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 // Initialize, and make an early exit in case of an aborted search,
1056 // an instant draw, maximum ply reached, etc.
1057 init_node(ss, ply, threadID);
1059 // After init_node() that calls poll()
1060 if (AbortSearch || TM.thread_should_stop(threadID))
1063 if (pos.is_draw() || ply >= PLY_MAX - 1)
1066 // Mate distance pruning
1068 alpha = Max(value_mated_in(ply), alpha);
1069 beta = Min(value_mate_in(ply+1), beta);
1073 // Transposition table lookup. At PV nodes, we don't use the TT for
1074 // pruning, but only for move ordering. This is to avoid problems in
1075 // the following areas:
1077 // * Repetition draw detection
1078 // * Fifty move rule detection
1079 // * Searching for a mate
1080 // * Printing of full PV line
1082 tte = TT.retrieve(pos.get_key());
1083 ttMove = (tte ? tte->move() : MOVE_NONE);
1085 // Go with internal iterative deepening if we don't have a TT move
1086 if ( UseIIDAtPVNodes
1087 && depth >= 5*OnePly
1088 && ttMove == MOVE_NONE)
1090 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1091 ttMove = ss[ply].pv[ply];
1092 tte = TT.retrieve(pos.get_key());
1095 isCheck = pos.is_check();
1098 // Update gain statistics of the previous move that lead
1099 // us in this position.
1101 ss[ply].eval = evaluate(pos, ei, threadID);
1102 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1105 // Initialize a MovePicker object for the current position, and prepare
1106 // to search all moves
1107 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1109 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1111 // Loop through all legal moves until no moves remain or a beta cutoff
1113 while ( alpha < beta
1114 && (move = mp.get_next_move()) != MOVE_NONE
1115 && !TM.thread_should_stop(threadID))
1117 assert(move_is_ok(move));
1119 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1120 moveIsCheck = pos.move_is_check(move, ci);
1121 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1123 // Decide the new search depth
1124 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1126 // Singular extension search. We extend the TT move if its value is much better than
1127 // its siblings. To verify this we do a reduced search on all the other moves but the
1128 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1129 if ( depth >= 6 * OnePly
1131 && move == tte->move()
1133 && is_lower_bound(tte->type())
1134 && tte->depth() >= depth - 3 * OnePly)
1136 Value ttValue = value_from_tt(tte->value(), ply);
1138 if (abs(ttValue) < VALUE_KNOWN_WIN)
1140 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1142 if (excValue < ttValue - SingleReplyMargin)
1147 newDepth = depth - OnePly + ext;
1149 // Update current move
1150 movesSearched[moveCount++] = ss[ply].currentMove = move;
1152 // Make and search the move
1153 pos.do_move(move, st, ci, moveIsCheck);
1155 if (moveCount == 1) // The first move in list is the PV
1156 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1159 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1160 // if the move fails high will be re-searched at full depth.
1161 bool doFullDepthSearch = true;
1163 if ( depth >= 3*OnePly
1165 && !captureOrPromotion
1166 && !move_is_castle(move)
1167 && !move_is_killer(move, ss[ply]))
1169 ss[ply].reduction = pv_reduction(depth, moveCount);
1170 if (ss[ply].reduction)
1172 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1173 doFullDepthSearch = (value > alpha);
1177 if (doFullDepthSearch) // Go with full depth non-pv search
1179 ss[ply].reduction = Depth(0);
1180 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1181 if (value > alpha && value < beta)
1182 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1185 pos.undo_move(move);
1187 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1190 if (value > bestValue)
1197 if (value == value_mate_in(ply + 1))
1198 ss[ply].mateKiller = move;
1203 if ( TM.active_threads() > 1
1205 && depth >= MinimumSplitDepth
1207 && TM.available_thread_exists(threadID)
1209 && !TM.thread_should_stop(threadID)
1210 && TM.split(pos, ss, ply, &alpha, beta, &bestValue, VALUE_NONE,
1211 depth, &moveCount, &mp, threadID, true))
1215 // All legal moves have been searched. A special case: If there were
1216 // no legal moves, it must be mate or stalemate.
1218 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1220 // If the search is not aborted, update the transposition table,
1221 // history counters, and killer moves.
1222 if (AbortSearch || TM.thread_should_stop(threadID))
1225 if (bestValue <= oldAlpha)
1226 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1228 else if (bestValue >= beta)
1230 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1231 move = ss[ply].pv[ply];
1232 if (!pos.move_is_capture_or_promotion(move))
1234 update_history(pos, move, depth, movesSearched, moveCount);
1235 update_killers(move, ss[ply]);
1237 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1240 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1246 // search() is the search function for zero-width nodes.
1248 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1249 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1251 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1252 assert(ply >= 0 && ply < PLY_MAX);
1253 assert(threadID >= 0 && threadID < TM.active_threads());
1255 Move movesSearched[256];
1260 Depth ext, newDepth;
1261 Value bestValue, staticValue, nullValue, value, futilityValue, futilityValueScaled;
1262 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1263 bool mateThreat = false;
1265 futilityValue = staticValue = bestValue = value = -VALUE_INFINITE;
1268 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1270 // Initialize, and make an early exit in case of an aborted search,
1271 // an instant draw, maximum ply reached, etc.
1272 init_node(ss, ply, threadID);
1274 // After init_node() that calls poll()
1275 if (AbortSearch || TM.thread_should_stop(threadID))
1278 if (pos.is_draw() || ply >= PLY_MAX - 1)
1281 // Mate distance pruning
1282 if (value_mated_in(ply) >= beta)
1285 if (value_mate_in(ply + 1) < beta)
1288 // We don't want the score of a partial search to overwrite a previous full search
1289 // TT value, so we use a different position key in case of an excluded move exsists.
1290 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1292 // Transposition table lookup
1293 tte = TT.retrieve(posKey);
1294 ttMove = (tte ? tte->move() : MOVE_NONE);
1296 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1298 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1299 return value_from_tt(tte->value(), ply);
1302 isCheck = pos.is_check();
1304 // Evaluate the position statically
1307 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1308 staticValue = value_from_tt(tte->value(), ply);
1310 staticValue = evaluate(pos, ei, threadID);
1312 ss[ply].eval = staticValue;
1313 futilityValue = staticValue + futility_margin(depth, 0); //FIXME: Remove me, only for split
1314 staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
1315 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1318 // Static null move pruning. We're betting that the opponent doesn't have
1319 // a move that will reduce the score by more than FutilityMargins[int(depth)]
1320 // if we do a null move.
