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];
101 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
103 Lock MPLock, WaitLock;
105 #if !defined(_MSC_VER)
106 pthread_cond_t WaitCond;
108 HANDLE SitIdleEvent[MAX_THREADS];
114 // RootMove struct is used for moves at the root at the tree. For each
115 // root move, we store a score, a node count, and a PV (really a refutation
116 // in the case of moves which fail low).
120 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
122 // RootMove::operator<() is the comparison function used when
123 // sorting the moves. A move m1 is considered to be better
124 // than a move m2 if it has a higher score, or if the moves
125 // have equal score but m1 has the higher beta cut-off count.
126 bool operator<(const RootMove& m) const {
128 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
133 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
134 Move pv[PLY_MAX_PLUS_2];
138 // The RootMoveList class is essentially an array of RootMove objects, with
139 // a handful of methods for accessing the data in the individual moves.
144 RootMoveList(Position& pos, Move searchMoves[]);
146 int move_count() const { return count; }
147 Move get_move(int moveNum) const { return moves[moveNum].move; }
148 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
149 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
150 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
151 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
153 void set_move_nodes(int moveNum, int64_t nodes);
154 void set_beta_counters(int moveNum, int64_t our, int64_t their);
155 void set_move_pv(int moveNum, const Move pv[]);
157 void sort_multipv(int n);
160 static const int MaxRootMoves = 500;
161 RootMove moves[MaxRootMoves];
170 // Maximum depth for razoring
171 const Depth RazorDepth = 4 * OnePly;
173 // Dynamic razoring margin based on depth
174 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
176 // Step 8. Null move search with verification search
178 // Null move margin. A null move search will not be done if the static
179 // evaluation of the position is more than NullMoveMargin below beta.
180 const Value NullMoveMargin = Value(0x200);
182 // Maximum depth for use of dynamic threat detection when null move fails low
183 const Depth ThreatDepth = 5 * OnePly;
185 // Step 9. Internal iterative deepening
187 // Minimum depth for use of internal iterative deepening
188 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
190 // At Non-PV nodes we do an internal iterative deepening search
191 // when the static evaluation is bigger then beta - IIDMargin.
192 const Value IIDMargin = Value(0x100);
194 // Step 11. Decide the new search depth
196 // Extensions. Configurable UCI options
197 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
198 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
199 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
201 // Minimum depth for use of singular extension
202 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
204 // If the TT move is at least SingularExtensionMargin better then the
205 // remaining ones we will extend it.
206 const Value SingularExtensionMargin = Value(0x20);
208 // Step 12. Futility pruning
210 // Futility margin for quiescence search
211 const Value FutilityMarginQS = Value(0x80);
213 // Futility lookup tables (initialized at startup) and their getter functions
214 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
215 int FutilityMoveCountArray[32]; // [depth]
217 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
218 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
220 // Step 14. Reduced search
222 // Reduction lookup tables (initialized at startup) and their getter functions
223 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
225 template <NodeType PV>
226 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
228 // Common adjustments
230 // Search depth at iteration 1
231 const Depth InitialDepth = OnePly;
233 // Easy move margin. An easy move candidate must be at least this much
234 // better than the second best move.
235 const Value EasyMoveMargin = Value(0x200);
237 // Last seconds noise filtering (LSN)
238 const bool UseLSNFiltering = false;
239 const int LSNTime = 100; // In milliseconds
240 const Value LSNValue = value_from_centipawns(200);
241 bool loseOnTime = false;
249 // Scores and number of times the best move changed for each iteration
250 Value ValueByIteration[PLY_MAX_PLUS_2];
251 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
253 // Search window management
259 // Time managment variables
260 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
261 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
262 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
263 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
267 std::ofstream LogFile;
269 // Multi-threads related variables
270 Depth MinimumSplitDepth;
271 int MaxThreadsPerSplitPoint;
274 // Node counters, used only by thread[0] but try to keep in different cache
275 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
277 int NodesBetweenPolls = 30000;
284 Value id_loop(const Position& pos, Move searchMoves[]);
285 Value root_search(Position& pos, SearchStack* ss, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
287 template <NodeType PvNode>
288 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
290 template <NodeType PvNode>
291 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
293 template <NodeType PvNode>
294 void sp_search(SplitPoint* sp, int threadID);
296 template <NodeType PvNode>
297 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
299 void update_pv(SearchStack* ss);
300 void sp_update_pv(SearchStack* pss, SearchStack* ss);
301 bool connected_moves(const Position& pos, Move m1, Move m2);
302 bool value_is_mate(Value value);
303 bool move_is_killer(Move m, SearchStack* ss);
304 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
305 bool connected_threat(const Position& pos, Move m, Move threat);
306 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
307 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
308 void update_killers(Move m, SearchStack* ss);
309 void update_gains(const Position& pos, Move move, Value before, Value after);
311 int current_search_time();
315 void wait_for_stop_or_ponderhit();
316 void init_ss_array(SearchStack* ss, int size);
317 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value);
319 #if !defined(_MSC_VER)
320 void *init_thread(void *threadID);
322 DWORD WINAPI init_thread(LPVOID threadID);
332 /// init_threads(), exit_threads() and nodes_searched() are helpers to
333 /// give accessibility to some TM methods from outside of current file.
335 void init_threads() { TM.init_threads(); }
336 void exit_threads() { TM.exit_threads(); }
337 int64_t nodes_searched() { return TM.nodes_searched(); }
340 /// init_search() is called during startup. It initializes various lookup tables
344 int d; // depth (OnePly == 2)
345 int hd; // half depth (OnePly == 1)
348 // Init reductions array
349 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
351 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
352 double nonPVRed = log(double(hd)) * log(double(mc)) / 1.5;
353 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
354 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
357 // Init futility margins array
358 for (d = 0; d < 16; d++) for (mc = 0; mc < 64; mc++)
359 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
361 // Init futility move count array
362 for (d = 0; d < 32; d++)
363 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
367 // SearchStack::init() initializes a search stack entry.
368 // Called at the beginning of search() when starting to examine a new node.
369 void SearchStack::init() {
371 pv[0] = pv[1] = MOVE_NONE;
372 currentMove = threatMove = MOVE_NONE;
373 reduction = Depth(0);
377 // SearchStack::initKillers() initializes killers for a search stack entry
378 void SearchStack::initKillers() {
380 mateKiller = MOVE_NONE;
381 for (int i = 0; i < KILLER_MAX; i++)
382 killers[i] = MOVE_NONE;
386 /// perft() is our utility to verify move generation is bug free. All the legal
387 /// moves up to given depth are generated and counted and the sum returned.
389 int perft(Position& pos, Depth depth)
394 MovePicker mp(pos, MOVE_NONE, depth, H);
396 // If we are at the last ply we don't need to do and undo
397 // the moves, just to count them.
398 if (depth <= OnePly) // Replace with '<' to test also qsearch
400 while (mp.get_next_move()) sum++;
404 // Loop through all legal moves
406 while ((move = mp.get_next_move()) != MOVE_NONE)
408 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
409 sum += perft(pos, depth - OnePly);
416 /// think() is the external interface to Stockfish's search, and is called when
417 /// the program receives the UCI 'go' command. It initializes various
418 /// search-related global variables, and calls root_search(). It returns false
419 /// when a quit command is received during the search.
