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()
742 << " hashfull " << TT.full() << endl;
744 // Print the best move and the ponder move to the standard output
745 if (pv[0] == MOVE_NONE)
747 pv[0] = rml.get_move(0);
751 assert(pv[0] != MOVE_NONE);
753 cout << "bestmove " << pv[0];
755 if (pv[1] != MOVE_NONE)
756 cout << " ponder " << pv[1];
763 dbg_print_mean(LogFile);
765 if (dbg_show_hit_rate)
766 dbg_print_hit_rate(LogFile);
768 LogFile << "\nNodes: " << TM.nodes_searched()
769 << "\nNodes/second: " << nps()
770 << "\nBest move: " << move_to_san(p, pv[0]);
773 p.do_move(pv[0], st);
774 LogFile << "\nPonder move: "
775 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
778 return rml.get_move_score(0);
782 // root_search() is the function which searches the root node. It is
783 // similar to search_pv except that it uses a different move ordering
784 // scheme, prints some information to the standard output and handles
785 // the fail low/high loops.
787 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
794 Depth depth, ext, newDepth;
795 Value value, alpha, beta;
796 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
797 int researchCountFH, researchCountFL;
799 researchCountFH = researchCountFL = 0;
802 isCheck = pos.is_check();
804 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
805 // Step 2. Check for aborted search (omitted at root)
806 // Step 3. Mate distance pruning (omitted at root)
807 // Step 4. Transposition table lookup (omitted at root)
809 // Step 5. Evaluate the position statically
810 // At root we do this only to get reference value for child nodes
812 ss->eval = evaluate(pos, ei);
814 // Step 6. Razoring (omitted at root)
815 // Step 7. Static null move pruning (omitted at root)
816 // Step 8. Null move search with verification search (omitted at root)
817 // Step 9. Internal iterative deepening (omitted at root)
819 // Step extra. Fail low loop
820 // We start with small aspiration window and in case of fail low, we research
821 // with bigger window until we are not failing low anymore.
824 // Sort the moves before to (re)search
827 // Step 10. Loop through all moves in the root move list
828 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
830 // This is used by time management
831 FirstRootMove = (i == 0);
833 // Save the current node count before the move is searched
834 nodes = TM.nodes_searched();
836 // Reset beta cut-off counters
837 TM.resetBetaCounters();
839 // Pick the next root move, and print the move and the move number to
840 // the standard output.
841 move = ss->currentMove = rml.get_move(i);
843 if (current_search_time() >= 1000)
844 cout << "info currmove " << move
845 << " currmovenumber " << i + 1 << endl;
847 moveIsCheck = pos.move_is_check(move);
848 captureOrPromotion = pos.move_is_capture_or_promotion(move);
850 // Step 11. Decide the new search depth
851 depth = (Iteration - 2) * OnePly + InitialDepth;
852 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
853 newDepth = depth + ext;
855 // Step 12. Futility pruning (omitted at root)
857 // Step extra. Fail high loop
858 // If move fails high, we research with bigger window until we are not failing
860 value = - VALUE_INFINITE;
864 // Step 13. Make the move
865 pos.do_move(move, st, ci, moveIsCheck);
867 // Step extra. pv search
868 // We do pv search for first moves (i < MultiPV)
869 // and for fail high research (value > alpha)
870 if (i < MultiPV || value > alpha)
872 // Aspiration window is disabled in multi-pv case
874 alpha = -VALUE_INFINITE;
876 // Full depth PV search, done on first move or after a fail high
877 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
881 // Step 14. Reduced search
882 // if the move fails high will be re-searched at full depth
883 bool doFullDepthSearch = true;
885 if ( depth >= 3 * OnePly
887 && !captureOrPromotion
888 && !move_is_castle(move))
890 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
893 assert(newDepth-ss->reduction >= OnePly);
895 // Reduced depth non-pv search using alpha as upperbound
896 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
897 doFullDepthSearch = (value > alpha);
900 // The move failed high, but if reduction is very big we could
901 // face a false positive, retry with a less aggressive reduction,
902 // if the move fails high again then go with full depth search.
903 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
905 assert(newDepth - OnePly >= OnePly);
907 ss->reduction = OnePly;
908 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
909 doFullDepthSearch = (value > alpha);
911 ss->reduction = Depth(0); // Restore original reduction
914 // Step 15. Full depth search
915 if (doFullDepthSearch)
917 // Full depth non-pv search using alpha as upperbound
918 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
920 // If we are above alpha then research at same depth but as PV
921 // to get a correct score or eventually a fail high above beta.
923 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
927 // Step 16. Undo move
930 // Can we exit fail high loop ?
931 if (AbortSearch || value < beta)
934 // We are failing high and going to do a research. It's important to update
935 // the score before research in case we run out of time while researching.
936 rml.set_move_score(i, value);
938 TT.extract_pv(pos, move, pv, PLY_MAX);
939 rml.set_move_pv(i, pv);
941 // Print information to the standard output
942 print_pv_info(pos, pv, alpha, beta, value);
944 // Prepare for a research after a fail high, each time with a wider window
945 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
948 } // End of fail high loop
950 // Finished searching the move. If AbortSearch is true, the search
951 // was aborted because the user interrupted the search or because we
952 // ran out of time. In this case, the return value of the search cannot
953 // be trusted, and we break out of the loop without updating the best
958 // Remember beta-cutoff and searched nodes counts for this move. The
959 // info is used to sort the root moves for the next iteration.
961 TM.get_beta_counters(pos.side_to_move(), our, their);
962 rml.set_beta_counters(i, our, their);
963 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
965 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
966 assert(value < beta);
968 // Step 17. Check for new best move
969 if (value <= alpha && i >= MultiPV)
970 rml.set_move_score(i, -VALUE_INFINITE);
973 // PV move or new best move!
976 rml.set_move_score(i, value);
978 TT.extract_pv(pos, move, pv, PLY_MAX);
979 rml.set_move_pv(i, pv);
983 // We record how often the best move has been changed in each
984 // iteration. This information is used for time managment: When
985 // the best move changes frequently, we allocate some more time.
