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, 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 = true;
239 const int LSNTime = 4000; // 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);
290 template <NodeType PvNode>
291 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
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, int ply);
300 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply);
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) - 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(int ply) {
371 pv[ply] = pv[ply + 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);
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);
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);
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);
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);
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);
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) {
1050 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1051 assert(beta > alpha && beta <= VALUE_INFINITE);
1052 assert(PvNode || alpha == beta - 1);
1053 assert(pos.ply() > 0 && pos.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 int ply = pos.ply();
1070 refinedValue = bestValue = value = -VALUE_INFINITE;
1073 // Step 1. Initialize node and poll. Polling can abort search
1074 TM.incrementNodeCounter(threadID);
1076 (ss + 2)->initKillers();
1078 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1084 // Step 2. Check for aborted search and immediate draw
1085 if (AbortSearch || TM.thread_should_stop(threadID))
1088 if (pos.is_draw() || ply >= PLY_MAX - 1)
1091 // Step 3. Mate distance pruning
1092 alpha = Max(value_mated_in(ply), alpha);
1093 beta = Min(value_mate_in(ply+1), beta);
1097 // Step 4. Transposition table lookup
1099 // We don't want the score of a partial search to overwrite a previous full search
1100 // TT value, so we use a different position key in case of an excluded move exists.
1101 excludedMove = ss->excludedMove;
1102 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1104 tte = TT.retrieve(posKey);
1105 ttMove = (tte ? tte->move() : MOVE_NONE);
1107 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1108 // This is to avoid problems in the following areas:
1110 // * Repetition draw detection
1111 // * Fifty move rule detection
1112 // * Searching for a mate
1113 // * Printing of full PV line
1115 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1117 // Refresh tte entry to avoid aging
1118 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1120 ss->currentMove = ttMove; // Can be MOVE_NONE
1121 return value_from_tt(tte->value(), ply);
1124 // Step 5. Evaluate the position statically
1125 // At PV nodes we do this only to update gain statistics
1126 isCheck = pos.is_check();
1129 if (tte && tte->static_value() != VALUE_NONE)
1131 ss->eval = tte->static_value();
1132 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1135 ss->eval = evaluate(pos, ei);
1137 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1138 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1141 // Step 6. Razoring (is omitted in PV nodes)
1143 && depth < RazorDepth
1145 && refinedValue < beta - razor_margin(depth)
1146 && ttMove == MOVE_NONE
1147 && (ss-1)->currentMove != MOVE_NULL
1148 && !value_is_mate(beta)
1149 && !pos.has_pawn_on_7th(pos.side_to_move()))
1151 Value rbeta = beta - razor_margin(depth);
1152 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0));
1154 // Logically we should return (v + razor_margin(depth)), but
1155 // surprisingly this did slightly weaker in tests.
1159 // Step 7. Static null move pruning (is omitted in PV nodes)
1160 // We're betting that the opponent doesn't have a move that will reduce
1161 // the score by more than futility_margin(depth) if we do a null move.
1163 && !ss->skipNullMove
1164 && depth < RazorDepth
1165 && refinedValue >= beta + futility_margin(depth, 0)
1167 && !value_is_mate(beta)
1168 && pos.non_pawn_material(pos.side_to_move()))
1169 return refinedValue - futility_margin(depth, 0);
1171 // Step 8. Null move search with verification search (is omitted in PV nodes)
1172 // When we jump directly to qsearch() we do a null move only if static value is
1173 // at least beta. Otherwise we do a null move if static value is not more than
1174 // NullMoveMargin under beta.
1176 && !ss->skipNullMove
1178 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1180 && !value_is_mate(beta)
1181 && pos.non_pawn_material(pos.side_to_move()))
1183 ss->currentMove = MOVE_NULL;
1185 // Null move dynamic reduction based on depth
1186 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1188 // Null move dynamic reduction based on value
1189 if (refinedValue - beta > PawnValueMidgame)
1192 pos.do_null_move(st);
1193 (ss+1)->skipNullMove = true;
1195 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0))
1196 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly);
1197 (ss+1)->skipNullMove = false;
1198 pos.undo_null_move();
1200 if (nullValue >= beta)
1202 // Do not return unproven mate scores
1203 if (nullValue >= value_mate_in(PLY_MAX))
1206 // Do zugzwang verification search at high depths
1207 if (depth < 6 * OnePly)
1210 ss->skipNullMove = true;
1211 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly);
1212 ss->skipNullMove = false;
1219 // The null move failed low, which means that we may be faced with
1220 // some kind of threat. If the previous move was reduced, check if
1221 // the move that refuted the null move was somehow connected to the
1222 // move which was reduced. If a connection is found, return a fail
1223 // low score (which will cause the reduced move to fail high in the
1224 // parent node, which will trigger a re-search with full depth).
