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 // Step 10. Loop through moves
1105 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1107 // Initialize a MovePicker object for the current position
1108 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1109 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1112 while ( alpha < beta
1113 && (move = mp.get_next_move()) != MOVE_NONE
1114 && !TM.thread_should_stop(threadID))
1116 assert(move_is_ok(move));
1118 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1119 moveIsCheck = pos.move_is_check(move, ci);
1120 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1122 // Step 11. Decide the new search depth
1123 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1125 // Singular extension search. We extend the TT move if its value is much better than
1126 // its siblings. To verify this we do a reduced search on all the other moves but the
1127 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1128 if ( depth >= SingularExtensionDepthAtPVNodes
1130 && move == tte->move()
1132 && is_lower_bound(tte->type())
1133 && tte->depth() >= depth - 3 * OnePly)
1135 Value ttValue = value_from_tt(tte->value(), ply);
1137 if (abs(ttValue) < VALUE_KNOWN_WIN)
1139 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1141 if (excValue < ttValue - SingularExtensionMargin)
1146 newDepth = depth - OnePly + ext;
1148 // Update current move (this must be done after singular extension search)
1149 movesSearched[moveCount++] = ss[ply].currentMove = move;
1151 // Step 12. Futility pruning (is omitted in PV nodes)
1153 // Step 13. Make the move
1154 pos.do_move(move, st, ci, moveIsCheck);
1156 // Step extra. pv search (only in PV nodes)
1157 // The first move in list is the expected PV
1159 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1162 // Step 14. Reduced search
1163 // if the move fails high will be re-searched at full depth.
1164 bool doFullDepthSearch = true;
1166 if ( depth >= 3 * OnePly
1168 && !captureOrPromotion
1169 && !move_is_castle(move)
1170 && !move_is_killer(move, ss[ply]))
1172 ss[ply].reduction = pv_reduction(depth, moveCount);
1173 if (ss[ply].reduction)
1175 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1176 doFullDepthSearch = (value > alpha);
1180 // Step 15. Full depth search
1181 if (doFullDepthSearch)
1183 ss[ply].reduction = Depth(0);
1184 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1186 // Step extra. pv search (only in PV nodes)
1187 if (value > alpha && value < beta)
1188 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1192 // Step 16. Undo move
1193 pos.undo_move(move);
1195 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1197 // Step 17. Check for new best move
1198 if (value > bestValue)
1205 if (value == value_mate_in(ply + 1))
1206 ss[ply].mateKiller = move;
1210 // Step 18. Check for split
1211 if ( TM.active_threads() > 1
1213 && depth >= MinimumSplitDepth
1215 && TM.available_thread_exists(threadID)
1217 && !TM.thread_should_stop(threadID)
1218 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1219 depth, mateThreat, &moveCount, &mp, threadID, true))
1223 // Step 19. Check for mate and stalemate
1224 // All legal moves have been searched and if there were
1225 // no legal moves, it must be mate or stalemate.
1227 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1229 // Step 20. Update tables
1230 // If the search is not aborted, update the transposition table,
1231 // history counters, and killer moves.
1232 if (AbortSearch || TM.thread_should_stop(threadID))
1235 if (bestValue <= oldAlpha)
1236 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1238 else if (bestValue >= beta)
1240 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1241 move = ss[ply].pv[ply];
1242 if (!pos.move_is_capture_or_promotion(move))
1244 update_history(pos, move, depth, movesSearched, moveCount);
1245 update_killers(move, ss[ply]);
1247 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1250 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1256 // search() is the search function for zero-width nodes.
1258 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1259 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1261 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1262 assert(ply >= 0 && ply < PLY_MAX);
1263 assert(threadID >= 0 && threadID < TM.active_threads());
1265 Move movesSearched[256];
1270 Depth ext, newDepth;
1271 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1272 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1273 bool mateThreat = false;
1275 refinedValue = bestValue = value = -VALUE_INFINITE;
1278 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1280 // Step 1. Initialize node and poll
1281 // Polling can abort search.
1282 init_node(ss, ply, threadID);
1284 // Step 2. Check for aborted search and immediate draw
1285 if (AbortSearch || TM.thread_should_stop(threadID))
1288 if (pos.is_draw() || ply >= PLY_MAX - 1)
1291 // Step 3. Mate distance pruning
1292 if (value_mated_in(ply) >= beta)
1295 if (value_mate_in(ply + 1) < beta)
1298 // Step 4. Transposition table lookup
1300 // We don't want the score of a partial search to overwrite a previous full search
1301 // TT value, so we use a different position key in case of an excluded move exists.
1302 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1304 tte = TT.retrieve(posKey);
1305 ttMove = (tte ? tte->move() : MOVE_NONE);
1307 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1309 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1310 return value_from_tt(tte->value(), ply);
1313 // Step 5. Evaluate the position statically
1314 isCheck = pos.is_check();
1318 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1319 ss[ply].eval = value_from_tt(tte->value(), ply);
1321 ss[ply].eval = evaluate(pos, ei, threadID);
1323 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1324 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1328 if ( !value_is_mate(beta)
1330 && depth < RazorDepth
1331 && refinedValue < beta - razor_margin(depth)
1332 && ss[ply - 1].currentMove != MOVE_NULL
1333 && ttMove == MOVE_NONE
1334 && !pos.has_pawn_on_7th(pos.side_to_move()))
1336 Value rbeta = beta - razor_margin(depth);
1337 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1339 // Logically we should return (v + razor_margin(depth)), but
1340 // surprisingly this did slightly weaker in tests.
1344 // Step 7. Static null move pruning
1345 // We're betting that the opponent doesn't have a move that will reduce
1346 // the score by more than fuility_margin(depth) if we do a null move.
1349 && depth < RazorDepth
1350 && refinedValue - futility_margin(depth, 0) >= beta)
1351 return refinedValue - futility_margin(depth, 0);
1353 // Step 8. Null move search with verification search
1354 // When we jump directly to qsearch() we do a null move only if static value is
1355 // at least beta. Otherwise we do a null move if static value is not more than
1356 // NullMoveMargin under beta.
