2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
43 #include "ucioption.h"
49 //// Local definitions
57 // ThreadsManager class is used to handle all the threads related stuff in search,
58 // init, starting, parking and, the most important, launching a slave thread at a
59 // split point are what this class does. All the access to shared thread data is
60 // done through this class, so that we avoid using global variables instead.
62 class ThreadsManager {
63 /* As long as the single ThreadsManager object is defined as a global we don't
64 need to explicitly initialize to zero its data members because variables with
65 static storage duration are automatically set to zero before enter main()
71 int active_threads() const { return ActiveThreads; }
72 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
73 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
74 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
75 void print_current_line(SearchStack ss[], int ply, int threadID);
77 void resetNodeCounters();
78 void resetBetaCounters();
79 int64_t nodes_searched() const;
80 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
81 bool available_thread_exists(int master) const;
82 bool thread_is_available(int slave, int master) const;
83 bool thread_should_stop(int threadID) const;
84 void wake_sleeping_threads();
85 void put_threads_to_sleep();
86 void idle_loop(int threadID, SplitPoint* waitSp);
87 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
88 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode);
94 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
95 Thread threads[MAX_THREADS];
96 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
100 #if !defined(_MSC_VER)
101 pthread_cond_t WaitCond;
102 pthread_mutex_t WaitLock;
104 HANDLE SitIdleEvent[MAX_THREADS];
110 // RootMove struct is used for moves at the root at the tree. For each
111 // root move, we store a score, a node count, and a PV (really a refutation
112 // in the case of moves which fail low).
116 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
118 // RootMove::operator<() is the comparison function used when
119 // sorting the moves. A move m1 is considered to be better
120 // than a move m2 if it has a higher score, or if the moves
121 // have equal score but m1 has the higher node count.
122 bool operator<(const RootMove& m) const {
124 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
129 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
130 Move pv[PLY_MAX_PLUS_2];
134 // The RootMoveList class is essentially an array of RootMove objects, with
135 // a handful of methods for accessing the data in the individual moves.
140 RootMoveList(Position& pos, Move searchMoves[]);
142 int move_count() const { return count; }
143 Move get_move(int moveNum) const { return moves[moveNum].move; }
144 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
145 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
146 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
147 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
149 void set_move_nodes(int moveNum, int64_t nodes);
150 void set_beta_counters(int moveNum, int64_t our, int64_t their);
151 void set_move_pv(int moveNum, const Move pv[]);
153 void sort_multipv(int n);
156 static const int MaxRootMoves = 500;
157 RootMove moves[MaxRootMoves];
164 // Search depth at iteration 1
165 const Depth InitialDepth = OnePly;
167 // Use internal iterative deepening?
168 const bool UseIIDAtPVNodes = true;
169 const bool UseIIDAtNonPVNodes = true;
171 // Internal iterative deepening margin. At Non-PV moves, when
172 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
173 // search when the static evaluation is at most IIDMargin below beta.
174 const Value IIDMargin = Value(0x100);
176 // Easy move margin. An easy move candidate must be at least this much
177 // better than the second best move.
178 const Value EasyMoveMargin = Value(0x200);
180 // Null move margin. A null move search will not be done if the static
181 // evaluation of the position is more than NullMoveMargin below beta.
182 const Value NullMoveMargin = Value(0x200);
184 // If the TT move is at least SingleReplyMargin better then the
185 // remaining ones we will extend it.
186 const Value SingleReplyMargin = Value(0x20);
188 // Depth limit for razoring
189 const Depth RazorDepth = 4 * OnePly;
191 /// Lookup tables initialized at startup
193 // Reduction lookup tables and their getter functions
194 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
195 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
197 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
198 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
200 // Futility lookup tables and their getter functions
201 const Value FutilityMarginQS = Value(0x80);
202 int32_t FutilityMarginsMatrix[14][64]; // [depth][moveNumber]
203 int FutilityMoveCountArray[32]; // [depth]
205 inline Value futility_margin(Depth d, int mn) { return Value(d < 7*OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
206 inline int futility_move_count(Depth d) { return d < 16*OnePly ? FutilityMoveCountArray[d] : 512; }
208 /// Variables initialized by UCI options
210 // Depth limit for use of dynamic threat detection
213 // Last seconds noise filtering (LSN)
214 const bool UseLSNFiltering = true;
215 const int LSNTime = 4000; // In milliseconds
216 const Value LSNValue = value_from_centipawns(200);
217 bool loseOnTime = false;
219 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
220 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
221 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
223 // Iteration counters
226 // Scores and number of times the best move changed for each iteration
227 Value ValueByIteration[PLY_MAX_PLUS_2];
228 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
230 // Search window management
236 // Time managment variables
239 int MaxNodes, MaxDepth;
240 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
241 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
242 bool AbortSearch, Quit;
243 bool AspirationFailLow;
245 // Show current line?
246 bool ShowCurrentLine;
250 std::ofstream LogFile;
252 // MP related variables
253 Depth MinimumSplitDepth;
254 int MaxThreadsPerSplitPoint;
257 // Node counters, used only by thread[0] but try to keep in different
258 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
260 int NodesBetweenPolls = 30000;
267 Value id_loop(const Position& pos, Move searchMoves[]);
268 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta);
269 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
270 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
271 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
272 void sp_search(SplitPoint* sp, int threadID);
273 void sp_search_pv(SplitPoint* sp, int threadID);
274 void init_node(SearchStack ss[], int ply, int threadID);
275 void update_pv(SearchStack ss[], int ply);
276 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
277 bool connected_moves(const Position& pos, Move m1, Move m2);
278 bool value_is_mate(Value value);
279 bool move_is_killer(Move m, const SearchStack& ss);
280 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
281 bool ok_to_do_nullmove(const Position& pos);
282 bool ok_to_prune(const Position& pos, Move m, Move threat);
283 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
284 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
285 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
286 void update_killers(Move m, SearchStack& ss);
287 void update_gains(const Position& pos, Move move, Value before, Value after);
289 int current_search_time();
293 void wait_for_stop_or_ponderhit();
294 void init_ss_array(SearchStack ss[]);
296 #if !defined(_MSC_VER)
297 void *init_thread(void *threadID);
299 DWORD WINAPI init_thread(LPVOID threadID);
309 /// init_threads(), exit_threads() and nodes_searched() are helpers to
310 /// give accessibility to some TM methods from outside of current file.
312 void init_threads() { TM.init_threads(); }
313 void exit_threads() { TM.exit_threads(); }
314 int64_t nodes_searched() { return TM.nodes_searched(); }
317 /// perft() is our utility to verify move generation is bug free. All the legal
318 /// moves up to given depth are generated and counted and the sum returned.
320 int perft(Position& pos, Depth depth)
324 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
326 // If we are at the last ply we don't need to do and undo
327 // the moves, just to count them.
328 if (depth <= OnePly) // Replace with '<' to test also qsearch
330 while (mp.get_next_move()) sum++;
334 // Loop through all legal moves
336 while ((move = mp.get_next_move()) != MOVE_NONE)
339 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
340 sum += perft(pos, depth - OnePly);
347 /// think() is the external interface to Stockfish's search, and is called when
348 /// the program receives the UCI 'go' command. It initializes various
349 /// search-related global variables, and calls root_search(). It returns false
350 /// when a quit command is received during the search.
