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++)
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 for 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);
1005 // Sort the moves before to return
1012 // search_pv() is the main search function for PV nodes.
1014 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1015 Depth depth, int ply, int threadID) {
1017 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1018 assert(beta > alpha && beta <= VALUE_INFINITE);
1019 assert(ply >= 0 && ply < PLY_MAX);
1020 assert(threadID >= 0 && threadID < TM.active_threads());
1022 Move movesSearched[256];
1027 Depth ext, newDepth;
1028 Value bestValue, value, oldAlpha;
1029 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1030 bool mateThreat = false;
1032 bestValue = value = -VALUE_INFINITE;
1035 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1037 // Step 1. Initialize node and poll
1038 // Polling can abort search.
1039 init_node(ss, ply, threadID);
1041 // Step 2. Check for aborted search and immediate draw
1042 if (AbortSearch || TM.thread_should_stop(threadID))
1045 if (pos.is_draw() || ply >= PLY_MAX - 1)
1048 // Step 3. Mate distance pruning
1050 alpha = Max(value_mated_in(ply), alpha);
1051 beta = Min(value_mate_in(ply+1), beta);
1055 // Step 4. Transposition table lookup
1056 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1057 // This is to avoid problems in the following areas:
1059 // * Repetition draw detection
1060 // * Fifty move rule detection
1061 // * Searching for a mate
1062 // * Printing of full PV line
1063 tte = TT.retrieve(pos.get_key());
1064 ttMove = (tte ? tte->move() : MOVE_NONE);
1066 // Step 5. Evaluate the position statically
1067 // At PV nodes we do this only to update gain statistics
1068 isCheck = pos.is_check();
1071 ss[ply].eval = evaluate(pos, ei, threadID);
1072 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1075 // Step 6. Razoring (is omitted in PV nodes)
1076 // Step 7. Static null move pruning (is omitted in PV nodes)
1077 // Step 8. Null move search with verification search (is omitted in PV nodes)
1079 // Step 9. Internal iterative deepening
1080 if ( depth >= IIDDepthAtPVNodes
1081 && ttMove == MOVE_NONE)
1083 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1084 ttMove = ss[ply].pv[ply];
1085 tte = TT.retrieve(pos.get_key());
1088 // Step 10. Loop through moves
1089 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1091 // Initialize a MovePicker object for the current position
1092 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1093 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1096 while ( alpha < beta
1097 && (move = mp.get_next_move()) != MOVE_NONE
1098 && !TM.thread_should_stop(threadID))
1100 assert(move_is_ok(move));
1102 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1103 moveIsCheck = pos.move_is_check(move, ci);
1104 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1106 // Step 11. Decide the new search depth
1107 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1109 // Singular extension search. We extend the TT move if its value is much better than
1110 // its siblings. To verify this we do a reduced search on all the other moves but the
1111 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1112 if ( depth >= SingularExtensionDepthAtPVNodes
1114 && move == tte->move()
1116 && is_lower_bound(tte->type())
1117 && tte->depth() >= depth - 3 * OnePly)
1119 Value ttValue = value_from_tt(tte->value(), ply);
1121 if (abs(ttValue) < VALUE_KNOWN_WIN)
1123 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1125 if (excValue < ttValue - SingularExtensionMargin)
1130 newDepth = depth - OnePly + ext;
1132 // Update current move (this must be done after singular extension search)
1133 movesSearched[moveCount++] = ss[ply].currentMove = move;
1135 // Step 12. Futility pruning (is omitted in PV nodes)
1137 // Step 13. Make the move
1138 pos.do_move(move, st, ci, moveIsCheck);
1140 // Step extra. pv search (only in PV nodes)
1141 // The first move in list is the expected PV
1143 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1146 // Step 14. Reduced search
1147 // if the move fails high will be re-searched at full depth.
1148 bool doFullDepthSearch = true;
1150 if ( depth >= 3 * OnePly
1152 && !captureOrPromotion
1153 && !move_is_castle(move)
1154 && !move_is_killer(move, ss[ply]))
1156 ss[ply].reduction = pv_reduction(depth, moveCount);
1157 if (ss[ply].reduction)
1159 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1160 doFullDepthSearch = (value > alpha);
1164 // Step 15. Full depth search
1165 if (doFullDepthSearch)
1167 ss[ply].reduction = Depth(0);
1168 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1170 // Step extra. pv search (only in PV nodes)
1171 if (value > alpha && value < beta)
1172 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1176 // Step 16. Undo move
1177 pos.undo_move(move);
1179 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1181 // Step 17. Check for new best move
1182 if (value > bestValue)
1189 if (value == value_mate_in(ply + 1))
1190 ss[ply].mateKiller = move;
1194 // Step 18. Check for split
1195 if ( TM.active_threads() > 1
1197 && depth >= MinimumSplitDepth
1199 && TM.available_thread_exists(threadID)
1201 && !TM.thread_should_stop(threadID)
1202 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1203 depth, &moveCount, &mp, threadID, true))
1207 // Step 19. Check for mate and stalemate
1208 // All legal moves have been searched and if there were
1209 // no legal moves, it must be mate or stalemate.
1211 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1213 // Step 20. Update tables
1214 // If the search is not aborted, update the transposition table,
1215 // history counters, and killer moves.
1216 if (AbortSearch || TM.thread_should_stop(threadID))
1219 if (bestValue <= oldAlpha)
1220 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1222 else if (bestValue >= beta)
1224 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1225 move = ss[ply].pv[ply];
1226 if (!pos.move_is_capture_or_promotion(move))
1228 update_history(pos, move, depth, movesSearched, moveCount);
1229 update_killers(move, ss[ply]);
1231 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1234 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1240 // search() is the search function for zero-width nodes.
1242 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1243 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1245 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1246 assert(ply >= 0 && ply < PLY_MAX);
1247 assert(threadID >= 0 && threadID < TM.active_threads());
1249 Move movesSearched[256];
1254 Depth ext, newDepth;
1255 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1256 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1257 bool mateThreat = false;
1259 refinedValue = bestValue = value = -VALUE_INFINITE;
1262 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1264 // Step 1. Initialize node and poll
1265 // Polling can abort search.