1360 && !value_is_mate(beta)
1361 && ok_to_do_nullmove(pos)
1362 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1364 ss[ply].currentMove = MOVE_NULL;
1366 pos.do_null_move(st);
1368 // Null move dynamic reduction based on depth
1369 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1371 // Null move dynamic reduction based on value
1372 if (refinedValue - beta > PawnValueMidgame)
1375 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1377 pos.undo_null_move();
1379 if (nullValue >= beta)
1381 if (depth < 6 * OnePly)
1384 // Do zugzwang verification search
1385 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1389 // The null move failed low, which means that we may be faced with
1390 // some kind of threat. If the previous move was reduced, check if
1391 // the move that refuted the null move was somehow connected to the
1392 // move which was reduced. If a connection is found, return a fail
1393 // low score (which will cause the reduced move to fail high in the
1394 // parent node, which will trigger a re-search with full depth).
1395 if (nullValue == value_mated_in(ply + 2))
1398 ss[ply].threatMove = ss[ply + 1].currentMove;
1399 if ( depth < ThreatDepth
1400 && ss[ply - 1].reduction
1401 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1406 // Step 9. Internal iterative deepening
1407 if ( depth >= IIDDepthAtNonPVNodes
1408 && ttMove == MOVE_NONE
1410 && ss[ply].eval >= beta - IIDMargin)
1412 search(pos, ss, beta, depth/2, ply, false, threadID);
1413 ttMove = ss[ply].pv[ply];
1414 tte = TT.retrieve(posKey);
1417 // Step 10. Loop through moves
1418 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1420 // Initialize a MovePicker object for the current position
1421 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1424 while ( bestValue < beta
1425 && (move = mp.get_next_move()) != MOVE_NONE
1426 && !TM.thread_should_stop(threadID))
1428 assert(move_is_ok(move));
1430 if (move == excludedMove)
1433 moveIsCheck = pos.move_is_check(move, ci);
1434 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1435 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1437 // Step 11. Decide the new search depth
1438 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1440 // Singular extension search. We extend the TT move if its value is much better than
1441 // its siblings. To verify this we do a reduced search on all the other moves but the
1442 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1443 if ( depth >= SingularExtensionDepthAtNonPVNodes
1445 && move == tte->move()
1446 && !excludedMove // Do not allow recursive single-reply search
1448 && is_lower_bound(tte->type())
1449 && tte->depth() >= depth - 3 * OnePly)
1451 Value ttValue = value_from_tt(tte->value(), ply);
1453 if (abs(ttValue) < VALUE_KNOWN_WIN)
1455 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1457 if (excValue < ttValue - SingularExtensionMargin)
1462 newDepth = depth - OnePly + ext;
1464 // Update current move (this must be done after singular extension search)
1465 movesSearched[moveCount++] = ss[ply].currentMove = move;
1467 // Step 12. Futility pruning
1470 && !captureOrPromotion
1471 && !move_is_castle(move)
1474 // Move count based pruning
1475 if ( moveCount >= futility_move_count(depth)
1476 && ok_to_prune(pos, move, ss[ply].threatMove)
1477 && bestValue > value_mated_in(PLY_MAX))
1480 // Value based pruning
1481 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1482 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1483 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1485 if (futilityValueScaled < beta)
1487 if (futilityValueScaled > bestValue)
1488 bestValue = futilityValueScaled;
1493 // Step 13. Make the move
1494 pos.do_move(move, st, ci, moveIsCheck);
1496 // Step 14. Reduced search
1497 // if the move fails high will be re-searched at full depth.
1498 bool doFullDepthSearch = true;
1500 if ( depth >= 3*OnePly
1502 && !captureOrPromotion
1503 && !move_is_castle(move)
1504 && !move_is_killer(move, ss[ply]))
1506 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1507 if (ss[ply].reduction)
1509 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1510 doFullDepthSearch = (value >= beta);
1514 // Step 15. Full depth search
1515 if (doFullDepthSearch)
1517 ss[ply].reduction = Depth(0);
1518 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1521 // Step 16. Undo move
1522 pos.undo_move(move);
1524 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1526 // Step 17. Check for new best move
1527 if (value > bestValue)
1533 if (value == value_mate_in(ply + 1))
1534 ss[ply].mateKiller = move;
1537 // Step 18. Check for split
1538 if ( TM.active_threads() > 1
1540 && depth >= MinimumSplitDepth
1542 && TM.available_thread_exists(threadID)
1544 && !TM.thread_should_stop(threadID)
1545 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1546 depth, mateThreat, &moveCount, &mp, threadID, false))
1550 // Step 19. Check for mate and stalemate
1551 // All legal moves have been searched and if there were
1552 // no legal moves, it must be mate or stalemate.
1553 // If one move was excluded return fail low.
1555 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1557 // Step 20. Update tables
1558 // If the search is not aborted, update the transposition table,
1559 // history counters, and killer moves.
1560 if (AbortSearch || TM.thread_should_stop(threadID))
1563 if (bestValue < beta)
1564 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1567 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1568 move = ss[ply].pv[ply];
1569 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1570 if (!pos.move_is_capture_or_promotion(move))
1572 update_history(pos, move, depth, movesSearched, moveCount);
1573 update_killers(move, ss[ply]);
1578 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1584 // qsearch() is the quiescence search function, which is called by the main
1585 // search function when the remaining depth is zero (or, to be more precise,
1586 // less than OnePly).
1588 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1589 Depth depth, int ply, int threadID) {
1591 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1592 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1594 assert(ply >= 0 && ply < PLY_MAX);
1595 assert(threadID >= 0 && threadID < TM.active_threads());
1600 Value staticValue, bestValue, value, futilityBase, futilityValue;
1601 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1602 const TTEntry* tte = NULL;
1604 bool pvNode = (beta - alpha != 1);
1605 Value oldAlpha = alpha;
1607 // Initialize, and make an early exit in case of an aborted search,
1608 // an instant draw, maximum ply reached, etc.
