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
57 // ThreadsManager class is used to handle all the threads related stuff in search,
58 // init, starting, parking and, the most important, launching a slave thread at a
59 // split point are what this class does. All the access to shared thread data is
60 // done through this class, so that we avoid using global variables instead.
62 class ThreadsManager {
63 /* As long as the single ThreadsManager object is defined as a global we don't
64 need to explicitly initialize to zero its data members because variables with
65 static storage duration are automatically set to zero before enter main()
71 int active_threads() const { return ActiveThreads; }
72 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
73 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
74 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
76 void resetNodeCounters();
77 void resetBetaCounters();
78 int64_t nodes_searched() const;
79 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
80 bool available_thread_exists(int master) const;
81 bool thread_is_available(int slave, int master) const;
82 bool thread_should_stop(int threadID) const;
83 void wake_sleeping_threads();
84 void put_threads_to_sleep();
85 void idle_loop(int threadID, SplitPoint* waitSp);
86 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode);
90 friend void poll(SearchStack ss[], int ply);
93 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
94 Thread threads[MAX_THREADS];
95 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
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 IIDDepthAtPVNodes = 5 * OnePly;
183 const Depth IIDDepthAtNonPVNodes = 8 * OnePly;
185 // At Non-PV nodes we do an internal iterative deepening search
186 // when the static evaluation is at most IIDMargin below beta.
187 const Value IIDMargin = Value(0x100);
189 // Step 11. Decide the new search depth
191 // Extensions. Configurable UCI options
192 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
193 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
194 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
196 // Minimum depth for use of singular extension
197 const Depth SingularExtensionDepthAtPVNodes = 6 * OnePly;
198 const Depth SingularExtensionDepthAtNonPVNodes = 8 * OnePly;
200 // If the TT move is at least SingularExtensionMargin better then the
201 // remaining ones we will extend it.
202 const Value SingularExtensionMargin = Value(0x20);
204 // Step 12. Futility pruning
206 // Futility margin for quiescence search
207 const Value FutilityMarginQS = Value(0x80);
209 // Futility lookup tables (initialized at startup) and their getter functions
210 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
211 int FutilityMoveCountArray[32]; // [depth]
213 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
214 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
216 // Step 14. Reduced search
218 // Reduction lookup tables (initialized at startup) and their getter functions
219 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
220 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
222 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
223 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
225 // Common adjustments
227 // Search depth at iteration 1
228 const Depth InitialDepth = OnePly;
230 // Easy move margin. An easy move candidate must be at least this much
231 // better than the second best move.
232 const Value EasyMoveMargin = Value(0x200);
234 // Last seconds noise filtering (LSN)
235 const bool UseLSNFiltering = true;
236 const int LSNTime = 4000; // In milliseconds
237 const Value LSNValue = value_from_centipawns(200);
238 bool loseOnTime = false;
246 // Scores and number of times the best move changed for each iteration
247 Value ValueByIteration[PLY_MAX_PLUS_2];
248 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
250 // Search window management
256 // Time managment variables
257 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
258 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
259 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
260 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
262 // Show current line?
263 bool ShowCurrentLine;
267 std::ofstream LogFile;
269 // Multi-threads related variables
270 Depth MinimumSplitDepth;
271 int MaxThreadsPerSplitPoint;
274 // Node counters, used only by thread[0] but try to keep in different cache
275 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
277 int NodesBetweenPolls = 30000;
284 Value id_loop(const Position& pos, Move searchMoves[]);
285 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
286 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
287 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
288 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
289 void sp_search(SplitPoint* sp, int threadID);
290 void sp_search_pv(SplitPoint* sp, int threadID);
291 void init_node(SearchStack ss[], int ply, int threadID);
292 void update_pv(SearchStack ss[], int ply);
293 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
294 bool connected_moves(const Position& pos, Move m1, Move m2);
295 bool value_is_mate(Value value);
296 bool move_is_killer(Move m, const SearchStack& ss);
297 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
298 bool ok_to_do_nullmove(const Position& pos);
299 bool ok_to_prune(const Position& pos, Move m, Move threat);
300 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
301 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
302 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
303 void update_killers(Move m, SearchStack& ss);
304 void update_gains(const Position& pos, Move move, Value before, Value after);
306 int current_search_time();
308 void poll(SearchStack ss[], int ply);
310 void wait_for_stop_or_ponderhit();
311 void init_ss_array(SearchStack ss[]);
312 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value);
314 #if !defined(_MSC_VER)
315 void *init_thread(void *threadID);
317 DWORD WINAPI init_thread(LPVOID threadID);
327 /// init_threads(), exit_threads() and nodes_searched() are helpers to
328 /// give accessibility to some TM methods from outside of current file.
330 void init_threads() { TM.init_threads(); }
331 void exit_threads() { TM.exit_threads(); }
332 int64_t nodes_searched() { return TM.nodes_searched(); }
335 /// perft() is our utility to verify move generation is bug free. All the legal
336 /// moves up to given depth are generated and counted and the sum returned.
338 int perft(Position& pos, Depth depth)
343 MovePicker mp(pos, MOVE_NONE, depth, H);
345 // If we are at the last ply we don't need to do and undo
346 // the moves, just to count them.
347 if (depth <= OnePly) // Replace with '<' to test also qsearch
349 while (mp.get_next_move()) sum++;
353 // Loop through all legal moves
355 while ((move = mp.get_next_move()) != MOVE_NONE)
357 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
358 sum += perft(pos, depth - OnePly);
365 /// think() is the external interface to Stockfish's search, and is called when
366 /// the program receives the UCI 'go' command. It initializes various
367 /// search-related global variables, and calls root_search(). It returns false
368 /// when a quit command is received during the search.
370 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
371 int time[], int increment[], int movesToGo, int maxDepth,
372 int maxNodes, int maxTime, Move searchMoves[]) {
374 // Initialize global search variables
375 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
376 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
378 TM.resetNodeCounters();
379 SearchStartTime = get_system_time();
380 ExactMaxTime = maxTime;
383 InfiniteSearch = infinite;
384 PonderSearch = ponder;
385 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
387 // Look for a book move, only during games, not tests
388 if (UseTimeManagement && get_option_value_bool("OwnBook"))
390 if (get_option_value_string("Book File") != OpeningBook.file_name())
391 OpeningBook.open(get_option_value_string("Book File"));
393 Move bookMove = OpeningBook.get_move(pos);
394 if (bookMove != MOVE_NONE)
397 wait_for_stop_or_ponderhit();
399 cout << "bestmove " << bookMove << endl;
404 // Reset loseOnTime flag at the beginning of a new game
405 if (button_was_pressed("New Game"))
408 // Read UCI option values
409 TT.set_size(get_option_value_int("Hash"));
410 if (button_was_pressed("Clear Hash"))
413 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
414 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
415 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
416 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
417 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
418 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
419 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
420 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
421 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
422 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
423 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
424 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
426 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
427 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
428 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
429 MultiPV = get_option_value_int("MultiPV");
430 Chess960 = get_option_value_bool("UCI_Chess960");
431 UseLogFile = get_option_value_bool("Use Search Log");
434 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
436 read_weights(pos.side_to_move());
438 // Set the number of active threads
439 int newActiveThreads = get_option_value_int("Threads");
440 if (newActiveThreads != TM.active_threads())
442 TM.set_active_threads(newActiveThreads);
443 init_eval(TM.active_threads());
446 // Wake up sleeping threads
447 TM.wake_sleeping_threads();
450 int myTime = time[side_to_move];
451 int myIncrement = increment[side_to_move];
452 if (UseTimeManagement)
454 if (!movesToGo) // Sudden death time control
458 MaxSearchTime = myTime / 30 + myIncrement;
459 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
461 else // Blitz game without increment
463 MaxSearchTime = myTime / 30;
464 AbsoluteMaxSearchTime = myTime / 8;
467 else // (x moves) / (y minutes)
471 MaxSearchTime = myTime / 2;
472 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
476 MaxSearchTime = myTime / Min(movesToGo, 20);
477 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
481 if (get_option_value_bool("Ponder"))
483 MaxSearchTime += MaxSearchTime / 4;
484 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
488 // Set best NodesBetweenPolls interval to avoid lagging under
489 // heavy time pressure.
491 NodesBetweenPolls = Min(MaxNodes, 30000);
492 else if (myTime && myTime < 1000)
493 NodesBetweenPolls = 1000;
494 else if (myTime && myTime < 5000)
495 NodesBetweenPolls = 5000;
497 NodesBetweenPolls = 30000;
499 // Write search information to log file
501 LogFile << "Searching: " << pos.to_fen() << endl
502 << "infinite: " << infinite
503 << " ponder: " << ponder
504 << " time: " << myTime
505 << " increment: " << myIncrement
506 << " moves to go: " << movesToGo << endl;
508 // LSN filtering. Used only for developing purposes, disabled by default
512 // Step 2. If after last move we decided to lose on time, do it now!