1266 init_node(ss, ply, threadID);
1268 // Step 2. Check for aborted search and immediate draw
1269 if (AbortSearch || TM.thread_should_stop(threadID))
1272 if (pos.is_draw() || ply >= PLY_MAX - 1)
1275 // Step 3. Mate distance pruning
1276 if (value_mated_in(ply) >= beta)
1279 if (value_mate_in(ply + 1) < beta)
1282 // Step 4. Transposition table lookup
1284 // We don't want the score of a partial search to overwrite a previous full search
1285 // TT value, so we use a different position key in case of an excluded move exists.
1286 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1288 tte = TT.retrieve(posKey);
1289 ttMove = (tte ? tte->move() : MOVE_NONE);
1291 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1293 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1294 return value_from_tt(tte->value(), ply);
1297 // Step 5. Evaluate the position statically
1298 isCheck = pos.is_check();
1302 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1303 ss[ply].eval = value_from_tt(tte->value(), ply);
1305 ss[ply].eval = evaluate(pos, ei, threadID);
1307 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1308 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1312 if ( !value_is_mate(beta)
1314 && depth < RazorDepth
1315 && refinedValue < beta - razor_margin(depth)
1316 && ss[ply - 1].currentMove != MOVE_NULL
1317 && ttMove == MOVE_NONE
1318 && !pos.has_pawn_on_7th(pos.side_to_move()))
1320 Value rbeta = beta - razor_margin(depth);
1321 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1323 return v; //FIXME: Logically should be: return (v + razor_margin(depth));
1326 // Step 7. Static null move pruning
1327 // We're betting that the opponent doesn't have a move that will reduce
1328 // the score by more than fuility_margin(depth) if we do a null move.
1331 && depth < RazorDepth
1332 && refinedValue - futility_margin(depth, 0) >= beta)
1333 return refinedValue - futility_margin(depth, 0);
1335 // Step 8. Null move search with verification search
1336 // When we jump directly to qsearch() we do a null move only if static value is
1337 // at least beta. Otherwise we do a null move if static value is not more than
1338 // NullMoveMargin under beta.
1342 && !value_is_mate(beta)
1343 && ok_to_do_nullmove(pos)
1344 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1346 ss[ply].currentMove = MOVE_NULL;
1348 pos.do_null_move(st);
1350 // Null move dynamic reduction based on depth
1351 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1353 // Null move dynamic reduction based on value
1354 if (refinedValue - beta > PawnValueMidgame)
1357 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1359 pos.undo_null_move();
1361 if (nullValue >= beta)
1363 if (depth < 6 * OnePly)
1366 // Do zugzwang verification search
1367 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1371 // The null move failed low, which means that we may be faced with
1372 // some kind of threat. If the previous move was reduced, check if
1373 // the move that refuted the null move was somehow connected to the
1374 // move which was reduced. If a connection is found, return a fail
1375 // low score (which will cause the reduced move to fail high in the
1376 // parent node, which will trigger a re-search with full depth).
1377 if (nullValue == value_mated_in(ply + 2))
1380 ss[ply].threatMove = ss[ply + 1].currentMove;
1381 if ( depth < ThreatDepth
1382 && ss[ply - 1].reduction
1383 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1388 // Step 9. Internal iterative deepening
1389 if ( depth >= IIDDepthAtNonPVNodes
1390 && ttMove == MOVE_NONE
1392 && ss[ply].eval >= beta - IIDMargin)
1394 search(pos, ss, beta, depth/2, ply, false, threadID);
1395 ttMove = ss[ply].pv[ply];
1396 tte = TT.retrieve(posKey);
1399 // Step 10. Loop through moves
1400 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1402 // Initialize a MovePicker object for the current position
1403 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1406 while ( bestValue < beta
1407 && (move = mp.get_next_move()) != MOVE_NONE
1408 && !TM.thread_should_stop(threadID))
1410 assert(move_is_ok(move));
1412 if (move == excludedMove)
1415 moveIsCheck = pos.move_is_check(move, ci);
1416 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1417 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1419 // Step 11. Decide the new search depth
1420 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1422 // Singular extension search. We extend the TT move if its value is much better than
1423 // its siblings. To verify this we do a reduced search on all the other moves but the
1424 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1425 if ( depth >= SingularExtensionDepthAtNonPVNodes
1427 && move == tte->move()
1428 && !excludedMove // Do not allow recursive single-reply search
1430 && is_lower_bound(tte->type())
1431 && tte->depth() >= depth - 3 * OnePly)
1433 Value ttValue = value_from_tt(tte->value(), ply);
1435 if (abs(ttValue) < VALUE_KNOWN_WIN)
1437 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1439 if (excValue < ttValue - SingularExtensionMargin)
1444 newDepth = depth - OnePly + ext;
1446 // Update current move (this must be done after singular extension search)
1447 movesSearched[moveCount++] = ss[ply].currentMove = move;
1449 // Step 12. Futility pruning
1452 && !captureOrPromotion
1453 && !move_is_castle(move)
1456 // Move count based pruning
1457 if ( moveCount >= futility_move_count(depth)
1458 && ok_to_prune(pos, move, ss[ply].threatMove)
1459 && bestValue > value_mated_in(PLY_MAX))
1462 // Value based pruning
1463 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1464 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1465 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1467 if (futilityValueScaled < beta)
1469 if (futilityValueScaled > bestValue)
1470 bestValue = futilityValueScaled;
1475 // Step 13. Make the move
1476 pos.do_move(move, st, ci, moveIsCheck);
1478 // Step 14. Reduced search
1479 // if the move fails high will be re-searched at full depth.
1480 bool doFullDepthSearch = true;
1482 if ( depth >= 3*OnePly
1484 && !captureOrPromotion
1485 && !move_is_castle(move)
1486 && !move_is_killer(move, ss[ply]))
1488 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1489 if (ss[ply].reduction)
1491 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1492 doFullDepthSearch = (value >= beta);
1496 // Step 15. Full depth search
1497 if (doFullDepthSearch)
1499 ss[ply].reduction = Depth(0);
1500 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1503 // Step 16. Undo move
1504 pos.undo_move(move);
1506 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1508 // Step 17. Check for new best move
1509 if (value > bestValue)
1515 if (value == value_mate_in(ply + 1))
1516 ss[ply].mateKiller = move;
1519 // Step 18. Check for split
1520 if ( TM.active_threads() > 1
1522 && depth >= MinimumSplitDepth
1524 && TM.available_thread_exists(threadID)
1526 && !TM.thread_should_stop(threadID)
1527 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1528 depth, &moveCount, &mp, threadID, false))
1532 // Step 19. Check for mate and stalemate
1533 // All legal moves have been searched and if there were
1534 // no legal moves, it must be mate or stalemate.
