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;
377 TM.resetNodeCounters();
378 SearchStartTime = get_system_time();
379 ExactMaxTime = maxTime;
382 InfiniteSearch = infinite;
383 PonderSearch = ponder;
384 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
386 // Look for a book move, only during games, not tests
387 if (UseTimeManagement && get_option_value_bool("OwnBook"))
389 if (get_option_value_string("Book File") != OpeningBook.file_name())
390 OpeningBook.open(get_option_value_string("Book File"));
392 Move bookMove = OpeningBook.get_move(pos);
393 if (bookMove != MOVE_NONE)
396 wait_for_stop_or_ponderhit();
398 cout << "bestmove " << bookMove << endl;
403 // Reset loseOnTime flag at the beginning of a new game
404 if (button_was_pressed("New Game"))
407 // Read UCI option values
408 TT.set_size(get_option_value_int("Hash"));
409 if (button_was_pressed("Clear Hash"))
412 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
413 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
414 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
415 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
416 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
417 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
418 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
419 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
420 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
421 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
422 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
423 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
425 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
426 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
427 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
428 MultiPV = get_option_value_int("MultiPV");
429 Chess960 = get_option_value_bool("UCI_Chess960");
430 UseLogFile = get_option_value_bool("Use Search Log");
433 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
435 read_weights(pos.side_to_move());
437 // Set the number of active threads
438 int newActiveThreads = get_option_value_int("Threads");
439 if (newActiveThreads != TM.active_threads())
441 TM.set_active_threads(newActiveThreads);
442 init_eval(TM.active_threads());
443 // HACK: init_eval() destroys the static castleRightsMask[] array in the
444 // Position class. The below line repairs the damage.
445 Position p(pos.to_fen());
449 // Wake up sleeping threads
450 TM.wake_sleeping_threads();
453 int myTime = time[side_to_move];
454 int myIncrement = increment[side_to_move];
455 if (UseTimeManagement)
457 if (!movesToGo) // Sudden death time control
461 MaxSearchTime = myTime / 30 + myIncrement;
462 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
464 else // Blitz game without increment
466 MaxSearchTime = myTime / 30;
467 AbsoluteMaxSearchTime = myTime / 8;
470 else // (x moves) / (y minutes)
474 MaxSearchTime = myTime / 2;
475 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
479 MaxSearchTime = myTime / Min(movesToGo, 20);
480 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
484 if (get_option_value_bool("Ponder"))
486 MaxSearchTime += MaxSearchTime / 4;
487 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
491 // Set best NodesBetweenPolls interval to avoid lagging under
492 // heavy time pressure.
494 NodesBetweenPolls = Min(MaxNodes, 30000);
495 else if (myTime && myTime < 1000)
496 NodesBetweenPolls = 1000;
497 else if (myTime && myTime < 5000)
498 NodesBetweenPolls = 5000;
500 NodesBetweenPolls = 30000;
502 // Write search information to log file
504 LogFile << "Searching: " << pos.to_fen() << endl
505 << "infinite: " << infinite
506 << " ponder: " << ponder
507 << " time: " << myTime
508 << " increment: " << myIncrement
509 << " moves to go: " << movesToGo << endl;
511 // LSN filtering. Used only for developing purposes, disabled by default
515 // Step 2. If after last move we decided to lose on time, do it now!
516 while (SearchStartTime + myTime + 1000 > get_system_time())
520 // We're ready to start thinking. Call the iterative deepening loop function
521 Value v = id_loop(pos, searchMoves);
525 // Step 1. If this is sudden death game and our position is hopeless,
526 // decide to lose on time.
527 if ( !loseOnTime // If we already lost on time, go to step 3.
537 // Step 3. Now after stepping over the time limit, reset flag for next match.
545 TM.put_threads_to_sleep();
551 /// init_search() is called during startup. It initializes various lookup tables
555 // Init our reduction lookup tables
556 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
557 for (int j = 1; j < 64; j++) // j == moveNumber
559 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
560 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
561 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
562 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
565 // Init futility margins array
566 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
567 for (int j = 0; j < 64; j++) // j == moveNumber
569 // FIXME: test using log instead of BSR
570 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j;
573 // Init futility move count array
574 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
575 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
579 // SearchStack::init() initializes a search stack. Used at the beginning of a
580 // new search from the root.
581 void SearchStack::init(int ply) {
583 pv[ply] = pv[ply + 1] = MOVE_NONE;
584 currentMove = threatMove = MOVE_NONE;
585 reduction = Depth(0);
589 void SearchStack::initKillers() {
591 mateKiller = MOVE_NONE;
592 for (int i = 0; i < KILLER_MAX; i++)
593 killers[i] = MOVE_NONE;
598 // id_loop() is the main iterative deepening loop. It calls root_search
599 // repeatedly with increasing depth until the allocated thinking time has
600 // been consumed, the user stops the search, or the maximum search depth is
603 Value id_loop(const Position& pos, Move searchMoves[]) {
606 SearchStack ss[PLY_MAX_PLUS_2];
607 Move EasyMove = MOVE_NONE;
608 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
610 // Moves to search are verified, copied, scored and sorted
611 RootMoveList rml(p, searchMoves);
613 // Handle special case of searching on a mate/stale position
614 if (rml.move_count() == 0)
617 wait_for_stop_or_ponderhit();
619 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
622 // Print RootMoveList startup scoring to the standard output,
623 // so to output information also for iteration 1.
624 cout << "info depth " << 1
625 << "\ninfo depth " << 1
626 << " score " << value_to_string(rml.get_move_score(0))
627 << " time " << current_search_time()
628 << " nodes " << TM.nodes_searched()
630 << " pv " << rml.get_move(0) << "\n";
636 ValueByIteration[1] = rml.get_move_score(0);
639 // Is one move significantly better than others after initial scoring ?
640 if ( rml.move_count() == 1
641 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
642 EasyMove = rml.get_move(0);
644 // Iterative deepening loop
645 while (Iteration < PLY_MAX)
647 // Initialize iteration
649 BestMoveChangesByIteration[Iteration] = 0;
653 cout << "info depth " << Iteration << endl;
655 // Calculate dynamic aspiration window based on previous iterations
656 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
658 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
659 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
661 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
662 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
664 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
665 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
668 // Search to the current depth, rml is updated and sorted, alpha and beta could change
669 value = root_search(p, ss, rml, &alpha, &beta);
671 // Write PV to transposition table, in case the relevant entries have
672 // been overwritten during the search.
673 TT.insert_pv(p, ss[0].pv);
676 break; // Value cannot be trusted. Break out immediately!
678 //Save info about search result
679 ValueByIteration[Iteration] = value;
681 // Drop the easy move if differs from the new best move
682 if (ss[0].pv[0] != EasyMove)
683 EasyMove = MOVE_NONE;
685 if (UseTimeManagement)
688 bool stopSearch = false;
690 // Stop search early if there is only a single legal move,
691 // we search up to Iteration 6 anyway to get a proper score.
692 if (Iteration >= 6 && rml.move_count() == 1)
695 // Stop search early when the last two iterations returned a mate score
697 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
698 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
701 // Stop search early if one move seems to be much better than the others
702 int64_t nodes = TM.nodes_searched();
704 && EasyMove == ss[0].pv[0]
705 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
706 && current_search_time() > MaxSearchTime / 16)
707 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
708 && current_search_time() > MaxSearchTime / 32)))
711 // Add some extra time if the best move has changed during the last two iterations
712 if (Iteration > 5 && Iteration <= 50)
713 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
714 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
716 // Stop search if most of MaxSearchTime is consumed at the end of the
717 // iteration. We probably don't have enough time to search the first
718 // move at the next iteration anyway.
719 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
725 StopOnPonderhit = true;
731 if (MaxDepth && Iteration >= MaxDepth)
735 // If we are pondering or in infinite search, we shouldn't print the
736 // best move before we are told to do so.