513 while (SearchStartTime + myTime + 1000 > get_system_time())
517 // We're ready to start thinking. Call the iterative deepening loop function
518 Value v = id_loop(pos, searchMoves);
522 // Step 1. If this is sudden death game and our position is hopeless,
523 // decide to lose on time.
524 if ( !loseOnTime // If we already lost on time, go to step 3.
534 // Step 3. Now after stepping over the time limit, reset flag for next match.
542 TM.put_threads_to_sleep();
548 /// init_search() is called during startup. It initializes various lookup tables
552 // Init our reduction lookup tables
553 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
554 for (int j = 1; j < 64; j++) // j == moveNumber
556 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
557 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
558 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
559 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
562 // Init futility margins array
563 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
564 for (int j = 0; j < 64; j++) // j == moveNumber
566 // FIXME: test using log instead of BSR
567 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j;
570 // Init futility move count array
571 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
572 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
576 // SearchStack::init() initializes a search stack. Used at the beginning of a
577 // new search from the root.
578 void SearchStack::init(int ply) {
580 pv[ply] = pv[ply + 1] = MOVE_NONE;
581 currentMove = threatMove = MOVE_NONE;
582 reduction = Depth(0);
586 void SearchStack::initKillers() {
588 mateKiller = MOVE_NONE;
589 for (int i = 0; i < KILLER_MAX; i++)
590 killers[i] = MOVE_NONE;
595 // id_loop() is the main iterative deepening loop. It calls root_search
596 // repeatedly with increasing depth until the allocated thinking time has
597 // been consumed, the user stops the search, or the maximum search depth is
600 Value id_loop(const Position& pos, Move searchMoves[]) {
603 SearchStack ss[PLY_MAX_PLUS_2];
604 Move EasyMove = MOVE_NONE;
605 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
607 // Moves to search are verified, copied, scored and sorted
608 RootMoveList rml(p, searchMoves);
610 // Handle special case of searching on a mate/stale position
611 if (rml.move_count() == 0)
614 wait_for_stop_or_ponderhit();
616 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
619 // Print RootMoveList startup scoring to the standard output,
620 // so to output information also for iteration 1.
621 cout << "info depth " << 1
622 << "\ninfo depth " << 1
623 << " score " << value_to_string(rml.get_move_score(0))
624 << " time " << current_search_time()
625 << " nodes " << TM.nodes_searched()
627 << " pv " << rml.get_move(0) << "\n";
633 ValueByIteration[1] = rml.get_move_score(0);
636 // Is one move significantly better than others after initial scoring ?
637 if ( rml.move_count() == 1
638 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
639 EasyMove = rml.get_move(0);
641 // Iterative deepening loop
642 while (Iteration < PLY_MAX)
644 // Initialize iteration
646 BestMoveChangesByIteration[Iteration] = 0;
648 cout << "info depth " << Iteration << endl;
650 // Calculate dynamic aspiration window based on previous iterations
651 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
653 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
654 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
656 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
657 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
659 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
660 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
663 // Search to the current depth, rml is updated and sorted, alpha and beta could change
664 value = root_search(p, ss, rml, &alpha, &beta);
666 // Write PV to transposition table, in case the relevant entries have
667 // been overwritten during the search.
668 TT.insert_pv(p, ss[0].pv);
671 break; // Value cannot be trusted. Break out immediately!
673 //Save info about search result
674 ValueByIteration[Iteration] = value;
676 // Drop the easy move if differs from the new best move
677 if (ss[0].pv[0] != EasyMove)
678 EasyMove = MOVE_NONE;
680 if (UseTimeManagement)
683 bool stopSearch = false;
685 // Stop search early if there is only a single legal move,
686 // we search up to Iteration 6 anyway to get a proper score.
687 if (Iteration >= 6 && rml.move_count() == 1)
690 // Stop search early when the last two iterations returned a mate score
692 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
693 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
696 // Stop search early if one move seems to be much better than the others
697 int64_t nodes = TM.nodes_searched();
699 && EasyMove == ss[0].pv[0]
700 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
701 && current_search_time() > MaxSearchTime / 16)
702 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
703 && current_search_time() > MaxSearchTime / 32)))
706 // Add some extra time if the best move has changed during the last two iterations
707 if (Iteration > 5 && Iteration <= 50)
708 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
709 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
711 // Stop search if most of MaxSearchTime is consumed at the end of the
712 // iteration. We probably don't have enough time to search the first
713 // move at the next iteration anyway.
714 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
720 StopOnPonderhit = true;
726 if (MaxDepth && Iteration >= MaxDepth)
730 // If we are pondering or in infinite search, we shouldn't print the
731 // best move before we are told to do so.
732 if (!AbortSearch && (PonderSearch || InfiniteSearch))
733 wait_for_stop_or_ponderhit();
735 // Print final search statistics
736 cout << "info nodes " << TM.nodes_searched()
738 << " time " << current_search_time()
739 << " hashfull " << TT.full() << endl;
741 // Print the best move and the ponder move to the standard output
742 if (ss[0].pv[0] == MOVE_NONE)
744 ss[0].pv[0] = rml.get_move(0);
745 ss[0].pv[1] = MOVE_NONE;
748 assert(ss[0].pv[0] != MOVE_NONE);
750 cout << "bestmove " << ss[0].pv[0];
752 if (ss[0].pv[1] != MOVE_NONE)
753 cout << " ponder " << ss[0].pv[1];
760 dbg_print_mean(LogFile);
762 if (dbg_show_hit_rate)
763 dbg_print_hit_rate(LogFile);
765 LogFile << "\nNodes: " << TM.nodes_searched()
766 << "\nNodes/second: " << nps()
767 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
770 p.do_move(ss[0].pv[0], st);
771 LogFile << "\nPonder move: "
772 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
775 return rml.get_move_score(0);
779 // root_search() is the function which searches the root node. It is
780 // similar to search_pv except that it uses a different move ordering
781 // scheme, prints some information to the standard output and handles
782 // the fail low/high loops.
784 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
791 Depth depth, ext, newDepth;
792 Value value, alpha, beta;
793 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
794 int researchCountFH, researchCountFL;
796 researchCountFH = researchCountFL = 0;
799 isCheck = pos.is_check();
801 // Step 1. Initialize node and poll (omitted at root, but I can see no good reason for this, FIXME)
802 // Step 2. Check for aborted search (omitted at root, because we do not initialize root node)
803 // Step 3. Mate distance pruning (omitted at root)
804 // Step 4. Transposition table lookup (omitted at root)
806 // Step 5. Evaluate the position statically
807 // At root we do this only to get reference value for child nodes
809 ss[0].eval = evaluate(pos, ei, 0);
811 ss[0].eval = VALUE_NONE; // HACK because we do not initialize root node
813 // Step 6. Razoring (omitted at root)
814 // Step 7. Static null move pruning (omitted at root)
815 // Step 8. Null move search with verification search (omitted at root)
816 // Step 9. Internal iterative deepening (omitted at root)
818 // Step extra. Fail low loop
819 // We start with small aspiration window and in case of fail low, we research
820 // with bigger window until we are not failing low anymore.
823 // Sort the moves before to (re)search
826 // Step 10. Loop through all moves in the root move list
827 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
829 // This is used by time management
830 FirstRootMove = (i == 0);
832 // Save the current node count before the move is searched
833 nodes = TM.nodes_searched();
835 // Reset beta cut-off counters
836 TM.resetBetaCounters();
838 // Pick the next root move, and print the move and the move number to
839 // the standard output.
840 move = ss[0].currentMove = rml.get_move(i);
842 if (current_search_time() >= 1000)
843 cout << "info currmove " << move
844 << " currmovenumber " << i + 1 << endl;
846 moveIsCheck = pos.move_is_check(move);
847 captureOrPromotion = pos.move_is_capture_or_promotion(move);
849 // Step 11. Decide the new search depth
850 depth = (Iteration - 2) * OnePly + InitialDepth;
851 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
852 newDepth = depth + ext;
854 // Step 12. Futility pruning (omitted at root)
856 // Step extra. Fail high loop
857 // If move fails high, we research with bigger window until we are not failing
859 value = - VALUE_INFINITE;
863 // Step 13. Make the move
864 pos.do_move(move, st, ci, moveIsCheck);
866 // Step extra. pv search
867 // We do pv search for first moves (i < MultiPV)
868 // and for fail high research (value > alpha)
869 if (i < MultiPV || value > alpha)
871 // Aspiration window is disabled in multi-pv case
873 alpha = -VALUE_INFINITE;
875 // Full depth PV search, done on first move or after a fail high
876 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
880 // Step 14. Reduced search
881 // if the move fails high will be re-searched at full depth
882 bool doFullDepthSearch = true;
884 if ( depth >= 3 * OnePly
886 && !captureOrPromotion
887 && !move_is_castle(move))
889 ss[0].reduction = pv_reduction(depth, i - MultiPV + 2);
892 // Reduced depth non-pv search using alpha as upperbound
893 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
894 doFullDepthSearch = (value > alpha);
898 // Step 15. Full depth search
899 if (doFullDepthSearch)
901 // Full depth non-pv search using alpha as upperbound
902 ss[0].reduction = Depth(0);
903 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
905 // If we are above alpha then research at same depth but as PV
906 // to get a correct score or eventually a fail high above beta.
