2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
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
57 // ThreadsManager class is used to handle all the threads related stuff in search,
58 // init, starting, parking and, the most important, launching a slave thread at a
59 // split point are what this class does. All the access to shared thread data is
60 // done through this class, so that we avoid using global variables instead.
62 class ThreadsManager {
63 /* As long as the single ThreadsManager object is defined as a global we don't
64 need to explicitly initialize to zero its data members because variables with
65 static storage duration are automatically set to zero before enter main()
71 int active_threads() const { return ActiveThreads; }
72 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
73 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
74 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
76 void resetNodeCounters();
77 void resetBetaCounters();
78 int64_t nodes_searched() const;
79 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
80 bool available_thread_exists(int master) const;
81 bool thread_is_available(int slave, int master) const;
82 bool thread_should_stop(int threadID) const;
83 void wake_sleeping_threads();
84 void put_threads_to_sleep();
85 void idle_loop(int threadID, SplitPoint* waitSp);
86 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode);
90 friend void poll(SearchStack ss[], int ply);
93 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
94 Thread threads[MAX_THREADS];
95 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
97 Lock MPLock, WaitLock;
99 #if !defined(_MSC_VER)
100 pthread_cond_t WaitCond;
102 HANDLE SitIdleEvent[MAX_THREADS];
108 // RootMove struct is used for moves at the root at the tree. For each
109 // root move, we store a score, a node count, and a PV (really a refutation
110 // in the case of moves which fail low).
114 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
116 // RootMove::operator<() is the comparison function used when
117 // sorting the moves. A move m1 is considered to be better
118 // than a move m2 if it has a higher score, or if the moves
119 // have equal score but m1 has the higher node count.
120 bool operator<(const RootMove& m) const {
122 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
127 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
128 Move pv[PLY_MAX_PLUS_2];
132 // The RootMoveList class is essentially an array of RootMove objects, with
133 // a handful of methods for accessing the data in the individual moves.
138 RootMoveList(Position& pos, Move searchMoves[]);
140 int move_count() const { return count; }
141 Move get_move(int moveNum) const { return moves[moveNum].move; }
142 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
143 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
144 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
145 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
147 void set_move_nodes(int moveNum, int64_t nodes);
148 void set_beta_counters(int moveNum, int64_t our, int64_t their);
149 void set_move_pv(int moveNum, const Move pv[]);
151 void sort_multipv(int n);
154 static const int MaxRootMoves = 500;
155 RootMove moves[MaxRootMoves];
164 // Maximum depth for razoring
165 const Depth RazorDepth = 4 * OnePly;
167 // Dynamic razoring margin based on depth
168 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
170 // Step 8. Null move search with verification search
172 // Null move margin. A null move search will not be done if the static
173 // evaluation of the position is more than NullMoveMargin below beta.
174 const Value NullMoveMargin = Value(0x200);
176 // Maximum depth for use of dynamic threat detection when null move fails low
177 const Depth ThreatDepth = 5 * OnePly;
179 // Step 9. Internal iterative deepening
181 // Minimum depth for use of internal iterative deepening
182 const Depth IIDDepthAtPVNodes = 5 * OnePly;
183 const Depth IIDDepthAtNonPVNodes = 8 * OnePly;
185 // At Non-PV nodes we do an internal iterative deepening search
186 // when the static evaluation is at most IIDMargin below beta.
187 const Value IIDMargin = Value(0x100);
189 // Step 11. Decide the new search depth
191 // Extensions. Configurable UCI options
192 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
193 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
194 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
196 // Minimum depth for use of singular extension
197 const Depth SingularExtensionDepthAtPVNodes = 6 * OnePly;
198 const Depth SingularExtensionDepthAtNonPVNodes = 8 * OnePly;
200 // If the TT move is at least SingularExtensionMargin better then the
201 // remaining ones we will extend it.
202 const Value SingularExtensionMargin = Value(0x20);
204 // Step 12. Futility pruning
206 // Futility margin for quiescence search
207 const Value FutilityMarginQS = Value(0x80);
209 // Futility lookup tables (initialized at startup) and their getter functions
210 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
211 int FutilityMoveCountArray[32]; // [depth]
213 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
214 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
216 // Step 14. Reduced search
218 // Reduction lookup tables (initialized at startup) and their getter functions
219 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
220 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
222 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
223 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
225 // Common adjustments
227 // Search depth at iteration 1
228 const Depth InitialDepth = OnePly;
230 // Easy move margin. An easy move candidate must be at least this much
231 // better than the second best move.
232 const Value EasyMoveMargin = Value(0x200);
234 // Last seconds noise filtering (LSN)
235 const bool UseLSNFiltering = true;
236 const int LSNTime = 4000; // In milliseconds
237 const Value LSNValue = value_from_centipawns(200);
238 bool loseOnTime = false;
246 // Scores and number of times the best move changed for each iteration
247 Value ValueByIteration[PLY_MAX_PLUS_2];
248 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
250 // Search window management
256 // Time managment variables
257 int RootMoveNumber, SearchStartTime, MaxNodes, MaxDepth;
258 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
259 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
260 bool AbortSearch, Quit, AspirationFailLow;
262 // Show current line?
263 bool ShowCurrentLine;
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& oldAlpha, Value& beta);
286 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
287 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
288 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
289 void sp_search(SplitPoint* sp, int threadID);
290 void sp_search_pv(SplitPoint* sp, int threadID);
291 void init_node(SearchStack ss[], int ply, int threadID);
292 void update_pv(SearchStack ss[], int ply);
293 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
294 bool connected_moves(const Position& pos, Move m1, Move m2);
295 bool value_is_mate(Value value);
296 bool move_is_killer(Move m, const SearchStack& ss);
297 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
298 bool ok_to_do_nullmove(const Position& pos);
299 bool ok_to_prune(const Position& pos, Move m, Move threat);
300 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
301 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
302 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
303 void update_killers(Move m, SearchStack& ss);
304 void update_gains(const Position& pos, Move move, Value before, Value after);
306 int current_search_time();
308 void poll(SearchStack ss[], int ply);
310 void wait_for_stop_or_ponderhit();
311 void init_ss_array(SearchStack ss[]);
312 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value);
314 #if !defined(_MSC_VER)
315 void *init_thread(void *threadID);
317 DWORD WINAPI init_thread(LPVOID threadID);
327 /// init_threads(), exit_threads() and nodes_searched() are helpers to
328 /// give accessibility to some TM methods from outside of current file.
330 void init_threads() { TM.init_threads(); }
331 void exit_threads() { TM.exit_threads(); }
332 int64_t nodes_searched() { return TM.nodes_searched(); }
335 /// perft() is our utility to verify move generation is bug free. All the legal
336 /// moves up to given depth are generated and counted and the sum returned.
338 int perft(Position& pos, Depth depth)
343 MovePicker mp(pos, MOVE_NONE, depth, H);
345 // If we are at the last ply we don't need to do and undo
346 // the moves, just to count them.
347 if (depth <= OnePly) // Replace with '<' to test also qsearch
349 while (mp.get_next_move()) sum++;
353 // Loop through all legal moves
355 while ((move = mp.get_next_move()) != MOVE_NONE)
357 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
358 sum += perft(pos, depth - OnePly);
365 /// think() is the external interface to Stockfish's search, and is called when
366 /// the program receives the UCI 'go' command. It initializes various
367 /// search-related global variables, and calls root_search(). It returns false
368 /// when a quit command is received during the search.
370 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
371 int time[], int increment[], int movesToGo, int maxDepth,
372 int maxNodes, int maxTime, Move searchMoves[]) {
374 // Initialize global search variables
375 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
377 TM.resetNodeCounters();
378 SearchStartTime = get_system_time();
379 ExactMaxTime = maxTime;
382 InfiniteSearch = infinite;
383 PonderSearch = ponder;
384 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
386 // Look for a book move, only during games, not tests
387 if (UseTimeManagement && get_option_value_bool("OwnBook"))
389 if (get_option_value_string("Book File") != OpeningBook.file_name())
390 OpeningBook.open(get_option_value_string("Book File"));
392 Move bookMove = OpeningBook.get_move(pos);
393 if (bookMove != MOVE_NONE)
396 wait_for_stop_or_ponderhit();
398 cout << "bestmove " << bookMove << endl;
403 // Reset loseOnTime flag at the beginning of a new game
404 if (button_was_pressed("New Game"))
407 // Read UCI option values
408 TT.set_size(get_option_value_int("Hash"));
409 if (button_was_pressed("Clear Hash"))
412 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
413 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
414 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
415 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
416 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
417 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
418 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
419 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
420 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
421 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
422 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
423 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
425 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
426 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
427 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
428 MultiPV = get_option_value_int("MultiPV");
429 Chess960 = get_option_value_bool("UCI_Chess960");
430 UseLogFile = get_option_value_bool("Use Search Log");
433 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
435 read_weights(pos.side_to_move());
437 // Set the number of active threads
438 int newActiveThreads = get_option_value_int("Threads");
439 if (newActiveThreads != TM.active_threads())
441 TM.set_active_threads(newActiveThreads);
442 init_eval(TM.active_threads());
443 // HACK: init_eval() destroys the static castleRightsMask[] array in the
444 // Position class. The below line repairs the damage.
