2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
43 #include "ucioption.h"
49 //// Local definitions
57 // ThreadsManager class is used to handle all the threads related stuff in search,
58 // init, starting, parking and, the most important, launching a slave thread at a
59 // split point are what this class does. All the access to shared thread data is
60 // done through this class, so that we avoid using global variables instead.
62 class ThreadsManager {
63 /* As long as the single ThreadsManager object is defined as a global we don't
64 need to explicitly initialize to zero its data members because variables with
65 static storage duration are automatically set to zero before enter main()
71 int active_threads() const { return ActiveThreads; }
72 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
73 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
74 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
75 void print_current_line(SearchStack ss[], int ply, int threadID);
77 void resetNodeCounters();
78 void resetBetaCounters();
79 int64_t nodes_searched() const;
80 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
81 bool available_thread_exists(int master) const;
82 bool thread_is_available(int slave, int master) const;
83 bool thread_should_stop(int threadID) const;
84 void wake_sleeping_threads();
85 void put_threads_to_sleep();
86 void idle_loop(int threadID, SplitPoint* waitSp);
87 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
88 const Value futilityValue, Depth depth, int* moves, MovePicker* mp, int master, bool pvNode);
94 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
95 Thread threads[MAX_THREADS];
96 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
100 #if !defined(_MSC_VER)
101 pthread_cond_t WaitCond;
102 pthread_mutex_t WaitLock;
104 HANDLE SitIdleEvent[MAX_THREADS];
110 // RootMove struct is used for moves at the root at the tree. For each
111 // root move, we store a score, a node count, and a PV (really a refutation
112 // in the case of moves which fail low).
116 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
118 // RootMove::operator<() is the comparison function used when
119 // sorting the moves. A move m1 is considered to be better
120 // than a move m2 if it has a higher score, or if the moves
121 // have equal score but m1 has the higher node count.
122 bool operator<(const RootMove& m) const {
124 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
129 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
130 Move pv[PLY_MAX_PLUS_2];
134 // The RootMoveList class is essentially an array of RootMove objects, with
135 // a handful of methods for accessing the data in the individual moves.
140 RootMoveList(Position& pos, Move searchMoves[]);
142 int move_count() const { return count; }
143 Move get_move(int moveNum) const { return moves[moveNum].move; }
144 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
145 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
146 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
147 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
149 void set_move_nodes(int moveNum, int64_t nodes);
150 void set_beta_counters(int moveNum, int64_t our, int64_t their);
151 void set_move_pv(int moveNum, const Move pv[]);
153 void sort_multipv(int n);
156 static const int MaxRootMoves = 500;
157 RootMove moves[MaxRootMoves];
164 // Search depth at iteration 1
165 const Depth InitialDepth = OnePly;
167 // Use internal iterative deepening?
168 const bool UseIIDAtPVNodes = true;
169 const bool UseIIDAtNonPVNodes = true;
171 // Internal iterative deepening margin. At Non-PV moves, when
172 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
173 // search when the static evaluation is at most IIDMargin below beta.
174 const Value IIDMargin = Value(0x100);
176 // Easy move margin. An easy move candidate must be at least this much
177 // better than the second best move.
178 const Value EasyMoveMargin = Value(0x200);
180 // Null move margin. A null move search will not be done if the static
181 // evaluation of the position is more than NullMoveMargin below beta.
182 const Value NullMoveMargin = Value(0x200);
184 // If the TT move is at least SingleReplyMargin better then the
185 // remaining ones we will extend it.
186 const Value SingleReplyMargin = Value(0x20);
188 // Depth limit for razoring
189 const Depth RazorDepth = 4 * OnePly;
191 /// Lookup tables initialized at startup
193 // Reduction lookup tables and their getter functions
194 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
195 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
197 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
198 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
200 // Futility lookup tables and their getter functions
201 const Value FutilityMarginQS = Value(0x80);
202 int32_t FutilityMarginsMatrix[14][64]; // [depth][moveNumber]
203 int FutilityMoveCountArray[32]; // [depth]
205 inline Value futility_margin(Depth d, int mn) { return Value(d < 7*OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
206 inline int futility_move_count(Depth d) { return d < 16*OnePly ? FutilityMoveCountArray[d] : 512; }
208 /// Variables initialized by UCI options
210 // Depth limit for use of dynamic threat detection
213 // Last seconds noise filtering (LSN)
214 const bool UseLSNFiltering = true;
215 const int LSNTime = 4000; // In milliseconds
216 const Value LSNValue = value_from_centipawns(200);
217 bool loseOnTime = false;
219 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
220 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
221 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
223 // Iteration counters
226 // Scores and number of times the best move changed for each iteration
227 Value ValueByIteration[PLY_MAX_PLUS_2];
228 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
230 // Search window management
236 // Time managment variables
239 int MaxNodes, MaxDepth;
240 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
241 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
242 bool AbortSearch, Quit;
243 bool AspirationFailLow;
245 // Show current line?
246 bool ShowCurrentLine;
250 std::ofstream LogFile;
252 // MP related variables
253 Depth MinimumSplitDepth;
254 int MaxThreadsPerSplitPoint;
257 // Node counters, used only by thread[0] but try to keep in different
258 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
260 int NodesBetweenPolls = 30000;
267 Value id_loop(const Position& pos, Move searchMoves[]);
268 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta);
269 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
270 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
271 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
272 void sp_search(SplitPoint* sp, int threadID);
273 void sp_search_pv(SplitPoint* sp, int threadID);
274 void init_node(SearchStack ss[], int ply, int threadID);
275 void update_pv(SearchStack ss[], int ply);
276 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
277 bool connected_moves(const Position& pos, Move m1, Move m2);
278 bool value_is_mate(Value value);
279 bool move_is_killer(Move m, const SearchStack& ss);
280 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
281 bool ok_to_do_nullmove(const Position& pos);
282 bool ok_to_prune(const Position& pos, Move m, Move threat);
283 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
284 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
285 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
286 void update_killers(Move m, SearchStack& ss);
287 void update_gains(const Position& pos, Move move, Value before, Value after);
289 int current_search_time();
293 void wait_for_stop_or_ponderhit();
294 void init_ss_array(SearchStack ss[]);
296 #if !defined(_MSC_VER)
297 void *init_thread(void *threadID);
299 DWORD WINAPI init_thread(LPVOID threadID);
309 /// init_threads(), exit_threads() and nodes_searched() are helpers to
310 /// give accessibility to some TM methods from outside of current file.
312 void init_threads() { TM.init_threads(); }
313 void exit_threads() { TM.exit_threads(); }
314 int64_t nodes_searched() { return TM.nodes_searched(); }
317 /// perft() is our utility to verify move generation is bug free. All the legal
318 /// moves up to given depth are generated and counted and the sum returned.
320 int perft(Position& pos, Depth depth)
324 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
326 // If we are at the last ply we don't need to do and undo
327 // the moves, just to count them.
328 if (depth <= OnePly) // Replace with '<' to test also qsearch
330 while (mp.get_next_move()) sum++;
334 // Loop through all legal moves
336 while ((move = mp.get_next_move()) != MOVE_NONE)
339 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
340 sum += perft(pos, depth - OnePly);
347 /// think() is the external interface to Stockfish's search, and is called when
348 /// the program receives the UCI 'go' command. It initializes various
349 /// search-related global variables, and calls root_search(). It returns false
350 /// when a quit command is received during the search.
352 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
353 int time[], int increment[], int movesToGo, int maxDepth,
354 int maxNodes, int maxTime, Move searchMoves[]) {
356 // Initialize global search variables
357 StopOnPonderhit = AbortSearch = Quit = false;
358 AspirationFailLow = false;
360 SearchStartTime = get_system_time();
361 ExactMaxTime = maxTime;
364 InfiniteSearch = infinite;
365 PonderSearch = ponder;
366 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
368 // Look for a book move, only during games, not tests
369 if (UseTimeManagement && get_option_value_bool("OwnBook"))
372 if (get_option_value_string("Book File") != OpeningBook.file_name())
373 OpeningBook.open(get_option_value_string("Book File"));
375 bookMove = OpeningBook.get_move(pos);
376 if (bookMove != MOVE_NONE)
379 wait_for_stop_or_ponderhit();
381 cout << "bestmove " << bookMove << endl;
386 TM.resetNodeCounters();
388 if (button_was_pressed("New Game"))
389 loseOnTime = false; // Reset at the beginning of a new game
391 // Read UCI option values
392 TT.set_size(get_option_value_int("Hash"));
393 if (button_was_pressed("Clear Hash"))
396 bool PonderingEnabled = get_option_value_bool("Ponder");
397 MultiPV = get_option_value_int("MultiPV");
399 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
400 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
402 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
403 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
405 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
406 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
408 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
409 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
411 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
412 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
414 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
415 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
417 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
419 Chess960 = get_option_value_bool("UCI_Chess960");
420 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
421 UseLogFile = get_option_value_bool("Use Search Log");
423 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
425 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
426 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
428 read_weights(pos.side_to_move());
430 // Set the number of active threads
431 int newActiveThreads = get_option_value_int("Threads");
432 if (newActiveThreads != TM.active_threads())
434 TM.set_active_threads(newActiveThreads);
435 init_eval(TM.active_threads());
436 // HACK: init_eval() destroys the static castleRightsMask[] array in the
437 // Position class. The below line repairs the damage.
