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,
1029 Depth depth, 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 (!PvNode && 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 excValue = search<NonPV>(pos, ss, ttValue - SingularExtensionMargin - 1, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1252 if (excValue < ttValue - SingularExtensionMargin)
1257 newDepth = depth - OnePly + ext;
1259 // Update current move (this must be done after singular extension search)
1260 movesSearched[moveCount++] = ss[ply].currentMove = move;
1262 // Step 12. Futility pruning (is omitted in PV nodes)
1266 && !captureOrPromotion
1267 && !move_is_castle(move)
1270 // Move count based pruning
1271 if ( moveCount >= futility_move_count(depth)
1272 && ok_to_prune(pos, move, ss[ply].threatMove)
1273 && bestValue > value_mated_in(PLY_MAX))
1276 // Value based pruning
1277 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1278 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1279 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1281 if (futilityValueScaled < beta)
1283 if (futilityValueScaled > bestValue)
1284 bestValue = futilityValueScaled;
1289 // Step 13. Make the move
1290 pos.do_move(move, st, ci, moveIsCheck);
1292 // Step extra. pv search (only in PV nodes)
1293 // The first move in list is the expected PV
1294 if (PvNode && moveCount == 1)
1295 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1298 // Step 14. Reduced search
1299 // if the move fails high will be re-searched at full depth.
1300 bool doFullDepthSearch = true;
1302 if ( depth >= 3 * OnePly
1304 && !captureOrPromotion
1305 && !move_is_castle(move)
1306 && !move_is_killer(move, ss[ply]))
1308 ss[ply].reduction = reduction<PvNode>(depth, moveCount);
1309 if (ss[ply].reduction)
1311 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1312 doFullDepthSearch = (value > alpha);
1316 // Step 15. Full depth search
1317 if (doFullDepthSearch)
1319 ss[ply].reduction = Depth(0);
1320 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, ply+1, true, threadID);
1322 // Step extra. pv search (only in PV nodes)
1323 if (PvNode && value > alpha && value < beta)
1324 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1328 // Step 16. Undo move
1329 pos.undo_move(move);
1331 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1333 // Step 17. Check for new best move
1334 if (value > bestValue)
1341 if (value == value_mate_in(ply + 1))
1342 ss[ply].mateKiller = move;
1346 // Step 18. Check for split
1347 if ( TM.active_threads() > 1
1349 && depth >= MinimumSplitDepth
1351 && TM.available_thread_exists(threadID)
1353 && !TM.thread_should_stop(threadID)
1354 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1355 depth, mateThreat, &moveCount, &mp, threadID, PvNode))
1359 // Step 19. Check for mate and stalemate
1360 // All legal moves have been searched and if there are
1361 // no legal moves, it must be mate or stalemate.
1362 // If one move was excluded return fail low score.
1364 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1366 // Step 20. Update tables
1367 // If the search is not aborted, update the transposition table,
1368 // history counters, and killer moves.
1369 if (AbortSearch || TM.thread_should_stop(threadID))
1372 if (bestValue <= oldAlpha)
1373 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1375 else if (bestValue >= beta)
1377 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1378 move = ss[ply].pv[ply];
1379 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1380 if (!pos.move_is_capture_or_promotion(move))
1382 update_history(pos, move, depth, movesSearched, moveCount);
1383 update_killers(move, ss[ply]);
1387 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1389 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1395 // qsearch() is the quiescence search function, which is called by the main
1396 // search function when the remaining depth is zero (or, to be more precise,
1397 // less than OnePly).
1399 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1400 Depth depth, int ply, int threadID) {
1402 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1403 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1405 assert(ply >= 0 && ply < PLY_MAX);
1406 assert(threadID >= 0 && threadID < TM.active_threads());
1411 Value staticValue, bestValue, value, futilityBase, futilityValue;
1412 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1413 const TTEntry* tte = NULL;
1415 bool pvNode = (beta - alpha != 1);
1416 Value oldAlpha = alpha;
1418 // Initialize, and make an early exit in case of an aborted search,
1419 // an instant draw, maximum ply reached, etc.
1420 init_node(ss, ply, threadID);
1422 // After init_node() that calls poll()
1423 if (AbortSearch || TM.thread_should_stop(threadID))
1426 if (pos.is_draw() || ply >= PLY_MAX - 1)
1429 // Transposition table lookup. At PV nodes, we don't use the TT for
1430 // pruning, but only for move ordering.
1431 tte = TT.retrieve(pos.get_key());
1432 ttMove = (tte ? tte->move() : MOVE_NONE);
1434 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1436 assert(tte->type() != VALUE_TYPE_EVAL);
1438 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1439 return value_from_tt(tte->value(), ply);
1442 isCheck = pos.is_check();
1444 // Evaluate the position statically
1446 staticValue = -VALUE_INFINITE;
1447 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1448 staticValue = value_from_tt(tte->value(), ply);
1450 staticValue = evaluate(pos, ei, threadID);
1454 ss[ply].eval = staticValue;
1455 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1458 // Initialize "stand pat score", and return it immediately if it is
1460 bestValue = staticValue;
1462 if (bestValue >= beta)
1464 // Store the score to avoid a future costly evaluation() call
1465 if (!isCheck && !tte && ei.kingDanger[pos.side_to_move()] == 0)
1466 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1471 if (bestValue > alpha)
1474 // If we are near beta then try to get a cutoff pushing checks a bit further
1475 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1477 // Initialize a MovePicker object for the current position, and prepare
1478 // to search the moves. Because the depth is <= 0 here, only captures,
1479 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1480 // and we are near beta) will be generated.