908 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
912 // Step 16. Undo move
915 // Can we exit fail high loop ?
916 if (AbortSearch || value < beta)
919 // We are failing high and going to do a research. It's important to update
920 // the score before research in case we run out of time while researching.
921 rml.set_move_score(i, value);
923 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
924 rml.set_move_pv(i, ss[0].pv);
926 // Print information to the standard output
927 print_pv_info(pos, ss, alpha, beta, value);
929 // Prepare for a research after a fail high, each time with a wider window
930 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
933 } // End of fail high loop
935 // Finished searching the move. If AbortSearch is true, the search
936 // was aborted because the user interrupted the search or because we
937 // ran out of time. In this case, the return value of the search cannot
938 // be trusted, and we break out of the loop without updating the best
943 // Remember beta-cutoff and searched nodes counts for this move. The
944 // info is used to sort the root moves for the next iteration.
946 TM.get_beta_counters(pos.side_to_move(), our, their);
947 rml.set_beta_counters(i, our, their);
948 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
950 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
951 assert(value < beta);
953 // Step 17. Check for new best move
954 if (value <= alpha && i >= MultiPV)
955 rml.set_move_score(i, -VALUE_INFINITE);
958 // PV move or new best move!
961 rml.set_move_score(i, value);
963 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
964 rml.set_move_pv(i, ss[0].pv);
968 // We record how often the best move has been changed in each
969 // iteration. This information is used for time managment: When
970 // the best move changes frequently, we allocate some more time.
972 BestMoveChangesByIteration[Iteration]++;
974 // Print information to the standard output
975 print_pv_info(pos, ss, alpha, beta, value);
977 // Raise alpha to setup proper non-pv search upper bound
984 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
986 cout << "info multipv " << j + 1
987 << " score " << value_to_string(rml.get_move_score(j))
988 << " depth " << (j <= i ? Iteration : Iteration - 1)
989 << " time " << current_search_time()
990 << " nodes " << TM.nodes_searched()
994 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
995 cout << rml.get_move_pv(j, k) << " ";
999 alpha = rml.get_move_score(Min(i, MultiPV - 1));
1001 } // PV move or new best move
1003 assert(alpha >= *alphaPtr);
1005 AspirationFailLow = (alpha == *alphaPtr);
1007 if (AspirationFailLow && StopOnPonderhit)
1008 StopOnPonderhit = false;
1011 // Can we exit fail low loop ?
1012 if (AbortSearch || !AspirationFailLow)
1015 // Prepare for a research after a fail low, each time with a wider window
1016 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1021 // Sort the moves before to return
1028 // search_pv() is the main search function for PV nodes.
1030 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1031 Depth depth, int ply, int threadID) {
1033 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1034 assert(beta > alpha && beta <= VALUE_INFINITE);
1035 assert(ply >= 0 && ply < PLY_MAX);
1036 assert(threadID >= 0 && threadID < TM.active_threads());
1038 Move movesSearched[256];
1043 Depth ext, newDepth;
1044 Value bestValue, value, oldAlpha;
1045 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1046 bool mateThreat = false;
1048 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
1066 alpha = Max(value_mated_in(ply), alpha);
1067 beta = Min(value_mate_in(ply+1), beta);
1071 // Step 4. Transposition table lookup
1072 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1073 // This is to avoid problems in the following areas:
1075 // * Repetition draw detection
1076 // * Fifty move rule detection
1077 // * Searching for a mate
1078 // * Printing of full PV line
1079 tte = TT.retrieve(pos.get_key());
1080 ttMove = (tte ? tte->move() : MOVE_NONE);
1082 // Step 5. Evaluate the position statically
1083 // At PV nodes we do this only to update gain statistics
1084 isCheck = pos.is_check();
1087 ss[ply].eval = evaluate(pos, ei, threadID);
1088 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1091 // Step 6. Razoring (is omitted in PV nodes)
1092 // Step 7. Static null move pruning (is omitted in PV nodes)
1093 // Step 8. Null move search with verification search (is omitted in PV nodes)
1095 // Step 9. Internal iterative deepening
1096 if ( depth >= IIDDepthAtPVNodes
1097 && ttMove == MOVE_NONE)
1099 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1100 ttMove = ss[ply].pv[ply];
1101 tte = TT.retrieve(pos.get_key());
1104 // Initialize a MovePicker object for the current position
1105 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1106 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1109 // Step 10. Loop through moves
1110 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1111 while ( alpha < beta
1112 && (move = mp.get_next_move()) != MOVE_NONE
1113 && !TM.thread_should_stop(threadID))
1115 assert(move_is_ok(move));
1117 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1118 moveIsCheck = pos.move_is_check(move, ci);
1119 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1121 // Step 11. Decide the new search depth
1122 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1124 // Singular extension search. We extend the TT move if its value is much better than
1125 // its siblings. To verify this we do a reduced search on all the other moves but the
1126 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1127 if ( depth >= SingularExtensionDepthAtPVNodes
1129 && move == tte->move()
1131 && is_lower_bound(tte->type())
1132 && tte->depth() >= depth - 3 * OnePly)
1134 Value ttValue = value_from_tt(tte->value(), ply);
1136 if (abs(ttValue) < VALUE_KNOWN_WIN)
1138 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1140 if (excValue < ttValue - SingularExtensionMargin)
1145 newDepth = depth - OnePly + ext;
1147 // Update current move (this must be done after singular extension search)
1148 movesSearched[moveCount++] = ss[ply].currentMove = move;
1150 // Step 12. Futility pruning (is omitted in PV nodes)
1152 // Step 13. Make the move
1153 pos.do_move(move, st, ci, moveIsCheck);
1155 // Step extra. pv search (only in PV nodes)
1156 // The first move in list is the expected PV
1158 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1161 // Step 14. Reduced search
1162 // if the move fails high will be re-searched at full depth.
1163 bool doFullDepthSearch = true;
1165 if ( depth >= 3 * OnePly
1167 && !captureOrPromotion
1168 && !move_is_castle(move)
1169 && !move_is_killer(move, ss[ply]))
1171 ss[ply].reduction = pv_reduction(depth, moveCount);
1172 if (ss[ply].reduction)
1174 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1175 doFullDepthSearch = (value > alpha);
1179 // Step 15. Full depth search
1180 if (doFullDepthSearch)
1182 ss[ply].reduction = Depth(0);
1183 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1185 // Step extra. pv search (only in PV nodes)
1186 if (value > alpha && value < beta)
1187 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1191 // Step 16. Undo move
1192 pos.undo_move(move);
1194 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1196 // Step 17. Check for new best move
1197 if (value > bestValue)
1204 if (value == value_mate_in(ply + 1))
1205 ss[ply].mateKiller = move;
1209 // Step 18. Check for split
1210 if ( TM.active_threads() > 1
1212 && depth >= MinimumSplitDepth
1214 && TM.available_thread_exists(threadID)
1216 && !TM.thread_should_stop(threadID)
1217 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1218 depth, mateThreat, &moveCount, &mp, threadID, true))
1222 // Step 19. Check for mate and stalemate
1223 // All legal moves have been searched and if there were
1224 // no legal moves, it must be mate or stalemate.
1226 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1228 // Step 20. Update tables
1229 // If the search is not aborted, update the transposition table,
1230 // history counters, and killer moves.
1231 if (AbortSearch || TM.thread_should_stop(threadID))
1234 if (bestValue <= oldAlpha)
1235 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1237 else if (bestValue >= beta)
1239 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1240 move = ss[ply].pv[ply];
1241 if (!pos.move_is_capture_or_promotion(move))
1243 update_history(pos, move, depth, movesSearched, moveCount);
1244 update_killers(move, ss[ply]);
1246 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1249 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1255 // search() is the search function for zero-width nodes.
1257 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1258 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1260 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1261 assert(ply >= 0 && ply < PLY_MAX);
1262 assert(threadID >= 0 && threadID < TM.active_threads());
1264 Move movesSearched[256];
1269 Depth ext, newDepth;
1270 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1271 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1272 bool mateThreat = false;
1274 refinedValue = bestValue = value = -VALUE_INFINITE;
1277 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1279 // Step 1. Initialize node and poll
1280 // Polling can abort search.
