2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
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
55 enum NodeType { NonPV, PV };
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* sp);
86 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode);
93 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
94 Thread threads[MAX_THREADS];
95 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
97 Lock MPLock, WaitLock;
99 #if !defined(_MSC_VER)
100 pthread_cond_t WaitCond;
102 HANDLE SitIdleEvent[MAX_THREADS];
108 // RootMove struct is used for moves at the root at the tree. For each
109 // root move, we store a score, a node count, and a PV (really a refutation
110 // in the case of moves which fail low).
114 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
116 // RootMove::operator<() is the comparison function used when
117 // sorting the moves. A move m1 is considered to be better
118 // than a move m2 if it has a higher score, or if the moves
119 // have equal score but m1 has the higher node count.
120 bool operator<(const RootMove& m) const {
122 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
127 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
128 Move pv[PLY_MAX_PLUS_2];
132 // The RootMoveList class is essentially an array of RootMove objects, with
133 // a handful of methods for accessing the data in the individual moves.
138 RootMoveList(Position& pos, Move searchMoves[]);
140 int move_count() const { return count; }
141 Move get_move(int moveNum) const { return moves[moveNum].move; }
142 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
143 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
144 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
145 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
147 void set_move_nodes(int moveNum, int64_t nodes);
148 void set_beta_counters(int moveNum, int64_t our, int64_t their);
149 void set_move_pv(int moveNum, const Move pv[]);
151 void sort_multipv(int n);
154 static const int MaxRootMoves = 500;
155 RootMove moves[MaxRootMoves];
164 // Maximum depth for razoring
165 const Depth RazorDepth = 4 * OnePly;
167 // Dynamic razoring margin based on depth
168 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
170 // Step 8. Null move search with verification search
172 // Null move margin. A null move search will not be done if the static
173 // evaluation of the position is more than NullMoveMargin below beta.
174 const Value NullMoveMargin = Value(0x200);
176 // Maximum depth for use of dynamic threat detection when null move fails low
177 const Depth ThreatDepth = 5 * OnePly;
179 // Step 9. Internal iterative deepening
181 // Minimum depth for use of internal iterative deepening
182 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
184 // At Non-PV nodes we do an internal iterative deepening search
185 // when the static evaluation is at most IIDMargin below beta.
186 const Value IIDMargin = Value(0x100);
188 // Step 11. Decide the new search depth
190 // Extensions. Configurable UCI options
191 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
192 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
193 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
195 // Minimum depth for use of singular extension
196 const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
198 // If the TT move is at least SingularExtensionMargin better then the
199 // remaining ones we will extend it.
200 const Value SingularExtensionMargin = Value(0x20);
202 // Step 12. Futility pruning
204 // Futility margin for quiescence search
205 const Value FutilityMarginQS = Value(0x80);
207 // Futility lookup tables (initialized at startup) and their getter functions
208 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
209 int FutilityMoveCountArray[32]; // [depth]
211 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
212 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
214 // Step 14. Reduced search
216 // Reduction lookup tables (initialized at startup) and their getter functions
217 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
219 template <NodeType PV>
220 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
222 // Common adjustments
224 // Search depth at iteration 1
225 const Depth InitialDepth = OnePly;
227 // Easy move margin. An easy move candidate must be at least this much
228 // better than the second best move.
229 const Value EasyMoveMargin = Value(0x200);
231 // Last seconds noise filtering (LSN)
232 const bool UseLSNFiltering = true;
233 const int LSNTime = 4000; // In milliseconds
234 const Value LSNValue = value_from_centipawns(200);
235 bool loseOnTime = false;
243 // Scores and number of times the best move changed for each iteration
244 Value ValueByIteration[PLY_MAX_PLUS_2];
245 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
247 // Search window management
253 // Time managment variables
254 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
255 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
256 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
257 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
261 std::ofstream LogFile;
263 // Multi-threads related variables
264 Depth MinimumSplitDepth;
265 int MaxThreadsPerSplitPoint;
268 // Node counters, used only by thread[0] but try to keep in different cache
269 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
271 int NodesBetweenPolls = 30000;
278 Value id_loop(const Position& pos, Move searchMoves[]);
279 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
281 template <NodeType PvNode>
282 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
284 template <NodeType PvNode>
285 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
287 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
288 void sp_search(SplitPoint* sp, int threadID);
289 void sp_search_pv(SplitPoint* sp, int threadID);
290 void init_node(SearchStack ss[], int ply, int threadID);
291 void update_pv(SearchStack ss[], int ply);
292 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
293 bool connected_moves(const Position& pos, Move m1, Move m2);
294 bool value_is_mate(Value value);
295 bool move_is_killer(Move m, const SearchStack& ss);
296 bool ok_to_do_nullmove(const Position& pos);
297 bool ok_to_prune(const Position& pos, Move m, Move threat);
298 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
299 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
300 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
301 void update_killers(Move m, SearchStack& ss);
302 void update_gains(const Position& pos, Move move, Value before, Value after);
304 int current_search_time();
308 void wait_for_stop_or_ponderhit();
309 void init_ss_array(SearchStack ss[]);
310 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value);
312 #if !defined(_MSC_VER)
313 void *init_thread(void *threadID);
315 DWORD WINAPI init_thread(LPVOID threadID);
325 /// init_threads(), exit_threads() and nodes_searched() are helpers to
326 /// give accessibility to some TM methods from outside of current file.
328 void init_threads() { TM.init_threads(); }
329 void exit_threads() { TM.exit_threads(); }
330 int64_t nodes_searched() { return TM.nodes_searched(); }
333 /// perft() is our utility to verify move generation is bug free. All the legal
334 /// moves up to given depth are generated and counted and the sum returned.
336 int perft(Position& pos, Depth depth)
341 MovePicker mp(pos, MOVE_NONE, depth, H);
343 // If we are at the last ply we don't need to do and undo
344 // the moves, just to count them.
345 if (depth <= OnePly) // Replace with '<' to test also qsearch
347 while (mp.get_next_move()) sum++;
351 // Loop through all legal moves
353 while ((move = mp.get_next_move()) != MOVE_NONE)
355 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
356 sum += perft(pos, depth - OnePly);
363 /// think() is the external interface to Stockfish's search, and is called when
364 /// the program receives the UCI 'go' command. It initializes various
365 /// search-related global variables, and calls root_search(). It returns false
366 /// when a quit command is received during the search.
368 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
369 int time[], int increment[], int movesToGo, int maxDepth,
370 int maxNodes, int maxTime, Move searchMoves[]) {
372 // Initialize global search variables
373 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
374 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
376 TM.resetNodeCounters();
377 SearchStartTime = get_system_time();
378 ExactMaxTime = maxTime;
381 InfiniteSearch = infinite;
382 PonderSearch = ponder;
383 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
385 // Look for a book move, only during games, not tests
386 if (UseTimeManagement && get_option_value_bool("OwnBook"))
388 if (get_option_value_string("Book File") != OpeningBook.file_name())
389 OpeningBook.open(get_option_value_string("Book File"));
391 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
392 if (bookMove != MOVE_NONE)
395 wait_for_stop_or_ponderhit();
397 cout << "bestmove " << bookMove << endl;
402 // Reset loseOnTime flag at the beginning of a new game
403 if (button_was_pressed("New Game"))
406 // Read UCI option values
407 TT.set_size(get_option_value_int("Hash"));
408 if (button_was_pressed("Clear Hash"))
411 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
412 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
413 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
414 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
415 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
416 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
417 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
418 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
419 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
420 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
421 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
422 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
424 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
425 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
426 MultiPV = get_option_value_int("MultiPV");
427 Chess960 = get_option_value_bool("UCI_Chess960");
428 UseLogFile = get_option_value_bool("Use Search Log");
431 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
433 read_weights(pos.side_to_move());
435 // Set the number of active threads
436 int newActiveThreads = get_option_value_int("Threads");
437 if (newActiveThreads != TM.active_threads())
439 TM.set_active_threads(newActiveThreads);
440 init_eval(TM.active_threads());
443 // Wake up sleeping threads
444 TM.wake_sleeping_threads();
447 int myTime = time[side_to_move];
448 int myIncrement = increment[side_to_move];
449 if (UseTimeManagement)
451 if (!movesToGo) // Sudden death time control
455 MaxSearchTime = myTime / 30 + myIncrement;
456 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
458 else // Blitz game without increment
460 MaxSearchTime = myTime / 30;
461 AbsoluteMaxSearchTime = myTime / 8;
464 else // (x moves) / (y minutes)
468 MaxSearchTime = myTime / 2;
469 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
473 MaxSearchTime = myTime / Min(movesToGo, 20);
474 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
478 if (get_option_value_bool("Ponder"))
480 MaxSearchTime += MaxSearchTime / 4;
481 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
485 // Set best NodesBetweenPolls interval to avoid lagging under
486 // heavy time pressure.
