2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
43 #include "ucioption.h"
49 //// Local definitions
55 enum NodeType { NonPV, PV};
57 // ThreadsManager class is used to handle all the threads related stuff in search,
58 // init, starting, parking and, the most important, launching a slave thread at a
59 // split point are what this class does. All the access to shared thread data is
60 // done through this class, so that we avoid using global variables instead.
62 class ThreadsManager {
63 /* As long as the single ThreadsManager object is defined as a global we don't
64 need to explicitly initialize to zero its data members because variables with
65 static storage duration are automatically set to zero before enter main()
71 int active_threads() const { return ActiveThreads; }
72 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
73 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
74 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
76 void resetNodeCounters();
77 void resetBetaCounters();
78 int64_t nodes_searched() const;
79 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
80 bool available_thread_exists(int master) const;
81 bool thread_is_available(int slave, int master) const;
82 bool thread_should_stop(int threadID) const;
83 void wake_sleeping_threads();
84 void put_threads_to_sleep();
85 void idle_loop(int threadID, SplitPoint* sp);
86 bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode);
93 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
94 Thread threads[MAX_THREADS];
95 SplitPoint SplitPointStack[MAX_THREADS][ACTIVE_SPLIT_POINTS_MAX];
97 Lock MPLock, WaitLock;
99 #if !defined(_MSC_VER)
100 pthread_cond_t WaitCond;
102 HANDLE SitIdleEvent[MAX_THREADS];
108 // RootMove struct is used for moves at the root at the tree. For each
109 // root move, we store a score, a node count, and a PV (really a refutation
110 // in the case of moves which fail low).
114 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
116 // RootMove::operator<() is the comparison function used when
117 // sorting the moves. A move m1 is considered to be better
118 // than a move m2 if it has a higher score, or if the moves
119 // have equal score but m1 has the higher node count.
120 bool operator<(const RootMove& m) const {
122 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
127 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
128 Move pv[PLY_MAX_PLUS_2];
132 // The RootMoveList class is essentially an array of RootMove objects, with
133 // a handful of methods for accessing the data in the individual moves.
138 RootMoveList(Position& pos, Move searchMoves[]);
140 int move_count() const { return count; }
141 Move get_move(int moveNum) const { return moves[moveNum].move; }
142 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
143 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
144 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
145 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
147 void set_move_nodes(int moveNum, int64_t nodes);
148 void set_beta_counters(int moveNum, int64_t our, int64_t their);
149 void set_move_pv(int moveNum, const Move pv[]);
151 void sort_multipv(int n);
154 static const int MaxRootMoves = 500;
155 RootMove moves[MaxRootMoves];
164 // Maximum depth for razoring
165 const Depth RazorDepth = 4 * OnePly;
167 // Dynamic razoring margin based on depth
168 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
170 // Step 8. Null move search with verification search
172 // Null move margin. A null move search will not be done if the static
173 // evaluation of the position is more than NullMoveMargin below beta.
174 const Value NullMoveMargin = Value(0x200);
176 // Maximum depth for use of dynamic threat detection when null move fails low
177 const Depth ThreatDepth = 5 * OnePly;
179 // Step 9. Internal iterative deepening
181 // Minimum depth for use of internal iterative deepening
182 const Depth 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 SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
199 // If the TT move is at least SingularExtensionMargin better then the
200 // remaining ones we will extend it.
201 const Value SingularExtensionMargin = Value(0x20);
203 // Step 12. Futility pruning
205 // Futility margin for quiescence search
206 const Value FutilityMarginQS = Value(0x80);
208 // Futility lookup tables (initialized at startup) and their getter functions
209 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
210 int FutilityMoveCountArray[32]; // [depth]
212 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 0)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
213 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
215 // Step 14. Reduced search
217 // Reduction lookup tables (initialized at startup) and their getter functions
218 int8_t PVReductionMatrix[64][64]; // [depth][moveNumber]
219 int8_t NonPVReductionMatrix[64][64]; // [depth][moveNumber]
221 inline Depth pv_reduction(Depth d, int mn) { return (Depth) PVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
222 inline Depth nonpv_reduction(Depth d, int mn) { return (Depth) NonPVReductionMatrix[Min(d / 2, 63)][Min(mn, 63)]; }
224 // Common adjustments
226 // Search depth at iteration 1
227 const Depth InitialDepth = OnePly;
229 // Easy move margin. An easy move candidate must be at least this much
230 // better than the second best move.
231 const Value EasyMoveMargin = Value(0x200);
233 // Last seconds noise filtering (LSN)
234 const bool UseLSNFiltering = true;
235 const int LSNTime = 4000; // In milliseconds
236 const Value LSNValue = value_from_centipawns(200);
237 bool loseOnTime = false;
245 // Scores and number of times the best move changed for each iteration
246 Value ValueByIteration[PLY_MAX_PLUS_2];
247 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
249 // Search window management
255 // Time managment variables
256 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
257 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
258 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
259 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
263 std::ofstream LogFile;
265 // Multi-threads related variables
266 Depth MinimumSplitDepth;
267 int MaxThreadsPerSplitPoint;
270 // Node counters, used only by thread[0] but try to keep in different cache
271 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
273 int NodesBetweenPolls = 30000;
280 Value id_loop(const Position& pos, Move searchMoves[]);
281 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
283 template <NodeType PvNode>
284 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
286 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
287 void sp_search(SplitPoint* sp, int threadID);
288 void sp_search_pv(SplitPoint* sp, int threadID);
289 void init_node(SearchStack ss[], int ply, int threadID);
290 void update_pv(SearchStack ss[], int ply);
291 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
292 bool connected_moves(const Position& pos, Move m1, Move m2);
293 bool value_is_mate(Value value);
294 bool move_is_killer(Move m, const SearchStack& ss);
295 Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
296 bool ok_to_do_nullmove(const Position& pos);
297 bool ok_to_prune(const Position& pos, Move m, Move threat);
298 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
299 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
300 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
301 void update_killers(Move m, SearchStack& ss);
302 void update_gains(const Position& pos, Move move, Value before, Value after);
304 int current_search_time();
308 void wait_for_stop_or_ponderhit();
309 void init_ss_array(SearchStack ss[]);
310 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value);
312 #if !defined(_MSC_VER)
313 void *init_thread(void *threadID);
315 DWORD WINAPI init_thread(LPVOID threadID);
325 /// init_threads(), exit_threads() and nodes_searched() are helpers to
326 /// give accessibility to some TM methods from outside of current file.
328 void init_threads() { TM.init_threads(); }
329 void exit_threads() { TM.exit_threads(); }
330 int64_t nodes_searched() { return TM.nodes_searched(); }
333 /// perft() is our utility to verify move generation is bug free. All the legal
334 /// moves up to given depth are generated and counted and the sum returned.
336 int perft(Position& pos, Depth depth)
341 MovePicker mp(pos, MOVE_NONE, depth, H);
343 // If we are at the last ply we don't need to do and undo
344 // the moves, just to count them.
345 if (depth <= OnePly) // Replace with '<' to test also qsearch
347 while (mp.get_next_move()) sum++;
351 // Loop through all legal moves
353 while ((move = mp.get_next_move()) != MOVE_NONE)
355 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
356 sum += perft(pos, depth - OnePly);
363 /// think() is the external interface to Stockfish's search, and is called when
364 /// the program receives the UCI 'go' command. It initializes various
365 /// search-related global variables, and calls root_search(). It returns false
366 /// when a quit command is received during the search.
