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 set_stop_request(int threadID) { threads[threadID].stopRequest = true; }
74 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
75 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
76 void print_current_line(SearchStack ss[], int ply, int threadID);
78 void resetNodeCounters();
79 void resetBetaCounters();
80 int64_t nodes_searched() const;
81 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
82 bool idle_thread_exists(int master) const;
83 bool thread_is_available(int slave, int master) const;
84 bool thread_should_stop(int threadID) const;
85 void wake_sleeping_threads();
86 void put_threads_to_sleep();
87 void idle_loop(int threadID, SplitPoint* waitSp);
88 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, Value* beta, Value* bestValue,
89 const Value futilityValue, Depth depth, int* moves, MovePicker* mp, int master, bool pvNode);
95 bool AllThreadsShouldExit, AllThreadsShouldSleep;
96 Thread threads[THREAD_MAX];
97 SplitPoint SplitPointStack[THREAD_MAX][ACTIVE_SPLIT_POINTS_MAX];
101 #if !defined(_MSC_VER)
102 pthread_cond_t WaitCond;
103 pthread_mutex_t WaitLock;
105 HANDLE SitIdleEvent[THREAD_MAX];
111 // RootMove struct is used for moves at the root at the tree. For each
112 // root move, we store a score, a node count, and a PV (really a refutation
113 // in the case of moves which fail low).
117 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
119 // RootMove::operator<() is the comparison function used when
120 // sorting the moves. A move m1 is considered to be better
121 // than a move m2 if it has a higher score, or if the moves
122 // have equal score but m1 has the higher node count.
123 bool operator<(const RootMove& m) const {
125 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
130 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
131 Move pv[PLY_MAX_PLUS_2];
135 // The RootMoveList class is essentially an array of RootMove objects, with
136 // a handful of methods for accessing the data in the individual moves.
141 RootMoveList(Position& pos, Move searchMoves[]);
143 int move_count() const { return count; }
144 Move get_move(int moveNum) const { return moves[moveNum].move; }
145 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
146 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
147 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
148 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
150 void set_move_nodes(int moveNum, int64_t nodes);
151 void set_beta_counters(int moveNum, int64_t our, int64_t their);
152 void set_move_pv(int moveNum, const Move pv[]);
154 void sort_multipv(int n);
157 static const int MaxRootMoves = 500;
158 RootMove moves[MaxRootMoves];
165 // Search depth at iteration 1
166 const Depth InitialDepth = OnePly;
168 // Use internal iterative deepening?
169 const bool UseIIDAtPVNodes = true;
170 const bool UseIIDAtNonPVNodes = true;
172 // Internal iterative deepening margin. At Non-PV moves, when
173 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
174 // search when the static evaluation is at most IIDMargin below beta.
175 const Value IIDMargin = Value(0x100);
177 // Easy move margin. An easy move candidate must be at least this much
178 // better than the second best move.
179 const Value EasyMoveMargin = Value(0x200);
181 // Null move margin. A null move search will not be done if the static
182 // evaluation of the position is more than NullMoveMargin below beta.
183 const Value NullMoveMargin = Value(0x200);
185 // If the TT move is at least SingleReplyMargin better then the
186 // remaining ones we will extend it.
187 const Value SingleReplyMargin = Value(0x20);
189 // Depth limit for razoring
190 const Depth RazorDepth = 4 * OnePly;
192 /// Lookup tables initialized at startup
194 // Reduction lookup tables and their getter functions
195 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
196 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
198 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
199 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
201 // Futility lookup tables and their getter functions
202 const Value FutilityMarginQS = Value(0x80);
203 int32_t FutilityMarginsMatrix[14][64]; // [depth][moveNumber]
204 int FutilityMoveCountArray[32]; // [depth]
206 inline Value futility_margin(Depth d, int mn) { return Value(d < 7*OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
207 inline int futility_move_count(Depth d) { return d < 16*OnePly ? FutilityMoveCountArray[d] : 512; }
209 /// Variables initialized by UCI options
211 // Depth limit for use of dynamic threat detection
214 // Last seconds noise filtering (LSN)
215 const bool UseLSNFiltering = true;
216 const int LSNTime = 4000; // In milliseconds
217 const Value LSNValue = value_from_centipawns(200);
218 bool loseOnTime = false;
220 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
221 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
222 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
224 // Iteration counters
227 // Scores and number of times the best move changed for each iteration
228 Value ValueByIteration[PLY_MAX_PLUS_2];
229 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
231 // Search window management
237 // Time managment variables
240 int MaxNodes, MaxDepth;
241 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
242 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
243 bool AbortSearch, Quit;
244 bool AspirationFailLow;
246 // Show current line?
247 bool ShowCurrentLine;
251 std::ofstream LogFile;
253 // MP related variables
254 Depth MinimumSplitDepth;
255 int MaxThreadsPerSplitPoint;
258 // Node counters, used only by thread[0] but try to keep in different
259 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
261 int NodesBetweenPolls = 30000;
268 Value id_loop(const Position& pos, Move searchMoves[]);
269 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta);
270 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
271 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
272 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
273 void sp_search(SplitPoint* sp, int threadID);
274 void sp_search_pv(SplitPoint* sp, int threadID);
275 void init_node(SearchStack ss[], int ply, int threadID);
276 void update_pv(SearchStack ss[], int ply);
277 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
278 bool connected_moves(const Position& pos, Move m1, Move m2);
279 bool value_is_mate(Value value);
280 bool move_is_killer(Move m, const SearchStack& ss);
281 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
282 bool ok_to_do_nullmove(const Position& pos);
283 bool ok_to_prune(const Position& pos, Move m, Move threat);
284 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
285 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
286 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
287 void update_killers(Move m, SearchStack& ss);
288 void update_gains(const Position& pos, Move move, Value before, Value after);
290 int current_search_time();
294 void wait_for_stop_or_ponderhit();
295 void init_ss_array(SearchStack ss[]);
297 #if !defined(_MSC_VER)
298 void *init_thread(void *threadID);
300 DWORD WINAPI init_thread(LPVOID threadID);
310 /// init_threads(), exit_threads() and nodes_searched() are helpers to
311 /// give accessibility to some TM methods from outside of current file.
313 void init_threads() { TM.init_threads(); }
314 void exit_threads() { TM.exit_threads(); }
315 int64_t nodes_searched() { return TM.nodes_searched(); }
318 /// perft() is our utility to verify move generation is bug free. All the legal
319 /// moves up to given depth are generated and counted and the sum returned.
321 int perft(Position& pos, Depth depth)
325 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
327 // If we are at the last ply we don't need to do and undo
328 // the moves, just to count them.
329 if (depth <= OnePly) // Replace with '<' to test also qsearch
331 while (mp.get_next_move()) sum++;
335 // Loop through all legal moves
337 while ((move = mp.get_next_move()) != MOVE_NONE)
340 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
341 sum += perft(pos, depth - OnePly);
348 /// think() is the external interface to Stockfish's search, and is called when
349 /// the program receives the UCI 'go' command. It initializes various
350 /// search-related global variables, and calls root_search(). It returns false
351 /// when a quit command is received during the search.
353 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
354 int time[], int increment[], int movesToGo, int maxDepth,
355 int maxNodes, int maxTime, Move searchMoves[]) {
357 // Initialize global search variables
358 StopOnPonderhit = AbortSearch = Quit = false;
359 AspirationFailLow = false;
361 SearchStartTime = get_system_time();
362 ExactMaxTime = maxTime;
365 InfiniteSearch = infinite;
366 PonderSearch = ponder;
367 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
369 // Look for a book move, only during games, not tests
370 if (UseTimeManagement && get_option_value_bool("OwnBook"))
373 if (get_option_value_string("Book File") != OpeningBook.file_name())
374 OpeningBook.open(get_option_value_string("Book File"));
376 bookMove = OpeningBook.get_move(pos);
377 if (bookMove != MOVE_NONE)
380 wait_for_stop_or_ponderhit();
382 cout << "bestmove " << bookMove << endl;
387 TM.resetNodeCounters();
389 if (button_was_pressed("New Game"))
390 loseOnTime = false; // Reset at the beginning of a new game
392 // Read UCI option values
393 TT.set_size(get_option_value_int("Hash"));
394 if (button_was_pressed("Clear Hash"))
397 bool PonderingEnabled = get_option_value_bool("Ponder");
398 MultiPV = get_option_value_int("MultiPV");
400 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
401 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
403 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
404 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
406 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
407 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
409 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
410 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
412 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
413 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
415 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
416 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
418 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
420 Chess960 = get_option_value_bool("UCI_Chess960");
421 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
422 UseLogFile = get_option_value_bool("Use Search Log");
424 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
426 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
427 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
429 read_weights(pos.side_to_move());
431 // Set the number of active threads
432 int newActiveThreads = get_option_value_int("Threads");
433 if (newActiveThreads != TM.active_threads())
435 TM.set_active_threads(newActiveThreads);
436 init_eval(TM.active_threads());
437 // HACK: init_eval() destroys the static castleRightsMask[] array in the
438 // Position class. The below line repairs the damage.