987 BestMoveChangesByIteration[Iteration]++;
989 // Print information to the standard output
990 print_pv_info(pos, pv, alpha, beta, value);
992 // Raise alpha to setup proper non-pv search upper bound
999 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1001 cout << "info multipv " << j + 1
1002 << " score " << value_to_string(rml.get_move_score(j))
1003 << " depth " << (j <= i ? Iteration : Iteration - 1)
1004 << " time " << current_search_time()
1005 << " nodes " << TM.nodes_searched()
1009 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1010 cout << rml.get_move_pv(j, k) << " ";
1014 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1016 } // PV move or new best move
1018 assert(alpha >= *alphaPtr);
1020 AspirationFailLow = (alpha == *alphaPtr);
1022 if (AspirationFailLow && StopOnPonderhit)
1023 StopOnPonderhit = false;
1026 // Can we exit fail low loop ?
1027 if (AbortSearch || !AspirationFailLow)
1030 // Prepare for a research after a fail low, each time with a wider window
1031 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1036 // Sort the moves before to return
1043 // search<>() is the main search function for both PV and non-PV nodes
1045 template <NodeType PvNode>
1046 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1048 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1049 assert(beta > alpha && beta <= VALUE_INFINITE);
1050 assert(PvNode || alpha == beta - 1);
1051 assert(ply > 0 && ply < PLY_MAX);
1052 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1054 Move movesSearched[256];
1059 Move ttMove, move, excludedMove;
1060 Depth ext, newDepth;
1061 Value bestValue, value, oldAlpha;
1062 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1063 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
1064 bool mateThreat = false;
1066 int threadID = pos.thread();
1067 refinedValue = bestValue = value = -VALUE_INFINITE;
1070 // Step 1. Initialize node and poll. Polling can abort search
1071 TM.incrementNodeCounter(threadID);
1073 (ss+2)->initKillers();
1075 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1081 // Step 2. Check for aborted search and immediate draw
1082 if (AbortSearch || TM.thread_should_stop(threadID))
1085 if (pos.is_draw() || ply >= PLY_MAX - 1)
1088 // Step 3. Mate distance pruning
1089 alpha = Max(value_mated_in(ply), alpha);
1090 beta = Min(value_mate_in(ply+1), beta);
1094 // Step 4. Transposition table lookup
1096 // We don't want the score of a partial search to overwrite a previous full search
1097 // TT value, so we use a different position key in case of an excluded move exists.
1098 excludedMove = ss->excludedMove;
1099 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1101 tte = TT.retrieve(posKey);
1102 ttMove = (tte ? tte->move() : MOVE_NONE);
1104 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1105 // This is to avoid problems in the following areas:
1107 // * Repetition draw detection
1108 // * Fifty move rule detection
1109 // * Searching for a mate
1110 // * Printing of full PV line
1112 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1114 // Refresh tte entry to avoid aging
1115 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1117 ss->currentMove = ttMove; // Can be MOVE_NONE
1118 return value_from_tt(tte->value(), ply);
1121 // Step 5. Evaluate the position statically
1122 // At PV nodes we do this only to update gain statistics
1123 isCheck = pos.is_check();
1126 if (tte && tte->static_value() != VALUE_NONE)
1128 ss->eval = tte->static_value();
1129 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1132 ss->eval = evaluate(pos, ei);
1134 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1135 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1138 // Step 6. Razoring (is omitted in PV nodes)
1140 && depth < RazorDepth
1142 && refinedValue < beta - razor_margin(depth)
1143 && ttMove == MOVE_NONE
1144 && (ss-1)->currentMove != MOVE_NULL
1145 && !value_is_mate(beta)
1146 && !pos.has_pawn_on_7th(pos.side_to_move()))
1148 // Pass ss->eval to qsearch() and avoid an evaluate call
1149 if (!tte || tte->static_value() == VALUE_NONE)
1150 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1152 Value rbeta = beta - razor_margin(depth);
1153 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1155 // Logically we should return (v + razor_margin(depth)), but
1156 // surprisingly this did slightly weaker in tests.
1160 // Step 7. Static null move pruning (is omitted in PV nodes)
1161 // We're betting that the opponent doesn't have a move that will reduce
1162 // the score by more than futility_margin(depth) if we do a null move.
1164 && !ss->skipNullMove
1165 && depth < RazorDepth
1166 && refinedValue >= beta + futility_margin(depth, 0)
1168 && !value_is_mate(beta)
1169 && pos.non_pawn_material(pos.side_to_move()))
1170 return refinedValue - futility_margin(depth, 0);
1172 // Step 8. Null move search with verification search (is omitted in PV nodes)
1173 // When we jump directly to qsearch() we do a null move only if static value is
1174 // at least beta. Otherwise we do a null move if static value is not more than
1175 // NullMoveMargin under beta.
1177 && !ss->skipNullMove
1179 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1181 && !value_is_mate(beta)
1182 && pos.non_pawn_material(pos.side_to_move()))
1184 ss->currentMove = MOVE_NULL;
1186 // Null move dynamic reduction based on depth
1187 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1189 // Null move dynamic reduction based on value
1190 if (refinedValue - beta > PawnValueMidgame)
1193 pos.do_null_move(st);
1194 (ss+1)->skipNullMove = true;
1196 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1197 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1198 (ss+1)->skipNullMove = false;
1199 pos.undo_null_move();
1201 if (nullValue >= beta)
1203 // Do not return unproven mate scores
1204 if (nullValue >= value_mate_in(PLY_MAX))
1207 // Do zugzwang verification search at high depths
1208 if (depth < 6 * OnePly)
1211 ss->skipNullMove = true;
1212 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply);
1213 ss->skipNullMove = false;
1220 // The null move failed low, which means that we may be faced with
1221 // some kind of threat. If the previous move was reduced, check if
1222 // the move that refuted the null move was somehow connected to the
1223 // move which was reduced. If a connection is found, return a fail
1224 // low score (which will cause the reduced move to fail high in the
1225 // parent node, which will trigger a re-search with full depth).