445 Position p(pos.to_fen());
449 // Wake up sleeping threads
450 TM.wake_sleeping_threads();
453 int myTime = time[side_to_move];
454 int myIncrement = increment[side_to_move];
455 if (UseTimeManagement)
457 if (!movesToGo) // Sudden death time control
461 MaxSearchTime = myTime / 30 + myIncrement;
462 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
464 else // Blitz game without increment
466 MaxSearchTime = myTime / 30;
467 AbsoluteMaxSearchTime = myTime / 8;
470 else // (x moves) / (y minutes)
474 MaxSearchTime = myTime / 2;
475 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
479 MaxSearchTime = myTime / Min(movesToGo, 20);
480 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
484 if (get_option_value_bool("Ponder"))
486 MaxSearchTime += MaxSearchTime / 4;
487 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
491 // Set best NodesBetweenPolls interval to avoid lagging under
492 // heavy time pressure.
494 NodesBetweenPolls = Min(MaxNodes, 30000);
495 else if (myTime && myTime < 1000)
496 NodesBetweenPolls = 1000;
497 else if (myTime && myTime < 5000)
498 NodesBetweenPolls = 5000;
500 NodesBetweenPolls = 30000;
502 // Write search information to log file
504 LogFile << "Searching: " << pos.to_fen() << endl
505 << "infinite: " << infinite
506 << " ponder: " << ponder
507 << " time: " << myTime
508 << " increment: " << myIncrement
509 << " moves to go: " << movesToGo << endl;
511 // LSN filtering. Used only for developing purposes, disabled by default
515 // Step 2. If after last move we decided to lose on time, do it now!
516 while (SearchStartTime + myTime + 1000 > get_system_time())
520 // We're ready to start thinking. Call the iterative deepening loop function
521 Value v = id_loop(pos, searchMoves);
525 // Step 1. If this is sudden death game and our position is hopeless,
526 // decide to lose on time.
527 if ( !loseOnTime // If we already lost on time, go to step 3.
537 // Step 3. Now after stepping over the time limit, reset flag for next match.
545 TM.put_threads_to_sleep();
551 /// init_search() is called during startup. It initializes various lookup tables
555 // Init our reduction lookup tables
556 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
557 for (int j = 1; j < 64; j++) // j == moveNumber
559 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
560 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
561 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
562 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
565 // Init futility margins array
566 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
567 for (int j = 0; j < 64; j++) // j == moveNumber
569 // FIXME: test using log instead of BSR
570 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j;
573 // Init futility move count array
574 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
575 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
579 // SearchStack::init() initializes a search stack. Used at the beginning of a
580 // new search from the root.
581 void SearchStack::init(int ply) {
583 pv[ply] = pv[ply + 1] = MOVE_NONE;
584 currentMove = threatMove = MOVE_NONE;
585 reduction = Depth(0);
589 void SearchStack::initKillers() {
591 mateKiller = MOVE_NONE;
592 for (int i = 0; i < KILLER_MAX; i++)
593 killers[i] = MOVE_NONE;
598 // id_loop() is the main iterative deepening loop. It calls root_search
599 // repeatedly with increasing depth until the allocated thinking time has
600 // been consumed, the user stops the search, or the maximum search depth is
603 Value id_loop(const Position& pos, Move searchMoves[]) {
606 SearchStack ss[PLY_MAX_PLUS_2];
607 Move EasyMove = MOVE_NONE;
608 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
610 // Moves to search are verified, copied, scored and sorted
611 RootMoveList rml(p, searchMoves);
613 // Handle special case of searching on a mate/stale position
614 if (rml.move_count() == 0)
617 wait_for_stop_or_ponderhit();
619 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
622 // Print RootMoveList startup scoring to the standard output,
623 // so to output information also for iteration 1.
624 cout << "info depth " << 1
625 << "\ninfo depth " << 1
626 << " score " << value_to_string(rml.get_move_score(0))
627 << " time " << current_search_time()
628 << " nodes " << TM.nodes_searched()
630 << " pv " << rml.get_move(0) << "\n";
636 ValueByIteration[1] = rml.get_move_score(0);
639 // Is one move significantly better than others after initial scoring ?
640 if ( rml.move_count() == 1
641 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
642 EasyMove = rml.get_move(0);
644 // Iterative deepening loop
645 while (Iteration < PLY_MAX)
647 // Initialize iteration
649 BestMoveChangesByIteration[Iteration] = 0;
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
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[0].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[0].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[0].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[0].pv[0] == MOVE_NONE)
749 ss[0].pv[0] = rml.get_move(0);
750 ss[0].pv[1] = MOVE_NONE;
753 assert(ss[0].pv[0] != MOVE_NONE);
755 cout << "bestmove " << ss[0].pv[0];
757 if (ss[0].pv[1] != MOVE_NONE)
758 cout << " ponder " << ss[0].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[0].pv[0]);
775 p.do_move(ss[0].pv[0], st);
776 LogFile << "\nPonder move: "
777 << move_to_san(p, ss[0].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& oldAlpha, Value& beta) {
795 Depth depth, ext, newDepth;
797 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
798 int researchCount = 0;
801 isCheck = pos.is_check();
803 // Evaluate the position statically
804 ss[0].eval = !isCheck ? evaluate(pos, ei, 0) : VALUE_NONE;
806 while (1) // Fail low loop
808 // Sort the moves before to (re)search
811 // Loop through all the moves in the root move list
812 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
814 // This is used by time management and starts from 1
815 RootMoveNumber = i + 1;
817 // Save the current node count before the move is searched
818 nodes = TM.nodes_searched();
820 // Reset beta cut-off counters
821 TM.resetBetaCounters();
823 // Pick the next root move, and print the move and the move number to
824 // the standard output.
825 move = ss[0].currentMove = rml.get_move(i);
827 if (current_search_time() >= 1000)
828 cout << "info currmove " << move
829 << " currmovenumber " << RootMoveNumber << endl;
831 // Decide search depth for this move
832 moveIsCheck = pos.move_is_check(move);
833 captureOrPromotion = pos.move_is_capture_or_promotion(move);
834 depth = (Iteration - 2) * OnePly + InitialDepth;
835 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
836 newDepth = depth + ext;
838 // Reset value before the search
839 value = - VALUE_INFINITE;
841 while (1) // Fail high loop
843 // Make the move, and search it
844 pos.do_move(move, st, ci, moveIsCheck);
846 if (i < MultiPV || value > alpha)
848 // Aspiration window is disabled in multi-pv case
850 alpha = -VALUE_INFINITE;
852 // Full depth PV search, done on first move or after a fail high
853 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
857 // Try to reduce non-pv search depth by one ply if move seems not problematic,
858 // if the move fails high will be re-searched at full depth.
859 bool doFullDepthSearch = true;
861 if ( depth >= 3 * OnePly // FIXME was newDepth
863 && !captureOrPromotion
864 && !move_is_castle(move))
866 ss[0].reduction = pv_reduction(depth, i - MultiPV + 2);
869 // Reduced depth non-pv search using alpha as upperbound
870 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
871 doFullDepthSearch = (value > alpha);
875 if (doFullDepthSearch)
877 // Full depth non-pv search using alpha as upperbound
878 ss[0].reduction = Depth(0);
879 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
881 // If we are above alpha then research at same depth but as PV
882 // to get a correct score or eventually a fail high above beta.
884 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
890 // Can we exit fail high loop ?
891 if (AbortSearch || value < beta)
894 // We are failing high and going to do a research. It's important to update
895 // the score before research in case we run out of time while researching.
896 rml.set_move_score(i, value);
898 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
899 rml.set_move_pv(i, ss[0].pv);
901 // Print information to the standard output
902 print_pv_info(pos, ss, alpha, beta, value);
904 // Prepare for a research after a fail high, each time with a wider window
906 beta = Min(beta + AspirationDelta * (1 << researchCount), VALUE_INFINITE);
908 } // End of fail high loop
910 // Finished searching the move. If AbortSearch is true, the search
911 // was aborted because the user interrupted the search or because we
912 // ran out of time. In this case, the return value of the search cannot
913 // be trusted, and we break out of the loop without updating the best
918 // Remember beta-cutoff and searched nodes counts for this move. The
919 // info is used to sort the root moves for the next iteration.
