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 // 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, VALUE_NONE,
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, staticValue, nullValue, value, futilityValue, futilityValueScaled;
1276 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1277 bool mateThreat = false;
1279 futilityValue = staticValue = 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 exsists.
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 staticValue = value_from_tt(tte->value(), ply);
1325 staticValue = evaluate(pos, ei, threadID);
1327 ss[ply].eval = staticValue;
1328 futilityValue = staticValue + futility_margin(depth, 0); //FIXME: Remove me, only for split
1329 staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
1330 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1334 if ( !value_is_mate(beta)
1336 && depth < RazorDepth
1337 && staticValue < beta - (0x200 + 16 * depth)
1338 && ss[ply - 1].currentMove != MOVE_NULL
1339 && ttMove == MOVE_NONE
1340 && !pos.has_pawn_on_7th(pos.side_to_move()))
1342 Value rbeta = beta - (0x200 + 16 * depth);
1343 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1345 return v; //FIXME: Logically should be: return (v + 0x200 + 16 * depth);
1348 // Step 7. Static null move pruning
1349 // We're betting that the opponent doesn't have a move that will reduce
1350 // the score by more than fuility_margin(depth) if we do a null move.
1353 && depth < RazorDepth
1354 && staticValue - futility_margin(depth, 0) >= beta)
1355 return staticValue - futility_margin(depth, 0);
1357 // Step 8. Null move search with verification search
1358 // When we jump directly to qsearch() we do a null move only if static value is
1359 // at least beta. Otherwise we do a null move if static value is not more than
1360 // NullMoveMargin under beta.
1364 && !value_is_mate(beta)
1365 && ok_to_do_nullmove(pos)
1366 && staticValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1368 ss[ply].currentMove = MOVE_NULL;
1370 pos.do_null_move(st);
1372 // Null move dynamic reduction based on depth
1373 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1375 // Null move dynamic reduction based on value
1376 if (staticValue - beta > PawnValueMidgame)
1379 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1381 pos.undo_null_move();
1383 if (nullValue >= beta)
1385 if (depth < 6 * OnePly)
1388 // Do zugzwang verification search
1389 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1393 // The null move failed low, which means that we may be faced with
1394 // some kind of threat. If the previous move was reduced, check if
1395 // the move that refuted the null move was somehow connected to the
1396 // move which was reduced. If a connection is found, return a fail
1397 // low score (which will cause the reduced move to fail high in the
1398 // parent node, which will trigger a re-search with full depth).
1399 if (nullValue == value_mated_in(ply + 2))
1402 ss[ply].threatMove = ss[ply + 1].currentMove;
1403 if ( depth < ThreatDepth
1404 && ss[ply - 1].reduction
1405 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1410 // Step 9. Internal iterative deepening
1411 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1412 !isCheck && ss[ply].eval >= beta - IIDMargin)
1414 search(pos, ss, beta, depth/2, ply, false, threadID);
1415 ttMove = ss[ply].pv[ply];
1416 tte = TT.retrieve(posKey);
1419 // Step 10. Loop through moves
1420 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1422 // Initialize a MovePicker object for the current position
1423 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1426 while ( bestValue < beta
1427 && (move = mp.get_next_move()) != MOVE_NONE
1428 && !TM.thread_should_stop(threadID))
1430 assert(move_is_ok(move));
1432 if (move == excludedMove)
1435 moveIsCheck = pos.move_is_check(move, ci);
1436 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1437 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1439 // Step 11. Decide the new search depth
1440 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1442 // Singular extension search. We extend the TT move if its value is much better than
1443 // its siblings. To verify this we do a reduced search on all the other moves but the
1444 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1445 if ( depth >= 8 * OnePly
1447 && move == tte->move()
1448 && !excludedMove // Do not allow recursive single-reply search
1450 && is_lower_bound(tte->type())
1451 && tte->depth() >= depth - 3 * OnePly)
1453 Value ttValue = value_from_tt(tte->value(), ply);
1455 if (abs(ttValue) < VALUE_KNOWN_WIN)
1457 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1459 if (excValue < ttValue - SingleReplyMargin)
1464 newDepth = depth - OnePly + ext;
1466 // Update current move (this must be done after singular extension search)
1467 movesSearched[moveCount++] = ss[ply].currentMove = move;
1469 // Step 12. Futility pruning
1472 && !captureOrPromotion
1473 && !move_is_castle(move)
1476 // Move count based pruning
1477 if ( moveCount >= futility_move_count(depth)
1478 && ok_to_prune(pos, move, ss[ply].threatMove)
1479 && bestValue > value_mated_in(PLY_MAX))
1482 // Value based pruning
1483 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1484 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1485 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1487 if (futilityValueScaled < beta)
1489 if (futilityValueScaled > bestValue)
1490 bestValue = futilityValueScaled;
1495 // Step 13. Make the move
1496 pos.do_move(move, st, ci, moveIsCheck);
1498 // Step 14. Reduced search
1499 // if the move fails high will be re-searched at full depth.
