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);
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 = false;
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, ZugDetection;
264 std::ofstream LogFile;
266 // Multi-threads related variables
267 Depth MinimumSplitDepth;
268 int MaxThreadsPerSplitPoint;
271 // Node counters, used only by thread[0] but try to keep in different cache
272 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
274 int NodesBetweenPolls = 30000;
281 Value id_loop(const Position& pos, Move searchMoves[]);
282 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
283 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
284 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
285 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
286 void sp_search(SplitPoint* sp, int threadID);
287 void sp_search_pv(SplitPoint* sp, int threadID);
288 void init_node(SearchStack ss[], int ply, int threadID);
289 void update_pv(SearchStack ss[], int ply);
290 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
291 bool connected_moves(const Position& pos, Move m1, Move m2);
292 bool value_is_mate(Value value);
293 bool move_is_killer(Move m, const SearchStack& ss);
294 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
295 bool ok_to_do_nullmove(const Position& pos);
296 bool ok_to_prune(const Position& pos, Move m, Move threat);
297 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply, bool allowNullmove);
298 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
299 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
300 void update_killers(Move m, SearchStack& ss);
301 void update_gains(const Position& pos, Move move, Value before, Value after);
303 int current_search_time();
307 void wait_for_stop_or_ponderhit();
308 void init_ss_array(SearchStack ss[]);
309 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value);
311 #if !defined(_MSC_VER)
312 void *init_thread(void *threadID);
314 DWORD WINAPI init_thread(LPVOID threadID);
324 /// init_threads(), exit_threads() and nodes_searched() are helpers to
325 /// give accessibility to some TM methods from outside of current file.
327 void init_threads() { TM.init_threads(); }
328 void exit_threads() { TM.exit_threads(); }
329 int64_t nodes_searched() { return TM.nodes_searched(); }
332 /// perft() is our utility to verify move generation is bug free. All the legal
333 /// moves up to given depth are generated and counted and the sum returned.
335 int perft(Position& pos, Depth depth)
340 MovePicker mp(pos, MOVE_NONE, depth, H);
342 // If we are at the last ply we don't need to do and undo
343 // the moves, just to count them.
344 if (depth <= OnePly) // Replace with '<' to test also qsearch
346 while (mp.get_next_move()) sum++;
350 // Loop through all legal moves
352 while ((move = mp.get_next_move()) != MOVE_NONE)
354 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
355 sum += perft(pos, depth - OnePly);
362 /// think() is the external interface to Stockfish's search, and is called when
363 /// the program receives the UCI 'go' command. It initializes various
364 /// search-related global variables, and calls root_search(). It returns false
365 /// when a quit command is received during the search.
367 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
368 int time[], int increment[], int movesToGo, int maxDepth,
369 int maxNodes, int maxTime, Move searchMoves[]) {
371 // Initialize global search variables
372 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
373 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
375 TM.resetNodeCounters();
376 SearchStartTime = get_system_time();
377 ExactMaxTime = maxTime;
380 InfiniteSearch = infinite;
381 PonderSearch = ponder;
382 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
384 // Look for a book move, only during games, not tests
385 if (UseTimeManagement && get_option_value_bool("OwnBook"))
387 if (get_option_value_string("Book File") != OpeningBook.file_name())
388 OpeningBook.open(get_option_value_string("Book File"));
390 Move bookMove = OpeningBook.get_move(pos);
391 if (bookMove != MOVE_NONE)
394 wait_for_stop_or_ponderhit();
396 cout << "bestmove " << bookMove << endl;
401 // Reset loseOnTime flag at the beginning of a new game
402 if (button_was_pressed("New Game"))
405 // Read UCI option values
406 TT.set_size(get_option_value_int("Hash"));
407 if (button_was_pressed("Clear Hash"))
410 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
411 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
412 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
413 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
414 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
415 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
416 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
417 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
418 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
419 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
420 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
421 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
423 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
424 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
425 MultiPV = get_option_value_int("MultiPV");
426 Chess960 = get_option_value_bool("UCI_Chess960");
427 UseLogFile = get_option_value_bool("Use Search Log");
428 ZugDetection = get_option_value_bool("Zugzwang detection"); // To be removed after 1.7.1
431 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
433 read_weights(pos.side_to_move());
435 // Set the number of active threads
436 int newActiveThreads = get_option_value_int("Threads");
437 if (newActiveThreads != TM.active_threads())
439 TM.set_active_threads(newActiveThreads);
440 init_eval(TM.active_threads());
443 // Wake up sleeping threads
444 TM.wake_sleeping_threads();
447 int myTime = time[side_to_move];
448 int myIncrement = increment[side_to_move];
449 if (UseTimeManagement)
451 if (!movesToGo) // Sudden death time control
455 MaxSearchTime = myTime / 30 + myIncrement;
456 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
458 else // Blitz game without increment
460 MaxSearchTime = myTime / 30;
461 AbsoluteMaxSearchTime = myTime / 8;
464 else // (x moves) / (y minutes)
468 MaxSearchTime = myTime / 2;
469 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
473 MaxSearchTime = myTime / Min(movesToGo, 20);
474 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
478 if (get_option_value_bool("Ponder"))
480 MaxSearchTime += MaxSearchTime / 4;
481 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
485 // Set best NodesBetweenPolls interval to avoid lagging under
486 // heavy time pressure.
488 NodesBetweenPolls = Min(MaxNodes, 30000);
489 else if (myTime && myTime < 1000)
490 NodesBetweenPolls = 1000;
491 else if (myTime && myTime < 5000)
492 NodesBetweenPolls = 5000;
494 NodesBetweenPolls = 30000;
496 // Write search information to log file
498 LogFile << "Searching: " << pos.to_fen() << endl
499 << "infinite: " << infinite
500 << " ponder: " << ponder
501 << " time: " << myTime
502 << " increment: " << myIncrement
503 << " moves to go: " << movesToGo << endl;
505 // LSN filtering. Used only for developing purposes, disabled by default
509 // Step 2. If after last move we decided to lose on time, do it now!
510 while (SearchStartTime + myTime + 1000 > get_system_time())
514 // We're ready to start thinking. Call the iterative deepening loop function
515 Value v = id_loop(pos, searchMoves);
519 // Step 1. If this is sudden death game and our position is hopeless,
520 // decide to lose on time.
521 if ( !loseOnTime // If we already lost on time, go to step 3.
531 // Step 3. Now after stepping over the time limit, reset flag for next match.
539 TM.put_threads_to_sleep();
545 /// init_search() is called during startup. It initializes various lookup tables
549 // Init our reduction lookup tables
550 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
551 for (int j = 1; j < 64; j++) // j == moveNumber
553 double pvRed = 0.5 + log(double(i)) * log(double(j)) / 6.0;
554 double nonPVRed = 0.5 + log(double(i)) * log(double(j)) / 3.0;
555 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
556 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
559 // Init futility margins array
560 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
561 for (int j = 0; j < 64; j++) // j == moveNumber
563 // FIXME: test using log instead of BSR
564 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j;
567 // Init futility move count array
568 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
569 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
573 // SearchStack::init() initializes a search stack. Used at the beginning of a
574 // new search from the root.
575 void SearchStack::init(int ply) {
577 pv[ply] = pv[ply + 1] = MOVE_NONE;
578 currentMove = threatMove = MOVE_NONE;
579 reduction = Depth(0);
583 void SearchStack::initKillers() {
585 mateKiller = MOVE_NONE;
586 for (int i = 0; i < KILLER_MAX; i++)
587 killers[i] = MOVE_NONE;
592 // id_loop() is the main iterative deepening loop. It calls root_search
593 // repeatedly with increasing depth until the allocated thinking time has
594 // been consumed, the user stops the search, or the maximum search depth is
597 Value id_loop(const Position& pos, Move searchMoves[]) {
600 SearchStack ss[PLY_MAX_PLUS_2];
601 Move EasyMove = MOVE_NONE;
602 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
604 // Moves to search are verified, copied, scored and sorted
605 RootMoveList rml(p, searchMoves);
607 // Handle special case of searching on a mate/stale position
608 if (rml.move_count() == 0)
611 wait_for_stop_or_ponderhit();
613 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
616 // Print RootMoveList startup scoring to the standard output,
617 // so to output information also for iteration 1.
618 cout << "info depth " << 1
619 << "\ninfo depth " << 1
620 << " score " << value_to_string(rml.get_move_score(0))
621 << " time " << current_search_time()
622 << " nodes " << TM.nodes_searched()
624 << " pv " << rml.get_move(0) << "\n";
630 ValueByIteration[1] = rml.get_move_score(0);
633 // Is one move significantly better than others after initial scoring ?