1226 if (nullValue == value_mated_in(ply + 2))
1229 ss->threatMove = (ss+1)->currentMove;
1230 if ( depth < ThreatDepth
1231 && (ss-1)->reduction
1232 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1237 // Step 9. Internal iterative deepening
1238 if ( depth >= IIDDepth[PvNode]
1239 && ttMove == MOVE_NONE
1240 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1242 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1244 ss->skipNullMove = true;
1245 search<PvNode>(pos, ss, alpha, beta, d, ply);
1246 ss->skipNullMove = false;
1248 ttMove = ss->bestMove;
1249 tte = TT.retrieve(posKey);
1252 // Expensive mate threat detection (only for PV nodes)
1254 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1256 // Initialize a MovePicker object for the current position
1257 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1259 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1260 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1261 && tte && tte->move()
1262 && !excludedMove // Do not allow recursive singular extension search
1263 && is_lower_bound(tte->type())
1264 && tte->depth() >= depth - 3 * OnePly;
1266 // Step 10. Loop through moves
1267 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1268 while ( bestValue < beta
1269 && (move = mp.get_next_move()) != MOVE_NONE
1270 && !TM.thread_should_stop(threadID))
1272 assert(move_is_ok(move));
1274 if (move == excludedMove)
1277 moveIsCheck = pos.move_is_check(move, ci);
1278 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1280 // Step 11. Decide the new search depth
1281 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1283 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1284 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1285 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1286 // lower then ttValue minus a margin then we extend ttMove.
1287 if ( singularExtensionNode
1288 && move == tte->move()
1291 Value ttValue = value_from_tt(tte->value(), ply);
1293 if (abs(ttValue) < VALUE_KNOWN_WIN)
1295 Value b = ttValue - SingularExtensionMargin;
1296 ss->excludedMove = move;
1297 ss->skipNullMove = true;
1298 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1299 ss->skipNullMove = false;
1300 ss->excludedMove = MOVE_NONE;
1306 newDepth = depth - OnePly + ext;
1308 // Update current move (this must be done after singular extension search)
1309 movesSearched[moveCount++] = ss->currentMove = move;
1311 // Step 12. Futility pruning (is omitted in PV nodes)
1313 && !captureOrPromotion
1317 && !move_is_castle(move))
1319 // Move count based pruning
1320 if ( moveCount >= futility_move_count(depth)
1321 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1322 && bestValue > value_mated_in(PLY_MAX))
1325 // Value based pruning
1326 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1327 // but fixing this made program slightly weaker.
1328 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1329 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1330 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1332 if (futilityValueScaled < beta)
1334 if (futilityValueScaled > bestValue)
1335 bestValue = futilityValueScaled;
1340 // Step 13. Make the move
1341 pos.do_move(move, st, ci, moveIsCheck);
1343 // Step extra. pv search (only in PV nodes)
1344 // The first move in list is the expected PV
1345 if (PvNode && moveCount == 1)
1346 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1347 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1350 // Step 14. Reduced depth search
1351 // If the move fails high will be re-searched at full depth.
1352 bool doFullDepthSearch = true;
1354 if ( depth >= 3 * OnePly
1355 && !captureOrPromotion
1357 && !move_is_castle(move)
1358 && !move_is_killer(move, ss))
1360 ss->reduction = reduction<PvNode>(depth, moveCount);
1363 Depth d = newDepth - ss->reduction;
1364 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1365 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1367 doFullDepthSearch = (value > alpha);
1370 // The move failed high, but if reduction is very big we could
1371 // face a false positive, retry with a less aggressive reduction,
1372 // if the move fails high again then go with full depth search.
1373 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1375 assert(newDepth - OnePly >= OnePly);
1377 ss->reduction = OnePly;
1378 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1379 doFullDepthSearch = (value > alpha);
1381 ss->reduction = Depth(0); // Restore original reduction
1384 // Step 15. Full depth search
1385 if (doFullDepthSearch)
1387 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1388 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1390 // Step extra. pv search (only in PV nodes)
1391 // Search only for possible new PV nodes, if instead value >= beta then
1392 // parent node fails low with value <= alpha and tries another move.
1393 if (PvNode && value > alpha && value < beta)
1394 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1395 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1399 // Step 16. Undo move
1400 pos.undo_move(move);
1402 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1404 // Step 17. Check for new best move
1405 if (value > bestValue)
1410 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1413 if (value == value_mate_in(ply + 1))
1414 ss->mateKiller = move;
1416 ss->bestMove = move;
1420 // Step 18. Check for split
1421 if ( depth >= MinimumSplitDepth
1422 && TM.active_threads() > 1
1424 && TM.available_thread_exists(threadID)
1426 && !TM.thread_should_stop(threadID)
1428 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1429 mateThreat, &moveCount, &mp, PvNode);
1432 // Step 19. Check for mate and stalemate
1433 // All legal moves have been searched and if there are
1434 // no legal moves, it must be mate or stalemate.
1435 // If one move was excluded return fail low score.
1437 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1439 // Step 20. Update tables
1440 // If the search is not aborted, update the transposition table,
1441 // history counters, and killer moves.
1442 if (AbortSearch || TM.thread_should_stop(threadID))
1445 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1446 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1447 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1449 // Update killers and history only for non capture moves that fails high
1450 if (bestValue >= beta)
1452 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1453 if (!pos.move_is_capture_or_promotion(move))
1455 update_history(pos, move, depth, movesSearched, moveCount);
1456 update_killers(move, ss);
1460 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1466 // qsearch() is the quiescence search function, which is called by the main
1467 // search function when the remaining depth is zero (or, to be more precise,
1468 // less than OnePly).
1470 template <NodeType PvNode>
1471 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1473 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1474 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1475 assert(PvNode || alpha == beta - 1);
1477 assert(ply > 0 && ply < PLY_MAX);
1478 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1483 Value bestValue, value, futilityValue, futilityBase;
1484 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1486 Value oldAlpha = alpha;
1488 TM.incrementNodeCounter(pos.thread());
1489 ss->bestMove = ss->currentMove = MOVE_NONE;
1490 ss->eval = VALUE_NONE;
1492 // Check for an instant draw or maximum ply reached
1493 if (pos.is_draw() || ply >= PLY_MAX - 1)
1496 // Transposition table lookup. At PV nodes, we don't use the TT for
1497 // pruning, but only for move ordering.
