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/>.
43 #include "ucioption.h"
49 //// Local definitions
55 enum NodeType { NonPV, PV };
57 // Set to true to force running with one thread.
58 // Used for debugging SMP code.
59 const bool FakeSplit = false;
61 // ThreadsManager class is used to handle all the threads related stuff in search,
62 // init, starting, parking and, the most important, launching a slave thread at a
63 // split point are what this class does. All the access to shared thread data is
64 // done through this class, so that we avoid using global variables instead.
66 class ThreadsManager {
67 /* As long as the single ThreadsManager object is defined as a global we don't
68 need to explicitly initialize to zero its data members because variables with
69 static storage duration are automatically set to zero before enter main()
75 int active_threads() const { return ActiveThreads; }
76 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
77 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
78 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
80 void resetNodeCounters();
81 void resetBetaCounters();
82 int64_t nodes_searched() const;
83 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
84 bool available_thread_exists(int master) const;
85 bool thread_is_available(int slave, int master) const;
86 bool thread_should_stop(int threadID) const;
87 void wake_sleeping_threads();
88 void put_threads_to_sleep();
89 void idle_loop(int threadID, SplitPoint* sp);
92 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
93 Depth depth, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
99 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
100 Thread threads[MAX_THREADS];
102 Lock MPLock, WaitLock;
104 #if !defined(_MSC_VER)
105 pthread_cond_t WaitCond;
107 HANDLE SitIdleEvent[MAX_THREADS];
113 // RootMove struct is used for moves at the root at the tree. For each
114 // root move, we store a score, a node count, and a PV (really a refutation
115 // in the case of moves which fail low).
119 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
121 // RootMove::operator<() is the comparison function used when
122 // sorting the moves. A move m1 is considered to be better
123 // than a move m2 if it has a higher score, or if the moves
124 // have equal score but m1 has the higher beta cut-off count.
125 bool operator<(const RootMove& m) const {
127 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
132 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
133 Move pv[PLY_MAX_PLUS_2];
137 // The RootMoveList class is essentially an array of RootMove objects, with
138 // a handful of methods for accessing the data in the individual moves.
143 RootMoveList(Position& pos, Move searchMoves[]);
145 int move_count() const { return count; }
146 Move get_move(int moveNum) const { return moves[moveNum].move; }
147 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
148 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
149 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
150 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
152 void set_move_nodes(int moveNum, int64_t nodes);
153 void set_beta_counters(int moveNum, int64_t our, int64_t their);
154 void set_move_pv(int moveNum, const Move pv[]);
156 void sort_multipv(int n);
159 static const int MaxRootMoves = 500;
160 RootMove moves[MaxRootMoves];
169 // Maximum depth for razoring
170 const Depth RazorDepth = 4 * OnePly;
172 // Dynamic razoring margin based on depth
173 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
175 // Step 8. Null move search with verification search
177 // Null move margin. A null move search will not be done if the static
178 // evaluation of the position is more than NullMoveMargin below beta.
179 const Value NullMoveMargin = Value(0x200);
181 // Maximum depth for use of dynamic threat detection when null move fails low
182 const Depth ThreatDepth = 5 * OnePly;
184 // Step 9. Internal iterative deepening
186 // Minimum depth for use of internal iterative deepening
187 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
189 // At Non-PV nodes we do an internal iterative deepening search
190 // when the static evaluation is bigger then beta - IIDMargin.
191 const Value IIDMargin = Value(0x100);
193 // Step 11. Decide the new search depth
195 // Extensions. Configurable UCI options
196 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
197 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
198 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
200 // Minimum depth for use of singular extension
201 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
203 // If the TT move is at least SingularExtensionMargin better then the
204 // remaining ones we will extend it.
205 const Value SingularExtensionMargin = Value(0x20);
207 // Step 12. Futility pruning
209 // Futility margin for quiescence search
210 const Value FutilityMarginQS = Value(0x80);
212 // Futility lookup tables (initialized at startup) and their getter functions
213 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
214 int FutilityMoveCountArray[32]; // [depth]
216 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
217 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
219 // Step 14. Reduced search
221 // Reduction lookup tables (initialized at startup) and their getter functions
222 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
224 template <NodeType PV>
225 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
227 // Common adjustments
229 // Search depth at iteration 1
230 const Depth InitialDepth = OnePly;
232 // Easy move margin. An easy move candidate must be at least this much
233 // better than the second best move.
234 const Value EasyMoveMargin = Value(0x200);
236 // Last seconds noise filtering (LSN)
237 const bool UseLSNFiltering = true;
238 const int LSNTime = 100; // In milliseconds
239 const Value LSNValue = value_from_centipawns(200);
240 bool loseOnTime = false;
248 // Scores and number of times the best move changed for each iteration
249 Value ValueByIteration[PLY_MAX_PLUS_2];
250 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
252 // Search window management
258 // Time managment variables
259 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
260 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
261 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
262 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
266 std::ofstream LogFile;
268 // Multi-threads related variables
269 Depth MinimumSplitDepth;
270 int MaxThreadsPerSplitPoint;
273 // Node counters, used only by thread[0] but try to keep in different cache
274 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
276 int NodesBetweenPolls = 30000;
283 Value id_loop(const Position& pos, Move searchMoves[]);
284 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
286 template <NodeType PvNode>
287 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
289 template <NodeType PvNode>
290 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
292 template <NodeType PvNode>
293 void sp_search(SplitPoint* sp, int threadID);
295 template <NodeType PvNode>
296 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
298 bool connected_moves(const Position& pos, Move m1, Move m2);
299 bool value_is_mate(Value value);
300 bool move_is_killer(Move m, SearchStack* ss);
301 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
302 bool connected_threat(const Position& pos, Move m, Move threat);
303 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
304 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
305 void update_killers(Move m, SearchStack* ss);
306 void update_gains(const Position& pos, Move move, Value before, Value after);
308 int current_search_time();
312 void wait_for_stop_or_ponderhit();
313 void init_ss_array(SearchStack* ss, int size);
314 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
316 #if !defined(_MSC_VER)
317 void *init_thread(void *threadID);
319 DWORD WINAPI init_thread(LPVOID threadID);
329 /// init_threads(), exit_threads() and nodes_searched() are helpers to
330 /// give accessibility to some TM methods from outside of current file.
332 void init_threads() { TM.init_threads(); }
333 void exit_threads() { TM.exit_threads(); }
334 int64_t nodes_searched() { return TM.nodes_searched(); }
337 /// init_search() is called during startup. It initializes various lookup tables
341 int d; // depth (OnePly == 2)
342 int hd; // half depth (OnePly == 1)
345 // Init reductions array
346 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
348 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
349 double nonPVRed = log(double(hd)) * log(double(mc)) / 1.5;
350 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
351 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
354 // Init futility margins array
355 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
356 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
358 // Init futility move count array
359 for (d = 0; d < 32; d++)
360 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
364 // SearchStack::init() initializes a search stack entry.
365 // Called at the beginning of search() when starting to examine a new node.
366 void SearchStack::init() {
368 currentMove = threatMove = bestMove = MOVE_NONE;
369 reduction = Depth(0);
373 // SearchStack::initKillers() initializes killers for a search stack entry
374 void SearchStack::initKillers() {
376 mateKiller = MOVE_NONE;
377 for (int i = 0; i < KILLER_MAX; i++)
378 killers[i] = MOVE_NONE;
382 /// perft() is our utility to verify move generation is bug free. All the legal
383 /// moves up to given depth are generated and counted and the sum returned.
385 int perft(Position& pos, Depth depth)
390 MovePicker mp(pos, MOVE_NONE, depth, H);
392 // If we are at the last ply we don't need to do and undo
393 // the moves, just to count them.
394 if (depth <= OnePly) // Replace with '<' to test also qsearch
396 while (mp.get_next_move()) sum++;
400 // Loop through all legal moves
402 while ((move = mp.get_next_move()) != MOVE_NONE)
404 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
405 sum += perft(pos, depth - OnePly);
412 /// think() is the external interface to Stockfish's search, and is called when
413 /// the program receives the UCI 'go' command. It initializes various
414 /// search-related global variables, and calls root_search(). It returns false
415 /// when a quit command is received during the search.