421 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
422 int time[], int increment[], int movesToGo, int maxDepth,
423 int maxNodes, int maxTime, Move searchMoves[]) {
425 // Initialize global search variables
426 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
427 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
429 TM.resetNodeCounters();
430 SearchStartTime = get_system_time();
431 ExactMaxTime = maxTime;
434 InfiniteSearch = infinite;
435 PonderSearch = ponder;
436 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
438 // Look for a book move, only during games, not tests
439 if (UseTimeManagement && get_option_value_bool("OwnBook"))
441 if (get_option_value_string("Book File") != OpeningBook.file_name())
442 OpeningBook.open(get_option_value_string("Book File"));
444 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
445 if (bookMove != MOVE_NONE)
448 wait_for_stop_or_ponderhit();
450 cout << "bestmove " << bookMove << endl;
455 // Reset loseOnTime flag at the beginning of a new game
456 if (button_was_pressed("New Game"))
459 // Read UCI option values
460 TT.set_size(get_option_value_int("Hash"));
461 if (button_was_pressed("Clear Hash"))
464 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
465 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
466 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
467 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
468 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
469 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
470 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
471 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
472 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
473 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
474 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
475 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
477 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
478 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
479 MultiPV = get_option_value_int("MultiPV");
480 Chess960 = get_option_value_bool("UCI_Chess960");
481 UseLogFile = get_option_value_bool("Use Search Log");
484 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
486 read_weights(pos.side_to_move());
488 // Set the number of active threads
489 int newActiveThreads = get_option_value_int("Threads");
490 if (newActiveThreads != TM.active_threads())
492 TM.set_active_threads(newActiveThreads);
493 init_eval(TM.active_threads());
496 // Wake up sleeping threads
497 TM.wake_sleeping_threads();
500 int myTime = time[side_to_move];
501 int myIncrement = increment[side_to_move];
502 if (UseTimeManagement)
504 if (!movesToGo) // Sudden death time control
508 MaxSearchTime = myTime / 30 + myIncrement;
509 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
511 else // Blitz game without increment
513 MaxSearchTime = myTime / 30;
514 AbsoluteMaxSearchTime = myTime / 8;
517 else // (x moves) / (y minutes)
521 MaxSearchTime = myTime / 2;
522 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
526 MaxSearchTime = myTime / Min(movesToGo, 20);
527 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
531 if (get_option_value_bool("Ponder"))
533 MaxSearchTime += MaxSearchTime / 4;
534 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
538 // Set best NodesBetweenPolls interval to avoid lagging under
539 // heavy time pressure.
541 NodesBetweenPolls = Min(MaxNodes, 30000);
542 else if (myTime && myTime < 1000)
543 NodesBetweenPolls = 1000;
544 else if (myTime && myTime < 5000)
545 NodesBetweenPolls = 5000;
547 NodesBetweenPolls = 30000;
549 // Write search information to log file
551 LogFile << "Searching: " << pos.to_fen() << endl
552 << "infinite: " << infinite
553 << " ponder: " << ponder
554 << " time: " << myTime
555 << " increment: " << myIncrement
556 << " moves to go: " << movesToGo << endl;
558 // LSN filtering. Used only for developing purposes, disabled by default
562 // Step 2. If after last move we decided to lose on time, do it now!
563 while (SearchStartTime + myTime + 1000 > get_system_time())
567 // We're ready to start thinking. Call the iterative deepening loop function
568 Value v = id_loop(pos, searchMoves);
572 // Step 1. If this is sudden death game and our position is hopeless,
573 // decide to lose on time.
574 if ( !loseOnTime // If we already lost on time, go to step 3.
584 // Step 3. Now after stepping over the time limit, reset flag for next match.
592 TM.put_threads_to_sleep();
600 // id_loop() is the main iterative deepening loop. It calls root_search
601 // repeatedly with increasing depth until the allocated thinking time has
602 // been consumed, the user stops the search, or the maximum search depth is
605 Value id_loop(const Position& pos, Move searchMoves[]) {
607 Position p(pos, pos.thread());
608 SearchStack ss[PLY_MAX_PLUS_2];
609 Move EasyMove = MOVE_NONE;
610 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
612 // Moves to search are verified, copied, scored and sorted
613 RootMoveList rml(p, searchMoves);
615 // Handle special case of searching on a mate/stale position
616 if (rml.move_count() == 0)
619 wait_for_stop_or_ponderhit();
621 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
624 // Print RootMoveList startup scoring to the standard output,
625 // so to output information also for iteration 1.
626 cout << "info depth " << 1
627 << "\ninfo depth " << 1
628 << " score " << value_to_string(rml.get_move_score(0))
629 << " time " << current_search_time()
630 << " nodes " << TM.nodes_searched()
632 << " pv " << rml.get_move(0) << "\n";
637 init_ss_array(ss, PLY_MAX_PLUS_2);
638 ValueByIteration[1] = rml.get_move_score(0);
641 // Is one move significantly better than others after initial scoring ?
642 if ( rml.move_count() == 1
643 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
644 EasyMove = rml.get_move(0);
646 // Iterative deepening loop
647 while (Iteration < PLY_MAX)
649 // Initialize iteration
651 BestMoveChangesByIteration[Iteration] = 0;
653 cout << "info depth " << Iteration << endl;
655 // Calculate dynamic aspiration window based on previous iterations
656 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
658 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
659 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
661 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
662 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
664 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
665 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
668 // Search to the current depth, rml is updated and sorted, alpha and beta could change
669 value = root_search(p, ss, rml, &alpha, &beta);
671 // Write PV to transposition table, in case the relevant entries have
672 // been overwritten during the search.
673 TT.insert_pv(p, ss->pv);
676 break; // Value cannot be trusted. Break out immediately!
678 //Save info about search result
679 ValueByIteration[Iteration] = value;
681 // Drop the easy move if differs from the new best move
682 if (ss->pv[0] != EasyMove)
683 EasyMove = MOVE_NONE;
685 if (UseTimeManagement)
688 bool stopSearch = false;
690 // Stop search early if there is only a single legal move,
691 // we search up to Iteration 6 anyway to get a proper score.
692 if (Iteration >= 6 && rml.move_count() == 1)
695 // Stop search early when the last two iterations returned a mate score
697 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
698 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
701 // Stop search early if one move seems to be much better than the others
702 int64_t nodes = TM.nodes_searched();
704 && EasyMove == ss->pv[0]
705 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
706 && current_search_time() > MaxSearchTime / 16)
707 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
708 && current_search_time() > MaxSearchTime / 32)))
711 // Add some extra time if the best move has changed during the last two iterations
712 if (Iteration > 5 && Iteration <= 50)
713 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
714 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
716 // Stop search if most of MaxSearchTime is consumed at the end of the
717 // iteration. We probably don't have enough time to search the first
718 // move at the next iteration anyway.
719 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
725 StopOnPonderhit = true;
731 if (MaxDepth && Iteration >= MaxDepth)
735 // If we are pondering or in infinite search, we shouldn't print the
736 // best move before we are told to do so.
737 if (!AbortSearch && (PonderSearch || InfiniteSearch))
738 wait_for_stop_or_ponderhit();
740 // Print final search statistics
741 cout << "info nodes " << TM.nodes_searched()
743 << " time " << current_search_time()
744 << " hashfull " << TT.full() << endl;
746 // Print the best move and the ponder move to the standard output
747 if (ss->pv[0] == MOVE_NONE)
749 ss->pv[0] = rml.get_move(0);
750 ss->pv[1] = MOVE_NONE;
753 assert(ss->pv[0] != MOVE_NONE);
755 cout << "bestmove " << ss->pv[0];
757 if (ss->pv[1] != MOVE_NONE)
758 cout << " ponder " << ss->pv[1];
765 dbg_print_mean(LogFile);
767 if (dbg_show_hit_rate)
768 dbg_print_hit_rate(LogFile);
770 LogFile << "\nNodes: " << TM.nodes_searched()
771 << "\nNodes/second: " << nps()
772 << "\nBest move: " << move_to_san(p, ss->pv[0]);
775 p.do_move(ss->pv[0], st);
776 LogFile << "\nPonder move: "
777 << move_to_san(p, ss->pv[1]) // Works also with MOVE_NONE
780 return rml.get_move_score(0);
784 // root_search() is the function which searches the root node. It is
785 // similar to search_pv except that it uses a different move ordering
786 // scheme, prints some information to the standard output and handles
787 // the fail low/high loops.
789 Value root_search(Position& pos, SearchStack* ss, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
796 Depth depth, ext, newDepth;
797 Value value, alpha, beta;
798 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
799 int researchCountFH, researchCountFL;
801 researchCountFH = researchCountFL = 0;
804 isCheck = pos.is_check();
806 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
807 // Step 2. Check for aborted search (omitted at root)
808 // Step 3. Mate distance pruning (omitted at root)
809 // Step 4. Transposition table lookup (omitted at root)
811 // Step 5. Evaluate the position statically
812 // At root we do this only to get reference value for child nodes
814 ss->eval = evaluate(pos, ei);
816 // Step 6. Razoring (omitted at root)
817 // Step 7. Static null move pruning (omitted at root)
818 // Step 8. Null move search with verification search (omitted at root)
819 // Step 9. Internal iterative deepening (omitted at root)
821 // Step extra. Fail low loop
822 // We start with small aspiration window and in case of fail low, we research
823 // with bigger window until we are not failing low anymore.
