to help the thread with threadID "master" at a split point. An
2523 // obvious requirement is that "slave" must be idle. With more than two
2524 // threads, this is not by itself sufficient: If "slave" is the master of
2525 // some active split point, it is only available as a slave to the other
2526 // threads which are busy searching the split point at the top of "slave"'s
2527 // split point stack (the "helpful master concept" in YBWC terminology).
2529 bool ThreadsManager::thread_is_available(int slave, int master) const {
2531 assert(slave >= 0 && slave < ActiveThreads);
2532 assert(master >= 0 && master < ActiveThreads);
2533 assert(ActiveThreads > 1);
2535 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2538 // Make a local copy to be sure doesn't change under our feet
2539 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2541 if (localActiveSplitPoints == 0)
2542 // No active split points means that the thread is available as
2543 // a slave for any other thread.
2546 if (ActiveThreads == 2)
2549 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2550 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2551 // could have been set to 0 by another thread leading to an out of bound access.
2552 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2559 // available_thread_exists() tries to find an idle thread which is available as
2560 // a slave for the thread with threadID "master".
2562 bool ThreadsManager::available_thread_exists(int master) const {
2564 assert(master >= 0 && master < ActiveThreads);
2565 assert(ActiveThreads > 1);
2567 for (int i = 0; i < ActiveThreads; i++)
2568 if (thread_is_available(i, master))
2575 // split() does the actual work of distributing the work at a node between
2576 // several available threads. If it does not succeed in splitting the
2577 // node (because no idle threads are available, or because we have no unused
2578 // split point objects), the function immediately returns. If splitting is
2579 // possible, a SplitPoint object is initialized with all the data that must be
2580 // copied to the helper threads and we tell our helper threads that they have
2581 // been assigned work. This will cause them to instantly leave their idle loops
2582 // and call sp_search(). When all threads have returned from sp_search() then
2585 template <bool Fake>
2586 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2587 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2588 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2590 assert(ply > 0 && ply < PLY_MAX);
2591 assert(*bestValue >= -VALUE_INFINITE);
2592 assert(*bestValue <= *alpha);
2593 assert(*alpha < beta);
2594 assert(beta <= VALUE_INFINITE);
2595 assert(depth > DEPTH_ZERO);
2596 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2597 assert(ActiveThreads > 1);
2599 int i, master = p.thread();
2600 Thread& masterThread = threads[master];
2604 // If no other thread is available to help us, or if we have too many
2605 // active split points, don't split.
2606 if ( !available_thread_exists(master)
2607 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2609 lock_release(&MPLock);
2613 // Pick the next available split point object from the split point stack
2614 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2616 // Initialize the split point object
2617 splitPoint.parent = masterThread.splitPoint;
2618 splitPoint.stopRequest = false;
2619 splitPoint.ply = ply;
2620 splitPoint.depth = depth;
2621 splitPoint.threatMove = threatMove;
2622 splitPoint.mateThreat = mateThreat;
2623 splitPoint.alpha = *alpha;
2624 splitPoint.beta = beta;
2625 splitPoint.pvNode = pvNode;
2626 splitPoint.bestValue = *bestValue;
2628 splitPoint.moveCount = *moveCount;
2629 splitPoint.pos = &p;
2630 splitPoint.parentSstack = ss;
2631 for (i = 0; i < ActiveThreads; i++)
2632 splitPoint.slaves[i] = 0;
2634 masterThread.splitPoint = &splitPoint;
2636 // If we are here it means we are not available
2637 assert(masterThread.state != THREAD_AVAILABLE);
2639 int workersCnt = 1; // At least the master is included
2641 // Allocate available threads setting state to THREAD_BOOKED
2642 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2643 if (thread_is_available(i, master))
2645 threads[i].state = THREAD_BOOKED;
2646 threads[i].splitPoint = &splitPoint;
2647 splitPoint.slaves[i] = 1;
2651 assert(Fake || workersCnt > 1);
2653 // We can release the lock because slave threads are already booked and master is not available
2654 lock_release(&MPLock);
2656 // Tell the threads that they have work to do. This will make them leave
2657 // their idle loop. But before copy search stack tail for each thread.