1498 tte = TT.retrieve(pos.get_key());
1499 ttMove = (tte ? tte->move() : MOVE_NONE);
1501 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1503 ss->currentMove = ttMove; // Can be MOVE_NONE
1504 return value_from_tt(tte->value(), ply);
1507 isCheck = pos.is_check();
1509 // Evaluate the position statically
1512 bestValue = futilityBase = -VALUE_INFINITE;
1513 deepChecks = enoughMaterial = false;
1517 if (tte && tte->static_value() != VALUE_NONE)
1519 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1520 bestValue = tte->static_value();
1523 bestValue = evaluate(pos, ei);
1525 ss->eval = bestValue;
1526 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1528 // Stand pat. Return immediately if static value is at least beta
1529 if (bestValue >= beta)
1532 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()]);
1537 if (PvNode && bestValue > alpha)
1540 // If we are near beta then try to get a cutoff pushing checks a bit further
1541 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1543 // Futility pruning parameters, not needed when in check
1544 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1545 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1548 // Initialize a MovePicker object for the current position, and prepare
1549 // to search the moves. Because the depth is <= 0 here, only captures,
1550 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1551 // and we are near beta) will be generated.
1552 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1555 // Loop through the moves until no moves remain or a beta cutoff occurs
1556 while ( alpha < beta
1557 && (move = mp.get_next_move()) != MOVE_NONE)
1559 assert(move_is_ok(move));
1561 moveIsCheck = pos.move_is_check(move, ci);
1569 && !move_is_promotion(move)
1570 && !pos.move_is_passed_pawn_push(move))
1572 futilityValue = futilityBase
1573 + pos.endgame_value_of_piece_on(move_to(move))
1574 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1576 if (futilityValue < alpha)
1578 if (futilityValue > bestValue)
1579 bestValue = futilityValue;
1584 // Detect blocking evasions that are candidate to be pruned
1585 evasionPrunable = isCheck
1586 && bestValue > value_mated_in(PLY_MAX)
1587 && !pos.move_is_capture(move)
1588 && pos.type_of_piece_on(move_from(move)) != KING
1589 && !pos.can_castle(pos.side_to_move());
1591 // Don't search moves with negative SEE values
1593 && (!isCheck || evasionPrunable)
1595 && !move_is_promotion(move)
1596 && pos.see_sign(move) < 0)
1599 // Update current move
1600 ss->currentMove = move;
1602 // Make and search the move
1603 pos.do_move(move, st, ci, moveIsCheck);
1604 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1605 pos.undo_move(move);
1607 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1610 if (value > bestValue)
1616 ss->bestMove = move;
1621 // All legal moves have been searched. A special case: If we're in check
1622 // and no legal moves were found, it is checkmate.
1623 if (isCheck && bestValue == -VALUE_INFINITE)
1624 return value_mated_in(ply);
1626 // Update transposition table
1627 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1628 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1629 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1631 // Update killers only for checking moves that fails high
1632 if ( bestValue >= beta
1633 && !pos.move_is_capture_or_promotion(ss->bestMove))
1634 update_killers(ss->bestMove, ss);
1636 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1642 // sp_search() is used to search from a split point. This function is called
1643 // by each thread working at the split point. It is similar to the normal
1644 // search() function, but simpler. Because we have already probed the hash
1645 // table, done a null move search, and searched the first move before
1646 // splitting, we don't have to repeat all this work in sp_search(). We
1647 // also don't need to store anything to the hash table here: This is taken
1648 // care of after we return from the split point.
1650 template <NodeType PvNode>
1651 void sp_search(SplitPoint* sp, int threadID) {
1653 assert(threadID >= 0 && threadID < TM.active_threads());
1654 assert(TM.active_threads() > 1);
1658 Depth ext, newDepth;
1660 Value futilityValueScaled; // NonPV specific
1661 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1663 value = -VALUE_INFINITE;
1665 Position pos(*sp->pos, threadID);
1667 SearchStack* ss = sp->sstack[threadID] + 1;
1668 isCheck = pos.is_check();
1670 // Step 10. Loop through moves
1671 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1672 lock_grab(&(sp->lock));
1674 while ( sp->bestValue < sp->beta
1675 && (move = sp->mp->get_next_move()) != MOVE_NONE
1676 && !TM.thread_should_stop(threadID))
1678 moveCount = ++sp->moveCount;
1679 lock_release(&(sp->lock));
1681 assert(move_is_ok(move));
1683 moveIsCheck = pos.move_is_check(move, ci);
1684 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1686 // Step 11. Decide the new search depth
1687 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1688 newDepth = sp->depth - OnePly + ext;
1690 // Update current move
1691 ss->currentMove = move;
1693 // Step 12. Futility pruning (is omitted in PV nodes)
1695 && !captureOrPromotion
1698 && !move_is_castle(move))
1700 // Move count based pruning
1701 if ( moveCount >= futility_move_count(sp->depth)
1702 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1703 && sp->bestValue > value_mated_in(PLY_MAX))
1705 lock_grab(&(sp->lock));
1709 // Value based pruning
1710 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1711 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1712 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1714 if (futilityValueScaled < sp->beta)
1716 lock_grab(&(sp->lock));
1718 if (futilityValueScaled > sp->bestValue)
1719 sp->bestValue = futilityValueScaled;
1724 // Step 13. Make the move
1725 pos.do_move(move, st, ci, moveIsCheck);
1727 // Step 14. Reduced search
1728 // If the move fails high will be re-searched at full depth.
1729 bool doFullDepthSearch = true;
1731 if ( !captureOrPromotion
1733 && !move_is_castle(move)
1734 && !move_is_killer(move, ss))
1736 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1739 Value localAlpha = sp->alpha;
1740 Depth d = newDepth - ss->reduction;
1741 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1742 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1744 doFullDepthSearch = (value > localAlpha);
1747 // The move failed high, but if reduction is very big we could
1748 // face a false positive, retry with a less aggressive reduction,
1749 // if the move fails high again then go with full depth search.
1750 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1752 assert(newDepth - OnePly >= OnePly);
1754 ss->reduction = OnePly;
1755 Value localAlpha = sp->alpha;
1756 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1757 doFullDepthSearch = (value > localAlpha);
1759 ss->reduction = Depth(0); // Restore original reduction
1762 // Step 15. Full depth search
1763 if (doFullDepthSearch)
1765 Value localAlpha = sp->alpha;
1766 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1767 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1769 // Step extra. pv search (only in PV nodes)
1770 // Search only for possible new PV nodes, if instead value >= beta then
1771 // parent node fails low with value <= alpha and tries another move.