826 // Sort the moves before to (re)search
829 // Step 10. Loop through all moves in the root move list
830 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
832 // This is used by time management
833 FirstRootMove = (i == 0);
835 // Save the current node count before the move is searched
836 nodes = TM.nodes_searched();
838 // Reset beta cut-off counters
839 TM.resetBetaCounters();
841 // Pick the next root move, and print the move and the move number to
842 // the standard output.
843 move = ss->currentMove = rml.get_move(i);
845 if (current_search_time() >= 1000)
846 cout << "info currmove " << move
847 << " currmovenumber " << i + 1 << endl;
849 moveIsCheck = pos.move_is_check(move);
850 captureOrPromotion = pos.move_is_capture_or_promotion(move);
852 // Step 11. Decide the new search depth
853 depth = (Iteration - 2) * OnePly + InitialDepth;
854 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
855 newDepth = depth + ext;
857 // Step 12. Futility pruning (omitted at root)
859 // Step extra. Fail high loop
860 // If move fails high, we research with bigger window until we are not failing
862 value = - VALUE_INFINITE;
866 // Step 13. Make the move
867 pos.do_move(move, st, ci, moveIsCheck);
869 // Step extra. pv search
870 // We do pv search for first moves (i < MultiPV)
871 // and for fail high research (value > alpha)
872 if (i < MultiPV || value > alpha)
874 // Aspiration window is disabled in multi-pv case
876 alpha = -VALUE_INFINITE;
878 // Full depth PV search, done on first move or after a fail high
879 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
883 // Step 14. Reduced search
884 // if the move fails high will be re-searched at full depth
885 bool doFullDepthSearch = true;
887 if ( depth >= 3 * OnePly
889 && !captureOrPromotion
890 && !move_is_castle(move))
892 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
895 assert(newDepth-ss->reduction >= OnePly);
897 // Reduced depth non-pv search using alpha as upperbound
898 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
899 doFullDepthSearch = (value > alpha);
902 // The move failed high, but if reduction is very big we could
903 // face a false positive, retry with a less aggressive reduction,
904 // if the move fails high again then go with full depth search.
905 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
907 assert(newDepth - OnePly >= OnePly);
909 ss->reduction = OnePly;
910 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
911 doFullDepthSearch = (value > alpha);
913 ss->reduction = Depth(0); // Restore original reduction
916 // Step 15. Full depth search
917 if (doFullDepthSearch)
919 // Full depth non-pv search using alpha as upperbound
920 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
922 // If we are above alpha then research at same depth but as PV
923 // to get a correct score or eventually a fail high above beta.
925 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
929 // Step 16. Undo move
932 // Can we exit fail high loop ?
933 if (AbortSearch || value < beta)
936 // We are failing high and going to do a research. It's important to update
937 // the score before research in case we run out of time while researching.
938 rml.set_move_score(i, value);
940 TT.extract_pv(pos, ss->pv, PLY_MAX);
941 rml.set_move_pv(i, ss->pv);
943 // Print information to the standard output
944 print_pv_info(pos, ss, alpha, beta, value);
946 // Prepare for a research after a fail high, each time with a wider window
947 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
950 } // End of fail high loop
952 // Finished searching the move. If AbortSearch is true, the search
953 // was aborted because the user interrupted the search or because we
954 // ran out of time. In this case, the return value of the search cannot
955 // be trusted, and we break out of the loop without updating the best
960 // Remember beta-cutoff and searched nodes counts for this move. The
961 // info is used to sort the root moves for the next iteration.
963 TM.get_beta_counters(pos.side_to_move(), our, their);
964 rml.set_beta_counters(i, our, their);
965 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
967 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
968 assert(value < beta);
970 // Step 17. Check for new best move
971 if (value <= alpha && i >= MultiPV)
972 rml.set_move_score(i, -VALUE_INFINITE);
975 // PV move or new best move!
978 rml.set_move_score(i, value);
980 TT.extract_pv(pos, ss->pv, PLY_MAX);
981 rml.set_move_pv(i, ss->pv);
985 // We record how often the best move has been changed in each
986 // iteration. This information is used for time managment: When
987 // the best move changes frequently, we allocate some more time.
989 BestMoveChangesByIteration[Iteration]++;
991 // Print information to the standard output
992 print_pv_info(pos, ss, alpha, beta, value);
994 // Raise alpha to setup proper non-pv search upper bound
1000 rml.sort_multipv(i);
1001 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1003 cout << "info multipv " << j + 1
1004 << " score " << value_to_string(rml.get_move_score(j))
1005 << " depth " << (j <= i ? Iteration : Iteration - 1)
1006 << " time " << current_search_time()
1007 << " nodes " << TM.nodes_searched()
1011 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1012 cout << rml.get_move_pv(j, k) << " ";
1016 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1018 } // PV move or new best move
1020 assert(alpha >= *alphaPtr);
1022 AspirationFailLow = (alpha == *alphaPtr);
1024 if (AspirationFailLow && StopOnPonderhit)
1025 StopOnPonderhit = false;
1028 // Can we exit fail low loop ?
1029 if (AbortSearch || !AspirationFailLow)
1032 // Prepare for a research after a fail low, each time with a wider window
1033 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1038 // Sort the moves before to return
1045 // search<>() is the main search function for both PV and non-PV nodes
1047 template <NodeType PvNode>
1048 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1050 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1051 assert(beta > alpha && beta <= VALUE_INFINITE);
1052 assert(PvNode || alpha == beta - 1);
1053 assert(ply > 0 && ply < PLY_MAX);
1054 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1056 Move movesSearched[256];
1061 Move ttMove, move, excludedMove;
1062 Depth ext, newDepth;
1063 Value bestValue, value, oldAlpha;
1064 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1065 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1066 bool mateThreat = false;
1068 int threadID = pos.thread();
1069 refinedValue = bestValue = value = -VALUE_INFINITE;
1072 // Step 1. Initialize node and poll. Polling can abort search
1073 TM.incrementNodeCounter(threadID);
1075 (ss+2)->initKillers();
1077 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1083 // Step 2. Check for aborted search and immediate draw
1084 if (AbortSearch || TM.thread_should_stop(threadID))
1087 if (pos.is_draw() || ply >= PLY_MAX - 1)
1090 // Step 3. Mate distance pruning
1091 alpha = Max(value_mated_in(ply), alpha);
1092 beta = Min(value_mate_in(ply+1), beta);
1096 // Step 4. Transposition table lookup
1098 // We don't want the score of a partial search to overwrite a previous full search
1099 // TT value, so we use a different position key in case of an excluded move exists.
1100 excludedMove = ss->excludedMove;
1101 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1103 tte = TT.retrieve(posKey);
1104 ttMove = (tte ? tte->move() : MOVE_NONE);
1106 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1107 // This is to avoid problems in the following areas:
1109 // * Repetition draw detection
1110 // * Fifty move rule detection
1111 // * Searching for a mate
1112 // * Printing of full PV line
1114 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1116 // Refresh tte entry to avoid aging
1117 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1119 ss->currentMove = ttMove; // Can be MOVE_NONE
1120 return value_from_tt(tte->value(), ply);
1123 // Step 5. Evaluate the position statically
1124 // At PV nodes we do this only to update gain statistics
1125 isCheck = pos.is_check();
1128 if (tte && tte->static_value() != VALUE_NONE)
1130 ss->eval = tte->static_value();
1131 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1134 ss->eval = evaluate(pos, ei);
1136 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1137 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1140 // Step 6. Razoring (is omitted in PV nodes)
1142 && depth < RazorDepth
1144 && refinedValue < beta - razor_margin(depth)
1145 && ttMove == MOVE_NONE
1146 && (ss-1)->currentMove != MOVE_NULL
1147 && !value_is_mate(beta)
1148 && !pos.has_pawn_on_7th(pos.side_to_move()))
1150 // Pass ss->eval to qsearch() and avoid an evaluate call
1151 if (!tte || tte->static_value() == VALUE_NONE)
1152 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1154 Value rbeta = beta - razor_margin(depth);
1155 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1157 // Logically we should return (v + razor_margin(depth)), but
1158 // surprisingly this did slightly weaker in tests.