1323 && depth < RazorDepth
1324 && staticValue - futility_margin(depth, 0) >= beta)
1325 return staticValue - futility_margin(depth, 0);
1331 && !value_is_mate(beta)
1332 && ok_to_do_nullmove(pos)
1333 && staticValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1335 ss[ply].currentMove = MOVE_NULL;
1337 pos.do_null_move(st);
1339 // Null move dynamic reduction based on depth
1340 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1342 // Null move dynamic reduction based on value
1343 if (staticValue - beta > PawnValueMidgame)
1346 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1348 pos.undo_null_move();
1350 if (nullValue >= beta)
1352 if (depth < 6 * OnePly)
1355 // Do zugzwang verification search
1356 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1360 // The null move failed low, which means that we may be faced with
1361 // some kind of threat. If the previous move was reduced, check if
1362 // the move that refuted the null move was somehow connected to the
1363 // move which was reduced. If a connection is found, return a fail
1364 // low score (which will cause the reduced move to fail high in the
1365 // parent node, which will trigger a re-search with full depth).
1366 if (nullValue == value_mated_in(ply + 2))
1369 ss[ply].threatMove = ss[ply + 1].currentMove;
1370 if ( depth < ThreatDepth
1371 && ss[ply - 1].reduction
1372 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1376 // Null move search not allowed, try razoring
1377 else if ( !value_is_mate(beta)
1379 && depth < RazorDepth
1380 && staticValue < beta - (NullMoveMargin + 16 * depth)
1381 && ss[ply - 1].currentMove != MOVE_NULL
1382 && ttMove == MOVE_NONE
1383 && !pos.has_pawn_on_7th(pos.side_to_move()))
1385 Value rbeta = beta - (NullMoveMargin + 16 * depth);
1386 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1391 // Go with internal iterative deepening if we don't have a TT move
1392 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1393 !isCheck && ss[ply].eval >= beta - IIDMargin)
1395 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1396 ttMove = ss[ply].pv[ply];
1397 tte = TT.retrieve(posKey);
1400 // Initialize a MovePicker object for the current position, and prepare
1401 // to search all moves.
1402 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1405 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1406 while ( bestValue < beta
1407 && (move = mp.get_next_move()) != MOVE_NONE
1408 && !TM.thread_should_stop(threadID))
1410 assert(move_is_ok(move));
1412 if (move == excludedMove)
1415 moveIsCheck = pos.move_is_check(move, ci);
1416 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1417 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1419 // Decide the new search depth
1420 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1422 // Singular extension search. We extend the TT move if its value is much better than
1423 // its siblings. To verify this we do a reduced search on all the other moves but the
1424 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1425 if ( depth >= 8 * OnePly
1427 && move == tte->move()
1428 && !excludedMove // Do not allow recursive single-reply search
1430 && is_lower_bound(tte->type())
1431 && tte->depth() >= depth - 3 * OnePly)
1433 Value ttValue = value_from_tt(tte->value(), ply);
1435 if (abs(ttValue) < VALUE_KNOWN_WIN)
1437 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1439 if (excValue < ttValue - SingleReplyMargin)
1444 newDepth = depth - OnePly + ext;
1446 // Update current move
1447 movesSearched[moveCount++] = ss[ply].currentMove = move;
1452 && !captureOrPromotion
1453 && !move_is_castle(move)
1456 // Move count based pruning
1457 if ( moveCount >= futility_move_count(depth)
1458 && ok_to_prune(pos, move, ss[ply].threatMove)
1459 && bestValue > value_mated_in(PLY_MAX))
1462 // Value based pruning
1463 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1464 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1465 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1467 if (futilityValueScaled < beta)
1469 if (futilityValueScaled > bestValue)
1470 bestValue = futilityValueScaled;
1475 // Make and search the move
1476 pos.do_move(move, st, ci, moveIsCheck);
1478 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1479 // if the move fails high will be re-searched at full depth.
1480 bool doFullDepthSearch = true;
1482 if ( depth >= 3*OnePly
1484 && !captureOrPromotion
1485 && !move_is_castle(move)
1486 && !move_is_killer(move, ss[ply]))
1488 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1489 if (ss[ply].reduction)
1491 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1492 doFullDepthSearch = (value >= beta);
1496 if (doFullDepthSearch) // Go with full depth non-pv search
1498 ss[ply].reduction = Depth(0);
1499 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1501 pos.undo_move(move);
1503 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1506 if (value > bestValue)
1512 if (value == value_mate_in(ply + 1))
1513 ss[ply].mateKiller = move;
1517 if ( TM.active_threads() > 1
1519 && depth >= MinimumSplitDepth
1521 && TM.available_thread_exists(threadID)
1523 && !TM.thread_should_stop(threadID)
1524 && TM.split(pos, ss, ply, NULL, beta, &bestValue, futilityValue, //FIXME: SMP & futilityValue
1525 depth, &moveCount, &mp, threadID, false))
1529 // All legal moves have been searched. A special case: If there were
1530 // no legal moves, it must be mate or stalemate.
1532 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1534 // If the search is not aborted, update the transposition table,
1535 // history counters, and killer moves.
1536 if (AbortSearch || TM.thread_should_stop(threadID))
1539 if (bestValue < beta)
1540 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1543 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1544 move = ss[ply].pv[ply];
1545 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1546 if (!pos.move_is_capture_or_promotion(move))
1548 update_history(pos, move, depth, movesSearched, moveCount);
1549 update_killers(move, ss[ply]);
1554 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1560 // qsearch() is the quiescence search function, which is called by the main
1561 // search function when the remaining depth is zero (or, to be more precise,
1562 // less than OnePly).