488 NodesBetweenPolls = Min(MaxNodes, 30000);
489 else if (myTime && myTime < 1000)
490 NodesBetweenPolls = 1000;
491 else if (myTime && myTime < 5000)
492 NodesBetweenPolls = 5000;
494 NodesBetweenPolls = 30000;
496 // Write search information to log file
498 LogFile << "Searching: " << pos.to_fen() << endl
499 << "infinite: " << infinite
500 << " ponder: " << ponder
501 << " time: " << myTime
502 << " increment: " << myIncrement
503 << " moves to go: " << movesToGo << endl;
505 // LSN filtering. Used only for developing purposes, disabled by default
509 // Step 2. If after last move we decided to lose on time, do it now!
510 while (SearchStartTime + myTime + 1000 > get_system_time())
514 // We're ready to start thinking. Call the iterative deepening loop function
515 Value v = id_loop(pos, searchMoves);
519 // Step 1. If this is sudden death game and our position is hopeless,
520 // decide to lose on time.
521 if ( !loseOnTime // If we already lost on time, go to step 3.
531 // Step 3. Now after stepping over the time limit, reset flag for next match.
539 TM.put_threads_to_sleep();
545 /// init_search() is called during startup. It initializes various lookup tables
549 // Init our reduction lookup tables
550 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
551 for (int j = 1; j < 64; j++) // j == moveNumber
553 double pvRed = log(double(i)) * log(double(j)) / 3.0;
554 double nonPVRed = log(double(i)) * log(double(j)) / 1.5;
555 ReductionMatrix[PV][i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
556 ReductionMatrix[NonPV][i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
559 // Init futility margins array
560 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
561 for (int j = 0; j < 64; j++) // j == moveNumber
563 // FIXME: test using log instead of BSR
564 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j + 45;
567 // Init futility move count array
568 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
569 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
573 // SearchStack::init() initializes a search stack. Used at the beginning of a
574 // new search from the root.
575 void SearchStack::init(int ply) {
577 pv[ply] = pv[ply + 1] = MOVE_NONE;
578 currentMove = threatMove = MOVE_NONE;
579 reduction = Depth(0);
583 void SearchStack::initKillers() {
585 mateKiller = MOVE_NONE;
586 for (int i = 0; i < KILLER_MAX; i++)
587 killers[i] = MOVE_NONE;
592 // id_loop() is the main iterative deepening loop. It calls root_search
593 // repeatedly with increasing depth until the allocated thinking time has
594 // been consumed, the user stops the search, or the maximum search depth is
597 Value id_loop(const Position& pos, Move searchMoves[]) {
600 SearchStack ss[PLY_MAX_PLUS_2];
601 Move EasyMove = MOVE_NONE;
602 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
604 // Moves to search are verified, copied, scored and sorted
605 RootMoveList rml(p, searchMoves);
607 // Handle special case of searching on a mate/stale position
608 if (rml.move_count() == 0)
611 wait_for_stop_or_ponderhit();
613 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
616 // Print RootMoveList startup scoring to the standard output,
617 // so to output information also for iteration 1.
618 cout << "info depth " << 1
619 << "\ninfo depth " << 1
620 << " score " << value_to_string(rml.get_move_score(0))
621 << " time " << current_search_time()
622 << " nodes " << TM.nodes_searched()
624 << " pv " << rml.get_move(0) << "\n";
630 ValueByIteration[1] = rml.get_move_score(0);
633 // Is one move significantly better than others after initial scoring ?
634 if ( rml.move_count() == 1
635 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
636 EasyMove = rml.get_move(0);
638 // Iterative deepening loop
639 while (Iteration < PLY_MAX)
641 // Initialize iteration
643 BestMoveChangesByIteration[Iteration] = 0;
645 cout << "info depth " << Iteration << endl;
647 // Calculate dynamic aspiration 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);
660 // Search to the current depth, rml is updated and sorted, alpha and beta could change
661 value = root_search(p, ss, rml, &alpha, &beta);
663 // Write PV to transposition table, in case the relevant entries have
664 // been overwritten during the search.
665 TT.insert_pv(p, ss[0].pv);
668 break; // Value cannot be trusted. Break out immediately!
670 //Save info about search result
671 ValueByIteration[Iteration] = value;
673 // Drop the easy move if differs from the new best move
674 if (ss[0].pv[0] != EasyMove)
675 EasyMove = MOVE_NONE;
677 if (UseTimeManagement)
680 bool stopSearch = false;
682 // Stop search early if there is only a single legal move,
683 // we search up to Iteration 6 anyway to get a proper score.
684 if (Iteration >= 6 && rml.move_count() == 1)
687 // Stop search early when the last two iterations returned a mate score
689 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
690 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
693 // Stop search early if one move seems to be much better than the others
694 int64_t nodes = TM.nodes_searched();
696 && EasyMove == ss[0].pv[0]
697 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
698 && current_search_time() > MaxSearchTime / 16)
699 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
700 && current_search_time() > MaxSearchTime / 32)))
703 // Add some extra time if the best move has changed during the last two iterations
704 if (Iteration > 5 && Iteration <= 50)
705 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
706 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
708 // Stop search if most of MaxSearchTime is consumed at the end of the
709 // iteration. We probably don't have enough time to search the first
710 // move at the next iteration anyway.
711 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
717 StopOnPonderhit = true;
723 if (MaxDepth && Iteration >= MaxDepth)
727 // If we are pondering or in infinite search, we shouldn't print the
728 // best move before we are told to do so.
729 if (!AbortSearch && (PonderSearch || InfiniteSearch))
730 wait_for_stop_or_ponderhit();
732 // Print final search statistics
733 cout << "info nodes " << TM.nodes_searched()
735 << " time " << current_search_time()
736 << " hashfull " << TT.full() << endl;
738 // Print the best move and the ponder move to the standard output
739 if (ss[0].pv[0] == MOVE_NONE)
741 ss[0].pv[0] = rml.get_move(0);
742 ss[0].pv[1] = MOVE_NONE;
745 assert(ss[0].pv[0] != MOVE_NONE);
747 cout << "bestmove " << ss[0].pv[0];
749 if (ss[0].pv[1] != MOVE_NONE)
750 cout << " ponder " << ss[0].pv[1];
757 dbg_print_mean(LogFile);
759 if (dbg_show_hit_rate)
760 dbg_print_hit_rate(LogFile);
762 LogFile << "\nNodes: " << TM.nodes_searched()
763 << "\nNodes/second: " << nps()
764 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
767 p.do_move(ss[0].pv[0], st);
768 LogFile << "\nPonder move: "
769 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
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, prints some information to the standard output and handles
779 // the fail low/high loops.
781 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
788 Depth depth, ext, newDepth;
789 Value value, alpha, beta;
790 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
791 int researchCountFH, researchCountFL;
793 researchCountFH = researchCountFL = 0;
796 isCheck = pos.is_check();
798 // Step 1. Initialize node and poll (omitted at root, but I can see no good reason for this, FIXME)
799 // Step 2. Check for aborted search (omitted at root, because we do not initialize root node)
800 // Step 3. Mate distance pruning (omitted at root)
801 // Step 4. Transposition table lookup (omitted at root)
803 // Step 5. Evaluate the position statically
804 // At root we do this only to get reference value for child nodes
806 ss[0].eval = evaluate(pos, ei, 0);
808 ss[0].eval = VALUE_NONE; // HACK because we do not initialize root node
810 // Step 6. Razoring (omitted at root)
811 // Step 7. Static null move pruning (omitted at root)
812 // Step 8. Null move search with verification search (omitted at root)
813 // Step 9. Internal iterative deepening (omitted at root)
815 // Step extra. Fail low loop
816 // We start with small aspiration window and in case of fail low, we research
817 // with bigger window until we are not failing low anymore.
820 // Sort the moves before to (re)search
823 // Step 10. Loop through all moves in the root move list
824 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
826 // This is used by time management
827 FirstRootMove = (i == 0);
829 // Save the current node count before the move is searched
830 nodes = TM.nodes_searched();
832 // Reset beta cut-off counters
833 TM.resetBetaCounters();
835 // Pick the next root move, and print the move and the move number to
836 // the standard output.