1225 if (nullValue == value_mated_in(ply + 2))
1228 ss->threatMove = (ss+1)->currentMove;
1229 if ( depth < ThreatDepth
1230 && (ss-1)->reduction
1231 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1236 // Step 9. Internal iterative deepening
1237 if ( depth >= IIDDepth[PvNode]
1238 && (ttMove == MOVE_NONE || (PvNode && tte->depth() <= depth - 4 * OnePly))
1239 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1241 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1243 ss->skipNullMove = true;
1244 search<PvNode>(pos, ss, alpha, beta, d);
1245 ss->skipNullMove = false;
1247 ttMove = ss->pv[ply];
1248 tte = TT.retrieve(posKey);
1251 // Expensive mate threat detection (only for PV nodes)
1253 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1255 // Initialize a MovePicker object for the current position
1256 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1258 bool singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1259 && tte && tte->move()
1260 && !excludedMove // Do not allow recursive singular extension search
1261 && is_lower_bound(tte->type())
1262 && tte->depth() >= depth - 3 * OnePly;
1264 // Step 10. Loop through moves
1265 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1266 while ( bestValue < beta
1267 && (move = mp.get_next_move()) != MOVE_NONE
1268 && !TM.thread_should_stop(threadID))
1270 assert(move_is_ok(move));
1272 if (move == excludedMove)
1275 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1276 moveIsCheck = pos.move_is_check(move, ci);
1277 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1279 // Step 11. Decide the new search depth
1280 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1282 // Singular extension search. We extend the TT move if its value is much better than
1283 // its siblings. To verify this we do a reduced search on all the other moves but the
1284 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1285 if ( singularExtensionNode
1286 && move == tte->move()
1289 Value ttValue = value_from_tt(tte->value(), ply);
1291 if (abs(ttValue) < VALUE_KNOWN_WIN)
1293 Value b = ttValue - SingularExtensionMargin;
1294 ss->excludedMove = move;
1295 ss->skipNullMove = true;
1296 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2);
1297 ss->skipNullMove = false;
1298 ss->excludedMove = MOVE_NONE;
1300 if (v < ttValue - SingularExtensionMargin)
1305 newDepth = depth - OnePly + ext;
1307 // Update current move (this must be done after singular extension search)
1308 movesSearched[moveCount++] = ss->currentMove = move;
1310 // Step 12. Futility pruning (is omitted in PV nodes)
1312 && !captureOrPromotion
1316 && !move_is_castle(move))
1318 // Move count based pruning
1319 if ( moveCount >= futility_move_count(depth)
1320 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1321 && bestValue > value_mated_in(PLY_MAX))
1324 // Value based pruning
1325 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1326 // but fixing this made program slightly weaker.
1327 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1328 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1329 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1331 if (futilityValueScaled < beta)
1333 if (futilityValueScaled > bestValue)
1334 bestValue = futilityValueScaled;
1339 // Step 13. Make the move
1340 pos.do_move(move, st, ci, moveIsCheck);
1342 // Step extra. pv search (only in PV nodes)
1343 // The first move in list is the expected PV
1344 if (PvNode && moveCount == 1)
1345 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0))
1346 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1349 // Step 14. Reduced depth search
1350 // If the move fails high will be re-searched at full depth.
1351 bool doFullDepthSearch = true;
1353 if ( depth >= 3 * OnePly
1354 && !captureOrPromotion
1356 && !move_is_castle(move)
1357 && !move_is_killer(move, ss))
1359 ss->reduction = reduction<PvNode>(depth, moveCount);
1362 Depth d = newDepth - ss->reduction;
1363 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0))
1364 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1366 doFullDepthSearch = (value > alpha);
1369 // The move failed high, but if reduction is very big we could
1370 // face a false positive, retry with a less aggressive reduction,
1371 // if the move fails high again then go with full depth search.
1372 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1374 assert(newDepth - OnePly >= OnePly);
1376 ss->reduction = OnePly;
1377 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction);
1378 doFullDepthSearch = (value > alpha);
1380 ss->reduction = Depth(0); // Restore original reduction
1383 // Step 15. Full depth search
1384 if (doFullDepthSearch)
1386 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0))
1387 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1389 // Step extra. pv search (only in PV nodes)
1390 // Search only for possible new PV nodes, if instead value >= beta then
1391 // parent node fails low with value <= alpha and tries another move.
1392 if (PvNode && value > alpha && value < beta)
1393 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0))
1394 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1398 // Step 16. Undo move
1399 pos.undo_move(move);
1401 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1403 // Step 17. Check for new best move
1404 if (value > bestValue)
1409 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1414 if (value == value_mate_in(ply + 1))
1415 ss->mateKiller = move;
1419 // Step 18. Check for split
1420 if ( depth >= MinimumSplitDepth
1421 && TM.active_threads() > 1
1423 && TM.available_thread_exists(threadID)
1425 && !TM.thread_should_stop(threadID)
1427 TM.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1428 mateThreat, &moveCount, &mp, PvNode);
1431 // Step 19. Check for mate and stalemate
1432 // All legal moves have been searched and if there are
1433 // no legal moves, it must be mate or stalemate.
1434 // If one move was excluded return fail low score.
1436 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1438 // Step 20. Update tables
1439 // If the search is not aborted, update the transposition table,
1440 // history counters, and killer moves.
1441 if (AbortSearch || TM.thread_should_stop(threadID))
1444 if (bestValue <= oldAlpha)
1445 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1447 else if (bestValue >= beta)
1449 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1451 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1452 if (!pos.move_is_capture_or_promotion(move))
1454 update_history(pos, move, depth, movesSearched, moveCount);
1455 update_killers(move, ss);
1459 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1461 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1467 // qsearch() is the quiescence search function, which is called by the main
1468 // search function when the remaining depth is zero (or, to be more precise,
1469 // less than OnePly).