1535 // If one move was excluded return fail low.
1537 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1539 // Step 20. Update tables
1540 // If the search is not aborted, update the transposition table,
1541 // history counters, and killer moves.
1542 if (AbortSearch || TM.thread_should_stop(threadID))
1545 if (bestValue < beta)
1546 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1549 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1550 move = ss[ply].pv[ply];
1551 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1552 if (!pos.move_is_capture_or_promotion(move))
1554 update_history(pos, move, depth, movesSearched, moveCount);
1555 update_killers(move, ss[ply]);
1560 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1566 // qsearch() is the quiescence search function, which is called by the main
1567 // search function when the remaining depth is zero (or, to be more precise,
1568 // less than OnePly).
1570 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1571 Depth depth, int ply, int threadID) {
1573 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1574 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1576 assert(ply >= 0 && ply < PLY_MAX);
1577 assert(threadID >= 0 && threadID < TM.active_threads());
1582 Value staticValue, bestValue, value, futilityBase, futilityValue;
1583 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1584 const TTEntry* tte = NULL;
1586 bool pvNode = (beta - alpha != 1);
1587 Value oldAlpha = alpha;
1589 // Initialize, and make an early exit in case of an aborted search,
1590 // an instant draw, maximum ply reached, etc.
1591 init_node(ss, ply, threadID);
1593 // After init_node() that calls poll()
1594 if (AbortSearch || TM.thread_should_stop(threadID))
1597 if (pos.is_draw() || ply >= PLY_MAX - 1)
1600 // Transposition table lookup. At PV nodes, we don't use the TT for
1601 // pruning, but only for move ordering.
1602 tte = TT.retrieve(pos.get_key());
1603 ttMove = (tte ? tte->move() : MOVE_NONE);
1605 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1607 assert(tte->type() != VALUE_TYPE_EVAL);
1609 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1610 return value_from_tt(tte->value(), ply);
1613 isCheck = pos.is_check();
1615 // Evaluate the position statically
1617 staticValue = -VALUE_INFINITE;
1618 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1619 staticValue = value_from_tt(tte->value(), ply);
1621 staticValue = evaluate(pos, ei, threadID);
1625 ss[ply].eval = staticValue;
1626 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1629 // Initialize "stand pat score", and return it immediately if it is
1631 bestValue = staticValue;
1633 if (bestValue >= beta)
1635 // Store the score to avoid a future costly evaluation() call
1636 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1637 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1642 if (bestValue > alpha)
1645 // If we are near beta then try to get a cutoff pushing checks a bit further
1646 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1648 // Initialize a MovePicker object for the current position, and prepare
1649 // to search the moves. Because the depth is <= 0 here, only captures,
1650 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1651 // and we are near beta) will be generated.
1652 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1654 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1655 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1657 // Loop through the moves until no moves remain or a beta cutoff
1659 while ( alpha < beta
1660 && (move = mp.get_next_move()) != MOVE_NONE)
1662 assert(move_is_ok(move));
1664 moveIsCheck = pos.move_is_check(move, ci);
1666 // Update current move
1668 ss[ply].currentMove = move;
1676 && !move_is_promotion(move)
1677 && !pos.move_is_passed_pawn_push(move))
1679 futilityValue = futilityBase
1680 + pos.endgame_value_of_piece_on(move_to(move))
1681 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1683 if (futilityValue < alpha)
1685 if (futilityValue > bestValue)
1686 bestValue = futilityValue;
1691 // Detect blocking evasions that are candidate to be pruned
1692 evasionPrunable = isCheck
1693 && bestValue != -VALUE_INFINITE
1694 && !pos.move_is_capture(move)
1695 && pos.type_of_piece_on(move_from(move)) != KING
1696 && !pos.can_castle(pos.side_to_move());
1698 // Don't search moves with negative SEE values
1699 if ( (!isCheck || evasionPrunable)
1702 && !move_is_promotion(move)
1703 && pos.see_sign(move) < 0)
1706 // Make and search the move
1707 pos.do_move(move, st, ci, moveIsCheck);
1708 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1709 pos.undo_move(move);
1711 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1714 if (value > bestValue)
1725 // All legal moves have been searched. A special case: If we're in check
1726 // and no legal moves were found, it is checkmate.
1727 if (!moveCount && pos.is_check()) // Mate!
1728 return value_mated_in(ply);
1730 // Update transposition table
1731 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1732 if (bestValue <= oldAlpha)
1734 // If bestValue isn't changed it means it is still the static evaluation
1735 // of the node, so keep this info to avoid a future evaluation() call.
1736 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1737 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1739 else if (bestValue >= beta)
1741 move = ss[ply].pv[ply];
1742 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1744 // Update killers only for good checking moves
1745 if (!pos.move_is_capture_or_promotion(move))
1746 update_killers(move, ss[ply]);
1749 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1751 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1757 // sp_search() is used to search from a split point. This function is called
1758 // by each thread working at the split point. It is similar to the normal
1759 // search() function, but simpler. Because we have already probed the hash
1760 // table, done a null move search, and searched the first move before
1761 // splitting, we don't have to repeat all this work in sp_search(). We
1762 // also don't need to store anything to the hash table here: This is taken
1763 // care of after we return from the split point.