439 Position p(pos.to_fen());
443 // Wake up sleeping threads
444 TM.wake_sleeping_threads();
446 for (int i = 1; i < TM.active_threads(); i++)
447 assert(TM.thread_is_available(i, 0));
450 int myTime = time[side_to_move];
451 int myIncrement = increment[side_to_move];
452 if (UseTimeManagement)
454 if (!movesToGo) // Sudden death time control
458 MaxSearchTime = myTime / 30 + myIncrement;
459 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
461 else // Blitz game without increment
463 MaxSearchTime = myTime / 30;
464 AbsoluteMaxSearchTime = myTime / 8;
467 else // (x moves) / (y minutes)
471 MaxSearchTime = myTime / 2;
472 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
476 MaxSearchTime = myTime / Min(movesToGo, 20);
477 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
481 if (PonderingEnabled)
483 MaxSearchTime += MaxSearchTime / 4;
484 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
488 // Set best NodesBetweenPolls interval
490 NodesBetweenPolls = Min(MaxNodes, 30000);
491 else if (myTime && myTime < 1000)
492 NodesBetweenPolls = 1000;
493 else if (myTime && myTime < 5000)
494 NodesBetweenPolls = 5000;
496 NodesBetweenPolls = 30000;
498 // Write information to search log file
500 LogFile << "Searching: " << pos.to_fen() << endl
501 << "infinite: " << infinite
502 << " ponder: " << ponder
503 << " time: " << myTime
504 << " increment: " << myIncrement
505 << " moves to go: " << movesToGo << endl;
507 // LSN filtering. Used only for developing purpose. Disabled by default.
511 // Step 2. If after last move we decided to lose on time, do it now!
512 while (SearchStartTime + myTime + 1000 > get_system_time())
516 // We're ready to start thinking. Call the iterative deepening loop function
517 Value v = id_loop(pos, searchMoves);
521 // Step 1. If this is sudden death game and our position is hopeless,
522 // decide to lose on time.
523 if ( !loseOnTime // If we already lost on time, go to step 3.
533 // Step 3. Now after stepping over the time limit, reset flag for next match.
541 TM.put_threads_to_sleep();
547 /// init_search() is called during startup. It initializes various lookup tables
551 // Init our reduction lookup tables
552 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
553 for (int j = 1; j < 64; j++) // j == moveNumber
555 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
556 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
557 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
558 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
561 // Init futility margins array
562 for (int i = 0; i < 14; i++) // i == depth (OnePly = 2)
563 for (int j = 0; j < 64; j++) // j == moveNumber
565 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j; // FIXME: test using log instead of BSR
568 // Init futility move count array
569 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
570 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
574 // SearchStack::init() initializes a search stack. Used at the beginning of a
575 // new search from the root.
576 void SearchStack::init(int ply) {
578 pv[ply] = pv[ply + 1] = MOVE_NONE;
579 currentMove = threatMove = MOVE_NONE;
580 reduction = Depth(0);
584 void SearchStack::initKillers() {
586 mateKiller = MOVE_NONE;
587 for (int i = 0; i < KILLER_MAX; i++)
588 killers[i] = MOVE_NONE;
593 // id_loop() is the main iterative deepening loop. It calls root_search
594 // repeatedly with increasing depth until the allocated thinking time has
595 // been consumed, the user stops the search, or the maximum search depth is
598 Value id_loop(const Position& pos, Move searchMoves[]) {
601 SearchStack ss[PLY_MAX_PLUS_2];
603 // searchMoves are verified, copied, scored and sorted
604 RootMoveList rml(p, searchMoves);
606 // Handle special case of searching on a mate/stale position
607 if (rml.move_count() == 0)
610 wait_for_stop_or_ponderhit();
612 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
615 // Print RootMoveList c'tor startup scoring to the standard output,
616 // so that we print information also for iteration 1.
617 cout << "info depth " << 1 << "\ninfo depth " << 1
618 << " score " << value_to_string(rml.get_move_score(0))
619 << " time " << current_search_time()
620 << " nodes " << TM.nodes_searched()
622 << " pv " << rml.get_move(0) << "\n";
628 ValueByIteration[1] = rml.get_move_score(0);
631 // Is one move significantly better than others after initial scoring ?
632 Move EasyMove = MOVE_NONE;
633 if ( rml.move_count() == 1
634 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
635 EasyMove = rml.get_move(0);
637 // Iterative deepening loop
638 while (Iteration < PLY_MAX)
640 // Initialize iteration
643 BestMoveChangesByIteration[Iteration] = 0;
647 cout << "info depth " << Iteration << endl;
649 // Calculate dynamic search window based on previous iterations
652 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
654 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
655 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
657 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
658 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
660 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
661 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
665 alpha = - VALUE_INFINITE;
666 beta = VALUE_INFINITE;
669 // Search to the current depth
670 Value value = root_search(p, ss, rml, alpha, beta);
672 // Write PV to transposition table, in case the relevant entries have
673 // been overwritten during the search.
674 TT.insert_pv(p, ss[0].pv);
677 break; // Value cannot be trusted. Break out immediately!
679 //Save info about search result
680 ValueByIteration[Iteration] = value;
682 // Drop the easy move if it differs from the new best move
683 if (ss[0].pv[0] != EasyMove)
684 EasyMove = MOVE_NONE;
686 if (UseTimeManagement)
689 bool stopSearch = false;
691 // Stop search early if there is only a single legal move,
692 // we search up to Iteration 6 anyway to get a proper score.
693 if (Iteration >= 6 && rml.move_count() == 1)
696 // Stop search early when the last two iterations returned a mate score
698 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
699 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
702 // Stop search early if one move seems to be much better than the rest
703 int64_t nodes = TM.nodes_searched();
705 && EasyMove == ss[0].pv[0]
706 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
707 && current_search_time() > MaxSearchTime / 16)
708 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
709 && current_search_time() > MaxSearchTime / 32)))
712 // Add some extra time if the best move has changed during the last two iterations
713 if (Iteration > 5 && Iteration <= 50)
714 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
715 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
717 // Stop search if most of MaxSearchTime is consumed at the end of the
718 // iteration. We probably don't have enough time to search the first
719 // move at the next iteration anyway.
720 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
728 StopOnPonderhit = true;
732 if (MaxDepth && Iteration >= MaxDepth)
738 // If we are pondering or in infinite search, we shouldn't print the
739 // best move before we are told to do so.
740 if (!AbortSearch && (PonderSearch || InfiniteSearch))
741 wait_for_stop_or_ponderhit();
743 // Print final search statistics
744 cout << "info nodes " << TM.nodes_searched()
746 << " time " << current_search_time()
747 << " hashfull " << TT.full() << endl;
749 // Print the best move and the ponder move to the standard output
750 if (ss[0].pv[0] == MOVE_NONE)
752 ss[0].pv[0] = rml.get_move(0);
753 ss[0].pv[1] = MOVE_NONE;
755 cout << "bestmove " << ss[0].pv[0];
756 if (ss[0].pv[1] != MOVE_NONE)
757 cout << " ponder " << ss[0].pv[1];
764 dbg_print_mean(LogFile);
766 if (dbg_show_hit_rate)
767 dbg_print_hit_rate(LogFile);
769 LogFile << "\nNodes: " << TM.nodes_searched()
770 << "\nNodes/second: " << nps()
771 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
774 p.do_move(ss[0].pv[0], st);
775 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
777 return rml.get_move_score(0);
781 // root_search() is the function which searches the root node. It is
782 // similar to search_pv except that it uses a different move ordering
783 // scheme and prints some information to the standard output.
785 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta) {
790 Depth depth, ext, newDepth;
793 int researchCount = 0;
794 bool moveIsCheck, captureOrPromotion, dangerous;
795 Value alpha = oldAlpha;
796 bool isCheck = pos.is_check();
798 // Evaluate the position statically
800 ss[0].eval = !isCheck ? evaluate(pos, ei, 0) : VALUE_NONE;
802 while (1) // Fail low loop
805 // Loop through all the moves in the root move list
806 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
810 // We failed high, invalidate and skip next moves, leave node-counters
811 // and beta-counters as they are and quickly return, we will try to do
812 // a research at the next iteration with a bigger aspiration window.
813 rml.set_move_score(i, -VALUE_INFINITE);
817 RootMoveNumber = i + 1;
819 // Save the current node count before the move is searched
820 nodes = TM.nodes_searched();
822 // Reset beta cut-off counters
823 TM.resetBetaCounters();
825 // Pick the next root move, and print the move and the move number to
826 // the standard output.