921 TM.get_beta_counters(pos.side_to_move(), our, their);
922 rml.set_beta_counters(i, our, their);
923 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
925 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
927 if (value <= alpha && i >= MultiPV)
928 rml.set_move_score(i, -VALUE_INFINITE);
931 // PV move or new best move!
934 rml.set_move_score(i, value);
936 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
937 rml.set_move_pv(i, ss[0].pv);
941 // We record how often the best move has been changed in each
942 // iteration. This information is used for time managment: When
943 // the best move changes frequently, we allocate some more time.
945 BestMoveChangesByIteration[Iteration]++;
947 // Print information to the standard output
948 print_pv_info(pos, ss, alpha, beta, value);
950 // Raise alpha to setup proper non-pv search upper bound, note
951 // that we can end up with alpha >= beta and so get a fail high.
958 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
960 cout << "info multipv " << j + 1
961 << " score " << value_to_string(rml.get_move_score(j))
962 << " depth " << (j <= i ? Iteration : Iteration - 1)
963 << " time " << current_search_time()
964 << " nodes " << TM.nodes_searched()
968 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
969 cout << rml.get_move_pv(j, k) << " ";
973 alpha = rml.get_move_score(Min(i, MultiPV - 1));
975 } // PV move or new best move
977 assert(alpha >= oldAlpha);
979 AspirationFailLow = (alpha == oldAlpha);
981 if (AspirationFailLow && StopOnPonderhit)
982 StopOnPonderhit = false;
985 // Can we exit fail low loop ?
986 if (AbortSearch || alpha > oldAlpha)
989 // Prepare for a research after a fail low, each time with a wider window
991 alpha = Max(alpha - AspirationDelta * (1 << researchCount), -VALUE_INFINITE);
996 // Sort the moves before to return
1003 // search_pv() is the main search function for PV nodes.
1005 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1006 Depth depth, int ply, int threadID) {
1008 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1009 assert(beta > alpha && beta <= VALUE_INFINITE);
1010 assert(ply >= 0 && ply < PLY_MAX);
1011 assert(threadID >= 0 && threadID < TM.active_threads());
1013 Move movesSearched[256];
1018 Depth ext, newDepth;
1019 Value bestValue, value, oldAlpha;
1020 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1021 bool mateThreat = false;
1023 bestValue = value = -VALUE_INFINITE;
1026 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1028 // Step 1. Initialize node and poll
1029 // Polling can abort search.
1030 init_node(ss, ply, threadID);
1032 // Step 2. Check for aborted search and immediate draw
1033 if (AbortSearch || TM.thread_should_stop(threadID))
1036 if (pos.is_draw() || ply >= PLY_MAX - 1)
1039 // Step 3. Mate distance pruning
1041 alpha = Max(value_mated_in(ply), alpha);
1042 beta = Min(value_mate_in(ply+1), beta);
1046 // Step 4. Transposition table lookup
1047 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1048 // This is to avoid problems in the following areas:
1050 // * Repetition draw detection
1051 // * Fifty move rule detection
1052 // * Searching for a mate
1053 // * Printing of full PV line
1054 tte = TT.retrieve(pos.get_key());
1055 ttMove = (tte ? tte->move() : MOVE_NONE);
1057 // Step 5. Evaluate the position statically
1058 // At PV nodes we do this only to update gain statistics
1059 isCheck = pos.is_check();
1062 ss[ply].eval = evaluate(pos, ei, threadID);
1063 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1066 // Step 6. Razoring (is omitted in PV nodes)
1067 // Step 7. Static null move pruning (is omitted in PV nodes)
1068 // Step 8. Null move search with verification search (is omitted in PV nodes)
1070 // Step 9. Internal iterative deepening
1071 if ( depth >= IIDDepthAtPVNodes
1072 && ttMove == MOVE_NONE)
1074 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1075 ttMove = ss[ply].pv[ply];
1076 tte = TT.retrieve(pos.get_key());
1079 // Step 10. Loop through moves
1080 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1082 // Initialize a MovePicker object for the current position
1083 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1084 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1087 while ( alpha < beta
1088 && (move = mp.get_next_move()) != MOVE_NONE
1089 && !TM.thread_should_stop(threadID))
1091 assert(move_is_ok(move));
1093 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1094 moveIsCheck = pos.move_is_check(move, ci);
1095 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1097 // Step 11. Decide the new search depth
1098 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1100 // Singular extension search. We extend the TT move if its value is much better than
1101 // its siblings. To verify this we do a reduced search on all the other moves but the
1102 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1103 if ( depth >= SingularExtensionDepthAtPVNodes
1105 && move == tte->move()
1107 && is_lower_bound(tte->type())
1108 && tte->depth() >= depth - 3 * OnePly)
1110 Value ttValue = value_from_tt(tte->value(), ply);
1112 if (abs(ttValue) < VALUE_KNOWN_WIN)
1114 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1116 if (excValue < ttValue - SingularExtensionMargin)
1121 newDepth = depth - OnePly + ext;
1123 // Update current move (this must be done after singular extension search)
1124 movesSearched[moveCount++] = ss[ply].currentMove = move;
1126 // Step 12. Futility pruning (is omitted in PV nodes)
1128 // Step 13. Make the move
1129 pos.do_move(move, st, ci, moveIsCheck);
1131 // Step extra. pv search (only in PV nodes)
1132 // The first move in list is the expected PV
1134 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1137 // Step 14. Reduced search
1138 // if the move fails high will be re-searched at full depth.
1139 bool doFullDepthSearch = true;
1141 if ( depth >= 3 * OnePly
1143 && !captureOrPromotion
1144 && !move_is_castle(move)
1145 && !move_is_killer(move, ss[ply]))
1147 ss[ply].reduction = pv_reduction(depth, moveCount);
1148 if (ss[ply].reduction)
1150 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1151 doFullDepthSearch = (value > alpha);
1155 // Step 15. Full depth search
1156 if (doFullDepthSearch)
1158 ss[ply].reduction = Depth(0);
1159 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1161 // Step extra. pv search (only in PV nodes)
1162 if (value > alpha && value < beta)
1163 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1167 // Step 16. Undo move
1168 pos.undo_move(move);
1170 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1172 // Step 17. Check for new best move
1173 if (value > bestValue)
1180 if (value == value_mate_in(ply + 1))
1181 ss[ply].mateKiller = move;
1185 // Step 18. Check for split
1186 if ( TM.active_threads() > 1
1188 && depth >= MinimumSplitDepth
1190 && TM.available_thread_exists(threadID)
1192 && !TM.thread_should_stop(threadID)
1193 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1194 depth, &moveCount, &mp, threadID, true))
1198 // Step 19. Check for mate and stalemate
1199 // All legal moves have been searched and if there were
1200 // no legal moves, it must be mate or stalemate.
1202 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1204 // Step 20. Update tables
1205 // If the search is not aborted, update the transposition table,
1206 // history counters, and killer moves.
1207 if (AbortSearch || TM.thread_should_stop(threadID))
1210 if (bestValue <= oldAlpha)
1211 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1213 else if (bestValue >= beta)
1215 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1216 move = ss[ply].pv[ply];
1217 if (!pos.move_is_capture_or_promotion(move))
1219 update_history(pos, move, depth, movesSearched, moveCount);
1220 update_killers(move, ss[ply]);
1222 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1225 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1231 // search() is the search function for zero-width nodes.
1233 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1234 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1236 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1237 assert(ply >= 0 && ply < PLY_MAX);
1238 assert(threadID >= 0 && threadID < TM.active_threads());
1240 Move movesSearched[256];
1245 Depth ext, newDepth;
1246 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1247 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1248 bool mateThreat = false;
1250 refinedValue = bestValue = value = -VALUE_INFINITE;
1253 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1255 // Step 1. Initialize node and poll
1256 // Polling can abort search.
1257 init_node(ss, ply, threadID);
1259 // Step 2. Check for aborted search and immediate draw
1260 if (AbortSearch || TM.thread_should_stop(threadID))
1263 if (pos.is_draw() || ply >= PLY_MAX - 1)
1266 // Step 3. Mate distance pruning
1267 if (value_mated_in(ply) >= beta)
1270 if (value_mate_in(ply + 1) < beta)
1273 // Step 4. Transposition table lookup
1275 // We don't want the score of a partial search to overwrite a previous full search
1276 // TT value, so we use a different position key in case of an excluded move exists.