1500 bool doFullDepthSearch = true;
1502 if ( depth >= 3*OnePly
1504 && !captureOrPromotion
1505 && !move_is_castle(move)
1506 && !move_is_killer(move, ss[ply]))
1508 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1509 if (ss[ply].reduction)
1511 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1512 doFullDepthSearch = (value >= beta);
1516 // Step 15. Full depth search
1517 if (doFullDepthSearch)
1519 ss[ply].reduction = Depth(0);
1520 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1523 // Step 16. Undo move
1524 pos.undo_move(move);
1526 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1528 // Step 17. Check for new best move
1529 if (value > bestValue)
1535 if (value == value_mate_in(ply + 1))
1536 ss[ply].mateKiller = move;
1539 // Step 18. Check for split
1540 if ( TM.active_threads() > 1
1542 && depth >= MinimumSplitDepth
1544 && TM.available_thread_exists(threadID)
1546 && !TM.thread_should_stop(threadID)
1547 && TM.split(pos, ss, ply, NULL, beta, &bestValue, futilityValue, //FIXME: SMP & futilityValue
1548 depth, &moveCount, &mp, threadID, false))
1552 // Step 19. Check for mate and stalemate
1553 // All legal moves have been searched and if there were
1554 // no legal moves, it must be mate or stalemate.
1555 // If one move was excluded return fail low.
1557 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1559 // Step 20. Update tables
1560 // If the search is not aborted, update the transposition table,
1561 // history counters, and killer moves.
1562 if (AbortSearch || TM.thread_should_stop(threadID))
1565 if (bestValue < beta)
1566 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1569 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1570 move = ss[ply].pv[ply];
1571 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1572 if (!pos.move_is_capture_or_promotion(move))
1574 update_history(pos, move, depth, movesSearched, moveCount);
1575 update_killers(move, ss[ply]);
1580 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1586 // qsearch() is the quiescence search function, which is called by the main
1587 // search function when the remaining depth is zero (or, to be more precise,
1588 // less than OnePly).
1590 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1591 Depth depth, int ply, int threadID) {
1593 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1594 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1596 assert(ply >= 0 && ply < PLY_MAX);
1597 assert(threadID >= 0 && threadID < TM.active_threads());
1602 Value staticValue, bestValue, value, futilityBase, futilityValue;
1603 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1604 const TTEntry* tte = NULL;
1606 bool pvNode = (beta - alpha != 1);
1607 Value oldAlpha = alpha;
1609 // Initialize, and make an early exit in case of an aborted search,
1610 // an instant draw, maximum ply reached, etc.
1611 init_node(ss, ply, threadID);
1613 // After init_node() that calls poll()
1614 if (AbortSearch || TM.thread_should_stop(threadID))
1617 if (pos.is_draw() || ply >= PLY_MAX - 1)
1620 // Transposition table lookup. At PV nodes, we don't use the TT for
1621 // pruning, but only for move ordering.
1622 tte = TT.retrieve(pos.get_key());
1623 ttMove = (tte ? tte->move() : MOVE_NONE);
1625 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1627 assert(tte->type() != VALUE_TYPE_EVAL);
1629 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1630 return value_from_tt(tte->value(), ply);
1633 isCheck = pos.is_check();
1635 // Evaluate the position statically
1637 staticValue = -VALUE_INFINITE;
1638 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1639 staticValue = value_from_tt(tte->value(), ply);
1641 staticValue = evaluate(pos, ei, threadID);
1645 ss[ply].eval = staticValue;
1646 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1649 // Initialize "stand pat score", and return it immediately if it is
1651 bestValue = staticValue;
1653 if (bestValue >= beta)
1655 // Store the score to avoid a future costly evaluation() call
1656 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1657 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1662 if (bestValue > alpha)
1665 // If we are near beta then try to get a cutoff pushing checks a bit further
1666 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1668 // Initialize a MovePicker object for the current position, and prepare
1669 // to search the moves. Because the depth is <= 0 here, only captures,
1670 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1671 // and we are near beta) will be generated.
1672 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1674 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1675 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1677 // Loop through the moves until no moves remain or a beta cutoff
1679 while ( alpha < beta
1680 && (move = mp.get_next_move()) != MOVE_NONE)
1682 assert(move_is_ok(move));
1684 moveIsCheck = pos.move_is_check(move, ci);
1686 // Update current move
1688 ss[ply].currentMove = move;
1696 && !move_is_promotion(move)
1697 && !pos.move_is_passed_pawn_push(move))
1699 futilityValue = futilityBase
1700 + pos.endgame_value_of_piece_on(move_to(move))
1701 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1703 if (futilityValue < alpha)
1705 if (futilityValue > bestValue)
1706 bestValue = futilityValue;
1711 // Detect blocking evasions that are candidate to be pruned
1712 evasionPrunable = isCheck
1713 && bestValue != -VALUE_INFINITE
1714 && !pos.move_is_capture(move)
1715 && pos.type_of_piece_on(move_from(move)) != KING
1716 && !pos.can_castle(pos.side_to_move());
1718 // Don't search moves with negative SEE values
1719 if ( (!isCheck || evasionPrunable)
1722 && !move_is_promotion(move)
1723 && pos.see_sign(move) < 0)
1726 // Make and search the move
1727 pos.do_move(move, st, ci, moveIsCheck);
1728 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1729 pos.undo_move(move);
1731 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1734 if (value > bestValue)
1745 // All legal moves have been searched. A special case: If we're in check
1746 // and no legal moves were found, it is checkmate.
1747 if (!moveCount && pos.is_check()) // Mate!
1748 return value_mated_in(ply);
1750 // Update transposition table
1751 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1752 if (bestValue <= oldAlpha)
1754 // If bestValue isn't changed it means it is still the static evaluation
1755 // of the node, so keep this info to avoid a future evaluation() call.
