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. Used at the beginning of a
368 // new search from the root.
369 void SearchStack::init() {
371 pv[0] = pv[1] = MOVE_NONE;
372 currentMove = threatMove = MOVE_NONE;
373 reduction = Depth(0);
377 void SearchStack::initKillers() {
379 mateKiller = MOVE_NONE;
380 for (int i = 0; i < KILLER_MAX; i++)
381 killers[i] = MOVE_NONE;
385 /// perft() is our utility to verify move generation is bug free. All the legal
386 /// moves up to given depth are generated and counted and the sum returned.
388 int perft(Position& pos, Depth depth)
393 MovePicker mp(pos, MOVE_NONE, depth, H);
395 // If we are at the last ply we don't need to do and undo
396 // the moves, just to count them.
397 if (depth <= OnePly) // Replace with '<' to test also qsearch
399 while (mp.get_next_move()) sum++;
403 // Loop through all legal moves
405 while ((move = mp.get_next_move()) != MOVE_NONE)
407 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
408 sum += perft(pos, depth - OnePly);
415 /// think() is the external interface to Stockfish's search, and is called when
416 /// the program receives the UCI 'go' command. It initializes various
417 /// search-related global variables, and calls root_search(). It returns false
418 /// when a quit command is received during the search.
420 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
421 int time[], int increment[], int movesToGo, int maxDepth,
422 int maxNodes, int maxTime, Move searchMoves[]) {
424 // Initialize global search variables
425 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
426 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
428 TM.resetNodeCounters();
429 SearchStartTime = get_system_time();
430 ExactMaxTime = maxTime;
433 InfiniteSearch = infinite;
434 PonderSearch = ponder;
435 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
437 // Look for a book move, only during games, not tests
438 if (UseTimeManagement && get_option_value_bool("OwnBook"))
440 if (get_option_value_string("Book File") != OpeningBook.file_name())
441 OpeningBook.open(get_option_value_string("Book File"));
443 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
444 if (bookMove != MOVE_NONE)
447 wait_for_stop_or_ponderhit();
449 cout << "bestmove " << bookMove << endl;
454 // Reset loseOnTime flag at the beginning of a new game
455 if (button_was_pressed("New Game"))
458 // Read UCI option values
459 TT.set_size(get_option_value_int("Hash"));
460 if (button_was_pressed("Clear Hash"))
463 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
464 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
465 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
466 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
467 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
468 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
469 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
470 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
471 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
472 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
473 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
474 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
476 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
477 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
478 MultiPV = get_option_value_int("MultiPV");
479 Chess960 = get_option_value_bool("UCI_Chess960");
480 UseLogFile = get_option_value_bool("Use Search Log");
483 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
485 read_weights(pos.side_to_move());
487 // Set the number of active threads
488 int newActiveThreads = get_option_value_int("Threads");
489 if (newActiveThreads != TM.active_threads())
491 TM.set_active_threads(newActiveThreads);
492 init_eval(TM.active_threads());
495 // Wake up sleeping threads
496 TM.wake_sleeping_threads();
499 int myTime = time[side_to_move];
500 int myIncrement = increment[side_to_move];
501 if (UseTimeManagement)
503 if (!movesToGo) // Sudden death time control
507 MaxSearchTime = myTime / 30 + myIncrement;
508 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
510 else // Blitz game without increment
512 MaxSearchTime = myTime / 30;
513 AbsoluteMaxSearchTime = myTime / 8;
516 else // (x moves) / (y minutes)
520 MaxSearchTime = myTime / 2;
521 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
525 MaxSearchTime = myTime / Min(movesToGo, 20);
526 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
530 if (get_option_value_bool("Ponder"))
532 MaxSearchTime += MaxSearchTime / 4;
533 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
537 // Set best NodesBetweenPolls interval to avoid lagging under
538 // heavy time pressure.
540 NodesBetweenPolls = Min(MaxNodes, 30000);
541 else if (myTime && myTime < 1000)
542 NodesBetweenPolls = 1000;
543 else if (myTime && myTime < 5000)
544 NodesBetweenPolls = 5000;
546 NodesBetweenPolls = 30000;
548 // Write search information to log file
550 LogFile << "Searching: " << pos.to_fen() << endl
551 << "infinite: " << infinite
552 << " ponder: " << ponder
553 << " time: " << myTime
554 << " increment: " << myIncrement
555 << " moves to go: " << movesToGo << endl;
557 // LSN filtering. Used only for developing purposes, disabled by default
561 // Step 2. If after last move we decided to lose on time, do it now!
562 while (SearchStartTime + myTime + 1000 > get_system_time())
566 // We're ready to start thinking. Call the iterative deepening loop function
567 Value v = id_loop(pos, searchMoves);
571 // Step 1. If this is sudden death game and our position is hopeless,
572 // decide to lose on time.
573 if ( !loseOnTime // If we already lost on time, go to step 3.
583 // Step 3. Now after stepping over the time limit, reset flag for next match.
591 TM.put_threads_to_sleep();
599 // id_loop() is the main iterative deepening loop. It calls root_search
600 // repeatedly with increasing depth until the allocated thinking time has
601 // been consumed, the user stops the search, or the maximum search depth is
604 Value id_loop(const Position& pos, Move searchMoves[]) {
606 Position p(pos, pos.thread());
607 SearchStack ss[PLY_MAX_PLUS_2];
608 Move EasyMove = MOVE_NONE;
609 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
611 // Moves to search are verified, copied, scored and sorted
612 RootMoveList rml(p, searchMoves);
614 // Handle special case of searching on a mate/stale position
615 if (rml.move_count() == 0)
618 wait_for_stop_or_ponderhit();
620 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
623 // Print RootMoveList startup scoring to the standard output,
624 // so to output information also for iteration 1.
625 cout << "info depth " << 1
626 << "\ninfo depth " << 1
627 << " score " << value_to_string(rml.get_move_score(0))
628 << " time " << current_search_time()
629 << " nodes " << TM.nodes_searched()
631 << " pv " << rml.get_move(0) << "\n";
636 init_ss_array(ss, PLY_MAX_PLUS_2);
637 ValueByIteration[1] = rml.get_move_score(0);
640 // Is one move significantly better than others after initial scoring ?
641 if ( rml.move_count() == 1
642 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
643 EasyMove = rml.get_move(0);
645 // Iterative deepening loop
646 while (Iteration < PLY_MAX)
648 // Initialize iteration
650 BestMoveChangesByIteration[Iteration] = 0;
652 cout << "info depth " << Iteration << endl;
654 // Calculate dynamic aspiration window based on previous iterations
655 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
657 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
658 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
660 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
661 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
663 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
664 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
667 // Search to the current depth, rml is updated and sorted, alpha and beta could change
668 value = root_search(p, ss, rml, &alpha, &beta);
670 // Write PV to transposition table, in case the relevant entries have
671 // been overwritten during the search.
672 TT.insert_pv(p, ss->pv);
675 break; // Value cannot be trusted. Break out immediately!
