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 const Value futilityValue, Depth depth, int* moves, MovePicker* mp, int master, bool pvNode);
94 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
95 Thread threads[MAX_THREADS];
96 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
100 #if !defined(_MSC_VER)
101 pthread_cond_t WaitCond;
102 pthread_mutex_t WaitLock;
104 HANDLE SitIdleEvent[MAX_THREADS];
110 // RootMove struct is used for moves at the root at the tree. For each
111 // root move, we store a score, a node count, and a PV (really a refutation
112 // in the case of moves which fail low).
116 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
118 // RootMove::operator<() is the comparison function used when
119 // sorting the moves. A move m1 is considered to be better
120 // than a move m2 if it has a higher score, or if the moves
121 // have equal score but m1 has the higher node count.
122 bool operator<(const RootMove& m) const {
124 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
129 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
130 Move pv[PLY_MAX_PLUS_2];
134 // The RootMoveList class is essentially an array of RootMove objects, with
135 // a handful of methods for accessing the data in the individual moves.
140 RootMoveList(Position& pos, Move searchMoves[]);
142 int move_count() const { return count; }
143 Move get_move(int moveNum) const { return moves[moveNum].move; }
144 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
145 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
146 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
147 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
149 void set_move_nodes(int moveNum, int64_t nodes);
150 void set_beta_counters(int moveNum, int64_t our, int64_t their);
151 void set_move_pv(int moveNum, const Move pv[]);
153 void sort_multipv(int n);
156 static const int MaxRootMoves = 500;
157 RootMove moves[MaxRootMoves];
164 // Search depth at iteration 1
165 const Depth InitialDepth = OnePly;
167 // Use internal iterative deepening?
168 const bool UseIIDAtPVNodes = true;
169 const bool UseIIDAtNonPVNodes = true;
171 // Internal iterative deepening margin. At Non-PV moves, when
172 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
173 // search when the static evaluation is at most IIDMargin below beta.
174 const Value IIDMargin = Value(0x100);
176 // Easy move margin. An easy move candidate must be at least this much
177 // better than the second best move.
178 const Value EasyMoveMargin = Value(0x200);
180 // Null move margin. A null move search will not be done if the static
181 // evaluation of the position is more than NullMoveMargin below beta.
182 const Value NullMoveMargin = Value(0x200);
184 // If the TT move is at least SingleReplyMargin better then the
185 // remaining ones we will extend it.
186 const Value SingleReplyMargin = Value(0x20);
188 // Depth limit for razoring
189 const Depth RazorDepth = 4 * OnePly;
191 /// Lookup tables initialized at startup
193 // Reduction lookup tables and their getter functions
194 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
195 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
197 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
198 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
200 // Futility lookup tables and their getter functions
201 const Value FutilityMarginQS = Value(0x80);
202 int32_t FutilityMarginsMatrix[14][64]; // [depth][moveNumber]
203 int FutilityMoveCountArray[32]; // [depth]
205 inline Value futility_margin(Depth d, int mn) { return Value(d < 7*OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
206 inline int futility_move_count(Depth d) { return d < 16*OnePly ? FutilityMoveCountArray[d] : 512; }
208 /// Variables initialized by UCI options
210 // Depth limit for use of dynamic threat detection
213 // Last seconds noise filtering (LSN)
214 const bool UseLSNFiltering = true;
215 const int LSNTime = 4000; // In milliseconds
216 const Value LSNValue = value_from_centipawns(200);
217 bool loseOnTime = false;
219 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
220 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
221 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
223 // Iteration counters
226 // Scores and number of times the best move changed for each iteration
227 Value ValueByIteration[PLY_MAX_PLUS_2];
228 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
230 // Search window management
236 // Time managment variables
239 int MaxNodes, MaxDepth;
240 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
241 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
242 bool AbortSearch, Quit;
243 bool AspirationFailLow;
245 // Show current line?
246 bool ShowCurrentLine;
250 std::ofstream LogFile;
252 // MP related variables
253 Depth MinimumSplitDepth;
254 int MaxThreadsPerSplitPoint;
257 // Node counters, used only by thread[0] but try to keep in different
258 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
260 int NodesBetweenPolls = 30000;
267 Value id_loop(const Position& pos, Move searchMoves[]);
268 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta);
269 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
270 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
271 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
272 void sp_search(SplitPoint* sp, int threadID);
273 void sp_search_pv(SplitPoint* sp, int threadID);
274 void init_node(SearchStack ss[], int ply, int threadID);
275 void update_pv(SearchStack ss[], int ply);
276 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
277 bool connected_moves(const Position& pos, Move m1, Move m2);
278 bool value_is_mate(Value value);
279 bool move_is_killer(Move m, const SearchStack& ss);
280 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
281 bool ok_to_do_nullmove(const Position& pos);
282 bool ok_to_prune(const Position& pos, Move m, Move threat);
283 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
284 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
285 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
286 void update_killers(Move m, SearchStack& ss);
287 void update_gains(const Position& pos, Move move, Value before, Value after);
289 int current_search_time();
293 void wait_for_stop_or_ponderhit();
294 void init_ss_array(SearchStack ss[]);
296 #if !defined(_MSC_VER)
297 void *init_thread(void *threadID);
299 DWORD WINAPI init_thread(LPVOID threadID);
309 /// init_threads(), exit_threads() and nodes_searched() are helpers to
310 /// give accessibility to some TM methods from outside of current file.
312 void init_threads() { TM.init_threads(); }
313 void exit_threads() { TM.exit_threads(); }
314 int64_t nodes_searched() { return TM.nodes_searched(); }
317 /// perft() is our utility to verify move generation is bug free. All the legal
318 /// moves up to given depth are generated and counted and the sum returned.
320 int perft(Position& pos, Depth depth)
324 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
326 // If we are at the last ply we don't need to do and undo
327 // the moves, just to count them.
328 if (depth <= OnePly) // Replace with '<' to test also qsearch
330 while (mp.get_next_move()) sum++;
334 // Loop through all legal moves
336 while ((move = mp.get_next_move()) != MOVE_NONE)
339 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
340 sum += perft(pos, depth - OnePly);
347 /// think() is the external interface to Stockfish's search, and is called when
348 /// the program receives the UCI 'go' command. It initializes various
349 /// search-related global variables, and calls root_search(). It returns false
350 /// when a quit command is received during the search.