1756 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1757 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1759 else if (bestValue >= beta)
1761 move = ss[ply].pv[ply];
1762 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1764 // Update killers only for good checking moves
1765 if (!pos.move_is_capture_or_promotion(move))
1766 update_killers(move, ss[ply]);
1769 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1771 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1777 // sp_search() is used to search from a split point. This function is called
1778 // by each thread working at the split point. It is similar to the normal
1779 // search() function, but simpler. Because we have already probed the hash
1780 // table, done a null move search, and searched the first move before
1781 // splitting, we don't have to repeat all this work in sp_search(). We
1782 // also don't need to store anything to the hash table here: This is taken
1783 // care of after we return from the split point.
1785 void sp_search(SplitPoint* sp, int threadID) {
1787 assert(threadID >= 0 && threadID < TM.active_threads());
1788 assert(TM.active_threads() > 1);
1790 Position pos(*sp->pos);
1792 SearchStack* ss = sp->sstack[threadID];
1794 Value value = -VALUE_INFINITE;
1797 bool isCheck = pos.is_check();
1798 bool useFutilityPruning = sp->depth < 7 * OnePly //FIXME: sync with search
1801 lock_grab(&(sp->lock));
1803 while ( sp->bestValue < sp->beta
1804 && !TM.thread_should_stop(threadID)
1805 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1807 moveCount = ++sp->moves;
1808 lock_release(&(sp->lock));
1810 assert(move_is_ok(move));
1812 bool moveIsCheck = pos.move_is_check(move, ci);
1813 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1815 ss[sp->ply].currentMove = move;
1817 // Decide the new search depth
1819 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1820 Depth newDepth = sp->depth - OnePly + ext;
1823 if ( useFutilityPruning
1825 && !captureOrPromotion)
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 Value futilityValueScaled = sp->futilityValue - moveCount * 8; //FIXME: sync with search
1839 if (futilityValueScaled < sp->beta)
1841 lock_grab(&(sp->lock));
1843 if (futilityValueScaled > sp->bestValue)
1844 sp->bestValue = futilityValueScaled;
1849 // Step 13. Make the move
1850 pos.do_move(move, st, ci, moveIsCheck);
1852 // Step 14. Reduced search
1853 // if the move fails high will be re-searched at full depth.
1854 bool doFullDepthSearch = true;
1857 && !captureOrPromotion
1858 && !move_is_castle(move)
1859 && !move_is_killer(move, ss[sp->ply]))
1861 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1862 if (ss[sp->ply].reduction)
1864 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1865 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1869 // Step 15. Full depth search
1870 if (doFullDepthSearch)
1872 ss[sp->ply].reduction = Depth(0);
1873 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1876 // Step 16. Undo move
1877 pos.undo_move(move);
1879 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1881 // Step 17. Check for new best move
1882 lock_grab(&(sp->lock));
1884 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1886 sp->bestValue = value;
1887 if (sp->bestValue >= sp->beta)
1889 sp->stopRequest = true;
1890 sp_update_pv(sp->parentSstack, ss, sp->ply);
1895 /* Here we have the lock still grabbed */
1897 sp->slaves[threadID] = 0;
1900 lock_release(&(sp->lock));
1904 // sp_search_pv() is used to search from a PV split point. This function
1905 // is called by each thread working at the split point. It is similar to
1906 // the normal search_pv() function, but simpler. Because we have already
1907 // probed the hash table and searched the first move before splitting, we
1908 // don't have to repeat all this work in sp_search_pv(). We also don't
1909 // need to store anything to the hash table here: This is taken care of
1910 // after we return from the split point.
1912 void sp_search_pv(SplitPoint* sp, int threadID) {
1914 assert(threadID >= 0 && threadID < TM.active_threads());
1915 assert(TM.active_threads() > 1);
1917 Position pos(*sp->pos);
1919 SearchStack* ss = sp->sstack[threadID];
1920 Value value = -VALUE_INFINITE;
1924 lock_grab(&(sp->lock));
1926 while ( sp->alpha < sp->beta
1927 && !TM.thread_should_stop(threadID)
1928 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1930 moveCount = ++sp->moves;
1931 lock_release(&(sp->lock));
1933 assert(move_is_ok(move));
1935 bool moveIsCheck = pos.move_is_check(move, ci);
1936 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1938 ss[sp->ply].currentMove = move;
1940 // Decide the new search depth
1942 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1943 Depth newDepth = sp->depth - OnePly + ext;
1945 // Make and search the move.
1947 pos.do_move(move, st, ci, moveIsCheck);
1949 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1950 // if the move fails high will be re-searched at full depth.
1951 bool doFullDepthSearch = true;
1954 && !captureOrPromotion
1955 && !move_is_castle(move)
1956 && !move_is_killer(move, ss[sp->ply]))
1958 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1959 if (ss[sp->ply].reduction)
1961 Value localAlpha = sp->alpha;
1962 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1963 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1967 if (doFullDepthSearch) // Go with full depth non-pv search
1969 Value localAlpha = sp->alpha;
1970 ss[sp->ply].reduction = Depth(0);
1971 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1973 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1975 // If another thread has failed high then sp->alpha has been increased
1976 // to be higher or equal then beta, if so, avoid to start a PV search.
