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
650 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
670 value = root_search(p, ss, rml, alpha, beta);
672 // Write PV to transposition table, in case the relevant entries have
673 // been overwritten during the search.
674 TT.insert_pv(p, ss[0].pv);
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 (ss[0].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();
705 && EasyMove == ss[0].pv[0]
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)
738 // If we are pondering or in infinite search, we shouldn't print the
739 // best move before we are told to do so.
740 if (!AbortSearch && (PonderSearch || InfiniteSearch))
741 wait_for_stop_or_ponderhit();
743 // Print final search statistics
744 cout << "info nodes " << TM.nodes_searched()
746 << " time " << current_search_time()
747 << " hashfull " << TT.full() << endl;
749 // Print the best move and the ponder move to the standard output
750 if (ss[0].pv[0] == MOVE_NONE)
752 ss[0].pv[0] = rml.get_move(0);
753 ss[0].pv[1] = MOVE_NONE;
756 assert(ss[0].pv[0] != MOVE_NONE);
758 cout << "bestmove " << ss[0].pv[0];
760 if (ss[0].pv[1] != MOVE_NONE)
761 cout << " ponder " << ss[0].pv[1];
768 dbg_print_mean(LogFile);
770 if (dbg_show_hit_rate)
771 dbg_print_hit_rate(LogFile);
773 LogFile << "\nNodes: " << TM.nodes_searched()
774 << "\nNodes/second: " << nps()
775 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
778 p.do_move(ss[0].pv[0], st);
779 LogFile << "\nPonder move: "
780 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
783 return rml.get_move_score(0);
787 // root_search() is the function which searches the root node. It is
788 // similar to search_pv except that it uses a different move ordering
789 // scheme, prints some information to the standard output and handles
790 // the fail low/high loops.
792 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta) {
798 Depth depth, ext, newDepth;
800 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
801 int researchCount = 0;
804 isCheck = pos.is_check();
806 // Evaluate the position statically
807 ss[0].eval = !isCheck ? evaluate(pos, ei, 0) : VALUE_NONE;
809 while (1) // Fail low loop
811 // Loop through all the moves in the root move list
812 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
816 // We failed high, invalidate and skip next moves, leave node-counters
817 // and beta-counters as they are and quickly return, we will try to do
818 // a research at the next iteration with a bigger aspiration window.
819 rml.set_move_score(i, -VALUE_INFINITE);
823 // This is used by time management and starts from 1
824 RootMoveNumber = i + 1;
826 // Save the current node count before the move is searched
827 nodes = TM.nodes_searched();
829 // Reset beta cut-off counters
830 TM.resetBetaCounters();
832 // Pick the next root move, and print the move and the move number to
833 // the standard output.
834 move = ss[0].currentMove = rml.get_move(i);
836 if (current_search_time() >= 1000)
837 cout << "info currmove " << move
838 << " currmovenumber " << RootMoveNumber << endl;
840 // Decide search depth for this move
841 moveIsCheck = pos.move_is_check(move);
842 captureOrPromotion = pos.move_is_capture_or_promotion(move);
843 depth = (Iteration - 2) * OnePly + InitialDepth;
844 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
845 newDepth = depth + ext;
847 // Reset value before the search
848 value = - VALUE_INFINITE;
850 while (1) // Fail high loop
852 // Make the move, and search it
853 pos.do_move(move, st, ci, moveIsCheck);
855 if (i < MultiPV || value > alpha)
857 // Aspiration window is disabled in multi-pv case
859 alpha = -VALUE_INFINITE;
861 // Full depth PV search, done on first move or after a fail high
862 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
866 // Try to reduce non-pv search depth by one ply if move seems not problematic,
867 // if the move fails high will be re-searched at full depth.
868 bool doFullDepthSearch = true;
870 if ( depth >= 3 * OnePly // FIXME was newDepth
872 && !captureOrPromotion
873 && !move_is_castle(move))
875 ss[0].reduction = pv_reduction(depth, i - MultiPV + 2);
878 // Reduced depth non-pv search using alpha as upperbound
879 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
880 doFullDepthSearch = (value > alpha);
884 if (doFullDepthSearch)
886 // Full depth non-pv search using alpha as upperbound
887 ss[0].reduction = Depth(0);
888 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
890 // If we are above alpha then research at same depth but as PV
891 // to get a correct score or eventually a fail high above beta.
893 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
899 // Can we exit fail high loop ?
900 if (AbortSearch || value < beta)
903 // We are failing high and going to do a research. It's important to update
904 // the score before research in case we run out of time while researching.
905 rml.set_move_score(i, value);
907 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
908 rml.set_move_pv(i, ss[0].pv);
910 // Print information to the standard output
911 print_pv_info(pos, ss, alpha, beta, value);
913 // Prepare for a research after a fail high, each time with a wider window
915 beta = Min(beta + AspirationDelta * (1 << researchCount), VALUE_INFINITE);
917 } // End of fail high loop
919 // Finished searching the move. If AbortSearch is true, the search
920 // was aborted because the user interrupted the search or because we
921 // ran out of time. In this case, the return value of the search cannot
922 // be trusted, and we break out of the loop without updating the best
927 // Remember beta-cutoff and searched nodes counts for this move. The
928 // info is used to sort the root moves at the next iteration.
930 TM.get_beta_counters(pos.side_to_move(), our, their);
931 rml.set_beta_counters(i, our, their);
932 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
934 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
936 if (value <= alpha && i >= MultiPV)
937 rml.set_move_score(i, -VALUE_INFINITE);
940 // PV move or new best move!
943 rml.set_move_score(i, value);
945 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
946 rml.set_move_pv(i, ss[0].pv);
950 // We record how often the best move has been changed in each
951 // iteration. This information is used for time managment: When
952 // the best move changes frequently, we allocate some more time.
954 BestMoveChangesByIteration[Iteration]++;
956 // Print information to the standard output
957 print_pv_info(pos, ss, alpha, beta, value);
959 // Raise alpha to setup proper non-pv search upper bound, note
960 // that we can end up with alpha >= beta and so get a fail high.
967 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
969 cout << "info multipv " << j + 1
970 << " score " << value_to_string(rml.get_move_score(j))
971 << " depth " << (j <= i ? Iteration : Iteration - 1)
972 << " time " << current_search_time()
973 << " nodes " << TM.nodes_searched()
977 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
978 cout << rml.get_move_pv(j, k) << " ";
982 alpha = rml.get_move_score(Min(i, MultiPV - 1));
984 } // PV move or new best move
986 assert(alpha >= oldAlpha);
988 AspirationFailLow = (alpha == oldAlpha);
990 if (AspirationFailLow && StopOnPonderhit)
991 StopOnPonderhit = false;
994 // Can we exit fail low loop ?
995 if (AbortSearch || alpha > oldAlpha)
998 // Prepare for a research after a fail low, each time with a wider window
1000 alpha = Max(alpha - AspirationDelta * (1 << researchCount), -VALUE_INFINITE);
1009 // search_pv() is the main search function for PV nodes.
