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* sp);
86 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode);
93 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
94 Thread threads[MAX_THREADS];
95 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
97 Lock MPLock, WaitLock;
99 #if !defined(_MSC_VER)
100 pthread_cond_t WaitCond;
102 HANDLE SitIdleEvent[MAX_THREADS];
108 // RootMove struct is used for moves at the root at the tree. For each
109 // root move, we store a score, a node count, and a PV (really a refutation
110 // in the case of moves which fail low).
114 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
116 // RootMove::operator<() is the comparison function used when
117 // sorting the moves. A move m1 is considered to be better
118 // than a move m2 if it has a higher score, or if the moves
119 // have equal score but m1 has the higher node count.
120 bool operator<(const RootMove& m) const {
122 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
127 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
128 Move pv[PLY_MAX_PLUS_2];
132 // The RootMoveList class is essentially an array of RootMove objects, with
133 // a handful of methods for accessing the data in the individual moves.
138 RootMoveList(Position& pos, Move searchMoves[]);
140 int move_count() const { return count; }
141 Move get_move(int moveNum) const { return moves[moveNum].move; }
142 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
143 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
144 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
145 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
147 void set_move_nodes(int moveNum, int64_t nodes);
148 void set_beta_counters(int moveNum, int64_t our, int64_t their);
149 void set_move_pv(int moveNum, const Move pv[]);
151 void sort_multipv(int n);
154 static const int MaxRootMoves = 500;
155 RootMove moves[MaxRootMoves];
164 // Maximum depth for razoring
165 const Depth RazorDepth = 4 * OnePly;
167 // Dynamic razoring margin based on depth
168 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
170 // Step 8. Null move search with verification search
172 // Null move margin. A null move search will not be done if the static
173 // evaluation of the position is more than NullMoveMargin below beta.
174 const Value NullMoveMargin = Value(0x200);
176 // Maximum depth for use of dynamic threat detection when null move fails low
177 const Depth ThreatDepth = 5 * OnePly;
179 // Step 9. Internal iterative deepening
181 // Minimum depth for use of internal iterative deepening
182 const Depth 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;
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);
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, get_option_value_bool("Best Book Move"));
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");
430 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
432 read_weights(pos.side_to_move());
434 // Set the number of active threads
435 int newActiveThreads = get_option_value_int("Threads");
436 if (newActiveThreads != TM.active_threads())
438 TM.set_active_threads(newActiveThreads);
439 init_eval(TM.active_threads());
442 // Wake up sleeping threads
443 TM.wake_sleeping_threads();
446 int myTime = time[side_to_move];
447 int myIncrement = increment[side_to_move];
448 if (UseTimeManagement)
450 if (!movesToGo) // Sudden death time control
454 MaxSearchTime = myTime / 30 + myIncrement;
455 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
457 else // Blitz game without increment
459 MaxSearchTime = myTime / 30;
460 AbsoluteMaxSearchTime = myTime / 8;
463 else // (x moves) / (y minutes)
467 MaxSearchTime = myTime / 2;
468 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
472 MaxSearchTime = myTime / Min(movesToGo, 20);
473 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
477 if (get_option_value_bool("Ponder"))
479 MaxSearchTime += MaxSearchTime / 4;
480 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
484 // Set best NodesBetweenPolls interval to avoid lagging under
485 // heavy time pressure.
487 NodesBetweenPolls = Min(MaxNodes, 30000);
488 else if (myTime && myTime < 1000)
489 NodesBetweenPolls = 1000;
490 else if (myTime && myTime < 5000)
491 NodesBetweenPolls = 5000;
493 NodesBetweenPolls = 30000;
495 // Write search information to log file
497 LogFile << "Searching: " << pos.to_fen() << endl
498 << "infinite: " << infinite
499 << " ponder: " << ponder
500 << " time: " << myTime
501 << " increment: " << myIncrement
502 << " moves to go: " << movesToGo << endl;
504 // LSN filtering. Used only for developing purposes, disabled by default
508 // Step 2. If after last move we decided to lose on time, do it now!
509 while (SearchStartTime + myTime + 1000 > get_system_time())
513 // We're ready to start thinking. Call the iterative deepening loop function
514 Value v = id_loop(pos, searchMoves);
518 // Step 1. If this is sudden death game and our position is hopeless,
519 // decide to lose on time.
520 if ( !loseOnTime // If we already lost on time, go to step 3.
530 // Step 3. Now after stepping over the time limit, reset flag for next match.
538 TM.put_threads_to_sleep();
544 /// init_search() is called during startup. It initializes various lookup tables
548 // Init our reduction lookup tables
549 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
550 for (int j = 1; j < 64; j++) // j == moveNumber
552 double pvRed = log(double(i)) * log(double(j)) / 3.0;
553 double nonPVRed = log(double(i)) * log(double(j)) / 1.5;
554 PVReductionMatrix[i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
555 NonPVReductionMatrix[i][j] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
558 // Init futility margins array
559 for (int i = 0; i < 16; i++) // i == depth (OnePly = 2)
560 for (int j = 0; j < 64; j++) // j == moveNumber
562 // FIXME: test using log instead of BSR
563 FutilityMarginsMatrix[i][j] = (i < 2 ? 0 : 112 * bitScanReverse32(i * i / 2)) - 8 * j + 45;
566 // Init futility move count array
567 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
568 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
572 // SearchStack::init() initializes a search stack. Used at the beginning of a
573 // new search from the root.
574 void SearchStack::init(int ply) {
576 pv[ply] = pv[ply + 1] = MOVE_NONE;
577 currentMove = threatMove = MOVE_NONE;
578 reduction = Depth(0);
582 void SearchStack::initKillers() {
584 mateKiller = MOVE_NONE;
585 for (int i = 0; i < KILLER_MAX; i++)
586 killers[i] = MOVE_NONE;
591 // id_loop() is the main iterative deepening loop. It calls root_search
592 // repeatedly with increasing depth until the allocated thinking time has
593 // been consumed, the user stops the search, or the maximum search depth is
596 Value id_loop(const Position& pos, Move searchMoves[]) {
599 SearchStack ss[PLY_MAX_PLUS_2];
600 Move EasyMove = MOVE_NONE;
601 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
603 // Moves to search are verified, copied, scored and sorted
604 RootMoveList rml(p, searchMoves);
606 // Handle special case of searching on a mate/stale position
607 if (rml.move_count() == 0)
610 wait_for_stop_or_ponderhit();
612 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
615 // Print RootMoveList startup scoring to the standard output,
616 // so to output information also for iteration 1.
617 cout << "info depth " << 1
618 << "\ninfo depth " << 1
619 << " score " << value_to_string(rml.get_move_score(0))
620 << " time " << current_search_time()
621 << " nodes " << TM.nodes_searched()
623 << " pv " << rml.get_move(0) << "\n";
629 ValueByIteration[1] = rml.get_move_score(0);
632 // Is one move significantly better than others after initial scoring ?
633 if ( rml.move_count() == 1
634 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
635 EasyMove = rml.get_move(0);
637 // Iterative deepening loop
638 while (Iteration < PLY_MAX)
640 // Initialize iteration
642 BestMoveChangesByIteration[Iteration] = 0;
644 cout << "info depth " << Iteration << endl;
646 // Calculate dynamic aspiration window based on previous iterations
647 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
649 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
650 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
652 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
653 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
655 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
656 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
659 // Search to the current depth, rml is updated and sorted, alpha and beta could change
660 value = root_search(p, ss, rml, &alpha, &beta);
662 // Write PV to transposition table, in case the relevant entries have
663 // been overwritten during the search.
664 TT.insert_pv(p, ss[0].pv);
667 break; // Value cannot be trusted. Break out immediately!
669 //Save info about search result
670 ValueByIteration[Iteration] = value;
672 // Drop the easy move if differs from the new best move
673 if (ss[0].pv[0] != EasyMove)
674 EasyMove = MOVE_NONE;
676 if (UseTimeManagement)
679 bool stopSearch = false;
681 // Stop search early if there is only a single legal move,
682 // we search up to Iteration 6 anyway to get a proper score.
