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); }
75 void print_current_line(SearchStack ss[], int ply, int threadID);
77 void resetNodeCounters();
78 void resetBetaCounters();
79 int64_t nodes_searched() const;
80 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
81 bool available_thread_exists(int master) const;
82 bool thread_is_available(int slave, int master) const;
83 bool thread_should_stop(int threadID) const;
84 void wake_sleeping_threads();
85 void put_threads_to_sleep();
86 void idle_loop(int threadID, SplitPoint* waitSp);
87 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, Value* beta, Value* bestValue,
88 const Value futilityValue, Depth depth, int* moves, MovePicker* mp, int master, bool pvNode);
94 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
95 Thread threads[MAX_THREADS];
96 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
100 #if !defined(_MSC_VER)
101 pthread_cond_t WaitCond;
102 pthread_mutex_t WaitLock;
104 HANDLE SitIdleEvent[MAX_THREADS];
110 // RootMove struct is used for moves at the root at the tree. For each
111 // root move, we store a score, a node count, and a PV (really a refutation
112 // in the case of moves which fail low).
116 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
118 // RootMove::operator<() is the comparison function used when
119 // sorting the moves. A move m1 is considered to be better
120 // than a move m2 if it has a higher score, or if the moves
121 // have equal score but m1 has the higher node count.
122 bool operator<(const RootMove& m) const {
124 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
129 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
130 Move pv[PLY_MAX_PLUS_2];
134 // The RootMoveList class is essentially an array of RootMove objects, with
135 // a handful of methods for accessing the data in the individual moves.
140 RootMoveList(Position& pos, Move searchMoves[]);
142 int move_count() const { return count; }
143 Move get_move(int moveNum) const { return moves[moveNum].move; }
144 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
145 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
146 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
147 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
149 void set_move_nodes(int moveNum, int64_t nodes);
150 void set_beta_counters(int moveNum, int64_t our, int64_t their);
151 void set_move_pv(int moveNum, const Move pv[]);
153 void sort_multipv(int n);
156 static const int MaxRootMoves = 500;
157 RootMove moves[MaxRootMoves];
164 // Search depth at iteration 1
165 const Depth InitialDepth = OnePly;
167 // Use internal iterative deepening?
168 const bool UseIIDAtPVNodes = true;
169 const bool UseIIDAtNonPVNodes = true;
171 // Internal iterative deepening margin. At Non-PV moves, when
172 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
173 // search when the static evaluation is at most IIDMargin below beta.
174 const Value IIDMargin = Value(0x100);
176 // Easy move margin. An easy move candidate must be at least this much
177 // better than the second best move.
178 const Value EasyMoveMargin = Value(0x200);
180 // Null move margin. A null move search will not be done if the static
181 // evaluation of the position is more than NullMoveMargin below beta.
182 const Value NullMoveMargin = Value(0x200);
184 // If the TT move is at least SingleReplyMargin better then the
185 // remaining ones we will extend it.
186 const Value SingleReplyMargin = Value(0x20);
188 // Depth limit for razoring
189 const Depth RazorDepth = 4 * OnePly;
191 /// Lookup tables initialized at startup
193 // Reduction lookup tables and their getter functions
194 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
195 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
197 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
198 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
200 // Futility lookup tables and their getter functions
201 const Value FutilityMarginQS = Value(0x80);
202 int32_t FutilityMarginsMatrix[14][64]; // [depth][moveNumber]
203 int FutilityMoveCountArray[32]; // [depth]
205 inline Value futility_margin(Depth d, int mn) { return Value(d < 7*OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
206 inline int futility_move_count(Depth d) { return d < 16*OnePly ? FutilityMoveCountArray[d] : 512; }
208 /// Variables initialized by UCI options
210 // Depth limit for use of dynamic threat detection
213 // Last seconds noise filtering (LSN)
214 const bool UseLSNFiltering = true;
215 const int LSNTime = 4000; // In milliseconds
216 const Value LSNValue = value_from_centipawns(200);
217 bool loseOnTime = false;
219 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
220 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
221 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
223 // Iteration counters
226 // Scores and number of times the best move changed for each iteration
227 Value ValueByIteration[PLY_MAX_PLUS_2];
228 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
230 // Search window management
236 // Time managment variables
239 int MaxNodes, MaxDepth;
240 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
241 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
242 bool AbortSearch, Quit;
243 bool AspirationFailLow;
245 // Show current line?
246 bool ShowCurrentLine;
250 std::ofstream LogFile;
252 // MP related variables
253 Depth MinimumSplitDepth;
254 int MaxThreadsPerSplitPoint;
257 // Node counters, used only by thread[0] but try to keep in different
258 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
260 int NodesBetweenPolls = 30000;
267 Value id_loop(const Position& pos, Move searchMoves[]);
268 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta);
269 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
270 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
271 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
272 void sp_search(SplitPoint* sp, int threadID);
273 void sp_search_pv(SplitPoint* sp, int threadID);
274 void init_node(SearchStack ss[], int ply, int threadID);
275 void update_pv(SearchStack ss[], int ply);
276 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
277 bool connected_moves(const Position& pos, Move m1, Move m2);
278 bool value_is_mate(Value value);
279 bool move_is_killer(Move m, const SearchStack& ss);
280 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
281 bool ok_to_do_nullmove(const Position& pos);
282 bool ok_to_prune(const Position& pos, Move m, Move threat);
283 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
284 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
285 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
286 void update_killers(Move m, SearchStack& ss);
287 void update_gains(const Position& pos, Move move, Value before, Value after);
289 int current_search_time();
293 void wait_for_stop_or_ponderhit();
294 void init_ss_array(SearchStack ss[]);
296 #if !defined(_MSC_VER)
297 void *init_thread(void *threadID);
299 DWORD WINAPI init_thread(LPVOID threadID);
309 /// init_threads(), exit_threads() and nodes_searched() are helpers to
310 /// give accessibility to some TM methods from outside of current file.
312 void init_threads() { TM.init_threads(); }
313 void exit_threads() { TM.exit_threads(); }
314 int64_t nodes_searched() { return TM.nodes_searched(); }
317 /// perft() is our utility to verify move generation is bug free. All the legal
318 /// moves up to given depth are generated and counted and the sum returned.
320 int perft(Position& pos, Depth depth)
324 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
326 // If we are at the last ply we don't need to do and undo
327 // the moves, just to count them.
328 if (depth <= OnePly) // Replace with '<' to test also qsearch
330 while (mp.get_next_move()) sum++;
334 // Loop through all legal moves
336 while ((move = mp.get_next_move()) != MOVE_NONE)
339 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
340 sum += perft(pos, depth - OnePly);
347 /// think() is the external interface to Stockfish's search, and is called when
348 /// the program receives the UCI 'go' command. It initializes various
349 /// search-related global variables, and calls root_search(). It returns false
350 /// when a quit command is received during the search.
352 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
353 int time[], int increment[], int movesToGo, int maxDepth,
354 int maxNodes, int maxTime, Move searchMoves[]) {
356 // Initialize global search variables
357 StopOnPonderhit = AbortSearch = Quit = false;
358 AspirationFailLow = false;
360 SearchStartTime = get_system_time();
361 ExactMaxTime = maxTime;
364 InfiniteSearch = infinite;
365 PonderSearch = ponder;
366 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
368 // Look for a book move, only during games, not tests
369 if (UseTimeManagement && get_option_value_bool("OwnBook"))
372 if (get_option_value_string("Book File") != OpeningBook.file_name())
373 OpeningBook.open(get_option_value_string("Book File"));
375 bookMove = OpeningBook.get_move(pos);
376 if (bookMove != MOVE_NONE)
379 wait_for_stop_or_ponderhit();
381 cout << "bestmove " << bookMove << endl;
386 TM.resetNodeCounters();
388 if (button_was_pressed("New Game"))
389 loseOnTime = false; // Reset at the beginning of a new game
391 // Read UCI option values
392 TT.set_size(get_option_value_int("Hash"));
393 if (button_was_pressed("Clear Hash"))
396 bool PonderingEnabled = get_option_value_bool("Ponder");
397 MultiPV = get_option_value_int("MultiPV");
399 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
400 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
402 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
403 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
405 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
406 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
408 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
409 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
411 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
412 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
414 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
415 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
417 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
419 Chess960 = get_option_value_bool("UCI_Chess960");
420 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
421 UseLogFile = get_option_value_bool("Use Search Log");
423 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
425 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
426 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
428 read_weights(pos.side_to_move());
430 // Set the number of active threads
431 int newActiveThreads = get_option_value_int("Threads");
432 if (newActiveThreads != TM.active_threads())
434 TM.set_active_threads(newActiveThreads);
435 init_eval(TM.active_threads());
436 // HACK: init_eval() destroys the static castleRightsMask[] array in the
437 // Position class. The below line repairs the damage.