1162 // Step 7. Static null move pruning (is omitted in PV nodes)
1163 // We're betting that the opponent doesn't have a move that will reduce
1164 // the score by more than futility_margin(depth) if we do a null move.
1166 && !ss->skipNullMove
1167 && depth < RazorDepth
1168 && refinedValue >= beta + futility_margin(depth, 0)
1170 && !value_is_mate(beta)
1171 && pos.non_pawn_material(pos.side_to_move()))
1172 return refinedValue - futility_margin(depth, 0);
1174 // Step 8. Null move search with verification search (is omitted in PV nodes)
1175 // When we jump directly to qsearch() we do a null move only if static value is
1176 // at least beta. Otherwise we do a null move if static value is not more than
1177 // NullMoveMargin under beta.
1179 && !ss->skipNullMove
1181 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1183 && !value_is_mate(beta)
1184 && pos.non_pawn_material(pos.side_to_move()))
1186 ss->currentMove = MOVE_NULL;
1188 // Null move dynamic reduction based on depth
1189 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1191 // Null move dynamic reduction based on value
1192 if (refinedValue - beta > PawnValueMidgame)
1195 pos.do_null_move(st);
1196 (ss+1)->skipNullMove = true;
1198 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1199 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1200 (ss+1)->skipNullMove = false;
1201 pos.undo_null_move();
1203 if (nullValue >= beta)
1205 // Do not return unproven mate scores
1206 if (nullValue >= value_mate_in(PLY_MAX))
1209 // Do zugzwang verification search at high depths
1210 if (depth < 6 * OnePly)
1213 ss->skipNullMove = true;
1214 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply);
1215 ss->skipNullMove = false;
1222 // The null move failed low, which means that we may be faced with
1223 // some kind of threat. If the previous move was reduced, check if
1224 // the move that refuted the null move was somehow connected to the
1225 // move which was reduced. If a connection is found, return a fail
1226 // low score (which will cause the reduced move to fail high in the
1227 // parent node, which will trigger a re-search with full depth).
1228 if (nullValue == value_mated_in(ply + 2))
1231 ss->threatMove = (ss+1)->currentMove;
1232 if ( depth < ThreatDepth
1233 && (ss-1)->reduction
1234 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1239 // Step 9. Internal iterative deepening
1240 if ( depth >= IIDDepth[PvNode]
1241 && ttMove == MOVE_NONE
1242 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1244 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1246 ss->skipNullMove = true;
1247 search<PvNode>(pos, ss, alpha, beta, d, ply);
1248 ss->skipNullMove = false;
1251 tte = TT.retrieve(posKey);
1254 // Expensive mate threat detection (only for PV nodes)
1256 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1258 // Initialize a MovePicker object for the current position
1259 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1261 bool singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1262 && tte && tte->move()
1263 && !excludedMove // Do not allow recursive singular extension search
1264 && is_lower_bound(tte->type())
1265 && tte->depth() >= depth - 3 * OnePly;
1267 // Step 10. Loop through moves
1268 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1269 while ( bestValue < beta
1270 && (move = mp.get_next_move()) != MOVE_NONE
1271 && !TM.thread_should_stop(threadID))
1273 assert(move_is_ok(move));
1275 if (move == excludedMove)
1278 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1279 moveIsCheck = pos.move_is_check(move, ci);
1280 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1282 // Step 11. Decide the new search depth
1283 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1285 // Singular extension search. We extend the TT move if its value is much better than
1286 // its siblings. To verify this we do a reduced search on all the other moves but the
1287 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1288 if ( singularExtensionNode
1289 && move == tte->move()
1292 Value ttValue = value_from_tt(tte->value(), ply);
1294 if (abs(ttValue) < VALUE_KNOWN_WIN)
1296 Value b = ttValue - SingularExtensionMargin;
1297 ss->excludedMove = move;
1298 ss->skipNullMove = true;
1299 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1300 ss->skipNullMove = false;
1301 ss->excludedMove = MOVE_NONE;
1302 if (v < ttValue - SingularExtensionMargin)
1307 newDepth = depth - OnePly + ext;
1309 // Update current move (this must be done after singular extension search)
1310 movesSearched[moveCount++] = ss->currentMove = move;
1312 // Step 12. Futility pruning (is omitted in PV nodes)
1314 && !captureOrPromotion
1318 && !move_is_castle(move))
1320 // Move count based pruning
1321 if ( moveCount >= futility_move_count(depth)
1322 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1323 && bestValue > value_mated_in(PLY_MAX))
1326 // Value based pruning
1327 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1328 // but fixing this made program slightly weaker.
1329 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1330 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1331 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1333 if (futilityValueScaled < beta)
1335 if (futilityValueScaled > bestValue)
1336 bestValue = futilityValueScaled;
1341 // Step 13. Make the move
1342 pos.do_move(move, st, ci, moveIsCheck);
1344 // Step extra. pv search (only in PV nodes)
1345 // The first move in list is the expected PV
1346 if (PvNode && moveCount == 1)
1347 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1348 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1351 // Step 14. Reduced depth search
1352 // If the move fails high will be re-searched at full depth.
1353 bool doFullDepthSearch = true;
1355 if ( depth >= 3 * OnePly
1356 && !captureOrPromotion
1358 && !move_is_castle(move)
1359 && !move_is_killer(move, ss))
1361 ss->reduction = reduction<PvNode>(depth, moveCount);
1364 Depth d = newDepth - ss->reduction;
1365 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1366 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1368 doFullDepthSearch = (value > alpha);
1371 // The move failed high, but if reduction is very big we could
1372 // face a false positive, retry with a less aggressive reduction,
1373 // if the move fails high again then go with full depth search.
1374 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1376 assert(newDepth - OnePly >= OnePly);
1378 ss->reduction = OnePly;
1379 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1380 doFullDepthSearch = (value > alpha);
1382 ss->reduction = Depth(0); // Restore original reduction
1385 // Step 15. Full depth search
1386 if (doFullDepthSearch)
1388 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1389 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1391 // Step extra. pv search (only in PV nodes)
1392 // Search only for possible new PV nodes, if instead value >= beta then
1393 // parent node fails low with value <= alpha and tries another move.
1394 if (PvNode && value > alpha && value < beta)
1395 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1396 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1400 // Step 16. Undo move
1401 pos.undo_move(move);
1403 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1405 // Step 17. Check for new best move
1406 if (value > bestValue)
1411 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1416 if (value == value_mate_in(ply + 1))
1417 ss->mateKiller = move;
1421 // Step 18. Check for split
1422 if ( depth >= MinimumSplitDepth
1423 && TM.active_threads() > 1
1425 && TM.available_thread_exists(threadID)
1427 && !TM.thread_should_stop(threadID)
1429 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1430 mateThreat, &moveCount, &mp, PvNode);
1433 // Step 19. Check for mate and stalemate
1434 // All legal moves have been searched and if there are
1435 // no legal moves, it must be mate or stalemate.
1436 // If one move was excluded return fail low score.
1438 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1440 // Step 20. Update tables
1441 // If the search is not aborted, update the transposition table,
1442 // history counters, and killer moves.
1443 if (AbortSearch || TM.thread_should_stop(threadID))
1446 if (bestValue <= oldAlpha)
1447 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1449 else if (bestValue >= beta)
1451 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1453 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1454 if (!pos.move_is_capture_or_promotion(move))
1456 update_history(pos, move, depth, movesSearched, moveCount);
1457 update_killers(move, ss);
1461 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss->pv[0], ss->eval, ei.kingDanger[pos.side_to_move()]);
1463 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1469 // qsearch() is the quiescence search function, which is called by the main
1470 // search function when the remaining depth is zero (or, to be more precise,
1471 // less than OnePly).
