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 // Step 1. Initialize node and poll
1271 // Polling can abort search.
1272 init_node(ss, ply, threadID);
1274 // Step 2. Check for aborted search and immediate draw
1275 if (AbortSearch || TM.thread_should_stop(threadID))
1278 if (pos.is_draw() || ply >= PLY_MAX - 1)
1281 // Step 3. Mate distance pruning
1282 if (value_mated_in(ply) >= beta)
1285 if (value_mate_in(ply + 1) < beta)
1288 // Step 4. Transposition table lookup
1290 // We don't want the score of a partial search to overwrite a previous full search
1291 // TT value, so we use a different position key in case of an excluded move exsists.
1292 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1294 tte = TT.retrieve(posKey);
1295 ttMove = (tte ? tte->move() : MOVE_NONE);
1297 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1299 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1300 return value_from_tt(tte->value(), ply);
1303 // Step 5. Evaluate the position statically
1304 isCheck = pos.is_check();
1308 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1309 staticValue = value_from_tt(tte->value(), ply);
1311 staticValue = evaluate(pos, ei, threadID);
1313 ss[ply].eval = staticValue;
1314 futilityValue = staticValue + futility_margin(depth, 0); //FIXME: Remove me, only for split
1315 staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
1316 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1320 if ( !value_is_mate(beta)
1322 && depth < RazorDepth
1323 && staticValue < beta - (0x200 + 16 * depth)
1324 && ss[ply - 1].currentMove != MOVE_NULL
1325 && ttMove == MOVE_NONE
1326 && !pos.has_pawn_on_7th(pos.side_to_move()))
1328 Value rbeta = beta - (0x200 + 16 * depth);
1329 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1331 return v; //FIXME: Logically should be: return (v + 0x200 + 16 * depth);
1334 // Step 7. Static null move pruning
1335 // We're betting that the opponent doesn't have a move that will reduce
1336 // the score by more than fuility_margin(depth) if we do a null move.
1339 && depth < RazorDepth
1340 && staticValue - futility_margin(depth, 0) >= beta)
1341 return staticValue - futility_margin(depth, 0);
1343 // Step 8. Null move search with verification search
1344 // When we jump directly to qsearch() we do a null move only if static value is
1345 // at least beta. Otherwise we do a null move if static value is not more than
1346 // NullMoveMargin under beta.
1350 && !value_is_mate(beta)
1351 && ok_to_do_nullmove(pos)
1352 && staticValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1354 ss[ply].currentMove = MOVE_NULL;
1356 pos.do_null_move(st);
1358 // Null move dynamic reduction based on depth
1359 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1361 // Null move dynamic reduction based on value
1362 if (staticValue - beta > PawnValueMidgame)
1365 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1367 pos.undo_null_move();
1369 if (nullValue >= beta)
1371 if (depth < 6 * OnePly)
1374 // Do zugzwang verification search
1375 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1379 // The null move failed low, which means that we may be faced with
1380 // some kind of threat. If the previous move was reduced, check if
1381 // the move that refuted the null move was somehow connected to the
1382 // move which was reduced. If a connection is found, return a fail
1383 // low score (which will cause the reduced move to fail high in the
1384 // parent node, which will trigger a re-search with full depth).
1385 if (nullValue == value_mated_in(ply + 2))
1388 ss[ply].threatMove = ss[ply + 1].currentMove;
1389 if ( depth < ThreatDepth
1390 && ss[ply - 1].reduction
1391 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1396 // Step 9. Internal iterative deepening
1397 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1398 !isCheck && ss[ply].eval >= beta - IIDMargin)
1400 search(pos, ss, beta, depth/2, ply, false, threadID);
1401 ttMove = ss[ply].pv[ply];
1402 tte = TT.retrieve(posKey);
1405 // Initialize a MovePicker object for the current position, and prepare
1406 // to search all moves.
1407 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1410 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1411 while ( bestValue < beta
1412 && (move = mp.get_next_move()) != MOVE_NONE
1413 && !TM.thread_should_stop(threadID))
1415 assert(move_is_ok(move));
1417 if (move == excludedMove)
1420 moveIsCheck = pos.move_is_check(move, ci);
1421 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1422 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1424 // Decide the new search depth
1425 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1427 // Singular extension search. We extend the TT move if its value is much better than
1428 // its siblings. To verify this we do a reduced search on all the other moves but the
1429 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1430 if ( depth >= 8 * OnePly
1432 && move == tte->move()
1433 && !excludedMove // Do not allow recursive single-reply search
1435 && is_lower_bound(tte->type())
1436 && tte->depth() >= depth - 3 * OnePly)
1438 Value ttValue = value_from_tt(tte->value(), ply);
1440 if (abs(ttValue) < VALUE_KNOWN_WIN)
1442 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1444 if (excValue < ttValue - SingleReplyMargin)
1449 newDepth = depth - OnePly + ext;
1451 // Update current move
1452 movesSearched[moveCount++] = ss[ply].currentMove = move;
1457 && !captureOrPromotion
1458 && !move_is_castle(move)
1461 // Move count based pruning
1462 if ( moveCount >= futility_move_count(depth)
1463 && ok_to_prune(pos, move, ss[ply].threatMove)
1464 && bestValue > value_mated_in(PLY_MAX))
1467 // Value based pruning
1468 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1469 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1470 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1472 if (futilityValueScaled < beta)
1474 if (futilityValueScaled > bestValue)
1475 bestValue = futilityValueScaled;
1480 // Make and search the move
1481 pos.do_move(move, st, ci, moveIsCheck);
1483 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1484 // if the move fails high will be re-searched at full depth.