1277 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1279 tte = TT.retrieve(posKey);
1280 ttMove = (tte ? tte->move() : MOVE_NONE);
1282 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1284 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1285 return value_from_tt(tte->value(), ply);
1288 // Step 5. Evaluate the position statically
1289 isCheck = pos.is_check();
1293 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1294 ss[ply].eval = value_from_tt(tte->value(), ply);
1296 ss[ply].eval = evaluate(pos, ei, threadID);
1298 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1299 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1303 if ( !value_is_mate(beta)
1305 && depth < RazorDepth
1306 && refinedValue < beta - razor_margin(depth)
1307 && ss[ply - 1].currentMove != MOVE_NULL
1308 && ttMove == MOVE_NONE
1309 && !pos.has_pawn_on_7th(pos.side_to_move()))
1311 Value rbeta = beta - razor_margin(depth);
1312 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1314 return v; //FIXME: Logically should be: return (v + razor_margin(depth));
1317 // Step 7. Static null move pruning
1318 // We're betting that the opponent doesn't have a move that will reduce
1319 // the score by more than fuility_margin(depth) if we do a null move.
1322 && depth < RazorDepth
1323 && refinedValue - futility_margin(depth, 0) >= beta)
1324 return refinedValue - futility_margin(depth, 0);
1326 // Step 8. Null move search with verification search
1327 // When we jump directly to qsearch() we do a null move only if static value is
1328 // at least beta. Otherwise we do a null move if static value is not more than
1329 // NullMoveMargin under beta.
1333 && !value_is_mate(beta)
1334 && ok_to_do_nullmove(pos)
1335 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1337 ss[ply].currentMove = MOVE_NULL;
1339 pos.do_null_move(st);
1341 // Null move dynamic reduction based on depth
1342 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1344 // Null move dynamic reduction based on value
1345 if (refinedValue - beta > PawnValueMidgame)
1348 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1350 pos.undo_null_move();
1352 if (nullValue >= beta)
1354 if (depth < 6 * OnePly)
1357 // Do zugzwang verification search
1358 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1362 // The null move failed low, which means that we may be faced with
1363 // some kind of threat. If the previous move was reduced, check if
1364 // the move that refuted the null move was somehow connected to the
1365 // move which was reduced. If a connection is found, return a fail
1366 // low score (which will cause the reduced move to fail high in the
1367 // parent node, which will trigger a re-search with full depth).
1368 if (nullValue == value_mated_in(ply + 2))
1371 ss[ply].threatMove = ss[ply + 1].currentMove;
1372 if ( depth < ThreatDepth
1373 && ss[ply - 1].reduction
1374 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1379 // Step 9. Internal iterative deepening
1380 if ( depth >= IIDDepthAtNonPVNodes
1381 && ttMove == MOVE_NONE
1383 && ss[ply].eval >= beta - IIDMargin)
1385 search(pos, ss, beta, depth/2, ply, false, threadID);
1386 ttMove = ss[ply].pv[ply];
1387 tte = TT.retrieve(posKey);
1390 // Step 10. Loop through moves
1391 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1393 // Initialize a MovePicker object for the current position
1394 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1397 while ( bestValue < beta
1398 && (move = mp.get_next_move()) != MOVE_NONE
1399 && !TM.thread_should_stop(threadID))
1401 assert(move_is_ok(move));
1403 if (move == excludedMove)
1406 moveIsCheck = pos.move_is_check(move, ci);
1407 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1408 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1410 // Step 11. Decide the new search depth
1411 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1413 // Singular extension search. We extend the TT move if its value is much better than
1414 // its siblings. To verify this we do a reduced search on all the other moves but the
1415 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1416 if ( depth >= SingularExtensionDepthAtNonPVNodes
1418 && move == tte->move()
1419 && !excludedMove // Do not allow recursive single-reply search
1421 && is_lower_bound(tte->type())
1422 && tte->depth() >= depth - 3 * OnePly)
1424 Value ttValue = value_from_tt(tte->value(), ply);
1426 if (abs(ttValue) < VALUE_KNOWN_WIN)
1428 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1430 if (excValue < ttValue - SingularExtensionMargin)
1435 newDepth = depth - OnePly + ext;
1437 // Update current move (this must be done after singular extension search)
1438 movesSearched[moveCount++] = ss[ply].currentMove = move;
1440 // Step 12. Futility pruning
1443 && !captureOrPromotion
1444 && !move_is_castle(move)
1447 // Move count based pruning
1448 if ( moveCount >= futility_move_count(depth)
1449 && ok_to_prune(pos, move, ss[ply].threatMove)
1450 && bestValue > value_mated_in(PLY_MAX))
1453 // Value based pruning
1454 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1455 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1456 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1458 if (futilityValueScaled < beta)
1460 if (futilityValueScaled > bestValue)
1461 bestValue = futilityValueScaled;
1466 // Step 13. Make the move
1467 pos.do_move(move, st, ci, moveIsCheck);
1469 // Step 14. Reduced search
1470 // if the move fails high will be re-searched at full depth.
1471 bool doFullDepthSearch = true;
1473 if ( depth >= 3*OnePly
1475 && !captureOrPromotion
1476 && !move_is_castle(move)
1477 && !move_is_killer(move, ss[ply]))
1479 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1480 if (ss[ply].reduction)
1482 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1483 doFullDepthSearch = (value >= beta);
1487 // Step 15. Full depth search
1488 if (doFullDepthSearch)
1490 ss[ply].reduction = Depth(0);
1491 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1494 // Step 16. Undo move
1495 pos.undo_move(move);
1497 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1499 // Step 17. Check for new best move
1500 if (value > bestValue)
1506 if (value == value_mate_in(ply + 1))
1507 ss[ply].mateKiller = move;
1510 // Step 18. Check for split
1511 if ( TM.active_threads() > 1
1513 && depth >= MinimumSplitDepth
1515 && TM.available_thread_exists(threadID)
1517 && !TM.thread_should_stop(threadID)
1518 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1519 depth, &moveCount, &mp, threadID, false))
1523 // Step 19. Check for mate and stalemate
1524 // All legal moves have been searched and if there were
1525 // no legal moves, it must be mate or stalemate.
1526 // If one move was excluded return fail low.
1528 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1530 // Step 20. Update tables
1531 // If the search is not aborted, update the transposition table,
1532 // history counters, and killer moves.
1533 if (AbortSearch || TM.thread_should_stop(threadID))
1536 if (bestValue < beta)
1537 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1540 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1541 move = ss[ply].pv[ply];
1542 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1543 if (!pos.move_is_capture_or_promotion(move))
1545 update_history(pos, move, depth, movesSearched, moveCount);
1546 update_killers(move, ss[ply]);
1551 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1557 // qsearch() is the quiescence search function, which is called by the main
1558 // search function when the remaining depth is zero (or, to be more precise,
1559 // less than OnePly).
1561 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1562 Depth depth, int ply, int threadID) {
1564 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1565 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1567 assert(ply >= 0 && ply < PLY_MAX);
1568 assert(threadID >= 0 && threadID < TM.active_threads());
1573 Value staticValue, bestValue, value, futilityBase, futilityValue;
1574 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1575 const TTEntry* tte = NULL;
1577 bool pvNode = (beta - alpha != 1);
1578 Value oldAlpha = alpha;
1580 // Initialize, and make an early exit in case of an aborted search,
1581 // an instant draw, maximum ply reached, etc.
1582 init_node(ss, ply, threadID);
1584 // After init_node() that calls poll()
1585 if (AbortSearch || TM.thread_should_stop(threadID))
1588 if (pos.is_draw() || ply >= PLY_MAX - 1)
1591 // Transposition table lookup. At PV nodes, we don't use the TT for
1592 // pruning, but only for move ordering.
1593 tte = TT.retrieve(pos.get_key());
1594 ttMove = (tte ? tte->move() : MOVE_NONE);
1596 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1598 assert(tte->type() != VALUE_TYPE_EVAL);
1600 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1601 return value_from_tt(tte->value(), ply);
1604 isCheck = pos.is_check();
1606 // Evaluate the position statically
1608 staticValue = -VALUE_INFINITE;
1609 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1610 staticValue = value_from_tt(tte->value(), ply);
1612 staticValue = evaluate(pos, ei, threadID);
1616 ss[ply].eval = staticValue;
1617 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1620 // Initialize "stand pat score", and return it immediately if it is
1622 bestValue = staticValue;
1624 if (bestValue >= beta)
1626 // Store the score to avoid a future costly evaluation() call
1627 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1628 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1633 if (bestValue > alpha)
1636 // If we are near beta then try to get a cutoff pushing checks a bit further
1637 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1639 // Initialize a MovePicker object for the current position, and prepare
1640 // to search the moves. Because the depth is <= 0 here, only captures,
1641 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1642 // and we are near beta) will be generated.
