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 ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
220 template <NodeType PV>
221 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
223 // Common adjustments
225 // Search depth at iteration 1
226 const Depth InitialDepth = OnePly;
228 // Easy move margin. An easy move candidate must be at least this much
229 // better than the second best move.
230 const Value EasyMoveMargin = Value(0x200);
232 // Last seconds noise filtering (LSN)
233 const bool UseLSNFiltering = true;
234 const int LSNTime = 4000; // In milliseconds
235 const Value LSNValue = value_from_centipawns(200);
236 bool loseOnTime = false;
244 // Scores and number of times the best move changed for each iteration
245 Value ValueByIteration[PLY_MAX_PLUS_2];
246 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
248 // Search window management
254 // Time managment variables
255 int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
256 int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
257 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
258 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
262 std::ofstream LogFile;
264 // Multi-threads related variables
265 Depth MinimumSplitDepth;
266 int MaxThreadsPerSplitPoint;
269 // Node counters, used only by thread[0] but try to keep in different cache
270 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
272 int NodesBetweenPolls = 30000;
279 Value id_loop(const Position& pos, Move searchMoves[]);
280 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
282 template <NodeType PvNode>
283 Value search(Position& pos, SearchStack ss[], Value alpha, 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 ReductionMatrix[PV][i][j] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
555 ReductionMatrix[NonPV][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, false, 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 = reduction<PV>(depth, i - MultiPV + 2);
888 // Reduced depth non-pv search using alpha as upperbound
889 value = -search<NonPV>(pos, ss, -(alpha+1), -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<NonPV>(pos, ss, -(alpha+1), -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, false, 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 template <NodeType PvNode>
1027 Value search(Position& pos, SearchStack ss[], Value alpha, Value beta,
1028 Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove) {
1030 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1031 assert(beta > alpha && beta <= VALUE_INFINITE);
1032 assert(ply >= 0 && ply < PLY_MAX);
1033 assert(threadID >= 0 && threadID < TM.active_threads());
1035 Move movesSearched[256];
1040 Depth ext, newDepth;
1041 Value bestValue, value, oldAlpha;
1042 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
1043 bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
1044 bool mateThreat = false;
1046 refinedValue = bestValue = value = -VALUE_INFINITE;
1050 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1052 // Step 1. Initialize node and poll
1053 // Polling can abort search.
1054 init_node(ss, ply, threadID);
1056 // Step 2. Check for aborted search and immediate draw
1057 if (AbortSearch || TM.thread_should_stop(threadID))
1060 if (pos.is_draw() || ply >= PLY_MAX - 1)
1063 // Step 3. Mate distance pruning
1064 alpha = Max(value_mated_in(ply), alpha);
1065 beta = Min(value_mate_in(ply+1), beta);
1069 // Step 4. Transposition table lookup
1071 // We don't want the score of a partial search to overwrite a previous full search
1072 // TT value, so we use a different position key in case of an excluded move exists.
1073 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1075 tte = TT.retrieve(posKey);
1076 ttMove = (tte ? tte->move() : MOVE_NONE);
1078 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1079 // This is to avoid problems in the following areas:
1081 // * Repetition draw detection
1082 // * Fifty move rule detection
1083 // * Searching for a mate
1084 // * Printing of full PV line
1086 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1088 // Refresh tte entry to avoid aging
1089 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove);
1091 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1092 return value_from_tt(tte->value(), ply);
1095 // Step 5. Evaluate the position statically
1096 // At PV nodes we do this only to update gain statistics
1097 isCheck = pos.is_check();
1100 if (!PvNode && tte && (tte->type() & VALUE_TYPE_EVAL))
1101 ss[ply].eval = value_from_tt(tte->value(), ply);
1103 ss[ply].eval = evaluate(pos, ei, threadID);
1105 refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
1106 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1109 // Step 6. Razoring (is omitted in PV nodes)
1111 && refinedValue < beta - razor_margin(depth)
1112 && ttMove == MOVE_NONE
1113 && ss[ply - 1].currentMove != MOVE_NULL
1114 && depth < RazorDepth
1116 && !value_is_mate(beta)
1117 && !pos.has_pawn_on_7th(pos.side_to_move()))
1119 Value rbeta = beta - razor_margin(depth);
1120 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1122 // Logically we should return (v + razor_margin(depth)), but
1123 // surprisingly this did slightly weaker in tests.
1127 // Step 7. Static null move pruning (is omitted in PV nodes)
1128 // We're betting that the opponent doesn't have a move that will reduce
1129 // the score by more than futility_margin(depth) if we do a null move.
1132 && depth < RazorDepth
1134 && !value_is_mate(beta)
1135 && ok_to_do_nullmove(pos)
1136 && refinedValue >= beta + futility_margin(depth, 0))
1137 return refinedValue - futility_margin(depth, 0);
1139 // Step 8. Null move search with verification search (is omitted in PV nodes)
1140 // When we jump directly to qsearch() we do a null move only if static value is
1141 // at least beta. Otherwise we do a null move if static value is not more than
1142 // NullMoveMargin under beta.
