2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
43 #include "ucioption.h"
49 //// Local definitions
57 // ThreadsManager class is used to handle all the threads related stuff in search,
58 // init, starting, parking and, the most important, launching a slave thread at a
59 // split point are what this class does. All the access to shared thread data is
60 // done through this class, so that we avoid using global variables instead.
62 class ThreadsManager {
63 /* As long as the single ThreadsManager object is defined as a global we don't
64 need to explicitly initialize to zero its data members because variables with
65 static storage duration are automatically set to zero before enter main()
71 int active_threads() const { return ActiveThreads; }
72 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
73 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
74 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
76 void resetNodeCounters();
77 void resetBetaCounters();
78 int64_t nodes_searched() const;
79 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
80 bool available_thread_exists(int master) const;
81 bool thread_is_available(int slave, int master) const;
82 bool thread_should_stop(int threadID) const;
83 void wake_sleeping_threads();
84 void put_threads_to_sleep();
85 void idle_loop(int threadID, SplitPoint* waitSp);
86 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode);
90 friend void poll(SearchStack ss[], int ply);
93 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
94 Thread threads[MAX_THREADS];
95 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
97 Lock MPLock, WaitLock;
99 #if !defined(_MSC_VER)
100 pthread_cond_t WaitCond;
102 HANDLE SitIdleEvent[MAX_THREADS];
108 // RootMove struct is used for moves at the root at the tree. For each
109 // root move, we store a score, a node count, and a PV (really a refutation
110 // in the case of moves which fail low).
114 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
116 // RootMove::operator<() is the comparison function used when
117 // sorting the moves. A move m1 is considered to be better
118 // than a move m2 if it has a higher score, or if the moves
119 // have equal score but m1 has the higher node count.
120 bool operator<(const RootMove& m) const {
122 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
127 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
128 Move pv[PLY_MAX_PLUS_2];
132 // The RootMoveList class is essentially an array of RootMove objects, with
133 // a handful of methods for accessing the data in the individual moves.
138 RootMoveList(Position& pos, Move searchMoves[]);
140 int move_count() const { return count; }
141 Move get_move(int moveNum) const { return moves[moveNum].move; }
142 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
143 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
144 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
145 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
147 void set_move_nodes(int moveNum, int64_t nodes);
148 void set_beta_counters(int moveNum, int64_t our, int64_t their);
149 void set_move_pv(int moveNum, const Move pv[]);
151 void sort_multipv(int n);
154 static const int MaxRootMoves = 500;
155 RootMove moves[MaxRootMoves];
164 // Maximum depth for razoring
165 const Depth RazorDepth = 4 * OnePly;
167 // Dynamic razoring margin based on depth
168 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
170 // Step 8. Null move search with verification search
172 // Null move margin. A null move search will not be done if the static
173 // evaluation of the position is more than NullMoveMargin below beta.
174 const Value NullMoveMargin = Value(0x200);
176 // Maximum depth for use of dynamic threat detection when null move fails low
177 const Depth ThreatDepth = 5 * OnePly;
179 // Step 9. Internal iterative deepening
181 // Minimum depth for use of internal iterative deepening
182 const Depth IIDDepthAtPVNodes = 5 * OnePly;
183 const Depth IIDDepthAtNonPVNodes = 8 * OnePly;
185 // At Non-PV nodes we do an internal iterative deepening search
186 // when the static evaluation is at most IIDMargin below beta.
187 const Value IIDMargin = Value(0x100);
189 // Step 11. Decide the new search depth
191 // Extensions. Configurable UCI options
192 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
193 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
194 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
196 // Minimum depth for use of singular extension
197 const Depth SingularExtensionDepthAtPVNodes = 6 * OnePly;
198 const Depth SingularExtensionDepthAtNonPVNodes = 8 * OnePly;
200 // If the TT move is at least SingularExtensionMargin better then the
201 // remaining ones we will extend it.
202 const Value SingularExtensionMargin = Value(0x20);
204 // Step 12. Futility pruning
206 // Futility margin for quiescence search
207 const Value FutilityMarginQS = Value(0x80);
209 // Futility lookup tables (initialized at startup) and their getter functions
210 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
211 int FutilityMoveCountArray[32]; // [depth]
213 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
214 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
216 // Step 14. Reduced search
218 // Reduction lookup tables (initialized at startup) and their getter functions
219 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
220 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
222 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
223 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
225 // Common adjustments
227 // Search depth at iteration 1
228 const Depth InitialDepth = OnePly;
230 // Easy move margin. An easy move candidate must be at least this much
231 // better than the second best move.
232 const Value EasyMoveMargin = Value(0x200);
234 // Last seconds noise filtering (LSN)
235 const bool UseLSNFiltering = true;
236 const int LSNTime = 4000; // In milliseconds
237 const Value LSNValue = value_from_centipawns(200);
238 bool loseOnTime = false;
246 // Scores and number of times the best move changed for each iteration
247 Value ValueByIteration[PLY_MAX_PLUS_2];
248 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
250 // Search window management
256 // Time managment variables
257 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
258 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
259 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
260 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
262 // Show current line?
263 bool ShowCurrentLine;
267 std::ofstream LogFile;
269 // Multi-threads related variables
270 Depth MinimumSplitDepth;
271 int MaxThreadsPerSplitPoint;
274 // Node counters, used only by thread[0] but try to keep in different cache
275 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
277 int NodesBetweenPolls = 30000;
284 Value id_loop(const Position& pos, Move searchMoves[]);
285 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
286 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
287 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
288 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
289 void sp_search(SplitPoint* sp, int threadID);
290 void sp_search_pv(SplitPoint* sp, int threadID);
291 void init_node(SearchStack ss[], int ply, int threadID);
292 void update_pv(SearchStack ss[], int ply);
293 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
294 bool connected_moves(const Position& pos, Move m1, Move m2);
295 bool value_is_mate(Value value);
296 bool move_is_killer(Move m, const SearchStack& ss);
297 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
298 bool ok_to_do_nullmove(const Position& pos);
299 bool ok_to_prune(const Position& pos, Move m, Move threat);
300 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
301 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
302 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
303 void update_killers(Move m, SearchStack& ss);
304 void update_gains(const Position& pos, Move move, Value before, Value after);
306 int current_search_time();
308 void poll(SearchStack ss[], int ply);
310 void wait_for_stop_or_ponderhit();
311 void init_ss_array(SearchStack ss[]);
312 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value);
314 #if !defined(_MSC_VER)
315 void *init_thread(void *threadID);
317 DWORD WINAPI init_thread(LPVOID threadID);
327 /// init_threads(), exit_threads() and nodes_searched() are helpers to
328 /// give accessibility to some TM methods from outside of current file.
330 void init_threads() { TM.init_threads(); }
331 void exit_threads() { TM.exit_threads(); }
332 int64_t nodes_searched() { return TM.nodes_searched(); }
335 /// perft() is our utility to verify move generation is bug free. All the legal
336 /// moves up to given depth are generated and counted and the sum returned.
338 int perft(Position& pos, Depth depth)
343 MovePicker mp(pos, MOVE_NONE, depth, H);
345 // If we are at the last ply we don't need to do and undo
346 // the moves, just to count them.
347 if (depth <= OnePly) // Replace with '<' to test also qsearch
349 while (mp.get_next_move()) sum++;
353 // Loop through all legal moves
355 while ((move = mp.get_next_move()) != MOVE_NONE)
357 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
358 sum += perft(pos, depth - OnePly);
365 /// think() is the external interface to Stockfish's search, and is called when
366 /// the program receives the UCI 'go' command. It initializes various
367 /// search-related global variables, and calls root_search(). It returns false
368 /// when a quit command is received during the search.
370 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
371 int time[], int increment[], int movesToGo, int maxDepth,
372 int maxNodes, int maxTime, Move searchMoves[]) {
374 // Initialize global search variables
375 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
376 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
378 TM.resetNodeCounters();
379 SearchStartTime = get_system_time();
380 ExactMaxTime = maxTime;
383 InfiniteSearch = infinite;
384 PonderSearch = ponder;
385 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
387 // Look for a book move, only during games, not tests
388 if (UseTimeManagement && get_option_value_bool("OwnBook"))
390 if (get_option_value_string("Book File") != OpeningBook.file_name())
391 OpeningBook.open(get_option_value_string("Book File"));
393 Move bookMove = OpeningBook.get_move(pos);
394 if (bookMove != MOVE_NONE)
397 wait_for_stop_or_ponderhit();
399 cout << "bestmove " << bookMove << endl;
404 // Reset loseOnTime flag at the beginning of a new game
405 if (button_was_pressed("New Game"))
408 // Read UCI option values
409 TT.set_size(get_option_value_int("Hash"));
410 if (button_was_pressed("Clear Hash"))
413 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
414 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
415 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
416 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
417 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
418 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
419 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
420 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
421 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
422 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
423 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
424 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
426 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
427 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
428 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
429 MultiPV = get_option_value_int("MultiPV");
430 Chess960 = get_option_value_bool("UCI_Chess960");
431 UseLogFile = get_option_value_bool("Use Search Log");
434 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
436 read_weights(pos.side_to_move());
438 // Set the number of active threads
439 int newActiveThreads = get_option_value_int("Threads");
440 if (newActiveThreads != TM.active_threads())
442 TM.set_active_threads(newActiveThreads);
443 init_eval(TM.active_threads());
444 // HACK: init_eval() destroys the static castleRightsMask[] array in the
445 // Position class. The below line repairs the damage.