368 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
369 int time[], int increment[], int movesToGo, int maxDepth,
370 int maxNodes, int maxTime, Move searchMoves[]) {
372 // Initialize global search variables
373 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
374 MaxSearchTime = AbsoluteMaxSearchTime = ExtraSearchTime = 0;
376 TM.resetNodeCounters();
377 SearchStartTime = get_system_time();
378 ExactMaxTime = maxTime;
381 InfiniteSearch = infinite;
382 PonderSearch = ponder;
383 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
385 // Look for a book move, only during games, not tests
386 if (UseTimeManagement && get_option_value_bool("OwnBook"))
388 if (get_option_value_string("Book File") != OpeningBook.file_name())
389 OpeningBook.open(get_option_value_string("Book File"));
391 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
392 if (bookMove != MOVE_NONE)
395 wait_for_stop_or_ponderhit();
397 cout << "bestmove " << bookMove << endl;
402 // Reset loseOnTime flag at the beginning of a new game
403 if (button_was_pressed("New Game"))
406 // Read UCI option values
407 TT.set_size(get_option_value_int("Hash"));
408 if (button_was_pressed("Clear Hash"))
411 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
412 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
413 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
414 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
415 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
416 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
417 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
418 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
419 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
420 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
421 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
422 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
424 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
425 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
426 MultiPV = get_option_value_int("MultiPV");
427 Chess960 = get_option_value_bool("UCI_Chess960");
428 UseLogFile = get_option_value_bool("Use Search Log");
431 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
433 read_weights(pos.side_to_move());
435 // Set the number of active threads
436 int newActiveThreads = get_option_value_int("Threads");
437 if (newActiveThreads != TM.active_threads())
439 TM.set_active_threads(newActiveThreads);
440 init_eval(TM.active_threads());
443 // Wake up sleeping threads
444 TM.wake_sleeping_threads();
447 int myTime = time[side_to_move];
448 int myIncrement = increment[side_to_move];
449 if (UseTimeManagement)
451 if (!movesToGo) // Sudden death time control
455 MaxSearchTime = myTime / 30 + myIncrement;
456 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
458 else // Blitz game without increment
460 MaxSearchTime = myTime / 30;
461 AbsoluteMaxSearchTime = myTime / 8;
464 else // (x moves) / (y minutes)
468 MaxSearchTime = myTime / 2;
469 AbsoluteMaxSearchTime = (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
473 MaxSearchTime = myTime / Min(movesToGo, 20);
474 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
478 if (get_option_value_bool("Ponder"))
480 MaxSearchTime += MaxSearchTime / 4;
481 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
485 // Set best NodesBetweenPolls interval to avoid lagging under
486 // heavy time pressure.
488 NodesBetweenPolls = Min(MaxNodes, 30000);
489 else if (myTime && myTime < 1000)
490 NodesBetweenPolls = 1000;
491 else if (myTime && myTime < 5000)
492 NodesBetweenPolls = 5000;
494 NodesBetweenPolls = 30000;
496 // Write search information to log file
498 LogFile << "Searching: " << pos.to_fen() << endl
499 << "infinite: " << infinite
500 << " ponder: " << ponder
501 << " time: " << myTime
502 << " increment: " << myIncrement
503 << " moves to go: " << movesToGo << endl;
505 // LSN filtering. Used only for developing purposes, disabled by default
509 // Step 2. If after last move we decided to lose on time, do it now!
510 while (SearchStartTime + myTime + 1000 > get_system_time())
514 // We're ready to start thinking. Call the iterative deepening loop function
515 Value v = id_loop(pos, searchMoves);
519 // Step 1. If this is sudden death game and our position is hopeless,
520 // decide to lose on time.
521 if ( !loseOnTime // If we already lost on time, go to step 3.
531 // Step 3. Now after stepping over the time limit, reset flag for next match.
539 TM.put_threads_to_sleep();
545 /// init_search() is called during startup. It initializes various lookup tables
549 // Init our reduction lookup tables
550 for (int i = 1; i < 64; i++) // i == depth (OnePly = 1)
551 for (int j = 1; j < 64; j++) // j == moveNumber
553 double pvRed = log(double(i)) * log(double(j)) / 3.0;
554 double nonPVRed = log(double(i)) * log(double(j)) / 1.5;
555 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 + 45;
567 // Init futility move count array
568 for (int i = 0; i < 32; i++) // i == depth (OnePly = 2)
569 FutilityMoveCountArray[i] = 3 + (1 << (3 * i / 8));
573 // SearchStack::init() initializes a search stack. Used at the beginning of a
574 // new search from the root.
575 void SearchStack::init(int ply) {
577 pv[ply] = pv[ply + 1] = MOVE_NONE;
578 currentMove = threatMove = MOVE_NONE;
579 reduction = Depth(0);
583 void SearchStack::initKillers() {
585 mateKiller = MOVE_NONE;
586 for (int i = 0; i < KILLER_MAX; i++)
587 killers[i] = MOVE_NONE;
592 // id_loop() is the main iterative deepening loop. It calls root_search
593 // repeatedly with increasing depth until the allocated thinking time has
594 // been consumed, the user stops the search, or the maximum search depth is
597 Value id_loop(const Position& pos, Move searchMoves[]) {
600 SearchStack ss[PLY_MAX_PLUS_2];
601 Move EasyMove = MOVE_NONE;
602 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
604 // Moves to search are verified, copied, scored and sorted
605 RootMoveList rml(p, searchMoves);
607 // Handle special case of searching on a mate/stale position
608 if (rml.move_count() == 0)
611 wait_for_stop_or_ponderhit();
613 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
616 // Print RootMoveList startup scoring to the standard output,
617 // so to output information also for iteration 1.
618 cout << "info depth " << 1
619 << "\ninfo depth " << 1
620 << " score " << value_to_string(rml.get_move_score(0))
621 << " time " << current_search_time()
622 << " nodes " << TM.nodes_searched()
624 << " pv " << rml.get_move(0) << "\n";
630 ValueByIteration[1] = rml.get_move_score(0);
633 // Is one move significantly better than others after initial scoring ?
634 if ( rml.move_count() == 1
635 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
636 EasyMove = rml.get_move(0);
638 // Iterative deepening loop
639 while (Iteration < PLY_MAX)
641 // Initialize iteration
643 BestMoveChangesByIteration[Iteration] = 0;
645 cout << "info depth " << Iteration << endl;
647 // Calculate dynamic aspiration window based on previous iterations
648 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
650 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
651 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
653 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
654 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
656 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
657 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
660 // Search to the current depth, rml is updated and sorted, alpha and beta could change
661 value = root_search(p, ss, rml, &alpha, &beta);
663 // Write PV to transposition table, in case the relevant entries have
664 // been overwritten during the search.
665 TT.insert_pv(p, ss[0].pv);
668 break; // Value cannot be trusted. Break out immediately!
670 //Save info about search result
671 ValueByIteration[Iteration] = value;
673 // Drop the easy move if differs from the new best move
674 if (ss[0].pv[0] != EasyMove)
675 EasyMove = MOVE_NONE;
677 if (UseTimeManagement)
680 bool stopSearch = false;
682 // Stop search early if there is only a single legal move,
683 // we search up to Iteration 6 anyway to get a proper score.
684 if (Iteration >= 6 && rml.move_count() == 1)
687 // Stop search early when the last two iterations returned a mate score
689 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
690 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
693 // Stop search early if one move seems to be much better than the others
694 int64_t nodes = TM.nodes_searched();
696 && EasyMove == ss[0].pv[0]
697 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
698 && current_search_time() > MaxSearchTime / 16)
699 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
700 && current_search_time() > MaxSearchTime / 32)))
703 // Add some extra time if the best move has changed during the last two iterations
704 if (Iteration > 5 && Iteration <= 50)
705 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
706 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
708 // Stop search if most of MaxSearchTime is consumed at the end of the
709 // iteration. We probably don't have enough time to search the first
710 // move at the next iteration anyway.
711 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime) * 80) / 128)
717 StopOnPonderhit = true;
723 if (MaxDepth && Iteration >= MaxDepth)
727 // If we are pondering or in infinite search, we shouldn't print the
728 // best move before we are told to do so.
729 if (!AbortSearch && (PonderSearch || InfiniteSearch))
730 wait_for_stop_or_ponderhit();
732 // Print final search statistics
733 cout << "info nodes " << TM.nodes_searched()
735 << " time " << current_search_time()
736 << " hashfull " << TT.full() << endl;
738 // Print the best move and the ponder move to the standard output
739 if (ss[0].pv[0] == MOVE_NONE)
741 ss[0].pv[0] = rml.get_move(0);
742 ss[0].pv[1] = MOVE_NONE;
745 assert(ss[0].pv[0] != MOVE_NONE);
747 cout << "bestmove " << ss[0].pv[0];
749 if (ss[0].pv[1] != MOVE_NONE)
750 cout << " ponder " << ss[0].pv[1];
757 dbg_print_mean(LogFile);
759 if (dbg_show_hit_rate)
760 dbg_print_hit_rate(LogFile);
762 LogFile << "\nNodes: " << TM.nodes_searched()
763 << "\nNodes/second: " << nps()
764 << "\nBest move: " << move_to_san(p, ss[0].pv[0]);
767 p.do_move(ss[0].pv[0], st);
768 LogFile << "\nPonder move: "
769 << move_to_san(p, ss[0].pv[1]) // Works also with MOVE_NONE
772 return rml.get_move_score(0);
776 // root_search() is the function which searches the root node. It is
777 // similar to search_pv except that it uses a different move ordering
778 // scheme, prints some information to the standard output and handles
779 // the fail low/high loops.