352 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
353 int time[], int increment[], int movesToGo, int maxDepth,
354 int maxNodes, int maxTime, Move searchMoves[]) {
356 // Initialize global search variables
357 StopOnPonderhit = AbortSearch = Quit = false;
358 AspirationFailLow = false;
360 SearchStartTime = get_system_time();
361 ExactMaxTime = maxTime;
364 InfiniteSearch = infinite;
365 PonderSearch = ponder;
366 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
368 // Look for a book move, only during games, not tests
369 if (UseTimeManagement && get_option_value_bool("OwnBook"))
372 if (get_option_value_string("Book File") != OpeningBook.file_name())
373 OpeningBook.open(get_option_value_string("Book File"));
375 bookMove = OpeningBook.get_move(pos);
376 if (bookMove != MOVE_NONE)
379 wait_for_stop_or_ponderhit();
381 cout << "bestmove " << bookMove << endl;
386 TM.resetNodeCounters();
388 if (button_was_pressed("New Game"))
389 loseOnTime = false; // Reset at the beginning of a new game
391 // Read UCI option values
392 TT.set_size(get_option_value_int("Hash"));
393 if (button_was_pressed("Clear Hash"))
396 bool PonderingEnabled = get_option_value_bool("Ponder");
397 MultiPV = get_option_value_int("MultiPV");
399 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
400 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
402 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
403 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
405 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
406 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
408 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
409 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
411 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
412 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
414 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
415 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
417 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
419 Chess960 = get_option_value_bool("UCI_Chess960");
420 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
421 UseLogFile = get_option_value_bool("Use Search Log");
423 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
425 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
426 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
428 read_weights(pos.side_to_move());
430 // Set the number of active threads
431 int newActiveThreads = get_option_value_int("Threads");
432 if (newActiveThreads != TM.active_threads())
434 TM.set_active_threads(newActiveThreads);
435 init_eval(TM.active_threads());
436 // HACK: init_eval() destroys the static castleRightsMask[] array in the
437 // Position class. The below line repairs the damage.
438 Position p(pos.to_fen());
442 // Wake up sleeping threads
443 TM.wake_sleeping_threads();
446 int myTime = time[side_to_move];
447 int myIncrement = increment[side_to_move];
448 if (UseTimeManagement)
450 if (!movesToGo) // Sudden death time control
454 MaxSearchTime = myTime / 30 + myIncrement;
455 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
457 else // Blitz game without increment
459 MaxSearchTime = myTime / 30;
460 AbsoluteMaxSearchTime = myTime / 8;
463 else // (x moves) / (y minutes)
467 MaxSearchTime = myTime / 2;
468 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
472 MaxSearchTime = myTime / Min(movesToGo, 20);
473 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
477 if (PonderingEnabled)
479 MaxSearchTime += MaxSearchTime / 4;
480 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
484 // Set best NodesBetweenPolls interval
486 NodesBetweenPolls = Min(MaxNodes, 30000);
487 else if (myTime && myTime < 1000)
488 NodesBetweenPolls = 1000;
489 else if (myTime && myTime < 5000)
490 NodesBetweenPolls = 5000;
492 NodesBetweenPolls = 30000;
494 // Write information to search log file
496 LogFile << "Searching: " << pos.to_fen() << endl
497 << "infinite: " << infinite
498 << " ponder: " << ponder
499 << " time: " << myTime
500 << " increment: " << myIncrement
501 << " moves to go: " << movesToGo << endl;
503 // LSN filtering. Used only for developing purpose. Disabled by default.
507 // Step 2. If after last move we decided to lose on time, do it now!
508 while (SearchStartTime + myTime + 1000 > get_system_time())
512 // We're ready to start thinking. Call the iterative deepening loop function
513 Value v = id_loop(pos, searchMoves);
517 // Step 1. If this is sudden death game and our position is hopeless,
518 // decide to lose on time.
519 if ( !loseOnTime // If we already lost on time, go to step 3.
529 // Step 3. Now after stepping over the time limit, reset flag for next match.
537 TM.put_threads_to_sleep();
543 /// init_search() is called during startup. It initializes various lookup tables
547 // Init our reduction lookup tables
548 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
549 for (int j = 1; j < 64; j++) // j == moveNumber
551 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
552 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
553 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
554 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
557 // Init futility margins array
558 for (int i = 0; i < 14; i++) // i == depth (OnePly = 2)
559 for (int j = 0; j < 64; j++) // j == moveNumber
561 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j; // FIXME: test using log instead of BSR
564 // Init futility move count array
565 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
566 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
570 // SearchStack::init() initializes a search stack. Used at the beginning of a
571 // new search from the root.
572 void SearchStack::init(int ply) {
574 pv[ply] = pv[ply + 1] = MOVE_NONE;
575 currentMove = threatMove = MOVE_NONE;
576 reduction = Depth(0);
580 void SearchStack::initKillers() {
582 mateKiller = MOVE_NONE;
583 for (int i = 0; i < KILLER_MAX; i++)
584 killers[i] = MOVE_NONE;
589 // id_loop() is the main iterative deepening loop. It calls root_search
590 // repeatedly with increasing depth until the allocated thinking time has
591 // been consumed, the user stops the search, or the maximum search depth is
594 Value id_loop(const Position& pos, Move searchMoves[]) {
597 SearchStack ss[PLY_MAX_PLUS_2];
599 // searchMoves are verified, copied, scored and sorted
600 RootMoveList rml(p, searchMoves);
602 // Handle special case of searching on a mate/stale position
603 if (rml.move_count() == 0)
606 wait_for_stop_or_ponderhit();
608 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
611 // Print RootMoveList c'tor startup scoring to the standard output,
612 // so that we print information also for iteration 1.
613 cout << "info depth " << 1 << "\ninfo depth " << 1
614 << " score " << value_to_string(rml.get_move_score(0))
615 << " time " << current_search_time()
616 << " nodes " << TM.nodes_searched()
618 << " pv " << rml.get_move(0) << "\n";
624 ValueByIteration[1] = rml.get_move_score(0);
627 // Is one move significantly better than others after initial scoring ?
628 Move EasyMove = MOVE_NONE;
629 if ( rml.move_count() == 1
630 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
631 EasyMove = rml.get_move(0);
633 // Iterative deepening loop
634 while (Iteration < PLY_MAX)
636 // Initialize iteration
639 BestMoveChangesByIteration[Iteration] = 0;
643 cout << "info depth " << Iteration << endl;
645 // Calculate dynamic search window based on previous iterations
648 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
650 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
651 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
653 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
654 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
656 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
657 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
661 alpha = - VALUE_INFINITE;
662 beta = VALUE_INFINITE;
665 // Search to the current depth
666 Value value = root_search(p, ss, rml, alpha, beta);
668 // Write PV to transposition table, in case the relevant entries have
669 // been overwritten during the search.
670 TT.insert_pv(p, ss[0].pv);
673 break; // Value cannot be trusted. Break out immediately!
675 //Save info about search result
676 ValueByIteration[Iteration] = value;
678 // Drop the easy move if it differs from the new best move
679 if (ss[0].pv[0] != EasyMove)
680 EasyMove = MOVE_NONE;
682 if (UseTimeManagement)
685 bool stopSearch = false;
687 // Stop search early if there is only a single legal move,
688 // we search up to Iteration 6 anyway to get a proper score.
689 if (Iteration >= 6 && rml.move_count() == 1)
692 // Stop search early when the last two iterations returned a mate score
694 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
695 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
698 // Stop search early if one move seems to be much better than the rest
699 int64_t nodes = TM.nodes_searched();
701 && EasyMove == ss[0].pv[0]
702 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
703 && current_search_time() > MaxSearchTime / 16)
704 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
705 && current_search_time() > MaxSearchTime / 32)))
708 // Add some extra time if the best move has changed during the last two iterations
709 if (Iteration > 5 && Iteration <= 50)
710 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
711 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
713 // Stop search if most of MaxSearchTime is consumed at the end of the
714 // iteration. We probably don't have enough time to search the first
715 // move at the next iteration anyway.
716 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
724 StopOnPonderhit = true;
728 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;
751 cout << "bestmove " << ss[0].pv[0];
752 if (ss[0].pv[1] != MOVE_NONE)
753 cout << " ponder " << ss[0].pv[1];
760 dbg_print_mean(LogFile);
762 if (dbg_show_hit_rate)
763 dbg_print_hit_rate(LogFile);
765 LogFile << "\nNodes: " << TM.nodes_searched()
766 << "\nNodes/second: " << nps()
767 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
770 p.do_move(ss[0].pv[0], st);
771 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
773 return rml.get_move_score(0);
777 // root_search() is the function which searches the root node. It is
778 // similar to search_pv except that it uses a different move ordering
779 // scheme and prints some information to the standard output.
781 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta) {
786 Depth depth, ext, newDepth;
789 int researchCount = 0;
790 bool moveIsCheck, captureOrPromotion, dangerous;
791 Value alpha = oldAlpha;
792 bool isCheck = pos.is_check();
794 // Evaluate the position statically
796 ss[0].eval = !isCheck ? evaluate(pos, ei, 0) : VALUE_NONE;
798 while (1) // Fail low loop
801 // Loop through all the moves in the root move list
802 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
806 // We failed high, invalidate and skip next moves, leave node-counters
807 // and beta-counters as they are and quickly return, we will try to do
808 // a research at the next iteration with a bigger aspiration window.