1485 bool doFullDepthSearch = true;
1487 if ( depth >= 3*OnePly
1489 && !captureOrPromotion
1490 && !move_is_castle(move)
1491 && !move_is_killer(move, ss[ply]))
1493 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1494 if (ss[ply].reduction)
1496 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1497 doFullDepthSearch = (value >= beta);
1501 if (doFullDepthSearch) // Go with full depth non-pv search
1503 ss[ply].reduction = Depth(0);
1504 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1506 pos.undo_move(move);
1508 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1511 if (value > bestValue)
1517 if (value == value_mate_in(ply + 1))
1518 ss[ply].mateKiller = move;
1522 if ( TM.active_threads() > 1
1524 && depth >= MinimumSplitDepth
1526 && TM.available_thread_exists(threadID)
1528 && !TM.thread_should_stop(threadID)
1529 && TM.split(pos, ss, ply, NULL, beta, &bestValue, futilityValue, //FIXME: SMP & futilityValue
1530 depth, &moveCount, &mp, threadID, false))
1534 // All legal moves have been searched. A special case: If there were
1535 // no legal moves, it must be mate or stalemate.
1537 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1539 // If the search is not aborted, update the transposition table,
1540 // history counters, and killer moves.
1541 if (AbortSearch || TM.thread_should_stop(threadID))
1544 if (bestValue < beta)
1545 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1548 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1549 move = ss[ply].pv[ply];
1550 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1551 if (!pos.move_is_capture_or_promotion(move))
1553 update_history(pos, move, depth, movesSearched, moveCount);
1554 update_killers(move, ss[ply]);
1559 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1565 // qsearch() is the quiescence search function, which is called by the main
1566 // search function when the remaining depth is zero (or, to be more precise,
1567 // less than OnePly).
1569 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1570 Depth depth, int ply, int threadID) {
1572 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1573 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1575 assert(ply >= 0 && ply < PLY_MAX);
1576 assert(threadID >= 0 && threadID < TM.active_threads());
1581 Value staticValue, bestValue, value, futilityBase, futilityValue;
1582 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1583 const TTEntry* tte = NULL;
1585 bool pvNode = (beta - alpha != 1);
1586 Value oldAlpha = alpha;
1588 // Initialize, and make an early exit in case of an aborted search,
1589 // an instant draw, maximum ply reached, etc.
1590 init_node(ss, ply, threadID);
1592 // After init_node() that calls poll()
1593 if (AbortSearch || TM.thread_should_stop(threadID))
1596 if (pos.is_draw() || ply >= PLY_MAX - 1)
1599 // Transposition table lookup. At PV nodes, we don't use the TT for
1600 // pruning, but only for move ordering.
1601 tte = TT.retrieve(pos.get_key());
1602 ttMove = (tte ? tte->move() : MOVE_NONE);
1604 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1606 assert(tte->type() != VALUE_TYPE_EVAL);
1608 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1609 return value_from_tt(tte->value(), ply);
1612 isCheck = pos.is_check();
1614 // Evaluate the position statically
1616 staticValue = -VALUE_INFINITE;
1617 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1618 staticValue = value_from_tt(tte->value(), ply);
1620 staticValue = evaluate(pos, ei, threadID);
1624 ss[ply].eval = staticValue;
1625 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1628 // Initialize "stand pat score", and return it immediately if it is
1630 bestValue = staticValue;
1632 if (bestValue >= beta)
1634 // Store the score to avoid a future costly evaluation() call
1635 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1636 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1641 if (bestValue > alpha)
1644 // If we are near beta then try to get a cutoff pushing checks a bit further
1645 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1647 // Initialize a MovePicker object for the current position, and prepare
1648 // to search the moves. Because the depth is <= 0 here, only captures,
1649 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1650 // and we are near beta) will be generated.
1651 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1653 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1654 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1656 // Loop through the moves until no moves remain or a beta cutoff
1658 while ( alpha < beta
1659 && (move = mp.get_next_move()) != MOVE_NONE)
1661 assert(move_is_ok(move));
1663 moveIsCheck = pos.move_is_check(move, ci);
1665 // Update current move
1667 ss[ply].currentMove = move;
1675 && !move_is_promotion(move)
1676 && !pos.move_is_passed_pawn_push(move))
1678 futilityValue = futilityBase
1679 + pos.endgame_value_of_piece_on(move_to(move))
1680 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1682 if (futilityValue < alpha)
1684 if (futilityValue > bestValue)
1685 bestValue = futilityValue;
1690 // Detect blocking evasions that are candidate to be pruned
1691 evasionPrunable = isCheck
1692 && bestValue != -VALUE_INFINITE
1693 && !pos.move_is_capture(move)
1694 && pos.type_of_piece_on(move_from(move)) != KING
1695 && !pos.can_castle(pos.side_to_move());
1697 // Don't search moves with negative SEE values
1698 if ( (!isCheck || evasionPrunable)
1701 && !move_is_promotion(move)
1702 && pos.see_sign(move) < 0)
1705 // Make and search the move
1706 pos.do_move(move, st, ci, moveIsCheck);
1707 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1708 pos.undo_move(move);
1710 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1713 if (value > bestValue)
1724 // All legal moves have been searched. A special case: If we're in check
1725 // and no legal moves were found, it is checkmate.
1726 if (!moveCount && pos.is_check()) // Mate!
1727 return value_mated_in(ply);
1729 // Update transposition table
1730 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1731 if (bestValue <= oldAlpha)
1733 // If bestValue isn't changed it means it is still the static evaluation
1734 // of the node, so keep this info to avoid a future evaluation() call.