634 if ( rml.move_count() == 1
635 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
636 EasyMove = rml.get_move(0);
638 // Iterative deepening loop
639 while (Iteration < PLY_MAX)
641 // Initialize iteration
643 BestMoveChangesByIteration[Iteration] = 0;
645 cout << "info depth " << Iteration << endl;
647 // Calculate dynamic aspiration window based on previous iterations
648 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
650 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
651 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
653 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
654 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
656 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
657 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
660 // Search to the current depth, rml is updated and sorted, alpha and beta could change
661 value = root_search(p, ss, rml, &alpha, &beta);
663 // Write PV to transposition table, in case the relevant entries have
664 // been overwritten during the search.
665 TT.insert_pv(p, ss[0].pv);
668 break; // Value cannot be trusted. Break out immediately!
670 //Save info about search result
671 ValueByIteration[Iteration] = value;
673 // Drop the easy move if differs from the new best move
674 if (ss[0].pv[0] != EasyMove)
675 EasyMove = MOVE_NONE;
677 if (UseTimeManagement)
680 bool stopSearch = false;
682 // Stop search early if there is only a single legal move,
683 // we search up to Iteration 6 anyway to get a proper score.
684 if (Iteration >= 6 && rml.move_count() == 1)
687 // Stop search early when the last two iterations returned a mate score
689 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
690 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
693 // Stop search early if one move seems to be much better than the others
694 int64_t nodes = TM.nodes_searched();
696 && EasyMove == ss[0].pv[0]
697 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
698 && current_search_time() > MaxSearchTime / 16)
699 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
700 && current_search_time() > MaxSearchTime / 32)))
703 // Add some extra time if the best move has changed during the last two iterations
704 if (Iteration > 5 && Iteration <= 50)
705 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
706 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
708 // Stop search if most of MaxSearchTime is consumed at the end of the
709 // iteration. We probably don't have enough time to search the first
710 // move at the next iteration anyway.
711 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
717 StopOnPonderhit = true;
723 if (MaxDepth && Iteration >= MaxDepth)
727 // If we are pondering or in infinite search, we shouldn't print the
728 // best move before we are told to do so.
729 if (!AbortSearch && (PonderSearch || InfiniteSearch))
730 wait_for_stop_or_ponderhit();
732 // Print final search statistics
733 cout << "info nodes " << TM.nodes_searched()
735 << " time " << current_search_time()
736 << " hashfull " << TT.full() << endl;
738 // Print the best move and the ponder move to the standard output
739 if (ss[0].pv[0] == MOVE_NONE)
741 ss[0].pv[0] = rml.get_move(0);
742 ss[0].pv[1] = MOVE_NONE;
745 assert(ss[0].pv[0] != MOVE_NONE);
747 cout << "bestmove " << ss[0].pv[0];
749 if (ss[0].pv[1] != MOVE_NONE)
750 cout << " ponder " << ss[0].pv[1];
757 dbg_print_mean(LogFile);
759 if (dbg_show_hit_rate)
760 dbg_print_hit_rate(LogFile);
762 LogFile << "\nNodes: " << TM.nodes_searched()
763 << "\nNodes/second: " << nps()
764 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
767 p.do_move(ss[0].pv[0], st);
768 LogFile << "\nPonder move: "
769 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
772 return rml.get_move_score(0);
776 // root_search() is the function which searches the root node. It is
777 // similar to search_pv except that it uses a different move ordering
778 // scheme, prints some information to the standard output and handles
779 // the fail low/high loops.
781 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
788 Depth depth, ext, newDepth;
789 Value value, alpha, beta;
790 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
791 int researchCountFH, researchCountFL;
793 researchCountFH = researchCountFL = 0;
796 isCheck = pos.is_check();
798 // Step 1. Initialize node and poll (omitted at root, but I can see no good reason for this, FIXME)
799 // Step 2. Check for aborted search (omitted at root, because we do not initialize root node)
800 // Step 3. Mate distance pruning (omitted at root)
801 // Step 4. Transposition table lookup (omitted at root)
803 // Step 5. Evaluate the position statically
804 // At root we do this only to get reference value for child nodes
806 ss[0].eval = evaluate(pos, ei, 0);
808 ss[0].eval = VALUE_NONE; // HACK because we do not initialize root node
810 // Step 6. Razoring (omitted at root)
811 // Step 7. Static null move pruning (omitted at root)
812 // Step 8. Null move search with verification search (omitted at root)
813 // Step 9. Internal iterative deepening (omitted at root)
815 // Step extra. Fail low loop
816 // We start with small aspiration window and in case of fail low, we research
817 // with bigger window until we are not failing low anymore.
820 // Sort the moves before to (re)search
823 // Step 10. Loop through all moves in the root move list
824 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
826 // This is used by time management
827 FirstRootMove = (i == 0);
829 // Save the current node count before the move is searched
830 nodes = TM.nodes_searched();
832 // Reset beta cut-off counters
833 TM.resetBetaCounters();
835 // Pick the next root move, and print the move and the move number to
836 // the standard output.
837 move = ss[0].currentMove = rml.get_move(i);
839 if (current_search_time() >= 1000)
840 cout << "info currmove " << move
841 << " currmovenumber " << i + 1 << endl;
843 moveIsCheck = pos.move_is_check(move);
844 captureOrPromotion = pos.move_is_capture_or_promotion(move);
846 // Step 11. Decide the new search depth
847 depth = (Iteration - 2) * OnePly + InitialDepth;
848 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
849 newDepth = depth + ext;
851 // Step 12. Futility pruning (omitted at root)
853 // Step extra. Fail high loop
854 // If move fails high, we research with bigger window until we are not failing
856 value = - VALUE_INFINITE;
860 // Step 13. Make the move
861 pos.do_move(move, st, ci, moveIsCheck);
863 // Step extra. pv search
864 // We do pv search for first moves (i < MultiPV)
865 // and for fail high research (value > alpha)
866 if (i < MultiPV || value > alpha)
868 // Aspiration window is disabled in multi-pv case
870 alpha = -VALUE_INFINITE;
872 // Full depth PV search, done on first move or after a fail high
873 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
877 // Step 14. Reduced search
878 // if the move fails high will be re-searched at full depth
879 bool doFullDepthSearch = true;
881 if ( depth >= 3 * OnePly
883 && !captureOrPromotion
884 && !move_is_castle(move))
886 ss[0].reduction = pv_reduction(depth, i - MultiPV + 2);
889 // Reduced depth non-pv search using alpha as upperbound
890 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
891 doFullDepthSearch = (value > alpha);
895 // Step 15. Full depth search
896 if (doFullDepthSearch)
898 // Full depth non-pv search using alpha as upperbound
899 ss[0].reduction = Depth(0);
900 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
902 // If we are above alpha then research at same depth but as PV
903 // to get a correct score or eventually a fail high above beta.
905 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
909 // Step 16. Undo move
912 // Can we exit fail high loop ?
913 if (AbortSearch || value < beta)
916 // We are failing high and going to do a research. It's important to update
917 // the score before research in case we run out of time while researching.
918 rml.set_move_score(i, value);
920 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
921 rml.set_move_pv(i, ss[0].pv);
923 // Print information to the standard output
924 print_pv_info(pos, ss, alpha, beta, value);
926 // Prepare for a research after a fail high, each time with a wider window
927 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
930 } // End of fail high loop
932 // Finished searching the move. If AbortSearch is true, the search
933 // was aborted because the user interrupted the search or because we
934 // ran out of time. In this case, the return value of the search cannot
935 // be trusted, and we break out of the loop without updating the best
940 // Remember beta-cutoff and searched nodes counts for this move. The
941 // info is used to sort the root moves for the next iteration.
943 TM.get_beta_counters(pos.side_to_move(), our, their);
944 rml.set_beta_counters(i, our, their);
945 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
947 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
948 assert(value < beta);
950 // Step 17. Check for new best move
951 if (value <= alpha && i >= MultiPV)
952 rml.set_move_score(i, -VALUE_INFINITE);
955 // PV move or new best move!
958 rml.set_move_score(i, value);
960 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
961 rml.set_move_pv(i, ss[0].pv);
965 // We record how often the best move has been changed in each
966 // iteration. This information is used for time managment: When
967 // the best move changes frequently, we allocate some more time.
