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, Move* pv, 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, Move* ss, Value alpha, Value beta, Value value);
319 #if !defined(_MSC_VER)
320 void *init_thread(void *threadID);
322 DWORD WINAPI init_thread(LPVOID threadID);
332 /// init_threads(), exit_threads() and nodes_searched() are helpers to
333 /// give accessibility to some TM methods from outside of current file.
335 void init_threads() { TM.init_threads(); }
336 void exit_threads() { TM.exit_threads(); }
337 int64_t nodes_searched() { return TM.nodes_searched(); }
340 /// init_search() is called during startup. It initializes various lookup tables
344 int d; // depth (OnePly == 2)
345 int hd; // half depth (OnePly == 1)
348 // Init reductions array
349 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
351 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
352 double nonPVRed = log(double(hd)) * log(double(mc)) / 1.5;
353 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
354 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
357 // Init futility margins array
358 for (d = 0; d < 16; d++) for (mc = 0; mc < 64; mc++)
359 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
361 // Init futility move count array
362 for (d = 0; d < 32; d++)
363 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
367 // SearchStack::init() initializes a search stack entry.
368 // Called at the beginning of search() when starting to examine a new node.
369 void SearchStack::init() {
371 currentMove = threatMove = bestMove = MOVE_NONE;
372 reduction = Depth(0);
376 // SearchStack::initKillers() initializes killers for a search stack entry
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 pv[PLY_MAX_PLUS_2];
609 Move EasyMove = MOVE_NONE;
610 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
612 // Moves to search are verified, copied, scored and sorted
613 RootMoveList rml(p, searchMoves);
615 // Handle special case of searching on a mate/stale position
616 if (rml.move_count() == 0)
619 wait_for_stop_or_ponderhit();
621 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
624 // Print RootMoveList startup scoring to the standard output,
625 // so to output information also for iteration 1.
626 cout << "info depth " << 1
627 << "\ninfo depth " << 1
628 << " score " << value_to_string(rml.get_move_score(0))
629 << " time " << current_search_time()
630 << " nodes " << TM.nodes_searched()
632 << " pv " << rml.get_move(0) << "\n";
637 init_ss_array(ss, PLY_MAX_PLUS_2);
638 pv[0] = pv[1] = MOVE_NONE;
639 ValueByIteration[1] = rml.get_move_score(0);
642 // Is one move significantly better than others after initial scoring ?
643 if ( rml.move_count() == 1
644 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
645 EasyMove = rml.get_move(0);
647 // Iterative deepening loop
648 while (Iteration < PLY_MAX)
650 // Initialize iteration
652 BestMoveChangesByIteration[Iteration] = 0;
654 cout << "info depth " << Iteration << endl;
656 // Calculate dynamic aspiration window based on previous iterations
657 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
659 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
660 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
662 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
663 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
665 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
666 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
669 // Search to the current depth, rml is updated and sorted, alpha and beta could change
670 value = root_search(p, ss, pv, rml, &alpha, &beta);
672 // Write PV to transposition table, in case the relevant entries have
673 // been overwritten during the search.
677 break; // Value cannot be trusted. Break out immediately!
679 //Save info about search result
680 ValueByIteration[Iteration] = value;
682 // Drop the easy move if differs from the new best move
683 if (pv[0] != EasyMove)
684 EasyMove = MOVE_NONE;
686 if (UseTimeManagement)
689 bool stopSearch = false;
691 // Stop search early if there is only a single legal move,
692 // we search up to Iteration 6 anyway to get a proper score.
693 if (Iteration >= 6 && rml.move_count() == 1)
696 // Stop search early when the last two iterations returned a mate score
698 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
699 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
702 // Stop search early if one move seems to be much better than the others
703 int64_t nodes = TM.nodes_searched();
706 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
707 && current_search_time() > MaxSearchTime / 16)
708 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
709 && current_search_time() > MaxSearchTime / 32)))
712 // Add some extra time if the best move has changed during the last two iterations
713 if (Iteration > 5 && Iteration <= 50)
714 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
715 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
717 // Stop search if most of MaxSearchTime is consumed at the end of the
718 // iteration. We probably don't have enough time to search the first
719 // move at the next iteration anyway.
720 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
726 StopOnPonderhit = true;
732 if (MaxDepth && Iteration >= MaxDepth)
736 // If we are pondering or in infinite search, we shouldn't print the
737 // best move before we are told to do so.
738 if (!AbortSearch && (PonderSearch || InfiniteSearch))
739 wait_for_stop_or_ponderhit();
741 // Print final search statistics
742 cout << "info nodes " << TM.nodes_searched()
744 << " time " << current_search_time()
745 << " hashfull " << TT.full() << endl;
747 // Print the best move and the ponder move to the standard output
748 if (pv[0] == MOVE_NONE)
750 pv[0] = rml.get_move(0);
754 assert(pv[0] != MOVE_NONE);
756 cout << "bestmove " << pv[0];
758 if (pv[1] != MOVE_NONE)
759 cout << " ponder " << pv[1];
766 dbg_print_mean(LogFile);
768 if (dbg_show_hit_rate)
769 dbg_print_hit_rate(LogFile);
771 LogFile << "\nNodes: " << TM.nodes_searched()
772 << "\nNodes/second: " << nps()
773 << "\nBest move: " << move_to_san(p, pv[0]);
776 p.do_move(pv[0], st);
777 LogFile << "\nPonder move: "
778 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
781 return rml.get_move_score(0);
785 // root_search() is the function which searches the root node. It is
786 // similar to search_pv except that it uses a different move ordering
787 // scheme, prints some information to the standard output and handles
788 // the fail low/high loops.
790 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
797 Depth depth, ext, newDepth;
798 Value value, alpha, beta;
799 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
800 int researchCountFH, researchCountFL;
802 researchCountFH = researchCountFL = 0;
805 isCheck = pos.is_check();
807 // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
808 // Step 2. Check for aborted search (omitted at root)
809 // Step 3. Mate distance pruning (omitted at root)
810 // Step 4. Transposition table lookup (omitted at root)
812 // Step 5. Evaluate the position statically
813 // At root we do this only to get reference value for child nodes
815 ss->eval = evaluate(pos, ei);
817 // Step 6. Razoring (omitted at root)
818 // Step 7. Static null move pruning (omitted at root)
819 // Step 8. Null move search with verification search (omitted at root)
820 // Step 9. Internal iterative deepening (omitted at root)
822 // Step extra. Fail low loop
823 // We start with small aspiration window and in case of fail low, we research
824 // with bigger window until we are not failing low anymore.
827 // Sort the moves before to (re)search
830 // Step 10. Loop through all moves in the root move list
831 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
833 // This is used by time management
834 FirstRootMove = (i == 0);
836 // Save the current node count before the move is searched
837 nodes = TM.nodes_searched();
839 // Reset beta cut-off counters
840 TM.resetBetaCounters();
842 // Pick the next root move, and print the move and the move number to
843 // the standard output.