1147 && !value_is_mate(beta)
1148 && ok_to_do_nullmove(pos)
1149 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
1151 ss[ply].currentMove = MOVE_NULL;
1153 // Null move dynamic reduction based on depth
1154 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1156 // Null move dynamic reduction based on value
1157 if (refinedValue - beta > PawnValueMidgame)
1160 pos.do_null_move(st);
1162 nullValue = -search<NonPV>(pos, ss, -beta, -alpha, depth-R*OnePly, ply+1, false, threadID);
1164 pos.undo_null_move();
1166 if (nullValue >= beta)
1168 // Do not return unproven mate scores
1169 if (nullValue >= value_mate_in(PLY_MAX))
1172 if (depth < 6 * OnePly)
1175 // Do zugzwang verification search
1176 Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply, false, threadID);
1180 // The null move failed low, which means that we may be faced with
1181 // some kind of threat. If the previous move was reduced, check if
1182 // the move that refuted the null move was somehow connected to the
1183 // move which was reduced. If a connection is found, return a fail
1184 // low score (which will cause the reduced move to fail high in the
1185 // parent node, which will trigger a re-search with full depth).
1186 if (nullValue == value_mated_in(ply + 2))
1189 ss[ply].threatMove = ss[ply + 1].currentMove;
1190 if ( depth < ThreatDepth
1191 && ss[ply - 1].reduction
1192 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1197 // Step 9. Internal iterative deepening
1198 // We have different rules for PV nodes and non-pv nodes
1200 && depth >= IIDDepthAtPVNodes
1201 && ttMove == MOVE_NONE)
1203 search<PV>(pos, ss, alpha, beta, depth-2*OnePly, ply, false, threadID);
1204 ttMove = ss[ply].pv[ply];
1205 tte = TT.retrieve(posKey);
1209 && depth >= IIDDepthAtNonPVNodes
1210 && ttMove == MOVE_NONE
1212 && ss[ply].eval >= beta - IIDMargin)
1214 search<NonPV>(pos, ss, alpha, beta, depth/2, ply, false, threadID);
1215 ttMove = ss[ply].pv[ply];
1216 tte = TT.retrieve(posKey);
1219 // Expensive mate threat detection (only for PV nodes)
1221 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1223 // Initialize a MovePicker object for the current position
1224 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], (PvNode ? -VALUE_INFINITE : beta));
1227 // Step 10. Loop through moves
1228 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1229 while ( bestValue < beta
1230 && (move = mp.get_next_move()) != MOVE_NONE
1231 && !TM.thread_should_stop(threadID))
1233 assert(move_is_ok(move));
1235 if (move == excludedMove)
1238 singleEvasion = (isCheck && mp.number_of_evasions() == 1);
1239 moveIsCheck = pos.move_is_check(move, ci);
1240 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1242 // Step 11. Decide the new search depth
1243 ext = extension(pos, move, PvNode, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1245 // Singular extension search. We extend the TT move if its value is much better than
1246 // its siblings. To verify this we do a reduced search on all the other moves but the
1247 // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
1248 if ( depth >= SingularExtensionDepth[PvNode]
1250 && move == tte->move()
1251 && !excludedMove // Do not allow recursive singular extension search
1253 && is_lower_bound(tte->type())
1254 && tte->depth() >= depth - 3 * OnePly)
1256 Value ttValue = value_from_tt(tte->value(), ply);
1258 if (abs(ttValue) < VALUE_KNOWN_WIN)
1260 Value excValue = search<NonPV>(pos, ss, ttValue - SingularExtensionMargin - 1, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
1262 if (excValue < ttValue - SingularExtensionMargin)
1267 newDepth = depth - OnePly + ext;
1269 // Update current move (this must be done after singular extension search)
1270 movesSearched[moveCount++] = ss[ply].currentMove = move;
1272 // Step 12. Futility pruning (is omitted in PV nodes)
1276 && !captureOrPromotion
1277 && !move_is_castle(move)
1280 // Move count based pruning
1281 if ( moveCount >= futility_move_count(depth)
1282 && ok_to_prune(pos, move, ss[ply].threatMove)
1283 && bestValue > value_mated_in(PLY_MAX))
1286 // Value based pruning
1287 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
1288 futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
1289 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1291 if (futilityValueScaled < beta)
1293 if (futilityValueScaled > bestValue)
1294 bestValue = futilityValueScaled;
1299 // Step 13. Make the move
1300 pos.do_move(move, st, ci, moveIsCheck);
1302 // Step extra. pv search (only in PV nodes)
1303 // The first move in list is the expected PV
1304 if (PvNode && moveCount == 1)
1305 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1308 // Step 14. Reduced search
1309 // if the move fails high will be re-searched at full depth.
1310 bool doFullDepthSearch = true;
1312 if ( depth >= 3 * OnePly
1314 && !captureOrPromotion
1315 && !move_is_castle(move)
1316 && !move_is_killer(move, ss[ply]))
1318 ss[ply].reduction = reduction<PvNode>(depth, moveCount);
1319 if (ss[ply].reduction)
1321 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
1322 doFullDepthSearch = (value > alpha);
1326 // Step 15. Full depth search
1327 if (doFullDepthSearch)
1329 ss[ply].reduction = Depth(0);
1330 value = -search<NonPV>(pos, ss, -(alpha+1), -alpha, newDepth, ply+1, true, threadID);
1332 // Step extra. pv search (only in PV nodes)
1333 if (PvNode && value > alpha && value < beta)
1334 value = -search<PV>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
1338 // Step 16. Undo move
1339 pos.undo_move(move);
1341 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1343 // Step 17. Check for new best move
1344 if (value > bestValue)
1351 if (value == value_mate_in(ply + 1))
1352 ss[ply].mateKiller = move;
1356 // Step 18. Check for split
1357 if ( TM.active_threads() > 1
1359 && depth >= MinimumSplitDepth
1361 && TM.available_thread_exists(threadID)
1363 && !TM.thread_should_stop(threadID)
1364 && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
1365 depth, mateThreat, &moveCount, &mp, threadID, PvNode))
1369 // Step 19. Check for mate and stalemate
1370 // All legal moves have been searched and if there are
1371 // no legal moves, it must be mate or stalemate.