781 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
788 Depth depth, ext, newDepth;
789 Value value, alpha, beta;
790 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
791 int researchCountFH, researchCountFL;
793 researchCountFH = researchCountFL = 0;
796 isCheck = pos.is_check();
798 // Step 1. Initialize node and poll (omitted at root, but I can see no good reason for this, FIXME)
799 // Step 2. Check for aborted search (omitted at root, because we do not initialize root node)
800 // Step 3. Mate distance pruning (omitted at root)
801 // Step 4. Transposition table lookup (omitted at root)
803 // Step 5. Evaluate the position statically
804 // At root we do this only to get reference value for child nodes
806 ss[0].eval = evaluate(pos, ei, 0);
808 ss[0].eval = VALUE_NONE; // HACK because we do not initialize root node
810 // Step 6. Razoring (omitted at root)
811 // Step 7. Static null move pruning (omitted at root)
812 // Step 8. Null move search with verification search (omitted at root)
813 // Step 9. Internal iterative deepening (omitted at root)
815 // Step extra. Fail low loop
816 // We start with small aspiration window and in case of fail low, we research
817 // with bigger window until we are not failing low anymore.
820 // Sort the moves before to (re)search
823 // Step 10. Loop through all moves in the root move list
824 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
826 // This is used by time management
827 FirstRootMove = (i == 0);
829 // Save the current node count before the move is searched
830 nodes = TM.nodes_searched();
832 // Reset beta cut-off counters
833 TM.resetBetaCounters();
835 // Pick the next root move, and print the move and the move number to
836 // the standard output.
837 move = ss[0].currentMove = rml.get_move(i);
839 if (current_search_time() >= 1000)
840 cout << "info currmove " << move
841 << " currmovenumber " << i + 1 << endl;
843 moveIsCheck = pos.move_is_check(move);
844 captureOrPromotion = pos.move_is_capture_or_promotion(move);
846 // Step 11. Decide the new search depth
847 depth = (Iteration - 2) * OnePly + InitialDepth;
848 ext = extension(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, false, 0);
877 // Step 14. Reduced search
878 // if the move fails high will be re-searched at full depth
879 bool doFullDepthSearch = true;
881 if ( depth >= 3 * OnePly
883 && !captureOrPromotion
884 && !move_is_castle(move))
886 ss[0].reduction = pv_reduction(depth, i - MultiPV + 2);
889 // Reduced depth non-pv search using alpha as upperbound
890 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[0].reduction, 1, true, 0);
891 doFullDepthSearch = (value > alpha);
895 // Step 15. Full depth search
896 if (doFullDepthSearch)
898 // Full depth non-pv search using alpha as upperbound
899 ss[0].reduction = Depth(0);
900 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, 1, true, 0);
902 // If we are above alpha then research at same depth but as PV
903 // to get a correct score or eventually a fail high above beta.
905 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
909 // Step 16. Undo move
912 // Can we exit fail high loop ?
913 if (AbortSearch || value < beta)
916 // We are failing high and going to do a research. It's important to update
917 // the score before research in case we run out of time while researching.
918 rml.set_move_score(i, value);
920 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
921 rml.set_move_pv(i, ss[0].pv);
923 // Print information to the standard output
924 print_pv_info(pos, ss, alpha, beta, value);
926 // Prepare for a research after a fail high, each time with a wider window
927 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
930 } // End of fail high loop
932 // Finished searching the move. If AbortSearch is true, the search
933 // was aborted because the user interrupted the search or because we
934 // ran out of time. In this case, the return value of the search cannot
935 // be trusted, and we break out of the loop without updating the best
940 // Remember beta-cutoff and searched nodes counts for this move. The
941 // info is used to sort the root moves for the next iteration.
943 TM.get_beta_counters(pos.side_to_move(), our, their);
944 rml.set_beta_counters(i, our, their);
945 rml.set_move_nodes(i, TM.nodes_searched() - nodes);
947 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
948 assert(value < beta);
950 // Step 17. Check for new best move
951 if (value <= alpha && i >= MultiPV)
952 rml.set_move_score(i, -VALUE_INFINITE);
955 // PV move or new best move!
958 rml.set_move_score(i, value);
960 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
961 rml.set_move_pv(i, ss[0].pv);
965 // We record how often the best move has been changed in each
966 // iteration. This information is used for time managment: When
967 // the best move changes frequently, we allocate some more time.
969 BestMoveChangesByIteration[Iteration]++;
971 // Print information to the standard output
972 print_pv_info(pos, ss, alpha, beta, value);
974 // Raise alpha to setup proper non-pv search upper bound
981 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
983 cout << "info multipv " << j + 1
984 << " score " << value_to_string(rml.get_move_score(j))
985 << " depth " << (j <= i ? Iteration : Iteration - 1)
986 << " time " << current_search_time()
987 << " nodes " << TM.nodes_searched()
991 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
992 cout << rml.get_move_pv(j, k) << " ";
996 alpha = rml.get_move_score(Min(i, MultiPV - 1));
998 } // PV move or new best move
1000 assert(alpha >= *alphaPtr);
1002 AspirationFailLow = (alpha == *alphaPtr);
1004 if (AspirationFailLow && StopOnPonderhit)
1005 StopOnPonderhit = false;
1008 // Can we exit fail low loop ?
1009 if (AbortSearch || !AspirationFailLow)
1012 // Prepare for a research after a fail low, each time with a wider window
1013 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
1018 // Sort the moves before to return
1025 // search_pv() is the main search function for PV nodes.
1027 template <NodeType PvNode>
1028 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta,
1029 Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove) {
1031 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1032 assert(beta > alpha && beta <= VALUE_INFINITE);
1033 assert(ply >= 0 && ply < PLY_MAX);
1034 assert(threadID >= 0 && threadID < TM.active_threads());
1036 Move movesSearched[256];
1041 Depth ext, newDepth;
1042 Value bestValue, value, oldAlpha;
1043 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1044 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1045 bool mateThreat = false;
1047 refinedValue = bestValue = value = -VALUE_INFINITE;
1051 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1053 // Step 1. Initialize node and poll
1054 // Polling can abort search.
1055 init_node(ss, ply, threadID);
1057 // Step 2. Check for aborted search and immediate draw
1058 if (AbortSearch || TM.thread_should_stop(threadID))
1061 if (pos.is_draw() || ply >= PLY_MAX - 1)
1064 // Step 3. Mate distance pruning
1065 alpha = Max(value_mated_in(ply), alpha);
1066 beta = Min(value_mate_in(ply+1), beta);
1070 // Step 4. Transposition table lookup
1072 // We don't want the score of a partial search to overwrite a previous full search
1073 // TT value, so we use a different position key in case of an excluded move exists.
1074 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1076 tte = TT.retrieve(posKey);
1077 ttMove = (tte ? tte->move() : MOVE_NONE);
1079 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1080 // This is to avoid problems in the following areas:
1082 // * Repetition draw detection
1083 // * Fifty move rule detection
1084 // * Searching for a mate
1085 // * Printing of full PV line
1087 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1089 // Refresh tte entry to avoid aging
1090 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove);
1092 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1093 return value_from_tt(tte->value(), ply);
1096 // Step 5. Evaluate the position statically
1097 // At PV nodes we do this only to update gain statistics
1098 isCheck = pos.is_check();
1101 if (!PvNode && tte && (tte->type() & VALUE_TYPE_EVAL))
1102 ss[ply].eval = value_from_tt(tte->value(), ply);
1104 ss[ply].eval = evaluate(pos, ei, threadID);
1106 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1107 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1110 // Step 6. Razoring (is omitted in PV nodes)
1112 && refinedValue < beta - razor_margin(depth)
1113 && ttMove == MOVE_NONE
1114 && ss[ply - 1].currentMove != MOVE_NULL
1115 && depth < RazorDepth
1117 && !value_is_mate(beta)
1118 && !pos.has_pawn_on_7th(pos.side_to_move()))
1120 Value rbeta = beta - razor_margin(depth);
1121 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1123 // Logically we should return (v + razor_margin(depth)), but
1124 // surprisingly this did slightly weaker in tests.
1128 // Step 7. Static null move pruning (is omitted in PV nodes)
1129 // We're betting that the opponent doesn't have a move that will reduce
1130 // the score by more than futility_margin(depth) if we do a null move.
1133 && depth < RazorDepth
1135 && !value_is_mate(beta)
1136 && ok_to_do_nullmove(pos)
1137 && refinedValue >= beta + futility_margin(depth, 0))
1138 return refinedValue - futility_margin(depth, 0);
1140 // Step 8. Null move search with verification search (is omitted in PV nodes)
1141 // When we jump directly to qsearch() we do a null move only if static value is
1142 // at least beta. Otherwise we do a null move if static value is not more than
1143 // NullMoveMargin under beta.
