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); }
76 void resetNodeCounters();
77 void resetBetaCounters();
78 int64_t nodes_searched() const;
79 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
80 bool available_thread_exists(int master) const;
81 bool thread_is_available(int slave, int master) const;
82 bool thread_should_stop(int threadID) const;
83 void wake_sleeping_threads();
84 void put_threads_to_sleep();
85 void idle_loop(int threadID, SplitPoint* waitSp);
86 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode);
90 friend void poll(SearchStack ss[], int ply);
93 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
94 Thread threads[MAX_THREADS];
95 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
99 #if !defined(_MSC_VER)
100 pthread_cond_t WaitCond;
101 pthread_mutex_t WaitLock;
103 HANDLE SitIdleEvent[MAX_THREADS];
109 // RootMove struct is used for moves at the root at the tree. For each
110 // root move, we store a score, a node count, and a PV (really a refutation
111 // in the case of moves which fail low).
115 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
117 // RootMove::operator<() is the comparison function used when
118 // sorting the moves. A move m1 is considered to be better
119 // than a move m2 if it has a higher score, or if the moves
120 // have equal score but m1 has the higher node count.
121 bool operator<(const RootMove& m) const {
123 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
128 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
129 Move pv[PLY_MAX_PLUS_2];
133 // The RootMoveList class is essentially an array of RootMove objects, with
134 // a handful of methods for accessing the data in the individual moves.
139 RootMoveList(Position& pos, Move searchMoves[]);
141 int move_count() const { return count; }
142 Move get_move(int moveNum) const { return moves[moveNum].move; }
143 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
144 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
145 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
146 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
148 void set_move_nodes(int moveNum, int64_t nodes);
149 void set_beta_counters(int moveNum, int64_t our, int64_t their);
150 void set_move_pv(int moveNum, const Move pv[]);
152 void sort_multipv(int n);
155 static const int MaxRootMoves = 500;
156 RootMove moves[MaxRootMoves];
163 // Search depth at iteration 1
164 const Depth InitialDepth = OnePly;
166 // Use internal iterative deepening?
167 const bool UseIIDAtPVNodes = true;
168 const bool UseIIDAtNonPVNodes = true;
170 // Internal iterative deepening margin. At Non-PV moves, when
171 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
172 // search when the static evaluation is at most IIDMargin below beta.
173 const Value IIDMargin = Value(0x100);
175 // Easy move margin. An easy move candidate must be at least this much
176 // better than the second best move.
177 const Value EasyMoveMargin = Value(0x200);
179 // Null move margin. A null move search will not be done if the static
180 // evaluation of the position is more than NullMoveMargin below beta.
181 const Value NullMoveMargin = Value(0x200);
183 // If the TT move is at least SingleReplyMargin better then the
184 // remaining ones we will extend it.
185 const Value SingleReplyMargin = Value(0x20);
187 // Depth limit for razoring
188 const Depth RazorDepth = 4 * OnePly;
190 /// Lookup tables initialized at startup
192 // Reduction lookup tables and their getter functions
193 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
194 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
196 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
197 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
199 // Futility lookup tables and their getter functions
200 const Value FutilityMarginQS = Value(0x80);
201 int32_t FutilityMarginsMatrix[14][64]; // [depth][moveNumber]
202 int FutilityMoveCountArray[32]; // [depth]
204 inline Value futility_margin(Depth d, int mn) { return Value(d < 7*OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
205 inline int futility_move_count(Depth d) { return d < 16*OnePly ? FutilityMoveCountArray[d] : 512; }
207 /// Variables initialized by UCI options
209 // Depth limit for use of dynamic threat detection
212 // Last seconds noise filtering (LSN)
213 const bool UseLSNFiltering = true;
214 const int LSNTime = 4000; // In milliseconds
215 const Value LSNValue = value_from_centipawns(200);
216 bool loseOnTime = false;
218 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
219 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
220 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
222 // Iteration counters
225 // Scores and number of times the best move changed for each iteration
226 Value ValueByIteration[PLY_MAX_PLUS_2];
227 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
229 // Search window management
235 // Time managment variables
238 int MaxNodes, MaxDepth;
239 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
240 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
241 bool AbortSearch, Quit;
242 bool AspirationFailLow;
244 // Show current line?
245 bool ShowCurrentLine;
249 std::ofstream LogFile;
251 // MP related variables
252 Depth MinimumSplitDepth;
253 int MaxThreadsPerSplitPoint;
256 // Node counters, used only by thread[0] but try to keep in different
257 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
259 int NodesBetweenPolls = 30000;
266 Value id_loop(const Position& pos, Move searchMoves[]);
267 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta);
268 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
269 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
270 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
271 void sp_search(SplitPoint* sp, int threadID);
272 void sp_search_pv(SplitPoint* sp, int threadID);
273 void init_node(SearchStack ss[], int ply, int threadID);
274 void update_pv(SearchStack ss[], int ply);
275 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
276 bool connected_moves(const Position& pos, Move m1, Move m2);
277 bool value_is_mate(Value value);
278 bool move_is_killer(Move m, const SearchStack& ss);
279 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
280 bool ok_to_do_nullmove(const Position& pos);
281 bool ok_to_prune(const Position& pos, Move m, Move threat);
282 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
283 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
284 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
285 void update_killers(Move m, SearchStack& ss);
286 void update_gains(const Position& pos, Move move, Value before, Value after);
288 int current_search_time();
290 void poll(SearchStack ss[], int ply);
292 void wait_for_stop_or_ponderhit();
293 void init_ss_array(SearchStack ss[]);
295 #if !defined(_MSC_VER)
296 void *init_thread(void *threadID);
298 DWORD WINAPI init_thread(LPVOID threadID);
308 /// init_threads(), exit_threads() and nodes_searched() are helpers to
309 /// give accessibility to some TM methods from outside of current file.
311 void init_threads() { TM.init_threads(); }
312 void exit_threads() { TM.exit_threads(); }
313 int64_t nodes_searched() { return TM.nodes_searched(); }
316 /// perft() is our utility to verify move generation is bug free. All the legal
317 /// moves up to given depth are generated and counted and the sum returned.
319 int perft(Position& pos, Depth depth)
323 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
325 // If we are at the last ply we don't need to do and undo
326 // the moves, just to count them.
327 if (depth <= OnePly) // Replace with '<' to test also qsearch
329 while (mp.get_next_move()) sum++;
333 // Loop through all legal moves
335 while ((move = mp.get_next_move()) != MOVE_NONE)
338 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
339 sum += perft(pos, depth - OnePly);
346 /// think() is the external interface to Stockfish's search, and is called when
347 /// the program receives the UCI 'go' command. It initializes various
348 /// search-related global variables, and calls root_search(). It returns false
349 /// when a quit command is received during the search.
351 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
352 int time[], int increment[], int movesToGo, int maxDepth,
353 int maxNodes, int maxTime, Move searchMoves[]) {
355 // Initialize global search variables
356 StopOnPonderhit = AbortSearch = Quit = false;
357 AspirationFailLow = false;
359 SearchStartTime = get_system_time();
360 ExactMaxTime = maxTime;
363 InfiniteSearch = infinite;
364 PonderSearch = ponder;
365 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
367 // Look for a book move, only during games, not tests
368 if (UseTimeManagement && get_option_value_bool("OwnBook"))
371 if (get_option_value_string("Book File") != OpeningBook.file_name())
372 OpeningBook.open(get_option_value_string("Book File"));
374 bookMove = OpeningBook.get_move(pos);
375 if (bookMove != MOVE_NONE)
378 wait_for_stop_or_ponderhit();
380 cout << "bestmove " << bookMove << endl;
385 TM.resetNodeCounters();
387 if (button_was_pressed("New Game"))
388 loseOnTime = false; // Reset at the beginning of a new game
390 // Read UCI option values
391 TT.set_size(get_option_value_int("Hash"));
392 if (button_was_pressed("Clear Hash"))
395 bool PonderingEnabled = get_option_value_bool("Ponder");
396 MultiPV = get_option_value_int("MultiPV");
398 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
399 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
401 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
402 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
404 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
405 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
407 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
408 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
410 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
411 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
413 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
414 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
416 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
418 Chess960 = get_option_value_bool("UCI_Chess960");
419 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
420 UseLogFile = get_option_value_bool("Use Search Log");
422 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
424 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
425 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
427 read_weights(pos.side_to_move());
429 // Set the number of active threads
430 int newActiveThreads = get_option_value_int("Threads");
431 if (newActiveThreads != TM.active_threads())
433 TM.set_active_threads(newActiveThreads);
434 init_eval(TM.active_threads());
435 // HACK: init_eval() destroys the static castleRightsMask[] array in the
436 // Position class. The below line repairs the damage.