446 Position p(pos.to_fen());
450 // Wake up sleeping threads
451 TM.wake_sleeping_threads();
454 int myTime = time[side_to_move];
455 int myIncrement = increment[side_to_move];
456 if (UseTimeManagement)
458 if (!movesToGo) // Sudden death time control
462 MaxSearchTime = myTime / 30 + myIncrement;
463 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
465 else // Blitz game without increment
467 MaxSearchTime = myTime / 30;
468 AbsoluteMaxSearchTime = myTime / 8;
471 else // (x moves) / (y minutes)
475 MaxSearchTime = myTime / 2;
476 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
480 MaxSearchTime = myTime / Min(movesToGo, 20);
481 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
485 if (get_option_value_bool("Ponder"))
487 MaxSearchTime += MaxSearchTime / 4;
488 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
492 // Set best NodesBetweenPolls interval to avoid lagging under
493 // heavy time pressure.
495 NodesBetweenPolls = Min(MaxNodes, 30000);
496 else if (myTime && myTime < 1000)
497 NodesBetweenPolls = 1000;
498 else if (myTime && myTime < 5000)
499 NodesBetweenPolls = 5000;
501 NodesBetweenPolls = 30000;
503 // Write search information to log file
505 LogFile << "Searching: " << pos.to_fen() << endl
506 << "infinite: " << infinite
507 << " ponder: " << ponder
508 << " time: " << myTime
509 << " increment: " << myIncrement
510 << " moves to go: " << movesToGo << endl;
512 // LSN filtering. Used only for developing purposes, disabled by default
516 // Step 2. If after last move we decided to lose on time, do it now!
517 while (SearchStartTime + myTime + 1000 > get_system_time())
521 // We're ready to start thinking. Call the iterative deepening loop function
522 Value v = id_loop(pos, searchMoves);
526 // Step 1. If this is sudden death game and our position is hopeless,
527 // decide to lose on time.
528 if ( !loseOnTime // If we already lost on time, go to step 3.
538 // Step 3. Now after stepping over the time limit, reset flag for next match.
546 TM.put_threads_to_sleep();
552 /// init_search() is called during startup. It initializes various lookup tables
556 // Init our reduction lookup tables
557 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
558 for (int j = 1; j < 64; j++) // j == moveNumber
560 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
561 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
562 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
563 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
566 // Init futility margins array
567 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
568 for (int j = 0; j < 64; j++) // j == moveNumber
570 // FIXME: test using log instead of BSR
571 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j;
574 // Init futility move count array
575 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
576 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
580 // SearchStack::init() initializes a search stack. Used at the beginning of a
581 // new search from the root.
582 void SearchStack::init(int ply) {
584 pv[ply] = pv[ply + 1] = MOVE_NONE;
585 currentMove = threatMove = MOVE_NONE;
586 reduction = Depth(0);
590 void SearchStack::initKillers() {
592 mateKiller = MOVE_NONE;
593 for (int i = 0; i < KILLER_MAX; i++)
594 killers[i] = MOVE_NONE;
599 // id_loop() is the main iterative deepening loop. It calls root_search
600 // repeatedly with increasing depth until the allocated thinking time has
601 // been consumed, the user stops the search, or the maximum search depth is
604 Value id_loop(const Position& pos, Move searchMoves[]) {
607 SearchStack ss[PLY_MAX_PLUS_2];
608 Move EasyMove = MOVE_NONE;
609 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
611 // Moves to search are verified, copied, scored and sorted
612 RootMoveList rml(p, searchMoves);
614 // Handle special case of searching on a mate/stale position
615 if (rml.move_count() == 0)
618 wait_for_stop_or_ponderhit();
620 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
623 // Print RootMoveList startup scoring to the standard output,
624 // so to output information also for iteration 1.
625 cout << "info depth " << 1
626 << "\ninfo depth " << 1
627 << " score " << value_to_string(rml.get_move_score(0))
628 << " time " << current_search_time()
629 << " nodes " << TM.nodes_searched()
631 << " pv " << rml.get_move(0) << "\n";
637 ValueByIteration[1] = rml.get_move_score(0);
640 // Is one move significantly better than others after initial scoring ?
641 if ( rml.move_count() == 1
642 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
643 EasyMove = rml.get_move(0);
645 // Iterative deepening loop
646 while (Iteration < PLY_MAX)
648 // Initialize iteration
650 BestMoveChangesByIteration[Iteration] = 0;
652 cout << "info depth " << Iteration << endl;
654 // Calculate dynamic aspiration window based on previous iterations
655 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
657 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
658 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
660 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
661 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
663 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
664 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
667 // Search to the current depth, rml is updated and sorted, alpha and beta could change
668 value = root_search(p, ss, rml, &alpha, &beta);
670 // Write PV to transposition table, in case the relevant entries have
671 // been overwritten during the search.
672 TT.insert_pv(p, ss[0].pv);
675 break; // Value cannot be trusted. Break out immediately!
677 //Save info about search result
678 ValueByIteration[Iteration] = value;
680 // Drop the easy move if differs from the new best move
681 if (ss[0].pv[0] != EasyMove)
682 EasyMove = MOVE_NONE;
684 if (UseTimeManagement)
687 bool stopSearch = false;
689 // Stop search early if there is only a single legal move,
690 // we search up to Iteration 6 anyway to get a proper score.
691 if (Iteration >= 6 && rml.move_count() == 1)
694 // Stop search early when the last two iterations returned a mate score
696 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
697 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
700 // Stop search early if one move seems to be much better than the others
701 int64_t nodes = TM.nodes_searched();
703 && EasyMove == ss[0].pv[0]
704 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
705 && current_search_time() > MaxSearchTime / 16)
706 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
707 && current_search_time() > MaxSearchTime / 32)))
710 // Add some extra time if the best move has changed during the last two iterations
711 if (Iteration > 5 && Iteration <= 50)
712 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
713 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
715 // Stop search if most of MaxSearchTime is consumed at the end of the
716 // iteration. We probably don't have enough time to search the first
717 // move at the next iteration anyway.
718 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
724 StopOnPonderhit = true;
730 if (MaxDepth && Iteration >= MaxDepth)
734 // If we are pondering or in infinite search, we shouldn't print the
735 // best move before we are told to do so.
736 if (!AbortSearch && (PonderSearch || InfiniteSearch))
737 wait_for_stop_or_ponderhit();
739 // Print final search statistics
740 cout << "info nodes " << TM.nodes_searched()
742 << " time " << current_search_time()
743 << " hashfull " << TT.full() << endl;
745 // Print the best move and the ponder move to the standard output
746 if (ss[0].pv[0] == MOVE_NONE)
748 ss[0].pv[0] = rml.get_move(0);
749 ss[0].pv[1] = MOVE_NONE;
752 assert(ss[0].pv[0] != MOVE_NONE);
754 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: "
776 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
779 return rml.get_move_score(0);
783 // root_search() is the function which searches the root node. It is
784 // similar to search_pv except that it uses a different move ordering
785 // scheme, prints some information to the standard output and handles
786 // the fail low/high loops.
788 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
795 Depth depth, ext, newDepth;
796 Value value, alpha, beta;
797 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
798 int researchCountFH, researchCountFL;
800 researchCountFH = researchCountFL = 0;
803 isCheck = pos.is_check();
805 // Step 1. Initialize node and poll (omitted at root, but I can see no good reason for this, FIXME)
806 // Step 2. Check for aborted search (omitted at root, because we do not initialize root node)
807 // Step 3. Mate distance pruning (omitted at root)
808 // Step 4. Transposition table lookup (omitted at root)
810 // Step 5. Evaluate the position statically
811 // At root we do this only to get reference value for child nodes
813 ss[0].eval = evaluate(pos, ei, 0);
815 ss[0].eval = VALUE_NONE; // HACK because we do not initialize root node
817 // Step 6. Razoring (omitted at root)
818 // Step 7. Static null move pruning (omitted at root)
819 // Step 8. Null move search with verification search (omitted at root)
820 // Step 9. Internal iterative deepening (omitted at root)
822 // Step extra. Fail low loop
823 // We start with small aspiration window and in case of fail low, we research
824 // with bigger window until we are not failing low anymore.