837 move = ss[0].currentMove = rml.get_move(i);
839 if (current_search_time() >= 1000)
840 cout << "info currmove " << move
841 << " currmovenumber " << i + 1 << endl;
843 moveIsCheck = pos.move_is_check(move);
844 captureOrPromotion = pos.move_is_capture_or_promotion(move);
846 // Step 11. Decide the new search depth
847 depth = (Iteration - 2) * OnePly + InitialDepth;
848 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
849 newDepth = depth + ext;
851 // Step 12. Futility pruning (omitted at root)
853 // Step extra. Fail high loop
854 // If move fails high, we research with bigger window until we are not failing
856 value = - VALUE_INFINITE;
860 // Step 13. Make the move
861 pos.do_move(move, st, ci, moveIsCheck);
863 // Step extra. pv search
864 // We do pv search for first moves (i < MultiPV)
865 // and for fail high research (value > alpha)
866 if (i < MultiPV || value > alpha)
868 // Aspiration window is disabled in multi-pv case
870 alpha = -VALUE_INFINITE;
872 // Full depth PV search, done on first move or after a fail high
873 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
877 // Step 14. Reduced search
878 // if the move fails high will be re-searched at full depth
879 bool doFullDepthSearch = true;
881 if ( depth >= 3 * OnePly
883 && !captureOrPromotion
884 && !move_is_castle(move))
886 ss[0].reduction = reduction<PV>(depth, i - MultiPV + 2);
889 // Reduced depth non-pv search using alpha as upperbound
890 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[0].reduction, 1, true, 0);
891 doFullDepthSearch = (value > alpha);
895 // Step 15. Full depth search
896 if (doFullDepthSearch)
898 // Full depth non-pv search using alpha as upperbound
899 ss[0].reduction = Depth(0);
900 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, 1, true, 0);
902 // If we are above alpha then research at same depth but as PV
903 // to get a correct score or eventually a fail high above beta.
905 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
909 // Step 16. Undo move
912 // Can we exit fail high loop ?
913 if (AbortSearch || value < beta)
916 // We are failing high and going to do a research. It's important to update
917 // the score before research in case we run out of time while researching.
918 rml.set_move_score(i, value);
920 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
921 rml.set_move_pv(i, ss[0].pv);
923 // Print information to the standard output
924 print_pv_info(pos, ss, alpha, beta, value);
926 // Prepare for a research after a fail high, each time with a wider window
927 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
930 } // End of fail high loop
932 // Finished searching the move. If AbortSearch is true, the search
933 // was aborted because the user interrupted the search or because we
934 // ran out of time. In this case, the return value of the search cannot
935 // be trusted, and we break out of the loop without updating the best
940 // Remember beta-cutoff and searched nodes counts for this move. The
941 // info is used to sort the root moves for the next iteration.
943 TM.get_beta_counters(pos.side_to_move(), our, their);
944 rml.set_beta_counters(i, our, their);
945 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
947 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
948 assert(value < beta);
950 // Step 17. Check for new best move
951 if (value <= alpha && i >= MultiPV)
952 rml.set_move_score(i, -VALUE_INFINITE);
955 // PV move or new best move!
958 rml.set_move_score(i, value);
960 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
961 rml.set_move_pv(i, ss[0].pv);
965 // We record how often the best move has been changed in each
966 // iteration. This information is used for time managment: When
967 // the best move changes frequently, we allocate some more time.
969 BestMoveChangesByIteration[Iteration]++;
971 // Print information to the standard output
972 print_pv_info(pos, ss, alpha, beta, value);
974 // Raise alpha to setup proper non-pv search upper bound
981 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
983 cout << "info multipv " << j + 1
984 << " score " << value_to_string(rml.get_move_score(j))
985 << " depth " << (j <= i ? Iteration : Iteration - 1)
986 << " time " << current_search_time()
987 << " nodes " << TM.nodes_searched()
991 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
992 cout << rml.get_move_pv(j, k) << " ";
996 alpha = rml.get_move_score(Min(i, MultiPV - 1));
998 } // PV move or new best move
1000 assert(alpha >= *alphaPtr);
1002 AspirationFailLow = (alpha == *alphaPtr);
1004 if (AspirationFailLow && StopOnPonderhit)
1005 StopOnPonderhit = false;
1008 // Can we exit fail low loop ?
1009 if (AbortSearch || !AspirationFailLow)
1012 // Prepare for a research after a fail low, each time with a wider window
1013 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1018 // Sort the moves before to return
1025 // search<>() is the main search function for both PV and non-PV nodes
1027 template <NodeType PvNode>
1028 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth,
1029 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1031 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1032 assert(beta > alpha && beta <= VALUE_INFINITE);
1033 assert(ply >= 0 && ply < PLY_MAX);
1034 assert(threadID >= 0 && threadID < TM.active_threads());
1036 Move movesSearched[256];
1041 Depth ext, newDepth;
1042 Value bestValue, value, oldAlpha;
1043 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1044 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1045 bool mateThreat = false;
1047 refinedValue = bestValue = value = -VALUE_INFINITE;
1051 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1053 // Step 1. Initialize node and poll
1054 // Polling can abort search.
1055 init_node(ss, ply, threadID);
1057 // Step 2. Check for aborted search and immediate draw
1058 if (AbortSearch || TM.thread_should_stop(threadID))
1061 if (pos.is_draw() || ply >= PLY_MAX - 1)
1064 // Step 3. Mate distance pruning
1065 alpha = Max(value_mated_in(ply), alpha);
1066 beta = Min(value_mate_in(ply+1), beta);
1070 // Step 4. Transposition table lookup
1072 // We don't want the score of a partial search to overwrite a previous full search
1073 // TT value, so we use a different position key in case of an excluded move exists.
1074 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1076 tte = TT.retrieve(posKey);
1077 ttMove = (tte ? tte->move() : MOVE_NONE);
1079 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1080 // This is to avoid problems in the following areas:
1082 // * Repetition draw detection
1083 // * Fifty move rule detection
1084 // * Searching for a mate
1085 // * Printing of full PV line
1087 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1089 // Refresh tte entry to avoid aging
1090 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove);
1092 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1093 return value_from_tt(tte->value(), ply);
1096 // Step 5. Evaluate the position statically
1097 // At PV nodes we do this only to update gain statistics
1098 isCheck = pos.is_check();
1101 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1102 ss[ply].eval = value_from_tt(tte->value(), ply);
1104 ss[ply].eval = evaluate(pos, ei, threadID);
1106 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1107 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1110 // Step 6. Razoring (is omitted in PV nodes)
1112 && refinedValue < beta - razor_margin(depth)
1113 && ttMove == MOVE_NONE
1114 && ss[ply - 1].currentMove != MOVE_NULL
1115 && depth < RazorDepth
1117 && !value_is_mate(beta)
1118 && !pos.has_pawn_on_7th(pos.side_to_move()))
1120 Value rbeta = beta - razor_margin(depth);
1121 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1123 // Logically we should return (v + razor_margin(depth)), but
1124 // surprisingly this did slightly weaker in tests.
1128 // Step 7. Static null move pruning (is omitted in PV nodes)
1129 // We're betting that the opponent doesn't have a move that will reduce
1130 // the score by more than futility_margin(depth) if we do a null move.
1133 && depth < RazorDepth
1135 && !value_is_mate(beta)
1136 && ok_to_do_nullmove(pos)
1137 && refinedValue >= beta + futility_margin(depth, 0))
1138 return refinedValue - futility_margin(depth, 0);
1140 // Step 8. Null move search with verification search (is omitted in PV nodes)
1141 // When we jump directly to qsearch() we do a null move only if static value is
1142 // at least beta. Otherwise we do a null move if static value is not more than
1143 // NullMoveMargin under beta.
1148 && !value_is_mate(beta)
1149 && ok_to_do_nullmove(pos)
1150 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1152 ss[ply].currentMove = MOVE_NULL;
1154 // Null move dynamic reduction based on depth
1155 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1157 // Null move dynamic reduction based on value
1158 if (refinedValue - beta > PawnValueMidgame)
1161 pos.do_null_move(st);
1163 nullValue = -search<NonPV>(pos, ss, -beta, -alpha, depth-R*OnePly, ply+1, false, threadID);
1165 pos.undo_null_move();
1167 if (nullValue >= beta)
1169 // Do not return unproven mate scores
1170 if (nullValue >= value_mate_in(PLY_MAX))
1173 if (depth < 6 * OnePly)
1176 // Do zugzwang verification search
1177 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply, false, threadID);
1181 // The null move failed low, which means that we may be faced with
1182 // some kind of threat. If the previous move was reduced, check if
1183 // the move that refuted the null move was somehow connected to the
1184 // move which was reduced. If a connection is found, return a fail
1185 // low score (which will cause the reduced move to fail high in the
1186 // parent node, which will trigger a re-search with full depth).