1764 // FIXME: We are currently ignoring mateThreat flag here
1766 void sp_search(SplitPoint* sp, int threadID) {
1768 assert(threadID >= 0 && threadID < TM.active_threads());
1769 assert(TM.active_threads() > 1);
1773 Depth ext, newDepth;
1774 Value value, futilityValueScaled;
1775 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1777 value = -VALUE_INFINITE;
1779 Position pos(*sp->pos);
1781 SearchStack* ss = sp->sstack[threadID];
1782 isCheck = pos.is_check();
1784 // Step 10. Loop through moves
1785 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1786 lock_grab(&(sp->lock));
1788 while ( sp->bestValue < sp->beta
1789 && !TM.thread_should_stop(threadID)
1790 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1792 moveCount = ++sp->moves;
1793 lock_release(&(sp->lock));
1795 assert(move_is_ok(move));
1797 moveIsCheck = pos.move_is_check(move, ci);
1798 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1800 // Step 11. Decide the new search depth
1801 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1802 newDepth = sp->depth - OnePly + ext;
1804 // Update current move
1805 ss[sp->ply].currentMove = move;
1807 // Step 12. Futility pruning
1810 && !captureOrPromotion
1811 && !move_is_castle(move))
1813 // Move count based pruning
1814 if ( moveCount >= futility_move_count(sp->depth)
1815 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1816 && sp->bestValue > value_mated_in(PLY_MAX))
1818 lock_grab(&(sp->lock));
1822 // Value based pruning
1823 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1824 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1825 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1827 if (futilityValueScaled < sp->beta)
1829 lock_grab(&(sp->lock));
1831 if (futilityValueScaled > sp->bestValue)
1832 sp->bestValue = futilityValueScaled;
1837 // Step 13. Make the move
1838 pos.do_move(move, st, ci, moveIsCheck);
1840 // Step 14. Reduced search
1841 // if the move fails high will be re-searched at full depth.
1842 bool doFullDepthSearch = true;
1845 && !captureOrPromotion
1846 && !move_is_castle(move)
1847 && !move_is_killer(move, ss[sp->ply]))
1849 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1850 if (ss[sp->ply].reduction)
1852 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1853 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1857 // Step 15. Full depth search
1858 if (doFullDepthSearch)
1860 ss[sp->ply].reduction = Depth(0);
1861 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1864 // Step 16. Undo move
1865 pos.undo_move(move);
1867 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1869 // Step 17. Check for new best move
1870 lock_grab(&(sp->lock));
1872 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1874 sp->bestValue = value;
1875 if (sp->bestValue >= sp->beta)
1877 sp->stopRequest = true;
1878 sp_update_pv(sp->parentSstack, ss, sp->ply);
1883 /* Here we have the lock still grabbed */
1885 sp->slaves[threadID] = 0;
1888 lock_release(&(sp->lock));
1892 // sp_search_pv() is used to search from a PV split point. This function
1893 // is called by each thread working at the split point. It is similar to
1894 // the normal search_pv() function, but simpler. Because we have already
1895 // probed the hash table and searched the first move before splitting, we
1896 // don't have to repeat all this work in sp_search_pv(). We also don't
1897 // need to store anything to the hash table here: This is taken care of
1898 // after we return from the split point.
1899 // FIXME: We are ignoring mateThreat flag!
1901 void sp_search_pv(SplitPoint* sp, int threadID) {
1903 assert(threadID >= 0 && threadID < TM.active_threads());
1904 assert(TM.active_threads() > 1);
1908 Depth ext, newDepth;
1910 bool moveIsCheck, captureOrPromotion, dangerous;
1912 value = -VALUE_INFINITE;
1914 Position pos(*sp->pos);
1916 SearchStack* ss = sp->sstack[threadID];
1918 // Step 10. Loop through moves
1919 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1920 lock_grab(&(sp->lock));
1922 while ( sp->alpha < sp->beta
1923 && !TM.thread_should_stop(threadID)
1924 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1926 moveCount = ++sp->moves;
1927 lock_release(&(sp->lock));
1929 assert(move_is_ok(move));
1931 moveIsCheck = pos.move_is_check(move, ci);
1932 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1934 // Step 11. Decide the new search depth
1935 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1936 newDepth = sp->depth - OnePly + ext;
1938 // Update current move
1939 ss[sp->ply].currentMove = move;
1941 // Step 12. Futility pruning (is omitted in PV nodes)
1943 // Step 13. Make the move
1944 pos.do_move(move, st, ci, moveIsCheck);
1946 // Step 14. Reduced search
1947 // if the move fails high will be re-searched at full depth.
1948 bool doFullDepthSearch = true;
1951 && !captureOrPromotion
1952 && !move_is_castle(move)
1953 && !move_is_killer(move, ss[sp->ply]))
1955 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1956 if (ss[sp->ply].reduction)
1958 Value localAlpha = sp->alpha;
1959 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1960 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1964 // Step 15. Full depth search
1965 if (doFullDepthSearch)
1967 Value localAlpha = sp->alpha;
1968 ss[sp->ply].reduction = Depth(0);
1969 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1971 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1973 // If another thread has failed high then sp->alpha has been increased
1974 // to be higher or equal then beta, if so, avoid to start a PV search.
1975 localAlpha = sp->alpha;
1976 if (localAlpha < sp->beta)
1977 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1981 // Step 16. Undo move
1982 pos.undo_move(move);
1984 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1986 // Step 17. Check for new best move
1987 lock_grab(&(sp->lock));
1989 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1991 sp->bestValue = value;
1992 if (value > sp->alpha)
1994 // Ask threads to stop before to modify sp->alpha
1995 if (value >= sp->beta)
1996 sp->stopRequest = true;
2000 sp_update_pv(sp->parentSstack, ss, sp->ply);
2001 if (value == value_mate_in(sp->ply + 1))
2002 ss[sp->ply].mateKiller = move;
2007 /* Here we have the lock still grabbed */
2009 sp->slaves[threadID] = 0;
2012 lock_release(&(sp->lock));
2016 // init_node() is called at the beginning of all the search functions
2017 // (search(), search_pv(), qsearch(), and so on) and initializes the
2018 // search stack object corresponding to the current node. Once every
2019 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2020 // for user input and checks whether it is time to stop the search.
2022 void init_node(SearchStack ss[], int ply, int threadID) {
2024 assert(ply >= 0 && ply < PLY_MAX);
2025 assert(threadID >= 0 && threadID < TM.active_threads());
2027 TM.incrementNodeCounter(threadID);
2032 if (NodesSincePoll >= NodesBetweenPolls)
2039 ss[ply + 2].initKillers();
2043 // update_pv() is called whenever a search returns a value > alpha.
2044 // It updates the PV in the SearchStack object corresponding to the
2047 void update_pv(SearchStack ss[], int ply) {
2049 assert(ply >= 0 && ply < PLY_MAX);
2053 ss[ply].pv[ply] = ss[ply].currentMove;
2055 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2056 ss[ply].pv[p] = ss[ply + 1].pv[p];
2058 ss[ply].pv[p] = MOVE_NONE;
2062 // sp_update_pv() is a variant of update_pv for use at split points. The
2063 // difference between the two functions is that sp_update_pv also updates
2064 // the PV at the parent node.