437 Position p(pos.to_fen());
441 // Wake up sleeping threads
442 TM.wake_sleeping_threads();
445 int myTime = time[side_to_move];
446 int myIncrement = increment[side_to_move];
447 if (UseTimeManagement)
449 if (!movesToGo) // Sudden death time control
453 MaxSearchTime = myTime / 30 + myIncrement;
454 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
456 else // Blitz game without increment
458 MaxSearchTime = myTime / 30;
459 AbsoluteMaxSearchTime = myTime / 8;
462 else // (x moves) / (y minutes)
466 MaxSearchTime = myTime / 2;
467 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
471 MaxSearchTime = myTime / Min(movesToGo, 20);
472 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
476 if (PonderingEnabled)
478 MaxSearchTime += MaxSearchTime / 4;
479 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
483 // Set best NodesBetweenPolls interval
485 NodesBetweenPolls = Min(MaxNodes, 30000);
486 else if (myTime && myTime < 1000)
487 NodesBetweenPolls = 1000;
488 else if (myTime && myTime < 5000)
489 NodesBetweenPolls = 5000;
491 NodesBetweenPolls = 30000;
493 // Write information to search log file
495 LogFile << "Searching: " << pos.to_fen() << endl
496 << "infinite: " << infinite
497 << " ponder: " << ponder
498 << " time: " << myTime
499 << " increment: " << myIncrement
500 << " moves to go: " << movesToGo << endl;
502 // LSN filtering. Used only for developing purpose. Disabled by default.
506 // Step 2. If after last move we decided to lose on time, do it now!
507 while (SearchStartTime + myTime + 1000 > get_system_time())
511 // We're ready to start thinking. Call the iterative deepening loop function
512 Value v = id_loop(pos, searchMoves);
516 // Step 1. If this is sudden death game and our position is hopeless,
517 // decide to lose on time.
518 if ( !loseOnTime // If we already lost on time, go to step 3.
528 // Step 3. Now after stepping over the time limit, reset flag for next match.
536 TM.put_threads_to_sleep();
542 /// init_search() is called during startup. It initializes various lookup tables
546 // Init our reduction lookup tables
547 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
548 for (int j = 1; j < 64; j++) // j == moveNumber
550 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
551 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
552 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
553 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
556 // Init futility margins array
557 for (int i = 0; i < 14; i++) // i == depth (OnePly = 2)
558 for (int j = 0; j < 64; j++) // j == moveNumber
560 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j; // FIXME: test using log instead of BSR
563 // Init futility move count array
564 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
565 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
569 // SearchStack::init() initializes a search stack. Used at the beginning of a
570 // new search from the root.
571 void SearchStack::init(int ply) {
573 pv[ply] = pv[ply + 1] = MOVE_NONE;
574 currentMove = threatMove = MOVE_NONE;
575 reduction = Depth(0);
579 void SearchStack::initKillers() {
581 mateKiller = MOVE_NONE;
582 for (int i = 0; i < KILLER_MAX; i++)
583 killers[i] = MOVE_NONE;
588 // id_loop() is the main iterative deepening loop. It calls root_search
589 // repeatedly with increasing depth until the allocated thinking time has
590 // been consumed, the user stops the search, or the maximum search depth is
593 Value id_loop(const Position& pos, Move searchMoves[]) {
596 SearchStack ss[PLY_MAX_PLUS_2];
598 // searchMoves are verified, copied, scored and sorted
599 RootMoveList rml(p, searchMoves);
601 // Handle special case of searching on a mate/stale position
602 if (rml.move_count() == 0)
605 wait_for_stop_or_ponderhit();
607 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
610 // Print RootMoveList c'tor startup scoring to the standard output,
611 // so that we print information also for iteration 1.
612 cout << "info depth " << 1 << "\ninfo depth " << 1
613 << " score " << value_to_string(rml.get_move_score(0))
614 << " time " << current_search_time()
615 << " nodes " << TM.nodes_searched()
617 << " pv " << rml.get_move(0) << "\n";
623 ValueByIteration[1] = rml.get_move_score(0);
626 // Is one move significantly better than others after initial scoring ?
627 Move EasyMove = MOVE_NONE;
628 if ( rml.move_count() == 1
629 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
630 EasyMove = rml.get_move(0);
632 // Iterative deepening loop
633 while (Iteration < PLY_MAX)
635 // Initialize iteration
638 BestMoveChangesByIteration[Iteration] = 0;
642 cout << "info depth " << Iteration << endl;
644 // Calculate dynamic search window based on previous iterations
647 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
649 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
650 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
652 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
653 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
655 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
656 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
660 alpha = - VALUE_INFINITE;
661 beta = VALUE_INFINITE;
664 // Search to the current depth
665 Value value = root_search(p, ss, rml, alpha, beta);
667 // Write PV to transposition table, in case the relevant entries have
668 // been overwritten during the search.
669 TT.insert_pv(p, ss[0].pv);
672 break; // Value cannot be trusted. Break out immediately!
674 //Save info about search result
675 ValueByIteration[Iteration] = value;
677 // Drop the easy move if it differs from the new best move
678 if (ss[0].pv[0] != EasyMove)
679 EasyMove = MOVE_NONE;
681 if (UseTimeManagement)
684 bool stopSearch = false;
686 // Stop search early if there is only a single legal move,
687 // we search up to Iteration 6 anyway to get a proper score.
688 if (Iteration >= 6 && rml.move_count() == 1)
691 // Stop search early when the last two iterations returned a mate score
693 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
694 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
697 // Stop search early if one move seems to be much better than the rest
698 int64_t nodes = TM.nodes_searched();
700 && EasyMove == ss[0].pv[0]
701 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
702 && current_search_time() > MaxSearchTime / 16)
703 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
704 && current_search_time() > MaxSearchTime / 32)))
707 // Add some extra time if the best move has changed during the last two iterations
708 if (Iteration > 5 && Iteration <= 50)
709 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
710 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
712 // Stop search if most of MaxSearchTime is consumed at the end of the
713 // iteration. We probably don't have enough time to search the first
714 // move at the next iteration anyway.
715 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
723 StopOnPonderhit = true;
727 if (MaxDepth && Iteration >= MaxDepth)
733 // If we are pondering or in infinite search, we shouldn't print the
734 // best move before we are told to do so.
735 if (!AbortSearch && (PonderSearch || InfiniteSearch))
736 wait_for_stop_or_ponderhit();
738 // Print final search statistics
739 cout << "info nodes " << TM.nodes_searched()
741 << " time " << current_search_time()
742 << " hashfull " << TT.full() << endl;
744 // Print the best move and the ponder move to the standard output
745 if (ss[0].pv[0] == MOVE_NONE)
747 ss[0].pv[0] = rml.get_move(0);
748 ss[0].pv[1] = MOVE_NONE;
750 cout << "bestmove " << ss[0].pv[0];
751 if (ss[0].pv[1] != MOVE_NONE)
752 cout << " ponder " << ss[0].pv[1];
759 dbg_print_mean(LogFile);
761 if (dbg_show_hit_rate)
762 dbg_print_hit_rate(LogFile);
764 LogFile << "\nNodes: " << TM.nodes_searched()
765 << "\nNodes/second: " << nps()
766 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
769 p.do_move(ss[0].pv[0], st);
770 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
772 return rml.get_move_score(0);
776 // root_search() is the function which searches the root node. It is
777 // similar to search_pv except that it uses a different move ordering
778 // scheme and prints some information to the standard output.
780 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta) {
785 Depth depth, ext, newDepth;
788 int researchCount = 0;
789 bool moveIsCheck, captureOrPromotion, dangerous;
790 Value alpha = oldAlpha;
791 bool isCheck = pos.is_check();
793 // Evaluate the position statically
795 ss[0].eval = !isCheck ? evaluate(pos, ei, 0) : VALUE_NONE;
797 while (1) // Fail low loop
800 // Loop through all the moves in the root move list
801 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
805 // We failed high, invalidate and skip next moves, leave node-counters
806 // and beta-counters as they are and quickly return, we will try to do
807 // a research at the next iteration with a bigger aspiration window.
808 rml.set_move_score(i, -VALUE_INFINITE);
812 RootMoveNumber = i + 1;
814 // Save the current node count before the move is searched
815 nodes = TM.nodes_searched();
817 // Reset beta cut-off counters
818 TM.resetBetaCounters();
820 // Pick the next root move, and print the move and the move number to
821 // the standard output.