352 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
353 int time[], int increment[], int movesToGo, int maxDepth,
354 int maxNodes, int maxTime, Move searchMoves[]) {
356 // Initialize global search variables
357 StopOnPonderhit = AbortSearch = Quit = false;
358 AspirationFailLow = false;
360 SearchStartTime = get_system_time();
361 ExactMaxTime = maxTime;
364 InfiniteSearch = infinite;
365 PonderSearch = ponder;
366 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
368 // Look for a book move, only during games, not tests
369 if (UseTimeManagement && get_option_value_bool("OwnBook"))
372 if (get_option_value_string("Book File") != OpeningBook.file_name())
373 OpeningBook.open(get_option_value_string("Book File"));
375 bookMove = OpeningBook.get_move(pos);
376 if (bookMove != MOVE_NONE)
379 wait_for_stop_or_ponderhit();
381 cout << "bestmove " << bookMove << endl;
386 TM.resetNodeCounters();
388 if (button_was_pressed("New Game"))
389 loseOnTime = false; // Reset at the beginning of a new game
391 // Read UCI option values
392 TT.set_size(get_option_value_int("Hash"));
393 if (button_was_pressed("Clear Hash"))
396 bool PonderingEnabled = get_option_value_bool("Ponder");
397 MultiPV = get_option_value_int("MultiPV");
399 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
400 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
402 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
403 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
405 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
406 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
408 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
409 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
411 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
412 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
414 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
415 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
417 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
419 Chess960 = get_option_value_bool("UCI_Chess960");
420 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
421 UseLogFile = get_option_value_bool("Use Search Log");
423 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
425 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
426 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
428 read_weights(pos.side_to_move());
430 // Set the number of active threads
431 int newActiveThreads = get_option_value_int("Threads");
432 if (newActiveThreads != TM.active_threads())
434 TM.set_active_threads(newActiveThreads);
435 init_eval(TM.active_threads());
436 // HACK: init_eval() destroys the static castleRightsMask[] array in the
437 // Position class. The below line repairs the damage.
438 Position p(pos.to_fen());
442 // Wake up sleeping threads
443 TM.wake_sleeping_threads();
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 // Decide the new search depth
1127 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1129 // Singular extension search. We extend the TT move if its value is much better than
1130 // its siblings. To verify this we do a reduced search on all the other moves but the
1131 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1132 if ( depth >= 6 * OnePly
1134 && move == tte->move()
1136 && is_lower_bound(tte->type())
1137 && tte->depth() >= depth - 3 * OnePly)
1139 Value ttValue = value_from_tt(tte->value(), ply);
1141 if (abs(ttValue) < VALUE_KNOWN_WIN)
1143 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1145 if (excValue < ttValue - SingleReplyMargin)
1150 newDepth = depth - OnePly + ext;
1152 // Update current move
1153 movesSearched[moveCount++] = ss[ply].currentMove = move;
1155 // Make and search the move
1156 pos.do_move(move, st, ci, moveIsCheck);
1158 if (moveCount == 1) // The first move in list is the PV
1159 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1162 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1163 // if the move fails high will be re-searched at full depth.
1164 bool doFullDepthSearch = true;
1166 if ( depth >= 3*OnePly
1168 && !captureOrPromotion
1169 && !move_is_castle(move)
1170 && !move_is_killer(move, ss[ply]))
1172 ss[ply].reduction = pv_reduction(depth, moveCount);
1173 if (ss[ply].reduction)
1175 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1176 doFullDepthSearch = (value > alpha);
1180 if (doFullDepthSearch) // Go with full depth non-pv search
1182 ss[ply].reduction = Depth(0);
1183 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1184 if (value > alpha && value < beta)
1185 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1188 pos.undo_move(move);
1190 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1193 if (value > bestValue)
1200 if (value == value_mate_in(ply + 1))
1201 ss[ply].mateKiller = move;
1206 if ( TM.active_threads() > 1
1208 && depth >= MinimumSplitDepth
1210 && TM.available_thread_exists(threadID)
1212 && !TM.thread_should_stop(threadID)
1213 && TM.split(pos, ss, ply, &alpha, beta, &bestValue, VALUE_NONE,
1214 depth, &moveCount, &mp, threadID, true))
1218 // All legal moves have been searched. A special case: If there were
1219 // no legal moves, it must be mate or stalemate.
1221 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1223 // If the search is not aborted, update the transposition table,
1224 // history counters, and killer moves.
1225 if (AbortSearch || TM.thread_should_stop(threadID))
1228 if (bestValue <= oldAlpha)
1229 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1231 else if (bestValue >= beta)
1233 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1234 move = ss[ply].pv[ply];
1235 if (!pos.move_is_capture_or_promotion(move))
1237 update_history(pos, move, depth, movesSearched, moveCount);
1238 update_killers(move, ss[ply]);
1240 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1243 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1249 // search() is the search function for zero-width nodes.
1251 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1252 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1254 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1255 assert(ply >= 0 && ply < PLY_MAX);
1256 assert(threadID >= 0 && threadID < TM.active_threads());
1258 Move movesSearched[256];
1263 Depth ext, newDepth;
1264 Value bestValue, staticValue, nullValue, value, futilityValue, futilityValueScaled;
1265 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1266 bool mateThreat = false;
1268 futilityValue = staticValue = bestValue = value = -VALUE_INFINITE;
1271 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1273 // Step 1. Initialize node and poll
1274 // Polling can abort search.
1275 init_node(ss, ply, threadID);
1277 // Step 2. Check for aborted search and immediate draw
1278 if (AbortSearch || TM.thread_should_stop(threadID))
1281 if (pos.is_draw() || ply >= PLY_MAX - 1)
1284 // Step 3. Mate distance pruning
1285 if (value_mated_in(ply) >= beta)
1288 if (value_mate_in(ply + 1) < beta)
1291 // Step 4. Transposition table lookup
1293 // We don't want the score of a partial search to overwrite a previous full search
1294 // TT value, so we use a different position key in case of an excluded move exsists.
1295 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1297 tte = TT.retrieve(posKey);
1298 ttMove = (tte ? tte->move() : MOVE_NONE);
1300 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1302 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1303 return value_from_tt(tte->value(), ply);
1306 // Step 5. Evaluate the position statically
1307 isCheck = pos.is_check();
1311 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1312 staticValue = value_from_tt(tte->value(), ply);
1314 staticValue = evaluate(pos, ei, threadID);
1316 ss[ply].eval = staticValue;
1317 futilityValue = staticValue + futility_margin(depth, 0); //FIXME: Remove me, only for split
1318 staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
1319 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1323 if ( !value_is_mate(beta)
1325 && depth < RazorDepth
1326 && staticValue < beta - (0x200 + 16 * depth)
1327 && ss[ply - 1].currentMove != MOVE_NULL
1328 && ttMove == MOVE_NONE
1329 && !pos.has_pawn_on_7th(pos.side_to_move()))
1331 Value rbeta = beta - (0x200 + 16 * depth);
1332 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1334 return v; //FIXME: Logically should be: return (v + 0x200 + 16 * depth);
1337 // Step 7. Static null move pruning
1338 // We're betting that the opponent doesn't have a move that will reduce
1339 // the score by more than fuility_margin(depth) if we do a null move.
1342 && depth < RazorDepth
1343 && staticValue - futility_margin(depth, 0) >= beta)
1344 return staticValue - futility_margin(depth, 0);
1346 // Step 8. Null move search with verification search
1347 // When we jump directly to qsearch() we do a null move only if static value is
1348 // at least beta. Otherwise we do a null move if static value is not more than
1349 // NullMoveMargin under beta.