438 Position p(pos.to_fen());
442 // Wake up sleeping threads
443 TM.wake_sleeping_threads();
445 for (int i = 1; i < TM.active_threads(); i++)
446 assert(TM.thread_is_available(i, 0));
449 int myTime = time[side_to_move];
450 int myIncrement = increment[side_to_move];
451 if (UseTimeManagement)
453 if (!movesToGo) // Sudden death time control
457 MaxSearchTime = myTime / 30 + myIncrement;
458 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
460 else // Blitz game without increment
462 MaxSearchTime = myTime / 30;
463 AbsoluteMaxSearchTime = myTime / 8;
466 else // (x moves) / (y minutes)
470 MaxSearchTime = myTime / 2;
471 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
475 MaxSearchTime = myTime / Min(movesToGo, 20);
476 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
480 if (PonderingEnabled)
482 MaxSearchTime += MaxSearchTime / 4;
483 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
487 // Set best NodesBetweenPolls interval
489 NodesBetweenPolls = Min(MaxNodes, 30000);
490 else if (myTime && myTime < 1000)
491 NodesBetweenPolls = 1000;
492 else if (myTime && myTime < 5000)
493 NodesBetweenPolls = 5000;
495 NodesBetweenPolls = 30000;
497 // Write information to search log file
499 LogFile << "Searching: " << pos.to_fen() << endl
500 << "infinite: " << infinite
501 << " ponder: " << ponder
502 << " time: " << myTime
503 << " increment: " << myIncrement
504 << " moves to go: " << movesToGo << endl;
506 // LSN filtering. Used only for developing purpose. Disabled by default.
510 // Step 2. If after last move we decided to lose on time, do it now!
511 while (SearchStartTime + myTime + 1000 > get_system_time())
515 // We're ready to start thinking. Call the iterative deepening loop function
516 Value v = id_loop(pos, searchMoves);
520 // Step 1. If this is sudden death game and our position is hopeless,
521 // decide to lose on time.
522 if ( !loseOnTime // If we already lost on time, go to step 3.
532 // Step 3. Now after stepping over the time limit, reset flag for next match.
540 TM.put_threads_to_sleep();
546 /// init_search() is called during startup. It initializes various lookup tables
550 // Init our reduction lookup tables
551 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
552 for (int j = 1; j < 64; j++) // j == moveNumber
554 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
555 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
556 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
557 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
560 // Init futility margins array
561 for (int i = 0; i < 14; i++) // i == depth (OnePly = 2)
562 for (int j = 0; j < 64; j++) // j == moveNumber
564 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j; // FIXME: test using log instead of BSR
567 // Init futility move count array
568 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
569 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
573 // SearchStack::init() initializes a search stack. Used at the beginning of a
574 // new search from the root.
575 void SearchStack::init(int ply) {
577 pv[ply] = pv[ply + 1] = MOVE_NONE;
578 currentMove = threatMove = MOVE_NONE;
579 reduction = Depth(0);
583 void SearchStack::initKillers() {
585 mateKiller = MOVE_NONE;
586 for (int i = 0; i < KILLER_MAX; i++)
587 killers[i] = MOVE_NONE;
592 // id_loop() is the main iterative deepening loop. It calls root_search
593 // repeatedly with increasing depth until the allocated thinking time has
594 // been consumed, the user stops the search, or the maximum search depth is
597 Value id_loop(const Position& pos, Move searchMoves[]) {
600 SearchStack ss[PLY_MAX_PLUS_2];
602 // searchMoves are verified, copied, scored and sorted
603 RootMoveList rml(p, searchMoves);
605 // Handle special case of searching on a mate/stale position
606 if (rml.move_count() == 0)
609 wait_for_stop_or_ponderhit();
611 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
614 // Print RootMoveList c'tor startup scoring to the standard output,
615 // so that we print information also for iteration 1.
616 cout << "info depth " << 1 << "\ninfo depth " << 1
617 << " score " << value_to_string(rml.get_move_score(0))
618 << " time " << current_search_time()
619 << " nodes " << TM.nodes_searched()
621 << " pv " << rml.get_move(0) << "\n";
627 ValueByIteration[1] = rml.get_move_score(0);
630 // Is one move significantly better than others after initial scoring ?
631 Move EasyMove = MOVE_NONE;
632 if ( rml.move_count() == 1
633 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
634 EasyMove = rml.get_move(0);
636 // Iterative deepening loop
637 while (Iteration < PLY_MAX)
639 // Initialize iteration
642 BestMoveChangesByIteration[Iteration] = 0;
646 cout << "info depth " << Iteration << endl;
648 // Calculate dynamic search window based on previous iterations
651 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
653 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
654 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
656 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
657 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
659 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
660 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
664 alpha = - VALUE_INFINITE;
665 beta = VALUE_INFINITE;
668 // Search to the current depth
669 Value 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 it 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 rest
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)
727 StopOnPonderhit = true;
731 if (MaxDepth && Iteration >= MaxDepth)
737 // If we are pondering or in infinite search, we shouldn't print the
738 // best move before we are told to do so.
739 if (!AbortSearch && (PonderSearch || InfiniteSearch))
740 wait_for_stop_or_ponderhit();
742 // Print final search statistics
743 cout << "info nodes " << TM.nodes_searched()
745 << " time " << current_search_time()
746 << " hashfull " << TT.full() << endl;
748 // Print the best move and the ponder move to the standard output
749 if (ss[0].pv[0] == MOVE_NONE)
751 ss[0].pv[0] = rml.get_move(0);
752 ss[0].pv[1] = MOVE_NONE;
754 cout << "bestmove " << ss[0].pv[0];
755 if (ss[0].pv[1] != MOVE_NONE)
756 cout << " ponder " << ss[0].pv[1];
763 dbg_print_mean(LogFile);
765 if (dbg_show_hit_rate)
766 dbg_print_hit_rate(LogFile);
768 LogFile << "\nNodes: " << TM.nodes_searched()
769 << "\nNodes/second: " << nps()
770 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
773 p.do_move(ss[0].pv[0], st);
774 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
776 return rml.get_move_score(0);
780 // root_search() is the function which searches the root node. It is
781 // similar to search_pv except that it uses a different move ordering
782 // scheme and prints some information to the standard output.
784 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta) {
789 Depth depth, ext, newDepth;
792 int researchCount = 0;
793 bool moveIsCheck, captureOrPromotion, dangerous;
794 Value alpha = oldAlpha;
795 bool isCheck = pos.is_check();
797 // Evaluate the position statically
799 ss[0].eval = !isCheck ? evaluate(pos, ei, 0) : VALUE_NONE;
801 while (1) // Fail low loop
804 // Loop through all the moves in the root move list
805 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
809 // We failed high, invalidate and skip next moves, leave node-counters
810 // and beta-counters as they are and quickly return, we will try to do
811 // a research at the next iteration with a bigger aspiration window.
812 rml.set_move_score(i, -VALUE_INFINITE);
816 RootMoveNumber = i + 1;
818 // Save the current node count before the move is searched
819 nodes = TM.nodes_searched();
821 // Reset beta cut-off counters
822 TM.resetBetaCounters();
824 // Pick the next root move, and print the move and the move number to
825 // the standard output.