1372 // If one move was excluded return fail low score.
1374 return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1376 // Step 20. Update tables
1377 // If the search is not aborted, update the transposition table,
1378 // history counters, and killer moves.
1379 if (AbortSearch || TM.thread_should_stop(threadID))
1382 if (bestValue <= oldAlpha)
1383 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1385 else if (bestValue >= beta)
1387 TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1388 move = ss[ply].pv[ply];
1389 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1390 if (!pos.move_is_capture_or_promotion(move))
1392 update_history(pos, move, depth, movesSearched, moveCount);
1393 update_killers(move, ss[ply]);
1397 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1399 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1405 // qsearch() is the quiescence search function, which is called by the main
1406 // search function when the remaining depth is zero (or, to be more precise,
1407 // less than OnePly).
1409 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1410 Depth depth, int ply, int threadID) {
1412 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1413 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1415 assert(ply >= 0 && ply < PLY_MAX);
1416 assert(threadID >= 0 && threadID < TM.active_threads());
1421 Value staticValue, bestValue, value, futilityBase, futilityValue;
1422 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1423 const TTEntry* tte = NULL;
1425 bool pvNode = (beta - alpha != 1);
1426 Value oldAlpha = alpha;
1428 // Initialize, and make an early exit in case of an aborted search,
1429 // an instant draw, maximum ply reached, etc.
1430 init_node(ss, ply, threadID);
1432 // After init_node() that calls poll()
1433 if (AbortSearch || TM.thread_should_stop(threadID))
1436 if (pos.is_draw() || ply >= PLY_MAX - 1)
1439 // Transposition table lookup. At PV nodes, we don't use the TT for
1440 // pruning, but only for move ordering.
1441 tte = TT.retrieve(pos.get_key());
1442 ttMove = (tte ? tte->move() : MOVE_NONE);
1444 if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1446 assert(tte->type() != VALUE_TYPE_EVAL);
1448 ss[ply].currentMove = ttMove; // Can be MOVE_NONE
1449 return value_from_tt(tte->value(), ply);
1452 isCheck = pos.is_check();
1454 // Evaluate the position statically
1456 staticValue = -VALUE_INFINITE;
1457 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1458 staticValue = value_from_tt(tte->value(), ply);
1460 staticValue = evaluate(pos, ei, threadID);
1464 ss[ply].eval = staticValue;
1465 update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
1468 // Initialize "stand pat score", and return it immediately if it is
1470 bestValue = staticValue;
1472 if (bestValue >= beta)
1474 // Store the score to avoid a future costly evaluation() call
1475 if (!isCheck && !tte && ei.kingDanger[pos.side_to_move()] == 0)
1476 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1481 if (bestValue > alpha)
1484 // If we are near beta then try to get a cutoff pushing checks a bit further
1485 bool deepChecks = (depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8);
1487 // Initialize a MovePicker object for the current position, and prepare
1488 // to search the moves. Because the depth is <= 0 here, only captures,
1489 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1490 // and we are near beta) will be generated.
1491 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1493 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1494 futilityBase = staticValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1496 // Loop through the moves until no moves remain or a beta cutoff occurs
1497 while ( alpha < beta
1498 && (move = mp.get_next_move()) != MOVE_NONE)
1500 assert(move_is_ok(move));
1502 moveIsCheck = pos.move_is_check(move, ci);
1504 // Update current move
1506 ss[ply].currentMove = move;
1514 && !move_is_promotion(move)
1515 && !pos.move_is_passed_pawn_push(move))
1517 futilityValue = futilityBase
1518 + pos.endgame_value_of_piece_on(move_to(move))
1519 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1521 if (futilityValue < alpha)
1523 if (futilityValue > bestValue)
1524 bestValue = futilityValue;
1529 // Detect blocking evasions that are candidate to be pruned
1530 evasionPrunable = isCheck
1531 && bestValue > value_mated_in(PLY_MAX)
1532 && !pos.move_is_capture(move)
1533 && pos.type_of_piece_on(move_from(move)) != KING
1534 && !pos.can_castle(pos.side_to_move());
1536 // Don't search moves with negative SEE values
1537 if ( (!isCheck || evasionPrunable)
1540 && !move_is_promotion(move)
1541 && pos.see_sign(move) < 0)
1544 // Make and search the move
1545 pos.do_move(move, st, ci, moveIsCheck);
1546 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1547 pos.undo_move(move);
1549 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1552 if (value > bestValue)
1563 // All legal moves have been searched. A special case: If we're in check
1564 // and no legal moves were found, it is checkmate.
1565 if (!moveCount && isCheck) // Mate!
1566 return value_mated_in(ply);
1568 // Update transposition table
1569 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1570 if (bestValue <= oldAlpha)
1572 // If bestValue isn't changed it means it is still the static evaluation
1573 // of the node, so keep this info to avoid a future evaluation() call.