737 if (!AbortSearch && (PonderSearch || InfiniteSearch))
738 wait_for_stop_or_ponderhit();
740 // Print final search statistics
741 cout << "info nodes " << TM.nodes_searched()
743 << " time " << current_search_time()
744 << " hashfull " << TT.full() << endl;
746 // Print the best move and the ponder move to the standard output
747 if (ss[0].pv[0] == MOVE_NONE)
749 ss[0].pv[0] = rml.get_move(0);
750 ss[0].pv[1] = MOVE_NONE;
753 assert(ss[0].pv[0] != MOVE_NONE);
755 cout << "bestmove " << ss[0].pv[0];
757 if (ss[0].pv[1] != MOVE_NONE)
758 cout << " ponder " << ss[0].pv[1];
765 dbg_print_mean(LogFile);
767 if (dbg_show_hit_rate)
768 dbg_print_hit_rate(LogFile);
770 LogFile << "\nNodes: " << TM.nodes_searched()
771 << "\nNodes/second: " << nps()
772 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
775 p.do_move(ss[0].pv[0], st);
776 LogFile << "\nPonder move: "
777 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
780 return rml.get_move_score(0);
784 // root_search() is the function which searches the root node. It is
785 // similar to search_pv except that it uses a different move ordering
786 // scheme, prints some information to the standard output and handles
787 // the fail low/high loops.
789 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
795 Depth depth, ext, newDepth;
796 Value value, alpha, beta;
797 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
798 int researchCount = 0;
802 isCheck = pos.is_check();
804 // Step 1. Initialize node and poll (omitted at root, but I can see no good reason for this, FIXME)
805 // Step 2. Check for aborted search (omitted at root, because we do not initialize root node)
806 // Step 3. Mate distance pruning (omitted at root)
807 // Step 4. Transposition table lookup (omitted at root)
809 // Step 5. Evaluate the position statically
810 // At root we do this only to get reference value for child nodes
812 ss[0].eval = evaluate(pos, ei, 0);
814 ss[0].eval = VALUE_NONE; // HACK because we do not initialize root node
816 // Step 6. Razoring (omitted at root)
817 // Step 7. Static null move pruning (omitted at root)
818 // Step 8. Null move search with verification search (omitted at root)
819 // Step 9. Internal iterative deepening (omitted at root)
821 // Step extra. Fail low loop
822 // We start with small aspiration window and in case of fail low, we research
823 // with bigger window until we are not failing low anymore.
826 // Sort the moves before to (re)search
829 // Step 10. Loop through all moves in the root move list
830 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
832 // This is used by time management
833 FirstRootMove = (i == 0);
835 // Save the current node count before the move is searched
836 nodes = TM.nodes_searched();
838 // Reset beta cut-off counters
839 TM.resetBetaCounters();
841 // Pick the next root move, and print the move and the move number to
842 // the standard output.
843 move = ss[0].currentMove = rml.get_move(i);
845 if (current_search_time() >= 1000)
846 cout << "info currmove " << move
847 << " currmovenumber " << i + 1 << endl;
849 moveIsCheck = pos.move_is_check(move);
850 captureOrPromotion = pos.move_is_capture_or_promotion(move);
852 // Step 11. Decide the new search depth
853 depth = (Iteration - 2) * OnePly + InitialDepth;
854 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
855 newDepth = depth + ext;
857 // Step 12. Futility pruning (omitted at root)
859 // Step extra. Fail high loop
860 // If move fails high, we research with bigger window until we are not failing
862 value = - VALUE_INFINITE;
866 // Step 13. Make the move
867 pos.do_move(move, st, ci, moveIsCheck);
869 // Step extra. pv search
870 // We do pv search for first moves (i < MultiPV)
871 // and for fail high research (value > alpha)
872 if (i < MultiPV || value > alpha)
874 // Aspiration window is disabled in multi-pv case
876 alpha = -VALUE_INFINITE;
878 // Full depth PV search, done on first move or after a fail high
879 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
883 // Step 14. Reduced search
884 // if the move fails high will be re-searched at full depth
885 bool doFullDepthSearch = true;
887 if ( depth >= 3 * OnePly
889 && !captureOrPromotion
890 && !move_is_castle(move))
892 ss[0].reduction = pv_reduction(depth, i - MultiPV + 2);
895 // Reduced depth non-pv search using alpha as upperbound
896 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
897 doFullDepthSearch = (value > alpha);
901 // Step 15. Full depth search
902 if (doFullDepthSearch)
904 // Full depth non-pv search using alpha as upperbound
905 ss[0].reduction = Depth(0);
906 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
908 // If we are above alpha then research at same depth but as PV
909 // to get a correct score or eventually a fail high above beta.
911 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
915 // Step 16. Undo move
918 // Can we exit fail high loop ?
919 if (AbortSearch || value < beta)
922 // We are failing high and going to do a research. It's important to update
923 // the score before research in case we run out of time while researching.
924 rml.set_move_score(i, value);
926 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
927 rml.set_move_pv(i, ss[0].pv);
929 // Print information to the standard output
930 print_pv_info(pos, ss, alpha, beta, value);
932 // Prepare for a research after a fail high, each time with a wider window
934 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCount), VALUE_INFINITE);
936 } // End of fail high loop
938 // Finished searching the move. If AbortSearch is true, the search
939 // was aborted because the user interrupted the search or because we
940 // ran out of time. In this case, the return value of the search cannot
941 // be trusted, and we break out of the loop without updating the best
946 // Remember beta-cutoff and searched nodes counts for this move. The
947 // info is used to sort the root moves for the next iteration.
949 TM.get_beta_counters(pos.side_to_move(), our, their);
950 rml.set_beta_counters(i, our, their);
951 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
953 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
954 assert(value < beta);
956 // Step 17. Check for new best move
957 if (value <= alpha && i >= MultiPV)
958 rml.set_move_score(i, -VALUE_INFINITE);
961 // PV move or new best move!
964 rml.set_move_score(i, value);
966 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
967 rml.set_move_pv(i, ss[0].pv);
971 // We record how often the best move has been changed in each
972 // iteration. This information is used for time managment: When
973 // the best move changes frequently, we allocate some more time.
975 BestMoveChangesByIteration[Iteration]++;
977 // Print information to the standard output
978 print_pv_info(pos, ss, alpha, beta, value);
980 // Raise alpha to setup proper non-pv search upper bound
987 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
989 cout << "info multipv " << j + 1
990 << " score " << value_to_string(rml.get_move_score(j))
991 << " depth " << (j <= i ? Iteration : Iteration - 1)
992 << " time " << current_search_time()
993 << " nodes " << TM.nodes_searched()
997 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
998 cout << rml.get_move_pv(j, k) << " ";
1002 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1004 } // PV move or new best move
1006 assert(alpha >= *alphaPtr);
1008 AspirationFailLow = (alpha == *alphaPtr);
1010 if (AspirationFailLow && StopOnPonderhit)
1011 StopOnPonderhit = false;
1014 // Can we exit fail low loop ?
1015 if (AbortSearch || !AspirationFailLow)
1018 // Prepare for a research after a fail low, each time with a wider window
1020 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCount), -VALUE_INFINITE);
1024 // Sort the moves before to return
1031 // search_pv() is the main search function for PV nodes.
1033 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1034 Depth depth, int ply, int threadID) {
1036 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1037 assert(beta > alpha && beta <= VALUE_INFINITE);
1038 assert(ply >= 0 && ply < PLY_MAX);
1039 assert(threadID >= 0 && threadID < TM.active_threads());
1041 Move movesSearched[256];
1046 Depth ext, newDepth;
1047 Value bestValue, value, oldAlpha;
1048 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1049 bool mateThreat = false;
1051 bestValue = value = -VALUE_INFINITE;
1054 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1056 // Step 1. Initialize node and poll
1057 // Polling can abort search.