1353 && !value_is_mate(beta)
1354 && ok_to_do_nullmove(pos)
1355 && staticValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1357 ss[ply].currentMove = MOVE_NULL;
1359 pos.do_null_move(st);
1361 // Null move dynamic reduction based on depth
1362 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1364 // Null move dynamic reduction based on value
1365 if (staticValue - beta > PawnValueMidgame)
1368 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1370 pos.undo_null_move();
1372 if (nullValue >= beta)
1374 if (depth < 6 * OnePly)
1377 // Do zugzwang verification search
1378 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1382 // The null move failed low, which means that we may be faced with
1383 // some kind of threat. If the previous move was reduced, check if
1384 // the move that refuted the null move was somehow connected to the
1385 // move which was reduced. If a connection is found, return a fail
1386 // low score (which will cause the reduced move to fail high in the
1387 // parent node, which will trigger a re-search with full depth).
1388 if (nullValue == value_mated_in(ply + 2))
1391 ss[ply].threatMove = ss[ply + 1].currentMove;
1392 if ( depth < ThreatDepth
1393 && ss[ply - 1].reduction
1394 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1399 // Step 9. Internal iterative deepening
1400 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1401 !isCheck && ss[ply].eval >= beta - IIDMargin)
1403 search(pos, ss, beta, depth/2, ply, false, threadID);
1404 ttMove = ss[ply].pv[ply];
1405 tte = TT.retrieve(posKey);
1408 // Step 10. Loop through moves
1409 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1411 // Initialize a MovePicker object for the current position
1412 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1415 while ( bestValue < beta
1416 && (move = mp.get_next_move()) != MOVE_NONE
1417 && !TM.thread_should_stop(threadID))
1419 assert(move_is_ok(move));
1421 if (move == excludedMove)
1424 moveIsCheck = pos.move_is_check(move, ci);
1425 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1426 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1428 // Step 11. Decide the new search depth
1429 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1431 // Singular extension search. We extend the TT move if its value is much better than
1432 // its siblings. To verify this we do a reduced search on all the other moves but the
1433 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1434 if ( depth >= 8 * OnePly
1436 && move == tte->move()
1437 && !excludedMove // Do not allow recursive single-reply search
1439 && is_lower_bound(tte->type())
1440 && tte->depth() >= depth - 3 * OnePly)
1442 Value ttValue = value_from_tt(tte->value(), ply);
1444 if (abs(ttValue) < VALUE_KNOWN_WIN)
1446 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1448 if (excValue < ttValue - SingleReplyMargin)
1453 newDepth = depth - OnePly + ext;
1455 // Update current move (this must be done after singular extension search)
1456 movesSearched[moveCount++] = ss[ply].currentMove = move;
1458 // Step 12. Futility pruning
1461 && !captureOrPromotion
1462 && !move_is_castle(move)
1465 // Move count based pruning
1466 if ( moveCount >= futility_move_count(depth)
1467 && ok_to_prune(pos, move, ss[ply].threatMove)
1468 && bestValue > value_mated_in(PLY_MAX))
1471 // Value based pruning
1472 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1473 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1474 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1476 if (futilityValueScaled < beta)
1478 if (futilityValueScaled > bestValue)
1479 bestValue = futilityValueScaled;
1484 // Step 13. Make the move
1485 pos.do_move(move, st, ci, moveIsCheck);
1487 // Step 14. Reduced search
1488 // if the move fails high will be re-searched at full depth.
1489 bool doFullDepthSearch = true;
1491 if ( depth >= 3*OnePly
1493 && !captureOrPromotion
1494 && !move_is_castle(move)
1495 && !move_is_killer(move, ss[ply]))
1497 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1498 if (ss[ply].reduction)
1500 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1501 doFullDepthSearch = (value >= beta);
1505 // Step 15. Full depth search
1506 if (doFullDepthSearch)
1508 ss[ply].reduction = Depth(0);
1509 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1512 // Step 16. Undo move
1513 pos.undo_move(move);
1515 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1517 // Step 17. Check for new best move
1518 if (value > bestValue)
1524 if (value == value_mate_in(ply + 1))
1525 ss[ply].mateKiller = move;
1528 // Step 18. Check for split
1529 if ( TM.active_threads() > 1
1531 && depth >= MinimumSplitDepth
1533 && TM.available_thread_exists(threadID)
1535 && !TM.thread_should_stop(threadID)
1536 && TM.split(pos, ss, ply, NULL, beta, &bestValue, futilityValue, //FIXME: SMP & futilityValue
1537 depth, &moveCount, &mp, threadID, false))
1541 // Step 19. Check for mate and stalemate
1542 // All legal moves have been searched and if there were
1543 // no legal moves, it must be mate or stalemate.
1544 // If one move was excluded return fail low.
1546 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1548 // Step 20. Update tables
1549 // If the search is not aborted, update the transposition table,
1550 // history counters, and killer moves.
1551 if (AbortSearch || TM.thread_should_stop(threadID))
1554 if (bestValue < beta)
1555 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1558 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1559 move = ss[ply].pv[ply];
1560 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1561 if (!pos.move_is_capture_or_promotion(move))
1563 update_history(pos, move, depth, movesSearched, moveCount);
1564 update_killers(move, ss[ply]);
1569 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1575 // qsearch() is the quiescence search function, which is called by the main
1576 // search function when the remaining depth is zero (or, to be more precise,
1577 // less than OnePly).
1579 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1580 Depth depth, int ply, int threadID) {
1582 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1583 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1585 assert(ply >= 0 && ply < PLY_MAX);
1586 assert(threadID >= 0 && threadID < TM.active_threads());
1591 Value staticValue, bestValue, value, futilityBase, futilityValue;
1592 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1593 const TTEntry* tte = NULL;
1595 bool pvNode = (beta - alpha != 1);
1596 Value oldAlpha = alpha;
1598 // Initialize, and make an early exit in case of an aborted search,
1599 // an instant draw, maximum ply reached, etc.
1600 init_node(ss, ply, threadID);
1602 // After init_node() that calls poll()
1603 if (AbortSearch || TM.thread_should_stop(threadID))
1606 if (pos.is_draw() || ply >= PLY_MAX - 1)
1609 // Transposition table lookup. At PV nodes, we don't use the TT for
1610 // pruning, but only for move ordering.
1611 tte = TT.retrieve(pos.get_key());
1612 ttMove = (tte ? tte->move() : MOVE_NONE);
1614 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1616 assert(tte->type() != VALUE_TYPE_EVAL);
1618 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1619 return value_from_tt(tte->value(), ply);
1622 isCheck = pos.is_check();
1624 // Evaluate the position statically
1626 staticValue = -VALUE_INFINITE;
1627 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1628 staticValue = value_from_tt(tte->value(), ply);
1630 staticValue = evaluate(pos, ei, threadID);
1634 ss[ply].eval = staticValue;
1635 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1638 // Initialize "stand pat score", and return it immediately if it is
1640 bestValue = staticValue;
1642 if (bestValue >= beta)
1644 // Store the score to avoid a future costly evaluation() call
1645 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1646 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1651 if (bestValue > alpha)
1654 // If we are near beta then try to get a cutoff pushing checks a bit further
1655 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1657 // Initialize a MovePicker object for the current position, and prepare
1658 // to search the moves. Because the depth is <= 0 here, only captures,
1659 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1660 // and we are near beta) will be generated.