969 BestMoveChangesByIteration[Iteration]++;
971 // Print information to the standard output
972 print_pv_info(pos, ss, alpha, beta, value);
974 // Raise alpha to setup proper non-pv search upper bound
981 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
983 cout << "info multipv " << j + 1
984 << " score " << value_to_string(rml.get_move_score(j))
985 << " depth " << (j <= i ? Iteration : Iteration - 1)
986 << " time " << current_search_time()
987 << " nodes " << TM.nodes_searched()
991 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
992 cout << rml.get_move_pv(j, k) << " ";
996 alpha = rml.get_move_score(Min(i, MultiPV - 1));
998 } // PV move or new best move
1000 assert(alpha >= *alphaPtr);
1002 AspirationFailLow = (alpha == *alphaPtr);
1004 if (AspirationFailLow && StopOnPonderhit)
1005 StopOnPonderhit = false;
1008 // Can we exit fail low loop ?
1009 if (AbortSearch || !AspirationFailLow)
1012 // Prepare for a research after a fail low, each time with a wider window
1013 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1018 // Sort the moves before to return
1025 // search_pv() is the main search function for PV nodes.
1027 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1028 Depth depth, int ply, int threadID) {
1030 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1031 assert(beta > alpha && beta <= VALUE_INFINITE);
1032 assert(ply >= 0 && ply < PLY_MAX);
1033 assert(threadID >= 0 && threadID < TM.active_threads());
1035 Move movesSearched[256];
1040 Depth ext, newDepth;
1041 Value bestValue, value, oldAlpha;
1042 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1043 bool mateThreat = false;
1045 bestValue = value = -VALUE_INFINITE;
1048 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1050 // Step 1. Initialize node and poll
1051 // Polling can abort search.
1052 init_node(ss, ply, threadID);
1054 // Step 2. Check for aborted search and immediate draw
1055 if (AbortSearch || TM.thread_should_stop(threadID))
1058 if (pos.is_draw() || ply >= PLY_MAX - 1)
1061 // Step 3. Mate distance pruning
1063 alpha = Max(value_mated_in(ply), alpha);
1064 beta = Min(value_mate_in(ply+1), beta);
1068 // Step 4. Transposition table lookup
1069 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1070 // This is to avoid problems in the following areas:
1072 // * Repetition draw detection
1073 // * Fifty move rule detection
1074 // * Searching for a mate
1075 // * Printing of full PV line
1076 tte = TT.retrieve(pos.get_key());
1077 ttMove = (tte ? tte->move() : MOVE_NONE);
1079 // Step 5. Evaluate the position statically
1080 // At PV nodes we do this only to update gain statistics
1081 isCheck = pos.is_check();
1084 ss[ply].eval = evaluate(pos, ei, threadID);
1085 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1088 // Step 6. Razoring (is omitted in PV nodes)
1089 // Step 7. Static null move pruning (is omitted in PV nodes)
1090 // Step 8. Null move search with verification search (is omitted in PV nodes)
1092 // Step 9. Internal iterative deepening
1093 if ( depth >= IIDDepthAtPVNodes
1094 && ttMove == MOVE_NONE)
1096 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1097 ttMove = ss[ply].pv[ply];
1098 tte = TT.retrieve(pos.get_key());
1101 // Initialize a MovePicker object for the current position
1102 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1103 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1106 // Step 10. Loop through moves
1107 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1108 while ( alpha < beta
1109 && (move = mp.get_next_move()) != MOVE_NONE
1110 && !TM.thread_should_stop(threadID))
1112 assert(move_is_ok(move));
1114 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1115 moveIsCheck = pos.move_is_check(move, ci);
1116 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1118 // Step 11. Decide the new search depth
1119 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1121 // Singular extension search. We extend the TT move if its value is much better than
1122 // its siblings. To verify this we do a reduced search on all the other moves but the
1123 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1124 if ( depth >= SingularExtensionDepthAtPVNodes
1126 && move == tte->move()
1128 && is_lower_bound(tte->type())
1129 && tte->depth() >= depth - 3 * OnePly)
1131 Value ttValue = value_from_tt(tte->value(), ply);
1133 if (abs(ttValue) < VALUE_KNOWN_WIN)
1135 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1137 if (excValue < ttValue - SingularExtensionMargin)
1142 newDepth = depth - OnePly + ext;
1144 // Update current move (this must be done after singular extension search)
1145 movesSearched[moveCount++] = ss[ply].currentMove = move;
1147 // Step 12. Futility pruning (is omitted in PV nodes)
1149 // Step 13. Make the move
1150 pos.do_move(move, st, ci, moveIsCheck);
1152 // Step extra. pv search (only in PV nodes)
1153 // The first move in list is the expected PV
1155 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1158 // Step 14. Reduced search
1159 // if the move fails high will be re-searched at full depth.
1160 bool doFullDepthSearch = true;
1162 if ( depth >= 3 * OnePly
1164 && !captureOrPromotion
1165 && !move_is_castle(move)
1166 && !move_is_killer(move, ss[ply]))
1168 ss[ply].reduction = pv_reduction(depth, moveCount);
1169 if (ss[ply].reduction)
1171 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1172 doFullDepthSearch = (value > alpha);
1176 // Step 15. Full depth search
1177 if (doFullDepthSearch)
1179 ss[ply].reduction = Depth(0);
1180 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1182 // Step extra. pv search (only in PV nodes)
1183 if (value > alpha && value < beta)
1184 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1188 // Step 16. Undo move
1189 pos.undo_move(move);
1191 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1193 // Step 17. Check for new best move
1194 if (value > bestValue)
1201 if (value == value_mate_in(ply + 1))
1202 ss[ply].mateKiller = move;
1206 // Step 18. Check for split
1207 if ( TM.active_threads() > 1
1209 && depth >= MinimumSplitDepth
1211 && TM.available_thread_exists(threadID)
1213 && !TM.thread_should_stop(threadID)
1214 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1215 depth, mateThreat, &moveCount, &mp, threadID, true))
1219 // Step 19. Check for mate and stalemate
1220 // All legal moves have been searched and if there were
1221 // no legal moves, it must be mate or stalemate.
1223 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1225 // Step 20. Update tables
1226 // If the search is not aborted, update the transposition table,
1227 // history counters, and killer moves.
1228 if (AbortSearch || TM.thread_should_stop(threadID))
1231 if (bestValue <= oldAlpha)
1232 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1234 else if (bestValue >= beta)
1236 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1237 move = ss[ply].pv[ply];
1238 if (!pos.move_is_capture_or_promotion(move))
1240 update_history(pos, move, depth, movesSearched, moveCount);
1241 update_killers(move, ss[ply]);
1243 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1246 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1252 // search() is the search function for zero-width nodes.
1254 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1255 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1257 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1258 assert(ply >= 0 && ply < PLY_MAX);
1259 assert(threadID >= 0 && threadID < TM.active_threads());
1261 Move movesSearched[256];
1266 Depth ext, newDepth;
1267 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1268 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1269 bool mateThreat = false;
1271 refinedValue = bestValue = value = -VALUE_INFINITE;
1274 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1276 // Step 1. Initialize node and poll
1277 // Polling can abort search.
1278 init_node(ss, ply, threadID);
1280 // Step 2. Check for aborted search and immediate draw
1281 if (AbortSearch || TM.thread_should_stop(threadID))
1284 if (pos.is_draw() || ply >= PLY_MAX - 1)
1287 // Step 3. Mate distance pruning
1288 if (value_mated_in(ply) >= beta)
1291 if (value_mate_in(ply + 1) < beta)
1294 // Step 4. Transposition table lookup
1296 // We don't want the score of a partial search to overwrite a previous full search
1297 // TT value, so we use a different position key in case of an excluded move exists.
1298 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1300 tte = TT.retrieve(posKey);
1301 ttMove = (tte ? tte->move() : MOVE_NONE);
1303 if (tte && ok_to_use_TT(tte, depth, beta, ply, allowNullmove))
1305 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1306 return value_from_tt(tte->value(), ply);
1309 // Step 5. Evaluate the position statically
1310 isCheck = pos.is_check();
1314 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1315 ss[ply].eval = value_from_tt(tte->value(), ply);
1317 ss[ply].eval = evaluate(pos, ei, threadID);
1319 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1320 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1324 if ( refinedValue < beta - razor_margin(depth)
1325 && ttMove == MOVE_NONE
1326 && ss[ply - 1].currentMove != MOVE_NULL
1327 && depth < RazorDepth
1329 && !value_is_mate(beta)
1330 && !pos.has_pawn_on_7th(pos.side_to_move()))
1332 Value rbeta = beta - razor_margin(depth);
1333 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1335 // Logically we should return (v + razor_margin(depth)), but
1336 // surprisingly this did slightly weaker in tests.