1058 init_node(ss, ply, threadID);
1060 // Step 2. Check for aborted search and immediate draw
1061 if (AbortSearch || TM.thread_should_stop(threadID))
1064 if (pos.is_draw() || ply >= PLY_MAX - 1)
1067 // Step 3. Mate distance pruning
1069 alpha = Max(value_mated_in(ply), alpha);
1070 beta = Min(value_mate_in(ply+1), beta);
1074 // Step 4. Transposition table lookup
1075 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1076 // This is to avoid problems in the following areas:
1078 // * Repetition draw detection
1079 // * Fifty move rule detection
1080 // * Searching for a mate
1081 // * Printing of full PV line
1082 tte = TT.retrieve(pos.get_key());
1083 ttMove = (tte ? tte->move() : MOVE_NONE);
1085 // Step 5. Evaluate the position statically
1086 // At PV nodes we do this only to update gain statistics
1087 isCheck = pos.is_check();
1090 ss[ply].eval = evaluate(pos, ei, threadID);
1091 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1094 // Step 6. Razoring (is omitted in PV nodes)
1095 // Step 7. Static null move pruning (is omitted in PV nodes)
1096 // Step 8. Null move search with verification search (is omitted in PV nodes)
1098 // Step 9. Internal iterative deepening
1099 if ( depth >= IIDDepthAtPVNodes
1100 && ttMove == MOVE_NONE)
1102 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1103 ttMove = ss[ply].pv[ply];
1104 tte = TT.retrieve(pos.get_key());
1107 // Step 10. Loop through moves
1108 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1110 // Initialize a MovePicker object for the current position
1111 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1112 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1115 while ( alpha < beta
1116 && (move = mp.get_next_move()) != MOVE_NONE
1117 && !TM.thread_should_stop(threadID))
1119 assert(move_is_ok(move));
1121 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1122 moveIsCheck = pos.move_is_check(move, ci);
1123 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1125 // Step 11. Decide the new search depth
1126 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1128 // Singular extension search. We extend the TT move if its value is much better than
1129 // its siblings. To verify this we do a reduced search on all the other moves but the
1130 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1131 if ( depth >= SingularExtensionDepthAtPVNodes
1133 && move == tte->move()
1135 && is_lower_bound(tte->type())
1136 && tte->depth() >= depth - 3 * OnePly)
1138 Value ttValue = value_from_tt(tte->value(), ply);
1140 if (abs(ttValue) < VALUE_KNOWN_WIN)
1142 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1144 if (excValue < ttValue - SingularExtensionMargin)
1149 newDepth = depth - OnePly + ext;
1151 // Update current move (this must be done after singular extension search)
1152 movesSearched[moveCount++] = ss[ply].currentMove = move;
1154 // Step 12. Futility pruning (is omitted in PV nodes)
1156 // Step 13. Make the move
1157 pos.do_move(move, st, ci, moveIsCheck);
1159 // Step extra. pv search (only in PV nodes)
1160 // The first move in list is the expected PV
1162 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1165 // Step 14. Reduced search
1166 // if the move fails high will be re-searched at full depth.
1167 bool doFullDepthSearch = true;
1169 if ( depth >= 3 * OnePly
1171 && !captureOrPromotion
1172 && !move_is_castle(move)
1173 && !move_is_killer(move, ss[ply]))
1175 ss[ply].reduction = pv_reduction(depth, moveCount);
1176 if (ss[ply].reduction)
1178 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1179 doFullDepthSearch = (value > alpha);
1183 // Step 15. Full depth search
1184 if (doFullDepthSearch)
1186 ss[ply].reduction = Depth(0);
1187 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1189 // Step extra. pv search (only in PV nodes)
1190 if (value > alpha && value < beta)
1191 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1195 // Step 16. Undo move
1196 pos.undo_move(move);
1198 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1200 // Step 17. Check for new best move
1201 if (value > bestValue)
1208 if (value == value_mate_in(ply + 1))
1209 ss[ply].mateKiller = move;
1213 // Step 18. Check for split
1214 if ( TM.active_threads() > 1
1216 && depth >= MinimumSplitDepth
1218 && TM.available_thread_exists(threadID)
1220 && !TM.thread_should_stop(threadID)
1221 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1222 depth, mateThreat, &moveCount, &mp, threadID, true))
1226 // Step 19. Check for mate and stalemate
1227 // All legal moves have been searched and if there were
1228 // no legal moves, it must be mate or stalemate.
1230 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1232 // Step 20. Update tables
1233 // If the search is not aborted, update the transposition table,
1234 // history counters, and killer moves.
1235 if (AbortSearch || TM.thread_should_stop(threadID))
1238 if (bestValue <= oldAlpha)
1239 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1241 else if (bestValue >= beta)
1243 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1244 move = ss[ply].pv[ply];
1245 if (!pos.move_is_capture_or_promotion(move))
1247 update_history(pos, move, depth, movesSearched, moveCount);
1248 update_killers(move, ss[ply]);
1250 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1253 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1259 // search() is the search function for zero-width nodes.
1261 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1262 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1264 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1265 assert(ply >= 0 && ply < PLY_MAX);
1266 assert(threadID >= 0 && threadID < TM.active_threads());
1268 Move movesSearched[256];
1273 Depth ext, newDepth;
1274 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1275 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1276 bool mateThreat = false;
1278 refinedValue = bestValue = value = -VALUE_INFINITE;
1281 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1283 // Step 1. Initialize node and poll
1284 // Polling can abort search.
1285 init_node(ss, ply, threadID);
1287 // Step 2. Check for aborted search and immediate draw
1288 if (AbortSearch || TM.thread_should_stop(threadID))
1291 if (pos.is_draw() || ply >= PLY_MAX - 1)
1294 // Step 3. Mate distance pruning
1295 if (value_mated_in(ply) >= beta)
1298 if (value_mate_in(ply + 1) < beta)
1301 // Step 4. Transposition table lookup
1303 // We don't want the score of a partial search to overwrite a previous full search
1304 // TT value, so we use a different position key in case of an excluded move exists.
1305 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1307 tte = TT.retrieve(posKey);
1308 ttMove = (tte ? tte->move() : MOVE_NONE);
1310 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1312 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1313 return value_from_tt(tte->value(), ply);
1316 // Step 5. Evaluate the position statically
1317 isCheck = pos.is_check();
1321 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1322 ss[ply].eval = value_from_tt(tte->value(), ply);
1324 ss[ply].eval = evaluate(pos, ei, threadID);
1326 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1327 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1331 if ( !value_is_mate(beta)
1333 && depth < RazorDepth
1334 && refinedValue < beta - razor_margin(depth)
1335 && ss[ply - 1].currentMove != MOVE_NULL
1336 && ttMove == MOVE_NONE
1337 && !pos.has_pawn_on_7th(pos.side_to_move()))
1339 Value rbeta = beta - razor_margin(depth);
1340 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1342 // Logically we should return (v + razor_margin(depth)), but
1343 // surprisingly this did slightly weaker in tests.
1347 // Step 7. Static null move pruning
1348 // We're betting that the opponent doesn't have a move that will reduce
1349 // the score by more than fuility_margin(depth) if we do a null move.
1352 && depth < RazorDepth
1353 && refinedValue - futility_margin(depth, 0) >= beta)
1354 return refinedValue - futility_margin(depth, 0);
1356 // Step 8. Null move search with verification search
1357 // When we jump directly to qsearch() we do a null move only if static value is
1358 // at least beta. Otherwise we do a null move if static value is not more than
1359 // NullMoveMargin under beta.
1363 && !value_is_mate(beta)
1364 && ok_to_do_nullmove(pos)
1365 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1367 ss[ply].currentMove = MOVE_NULL;
1369 pos.do_null_move(st);
1371 // Null move dynamic reduction based on depth
1372 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1374 // Null move dynamic reduction based on value
1375 if (refinedValue - beta > PawnValueMidgame)
1378 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1380 pos.undo_null_move();
1382 if (nullValue >= beta)
1384 if (depth < 6 * OnePly)
1387 // Do zugzwang verification search
1388 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1392 // The null move failed low, which means that we may be faced with
1393 // some kind of threat. If the previous move was reduced, check if
1394 // the move that refuted the null move was somehow connected to the
1395 // move which was reduced. If a connection is found, return a fail
1396 // low score (which will cause the reduced move to fail high in the
1397 // parent node, which will trigger a re-search with full depth).