827 // Sort the moves before to (re)search
830 // Step 10. Loop through all moves in the root move list
831 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
833 // This is used by time management
834 FirstRootMove = (i == 0);
836 // Save the current node count before the move is searched
837 nodes = TM.nodes_searched();
839 // Reset beta cut-off counters
840 TM.resetBetaCounters();
842 // Pick the next root move, and print the move and the move number to
843 // the standard output.
844 move = ss[0].currentMove = rml.get_move(i);
846 if (current_search_time() >= 1000)
847 cout << "info currmove " << move
848 << " currmovenumber " << i + 1 << endl;
850 moveIsCheck = pos.move_is_check(move);
851 captureOrPromotion = pos.move_is_capture_or_promotion(move);
853 // Step 11. Decide the new search depth
854 depth = (Iteration - 2) * OnePly + InitialDepth;
855 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
856 newDepth = depth + ext;
858 // Step 12. Futility pruning (omitted at root)
860 // Step extra. Fail high loop
861 // If move fails high, we research with bigger window until we are not failing
863 value = - VALUE_INFINITE;
867 // Step 13. Make the move
868 pos.do_move(move, st, ci, moveIsCheck);
870 // Step extra. pv search
871 // We do pv search for first moves (i < MultiPV)
872 // and for fail high research (value > alpha)
873 if (i < MultiPV || value > alpha)
875 // Aspiration window is disabled in multi-pv case
877 alpha = -VALUE_INFINITE;
879 // Full depth PV search, done on first move or after a fail high
880 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
884 // Step 14. Reduced search
885 // if the move fails high will be re-searched at full depth
886 bool doFullDepthSearch = true;
888 if ( depth >= 3 * OnePly
890 && !captureOrPromotion
891 && !move_is_castle(move))
893 ss[0].reduction = pv_reduction(depth, i - MultiPV + 2);
896 // Reduced depth non-pv search using alpha as upperbound
897 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
898 doFullDepthSearch = (value > alpha);
902 // Step 15. Full depth search
903 if (doFullDepthSearch)
905 // Full depth non-pv search using alpha as upperbound
906 ss[0].reduction = Depth(0);
907 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
909 // If we are above alpha then research at same depth but as PV
910 // to get a correct score or eventually a fail high above beta.
912 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
916 // Step 16. Undo move
919 // Can we exit fail high loop ?
920 if (AbortSearch || value < beta)
923 // We are failing high and going to do a research. It's important to update
924 // the score before research in case we run out of time while researching.
925 rml.set_move_score(i, value);
927 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
928 rml.set_move_pv(i, ss[0].pv);
930 // Print information to the standard output
931 print_pv_info(pos, ss, alpha, beta, value);
933 // Prepare for a research after a fail high, each time with a wider window
934 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
937 } // End of fail high loop
939 // Finished searching the move. If AbortSearch is true, the search
940 // was aborted because the user interrupted the search or because we
941 // ran out of time. In this case, the return value of the search cannot
942 // be trusted, and we break out of the loop without updating the best
947 // Remember beta-cutoff and searched nodes counts for this move. The
948 // info is used to sort the root moves for the next iteration.
950 TM.get_beta_counters(pos.side_to_move(), our, their);
951 rml.set_beta_counters(i, our, their);
952 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
954 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
955 assert(value < beta);
957 // Step 17. Check for new best move
958 if (value <= alpha && i >= MultiPV)
959 rml.set_move_score(i, -VALUE_INFINITE);
962 // PV move or new best move!
965 rml.set_move_score(i, value);
967 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
968 rml.set_move_pv(i, ss[0].pv);
972 // We record how often the best move has been changed in each
973 // iteration. This information is used for time managment: When
974 // the best move changes frequently, we allocate some more time.
976 BestMoveChangesByIteration[Iteration]++;
978 // Print information to the standard output
979 print_pv_info(pos, ss, alpha, beta, value);
981 // Raise alpha to setup proper non-pv search upper bound
988 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
990 cout << "info multipv " << j + 1
991 << " score " << value_to_string(rml.get_move_score(j))
992 << " depth " << (j <= i ? Iteration : Iteration - 1)
993 << " time " << current_search_time()
994 << " nodes " << TM.nodes_searched()
998 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
999 cout << rml.get_move_pv(j, k) << " ";
1003 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1005 } // PV move or new best move
1007 assert(alpha >= *alphaPtr);
1009 AspirationFailLow = (alpha == *alphaPtr);
1011 if (AspirationFailLow && StopOnPonderhit)
1012 StopOnPonderhit = false;
1015 // Can we exit fail low loop ?
1016 if (AbortSearch || !AspirationFailLow)
1019 // Prepare for a research after a fail low, each time with a wider window
1020 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1025 // Sort the moves before to return
1032 // search_pv() is the main search function for PV nodes.
1034 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1035 Depth depth, int ply, int threadID) {
1037 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1038 assert(beta > alpha && beta <= VALUE_INFINITE);
1039 assert(ply >= 0 && ply < PLY_MAX);
1040 assert(threadID >= 0 && threadID < TM.active_threads());
1042 Move movesSearched[256];
1047 Depth ext, newDepth;
1048 Value bestValue, value, oldAlpha;
1049 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1050 bool mateThreat = false;
1052 bestValue = value = -VALUE_INFINITE;
1055 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1057 // Step 1. Initialize node and poll
1058 // Polling can abort search.
1059 init_node(ss, ply, threadID);
1061 // Step 2. Check for aborted search and immediate draw
1062 if (AbortSearch || TM.thread_should_stop(threadID))
1065 if (pos.is_draw() || ply >= PLY_MAX - 1)
1068 // Step 3. Mate distance pruning
1070 alpha = Max(value_mated_in(ply), alpha);
1071 beta = Min(value_mate_in(ply+1), beta);
1075 // Step 4. Transposition table lookup
1076 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1077 // This is to avoid problems in the following areas:
1079 // * Repetition draw detection
1080 // * Fifty move rule detection
1081 // * Searching for a mate
1082 // * Printing of full PV line
1083 tte = TT.retrieve(pos.get_key());
1084 ttMove = (tte ? tte->move() : MOVE_NONE);
1086 // Step 5. Evaluate the position statically
1087 // At PV nodes we do this only to update gain statistics
1088 isCheck = pos.is_check();
1091 ss[ply].eval = evaluate(pos, ei, threadID);
1092 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1095 // Step 6. Razoring (is omitted in PV nodes)
1096 // Step 7. Static null move pruning (is omitted in PV nodes)
1097 // Step 8. Null move search with verification search (is omitted in PV nodes)
1099 // Step 9. Internal iterative deepening
1100 if ( depth >= IIDDepthAtPVNodes
1101 && ttMove == MOVE_NONE)
1103 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1104 ttMove = ss[ply].pv[ply];
1105 tte = TT.retrieve(pos.get_key());
1108 // Step 10. Loop through moves
1109 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1111 // Initialize a MovePicker object for the current position
1112 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1113 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
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 // Step 11. 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 >= SingularExtensionDepthAtPVNodes
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 - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1145 if (excValue < ttValue - SingularExtensionMargin)
1150 newDepth = depth - OnePly + ext;
1152 // Update current move (this must be done after singular extension search)
1153 movesSearched[moveCount++] = ss[ply].currentMove = move;
1155 // Step 12. Futility pruning (is omitted in PV nodes)
1157 // Step 13. Make the move
1158 pos.do_move(move, st, ci, moveIsCheck);
1160 // Step extra. pv search (only in PV nodes)
1161 // The first move in list is the expected PV
1163 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1166 // Step 14. Reduced search
1167 // if the move fails high will be re-searched at full depth.
1168 bool doFullDepthSearch = true;
1170 if ( depth >= 3 * OnePly
1172 && !captureOrPromotion
1173 && !move_is_castle(move)
1174 && !move_is_killer(move, ss[ply]))
1176 ss[ply].reduction = pv_reduction(depth, moveCount);
1177 if (ss[ply].reduction)
1179 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1180 doFullDepthSearch = (value > alpha);
1184 // Step 15. Full depth search
1185 if (doFullDepthSearch)
1187 ss[ply].reduction = Depth(0);
1188 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1190 // Step extra. pv search (only in PV nodes)
1191 if (value > alpha && value < beta)
1192 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1196 // Step 16. Undo move
1197 pos.undo_move(move);
1199 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1201 // Step 17. Check for new best move
1202 if (value > bestValue)
1209 if (value == value_mate_in(ply + 1))
1210 ss[ply].mateKiller = move;
1214 // Step 18. Check for split
1215 if ( TM.active_threads() > 1
1217 && depth >= MinimumSplitDepth
1219 && TM.available_thread_exists(threadID)
1221 && !TM.thread_should_stop(threadID)
1222 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1223 depth, mateThreat, &moveCount, &mp, threadID, true))
1227 // Step 19. Check for mate and stalemate
1228 // All legal moves have been searched and if there were
1229 // no legal moves, it must be mate or stalemate.