844 move = ss->currentMove = rml.get_move(i);
846 if (current_search_time() >= 1000)
847 cout << "info currmove " << move
848 << " currmovenumber " << i + 1 << endl;
850 moveIsCheck = pos.move_is_check(move);
851 captureOrPromotion = pos.move_is_capture_or_promotion(move);
853 // Step 11. Decide the new search depth
854 depth = (Iteration - 2) * OnePly + InitialDepth;
855 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
856 newDepth = depth + ext;
858 // Step 12. Futility pruning (omitted at root)
860 // Step extra. Fail high loop
861 // If move fails high, we research with bigger window until we are not failing
863 value = - VALUE_INFINITE;
867 // Step 13. Make the move
868 pos.do_move(move, st, ci, moveIsCheck);
870 // Step extra. pv search
871 // We do pv search for first moves (i < MultiPV)
872 // and for fail high research (value > alpha)
873 if (i < MultiPV || value > alpha)
875 // Aspiration window is disabled in multi-pv case
877 alpha = -VALUE_INFINITE;
879 // Full depth PV search, done on first move or after a fail high
880 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
884 // Step 14. Reduced search
885 // if the move fails high will be re-searched at full depth
886 bool doFullDepthSearch = true;
888 if ( depth >= 3 * OnePly
890 && !captureOrPromotion
891 && !move_is_castle(move))
893 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
896 assert(newDepth-ss->reduction >= OnePly);
898 // Reduced depth non-pv search using alpha as upperbound
899 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
900 doFullDepthSearch = (value > alpha);
903 // The move failed high, but if reduction is very big we could
904 // face a false positive, retry with a less aggressive reduction,
905 // if the move fails high again then go with full depth search.
906 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
908 assert(newDepth - OnePly >= OnePly);
910 ss->reduction = OnePly;
911 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
912 doFullDepthSearch = (value > alpha);
914 ss->reduction = Depth(0); // Restore original reduction
917 // Step 15. Full depth search
918 if (doFullDepthSearch)
920 // Full depth non-pv search using alpha as upperbound
921 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
923 // If we are above alpha then research at same depth but as PV
924 // to get a correct score or eventually a fail high above beta.
926 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
930 // Step 16. Undo move
933 // Can we exit fail high loop ?
934 if (AbortSearch || value < beta)
937 // We are failing high and going to do a research. It's important to update
938 // the score before research in case we run out of time while researching.
939 rml.set_move_score(i, value);
941 pv[0] = ss->bestMove;
942 TT.extract_pv(pos, pv, PLY_MAX);
943 rml.set_move_pv(i, pv);
945 // Print information to the standard output
946 print_pv_info(pos, pv, alpha, beta, value);
948 // Prepare for a research after a fail high, each time with a wider window
949 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
952 } // End of fail high loop
954 // Finished searching the move. If AbortSearch is true, the search
955 // was aborted because the user interrupted the search or because we
956 // ran out of time. In this case, the return value of the search cannot
957 // be trusted, and we break out of the loop without updating the best
962 // Remember beta-cutoff and searched nodes counts for this move. The
963 // info is used to sort the root moves for the next iteration.
965 TM.get_beta_counters(pos.side_to_move(), our, their);
966 rml.set_beta_counters(i, our, their);
967 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
969 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
970 assert(value < beta);
972 // Step 17. Check for new best move
973 if (value <= alpha && i >= MultiPV)
974 rml.set_move_score(i, -VALUE_INFINITE);
977 // PV move or new best move!
980 rml.set_move_score(i, value);
982 pv[0] = ss->bestMove;
983 TT.extract_pv(pos, pv, PLY_MAX);
984 rml.set_move_pv(i, pv);
988 // We record how often the best move has been changed in each
989 // iteration. This information is used for time managment: When
990 // the best move changes frequently, we allocate some more time.
992 BestMoveChangesByIteration[Iteration]++;
994 // Print information to the standard output
995 print_pv_info(pos, pv, alpha, beta, value);
997 // Raise alpha to setup proper non-pv search upper bound
1003 rml.sort_multipv(i);
1004 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1006 cout << "info multipv " << j + 1
1007 << " score " << value_to_string(rml.get_move_score(j))
1008 << " depth " << (j <= i ? Iteration : Iteration - 1)
1009 << " time " << current_search_time()
1010 << " nodes " << TM.nodes_searched()
1014 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1015 cout << rml.get_move_pv(j, k) << " ";
1019 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1021 } // PV move or new best move
1023 assert(alpha >= *alphaPtr);
1025 AspirationFailLow = (alpha == *alphaPtr);
1027 if (AspirationFailLow && StopOnPonderhit)
1028 StopOnPonderhit = false;
1031 // Can we exit fail low loop ?
1032 if (AbortSearch || !AspirationFailLow)
1035 // Prepare for a research after a fail low, each time with a wider window
1036 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1041 // Sort the moves before to return
1048 // search<>() is the main search function for both PV and non-PV nodes
1050 template <NodeType PvNode>
1051 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1053 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1054 assert(beta > alpha && beta <= VALUE_INFINITE);
1055 assert(PvNode || alpha == beta - 1);
1056 assert(ply > 0 && ply < PLY_MAX);
1057 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1059 Move movesSearched[256];
1064 Move ttMove, move, excludedMove;
1065 Depth ext, newDepth;
1066 Value bestValue, value, oldAlpha;
1067 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1068 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1069 bool mateThreat = false;
1071 int threadID = pos.thread();
1072 refinedValue = bestValue = value = -VALUE_INFINITE;
1075 // Step 1. Initialize node and poll. Polling can abort search
1076 TM.incrementNodeCounter(threadID);
1078 (ss+2)->initKillers();
1080 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
1086 // Step 2. Check for aborted search and immediate draw
1087 if (AbortSearch || TM.thread_should_stop(threadID))
1090 if (pos.is_draw() || ply >= PLY_MAX - 1)
1093 // Step 3. Mate distance pruning
1094 alpha = Max(value_mated_in(ply), alpha);
1095 beta = Min(value_mate_in(ply+1), beta);
1099 // Step 4. Transposition table lookup
1101 // We don't want the score of a partial search to overwrite a previous full search
1102 // TT value, so we use a different position key in case of an excluded move exists.