822 move = ss[0].currentMove = rml.get_move(i);
824 if (current_search_time() >= 1000)
825 cout << "info currmove " << move
826 << " currmovenumber " << RootMoveNumber << endl;
828 // Decide search depth for this move
829 moveIsCheck = pos.move_is_check(move);
830 captureOrPromotion = pos.move_is_capture_or_promotion(move);
831 depth = (Iteration - 2) * OnePly + InitialDepth;
832 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
833 newDepth = depth + ext;
835 value = - VALUE_INFINITE;
837 while (1) // Fail high loop
840 // Make the move, and search it
841 pos.do_move(move, st, ci, moveIsCheck);
843 if (i < MultiPV || value > alpha)
845 // Aspiration window is disabled in multi-pv case
847 alpha = -VALUE_INFINITE;
849 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
853 // Try to reduce non-pv search depth by one ply if move seems not problematic,
854 // if the move fails high will be re-searched at full depth.
855 bool doFullDepthSearch = true;
857 if ( depth >= 3*OnePly // FIXME was newDepth
859 && !captureOrPromotion
860 && !move_is_castle(move))
862 ss[0].reduction = pv_reduction(depth, RootMoveNumber - MultiPV + 1);
865 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
866 doFullDepthSearch = (value > alpha);
870 if (doFullDepthSearch)
872 ss[0].reduction = Depth(0);
873 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
876 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
882 // Can we exit fail high loop ?
883 if (AbortSearch || value < beta)
886 // We are failing high and going to do a research. It's important to update score
887 // before research in case we run out of time while researching.
888 rml.set_move_score(i, value);
890 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
891 rml.set_move_pv(i, ss[0].pv);
893 // Print search information to the standard output
894 cout << "info depth " << Iteration
895 << " score " << value_to_string(value)
896 << ((value >= beta) ? " lowerbound" :
897 ((value <= alpha)? " upperbound" : ""))
898 << " time " << current_search_time()
899 << " nodes " << TM.nodes_searched()
903 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
904 cout << ss[0].pv[j] << " ";
910 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
911 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
913 LogFile << pretty_pv(pos, current_search_time(), Iteration,
914 TM.nodes_searched(), value, type, ss[0].pv) << endl;
917 // Prepare for a research after a fail high, each time with a wider window
919 beta = Min(beta + AspirationDelta * (1 << researchCount), VALUE_INFINITE);
921 } // End of fail high loop
923 // Finished searching the move. If AbortSearch is true, the search
924 // was aborted because the user interrupted the search or because we
925 // ran out of time. In this case, the return value of the search cannot
926 // be trusted, and we break out of the loop without updating the best
931 // Remember beta-cutoff and searched nodes counts for this move. The
932 // info is used to sort the root moves at the next iteration.
934 TM.get_beta_counters(pos.side_to_move(), our, their);
935 rml.set_beta_counters(i, our, their);
936 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
938 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
940 if (value <= alpha && i >= MultiPV)
941 rml.set_move_score(i, -VALUE_INFINITE);
944 // PV move or new best move!
947 rml.set_move_score(i, value);
949 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
950 rml.set_move_pv(i, ss[0].pv);
954 // We record how often the best move has been changed in each
955 // iteration. This information is used for time managment: When
956 // the best move changes frequently, we allocate some more time.
958 BestMoveChangesByIteration[Iteration]++;
960 // Print search information to the standard output
961 cout << "info depth " << Iteration
962 << " score " << value_to_string(value)
963 << ((value >= beta) ? " lowerbound" :
964 ((value <= alpha)? " upperbound" : ""))
965 << " time " << current_search_time()
966 << " nodes " << TM.nodes_searched()
970 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
971 cout << ss[0].pv[j] << " ";
977 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
978 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
980 LogFile << pretty_pv(pos, current_search_time(), Iteration,
981 TM.nodes_searched(), value, type, ss[0].pv) << endl;
989 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
991 cout << "info multipv " << j + 1
992 << " score " << value_to_string(rml.get_move_score(j))
993 << " depth " << ((j <= i)? Iteration : Iteration - 1)
994 << " time " << current_search_time()
995 << " nodes " << TM.nodes_searched()
999 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1000 cout << rml.get_move_pv(j, k) << " ";
1004 alpha = rml.get_move_score(Min(i, MultiPV-1));
1006 } // PV move or new best move
1008 assert(alpha >= oldAlpha);
1010 AspirationFailLow = (alpha == oldAlpha);
1012 if (AspirationFailLow && StopOnPonderhit)
1013 StopOnPonderhit = false;
1016 // Can we exit fail low loop ?
1017 if (AbortSearch || alpha > oldAlpha)
1020 // Prepare for a research after a fail low, each time with a wider window
1022 alpha = Max(alpha - AspirationDelta * (1 << researchCount), -VALUE_INFINITE);
1031 // search_pv() is the main search function for PV nodes.
1033 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1034 Depth depth, int ply, int threadID) {
1036 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1037 assert(beta > alpha && beta <= VALUE_INFINITE);
1038 assert(ply >= 0 && ply < PLY_MAX);
1039 assert(threadID >= 0 && threadID < TM.active_threads());
1041 Move movesSearched[256];
1046 Depth ext, newDepth;
1047 Value bestValue, value, oldAlpha;
1048 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1049 bool mateThreat = false;
1051 bestValue = value = -VALUE_INFINITE;
1054 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1056 // Step 1. Initialize node and poll
1057 // Polling can abort search.
1058 init_node(ss, ply, threadID);
1060 // Step 2. Check for aborted search and immediate draw
1061 if (AbortSearch || TM.thread_should_stop(threadID))
1064 if (pos.is_draw() || ply >= PLY_MAX - 1)
1067 // Step 3. Mate distance pruning
1069 alpha = Max(value_mated_in(ply), alpha);
1070 beta = Min(value_mate_in(ply+1), beta);
1074 // Step 4. Transposition table lookup
1075 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1076 // This is to avoid problems in the following areas:
1078 // * Repetition draw detection
1079 // * Fifty move rule detection
1080 // * Searching for a mate
1081 // * Printing of full PV line
1082 tte = TT.retrieve(pos.get_key());
1083 ttMove = (tte ? tte->move() : MOVE_NONE);
1085 // Step 5. Evaluate the position statically
1086 // At PV nodes we do this only to update gain statistics
1087 isCheck = pos.is_check();
1090 ss[ply].eval = evaluate(pos, ei, threadID);
1091 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1094 // Step 6. Razoring (is omitted in PV nodes)
1095 // Step 7. Static null move pruning (is omitted in PV nodes)
1096 // Step 8. Null move search with verification search (is omitted in PV nodes)
1098 // Step 9. Internal iterative deepening
1099 if ( UseIIDAtPVNodes
1100 && depth >= 5*OnePly
1101 && ttMove == MOVE_NONE)
1103 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1104 ttMove = ss[ply].pv[ply];
1105 tte = TT.retrieve(pos.get_key());
1108 // Step 10. Loop through moves
1109 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1111 // Initialize a MovePicker object for the current position
1112 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1113 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1116 while ( alpha < beta
1117 && (move = mp.get_next_move()) != MOVE_NONE
1118 && !TM.thread_should_stop(threadID))
1120 assert(move_is_ok(move));
1122 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1123 moveIsCheck = pos.move_is_check(move, ci);
1124 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1126 // Step 11. Decide the new search depth
1127 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1129 // Singular extension search. We extend the TT move if its value is much better than
1130 // its siblings. To verify this we do a reduced search on all the other moves but the
1131 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1132 if ( depth >= 6 * OnePly
1134 && move == tte->move()
1136 && is_lower_bound(tte->type())
1137 && tte->depth() >= depth - 3 * OnePly)
1139 Value ttValue = value_from_tt(tte->value(), ply);
1141 if (abs(ttValue) < VALUE_KNOWN_WIN)
1143 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1145 if (excValue < ttValue - SingleReplyMargin)
1150 newDepth = depth - OnePly + ext;
1152 // Update current move (this must be done after singular extension search)
1153 movesSearched[moveCount++] = ss[ply].currentMove = move;
1155 // Step 12. Futility pruning (is omitted in PV nodes)
1157 // Step 13. Make the move
1158 pos.do_move(move, st, ci, moveIsCheck);
1160 // Step extra. pv search (only in PV nodes)
1161 // The first move in list is the expected PV
1163 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1166 // Step 14. Reduced search
1167 // if the move fails high will be re-searched at full depth.