1148 && !value_is_mate(beta)
1149 && ok_to_do_nullmove(pos)
1150 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1152 ss[ply].currentMove = MOVE_NULL;
1154 // Null move dynamic reduction based on depth
1155 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1157 // Null move dynamic reduction based on value
1158 if (refinedValue - beta > PawnValueMidgame)
1161 pos.do_null_move(st);
1163 nullValue = -search<NonPV>(pos, ss, -beta, -alpha, depth-R*OnePly, ply+1, false, threadID);
1165 pos.undo_null_move();
1167 if (nullValue >= beta)
1169 // Do not return unproven mate scores
1170 if (nullValue >= value_mate_in(PLY_MAX))
1173 if (depth < 6 * OnePly)
1176 // Do zugzwang verification search
1177 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply, false, threadID);
1181 // The null move failed low, which means that we may be faced with
1182 // some kind of threat. If the previous move was reduced, check if
1183 // the move that refuted the null move was somehow connected to the
1184 // move which was reduced. If a connection is found, return a fail
1185 // low score (which will cause the reduced move to fail high in the
1186 // parent node, which will trigger a re-search with full depth).
1187 if (nullValue == value_mated_in(ply + 2))
1190 ss[ply].threatMove = ss[ply + 1].currentMove;
1191 if ( depth < ThreatDepth
1192 && ss[ply - 1].reduction
1193 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1198 // Step 9. Internal iterative deepening
1199 // We have different rules for PV nodes and non-pv nodes
1201 && depth >= IIDDepthAtPVNodes
1202 && ttMove == MOVE_NONE)
1204 search<PV>(pos, ss, alpha, beta, depth-2*OnePly, ply, false, threadID);
1205 ttMove = ss[ply].pv[ply];
1206 tte = TT.retrieve(posKey);
1210 && depth >= IIDDepthAtNonPVNodes
1211 && ttMove == MOVE_NONE
1213 && ss[ply].eval >= beta - IIDMargin)
1215 search<NonPV>(pos, ss, alpha, beta, depth/2, ply, false, threadID);
1216 ttMove = ss[ply].pv[ply];
1217 tte = TT.retrieve(posKey);
1220 // Expensive mate threat detection (only for PV nodes)
1222 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1224 // Initialize a MovePicker object for the current position
1225 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], (PvNode ? -VALUE_INFINITE : beta));
1228 // Step 10. Loop through moves
1229 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1230 while ( bestValue < beta
1231 && (move = mp.get_next_move()) != MOVE_NONE
1232 && !TM.thread_should_stop(threadID))
1234 assert(move_is_ok(move));
1236 if (move == excludedMove)
1239 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1240 moveIsCheck = pos.move_is_check(move, ci);
1241 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1243 // Step 11. Decide the new search depth
1244 ext = extension(pos, move, PvNode, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1246 // Singular extension search. We extend the TT move if its value is much better than
1247 // its siblings. To verify this we do a reduced search on all the other moves but the
1248 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1249 if ( depth >= SingularExtensionDepth[PvNode]
1251 && move == tte->move()
1252 && !excludedMove // Do not allow recursive singular extension search
1254 && is_lower_bound(tte->type())
1255 && tte->depth() >= depth - 3 * OnePly)
1257 Value ttValue = value_from_tt(tte->value(), ply);
1259 if (abs(ttValue) < VALUE_KNOWN_WIN)
1261 Value excValue = search<NonPV>(pos, ss, ttValue - SingularExtensionMargin - 1, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1263 if (excValue < ttValue - SingularExtensionMargin)
1268 newDepth = depth - OnePly + ext;
1270 // Update current move (this must be done after singular extension search)
1271 movesSearched[moveCount++] = ss[ply].currentMove = move;
1273 // Step 12. Futility pruning (is omitted in PV nodes)
1277 && !captureOrPromotion
1278 && !move_is_castle(move)
1281 // Move count based pruning
1282 if ( moveCount >= futility_move_count(depth)
1283 && ok_to_prune(pos, move, ss[ply].threatMove)
1284 && bestValue > value_mated_in(PLY_MAX))
1287 // Value based pruning
1288 Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1289 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1290 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1292 if (futilityValueScaled < beta)
1294 if (futilityValueScaled > bestValue)
1295 bestValue = futilityValueScaled;
1300 // Step 13. Make the move
1301 pos.do_move(move, st, ci, moveIsCheck);
1303 // Step extra. pv search (only in PV nodes)
1304 // The first move in list is the expected PV
1305 if (PvNode && moveCount == 1)
1306 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1309 // Step 14. Reduced search
1310 // if the move fails high will be re-searched at full depth.
1311 bool doFullDepthSearch = true;
1313 if ( depth >= 3 * OnePly
1315 && !captureOrPromotion
1316 && !move_is_castle(move)
1317 && !move_is_killer(move, ss[ply]))
1319 ss[ply].reduction = (PvNode ? pv_reduction(depth, moveCount) : nonpv_reduction(depth, moveCount));
1320 if (ss[ply].reduction)
1322 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1323 doFullDepthSearch = (value > alpha);
1327 // Step 15. Full depth search
1328 if (doFullDepthSearch)
1330 ss[ply].reduction = Depth(0);
1331 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, ply+1, true, threadID);
1333 // Step extra. pv search (only in PV nodes)
1334 if (PvNode && value > alpha && value < beta)
1335 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1339 // Step 16. Undo move
1340 pos.undo_move(move);
1342 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1344 // Step 17. Check for new best move
1345 if (value > bestValue)
1352 if (value == value_mate_in(ply + 1))
1353 ss[ply].mateKiller = move;
1357 // Step 18. Check for split
1358 if ( TM.active_threads() > 1
1360 && depth >= MinimumSplitDepth
1362 && TM.available_thread_exists(threadID)
1364 && !TM.thread_should_stop(threadID)
1365 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1366 depth, mateThreat, &moveCount, &mp, threadID, PvNode))
1370 // Step 19. Check for mate and stalemate
1371 // All legal moves have been searched and if there are
1372 // no legal moves, it must be mate or stalemate.
1373 // If one move was excluded return fail low score.
1375 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1377 // Step 20. Update tables
1378 // If the search is not aborted, update the transposition table,
1379 // history counters, and killer moves.
1380 if (AbortSearch || TM.thread_should_stop(threadID))
1383 if (bestValue <= oldAlpha)
1384 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1386 else if (bestValue >= beta)
1388 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1389 move = ss[ply].pv[ply];
1390 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1391 if (!pos.move_is_capture_or_promotion(move))
1393 update_history(pos, move, depth, movesSearched, moveCount);
1394 update_killers(move, ss[ply]);
1398 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1400 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1406 // qsearch() is the quiescence search function, which is called by the main
1407 // search function when the remaining depth is zero (or, to be more precise,
1408 // less than OnePly).
1410 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1411 Depth depth, int ply, int threadID) {
1413 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1414 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1416 assert(ply >= 0 && ply < PLY_MAX);
1417 assert(threadID >= 0 && threadID < TM.active_threads());
1422 Value staticValue, bestValue, value, futilityBase, futilityValue;
1423 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1424 const TTEntry* tte = NULL;
1426 bool pvNode = (beta - alpha != 1);
1427 Value oldAlpha = alpha;
1429 // Initialize, and make an early exit in case of an aborted search,
1430 // an instant draw, maximum ply reached, etc.
1431 init_node(ss, ply, threadID);
1433 // After init_node() that calls poll()
1434 if (AbortSearch || TM.thread_should_stop(threadID))
1437 if (pos.is_draw() || ply >= PLY_MAX - 1)
1440 // Transposition table lookup. At PV nodes, we don't use the TT for
1441 // pruning, but only for move ordering.
1442 tte = TT.retrieve(pos.get_key());
1443 ttMove = (tte ? tte->move() : MOVE_NONE);
1445 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1447 assert(tte->type() != VALUE_TYPE_EVAL);
1449 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1450 return value_from_tt(tte->value(), ply);
1453 isCheck = pos.is_check();
1455 // Evaluate the position statically
1457 staticValue = -VALUE_INFINITE;
1458 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1459 staticValue = value_from_tt(tte->value(), ply);
1461 staticValue = evaluate(pos, ei, threadID);
1465 ss[ply].eval = staticValue;
1466 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1469 // Initialize "stand pat score", and return it immediately if it is
1471 bestValue = staticValue;
1473 if (bestValue >= beta)
1475 // Store the score to avoid a future costly evaluation() call
1476 if (!isCheck && !tte && ei.kingDanger[pos.side_to_move()] == 0)
1477 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1482 if (bestValue > alpha)
1485 // If we are near beta then try to get a cutoff pushing checks a bit further
1486 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1488 // Initialize a MovePicker object for the current position, and prepare
1489 // to search the moves. Because the depth is <= 0 here, only captures,
1490 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1491 // and we are near beta) will be generated.