1103 excludedMove = ss->excludedMove;
1104 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1106 tte = TT.retrieve(posKey);
1107 ttMove = (tte ? tte->move() : MOVE_NONE);
1109 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1110 // This is to avoid problems in the following areas:
1112 // * Repetition draw detection
1113 // * Fifty move rule detection
1114 // * Searching for a mate
1115 // * Printing of full PV line
1117 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1119 // Refresh tte entry to avoid aging
1120 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1122 ss->currentMove = ttMove; // Can be MOVE_NONE
1123 return value_from_tt(tte->value(), ply);
1126 // Step 5. Evaluate the position statically
1127 // At PV nodes we do this only to update gain statistics
1128 isCheck = pos.is_check();
1131 if (tte && tte->static_value() != VALUE_NONE)
1133 ss->eval = tte->static_value();
1134 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1137 ss->eval = evaluate(pos, ei);
1139 refinedValue = refine_eval(tte, ss->eval, ply); // Enhance accuracy with TT value if possible
1140 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1143 // Step 6. Razoring (is omitted in PV nodes)
1145 && depth < RazorDepth
1147 && refinedValue < beta - razor_margin(depth)
1148 && ttMove == MOVE_NONE
1149 && (ss-1)->currentMove != MOVE_NULL
1150 && !value_is_mate(beta)
1151 && !pos.has_pawn_on_7th(pos.side_to_move()))
1153 // Pass ss->eval to qsearch() and avoid an evaluate call
1154 if (!tte || tte->static_value() == VALUE_NONE)
1155 TT.store(posKey, ss->eval, VALUE_TYPE_EXACT, Depth(-127*OnePly), MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1157 Value rbeta = beta - razor_margin(depth);
1158 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1160 // Logically we should return (v + razor_margin(depth)), but
1161 // surprisingly this did slightly weaker in tests.
1165 // Step 7. Static null move pruning (is omitted in PV nodes)
1166 // We're betting that the opponent doesn't have a move that will reduce
1167 // the score by more than futility_margin(depth) if we do a null move.
1169 && !ss->skipNullMove
1170 && depth < RazorDepth
1171 && refinedValue >= beta + futility_margin(depth, 0)
1173 && !value_is_mate(beta)
1174 && pos.non_pawn_material(pos.side_to_move()))
1175 return refinedValue - futility_margin(depth, 0);
1177 // Step 8. Null move search with verification search (is omitted in PV nodes)
1178 // When we jump directly to qsearch() we do a null move only if static value is
1179 // at least beta. Otherwise we do a null move if static value is not more than
1180 // NullMoveMargin under beta.
1182 && !ss->skipNullMove
1184 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1186 && !value_is_mate(beta)
1187 && pos.non_pawn_material(pos.side_to_move()))
1189 ss->currentMove = MOVE_NULL;
1191 // Null move dynamic reduction based on depth
1192 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1194 // Null move dynamic reduction based on value
1195 if (refinedValue - beta > PawnValueMidgame)
1198 pos.do_null_move(st);
1199 (ss+1)->skipNullMove = true;
1201 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1202 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1203 (ss+1)->skipNullMove = false;
1204 pos.undo_null_move();
1206 if (nullValue >= beta)
1208 // Do not return unproven mate scores
1209 if (nullValue >= value_mate_in(PLY_MAX))
1212 // Do zugzwang verification search at high depths
1213 if (depth < 6 * OnePly)
1216 ss->skipNullMove = true;
1217 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply);
1218 ss->skipNullMove = false;
1225 // The null move failed low, which means that we may be faced with
1226 // some kind of threat. If the previous move was reduced, check if
1227 // the move that refuted the null move was somehow connected to the
1228 // move which was reduced. If a connection is found, return a fail
1229 // low score (which will cause the reduced move to fail high in the
1230 // parent node, which will trigger a re-search with full depth).
1231 if (nullValue == value_mated_in(ply + 2))
1234 ss->threatMove = (ss+1)->currentMove;
1235 if ( depth < ThreatDepth
1236 && (ss-1)->reduction
1237 && connected_moves(pos, (ss-1)->currentMove, ss->threatMove))
1242 // Step 9. Internal iterative deepening
1243 if ( depth >= IIDDepth[PvNode]
1244 && ttMove == MOVE_NONE
1245 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1247 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1249 ss->skipNullMove = true;
1250 search<PvNode>(pos, ss, alpha, beta, d, ply);
1251 ss->skipNullMove = false;
1253 ttMove = ss->bestMove;
1254 tte = TT.retrieve(posKey);
1257 // Expensive mate threat detection (only for PV nodes)
1259 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1261 // Initialize a MovePicker object for the current position
1262 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1264 bool singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1265 && tte && tte->move()
1266 && !excludedMove // Do not allow recursive singular extension search
1267 && is_lower_bound(tte->type())
1268 && tte->depth() >= depth - 3 * OnePly;
1270 // Step 10. Loop through moves
1271 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1272 while ( bestValue < beta
1273 && (move = mp.get_next_move()) != MOVE_NONE
1274 && !TM.thread_should_stop(threadID))
1276 assert(move_is_ok(move));
1278 if (move == excludedMove)
1281 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1282 moveIsCheck = pos.move_is_check(move, ci);
1283 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1285 // Step 11. Decide the new search depth
1286 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1288 // Singular extension search. We extend the TT move if its value is much better than
1289 // its siblings. To verify this we do a reduced search on all the other moves but the
1290 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1291 if ( singularExtensionNode
1292 && move == tte->move()
1295 Value ttValue = value_from_tt(tte->value(), ply);
1297 if (abs(ttValue) < VALUE_KNOWN_WIN)
1299 Value b = ttValue - SingularExtensionMargin;
1300 ss->excludedMove = move;
1301 ss->skipNullMove = true;
1302 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1303 ss->skipNullMove = false;
1304 ss->excludedMove = MOVE_NONE;
1305 if (v < ttValue - SingularExtensionMargin)
1310 newDepth = depth - OnePly + ext;
1312 // Update current move (this must be done after singular extension search)
1313 movesSearched[moveCount++] = ss->currentMove = move;
1315 // Step 12. Futility pruning (is omitted in PV nodes)
1317 && !captureOrPromotion
1321 && !move_is_castle(move))
1323 // Move count based pruning
1324 if ( moveCount >= futility_move_count(depth)
1325 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1326 && bestValue > value_mated_in(PLY_MAX))
1329 // Value based pruning
1330 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1331 // but fixing this made program slightly weaker.
1332 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1333 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1334 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1336 if (futilityValueScaled < beta)
1338 if (futilityValueScaled > bestValue)
1339 bestValue = futilityValueScaled;
1344 // Step 13. Make the move
1345 pos.do_move(move, st, ci, moveIsCheck);
1347 // Step extra. pv search (only in PV nodes)
1348 // The first move in list is the expected PV
1349 if (PvNode && moveCount == 1)
1350 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1351 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1354 // Step 14. Reduced depth search
1355 // If the move fails high will be re-searched at full depth.
1356 bool doFullDepthSearch = true;
1358 if ( depth >= 3 * OnePly
1359 && !captureOrPromotion
1361 && !move_is_castle(move)
1362 && !move_is_killer(move, ss))
1364 ss->reduction = reduction<PvNode>(depth, moveCount);
1367 Depth d = newDepth - ss->reduction;
1368 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1369 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1371 doFullDepthSearch = (value > alpha);
1374 // The move failed high, but if reduction is very big we could
1375 // face a false positive, retry with a less aggressive reduction,
1376 // if the move fails high again then go with full depth search.