1643 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1645 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1646 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1648 // Loop through the moves until no moves remain or a beta cutoff
1650 while ( alpha < beta
1651 && (move = mp.get_next_move()) != MOVE_NONE)
1653 assert(move_is_ok(move));
1655 moveIsCheck = pos.move_is_check(move, ci);
1657 // Update current move
1659 ss[ply].currentMove = move;
1667 && !move_is_promotion(move)
1668 && !pos.move_is_passed_pawn_push(move))
1670 futilityValue = futilityBase
1671 + pos.endgame_value_of_piece_on(move_to(move))
1672 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1674 if (futilityValue < alpha)
1676 if (futilityValue > bestValue)
1677 bestValue = futilityValue;
1682 // Detect blocking evasions that are candidate to be pruned
1683 evasionPrunable = isCheck
1684 && bestValue != -VALUE_INFINITE
1685 && !pos.move_is_capture(move)
1686 && pos.type_of_piece_on(move_from(move)) != KING
1687 && !pos.can_castle(pos.side_to_move());
1689 // Don't search moves with negative SEE values
1690 if ( (!isCheck || evasionPrunable)
1693 && !move_is_promotion(move)
1694 && pos.see_sign(move) < 0)
1697 // Make and search the move
1698 pos.do_move(move, st, ci, moveIsCheck);
1699 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1700 pos.undo_move(move);
1702 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1705 if (value > bestValue)
1716 // All legal moves have been searched. A special case: If we're in check
1717 // and no legal moves were found, it is checkmate.
1718 if (!moveCount && pos.is_check()) // Mate!
1719 return value_mated_in(ply);
1721 // Update transposition table
1722 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1723 if (bestValue <= oldAlpha)
1725 // If bestValue isn't changed it means it is still the static evaluation
1726 // of the node, so keep this info to avoid a future evaluation() call.
1727 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1728 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1730 else if (bestValue >= beta)
1732 move = ss[ply].pv[ply];
1733 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1735 // Update killers only for good checking moves
1736 if (!pos.move_is_capture_or_promotion(move))
1737 update_killers(move, ss[ply]);
1740 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1742 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1748 // sp_search() is used to search from a split point. This function is called
1749 // by each thread working at the split point. It is similar to the normal
1750 // search() function, but simpler. Because we have already probed the hash
1751 // table, done a null move search, and searched the first move before
1752 // splitting, we don't have to repeat all this work in sp_search(). We
1753 // also don't need to store anything to the hash table here: This is taken
1754 // care of after we return from the split point.
1755 // FIXME: We are currently ignoring mateThreat flag here
1757 void sp_search(SplitPoint* sp, int threadID) {
1759 assert(threadID >= 0 && threadID < TM.active_threads());
1760 assert(TM.active_threads() > 1);
1764 Depth ext, newDepth;
1765 Value value, futilityValueScaled;
1766 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1768 value = -VALUE_INFINITE;
1770 Position pos(*sp->pos);
1772 SearchStack* ss = sp->sstack[threadID];
1773 isCheck = pos.is_check();
1775 // Step 10. Loop through moves
1776 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1777 lock_grab(&(sp->lock));
1779 while ( sp->bestValue < sp->beta
1780 && !TM.thread_should_stop(threadID)
1781 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1783 moveCount = ++sp->moves;
1784 lock_release(&(sp->lock));
1786 assert(move_is_ok(move));
1788 moveIsCheck = pos.move_is_check(move, ci);
1789 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1791 // Step 11. Decide the new search depth
1792 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1793 newDepth = sp->depth - OnePly + ext;
1795 // Update current move
1796 ss[sp->ply].currentMove = move;
1798 // Step 12. Futility pruning
1801 && !captureOrPromotion
1802 && !move_is_castle(move))
1804 // Move count based pruning
1805 if ( moveCount >= futility_move_count(sp->depth)
1806 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1807 && sp->bestValue > value_mated_in(PLY_MAX))
1809 lock_grab(&(sp->lock));
1813 // Value based pruning
1814 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1815 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1816 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1818 if (futilityValueScaled < sp->beta)
1820 lock_grab(&(sp->lock));
1822 if (futilityValueScaled > sp->bestValue)
1823 sp->bestValue = futilityValueScaled;
1828 // Step 13. Make the move
1829 pos.do_move(move, st, ci, moveIsCheck);
1831 // Step 14. Reduced search
1832 // if the move fails high will be re-searched at full depth.
1833 bool doFullDepthSearch = true;
1836 && !captureOrPromotion
1837 && !move_is_castle(move)
1838 && !move_is_killer(move, ss[sp->ply]))
1840 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1841 if (ss[sp->ply].reduction)
1843 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1844 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1848 // Step 15. Full depth search
1849 if (doFullDepthSearch)
1851 ss[sp->ply].reduction = Depth(0);
1852 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1855 // Step 16. Undo move
1856 pos.undo_move(move);
1858 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1860 // Step 17. Check for new best move
1861 lock_grab(&(sp->lock));
1863 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1865 sp->bestValue = value;
1866 if (sp->bestValue >= sp->beta)
1868 sp->stopRequest = true;
1869 sp_update_pv(sp->parentSstack, ss, sp->ply);
1874 /* Here we have the lock still grabbed */
1876 sp->slaves[threadID] = 0;
1879 lock_release(&(sp->lock));
1883 // sp_search_pv() is used to search from a PV split point. This function
1884 // is called by each thread working at the split point. It is similar to
1885 // the normal search_pv() function, but simpler. Because we have already
1886 // probed the hash table and searched the first move before splitting, we
1887 // don't have to repeat all this work in sp_search_pv(). We also don't
1888 // need to store anything to the hash table here: This is taken care of
1889 // after we return from the split point.
1890 // FIXME: We are ignoring mateThreat flag!
1892 void sp_search_pv(SplitPoint* sp, int threadID) {
1894 assert(threadID >= 0 && threadID < TM.active_threads());
1895 assert(TM.active_threads() > 1);
1899 Depth ext, newDepth;
1901 bool moveIsCheck, captureOrPromotion, dangerous;
1903 value = -VALUE_INFINITE;
1905 Position pos(*sp->pos);
1907 SearchStack* ss = sp->sstack[threadID];
1909 // Step 10. Loop through moves
1910 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1911 lock_grab(&(sp->lock));
1913 while ( sp->alpha < sp->beta
1914 && !TM.thread_should_stop(threadID)
1915 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1917 moveCount = ++sp->moves;
1918 lock_release(&(sp->lock));
1920 assert(move_is_ok(move));
1922 moveIsCheck = pos.move_is_check(move, ci);
1923 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1925 // Step 11. Decide the new search depth
1926 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1927 newDepth = sp->depth - OnePly + ext;
1929 // Update current move
1930 ss[sp->ply].currentMove = move;
1932 // Step 12. Futility pruning (is omitted in PV nodes)
1934 // Step 13. Make the move
1935 pos.do_move(move, st, ci, moveIsCheck);
1937 // Step 14. Reduced search
1938 // if the move fails high will be re-searched at full depth.
1939 bool doFullDepthSearch = true;
1942 && !captureOrPromotion
1943 && !move_is_castle(move)
1944 && !move_is_killer(move, ss[sp->ply]))
1946 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1947 if (ss[sp->ply].reduction)
1949 Value localAlpha = sp->alpha;
1950 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1951 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1955 // Step 15. Full depth search
1956 if (doFullDepthSearch)
1958 Value localAlpha = sp->alpha;
1959 ss[sp->ply].reduction = Depth(0);
1960 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1962 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1964 // If another thread has failed high then sp->alpha has been increased
1965 // to be higher or equal then beta, if so, avoid to start a PV search.
1966 localAlpha = sp->alpha;
1967 if (localAlpha < sp->beta)
1968 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1972 // Step 16. Undo move
1973 pos.undo_move(move);
1975 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1977 // Step 17. Check for new best move
1978 lock_grab(&(sp->lock));
1980 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1982 sp->bestValue = value;
1983 if (value > sp->alpha)
1985 // Ask threads to stop before to modify sp->alpha
1986 if (value >= sp->beta)
1987 sp->stopRequest = true;
1991 sp_update_pv(sp->parentSstack, ss, sp->ply);
1992 if (value == value_mate_in(sp->ply + 1))
1993 ss[sp->ply].mateKiller = move;
1998 /* Here we have the lock still grabbed */
2000 sp->slaves[threadID] = 0;
2003 lock_release(&(sp->lock));
2007 // init_node() is called at the beginning of all the search functions
2008 // (search(), search_pv(), qsearch(), and so on) and initializes the
2009 // search stack object corresponding to the current node. Once every
2010 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2011 // for user input and checks whether it is time to stop the search.