683 if (Iteration >= 6 && rml.move_count() == 1)
686 // Stop search early when the last two iterations returned a mate score
688 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
689 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
692 // Stop search early if one move seems to be much better than the others
693 int64_t nodes = TM.nodes_searched();
695 && EasyMove == ss[0].pv[0]
696 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
697 && current_search_time() > MaxSearchTime / 16)
698 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
699 && current_search_time() > MaxSearchTime / 32)))
702 // Add some extra time if the best move has changed during the last two iterations
703 if (Iteration > 5 && Iteration <= 50)
704 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
705 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
707 // Stop search if most of MaxSearchTime is consumed at the end of the
708 // iteration. We probably don't have enough time to search the first
709 // move at the next iteration anyway.
710 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
716 StopOnPonderhit = true;
722 if (MaxDepth && Iteration >= MaxDepth)
726 // If we are pondering or in infinite search, we shouldn't print the
727 // best move before we are told to do so.
728 if (!AbortSearch && (PonderSearch || InfiniteSearch))
729 wait_for_stop_or_ponderhit();
731 // Print final search statistics
732 cout << "info nodes " << TM.nodes_searched()
734 << " time " << current_search_time()
735 << " hashfull " << TT.full() << endl;
737 // Print the best move and the ponder move to the standard output
738 if (ss[0].pv[0] == MOVE_NONE)
740 ss[0].pv[0] = rml.get_move(0);
741 ss[0].pv[1] = MOVE_NONE;
744 assert(ss[0].pv[0] != MOVE_NONE);
746 cout << "bestmove " << ss[0].pv[0];
748 if (ss[0].pv[1] != MOVE_NONE)
749 cout << " ponder " << ss[0].pv[1];
756 dbg_print_mean(LogFile);
758 if (dbg_show_hit_rate)
759 dbg_print_hit_rate(LogFile);
761 LogFile << "\nNodes: " << TM.nodes_searched()
762 << "\nNodes/second: " << nps()
763 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
766 p.do_move(ss[0].pv[0], st);
767 LogFile << "\nPonder move: "
768 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
771 return rml.get_move_score(0);
775 // root_search() is the function which searches the root node. It is
776 // similar to search_pv except that it uses a different move ordering
777 // scheme, prints some information to the standard output and handles
778 // the fail low/high loops.
780 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
787 Depth depth, ext, newDepth;
788 Value value, alpha, beta;
789 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
790 int researchCountFH, researchCountFL;
792 researchCountFH = researchCountFL = 0;
795 isCheck = pos.is_check();
797 // Step 1. Initialize node and poll (omitted at root, but I can see no good reason for this, FIXME)
798 // Step 2. Check for aborted search (omitted at root, because we do not initialize root node)
799 // Step 3. Mate distance pruning (omitted at root)
800 // Step 4. Transposition table lookup (omitted at root)
802 // Step 5. Evaluate the position statically
803 // At root we do this only to get reference value for child nodes
805 ss[0].eval = evaluate(pos, ei, 0);
807 ss[0].eval = VALUE_NONE; // HACK because we do not initialize root node
809 // Step 6. Razoring (omitted at root)
810 // Step 7. Static null move pruning (omitted at root)
811 // Step 8. Null move search with verification search (omitted at root)
812 // Step 9. Internal iterative deepening (omitted at root)
814 // Step extra. Fail low loop
815 // We start with small aspiration window and in case of fail low, we research
816 // with bigger window until we are not failing low anymore.
819 // Sort the moves before to (re)search
822 // Step 10. Loop through all moves in the root move list
823 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
825 // This is used by time management
826 FirstRootMove = (i == 0);
828 // Save the current node count before the move is searched
829 nodes = TM.nodes_searched();
831 // Reset beta cut-off counters
832 TM.resetBetaCounters();
834 // Pick the next root move, and print the move and the move number to
835 // the standard output.
836 move = ss[0].currentMove = rml.get_move(i);
838 if (current_search_time() >= 1000)
839 cout << "info currmove " << move
840 << " currmovenumber " << i + 1 << endl;
842 moveIsCheck = pos.move_is_check(move);
843 captureOrPromotion = pos.move_is_capture_or_promotion(move);
845 // Step 11. Decide the new search depth
846 depth = (Iteration - 2) * OnePly + InitialDepth;
847 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
848 newDepth = depth + ext;
850 // Step 12. Futility pruning (omitted at root)
852 // Step extra. Fail high loop
853 // If move fails high, we research with bigger window until we are not failing
855 value = - VALUE_INFINITE;
859 // Step 13. Make the move
860 pos.do_move(move, st, ci, moveIsCheck);
862 // Step extra. pv search
863 // We do pv search for first moves (i < MultiPV)
864 // and for fail high research (value > alpha)
865 if (i < MultiPV || value > alpha)
867 // Aspiration window is disabled in multi-pv case
869 alpha = -VALUE_INFINITE;
871 // Full depth PV search, done on first move or after a fail high
872 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
876 // Step 14. Reduced search
877 // if the move fails high will be re-searched at full depth
878 bool doFullDepthSearch = true;
880 if ( depth >= 3 * OnePly
882 && !captureOrPromotion
883 && !move_is_castle(move))
885 ss[0].reduction = pv_reduction(depth, i - MultiPV + 2);
888 // Reduced depth non-pv search using alpha as upperbound
889 value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0);
890 doFullDepthSearch = (value > alpha);
894 // Step 15. Full depth search
895 if (doFullDepthSearch)
897 // Full depth non-pv search using alpha as upperbound
898 ss[0].reduction = Depth(0);
899 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
901 // If we are above alpha then research at same depth but as PV
902 // to get a correct score or eventually a fail high above beta.
904 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
908 // Step 16. Undo move
911 // Can we exit fail high loop ?
912 if (AbortSearch || value < beta)
915 // We are failing high and going to do a research. It's important to update
916 // the score before research in case we run out of time while researching.
917 rml.set_move_score(i, value);
919 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
920 rml.set_move_pv(i, ss[0].pv);
922 // Print information to the standard output
923 print_pv_info(pos, ss, alpha, beta, value);
925 // Prepare for a research after a fail high, each time with a wider window
926 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
929 } // End of fail high loop
931 // Finished searching the move. If AbortSearch is true, the search
932 // was aborted because the user interrupted the search or because we
933 // ran out of time. In this case, the return value of the search cannot
934 // be trusted, and we break out of the loop without updating the best
939 // Remember beta-cutoff and searched nodes counts for this move. The
940 // info is used to sort the root moves for the next iteration.
942 TM.get_beta_counters(pos.side_to_move(), our, their);
943 rml.set_beta_counters(i, our, their);
944 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
946 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
947 assert(value < beta);
949 // Step 17. Check for new best move
950 if (value <= alpha && i >= MultiPV)
951 rml.set_move_score(i, -VALUE_INFINITE);
954 // PV move or new best move!
957 rml.set_move_score(i, value);
959 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
960 rml.set_move_pv(i, ss[0].pv);
964 // We record how often the best move has been changed in each
965 // iteration. This information is used for time managment: When
966 // the best move changes frequently, we allocate some more time.
968 BestMoveChangesByIteration[Iteration]++;
970 // Print information to the standard output
971 print_pv_info(pos, ss, alpha, beta, value);
973 // Raise alpha to setup proper non-pv search upper bound
980 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
982 cout << "info multipv " << j + 1
983 << " score " << value_to_string(rml.get_move_score(j))
984 << " depth " << (j <= i ? Iteration : Iteration - 1)
985 << " time " << current_search_time()
986 << " nodes " << TM.nodes_searched()
990 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
991 cout << rml.get_move_pv(j, k) << " ";
995 alpha = rml.get_move_score(Min(i, MultiPV - 1));
997 } // PV move or new best move
999 assert(alpha >= *alphaPtr);
1001 AspirationFailLow = (alpha == *alphaPtr);
1003 if (AspirationFailLow && StopOnPonderhit)
1004 StopOnPonderhit = false;
1007 // Can we exit fail low loop ?
1008 if (AbortSearch || !AspirationFailLow)
1011 // Prepare for a research after a fail low, each time with a wider window
1012 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1017 // Sort the moves before to return
1024 // search_pv() is the main search function for PV nodes.
1026 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1027 Depth depth, int ply, int threadID) {
1029 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1030 assert(beta > alpha && beta <= VALUE_INFINITE);
1031 assert(ply >= 0 && ply < PLY_MAX);
1032 assert(threadID >= 0 && threadID < TM.active_threads());
1034 Move movesSearched[256];
1039 Depth ext, newDepth;
1040 Value bestValue, value, oldAlpha;
1041 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1042 bool mateThreat = false;
1044 bestValue = value = -VALUE_INFINITE;
1047 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1049 // Step 1. Initialize node and poll
1050 // Polling can abort search.