417 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
418 int time[], int increment[], int movesToGo, int maxDepth,
419 int maxNodes, int maxTime, Move searchMoves[]) {
421 // Initialize global search variables
422 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
423 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
425 TM.resetNodeCounters();
426 SearchStartTime = get_system_time();
427 ExactMaxTime = maxTime;
430 InfiniteSearch = infinite;
431 PonderSearch = ponder;
432 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
434 // Look for a book move, only during games, not tests
435 if (UseTimeManagement && get_option_value_bool("OwnBook"))
437 if (get_option_value_string("Book File") != OpeningBook.file_name())
438 OpeningBook.open(get_option_value_string("Book File"));
440 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
441 if (bookMove != MOVE_NONE)
444 wait_for_stop_or_ponderhit();
446 cout << "bestmove " << bookMove << endl;
451 // Reset loseOnTime flag at the beginning of a new game
452 if (button_was_pressed("New Game"))
455 // Read UCI option values
456 TT.set_size(get_option_value_int("Hash"));
457 if (button_was_pressed("Clear Hash"))
460 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
461 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
462 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
463 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
464 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
465 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
466 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
467 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
468 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
469 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
470 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
471 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
473 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
474 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
475 MultiPV = get_option_value_int("MultiPV");
476 Chess960 = get_option_value_bool("UCI_Chess960");
477 UseLogFile = get_option_value_bool("Use Search Log");
480 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
482 read_weights(pos.side_to_move());
484 // Set the number of active threads
485 int newActiveThreads = get_option_value_int("Threads");
486 if (newActiveThreads != TM.active_threads())
488 TM.set_active_threads(newActiveThreads);
489 init_eval(TM.active_threads());
492 // Wake up sleeping threads
493 TM.wake_sleeping_threads();
496 int myTime = time[side_to_move];
497 int myIncrement = increment[side_to_move];
498 if (UseTimeManagement)
500 if (!movesToGo) // Sudden death time control
504 MaxSearchTime = myTime / 30 + myIncrement;
505 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
507 else // Blitz game without increment
509 MaxSearchTime = myTime / 30;
510 AbsoluteMaxSearchTime = myTime / 8;
513 else // (x moves) / (y minutes)
517 MaxSearchTime = myTime / 2;
518 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
522 MaxSearchTime = myTime / Min(movesToGo, 20);
523 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
527 if (get_option_value_bool("Ponder"))
529 MaxSearchTime += MaxSearchTime / 4;
530 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
534 // Set best NodesBetweenPolls interval to avoid lagging under
535 // heavy time pressure.
537 NodesBetweenPolls = Min(MaxNodes, 30000);
538 else if (myTime && myTime < 1000)
539 NodesBetweenPolls = 1000;
540 else if (myTime && myTime < 5000)
541 NodesBetweenPolls = 5000;
543 NodesBetweenPolls = 30000;
545 // Write search information to log file
547 LogFile << "Searching: " << pos.to_fen() << endl
548 << "infinite: " << infinite
549 << " ponder: " << ponder
550 << " time: " << myTime
551 << " increment: " << myIncrement
552 << " moves to go: " << movesToGo << endl;
554 // LSN filtering. Used only for developing purposes, disabled by default
558 // Step 2. If after last move we decided to lose on time, do it now!
559 while (SearchStartTime + myTime + 1000 > get_system_time())
563 // We're ready to start thinking. Call the iterative deepening loop function
564 Value v = id_loop(pos, searchMoves);
568 // Step 1. If this is sudden death game and our position is hopeless,
569 // decide to lose on time.
570 if ( !loseOnTime // If we already lost on time, go to step 3.
580 // Step 3. Now after stepping over the time limit, reset flag for next match.
588 TM.put_threads_to_sleep();
596 // id_loop() is the main iterative deepening loop. It calls root_search
597 // repeatedly with increasing depth until the allocated thinking time has
598 // been consumed, the user stops the search, or the maximum search depth is
601 Value id_loop(const Position& pos, Move searchMoves[]) {
603 Position p(pos, pos.thread());
604 SearchStack ss[PLY_MAX_PLUS_2];
605 Move pv[PLY_MAX_PLUS_2];
606 Move EasyMove = MOVE_NONE;
607 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
609 // Moves to search are verified, copied, scored and sorted
610 RootMoveList rml(p, searchMoves);
612 // Handle special case of searching on a mate/stale position
613 if (rml.move_count() == 0)
616 wait_for_stop_or_ponderhit();
618 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
621 // Print RootMoveList startup scoring to the standard output,
622 // so to output information also for iteration 1.
623 cout << "info depth " << 1
624 << "\ninfo depth " << 1
625 << " score " << value_to_string(rml.get_move_score(0))
626 << " time " << current_search_time()
627 << " nodes " << TM.nodes_searched()
629 << " pv " << rml.get_move(0) << "\n";
634 init_ss_array(ss, PLY_MAX_PLUS_2);
635 pv[0] = pv[1] = MOVE_NONE;
636 ValueByIteration[1] = rml.get_move_score(0);
639 // Is one move significantly better than others after initial scoring ?
640 if ( rml.move_count() == 1
641 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
642 EasyMove = rml.get_move(0);
644 // Iterative deepening loop
645 while (Iteration < PLY_MAX)
647 // Initialize iteration
649 BestMoveChangesByIteration[Iteration] = 0;
651 cout << "info depth " << Iteration << endl;
653 // Calculate dynamic aspiration window based on previous iterations
654 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
656 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
657 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
659 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
660 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
662 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
663 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
666 // Search to the current depth, rml is updated and sorted, alpha and beta could change
667 value = root_search(p, ss, pv, rml, &alpha, &beta);
669 // Write PV to transposition table, in case the relevant entries have
670 // been overwritten during the search.
674 break; // Value cannot be trusted. Break out immediately!
676 //Save info about search result
677 ValueByIteration[Iteration] = value;
679 // Drop the easy move if differs from the new best move
680 if (pv[0] != EasyMove)
681 EasyMove = MOVE_NONE;
683 if (UseTimeManagement)
686 bool stopSearch = false;
688 // Stop search early if there is only a single legal move,
689 // we search up to Iteration 6 anyway to get a proper score.
690 if (Iteration >= 6 && rml.move_count() == 1)
693 // Stop search early when the last two iterations returned a mate score
695 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
696 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
699 // Stop search early if one move seems to be much better than the others
700 int64_t nodes = TM.nodes_searched();
703 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
704 && current_search_time() > MaxSearchTime / 16)
705 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
706 && current_search_time() > MaxSearchTime / 32)))
709 // Add some extra time if the best move has changed during the last two iterations
710 if (Iteration > 5 && Iteration <= 50)
711 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
712 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
714 // Stop search if most of MaxSearchTime is consumed at the end of the
715 // iteration. We probably don't have enough time to search the first
716 // move at the next iteration anyway.
717 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
723 StopOnPonderhit = true;
729 if (MaxDepth && Iteration >= MaxDepth)
733 // If we are pondering or in infinite search, we shouldn't print the
734 // best move before we are told to do so.
735 if (!AbortSearch && (PonderSearch || InfiniteSearch))
736 wait_for_stop_or_ponderhit();
738 // Print final search statistics
739 cout << "info nodes " << TM.nodes_searched()
741 << " time " << current_search_time() << endl;
743 // Print the best move and the ponder move to the standard output
744 if (pv[0] == MOVE_NONE)
746 pv[0] = rml.get_move(0);
750 assert(pv[0] != MOVE_NONE);
752 cout << "bestmove " << pv[0];
754 if (pv[1] != MOVE_NONE)
755 cout << " ponder " << pv[1];
762 dbg_print_mean(LogFile);
764 if (dbg_show_hit_rate)
765 dbg_print_hit_rate(LogFile);
767 LogFile << "\nNodes: " << TM.nodes_searched()
768 << "\nNodes/second: " << nps()
769 << "\nBest move: " << move_to_san(p, pv[0]);
772 p.do_move(pv[0], st);
773 LogFile << "\nPonder move: "
774 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
777 return rml.get_move_score(0);
781 // root_search() is the function which searches the root node. It is
782 // similar to search_pv except that it uses a different move ordering
783 // scheme, prints some information to the standard output and handles
784 // the fail low/high loops.