1564 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1565 Depth depth, int ply, int threadID) {
1567 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1568 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1570 assert(ply >= 0 && ply < PLY_MAX);
1571 assert(threadID >= 0 && threadID < TM.active_threads());
1576 Value staticValue, bestValue, value, futilityBase, futilityValue;
1577 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1578 const TTEntry* tte = NULL;
1580 bool pvNode = (beta - alpha != 1);
1581 Value oldAlpha = alpha;
1583 // Initialize, and make an early exit in case of an aborted search,
1584 // an instant draw, maximum ply reached, etc.
1585 init_node(ss, ply, threadID);
1587 // After init_node() that calls poll()
1588 if (AbortSearch || TM.thread_should_stop(threadID))
1591 if (pos.is_draw() || ply >= PLY_MAX - 1)
1594 // Transposition table lookup. At PV nodes, we don't use the TT for
1595 // pruning, but only for move ordering.
1596 tte = TT.retrieve(pos.get_key());
1597 ttMove = (tte ? tte->move() : MOVE_NONE);
1599 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1601 assert(tte->type() != VALUE_TYPE_EVAL);
1603 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1604 return value_from_tt(tte->value(), ply);
1607 isCheck = pos.is_check();
1609 // Evaluate the position statically
1611 staticValue = -VALUE_INFINITE;
1612 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1613 staticValue = value_from_tt(tte->value(), ply);
1615 staticValue = evaluate(pos, ei, threadID);
1619 ss[ply].eval = staticValue;
1620 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1623 // Initialize "stand pat score", and return it immediately if it is
1625 bestValue = staticValue;
1627 if (bestValue >= beta)
1629 // Store the score to avoid a future costly evaluation() call
1630 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1631 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1636 if (bestValue > alpha)
1639 // If we are near beta then try to get a cutoff pushing checks a bit further
1640 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1642 // Initialize a MovePicker object for the current position, and prepare
1643 // to search the moves. Because the depth is <= 0 here, only captures,
1644 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1645 // and we are near beta) will be generated.
1646 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1648 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1649 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1651 // Loop through the moves until no moves remain or a beta cutoff
1653 while ( alpha < beta
1654 && (move = mp.get_next_move()) != MOVE_NONE)
1656 assert(move_is_ok(move));
1658 moveIsCheck = pos.move_is_check(move, ci);
1660 // Update current move
1662 ss[ply].currentMove = move;
1670 && !move_is_promotion(move)
1671 && !pos.move_is_passed_pawn_push(move))
1673 futilityValue = futilityBase
1674 + pos.endgame_value_of_piece_on(move_to(move))
1675 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1677 if (futilityValue < alpha)
1679 if (futilityValue > bestValue)
1680 bestValue = futilityValue;
1685 // Detect blocking evasions that are candidate to be pruned
1686 evasionPrunable = isCheck
1687 && bestValue != -VALUE_INFINITE
1688 && !pos.move_is_capture(move)
1689 && pos.type_of_piece_on(move_from(move)) != KING
1690 && !pos.can_castle(pos.side_to_move());
1692 // Don't search moves with negative SEE values
1693 if ( (!isCheck || evasionPrunable)
1696 && !move_is_promotion(move)
1697 && pos.see_sign(move) < 0)
1700 // Make and search the move
1701 pos.do_move(move, st, ci, moveIsCheck);
1702 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1703 pos.undo_move(move);
1705 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1708 if (value > bestValue)
1719 // All legal moves have been searched. A special case: If we're in check
1720 // and no legal moves were found, it is checkmate.
1721 if (!moveCount && pos.is_check()) // Mate!
1722 return value_mated_in(ply);
1724 // Update transposition table
1725 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1726 if (bestValue <= oldAlpha)
1728 // If bestValue isn't changed it means it is still the static evaluation
1729 // of the node, so keep this info to avoid a future evaluation() call.
1730 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1731 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1733 else if (bestValue >= beta)
1735 move = ss[ply].pv[ply];
1736 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1738 // Update killers only for good checking moves
1739 if (!pos.move_is_capture_or_promotion(move))
1740 update_killers(move, ss[ply]);
1743 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1745 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1751 // sp_search() is used to search from a split point. This function is called
1752 // by each thread working at the split point. It is similar to the normal
1753 // search() function, but simpler. Because we have already probed the hash
1754 // table, done a null move search, and searched the first move before
1755 // splitting, we don't have to repeat all this work in sp_search(). We
1756 // also don't need to store anything to the hash table here: This is taken
1757 // care of after we return from the split point.
1759 void sp_search(SplitPoint* sp, int threadID) {
1761 assert(threadID >= 0 && threadID < TM.active_threads());
1762 assert(TM.active_threads() > 1);
1764 Position pos(*sp->pos);
1766 SearchStack* ss = sp->sstack[threadID];
1767 Value value = -VALUE_INFINITE;
1770 bool isCheck = pos.is_check();
1771 bool useFutilityPruning = sp->depth < 7 * OnePly //FIXME: sync with search
1774 while ( lock_grab_bool(&(sp->lock))
1775 && sp->bestValue < sp->beta
1776 && !TM.thread_should_stop(threadID)
1777 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1779 moveCount = ++sp->moves;
1780 lock_release(&(sp->lock));
1782 assert(move_is_ok(move));
1784 bool moveIsCheck = pos.move_is_check(move, ci);
1785 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1787 ss[sp->ply].currentMove = move;
1789 // Decide the new search depth
1791 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1792 Depth newDepth = sp->depth - OnePly + ext;
1795 if ( useFutilityPruning
1797 && !captureOrPromotion)
1799 // Move count based pruning
1800 if ( moveCount >= futility_move_count(sp->depth)
1801 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1802 && sp->bestValue > value_mated_in(PLY_MAX))
1805 // Value based pruning
1806 Value futilityValueScaled = sp->futilityValue - moveCount * 8; //FIXME: sync with search
1808 if (futilityValueScaled < sp->beta)
1810 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1812 lock_grab(&(sp->lock));
1813 if (futilityValueScaled > sp->bestValue)
1814 sp->bestValue = futilityValueScaled;
1815 lock_release(&(sp->lock));
1821 // Make and search the move.
1823 pos.do_move(move, st, ci, moveIsCheck);
1825 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1826 // if the move fails high will be re-searched at full depth.