1011 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1012 Depth depth, int ply, int threadID) {
1014 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1015 assert(beta > alpha && beta <= VALUE_INFINITE);
1016 assert(ply >= 0 && ply < PLY_MAX);
1017 assert(threadID >= 0 && threadID < TM.active_threads());
1019 Move movesSearched[256];
1024 Depth ext, newDepth;
1025 Value bestValue, value, oldAlpha;
1026 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1027 bool mateThreat = false;
1029 bestValue = value = -VALUE_INFINITE;
1032 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1034 // Step 1. Initialize node and poll
1035 // Polling can abort search.
1036 init_node(ss, ply, threadID);
1038 // Step 2. Check for aborted search and immediate draw
1039 if (AbortSearch || TM.thread_should_stop(threadID))
1042 if (pos.is_draw() || ply >= PLY_MAX - 1)
1045 // Step 3. Mate distance pruning
1047 alpha = Max(value_mated_in(ply), alpha);
1048 beta = Min(value_mate_in(ply+1), beta);
1052 // Step 4. Transposition table lookup
1053 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1054 // This is to avoid problems in the following areas:
1056 // * Repetition draw detection
1057 // * Fifty move rule detection
1058 // * Searching for a mate
1059 // * Printing of full PV line
1060 tte = TT.retrieve(pos.get_key());
1061 ttMove = (tte ? tte->move() : MOVE_NONE);
1063 // Step 5. Evaluate the position statically
1064 // At PV nodes we do this only to update gain statistics
1065 isCheck = pos.is_check();
1068 ss[ply].eval = evaluate(pos, ei, threadID);
1069 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1072 // Step 6. Razoring (is omitted in PV nodes)
1073 // Step 7. Static null move pruning (is omitted in PV nodes)
1074 // Step 8. Null move search with verification search (is omitted in PV nodes)
1076 // Step 9. Internal iterative deepening
1077 if ( depth >= IIDDepthAtPVNodes
1078 && ttMove == MOVE_NONE)
1080 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1081 ttMove = ss[ply].pv[ply];
1082 tte = TT.retrieve(pos.get_key());
1085 // Step 10. Loop through moves
1086 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1088 // Initialize a MovePicker object for the current position
1089 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1090 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1093 while ( alpha < beta
1094 && (move = mp.get_next_move()) != MOVE_NONE
1095 && !TM.thread_should_stop(threadID))
1097 assert(move_is_ok(move));
1099 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1100 moveIsCheck = pos.move_is_check(move, ci);
1101 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1103 // Step 11. Decide the new search depth
1104 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1106 // Singular extension search. We extend the TT move if its value is much better than
1107 // its siblings. To verify this we do a reduced search on all the other moves but the
1108 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1109 if ( depth >= SingularExtensionDepthAtPVNodes
1111 && move == tte->move()
1113 && is_lower_bound(tte->type())
1114 && tte->depth() >= depth - 3 * OnePly)
1116 Value ttValue = value_from_tt(tte->value(), ply);
1118 if (abs(ttValue) < VALUE_KNOWN_WIN)
1120 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1122 if (excValue < ttValue - SingularExtensionMargin)
1127 newDepth = depth - OnePly + ext;
1129 // Update current move (this must be done after singular extension search)
1130 movesSearched[moveCount++] = ss[ply].currentMove = move;
1132 // Step 12. Futility pruning (is omitted in PV nodes)
1134 // Step 13. Make the move
1135 pos.do_move(move, st, ci, moveIsCheck);
1137 // Step extra. pv search (only in PV nodes)
1138 // The first move in list is the expected PV
1140 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1143 // Step 14. Reduced search
1144 // if the move fails high will be re-searched at full depth.
1145 bool doFullDepthSearch = true;
1147 if ( depth >= 3 * OnePly
1149 && !captureOrPromotion
1150 && !move_is_castle(move)
1151 && !move_is_killer(move, ss[ply]))
1153 ss[ply].reduction = pv_reduction(depth, moveCount);
1154 if (ss[ply].reduction)
1156 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1157 doFullDepthSearch = (value > alpha);
1161 // Step 15. Full depth search
1162 if (doFullDepthSearch)
1164 ss[ply].reduction = Depth(0);
1165 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1167 // Step extra. pv search (only in PV nodes)
1168 if (value > alpha && value < beta)
1169 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1173 // Step 16. Undo move
1174 pos.undo_move(move);
1176 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1178 // Step 17. Check for new best move
1179 if (value > bestValue)
1186 if (value == value_mate_in(ply + 1))
1187 ss[ply].mateKiller = move;
1191 // Step 18. Check for split
1192 if ( TM.active_threads() > 1
1194 && depth >= MinimumSplitDepth
1196 && TM.available_thread_exists(threadID)
1198 && !TM.thread_should_stop(threadID)
1199 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1200 depth, &moveCount, &mp, threadID, true))
1204 // Step 19. Check for mate and stalemate
1205 // All legal moves have been searched and if there were
1206 // no legal moves, it must be mate or stalemate.
1208 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1210 // Step 20. Update tables
1211 // If the search is not aborted, update the transposition table,
1212 // history counters, and killer moves.
1213 if (AbortSearch || TM.thread_should_stop(threadID))
1216 if (bestValue <= oldAlpha)
1217 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1219 else if (bestValue >= beta)
1221 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1222 move = ss[ply].pv[ply];
1223 if (!pos.move_is_capture_or_promotion(move))
1225 update_history(pos, move, depth, movesSearched, moveCount);
1226 update_killers(move, ss[ply]);
1228 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1231 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1237 // search() is the search function for zero-width nodes.
1239 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1240 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1242 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1243 assert(ply >= 0 && ply < PLY_MAX);
1244 assert(threadID >= 0 && threadID < TM.active_threads());
1246 Move movesSearched[256];
1251 Depth ext, newDepth;
1252 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1253 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1254 bool mateThreat = false;
1256 refinedValue = bestValue = value = -VALUE_INFINITE;
1259 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1261 // Step 1. Initialize node and poll
1262 // Polling can abort search.
1263 init_node(ss, ply, threadID);
1265 // Step 2. Check for aborted search and immediate draw
1266 if (AbortSearch || TM.thread_should_stop(threadID))
1269 if (pos.is_draw() || ply >= PLY_MAX - 1)
1272 // Step 3. Mate distance pruning
1273 if (value_mated_in(ply) >= beta)
1276 if (value_mate_in(ply + 1) < beta)
1279 // Step 4. Transposition table lookup
1281 // We don't want the score of a partial search to overwrite a previous full search
1282 // TT value, so we use a different position key in case of an excluded move exists.
1283 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1285 tte = TT.retrieve(posKey);
1286 ttMove = (tte ? tte->move() : MOVE_NONE);
1288 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1290 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1291 return value_from_tt(tte->value(), ply);
1294 // Step 5. Evaluate the position statically
1295 isCheck = pos.is_check();
1299 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1300 ss[ply].eval = value_from_tt(tte->value(), ply);
1302 ss[ply].eval = evaluate(pos, ei, threadID);
1304 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1305 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1309 if ( !value_is_mate(beta)
1311 && depth < RazorDepth
1312 && refinedValue < beta - razor_margin(depth)
1313 && ss[ply - 1].currentMove != MOVE_NULL
1314 && ttMove == MOVE_NONE
1315 && !pos.has_pawn_on_7th(pos.side_to_move()))
1317 Value rbeta = beta - razor_margin(depth);
1318 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1320 return v; //FIXME: Logically should be: return (v + razor_margin(depth));
1323 // Step 7. Static null move pruning
1324 // We're betting that the opponent doesn't have a move that will reduce
1325 // the score by more than fuility_margin(depth) if we do a null move.