1168 bool doFullDepthSearch = true;
1170 if ( depth >= 3*OnePly
1172 && !captureOrPromotion
1173 && !move_is_castle(move)
1174 && !move_is_killer(move, ss[ply]))
1176 ss[ply].reduction = pv_reduction(depth, moveCount);
1177 if (ss[ply].reduction)
1179 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1180 doFullDepthSearch = (value > alpha);
1184 // Step 15. Full depth search
1185 if (doFullDepthSearch)
1187 ss[ply].reduction = Depth(0);
1188 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1190 // Step extra. pv search (only in PV nodes)
1191 if (value > alpha && value < beta)
1192 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1196 // Step 16. Undo move
1197 pos.undo_move(move);
1199 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1201 // Step 17. Check for new best move
1202 if (value > bestValue)
1209 if (value == value_mate_in(ply + 1))
1210 ss[ply].mateKiller = move;
1214 // Step 18. Check for split
1215 if ( TM.active_threads() > 1
1217 && depth >= MinimumSplitDepth
1219 && TM.available_thread_exists(threadID)
1221 && !TM.thread_should_stop(threadID)
1222 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1223 depth, &moveCount, &mp, threadID, true))
1227 // Step 19. Check for mate and stalemate
1228 // All legal moves have been searched and if there were
1229 // no legal moves, it must be mate or stalemate.
1231 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1233 // Step 20. Update tables
1234 // If the search is not aborted, update the transposition table,
1235 // history counters, and killer moves.
1236 if (AbortSearch || TM.thread_should_stop(threadID))
1239 if (bestValue <= oldAlpha)
1240 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1242 else if (bestValue >= beta)
1244 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1245 move = ss[ply].pv[ply];
1246 if (!pos.move_is_capture_or_promotion(move))
1248 update_history(pos, move, depth, movesSearched, moveCount);
1249 update_killers(move, ss[ply]);
1251 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1254 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1260 // search() is the search function for zero-width nodes.
1262 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1263 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1265 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1266 assert(ply >= 0 && ply < PLY_MAX);
1267 assert(threadID >= 0 && threadID < TM.active_threads());
1269 Move movesSearched[256];
1274 Depth ext, newDepth;
1275 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1276 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1277 bool mateThreat = false;
1279 refinedValue = bestValue = value = -VALUE_INFINITE;
1282 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1284 // Step 1. Initialize node and poll
1285 // Polling can abort search.
1286 init_node(ss, ply, threadID);
1288 // Step 2. Check for aborted search and immediate draw
1289 if (AbortSearch || TM.thread_should_stop(threadID))
1292 if (pos.is_draw() || ply >= PLY_MAX - 1)
1295 // Step 3. Mate distance pruning
1296 if (value_mated_in(ply) >= beta)
1299 if (value_mate_in(ply + 1) < beta)
1302 // Step 4. Transposition table lookup
1304 // We don't want the score of a partial search to overwrite a previous full search
1305 // TT value, so we use a different position key in case of an excluded move exists.
1306 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1308 tte = TT.retrieve(posKey);
1309 ttMove = (tte ? tte->move() : MOVE_NONE);
1311 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1313 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1314 return value_from_tt(tte->value(), ply);
1317 // Step 5. Evaluate the position statically
1318 isCheck = pos.is_check();
1322 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1323 ss[ply].eval = value_from_tt(tte->value(), ply);
1325 ss[ply].eval = evaluate(pos, ei, threadID);
1327 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1328 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1332 if ( !value_is_mate(beta)
1334 && depth < RazorDepth
1335 && refinedValue < beta - (0x200 + 16 * depth)
1336 && ss[ply - 1].currentMove != MOVE_NULL
1337 && ttMove == MOVE_NONE
1338 && !pos.has_pawn_on_7th(pos.side_to_move()))
1340 Value rbeta = beta - (0x200 + 16 * depth);
1341 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1343 return v; //FIXME: Logically should be: return (v + 0x200 + 16 * depth);
1346 // Step 7. Static null move pruning
1347 // We're betting that the opponent doesn't have a move that will reduce
1348 // the score by more than fuility_margin(depth) if we do a null move.
1351 && depth < RazorDepth
1352 && refinedValue - futility_margin(depth, 0) >= beta)
1353 return refinedValue - futility_margin(depth, 0);
1355 // Step 8. Null move search with verification search
1356 // When we jump directly to qsearch() we do a null move only if static value is
1357 // at least beta. Otherwise we do a null move if static value is not more than
1358 // NullMoveMargin under beta.
1362 && !value_is_mate(beta)
1363 && ok_to_do_nullmove(pos)
1364 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1366 ss[ply].currentMove = MOVE_NULL;
1368 pos.do_null_move(st);
1370 // Null move dynamic reduction based on depth
1371 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1373 // Null move dynamic reduction based on value
1374 if (refinedValue - beta > PawnValueMidgame)
1377 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1379 pos.undo_null_move();
1381 if (nullValue >= beta)
1383 if (depth < 6 * OnePly)
1386 // Do zugzwang verification search
1387 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1391 // The null move failed low, which means that we may be faced with
1392 // some kind of threat. If the previous move was reduced, check if
1393 // the move that refuted the null move was somehow connected to the
1394 // move which was reduced. If a connection is found, return a fail
1395 // low score (which will cause the reduced move to fail high in the
1396 // parent node, which will trigger a re-search with full depth).
1397 if (nullValue == value_mated_in(ply + 2))
1400 ss[ply].threatMove = ss[ply + 1].currentMove;
1401 if ( depth < ThreatDepth
1402 && ss[ply - 1].reduction
1403 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1408 // Step 9. Internal iterative deepening
1409 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1410 !isCheck && ss[ply].eval >= beta - IIDMargin)
1412 search(pos, ss, beta, depth/2, ply, false, threadID);
1413 ttMove = ss[ply].pv[ply];
1414 tte = TT.retrieve(posKey);
1417 // Step 10. Loop through moves
1418 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1420 // Initialize a MovePicker object for the current position
1421 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1424 while ( bestValue < beta
1425 && (move = mp.get_next_move()) != MOVE_NONE
1426 && !TM.thread_should_stop(threadID))
1428 assert(move_is_ok(move));
1430 if (move == excludedMove)
1433 moveIsCheck = pos.move_is_check(move, ci);
1434 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1435 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1437 // Step 11. Decide the new search depth
1438 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1440 // Singular extension search. We extend the TT move if its value is much better than
1441 // its siblings. To verify this we do a reduced search on all the other moves but the
1442 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1443 if ( depth >= 8 * OnePly
1445 && move == tte->move()
1446 && !excludedMove // Do not allow recursive single-reply search
1448 && is_lower_bound(tte->type())
1449 && tte->depth() >= depth - 3 * OnePly)
1451 Value ttValue = value_from_tt(tte->value(), ply);
1453 if (abs(ttValue) < VALUE_KNOWN_WIN)
1455 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1457 if (excValue < ttValue - SingleReplyMargin)
1462 newDepth = depth - OnePly + ext;
1464 // Update current move (this must be done after singular extension search)
1465 movesSearched[moveCount++] = ss[ply].currentMove = move;
1467 // Step 12. Futility pruning
1470 && !captureOrPromotion
1471 && !move_is_castle(move)
1474 // Move count based pruning
1475 if ( moveCount >= futility_move_count(depth)
1476 && ok_to_prune(pos, move, ss[ply].threatMove)
1477 && bestValue > value_mated_in(PLY_MAX))
1480 // Value based pruning
1481 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1482 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1483 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1485 if (futilityValueScaled < beta)
1487 if (futilityValueScaled > bestValue)
1488 bestValue = futilityValueScaled;
1493 // Step 13. Make the move
1494 pos.do_move(move, st, ci, moveIsCheck);
1496 // Step 14. Reduced search
1497 // if the move fails high will be re-searched at full depth.
1498 bool doFullDepthSearch = true;
1500 if ( depth >= 3*OnePly
1502 && !captureOrPromotion
1503 && !move_is_castle(move)
1504 && !move_is_killer(move, ss[ply]))
1506 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1507 if (ss[ply].reduction)
1509 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1510 doFullDepthSearch = (value >= beta);
1514 // Step 15. Full depth search
1515 if (doFullDepthSearch)
1517 ss[ply].reduction = Depth(0);
1518 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1521 // Step 16. Undo move
1522 pos.undo_move(move);
1524 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1526 // Step 17. Check for new best move
1527 if (value > bestValue)
1533 if (value == value_mate_in(ply + 1))
1534 ss[ply].mateKiller = move;
1537 // Step 18. Check for split
1538 if ( TM.active_threads() > 1
1540 && depth >= MinimumSplitDepth
1542 && TM.available_thread_exists(threadID)
1544 && !TM.thread_should_stop(threadID)
1545 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1546 depth, &moveCount, &mp, threadID, false))
1550 // Step 19. Check for mate and stalemate
1551 // All legal moves have been searched and if there were
1552 // no legal moves, it must be mate or stalemate.
1553 // If one move was excluded return fail low.
1555 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1557 // Step 20. Update tables
1558 // If the search is not aborted, update the transposition table,
1559 // history counters, and killer moves.