438 Position p(pos.to_fen());
442 // Wake up sleeping threads
443 TM.wake_sleeping_threads();
446 int myTime = time[side_to_move];
447 int myIncrement = increment[side_to_move];
448 if (UseTimeManagement)
450 if (!movesToGo) // Sudden death time control
454 MaxSearchTime = myTime / 30 + myIncrement;
455 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
457 else // Blitz game without increment
459 MaxSearchTime = myTime / 30;
460 AbsoluteMaxSearchTime = myTime / 8;
463 else // (x moves) / (y minutes)
467 MaxSearchTime = myTime / 2;
468 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
472 MaxSearchTime = myTime / Min(movesToGo, 20);
473 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
477 if (PonderingEnabled)
479 MaxSearchTime += MaxSearchTime / 4;
480 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
484 // Set best NodesBetweenPolls interval
486 NodesBetweenPolls = Min(MaxNodes, 30000);
487 else if (myTime && myTime < 1000)
488 NodesBetweenPolls = 1000;
489 else if (myTime && myTime < 5000)
490 NodesBetweenPolls = 5000;
492 NodesBetweenPolls = 30000;
494 // Write information to search log file
496 LogFile << "Searching: " << pos.to_fen() << endl
497 << "infinite: " << infinite
498 << " ponder: " << ponder
499 << " time: " << myTime
500 << " increment: " << myIncrement
501 << " moves to go: " << movesToGo << endl;
503 // LSN filtering. Used only for developing purpose. Disabled by default.
507 // Step 2. If after last move we decided to lose on time, do it now!
508 while (SearchStartTime + myTime + 1000 > get_system_time())
512 // We're ready to start thinking. Call the iterative deepening loop function
513 Value v = id_loop(pos, searchMoves);
517 // Step 1. If this is sudden death game and our position is hopeless,
518 // decide to lose on time.
519 if ( !loseOnTime // If we already lost on time, go to step 3.
529 // Step 3. Now after stepping over the time limit, reset flag for next match.
537 TM.put_threads_to_sleep();
543 /// init_search() is called during startup. It initializes various lookup tables
547 // Init our reduction lookup tables
548 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
549 for (int j = 1; j < 64; j++) // j == moveNumber
551 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
552 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
553 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
554 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
557 // Init futility margins array
558 for (int i = 0; i < 14; i++) // i == depth (OnePly = 2)
559 for (int j = 0; j < 64; j++) // j == moveNumber
561 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j; // FIXME: test using log instead of BSR
564 // Init futility move count array
565 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
566 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
570 // SearchStack::init() initializes a search stack. Used at the beginning of a
571 // new search from the root.
572 void SearchStack::init(int ply) {
574 pv[ply] = pv[ply + 1] = MOVE_NONE;
575 currentMove = threatMove = MOVE_NONE;
576 reduction = Depth(0);
580 void SearchStack::initKillers() {
582 mateKiller = MOVE_NONE;
583 for (int i = 0; i < KILLER_MAX; i++)
584 killers[i] = MOVE_NONE;
589 // id_loop() is the main iterative deepening loop. It calls root_search
590 // repeatedly with increasing depth until the allocated thinking time has
591 // been consumed, the user stops the search, or the maximum search depth is
594 Value id_loop(const Position& pos, Move searchMoves[]) {
597 SearchStack ss[PLY_MAX_PLUS_2];
599 // searchMoves are verified, copied, scored and sorted
600 RootMoveList rml(p, searchMoves);
602 // Handle special case of searching on a mate/stale position
603 if (rml.move_count() == 0)
606 wait_for_stop_or_ponderhit();
608 return pos.is_check()? -VALUE_MATE : VALUE_DRAW;
611 // Print RootMoveList c'tor startup scoring to the standard output,
612 // so that we print information also for iteration 1.
613 cout << "info depth " << 1 << "\ninfo depth " << 1
614 << " score " << value_to_string(rml.get_move_score(0))
615 << " time " << current_search_time()
616 << " nodes " << TM.nodes_searched()
618 << " pv " << rml.get_move(0) << "\n";
624 ValueByIteration[1] = rml.get_move_score(0);
627 // Is one move significantly better than others after initial scoring ?
628 Move EasyMove = MOVE_NONE;
629 if ( rml.move_count() == 1
630 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
631 EasyMove = rml.get_move(0);
633 // Iterative deepening loop
634 while (Iteration < PLY_MAX)
636 // Initialize iteration
639 BestMoveChangesByIteration[Iteration] = 0;
643 cout << "info depth " << Iteration << endl;
645 // Calculate dynamic search window based on previous iterations
648 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
650 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
651 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
653 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
654 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
656 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
657 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
661 alpha = - VALUE_INFINITE;
662 beta = VALUE_INFINITE;
665 // Search to the current depth
666 Value value = root_search(p, ss, rml, alpha, beta);
668 // Write PV to transposition table, in case the relevant entries have
669 // been overwritten during the search.
670 TT.insert_pv(p, ss[0].pv);
673 break; // Value cannot be trusted. Break out immediately!
675 //Save info about search result
676 ValueByIteration[Iteration] = value;
678 // Drop the easy move if it differs from the new best move
679 if (ss[0].pv[0] != EasyMove)
680 EasyMove = MOVE_NONE;
682 if (UseTimeManagement)
685 bool stopSearch = false;
687 // Stop search early if there is only a single legal move,
688 // we search up to Iteration 6 anyway to get a proper score.
689 if (Iteration >= 6 && rml.move_count() == 1)
692 // Stop search early when the last two iterations returned a mate score
694 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
695 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
698 // Stop search early if one move seems to be much better than the rest
699 int64_t nodes = TM.nodes_searched();
701 && EasyMove == ss[0].pv[0]
702 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
703 && current_search_time() > MaxSearchTime / 16)
704 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
705 && current_search_time() > MaxSearchTime / 32)))
708 // Add some extra time if the best move has changed during the last two iterations
709 if (Iteration > 5 && Iteration <= 50)
710 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
711 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
713 // Stop search if most of MaxSearchTime is consumed at the end of the
714 // iteration. We probably don't have enough time to search the first
715 // move at the next iteration anyway.
716 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
724 StopOnPonderhit = true;
728 if (MaxDepth && Iteration >= MaxDepth)
734 // If we are pondering or in infinite search, we shouldn't print the
735 // best move before we are told to do so.
736 if (!AbortSearch && (PonderSearch || InfiniteSearch))
737 wait_for_stop_or_ponderhit();
739 // Print final search statistics
740 cout << "info nodes " << TM.nodes_searched()
742 << " time " << current_search_time()
743 << " hashfull " << TT.full() << endl;
745 // Print the best move and the ponder move to the standard output
746 if (ss[0].pv[0] == MOVE_NONE)
748 ss[0].pv[0] = rml.get_move(0);
749 ss[0].pv[1] = MOVE_NONE;
751 cout << "bestmove " << ss[0].pv[0];
752 if (ss[0].pv[1] != MOVE_NONE)
753 cout << " ponder " << ss[0].pv[1];
760 dbg_print_mean(LogFile);
762 if (dbg_show_hit_rate)
763 dbg_print_hit_rate(LogFile);
765 LogFile << "\nNodes: " << TM.nodes_searched()
766 << "\nNodes/second: " << nps()
767 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
770 p.do_move(ss[0].pv[0], st);
771 LogFile << "\nPonder move: " << move_to_san(p, ss[0].pv[1]) << endl;
773 return rml.get_move_score(0);
777 // root_search() is the function which searches the root node. It is
778 // similar to search_pv except that it uses a different move ordering
779 // scheme and prints some information to the standard output.
781 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value& oldAlpha, Value& beta) {
786 Depth depth, ext, newDepth;
789 int researchCount = 0;
790 bool moveIsCheck, captureOrPromotion, dangerous;
791 Value alpha = oldAlpha;
792 bool isCheck = pos.is_check();
794 // Evaluate the position statically
796 ss[0].eval = !isCheck ? evaluate(pos, ei, 0) : VALUE_NONE;
798 while (1) // Fail low loop
801 // Loop through all the moves in the root move list
802 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
806 // We failed high, invalidate and skip next moves, leave node-counters
807 // and beta-counters as they are and quickly return, we will try to do
808 // a research at the next iteration with a bigger aspiration window.
809 rml.set_move_score(i, -VALUE_INFINITE);
813 RootMoveNumber = i + 1;
815 // Save the current node count before the move is searched
816 nodes = TM.nodes_searched();
818 // Reset beta cut-off counters
819 TM.resetBetaCounters();
821 // Pick the next root move, and print the move and the move number to
822 // the standard output.