1328 && depth < RazorDepth
1329 && refinedValue - futility_margin(depth, 0) >= beta)
1330 return refinedValue - futility_margin(depth, 0);
1332 // Step 8. Null move search with verification search
1333 // When we jump directly to qsearch() we do a null move only if static value is
1334 // at least beta. Otherwise we do a null move if static value is not more than
1335 // NullMoveMargin under beta.
1339 && !value_is_mate(beta)
1340 && ok_to_do_nullmove(pos)
1341 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1343 ss[ply].currentMove = MOVE_NULL;
1345 pos.do_null_move(st);
1347 // Null move dynamic reduction based on depth
1348 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1350 // Null move dynamic reduction based on value
1351 if (refinedValue - beta > PawnValueMidgame)
1354 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1356 pos.undo_null_move();
1358 if (nullValue >= beta)
1360 if (depth < 6 * OnePly)
1363 // Do zugzwang verification search
1364 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1368 // The null move failed low, which means that we may be faced with
1369 // some kind of threat. If the previous move was reduced, check if
1370 // the move that refuted the null move was somehow connected to the
1371 // move which was reduced. If a connection is found, return a fail
1372 // low score (which will cause the reduced move to fail high in the
1373 // parent node, which will trigger a re-search with full depth).
1374 if (nullValue == value_mated_in(ply + 2))
1377 ss[ply].threatMove = ss[ply + 1].currentMove;
1378 if ( depth < ThreatDepth
1379 && ss[ply - 1].reduction
1380 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1385 // Step 9. Internal iterative deepening
1386 if ( depth >= IIDDepthAtNonPVNodes
1387 && ttMove == MOVE_NONE
1389 && ss[ply].eval >= beta - IIDMargin)
1391 search(pos, ss, beta, depth/2, ply, false, threadID);
1392 ttMove = ss[ply].pv[ply];
1393 tte = TT.retrieve(posKey);
1396 // Step 10. Loop through moves
1397 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1399 // Initialize a MovePicker object for the current position
1400 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1403 while ( bestValue < beta
1404 && (move = mp.get_next_move()) != MOVE_NONE
1405 && !TM.thread_should_stop(threadID))
1407 assert(move_is_ok(move));
1409 if (move == excludedMove)
1412 moveIsCheck = pos.move_is_check(move, ci);
1413 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1414 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1416 // Step 11. Decide the new search depth
1417 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1419 // Singular extension search. We extend the TT move if its value is much better than
1420 // its siblings. To verify this we do a reduced search on all the other moves but the
1421 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1422 if ( depth >= SingularExtensionDepthAtNonPVNodes
1424 && move == tte->move()
1425 && !excludedMove // Do not allow recursive single-reply search
1427 && is_lower_bound(tte->type())
1428 && tte->depth() >= depth - 3 * OnePly)
1430 Value ttValue = value_from_tt(tte->value(), ply);
1432 if (abs(ttValue) < VALUE_KNOWN_WIN)
1434 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1436 if (excValue < ttValue - SingularExtensionMargin)
1441 newDepth = depth - OnePly + ext;
1443 // Update current move (this must be done after singular extension search)
1444 movesSearched[moveCount++] = ss[ply].currentMove = move;
1446 // Step 12. Futility pruning
1449 && !captureOrPromotion
1450 && !move_is_castle(move)
1453 // Move count based pruning
1454 if ( moveCount >= futility_move_count(depth)
1455 && ok_to_prune(pos, move, ss[ply].threatMove)
1456 && bestValue > value_mated_in(PLY_MAX))
1459 // Value based pruning
1460 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1461 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1462 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1464 if (futilityValueScaled < beta)
1466 if (futilityValueScaled > bestValue)
1467 bestValue = futilityValueScaled;
1472 // Step 13. Make the move
1473 pos.do_move(move, st, ci, moveIsCheck);
1475 // Step 14. Reduced search
1476 // if the move fails high will be re-searched at full depth.
1477 bool doFullDepthSearch = true;
1479 if ( depth >= 3*OnePly
1481 && !captureOrPromotion
1482 && !move_is_castle(move)
1483 && !move_is_killer(move, ss[ply]))
1485 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1486 if (ss[ply].reduction)
1488 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1489 doFullDepthSearch = (value >= beta);
1493 // Step 15. Full depth search
1494 if (doFullDepthSearch)
1496 ss[ply].reduction = Depth(0);
1497 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1500 // Step 16. Undo move
1501 pos.undo_move(move);
1503 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1505 // Step 17. Check for new best move
1506 if (value > bestValue)
1512 if (value == value_mate_in(ply + 1))
1513 ss[ply].mateKiller = move;
1516 // Step 18. Check for split
1517 if ( TM.active_threads() > 1
1519 && depth >= MinimumSplitDepth
1521 && TM.available_thread_exists(threadID)
1523 && !TM.thread_should_stop(threadID)
1524 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1525 depth, &moveCount, &mp, threadID, false))
1529 // Step 19. Check for mate and stalemate
1530 // All legal moves have been searched and if there were
1531 // no legal moves, it must be mate or stalemate.
1532 // If one move was excluded return fail low.
1534 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1536 // Step 20. Update tables
1537 // If the search is not aborted, update the transposition table,
1538 // history counters, and killer moves.
1539 if (AbortSearch || TM.thread_should_stop(threadID))
1542 if (bestValue < beta)
1543 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1546 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1547 move = ss[ply].pv[ply];
1548 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1549 if (!pos.move_is_capture_or_promotion(move))
1551 update_history(pos, move, depth, movesSearched, moveCount);
1552 update_killers(move, ss[ply]);
1557 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1563 // qsearch() is the quiescence search function, which is called by the main
1564 // search function when the remaining depth is zero (or, to be more precise,
1565 // less than OnePly).
1567 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1568 Depth depth, int ply, int threadID) {
1570 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1571 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1573 assert(ply >= 0 && ply < PLY_MAX);
1574 assert(threadID >= 0 && threadID < TM.active_threads());
1579 Value staticValue, bestValue, value, futilityBase, futilityValue;
1580 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1581 const TTEntry* tte = NULL;
1583 bool pvNode = (beta - alpha != 1);
1584 Value oldAlpha = alpha;
1586 // Initialize, and make an early exit in case of an aborted search,
1587 // an instant draw, maximum ply reached, etc.
1588 init_node(ss, ply, threadID);
1590 // After init_node() that calls poll()
1591 if (AbortSearch || TM.thread_should_stop(threadID))
1594 if (pos.is_draw() || ply >= PLY_MAX - 1)
1597 // Transposition table lookup. At PV nodes, we don't use the TT for
1598 // pruning, but only for move ordering.