1398 if (nullValue == value_mated_in(ply + 2))
1401 ss[ply].threatMove = ss[ply + 1].currentMove;
1402 if ( depth < ThreatDepth
1403 && ss[ply - 1].reduction
1404 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1409 // Step 9. Internal iterative deepening
1410 if ( depth >= IIDDepthAtNonPVNodes
1411 && ttMove == MOVE_NONE
1413 && ss[ply].eval >= beta - IIDMargin)
1415 search(pos, ss, beta, depth/2, ply, false, threadID);
1416 ttMove = ss[ply].pv[ply];
1417 tte = TT.retrieve(posKey);
1420 // Step 10. Loop through moves
1421 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1423 // Initialize a MovePicker object for the current position
1424 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1427 while ( bestValue < beta
1428 && (move = mp.get_next_move()) != MOVE_NONE
1429 && !TM.thread_should_stop(threadID))
1431 assert(move_is_ok(move));
1433 if (move == excludedMove)
1436 moveIsCheck = pos.move_is_check(move, ci);
1437 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1438 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1440 // Step 11. Decide the new search depth
1441 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1443 // Singular extension search. We extend the TT move if its value is much better than
1444 // its siblings. To verify this we do a reduced search on all the other moves but the
1445 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1446 if ( depth >= SingularExtensionDepthAtNonPVNodes
1448 && move == tte->move()
1449 && !excludedMove // Do not allow recursive single-reply search
1451 && is_lower_bound(tte->type())
1452 && tte->depth() >= depth - 3 * OnePly)
1454 Value ttValue = value_from_tt(tte->value(), ply);
1456 if (abs(ttValue) < VALUE_KNOWN_WIN)
1458 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1460 if (excValue < ttValue - SingularExtensionMargin)
1465 newDepth = depth - OnePly + ext;
1467 // Update current move (this must be done after singular extension search)
1468 movesSearched[moveCount++] = ss[ply].currentMove = move;
1470 // Step 12. Futility pruning
1473 && !captureOrPromotion
1474 && !move_is_castle(move)
1477 // Move count based pruning
1478 if ( moveCount >= futility_move_count(depth)
1479 && ok_to_prune(pos, move, ss[ply].threatMove)
1480 && bestValue > value_mated_in(PLY_MAX))
1483 // Value based pruning
1484 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1485 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1486 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1488 if (futilityValueScaled < beta)
1490 if (futilityValueScaled > bestValue)
1491 bestValue = futilityValueScaled;
1496 // Step 13. Make the move
1497 pos.do_move(move, st, ci, moveIsCheck);
1499 // Step 14. Reduced search
1500 // if the move fails high will be re-searched at full depth.
1501 bool doFullDepthSearch = true;
1503 if ( depth >= 3*OnePly
1505 && !captureOrPromotion
1506 && !move_is_castle(move)
1507 && !move_is_killer(move, ss[ply]))
1509 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1510 if (ss[ply].reduction)
1512 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1513 doFullDepthSearch = (value >= beta);
1517 // Step 15. Full depth search
1518 if (doFullDepthSearch)
1520 ss[ply].reduction = Depth(0);
1521 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1524 // Step 16. Undo move
1525 pos.undo_move(move);
1527 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1529 // Step 17. Check for new best move
1530 if (value > bestValue)
1536 if (value == value_mate_in(ply + 1))
1537 ss[ply].mateKiller = move;
1540 // Step 18. Check for split
1541 if ( TM.active_threads() > 1
1543 && depth >= MinimumSplitDepth
1545 && TM.available_thread_exists(threadID)
1547 && !TM.thread_should_stop(threadID)
1548 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1549 depth, mateThreat, &moveCount, &mp, threadID, false))
1553 // Step 19. Check for mate and stalemate
1554 // All legal moves have been searched and if there were
1555 // no legal moves, it must be mate or stalemate.
1556 // If one move was excluded return fail low.
1558 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1560 // Step 20. Update tables
1561 // If the search is not aborted, update the transposition table,
1562 // history counters, and killer moves.
1563 if (AbortSearch || TM.thread_should_stop(threadID))
1566 if (bestValue < beta)
1567 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1570 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1571 move = ss[ply].pv[ply];
1572 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1573 if (!pos.move_is_capture_or_promotion(move))
1575 update_history(pos, move, depth, movesSearched, moveCount);
1576 update_killers(move, ss[ply]);
1581 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1587 // qsearch() is the quiescence search function, which is called by the main
1588 // search function when the remaining depth is zero (or, to be more precise,
1589 // less than OnePly).
1591 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1592 Depth depth, int ply, int threadID) {
1594 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1595 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1597 assert(ply >= 0 && ply < PLY_MAX);
1598 assert(threadID >= 0 && threadID < TM.active_threads());
1603 Value staticValue, bestValue, value, futilityBase, futilityValue;
1604 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1605 const TTEntry* tte = NULL;
1607 bool pvNode = (beta - alpha != 1);
1608 Value oldAlpha = alpha;
1610 // Initialize, and make an early exit in case of an aborted search,
1611 // an instant draw, maximum ply reached, etc.
1612 init_node(ss, ply, threadID);
1614 // After init_node() that calls poll()
1615 if (AbortSearch || TM.thread_should_stop(threadID))
1618 if (pos.is_draw() || ply >= PLY_MAX - 1)
1621 // Transposition table lookup. At PV nodes, we don't use the TT for
1622 // pruning, but only for move ordering.
1623 tte = TT.retrieve(pos.get_key());
1624 ttMove = (tte ? tte->move() : MOVE_NONE);
1626 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1628 assert(tte->type() != VALUE_TYPE_EVAL);
1630 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1631 return value_from_tt(tte->value(), ply);
1634 isCheck = pos.is_check();
1636 // Evaluate the position statically
1638 staticValue = -VALUE_INFINITE;
1639 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1640 staticValue = value_from_tt(tte->value(), ply);
1642 staticValue = evaluate(pos, ei, threadID);
1646 ss[ply].eval = staticValue;
1647 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1650 // Initialize "stand pat score", and return it immediately if it is
1652 bestValue = staticValue;
1654 if (bestValue >= beta)
1656 // Store the score to avoid a future costly evaluation() call
1657 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1658 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1663 if (bestValue > alpha)
1666 // If we are near beta then try to get a cutoff pushing checks a bit further
1667 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1669 // Initialize a MovePicker object for the current position, and prepare
1670 // to search the moves. Because the depth is <= 0 here, only captures,
1671 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1672 // and we are near beta) will be generated.
1673 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1675 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1676 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1678 // Loop through the moves until no moves remain or a beta cutoff
1680 while ( alpha < beta
1681 && (move = mp.get_next_move()) != MOVE_NONE)
1683 assert(move_is_ok(move));
1685 moveIsCheck = pos.move_is_check(move, ci);
1687 // Update current move
1689 ss[ply].currentMove = move;
1697 && !move_is_promotion(move)
1698 && !pos.move_is_passed_pawn_push(move))
1700 futilityValue = futilityBase
1701 + pos.endgame_value_of_piece_on(move_to(move))
1702 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1704 if (futilityValue < alpha)
1706 if (futilityValue > bestValue)
1707 bestValue = futilityValue;
1712 // Detect blocking evasions that are candidate to be pruned
1713 evasionPrunable = isCheck
1714 && bestValue != -VALUE_INFINITE
1715 && !pos.move_is_capture(move)
1716 && pos.type_of_piece_on(move_from(move)) != KING
1717 && !pos.can_castle(pos.side_to_move());
1719 // Don't search moves with negative SEE values
1720 if ( (!isCheck || evasionPrunable)
1723 && !move_is_promotion(move)
1724 && pos.see_sign(move) < 0)
1727 // Make and search the move
1728 pos.do_move(move, st, ci, moveIsCheck);
1729 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1730 pos.undo_move(move);
1732 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1735 if (value > bestValue)
1746 // All legal moves have been searched. A special case: If we're in check
1747 // and no legal moves were found, it is checkmate.
1748 if (!moveCount && pos.is_check()) // Mate!
1749 return value_mated_in(ply);
1751 // Update transposition table
1752 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1753 if (bestValue <= oldAlpha)
1755 // If bestValue isn't changed it means it is still the static evaluation
1756 // of the node, so keep this info to avoid a future evaluation() call.