1051 init_node(ss, ply, threadID);
1053 // Step 2. Check for aborted search and immediate draw
1054 if (AbortSearch || TM.thread_should_stop(threadID))
1057 if (pos.is_draw() || ply >= PLY_MAX - 1)
1060 // Step 3. Mate distance pruning
1062 alpha = Max(value_mated_in(ply), alpha);
1063 beta = Min(value_mate_in(ply+1), beta);
1067 // Step 4. Transposition table lookup
1068 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1069 // This is to avoid problems in the following areas:
1071 // * Repetition draw detection
1072 // * Fifty move rule detection
1073 // * Searching for a mate
1074 // * Printing of full PV line
1075 tte = TT.retrieve(pos.get_key());
1076 ttMove = (tte ? tte->move() : MOVE_NONE);
1078 // Step 5. Evaluate the position statically
1079 // At PV nodes we do this only to update gain statistics
1080 isCheck = pos.is_check();
1083 ss[ply].eval = evaluate(pos, ei, threadID);
1084 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1087 // Step 6. Razoring (is omitted in PV nodes)
1088 // Step 7. Static null move pruning (is omitted in PV nodes)
1089 // Step 8. Null move search with verification search (is omitted in PV nodes)
1091 // Step 9. Internal iterative deepening
1092 if ( depth >= IIDDepthAtPVNodes
1093 && ttMove == MOVE_NONE)
1095 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1096 ttMove = ss[ply].pv[ply];
1097 tte = TT.retrieve(pos.get_key());
1100 // Initialize a MovePicker object for the current position
1101 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1102 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1105 // Step 10. Loop through moves
1106 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1107 while ( alpha < beta
1108 && (move = mp.get_next_move()) != MOVE_NONE
1109 && !TM.thread_should_stop(threadID))
1111 assert(move_is_ok(move));
1113 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1114 moveIsCheck = pos.move_is_check(move, ci);
1115 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1117 // Step 11. Decide the new search depth
1118 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1120 // Singular extension search. We extend the TT move if its value is much better than
1121 // its siblings. To verify this we do a reduced search on all the other moves but the
1122 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1123 if ( depth >= SingularExtensionDepthAtPVNodes
1125 && move == tte->move()
1127 && is_lower_bound(tte->type())
1128 && tte->depth() >= depth - 3 * OnePly)
1130 Value ttValue = value_from_tt(tte->value(), ply);
1132 if (abs(ttValue) < VALUE_KNOWN_WIN)
1134 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1136 if (excValue < ttValue - SingularExtensionMargin)
1141 newDepth = depth - OnePly + ext;
1143 // Update current move (this must be done after singular extension search)
1144 movesSearched[moveCount++] = ss[ply].currentMove = move;
1146 // Step 12. Futility pruning (is omitted in PV nodes)
1148 // Step 13. Make the move
1149 pos.do_move(move, st, ci, moveIsCheck);
1151 // Step extra. pv search (only in PV nodes)
1152 // The first move in list is the expected PV
1154 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1157 // Step 14. Reduced search
1158 // if the move fails high will be re-searched at full depth.
1159 bool doFullDepthSearch = true;
1161 if ( depth >= 3 * OnePly
1163 && !captureOrPromotion
1164 && !move_is_castle(move)
1165 && !move_is_killer(move, ss[ply]))
1167 ss[ply].reduction = pv_reduction(depth, moveCount);
1168 if (ss[ply].reduction)
1170 value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1171 doFullDepthSearch = (value > alpha);
1175 // Step 15. Full depth search
1176 if (doFullDepthSearch)
1178 ss[ply].reduction = Depth(0);
1179 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1181 // Step extra. pv search (only in PV nodes)
1182 if (value > alpha && value < beta)
1183 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1187 // Step 16. Undo move
1188 pos.undo_move(move);
1190 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1192 // Step 17. Check for new best move
1193 if (value > bestValue)
1200 if (value == value_mate_in(ply + 1))
1201 ss[ply].mateKiller = move;
1205 // Step 18. Check for split
1206 if ( TM.active_threads() > 1
1208 && depth >= MinimumSplitDepth
1210 && TM.available_thread_exists(threadID)
1212 && !TM.thread_should_stop(threadID)
1213 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1214 depth, mateThreat, &moveCount, &mp, threadID, true))
1218 // Step 19. Check for mate and stalemate
1219 // All legal moves have been searched and if there were
1220 // no legal moves, it must be mate or stalemate.
1222 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1224 // Step 20. Update tables
1225 // If the search is not aborted, update the transposition table,
1226 // history counters, and killer moves.
1227 if (AbortSearch || TM.thread_should_stop(threadID))
1230 if (bestValue <= oldAlpha)
1231 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1233 else if (bestValue >= beta)
1235 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1236 move = ss[ply].pv[ply];
1237 if (!pos.move_is_capture_or_promotion(move))
1239 update_history(pos, move, depth, movesSearched, moveCount);
1240 update_killers(move, ss[ply]);
1242 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1245 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1251 // search() is the search function for zero-width nodes.
1253 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1254 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1256 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1257 assert(ply >= 0 && ply < PLY_MAX);
1258 assert(threadID >= 0 && threadID < TM.active_threads());
1260 Move movesSearched[256];
1265 Depth ext, newDepth;
1266 Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
1267 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1268 bool mateThreat = false;
1270 refinedValue = bestValue = value = -VALUE_INFINITE;
1273 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1275 // Step 1. Initialize node and poll
1276 // Polling can abort search.
1277 init_node(ss, ply, threadID);
1279 // Step 2. Check for aborted search and immediate draw
1280 if (AbortSearch || TM.thread_should_stop(threadID))
1283 if (pos.is_draw() || ply >= PLY_MAX - 1)
1286 // Step 3. Mate distance pruning
1287 if (value_mated_in(ply) >= beta)
1290 if (value_mate_in(ply + 1) < beta)
1293 // Step 4. Transposition table lookup
1295 // We don't want the score of a partial search to overwrite a previous full search
1296 // TT value, so we use a different position key in case of an excluded move exists.
1297 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1299 tte = TT.retrieve(posKey);
1300 ttMove = (tte ? tte->move() : MOVE_NONE);
1302 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1304 // Refresh tte entry to avoid aging
1305 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove);
1307 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1308 return value_from_tt(tte->value(), ply);
1311 // Step 5. Evaluate the position statically
1312 isCheck = pos.is_check();
1316 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1317 ss[ply].eval = value_from_tt(tte->value(), ply);
1319 ss[ply].eval = evaluate(pos, ei, threadID);
1321 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1322 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1326 if ( refinedValue < beta - razor_margin(depth)
1327 && ttMove == MOVE_NONE
1328 && ss[ply - 1].currentMove != MOVE_NULL
1329 && depth < RazorDepth
1331 && !value_is_mate(beta)
1332 && !pos.has_pawn_on_7th(pos.side_to_move()))
1334 Value rbeta = beta - razor_margin(depth);
1335 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1337 // Logically we should return (v + razor_margin(depth)), but
1338 // surprisingly this did slightly weaker in tests.
1342 // Step 7. Static null move pruning
1343 // We're betting that the opponent doesn't have a move that will reduce
1344 // the score by more than futility_margin(depth) if we do a null move.
1346 && depth < RazorDepth
1348 && !value_is_mate(beta)
1349 && ok_to_do_nullmove(pos)
1350 && refinedValue >= beta + futility_margin(depth, 0))
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 // Null move dynamic reduction based on depth
1367 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1369 // Null move dynamic reduction based on value
1370 if (refinedValue - beta > PawnValueMidgame)
1373 pos.do_null_move(st);
1375 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1377 pos.undo_null_move();
1379 if (nullValue >= beta)
1381 // Do not return unproven mate scores
1382 if (nullValue >= value_mate_in(PLY_MAX))
1385 if (depth < 6 * OnePly)
1388 // Do zugzwang verification search
1389 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1393 // The null move failed low, which means that we may be faced with
1394 // some kind of threat. If the previous move was reduced, check if
1395 // the move that refuted the null move was somehow connected to the
1396 // move which was reduced. If a connection is found, return a fail
1397 // low score (which will cause the reduced move to fail high in the
1398 // parent node, which will trigger a re-search with full depth).