1492 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1494 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1495 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1497 // Loop through the moves until no moves remain or a beta cutoff occurs
1498 while ( alpha < beta
1499 && (move = mp.get_next_move()) != MOVE_NONE)
1501 assert(move_is_ok(move));
1503 moveIsCheck = pos.move_is_check(move, ci);
1505 // Update current move
1507 ss[ply].currentMove = move;
1515 && !move_is_promotion(move)
1516 && !pos.move_is_passed_pawn_push(move))
1518 futilityValue = futilityBase
1519 + pos.endgame_value_of_piece_on(move_to(move))
1520 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1522 if (futilityValue < alpha)
1524 if (futilityValue > bestValue)
1525 bestValue = futilityValue;
1530 // Detect blocking evasions that are candidate to be pruned
1531 evasionPrunable = isCheck
1532 && bestValue > value_mated_in(PLY_MAX)
1533 && !pos.move_is_capture(move)
1534 && pos.type_of_piece_on(move_from(move)) != KING
1535 && !pos.can_castle(pos.side_to_move());
1537 // Don't search moves with negative SEE values
1538 if ( (!isCheck || evasionPrunable)
1541 && !move_is_promotion(move)
1542 && pos.see_sign(move) < 0)
1545 // Make and search the move
1546 pos.do_move(move, st, ci, moveIsCheck);
1547 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1548 pos.undo_move(move);
1550 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1553 if (value > bestValue)
1564 // All legal moves have been searched. A special case: If we're in check
1565 // and no legal moves were found, it is checkmate.
1566 if (!moveCount && isCheck) // Mate!
1567 return value_mated_in(ply);
1569 // Update transposition table
1570 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1571 if (bestValue <= oldAlpha)
1573 // If bestValue isn't changed it means it is still the static evaluation
1574 // of the node, so keep this info to avoid a future evaluation() call.
1575 ValueType type = (bestValue == staticValue && !ei.kingDanger[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1576 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1578 else if (bestValue >= beta)
1580 move = ss[ply].pv[ply];
1581 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1583 // Update killers only for good checking moves
1584 if (!pos.move_is_capture_or_promotion(move))
1585 update_killers(move, ss[ply]);
1588 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1590 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1596 // sp_search() is used to search from a split point. This function is called
1597 // by each thread working at the split point. It is similar to the normal
1598 // search() function, but simpler. Because we have already probed the hash
1599 // table, done a null move search, and searched the first move before
1600 // splitting, we don't have to repeat all this work in sp_search(). We
1601 // also don't need to store anything to the hash table here: This is taken
1602 // care of after we return from the split point.
1604 void sp_search(SplitPoint* sp, int threadID) {
1606 assert(threadID >= 0 && threadID < TM.active_threads());
1607 assert(TM.active_threads() > 1);
1611 Depth ext, newDepth;
1612 Value value, futilityValueScaled;
1613 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1615 value = -VALUE_INFINITE;
1617 Position pos(*sp->pos);
1619 SearchStack* ss = sp->sstack[threadID];
1620 isCheck = pos.is_check();
1622 // Step 10. Loop through moves
1623 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1624 lock_grab(&(sp->lock));
1626 while ( sp->bestValue < sp->beta
1627 && !TM.thread_should_stop(threadID)
1628 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1630 moveCount = ++sp->moves;
1631 lock_release(&(sp->lock));
1633 assert(move_is_ok(move));
1635 moveIsCheck = pos.move_is_check(move, ci);
1636 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1638 // Step 11. Decide the new search depth
1639 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1640 newDepth = sp->depth - OnePly + ext;
1642 // Update current move
1643 ss[sp->ply].currentMove = move;
1645 // Step 12. Futility pruning
1648 && !captureOrPromotion
1649 && !move_is_castle(move))
1651 // Move count based pruning
1652 if ( moveCount >= futility_move_count(sp->depth)
1653 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1654 && sp->bestValue > value_mated_in(PLY_MAX))
1656 lock_grab(&(sp->lock));
1660 // Value based pruning
1661 Depth predictedDepth = newDepth - nonpv_reduction(sp->depth, moveCount);
1662 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1663 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1665 if (futilityValueScaled < sp->beta)
1667 lock_grab(&(sp->lock));
1669 if (futilityValueScaled > sp->bestValue)
1670 sp->bestValue = futilityValueScaled;
1675 // Step 13. Make the move
1676 pos.do_move(move, st, ci, moveIsCheck);
1678 // Step 14. Reduced search
1679 // if the move fails high will be re-searched at full depth.
1680 bool doFullDepthSearch = true;
1683 && !captureOrPromotion
1684 && !move_is_castle(move)
1685 && !move_is_killer(move, ss[sp->ply]))
1687 ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
1688 if (ss[sp->ply].reduction)
1690 value = -search<NonPV>(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1691 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1695 // Step 15. Full depth search
1696 if (doFullDepthSearch)
1698 ss[sp->ply].reduction = Depth(0);
1699 value = -search<NonPV>(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth, sp->ply+1, true, threadID);
1702 // Step 16. Undo move
1703 pos.undo_move(move);
1705 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1707 // Step 17. Check for new best move
1708 lock_grab(&(sp->lock));
1710 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1712 sp->bestValue = value;
1713 if (sp->bestValue >= sp->beta)
1715 sp->stopRequest = true;
1716 sp_update_pv(sp->parentSstack, ss, sp->ply);
1721 /* Here we have the lock still grabbed */
1723 sp->slaves[threadID] = 0;
1726 lock_release(&(sp->lock));
1730 // sp_search_pv() is used to search from a PV split point. This function
1731 // is called by each thread working at the split point. It is similar to
1732 // the normal search_pv() function, but simpler. Because we have already
1733 // probed the hash table and searched the first move before splitting, we
1734 // don't have to repeat all this work in sp_search_pv(). We also don't
1735 // need to store anything to the hash table here: This is taken care of
1736 // after we return from the split point.
1738 void sp_search_pv(SplitPoint* sp, int threadID) {
1740 assert(threadID >= 0 && threadID < TM.active_threads());
1741 assert(TM.active_threads() > 1);
1745 Depth ext, newDepth;
1747 bool moveIsCheck, captureOrPromotion, dangerous;
1749 value = -VALUE_INFINITE;
1751 Position pos(*sp->pos);
1753 SearchStack* ss = sp->sstack[threadID];
1755 // Step 10. Loop through moves
1756 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1757 lock_grab(&(sp->lock));
1759 while ( sp->alpha < sp->beta
1760 && !TM.thread_should_stop(threadID)
1761 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1763 moveCount = ++sp->moves;
1764 lock_release(&(sp->lock));
1766 assert(move_is_ok(move));
1768 moveIsCheck = pos.move_is_check(move, ci);
1769 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1771 // Step 11. Decide the new search depth
1772 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1773 newDepth = sp->depth - OnePly + ext;
1775 // Update current move
1776 ss[sp->ply].currentMove = move;
1778 // Step 12. Futility pruning (is omitted in PV nodes)
1780 // Step 13. Make the move
1781 pos.do_move(move, st, ci, moveIsCheck);
1783 // Step 14. Reduced search
1784 // if the move fails high will be re-searched at full depth.
1785 bool doFullDepthSearch = true;
1788 && !captureOrPromotion
1789 && !move_is_castle(move)
1790 && !move_is_killer(move, ss[sp->ply]))
1792 ss[sp->ply].reduction = pv_reduction(sp->depth, moveCount);
1793 if (ss[sp->ply].reduction)
1795 Value localAlpha = sp->alpha;
1796 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1797 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1801 // Step 15. Full depth search
1802 if (doFullDepthSearch)
1804 Value localAlpha = sp->alpha;
1805 ss[sp->ply].reduction = Depth(0);
1806 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1, true, threadID);
1808 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1810 // If another thread has failed high then sp->alpha has been increased
1811 // to be higher or equal then beta, if so, avoid to start a PV search.
1812 localAlpha = sp->alpha;
1813 if (localAlpha < sp->beta)
1814 value = -search<PV>(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, false, threadID);
1818 // Step 16. Undo move
1819 pos.undo_move(move);
1821 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1823 // Step 17. Check for new best move
1824 lock_grab(&(sp->lock));
1826 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1828 sp->bestValue = value;
1829 if (value > sp->alpha)
1831 // Ask threads to stop before to modify sp->alpha
1832 if (value >= sp->beta)
1833 sp->stopRequest = true;
1837 sp_update_pv(sp->parentSstack, ss, sp->ply);
1838 if (value == value_mate_in(sp->ply + 1))
1839 ss[sp->ply].mateKiller = move;
1844 /* Here we have the lock still grabbed */
1846 sp->slaves[threadID] = 0;
1849 lock_release(&(sp->lock));
1853 // init_node() is called at the beginning of all the search functions
1854 // (search() qsearch(), and so on) and initializes the
1855 // search stack object corresponding to the current node. Once every
1856 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1857 // for user input and checks whether it is time to stop the search.