826 move = ss[0].currentMove = rml.get_move(i);
828 if (current_search_time() >= 1000)
829 cout << "info currmove " << move
830 << " currmovenumber " << RootMoveNumber << endl;
832 // Decide search depth for this move
833 moveIsCheck = pos.move_is_check(move);
834 captureOrPromotion = pos.move_is_capture_or_promotion(move);
835 depth = (Iteration - 2) * OnePly + InitialDepth;
836 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
837 newDepth = depth + ext;
839 value = - VALUE_INFINITE;
841 while (1) // Fail high loop
844 // Make the move, and search it
845 pos.do_move(move, st, ci, moveIsCheck);
847 if (i < MultiPV || value > alpha)
849 // Aspiration window is disabled in multi-pv case
851 alpha = -VALUE_INFINITE;
853 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
857 // Try to reduce non-pv search depth by one ply if move seems not problematic,
858 // if the move fails high will be re-searched at full depth.
859 bool doFullDepthSearch = true;
861 if ( depth >= 3*OnePly // FIXME was newDepth
863 && !captureOrPromotion
864 && !move_is_castle(move))
866 ss[0].reduction = pv_reduction(depth, RootMoveNumber - MultiPV + 1);
869 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
870 doFullDepthSearch = (value > alpha);
874 if (doFullDepthSearch)
876 ss[0].reduction = Depth(0);
877 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
880 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
886 // Can we exit fail high loop ?
887 if (AbortSearch || value < beta)
890 // We are failing high and going to do a research. It's important to update score
891 // before research in case we run out of time while researching.
892 rml.set_move_score(i, value);
894 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
895 rml.set_move_pv(i, ss[0].pv);
897 // Print search information to the standard output
898 cout << "info depth " << Iteration
899 << " score " << value_to_string(value)
900 << ((value >= beta) ? " lowerbound" :
901 ((value <= alpha)? " upperbound" : ""))
902 << " time " << current_search_time()
903 << " nodes " << TM.nodes_searched()
907 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
908 cout << ss[0].pv[j] << " ";
914 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
915 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
917 LogFile << pretty_pv(pos, current_search_time(), Iteration,
918 TM.nodes_searched(), value, type, ss[0].pv) << endl;
921 // Prepare for a research after a fail high, each time with a wider window
923 beta = Min(beta + AspirationDelta * (1 << researchCount), VALUE_INFINITE);
925 } // End of fail high loop
927 // Finished searching the move. If AbortSearch is true, the search
928 // was aborted because the user interrupted the search or because we
929 // ran out of time. In this case, the return value of the search cannot
930 // be trusted, and we break out of the loop without updating the best
935 // Remember beta-cutoff and searched nodes counts for this move. The
936 // info is used to sort the root moves at the next iteration.
938 TM.get_beta_counters(pos.side_to_move(), our, their);
939 rml.set_beta_counters(i, our, their);
940 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
942 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
944 if (value <= alpha && i >= MultiPV)
945 rml.set_move_score(i, -VALUE_INFINITE);
948 // PV move or new best move!
951 rml.set_move_score(i, value);
953 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
954 rml.set_move_pv(i, ss[0].pv);
958 // We record how often the best move has been changed in each
959 // iteration. This information is used for time managment: When
960 // the best move changes frequently, we allocate some more time.
962 BestMoveChangesByIteration[Iteration]++;
964 // Print search information to the standard output
965 cout << "info depth " << Iteration
966 << " score " << value_to_string(value)
967 << ((value >= beta) ? " lowerbound" :
968 ((value <= alpha)? " upperbound" : ""))
969 << " time " << current_search_time()
970 << " nodes " << TM.nodes_searched()
974 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
975 cout << ss[0].pv[j] << " ";
981 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
982 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
984 LogFile << pretty_pv(pos, current_search_time(), Iteration,
985 TM.nodes_searched(), value, type, ss[0].pv) << endl;
993 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
995 cout << "info multipv " << j + 1
996 << " score " << value_to_string(rml.get_move_score(j))
997 << " depth " << ((j <= i)? Iteration : Iteration - 1)
998 << " time " << current_search_time()
999 << " nodes " << TM.nodes_searched()
1003 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1004 cout << rml.get_move_pv(j, k) << " ";
1008 alpha = rml.get_move_score(Min(i, MultiPV-1));
1010 } // PV move or new best move
1012 assert(alpha >= oldAlpha);
1014 AspirationFailLow = (alpha == oldAlpha);
1016 if (AspirationFailLow && StopOnPonderhit)
1017 StopOnPonderhit = false;
1020 // Can we exit fail low loop ?
1021 if (AbortSearch || alpha > oldAlpha)
1024 // Prepare for a research after a fail low, each time with a wider window
1026 alpha = Max(alpha - AspirationDelta * (1 << researchCount), -VALUE_INFINITE);
1035 // search_pv() is the main search function for PV nodes.
1037 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1038 Depth depth, int ply, int threadID) {
1040 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1041 assert(beta > alpha && beta <= VALUE_INFINITE);
1042 assert(ply >= 0 && ply < PLY_MAX);
1043 assert(threadID >= 0 && threadID < TM.active_threads());
1045 Move movesSearched[256];
1049 Depth ext, newDepth;
1050 Value oldAlpha, value;
1051 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1053 Value bestValue = value = -VALUE_INFINITE;
1056 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1058 // Initialize, and make an early exit in case of an aborted search,
1059 // an instant draw, maximum ply reached, etc.
1060 init_node(ss, ply, threadID);
1062 // After init_node() that calls poll()
1063 if (AbortSearch || TM.thread_should_stop(threadID))
1066 if (pos.is_draw() || ply >= PLY_MAX - 1)
1069 // Mate distance pruning
1071 alpha = Max(value_mated_in(ply), alpha);
1072 beta = Min(value_mate_in(ply+1), beta);
1076 // Transposition table lookup. At PV nodes, we don't use the TT for
1077 // pruning, but only for move ordering. This is to avoid problems in
1078 // the following areas:
1080 // * Repetition draw detection
1081 // * Fifty move rule detection
1082 // * Searching for a mate
1083 // * Printing of full PV line
1085 tte = TT.retrieve(pos.get_key());
1086 ttMove = (tte ? tte->move() : MOVE_NONE);
1088 // Go with internal iterative deepening if we don't have a TT move
1089 if ( UseIIDAtPVNodes
1090 && depth >= 5*OnePly
1091 && ttMove == MOVE_NONE)
1093 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1094 ttMove = ss[ply].pv[ply];
1095 tte = TT.retrieve(pos.get_key());
1098 isCheck = pos.is_check();
1101 // Update gain statistics of the previous move that lead
1102 // us in this position.
1104 ss[ply].eval = evaluate(pos, ei, threadID);
1105 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1108 // Initialize a MovePicker object for the current position, and prepare
1109 // to search all moves
1110 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1112 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1114 // Loop through all legal moves until no moves remain or a beta cutoff
1116 while ( alpha < beta
1117 && (move = mp.get_next_move()) != MOVE_NONE
1118 && !TM.thread_should_stop(threadID))
1120 assert(move_is_ok(move));
1122 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1123 moveIsCheck = pos.move_is_check(move, ci);
1124 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1126 // Decide the new search depth
1127 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1129 // Singular extension search. We extend the TT move if its value is much better than
1130 // its siblings. To verify this we do a reduced search on all the other moves but the
1131 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1132 if ( depth >= 6 * OnePly
1134 && move == tte->move()
1136 && is_lower_bound(tte->type())
1137 && tte->depth() >= depth - 3 * OnePly)
1139 Value ttValue = value_from_tt(tte->value(), ply);
1141 if (abs(ttValue) < VALUE_KNOWN_WIN)
1143 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1145 if (excValue < ttValue - SingleReplyMargin)
1150 newDepth = depth - OnePly + ext;
1152 // Update current move
1153 movesSearched[moveCount++] = ss[ply].currentMove = move;
1155 // Make and search the move
1156 pos.do_move(move, st, ci, moveIsCheck);
1158 if (moveCount == 1) // The first move in list is the PV
1159 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1162 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1163 // if the move fails high will be re-searched at full depth.