1560 if (AbortSearch || TM.thread_should_stop(threadID))
1563 if (bestValue < beta)
1564 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1567 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1568 move = ss[ply].pv[ply];
1569 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1570 if (!pos.move_is_capture_or_promotion(move))
1572 update_history(pos, move, depth, movesSearched, moveCount);
1573 update_killers(move, ss[ply]);
1578 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1584 // qsearch() is the quiescence search function, which is called by the main
1585 // search function when the remaining depth is zero (or, to be more precise,
1586 // less than OnePly).
1588 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1589 Depth depth, int ply, int threadID) {
1591 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1592 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1594 assert(ply >= 0 && ply < PLY_MAX);
1595 assert(threadID >= 0 && threadID < TM.active_threads());
1600 Value staticValue, bestValue, value, futilityBase, futilityValue;
1601 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1602 const TTEntry* tte = NULL;
1604 bool pvNode = (beta - alpha != 1);
1605 Value oldAlpha = alpha;
1607 // Initialize, and make an early exit in case of an aborted search,
1608 // an instant draw, maximum ply reached, etc.
1609 init_node(ss, ply, threadID);
1611 // After init_node() that calls poll()
1612 if (AbortSearch || TM.thread_should_stop(threadID))
1615 if (pos.is_draw() || ply >= PLY_MAX - 1)
1618 // Transposition table lookup. At PV nodes, we don't use the TT for
1619 // pruning, but only for move ordering.
1620 tte = TT.retrieve(pos.get_key());
1621 ttMove = (tte ? tte->move() : MOVE_NONE);
1623 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1625 assert(tte->type() != VALUE_TYPE_EVAL);
1627 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1628 return value_from_tt(tte->value(), ply);
1631 isCheck = pos.is_check();
1633 // Evaluate the position statically
1635 staticValue = -VALUE_INFINITE;
1636 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1637 staticValue = value_from_tt(tte->value(), ply);
1639 staticValue = evaluate(pos, ei, threadID);
1643 ss[ply].eval = staticValue;
1644 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1647 // Initialize "stand pat score", and return it immediately if it is
1649 bestValue = staticValue;
1651 if (bestValue >= beta)
1653 // Store the score to avoid a future costly evaluation() call
1654 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1655 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1660 if (bestValue > alpha)
1663 // If we are near beta then try to get a cutoff pushing checks a bit further
1664 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1666 // Initialize a MovePicker object for the current position, and prepare
1667 // to search the moves. Because the depth is <= 0 here, only captures,
1668 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1669 // and we are near beta) will be generated.
1670 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1672 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1673 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1675 // Loop through the moves until no moves remain or a beta cutoff
1677 while ( alpha < beta
1678 && (move = mp.get_next_move()) != MOVE_NONE)
1680 assert(move_is_ok(move));
1682 moveIsCheck = pos.move_is_check(move, ci);
1684 // Update current move
1686 ss[ply].currentMove = move;
1694 && !move_is_promotion(move)
1695 && !pos.move_is_passed_pawn_push(move))
1697 futilityValue = futilityBase
1698 + pos.endgame_value_of_piece_on(move_to(move))
1699 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1701 if (futilityValue < alpha)
1703 if (futilityValue > bestValue)
1704 bestValue = futilityValue;
1709 // Detect blocking evasions that are candidate to be pruned
1710 evasionPrunable = isCheck
1711 && bestValue != -VALUE_INFINITE
1712 && !pos.move_is_capture(move)
1713 && pos.type_of_piece_on(move_from(move)) != KING
1714 && !pos.can_castle(pos.side_to_move());
1716 // Don't search moves with negative SEE values
1717 if ( (!isCheck || evasionPrunable)
1720 && !move_is_promotion(move)
1721 && pos.see_sign(move) < 0)
1724 // Make and search the move
1725 pos.do_move(move, st, ci, moveIsCheck);
1726 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1727 pos.undo_move(move);
1729 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1732 if (value > bestValue)
1743 // All legal moves have been searched. A special case: If we're in check
1744 // and no legal moves were found, it is checkmate.
1745 if (!moveCount && pos.is_check()) // Mate!
1746 return value_mated_in(ply);
1748 // Update transposition table
1749 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1750 if (bestValue <= oldAlpha)
1752 // If bestValue isn't changed it means it is still the static evaluation
1753 // of the node, so keep this info to avoid a future evaluation() call.
1754 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1755 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1757 else if (bestValue >= beta)
1759 move = ss[ply].pv[ply];
1760 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1762 // Update killers only for good checking moves
1763 if (!pos.move_is_capture_or_promotion(move))
1764 update_killers(move, ss[ply]);
1767 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1769 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1775 // sp_search() is used to search from a split point. This function is called
1776 // by each thread working at the split point. It is similar to the normal
1777 // search() function, but simpler. Because we have already probed the hash
1778 // table, done a null move search, and searched the first move before
1779 // splitting, we don't have to repeat all this work in sp_search(). We
1780 // also don't need to store anything to the hash table here: This is taken
1781 // care of after we return from the split point.
1782 // FIXME: We are currently ignoring mateThreat flag here
1784 void sp_search(SplitPoint* sp, int threadID) {
1786 assert(threadID >= 0 && threadID < TM.active_threads());
1787 assert(TM.active_threads() > 1);
1791 Depth ext, newDepth;
1792 Value value, futilityValueScaled;
1793 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1795 value = -VALUE_INFINITE;
1797 Position pos(*sp->pos);
1799 SearchStack* ss = sp->sstack[threadID];
1800 isCheck = pos.is_check();
1802 // Step 10. Loop through moves
1803 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1804 lock_grab(&(sp->lock));
1806 while ( sp->bestValue < sp->beta
1807 && !TM.thread_should_stop(threadID)
1808 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1810 moveCount = ++sp->moves;
1811 lock_release(&(sp->lock));
1813 assert(move_is_ok(move));
1815 moveIsCheck = pos.move_is_check(move, ci);
1816 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1818 // Step 11. Decide the new search depth
1819 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1820 newDepth = sp->depth - OnePly + ext;
1822 // Update current move
1823 ss[sp->ply].currentMove = move;
1825 // Step 12. Futility pruning
1828 && !captureOrPromotion
1829 && !move_is_castle(move))
1831 // Move count based pruning
1832 if ( moveCount >= futility_move_count(sp->depth)
1833 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1834 && sp->bestValue > value_mated_in(PLY_MAX))
1836 lock_grab(&(sp->lock));
1840 // Value based pruning
1841 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1842 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1843 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1845 if (futilityValueScaled < sp->beta)
1847 lock_grab(&(sp->lock));
1849 if (futilityValueScaled > sp->bestValue)
1850 sp->bestValue = futilityValueScaled;
1855 // Step 13. Make the move
1856 pos.do_move(move, st, ci, moveIsCheck);
1858 // Step 14. Reduced search
1859 // if the move fails high will be re-searched at full depth.
1860 bool doFullDepthSearch = true;
1863 && !captureOrPromotion
1864 && !move_is_castle(move)
1865 && !move_is_killer(move, ss[sp->ply]))
1867 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1868 if (ss[sp->ply].reduction)
1870 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1871 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1875 // Step 15. Full depth search
1876 if (doFullDepthSearch)
1878 ss[sp->ply].reduction = Depth(0);
1879 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1882 // Step 16. Undo move
1883 pos.undo_move(move);
1885 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1887 // Step 17. Check for new best move
1888 lock_grab(&(sp->lock));
1890 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1892 sp->bestValue = value;
1893 if (sp->bestValue >= sp->beta)
1895 sp->stopRequest = true;
1896 sp_update_pv(sp->parentSstack, ss, sp->ply);
1901 /* Here we have the lock still grabbed */
1903 sp->slaves[threadID] = 0;
1906 lock_release(&(sp->lock));
1910 // sp_search_pv() is used to search from a PV split point. This function
1911 // is called by each thread working at the split point. It is similar to
1912 // the normal search_pv() function, but simpler. Because we have already
1913 // probed the hash table and searched the first move before splitting, we
1914 // don't have to repeat all this work in sp_search_pv(). We also don't
1915 // need to store anything to the hash table here: This is taken care of
1916 // after we return from the split point.
1917 // FIXME: We are ignoring mateThreat flag!