1481 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1483 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1484 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1486 // Loop through the moves until no moves remain or a beta cutoff occurs
1487 while ( alpha < beta
1488 && (move = mp.get_next_move()) != MOVE_NONE)
1490 assert(move_is_ok(move));
1492 moveIsCheck = pos.move_is_check(move, ci);
1494 // Update current move
1496 ss[ply].currentMove = move;
1504 && !move_is_promotion(move)
1505 && !pos.move_is_passed_pawn_push(move))
1507 futilityValue = futilityBase
1508 + pos.endgame_value_of_piece_on(move_to(move))
1509 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1511 if (futilityValue < alpha)
1513 if (futilityValue > bestValue)
1514 bestValue = futilityValue;
1519 // Detect blocking evasions that are candidate to be pruned
1520 evasionPrunable = isCheck
1521 && bestValue > value_mated_in(PLY_MAX)
1522 && !pos.move_is_capture(move)
1523 && pos.type_of_piece_on(move_from(move)) != KING
1524 && !pos.can_castle(pos.side_to_move());
1526 // Don't search moves with negative SEE values
1527 if ( (!isCheck || evasionPrunable)
1530 && !move_is_promotion(move)
1531 && pos.see_sign(move) < 0)
1534 // Make and search the move
1535 pos.do_move(move, st, ci, moveIsCheck);
1536 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1537 pos.undo_move(move);
1539 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1542 if (value > bestValue)
1553 // All legal moves have been searched. A special case: If we're in check
1554 // and no legal moves were found, it is checkmate.
1555 if (!moveCount && isCheck) // Mate!
1556 return value_mated_in(ply);
1558 // Update transposition table
1559 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1560 if (bestValue <= oldAlpha)
1562 // If bestValue isn't changed it means it is still the static evaluation
1563 // of the node, so keep this info to avoid a future evaluation() call.
1564 ValueType type = (bestValue == staticValue && !ei.kingDanger[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1565 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1567 else if (bestValue >= beta)
1569 move = ss[ply].pv[ply];
1570 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1572 // Update killers only for good checking moves
1573 if (!pos.move_is_capture_or_promotion(move))
1574 update_killers(move, ss[ply]);
1577 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1579 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1585 // sp_search() is used to search from a split point. This function is called
1586 // by each thread working at the split point. It is similar to the normal
1587 // search() function, but simpler. Because we have already probed the hash
1588 // table, done a null move search, and searched the first move before
1589 // splitting, we don't have to repeat all this work in sp_search(). We
1590 // also don't need to store anything to the hash table here: This is taken
1591 // care of after we return from the split point.
1593 void sp_search(SplitPoint* sp, int threadID) {
1595 assert(threadID >= 0 && threadID < TM.active_threads());
1596 assert(TM.active_threads() > 1);
1600 Depth ext, newDepth;
1601 Value value, futilityValueScaled;
1602 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1604 value = -VALUE_INFINITE;
1606 Position pos(*sp->pos);
1608 SearchStack* ss = sp->sstack[threadID];
1609 isCheck = pos.is_check();
1611 // Step 10. Loop through moves
1612 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1613 lock_grab(&(sp->lock));
1615 while ( sp->bestValue < sp->beta
1616 && !TM.thread_should_stop(threadID)
1617 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1619 moveCount = ++sp->moves;
1620 lock_release(&(sp->lock));
1622 assert(move_is_ok(move));
1624 moveIsCheck = pos.move_is_check(move, ci);
1625 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1627 // Step 11. Decide the new search depth
1628 ext = extension<NonPV>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1629 newDepth = sp->depth - OnePly + ext;
1631 // Update current move
1632 ss[sp->ply].currentMove = move;
1634 // Step 12. Futility pruning
1637 && !captureOrPromotion
1638 && !move_is_castle(move))
1640 // Move count based pruning
1641 if ( moveCount >= futility_move_count(sp->depth)
1642 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1643 && sp->bestValue > value_mated_in(PLY_MAX))
1645 lock_grab(&(sp->lock));
1649 // Value based pruning
1650 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1651 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1652 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1654 if (futilityValueScaled < sp->beta)
1656 lock_grab(&(sp->lock));
1658 if (futilityValueScaled > sp->bestValue)
1659 sp->bestValue = futilityValueScaled;
1664 // Step 13. Make the move
1665 pos.do_move(move, st, ci, moveIsCheck);
1667 // Step 14. Reduced search
1668 // if the move fails high will be re-searched at full depth.