2013 void init_node(SearchStack ss[], int ply, int threadID) {
2015 assert(ply >= 0 && ply < PLY_MAX);
2016 assert(threadID >= 0 && threadID < TM.active_threads());
2018 TM.incrementNodeCounter(threadID);
2023 if (NodesSincePoll >= NodesBetweenPolls)
2030 ss[ply + 2].initKillers();
2034 // update_pv() is called whenever a search returns a value > alpha.
2035 // It updates the PV in the SearchStack object corresponding to the
2038 void update_pv(SearchStack ss[], int ply) {
2040 assert(ply >= 0 && ply < PLY_MAX);
2044 ss[ply].pv[ply] = ss[ply].currentMove;
2046 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2047 ss[ply].pv[p] = ss[ply + 1].pv[p];
2049 ss[ply].pv[p] = MOVE_NONE;
2053 // sp_update_pv() is a variant of update_pv for use at split points. The
2054 // difference between the two functions is that sp_update_pv also updates
2055 // the PV at the parent node.
2057 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2059 assert(ply >= 0 && ply < PLY_MAX);
2063 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2065 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2066 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2068 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2072 // connected_moves() tests whether two moves are 'connected' in the sense
2073 // that the first move somehow made the second move possible (for instance
2074 // if the moving piece is the same in both moves). The first move is assumed
2075 // to be the move that was made to reach the current position, while the
2076 // second move is assumed to be a move from the current position.
2078 bool connected_moves(const Position& pos, Move m1, Move m2) {
2080 Square f1, t1, f2, t2;
2083 assert(move_is_ok(m1));
2084 assert(move_is_ok(m2));
2086 if (m2 == MOVE_NONE)
2089 // Case 1: The moving piece is the same in both moves
2095 // Case 2: The destination square for m2 was vacated by m1
2101 // Case 3: Moving through the vacated square
2102 if ( piece_is_slider(pos.piece_on(f2))
2103 && bit_is_set(squares_between(f2, t2), f1))
2106 // Case 4: The destination square for m2 is defended by the moving piece in m1
2107 p = pos.piece_on(t1);
2108 if (bit_is_set(pos.attacks_from(p, t1), t2))
2111 // Case 5: Discovered check, checking piece is the piece moved in m1
2112 if ( piece_is_slider(p)
2113 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2114 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2116 // discovered_check_candidates() works also if the Position's side to
2117 // move is the opposite of the checking piece.
2118 Color them = opposite_color(pos.side_to_move());
2119 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2121 if (bit_is_set(dcCandidates, f2))
2128 // value_is_mate() checks if the given value is a mate one
2129 // eventually compensated for the ply.
2131 bool value_is_mate(Value value) {
2133 assert(abs(value) <= VALUE_INFINITE);
2135 return value <= value_mated_in(PLY_MAX)
2136 || value >= value_mate_in(PLY_MAX);
2140 // move_is_killer() checks if the given move is among the
2141 // killer moves of that ply.
2143 bool move_is_killer(Move m, const SearchStack& ss) {
2145 const Move* k = ss.killers;
2146 for (int i = 0; i < KILLER_MAX; i++, k++)
2154 // extension() decides whether a move should be searched with normal depth,
2155 // or with extended depth. Certain classes of moves (checking moves, in
2156 // particular) are searched with bigger depth than ordinary moves and in
2157 // any case are marked as 'dangerous'. Note that also if a move is not
2158 // extended, as example because the corresponding UCI option is set to zero,
2159 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2161 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2162 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2164 assert(m != MOVE_NONE);
2166 Depth result = Depth(0);
2167 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2172 result += CheckExtension[pvNode];
2175 result += SingleEvasionExtension[pvNode];
2178 result += MateThreatExtension[pvNode];
2181 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2183 Color c = pos.side_to_move();
2184 if (relative_rank(c, move_to(m)) == RANK_7)
2186 result += PawnPushTo7thExtension[pvNode];
2189 if (pos.pawn_is_passed(c, move_to(m)))
2191 result += PassedPawnExtension[pvNode];
2196 if ( captureOrPromotion
2197 && pos.type_of_piece_on(move_to(m)) != PAWN
2198 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2199 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2200 && !move_is_promotion(m)
2203 result += PawnEndgameExtension[pvNode];
2208 && captureOrPromotion
2209 && pos.type_of_piece_on(move_to(m)) != PAWN
2210 && pos.see_sign(m) >= 0)
2216 return Min(result, OnePly);
2220 // ok_to_do_nullmove() looks at the current position and decides whether
2221 // doing a 'null move' should be allowed. In order to avoid zugzwang
2222 // problems, null moves are not allowed when the side to move has very
2223 // little material left. Currently, the test is a bit too simple: Null
2224 // moves are avoided only when the side to move has only pawns left.
2225 // It's probably a good idea to avoid null moves in at least some more
2226 // complicated endgames, e.g. KQ vs KR. FIXME
2228 bool ok_to_do_nullmove(const Position& pos) {
2230 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2234 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2235 // non-tactical moves late in the move list close to the leaves are
2236 // candidates for pruning.
2238 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2240 assert(move_is_ok(m));
2241 assert(threat == MOVE_NONE || move_is_ok(threat));
2242 assert(!pos.move_is_check(m));
2243 assert(!pos.move_is_capture_or_promotion(m));
2244 assert(!pos.move_is_passed_pawn_push(m));
2246 Square mfrom, mto, tfrom, tto;
2248 // Prune if there isn't any threat move
2249 if (threat == MOVE_NONE)
2252 mfrom = move_from(m);
2254 tfrom = move_from(threat);
2255 tto = move_to(threat);
2257 // Case 1: Don't prune moves which move the threatened piece
2261 // Case 2: If the threatened piece has value less than or equal to the
2262 // value of the threatening piece, don't prune move which defend it.
2263 if ( pos.move_is_capture(threat)
2264 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2265 || pos.type_of_piece_on(tfrom) == KING)
2266 && pos.move_attacks_square(m, tto))
2269 // Case 3: If the moving piece in the threatened move is a slider, don't
2270 // prune safe moves which block its ray.
2271 if ( piece_is_slider(pos.piece_on(tfrom))
2272 && bit_is_set(squares_between(tfrom, tto), mto)
2273 && pos.see_sign(m) >= 0)
2280 // ok_to_use_TT() returns true if a transposition table score
2281 // can be used at a given point in search.
2283 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2285 Value v = value_from_tt(tte->value(), ply);
2287 return ( tte->depth() >= depth
2288 || v >= Max(value_mate_in(PLY_MAX), beta)
2289 || v < Min(value_mated_in(PLY_MAX), beta))
2291 && ( (is_lower_bound(tte->type()) && v >= beta)
2292 || (is_upper_bound(tte->type()) && v < beta));
2296 // refine_eval() returns the transposition table score if
2297 // possible otherwise falls back on static position evaluation.
2299 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2304 Value v = value_from_tt(tte->value(), ply);
2306 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2307 || (is_upper_bound(tte->type()) && v < defaultEval))
2314 // update_history() registers a good move that produced a beta-cutoff
2315 // in history and marks as failures all the other moves of that ply.
2317 void update_history(const Position& pos, Move move, Depth depth,
2318 Move movesSearched[], int moveCount) {
2322 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2324 for (int i = 0; i < moveCount - 1; i++)
2326 m = movesSearched[i];
2330 if (!pos.move_is_capture_or_promotion(m))
2331 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2336 // update_killers() add a good move that produced a beta-cutoff
2337 // among the killer moves of that ply.
2339 void update_killers(Move m, SearchStack& ss) {
2341 if (m == ss.killers[0])
2344 for (int i = KILLER_MAX - 1; i > 0; i--)
2345 ss.killers[i] = ss.killers[i - 1];
2351 // update_gains() updates the gains table of a non-capture move given
2352 // the static position evaluation before and after the move.
2354 void update_gains(const Position& pos, Move m, Value before, Value after) {
2357 && before != VALUE_NONE
2358 && after != VALUE_NONE
2359 && pos.captured_piece() == NO_PIECE_TYPE
2360 && !move_is_castle(m)
2361 && !move_is_promotion(m))
2362 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2366 // current_search_time() returns the number of milliseconds which have passed
2367 // since the beginning of the current search.
2369 int current_search_time() {
2371 return get_system_time() - SearchStartTime;
2375 // nps() computes the current nodes/second count.