1977 localAlpha = sp->alpha;
1978 if (localAlpha < sp->beta)
1979 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1982 pos.undo_move(move);
1984 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1987 lock_grab(&(sp->lock));
1989 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1991 sp->bestValue = value;
1992 if (value > sp->alpha)
1994 // Ask threads to stop before to modify sp->alpha
1995 if (value >= sp->beta)
1996 sp->stopRequest = true;
2000 sp_update_pv(sp->parentSstack, ss, sp->ply);
2001 if (value == value_mate_in(sp->ply + 1))
2002 ss[sp->ply].mateKiller = move;
2007 /* Here we have the lock still grabbed */
2009 sp->slaves[threadID] = 0;
2012 lock_release(&(sp->lock));
2016 // init_node() is called at the beginning of all the search functions
2017 // (search(), search_pv(), qsearch(), and so on) and initializes the
2018 // search stack object corresponding to the current node. Once every
2019 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2020 // for user input and checks whether it is time to stop the search.
2022 void init_node(SearchStack ss[], int ply, int threadID) {
2024 assert(ply >= 0 && ply < PLY_MAX);
2025 assert(threadID >= 0 && threadID < TM.active_threads());
2027 TM.incrementNodeCounter(threadID);
2032 if (NodesSincePoll >= NodesBetweenPolls)
2039 ss[ply + 2].initKillers();
2040 TM.print_current_line(ss, ply, threadID);
2044 // update_pv() is called whenever a search returns a value > alpha.
2045 // It updates the PV in the SearchStack object corresponding to the
2048 void update_pv(SearchStack ss[], int ply) {
2050 assert(ply >= 0 && ply < PLY_MAX);
2054 ss[ply].pv[ply] = ss[ply].currentMove;
2056 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2057 ss[ply].pv[p] = ss[ply + 1].pv[p];
2059 ss[ply].pv[p] = MOVE_NONE;
2063 // sp_update_pv() is a variant of update_pv for use at split points. The
2064 // difference between the two functions is that sp_update_pv also updates
2065 // the PV at the parent node.
2067 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2069 assert(ply >= 0 && ply < PLY_MAX);
2073 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2075 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2076 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2078 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2082 // connected_moves() tests whether two moves are 'connected' in the sense
2083 // that the first move somehow made the second move possible (for instance
2084 // if the moving piece is the same in both moves). The first move is assumed
2085 // to be the move that was made to reach the current position, while the
2086 // second move is assumed to be a move from the current position.
2088 bool connected_moves(const Position& pos, Move m1, Move m2) {
2090 Square f1, t1, f2, t2;
2093 assert(move_is_ok(m1));
2094 assert(move_is_ok(m2));
2096 if (m2 == MOVE_NONE)
2099 // Case 1: The moving piece is the same in both moves
2105 // Case 2: The destination square for m2 was vacated by m1
2111 // Case 3: Moving through the vacated square
2112 if ( piece_is_slider(pos.piece_on(f2))
2113 && bit_is_set(squares_between(f2, t2), f1))
2116 // Case 4: The destination square for m2 is defended by the moving piece in m1
2117 p = pos.piece_on(t1);
2118 if (bit_is_set(pos.attacks_from(p, t1), t2))
2121 // Case 5: Discovered check, checking piece is the piece moved in m1
2122 if ( piece_is_slider(p)
2123 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2124 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2126 // discovered_check_candidates() works also if the Position's side to
2127 // move is the opposite of the checking piece.
2128 Color them = opposite_color(pos.side_to_move());
2129 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2131 if (bit_is_set(dcCandidates, f2))
2138 // value_is_mate() checks if the given value is a mate one
2139 // eventually compensated for the ply.
2141 bool value_is_mate(Value value) {
2143 assert(abs(value) <= VALUE_INFINITE);
2145 return value <= value_mated_in(PLY_MAX)
2146 || value >= value_mate_in(PLY_MAX);
2150 // move_is_killer() checks if the given move is among the
2151 // killer moves of that ply.
2153 bool move_is_killer(Move m, const SearchStack& ss) {
2155 const Move* k = ss.killers;
2156 for (int i = 0; i < KILLER_MAX; i++, k++)
2164 // extension() decides whether a move should be searched with normal depth,
2165 // or with extended depth. Certain classes of moves (checking moves, in
2166 // particular) are searched with bigger depth than ordinary moves and in
2167 // any case are marked as 'dangerous'. Note that also if a move is not
2168 // extended, as example because the corresponding UCI option is set to zero,
2169 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2171 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2172 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2174 assert(m != MOVE_NONE);
2176 Depth result = Depth(0);
2177 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2182 result += CheckExtension[pvNode];
2185 result += SingleEvasionExtension[pvNode];
2188 result += MateThreatExtension[pvNode];
2191 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2193 Color c = pos.side_to_move();
2194 if (relative_rank(c, move_to(m)) == RANK_7)
2196 result += PawnPushTo7thExtension[pvNode];
2199 if (pos.pawn_is_passed(c, move_to(m)))
2201 result += PassedPawnExtension[pvNode];
2206 if ( captureOrPromotion
2207 && pos.type_of_piece_on(move_to(m)) != PAWN
2208 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2209 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2210 && !move_is_promotion(m)
2213 result += PawnEndgameExtension[pvNode];
2218 && captureOrPromotion
2219 && pos.type_of_piece_on(move_to(m)) != PAWN
2220 && pos.see_sign(m) >= 0)
2226 return Min(result, OnePly);
2230 // ok_to_do_nullmove() looks at the current position and decides whether
2231 // doing a 'null move' should be allowed. In order to avoid zugzwang
2232 // problems, null moves are not allowed when the side to move has very
2233 // little material left. Currently, the test is a bit too simple: Null
2234 // moves are avoided only when the side to move has only pawns left.