1919 void sp_search_pv(SplitPoint* sp, int threadID) {
1921 assert(threadID >= 0 && threadID < TM.active_threads());
1922 assert(TM.active_threads() > 1);
1926 Depth ext, newDepth;
1928 bool moveIsCheck, captureOrPromotion, dangerous;
1930 value = -VALUE_INFINITE;
1932 Position pos(*sp->pos);
1934 SearchStack* ss = sp->sstack[threadID];
1936 // Step 10. Loop through moves
1937 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1938 lock_grab(&(sp->lock));
1940 while ( sp->alpha < sp->beta
1941 && !TM.thread_should_stop(threadID)
1942 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1944 moveCount = ++sp->moves;
1945 lock_release(&(sp->lock));
1947 assert(move_is_ok(move));
1949 moveIsCheck = pos.move_is_check(move, ci);
1950 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1952 // Step 11. Decide the new search depth
1953 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1954 newDepth = sp->depth - OnePly + ext;
1956 // Update current move
1957 ss[sp->ply].currentMove = move;
1959 // Step 12. Futility pruning (is omitted in PV nodes)
1961 // Step 13. Make the move
1962 pos.do_move(move, st, ci, moveIsCheck);
1964 // Step 14. Reduced search
1965 // if the move fails high will be re-searched at full depth.
1966 bool doFullDepthSearch = true;
1969 && !captureOrPromotion
1970 && !move_is_castle(move)
1971 && !move_is_killer(move, ss[sp->ply]))
1973 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1974 if (ss[sp->ply].reduction)
1976 Value localAlpha = sp->alpha;
1977 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1978 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1982 // Step 15. Full depth search
1983 if (doFullDepthSearch)
1985 Value localAlpha = sp->alpha;
1986 ss[sp->ply].reduction = Depth(0);
1987 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1989 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1991 // If another thread has failed high then sp->alpha has been increased
1992 // to be higher or equal then beta, if so, avoid to start a PV search.
1993 localAlpha = sp->alpha;
1994 if (localAlpha < sp->beta)
1995 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1999 // Step 16. Undo move
2000 pos.undo_move(move);
2002 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2004 // Step 17. Check for new best move
2005 lock_grab(&(sp->lock));
2007 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
2009 sp->bestValue = value;
2010 if (value > sp->alpha)
2012 // Ask threads to stop before to modify sp->alpha
2013 if (value >= sp->beta)
2014 sp->stopRequest = true;
2018 sp_update_pv(sp->parentSstack, ss, sp->ply);
2019 if (value == value_mate_in(sp->ply + 1))
2020 ss[sp->ply].mateKiller = move;
2025 /* Here we have the lock still grabbed */
2027 sp->slaves[threadID] = 0;
2030 lock_release(&(sp->lock));
2034 // init_node() is called at the beginning of all the search functions
2035 // (search(), search_pv(), qsearch(), and so on) and initializes the
2036 // search stack object corresponding to the current node. Once every
2037 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2038 // for user input and checks whether it is time to stop the search.
2040 void init_node(SearchStack ss[], int ply, int threadID) {
2042 assert(ply >= 0 && ply < PLY_MAX);
2043 assert(threadID >= 0 && threadID < TM.active_threads());
2045 TM.incrementNodeCounter(threadID);
2050 if (NodesSincePoll >= NodesBetweenPolls)
2057 ss[ply + 2].initKillers();
2061 // update_pv() is called whenever a search returns a value > alpha.
2062 // It updates the PV in the SearchStack object corresponding to the
2065 void update_pv(SearchStack ss[], int ply) {
2067 assert(ply >= 0 && ply < PLY_MAX);
2071 ss[ply].pv[ply] = ss[ply].currentMove;
2073 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2074 ss[ply].pv[p] = ss[ply + 1].pv[p];
2076 ss[ply].pv[p] = MOVE_NONE;
2080 // sp_update_pv() is a variant of update_pv for use at split points. The
2081 // difference between the two functions is that sp_update_pv also updates
2082 // the PV at the parent node.
2084 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2086 assert(ply >= 0 && ply < PLY_MAX);
2090 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2092 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2093 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2095 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2099 // connected_moves() tests whether two moves are 'connected' in the sense
2100 // that the first move somehow made the second move possible (for instance
2101 // if the moving piece is the same in both moves). The first move is assumed
2102 // to be the move that was made to reach the current position, while the
2103 // second move is assumed to be a move from the current position.
2105 bool connected_moves(const Position& pos, Move m1, Move m2) {
2107 Square f1, t1, f2, t2;
2110 assert(move_is_ok(m1));
2111 assert(move_is_ok(m2));
2113 if (m2 == MOVE_NONE)
2116 // Case 1: The moving piece is the same in both moves
2122 // Case 2: The destination square for m2 was vacated by m1
2128 // Case 3: Moving through the vacated square
2129 if ( piece_is_slider(pos.piece_on(f2))
2130 && bit_is_set(squares_between(f2, t2), f1))
2133 // Case 4: The destination square for m2 is defended by the moving piece in m1
2134 p = pos.piece_on(t1);
2135 if (bit_is_set(pos.attacks_from(p, t1), t2))
2138 // Case 5: Discovered check, checking piece is the piece moved in m1
2139 if ( piece_is_slider(p)
2140 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2141 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2143 // discovered_check_candidates() works also if the Position's side to
2144 // move is the opposite of the checking piece.
2145 Color them = opposite_color(pos.side_to_move());
2146 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2148 if (bit_is_set(dcCandidates, f2))
2155 // value_is_mate() checks if the given value is a mate one
2156 // eventually compensated for the ply.
2158 bool value_is_mate(Value value) {
2160 assert(abs(value) <= VALUE_INFINITE);
2162 return value <= value_mated_in(PLY_MAX)
2163 || value >= value_mate_in(PLY_MAX);
2167 // move_is_killer() checks if the given move is among the
2168 // killer moves of that ply.
2170 bool move_is_killer(Move m, const SearchStack& ss) {
2172 const Move* k = ss.killers;
2173 for (int i = 0; i < KILLER_MAX; i++, k++)
2181 // extension() decides whether a move should be searched with normal depth,
2182 // or with extended depth. Certain classes of moves (checking moves, in
2183 // particular) are searched with bigger depth than ordinary moves and in
2184 // any case are marked as 'dangerous'. Note that also if a move is not
2185 // extended, as example because the corresponding UCI option is set to zero,
2186 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2188 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2189 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2191 assert(m != MOVE_NONE);
2193 Depth result = Depth(0);
2194 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2199 result += CheckExtension[pvNode];
2202 result += SingleEvasionExtension[pvNode];
2205 result += MateThreatExtension[pvNode];
2208 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2210 Color c = pos.side_to_move();
2211 if (relative_rank(c, move_to(m)) == RANK_7)
2213 result += PawnPushTo7thExtension[pvNode];
2216 if (pos.pawn_is_passed(c, move_to(m)))
2218 result += PassedPawnExtension[pvNode];
2223 if ( captureOrPromotion
2224 && pos.type_of_piece_on(move_to(m)) != PAWN
2225 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2226 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2227 && !move_is_promotion(m)
2230 result += PawnEndgameExtension[pvNode];
2235 && captureOrPromotion
2236 && pos.type_of_piece_on(move_to(m)) != PAWN
2237 && pos.see_sign(m) >= 0)
2243 return Min(result, OnePly);
2247 // ok_to_do_nullmove() looks at the current position and decides whether
2248 // doing a 'null move' should be allowed. In order to avoid zugzwang
2249 // problems, null moves are not allowed when the side to move has very
2250 // little material left. Currently, the test is a bit too simple: Null
2251 // moves are avoided only when the side to move has only pawns left.
2252 // It's probably a good idea to avoid null moves in at least some more
2253 // complicated endgames, e.g. KQ vs KR. FIXME
2255 bool ok_to_do_nullmove(const Position& pos) {
2257 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2261 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2262 // non-tactical moves late in the move list close to the leaves are
2263 // candidates for pruning.
2265 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2267 assert(move_is_ok(m));
2268 assert(threat == MOVE_NONE || move_is_ok(threat));
2269 assert(!pos.move_is_check(m));
2270 assert(!pos.move_is_capture_or_promotion(m));
2271 assert(!pos.move_is_passed_pawn_push(m));
2273 Square mfrom, mto, tfrom, tto;
2275 // Prune if there isn't any threat move
2276 if (threat == MOVE_NONE)
2279 mfrom = move_from(m);
2281 tfrom = move_from(threat);
2282 tto = move_to(threat);
2284 // Case 1: Don't prune moves which move the threatened piece
2288 // Case 2: If the threatened piece has value less than or equal to the
2289 // value of the threatening piece, don't prune move which defend it.
2290 if ( pos.move_is_capture(threat)
2291 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2292 || pos.type_of_piece_on(tfrom) == KING)
2293 && pos.move_attacks_square(m, tto))
2296 // Case 3: If the moving piece in the threatened move is a slider, don't
2297 // prune safe moves which block its ray.