1735 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1736 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1738 else if (bestValue >= beta)
1740 move = ss[ply].pv[ply];
1741 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1743 // Update killers only for good checking moves
1744 if (!pos.move_is_capture_or_promotion(move))
1745 update_killers(move, ss[ply]);
1748 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1750 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1756 // sp_search() is used to search from a split point. This function is called
1757 // by each thread working at the split point. It is similar to the normal
1758 // search() function, but simpler. Because we have already probed the hash
1759 // table, done a null move search, and searched the first move before
1760 // splitting, we don't have to repeat all this work in sp_search(). We
1761 // also don't need to store anything to the hash table here: This is taken
1762 // care of after we return from the split point.
1764 void sp_search(SplitPoint* sp, int threadID) {
1766 assert(threadID >= 0 && threadID < TM.active_threads());
1767 assert(TM.active_threads() > 1);
1769 Position pos(*sp->pos);
1771 SearchStack* ss = sp->sstack[threadID];
1772 Value value = -VALUE_INFINITE;
1775 bool isCheck = pos.is_check();
1776 bool useFutilityPruning = sp->depth < 7 * OnePly //FIXME: sync with search
1779 while ( lock_grab_bool(&(sp->lock))
1780 && sp->bestValue < sp->beta
1781 && !TM.thread_should_stop(threadID)
1782 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1784 moveCount = ++sp->moves;
1785 lock_release(&(sp->lock));
1787 assert(move_is_ok(move));
1789 bool moveIsCheck = pos.move_is_check(move, ci);
1790 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1792 ss[sp->ply].currentMove = move;
1794 // Decide the new search depth
1796 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1797 Depth newDepth = sp->depth - OnePly + ext;
1800 if ( useFutilityPruning
1802 && !captureOrPromotion)
1804 // Move count based pruning
1805 if ( moveCount >= futility_move_count(sp->depth)
1806 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1807 && sp->bestValue > value_mated_in(PLY_MAX))
1810 // Value based pruning
1811 Value futilityValueScaled = sp->futilityValue - moveCount * 8; //FIXME: sync with search
1813 if (futilityValueScaled < sp->beta)
1815 if (futilityValueScaled > sp->bestValue) // Less then 1% of cases
1817 lock_grab(&(sp->lock));
1818 if (futilityValueScaled > sp->bestValue)
1819 sp->bestValue = futilityValueScaled;
1820 lock_release(&(sp->lock));
1826 // Make and search the move.
1828 pos.do_move(move, st, ci, moveIsCheck);
1830 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1831 // if the move fails high will be re-searched at full depth.
1832 bool doFullDepthSearch = true;
1835 && !captureOrPromotion
1836 && !move_is_castle(move)
1837 && !move_is_killer(move, ss[sp->ply]))
1839 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1840 if (ss[sp->ply].reduction)
1842 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1843 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1847 if (doFullDepthSearch) // Go with full depth non-pv search
1849 ss[sp->ply].reduction = Depth(0);
1850 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1852 pos.undo_move(move);
1854 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1857 if (value > sp->bestValue) // Less then 2% of cases
1859 lock_grab(&(sp->lock));
1860 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1862 sp->bestValue = value;
1863 if (sp->bestValue >= sp->beta)
1865 sp->stopRequest = true;
1866 sp_update_pv(sp->parentSstack, ss, sp->ply);
1869 lock_release(&(sp->lock));
1873 /* Here we have the lock still grabbed */
1876 sp->slaves[threadID] = 0;
1878 lock_release(&(sp->lock));
1882 // sp_search_pv() is used to search from a PV split point. This function
1883 // is called by each thread working at the split point. It is similar to
1884 // the normal search_pv() function, but simpler. Because we have already
1885 // probed the hash table and searched the first move before splitting, we
1886 // don't have to repeat all this work in sp_search_pv(). We also don't
1887 // need to store anything to the hash table here: This is taken care of
1888 // after we return from the split point.
1890 void sp_search_pv(SplitPoint* sp, int threadID) {
1892 assert(threadID >= 0 && threadID < TM.active_threads());
1893 assert(TM.active_threads() > 1);
1895 Position pos(*sp->pos);
1897 SearchStack* ss = sp->sstack[threadID];
1898 Value value = -VALUE_INFINITE;
1902 while ( lock_grab_bool(&(sp->lock))
1903 && sp->alpha < sp->beta
1904 && !TM.thread_should_stop(threadID)
1905 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1907 moveCount = ++sp->moves;
1908 lock_release(&(sp->lock));
1910 assert(move_is_ok(move));
1912 bool moveIsCheck = pos.move_is_check(move, ci);
1913 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1915 ss[sp->ply].currentMove = move;
1917 // Decide the new search depth
1919 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1920 Depth newDepth = sp->depth - OnePly + ext;
1922 // Make and search the move.
1924 pos.do_move(move, st, ci, moveIsCheck);
1926 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1927 // if the move fails high will be re-searched at full depth.
1928 bool doFullDepthSearch = true;
1931 && !captureOrPromotion
1932 && !move_is_castle(move)
1933 && !move_is_killer(move, ss[sp->ply]))
1935 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1936 if (ss[sp->ply].reduction)
1938 Value localAlpha = sp->alpha;
1939 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1940 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1944 if (doFullDepthSearch) // Go with full depth non-pv search
1946 Value localAlpha = sp->alpha;
1947 ss[sp->ply].reduction = Depth(0);
1948 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1950 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1952 // If another thread has failed high then sp->alpha has been increased
1953 // to be higher or equal then beta, if so, avoid to start a PV search.