1661 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1663 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1664 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1666 // Loop through the moves until no moves remain or a beta cutoff
1668 while ( alpha < beta
1669 && (move = mp.get_next_move()) != MOVE_NONE)
1671 assert(move_is_ok(move));
1673 moveIsCheck = pos.move_is_check(move, ci);
1675 // Update current move
1677 ss[ply].currentMove = move;
1685 && !move_is_promotion(move)
1686 && !pos.move_is_passed_pawn_push(move))
1688 futilityValue = futilityBase
1689 + pos.endgame_value_of_piece_on(move_to(move))
1690 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1692 if (futilityValue < alpha)
1694 if (futilityValue > bestValue)
1695 bestValue = futilityValue;
1700 // Detect blocking evasions that are candidate to be pruned
1701 evasionPrunable = isCheck
1702 && bestValue != -VALUE_INFINITE
1703 && !pos.move_is_capture(move)
1704 && pos.type_of_piece_on(move_from(move)) != KING
1705 && !pos.can_castle(pos.side_to_move());
1707 // Don't search moves with negative SEE values
1708 if ( (!isCheck || evasionPrunable)
1711 && !move_is_promotion(move)
1712 && pos.see_sign(move) < 0)
1715 // Make and search the move
1716 pos.do_move(move, st, ci, moveIsCheck);
1717 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1718 pos.undo_move(move);
1720 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1723 if (value > bestValue)
1734 // All legal moves have been searched. A special case: If we're in check
1735 // and no legal moves were found, it is checkmate.
1736 if (!moveCount && pos.is_check()) // Mate!
1737 return value_mated_in(ply);
1739 // Update transposition table
1740 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1741 if (bestValue <= oldAlpha)
1743 // If bestValue isn't changed it means it is still the static evaluation
1744 // of the node, so keep this info to avoid a future evaluation() call.
1745 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1746 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1748 else if (bestValue >= beta)
1750 move = ss[ply].pv[ply];
1751 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1753 // Update killers only for good checking moves
1754 if (!pos.move_is_capture_or_promotion(move))
1755 update_killers(move, ss[ply]);
1758 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1760 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1766 // sp_search() is used to search from a split point. This function is called
1767 // by each thread working at the split point. It is similar to the normal
1768 // search() function, but simpler. Because we have already probed the hash
1769 // table, done a null move search, and searched the first move before
1770 // splitting, we don't have to repeat all this work in sp_search(). We
1771 // also don't need to store anything to the hash table here: This is taken
1772 // care of after we return from the split point.
1774 void sp_search(SplitPoint* sp, int threadID) {
1776 assert(threadID >= 0 && threadID < TM.active_threads());
1777 assert(TM.active_threads() > 1);
1779 Position pos(*sp->pos);
1781 SearchStack* ss = sp->sstack[threadID];
1782 Value value = -VALUE_INFINITE;
1785 bool isCheck = pos.is_check();
1786 bool useFutilityPruning = sp->depth < 7 * OnePly //FIXME: sync with search
1789 while ( lock_grab_bool(&(sp->lock))
1790 && sp->bestValue < sp->beta
1791 && !TM.thread_should_stop(threadID)
1792 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1794 moveCount = ++sp->moves;
1795 lock_release(&(sp->lock));
1797 assert(move_is_ok(move));
1799 bool moveIsCheck = pos.move_is_check(move, ci);
1800 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1802 ss[sp->ply].currentMove = move;
1804 // Decide the new search depth
1806 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1807 Depth newDepth = sp->depth - OnePly + ext;
1810 if ( useFutilityPruning
1812 && !captureOrPromotion)
1814 // Move count based pruning
1815 if ( moveCount >= futility_move_count(sp->depth)
1816 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1817 && sp->bestValue > value_mated_in(PLY_MAX))
1820 // Value based pruning
1821 Value futilityValueScaled = sp->futilityValue - moveCount * 8; //FIXME: sync with search
1823 if (futilityValueScaled < sp->beta)
1825 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1827 lock_grab(&(sp->lock));
1828 if (futilityValueScaled > sp->bestValue)
1829 sp->bestValue = futilityValueScaled;
1830 lock_release(&(sp->lock));
1836 // Make and search the move.
1838 pos.do_move(move, st, ci, moveIsCheck);
1840 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1841 // if the move fails high will be re-searched at full depth.
1842 bool doFullDepthSearch = true;
1845 && !captureOrPromotion
1846 && !move_is_castle(move)
1847 && !move_is_killer(move, ss[sp->ply]))
1849 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1850 if (ss[sp->ply].reduction)
1852 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1853 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1857 if (doFullDepthSearch) // Go with full depth non-pv search
1859 ss[sp->ply].reduction = Depth(0);
1860 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1862 pos.undo_move(move);
1864 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1867 if (value > sp->bestValue) // Less then 2% of cases
1869 lock_grab(&(sp->lock));
1870 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1872 sp->bestValue = value;
1873 if (sp->bestValue >= sp->beta)
1875 sp->stopRequest = true;
1876 sp_update_pv(sp->parentSstack, ss, sp->ply);
1879 lock_release(&(sp->lock));
1883 /* Here we have the lock still grabbed */
1886 sp->slaves[threadID] = 0;
1888 lock_release(&(sp->lock));
1892 // sp_search_pv() is used to search from a PV split point. This function
1893 // is called by each thread working at the split point. It is similar to
1894 // the normal search_pv() function, but simpler. Because we have already
1895 // probed the hash table and searched the first move before splitting, we
1896 // don't have to repeat all this work in sp_search_pv(). We also don't
1897 // need to store anything to the hash table here: This is taken care of
1898 // after we return from the split point.
1900 void sp_search_pv(SplitPoint* sp, int threadID) {
1902 assert(threadID >= 0 && threadID < TM.active_threads());
1903 assert(TM.active_threads() > 1);
1905 Position pos(*sp->pos);
1907 SearchStack* ss = sp->sstack[threadID];
1908 Value value = -VALUE_INFINITE;
1912 while ( lock_grab_bool(&(sp->lock))
1913 && sp->alpha < sp->beta
1914 && !TM.thread_should_stop(threadID)
1915 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1917 moveCount = ++sp->moves;
1918 lock_release(&(sp->lock));
1920 assert(move_is_ok(move));
1922 bool moveIsCheck = pos.move_is_check(move, ci);
1923 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1925 ss[sp->ply].currentMove = move;
1927 // Decide the new search depth
1929 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1930 Depth newDepth = sp->depth - OnePly + ext;
1932 // Make and search the move.
1934 pos.do_move(move, st, ci, moveIsCheck);
1936 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1937 // if the move fails high will be re-searched at full depth.