1827 bool doFullDepthSearch = true;
1830 && !captureOrPromotion
1831 && !move_is_castle(move)
1832 && !move_is_killer(move, ss[sp->ply]))
1834 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1835 if (ss[sp->ply].reduction)
1837 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1838 doFullDepthSearch = (value >= sp->beta);
1842 if (doFullDepthSearch) // Go with full depth non-pv search
1844 ss[sp->ply].reduction = Depth(0);
1845 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1847 pos.undo_move(move);
1849 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1852 if (value > sp->bestValue) // Less then 2% of cases
1854 lock_grab(&(sp->lock));
1855 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1857 sp->bestValue = value;
1858 if (sp->bestValue >= sp->beta)
1860 sp->stopRequest = true;
1861 sp_update_pv(sp->parentSstack, ss, sp->ply);
1864 lock_release(&(sp->lock));
1868 /* Here we have the lock still grabbed */
1871 sp->slaves[threadID] = 0;
1873 lock_release(&(sp->lock));
1877 // sp_search_pv() is used to search from a PV split point. This function
1878 // is called by each thread working at the split point. It is similar to
1879 // the normal search_pv() function, but simpler. Because we have already
1880 // probed the hash table and searched the first move before splitting, we
1881 // don't have to repeat all this work in sp_search_pv(). We also don't
1882 // need to store anything to the hash table here: This is taken care of
1883 // after we return from the split point.
1885 void sp_search_pv(SplitPoint* sp, int threadID) {
1887 assert(threadID >= 0 && threadID < TM.active_threads());
1888 assert(TM.active_threads() > 1);
1890 Position pos(*sp->pos);
1892 SearchStack* ss = sp->sstack[threadID];
1893 Value value = -VALUE_INFINITE;
1897 while ( lock_grab_bool(&(sp->lock))
1898 && sp->alpha < sp->beta
1899 && !TM.thread_should_stop(threadID)
1900 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1902 moveCount = ++sp->moves;
1903 lock_release(&(sp->lock));
1905 assert(move_is_ok(move));
1907 bool moveIsCheck = pos.move_is_check(move, ci);
1908 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1910 ss[sp->ply].currentMove = move;
1912 // Decide the new search depth
1914 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1915 Depth newDepth = sp->depth - OnePly + ext;
1917 // Make and search the move.
1919 pos.do_move(move, st, ci, moveIsCheck);
1921 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1922 // if the move fails high will be re-searched at full depth.
1923 bool doFullDepthSearch = true;
1926 && !captureOrPromotion
1927 && !move_is_castle(move)
1928 && !move_is_killer(move, ss[sp->ply]))
1930 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1931 if (ss[sp->ply].reduction)
1933 Value localAlpha = sp->alpha;
1934 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1935 doFullDepthSearch = (value > localAlpha);
1939 if (doFullDepthSearch) // Go with full depth non-pv search
1941 Value localAlpha = sp->alpha;
1942 ss[sp->ply].reduction = Depth(0);
1943 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1945 if (value > localAlpha && value < sp->beta)
1947 // If another thread has failed high then sp->alpha has been increased
1948 // to be higher or equal then beta, if so, avoid to start a PV search.
1949 localAlpha = sp->alpha;
1950 if (localAlpha < sp->beta)
1951 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1953 assert(TM.thread_should_stop(threadID));
1956 pos.undo_move(move);
1958 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1961 if (value > sp->bestValue) // Less then 2% of cases
1963 lock_grab(&(sp->lock));
1964 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1966 sp->bestValue = value;
1967 if (value > sp->alpha)
1969 // Ask threads to stop before to modify sp->alpha
1970 if (value >= sp->beta)
1971 sp->stopRequest = true;
1975 sp_update_pv(sp->parentSstack, ss, sp->ply);
1976 if (value == value_mate_in(sp->ply + 1))
1977 ss[sp->ply].mateKiller = move;
1980 lock_release(&(sp->lock));
1984 /* Here we have the lock still grabbed */
1987 sp->slaves[threadID] = 0;
1989 lock_release(&(sp->lock));
1993 // init_node() is called at the beginning of all the search functions
1994 // (search(), search_pv(), qsearch(), and so on) and initializes the
1995 // search stack object corresponding to the current node. Once every
1996 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1997 // for user input and checks whether it is time to stop the search.
1999 void init_node(SearchStack ss[], int ply, int threadID) {
2001 assert(ply >= 0 && ply < PLY_MAX);
2002 assert(threadID >= 0 && threadID < TM.active_threads());
2004 TM.incrementNodeCounter(threadID);
2009 if (NodesSincePoll >= NodesBetweenPolls)
2016 ss[ply + 2].initKillers();
2017 TM.print_current_line(ss, ply, threadID);
2021 // update_pv() is called whenever a search returns a value > alpha.
2022 // It updates the PV in the SearchStack object corresponding to the
2025 void update_pv(SearchStack ss[], int ply) {
2027 assert(ply >= 0 && ply < PLY_MAX);
2031 ss[ply].pv[ply] = ss[ply].currentMove;
2033 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2034 ss[ply].pv[p] = ss[ply + 1].pv[p];
2036 ss[ply].pv[p] = MOVE_NONE;
2040 // sp_update_pv() is a variant of update_pv for use at split points. The
2041 // difference between the two functions is that sp_update_pv also updates
2042 // the PV at the parent node.
2044 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2046 assert(ply >= 0 && ply < PLY_MAX);
2050 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2052 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2053 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2055 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2059 // connected_moves() tests whether two moves are 'connected' in the sense
2060 // that the first move somehow made the second move possible (for instance
2061 // if the moving piece is the same in both moves). The first move is assumed
2062 // to be the move that was made to reach the current position, while the
2063 // second move is assumed to be a move from the current position.
2065 bool connected_moves(const Position& pos, Move m1, Move m2) {
2067 Square f1, t1, f2, t2;
2070 assert(move_is_ok(m1));
2071 assert(move_is_ok(m2));
2073 if (m2 == MOVE_NONE)
2076 // Case 1: The moving piece is the same in both moves
2082 // Case 2: The destination square for m2 was vacated by m1
2088 // Case 3: Moving through the vacated square
2089 if ( piece_is_slider(pos.piece_on(f2))
2090 && bit_is_set(squares_between(f2, t2), f1))
2093 // Case 4: The destination square for m2 is defended by the moving piece in m1
2094 p = pos.piece_on(t1);
2095 if (bit_is_set(pos.attacks_from(p, t1), t2))
2098 // Case 5: Discovered check, checking piece is the piece moved in m1
2099 if ( piece_is_slider(p)
2100 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2101 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2103 // discovered_check_candidates() works also if the Position's side to
2104 // move is the opposite of the checking piece.