1954 localAlpha = sp->alpha;
1955 if (localAlpha < sp->beta)
1956 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1959 pos.undo_move(move);
1961 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1964 if (value > sp->bestValue) // Less then 2% of cases
1966 lock_grab(&(sp->lock));
1967 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1969 sp->bestValue = value;
1970 if (value > sp->alpha)
1972 // Ask threads to stop before to modify sp->alpha
1973 if (value >= sp->beta)
1974 sp->stopRequest = true;
1978 sp_update_pv(sp->parentSstack, ss, sp->ply);
1979 if (value == value_mate_in(sp->ply + 1))
1980 ss[sp->ply].mateKiller = move;
1983 lock_release(&(sp->lock));
1987 /* Here we have the lock still grabbed */
1990 sp->slaves[threadID] = 0;
1992 lock_release(&(sp->lock));
1996 // init_node() is called at the beginning of all the search functions
1997 // (search(), search_pv(), qsearch(), and so on) and initializes the
1998 // search stack object corresponding to the current node. Once every
1999 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2000 // for user input and checks whether it is time to stop the search.
2002 void init_node(SearchStack ss[], int ply, int threadID) {
2004 assert(ply >= 0 && ply < PLY_MAX);
2005 assert(threadID >= 0 && threadID < TM.active_threads());
2007 TM.incrementNodeCounter(threadID);
2012 if (NodesSincePoll >= NodesBetweenPolls)
2019 ss[ply + 2].initKillers();
2020 TM.print_current_line(ss, ply, threadID);
2024 // update_pv() is called whenever a search returns a value > alpha.
2025 // It updates the PV in the SearchStack object corresponding to the
2028 void update_pv(SearchStack ss[], int ply) {
2030 assert(ply >= 0 && ply < PLY_MAX);
2034 ss[ply].pv[ply] = ss[ply].currentMove;
2036 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2037 ss[ply].pv[p] = ss[ply + 1].pv[p];
2039 ss[ply].pv[p] = MOVE_NONE;
2043 // sp_update_pv() is a variant of update_pv for use at split points. The
2044 // difference between the two functions is that sp_update_pv also updates
2045 // the PV at the parent node.
2047 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2049 assert(ply >= 0 && ply < PLY_MAX);
2053 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2055 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2056 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2058 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2062 // connected_moves() tests whether two moves are 'connected' in the sense
2063 // that the first move somehow made the second move possible (for instance
2064 // if the moving piece is the same in both moves). The first move is assumed
2065 // to be the move that was made to reach the current position, while the
2066 // second move is assumed to be a move from the current position.
2068 bool connected_moves(const Position& pos, Move m1, Move m2) {
2070 Square f1, t1, f2, t2;
2073 assert(move_is_ok(m1));
2074 assert(move_is_ok(m2));
2076 if (m2 == MOVE_NONE)
2079 // Case 1: The moving piece is the same in both moves
2085 // Case 2: The destination square for m2 was vacated by m1
2091 // Case 3: Moving through the vacated square
2092 if ( piece_is_slider(pos.piece_on(f2))
2093 && bit_is_set(squares_between(f2, t2), f1))
2096 // Case 4: The destination square for m2 is defended by the moving piece in m1
2097 p = pos.piece_on(t1);
2098 if (bit_is_set(pos.attacks_from(p, t1), t2))
2101 // Case 5: Discovered check, checking piece is the piece moved in m1
2102 if ( piece_is_slider(p)
2103 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2104 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2106 // discovered_check_candidates() works also if the Position's side to
2107 // move is the opposite of the checking piece.
2108 Color them = opposite_color(pos.side_to_move());
2109 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2111 if (bit_is_set(dcCandidates, f2))
2118 // value_is_mate() checks if the given value is a mate one
2119 // eventually compensated for the ply.
2121 bool value_is_mate(Value value) {
2123 assert(abs(value) <= VALUE_INFINITE);
2125 return value <= value_mated_in(PLY_MAX)
2126 || value >= value_mate_in(PLY_MAX);
2130 // move_is_killer() checks if the given move is among the
2131 // killer moves of that ply.
2133 bool move_is_killer(Move m, const SearchStack& ss) {
2135 const Move* k = ss.killers;
2136 for (int i = 0; i < KILLER_MAX; i++, k++)
2144 // extension() decides whether a move should be searched with normal depth,
2145 // or with extended depth. Certain classes of moves (checking moves, in
2146 // particular) are searched with bigger depth than ordinary moves and in
2147 // any case are marked as 'dangerous'. Note that also if a move is not
2148 // extended, as example because the corresponding UCI option is set to zero,
2149 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2151 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2152 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2154 assert(m != MOVE_NONE);
2156 Depth result = Depth(0);
2157 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2162 result += CheckExtension[pvNode];
2165 result += SingleEvasionExtension[pvNode];
2168 result += MateThreatExtension[pvNode];
2171 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2173 Color c = pos.side_to_move();
2174 if (relative_rank(c, move_to(m)) == RANK_7)
2176 result += PawnPushTo7thExtension[pvNode];
2179 if (pos.pawn_is_passed(c, move_to(m)))
2181 result += PassedPawnExtension[pvNode];
2186 if ( captureOrPromotion
2187 && pos.type_of_piece_on(move_to(m)) != PAWN
2188 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2189 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2190 && !move_is_promotion(m)
2193 result += PawnEndgameExtension[pvNode];
2198 && captureOrPromotion
2199 && pos.type_of_piece_on(move_to(m)) != PAWN
2200 && pos.see_sign(m) >= 0)
2206 return Min(result, OnePly);
2210 // ok_to_do_nullmove() looks at the current position and decides whether
2211 // doing a 'null move' should be allowed. In order to avoid zugzwang
2212 // problems, null moves are not allowed when the side to move has very
2213 // little material left. Currently, the test is a bit too simple: Null
2214 // moves are avoided only when the side to move has only pawns left.