786 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
793 Depth depth, ext, newDepth;
794 Value value, alpha, beta;
795 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
796 int researchCountFH, researchCountFL;
798 researchCountFH = researchCountFL = 0;
801 isCheck = pos.is_check();
803 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
804 // Step 2. Check for aborted search (omitted at root)
805 // Step 3. Mate distance pruning (omitted at root)
806 // Step 4. Transposition table lookup (omitted at root)
808 // Step 5. Evaluate the position statically
809 // At root we do this only to get reference value for child nodes
811 ss->eval = evaluate(pos, ei);
813 // Step 6. Razoring (omitted at root)
814 // Step 7. Static null move pruning (omitted at root)
815 // Step 8. Null move search with verification search (omitted at root)
816 // Step 9. Internal iterative deepening (omitted at root)
818 // Step extra. Fail low loop
819 // We start with small aspiration window and in case of fail low, we research
820 // with bigger window until we are not failing low anymore.
823 // Sort the moves before to (re)search
826 // Step 10. Loop through all moves in the root move list
827 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
829 // This is used by time management
830 FirstRootMove = (i == 0);
832 // Save the current node count before the move is searched
833 nodes = TM.nodes_searched();
835 // Reset beta cut-off counters
836 TM.resetBetaCounters();
838 // Pick the next root move, and print the move and the move number to
839 // the standard output.
840 move = ss->currentMove = rml.get_move(i);
842 if (current_search_time() >= 1000)
843 cout << "info currmove " << move
844 << " currmovenumber " << i + 1 << endl;
846 moveIsCheck = pos.move_is_check(move);
847 captureOrPromotion = pos.move_is_capture_or_promotion(move);
849 // Step 11. Decide the new search depth
850 depth = (Iteration - 2) * OnePly + InitialDepth;
851 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
852 newDepth = depth + ext;
854 // Step 12. Futility pruning (omitted at root)
856 // Step extra. Fail high loop
857 // If move fails high, we research with bigger window until we are not failing
859 value = - VALUE_INFINITE;
863 // Step 13. Make the move
864 pos.do_move(move, st, ci, moveIsCheck);
866 // Step extra. pv search
867 // We do pv search for first moves (i < MultiPV)
868 // and for fail high research (value > alpha)
869 if (i < MultiPV || value > alpha)
871 // Aspiration window is disabled in multi-pv case
873 alpha = -VALUE_INFINITE;
875 // Full depth PV search, done on first move or after a fail high
876 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
880 // Step 14. Reduced search
881 // if the move fails high will be re-searched at full depth
882 bool doFullDepthSearch = true;
884 if ( depth >= 3 * OnePly
886 && !captureOrPromotion
887 && !move_is_castle(move))
889 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
892 assert(newDepth-ss->reduction >= OnePly);
894 // Reduced depth non-pv search using alpha as upperbound
895 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
896 doFullDepthSearch = (value > alpha);
899 // The move failed high, but if reduction is very big we could
900 // face a false positive, retry with a less aggressive reduction,
901 // if the move fails high again then go with full depth search.
902 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
904 assert(newDepth - OnePly >= OnePly);
906 ss->reduction = OnePly;
907 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
908 doFullDepthSearch = (value > alpha);
910 ss->reduction = Depth(0); // Restore original reduction
913 // Step 15. Full depth search
914 if (doFullDepthSearch)
916 // Full depth non-pv search using alpha as upperbound
917 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
919 // If we are above alpha then research at same depth but as PV
920 // to get a correct score or eventually a fail high above beta.
922 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
926 // Step 16. Undo move
929 // Can we exit fail high loop ?
930 if (AbortSearch || value < beta)
933 // We are failing high and going to do a research. It's important to update
934 // the score before research in case we run out of time while researching.
935 rml.set_move_score(i, value);
937 TT.extract_pv(pos, move, pv, PLY_MAX);
938 rml.set_move_pv(i, pv);
940 // Print information to the standard output
941 print_pv_info(pos, pv, alpha, beta, value);
943 // Prepare for a research after a fail high, each time with a wider window
944 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
947 } // End of fail high loop
949 // Finished searching the move. If AbortSearch is true, the search
950 // was aborted because the user interrupted the search or because we
951 // ran out of time. In this case, the return value of the search cannot
952 // be trusted, and we break out of the loop without updating the best
957 // Remember beta-cutoff and searched nodes counts for this move. The
958 // info is used to sort the root moves for the next iteration.
960 TM.get_beta_counters(pos.side_to_move(), our, their);
961 rml.set_beta_counters(i, our, their);
962 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
964 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
965 assert(value < beta);
967 // Step 17. Check for new best move
968 if (value <= alpha && i >= MultiPV)
969 rml.set_move_score(i, -VALUE_INFINITE);
972 // PV move or new best move!
975 rml.set_move_score(i, value);
977 TT.extract_pv(pos, move, pv, PLY_MAX);
978 rml.set_move_pv(i, pv);
982 // We record how often the best move has been changed in each
983 // iteration. This information is used for time managment: When
984 // the best move changes frequently, we allocate some more time.
986 BestMoveChangesByIteration[Iteration]++;
988 // Print information to the standard output
989 print_pv_info(pos, pv, alpha, beta, value);
991 // Raise alpha to setup proper non-pv search upper bound
998 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1000 cout << "info multipv " << j + 1
1001 << " score " << value_to_string(rml.get_move_score(j))
1002 << " depth " << (j <= i ? Iteration : Iteration - 1)
1003 << " time " << current_search_time()
1004 << " nodes " << TM.nodes_searched()
1008 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1009 cout << rml.get_move_pv(j, k) << " ";
1013 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1015 } // PV move or new best move
1017 assert(alpha >= *alphaPtr);
1019 AspirationFailLow = (alpha == *alphaPtr);
1021 if (AspirationFailLow && StopOnPonderhit)
1022 StopOnPonderhit = false;
1025 // Can we exit fail low loop ?
1026 if (AbortSearch || !AspirationFailLow)
1029 // Prepare for a research after a fail low, each time with a wider window
1030 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1035 // Sort the moves before to return
1042 // search<>() is the main search function for both PV and non-PV nodes
1044 template <NodeType PvNode>
1045 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1047 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1048 assert(beta > alpha && beta <= VALUE_INFINITE);
1049 assert(PvNode || alpha == beta - 1);
1050 assert(ply > 0 && ply < PLY_MAX);
1051 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1053 Move movesSearched[256];
1058 Move ttMove, move, excludedMove;
1059 Depth ext, newDepth;
1060 Value bestValue, value, oldAlpha;
1061 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1062 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
1063 bool mateThreat = false;
1065 int threadID = pos.thread();
1066 refinedValue = bestValue = value = -VALUE_INFINITE;
1069 // Step 1. Initialize node and poll. Polling can abort search
1070 TM.incrementNodeCounter(threadID);
1072 (ss+2)->initKillers();
1074 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1080 // Step 2. Check for aborted search and immediate draw
1081 if (AbortSearch || TM.thread_should_stop(threadID))
1084 if (pos.is_draw() || ply >= PLY_MAX - 1)
1087 // Step 3. Mate distance pruning
1088 alpha = Max(value_mated_in(ply), alpha);
1089 beta = Min(value_mate_in(ply+1), beta);
1093 // Step 4. Transposition table lookup
1095 // We don't want the score of a partial search to overwrite a previous full search
1096 // TT value, so we use a different position key in case of an excluded move exists.