1231 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1233 // Step 20. Update tables
1234 // If the search is not aborted, update the transposition table,
1235 // history counters, and killer moves.
1236 if (AbortSearch || TM.thread_should_stop(threadID))
1239 if (bestValue <= oldAlpha)
1240 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1242 else if (bestValue >= beta)
1244 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1245 move = ss[ply].pv[ply];
1246 if (!pos.move_is_capture_or_promotion(move))
1248 update_history(pos, move, depth, movesSearched, moveCount);
1249 update_killers(move, ss[ply]);
1251 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1254 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1260 // search() is the search function for zero-width nodes.
1262 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1263 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1265 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1266 assert(ply >= 0 && ply < PLY_MAX);
1267 assert(threadID >= 0 && threadID < TM.active_threads());
1269 Move movesSearched[256];
1274 Depth ext, newDepth;
1275 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1276 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1277 bool mateThreat = false;
1279 refinedValue = bestValue = value = -VALUE_INFINITE;
1282 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1284 // Step 1. Initialize node and poll
1285 // Polling can abort search.
1286 init_node(ss, ply, threadID);
1288 // Step 2. Check for aborted search and immediate draw
1289 if (AbortSearch || TM.thread_should_stop(threadID))
1292 if (pos.is_draw() || ply >= PLY_MAX - 1)
1295 // Step 3. Mate distance pruning
1296 if (value_mated_in(ply) >= beta)
1299 if (value_mate_in(ply + 1) < beta)
1302 // Step 4. Transposition table lookup
1304 // We don't want the score of a partial search to overwrite a previous full search
1305 // TT value, so we use a different position key in case of an excluded move exists.
1306 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1308 tte = TT.retrieve(posKey);
1309 ttMove = (tte ? tte->move() : MOVE_NONE);
1311 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1313 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1314 return value_from_tt(tte->value(), ply);
1317 // Step 5. Evaluate the position statically
1318 isCheck = pos.is_check();
1322 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1323 ss[ply].eval = value_from_tt(tte->value(), ply);
1325 ss[ply].eval = evaluate(pos, ei, threadID);
1327 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1328 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1332 if ( !value_is_mate(beta)
1334 && depth < RazorDepth
1335 && refinedValue < beta - razor_margin(depth)
1336 && ss[ply - 1].currentMove != MOVE_NULL
1337 && ttMove == MOVE_NONE
1338 && !pos.has_pawn_on_7th(pos.side_to_move()))
1340 Value rbeta = beta - razor_margin(depth);
1341 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1343 // Logically we should return (v + razor_margin(depth)), but
1344 // surprisingly this did slightly weaker in tests.
1348 // Step 7. Static null move pruning
1349 // We're betting that the opponent doesn't have a move that will reduce
1350 // the score by more than fuility_margin(depth) if we do a null move.
1353 && depth < RazorDepth
1354 && refinedValue - futility_margin(depth, 0) >= beta)
1355 return refinedValue - futility_margin(depth, 0);
1357 // Step 8. Null move search with verification search
1358 // When we jump directly to qsearch() we do a null move only if static value is
1359 // at least beta. Otherwise we do a null move if static value is not more than
1360 // NullMoveMargin under beta.
1364 && !value_is_mate(beta)
1365 && ok_to_do_nullmove(pos)
1366 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1368 ss[ply].currentMove = MOVE_NULL;
1370 pos.do_null_move(st);
1372 // Null move dynamic reduction based on depth
1373 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1375 // Null move dynamic reduction based on value
1376 if (refinedValue - beta > PawnValueMidgame)
1379 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1381 pos.undo_null_move();
1383 if (nullValue >= beta)
1385 if (depth < 6 * OnePly)
1388 // Do zugzwang verification search
1389 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1393 // The null move failed low, which means that we may be faced with
1394 // some kind of threat. If the previous move was reduced, check if
1395 // the move that refuted the null move was somehow connected to the
1396 // move which was reduced. If a connection is found, return a fail
1397 // low score (which will cause the reduced move to fail high in the
1398 // parent node, which will trigger a re-search with full depth).
1399 if (nullValue == value_mated_in(ply + 2))
1402 ss[ply].threatMove = ss[ply + 1].currentMove;
1403 if ( depth < ThreatDepth
1404 && ss[ply - 1].reduction
1405 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1410 // Step 9. Internal iterative deepening
1411 if ( depth >= IIDDepthAtNonPVNodes
1412 && ttMove == MOVE_NONE
1414 && ss[ply].eval >= beta - IIDMargin)
1416 search(pos, ss, beta, depth/2, ply, false, threadID);
1417 ttMove = ss[ply].pv[ply];
1418 tte = TT.retrieve(posKey);
1421 // Step 10. Loop through moves
1422 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1424 // Initialize a MovePicker object for the current position
1425 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1428 while ( bestValue < beta
1429 && (move = mp.get_next_move()) != MOVE_NONE
1430 && !TM.thread_should_stop(threadID))
1432 assert(move_is_ok(move));
1434 if (move == excludedMove)
1437 moveIsCheck = pos.move_is_check(move, ci);
1438 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1439 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1441 // Step 11. Decide the new search depth
1442 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1444 // Singular extension search. We extend the TT move if its value is much better than
1445 // its siblings. To verify this we do a reduced search on all the other moves but the
1446 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1447 if ( depth >= SingularExtensionDepthAtNonPVNodes
1449 && move == tte->move()
1450 && !excludedMove // Do not allow recursive single-reply search
1452 && is_lower_bound(tte->type())
1453 && tte->depth() >= depth - 3 * OnePly)
1455 Value ttValue = value_from_tt(tte->value(), ply);
1457 if (abs(ttValue) < VALUE_KNOWN_WIN)
1459 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1461 if (excValue < ttValue - SingularExtensionMargin)
1466 newDepth = depth - OnePly + ext;
1468 // Update current move (this must be done after singular extension search)
1469 movesSearched[moveCount++] = ss[ply].currentMove = move;
1471 // Step 12. Futility pruning
1474 && !captureOrPromotion
1475 && !move_is_castle(move)
1478 // Move count based pruning
1479 if ( moveCount >= futility_move_count(depth)
1480 && ok_to_prune(pos, move, ss[ply].threatMove)
1481 && bestValue > value_mated_in(PLY_MAX))
1484 // Value based pruning
1485 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1486 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1487 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1489 if (futilityValueScaled < beta)
1491 if (futilityValueScaled > bestValue)
1492 bestValue = futilityValueScaled;
1497 // Step 13. Make the move
1498 pos.do_move(move, st, ci, moveIsCheck);
1500 // Step 14. Reduced search
1501 // if the move fails high will be re-searched at full depth.
1502 bool doFullDepthSearch = true;
1504 if ( depth >= 3*OnePly
1506 && !captureOrPromotion
1507 && !move_is_castle(move)
1508 && !move_is_killer(move, ss[ply]))
1510 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1511 if (ss[ply].reduction)
1513 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1514 doFullDepthSearch = (value >= beta);
1518 // Step 15. Full depth search
1519 if (doFullDepthSearch)
1521 ss[ply].reduction = Depth(0);
1522 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1525 // Step 16. Undo move
1526 pos.undo_move(move);
1528 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1530 // Step 17. Check for new best move
1531 if (value > bestValue)
1537 if (value == value_mate_in(ply + 1))
1538 ss[ply].mateKiller = move;
1541 // Step 18. Check for split
1542 if ( TM.active_threads() > 1
1544 && depth >= MinimumSplitDepth
1546 && TM.available_thread_exists(threadID)
1548 && !TM.thread_should_stop(threadID)
1549 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1550 depth, mateThreat, &moveCount, &mp, threadID, false))
1554 // Step 19. Check for mate and stalemate
1555 // All legal moves have been searched and if there were
1556 // no legal moves, it must be mate or stalemate.
1557 // If one move was excluded return fail low.
1559 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1561 // Step 20. Update tables
1562 // If the search is not aborted, update the transposition table,
1563 // history counters, and killer moves.
1564 if (AbortSearch || TM.thread_should_stop(threadID))
1567 if (bestValue < beta)
1568 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1571 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1572 move = ss[ply].pv[ply];
1573 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1574 if (!pos.move_is_capture_or_promotion(move))
1576 update_history(pos, move, depth, movesSearched, moveCount);
1577 update_killers(move, ss[ply]);
1582 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1588 // qsearch() is the quiescence search function, which is called by the main
1589 // search function when the remaining depth is zero (or, to be more precise,
1590 // less than OnePly).