1757 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1758 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1760 else if (bestValue >= beta)
1762 move = ss[ply].pv[ply];
1763 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1765 // Update killers only for good checking moves
1766 if (!pos.move_is_capture_or_promotion(move))
1767 update_killers(move, ss[ply]);
1770 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1772 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1778 // sp_search() is used to search from a split point. This function is called
1779 // by each thread working at the split point. It is similar to the normal
1780 // search() function, but simpler. Because we have already probed the hash
1781 // table, done a null move search, and searched the first move before
1782 // splitting, we don't have to repeat all this work in sp_search(). We
1783 // also don't need to store anything to the hash table here: This is taken
1784 // care of after we return from the split point.
1786 void sp_search(SplitPoint* sp, int threadID) {
1788 assert(threadID >= 0 && threadID < TM.active_threads());
1789 assert(TM.active_threads() > 1);
1793 Depth ext, newDepth;
1794 Value value, futilityValueScaled;
1795 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1797 value = -VALUE_INFINITE;
1799 Position pos(*sp->pos);
1801 SearchStack* ss = sp->sstack[threadID];
1802 isCheck = pos.is_check();
1804 // Step 10. Loop through moves
1805 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1806 lock_grab(&(sp->lock));
1808 while ( sp->bestValue < sp->beta
1809 && !TM.thread_should_stop(threadID)
1810 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1812 moveCount = ++sp->moves;
1813 lock_release(&(sp->lock));
1815 assert(move_is_ok(move));
1817 moveIsCheck = pos.move_is_check(move, ci);
1818 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1820 // Step 11. Decide the new search depth
1821 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1822 newDepth = sp->depth - OnePly + ext;
1824 // Update current move
1825 ss[sp->ply].currentMove = move;
1827 // Step 12. Futility pruning
1830 && !captureOrPromotion
1831 && !move_is_castle(move))
1833 // Move count based pruning
1834 if ( moveCount >= futility_move_count(sp->depth)
1835 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1836 && sp->bestValue > value_mated_in(PLY_MAX))
1838 lock_grab(&(sp->lock));
1842 // Value based pruning
1843 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1844 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1845 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1847 if (futilityValueScaled < sp->beta)
1849 lock_grab(&(sp->lock));
1851 if (futilityValueScaled > sp->bestValue)
1852 sp->bestValue = futilityValueScaled;
1857 // Step 13. Make the move
1858 pos.do_move(move, st, ci, moveIsCheck);
1860 // Step 14. Reduced search
1861 // if the move fails high will be re-searched at full depth.
1862 bool doFullDepthSearch = true;
1865 && !captureOrPromotion
1866 && !move_is_castle(move)
1867 && !move_is_killer(move, ss[sp->ply]))
1869 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1870 if (ss[sp->ply].reduction)
1872 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1873 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1877 // Step 15. Full depth search
1878 if (doFullDepthSearch)
1880 ss[sp->ply].reduction = Depth(0);
1881 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1884 // Step 16. Undo move
1885 pos.undo_move(move);
1887 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1889 // Step 17. Check for new best move
1890 lock_grab(&(sp->lock));
1892 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1894 sp->bestValue = value;
1895 if (sp->bestValue >= sp->beta)
1897 sp->stopRequest = true;
1898 sp_update_pv(sp->parentSstack, ss, sp->ply);
1903 /* Here we have the lock still grabbed */
1905 sp->slaves[threadID] = 0;
1908 lock_release(&(sp->lock));
1912 // sp_search_pv() is used to search from a PV split point. This function
1913 // is called by each thread working at the split point. It is similar to
1914 // the normal search_pv() function, but simpler. Because we have already
1915 // probed the hash table and searched the first move before splitting, we
1916 // don't have to repeat all this work in sp_search_pv(). We also don't
1917 // need to store anything to the hash table here: This is taken care of
1918 // after we return from the split point.
1920 void sp_search_pv(SplitPoint* sp, int threadID) {
1922 assert(threadID >= 0 && threadID < TM.active_threads());
1923 assert(TM.active_threads() > 1);
1927 Depth ext, newDepth;
1929 bool moveIsCheck, captureOrPromotion, dangerous;
1931 value = -VALUE_INFINITE;
1933 Position pos(*sp->pos);
1935 SearchStack* ss = sp->sstack[threadID];
1937 // Step 10. Loop through moves
1938 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1939 lock_grab(&(sp->lock));
1941 while ( sp->alpha < sp->beta
1942 && !TM.thread_should_stop(threadID)
1943 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1945 moveCount = ++sp->moves;
1946 lock_release(&(sp->lock));
1948 assert(move_is_ok(move));
1950 moveIsCheck = pos.move_is_check(move, ci);
1951 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1953 // Step 11. Decide the new search depth
1954 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1955 newDepth = sp->depth - OnePly + ext;
1957 // Update current move
1958 ss[sp->ply].currentMove = move;
1960 // Step 12. Futility pruning (is omitted in PV nodes)
1962 // Step 13. Make the move
1963 pos.do_move(move, st, ci, moveIsCheck);
1965 // Step 14. Reduced search
1966 // if the move fails high will be re-searched at full depth.
1967 bool doFullDepthSearch = true;
1970 && !captureOrPromotion
1971 && !move_is_castle(move)
1972 && !move_is_killer(move, ss[sp->ply]))
1974 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1975 if (ss[sp->ply].reduction)
1977 Value localAlpha = sp->alpha;
1978 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1979 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1983 // Step 15. Full depth search
1984 if (doFullDepthSearch)
1986 Value localAlpha = sp->alpha;
1987 ss[sp->ply].reduction = Depth(0);
1988 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1990 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1992 // If another thread has failed high then sp->alpha has been increased
1993 // to be higher or equal then beta, if so, avoid to start a PV search.
1994 localAlpha = sp->alpha;
1995 if (localAlpha < sp->beta)
1996 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2000 // Step 16. Undo move
2001 pos.undo_move(move);
2003 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2005 // Step 17. Check for new best move
2006 lock_grab(&(sp->lock));
2008 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
2010 sp->bestValue = value;
2011 if (value > sp->alpha)
2013 // Ask threads to stop before to modify sp->alpha
2014 if (value >= sp->beta)
2015 sp->stopRequest = true;
2019 sp_update_pv(sp->parentSstack, ss, sp->ply);
2020 if (value == value_mate_in(sp->ply + 1))
2021 ss[sp->ply].mateKiller = move;
2026 /* Here we have the lock still grabbed */
2028 sp->slaves[threadID] = 0;
2031 lock_release(&(sp->lock));
2035 // init_node() is called at the beginning of all the search functions
2036 // (search(), search_pv(), qsearch(), and so on) and initializes the
2037 // search stack object corresponding to the current node. Once every
2038 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2039 // for user input and checks whether it is time to stop the search.
2041 void init_node(SearchStack ss[], int ply, int threadID) {
2043 assert(ply >= 0 && ply < PLY_MAX);
2044 assert(threadID >= 0 && threadID < TM.active_threads());
2046 TM.incrementNodeCounter(threadID);
2051 if (NodesSincePoll >= NodesBetweenPolls)
2058 ss[ply + 2].initKillers();
2062 // update_pv() is called whenever a search returns a value > alpha.
2063 // It updates the PV in the SearchStack object corresponding to the
2066 void update_pv(SearchStack ss[], int ply) {
2068 assert(ply >= 0 && ply < PLY_MAX);
2072 ss[ply].pv[ply] = ss[ply].currentMove;
2074 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2075 ss[ply].pv[p] = ss[ply + 1].pv[p];
2077 ss[ply].pv[p] = MOVE_NONE;
2081 // sp_update_pv() is a variant of update_pv for use at split points. The
2082 // difference between the two functions is that sp_update_pv also updates
2083 // the PV at the parent node.
2085 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2087 assert(ply >= 0 && ply < PLY_MAX);
2091 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2093 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2094 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2096 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2100 // connected_moves() tests whether two moves are 'connected' in the sense
2101 // that the first move somehow made the second move possible (for instance
2102 // if the moving piece is the same in both moves). The first move is assumed
2103 // to be the move that was made to reach the current position, while the
2104 // second move is assumed to be a move from the current position.