827 move = ss[0].currentMove = rml.get_move(i);
829 if (current_search_time() >= 1000)
830 cout << "info currmove " << move
831 << " currmovenumber " << RootMoveNumber << endl;
833 // Decide search depth for this move
834 moveIsCheck = pos.move_is_check(move);
835 captureOrPromotion = pos.move_is_capture_or_promotion(move);
836 depth = (Iteration - 2) * OnePly + InitialDepth;
837 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
838 newDepth = depth + ext;
840 value = - VALUE_INFINITE;
842 while (1) // Fail high loop
845 // Make the move, and search it
846 pos.do_move(move, st, ci, moveIsCheck);
848 if (i < MultiPV || value > alpha)
850 // Aspiration window is disabled in multi-pv case
852 alpha = -VALUE_INFINITE;
854 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
858 // Try to reduce non-pv search depth by one ply if move seems not problematic,
859 // if the move fails high will be re-searched at full depth.
860 bool doFullDepthSearch = true;
862 if ( depth >= 3*OnePly // FIXME was newDepth
864 && !captureOrPromotion
865 && !move_is_castle(move))
867 ss[0].reduction = pv_reduction(depth, RootMoveNumber - MultiPV + 1);
870 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
871 doFullDepthSearch = (value > alpha);
875 if (doFullDepthSearch)
877 ss[0].reduction = Depth(0);
878 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
881 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
887 // Can we exit fail high loop ?
888 if (AbortSearch || value < beta)
891 // We are failing high and going to do a research. It's important to update score
892 // before research in case we run out of time while researching.
893 rml.set_move_score(i, value);
895 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
896 rml.set_move_pv(i, ss[0].pv);
898 // Print search information to the standard output
899 cout << "info depth " << Iteration
900 << " score " << value_to_string(value)
901 << ((value >= beta) ? " lowerbound" :
902 ((value <= alpha)? " upperbound" : ""))
903 << " time " << current_search_time()
904 << " nodes " << TM.nodes_searched()
908 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
909 cout << ss[0].pv[j] << " ";
915 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
916 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
918 LogFile << pretty_pv(pos, current_search_time(), Iteration,
919 TM.nodes_searched(), value, type, ss[0].pv) << endl;
922 // Prepare for a research after a fail high, each time with a wider window
924 beta = Min(beta + AspirationDelta * (1 << researchCount), VALUE_INFINITE);
926 } // End of fail high loop
928 // Finished searching the move. If AbortSearch is true, the search
929 // was aborted because the user interrupted the search or because we
930 // ran out of time. In this case, the return value of the search cannot
931 // be trusted, and we break out of the loop without updating the best
936 // Remember beta-cutoff and searched nodes counts for this move. The
937 // info is used to sort the root moves at the next iteration.
939 TM.get_beta_counters(pos.side_to_move(), our, their);
940 rml.set_beta_counters(i, our, their);
941 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
943 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
945 if (value <= alpha && i >= MultiPV)
946 rml.set_move_score(i, -VALUE_INFINITE);
949 // PV move or new best move!
952 rml.set_move_score(i, value);
954 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
955 rml.set_move_pv(i, ss[0].pv);
959 // We record how often the best move has been changed in each
960 // iteration. This information is used for time managment: When
961 // the best move changes frequently, we allocate some more time.
963 BestMoveChangesByIteration[Iteration]++;
965 // Print search information to the standard output
966 cout << "info depth " << Iteration
967 << " score " << value_to_string(value)
968 << ((value >= beta) ? " lowerbound" :
969 ((value <= alpha)? " upperbound" : ""))
970 << " time " << current_search_time()
971 << " nodes " << TM.nodes_searched()
975 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
976 cout << ss[0].pv[j] << " ";
982 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
983 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
985 LogFile << pretty_pv(pos, current_search_time(), Iteration,
986 TM.nodes_searched(), value, type, ss[0].pv) << endl;
994 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
996 cout << "info multipv " << j + 1
997 << " score " << value_to_string(rml.get_move_score(j))
998 << " depth " << ((j <= i)? Iteration : Iteration - 1)
999 << " time " << current_search_time()
1000 << " nodes " << TM.nodes_searched()
1004 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1005 cout << rml.get_move_pv(j, k) << " ";
1009 alpha = rml.get_move_score(Min(i, MultiPV-1));
1011 } // PV move or new best move
1013 assert(alpha >= oldAlpha);
1015 AspirationFailLow = (alpha == oldAlpha);
1017 if (AspirationFailLow && StopOnPonderhit)
1018 StopOnPonderhit = false;
1021 // Can we exit fail low loop ?
1022 if (AbortSearch || alpha > oldAlpha)
1025 // Prepare for a research after a fail low, each time with a wider window
1027 alpha = Max(alpha - AspirationDelta * (1 << researchCount), -VALUE_INFINITE);
1036 // search_pv() is the main search function for PV nodes.
1038 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1039 Depth depth, int ply, int threadID) {
1041 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1042 assert(beta > alpha && beta <= VALUE_INFINITE);
1043 assert(ply >= 0 && ply < PLY_MAX);
1044 assert(threadID >= 0 && threadID < TM.active_threads());
1046 Move movesSearched[256];
1050 Depth ext, newDepth;
1051 Value oldAlpha, value;
1052 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1054 Value bestValue = value = -VALUE_INFINITE;
1057 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1059 // Initialize, and make an early exit in case of an aborted search,
1060 // an instant draw, maximum ply reached, etc.
1061 init_node(ss, ply, threadID);
1063 // After init_node() that calls poll()
1064 if (AbortSearch || TM.thread_should_stop(threadID))
1067 if (pos.is_draw() || ply >= PLY_MAX - 1)
1070 // Mate distance pruning
1072 alpha = Max(value_mated_in(ply), alpha);
1073 beta = Min(value_mate_in(ply+1), beta);
1077 // Transposition table lookup. At PV nodes, we don't use the TT for
1078 // pruning, but only for move ordering. This is to avoid problems in
1079 // the following areas:
1081 // * Repetition draw detection
1082 // * Fifty move rule detection
1083 // * Searching for a mate
1084 // * Printing of full PV line
1086 tte = TT.retrieve(pos.get_key());
1087 ttMove = (tte ? tte->move() : MOVE_NONE);
1089 // Go with internal iterative deepening if we don't have a TT move
1090 if ( UseIIDAtPVNodes
1091 && depth >= 5*OnePly
1092 && ttMove == MOVE_NONE)
1094 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1095 ttMove = ss[ply].pv[ply];
1096 tte = TT.retrieve(pos.get_key());
1099 isCheck = pos.is_check();
1102 // Update gain statistics of the previous move that lead
1103 // us in this position.
1105 ss[ply].eval = evaluate(pos, ei, threadID);
1106 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1109 // Initialize a MovePicker object for the current position, and prepare
1110 // to search all moves
1111 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1113 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1115 // Loop through all legal moves until no moves remain or a beta cutoff
1117 while ( alpha < beta
1118 && (move = mp.get_next_move()) != MOVE_NONE
1119 && !TM.thread_should_stop(threadID))
1121 assert(move_is_ok(move));
1123 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1124 moveIsCheck = pos.move_is_check(move, ci);
1125 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1127 // Decide the new search depth
1128 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1130 // Singular extension search. We extend the TT move if its value is much better than
1131 // its siblings. To verify this we do a reduced search on all the other moves but the
1132 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1133 if ( depth >= 6 * OnePly
1135 && move == tte->move()
1137 && is_lower_bound(tte->type())
1138 && tte->depth() >= depth - 3 * OnePly)
1140 Value ttValue = value_from_tt(tte->value(), ply);
1142 if (abs(ttValue) < VALUE_KNOWN_WIN)
1144 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1146 if (excValue < ttValue - SingleReplyMargin)
1151 newDepth = depth - OnePly + ext;
1153 // Update current move
1154 movesSearched[moveCount++] = ss[ply].currentMove = move;
1156 // Make and search the move
1157 pos.do_move(move, st, ci, moveIsCheck);
1159 if (moveCount == 1) // The first move in list is the PV
1160 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1163 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1164 // if the move fails high will be re-searched at full depth.
1165 bool doFullDepthSearch = true;
1167 if ( depth >= 3*OnePly
1169 && !captureOrPromotion
1170 && !move_is_castle(move)
1171 && !move_is_killer(move, ss[ply]))
1173 ss[ply].reduction = pv_reduction(depth, moveCount);
1174 if (ss[ply].reduction)
1176 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1177 doFullDepthSearch = (value > alpha);
1181 if (doFullDepthSearch) // Go with full depth non-pv search
1183 ss[ply].reduction = Depth(0);
1184 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1185 if (value > alpha && value < beta)
1186 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1189 pos.undo_move(move);
1191 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1194 if (value > bestValue)
1201 if (value == value_mate_in(ply + 1))
1202 ss[ply].mateKiller = move;
1207 if ( TM.active_threads() > 1
1209 && depth >= MinimumSplitDepth
1211 && TM.idle_thread_exists(threadID)
1213 && !TM.thread_should_stop(threadID)
1214 && TM.split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
1215 depth, &moveCount, &mp, threadID, true))
1219 // All legal moves have been searched. A special case: If there were
1220 // no legal moves, it must be mate or stalemate.