1399 if (nullValue == value_mated_in(ply + 2))
1402 ss[ply].threatMove = ss[ply + 1].currentMove;
1403 if ( depth < ThreatDepth
1404 && ss[ply - 1].reduction
1405 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1410 // Step 9. Internal iterative deepening
1411 if ( depth >= IIDDepthAtNonPVNodes
1412 && ttMove == MOVE_NONE
1414 && ss[ply].eval >= beta - IIDMargin)
1416 search(pos, ss, beta, depth/2, ply, false, threadID);
1417 ttMove = ss[ply].pv[ply];
1418 tte = TT.retrieve(posKey);
1421 // Initialize a MovePicker object for the current position
1422 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
1425 // Step 10. Loop through moves
1426 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1427 while ( bestValue < beta
1428 && (move = mp.get_next_move()) != MOVE_NONE
1429 && !TM.thread_should_stop(threadID))
1431 assert(move_is_ok(move));
1433 if (move == excludedMove)
1436 moveIsCheck = pos.move_is_check(move, ci);
1437 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1438 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1440 // Step 11. Decide the new search depth
1441 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1443 // Singular extension search. We extend the TT move if its value is much better than
1444 // its siblings. To verify this we do a reduced search on all the other moves but the
1445 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1446 if ( depth >= SingularExtensionDepthAtNonPVNodes
1448 && move == tte->move()
1449 && !excludedMove // Do not allow recursive singular extension search
1451 && is_lower_bound(tte->type())
1452 && tte->depth() >= depth - 3 * OnePly)
1454 Value ttValue = value_from_tt(tte->value(), ply);
1456 if (abs(ttValue) < VALUE_KNOWN_WIN)
1458 Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1460 if (excValue < ttValue - SingularExtensionMargin)
1465 newDepth = depth - OnePly + ext;
1467 // Update current move (this must be done after singular extension search)
1468 movesSearched[moveCount++] = ss[ply].currentMove = move;
1470 // Step 12. Futility pruning
1473 && !captureOrPromotion
1474 && !move_is_castle(move)
1477 // Move count based pruning
1478 if ( moveCount >= futility_move_count(depth)
1479 && ok_to_prune(pos, move, ss[ply].threatMove)
1480 && bestValue > value_mated_in(PLY_MAX))
1483 // Value based pruning
1484 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1485 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1486 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1488 if (futilityValueScaled < beta)
1490 if (futilityValueScaled > bestValue)
1491 bestValue = futilityValueScaled;
1496 // Step 13. Make the move
1497 pos.do_move(move, st, ci, moveIsCheck);
1499 // Step 14. Reduced search, if the move fails high
1500 // will be re-searched at full depth.
1501 bool doFullDepthSearch = true;
1503 if ( depth >= 3*OnePly
1505 && !captureOrPromotion
1506 && !move_is_castle(move)
1507 && !move_is_killer(move, ss[ply]))
1509 ss[ply].reduction = nonpv_reduction(depth, moveCount);
1510 if (ss[ply].reduction)
1512 value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
1513 doFullDepthSearch = (value >= beta);
1517 // Step 15. Full depth search
1518 if (doFullDepthSearch)
1520 ss[ply].reduction = Depth(0);
1521 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1524 // Step 16. Undo move
1525 pos.undo_move(move);
1527 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1529 // Step 17. Check for new best move
1530 if (value > bestValue)
1536 if (value == value_mate_in(ply + 1))
1537 ss[ply].mateKiller = move;
1540 // Step 18. Check for split
1541 if ( TM.active_threads() > 1
1543 && depth >= MinimumSplitDepth
1545 && TM.available_thread_exists(threadID)
1547 && !TM.thread_should_stop(threadID)
1548 && TM.split(pos, ss, ply, NULL, beta, &bestValue,
1549 depth, mateThreat, &moveCount, &mp, threadID, false))
1553 // Step 19. Check for mate and stalemate
1554 // All legal moves have been searched and if there are
1555 // no legal moves, it must be mate or stalemate.
1556 // If one move was excluded return fail low score.
1558 return excludedMove ? beta - 1 : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1560 // Step 20. Update tables
1561 // If the search is not aborted, update the transposition table,
1562 // history counters, and killer moves.
1563 if (AbortSearch || TM.thread_should_stop(threadID))
1566 if (bestValue < beta)
1567 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1570 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1571 move = ss[ply].pv[ply];
1572 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1573 if (!pos.move_is_capture_or_promotion(move))
1575 update_history(pos, move, depth, movesSearched, moveCount);
1576 update_killers(move, ss[ply]);
1581 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1587 // qsearch() is the quiescence search function, which is called by the main
1588 // search function when the remaining depth is zero (or, to be more precise,
1589 // less than OnePly).
1591 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1592 Depth depth, int ply, int threadID) {
1594 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1595 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1597 assert(ply >= 0 && ply < PLY_MAX);
1598 assert(threadID >= 0 && threadID < TM.active_threads());
1603 Value staticValue, bestValue, value, futilityBase, futilityValue;
1604 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1605 const TTEntry* tte = NULL;
1607 bool pvNode = (beta - alpha != 1);
1608 Value oldAlpha = alpha;
1610 // Initialize, and make an early exit in case of an aborted search,
1611 // an instant draw, maximum ply reached, etc.
1612 init_node(ss, ply, threadID);
1614 // After init_node() that calls poll()
1615 if (AbortSearch || TM.thread_should_stop(threadID))
1618 if (pos.is_draw() || ply >= PLY_MAX - 1)
1621 // Transposition table lookup. At PV nodes, we don't use the TT for
1622 // pruning, but only for move ordering.
1623 tte = TT.retrieve(pos.get_key());
1624 ttMove = (tte ? tte->move() : MOVE_NONE);
1626 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1628 assert(tte->type() != VALUE_TYPE_EVAL);
1630 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1631 return value_from_tt(tte->value(), ply);
1634 isCheck = pos.is_check();
1636 // Evaluate the position statically
1638 staticValue = -VALUE_INFINITE;
1639 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1640 staticValue = value_from_tt(tte->value(), ply);
1642 staticValue = evaluate(pos, ei, threadID);
1646 ss[ply].eval = staticValue;
1647 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1650 // Initialize "stand pat score", and return it immediately if it is
1652 bestValue = staticValue;
1654 if (bestValue >= beta)
1656 // Store the score to avoid a future costly evaluation() call
1657 if (!isCheck && !tte && ei.futilityMargin[pos.side_to_move()] == 0)
1658 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1663 if (bestValue > alpha)
1666 // If we are near beta then try to get a cutoff pushing checks a bit further
1667 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1669 // Initialize a MovePicker object for the current position, and prepare
1670 // to search the moves. Because the depth is <= 0 here, only captures,
1671 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1672 // and we are near beta) will be generated.
1673 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1675 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1676 futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin[pos.side_to_move()];
1678 // Loop through the moves until no moves remain or a beta cutoff occurs
1679 while ( alpha < beta
1680 && (move = mp.get_next_move()) != MOVE_NONE)
1682 assert(move_is_ok(move));
1684 moveIsCheck = pos.move_is_check(move, ci);
1686 // Update current move
1688 ss[ply].currentMove = move;
1696 && !move_is_promotion(move)
1697 && !pos.move_is_passed_pawn_push(move))
1699 futilityValue = futilityBase
1700 + pos.endgame_value_of_piece_on(move_to(move))
1701 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1703 if (futilityValue < alpha)
1705 if (futilityValue > bestValue)
1706 bestValue = futilityValue;
1711 // Detect blocking evasions that are candidate to be pruned
1712 evasionPrunable = isCheck
1713 && bestValue > value_mated_in(PLY_MAX)
1714 && !pos.move_is_capture(move)
1715 && pos.type_of_piece_on(move_from(move)) != KING
1716 && !pos.can_castle(pos.side_to_move());
1718 // Don't search moves with negative SEE values
1719 if ( (!isCheck || evasionPrunable)
1722 && !move_is_promotion(move)
1723 && pos.see_sign(move) < 0)
1726 // Make and search the move
1727 pos.do_move(move, st, ci, moveIsCheck);
1728 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1729 pos.undo_move(move);
1731 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1734 if (value > bestValue)
1745 // All legal moves have been searched. A special case: If we're in check
1746 // and no legal moves were found, it is checkmate.