1281 init_node(ss, ply, threadID);
1283 // Step 2. Check for aborted search and immediate draw
1284 if (AbortSearch || TM.thread_should_stop(threadID))
1287 if (pos.is_draw() || ply >= PLY_MAX - 1)
1290 // Step 3. Mate distance pruning
1291 if (value_mated_in(ply) >= beta)
1294 if (value_mate_in(ply + 1) < beta)
1297 // Step 4. Transposition table lookup
1299 // We don't want the score of a partial search to overwrite a previous full search
1300 // TT value, so we use a different position key in case of an excluded move exists.
1301 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1303 tte = TT.retrieve(posKey);
1304 ttMove = (tte ? tte->move() : MOVE_NONE);
1306 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1308 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1309 return value_from_tt(tte->value(), ply);
1312 // Step 5. Evaluate the position statically
1313 isCheck = pos.is_check();
1317 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1318 ss[ply].eval = value_from_tt(tte->value(), ply);
1320 ss[ply].eval = evaluate(pos, ei, threadID);
1322 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1323 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1327 if ( refinedValue < beta - razor_margin(depth)
1328 && ttMove == MOVE_NONE
1329 && ss[ply - 1].currentMove != MOVE_NULL
1330 && depth < RazorDepth
1332 && !value_is_mate(beta)
1333 && !pos.has_pawn_on_7th(pos.side_to_move()))
1335 Value rbeta = beta - razor_margin(depth);
1336 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1338 // Logically we should return (v + razor_margin(depth)), but
1339 // surprisingly this did slightly weaker in tests.
1343 // Step 7. Static null move pruning
1344 // We're betting that the opponent doesn't have a move that will reduce
1345 // the score by more than futility_margin(depth) if we do a null move.
1347 && depth < RazorDepth
1349 && !value_is_mate(beta)
1350 && ok_to_do_nullmove(pos)
1351 && refinedValue >= beta + futility_margin(depth, 0))
1352 return refinedValue - futility_margin(depth, 0);
1354 // Step 8. Null move search with verification search
1355 // When we jump directly to qsearch() we do a null move only if static value is
1356 // at least beta. Otherwise we do a null move if static value is not more than
1357 // NullMoveMargin under beta.
1361 && !value_is_mate(beta)
1362 && ok_to_do_nullmove(pos)
1363 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1365 ss[ply].currentMove = MOVE_NULL;
1367 // Null move dynamic reduction based on depth
1368 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1370 // Null move dynamic reduction based on value
1371 if (refinedValue - beta > PawnValueMidgame)
1374 pos.do_null_move(st);
1376 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1378 pos.undo_null_move();
1380 if (nullValue >= beta)
1382 // Do not return unproven mate scores
1383 if (nullValue >= value_mate_in(PLY_MAX))
1386 if (depth < 6 * OnePly)
1389 // Do zugzwang verification search
1390 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1394 // The null move failed low, which means that we may be faced with
1395 // some kind of threat. If the previous move was reduced, check if
1396 // the move that refuted the null move was somehow connected to the
1397 // move which was reduced. If a connection is found, return a fail
1398 // low score (which will cause the reduced move to fail high in the
1399 // parent node, which will trigger a re-search with full depth).
1400 if (nullValue == value_mated_in(ply + 2))
1403 ss[ply].threatMove = ss[ply + 1].currentMove;
1404 if ( depth < ThreatDepth
1405 && ss[ply - 1].reduction
1406 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1411 // Step 9. Internal iterative deepening
1412 if ( depth >= IIDDepthAtNonPVNodes
1413 && ttMove == MOVE_NONE
1415 && ss[ply].eval >= beta - IIDMargin)
1417 search(pos, ss, beta, depth/2, ply, false, threadID);
1418 ttMove = ss[ply].pv[ply];
1419 tte = TT.retrieve(posKey);
1422 // Initialize a MovePicker object for the current position
1423 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1426 // Step 10. Loop through moves
1427 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1428 while ( bestValue < beta
1429 && (move = mp.get_next_move()) != MOVE_NONE
1430 && !TM.thread_should_stop(threadID))
1432 assert(move_is_ok(move));
1434 if (move == excludedMove)
1437 moveIsCheck = pos.move_is_check(move, ci);
1438 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1439 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1441 // Step 11. Decide the new search depth
1442 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1444 // Singular extension search. We extend the TT move if its value is much better than
1445 // its siblings. To verify this we do a reduced search on all the other moves but the
1446 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1447 if ( depth >= SingularExtensionDepthAtNonPVNodes
1449 && move == tte->move()
1450 && !excludedMove // Do not allow recursive singular extension search
1452 && is_lower_bound(tte->type())
1453 && tte->depth() >= depth - 3 * OnePly)
1455 Value ttValue = value_from_tt(tte->value(), ply);
1457 if (abs(ttValue) < VALUE_KNOWN_WIN)
1459 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1461 if (excValue < ttValue - SingularExtensionMargin)
1466 newDepth = depth - OnePly + ext;
1468 // Update current move (this must be done after singular extension search)
1469 movesSearched[moveCount++] = ss[ply].currentMove = move;
1471 // Step 12. Futility pruning
1474 && !captureOrPromotion
1475 && !move_is_castle(move)
1478 // Move count based pruning
1479 if ( moveCount >= futility_move_count(depth)
1480 && ok_to_prune(pos, move, ss[ply].threatMove)
1481 && bestValue > value_mated_in(PLY_MAX))
1484 // Value based pruning
1485 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1486 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1487 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1489 if (futilityValueScaled < beta)
1491 if (futilityValueScaled > bestValue)
1492 bestValue = futilityValueScaled;
1497 // Step 13. Make the move
1498 pos.do_move(move, st, ci, moveIsCheck);
1500 // Step 14. Reduced search, if the move fails high
1501 // will be re-searched at full depth.
1502 bool doFullDepthSearch = true;
1504 if ( depth >= 3*OnePly
1506 && !captureOrPromotion
1507 && !move_is_castle(move)
1508 && !move_is_killer(move, ss[ply]))
1510 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1511 if (ss[ply].reduction)
1513 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1514 doFullDepthSearch = (value >= beta);
1518 // Step 15. Full depth search
1519 if (doFullDepthSearch)
1521 ss[ply].reduction = Depth(0);
1522 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1525 // Step 16. Undo move
1526 pos.undo_move(move);
1528 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1530 // Step 17. Check for new best move
1531 if (value > bestValue)
1537 if (value == value_mate_in(ply + 1))
1538 ss[ply].mateKiller = move;
1541 // Step 18. Check for split
1542 if ( TM.active_threads() > 1
1544 && depth >= MinimumSplitDepth
1546 && TM.available_thread_exists(threadID)
1548 && !TM.thread_should_stop(threadID)
1549 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1550 depth, mateThreat, &moveCount, &mp, threadID, false))
1554 // Step 19. Check for mate and stalemate
1555 // All legal moves have been searched and if there are
1556 // no legal moves, it must be mate or stalemate.
1557 // If one move was excluded return fail low score.
1559 return excludedMove ? beta - 1 : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1561 // Step 20. Update tables
1562 // If the search is not aborted, update the transposition table,
1563 // history counters, and killer moves.
1564 if (AbortSearch || TM.thread_should_stop(threadID))
1567 if (bestValue < beta)
1568 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1571 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1572 move = ss[ply].pv[ply];
1573 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1574 if (!pos.move_is_capture_or_promotion(move))
1576 update_history(pos, move, depth, movesSearched, moveCount);
1577 update_killers(move, ss[ply]);
1582 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1588 // qsearch() is the quiescence search function, which is called by the main
1589 // search function when the remaining depth is zero (or, to be more precise,
1590 // less than OnePly).
1592 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1593 Depth depth, int ply, int threadID) {
1595 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1596 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1598 assert(ply >= 0 && ply < PLY_MAX);
1599 assert(threadID >= 0 && threadID < TM.active_threads());
1604 Value staticValue, bestValue, value, futilityBase, futilityValue;
1605 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1606 const TTEntry* tte = NULL;
1608 bool pvNode = (beta - alpha != 1);
1609 Value oldAlpha = alpha;
1611 // Initialize, and make an early exit in case of an aborted search,
1612 // an instant draw, maximum ply reached, etc.
1613 init_node(ss, ply, threadID);
1615 // After init_node() that calls poll()
1616 if (AbortSearch || TM.thread_should_stop(threadID))
1619 if (pos.is_draw() || ply >= PLY_MAX - 1)
1622 // Transposition table lookup. At PV nodes, we don't use the TT for
1623 // pruning, but only for move ordering.