1599 tte = TT.retrieve(pos.get_key());
1600 ttMove = (tte ? tte->move() : MOVE_NONE);
1602 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1604 assert(tte->type() != VALUE_TYPE_EVAL);
1606 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1607 return value_from_tt(tte->value(), ply);
1610 isCheck = pos.is_check();
1612 // Evaluate the position statically
1614 staticValue = -VALUE_INFINITE;
1615 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1616 staticValue = value_from_tt(tte->value(), ply);
1618 staticValue = evaluate(pos, ei, threadID);
1622 ss[ply].eval = staticValue;
1623 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1626 // Initialize "stand pat score", and return it immediately if it is
1628 bestValue = staticValue;
1630 if (bestValue >= beta)
1632 // Store the score to avoid a future costly evaluation() call
1633 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1634 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1639 if (bestValue > alpha)
1642 // If we are near beta then try to get a cutoff pushing checks a bit further
1643 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1645 // Initialize a MovePicker object for the current position, and prepare
1646 // to search the moves. Because the depth is <= 0 here, only captures,
1647 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1648 // and we are near beta) will be generated.
1649 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1651 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1652 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1654 // Loop through the moves until no moves remain or a beta cutoff
1656 while ( alpha < beta
1657 && (move = mp.get_next_move()) != MOVE_NONE)
1659 assert(move_is_ok(move));
1661 moveIsCheck = pos.move_is_check(move, ci);
1663 // Update current move
1665 ss[ply].currentMove = move;
1673 && !move_is_promotion(move)
1674 && !pos.move_is_passed_pawn_push(move))
1676 futilityValue = futilityBase
1677 + pos.endgame_value_of_piece_on(move_to(move))
1678 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1680 if (futilityValue < alpha)
1682 if (futilityValue > bestValue)
1683 bestValue = futilityValue;
1688 // Detect blocking evasions that are candidate to be pruned
1689 evasionPrunable = isCheck
1690 && bestValue != -VALUE_INFINITE
1691 && !pos.move_is_capture(move)
1692 && pos.type_of_piece_on(move_from(move)) != KING
1693 && !pos.can_castle(pos.side_to_move());
1695 // Don't search moves with negative SEE values
1696 if ( (!isCheck || evasionPrunable)
1699 && !move_is_promotion(move)
1700 && pos.see_sign(move) < 0)
1703 // Make and search the move
1704 pos.do_move(move, st, ci, moveIsCheck);
1705 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1706 pos.undo_move(move);
1708 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1711 if (value > bestValue)
1722 // All legal moves have been searched. A special case: If we're in check
1723 // and no legal moves were found, it is checkmate.
1724 if (!moveCount && pos.is_check()) // Mate!
1725 return value_mated_in(ply);
1727 // Update transposition table
1728 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1729 if (bestValue <= oldAlpha)
1731 // If bestValue isn't changed it means it is still the static evaluation
1732 // of the node, so keep this info to avoid a future evaluation() call.
1733 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1734 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1736 else if (bestValue >= beta)
1738 move = ss[ply].pv[ply];
1739 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1741 // Update killers only for good checking moves
1742 if (!pos.move_is_capture_or_promotion(move))
1743 update_killers(move, ss[ply]);
1746 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1748 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1754 // sp_search() is used to search from a split point. This function is called
1755 // by each thread working at the split point. It is similar to the normal
1756 // search() function, but simpler. Because we have already probed the hash
1757 // table, done a null move search, and searched the first move before
1758 // splitting, we don't have to repeat all this work in sp_search(). We
1759 // also don't need to store anything to the hash table here: This is taken
1760 // care of after we return from the split point.
1761 // FIXME: We are currently ignoring mateThreat flag here
1763 void sp_search(SplitPoint* sp, int threadID) {
1765 assert(threadID >= 0 && threadID < TM.active_threads());
1766 assert(TM.active_threads() > 1);
1770 Depth ext, newDepth;
1771 Value value, futilityValueScaled;
1772 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1774 value = -VALUE_INFINITE;
1776 Position pos(*sp->pos);
1778 SearchStack* ss = sp->sstack[threadID];
1779 isCheck = pos.is_check();
1781 // Step 10. Loop through moves
1782 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1783 lock_grab(&(sp->lock));
1785 while ( sp->bestValue < sp->beta
1786 && !TM.thread_should_stop(threadID)
1787 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1789 moveCount = ++sp->moves;
1790 lock_release(&(sp->lock));
1792 assert(move_is_ok(move));
1794 moveIsCheck = pos.move_is_check(move, ci);
1795 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1797 // Step 11. Decide the new search depth
1798 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1799 newDepth = sp->depth - OnePly + ext;
1801 // Update current move
1802 ss[sp->ply].currentMove = move;
1804 // Step 12. Futility pruning
1807 && !captureOrPromotion
1808 && !move_is_castle(move))
1810 // Move count based pruning
1811 if ( moveCount >= futility_move_count(sp->depth)
1812 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1813 && sp->bestValue > value_mated_in(PLY_MAX))
1815 lock_grab(&(sp->lock));
1819 // Value based pruning
1820 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1821 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1822 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1824 if (futilityValueScaled < sp->beta)
1826 lock_grab(&(sp->lock));
1828 if (futilityValueScaled > sp->bestValue)
1829 sp->bestValue = futilityValueScaled;
1834 // Step 13. Make the move
1835 pos.do_move(move, st, ci, moveIsCheck);
1837 // Step 14. Reduced search
1838 // if the move fails high will be re-searched at full depth.
1839 bool doFullDepthSearch = true;
1842 && !captureOrPromotion
1843 && !move_is_castle(move)
1844 && !move_is_killer(move, ss[sp->ply]))
1846 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1847 if (ss[sp->ply].reduction)
1849 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1850 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1854 // Step 15. Full depth search
1855 if (doFullDepthSearch)
1857 ss[sp->ply].reduction = Depth(0);
1858 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1861 // Step 16. Undo move
1862 pos.undo_move(move);
1864 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1866 // Step 17. Check for new best move
1867 lock_grab(&(sp->lock));
1869 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1871 sp->bestValue = value;
1872 if (sp->bestValue >= sp->beta)
1874 sp->stopRequest = true;
1875 sp_update_pv(sp->parentSstack, ss, sp->ply);
1880 /* Here we have the lock still grabbed */
1882 sp->slaves[threadID] = 0;
1885 lock_release(&(sp->lock));
1889 // sp_search_pv() is used to search from a PV split point. This function
1890 // is called by each thread working at the split point. It is similar to
1891 // the normal search_pv() function, but simpler. Because we have already
1892 // probed the hash table and searched the first move before splitting, we
1893 // don't have to repeat all this work in sp_search_pv(). We also don't
1894 // need to store anything to the hash table here: This is taken care of
1895 // after we return from the split point.
1896 // FIXME: We are ignoring mateThreat flag!