1747 if (!moveCount && isCheck) // Mate!
1748 return value_mated_in(ply);
1750 // Update transposition table
1751 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1752 if (bestValue <= oldAlpha)
1754 // If bestValue isn't changed it means it is still the static evaluation
1755 // of the node, so keep this info to avoid a future evaluation() call.
1756 ValueType type = (bestValue == staticValue && !ei.futilityMargin[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1757 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1759 else if (bestValue >= beta)
1761 move = ss[ply].pv[ply];
1762 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1764 // Update killers only for good checking moves
1765 if (!pos.move_is_capture_or_promotion(move))
1766 update_killers(move, ss[ply]);
1769 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1771 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1777 // sp_search() is used to search from a split point. This function is called
1778 // by each thread working at the split point. It is similar to the normal
1779 // search() function, but simpler. Because we have already probed the hash
1780 // table, done a null move search, and searched the first move before
1781 // splitting, we don't have to repeat all this work in sp_search(). We
1782 // also don't need to store anything to the hash table here: This is taken
1783 // care of after we return from the split point.
1785 void sp_search(SplitPoint* sp, int threadID) {
1787 assert(threadID >= 0 && threadID < TM.active_threads());
1788 assert(TM.active_threads() > 1);
1792 Depth ext, newDepth;
1793 Value value, futilityValueScaled;
1794 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1796 value = -VALUE_INFINITE;
1798 Position pos(*sp->pos);
1800 SearchStack* ss = sp->sstack[threadID];
1801 isCheck = pos.is_check();
1803 // Step 10. Loop through moves
1804 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1805 lock_grab(&(sp->lock));
1807 while ( sp->bestValue < sp->beta
1808 && !TM.thread_should_stop(threadID)
1809 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1811 moveCount = ++sp->moves;
1812 lock_release(&(sp->lock));
1814 assert(move_is_ok(move));
1816 moveIsCheck = pos.move_is_check(move, ci);
1817 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1819 // Step 11. Decide the new search depth
1820 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1821 newDepth = sp->depth - OnePly + ext;
1823 // Update current move
1824 ss[sp->ply].currentMove = move;
1826 // Step 12. Futility pruning
1829 && !captureOrPromotion
1830 && !move_is_castle(move))
1832 // Move count based pruning
1833 if ( moveCount >= futility_move_count(sp->depth)
1834 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1835 && sp->bestValue > value_mated_in(PLY_MAX))
1837 lock_grab(&(sp->lock));
1841 // Value based pruning
1842 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1843 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1844 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1846 if (futilityValueScaled < sp->beta)
1848 lock_grab(&(sp->lock));
1850 if (futilityValueScaled > sp->bestValue)
1851 sp->bestValue = futilityValueScaled;
1856 // Step 13. Make the move
1857 pos.do_move(move, st, ci, moveIsCheck);
1859 // Step 14. Reduced search
1860 // if the move fails high will be re-searched at full depth.
1861 bool doFullDepthSearch = true;
1864 && !captureOrPromotion
1865 && !move_is_castle(move)
1866 && !move_is_killer(move, ss[sp->ply]))
1868 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1869 if (ss[sp->ply].reduction)
1871 value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1872 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1876 // Step 15. Full depth search
1877 if (doFullDepthSearch)
1879 ss[sp->ply].reduction = Depth(0);
1880 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1883 // Step 16. Undo move
1884 pos.undo_move(move);
1886 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1888 // Step 17. Check for new best move
1889 lock_grab(&(sp->lock));
1891 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1893 sp->bestValue = value;
1894 if (sp->bestValue >= sp->beta)
1896 sp->stopRequest = true;
1897 sp_update_pv(sp->parentSstack, ss, sp->ply);
1902 /* Here we have the lock still grabbed */
1904 sp->slaves[threadID] = 0;
1907 lock_release(&(sp->lock));
1911 // sp_search_pv() is used to search from a PV split point. This function
1912 // is called by each thread working at the split point. It is similar to
1913 // the normal search_pv() function, but simpler. Because we have already
1914 // probed the hash table and searched the first move before splitting, we
1915 // don't have to repeat all this work in sp_search_pv(). We also don't
1916 // need to store anything to the hash table here: This is taken care of
1917 // after we return from the split point.
1919 void sp_search_pv(SplitPoint* sp, int threadID) {
1921 assert(threadID >= 0 && threadID < TM.active_threads());
1922 assert(TM.active_threads() > 1);
1926 Depth ext, newDepth;
1928 bool moveIsCheck, captureOrPromotion, dangerous;
1930 value = -VALUE_INFINITE;
1932 Position pos(*sp->pos);
1934 SearchStack* ss = sp->sstack[threadID];
1936 // Step 10. Loop through moves
1937 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1938 lock_grab(&(sp->lock));
1940 while ( sp->alpha < sp->beta
1941 && !TM.thread_should_stop(threadID)
1942 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1944 moveCount = ++sp->moves;
1945 lock_release(&(sp->lock));
1947 assert(move_is_ok(move));
1949 moveIsCheck = pos.move_is_check(move, ci);
1950 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1952 // Step 11. Decide the new search depth
1953 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1954 newDepth = sp->depth - OnePly + ext;
1956 // Update current move
1957 ss[sp->ply].currentMove = move;
1959 // Step 12. Futility pruning (is omitted in PV nodes)
1961 // Step 13. Make the move
1962 pos.do_move(move, st, ci, moveIsCheck);
1964 // Step 14. Reduced search
1965 // if the move fails high will be re-searched at full depth.
1966 bool doFullDepthSearch = true;
1969 && !captureOrPromotion
1970 && !move_is_castle(move)
1971 && !move_is_killer(move, ss[sp->ply]))
1973 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1974 if (ss[sp->ply].reduction)
1976 Value localAlpha = sp->alpha;
1977 value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1978 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1982 // Step 15. Full depth search
1983 if (doFullDepthSearch)
1985 Value localAlpha = sp->alpha;
1986 ss[sp->ply].reduction = Depth(0);
1987 value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID);
1989 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1991 // If another thread has failed high then sp->alpha has been increased
1992 // to be higher or equal then beta, if so, avoid to start a PV search.
1993 localAlpha = sp->alpha;
1994 if (localAlpha < sp->beta)
1995 value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
1999 // Step 16. Undo move
2000 pos.undo_move(move);
2002 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
2004 // Step 17. Check for new best move
2005 lock_grab(&(sp->lock));
2007 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
2009 sp->bestValue = value;
2010 if (value > sp->alpha)
2012 // Ask threads to stop before to modify sp->alpha
2013 if (value >= sp->beta)
2014 sp->stopRequest = true;
2018 sp_update_pv(sp->parentSstack, ss, sp->ply);
2019 if (value == value_mate_in(sp->ply + 1))
2020 ss[sp->ply].mateKiller = move;
2025 /* Here we have the lock still grabbed */
2027 sp->slaves[threadID] = 0;
2030 lock_release(&(sp->lock));
2034 // init_node() is called at the beginning of all the search functions
2035 // (search(), search_pv(), qsearch(), and so on) and initializes the
2036 // search stack object corresponding to the current node. Once every
2037 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2038 // for user input and checks whether it is time to stop the search.
2040 void init_node(SearchStack ss[], int ply, int threadID) {
2042 assert(ply >= 0 && ply < PLY_MAX);
2043 assert(threadID >= 0 && threadID < TM.active_threads());
2045 TM.incrementNodeCounter(threadID);
2050 if (NodesSincePoll >= NodesBetweenPolls)
2057 ss[ply + 2].initKillers();
2061 // update_pv() is called whenever a search returns a value > alpha.
2062 // It updates the PV in the SearchStack object corresponding to the
2065 void update_pv(SearchStack ss[], int ply) {
2067 assert(ply >= 0 && ply < PLY_MAX);
2071 ss[ply].pv[ply] = ss[ply].currentMove;
2073 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2074 ss[ply].pv[p] = ss[ply + 1].pv[p];
2076 ss[ply].pv[p] = MOVE_NONE;
2080 // sp_update_pv() is a variant of update_pv for use at split points. The
2081 // difference between the two functions is that sp_update_pv also updates
2082 // the PV at the parent node.