1187 if (nullValue == value_mated_in(ply + 2))
1190 ss[ply].threatMove = ss[ply + 1].currentMove;
1191 if ( depth < ThreatDepth
1192 && ss[ply - 1].reduction
1193 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1198 // Step 9. Internal iterative deepening
1199 if ( depth >= IIDDepth[PvNode]
1200 && ttMove == MOVE_NONE
1201 && (PvNode || (!isCheck && ss[ply].eval >= beta - IIDMargin)))
1203 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1204 search<PvNode>(pos, ss, alpha, beta, d, ply, false, threadID);
1205 ttMove = ss[ply].pv[ply];
1206 tte = TT.retrieve(posKey);
1209 // Expensive mate threat detection (only for PV nodes)
1211 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1213 // Initialize a MovePicker object for the current position
1214 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], (PvNode ? -VALUE_INFINITE : beta));
1217 // Step 10. Loop through moves
1218 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1219 while ( bestValue < beta
1220 && (move = mp.get_next_move()) != MOVE_NONE
1221 && !TM.thread_should_stop(threadID))
1223 assert(move_is_ok(move));
1225 if (move == excludedMove)
1228 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1229 moveIsCheck = pos.move_is_check(move, ci);
1230 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1232 // Step 11. Decide the new search depth
1233 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1235 // Singular extension search. We extend the TT move if its value is much better than
1236 // its siblings. To verify this we do a reduced search on all the other moves but the
1237 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1238 if ( depth >= SingularExtensionDepth[PvNode]
1240 && move == tte->move()
1241 && !excludedMove // Do not allow recursive singular extension search
1243 && is_lower_bound(tte->type())
1244 && tte->depth() >= depth - 3 * OnePly)
1246 Value ttValue = value_from_tt(tte->value(), ply);
1248 if (abs(ttValue) < VALUE_KNOWN_WIN)
1250 Value b = ttValue - SingularExtensionMargin;
1251 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply, false, threadID, move);
1253 if (v < ttValue - SingularExtensionMargin)
1258 newDepth = depth - OnePly + ext;
1260 // Update current move (this must be done after singular extension search)
1261 movesSearched[moveCount++] = ss[ply].currentMove = move;
1263 // Step 12. Futility pruning (is omitted in PV nodes)
1267 && !captureOrPromotion
1268 && !move_is_castle(move)
1271 // Move count based pruning
1272 if ( moveCount >= futility_move_count(depth)
1273 && ok_to_prune(pos, move, ss[ply].threatMove)
1274 && bestValue > value_mated_in(PLY_MAX))
1277 // Value based pruning
1278 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount); // FIXME We illogically ignore reduction condition depth >= 3*OnePly
1279 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1280 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1282 if (futilityValueScaled < beta)
1284 if (futilityValueScaled > bestValue)
1285 bestValue = futilityValueScaled;
1290 // Step 13. Make the move
1291 pos.do_move(move, st, ci, moveIsCheck);
1293 // Step extra. pv search (only in PV nodes)
1294 // The first move in list is the expected PV
1295 if (PvNode && moveCount == 1)
1296 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1299 // Step 14. Reduced search
1300 // if the move fails high will be re-searched at full depth.
1301 bool doFullDepthSearch = true;
1303 if ( depth >= 3 * OnePly
1305 && !captureOrPromotion
1306 && !move_is_castle(move)
1307 && !move_is_killer(move, ss[ply]))
1309 ss[ply].reduction = reduction<PvNode>(depth, moveCount);
1310 if (ss[ply].reduction)
1312 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1313 doFullDepthSearch = (value > alpha);
1317 // Step 15. Full depth search
1318 if (doFullDepthSearch)
1320 ss[ply].reduction = Depth(0);
1321 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, ply+1, true, threadID);
1323 // Step extra. pv search (only in PV nodes)
1324 // Search only for possible new PV nodes, if instead value >= beta then
1325 // parent node fails low with value <= alpha and tries another move.
1326 if (PvNode && value > alpha && value < beta)
1327 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1331 // Step 16. Undo move
1332 pos.undo_move(move);
1334 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1336 // Step 17. Check for new best move
1337 if (value > bestValue)
1344 if (value == value_mate_in(ply + 1))
1345 ss[ply].mateKiller = move;
1349 // Step 18. Check for split
1350 if ( TM.active_threads() > 1
1352 && depth >= MinimumSplitDepth
1354 && TM.available_thread_exists(threadID)
1356 && !TM.thread_should_stop(threadID)
1357 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1358 depth, mateThreat, &moveCount, &mp, threadID, PvNode))
1362 // Step 19. Check for mate and stalemate
1363 // All legal moves have been searched and if there are
1364 // no legal moves, it must be mate or stalemate.
1365 // If one move was excluded return fail low score.
1367 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1369 // Step 20. Update tables
1370 // If the search is not aborted, update the transposition table,
1371 // history counters, and killer moves.
1372 if (AbortSearch || TM.thread_should_stop(threadID))
1375 if (bestValue <= oldAlpha)
1376 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1378 else if (bestValue >= beta)
1380 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1381 move = ss[ply].pv[ply];
1382 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1383 if (!pos.move_is_capture_or_promotion(move))
1385 update_history(pos, move, depth, movesSearched, moveCount);
1386 update_killers(move, ss[ply]);
1390 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1392 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1398 // qsearch() is the quiescence search function, which is called by the main
1399 // search function when the remaining depth is zero (or, to be more precise,
1400 // less than OnePly).
1402 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1403 Depth depth, int ply, int threadID) {
1405 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1406 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1408 assert(ply >= 0 && ply < PLY_MAX);
1409 assert(threadID >= 0 && threadID < TM.active_threads());
1414 Value staticValue, bestValue, value, futilityBase, futilityValue;
1415 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1416 const TTEntry* tte = NULL;
1418 bool pvNode = (beta - alpha != 1);
1419 Value oldAlpha = alpha;
1421 // Initialize, and make an early exit in case of an aborted search,
1422 // an instant draw, maximum ply reached, etc.
1423 init_node(ss, ply, threadID);
1425 // After init_node() that calls poll()
1426 if (AbortSearch || TM.thread_should_stop(threadID))
1429 if (pos.is_draw() || ply >= PLY_MAX - 1)
1432 // Transposition table lookup. At PV nodes, we don't use the TT for
1433 // pruning, but only for move ordering.
1434 tte = TT.retrieve(pos.get_key());
1435 ttMove = (tte ? tte->move() : MOVE_NONE);
1437 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1439 assert(tte->type() != VALUE_TYPE_EVAL);
1441 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1442 return value_from_tt(tte->value(), ply);
1445 isCheck = pos.is_check();
1447 // Evaluate the position statically
1449 staticValue = -VALUE_INFINITE;
1450 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1451 staticValue = value_from_tt(tte->value(), ply);
1453 staticValue = evaluate(pos, ei, threadID);
1457 ss[ply].eval = staticValue;
1458 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1461 // Initialize "stand pat score", and return it immediately if it is
1463 bestValue = staticValue;
1465 if (bestValue >= beta)
1467 // Store the score to avoid a future costly evaluation() call
1468 if (!isCheck && !tte && ei.kingDanger[pos.side_to_move()] == 0)
1469 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1474 if (bestValue > alpha)
1477 // If we are near beta then try to get a cutoff pushing checks a bit further
1478 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1480 // Initialize a MovePicker object for the current position, and prepare
1481 // to search the moves. Because the depth is <= 0 here, only captures,
1482 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1483 // and we are near beta) will be generated.