1859 void init_node(SearchStack ss[], int ply, int threadID) {
1861 assert(ply >= 0 && ply < PLY_MAX);
1862 assert(threadID >= 0 && threadID < TM.active_threads());
1864 TM.incrementNodeCounter(threadID);
1869 if (NodesSincePoll >= NodesBetweenPolls)
1876 ss[ply + 2].initKillers();
1880 // update_pv() is called whenever a search returns a value > alpha.
1881 // It updates the PV in the SearchStack object corresponding to the
1884 void update_pv(SearchStack ss[], int ply) {
1886 assert(ply >= 0 && ply < PLY_MAX);
1890 ss[ply].pv[ply] = ss[ply].currentMove;
1892 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1893 ss[ply].pv[p] = ss[ply + 1].pv[p];
1895 ss[ply].pv[p] = MOVE_NONE;
1899 // sp_update_pv() is a variant of update_pv for use at split points. The
1900 // difference between the two functions is that sp_update_pv also updates
1901 // the PV at the parent node.
1903 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
1905 assert(ply >= 0 && ply < PLY_MAX);
1909 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
1911 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1912 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
1914 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
1918 // connected_moves() tests whether two moves are 'connected' in the sense
1919 // that the first move somehow made the second move possible (for instance
1920 // if the moving piece is the same in both moves). The first move is assumed
1921 // to be the move that was made to reach the current position, while the
1922 // second move is assumed to be a move from the current position.
1924 bool connected_moves(const Position& pos, Move m1, Move m2) {
1926 Square f1, t1, f2, t2;
1929 assert(move_is_ok(m1));
1930 assert(move_is_ok(m2));
1932 if (m2 == MOVE_NONE)
1935 // Case 1: The moving piece is the same in both moves
1941 // Case 2: The destination square for m2 was vacated by m1
1947 // Case 3: Moving through the vacated square
1948 if ( piece_is_slider(pos.piece_on(f2))
1949 && bit_is_set(squares_between(f2, t2), f1))
1952 // Case 4: The destination square for m2 is defended by the moving piece in m1
1953 p = pos.piece_on(t1);
1954 if (bit_is_set(pos.attacks_from(p, t1), t2))
1957 // Case 5: Discovered check, checking piece is the piece moved in m1
1958 if ( piece_is_slider(p)
1959 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1960 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1962 // discovered_check_candidates() works also if the Position's side to
1963 // move is the opposite of the checking piece.
1964 Color them = opposite_color(pos.side_to_move());
1965 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1967 if (bit_is_set(dcCandidates, f2))
1974 // value_is_mate() checks if the given value is a mate one
1975 // eventually compensated for the ply.
1977 bool value_is_mate(Value value) {
1979 assert(abs(value) <= VALUE_INFINITE);
1981 return value <= value_mated_in(PLY_MAX)
1982 || value >= value_mate_in(PLY_MAX);
1986 // move_is_killer() checks if the given move is among the
1987 // killer moves of that ply.
1989 bool move_is_killer(Move m, const SearchStack& ss) {
1991 const Move* k = ss.killers;
1992 for (int i = 0; i < KILLER_MAX; i++, k++)
2000 // extension() decides whether a move should be searched with normal depth,
2001 // or with extended depth. Certain classes of moves (checking moves, in
2002 // particular) are searched with bigger depth than ordinary moves and in
2003 // any case are marked as 'dangerous'. Note that also if a move is not
2004 // extended, as example because the corresponding UCI option is set to zero,
2005 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2007 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2008 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2010 assert(m != MOVE_NONE);
2012 Depth result = Depth(0);
2013 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2018 result += CheckExtension[pvNode];
2021 result += SingleEvasionExtension[pvNode];
2024 result += MateThreatExtension[pvNode];
2027 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2029 Color c = pos.side_to_move();
2030 if (relative_rank(c, move_to(m)) == RANK_7)
2032 result += PawnPushTo7thExtension[pvNode];
2035 if (pos.pawn_is_passed(c, move_to(m)))
2037 result += PassedPawnExtension[pvNode];
2042 if ( captureOrPromotion
2043 && pos.type_of_piece_on(move_to(m)) != PAWN
2044 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2045 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2046 && !move_is_promotion(m)
2049 result += PawnEndgameExtension[pvNode];
2054 && captureOrPromotion
2055 && pos.type_of_piece_on(move_to(m)) != PAWN
2056 && pos.see_sign(m) >= 0)
2062 return Min(result, OnePly);
2066 // ok_to_do_nullmove() looks at the current position and decides whether
2067 // doing a 'null move' should be allowed. In order to avoid zugzwang
2068 // problems, null moves are not allowed when the side to move has very
2069 // little material left. Currently, the test is a bit too simple: Null
2070 // moves are avoided only when the side to move has only pawns left.
2071 // It's probably a good idea to avoid null moves in at least some more
2072 // complicated endgames, e.g. KQ vs KR. FIXME
2074 bool ok_to_do_nullmove(const Position& pos) {
2076 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2080 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2081 // non-tactical moves late in the move list close to the leaves are
2082 // candidates for pruning.
2084 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2086 assert(move_is_ok(m));
2087 assert(threat == MOVE_NONE || move_is_ok(threat));
2088 assert(!pos.move_is_check(m));
2089 assert(!pos.move_is_capture_or_promotion(m));
2090 assert(!pos.move_is_passed_pawn_push(m));
2092 Square mfrom, mto, tfrom, tto;
2094 // Prune if there isn't any threat move
2095 if (threat == MOVE_NONE)
2098 mfrom = move_from(m);
2100 tfrom = move_from(threat);
2101 tto = move_to(threat);
2103 // Case 1: Don't prune moves which move the threatened piece
2107 // Case 2: If the threatened piece has value less than or equal to the
2108 // value of the threatening piece, don't prune move which defend it.
2109 if ( pos.move_is_capture(threat)
2110 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2111 || pos.type_of_piece_on(tfrom) == KING)
2112 && pos.move_attacks_square(m, tto))
2115 // Case 3: If the moving piece in the threatened move is a slider, don't
2116 // prune safe moves which block its ray.
2117 if ( piece_is_slider(pos.piece_on(tfrom))
2118 && bit_is_set(squares_between(tfrom, tto), mto)
2119 && pos.see_sign(m) >= 0)
2126 // ok_to_use_TT() returns true if a transposition table score
2127 // can be used at a given point in search.
2129 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2131 Value v = value_from_tt(tte->value(), ply);
2133 return ( tte->depth() >= depth
2134 || v >= Max(value_mate_in(PLY_MAX), beta)
2135 || v < Min(value_mated_in(PLY_MAX), beta))
2137 && ( (is_lower_bound(tte->type()) && v >= beta)
2138 || (is_upper_bound(tte->type()) && v < beta));
2142 // refine_eval() returns the transposition table score if
2143 // possible otherwise falls back on static position evaluation.
2145 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2150 Value v = value_from_tt(tte->value(), ply);
2152 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2153 || (is_upper_bound(tte->type()) && v < defaultEval))
2160 // update_history() registers a good move that produced a beta-cutoff
2161 // in history and marks as failures all the other moves of that ply.
2163 void update_history(const Position& pos, Move move, Depth depth,
2164 Move movesSearched[], int moveCount) {
2168 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2170 for (int i = 0; i < moveCount - 1; i++)
2172 m = movesSearched[i];
2176 if (!pos.move_is_capture_or_promotion(m))
2177 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2182 // update_killers() add a good move that produced a beta-cutoff
2183 // among the killer moves of that ply.
2185 void update_killers(Move m, SearchStack& ss) {
2187 if (m == ss.killers[0])
2190 for (int i = KILLER_MAX - 1; i > 0; i--)
2191 ss.killers[i] = ss.killers[i - 1];
2197 // update_gains() updates the gains table of a non-capture move given
2198 // the static position evaluation before and after the move.
2200 void update_gains(const Position& pos, Move m, Value before, Value after) {
2203 && before != VALUE_NONE
2204 && after != VALUE_NONE
2205 && pos.captured_piece() == NO_PIECE_TYPE
2206 && !move_is_castle(m)
2207 && !move_is_promotion(m))
2208 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2212 // current_search_time() returns the number of milliseconds which have passed
2213 // since the beginning of the current search.
2215 int current_search_time() {
2217 return get_system_time() - SearchStartTime;
2221 // nps() computes the current nodes/second count.