2066 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2068 assert(ply >= 0 && ply < PLY_MAX);
2072 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2074 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2075 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2077 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2081 // connected_moves() tests whether two moves are 'connected' in the sense
2082 // that the first move somehow made the second move possible (for instance
2083 // if the moving piece is the same in both moves). The first move is assumed
2084 // to be the move that was made to reach the current position, while the
2085 // second move is assumed to be a move from the current position.
2087 bool connected_moves(const Position& pos, Move m1, Move m2) {
2089 Square f1, t1, f2, t2;
2092 assert(move_is_ok(m1));
2093 assert(move_is_ok(m2));
2095 if (m2 == MOVE_NONE)
2098 // Case 1: The moving piece is the same in both moves
2104 // Case 2: The destination square for m2 was vacated by m1
2110 // Case 3: Moving through the vacated square
2111 if ( piece_is_slider(pos.piece_on(f2))
2112 && bit_is_set(squares_between(f2, t2), f1))
2115 // Case 4: The destination square for m2 is defended by the moving piece in m1
2116 p = pos.piece_on(t1);
2117 if (bit_is_set(pos.attacks_from(p, t1), t2))
2120 // Case 5: Discovered check, checking piece is the piece moved in m1
2121 if ( piece_is_slider(p)
2122 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2123 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2125 // discovered_check_candidates() works also if the Position's side to
2126 // move is the opposite of the checking piece.
2127 Color them = opposite_color(pos.side_to_move());
2128 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2130 if (bit_is_set(dcCandidates, f2))
2137 // value_is_mate() checks if the given value is a mate one
2138 // eventually compensated for the ply.
2140 bool value_is_mate(Value value) {
2142 assert(abs(value) <= VALUE_INFINITE);
2144 return value <= value_mated_in(PLY_MAX)
2145 || value >= value_mate_in(PLY_MAX);
2149 // move_is_killer() checks if the given move is among the
2150 // killer moves of that ply.
2152 bool move_is_killer(Move m, const SearchStack& ss) {
2154 const Move* k = ss.killers;
2155 for (int i = 0; i < KILLER_MAX; i++, k++)
2163 // extension() decides whether a move should be searched with normal depth,
2164 // or with extended depth. Certain classes of moves (checking moves, in
2165 // particular) are searched with bigger depth than ordinary moves and in
2166 // any case are marked as 'dangerous'. Note that also if a move is not
2167 // extended, as example because the corresponding UCI option is set to zero,
2168 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2170 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2171 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2173 assert(m != MOVE_NONE);
2175 Depth result = Depth(0);
2176 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2181 result += CheckExtension[pvNode];
2184 result += SingleEvasionExtension[pvNode];
2187 result += MateThreatExtension[pvNode];
2190 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2192 Color c = pos.side_to_move();
2193 if (relative_rank(c, move_to(m)) == RANK_7)
2195 result += PawnPushTo7thExtension[pvNode];
2198 if (pos.pawn_is_passed(c, move_to(m)))
2200 result += PassedPawnExtension[pvNode];
2205 if ( captureOrPromotion
2206 && pos.type_of_piece_on(move_to(m)) != PAWN
2207 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2208 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2209 && !move_is_promotion(m)
2212 result += PawnEndgameExtension[pvNode];
2217 && captureOrPromotion
2218 && pos.type_of_piece_on(move_to(m)) != PAWN
2219 && pos.see_sign(m) >= 0)
2225 return Min(result, OnePly);
2229 // ok_to_do_nullmove() looks at the current position and decides whether
2230 // doing a 'null move' should be allowed. In order to avoid zugzwang
2231 // problems, null moves are not allowed when the side to move has very
2232 // little material left. Currently, the test is a bit too simple: Null
2233 // moves are avoided only when the side to move has only pawns left.
2234 // It's probably a good idea to avoid null moves in at least some more
2235 // complicated endgames, e.g. KQ vs KR. FIXME
2237 bool ok_to_do_nullmove(const Position& pos) {
2239 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2243 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2244 // non-tactical moves late in the move list close to the leaves are
2245 // candidates for pruning.
2247 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2249 assert(move_is_ok(m));
2250 assert(threat == MOVE_NONE || move_is_ok(threat));
2251 assert(!pos.move_is_check(m));
2252 assert(!pos.move_is_capture_or_promotion(m));
2253 assert(!pos.move_is_passed_pawn_push(m));
2255 Square mfrom, mto, tfrom, tto;
2257 // Prune if there isn't any threat move
2258 if (threat == MOVE_NONE)
2261 mfrom = move_from(m);
2263 tfrom = move_from(threat);
2264 tto = move_to(threat);
2266 // Case 1: Don't prune moves which move the threatened piece
2270 // Case 2: If the threatened piece has value less than or equal to the
2271 // value of the threatening piece, don't prune move which defend it.
2272 if ( pos.move_is_capture(threat)
2273 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2274 || pos.type_of_piece_on(tfrom) == KING)
2275 && pos.move_attacks_square(m, tto))
2278 // Case 3: If the moving piece in the threatened move is a slider, don't
2279 // prune safe moves which block its ray.
2280 if ( piece_is_slider(pos.piece_on(tfrom))
2281 && bit_is_set(squares_between(tfrom, tto), mto)
2282 && pos.see_sign(m) >= 0)
2289 // ok_to_use_TT() returns true if a transposition table score
2290 // can be used at a given point in search.
2292 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2294 Value v = value_from_tt(tte->value(), ply);
2296 return ( tte->depth() >= depth
2297 || v >= Max(value_mate_in(PLY_MAX), beta)
2298 || v < Min(value_mated_in(PLY_MAX), beta))
2300 && ( (is_lower_bound(tte->type()) && v >= beta)
2301 || (is_upper_bound(tte->type()) && v < beta));
2305 // refine_eval() returns the transposition table score if
2306 // possible otherwise falls back on static position evaluation.
2308 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2313 Value v = value_from_tt(tte->value(), ply);
2315 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2316 || (is_upper_bound(tte->type()) && v < defaultEval))
2323 // update_history() registers a good move that produced a beta-cutoff
2324 // in history and marks as failures all the other moves of that ply.