1097 excludedMove = ss->excludedMove;
1098 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1100 tte = TT.retrieve(posKey);
1101 ttMove = (tte ? tte->move() : MOVE_NONE);
1103 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1104 // This is to avoid problems in the following areas:
1106 // * Repetition draw detection
1107 // * Fifty move rule detection
1108 // * Searching for a mate
1109 // * Printing of full PV line
1111 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1113 // Refresh tte entry to avoid aging
1114 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1116 ss->currentMove = ttMove; // Can be MOVE_NONE
1117 return value_from_tt(tte->value(), ply);
1120 // Step 5. Evaluate the position statically
1121 // At PV nodes we do this only to update gain statistics
1122 isCheck = pos.is_check();
1125 if (tte && tte->static_value() != VALUE_NONE)
1127 ss->eval = tte->static_value();
1128 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1131 ss->eval = evaluate(pos, ei);
1133 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1134 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1137 // Step 6. Razoring (is omitted in PV nodes)
1139 && depth < RazorDepth
1141 && refinedValue < beta - razor_margin(depth)
1142 && ttMove == MOVE_NONE
1143 && (ss-1)->currentMove != MOVE_NULL
1144 && !value_is_mate(beta)
1145 && !pos.has_pawn_on_7th(pos.side_to_move()))
1147 // Pass ss->eval to qsearch() and avoid an evaluate call
1148 if (!tte || tte->static_value() == VALUE_NONE)
1149 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1151 Value rbeta = beta - razor_margin(depth);
1152 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1154 // Logically we should return (v + razor_margin(depth)), but
1155 // surprisingly this did slightly weaker in tests.
1159 // Step 7. Static null move pruning (is omitted in PV nodes)
1160 // We're betting that the opponent doesn't have a move that will reduce
1161 // the score by more than futility_margin(depth) if we do a null move.
1163 && !ss->skipNullMove
1164 && depth < RazorDepth
1165 && refinedValue >= beta + futility_margin(depth, 0)
1167 && !value_is_mate(beta)
1168 && pos.non_pawn_material(pos.side_to_move()))
1169 return refinedValue - futility_margin(depth, 0);
1171 // Step 8. Null move search with verification search (is omitted in PV nodes)
1172 // When we jump directly to qsearch() we do a null move only if static value is
1173 // at least beta. Otherwise we do a null move if static value is not more than
1174 // NullMoveMargin under beta.
1176 && !ss->skipNullMove
1178 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1180 && !value_is_mate(beta)
1181 && pos.non_pawn_material(pos.side_to_move()))
1183 ss->currentMove = MOVE_NULL;
1185 // Null move dynamic reduction based on depth
1186 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1188 // Null move dynamic reduction based on value
1189 if (refinedValue - beta > PawnValueMidgame)
1192 pos.do_null_move(st);
1193 (ss+1)->skipNullMove = true;
1195 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1196 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1197 (ss+1)->skipNullMove = false;
1198 pos.undo_null_move();
1200 if (nullValue >= beta)
1202 // Do not return unproven mate scores
1203 if (nullValue >= value_mate_in(PLY_MAX))
1206 if (depth < 6 * OnePly)
1209 // Do verification search at high depths
1210 ss->skipNullMove = true;
1211 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1212 ss->skipNullMove = false;
1219 // The null move failed low, which means that we may be faced with
1220 // some kind of threat. If the previous move was reduced, check if
1221 // the move that refuted the null move was somehow connected to the
1222 // move which was reduced. If a connection is found, return a fail
1223 // low score (which will cause the reduced move to fail high in the
1224 // parent node, which will trigger a re-search with full depth).
1225 if (nullValue == value_mated_in(ply + 2))
1228 ss->threatMove = (ss+1)->currentMove;
1229 if ( depth < ThreatDepth
1230 && (ss-1)->reduction
1231 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1236 // Step 9. Internal iterative deepening
1237 if ( depth >= IIDDepth[PvNode]
1238 && ttMove == MOVE_NONE
1239 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1241 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1243 ss->skipNullMove = true;
1244 search<PvNode>(pos, ss, alpha, beta, d, ply);
1245 ss->skipNullMove = false;
1247 ttMove = ss->bestMove;
1248 tte = TT.retrieve(posKey);
1251 // Expensive mate threat detection (only for PV nodes)
1253 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1255 // Initialize a MovePicker object for the current position
1256 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1258 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1259 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1260 && tte && tte->move()
1261 && !excludedMove // Do not allow recursive singular extension search
1262 && is_lower_bound(tte->type())
1263 && tte->depth() >= depth - 3 * OnePly;
1265 // Step 10. Loop through moves
1266 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1267 while ( bestValue < beta
1268 && (move = mp.get_next_move()) != MOVE_NONE
1269 && !TM.thread_should_stop(threadID))
1271 assert(move_is_ok(move));
1273 if (move == excludedMove)
1276 moveIsCheck = pos.move_is_check(move, ci);
1277 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1279 // Step 11. Decide the new search depth
1280 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1282 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1283 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1284 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1285 // lower then ttValue minus a margin then we extend ttMove.
1286 if ( singularExtensionNode
1287 && move == tte->move()
1290 Value ttValue = value_from_tt(tte->value(), ply);
1292 if (abs(ttValue) < VALUE_KNOWN_WIN)
1294 Value b = ttValue - SingularExtensionMargin;
1295 ss->excludedMove = move;
1296 ss->skipNullMove = true;
1297 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1298 ss->skipNullMove = false;
1299 ss->excludedMove = MOVE_NONE;
1305 newDepth = depth - OnePly + ext;
1307 // Update current move (this must be done after singular extension search)
1308 movesSearched[moveCount++] = ss->currentMove = move;
1310 // Step 12. Futility pruning (is omitted in PV nodes)
1312 && !captureOrPromotion
1316 && !move_is_castle(move))
1318 // Move count based pruning
1319 if ( moveCount >= futility_move_count(depth)
1320 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1321 && bestValue > value_mated_in(PLY_MAX))
1324 // Value based pruning
1325 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1326 // but fixing this made program slightly weaker.
1327 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1328 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1329 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1331 if (futilityValueScaled < beta)
1333 if (futilityValueScaled > bestValue)
1334 bestValue = futilityValueScaled;
1339 // Step 13. Make the move
1340 pos.do_move(move, st, ci, moveIsCheck);
1342 // Step extra. pv search (only in PV nodes)
1343 // The first move in list is the expected PV
1344 if (PvNode && moveCount == 1)
1345 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1346 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1349 // Step 14. Reduced depth search
1350 // If the move fails high will be re-searched at full depth.
1351 bool doFullDepthSearch = true;
1353 if ( depth >= 3 * OnePly
1354 && !captureOrPromotion
1356 && !move_is_castle(move)
1357 && !move_is_killer(move, ss))
1359 ss->reduction = reduction<PvNode>(depth, moveCount);
1362 Depth d = newDepth - ss->reduction;
1363 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1364 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1366 doFullDepthSearch = (value > alpha);
1369 // The move failed high, but if reduction is very big we could
1370 // face a false positive, retry with a less aggressive reduction,
1371 // if the move fails high again then go with full depth search.
1372 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1374 assert(newDepth - OnePly >= OnePly);
1376 ss->reduction = OnePly;
1377 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1378 doFullDepthSearch = (value > alpha);
1380 ss->reduction = Depth(0); // Restore original reduction
1383 // Step 15. Full depth search
1384 if (doFullDepthSearch)
1386 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1387 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1389 // Step extra. pv search (only in PV nodes)
1390 // Search only for possible new PV nodes, if instead value >= beta then
1391 // parent node fails low with value <= alpha and tries another move.
1392 if (PvNode && value > alpha && value < beta)
1393 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1394 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1398 // Step 16. Undo move
1399 pos.undo_move(move);
1401 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1403 // Step 17. Check for new best move
1404 if (value > bestValue)
1409 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1412 if (value == value_mate_in(ply + 1))
1413 ss->mateKiller = move;
1415 ss->bestMove = move;
1419 // Step 18. Check for split
1420 if ( depth >= MinimumSplitDepth
1421 && TM.active_threads() > 1
1423 && TM.available_thread_exists(threadID)
1425 && !TM.thread_should_stop(threadID)
1427 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1428 mateThreat, &moveCount, &mp, PvNode);
1431 // Step 19. Check for mate and stalemate
1432 // All legal moves have been searched and if there are
1433 // no legal moves, it must be mate or stalemate.
1434 // If one move was excluded return fail low score.