823 move = ss[0].currentMove = rml.get_move(i);
825 if (current_search_time() >= 1000)
826 cout << "info currmove " << move
827 << " currmovenumber " << RootMoveNumber << endl;
829 // Decide search depth for this move
830 moveIsCheck = pos.move_is_check(move);
831 captureOrPromotion = pos.move_is_capture_or_promotion(move);
832 depth = (Iteration - 2) * OnePly + InitialDepth;
833 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
834 newDepth = depth + ext;
836 value = - VALUE_INFINITE;
838 while (1) // Fail high loop
841 // Make the move, and search it
842 pos.do_move(move, st, ci, moveIsCheck);
844 if (i < MultiPV || value > alpha)
846 // Aspiration window is disabled in multi-pv case
848 alpha = -VALUE_INFINITE;
850 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
854 // Try to reduce non-pv search depth by one ply if move seems not problematic,
855 // if the move fails high will be re-searched at full depth.
856 bool doFullDepthSearch = true;
858 if ( depth >= 3*OnePly // FIXME was newDepth
860 && !captureOrPromotion
861 && !move_is_castle(move))
863 ss[0].reduction = pv_reduction(depth, RootMoveNumber - MultiPV + 1);
866 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
867 doFullDepthSearch = (value > alpha);
871 if (doFullDepthSearch)
873 ss[0].reduction = Depth(0);
874 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
877 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
883 // Can we exit fail high loop ?
884 if (AbortSearch || value < beta)
887 // We are failing high and going to do a research. It's important to update score
888 // before research in case we run out of time while researching.
889 rml.set_move_score(i, value);
891 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
892 rml.set_move_pv(i, ss[0].pv);
894 // Print search information to the standard output
895 cout << "info depth " << Iteration
896 << " score " << value_to_string(value)
897 << ((value >= beta) ? " lowerbound" :
898 ((value <= alpha)? " upperbound" : ""))
899 << " time " << current_search_time()
900 << " nodes " << TM.nodes_searched()
904 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
905 cout << ss[0].pv[j] << " ";
911 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
912 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
914 LogFile << pretty_pv(pos, current_search_time(), Iteration,
915 TM.nodes_searched(), value, type, ss[0].pv) << endl;
918 // Prepare for a research after a fail high, each time with a wider window
920 beta = Min(beta + AspirationDelta * (1 << researchCount), VALUE_INFINITE);
922 } // End of fail high loop
924 // Finished searching the move. If AbortSearch is true, the search
925 // was aborted because the user interrupted the search or because we
926 // ran out of time. In this case, the return value of the search cannot
927 // be trusted, and we break out of the loop without updating the best
932 // Remember beta-cutoff and searched nodes counts for this move. The
933 // info is used to sort the root moves at the next iteration.
935 TM.get_beta_counters(pos.side_to_move(), our, their);
936 rml.set_beta_counters(i, our, their);
937 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
939 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
941 if (value <= alpha && i >= MultiPV)
942 rml.set_move_score(i, -VALUE_INFINITE);
945 // PV move or new best move!
948 rml.set_move_score(i, value);
950 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
951 rml.set_move_pv(i, ss[0].pv);
955 // We record how often the best move has been changed in each
956 // iteration. This information is used for time managment: When
957 // the best move changes frequently, we allocate some more time.
959 BestMoveChangesByIteration[Iteration]++;
961 // Print search information to the standard output
962 cout << "info depth " << Iteration
963 << " score " << value_to_string(value)
964 << ((value >= beta) ? " lowerbound" :
965 ((value <= alpha)? " upperbound" : ""))
966 << " time " << current_search_time()
967 << " nodes " << TM.nodes_searched()
971 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
972 cout << ss[0].pv[j] << " ";
978 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
979 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
981 LogFile << pretty_pv(pos, current_search_time(), Iteration,
982 TM.nodes_searched(), value, type, ss[0].pv) << endl;
990 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
992 cout << "info multipv " << j + 1
993 << " score " << value_to_string(rml.get_move_score(j))
994 << " depth " << ((j <= i)? Iteration : Iteration - 1)
995 << " time " << current_search_time()
996 << " nodes " << TM.nodes_searched()
1000 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1001 cout << rml.get_move_pv(j, k) << " ";
1005 alpha = rml.get_move_score(Min(i, MultiPV-1));
1007 } // PV move or new best move
1009 assert(alpha >= oldAlpha);
1011 AspirationFailLow = (alpha == oldAlpha);
1013 if (AspirationFailLow && StopOnPonderhit)
1014 StopOnPonderhit = false;
1017 // Can we exit fail low loop ?
1018 if (AbortSearch || alpha > oldAlpha)
1021 // Prepare for a research after a fail low, each time with a wider window
1023 alpha = Max(alpha - AspirationDelta * (1 << researchCount), -VALUE_INFINITE);
1032 // search_pv() is the main search function for PV nodes.
1034 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1035 Depth depth, int ply, int threadID) {
1037 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1038 assert(beta > alpha && beta <= VALUE_INFINITE);
1039 assert(ply >= 0 && ply < PLY_MAX);
1040 assert(threadID >= 0 && threadID < TM.active_threads());
1042 Move movesSearched[256];
1046 Depth ext, newDepth;
1047 Value oldAlpha, value;
1048 bool isCheck, mateThreat, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1050 Value bestValue = value = -VALUE_INFINITE;
1053 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1055 // Step 1. Initialize node and poll
1056 // Polling can abort search.
1057 init_node(ss, ply, threadID);
1059 // Step 2. Check for aborted search and immediate draw
1060 if (AbortSearch || TM.thread_should_stop(threadID))
1063 if (pos.is_draw() || ply >= PLY_MAX - 1)
1066 // Step 3. Mate distance pruning
1068 alpha = Max(value_mated_in(ply), alpha);
1069 beta = Min(value_mate_in(ply+1), beta);
1073 // Step 4. Transposition table lookup
1074 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1075 // This is to avoid problems in the following areas:
1077 // * Repetition draw detection
1078 // * Fifty move rule detection
1079 // * Searching for a mate
1080 // * Printing of full PV line
1081 tte = TT.retrieve(pos.get_key());
1082 ttMove = (tte ? tte->move() : MOVE_NONE);
1084 // Step 5. Evaluate the position statically
1085 // At PV nodes we do this only to update gain statistics
1086 isCheck = pos.is_check();
1090 ss[ply].eval = evaluate(pos, ei, threadID);
1091 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1094 // Step 6. Razoring (is omitted in PV nodes)
1095 // Step 7. Static null move pruning (is omitted in PV nodes)
1096 // Step 8. Null move search with verification search (is omitted in PV nodes)
1098 // Step 9. Internal iterative deepening
1099 if ( UseIIDAtPVNodes
1100 && depth >= 5*OnePly
1101 && ttMove == MOVE_NONE)
1103 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1104 ttMove = ss[ply].pv[ply];
1105 tte = TT.retrieve(pos.get_key());
1108 // Step 10. Loop through moves
1109 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1111 // Initialize a MovePicker object for the current position
1112 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1113 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1116 while ( alpha < beta
1117 && (move = mp.get_next_move()) != MOVE_NONE
1118 && !TM.thread_should_stop(threadID))
1120 assert(move_is_ok(move));
1122 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1123 moveIsCheck = pos.move_is_check(move, ci);
1124 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1126 // Step 11. Decide the new search depth
1127 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1129 // Singular extension search. We extend the TT move if its value is much better than
1130 // its siblings. To verify this we do a reduced search on all the other moves but the
1131 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1132 if ( depth >= 6 * OnePly
1134 && move == tte->move()
1136 && is_lower_bound(tte->type())
1137 && tte->depth() >= depth - 3 * OnePly)
1139 Value ttValue = value_from_tt(tte->value(), ply);
1141 if (abs(ttValue) < VALUE_KNOWN_WIN)
1143 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1145 if (excValue < ttValue - SingleReplyMargin)
1150 newDepth = depth - OnePly + ext;
1152 // Update current move (this must be done after singular extension search)
1153 movesSearched[moveCount++] = ss[ply].currentMove = move;
1155 // Step 12. Futility pruning (is omitted in PV nodes)
1157 // Step 13. Make the move
1158 pos.do_move(move, st, ci, moveIsCheck);
1160 // Step extra. pv search (only in PV nodes)
1161 // The first move in list is the expected PV
1163 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1166 // Step 14. Reduced search
1167 // if the move fails high will be re-searched at full depth.
1168 bool doFullDepthSearch = true;
1170 if ( depth >= 3*OnePly
1172 && !captureOrPromotion
1173 && !move_is_castle(move)
1174 && !move_is_killer(move, ss[ply]))
1176 ss[ply].reduction = pv_reduction(depth, moveCount);
1177 if (ss[ply].reduction)
1179 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1180 doFullDepthSearch = (value > alpha);
1184 // Step 15. Full depth search
1185 if (doFullDepthSearch)
1187 ss[ply].reduction = Depth(0);
1188 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1190 // Step extra. pv search (only in PV nodes)
1191 if (value > alpha && value < beta)
1192 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1196 // Step 16. Undo move
1197 pos.undo_move(move);
1199 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1201 // Step 17. Check for new best move
1202 if (value > bestValue)
1209 if (value == value_mate_in(ply + 1))
1210 ss[ply].mateKiller = move;
1214 // Step 18. Check for split
1215 if ( TM.active_threads() > 1
1217 && depth >= MinimumSplitDepth
1219 && TM.available_thread_exists(threadID)
1221 && !TM.thread_should_stop(threadID)
1222 && TM.split(pos, ss, ply, &alpha, beta, &bestValue, VALUE_NONE,
1223 depth, &moveCount, &mp, threadID, true))
1227 // Step 19. Check for mate and stalemate
1228 // All legal moves have been searched and if there were
1229 // no legal moves, it must be mate or stalemate.