1222 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1224 // If the search is not aborted, update the transposition table,
1225 // history counters, and killer moves.
1226 if (AbortSearch || TM.thread_should_stop(threadID))
1229 if (bestValue <= oldAlpha)
1230 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1232 else if (bestValue >= beta)
1234 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1235 move = ss[ply].pv[ply];
1236 if (!pos.move_is_capture_or_promotion(move))
1238 update_history(pos, move, depth, movesSearched, moveCount);
1239 update_killers(move, ss[ply]);
1241 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1244 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1250 // search() is the search function for zero-width nodes.
1252 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1253 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1255 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1256 assert(ply >= 0 && ply < PLY_MAX);
1257 assert(threadID >= 0 && threadID < TM.active_threads());
1259 Move movesSearched[256];
1264 Depth ext, newDepth;
1265 Value bestValue, staticValue, nullValue, value, futilityValue, futilityValueScaled;
1266 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1267 bool mateThreat = false;
1269 futilityValue = staticValue = bestValue = value = -VALUE_INFINITE;
1272 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1274 // Initialize, and make an early exit in case of an aborted search,
1275 // an instant draw, maximum ply reached, etc.
1276 init_node(ss, ply, threadID);
1278 // After init_node() that calls poll()
1279 if (AbortSearch || TM.thread_should_stop(threadID))
1282 if (pos.is_draw() || ply >= PLY_MAX - 1)
1285 // Mate distance pruning
1286 if (value_mated_in(ply) >= beta)
1289 if (value_mate_in(ply + 1) < beta)
1292 // We don't want the score of a partial search to overwrite a previous full search
1293 // TT value, so we use a different position key in case of an excluded move exsists.
1294 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1296 // Transposition table lookup
1297 tte = TT.retrieve(posKey);
1298 ttMove = (tte ? tte->move() : MOVE_NONE);
1300 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1302 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1303 return value_from_tt(tte->value(), ply);
1306 isCheck = pos.is_check();
1308 // Evaluate the position statically
1311 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1312 staticValue = value_from_tt(tte->value(), ply);
1314 staticValue = evaluate(pos, ei, threadID);
1316 ss[ply].eval = staticValue;
1317 futilityValue = staticValue + futility_margin(depth, 0); //FIXME: Remove me, only for split
1318 staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
1319 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1322 // Static null move pruning. We're betting that the opponent doesn't have
1323 // a move that will reduce the score by more than FutilityMargins[int(depth)]
1324 // if we do a null move.
1327 && depth < RazorDepth
1328 && staticValue - futility_margin(depth, 0) >= beta)
1329 return staticValue - futility_margin(depth, 0);
1335 && !value_is_mate(beta)
1336 && ok_to_do_nullmove(pos)
1337 && staticValue >= beta - NullMoveMargin)
1339 ss[ply].currentMove = MOVE_NULL;
1341 pos.do_null_move(st);
1343 // Null move dynamic reduction based on depth
1344 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1346 // Null move dynamic reduction based on value
1347 if (staticValue - beta > PawnValueMidgame)
1350 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1352 pos.undo_null_move();
1354 if (nullValue >= beta)
1356 if (depth < 6 * OnePly)
1359 // Do zugzwang verification search
1360 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1364 // The null move failed low, which means that we may be faced with
1365 // some kind of threat. If the previous move was reduced, check if
1366 // the move that refuted the null move was somehow connected to the
1367 // move which was reduced. If a connection is found, return a fail
1368 // low score (which will cause the reduced move to fail high in the
1369 // parent node, which will trigger a re-search with full depth).
1370 if (nullValue == value_mated_in(ply + 2))
1373 ss[ply].threatMove = ss[ply + 1].currentMove;
1374 if ( depth < ThreatDepth
1375 && ss[ply - 1].reduction
1376 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1380 // Null move search not allowed, try razoring
1381 else if ( !value_is_mate(beta)
1383 && depth < RazorDepth
1384 && staticValue < beta - (NullMoveMargin + 16 * depth)
1385 && ss[ply - 1].currentMove != MOVE_NULL
1386 && ttMove == MOVE_NONE
1387 && !pos.has_pawn_on_7th(pos.side_to_move()))
1389 Value rbeta = beta - (NullMoveMargin + 16 * depth);
1390 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1395 // Go with internal iterative deepening if we don't have a TT move
1396 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1397 !isCheck && ss[ply].eval >= beta - IIDMargin)
1399 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1400 ttMove = ss[ply].pv[ply];
1401 tte = TT.retrieve(posKey);
1404 // Initialize a MovePicker object for the current position, and prepare
1405 // to search all moves.
1406 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1409 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1410 while ( bestValue < beta
1411 && (move = mp.get_next_move()) != MOVE_NONE
1412 && !TM.thread_should_stop(threadID))
1414 assert(move_is_ok(move));
1416 if (move == excludedMove)
1419 moveIsCheck = pos.move_is_check(move, ci);
1420 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1421 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1423 // Decide the new search depth
1424 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1426 // Singular extension search. We extend the TT move if its value is much better than
1427 // its siblings. To verify this we do a reduced search on all the other moves but the
1428 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1429 if ( depth >= 8 * OnePly
1431 && move == tte->move()
1432 && !excludedMove // Do not allow recursive single-reply search
1434 && is_lower_bound(tte->type())
1435 && tte->depth() >= depth - 3 * OnePly)
1437 Value ttValue = value_from_tt(tte->value(), ply);
1439 if (abs(ttValue) < VALUE_KNOWN_WIN)
1441 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1443 if (excValue < ttValue - SingleReplyMargin)
1448 newDepth = depth - OnePly + ext;
1450 // Update current move
1451 movesSearched[moveCount++] = ss[ply].currentMove = move;
1456 && !captureOrPromotion
1457 && !move_is_castle(move)
1460 // Move count based pruning
1461 if ( moveCount >= futility_move_count(depth)
1462 && ok_to_prune(pos, move, ss[ply].threatMove)
1463 && bestValue > value_mated_in(PLY_MAX))
1466 // Value based pruning
1467 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1468 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1469 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1471 if (futilityValueScaled < beta)
1473 if (futilityValueScaled > bestValue)
1474 bestValue = futilityValueScaled;
1479 // Make and search the move
1480 pos.do_move(move, st, ci, moveIsCheck);
1482 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1483 // if the move fails high will be re-searched at full depth.
1484 bool doFullDepthSearch = true;
1486 if ( depth >= 3*OnePly
1488 && !captureOrPromotion
1489 && !move_is_castle(move)
1490 && !move_is_killer(move, ss[ply]))
1492 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1493 if (ss[ply].reduction)
1495 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1496 doFullDepthSearch = (value >= beta);
1500 if (doFullDepthSearch) // Go with full depth non-pv search
1502 ss[ply].reduction = Depth(0);
1503 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1505 pos.undo_move(move);
1507 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1510 if (value > bestValue)
1516 if (value == value_mate_in(ply + 1))
1517 ss[ply].mateKiller = move;
1521 if ( TM.active_threads() > 1
1523 && depth >= MinimumSplitDepth
1525 && TM.idle_thread_exists(threadID)
1527 && !TM.thread_should_stop(threadID)
1528 && TM.split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue, //FIXME: SMP & futilityValue
1529 depth, &moveCount, &mp, threadID, false))
1533 // All legal moves have been searched. A special case: If there were
1534 // no legal moves, it must be mate or stalemate.
1536 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1538 // If the search is not aborted, update the transposition table,
1539 // history counters, and killer moves.
1540 if (AbortSearch || TM.thread_should_stop(threadID))
1543 if (bestValue < beta)
1544 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1547 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1548 move = ss[ply].pv[ply];
1549 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1550 if (!pos.move_is_capture_or_promotion(move))
1552 update_history(pos, move, depth, movesSearched, moveCount);
1553 update_killers(move, ss[ply]);
1558 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1564 // qsearch() is the quiescence search function, which is called by the main
1565 // search function when the remaining depth is zero (or, to be more precise,
1566 // less than OnePly).
1568 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1569 Depth depth, int ply, int threadID) {
1571 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1572 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1574 assert(ply >= 0 && ply < PLY_MAX);
1575 assert(threadID >= 0 && threadID < TM.active_threads());
1580 Value staticValue, bestValue, value, futilityBase, futilityValue;
1581 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1582 const TTEntry* tte = NULL;
1584 bool pvNode = (beta - alpha != 1);
1585 Value oldAlpha = alpha;
1587 // Initialize, and make an early exit in case of an aborted search,
1588 // an instant draw, maximum ply reached, etc.