1471 template <NodeType PvNode>
1472 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1474 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1475 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1476 assert(PvNode || alpha == beta - 1);
1478 assert(pos.ply() > 0 && pos.ply() < PLY_MAX);
1479 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1484 Value staticValue, bestValue, value, futilityBase;
1485 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1486 const TTEntry* tte = NULL;
1488 int ply = pos.ply();
1489 Value oldAlpha = alpha;
1490 Value futilityValue = VALUE_INFINITE;
1492 TM.incrementNodeCounter(pos.thread());
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
1514 staticValue = -VALUE_INFINITE;
1515 else if (tte && tte->static_value() != VALUE_NONE)
1517 staticValue = tte->static_value();
1518 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1521 staticValue = evaluate(pos, ei);
1525 ss->eval = staticValue;
1526 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1529 // Initialize "stand pat score", and return it immediately if it is
1531 bestValue = staticValue;
1533 if (bestValue >= beta)
1535 // Store the score to avoid a future costly evaluation() call
1536 if (!isCheck && !tte)
1537 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()]);
1542 if (PvNode && bestValue > alpha)
1545 // If we are near beta then try to get a cutoff pushing checks a bit further
1546 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1548 // Initialize a MovePicker object for the current position, and prepare
1549 // to search the moves. Because the depth is <= 0 here, only captures,
1550 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1551 // and we are near beta) will be generated.
1552 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1554 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1555 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
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);
1565 // Update current move
1567 ss->currentMove = move;
1575 && !move_is_promotion(move)
1576 && !pos.move_is_passed_pawn_push(move))
1578 // Can only decrease from previous move because of
1579 // MVV ordering so we don't need to recheck.
1580 if (futilityValue < alpha)
1583 futilityValue = futilityBase
1584 + pos.endgame_value_of_piece_on(move_to(move))
1585 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1587 if (futilityValue < alpha)
1589 if (futilityValue > bestValue)
1590 bestValue = futilityValue;
1595 // Detect blocking evasions that are candidate to be pruned
1596 evasionPrunable = isCheck
1597 && bestValue > value_mated_in(PLY_MAX)
1598 && !pos.move_is_capture(move)
1599 && pos.type_of_piece_on(move_from(move)) != KING
1600 && !pos.can_castle(pos.side_to_move());
1602 // Don't search moves with negative SEE values
1604 && (!isCheck || evasionPrunable)
1606 && !move_is_promotion(move)
1607 && pos.see_sign(move) < 0)
1610 // Make and search the move
1611 pos.do_move(move, st, ci, moveIsCheck);
1612 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly);
1613 pos.undo_move(move);
1615 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1618 if (value > bestValue)
1629 // All legal moves have been searched. A special case: If we're in check
1630 // and no legal moves were found, it is checkmate.
1631 if (!moveCount && isCheck) // Mate!
1632 return value_mated_in(ply);
1634 // Update transposition table
1635 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1636 if (bestValue <= oldAlpha)
1638 // If bestValue isn't changed it means it is still the static evaluation
1639 // of the node, so keep this info to avoid a future evaluation() call.
1640 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1642 else if (bestValue >= beta)
1645 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1647 // Update killers only for good checking moves
1648 if (!pos.move_is_capture_or_promotion(move))
1649 update_killers(move, ss);
1652 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss->pv[ply], ss->eval, ei.kingDanger[pos.side_to_move()]);
1654 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1660 // sp_search() is used to search from a split point. This function is called
1661 // by each thread working at the split point. It is similar to the normal
1662 // search() function, but simpler. Because we have already probed the hash
1663 // table, done a null move search, and searched the first move before
1664 // splitting, we don't have to repeat all this work in sp_search(). We
1665 // also don't need to store anything to the hash table here: This is taken
1666 // care of after we return from the split point.
1668 template <NodeType PvNode>
1669 void sp_search(SplitPoint* sp, int threadID) {
1671 assert(threadID >= 0 && threadID < TM.active_threads());
1672 assert(TM.active_threads() > 1);
1676 Depth ext, newDepth;
1678 Value futilityValueScaled; // NonPV specific
1679 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1681 value = -VALUE_INFINITE;
1683 Position pos(*sp->pos, threadID);
1685 int ply = pos.ply();
1686 SearchStack* ss = sp->sstack[threadID] + 1;
1687 isCheck = pos.is_check();
1689 // Step 10. Loop through moves
1690 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1691 lock_grab(&(sp->lock));
1693 while ( sp->bestValue < sp->beta
1694 && (move = sp->mp->get_next_move()) != MOVE_NONE
1695 && !TM.thread_should_stop(threadID))
1697 moveCount = ++sp->moveCount;
1698 lock_release(&(sp->lock));
1700 assert(move_is_ok(move));
1702 moveIsCheck = pos.move_is_check(move, ci);
1703 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1705 // Step 11. Decide the new search depth
1706 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1707 newDepth = sp->depth - OnePly + ext;
1709 // Update current move
1710 ss->currentMove = move;
1712 // Step 12. Futility pruning (is omitted in PV nodes)
1714 && !captureOrPromotion
1717 && !move_is_castle(move))
1719 // Move count based pruning
1720 if ( moveCount >= futility_move_count(sp->depth)
1721 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1722 && sp->bestValue > value_mated_in(PLY_MAX))
1724 lock_grab(&(sp->lock));
1728 // Value based pruning
1729 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1730 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1731 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1733 if (futilityValueScaled < sp->beta)
1735 lock_grab(&(sp->lock));
1737 if (futilityValueScaled > sp->bestValue)
1738 sp->bestValue = futilityValueScaled;
1743 // Step 13. Make the move
1744 pos.do_move(move, st, ci, moveIsCheck);
1746 // Step 14. Reduced search
1747 // If the move fails high will be re-searched at full depth.