2225 int t = current_search_time();
2226 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2230 // poll() performs two different functions: It polls for user input, and it
2231 // looks at the time consumed so far and decides if it's time to abort the
2236 static int lastInfoTime;
2237 int t = current_search_time();
2242 // We are line oriented, don't read single chars
2243 std::string command;
2245 if (!std::getline(std::cin, command))
2248 if (command == "quit")
2251 PonderSearch = false;
2255 else if (command == "stop")
2258 PonderSearch = false;
2260 else if (command == "ponderhit")
2264 // Print search information
2268 else if (lastInfoTime > t)
2269 // HACK: Must be a new search where we searched less than
2270 // NodesBetweenPolls nodes during the first second of search.
2273 else if (t - lastInfoTime >= 1000)
2280 if (dbg_show_hit_rate)
2281 dbg_print_hit_rate();
2283 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2284 << " time " << t << " hashfull " << TT.full() << endl;
2287 // Should we stop the search?
2291 bool stillAtFirstMove = FirstRootMove
2292 && !AspirationFailLow
2293 && t > MaxSearchTime + ExtraSearchTime;
2295 bool noMoreTime = t > AbsoluteMaxSearchTime
2296 || stillAtFirstMove;
2298 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2299 || (ExactMaxTime && t >= ExactMaxTime)
2300 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2305 // ponderhit() is called when the program is pondering (i.e. thinking while
2306 // it's the opponent's turn to move) in order to let the engine know that
2307 // it correctly predicted the opponent's move.
2311 int t = current_search_time();
2312 PonderSearch = false;
2314 bool stillAtFirstMove = FirstRootMove
2315 && !AspirationFailLow
2316 && t > MaxSearchTime + ExtraSearchTime;
2318 bool noMoreTime = t > AbsoluteMaxSearchTime
2319 || stillAtFirstMove;
2321 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2326 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2328 void init_ss_array(SearchStack ss[]) {
2330 for (int i = 0; i < 3; i++)
2333 ss[i].initKillers();
2338 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2339 // while the program is pondering. The point is to work around a wrinkle in
2340 // the UCI protocol: When pondering, the engine is not allowed to give a
2341 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2342 // We simply wait here until one of these commands is sent, and return,
2343 // after which the bestmove and pondermove will be printed (in id_loop()).
2345 void wait_for_stop_or_ponderhit() {
2347 std::string command;
2351 if (!std::getline(std::cin, command))
2354 if (command == "quit")
2359 else if (command == "ponderhit" || command == "stop")
2365 // print_pv_info() prints to standard output and eventually to log file information on
2366 // the current PV line. It is called at each iteration or after a new pv is found.
2368 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2370 cout << "info depth " << Iteration
2371 << " score " << value_to_string(value)
2372 << ((value >= beta) ? " lowerbound" :
2373 ((value <= alpha)? " upperbound" : ""))
2374 << " time " << current_search_time()
2375 << " nodes " << TM.nodes_searched()
2379 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2380 cout << ss[0].pv[j] << " ";
2386 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2387 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2389 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2390 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2395 // init_thread() is the function which is called when a new thread is
2396 // launched. It simply calls the idle_loop() function with the supplied
2397 // threadID. There are two versions of this function; one for POSIX
2398 // threads and one for Windows threads.
2400 #if !defined(_MSC_VER)
2402 void* init_thread(void *threadID) {
2404 TM.idle_loop(*(int*)threadID, NULL);
2410 DWORD WINAPI init_thread(LPVOID threadID) {
2412 TM.idle_loop(*(int*)threadID, NULL);
2419 /// The ThreadsManager class
2421 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2422 // get_beta_counters() are getters/setters for the per thread
2423 // counters used to sort the moves at root.
2425 void ThreadsManager::resetNodeCounters() {
2427 for (int i = 0; i < MAX_THREADS; i++)
2428 threads[i].nodes = 0ULL;
2431 void ThreadsManager::resetBetaCounters() {
2433 for (int i = 0; i < MAX_THREADS; i++)
2434 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2437 int64_t ThreadsManager::nodes_searched() const {
2439 int64_t result = 0ULL;
2440 for (int i = 0; i < ActiveThreads; i++)
2441 result += threads[i].nodes;
2446 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2449 for (int i = 0; i < MAX_THREADS; i++)
2451 our += threads[i].betaCutOffs[us];
2452 their += threads[i].betaCutOffs[opposite_color(us)];
2457 // idle_loop() is where the threads are parked when they have no work to do.
2458 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2459 // object for which the current thread is the master.
2461 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2463 assert(threadID >= 0 && threadID < MAX_THREADS);
2467 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2468 // master should exit as last one.
2469 if (AllThreadsShouldExit)
2472 threads[threadID].state = THREAD_TERMINATED;
2476 // If we are not thinking, wait for a condition to be signaled
2477 // instead of wasting CPU time polling for work.
2478 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2481 assert(threadID != 0);
2482 threads[threadID].state = THREAD_SLEEPING;
2484 #if !defined(_MSC_VER)
2485 lock_grab(&WaitLock);
2486 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2487 pthread_cond_wait(&WaitCond, &WaitLock);
2488 lock_release(&WaitLock);
2490 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2494 // If thread has just woken up, mark it as available
2495 if (threads[threadID].state == THREAD_SLEEPING)
2496 threads[threadID].state = THREAD_AVAILABLE;
2498 // If this thread has been assigned work, launch a search
2499 if (threads[threadID].state == THREAD_WORKISWAITING)
2501 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2503 threads[threadID].state = THREAD_SEARCHING;
2505 if (threads[threadID].splitPoint->pvNode)
2506 sp_search_pv(threads[threadID].splitPoint, threadID);
2508 sp_search(threads[threadID].splitPoint, threadID);
2510 assert(threads[threadID].state == THREAD_SEARCHING);
2512 threads[threadID].state = THREAD_AVAILABLE;
2515 // If this thread is the master of a split point and all threads have
2516 // finished their work at this split point, return from the idle loop.
2517 if (sp && sp->cpus == 0)
2519 // Because sp->cpus is decremented under lock protection,
2520 // be sure sp->lock has been released before to proceed.
2521 lock_grab(&(sp->lock));
2522 lock_release(&(sp->lock));
2524 assert(threads[threadID].state == THREAD_AVAILABLE);
2526 threads[threadID].state = THREAD_SEARCHING;
2533 // init_threads() is called during startup. It launches all helper threads,
2534 // and initializes the split point stack and the global locks and condition
2537 void ThreadsManager::init_threads() {
2542 #if !defined(_MSC_VER)
2543 pthread_t pthread[1];
2546 // Initialize global locks
2547 lock_init(&MPLock, NULL);
2548 lock_init(&WaitLock, NULL);
2550 #if !defined(_MSC_VER)
2551 pthread_cond_init(&WaitCond, NULL);
2553 for (i = 0; i < MAX_THREADS; i++)
2554 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2557 // Initialize SplitPointStack locks
2558 for (i = 0; i < MAX_THREADS; i++)
2559 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2561 SplitPointStack[i][j].parent = NULL;
2562 lock_init(&(SplitPointStack[i][j].lock), NULL);
2565 // Will be set just before program exits to properly end the threads
2566 AllThreadsShouldExit = false;
2568 // Threads will be put to sleep as soon as created
2569 AllThreadsShouldSleep = true;
2571 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2573 threads[0].state = THREAD_SEARCHING;
2574 for (i = 1; i < MAX_THREADS; i++)
2575 threads[i].state = THREAD_AVAILABLE;
2577 // Launch the helper threads
2578 for (i = 1; i < MAX_THREADS; i++)
2581 #if !defined(_MSC_VER)
2582 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2584 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2589 cout << "Failed to create thread number " << i << endl;
2590 Application::exit_with_failure();
2593 // Wait until the thread has finished launching and is gone to sleep
2594 while (threads[i].state != THREAD_SLEEPING) {}
2599 // exit_threads() is called when the program exits. It makes all the
2600 // helper threads exit cleanly.
2602 void ThreadsManager::exit_threads() {
2604 ActiveThreads = MAX_THREADS; // HACK
2605 AllThreadsShouldSleep = true; // HACK
2606 wake_sleeping_threads();
2608 // This makes the threads to exit idle_loop()
2609 AllThreadsShouldExit = true;
2611 // Wait for thread termination
2612 for (int i = 1; i < MAX_THREADS; i++)
2613 while (threads[i].state != THREAD_TERMINATED);
2615 // Now we can safely destroy the locks
2616 for (int i = 0; i < MAX_THREADS; i++)
2617 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2618 lock_destroy(&(SplitPointStack[i][j].lock));
2620 lock_destroy(&WaitLock);
2621 lock_destroy(&MPLock);
2625 // thread_should_stop() checks whether the thread should stop its search.