1898 void sp_search_pv(SplitPoint* sp, int threadID) {
1900 assert(threadID >= 0 && threadID < TM.active_threads());
1901 assert(TM.active_threads() > 1);
1905 Depth ext, newDepth;
1907 bool moveIsCheck, captureOrPromotion, dangerous;
1909 value = -VALUE_INFINITE;
1911 Position pos(*sp->pos);
1913 SearchStack* ss = sp->sstack[threadID];
1915 // Step 10. Loop through moves
1916 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1917 lock_grab(&(sp->lock));
1919 while ( sp->alpha < sp->beta
1920 && !TM.thread_should_stop(threadID)
1921 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1923 moveCount = ++sp->moves;
1924 lock_release(&(sp->lock));
1926 assert(move_is_ok(move));
1928 moveIsCheck = pos.move_is_check(move, ci);
1929 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1931 // Step 11. Decide the new search depth
1932 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1933 newDepth = sp->depth - OnePly + ext;
1935 // Update current move
1936 ss[sp->ply].currentMove = move;
1938 // Step 12. Futility pruning (is omitted in PV nodes)
1940 // Step 13. Make the move
1941 pos.do_move(move, st, ci, moveIsCheck);
1943 // Step 14. Reduced search
1944 // if the move fails high will be re-searched at full depth.
1945 bool doFullDepthSearch = true;
1948 && !captureOrPromotion
1949 && !move_is_castle(move)
1950 && !move_is_killer(move, ss[sp->ply]))
1952 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1953 if (ss[sp->ply].reduction)
1955 Value localAlpha = sp->alpha;
1956 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1957 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1961 // Step 15. Full depth search
1962 if (doFullDepthSearch)
1964 Value localAlpha = sp->alpha;
1965 ss[sp->ply].reduction = Depth(0);
1966 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1968 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1970 // If another thread has failed high then sp->alpha has been increased
1971 // to be higher or equal then beta, if so, avoid to start a PV search.
1972 localAlpha = sp->alpha;
1973 if (localAlpha < sp->beta)
1974 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1978 // Step 16. Undo move
1979 pos.undo_move(move);
1981 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1983 // Step 17. Check for new best move
1984 lock_grab(&(sp->lock));
1986 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1988 sp->bestValue = value;
1989 if (value > sp->alpha)
1991 // Ask threads to stop before to modify sp->alpha
1992 if (value >= sp->beta)
1993 sp->stopRequest = true;
1997 sp_update_pv(sp->parentSstack, ss, sp->ply);
1998 if (value == value_mate_in(sp->ply + 1))
1999 ss[sp->ply].mateKiller = move;
2004 /* Here we have the lock still grabbed */
2006 sp->slaves[threadID] = 0;
2009 lock_release(&(sp->lock));
2013 // init_node() is called at the beginning of all the search functions
2014 // (search(), search_pv(), qsearch(), and so on) and initializes the
2015 // search stack object corresponding to the current node. Once every
2016 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2017 // for user input and checks whether it is time to stop the search.
2019 void init_node(SearchStack ss[], int ply, int threadID) {
2021 assert(ply >= 0 && ply < PLY_MAX);
2022 assert(threadID >= 0 && threadID < TM.active_threads());
2024 TM.incrementNodeCounter(threadID);
2029 if (NodesSincePoll >= NodesBetweenPolls)
2036 ss[ply + 2].initKillers();
2040 // update_pv() is called whenever a search returns a value > alpha.
2041 // It updates the PV in the SearchStack object corresponding to the
2044 void update_pv(SearchStack ss[], int ply) {
2046 assert(ply >= 0 && ply < PLY_MAX);
2050 ss[ply].pv[ply] = ss[ply].currentMove;
2052 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2053 ss[ply].pv[p] = ss[ply + 1].pv[p];
2055 ss[ply].pv[p] = MOVE_NONE;
2059 // sp_update_pv() is a variant of update_pv for use at split points. The
2060 // difference between the two functions is that sp_update_pv also updates
2061 // the PV at the parent node.
2063 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2065 assert(ply >= 0 && ply < PLY_MAX);
2069 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2071 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2072 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2074 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2078 // connected_moves() tests whether two moves are 'connected' in the sense
2079 // that the first move somehow made the second move possible (for instance
2080 // if the moving piece is the same in both moves). The first move is assumed
2081 // to be the move that was made to reach the current position, while the
2082 // second move is assumed to be a move from the current position.
2084 bool connected_moves(const Position& pos, Move m1, Move m2) {
2086 Square f1, t1, f2, t2;
2089 assert(move_is_ok(m1));
2090 assert(move_is_ok(m2));
2092 if (m2 == MOVE_NONE)
2095 // Case 1: The moving piece is the same in both moves
2101 // Case 2: The destination square for m2 was vacated by m1
2107 // Case 3: Moving through the vacated square
2108 if ( piece_is_slider(pos.piece_on(f2))
2109 && bit_is_set(squares_between(f2, t2), f1))
2112 // Case 4: The destination square for m2 is defended by the moving piece in m1
2113 p = pos.piece_on(t1);
2114 if (bit_is_set(pos.attacks_from(p, t1), t2))
2117 // Case 5: Discovered check, checking piece is the piece moved in m1
2118 if ( piece_is_slider(p)
2119 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2120 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2122 // discovered_check_candidates() works also if the Position's side to
2123 // move is the opposite of the checking piece.
2124 Color them = opposite_color(pos.side_to_move());
2125 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2127 if (bit_is_set(dcCandidates, f2))
2134 // value_is_mate() checks if the given value is a mate one
2135 // eventually compensated for the ply.
2137 bool value_is_mate(Value value) {
2139 assert(abs(value) <= VALUE_INFINITE);
2141 return value <= value_mated_in(PLY_MAX)
2142 || value >= value_mate_in(PLY_MAX);
2146 // move_is_killer() checks if the given move is among the
2147 // killer moves of that ply.
2149 bool move_is_killer(Move m, const SearchStack& ss) {
2151 const Move* k = ss.killers;
2152 for (int i = 0; i < KILLER_MAX; i++, k++)
2160 // extension() decides whether a move should be searched with normal depth,
2161 // or with extended depth. Certain classes of moves (checking moves, in
2162 // particular) are searched with bigger depth than ordinary moves and in
2163 // any case are marked as 'dangerous'. Note that also if a move is not
2164 // extended, as example because the corresponding UCI option is set to zero,
2165 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2167 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2168 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2170 assert(m != MOVE_NONE);
2172 Depth result = Depth(0);
2173 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2178 result += CheckExtension[pvNode];
2181 result += SingleEvasionExtension[pvNode];
2184 result += MateThreatExtension[pvNode];
2187 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2189 Color c = pos.side_to_move();
2190 if (relative_rank(c, move_to(m)) == RANK_7)
2192 result += PawnPushTo7thExtension[pvNode];
2195 if (pos.pawn_is_passed(c, move_to(m)))
2197 result += PassedPawnExtension[pvNode];
2202 if ( captureOrPromotion
2203 && pos.type_of_piece_on(move_to(m)) != PAWN
2204 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2205 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2206 && !move_is_promotion(m)
2209 result += PawnEndgameExtension[pvNode];
2214 && captureOrPromotion
2215 && pos.type_of_piece_on(move_to(m)) != PAWN
2216 && pos.see_sign(m) >= 0)
2222 return Min(result, OnePly);
2226 // ok_to_do_nullmove() looks at the current position and decides whether
2227 // doing a 'null move' should be allowed. In order to avoid zugzwang
2228 // problems, null moves are not allowed when the side to move has very
2229 // little material left. Currently, the test is a bit too simple: Null
2230 // moves are avoided only when the side to move has only pawns left.