1609 init_node(ss, ply, threadID);
1611 // After init_node() that calls poll()
1612 if (AbortSearch || TM.thread_should_stop(threadID))
1615 if (pos.is_draw() || ply >= PLY_MAX - 1)
1618 // Transposition table lookup. At PV nodes, we don't use the TT for
1619 // pruning, but only for move ordering.
1620 tte = TT.retrieve(pos.get_key());
1621 ttMove = (tte ? tte->move() : MOVE_NONE);
1623 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1625 assert(tte->type() != VALUE_TYPE_EVAL);
1627 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1628 return value_from_tt(tte->value(), ply);
1631 isCheck = pos.is_check();
1633 // Evaluate the position statically
1635 staticValue = -VALUE_INFINITE;
1636 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1637 staticValue = value_from_tt(tte->value(), ply);
1639 staticValue = evaluate(pos, ei, threadID);
1643 ss[ply].eval = staticValue;
1644 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1647 // Initialize "stand pat score", and return it immediately if it is
1649 bestValue = staticValue;
1651 if (bestValue >= beta)
1653 // Store the score to avoid a future costly evaluation() call
1654 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1655 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1660 if (bestValue > alpha)
1663 // If we are near beta then try to get a cutoff pushing checks a bit further
1664 bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
1666 // Initialize a MovePicker object for the current position, and prepare
1667 // to search the moves. Because the depth is <= 0 here, only captures,
1668 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1669 // and we are near beta) will be generated.
1670 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1672 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1673 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1675 // Loop through the moves until no moves remain or a beta cutoff
1677 while ( alpha < beta
1678 && (move = mp.get_next_move()) != MOVE_NONE)
1680 assert(move_is_ok(move));
1682 moveIsCheck = pos.move_is_check(move, ci);
1684 // Update current move
1686 ss[ply].currentMove = move;
1694 && !move_is_promotion(move)
1695 && !pos.move_is_passed_pawn_push(move))
1697 futilityValue = futilityBase
1698 + pos.endgame_value_of_piece_on(move_to(move))
1699 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1701 if (futilityValue < alpha)
1703 if (futilityValue > bestValue)
1704 bestValue = futilityValue;
1709 // Detect blocking evasions that are candidate to be pruned
1710 evasionPrunable = isCheck
1711 && bestValue != -VALUE_INFINITE
1712 && !pos.move_is_capture(move)
1713 && pos.type_of_piece_on(move_from(move)) != KING
1714 && !pos.can_castle(pos.side_to_move());
1716 // Don't search moves with negative SEE values
1717 if ( (!isCheck || evasionPrunable)
1720 && !move_is_promotion(move)
1721 && pos.see_sign(move) < 0)
1724 // Make and search the move
1725 pos.do_move(move, st, ci, moveIsCheck);
1726 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1727 pos.undo_move(move);
1729 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1732 if (value > bestValue)
1743 // All legal moves have been searched. A special case: If we're in check
1744 // and no legal moves were found, it is checkmate.
1745 if (!moveCount && pos.is_check()) // Mate!
1746 return value_mated_in(ply);
1748 // Update transposition table
1749 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1750 if (bestValue <= oldAlpha)
1752 // If bestValue isn't changed it means it is still the static evaluation
1753 // of the node, so keep this info to avoid a future evaluation() call.
1754 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1755 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1757 else if (bestValue >= beta)
1759 move = ss[ply].pv[ply];
1760 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1762 // Update killers only for good checking moves
1763 if (!pos.move_is_capture_or_promotion(move))
1764 update_killers(move, ss[ply]);
1767 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1769 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1775 // sp_search() is used to search from a split point. This function is called
1776 // by each thread working at the split point. It is similar to the normal
1777 // search() function, but simpler. Because we have already probed the hash
1778 // table, done a null move search, and searched the first move before
1779 // splitting, we don't have to repeat all this work in sp_search(). We
1780 // also don't need to store anything to the hash table here: This is taken
1781 // care of after we return from the split point.
1783 void sp_search(SplitPoint* sp, int threadID) {
1785 assert(threadID >= 0 && threadID < TM.active_threads());
1786 assert(TM.active_threads() > 1);
1790 Depth ext, newDepth;
1791 Value value, futilityValueScaled;
1792 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1794 value = -VALUE_INFINITE;
1796 Position pos(*sp->pos);
1798 SearchStack* ss = sp->sstack[threadID];
1799 isCheck = pos.is_check();
1801 // Step 10. Loop through moves
1802 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1803 lock_grab(&(sp->lock));
1805 while ( sp->bestValue < sp->beta
1806 && !TM.thread_should_stop(threadID)
1807 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1809 moveCount = ++sp->moves;
1810 lock_release(&(sp->lock));
1812 assert(move_is_ok(move));
1814 moveIsCheck = pos.move_is_check(move, ci);
1815 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1817 // Step 11. Decide the new search depth
1818 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1819 newDepth = sp->depth - OnePly + ext;
1821 // Update current move
1822 ss[sp->ply].currentMove = move;
1824 // Step 12. Futility pruning
1827 && !captureOrPromotion
1828 && !move_is_castle(move))
1830 // Move count based pruning
1831 if ( moveCount >= futility_move_count(sp->depth)
1832 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1833 && sp->bestValue > value_mated_in(PLY_MAX))
1835 lock_grab(&(sp->lock));
1839 // Value based pruning
1840 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1841 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1842 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1844 if (futilityValueScaled < sp->beta)
1846 lock_grab(&(sp->lock));
1848 if (futilityValueScaled > sp->bestValue)
1849 sp->bestValue = futilityValueScaled;
1854 // Step 13. Make the move
1855 pos.do_move(move, st, ci, moveIsCheck);
1857 // Step 14. Reduced search
1858 // if the move fails high will be re-searched at full depth.