2626 // This can happen if a beta cutoff has occurred in the thread's currently
2627 // active split point, or in some ancestor of the current split point.
2629 bool ThreadsManager::thread_should_stop(int threadID) const {
2631 assert(threadID >= 0 && threadID < ActiveThreads);
2635 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2640 // thread_is_available() checks whether the thread with threadID "slave" is
2641 // available to help the thread with threadID "master" at a split point. An
2642 // obvious requirement is that "slave" must be idle. With more than two
2643 // threads, this is not by itself sufficient: If "slave" is the master of
2644 // some active split point, it is only available as a slave to the other
2645 // threads which are busy searching the split point at the top of "slave"'s
2646 // split point stack (the "helpful master concept" in YBWC terminology).
2648 bool ThreadsManager::thread_is_available(int slave, int master) const {
2650 assert(slave >= 0 && slave < ActiveThreads);
2651 assert(master >= 0 && master < ActiveThreads);
2652 assert(ActiveThreads > 1);
2654 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2657 // Make a local copy to be sure doesn't change under our feet
2658 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2660 if (localActiveSplitPoints == 0)
2661 // No active split points means that the thread is available as
2662 // a slave for any other thread.
2665 if (ActiveThreads == 2)
2668 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2669 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2670 // could have been set to 0 by another thread leading to an out of bound access.
2671 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2678 // available_thread_exists() tries to find an idle thread which is available as
2679 // a slave for the thread with threadID "master".
2681 bool ThreadsManager::available_thread_exists(int master) const {
2683 assert(master >= 0 && master < ActiveThreads);
2684 assert(ActiveThreads > 1);
2686 for (int i = 0; i < ActiveThreads; i++)
2687 if (thread_is_available(i, master))
2694 // split() does the actual work of distributing the work at a node between
2695 // several threads at PV nodes. If it does not succeed in splitting the
2696 // node (because no idle threads are available, or because we have no unused
2697 // split point objects), the function immediately returns false. If
2698 // splitting is possible, a SplitPoint object is initialized with all the
2699 // data that must be copied to the helper threads (the current position and
2700 // search stack, alpha, beta, the search depth, etc.), and we tell our
2701 // helper threads that they have been assigned work. This will cause them
2702 // to instantly leave their idle loops and call sp_search_pv(). When all
2703 // threads have returned from sp_search_pv (or, equivalently, when
2704 // splitPoint->cpus becomes 0), split() returns true.
2706 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2707 Value* alpha, const Value beta, Value* bestValue,
2708 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2711 assert(sstck != NULL);
2712 assert(ply >= 0 && ply < PLY_MAX);
2713 assert(*bestValue >= -VALUE_INFINITE);
2714 assert( ( pvNode && *bestValue <= *alpha)
2715 || (!pvNode && *bestValue < beta ));
2716 assert(!pvNode || *alpha < beta);
2717 assert(beta <= VALUE_INFINITE);
2718 assert(depth > Depth(0));
2719 assert(master >= 0 && master < ActiveThreads);
2720 assert(ActiveThreads > 1);
2722 SplitPoint* splitPoint;
2726 // If no other thread is available to help us, or if we have too many
2727 // active split points, don't split.
2728 if ( !available_thread_exists(master)
2729 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2731 lock_release(&MPLock);
2735 // Pick the next available split point object from the split point stack
2736 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2738 // Initialize the split point object
2739 splitPoint->parent = threads[master].splitPoint;
2740 splitPoint->stopRequest = false;
2741 splitPoint->ply = ply;
2742 splitPoint->depth = depth;
2743 splitPoint->mateThreat = mateThreat;
2744 splitPoint->alpha = *alpha;
2745 splitPoint->beta = beta;
2746 splitPoint->pvNode = pvNode;
2747 splitPoint->bestValue = *bestValue;
2748 splitPoint->master = master;
2749 splitPoint->mp = mp;
2750 splitPoint->moves = *moves;
2751 splitPoint->cpus = 1;
2752 splitPoint->pos = &p;
2753 splitPoint->parentSstack = sstck;
2754 for (int i = 0; i < ActiveThreads; i++)
2755 splitPoint->slaves[i] = 0;
2757 threads[master].splitPoint = splitPoint;
2758 threads[master].activeSplitPoints++;
2760 // If we are here it means we are not available
2761 assert(threads[master].state != THREAD_AVAILABLE);
2763 // Allocate available threads setting state to THREAD_BOOKED
2764 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2765 if (thread_is_available(i, master))
2767 threads[i].state = THREAD_BOOKED;
2768 threads[i].splitPoint = splitPoint;
2769 splitPoint->slaves[i] = 1;
2773 assert(splitPoint->cpus > 1);
2775 // We can release the lock because slave threads are already booked and master is not available
2776 lock_release(&MPLock);
2778 // Tell the threads that they have work to do. This will make them leave
2779 // their idle loop. But before copy search stack tail for each thread.
2780 for (int i = 0; i < ActiveThreads; i++)
2781 if (i == master || splitPoint->slaves[i])
2783 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2785 assert(i == master || threads[i].state == THREAD_BOOKED);
2787 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2790 // Everything is set up. The master thread enters the idle loop, from
2791 // which it will instantly launch a search, because its state is
2792 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2793 // idle loop, which means that the main thread will return from the idle
2794 // loop when all threads have finished their work at this split point
2795 // (i.e. when splitPoint->cpus == 0).
2796 idle_loop(master, splitPoint);
2798 // We have returned from the idle loop, which means that all threads are
2799 // finished. Update alpha and bestValue, and return.
2802 *alpha = splitPoint->alpha;
2803 *bestValue = splitPoint->bestValue;
2804 threads[master].activeSplitPoints--;
2805 threads[master].splitPoint = splitPoint->parent;
2807 lock_release(&MPLock);
2812 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2813 // to start a new search from the root.
2815 void ThreadsManager::wake_sleeping_threads() {
2817 assert(AllThreadsShouldSleep);
2818 assert(ActiveThreads > 0);
2820 AllThreadsShouldSleep = false;
2822 if (ActiveThreads == 1)
2825 #if !defined(_MSC_VER)
2826 pthread_mutex_lock(&WaitLock);
2827 pthread_cond_broadcast(&WaitCond);
2828 pthread_mutex_unlock(&WaitLock);
2830 for (int i = 1; i < MAX_THREADS; i++)
2831 SetEvent(SitIdleEvent[i]);
2837 // put_threads_to_sleep() makes all the threads go to sleep just before
2838 // to leave think(), at the end of the search. Threads should have already
2839 // finished the job and should be idle.
2841 void ThreadsManager::put_threads_to_sleep() {
2843 assert(!AllThreadsShouldSleep);
2845 // This makes the threads to go to sleep
2846 AllThreadsShouldSleep = true;
2849 /// The RootMoveList class
2851 // RootMoveList c'tor
2853 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2855 SearchStack ss[PLY_MAX_PLUS_2];
2856 MoveStack mlist[MaxRootMoves];
2858 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2860 // Generate all legal moves
2861 MoveStack* last = generate_moves(pos, mlist);
2863 // Add each move to the moves[] array
2864 for (MoveStack* cur = mlist; cur != last; cur++)
2866 bool includeMove = includeAllMoves;
2868 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2869 includeMove = (searchMoves[k] == cur->move);
2874 // Find a quick score for the move
2876 pos.do_move(cur->move, st);
2877 moves[count].move = cur->move;
2878 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2879 moves[count].pv[0] = cur->move;
2880 moves[count].pv[1] = MOVE_NONE;
2881 pos.undo_move(cur->move);
2888 // RootMoveList simple methods definitions
2890 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2892 moves[moveNum].nodes = nodes;
2893 moves[moveNum].cumulativeNodes += nodes;
2896 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2898 moves[moveNum].ourBeta = our;
2899 moves[moveNum].theirBeta = their;
2902 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2906 for (j = 0; pv[j] != MOVE_NONE; j++)
2907 moves[moveNum].pv[j] = pv[j];
2909 moves[moveNum].pv[j] = MOVE_NONE;
2913 // RootMoveList::sort() sorts the root move list at the beginning of a new
2916 void RootMoveList::sort() {
2918 sort_multipv(count - 1); // Sort all items
2922 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2923 // list by their scores and depths. It is used to order the different PVs
2924 // correctly in MultiPV mode.
2926 void RootMoveList::sort_multipv(int n) {
2930 for (i = 1; i <= n; i++)
2932 RootMove rm = moves[i];
2933 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2934 moves[j] = moves[j - 1];