1772 if (PvNode && value > localAlpha && value < sp->beta)
1773 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1774 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1777 // Step 16. Undo move
1778 pos.undo_move(move);
1780 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1782 // Step 17. Check for new best move
1783 lock_grab(&(sp->lock));
1785 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1787 sp->bestValue = value;
1789 if (sp->bestValue > sp->alpha)
1791 if (!PvNode || value >= sp->beta)
1792 sp->stopRequest = true;
1794 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1797 sp->parentSstack->bestMove = ss->bestMove = move;
1802 /* Here we have the lock still grabbed */
1804 sp->slaves[threadID] = 0;
1806 lock_release(&(sp->lock));
1810 // connected_moves() tests whether two moves are 'connected' in the sense
1811 // that the first move somehow made the second move possible (for instance
1812 // if the moving piece is the same in both moves). The first move is assumed
1813 // to be the move that was made to reach the current position, while the
1814 // second move is assumed to be a move from the current position.
1816 bool connected_moves(const Position& pos, Move m1, Move m2) {
1818 Square f1, t1, f2, t2;
1821 assert(move_is_ok(m1));
1822 assert(move_is_ok(m2));
1824 if (m2 == MOVE_NONE)
1827 // Case 1: The moving piece is the same in both moves
1833 // Case 2: The destination square for m2 was vacated by m1
1839 // Case 3: Moving through the vacated square
1840 if ( piece_is_slider(pos.piece_on(f2))
1841 && bit_is_set(squares_between(f2, t2), f1))
1844 // Case 4: The destination square for m2 is defended by the moving piece in m1
1845 p = pos.piece_on(t1);
1846 if (bit_is_set(pos.attacks_from(p, t1), t2))
1849 // Case 5: Discovered check, checking piece is the piece moved in m1
1850 if ( piece_is_slider(p)
1851 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1852 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1854 // discovered_check_candidates() works also if the Position's side to
1855 // move is the opposite of the checking piece.
1856 Color them = opposite_color(pos.side_to_move());
1857 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1859 if (bit_is_set(dcCandidates, f2))
1866 // value_is_mate() checks if the given value is a mate one
1867 // eventually compensated for the ply.
1869 bool value_is_mate(Value value) {
1871 assert(abs(value) <= VALUE_INFINITE);
1873 return value <= value_mated_in(PLY_MAX)
1874 || value >= value_mate_in(PLY_MAX);
1878 // move_is_killer() checks if the given move is among the
1879 // killer moves of that ply.
1881 bool move_is_killer(Move m, SearchStack* ss) {
1883 const Move* k = ss->killers;
1884 for (int i = 0; i < KILLER_MAX; i++, k++)
1892 // extension() decides whether a move should be searched with normal depth,
1893 // or with extended depth. Certain classes of moves (checking moves, in
1894 // particular) are searched with bigger depth than ordinary moves and in
1895 // any case are marked as 'dangerous'. Note that also if a move is not
1896 // extended, as example because the corresponding UCI option is set to zero,
1897 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1898 template <NodeType PvNode>
1899 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1900 bool singleEvasion, bool mateThreat, bool* dangerous) {
1902 assert(m != MOVE_NONE);
1904 Depth result = Depth(0);
1905 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1909 if (moveIsCheck && pos.see_sign(m) >= 0)
1910 result += CheckExtension[PvNode];
1913 result += SingleEvasionExtension[PvNode];
1916 result += MateThreatExtension[PvNode];
1919 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1921 Color c = pos.side_to_move();
1922 if (relative_rank(c, move_to(m)) == RANK_7)
1924 result += PawnPushTo7thExtension[PvNode];
1927 if (pos.pawn_is_passed(c, move_to(m)))
1929 result += PassedPawnExtension[PvNode];
1934 if ( captureOrPromotion
1935 && pos.type_of_piece_on(move_to(m)) != PAWN
1936 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1937 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1938 && !move_is_promotion(m)
1941 result += PawnEndgameExtension[PvNode];
1946 && captureOrPromotion
1947 && pos.type_of_piece_on(move_to(m)) != PAWN
1948 && pos.see_sign(m) >= 0)
1954 return Min(result, OnePly);
1958 // connected_threat() tests whether it is safe to forward prune a move or if
1959 // is somehow coonected to the threat move returned by null search.
1961 bool connected_threat(const Position& pos, Move m, Move threat) {
1963 assert(move_is_ok(m));
1964 assert(threat && move_is_ok(threat));
1965 assert(!pos.move_is_check(m));
1966 assert(!pos.move_is_capture_or_promotion(m));
1967 assert(!pos.move_is_passed_pawn_push(m));
1969 Square mfrom, mto, tfrom, tto;
1971 mfrom = move_from(m);
1973 tfrom = move_from(threat);
1974 tto = move_to(threat);
1976 // Case 1: Don't prune moves which move the threatened piece
1980 // Case 2: If the threatened piece has value less than or equal to the
1981 // value of the threatening piece, don't prune move which defend it.
1982 if ( pos.move_is_capture(threat)
1983 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1984 || pos.type_of_piece_on(tfrom) == KING)
1985 && pos.move_attacks_square(m, tto))
1988 // Case 3: If the moving piece in the threatened move is a slider, don't
1989 // prune safe moves which block its ray.
1990 if ( piece_is_slider(pos.piece_on(tfrom))
1991 && bit_is_set(squares_between(tfrom, tto), mto)
1992 && pos.see_sign(m) >= 0)
1999 // ok_to_use_TT() returns true if a transposition table score
2000 // can be used at a given point in search.
2002 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2004 Value v = value_from_tt(tte->value(), ply);
2006 return ( tte->depth() >= depth
2007 || v >= Max(value_mate_in(PLY_MAX), beta)
2008 || v < Min(value_mated_in(PLY_MAX), beta))
2010 && ( (is_lower_bound(tte->type()) && v >= beta)
2011 || (is_upper_bound(tte->type()) && v < beta));
2015 // refine_eval() returns the transposition table score if
2016 // possible otherwise falls back on static position evaluation.