1859 bool doFullDepthSearch = true;
1862 && !captureOrPromotion
1863 && !move_is_castle(move)
1864 && !move_is_killer(move, ss[sp->ply]))
1866 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1867 if (ss[sp->ply].reduction)
1869 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1870 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1874 // Step 15. Full depth search
1875 if (doFullDepthSearch)
1877 ss[sp->ply].reduction = Depth(0);
1878 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1881 // Step 16. Undo move
1882 pos.undo_move(move);
1884 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1886 // Step 17. Check for new best move
1887 lock_grab(&(sp->lock));
1889 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1891 sp->bestValue = value;
1892 if (sp->bestValue >= sp->beta)
1894 sp->stopRequest = true;
1895 sp_update_pv(sp->parentSstack, ss, sp->ply);
1900 /* Here we have the lock still grabbed */
1902 sp->slaves[threadID] = 0;
1905 lock_release(&(sp->lock));
1909 // sp_search_pv() is used to search from a PV split point. This function
1910 // is called by each thread working at the split point. It is similar to
1911 // the normal search_pv() function, but simpler. Because we have already
1912 // probed the hash table and searched the first move before splitting, we
1913 // don't have to repeat all this work in sp_search_pv(). We also don't
1914 // need to store anything to the hash table here: This is taken care of
1915 // after we return from the split point.
1917 void sp_search_pv(SplitPoint* sp, int threadID) {
1919 assert(threadID >= 0 && threadID < TM.active_threads());
1920 assert(TM.active_threads() > 1);
1924 Depth ext, newDepth;
1926 bool moveIsCheck, captureOrPromotion, dangerous;
1928 value = -VALUE_INFINITE;
1930 Position pos(*sp->pos);
1932 SearchStack* ss = sp->sstack[threadID];
1934 // Step 10. Loop through moves
1935 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1936 lock_grab(&(sp->lock));
1938 while ( sp->alpha < sp->beta
1939 && !TM.thread_should_stop(threadID)
1940 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1942 moveCount = ++sp->moves;
1943 lock_release(&(sp->lock));
1945 assert(move_is_ok(move));
1947 moveIsCheck = pos.move_is_check(move, ci);
1948 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1950 // Step 11. Decide the new search depth
1951 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1952 newDepth = sp->depth - OnePly + ext;
1954 // Update current move
1955 ss[sp->ply].currentMove = move;
1957 // Step 12. Futility pruning (is omitted in PV nodes)
1959 // Step 13. Make the move
1960 pos.do_move(move, st, ci, moveIsCheck);
1962 // Step 14. Reduced search
1963 // if the move fails high will be re-searched at full depth.
1964 bool doFullDepthSearch = true;
1967 && !captureOrPromotion
1968 && !move_is_castle(move)
1969 && !move_is_killer(move, ss[sp->ply]))
1971 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1972 if (ss[sp->ply].reduction)
1974 Value localAlpha = sp->alpha;
1975 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1976 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1980 // Step 15. Full depth search
1981 if (doFullDepthSearch)
1983 Value localAlpha = sp->alpha;
1984 ss[sp->ply].reduction = Depth(0);
1985 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1987 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1989 // If another thread has failed high then sp->alpha has been increased
1990 // to be higher or equal then beta, if so, avoid to start a PV search.
1991 localAlpha = sp->alpha;
1992 if (localAlpha < sp->beta)
1993 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1997 // Step 16. Undo move
1998 pos.undo_move(move);
2000 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2002 // Step 17. Check for new best move
2003 lock_grab(&(sp->lock));
2005 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
2007 sp->bestValue = value;
2008 if (value > sp->alpha)
2010 // Ask threads to stop before to modify sp->alpha
2011 if (value >= sp->beta)
2012 sp->stopRequest = true;
2016 sp_update_pv(sp->parentSstack, ss, sp->ply);
2017 if (value == value_mate_in(sp->ply + 1))
2018 ss[sp->ply].mateKiller = move;
2023 /* Here we have the lock still grabbed */
2025 sp->slaves[threadID] = 0;
2028 lock_release(&(sp->lock));
2032 // init_node() is called at the beginning of all the search functions
2033 // (search(), search_pv(), qsearch(), and so on) and initializes the
2034 // search stack object corresponding to the current node. Once every
2035 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2036 // for user input and checks whether it is time to stop the search.
2038 void init_node(SearchStack ss[], int ply, int threadID) {
2040 assert(ply >= 0 && ply < PLY_MAX);
2041 assert(threadID >= 0 && threadID < TM.active_threads());
2043 TM.incrementNodeCounter(threadID);
2048 if (NodesSincePoll >= NodesBetweenPolls)
2055 ss[ply + 2].initKillers();
2059 // update_pv() is called whenever a search returns a value > alpha.
2060 // It updates the PV in the SearchStack object corresponding to the
2063 void update_pv(SearchStack ss[], int ply) {
2065 assert(ply >= 0 && ply < PLY_MAX);
2069 ss[ply].pv[ply] = ss[ply].currentMove;
2071 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2072 ss[ply].pv[p] = ss[ply + 1].pv[p];
2074 ss[ply].pv[p] = MOVE_NONE;
2078 // sp_update_pv() is a variant of update_pv for use at split points. The
2079 // difference between the two functions is that sp_update_pv also updates
2080 // the PV at the parent node.
2082 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2084 assert(ply >= 0 && ply < PLY_MAX);
2088 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2090 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2091 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2093 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2097 // connected_moves() tests whether two moves are 'connected' in the sense
2098 // that the first move somehow made the second move possible (for instance
2099 // if the moving piece is the same in both moves). The first move is assumed
2100 // to be the move that was made to reach the current position, while the
2101 // second move is assumed to be a move from the current position.