2231 // It's probably a good idea to avoid null moves in at least some more
2232 // complicated endgames, e.g. KQ vs KR. FIXME
2234 bool ok_to_do_nullmove(const Position& pos) {
2236 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2240 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2241 // non-tactical moves late in the move list close to the leaves are
2242 // candidates for pruning.
2244 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2246 assert(move_is_ok(m));
2247 assert(threat == MOVE_NONE || move_is_ok(threat));
2248 assert(!pos.move_is_check(m));
2249 assert(!pos.move_is_capture_or_promotion(m));
2250 assert(!pos.move_is_passed_pawn_push(m));
2252 Square mfrom, mto, tfrom, tto;
2254 // Prune if there isn't any threat move
2255 if (threat == MOVE_NONE)
2258 mfrom = move_from(m);
2260 tfrom = move_from(threat);
2261 tto = move_to(threat);
2263 // Case 1: Don't prune moves which move the threatened piece
2267 // Case 2: If the threatened piece has value less than or equal to the
2268 // value of the threatening piece, don't prune move which defend it.
2269 if ( pos.move_is_capture(threat)
2270 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2271 || pos.type_of_piece_on(tfrom) == KING)
2272 && pos.move_attacks_square(m, tto))
2275 // Case 3: If the moving piece in the threatened move is a slider, don't
2276 // prune safe moves which block its ray.
2277 if ( piece_is_slider(pos.piece_on(tfrom))
2278 && bit_is_set(squares_between(tfrom, tto), mto)
2279 && pos.see_sign(m) >= 0)
2286 // ok_to_use_TT() returns true if a transposition table score
2287 // can be used at a given point in search.
2289 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2291 Value v = value_from_tt(tte->value(), ply);
2293 return ( tte->depth() >= depth
2294 || v >= Max(value_mate_in(PLY_MAX), beta)
2295 || v < Min(value_mated_in(PLY_MAX), beta))
2297 && ( (is_lower_bound(tte->type()) && v >= beta)
2298 || (is_upper_bound(tte->type()) && v < beta));
2302 // refine_eval() returns the transposition table score if
2303 // possible otherwise falls back on static position evaluation.
2305 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2310 Value v = value_from_tt(tte->value(), ply);
2312 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2313 || (is_upper_bound(tte->type()) && v < defaultEval))
2320 // update_history() registers a good move that produced a beta-cutoff
2321 // in history and marks as failures all the other moves of that ply.
2323 void update_history(const Position& pos, Move move, Depth depth,
2324 Move movesSearched[], int moveCount) {
2328 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2330 for (int i = 0; i < moveCount - 1; i++)
2332 m = movesSearched[i];
2336 if (!pos.move_is_capture_or_promotion(m))
2337 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2342 // update_killers() add a good move that produced a beta-cutoff
2343 // among the killer moves of that ply.
2345 void update_killers(Move m, SearchStack& ss) {
2347 if (m == ss.killers[0])
2350 for (int i = KILLER_MAX - 1; i > 0; i--)
2351 ss.killers[i] = ss.killers[i - 1];
2357 // update_gains() updates the gains table of a non-capture move given
2358 // the static position evaluation before and after the move.
2360 void update_gains(const Position& pos, Move m, Value before, Value after) {
2363 && before != VALUE_NONE
2364 && after != VALUE_NONE
2365 && pos.captured_piece() == NO_PIECE_TYPE
2366 && !move_is_castle(m)
2367 && !move_is_promotion(m))
2368 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2372 // current_search_time() returns the number of milliseconds which have passed
2373 // since the beginning of the current search.
2375 int current_search_time() {
2377 return get_system_time() - SearchStartTime;
2381 // nps() computes the current nodes/second count.
2385 int t = current_search_time();
2386 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2390 // poll() performs two different functions: It polls for user input, and it
2391 // looks at the time consumed so far and decides if it's time to abort the
2394 void poll(SearchStack ss[], int ply) {
2396 static int lastInfoTime;
2397 int t = current_search_time();
2402 // We are line oriented, don't read single chars
2403 std::string command;
2405 if (!std::getline(std::cin, command))
2408 if (command == "quit")
2411 PonderSearch = false;
2415 else if (command == "stop")
2418 PonderSearch = false;
2420 else if (command == "ponderhit")
2424 // Print search information
2428 else if (lastInfoTime > t)
2429 // HACK: Must be a new search where we searched less than
2430 // NodesBetweenPolls nodes during the first second of search.
2433 else if (t - lastInfoTime >= 1000)
2440 if (dbg_show_hit_rate)
2441 dbg_print_hit_rate();
2443 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2444 << " time " << t << " hashfull " << TT.full() << endl;
2446 // We only support current line printing in single thread mode
2447 if (ShowCurrentLine && TM.active_threads() == 1)
2449 cout << "info currline";
2450 for (int p = 0; p < ply; p++)
2451 cout << " " << ss[p].currentMove;
2457 // Should we stop the search?
2461 bool stillAtFirstMove = RootMoveNumber == 1
2462 && !AspirationFailLow
2463 && t > MaxSearchTime + ExtraSearchTime;
2465 bool noMoreTime = t > AbsoluteMaxSearchTime
2466 || stillAtFirstMove;
2468 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2469 || (ExactMaxTime && t >= ExactMaxTime)
2470 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2475 // ponderhit() is called when the program is pondering (i.e. thinking while
2476 // it's the opponent's turn to move) in order to let the engine know that
2477 // it correctly predicted the opponent's move.
2481 int t = current_search_time();
2482 PonderSearch = false;
2484 bool stillAtFirstMove = RootMoveNumber == 1
2485 && !AspirationFailLow
2486 && t > MaxSearchTime + ExtraSearchTime;
2488 bool noMoreTime = t > AbsoluteMaxSearchTime
2489 || stillAtFirstMove;
2491 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2496 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2498 void init_ss_array(SearchStack ss[]) {
2500 for (int i = 0; i < 3; i++)
2503 ss[i].initKillers();
2508 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2509 // while the program is pondering. The point is to work around a wrinkle in
2510 // the UCI protocol: When pondering, the engine is not allowed to give a
2511 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2512 // We simply wait here until one of these commands is sent, and return,
2513 // after which the bestmove and pondermove will be printed (in id_loop()).
2515 void wait_for_stop_or_ponderhit() {
2517 std::string command;
2521 if (!std::getline(std::cin, command))
2524 if (command == "quit")
2529 else if (command == "ponderhit" || command == "stop")
2535 // print_pv_info() prints to standard output and eventually to log file information on
2536 // the current PV line. It is called at each iteration or after a new pv is found.