2326 void update_history(const Position& pos, Move move, Depth depth,
2327 Move movesSearched[], int moveCount) {
2331 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2333 for (int i = 0; i < moveCount - 1; i++)
2335 m = movesSearched[i];
2339 if (!pos.move_is_capture_or_promotion(m))
2340 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2345 // update_killers() add a good move that produced a beta-cutoff
2346 // among the killer moves of that ply.
2348 void update_killers(Move m, SearchStack& ss) {
2350 if (m == ss.killers[0])
2353 for (int i = KILLER_MAX - 1; i > 0; i--)
2354 ss.killers[i] = ss.killers[i - 1];
2360 // update_gains() updates the gains table of a non-capture move given
2361 // the static position evaluation before and after the move.
2363 void update_gains(const Position& pos, Move m, Value before, Value after) {
2366 && before != VALUE_NONE
2367 && after != VALUE_NONE
2368 && pos.captured_piece() == NO_PIECE_TYPE
2369 && !move_is_castle(m)
2370 && !move_is_promotion(m))
2371 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2375 // current_search_time() returns the number of milliseconds which have passed
2376 // since the beginning of the current search.
2378 int current_search_time() {
2380 return get_system_time() - SearchStartTime;
2384 // nps() computes the current nodes/second count.
2388 int t = current_search_time();
2389 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2393 // poll() performs two different functions: It polls for user input, and it
2394 // looks at the time consumed so far and decides if it's time to abort the
2397 void poll(SearchStack ss[], int ply) {
2399 static int lastInfoTime;
2400 int t = current_search_time();
2405 // We are line oriented, don't read single chars
2406 std::string command;
2408 if (!std::getline(std::cin, command))
2411 if (command == "quit")
2414 PonderSearch = false;
2418 else if (command == "stop")
2421 PonderSearch = false;
2423 else if (command == "ponderhit")
2427 // Print search information
2431 else if (lastInfoTime > t)
2432 // HACK: Must be a new search where we searched less than
2433 // NodesBetweenPolls nodes during the first second of search.
2436 else if (t - lastInfoTime >= 1000)
2443 if (dbg_show_hit_rate)
2444 dbg_print_hit_rate();
2446 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2447 << " time " << t << " hashfull " << TT.full() << endl;
2449 // We only support current line printing in single thread mode
2450 if (ShowCurrentLine && TM.active_threads() == 1)
2452 cout << "info currline";
2453 for (int p = 0; p < ply; p++)
2454 cout << " " << ss[p].currentMove;
2460 // Should we stop the search?
2464 bool stillAtFirstMove = RootMoveNumber == 1
2465 && !AspirationFailLow
2466 && t > MaxSearchTime + ExtraSearchTime;
2468 bool noMoreTime = t > AbsoluteMaxSearchTime
2469 || stillAtFirstMove;
2471 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2472 || (ExactMaxTime && t >= ExactMaxTime)
2473 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2478 // ponderhit() is called when the program is pondering (i.e. thinking while
2479 // it's the opponent's turn to move) in order to let the engine know that
2480 // it correctly predicted the opponent's move.
2484 int t = current_search_time();
2485 PonderSearch = false;
2487 bool stillAtFirstMove = RootMoveNumber == 1
2488 && !AspirationFailLow
2489 && t > MaxSearchTime + ExtraSearchTime;
2491 bool noMoreTime = t > AbsoluteMaxSearchTime
2492 || stillAtFirstMove;
2494 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2499 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2501 void init_ss_array(SearchStack ss[]) {
2503 for (int i = 0; i < 3; i++)
2506 ss[i].initKillers();
2511 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2512 // while the program is pondering. The point is to work around a wrinkle in
2513 // the UCI protocol: When pondering, the engine is not allowed to give a
2514 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2515 // We simply wait here until one of these commands is sent, and return,
2516 // after which the bestmove and pondermove will be printed (in id_loop()).
2518 void wait_for_stop_or_ponderhit() {
2520 std::string command;
2524 if (!std::getline(std::cin, command))
2527 if (command == "quit")
2532 else if (command == "ponderhit" || command == "stop")
2538 // print_pv_info() prints to standard output and eventually to log file information on
2539 // the current PV line. It is called at each iteration or after a new pv is found.
2541 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2543 cout << "info depth " << Iteration
2544 << " score " << value_to_string(value)
2545 << ((value >= beta) ? " lowerbound" :
2546 ((value <= alpha)? " upperbound" : ""))
2547 << " time " << current_search_time()
2548 << " nodes " << TM.nodes_searched()
2552 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2553 cout << ss[0].pv[j] << " ";
2559 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2560 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2562 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2563 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2568 // init_thread() is the function which is called when a new thread is
2569 // launched. It simply calls the idle_loop() function with the supplied
2570 // threadID. There are two versions of this function; one for POSIX
2571 // threads and one for Windows threads.
2573 #if !defined(_MSC_VER)
2575 void* init_thread(void *threadID) {
2577 TM.idle_loop(*(int*)threadID, NULL);
2583 DWORD WINAPI init_thread(LPVOID threadID) {
2585 TM.idle_loop(*(int*)threadID, NULL);
2592 /// The ThreadsManager class
2594 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2595 // get_beta_counters() are getters/setters for the per thread
2596 // counters used to sort the moves at root.
2598 void ThreadsManager::resetNodeCounters() {
2600 for (int i = 0; i < MAX_THREADS; i++)
2601 threads[i].nodes = 0ULL;
2604 void ThreadsManager::resetBetaCounters() {
2606 for (int i = 0; i < MAX_THREADS; i++)
2607 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2610 int64_t ThreadsManager::nodes_searched() const {
2612 int64_t result = 0ULL;
2613 for (int i = 0; i < ActiveThreads; i++)
2614 result += threads[i].nodes;
2619 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2622 for (int i = 0; i < MAX_THREADS; i++)
2624 our += threads[i].betaCutOffs[us];
2625 their += threads[i].betaCutOffs[opposite_color(us)];
2630 // idle_loop() is where the threads are parked when they have no work to do.
2631 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2632 // object for which the current thread is the master.
2634 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2636 assert(threadID >= 0 && threadID < MAX_THREADS);
2640 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2641 // master should exit as last one.