2106 bool connected_moves(const Position& pos, Move m1, Move m2) {
2108 Square f1, t1, f2, t2;
2111 assert(move_is_ok(m1));
2112 assert(move_is_ok(m2));
2114 if (m2 == MOVE_NONE)
2117 // Case 1: The moving piece is the same in both moves
2123 // Case 2: The destination square for m2 was vacated by m1
2129 // Case 3: Moving through the vacated square
2130 if ( piece_is_slider(pos.piece_on(f2))
2131 && bit_is_set(squares_between(f2, t2), f1))
2134 // Case 4: The destination square for m2 is defended by the moving piece in m1
2135 p = pos.piece_on(t1);
2136 if (bit_is_set(pos.attacks_from(p, t1), t2))
2139 // Case 5: Discovered check, checking piece is the piece moved in m1
2140 if ( piece_is_slider(p)
2141 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2142 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2144 // discovered_check_candidates() works also if the Position's side to
2145 // move is the opposite of the checking piece.
2146 Color them = opposite_color(pos.side_to_move());
2147 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2149 if (bit_is_set(dcCandidates, f2))
2156 // value_is_mate() checks if the given value is a mate one
2157 // eventually compensated for the ply.
2159 bool value_is_mate(Value value) {
2161 assert(abs(value) <= VALUE_INFINITE);
2163 return value <= value_mated_in(PLY_MAX)
2164 || value >= value_mate_in(PLY_MAX);
2168 // move_is_killer() checks if the given move is among the
2169 // killer moves of that ply.
2171 bool move_is_killer(Move m, const SearchStack& ss) {
2173 const Move* k = ss.killers;
2174 for (int i = 0; i < KILLER_MAX; i++, k++)
2182 // extension() decides whether a move should be searched with normal depth,
2183 // or with extended depth. Certain classes of moves (checking moves, in
2184 // particular) are searched with bigger depth than ordinary moves and in
2185 // any case are marked as 'dangerous'. Note that also if a move is not
2186 // extended, as example because the corresponding UCI option is set to zero,
2187 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2189 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2190 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2192 assert(m != MOVE_NONE);
2194 Depth result = Depth(0);
2195 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2200 result += CheckExtension[pvNode];
2203 result += SingleEvasionExtension[pvNode];
2206 result += MateThreatExtension[pvNode];
2209 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2211 Color c = pos.side_to_move();
2212 if (relative_rank(c, move_to(m)) == RANK_7)
2214 result += PawnPushTo7thExtension[pvNode];
2217 if (pos.pawn_is_passed(c, move_to(m)))
2219 result += PassedPawnExtension[pvNode];
2224 if ( captureOrPromotion
2225 && pos.type_of_piece_on(move_to(m)) != PAWN
2226 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2227 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2228 && !move_is_promotion(m)
2231 result += PawnEndgameExtension[pvNode];
2236 && captureOrPromotion
2237 && pos.type_of_piece_on(move_to(m)) != PAWN
2238 && pos.see_sign(m) >= 0)
2244 return Min(result, OnePly);
2248 // ok_to_do_nullmove() looks at the current position and decides whether
2249 // doing a 'null move' should be allowed. In order to avoid zugzwang
2250 // problems, null moves are not allowed when the side to move has very
2251 // little material left. Currently, the test is a bit too simple: Null
2252 // moves are avoided only when the side to move has only pawns left.
2253 // It's probably a good idea to avoid null moves in at least some more
2254 // complicated endgames, e.g. KQ vs KR. FIXME
2256 bool ok_to_do_nullmove(const Position& pos) {
2258 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2262 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2263 // non-tactical moves late in the move list close to the leaves are
2264 // candidates for pruning.
2266 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2268 assert(move_is_ok(m));
2269 assert(threat == MOVE_NONE || move_is_ok(threat));
2270 assert(!pos.move_is_check(m));
2271 assert(!pos.move_is_capture_or_promotion(m));
2272 assert(!pos.move_is_passed_pawn_push(m));
2274 Square mfrom, mto, tfrom, tto;
2276 // Prune if there isn't any threat move
2277 if (threat == MOVE_NONE)
2280 mfrom = move_from(m);
2282 tfrom = move_from(threat);
2283 tto = move_to(threat);
2285 // Case 1: Don't prune moves which move the threatened piece
2289 // Case 2: If the threatened piece has value less than or equal to the
2290 // value of the threatening piece, don't prune move which defend it.
2291 if ( pos.move_is_capture(threat)
2292 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2293 || pos.type_of_piece_on(tfrom) == KING)
2294 && pos.move_attacks_square(m, tto))
2297 // Case 3: If the moving piece in the threatened move is a slider, don't
2298 // prune safe moves which block its ray.
2299 if ( piece_is_slider(pos.piece_on(tfrom))
2300 && bit_is_set(squares_between(tfrom, tto), mto)
2301 && pos.see_sign(m) >= 0)
2308 // ok_to_use_TT() returns true if a transposition table score
2309 // can be used at a given point in search.
2311 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2313 Value v = value_from_tt(tte->value(), ply);
2315 return ( tte->depth() >= depth
2316 || v >= Max(value_mate_in(PLY_MAX), beta)
2317 || v < Min(value_mated_in(PLY_MAX), beta))
2319 && ( (is_lower_bound(tte->type()) && v >= beta)
2320 || (is_upper_bound(tte->type()) && v < beta));
2324 // refine_eval() returns the transposition table score if
2325 // possible otherwise falls back on static position evaluation.
2327 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2332 Value v = value_from_tt(tte->value(), ply);
2334 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2335 || (is_upper_bound(tte->type()) && v < defaultEval))
2342 // update_history() registers a good move that produced a beta-cutoff
2343 // in history and marks as failures all the other moves of that ply.
2345 void update_history(const Position& pos, Move move, Depth depth,
2346 Move movesSearched[], int moveCount) {
2350 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2352 for (int i = 0; i < moveCount - 1; i++)
2354 m = movesSearched[i];
2358 if (!pos.move_is_capture_or_promotion(m))
2359 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2364 // update_killers() add a good move that produced a beta-cutoff
2365 // among the killer moves of that ply.
2367 void update_killers(Move m, SearchStack& ss) {
2369 if (m == ss.killers[0])
2372 for (int i = KILLER_MAX - 1; i > 0; i--)
2373 ss.killers[i] = ss.killers[i - 1];
2379 // update_gains() updates the gains table of a non-capture move given
2380 // the static position evaluation before and after the move.
2382 void update_gains(const Position& pos, Move m, Value before, Value after) {
2385 && before != VALUE_NONE
2386 && after != VALUE_NONE
2387 && pos.captured_piece() == NO_PIECE_TYPE
2388 && !move_is_castle(m)
2389 && !move_is_promotion(m))
2390 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2394 // current_search_time() returns the number of milliseconds which have passed
2395 // since the beginning of the current search.
2397 int current_search_time() {
2399 return get_system_time() - SearchStartTime;
2403 // nps() computes the current nodes/second count.
2407 int t = current_search_time();
2408 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2412 // poll() performs two different functions: It polls for user input, and it
2413 // looks at the time consumed so far and decides if it's time to abort the
2416 void poll(SearchStack ss[], int ply) {
2418 static int lastInfoTime;
2419 int t = current_search_time();
2424 // We are line oriented, don't read single chars
2425 std::string command;
2427 if (!std::getline(std::cin, command))
2430 if (command == "quit")
2433 PonderSearch = false;
2437 else if (command == "stop")
2440 PonderSearch = false;
2442 else if (command == "ponderhit")
2446 // Print search information
2450 else if (lastInfoTime > t)
2451 // HACK: Must be a new search where we searched less than
2452 // NodesBetweenPolls nodes during the first second of search.
2455 else if (t - lastInfoTime >= 1000)
2462 if (dbg_show_hit_rate)
2463 dbg_print_hit_rate();
2465 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2466 << " time " << t << " hashfull " << TT.full() << endl;
2468 // We only support current line printing in single thread mode
2469 if (ShowCurrentLine && TM.active_threads() == 1)
2471 cout << "info currline";
2472 for (int p = 0; p < ply; p++)
2473 cout << " " << ss[p].currentMove;
2479 // Should we stop the search?