1231 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1233 // Step 20. Update tables
1234 // If the search is not aborted, update the transposition table,
1235 // history counters, and killer moves.
1236 if (AbortSearch || TM.thread_should_stop(threadID))
1239 if (bestValue <= oldAlpha)
1240 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1242 else if (bestValue >= beta)
1244 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1245 move = ss[ply].pv[ply];
1246 if (!pos.move_is_capture_or_promotion(move))
1248 update_history(pos, move, depth, movesSearched, moveCount);
1249 update_killers(move, ss[ply]);
1251 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1254 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1260 // search() is the search function for zero-width nodes.
1262 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1263 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1265 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1266 assert(ply >= 0 && ply < PLY_MAX);
1267 assert(threadID >= 0 && threadID < TM.active_threads());
1269 Move movesSearched[256];
1274 Depth ext, newDepth;
1275 Value bestValue, refinedValue, nullValue, value, futilityValue, futilityValueScaled;
1276 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1277 bool mateThreat = false;
1279 futilityValue = 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 futilityValue = ss[ply].eval + futility_margin(depth, 0); //FIXME: Remove me, only for split
1328 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1329 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1333 if ( !value_is_mate(beta)
1335 && depth < RazorDepth
1336 && refinedValue < beta - (0x200 + 16 * depth)
1337 && ss[ply - 1].currentMove != MOVE_NULL
1338 && ttMove == MOVE_NONE
1339 && !pos.has_pawn_on_7th(pos.side_to_move()))
1341 Value rbeta = beta - (0x200 + 16 * depth);
1342 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1344 return v; //FIXME: Logically should be: return (v + 0x200 + 16 * depth);
1347 // Step 7. Static null move pruning
1348 // We're betting that the opponent doesn't have a move that will reduce
1349 // the score by more than fuility_margin(depth) if we do a null move.
1352 && depth < RazorDepth
1353 && refinedValue - futility_margin(depth, 0) >= beta)
1354 return refinedValue - futility_margin(depth, 0);
1356 // Step 8. Null move search with verification search
1357 // When we jump directly to qsearch() we do a null move only if static value is
1358 // at least beta. Otherwise we do a null move if static value is not more than
1359 // NullMoveMargin under beta.
1363 && !value_is_mate(beta)
1364 && ok_to_do_nullmove(pos)
1365 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1367 ss[ply].currentMove = MOVE_NULL;
1369 pos.do_null_move(st);
1371 // Null move dynamic reduction based on depth
1372 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1374 // Null move dynamic reduction based on value
1375 if (refinedValue - beta > PawnValueMidgame)
1378 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1380 pos.undo_null_move();
1382 if (nullValue >= beta)
1384 if (depth < 6 * OnePly)
1387 // Do zugzwang verification search
1388 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1392 // The null move failed low, which means that we may be faced with
1393 // some kind of threat. If the previous move was reduced, check if
1394 // the move that refuted the null move was somehow connected to the
1395 // move which was reduced. If a connection is found, return a fail
1396 // low score (which will cause the reduced move to fail high in the
1397 // parent node, which will trigger a re-search with full depth).
1398 if (nullValue == value_mated_in(ply + 2))
1401 ss[ply].threatMove = ss[ply + 1].currentMove;
1402 if ( depth < ThreatDepth
1403 && ss[ply - 1].reduction
1404 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1409 // Step 9. Internal iterative deepening
1410 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1411 !isCheck && ss[ply].eval >= beta - IIDMargin)
1413 search(pos, ss, beta, depth/2, ply, false, threadID);
1414 ttMove = ss[ply].pv[ply];
1415 tte = TT.retrieve(posKey);
1418 // Step 10. Loop through moves
1419 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1421 // Initialize a MovePicker object for the current position
1422 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1425 while ( bestValue < beta
1426 && (move = mp.get_next_move()) != MOVE_NONE
1427 && !TM.thread_should_stop(threadID))
1429 assert(move_is_ok(move));
1431 if (move == excludedMove)
1434 moveIsCheck = pos.move_is_check(move, ci);
1435 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1436 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1438 // Step 11. Decide the new search depth
1439 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1441 // Singular extension search. We extend the TT move if its value is much better than
1442 // its siblings. To verify this we do a reduced search on all the other moves but the
1443 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1444 if ( depth >= 8 * OnePly
1446 && move == tte->move()
1447 && !excludedMove // Do not allow recursive single-reply search
1449 && is_lower_bound(tte->type())
1450 && tte->depth() >= depth - 3 * OnePly)
1452 Value ttValue = value_from_tt(tte->value(), ply);
1454 if (abs(ttValue) < VALUE_KNOWN_WIN)
1456 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, depth / 2, ply, false, threadID, move);
1458 if (excValue < ttValue - SingleReplyMargin)
1463 newDepth = depth - OnePly + ext;
1465 // Update current move (this must be done after singular extension search)
1466 movesSearched[moveCount++] = ss[ply].currentMove = move;
1468 // Step 12. Futility pruning
1471 && !captureOrPromotion
1472 && !move_is_castle(move)
1475 // Move count based pruning
1476 if ( moveCount >= futility_move_count(depth)
1477 && ok_to_prune(pos, move, ss[ply].threatMove)
1478 && bestValue > value_mated_in(PLY_MAX))
1481 // Value based pruning
1482 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); //FIXME: We are ignoring condition: depth >= 3*OnePly, BUG??
1483 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1484 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1486 if (futilityValueScaled < beta)
1488 if (futilityValueScaled > bestValue)
1489 bestValue = futilityValueScaled;
1494 // Step 13. Make the move
1495 pos.do_move(move, st, ci, moveIsCheck);
1497 // Step 14. Reduced search
1498 // if the move fails high will be re-searched at full depth.
1499 bool doFullDepthSearch = true;
1501 if ( depth >= 3*OnePly
1503 && !captureOrPromotion
1504 && !move_is_castle(move)
1505 && !move_is_killer(move, ss[ply]))
1507 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1508 if (ss[ply].reduction)
1510 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1511 doFullDepthSearch = (value >= beta);
1515 // Step 15. Full depth search
1516 if (doFullDepthSearch)
1518 ss[ply].reduction = Depth(0);
1519 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1522 // Step 16. Undo move
1523 pos.undo_move(move);
1525 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1527 // Step 17. Check for new best move
1528 if (value > bestValue)
1534 if (value == value_mate_in(ply + 1))
1535 ss[ply].mateKiller = move;
1538 // Step 18. Check for split
1539 if ( TM.active_threads() > 1
1541 && depth >= MinimumSplitDepth
1543 && TM.available_thread_exists(threadID)
1545 && !TM.thread_should_stop(threadID)
1546 && TM.split(pos, ss, ply, NULL, beta, &bestValue, futilityValue, //FIXME: SMP & futilityValue
1547 depth, &moveCount, &mp, threadID, false))
1551 // Step 19. Check for mate and stalemate
1552 // All legal moves have been searched and if there were
1553 // no legal moves, it must be mate or stalemate.
1554 // If one move was excluded return fail low.
1556 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1558 // Step 20. Update tables
1559 // If the search is not aborted, update the transposition table,
1560 // history counters, and killer moves.
1561 if (AbortSearch || TM.thread_should_stop(threadID))
1564 if (bestValue < beta)
1565 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1568 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1569 move = ss[ply].pv[ply];
1570 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1571 if (!pos.move_is_capture_or_promotion(move))
1573 update_history(pos, move, depth, movesSearched, moveCount);
1574 update_killers(move, ss[ply]);
1579 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1585 // qsearch() is the quiescence search function, which is called by the main
1586 // search function when the remaining depth is zero (or, to be more precise,
1587 // less than OnePly).
1589 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1590 Depth depth, int ply, int threadID) {
1592 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1593 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1595 assert(ply >= 0 && ply < PLY_MAX);
1596 assert(threadID >= 0 && threadID < TM.active_threads());
1601 Value staticValue, bestValue, value, futilityBase, futilityValue;
1602 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1603 const TTEntry* tte = NULL;
1605 bool pvNode = (beta - alpha != 1);
1606 Value oldAlpha = alpha;
1608 // Initialize, and make an early exit in case of an aborted search,
1609 // an instant draw, maximum ply reached, etc.
1610 init_node(ss, ply, threadID);
1612 // After init_node() that calls poll()
1613 if (AbortSearch || TM.thread_should_stop(threadID))
1616 if (pos.is_draw() || ply >= PLY_MAX - 1)
1619 // Transposition table lookup. At PV nodes, we don't use the TT for
1620 // pruning, but only for move ordering.