2235 // It's probably a good idea to avoid null moves in at least some more
2236 // complicated endgames, e.g. KQ vs KR. FIXME
2238 bool ok_to_do_nullmove(const Position& pos) {
2240 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2244 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2245 // non-tactical moves late in the move list close to the leaves are
2246 // candidates for pruning.
2248 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2250 assert(move_is_ok(m));
2251 assert(threat == MOVE_NONE || move_is_ok(threat));
2252 assert(!pos.move_is_check(m));
2253 assert(!pos.move_is_capture_or_promotion(m));
2254 assert(!pos.move_is_passed_pawn_push(m));
2256 Square mfrom, mto, tfrom, tto;
2258 // Prune if there isn't any threat move
2259 if (threat == MOVE_NONE)
2262 mfrom = move_from(m);
2264 tfrom = move_from(threat);
2265 tto = move_to(threat);
2267 // Case 1: Don't prune moves which move the threatened piece
2271 // Case 2: If the threatened piece has value less than or equal to the
2272 // value of the threatening piece, don't prune move which defend it.
2273 if ( pos.move_is_capture(threat)
2274 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2275 || pos.type_of_piece_on(tfrom) == KING)
2276 && pos.move_attacks_square(m, tto))
2279 // Case 3: If the moving piece in the threatened move is a slider, don't
2280 // prune safe moves which block its ray.
2281 if ( piece_is_slider(pos.piece_on(tfrom))
2282 && bit_is_set(squares_between(tfrom, tto), mto)
2283 && pos.see_sign(m) >= 0)
2290 // ok_to_use_TT() returns true if a transposition table score
2291 // can be used at a given point in search.
2293 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2295 Value v = value_from_tt(tte->value(), ply);
2297 return ( tte->depth() >= depth
2298 || v >= Max(value_mate_in(PLY_MAX), beta)
2299 || v < Min(value_mated_in(PLY_MAX), beta))
2301 && ( (is_lower_bound(tte->type()) && v >= beta)
2302 || (is_upper_bound(tte->type()) && v < beta));
2306 // refine_eval() returns the transposition table score if
2307 // possible otherwise falls back on static position evaluation.
2309 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2314 Value v = value_from_tt(tte->value(), ply);
2316 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2317 || (is_upper_bound(tte->type()) && v < defaultEval))
2324 // update_history() registers a good move that produced a beta-cutoff
2325 // in history and marks as failures all the other moves of that ply.
2327 void update_history(const Position& pos, Move move, Depth depth,
2328 Move movesSearched[], int moveCount) {
2332 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2334 for (int i = 0; i < moveCount - 1; i++)
2336 m = movesSearched[i];
2340 if (!pos.move_is_capture_or_promotion(m))
2341 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2346 // update_killers() add a good move that produced a beta-cutoff
2347 // among the killer moves of that ply.
2349 void update_killers(Move m, SearchStack& ss) {
2351 if (m == ss.killers[0])
2354 for (int i = KILLER_MAX - 1; i > 0; i--)
2355 ss.killers[i] = ss.killers[i - 1];
2361 // update_gains() updates the gains table of a non-capture move given
2362 // the static position evaluation before and after the move.
2364 void update_gains(const Position& pos, Move m, Value before, Value after) {
2367 && before != VALUE_NONE
2368 && after != VALUE_NONE
2369 && pos.captured_piece() == NO_PIECE_TYPE
2370 && !move_is_castle(m)
2371 && !move_is_promotion(m))
2372 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2376 // current_search_time() returns the number of milliseconds which have passed
2377 // since the beginning of the current search.
2379 int current_search_time() {
2381 return get_system_time() - SearchStartTime;
2385 // nps() computes the current nodes/second count.
2389 int t = current_search_time();
2390 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2394 // poll() performs two different functions: It polls for user input, and it
2395 // looks at the time consumed so far and decides if it's time to abort the
2400 static int lastInfoTime;
2401 int t = current_search_time();
2406 // We are line oriented, don't read single chars
2407 std::string command;
2409 if (!std::getline(std::cin, command))
2412 if (command == "quit")
2415 PonderSearch = false;
2419 else if (command == "stop")
2422 PonderSearch = false;
2424 else if (command == "ponderhit")
2428 // Print search information
2432 else if (lastInfoTime > t)
2433 // HACK: Must be a new search where we searched less than
2434 // NodesBetweenPolls nodes during the first second of search.
2437 else if (t - lastInfoTime >= 1000)
2440 lock_grab(&TM.IOLock);
2445 if (dbg_show_hit_rate)
2446 dbg_print_hit_rate();
2448 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2449 << " time " << t << " hashfull " << TT.full() << endl;
2451 lock_release(&TM.IOLock);
2453 if (ShowCurrentLine)
2454 TM.threads[0].printCurrentLineRequest = true;
2457 // Should we stop the search?
2461 bool stillAtFirstMove = RootMoveNumber == 1
2462 && !AspirationFailLow
2463 && t > MaxSearchTime + ExtraSearchTime;
2465 bool noMoreTime = t > AbsoluteMaxSearchTime
2466 || stillAtFirstMove;
2468 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2469 || (ExactMaxTime && t >= ExactMaxTime)
2470 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2475 // ponderhit() is called when the program is pondering (i.e. thinking while
2476 // it's the opponent's turn to move) in order to let the engine know that
2477 // it correctly predicted the opponent's move.