2105 Color them = opposite_color(pos.side_to_move());
2106 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2108 if (bit_is_set(dcCandidates, f2))
2115 // value_is_mate() checks if the given value is a mate one
2116 // eventually compensated for the ply.
2118 bool value_is_mate(Value value) {
2120 assert(abs(value) <= VALUE_INFINITE);
2122 return value <= value_mated_in(PLY_MAX)
2123 || value >= value_mate_in(PLY_MAX);
2127 // move_is_killer() checks if the given move is among the
2128 // killer moves of that ply.
2130 bool move_is_killer(Move m, const SearchStack& ss) {
2132 const Move* k = ss.killers;
2133 for (int i = 0; i < KILLER_MAX; i++, k++)
2141 // extension() decides whether a move should be searched with normal depth,
2142 // or with extended depth. Certain classes of moves (checking moves, in
2143 // particular) are searched with bigger depth than ordinary moves and in
2144 // any case are marked as 'dangerous'. Note that also if a move is not
2145 // extended, as example because the corresponding UCI option is set to zero,
2146 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2148 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2149 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2151 assert(m != MOVE_NONE);
2153 Depth result = Depth(0);
2154 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2159 result += CheckExtension[pvNode];
2162 result += SingleEvasionExtension[pvNode];
2165 result += MateThreatExtension[pvNode];
2168 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2170 Color c = pos.side_to_move();
2171 if (relative_rank(c, move_to(m)) == RANK_7)
2173 result += PawnPushTo7thExtension[pvNode];
2176 if (pos.pawn_is_passed(c, move_to(m)))
2178 result += PassedPawnExtension[pvNode];
2183 if ( captureOrPromotion
2184 && pos.type_of_piece_on(move_to(m)) != PAWN
2185 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2186 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2187 && !move_is_promotion(m)
2190 result += PawnEndgameExtension[pvNode];
2195 && captureOrPromotion
2196 && pos.type_of_piece_on(move_to(m)) != PAWN
2197 && pos.see_sign(m) >= 0)
2203 return Min(result, OnePly);
2207 // ok_to_do_nullmove() looks at the current position and decides whether
2208 // doing a 'null move' should be allowed. In order to avoid zugzwang
2209 // problems, null moves are not allowed when the side to move has very
2210 // little material left. Currently, the test is a bit too simple: Null
2211 // moves are avoided only when the side to move has only pawns left.
2212 // It's probably a good idea to avoid null moves in at least some more
2213 // complicated endgames, e.g. KQ vs KR. FIXME
2215 bool ok_to_do_nullmove(const Position& pos) {
2217 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2221 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2222 // non-tactical moves late in the move list close to the leaves are
2223 // candidates for pruning.
2225 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2227 assert(move_is_ok(m));
2228 assert(threat == MOVE_NONE || move_is_ok(threat));
2229 assert(!pos.move_is_check(m));
2230 assert(!pos.move_is_capture_or_promotion(m));
2231 assert(!pos.move_is_passed_pawn_push(m));
2233 Square mfrom, mto, tfrom, tto;
2235 // Prune if there isn't any threat move
2236 if (threat == MOVE_NONE)
2239 mfrom = move_from(m);
2241 tfrom = move_from(threat);
2242 tto = move_to(threat);
2244 // Case 1: Don't prune moves which move the threatened piece
2248 // Case 2: If the threatened piece has value less than or equal to the
2249 // value of the threatening piece, don't prune move which defend it.
2250 if ( pos.move_is_capture(threat)
2251 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2252 || pos.type_of_piece_on(tfrom) == KING)
2253 && pos.move_attacks_square(m, tto))
2256 // Case 3: If the moving piece in the threatened move is a slider, don't
2257 // prune safe moves which block its ray.
2258 if ( piece_is_slider(pos.piece_on(tfrom))
2259 && bit_is_set(squares_between(tfrom, tto), mto)
2260 && pos.see_sign(m) >= 0)
2267 // ok_to_use_TT() returns true if a transposition table score
2268 // can be used at a given point in search.
2270 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2272 Value v = value_from_tt(tte->value(), ply);
2274 return ( tte->depth() >= depth
2275 || v >= Max(value_mate_in(PLY_MAX), beta)
2276 || v < Min(value_mated_in(PLY_MAX), beta))
2278 && ( (is_lower_bound(tte->type()) && v >= beta)
2279 || (is_upper_bound(tte->type()) && v < beta));
2283 // refine_eval() returns the transposition table score if
2284 // possible otherwise falls back on static position evaluation.
2286 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2291 Value v = value_from_tt(tte->value(), ply);
2293 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2294 || (is_upper_bound(tte->type()) && v < defaultEval))
2301 // update_history() registers a good move that produced a beta-cutoff
2302 // in history and marks as failures all the other moves of that ply.
2304 void update_history(const Position& pos, Move move, Depth depth,
2305 Move movesSearched[], int moveCount) {
2309 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2311 for (int i = 0; i < moveCount - 1; i++)
2313 m = movesSearched[i];
2317 if (!pos.move_is_capture_or_promotion(m))
2318 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2323 // update_killers() add a good move that produced a beta-cutoff
2324 // among the killer moves of that ply.
2326 void update_killers(Move m, SearchStack& ss) {
2328 if (m == ss.killers[0])
2331 for (int i = KILLER_MAX - 1; i > 0; i--)
2332 ss.killers[i] = ss.killers[i - 1];
2338 // update_gains() updates the gains table of a non-capture move given
2339 // the static position evaluation before and after the move.
2341 void update_gains(const Position& pos, Move m, Value before, Value after) {
2344 && before != VALUE_NONE
2345 && after != VALUE_NONE
2346 && pos.captured_piece() == NO_PIECE_TYPE
2347 && !move_is_castle(m)
2348 && !move_is_promotion(m))
2349 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2353 // current_search_time() returns the number of milliseconds which have passed
2354 // since the beginning of the current search.