1589 init_node(ss, ply, threadID);
1591 // After init_node() that calls poll()
1592 if (AbortSearch || TM.thread_should_stop(threadID))
1595 if (pos.is_draw() || ply >= PLY_MAX - 1)
1598 // Transposition table lookup. At PV nodes, we don't use the TT for
1599 // pruning, but only for move ordering.
1600 tte = TT.retrieve(pos.get_key());
1601 ttMove = (tte ? tte->move() : MOVE_NONE);
1603 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1605 assert(tte->type() != VALUE_TYPE_EVAL);
1607 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1608 return value_from_tt(tte->value(), ply);
1611 isCheck = pos.is_check();
1613 // Evaluate the position statically
1615 staticValue = -VALUE_INFINITE;
1616 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1617 staticValue = value_from_tt(tte->value(), ply);
1619 staticValue = evaluate(pos, ei, threadID);
1623 ss[ply].eval = staticValue;
1624 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1627 // Initialize "stand pat score", and return it immediately if it is
1629 bestValue = staticValue;
1631 if (bestValue >= beta)
1633 // Store the score to avoid a future costly evaluation() call
1634 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1635 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1640 if (bestValue > alpha)
1643 // If we are near beta then try to get a cutoff pushing checks a bit further
1644 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1646 // Initialize a MovePicker object for the current position, and prepare
1647 // to search the moves. Because the depth is <= 0 here, only captures,
1648 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1649 // and we are near beta) will be generated.
1650 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1652 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1653 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1655 // Loop through the moves until no moves remain or a beta cutoff
1657 while ( alpha < beta
1658 && (move = mp.get_next_move()) != MOVE_NONE)
1660 assert(move_is_ok(move));
1662 moveIsCheck = pos.move_is_check(move, ci);
1664 // Update current move
1666 ss[ply].currentMove = move;
1674 && !move_is_promotion(move)
1675 && !pos.move_is_passed_pawn_push(move))
1677 futilityValue = futilityBase
1678 + pos.endgame_value_of_piece_on(move_to(move))
1679 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1681 if (futilityValue < alpha)
1683 if (futilityValue > bestValue)
1684 bestValue = futilityValue;
1689 // Detect blocking evasions that are candidate to be pruned
1690 evasionPrunable = isCheck
1691 && bestValue != -VALUE_INFINITE
1692 && !pos.move_is_capture(move)
1693 && pos.type_of_piece_on(move_from(move)) != KING
1694 && !pos.can_castle(pos.side_to_move());
1696 // Don't search moves with negative SEE values
1697 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);
1854 if (TM.thread_should_stop(threadID))
1856 lock_grab(&(sp->lock));
1861 if (value > sp->bestValue) // Less then 2% of cases
1863 lock_grab(&(sp->lock));
1864 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1866 sp->bestValue = value;
1867 if (sp->bestValue >= sp->beta)
1869 sp_update_pv(sp->parentSstack, ss, sp->ply);
1870 for (int i = 0; i < TM.active_threads(); i++)
1871 if (i != threadID && (i == sp->master || sp->slaves[i]))
1872 TM.set_stop_request(i);
1874 sp->finished = true;
1877 lock_release(&(sp->lock));
1881 /* Here we have the lock still grabbed */
1883 // If this is the master thread and we have been asked to stop because of
1884 // a beta cutoff higher up in the tree, stop all slave threads. Note that
1885 // thread_should_stop(threadID) does not imply that 'stop' flag is set, so
1886 // do this explicitly now, under lock protection.
1887 if (sp->master == threadID && TM.thread_should_stop(threadID))
1888 for (int i = 0; i < TM.active_threads(); i++)
1889 if (sp->slaves[i] || i == threadID)
1890 TM.set_stop_request(i);
1893 sp->slaves[threadID] = 0;
1895 lock_release(&(sp->lock));
1899 // sp_search_pv() is used to search from a PV split point. This function
1900 // is called by each thread working at the split point. It is similar to
1901 // the normal search_pv() function, but simpler. Because we have already
1902 // probed the hash table and searched the first move before splitting, we
1903 // don't have to repeat all this work in sp_search_pv(). We also don't
1904 // need to store anything to the hash table here: This is taken care of
1905 // after we return from the split point.
1907 void sp_search_pv(SplitPoint* sp, int threadID) {
1909 assert(threadID >= 0 && threadID < TM.active_threads());
1910 assert(TM.active_threads() > 1);
1912 Position pos(*sp->pos);
1914 SearchStack* ss = sp->sstack[threadID];
1915 Value value = -VALUE_INFINITE;
1919 while ( lock_grab_bool(&(sp->lock))
1920 && sp->alpha < sp->beta
1921 && !TM.thread_should_stop(threadID)
1922 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1924 moveCount = ++sp->moves;
1925 lock_release(&(sp->lock));
1927 assert(move_is_ok(move));
1929 bool moveIsCheck = pos.move_is_check(move, ci);
1930 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1932 ss[sp->ply].currentMove = move;
1934 // Decide the new search depth
1936 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1937 Depth newDepth = sp->depth - OnePly + ext;
1939 // Make and search the move.
1941 pos.do_move(move, st, ci, moveIsCheck);
1943 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1944 // if the move fails high will be re-searched at full depth.
1945 bool doFullDepthSearch = true;
1948 && !captureOrPromotion
1949 && !move_is_castle(move)
1950 && !move_is_killer(move, ss[sp->ply]))
1952 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1953 if (ss[sp->ply].reduction)
1955 Value localAlpha = sp->alpha;
1956 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1957 doFullDepthSearch = (value > localAlpha);
1961 if (doFullDepthSearch) // Go with full depth non-pv search
1963 Value localAlpha = sp->alpha;
1964 ss[sp->ply].reduction = Depth(0);
1965 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1967 if (value > localAlpha && value < sp->beta)
1969 // If another thread has failed high then sp->alpha has been increased
1970 // to be higher or equal then beta, if so, avoid to start a PV search.
1971 localAlpha = sp->alpha;
1972 if (localAlpha < sp->beta)
1973 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1975 assert(TM.thread_should_stop(threadID));
1978 pos.undo_move(move);
1980 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1982 if (TM.thread_should_stop(threadID))
1984 lock_grab(&(sp->lock));
1989 if (value > sp->bestValue) // Less then 2% of cases
1991 lock_grab(&(sp->lock));
1992 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1994 sp->bestValue = value;
1995 if (value > sp->alpha)
1997 // Ask threads to stop before to modify sp->alpha
1998 if (value >= sp->beta)
2000 for (int i = 0; i < TM.active_threads(); i++)
2001 if (i != threadID && (i == sp->master || sp->slaves[i]))
2002 TM.set_stop_request(i);
2004 sp->finished = true;
2009 sp_update_pv(sp->parentSstack, ss, sp->ply);
2010 if (value == value_mate_in(sp->ply + 1))
2011 ss[sp->ply].mateKiller = move;
2014 lock_release(&(sp->lock));
2018 /* Here we have the lock still grabbed */
2020 // If this is the master thread and we have been asked to stop because of
2021 // a beta cutoff higher up in the tree, stop all slave threads. Note that
2022 // thread_should_stop(threadID) does not imply that 'stop' flag is set, so
2023 // do this explicitly now, under lock protection.
2024 if (sp->master == threadID && TM.thread_should_stop(threadID))
2025 for (int i = 0; i < TM.active_threads(); i++)
2026 if (sp->slaves[i] || i == threadID)
2027 TM.set_stop_request(i);
2030 sp->slaves[threadID] = 0;
2032 lock_release(&(sp->lock));
2036 // init_node() is called at the beginning of all the search functions
2037 // (search(), search_pv(), qsearch(), and so on) and initializes the
2038 // search stack object corresponding to the current node. Once every
2039 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2040 // for user input and checks whether it is time to stop the search.
2042 void init_node(SearchStack ss[], int ply, int threadID) {
2044 assert(ply >= 0 && ply < PLY_MAX);
2045 assert(threadID >= 0 && threadID < TM.active_threads());
2047 TM.incrementNodeCounter(threadID);
2052 if (NodesSincePoll >= NodesBetweenPolls)
2059 ss[ply + 2].initKillers();
2060 TM.print_current_line(ss, ply, threadID);
2064 // update_pv() is called whenever a search returns a value > alpha.