1592 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1593 Depth depth, int ply, int threadID) {
1595 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1596 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1598 assert(ply >= 0 && ply < PLY_MAX);
1599 assert(threadID >= 0 && threadID < TM.active_threads());
1604 Value staticValue, bestValue, value, futilityBase, futilityValue;
1605 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1606 const TTEntry* tte = NULL;
1608 bool pvNode = (beta - alpha != 1);
1609 Value oldAlpha = alpha;
1611 // Initialize, and make an early exit in case of an aborted search,
1612 // an instant draw, maximum ply reached, etc.
1613 init_node(ss, ply, threadID);
1615 // After init_node() that calls poll()
1616 if (AbortSearch || TM.thread_should_stop(threadID))
1619 if (pos.is_draw() || ply >= PLY_MAX - 1)
1622 // Transposition table lookup. At PV nodes, we don't use the TT for
1623 // pruning, but only for move ordering.
1624 tte = TT.retrieve(pos.get_key());
1625 ttMove = (tte ? tte->move() : MOVE_NONE);
1627 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1629 assert(tte->type() != VALUE_TYPE_EVAL);
1631 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1632 return value_from_tt(tte->value(), ply);
1635 isCheck = pos.is_check();
1637 // Evaluate the position statically
1639 staticValue = -VALUE_INFINITE;
1640 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1641 staticValue = value_from_tt(tte->value(), ply);
1643 staticValue = evaluate(pos, ei, threadID);
1647 ss[ply].eval = staticValue;
1648 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1651 // Initialize "stand pat score", and return it immediately if it is
1653 bestValue = staticValue;
1655 if (bestValue >= beta)
1657 // Store the score to avoid a future costly evaluation() call
1658 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1659 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1664 if (bestValue > alpha)
1667 // If we are near beta then try to get a cutoff pushing checks a bit further
1668 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1670 // Initialize a MovePicker object for the current position, and prepare
1671 // to search the moves. Because the depth is <= 0 here, only captures,
1672 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1673 // and we are near beta) will be generated.
1674 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1676 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1677 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1679 // Loop through the moves until no moves remain or a beta cutoff
1681 while ( alpha < beta
1682 && (move = mp.get_next_move()) != MOVE_NONE)
1684 assert(move_is_ok(move));
1686 moveIsCheck = pos.move_is_check(move, ci);
1688 // Update current move
1690 ss[ply].currentMove = move;
1698 && !move_is_promotion(move)
1699 && !pos.move_is_passed_pawn_push(move))
1701 futilityValue = futilityBase
1702 + pos.endgame_value_of_piece_on(move_to(move))
1703 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1705 if (futilityValue < alpha)
1707 if (futilityValue > bestValue)
1708 bestValue = futilityValue;
1713 // Detect blocking evasions that are candidate to be pruned
1714 evasionPrunable = isCheck
1715 && bestValue != -VALUE_INFINITE
1716 && !pos.move_is_capture(move)
1717 && pos.type_of_piece_on(move_from(move)) != KING
1718 && !pos.can_castle(pos.side_to_move());
1720 // Don't search moves with negative SEE values
1721 if ( (!isCheck || evasionPrunable)
1724 && !move_is_promotion(move)
1725 && pos.see_sign(move) < 0)
1728 // Make and search the move
1729 pos.do_move(move, st, ci, moveIsCheck);
1730 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1731 pos.undo_move(move);
1733 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1736 if (value > bestValue)
1747 // All legal moves have been searched. A special case: If we're in check
1748 // and no legal moves were found, it is checkmate.
1749 if (!moveCount && pos.is_check()) // Mate!
1750 return value_mated_in(ply);
1752 // Update transposition table
1753 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1754 if (bestValue <= oldAlpha)
1756 // If bestValue isn't changed it means it is still the static evaluation
1757 // of the node, so keep this info to avoid a future evaluation() call.
1758 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1759 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1761 else if (bestValue >= beta)
1763 move = ss[ply].pv[ply];
1764 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1766 // Update killers only for good checking moves
1767 if (!pos.move_is_capture_or_promotion(move))
1768 update_killers(move, ss[ply]);
1771 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1773 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1779 // sp_search() is used to search from a split point. This function is called
1780 // by each thread working at the split point. It is similar to the normal
1781 // search() function, but simpler. Because we have already probed the hash
1782 // table, done a null move search, and searched the first move before
1783 // splitting, we don't have to repeat all this work in sp_search(). We
1784 // also don't need to store anything to the hash table here: This is taken
1785 // care of after we return from the split point.
1787 void sp_search(SplitPoint* sp, int threadID) {
1789 assert(threadID >= 0 && threadID < TM.active_threads());
1790 assert(TM.active_threads() > 1);
1794 Depth ext, newDepth;
1795 Value value, futilityValueScaled;
1796 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1798 value = -VALUE_INFINITE;
1800 Position pos(*sp->pos);
1802 SearchStack* ss = sp->sstack[threadID];
1803 isCheck = pos.is_check();
1805 // Step 10. Loop through moves
1806 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1807 lock_grab(&(sp->lock));
1809 while ( sp->bestValue < sp->beta
1810 && !TM.thread_should_stop(threadID)
1811 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1813 moveCount = ++sp->moves;
1814 lock_release(&(sp->lock));
1816 assert(move_is_ok(move));
1818 moveIsCheck = pos.move_is_check(move, ci);
1819 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1821 // Step 11. Decide the new search depth
1822 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1823 newDepth = sp->depth - OnePly + ext;
1825 // Update current move
1826 ss[sp->ply].currentMove = move;
1828 // Step 12. Futility pruning
1831 && !captureOrPromotion
1832 && !move_is_castle(move))
1834 // Move count based pruning
1835 if ( moveCount >= futility_move_count(sp->depth)
1836 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1837 && sp->bestValue > value_mated_in(PLY_MAX))
1839 lock_grab(&(sp->lock));
1843 // Value based pruning
1844 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1845 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1846 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1848 if (futilityValueScaled < sp->beta)
1850 lock_grab(&(sp->lock));
1852 if (futilityValueScaled > sp->bestValue)
1853 sp->bestValue = futilityValueScaled;
1858 // Step 13. Make the move
1859 pos.do_move(move, st, ci, moveIsCheck);
1861 // Step 14. Reduced search
1862 // if the move fails high will be re-searched at full depth.
1863 bool doFullDepthSearch = true;
1866 && !captureOrPromotion
1867 && !move_is_castle(move)
1868 && !move_is_killer(move, ss[sp->ply]))
1870 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1871 if (ss[sp->ply].reduction)
1873 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1874 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1878 // Step 15. Full depth search
1879 if (doFullDepthSearch)
1881 ss[sp->ply].reduction = Depth(0);
1882 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1885 // Step 16. Undo move
1886 pos.undo_move(move);
1888 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1890 // Step 17. Check for new best move
1891 lock_grab(&(sp->lock));
1893 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1895 sp->bestValue = value;
1896 if (sp->bestValue >= sp->beta)
1898 sp->stopRequest = true;
1899 sp_update_pv(sp->parentSstack, ss, sp->ply);
1904 /* Here we have the lock still grabbed */
1906 sp->slaves[threadID] = 0;
1909 lock_release(&(sp->lock));
1913 // sp_search_pv() is used to search from a PV split point. This function
1914 // is called by each thread working at the split point. It is similar to
1915 // the normal search_pv() function, but simpler. Because we have already
1916 // probed the hash table and searched the first move before splitting, we
1917 // don't have to repeat all this work in sp_search_pv(). We also don't
1918 // need to store anything to the hash table here: This is taken care of
1919 // after we return from the split point.
1921 void sp_search_pv(SplitPoint* sp, int threadID) {
1923 assert(threadID >= 0 && threadID < TM.active_threads());
1924 assert(TM.active_threads() > 1);
1928 Depth ext, newDepth;
1930 bool moveIsCheck, captureOrPromotion, dangerous;
1932 value = -VALUE_INFINITE;
1934 Position pos(*sp->pos);
1936 SearchStack* ss = sp->sstack[threadID];
1938 // Step 10. Loop through moves
1939 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1940 lock_grab(&(sp->lock));
1942 while ( sp->alpha < sp->beta
1943 && !TM.thread_should_stop(threadID)
1944 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1946 moveCount = ++sp->moves;
1947 lock_release(&(sp->lock));
1949 assert(move_is_ok(move));
1951 moveIsCheck = pos.move_is_check(move, ci);
1952 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1954 // Step 11. Decide the new search depth
1955 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1956 newDepth = sp->depth - OnePly + ext;
1958 // Update current move
1959 ss[sp->ply].currentMove = move;
1961 // Step 12. Futility pruning (is omitted in PV nodes)
1963 // Step 13. Make the move
1964 pos.do_move(move, st, ci, moveIsCheck);
1966 // Step 14. Reduced search
1967 // if the move fails high will be re-searched at full depth.