2298 if ( piece_is_slider(pos.piece_on(tfrom))
2299 && bit_is_set(squares_between(tfrom, tto), mto)
2300 && pos.see_sign(m) >= 0)
2307 // ok_to_use_TT() returns true if a transposition table score
2308 // can be used at a given point in search.
2310 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2312 Value v = value_from_tt(tte->value(), ply);
2314 return ( tte->depth() >= depth
2315 || v >= Max(value_mate_in(PLY_MAX), beta)
2316 || v < Min(value_mated_in(PLY_MAX), beta))
2318 && ( (is_lower_bound(tte->type()) && v >= beta)
2319 || (is_upper_bound(tte->type()) && v < beta));
2323 // refine_eval() returns the transposition table score if
2324 // possible otherwise falls back on static position evaluation.
2326 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2331 Value v = value_from_tt(tte->value(), ply);
2333 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2334 || (is_upper_bound(tte->type()) && v < defaultEval))
2341 // update_history() registers a good move that produced a beta-cutoff
2342 // in history and marks as failures all the other moves of that ply.
2344 void update_history(const Position& pos, Move move, Depth depth,
2345 Move movesSearched[], int moveCount) {
2349 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2351 for (int i = 0; i < moveCount - 1; i++)
2353 m = movesSearched[i];
2357 if (!pos.move_is_capture_or_promotion(m))
2358 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2363 // update_killers() add a good move that produced a beta-cutoff
2364 // among the killer moves of that ply.
2366 void update_killers(Move m, SearchStack& ss) {
2368 if (m == ss.killers[0])
2371 for (int i = KILLER_MAX - 1; i > 0; i--)
2372 ss.killers[i] = ss.killers[i - 1];
2378 // update_gains() updates the gains table of a non-capture move given
2379 // the static position evaluation before and after the move.
2381 void update_gains(const Position& pos, Move m, Value before, Value after) {
2384 && before != VALUE_NONE
2385 && after != VALUE_NONE
2386 && pos.captured_piece() == NO_PIECE_TYPE
2387 && !move_is_castle(m)
2388 && !move_is_promotion(m))
2389 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2393 // current_search_time() returns the number of milliseconds which have passed
2394 // since the beginning of the current search.
2396 int current_search_time() {
2398 return get_system_time() - SearchStartTime;
2402 // nps() computes the current nodes/second count.
2406 int t = current_search_time();
2407 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2411 // poll() performs two different functions: It polls for user input, and it
2412 // looks at the time consumed so far and decides if it's time to abort the
2415 void poll(SearchStack ss[], int ply) {
2417 static int lastInfoTime;
2418 int t = current_search_time();
2423 // We are line oriented, don't read single chars
2424 std::string command;
2426 if (!std::getline(std::cin, command))
2429 if (command == "quit")
2432 PonderSearch = false;
2436 else if (command == "stop")
2439 PonderSearch = false;
2441 else if (command == "ponderhit")
2445 // Print search information
2449 else if (lastInfoTime > t)
2450 // HACK: Must be a new search where we searched less than
2451 // NodesBetweenPolls nodes during the first second of search.
2454 else if (t - lastInfoTime >= 1000)
2461 if (dbg_show_hit_rate)
2462 dbg_print_hit_rate();
2464 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2465 << " time " << t << " hashfull " << TT.full() << endl;
2467 // We only support current line printing in single thread mode
2468 if (ShowCurrentLine && TM.active_threads() == 1)
2470 cout << "info currline";
2471 for (int p = 0; p < ply; p++)
2472 cout << " " << ss[p].currentMove;
2478 // Should we stop the search?
2482 bool stillAtFirstMove = RootMoveNumber == 1
2483 && !AspirationFailLow
2484 && t > MaxSearchTime + ExtraSearchTime;
2486 bool noMoreTime = t > AbsoluteMaxSearchTime
2487 || stillAtFirstMove;
2489 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2490 || (ExactMaxTime && t >= ExactMaxTime)
2491 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2496 // ponderhit() is called when the program is pondering (i.e. thinking while
2497 // it's the opponent's turn to move) in order to let the engine know that
2498 // it correctly predicted the opponent's move.
2502 int t = current_search_time();
2503 PonderSearch = false;
2505 bool stillAtFirstMove = RootMoveNumber == 1
2506 && !AspirationFailLow
2507 && t > MaxSearchTime + ExtraSearchTime;
2509 bool noMoreTime = t > AbsoluteMaxSearchTime
2510 || stillAtFirstMove;
2512 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2517 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2519 void init_ss_array(SearchStack ss[]) {
2521 for (int i = 0; i < 3; i++)
2524 ss[i].initKillers();
2529 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2530 // while the program is pondering. The point is to work around a wrinkle in
2531 // the UCI protocol: When pondering, the engine is not allowed to give a
2532 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2533 // We simply wait here until one of these commands is sent, and return,
2534 // after which the bestmove and pondermove will be printed (in id_loop()).
2536 void wait_for_stop_or_ponderhit() {
2538 std::string command;
2542 if (!std::getline(std::cin, command))
2545 if (command == "quit")
2550 else if (command == "ponderhit" || command == "stop")
2556 // init_thread() is the function which is called when a new thread is
2557 // launched. It simply calls the idle_loop() function with the supplied
2558 // threadID. There are two versions of this function; one for POSIX
2559 // threads and one for Windows threads.
2561 #if !defined(_MSC_VER)
2563 void* init_thread(void *threadID) {
2565 TM.idle_loop(*(int*)threadID, NULL);
2571 DWORD WINAPI init_thread(LPVOID threadID) {
2573 TM.idle_loop(*(int*)threadID, NULL);
2580 /// The ThreadsManager class
2582 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2583 // get_beta_counters() are getters/setters for the per thread
2584 // counters used to sort the moves at root.
2586 void ThreadsManager::resetNodeCounters() {
2588 for (int i = 0; i < MAX_THREADS; i++)
2589 threads[i].nodes = 0ULL;
2592 void ThreadsManager::resetBetaCounters() {
2594 for (int i = 0; i < MAX_THREADS; i++)
2595 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2598 int64_t ThreadsManager::nodes_searched() const {
2600 int64_t result = 0ULL;
2601 for (int i = 0; i < ActiveThreads; i++)
2602 result += threads[i].nodes;
2607 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2610 for (int i = 0; i < MAX_THREADS; i++)
2612 our += threads[i].betaCutOffs[us];
2613 their += threads[i].betaCutOffs[opposite_color(us)];
2618 // idle_loop() is where the threads are parked when they have no work to do.
2619 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2620 // object for which the current thread is the master.
2622 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2624 assert(threadID >= 0 && threadID < MAX_THREADS);
2628 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2629 // master should exit as last one.
2630 if (AllThreadsShouldExit)
2633 threads[threadID].state = THREAD_TERMINATED;
2637 // If we are not thinking, wait for a condition to be signaled
2638 // instead of wasting CPU time polling for work.
2639 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2642 assert(threadID != 0);
2643 threads[threadID].state = THREAD_SLEEPING;
2645 #if !defined(_MSC_VER)
2646 pthread_mutex_lock(&WaitLock);
2647 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2648 pthread_cond_wait(&WaitCond, &WaitLock);
2649 pthread_mutex_unlock(&WaitLock);
2651 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2655 // If thread has just woken up, mark it as available
2656 if (threads[threadID].state == THREAD_SLEEPING)
2657 threads[threadID].state = THREAD_AVAILABLE;
2659 // If this thread has been assigned work, launch a search
2660 if (threads[threadID].state == THREAD_WORKISWAITING)
2662 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2664 threads[threadID].state = THREAD_SEARCHING;
2666 if (threads[threadID].splitPoint->pvNode)
2667 sp_search_pv(threads[threadID].splitPoint, threadID);
2669 sp_search(threads[threadID].splitPoint, threadID);
2671 assert(threads[threadID].state == THREAD_SEARCHING);
2673 threads[threadID].state = THREAD_AVAILABLE;
2676 // If this thread is the master of a split point and all threads have
2677 // finished their work at this split point, return from the idle loop.