1484 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1486 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1487 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1489 // Loop through the moves until no moves remain or a beta cutoff occurs
1490 while ( alpha < beta
1491 && (move = mp.get_next_move()) != MOVE_NONE)
1493 assert(move_is_ok(move));
1495 moveIsCheck = pos.move_is_check(move, ci);
1497 // Update current move
1499 ss[ply].currentMove = move;
1507 && !move_is_promotion(move)
1508 && !pos.move_is_passed_pawn_push(move))
1510 futilityValue = futilityBase
1511 + pos.endgame_value_of_piece_on(move_to(move))
1512 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1514 if (futilityValue < alpha)
1516 if (futilityValue > bestValue)
1517 bestValue = futilityValue;
1522 // Detect blocking evasions that are candidate to be pruned
1523 evasionPrunable = isCheck
1524 && bestValue > value_mated_in(PLY_MAX)
1525 && !pos.move_is_capture(move)
1526 && pos.type_of_piece_on(move_from(move)) != KING
1527 && !pos.can_castle(pos.side_to_move());
1529 // Don't search moves with negative SEE values
1530 if ( (!isCheck || evasionPrunable)
1533 && !move_is_promotion(move)
1534 && pos.see_sign(move) < 0)
1537 // Make and search the move
1538 pos.do_move(move, st, ci, moveIsCheck);
1539 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1540 pos.undo_move(move);
1542 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1545 if (value > bestValue)
1556 // All legal moves have been searched. A special case: If we're in check
1557 // and no legal moves were found, it is checkmate.
1558 if (!moveCount && isCheck) // Mate!
1559 return value_mated_in(ply);
1561 // Update transposition table
1562 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1563 if (bestValue <= oldAlpha)
1565 // If bestValue isn't changed it means it is still the static evaluation
1566 // of the node, so keep this info to avoid a future evaluation() call.
1567 ValueType type = (bestValue == staticValue && !ei.kingDanger[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1568 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1570 else if (bestValue >= beta)
1572 move = ss[ply].pv[ply];
1573 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1575 // Update killers only for good checking moves
1576 if (!pos.move_is_capture_or_promotion(move))
1577 update_killers(move, ss[ply]);
1580 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1582 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1588 // sp_search() is used to search from a split point. This function is called
1589 // by each thread working at the split point. It is similar to the normal
1590 // search() function, but simpler. Because we have already probed the hash
1591 // table, done a null move search, and searched the first move before
1592 // splitting, we don't have to repeat all this work in sp_search(). We
1593 // also don't need to store anything to the hash table here: This is taken
1594 // care of after we return from the split point.
1596 void sp_search(SplitPoint* sp, int threadID) {
1598 assert(threadID >= 0 && threadID < TM.active_threads());
1599 assert(TM.active_threads() > 1);
1603 Depth ext, newDepth;
1604 Value value, futilityValueScaled;
1605 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1607 value = -VALUE_INFINITE;
1609 Position pos(*sp->pos);
1611 SearchStack* ss = sp->sstack[threadID];
1612 isCheck = pos.is_check();
1614 // Step 10. Loop through moves
1615 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1616 lock_grab(&(sp->lock));
1618 while ( sp->bestValue < sp->beta
1619 && !TM.thread_should_stop(threadID)
1620 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1622 moveCount = ++sp->moves;
1623 lock_release(&(sp->lock));
1625 assert(move_is_ok(move));
1627 moveIsCheck = pos.move_is_check(move, ci);
1628 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1630 // Step 11. Decide the new search depth
1631 ext = extension<NonPV>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1632 newDepth = sp->depth - OnePly + ext;
1634 // Update current move
1635 ss[sp->ply].currentMove = move;
1637 // Step 12. Futility pruning
1640 && !captureOrPromotion
1641 && !move_is_castle(move))
1643 // Move count based pruning
1644 if ( moveCount >= futility_move_count(sp->depth)
1645 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1646 && sp->bestValue > value_mated_in(PLY_MAX))
1648 lock_grab(&(sp->lock));
1652 // Value based pruning
1653 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1654 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1655 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1657 if (futilityValueScaled < sp->beta)
1659 lock_grab(&(sp->lock));
1661 if (futilityValueScaled > sp->bestValue)
1662 sp->bestValue = futilityValueScaled;
1667 // Step 13. Make the move
1668 pos.do_move(move, st, ci, moveIsCheck);
1670 // Step 14. Reduced search
1671 // if the move fails high will be re-searched at full depth.
1672 bool doFullDepthSearch = true;
1675 && !captureOrPromotion
1676 && !move_is_castle(move)
1677 && !move_is_killer(move, ss[sp->ply]))
1679 ss[sp->ply].reduction = reduction<NonPV>(sp->depth, moveCount);
1680 if (ss[sp->ply].reduction)
1682 value = -search<NonPV>(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1683 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1687 // Step 15. Full depth search
1688 if (doFullDepthSearch)
1690 ss[sp->ply].reduction = Depth(0);
1691 value = -search<NonPV>(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth, sp->ply+1, true, threadID);
1694 // Step 16. Undo move
1695 pos.undo_move(move);
1697 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1699 // Step 17. Check for new best move
1700 lock_grab(&(sp->lock));
1702 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1704 sp->bestValue = value;
1705 if (sp->bestValue >= sp->beta)
1707 sp->stopRequest = true;
1708 sp_update_pv(sp->parentSstack, ss, sp->ply);
1713 /* Here we have the lock still grabbed */
1715 sp->slaves[threadID] = 0;
1718 lock_release(&(sp->lock));
1722 // sp_search_pv() is used to search from a PV split point. This function
1723 // is called by each thread working at the split point. It is similar to
1724 // the normal search_pv() function, but simpler. Because we have already
1725 // probed the hash table and searched the first move before splitting, we
1726 // don't have to repeat all this work in sp_search_pv(). We also don't
1727 // need to store anything to the hash table here: This is taken care of
1728 // after we return from the split point.
1730 void sp_search_pv(SplitPoint* sp, int threadID) {
1732 assert(threadID >= 0 && threadID < TM.active_threads());
1733 assert(TM.active_threads() > 1);
1737 Depth ext, newDepth;
1739 bool moveIsCheck, captureOrPromotion, dangerous;
1741 value = -VALUE_INFINITE;
1743 Position pos(*sp->pos);
1745 SearchStack* ss = sp->sstack[threadID];
1747 // Step 10. Loop through moves
1748 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1749 lock_grab(&(sp->lock));
1751 while ( sp->alpha < sp->beta
1752 && !TM.thread_should_stop(threadID)
1753 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1755 moveCount = ++sp->moves;
1756 lock_release(&(sp->lock));
1758 assert(move_is_ok(move));
1760 moveIsCheck = pos.move_is_check(move, ci);
1761 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1763 // Step 11. Decide the new search depth
1764 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1765 newDepth = sp->depth - OnePly + ext;
1767 // Update current move
1768 ss[sp->ply].currentMove = move;
1770 // Step 12. Futility pruning (is omitted in PV nodes)
1772 // Step 13. Make the move
1773 pos.do_move(move, st, ci, moveIsCheck);
1775 // Step 14. Reduced search
1776 // if the move fails high will be re-searched at full depth.
1777 bool doFullDepthSearch = true;
1780 && !captureOrPromotion
1781 && !move_is_castle(move)
1782 && !move_is_killer(move, ss[sp->ply]))
1784 ss[sp->ply].reduction = reduction<PV>(sp->depth, moveCount);
1785 if (ss[sp->ply].reduction)
1787 Value localAlpha = sp->alpha;
1788 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1789 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1793 // Step 15. Full depth search
1794 if (doFullDepthSearch)
1796 Value localAlpha = sp->alpha;
1797 ss[sp->ply].reduction = Depth(0);
1798 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1, true, threadID);
1800 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1802 // If another thread has failed high then sp->alpha has been increased
1803 // to be higher or equal then beta, if so, avoid to start a PV search.
1804 localAlpha = sp->alpha;
1805 if (localAlpha < sp->beta)
1806 value = -search<PV>(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, false, threadID);
1810 // Step 16. Undo move
1811 pos.undo_move(move);
1813 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1815 // Step 17. Check for new best move
1816 lock_grab(&(sp->lock));
1818 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1820 sp->bestValue = value;
1821 if (value > sp->alpha)
1823 // Ask threads to stop before to modify sp->alpha
1824 if (value >= sp->beta)
1825 sp->stopRequest = true;
1829 sp_update_pv(sp->parentSstack, ss, sp->ply);
1830 if (value == value_mate_in(sp->ply + 1))
1831 ss[sp->ply].mateKiller = move;
1836 /* Here we have the lock still grabbed */
1838 sp->slaves[threadID] = 0;
1841 lock_release(&(sp->lock));
1845 // init_node() is called at the beginning of all the search functions
1846 // (search() qsearch(), and so on) and initializes the
1847 // search stack object corresponding to the current node. Once every
1848 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1849 // for user input and checks whether it is time to stop the search.