1938 bool doFullDepthSearch = true;
1941 && !captureOrPromotion
1942 && !move_is_castle(move)
1943 && !move_is_killer(move, ss[sp->ply]))
1945 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1946 if (ss[sp->ply].reduction)
1948 Value localAlpha = sp->alpha;
1949 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1950 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1954 if (doFullDepthSearch) // Go with full depth non-pv search
1956 Value localAlpha = sp->alpha;
1957 ss[sp->ply].reduction = Depth(0);
1958 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1960 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1962 // If another thread has failed high then sp->alpha has been increased
1963 // to be higher or equal then beta, if so, avoid to start a PV search.
1964 localAlpha = sp->alpha;
1965 if (localAlpha < sp->beta)
1966 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1969 pos.undo_move(move);
1971 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1974 if (value > sp->bestValue) // Less then 2% of cases
1976 lock_grab(&(sp->lock));
1977 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1979 sp->bestValue = value;
1980 if (value > sp->alpha)
1982 // Ask threads to stop before to modify sp->alpha
1983 if (value >= sp->beta)
1984 sp->stopRequest = true;
1988 sp_update_pv(sp->parentSstack, ss, sp->ply);
1989 if (value == value_mate_in(sp->ply + 1))
1990 ss[sp->ply].mateKiller = move;
1993 lock_release(&(sp->lock));
1997 /* Here we have the lock still grabbed */
2000 sp->slaves[threadID] = 0;
2002 lock_release(&(sp->lock));
2006 // init_node() is called at the beginning of all the search functions
2007 // (search(), search_pv(), qsearch(), and so on) and initializes the
2008 // search stack object corresponding to the current node. Once every
2009 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2010 // for user input and checks whether it is time to stop the search.
2012 void init_node(SearchStack ss[], int ply, int threadID) {
2014 assert(ply >= 0 && ply < PLY_MAX);
2015 assert(threadID >= 0 && threadID < TM.active_threads());
2017 TM.incrementNodeCounter(threadID);
2022 if (NodesSincePoll >= NodesBetweenPolls)
2029 ss[ply + 2].initKillers();
2030 TM.print_current_line(ss, ply, threadID);
2034 // update_pv() is called whenever a search returns a value > alpha.
2035 // It updates the PV in the SearchStack object corresponding to the
2038 void update_pv(SearchStack ss[], int ply) {
2040 assert(ply >= 0 && ply < PLY_MAX);
2044 ss[ply].pv[ply] = ss[ply].currentMove;
2046 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2047 ss[ply].pv[p] = ss[ply + 1].pv[p];
2049 ss[ply].pv[p] = MOVE_NONE;
2053 // sp_update_pv() is a variant of update_pv for use at split points. The
2054 // difference between the two functions is that sp_update_pv also updates
2055 // the PV at the parent node.
2057 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2059 assert(ply >= 0 && ply < PLY_MAX);
2063 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2065 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2066 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2068 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2072 // connected_moves() tests whether two moves are 'connected' in the sense
2073 // that the first move somehow made the second move possible (for instance
2074 // if the moving piece is the same in both moves). The first move is assumed
2075 // to be the move that was made to reach the current position, while the
2076 // second move is assumed to be a move from the current position.
2078 bool connected_moves(const Position& pos, Move m1, Move m2) {
2080 Square f1, t1, f2, t2;
2083 assert(move_is_ok(m1));
2084 assert(move_is_ok(m2));
2086 if (m2 == MOVE_NONE)
2089 // Case 1: The moving piece is the same in both moves
2095 // Case 2: The destination square for m2 was vacated by m1
2101 // Case 3: Moving through the vacated square
2102 if ( piece_is_slider(pos.piece_on(f2))
2103 && bit_is_set(squares_between(f2, t2), f1))
2106 // Case 4: The destination square for m2 is defended by the moving piece in m1
2107 p = pos.piece_on(t1);
2108 if (bit_is_set(pos.attacks_from(p, t1), t2))
2111 // Case 5: Discovered check, checking piece is the piece moved in m1
2112 if ( piece_is_slider(p)
2113 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2114 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2116 // discovered_check_candidates() works also if the Position's side to
2117 // move is the opposite of the checking piece.
2118 Color them = opposite_color(pos.side_to_move());
2119 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2121 if (bit_is_set(dcCandidates, f2))
2128 // value_is_mate() checks if the given value is a mate one
2129 // eventually compensated for the ply.
2131 bool value_is_mate(Value value) {
2133 assert(abs(value) <= VALUE_INFINITE);
2135 return value <= value_mated_in(PLY_MAX)
2136 || value >= value_mate_in(PLY_MAX);
2140 // move_is_killer() checks if the given move is among the
2141 // killer moves of that ply.
2143 bool move_is_killer(Move m, const SearchStack& ss) {
2145 const Move* k = ss.killers;
2146 for (int i = 0; i < KILLER_MAX; i++, k++)
2154 // extension() decides whether a move should be searched with normal depth,
2155 // or with extended depth. Certain classes of moves (checking moves, in
2156 // particular) are searched with bigger depth than ordinary moves and in
2157 // any case are marked as 'dangerous'. Note that also if a move is not
2158 // extended, as example because the corresponding UCI option is set to zero,
2159 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2161 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2162 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2164 assert(m != MOVE_NONE);
2166 Depth result = Depth(0);
2167 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2172 result += CheckExtension[pvNode];
2175 result += SingleEvasionExtension[pvNode];
2178 result += MateThreatExtension[pvNode];
2181 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2183 Color c = pos.side_to_move();
2184 if (relative_rank(c, move_to(m)) == RANK_7)
2186 result += PawnPushTo7thExtension[pvNode];
2189 if (pos.pawn_is_passed(c, move_to(m)))
2191 result += PassedPawnExtension[pvNode];
2196 if ( captureOrPromotion
2197 && pos.type_of_piece_on(move_to(m)) != PAWN
2198 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2199 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2200 && !move_is_promotion(m)
2203 result += PawnEndgameExtension[pvNode];
2208 && captureOrPromotion
2209 && pos.type_of_piece_on(move_to(m)) != PAWN
2210 && pos.see_sign(m) >= 0)
2216 return Min(result, OnePly);
2220 // ok_to_do_nullmove() looks at the current position and decides whether
2221 // doing a 'null move' should be allowed. In order to avoid zugzwang
2222 // problems, null moves are not allowed when the side to move has very
2223 // little material left. Currently, the test is a bit too simple: Null
2224 // moves are avoided only when the side to move has only pawns left.
2225 // It's probably a good idea to avoid null moves in at least some more
2226 // complicated endgames, e.g. KQ vs KR. FIXME
2228 bool ok_to_do_nullmove(const Position& pos) {
2230 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2234 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2235 // non-tactical moves late in the move list close to the leaves are
2236 // candidates for pruning.
2238 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2240 assert(move_is_ok(m));
2241 assert(threat == MOVE_NONE || move_is_ok(threat));
2242 assert(!pos.move_is_check(m));
2243 assert(!pos.move_is_capture_or_promotion(m));
2244 assert(!pos.move_is_passed_pawn_push(m));
2246 Square mfrom, mto, tfrom, tto;
2248 // Prune if there isn't any threat move
2249 if (threat == MOVE_NONE)
2252 mfrom = move_from(m);
2254 tfrom = move_from(threat);
2255 tto = move_to(threat);
2257 // Case 1: Don't prune moves which move the threatened piece
2261 // Case 2: If the threatened piece has value less than or equal to the
2262 // value of the threatening piece, don't prune move which defend it.