1340 // Step 7. Static null move pruning
1341 // We're betting that the opponent doesn't have a move that will reduce
1342 // the score by more than futility_margin(depth) if we do a null move.
1344 && depth < RazorDepth
1346 && !value_is_mate(beta)
1347 && ok_to_do_nullmove(pos)
1348 && refinedValue >= beta + futility_margin(depth, 0))
1349 return refinedValue - futility_margin(depth, 0);
1351 // Step 8. Null move search with verification search
1352 // When we jump directly to qsearch() we do a null move only if static value is
1353 // at least beta. Otherwise we do a null move if static value is not more than
1354 // NullMoveMargin under beta.
1358 && !value_is_mate(beta)
1359 && ok_to_do_nullmove(pos)
1360 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1362 ss[ply].currentMove = MOVE_NULL;
1364 // Null move dynamic reduction based on depth
1365 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1367 // Null move dynamic reduction based on value
1368 if (refinedValue - beta > PawnValueMidgame)
1371 pos.do_null_move(st);
1373 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1375 pos.undo_null_move();
1377 if (nullValue >= beta)
1379 // Do not return unproven mate scores
1380 if (nullValue >= value_mate_in(PLY_MAX))
1383 // Do zugzwang verification search for high depths, don't store in TT
1384 // if search was stopped.
1385 if ( ( depth < 6 * OnePly
1386 || search(pos, ss, beta, depth-5*OnePly, ply, false, threadID) >= beta)
1388 && !TM.thread_should_stop(threadID))
1390 assert(value_to_tt(nullValue, ply) == nullValue);
1392 TT.store(posKey, nullValue, VALUE_TYPE_NS_LO, depth, MOVE_NONE);
1396 // The null move failed low, which means that we may be faced with
1397 // some kind of threat. If the previous move was reduced, check if
1398 // the move that refuted the null move was somehow connected to the
1399 // move which was reduced. If a connection is found, return a fail
1400 // low score (which will cause the reduced move to fail high in the
1401 // parent node, which will trigger a re-search with full depth).
1402 if (nullValue == value_mated_in(ply + 2))
1405 ss[ply].threatMove = ss[ply + 1].currentMove;
1406 if ( depth < ThreatDepth
1407 && ss[ply - 1].reduction
1408 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1413 // Step 9. Internal iterative deepening
1414 if ( depth >= IIDDepthAtNonPVNodes
1415 && ttMove == MOVE_NONE
1417 && ss[ply].eval >= beta - IIDMargin)
1419 search(pos, ss, beta, depth/2, ply, false, threadID);
1420 ttMove = ss[ply].pv[ply];
1421 tte = TT.retrieve(posKey);
1424 // Initialize a MovePicker object for the current position
1425 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1428 // Step 10. Loop through moves
1429 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1430 while ( bestValue < beta
1431 && (move = mp.get_next_move()) != MOVE_NONE
1432 && !TM.thread_should_stop(threadID))
1434 assert(move_is_ok(move));
1436 if (move == excludedMove)
1439 moveIsCheck = pos.move_is_check(move, ci);
1440 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1441 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1443 // Step 11. Decide the new search depth
1444 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1446 // Singular extension search. We extend the TT move if its value is much better than
1447 // its siblings. To verify this we do a reduced search on all the other moves but the
1448 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1449 if ( depth >= SingularExtensionDepthAtNonPVNodes
1451 && move == tte->move()
1452 && !excludedMove // Do not allow recursive singular extension search
1454 && is_lower_bound(tte->type())
1455 && tte->depth() >= depth - 3 * OnePly)
1457 Value ttValue = value_from_tt(tte->value(), ply);
1459 if (abs(ttValue) < VALUE_KNOWN_WIN)
1461 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1463 if (excValue < ttValue - SingularExtensionMargin)
1468 newDepth = depth - OnePly + ext;
1470 // Update current move (this must be done after singular extension search)
1471 movesSearched[moveCount++] = ss[ply].currentMove = move;
1473 // Step 12. Futility pruning
1476 && !captureOrPromotion
1477 && !move_is_castle(move)
1480 // Move count based pruning
1481 if ( moveCount >= futility_move_count(depth)
1482 && ok_to_prune(pos, move, ss[ply].threatMove)
1483 && bestValue > value_mated_in(PLY_MAX))
1486 // Value based pruning
1487 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1488 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1489 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1491 if (futilityValueScaled < beta)
1493 if (futilityValueScaled > bestValue)
1494 bestValue = futilityValueScaled;
1499 // Step 13. Make the move
1500 pos.do_move(move, st, ci, moveIsCheck);
1502 // Step 14. Reduced search, if the move fails high
1503 // will be re-searched at full depth.
1504 bool doFullDepthSearch = true;
1506 if ( depth >= 3*OnePly
1508 && !captureOrPromotion
1509 && !move_is_castle(move)
1510 && !move_is_killer(move, ss[ply]))
1512 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1513 if (ss[ply].reduction)
1515 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1516 doFullDepthSearch = (value >= beta);
1520 // Step 15. Full depth search
1521 if (doFullDepthSearch)
1523 ss[ply].reduction = Depth(0);
1524 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1527 // Step 16. Undo move
1528 pos.undo_move(move);
1530 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1532 // Step 17. Check for new best move
1533 if (value > bestValue)
1539 if (value == value_mate_in(ply + 1))
1540 ss[ply].mateKiller = move;
1543 // Step 18. Check for split
1544 if ( TM.active_threads() > 1
1546 && depth >= MinimumSplitDepth
1548 && TM.available_thread_exists(threadID)
1550 && !TM.thread_should_stop(threadID)
1551 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1552 depth, mateThreat, &moveCount, &mp, threadID, false))
1556 // Step 19. Check for mate and stalemate
1557 // All legal moves have been searched and if there are
1558 // no legal moves, it must be mate or stalemate.
1559 // If one move was excluded return fail low score.
1561 return excludedMove ? beta - 1 : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1563 // Step 20. Update tables
1564 // If the search is not aborted, update the transposition table,
1565 // history counters, and killer moves.
1566 if (AbortSearch || TM.thread_should_stop(threadID))
1569 if (bestValue < beta)
1570 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1573 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1574 move = ss[ply].pv[ply];
1575 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1576 if (!pos.move_is_capture_or_promotion(move))
1578 update_history(pos, move, depth, movesSearched, moveCount);
1579 update_killers(move, ss[ply]);
1584 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1590 // qsearch() is the quiescence search function, which is called by the main
1591 // search function when the remaining depth is zero (or, to be more precise,
1592 // less than OnePly).
1594 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1595 Depth depth, int ply, int threadID) {
1597 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1598 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1600 assert(ply >= 0 && ply < PLY_MAX);
1601 assert(threadID >= 0 && threadID < TM.active_threads());
1606 Value staticValue, bestValue, value, futilityBase, futilityValue;
1607 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1608 const TTEntry* tte = NULL;
1610 bool pvNode = (beta - alpha != 1);
1611 Value oldAlpha = alpha;
1613 // Initialize, and make an early exit in case of an aborted search,
1614 // an instant draw, maximum ply reached, etc.
1615 init_node(ss, ply, threadID);
1617 // After init_node() that calls poll()
1618 if (AbortSearch || TM.thread_should_stop(threadID))
1621 if (pos.is_draw() || ply >= PLY_MAX - 1)
1624 // Transposition table lookup. At PV nodes, we don't use the TT for
1625 // pruning, but only for move ordering.
1626 tte = TT.retrieve(pos.get_key());
1627 ttMove = (tte ? tte->move() : MOVE_NONE);
1629 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply, true))
1631 assert(tte->type() != VALUE_TYPE_EVAL);
1633 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1634 return value_from_tt(tte->value(), ply);
1637 isCheck = pos.is_check();
1639 // Evaluate the position statically
1641 staticValue = -VALUE_INFINITE;
1642 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1643 staticValue = value_from_tt(tte->value(), ply);
1645 staticValue = evaluate(pos, ei, threadID);
1649 ss[ply].eval = staticValue;
1650 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1653 // Initialize "stand pat score", and return it immediately if it is
1655 bestValue = staticValue;
1657 if (bestValue >= beta)
1659 // Store the score to avoid a future costly evaluation() call
1660 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1661 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1666 if (bestValue > alpha)
1669 // If we are near beta then try to get a cutoff pushing checks a bit further
1670 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1672 // Initialize a MovePicker object for the current position, and prepare
1673 // to search the moves. Because the depth is <= 0 here, only captures,
1674 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1675 // and we are near beta) will be generated.