809 rml.set_move_score(i, -VALUE_INFINITE);
813 RootMoveNumber = i + 1;
815 // Save the current node count before the move is searched
816 nodes = TM.nodes_searched();
818 // Reset beta cut-off counters
819 TM.resetBetaCounters();
821 // Pick the next root move, and print the move and the move number to
822 // the standard output.
823 move = ss[0].currentMove = rml.get_move(i);
825 if (current_search_time() >= 1000)
826 cout << "info currmove " << move
827 << " currmovenumber " << RootMoveNumber << endl;
829 // Decide search depth for this move
830 moveIsCheck = pos.move_is_check(move);
831 captureOrPromotion = pos.move_is_capture_or_promotion(move);
832 depth = (Iteration - 2) * OnePly + InitialDepth;
833 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
834 newDepth = depth + ext;
836 value = - VALUE_INFINITE;
838 while (1) // Fail high loop
841 // Make the move, and search it
842 pos.do_move(move, st, ci, moveIsCheck);
844 if (i < MultiPV || value > alpha)
846 // Aspiration window is disabled in multi-pv case
848 alpha = -VALUE_INFINITE;
850 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
854 // Try to reduce non-pv search depth by one ply if move seems not problematic,
855 // if the move fails high will be re-searched at full depth.
856 bool doFullDepthSearch = true;
858 if ( depth >= 3*OnePly // FIXME was newDepth
860 && !captureOrPromotion
861 && !move_is_castle(move))
863 ss[0].reduction = pv_reduction(depth, RootMoveNumber - MultiPV + 1);
866 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
867 doFullDepthSearch = (value > alpha);
871 if (doFullDepthSearch)
873 ss[0].reduction = Depth(0);
874 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
877 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
883 // Can we exit fail high loop ?
884 if (AbortSearch || value < beta)
887 // We are failing high and going to do a research. It's important to update score
888 // before research in case we run out of time while researching.
889 rml.set_move_score(i, value);
891 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
892 rml.set_move_pv(i, ss[0].pv);
894 // Print search information to the standard output
895 cout << "info depth " << Iteration
896 << " score " << value_to_string(value)
897 << ((value >= beta) ? " lowerbound" :
898 ((value <= alpha)? " upperbound" : ""))
899 << " time " << current_search_time()
900 << " nodes " << TM.nodes_searched()
904 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
905 cout << ss[0].pv[j] << " ";
911 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
912 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
914 LogFile << pretty_pv(pos, current_search_time(), Iteration,
915 TM.nodes_searched(), value, type, ss[0].pv) << endl;
918 // Prepare for a research after a fail high, each time with a wider window
920 beta = Min(beta + AspirationDelta * (1 << researchCount), VALUE_INFINITE);
922 } // End of fail high loop
924 // Finished searching the move. If AbortSearch is true, the search
925 // was aborted because the user interrupted the search or because we
926 // ran out of time. In this case, the return value of the search cannot
927 // be trusted, and we break out of the loop without updating the best
932 // Remember beta-cutoff and searched nodes counts for this move. The
933 // info is used to sort the root moves at the next iteration.
935 TM.get_beta_counters(pos.side_to_move(), our, their);
936 rml.set_beta_counters(i, our, their);
937 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
939 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
941 if (value <= alpha && i >= MultiPV)
942 rml.set_move_score(i, -VALUE_INFINITE);
945 // PV move or new best move!
948 rml.set_move_score(i, value);
950 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
951 rml.set_move_pv(i, ss[0].pv);
955 // We record how often the best move has been changed in each
956 // iteration. This information is used for time managment: When
957 // the best move changes frequently, we allocate some more time.
959 BestMoveChangesByIteration[Iteration]++;
961 // Print search information to the standard output
962 cout << "info depth " << Iteration
963 << " score " << value_to_string(value)
964 << ((value >= beta) ? " lowerbound" :
965 ((value <= alpha)? " upperbound" : ""))
966 << " time " << current_search_time()
967 << " nodes " << TM.nodes_searched()
971 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
972 cout << ss[0].pv[j] << " ";
978 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
979 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
981 LogFile << pretty_pv(pos, current_search_time(), Iteration,
982 TM.nodes_searched(), value, type, ss[0].pv) << endl;
990 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
992 cout << "info multipv " << j + 1
993 << " score " << value_to_string(rml.get_move_score(j))
994 << " depth " << ((j <= i)? Iteration : Iteration - 1)
995 << " time " << current_search_time()
996 << " nodes " << TM.nodes_searched()
1000 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1001 cout << rml.get_move_pv(j, k) << " ";
1005 alpha = rml.get_move_score(Min(i, MultiPV-1));
1007 } // PV move or new best move
1009 assert(alpha >= oldAlpha);
1011 AspirationFailLow = (alpha == oldAlpha);
1013 if (AspirationFailLow && StopOnPonderhit)
1014 StopOnPonderhit = false;
1017 // Can we exit fail low loop ?
1018 if (AbortSearch || alpha > oldAlpha)
1021 // Prepare for a research after a fail low, each time with a wider window
1023 alpha = Max(alpha - AspirationDelta * (1 << researchCount), -VALUE_INFINITE);
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];
1046 Depth ext, newDepth;
1047 Value oldAlpha, value;
1048 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1050 Value bestValue = value = -VALUE_INFINITE;
1053 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1055 // Step 1. Initialize node and poll
1056 // Polling can abort search.
1057 init_node(ss, ply, threadID);
1059 // Step 2. Check for aborted search and immediate draw
1060 if (AbortSearch || TM.thread_should_stop(threadID))
1063 if (pos.is_draw() || ply >= PLY_MAX - 1)
1066 // Step 3. Mate distance pruning
1068 alpha = Max(value_mated_in(ply), alpha);
1069 beta = Min(value_mate_in(ply+1), beta);
1073 // Step 4. Transposition table lookup
1074 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1075 // This is to avoid problems in the following areas:
1077 // * Repetition draw detection
1078 // * Fifty move rule detection
1079 // * Searching for a mate
1080 // * Printing of full PV line
1081 tte = TT.retrieve(pos.get_key());
1082 ttMove = (tte ? tte->move() : MOVE_NONE);
1084 // Step 5. Evaluate the position statically
1085 // At PV nodes we do this only to update gain statistics
1086 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 ( UseIIDAtPVNodes
1100 && depth >= 5*OnePly
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 >= 6 * OnePly
1134 && move == tte->move()
1136 && is_lower_bound(tte->type())
1137 && tte->depth() >= depth - 3 * OnePly)
1139 Value ttValue = value_from_tt(tte->value(), ply);
1141 if (abs(ttValue) < VALUE_KNOWN_WIN)
1143 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1145 if (excValue < ttValue - SingleReplyMargin)
1150 newDepth = depth - OnePly + ext;
1152 // Update current move (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, &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 - (0x200 + 16 * 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 - (0x200 + 16 * depth);
1341 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1343 return v; //FIXME: Logically should be: return (v + 0x200 + 16 * depth);
1346 // Step 7. Static null move pruning
1347 // We're betting that the opponent doesn't have a move that will reduce
1348 // the score by more than fuility_margin(depth) if we do a null move.
1351 && depth < RazorDepth
1352 && refinedValue - futility_margin(depth, 0) >= beta)
1353 return refinedValue - futility_margin(depth, 0);
1355 // Step 8. Null move search with verification search
1356 // When we jump directly to qsearch() we do a null move only if static value is
1357 // at least beta. Otherwise we do a null move if static value is not more than
1358 // NullMoveMargin under beta.
1362 && !value_is_mate(beta)
1363 && ok_to_do_nullmove(pos)
1364 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1366 ss[ply].currentMove = MOVE_NULL;
1368 pos.do_null_move(st);
1370 // Null move dynamic reduction based on depth
1371 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1373 // Null move dynamic reduction based on value
1374 if (refinedValue - beta > PawnValueMidgame)
1377 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1379 pos.undo_null_move();
1381 if (nullValue >= beta)
1383 if (depth < 6 * OnePly)
1386 // Do zugzwang verification search
1387 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1391 // The null move failed low, which means that we may be faced with
1392 // some kind of threat. If the previous move was reduced, check if
1393 // the move that refuted the null move was somehow connected to the
1394 // move which was reduced. If a connection is found, return a fail
1395 // low score (which will cause the reduced move to fail high in the
1396 // parent node, which will trigger a re-search with full depth).