2263 if ( pos.move_is_capture(threat)
2264 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2265 || pos.type_of_piece_on(tfrom) == KING)
2266 && pos.move_attacks_square(m, tto))
2269 // Case 3: If the moving piece in the threatened move is a slider, don't
2270 // prune safe moves which block its ray.
2271 if ( piece_is_slider(pos.piece_on(tfrom))
2272 && bit_is_set(squares_between(tfrom, tto), mto)
2273 && pos.see_sign(m) >= 0)
2280 // ok_to_use_TT() returns true if a transposition table score
2281 // can be used at a given point in search.
2283 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2285 Value v = value_from_tt(tte->value(), ply);
2287 return ( tte->depth() >= depth
2288 || v >= Max(value_mate_in(PLY_MAX), beta)
2289 || v < Min(value_mated_in(PLY_MAX), beta))
2291 && ( (is_lower_bound(tte->type()) && v >= beta)
2292 || (is_upper_bound(tte->type()) && v < beta));
2296 // refine_eval() returns the transposition table score if
2297 // possible otherwise falls back on static position evaluation.
2299 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2304 Value v = value_from_tt(tte->value(), ply);
2306 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2307 || (is_upper_bound(tte->type()) && v < defaultEval))
2314 // update_history() registers a good move that produced a beta-cutoff
2315 // in history and marks as failures all the other moves of that ply.
2317 void update_history(const Position& pos, Move move, Depth depth,
2318 Move movesSearched[], int moveCount) {
2322 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2324 for (int i = 0; i < moveCount - 1; i++)
2326 m = movesSearched[i];
2330 if (!pos.move_is_capture_or_promotion(m))
2331 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2336 // update_killers() add a good move that produced a beta-cutoff
2337 // among the killer moves of that ply.
2339 void update_killers(Move m, SearchStack& ss) {
2341 if (m == ss.killers[0])
2344 for (int i = KILLER_MAX - 1; i > 0; i--)
2345 ss.killers[i] = ss.killers[i - 1];
2351 // update_gains() updates the gains table of a non-capture move given
2352 // the static position evaluation before and after the move.
2354 void update_gains(const Position& pos, Move m, Value before, Value after) {
2357 && before != VALUE_NONE
2358 && after != VALUE_NONE
2359 && pos.captured_piece() == NO_PIECE_TYPE
2360 && !move_is_castle(m)
2361 && !move_is_promotion(m))
2362 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2366 // current_search_time() returns the number of milliseconds which have passed
2367 // since the beginning of the current search.
2369 int current_search_time() {
2371 return get_system_time() - SearchStartTime;
2375 // nps() computes the current nodes/second count.
2379 int t = current_search_time();
2380 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2384 // poll() performs two different functions: It polls for user input, and it
2385 // looks at the time consumed so far and decides if it's time to abort the
2390 static int lastInfoTime;
2391 int t = current_search_time();
2396 // We are line oriented, don't read single chars
2397 std::string command;
2399 if (!std::getline(std::cin, command))
2402 if (command == "quit")
2405 PonderSearch = false;
2409 else if (command == "stop")
2412 PonderSearch = false;
2414 else if (command == "ponderhit")
2418 // Print search information
2422 else if (lastInfoTime > t)
2423 // HACK: Must be a new search where we searched less than
2424 // NodesBetweenPolls nodes during the first second of search.
2427 else if (t - lastInfoTime >= 1000)
2430 lock_grab(&TM.IOLock);
2435 if (dbg_show_hit_rate)
2436 dbg_print_hit_rate();
2438 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2439 << " time " << t << " hashfull " << TT.full() << endl;
2441 lock_release(&TM.IOLock);
2443 if (ShowCurrentLine)
2444 TM.threads[0].printCurrentLineRequest = true;
2447 // Should we stop the search?
2451 bool stillAtFirstMove = RootMoveNumber == 1
2452 && !AspirationFailLow
2453 && t > MaxSearchTime + ExtraSearchTime;
2455 bool noMoreTime = t > AbsoluteMaxSearchTime
2456 || stillAtFirstMove;
2458 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2459 || (ExactMaxTime && t >= ExactMaxTime)
2460 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2465 // ponderhit() is called when the program is pondering (i.e. thinking while
2466 // it's the opponent's turn to move) in order to let the engine know that
2467 // it correctly predicted the opponent's move.
2471 int t = current_search_time();
2472 PonderSearch = false;
2474 bool stillAtFirstMove = RootMoveNumber == 1
2475 && !AspirationFailLow
2476 && t > MaxSearchTime + ExtraSearchTime;
2478 bool noMoreTime = t > AbsoluteMaxSearchTime
2479 || stillAtFirstMove;
2481 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2486 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2488 void init_ss_array(SearchStack ss[]) {
2490 for (int i = 0; i < 3; i++)
2493 ss[i].initKillers();
2498 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2499 // while the program is pondering. The point is to work around a wrinkle in
2500 // the UCI protocol: When pondering, the engine is not allowed to give a
2501 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2502 // We simply wait here until one of these commands is sent, and return,
2503 // after which the bestmove and pondermove will be printed (in id_loop()).
2505 void wait_for_stop_or_ponderhit() {
2507 std::string command;
2511 if (!std::getline(std::cin, command))
2514 if (command == "quit")
2519 else if (command == "ponderhit" || command == "stop")
2525 // init_thread() is the function which is called when a new thread is
2526 // launched. It simply calls the idle_loop() function with the supplied
2527 // threadID. There are two versions of this function; one for POSIX
2528 // threads and one for Windows threads.
2530 #if !defined(_MSC_VER)
2532 void* init_thread(void *threadID) {
2534 TM.idle_loop(*(int*)threadID, NULL);
2540 DWORD WINAPI init_thread(LPVOID threadID) {
2542 TM.idle_loop(*(int*)threadID, NULL);
2549 /// The ThreadsManager class
2551 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2552 // get_beta_counters() are getters/setters for the per thread
2553 // counters used to sort the moves at root.
2555 void ThreadsManager::resetNodeCounters() {
2557 for (int i = 0; i < MAX_THREADS; i++)
2558 threads[i].nodes = 0ULL;
2561 void ThreadsManager::resetBetaCounters() {
2563 for (int i = 0; i < MAX_THREADS; i++)
2564 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2567 int64_t ThreadsManager::nodes_searched() const {
2569 int64_t result = 0ULL;
2570 for (int i = 0; i < ActiveThreads; i++)
2571 result += threads[i].nodes;
2576 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2579 for (int i = 0; i < MAX_THREADS; i++)
2581 our += threads[i].betaCutOffs[us];
2582 their += threads[i].betaCutOffs[opposite_color(us)];
2587 // idle_loop() is where the threads are parked when they have no work to do.