1676 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1678 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1679 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1681 // Loop through the moves until no moves remain or a beta cutoff occurs
1682 while ( alpha < beta
1683 && (move = mp.get_next_move()) != MOVE_NONE)
1685 assert(move_is_ok(move));
1687 moveIsCheck = pos.move_is_check(move, ci);
1689 // Update current move
1691 ss[ply].currentMove = move;
1699 && !move_is_promotion(move)
1700 && !pos.move_is_passed_pawn_push(move))
1702 futilityValue = futilityBase
1703 + pos.endgame_value_of_piece_on(move_to(move))
1704 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1706 if (futilityValue < alpha)
1708 if (futilityValue > bestValue)
1709 bestValue = futilityValue;
1714 // Detect blocking evasions that are candidate to be pruned
1715 evasionPrunable = isCheck
1716 && bestValue != -VALUE_INFINITE
1717 && !pos.move_is_capture(move)
1718 && pos.type_of_piece_on(move_from(move)) != KING
1719 && !pos.can_castle(pos.side_to_move());
1721 // Don't search moves with negative SEE values
1722 if ( (!isCheck || evasionPrunable)
1725 && !move_is_promotion(move)
1726 && pos.see_sign(move) < 0)
1729 // Make and search the move
1730 pos.do_move(move, st, ci, moveIsCheck);
1731 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1732 pos.undo_move(move);
1734 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1737 if (value > bestValue)
1748 // All legal moves have been searched. A special case: If we're in check
1749 // and no legal moves were found, it is checkmate.
1750 if (!moveCount && isCheck) // Mate!
1751 return value_mated_in(ply);
1753 // Update transposition table
1754 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1755 if (bestValue <= oldAlpha)
1757 // If bestValue isn't changed it means it is still the static evaluation
1758 // of the node, so keep this info to avoid a future evaluation() call.
1759 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1760 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1762 else if (bestValue >= beta)
1764 move = ss[ply].pv[ply];
1765 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1767 // Update killers only for good checking moves
1768 if (!pos.move_is_capture_or_promotion(move))
1769 update_killers(move, ss[ply]);
1772 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1774 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1780 // sp_search() is used to search from a split point. This function is called
1781 // by each thread working at the split point. It is similar to the normal
1782 // search() function, but simpler. Because we have already probed the hash
1783 // table, done a null move search, and searched the first move before
1784 // splitting, we don't have to repeat all this work in sp_search(). We
1785 // also don't need to store anything to the hash table here: This is taken
1786 // care of after we return from the split point.
1788 void sp_search(SplitPoint* sp, int threadID) {
1790 assert(threadID >= 0 && threadID < TM.active_threads());
1791 assert(TM.active_threads() > 1);
1795 Depth ext, newDepth;
1796 Value value, futilityValueScaled;
1797 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1799 value = -VALUE_INFINITE;
1801 Position pos(*sp->pos);
1803 SearchStack* ss = sp->sstack[threadID];
1804 isCheck = pos.is_check();
1806 // Step 10. Loop through moves
1807 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1808 lock_grab(&(sp->lock));
1810 while ( sp->bestValue < sp->beta
1811 && !TM.thread_should_stop(threadID)
1812 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1814 moveCount = ++sp->moves;
1815 lock_release(&(sp->lock));
1817 assert(move_is_ok(move));
1819 moveIsCheck = pos.move_is_check(move, ci);
1820 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1822 // Step 11. Decide the new search depth
1823 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1824 newDepth = sp->depth - OnePly + ext;
1826 // Update current move
1827 ss[sp->ply].currentMove = move;
1829 // Step 12. Futility pruning
1832 && !captureOrPromotion
1833 && !move_is_castle(move))
1835 // Move count based pruning
1836 if ( moveCount >= futility_move_count(sp->depth)
1837 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1838 && sp->bestValue > value_mated_in(PLY_MAX))
1840 lock_grab(&(sp->lock));
1844 // Value based pruning
1845 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1846 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1847 + H.gain(pos.piece_on(move_from(move)), move_to(move)) + 45;
1849 if (futilityValueScaled < sp->beta)
1851 lock_grab(&(sp->lock));
1853 if (futilityValueScaled > sp->bestValue)
1854 sp->bestValue = futilityValueScaled;
1859 // Step 13. Make the move
1860 pos.do_move(move, st, ci, moveIsCheck);
1862 // Step 14. Reduced search
1863 // if the move fails high will be re-searched at full depth.
1864 bool doFullDepthSearch = true;
1867 && !captureOrPromotion
1868 && !move_is_castle(move)
1869 && !move_is_killer(move, ss[sp->ply]))
1871 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1872 if (ss[sp->ply].reduction)
1874 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1875 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1879 // Step 15. Full depth search
1880 if (doFullDepthSearch)
1882 ss[sp->ply].reduction = Depth(0);
1883 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1886 // Step 16. Undo move
1887 pos.undo_move(move);
1889 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1891 // Step 17. Check for new best move
1892 lock_grab(&(sp->lock));
1894 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1896 sp->bestValue = value;
1897 if (sp->bestValue >= sp->beta)
1899 sp->stopRequest = true;
1900 sp_update_pv(sp->parentSstack, ss, sp->ply);
1905 /* Here we have the lock still grabbed */
1907 sp->slaves[threadID] = 0;
1910 lock_release(&(sp->lock));
1914 // sp_search_pv() is used to search from a PV split point. This function
1915 // is called by each thread working at the split point. It is similar to
1916 // the normal search_pv() function, but simpler. Because we have already
1917 // probed the hash table and searched the first move before splitting, we
1918 // don't have to repeat all this work in sp_search_pv(). We also don't
1919 // need to store anything to the hash table here: This is taken care of
1920 // after we return from the split point.
1922 void sp_search_pv(SplitPoint* sp, int threadID) {
1924 assert(threadID >= 0 && threadID < TM.active_threads());
1925 assert(TM.active_threads() > 1);
1929 Depth ext, newDepth;
1931 bool moveIsCheck, captureOrPromotion, dangerous;
1933 value = -VALUE_INFINITE;
1935 Position pos(*sp->pos);
1937 SearchStack* ss = sp->sstack[threadID];
1939 // Step 10. Loop through moves
1940 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1941 lock_grab(&(sp->lock));
1943 while ( sp->alpha < sp->beta
1944 && !TM.thread_should_stop(threadID)
1945 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1947 moveCount = ++sp->moves;
1948 lock_release(&(sp->lock));
1950 assert(move_is_ok(move));
1952 moveIsCheck = pos.move_is_check(move, ci);
1953 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1955 // Step 11. Decide the new search depth
1956 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1957 newDepth = sp->depth - OnePly + ext;
1959 // Update current move
1960 ss[sp->ply].currentMove = move;
1962 // Step 12. Futility pruning (is omitted in PV nodes)
1964 // Step 13. Make the move
1965 pos.do_move(move, st, ci, moveIsCheck);
1967 // Step 14. Reduced search
1968 // if the move fails high will be re-searched at full depth.
1969 bool doFullDepthSearch = true;
1972 && !captureOrPromotion
1973 && !move_is_castle(move)
1974 && !move_is_killer(move, ss[sp->ply]))
1976 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1977 if (ss[sp->ply].reduction)
1979 Value localAlpha = sp->alpha;
1980 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1981 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1985 // Step 15. Full depth search
1986 if (doFullDepthSearch)
1988 Value localAlpha = sp->alpha;
1989 ss[sp->ply].reduction = Depth(0);
1990 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1992 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1994 // If another thread has failed high then sp->alpha has been increased
1995 // to be higher or equal then beta, if so, avoid to start a PV search.
1996 localAlpha = sp->alpha;
1997 if (localAlpha < sp->beta)
1998 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
2002 // Step 16. Undo move
2003 pos.undo_move(move);
2005 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2007 // Step 17. Check for new best move
2008 lock_grab(&(sp->lock));
2010 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
2012 sp->bestValue = value;
2013 if (value > sp->alpha)
2015 // Ask threads to stop before to modify sp->alpha
2016 if (value >= sp->beta)
2017 sp->stopRequest = true;
2021 sp_update_pv(sp->parentSstack, ss, sp->ply);
2022 if (value == value_mate_in(sp->ply + 1))
2023 ss[sp->ply].mateKiller = move;
2028 /* Here we have the lock still grabbed */
2030 sp->slaves[threadID] = 0;
2033 lock_release(&(sp->lock));
2037 // init_node() is called at the beginning of all the search functions
2038 // (search(), search_pv(), qsearch(), and so on) and initializes the
2039 // search stack object corresponding to the current node. Once every
2040 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2041 // for user input and checks whether it is time to stop the search.