2379 int t = current_search_time();
2380 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2384 // poll() performs two different functions: It polls for user input, and it
2385 // looks at the time consumed so far and decides if it's time to abort the
2388 void poll(SearchStack ss[], int ply) {
2390 static int lastInfoTime;
2391 int t = current_search_time();
2396 // We are line oriented, don't read single chars
2397 std::string command;
2399 if (!std::getline(std::cin, command))
2402 if (command == "quit")
2405 PonderSearch = false;
2409 else if (command == "stop")
2412 PonderSearch = false;
2414 else if (command == "ponderhit")
2418 // Print search information
2422 else if (lastInfoTime > t)
2423 // HACK: Must be a new search where we searched less than
2424 // NodesBetweenPolls nodes during the first second of search.
2427 else if (t - lastInfoTime >= 1000)
2434 if (dbg_show_hit_rate)
2435 dbg_print_hit_rate();
2437 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2438 << " time " << t << " hashfull " << TT.full() << endl;
2440 // We only support current line printing in single thread mode
2441 if (ShowCurrentLine && TM.active_threads() == 1)
2443 cout << "info currline";
2444 for (int p = 0; p < ply; p++)
2445 cout << " " << ss[p].currentMove;
2451 // Should we stop the search?
2455 bool stillAtFirstMove = RootMoveNumber == 1
2456 && !AspirationFailLow
2457 && t > MaxSearchTime + ExtraSearchTime;
2459 bool noMoreTime = t > AbsoluteMaxSearchTime
2460 || stillAtFirstMove;
2462 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2463 || (ExactMaxTime && t >= ExactMaxTime)
2464 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2469 // ponderhit() is called when the program is pondering (i.e. thinking while
2470 // it's the opponent's turn to move) in order to let the engine know that
2471 // it correctly predicted the opponent's move.
2475 int t = current_search_time();
2476 PonderSearch = false;
2478 bool stillAtFirstMove = RootMoveNumber == 1
2479 && !AspirationFailLow
2480 && t > MaxSearchTime + ExtraSearchTime;
2482 bool noMoreTime = t > AbsoluteMaxSearchTime
2483 || stillAtFirstMove;
2485 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2490 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2492 void init_ss_array(SearchStack ss[]) {
2494 for (int i = 0; i < 3; i++)
2497 ss[i].initKillers();
2502 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2503 // while the program is pondering. The point is to work around a wrinkle in
2504 // the UCI protocol: When pondering, the engine is not allowed to give a
2505 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2506 // We simply wait here until one of these commands is sent, and return,
2507 // after which the bestmove and pondermove will be printed (in id_loop()).
2509 void wait_for_stop_or_ponderhit() {
2511 std::string command;
2515 if (!std::getline(std::cin, command))
2518 if (command == "quit")
2523 else if (command == "ponderhit" || command == "stop")
2529 // print_pv_info() prints to standard output and eventually to log file information on
2530 // the current PV line. It is called at each iteration or after a new pv is found.
2532 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2534 cout << "info depth " << Iteration
2535 << " score " << value_to_string(value)
2536 << ((value >= beta) ? " lowerbound" :
2537 ((value <= alpha)? " upperbound" : ""))
2538 << " time " << current_search_time()
2539 << " nodes " << TM.nodes_searched()
2543 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2544 cout << ss[0].pv[j] << " ";
2550 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2551 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2553 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2554 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2559 // init_thread() is the function which is called when a new thread is
2560 // launched. It simply calls the idle_loop() function with the supplied
2561 // threadID. There are two versions of this function; one for POSIX
2562 // threads and one for Windows threads.
2564 #if !defined(_MSC_VER)
2566 void* init_thread(void *threadID) {
2568 TM.idle_loop(*(int*)threadID, NULL);
2574 DWORD WINAPI init_thread(LPVOID threadID) {
2576 TM.idle_loop(*(int*)threadID, NULL);
2583 /// The ThreadsManager class
2585 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2586 // get_beta_counters() are getters/setters for the per thread
2587 // counters used to sort the moves at root.
2589 void ThreadsManager::resetNodeCounters() {
2591 for (int i = 0; i < MAX_THREADS; i++)
2592 threads[i].nodes = 0ULL;
2595 void ThreadsManager::resetBetaCounters() {
2597 for (int i = 0; i < MAX_THREADS; i++)
2598 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2601 int64_t ThreadsManager::nodes_searched() const {
2603 int64_t result = 0ULL;
2604 for (int i = 0; i < ActiveThreads; i++)
2605 result += threads[i].nodes;
2610 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2613 for (int i = 0; i < MAX_THREADS; i++)
2615 our += threads[i].betaCutOffs[us];
2616 their += threads[i].betaCutOffs[opposite_color(us)];
2621 // idle_loop() is where the threads are parked when they have no work to do.
2622 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2623 // object for which the current thread is the master.
2625 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2627 assert(threadID >= 0 && threadID < MAX_THREADS);
2631 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2632 // master should exit as last one.
2633 if (AllThreadsShouldExit)
2636 threads[threadID].state = THREAD_TERMINATED;
2640 // If we are not thinking, wait for a condition to be signaled
2641 // instead of wasting CPU time polling for work.
2642 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2645 assert(threadID != 0);
2646 threads[threadID].state = THREAD_SLEEPING;
2648 #if !defined(_MSC_VER)
2649 lock_grab(&WaitLock);
2650 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2651 pthread_cond_wait(&WaitCond, &WaitLock);
2652 lock_release(&WaitLock);
2654 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2658 // If thread has just woken up, mark it as available
2659 if (threads[threadID].state == THREAD_SLEEPING)
2660 threads[threadID].state = THREAD_AVAILABLE;
2662 // If this thread has been assigned work, launch a search
2663 if (threads[threadID].state == THREAD_WORKISWAITING)
2665 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2667 threads[threadID].state = THREAD_SEARCHING;
2669 if (threads[threadID].splitPoint->pvNode)
2670 sp_search_pv(threads[threadID].splitPoint, threadID);
2672 sp_search(threads[threadID].splitPoint, threadID);
2674 assert(threads[threadID].state == THREAD_SEARCHING);
2676 threads[threadID].state = THREAD_AVAILABLE;
2679 // If this thread is the master of a split point and all threads have
2680 // finished their work at this split point, return from the idle loop.
2681 if (waitSp != NULL && waitSp->cpus == 0)
2683 assert(threads[threadID].state == THREAD_AVAILABLE);
2685 threads[threadID].state = THREAD_SEARCHING;
2692 // init_threads() is called during startup. It launches all helper threads,
2693 // and initializes the split point stack and the global locks and condition
2696 void ThreadsManager::init_threads() {
2701 #if !defined(_MSC_VER)
2702 pthread_t pthread[1];
2705 // Initialize global locks
2706 lock_init(&MPLock, NULL);
2707 lock_init(&WaitLock, NULL);
2709 #if !defined(_MSC_VER)
2710 pthread_cond_init(&WaitCond, NULL);
2712 for (i = 0; i < MAX_THREADS; i++)
2713 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2716 // Initialize SplitPointStack locks
2717 for (i = 0; i < MAX_THREADS; i++)
2718 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2720 SplitPointStack[i][j].parent = NULL;
2721 lock_init(&(SplitPointStack[i][j].lock), NULL);
2724 // Will be set just before program exits to properly end the threads
2725 AllThreadsShouldExit = false;
2727 // Threads will be put to sleep as soon as created
2728 AllThreadsShouldSleep = true;
2730 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2732 threads[0].state = THREAD_SEARCHING;
2733 for (i = 1; i < MAX_THREADS; i++)
2734 threads[i].state = THREAD_AVAILABLE;
2736 // Launch the helper threads
2737 for (i = 1; i < MAX_THREADS; i++)
2740 #if !defined(_MSC_VER)
2741 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2743 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2748 cout << "Failed to create thread number " << i << endl;
2749 Application::exit_with_failure();
2752 // Wait until the thread has finished launching and is gone to sleep
2753 while (threads[i].state != THREAD_SLEEPING);
2758 // exit_threads() is called when the program exits. It makes all the
2759 // helper threads exit cleanly.
2761 void ThreadsManager::exit_threads() {
2763 ActiveThreads = MAX_THREADS; // HACK
2764 AllThreadsShouldSleep = true; // HACK
2765 wake_sleeping_threads();
2767 // This makes the threads to exit idle_loop()
2768 AllThreadsShouldExit = true;
2770 // Wait for thread termination
2771 for (int i = 1; i < MAX_THREADS; i++)
2772 while (threads[i].state != THREAD_TERMINATED);
2774 // Now we can safely destroy the locks
2775 for (int i = 0; i < MAX_THREADS; i++)
2776 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2777 lock_destroy(&(SplitPointStack[i][j].lock));
2779 lock_destroy(&WaitLock);
2780 lock_destroy(&MPLock);
2784 // thread_should_stop() checks whether the thread should stop its search.