2356 int current_search_time() {
2358 return get_system_time() - SearchStartTime;
2362 // nps() computes the current nodes/second count.
2366 int t = current_search_time();
2367 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2371 // poll() performs two different functions: It polls for user input, and it
2372 // looks at the time consumed so far and decides if it's time to abort the
2377 static int lastInfoTime;
2378 int t = current_search_time();
2383 // We are line oriented, don't read single chars
2384 std::string command;
2386 if (!std::getline(std::cin, command))
2389 if (command == "quit")
2392 PonderSearch = false;
2396 else if (command == "stop")
2399 PonderSearch = false;
2401 else if (command == "ponderhit")
2405 // Print search information
2409 else if (lastInfoTime > t)
2410 // HACK: Must be a new search where we searched less than
2411 // NodesBetweenPolls nodes during the first second of search.
2414 else if (t - lastInfoTime >= 1000)
2417 lock_grab(&TM.IOLock);
2422 if (dbg_show_hit_rate)
2423 dbg_print_hit_rate();
2425 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2426 << " time " << t << " hashfull " << TT.full() << endl;
2428 lock_release(&TM.IOLock);
2430 if (ShowCurrentLine)
2431 TM.threads[0].printCurrentLineRequest = true;
2434 // Should we stop the search?
2438 bool stillAtFirstMove = RootMoveNumber == 1
2439 && !AspirationFailLow
2440 && t > MaxSearchTime + ExtraSearchTime;
2442 bool noMoreTime = t > AbsoluteMaxSearchTime
2443 || stillAtFirstMove;
2445 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2446 || (ExactMaxTime && t >= ExactMaxTime)
2447 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2452 // ponderhit() is called when the program is pondering (i.e. thinking while
2453 // it's the opponent's turn to move) in order to let the engine know that
2454 // it correctly predicted the opponent's move.
2458 int t = current_search_time();
2459 PonderSearch = false;
2461 bool stillAtFirstMove = RootMoveNumber == 1
2462 && !AspirationFailLow
2463 && t > MaxSearchTime + ExtraSearchTime;
2465 bool noMoreTime = t > AbsoluteMaxSearchTime
2466 || stillAtFirstMove;
2468 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2473 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2475 void init_ss_array(SearchStack ss[]) {
2477 for (int i = 0; i < 3; i++)
2480 ss[i].initKillers();
2485 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2486 // while the program is pondering. The point is to work around a wrinkle in
2487 // the UCI protocol: When pondering, the engine is not allowed to give a
2488 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2489 // We simply wait here until one of these commands is sent, and return,
2490 // after which the bestmove and pondermove will be printed (in id_loop()).
2492 void wait_for_stop_or_ponderhit() {
2494 std::string command;
2498 if (!std::getline(std::cin, command))
2501 if (command == "quit")
2506 else if (command == "ponderhit" || command == "stop")
2512 // init_thread() is the function which is called when a new thread is
2513 // launched. It simply calls the idle_loop() function with the supplied
2514 // threadID. There are two versions of this function; one for POSIX
2515 // threads and one for Windows threads.
2517 #if !defined(_MSC_VER)
2519 void* init_thread(void *threadID) {
2521 TM.idle_loop(*(int*)threadID, NULL);
2527 DWORD WINAPI init_thread(LPVOID threadID) {
2529 TM.idle_loop(*(int*)threadID, NULL);
2536 /// The ThreadsManager class
2538 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2539 // get_beta_counters() are getters/setters for the per thread
2540 // counters used to sort the moves at root.
2542 void ThreadsManager::resetNodeCounters() {
2544 for (int i = 0; i < MAX_THREADS; i++)
2545 threads[i].nodes = 0ULL;
2548 void ThreadsManager::resetBetaCounters() {
2550 for (int i = 0; i < MAX_THREADS; i++)
2551 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2554 int64_t ThreadsManager::nodes_searched() const {
2556 int64_t result = 0ULL;
2557 for (int i = 0; i < ActiveThreads; i++)
2558 result += threads[i].nodes;
2563 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2566 for (int i = 0; i < MAX_THREADS; i++)
2568 our += threads[i].betaCutOffs[us];
2569 their += threads[i].betaCutOffs[opposite_color(us)];
2574 // idle_loop() is where the threads are parked when they have no work to do.
2575 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2576 // object for which the current thread is the master.
2578 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2580 assert(threadID >= 0 && threadID < MAX_THREADS);
2584 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2585 // master should exit as last one.
2586 if (AllThreadsShouldExit)
2589 threads[threadID].state = THREAD_TERMINATED;
2593 // If we are not thinking, wait for a condition to be signaled
2594 // instead of wasting CPU time polling for work.
2595 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2597 assert(threadID != 0);
2598 threads[threadID].state = THREAD_SLEEPING;
2600 #if !defined(_MSC_VER)
2601 pthread_mutex_lock(&WaitLock);
2602 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2603 pthread_cond_wait(&WaitCond, &WaitLock);
2604 pthread_mutex_unlock(&WaitLock);
2606 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2610 // If thread has just woken up, mark it as available
2611 if (threads[threadID].state == THREAD_SLEEPING)
2612 threads[threadID].state = THREAD_AVAILABLE;
2614 // If this thread has been assigned work, launch a search
2615 if (threads[threadID].state == THREAD_WORKISWAITING)
2617 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2619 threads[threadID].state = THREAD_SEARCHING;
2621 if (threads[threadID].splitPoint->pvNode)
2622 sp_search_pv(threads[threadID].splitPoint, threadID);
2624 sp_search(threads[threadID].splitPoint, threadID);
2626 assert(threads[threadID].state == THREAD_SEARCHING);
2628 threads[threadID].state = THREAD_AVAILABLE;
2631 // If this thread is the master of a split point and all threads have
2632 // finished their work at this split point, return from the idle loop.