2658 for (i = 0; i < ActiveThreads; i++)
2659 if (i == master || splitPoint.slaves[i])
2661 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2663 assert(i == master || threads[i].state == THREAD_BOOKED);
2665 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2668 // Everything is set up. The master thread enters the idle loop, from
2669 // which it will instantly launch a search, because its state is
2670 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2671 // idle loop, which means that the main thread will return from the idle
2672 // loop when all threads have finished their work at this split point.
2673 idle_loop(master, &splitPoint);
2675 // We have returned from the idle loop, which means that all threads are
2676 // finished. Update alpha and bestValue, and return.
2679 *alpha = splitPoint.alpha;
2680 *bestValue = splitPoint.bestValue;
2681 masterThread.activeSplitPoints--;
2682 masterThread.splitPoint = splitPoint.parent;
2684 lock_release(&MPLock);
2688 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2689 // to start a new search from the root.
2691 void ThreadsManager::wake_sleeping_threads() {
2693 assert(AllThreadsShouldSleep);
2694 assert(ActiveThreads > 0);
2696 AllThreadsShouldSleep = false;
2698 if (ActiveThreads == 1)
2701 #if !defined(_MSC_VER)
2702 pthread_mutex_lock(&WaitLock);
2703 pthread_cond_broadcast(&WaitCond);
2704 pthread_mutex_unlock(&WaitLock);
2706 for (int i = 1; i < MAX_THREADS; i++)
2707 SetEvent(SitIdleEvent[i]);
2713 // put_threads_to_sleep() makes all the threads go to sleep just before
2714 // to leave think(), at the end of the search. Threads should have already
2715 // finished the job and should be idle.
2717 void ThreadsManager::put_threads_to_sleep() {
2719 assert(!AllThreadsShouldSleep);
2721 // This makes the threads to go to sleep
2722 AllThreadsShouldSleep = true;
2725 /// The RootMoveList class
2727 // RootMoveList c'tor
2729 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2731 SearchStack ss[PLY_MAX_PLUS_2];
2732 MoveStack mlist[MaxRootMoves];
2734 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2736 // Initialize search stack
2737 init_ss_array(ss, PLY_MAX_PLUS_2);
2738 ss[0].currentMove = ss[0].bestMove = MOVE_NONE;
2739 ss[0].eval = VALUE_NONE;
2741 // Generate all legal moves
2742 MoveStack* last = generate_moves(pos, mlist);
2744 // Add each move to the moves[] array
2745 for (MoveStack* cur = mlist; cur != last; cur++)
2747 bool includeMove = includeAllMoves;
2749 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2750 includeMove = (searchMoves[k] == cur->move);
2755 // Find a quick score for the move
2756 pos.do_move(cur->move, st);
2757 ss[0].currentMove = cur->move;
2758 moves[count].move = cur->move;
2759 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2760 moves[count].pv[0] = cur->move;
2761 moves[count].pv[1] = MOVE_NONE;
2762 pos.undo_move(cur->move);
2768 // Score root moves using the standard way used in main search, the moves
2769 // are scored according to the order in which are returned by MovePicker.
2771 void RootMoveList::score_moves(const Position& pos)
2775 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2777 while ((move = mp.get_next_move()) != MOVE_NONE)
2778 for (int i = 0; i < count; i++)
2779 if (moves[i].move == move)
2781 moves[i].mp_score = score--;
2786 // RootMoveList simple methods definitions
2788 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2790 moves[moveNum].nodes = nodes;
2791 moves[moveNum].cumulativeNodes += nodes;
2794 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2798 for (j = 0; pv[j] != MOVE_NONE; j++)
2799 moves[moveNum].pv[j] = pv[j];
2801 moves[moveNum].pv[j] = MOVE_NONE;
2805 // RootMoveList::sort() sorts the root move list at the beginning of a new
2808 void RootMoveList::sort() {
2810 sort_multipv(count - 1); // Sort all items
2814 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2815 // list by their scores and depths. It is used to order the different PVs
2816 // correctly in MultiPV mode.
2818 void RootMoveList::sort_multipv(int n) {
2822 for (i = 1; i <= n; i++)
2824 RootMove rm = moves[i];
2825 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2826 moves[j] = moves[j - 1];