1624 tte = TT.retrieve(pos.get_key());
1625 ttMove = (tte ? tte->move() : MOVE_NONE);
1627 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1629 assert(tte->type() != VALUE_TYPE_EVAL);
1631 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1632 return value_from_tt(tte->value(), ply);
1635 isCheck = pos.is_check();
1637 // Evaluate the position statically
1639 staticValue = -VALUE_INFINITE;
1640 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1641 staticValue = value_from_tt(tte->value(), ply);
1643 staticValue = evaluate(pos, ei, threadID);
1647 ss[ply].eval = staticValue;
1648 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1651 // Initialize "stand pat score", and return it immediately if it is
1653 bestValue = staticValue;
1655 if (bestValue >= beta)
1657 // Store the score to avoid a future costly evaluation() call
1658 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1659 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1664 if (bestValue > alpha)
1667 // If we are near beta then try to get a cutoff pushing checks a bit further
1668 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1670 // Initialize a MovePicker object for the current position, and prepare
1671 // to search the moves. Because the depth is <= 0 here, only captures,
1672 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1673 // and we are near beta) will be generated.
1674 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1676 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1677 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1679 // Loop through the moves until no moves remain or a beta cutoff occurs
1680 while ( alpha < beta
1681 && (move = mp.get_next_move()) != MOVE_NONE)
1683 assert(move_is_ok(move));
1685 moveIsCheck = pos.move_is_check(move, ci);
1687 // Update current move
1689 ss[ply].currentMove = move;
1697 && !move_is_promotion(move)
1698 && !pos.move_is_passed_pawn_push(move))
1700 futilityValue = futilityBase
1701 + pos.endgame_value_of_piece_on(move_to(move))
1702 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1704 if (futilityValue < alpha)
1706 if (futilityValue > bestValue)
1707 bestValue = futilityValue;
1712 // Detect blocking evasions that are candidate to be pruned
1713 evasionPrunable = isCheck
1714 && bestValue != -VALUE_INFINITE
1715 && !pos.move_is_capture(move)
1716 && pos.type_of_piece_on(move_from(move)) != KING
1717 && !pos.can_castle(pos.side_to_move());
1719 // Don't search moves with negative SEE values
1720 if ( (!isCheck || evasionPrunable)
1723 && !move_is_promotion(move)
1724 && pos.see_sign(move) < 0)
1727 // Make and search the move
1728 pos.do_move(move, st, ci, moveIsCheck);
1729 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1730 pos.undo_move(move);
1732 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1735 if (value > bestValue)
1746 // All legal moves have been searched. A special case: If we're in check
1747 // and no legal moves were found, it is checkmate.
1748 if (!moveCount && isCheck) // Mate!
1749 return value_mated_in(ply);
1751 // Update transposition table
1752 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1753 if (bestValue <= oldAlpha)
1755 // If bestValue isn't changed it means it is still the static evaluation
1756 // of the node, so keep this info to avoid a future evaluation() call.
1757 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1758 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1760 else if (bestValue >= beta)
1762 move = ss[ply].pv[ply];
1763 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1765 // Update killers only for good checking moves
1766 if (!pos.move_is_capture_or_promotion(move))
1767 update_killers(move, ss[ply]);
1770 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1772 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1778 // sp_search() is used to search from a split point. This function is called
1779 // by each thread working at the split point. It is similar to the normal
1780 // search() function, but simpler. Because we have already probed the hash
1781 // table, done a null move search, and searched the first move before
1782 // splitting, we don't have to repeat all this work in sp_search(). We
1783 // also don't need to store anything to the hash table here: This is taken
1784 // care of after we return from the split point.
1786 void sp_search(SplitPoint* sp, int threadID) {
1788 assert(threadID >= 0 && threadID < TM.active_threads());
1789 assert(TM.active_threads() > 1);
1793 Depth ext, newDepth;
1794 Value value, futilityValueScaled;
1795 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1797 value = -VALUE_INFINITE;
1799 Position pos(*sp->pos);
1801 SearchStack* ss = sp->sstack[threadID];
1802 isCheck = pos.is_check();
1804 // Step 10. Loop through moves
1805 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1806 lock_grab(&(sp->lock));
1808 while ( sp->bestValue < sp->beta
1809 && !TM.thread_should_stop(threadID)
1810 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1812 moveCount = ++sp->moves;
1813 lock_release(&(sp->lock));
1815 assert(move_is_ok(move));
1817 moveIsCheck = pos.move_is_check(move, ci);
1818 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1820 // Step 11. Decide the new search depth
1821 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1822 newDepth = sp->depth - OnePly + ext;
1824 // Update current move
1825 ss[sp->ply].currentMove = move;
1827 // Step 12. Futility pruning
1830 && !captureOrPromotion
1831 && !move_is_castle(move))
1833 // Move count based pruning
1834 if ( moveCount >= futility_move_count(sp->depth)
1835 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1836 && sp->bestValue > value_mated_in(PLY_MAX))
1838 lock_grab(&(sp->lock));
1842 // Value based pruning
1843 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1844 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1845 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1847 if (futilityValueScaled < sp->beta)
1849 lock_grab(&(sp->lock));
1851 if (futilityValueScaled > sp->bestValue)
1852 sp->bestValue = futilityValueScaled;
1857 // Step 13. Make the move
1858 pos.do_move(move, st, ci, moveIsCheck);
1860 // Step 14. Reduced search
1861 // if the move fails high will be re-searched at full depth.
1862 bool doFullDepthSearch = true;
1865 && !captureOrPromotion
1866 && !move_is_castle(move)
1867 && !move_is_killer(move, ss[sp->ply]))
1869 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1870 if (ss[sp->ply].reduction)
1872 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1873 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1877 // Step 15. Full depth search
1878 if (doFullDepthSearch)
1880 ss[sp->ply].reduction = Depth(0);
1881 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1884 // Step 16. Undo move
1885 pos.undo_move(move);
1887 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1889 // Step 17. Check for new best move
1890 lock_grab(&(sp->lock));
1892 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1894 sp->bestValue = value;
1895 if (sp->bestValue >= sp->beta)
1897 sp->stopRequest = true;
1898 sp_update_pv(sp->parentSstack, ss, sp->ply);
1903 /* Here we have the lock still grabbed */
1905 sp->slaves[threadID] = 0;
1908 lock_release(&(sp->lock));
1912 // sp_search_pv() is used to search from a PV split point. This function
1913 // is called by each thread working at the split point. It is similar to
1914 // the normal search_pv() function, but simpler. Because we have already
1915 // probed the hash table and searched the first move before splitting, we
1916 // don't have to repeat all this work in sp_search_pv(). We also don't
1917 // need to store anything to the hash table here: This is taken care of
1918 // after we return from the split point.
1920 void sp_search_pv(SplitPoint* sp, int threadID) {
1922 assert(threadID >= 0 && threadID < TM.active_threads());
1923 assert(TM.active_threads() > 1);
1927 Depth ext, newDepth;
1929 bool moveIsCheck, captureOrPromotion, dangerous;
1931 value = -VALUE_INFINITE;
1933 Position pos(*sp->pos);
1935 SearchStack* ss = sp->sstack[threadID];
1937 // Step 10. Loop through moves
1938 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1939 lock_grab(&(sp->lock));
1941 while ( sp->alpha < sp->beta
1942 && !TM.thread_should_stop(threadID)
1943 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1945 moveCount = ++sp->moves;
1946 lock_release(&(sp->lock));
1948 assert(move_is_ok(move));
1950 moveIsCheck = pos.move_is_check(move, ci);
1951 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1953 // Step 11. Decide the new search depth
1954 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1955 newDepth = sp->depth - OnePly + ext;
1957 // Update current move
1958 ss[sp->ply].currentMove = move;
1960 // Step 12. Futility pruning (is omitted in PV nodes)
1962 // Step 13. Make the move
1963 pos.do_move(move, st, ci, moveIsCheck);
1965 // Step 14. Reduced search
1966 // if the move fails high will be re-searched at full depth.
1967 bool doFullDepthSearch = true;
1970 && !captureOrPromotion
1971 && !move_is_castle(move)
1972 && !move_is_killer(move, ss[sp->ply]))
1974 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1975 if (ss[sp->ply].reduction)
1977 Value localAlpha = sp->alpha;
1978 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1979 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1983 // Step 15. Full depth search
1984 if (doFullDepthSearch)
1986 Value localAlpha = sp->alpha;
1987 ss[sp->ply].reduction = Depth(0);
1988 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1990 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1992 // If another thread has failed high then sp->alpha has been increased
1993 // to be higher or equal then beta, if so, avoid to start a PV search.