2215 // It's probably a good idea to avoid null moves in at least some more
2216 // complicated endgames, e.g. KQ vs KR. FIXME
2218 bool ok_to_do_nullmove(const Position& pos) {
2220 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2224 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2225 // non-tactical moves late in the move list close to the leaves are
2226 // candidates for pruning.
2228 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2230 assert(move_is_ok(m));
2231 assert(threat == MOVE_NONE || move_is_ok(threat));
2232 assert(!pos.move_is_check(m));
2233 assert(!pos.move_is_capture_or_promotion(m));
2234 assert(!pos.move_is_passed_pawn_push(m));
2236 Square mfrom, mto, tfrom, tto;
2238 // Prune if there isn't any threat move
2239 if (threat == MOVE_NONE)
2242 mfrom = move_from(m);
2244 tfrom = move_from(threat);
2245 tto = move_to(threat);
2247 // Case 1: Don't prune moves which move the threatened piece
2251 // Case 2: If the threatened piece has value less than or equal to the
2252 // value of the threatening piece, don't prune move which defend it.
2253 if ( pos.move_is_capture(threat)
2254 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2255 || pos.type_of_piece_on(tfrom) == KING)
2256 && pos.move_attacks_square(m, tto))
2259 // Case 3: If the moving piece in the threatened move is a slider, don't
2260 // prune safe moves which block its ray.
2261 if ( piece_is_slider(pos.piece_on(tfrom))
2262 && bit_is_set(squares_between(tfrom, tto), mto)
2263 && pos.see_sign(m) >= 0)
2270 // ok_to_use_TT() returns true if a transposition table score
2271 // can be used at a given point in search.
2273 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2275 Value v = value_from_tt(tte->value(), ply);
2277 return ( tte->depth() >= depth
2278 || v >= Max(value_mate_in(PLY_MAX), beta)
2279 || v < Min(value_mated_in(PLY_MAX), beta))
2281 && ( (is_lower_bound(tte->type()) && v >= beta)
2282 || (is_upper_bound(tte->type()) && v < beta));
2286 // refine_eval() returns the transposition table score if
2287 // possible otherwise falls back on static position evaluation.
2289 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2294 Value v = value_from_tt(tte->value(), ply);
2296 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2297 || (is_upper_bound(tte->type()) && v < defaultEval))
2304 // update_history() registers a good move that produced a beta-cutoff
2305 // in history and marks as failures all the other moves of that ply.
2307 void update_history(const Position& pos, Move move, Depth depth,
2308 Move movesSearched[], int moveCount) {
2312 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2314 for (int i = 0; i < moveCount - 1; i++)
2316 m = movesSearched[i];
2320 if (!pos.move_is_capture_or_promotion(m))
2321 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2326 // update_killers() add a good move that produced a beta-cutoff
2327 // among the killer moves of that ply.
2329 void update_killers(Move m, SearchStack& ss) {
2331 if (m == ss.killers[0])
2334 for (int i = KILLER_MAX - 1; i > 0; i--)
2335 ss.killers[i] = ss.killers[i - 1];
2341 // update_gains() updates the gains table of a non-capture move given
2342 // the static position evaluation before and after the move.
2344 void update_gains(const Position& pos, Move m, Value before, Value after) {
2347 && before != VALUE_NONE
2348 && after != VALUE_NONE
2349 && pos.captured_piece() == NO_PIECE_TYPE
2350 && !move_is_castle(m)
2351 && !move_is_promotion(m))
2352 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2356 // current_search_time() returns the number of milliseconds which have passed
2357 // since the beginning of the current search.
2359 int current_search_time() {
2361 return get_system_time() - SearchStartTime;
2365 // nps() computes the current nodes/second count.
2369 int t = current_search_time();
2370 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2374 // poll() performs two different functions: It polls for user input, and it
2375 // looks at the time consumed so far and decides if it's time to abort the
2380 static int lastInfoTime;
2381 int t = current_search_time();
2386 // We are line oriented, don't read single chars
2387 std::string command;
2389 if (!std::getline(std::cin, command))
2392 if (command == "quit")
2395 PonderSearch = false;
2399 else if (command == "stop")
2402 PonderSearch = false;
2404 else if (command == "ponderhit")
2408 // Print search information
2412 else if (lastInfoTime > t)
2413 // HACK: Must be a new search where we searched less than
2414 // NodesBetweenPolls nodes during the first second of search.
2417 else if (t - lastInfoTime >= 1000)
2420 lock_grab(&TM.IOLock);
2425 if (dbg_show_hit_rate)
2426 dbg_print_hit_rate();
2428 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2429 << " time " << t << " hashfull " << TT.full() << endl;
2431 lock_release(&TM.IOLock);
2433 if (ShowCurrentLine)
2434 TM.threads[0].printCurrentLineRequest = true;
2437 // Should we stop the search?
2441 bool stillAtFirstMove = RootMoveNumber == 1
2442 && !AspirationFailLow
2443 && t > MaxSearchTime + ExtraSearchTime;
2445 bool noMoreTime = t > AbsoluteMaxSearchTime
2446 || stillAtFirstMove;
2448 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2449 || (ExactMaxTime && t >= ExactMaxTime)
2450 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2455 // ponderhit() is called when the program is pondering (i.e. thinking while
2456 // it's the opponent's turn to move) in order to let the engine know that
2457 // it correctly predicted the opponent's move.