1377 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1379 assert(newDepth - OnePly >= OnePly);
1381 ss->reduction = OnePly;
1382 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1383 doFullDepthSearch = (value > alpha);
1385 ss->reduction = Depth(0); // Restore original reduction
1388 // Step 15. Full depth search
1389 if (doFullDepthSearch)
1391 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1392 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1394 // Step extra. pv search (only in PV nodes)
1395 // Search only for possible new PV nodes, if instead value >= beta then
1396 // parent node fails low with value <= alpha and tries another move.
1397 if (PvNode && value > alpha && value < beta)
1398 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1399 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1403 // Step 16. Undo move
1404 pos.undo_move(move);
1406 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1408 // Step 17. Check for new best move
1409 if (value > bestValue)
1414 if (PvNode && value < beta) // This guarantees that always: alpha < beta
1419 if (value == value_mate_in(ply + 1))
1420 ss->mateKiller = move;
1424 // Step 18. Check for split
1425 if ( depth >= MinimumSplitDepth
1426 && TM.active_threads() > 1
1428 && TM.available_thread_exists(threadID)
1430 && !TM.thread_should_stop(threadID)
1432 TM.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1433 mateThreat, &moveCount, &mp, PvNode);
1436 // Step 19. Check for mate and stalemate
1437 // All legal moves have been searched and if there are
1438 // no legal moves, it must be mate or stalemate.
1439 // If one move was excluded return fail low score.
1441 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1443 // Step 20. Update tables
1444 // If the search is not aborted, update the transposition table,
1445 // history counters, and killer moves.
1446 if (AbortSearch || TM.thread_should_stop(threadID))
1449 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1450 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1451 TT.store(posKey, value_to_tt(bestValue, ply), f, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1453 // Update killers and history only for non capture moves that fails high
1454 if (bestValue >= beta)
1456 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1457 if (!pos.move_is_capture_or_promotion(move))
1459 update_history(pos, move, depth, movesSearched, moveCount);
1460 update_killers(move, ss);
1464 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1470 // qsearch() is the quiescence search function, which is called by the main
1471 // search function when the remaining depth is zero (or, to be more precise,
1472 // less than OnePly).
1474 template <NodeType PvNode>
1475 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1477 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1478 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1479 assert(PvNode || alpha == beta - 1);
1481 assert(ply > 0 && ply < PLY_MAX);
1482 assert(pos.thread() >= 0 && pos.thread() < TM.active_threads());
1487 Value bestValue, value, futilityValue, futilityBase;
1488 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1490 Value oldAlpha = alpha;
1492 TM.incrementNodeCounter(pos.thread());
1493 ss->bestMove = ss->currentMove = MOVE_NONE;
1494 ss->eval = VALUE_NONE;
1496 // Check for an instant draw or maximum ply reached
1497 if (pos.is_draw() || ply >= PLY_MAX - 1)
1500 // Transposition table lookup. At PV nodes, we don't use the TT for
1501 // pruning, but only for move ordering.
1502 tte = TT.retrieve(pos.get_key());
1503 ttMove = (tte ? tte->move() : MOVE_NONE);
1505 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1507 ss->currentMove = ttMove; // Can be MOVE_NONE
1508 return value_from_tt(tte->value(), ply);
1511 isCheck = pos.is_check();
1513 // Evaluate the position statically
1516 bestValue = futilityBase = -VALUE_INFINITE;
1517 deepChecks = enoughMaterial = false;
1521 if (tte && tte->static_value() != VALUE_NONE)
1523 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1524 bestValue = tte->static_value();
1527 bestValue = evaluate(pos, ei);
1529 ss->eval = bestValue;
1530 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1532 // Stand pat. Return immediately if static value is at least beta
1533 if (bestValue >= beta)
1536 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()]);
1541 if (PvNode && bestValue > alpha)
1544 // If we are near beta then try to get a cutoff pushing checks a bit further
1545 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1547 // Futility pruning parameters, not needed when in check
1548 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1549 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1552 // Initialize a MovePicker object for the current position, and prepare
1553 // to search the moves. Because the depth is <= 0 here, only captures,
1554 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1555 // and we are near beta) will be generated.
1556 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1559 // Loop through the moves until no moves remain or a beta cutoff occurs
1560 while ( alpha < beta
1561 && (move = mp.get_next_move()) != MOVE_NONE)
1563 assert(move_is_ok(move));
1565 moveIsCheck = pos.move_is_check(move, ci);
1573 && !move_is_promotion(move)
1574 && !pos.move_is_passed_pawn_push(move))
1576 futilityValue = futilityBase
1577 + pos.endgame_value_of_piece_on(move_to(move))
1578 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1580 if (futilityValue < alpha)
1582 if (futilityValue > bestValue)
1583 bestValue = futilityValue;
1588 // Detect blocking evasions that are candidate to be pruned
1589 evasionPrunable = isCheck
1590 && bestValue > value_mated_in(PLY_MAX)
1591 && !pos.move_is_capture(move)
1592 && pos.type_of_piece_on(move_from(move)) != KING
1593 && !pos.can_castle(pos.side_to_move());
1595 // Don't search moves with negative SEE values
1597 && (!isCheck || evasionPrunable)
1599 && !move_is_promotion(move)
1600 && pos.see_sign(move) < 0)
1603 // Update current move
1604 ss->currentMove = move;
1606 // Make and search the move
1607 pos.do_move(move, st, ci, moveIsCheck);
1608 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1609 pos.undo_move(move);
1611 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1614 if (value > bestValue)
1625 // All legal moves have been searched. A special case: If we're in check
1626 // and no legal moves were found, it is checkmate.
1627 if (isCheck && bestValue == -VALUE_INFINITE)
1628 return value_mated_in(ply);
1630 // Update transposition table
1631 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1632 ValueType f = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1633 TT.store(pos.get_key(), value_to_tt(bestValue, ply), f, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1635 // Update killers only for checking moves that fails high
1636 if ( bestValue >= beta
1637 && !pos.move_is_capture_or_promotion(ss->bestMove))
1638 update_killers(ss->bestMove, ss);
1640 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1646 // sp_search() is used to search from a split point. This function is called
1647 // by each thread working at the split point. It is similar to the normal
1648 // search() function, but simpler. Because we have already probed the hash
1649 // table, done a null move search, and searched the first move before
1650 // splitting, we don't have to repeat all this work in sp_search(). We
1651 // also don't need to store anything to the hash table here: This is taken
1652 // care of after we return from the split point.