2018 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2023 Value v = value_from_tt(tte->value(), ply);
2025 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2026 || (is_upper_bound(tte->type()) && v < defaultEval))
2033 // update_history() registers a good move that produced a beta-cutoff
2034 // in history and marks as failures all the other moves of that ply.
2036 void update_history(const Position& pos, Move move, Depth depth,
2037 Move movesSearched[], int moveCount) {
2041 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2043 for (int i = 0; i < moveCount - 1; i++)
2045 m = movesSearched[i];
2049 if (!pos.move_is_capture_or_promotion(m))
2050 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2055 // update_killers() add a good move that produced a beta-cutoff
2056 // among the killer moves of that ply.
2058 void update_killers(Move m, SearchStack* ss) {
2060 if (m == ss->killers[0])
2063 for (int i = KILLER_MAX - 1; i > 0; i--)
2064 ss->killers[i] = ss->killers[i - 1];
2070 // update_gains() updates the gains table of a non-capture move given
2071 // the static position evaluation before and after the move.
2073 void update_gains(const Position& pos, Move m, Value before, Value after) {
2076 && before != VALUE_NONE
2077 && after != VALUE_NONE
2078 && pos.captured_piece() == NO_PIECE_TYPE
2079 && !move_is_castle(m)
2080 && !move_is_promotion(m))
2081 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2085 // current_search_time() returns the number of milliseconds which have passed
2086 // since the beginning of the current search.
2088 int current_search_time() {
2090 return get_system_time() - SearchStartTime;
2094 // nps() computes the current nodes/second count.
2098 int t = current_search_time();
2099 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2103 // poll() performs two different functions: It polls for user input, and it
2104 // looks at the time consumed so far and decides if it's time to abort the
2109 static int lastInfoTime;
2110 int t = current_search_time();
2115 // We are line oriented, don't read single chars
2116 std::string command;
2118 if (!std::getline(std::cin, command))
2121 if (command == "quit")
2124 PonderSearch = false;
2128 else if (command == "stop")
2131 PonderSearch = false;
2133 else if (command == "ponderhit")
2137 // Print search information
2141 else if (lastInfoTime > t)
2142 // HACK: Must be a new search where we searched less than
2143 // NodesBetweenPolls nodes during the first second of search.
2146 else if (t - lastInfoTime >= 1000)
2153 if (dbg_show_hit_rate)
2154 dbg_print_hit_rate();
2156 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2157 << " time " << t << " hashfull " << TT.full() << endl;
2160 // Should we stop the search?
2164 bool stillAtFirstMove = FirstRootMove
2165 && !AspirationFailLow
2166 && t > MaxSearchTime + ExtraSearchTime;
2168 bool noMoreTime = t > AbsoluteMaxSearchTime
2169 || stillAtFirstMove;
2171 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2172 || (ExactMaxTime && t >= ExactMaxTime)
2173 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2178 // ponderhit() is called when the program is pondering (i.e. thinking while
2179 // it's the opponent's turn to move) in order to let the engine know that
2180 // it correctly predicted the opponent's move.
2184 int t = current_search_time();
2185 PonderSearch = false;
2187 bool stillAtFirstMove = FirstRootMove
2188 && !AspirationFailLow
2189 && t > MaxSearchTime + ExtraSearchTime;
2191 bool noMoreTime = t > AbsoluteMaxSearchTime
2192 || stillAtFirstMove;
2194 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2199 // init_ss_array() does a fast reset of the first entries of a SearchStack
2200 // array and of all the excludedMove and skipNullMove entries.
2202 void init_ss_array(SearchStack* ss, int size) {
2204 for (int i = 0; i < size; i++, ss++)
2206 ss->excludedMove = MOVE_NONE;
2207 ss->skipNullMove = false;
2218 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2219 // while the program is pondering. The point is to work around a wrinkle in
2220 // the UCI protocol: When pondering, the engine is not allowed to give a
2221 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2222 // We simply wait here until one of these commands is sent, and return,
2223 // after which the bestmove and pondermove will be printed (in id_loop()).
2225 void wait_for_stop_or_ponderhit() {
2227 std::string command;
2231 if (!std::getline(std::cin, command))
2234 if (command == "quit")
2239 else if (command == "ponderhit" || command == "stop")
2245 // print_pv_info() prints to standard output and eventually to log file information on
2246 // the current PV line. It is called at each iteration or after a new pv is found.
2248 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2250 cout << "info depth " << Iteration
2251 << " score " << value_to_string(value)
2252 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2253 << " time " << current_search_time()
2254 << " nodes " << TM.nodes_searched()
2258 for (Move* m = pv; *m != MOVE_NONE; m++)
2265 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2266 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2268 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2269 TM.nodes_searched(), value, t, pv) << endl;
2274 // init_thread() is the function which is called when a new thread is
2275 // launched. It simply calls the idle_loop() function with the supplied
2276 // threadID. There are two versions of this function; one for POSIX
2277 // threads and one for Windows threads.
2279 #if !defined(_MSC_VER)
2281 void* init_thread(void *threadID) {
2283 TM.idle_loop(*(int*)threadID, NULL);
2289 DWORD WINAPI init_thread(LPVOID threadID) {
2291 TM.idle_loop(*(int*)threadID, NULL);
2298 /// The ThreadsManager class
2300 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2301 // get_beta_counters() are getters/setters for the per thread
2302 // counters used to sort the moves at root.
2304 void ThreadsManager::resetNodeCounters() {
2306 for (int i = 0; i < MAX_THREADS; i++)
2307 threads[i].nodes = 0ULL;
2310 void ThreadsManager::resetBetaCounters() {
2312 for (int i = 0; i < MAX_THREADS; i++)
2313 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2316 int64_t ThreadsManager::nodes_searched() const {
2318 int64_t result = 0ULL;
2319 for (int i = 0; i < ActiveThreads; i++)
2320 result += threads[i].nodes;
2325 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2328 for (int i = 0; i < MAX_THREADS; i++)
2330 our += threads[i].betaCutOffs[us];
2331 their += threads[i].betaCutOffs[opposite_color(us)];
2336 // idle_loop() is where the threads are parked when they have no work to do.
2337 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2338 // object for which the current thread is the master.