1748 bool doFullDepthSearch = true;
1750 if ( !captureOrPromotion
1752 && !move_is_castle(move)
1753 && !move_is_killer(move, ss))
1755 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1758 Value localAlpha = sp->alpha;
1759 Depth d = newDepth - ss->reduction;
1760 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0))
1761 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d);
1762 doFullDepthSearch = (value > localAlpha);
1765 // The move failed high, but if reduction is very big we could
1766 // face a false positive, retry with a less aggressive reduction,
1767 // if the move fails high again then go with full depth search.
1768 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1770 assert(newDepth - OnePly >= OnePly);
1772 ss->reduction = OnePly;
1773 Value localAlpha = sp->alpha;
1774 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction);
1775 doFullDepthSearch = (value > localAlpha);
1777 ss->reduction = Depth(0); // Restore original reduction
1780 // Step 15. Full depth search
1781 if (doFullDepthSearch)
1783 Value localAlpha = sp->alpha;
1784 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0))
1785 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth);
1787 // Step extra. pv search (only in PV nodes)
1788 // Search only for possible new PV nodes, if instead value >= beta then
1789 // parent node fails low with value <= alpha and tries another move.
1790 if (PvNode && value > localAlpha && value < sp->beta)
1791 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0))
1792 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth);
1795 // Step 16. Undo move
1796 pos.undo_move(move);
1798 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1800 // Step 17. Check for new best move
1801 lock_grab(&(sp->lock));
1803 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1805 sp->bestValue = value;
1807 if (sp->bestValue > sp->alpha)
1809 if (!PvNode || value >= sp->beta)
1810 sp->stopRequest = true;
1812 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1815 sp_update_pv(sp->parentSstack, ss, ply);
1820 /* Here we have the lock still grabbed */
1822 sp->slaves[threadID] = 0;
1824 lock_release(&(sp->lock));
1827 // update_pv() is called whenever a search returns a value > alpha.
1828 // It updates the PV in the SearchStack object corresponding to the
1831 void update_pv(SearchStack* ss, int ply) {
1833 assert(ply >= 0 && ply < PLY_MAX);
1837 ss->pv[ply] = ss->currentMove;
1839 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1840 ss->pv[p] = (ss+1)->pv[p];
1842 ss->pv[p] = MOVE_NONE;
1846 // sp_update_pv() is a variant of update_pv for use at split points. The
1847 // difference between the two functions is that sp_update_pv also updates
1848 // the PV at the parent node.
1850 void sp_update_pv(SearchStack* pss, SearchStack* ss, int ply) {
1852 assert(ply >= 0 && ply < PLY_MAX);
1856 ss->pv[ply] = pss->pv[ply] = ss->currentMove;
1858 for (p = ply + 1; (ss+1)->pv[p] != MOVE_NONE; p++)
1859 ss->pv[p] = pss->pv[p] = (ss+1)->pv[p];
1861 ss->pv[p] = pss->pv[p] = MOVE_NONE;
1865 // connected_moves() tests whether two moves are 'connected' in the sense
1866 // that the first move somehow made the second move possible (for instance
1867 // if the moving piece is the same in both moves). The first move is assumed
1868 // to be the move that was made to reach the current position, while the
1869 // second move is assumed to be a move from the current position.
1871 bool connected_moves(const Position& pos, Move m1, Move m2) {
1873 Square f1, t1, f2, t2;
1876 assert(move_is_ok(m1));
1877 assert(move_is_ok(m2));
1879 if (m2 == MOVE_NONE)
1882 // Case 1: The moving piece is the same in both moves
1888 // Case 2: The destination square for m2 was vacated by m1
1894 // Case 3: Moving through the vacated square
1895 if ( piece_is_slider(pos.piece_on(f2))
1896 && bit_is_set(squares_between(f2, t2), f1))
1899 // Case 4: The destination square for m2 is defended by the moving piece in m1
1900 p = pos.piece_on(t1);
1901 if (bit_is_set(pos.attacks_from(p, t1), t2))
1904 // Case 5: Discovered check, checking piece is the piece moved in m1
1905 if ( piece_is_slider(p)
1906 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1907 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1909 // discovered_check_candidates() works also if the Position's side to
1910 // move is the opposite of the checking piece.
1911 Color them = opposite_color(pos.side_to_move());
1912 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1914 if (bit_is_set(dcCandidates, f2))
1921 // value_is_mate() checks if the given value is a mate one
1922 // eventually compensated for the ply.
1924 bool value_is_mate(Value value) {
1926 assert(abs(value) <= VALUE_INFINITE);
1928 return value <= value_mated_in(PLY_MAX)
1929 || value >= value_mate_in(PLY_MAX);
1933 // move_is_killer() checks if the given move is among the
1934 // killer moves of that ply.