1994 localAlpha = sp->alpha;
1995 if (localAlpha < sp->beta)
1996 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2000 // Step 16. Undo move
2001 pos.undo_move(move);
2003 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2005 // Step 17. Check for new best move
2006 lock_grab(&(sp->lock));
2008 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
2010 sp->bestValue = value;
2011 if (value > sp->alpha)
2013 // Ask threads to stop before to modify sp->alpha
2014 if (value >= sp->beta)
2015 sp->stopRequest = true;
2019 sp_update_pv(sp->parentSstack, ss, sp->ply);
2020 if (value == value_mate_in(sp->ply + 1))
2021 ss[sp->ply].mateKiller = move;
2026 /* Here we have the lock still grabbed */
2028 sp->slaves[threadID] = 0;
2031 lock_release(&(sp->lock));
2035 // init_node() is called at the beginning of all the search functions
2036 // (search(), search_pv(), qsearch(), and so on) and initializes the
2037 // search stack object corresponding to the current node. Once every
2038 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2039 // for user input and checks whether it is time to stop the search.
2041 void init_node(SearchStack ss[], int ply, int threadID) {
2043 assert(ply >= 0 && ply < PLY_MAX);
2044 assert(threadID >= 0 && threadID < TM.active_threads());
2046 TM.incrementNodeCounter(threadID);
2051 if (NodesSincePoll >= NodesBetweenPolls)
2058 ss[ply + 2].initKillers();
2062 // update_pv() is called whenever a search returns a value > alpha.
2063 // It updates the PV in the SearchStack object corresponding to the
2066 void update_pv(SearchStack ss[], int ply) {
2068 assert(ply >= 0 && ply < PLY_MAX);
2072 ss[ply].pv[ply] = ss[ply].currentMove;
2074 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2075 ss[ply].pv[p] = ss[ply + 1].pv[p];
2077 ss[ply].pv[p] = MOVE_NONE;
2081 // sp_update_pv() is a variant of update_pv for use at split points. The
2082 // difference between the two functions is that sp_update_pv also updates
2083 // the PV at the parent node.
2085 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2087 assert(ply >= 0 && ply < PLY_MAX);
2091 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2093 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2094 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2096 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2100 // connected_moves() tests whether two moves are 'connected' in the sense
2101 // that the first move somehow made the second move possible (for instance
2102 // if the moving piece is the same in both moves). The first move is assumed
2103 // to be the move that was made to reach the current position, while the
2104 // second move is assumed to be a move from the current position.
2106 bool connected_moves(const Position& pos, Move m1, Move m2) {
2108 Square f1, t1, f2, t2;
2111 assert(move_is_ok(m1));
2112 assert(move_is_ok(m2));
2114 if (m2 == MOVE_NONE)
2117 // Case 1: The moving piece is the same in both moves
2123 // Case 2: The destination square for m2 was vacated by m1
2129 // Case 3: Moving through the vacated square
2130 if ( piece_is_slider(pos.piece_on(f2))
2131 && bit_is_set(squares_between(f2, t2), f1))
2134 // Case 4: The destination square for m2 is defended by the moving piece in m1
2135 p = pos.piece_on(t1);
2136 if (bit_is_set(pos.attacks_from(p, t1), t2))
2139 // Case 5: Discovered check, checking piece is the piece moved in m1
2140 if ( piece_is_slider(p)
2141 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2142 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2144 // discovered_check_candidates() works also if the Position's side to
2145 // move is the opposite of the checking piece.
2146 Color them = opposite_color(pos.side_to_move());
2147 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2149 if (bit_is_set(dcCandidates, f2))
2156 // value_is_mate() checks if the given value is a mate one
2157 // eventually compensated for the ply.
2159 bool value_is_mate(Value value) {
2161 assert(abs(value) <= VALUE_INFINITE);
2163 return value <= value_mated_in(PLY_MAX)
2164 || value >= value_mate_in(PLY_MAX);
2168 // move_is_killer() checks if the given move is among the
2169 // killer moves of that ply.
2171 bool move_is_killer(Move m, const SearchStack& ss) {
2173 const Move* k = ss.killers;
2174 for (int i = 0; i < KILLER_MAX; i++, k++)
2182 // extension() decides whether a move should be searched with normal depth,
2183 // or with extended depth. Certain classes of moves (checking moves, in
2184 // particular) are searched with bigger depth than ordinary moves and in
2185 // any case are marked as 'dangerous'. Note that also if a move is not
2186 // extended, as example because the corresponding UCI option is set to zero,
2187 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2189 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2190 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2192 assert(m != MOVE_NONE);
2194 Depth result = Depth(0);
2195 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2200 result += CheckExtension[pvNode];
2203 result += SingleEvasionExtension[pvNode];
2206 result += MateThreatExtension[pvNode];
2209 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2211 Color c = pos.side_to_move();
2212 if (relative_rank(c, move_to(m)) == RANK_7)
2214 result += PawnPushTo7thExtension[pvNode];
2217 if (pos.pawn_is_passed(c, move_to(m)))
2219 result += PassedPawnExtension[pvNode];
2224 if ( captureOrPromotion
2225 && pos.type_of_piece_on(move_to(m)) != PAWN
2226 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2227 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2228 && !move_is_promotion(m)
2231 result += PawnEndgameExtension[pvNode];
2236 && captureOrPromotion
2237 && pos.type_of_piece_on(move_to(m)) != PAWN
2238 && pos.see_sign(m) >= 0)
2244 return Min(result, OnePly);
2248 // ok_to_do_nullmove() looks at the current position and decides whether
2249 // doing a 'null move' should be allowed. In order to avoid zugzwang
2250 // problems, null moves are not allowed when the side to move has very
2251 // little material left. Currently, the test is a bit too simple: Null
2252 // moves are avoided only when the side to move has only pawns left.
2253 // It's probably a good idea to avoid null moves in at least some more
2254 // complicated endgames, e.g. KQ vs KR. FIXME
2256 bool ok_to_do_nullmove(const Position& pos) {
2258 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2262 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2263 // non-tactical moves late in the move list close to the leaves are
2264 // candidates for pruning.
2266 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2268 assert(move_is_ok(m));
2269 assert(threat == MOVE_NONE || move_is_ok(threat));
2270 assert(!pos.move_is_check(m));
2271 assert(!pos.move_is_capture_or_promotion(m));
2272 assert(!pos.move_is_passed_pawn_push(m));
2274 Square mfrom, mto, tfrom, tto;
2276 // Prune if there isn't any threat move
2277 if (threat == MOVE_NONE)
2280 mfrom = move_from(m);
2282 tfrom = move_from(threat);
2283 tto = move_to(threat);
2285 // Case 1: Don't prune moves which move the threatened piece
2289 // Case 2: If the threatened piece has value less than or equal to the
2290 // value of the threatening piece, don't prune move which defend it.
2291 if ( pos.move_is_capture(threat)
2292 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2293 || pos.type_of_piece_on(tfrom) == KING)
2294 && pos.move_attacks_square(m, tto))
2297 // Case 3: If the moving piece in the threatened move is a slider, don't
2298 // prune safe moves which block its ray.
2299 if ( piece_is_slider(pos.piece_on(tfrom))
2300 && bit_is_set(squares_between(tfrom, tto), mto)
2301 && pos.see_sign(m) >= 0)
2308 // ok_to_use_TT() returns true if a transposition table score
2309 // can be used at a given point in search.
2311 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2313 Value v = value_from_tt(tte->value(), ply);
2315 return ( tte->depth() >= depth
2316 || v >= Max(value_mate_in(PLY_MAX), beta)
2317 || v < Min(value_mated_in(PLY_MAX), beta))
2319 && ( (is_lower_bound(tte->type()) && v >= beta)
2320 || (is_upper_bound(tte->type()) && v < beta));
2324 // refine_eval() returns the transposition table score if
2325 // possible otherwise falls back on static position evaluation.
2327 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2332 Value v = value_from_tt(tte->value(), ply);
2334 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2335 || (is_upper_bound(tte->type()) && v < defaultEval))
2342 // update_history() registers a good move that produced a beta-cutoff
2343 // in history and marks as failures all the other moves of that ply.
2345 void update_history(const Position& pos, Move move, Depth depth,
2346 Move movesSearched[], int moveCount) {
2350 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2352 for (int i = 0; i < moveCount - 1; i++)
2354 m = movesSearched[i];
2358 if (!pos.move_is_capture_or_promotion(m))
2359 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2364 // update_killers() add a good move that produced a beta-cutoff
2365 // among the killer moves of that ply.
2367 void update_killers(Move m, SearchStack& ss) {
2369 if (m == ss.killers[0])
2372 for (int i = KILLER_MAX - 1; i > 0; i--)
2373 ss.killers[i] = ss.killers[i - 1];
2379 // update_gains() updates the gains table of a non-capture move given
2380 // the static position evaluation before and after the move.
2382 void update_gains(const Position& pos, Move m, Value before, Value after) {
2385 && before != VALUE_NONE
2386 && after != VALUE_NONE
2387 && pos.captured_piece() == NO_PIECE_TYPE
2388 && !move_is_castle(m)
2389 && !move_is_promotion(m))
2390 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2394 // current_search_time() returns the number of milliseconds which have passed
2395 // since the beginning of the current search.