2461 int t = current_search_time();
2462 PonderSearch = false;
2464 bool stillAtFirstMove = RootMoveNumber == 1
2465 && !AspirationFailLow
2466 && t > MaxSearchTime + ExtraSearchTime;
2468 bool noMoreTime = t > AbsoluteMaxSearchTime
2469 || stillAtFirstMove;
2471 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2476 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2478 void init_ss_array(SearchStack ss[]) {
2480 for (int i = 0; i < 3; i++)
2483 ss[i].initKillers();
2488 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2489 // while the program is pondering. The point is to work around a wrinkle in
2490 // the UCI protocol: When pondering, the engine is not allowed to give a
2491 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2492 // We simply wait here until one of these commands is sent, and return,
2493 // after which the bestmove and pondermove will be printed (in id_loop()).
2495 void wait_for_stop_or_ponderhit() {
2497 std::string command;
2501 if (!std::getline(std::cin, command))
2504 if (command == "quit")
2509 else if (command == "ponderhit" || command == "stop")
2515 // init_thread() is the function which is called when a new thread is
2516 // launched. It simply calls the idle_loop() function with the supplied
2517 // threadID. There are two versions of this function; one for POSIX
2518 // threads and one for Windows threads.
2520 #if !defined(_MSC_VER)
2522 void* init_thread(void *threadID) {
2524 TM.idle_loop(*(int*)threadID, NULL);
2530 DWORD WINAPI init_thread(LPVOID threadID) {
2532 TM.idle_loop(*(int*)threadID, NULL);
2539 /// The ThreadsManager class
2541 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2542 // get_beta_counters() are getters/setters for the per thread
2543 // counters used to sort the moves at root.
2545 void ThreadsManager::resetNodeCounters() {
2547 for (int i = 0; i < MAX_THREADS; i++)
2548 threads[i].nodes = 0ULL;
2551 void ThreadsManager::resetBetaCounters() {
2553 for (int i = 0; i < MAX_THREADS; i++)
2554 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2557 int64_t ThreadsManager::nodes_searched() const {
2559 int64_t result = 0ULL;
2560 for (int i = 0; i < ActiveThreads; i++)
2561 result += threads[i].nodes;
2566 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2569 for (int i = 0; i < MAX_THREADS; i++)
2571 our += threads[i].betaCutOffs[us];
2572 their += threads[i].betaCutOffs[opposite_color(us)];
2577 // idle_loop() is where the threads are parked when they have no work to do.
2578 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2579 // object for which the current thread is the master.
2581 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2583 assert(threadID >= 0 && threadID < MAX_THREADS);
2587 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2588 // master should exit as last one.
2589 if (AllThreadsShouldExit)
2592 threads[threadID].state = THREAD_TERMINATED;
2596 // If we are not thinking, wait for a condition to be signaled
2597 // instead of wasting CPU time polling for work.
2598 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2601 assert(threadID != 0);
2602 threads[threadID].state = THREAD_SLEEPING;
2604 #if !defined(_MSC_VER)
2605 pthread_mutex_lock(&WaitLock);
2606 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2607 pthread_cond_wait(&WaitCond, &WaitLock);
2608 pthread_mutex_unlock(&WaitLock);
2610 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2614 // If thread has just woken up, mark it as available
2615 if (threads[threadID].state == THREAD_SLEEPING)
2616 threads[threadID].state = THREAD_AVAILABLE;
2618 // If this thread has been assigned work, launch a search
2619 if (threads[threadID].state == THREAD_WORKISWAITING)
2621 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2623 threads[threadID].state = THREAD_SEARCHING;
2625 if (threads[threadID].splitPoint->pvNode)
2626 sp_search_pv(threads[threadID].splitPoint, threadID);
2628 sp_search(threads[threadID].splitPoint, threadID);
2630 assert(threads[threadID].state == THREAD_SEARCHING);
2632 threads[threadID].state = THREAD_AVAILABLE;
2635 // If this thread is the master of a split point and all threads have
2636 // finished their work at this split point, return from the idle loop.
2637 if (waitSp != NULL && waitSp->cpus == 0)
2639 assert(threads[threadID].state == THREAD_AVAILABLE);
2641 threads[threadID].state = THREAD_SEARCHING;
2648 // init_threads() is called during startup. It launches all helper threads,
2649 // and initializes the split point stack and the global locks and condition
2652 void ThreadsManager::init_threads() {
2657 #if !defined(_MSC_VER)
2658 pthread_t pthread[1];
2661 // Initialize global locks
2662 lock_init(&MPLock, NULL);
2663 lock_init(&IOLock, NULL);
2665 // Initialize SplitPointStack locks
2666 for (i = 0; i < MAX_THREADS; i++)
2667 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2669 SplitPointStack[i][j].parent = NULL;
2670 lock_init(&(SplitPointStack[i][j].lock), NULL);
2673 #if !defined(_MSC_VER)
2674 pthread_mutex_init(&WaitLock, NULL);
2675 pthread_cond_init(&WaitCond, NULL);
2677 for (i = 0; i < MAX_THREADS; i++)
2678 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2681 // Will be set just before program exits to properly end the threads
2682 AllThreadsShouldExit = false;
2684 // Threads will be put to sleep as soon as created
2685 AllThreadsShouldSleep = true;
2687 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2689 threads[0].state = THREAD_SEARCHING;
2690 for (i = 1; i < MAX_THREADS; i++)
2691 threads[i].state = THREAD_AVAILABLE;
2693 // Launch the helper threads
2694 for (i = 1; i < MAX_THREADS; i++)
2697 #if !defined(_MSC_VER)
2698 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2701 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
2706 cout << "Failed to create thread number " << i << endl;
2707 Application::exit_with_failure();
2710 // Wait until the thread has finished launching and is gone to sleep
2711 while (threads[i].state != THREAD_SLEEPING);
2716 // exit_threads() is called when the program exits. It makes all the
2717 // helper threads exit cleanly.