1473 template <NodeType PvNode>
1474 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1476 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1477 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1478 assert(PvNode || alpha == beta - 1);
1480 assert(ply > 0 && ply < PLY_MAX);
1481 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1486 Value bestValue, value, futilityValue, futilityBase;
1487 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1489 Value oldAlpha = alpha;
1491 TM.incrementNodeCounter(pos.thread());
1492 ss->pv[0] = ss->pv[1] = ss->currentMove = MOVE_NONE;
1493 ss->eval = VALUE_NONE;
1495 // Check for an instant draw or maximum ply reached
1496 if (pos.is_draw() || ply >= PLY_MAX - 1)
1499 // Transposition table lookup. At PV nodes, we don't use the TT for
1500 // pruning, but only for move ordering.
1501 tte = TT.retrieve(pos.get_key());
1502 ttMove = (tte ? tte->move() : MOVE_NONE);
1504 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1506 ss->currentMove = ttMove; // Can be MOVE_NONE
1507 return value_from_tt(tte->value(), ply);
1510 isCheck = pos.is_check();
1512 // Evaluate the position statically
1515 bestValue = futilityBase = -VALUE_INFINITE;
1516 deepChecks = enoughMaterial = false;
1520 if (tte && tte->static_value() != VALUE_NONE)
1522 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1523 bestValue = tte->static_value();
1526 bestValue = evaluate(pos, ei);
1528 ss->eval = bestValue;
1529 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1531 // Stand pat. Return immediately if static value is at least beta
1532 if (bestValue >= beta)
1535 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()]);
1540 if (PvNode && bestValue > alpha)
1543 // If we are near beta then try to get a cutoff pushing checks a bit further
1544 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1546 // Futility pruning parameters, not needed when in check
1547 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1548 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1551 // Initialize a MovePicker object for the current position, and prepare
1552 // to search the moves. Because the depth is <= 0 here, only captures,
1553 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1554 // and we are near beta) will be generated.
1555 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1558 // Loop through the moves until no moves remain or a beta cutoff occurs
1559 while ( alpha < beta
1560 && (move = mp.get_next_move()) != MOVE_NONE)
1562 assert(move_is_ok(move));
1564 moveIsCheck = pos.move_is_check(move, ci);
1572 && !move_is_promotion(move)
1573 && !pos.move_is_passed_pawn_push(move))
1575 futilityValue = futilityBase
1576 + pos.endgame_value_of_piece_on(move_to(move))
1577 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1579 if (futilityValue < alpha)
1581 if (futilityValue > bestValue)
1582 bestValue = futilityValue;
1587 // Detect blocking evasions that are candidate to be pruned
1588 evasionPrunable = isCheck
1589 && bestValue > value_mated_in(PLY_MAX)
1590 && !pos.move_is_capture(move)
1591 && pos.type_of_piece_on(move_from(move)) != KING
1592 && !pos.can_castle(pos.side_to_move());
1594 // Don't search moves with negative SEE values
1596 && (!isCheck || evasionPrunable)
1598 && !move_is_promotion(move)
1599 && pos.see_sign(move) < 0)
1602 // Update current move
1603 ss->currentMove = move;
1605 // Make and search the move
1606 pos.do_move(move, st, ci, moveIsCheck);
1607 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1608 pos.undo_move(move);
1610 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1613 if (value > bestValue)
1624 // All legal moves have been searched. A special case: If we're in check
1625 // and no legal moves were found, it is checkmate.
1626 if (isCheck && bestValue == -VALUE_INFINITE)
1627 return value_mated_in(ply);
1629 // Update transposition table
1630 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1631 if (bestValue <= oldAlpha)
1632 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1633 else if (bestValue >= beta)
1636 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1638 // Update killers only for good checking moves
1639 if (!pos.move_is_capture_or_promotion(move))
1640 update_killers(move, ss);
1643 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss->pv[0], ss->eval, ei.kingDanger[pos.side_to_move()]);
1645 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1651 // sp_search() is used to search from a split point. This function is called
1652 // by each thread working at the split point. It is similar to the normal
1653 // search() function, but simpler. Because we have already probed the hash
1654 // table, done a null move search, and searched the first move before
1655 // splitting, we don't have to repeat all this work in sp_search(). We
1656 // also don't need to store anything to the hash table here: This is taken
1657 // care of after we return from the split point.
1659 template <NodeType PvNode>
1660 void sp_search(SplitPoint* sp, int threadID) {
1662 assert(threadID >= 0 && threadID < TM.active_threads());
1663 assert(TM.active_threads() > 1);
1667 Depth ext, newDepth;
1669 Value futilityValueScaled; // NonPV specific
1670 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1672 value = -VALUE_INFINITE;
1674 Position pos(*sp->pos, threadID);
1676 SearchStack* ss = sp->sstack[threadID] + 1;
1677 isCheck = pos.is_check();
1679 // Step 10. Loop through moves
1680 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1681 lock_grab(&(sp->lock));
1683 while ( sp->bestValue < sp->beta
1684 && (move = sp->mp->get_next_move()) != MOVE_NONE
1685 && !TM.thread_should_stop(threadID))
1687 moveCount = ++sp->moveCount;
1688 lock_release(&(sp->lock));
1690 assert(move_is_ok(move));
1692 moveIsCheck = pos.move_is_check(move, ci);
1693 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1695 // Step 11. Decide the new search depth
1696 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1697 newDepth = sp->depth - OnePly + ext;
1699 // Update current move
1700 ss->currentMove = move;
1702 // Step 12. Futility pruning (is omitted in PV nodes)
1704 && !captureOrPromotion
1707 && !move_is_castle(move))
1709 // Move count based pruning
1710 if ( moveCount >= futility_move_count(sp->depth)
1711 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1712 && sp->bestValue > value_mated_in(PLY_MAX))
1714 lock_grab(&(sp->lock));
1718 // Value based pruning
1719 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1720 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1721 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1723 if (futilityValueScaled < sp->beta)
1725 lock_grab(&(sp->lock));
1727 if (futilityValueScaled > sp->bestValue)
1728 sp->bestValue = futilityValueScaled;
1733 // Step 13. Make the move
1734 pos.do_move(move, st, ci, moveIsCheck);
1736 // Step 14. Reduced search
1737 // If the move fails high will be re-searched at full depth.
1738 bool doFullDepthSearch = true;
1740 if ( !captureOrPromotion
1742 && !move_is_castle(move)
1743 && !move_is_killer(move, ss))
1745 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1748 Value localAlpha = sp->alpha;
1749 Depth d = newDepth - ss->reduction;
1750 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1751 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1753 doFullDepthSearch = (value > localAlpha);
1756 // The move failed high, but if reduction is very big we could
1757 // face a false positive, retry with a less aggressive reduction,
1758 // if the move fails high again then go with full depth search.
1759 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1761 assert(newDepth - OnePly >= OnePly);
1763 ss->reduction = OnePly;
1764 Value localAlpha = sp->alpha;
1765 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1766 doFullDepthSearch = (value > localAlpha);
1768 ss->reduction = Depth(0); // Restore original reduction
1771 // Step 15. Full depth search
1772 if (doFullDepthSearch)
1774 Value localAlpha = sp->alpha;
1775 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1776 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1778 // Step extra. pv search (only in PV nodes)
1779 // Search only for possible new PV nodes, if instead value >= beta then
1780 // parent node fails low with value <= alpha and tries another move.
1781 if (PvNode && value > localAlpha && value < sp->beta)
1782 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1783 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1786 // Step 16. Undo move
1787 pos.undo_move(move);
1789 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1791 // Step 17. Check for new best move
1792 lock_grab(&(sp->lock));
1794 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1796 sp->bestValue = value;
1798 if (sp->bestValue > sp->alpha)
1800 if (!PvNode || value >= sp->beta)
1801 sp->stopRequest = true;
1803 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1806 sp_update_pv(sp->parentSstack, ss);
1811 /* Here we have the lock still grabbed */
1813 sp->slaves[threadID] = 0;
1815 lock_release(&(sp->lock));
1818 // update_pv() is called whenever a search returns a value > alpha.