1436 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1438 // Step 20. Update tables
1439 // If the search is not aborted, update the transposition table,
1440 // history counters, and killer moves.
1441 if (AbortSearch || TM.thread_should_stop(threadID))
1444 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1445 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1446 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1448 // Update killers and history only for non capture moves that fails high
1449 if (bestValue >= beta)
1451 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1452 if (!pos.move_is_capture_or_promotion(move))
1454 update_history(pos, move, depth, movesSearched, moveCount);
1455 update_killers(move, ss);
1459 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1465 // qsearch() is the quiescence search function, which is called by the main
1466 // search function when the remaining depth is zero (or, to be more precise,
1467 // less than OnePly).
1469 template <NodeType PvNode>
1470 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1472 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1473 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1474 assert(PvNode || alpha == beta - 1);
1476 assert(ply > 0 && ply < PLY_MAX);
1477 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1482 Value bestValue, value, futilityValue, futilityBase;
1483 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1485 Value oldAlpha = alpha;
1487 TM.incrementNodeCounter(pos.thread());
1488 ss->bestMove = ss->currentMove = MOVE_NONE;
1489 ss->eval = VALUE_NONE;
1491 // Check for an instant draw or maximum ply reached
1492 if (pos.is_draw() || ply >= PLY_MAX - 1)
1495 // Transposition table lookup. At PV nodes, we don't use the TT for
1496 // pruning, but only for move ordering.
1497 tte = TT.retrieve(pos.get_key());
1498 ttMove = (tte ? tte->move() : MOVE_NONE);
1500 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1502 ss->currentMove = ttMove; // Can be MOVE_NONE
1503 return value_from_tt(tte->value(), ply);
1506 isCheck = pos.is_check();
1508 // Evaluate the position statically
1511 bestValue = futilityBase = -VALUE_INFINITE;
1512 deepChecks = enoughMaterial = false;
1516 if (tte && tte->static_value() != VALUE_NONE)
1518 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1519 bestValue = tte->static_value();
1522 bestValue = evaluate(pos, ei);
1524 ss->eval = bestValue;
1525 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1527 // Stand pat. Return immediately if static value is at least beta
1528 if (bestValue >= beta)
1531 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1536 if (PvNode && bestValue > alpha)
1539 // If we are near beta then try to get a cutoff pushing checks a bit further
1540 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1542 // Futility pruning parameters, not needed when in check
1543 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1544 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1547 // Initialize a MovePicker object for the current position, and prepare
1548 // to search the moves. Because the depth is <= 0 here, only captures,
1549 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1550 // and we are near beta) will be generated.
1551 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1554 // Loop through the moves until no moves remain or a beta cutoff occurs
1555 while ( alpha < beta
1556 && (move = mp.get_next_move()) != MOVE_NONE)
1558 assert(move_is_ok(move));
1560 moveIsCheck = pos.move_is_check(move, ci);
1568 && !move_is_promotion(move)
1569 && !pos.move_is_passed_pawn_push(move))
1571 futilityValue = futilityBase
1572 + pos.endgame_value_of_piece_on(move_to(move))
1573 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1575 if (futilityValue < alpha)
1577 if (futilityValue > bestValue)
1578 bestValue = futilityValue;
1583 // Detect blocking evasions that are candidate to be pruned
1584 evasionPrunable = isCheck
1585 && bestValue > value_mated_in(PLY_MAX)
1586 && !pos.move_is_capture(move)
1587 && pos.type_of_piece_on(move_from(move)) != KING
1588 && !pos.can_castle(pos.side_to_move());
1590 // Don't search moves with negative SEE values
1592 && (!isCheck || evasionPrunable)
1594 && !move_is_promotion(move)
1595 && pos.see_sign(move) < 0)
1598 // Update current move
1599 ss->currentMove = move;
1601 // Make and search the move
1602 pos.do_move(move, st, ci, moveIsCheck);
1603 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1604 pos.undo_move(move);
1606 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1609 if (value > bestValue)
1615 ss->bestMove = move;
1620 // All legal moves have been searched. A special case: If we're in check
1621 // and no legal moves were found, it is checkmate.
1622 if (isCheck && bestValue == -VALUE_INFINITE)
1623 return value_mated_in(ply);
1625 // Update transposition table
1626 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1627 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1628 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1630 // Update killers only for checking moves that fails high
1631 if ( bestValue >= beta
1632 && !pos.move_is_capture_or_promotion(ss->bestMove))
1633 update_killers(ss->bestMove, ss);
1635 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1641 // sp_search() is used to search from a split point. This function is called
1642 // by each thread working at the split point. It is similar to the normal
1643 // search() function, but simpler. Because we have already probed the hash
1644 // table, done a null move search, and searched the first move before
1645 // splitting, we don't have to repeat all this work in sp_search(). We
1646 // also don't need to store anything to the hash table here: This is taken
1647 // care of after we return from the split point.
1649 template <NodeType PvNode>
1650 void sp_search(SplitPoint* sp, int threadID) {
1652 assert(threadID >= 0 && threadID < TM.active_threads());
1653 assert(TM.active_threads() > 1);
1657 Depth ext, newDepth;
1659 Value futilityValueScaled; // NonPV specific
1660 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1662 value = -VALUE_INFINITE;
1664 Position pos(*sp->pos, threadID);
1666 SearchStack* ss = sp->sstack[threadID] + 1;
1667 isCheck = pos.is_check();
1669 // Step 10. Loop through moves
1670 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1671 lock_grab(&(sp->lock));
1673 while ( sp->bestValue < sp->beta
1674 && (move = sp->mp->get_next_move()) != MOVE_NONE
1675 && !TM.thread_should_stop(threadID))
1677 moveCount = ++sp->moveCount;
1678 lock_release(&(sp->lock));
1680 assert(move_is_ok(move));
1682 moveIsCheck = pos.move_is_check(move, ci);
1683 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1685 // Step 11. Decide the new search depth
1686 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1687 newDepth = sp->depth - OnePly + ext;
1689 // Update current move
1690 ss->currentMove = move;
1692 // Step 12. Futility pruning (is omitted in PV nodes)
1694 && !captureOrPromotion
1697 && !move_is_castle(move))
1699 // Move count based pruning
1700 if ( moveCount >= futility_move_count(sp->depth)
1701 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1702 && sp->bestValue > value_mated_in(PLY_MAX))
1704 lock_grab(&(sp->lock));
1708 // Value based pruning
1709 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1710 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1711 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1713 if (futilityValueScaled < sp->beta)
1715 lock_grab(&(sp->lock));
1717 if (futilityValueScaled > sp->bestValue)
1718 sp->bestValue = futilityValueScaled;
1723 // Step 13. Make the move
1724 pos.do_move(move, st, ci, moveIsCheck);
1726 // Step 14. Reduced search
1727 // If the move fails high will be re-searched at full depth.
1728 bool doFullDepthSearch = true;
1730 if ( !captureOrPromotion
1732 && !move_is_castle(move)
1733 && !move_is_killer(move, ss))
1735 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1738 Value localAlpha = sp->alpha;
1739 Depth d = newDepth - ss->reduction;
1740 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1741 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1743 doFullDepthSearch = (value > localAlpha);
1746 // The move failed high, but if reduction is very big we could
1747 // face a false positive, retry with a less aggressive reduction,
1748 // if the move fails high again then go with full depth search.
1749 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1751 assert(newDepth - OnePly >= OnePly);
1753 ss->reduction = OnePly;
1754 Value localAlpha = sp->alpha;
1755 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1756 doFullDepthSearch = (value > localAlpha);
1758 ss->reduction = Depth(0); // Restore original reduction
1761 // Step 15. Full depth search
1762 if (doFullDepthSearch)
1764 Value localAlpha = sp->alpha;
1765 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1766 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1768 // Step extra. pv search (only in PV nodes)
1769 // Search only for possible new PV nodes, if instead value >= beta then
1770 // parent node fails low with value <= alpha and tries another move.