1164 bool doFullDepthSearch = true;
1166 if ( depth >= 3*OnePly
1168 && !captureOrPromotion
1169 && !move_is_castle(move)
1170 && !move_is_killer(move, ss[ply]))
1172 ss[ply].reduction = pv_reduction(depth, moveCount);
1173 if (ss[ply].reduction)
1175 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1176 doFullDepthSearch = (value > alpha);
1180 if (doFullDepthSearch) // Go with full depth non-pv search
1182 ss[ply].reduction = Depth(0);
1183 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1184 if (value > alpha && value < beta)
1185 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1188 pos.undo_move(move);
1190 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1193 if (value > bestValue)
1200 if (value == value_mate_in(ply + 1))
1201 ss[ply].mateKiller = move;
1206 if ( TM.active_threads() > 1
1208 && depth >= MinimumSplitDepth
1210 && TM.available_thread_exists(threadID)
1212 && !TM.thread_should_stop(threadID)
1213 && TM.split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1214 depth, &moveCount, &mp, threadID, true))
1218 // All legal moves have been searched. A special case: If there were
1219 // no legal moves, it must be mate or stalemate.
1221 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1223 // If the search is not aborted, update the transposition table,
1224 // history counters, and killer moves.
1225 if (AbortSearch || TM.thread_should_stop(threadID))
1228 if (bestValue <= oldAlpha)
1229 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1231 else if (bestValue >= beta)
1233 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1234 move = ss[ply].pv[ply];
1235 if (!pos.move_is_capture_or_promotion(move))
1237 update_history(pos, move, depth, movesSearched, moveCount);
1238 update_killers(move, ss[ply]);
1240 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1243 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1249 // search() is the search function for zero-width nodes.
1251 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1252 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1254 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1255 assert(ply >= 0 && ply < PLY_MAX);
1256 assert(threadID >= 0 && threadID < TM.active_threads());
1258 Move movesSearched[256];
1263 Depth ext, newDepth;
1264 Value bestValue, staticValue, nullValue, value, futilityValue, futilityValueScaled;
1265 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1266 bool mateThreat = false;
1268 futilityValue = staticValue = bestValue = value = -VALUE_INFINITE;
1271 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1273 // Initialize, and make an early exit in case of an aborted search,
1274 // an instant draw, maximum ply reached, etc.
1275 init_node(ss, ply, threadID);
1277 // After init_node() that calls poll()
1278 if (AbortSearch || TM.thread_should_stop(threadID))
1281 if (pos.is_draw() || ply >= PLY_MAX - 1)
1284 // Mate distance pruning
1285 if (value_mated_in(ply) >= beta)
1288 if (value_mate_in(ply + 1) < beta)
1291 // We don't want the score of a partial search to overwrite a previous full search
1292 // TT value, so we use a different position key in case of an excluded move exsists.
1293 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1295 // Transposition table lookup
1296 tte = TT.retrieve(posKey);
1297 ttMove = (tte ? tte->move() : MOVE_NONE);
1299 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1301 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1302 return value_from_tt(tte->value(), ply);
1305 isCheck = pos.is_check();
1307 // Evaluate the position statically
1310 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1311 staticValue = value_from_tt(tte->value(), ply);
1313 staticValue = evaluate(pos, ei, threadID);
1315 ss[ply].eval = staticValue;
1316 futilityValue = staticValue + futility_margin(depth, 0); //FIXME: Remove me, only for split
1317 staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
1318 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1321 // Static null move pruning. We're betting that the opponent doesn't have
1322 // a move that will reduce the score by more than FutilityMargins[int(depth)]
1323 // if we do a null move.
1326 && depth < RazorDepth
1327 && staticValue - futility_margin(depth, 0) >= beta)
1328 return staticValue - futility_margin(depth, 0);
1334 && !value_is_mate(beta)
1335 && ok_to_do_nullmove(pos)
1336 && staticValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1338 ss[ply].currentMove = MOVE_NULL;
1340 pos.do_null_move(st);
1342 // Null move dynamic reduction based on depth
1343 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1345 // Null move dynamic reduction based on value
1346 if (staticValue - beta > PawnValueMidgame)
1349 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1351 pos.undo_null_move();
1353 if (nullValue >= beta)
1355 if (depth < 6 * OnePly)
1358 // Do zugzwang verification search
1359 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1363 // The null move failed low, which means that we may be faced with
1364 // some kind of threat. If the previous move was reduced, check if
1365 // the move that refuted the null move was somehow connected to the
1366 // move which was reduced. If a connection is found, return a fail
1367 // low score (which will cause the reduced move to fail high in the
1368 // parent node, which will trigger a re-search with full depth).
1369 if (nullValue == value_mated_in(ply + 2))
1372 ss[ply].threatMove = ss[ply + 1].currentMove;
1373 if ( depth < ThreatDepth
1374 && ss[ply - 1].reduction
1375 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1379 // Null move search not allowed, try razoring
1380 else if ( !value_is_mate(beta)
1382 && depth < RazorDepth
1383 && staticValue < beta - (NullMoveMargin + 16 * depth)
1384 && ss[ply - 1].currentMove != MOVE_NULL
1385 && ttMove == MOVE_NONE
1386 && !pos.has_pawn_on_7th(pos.side_to_move()))
1388 Value rbeta = beta - (NullMoveMargin + 16 * depth);
1389 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1394 // Go with internal iterative deepening if we don't have a TT move
1395 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1396 !isCheck && ss[ply].eval >= beta - IIDMargin)
1398 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1399 ttMove = ss[ply].pv[ply];
1400 tte = TT.retrieve(posKey);
1403 // Initialize a MovePicker object for the current position, and prepare
1404 // to search all moves.
1405 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1408 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1409 while ( bestValue < beta
1410 && (move = mp.get_next_move()) != MOVE_NONE
1411 && !TM.thread_should_stop(threadID))
1413 assert(move_is_ok(move));
1415 if (move == excludedMove)
1418 moveIsCheck = pos.move_is_check(move, ci);
1419 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1420 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1422 // Decide the new search depth
1423 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1425 // Singular extension search. We extend the TT move if its value is much better than
1426 // its siblings. To verify this we do a reduced search on all the other moves but the
1427 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1428 if ( depth >= 8 * OnePly
1430 && move == tte->move()
1431 && !excludedMove // Do not allow recursive single-reply search
1433 && is_lower_bound(tte->type())
1434 && tte->depth() >= depth - 3 * OnePly)
1436 Value ttValue = value_from_tt(tte->value(), ply);
1438 if (abs(ttValue) < VALUE_KNOWN_WIN)
1440 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1442 if (excValue < ttValue - SingleReplyMargin)
1447 newDepth = depth - OnePly + ext;
1449 // Update current move
1450 movesSearched[moveCount++] = ss[ply].currentMove = move;
1455 && !captureOrPromotion
1456 && !move_is_castle(move)
1459 // Move count based pruning
1460 if ( moveCount >= futility_move_count(depth)
1461 && ok_to_prune(pos, move, ss[ply].threatMove)
1462 && bestValue > value_mated_in(PLY_MAX))
1465 // Value based pruning
1466 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1467 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1468 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1470 if (futilityValueScaled < beta)
1472 if (futilityValueScaled > bestValue)
1473 bestValue = futilityValueScaled;
1478 // Make and search the move
1479 pos.do_move(move, st, ci, moveIsCheck);
1481 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1482 // if the move fails high will be re-searched at full depth.
1483 bool doFullDepthSearch = true;
1485 if ( depth >= 3*OnePly
1487 && !captureOrPromotion
1488 && !move_is_castle(move)
1489 && !move_is_killer(move, ss[ply]))
1491 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1492 if (ss[ply].reduction)
1494 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1495 doFullDepthSearch = (value >= beta);
1499 if (doFullDepthSearch) // Go with full depth non-pv search
1501 ss[ply].reduction = Depth(0);
1502 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1504 pos.undo_move(move);
1506 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1509 if (value > bestValue)
1515 if (value == value_mate_in(ply + 1))
1516 ss[ply].mateKiller = move;
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, &beta, &beta, &bestValue, futilityValue, //FIXME: SMP & futilityValue
1528 depth, &moveCount, &mp, threadID, false))
1532 // All legal moves have been searched. A special case: If there were
1533 // no legal moves, it must be mate or stalemate.
1535 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
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.