2340 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2342 assert(threadID >= 0 && threadID < MAX_THREADS);
2346 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2347 // master should exit as last one.
2348 if (AllThreadsShouldExit)
2351 threads[threadID].state = THREAD_TERMINATED;
2355 // If we are not thinking, wait for a condition to be signaled
2356 // instead of wasting CPU time polling for work.
2357 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2360 assert(threadID != 0);
2361 threads[threadID].state = THREAD_SLEEPING;
2363 #if !defined(_MSC_VER)
2364 lock_grab(&WaitLock);
2365 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2366 pthread_cond_wait(&WaitCond, &WaitLock);
2367 lock_release(&WaitLock);
2369 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2373 // If thread has just woken up, mark it as available
2374 if (threads[threadID].state == THREAD_SLEEPING)
2375 threads[threadID].state = THREAD_AVAILABLE;
2377 // If this thread has been assigned work, launch a search
2378 if (threads[threadID].state == THREAD_WORKISWAITING)
2380 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2382 threads[threadID].state = THREAD_SEARCHING;
2384 if (threads[threadID].splitPoint->pvNode)
2385 sp_search<PV>(threads[threadID].splitPoint, threadID);
2387 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2389 assert(threads[threadID].state == THREAD_SEARCHING);
2391 threads[threadID].state = THREAD_AVAILABLE;
2394 // If this thread is the master of a split point and all slaves have
2395 // finished their work at this split point, return from the idle loop.
2397 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2399 if (i == ActiveThreads)
2401 // Because sp->slaves[] is reset under lock protection,
2402 // be sure sp->lock has been released before to return.
2403 lock_grab(&(sp->lock));
2404 lock_release(&(sp->lock));
2406 assert(threads[threadID].state == THREAD_AVAILABLE);
2408 threads[threadID].state = THREAD_SEARCHING;
2415 // init_threads() is called during startup. It launches all helper threads,
2416 // and initializes the split point stack and the global locks and condition
2419 void ThreadsManager::init_threads() {
2424 #if !defined(_MSC_VER)
2425 pthread_t pthread[1];
2428 // Initialize global locks
2429 lock_init(&MPLock, NULL);
2430 lock_init(&WaitLock, NULL);
2432 #if !defined(_MSC_VER)
2433 pthread_cond_init(&WaitCond, NULL);
2435 for (i = 0; i < MAX_THREADS; i++)
2436 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2439 // Initialize splitPoints[] locks
2440 for (i = 0; i < MAX_THREADS; i++)
2441 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2442 lock_init(&(threads[i].splitPoints[j].lock), NULL);
2444 // Will be set just before program exits to properly end the threads
2445 AllThreadsShouldExit = false;
2447 // Threads will be put to sleep as soon as created
2448 AllThreadsShouldSleep = true;
2450 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2452 threads[0].state = THREAD_SEARCHING;
2453 for (i = 1; i < MAX_THREADS; i++)
2454 threads[i].state = THREAD_AVAILABLE;
2456 // Launch the helper threads
2457 for (i = 1; i < MAX_THREADS; i++)
2460 #if !defined(_MSC_VER)
2461 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2463 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2468 cout << "Failed to create thread number " << i << endl;
2469 Application::exit_with_failure();
2472 // Wait until the thread has finished launching and is gone to sleep
2473 while (threads[i].state != THREAD_SLEEPING) {}
2478 // exit_threads() is called when the program exits. It makes all the
2479 // helper threads exit cleanly.
2481 void ThreadsManager::exit_threads() {
2483 ActiveThreads = MAX_THREADS; // HACK
2484 AllThreadsShouldSleep = true; // HACK
2485 wake_sleeping_threads();
2487 // This makes the threads to exit idle_loop()
2488 AllThreadsShouldExit = true;
2490 // Wait for thread termination
2491 for (int i = 1; i < MAX_THREADS; i++)
2492 while (threads[i].state != THREAD_TERMINATED) {}
2494 // Now we can safely destroy the locks
2495 for (int i = 0; i < MAX_THREADS; i++)
2496 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2497 lock_destroy(&(threads[i].splitPoints[j].lock));
2499 lock_destroy(&WaitLock);
2500 lock_destroy(&MPLock);
2504 // thread_should_stop() checks whether the thread should stop its search.
2505 // This can happen if a beta cutoff has occurred in the thread's currently
2506 // active split point, or in some ancestor of the current split point.
2508 bool ThreadsManager::thread_should_stop(int threadID) const {
2510 assert(threadID >= 0 && threadID < ActiveThreads);
2514 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2519 // thread_is_available() checks whether the thread with threadID "slave" is
2520 // available to help the thread with threadID "master" at a split point. An
2521 // obvious requirement is that "slave" must be idle. With more than two
2522 // threads, this is not by itself sufficient: If "slave" is the master of
2523 // some active split point, it is only available as a slave to the other
2524 // threads which are busy searching the split point at the top of "slave"'s
2525 // split point stack (the "helpful master concept" in YBWC terminology).
2527 bool ThreadsManager::thread_is_available(int slave, int master) const {
2529 assert(slave >= 0 && slave < ActiveThreads);
2530 assert(master >= 0 && master < ActiveThreads);
2531 assert(ActiveThreads > 1);
2533 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2536 // Make a local copy to be sure doesn't change under our feet
2537 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2539 if (localActiveSplitPoints == 0)
2540 // No active split points means that the thread is available as
2541 // a slave for any other thread.
2544 if (ActiveThreads == 2)
2547 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2548 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2549 // could have been set to 0 by another thread leading to an out of bound access.
2550 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2557 // available_thread_exists() tries to find an idle thread which is available as
2558 // a slave for the thread with threadID "master".