1654 template <NodeType PvNode>
1655 void sp_search(SplitPoint* sp, int threadID) {
1657 assert(threadID >= 0 && threadID < TM.active_threads());
1658 assert(TM.active_threads() > 1);
1662 Depth ext, newDepth;
1664 Value futilityValueScaled; // NonPV specific
1665 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1667 value = -VALUE_INFINITE;
1669 Position pos(*sp->pos, threadID);
1671 SearchStack* ss = sp->sstack[threadID] + 1;
1672 isCheck = pos.is_check();
1674 // Step 10. Loop through moves
1675 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1676 lock_grab(&(sp->lock));
1678 while ( sp->bestValue < sp->beta
1679 && (move = sp->mp->get_next_move()) != MOVE_NONE
1680 && !TM.thread_should_stop(threadID))
1682 moveCount = ++sp->moveCount;
1683 lock_release(&(sp->lock));
1685 assert(move_is_ok(move));
1687 moveIsCheck = pos.move_is_check(move, ci);
1688 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1690 // Step 11. Decide the new search depth
1691 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1692 newDepth = sp->depth - OnePly + ext;
1694 // Update current move
1695 ss->currentMove = move;
1697 // Step 12. Futility pruning (is omitted in PV nodes)
1699 && !captureOrPromotion
1702 && !move_is_castle(move))
1704 // Move count based pruning
1705 if ( moveCount >= futility_move_count(sp->depth)
1706 && !(ss->threatMove && connected_threat(pos, move, ss->threatMove))
1707 && sp->bestValue > value_mated_in(PLY_MAX))
1709 lock_grab(&(sp->lock));
1713 // Value based pruning
1714 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1715 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1716 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1718 if (futilityValueScaled < sp->beta)
1720 lock_grab(&(sp->lock));
1722 if (futilityValueScaled > sp->bestValue)
1723 sp->bestValue = futilityValueScaled;
1728 // Step 13. Make the move
1729 pos.do_move(move, st, ci, moveIsCheck);
1731 // Step 14. Reduced search
1732 // If the move fails high will be re-searched at full depth.
1733 bool doFullDepthSearch = true;
1735 if ( !captureOrPromotion
1737 && !move_is_castle(move)
1738 && !move_is_killer(move, ss))
1740 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1743 Value localAlpha = sp->alpha;
1744 Depth d = newDepth - ss->reduction;
1745 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1746 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1748 doFullDepthSearch = (value > localAlpha);
1751 // The move failed high, but if reduction is very big we could
1752 // face a false positive, retry with a less aggressive reduction,
1753 // if the move fails high again then go with full depth search.
1754 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1756 assert(newDepth - OnePly >= OnePly);
1758 ss->reduction = OnePly;
1759 Value localAlpha = sp->alpha;
1760 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1761 doFullDepthSearch = (value > localAlpha);
1763 ss->reduction = Depth(0); // Restore original reduction
1766 // Step 15. Full depth search
1767 if (doFullDepthSearch)
1769 Value localAlpha = sp->alpha;
1770 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1771 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1773 // Step extra. pv search (only in PV nodes)
1774 // Search only for possible new PV nodes, if instead value >= beta then
1775 // parent node fails low with value <= alpha and tries another move.
1776 if (PvNode && value > localAlpha && value < sp->beta)
1777 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1778 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1781 // Step 16. Undo move
1782 pos.undo_move(move);
1784 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1786 // Step 17. Check for new best move
1787 lock_grab(&(sp->lock));
1789 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1791 sp->bestValue = value;
1793 if (sp->bestValue > sp->alpha)
1795 if (!PvNode || value >= sp->beta)
1796 sp->stopRequest = true;
1798 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1801 sp_update_pv(sp->parentSstack, ss);
1806 /* Here we have the lock still grabbed */
1808 sp->slaves[threadID] = 0;
1810 lock_release(&(sp->lock));
1813 // update_pv() is called whenever a search returns a value > alpha.
1814 // It updates the PV in the SearchStack object corresponding to the
1817 void update_pv(SearchStack* ss) {
1819 ss->bestMove = ss->currentMove;
1823 // sp_update_pv() is a variant of update_pv for use at split points. The
1824 // difference between the two functions is that sp_update_pv also updates
1825 // the PV at the parent node.
1827 void sp_update_pv(SearchStack* pss, SearchStack* ss) {
1829 pss->bestMove = ss->bestMove = ss->currentMove;
1833 // connected_moves() tests whether two moves are 'connected' in the sense
1834 // that the first move somehow made the second move possible (for instance
1835 // if the moving piece is the same in both moves). The first move is assumed
1836 // to be the move that was made to reach the current position, while the
1837 // second move is assumed to be a move from the current position.
1839 bool connected_moves(const Position& pos, Move m1, Move m2) {
1841 Square f1, t1, f2, t2;
1844 assert(move_is_ok(m1));
1845 assert(move_is_ok(m2));
1847 if (m2 == MOVE_NONE)
1850 // Case 1: The moving piece is the same in both moves
1856 // Case 2: The destination square for m2 was vacated by m1
1862 // Case 3: Moving through the vacated square
1863 if ( piece_is_slider(pos.piece_on(f2))
1864 && bit_is_set(squares_between(f2, t2), f1))
1867 // Case 4: The destination square for m2 is defended by the moving piece in m1
1868 p = pos.piece_on(t1);
1869 if (bit_is_set(pos.attacks_from(p, t1), t2))
1872 // Case 5: Discovered check, checking piece is the piece moved in m1
1873 if ( piece_is_slider(p)
1874 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1875 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1877 // discovered_check_candidates() works also if the Position's side to
1878 // move is the opposite of the checking piece.
1879 Color them = opposite_color(pos.side_to_move());
1880 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1882 if (bit_is_set(dcCandidates, f2))
1889 // value_is_mate() checks if the given value is a mate one
1890 // eventually compensated for the ply.
1892 bool value_is_mate(Value value) {
1894 assert(abs(value) <= VALUE_INFINITE);
1896 return value <= value_mated_in(PLY_MAX)
1897 || value >= value_mate_in(PLY_MAX);
1901 // move_is_killer() checks if the given move is among the
1902 // killer moves of that ply.
1904 bool move_is_killer(Move m, SearchStack* ss) {
1906 const Move* k = ss->killers;
1907 for (int i = 0; i < KILLER_MAX; i++, k++)
1915 // extension() decides whether a move should be searched with normal depth,
1916 // or with extended depth. Certain classes of moves (checking moves, in
1917 // particular) are searched with bigger depth than ordinary moves and in
1918 // any case are marked as 'dangerous'. Note that also if a move is not
1919 // extended, as example because the corresponding UCI option is set to zero,
1920 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1921 template <NodeType PvNode>
1922 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1923 bool singleEvasion, bool mateThreat, bool* dangerous) {
1925 assert(m != MOVE_NONE);
1927 Depth result = Depth(0);
1928 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1932 if (moveIsCheck && pos.see_sign(m) >= 0)
1933 result += CheckExtension[PvNode];
1936 result += SingleEvasionExtension[PvNode];
1939 result += MateThreatExtension[PvNode];
1942 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1944 Color c = pos.side_to_move();
1945 if (relative_rank(c, move_to(m)) == RANK_7)
1947 result += PawnPushTo7thExtension[PvNode];
1950 if (pos.pawn_is_passed(c, move_to(m)))
1952 result += PassedPawnExtension[PvNode];
1957 if ( captureOrPromotion
1958 && pos.type_of_piece_on(move_to(m)) != PAWN
1959 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1960 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1961 && !move_is_promotion(m)
1964 result += PawnEndgameExtension[PvNode];
1969 && captureOrPromotion
1970 && pos.type_of_piece_on(move_to(m)) != PAWN
1971 && pos.see_sign(m) >= 0)
1977 return Min(result, OnePly);
1981 // connected_threat() tests whether it is safe to forward prune a move or if
1982 // is somehow coonected to the threat move returned by null search.