2538 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2540 cout << "info depth " << Iteration
2541 << " score " << value_to_string(value)
2542 << ((value >= beta) ? " lowerbound" :
2543 ((value <= alpha)? " upperbound" : ""))
2544 << " time " << current_search_time()
2545 << " nodes " << TM.nodes_searched()
2549 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2550 cout << ss[0].pv[j] << " ";
2556 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2557 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2559 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2560 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2565 // init_thread() is the function which is called when a new thread is
2566 // launched. It simply calls the idle_loop() function with the supplied
2567 // threadID. There are two versions of this function; one for POSIX
2568 // threads and one for Windows threads.
2570 #if !defined(_MSC_VER)
2572 void* init_thread(void *threadID) {
2574 TM.idle_loop(*(int*)threadID, NULL);
2580 DWORD WINAPI init_thread(LPVOID threadID) {
2582 TM.idle_loop(*(int*)threadID, NULL);
2589 /// The ThreadsManager class
2591 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2592 // get_beta_counters() are getters/setters for the per thread
2593 // counters used to sort the moves at root.
2595 void ThreadsManager::resetNodeCounters() {
2597 for (int i = 0; i < MAX_THREADS; i++)
2598 threads[i].nodes = 0ULL;
2601 void ThreadsManager::resetBetaCounters() {
2603 for (int i = 0; i < MAX_THREADS; i++)
2604 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2607 int64_t ThreadsManager::nodes_searched() const {
2609 int64_t result = 0ULL;
2610 for (int i = 0; i < ActiveThreads; i++)
2611 result += threads[i].nodes;
2616 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2619 for (int i = 0; i < MAX_THREADS; i++)
2621 our += threads[i].betaCutOffs[us];
2622 their += threads[i].betaCutOffs[opposite_color(us)];
2627 // idle_loop() is where the threads are parked when they have no work to do.
2628 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2629 // object for which the current thread is the master.
2631 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2633 assert(threadID >= 0 && threadID < MAX_THREADS);
2637 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2638 // master should exit as last one.
2639 if (AllThreadsShouldExit)
2642 threads[threadID].state = THREAD_TERMINATED;
2646 // If we are not thinking, wait for a condition to be signaled
2647 // instead of wasting CPU time polling for work.
2648 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2651 assert(threadID != 0);
2652 threads[threadID].state = THREAD_SLEEPING;
2654 #if !defined(_MSC_VER)
2655 lock_grab(&WaitLock);
2656 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2657 pthread_cond_wait(&WaitCond, &WaitLock);
2658 lock_release(&WaitLock);
2660 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2664 // If thread has just woken up, mark it as available
2665 if (threads[threadID].state == THREAD_SLEEPING)
2666 threads[threadID].state = THREAD_AVAILABLE;
2668 // If this thread has been assigned work, launch a search
2669 if (threads[threadID].state == THREAD_WORKISWAITING)
2671 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2673 threads[threadID].state = THREAD_SEARCHING;
2675 if (threads[threadID].splitPoint->pvNode)
2676 sp_search_pv(threads[threadID].splitPoint, threadID);
2678 sp_search(threads[threadID].splitPoint, threadID);
2680 assert(threads[threadID].state == THREAD_SEARCHING);
2682 threads[threadID].state = THREAD_AVAILABLE;
2685 // If this thread is the master of a split point and all threads have
2686 // finished their work at this split point, return from the idle loop.
2687 if (waitSp != NULL && waitSp->cpus == 0)
2689 assert(threads[threadID].state == THREAD_AVAILABLE);
2691 threads[threadID].state = THREAD_SEARCHING;
2698 // init_threads() is called during startup. It launches all helper threads,
2699 // and initializes the split point stack and the global locks and condition
2702 void ThreadsManager::init_threads() {
2707 #if !defined(_MSC_VER)
2708 pthread_t pthread[1];
2711 // Initialize global locks
2712 lock_init(&MPLock, NULL);
2713 lock_init(&WaitLock, NULL);
2715 #if !defined(_MSC_VER)
2716 pthread_cond_init(&WaitCond, NULL);
2718 for (i = 0; i < MAX_THREADS; i++)
2719 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2722 // Initialize SplitPointStack locks
2723 for (i = 0; i < MAX_THREADS; i++)
2724 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2726 SplitPointStack[i][j].parent = NULL;
2727 lock_init(&(SplitPointStack[i][j].lock), NULL);
2730 // Will be set just before program exits to properly end the threads
2731 AllThreadsShouldExit = false;
2733 // Threads will be put to sleep as soon as created
2734 AllThreadsShouldSleep = true;
2736 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2738 threads[0].state = THREAD_SEARCHING;
2739 for (i = 1; i < MAX_THREADS; i++)
2740 threads[i].state = THREAD_AVAILABLE;
2742 // Launch the helper threads
2743 for (i = 1; i < MAX_THREADS; i++)
2746 #if !defined(_MSC_VER)
2747 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2749 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2754 cout << "Failed to create thread number " << i << endl;
2755 Application::exit_with_failure();
2758 // Wait until the thread has finished launching and is gone to sleep
2759 while (threads[i].state != THREAD_SLEEPING);
2764 // exit_threads() is called when the program exits. It makes all the
2765 // helper threads exit cleanly.
2767 void ThreadsManager::exit_threads() {
2769 ActiveThreads = MAX_THREADS; // HACK
2770 AllThreadsShouldSleep = true; // HACK
2771 wake_sleeping_threads();
2773 // This makes the threads to exit idle_loop()
2774 AllThreadsShouldExit = true;
2776 // Wait for thread termination
2777 for (int i = 1; i < MAX_THREADS; i++)
2778 while (threads[i].state != THREAD_TERMINATED);
2780 // Now we can safely destroy the locks
2781 for (int i = 0; i < MAX_THREADS; i++)
2782 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2783 lock_destroy(&(SplitPointStack[i][j].lock));
2785 lock_destroy(&WaitLock);
2786 lock_destroy(&MPLock);
2790 // thread_should_stop() checks whether the thread should stop its search.
2791 // This can happen if a beta cutoff has occurred in the thread's currently
2792 // active split point, or in some ancestor of the current split point.
2794 bool ThreadsManager::thread_should_stop(int threadID) const {
2796 assert(threadID >= 0 && threadID < ActiveThreads);
2800 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2805 // thread_is_available() checks whether the thread with threadID "slave" is
2806 // available to help the thread with threadID "master" at a split point. An
2807 // obvious requirement is that "slave" must be idle. With more than two
2808 // threads, this is not by itself sufficient: If "slave" is the master of
2809 // some active split point, it is only available as a slave to the other
2810 // threads which are busy searching the split point at the top of "slave"'s
2811 // split point stack (the "helpful master concept" in YBWC terminology).
2813 bool ThreadsManager::thread_is_available(int slave, int master) const {
2815 assert(slave >= 0 && slave < ActiveThreads);
2816 assert(master >= 0 && master < ActiveThreads);
2817 assert(ActiveThreads > 1);
2819 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2822 // Make a local copy to be sure doesn't change under our feet
2823 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2825 if (localActiveSplitPoints == 0)
2826 // No active split points means that the thread is available as
2827 // a slave for any other thread.
2830 if (ActiveThreads == 2)
2833 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2834 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2835 // could have been set to 0 by another thread leading to an out of bound access.