677 //Save info about search result
678 ValueByIteration[Iteration] = value;
680 // Drop the easy move if differs from the new best move
681 if (ss->pv[0] != EasyMove)
682 EasyMove = MOVE_NONE;
684 if (UseTimeManagement)
687 bool stopSearch = false;
689 // Stop search early if there is only a single legal move,
690 // we search up to Iteration 6 anyway to get a proper score.
691 if (Iteration >= 6 && rml.move_count() == 1)
694 // Stop search early when the last two iterations returned a mate score
696 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
697 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
700 // Stop search early if one move seems to be much better than the others
701 int64_t nodes = TM.nodes_searched();
703 && EasyMove == ss->pv[0]
704 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
705 && current_search_time() > MaxSearchTime / 16)
706 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
707 && current_search_time() > MaxSearchTime / 32)))
710 // Add some extra time if the best move has changed during the last two iterations
711 if (Iteration > 5 && Iteration <= 50)
712 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
713 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
715 // Stop search if most of MaxSearchTime is consumed at the end of the
716 // iteration. We probably don't have enough time to search the first
717 // move at the next iteration anyway.
718 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
724 StopOnPonderhit = true;
730 if (MaxDepth && Iteration >= MaxDepth)
734 // If we are pondering or in infinite search, we shouldn't print the
735 // best move before we are told to do so.
736 if (!AbortSearch && (PonderSearch || InfiniteSearch))
737 wait_for_stop_or_ponderhit();
739 // Print final search statistics
740 cout << "info nodes " << TM.nodes_searched()
742 << " time " << current_search_time()
743 << " hashfull " << TT.full() << endl;
745 // Print the best move and the ponder move to the standard output
746 if (ss->pv[0] == MOVE_NONE)
748 ss->pv[0] = rml.get_move(0);
749 ss->pv[1] = MOVE_NONE;
752 assert(ss->pv[0] != MOVE_NONE);
754 cout << "bestmove " << ss->pv[0];
756 if (ss->pv[1] != MOVE_NONE)
757 cout << " ponder " << ss->pv[1];
764 dbg_print_mean(LogFile);
766 if (dbg_show_hit_rate)
767 dbg_print_hit_rate(LogFile);
769 LogFile << "\nNodes: " << TM.nodes_searched()
770 << "\nNodes/second: " << nps()
771 << "\nBest move: " << move_to_san(p, ss->pv[0]);
774 p.do_move(ss->pv[0], st);
775 LogFile << "\nPonder move: "
776 << move_to_san(p, ss->pv[1]) // Works also with MOVE_NONE
779 return rml.get_move_score(0);
783 // root_search() is the function which searches the root node. It is
784 // similar to search_pv except that it uses a different move ordering
785 // scheme, prints some information to the standard output and handles
786 // the fail low/high loops.
788 Value root_search(Position& pos, SearchStack* ss, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
795 Depth depth, ext, newDepth;
796 Value value, alpha, beta;
797 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
798 int researchCountFH, researchCountFL;
800 researchCountFH = researchCountFL = 0;
803 isCheck = pos.is_check();
805 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
806 // Step 2. Check for aborted search (omitted at root)
807 // Step 3. Mate distance pruning (omitted at root)
808 // Step 4. Transposition table lookup (omitted at root)
810 // Step 5. Evaluate the position statically
811 // At root we do this only to get reference value for child nodes
813 ss->eval = evaluate(pos, ei);
815 // Step 6. Razoring (omitted at root)
816 // Step 7. Static null move pruning (omitted at root)
817 // Step 8. Null move search with verification search (omitted at root)
818 // Step 9. Internal iterative deepening (omitted at root)
820 // Step extra. Fail low loop
821 // We start with small aspiration window and in case of fail low, we research
822 // with bigger window until we are not failing low anymore.
825 // Sort the moves before to (re)search
828 // Step 10. Loop through all moves in the root move list
829 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
831 // This is used by time management
832 FirstRootMove = (i == 0);
834 // Save the current node count before the move is searched
835 nodes = TM.nodes_searched();
837 // Reset beta cut-off counters
838 TM.resetBetaCounters();
840 // Pick the next root move, and print the move and the move number to
841 // the standard output.
842 move = ss->currentMove = rml.get_move(i);
844 if (current_search_time() >= 1000)
845 cout << "info currmove " << move
846 << " currmovenumber " << i + 1 << endl;
848 moveIsCheck = pos.move_is_check(move);
849 captureOrPromotion = pos.move_is_capture_or_promotion(move);
851 // Step 11. Decide the new search depth
852 depth = (Iteration - 2) * OnePly + InitialDepth;
853 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
854 newDepth = depth + ext;
856 // Step 12. Futility pruning (omitted at root)
858 // Step extra. Fail high loop
859 // If move fails high, we research with bigger window until we are not failing
861 value = - VALUE_INFINITE;
865 // Step 13. Make the move
866 pos.do_move(move, st, ci, moveIsCheck);
868 // Step extra. pv search
869 // We do pv search for first moves (i < MultiPV)
870 // and for fail high research (value > alpha)
871 if (i < MultiPV || value > alpha)
873 // Aspiration window is disabled in multi-pv case
875 alpha = -VALUE_INFINITE;
877 // Full depth PV search, done on first move or after a fail high
878 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
882 // Step 14. Reduced search
883 // if the move fails high will be re-searched at full depth
884 bool doFullDepthSearch = true;
886 if ( depth >= 3 * OnePly
888 && !captureOrPromotion
889 && !move_is_castle(move))
891 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
894 assert(newDepth-ss->reduction >= OnePly);
896 // Reduced depth non-pv search using alpha as upperbound
897 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
898 doFullDepthSearch = (value > alpha);
901 // The move failed high, but if reduction is very big we could
902 // face a false positive, retry with a less aggressive reduction,
903 // if the move fails high again then go with full depth search.
904 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
906 assert(newDepth - OnePly >= OnePly);
908 ss->reduction = OnePly;
909 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
910 doFullDepthSearch = (value > alpha);
912 ss->reduction = Depth(0); // Restore original reduction
915 // Step 15. Full depth search
916 if (doFullDepthSearch)
918 // Full depth non-pv search using alpha as upperbound
919 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
921 // If we are above alpha then research at same depth but as PV
922 // to get a correct score or eventually a fail high above beta.
924 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
928 // Step 16. Undo move
931 // Can we exit fail high loop ?
932 if (AbortSearch || value < beta)
935 // We are failing high and going to do a research. It's important to update
936 // the score before research in case we run out of time while researching.
937 rml.set_move_score(i, value);
939 TT.extract_pv(pos, ss->pv, PLY_MAX);
940 rml.set_move_pv(i, ss->pv);
942 // Print information to the standard output
943 print_pv_info(pos, ss, alpha, beta, value);
945 // Prepare for a research after a fail high, each time with a wider window
946 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
949 } // End of fail high loop
951 // Finished searching the move. If AbortSearch is true, the search
952 // was aborted because the user interrupted the search or because we
953 // ran out of time. In this case, the return value of the search cannot
954 // be trusted, and we break out of the loop without updating the best
959 // Remember beta-cutoff and searched nodes counts for this move. The
960 // info is used to sort the root moves for the next iteration.