1819 // It updates the PV in the SearchStack object corresponding to the
1822 void update_pv(SearchStack* ss) {
1824 Move* src = (ss+1)->pv;
1827 *dst = ss->currentMove;
1831 while (*src++ != MOVE_NONE);
1835 // sp_update_pv() is a variant of update_pv for use at split points. The
1836 // difference between the two functions is that sp_update_pv also updates
1837 // the PV at the parent node.
1839 void sp_update_pv(SearchStack* pss, SearchStack* ss) {
1841 Move* src = (ss+1)->pv;
1843 Move* pdst = pss->pv;
1845 *dst = *pdst = ss->currentMove;
1848 *++dst = *++pdst = *src;
1849 while (*src++ != MOVE_NONE);
1853 // connected_moves() tests whether two moves are 'connected' in the sense
1854 // that the first move somehow made the second move possible (for instance
1855 // if the moving piece is the same in both moves). The first move is assumed
1856 // to be the move that was made to reach the current position, while the
1857 // second move is assumed to be a move from the current position.
1859 bool connected_moves(const Position& pos, Move m1, Move m2) {
1861 Square f1, t1, f2, t2;
1864 assert(move_is_ok(m1));
1865 assert(move_is_ok(m2));
1867 if (m2 == MOVE_NONE)
1870 // Case 1: The moving piece is the same in both moves
1876 // Case 2: The destination square for m2 was vacated by m1
1882 // Case 3: Moving through the vacated square
1883 if ( piece_is_slider(pos.piece_on(f2))
1884 && bit_is_set(squares_between(f2, t2), f1))
1887 // Case 4: The destination square for m2 is defended by the moving piece in m1
1888 p = pos.piece_on(t1);
1889 if (bit_is_set(pos.attacks_from(p, t1), t2))
1892 // Case 5: Discovered check, checking piece is the piece moved in m1
1893 if ( piece_is_slider(p)
1894 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1895 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1897 // discovered_check_candidates() works also if the Position's side to
1898 // move is the opposite of the checking piece.
1899 Color them = opposite_color(pos.side_to_move());
1900 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1902 if (bit_is_set(dcCandidates, f2))
1909 // value_is_mate() checks if the given value is a mate one
1910 // eventually compensated for the ply.
1912 bool value_is_mate(Value value) {
1914 assert(abs(value) <= VALUE_INFINITE);
1916 return value <= value_mated_in(PLY_MAX)
1917 || value >= value_mate_in(PLY_MAX);
1921 // move_is_killer() checks if the given move is among the
1922 // killer moves of that ply.
1924 bool move_is_killer(Move m, SearchStack* ss) {
1926 const Move* k = ss->killers;
1927 for (int i = 0; i < KILLER_MAX; i++, k++)
1935 // extension() decides whether a move should be searched with normal depth,
1936 // or with extended depth. Certain classes of moves (checking moves, in
1937 // particular) are searched with bigger depth than ordinary moves and in
1938 // any case are marked as 'dangerous'. Note that also if a move is not
1939 // extended, as example because the corresponding UCI option is set to zero,
1940 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1941 template <NodeType PvNode>
1942 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1943 bool singleEvasion, bool mateThreat, bool* dangerous) {
1945 assert(m != MOVE_NONE);
1947 Depth result = Depth(0);
1948 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1952 if (moveIsCheck && pos.see_sign(m)>= 0)
1953 result += CheckExtension[PvNode];
1956 result += SingleEvasionExtension[PvNode];
1959 result += MateThreatExtension[PvNode];
1962 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1964 Color c = pos.side_to_move();
1965 if (relative_rank(c, move_to(m)) == RANK_7)
1967 result += PawnPushTo7thExtension[PvNode];
1970 if (pos.pawn_is_passed(c, move_to(m)))
1972 result += PassedPawnExtension[PvNode];
1977 if ( captureOrPromotion
1978 && pos.type_of_piece_on(move_to(m)) != PAWN
1979 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1980 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1981 && !move_is_promotion(m)
1984 result += PawnEndgameExtension[PvNode];
1989 && captureOrPromotion
1990 && pos.type_of_piece_on(move_to(m)) != PAWN
1991 && pos.see_sign(m) >= 0)
1997 return Min(result, OnePly);
2001 // connected_threat() tests whether it is safe to forward prune a move or if
2002 // is somehow coonected to the threat move returned by null search.
2004 bool connected_threat(const Position& pos, Move m, Move threat) {
2006 assert(move_is_ok(m));
2007 assert(threat && move_is_ok(threat));
2008 assert(!pos.move_is_check(m));
2009 assert(!pos.move_is_capture_or_promotion(m));
2010 assert(!pos.move_is_passed_pawn_push(m));
2012 Square mfrom, mto, tfrom, tto;
2014 mfrom = move_from(m);
2016 tfrom = move_from(threat);
2017 tto = move_to(threat);
2019 // Case 1: Don't prune moves which move the threatened piece
2023 // Case 2: If the threatened piece has value less than or equal to the
2024 // value of the threatening piece, don't prune move which defend it.
2025 if ( pos.move_is_capture(threat)
2026 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2027 || pos.type_of_piece_on(tfrom) == KING)
2028 && pos.move_attacks_square(m, tto))
2031 // Case 3: If the moving piece in the threatened move is a slider, don't
2032 // prune safe moves which block its ray.
2033 if ( piece_is_slider(pos.piece_on(tfrom))
2034 && bit_is_set(squares_between(tfrom, tto), mto)
2035 && pos.see_sign(m) >= 0)
2042 // ok_to_use_TT() returns true if a transposition table score
2043 // can be used at a given point in search.
2045 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2047 Value v = value_from_tt(tte->value(), ply);
2049 return ( tte->depth() >= depth
2050 || v >= Max(value_mate_in(PLY_MAX), beta)
2051 || v < Min(value_mated_in(PLY_MAX), beta))
2053 && ( (is_lower_bound(tte->type()) && v >= beta)
2054 || (is_upper_bound(tte->type()) && v < beta));
2058 // refine_eval() returns the transposition table score if
2059 // possible otherwise falls back on static position evaluation.
2061 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2066 Value v = value_from_tt(tte->value(), ply);
2068 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2069 || (is_upper_bound(tte->type()) && v < defaultEval))
2076 // update_history() registers a good move that produced a beta-cutoff
2077 // in history and marks as failures all the other moves of that ply.
2079 void update_history(const Position& pos, Move move, Depth depth,
2080 Move movesSearched[], int moveCount) {
2084 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2086 for (int i = 0; i < moveCount - 1; i++)
2088 m = movesSearched[i];
2092 if (!pos.move_is_capture_or_promotion(m))
2093 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2098 // update_killers() add a good move that produced a beta-cutoff
2099 // among the killer moves of that ply.
2101 void update_killers(Move m, SearchStack* ss) {
2103 if (m == ss->killers[0])
2106 for (int i = KILLER_MAX - 1; i > 0; i--)
2107 ss->killers[i] = ss->killers[i - 1];
2113 // update_gains() updates the gains table of a non-capture move given
2114 // the static position evaluation before and after the move.
2116 void update_gains(const Position& pos, Move m, Value before, Value after) {
2119 && before != VALUE_NONE
2120 && after != VALUE_NONE
2121 && pos.captured_piece() == NO_PIECE_TYPE
2122 && !move_is_castle(m)
2123 && !move_is_promotion(m))
2124 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2128 // current_search_time() returns the number of milliseconds which have passed
2129 // since the beginning of the current search.
2131 int current_search_time() {
2133 return get_system_time() - SearchStartTime;
2137 // nps() computes the current nodes/second count.
2141 int t = current_search_time();
2142 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2146 // poll() performs two different functions: It polls for user input, and it
2147 // looks at the time consumed so far and decides if it's time to abort the
2152 static int lastInfoTime;
2153 int t = current_search_time();
2158 // We are line oriented, don't read single chars
2159 std::string command;
2161 if (!std::getline(std::cin, command))
2164 if (command == "quit")
2167 PonderSearch = false;
2171 else if (command == "stop")
2174 PonderSearch = false;
2176 else if (command == "ponderhit")
2180 // Print search information
2184 else if (lastInfoTime > t)
2185 // HACK: Must be a new search where we searched less than
2186 // NodesBetweenPolls nodes during the first second of search.