1621 tte = TT.retrieve(pos.get_key());
1622 ttMove = (tte ? tte->move() : MOVE_NONE);
1624 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1626 assert(tte->type() != VALUE_TYPE_EVAL);
1628 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1629 return value_from_tt(tte->value(), ply);
1632 isCheck = pos.is_check();
1634 // Evaluate the position statically
1636 staticValue = -VALUE_INFINITE;
1637 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1638 staticValue = value_from_tt(tte->value(), ply);
1640 staticValue = evaluate(pos, ei, threadID);
1644 ss[ply].eval = staticValue;
1645 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1648 // Initialize "stand pat score", and return it immediately if it is
1650 bestValue = staticValue;
1652 if (bestValue >= beta)
1654 // Store the score to avoid a future costly evaluation() call
1655 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1656 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1661 if (bestValue > alpha)
1664 // If we are near beta then try to get a cutoff pushing checks a bit further
1665 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1667 // Initialize a MovePicker object for the current position, and prepare
1668 // to search the moves. Because the depth is <= 0 here, only captures,
1669 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1670 // and we are near beta) will be generated.
1671 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1673 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1674 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1676 // Loop through the moves until no moves remain or a beta cutoff
1678 while ( alpha < beta
1679 && (move = mp.get_next_move()) != MOVE_NONE)
1681 assert(move_is_ok(move));
1683 moveIsCheck = pos.move_is_check(move, ci);
1685 // Update current move
1687 ss[ply].currentMove = move;
1695 && !move_is_promotion(move)
1696 && !pos.move_is_passed_pawn_push(move))
1698 futilityValue = futilityBase
1699 + pos.endgame_value_of_piece_on(move_to(move))
1700 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1702 if (futilityValue < alpha)
1704 if (futilityValue > bestValue)
1705 bestValue = futilityValue;
1710 // Detect blocking evasions that are candidate to be pruned
1711 evasionPrunable = isCheck
1712 && bestValue != -VALUE_INFINITE
1713 && !pos.move_is_capture(move)
1714 && pos.type_of_piece_on(move_from(move)) != KING
1715 && !pos.can_castle(pos.side_to_move());
1717 // Don't search moves with negative SEE values
1718 if ( (!isCheck || evasionPrunable)
1721 && !move_is_promotion(move)
1722 && pos.see_sign(move) < 0)
1725 // Make and search the move
1726 pos.do_move(move, st, ci, moveIsCheck);
1727 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1728 pos.undo_move(move);
1730 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1733 if (value > bestValue)
1744 // All legal moves have been searched. A special case: If we're in check
1745 // and no legal moves were found, it is checkmate.
1746 if (!moveCount && pos.is_check()) // Mate!
1747 return value_mated_in(ply);
1749 // Update transposition table
1750 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1751 if (bestValue <= oldAlpha)
1753 // If bestValue isn't changed it means it is still the static evaluation
1754 // of the node, so keep this info to avoid a future evaluation() call.
1755 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1756 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1758 else if (bestValue >= beta)
1760 move = ss[ply].pv[ply];
1761 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1763 // Update killers only for good checking moves
1764 if (!pos.move_is_capture_or_promotion(move))
1765 update_killers(move, ss[ply]);
1768 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1770 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1776 // sp_search() is used to search from a split point. This function is called
1777 // by each thread working at the split point. It is similar to the normal
1778 // search() function, but simpler. Because we have already probed the hash
1779 // table, done a null move search, and searched the first move before
1780 // splitting, we don't have to repeat all this work in sp_search(). We
1781 // also don't need to store anything to the hash table here: This is taken
1782 // care of after we return from the split point.
1784 void sp_search(SplitPoint* sp, int threadID) {
1786 assert(threadID >= 0 && threadID < TM.active_threads());
1787 assert(TM.active_threads() > 1);
1789 Position pos(*sp->pos);
1791 SearchStack* ss = sp->sstack[threadID];
1793 Value value = -VALUE_INFINITE;
1796 bool isCheck = pos.is_check();
1797 bool useFutilityPruning = sp->depth < 7 * OnePly //FIXME: sync with search
1800 lock_grab(&(sp->lock));
1802 while ( sp->bestValue < sp->beta
1803 && !TM.thread_should_stop(threadID)
1804 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1806 moveCount = ++sp->moves;
1807 lock_release(&(sp->lock));
1809 assert(move_is_ok(move));
1811 bool moveIsCheck = pos.move_is_check(move, ci);
1812 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1814 ss[sp->ply].currentMove = move;
1816 // Decide the new search depth
1818 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1819 Depth newDepth = sp->depth - OnePly + ext;
1822 if ( useFutilityPruning
1824 && !captureOrPromotion)
1826 // Move count based pruning
1827 if ( moveCount >= futility_move_count(sp->depth)
1828 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1829 && sp->bestValue > value_mated_in(PLY_MAX))
1831 lock_grab(&(sp->lock));
1835 // Value based pruning
1836 Value futilityValueScaled = sp->futilityValue - moveCount * 8; //FIXME: sync with search
1838 if (futilityValueScaled < sp->beta)
1840 lock_grab(&(sp->lock));
1842 if (futilityValueScaled > sp->bestValue)
1843 sp->bestValue = futilityValueScaled;
1848 // Step 13. Make the move
1849 pos.do_move(move, st, ci, moveIsCheck);
1851 // Step 14. Reduced search
1852 // if the move fails high will be re-searched at full depth.
1853 bool doFullDepthSearch = true;
1856 && !captureOrPromotion
1857 && !move_is_castle(move)
1858 && !move_is_killer(move, ss[sp->ply]))
1860 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1861 if (ss[sp->ply].reduction)
1863 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1864 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1868 // Step 15. Full depth search
1869 if (doFullDepthSearch)
1871 ss[sp->ply].reduction = Depth(0);
1872 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1875 // Step 16. Undo move
1876 pos.undo_move(move);
1878 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1880 // Step 17. Check for new best move
1881 lock_grab(&(sp->lock));
1883 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1885 sp->bestValue = value;
1886 if (sp->bestValue >= sp->beta)
1888 sp->stopRequest = true;
1889 sp_update_pv(sp->parentSstack, ss, sp->ply);
1894 /* Here we have the lock still grabbed */
1896 sp->slaves[threadID] = 0;
1899 lock_release(&(sp->lock));
1903 // sp_search_pv() is used to search from a PV split point. This function
1904 // is called by each thread working at the split point. It is similar to
1905 // the normal search_pv() function, but simpler. Because we have already
1906 // probed the hash table and searched the first move before splitting, we
1907 // don't have to repeat all this work in sp_search_pv(). We also don't
1908 // need to store anything to the hash table here: This is taken care of
1909 // after we return from the split point.
1911 void sp_search_pv(SplitPoint* sp, int threadID) {
1913 assert(threadID >= 0 && threadID < TM.active_threads());
1914 assert(TM.active_threads() > 1);
1916 Position pos(*sp->pos);
1918 SearchStack* ss = sp->sstack[threadID];
1920 Value value = -VALUE_INFINITE;
1924 // Step 10. Loop through moves
1925 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1926 lock_grab(&(sp->lock));
1928 while ( sp->alpha < sp->beta
1929 && !TM.thread_should_stop(threadID)
1930 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1932 moveCount = ++sp->moves;
1933 lock_release(&(sp->lock));
1935 assert(move_is_ok(move));
1937 bool moveIsCheck = pos.move_is_check(move, ci);
1938 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1940 // Step 11. Decide the new search depth
1942 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1943 Depth newDepth = sp->depth - OnePly + ext;
1945 // Update current move
1946 ss[sp->ply].currentMove = move;
1948 // Step 12. Futility pruning (is omitted in PV nodes)
1950 // Step 13. Make the move
1951 pos.do_move(move, st, ci, moveIsCheck);
1953 // Step 14. Reduced search
1954 // if the move fails high will be re-searched at full depth.
1955 bool doFullDepthSearch = true;
1958 && !captureOrPromotion
1959 && !move_is_castle(move)
1960 && !move_is_killer(move, ss[sp->ply]))
1962 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1963 if (ss[sp->ply].reduction)
1965 Value localAlpha = sp->alpha;
1966 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1967 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1971 // Step 15. Full depth search
1972 if (doFullDepthSearch)
1974 Value localAlpha = sp->alpha;
1975 ss[sp->ply].reduction = Depth(0);
1976 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1978 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1980 // If another thread has failed high then sp->alpha has been increased
1981 // to be higher or equal then beta, if so, avoid to start a PV search.