2719 void ThreadsManager::exit_threads() {
2721 ActiveThreads = MAX_THREADS; // HACK
2722 AllThreadsShouldSleep = true; // HACK
2723 wake_sleeping_threads();
2725 // This makes the threads to exit idle_loop()
2726 AllThreadsShouldExit = true;
2728 // Wait for thread termination
2729 for (int i = 1; i < MAX_THREADS; i++)
2730 while (threads[i].state != THREAD_TERMINATED);
2732 // Now we can safely destroy the locks
2733 for (int i = 0; i < MAX_THREADS; i++)
2734 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2735 lock_destroy(&(SplitPointStack[i][j].lock));
2739 // thread_should_stop() checks whether the thread should stop its search.
2740 // This can happen if a beta cutoff has occurred in the thread's currently
2741 // active split point, or in some ancestor of the current split point.
2743 bool ThreadsManager::thread_should_stop(int threadID) const {
2745 assert(threadID >= 0 && threadID < ActiveThreads);
2749 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2754 // thread_is_available() checks whether the thread with threadID "slave" is
2755 // available to help the thread with threadID "master" at a split point. An
2756 // obvious requirement is that "slave" must be idle. With more than two
2757 // threads, this is not by itself sufficient: If "slave" is the master of
2758 // some active split point, it is only available as a slave to the other
2759 // threads which are busy searching the split point at the top of "slave"'s
2760 // split point stack (the "helpful master concept" in YBWC terminology).
2762 bool ThreadsManager::thread_is_available(int slave, int master) const {
2764 assert(slave >= 0 && slave < ActiveThreads);
2765 assert(master >= 0 && master < ActiveThreads);
2766 assert(ActiveThreads > 1);
2768 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2771 // Make a local copy to be sure doesn't change under our feet
2772 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2774 if (localActiveSplitPoints == 0)
2775 // No active split points means that the thread is available as
2776 // a slave for any other thread.
2779 if (ActiveThreads == 2)
2782 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2783 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2784 // could have been set to 0 by another thread leading to an out of bound access.
2785 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2792 // available_thread_exists() tries to find an idle thread which is available as
2793 // a slave for the thread with threadID "master".
2795 bool ThreadsManager::available_thread_exists(int master) const {
2797 assert(master >= 0 && master < ActiveThreads);
2798 assert(ActiveThreads > 1);
2800 for (int i = 0; i < ActiveThreads; i++)
2801 if (thread_is_available(i, master))
2808 // split() does the actual work of distributing the work at a node between
2809 // several threads at PV nodes. If it does not succeed in splitting the
2810 // node (because no idle threads are available, or because we have no unused
2811 // split point objects), the function immediately returns false. If
2812 // splitting is possible, a SplitPoint object is initialized with all the
2813 // data that must be copied to the helper threads (the current position and
2814 // search stack, alpha, beta, the search depth, etc.), and we tell our
2815 // helper threads that they have been assigned work. This will cause them
2816 // to instantly leave their idle loops and call sp_search_pv(). When all
2817 // threads have returned from sp_search_pv (or, equivalently, when
2818 // splitPoint->cpus becomes 0), split() returns true.
2820 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2821 Value* alpha, const Value beta, Value* bestValue, const Value futilityValue,
2822 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2825 assert(sstck != NULL);
2826 assert(ply >= 0 && ply < PLY_MAX);
2827 assert(*bestValue >= -VALUE_INFINITE);
2828 assert( ( pvNode && *bestValue <= *alpha)
2829 || (!pvNode && *bestValue < beta ));
2830 assert(!pvNode || *alpha < beta);
2831 assert(beta <= VALUE_INFINITE);
2832 assert(depth > Depth(0));
2833 assert(master >= 0 && master < ActiveThreads);
2834 assert(ActiveThreads > 1);
2836 SplitPoint* splitPoint;
2840 // If no other thread is available to help us, or if we have too many
2841 // active split points, don't split.
2842 if ( !available_thread_exists(master)
2843 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2845 lock_release(&MPLock);
2849 // Pick the next available split point object from the split point stack
2850 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2852 // Initialize the split point object
2853 splitPoint->parent = threads[master].splitPoint;
2854 splitPoint->stopRequest = false;
2855 splitPoint->ply = ply;
2856 splitPoint->depth = depth;
2857 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2858 splitPoint->beta = beta;
2859 splitPoint->pvNode = pvNode;
2860 splitPoint->bestValue = *bestValue;
2861 splitPoint->futilityValue = futilityValue;
2862 splitPoint->master = master;
2863 splitPoint->mp = mp;
2864 splitPoint->moves = *moves;
2865 splitPoint->cpus = 1;
2866 splitPoint->pos = &p;
2867 splitPoint->parentSstack = sstck;
2868 for (int i = 0; i < ActiveThreads; i++)
2869 splitPoint->slaves[i] = 0;
2871 threads[master].splitPoint = splitPoint;
2872 threads[master].activeSplitPoints++;
2874 // If we are here it means we are not available
2875 assert(threads[master].state != THREAD_AVAILABLE);
2877 // Allocate available threads setting state to THREAD_BOOKED
2878 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2879 if (thread_is_available(i, master))
2881 threads[i].state = THREAD_BOOKED;
2882 threads[i].splitPoint = splitPoint;
2883 splitPoint->slaves[i] = 1;
2887 assert(splitPoint->cpus > 1);
2889 // We can release the lock because slave threads are already booked and master is not available
2890 lock_release(&MPLock);
2892 // Tell the threads that they have work to do. This will make them leave
2893 // their idle loop. But before copy search stack tail for each thread.