1771 if (PvNode && value > localAlpha && value < sp->beta)
1772 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1773 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1776 // Step 16. Undo move
1777 pos.undo_move(move);
1779 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1781 // Step 17. Check for new best move
1782 lock_grab(&(sp->lock));
1784 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1786 sp->bestValue = value;
1788 if (sp->bestValue > sp->alpha)
1790 if (!PvNode || value >= sp->beta)
1791 sp->stopRequest = true;
1793 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1796 sp->parentSstack->bestMove = ss->bestMove = move;
1801 /* Here we have the lock still grabbed */
1803 sp->slaves[threadID] = 0;
1805 lock_release(&(sp->lock));
1809 // connected_moves() tests whether two moves are 'connected' in the sense
1810 // that the first move somehow made the second move possible (for instance
1811 // if the moving piece is the same in both moves). The first move is assumed
1812 // to be the move that was made to reach the current position, while the
1813 // second move is assumed to be a move from the current position.
1815 bool connected_moves(const Position& pos, Move m1, Move m2) {
1817 Square f1, t1, f2, t2;
1820 assert(move_is_ok(m1));
1821 assert(move_is_ok(m2));
1823 if (m2 == MOVE_NONE)
1826 // Case 1: The moving piece is the same in both moves
1832 // Case 2: The destination square for m2 was vacated by m1
1838 // Case 3: Moving through the vacated square
1839 if ( piece_is_slider(pos.piece_on(f2))
1840 && bit_is_set(squares_between(f2, t2), f1))
1843 // Case 4: The destination square for m2 is defended by the moving piece in m1
1844 p = pos.piece_on(t1);
1845 if (bit_is_set(pos.attacks_from(p, t1), t2))
1848 // Case 5: Discovered check, checking piece is the piece moved in m1
1849 if ( piece_is_slider(p)
1850 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1851 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1853 // discovered_check_candidates() works also if the Position's side to
1854 // move is the opposite of the checking piece.
1855 Color them = opposite_color(pos.side_to_move());
1856 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1858 if (bit_is_set(dcCandidates, f2))
1865 // value_is_mate() checks if the given value is a mate one
1866 // eventually compensated for the ply.
1868 bool value_is_mate(Value value) {
1870 assert(abs(value) <= VALUE_INFINITE);
1872 return value <= value_mated_in(PLY_MAX)
1873 || value >= value_mate_in(PLY_MAX);
1877 // move_is_killer() checks if the given move is among the
1878 // killer moves of that ply.
1880 bool move_is_killer(Move m, SearchStack* ss) {
1882 const Move* k = ss->killers;
1883 for (int i = 0; i < KILLER_MAX; i++, k++)
1891 // extension() decides whether a move should be searched with normal depth,
1892 // or with extended depth. Certain classes of moves (checking moves, in
1893 // particular) are searched with bigger depth than ordinary moves and in
1894 // any case are marked as 'dangerous'. Note that also if a move is not
1895 // extended, as example because the corresponding UCI option is set to zero,
1896 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1897 template <NodeType PvNode>
1898 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1899 bool singleEvasion, bool mateThreat, bool* dangerous) {
1901 assert(m != MOVE_NONE);
1903 Depth result = Depth(0);
1904 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1908 if (moveIsCheck && pos.see_sign(m) >= 0)
1909 result += CheckExtension[PvNode];
1912 result += SingleEvasionExtension[PvNode];
1915 result += MateThreatExtension[PvNode];
1918 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1920 Color c = pos.side_to_move();
1921 if (relative_rank(c, move_to(m)) == RANK_7)
1923 result += PawnPushTo7thExtension[PvNode];
1926 if (pos.pawn_is_passed(c, move_to(m)))
1928 result += PassedPawnExtension[PvNode];
1933 if ( captureOrPromotion
1934 && pos.type_of_piece_on(move_to(m)) != PAWN
1935 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1936 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1937 && !move_is_promotion(m)
1940 result += PawnEndgameExtension[PvNode];
1945 && captureOrPromotion
1946 && pos.type_of_piece_on(move_to(m)) != PAWN
1947 && pos.see_sign(m) >= 0)
1953 return Min(result, OnePly);
1957 // connected_threat() tests whether it is safe to forward prune a move or if
1958 // is somehow coonected to the threat move returned by null search.
1960 bool connected_threat(const Position& pos, Move m, Move threat) {
1962 assert(move_is_ok(m));
1963 assert(threat && move_is_ok(threat));
1964 assert(!pos.move_is_check(m));
1965 assert(!pos.move_is_capture_or_promotion(m));
1966 assert(!pos.move_is_passed_pawn_push(m));
1968 Square mfrom, mto, tfrom, tto;
1970 mfrom = move_from(m);
1972 tfrom = move_from(threat);
1973 tto = move_to(threat);
1975 // Case 1: Don't prune moves which move the threatened piece
1979 // Case 2: If the threatened piece has value less than or equal to the
1980 // value of the threatening piece, don't prune move which defend it.
1981 if ( pos.move_is_capture(threat)
1982 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1983 || pos.type_of_piece_on(tfrom) == KING)
1984 && pos.move_attacks_square(m, tto))
1987 // Case 3: If the moving piece in the threatened move is a slider, don't
1988 // prune safe moves which block its ray.
1989 if ( piece_is_slider(pos.piece_on(tfrom))
1990 && bit_is_set(squares_between(tfrom, tto), mto)
1991 && pos.see_sign(m) >= 0)
1998 // ok_to_use_TT() returns true if a transposition table score
1999 // can be used at a given point in search.
2001 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2003 Value v = value_from_tt(tte->value(), ply);
2005 return ( tte->depth() >= depth
2006 || v >= Max(value_mate_in(PLY_MAX), beta)
2007 || v < Min(value_mated_in(PLY_MAX), beta))
2009 && ( (is_lower_bound(tte->type()) && v >= beta)
2010 || (is_upper_bound(tte->type()) && v < beta));
2014 // refine_eval() returns the transposition table score if
2015 // possible otherwise falls back on static position evaluation.
2017 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2022 Value v = value_from_tt(tte->value(), ply);
2024 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2025 || (is_upper_bound(tte->type()) && v < defaultEval))
2032 // update_history() registers a good move that produced a beta-cutoff
2033 // in history and marks as failures all the other moves of that ply.
2035 void update_history(const Position& pos, Move move, Depth depth,
2036 Move movesSearched[], int moveCount) {
2040 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2042 for (int i = 0; i < moveCount - 1; i++)
2044 m = movesSearched[i];
2048 if (!pos.move_is_capture_or_promotion(m))
2049 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2054 // update_killers() add a good move that produced a beta-cutoff
2055 // among the killer moves of that ply.
2057 void update_killers(Move m, SearchStack* ss) {
2059 if (m == ss->killers[0])
2062 for (int i = KILLER_MAX - 1; i > 0; i--)
2063 ss->killers[i] = ss->killers[i - 1];
2069 // update_gains() updates the gains table of a non-capture move given
2070 // the static position evaluation before and after the move.
2072 void update_gains(const Position& pos, Move m, Value before, Value after) {
2075 && before != VALUE_NONE
2076 && after != VALUE_NONE
2077 && pos.captured_piece() == NO_PIECE_TYPE
2078 && !move_is_castle(m)
2079 && !move_is_promotion(m))
2080 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2084 // current_search_time() returns the number of milliseconds which have passed
2085 // since the beginning of the current search.
2087 int current_search_time() {
2089 return get_system_time() - SearchStartTime;
2093 // nps() computes the current nodes/second count.
2097 int t = current_search_time();
2098 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2102 // poll() performs two different functions: It polls for user input, and it
2103 // looks at the time consumed so far and decides if it's time to abort the
2108 static int lastInfoTime;
2109 int t = current_search_time();
2114 // We are line oriented, don't read single chars
2115 std::string command;
2117 if (!std::getline(std::cin, command))
2120 if (command == "quit")
2123 PonderSearch = false;
2127 else if (command == "stop")
2130 PonderSearch = false;
2132 else if (command == "ponderhit")
2136 // Print search information
2140 else if (lastInfoTime > t)
2141 // HACK: Must be a new search where we searched less than
2142 // NodesBetweenPolls nodes during the first second of search.