1574 ValueType type = (bestValue == staticValue && !ei.kingDanger[pos.side_to_move()] ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1575 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1577 else if (bestValue >= beta)
1579 move = ss[ply].pv[ply];
1580 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1582 // Update killers only for good checking moves
1583 if (!pos.move_is_capture_or_promotion(move))
1584 update_killers(move, ss[ply]);
1587 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);
1589 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1595 // sp_search() is used to search from a split point. This function is called
1596 // by each thread working at the split point. It is similar to the normal
1597 // search() function, but simpler. Because we have already probed the hash
1598 // table, done a null move search, and searched the first move before
1599 // splitting, we don't have to repeat all this work in sp_search(). We
1600 // also don't need to store anything to the hash table here: This is taken
1601 // care of after we return from the split point.
1603 void sp_search(SplitPoint* sp, int threadID) {
1605 assert(threadID >= 0 && threadID < TM.active_threads());
1606 assert(TM.active_threads() > 1);
1610 Depth ext, newDepth;
1611 Value value, futilityValueScaled;
1612 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1614 value = -VALUE_INFINITE;
1616 Position pos(*sp->pos);
1618 SearchStack* ss = sp->sstack[threadID];
1619 isCheck = pos.is_check();
1621 // Step 10. Loop through moves
1622 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1623 lock_grab(&(sp->lock));
1625 while ( sp->bestValue < sp->beta
1626 && !TM.thread_should_stop(threadID)
1627 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1629 moveCount = ++sp->moves;
1630 lock_release(&(sp->lock));
1632 assert(move_is_ok(move));
1634 moveIsCheck = pos.move_is_check(move, ci);
1635 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1637 // Step 11. Decide the new search depth
1638 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1639 newDepth = sp->depth - OnePly + ext;
1641 // Update current move
1642 ss[sp->ply].currentMove = move;
1644 // Step 12. Futility pruning
1647 && !captureOrPromotion
1648 && !move_is_castle(move))
1650 // Move count based pruning
1651 if ( moveCount >= futility_move_count(sp->depth)
1652 && ok_to_prune(pos, move, ss[sp->ply].threatMove)
1653 && sp->bestValue > value_mated_in(PLY_MAX))
1655 lock_grab(&(sp->lock));
1659 // Value based pruning
1660 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1661 futilityValueScaled = ss[sp->ply].eval + futility_margin(predictedDepth, moveCount)
1662 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1664 if (futilityValueScaled < sp->beta)
1666 lock_grab(&(sp->lock));
1668 if (futilityValueScaled > sp->bestValue)
1669 sp->bestValue = futilityValueScaled;
1674 // Step 13. Make the move
1675 pos.do_move(move, st, ci, moveIsCheck);
1677 // Step 14. Reduced search
1678 // if the move fails high will be re-searched at full depth.
1679 bool doFullDepthSearch = true;
1682 && !captureOrPromotion
1683 && !move_is_castle(move)
1684 && !move_is_killer(move, ss[sp->ply]))
1686 ss[sp->ply].reduction = reduction<NonPV>(sp->depth, moveCount);
1687 if (ss[sp->ply].reduction)
1689 value = -search<NonPV>(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1690 doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
1694 // Step 15. Full depth search
1695 if (doFullDepthSearch)
1697 ss[sp->ply].reduction = Depth(0);
1698 value = -search<NonPV>(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth, sp->ply+1, true, threadID);
1701 // Step 16. Undo move
1702 pos.undo_move(move);
1704 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1706 // Step 17. Check for new best move
1707 lock_grab(&(sp->lock));
1709 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1711 sp->bestValue = value;
1712 if (sp->bestValue >= sp->beta)
1714 sp->stopRequest = true;
1715 sp_update_pv(sp->parentSstack, ss, sp->ply);
1720 /* Here we have the lock still grabbed */
1722 sp->slaves[threadID] = 0;
1725 lock_release(&(sp->lock));
1729 // sp_search_pv() is used to search from a PV split point. This function
1730 // is called by each thread working at the split point. It is similar to
1731 // the normal search_pv() function, but simpler. Because we have already
1732 // probed the hash table and searched the first move before splitting, we
1733 // don't have to repeat all this work in sp_search_pv(). We also don't
1734 // need to store anything to the hash table here: This is taken care of
1735 // after we return from the split point.
1737 void sp_search_pv(SplitPoint* sp, int threadID) {
1739 assert(threadID >= 0 && threadID < TM.active_threads());
1740 assert(TM.active_threads() > 1);
1744 Depth ext, newDepth;
1746 bool moveIsCheck, captureOrPromotion, dangerous;
1748 value = -VALUE_INFINITE;
1750 Position pos(*sp->pos);
1752 SearchStack* ss = sp->sstack[threadID];
1754 // Step 10. Loop through moves
1755 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1756 lock_grab(&(sp->lock));
1758 while ( sp->alpha < sp->beta
1759 && !TM.thread_should_stop(threadID)
1760 && (move = sp->mp->get_next_move()) != MOVE_NONE)
1762 moveCount = ++sp->moves;
1763 lock_release(&(sp->lock));
1765 assert(move_is_ok(move));
1767 moveIsCheck = pos.move_is_check(move, ci);
1768 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1770 // Step 11. Decide the new search depth
1771 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1772 newDepth = sp->depth - OnePly + ext;
1774 // Update current move
1775 ss[sp->ply].currentMove = move;
1777 // Step 12. Futility pruning (is omitted in PV nodes)
1779 // Step 13. Make the move
1780 pos.do_move(move, st, ci, moveIsCheck);
1782 // Step 14. Reduced search
1783 // if the move fails high will be re-searched at full depth.