2189 else if (t - lastInfoTime >= 1000)
2196 if (dbg_show_hit_rate)
2197 dbg_print_hit_rate();
2199 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2200 << " time " << t << " hashfull " << TT.full() << endl;
2203 // Should we stop the search?
2207 bool stillAtFirstMove = FirstRootMove
2208 && !AspirationFailLow
2209 && t > MaxSearchTime + ExtraSearchTime;
2211 bool noMoreTime = t > AbsoluteMaxSearchTime
2212 || stillAtFirstMove;
2214 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2215 || (ExactMaxTime && t >= ExactMaxTime)
2216 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2221 // ponderhit() is called when the program is pondering (i.e. thinking while
2222 // it's the opponent's turn to move) in order to let the engine know that
2223 // it correctly predicted the opponent's move.
2227 int t = current_search_time();
2228 PonderSearch = false;
2230 bool stillAtFirstMove = FirstRootMove
2231 && !AspirationFailLow
2232 && t > MaxSearchTime + ExtraSearchTime;
2234 bool noMoreTime = t > AbsoluteMaxSearchTime
2235 || stillAtFirstMove;
2237 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2242 // init_ss_array() does a fast reset of the first entries of a SearchStack
2243 // array and of all the excludedMove and skipNullMove entries.
2245 void init_ss_array(SearchStack* ss, int size) {
2247 for (int i = 0; i < size; i++, ss++)
2249 ss->excludedMove = MOVE_NONE;
2250 ss->skipNullMove = false;
2261 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2262 // while the program is pondering. The point is to work around a wrinkle in
2263 // the UCI protocol: When pondering, the engine is not allowed to give a
2264 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2265 // We simply wait here until one of these commands is sent, and return,
2266 // after which the bestmove and pondermove will be printed (in id_loop()).
2268 void wait_for_stop_or_ponderhit() {
2270 std::string command;
2274 if (!std::getline(std::cin, command))
2277 if (command == "quit")
2282 else if (command == "ponderhit" || command == "stop")
2288 // print_pv_info() prints to standard output and eventually to log file information on
2289 // the current PV line. It is called at each iteration or after a new pv is found.
2291 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2293 cout << "info depth " << Iteration
2294 << " score " << value_to_string(value)
2295 << ((value >= beta) ? " lowerbound" :
2296 ((value <= alpha)? " upperbound" : ""))
2297 << " time " << current_search_time()
2298 << " nodes " << TM.nodes_searched()
2302 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2303 cout << ss->pv[j] << " ";
2309 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2310 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2312 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2313 TM.nodes_searched(), value, type, ss->pv) << endl;
2318 // init_thread() is the function which is called when a new thread is
2319 // launched. It simply calls the idle_loop() function with the supplied
2320 // threadID. There are two versions of this function; one for POSIX
2321 // threads and one for Windows threads.
2323 #if !defined(_MSC_VER)
2325 void* init_thread(void *threadID) {
2327 TM.idle_loop(*(int*)threadID, NULL);
2333 DWORD WINAPI init_thread(LPVOID threadID) {
2335 TM.idle_loop(*(int*)threadID, NULL);
2342 /// The ThreadsManager class
2344 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2345 // get_beta_counters() are getters/setters for the per thread
2346 // counters used to sort the moves at root.
2348 void ThreadsManager::resetNodeCounters() {
2350 for (int i = 0; i < MAX_THREADS; i++)
2351 threads[i].nodes = 0ULL;
2354 void ThreadsManager::resetBetaCounters() {
2356 for (int i = 0; i < MAX_THREADS; i++)
2357 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2360 int64_t ThreadsManager::nodes_searched() const {
2362 int64_t result = 0ULL;
2363 for (int i = 0; i < ActiveThreads; i++)
2364 result += threads[i].nodes;
2369 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2372 for (int i = 0; i < MAX_THREADS; i++)
2374 our += threads[i].betaCutOffs[us];
2375 their += threads[i].betaCutOffs[opposite_color(us)];
2380 // idle_loop() is where the threads are parked when they have no work to do.
2381 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2382 // object for which the current thread is the master.
2384 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2386 assert(threadID >= 0 && threadID < MAX_THREADS);
2390 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2391 // master should exit as last one.
2392 if (AllThreadsShouldExit)
2395 threads[threadID].state = THREAD_TERMINATED;
2399 // If we are not thinking, wait for a condition to be signaled
2400 // instead of wasting CPU time polling for work.
2401 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2404 assert(threadID != 0);
2405 threads[threadID].state = THREAD_SLEEPING;
2407 #if !defined(_MSC_VER)
2408 lock_grab(&WaitLock);
2409 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2410 pthread_cond_wait(&WaitCond, &WaitLock);
2411 lock_release(&WaitLock);
2413 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2417 // If thread has just woken up, mark it as available
2418 if (threads[threadID].state == THREAD_SLEEPING)
2419 threads[threadID].state = THREAD_AVAILABLE;
2421 // If this thread has been assigned work, launch a search
2422 if (threads[threadID].state == THREAD_WORKISWAITING)
2424 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2426 threads[threadID].state = THREAD_SEARCHING;
2428 if (threads[threadID].splitPoint->pvNode)
2429 sp_search<PV>(threads[threadID].splitPoint, threadID);
2431 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2433 assert(threads[threadID].state == THREAD_SEARCHING);
2435 threads[threadID].state = THREAD_AVAILABLE;
2438 // If this thread is the master of a split point and all slaves have
2439 // finished their work at this split point, return from the idle loop.
2441 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2443 if (i == ActiveThreads)
2445 // Because sp->slaves[] is reset under lock protection,
2446 // be sure sp->lock has been released before to return.
2447 lock_grab(&(sp->lock));
2448 lock_release(&(sp->lock));
2450 assert(threads[threadID].state == THREAD_AVAILABLE);
2452 threads[threadID].state = THREAD_SEARCHING;
2459 // init_threads() is called during startup. It launches all helper threads,
2460 // and initializes the split point stack and the global locks and condition
2463 void ThreadsManager::init_threads() {
2468 #if !defined(_MSC_VER)
2469 pthread_t pthread[1];
2472 // Initialize global locks
2473 lock_init(&MPLock, NULL);
2474 lock_init(&WaitLock, NULL);
2476 #if !defined(_MSC_VER)
2477 pthread_cond_init(&WaitCond, NULL);
2479 for (i = 0; i < MAX_THREADS; i++)
2480 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2483 // Initialize SplitPointStack locks
2484 for (i = 0; i < MAX_THREADS; i++)
2485 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2486 lock_init(&(SplitPointStack[i][j].lock), NULL);
2488 // Will be set just before program exits to properly end the threads
2489 AllThreadsShouldExit = false;
2491 // Threads will be put to sleep as soon as created
2492 AllThreadsShouldSleep = true;
2494 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2496 threads[0].state = THREAD_SEARCHING;
2497 for (i = 1; i < MAX_THREADS; i++)
2498 threads[i].state = THREAD_AVAILABLE;
2500 // Launch the helper threads
2501 for (i = 1; i < MAX_THREADS; i++)
2504 #if !defined(_MSC_VER)
2505 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2507 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2512 cout << "Failed to create thread number " << i << endl;
2513 Application::exit_with_failure();
2516 // Wait until the thread has finished launching and is gone to sleep
2517 while (threads[i].state != THREAD_SLEEPING) {}
2522 // exit_threads() is called when the program exits. It makes all the
2523 // helper threads exit cleanly.
2525 void ThreadsManager::exit_threads() {
2527 ActiveThreads = MAX_THREADS; // HACK
2528 AllThreadsShouldSleep = true; // HACK
2529 wake_sleeping_threads();
2531 // This makes the threads to exit idle_loop()
2532 AllThreadsShouldExit = true;
2534 // Wait for thread termination
2535 for (int i = 1; i < MAX_THREADS; i++)
2536 while (threads[i].state != THREAD_TERMINATED) {}
2538 // Now we can safely destroy the locks
2539 for (int i = 0; i < MAX_THREADS; i++)
2540 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2541 lock_destroy(&(SplitPointStack[i][j].lock));
2543 lock_destroy(&WaitLock);
2544 lock_destroy(&MPLock);
2548 // thread_should_stop() checks whether the thread should stop its search.