2836 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2843 // available_thread_exists() tries to find an idle thread which is available as
2844 // a slave for the thread with threadID "master".
2846 bool ThreadsManager::available_thread_exists(int master) const {
2848 assert(master >= 0 && master < ActiveThreads);
2849 assert(ActiveThreads > 1);
2851 for (int i = 0; i < ActiveThreads; i++)
2852 if (thread_is_available(i, master))
2859 // split() does the actual work of distributing the work at a node between
2860 // several threads at PV nodes. If it does not succeed in splitting the
2861 // node (because no idle threads are available, or because we have no unused
2862 // split point objects), the function immediately returns false. If
2863 // splitting is possible, a SplitPoint object is initialized with all the
2864 // data that must be copied to the helper threads (the current position and
2865 // search stack, alpha, beta, the search depth, etc.), and we tell our
2866 // helper threads that they have been assigned work. This will cause them
2867 // to instantly leave their idle loops and call sp_search_pv(). When all
2868 // threads have returned from sp_search_pv (or, equivalently, when
2869 // splitPoint->cpus becomes 0), split() returns true.
2871 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2872 Value* alpha, const Value beta, Value* bestValue,
2873 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2876 assert(sstck != NULL);
2877 assert(ply >= 0 && ply < PLY_MAX);
2878 assert(*bestValue >= -VALUE_INFINITE);
2879 assert( ( pvNode && *bestValue <= *alpha)
2880 || (!pvNode && *bestValue < beta ));
2881 assert(!pvNode || *alpha < beta);
2882 assert(beta <= VALUE_INFINITE);
2883 assert(depth > Depth(0));
2884 assert(master >= 0 && master < ActiveThreads);
2885 assert(ActiveThreads > 1);
2887 SplitPoint* splitPoint;
2891 // If no other thread is available to help us, or if we have too many
2892 // active split points, don't split.
2893 if ( !available_thread_exists(master)
2894 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2896 lock_release(&MPLock);
2900 // Pick the next available split point object from the split point stack
2901 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2903 // Initialize the split point object
2904 splitPoint->parent = threads[master].splitPoint;
2905 splitPoint->stopRequest = false;
2906 splitPoint->ply = ply;
2907 splitPoint->depth = depth;
2908 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2909 splitPoint->beta = beta;
2910 splitPoint->pvNode = pvNode;
2911 splitPoint->bestValue = *bestValue;
2912 splitPoint->master = master;
2913 splitPoint->mp = mp;
2914 splitPoint->moves = *moves;
2915 splitPoint->cpus = 1;
2916 splitPoint->pos = &p;
2917 splitPoint->parentSstack = sstck;
2918 for (int i = 0; i < ActiveThreads; i++)
2919 splitPoint->slaves[i] = 0;
2921 threads[master].splitPoint = splitPoint;
2922 threads[master].activeSplitPoints++;
2924 // If we are here it means we are not available
2925 assert(threads[master].state != THREAD_AVAILABLE);
2927 // Allocate available threads setting state to THREAD_BOOKED
2928 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2929 if (thread_is_available(i, master))
2931 threads[i].state = THREAD_BOOKED;
2932 threads[i].splitPoint = splitPoint;
2933 splitPoint->slaves[i] = 1;
2937 assert(splitPoint->cpus > 1);
2939 // We can release the lock because slave threads are already booked and master is not available
2940 lock_release(&MPLock);
2942 // Tell the threads that they have work to do. This will make them leave
2943 // their idle loop. But before copy search stack tail for each thread.
2944 for (int i = 0; i < ActiveThreads; i++)
2945 if (i == master || splitPoint->slaves[i])
2947 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2949 assert(i == master || threads[i].state == THREAD_BOOKED);
2951 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2954 // Everything is set up. The master thread enters the idle loop, from
2955 // which it will instantly launch a search, because its state is
2956 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2957 // idle loop, which means that the main thread will return from the idle
2958 // loop when all threads have finished their work at this split point
2959 // (i.e. when splitPoint->cpus == 0).
2960 idle_loop(master, splitPoint);
2962 // We have returned from the idle loop, which means that all threads are
2963 // finished. Update alpha, beta and bestValue, and return.
2967 *alpha = splitPoint->alpha;
2969 *bestValue = splitPoint->bestValue;
2970 threads[master].activeSplitPoints--;
2971 threads[master].splitPoint = splitPoint->parent;
2973 lock_release(&MPLock);
2978 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2979 // to start a new search from the root.
2981 void ThreadsManager::wake_sleeping_threads() {
2983 assert(AllThreadsShouldSleep);
2984 assert(ActiveThreads > 0);
2986 AllThreadsShouldSleep = false;
2988 if (ActiveThreads == 1)
2991 #if !defined(_MSC_VER)
2992 pthread_mutex_lock(&WaitLock);
2993 pthread_cond_broadcast(&WaitCond);
2994 pthread_mutex_unlock(&WaitLock);
2996 for (int i = 1; i < MAX_THREADS; i++)
2997 SetEvent(SitIdleEvent[i]);
3003 // put_threads_to_sleep() makes all the threads go to sleep just before
3004 // to leave think(), at the end of the search. Threads should have already
3005 // finished the job and should be idle.
3007 void ThreadsManager::put_threads_to_sleep() {
3009 assert(!AllThreadsShouldSleep);
3011 // This makes the threads to go to sleep
3012 AllThreadsShouldSleep = true;
3015 /// The RootMoveList class
3017 // RootMoveList c'tor
3019 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3021 SearchStack ss[PLY_MAX_PLUS_2];
3022 MoveStack mlist[MaxRootMoves];
3024 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3026 // Generate all legal moves
3027 MoveStack* last = generate_moves(pos, mlist);
3029 // Add each move to the moves[] array
3030 for (MoveStack* cur = mlist; cur != last; cur++)
3032 bool includeMove = includeAllMoves;
3034 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3035 includeMove = (searchMoves[k] == cur->move);
3040 // Find a quick score for the move
3042 pos.do_move(cur->move, st);
3043 moves[count].move = cur->move;
3044 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3045 moves[count].pv[0] = cur->move;
3046 moves[count].pv[1] = MOVE_NONE;
3047 pos.undo_move(cur->move);
3054 // RootMoveList simple methods definitions
3056 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3058 moves[moveNum].nodes = nodes;
3059 moves[moveNum].cumulativeNodes += nodes;
3062 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3064 moves[moveNum].ourBeta = our;
3065 moves[moveNum].theirBeta = their;
3068 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3072 for (j = 0; pv[j] != MOVE_NONE; j++)
3073 moves[moveNum].pv[j] = pv[j];
3075 moves[moveNum].pv[j] = MOVE_NONE;
3079 // RootMoveList::sort() sorts the root move list at the beginning of a new
3082 void RootMoveList::sort() {
3084 sort_multipv(count - 1); // Sort all items
3088 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3089 // list by their scores and depths. It is used to order the different PVs
3090 // correctly in MultiPV mode.
3092 void RootMoveList::sort_multipv(int n) {
3096 for (i = 1; i <= n; i++)
3098 RootMove rm = moves[i];
3099 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3100 moves[j] = moves[j - 1];