2145 else if (t - lastInfoTime >= 1000)
2152 if (dbg_show_hit_rate)
2153 dbg_print_hit_rate();
2155 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2156 << " time " << t << endl;
2159 // Should we stop the search?
2163 bool stillAtFirstMove = FirstRootMove
2164 && !AspirationFailLow
2165 && t > MaxSearchTime + ExtraSearchTime;
2167 bool noMoreTime = t > AbsoluteMaxSearchTime
2168 || stillAtFirstMove;
2170 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2171 || (ExactMaxTime && t >= ExactMaxTime)
2172 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2177 // ponderhit() is called when the program is pondering (i.e. thinking while
2178 // it's the opponent's turn to move) in order to let the engine know that
2179 // it correctly predicted the opponent's move.
2183 int t = current_search_time();
2184 PonderSearch = false;
2186 bool stillAtFirstMove = FirstRootMove
2187 && !AspirationFailLow
2188 && t > MaxSearchTime + ExtraSearchTime;
2190 bool noMoreTime = t > AbsoluteMaxSearchTime
2191 || stillAtFirstMove;
2193 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2198 // init_ss_array() does a fast reset of the first entries of a SearchStack
2199 // array and of all the excludedMove and skipNullMove entries.
2201 void init_ss_array(SearchStack* ss, int size) {
2203 for (int i = 0; i < size; i++, ss++)
2205 ss->excludedMove = MOVE_NONE;
2206 ss->skipNullMove = false;
2217 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2218 // while the program is pondering. The point is to work around a wrinkle in
2219 // the UCI protocol: When pondering, the engine is not allowed to give a
2220 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2221 // We simply wait here until one of these commands is sent, and return,
2222 // after which the bestmove and pondermove will be printed (in id_loop()).
2224 void wait_for_stop_or_ponderhit() {
2226 std::string command;
2230 if (!std::getline(std::cin, command))
2233 if (command == "quit")
2238 else if (command == "ponderhit" || command == "stop")
2244 // print_pv_info() prints to standard output and eventually to log file information on
2245 // the current PV line. It is called at each iteration or after a new pv is found.
2247 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2249 cout << "info depth " << Iteration
2250 << " score " << value_to_string(value)
2251 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2252 << " time " << current_search_time()
2253 << " nodes " << TM.nodes_searched()
2257 for (Move* m = pv; *m != MOVE_NONE; m++)
2264 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2265 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2267 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2268 TM.nodes_searched(), value, t, pv) << endl;
2273 // init_thread() is the function which is called when a new thread is
2274 // launched. It simply calls the idle_loop() function with the supplied
2275 // threadID. There are two versions of this function; one for POSIX
2276 // threads and one for Windows threads.
2278 #if !defined(_MSC_VER)
2280 void* init_thread(void *threadID) {
2282 TM.idle_loop(*(int*)threadID, NULL);
2288 DWORD WINAPI init_thread(LPVOID threadID) {
2290 TM.idle_loop(*(int*)threadID, NULL);
2297 /// The ThreadsManager class
2299 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2300 // get_beta_counters() are getters/setters for the per thread
2301 // counters used to sort the moves at root.
2303 void ThreadsManager::resetNodeCounters() {
2305 for (int i = 0; i < MAX_THREADS; i++)
2306 threads[i].nodes = 0ULL;
2309 void ThreadsManager::resetBetaCounters() {
2311 for (int i = 0; i < MAX_THREADS; i++)
2312 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2315 int64_t ThreadsManager::nodes_searched() const {
2317 int64_t result = 0ULL;
2318 for (int i = 0; i < ActiveThreads; i++)
2319 result += threads[i].nodes;
2324 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2327 for (int i = 0; i < MAX_THREADS; i++)
2329 our += threads[i].betaCutOffs[us];
2330 their += threads[i].betaCutOffs[opposite_color(us)];
2335 // idle_loop() is where the threads are parked when they have no work to do.
2336 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2337 // object for which the current thread is the master.
2339 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2341 assert(threadID >= 0 && threadID < MAX_THREADS);
2345 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2346 // master should exit as last one.
2347 if (AllThreadsShouldExit)
2350 threads[threadID].state = THREAD_TERMINATED;
2354 // If we are not thinking, wait for a condition to be signaled
2355 // instead of wasting CPU time polling for work.
2356 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2359 assert(threadID != 0);
2360 threads[threadID].state = THREAD_SLEEPING;
2362 #if !defined(_MSC_VER)
2363 lock_grab(&WaitLock);
2364 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2365 pthread_cond_wait(&WaitCond, &WaitLock);
2366 lock_release(&WaitLock);
2368 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2372 // If thread has just woken up, mark it as available
2373 if (threads[threadID].state == THREAD_SLEEPING)
2374 threads[threadID].state = THREAD_AVAILABLE;
2376 // If this thread has been assigned work, launch a search
2377 if (threads[threadID].state == THREAD_WORKISWAITING)
2379 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2381 threads[threadID].state = THREAD_SEARCHING;
2383 if (threads[threadID].splitPoint->pvNode)
2384 sp_search<PV>(threads[threadID].splitPoint, threadID);
2386 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2388 assert(threads[threadID].state == THREAD_SEARCHING);
2390 threads[threadID].state = THREAD_AVAILABLE;
2393 // If this thread is the master of a split point and all slaves have
2394 // finished their work at this split point, return from the idle loop.
2396 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2398 if (i == ActiveThreads)
2400 // Because sp->slaves[] is reset under lock protection,
2401 // be sure sp->lock has been released before to return.
2402 lock_grab(&(sp->lock));
2403 lock_release(&(sp->lock));
2405 assert(threads[threadID].state == THREAD_AVAILABLE);
2407 threads[threadID].state = THREAD_SEARCHING;
2414 // init_threads() is called during startup. It launches all helper threads,
2415 // and initializes the split point stack and the global locks and condition
2418 void ThreadsManager::init_threads() {
2423 #if !defined(_MSC_VER)
2424 pthread_t pthread[1];
2427 // Initialize global locks
2428 lock_init(&MPLock, NULL);
2429 lock_init(&WaitLock, NULL);
2431 #if !defined(_MSC_VER)
2432 pthread_cond_init(&WaitCond, NULL);
2434 for (i = 0; i < MAX_THREADS; i++)
2435 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2438 // Initialize splitPoints[] locks
2439 for (i = 0; i < MAX_THREADS; i++)
2440 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2441 lock_init(&(threads[i].splitPoints[j].lock), NULL);
2443 // Will be set just before program exits to properly end the threads
2444 AllThreadsShouldExit = false;
2446 // Threads will be put to sleep as soon as created
2447 AllThreadsShouldSleep = true;
2449 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2451 threads[0].state = THREAD_SEARCHING;
2452 for (i = 1; i < MAX_THREADS; i++)
2453 threads[i].state = THREAD_AVAILABLE;
2455 // Launch the helper threads
2456 for (i = 1; i < MAX_THREADS; i++)
2459 #if !defined(_MSC_VER)
2460 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2462 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2467 cout << "Failed to create thread number " << i << endl;
2468 Application::exit_with_failure();
2471 // Wait until the thread has finished launching and is gone to sleep
2472 while (threads[i].state != THREAD_SLEEPING) {}
2477 // exit_threads() is called when the program exits. It makes all the
2478 // helper threads exit cleanly.
2480 void ThreadsManager::exit_threads() {
2482 ActiveThreads = MAX_THREADS; // HACK
2483 AllThreadsShouldSleep = true; // HACK
2484 wake_sleeping_threads();
2486 // This makes the threads to exit idle_loop()
2487 AllThreadsShouldExit = true;
2489 // Wait for thread termination
2490 for (int i = 1; i < MAX_THREADS; i++)
2491 while (threads[i].state != THREAD_TERMINATED) {}
2493 // Now we can safely destroy the locks
2494 for (int i = 0; i < MAX_THREADS; i++)
2495 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2496 lock_destroy(&(threads[i].splitPoints[j].lock));
2498 lock_destroy(&WaitLock);
2499 lock_destroy(&MPLock);
2503 // thread_should_stop() checks whether the thread should stop its search.