1982 localAlpha = sp->alpha;
1983 if (localAlpha < sp->beta)
1984 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1988 // Step 16. Undo move
1989 pos.undo_move(move);
1991 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1993 // Step 17. Check for new best move
1994 lock_grab(&(sp->lock));
1996 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1998 sp->bestValue = value;
1999 if (value > sp->alpha)
2001 // Ask threads to stop before to modify sp->alpha
2002 if (value >= sp->beta)
2003 sp->stopRequest = true;
2007 sp_update_pv(sp->parentSstack, ss, sp->ply);
2008 if (value == value_mate_in(sp->ply + 1))
2009 ss[sp->ply].mateKiller = move;
2014 /* Here we have the lock still grabbed */
2016 sp->slaves[threadID] = 0;
2019 lock_release(&(sp->lock));
2023 // init_node() is called at the beginning of all the search functions
2024 // (search(), search_pv(), qsearch(), and so on) and initializes the
2025 // search stack object corresponding to the current node. Once every
2026 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2027 // for user input and checks whether it is time to stop the search.
2029 void init_node(SearchStack ss[], int ply, int threadID) {
2031 assert(ply >= 0 && ply < PLY_MAX);
2032 assert(threadID >= 0 && threadID < TM.active_threads());
2034 TM.incrementNodeCounter(threadID);
2039 if (NodesSincePoll >= NodesBetweenPolls)
2046 ss[ply + 2].initKillers();
2047 TM.print_current_line(ss, ply, threadID);
2051 // update_pv() is called whenever a search returns a value > alpha.
2052 // It updates the PV in the SearchStack object corresponding to the
2055 void update_pv(SearchStack ss[], int ply) {
2057 assert(ply >= 0 && ply < PLY_MAX);
2061 ss[ply].pv[ply] = ss[ply].currentMove;
2063 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2064 ss[ply].pv[p] = ss[ply + 1].pv[p];
2066 ss[ply].pv[p] = MOVE_NONE;
2070 // sp_update_pv() is a variant of update_pv for use at split points. The
2071 // difference between the two functions is that sp_update_pv also updates
2072 // the PV at the parent node.
2074 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2076 assert(ply >= 0 && ply < PLY_MAX);
2080 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2082 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2083 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2085 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2089 // connected_moves() tests whether two moves are 'connected' in the sense
2090 // that the first move somehow made the second move possible (for instance
2091 // if the moving piece is the same in both moves). The first move is assumed
2092 // to be the move that was made to reach the current position, while the
2093 // second move is assumed to be a move from the current position.
2095 bool connected_moves(const Position& pos, Move m1, Move m2) {
2097 Square f1, t1, f2, t2;
2100 assert(move_is_ok(m1));
2101 assert(move_is_ok(m2));
2103 if (m2 == MOVE_NONE)
2106 // Case 1: The moving piece is the same in both moves
2112 // Case 2: The destination square for m2 was vacated by m1
2118 // Case 3: Moving through the vacated square
2119 if ( piece_is_slider(pos.piece_on(f2))
2120 && bit_is_set(squares_between(f2, t2), f1))
2123 // Case 4: The destination square for m2 is defended by the moving piece in m1
2124 p = pos.piece_on(t1);
2125 if (bit_is_set(pos.attacks_from(p, t1), t2))
2128 // Case 5: Discovered check, checking piece is the piece moved in m1
2129 if ( piece_is_slider(p)
2130 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2131 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2133 // discovered_check_candidates() works also if the Position's side to
2134 // move is the opposite of the checking piece.
2135 Color them = opposite_color(pos.side_to_move());
2136 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2138 if (bit_is_set(dcCandidates, f2))
2145 // value_is_mate() checks if the given value is a mate one
2146 // eventually compensated for the ply.
2148 bool value_is_mate(Value value) {
2150 assert(abs(value) <= VALUE_INFINITE);
2152 return value <= value_mated_in(PLY_MAX)
2153 || value >= value_mate_in(PLY_MAX);
2157 // move_is_killer() checks if the given move is among the
2158 // killer moves of that ply.
2160 bool move_is_killer(Move m, const SearchStack& ss) {
2162 const Move* k = ss.killers;
2163 for (int i = 0; i < KILLER_MAX; i++, k++)
2171 // extension() decides whether a move should be searched with normal depth,
2172 // or with extended depth. Certain classes of moves (checking moves, in
2173 // particular) are searched with bigger depth than ordinary moves and in
2174 // any case are marked as 'dangerous'. Note that also if a move is not
2175 // extended, as example because the corresponding UCI option is set to zero,
2176 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2178 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2179 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2181 assert(m != MOVE_NONE);
2183 Depth result = Depth(0);
2184 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2189 result += CheckExtension[pvNode];
2192 result += SingleEvasionExtension[pvNode];
2195 result += MateThreatExtension[pvNode];
2198 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2200 Color c = pos.side_to_move();
2201 if (relative_rank(c, move_to(m)) == RANK_7)
2203 result += PawnPushTo7thExtension[pvNode];
2206 if (pos.pawn_is_passed(c, move_to(m)))
2208 result += PassedPawnExtension[pvNode];
2213 if ( captureOrPromotion
2214 && pos.type_of_piece_on(move_to(m)) != PAWN
2215 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2216 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2217 && !move_is_promotion(m)
2220 result += PawnEndgameExtension[pvNode];
2225 && captureOrPromotion
2226 && pos.type_of_piece_on(move_to(m)) != PAWN
2227 && pos.see_sign(m) >= 0)
2233 return Min(result, OnePly);
2237 // ok_to_do_nullmove() looks at the current position and decides whether
2238 // doing a 'null move' should be allowed. In order to avoid zugzwang
2239 // problems, null moves are not allowed when the side to move has very
2240 // little material left. Currently, the test is a bit too simple: Null
2241 // moves are avoided only when the side to move has only pawns left.
2242 // It's probably a good idea to avoid null moves in at least some more
2243 // complicated endgames, e.g. KQ vs KR. FIXME
2245 bool ok_to_do_nullmove(const Position& pos) {
2247 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2251 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2252 // non-tactical moves late in the move list close to the leaves are
2253 // candidates for pruning.
2255 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2257 assert(move_is_ok(m));
2258 assert(threat == MOVE_NONE || move_is_ok(threat));
2259 assert(!pos.move_is_check(m));
2260 assert(!pos.move_is_capture_or_promotion(m));
2261 assert(!pos.move_is_passed_pawn_push(m));
2263 Square mfrom, mto, tfrom, tto;
2265 // Prune if there isn't any threat move
2266 if (threat == MOVE_NONE)
2269 mfrom = move_from(m);
2271 tfrom = move_from(threat);
2272 tto = move_to(threat);
2274 // Case 1: Don't prune moves which move the threatened piece
2278 // Case 2: If the threatened piece has value less than or equal to the
2279 // value of the threatening piece, don't prune move which defend it.
2280 if ( pos.move_is_capture(threat)
2281 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2282 || pos.type_of_piece_on(tfrom) == KING)
2283 && pos.move_attacks_square(m, tto))
2286 // Case 3: If the moving piece in the threatened move is a slider, don't
2287 // prune safe moves which block its ray.
2288 if ( piece_is_slider(pos.piece_on(tfrom))
2289 && bit_is_set(squares_between(tfrom, tto), mto)
2290 && pos.see_sign(m) >= 0)
2297 // ok_to_use_TT() returns true if a transposition table score
2298 // can be used at a given point in search.
2300 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2302 Value v = value_from_tt(tte->value(), ply);
2304 return ( tte->depth() >= depth
2305 || v >= Max(value_mate_in(PLY_MAX), beta)
2306 || v < Min(value_mated_in(PLY_MAX), beta))
2308 && ( (is_lower_bound(tte->type()) && v >= beta)
2309 || (is_upper_bound(tte->type()) && v < beta));
2313 // refine_eval() returns the transposition table score if
2314 // possible otherwise falls back on static position evaluation.
2316 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2321 Value v = value_from_tt(tte->value(), ply);
2323 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2324 || (is_upper_bound(tte->type()) && v < defaultEval))
2331 // update_history() registers a good move that produced a beta-cutoff
2332 // in history and marks as failures all the other moves of that ply.
2334 void update_history(const Position& pos, Move move, Depth depth,
2335 Move movesSearched[], int moveCount) {
2339 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2341 for (int i = 0; i < moveCount - 1; i++)
2343 m = movesSearched[i];
2347 if (!pos.move_is_capture_or_promotion(m))
2348 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2353 // update_killers() add a good move that produced a beta-cutoff
2354 // among the killer moves of that ply.
2356 void update_killers(Move m, SearchStack& ss) {
2358 if (m == ss.killers[0])
2361 for (int i = KILLER_MAX - 1; i > 0; i--)
2362 ss.killers[i] = ss.killers[i - 1];
2368 // update_gains() updates the gains table of a non-capture move given
2369 // the static position evaluation before and after the move.
2371 void update_gains(const Position& pos, Move m, Value before, Value after) {
2374 && before != VALUE_NONE
2375 && after != VALUE_NONE
2376 && pos.captured_piece() == NO_PIECE_TYPE
2377 && !move_is_castle(m)
2378 && !move_is_promotion(m))
2379 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2383 // current_search_time() returns the number of milliseconds which have passed
2384 // since the beginning of the current search.
2386 int current_search_time() {
2388 return get_system_time() - SearchStartTime;
2392 // nps() computes the current nodes/second count.