2103 bool connected_moves(const Position& pos, Move m1, Move m2) {
2105 Square f1, t1, f2, t2;
2108 assert(move_is_ok(m1));
2109 assert(move_is_ok(m2));
2111 if (m2 == MOVE_NONE)
2114 // Case 1: The moving piece is the same in both moves
2120 // Case 2: The destination square for m2 was vacated by m1
2126 // Case 3: Moving through the vacated square
2127 if ( piece_is_slider(pos.piece_on(f2))
2128 && bit_is_set(squares_between(f2, t2), f1))
2131 // Case 4: The destination square for m2 is defended by the moving piece in m1
2132 p = pos.piece_on(t1);
2133 if (bit_is_set(pos.attacks_from(p, t1), t2))
2136 // Case 5: Discovered check, checking piece is the piece moved in m1
2137 if ( piece_is_slider(p)
2138 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2139 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2141 // discovered_check_candidates() works also if the Position's side to
2142 // move is the opposite of the checking piece.
2143 Color them = opposite_color(pos.side_to_move());
2144 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2146 if (bit_is_set(dcCandidates, f2))
2153 // value_is_mate() checks if the given value is a mate one
2154 // eventually compensated for the ply.
2156 bool value_is_mate(Value value) {
2158 assert(abs(value) <= VALUE_INFINITE);
2160 return value <= value_mated_in(PLY_MAX)
2161 || value >= value_mate_in(PLY_MAX);
2165 // move_is_killer() checks if the given move is among the
2166 // killer moves of that ply.
2168 bool move_is_killer(Move m, const SearchStack& ss) {
2170 const Move* k = ss.killers;
2171 for (int i = 0; i < KILLER_MAX; i++, k++)
2179 // extension() decides whether a move should be searched with normal depth,
2180 // or with extended depth. Certain classes of moves (checking moves, in
2181 // particular) are searched with bigger depth than ordinary moves and in
2182 // any case are marked as 'dangerous'. Note that also if a move is not
2183 // extended, as example because the corresponding UCI option is set to zero,
2184 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2186 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2187 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2189 assert(m != MOVE_NONE);
2191 Depth result = Depth(0);
2192 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2197 result += CheckExtension[pvNode];
2200 result += SingleEvasionExtension[pvNode];
2203 result += MateThreatExtension[pvNode];
2206 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2208 Color c = pos.side_to_move();
2209 if (relative_rank(c, move_to(m)) == RANK_7)
2211 result += PawnPushTo7thExtension[pvNode];
2214 if (pos.pawn_is_passed(c, move_to(m)))
2216 result += PassedPawnExtension[pvNode];
2221 if ( captureOrPromotion
2222 && pos.type_of_piece_on(move_to(m)) != PAWN
2223 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2224 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2225 && !move_is_promotion(m)
2228 result += PawnEndgameExtension[pvNode];
2233 && captureOrPromotion
2234 && pos.type_of_piece_on(move_to(m)) != PAWN
2235 && pos.see_sign(m) >= 0)
2241 return Min(result, OnePly);
2245 // ok_to_do_nullmove() looks at the current position and decides whether
2246 // doing a 'null move' should be allowed. In order to avoid zugzwang
2247 // problems, null moves are not allowed when the side to move has very
2248 // little material left. Currently, the test is a bit too simple: Null
2249 // moves are avoided only when the side to move has only pawns left.
2250 // It's probably a good idea to avoid null moves in at least some more
2251 // complicated endgames, e.g. KQ vs KR. FIXME
2253 bool ok_to_do_nullmove(const Position& pos) {
2255 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2259 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2260 // non-tactical moves late in the move list close to the leaves are
2261 // candidates for pruning.
2263 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2265 assert(move_is_ok(m));
2266 assert(threat == MOVE_NONE || move_is_ok(threat));
2267 assert(!pos.move_is_check(m));
2268 assert(!pos.move_is_capture_or_promotion(m));
2269 assert(!pos.move_is_passed_pawn_push(m));
2271 Square mfrom, mto, tfrom, tto;
2273 // Prune if there isn't any threat move
2274 if (threat == MOVE_NONE)
2277 mfrom = move_from(m);
2279 tfrom = move_from(threat);
2280 tto = move_to(threat);
2282 // Case 1: Don't prune moves which move the threatened piece
2286 // Case 2: If the threatened piece has value less than or equal to the
2287 // value of the threatening piece, don't prune move which defend it.
2288 if ( pos.move_is_capture(threat)
2289 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2290 || pos.type_of_piece_on(tfrom) == KING)
2291 && pos.move_attacks_square(m, tto))
2294 // Case 3: If the moving piece in the threatened move is a slider, don't
2295 // prune safe moves which block its ray.
2296 if ( piece_is_slider(pos.piece_on(tfrom))
2297 && bit_is_set(squares_between(tfrom, tto), mto)
2298 && pos.see_sign(m) >= 0)
2305 // ok_to_use_TT() returns true if a transposition table score
2306 // can be used at a given point in search.
2308 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2310 Value v = value_from_tt(tte->value(), ply);
2312 return ( tte->depth() >= depth
2313 || v >= Max(value_mate_in(PLY_MAX), beta)
2314 || v < Min(value_mated_in(PLY_MAX), beta))
2316 && ( (is_lower_bound(tte->type()) && v >= beta)
2317 || (is_upper_bound(tte->type()) && v < beta));
2321 // refine_eval() returns the transposition table score if
2322 // possible otherwise falls back on static position evaluation.
2324 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2329 Value v = value_from_tt(tte->value(), ply);
2331 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2332 || (is_upper_bound(tte->type()) && v < defaultEval))
2339 // update_history() registers a good move that produced a beta-cutoff
2340 // in history and marks as failures all the other moves of that ply.
2342 void update_history(const Position& pos, Move move, Depth depth,
2343 Move movesSearched[], int moveCount) {
2347 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2349 for (int i = 0; i < moveCount - 1; i++)
2351 m = movesSearched[i];
2355 if (!pos.move_is_capture_or_promotion(m))
2356 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2361 // update_killers() add a good move that produced a beta-cutoff
2362 // among the killer moves of that ply.
2364 void update_killers(Move m, SearchStack& ss) {
2366 if (m == ss.killers[0])
2369 for (int i = KILLER_MAX - 1; i > 0; i--)
2370 ss.killers[i] = ss.killers[i - 1];
2376 // update_gains() updates the gains table of a non-capture move given
2377 // the static position evaluation before and after the move.