1397 if (nullValue == value_mated_in(ply + 2))
1400 ss[ply].threatMove = ss[ply + 1].currentMove;
1401 if ( depth < ThreatDepth
1402 && ss[ply - 1].reduction
1403 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1408 // Step 9. Internal iterative deepening
1409 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1410 !isCheck && ss[ply].eval >= beta - IIDMargin)
1412 search(pos, ss, beta, depth/2, ply, false, threadID);
1413 ttMove = ss[ply].pv[ply];
1414 tte = TT.retrieve(posKey);
1417 // Step 10. Loop through moves
1418 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1420 // Initialize a MovePicker object for the current position
1421 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1424 while ( bestValue < beta
1425 && (move = mp.get_next_move()) != MOVE_NONE
1426 && !TM.thread_should_stop(threadID))
1428 assert(move_is_ok(move));
1430 if (move == excludedMove)
1433 moveIsCheck = pos.move_is_check(move, ci);
1434 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1435 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1437 // Step 11. Decide the new search depth
1438 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1440 // Singular extension search. We extend the TT move if its value is much better than
1441 // its siblings. To verify this we do a reduced search on all the other moves but the
1442 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1443 if ( depth >= 8 * OnePly
1445 && move == tte->move()
1446 && !excludedMove // Do not allow recursive single-reply search
1448 && is_lower_bound(tte->type())
1449 && tte->depth() >= depth - 3 * OnePly)
1451 Value ttValue = value_from_tt(tte->value(), ply);
1453 if (abs(ttValue) < VALUE_KNOWN_WIN)
1455 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1457 if (excValue < ttValue - SingleReplyMargin)
1462 newDepth = depth - OnePly + ext;
1464 // Update current move (this must be done after singular extension search)
1465 movesSearched[moveCount++] = ss[ply].currentMove = move;
1467 // Step 12. Futility pruning
1470 && !captureOrPromotion
1471 && !move_is_castle(move)
1474 // Move count based pruning
1475 if ( moveCount >= futility_move_count(depth)
1476 && ok_to_prune(pos, move, ss[ply].threatMove)
1477 && bestValue > value_mated_in(PLY_MAX))
1480 // Value based pruning
1481 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1482 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1483 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1485 if (futilityValueScaled < beta)
1487 if (futilityValueScaled > bestValue)
1488 bestValue = futilityValueScaled;
1493 // Step 13. Make the move
1494 pos.do_move(move, st, ci, moveIsCheck);
1496 // Step 14. Reduced search
1497 // if the move fails high will be re-searched at full depth.
1498 bool doFullDepthSearch = true;
1500 if ( depth >= 3*OnePly
1502 && !captureOrPromotion
1503 && !move_is_castle(move)
1504 && !move_is_killer(move, ss[ply]))
1506 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1507 if (ss[ply].reduction)
1509 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1510 doFullDepthSearch = (value >= beta);
1514 // Step 15. Full depth search
1515 if (doFullDepthSearch)
1517 ss[ply].reduction = Depth(0);
1518 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1521 // Step 16. Undo move
1522 pos.undo_move(move);
1524 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1526 // Step 17. Check for new best move
1527 if (value > bestValue)
1533 if (value == value_mate_in(ply + 1))
1534 ss[ply].mateKiller = move;
1537 // Step 18. Check for split
1538 if ( TM.active_threads() > 1
1540 && depth >= MinimumSplitDepth
1542 && TM.available_thread_exists(threadID)
1544 && !TM.thread_should_stop(threadID)
1545 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1546 depth, &moveCount, &mp, threadID, false))
1550 // Step 19. Check for mate and stalemate
1551 // All legal moves have been searched and if there were
1552 // no legal moves, it must be mate or stalemate.
1553 // If one move was excluded return fail low.
1555 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1557 // Step 20. Update tables
1558 // If the search is not aborted, update the transposition table,
1559 // history counters, and killer moves.
1560 if (AbortSearch || TM.thread_should_stop(threadID))
1563 if (bestValue < beta)
1564 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1567 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1568 move = ss[ply].pv[ply];
1569 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1570 if (!pos.move_is_capture_or_promotion(move))
1572 update_history(pos, move, depth, movesSearched, moveCount);
1573 update_killers(move, ss[ply]);
1578 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1584 // qsearch() is the quiescence search function, which is called by the main
1585 // search function when the remaining depth is zero (or, to be more precise,
1586 // less than OnePly).
1588 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1589 Depth depth, int ply, int threadID) {
1591 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1592 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1594 assert(ply >= 0 && ply < PLY_MAX);
1595 assert(threadID >= 0 && threadID < TM.active_threads());
1600 Value staticValue, bestValue, value, futilityBase, futilityValue;
1601 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1602 const TTEntry* tte = NULL;
1604 bool pvNode = (beta - alpha != 1);
1605 Value oldAlpha = alpha;
1607 // Initialize, and make an early exit in case of an aborted search,
1608 // an instant draw, maximum ply reached, etc.
1609 init_node(ss, ply, threadID);
1611 // After init_node() that calls poll()
1612 if (AbortSearch || TM.thread_should_stop(threadID))
1615 if (pos.is_draw() || ply >= PLY_MAX - 1)
1618 // Transposition table lookup. At PV nodes, we don't use the TT for
1619 // pruning, but only for move ordering.
1620 tte = TT.retrieve(pos.get_key());
1621 ttMove = (tte ? tte->move() : MOVE_NONE);
1623 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1625 assert(tte->type() != VALUE_TYPE_EVAL);
1627 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1628 return value_from_tt(tte->value(), ply);
1631 isCheck = pos.is_check();
1633 // Evaluate the position statically
1635 staticValue = -VALUE_INFINITE;
1636 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1637 staticValue = value_from_tt(tte->value(), ply);
1639 staticValue = evaluate(pos, ei, threadID);
1643 ss[ply].eval = staticValue;
1644 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1647 // Initialize "stand pat score", and return it immediately if it is
1649 bestValue = staticValue;
1651 if (bestValue >= beta)
1653 // Store the score to avoid a future costly evaluation() call
1654 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1655 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1660 if (bestValue > alpha)
1663 // If we are near beta then try to get a cutoff pushing checks a bit further
1664 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1666 // Initialize a MovePicker object for the current position, and prepare
1667 // to search the moves. Because the depth is <= 0 here, only captures,
1668 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1669 // and we are near beta) will be generated.
1670 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1672 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1673 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1675 // Loop through the moves until no moves remain or a beta cutoff
1677 while ( alpha < beta
1678 && (move = mp.get_next_move()) != MOVE_NONE)
1680 assert(move_is_ok(move));
1682 moveIsCheck = pos.move_is_check(move, ci);
1684 // Update current move
1686 ss[ply].currentMove = move;
1694 && !move_is_promotion(move)
1695 && !pos.move_is_passed_pawn_push(move))
1697 futilityValue = futilityBase
1698 + pos.endgame_value_of_piece_on(move_to(move))
1699 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1701 if (futilityValue < alpha)
1703 if (futilityValue > bestValue)
1704 bestValue = futilityValue;
1709 // Detect blocking evasions that are candidate to be pruned
1710 evasionPrunable = isCheck
1711 && bestValue != -VALUE_INFINITE
1712 && !pos.move_is_capture(move)
1713 && pos.type_of_piece_on(move_from(move)) != KING
1714 && !pos.can_castle(pos.side_to_move());
1716 // Don't search moves with negative SEE values
1717 if ( (!isCheck || evasionPrunable)
1720 && !move_is_promotion(move)
1721 && pos.see_sign(move) < 0)
1724 // Make and search the move
1725 pos.do_move(move, st, ci, moveIsCheck);
1726 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1727 pos.undo_move(move);
1729 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1732 if (value > bestValue)
1743 // All legal moves have been searched. A special case: If we're in check
1744 // and no legal moves were found, it is checkmate.
1745 if (!moveCount && pos.is_check()) // Mate!
1746 return value_mated_in(ply);
1748 // Update transposition table
1749 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1750 if (bestValue <= oldAlpha)
1752 // If bestValue isn't changed it means it is still the static evaluation
1753 // of the node, so keep this info to avoid a future evaluation() call.