2588 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2589 // object for which the current thread is the master.
2591 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2593 assert(threadID >= 0 && threadID < MAX_THREADS);
2597 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2598 // master should exit as last one.
2599 if (AllThreadsShouldExit)
2602 threads[threadID].state = THREAD_TERMINATED;
2606 // If we are not thinking, wait for a condition to be signaled
2607 // instead of wasting CPU time polling for work.
2608 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2611 assert(threadID != 0);
2612 threads[threadID].state = THREAD_SLEEPING;
2614 #if !defined(_MSC_VER)
2615 pthread_mutex_lock(&WaitLock);
2616 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2617 pthread_cond_wait(&WaitCond, &WaitLock);
2618 pthread_mutex_unlock(&WaitLock);
2620 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2624 // If thread has just woken up, mark it as available
2625 if (threads[threadID].state == THREAD_SLEEPING)
2626 threads[threadID].state = THREAD_AVAILABLE;
2628 // If this thread has been assigned work, launch a search
2629 if (threads[threadID].state == THREAD_WORKISWAITING)
2631 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2633 threads[threadID].state = THREAD_SEARCHING;
2635 if (threads[threadID].splitPoint->pvNode)
2636 sp_search_pv(threads[threadID].splitPoint, threadID);
2638 sp_search(threads[threadID].splitPoint, threadID);
2640 assert(threads[threadID].state == THREAD_SEARCHING);
2642 threads[threadID].state = THREAD_AVAILABLE;
2645 // If this thread is the master of a split point and all threads have
2646 // finished their work at this split point, return from the idle loop.
2647 if (waitSp != NULL && waitSp->cpus == 0)
2649 assert(threads[threadID].state == THREAD_AVAILABLE);
2651 threads[threadID].state = THREAD_SEARCHING;
2658 // init_threads() is called during startup. It launches all helper threads,
2659 // and initializes the split point stack and the global locks and condition
2662 void ThreadsManager::init_threads() {
2667 #if !defined(_MSC_VER)
2668 pthread_t pthread[1];
2671 // Initialize global locks
2672 lock_init(&MPLock, NULL);
2673 lock_init(&IOLock, NULL);
2675 // Initialize SplitPointStack locks
2676 for (i = 0; i < MAX_THREADS; i++)
2677 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2679 SplitPointStack[i][j].parent = NULL;
2680 lock_init(&(SplitPointStack[i][j].lock), NULL);
2683 #if !defined(_MSC_VER)
2684 pthread_mutex_init(&WaitLock, NULL);
2685 pthread_cond_init(&WaitCond, NULL);
2687 for (i = 0; i < MAX_THREADS; i++)
2688 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2691 // Will be set just before program exits to properly end the threads
2692 AllThreadsShouldExit = false;
2694 // Threads will be put to sleep as soon as created
2695 AllThreadsShouldSleep = true;
2697 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2699 threads[0].state = THREAD_SEARCHING;
2700 for (i = 1; i < MAX_THREADS; i++)
2701 threads[i].state = THREAD_AVAILABLE;
2703 // Launch the helper threads
2704 for (i = 1; i < MAX_THREADS; i++)
2707 #if !defined(_MSC_VER)
2708 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2711 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
2716 cout << "Failed to create thread number " << i << endl;
2717 Application::exit_with_failure();
2720 // Wait until the thread has finished launching and is gone to sleep
2721 while (threads[i].state != THREAD_SLEEPING);
2726 // exit_threads() is called when the program exits. It makes all the
2727 // helper threads exit cleanly.
2729 void ThreadsManager::exit_threads() {
2731 ActiveThreads = MAX_THREADS; // HACK
2732 AllThreadsShouldSleep = true; // HACK
2733 wake_sleeping_threads();
2735 // This makes the threads to exit idle_loop()
2736 AllThreadsShouldExit = true;
2738 // Wait for thread termination
2739 for (int i = 1; i < MAX_THREADS; i++)
2740 while (threads[i].state != THREAD_TERMINATED);
2742 // Now we can safely destroy the locks
2743 for (int i = 0; i < MAX_THREADS; i++)
2744 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2745 lock_destroy(&(SplitPointStack[i][j].lock));
2749 // thread_should_stop() checks whether the thread should stop its search.
2750 // This can happen if a beta cutoff has occurred in the thread's currently
2751 // active split point, or in some ancestor of the current split point.
2753 bool ThreadsManager::thread_should_stop(int threadID) const {
2755 assert(threadID >= 0 && threadID < ActiveThreads);
2759 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2764 // thread_is_available() checks whether the thread with threadID "slave" is
2765 // available to help the thread with threadID "master" at a split point. An
2766 // obvious requirement is that "slave" must be idle. With more than two
2767 // threads, this is not by itself sufficient: If "slave" is the master of
2768 // some active split point, it is only available as a slave to the other
2769 // threads which are busy searching the split point at the top of "slave"'s
2770 // split point stack (the "helpful master concept" in YBWC terminology).
2772 bool ThreadsManager::thread_is_available(int slave, int master) const {
2774 assert(slave >= 0 && slave < ActiveThreads);
2775 assert(master >= 0 && master < ActiveThreads);
2776 assert(ActiveThreads > 1);
2778 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2781 // Make a local copy to be sure doesn't change under our feet
2782 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2784 if (localActiveSplitPoints == 0)
2785 // No active split points means that the thread is available as
2786 // a slave for any other thread.
2789 if (ActiveThreads == 2)
2792 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2793 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2794 // could have been set to 0 by another thread leading to an out of bound access.
2795 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2802 // available_thread_exists() tries to find an idle thread which is available as
2803 // a slave for the thread with threadID "master".
2805 bool ThreadsManager::available_thread_exists(int master) const {
2807 assert(master >= 0 && master < ActiveThreads);
2808 assert(ActiveThreads > 1);
2810 for (int i = 0; i < ActiveThreads; i++)
2811 if (thread_is_available(i, master))
2818 // split() does the actual work of distributing the work at a node between
2819 // several threads at PV nodes. If it does not succeed in splitting the
2820 // node (because no idle threads are available, or because we have no unused
2821 // split point objects), the function immediately returns false. If
2822 // splitting is possible, a SplitPoint object is initialized with all the
2823 // data that must be copied to the helper threads (the current position and
2824 // search stack, alpha, beta, the search depth, etc.), and we tell our
2825 // helper threads that they have been assigned work. This will cause them
2826 // to instantly leave their idle loops and call sp_search_pv(). When all
2827 // threads have returned from sp_search_pv (or, equivalently, when
2828 // splitPoint->cpus becomes 0), split() returns true.