2379 void update_gains(const Position& pos, Move m, Value before, Value after) {
2382 && before != VALUE_NONE
2383 && after != VALUE_NONE
2384 && pos.captured_piece() == NO_PIECE_TYPE
2385 && !move_is_castle(m)
2386 && !move_is_promotion(m))
2387 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2391 // current_search_time() returns the number of milliseconds which have passed
2392 // since the beginning of the current search.
2394 int current_search_time() {
2396 return get_system_time() - SearchStartTime;
2400 // nps() computes the current nodes/second count.
2404 int t = current_search_time();
2405 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2409 // poll() performs two different functions: It polls for user input, and it
2410 // looks at the time consumed so far and decides if it's time to abort the
2413 void poll(SearchStack ss[], int ply) {
2415 static int lastInfoTime;
2416 int t = current_search_time();
2421 // We are line oriented, don't read single chars
2422 std::string command;
2424 if (!std::getline(std::cin, command))
2427 if (command == "quit")
2430 PonderSearch = false;
2434 else if (command == "stop")
2437 PonderSearch = false;
2439 else if (command == "ponderhit")
2443 // Print search information
2447 else if (lastInfoTime > t)
2448 // HACK: Must be a new search where we searched less than
2449 // NodesBetweenPolls nodes during the first second of search.
2452 else if (t - lastInfoTime >= 1000)
2459 if (dbg_show_hit_rate)
2460 dbg_print_hit_rate();
2462 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2463 << " time " << t << " hashfull " << TT.full() << endl;
2465 // We only support current line printing in single thread mode
2466 if (ShowCurrentLine && TM.active_threads() == 1)
2468 cout << "info currline";
2469 for (int p = 0; p < ply; p++)
2470 cout << " " << ss[p].currentMove;
2476 // Should we stop the search?
2480 bool stillAtFirstMove = FirstRootMove
2481 && !AspirationFailLow
2482 && t > MaxSearchTime + ExtraSearchTime;
2484 bool noMoreTime = t > AbsoluteMaxSearchTime
2485 || stillAtFirstMove;
2487 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2488 || (ExactMaxTime && t >= ExactMaxTime)
2489 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2494 // ponderhit() is called when the program is pondering (i.e. thinking while
2495 // it's the opponent's turn to move) in order to let the engine know that
2496 // it correctly predicted the opponent's move.
2500 int t = current_search_time();
2501 PonderSearch = false;
2503 bool stillAtFirstMove = FirstRootMove
2504 && !AspirationFailLow
2505 && t > MaxSearchTime + ExtraSearchTime;
2507 bool noMoreTime = t > AbsoluteMaxSearchTime
2508 || stillAtFirstMove;
2510 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2515 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2517 void init_ss_array(SearchStack ss[]) {
2519 for (int i = 0; i < 3; i++)
2522 ss[i].initKillers();
2527 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2528 // while the program is pondering. The point is to work around a wrinkle in
2529 // the UCI protocol: When pondering, the engine is not allowed to give a
2530 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2531 // We simply wait here until one of these commands is sent, and return,
2532 // after which the bestmove and pondermove will be printed (in id_loop()).
2534 void wait_for_stop_or_ponderhit() {
2536 std::string command;
2540 if (!std::getline(std::cin, command))
2543 if (command == "quit")
2548 else if (command == "ponderhit" || command == "stop")
2554 // print_pv_info() prints to standard output and eventually to log file information on
2555 // the current PV line. It is called at each iteration or after a new pv is found.
2557 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2559 cout << "info depth " << Iteration
2560 << " score " << value_to_string(value)
2561 << ((value >= beta) ? " lowerbound" :
2562 ((value <= alpha)? " upperbound" : ""))
2563 << " time " << current_search_time()
2564 << " nodes " << TM.nodes_searched()
2568 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2569 cout << ss[0].pv[j] << " ";
2575 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2576 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2578 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2579 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2584 // init_thread() is the function which is called when a new thread is
2585 // launched. It simply calls the idle_loop() function with the supplied
2586 // threadID. There are two versions of this function; one for POSIX
2587 // threads and one for Windows threads.
2589 #if !defined(_MSC_VER)
2591 void* init_thread(void *threadID) {
2593 TM.idle_loop(*(int*)threadID, NULL);
2599 DWORD WINAPI init_thread(LPVOID threadID) {
2601 TM.idle_loop(*(int*)threadID, NULL);
2608 /// The ThreadsManager class
2610 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2611 // get_beta_counters() are getters/setters for the per thread
2612 // counters used to sort the moves at root.
2614 void ThreadsManager::resetNodeCounters() {
2616 for (int i = 0; i < MAX_THREADS; i++)
2617 threads[i].nodes = 0ULL;
2620 void ThreadsManager::resetBetaCounters() {
2622 for (int i = 0; i < MAX_THREADS; i++)
2623 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2626 int64_t ThreadsManager::nodes_searched() const {
2628 int64_t result = 0ULL;
2629 for (int i = 0; i < ActiveThreads; i++)
2630 result += threads[i].nodes;
2635 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2638 for (int i = 0; i < MAX_THREADS; i++)
2640 our += threads[i].betaCutOffs[us];
2641 their += threads[i].betaCutOffs[opposite_color(us)];
2646 // idle_loop() is where the threads are parked when they have no work to do.
2647 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2648 // object for which the current thread is the master.
2650 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2652 assert(threadID >= 0 && threadID < MAX_THREADS);
2656 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2657 // master should exit as last one.
2658 if (AllThreadsShouldExit)
2661 threads[threadID].state = THREAD_TERMINATED;
2665 // If we are not thinking, wait for a condition to be signaled
2666 // instead of wasting CPU time polling for work.