1762 void sp_search(SplitPoint* sp, int threadID) {
1764 assert(threadID >= 0 && threadID < TM.active_threads());
1765 assert(TM.active_threads() > 1);
1767 Position pos(*sp->pos);
1769 SearchStack* ss = sp->sstack[threadID];
1770 Value value = -VALUE_INFINITE;
1773 bool isCheck = pos.is_check();
1774 bool useFutilityPruning = sp->depth < 7 * OnePly //FIXME: sync with search
1777 while ( lock_grab_bool(&(sp->lock))
1778 && sp->bestValue < sp->beta
1779 && !TM.thread_should_stop(threadID)
1780 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1782 moveCount = ++sp->moves;
1783 lock_release(&(sp->lock));
1785 assert(move_is_ok(move));
1787 bool moveIsCheck = pos.move_is_check(move, ci);
1788 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1790 ss[sp->ply].currentMove = move;
1792 // Decide the new search depth
1794 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1795 Depth newDepth = sp->depth - OnePly + ext;
1798 if ( useFutilityPruning
1800 && !captureOrPromotion)
1802 // Move count based pruning
1803 if ( moveCount >= futility_move_count(sp->depth)
1804 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1805 && sp->bestValue > value_mated_in(PLY_MAX))
1808 // Value based pruning
1809 Value futilityValueScaled = sp->futilityValue - moveCount * 8; //FIXME: sync with search
1811 if (futilityValueScaled < sp->beta)
1813 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1815 lock_grab(&(sp->lock));
1816 if (futilityValueScaled > sp->bestValue)
1817 sp->bestValue = futilityValueScaled;
1818 lock_release(&(sp->lock));
1824 // Make and search the move.
1826 pos.do_move(move, st, ci, moveIsCheck);
1828 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1829 // if the move fails high will be re-searched at full depth.
1830 bool doFullDepthSearch = true;
1833 && !captureOrPromotion
1834 && !move_is_castle(move)
1835 && !move_is_killer(move, ss[sp->ply]))
1837 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1838 if (ss[sp->ply].reduction)
1840 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1841 doFullDepthSearch = (value >= sp->beta);
1845 if (doFullDepthSearch) // Go with full depth non-pv search
1847 ss[sp->ply].reduction = Depth(0);
1848 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1850 pos.undo_move(move);
1852 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1855 if (value > sp->bestValue) // Less then 2% of cases
1857 // Recursive locking, lock current split point and its ancestors to
1858 // guarantee thread_should_stop() and sp_update_pv() are race free.
1859 SplitPoint* spChain[MAX_THREADS * ACTIVE_SPLIT_POINTS_MAX];
1861 for (spChain[cnt] = sp; spChain[cnt]; )
1863 lock_grab(&(spChain[cnt++]->lock));
1864 spChain[cnt] = spChain[cnt - 1]->parent;
1867 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1869 sp->bestValue = value;
1870 if (sp->bestValue >= sp->beta)
1872 sp->stopRequest = true;
1873 sp_update_pv(sp->parentSstack, ss, sp->ply);
1877 // Release locks in reverse order
1879 lock_release(&(spChain[--cnt]->lock));
1883 /* Here we have the lock still grabbed */
1886 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.
1900 void sp_search_pv(SplitPoint* sp, int threadID) {
1902 assert(threadID >= 0 && threadID < TM.active_threads());
1903 assert(TM.active_threads() > 1);
1905 Position pos(*sp->pos);
1907 SearchStack* ss = sp->sstack[threadID];
1908 Value value = -VALUE_INFINITE;
1912 while ( lock_grab_bool(&(sp->lock))
1913 && sp->alpha < sp->beta
1914 && !TM.thread_should_stop(threadID)
1915 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1917 moveCount = ++sp->moves;
1918 lock_release(&(sp->lock));
1920 assert(move_is_ok(move));
1922 bool moveIsCheck = pos.move_is_check(move, ci);
1923 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1925 ss[sp->ply].currentMove = move;
1927 // Decide the new search depth
1929 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1930 Depth newDepth = sp->depth - OnePly + ext;
1932 // Make and search the move.
1934 pos.do_move(move, st, ci, moveIsCheck);
1936 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1937 // if the move fails high will be re-searched at full depth.
1938 bool doFullDepthSearch = true;
1941 && !captureOrPromotion
1942 && !move_is_castle(move)
1943 && !move_is_killer(move, ss[sp->ply]))
1945 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1946 if (ss[sp->ply].reduction)
1948 Value localAlpha = sp->alpha;
1949 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1950 doFullDepthSearch = (value > localAlpha);
1954 if (doFullDepthSearch) // Go with full depth non-pv search
1956 Value localAlpha = sp->alpha;
1957 ss[sp->ply].reduction = Depth(0);
1958 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1960 if (value > localAlpha && value < sp->beta)
1962 // If another thread has failed high then sp->alpha has been increased
1963 // to be higher or equal then beta, if so, avoid to start a PV search.
1964 localAlpha = sp->alpha;
1965 if (localAlpha < sp->beta)
1966 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1968 assert(TM.thread_should_stop(threadID));
1971 pos.undo_move(move);
1973 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1976 if (value > sp->bestValue) // Less then 2% of cases
1978 // Recursive locking, lock current split point and its ancestors to
1979 // guarantee thread_should_stop() and sp_update_pv() are race free.
1980 SplitPoint* spChain[MAX_THREADS * ACTIVE_SPLIT_POINTS_MAX];
1982 for (spChain[cnt] = sp; spChain[cnt]; )
1984 lock_grab(&(spChain[cnt++]->lock));
1985 spChain[cnt] = spChain[cnt - 1]->parent;
1988 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1990 sp->bestValue = value;
1991 if (value > sp->alpha)
1993 // Ask threads to stop before to modify sp->alpha
1994 if (value >= sp->beta)
1995 sp->stopRequest = true;
1999 sp_update_pv(sp->parentSstack, ss, sp->ply);
2000 if (value == value_mate_in(sp->ply + 1))
2001 ss[sp->ply].mateKiller = move;
2005 // Release locks in reverse order
2007 lock_release(&(spChain[--cnt]->lock));
2011 /* Here we have the lock still grabbed */
2014 sp->slaves[threadID] = 0;
2016 lock_release(&(sp->lock));
2020 // init_node() is called at the beginning of all the search functions
2021 // (search(), search_pv(), qsearch(), and so on) and initializes the
2022 // search stack object corresponding to the current node. Once every
2023 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2024 // for user input and checks whether it is time to stop the search.
2026 void init_node(SearchStack ss[], int ply, int threadID) {
2028 assert(ply >= 0 && ply < PLY_MAX);
2029 assert(threadID >= 0 && threadID < TM.active_threads());
2031 TM.incrementNodeCounter(threadID);
2036 if (NodesSincePoll >= NodesBetweenPolls)
2043 ss[ply + 2].initKillers();
2044 TM.print_current_line(ss, ply, threadID);
2048 // update_pv() is called whenever a search returns a value > alpha.
2049 // It updates the PV in the SearchStack object corresponding to the
2052 void update_pv(SearchStack ss[], int ply) {
2054 assert(ply >= 0 && ply < PLY_MAX);
2058 ss[ply].pv[ply] = ss[ply].currentMove;
2060 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2061 ss[ply].pv[p] = ss[ply + 1].pv[p];
2063 ss[ply].pv[p] = MOVE_NONE;
2067 // sp_update_pv() is a variant of update_pv for use at split points. The
2068 // difference between the two functions is that sp_update_pv also updates
2069 // the PV at the parent node.
2071 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2073 assert(ply >= 0 && ply < PLY_MAX);
2077 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2079 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2080 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2082 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2086 // connected_moves() tests whether two moves are 'connected' in the sense
2087 // that the first move somehow made the second move possible (for instance
2088 // if the moving piece is the same in both moves). The first move is assumed
2089 // to be the move that was made to reach the current position, while the
2090 // second move is assumed to be a move from the current position.
2092 bool connected_moves(const Position& pos, Move m1, Move m2) {
2094 Square f1, t1, f2, t2;
2097 assert(move_is_ok(m1));
2098 assert(move_is_ok(m2));
2100 if (m2 == MOVE_NONE)
2103 // Case 1: The moving piece is the same in both moves
2109 // Case 2: The destination square for m2 was vacated by m1
2115 // Case 3: Moving through the vacated square
2116 if ( piece_is_slider(pos.piece_on(f2))
2117 && bit_is_set(squares_between(f2, t2), f1))
2120 // Case 4: The destination square for m2 is defended by the moving piece in m1
2121 p = pos.piece_on(t1);
2122 if (bit_is_set(pos.attacks_from(p, t1), t2))
2125 // Case 5: Discovered check, checking piece is the piece moved in m1
2126 if ( piece_is_slider(p)
2127 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2128 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2130 // discovered_check_candidates() works also if the Position's side to
2131 // move is the opposite of the checking piece.