1936 bool move_is_killer(Move m, SearchStack* ss) {
1938 const Move* k = ss->killers;
1939 for (int i = 0; i < KILLER_MAX; i++, k++)
1947 // extension() decides whether a move should be searched with normal depth,
1948 // or with extended depth. Certain classes of moves (checking moves, in
1949 // particular) are searched with bigger depth than ordinary moves and in
1950 // any case are marked as 'dangerous'. Note that also if a move is not
1951 // extended, as example because the corresponding UCI option is set to zero,
1952 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1953 template <NodeType PvNode>
1954 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1955 bool singleEvasion, bool mateThreat, bool* dangerous) {
1957 assert(m != MOVE_NONE);
1959 Depth result = Depth(0);
1960 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1965 result += CheckExtension[PvNode];
1968 result += SingleEvasionExtension[PvNode];
1971 result += MateThreatExtension[PvNode];
1974 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1976 Color c = pos.side_to_move();
1977 if (relative_rank(c, move_to(m)) == RANK_7)
1979 result += PawnPushTo7thExtension[PvNode];
1982 if (pos.pawn_is_passed(c, move_to(m)))
1984 result += PassedPawnExtension[PvNode];
1989 if ( captureOrPromotion
1990 && pos.type_of_piece_on(move_to(m)) != PAWN
1991 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1992 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1993 && !move_is_promotion(m)
1996 result += PawnEndgameExtension[PvNode];
2001 && captureOrPromotion
2002 && pos.type_of_piece_on(move_to(m)) != PAWN
2003 && pos.see_sign(m) >= 0)
2009 return Min(result, OnePly);
2013 // connected_threat() tests whether it is safe to forward prune a move or if
2014 // is somehow coonected to the threat move returned by null search.
2016 bool connected_threat(const Position& pos, Move m, Move threat) {
2018 assert(move_is_ok(m));
2019 assert(threat && move_is_ok(threat));
2020 assert(!pos.move_is_check(m));
2021 assert(!pos.move_is_capture_or_promotion(m));
2022 assert(!pos.move_is_passed_pawn_push(m));
2024 Square mfrom, mto, tfrom, tto;
2026 mfrom = move_from(m);
2028 tfrom = move_from(threat);
2029 tto = move_to(threat);
2031 // Case 1: Don't prune moves which move the threatened piece
2035 // Case 2: If the threatened piece has value less than or equal to the
2036 // value of the threatening piece, don't prune move which defend it.
2037 if ( pos.move_is_capture(threat)
2038 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2039 || pos.type_of_piece_on(tfrom) == KING)
2040 && pos.move_attacks_square(m, tto))
2043 // Case 3: If the moving piece in the threatened move is a slider, don't
2044 // prune safe moves which block its ray.
2045 if ( piece_is_slider(pos.piece_on(tfrom))
2046 && bit_is_set(squares_between(tfrom, tto), mto)
2047 && pos.see_sign(m) >= 0)
2054 // ok_to_use_TT() returns true if a transposition table score
2055 // can be used at a given point in search.
2057 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2059 Value v = value_from_tt(tte->value(), ply);
2061 return ( tte->depth() >= depth
2062 || v >= Max(value_mate_in(PLY_MAX), beta)
2063 || v < Min(value_mated_in(PLY_MAX), beta))
2065 && ( (is_lower_bound(tte->type()) && v >= beta)
2066 || (is_upper_bound(tte->type()) && v < beta));
2070 // refine_eval() returns the transposition table score if
2071 // possible otherwise falls back on static position evaluation.
2073 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2078 Value v = value_from_tt(tte->value(), ply);
2080 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2081 || (is_upper_bound(tte->type()) && v < defaultEval))
2088 // update_history() registers a good move that produced a beta-cutoff
2089 // in history and marks as failures all the other moves of that ply.
2091 void update_history(const Position& pos, Move move, Depth depth,
2092 Move movesSearched[], int moveCount) {
2096 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2098 for (int i = 0; i < moveCount - 1; i++)
2100 m = movesSearched[i];
2104 if (!pos.move_is_capture_or_promotion(m))
2105 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2110 // update_killers() add a good move that produced a beta-cutoff
2111 // among the killer moves of that ply.
2113 void update_killers(Move m, SearchStack* ss) {
2115 if (m == ss->killers[0])
2118 for (int i = KILLER_MAX - 1; i > 0; i--)
2119 ss->killers[i] = ss->killers[i - 1];
2125 // update_gains() updates the gains table of a non-capture move given
2126 // the static position evaluation before and after the move.
2128 void update_gains(const Position& pos, Move m, Value before, Value after) {
2131 && before != VALUE_NONE
2132 && after != VALUE_NONE
2133 && pos.captured_piece() == NO_PIECE_TYPE
2134 && !move_is_castle(m)
2135 && !move_is_promotion(m))
2136 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2140 // current_search_time() returns the number of milliseconds which have passed
2141 // since the beginning of the current search.
2143 int current_search_time() {
2145 return get_system_time() - SearchStartTime;
2149 // nps() computes the current nodes/second count.
2153 int t = current_search_time();
2154 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2158 // poll() performs two different functions: It polls for user input, and it
2159 // looks at the time consumed so far and decides if it's time to abort the
2164 static int lastInfoTime;
2165 int t = current_search_time();
2170 // We are line oriented, don't read single chars
2171 std::string command;
2173 if (!std::getline(std::cin, command))
2176 if (command == "quit")
2179 PonderSearch = false;
2183 else if (command == "stop")
2186 PonderSearch = false;
2188 else if (command == "ponderhit")
2192 // Print search information
2196 else if (lastInfoTime > t)
2197 // HACK: Must be a new search where we searched less than
2198 // NodesBetweenPolls nodes during the first second of search.
2201 else if (t - lastInfoTime >= 1000)
2208 if (dbg_show_hit_rate)
2209 dbg_print_hit_rate();
2211 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2212 << " time " << t << " hashfull " << TT.full() << endl;
2215 // Should we stop the search?