1968 bool doFullDepthSearch = true;
1971 && !captureOrPromotion
1972 && !move_is_castle(move)
1973 && !move_is_killer(move, ss[sp->ply]))
1975 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1976 if (ss[sp->ply].reduction)
1978 Value localAlpha = sp->alpha;
1979 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1980 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1984 // Step 15. Full depth search
1985 if (doFullDepthSearch)
1987 Value localAlpha = sp->alpha;
1988 ss[sp->ply].reduction = Depth(0);
1989 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1991 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1993 // If another thread has failed high then sp->alpha has been increased
1994 // to be higher or equal then beta, if so, avoid to start a PV search.
1995 localAlpha = sp->alpha;
1996 if (localAlpha < sp->beta)
1997 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2001 // Step 16. Undo move
2002 pos.undo_move(move);
2004 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2006 // Step 17. Check for new best move
2007 lock_grab(&(sp->lock));
2009 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
2011 sp->bestValue = value;
2012 if (value > sp->alpha)
2014 // Ask threads to stop before to modify sp->alpha
2015 if (value >= sp->beta)
2016 sp->stopRequest = true;
2020 sp_update_pv(sp->parentSstack, ss, sp->ply);
2021 if (value == value_mate_in(sp->ply + 1))
2022 ss[sp->ply].mateKiller = move;
2027 /* Here we have the lock still grabbed */
2029 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();
2063 // update_pv() is called whenever a search returns a value > alpha.
2064 // It updates the PV in the SearchStack object corresponding to the
2067 void update_pv(SearchStack ss[], int ply) {
2069 assert(ply >= 0 && ply < PLY_MAX);
2073 ss[ply].pv[ply] = ss[ply].currentMove;
2075 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2076 ss[ply].pv[p] = ss[ply + 1].pv[p];
2078 ss[ply].pv[p] = MOVE_NONE;
2082 // sp_update_pv() is a variant of update_pv for use at split points. The
2083 // difference between the two functions is that sp_update_pv also updates
2084 // the PV at the parent node.
2086 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2088 assert(ply >= 0 && ply < PLY_MAX);
2092 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2094 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2095 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2097 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2101 // connected_moves() tests whether two moves are 'connected' in the sense
2102 // that the first move somehow made the second move possible (for instance
2103 // if the moving piece is the same in both moves). The first move is assumed
2104 // to be the move that was made to reach the current position, while the
2105 // second move is assumed to be a move from the current position.
2107 bool connected_moves(const Position& pos, Move m1, Move m2) {
2109 Square f1, t1, f2, t2;
2112 assert(move_is_ok(m1));
2113 assert(move_is_ok(m2));
2115 if (m2 == MOVE_NONE)
2118 // Case 1: The moving piece is the same in both moves
2124 // Case 2: The destination square for m2 was vacated by m1
2130 // Case 3: Moving through the vacated square
2131 if ( piece_is_slider(pos.piece_on(f2))
2132 && bit_is_set(squares_between(f2, t2), f1))
2135 // Case 4: The destination square for m2 is defended by the moving piece in m1
2136 p = pos.piece_on(t1);
2137 if (bit_is_set(pos.attacks_from(p, t1), t2))
2140 // Case 5: Discovered check, checking piece is the piece moved in m1
2141 if ( piece_is_slider(p)
2142 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2143 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2145 // discovered_check_candidates() works also if the Position's side to
2146 // move is the opposite of the checking piece.
2147 Color them = opposite_color(pos.side_to_move());
2148 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2150 if (bit_is_set(dcCandidates, f2))
2157 // value_is_mate() checks if the given value is a mate one
2158 // eventually compensated for the ply.
2160 bool value_is_mate(Value value) {
2162 assert(abs(value) <= VALUE_INFINITE);
2164 return value <= value_mated_in(PLY_MAX)
2165 || value >= value_mate_in(PLY_MAX);
2169 // move_is_killer() checks if the given move is among the
2170 // killer moves of that ply.
2172 bool move_is_killer(Move m, const SearchStack& ss) {
2174 const Move* k = ss.killers;
2175 for (int i = 0; i < KILLER_MAX; i++, k++)
2183 // extension() decides whether a move should be searched with normal depth,
2184 // or with extended depth. Certain classes of moves (checking moves, in
2185 // particular) are searched with bigger depth than ordinary moves and in
2186 // any case are marked as 'dangerous'. Note that also if a move is not
2187 // extended, as example because the corresponding UCI option is set to zero,
2188 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2190 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2191 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2193 assert(m != MOVE_NONE);
2195 Depth result = Depth(0);
2196 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2201 result += CheckExtension[pvNode];
2204 result += SingleEvasionExtension[pvNode];
2207 result += MateThreatExtension[pvNode];
2210 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2212 Color c = pos.side_to_move();
2213 if (relative_rank(c, move_to(m)) == RANK_7)
2215 result += PawnPushTo7thExtension[pvNode];
2218 if (pos.pawn_is_passed(c, move_to(m)))
2220 result += PassedPawnExtension[pvNode];
2225 if ( captureOrPromotion
2226 && pos.type_of_piece_on(move_to(m)) != PAWN
2227 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2228 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2229 && !move_is_promotion(m)
2232 result += PawnEndgameExtension[pvNode];
2237 && captureOrPromotion
2238 && pos.type_of_piece_on(move_to(m)) != PAWN
2239 && pos.see_sign(m) >= 0)
2245 return Min(result, OnePly);
2249 // ok_to_do_nullmove() looks at the current position and decides whether
2250 // doing a 'null move' should be allowed. In order to avoid zugzwang
2251 // problems, null moves are not allowed when the side to move has very
2252 // little material left. Currently, the test is a bit too simple: Null
2253 // moves are avoided only when the side to move has only pawns left.
2254 // It's probably a good idea to avoid null moves in at least some more
2255 // complicated endgames, e.g. KQ vs KR. FIXME
2257 bool ok_to_do_nullmove(const Position& pos) {
2259 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2263 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2264 // non-tactical moves late in the move list close to the leaves are
2265 // candidates for pruning.
2267 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2269 assert(move_is_ok(m));
2270 assert(threat == MOVE_NONE || move_is_ok(threat));
2271 assert(!pos.move_is_check(m));
2272 assert(!pos.move_is_capture_or_promotion(m));
2273 assert(!pos.move_is_passed_pawn_push(m));
2275 Square mfrom, mto, tfrom, tto;
2277 // Prune if there isn't any threat move
2278 if (threat == MOVE_NONE)
2281 mfrom = move_from(m);
2283 tfrom = move_from(threat);
2284 tto = move_to(threat);
2286 // Case 1: Don't prune moves which move the threatened piece
2290 // Case 2: If the threatened piece has value less than or equal to the
2291 // value of the threatening piece, don't prune move which defend it.
2292 if ( pos.move_is_capture(threat)
2293 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2294 || pos.type_of_piece_on(tfrom) == KING)
2295 && pos.move_attacks_square(m, tto))
2298 // Case 3: If the moving piece in the threatened move is a slider, don't
2299 // prune safe moves which block its ray.
2300 if ( piece_is_slider(pos.piece_on(tfrom))
2301 && bit_is_set(squares_between(tfrom, tto), mto)
2302 && pos.see_sign(m) >= 0)
2309 // ok_to_use_TT() returns true if a transposition table score
2310 // can be used at a given point in search.
2312 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2314 Value v = value_from_tt(tte->value(), ply);
2316 return ( tte->depth() >= depth
2317 || v >= Max(value_mate_in(PLY_MAX), beta)
2318 || v < Min(value_mated_in(PLY_MAX), beta))
2320 && ( (is_lower_bound(tte->type()) && v >= beta)
2321 || (is_upper_bound(tte->type()) && v < beta));
2325 // refine_eval() returns the transposition table score if
2326 // possible otherwise falls back on static position evaluation.
2328 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2333 Value v = value_from_tt(tte->value(), ply);
2335 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2336 || (is_upper_bound(tte->type()) && v < defaultEval))
2343 // update_history() registers a good move that produced a beta-cutoff
2344 // in history and marks as failures all the other moves of that ply.
2346 void update_history(const Position& pos, Move move, Depth depth,
2347 Move movesSearched[], int moveCount) {
2351 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2353 for (int i = 0; i < moveCount - 1; i++)
2355 m = movesSearched[i];
2359 if (!pos.move_is_capture_or_promotion(m))
2360 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2365 // update_killers() add a good move that produced a beta-cutoff
2366 // among the killer moves of that ply.
2368 void update_killers(Move m, SearchStack& ss) {
2370 if (m == ss.killers[0])
2373 for (int i = KILLER_MAX - 1; i > 0; i--)
2374 ss.killers[i] = ss.killers[i - 1];
2380 // update_gains() updates the gains table of a non-capture move given
2381 // the static position evaluation before and after the move.
2383 void update_gains(const Position& pos, Move m, Value before, Value after) {
2386 && before != VALUE_NONE
2387 && after != VALUE_NONE
2388 && pos.captured_piece() == NO_PIECE_TYPE
2389 && !move_is_castle(m)
2390 && !move_is_promotion(m))
2391 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2395 // current_search_time() returns the number of milliseconds which have passed
2396 // since the beginning of the current search.