2894 for (int i = 0; i < ActiveThreads; i++)
2895 if (i == master || splitPoint->slaves[i])
2897 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2899 assert(i == master || threads[i].state == THREAD_BOOKED);
2901 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2904 // Everything is set up. The master thread enters the idle loop, from
2905 // which it will instantly launch a search, because its state is
2906 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2907 // idle loop, which means that the main thread will return from the idle
2908 // loop when all threads have finished their work at this split point
2909 // (i.e. when splitPoint->cpus == 0).
2910 idle_loop(master, splitPoint);
2912 // We have returned from the idle loop, which means that all threads are
2913 // finished. Update alpha, beta and bestValue, and return.
2917 *alpha = splitPoint->alpha;
2919 *bestValue = splitPoint->bestValue;
2920 threads[master].activeSplitPoints--;
2921 threads[master].splitPoint = splitPoint->parent;
2923 lock_release(&MPLock);
2928 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2929 // to start a new search from the root.
2931 void ThreadsManager::wake_sleeping_threads() {
2933 assert(AllThreadsShouldSleep);
2934 assert(ActiveThreads > 0);
2936 AllThreadsShouldSleep = false;
2938 if (ActiveThreads == 1)
2941 for (int i = 1; i < ActiveThreads; i++)
2942 assert(threads[i].state == THREAD_SLEEPING);
2944 #if !defined(_MSC_VER)
2945 pthread_mutex_lock(&WaitLock);
2946 pthread_cond_broadcast(&WaitCond);
2947 pthread_mutex_unlock(&WaitLock);
2949 for (int i = 1; i < MAX_THREADS; i++)
2950 SetEvent(SitIdleEvent[i]);
2956 // put_threads_to_sleep() makes all the threads go to sleep just before
2957 // to leave think(), at the end of the search. Threads should have already
2958 // finished the job and should be idle.
2960 void ThreadsManager::put_threads_to_sleep() {
2962 assert(!AllThreadsShouldSleep);
2964 // This makes the threads to go to sleep
2965 AllThreadsShouldSleep = true;
2967 // Reset flags to a known state.
2968 for (int i = 1; i < ActiveThreads; i++)
2970 // This flag can be in a random state
2971 threads[i].printCurrentLineRequest = false;
2975 // print_current_line() prints _once_ the current line of search for a
2976 // given thread and then setup the print request for the next thread.
2977 // Called when the UCI option UCI_ShowCurrLine is 'true'.
2979 void ThreadsManager::print_current_line(SearchStack ss[], int ply, int threadID) {
2981 assert(ply >= 0 && ply < PLY_MAX);
2982 assert(threadID >= 0 && threadID < ActiveThreads);
2984 if (!threads[threadID].printCurrentLineRequest)
2988 threads[threadID].printCurrentLineRequest = false;
2990 if (threads[threadID].state == THREAD_SEARCHING)
2993 cout << "info currline " << (threadID + 1);
2994 for (int p = 0; p < ply; p++)
2995 cout << " " << ss[p].currentMove;
2998 lock_release(&IOLock);
3001 // Setup print request for the next thread ID
3002 if (threadID + 1 < ActiveThreads)
3003 threads[threadID + 1].printCurrentLineRequest = true;
3007 /// The RootMoveList class
3009 // RootMoveList c'tor
3011 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3013 SearchStack ss[PLY_MAX_PLUS_2];
3014 MoveStack mlist[MaxRootMoves];
3016 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3018 // Generate all legal moves
3019 MoveStack* last = generate_moves(pos, mlist);
3021 // Add each move to the moves[] array
3022 for (MoveStack* cur = mlist; cur != last; cur++)
3024 bool includeMove = includeAllMoves;
3026 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3027 includeMove = (searchMoves[k] == cur->move);
3032 // Find a quick score for the move
3034 pos.do_move(cur->move, st);
3035 moves[count].move = cur->move;
3036 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3037 moves[count].pv[0] = cur->move;
3038 moves[count].pv[1] = MOVE_NONE;
3039 pos.undo_move(cur->move);
3046 // RootMoveList simple methods definitions
3048 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3050 moves[moveNum].nodes = nodes;
3051 moves[moveNum].cumulativeNodes += nodes;
3054 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3056 moves[moveNum].ourBeta = our;
3057 moves[moveNum].theirBeta = their;
3060 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3064 for (j = 0; pv[j] != MOVE_NONE; j++)
3065 moves[moveNum].pv[j] = pv[j];
3067 moves[moveNum].pv[j] = MOVE_NONE;
3071 // RootMoveList::sort() sorts the root move list at the beginning of a new
3074 void RootMoveList::sort() {
3076 sort_multipv(count - 1); // Sort all items
3080 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3081 // list by their scores and depths. It is used to order the different PVs
3082 // correctly in MultiPV mode.
3084 void RootMoveList::sort_multipv(int n) {
3088 for (i = 1; i <= n; i++)
3090 RootMove rm = moves[i];
3091 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3092 moves[j] = moves[j - 1];