2504 // This can happen if a beta cutoff has occurred in the thread's currently
2505 // active split point, or in some ancestor of the current split point.
2507 bool ThreadsManager::thread_should_stop(int threadID) const {
2509 assert(threadID >= 0 && threadID < ActiveThreads);
2513 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2518 // thread_is_available() checks whether the thread with threadID "slave" is
2519 // available to help the thread with threadID "master" at a split point. An
2520 // obvious requirement is that "slave" must be idle. With more than two
2521 // threads, this is not by itself sufficient: If "slave" is the master of
2522 // some active split point, it is only available as a slave to the other
2523 // threads which are busy searching the split point at the top of "slave"'s
2524 // split point stack (the "helpful master concept" in YBWC terminology).
2526 bool ThreadsManager::thread_is_available(int slave, int master) const {
2528 assert(slave >= 0 && slave < ActiveThreads);
2529 assert(master >= 0 && master < ActiveThreads);
2530 assert(ActiveThreads > 1);
2532 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2535 // Make a local copy to be sure doesn't change under our feet
2536 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2538 if (localActiveSplitPoints == 0)
2539 // No active split points means that the thread is available as
2540 // a slave for any other thread.
2543 if (ActiveThreads == 2)
2546 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2547 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2548 // could have been set to 0 by another thread leading to an out of bound access.
2549 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2556 // available_thread_exists() tries to find an idle thread which is available as
2557 // a slave for the thread with threadID "master".
2559 bool ThreadsManager::available_thread_exists(int master) const {
2561 assert(master >= 0 && master < ActiveThreads);
2562 assert(ActiveThreads > 1);
2564 for (int i = 0; i < ActiveThreads; i++)
2565 if (thread_is_available(i, master))
2572 // split() does the actual work of distributing the work at a node between
2573 // several available threads. If it does not succeed in splitting the
2574 // node (because no idle threads are available, or because we have no unused
2575 // split point objects), the function immediately returns. If splitting is
2576 // possible, a SplitPoint object is initialized with all the data that must be
2577 // copied to the helper threads and we tell our helper threads that they have
2578 // been assigned work. This will cause them to instantly leave their idle loops
2579 // and call sp_search(). When all threads have returned from sp_search() then
2582 template <bool Fake>
2583 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2584 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2585 int* moveCount, MovePicker* mp, bool pvNode) {
2587 assert(ply > 0 && ply < PLY_MAX);
2588 assert(*bestValue >= -VALUE_INFINITE);
2589 assert(*bestValue <= *alpha);
2590 assert(*alpha < beta);
2591 assert(beta <= VALUE_INFINITE);
2592 assert(depth > Depth(0));
2593 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2594 assert(ActiveThreads > 1);
2596 int i, master = p.thread();
2597 Thread& masterThread = threads[master];
2601 // If no other thread is available to help us, or if we have too many
2602 // active split points, don't split.
2603 if ( !available_thread_exists(master)
2604 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2606 lock_release(&MPLock);
2610 // Pick the next available split point object from the split point stack
2611 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2613 // Initialize the split point object
2614 splitPoint.parent = masterThread.splitPoint;
2615 splitPoint.stopRequest = false;
2616 splitPoint.ply = ply;
2617 splitPoint.depth = depth;
2618 splitPoint.mateThreat = mateThreat;
2619 splitPoint.alpha = *alpha;
2620 splitPoint.beta = beta;
2621 splitPoint.pvNode = pvNode;
2622 splitPoint.bestValue = *bestValue;
2624 splitPoint.moveCount = *moveCount;
2625 splitPoint.pos = &p;
2626 splitPoint.parentSstack = ss;
2627 for (i = 0; i < ActiveThreads; i++)
2628 splitPoint.slaves[i] = 0;
2630 masterThread.splitPoint = &splitPoint;
2632 // If we are here it means we are not available
2633 assert(masterThread.state != THREAD_AVAILABLE);
2635 int workersCnt = 1; // At least the master is included
2637 // Allocate available threads setting state to THREAD_BOOKED
2638 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2639 if (thread_is_available(i, master))
2641 threads[i].state = THREAD_BOOKED;
2642 threads[i].splitPoint = &splitPoint;
2643 splitPoint.slaves[i] = 1;
2647 assert(Fake || workersCnt > 1);
2649 // We can release the lock because slave threads are already booked and master is not available
2650 lock_release(&MPLock);
2652 // Tell the threads that they have work to do. This will make them leave
2653 // their idle loop. But before copy search stack tail for each thread.
2654 for (i = 0; i < ActiveThreads; i++)
2655 if (i == master || splitPoint.slaves[i])
2657 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2659 assert(i == master || threads[i].state == THREAD_BOOKED);
2661 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2664 // Everything is set up. The master thread enters the idle loop, from
2665 // which it will instantly launch a search, because its state is
2666 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2667 // idle loop, which means that the main thread will return from the idle
2668 // loop when all threads have finished their work at this split point.
2669 idle_loop(master, &splitPoint);
2671 // We have returned from the idle loop, which means that all threads are
2672 // finished. Update alpha and bestValue, and return.
2675 *alpha = splitPoint.alpha;
2676 *bestValue = splitPoint.bestValue;
2677 masterThread.activeSplitPoints--;
2678 masterThread.splitPoint = splitPoint.parent;
2680 lock_release(&MPLock);
2684 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2685 // to start a new search from the root.
2687 void ThreadsManager::wake_sleeping_threads() {
2689 assert(AllThreadsShouldSleep);
2690 assert(ActiveThreads > 0);
2692 AllThreadsShouldSleep = false;
2694 if (ActiveThreads == 1)
2697 #if !defined(_MSC_VER)
2698 pthread_mutex_lock(&WaitLock);
2699 pthread_cond_broadcast(&WaitCond);
2700 pthread_mutex_unlock(&WaitLock);
2702 for (int i = 1; i < MAX_THREADS; i++)
2703 SetEvent(SitIdleEvent[i]);
2709 // put_threads_to_sleep() makes all the threads go to sleep just before
2710 // to leave think(), at the end of the search. Threads should have already
2711 // finished the job and should be idle.
2713 void ThreadsManager::put_threads_to_sleep() {
2715 assert(!AllThreadsShouldSleep);
2717 // This makes the threads to go to sleep
2718 AllThreadsShouldSleep = true;
2721 /// The RootMoveList class
2723 // RootMoveList c'tor
2725 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2727 SearchStack ss[PLY_MAX_PLUS_2];
2728 MoveStack mlist[MaxRootMoves];
2730 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2732 // Generate all legal moves
2733 MoveStack* last = generate_moves(pos, mlist);
2735 // Add each move to the moves[] array
2736 for (MoveStack* cur = mlist; cur != last; cur++)
2738 bool includeMove = includeAllMoves;
2740 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2741 includeMove = (searchMoves[k] == cur->move);
2746 // Find a quick score for the move
2747 init_ss_array(ss, PLY_MAX_PLUS_2);
2748 pos.do_move(cur->move, st);
2749 moves[count].move = cur->move;
2750 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2751 moves[count].pv[0] = cur->move;
2752 moves[count].pv[1] = MOVE_NONE;
2753 pos.undo_move(cur->move);
2760 // RootMoveList simple methods definitions
2762 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2764 moves[moveNum].nodes = nodes;
2765 moves[moveNum].cumulativeNodes += nodes;
2768 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2770 moves[moveNum].ourBeta = our;
2771 moves[moveNum].theirBeta = their;
2774 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2778 for (j = 0; pv[j] != MOVE_NONE; j++)
2779 moves[moveNum].pv[j] = pv[j];
2781 moves[moveNum].pv[j] = MOVE_NONE;
2785 // RootMoveList::sort() sorts the root move list at the beginning of a new
2788 void RootMoveList::sort() {
2790 sort_multipv(count - 1); // Sort all items
2794 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2795 // list by their scores and depths. It is used to order the different PVs
2796 // correctly in MultiPV mode.
2798 void RootMoveList::sort_multipv(int n) {
2802 for (i = 1; i <= n; i++)
2804 RootMove rm = moves[i];
2805 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2806 moves[j] = moves[j - 1];