2481 int t = current_search_time();
2482 PonderSearch = false;
2484 bool stillAtFirstMove = RootMoveNumber == 1
2485 && !AspirationFailLow
2486 && t > MaxSearchTime + ExtraSearchTime;
2488 bool noMoreTime = t > AbsoluteMaxSearchTime
2489 || stillAtFirstMove;
2491 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2496 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2498 void init_ss_array(SearchStack ss[]) {
2500 for (int i = 0; i < 3; i++)
2503 ss[i].initKillers();
2508 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2509 // while the program is pondering. The point is to work around a wrinkle in
2510 // the UCI protocol: When pondering, the engine is not allowed to give a
2511 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2512 // We simply wait here until one of these commands is sent, and return,
2513 // after which the bestmove and pondermove will be printed (in id_loop()).
2515 void wait_for_stop_or_ponderhit() {
2517 std::string command;
2521 if (!std::getline(std::cin, command))
2524 if (command == "quit")
2529 else if (command == "ponderhit" || command == "stop")
2535 // init_thread() is the function which is called when a new thread is
2536 // launched. It simply calls the idle_loop() function with the supplied
2537 // threadID. There are two versions of this function; one for POSIX
2538 // threads and one for Windows threads.
2540 #if !defined(_MSC_VER)
2542 void* init_thread(void *threadID) {
2544 TM.idle_loop(*(int*)threadID, NULL);
2550 DWORD WINAPI init_thread(LPVOID threadID) {
2552 TM.idle_loop(*(int*)threadID, NULL);
2559 /// The ThreadsManager class
2561 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2562 // get_beta_counters() are getters/setters for the per thread
2563 // counters used to sort the moves at root.
2565 void ThreadsManager::resetNodeCounters() {
2567 for (int i = 0; i < MAX_THREADS; i++)
2568 threads[i].nodes = 0ULL;
2571 void ThreadsManager::resetBetaCounters() {
2573 for (int i = 0; i < MAX_THREADS; i++)
2574 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2577 int64_t ThreadsManager::nodes_searched() const {
2579 int64_t result = 0ULL;
2580 for (int i = 0; i < ActiveThreads; i++)
2581 result += threads[i].nodes;
2586 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2589 for (int i = 0; i < MAX_THREADS; i++)
2591 our += threads[i].betaCutOffs[us];
2592 their += threads[i].betaCutOffs[opposite_color(us)];
2597 // idle_loop() is where the threads are parked when they have no work to do.
2598 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2599 // object for which the current thread is the master.
2601 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2603 assert(threadID >= 0 && threadID < MAX_THREADS);
2607 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2608 // master should exit as last one.
2609 if (AllThreadsShouldExit)
2612 threads[threadID].state = THREAD_TERMINATED;
2616 // If we are not thinking, wait for a condition to be signaled
2617 // instead of wasting CPU time polling for work.
2618 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2621 assert(threadID != 0);
2622 threads[threadID].state = THREAD_SLEEPING;
2624 #if !defined(_MSC_VER)
2625 pthread_mutex_lock(&WaitLock);
2626 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2627 pthread_cond_wait(&WaitCond, &WaitLock);
2628 pthread_mutex_unlock(&WaitLock);
2630 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2634 // If thread has just woken up, mark it as available
2635 if (threads[threadID].state == THREAD_SLEEPING)
2636 threads[threadID].state = THREAD_AVAILABLE;
2638 // If this thread has been assigned work, launch a search
2639 if (threads[threadID].state == THREAD_WORKISWAITING)
2641 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2643 threads[threadID].state = THREAD_SEARCHING;
2645 if (threads[threadID].splitPoint->pvNode)
2646 sp_search_pv(threads[threadID].splitPoint, threadID);
2648 sp_search(threads[threadID].splitPoint, threadID);
2650 assert(threads[threadID].state == THREAD_SEARCHING);
2652 threads[threadID].state = THREAD_AVAILABLE;
2655 // If this thread is the master of a split point and all threads have
2656 // finished their work at this split point, return from the idle loop.
2657 if (waitSp != NULL && waitSp->cpus == 0)
2659 assert(threads[threadID].state == THREAD_AVAILABLE);
2661 threads[threadID].state = THREAD_SEARCHING;
2668 // init_threads() is called during startup. It launches all helper threads,
2669 // and initializes the split point stack and the global locks and condition
2672 void ThreadsManager::init_threads() {
2677 #if !defined(_MSC_VER)
2678 pthread_t pthread[1];
2681 // Initialize global locks
2682 lock_init(&MPLock, NULL);
2683 lock_init(&IOLock, NULL);
2685 // Initialize SplitPointStack locks
2686 for (i = 0; i < MAX_THREADS; i++)
2687 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2689 SplitPointStack[i][j].parent = NULL;
2690 lock_init(&(SplitPointStack[i][j].lock), NULL);
2693 #if !defined(_MSC_VER)
2694 pthread_mutex_init(&WaitLock, NULL);
2695 pthread_cond_init(&WaitCond, NULL);
2697 for (i = 0; i < MAX_THREADS; i++)
2698 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2701 // Will be set just before program exits to properly end the threads
2702 AllThreadsShouldExit = false;
2704 // Threads will be put to sleep as soon as created
2705 AllThreadsShouldSleep = true;
2707 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2709 threads[0].state = THREAD_SEARCHING;
2710 for (i = 1; i < MAX_THREADS; i++)
2711 threads[i].state = THREAD_AVAILABLE;
2713 // Launch the helper threads
2714 for (i = 1; i < MAX_THREADS; i++)
2717 #if !defined(_MSC_VER)
2718 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2721 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
2726 cout << "Failed to create thread number " << i << endl;
2727 Application::exit_with_failure();
2730 // Wait until the thread has finished launching and is gone to sleep
2731 while (threads[i].state != THREAD_SLEEPING);
2736 // exit_threads() is called when the program exits. It makes all the
2737 // helper threads exit cleanly.