2043 void init_node(SearchStack ss[], int ply, int threadID) {
2045 assert(ply >= 0 && ply < PLY_MAX);
2046 assert(threadID >= 0 && threadID < TM.active_threads());
2048 TM.incrementNodeCounter(threadID);
2053 if (NodesSincePoll >= NodesBetweenPolls)
2060 ss[ply + 2].initKillers();
2064 // update_pv() is called whenever a search returns a value > alpha.
2065 // It updates the PV in the SearchStack object corresponding to the
2068 void update_pv(SearchStack ss[], int ply) {
2070 assert(ply >= 0 && ply < PLY_MAX);
2074 ss[ply].pv[ply] = ss[ply].currentMove;
2076 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2077 ss[ply].pv[p] = ss[ply + 1].pv[p];
2079 ss[ply].pv[p] = MOVE_NONE;
2083 // sp_update_pv() is a variant of update_pv for use at split points. The
2084 // difference between the two functions is that sp_update_pv also updates
2085 // the PV at the parent node.
2087 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2089 assert(ply >= 0 && ply < PLY_MAX);
2093 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2095 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2096 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2098 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2102 // connected_moves() tests whether two moves are 'connected' in the sense
2103 // that the first move somehow made the second move possible (for instance
2104 // if the moving piece is the same in both moves). The first move is assumed
2105 // to be the move that was made to reach the current position, while the
2106 // second move is assumed to be a move from the current position.
2108 bool connected_moves(const Position& pos, Move m1, Move m2) {
2110 Square f1, t1, f2, t2;
2113 assert(move_is_ok(m1));
2114 assert(move_is_ok(m2));
2116 if (m2 == MOVE_NONE)
2119 // Case 1: The moving piece is the same in both moves
2125 // Case 2: The destination square for m2 was vacated by m1
2131 // Case 3: Moving through the vacated square
2132 if ( piece_is_slider(pos.piece_on(f2))
2133 && bit_is_set(squares_between(f2, t2), f1))
2136 // Case 4: The destination square for m2 is defended by the moving piece in m1
2137 p = pos.piece_on(t1);
2138 if (bit_is_set(pos.attacks_from(p, t1), t2))
2141 // Case 5: Discovered check, checking piece is the piece moved in m1
2142 if ( piece_is_slider(p)
2143 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2144 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2146 // discovered_check_candidates() works also if the Position's side to
2147 // move is the opposite of the checking piece.
2148 Color them = opposite_color(pos.side_to_move());
2149 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2151 if (bit_is_set(dcCandidates, f2))
2158 // value_is_mate() checks if the given value is a mate one
2159 // eventually compensated for the ply.
2161 bool value_is_mate(Value value) {
2163 assert(abs(value) <= VALUE_INFINITE);
2165 return value <= value_mated_in(PLY_MAX)
2166 || value >= value_mate_in(PLY_MAX);
2170 // move_is_killer() checks if the given move is among the
2171 // killer moves of that ply.
2173 bool move_is_killer(Move m, const SearchStack& ss) {
2175 const Move* k = ss.killers;
2176 for (int i = 0; i < KILLER_MAX; i++, k++)
2184 // extension() decides whether a move should be searched with normal depth,
2185 // or with extended depth. Certain classes of moves (checking moves, in
2186 // particular) are searched with bigger depth than ordinary moves and in
2187 // any case are marked as 'dangerous'. Note that also if a move is not
2188 // extended, as example because the corresponding UCI option is set to zero,
2189 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2191 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2192 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2194 assert(m != MOVE_NONE);
2196 Depth result = Depth(0);
2197 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2202 result += CheckExtension[pvNode];
2205 result += SingleEvasionExtension[pvNode];
2208 result += MateThreatExtension[pvNode];
2211 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2213 Color c = pos.side_to_move();
2214 if (relative_rank(c, move_to(m)) == RANK_7)
2216 result += PawnPushTo7thExtension[pvNode];
2219 if (pos.pawn_is_passed(c, move_to(m)))
2221 result += PassedPawnExtension[pvNode];
2226 if ( captureOrPromotion
2227 && pos.type_of_piece_on(move_to(m)) != PAWN
2228 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2229 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2230 && !move_is_promotion(m)
2233 result += PawnEndgameExtension[pvNode];
2238 && captureOrPromotion
2239 && pos.type_of_piece_on(move_to(m)) != PAWN
2240 && pos.see_sign(m) >= 0)
2246 return Min(result, OnePly);
2250 // ok_to_do_nullmove() looks at the current position and decides whether
2251 // doing a 'null move' should be allowed. In order to avoid zugzwang
2252 // problems, null moves are not allowed when the side to move has very
2253 // little material left. Currently, the test is a bit too simple: Null
2254 // moves are avoided only when the side to move has only pawns left.
2255 // It's probably a good idea to avoid null moves in at least some more
2256 // complicated endgames, e.g. KQ vs KR. FIXME
2258 bool ok_to_do_nullmove(const Position& pos) {
2260 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2264 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2265 // non-tactical moves late in the move list close to the leaves are
2266 // candidates for pruning.
2268 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2270 assert(move_is_ok(m));
2271 assert(threat == MOVE_NONE || move_is_ok(threat));
2272 assert(!pos.move_is_check(m));
2273 assert(!pos.move_is_capture_or_promotion(m));
2274 assert(!pos.move_is_passed_pawn_push(m));
2276 Square mfrom, mto, tfrom, tto;
2278 // Prune if there isn't any threat move
2279 if (threat == MOVE_NONE)
2282 mfrom = move_from(m);
2284 tfrom = move_from(threat);
2285 tto = move_to(threat);
2287 // Case 1: Don't prune moves which move the threatened piece
2291 // Case 2: If the threatened piece has value less than or equal to the
2292 // value of the threatening piece, don't prune move which defend it.
2293 if ( pos.move_is_capture(threat)
2294 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2295 || pos.type_of_piece_on(tfrom) == KING)
2296 && pos.move_attacks_square(m, tto))
2299 // Case 3: If the moving piece in the threatened move is a slider, don't
2300 // prune safe moves which block its ray.
2301 if ( piece_is_slider(pos.piece_on(tfrom))
2302 && bit_is_set(squares_between(tfrom, tto), mto)
2303 && pos.see_sign(m) >= 0)
2310 // ok_to_use_TT() returns true if a transposition table score can be used at a
2311 // given point in search. To avoid zugzwang issues TT cutoffs at the root node
2312 // of a null move verification search are not allowed if the TT value was found
2313 // by a null search, this is implemented testing allowNullmove and TT entry type.
2315 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply, bool allowNullmove) {
2317 Value v = value_from_tt(tte->value(), ply);
2319 return (allowNullmove || !(tte->type() & VALUE_TYPE_NULL) || !ZugDetection)
2321 && ( tte->depth() >= depth
2322 || v >= Max(value_mate_in(PLY_MAX), beta)
2323 || v < Min(value_mated_in(PLY_MAX), beta))
2325 && ( (is_lower_bound(tte->type()) && v >= beta)
2326 || (is_upper_bound(tte->type()) && v < beta));
2330 // refine_eval() returns the transposition table score if
2331 // possible otherwise falls back on static position evaluation.
2333 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2338 Value v = value_from_tt(tte->value(), ply);
2340 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2341 || (is_upper_bound(tte->type()) && v < defaultEval))
2348 // update_history() registers a good move that produced a beta-cutoff
2349 // in history and marks as failures all the other moves of that ply.
2351 void update_history(const Position& pos, Move move, Depth depth,
2352 Move movesSearched[], int moveCount) {
2356 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2358 for (int i = 0; i < moveCount - 1; i++)
2360 m = movesSearched[i];
2364 if (!pos.move_is_capture_or_promotion(m))
2365 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2370 // update_killers() add a good move that produced a beta-cutoff
2371 // among the killer moves of that ply.
2373 void update_killers(Move m, SearchStack& ss) {
2375 if (m == ss.killers[0])
2378 for (int i = KILLER_MAX - 1; i > 0; i--)
2379 ss.killers[i] = ss.killers[i - 1];
2385 // update_gains() updates the gains table of a non-capture move given
2386 // the static position evaluation before and after the move.
2388 void update_gains(const Position& pos, Move m, Value before, Value after) {
2391 && before != VALUE_NONE
2392 && after != VALUE_NONE
2393 && pos.captured_piece() == NO_PIECE_TYPE
2394 && !move_is_castle(m)
2395 && !move_is_promotion(m))
2396 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2400 // current_search_time() returns the number of milliseconds which have passed
2401 // since the beginning of the current search.