1669 bool doFullDepthSearch = true;
1672 && !captureOrPromotion
1673 && !move_is_castle(move)
1674 && !move_is_killer(move, ss[sp->ply]))
1676 ss[sp->ply].reduction = reduction<NonPV>(sp->depth, moveCount);
1677 if (ss[sp->ply].reduction)
1679 value = -search<NonPV>(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1680 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1684 // Step 15. Full depth search
1685 if (doFullDepthSearch)
1687 ss[sp->ply].reduction = Depth(0);
1688 value = -search<NonPV>(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth, sp->ply+1, true, threadID);
1691 // Step 16. Undo move
1692 pos.undo_move(move);
1694 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1696 // Step 17. Check for new best move
1697 lock_grab(&(sp->lock));
1699 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1701 sp->bestValue = value;
1702 if (sp->bestValue >= sp->beta)
1704 sp->stopRequest = true;
1705 sp_update_pv(sp->parentSstack, ss, sp->ply);
1710 /* Here we have the lock still grabbed */
1712 sp->slaves[threadID] = 0;
1715 lock_release(&(sp->lock));
1719 // sp_search_pv() is used to search from a PV split point. This function
1720 // is called by each thread working at the split point. It is similar to
1721 // the normal search_pv() function, but simpler. Because we have already
1722 // probed the hash table and searched the first move before splitting, we
1723 // don't have to repeat all this work in sp_search_pv(). We also don't
1724 // need to store anything to the hash table here: This is taken care of
1725 // after we return from the split point.
1727 void sp_search_pv(SplitPoint* sp, int threadID) {
1729 assert(threadID >= 0 && threadID < TM.active_threads());
1730 assert(TM.active_threads() > 1);
1734 Depth ext, newDepth;
1736 bool moveIsCheck, captureOrPromotion, dangerous;
1738 value = -VALUE_INFINITE;
1740 Position pos(*sp->pos);
1742 SearchStack* ss = sp->sstack[threadID];
1744 // Step 10. Loop through moves
1745 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1746 lock_grab(&(sp->lock));
1748 while ( sp->alpha < sp->beta
1749 && !TM.thread_should_stop(threadID)
1750 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1752 moveCount = ++sp->moves;
1753 lock_release(&(sp->lock));
1755 assert(move_is_ok(move));
1757 moveIsCheck = pos.move_is_check(move, ci);
1758 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1760 // Step 11. Decide the new search depth
1761 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1762 newDepth = sp->depth - OnePly + ext;
1764 // Update current move
1765 ss[sp->ply].currentMove = move;
1767 // Step 12. Futility pruning (is omitted in PV nodes)
1769 // Step 13. Make the move
1770 pos.do_move(move, st, ci, moveIsCheck);
1772 // Step 14. Reduced search
1773 // if the move fails high will be re-searched at full depth.
1774 bool doFullDepthSearch = true;
1777 && !captureOrPromotion
1778 && !move_is_castle(move)
1779 && !move_is_killer(move, ss[sp->ply]))
1781 ss[sp->ply].reduction = reduction<PV>(sp->depth, moveCount);
1782 if (ss[sp->ply].reduction)
1784 Value localAlpha = sp->alpha;
1785 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1786 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1790 // Step 15. Full depth search
1791 if (doFullDepthSearch)
1793 Value localAlpha = sp->alpha;
1794 ss[sp->ply].reduction = Depth(0);
1795 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1, true, threadID);
1797 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1799 // If another thread has failed high then sp->alpha has been increased
1800 // to be higher or equal then beta, if so, avoid to start a PV search.
1801 localAlpha = sp->alpha;
1802 if (localAlpha < sp->beta)
1803 value = -search<PV>(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, false, threadID);
1807 // Step 16. Undo move
1808 pos.undo_move(move);
1810 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1812 // Step 17. Check for new best move
1813 lock_grab(&(sp->lock));
1815 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1817 sp->bestValue = value;
1818 if (value > sp->alpha)
1820 // Ask threads to stop before to modify sp->alpha
1821 if (value >= sp->beta)
1822 sp->stopRequest = true;
1826 sp_update_pv(sp->parentSstack, ss, sp->ply);
1827 if (value == value_mate_in(sp->ply + 1))
1828 ss[sp->ply].mateKiller = move;
1833 /* Here we have the lock still grabbed */
1835 sp->slaves[threadID] = 0;
1838 lock_release(&(sp->lock));
1842 // init_node() is called at the beginning of all the search functions
1843 // (search() qsearch(), and so on) and initializes the
1844 // search stack object corresponding to the current node. Once every
1845 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1846 // for user input and checks whether it is time to stop the search.
1848 void init_node(SearchStack ss[], int ply, int threadID) {
1850 assert(ply >= 0 && ply < PLY_MAX);
1851 assert(threadID >= 0 && threadID < TM.active_threads());
1853 TM.incrementNodeCounter(threadID);
1858 if (NodesSincePoll >= NodesBetweenPolls)
1865 ss[ply + 2].initKillers();
1869 // update_pv() is called whenever a search returns a value > alpha.