962 TM.get_beta_counters(pos.side_to_move(), our, their);
963 rml.set_beta_counters(i, our, their);
964 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
966 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
967 assert(value < beta);
969 // Step 17. Check for new best move
970 if (value <= alpha && i >= MultiPV)
971 rml.set_move_score(i, -VALUE_INFINITE);
974 // PV move or new best move!
977 rml.set_move_score(i, value);
979 TT.extract_pv(pos, ss->pv, PLY_MAX);
980 rml.set_move_pv(i, ss->pv);
984 // We record how often the best move has been changed in each
985 // iteration. This information is used for time managment: When
986 // the best move changes frequently, we allocate some more time.
988 BestMoveChangesByIteration[Iteration]++;
990 // Print information to the standard output
991 print_pv_info(pos, ss, alpha, beta, value);
993 // Raise alpha to setup proper non-pv search upper bound
1000 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1002 cout << "info multipv " << j + 1
1003 << " score " << value_to_string(rml.get_move_score(j))
1004 << " depth " << (j <= i ? Iteration : Iteration - 1)
1005 << " time " << current_search_time()
1006 << " nodes " << TM.nodes_searched()
1010 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1011 cout << rml.get_move_pv(j, k) << " ";
1015 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1017 } // PV move or new best move
1019 assert(alpha >= *alphaPtr);
1021 AspirationFailLow = (alpha == *alphaPtr);
1023 if (AspirationFailLow && StopOnPonderhit)
1024 StopOnPonderhit = false;
1027 // Can we exit fail low loop ?
1028 if (AbortSearch || !AspirationFailLow)
1031 // Prepare for a research after a fail low, each time with a wider window
1032 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1037 // Sort the moves before to return
1044 // search<>() is the main search function for both PV and non-PV nodes
1046 template <NodeType PvNode>
1047 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1049 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1050 assert(beta > alpha && beta <= VALUE_INFINITE);
1051 assert(PvNode || alpha == beta - 1);
1052 assert(ply > 0 && ply < PLY_MAX);
1053 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1055 Move movesSearched[256];
1060 Move ttMove, move, excludedMove;
1061 Depth ext, newDepth;
1062 Value bestValue, value, oldAlpha;
1063 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1064 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1065 bool mateThreat = false;
1067 int threadID = pos.thread();
1068 refinedValue = bestValue = value = -VALUE_INFINITE;
1071 // Step 1. Initialize node and poll. Polling can abort search
1072 TM.incrementNodeCounter(threadID);
1074 (ss+2)->initKillers();
1076 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1082 // Step 2. Check for aborted search and immediate draw
1083 if (AbortSearch || TM.thread_should_stop(threadID))
1086 if (pos.is_draw() || ply >= PLY_MAX - 1)
1089 // Step 3. Mate distance pruning
1090 alpha = Max(value_mated_in(ply), alpha);
1091 beta = Min(value_mate_in(ply+1), beta);
1095 // Step 4. Transposition table lookup
1097 // We don't want the score of a partial search to overwrite a previous full search
1098 // TT value, so we use a different position key in case of an excluded move exists.
1099 excludedMove = ss->excludedMove;
1100 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1102 tte = TT.retrieve(posKey);
1103 ttMove = (tte ? tte->move() : MOVE_NONE);
1105 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1106 // This is to avoid problems in the following areas:
1108 // * Repetition draw detection
1109 // * Fifty move rule detection
1110 // * Searching for a mate
1111 // * Printing of full PV line
1113 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1115 // Refresh tte entry to avoid aging
1116 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1118 ss->currentMove = ttMove; // Can be MOVE_NONE
1119 return value_from_tt(tte->value(), ply);
1122 // Step 5. Evaluate the position statically
1123 // At PV nodes we do this only to update gain statistics
1124 isCheck = pos.is_check();
1127 if (tte && tte->static_value() != VALUE_NONE)
1129 ss->eval = tte->static_value();
1130 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1133 ss->eval = evaluate(pos, ei);
1135 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1136 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1139 // Step 6. Razoring (is omitted in PV nodes)
1141 && depth < RazorDepth
1143 && refinedValue < beta - razor_margin(depth)
1144 && ttMove == MOVE_NONE
1145 && (ss-1)->currentMove != MOVE_NULL
1146 && !value_is_mate(beta)
1147 && !pos.has_pawn_on_7th(pos.side_to_move()))
1149 // Pass ss->eval to qsearch() and avoid an evaluate call
1150 if (!tte || tte->static_value() == VALUE_NONE)
1151 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1153 Value rbeta = beta - razor_margin(depth);
1154 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1156 // Logically we should return (v + razor_margin(depth)), but
1157 // surprisingly this did slightly weaker in tests.
1161 // Step 7. Static null move pruning (is omitted in PV nodes)
1162 // We're betting that the opponent doesn't have a move that will reduce
1163 // the score by more than futility_margin(depth) if we do a null move.
1165 && !ss->skipNullMove
1166 && depth < RazorDepth
1167 && refinedValue >= beta + futility_margin(depth, 0)
1169 && !value_is_mate(beta)
1170 && pos.non_pawn_material(pos.side_to_move()))
1171 return refinedValue - futility_margin(depth, 0);
1173 // Step 8. Null move search with verification search (is omitted in PV nodes)
1174 // When we jump directly to qsearch() we do a null move only if static value is
1175 // at least beta. Otherwise we do a null move if static value is not more than
1176 // NullMoveMargin under beta.
1178 && !ss->skipNullMove
1180 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1182 && !value_is_mate(beta)
1183 && pos.non_pawn_material(pos.side_to_move()))
1185 ss->currentMove = MOVE_NULL;
1187 // Null move dynamic reduction based on depth
1188 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1190 // Null move dynamic reduction based on value
1191 if (refinedValue - beta > PawnValueMidgame)
1194 pos.do_null_move(st);
1195 (ss+1)->skipNullMove = true;
1197 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1198 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1199 (ss+1)->skipNullMove = false;
1200 pos.undo_null_move();
1202 if (nullValue >= beta)
1204 // Do not return unproven mate scores
1205 if (nullValue >= value_mate_in(PLY_MAX))
1208 // Do zugzwang verification search at high depths
1209 if (depth < 6 * OnePly)
1212 ss->skipNullMove = true;
1213 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply);
1214 ss->skipNullMove = false;
1221 // The null move failed low, which means that we may be faced with
1222 // some kind of threat. If the previous move was reduced, check if
1223 // the move that refuted the null move was somehow connected to the
1224 // move which was reduced. If a connection is found, return a fail
1225 // low score (which will cause the reduced move to fail high in the
1226 // parent node, which will trigger a re-search with full depth).