2403 int current_search_time() {
2405 return get_system_time() - SearchStartTime;
2409 // nps() computes the current nodes/second count.
2413 int t = current_search_time();
2414 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2418 // poll() performs two different functions: It polls for user input, and it
2419 // looks at the time consumed so far and decides if it's time to abort the
2424 static int lastInfoTime;
2425 int t = current_search_time();
2430 // We are line oriented, don't read single chars
2431 std::string command;
2433 if (!std::getline(std::cin, command))
2436 if (command == "quit")
2439 PonderSearch = false;
2443 else if (command == "stop")
2446 PonderSearch = false;
2448 else if (command == "ponderhit")
2452 // Print search information
2456 else if (lastInfoTime > t)
2457 // HACK: Must be a new search where we searched less than
2458 // NodesBetweenPolls nodes during the first second of search.
2461 else if (t - lastInfoTime >= 1000)
2468 if (dbg_show_hit_rate)
2469 dbg_print_hit_rate();
2471 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2472 << " time " << t << " hashfull " << TT.full() << endl;
2475 // Should we stop the search?
2479 bool stillAtFirstMove = FirstRootMove
2480 && !AspirationFailLow
2481 && t > MaxSearchTime + ExtraSearchTime;
2483 bool noMoreTime = t > AbsoluteMaxSearchTime
2484 || stillAtFirstMove;
2486 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2487 || (ExactMaxTime && t >= ExactMaxTime)
2488 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2493 // ponderhit() is called when the program is pondering (i.e. thinking while
2494 // it's the opponent's turn to move) in order to let the engine know that
2495 // it correctly predicted the opponent's move.
2499 int t = current_search_time();
2500 PonderSearch = false;
2502 bool stillAtFirstMove = FirstRootMove
2503 && !AspirationFailLow
2504 && t > MaxSearchTime + ExtraSearchTime;
2506 bool noMoreTime = t > AbsoluteMaxSearchTime
2507 || stillAtFirstMove;
2509 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2514 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2516 void init_ss_array(SearchStack ss[]) {
2518 for (int i = 0; i < 3; i++)
2521 ss[i].initKillers();
2526 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2527 // while the program is pondering. The point is to work around a wrinkle in
2528 // the UCI protocol: When pondering, the engine is not allowed to give a
2529 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2530 // We simply wait here until one of these commands is sent, and return,
2531 // after which the bestmove and pondermove will be printed (in id_loop()).
2533 void wait_for_stop_or_ponderhit() {
2535 std::string command;
2539 if (!std::getline(std::cin, command))
2542 if (command == "quit")
2547 else if (command == "ponderhit" || command == "stop")
2553 // print_pv_info() prints to standard output and eventually to log file information on
2554 // the current PV line. It is called at each iteration or after a new pv is found.
2556 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2558 cout << "info depth " << Iteration
2559 << " score " << value_to_string(value)
2560 << ((value >= beta) ? " lowerbound" :
2561 ((value <= alpha)? " upperbound" : ""))
2562 << " time " << current_search_time()
2563 << " nodes " << TM.nodes_searched()
2567 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2568 cout << ss[0].pv[j] << " ";
2574 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2575 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2577 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2578 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2583 // init_thread() is the function which is called when a new thread is
2584 // launched. It simply calls the idle_loop() function with the supplied
2585 // threadID. There are two versions of this function; one for POSIX
2586 // threads and one for Windows threads.
2588 #if !defined(_MSC_VER)
2590 void* init_thread(void *threadID) {
2592 TM.idle_loop(*(int*)threadID, NULL);
2598 DWORD WINAPI init_thread(LPVOID threadID) {
2600 TM.idle_loop(*(int*)threadID, NULL);
2607 /// The ThreadsManager class
2609 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2610 // get_beta_counters() are getters/setters for the per thread
2611 // counters used to sort the moves at root.
2613 void ThreadsManager::resetNodeCounters() {
2615 for (int i = 0; i < MAX_THREADS; i++)
2616 threads[i].nodes = 0ULL;
2619 void ThreadsManager::resetBetaCounters() {
2621 for (int i = 0; i < MAX_THREADS; i++)
2622 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2625 int64_t ThreadsManager::nodes_searched() const {
2627 int64_t result = 0ULL;
2628 for (int i = 0; i < ActiveThreads; i++)
2629 result += threads[i].nodes;
2634 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2637 for (int i = 0; i < MAX_THREADS; i++)
2639 our += threads[i].betaCutOffs[us];
2640 their += threads[i].betaCutOffs[opposite_color(us)];
2645 // idle_loop() is where the threads are parked when they have no work to do.
2646 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2647 // object for which the current thread is the master.
2649 void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
2651 assert(threadID >= 0 && threadID < MAX_THREADS);
2655 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2656 // master should exit as last one.
2657 if (AllThreadsShouldExit)
2660 threads[threadID].state = THREAD_TERMINATED;
2664 // If we are not thinking, wait for a condition to be signaled
2665 // instead of wasting CPU time polling for work.
2666 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2669 assert(threadID != 0);
2670 threads[threadID].state = THREAD_SLEEPING;
2672 #if !defined(_MSC_VER)
2673 lock_grab(&WaitLock);
2674 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2675 pthread_cond_wait(&WaitCond, &WaitLock);
2676 lock_release(&WaitLock);
2678 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2682 // If thread has just woken up, mark it as available
2683 if (threads[threadID].state == THREAD_SLEEPING)
2684 threads[threadID].state = THREAD_AVAILABLE;
2686 // If this thread has been assigned work, launch a search
2687 if (threads[threadID].state == THREAD_WORKISWAITING)
2689 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2691 threads[threadID].state = THREAD_SEARCHING;
2693 if (threads[threadID].splitPoint->pvNode)
2694 sp_search_pv(threads[threadID].splitPoint, threadID);
2696 sp_search(threads[threadID].splitPoint, threadID);
2698 assert(threads[threadID].state == THREAD_SEARCHING);
2700 threads[threadID].state = THREAD_AVAILABLE;
2703 // If this thread is the master of a split point and all threads have
2704 // finished their work at this split point, return from the idle loop.
2705 if (waitSp != NULL && waitSp->cpus == 0)
2707 assert(threads[threadID].state == THREAD_AVAILABLE);
2709 threads[threadID].state = THREAD_SEARCHING;
2716 // init_threads() is called during startup. It launches all helper threads,
2717 // and initializes the split point stack and the global locks and condition
2720 void ThreadsManager::init_threads() {
2725 #if !defined(_MSC_VER)
2726 pthread_t pthread[1];
2729 // Initialize global locks
2730 lock_init(&MPLock, NULL);
2731 lock_init(&WaitLock, NULL);
2733 #if !defined(_MSC_VER)
2734 pthread_cond_init(&WaitCond, NULL);
2736 for (i = 0; i < MAX_THREADS; i++)
2737 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2740 // Initialize SplitPointStack locks
2741 for (i = 0; i < MAX_THREADS; i++)
2742 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2744 SplitPointStack[i][j].parent = NULL;
2745 lock_init(&(SplitPointStack[i][j].lock), NULL);
2748 // Will be set just before program exits to properly end the threads
2749 AllThreadsShouldExit = false;
2751 // Threads will be put to sleep as soon as created
2752 AllThreadsShouldSleep = true;
2754 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2756 threads[0].state = THREAD_SEARCHING;
2757 for (i = 1; i < MAX_THREADS; i++)
2758 threads[i].state = THREAD_AVAILABLE;
2760 // Launch the helper threads
2761 for (i = 1; i < MAX_THREADS; i++)
2764 #if !defined(_MSC_VER)
2765 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2767 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2772 cout << "Failed to create thread number " << i << endl;
2773 Application::exit_with_failure();
2776 // Wait until the thread has finished launching and is gone to sleep
2777 while (threads[i].state != THREAD_SLEEPING);
2782 // exit_threads() is called when the program exits. It makes all the
2783 // helper threads exit cleanly.
2785 void ThreadsManager::exit_threads() {
2787 ActiveThreads = MAX_THREADS; // HACK
2788 AllThreadsShouldSleep = true; // HACK
2789 wake_sleeping_threads();
2791 // This makes the threads to exit idle_loop()
2792 AllThreadsShouldExit = true;
2794 // Wait for thread termination
2795 for (int i = 1; i < MAX_THREADS; i++)
2796 while (threads[i].state != THREAD_TERMINATED);
2798 // Now we can safely destroy the locks
2799 for (int i = 0; i < MAX_THREADS; i++)
2800 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2801 lock_destroy(&(SplitPointStack[i][j].lock));
2803 lock_destroy(&WaitLock);
2804 lock_destroy(&MPLock);
2808 // thread_should_stop() checks whether the thread should stop its search.