1754 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1755 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1757 else if (bestValue >= beta)
1759 move = ss[ply].pv[ply];
1760 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1762 // Update killers only for good checking moves
1763 if (!pos.move_is_capture_or_promotion(move))
1764 update_killers(move, ss[ply]);
1767 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1769 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1775 // sp_search() is used to search from a split point. This function is called
1776 // by each thread working at the split point. It is similar to the normal
1777 // search() function, but simpler. Because we have already probed the hash
1778 // table, done a null move search, and searched the first move before
1779 // splitting, we don't have to repeat all this work in sp_search(). We
1780 // also don't need to store anything to the hash table here: This is taken
1781 // care of after we return from the split point.
1783 void sp_search(SplitPoint* sp, int threadID) {
1785 assert(threadID >= 0 && threadID < TM.active_threads());
1786 assert(TM.active_threads() > 1);
1788 Position pos(*sp->pos);
1790 SearchStack* ss = sp->sstack[threadID];
1792 Value value = -VALUE_INFINITE;
1795 bool isCheck = pos.is_check();
1797 // Step 10. Loop through moves
1798 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1799 lock_grab(&(sp->lock));
1801 while ( sp->bestValue < sp->beta
1802 && !TM.thread_should_stop(threadID)
1803 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1805 moveCount = ++sp->moves;
1806 lock_release(&(sp->lock));
1808 assert(move_is_ok(move));
1810 bool moveIsCheck = pos.move_is_check(move, ci);
1811 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1813 // Step 11. Decide the new search depth
1815 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1816 Depth newDepth = sp->depth - OnePly + ext;
1818 // Update current move
1819 ss[sp->ply].currentMove = move;
1821 // Step 12. Futility pruning
1824 && !captureOrPromotion
1825 && !move_is_castle(move))
1827 // Move count based pruning
1828 if ( moveCount >= futility_move_count(sp->depth)
1829 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1830 && sp->bestValue > value_mated_in(PLY_MAX))
1832 lock_grab(&(sp->lock));
1836 // Value based pruning
1837 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1838 Value futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1839 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1841 if (futilityValueScaled < sp->beta)
1843 lock_grab(&(sp->lock));
1845 if (futilityValueScaled > sp->bestValue)
1846 sp->bestValue = futilityValueScaled;
1851 // Step 13. Make the move
1852 pos.do_move(move, st, ci, moveIsCheck);
1854 // Step 14. Reduced search
1855 // if the move fails high will be re-searched at full depth.
1856 bool doFullDepthSearch = true;
1859 && !captureOrPromotion
1860 && !move_is_castle(move)
1861 && !move_is_killer(move, ss[sp->ply]))
1863 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1864 if (ss[sp->ply].reduction)
1866 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1867 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1871 // Step 15. Full depth search
1872 if (doFullDepthSearch)
1874 ss[sp->ply].reduction = Depth(0);
1875 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1878 // Step 16. Undo move
1879 pos.undo_move(move);
1881 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1883 // Step 17. Check for new best move
1884 lock_grab(&(sp->lock));
1886 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1888 sp->bestValue = value;
1889 if (sp->bestValue >= sp->beta)
1891 sp->stopRequest = true;
1892 sp_update_pv(sp->parentSstack, ss, sp->ply);
1897 /* Here we have the lock still grabbed */
1899 sp->slaves[threadID] = 0;
1902 lock_release(&(sp->lock));
1906 // sp_search_pv() is used to search from a PV split point. This function
1907 // is called by each thread working at the split point. It is similar to
1908 // the normal search_pv() function, but simpler. Because we have already
1909 // probed the hash table and searched the first move before splitting, we
1910 // don't have to repeat all this work in sp_search_pv(). We also don't
1911 // need to store anything to the hash table here: This is taken care of
1912 // after we return from the split point.
1914 void sp_search_pv(SplitPoint* sp, int threadID) {
1916 assert(threadID >= 0 && threadID < TM.active_threads());
1917 assert(TM.active_threads() > 1);
1919 Position pos(*sp->pos);
1921 SearchStack* ss = sp->sstack[threadID];
1923 Value value = -VALUE_INFINITE;
1927 // Step 10. Loop through moves
1928 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1929 lock_grab(&(sp->lock));
1931 while ( sp->alpha < sp->beta
1932 && !TM.thread_should_stop(threadID)
1933 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1935 moveCount = ++sp->moves;
1936 lock_release(&(sp->lock));
1938 assert(move_is_ok(move));
1940 bool moveIsCheck = pos.move_is_check(move, ci);
1941 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1943 // Step 11. Decide the new search depth
1945 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1946 Depth newDepth = sp->depth - OnePly + ext;
1948 // Update current move
1949 ss[sp->ply].currentMove = move;
1951 // Step 12. Futility pruning (is omitted in PV nodes)
1953 // Step 13. Make the move
1954 pos.do_move(move, st, ci, moveIsCheck);
1956 // Step 14. Reduced search
1957 // if the move fails high will be re-searched at full depth.
1958 bool doFullDepthSearch = true;
1961 && !captureOrPromotion
1962 && !move_is_castle(move)
1963 && !move_is_killer(move, ss[sp->ply]))
1965 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1966 if (ss[sp->ply].reduction)
1968 Value localAlpha = sp->alpha;
1969 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1970 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1974 // Step 15. Full depth search
1975 if (doFullDepthSearch)
1977 Value localAlpha = sp->alpha;
1978 ss[sp->ply].reduction = Depth(0);
1979 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1981 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1983 // If another thread has failed high then sp->alpha has been increased
1984 // to be higher or equal then beta, if so, avoid to start a PV search.
1985 localAlpha = sp->alpha;
1986 if (localAlpha < sp->beta)
1987 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1991 // Step 16. Undo move
1992 pos.undo_move(move);
1994 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1996 // Step 17. Check for new best move
1997 lock_grab(&(sp->lock));
1999 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
2001 sp->bestValue = value;
2002 if (value > sp->alpha)
2004 // Ask threads to stop before to modify sp->alpha
2005 if (value >= sp->beta)
2006 sp->stopRequest = true;
2010 sp_update_pv(sp->parentSstack, ss, sp->ply);
2011 if (value == value_mate_in(sp->ply + 1))
2012 ss[sp->ply].mateKiller = move;
2017 /* Here we have the lock still grabbed */
2019 sp->slaves[threadID] = 0;
2022 lock_release(&(sp->lock));
2026 // init_node() is called at the beginning of all the search functions
2027 // (search(), search_pv(), qsearch(), and so on) and initializes the
2028 // search stack object corresponding to the current node. Once every
2029 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2030 // for user input and checks whether it is time to stop the search.
2032 void init_node(SearchStack ss[], int ply, int threadID) {
2034 assert(ply >= 0 && ply < PLY_MAX);
2035 assert(threadID >= 0 && threadID < TM.active_threads());
2037 TM.incrementNodeCounter(threadID);
2042 if (NodesSincePoll >= NodesBetweenPolls)
2049 ss[ply + 2].initKillers();
2050 TM.print_current_line(ss, ply, threadID);
2054 // update_pv() is called whenever a search returns a value > alpha.
2055 // It updates the PV in the SearchStack object corresponding to the
2058 void update_pv(SearchStack ss[], int ply) {
2060 assert(ply >= 0 && ply < PLY_MAX);
2064 ss[ply].pv[ply] = ss[ply].currentMove;
2066 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2067 ss[ply].pv[p] = ss[ply + 1].pv[p];
2069 ss[ply].pv[p] = MOVE_NONE;
2073 // sp_update_pv() is a variant of update_pv for use at split points. The
2074 // difference between the two functions is that sp_update_pv also updates
2075 // the PV at the parent node.
2077 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2079 assert(ply >= 0 && ply < PLY_MAX);
2083 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2085 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2086 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2088 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2092 // connected_moves() tests whether two moves are 'connected' in the sense
2093 // that the first move somehow made the second move possible (for instance
2094 // if the moving piece is the same in both moves). The first move is assumed
2095 // to be the move that was made to reach the current position, while the
2096 // second move is assumed to be a move from the current position.