2396 int t = current_search_time();
2397 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2401 // poll() performs two different functions: It polls for user input, and it
2402 // looks at the time consumed so far and decides if it's time to abort the
2407 static int lastInfoTime;
2408 int t = current_search_time();
2413 // We are line oriented, don't read single chars
2414 std::string command;
2416 if (!std::getline(std::cin, command))
2419 if (command == "quit")
2422 PonderSearch = false;
2426 else if (command == "stop")
2429 PonderSearch = false;
2431 else if (command == "ponderhit")
2435 // Print search information
2439 else if (lastInfoTime > t)
2440 // HACK: Must be a new search where we searched less than
2441 // NodesBetweenPolls nodes during the first second of search.
2444 else if (t - lastInfoTime >= 1000)
2447 lock_grab(&TM.IOLock);
2452 if (dbg_show_hit_rate)
2453 dbg_print_hit_rate();
2455 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2456 << " time " << t << " hashfull " << TT.full() << endl;
2458 lock_release(&TM.IOLock);
2460 if (ShowCurrentLine)
2461 TM.threads[0].printCurrentLineRequest = true;
2464 // Should we stop the search?
2468 bool stillAtFirstMove = RootMoveNumber == 1
2469 && !AspirationFailLow
2470 && t > MaxSearchTime + ExtraSearchTime;
2472 bool noMoreTime = t > AbsoluteMaxSearchTime
2473 || stillAtFirstMove;
2475 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2476 || (ExactMaxTime && t >= ExactMaxTime)
2477 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2482 // ponderhit() is called when the program is pondering (i.e. thinking while
2483 // it's the opponent's turn to move) in order to let the engine know that
2484 // it correctly predicted the opponent's move.
2488 int t = current_search_time();
2489 PonderSearch = false;
2491 bool stillAtFirstMove = RootMoveNumber == 1
2492 && !AspirationFailLow
2493 && t > MaxSearchTime + ExtraSearchTime;
2495 bool noMoreTime = t > AbsoluteMaxSearchTime
2496 || stillAtFirstMove;
2498 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2503 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2505 void init_ss_array(SearchStack ss[]) {
2507 for (int i = 0; i < 3; i++)
2510 ss[i].initKillers();
2515 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2516 // while the program is pondering. The point is to work around a wrinkle in
2517 // the UCI protocol: When pondering, the engine is not allowed to give a
2518 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2519 // We simply wait here until one of these commands is sent, and return,
2520 // after which the bestmove and pondermove will be printed (in id_loop()).
2522 void wait_for_stop_or_ponderhit() {
2524 std::string command;
2528 if (!std::getline(std::cin, command))
2531 if (command == "quit")
2536 else if (command == "ponderhit" || command == "stop")
2542 // init_thread() is the function which is called when a new thread is
2543 // launched. It simply calls the idle_loop() function with the supplied
2544 // threadID. There are two versions of this function; one for POSIX
2545 // threads and one for Windows threads.
2547 #if !defined(_MSC_VER)
2549 void* init_thread(void *threadID) {
2551 TM.idle_loop(*(int*)threadID, NULL);
2557 DWORD WINAPI init_thread(LPVOID threadID) {
2559 TM.idle_loop(*(int*)threadID, NULL);
2566 /// The ThreadsManager class
2568 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2569 // get_beta_counters() are getters/setters for the per thread
2570 // counters used to sort the moves at root.
2572 void ThreadsManager::resetNodeCounters() {
2574 for (int i = 0; i < MAX_THREADS; i++)
2575 threads[i].nodes = 0ULL;
2578 void ThreadsManager::resetBetaCounters() {
2580 for (int i = 0; i < MAX_THREADS; i++)
2581 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2584 int64_t ThreadsManager::nodes_searched() const {
2586 int64_t result = 0ULL;
2587 for (int i = 0; i < ActiveThreads; i++)
2588 result += threads[i].nodes;
2593 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2596 for (int i = 0; i < MAX_THREADS; i++)
2598 our += threads[i].betaCutOffs[us];
2599 their += threads[i].betaCutOffs[opposite_color(us)];
2604 // idle_loop() is where the threads are parked when they have no work to do.
2605 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2606 // object for which the current thread is the master.
2608 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2610 assert(threadID >= 0 && threadID < MAX_THREADS);
2614 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2615 // master should exit as last one.
2616 if (AllThreadsShouldExit)
2619 threads[threadID].state = THREAD_TERMINATED;
2623 // If we are not thinking, wait for a condition to be signaled
2624 // instead of wasting CPU time polling for work.
2625 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2628 assert(threadID != 0);
2629 threads[threadID].state = THREAD_SLEEPING;
2631 #if !defined(_MSC_VER)
2632 pthread_mutex_lock(&WaitLock);
2633 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2634 pthread_cond_wait(&WaitCond, &WaitLock);
2635 pthread_mutex_unlock(&WaitLock);
2637 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2641 // If thread has just woken up, mark it as available
2642 if (threads[threadID].state == THREAD_SLEEPING)
2643 threads[threadID].state = THREAD_AVAILABLE;
2645 // If this thread has been assigned work, launch a search
2646 if (threads[threadID].state == THREAD_WORKISWAITING)
2648 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2650 threads[threadID].state = THREAD_SEARCHING;
2652 if (threads[threadID].splitPoint->pvNode)
2653 sp_search_pv(threads[threadID].splitPoint, threadID);
2655 sp_search(threads[threadID].splitPoint, threadID);
2657 assert(threads[threadID].state == THREAD_SEARCHING);
2659 threads[threadID].state = THREAD_AVAILABLE;
2662 // If this thread is the master of a split point and all threads have
2663 // finished their work at this split point, return from the idle loop.
2664 if (waitSp != NULL && waitSp->cpus == 0)
2666 assert(threads[threadID].state == THREAD_AVAILABLE);
2668 threads[threadID].state = THREAD_SEARCHING;
2675 // init_threads() is called during startup. It launches all helper threads,
2676 // and initializes the split point stack and the global locks and condition
2679 void ThreadsManager::init_threads() {
2684 #if !defined(_MSC_VER)
2685 pthread_t pthread[1];
2688 // Initialize global locks
2689 lock_init(&MPLock, NULL);
2690 lock_init(&IOLock, NULL);
2692 // Initialize SplitPointStack locks
2693 for (i = 0; i < MAX_THREADS; i++)
2694 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2696 SplitPointStack[i][j].parent = NULL;
2697 lock_init(&(SplitPointStack[i][j].lock), NULL);
2700 #if !defined(_MSC_VER)
2701 pthread_mutex_init(&WaitLock, NULL);
2702 pthread_cond_init(&WaitCond, NULL);
2704 for (i = 0; i < MAX_THREADS; i++)
2705 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2708 // Will be set just before program exits to properly end the threads
2709 AllThreadsShouldExit = false;
2711 // Threads will be put to sleep as soon as created
2712 AllThreadsShouldSleep = true;
2714 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2716 threads[0].state = THREAD_SEARCHING;
2717 for (i = 1; i < MAX_THREADS; i++)
2718 threads[i].state = THREAD_AVAILABLE;
2720 // Launch the helper threads
2721 for (i = 1; i < MAX_THREADS; i++)
2724 #if !defined(_MSC_VER)
2725 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2728 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID) != NULL);
2733 cout << "Failed to create thread number " << i << endl;
2734 Application::exit_with_failure();
2737 // Wait until the thread has finished launching and is gone to sleep
2738 while (threads[i].state != THREAD_SLEEPING);
2743 // exit_threads() is called when the program exits. It makes all the
2744 // helper threads exit cleanly.
2746 void ThreadsManager::exit_threads() {
2748 ActiveThreads = MAX_THREADS; // HACK
2749 AllThreadsShouldSleep = true; // HACK
2750 wake_sleeping_threads();
2752 // This makes the threads to exit idle_loop()
2753 AllThreadsShouldExit = true;
2755 // Wait for thread termination
2756 for (int i = 1; i < MAX_THREADS; i++)
2757 while (threads[i].state != THREAD_TERMINATED);
2759 // Now we can safely destroy the locks
2760 for (int i = 0; i < MAX_THREADS; i++)
2761 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2762 lock_destroy(&(SplitPointStack[i][j].lock));
2766 // thread_should_stop() checks whether the thread should stop its search.
2767 // This can happen if a beta cutoff has occurred in the thread's currently
2768 // active split point, or in some ancestor of the current split point.
2770 bool ThreadsManager::thread_should_stop(int threadID) const {
2772 assert(threadID >= 0 && threadID < ActiveThreads);
2776 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2781 // thread_is_available() checks whether the thread with threadID "slave" is
2782 // available to help the thread with threadID "master" at a split point. An
2783 // obvious requirement is that "slave" must be idle. With more than two
2784 // threads, this is not by itself sufficient: If "slave" is the master of
2785 // some active split point, it is only available as a slave to the other
2786 // threads which are busy searching the split point at the top of "slave"'s
2787 // split point stack (the "helpful master concept" in YBWC terminology).