1870 // It updates the PV in the SearchStack object corresponding to the
1873 void update_pv(SearchStack ss[], int ply) {
1875 assert(ply >= 0 && ply < PLY_MAX);
1879 ss[ply].pv[ply] = ss[ply].currentMove;
1881 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1882 ss[ply].pv[p] = ss[ply + 1].pv[p];
1884 ss[ply].pv[p] = MOVE_NONE;
1888 // sp_update_pv() is a variant of update_pv for use at split points. The
1889 // difference between the two functions is that sp_update_pv also updates
1890 // the PV at the parent node.
1892 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
1894 assert(ply >= 0 && ply < PLY_MAX);
1898 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
1900 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1901 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
1903 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
1907 // connected_moves() tests whether two moves are 'connected' in the sense
1908 // that the first move somehow made the second move possible (for instance
1909 // if the moving piece is the same in both moves). The first move is assumed
1910 // to be the move that was made to reach the current position, while the
1911 // second move is assumed to be a move from the current position.
1913 bool connected_moves(const Position& pos, Move m1, Move m2) {
1915 Square f1, t1, f2, t2;
1918 assert(move_is_ok(m1));
1919 assert(move_is_ok(m2));
1921 if (m2 == MOVE_NONE)
1924 // Case 1: The moving piece is the same in both moves
1930 // Case 2: The destination square for m2 was vacated by m1
1936 // Case 3: Moving through the vacated square
1937 if ( piece_is_slider(pos.piece_on(f2))
1938 && bit_is_set(squares_between(f2, t2), f1))
1941 // Case 4: The destination square for m2 is defended by the moving piece in m1
1942 p = pos.piece_on(t1);
1943 if (bit_is_set(pos.attacks_from(p, t1), t2))
1946 // Case 5: Discovered check, checking piece is the piece moved in m1
1947 if ( piece_is_slider(p)
1948 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1949 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1951 // discovered_check_candidates() works also if the Position's side to
1952 // move is the opposite of the checking piece.
1953 Color them = opposite_color(pos.side_to_move());
1954 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1956 if (bit_is_set(dcCandidates, f2))
1963 // value_is_mate() checks if the given value is a mate one
1964 // eventually compensated for the ply.
1966 bool value_is_mate(Value value) {
1968 assert(abs(value) <= VALUE_INFINITE);
1970 return value <= value_mated_in(PLY_MAX)
1971 || value >= value_mate_in(PLY_MAX);
1975 // move_is_killer() checks if the given move is among the
1976 // killer moves of that ply.
1978 bool move_is_killer(Move m, const SearchStack& ss) {
1980 const Move* k = ss.killers;
1981 for (int i = 0; i < KILLER_MAX; i++, k++)
1989 // extension() decides whether a move should be searched with normal depth,
1990 // or with extended depth. Certain classes of moves (checking moves, in
1991 // particular) are searched with bigger depth than ordinary moves and in
1992 // any case are marked as 'dangerous'. Note that also if a move is not
1993 // extended, as example because the corresponding UCI option is set to zero,
1994 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1995 template <NodeType PvNode>
1996 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1997 bool singleEvasion, bool mateThreat, bool* dangerous) {
1999 assert(m != MOVE_NONE);
2001 Depth result = Depth(0);
2002 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2007 result += CheckExtension[PvNode];
2010 result += SingleEvasionExtension[PvNode];
2013 result += MateThreatExtension[PvNode];
2016 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2018 Color c = pos.side_to_move();
2019 if (relative_rank(c, move_to(m)) == RANK_7)
2021 result += PawnPushTo7thExtension[PvNode];
2024 if (pos.pawn_is_passed(c, move_to(m)))
2026 result += PassedPawnExtension[PvNode];
2031 if ( captureOrPromotion
2032 && pos.type_of_piece_on(move_to(m)) != PAWN
2033 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2034 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2035 && !move_is_promotion(m)
2038 result += PawnEndgameExtension[PvNode];
2043 && captureOrPromotion
2044 && pos.type_of_piece_on(move_to(m)) != PAWN
2045 && pos.see_sign(m) >= 0)
2051 return Min(result, OnePly);
2055 // ok_to_do_nullmove() looks at the current position and decides whether
2056 // doing a 'null move' should be allowed. In order to avoid zugzwang
2057 // problems, null moves are not allowed when the side to move has very
2058 // little material left. Currently, the test is a bit too simple: Null
2059 // moves are avoided only when the side to move has only pawns left.
2060 // It's probably a good idea to avoid null moves in at least some more
2061 // complicated endgames, e.g. KQ vs KR. FIXME
2063 bool ok_to_do_nullmove(const Position& pos) {
2065 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2069 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2070 // non-tactical moves late in the move list close to the leaves are
2071 // candidates for pruning.
2073 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2075 assert(move_is_ok(m));
2076 assert(threat == MOVE_NONE || move_is_ok(threat));
2077 assert(!pos.move_is_check(m));
2078 assert(!pos.move_is_capture_or_promotion(m));
2079 assert(!pos.move_is_passed_pawn_push(m));
2081 Square mfrom, mto, tfrom, tto;
2083 // Prune if there isn't any threat move
2084 if (threat == MOVE_NONE)
2087 mfrom = move_from(m);
2089 tfrom = move_from(threat);
2090 tto = move_to(threat);
2092 // Case 1: Don't prune moves which move the threatened piece
2096 // Case 2: If the threatened piece has value less than or equal to the
2097 // value of the threatening piece, don't prune move which defend it.