2633 if (waitSp != NULL && waitSp->cpus == 0)
2635 assert(threads[threadID].state == THREAD_AVAILABLE);
2637 threads[threadID].state = THREAD_SEARCHING;
2644 // init_threads() is called during startup. It launches all helper threads,
2645 // and initializes the split point stack and the global locks and condition
2648 void ThreadsManager::init_threads() {
2653 #if !defined(_MSC_VER)
2654 pthread_t pthread[1];
2657 // Initialize global locks
2658 lock_init(&MPLock, NULL);
2659 lock_init(&IOLock, NULL);
2661 // Initialize SplitPointStack locks
2662 for (i = 0; i < MAX_THREADS; i++)
2663 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2665 SplitPointStack[i][j].parent = NULL;
2666 lock_init(&(SplitPointStack[i][j].lock), NULL);
2669 #if !defined(_MSC_VER)
2670 pthread_mutex_init(&WaitLock, NULL);
2671 pthread_cond_init(&WaitCond, NULL);
2673 for (i = 0; i < MAX_THREADS; i++)
2674 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2677 // Will be set just before program exits to properly end the threads
2678 AllThreadsShouldExit = false;
2680 // Threads will be put to sleep as soon as created
2681 AllThreadsShouldSleep = true;
2683 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2685 threads[0].state = THREAD_SEARCHING;
2686 for (i = 1; i < MAX_THREADS; i++)
2687 threads[i].state = THREAD_AVAILABLE;
2689 // Launch the helper threads
2690 for (i = 1; i < MAX_THREADS; i++)
2693 #if !defined(_MSC_VER)
2694 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2697 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
2702 cout << "Failed to create thread number " << i << endl;
2703 Application::exit_with_failure();
2706 // Wait until the thread has finished launching and is gone to sleep
2707 while (threads[i].state != THREAD_SLEEPING);
2712 // exit_threads() is called when the program exits. It makes all the
2713 // helper threads exit cleanly.
2715 void ThreadsManager::exit_threads() {
2717 ActiveThreads = MAX_THREADS; // HACK
2718 AllThreadsShouldSleep = true; // HACK
2719 wake_sleeping_threads();
2721 // This makes the threads to exit idle_loop()
2722 AllThreadsShouldExit = true;
2724 // Wait for thread termination
2725 for (int i = 1; i < MAX_THREADS; i++)
2726 while (threads[i].state != THREAD_TERMINATED);
2728 // Now we can safely destroy the locks
2729 for (int i = 0; i < MAX_THREADS; i++)
2730 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2731 lock_destroy(&(SplitPointStack[i][j].lock));
2735 // thread_should_stop() checks whether the thread should stop its search.
2736 // This can happen if a beta cutoff has occurred in the thread's currently
2737 // active split point, or in some ancestor of the current split point.
2739 bool ThreadsManager::thread_should_stop(int threadID) const {
2741 assert(threadID >= 0 && threadID < ActiveThreads);
2745 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2750 // thread_is_available() checks whether the thread with threadID "slave" is
2751 // available to help the thread with threadID "master" at a split point. An
2752 // obvious requirement is that "slave" must be idle. With more than two
2753 // threads, this is not by itself sufficient: If "slave" is the master of
2754 // some active split point, it is only available as a slave to the other
2755 // threads which are busy searching the split point at the top of "slave"'s
2756 // split point stack (the "helpful master concept" in YBWC terminology).
2758 bool ThreadsManager::thread_is_available(int slave, int master) const {
2760 assert(slave >= 0 && slave < ActiveThreads);
2761 assert(master >= 0 && master < ActiveThreads);
2762 assert(ActiveThreads > 1);
2764 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2767 // Make a local copy to be sure doesn't change under our feet
2768 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2770 if (localActiveSplitPoints == 0)
2771 // No active split points means that the thread is available as
2772 // a slave for any other thread.
2775 if (ActiveThreads == 2)
2778 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2779 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2780 // could have been set to 0 by another thread leading to an out of bound access.
2781 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2788 // available_thread_exists() tries to find an idle thread which is available as
2789 // a slave for the thread with threadID "master".
2791 bool ThreadsManager::available_thread_exists(int master) const {
2793 assert(master >= 0 && master < ActiveThreads);
2794 assert(ActiveThreads > 1);
2796 for (int i = 0; i < ActiveThreads; i++)
2797 if (thread_is_available(i, master))
2804 // split() does the actual work of distributing the work at a node between
2805 // several threads at PV nodes. If it does not succeed in splitting the
2806 // node (because no idle threads are available, or because we have no unused
2807 // split point objects), the function immediately returns false. If
2808 // splitting is possible, a SplitPoint object is initialized with all the
2809 // data that must be copied to the helper threads (the current position and
2810 // search stack, alpha, beta, the search depth, etc.), and we tell our
2811 // helper threads that they have been assigned work. This will cause them
2812 // to instantly leave their idle loops and call sp_search_pv(). When all
2813 // threads have returned from sp_search_pv (or, equivalently, when
2814 // splitPoint->cpus becomes 0), split() returns true.
2816 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2817 Value* alpha, const Value beta, Value* bestValue, const Value futilityValue,
2818 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2821 assert(sstck != NULL);
2822 assert(ply >= 0 && ply < PLY_MAX);
2823 assert(*bestValue >= -VALUE_INFINITE);
2824 assert( ( pvNode && *bestValue <= *alpha)
2825 || (!pvNode && *bestValue < beta ));
2826 assert(!pvNode || *alpha < beta);
2827 assert(beta <= VALUE_INFINITE);
2828 assert(depth > Depth(0));
2829 assert(master >= 0 && master < ActiveThreads);
2830 assert(ActiveThreads > 1);
2832 SplitPoint* splitPoint;
2836 // If no other thread is available to help us, or if we have too many
2837 // active split points, don't split.