2483 bool stillAtFirstMove = FirstRootMove
2484 && !AspirationFailLow
2485 && t > MaxSearchTime + ExtraSearchTime;
2487 bool noMoreTime = t > AbsoluteMaxSearchTime
2488 || stillAtFirstMove;
2490 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2491 || (ExactMaxTime && t >= ExactMaxTime)
2492 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2497 // ponderhit() is called when the program is pondering (i.e. thinking while
2498 // it's the opponent's turn to move) in order to let the engine know that
2499 // it correctly predicted the opponent's move.
2503 int t = current_search_time();
2504 PonderSearch = false;
2506 bool stillAtFirstMove = FirstRootMove
2507 && !AspirationFailLow
2508 && t > MaxSearchTime + ExtraSearchTime;
2510 bool noMoreTime = t > AbsoluteMaxSearchTime
2511 || stillAtFirstMove;
2513 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2518 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2520 void init_ss_array(SearchStack ss[]) {
2522 for (int i = 0; i < 3; i++)
2525 ss[i].initKillers();
2530 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2531 // while the program is pondering. The point is to work around a wrinkle in
2532 // the UCI protocol: When pondering, the engine is not allowed to give a
2533 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2534 // We simply wait here until one of these commands is sent, and return,
2535 // after which the bestmove and pondermove will be printed (in id_loop()).
2537 void wait_for_stop_or_ponderhit() {
2539 std::string command;
2543 if (!std::getline(std::cin, command))
2546 if (command == "quit")
2551 else if (command == "ponderhit" || command == "stop")
2557 // print_pv_info() prints to standard output and eventually to log file information on
2558 // the current PV line. It is called at each iteration or after a new pv is found.
2560 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2562 cout << "info depth " << Iteration
2563 << " score " << value_to_string(value)
2564 << ((value >= beta) ? " lowerbound" :
2565 ((value <= alpha)? " upperbound" : ""))
2566 << " time " << current_search_time()
2567 << " nodes " << TM.nodes_searched()
2571 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2572 cout << ss[0].pv[j] << " ";
2578 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2579 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2581 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2582 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2587 // init_thread() is the function which is called when a new thread is
2588 // launched. It simply calls the idle_loop() function with the supplied
2589 // threadID. There are two versions of this function; one for POSIX
2590 // threads and one for Windows threads.
2592 #if !defined(_MSC_VER)
2594 void* init_thread(void *threadID) {
2596 TM.idle_loop(*(int*)threadID, NULL);
2602 DWORD WINAPI init_thread(LPVOID threadID) {
2604 TM.idle_loop(*(int*)threadID, NULL);
2611 /// The ThreadsManager class
2613 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2614 // get_beta_counters() are getters/setters for the per thread
2615 // counters used to sort the moves at root.
2617 void ThreadsManager::resetNodeCounters() {
2619 for (int i = 0; i < MAX_THREADS; i++)
2620 threads[i].nodes = 0ULL;
2623 void ThreadsManager::resetBetaCounters() {
2625 for (int i = 0; i < MAX_THREADS; i++)
2626 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2629 int64_t ThreadsManager::nodes_searched() const {
2631 int64_t result = 0ULL;
2632 for (int i = 0; i < ActiveThreads; i++)
2633 result += threads[i].nodes;
2638 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2641 for (int i = 0; i < MAX_THREADS; i++)
2643 our += threads[i].betaCutOffs[us];
2644 their += threads[i].betaCutOffs[opposite_color(us)];
2649 // idle_loop() is where the threads are parked when they have no work to do.
2650 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2651 // object for which the current thread is the master.
2653 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2655 assert(threadID >= 0 && threadID < MAX_THREADS);
2659 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2660 // master should exit as last one.
2661 if (AllThreadsShouldExit)
2664 threads[threadID].state = THREAD_TERMINATED;
2668 // If we are not thinking, wait for a condition to be signaled
2669 // instead of wasting CPU time polling for work.
2670 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2673 assert(threadID != 0);
2674 threads[threadID].state = THREAD_SLEEPING;
2676 #if !defined(_MSC_VER)
2677 lock_grab(&WaitLock);
2678 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2679 pthread_cond_wait(&WaitCond, &WaitLock);
2680 lock_release(&WaitLock);
2682 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2686 // If thread has just woken up, mark it as available
2687 if (threads[threadID].state == THREAD_SLEEPING)
2688 threads[threadID].state = THREAD_AVAILABLE;
2690 // If this thread has been assigned work, launch a search
2691 if (threads[threadID].state == THREAD_WORKISWAITING)
2693 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2695 threads[threadID].state = THREAD_SEARCHING;
2697 if (threads[threadID].splitPoint->pvNode)
2698 sp_search_pv(threads[threadID].splitPoint, threadID);
2700 sp_search(threads[threadID].splitPoint, threadID);
2702 assert(threads[threadID].state == THREAD_SEARCHING);
2704 threads[threadID].state = THREAD_AVAILABLE;
2707 // If this thread is the master of a split point and all threads have
2708 // finished their work at this split point, return from the idle loop.
2709 if (waitSp != NULL && waitSp->cpus == 0)
2711 assert(threads[threadID].state == THREAD_AVAILABLE);
2713 threads[threadID].state = THREAD_SEARCHING;
2720 // init_threads() is called during startup. It launches all helper threads,
2721 // and initializes the split point stack and the global locks and condition
2724 void ThreadsManager::init_threads() {
2729 #if !defined(_MSC_VER)
2730 pthread_t pthread[1];
2733 // Initialize global locks
2734 lock_init(&MPLock, NULL);
2735 lock_init(&WaitLock, NULL);
2737 #if !defined(_MSC_VER)
2738 pthread_cond_init(&WaitCond, NULL);
2740 for (i = 0; i < MAX_THREADS; i++)
2741 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2744 // Initialize SplitPointStack locks
2745 for (i = 0; i < MAX_THREADS; i++)
2746 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2748 SplitPointStack[i][j].parent = NULL;
2749 lock_init(&(SplitPointStack[i][j].lock), NULL);
2752 // Will be set just before program exits to properly end the threads
2753 AllThreadsShouldExit = false;
2755 // Threads will be put to sleep as soon as created
2756 AllThreadsShouldSleep = true;
2758 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2760 threads[0].state = THREAD_SEARCHING;
2761 for (i = 1; i < MAX_THREADS; i++)
2762 threads[i].state = THREAD_AVAILABLE;
2764 // Launch the helper threads
2765 for (i = 1; i < MAX_THREADS; i++)
2768 #if !defined(_MSC_VER)
2769 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2771 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2776 cout << "Failed to create thread number " << i << endl;
2777 Application::exit_with_failure();
2780 // Wait until the thread has finished launching and is gone to sleep
2781 while (threads[i].state != THREAD_SLEEPING);
2786 // exit_threads() is called when the program exits. It makes all the
2787 // helper threads exit cleanly.
2789 void ThreadsManager::exit_threads() {
2791 ActiveThreads = MAX_THREADS; // HACK
2792 AllThreadsShouldSleep = true; // HACK
2793 wake_sleeping_threads();
2795 // This makes the threads to exit idle_loop()
2796 AllThreadsShouldExit = true;
2798 // Wait for thread termination
2799 for (int i = 1; i < MAX_THREADS; i++)
2800 while (threads[i].state != THREAD_TERMINATED);
2802 // Now we can safely destroy the locks
2803 for (int i = 0; i < MAX_THREADS; i++)
2804 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2805 lock_destroy(&(SplitPointStack[i][j].lock));
2807 lock_destroy(&WaitLock);
2808 lock_destroy(&MPLock);
2812 // thread_should_stop() checks whether the thread should stop its search.
2813 // This can happen if a beta cutoff has occurred in the thread's currently
2814 // active split point, or in some ancestor of the current split point.