2098 if ( pos.move_is_capture(threat)
2099 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2100 || pos.type_of_piece_on(tfrom) == KING)
2101 && pos.move_attacks_square(m, tto))
2104 // Case 3: If the moving piece in the threatened move is a slider, don't
2105 // prune safe moves which block its ray.
2106 if ( piece_is_slider(pos.piece_on(tfrom))
2107 && bit_is_set(squares_between(tfrom, tto), mto)
2108 && pos.see_sign(m) >= 0)
2115 // ok_to_use_TT() returns true if a transposition table score
2116 // can be used at a given point in search.
2118 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2120 Value v = value_from_tt(tte->value(), ply);
2122 return ( tte->depth() >= depth
2123 || v >= Max(value_mate_in(PLY_MAX), beta)
2124 || v < Min(value_mated_in(PLY_MAX), beta))
2126 && ( (is_lower_bound(tte->type()) && v >= beta)
2127 || (is_upper_bound(tte->type()) && v < beta));
2131 // refine_eval() returns the transposition table score if
2132 // possible otherwise falls back on static position evaluation.
2134 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2139 Value v = value_from_tt(tte->value(), ply);
2141 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2142 || (is_upper_bound(tte->type()) && v < defaultEval))
2149 // update_history() registers a good move that produced a beta-cutoff
2150 // in history and marks as failures all the other moves of that ply.
2152 void update_history(const Position& pos, Move move, Depth depth,
2153 Move movesSearched[], int moveCount) {
2157 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2159 for (int i = 0; i < moveCount - 1; i++)
2161 m = movesSearched[i];
2165 if (!pos.move_is_capture_or_promotion(m))
2166 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2171 // update_killers() add a good move that produced a beta-cutoff
2172 // among the killer moves of that ply.
2174 void update_killers(Move m, SearchStack& ss) {
2176 if (m == ss.killers[0])
2179 for (int i = KILLER_MAX - 1; i > 0; i--)
2180 ss.killers[i] = ss.killers[i - 1];
2186 // update_gains() updates the gains table of a non-capture move given
2187 // the static position evaluation before and after the move.
2189 void update_gains(const Position& pos, Move m, Value before, Value after) {
2192 && before != VALUE_NONE
2193 && after != VALUE_NONE
2194 && pos.captured_piece() == NO_PIECE_TYPE
2195 && !move_is_castle(m)
2196 && !move_is_promotion(m))
2197 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2201 // current_search_time() returns the number of milliseconds which have passed
2202 // since the beginning of the current search.
2204 int current_search_time() {
2206 return get_system_time() - SearchStartTime;
2210 // nps() computes the current nodes/second count.
2214 int t = current_search_time();
2215 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2219 // poll() performs two different functions: It polls for user input, and it
2220 // looks at the time consumed so far and decides if it's time to abort the
2225 static int lastInfoTime;
2226 int t = current_search_time();
2231 // We are line oriented, don't read single chars
2232 std::string command;
2234 if (!std::getline(std::cin, command))
2237 if (command == "quit")
2240 PonderSearch = false;
2244 else if (command == "stop")
2247 PonderSearch = false;
2249 else if (command == "ponderhit")
2253 // Print search information
2257 else if (lastInfoTime > t)
2258 // HACK: Must be a new search where we searched less than
2259 // NodesBetweenPolls nodes during the first second of search.
2262 else if (t - lastInfoTime >= 1000)
2269 if (dbg_show_hit_rate)
2270 dbg_print_hit_rate();
2272 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2273 << " time " << t << " hashfull " << TT.full() << endl;
2276 // Should we stop the search?
2280 bool stillAtFirstMove = FirstRootMove
2281 && !AspirationFailLow
2282 && t > MaxSearchTime + ExtraSearchTime;
2284 bool noMoreTime = t > AbsoluteMaxSearchTime
2285 || stillAtFirstMove;
2287 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2288 || (ExactMaxTime && t >= ExactMaxTime)
2289 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2294 // ponderhit() is called when the program is pondering (i.e. thinking while
2295 // it's the opponent's turn to move) in order to let the engine know that
2296 // it correctly predicted the opponent's move.
2300 int t = current_search_time();
2301 PonderSearch = false;
2303 bool stillAtFirstMove = FirstRootMove
2304 && !AspirationFailLow
2305 && t > MaxSearchTime + ExtraSearchTime;
2307 bool noMoreTime = t > AbsoluteMaxSearchTime
2308 || stillAtFirstMove;
2310 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2315 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2317 void init_ss_array(SearchStack ss[]) {
2319 for (int i = 0; i < 3; i++)
2322 ss[i].initKillers();
2327 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2328 // while the program is pondering. The point is to work around a wrinkle in
2329 // the UCI protocol: When pondering, the engine is not allowed to give a
2330 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2331 // We simply wait here until one of these commands is sent, and return,
2332 // after which the bestmove and pondermove will be printed (in id_loop()).