2560 bool ThreadsManager::available_thread_exists(int master) const {
2562 assert(master >= 0 && master < ActiveThreads);
2563 assert(ActiveThreads > 1);
2565 for (int i = 0; i < ActiveThreads; i++)
2566 if (thread_is_available(i, master))
2573 // split() does the actual work of distributing the work at a node between
2574 // several available threads. If it does not succeed in splitting the
2575 // node (because no idle threads are available, or because we have no unused
2576 // split point objects), the function immediately returns. If splitting is
2577 // possible, a SplitPoint object is initialized with all the data that must be
2578 // copied to the helper threads and we tell our helper threads that they have
2579 // been assigned work. This will cause them to instantly leave their idle loops
2580 // and call sp_search(). When all threads have returned from sp_search() then
2583 template <bool Fake>
2584 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2585 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2586 int* moveCount, MovePicker* mp, bool pvNode) {
2588 assert(ply > 0 && ply < PLY_MAX);
2589 assert(*bestValue >= -VALUE_INFINITE);
2590 assert(*bestValue <= *alpha);
2591 assert(*alpha < beta);
2592 assert(beta <= VALUE_INFINITE);
2593 assert(depth > Depth(0));
2594 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2595 assert(ActiveThreads > 1);
2597 int i, master = p.thread();
2598 Thread& masterThread = threads[master];
2602 // If no other thread is available to help us, or if we have too many
2603 // active split points, don't split.
2604 if ( !available_thread_exists(master)
2605 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2607 lock_release(&MPLock);
2611 // Pick the next available split point object from the split point stack
2612 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2614 // Initialize the split point object
2615 splitPoint.parent = masterThread.splitPoint;
2616 splitPoint.stopRequest = false;
2617 splitPoint.ply = ply;
2618 splitPoint.depth = depth;
2619 splitPoint.mateThreat = mateThreat;
2620 splitPoint.alpha = *alpha;
2621 splitPoint.beta = beta;
2622 splitPoint.pvNode = pvNode;
2623 splitPoint.bestValue = *bestValue;
2625 splitPoint.moveCount = *moveCount;
2626 splitPoint.pos = &p;
2627 splitPoint.parentSstack = ss;
2628 for (i = 0; i < ActiveThreads; i++)
2629 splitPoint.slaves[i] = 0;
2631 masterThread.splitPoint = &splitPoint;
2633 // If we are here it means we are not available
2634 assert(masterThread.state != THREAD_AVAILABLE);
2636 int workersCnt = 1; // At least the master is included
2638 // Allocate available threads setting state to THREAD_BOOKED
2639 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2640 if (thread_is_available(i, master))
2642 threads[i].state = THREAD_BOOKED;
2643 threads[i].splitPoint = &splitPoint;
2644 splitPoint.slaves[i] = 1;
2648 assert(Fake || workersCnt > 1);
2650 // We can release the lock because slave threads are already booked and master is not available
2651 lock_release(&MPLock);
2653 // Tell the threads that they have work to do. This will make them leave
2654 // their idle loop. But before copy search stack tail for each thread.
2655 for (i = 0; i < ActiveThreads; i++)
2656 if (i == master || splitPoint.slaves[i])
2658 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2660 assert(i == master || threads[i].state == THREAD_BOOKED);
2662 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2665 // Everything is set up. The master thread enters the idle loop, from
2666 // which it will instantly launch a search, because its state is
2667 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2668 // idle loop, which means that the main thread will return from the idle
2669 // loop when all threads have finished their work at this split point.
2670 idle_loop(master, &splitPoint);
2672 // We have returned from the idle loop, which means that all threads are
2673 // finished. Update alpha and bestValue, and return.
2676 *alpha = splitPoint.alpha;
2677 *bestValue = splitPoint.bestValue;
2678 masterThread.activeSplitPoints--;
2679 masterThread.splitPoint = splitPoint.parent;
2681 lock_release(&MPLock);
2685 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2686 // to start a new search from the root.
2688 void ThreadsManager::wake_sleeping_threads() {
2690 assert(AllThreadsShouldSleep);
2691 assert(ActiveThreads > 0);
2693 AllThreadsShouldSleep = false;
2695 if (ActiveThreads == 1)
2698 #if !defined(_MSC_VER)
2699 pthread_mutex_lock(&WaitLock);
2700 pthread_cond_broadcast(&WaitCond);
2701 pthread_mutex_unlock(&WaitLock);
2703 for (int i = 1; i < MAX_THREADS; i++)
2704 SetEvent(SitIdleEvent[i]);
2710 // put_threads_to_sleep() makes all the threads go to sleep just before
2711 // to leave think(), at the end of the search. Threads should have already
2712 // finished the job and should be idle.
2714 void ThreadsManager::put_threads_to_sleep() {
2716 assert(!AllThreadsShouldSleep);
2718 // This makes the threads to go to sleep
2719 AllThreadsShouldSleep = true;
2722 /// The RootMoveList class
2724 // RootMoveList c'tor
2726 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2728 SearchStack ss[PLY_MAX_PLUS_2];
2729 MoveStack mlist[MaxRootMoves];
2731 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2733 // Generate all legal moves
2734 MoveStack* last = generate_moves(pos, mlist);
2736 // Add each move to the moves[] array
2737 for (MoveStack* cur = mlist; cur != last; cur++)
2739 bool includeMove = includeAllMoves;
2741 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2742 includeMove = (searchMoves[k] == cur->move);
2747 // Find a quick score for the move
2748 init_ss_array(ss, PLY_MAX_PLUS_2);
2749 pos.do_move(cur->move, st);
2750 moves[count].move = cur->move;
2751 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2752 moves[count].pv[0] = cur->move;
2753 moves[count].pv[1] = MOVE_NONE;
2754 pos.undo_move(cur->move);
2761 // RootMoveList simple methods definitions
2763 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2765 moves[moveNum].nodes = nodes;
2766 moves[moveNum].cumulativeNodes += nodes;
2769 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2771 moves[moveNum].ourBeta = our;
2772 moves[moveNum].theirBeta = their;
2775 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2779 for (j = 0; pv[j] != MOVE_NONE; j++)
2780 moves[moveNum].pv[j] = pv[j];
2782 moves[moveNum].pv[j] = MOVE_NONE;
2786 // RootMoveList::sort() sorts the root move list at the beginning of a new
2789 void RootMoveList::sort() {
2791 sort_multipv(count - 1); // Sort all items
2795 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2796 // list by their scores and depths. It is used to order the different PVs
2797 // correctly in MultiPV mode.
2799 void RootMoveList::sort_multipv(int n) {
2803 for (i = 1; i <= n; i++)
2805 RootMove rm = moves[i];
2806 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2807 moves[j] = moves[j - 1];