2642 if (AllThreadsShouldExit)
2645 threads[threadID].state = THREAD_TERMINATED;
2649 // If we are not thinking, wait for a condition to be signaled
2650 // instead of wasting CPU time polling for work.
2651 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2654 assert(threadID != 0);
2655 threads[threadID].state = THREAD_SLEEPING;
2657 #if !defined(_MSC_VER)
2658 lock_grab(&WaitLock);
2659 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2660 pthread_cond_wait(&WaitCond, &WaitLock);
2661 lock_release(&WaitLock);
2663 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2667 // If thread has just woken up, mark it as available
2668 if (threads[threadID].state == THREAD_SLEEPING)
2669 threads[threadID].state = THREAD_AVAILABLE;
2671 // If this thread has been assigned work, launch a search
2672 if (threads[threadID].state == THREAD_WORKISWAITING)
2674 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2676 threads[threadID].state = THREAD_SEARCHING;
2678 if (threads[threadID].splitPoint->pvNode)
2679 sp_search_pv(threads[threadID].splitPoint, threadID);
2681 sp_search(threads[threadID].splitPoint, threadID);
2683 assert(threads[threadID].state == THREAD_SEARCHING);
2685 threads[threadID].state = THREAD_AVAILABLE;
2688 // If this thread is the master of a split point and all threads have
2689 // finished their work at this split point, return from the idle loop.
2690 if (waitSp != NULL && waitSp->cpus == 0)
2692 assert(threads[threadID].state == THREAD_AVAILABLE);
2694 threads[threadID].state = THREAD_SEARCHING;
2701 // init_threads() is called during startup. It launches all helper threads,
2702 // and initializes the split point stack and the global locks and condition
2705 void ThreadsManager::init_threads() {
2710 #if !defined(_MSC_VER)
2711 pthread_t pthread[1];
2714 // Initialize global locks
2715 lock_init(&MPLock, NULL);
2716 lock_init(&WaitLock, NULL);
2718 #if !defined(_MSC_VER)
2719 pthread_cond_init(&WaitCond, NULL);
2721 for (i = 0; i < MAX_THREADS; i++)
2722 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2725 // Initialize SplitPointStack locks
2726 for (i = 0; i < MAX_THREADS; i++)
2727 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2729 SplitPointStack[i][j].parent = NULL;
2730 lock_init(&(SplitPointStack[i][j].lock), NULL);
2733 // Will be set just before program exits to properly end the threads
2734 AllThreadsShouldExit = false;
2736 // Threads will be put to sleep as soon as created
2737 AllThreadsShouldSleep = true;
2739 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2741 threads[0].state = THREAD_SEARCHING;
2742 for (i = 1; i < MAX_THREADS; i++)
2743 threads[i].state = THREAD_AVAILABLE;
2745 // Launch the helper threads
2746 for (i = 1; i < MAX_THREADS; i++)
2749 #if !defined(_MSC_VER)
2750 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2752 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2757 cout << "Failed to create thread number " << i << endl;
2758 Application::exit_with_failure();
2761 // Wait until the thread has finished launching and is gone to sleep
2762 while (threads[i].state != THREAD_SLEEPING);
2767 // exit_threads() is called when the program exits. It makes all the
2768 // helper threads exit cleanly.
2770 void ThreadsManager::exit_threads() {
2772 ActiveThreads = MAX_THREADS; // HACK
2773 AllThreadsShouldSleep = true; // HACK
2774 wake_sleeping_threads();
2776 // This makes the threads to exit idle_loop()
2777 AllThreadsShouldExit = true;
2779 // Wait for thread termination
2780 for (int i = 1; i < MAX_THREADS; i++)
2781 while (threads[i].state != THREAD_TERMINATED);
2783 // Now we can safely destroy the locks
2784 for (int i = 0; i < MAX_THREADS; i++)
2785 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2786 lock_destroy(&(SplitPointStack[i][j].lock));
2788 lock_destroy(&WaitLock);
2789 lock_destroy(&MPLock);
2793 // thread_should_stop() checks whether the thread should stop its search.
2794 // This can happen if a beta cutoff has occurred in the thread's currently
2795 // active split point, or in some ancestor of the current split point.
2797 bool ThreadsManager::thread_should_stop(int threadID) const {
2799 assert(threadID >= 0 && threadID < ActiveThreads);
2803 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2808 // thread_is_available() checks whether the thread with threadID "slave" is
2809 // available to help the thread with threadID "master" at a split point. An
2810 // obvious requirement is that "slave" must be idle. With more than two
2811 // threads, this is not by itself sufficient: If "slave" is the master of
2812 // some active split point, it is only available as a slave to the other
2813 // threads which are busy searching the split point at the top of "slave"'s
2814 // split point stack (the "helpful master concept" in YBWC terminology).
2816 bool ThreadsManager::thread_is_available(int slave, int master) const {
2818 assert(slave >= 0 && slave < ActiveThreads);
2819 assert(master >= 0 && master < ActiveThreads);
2820 assert(ActiveThreads > 1);
2822 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2825 // Make a local copy to be sure doesn't change under our feet
2826 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2828 if (localActiveSplitPoints == 0)
2829 // No active split points means that the thread is available as
2830 // a slave for any other thread.
2833 if (ActiveThreads == 2)
2836 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2837 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2838 // could have been set to 0 by another thread leading to an out of bound access.
2839 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2846 // available_thread_exists() tries to find an idle thread which is available as
2847 // a slave for the thread with threadID "master".
2849 bool ThreadsManager::available_thread_exists(int master) const {
2851 assert(master >= 0 && master < ActiveThreads);
2852 assert(ActiveThreads > 1);
2854 for (int i = 0; i < ActiveThreads; i++)
2855 if (thread_is_available(i, master))
2862 // split() does the actual work of distributing the work at a node between
2863 // several threads at PV nodes. If it does not succeed in splitting the
2864 // node (because no idle threads are available, or because we have no unused
2865 // split point objects), the function immediately returns false. If
2866 // splitting is possible, a SplitPoint object is initialized with all the
2867 // data that must be copied to the helper threads (the current position and
2868 // search stack, alpha, beta, the search depth, etc.), and we tell our
2869 // helper threads that they have been assigned work. This will cause them
2870 // to instantly leave their idle loops and call sp_search_pv(). When all
2871 // threads have returned from sp_search_pv (or, equivalently, when
2872 // splitPoint->cpus becomes 0), split() returns true.