2809 // This can happen if a beta cutoff has occurred in the thread's currently
2810 // active split point, or in some ancestor of the current split point.
2812 bool ThreadsManager::thread_should_stop(int threadID) const {
2814 assert(threadID >= 0 && threadID < ActiveThreads);
2818 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
2823 // thread_is_available() checks whether the thread with threadID "slave" is
2824 // available to help the thread with threadID "master" at a split point. An
2825 // obvious requirement is that "slave" must be idle. With more than two
2826 // threads, this is not by itself sufficient: If "slave" is the master of
2827 // some active split point, it is only available as a slave to the other
2828 // threads which are busy searching the split point at the top of "slave"'s
2829 // split point stack (the "helpful master concept" in YBWC terminology).
2831 bool ThreadsManager::thread_is_available(int slave, int master) const {
2833 assert(slave >= 0 && slave < ActiveThreads);
2834 assert(master >= 0 && master < ActiveThreads);
2835 assert(ActiveThreads > 1);
2837 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2840 // Make a local copy to be sure doesn't change under our feet
2841 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2843 if (localActiveSplitPoints == 0)
2844 // No active split points means that the thread is available as
2845 // a slave for any other thread.
2848 if (ActiveThreads == 2)
2851 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2852 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2853 // could have been set to 0 by another thread leading to an out of bound access.
2854 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2861 // available_thread_exists() tries to find an idle thread which is available as
2862 // a slave for the thread with threadID "master".
2864 bool ThreadsManager::available_thread_exists(int master) const {
2866 assert(master >= 0 && master < ActiveThreads);
2867 assert(ActiveThreads > 1);
2869 for (int i = 0; i < ActiveThreads; i++)
2870 if (thread_is_available(i, master))
2877 // split() does the actual work of distributing the work at a node between
2878 // several threads at PV nodes. If it does not succeed in splitting the
2879 // node (because no idle threads are available, or because we have no unused
2880 // split point objects), the function immediately returns false. If
2881 // splitting is possible, a SplitPoint object is initialized with all the
2882 // data that must be copied to the helper threads (the current position and
2883 // search stack, alpha, beta, the search depth, etc.), and we tell our
2884 // helper threads that they have been assigned work. This will cause them
2885 // to instantly leave their idle loops and call sp_search_pv(). When all
2886 // threads have returned from sp_search_pv (or, equivalently, when
2887 // splitPoint->cpus becomes 0), split() returns true.
2889 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2890 Value* alpha, const Value beta, Value* bestValue,
2891 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2894 assert(sstck != NULL);
2895 assert(ply >= 0 && ply < PLY_MAX);
2896 assert(*bestValue >= -VALUE_INFINITE);
2897 assert( ( pvNode && *bestValue <= *alpha)
2898 || (!pvNode && *bestValue < beta ));
2899 assert(!pvNode || *alpha < beta);
2900 assert(beta <= VALUE_INFINITE);
2901 assert(depth > Depth(0));
2902 assert(master >= 0 && master < ActiveThreads);
2903 assert(ActiveThreads > 1);
2905 SplitPoint* splitPoint;
2909 // If no other thread is available to help us, or if we have too many
2910 // active split points, don't split.
2911 if ( !available_thread_exists(master)
2912 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2914 lock_release(&MPLock);
2918 // Pick the next available split point object from the split point stack
2919 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2921 // Initialize the split point object
2922 splitPoint->parent = threads[master].splitPoint;
2923 splitPoint->stopRequest = false;
2924 splitPoint->ply = ply;
2925 splitPoint->depth = depth;
2926 splitPoint->mateThreat = mateThreat;
2927 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2928 splitPoint->beta = beta;
2929 splitPoint->pvNode = pvNode;
2930 splitPoint->bestValue = *bestValue;
2931 splitPoint->master = master;
2932 splitPoint->mp = mp;
2933 splitPoint->moves = *moves;
2934 splitPoint->cpus = 1;
2935 splitPoint->pos = &p;
2936 splitPoint->parentSstack = sstck;
2937 for (int i = 0; i < ActiveThreads; i++)
2938 splitPoint->slaves[i] = 0;
2940 threads[master].splitPoint = splitPoint;
2941 threads[master].activeSplitPoints++;
2943 // If we are here it means we are not available
2944 assert(threads[master].state != THREAD_AVAILABLE);
2946 // Allocate available threads setting state to THREAD_BOOKED
2947 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2948 if (thread_is_available(i, master))
2950 threads[i].state = THREAD_BOOKED;
2951 threads[i].splitPoint = splitPoint;
2952 splitPoint->slaves[i] = 1;
2956 assert(splitPoint->cpus > 1);
2958 // We can release the lock because slave threads are already booked and master is not available
2959 lock_release(&MPLock);
2961 // Tell the threads that they have work to do. This will make them leave
2962 // their idle loop. But before copy search stack tail for each thread.
2963 for (int i = 0; i < ActiveThreads; i++)
2964 if (i == master || splitPoint->slaves[i])
2966 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2968 assert(i == master || threads[i].state == THREAD_BOOKED);
2970 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2973 // Everything is set up. The master thread enters the idle loop, from
2974 // which it will instantly launch a search, because its state is
2975 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2976 // idle loop, which means that the main thread will return from the idle
2977 // loop when all threads have finished their work at this split point
2978 // (i.e. when splitPoint->cpus == 0).
2979 idle_loop(master, splitPoint);
2981 // We have returned from the idle loop, which means that all threads are
2982 // finished. Update alpha, beta and bestValue, and return.
2986 *alpha = splitPoint->alpha;
2988 *bestValue = splitPoint->bestValue;
2989 threads[master].activeSplitPoints--;
2990 threads[master].splitPoint = splitPoint->parent;
2992 lock_release(&MPLock);
2997 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2998 // to start a new search from the root.
3000 void ThreadsManager::wake_sleeping_threads() {
3002 assert(AllThreadsShouldSleep);
3003 assert(ActiveThreads > 0);
3005 AllThreadsShouldSleep = false;
3007 if (ActiveThreads == 1)
3010 #if !defined(_MSC_VER)
3011 pthread_mutex_lock(&WaitLock);
3012 pthread_cond_broadcast(&WaitCond);
3013 pthread_mutex_unlock(&WaitLock);
3015 for (int i = 1; i < MAX_THREADS; i++)
3016 SetEvent(SitIdleEvent[i]);
3022 // put_threads_to_sleep() makes all the threads go to sleep just before
3023 // to leave think(), at the end of the search. Threads should have already
3024 // finished the job and should be idle.
3026 void ThreadsManager::put_threads_to_sleep() {
3028 assert(!AllThreadsShouldSleep);
3030 // This makes the threads to go to sleep
3031 AllThreadsShouldSleep = true;
3034 /// The RootMoveList class
3036 // RootMoveList c'tor
3038 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3040 SearchStack ss[PLY_MAX_PLUS_2];
3041 MoveStack mlist[MaxRootMoves];
3043 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3045 // Generate all legal moves
3046 MoveStack* last = generate_moves(pos, mlist);
3048 // Add each move to the moves[] array
3049 for (MoveStack* cur = mlist; cur != last; cur++)
3051 bool includeMove = includeAllMoves;
3053 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3054 includeMove = (searchMoves[k] == cur->move);
3059 // Find a quick score for the move
3061 pos.do_move(cur->move, st);
3062 moves[count].move = cur->move;
3063 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3064 moves[count].pv[0] = cur->move;
3065 moves[count].pv[1] = MOVE_NONE;
3066 pos.undo_move(cur->move);
3073 // RootMoveList simple methods definitions
3075 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3077 moves[moveNum].nodes = nodes;
3078 moves[moveNum].cumulativeNodes += nodes;
3081 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3083 moves[moveNum].ourBeta = our;
3084 moves[moveNum].theirBeta = their;
3087 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3091 for (j = 0; pv[j] != MOVE_NONE; j++)
3092 moves[moveNum].pv[j] = pv[j];
3094 moves[moveNum].pv[j] = MOVE_NONE;
3098 // RootMoveList::sort() sorts the root move list at the beginning of a new
3101 void RootMoveList::sort() {
3103 sort_multipv(count - 1); // Sort all items
3107 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3108 // list by their scores and depths. It is used to order the different PVs
3109 // correctly in MultiPV mode.
3111 void RootMoveList::sort_multipv(int n) {
3115 for (i = 1; i <= n; i++)
3117 RootMove rm = moves[i];
3118 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3119 moves[j] = moves[j - 1];