2678 if (waitSp != NULL && waitSp->cpus == 0)
2680 assert(threads[threadID].state == THREAD_AVAILABLE);
2682 threads[threadID].state = THREAD_SEARCHING;
2689 // init_threads() is called during startup. It launches all helper threads,
2690 // and initializes the split point stack and the global locks and condition
2693 void ThreadsManager::init_threads() {
2698 #if !defined(_MSC_VER)
2699 pthread_t pthread[1];
2702 // Initialize global locks
2703 lock_init(&MPLock, NULL);
2705 // Initialize SplitPointStack locks
2706 for (i = 0; i < MAX_THREADS; i++)
2707 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2709 SplitPointStack[i][j].parent = NULL;
2710 lock_init(&(SplitPointStack[i][j].lock), NULL);
2713 #if !defined(_MSC_VER)
2714 pthread_mutex_init(&WaitLock, NULL);
2715 pthread_cond_init(&WaitCond, NULL);
2717 for (i = 0; i < MAX_THREADS; i++)
2718 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2721 // Will be set just before program exits to properly end the threads
2722 AllThreadsShouldExit = false;
2724 // Threads will be put to sleep as soon as created
2725 AllThreadsShouldSleep = true;
2727 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2729 threads[0].state = THREAD_SEARCHING;
2730 for (i = 1; i < MAX_THREADS; i++)
2731 threads[i].state = THREAD_AVAILABLE;
2733 // Launch the helper threads
2734 for (i = 1; i < MAX_THREADS; i++)
2737 #if !defined(_MSC_VER)
2738 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2741 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
2746 cout << "Failed to create thread number " << i << endl;
2747 Application::exit_with_failure();
2750 // Wait until the thread has finished launching and is gone to sleep
2751 while (threads[i].state != THREAD_SLEEPING);
2756 // exit_threads() is called when the program exits. It makes all the
2757 // helper threads exit cleanly.
2759 void ThreadsManager::exit_threads() {
2761 ActiveThreads = MAX_THREADS; // HACK
2762 AllThreadsShouldSleep = true; // HACK
2763 wake_sleeping_threads();
2765 // This makes the threads to exit idle_loop()
2766 AllThreadsShouldExit = true;
2768 // Wait for thread termination
2769 for (int i = 1; i < MAX_THREADS; i++)
2770 while (threads[i].state != THREAD_TERMINATED);
2772 // Now we can safely destroy the locks
2773 for (int i = 0; i < MAX_THREADS; i++)
2774 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2775 lock_destroy(&(SplitPointStack[i][j].lock));
2779 // thread_should_stop() checks whether the thread should stop its search.
2780 // This can happen if a beta cutoff has occurred in the thread's currently
2781 // active split point, or in some ancestor of the current split point.
2783 bool ThreadsManager::thread_should_stop(int threadID) const {
2785 assert(threadID >= 0 && threadID < ActiveThreads);
2789 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2794 // thread_is_available() checks whether the thread with threadID "slave" is
2795 // available to help the thread with threadID "master" at a split point. An
2796 // obvious requirement is that "slave" must be idle. With more than two
2797 // threads, this is not by itself sufficient: If "slave" is the master of
2798 // some active split point, it is only available as a slave to the other
2799 // threads which are busy searching the split point at the top of "slave"'s
2800 // split point stack (the "helpful master concept" in YBWC terminology).
2802 bool ThreadsManager::thread_is_available(int slave, int master) const {
2804 assert(slave >= 0 && slave < ActiveThreads);
2805 assert(master >= 0 && master < ActiveThreads);
2806 assert(ActiveThreads > 1);
2808 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2811 // Make a local copy to be sure doesn't change under our feet
2812 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2814 if (localActiveSplitPoints == 0)
2815 // No active split points means that the thread is available as
2816 // a slave for any other thread.
2819 if (ActiveThreads == 2)
2822 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2823 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2824 // could have been set to 0 by another thread leading to an out of bound access.
2825 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2832 // available_thread_exists() tries to find an idle thread which is available as
2833 // a slave for the thread with threadID "master".
2835 bool ThreadsManager::available_thread_exists(int master) const {
2837 assert(master >= 0 && master < ActiveThreads);
2838 assert(ActiveThreads > 1);
2840 for (int i = 0; i < ActiveThreads; i++)
2841 if (thread_is_available(i, master))
2848 // split() does the actual work of distributing the work at a node between
2849 // several threads at PV nodes. If it does not succeed in splitting the
2850 // node (because no idle threads are available, or because we have no unused
2851 // split point objects), the function immediately returns false. If
2852 // splitting is possible, a SplitPoint object is initialized with all the
2853 // data that must be copied to the helper threads (the current position and
2854 // search stack, alpha, beta, the search depth, etc.), and we tell our
2855 // helper threads that they have been assigned work. This will cause them
2856 // to instantly leave their idle loops and call sp_search_pv(). When all
2857 // threads have returned from sp_search_pv (or, equivalently, when
2858 // splitPoint->cpus becomes 0), split() returns true.
2860 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2861 Value* alpha, const Value beta, Value* bestValue,
2862 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2865 assert(sstck != NULL);
2866 assert(ply >= 0 && ply < PLY_MAX);
2867 assert(*bestValue >= -VALUE_INFINITE);
2868 assert( ( pvNode && *bestValue <= *alpha)
2869 || (!pvNode && *bestValue < beta ));
2870 assert(!pvNode || *alpha < beta);
2871 assert(beta <= VALUE_INFINITE);
2872 assert(depth > Depth(0));
2873 assert(master >= 0 && master < ActiveThreads);
2874 assert(ActiveThreads > 1);
2876 SplitPoint* splitPoint;
2880 // If no other thread is available to help us, or if we have too many
2881 // active split points, don't split.
2882 if ( !available_thread_exists(master)
2883 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2885 lock_release(&MPLock);
2889 // Pick the next available split point object from the split point stack
2890 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2892 // Initialize the split point object
2893 splitPoint->parent = threads[master].splitPoint;
2894 splitPoint->stopRequest = false;
2895 splitPoint->ply = ply;
2896 splitPoint->depth = depth;
2897 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2898 splitPoint->beta = beta;
2899 splitPoint->pvNode = pvNode;
2900 splitPoint->bestValue = *bestValue;
2901 splitPoint->master = master;
2902 splitPoint->mp = mp;
2903 splitPoint->moves = *moves;
2904 splitPoint->cpus = 1;
2905 splitPoint->pos = &p;
2906 splitPoint->parentSstack = sstck;
2907 for (int i = 0; i < ActiveThreads; i++)
2908 splitPoint->slaves[i] = 0;
2910 threads[master].splitPoint = splitPoint;
2911 threads[master].activeSplitPoints++;
2913 // If we are here it means we are not available
2914 assert(threads[master].state != THREAD_AVAILABLE);
2916 // Allocate available threads setting state to THREAD_BOOKED
2917 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2918 if (thread_is_available(i, master))
2920 threads[i].state = THREAD_BOOKED;
2921 threads[i].splitPoint = splitPoint;
2922 splitPoint->slaves[i] = 1;
2926 assert(splitPoint->cpus > 1);
2928 // We can release the lock because slave threads are already booked and master is not available
2929 lock_release(&MPLock);
2931 // Tell the threads that they have work to do. This will make them leave
2932 // their idle loop. But before copy search stack tail for each thread.
2933 for (int i = 0; i < ActiveThreads; i++)
2934 if (i == master || splitPoint->slaves[i])
2936 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2938 assert(i == master || threads[i].state == THREAD_BOOKED);
2940 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2943 // Everything is set up. The master thread enters the idle loop, from
2944 // which it will instantly launch a search, because its state is
2945 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2946 // idle loop, which means that the main thread will return from the idle
2947 // loop when all threads have finished their work at this split point
2948 // (i.e. when splitPoint->cpus == 0).
2949 idle_loop(master, splitPoint);
2951 // We have returned from the idle loop, which means that all threads are
2952 // finished. Update alpha, beta and bestValue, and return.
2956 *alpha = splitPoint->alpha;
2958 *bestValue = splitPoint->bestValue;
2959 threads[master].activeSplitPoints--;
2960 threads[master].splitPoint = splitPoint->parent;
2962 lock_release(&MPLock);
2967 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2968 // to start a new search from the root.
2970 void ThreadsManager::wake_sleeping_threads() {
2972 assert(AllThreadsShouldSleep);
2973 assert(ActiveThreads > 0);
2975 AllThreadsShouldSleep = false;
2977 if (ActiveThreads == 1)
2980 for (int i = 1; i < ActiveThreads; i++)
2981 assert(threads[i].state == THREAD_SLEEPING);
2983 #if !defined(_MSC_VER)
2984 pthread_mutex_lock(&WaitLock);
2985 pthread_cond_broadcast(&WaitCond);
2986 pthread_mutex_unlock(&WaitLock);
2988 for (int i = 1; i < MAX_THREADS; i++)
2989 SetEvent(SitIdleEvent[i]);
2995 // put_threads_to_sleep() makes all the threads go to sleep just before
2996 // to leave think(), at the end of the search. Threads should have already
2997 // finished the job and should be idle.
2999 void ThreadsManager::put_threads_to_sleep() {
3001 assert(!AllThreadsShouldSleep);
3003 // This makes the threads to go to sleep
3004 AllThreadsShouldSleep = 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];