2219 bool stillAtFirstMove = FirstRootMove
2220 && !AspirationFailLow
2221 && t > MaxSearchTime + ExtraSearchTime;
2223 bool noMoreTime = t > AbsoluteMaxSearchTime
2224 || stillAtFirstMove;
2226 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2227 || (ExactMaxTime && t >= ExactMaxTime)
2228 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2233 // ponderhit() is called when the program is pondering (i.e. thinking while
2234 // it's the opponent's turn to move) in order to let the engine know that
2235 // it correctly predicted the opponent's move.
2239 int t = current_search_time();
2240 PonderSearch = false;
2242 bool stillAtFirstMove = FirstRootMove
2243 && !AspirationFailLow
2244 && t > MaxSearchTime + ExtraSearchTime;
2246 bool noMoreTime = t > AbsoluteMaxSearchTime
2247 || stillAtFirstMove;
2249 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2254 // init_ss_array() does a fast reset of the first entries of a SearchStack
2255 // array and of all the excludedMove and skipNullMove entries.
2257 void init_ss_array(SearchStack* ss, int size) {
2259 for (int i = 0; i < size; i++, ss++)
2261 ss->excludedMove = MOVE_NONE;
2262 ss->skipNullMove = false;
2273 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2274 // while the program is pondering. The point is to work around a wrinkle in
2275 // the UCI protocol: When pondering, the engine is not allowed to give a
2276 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2277 // We simply wait here until one of these commands is sent, and return,
2278 // after which the bestmove and pondermove will be printed (in id_loop()).
2280 void wait_for_stop_or_ponderhit() {
2282 std::string command;
2286 if (!std::getline(std::cin, command))
2289 if (command == "quit")
2294 else if (command == "ponderhit" || command == "stop")
2300 // print_pv_info() prints to standard output and eventually to log file information on
2301 // the current PV line. It is called at each iteration or after a new pv is found.
2303 void print_pv_info(const Position& pos, SearchStack* ss, Value alpha, Value beta, Value value) {
2305 cout << "info depth " << Iteration
2306 << " score " << value_to_string(value)
2307 << ((value >= beta) ? " lowerbound" :
2308 ((value <= alpha)? " upperbound" : ""))
2309 << " time " << current_search_time()
2310 << " nodes " << TM.nodes_searched()
2314 for (int j = 0; ss->pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2315 cout << ss->pv[j] << " ";
2321 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2322 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2324 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2325 TM.nodes_searched(), value, type, ss->pv) << endl;
2330 // init_thread() is the function which is called when a new thread is
2331 // launched. It simply calls the idle_loop() function with the supplied
2332 // threadID. There are two versions of this function; one for POSIX
2333 // threads and one for Windows threads.
2335 #if !defined(_MSC_VER)
2337 void* init_thread(void *threadID) {
2339 TM.idle_loop(*(int*)threadID, NULL);
2345 DWORD WINAPI init_thread(LPVOID threadID) {
2347 TM.idle_loop(*(int*)threadID, NULL);
2354 /// The ThreadsManager class
2356 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2357 // get_beta_counters() are getters/setters for the per thread
2358 // counters used to sort the moves at root.
2360 void ThreadsManager::resetNodeCounters() {
2362 for (int i = 0; i < MAX_THREADS; i++)
2363 threads[i].nodes = 0ULL;
2366 void ThreadsManager::resetBetaCounters() {
2368 for (int i = 0; i < MAX_THREADS; i++)
2369 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2372 int64_t ThreadsManager::nodes_searched() const {
2374 int64_t result = 0ULL;
2375 for (int i = 0; i < ActiveThreads; i++)
2376 result += threads[i].nodes;
2381 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2384 for (int i = 0; i < MAX_THREADS; i++)
2386 our += threads[i].betaCutOffs[us];
2387 their += threads[i].betaCutOffs[opposite_color(us)];
2392 // idle_loop() is where the threads are parked when they have no work to do.
2393 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2394 // object for which the current thread is the master.
2396 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2398 assert(threadID >= 0 && threadID < MAX_THREADS);
2402 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2403 // master should exit as last one.
2404 if (AllThreadsShouldExit)
2407 threads[threadID].state = THREAD_TERMINATED;
2411 // If we are not thinking, wait for a condition to be signaled
2412 // instead of wasting CPU time polling for work.
2413 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2416 assert(threadID != 0);
2417 threads[threadID].state = THREAD_SLEEPING;
2419 #if !defined(_MSC_VER)
2420 lock_grab(&WaitLock);
2421 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2422 pthread_cond_wait(&WaitCond, &WaitLock);
2423 lock_release(&WaitLock);
2425 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2429 // If thread has just woken up, mark it as available
2430 if (threads[threadID].state == THREAD_SLEEPING)
2431 threads[threadID].state = THREAD_AVAILABLE;
2433 // If this thread has been assigned work, launch a search
2434 if (threads[threadID].state == THREAD_WORKISWAITING)
2436 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2438 threads[threadID].state = THREAD_SEARCHING;
2440 if (threads[threadID].splitPoint->pvNode)
2441 sp_search<PV>(threads[threadID].splitPoint, threadID);
2443 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2445 assert(threads[threadID].state == THREAD_SEARCHING);
2447 threads[threadID].state = THREAD_AVAILABLE;
2450 // If this thread is the master of a split point and all slaves have
2451 // finished their work at this split point, return from the idle loop.
2453 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2455 if (i == ActiveThreads)
2457 // Because sp->slaves[] is reset under lock protection,
2458 // be sure sp->lock has been released before to return.