2334 void wait_for_stop_or_ponderhit() {
2336 std::string command;
2340 if (!std::getline(std::cin, command))
2343 if (command == "quit")
2348 else if (command == "ponderhit" || command == "stop")
2354 // print_pv_info() prints to standard output and eventually to log file information on
2355 // the current PV line. It is called at each iteration or after a new pv is found.
2357 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2359 cout << "info depth " << Iteration
2360 << " score " << value_to_string(value)
2361 << ((value >= beta) ? " lowerbound" :
2362 ((value <= alpha)? " upperbound" : ""))
2363 << " time " << current_search_time()
2364 << " nodes " << TM.nodes_searched()
2368 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2369 cout << ss[0].pv[j] << " ";
2375 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2376 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2378 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2379 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2384 // init_thread() is the function which is called when a new thread is
2385 // launched. It simply calls the idle_loop() function with the supplied
2386 // threadID. There are two versions of this function; one for POSIX
2387 // threads and one for Windows threads.
2389 #if !defined(_MSC_VER)
2391 void* init_thread(void *threadID) {
2393 TM.idle_loop(*(int*)threadID, NULL);
2399 DWORD WINAPI init_thread(LPVOID threadID) {
2401 TM.idle_loop(*(int*)threadID, NULL);
2408 /// The ThreadsManager class
2410 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2411 // get_beta_counters() are getters/setters for the per thread
2412 // counters used to sort the moves at root.
2414 void ThreadsManager::resetNodeCounters() {
2416 for (int i = 0; i < MAX_THREADS; i++)
2417 threads[i].nodes = 0ULL;
2420 void ThreadsManager::resetBetaCounters() {
2422 for (int i = 0; i < MAX_THREADS; i++)
2423 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2426 int64_t ThreadsManager::nodes_searched() const {
2428 int64_t result = 0ULL;
2429 for (int i = 0; i < ActiveThreads; i++)
2430 result += threads[i].nodes;
2435 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2438 for (int i = 0; i < MAX_THREADS; i++)
2440 our += threads[i].betaCutOffs[us];
2441 their += threads[i].betaCutOffs[opposite_color(us)];
2446 // idle_loop() is where the threads are parked when they have no work to do.
2447 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2448 // object for which the current thread is the master.
2450 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2452 assert(threadID >= 0 && threadID < MAX_THREADS);
2456 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2457 // master should exit as last one.
2458 if (AllThreadsShouldExit)
2461 threads[threadID].state = THREAD_TERMINATED;
2465 // If we are not thinking, wait for a condition to be signaled
2466 // instead of wasting CPU time polling for work.
2467 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2470 assert(threadID != 0);
2471 threads[threadID].state = THREAD_SLEEPING;
2473 #if !defined(_MSC_VER)
2474 lock_grab(&WaitLock);
2475 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2476 pthread_cond_wait(&WaitCond, &WaitLock);
2477 lock_release(&WaitLock);
2479 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2483 // If thread has just woken up, mark it as available
2484 if (threads[threadID].state == THREAD_SLEEPING)
2485 threads[threadID].state = THREAD_AVAILABLE;
2487 // If this thread has been assigned work, launch a search
2488 if (threads[threadID].state == THREAD_WORKISWAITING)
2490 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2492 threads[threadID].state = THREAD_SEARCHING;
2494 if (threads[threadID].splitPoint->pvNode)
2495 sp_search_pv(threads[threadID].splitPoint, threadID);
2497 sp_search(threads[threadID].splitPoint, threadID);
2499 assert(threads[threadID].state == THREAD_SEARCHING);
2501 threads[threadID].state = THREAD_AVAILABLE;
2504 // If this thread is the master of a split point and all threads have
2505 // finished their work at this split point, return from the idle loop.
2506 if (sp && sp->cpus == 0)
2508 // Because sp->cpus is decremented under lock protection,
2509 // be sure sp->lock has been released before to proceed.
2510 lock_grab(&(sp->lock));
2511 lock_release(&(sp->lock));
2513 assert(threads[threadID].state == THREAD_AVAILABLE);
2515 threads[threadID].state = THREAD_SEARCHING;
2522 // init_threads() is called during startup. It launches all helper threads,
2523 // and initializes the split point stack and the global locks and condition
2526 void ThreadsManager::init_threads() {
2531 #if !defined(_MSC_VER)
2532 pthread_t pthread[1];
2535 // Initialize global locks
2536 lock_init(&MPLock, NULL);
2537 lock_init(&WaitLock, NULL);
2539 #if !defined(_MSC_VER)
2540 pthread_cond_init(&WaitCond, NULL);
2542 for (i = 0; i < MAX_THREADS; i++)
2543 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2546 // Initialize SplitPointStack locks
2547 for (i = 0; i < MAX_THREADS; i++)
2548 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2550 SplitPointStack[i][j].parent = NULL;
2551 lock_init(&(SplitPointStack[i][j].lock), NULL);
2554 // Will be set just before program exits to properly end the threads
2555 AllThreadsShouldExit = false;
2557 // Threads will be put to sleep as soon as created
2558 AllThreadsShouldSleep = true;
2560 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2562 threads[0].state = THREAD_SEARCHING;
2563 for (i = 1; i < MAX_THREADS; i++)
2564 threads[i].state = THREAD_AVAILABLE;
2566 // Launch the helper threads
2567 for (i = 1; i < MAX_THREADS; i++)
2570 #if !defined(_MSC_VER)
2571 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2573 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2578 cout << "Failed to create thread number " << i << endl;
2579 Application::exit_with_failure();
2582 // Wait until the thread has finished launching and is gone to sleep
2583 while (threads[i].state != THREAD_SLEEPING) {}
2588 // exit_threads() is called when the program exits. It makes all the
2589 // helper threads exit cleanly.