1784 bool doFullDepthSearch = true;
1787 && !captureOrPromotion
1788 && !move_is_castle(move)
1789 && !move_is_killer(move, ss[sp->ply]))
1791 ss[sp->ply].reduction = reduction<PV>(sp->depth, moveCount);
1792 if (ss[sp->ply].reduction)
1794 Value localAlpha = sp->alpha;
1795 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
1796 doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
1800 // Step 15. Full depth search
1801 if (doFullDepthSearch)
1803 Value localAlpha = sp->alpha;
1804 ss[sp->ply].reduction = Depth(0);
1805 value = -search<NonPV>(pos, ss, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1, true, threadID);
1807 if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
1809 // If another thread has failed high then sp->alpha has been increased
1810 // to be higher or equal then beta, if so, avoid to start a PV search.
1811 localAlpha = sp->alpha;
1812 if (localAlpha < sp->beta)
1813 value = -search<PV>(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, false, threadID);
1817 // Step 16. Undo move
1818 pos.undo_move(move);
1820 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1822 // Step 17. Check for new best move
1823 lock_grab(&(sp->lock));
1825 if (value > sp->bestValue && !TM.thread_should_stop(threadID))
1827 sp->bestValue = value;
1828 if (value > sp->alpha)
1830 // Ask threads to stop before to modify sp->alpha
1831 if (value >= sp->beta)
1832 sp->stopRequest = true;
1836 sp_update_pv(sp->parentSstack, ss, sp->ply);
1837 if (value == value_mate_in(sp->ply + 1))
1838 ss[sp->ply].mateKiller = move;
1843 /* Here we have the lock still grabbed */
1845 sp->slaves[threadID] = 0;
1848 lock_release(&(sp->lock));
1852 // init_node() is called at the beginning of all the search functions
1853 // (search() qsearch(), and so on) and initializes the
1854 // search stack object corresponding to the current node. Once every
1855 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1856 // for user input and checks whether it is time to stop the search.
1858 void init_node(SearchStack ss[], int ply, int threadID) {
1860 assert(ply >= 0 && ply < PLY_MAX);
1861 assert(threadID >= 0 && threadID < TM.active_threads());
1863 TM.incrementNodeCounter(threadID);
1868 if (NodesSincePoll >= NodesBetweenPolls)
1875 ss[ply + 2].initKillers();
1879 // update_pv() is called whenever a search returns a value > alpha.
1880 // It updates the PV in the SearchStack object corresponding to the
1883 void update_pv(SearchStack ss[], int ply) {
1885 assert(ply >= 0 && ply < PLY_MAX);
1889 ss[ply].pv[ply] = ss[ply].currentMove;
1891 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1892 ss[ply].pv[p] = ss[ply + 1].pv[p];
1894 ss[ply].pv[p] = MOVE_NONE;
1898 // sp_update_pv() is a variant of update_pv for use at split points. The
1899 // difference between the two functions is that sp_update_pv also updates
1900 // the PV at the parent node.
1902 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
1904 assert(ply >= 0 && ply < PLY_MAX);
1908 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
1910 for (p = ply + 1; ss[ply + 1].pv[p] != MOVE_NONE; p++)
1911 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply + 1].pv[p];
1913 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
1917 // connected_moves() tests whether two moves are 'connected' in the sense
1918 // that the first move somehow made the second move possible (for instance
1919 // if the moving piece is the same in both moves). The first move is assumed
1920 // to be the move that was made to reach the current position, while the
1921 // second move is assumed to be a move from the current position.
1923 bool connected_moves(const Position& pos, Move m1, Move m2) {
1925 Square f1, t1, f2, t2;
1928 assert(move_is_ok(m1));
1929 assert(move_is_ok(m2));
1931 if (m2 == MOVE_NONE)
1934 // Case 1: The moving piece is the same in both moves
1940 // Case 2: The destination square for m2 was vacated by m1
1946 // Case 3: Moving through the vacated square
1947 if ( piece_is_slider(pos.piece_on(f2))
1948 && bit_is_set(squares_between(f2, t2), f1))
1951 // Case 4: The destination square for m2 is defended by the moving piece in m1
1952 p = pos.piece_on(t1);
1953 if (bit_is_set(pos.attacks_from(p, t1), t2))
1956 // Case 5: Discovered check, checking piece is the piece moved in m1
1957 if ( piece_is_slider(p)
1958 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1959 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1961 // discovered_check_candidates() works also if the Position's side to
1962 // move is the opposite of the checking piece.
1963 Color them = opposite_color(pos.side_to_move());
1964 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1966 if (bit_is_set(dcCandidates, f2))
1973 // value_is_mate() checks if the given value is a mate one
1974 // eventually compensated for the ply.
1976 bool value_is_mate(Value value) {
1978 assert(abs(value) <= VALUE_INFINITE);
1980 return value <= value_mated_in(PLY_MAX)
1981 || value >= value_mate_in(PLY_MAX);
1985 // move_is_killer() checks if the given move is among the
1986 // killer moves of that ply.