2132 Color them = opposite_color(pos.side_to_move());
2133 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2135 if (bit_is_set(dcCandidates, f2))
2142 // value_is_mate() checks if the given value is a mate one
2143 // eventually compensated for the ply.
2145 bool value_is_mate(Value value) {
2147 assert(abs(value) <= VALUE_INFINITE);
2149 return value <= value_mated_in(PLY_MAX)
2150 || value >= value_mate_in(PLY_MAX);
2154 // move_is_killer() checks if the given move is among the
2155 // killer moves of that ply.
2157 bool move_is_killer(Move m, const SearchStack& ss) {
2159 const Move* k = ss.killers;
2160 for (int i = 0; i < KILLER_MAX; i++, k++)
2168 // extension() decides whether a move should be searched with normal depth,
2169 // or with extended depth. Certain classes of moves (checking moves, in
2170 // particular) are searched with bigger depth than ordinary moves and in
2171 // any case are marked as 'dangerous'. Note that also if a move is not
2172 // extended, as example because the corresponding UCI option is set to zero,
2173 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2175 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2176 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2178 assert(m != MOVE_NONE);
2180 Depth result = Depth(0);
2181 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2186 result += CheckExtension[pvNode];
2189 result += SingleEvasionExtension[pvNode];
2192 result += MateThreatExtension[pvNode];
2195 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2197 Color c = pos.side_to_move();
2198 if (relative_rank(c, move_to(m)) == RANK_7)
2200 result += PawnPushTo7thExtension[pvNode];
2203 if (pos.pawn_is_passed(c, move_to(m)))
2205 result += PassedPawnExtension[pvNode];
2210 if ( captureOrPromotion
2211 && pos.type_of_piece_on(move_to(m)) != PAWN
2212 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2213 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2214 && !move_is_promotion(m)
2217 result += PawnEndgameExtension[pvNode];
2222 && captureOrPromotion
2223 && pos.type_of_piece_on(move_to(m)) != PAWN
2224 && pos.see_sign(m) >= 0)
2230 return Min(result, OnePly);
2234 // ok_to_do_nullmove() looks at the current position and decides whether
2235 // doing a 'null move' should be allowed. In order to avoid zugzwang
2236 // problems, null moves are not allowed when the side to move has very
2237 // little material left. Currently, the test is a bit too simple: Null
2238 // moves are avoided only when the side to move has only pawns left.
2239 // It's probably a good idea to avoid null moves in at least some more
2240 // complicated endgames, e.g. KQ vs KR. FIXME
2242 bool ok_to_do_nullmove(const Position& pos) {
2244 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2248 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2249 // non-tactical moves late in the move list close to the leaves are
2250 // candidates for pruning.
2252 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2254 assert(move_is_ok(m));
2255 assert(threat == MOVE_NONE || move_is_ok(threat));
2256 assert(!pos.move_is_check(m));
2257 assert(!pos.move_is_capture_or_promotion(m));
2258 assert(!pos.move_is_passed_pawn_push(m));
2260 Square mfrom, mto, tfrom, tto;
2262 // Prune if there isn't any threat move
2263 if (threat == MOVE_NONE)
2266 mfrom = move_from(m);
2268 tfrom = move_from(threat);
2269 tto = move_to(threat);
2271 // Case 1: Don't prune moves which move the threatened piece
2275 // Case 2: If the threatened piece has value less than or equal to the
2276 // value of the threatening piece, don't prune move which defend it.
2277 if ( pos.move_is_capture(threat)
2278 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2279 || pos.type_of_piece_on(tfrom) == KING)
2280 && pos.move_attacks_square(m, tto))
2283 // Case 3: If the moving piece in the threatened move is a slider, don't
2284 // prune safe moves which block its ray.
2285 if ( piece_is_slider(pos.piece_on(tfrom))
2286 && bit_is_set(squares_between(tfrom, tto), mto)
2287 && pos.see_sign(m) >= 0)
2294 // ok_to_use_TT() returns true if a transposition table score
2295 // can be used at a given point in search.
2297 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2299 Value v = value_from_tt(tte->value(), ply);
2301 return ( tte->depth() >= depth
2302 || v >= Max(value_mate_in(PLY_MAX), beta)
2303 || v < Min(value_mated_in(PLY_MAX), beta))
2305 && ( (is_lower_bound(tte->type()) && v >= beta)
2306 || (is_upper_bound(tte->type()) && v < beta));
2310 // refine_eval() returns the transposition table score if
2311 // possible otherwise falls back on static position evaluation.
2313 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2318 Value v = value_from_tt(tte->value(), ply);
2320 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2321 || (is_upper_bound(tte->type()) && v < defaultEval))
2328 // update_history() registers a good move that produced a beta-cutoff
2329 // in history and marks as failures all the other moves of that ply.
2331 void update_history(const Position& pos, Move move, Depth depth,
2332 Move movesSearched[], int moveCount) {
2336 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2338 for (int i = 0; i < moveCount - 1; i++)
2340 m = movesSearched[i];
2344 if (!pos.move_is_capture_or_promotion(m))
2345 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2350 // update_killers() add a good move that produced a beta-cutoff
2351 // among the killer moves of that ply.
2353 void update_killers(Move m, SearchStack& ss) {
2355 if (m == ss.killers[0])
2358 for (int i = KILLER_MAX - 1; i > 0; i--)
2359 ss.killers[i] = ss.killers[i - 1];
2365 // update_gains() updates the gains table of a non-capture move given
2366 // the static position evaluation before and after the move.
2368 void update_gains(const Position& pos, Move m, Value before, Value after) {
2371 && before != VALUE_NONE
2372 && after != VALUE_NONE
2373 && pos.captured_piece() == NO_PIECE_TYPE
2374 && !move_is_castle(m)
2375 && !move_is_promotion(m))
2376 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2380 // current_search_time() returns the number of milliseconds which have passed
2381 // since the beginning of the current search.
2383 int current_search_time() {
2385 return get_system_time() - SearchStartTime;
2389 // nps() computes the current nodes/second count.
2393 int t = current_search_time();
2394 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2398 // poll() performs two different functions: It polls for user input, and it
2399 // looks at the time consumed so far and decides if it's time to abort the
2404 static int lastInfoTime;
2405 int t = current_search_time();
2410 // We are line oriented, don't read single chars
2411 std::string command;
2413 if (!std::getline(std::cin, command))
2416 if (command == "quit")
2419 PonderSearch = false;
2423 else if (command == "stop")
2426 PonderSearch = false;
2428 else if (command == "ponderhit")
2432 // Print search information
2436 else if (lastInfoTime > t)
2437 // HACK: Must be a new search where we searched less than
2438 // NodesBetweenPolls nodes during the first second of search.
2441 else if (t - lastInfoTime >= 1000)
2444 lock_grab(&TM.IOLock);
2449 if (dbg_show_hit_rate)
2450 dbg_print_hit_rate();
2452 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2453 << " time " << t << " hashfull " << TT.full() << endl;
2455 lock_release(&TM.IOLock);
2457 if (ShowCurrentLine)
2458 TM.threads[0].printCurrentLineRequest = true;
2461 // Should we stop the search?
2465 bool stillAtFirstMove = RootMoveNumber == 1
2466 && !AspirationFailLow
2467 && t > MaxSearchTime + ExtraSearchTime;
2469 bool noMoreTime = t > AbsoluteMaxSearchTime
2470 || stillAtFirstMove;
2472 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2473 || (ExactMaxTime && t >= ExactMaxTime)
2474 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2479 // ponderhit() is called when the program is pondering (i.e. thinking while
2480 // it's the opponent's turn to move) in order to let the engine know that
2481 // it correctly predicted the opponent's move.