2874 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2875 Value* alpha, const Value beta, Value* bestValue,
2876 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2879 assert(sstck != NULL);
2880 assert(ply >= 0 && ply < PLY_MAX);
2881 assert(*bestValue >= -VALUE_INFINITE);
2882 assert( ( pvNode && *bestValue <= *alpha)
2883 || (!pvNode && *bestValue < beta ));
2884 assert(!pvNode || *alpha < beta);
2885 assert(beta <= VALUE_INFINITE);
2886 assert(depth > Depth(0));
2887 assert(master >= 0 && master < ActiveThreads);
2888 assert(ActiveThreads > 1);
2890 SplitPoint* splitPoint;
2894 // If no other thread is available to help us, or if we have too many
2895 // active split points, don't split.
2896 if ( !available_thread_exists(master)
2897 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2899 lock_release(&MPLock);
2903 // Pick the next available split point object from the split point stack
2904 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2906 // Initialize the split point object
2907 splitPoint->parent = threads[master].splitPoint;
2908 splitPoint->stopRequest = false;
2909 splitPoint->ply = ply;
2910 splitPoint->depth = depth;
2911 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2912 splitPoint->beta = beta;
2913 splitPoint->pvNode = pvNode;
2914 splitPoint->bestValue = *bestValue;
2915 splitPoint->master = master;
2916 splitPoint->mp = mp;
2917 splitPoint->moves = *moves;
2918 splitPoint->cpus = 1;
2919 splitPoint->pos = &p;
2920 splitPoint->parentSstack = sstck;
2921 for (int i = 0; i < ActiveThreads; i++)
2922 splitPoint->slaves[i] = 0;
2924 threads[master].splitPoint = splitPoint;
2925 threads[master].activeSplitPoints++;
2927 // If we are here it means we are not available
2928 assert(threads[master].state != THREAD_AVAILABLE);
2930 // Allocate available threads setting state to THREAD_BOOKED
2931 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2932 if (thread_is_available(i, master))
2934 threads[i].state = THREAD_BOOKED;
2935 threads[i].splitPoint = splitPoint;
2936 splitPoint->slaves[i] = 1;
2940 assert(splitPoint->cpus > 1);
2942 // We can release the lock because slave threads are already booked and master is not available
2943 lock_release(&MPLock);
2945 // Tell the threads that they have work to do. This will make them leave
2946 // their idle loop. But before copy search stack tail for each thread.
2947 for (int i = 0; i < ActiveThreads; i++)
2948 if (i == master || splitPoint->slaves[i])
2950 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2952 assert(i == master || threads[i].state == THREAD_BOOKED);
2954 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2957 // Everything is set up. The master thread enters the idle loop, from
2958 // which it will instantly launch a search, because its state is
2959 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2960 // idle loop, which means that the main thread will return from the idle
2961 // loop when all threads have finished their work at this split point
2962 // (i.e. when splitPoint->cpus == 0).
2963 idle_loop(master, splitPoint);
2965 // We have returned from the idle loop, which means that all threads are
2966 // finished. Update alpha, beta and bestValue, and return.
2970 *alpha = splitPoint->alpha;
2972 *bestValue = splitPoint->bestValue;
2973 threads[master].activeSplitPoints--;
2974 threads[master].splitPoint = splitPoint->parent;
2976 lock_release(&MPLock);
2981 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2982 // to start a new search from the root.
2984 void ThreadsManager::wake_sleeping_threads() {
2986 assert(AllThreadsShouldSleep);
2987 assert(ActiveThreads > 0);
2989 AllThreadsShouldSleep = false;
2991 if (ActiveThreads == 1)
2994 #if !defined(_MSC_VER)
2995 pthread_mutex_lock(&WaitLock);
2996 pthread_cond_broadcast(&WaitCond);
2997 pthread_mutex_unlock(&WaitLock);
2999 for (int i = 1; i < MAX_THREADS; i++)
3000 SetEvent(SitIdleEvent[i]);
3006 // put_threads_to_sleep() makes all the threads go to sleep just before
3007 // to leave think(), at the end of the search. Threads should have already
3008 // finished the job and should be idle.
3010 void ThreadsManager::put_threads_to_sleep() {
3012 assert(!AllThreadsShouldSleep);
3014 // This makes the threads to go to sleep
3015 AllThreadsShouldSleep = true;
3018 /// The RootMoveList class
3020 // RootMoveList c'tor
3022 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3024 SearchStack ss[PLY_MAX_PLUS_2];
3025 MoveStack mlist[MaxRootMoves];
3027 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3029 // Generate all legal moves
3030 MoveStack* last = generate_moves(pos, mlist);
3032 // Add each move to the moves[] array
3033 for (MoveStack* cur = mlist; cur != last; cur++)
3035 bool includeMove = includeAllMoves;
3037 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3038 includeMove = (searchMoves[k] == cur->move);
3043 // Find a quick score for the move
3045 pos.do_move(cur->move, st);
3046 moves[count].move = cur->move;
3047 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3048 moves[count].pv[0] = cur->move;
3049 moves[count].pv[1] = MOVE_NONE;
3050 pos.undo_move(cur->move);
3057 // RootMoveList simple methods definitions
3059 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3061 moves[moveNum].nodes = nodes;
3062 moves[moveNum].cumulativeNodes += nodes;
3065 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3067 moves[moveNum].ourBeta = our;
3068 moves[moveNum].theirBeta = their;
3071 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3075 for (j = 0; pv[j] != MOVE_NONE; j++)
3076 moves[moveNum].pv[j] = pv[j];
3078 moves[moveNum].pv[j] = MOVE_NONE;
3082 // RootMoveList::sort() sorts the root move list at the beginning of a new
3085 void RootMoveList::sort() {
3087 sort_multipv(count - 1); // Sort all items
3091 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3092 // list by their scores and depths. It is used to order the different PVs
3093 // correctly in MultiPV mode.
3095 void RootMoveList::sort_multipv(int n) {
3099 for (i = 1; i <= n; i++)
3101 RootMove rm = moves[i];
3102 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3103 moves[j] = moves[j - 1];