2816 bool ThreadsManager::thread_should_stop(int threadID) const {
2818 assert(threadID >= 0 && threadID < ActiveThreads);
2822 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2827 // thread_is_available() checks whether the thread with threadID "slave" is
2828 // available to help the thread with threadID "master" at a split point. An
2829 // obvious requirement is that "slave" must be idle. With more than two
2830 // threads, this is not by itself sufficient: If "slave" is the master of
2831 // some active split point, it is only available as a slave to the other
2832 // threads which are busy searching the split point at the top of "slave"'s
2833 // split point stack (the "helpful master concept" in YBWC terminology).
2835 bool ThreadsManager::thread_is_available(int slave, int master) const {
2837 assert(slave >= 0 && slave < ActiveThreads);
2838 assert(master >= 0 && master < ActiveThreads);
2839 assert(ActiveThreads > 1);
2841 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2844 // Make a local copy to be sure doesn't change under our feet
2845 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2847 if (localActiveSplitPoints == 0)
2848 // No active split points means that the thread is available as
2849 // a slave for any other thread.
2852 if (ActiveThreads == 2)
2855 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2856 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2857 // could have been set to 0 by another thread leading to an out of bound access.
2858 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2865 // available_thread_exists() tries to find an idle thread which is available as
2866 // a slave for the thread with threadID "master".
2868 bool ThreadsManager::available_thread_exists(int master) const {
2870 assert(master >= 0 && master < ActiveThreads);
2871 assert(ActiveThreads > 1);
2873 for (int i = 0; i < ActiveThreads; i++)
2874 if (thread_is_available(i, master))
2881 // split() does the actual work of distributing the work at a node between
2882 // several threads at PV nodes. If it does not succeed in splitting the
2883 // node (because no idle threads are available, or because we have no unused
2884 // split point objects), the function immediately returns false. If
2885 // splitting is possible, a SplitPoint object is initialized with all the
2886 // data that must be copied to the helper threads (the current position and
2887 // search stack, alpha, beta, the search depth, etc.), and we tell our
2888 // helper threads that they have been assigned work. This will cause them
2889 // to instantly leave their idle loops and call sp_search_pv(). When all
2890 // threads have returned from sp_search_pv (or, equivalently, when
2891 // splitPoint->cpus becomes 0), split() returns true.
2893 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2894 Value* alpha, const Value beta, Value* bestValue,
2895 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2898 assert(sstck != NULL);
2899 assert(ply >= 0 && ply < PLY_MAX);
2900 assert(*bestValue >= -VALUE_INFINITE);
2901 assert( ( pvNode && *bestValue <= *alpha)
2902 || (!pvNode && *bestValue < beta ));
2903 assert(!pvNode || *alpha < beta);
2904 assert(beta <= VALUE_INFINITE);
2905 assert(depth > Depth(0));
2906 assert(master >= 0 && master < ActiveThreads);
2907 assert(ActiveThreads > 1);
2909 SplitPoint* splitPoint;
2913 // If no other thread is available to help us, or if we have too many
2914 // active split points, don't split.
2915 if ( !available_thread_exists(master)
2916 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2918 lock_release(&MPLock);
2922 // Pick the next available split point object from the split point stack
2923 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2925 // Initialize the split point object
2926 splitPoint->parent = threads[master].splitPoint;
2927 splitPoint->stopRequest = false;
2928 splitPoint->ply = ply;
2929 splitPoint->depth = depth;
2930 splitPoint->mateThreat = mateThreat;
2931 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2932 splitPoint->beta = beta;
2933 splitPoint->pvNode = pvNode;
2934 splitPoint->bestValue = *bestValue;
2935 splitPoint->master = master;
2936 splitPoint->mp = mp;
2937 splitPoint->moves = *moves;
2938 splitPoint->cpus = 1;
2939 splitPoint->pos = &p;
2940 splitPoint->parentSstack = sstck;
2941 for (int i = 0; i < ActiveThreads; i++)
2942 splitPoint->slaves[i] = 0;
2944 threads[master].splitPoint = splitPoint;
2945 threads[master].activeSplitPoints++;
2947 // If we are here it means we are not available
2948 assert(threads[master].state != THREAD_AVAILABLE);
2950 // Allocate available threads setting state to THREAD_BOOKED
2951 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2952 if (thread_is_available(i, master))
2954 threads[i].state = THREAD_BOOKED;
2955 threads[i].splitPoint = splitPoint;
2956 splitPoint->slaves[i] = 1;
2960 assert(splitPoint->cpus > 1);
2962 // We can release the lock because slave threads are already booked and master is not available
2963 lock_release(&MPLock);
2965 // Tell the threads that they have work to do. This will make them leave
2966 // their idle loop. But before copy search stack tail for each thread.
2967 for (int i = 0; i < ActiveThreads; i++)
2968 if (i == master || splitPoint->slaves[i])
2970 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2972 assert(i == master || threads[i].state == THREAD_BOOKED);
2974 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2977 // Everything is set up. The master thread enters the idle loop, from
2978 // which it will instantly launch a search, because its state is
2979 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2980 // idle loop, which means that the main thread will return from the idle
2981 // loop when all threads have finished their work at this split point
2982 // (i.e. when splitPoint->cpus == 0).
2983 idle_loop(master, splitPoint);
2985 // We have returned from the idle loop, which means that all threads are
2986 // finished. Update alpha, beta and bestValue, and return.
2990 *alpha = splitPoint->alpha;
2992 *bestValue = splitPoint->bestValue;
2993 threads[master].activeSplitPoints--;
2994 threads[master].splitPoint = splitPoint->parent;
2996 lock_release(&MPLock);
3001 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3002 // to start a new search from the root.
3004 void ThreadsManager::wake_sleeping_threads() {
3006 assert(AllThreadsShouldSleep);
3007 assert(ActiveThreads > 0);
3009 AllThreadsShouldSleep = false;
3011 if (ActiveThreads == 1)
3014 #if !defined(_MSC_VER)
3015 pthread_mutex_lock(&WaitLock);
3016 pthread_cond_broadcast(&WaitCond);
3017 pthread_mutex_unlock(&WaitLock);
3019 for (int i = 1; i < MAX_THREADS; i++)
3020 SetEvent(SitIdleEvent[i]);
3026 // put_threads_to_sleep() makes all the threads go to sleep just before
3027 // to leave think(), at the end of the search. Threads should have already
3028 // finished the job and should be idle.
3030 void ThreadsManager::put_threads_to_sleep() {
3032 assert(!AllThreadsShouldSleep);
3034 // This makes the threads to go to sleep
3035 AllThreadsShouldSleep = true;
3038 /// The RootMoveList class
3040 // RootMoveList c'tor
3042 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3044 SearchStack ss[PLY_MAX_PLUS_2];
3045 MoveStack mlist[MaxRootMoves];
3047 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3049 // Generate all legal moves
3050 MoveStack* last = generate_moves(pos, mlist);
3052 // Add each move to the moves[] array
3053 for (MoveStack* cur = mlist; cur != last; cur++)
3055 bool includeMove = includeAllMoves;
3057 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3058 includeMove = (searchMoves[k] == cur->move);
3063 // Find a quick score for the move
3065 pos.do_move(cur->move, st);
3066 moves[count].move = cur->move;
3067 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3068 moves[count].pv[0] = cur->move;
3069 moves[count].pv[1] = MOVE_NONE;
3070 pos.undo_move(cur->move);
3077 // RootMoveList simple methods definitions
3079 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3081 moves[moveNum].nodes = nodes;
3082 moves[moveNum].cumulativeNodes += nodes;
3085 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3087 moves[moveNum].ourBeta = our;
3088 moves[moveNum].theirBeta = their;
3091 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3095 for (j = 0; pv[j] != MOVE_NONE; j++)
3096 moves[moveNum].pv[j] = pv[j];
3098 moves[moveNum].pv[j] = MOVE_NONE;
3102 // RootMoveList::sort() sorts the root move list at the beginning of a new
3105 void RootMoveList::sort() {
3107 sort_multipv(count - 1); // Sort all items
3111 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3112 // list by their scores and depths. It is used to order the different PVs
3113 // correctly in MultiPV mode.
3115 void RootMoveList::sort_multipv(int n) {
3119 for (i = 1; i <= n; i++)
3121 RootMove rm = moves[i];
3122 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3123 moves[j] = moves[j - 1];