2591 void ThreadsManager::exit_threads() {
2593 ActiveThreads = MAX_THREADS; // HACK
2594 AllThreadsShouldSleep = true; // HACK
2595 wake_sleeping_threads();
2597 // This makes the threads to exit idle_loop()
2598 AllThreadsShouldExit = true;
2600 // Wait for thread termination
2601 for (int i = 1; i < MAX_THREADS; i++)
2602 while (threads[i].state != THREAD_TERMINATED);
2604 // Now we can safely destroy the locks
2605 for (int i = 0; i < MAX_THREADS; i++)
2606 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2607 lock_destroy(&(SplitPointStack[i][j].lock));
2609 lock_destroy(&WaitLock);
2610 lock_destroy(&MPLock);
2614 // thread_should_stop() checks whether the thread should stop its search.
2615 // This can happen if a beta cutoff has occurred in the thread's currently
2616 // active split point, or in some ancestor of the current split point.
2618 bool ThreadsManager::thread_should_stop(int threadID) const {
2620 assert(threadID >= 0 && threadID < ActiveThreads);
2624 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2629 // thread_is_available() checks whether the thread with threadID "slave" is
2630 // available to help the thread with threadID "master" at a split point. An
2631 // obvious requirement is that "slave" must be idle. With more than two
2632 // threads, this is not by itself sufficient: If "slave" is the master of
2633 // some active split point, it is only available as a slave to the other
2634 // threads which are busy searching the split point at the top of "slave"'s
2635 // split point stack (the "helpful master concept" in YBWC terminology).
2637 bool ThreadsManager::thread_is_available(int slave, int master) const {
2639 assert(slave >= 0 && slave < ActiveThreads);
2640 assert(master >= 0 && master < ActiveThreads);
2641 assert(ActiveThreads > 1);
2643 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2646 // Make a local copy to be sure doesn't change under our feet
2647 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2649 if (localActiveSplitPoints == 0)
2650 // No active split points means that the thread is available as
2651 // a slave for any other thread.
2654 if (ActiveThreads == 2)
2657 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2658 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2659 // could have been set to 0 by another thread leading to an out of bound access.
2660 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2667 // available_thread_exists() tries to find an idle thread which is available as
2668 // a slave for the thread with threadID "master".
2670 bool ThreadsManager::available_thread_exists(int master) const {
2672 assert(master >= 0 && master < ActiveThreads);
2673 assert(ActiveThreads > 1);
2675 for (int i = 0; i < ActiveThreads; i++)
2676 if (thread_is_available(i, master))
2683 // split() does the actual work of distributing the work at a node between
2684 // several threads at PV nodes. If it does not succeed in splitting the
2685 // node (because no idle threads are available, or because we have no unused
2686 // split point objects), the function immediately returns false. If
2687 // splitting is possible, a SplitPoint object is initialized with all the
2688 // data that must be copied to the helper threads (the current position and
2689 // search stack, alpha, beta, the search depth, etc.), and we tell our
2690 // helper threads that they have been assigned work. This will cause them
2691 // to instantly leave their idle loops and call sp_search_pv(). When all
2692 // threads have returned from sp_search_pv (or, equivalently, when
2693 // splitPoint->cpus becomes 0), split() returns true.
2695 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2696 Value* alpha, const Value beta, Value* bestValue,
2697 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2700 assert(sstck != NULL);
2701 assert(ply >= 0 && ply < PLY_MAX);
2702 assert(*bestValue >= -VALUE_INFINITE);
2703 assert( ( pvNode && *bestValue <= *alpha)
2704 || (!pvNode && *bestValue < beta ));
2705 assert(!pvNode || *alpha < beta);
2706 assert(beta <= VALUE_INFINITE);
2707 assert(depth > Depth(0));
2708 assert(master >= 0 && master < ActiveThreads);
2709 assert(ActiveThreads > 1);
2711 SplitPoint* splitPoint;
2715 // If no other thread is available to help us, or if we have too many
2716 // active split points, don't split.