2084 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2086 assert(ply >= 0 && ply < PLY_MAX);
2090 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2092 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
2093 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
2095 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2099 // connected_moves() tests whether two moves are 'connected' in the sense
2100 // that the first move somehow made the second move possible (for instance
2101 // if the moving piece is the same in both moves). The first move is assumed
2102 // to be the move that was made to reach the current position, while the
2103 // second move is assumed to be a move from the current position.
2105 bool connected_moves(const Position& pos, Move m1, Move m2) {
2107 Square f1, t1, f2, t2;
2110 assert(move_is_ok(m1));
2111 assert(move_is_ok(m2));
2113 if (m2 == MOVE_NONE)
2116 // Case 1: The moving piece is the same in both moves
2122 // Case 2: The destination square for m2 was vacated by m1
2128 // Case 3: Moving through the vacated square
2129 if ( piece_is_slider(pos.piece_on(f2))
2130 && bit_is_set(squares_between(f2, t2), f1))
2133 // Case 4: The destination square for m2 is defended by the moving piece in m1
2134 p = pos.piece_on(t1);
2135 if (bit_is_set(pos.attacks_from(p, t1), t2))
2138 // Case 5: Discovered check, checking piece is the piece moved in m1
2139 if ( piece_is_slider(p)
2140 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2141 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2143 // discovered_check_candidates() works also if the Position's side to
2144 // move is the opposite of the checking piece.
2145 Color them = opposite_color(pos.side_to_move());
2146 Bitboard dcCandidates = pos.discovered_check_candidates(them);
2148 if (bit_is_set(dcCandidates, f2))
2155 // value_is_mate() checks if the given value is a mate one
2156 // eventually compensated for the ply.
2158 bool value_is_mate(Value value) {
2160 assert(abs(value) <= VALUE_INFINITE);
2162 return value <= value_mated_in(PLY_MAX)
2163 || value >= value_mate_in(PLY_MAX);
2167 // move_is_killer() checks if the given move is among the
2168 // killer moves of that ply.
2170 bool move_is_killer(Move m, const SearchStack& ss) {
2172 const Move* k = ss.killers;
2173 for (int i = 0; i < KILLER_MAX; i++, k++)
2181 // extension() decides whether a move should be searched with normal depth,
2182 // or with extended depth. Certain classes of moves (checking moves, in
2183 // particular) are searched with bigger depth than ordinary moves and in
2184 // any case are marked as 'dangerous'. Note that also if a move is not
2185 // extended, as example because the corresponding UCI option is set to zero,
2186 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2188 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2189 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2191 assert(m != MOVE_NONE);
2193 Depth result = Depth(0);
2194 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2199 result += CheckExtension[pvNode];
2202 result += SingleEvasionExtension[pvNode];
2205 result += MateThreatExtension[pvNode];
2208 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2210 Color c = pos.side_to_move();
2211 if (relative_rank(c, move_to(m)) == RANK_7)
2213 result += PawnPushTo7thExtension[pvNode];
2216 if (pos.pawn_is_passed(c, move_to(m)))
2218 result += PassedPawnExtension[pvNode];
2223 if ( captureOrPromotion
2224 && pos.type_of_piece_on(move_to(m)) != PAWN
2225 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2226 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2227 && !move_is_promotion(m)
2230 result += PawnEndgameExtension[pvNode];
2235 && captureOrPromotion
2236 && pos.type_of_piece_on(move_to(m)) != PAWN
2237 && pos.see_sign(m) >= 0)
2243 return Min(result, OnePly);
2247 // ok_to_do_nullmove() looks at the current position and decides whether
2248 // doing a 'null move' should be allowed. In order to avoid zugzwang
2249 // problems, null moves are not allowed when the side to move has very
2250 // little material left. Currently, the test is a bit too simple: Null
2251 // moves are avoided only when the side to move has only pawns left.
2252 // It's probably a good idea to avoid null moves in at least some more
2253 // complicated endgames, e.g. KQ vs KR. FIXME
2255 bool ok_to_do_nullmove(const Position& pos) {
2257 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2261 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2262 // non-tactical moves late in the move list close to the leaves are
2263 // candidates for pruning.
2265 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2267 assert(move_is_ok(m));
2268 assert(threat == MOVE_NONE || move_is_ok(threat));
2269 assert(!pos.move_is_check(m));
2270 assert(!pos.move_is_capture_or_promotion(m));
2271 assert(!pos.move_is_passed_pawn_push(m));
2273 Square mfrom, mto, tfrom, tto;
2275 // Prune if there isn't any threat move
2276 if (threat == MOVE_NONE)
2279 mfrom = move_from(m);
2281 tfrom = move_from(threat);
2282 tto = move_to(threat);
2284 // Case 1: Don't prune moves which move the threatened piece
2288 // Case 2: If the threatened piece has value less than or equal to the
2289 // value of the threatening piece, don't prune move which defend it.
2290 if ( pos.move_is_capture(threat)
2291 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2292 || pos.type_of_piece_on(tfrom) == KING)
2293 && pos.move_attacks_square(m, tto))
2296 // Case 3: If the moving piece in the threatened move is a slider, don't
2297 // prune safe moves which block its ray.
2298 if ( piece_is_slider(pos.piece_on(tfrom))
2299 && bit_is_set(squares_between(tfrom, tto), mto)
2300 && pos.see_sign(m) >= 0)
2307 // ok_to_use_TT() returns true if a transposition table score
2308 // can be used at a given point in search.
2310 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2312 Value v = value_from_tt(tte->value(), ply);
2314 return ( tte->depth() >= depth
2315 || v >= Max(value_mate_in(PLY_MAX), beta)
2316 || v < Min(value_mated_in(PLY_MAX), beta))
2318 && ( (is_lower_bound(tte->type()) && v >= beta)
2319 || (is_upper_bound(tte->type()) && v < beta));
2323 // refine_eval() returns the transposition table score if
2324 // possible otherwise falls back on static position evaluation.
2326 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2331 Value v = value_from_tt(tte->value(), ply);
2333 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2334 || (is_upper_bound(tte->type()) && v < defaultEval))
2341 // update_history() registers a good move that produced a beta-cutoff
2342 // in history and marks as failures all the other moves of that ply.
2344 void update_history(const Position& pos, Move move, Depth depth,
2345 Move movesSearched[], int moveCount) {
2349 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2351 for (int i = 0; i < moveCount - 1; i++)
2353 m = movesSearched[i];
2357 if (!pos.move_is_capture_or_promotion(m))
2358 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2363 // update_killers() add a good move that produced a beta-cutoff
2364 // among the killer moves of that ply.
2366 void update_killers(Move m, SearchStack& ss) {
2368 if (m == ss.killers[0])
2371 for (int i = KILLER_MAX - 1; i > 0; i--)
2372 ss.killers[i] = ss.killers[i - 1];
2378 // update_gains() updates the gains table of a non-capture move given
2379 // the static position evaluation before and after the move.
2381 void update_gains(const Position& pos, Move m, Value before, Value after) {
2384 && before != VALUE_NONE
2385 && after != VALUE_NONE
2386 && pos.captured_piece() == NO_PIECE_TYPE
2387 && !move_is_castle(m)
2388 && !move_is_promotion(m))
2389 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2393 // current_search_time() returns the number of milliseconds which have passed
2394 // since the beginning of the current search.
2396 int current_search_time() {
2398 return get_system_time() - SearchStartTime;
2402 // nps() computes the current nodes/second count.
2406 int t = current_search_time();
2407 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2411 // poll() performs two different functions: It polls for user input, and it
2412 // looks at the time consumed so far and decides if it's time to abort the
2417 static int lastInfoTime;
2418 int t = current_search_time();
2423 // We are line oriented, don't read single chars
2424 std::string command;
2426 if (!std::getline(std::cin, command))
2429 if (command == "quit")
2432 PonderSearch = false;
2436 else if (command == "stop")
2439 PonderSearch = false;
2441 else if (command == "ponderhit")
2445 // Print search information
2449 else if (lastInfoTime > t)
2450 // HACK: Must be a new search where we searched less than
2451 // NodesBetweenPolls nodes during the first second of search.
2454 else if (t - lastInfoTime >= 1000)
2461 if (dbg_show_hit_rate)
2462 dbg_print_hit_rate();
2464 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2465 << " time " << t << " hashfull " << TT.full() << endl;
2468 // Should we stop the search?