2549 // This can happen if a beta cutoff has occurred in the thread's currently
2550 // active split point, or in some ancestor of the current split point.
2552 bool ThreadsManager::thread_should_stop(int threadID) const {
2554 assert(threadID >= 0 && threadID < ActiveThreads);
2558 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2563 // thread_is_available() checks whether the thread with threadID "slave" is
2564 // available to help the thread with threadID "master" at a split point. An
2565 // obvious requirement is that "slave" must be idle. With more than two
2566 // threads, this is not by itself sufficient: If "slave" is the master of
2567 // some active split point, it is only available as a slave to the other
2568 // threads which are busy searching the split point at the top of "slave"'s
2569 // split point stack (the "helpful master concept" in YBWC terminology).
2571 bool ThreadsManager::thread_is_available(int slave, int master) const {
2573 assert(slave >= 0 && slave < ActiveThreads);
2574 assert(master >= 0 && master < ActiveThreads);
2575 assert(ActiveThreads > 1);
2577 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2580 // Make a local copy to be sure doesn't change under our feet
2581 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2583 if (localActiveSplitPoints == 0)
2584 // No active split points means that the thread is available as
2585 // a slave for any other thread.
2588 if (ActiveThreads == 2)
2591 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2592 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2593 // could have been set to 0 by another thread leading to an out of bound access.
2594 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2601 // available_thread_exists() tries to find an idle thread which is available as
2602 // a slave for the thread with threadID "master".
2604 bool ThreadsManager::available_thread_exists(int master) const {
2606 assert(master >= 0 && master < ActiveThreads);
2607 assert(ActiveThreads > 1);
2609 for (int i = 0; i < ActiveThreads; i++)
2610 if (thread_is_available(i, master))
2617 // split() does the actual work of distributing the work at a node between
2618 // several available threads. If it does not succeed in splitting the
2619 // node (because no idle threads are available, or because we have no unused
2620 // split point objects), the function immediately returns. If splitting is
2621 // possible, a SplitPoint object is initialized with all the data that must be
2622 // copied to the helper threads and we tell our helper threads that they have
2623 // been assigned work. This will cause them to instantly leave their idle loops
2624 // and call sp_search(). When all threads have returned from sp_search() then
2627 template <bool Fake>
2628 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2629 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2630 int* moveCount, MovePicker* mp, bool pvNode) {
2632 assert(ply > 0 && ply < PLY_MAX);
2633 assert(*bestValue >= -VALUE_INFINITE);
2634 assert(*bestValue <= *alpha);
2635 assert(*alpha < beta);
2636 assert(beta <= VALUE_INFINITE);
2637 assert(depth > Depth(0));
2638 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2639 assert(ActiveThreads > 1);
2641 int master = p.thread();
2645 // If no other thread is available to help us, or if we have too many
2646 // active split points, don't split.
2647 if ( !available_thread_exists(master)
2648 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2650 lock_release(&MPLock);
2654 // Pick the next available split point object from the split point stack
2655 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2657 // Initialize the split point object
2658 splitPoint->parent = threads[master].splitPoint;
2659 splitPoint->stopRequest = false;
2660 splitPoint->ply = ply;
2661 splitPoint->depth = depth;
2662 splitPoint->mateThreat = mateThreat;
2663 splitPoint->alpha = *alpha;
2664 splitPoint->beta = beta;
2665 splitPoint->pvNode = pvNode;
2666 splitPoint->bestValue = *bestValue;
2667 splitPoint->mp = mp;
2668 splitPoint->moveCount = *moveCount;
2669 splitPoint->pos = &p;
2670 splitPoint->parentSstack = ss;
2671 for (int i = 0; i < ActiveThreads; i++)
2672 splitPoint->slaves[i] = 0;
2674 threads[master].splitPoint = splitPoint;
2675 threads[master].activeSplitPoints++;
2677 // If we are here it means we are not available
2678 assert(threads[master].state != THREAD_AVAILABLE);
2680 int workersCnt = 1; // At least the master is included
2682 // Allocate available threads setting state to THREAD_BOOKED
2683 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2684 if (thread_is_available(i, master))
2686 threads[i].state = THREAD_BOOKED;
2687 threads[i].splitPoint = splitPoint;
2688 splitPoint->slaves[i] = 1;
2692 assert(Fake || workersCnt > 1);
2694 // We can release the lock because slave threads are already booked and master is not available
2695 lock_release(&MPLock);
2697 // Tell the threads that they have work to do. This will make them leave
2698 // their idle loop. But before copy search stack tail for each thread.
2699 for (int i = 0; i < ActiveThreads; i++)
2700 if (i == master || splitPoint->slaves[i])
2702 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2704 assert(i == master || threads[i].state == THREAD_BOOKED);
2706 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2709 // Everything is set up. The master thread enters the idle loop, from
2710 // which it will instantly launch a search, because its state is
2711 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2712 // idle loop, which means that the main thread will return from the idle
2713 // loop when all threads have finished their work at this split point.
2714 idle_loop(master, splitPoint);
2716 // We have returned from the idle loop, which means that all threads are
2717 // finished. Update alpha and bestValue, and return.
2720 *alpha = splitPoint->alpha;
2721 *bestValue = splitPoint->bestValue;
2722 threads[master].activeSplitPoints--;
2723 threads[master].splitPoint = splitPoint->parent;
2725 lock_release(&MPLock);
2729 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2730 // to start a new search from the root.
2732 void ThreadsManager::wake_sleeping_threads() {
2734 assert(AllThreadsShouldSleep);
2735 assert(ActiveThreads > 0);
2737 AllThreadsShouldSleep = false;
2739 if (ActiveThreads == 1)
2742 #if !defined(_MSC_VER)
2743 pthread_mutex_lock(&WaitLock);
2744 pthread_cond_broadcast(&WaitCond);
2745 pthread_mutex_unlock(&WaitLock);
2747 for (int i = 1; i < MAX_THREADS; i++)
2748 SetEvent(SitIdleEvent[i]);
2754 // put_threads_to_sleep() makes all the threads go to sleep just before
2755 // to leave think(), at the end of the search. Threads should have already
2756 // finished the job and should be idle.
2758 void ThreadsManager::put_threads_to_sleep() {
2760 assert(!AllThreadsShouldSleep);
2762 // This makes the threads to go to sleep
2763 AllThreadsShouldSleep = true;
2766 /// The RootMoveList class
2768 // RootMoveList c'tor
2770 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2772 SearchStack ss[PLY_MAX_PLUS_2];
2773 MoveStack mlist[MaxRootMoves];
2775 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2777 // Generate all legal moves
2778 MoveStack* last = generate_moves(pos, mlist);
2780 // Add each move to the moves[] array
2781 for (MoveStack* cur = mlist; cur != last; cur++)
2783 bool includeMove = includeAllMoves;
2785 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2786 includeMove = (searchMoves[k] == cur->move);
2791 // Find a quick score for the move
2792 init_ss_array(ss, PLY_MAX_PLUS_2);
2793 pos.do_move(cur->move, st);
2794 moves[count].move = cur->move;
2795 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2796 moves[count].pv[0] = cur->move;
2797 moves[count].pv[1] = MOVE_NONE;
2798 pos.undo_move(cur->move);
2805 // RootMoveList simple methods definitions
2807 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2809 moves[moveNum].nodes = nodes;
2810 moves[moveNum].cumulativeNodes += nodes;
2813 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2815 moves[moveNum].ourBeta = our;
2816 moves[moveNum].theirBeta = their;
2819 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2823 for (j = 0; pv[j] != MOVE_NONE; j++)
2824 moves[moveNum].pv[j] = pv[j];
2826 moves[moveNum].pv[j] = MOVE_NONE;
2830 // RootMoveList::sort() sorts the root move list at the beginning of a new
2833 void RootMoveList::sort() {
2835 sort_multipv(count - 1); // Sort all items
2839 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2840 // list by their scores and depths. It is used to order the different PVs
2841 // correctly in MultiPV mode.
2843 void RootMoveList::sort_multipv(int n) {
2847 for (i = 1; i <= n; i++)
2849 RootMove rm = moves[i];
2850 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2851 moves[j] = moves[j - 1];