2485 int t = current_search_time();
2486 PonderSearch = false;
2488 bool stillAtFirstMove = RootMoveNumber == 1
2489 && !AspirationFailLow
2490 && t > MaxSearchTime + ExtraSearchTime;
2492 bool noMoreTime = t > AbsoluteMaxSearchTime
2493 || stillAtFirstMove;
2495 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2500 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2502 void init_ss_array(SearchStack ss[]) {
2504 for (int i = 0; i < 3; i++)
2507 ss[i].initKillers();
2512 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2513 // while the program is pondering. The point is to work around a wrinkle in
2514 // the UCI protocol: When pondering, the engine is not allowed to give a
2515 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2516 // We simply wait here until one of these commands is sent, and return,
2517 // after which the bestmove and pondermove will be printed (in id_loop()).
2519 void wait_for_stop_or_ponderhit() {
2521 std::string command;
2525 if (!std::getline(std::cin, command))
2528 if (command == "quit")
2533 else if (command == "ponderhit" || command == "stop")
2539 // init_thread() is the function which is called when a new thread is
2540 // launched. It simply calls the idle_loop() function with the supplied
2541 // threadID. There are two versions of this function; one for POSIX
2542 // threads and one for Windows threads.
2544 #if !defined(_MSC_VER)
2546 void* init_thread(void *threadID) {
2548 TM.idle_loop(*(int*)threadID, NULL);
2554 DWORD WINAPI init_thread(LPVOID threadID) {
2556 TM.idle_loop(*(int*)threadID, NULL);
2563 /// The ThreadsManager class
2565 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2566 // get_beta_counters() are getters/setters for the per thread
2567 // counters used to sort the moves at root.
2569 void ThreadsManager::resetNodeCounters() {
2571 for (int i = 0; i < MAX_THREADS; i++)
2572 threads[i].nodes = 0ULL;
2575 void ThreadsManager::resetBetaCounters() {
2577 for (int i = 0; i < MAX_THREADS; i++)
2578 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2581 int64_t ThreadsManager::nodes_searched() const {
2583 int64_t result = 0ULL;
2584 for (int i = 0; i < ActiveThreads; i++)
2585 result += threads[i].nodes;
2590 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2593 for (int i = 0; i < MAX_THREADS; i++)
2595 our += threads[i].betaCutOffs[us];
2596 their += threads[i].betaCutOffs[opposite_color(us)];
2601 // idle_loop() is where the threads are parked when they have no work to do.
2602 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2603 // object for which the current thread is the master.
2605 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2607 assert(threadID >= 0 && threadID < MAX_THREADS);
2611 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2612 // master should exit as last one.
2613 if (AllThreadsShouldExit && !waitSp)
2615 threads[threadID].state = THREAD_TERMINATED;
2619 // If we are not thinking, wait for a condition to be signaled
2620 // instead of wasting CPU time polling for work.
2621 while ( threadID != 0
2622 && !AllThreadsShouldExit
2623 && (AllThreadsShouldSleep || threadID >= ActiveThreads))
2625 threads[threadID].state = THREAD_SLEEPING;
2627 #if !defined(_MSC_VER)
2628 pthread_mutex_lock(&WaitLock);
2629 pthread_cond_wait(&WaitCond, &WaitLock);
2630 pthread_mutex_unlock(&WaitLock);
2632 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2634 // State is already changed by wake_sleeping_threads()
2635 assert(threads[threadID].state == THREAD_AVAILABLE || threadID >= ActiveThreads);
2638 // If this thread has been assigned work, launch a search
2639 if (threads[threadID].state == THREAD_WORKISWAITING)
2641 assert(!AllThreadsShouldExit);
2643 threads[threadID].state = THREAD_SEARCHING;
2645 if (threads[threadID].splitPoint->pvNode)
2646 sp_search_pv(threads[threadID].splitPoint, threadID);
2648 sp_search(threads[threadID].splitPoint, threadID);
2650 assert(threads[threadID].state == THREAD_SEARCHING);
2652 threads[threadID].state = THREAD_AVAILABLE;
2655 // If this thread is the master of a split point and all threads have
2656 // finished their work at this split point, return from the idle loop.
2657 if (waitSp != NULL && waitSp->cpus == 0)
2659 assert( threads[threadID].state == THREAD_AVAILABLE
2660 || threads[threadID].state == THREAD_SEARCHING);
2662 threads[threadID].state = THREAD_SEARCHING;
2669 // init_threads() is called during startup. It launches all helper threads,
2670 // and initializes the split point stack and the global locks and condition
2673 void ThreadsManager::init_threads() {
2678 #if !defined(_MSC_VER)
2679 pthread_t pthread[1];
2682 // Initialize global locks
2683 lock_init(&MPLock, NULL);
2684 lock_init(&IOLock, NULL);
2686 // Initialize SplitPointStack locks
2687 for (int i = 0; i < MAX_THREADS; i++)
2688 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2690 SplitPointStack[i][j].parent = NULL;
2691 lock_init(&(SplitPointStack[i][j].lock), NULL);
2694 #if !defined(_MSC_VER)
2695 pthread_mutex_init(&WaitLock, NULL);
2696 pthread_cond_init(&WaitCond, NULL);
2698 for (i = 0; i < MAX_THREADS; i++)
2699 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2702 // Will be set just before program exits to properly end the threads
2703 AllThreadsShouldExit = false;
2705 // Threads will be put to sleep as soon as created
2706 AllThreadsShouldSleep = true;
2708 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2710 threads[0].state = THREAD_SEARCHING;
2711 for (i = 1; i < MAX_THREADS; i++)
2712 threads[i].state = THREAD_AVAILABLE;
2714 // Launch the helper threads
2715 for (i = 1; i < MAX_THREADS; i++)
2718 #if !defined(_MSC_VER)
2719 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2722 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
2727 cout << "Failed to create thread number " << i << endl;
2728 Application::exit_with_failure();
2731 // Wait until the thread has finished launching and is gone to sleep
2732 while (threads[i].state != THREAD_SLEEPING);
2737 // exit_threads() is called when the program exits. It makes all the
2738 // helper threads exit cleanly.
2740 void ThreadsManager::exit_threads() {
2742 ActiveThreads = MAX_THREADS; // HACK
2743 AllThreadsShouldSleep = true; // HACK
2744 wake_sleeping_threads();
2746 // This makes the threads to exit idle_loop()
2747 AllThreadsShouldExit = true;
2749 // Wait for thread termination
2750 for (int i = 1; i < MAX_THREADS; i++)
2751 while (threads[i].state != THREAD_TERMINATED);
2753 // Now we can safely destroy the locks
2754 for (int i = 0; i < MAX_THREADS; i++)
2755 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2756 lock_destroy(&(SplitPointStack[i][j].lock));
2760 // thread_should_stop() checks whether the thread should stop its search.
2761 // This can happen if a beta cutoff has occurred in the thread's currently
2762 // active split point, or in some ancestor of the current split point.
2764 bool ThreadsManager::thread_should_stop(int threadID) const {
2766 assert(threadID >= 0 && threadID < ActiveThreads);
2770 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2775 // thread_is_available() checks whether the thread with threadID "slave" is
2776 // available to help the thread with threadID "master" at a split point. An
2777 // obvious requirement is that "slave" must be idle. With more than two
2778 // threads, this is not by itself sufficient: If "slave" is the master of
2779 // some active split point, it is only available as a slave to the other
2780 // threads which are busy searching the split point at the top of "slave"'s
2781 // split point stack (the "helpful master concept" in YBWC terminology).
2783 bool ThreadsManager::thread_is_available(int slave, int master) const {
2785 assert(slave >= 0 && slave < ActiveThreads);
2786 assert(master >= 0 && master < ActiveThreads);
2787 assert(ActiveThreads > 1);
2789 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2792 // Make a local copy to be sure doesn't change under our feet
2793 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2795 if (localActiveSplitPoints == 0)
2796 // No active split points means that the thread is available as
2797 // a slave for any other thread.
2800 if (ActiveThreads == 2)
2803 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2804 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2805 // could have been set to 0 by another thread leading to an out of bound access.
2806 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2813 // available_thread_exists() tries to find an idle thread which is available as
2814 // a slave for the thread with threadID "master".