2472 bool stillAtFirstMove = FirstRootMove
2473 && !AspirationFailLow
2474 && t > MaxSearchTime + ExtraSearchTime;
2476 bool noMoreTime = t > AbsoluteMaxSearchTime
2477 || stillAtFirstMove;
2479 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2480 || (ExactMaxTime && t >= ExactMaxTime)
2481 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2486 // ponderhit() is called when the program is pondering (i.e. thinking while
2487 // it's the opponent's turn to move) in order to let the engine know that
2488 // it correctly predicted the opponent's move.
2492 int t = current_search_time();
2493 PonderSearch = false;
2495 bool stillAtFirstMove = FirstRootMove
2496 && !AspirationFailLow
2497 && t > MaxSearchTime + ExtraSearchTime;
2499 bool noMoreTime = t > AbsoluteMaxSearchTime
2500 || stillAtFirstMove;
2502 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2507 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2509 void init_ss_array(SearchStack ss[]) {
2511 for (int i = 0; i < 3; i++)
2514 ss[i].initKillers();
2519 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2520 // while the program is pondering. The point is to work around a wrinkle in
2521 // the UCI protocol: When pondering, the engine is not allowed to give a
2522 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2523 // We simply wait here until one of these commands is sent, and return,
2524 // after which the bestmove and pondermove will be printed (in id_loop()).
2526 void wait_for_stop_or_ponderhit() {
2528 std::string command;
2532 if (!std::getline(std::cin, command))
2535 if (command == "quit")
2540 else if (command == "ponderhit" || command == "stop")
2546 // print_pv_info() prints to standard output and eventually to log file information on
2547 // the current PV line. It is called at each iteration or after a new pv is found.
2549 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2551 cout << "info depth " << Iteration
2552 << " score " << value_to_string(value)
2553 << ((value >= beta) ? " lowerbound" :
2554 ((value <= alpha)? " upperbound" : ""))
2555 << " time " << current_search_time()
2556 << " nodes " << TM.nodes_searched()
2560 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2561 cout << ss[0].pv[j] << " ";
2567 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2568 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2570 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2571 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2576 // init_thread() is the function which is called when a new thread is
2577 // launched. It simply calls the idle_loop() function with the supplied
2578 // threadID. There are two versions of this function; one for POSIX
2579 // threads and one for Windows threads.
2581 #if !defined(_MSC_VER)
2583 void* init_thread(void *threadID) {
2585 TM.idle_loop(*(int*)threadID, NULL);
2591 DWORD WINAPI init_thread(LPVOID threadID) {
2593 TM.idle_loop(*(int*)threadID, NULL);
2600 /// The ThreadsManager class
2602 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2603 // get_beta_counters() are getters/setters for the per thread
2604 // counters used to sort the moves at root.
2606 void ThreadsManager::resetNodeCounters() {
2608 for (int i = 0; i < MAX_THREADS; i++)
2609 threads[i].nodes = 0ULL;
2612 void ThreadsManager::resetBetaCounters() {
2614 for (int i = 0; i < MAX_THREADS; i++)
2615 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2618 int64_t ThreadsManager::nodes_searched() const {
2620 int64_t result = 0ULL;
2621 for (int i = 0; i < ActiveThreads; i++)
2622 result += threads[i].nodes;
2627 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2630 for (int i = 0; i < MAX_THREADS; i++)
2632 our += threads[i].betaCutOffs[us];
2633 their += threads[i].betaCutOffs[opposite_color(us)];
2638 // idle_loop() is where the threads are parked when they have no work to do.
2639 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2640 // object for which the current thread is the master.
2642 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2644 assert(threadID >= 0 && threadID < MAX_THREADS);
2648 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2649 // master should exit as last one.
2650 if (AllThreadsShouldExit)
2653 threads[threadID].state = THREAD_TERMINATED;
2657 // If we are not thinking, wait for a condition to be signaled
2658 // instead of wasting CPU time polling for work.
2659 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2662 assert(threadID != 0);
2663 threads[threadID].state = THREAD_SLEEPING;
2665 #if !defined(_MSC_VER)
2666 lock_grab(&WaitLock);
2667 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2668 pthread_cond_wait(&WaitCond, &WaitLock);
2669 lock_release(&WaitLock);
2671 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2675 // If thread has just woken up, mark it as available
2676 if (threads[threadID].state == THREAD_SLEEPING)
2677 threads[threadID].state = THREAD_AVAILABLE;
2679 // If this thread has been assigned work, launch a search
2680 if (threads[threadID].state == THREAD_WORKISWAITING)
2682 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2684 threads[threadID].state = THREAD_SEARCHING;
2686 if (threads[threadID].splitPoint->pvNode)
2687 sp_search_pv(threads[threadID].splitPoint, threadID);
2689 sp_search(threads[threadID].splitPoint, threadID);
2691 assert(threads[threadID].state == THREAD_SEARCHING);
2693 threads[threadID].state = THREAD_AVAILABLE;
2696 // If this thread is the master of a split point and all threads have
2697 // finished their work at this split point, return from the idle loop.
2698 if (sp && sp->cpus == 0)
2700 // Because sp->cpus is decremented under lock protection,
2701 // be sure sp->lock has been released before to proceed.
2702 lock_grab(&(sp->lock));
2703 lock_release(&(sp->lock));
2705 assert(threads[threadID].state == THREAD_AVAILABLE);
2707 threads[threadID].state = THREAD_SEARCHING;
2714 // init_threads() is called during startup. It launches all helper threads,
2715 // and initializes the split point stack and the global locks and condition
2718 void ThreadsManager::init_threads() {
2723 #if !defined(_MSC_VER)
2724 pthread_t pthread[1];
2727 // Initialize global locks
2728 lock_init(&MPLock, NULL);
2729 lock_init(&WaitLock, NULL);
2731 #if !defined(_MSC_VER)
2732 pthread_cond_init(&WaitCond, NULL);
2734 for (i = 0; i < MAX_THREADS; i++)
2735 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2738 // Initialize SplitPointStack locks
2739 for (i = 0; i < MAX_THREADS; i++)
2740 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2742 SplitPointStack[i][j].parent = NULL;
2743 lock_init(&(SplitPointStack[i][j].lock), NULL);
2746 // Will be set just before program exits to properly end the threads
2747 AllThreadsShouldExit = false;
2749 // Threads will be put to sleep as soon as created
2750 AllThreadsShouldSleep = true;
2752 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2754 threads[0].state = THREAD_SEARCHING;
2755 for (i = 1; i < MAX_THREADS; i++)
2756 threads[i].state = THREAD_AVAILABLE;
2758 // Launch the helper threads
2759 for (i = 1; i < MAX_THREADS; i++)
2762 #if !defined(_MSC_VER)
2763 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2765 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2770 cout << "Failed to create thread number " << i << endl;
2771 Application::exit_with_failure();
2774 // Wait until the thread has finished launching and is gone to sleep
2775 while (threads[i].state != THREAD_SLEEPING) {}
2780 // exit_threads() is called when the program exits. It makes all the
2781 // helper threads exit cleanly.
2783 void ThreadsManager::exit_threads() {
2785 ActiveThreads = MAX_THREADS; // HACK
2786 AllThreadsShouldSleep = true; // HACK
2787 wake_sleeping_threads();
2789 // This makes the threads to exit idle_loop()
2790 AllThreadsShouldExit = true;
2792 // Wait for thread termination
2793 for (int i = 1; i < MAX_THREADS; i++)
2794 while (threads[i].state != THREAD_TERMINATED);
2796 // Now we can safely destroy the locks
2797 for (int i = 0; i < MAX_THREADS; i++)
2798 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2799 lock_destroy(&(SplitPointStack[i][j].lock));
2801 lock_destroy(&WaitLock);
2802 lock_destroy(&MPLock);
2806 // thread_should_stop() checks whether the thread should stop its search.
2807 // This can happen if a beta cutoff has occurred in the thread's currently
2808 // active split point, or in some ancestor of the current split point.