1988 bool move_is_killer(Move m, const SearchStack& ss) {
1990 const Move* k = ss.killers;
1991 for (int i = 0; i < KILLER_MAX; i++, k++)
1999 // extension() decides whether a move should be searched with normal depth,
2000 // or with extended depth. Certain classes of moves (checking moves, in
2001 // particular) are searched with bigger depth than ordinary moves and in
2002 // any case are marked as 'dangerous'. Note that also if a move is not
2003 // extended, as example because the corresponding UCI option is set to zero,
2004 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2006 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2007 bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous) {
2009 assert(m != MOVE_NONE);
2011 Depth result = Depth(0);
2012 *dangerous = moveIsCheck | singleEvasion | mateThreat;
2017 result += CheckExtension[pvNode];
2020 result += SingleEvasionExtension[pvNode];
2023 result += MateThreatExtension[pvNode];
2026 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2028 Color c = pos.side_to_move();
2029 if (relative_rank(c, move_to(m)) == RANK_7)
2031 result += PawnPushTo7thExtension[pvNode];
2034 if (pos.pawn_is_passed(c, move_to(m)))
2036 result += PassedPawnExtension[pvNode];
2041 if ( captureOrPromotion
2042 && pos.type_of_piece_on(move_to(m)) != PAWN
2043 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2044 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2045 && !move_is_promotion(m)
2048 result += PawnEndgameExtension[pvNode];
2053 && captureOrPromotion
2054 && pos.type_of_piece_on(move_to(m)) != PAWN
2055 && pos.see_sign(m) >= 0)
2061 return Min(result, OnePly);
2065 // ok_to_do_nullmove() looks at the current position and decides whether
2066 // doing a 'null move' should be allowed. In order to avoid zugzwang
2067 // problems, null moves are not allowed when the side to move has very
2068 // little material left. Currently, the test is a bit too simple: Null
2069 // moves are avoided only when the side to move has only pawns left.
2070 // It's probably a good idea to avoid null moves in at least some more
2071 // complicated endgames, e.g. KQ vs KR. FIXME
2073 bool ok_to_do_nullmove(const Position& pos) {
2075 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2079 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2080 // non-tactical moves late in the move list close to the leaves are
2081 // candidates for pruning.
2083 bool ok_to_prune(const Position& pos, Move m, Move threat) {
2085 assert(move_is_ok(m));
2086 assert(threat == MOVE_NONE || move_is_ok(threat));
2087 assert(!pos.move_is_check(m));
2088 assert(!pos.move_is_capture_or_promotion(m));
2089 assert(!pos.move_is_passed_pawn_push(m));
2091 Square mfrom, mto, tfrom, tto;
2093 // Prune if there isn't any threat move
2094 if (threat == MOVE_NONE)
2097 mfrom = move_from(m);
2099 tfrom = move_from(threat);
2100 tto = move_to(threat);
2102 // Case 1: Don't prune moves which move the threatened piece
2106 // Case 2: If the threatened piece has value less than or equal to the
2107 // value of the threatening piece, don't prune move which defend it.
2108 if ( pos.move_is_capture(threat)
2109 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2110 || pos.type_of_piece_on(tfrom) == KING)
2111 && pos.move_attacks_square(m, tto))
2114 // Case 3: If the moving piece in the threatened move is a slider, don't
2115 // prune safe moves which block its ray.
2116 if ( piece_is_slider(pos.piece_on(tfrom))
2117 && bit_is_set(squares_between(tfrom, tto), mto)
2118 && pos.see_sign(m) >= 0)
2125 // ok_to_use_TT() returns true if a transposition table score
2126 // can be used at a given point in search.
2128 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2130 Value v = value_from_tt(tte->value(), ply);
2132 return ( tte->depth() >= depth
2133 || v >= Max(value_mate_in(PLY_MAX), beta)
2134 || v < Min(value_mated_in(PLY_MAX), beta))
2136 && ( (is_lower_bound(tte->type()) && v >= beta)
2137 || (is_upper_bound(tte->type()) && v < beta));
2141 // refine_eval() returns the transposition table score if
2142 // possible otherwise falls back on static position evaluation.
2144 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
2149 Value v = value_from_tt(tte->value(), ply);
2151 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
2152 || (is_upper_bound(tte->type()) && v < defaultEval))
2159 // update_history() registers a good move that produced a beta-cutoff
2160 // in history and marks as failures all the other moves of that ply.
2162 void update_history(const Position& pos, Move move, Depth depth,
2163 Move movesSearched[], int moveCount) {
2167 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2169 for (int i = 0; i < moveCount - 1; i++)
2171 m = movesSearched[i];
2175 if (!pos.move_is_capture_or_promotion(m))
2176 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2181 // update_killers() add a good move that produced a beta-cutoff
2182 // among the killer moves of that ply.
2184 void update_killers(Move m, SearchStack& ss) {
2186 if (m == ss.killers[0])
2189 for (int i = KILLER_MAX - 1; i > 0; i--)
2190 ss.killers[i] = ss.killers[i - 1];
2196 // update_gains() updates the gains table of a non-capture move given
2197 // the static position evaluation before and after the move.
2199 void update_gains(const Position& pos, Move m, Value before, Value after) {
2202 && before != VALUE_NONE
2203 && after != VALUE_NONE
2204 && pos.captured_piece() == NO_PIECE_TYPE
2205 && !move_is_castle(m)
2206 && !move_is_promotion(m))
2207 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2211 // current_search_time() returns the number of milliseconds which have passed
2212 // since the beginning of the current search.