1851 void init_node(SearchStack ss[], int ply, int threadID) {
1853 assert(ply >= 0 && ply < PLY_MAX);
1854 assert(threadID >= 0 && threadID < TM.active_threads());
1856 TM.incrementNodeCounter(threadID);
1861 if (NodesSincePoll >= NodesBetweenPolls)
1868 ss[ply + 2].initKillers();
1872 // update_pv() is called whenever a search returns a value > alpha.
1873 // It updates the PV in the SearchStack object corresponding to the
1876 void update_pv(SearchStack ss[], int ply) {
1878 assert(ply >= 0 && ply < PLY_MAX);
1882 ss[ply].pv[ply] = ss[ply].currentMove;
1884 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1885 ss[ply].pv[p] = ss[ply + 1].pv[p];
1887 ss[ply].pv[p] = MOVE_NONE;
1891 // sp_update_pv() is a variant of update_pv for use at split points. The
1892 // difference between the two functions is that sp_update_pv also updates
1893 // the PV at the parent node.
1895 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
1897 assert(ply >= 0 && ply < PLY_MAX);
1901 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
1903 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1904 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
1906 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
1910 // connected_moves() tests whether two moves are 'connected' in the sense
1911 // that the first move somehow made the second move possible (for instance
1912 // if the moving piece is the same in both moves). The first move is assumed
1913 // to be the move that was made to reach the current position, while the
1914 // second move is assumed to be a move from the current position.
1916 bool connected_moves(const Position& pos, Move m1, Move m2) {
1918 Square f1, t1, f2, t2;
1921 assert(move_is_ok(m1));
1922 assert(move_is_ok(m2));
1924 if (m2 == MOVE_NONE)
1927 // Case 1: The moving piece is the same in both moves
1933 // Case 2: The destination square for m2 was vacated by m1
1939 // Case 3: Moving through the vacated square
1940 if ( piece_is_slider(pos.piece_on(f2))
1941 && bit_is_set(squares_between(f2, t2), f1))
1944 // Case 4: The destination square for m2 is defended by the moving piece in m1
1945 p = pos.piece_on(t1);
1946 if (bit_is_set(pos.attacks_from(p, t1), t2))
1949 // Case 5: Discovered check, checking piece is the piece moved in m1
1950 if ( piece_is_slider(p)
1951 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1952 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1954 // discovered_check_candidates() works also if the Position's side to
1955 // move is the opposite of the checking piece.
1956 Color them = opposite_color(pos.side_to_move());
1957 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1959 if (bit_is_set(dcCandidates, f2))
1966 // value_is_mate() checks if the given value is a mate one
1967 // eventually compensated for the ply.
1969 bool value_is_mate(Value value) {
1971 assert(abs(value) <= VALUE_INFINITE);
1973 return value <= value_mated_in(PLY_MAX)
1974 || value >= value_mate_in(PLY_MAX);
1978 // move_is_killer() checks if the given move is among the
1979 // killer moves of that ply.
1981 bool move_is_killer(Move m, const SearchStack& ss) {
1983 const Move* k = ss.killers;
1984 for (int i = 0; i < KILLER_MAX; i++, k++)
1992 // extension() decides whether a move should be searched with normal depth,
1993 // or with extended depth. Certain classes of moves (checking moves, in
1994 // particular) are searched with bigger depth than ordinary moves and in
1995 // any case are marked as 'dangerous'. Note that also if a move is not
1996 // extended, as example because the corresponding UCI option is set to zero,
1997 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1998 template <NodeType PvNode>
1999 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
2000 bool singleEvasion, bool mateThreat, bool* dangerous) {
2002 assert(m != MOVE_NONE);
2004 Depth result = Depth(0);
2005 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2010 result += CheckExtension[PvNode];
2013 result += SingleEvasionExtension[PvNode];
2016 result += MateThreatExtension[PvNode];
2019 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2021 Color c = pos.side_to_move();
2022 if (relative_rank(c, move_to(m)) == RANK_7)
2024 result += PawnPushTo7thExtension[PvNode];
2027 if (pos.pawn_is_passed(c, move_to(m)))
2029 result += PassedPawnExtension[PvNode];
2034 if ( captureOrPromotion
2035 && pos.type_of_piece_on(move_to(m)) != PAWN
2036 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2037 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2038 && !move_is_promotion(m)
2041 result += PawnEndgameExtension[PvNode];
2046 && captureOrPromotion
2047 && pos.type_of_piece_on(move_to(m)) != PAWN
2048 && pos.see_sign(m) >= 0)
2054 return Min(result, OnePly);
2058 // ok_to_do_nullmove() looks at the current position and decides whether
2059 // doing a 'null move' should be allowed. In order to avoid zugzwang
2060 // problems, null moves are not allowed when the side to move has very
2061 // little material left. Currently, the test is a bit too simple: Null
2062 // moves are avoided only when the side to move has only pawns left.
2063 // It's probably a good idea to avoid null moves in at least some more
2064 // complicated endgames, e.g. KQ vs KR. FIXME
2066 bool ok_to_do_nullmove(const Position& pos) {
2068 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2072 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2073 // non-tactical moves late in the move list close to the leaves are
2074 // candidates for pruning.
2076 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2078 assert(move_is_ok(m));
2079 assert(threat == MOVE_NONE || move_is_ok(threat));
2080 assert(!pos.move_is_check(m));
2081 assert(!pos.move_is_capture_or_promotion(m));
2082 assert(!pos.move_is_passed_pawn_push(m));
2084 Square mfrom, mto, tfrom, tto;
2086 // Prune if there isn't any threat move
2087 if (threat == MOVE_NONE)
2090 mfrom = move_from(m);
2092 tfrom = move_from(threat);
2093 tto = move_to(threat);
2095 // Case 1: Don't prune moves which move the threatened piece
2099 // Case 2: If the threatened piece has value less than or equal to the
2100 // value of the threatening piece, don't prune move which defend it.
2101 if ( pos.move_is_capture(threat)
2102 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2103 || pos.type_of_piece_on(tfrom) == KING)
2104 && pos.move_attacks_square(m, tto))
2107 // Case 3: If the moving piece in the threatened move is a slider, don't
2108 // prune safe moves which block its ray.
2109 if ( piece_is_slider(pos.piece_on(tfrom))
2110 && bit_is_set(squares_between(tfrom, tto), mto)
2111 && pos.see_sign(m) >= 0)
2118 // ok_to_use_TT() returns true if a transposition table score
2119 // can be used at a given point in search.
2121 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2123 Value v = value_from_tt(tte->value(), ply);
2125 return ( tte->depth() >= depth
2126 || v >= Max(value_mate_in(PLY_MAX), beta)
2127 || v < Min(value_mated_in(PLY_MAX), beta))
2129 && ( (is_lower_bound(tte->type()) && v >= beta)
2130 || (is_upper_bound(tte->type()) && v < beta));
2134 // refine_eval() returns the transposition table score if
2135 // possible otherwise falls back on static position evaluation.
2137 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2142 Value v = value_from_tt(tte->value(), ply);
2144 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2145 || (is_upper_bound(tte->type()) && v < defaultEval))
2152 // update_history() registers a good move that produced a beta-cutoff
2153 // in history and marks as failures all the other moves of that ply.
2155 void update_history(const Position& pos, Move move, Depth depth,
2156 Move movesSearched[], int moveCount) {
2160 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2162 for (int i = 0; i < moveCount - 1; i++)
2164 m = movesSearched[i];
2168 if (!pos.move_is_capture_or_promotion(m))
2169 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2174 // update_killers() add a good move that produced a beta-cutoff
2175 // among the killer moves of that ply.
2177 void update_killers(Move m, SearchStack& ss) {
2179 if (m == ss.killers[0])
2182 for (int i = KILLER_MAX - 1; i > 0; i--)
2183 ss.killers[i] = ss.killers[i - 1];
2189 // update_gains() updates the gains table of a non-capture move given
2190 // the static position evaluation before and after the move.
2192 void update_gains(const Position& pos, Move m, Value before, Value after) {
2195 && before != VALUE_NONE
2196 && after != VALUE_NONE
2197 && pos.captured_piece() == NO_PIECE_TYPE
2198 && !move_is_castle(m)
2199 && !move_is_promotion(m))
2200 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2204 // current_search_time() returns the number of milliseconds which have passed
2205 // since the beginning of the current search.
2207 int current_search_time() {
2209 return get_system_time() - SearchStartTime;
2213 // nps() computes the current nodes/second count.