2397 int current_search_time() {
2399 return get_system_time() - SearchStartTime;
2403 // nps() computes the current nodes/second count.
2407 int t = current_search_time();
2408 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2412 // poll() performs two different functions: It polls for user input, and it
2413 // looks at the time consumed so far and decides if it's time to abort the
2416 void poll(SearchStack ss[], int ply) {
2418 static int lastInfoTime;
2419 int t = current_search_time();
2424 // We are line oriented, don't read single chars
2425 std::string command;
2427 if (!std::getline(std::cin, command))
2430 if (command == "quit")
2433 PonderSearch = false;
2437 else if (command == "stop")
2440 PonderSearch = false;
2442 else if (command == "ponderhit")
2446 // Print search information
2450 else if (lastInfoTime > t)
2451 // HACK: Must be a new search where we searched less than
2452 // NodesBetweenPolls nodes during the first second of search.
2455 else if (t - lastInfoTime >= 1000)
2462 if (dbg_show_hit_rate)
2463 dbg_print_hit_rate();
2465 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2466 << " time " << t << " hashfull " << TT.full() << endl;
2468 // We only support current line printing in single thread mode
2469 if (ShowCurrentLine && TM.active_threads() == 1)
2471 cout << "info currline";
2472 for (int p = 0; p < ply; p++)
2473 cout << " " << ss[p].currentMove;
2479 // Should we stop the search?
2483 bool stillAtFirstMove = FirstRootMove
2484 && !AspirationFailLow
2485 && t > MaxSearchTime + ExtraSearchTime;
2487 bool noMoreTime = t > AbsoluteMaxSearchTime
2488 || stillAtFirstMove;
2490 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2491 || (ExactMaxTime && t >= ExactMaxTime)
2492 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2497 // ponderhit() is called when the program is pondering (i.e. thinking while
2498 // it's the opponent's turn to move) in order to let the engine know that
2499 // it correctly predicted the opponent's move.
2503 int t = current_search_time();
2504 PonderSearch = false;
2506 bool stillAtFirstMove = FirstRootMove
2507 && !AspirationFailLow
2508 && t > MaxSearchTime + ExtraSearchTime;
2510 bool noMoreTime = t > AbsoluteMaxSearchTime
2511 || stillAtFirstMove;
2513 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2518 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2520 void init_ss_array(SearchStack ss[]) {
2522 for (int i = 0; i < 3; i++)
2525 ss[i].initKillers();
2530 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2531 // while the program is pondering. The point is to work around a wrinkle in
2532 // the UCI protocol: When pondering, the engine is not allowed to give a
2533 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2534 // We simply wait here until one of these commands is sent, and return,
2535 // after which the bestmove and pondermove will be printed (in id_loop()).
2537 void wait_for_stop_or_ponderhit() {
2539 std::string command;
2543 if (!std::getline(std::cin, command))
2546 if (command == "quit")
2551 else if (command == "ponderhit" || command == "stop")
2557 // print_pv_info() prints to standard output and eventually to log file information on
2558 // the current PV line. It is called at each iteration or after a new pv is found.
2560 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2562 cout << "info depth " << Iteration
2563 << " score " << value_to_string(value)
2564 << ((value >= beta) ? " lowerbound" :
2565 ((value <= alpha)? " upperbound" : ""))
2566 << " time " << current_search_time()
2567 << " nodes " << TM.nodes_searched()
2571 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2572 cout << ss[0].pv[j] << " ";
2578 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2579 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2581 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2582 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2587 // init_thread() is the function which is called when a new thread is
2588 // launched. It simply calls the idle_loop() function with the supplied
2589 // threadID. There are two versions of this function; one for POSIX
2590 // threads and one for Windows threads.
2592 #if !defined(_MSC_VER)
2594 void* init_thread(void *threadID) {
2596 TM.idle_loop(*(int*)threadID, NULL);
2602 DWORD WINAPI init_thread(LPVOID threadID) {
2604 TM.idle_loop(*(int*)threadID, NULL);
2611 /// The ThreadsManager class
2613 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2614 // get_beta_counters() are getters/setters for the per thread
2615 // counters used to sort the moves at root.
2617 void ThreadsManager::resetNodeCounters() {
2619 for (int i = 0; i < MAX_THREADS; i++)
2620 threads[i].nodes = 0ULL;
2623 void ThreadsManager::resetBetaCounters() {
2625 for (int i = 0; i < MAX_THREADS; i++)
2626 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2629 int64_t ThreadsManager::nodes_searched() const {
2631 int64_t result = 0ULL;
2632 for (int i = 0; i < ActiveThreads; i++)
2633 result += threads[i].nodes;
2638 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2641 for (int i = 0; i < MAX_THREADS; i++)
2643 our += threads[i].betaCutOffs[us];
2644 their += threads[i].betaCutOffs[opposite_color(us)];
2649 // idle_loop() is where the threads are parked when they have no work to do.
2650 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2651 // object for which the current thread is the master.
2653 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2655 assert(threadID >= 0 && threadID < MAX_THREADS);
2659 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2660 // master should exit as last one.
2661 if (AllThreadsShouldExit)
2664 threads[threadID].state = THREAD_TERMINATED;
2668 // If we are not thinking, wait for a condition to be signaled
2669 // instead of wasting CPU time polling for work.
2670 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2673 assert(threadID != 0);
2674 threads[threadID].state = THREAD_SLEEPING;
2676 #if !defined(_MSC_VER)
2677 lock_grab(&WaitLock);
2678 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2679 pthread_cond_wait(&WaitCond, &WaitLock);
2680 lock_release(&WaitLock);
2682 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2686 // If thread has just woken up, mark it as available
2687 if (threads[threadID].state == THREAD_SLEEPING)
2688 threads[threadID].state = THREAD_AVAILABLE;
2690 // If this thread has been assigned work, launch a search
2691 if (threads[threadID].state == THREAD_WORKISWAITING)
2693 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2695 threads[threadID].state = THREAD_SEARCHING;
2697 if (threads[threadID].splitPoint->pvNode)
2698 sp_search_pv(threads[threadID].splitPoint, threadID);
2700 sp_search(threads[threadID].splitPoint, threadID);
2702 assert(threads[threadID].state == THREAD_SEARCHING);
2704 threads[threadID].state = THREAD_AVAILABLE;
2707 // If this thread is the master of a split point and all threads have
2708 // finished their work at this split point, return from the idle loop.
2709 if (waitSp != NULL && waitSp->cpus == 0)
2711 assert(threads[threadID].state == THREAD_AVAILABLE);
2713 threads[threadID].state = THREAD_SEARCHING;
2720 // init_threads() is called during startup. It launches all helper threads,
2721 // and initializes the split point stack and the global locks and condition
2724 void ThreadsManager::init_threads() {
2729 #if !defined(_MSC_VER)
2730 pthread_t pthread[1];
2733 // Initialize global locks
2734 lock_init(&MPLock, NULL);
2735 lock_init(&WaitLock, NULL);
2737 #if !defined(_MSC_VER)
2738 pthread_cond_init(&WaitCond, NULL);
2740 for (i = 0; i < MAX_THREADS; i++)
2741 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2744 // Initialize SplitPointStack locks
2745 for (i = 0; i < MAX_THREADS; i++)
2746 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2748 SplitPointStack[i][j].parent = NULL;
2749 lock_init(&(SplitPointStack[i][j].lock), NULL);
2752 // Will be set just before program exits to properly end the threads
2753 AllThreadsShouldExit = false;
2755 // Threads will be put to sleep as soon as created
2756 AllThreadsShouldSleep = true;
2758 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2760 threads[0].state = THREAD_SEARCHING;
2761 for (i = 1; i < MAX_THREADS; i++)
2762 threads[i].state = THREAD_AVAILABLE;
2764 // Launch the helper threads
2765 for (i = 1; i < MAX_THREADS; i++)
2768 #if !defined(_MSC_VER)
2769 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2771 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2776 cout << "Failed to create thread number " << i << endl;
2777 Application::exit_with_failure();
2780 // Wait until the thread has finished launching and is gone to sleep
2781 while (threads[i].state != THREAD_SLEEPING);
2786 // exit_threads() is called when the program exits. It makes all the
2787 // helper threads exit cleanly.
2789 void ThreadsManager::exit_threads() {
2791 ActiveThreads = MAX_THREADS; // HACK
2792 AllThreadsShouldSleep = true; // HACK
2793 wake_sleeping_threads();
2795 // This makes the threads to exit idle_loop()
2796 AllThreadsShouldExit = true;
2798 // Wait for thread termination
2799 for (int i = 1; i < MAX_THREADS; i++)
2800 while (threads[i].state != THREAD_TERMINATED);
2802 // Now we can safely destroy the locks
2803 for (int i = 0; i < MAX_THREADS; i++)
2804 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2805 lock_destroy(&(SplitPointStack[i][j].lock));
2807 lock_destroy(&WaitLock);
2808 lock_destroy(&MPLock);
2812 // thread_should_stop() checks whether the thread should stop its search.