2667 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2670 assert(threadID != 0);
2671 threads[threadID].state = THREAD_SLEEPING;
2673 #if !defined(_MSC_VER)
2674 lock_grab(&WaitLock);
2675 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2676 pthread_cond_wait(&WaitCond, &WaitLock);
2677 lock_release(&WaitLock);
2679 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2683 // If thread has just woken up, mark it as available
2684 if (threads[threadID].state == THREAD_SLEEPING)
2685 threads[threadID].state = THREAD_AVAILABLE;
2687 // If this thread has been assigned work, launch a search
2688 if (threads[threadID].state == THREAD_WORKISWAITING)
2690 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2692 threads[threadID].state = THREAD_SEARCHING;
2694 if (threads[threadID].splitPoint->pvNode)
2695 sp_search_pv(threads[threadID].splitPoint, threadID);
2697 sp_search(threads[threadID].splitPoint, threadID);
2699 assert(threads[threadID].state == THREAD_SEARCHING);
2701 threads[threadID].state = THREAD_AVAILABLE;
2704 // If this thread is the master of a split point and all threads have
2705 // finished their work at this split point, return from the idle loop.
2706 if (waitSp != NULL && waitSp->cpus == 0)
2708 assert(threads[threadID].state == THREAD_AVAILABLE);
2710 threads[threadID].state = THREAD_SEARCHING;
2717 // init_threads() is called during startup. It launches all helper threads,
2718 // and initializes the split point stack and the global locks and condition
2721 void ThreadsManager::init_threads() {
2726 #if !defined(_MSC_VER)
2727 pthread_t pthread[1];
2730 // Initialize global locks
2731 lock_init(&MPLock, NULL);
2732 lock_init(&WaitLock, NULL);
2734 #if !defined(_MSC_VER)
2735 pthread_cond_init(&WaitCond, NULL);
2737 for (i = 0; i < MAX_THREADS; i++)
2738 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2741 // Initialize SplitPointStack locks
2742 for (i = 0; i < MAX_THREADS; i++)
2743 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2745 SplitPointStack[i][j].parent = NULL;
2746 lock_init(&(SplitPointStack[i][j].lock), NULL);
2749 // Will be set just before program exits to properly end the threads
2750 AllThreadsShouldExit = false;
2752 // Threads will be put to sleep as soon as created
2753 AllThreadsShouldSleep = true;
2755 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2757 threads[0].state = THREAD_SEARCHING;
2758 for (i = 1; i < MAX_THREADS; i++)
2759 threads[i].state = THREAD_AVAILABLE;
2761 // Launch the helper threads
2762 for (i = 1; i < MAX_THREADS; i++)
2765 #if !defined(_MSC_VER)
2766 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2768 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2773 cout << "Failed to create thread number " << i << endl;
2774 Application::exit_with_failure();
2777 // Wait until the thread has finished launching and is gone to sleep
2778 while (threads[i].state != THREAD_SLEEPING);
2783 // exit_threads() is called when the program exits. It makes all the
2784 // helper threads exit cleanly.
2786 void ThreadsManager::exit_threads() {
2788 ActiveThreads = MAX_THREADS; // HACK
2789 AllThreadsShouldSleep = true; // HACK
2790 wake_sleeping_threads();
2792 // This makes the threads to exit idle_loop()
2793 AllThreadsShouldExit = true;
2795 // Wait for thread termination
2796 for (int i = 1; i < MAX_THREADS; i++)
2797 while (threads[i].state != THREAD_TERMINATED);
2799 // Now we can safely destroy the locks
2800 for (int i = 0; i < MAX_THREADS; i++)
2801 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2802 lock_destroy(&(SplitPointStack[i][j].lock));
2804 lock_destroy(&WaitLock);
2805 lock_destroy(&MPLock);
2809 // thread_should_stop() checks whether the thread should stop its search.
2810 // This can happen if a beta cutoff has occurred in the thread's currently
2811 // active split point, or in some ancestor of the current split point.
2813 bool ThreadsManager::thread_should_stop(int threadID) const {
2815 assert(threadID >= 0 && threadID < ActiveThreads);
2819 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2824 // thread_is_available() checks whether the thread with threadID "slave" is
2825 // available to help the thread with threadID "master" at a split point. An
2826 // obvious requirement is that "slave" must be idle. With more than two
2827 // threads, this is not by itself sufficient: If "slave" is the master of
2828 // some active split point, it is only available as a slave to the other
2829 // threads which are busy searching the split point at the top of "slave"'s
2830 // split point stack (the "helpful master concept" in YBWC terminology).
2832 bool ThreadsManager::thread_is_available(int slave, int master) const {
2834 assert(slave >= 0 && slave < ActiveThreads);
2835 assert(master >= 0 && master < ActiveThreads);
2836 assert(ActiveThreads > 1);
2838 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2841 // Make a local copy to be sure doesn't change under our feet
2842 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2844 if (localActiveSplitPoints == 0)
2845 // No active split points means that the thread is available as
2846 // a slave for any other thread.
2849 if (ActiveThreads == 2)
2852 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2853 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2854 // could have been set to 0 by another thread leading to an out of bound access.
2855 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2862 // available_thread_exists() tries to find an idle thread which is available as
2863 // a slave for the thread with threadID "master".
2865 bool ThreadsManager::available_thread_exists(int master) const {
2867 assert(master >= 0 && master < ActiveThreads);
2868 assert(ActiveThreads > 1);
2870 for (int i = 0; i < ActiveThreads; i++)
2871 if (thread_is_available(i, master))
2878 // split() does the actual work of distributing the work at a node between
2879 // several threads at PV nodes. If it does not succeed in splitting the
2880 // node (because no idle threads are available, or because we have no unused
2881 // split point objects), the function immediately returns false. If
2882 // splitting is possible, a SplitPoint object is initialized with all the
2883 // data that must be copied to the helper threads (the current position and
2884 // search stack, alpha, beta, the search depth, etc.), and we tell our
2885 // helper threads that they have been assigned work. This will cause them
2886 // to instantly leave their idle loops and call sp_search_pv(). When all
2887 // threads have returned from sp_search_pv (or, equivalently, when
2888 // splitPoint->cpus becomes 0), split() returns true.