2459 lock_grab(&(sp->lock));
2460 lock_release(&(sp->lock));
2462 assert(threads[threadID].state == THREAD_AVAILABLE);
2464 threads[threadID].state = THREAD_SEARCHING;
2471 // init_threads() is called during startup. It launches all helper threads,
2472 // and initializes the split point stack and the global locks and condition
2475 void ThreadsManager::init_threads() {
2480 #if !defined(_MSC_VER)
2481 pthread_t pthread[1];
2484 // Initialize global locks
2485 lock_init(&MPLock, NULL);
2486 lock_init(&WaitLock, NULL);
2488 #if !defined(_MSC_VER)
2489 pthread_cond_init(&WaitCond, NULL);
2491 for (i = 0; i < MAX_THREADS; i++)
2492 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2495 // Initialize SplitPointStack locks
2496 for (i = 0; i < MAX_THREADS; i++)
2497 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2498 lock_init(&(SplitPointStack[i][j].lock), NULL);
2500 // Will be set just before program exits to properly end the threads
2501 AllThreadsShouldExit = false;
2503 // Threads will be put to sleep as soon as created
2504 AllThreadsShouldSleep = true;
2506 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2508 threads[0].state = THREAD_SEARCHING;
2509 for (i = 1; i < MAX_THREADS; i++)
2510 threads[i].state = THREAD_AVAILABLE;
2512 // Launch the helper threads
2513 for (i = 1; i < MAX_THREADS; i++)
2516 #if !defined(_MSC_VER)
2517 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2519 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2524 cout << "Failed to create thread number " << i << endl;
2525 Application::exit_with_failure();
2528 // Wait until the thread has finished launching and is gone to sleep
2529 while (threads[i].state != THREAD_SLEEPING) {}
2534 // exit_threads() is called when the program exits. It makes all the
2535 // helper threads exit cleanly.
2537 void ThreadsManager::exit_threads() {
2539 ActiveThreads = MAX_THREADS; // HACK
2540 AllThreadsShouldSleep = true; // HACK
2541 wake_sleeping_threads();
2543 // This makes the threads to exit idle_loop()
2544 AllThreadsShouldExit = true;
2546 // Wait for thread termination
2547 for (int i = 1; i < MAX_THREADS; i++)
2548 while (threads[i].state != THREAD_TERMINATED) {}
2550 // Now we can safely destroy the locks
2551 for (int i = 0; i < MAX_THREADS; i++)
2552 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2553 lock_destroy(&(SplitPointStack[i][j].lock));
2555 lock_destroy(&WaitLock);
2556 lock_destroy(&MPLock);
2560 // thread_should_stop() checks whether the thread should stop its search.
2561 // This can happen if a beta cutoff has occurred in the thread's currently
2562 // active split point, or in some ancestor of the current split point.
2564 bool ThreadsManager::thread_should_stop(int threadID) const {
2566 assert(threadID >= 0 && threadID < ActiveThreads);
2570 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2575 // thread_is_available() checks whether the thread with threadID "slave" is
2576 // available to help the thread with threadID "master" at a split point. An
2577 // obvious requirement is that "slave" must be idle. With more than two
2578 // threads, this is not by itself sufficient: If "slave" is the master of
2579 // some active split point, it is only available as a slave to the other
2580 // threads which are busy searching the split point at the top of "slave"'s
2581 // split point stack (the "helpful master concept" in YBWC terminology).
2583 bool ThreadsManager::thread_is_available(int slave, int master) const {
2585 assert(slave >= 0 && slave < ActiveThreads);
2586 assert(master >= 0 && master < ActiveThreads);
2587 assert(ActiveThreads > 1);
2589 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2592 // Make a local copy to be sure doesn't change under our feet
2593 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2595 if (localActiveSplitPoints == 0)
2596 // No active split points means that the thread is available as
2597 // a slave for any other thread.
2600 if (ActiveThreads == 2)
2603 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2604 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2605 // could have been set to 0 by another thread leading to an out of bound access.
2606 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2613 // available_thread_exists() tries to find an idle thread which is available as
2614 // a slave for the thread with threadID "master".
2616 bool ThreadsManager::available_thread_exists(int master) const {
2618 assert(master >= 0 && master < ActiveThreads);
2619 assert(ActiveThreads > 1);
2621 for (int i = 0; i < ActiveThreads; i++)
2622 if (thread_is_available(i, master))
2629 // split() does the actual work of distributing the work at a node between
2630 // several available threads. If it does not succeed in splitting the
2631 // node (because no idle threads are available, or because we have no unused
2632 // split point objects), the function immediately returns. If splitting is
2633 // possible, a SplitPoint object is initialized with all the data that must be
2634 // copied to the helper threads and we tell our helper threads that they have
2635 // been assigned work. This will cause them to instantly leave their idle loops
2636 // and call sp_search(). When all threads have returned from sp_search() then
2639 template <bool Fake>
2640 void ThreadsManager::split(const Position& p, SearchStack* ss, Value* alpha, const Value beta,
2641 Value* bestValue, Depth depth, bool mateThreat, int* moveCount,
2642 MovePicker* mp, bool pvNode) {
2644 assert(*bestValue >= -VALUE_INFINITE);
2645 assert(*bestValue <= *alpha);
2646 assert(*alpha < beta);
2647 assert(beta <= VALUE_INFINITE);
2648 assert(depth > Depth(0));
2649 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2650 assert(ActiveThreads > 1);
2652 int master = p.thread();
2656 // If no other thread is available to help us, or if we have too many
2657 // active split points, don't split.