2214 int current_search_time() {
2216 return get_system_time() - SearchStartTime;
2220 // nps() computes the current nodes/second count.
2224 int t = current_search_time();
2225 return (t > 0 ? int((TM.nodes_searched() * 1000) / t) : 0);
2229 // poll() performs two different functions: It polls for user input, and it
2230 // looks at the time consumed so far and decides if it's time to abort the
2235 static int lastInfoTime;
2236 int t = current_search_time();
2241 // We are line oriented, don't read single chars
2242 std::string command;
2244 if (!std::getline(std::cin, command))
2247 if (command == "quit")
2250 PonderSearch = false;
2254 else if (command == "stop")
2257 PonderSearch = false;
2259 else if (command == "ponderhit")
2263 // Print search information
2267 else if (lastInfoTime > t)
2268 // HACK: Must be a new search where we searched less than
2269 // NodesBetweenPolls nodes during the first second of search.
2272 else if (t - lastInfoTime >= 1000)
2279 if (dbg_show_hit_rate)
2280 dbg_print_hit_rate();
2282 cout << "info nodes " << TM.nodes_searched() << " nps " << nps()
2283 << " time " << t << " hashfull " << TT.full() << endl;
2286 // Should we stop the search?
2290 bool stillAtFirstMove = FirstRootMove
2291 && !AspirationFailLow
2292 && t > MaxSearchTime + ExtraSearchTime;
2294 bool noMoreTime = t > AbsoluteMaxSearchTime
2295 || stillAtFirstMove;
2297 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2298 || (ExactMaxTime && t >= ExactMaxTime)
2299 || (Iteration >= 3 && MaxNodes && TM.nodes_searched() >= MaxNodes))
2304 // ponderhit() is called when the program is pondering (i.e. thinking while
2305 // it's the opponent's turn to move) in order to let the engine know that
2306 // it correctly predicted the opponent's move.
2310 int t = current_search_time();
2311 PonderSearch = false;
2313 bool stillAtFirstMove = FirstRootMove
2314 && !AspirationFailLow
2315 && t > MaxSearchTime + ExtraSearchTime;
2317 bool noMoreTime = t > AbsoluteMaxSearchTime
2318 || stillAtFirstMove;
2320 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2325 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2327 void init_ss_array(SearchStack ss[]) {
2329 for (int i = 0; i < 3; i++)
2332 ss[i].initKillers();
2337 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2338 // while the program is pondering. The point is to work around a wrinkle in
2339 // the UCI protocol: When pondering, the engine is not allowed to give a
2340 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2341 // We simply wait here until one of these commands is sent, and return,
2342 // after which the bestmove and pondermove will be printed (in id_loop()).
2344 void wait_for_stop_or_ponderhit() {
2346 std::string command;
2350 if (!std::getline(std::cin, command))
2353 if (command == "quit")
2358 else if (command == "ponderhit" || command == "stop")
2364 // print_pv_info() prints to standard output and eventually to log file information on
2365 // the current PV line. It is called at each iteration or after a new pv is found.
2367 void print_pv_info(const Position& pos, SearchStack ss[], Value alpha, Value beta, Value value) {
2369 cout << "info depth " << Iteration
2370 << " score " << value_to_string(value)
2371 << ((value >= beta) ? " lowerbound" :
2372 ((value <= alpha)? " upperbound" : ""))
2373 << " time " << current_search_time()
2374 << " nodes " << TM.nodes_searched()
2378 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
2379 cout << ss[0].pv[j] << " ";
2385 ValueType type = (value >= beta ? VALUE_TYPE_LOWER
2386 : (value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT));
2388 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2389 TM.nodes_searched(), value, type, ss[0].pv) << endl;
2394 // init_thread() is the function which is called when a new thread is
2395 // launched. It simply calls the idle_loop() function with the supplied
2396 // threadID. There are two versions of this function; one for POSIX
2397 // threads and one for Windows threads.
2399 #if !defined(_MSC_VER)
2401 void* init_thread(void *threadID) {
2403 TM.idle_loop(*(int*)threadID, NULL);
2409 DWORD WINAPI init_thread(LPVOID threadID) {
2411 TM.idle_loop(*(int*)threadID, NULL);
2418 /// The ThreadsManager class
2420 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2421 // get_beta_counters() are getters/setters for the per thread
2422 // counters used to sort the moves at root.
2424 void ThreadsManager::resetNodeCounters() {
2426 for (int i = 0; i < MAX_THREADS; i++)
2427 threads[i].nodes = 0ULL;
2430 void ThreadsManager::resetBetaCounters() {
2432 for (int i = 0; i < MAX_THREADS; i++)
2433 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2436 int64_t ThreadsManager::nodes_searched() const {
2438 int64_t result = 0ULL;
2439 for (int i = 0; i < ActiveThreads; i++)
2440 result += threads[i].nodes;
2445 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2448 for (int i = 0; i < MAX_THREADS; i++)
2450 our += threads[i].betaCutOffs[us];
2451 their += threads[i].betaCutOffs[opposite_color(us)];
2456 // idle_loop() is where the threads are parked when they have no work to do.
2457 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2458 // object for which the current thread is the master.
2460 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2462 assert(threadID >= 0 && threadID < MAX_THREADS);
2466 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2467 // master should exit as last one.