2739 void ThreadsManager::exit_threads() {
2741 ActiveThreads = MAX_THREADS; // HACK
2742 AllThreadsShouldSleep = true; // HACK
2743 wake_sleeping_threads();
2745 // This makes the threads to exit idle_loop()
2746 AllThreadsShouldExit = true;
2748 // Wait for thread termination
2749 for (int i = 1; i < MAX_THREADS; i++)
2750 while (threads[i].state != THREAD_TERMINATED);
2752 // Now we can safely destroy the locks
2753 for (int i = 0; i < MAX_THREADS; i++)
2754 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2755 lock_destroy(&(SplitPointStack[i][j].lock));
2759 // thread_should_stop() checks whether the thread should stop its search.
2760 // This can happen if a beta cutoff has occurred in the thread's currently
2761 // active split point, or in some ancestor of the current split point.
2763 bool ThreadsManager::thread_should_stop(int threadID) const {
2765 assert(threadID >= 0 && threadID < ActiveThreads);
2769 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2774 // thread_is_available() checks whether the thread with threadID "slave" is
2775 // available to help the thread with threadID "master" at a split point. An
2776 // obvious requirement is that "slave" must be idle. With more than two
2777 // threads, this is not by itself sufficient: If "slave" is the master of
2778 // some active split point, it is only available as a slave to the other
2779 // threads which are busy searching the split point at the top of "slave"'s
2780 // split point stack (the "helpful master concept" in YBWC terminology).
2782 bool ThreadsManager::thread_is_available(int slave, int master) const {
2784 assert(slave >= 0 && slave < ActiveThreads);
2785 assert(master >= 0 && master < ActiveThreads);
2786 assert(ActiveThreads > 1);
2788 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2791 // Make a local copy to be sure doesn't change under our feet
2792 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2794 if (localActiveSplitPoints == 0)
2795 // No active split points means that the thread is available as
2796 // a slave for any other thread.
2799 if (ActiveThreads == 2)
2802 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2803 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2804 // could have been set to 0 by another thread leading to an out of bound access.
2805 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2812 // available_thread_exists() tries to find an idle thread which is available as
2813 // a slave for the thread with threadID "master".
2815 bool ThreadsManager::available_thread_exists(int master) const {
2817 assert(master >= 0 && master < ActiveThreads);
2818 assert(ActiveThreads > 1);
2820 for (int i = 0; i < ActiveThreads; i++)
2821 if (thread_is_available(i, master))
2828 // split() does the actual work of distributing the work at a node between
2829 // several threads at PV nodes. If it does not succeed in splitting the
2830 // node (because no idle threads are available, or because we have no unused
2831 // split point objects), the function immediately returns false. If
2832 // splitting is possible, a SplitPoint object is initialized with all the
2833 // data that must be copied to the helper threads (the current position and
2834 // search stack, alpha, beta, the search depth, etc.), and we tell our
2835 // helper threads that they have been assigned work. This will cause them
2836 // to instantly leave their idle loops and call sp_search_pv(). When all
2837 // threads have returned from sp_search_pv (or, equivalently, when
2838 // splitPoint->cpus becomes 0), split() returns true.
2840 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2841 Value* alpha, const Value beta, Value* bestValue, const Value futilityValue,
2842 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2845 assert(sstck != NULL);
2846 assert(ply >= 0 && ply < PLY_MAX);
2847 assert(*bestValue >= -VALUE_INFINITE);
2848 assert( ( pvNode && *bestValue <= *alpha)
2849 || (!pvNode && *bestValue < beta ));
2850 assert(!pvNode || *alpha < beta);
2851 assert(beta <= VALUE_INFINITE);
2852 assert(depth > Depth(0));
2853 assert(master >= 0 && master < ActiveThreads);
2854 assert(ActiveThreads > 1);
2856 SplitPoint* splitPoint;
2860 // If no other thread is available to help us, or if we have too many
2861 // active split points, don't split.
2862 if ( !available_thread_exists(master)
2863 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2865 lock_release(&MPLock);
2869 // Pick the next available split point object from the split point stack
2870 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2872 // Initialize the split point object
2873 splitPoint->parent = threads[master].splitPoint;
2874 splitPoint->stopRequest = false;
2875 splitPoint->ply = ply;
2876 splitPoint->depth = depth;
2877 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2878 splitPoint->beta = beta;
2879 splitPoint->pvNode = pvNode;
2880 splitPoint->bestValue = *bestValue;
2881 splitPoint->futilityValue = futilityValue;
2882 splitPoint->master = master;
2883 splitPoint->mp = mp;
2884 splitPoint->moves = *moves;
2885 splitPoint->cpus = 1;
2886 splitPoint->pos = &p;
2887 splitPoint->parentSstack = sstck;
2888 for (int i = 0; i < ActiveThreads; i++)
2889 splitPoint->slaves[i] = 0;
2891 threads[master].splitPoint = splitPoint;
2892 threads[master].activeSplitPoints++;
2894 // If we are here it means we are not available
2895 assert(threads[master].state != THREAD_AVAILABLE);
2897 // Allocate available threads setting state to THREAD_BOOKED
2898 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2899 if (thread_is_available(i, master))
2901 threads[i].state = THREAD_BOOKED;
2902 threads[i].splitPoint = splitPoint;
2903 splitPoint->slaves[i] = 1;
2907 assert(splitPoint->cpus > 1);
2909 // We can release the lock because slave threads are already booked and master is not available
2910 lock_release(&MPLock);
2912 // Tell the threads that they have work to do. This will make them leave
2913 // their idle loop. But before copy search stack tail for each thread.