2789 bool ThreadsManager::thread_is_available(int slave, int master) const {
2791 assert(slave >= 0 && slave < ActiveThreads);
2792 assert(master >= 0 && master < ActiveThreads);
2793 assert(ActiveThreads > 1);
2795 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2798 // Make a local copy to be sure doesn't change under our feet
2799 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2801 if (localActiveSplitPoints == 0)
2802 // No active split points means that the thread is available as
2803 // a slave for any other thread.
2806 if (ActiveThreads == 2)
2809 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2810 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2811 // could have been set to 0 by another thread leading to an out of bound access.
2812 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2819 // available_thread_exists() tries to find an idle thread which is available as
2820 // a slave for the thread with threadID "master".
2822 bool ThreadsManager::available_thread_exists(int master) const {
2824 assert(master >= 0 && master < ActiveThreads);
2825 assert(ActiveThreads > 1);
2827 for (int i = 0; i < ActiveThreads; i++)
2828 if (thread_is_available(i, master))
2835 // split() does the actual work of distributing the work at a node between
2836 // several threads at PV nodes. If it does not succeed in splitting the
2837 // node (because no idle threads are available, or because we have no unused
2838 // split point objects), the function immediately returns false. If
2839 // splitting is possible, a SplitPoint object is initialized with all the
2840 // data that must be copied to the helper threads (the current position and
2841 // search stack, alpha, beta, the search depth, etc.), and we tell our
2842 // helper threads that they have been assigned work. This will cause them
2843 // to instantly leave their idle loops and call sp_search_pv(). When all
2844 // threads have returned from sp_search_pv (or, equivalently, when
2845 // splitPoint->cpus becomes 0), split() returns true.
2847 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2848 Value* alpha, const Value beta, Value* bestValue, const Value futilityValue,
2849 Depth depth, int* moves, MovePicker* mp, int master, bool pvNode) {
2852 assert(sstck != NULL);
2853 assert(ply >= 0 && ply < PLY_MAX);
2854 assert(*bestValue >= -VALUE_INFINITE);
2855 assert( ( pvNode && *bestValue <= *alpha)
2856 || (!pvNode && *bestValue < beta ));
2857 assert(!pvNode || *alpha < beta);
2858 assert(beta <= VALUE_INFINITE);
2859 assert(depth > Depth(0));
2860 assert(master >= 0 && master < ActiveThreads);
2861 assert(ActiveThreads > 1);
2863 SplitPoint* splitPoint;
2867 // If no other thread is available to help us, or if we have too many
2868 // active split points, don't split.
2869 if ( !available_thread_exists(master)
2870 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2872 lock_release(&MPLock);
2876 // Pick the next available split point object from the split point stack
2877 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2879 // Initialize the split point object
2880 splitPoint->parent = threads[master].splitPoint;
2881 splitPoint->stopRequest = false;
2882 splitPoint->ply = ply;
2883 splitPoint->depth = depth;
2884 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2885 splitPoint->beta = beta;
2886 splitPoint->pvNode = pvNode;
2887 splitPoint->bestValue = *bestValue;
2888 splitPoint->futilityValue = futilityValue;
2889 splitPoint->master = master;
2890 splitPoint->mp = mp;
2891 splitPoint->moves = *moves;
2892 splitPoint->cpus = 1;
2893 splitPoint->pos = &p;
2894 splitPoint->parentSstack = sstck;
2895 for (int i = 0; i < ActiveThreads; i++)
2896 splitPoint->slaves[i] = 0;
2898 threads[master].splitPoint = splitPoint;
2899 threads[master].activeSplitPoints++;
2901 // If we are here it means we are not available
2902 assert(threads[master].state != THREAD_AVAILABLE);
2904 // Allocate available threads setting state to THREAD_BOOKED
2905 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2906 if (thread_is_available(i, master))
2908 threads[i].state = THREAD_BOOKED;
2909 threads[i].splitPoint = splitPoint;
2910 splitPoint->slaves[i] = 1;
2914 assert(splitPoint->cpus > 1);
2916 // We can release the lock because slave threads are already booked and master is not available
2917 lock_release(&MPLock);
2919 // Tell the threads that they have work to do. This will make them leave
2920 // their idle loop. But before copy search stack tail for each thread.
2921 for (int i = 0; i < ActiveThreads; i++)
2922 if (i == master || splitPoint->slaves[i])
2924 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2926 assert(i == master || threads[i].state == THREAD_BOOKED);
2928 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2931 // Everything is set up. The master thread enters the idle loop, from
2932 // which it will instantly launch a search, because its state is
2933 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2934 // idle loop, which means that the main thread will return from the idle
2935 // loop when all threads have finished their work at this split point
2936 // (i.e. when splitPoint->cpus == 0).
2937 idle_loop(master, splitPoint);
2939 // We have returned from the idle loop, which means that all threads are
2940 // finished. Update alpha, beta and bestValue, and return.
2944 *alpha = splitPoint->alpha;
2946 *bestValue = splitPoint->bestValue;
2947 threads[master].activeSplitPoints--;
2948 threads[master].splitPoint = splitPoint->parent;
2950 lock_release(&MPLock);
2955 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2956 // to start a new search from the root.
2958 void ThreadsManager::wake_sleeping_threads() {
2960 assert(AllThreadsShouldSleep);
2961 assert(ActiveThreads > 0);
2963 AllThreadsShouldSleep = false;
2965 if (ActiveThreads == 1)
2968 for (int i = 1; i < ActiveThreads; i++)
2969 assert(threads[i].state == THREAD_SLEEPING);
2971 #if !defined(_MSC_VER)
2972 pthread_mutex_lock(&WaitLock);
2973 pthread_cond_broadcast(&WaitCond);
2974 pthread_mutex_unlock(&WaitLock);
2976 for (int i = 1; i < MAX_THREADS; i++)
2977 SetEvent(SitIdleEvent[i]);
2983 // put_threads_to_sleep() makes all the threads go to sleep just before
2984 // to leave think(), at the end of the search. Threads should have already
2985 // finished the job and should be idle.
2987 void ThreadsManager::put_threads_to_sleep() {
2989 assert(!AllThreadsShouldSleep);
2991 // This makes the threads to go to sleep
2992 AllThreadsShouldSleep = true;
2994 // Reset flags to a known state.
2995 for (int i = 1; i < ActiveThreads; i++)
2997 // This flag can be in a random state
2998 threads[i].printCurrentLineRequest = false;
3002 // print_current_line() prints _once_ the current line of search for a
3003 // given thread and then setup the print request for the next thread.
3004 // Called when the UCI option UCI_ShowCurrLine is 'true'.
3006 void ThreadsManager::print_current_line(SearchStack ss[], int ply, int threadID) {
3008 assert(ply >= 0 && ply < PLY_MAX);
3009 assert(threadID >= 0 && threadID < ActiveThreads);
3011 if (!threads[threadID].printCurrentLineRequest)
3015 threads[threadID].printCurrentLineRequest = false;
3017 if (threads[threadID].state == THREAD_SEARCHING)
3020 cout << "info currline " << (threadID + 1);
3021 for (int p = 0; p < ply; p++)
3022 cout << " " << ss[p].currentMove;
3025 lock_release(&IOLock);
3028 // Setup print request for the next thread ID
3029 if (threadID + 1 < ActiveThreads)
3030 threads[threadID + 1].printCurrentLineRequest = true;
3034 /// The RootMoveList class
3036 // RootMoveList c'tor
3038 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3040 SearchStack ss[PLY_MAX_PLUS_2];
3041 MoveStack mlist[MaxRootMoves];
3043 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3045 // Generate all legal moves
3046 MoveStack* last = generate_moves(pos, mlist);
3048 // Add each move to the moves[] array
3049 for (MoveStack* cur = mlist; cur != last; cur++)
3051 bool includeMove = includeAllMoves;
3053 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3054 includeMove = (searchMoves[k] == cur->move);
3059 // Find a quick score for the move
3061 pos.do_move(cur->move, st);
3062 moves[count].move = cur->move;
3063 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3064 moves[count].pv[0] = cur->move;
3065 moves[count].pv[1] = MOVE_NONE;
3066 pos.undo_move(cur->move);
3073 // RootMoveList simple methods definitions
3075 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3077 moves[moveNum].nodes = nodes;
3078 moves[moveNum].cumulativeNodes += nodes;
3081 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3083 moves[moveNum].ourBeta = our;
3084 moves[moveNum].theirBeta = their;
3087 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3091 for (j = 0; pv[j] != MOVE_NONE; j++)
3092 moves[moveNum].pv[j] = pv[j];
3094 moves[moveNum].pv[j] = MOVE_NONE;
3098 // RootMoveList::sort() sorts the root move list at the beginning of a new
3101 void RootMoveList::sort() {
3103 sort_multipv(count - 1); // Sort all items
3107 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3108 // list by their scores and depths. It is used to order the different PVs
3109 // correctly in MultiPV mode.
3111 void RootMoveList::sort_multipv(int n) {
3115 for (i = 1; i <= n; i++)
3117 RootMove rm = moves[i];
3118 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3119 moves[j] = moves[j - 1];