2830 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2831 Value* alpha, const Value beta, Value* bestValue, const Value futilityValue,
2832 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2835 assert(sstck != NULL);
2836 assert(ply >= 0 && ply < PLY_MAX);
2837 assert(*bestValue >= -VALUE_INFINITE);
2838 assert( ( pvNode && *bestValue <= *alpha)
2839 || (!pvNode && *bestValue < beta ));
2840 assert(!pvNode || *alpha < beta);
2841 assert(beta <= VALUE_INFINITE);
2842 assert(depth > Depth(0));
2843 assert(master >= 0 && master < ActiveThreads);
2844 assert(ActiveThreads > 1);
2846 SplitPoint* splitPoint;
2850 // If no other thread is available to help us, or if we have too many
2851 // active split points, don't split.
2852 if ( !available_thread_exists(master)
2853 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2855 lock_release(&MPLock);
2859 // Pick the next available split point object from the split point stack
2860 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2862 // Initialize the split point object
2863 splitPoint->parent = threads[master].splitPoint;
2864 splitPoint->stopRequest = false;
2865 splitPoint->ply = ply;
2866 splitPoint->depth = depth;
2867 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2868 splitPoint->beta = beta;
2869 splitPoint->pvNode = pvNode;
2870 splitPoint->bestValue = *bestValue;
2871 splitPoint->futilityValue = futilityValue;
2872 splitPoint->master = master;
2873 splitPoint->mp = mp;
2874 splitPoint->moves = *moves;
2875 splitPoint->cpus = 1;
2876 splitPoint->pos = &p;
2877 splitPoint->parentSstack = sstck;
2878 for (int i = 0; i < ActiveThreads; i++)
2879 splitPoint->slaves[i] = 0;
2881 threads[master].splitPoint = splitPoint;
2882 threads[master].activeSplitPoints++;
2884 // If we are here it means we are not available
2885 assert(threads[master].state != THREAD_AVAILABLE);
2887 // Allocate available threads setting state to THREAD_BOOKED
2888 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2889 if (thread_is_available(i, master))
2891 threads[i].state = THREAD_BOOKED;
2892 threads[i].splitPoint = splitPoint;
2893 splitPoint->slaves[i] = 1;
2897 assert(splitPoint->cpus > 1);
2899 // We can release the lock because slave threads are already booked and master is not available
2900 lock_release(&MPLock);
2902 // Tell the threads that they have work to do. This will make them leave
2903 // their idle loop. But before copy search stack tail for each thread.
2904 for (int i = 0; i < ActiveThreads; i++)
2905 if (i == master || splitPoint->slaves[i])
2907 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2909 assert(i == master || threads[i].state == THREAD_BOOKED);
2911 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2914 // Everything is set up. The master thread enters the idle loop, from
2915 // which it will instantly launch a search, because its state is
2916 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2917 // idle loop, which means that the main thread will return from the idle
2918 // loop when all threads have finished their work at this split point
2919 // (i.e. when splitPoint->cpus == 0).
2920 idle_loop(master, splitPoint);
2922 // We have returned from the idle loop, which means that all threads are
2923 // finished. Update alpha, beta and bestValue, and return.
2927 *alpha = splitPoint->alpha;
2929 *bestValue = splitPoint->bestValue;
2930 threads[master].activeSplitPoints--;
2931 threads[master].splitPoint = splitPoint->parent;
2933 lock_release(&MPLock);
2938 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2939 // to start a new search from the root.
2941 void ThreadsManager::wake_sleeping_threads() {
2943 assert(AllThreadsShouldSleep);
2944 assert(ActiveThreads > 0);
2946 AllThreadsShouldSleep = false;
2948 if (ActiveThreads == 1)
2951 for (int i = 1; i < ActiveThreads; i++)
2952 assert(threads[i].state == THREAD_SLEEPING);
2954 #if !defined(_MSC_VER)
2955 pthread_mutex_lock(&WaitLock);
2956 pthread_cond_broadcast(&WaitCond);
2957 pthread_mutex_unlock(&WaitLock);
2959 for (int i = 1; i < MAX_THREADS; i++)
2960 SetEvent(SitIdleEvent[i]);
2966 // put_threads_to_sleep() makes all the threads go to sleep just before
2967 // to leave think(), at the end of the search. Threads should have already
2968 // finished the job and should be idle.
2970 void ThreadsManager::put_threads_to_sleep() {
2972 assert(!AllThreadsShouldSleep);
2974 // This makes the threads to go to sleep
2975 AllThreadsShouldSleep = true;
2977 // Reset flags to a known state.
2978 for (int i = 1; i < ActiveThreads; i++)
2980 // This flag can be in a random state
2981 threads[i].printCurrentLineRequest = false;
2985 // print_current_line() prints _once_ the current line of search for a
2986 // given thread and then setup the print request for the next thread.
2987 // Called when the UCI option UCI_ShowCurrLine is 'true'.
2989 void ThreadsManager::print_current_line(SearchStack ss[], int ply, int threadID) {
2991 assert(ply >= 0 && ply < PLY_MAX);
2992 assert(threadID >= 0 && threadID < ActiveThreads);
2994 if (!threads[threadID].printCurrentLineRequest)
2998 threads[threadID].printCurrentLineRequest = false;
3000 if (threads[threadID].state == THREAD_SEARCHING)
3003 cout << "info currline " << (threadID + 1);
3004 for (int p = 0; p < ply; p++)
3005 cout << " " << ss[p].currentMove;
3008 lock_release(&IOLock);
3011 // Setup print request for the next thread ID
3012 if (threadID + 1 < ActiveThreads)
3013 threads[threadID + 1].printCurrentLineRequest = true;
3017 /// The RootMoveList class
3019 // RootMoveList c'tor
3021 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3023 SearchStack ss[PLY_MAX_PLUS_2];
3024 MoveStack mlist[MaxRootMoves];
3026 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3028 // Generate all legal moves
3029 MoveStack* last = generate_moves(pos, mlist);
3031 // Add each move to the moves[] array
3032 for (MoveStack* cur = mlist; cur != last; cur++)
3034 bool includeMove = includeAllMoves;
3036 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3037 includeMove = (searchMoves[k] == cur->move);
3042 // Find a quick score for the move
3044 pos.do_move(cur->move, st);
3045 moves[count].move = cur->move;
3046 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3047 moves[count].pv[0] = cur->move;
3048 moves[count].pv[1] = MOVE_NONE;
3049 pos.undo_move(cur->move);
3056 // RootMoveList simple methods definitions
3058 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3060 moves[moveNum].nodes = nodes;
3061 moves[moveNum].cumulativeNodes += nodes;
3064 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3066 moves[moveNum].ourBeta = our;
3067 moves[moveNum].theirBeta = their;
3070 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3074 for (j = 0; pv[j] != MOVE_NONE; j++)
3075 moves[moveNum].pv[j] = pv[j];
3077 moves[moveNum].pv[j] = MOVE_NONE;
3081 // RootMoveList::sort() sorts the root move list at the beginning of a new
3084 void RootMoveList::sort() {
3086 sort_multipv(count - 1); // Sort all items
3090 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3091 // list by their scores and depths. It is used to order the different PVs
3092 // correctly in MultiPV mode.
3094 void RootMoveList::sort_multipv(int n) {
3098 for (i = 1; i <= n; i++)
3100 RootMove rm = moves[i];
3101 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3102 moves[j] = moves[j - 1];