2810 bool ThreadsManager::thread_should_stop(int threadID) const {
2812 assert(threadID >= 0 && threadID < ActiveThreads);
2816 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2821 // thread_is_available() checks whether the thread with threadID "slave" is
2822 // available to help the thread with threadID "master" at a split point. An
2823 // obvious requirement is that "slave" must be idle. With more than two
2824 // threads, this is not by itself sufficient: If "slave" is the master of
2825 // some active split point, it is only available as a slave to the other
2826 // threads which are busy searching the split point at the top of "slave"'s
2827 // split point stack (the "helpful master concept" in YBWC terminology).
2829 bool ThreadsManager::thread_is_available(int slave, int master) const {
2831 assert(slave >= 0 && slave < ActiveThreads);
2832 assert(master >= 0 && master < ActiveThreads);
2833 assert(ActiveThreads > 1);
2835 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2838 // Make a local copy to be sure doesn't change under our feet
2839 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2841 if (localActiveSplitPoints == 0)
2842 // No active split points means that the thread is available as
2843 // a slave for any other thread.
2846 if (ActiveThreads == 2)
2849 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2850 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2851 // could have been set to 0 by another thread leading to an out of bound access.
2852 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2859 // available_thread_exists() tries to find an idle thread which is available as
2860 // a slave for the thread with threadID "master".
2862 bool ThreadsManager::available_thread_exists(int master) const {
2864 assert(master >= 0 && master < ActiveThreads);
2865 assert(ActiveThreads > 1);
2867 for (int i = 0; i < ActiveThreads; i++)
2868 if (thread_is_available(i, master))
2875 // split() does the actual work of distributing the work at a node between
2876 // several threads at PV nodes. If it does not succeed in splitting the
2877 // node (because no idle threads are available, or because we have no unused
2878 // split point objects), the function immediately returns false. If
2879 // splitting is possible, a SplitPoint object is initialized with all the
2880 // data that must be copied to the helper threads (the current position and
2881 // search stack, alpha, beta, the search depth, etc.), and we tell our
2882 // helper threads that they have been assigned work. This will cause them
2883 // to instantly leave their idle loops and call sp_search_pv(). When all
2884 // threads have returned from sp_search_pv (or, equivalently, when
2885 // splitPoint->cpus becomes 0), split() returns true.
2887 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2888 Value* alpha, const Value beta, Value* bestValue,
2889 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2892 assert(sstck != NULL);
2893 assert(ply >= 0 && ply < PLY_MAX);
2894 assert(*bestValue >= -VALUE_INFINITE);
2895 assert( ( pvNode && *bestValue <= *alpha)
2896 || (!pvNode && *bestValue < beta ));
2897 assert(!pvNode || *alpha < beta);
2898 assert(beta <= VALUE_INFINITE);
2899 assert(depth > Depth(0));
2900 assert(master >= 0 && master < ActiveThreads);
2901 assert(ActiveThreads > 1);
2903 SplitPoint* splitPoint;
2907 // If no other thread is available to help us, or if we have too many
2908 // active split points, don't split.
2909 if ( !available_thread_exists(master)
2910 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2912 lock_release(&MPLock);
2916 // Pick the next available split point object from the split point stack
2917 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2919 // Initialize the split point object
2920 splitPoint->parent = threads[master].splitPoint;
2921 splitPoint->stopRequest = false;
2922 splitPoint->ply = ply;
2923 splitPoint->depth = depth;
2924 splitPoint->mateThreat = mateThreat;
2925 splitPoint->alpha = pvNode ? *alpha : beta - 1;
2926 splitPoint->beta = beta;
2927 splitPoint->pvNode = pvNode;
2928 splitPoint->bestValue = *bestValue;
2929 splitPoint->master = master;
2930 splitPoint->mp = mp;
2931 splitPoint->moves = *moves;
2932 splitPoint->cpus = 1;
2933 splitPoint->pos = &p;
2934 splitPoint->parentSstack = sstck;
2935 for (int i = 0; i < ActiveThreads; i++)
2936 splitPoint->slaves[i] = 0;
2938 threads[master].splitPoint = splitPoint;
2939 threads[master].activeSplitPoints++;
2941 // If we are here it means we are not available
2942 assert(threads[master].state != THREAD_AVAILABLE);
2944 // Allocate available threads setting state to THREAD_BOOKED
2945 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2946 if (thread_is_available(i, master))
2948 threads[i].state = THREAD_BOOKED;
2949 threads[i].splitPoint = splitPoint;
2950 splitPoint->slaves[i] = 1;
2954 assert(splitPoint->cpus > 1);
2956 // We can release the lock because slave threads are already booked and master is not available
2957 lock_release(&MPLock);
2959 // Tell the threads that they have work to do. This will make them leave
2960 // their idle loop. But before copy search stack tail for each thread.
2961 for (int i = 0; i < ActiveThreads; i++)
2962 if (i == master || splitPoint->slaves[i])
2964 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2966 assert(i == master || threads[i].state == THREAD_BOOKED);
2968 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2971 // Everything is set up. The master thread enters the idle loop, from
2972 // which it will instantly launch a search, because its state is
2973 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2974 // idle loop, which means that the main thread will return from the idle
2975 // loop when all threads have finished their work at this split point
2976 // (i.e. when splitPoint->cpus == 0).
2977 idle_loop(master, splitPoint);
2979 // We have returned from the idle loop, which means that all threads are
2980 // finished. Update alpha, beta and bestValue, and return.
2984 *alpha = splitPoint->alpha;
2986 *bestValue = splitPoint->bestValue;
2987 threads[master].activeSplitPoints--;
2988 threads[master].splitPoint = splitPoint->parent;
2990 lock_release(&MPLock);
2995 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2996 // to start a new search from the root.
2998 void ThreadsManager::wake_sleeping_threads() {
3000 assert(AllThreadsShouldSleep);
3001 assert(ActiveThreads > 0);
3003 AllThreadsShouldSleep = false;
3005 if (ActiveThreads == 1)
3008 #if !defined(_MSC_VER)
3009 pthread_mutex_lock(&WaitLock);
3010 pthread_cond_broadcast(&WaitCond);
3011 pthread_mutex_unlock(&WaitLock);
3013 for (int i = 1; i < MAX_THREADS; i++)
3014 SetEvent(SitIdleEvent[i]);
3020 // put_threads_to_sleep() makes all the threads go to sleep just before
3021 // to leave think(), at the end of the search. Threads should have already
3022 // finished the job and should be idle.
3024 void ThreadsManager::put_threads_to_sleep() {
3026 assert(!AllThreadsShouldSleep);
3028 // This makes the threads to go to sleep
3029 AllThreadsShouldSleep = true;
3032 /// The RootMoveList class
3034 // RootMoveList c'tor
3036 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
3038 SearchStack ss[PLY_MAX_PLUS_2];
3039 MoveStack mlist[MaxRootMoves];
3041 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
3043 // Generate all legal moves
3044 MoveStack* last = generate_moves(pos, mlist);
3046 // Add each move to the moves[] array
3047 for (MoveStack* cur = mlist; cur != last; cur++)
3049 bool includeMove = includeAllMoves;
3051 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
3052 includeMove = (searchMoves[k] == cur->move);
3057 // Find a quick score for the move
3059 pos.do_move(cur->move, st);
3060 moves[count].move = cur->move;
3061 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
3062 moves[count].pv[0] = cur->move;
3063 moves[count].pv[1] = MOVE_NONE;
3064 pos.undo_move(cur->move);
3071 // RootMoveList simple methods definitions
3073 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
3075 moves[moveNum].nodes = nodes;
3076 moves[moveNum].cumulativeNodes += nodes;
3079 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
3081 moves[moveNum].ourBeta = our;
3082 moves[moveNum].theirBeta = their;
3085 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
3089 for (j = 0; pv[j] != MOVE_NONE; j++)
3090 moves[moveNum].pv[j] = pv[j];
3092 moves[moveNum].pv[j] = MOVE_NONE;
3096 // RootMoveList::sort() sorts the root move list at the beginning of a new
3099 void RootMoveList::sort() {
3101 sort_multipv(count - 1); // Sort all items
3105 // RootMoveList::sort_multipv() sorts the first few moves in the root move
3106 // list by their scores and depths. It is used to order the different PVs
3107 // correctly in MultiPV mode.
3109 void RootMoveList::sort_multipv(int n) {
3113 for (i = 1; i <= n; i++)
3115 RootMove rm = moves[i];
3116 for (j = i; j > 0 && moves[j - 1] < rm; j--)
3117 moves[j] = moves[j - 1];