2098 bool connected_moves(const Position& pos, Move m1, Move m2) {
2100 Square f1, t1, f2, t2;
2103 assert(move_is_ok(m1));
2104 assert(move_is_ok(m2));
2106 if (m2 == MOVE_NONE)
2109 // Case 1: The moving piece is the same in both moves
2115 // Case 2: The destination square for m2 was vacated by m1
2121 // Case 3: Moving through the vacated square
2122 if ( piece_is_slider(pos.piece_on(f2))
2123 && bit_is_set(squares_between(f2, t2), f1))
2126 // Case 4: The destination square for m2 is defended by the moving piece in m1
2127 p = pos.piece_on(t1);
2128 if (bit_is_set(pos.attacks_from(p, t1), t2))
2131 // Case 5: Discovered check, checking piece is the piece moved in m1
2132 if ( piece_is_slider(p)
2133 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2134 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2136 // discovered_check_candidates() works also if the Position's side to
2137 // move is the opposite of the checking piece.
2138 Color them = opposite_color(pos.side_to_move());
2139 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2141 if (bit_is_set(dcCandidates, f2))
2148 // value_is_mate() checks if the given value is a mate one
2149 // eventually compensated for the ply.
2151 bool value_is_mate(Value value) {
2153 assert(abs(value) <= VALUE_INFINITE);
2155 return value <= value_mated_in(PLY_MAX)
2156 || value >= value_mate_in(PLY_MAX);
2160 // move_is_killer() checks if the given move is among the
2161 // killer moves of that ply.
2163 bool move_is_killer(Move m, const SearchStack& ss) {
2165 const Move* k = ss.killers;
2166 for (int i = 0; i < KILLER_MAX; i++, k++)
2174 // extension() decides whether a move should be searched with normal depth,
2175 // or with extended depth. Certain classes of moves (checking moves, in
2176 // particular) are searched with bigger depth than ordinary moves and in
2177 // any case are marked as 'dangerous'. Note that also if a move is not
2178 // extended, as example because the corresponding UCI option is set to zero,
2179 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2181 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2182 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2184 assert(m != MOVE_NONE);
2186 Depth result = Depth(0);
2187 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2192 result += CheckExtension[pvNode];
2195 result += SingleEvasionExtension[pvNode];
2198 result += MateThreatExtension[pvNode];
2201 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2203 Color c = pos.side_to_move();
2204 if (relative_rank(c, move_to(m)) == RANK_7)
2206 result += PawnPushTo7thExtension[pvNode];
2209 if (pos.pawn_is_passed(c, move_to(m)))
2211 result += PassedPawnExtension[pvNode];
2216 if ( captureOrPromotion
2217 && pos.type_of_piece_on(move_to(m)) != PAWN
2218 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2219 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2220 && !move_is_promotion(m)
2223 result += PawnEndgameExtension[pvNode];
2228 && captureOrPromotion
2229 && pos.type_of_piece_on(move_to(m)) != PAWN
2230 && pos.see_sign(m) >= 0)
2236 return Min(result, OnePly);
2240 // ok_to_do_nullmove() looks at the current position and decides whether
2241 // doing a 'null move' should be allowed. In order to avoid zugzwang
2242 // problems, null moves are not allowed when the side to move has very
2243 // little material left. Currently, the test is a bit too simple: Null
2244 // moves are avoided only when the side to move has only pawns left.
2245 // It's probably a good idea to avoid null moves in at least some more
2246 // complicated endgames, e.g. KQ vs KR. FIXME
2248 bool ok_to_do_nullmove(const Position& pos) {
2250 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2254 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2255 // non-tactical moves late in the move list close to the leaves are
2256 // candidates for pruning.
2258 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2260 assert(move_is_ok(m));
2261 assert(threat == MOVE_NONE || move_is_ok(threat));
2262 assert(!pos.move_is_check(m));
2263 assert(!pos.move_is_capture_or_promotion(m));
2264 assert(!pos.move_is_passed_pawn_push(m));
2266 Square mfrom, mto, tfrom, tto;
2268 // Prune if there isn't any threat move
2269 if (threat == MOVE_NONE)
2272 mfrom = move_from(m);
2274 tfrom = move_from(threat);
2275 tto = move_to(threat);
2277 // Case 1: Don't prune moves which move the threatened piece
2281 // Case 2: If the threatened piece has value less than or equal to the
2282 // value of the threatening piece, don't prune move which defend it.
2283 if ( pos.move_is_capture(threat)
2284 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2285 || pos.type_of_piece_on(tfrom) == KING)
2286 && pos.move_attacks_square(m, tto))
2289 // Case 3: If the moving piece in the threatened move is a slider, don't
2290 // prune safe moves which block its ray.
2291 if ( piece_is_slider(pos.piece_on(tfrom))
2292 && bit_is_set(squares_between(tfrom, tto), mto)
2293 && pos.see_sign(m) >= 0)
2300 // ok_to_use_TT() returns true if a transposition table score
2301 // can be used at a given point in search.
2303 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2305 Value v = value_from_tt(tte->value(), ply);
2307 return ( tte->depth() >= depth
2308 || v >= Max(value_mate_in(PLY_MAX), beta)
2309 || v < Min(value_mated_in(PLY_MAX), beta))
2311 && ( (is_lower_bound(tte->type()) && v >= beta)
2312 || (is_upper_bound(tte->type()) && v < beta));
2316 // refine_eval() returns the transposition table score if
2317 // possible otherwise falls back on static position evaluation.
2319 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2324 Value v = value_from_tt(tte->value(), ply);
2326 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2327 || (is_upper_bound(tte->type()) && v < defaultEval))
2334 // update_history() registers a good move that produced a beta-cutoff
2335 // in history and marks as failures all the other moves of that ply.
2337 void update_history(const Position& pos, Move move, Depth depth,
2338 Move movesSearched[], int moveCount) {
2342 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2344 for (int i = 0; i < moveCount - 1; i++)
2346 m = movesSearched[i];
2350 if (!pos.move_is_capture_or_promotion(m))
2351 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2356 // update_killers() add a good move that produced a beta-cutoff
2357 // among the killer moves of that ply.
2359 void update_killers(Move m, SearchStack& ss) {
2361 if (m == ss.killers[0])
2364 for (int i = KILLER_MAX - 1; i > 0; i--)
2365 ss.killers[i] = ss.killers[i - 1];
2371 // update_gains() updates the gains table of a non-capture move given
2372 // the static position evaluation before and after the move.
2374 void update_gains(const Position& pos, Move m, Value before, Value after) {
2377 && before != VALUE_NONE
2378 && after != VALUE_NONE
2379 && pos.captured_piece() == NO_PIECE_TYPE
2380 && !move_is_castle(m)
2381 && !move_is_promotion(m))
2382 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2386 // current_search_time() returns the number of milliseconds which have passed
2387 // since the beginning of the current search.
2389 int current_search_time() {
2391 return get_system_time() - SearchStartTime;
2395 // nps() computes the current nodes/second count.
2399 int t = current_search_time();
2400 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2404 // poll() performs two different functions: It polls for user input, and it
2405 // looks at the time consumed so far and decides if it's time to abort the
2410 static int lastInfoTime;
2411 int t = current_search_time();
2416 // We are line oriented, don't read single chars
2417 std::string command;
2419 if (!std::getline(std::cin, command))
2422 if (command == "quit")
2425 PonderSearch = false;
2429 else if (command == "stop")
2432 PonderSearch = false;
2434 else if (command == "ponderhit")
2438 // Print search information
2442 else if (lastInfoTime > t)
2443 // HACK: Must be a new search where we searched less than
2444 // NodesBetweenPolls nodes during the first second of search.
2447 else if (t - lastInfoTime >= 1000)
2450 lock_grab(&TM.IOLock);
2455 if (dbg_show_hit_rate)
2456 dbg_print_hit_rate();
2458 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2459 << " time " << t << " hashfull " << TT.full() << endl;
2461 lock_release(&TM.IOLock);
2463 if (ShowCurrentLine)
2464 TM.threads[0].printCurrentLineRequest = true;
2467 // Should we stop the search?