2658 if ( !available_thread_exists(master)
2659 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2661 lock_release(&MPLock);
2665 // Pick the next available split point object from the split point stack
2666 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2668 // Initialize the split point object
2669 splitPoint->parent = threads[master].splitPoint;
2670 splitPoint->stopRequest = false;
2671 splitPoint->depth = depth;
2672 splitPoint->mateThreat = mateThreat;
2673 splitPoint->alpha = *alpha;
2674 splitPoint->beta = beta;
2675 splitPoint->pvNode = pvNode;
2676 splitPoint->bestValue = *bestValue;
2677 splitPoint->mp = mp;
2678 splitPoint->moveCount = *moveCount;
2679 splitPoint->pos = &p;
2680 splitPoint->parentSstack = ss;
2681 for (int i = 0; i < ActiveThreads; i++)
2682 splitPoint->slaves[i] = 0;
2684 threads[master].splitPoint = splitPoint;
2685 threads[master].activeSplitPoints++;
2687 // If we are here it means we are not available
2688 assert(threads[master].state != THREAD_AVAILABLE);
2690 int workersCnt = 1; // At least the master is included
2692 // Allocate available threads setting state to THREAD_BOOKED
2693 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2694 if (thread_is_available(i, master))
2696 threads[i].state = THREAD_BOOKED;
2697 threads[i].splitPoint = splitPoint;
2698 splitPoint->slaves[i] = 1;
2702 assert(Fake || workersCnt > 1);
2704 // We can release the lock because slave threads are already booked and master is not available
2705 lock_release(&MPLock);
2707 // Tell the threads that they have work to do. This will make them leave
2708 // their idle loop. But before copy search stack tail for each thread.
2709 for (int i = 0; i < ActiveThreads; i++)
2710 if (i == master || splitPoint->slaves[i])
2712 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2714 assert(i == master || threads[i].state == THREAD_BOOKED);
2716 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2719 // Everything is set up. The master thread enters the idle loop, from
2720 // which it will instantly launch a search, because its state is
2721 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2722 // idle loop, which means that the main thread will return from the idle
2723 // loop when all threads have finished their work at this split point.
2724 idle_loop(master, splitPoint);
2726 // We have returned from the idle loop, which means that all threads are
2727 // finished. Update alpha and bestValue, and return.
2730 *alpha = splitPoint->alpha;
2731 *bestValue = splitPoint->bestValue;
2732 threads[master].activeSplitPoints--;
2733 threads[master].splitPoint = splitPoint->parent;
2735 lock_release(&MPLock);
2739 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2740 // to start a new search from the root.
2742 void ThreadsManager::wake_sleeping_threads() {
2744 assert(AllThreadsShouldSleep);
2745 assert(ActiveThreads > 0);
2747 AllThreadsShouldSleep = false;
2749 if (ActiveThreads == 1)
2752 #if !defined(_MSC_VER)
2753 pthread_mutex_lock(&WaitLock);
2754 pthread_cond_broadcast(&WaitCond);
2755 pthread_mutex_unlock(&WaitLock);
2757 for (int i = 1; i < MAX_THREADS; i++)
2758 SetEvent(SitIdleEvent[i]);
2764 // put_threads_to_sleep() makes all the threads go to sleep just before
2765 // to leave think(), at the end of the search. Threads should have already
2766 // finished the job and should be idle.
2768 void ThreadsManager::put_threads_to_sleep() {
2770 assert(!AllThreadsShouldSleep);
2772 // This makes the threads to go to sleep
2773 AllThreadsShouldSleep = true;
2776 /// The RootMoveList class
2778 // RootMoveList c'tor
2780 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2782 SearchStack ss[PLY_MAX_PLUS_2];
2783 MoveStack mlist[MaxRootMoves];
2785 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2787 // Generate all legal moves
2788 MoveStack* last = generate_moves(pos, mlist);
2790 // Add each move to the moves[] array
2791 for (MoveStack* cur = mlist; cur != last; cur++)
2793 bool includeMove = includeAllMoves;
2795 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2796 includeMove = (searchMoves[k] == cur->move);
2801 // Find a quick score for the move
2802 init_ss_array(ss, PLY_MAX_PLUS_2);
2803 pos.do_move(cur->move, st);
2804 moves[count].move = cur->move;
2805 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0));
2806 moves[count].pv[0] = cur->move;
2807 moves[count].pv[1] = MOVE_NONE;
2808 pos.undo_move(cur->move);
2815 // RootMoveList simple methods definitions
2817 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2819 moves[moveNum].nodes = nodes;
2820 moves[moveNum].cumulativeNodes += nodes;
2823 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2825 moves[moveNum].ourBeta = our;
2826 moves[moveNum].theirBeta = their;
2829 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2833 for (j = 0; pv[j] != MOVE_NONE; j++)
2834 moves[moveNum].pv[j] = pv[j];
2836 moves[moveNum].pv[j] = MOVE_NONE;
2840 // RootMoveList::sort() sorts the root move list at the beginning of a new
2843 void RootMoveList::sort() {
2845 sort_multipv(count - 1); // Sort all items
2849 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2850 // list by their scores and depths. It is used to order the different PVs
2851 // correctly in MultiPV mode.
2853 void RootMoveList::sort_multipv(int n) {
2857 for (i = 1; i <= n; i++)
2859 RootMove rm = moves[i];
2860 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2861 moves[j] = moves[j - 1];