1984 bool connected_threat(const Position& pos, Move m, Move threat) {
1986 assert(move_is_ok(m));
1987 assert(threat && move_is_ok(threat));
1988 assert(!pos.move_is_check(m));
1989 assert(!pos.move_is_capture_or_promotion(m));
1990 assert(!pos.move_is_passed_pawn_push(m));
1992 Square mfrom, mto, tfrom, tto;
1994 mfrom = move_from(m);
1996 tfrom = move_from(threat);
1997 tto = move_to(threat);
1999 // Case 1: Don't prune moves which move the threatened piece
2003 // Case 2: If the threatened piece has value less than or equal to the
2004 // value of the threatening piece, don't prune move which defend it.
2005 if ( pos.move_is_capture(threat)
2006 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2007 || pos.type_of_piece_on(tfrom) == KING)
2008 && pos.move_attacks_square(m, tto))
2011 // Case 3: If the moving piece in the threatened move is a slider, don't
2012 // prune safe moves which block its ray.
2013 if ( piece_is_slider(pos.piece_on(tfrom))
2014 && bit_is_set(squares_between(tfrom, tto), mto)
2015 && pos.see_sign(m) >= 0)
2022 // ok_to_use_TT() returns true if a transposition table score
2023 // can be used at a given point in search.
2025 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2027 Value v = value_from_tt(tte->value(), ply);
2029 return ( tte->depth() >= depth
2030 || v >= Max(value_mate_in(PLY_MAX), beta)
2031 || v < Min(value_mated_in(PLY_MAX), beta))
2033 && ( (is_lower_bound(tte->type()) && v >= beta)
2034 || (is_upper_bound(tte->type()) && v < beta));
2038 // refine_eval() returns the transposition table score if
2039 // possible otherwise falls back on static position evaluation.
2041 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2046 Value v = value_from_tt(tte->value(), ply);
2048 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2049 || (is_upper_bound(tte->type()) && v < defaultEval))
2056 // update_history() registers a good move that produced a beta-cutoff
2057 // in history and marks as failures all the other moves of that ply.
2059 void update_history(const Position& pos, Move move, Depth depth,
2060 Move movesSearched[], int moveCount) {
2064 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2066 for (int i = 0; i < moveCount - 1; i++)
2068 m = movesSearched[i];
2072 if (!pos.move_is_capture_or_promotion(m))
2073 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2078 // update_killers() add a good move that produced a beta-cutoff
2079 // among the killer moves of that ply.
2081 void update_killers(Move m, SearchStack* ss) {
2083 if (m == ss->killers[0])
2086 for (int i = KILLER_MAX - 1; i > 0; i--)
2087 ss->killers[i] = ss->killers[i - 1];
2093 // update_gains() updates the gains table of a non-capture move given
2094 // the static position evaluation before and after the move.
2096 void update_gains(const Position& pos, Move m, Value before, Value after) {
2099 && before != VALUE_NONE
2100 && after != VALUE_NONE
2101 && pos.captured_piece() == NO_PIECE_TYPE
2102 && !move_is_castle(m)
2103 && !move_is_promotion(m))
2104 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2108 // current_search_time() returns the number of milliseconds which have passed
2109 // since the beginning of the current search.
2111 int current_search_time() {
2113 return get_system_time() - SearchStartTime;
2117 // nps() computes the current nodes/second count.
2121 int t = current_search_time();
2122 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2126 // poll() performs two different functions: It polls for user input, and it
2127 // looks at the time consumed so far and decides if it's time to abort the
2132 static int lastInfoTime;
2133 int t = current_search_time();
2138 // We are line oriented, don't read single chars
2139 std::string command;
2141 if (!std::getline(std::cin, command))
2144 if (command == "quit")
2147 PonderSearch = false;
2151 else if (command == "stop")
2154 PonderSearch = false;
2156 else if (command == "ponderhit")
2160 // Print search information
2164 else if (lastInfoTime > t)
2165 // HACK: Must be a new search where we searched less than
2166 // NodesBetweenPolls nodes during the first second of search.
2169 else if (t - lastInfoTime >= 1000)
2176 if (dbg_show_hit_rate)
2177 dbg_print_hit_rate();
2179 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2180 << " time " << t << " hashfull " << TT.full() << endl;
2183 // Should we stop the search?
2187 bool stillAtFirstMove = FirstRootMove
2188 && !AspirationFailLow
2189 && t > MaxSearchTime + ExtraSearchTime;
2191 bool noMoreTime = t > AbsoluteMaxSearchTime
2192 || stillAtFirstMove;
2194 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2195 || (ExactMaxTime && t >= ExactMaxTime)
2196 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2201 // ponderhit() is called when the program is pondering (i.e. thinking while
2202 // it's the opponent's turn to move) in order to let the engine know that
2203 // it correctly predicted the opponent's move.
2207 int t = current_search_time();
2208 PonderSearch = false;
2210 bool stillAtFirstMove = FirstRootMove
2211 && !AspirationFailLow
2212 && t > MaxSearchTime + ExtraSearchTime;
2214 bool noMoreTime = t > AbsoluteMaxSearchTime
2215 || stillAtFirstMove;
2217 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2222 // init_ss_array() does a fast reset of the first entries of a SearchStack
2223 // array and of all the excludedMove and skipNullMove entries.
2225 void init_ss_array(SearchStack* ss, int size) {
2227 for (int i = 0; i < size; i++, ss++)
2229 ss->excludedMove = MOVE_NONE;
2230 ss->skipNullMove = false;
2241 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2242 // while the program is pondering. The point is to work around a wrinkle in
2243 // the UCI protocol: When pondering, the engine is not allowed to give a
2244 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2245 // We simply wait here until one of these commands is sent, and return,
2246 // after which the bestmove and pondermove will be printed (in id_loop()).
2248 void wait_for_stop_or_ponderhit() {
2250 std::string command;
2254 if (!std::getline(std::cin, command))
2257 if (command == "quit")
2262 else if (command == "ponderhit" || command == "stop")
2268 // print_pv_info() prints to standard output and eventually to log file information on
2269 // the current PV line. It is called at each iteration or after a new pv is found.
2271 void print_pv_info(const Position& pos, Move* pv, Value alpha, Value beta, Value value) {
2273 cout << "info depth " << Iteration
2274 << " score " << value_to_string(value)
2275 << ((value >= beta) ? " lowerbound" :
2276 ((value <= alpha)? " upperbound" : ""))
2277 << " time " << current_search_time()
2278 << " nodes " << TM.nodes_searched()
2282 for (int j = 0; pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2283 cout << pv[j] << " ";
2289 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2290 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2292 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2293 TM.nodes_searched(), value, type, pv) << endl;
2298 // init_thread() is the function which is called when a new thread is
2299 // launched. It simply calls the idle_loop() function with the supplied
2300 // threadID. There are two versions of this function; one for POSIX
2301 // threads and one for Windows threads.