2398 int current_search_time() {
2400 return get_system_time() - SearchStartTime;
2404 // nps() computes the current nodes/second count.
2408 int t = current_search_time();
2409 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2413 // poll() performs two different functions: It polls for user input, and it
2414 // looks at the time consumed so far and decides if it's time to abort the
2417 void poll(SearchStack ss[], int ply) {
2419 static int lastInfoTime;
2420 int t = current_search_time();
2425 // We are line oriented, don't read single chars
2426 std::string command;
2428 if (!std::getline(std::cin, command))
2431 if (command == "quit")
2434 PonderSearch = false;
2438 else if (command == "stop")
2441 PonderSearch = false;
2443 else if (command == "ponderhit")
2447 // Print search information
2451 else if (lastInfoTime > t)
2452 // HACK: Must be a new search where we searched less than
2453 // NodesBetweenPolls nodes during the first second of search.
2456 else if (t - lastInfoTime >= 1000)
2463 if (dbg_show_hit_rate)
2464 dbg_print_hit_rate();
2466 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2467 << " time " << t << " hashfull " << TT.full() << endl;
2469 // We only support current line printing in single thread mode
2470 if (ShowCurrentLine && TM.active_threads() == 1)
2472 cout << "info currline";
2473 for (int p = 0; p < ply; p++)
2474 cout << " " << ss[p].currentMove;
2480 // Should we stop the search?
2484 bool stillAtFirstMove = FirstRootMove
2485 && !AspirationFailLow
2486 && t > MaxSearchTime + ExtraSearchTime;
2488 bool noMoreTime = t > AbsoluteMaxSearchTime
2489 || stillAtFirstMove;
2491 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2492 || (ExactMaxTime && t >= ExactMaxTime)
2493 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2498 // ponderhit() is called when the program is pondering (i.e. thinking while
2499 // it's the opponent's turn to move) in order to let the engine know that
2500 // it correctly predicted the opponent's move.
2504 int t = current_search_time();
2505 PonderSearch = false;
2507 bool stillAtFirstMove = FirstRootMove
2508 && !AspirationFailLow
2509 && t > MaxSearchTime + ExtraSearchTime;
2511 bool noMoreTime = t > AbsoluteMaxSearchTime
2512 || stillAtFirstMove;
2514 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2519 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2521 void init_ss_array(SearchStack ss[]) {
2523 for (int i = 0; i < 3; i++)
2526 ss[i].initKillers();
2531 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2532 // while the program is pondering. The point is to work around a wrinkle in
2533 // the UCI protocol: When pondering, the engine is not allowed to give a
2534 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2535 // We simply wait here until one of these commands is sent, and return,
2536 // after which the bestmove and pondermove will be printed (in id_loop()).
2538 void wait_for_stop_or_ponderhit() {
2540 std::string command;
2544 if (!std::getline(std::cin, command))
2547 if (command == "quit")
2552 else if (command == "ponderhit" || command == "stop")
2558 // print_pv_info() prints to standard output and eventually to log file information on
2559 // the current PV line. It is called at each iteration or after a new pv is found.
2561 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2563 cout << "info depth " << Iteration
2564 << " score " << value_to_string(value)
2565 << ((value >= beta) ? " lowerbound" :
2566 ((value <= alpha)? " upperbound" : ""))
2567 << " time " << current_search_time()
2568 << " nodes " << TM.nodes_searched()
2572 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2573 cout << ss[0].pv[j] << " ";
2579 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2580 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2582 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2583 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2588 // init_thread() is the function which is called when a new thread is
2589 // launched. It simply calls the idle_loop() function with the supplied
2590 // threadID. There are two versions of this function; one for POSIX
2591 // threads and one for Windows threads.
2593 #if !defined(_MSC_VER)
2595 void* init_thread(void *threadID) {
2597 TM.idle_loop(*(int*)threadID, NULL);
2603 DWORD WINAPI init_thread(LPVOID threadID) {
2605 TM.idle_loop(*(int*)threadID, NULL);
2612 /// The ThreadsManager class
2614 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2615 // get_beta_counters() are getters/setters for the per thread
2616 // counters used to sort the moves at root.
2618 void ThreadsManager::resetNodeCounters() {
2620 for (int i = 0; i < MAX_THREADS; i++)
2621 threads[i].nodes = 0ULL;
2624 void ThreadsManager::resetBetaCounters() {
2626 for (int i = 0; i < MAX_THREADS; i++)
2627 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2630 int64_t ThreadsManager::nodes_searched() const {
2632 int64_t result = 0ULL;
2633 for (int i = 0; i < ActiveThreads; i++)
2634 result += threads[i].nodes;
2639 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2642 for (int i = 0; i < MAX_THREADS; i++)
2644 our += threads[i].betaCutOffs[us];
2645 their += threads[i].betaCutOffs[opposite_color(us)];
2650 // idle_loop() is where the threads are parked when they have no work to do.
2651 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2652 // object for which the current thread is the master.
2654 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2656 assert(threadID >= 0 && threadID < MAX_THREADS);
2660 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2661 // master should exit as last one.
2662 if (AllThreadsShouldExit)
2665 threads[threadID].state = THREAD_TERMINATED;
2669 // If we are not thinking, wait for a condition to be signaled
2670 // instead of wasting CPU time polling for work.
2671 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2674 assert(threadID != 0);
2675 threads[threadID].state = THREAD_SLEEPING;
2677 #if !defined(_MSC_VER)
2678 lock_grab(&WaitLock);
2679 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2680 pthread_cond_wait(&WaitCond, &WaitLock);
2681 lock_release(&WaitLock);
2683 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2687 // If thread has just woken up, mark it as available
2688 if (threads[threadID].state == THREAD_SLEEPING)
2689 threads[threadID].state = THREAD_AVAILABLE;
2691 // If this thread has been assigned work, launch a search
2692 if (threads[threadID].state == THREAD_WORKISWAITING)
2694 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2696 threads[threadID].state = THREAD_SEARCHING;
2698 if (threads[threadID].splitPoint->pvNode)
2699 sp_search_pv(threads[threadID].splitPoint, threadID);
2701 sp_search(threads[threadID].splitPoint, threadID);
2703 assert(threads[threadID].state == THREAD_SEARCHING);
2705 threads[threadID].state = THREAD_AVAILABLE;
2708 // If this thread is the master of a split point and all threads have
2709 // finished their work at this split point, return from the idle loop.
2710 if (waitSp != NULL && waitSp->cpus == 0)
2712 assert(threads[threadID].state == THREAD_AVAILABLE);
2714 threads[threadID].state = THREAD_SEARCHING;
2721 // init_threads() is called during startup. It launches all helper threads,
2722 // and initializes the split point stack and the global locks and condition
2725 void ThreadsManager::init_threads() {
2730 #if !defined(_MSC_VER)
2731 pthread_t pthread[1];
2734 // Initialize global locks
2735 lock_init(&MPLock, NULL);
2736 lock_init(&WaitLock, NULL);
2738 #if !defined(_MSC_VER)
2739 pthread_cond_init(&WaitCond, NULL);
2741 for (i = 0; i < MAX_THREADS; i++)
2742 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2745 // Initialize SplitPointStack locks
2746 for (i = 0; i < MAX_THREADS; i++)
2747 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2749 SplitPointStack[i][j].parent = NULL;
2750 lock_init(&(SplitPointStack[i][j].lock), NULL);
2753 // Will be set just before program exits to properly end the threads
2754 AllThreadsShouldExit = false;
2756 // Threads will be put to sleep as soon as created
2757 AllThreadsShouldSleep = true;
2759 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2761 threads[0].state = THREAD_SEARCHING;
2762 for (i = 1; i < MAX_THREADS; i++)
2763 threads[i].state = THREAD_AVAILABLE;
2765 // Launch the helper threads
2766 for (i = 1; i < MAX_THREADS; i++)
2769 #if !defined(_MSC_VER)
2770 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2772 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2777 cout << "Failed to create thread number " << i << endl;
2778 Application::exit_with_failure();
2781 // Wait until the thread has finished launching and is gone to sleep
2782 while (threads[i].state != THREAD_SLEEPING);
2787 // exit_threads() is called when the program exits. It makes all the
2788 // helper threads exit cleanly.
2790 void ThreadsManager::exit_threads() {
2792 ActiveThreads = MAX_THREADS; // HACK
2793 AllThreadsShouldSleep = true; // HACK
2794 wake_sleeping_threads();
2796 // This makes the threads to exit idle_loop()
2797 AllThreadsShouldExit = true;
2799 // Wait for thread termination
2800 for (int i = 1; i < MAX_THREADS; i++)
2801 while (threads[i].state != THREAD_TERMINATED);
2803 // Now we can safely destroy the locks
2804 for (int i = 0; i < MAX_THREADS; i++)
2805 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2806 lock_destroy(&(SplitPointStack[i][j].lock));
2808 lock_destroy(&WaitLock);
2809 lock_destroy(&MPLock);
2813 // thread_should_stop() checks whether the thread should stop its search.