2717 if ( !available_thread_exists(master)
2718 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2720 lock_release(&MPLock);
2724 // Pick the next available split point object from the split point stack
2725 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2727 // Initialize the split point object
2728 splitPoint->parent = threads[master].splitPoint;
2729 splitPoint->stopRequest = false;
2730 splitPoint->ply = ply;
2731 splitPoint->depth = depth;
2732 splitPoint->mateThreat = mateThreat;
2733 splitPoint->alpha = *alpha;
2734 splitPoint->beta = beta;
2735 splitPoint->pvNode = pvNode;
2736 splitPoint->bestValue = *bestValue;
2737 splitPoint->master = master;
2738 splitPoint->mp = mp;
2739 splitPoint->moves = *moves;
2740 splitPoint->cpus = 1;
2741 splitPoint->pos = &p;
2742 splitPoint->parentSstack = sstck;
2743 for (int i = 0; i < ActiveThreads; i++)
2744 splitPoint->slaves[i] = 0;
2746 threads[master].splitPoint = splitPoint;
2747 threads[master].activeSplitPoints++;
2749 // If we are here it means we are not available
2750 assert(threads[master].state != THREAD_AVAILABLE);
2752 // Allocate available threads setting state to THREAD_BOOKED
2753 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2754 if (thread_is_available(i, master))
2756 threads[i].state = THREAD_BOOKED;
2757 threads[i].splitPoint = splitPoint;
2758 splitPoint->slaves[i] = 1;
2762 assert(splitPoint->cpus > 1);
2764 // We can release the lock because slave threads are already booked and master is not available
2765 lock_release(&MPLock);
2767 // Tell the threads that they have work to do. This will make them leave
2768 // their idle loop. But before copy search stack tail for each thread.
2769 for (int i = 0; i < ActiveThreads; i++)
2770 if (i == master || splitPoint->slaves[i])
2772 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2774 assert(i == master || threads[i].state == THREAD_BOOKED);
2776 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2779 // Everything is set up. The master thread enters the idle loop, from
2780 // which it will instantly launch a search, because its state is
2781 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2782 // idle loop, which means that the main thread will return from the idle
2783 // loop when all threads have finished their work at this split point
2784 // (i.e. when splitPoint->cpus == 0).
2785 idle_loop(master, splitPoint);
2787 // We have returned from the idle loop, which means that all threads are
2788 // finished. Update alpha and bestValue, and return.
2791 *alpha = splitPoint->alpha;
2792 *bestValue = splitPoint->bestValue;
2793 threads[master].activeSplitPoints--;
2794 threads[master].splitPoint = splitPoint->parent;
2796 lock_release(&MPLock);
2801 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2802 // to start a new search from the root.
2804 void ThreadsManager::wake_sleeping_threads() {
2806 assert(AllThreadsShouldSleep);
2807 assert(ActiveThreads > 0);
2809 AllThreadsShouldSleep = false;
2811 if (ActiveThreads == 1)
2814 #if !defined(_MSC_VER)
2815 pthread_mutex_lock(&WaitLock);
2816 pthread_cond_broadcast(&WaitCond);
2817 pthread_mutex_unlock(&WaitLock);
2819 for (int i = 1; i < MAX_THREADS; i++)
2820 SetEvent(SitIdleEvent[i]);
2826 // put_threads_to_sleep() makes all the threads go to sleep just before
2827 // to leave think(), at the end of the search. Threads should have already
2828 // finished the job and should be idle.
2830 void ThreadsManager::put_threads_to_sleep() {
2832 assert(!AllThreadsShouldSleep);
2834 // This makes the threads to go to sleep
2835 AllThreadsShouldSleep = true;
2838 /// The RootMoveList class
2840 // RootMoveList c'tor
2842 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2844 SearchStack ss[PLY_MAX_PLUS_2];
2845 MoveStack mlist[MaxRootMoves];
2847 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2849 // Generate all legal moves
2850 MoveStack* last = generate_moves(pos, mlist);
2852 // Add each move to the moves[] array
2853 for (MoveStack* cur = mlist; cur != last; cur++)
2855 bool includeMove = includeAllMoves;
2857 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2858 includeMove = (searchMoves[k] == cur->move);
2863 // Find a quick score for the move
2865 pos.do_move(cur->move, st);
2866 moves[count].move = cur->move;
2867 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2868 moves[count].pv[0] = cur->move;
2869 moves[count].pv[1] = MOVE_NONE;
2870 pos.undo_move(cur->move);
2877 // RootMoveList simple methods definitions
2879 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2881 moves[moveNum].nodes = nodes;
2882 moves[moveNum].cumulativeNodes += nodes;
2885 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2887 moves[moveNum].ourBeta = our;
2888 moves[moveNum].theirBeta = their;
2891 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2895 for (j = 0; pv[j] != MOVE_NONE; j++)
2896 moves[moveNum].pv[j] = pv[j];
2898 moves[moveNum].pv[j] = MOVE_NONE;
2902 // RootMoveList::sort() sorts the root move list at the beginning of a new
2905 void RootMoveList::sort() {
2907 sort_multipv(count - 1); // Sort all items
2911 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2912 // list by their scores and depths. It is used to order the different PVs
2913 // correctly in MultiPV mode.
2915 void RootMoveList::sort_multipv(int n) {
2919 for (i = 1; i <= n; i++)
2921 RootMove rm = moves[i];
2922 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2923 moves[j] = moves[j - 1];