2303 #if !defined(_MSC_VER)
2305 void* init_thread(void *threadID) {
2307 TM.idle_loop(*(int*)threadID, NULL);
2313 DWORD WINAPI init_thread(LPVOID threadID) {
2315 TM.idle_loop(*(int*)threadID, NULL);
2322 /// The ThreadsManager class
2324 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2325 // get_beta_counters() are getters/setters for the per thread
2326 // counters used to sort the moves at root.
2328 void ThreadsManager::resetNodeCounters() {
2330 for (int i = 0; i < MAX_THREADS; i++)
2331 threads[i].nodes = 0ULL;
2334 void ThreadsManager::resetBetaCounters() {
2336 for (int i = 0; i < MAX_THREADS; i++)
2337 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2340 int64_t ThreadsManager::nodes_searched() const {
2342 int64_t result = 0ULL;
2343 for (int i = 0; i < ActiveThreads; i++)
2344 result += threads[i].nodes;
2349 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2352 for (int i = 0; i < MAX_THREADS; i++)
2354 our += threads[i].betaCutOffs[us];
2355 their += threads[i].betaCutOffs[opposite_color(us)];
2360 // idle_loop() is where the threads are parked when they have no work to do.
2361 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2362 // object for which the current thread is the master.
2364 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2366 assert(threadID >= 0 && threadID < MAX_THREADS);
2370 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2371 // master should exit as last one.
2372 if (AllThreadsShouldExit)
2375 threads[threadID].state = THREAD_TERMINATED;
2379 // If we are not thinking, wait for a condition to be signaled
2380 // instead of wasting CPU time polling for work.
2381 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2384 assert(threadID != 0);
2385 threads[threadID].state = THREAD_SLEEPING;
2387 #if !defined(_MSC_VER)
2388 lock_grab(&WaitLock);
2389 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2390 pthread_cond_wait(&WaitCond, &WaitLock);
2391 lock_release(&WaitLock);
2393 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2397 // If thread has just woken up, mark it as available
2398 if (threads[threadID].state == THREAD_SLEEPING)
2399 threads[threadID].state = THREAD_AVAILABLE;
2401 // If this thread has been assigned work, launch a search
2402 if (threads[threadID].state == THREAD_WORKISWAITING)
2404 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2406 threads[threadID].state = THREAD_SEARCHING;
2408 if (threads[threadID].splitPoint->pvNode)
2409 sp_search<PV>(threads[threadID].splitPoint, threadID);
2411 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2413 assert(threads[threadID].state == THREAD_SEARCHING);
2415 threads[threadID].state = THREAD_AVAILABLE;
2418 // If this thread is the master of a split point and all slaves have
2419 // finished their work at this split point, return from the idle loop.
2421 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2423 if (i == ActiveThreads)
2425 // Because sp->slaves[] is reset under lock protection,
2426 // be sure sp->lock has been released before to return.
2427 lock_grab(&(sp->lock));
2428 lock_release(&(sp->lock));
2430 assert(threads[threadID].state == THREAD_AVAILABLE);
2432 threads[threadID].state = THREAD_SEARCHING;
2439 // init_threads() is called during startup. It launches all helper threads,
2440 // and initializes the split point stack and the global locks and condition
2443 void ThreadsManager::init_threads() {
2448 #if !defined(_MSC_VER)
2449 pthread_t pthread[1];
2452 // Initialize global locks
2453 lock_init(&MPLock, NULL);
2454 lock_init(&WaitLock, NULL);
2456 #if !defined(_MSC_VER)
2457 pthread_cond_init(&WaitCond, NULL);
2459 for (i = 0; i < MAX_THREADS; i++)
2460 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2463 // Initialize SplitPointStack locks
2464 for (i = 0; i < MAX_THREADS; i++)
2465 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2466 lock_init(&(SplitPointStack[i][j].lock), NULL);
2468 // Will be set just before program exits to properly end the threads
2469 AllThreadsShouldExit = false;
2471 // Threads will be put to sleep as soon as created
2472 AllThreadsShouldSleep = true;
2474 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2476 threads[0].state = THREAD_SEARCHING;
2477 for (i = 1; i < MAX_THREADS; i++)
2478 threads[i].state = THREAD_AVAILABLE;
2480 // Launch the helper threads
2481 for (i = 1; i < MAX_THREADS; i++)
2484 #if !defined(_MSC_VER)
2485 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2487 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2492 cout << "Failed to create thread number " << i << endl;
2493 Application::exit_with_failure();
2496 // Wait until the thread has finished launching and is gone to sleep
2497 while (threads[i].state != THREAD_SLEEPING) {}
2502 // exit_threads() is called when the program exits. It makes all the
2503 // helper threads exit cleanly.
2505 void ThreadsManager::exit_threads() {
2507 ActiveThreads = MAX_THREADS; // HACK
2508 AllThreadsShouldSleep = true; // HACK
2509 wake_sleeping_threads();
2511 // This makes the threads to exit idle_loop()
2512 AllThreadsShouldExit = true;
2514 // Wait for thread termination
2515 for (int i = 1; i < MAX_THREADS; i++)
2516 while (threads[i].state != THREAD_TERMINATED) {}
2518 // Now we can safely destroy the locks
2519 for (int i = 0; i < MAX_THREADS; i++)
2520 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2521 lock_destroy(&(SplitPointStack[i][j].lock));
2523 lock_destroy(&WaitLock);
2524 lock_destroy(&MPLock);
2528 // thread_should_stop() checks whether the thread should stop its search.
2529 // This can happen if a beta cutoff has occurred in the thread's currently
2530 // active split point, or in some ancestor of the current split point.
2532 bool ThreadsManager::thread_should_stop(int threadID) const {
2534 assert(threadID >= 0 && threadID < ActiveThreads);
2538 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2543 // thread_is_available() checks whether the thread with threadID "slave" is
2544 // available to help the thread with threadID "master" at a split point. An
2545 // obvious requirement is that "slave" must be idle. With more than two
2546 // threads, this is not by itself sufficient: If "slave" is the master of
2547 // some active split point, it is only available as a slave to the other
2548 // threads which are busy searching the split point at the top of "slave"'s
2549 // split point stack (the "helpful master concept" in YBWC terminology).
2551 bool ThreadsManager::thread_is_available(int slave, int master) const {
2553 assert(slave >= 0 && slave < ActiveThreads);
2554 assert(master >= 0 && master < ActiveThreads);
2555 assert(ActiveThreads > 1);
2557 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2560 // Make a local copy to be sure doesn't change under our feet
2561 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2563 if (localActiveSplitPoints == 0)
2564 // No active split points means that the thread is available as
2565 // a slave for any other thread.
2568 if (ActiveThreads == 2)
2571 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2572 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2573 // could have been set to 0 by another thread leading to an out of bound access.
2574 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2581 // available_thread_exists() tries to find an idle thread which is available as
2582 // a slave for the thread with threadID "master".