1227 if (nullValue == value_mated_in(ply + 2))
1230 ss->threatMove = (ss+1)->currentMove;
1231 if ( depth < ThreatDepth
1232 && (ss-1)->reduction
1233 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1238 // Step 9. Internal iterative deepening
1239 if ( depth >= IIDDepth[PvNode]
1240 && ttMove == MOVE_NONE
1241 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1243 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1245 ss->skipNullMove = true;
1246 search<PvNode>(pos, ss, alpha, beta, d, ply);
1247 ss->skipNullMove = false;
1250 tte = TT.retrieve(posKey);
1253 // Expensive mate threat detection (only for PV nodes)
1255 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1257 // Initialize a MovePicker object for the current position
1258 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1260 bool 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 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1278 moveIsCheck = pos.move_is_check(move, ci);
1279 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1281 // Step 11. Decide the new search depth
1282 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1284 // Singular extension search. We extend the TT move if its value is much better than
1285 // its siblings. To verify this we do a reduced search on all the other moves but the
1286 // ttMove, if result is 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;
1301 if (v < ttValue - SingularExtensionMargin)
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
1415 if (value == value_mate_in(ply + 1))
1416 ss->mateKiller = 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 if (bestValue <= oldAlpha)
1446 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1448 else if (bestValue >= beta)
1450 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1452 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1453 if (!pos.move_is_capture_or_promotion(move))
1455 update_history(pos, move, depth, movesSearched, moveCount);
1456 update_killers(move, ss);
1460 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss->pv[0], ss->eval, ei.kingDanger[pos.side_to_move()]);
1462 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1468 // qsearch() is the quiescence search function, which is called by the main
1469 // search function when the remaining depth is zero (or, to be more precise,
1470 // less than OnePly).
1472 template <NodeType PvNode>
1473 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1475 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1476 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1477 assert(PvNode || alpha == beta - 1);
1479 assert(ply > 0 && ply < PLY_MAX);
1480 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1485 Value bestValue, value, futilityValue, futilityBase;
1486 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1488 Value oldAlpha = alpha;
1490 TM.incrementNodeCounter(pos.thread());
1491 ss->pv[0] = ss->pv[1] = ss->currentMove = MOVE_NONE;
1492 ss->eval = VALUE_NONE;
1494 // Check for an instant draw or maximum ply reached
1495 if (pos.is_draw() || ply >= PLY_MAX - 1)
1498 // Transposition table lookup. At PV nodes, we don't use the TT for
1499 // pruning, but only for move ordering.
1500 tte = TT.retrieve(pos.get_key());
1501 ttMove = (tte ? tte->move() : MOVE_NONE);
1503 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1505 ss->currentMove = ttMove; // Can be MOVE_NONE
1506 return value_from_tt(tte->value(), ply);
1509 isCheck = pos.is_check();
1511 // Evaluate the position statically
1514 bestValue = futilityBase = -VALUE_INFINITE;
1515 deepChecks = enoughMaterial = false;
1519 if (tte && tte->static_value() != VALUE_NONE)
1521 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1522 bestValue = tte->static_value();
1525 bestValue = evaluate(pos, ei);
1527 ss->eval = bestValue;
1528 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1530 // Stand pat. Return immediately if static value is at least beta
1531 if (bestValue >= beta)
1534 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()]);
1539 if (PvNode && bestValue > alpha)
1542 // If we are near beta then try to get a cutoff pushing checks a bit further
1543 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1545 // Futility pruning parameters, not needed when in check
1546 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1547 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1550 // Initialize a MovePicker object for the current position, and prepare
1551 // to search the moves. Because the depth is <= 0 here, only captures,
1552 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1553 // and we are near beta) will be generated.
1554 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1557 // Loop through the moves until no moves remain or a beta cutoff occurs
1558 while ( alpha < beta
1559 && (move = mp.get_next_move()) != MOVE_NONE)
1561 assert(move_is_ok(move));
1563 moveIsCheck = pos.move_is_check(move, ci);
1571 && !move_is_promotion(move)
1572 && !pos.move_is_passed_pawn_push(move))
1574 futilityValue = futilityBase
1575 + pos.endgame_value_of_piece_on(move_to(move))
1576 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1578 if (futilityValue < alpha)
1580 if (futilityValue > bestValue)
1581 bestValue = futilityValue;
1586 // Detect blocking evasions that are candidate to be pruned
1587 evasionPrunable = isCheck
1588 && bestValue > value_mated_in(PLY_MAX)
1589 && !pos.move_is_capture(move)
1590 && pos.type_of_piece_on(move_from(move)) != KING
1591 && !pos.can_castle(pos.side_to_move());
1593 // Don't search moves with negative SEE values
1595 && (!isCheck || evasionPrunable)
1597 && !move_is_promotion(move)
1598 && pos.see_sign(move) < 0)
1601 // Update current move
1602 ss->currentMove = move;
1604 // Make and search the move
1605 pos.do_move(move, st, ci, moveIsCheck);
1606 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1607 pos.undo_move(move);
1609 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1612 if (value > bestValue)
1623 // All legal moves have been searched. A special case: If we're in check
1624 // and no legal moves were found, it is checkmate.
1625 if (isCheck && bestValue == -VALUE_INFINITE)
1626 return value_mated_in(ply);
1628 // Update transposition table
1629 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1630 if (bestValue <= oldAlpha)
1631 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1632 else if (bestValue >= beta)
1635 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1637 // Update killers only for good checking moves
1638 if (!pos.move_is_capture_or_promotion(move))
1639 update_killers(move, ss);
1642 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()]);
1644 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1650 // sp_search() is used to search from a split point. This function is called
1651 // by each thread working at the split point. It is similar to the normal
1652 // search() function, but simpler. Because we have already probed the hash
1653 // table, done a null move search, and searched the first move before
1654 // splitting, we don't have to repeat all this work in sp_search(). We
1655 // also don't need to store anything to the hash table here: This is taken
1656 // care of after we return from the split point.