2816 bool ThreadsManager::available_thread_exists(int master) const {
2818 assert(master >= 0 && master < ActiveThreads);
2819 assert(ActiveThreads > 1);
2821 for (int i = 0; i < ActiveThreads; i++)
2822 if (thread_is_available(i, master))
2829 // split() does the actual work of distributing the work at a node between
2830 // several threads at PV nodes. If it does not succeed in splitting the
2831 // node (because no idle threads are available, or because we have no unused
2832 // split point objects), the function immediately returns false. If
2833 // splitting is possible, a SplitPoint object is initialized with all the
2834 // data that must be copied to the helper threads (the current position and
2835 // search stack, alpha, beta, the search depth, etc.), and we tell our
2836 // helper threads that they have been assigned work. This will cause them
2837 // to instantly leave their idle loops and call sp_search_pv(). When all
2838 // threads have returned from sp_search_pv (or, equivalently, when
2839 // splitPoint->cpus becomes 0), split() returns true.
2841 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2842 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2843 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2846 assert(sstck != NULL);
2847 assert(ply >= 0 && ply < PLY_MAX);
2848 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2849 assert(!pvNode || *alpha < *beta);
2850 assert(*beta <= VALUE_INFINITE);
2851 assert(depth > Depth(0));
2852 assert(master >= 0 && master < ActiveThreads);
2853 assert(ActiveThreads > 1);
2855 SplitPoint* splitPoint;
2859 // If no other thread is available to help us, or if we have too many
2860 // active split points, don't split.
2861 if ( !available_thread_exists(master)
2862 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2864 lock_release(&MPLock);
2868 // Pick the next available split point object from the split point stack
2869 splitPoint = SplitPointStack[master] + threads[master].activeSplitPoints;
2870 threads[master].activeSplitPoints++;
2872 // Initialize the split point object
2873 splitPoint->parent = threads[master].splitPoint;
2874 splitPoint->stopRequest = false;
2875 splitPoint->ply = ply;
2876 splitPoint->depth = depth;
2877 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
2878 splitPoint->beta = *beta;
2879 splitPoint->pvNode = pvNode;
2880 splitPoint->bestValue = *bestValue;
2881 splitPoint->futilityValue = futilityValue;
2882 splitPoint->master = master;
2883 splitPoint->mp = mp;
2884 splitPoint->moves = *moves;
2885 splitPoint->cpus = 1;
2886 splitPoint->pos = &p;
2887 splitPoint->parentSstack = sstck;
2888 for (int i = 0; i < ActiveThreads; i++)
2889 splitPoint->slaves[i] = 0;
2891 threads[master].splitPoint = splitPoint;
2893 // If we are here it means we are not available
2894 assert(threads[master].state != THREAD_AVAILABLE);
2896 // Allocate available threads setting state to THREAD_BOOKED
2897 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2898 if (thread_is_available(i, master))
2900 threads[i].state = THREAD_BOOKED;
2901 threads[i].splitPoint = splitPoint;
2902 splitPoint->slaves[i] = 1;
2906 assert(splitPoint->cpus > 1);
2908 // We can release the lock because slave threads are already booked and master is not available
2909 lock_release(&MPLock);
2911 // Tell the threads that they have work to do. This will make them leave
2912 // their idle loop. But before copy search stack tail for each thread.
2913 for (int i = 0; i < ActiveThreads; i++)
2914 if (i == master || splitPoint->slaves[i])
2916 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2918 assert(i == master || threads[i].state == THREAD_BOOKED);
2920 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2923 // Everything is set up. The master thread enters the idle loop, from
2924 // which it will instantly launch a search, because its state is
2925 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2926 // idle loop, which means that the main thread will return from the idle
2927 // loop when all threads have finished their work at this split point
2928 // (i.e. when splitPoint->cpus == 0).
2929 idle_loop(master, splitPoint);
2931 // We have returned from the idle loop, which means that all threads are
2932 // finished. Update alpha, beta and bestValue, and return.
2936 *alpha = splitPoint->alpha;
2938 *beta = splitPoint->beta;
2939 *bestValue = splitPoint->bestValue;
2940 threads[master].activeSplitPoints--;
2941 threads[master].splitPoint = splitPoint->parent;
2943 lock_release(&MPLock);
2948 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2949 // to start a new search from the root.
2951 void ThreadsManager::wake_sleeping_threads() {
2953 assert(AllThreadsShouldSleep);
2954 assert(ActiveThreads > 0);
2956 AllThreadsShouldSleep = false;
2958 if (ActiveThreads == 1)
2961 for (int i = 1; i < ActiveThreads; i++)
2963 assert(threads[i].state == THREAD_SLEEPING);
2965 threads[i].state = THREAD_AVAILABLE;
2968 #if !defined(_MSC_VER)
2969 pthread_mutex_lock(&WaitLock);
2970 pthread_cond_broadcast(&WaitCond);
2971 pthread_mutex_unlock(&WaitLock);
2973 for (int i = 1; i < MAX_THREADS; i++)
2974 SetEvent(SitIdleEvent[i]);
2980 // put_threads_to_sleep() makes all the threads go to sleep just before
2981 // to leave think(), at the end of the search. Threads should have already
2982 // finished the job and should be idle.
2984 void ThreadsManager::put_threads_to_sleep() {
2986 assert(!AllThreadsShouldSleep);
2988 // This makes the threads to go to sleep
2989 AllThreadsShouldSleep = true;
2991 // Wait for the threads to be all sleeping and reset flags
2992 // to a known state.
2993 for (int i = 1; i < ActiveThreads; i++)
2995 while (threads[i].state != THREAD_SLEEPING);
2997 // This flag can be in a random state
2998 threads[i].printCurrentLineRequest = false;
3002 // print_current_line() prints _once_ the current line of search for a
3003 // given thread and then setup the print request for the next thread.
3004 // Called when the UCI option UCI_ShowCurrLine is 'true'.
3006 void ThreadsManager::print_current_line(SearchStack ss[], int ply, int threadID) {
3008 assert(ply >= 0 && ply < PLY_MAX);
3009 assert(threadID >= 0 && threadID < ActiveThreads);
3011 if (!threads[threadID].printCurrentLineRequest)
3015 threads[threadID].printCurrentLineRequest = false;
3017 if (threads[threadID].state == THREAD_SEARCHING)
3020 cout << "info currline " << (threadID + 1);
3021 for (int p = 0; p < ply; p++)
3022 cout << " " << ss[p].currentMove;
3025 lock_release(&IOLock);
3028 // Setup print request for the next thread ID
3029 if (threadID + 1 < ActiveThreads)
3030 threads[threadID + 1].printCurrentLineRequest = true;
3034 /// The RootMoveList class
3036 // RootMoveList c'tor
3038 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3040 SearchStack ss[PLY_MAX_PLUS_2];
3041 MoveStack mlist[MaxRootMoves];
3043 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3045 // Generate all legal moves
3046 MoveStack* last = generate_moves(pos, mlist);
3048 // Add each move to the moves[] array
3049 for (MoveStack* cur = mlist; cur != last; cur++)
3051 bool includeMove = includeAllMoves;
3053 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3054 includeMove = (searchMoves[k] == cur->move);
3059 // Find a quick score for the move
3061 pos.do_move(cur->move, st);
3062 moves[count].move = cur->move;
3063 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3064 moves[count].pv[0] = cur->move;
3065 moves[count].pv[1] = MOVE_NONE;
3066 pos.undo_move(cur->move);
3073 // RootMoveList simple methods definitions
3075 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3077 moves[moveNum].nodes = nodes;
3078 moves[moveNum].cumulativeNodes += nodes;
3081 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3083 moves[moveNum].ourBeta = our;
3084 moves[moveNum].theirBeta = their;
3087 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3091 for (j = 0; pv[j] != MOVE_NONE; j++)
3092 moves[moveNum].pv[j] = pv[j];
3094 moves[moveNum].pv[j] = MOVE_NONE;
3098 // RootMoveList::sort() sorts the root move list at the beginning of a new
3101 void RootMoveList::sort() {
3103 sort_multipv(count - 1); // Sort all items
3107 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3108 // list by their scores and depths. It is used to order the different PVs
3109 // correctly in MultiPV mode.
3111 void RootMoveList::sort_multipv(int n) {
3115 for (i = 1; i <= n; i++)
3117 RootMove rm = moves[i];
3118 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3119 moves[j] = moves[j - 1];