2065 // It updates the PV in the SearchStack object corresponding to the
2068 void update_pv(SearchStack ss[], int ply) {
2070 assert(ply >= 0 && ply < PLY_MAX);
2074 ss[ply].pv[ply] = ss[ply].currentMove;
2076 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2077 ss[ply].pv[p] = ss[ply + 1].pv[p];
2079 ss[ply].pv[p] = MOVE_NONE;
2083 // sp_update_pv() is a variant of update_pv for use at split points. The
2084 // difference between the two functions is that sp_update_pv also updates
2085 // the PV at the parent node.
2087 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2089 assert(ply >= 0 && ply < PLY_MAX);
2093 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2095 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2096 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2098 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2102 // connected_moves() tests whether two moves are 'connected' in the sense
2103 // that the first move somehow made the second move possible (for instance
2104 // if the moving piece is the same in both moves). The first move is assumed
2105 // to be the move that was made to reach the current position, while the
2106 // second move is assumed to be a move from the current position.
2108 bool connected_moves(const Position& pos, Move m1, Move m2) {
2110 Square f1, t1, f2, t2;
2113 assert(move_is_ok(m1));
2114 assert(move_is_ok(m2));
2116 if (m2 == MOVE_NONE)
2119 // Case 1: The moving piece is the same in both moves
2125 // Case 2: The destination square for m2 was vacated by m1
2131 // Case 3: Moving through the vacated square
2132 if ( piece_is_slider(pos.piece_on(f2))
2133 && bit_is_set(squares_between(f2, t2), f1))
2136 // Case 4: The destination square for m2 is defended by the moving piece in m1
2137 p = pos.piece_on(t1);
2138 if (bit_is_set(pos.attacks_from(p, t1), t2))
2141 // Case 5: Discovered check, checking piece is the piece moved in m1
2142 if ( piece_is_slider(p)
2143 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2144 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2146 // discovered_check_candidates() works also if the Position's side to
2147 // move is the opposite of the checking piece.
2148 Color them = opposite_color(pos.side_to_move());
2149 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2151 if (bit_is_set(dcCandidates, f2))
2158 // value_is_mate() checks if the given value is a mate one
2159 // eventually compensated for the ply.
2161 bool value_is_mate(Value value) {
2163 assert(abs(value) <= VALUE_INFINITE);
2165 return value <= value_mated_in(PLY_MAX)
2166 || value >= value_mate_in(PLY_MAX);
2170 // move_is_killer() checks if the given move is among the
2171 // killer moves of that ply.
2173 bool move_is_killer(Move m, const SearchStack& ss) {
2175 const Move* k = ss.killers;
2176 for (int i = 0; i < KILLER_MAX; i++, k++)
2184 // extension() decides whether a move should be searched with normal depth,
2185 // or with extended depth. Certain classes of moves (checking moves, in
2186 // particular) are searched with bigger depth than ordinary moves and in
2187 // any case are marked as 'dangerous'. Note that also if a move is not
2188 // extended, as example because the corresponding UCI option is set to zero,
2189 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2191 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2192 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2194 assert(m != MOVE_NONE);
2196 Depth result = Depth(0);
2197 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2202 result += CheckExtension[pvNode];
2205 result += SingleEvasionExtension[pvNode];
2208 result += MateThreatExtension[pvNode];
2211 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2213 Color c = pos.side_to_move();
2214 if (relative_rank(c, move_to(m)) == RANK_7)
2216 result += PawnPushTo7thExtension[pvNode];
2219 if (pos.pawn_is_passed(c, move_to(m)))
2221 result += PassedPawnExtension[pvNode];
2226 if ( captureOrPromotion
2227 && pos.type_of_piece_on(move_to(m)) != PAWN
2228 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2229 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2230 && !move_is_promotion(m)
2233 result += PawnEndgameExtension[pvNode];
2238 && captureOrPromotion
2239 && pos.type_of_piece_on(move_to(m)) != PAWN
2240 && pos.see_sign(m) >= 0)
2246 return Min(result, OnePly);
2250 // ok_to_do_nullmove() looks at the current position and decides whether
2251 // doing a 'null move' should be allowed. In order to avoid zugzwang
2252 // problems, null moves are not allowed when the side to move has very
2253 // little material left. Currently, the test is a bit too simple: Null
2254 // moves are avoided only when the side to move has only pawns left.
2255 // It's probably a good idea to avoid null moves in at least some more
2256 // complicated endgames, e.g. KQ vs KR. FIXME
2258 bool ok_to_do_nullmove(const Position& pos) {
2260 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2264 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2265 // non-tactical moves late in the move list close to the leaves are
2266 // candidates for pruning.
2268 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2270 assert(move_is_ok(m));
2271 assert(threat == MOVE_NONE || move_is_ok(threat));
2272 assert(!pos.move_is_check(m));
2273 assert(!pos.move_is_capture_or_promotion(m));
2274 assert(!pos.move_is_passed_pawn_push(m));
2276 Square mfrom, mto, tfrom, tto;
2278 // Prune if there isn't any threat move
2279 if (threat == MOVE_NONE)
2282 mfrom = move_from(m);
2284 tfrom = move_from(threat);
2285 tto = move_to(threat);
2287 // Case 1: Don't prune moves which move the threatened piece
2291 // Case 2: If the threatened piece has value less than or equal to the
2292 // value of the threatening piece, don't prune move which defend it.
2293 if ( pos.move_is_capture(threat)
2294 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2295 || pos.type_of_piece_on(tfrom) == KING)
2296 && pos.move_attacks_square(m, tto))
2299 // Case 3: If the moving piece in the threatened move is a slider, don't
2300 // prune safe moves which block its ray.
2301 if ( piece_is_slider(pos.piece_on(tfrom))
2302 && bit_is_set(squares_between(tfrom, tto), mto)
2303 && pos.see_sign(m) >= 0)
2310 // ok_to_use_TT() returns true if a transposition table score
2311 // can be used at a given point in search.
2313 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2315 Value v = value_from_tt(tte->value(), ply);
2317 return ( tte->depth() >= depth
2318 || v >= Max(value_mate_in(PLY_MAX), beta)
2319 || v < Min(value_mated_in(PLY_MAX), beta))
2321 && ( (is_lower_bound(tte->type()) && v >= beta)
2322 || (is_upper_bound(tte->type()) && v < beta));
2326 // refine_eval() returns the transposition table score if
2327 // possible otherwise falls back on static position evaluation.
2329 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2334 Value v = value_from_tt(tte->value(), ply);
2336 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2337 || (is_upper_bound(tte->type()) && v < defaultEval))
2344 // update_history() registers a good move that produced a beta-cutoff
2345 // in history and marks as failures all the other moves of that ply.
2347 void update_history(const Position& pos, Move move, Depth depth,
2348 Move movesSearched[], int moveCount) {
2352 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2354 for (int i = 0; i < moveCount - 1; i++)
2356 m = movesSearched[i];
2360 if (!pos.move_is_capture_or_promotion(m))
2361 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2366 // update_killers() add a good move that produced a beta-cutoff
2367 // among the killer moves of that ply.
2369 void update_killers(Move m, SearchStack& ss) {
2371 if (m == ss.killers[0])
2374 for (int i = KILLER_MAX - 1; i > 0; i--)
2375 ss.killers[i] = ss.killers[i - 1];
2381 // update_gains() updates the gains table of a non-capture move given
2382 // the static position evaluation before and after the move.
2384 void update_gains(const Position& pos, Move m, Value before, Value after) {
2387 && before != VALUE_NONE
2388 && after != VALUE_NONE
2389 && pos.captured_piece() == NO_PIECE_TYPE
2390 && !move_is_castle(m)
2391 && !move_is_promotion(m))
2392 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2396 // current_search_time() returns the number of milliseconds which have passed
2397 // since the beginning of the current search.
2399 int current_search_time() {
2401 return get_system_time() - SearchStartTime;
2405 // nps() computes the current nodes/second count.
2409 int t = current_search_time();
2410 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2414 // poll() performs two different functions: It polls for user input, and it
2415 // looks at the time consumed so far and decides if it's time to abort the
2420 static int lastInfoTime;
2421 int t = current_search_time();
2426 // We are line oriented, don't read single chars
2427 std::string command;
2429 if (!std::getline(std::cin, command))
2432 if (command == "quit")
2435 PonderSearch = false;
2439 else if (command == "stop")
2442 PonderSearch = false;
2444 else if (command == "ponderhit")
2448 // Print search information
2452 else if (lastInfoTime > t)
2453 // HACK: Must be a new search where we searched less than
2454 // NodesBetweenPolls nodes during the first second of search.
2457 else if (t - lastInfoTime >= 1000)
2460 lock_grab(&TM.IOLock);
2465 if (dbg_show_hit_rate)
2466 dbg_print_hit_rate();
2468 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2469 << " time " << t << " hashfull " << TT.full() << endl;
2471 lock_release(&TM.IOLock);
2473 if (ShowCurrentLine)
2474 TM.threads[0].printCurrentLineRequest = true;
2477 // Should we stop the search?