2813 // This can happen if a beta cutoff has occurred in the thread's currently
2814 // active split point, or in some ancestor of the current split point.
2816 bool ThreadsManager::thread_should_stop(int threadID) const {
2818 assert(threadID >= 0 && threadID < ActiveThreads);
2822 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2827 // thread_is_available() checks whether the thread with threadID "slave" is
2828 // available to help the thread with threadID "master" at a split point. An
2829 // obvious requirement is that "slave" must be idle. With more than two
2830 // threads, this is not by itself sufficient: If "slave" is the master of
2831 // some active split point, it is only available as a slave to the other
2832 // threads which are busy searching the split point at the top of "slave"'s
2833 // split point stack (the "helpful master concept" in YBWC terminology).
2835 bool ThreadsManager::thread_is_available(int slave, int master) const {
2837 assert(slave >= 0 && slave < ActiveThreads);
2838 assert(master >= 0 && master < ActiveThreads);
2839 assert(ActiveThreads > 1);
2841 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2844 // Make a local copy to be sure doesn't change under our feet
2845 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2847 if (localActiveSplitPoints == 0)
2848 // No active split points means that the thread is available as
2849 // a slave for any other thread.
2852 if (ActiveThreads == 2)
2855 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2856 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2857 // could have been set to 0 by another thread leading to an out of bound access.
2858 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2865 // available_thread_exists() tries to find an idle thread which is available as
2866 // a slave for the thread with threadID "master".
2868 bool ThreadsManager::available_thread_exists(int master) const {
2870 assert(master >= 0 && master < ActiveThreads);
2871 assert(ActiveThreads > 1);
2873 for (int i = 0; i < ActiveThreads; i++)
2874 if (thread_is_available(i, master))
2881 // split() does the actual work of distributing the work at a node between
2882 // several threads at PV nodes. If it does not succeed in splitting the
2883 // node (because no idle threads are available, or because we have no unused
2884 // split point objects), the function immediately returns false. If
2885 // splitting is possible, a SplitPoint object is initialized with all the
2886 // data that must be copied to the helper threads (the current position and
2887 // search stack, alpha, beta, the search depth, etc.), and we tell our
2888 // helper threads that they have been assigned work. This will cause them
2889 // to instantly leave their idle loops and call sp_search_pv(). When all
2890 // threads have returned from sp_search_pv (or, equivalently, when
2891 // splitPoint->cpus becomes 0), split() returns true.
2893 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2894 Value* alpha, const Value beta, Value* bestValue,
2895 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2898 assert(sstck != NULL);
2899 assert(ply >= 0 && ply < PLY_MAX);
2900 assert(*bestValue >= -VALUE_INFINITE);
2901 assert( ( pvNode && *bestValue <= *alpha)
2902 || (!pvNode && *bestValue < beta ));
2903 assert(!pvNode || *alpha < beta);
2904 assert(beta <= VALUE_INFINITE);
2905 assert(depth > Depth(0));
2906 assert(master >= 0 && master < ActiveThreads);
2907 assert(ActiveThreads > 1);
2909 SplitPoint* splitPoint;
2913 // If no other thread is available to help us, or if we have too many
2914 // active split points, don't split.
2915 if ( !available_thread_exists(master)
2916 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2918 lock_release(&MPLock);
2922 // Pick the next available split point object from the split point stack
2923 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2925 // Initialize the split point object
2926 splitPoint->parent = threads[master].splitPoint;
2927 splitPoint->stopRequest = false;
2928 splitPoint->ply = ply;
2929 splitPoint->depth = depth;
2930 splitPoint->mateThreat = mateThreat;
2931 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2932 splitPoint->beta = beta;
2933 splitPoint->pvNode = pvNode;
2934 splitPoint->bestValue = *bestValue;
2935 splitPoint->master = master;
2936 splitPoint->mp = mp;
2937 splitPoint->moves = *moves;
2938 splitPoint->cpus = 1;
2939 splitPoint->pos = &p;
2940 splitPoint->parentSstack = sstck;
2941 for (int i = 0; i < ActiveThreads; i++)
2942 splitPoint->slaves[i] = 0;
2944 threads[master].splitPoint = splitPoint;
2945 threads[master].activeSplitPoints++;
2947 // If we are here it means we are not available
2948 assert(threads[master].state != THREAD_AVAILABLE);
2950 // Allocate available threads setting state to THREAD_BOOKED
2951 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2952 if (thread_is_available(i, master))
2954 threads[i].state = THREAD_BOOKED;
2955 threads[i].splitPoint = splitPoint;
2956 splitPoint->slaves[i] = 1;
2960 assert(splitPoint->cpus > 1);
2962 // We can release the lock because slave threads are already booked and master is not available
2963 lock_release(&MPLock);
2965 // Tell the threads that they have work to do. This will make them leave
2966 // their idle loop. But before copy search stack tail for each thread.
2967 for (int i = 0; i < ActiveThreads; i++)
2968 if (i == master || splitPoint->slaves[i])
2970 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2972 assert(i == master || threads[i].state == THREAD_BOOKED);
2974 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2977 // Everything is set up. The master thread enters the idle loop, from
2978 // which it will instantly launch a search, because its state is
2979 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2980 // idle loop, which means that the main thread will return from the idle
2981 // loop when all threads have finished their work at this split point
2982 // (i.e. when splitPoint->cpus == 0).
2983 idle_loop(master, splitPoint);
2985 // We have returned from the idle loop, which means that all threads are
2986 // finished. Update alpha, beta and bestValue, and return.
2990 *alpha = splitPoint->alpha;
2992 *bestValue = splitPoint->bestValue;
2993 threads[master].activeSplitPoints--;
2994 threads[master].splitPoint = splitPoint->parent;
2996 lock_release(&MPLock);
3001 // wake_sleeping_threads() wakes up all sleeping threads when it is time
3002 // to start a new search from the root.
3004 void ThreadsManager::wake_sleeping_threads() {
3006 assert(AllThreadsShouldSleep);
3007 assert(ActiveThreads > 0);
3009 AllThreadsShouldSleep = false;
3011 if (ActiveThreads == 1)
3014 #if !defined(_MSC_VER)
3015 pthread_mutex_lock(&WaitLock);
3016 pthread_cond_broadcast(&WaitCond);
3017 pthread_mutex_unlock(&WaitLock);
3019 for (int i = 1; i < MAX_THREADS; i++)
3020 SetEvent(SitIdleEvent[i]);
3026 // put_threads_to_sleep() makes all the threads go to sleep just before
3027 // to leave think(), at the end of the search. Threads should have already
3028 // finished the job and should be idle.
3030 void ThreadsManager::put_threads_to_sleep() {
3032 assert(!AllThreadsShouldSleep);
3034 // This makes the threads to go to sleep
3035 AllThreadsShouldSleep = true;
3038 /// The RootMoveList class
3040 // RootMoveList c'tor
3042 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3044 SearchStack ss[PLY_MAX_PLUS_2];
3045 MoveStack mlist[MaxRootMoves];
3047 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3049 // Generate all legal moves
3050 MoveStack* last = generate_moves(pos, mlist);
3052 // Add each move to the moves[] array
3053 for (MoveStack* cur = mlist; cur != last; cur++)
3055 bool includeMove = includeAllMoves;
3057 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3058 includeMove = (searchMoves[k] == cur->move);
3063 // Find a quick score for the move
3065 pos.do_move(cur->move, st);
3066 moves[count].move = cur->move;
3067 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3068 moves[count].pv[0] = cur->move;
3069 moves[count].pv[1] = MOVE_NONE;
3070 pos.undo_move(cur->move);
3077 // RootMoveList simple methods definitions
3079 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3081 moves[moveNum].nodes = nodes;
3082 moves[moveNum].cumulativeNodes += nodes;
3085 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3087 moves[moveNum].ourBeta = our;
3088 moves[moveNum].theirBeta = their;
3091 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3095 for (j = 0; pv[j] != MOVE_NONE; j++)
3096 moves[moveNum].pv[j] = pv[j];
3098 moves[moveNum].pv[j] = MOVE_NONE;
3102 // RootMoveList::sort() sorts the root move list at the beginning of a new
3105 void RootMoveList::sort() {
3107 sort_multipv(count - 1); // Sort all items
3111 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3112 // list by their scores and depths. It is used to order the different PVs
3113 // correctly in MultiPV mode.
3115 void RootMoveList::sort_multipv(int n) {
3119 for (i = 1; i <= n; i++)
3121 RootMove rm = moves[i];
3122 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3123 moves[j] = moves[j - 1];