2785 // This can happen if a beta cutoff has occurred in the thread's currently
2786 // active split point, or in some ancestor of the current split point.
2788 bool ThreadsManager::thread_should_stop(int threadID) const {
2790 assert(threadID >= 0 && threadID < ActiveThreads);
2794 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2799 // thread_is_available() checks whether the thread with threadID "slave" is
2800 // available to help the thread with threadID "master" at a split point. An
2801 // obvious requirement is that "slave" must be idle. With more than two
2802 // threads, this is not by itself sufficient: If "slave" is the master of
2803 // some active split point, it is only available as a slave to the other
2804 // threads which are busy searching the split point at the top of "slave"'s
2805 // split point stack (the "helpful master concept" in YBWC terminology).
2807 bool ThreadsManager::thread_is_available(int slave, int master) const {
2809 assert(slave >= 0 && slave < ActiveThreads);
2810 assert(master >= 0 && master < ActiveThreads);
2811 assert(ActiveThreads > 1);
2813 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2816 // Make a local copy to be sure doesn't change under our feet
2817 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2819 if (localActiveSplitPoints == 0)
2820 // No active split points means that the thread is available as
2821 // a slave for any other thread.
2824 if (ActiveThreads == 2)
2827 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2828 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2829 // could have been set to 0 by another thread leading to an out of bound access.
2830 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2837 // available_thread_exists() tries to find an idle thread which is available as
2838 // a slave for the thread with threadID "master".
2840 bool ThreadsManager::available_thread_exists(int master) const {
2842 assert(master >= 0 && master < ActiveThreads);
2843 assert(ActiveThreads > 1);
2845 for (int i = 0; i < ActiveThreads; i++)
2846 if (thread_is_available(i, master))
2853 // split() does the actual work of distributing the work at a node between
2854 // several threads at PV nodes. If it does not succeed in splitting the
2855 // node (because no idle threads are available, or because we have no unused
2856 // split point objects), the function immediately returns false. If
2857 // splitting is possible, a SplitPoint object is initialized with all the
2858 // data that must be copied to the helper threads (the current position and
2859 // search stack, alpha, beta, the search depth, etc.), and we tell our
2860 // helper threads that they have been assigned work. This will cause them
2861 // to instantly leave their idle loops and call sp_search_pv(). When all
2862 // threads have returned from sp_search_pv (or, equivalently, when
2863 // splitPoint->cpus becomes 0), split() returns true.
2865 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2866 Value* alpha, const Value beta, Value* bestValue,
2867 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2870 assert(sstck != NULL);
2871 assert(ply >= 0 && ply < PLY_MAX);
2872 assert(*bestValue >= -VALUE_INFINITE);
2873 assert( ( pvNode && *bestValue <= *alpha)
2874 || (!pvNode && *bestValue < beta ));
2875 assert(!pvNode || *alpha < beta);
2876 assert(beta <= VALUE_INFINITE);
2877 assert(depth > Depth(0));
2878 assert(master >= 0 && master < ActiveThreads);
2879 assert(ActiveThreads > 1);
2881 SplitPoint* splitPoint;
2885 // If no other thread is available to help us, or if we have too many
2886 // active split points, don't split.
2887 if ( !available_thread_exists(master)
2888 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2890 lock_release(&MPLock);
2894 // Pick the next available split point object from the split point stack
2895 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2897 // Initialize the split point object
2898 splitPoint->parent = threads[master].splitPoint;
2899 splitPoint->stopRequest = false;
2900 splitPoint->ply = ply;
2901 splitPoint->depth = depth;
2902 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2903 splitPoint->beta = beta;
2904 splitPoint->pvNode = pvNode;
2905 splitPoint->bestValue = *bestValue;
2906 splitPoint->master = master;
2907 splitPoint->mp = mp;
2908 splitPoint->moves = *moves;
2909 splitPoint->cpus = 1;
2910 splitPoint->pos = &p;
2911 splitPoint->parentSstack = sstck;
2912 for (int i = 0; i < ActiveThreads; i++)
2913 splitPoint->slaves[i] = 0;
2915 threads[master].splitPoint = splitPoint;
2916 threads[master].activeSplitPoints++;
2918 // If we are here it means we are not available
2919 assert(threads[master].state != THREAD_AVAILABLE);
2921 // Allocate available threads setting state to THREAD_BOOKED
2922 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2923 if (thread_is_available(i, master))
2925 threads[i].state = THREAD_BOOKED;
2926 threads[i].splitPoint = splitPoint;
2927 splitPoint->slaves[i] = 1;
2931 assert(splitPoint->cpus > 1);
2933 // We can release the lock because slave threads are already booked and master is not available
2934 lock_release(&MPLock);
2936 // Tell the threads that they have work to do. This will make them leave
2937 // their idle loop. But before copy search stack tail for each thread.
2938 for (int i = 0; i < ActiveThreads; i++)
2939 if (i == master || splitPoint->slaves[i])
2941 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2943 assert(i == master || threads[i].state == THREAD_BOOKED);
2945 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2948 // Everything is set up. The master thread enters the idle loop, from
2949 // which it will instantly launch a search, because its state is
2950 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2951 // idle loop, which means that the main thread will return from the idle
2952 // loop when all threads have finished their work at this split point
2953 // (i.e. when splitPoint->cpus == 0).
2954 idle_loop(master, splitPoint);
2956 // We have returned from the idle loop, which means that all threads are
2957 // finished. Update alpha, beta and bestValue, and return.
2961 *alpha = splitPoint->alpha;
2963 *bestValue = splitPoint->bestValue;
2964 threads[master].activeSplitPoints--;
2965 threads[master].splitPoint = splitPoint->parent;
2967 lock_release(&MPLock);
2972 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2973 // to start a new search from the root.
2975 void ThreadsManager::wake_sleeping_threads() {
2977 assert(AllThreadsShouldSleep);
2978 assert(ActiveThreads > 0);
2980 AllThreadsShouldSleep = false;
2982 if (ActiveThreads == 1)
2985 #if !defined(_MSC_VER)
2986 pthread_mutex_lock(&WaitLock);
2987 pthread_cond_broadcast(&WaitCond);
2988 pthread_mutex_unlock(&WaitLock);
2990 for (int i = 1; i < MAX_THREADS; i++)
2991 SetEvent(SitIdleEvent[i]);
2997 // put_threads_to_sleep() makes all the threads go to sleep just before
2998 // to leave think(), at the end of the search. Threads should have already
2999 // finished the job and should be idle.
3001 void ThreadsManager::put_threads_to_sleep() {
3003 assert(!AllThreadsShouldSleep);
3005 // This makes the threads to go to sleep
3006 AllThreadsShouldSleep = true;
3009 /// The RootMoveList class
3011 // RootMoveList c'tor
3013 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3015 SearchStack ss[PLY_MAX_PLUS_2];
3016 MoveStack mlist[MaxRootMoves];
3018 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3020 // Generate all legal moves
3021 MoveStack* last = generate_moves(pos, mlist);
3023 // Add each move to the moves[] array
3024 for (MoveStack* cur = mlist; cur != last; cur++)
3026 bool includeMove = includeAllMoves;
3028 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3029 includeMove = (searchMoves[k] == cur->move);
3034 // Find a quick score for the move
3036 pos.do_move(cur->move, st);
3037 moves[count].move = cur->move;
3038 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3039 moves[count].pv[0] = cur->move;
3040 moves[count].pv[1] = MOVE_NONE;
3041 pos.undo_move(cur->move);
3048 // RootMoveList simple methods definitions
3050 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3052 moves[moveNum].nodes = nodes;
3053 moves[moveNum].cumulativeNodes += nodes;
3056 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3058 moves[moveNum].ourBeta = our;
3059 moves[moveNum].theirBeta = their;
3062 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3066 for (j = 0; pv[j] != MOVE_NONE; j++)
3067 moves[moveNum].pv[j] = pv[j];
3069 moves[moveNum].pv[j] = MOVE_NONE;
3073 // RootMoveList::sort() sorts the root move list at the beginning of a new
3076 void RootMoveList::sort() {
3078 sort_multipv(count - 1); // Sort all items
3082 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3083 // list by their scores and depths. It is used to order the different PVs
3084 // correctly in MultiPV mode.
3086 void RootMoveList::sort_multipv(int n) {
3090 for (i = 1; i <= n; i++)
3092 RootMove rm = moves[i];
3093 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3094 moves[j] = moves[j - 1];