2584 bool ThreadsManager::available_thread_exists(int master) const {
2586 assert(master >= 0 && master < ActiveThreads);
2587 assert(ActiveThreads > 1);
2589 for (int i = 0; i < ActiveThreads; i++)
2590 if (thread_is_available(i, master))
2597 // split() does the actual work of distributing the work at a node between
2598 // several available threads. If it does not succeed in splitting the
2599 // node (because no idle threads are available, or because we have no unused
2600 // split point objects), the function immediately returns. If splitting is
2601 // possible, a SplitPoint object is initialized with all the data that must be
2602 // copied to the helper threads and we tell our helper threads that they have
2603 // been assigned work. This will cause them to instantly leave their idle loops
2604 // and call sp_search(). When all threads have returned from sp_search() then
2607 template <bool Fake>
2608 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2609 const Value beta, Value* bestValue, Depth depth, bool mateThreat,
2610 int* moveCount, MovePicker* mp, bool pvNode) {
2612 assert(ply > 0 && ply < PLY_MAX);
2613 assert(*bestValue >= -VALUE_INFINITE);
2614 assert(*bestValue <= *alpha);
2615 assert(*alpha < beta);
2616 assert(beta <= VALUE_INFINITE);
2617 assert(depth > Depth(0));
2618 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2619 assert(ActiveThreads > 1);
2621 int master = p.thread();
2625 // If no other thread is available to help us, or if we have too many
2626 // active split points, don't split.
2627 if ( !available_thread_exists(master)
2628 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2630 lock_release(&MPLock);
2634 // Pick the next available split point object from the split point stack
2635 SplitPoint* splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2637 // Initialize the split point object
2638 splitPoint->parent = threads[master].splitPoint;
2639 splitPoint->stopRequest = false;
2640 splitPoint->ply = ply;
2641 splitPoint->depth = depth;
2642 splitPoint->mateThreat = mateThreat;
2643 splitPoint->alpha = *alpha;
2644 splitPoint->beta = beta;
2645 splitPoint->pvNode = pvNode;
2646 splitPoint->bestValue = *bestValue;
2647 splitPoint->mp = mp;
2648 splitPoint->moveCount = *moveCount;
2649 splitPoint->pos = &p;
2650 splitPoint->parentSstack = ss;
2651 for (int i = 0; i < ActiveThreads; i++)
2652 splitPoint->slaves[i] = 0;
2654 threads[master].splitPoint = splitPoint;
2655 threads[master].activeSplitPoints++;
2657 // If we are here it means we are not available
2658 assert(threads[master].state != THREAD_AVAILABLE);
2660 int workersCnt = 1; // At least the master is included
2662 // Allocate available threads setting state to THREAD_BOOKED
2663 for (int i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2664 if (thread_is_available(i, master))
2666 threads[i].state = THREAD_BOOKED;
2667 threads[i].splitPoint = splitPoint;
2668 splitPoint->slaves[i] = 1;
2672 assert(Fake || workersCnt > 1);
2674 // We can release the lock because slave threads are already booked and master is not available
2675 lock_release(&MPLock);
2677 // Tell the threads that they have work to do. This will make them leave
2678 // their idle loop. But before copy search stack tail for each thread.
2679 for (int i = 0; i < ActiveThreads; i++)
2680 if (i == master || splitPoint->slaves[i])
2682 memcpy(splitPoint->sstack[i], ss - 1, 4 * sizeof(SearchStack));
2684 assert(i == master || threads[i].state == THREAD_BOOKED);
2686 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2689 // Everything is set up. The master thread enters the idle loop, from
2690 // which it will instantly launch a search, because its state is
2691 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2692 // idle loop, which means that the main thread will return from the idle
2693 // loop when all threads have finished their work at this split point.
2694 idle_loop(master, splitPoint);
2696 // We have returned from the idle loop, which means that all threads are
2697 // finished. Update alpha and bestValue, and return.
2700 *alpha = splitPoint->alpha;
2701 *bestValue = splitPoint->bestValue;
2702 threads[master].activeSplitPoints--;
2703 threads[master].splitPoint = splitPoint->parent;
2705 lock_release(&MPLock);
2709 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2710 // to start a new search from the root.
2712 void ThreadsManager::wake_sleeping_threads() {
2714 assert(AllThreadsShouldSleep);
2715 assert(ActiveThreads > 0);
2717 AllThreadsShouldSleep = false;
2719 if (ActiveThreads == 1)
2722 #if !defined(_MSC_VER)
2723 pthread_mutex_lock(&WaitLock);
2724 pthread_cond_broadcast(&WaitCond);
2725 pthread_mutex_unlock(&WaitLock);
2727 for (int i = 1; i < MAX_THREADS; i++)
2728 SetEvent(SitIdleEvent[i]);
2734 // put_threads_to_sleep() makes all the threads go to sleep just before
2735 // to leave think(), at the end of the search. Threads should have already
2736 // finished the job and should be idle.
2738 void ThreadsManager::put_threads_to_sleep() {
2740 assert(!AllThreadsShouldSleep);
2742 // This makes the threads to go to sleep
2743 AllThreadsShouldSleep = true;
2746 /// The RootMoveList class
2748 // RootMoveList c'tor
2750 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2752 SearchStack ss[PLY_MAX_PLUS_2];
2753 MoveStack mlist[MaxRootMoves];
2755 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2757 // Generate all legal moves
2758 MoveStack* last = generate_moves(pos, mlist);
2760 // Add each move to the moves[] array
2761 for (MoveStack* cur = mlist; cur != last; cur++)
2763 bool includeMove = includeAllMoves;
2765 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2766 includeMove = (searchMoves[k] == cur->move);
2771 // Find a quick score for the move
2772 init_ss_array(ss, PLY_MAX_PLUS_2);
2773 pos.do_move(cur->move, st);
2774 moves[count].move = cur->move;
2775 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2776 moves[count].pv[0] = cur->move;
2777 moves[count].pv[1] = MOVE_NONE;
2778 pos.undo_move(cur->move);
2785 // RootMoveList simple methods definitions
2787 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2789 moves[moveNum].nodes = nodes;
2790 moves[moveNum].cumulativeNodes += nodes;
2793 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2795 moves[moveNum].ourBeta = our;
2796 moves[moveNum].theirBeta = their;
2799 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2803 for (j = 0; pv[j] != MOVE_NONE; j++)
2804 moves[moveNum].pv[j] = pv[j];
2806 moves[moveNum].pv[j] = MOVE_NONE;
2810 // RootMoveList::sort() sorts the root move list at the beginning of a new
2813 void RootMoveList::sort() {
2815 sort_multipv(count - 1); // Sort all items
2819 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2820 // list by their scores and depths. It is used to order the different PVs
2821 // correctly in MultiPV mode.
2823 void RootMoveList::sort_multipv(int n) {
2827 for (i = 1; i <= n; i++)
2829 RootMove rm = moves[i];
2830 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2831 moves[j] = moves[j - 1];