2481 bool stillAtFirstMove = RootMoveNumber == 1
2482 && !AspirationFailLow
2483 && t > MaxSearchTime + ExtraSearchTime;
2485 bool noMoreTime = t > AbsoluteMaxSearchTime
2486 || stillAtFirstMove;
2488 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2489 || (ExactMaxTime && t >= ExactMaxTime)
2490 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2495 // ponderhit() is called when the program is pondering (i.e. thinking while
2496 // it's the opponent's turn to move) in order to let the engine know that
2497 // it correctly predicted the opponent's move.
2501 int t = current_search_time();
2502 PonderSearch = false;
2504 bool stillAtFirstMove = RootMoveNumber == 1
2505 && !AspirationFailLow
2506 && t > MaxSearchTime + ExtraSearchTime;
2508 bool noMoreTime = t > AbsoluteMaxSearchTime
2509 || stillAtFirstMove;
2511 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2516 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2518 void init_ss_array(SearchStack ss[]) {
2520 for (int i = 0; i < 3; i++)
2523 ss[i].initKillers();
2528 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2529 // while the program is pondering. The point is to work around a wrinkle in
2530 // the UCI protocol: When pondering, the engine is not allowed to give a
2531 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2532 // We simply wait here until one of these commands is sent, and return,
2533 // after which the bestmove and pondermove will be printed (in id_loop()).
2535 void wait_for_stop_or_ponderhit() {
2537 std::string command;
2541 if (!std::getline(std::cin, command))
2544 if (command == "quit")
2549 else if (command == "ponderhit" || command == "stop")
2555 // init_thread() is the function which is called when a new thread is
2556 // launched. It simply calls the idle_loop() function with the supplied
2557 // threadID. There are two versions of this function; one for POSIX
2558 // threads and one for Windows threads.
2560 #if !defined(_MSC_VER)
2562 void* init_thread(void *threadID) {
2564 TM.idle_loop(*(int*)threadID, NULL);
2570 DWORD WINAPI init_thread(LPVOID threadID) {
2572 TM.idle_loop(*(int*)threadID, NULL);
2579 /// The ThreadsManager class
2581 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2582 // get_beta_counters() are getters/setters for the per thread
2583 // counters used to sort the moves at root.
2585 void ThreadsManager::resetNodeCounters() {
2587 for (int i = 0; i < THREAD_MAX; i++)
2588 threads[i].nodes = 0ULL;
2591 void ThreadsManager::resetBetaCounters() {
2593 for (int i = 0; i < THREAD_MAX; i++)
2594 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2597 int64_t ThreadsManager::nodes_searched() const {
2599 int64_t result = 0ULL;
2600 for (int i = 0; i < ActiveThreads; i++)
2601 result += threads[i].nodes;
2606 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2609 for (int i = 0; i < THREAD_MAX; i++)
2611 our += threads[i].betaCutOffs[us];
2612 their += threads[i].betaCutOffs[opposite_color(us)];
2617 // idle_loop() is where the threads are parked when they have no work to do.
2618 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2619 // object for which the current thread is the master.
2621 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2623 assert(threadID >= 0 && threadID < THREAD_MAX);
2625 threads[threadID].running = true;
2627 while (!AllThreadsShouldExit || threadID == 0)
2629 // If we are not thinking, wait for a condition to be signaled
2630 // instead of wasting CPU time polling for work.
2631 while ( threadID != 0
2632 && !AllThreadsShouldExit
2633 && (AllThreadsShouldSleep || threadID >= ActiveThreads))
2636 threads[threadID].sleeping = true;
2638 #if !defined(_MSC_VER)
2639 pthread_mutex_lock(&WaitLock);
2640 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2641 pthread_cond_wait(&WaitCond, &WaitLock);
2643 pthread_mutex_unlock(&WaitLock);
2645 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2649 // Out of the while loop to avoid races in case thread is woken up but
2650 // while condition still holds true so that is put to sleep again.
2651 threads[threadID].sleeping = false;
2653 // If this thread has been assigned work, launch a search
2654 if (threads[threadID].workIsWaiting)
2656 assert(!threads[threadID].idle);
2658 threads[threadID].workIsWaiting = false;
2659 if (threads[threadID].splitPoint->pvNode)
2660 sp_search_pv(threads[threadID].splitPoint, threadID);
2662 sp_search(threads[threadID].splitPoint, threadID);
2664 threads[threadID].idle = true;
2667 // If this thread is the master of a split point and all threads have
2668 // finished their work at this split point, return from the idle loop.
2669 if (waitSp != NULL && waitSp->cpus == 0)
2673 threads[threadID].running = false;
2677 // init_threads() is called during startup. It launches all helper threads,
2678 // and initializes the split point stack and the global locks and condition
2681 void ThreadsManager::init_threads() {
2686 #if !defined(_MSC_VER)
2687 pthread_t pthread[1];
2690 // Initialize global locks
2691 lock_init(&MPLock, NULL);
2692 lock_init(&IOLock, NULL);
2694 // Initialize SplitPointStack locks
2695 for (int i = 0; i < THREAD_MAX; i++)
2696 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2698 SplitPointStack[i][j].parent = NULL;
2699 lock_init(&(SplitPointStack[i][j].lock), NULL);
2702 #if !defined(_MSC_VER)
2703 pthread_mutex_init(&WaitLock, NULL);
2704 pthread_cond_init(&WaitCond, NULL);
2706 for (i = 0; i < THREAD_MAX; i++)
2707 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2710 // Will be set just before program exits to properly end the threads
2711 AllThreadsShouldExit = false;
2713 // Threads will be put to sleep as soon as created
2714 AllThreadsShouldSleep = true;
2716 // All threads except the main thread should be initialized to idle state
2718 for (i = 1; i < THREAD_MAX; i++)
2719 threads[i].idle = true;
2721 // Launch the helper threads
2722 for (i = 1; i < THREAD_MAX; i++)
2725 #if !defined(_MSC_VER)
2726 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2729 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
2734 cout << "Failed to create thread number " << i << endl;
2735 Application::exit_with_failure();
2738 // Wait until the thread has finished launching and is gone to sleep
2739 while (!threads[i].running || !threads[i].sleeping);
2744 // exit_threads() is called when the program exits. It makes all the
2745 // helper threads exit cleanly.
2747 void ThreadsManager::exit_threads() {
2749 ActiveThreads = THREAD_MAX; // HACK
2750 AllThreadsShouldSleep = true; // HACK
2751 wake_sleeping_threads();
2752 AllThreadsShouldExit = true;
2753 for (int i = 1; i < THREAD_MAX; i++)
2755 threads[i].stopRequest = true;
2756 while (threads[i].running);
2759 // Now we can safely destroy the locks
2760 for (int i = 0; i < THREAD_MAX; i++)
2761 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2762 lock_destroy(&(SplitPointStack[i][j].lock));
2766 // thread_should_stop() checks whether the thread with a given threadID has
2767 // been asked to stop, directly or indirectly. This can happen if a beta
2768 // cutoff has occurred in the thread's currently active split point, or in
2769 // some ancestor of the current split point.
2771 bool ThreadsManager::thread_should_stop(int threadID) const {
2773 assert(threadID >= 0 && threadID < ActiveThreads);
2777 if (threads[threadID].stopRequest)
2780 if (ActiveThreads <= 2)
2783 for (sp = threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2791 // thread_is_available() checks whether the thread with threadID "slave" is
2792 // available to help the thread with threadID "master" at a split point. An
2793 // obvious requirement is that "slave" must be idle. With more than two
2794 // threads, this is not by itself sufficient: If "slave" is the master of
2795 // some active split point, it is only available as a slave to the other
2796 // threads which are busy searching the split point at the top of "slave"'s
2797 // split point stack (the "helpful master concept" in YBWC terminology).
2799 bool ThreadsManager::thread_is_available(int slave, int master) const {
2801 assert(slave >= 0 && slave < ActiveThreads);
2802 assert(master >= 0 && master < ActiveThreads);
2803 assert(ActiveThreads > 1);
2805 if (!threads[slave].idle || slave == master)
2808 // Make a local copy to be sure doesn't change under our feet
2809 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2811 if (localActiveSplitPoints == 0)
2812 // No active split points means that the thread is available as
2813 // a slave for any other thread.
2816 if (ActiveThreads == 2)
2819 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2820 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2821 // could have been set to 0 by another thread leading to an out of bound access.
2822 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2829 // idle_thread_exists() tries to find an idle thread which is available as
2830 // a slave for the thread with threadID "master".