1658 template <NodeType PvNode>
1659 void sp_search(SplitPoint* sp, int threadID) {
1661 assert(threadID >= 0 && threadID < TM.active_threads());
1662 assert(TM.active_threads() > 1);
1666 Depth ext, newDepth;
1668 Value futilityValueScaled; // NonPV specific
1669 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1671 value = -VALUE_INFINITE;
1673 Position pos(*sp->pos, threadID);
1675 SearchStack* ss = sp->sstack[threadID] + 1;
1676 isCheck = pos.is_check();
1678 // Step 10. Loop through moves
1679 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1680 lock_grab(&(sp->lock));
1682 while ( sp->bestValue < sp->beta
1683 && (move = sp->mp->get_next_move()) != MOVE_NONE
1684 && !TM.thread_should_stop(threadID))
1686 moveCount = ++sp->moveCount;
1687 lock_release(&(sp->lock));
1689 assert(move_is_ok(move));
1691 moveIsCheck = pos.move_is_check(move, ci);
1692 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1694 // Step 11. Decide the new search depth
1695 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1696 newDepth = sp->depth - OnePly + ext;
1698 // Update current move
1699 ss->currentMove = move;
1701 // Step 12. Futility pruning (is omitted in PV nodes)
1703 && !captureOrPromotion
1706 && !move_is_castle(move))
1708 // Move count based pruning
1709 if ( moveCount >= futility_move_count(sp->depth)
1710 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1711 && sp->bestValue > value_mated_in(PLY_MAX))
1713 lock_grab(&(sp->lock));
1717 // Value based pruning
1718 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1719 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1720 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1722 if (futilityValueScaled < sp->beta)
1724 lock_grab(&(sp->lock));
1726 if (futilityValueScaled > sp->bestValue)
1727 sp->bestValue = futilityValueScaled;
1732 // Step 13. Make the move
1733 pos.do_move(move, st, ci, moveIsCheck);
1735 // Step 14. Reduced search
1736 // If the move fails high will be re-searched at full depth.
1737 bool doFullDepthSearch = true;
1739 if ( !captureOrPromotion
1741 && !move_is_castle(move)
1742 && !move_is_killer(move, ss))
1744 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1747 Value localAlpha = sp->alpha;
1748 Depth d = newDepth - ss->reduction;
1749 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1750 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1752 doFullDepthSearch = (value > localAlpha);
1755 // The move failed high, but if reduction is very big we could
1756 // face a false positive, retry with a less aggressive reduction,
1757 // if the move fails high again then go with full depth search.
1758 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1760 assert(newDepth - OnePly >= OnePly);
1762 ss->reduction = OnePly;
1763 Value localAlpha = sp->alpha;
1764 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1765 doFullDepthSearch = (value > localAlpha);
1767 ss->reduction = Depth(0); // Restore original reduction
1770 // Step 15. Full depth search
1771 if (doFullDepthSearch)
1773 Value localAlpha = sp->alpha;
1774 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1775 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1777 // Step extra. pv search (only in PV nodes)
1778 // Search only for possible new PV nodes, if instead value >= beta then
1779 // parent node fails low with value <= alpha and tries another move.
1780 if (PvNode && value > localAlpha && value < sp->beta)
1781 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1782 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1785 // Step 16. Undo move
1786 pos.undo_move(move);
1788 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1790 // Step 17. Check for new best move
1791 lock_grab(&(sp->lock));
1793 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1795 sp->bestValue = value;
1797 if (sp->bestValue > sp->alpha)
1799 if (!PvNode || value >= sp->beta)
1800 sp->stopRequest = true;
1802 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1805 sp_update_pv(sp->parentSstack, ss);
1810 /* Here we have the lock still grabbed */
1812 sp->slaves[threadID] = 0;
1814 lock_release(&(sp->lock));
1817 // update_pv() is called whenever a search returns a value > alpha.
1818 // It updates the PV in the SearchStack object corresponding to the
1821 void update_pv(SearchStack* ss) {
1823 Move* src = (ss+1)->pv;
1826 *dst = ss->currentMove;
1830 while (*src++ != MOVE_NONE);
1834 // sp_update_pv() is a variant of update_pv for use at split points. The
1835 // difference between the two functions is that sp_update_pv also updates
1836 // the PV at the parent node.
1838 void sp_update_pv(SearchStack* pss, SearchStack* ss) {
1840 Move* src = (ss+1)->pv;
1842 Move* pdst = pss->pv;
1844 *dst = *pdst = ss->currentMove;
1847 *++dst = *++pdst = *src;
1848 while (*src++ != MOVE_NONE);
1852 // connected_moves() tests whether two moves are 'connected' in the sense
1853 // that the first move somehow made the second move possible (for instance
1854 // if the moving piece is the same in both moves). The first move is assumed
1855 // to be the move that was made to reach the current position, while the
1856 // second move is assumed to be a move from the current position.
1858 bool connected_moves(const Position& pos, Move m1, Move m2) {
1860 Square f1, t1, f2, t2;
1863 assert(move_is_ok(m1));
1864 assert(move_is_ok(m2));
1866 if (m2 == MOVE_NONE)
1869 // Case 1: The moving piece is the same in both moves
1875 // Case 2: The destination square for m2 was vacated by m1
1881 // Case 3: Moving through the vacated square
1882 if ( piece_is_slider(pos.piece_on(f2))
1883 && bit_is_set(squares_between(f2, t2), f1))
1886 // Case 4: The destination square for m2 is defended by the moving piece in m1
1887 p = pos.piece_on(t1);
1888 if (bit_is_set(pos.attacks_from(p, t1), t2))
1891 // Case 5: Discovered check, checking piece is the piece moved in m1
1892 if ( piece_is_slider(p)
1893 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1894 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1896 // discovered_check_candidates() works also if the Position's side to
1897 // move is the opposite of the checking piece.
1898 Color them = opposite_color(pos.side_to_move());
1899 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1901 if (bit_is_set(dcCandidates, f2))
1908 // value_is_mate() checks if the given value is a mate one
1909 // eventually compensated for the ply.
1911 bool value_is_mate(Value value) {
1913 assert(abs(value) <= VALUE_INFINITE);
1915 return value <= value_mated_in(PLY_MAX)
1916 || value >= value_mate_in(PLY_MAX);
1920 // move_is_killer() checks if the given move is among the
1921 // killer moves of that ply.
1923 bool move_is_killer(Move m, SearchStack* ss) {
1925 const Move* k = ss->killers;
1926 for (int i = 0; i < KILLER_MAX; i++, k++)
1934 // extension() decides whether a move should be searched with normal depth,
1935 // or with extended depth. Certain classes of moves (checking moves, in
1936 // particular) are searched with bigger depth than ordinary moves and in
1937 // any case are marked as 'dangerous'. Note that also if a move is not
1938 // extended, as example because the corresponding UCI option is set to zero,
1939 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1940 template <NodeType PvNode>
1941 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1942 bool singleEvasion, bool mateThreat, bool* dangerous) {
1944 assert(m != MOVE_NONE);
1946 Depth result = Depth(0);
1947 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1951 if (moveIsCheck && pos.see_sign(m)>= 0)
1952 result += CheckExtension[PvNode];
1955 result += SingleEvasionExtension[PvNode];
1958 result += MateThreatExtension[PvNode];
1961 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1963 Color c = pos.side_to_move();
1964 if (relative_rank(c, move_to(m)) == RANK_7)
1966 result += PawnPushTo7thExtension[PvNode];
1969 if (pos.pawn_is_passed(c, move_to(m)))
1971 result += PassedPawnExtension[PvNode];
1976 if ( captureOrPromotion
1977 && pos.type_of_piece_on(move_to(m)) != PAWN
1978 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1979 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1980 && !move_is_promotion(m)
1983 result += PawnEndgameExtension[PvNode];
1988 && captureOrPromotion
1989 && pos.type_of_piece_on(move_to(m)) != PAWN
1990 && pos.see_sign(m) >= 0)
1996 return Min(result, OnePly);
2000 // connected_threat() tests whether it is safe to forward prune a move or if
2001 // is somehow coonected to the threat move returned by null search.