2838 if ( !available_thread_exists(master)
2839 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2841 lock_release(&MPLock);
2845 // Pick the next available split point object from the split point stack
2846 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2848 // Initialize the split point object
2849 splitPoint->parent = threads[master].splitPoint;
2850 splitPoint->stopRequest = false;
2851 splitPoint->ply = ply;
2852 splitPoint->depth = depth;
2853 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2854 splitPoint->beta = beta;
2855 splitPoint->pvNode = pvNode;
2856 splitPoint->bestValue = *bestValue;
2857 splitPoint->futilityValue = futilityValue;
2858 splitPoint->master = master;
2859 splitPoint->mp = mp;
2860 splitPoint->moves = *moves;
2861 splitPoint->cpus = 1;
2862 splitPoint->pos = &p;
2863 splitPoint->parentSstack = sstck;
2864 for (int i = 0; i < ActiveThreads; i++)
2865 splitPoint->slaves[i] = 0;
2867 threads[master].splitPoint = splitPoint;
2868 threads[master].activeSplitPoints++;
2870 // If we are here it means we are not available
2871 assert(threads[master].state != THREAD_AVAILABLE);
2873 // Allocate available threads setting state to THREAD_BOOKED
2874 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2875 if (thread_is_available(i, master))
2877 threads[i].state = THREAD_BOOKED;
2878 threads[i].splitPoint = splitPoint;
2879 splitPoint->slaves[i] = 1;
2883 assert(splitPoint->cpus > 1);
2885 // We can release the lock because slave threads are already booked and master is not available
2886 lock_release(&MPLock);
2888 // Tell the threads that they have work to do. This will make them leave
2889 // their idle loop. But before copy search stack tail for each thread.
2890 for (int i = 0; i < ActiveThreads; i++)
2891 if (i == master || splitPoint->slaves[i])
2893 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2895 assert(i == master || threads[i].state == THREAD_BOOKED);
2897 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2900 // Everything is set up. The master thread enters the idle loop, from
2901 // which it will instantly launch a search, because its state is
2902 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2903 // idle loop, which means that the main thread will return from the idle
2904 // loop when all threads have finished their work at this split point
2905 // (i.e. when splitPoint->cpus == 0).
2906 idle_loop(master, splitPoint);
2908 // We have returned from the idle loop, which means that all threads are
2909 // finished. Update alpha, beta and bestValue, and return.
2913 *alpha = splitPoint->alpha;
2915 *bestValue = splitPoint->bestValue;
2916 threads[master].activeSplitPoints--;
2917 threads[master].splitPoint = splitPoint->parent;
2919 lock_release(&MPLock);
2924 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2925 // to start a new search from the root.
2927 void ThreadsManager::wake_sleeping_threads() {
2929 assert(AllThreadsShouldSleep);
2930 assert(ActiveThreads > 0);
2932 AllThreadsShouldSleep = false;
2934 if (ActiveThreads == 1)
2937 for (int i = 1; i < ActiveThreads; i++)
2938 assert(threads[i].state == THREAD_SLEEPING);
2940 #if !defined(_MSC_VER)
2941 pthread_mutex_lock(&WaitLock);
2942 pthread_cond_broadcast(&WaitCond);
2943 pthread_mutex_unlock(&WaitLock);
2945 for (int i = 1; i < MAX_THREADS; i++)
2946 SetEvent(SitIdleEvent[i]);
2952 // put_threads_to_sleep() makes all the threads go to sleep just before
2953 // to leave think(), at the end of the search. Threads should have already
2954 // finished the job and should be idle.
2956 void ThreadsManager::put_threads_to_sleep() {
2958 assert(!AllThreadsShouldSleep);
2960 // This makes the threads to go to sleep
2961 AllThreadsShouldSleep = true;
2963 // Wait for the threads to be all sleeping and reset flags
2964 // to a known state.
2965 for (int i = 1; i < ActiveThreads; i++)
2967 while (threads[i].state != THREAD_SLEEPING);
2969 // This flag can be in a random state
2970 threads[i].printCurrentLineRequest = false;
2974 // print_current_line() prints _once_ the current line of search for a
2975 // given thread and then setup the print request for the next thread.
2976 // Called when the UCI option UCI_ShowCurrLine is 'true'.
2978 void ThreadsManager::print_current_line(SearchStack ss[], int ply, int threadID) {
2980 assert(ply >= 0 && ply < PLY_MAX);
2981 assert(threadID >= 0 && threadID < ActiveThreads);
2983 if (!threads[threadID].printCurrentLineRequest)
2987 threads[threadID].printCurrentLineRequest = false;
2989 if (threads[threadID].state == THREAD_SEARCHING)
2992 cout << "info currline " << (threadID + 1);
2993 for (int p = 0; p < ply; p++)
2994 cout << " " << ss[p].currentMove;
2997 lock_release(&IOLock);
3000 // Setup print request for the next thread ID
3001 if (threadID + 1 < ActiveThreads)
3002 threads[threadID + 1].printCurrentLineRequest = true;
3006 /// The RootMoveList class
3008 // RootMoveList c'tor
3010 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3012 SearchStack ss[PLY_MAX_PLUS_2];
3013 MoveStack mlist[MaxRootMoves];
3015 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3017 // Generate all legal moves
3018 MoveStack* last = generate_moves(pos, mlist);
3020 // Add each move to the moves[] array
3021 for (MoveStack* cur = mlist; cur != last; cur++)
3023 bool includeMove = includeAllMoves;
3025 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3026 includeMove = (searchMoves[k] == cur->move);
3031 // Find a quick score for the move
3033 pos.do_move(cur->move, st);
3034 moves[count].move = cur->move;
3035 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3036 moves[count].pv[0] = cur->move;
3037 moves[count].pv[1] = MOVE_NONE;
3038 pos.undo_move(cur->move);
3045 // RootMoveList simple methods definitions
3047 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3049 moves[moveNum].nodes = nodes;
3050 moves[moveNum].cumulativeNodes += nodes;
3053 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3055 moves[moveNum].ourBeta = our;
3056 moves[moveNum].theirBeta = their;
3059 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3063 for (j = 0; pv[j] != MOVE_NONE; j++)
3064 moves[moveNum].pv[j] = pv[j];
3066 moves[moveNum].pv[j] = MOVE_NONE;
3070 // RootMoveList::sort() sorts the root move list at the beginning of a new
3073 void RootMoveList::sort() {
3075 sort_multipv(count - 1); // Sort all items
3079 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3080 // list by their scores and depths. It is used to order the different PVs
3081 // correctly in MultiPV mode.
3083 void RootMoveList::sort_multipv(int n) {
3087 for (i = 1; i <= n; i++)
3089 RootMove rm = moves[i];
3090 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3091 moves[j] = moves[j - 1];