2217 int t = current_search_time();
2218 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2222 // poll() performs two different functions: It polls for user input, and it
2223 // looks at the time consumed so far and decides if it's time to abort the
2228 static int lastInfoTime;
2229 int t = current_search_time();
2234 // We are line oriented, don't read single chars
2235 std::string command;
2237 if (!std::getline(std::cin, command))
2240 if (command == "quit")
2243 PonderSearch = false;
2247 else if (command == "stop")
2250 PonderSearch = false;
2252 else if (command == "ponderhit")
2256 // Print search information
2260 else if (lastInfoTime > t)
2261 // HACK: Must be a new search where we searched less than
2262 // NodesBetweenPolls nodes during the first second of search.
2265 else if (t - lastInfoTime >= 1000)
2272 if (dbg_show_hit_rate)
2273 dbg_print_hit_rate();
2275 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2276 << " time " << t << " hashfull " << TT.full() << endl;
2279 // Should we stop the search?
2283 bool stillAtFirstMove = FirstRootMove
2284 && !AspirationFailLow
2285 && t > MaxSearchTime + ExtraSearchTime;
2287 bool noMoreTime = t > AbsoluteMaxSearchTime
2288 || stillAtFirstMove;
2290 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2291 || (ExactMaxTime && t >= ExactMaxTime)
2292 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2297 // ponderhit() is called when the program is pondering (i.e. thinking while
2298 // it's the opponent's turn to move) in order to let the engine know that
2299 // it correctly predicted the opponent's move.
2303 int t = current_search_time();
2304 PonderSearch = false;
2306 bool stillAtFirstMove = FirstRootMove
2307 && !AspirationFailLow
2308 && t > MaxSearchTime + ExtraSearchTime;
2310 bool noMoreTime = t > AbsoluteMaxSearchTime
2311 || stillAtFirstMove;
2313 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2318 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2320 void init_ss_array(SearchStack ss[]) {
2322 for (int i = 0; i < 3; i++)
2325 ss[i].initKillers();
2330 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2331 // while the program is pondering. The point is to work around a wrinkle in
2332 // the UCI protocol: When pondering, the engine is not allowed to give a
2333 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2334 // We simply wait here until one of these commands is sent, and return,
2335 // after which the bestmove and pondermove will be printed (in id_loop()).
2337 void wait_for_stop_or_ponderhit() {
2339 std::string command;
2343 if (!std::getline(std::cin, command))
2346 if (command == "quit")
2351 else if (command == "ponderhit" || command == "stop")
2357 // print_pv_info() prints to standard output and eventually to log file information on
2358 // the current PV line. It is called at each iteration or after a new pv is found.
2360 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2362 cout << "info depth " << Iteration
2363 << " score " << value_to_string(value)
2364 << ((value >= beta) ? " lowerbound" :
2365 ((value <= alpha)? " upperbound" : ""))
2366 << " time " << current_search_time()
2367 << " nodes " << TM.nodes_searched()
2371 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2372 cout << ss[0].pv[j] << " ";
2378 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2379 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2381 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2382 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2387 // init_thread() is the function which is called when a new thread is
2388 // launched. It simply calls the idle_loop() function with the supplied
2389 // threadID. There are two versions of this function; one for POSIX
2390 // threads and one for Windows threads.
2392 #if !defined(_MSC_VER)
2394 void* init_thread(void *threadID) {
2396 TM.idle_loop(*(int*)threadID, NULL);
2402 DWORD WINAPI init_thread(LPVOID threadID) {
2404 TM.idle_loop(*(int*)threadID, NULL);
2411 /// The ThreadsManager class
2413 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2414 // get_beta_counters() are getters/setters for the per thread
2415 // counters used to sort the moves at root.
2417 void ThreadsManager::resetNodeCounters() {
2419 for (int i = 0; i < MAX_THREADS; i++)
2420 threads[i].nodes = 0ULL;
2423 void ThreadsManager::resetBetaCounters() {
2425 for (int i = 0; i < MAX_THREADS; i++)
2426 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2429 int64_t ThreadsManager::nodes_searched() const {
2431 int64_t result = 0ULL;
2432 for (int i = 0; i < ActiveThreads; i++)
2433 result += threads[i].nodes;
2438 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2441 for (int i = 0; i < MAX_THREADS; i++)
2443 our += threads[i].betaCutOffs[us];
2444 their += threads[i].betaCutOffs[opposite_color(us)];
2449 // idle_loop() is where the threads are parked when they have no work to do.
2450 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2451 // object for which the current thread is the master.
2453 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2455 assert(threadID >= 0 && threadID < MAX_THREADS);
2459 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2460 // master should exit as last one.
2461 if (AllThreadsShouldExit)
2464 threads[threadID].state = THREAD_TERMINATED;
2468 // If we are not thinking, wait for a condition to be signaled
2469 // instead of wasting CPU time polling for work.
2470 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2473 assert(threadID != 0);
2474 threads[threadID].state = THREAD_SLEEPING;
2476 #if !defined(_MSC_VER)
2477 lock_grab(&WaitLock);
2478 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2479 pthread_cond_wait(&WaitCond, &WaitLock);
2480 lock_release(&WaitLock);
2482 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2486 // If thread has just woken up, mark it as available
2487 if (threads[threadID].state == THREAD_SLEEPING)
2488 threads[threadID].state = THREAD_AVAILABLE;
2490 // If this thread has been assigned work, launch a search
2491 if (threads[threadID].state == THREAD_WORKISWAITING)
2493 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2495 threads[threadID].state = THREAD_SEARCHING;
2497 if (threads[threadID].splitPoint->pvNode)
2498 sp_search_pv(threads[threadID].splitPoint, threadID);
2500 sp_search(threads[threadID].splitPoint, threadID);
2502 assert(threads[threadID].state == THREAD_SEARCHING);
2504 threads[threadID].state = THREAD_AVAILABLE;
2507 // If this thread is the master of a split point and all threads have
2508 // finished their work at this split point, return from the idle loop.
2509 if (sp && sp->cpus == 0)
2511 // Because sp->cpus is decremented under lock protection,
2512 // be sure sp->lock has been released before to proceed.
2513 lock_grab(&(sp->lock));
2514 lock_release(&(sp->lock));
2516 assert(threads[threadID].state == THREAD_AVAILABLE);
2518 threads[threadID].state = THREAD_SEARCHING;
2525 // init_threads() is called during startup. It launches all helper threads,
2526 // and initializes the split point stack and the global locks and condition
2529 void ThreadsManager::init_threads() {
2534 #if !defined(_MSC_VER)
2535 pthread_t pthread[1];
2538 // Initialize global locks
2539 lock_init(&MPLock, NULL);
2540 lock_init(&WaitLock, NULL);
2542 #if !defined(_MSC_VER)
2543 pthread_cond_init(&WaitCond, NULL);
2545 for (i = 0; i < MAX_THREADS; i++)
2546 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2549 // Initialize SplitPointStack locks
2550 for (i = 0; i < MAX_THREADS; i++)
2551 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2553 SplitPointStack[i][j].parent = NULL;
2554 lock_init(&(SplitPointStack[i][j].lock), NULL);
2557 // Will be set just before program exits to properly end the threads
2558 AllThreadsShouldExit = false;
2560 // Threads will be put to sleep as soon as created
2561 AllThreadsShouldSleep = true;
2563 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2565 threads[0].state = THREAD_SEARCHING;
2566 for (i = 1; i < MAX_THREADS; i++)
2567 threads[i].state = THREAD_AVAILABLE;
2569 // Launch the helper threads
2570 for (i = 1; i < MAX_THREADS; i++)
2573 #if !defined(_MSC_VER)
2574 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2576 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2581 cout << "Failed to create thread number " << i << endl;
2582 Application::exit_with_failure();
2585 // Wait until the thread has finished launching and is gone to sleep
2586 while (threads[i].state != THREAD_SLEEPING) {}
2591 // exit_threads() is called when the program exits. It makes all the
2592 // helper threads exit cleanly.
2594 void ThreadsManager::exit_threads() {
2596 ActiveThreads = MAX_THREADS; // HACK
2597 AllThreadsShouldSleep = true; // HACK
2598 wake_sleeping_threads();
2600 // This makes the threads to exit idle_loop()
2601 AllThreadsShouldExit = true;
2603 // Wait for thread termination
2604 for (int i = 1; i < MAX_THREADS; i++)
2605 while (threads[i].state != THREAD_TERMINATED);
2607 // Now we can safely destroy the locks
2608 for (int i = 0; i < MAX_THREADS; i++)
2609 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2610 lock_destroy(&(SplitPointStack[i][j].lock));
2612 lock_destroy(&WaitLock);
2613 lock_destroy(&MPLock);
2617 // thread_should_stop() checks whether the thread should stop its search.