2003 bool connected_threat(const Position& pos, Move m, Move threat) {
2005 assert(move_is_ok(m));
2006 assert(threat && move_is_ok(threat));
2007 assert(!pos.move_is_check(m));
2008 assert(!pos.move_is_capture_or_promotion(m));
2009 assert(!pos.move_is_passed_pawn_push(m));
2011 Square mfrom, mto, tfrom, tto;
2013 mfrom = move_from(m);
2015 tfrom = move_from(threat);
2016 tto = move_to(threat);
2018 // Case 1: Don't prune moves which move the threatened piece
2022 // Case 2: If the threatened piece has value less than or equal to the
2023 // value of the threatening piece, don't prune move which defend it.
2024 if ( pos.move_is_capture(threat)
2025 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2026 || pos.type_of_piece_on(tfrom) == KING)
2027 && pos.move_attacks_square(m, tto))
2030 // Case 3: If the moving piece in the threatened move is a slider, don't
2031 // prune safe moves which block its ray.
2032 if ( piece_is_slider(pos.piece_on(tfrom))
2033 && bit_is_set(squares_between(tfrom, tto), mto)
2034 && pos.see_sign(m) >= 0)
2041 // ok_to_use_TT() returns true if a transposition table score
2042 // can be used at a given point in search.
2044 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2046 Value v = value_from_tt(tte->value(), ply);
2048 return ( tte->depth() >= depth
2049 || v >= Max(value_mate_in(PLY_MAX), beta)
2050 || v < Min(value_mated_in(PLY_MAX), beta))
2052 && ( (is_lower_bound(tte->type()) && v >= beta)
2053 || (is_upper_bound(tte->type()) && v < beta));
2057 // refine_eval() returns the transposition table score if
2058 // possible otherwise falls back on static position evaluation.
2060 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2065 Value v = value_from_tt(tte->value(), ply);
2067 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2068 || (is_upper_bound(tte->type()) && v < defaultEval))
2075 // update_history() registers a good move that produced a beta-cutoff
2076 // in history and marks as failures all the other moves of that ply.
2078 void update_history(const Position& pos, Move move, Depth depth,
2079 Move movesSearched[], int moveCount) {
2083 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2085 for (int i = 0; i < moveCount - 1; i++)
2087 m = movesSearched[i];
2091 if (!pos.move_is_capture_or_promotion(m))
2092 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2097 // update_killers() add a good move that produced a beta-cutoff
2098 // among the killer moves of that ply.
2100 void update_killers(Move m, SearchStack* ss) {
2102 if (m == ss->killers[0])
2105 for (int i = KILLER_MAX - 1; i > 0; i--)
2106 ss->killers[i] = ss->killers[i - 1];
2112 // update_gains() updates the gains table of a non-capture move given
2113 // the static position evaluation before and after the move.
2115 void update_gains(const Position& pos, Move m, Value before, Value after) {
2118 && before != VALUE_NONE
2119 && after != VALUE_NONE
2120 && pos.captured_piece() == NO_PIECE_TYPE
2121 && !move_is_castle(m)
2122 && !move_is_promotion(m))
2123 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2127 // current_search_time() returns the number of milliseconds which have passed
2128 // since the beginning of the current search.
2130 int current_search_time() {
2132 return get_system_time() - SearchStartTime;
2136 // nps() computes the current nodes/second count.
2140 int t = current_search_time();
2141 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2145 // poll() performs two different functions: It polls for user input, and it
2146 // looks at the time consumed so far and decides if it's time to abort the
2151 static int lastInfoTime;
2152 int t = current_search_time();
2157 // We are line oriented, don't read single chars
2158 std::string command;
2160 if (!std::getline(std::cin, command))
2163 if (command == "quit")
2166 PonderSearch = false;
2170 else if (command == "stop")
2173 PonderSearch = false;
2175 else if (command == "ponderhit")
2179 // Print search information
2183 else if (lastInfoTime > t)
2184 // HACK: Must be a new search where we searched less than
2185 // NodesBetweenPolls nodes during the first second of search.
2188 else if (t - lastInfoTime >= 1000)
2195 if (dbg_show_hit_rate)
2196 dbg_print_hit_rate();
2198 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2199 << " time " << t << " hashfull " << TT.full() << endl;
2202 // Should we stop the search?
2206 bool stillAtFirstMove = FirstRootMove
2207 && !AspirationFailLow
2208 && t > MaxSearchTime + ExtraSearchTime;
2210 bool noMoreTime = t > AbsoluteMaxSearchTime
2211 || stillAtFirstMove;
2213 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2214 || (ExactMaxTime && t >= ExactMaxTime)
2215 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2220 // ponderhit() is called when the program is pondering (i.e. thinking while
2221 // it's the opponent's turn to move) in order to let the engine know that
2222 // it correctly predicted the opponent's move.
2226 int t = current_search_time();
2227 PonderSearch = false;
2229 bool stillAtFirstMove = FirstRootMove
2230 && !AspirationFailLow
2231 && t > MaxSearchTime + ExtraSearchTime;
2233 bool noMoreTime = t > AbsoluteMaxSearchTime
2234 || stillAtFirstMove;
2236 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2241 // init_ss_array() does a fast reset of the first entries of a SearchStack
2242 // array and of all the excludedMove and skipNullMove entries.
2244 void init_ss_array(SearchStack* ss, int size) {
2246 for (int i = 0; i < size; i++, ss++)
2248 ss->excludedMove = MOVE_NONE;
2249 ss->skipNullMove = false;
2260 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2261 // while the program is pondering. The point is to work around a wrinkle in
2262 // the UCI protocol: When pondering, the engine is not allowed to give a
2263 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2264 // We simply wait here until one of these commands is sent, and return,
2265 // after which the bestmove and pondermove will be printed (in id_loop()).
2267 void wait_for_stop_or_ponderhit() {
2269 std::string command;
2273 if (!std::getline(std::cin, command))
2276 if (command == "quit")
2281 else if (command == "ponderhit" || command == "stop")
2287 // print_pv_info() prints to standard output and eventually to log file information on
2288 // the current PV line. It is called at each iteration or after a new pv is found.
2290 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2292 cout << "info depth " << Iteration
2293 << " score " << value_to_string(value)
2294 << ((value >= beta) ? " lowerbound" :
2295 ((value <= alpha)? " upperbound" : ""))
2296 << " time " << current_search_time()
2297 << " nodes " << TM.nodes_searched()
2301 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2302 cout << ss->pv[j] << " ";
2308 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2309 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2311 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2312 TM.nodes_searched(), value, type, ss->pv) << endl;
2317 // init_thread() is the function which is called when a new thread is
2318 // launched. It simply calls the idle_loop() function with the supplied
2319 // threadID. There are two versions of this function; one for POSIX
2320 // threads and one for Windows threads.