2890 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2891 Value* alpha, const Value beta, Value* bestValue,
2892 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2895 assert(sstck != NULL);
2896 assert(ply >= 0 && ply < PLY_MAX);
2897 assert(*bestValue >= -VALUE_INFINITE);
2898 assert( ( pvNode && *bestValue <= *alpha)
2899 || (!pvNode && *bestValue < beta ));
2900 assert(!pvNode || *alpha < beta);
2901 assert(beta <= VALUE_INFINITE);
2902 assert(depth > Depth(0));
2903 assert(master >= 0 && master < ActiveThreads);
2904 assert(ActiveThreads > 1);
2906 SplitPoint* splitPoint;
2910 // If no other thread is available to help us, or if we have too many
2911 // active split points, don't split.
2912 if ( !available_thread_exists(master)
2913 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2915 lock_release(&MPLock);
2919 // Pick the next available split point object from the split point stack
2920 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2922 // Initialize the split point object
2923 splitPoint->parent = threads[master].splitPoint;
2924 splitPoint->stopRequest = false;
2925 splitPoint->ply = ply;
2926 splitPoint->depth = depth;
2927 splitPoint->mateThreat = mateThreat;
2928 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2929 splitPoint->beta = beta;
2930 splitPoint->pvNode = pvNode;
2931 splitPoint->bestValue = *bestValue;
2932 splitPoint->master = master;
2933 splitPoint->mp = mp;
2934 splitPoint->moves = *moves;
2935 splitPoint->cpus = 1;
2936 splitPoint->pos = &p;
2937 splitPoint->parentSstack = sstck;
2938 for (int i = 0; i < ActiveThreads; i++)
2939 splitPoint->slaves[i] = 0;
2941 threads[master].splitPoint = splitPoint;
2942 threads[master].activeSplitPoints++;
2944 // If we are here it means we are not available
2945 assert(threads[master].state != THREAD_AVAILABLE);
2947 // Allocate available threads setting state to THREAD_BOOKED
2948 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2949 if (thread_is_available(i, master))
2951 threads[i].state = THREAD_BOOKED;
2952 threads[i].splitPoint = splitPoint;
2953 splitPoint->slaves[i] = 1;
2957 assert(splitPoint->cpus > 1);
2959 // We can release the lock because slave threads are already booked and master is not available
2960 lock_release(&MPLock);
2962 // Tell the threads that they have work to do. This will make them leave
2963 // their idle loop. But before copy search stack tail for each thread.
2964 for (int i = 0; i < ActiveThreads; i++)
2965 if (i == master || splitPoint->slaves[i])
2967 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2969 assert(i == master || threads[i].state == THREAD_BOOKED);
2971 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2974 // Everything is set up. The master thread enters the idle loop, from
2975 // which it will instantly launch a search, because its state is
2976 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2977 // idle loop, which means that the main thread will return from the idle
2978 // loop when all threads have finished their work at this split point
2979 // (i.e. when splitPoint->cpus == 0).
2980 idle_loop(master, splitPoint);
2982 // We have returned from the idle loop, which means that all threads are
2983 // finished. Update alpha, beta and bestValue, and return.
2987 *alpha = splitPoint->alpha;
2989 *bestValue = splitPoint->bestValue;
2990 threads[master].activeSplitPoints--;
2991 threads[master].splitPoint = splitPoint->parent;
2993 lock_release(&MPLock);
2998 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2999 // to start a new search from the root.
3001 void ThreadsManager::wake_sleeping_threads() {
3003 assert(AllThreadsShouldSleep);
3004 assert(ActiveThreads > 0);
3006 AllThreadsShouldSleep = false;
3008 if (ActiveThreads == 1)
3011 #if !defined(_MSC_VER)
3012 pthread_mutex_lock(&WaitLock);
3013 pthread_cond_broadcast(&WaitCond);
3014 pthread_mutex_unlock(&WaitLock);
3016 for (int i = 1; i < MAX_THREADS; i++)
3017 SetEvent(SitIdleEvent[i]);
3023 // put_threads_to_sleep() makes all the threads go to sleep just before
3024 // to leave think(), at the end of the search. Threads should have already
3025 // finished the job and should be idle.
3027 void ThreadsManager::put_threads_to_sleep() {
3029 assert(!AllThreadsShouldSleep);
3031 // This makes the threads to go to sleep
3032 AllThreadsShouldSleep = true;
3035 /// The RootMoveList class
3037 // RootMoveList c'tor
3039 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3041 SearchStack ss[PLY_MAX_PLUS_2];
3042 MoveStack mlist[MaxRootMoves];
3044 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3046 // Generate all legal moves
3047 MoveStack* last = generate_moves(pos, mlist);
3049 // Add each move to the moves[] array
3050 for (MoveStack* cur = mlist; cur != last; cur++)
3052 bool includeMove = includeAllMoves;
3054 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3055 includeMove = (searchMoves[k] == cur->move);
3060 // Find a quick score for the move
3062 pos.do_move(cur->move, st);
3063 moves[count].move = cur->move;
3064 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3065 moves[count].pv[0] = cur->move;
3066 moves[count].pv[1] = MOVE_NONE;
3067 pos.undo_move(cur->move);
3074 // RootMoveList simple methods definitions
3076 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3078 moves[moveNum].nodes = nodes;
3079 moves[moveNum].cumulativeNodes += nodes;
3082 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3084 moves[moveNum].ourBeta = our;
3085 moves[moveNum].theirBeta = their;
3088 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3092 for (j = 0; pv[j] != MOVE_NONE; j++)
3093 moves[moveNum].pv[j] = pv[j];
3095 moves[moveNum].pv[j] = MOVE_NONE;
3099 // RootMoveList::sort() sorts the root move list at the beginning of a new
3102 void RootMoveList::sort() {
3104 sort_multipv(count - 1); // Sort all items
3108 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3109 // list by their scores and depths. It is used to order the different PVs
3110 // correctly in MultiPV mode.
3112 void RootMoveList::sort_multipv(int n) {
3116 for (i = 1; i <= n; i++)
3118 RootMove rm = moves[i];
3119 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3120 moves[j] = moves[j - 1];