2814 // This can happen if a beta cutoff has occurred in the thread's currently
2815 // active split point, or in some ancestor of the current split point.
2817 bool ThreadsManager::thread_should_stop(int threadID) const {
2819 assert(threadID >= 0 && threadID < ActiveThreads);
2823 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2828 // thread_is_available() checks whether the thread with threadID "slave" is
2829 // available to help the thread with threadID "master" at a split point. An
2830 // obvious requirement is that "slave" must be idle. With more than two
2831 // threads, this is not by itself sufficient: If "slave" is the master of
2832 // some active split point, it is only available as a slave to the other
2833 // threads which are busy searching the split point at the top of "slave"'s
2834 // split point stack (the "helpful master concept" in YBWC terminology).
2836 bool ThreadsManager::thread_is_available(int slave, int master) const {
2838 assert(slave >= 0 && slave < ActiveThreads);
2839 assert(master >= 0 && master < ActiveThreads);
2840 assert(ActiveThreads > 1);
2842 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2845 // Make a local copy to be sure doesn't change under our feet
2846 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2848 if (localActiveSplitPoints == 0)
2849 // No active split points means that the thread is available as
2850 // a slave for any other thread.
2853 if (ActiveThreads == 2)
2856 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2857 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2858 // could have been set to 0 by another thread leading to an out of bound access.
2859 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2866 // available_thread_exists() tries to find an idle thread which is available as
2867 // a slave for the thread with threadID "master".
2869 bool ThreadsManager::available_thread_exists(int master) const {
2871 assert(master >= 0 && master < ActiveThreads);
2872 assert(ActiveThreads > 1);
2874 for (int i = 0; i < ActiveThreads; i++)
2875 if (thread_is_available(i, master))
2882 // split() does the actual work of distributing the work at a node between
2883 // several threads at PV nodes. If it does not succeed in splitting the
2884 // node (because no idle threads are available, or because we have no unused
2885 // split point objects), the function immediately returns false. If
2886 // splitting is possible, a SplitPoint object is initialized with all the
2887 // data that must be copied to the helper threads (the current position and
2888 // search stack, alpha, beta, the search depth, etc.), and we tell our
2889 // helper threads that they have been assigned work. This will cause them
2890 // to instantly leave their idle loops and call sp_search_pv(). When all
2891 // threads have returned from sp_search_pv (or, equivalently, when
2892 // splitPoint->cpus becomes 0), split() returns true.
2894 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2895 Value* alpha, const Value beta, Value* bestValue,
2896 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2899 assert(sstck != NULL);
2900 assert(ply >= 0 && ply < PLY_MAX);
2901 assert(*bestValue >= -VALUE_INFINITE);
2902 assert( ( pvNode && *bestValue <= *alpha)
2903 || (!pvNode && *bestValue < beta ));
2904 assert(!pvNode || *alpha < beta);
2905 assert(beta <= VALUE_INFINITE);
2906 assert(depth > Depth(0));
2907 assert(master >= 0 && master < ActiveThreads);
2908 assert(ActiveThreads > 1);
2910 SplitPoint* splitPoint;
2914 // If no other thread is available to help us, or if we have too many
2915 // active split points, don't split.
2916 if ( !available_thread_exists(master)
2917 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2919 lock_release(&MPLock);
2923 // Pick the next available split point object from the split point stack
2924 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2926 // Initialize the split point object
2927 splitPoint->parent = threads[master].splitPoint;
2928 splitPoint->stopRequest = false;
2929 splitPoint->ply = ply;
2930 splitPoint->depth = depth;
2931 splitPoint->mateThreat = mateThreat;
2932 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2933 splitPoint->beta = beta;
2934 splitPoint->pvNode = pvNode;
2935 splitPoint->bestValue = *bestValue;
2936 splitPoint->master = master;
2937 splitPoint->mp = mp;
2938 splitPoint->moves = *moves;
2939 splitPoint->cpus = 1;
2940 splitPoint->pos = &p;
2941 splitPoint->parentSstack = sstck;
2942 for (int i = 0; i < ActiveThreads; i++)
2943 splitPoint->slaves[i] = 0;
2945 threads[master].splitPoint = splitPoint;
2946 threads[master].activeSplitPoints++;
2948 // If we are here it means we are not available
2949 assert(threads[master].state != THREAD_AVAILABLE);
2951 // Allocate available threads setting state to THREAD_BOOKED
2952 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2953 if (thread_is_available(i, master))
2955 threads[i].state = THREAD_BOOKED;
2956 threads[i].splitPoint = splitPoint;
2957 splitPoint->slaves[i] = 1;
2961 assert(splitPoint->cpus > 1);
2963 // We can release the lock because slave threads are already booked and master is not available
2964 lock_release(&MPLock);
2966 // Tell the threads that they have work to do. This will make them leave
2967 // their idle loop. But before copy search stack tail for each thread.
2968 for (int i = 0; i < ActiveThreads; i++)
2969 if (i == master || splitPoint->slaves[i])
2971 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2973 assert(i == master || threads[i].state == THREAD_BOOKED);
2975 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2978 // Everything is set up. The master thread enters the idle loop, from
2979 // which it will instantly launch a search, because its state is
2980 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2981 // idle loop, which means that the main thread will return from the idle
2982 // loop when all threads have finished their work at this split point
2983 // (i.e. when splitPoint->cpus == 0).
2984 idle_loop(master, splitPoint);
2986 // We have returned from the idle loop, which means that all threads are
2987 // finished. Update alpha, beta and bestValue, and return.
2991 *alpha = splitPoint->alpha;
2993 *bestValue = splitPoint->bestValue;
2994 threads[master].activeSplitPoints--;
2995 threads[master].splitPoint = splitPoint->parent;
2997 lock_release(&MPLock);
3002 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3003 // to start a new search from the root.
3005 void ThreadsManager::wake_sleeping_threads() {
3007 assert(AllThreadsShouldSleep);
3008 assert(ActiveThreads > 0);
3010 AllThreadsShouldSleep = false;
3012 if (ActiveThreads == 1)
3015 #if !defined(_MSC_VER)
3016 pthread_mutex_lock(&WaitLock);
3017 pthread_cond_broadcast(&WaitCond);
3018 pthread_mutex_unlock(&WaitLock);
3020 for (int i = 1; i < MAX_THREADS; i++)
3021 SetEvent(SitIdleEvent[i]);
3027 // put_threads_to_sleep() makes all the threads go to sleep just before
3028 // to leave think(), at the end of the search. Threads should have already
3029 // finished the job and should be idle.
3031 void ThreadsManager::put_threads_to_sleep() {
3033 assert(!AllThreadsShouldSleep);
3035 // This makes the threads to go to sleep
3036 AllThreadsShouldSleep = true;
3039 /// The RootMoveList class
3041 // RootMoveList c'tor
3043 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3045 SearchStack ss[PLY_MAX_PLUS_2];
3046 MoveStack mlist[MaxRootMoves];
3048 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3050 // Generate all legal moves
3051 MoveStack* last = generate_moves(pos, mlist);
3053 // Add each move to the moves[] array
3054 for (MoveStack* cur = mlist; cur != last; cur++)
3056 bool includeMove = includeAllMoves;
3058 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3059 includeMove = (searchMoves[k] == cur->move);
3064 // Find a quick score for the move
3066 pos.do_move(cur->move, st);
3067 moves[count].move = cur->move;
3068 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3069 moves[count].pv[0] = cur->move;
3070 moves[count].pv[1] = MOVE_NONE;
3071 pos.undo_move(cur->move);
3078 // RootMoveList simple methods definitions
3080 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3082 moves[moveNum].nodes = nodes;
3083 moves[moveNum].cumulativeNodes += nodes;
3086 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3088 moves[moveNum].ourBeta = our;
3089 moves[moveNum].theirBeta = their;
3092 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3096 for (j = 0; pv[j] != MOVE_NONE; j++)
3097 moves[moveNum].pv[j] = pv[j];
3099 moves[moveNum].pv[j] = MOVE_NONE;
3103 // RootMoveList::sort() sorts the root move list at the beginning of a new
3106 void RootMoveList::sort() {
3108 sort_multipv(count - 1); // Sort all items
3112 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3113 // list by their scores and depths. It is used to order the different PVs
3114 // correctly in MultiPV mode.
3116 void RootMoveList::sort_multipv(int n) {
3120 for (i = 1; i <= n; i++)
3122 RootMove rm = moves[i];
3123 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3124 moves[j] = moves[j - 1];