2322 #if !defined(_MSC_VER)
2324 void* init_thread(void *threadID) {
2326 TM.idle_loop(*(int*)threadID, NULL);
2332 DWORD WINAPI init_thread(LPVOID threadID) {
2334 TM.idle_loop(*(int*)threadID, NULL);
2341 /// The ThreadsManager class
2343 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2344 // get_beta_counters() are getters/setters for the per thread
2345 // counters used to sort the moves at root.
2347 void ThreadsManager::resetNodeCounters() {
2349 for (int i = 0; i < MAX_THREADS; i++)
2350 threads[i].nodes = 0ULL;
2353 void ThreadsManager::resetBetaCounters() {
2355 for (int i = 0; i < MAX_THREADS; i++)
2356 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2359 int64_t ThreadsManager::nodes_searched() const {
2361 int64_t result = 0ULL;
2362 for (int i = 0; i < ActiveThreads; i++)
2363 result += threads[i].nodes;
2368 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2371 for (int i = 0; i < MAX_THREADS; i++)
2373 our += threads[i].betaCutOffs[us];
2374 their += threads[i].betaCutOffs[opposite_color(us)];
2379 // idle_loop() is where the threads are parked when they have no work to do.
2380 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2381 // object for which the current thread is the master.
2383 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2385 assert(threadID >= 0 && threadID < MAX_THREADS);
2389 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2390 // master should exit as last one.
2391 if (AllThreadsShouldExit)
2394 threads[threadID].state = THREAD_TERMINATED;
2398 // If we are not thinking, wait for a condition to be signaled
2399 // instead of wasting CPU time polling for work.
2400 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2403 assert(threadID != 0);
2404 threads[threadID].state = THREAD_SLEEPING;
2406 #if !defined(_MSC_VER)
2407 lock_grab(&WaitLock);
2408 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2409 pthread_cond_wait(&WaitCond, &WaitLock);
2410 lock_release(&WaitLock);
2412 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2416 // If thread has just woken up, mark it as available
2417 if (threads[threadID].state == THREAD_SLEEPING)
2418 threads[threadID].state = THREAD_AVAILABLE;
2420 // If this thread has been assigned work, launch a search
2421 if (threads[threadID].state == THREAD_WORKISWAITING)
2423 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2425 threads[threadID].state = THREAD_SEARCHING;
2427 if (threads[threadID].splitPoint->pvNode)
2428 sp_search<PV>(threads[threadID].splitPoint, threadID);
2430 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2432 assert(threads[threadID].state == THREAD_SEARCHING);
2434 threads[threadID].state = THREAD_AVAILABLE;
2437 // If this thread is the master of a split point and all slaves have
2438 // finished their work at this split point, return from the idle loop.
2440 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2442 if (i == ActiveThreads)
2444 // Because sp->slaves[] is reset under lock protection,
2445 // be sure sp->lock has been released before to return.
2446 lock_grab(&(sp->lock));
2447 lock_release(&(sp->lock));
2449 assert(threads[threadID].state == THREAD_AVAILABLE);
2451 threads[threadID].state = THREAD_SEARCHING;
2458 // init_threads() is called during startup. It launches all helper threads,
2459 // and initializes the split point stack and the global locks and condition
2462 void ThreadsManager::init_threads() {
2467 #if !defined(_MSC_VER)
2468 pthread_t pthread[1];
2471 // Initialize global locks
2472 lock_init(&MPLock, NULL);
2473 lock_init(&WaitLock, NULL);
2475 #if !defined(_MSC_VER)
2476 pthread_cond_init(&WaitCond, NULL);
2478 for (i = 0; i < MAX_THREADS; i++)
2479 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2482 // Initialize SplitPointStack locks
2483 for (i = 0; i < MAX_THREADS; i++)
2484 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2485 lock_init(&(SplitPointStack[i][j].lock), NULL);
2487 // Will be set just before program exits to properly end the threads
2488 AllThreadsShouldExit = false;
2490 // Threads will be put to sleep as soon as created
2491 AllThreadsShouldSleep = true;
2493 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2495 threads[0].state = THREAD_SEARCHING;
2496 for (i = 1; i < MAX_THREADS; i++)
2497 threads[i].state = THREAD_AVAILABLE;
2499 // Launch the helper threads
2500 for (i = 1; i < MAX_THREADS; i++)
2503 #if !defined(_MSC_VER)
2504 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2506 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2511 cout << "Failed to create thread number " << i << endl;
2512 Application::exit_with_failure();
2515 // Wait until the thread has finished launching and is gone to sleep
2516 while (threads[i].state != THREAD_SLEEPING) {}
2521 // exit_threads() is called when the program exits. It makes all the
2522 // helper threads exit cleanly.
2524 void ThreadsManager::exit_threads() {
2526 ActiveThreads = MAX_THREADS; // HACK
2527 AllThreadsShouldSleep = true; // HACK
2528 wake_sleeping_threads();
2530 // This makes the threads to exit idle_loop()
2531 AllThreadsShouldExit = true;
2533 // Wait for thread termination
2534 for (int i = 1; i < MAX_THREADS; i++)
2535 while (threads[i].state != THREAD_TERMINATED) {}
2537 // Now we can safely destroy the locks
2538 for (int i = 0; i < MAX_THREADS; i++)
2539 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2540 lock_destroy(&(SplitPointStack[i][j].lock));
2542 lock_destroy(&WaitLock);
2543 lock_destroy(&MPLock);
2547 // thread_should_stop() checks whether the thread should stop its search.
2548 // This can happen if a beta cutoff has occurred in the thread's currently
2549 // active split point, or in some ancestor of the current split point.
2551 bool ThreadsManager::thread_should_stop(int threadID) const {
2553 assert(threadID >= 0 && threadID < ActiveThreads);
2557 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2562 // thread_is_available() checks whether the thread with threadID "slave" is
2563 // available to help the thread with threadID "master" at a split point. An
2564 // obvious requirement is that "slave" must be idle. With more than two
2565 // threads, this is not by itself sufficient: If "slave" is the master of
2566 // some active split point, it is only available as a slave to the other
2567 // threads which are busy searching the split point at the top of "slave"'s
2568 // split point stack (the "helpful master concept" in YBWC terminology).
2570 bool ThreadsManager::thread_is_available(int slave, int master) const {
2572 assert(slave >= 0 && slave < ActiveThreads);
2573 assert(master >= 0 && master < ActiveThreads);
2574 assert(ActiveThreads > 1);
2576 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2579 // Make a local copy to be sure doesn't change under our feet
2580 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2582 if (localActiveSplitPoints == 0)
2583 // No active split points means that the thread is available as
2584 // a slave for any other thread.
2587 if (ActiveThreads == 2)
2590 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2591 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2592 // could have been set to 0 by another thread leading to an out of bound access.