2471 bool stillAtFirstMove = RootMoveNumber == 1
2472 && !AspirationFailLow
2473 && t > MaxSearchTime + ExtraSearchTime;
2475 bool noMoreTime = t > AbsoluteMaxSearchTime
2476 || stillAtFirstMove;
2478 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2479 || (ExactMaxTime && t >= ExactMaxTime)
2480 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2485 // ponderhit() is called when the program is pondering (i.e. thinking while
2486 // it's the opponent's turn to move) in order to let the engine know that
2487 // it correctly predicted the opponent's move.
2491 int t = current_search_time();
2492 PonderSearch = false;
2494 bool stillAtFirstMove = RootMoveNumber == 1
2495 && !AspirationFailLow
2496 && t > MaxSearchTime + ExtraSearchTime;
2498 bool noMoreTime = t > AbsoluteMaxSearchTime
2499 || stillAtFirstMove;
2501 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2506 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2508 void init_ss_array(SearchStack ss[]) {
2510 for (int i = 0; i < 3; i++)
2513 ss[i].initKillers();
2518 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2519 // while the program is pondering. The point is to work around a wrinkle in
2520 // the UCI protocol: When pondering, the engine is not allowed to give a
2521 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2522 // We simply wait here until one of these commands is sent, and return,
2523 // after which the bestmove and pondermove will be printed (in id_loop()).
2525 void wait_for_stop_or_ponderhit() {
2527 std::string command;
2531 if (!std::getline(std::cin, command))
2534 if (command == "quit")
2539 else if (command == "ponderhit" || command == "stop")
2545 // init_thread() is the function which is called when a new thread is
2546 // launched. It simply calls the idle_loop() function with the supplied
2547 // threadID. There are two versions of this function; one for POSIX
2548 // threads and one for Windows threads.
2550 #if !defined(_MSC_VER)
2552 void* init_thread(void *threadID) {
2554 TM.idle_loop(*(int*)threadID, NULL);
2560 DWORD WINAPI init_thread(LPVOID threadID) {
2562 TM.idle_loop(*(int*)threadID, NULL);
2569 /// The ThreadsManager class
2571 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2572 // get_beta_counters() are getters/setters for the per thread
2573 // counters used to sort the moves at root.
2575 void ThreadsManager::resetNodeCounters() {
2577 for (int i = 0; i < MAX_THREADS; i++)
2578 threads[i].nodes = 0ULL;
2581 void ThreadsManager::resetBetaCounters() {
2583 for (int i = 0; i < MAX_THREADS; i++)
2584 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2587 int64_t ThreadsManager::nodes_searched() const {
2589 int64_t result = 0ULL;
2590 for (int i = 0; i < ActiveThreads; i++)
2591 result += threads[i].nodes;
2596 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2599 for (int i = 0; i < MAX_THREADS; i++)
2601 our += threads[i].betaCutOffs[us];
2602 their += threads[i].betaCutOffs[opposite_color(us)];
2607 // idle_loop() is where the threads are parked when they have no work to do.
2608 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2609 // object for which the current thread is the master.
2611 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2613 assert(threadID >= 0 && threadID < MAX_THREADS);
2617 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2618 // master should exit as last one.
2619 if (AllThreadsShouldExit)
2622 threads[threadID].state = THREAD_TERMINATED;
2626 // If we are not thinking, wait for a condition to be signaled
2627 // instead of wasting CPU time polling for work.
2628 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2631 assert(threadID != 0);
2632 threads[threadID].state = THREAD_SLEEPING;
2634 #if !defined(_MSC_VER)
2635 pthread_mutex_lock(&WaitLock);
2636 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2637 pthread_cond_wait(&WaitCond, &WaitLock);
2638 pthread_mutex_unlock(&WaitLock);
2640 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2644 // If thread has just woken up, mark it as available
2645 if (threads[threadID].state == THREAD_SLEEPING)
2646 threads[threadID].state = THREAD_AVAILABLE;
2648 // If this thread has been assigned work, launch a search
2649 if (threads[threadID].state == THREAD_WORKISWAITING)
2651 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2653 threads[threadID].state = THREAD_SEARCHING;
2655 if (threads[threadID].splitPoint->pvNode)
2656 sp_search_pv(threads[threadID].splitPoint, threadID);
2658 sp_search(threads[threadID].splitPoint, threadID);
2660 assert(threads[threadID].state == THREAD_SEARCHING);
2662 threads[threadID].state = THREAD_AVAILABLE;
2665 // If this thread is the master of a split point and all threads have
2666 // finished their work at this split point, return from the idle loop.
2667 if (waitSp != NULL && waitSp->cpus == 0)
2669 assert(threads[threadID].state == THREAD_AVAILABLE);
2671 threads[threadID].state = THREAD_SEARCHING;
2678 // init_threads() is called during startup. It launches all helper threads,
2679 // and initializes the split point stack and the global locks and condition
2682 void ThreadsManager::init_threads() {
2687 #if !defined(_MSC_VER)
2688 pthread_t pthread[1];
2691 // Initialize global locks
2692 lock_init(&MPLock, NULL);
2693 lock_init(&IOLock, NULL);
2695 // Initialize SplitPointStack locks
2696 for (i = 0; i < MAX_THREADS; i++)
2697 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2699 SplitPointStack[i][j].parent = NULL;
2700 lock_init(&(SplitPointStack[i][j].lock), NULL);
2703 #if !defined(_MSC_VER)
2704 pthread_mutex_init(&WaitLock, NULL);
2705 pthread_cond_init(&WaitCond, NULL);
2707 for (i = 0; i < MAX_THREADS; i++)
2708 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2711 // Will be set just before program exits to properly end the threads
2712 AllThreadsShouldExit = false;
2714 // Threads will be put to sleep as soon as created
2715 AllThreadsShouldSleep = true;
2717 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2719 threads[0].state = THREAD_SEARCHING;
2720 for (i = 1; i < MAX_THREADS; i++)
2721 threads[i].state = THREAD_AVAILABLE;
2723 // Launch the helper threads
2724 for (i = 1; i < MAX_THREADS; i++)
2727 #if !defined(_MSC_VER)
2728 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2731 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
2736 cout << "Failed to create thread number " << i << endl;
2737 Application::exit_with_failure();
2740 // Wait until the thread has finished launching and is gone to sleep
2741 while (threads[i].state != THREAD_SLEEPING);
2746 // exit_threads() is called when the program exits. It makes all the
2747 // helper threads exit cleanly.
2749 void ThreadsManager::exit_threads() {
2751 ActiveThreads = MAX_THREADS; // HACK
2752 AllThreadsShouldSleep = true; // HACK
2753 wake_sleeping_threads();
2755 // This makes the threads to exit idle_loop()
2756 AllThreadsShouldExit = true;
2758 // Wait for thread termination
2759 for (int i = 1; i < MAX_THREADS; i++)
2760 while (threads[i].state != THREAD_TERMINATED);
2762 // Now we can safely destroy the locks
2763 for (int i = 0; i < MAX_THREADS; i++)
2764 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2765 lock_destroy(&(SplitPointStack[i][j].lock));
2769 // thread_should_stop() checks whether the thread should stop its search.
2770 // This can happen if a beta cutoff has occurred in the thread's currently
2771 // active split point, or in some ancestor of the current split point.
2773 bool ThreadsManager::thread_should_stop(int threadID) const {
2775 assert(threadID >= 0 && threadID < ActiveThreads);
2779 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2784 // thread_is_available() checks whether the thread with threadID "slave" is
2785 // available to help the thread with threadID "master" at a split point. An
2786 // obvious requirement is that "slave" must be idle. With more than two
2787 // threads, this is not by itself sufficient: If "slave" is the master of
2788 // some active split point, it is only available as a slave to the other
2789 // threads which are busy searching the split point at the top of "slave"'s
2790 // split point stack (the "helpful master concept" in YBWC terminology).
2792 bool ThreadsManager::thread_is_available(int slave, int master) const {
2794 assert(slave >= 0 && slave < ActiveThreads);
2795 assert(master >= 0 && master < ActiveThreads);
2796 assert(ActiveThreads > 1);
2798 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2801 // Make a local copy to be sure doesn't change under our feet
2802 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2804 if (localActiveSplitPoints == 0)
2805 // No active split points means that the thread is available as
2806 // a slave for any other thread.
2809 if (ActiveThreads == 2)
2812 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2813 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2814 // could have been set to 0 by another thread leading to an out of bound access.
2815 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2822 // available_thread_exists() tries to find an idle thread which is available as
2823 // a slave for the thread with threadID "master".