2618 // This can happen if a beta cutoff has occurred in the thread's currently
2619 // active split point, or in some ancestor of the current split point.
2621 bool ThreadsManager::thread_should_stop(int threadID) const {
2623 assert(threadID >= 0 && threadID < ActiveThreads);
2627 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2632 // thread_is_available() checks whether the thread with threadID "slave" is
2633 // available to help the thread with threadID "master" at a split point. An
2634 // obvious requirement is that "slave" must be idle. With more than two
2635 // threads, this is not by itself sufficient: If "slave" is the master of
2636 // some active split point, it is only available as a slave to the other
2637 // threads which are busy searching the split point at the top of "slave"'s
2638 // split point stack (the "helpful master concept" in YBWC terminology).
2640 bool ThreadsManager::thread_is_available(int slave, int master) const {
2642 assert(slave >= 0 && slave < ActiveThreads);
2643 assert(master >= 0 && master < ActiveThreads);
2644 assert(ActiveThreads > 1);
2646 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2649 // Make a local copy to be sure doesn't change under our feet
2650 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2652 if (localActiveSplitPoints == 0)
2653 // No active split points means that the thread is available as
2654 // a slave for any other thread.
2657 if (ActiveThreads == 2)
2660 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2661 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2662 // could have been set to 0 by another thread leading to an out of bound access.
2663 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2670 // available_thread_exists() tries to find an idle thread which is available as
2671 // a slave for the thread with threadID "master".
2673 bool ThreadsManager::available_thread_exists(int master) const {
2675 assert(master >= 0 && master < ActiveThreads);
2676 assert(ActiveThreads > 1);
2678 for (int i = 0; i < ActiveThreads; i++)
2679 if (thread_is_available(i, master))
2686 // split() does the actual work of distributing the work at a node between
2687 // several threads at PV nodes. If it does not succeed in splitting the
2688 // node (because no idle threads are available, or because we have no unused
2689 // split point objects), the function immediately returns false. If
2690 // splitting is possible, a SplitPoint object is initialized with all the
2691 // data that must be copied to the helper threads (the current position and
2692 // search stack, alpha, beta, the search depth, etc.), and we tell our
2693 // helper threads that they have been assigned work. This will cause them
2694 // to instantly leave their idle loops and call sp_search_pv(). When all
2695 // threads have returned from sp_search_pv (or, equivalently, when
2696 // splitPoint->cpus becomes 0), split() returns true.
2698 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2699 Value* alpha, const Value beta, Value* bestValue,
2700 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2703 assert(sstck != NULL);
2704 assert(ply >= 0 && ply < PLY_MAX);
2705 assert(*bestValue >= -VALUE_INFINITE);
2706 assert( ( pvNode && *bestValue <= *alpha)
2707 || (!pvNode && *bestValue < beta ));
2708 assert(!pvNode || *alpha < beta);
2709 assert(beta <= VALUE_INFINITE);
2710 assert(depth > Depth(0));
2711 assert(master >= 0 && master < ActiveThreads);
2712 assert(ActiveThreads > 1);
2714 SplitPoint* splitPoint;
2718 // If no other thread is available to help us, or if we have too many
2719 // active split points, don't split.
2720 if ( !available_thread_exists(master)
2721 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2723 lock_release(&MPLock);
2727 // Pick the next available split point object from the split point stack
2728 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2730 // Initialize the split point object
2731 splitPoint->parent = threads[master].splitPoint;
2732 splitPoint->stopRequest = false;
2733 splitPoint->ply = ply;
2734 splitPoint->depth = depth;
2735 splitPoint->mateThreat = mateThreat;
2736 splitPoint->alpha = *alpha;
2737 splitPoint->beta = beta;
2738 splitPoint->pvNode = pvNode;
2739 splitPoint->bestValue = *bestValue;
2740 splitPoint->master = master;
2741 splitPoint->mp = mp;
2742 splitPoint->moves = *moves;
2743 splitPoint->cpus = 1;
2744 splitPoint->pos = &p;
2745 splitPoint->parentSstack = sstck;
2746 for (int i = 0; i < ActiveThreads; i++)
2747 splitPoint->slaves[i] = 0;
2749 threads[master].splitPoint = splitPoint;
2750 threads[master].activeSplitPoints++;
2752 // If we are here it means we are not available
2753 assert(threads[master].state != THREAD_AVAILABLE);
2755 // Allocate available threads setting state to THREAD_BOOKED
2756 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2757 if (thread_is_available(i, master))
2759 threads[i].state = THREAD_BOOKED;
2760 threads[i].splitPoint = splitPoint;
2761 splitPoint->slaves[i] = 1;
2765 assert(splitPoint->cpus > 1);
2767 // We can release the lock because slave threads are already booked and master is not available
2768 lock_release(&MPLock);
2770 // Tell the threads that they have work to do. This will make them leave
2771 // their idle loop. But before copy search stack tail for each thread.
2772 for (int i = 0; i < ActiveThreads; i++)
2773 if (i == master || splitPoint->slaves[i])
2775 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2777 assert(i == master || threads[i].state == THREAD_BOOKED);
2779 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2782 // Everything is set up. The master thread enters the idle loop, from
2783 // which it will instantly launch a search, because its state is
2784 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2785 // idle loop, which means that the main thread will return from the idle
2786 // loop when all threads have finished their work at this split point
2787 // (i.e. when splitPoint->cpus == 0).
2788 idle_loop(master, splitPoint);
2790 // We have returned from the idle loop, which means that all threads are
2791 // finished. Update alpha and bestValue, and return.
2794 *alpha = splitPoint->alpha;
2795 *bestValue = splitPoint->bestValue;
2796 threads[master].activeSplitPoints--;
2797 threads[master].splitPoint = splitPoint->parent;
2799 lock_release(&MPLock);
2804 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2805 // to start a new search from the root.
2807 void ThreadsManager::wake_sleeping_threads() {
2809 assert(AllThreadsShouldSleep);
2810 assert(ActiveThreads > 0);
2812 AllThreadsShouldSleep = false;
2814 if (ActiveThreads == 1)
2817 #if !defined(_MSC_VER)
2818 pthread_mutex_lock(&WaitLock);
2819 pthread_cond_broadcast(&WaitCond);
2820 pthread_mutex_unlock(&WaitLock);
2822 for (int i = 1; i < MAX_THREADS; i++)
2823 SetEvent(SitIdleEvent[i]);
2829 // put_threads_to_sleep() makes all the threads go to sleep just before
2830 // to leave think(), at the end of the search. Threads should have already
2831 // finished the job and should be idle.
2833 void ThreadsManager::put_threads_to_sleep() {
2835 assert(!AllThreadsShouldSleep);
2837 // This makes the threads to go to sleep
2838 AllThreadsShouldSleep = true;
2841 /// The RootMoveList class
2843 // RootMoveList c'tor
2845 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2847 SearchStack ss[PLY_MAX_PLUS_2];
2848 MoveStack mlist[MaxRootMoves];
2850 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2852 // Generate all legal moves
2853 MoveStack* last = generate_moves(pos, mlist);
2855 // Add each move to the moves[] array
2856 for (MoveStack* cur = mlist; cur != last; cur++)
2858 bool includeMove = includeAllMoves;
2860 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2861 includeMove = (searchMoves[k] == cur->move);
2866 // Find a quick score for the move
2868 pos.do_move(cur->move, st);
2869 moves[count].move = cur->move;
2870 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2871 moves[count].pv[0] = cur->move;
2872 moves[count].pv[1] = MOVE_NONE;
2873 pos.undo_move(cur->move);
2880 // RootMoveList simple methods definitions
2882 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2884 moves[moveNum].nodes = nodes;
2885 moves[moveNum].cumulativeNodes += nodes;
2888 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2890 moves[moveNum].ourBeta = our;
2891 moves[moveNum].theirBeta = their;
2894 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2898 for (j = 0; pv[j] != MOVE_NONE; j++)
2899 moves[moveNum].pv[j] = pv[j];
2901 moves[moveNum].pv[j] = MOVE_NONE;
2905 // RootMoveList::sort() sorts the root move list at the beginning of a new
2908 void RootMoveList::sort() {
2910 sort_multipv(count - 1); // Sort all items
2914 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2915 // list by their scores and depths. It is used to order the different PVs
2916 // correctly in MultiPV mode.
2918 void RootMoveList::sort_multipv(int n) {
2922 for (i = 1; i <= n; i++)
2924 RootMove rm = moves[i];
2925 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2926 moves[j] = moves[j - 1];