2593 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2600 // available_thread_exists() tries to find an idle thread which is available as
2601 // a slave for the thread with threadID "master".
2603 bool ThreadsManager::available_thread_exists(int master) const {
2605 assert(master >= 0 && master < ActiveThreads);
2606 assert(ActiveThreads > 1);
2608 for (int i = 0; i < ActiveThreads; i++)
2609 if (thread_is_available(i, master))
2616 // split() does the actual work of distributing the work at a node between
2617 // several available threads. If it does not succeed in splitting the
2618 // node (because no idle threads are available, or because we have no unused
2619 // split point objects), the function immediately returns. If splitting is
2620 // possible, a SplitPoint object is initialized with all the data that must be
2621 // copied to the helper threads and we tell our helper threads that they have
2622 // been assigned work. This will cause them to instantly leave their idle loops
2623 // and call sp_search(). When all threads have returned from sp_search() then
2626 template <bool Fake>
2627 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2628 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2629 int* moveCount, MovePicker* mp, bool pvNode) {
2631 assert(ply > 0 && ply < PLY_MAX);
2632 assert(*bestValue >= -VALUE_INFINITE);
2633 assert(*bestValue <= *alpha);
2634 assert(*alpha < beta);
2635 assert(beta <= VALUE_INFINITE);
2636 assert(depth > Depth(0));
2637 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2638 assert(ActiveThreads > 1);
2640 int master = p.thread();
2644 // If no other thread is available to help us, or if we have too many
2645 // active split points, don't split.
2646 if ( !available_thread_exists(master)
2647 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2649 lock_release(&MPLock);
2653 // Pick the next available split point object from the split point stack
2654 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2656 // Initialize the split point object
2657 splitPoint->parent = threads[master].splitPoint;
2658 splitPoint->stopRequest = false;
2659 splitPoint->ply = ply;
2660 splitPoint->depth = depth;
2661 splitPoint->mateThreat = mateThreat;
2662 splitPoint->alpha = *alpha;
2663 splitPoint->beta = beta;
2664 splitPoint->pvNode = pvNode;
2665 splitPoint->bestValue = *bestValue;
2666 splitPoint->mp = mp;
2667 splitPoint->moveCount = *moveCount;
2668 splitPoint->pos = &p;
2669 splitPoint->parentSstack = ss;
2670 for (int i = 0; i < ActiveThreads; i++)
2671 splitPoint->slaves[i] = 0;
2673 threads[master].splitPoint = splitPoint;
2674 threads[master].activeSplitPoints++;
2676 // If we are here it means we are not available
2677 assert(threads[master].state != THREAD_AVAILABLE);
2679 int workersCnt = 1; // At least the master is included
2681 // Allocate available threads setting state to THREAD_BOOKED
2682 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2683 if (thread_is_available(i, master))
2685 threads[i].state = THREAD_BOOKED;
2686 threads[i].splitPoint = splitPoint;
2687 splitPoint->slaves[i] = 1;
2691 assert(Fake || workersCnt > 1);
2693 // We can release the lock because slave threads are already booked and master is not available
2694 lock_release(&MPLock);
2696 // Tell the threads that they have work to do. This will make them leave
2697 // their idle loop. But before copy search stack tail for each thread.
2698 for (int i = 0; i < ActiveThreads; i++)
2699 if (i == master || splitPoint->slaves[i])
2701 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2703 assert(i == master || threads[i].state == THREAD_BOOKED);
2705 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2708 // Everything is set up. The master thread enters the idle loop, from
2709 // which it will instantly launch a search, because its state is
2710 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2711 // idle loop, which means that the main thread will return from the idle
2712 // loop when all threads have finished their work at this split point.
2713 idle_loop(master, splitPoint);
2715 // We have returned from the idle loop, which means that all threads are
2716 // finished. Update alpha and bestValue, and return.
2719 *alpha = splitPoint->alpha;
2720 *bestValue = splitPoint->bestValue;
2721 threads[master].activeSplitPoints--;
2722 threads[master].splitPoint = splitPoint->parent;
2724 lock_release(&MPLock);
2728 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2729 // to start a new search from the root.
2731 void ThreadsManager::wake_sleeping_threads() {
2733 assert(AllThreadsShouldSleep);
2734 assert(ActiveThreads > 0);
2736 AllThreadsShouldSleep = false;
2738 if (ActiveThreads == 1)
2741 #if !defined(_MSC_VER)
2742 pthread_mutex_lock(&WaitLock);
2743 pthread_cond_broadcast(&WaitCond);
2744 pthread_mutex_unlock(&WaitLock);
2746 for (int i = 1; i < MAX_THREADS; i++)
2747 SetEvent(SitIdleEvent[i]);
2753 // put_threads_to_sleep() makes all the threads go to sleep just before
2754 // to leave think(), at the end of the search. Threads should have already
2755 // finished the job and should be idle.
2757 void ThreadsManager::put_threads_to_sleep() {
2759 assert(!AllThreadsShouldSleep);
2761 // This makes the threads to go to sleep
2762 AllThreadsShouldSleep = true;
2765 /// The RootMoveList class
2767 // RootMoveList c'tor
2769 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2771 SearchStack ss[PLY_MAX_PLUS_2];
2772 MoveStack mlist[MaxRootMoves];
2774 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2776 // Generate all legal moves
2777 MoveStack* last = generate_moves(pos, mlist);
2779 // Add each move to the moves[] array
2780 for (MoveStack* cur = mlist; cur != last; cur++)
2782 bool includeMove = includeAllMoves;
2784 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2785 includeMove = (searchMoves[k] == cur->move);
2790 // Find a quick score for the move
2791 init_ss_array(ss, PLY_MAX_PLUS_2);
2792 pos.do_move(cur->move, st);
2793 moves[count].move = cur->move;
2794 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2795 moves[count].pv[0] = cur->move;
2796 moves[count].pv[1] = MOVE_NONE;
2797 pos.undo_move(cur->move);
2804 // RootMoveList simple methods definitions
2806 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2808 moves[moveNum].nodes = nodes;
2809 moves[moveNum].cumulativeNodes += nodes;
2812 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2814 moves[moveNum].ourBeta = our;
2815 moves[moveNum].theirBeta = their;
2818 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2822 for (j = 0; pv[j] != MOVE_NONE; j++)
2823 moves[moveNum].pv[j] = pv[j];
2825 moves[moveNum].pv[j] = MOVE_NONE;
2829 // RootMoveList::sort() sorts the root move list at the beginning of a new
2832 void RootMoveList::sort() {
2834 sort_multipv(count - 1); // Sort all items
2838 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2839 // list by their scores and depths. It is used to order the different PVs
2840 // correctly in MultiPV mode.
2842 void RootMoveList::sort_multipv(int n) {
2846 for (i = 1; i <= n; i++)
2848 RootMove rm = moves[i];
2849 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2850 moves[j] = moves[j - 1];