2914 for (int i = 0; i < ActiveThreads; i++)
2915 if (i == master || splitPoint->slaves[i])
2917 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2919 assert(i == master || threads[i].state == THREAD_BOOKED);
2921 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2924 // Everything is set up. The master thread enters the idle loop, from
2925 // which it will instantly launch a search, because its state is
2926 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2927 // idle loop, which means that the main thread will return from the idle
2928 // loop when all threads have finished their work at this split point
2929 // (i.e. when splitPoint->cpus == 0).
2930 idle_loop(master, splitPoint);
2932 // We have returned from the idle loop, which means that all threads are
2933 // finished. Update alpha, beta and bestValue, and return.
2937 *alpha = splitPoint->alpha;
2939 *bestValue = splitPoint->bestValue;
2940 threads[master].activeSplitPoints--;
2941 threads[master].splitPoint = splitPoint->parent;
2943 lock_release(&MPLock);
2948 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2949 // to start a new search from the root.
2951 void ThreadsManager::wake_sleeping_threads() {
2953 assert(AllThreadsShouldSleep);
2954 assert(ActiveThreads > 0);
2956 AllThreadsShouldSleep = false;
2958 if (ActiveThreads == 1)
2961 for (int i = 1; i < ActiveThreads; i++)
2962 assert(threads[i].state == THREAD_SLEEPING);
2964 #if !defined(_MSC_VER)
2965 pthread_mutex_lock(&WaitLock);
2966 pthread_cond_broadcast(&WaitCond);
2967 pthread_mutex_unlock(&WaitLock);
2969 for (int i = 1; i < MAX_THREADS; i++)
2970 SetEvent(SitIdleEvent[i]);
2976 // put_threads_to_sleep() makes all the threads go to sleep just before
2977 // to leave think(), at the end of the search. Threads should have already
2978 // finished the job and should be idle.
2980 void ThreadsManager::put_threads_to_sleep() {
2982 assert(!AllThreadsShouldSleep);
2984 // This makes the threads to go to sleep
2985 AllThreadsShouldSleep = true;
2987 // Reset flags to a known state.
2988 for (int i = 1; i < ActiveThreads; i++)
2990 // This flag can be in a random state
2991 threads[i].printCurrentLineRequest = false;
2995 // print_current_line() prints _once_ the current line of search for a
2996 // given thread and then setup the print request for the next thread.
2997 // Called when the UCI option UCI_ShowCurrLine is 'true'.
2999 void ThreadsManager::print_current_line(SearchStack ss[], int ply, int threadID) {
3001 assert(ply >= 0 && ply < PLY_MAX);
3002 assert(threadID >= 0 && threadID < ActiveThreads);
3004 if (!threads[threadID].printCurrentLineRequest)
3008 threads[threadID].printCurrentLineRequest = false;
3010 if (threads[threadID].state == THREAD_SEARCHING)
3013 cout << "info currline " << (threadID + 1);
3014 for (int p = 0; p < ply; p++)
3015 cout << " " << ss[p].currentMove;
3018 lock_release(&IOLock);
3021 // Setup print request for the next thread ID
3022 if (threadID + 1 < ActiveThreads)
3023 threads[threadID + 1].printCurrentLineRequest = true;
3027 /// The RootMoveList class
3029 // RootMoveList c'tor
3031 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3033 SearchStack ss[PLY_MAX_PLUS_2];
3034 MoveStack mlist[MaxRootMoves];
3036 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3038 // Generate all legal moves
3039 MoveStack* last = generate_moves(pos, mlist);
3041 // Add each move to the moves[] array
3042 for (MoveStack* cur = mlist; cur != last; cur++)
3044 bool includeMove = includeAllMoves;
3046 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3047 includeMove = (searchMoves[k] == cur->move);
3052 // Find a quick score for the move
3054 pos.do_move(cur->move, st);
3055 moves[count].move = cur->move;
3056 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3057 moves[count].pv[0] = cur->move;
3058 moves[count].pv[1] = MOVE_NONE;
3059 pos.undo_move(cur->move);
3066 // RootMoveList simple methods definitions
3068 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3070 moves[moveNum].nodes = nodes;
3071 moves[moveNum].cumulativeNodes += nodes;
3074 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3076 moves[moveNum].ourBeta = our;
3077 moves[moveNum].theirBeta = their;
3080 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3084 for (j = 0; pv[j] != MOVE_NONE; j++)
3085 moves[moveNum].pv[j] = pv[j];
3087 moves[moveNum].pv[j] = MOVE_NONE;
3091 // RootMoveList::sort() sorts the root move list at the beginning of a new
3094 void RootMoveList::sort() {
3096 sort_multipv(count - 1); // Sort all items
3100 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3101 // list by their scores and depths. It is used to order the different PVs
3102 // correctly in MultiPV mode.
3104 void RootMoveList::sort_multipv(int n) {
3108 for (i = 1; i <= n; i++)
3110 RootMove rm = moves[i];
3111 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3112 moves[j] = moves[j - 1];