2825 bool ThreadsManager::available_thread_exists(int master) const {
2827 assert(master >= 0 && master < ActiveThreads);
2828 assert(ActiveThreads > 1);
2830 for (int i = 0; i < ActiveThreads; i++)
2831 if (thread_is_available(i, master))
2838 // split() does the actual work of distributing the work at a node between
2839 // several threads at PV nodes. If it does not succeed in splitting the
2840 // node (because no idle threads are available, or because we have no unused
2841 // split point objects), the function immediately returns false. If
2842 // splitting is possible, a SplitPoint object is initialized with all the
2843 // data that must be copied to the helper threads (the current position and
2844 // search stack, alpha, beta, the search depth, etc.), and we tell our
2845 // helper threads that they have been assigned work. This will cause them
2846 // to instantly leave their idle loops and call sp_search_pv(). When all
2847 // threads have returned from sp_search_pv (or, equivalently, when
2848 // splitPoint->cpus becomes 0), split() returns true.
2850 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2851 Value* alpha, const Value beta, Value* bestValue,
2852 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2855 assert(sstck != NULL);
2856 assert(ply >= 0 && ply < PLY_MAX);
2857 assert(*bestValue >= -VALUE_INFINITE);
2858 assert( ( pvNode && *bestValue <= *alpha)
2859 || (!pvNode && *bestValue < beta ));
2860 assert(!pvNode || *alpha < beta);
2861 assert(beta <= VALUE_INFINITE);
2862 assert(depth > Depth(0));
2863 assert(master >= 0 && master < ActiveThreads);
2864 assert(ActiveThreads > 1);
2866 SplitPoint* splitPoint;
2870 // If no other thread is available to help us, or if we have too many
2871 // active split points, don't split.
2872 if ( !available_thread_exists(master)
2873 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2875 lock_release(&MPLock);
2879 // Pick the next available split point object from the split point stack
2880 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2882 // Initialize the split point object
2883 splitPoint->parent = threads[master].splitPoint;
2884 splitPoint->stopRequest = false;
2885 splitPoint->ply = ply;
2886 splitPoint->depth = depth;
2887 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2888 splitPoint->beta = beta;
2889 splitPoint->pvNode = pvNode;
2890 splitPoint->bestValue = *bestValue;
2891 splitPoint->master = master;
2892 splitPoint->mp = mp;
2893 splitPoint->moves = *moves;
2894 splitPoint->cpus = 1;
2895 splitPoint->pos = &p;
2896 splitPoint->parentSstack = sstck;
2897 for (int i = 0; i < ActiveThreads; i++)
2898 splitPoint->slaves[i] = 0;
2900 threads[master].splitPoint = splitPoint;
2901 threads[master].activeSplitPoints++;
2903 // If we are here it means we are not available
2904 assert(threads[master].state != THREAD_AVAILABLE);
2906 // Allocate available threads setting state to THREAD_BOOKED
2907 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2908 if (thread_is_available(i, master))
2910 threads[i].state = THREAD_BOOKED;
2911 threads[i].splitPoint = splitPoint;
2912 splitPoint->slaves[i] = 1;
2916 assert(splitPoint->cpus > 1);
2918 // We can release the lock because slave threads are already booked and master is not available
2919 lock_release(&MPLock);
2921 // Tell the threads that they have work to do. This will make them leave
2922 // their idle loop. But before copy search stack tail for each thread.
2923 for (int i = 0; i < ActiveThreads; i++)
2924 if (i == master || splitPoint->slaves[i])
2926 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2928 assert(i == master || threads[i].state == THREAD_BOOKED);
2930 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2933 // Everything is set up. The master thread enters the idle loop, from
2934 // which it will instantly launch a search, because its state is
2935 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2936 // idle loop, which means that the main thread will return from the idle
2937 // loop when all threads have finished their work at this split point
2938 // (i.e. when splitPoint->cpus == 0).
2939 idle_loop(master, splitPoint);
2941 // We have returned from the idle loop, which means that all threads are
2942 // finished. Update alpha, beta and bestValue, and return.
2946 *alpha = splitPoint->alpha;
2948 *bestValue = splitPoint->bestValue;
2949 threads[master].activeSplitPoints--;
2950 threads[master].splitPoint = splitPoint->parent;
2952 lock_release(&MPLock);
2957 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2958 // to start a new search from the root.
2960 void ThreadsManager::wake_sleeping_threads() {
2962 assert(AllThreadsShouldSleep);
2963 assert(ActiveThreads > 0);
2965 AllThreadsShouldSleep = false;
2967 if (ActiveThreads == 1)
2970 for (int i = 1; i < ActiveThreads; i++)
2971 assert(threads[i].state == THREAD_SLEEPING);
2973 #if !defined(_MSC_VER)
2974 pthread_mutex_lock(&WaitLock);
2975 pthread_cond_broadcast(&WaitCond);
2976 pthread_mutex_unlock(&WaitLock);
2978 for (int i = 1; i < MAX_THREADS; i++)
2979 SetEvent(SitIdleEvent[i]);
2985 // put_threads_to_sleep() makes all the threads go to sleep just before
2986 // to leave think(), at the end of the search. Threads should have already
2987 // finished the job and should be idle.
2989 void ThreadsManager::put_threads_to_sleep() {
2991 assert(!AllThreadsShouldSleep);
2993 // This makes the threads to go to sleep
2994 AllThreadsShouldSleep = true;
2996 // Reset flags to a known state.
2997 for (int i = 1; i < ActiveThreads; i++)
2999 // This flag can be in a random state
3000 threads[i].printCurrentLineRequest = false;
3004 // print_current_line() prints _once_ the current line of search for a
3005 // given thread and then setup the print request for the next thread.
3006 // Called when the UCI option UCI_ShowCurrLine is 'true'.
3008 void ThreadsManager::print_current_line(SearchStack ss[], int ply, int threadID) {
3010 assert(ply >= 0 && ply < PLY_MAX);
3011 assert(threadID >= 0 && threadID < ActiveThreads);
3013 if (!threads[threadID].printCurrentLineRequest)
3017 threads[threadID].printCurrentLineRequest = false;
3019 if (threads[threadID].state == THREAD_SEARCHING)
3022 cout << "info currline " << (threadID + 1);
3023 for (int p = 0; p < ply; p++)
3024 cout << " " << ss[p].currentMove;
3027 lock_release(&IOLock);
3030 // Setup print request for the next thread ID
3031 if (threadID + 1 < ActiveThreads)
3032 threads[threadID + 1].printCurrentLineRequest = true;
3036 /// The RootMoveList class
3038 // RootMoveList c'tor
3040 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3042 SearchStack ss[PLY_MAX_PLUS_2];
3043 MoveStack mlist[MaxRootMoves];
3045 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3047 // Generate all legal moves
3048 MoveStack* last = generate_moves(pos, mlist);
3050 // Add each move to the moves[] array
3051 for (MoveStack* cur = mlist; cur != last; cur++)
3053 bool includeMove = includeAllMoves;
3055 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3056 includeMove = (searchMoves[k] == cur->move);
3061 // Find a quick score for the move
3063 pos.do_move(cur->move, st);
3064 moves[count].move = cur->move;
3065 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3066 moves[count].pv[0] = cur->move;
3067 moves[count].pv[1] = MOVE_NONE;
3068 pos.undo_move(cur->move);
3075 // RootMoveList simple methods definitions
3077 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3079 moves[moveNum].nodes = nodes;
3080 moves[moveNum].cumulativeNodes += nodes;
3083 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3085 moves[moveNum].ourBeta = our;
3086 moves[moveNum].theirBeta = their;
3089 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3093 for (j = 0; pv[j] != MOVE_NONE; j++)
3094 moves[moveNum].pv[j] = pv[j];
3096 moves[moveNum].pv[j] = MOVE_NONE;
3100 // RootMoveList::sort() sorts the root move list at the beginning of a new
3103 void RootMoveList::sort() {
3105 sort_multipv(count - 1); // Sort all items
3109 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3110 // list by their scores and depths. It is used to order the different PVs
3111 // correctly in MultiPV mode.
3113 void RootMoveList::sort_multipv(int n) {
3117 for (i = 1; i <= n; i++)
3119 RootMove rm = moves[i];
3120 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3121 moves[j] = moves[j - 1];