2832 bool ThreadsManager::idle_thread_exists(int master) const {
2834 assert(master >= 0 && master < ActiveThreads);
2835 assert(ActiveThreads > 1);
2837 for (int i = 0; i < ActiveThreads; i++)
2838 if (thread_is_available(i, master))
2845 // split() does the actual work of distributing the work at a node between
2846 // several threads at PV nodes. If it does not succeed in splitting the
2847 // node (because no idle threads are available, or because we have no unused
2848 // split point objects), the function immediately returns false. If
2849 // splitting is possible, a SplitPoint object is initialized with all the
2850 // data that must be copied to the helper threads (the current position and
2851 // search stack, alpha, beta, the search depth, etc.), and we tell our
2852 // helper threads that they have been assigned work. This will cause them
2853 // to instantly leave their idle loops and call sp_search_pv(). When all
2854 // threads have returned from sp_search_pv (or, equivalently, when
2855 // splitPoint->cpus becomes 0), split() returns true.
2857 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2858 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2859 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2862 assert(sstck != NULL);
2863 assert(ply >= 0 && ply < PLY_MAX);
2864 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2865 assert(!pvNode || *alpha < *beta);
2866 assert(*beta <= VALUE_INFINITE);
2867 assert(depth > Depth(0));
2868 assert(master >= 0 && master < ActiveThreads);
2869 assert(ActiveThreads > 1);
2871 SplitPoint* splitPoint;
2875 // If no other thread is available to help us, or if we have too many
2876 // active split points, don't split.
2877 if ( !idle_thread_exists(master)
2878 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2880 lock_release(&MPLock);
2884 // Pick the next available split point object from the split point stack
2885 splitPoint = SplitPointStack[master] + threads[master].activeSplitPoints;
2886 threads[master].activeSplitPoints++;
2888 // Initialize the split point object
2889 splitPoint->parent = threads[master].splitPoint;
2890 splitPoint->finished = false;
2891 splitPoint->ply = ply;
2892 splitPoint->depth = depth;
2893 splitPoint->alpha = pvNode ? *alpha : (*beta - 1);
2894 splitPoint->beta = *beta;
2895 splitPoint->pvNode = pvNode;
2896 splitPoint->bestValue = *bestValue;
2897 splitPoint->futilityValue = futilityValue;
2898 splitPoint->master = master;
2899 splitPoint->mp = mp;
2900 splitPoint->moves = *moves;
2901 splitPoint->cpus = 1;
2902 splitPoint->pos = &p;
2903 splitPoint->parentSstack = sstck;
2904 for (int i = 0; i < ActiveThreads; i++)
2905 splitPoint->slaves[i] = 0;
2907 threads[master].splitPoint = splitPoint;
2909 // If we are here it means we are not idle
2910 assert(!threads[master].idle);
2912 // Following assert could fail because we could be slave of a master
2913 // thread that has just raised a stop request. Note that stopRequest
2914 // can be changed with only splitPoint::lock held, not with MPLock.
2915 /* assert(!threads[master].stopRequest); */
2917 // Allocate available threads setting idle flag to false
2918 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2919 if (thread_is_available(i, master))
2921 threads[i].idle = false;
2922 threads[i].stopRequest = false;
2923 threads[i].splitPoint = splitPoint;
2924 splitPoint->slaves[i] = 1;
2928 assert(splitPoint->cpus > 1);
2930 // We can release the lock because master and slave threads are already booked
2931 lock_release(&MPLock);
2933 // Tell the threads that they have work to do. This will make them leave
2934 // their idle loop. But before copy search stack tail for each thread.
2935 for (int i = 0; i < ActiveThreads; i++)
2936 if (i == master || splitPoint->slaves[i])
2938 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2939 threads[i].workIsWaiting = true; // This makes the slave to exit from idle_loop()
2942 // Everything is set up. The master thread enters the idle loop, from
2943 // which it will instantly launch a search, because its workIsWaiting
2944 // slot is 'true'. We send the split point as a second parameter to the
2945 // idle loop, which means that the main thread will return from the idle
2946 // loop when all threads have finished their work at this split point
2947 // (i.e. when splitPoint->cpus == 0).
2948 idle_loop(master, splitPoint);
2950 // We have returned from the idle loop, which means that all threads are
2951 // finished. Update alpha, beta and bestValue, and return.
2955 *alpha = splitPoint->alpha;
2957 *beta = splitPoint->beta;
2958 *bestValue = splitPoint->bestValue;
2959 threads[master].stopRequest = false;
2960 threads[master].idle = false;
2961 threads[master].activeSplitPoints--;
2962 threads[master].splitPoint = splitPoint->parent;
2964 lock_release(&MPLock);
2969 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2970 // to start a new search from the root.
2972 void ThreadsManager::wake_sleeping_threads() {
2974 assert(AllThreadsShouldSleep);
2975 assert(ActiveThreads > 0);
2977 AllThreadsShouldSleep = false;
2979 if (ActiveThreads == 1)
2982 for (int i = 1; i < ActiveThreads; i++)
2984 assert(threads[i].sleeping == true);
2986 threads[i].idle = true;
2987 threads[i].workIsWaiting = false;
2990 #if !defined(_MSC_VER)
2991 pthread_mutex_lock(&WaitLock);
2992 pthread_cond_broadcast(&WaitCond);
2993 pthread_mutex_unlock(&WaitLock);
2995 for (int i = 1; i < THREAD_MAX; i++)
2996 SetEvent(SitIdleEvent[i]);
2999 // Wait for the threads to be all woken up
3000 for (int i = 1; i < ActiveThreads; i++)
3001 while (threads[i].sleeping);
3005 // put_threads_to_sleep() makes all the threads go to sleep just before
3006 // to leave think(), at the end of the search. threads should have already
3007 // finished the job and should be idle.
3009 void ThreadsManager::put_threads_to_sleep() {
3011 assert(!AllThreadsShouldSleep);
3013 AllThreadsShouldSleep = true;
3015 // Wait for the threads to be all sleeping and reset flags
3016 // to a known state.
3017 for (int i = 1; i < ActiveThreads; i++)
3019 while (!threads[i].sleeping);
3021 assert(threads[i].idle);
3022 assert(threads[i].running);
3023 assert(!threads[i].workIsWaiting);
3025 // These two flags can be in a random state
3026 threads[i].stopRequest = threads[i].printCurrentLineRequest = false;
3030 // print_current_line() prints _once_ the current line of search for a
3031 // given thread and then setup the print request for the next thread.
3032 // Called when the UCI option UCI_ShowCurrLine is 'true'.
3034 void ThreadsManager::print_current_line(SearchStack ss[], int ply, int threadID) {
3036 assert(ply >= 0 && ply < PLY_MAX);
3037 assert(threadID >= 0 && threadID < ActiveThreads);
3039 if (!threads[threadID].printCurrentLineRequest)
3043 threads[threadID].printCurrentLineRequest = false;
3045 if (!threads[threadID].idle)
3048 cout << "info currline " << (threadID + 1);
3049 for (int p = 0; p < ply; p++)
3050 cout << " " << ss[p].currentMove;
3053 lock_release(&IOLock);
3056 // Setup print request for the next thread ID
3057 if (threadID + 1 < ActiveThreads)
3058 threads[threadID + 1].printCurrentLineRequest = true;
3062 /// The RootMoveList class
3064 // RootMoveList c'tor
3066 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3068 SearchStack ss[PLY_MAX_PLUS_2];
3069 MoveStack mlist[MaxRootMoves];
3071 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3073 // Generate all legal moves
3074 MoveStack* last = generate_moves(pos, mlist);
3076 // Add each move to the moves[] array
3077 for (MoveStack* cur = mlist; cur != last; cur++)
3079 bool includeMove = includeAllMoves;
3081 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3082 includeMove = (searchMoves[k] == cur->move);
3087 // Find a quick score for the move
3089 pos.do_move(cur->move, st);
3090 moves[count].move = cur->move;
3091 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3092 moves[count].pv[0] = cur->move;
3093 moves[count].pv[1] = MOVE_NONE;
3094 pos.undo_move(cur->move);
3101 // RootMoveList simple methods definitions
3103 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3105 moves[moveNum].nodes = nodes;
3106 moves[moveNum].cumulativeNodes += nodes;
3109 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3111 moves[moveNum].ourBeta = our;
3112 moves[moveNum].theirBeta = their;
3115 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3119 for (j = 0; pv[j] != MOVE_NONE; j++)
3120 moves[moveNum].pv[j] = pv[j];
3122 moves[moveNum].pv[j] = MOVE_NONE;
3126 // RootMoveList::sort() sorts the root move list at the beginning of a new
3129 void RootMoveList::sort() {
3131 sort_multipv(count - 1); // Sort all items
3135 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3136 // list by their scores and depths. It is used to order the different PVs
3137 // correctly in MultiPV mode.
3139 void RootMoveList::sort_multipv(int n) {
3143 for (i = 1; i <= n; i++)
3145 RootMove rm = moves[i];
3146 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3147 moves[j] = moves[j - 1];