2468 if (AllThreadsShouldExit)
2471 threads[threadID].state = THREAD_TERMINATED;
2475 // If we are not thinking, wait for a condition to be signaled
2476 // instead of wasting CPU time polling for work.
2477 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2480 assert(threadID != 0);
2481 threads[threadID].state = THREAD_SLEEPING;
2483 #if !defined(_MSC_VER)
2484 lock_grab(&WaitLock);
2485 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2486 pthread_cond_wait(&WaitCond, &WaitLock);
2487 lock_release(&WaitLock);
2489 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2493 // If thread has just woken up, mark it as available
2494 if (threads[threadID].state == THREAD_SLEEPING)
2495 threads[threadID].state = THREAD_AVAILABLE;
2497 // If this thread has been assigned work, launch a search
2498 if (threads[threadID].state == THREAD_WORKISWAITING)
2500 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2502 threads[threadID].state = THREAD_SEARCHING;
2504 if (threads[threadID].splitPoint->pvNode)
2505 sp_search_pv(threads[threadID].splitPoint, threadID);
2507 sp_search(threads[threadID].splitPoint, threadID);
2509 assert(threads[threadID].state == THREAD_SEARCHING);
2511 threads[threadID].state = THREAD_AVAILABLE;
2514 // If this thread is the master of a split point and all threads have
2515 // finished their work at this split point, return from the idle loop.
2516 if (sp && sp->cpus == 0)
2518 // Because sp->cpus is decremented under lock protection,
2519 // be sure sp->lock has been released before to proceed.
2520 lock_grab(&(sp->lock));
2521 lock_release(&(sp->lock));
2523 assert(threads[threadID].state == THREAD_AVAILABLE);
2525 threads[threadID].state = THREAD_SEARCHING;
2532 // init_threads() is called during startup. It launches all helper threads,
2533 // and initializes the split point stack and the global locks and condition
2536 void ThreadsManager::init_threads() {
2541 #if !defined(_MSC_VER)
2542 pthread_t pthread[1];
2545 // Initialize global locks
2546 lock_init(&MPLock, NULL);
2547 lock_init(&WaitLock, NULL);
2549 #if !defined(_MSC_VER)
2550 pthread_cond_init(&WaitCond, NULL);
2552 for (i = 0; i < MAX_THREADS; i++)
2553 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2556 // Initialize SplitPointStack locks
2557 for (i = 0; i < MAX_THREADS; i++)
2558 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2560 SplitPointStack[i][j].parent = NULL;
2561 lock_init(&(SplitPointStack[i][j].lock), NULL);
2564 // Will be set just before program exits to properly end the threads
2565 AllThreadsShouldExit = false;
2567 // Threads will be put to sleep as soon as created
2568 AllThreadsShouldSleep = true;
2570 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2572 threads[0].state = THREAD_SEARCHING;
2573 for (i = 1; i < MAX_THREADS; i++)
2574 threads[i].state = THREAD_AVAILABLE;
2576 // Launch the helper threads
2577 for (i = 1; i < MAX_THREADS; i++)
2580 #if !defined(_MSC_VER)
2581 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2583 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2588 cout << "Failed to create thread number " << i << endl;
2589 Application::exit_with_failure();
2592 // Wait until the thread has finished launching and is gone to sleep
2593 while (threads[i].state != THREAD_SLEEPING) {}
2598 // exit_threads() is called when the program exits. It makes all the
2599 // helper threads exit cleanly.
2601 void ThreadsManager::exit_threads() {
2603 ActiveThreads = MAX_THREADS; // HACK
2604 AllThreadsShouldSleep = true; // HACK
2605 wake_sleeping_threads();
2607 // This makes the threads to exit idle_loop()
2608 AllThreadsShouldExit = true;
2610 // Wait for thread termination
2611 for (int i = 1; i < MAX_THREADS; i++)
2612 while (threads[i].state != THREAD_TERMINATED);
2614 // Now we can safely destroy the locks
2615 for (int i = 0; i < MAX_THREADS; i++)
2616 for (int j = 0; j < ACTIVE_SPLIT_POINTS_MAX; j++)
2617 lock_destroy(&(SplitPointStack[i][j].lock));
2619 lock_destroy(&WaitLock);
2620 lock_destroy(&MPLock);
2624 // thread_should_stop() checks whether the thread should stop its search.
2625 // This can happen if a beta cutoff has occurred in the thread's currently
2626 // active split point, or in some ancestor of the current split point.
2628 bool ThreadsManager::thread_should_stop(int threadID) const {
2630 assert(threadID >= 0 && threadID < ActiveThreads);
2634 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2639 // thread_is_available() checks whether the thread with threadID "slave" is
2640 // available to help the thread with threadID "master" at a split point. An
2641 // obvious requirement is that "slave" must be idle. With more than two
2642 // threads, this is not by itself sufficient: If "slave" is the master of
2643 // some active split point, it is only available as a slave to the other
2644 // threads which are busy searching the split point at the top of "slave"'s
2645 // split point stack (the "helpful master concept" in YBWC terminology).
2647 bool ThreadsManager::thread_is_available(int slave, int master) const {
2649 assert(slave >= 0 && slave < ActiveThreads);
2650 assert(master >= 0 && master < ActiveThreads);
2651 assert(ActiveThreads > 1);
2653 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2656 // Make a local copy to be sure doesn't change under our feet
2657 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2659 if (localActiveSplitPoints == 0)
2660 // No active split points means that the thread is available as
2661 // a slave for any other thread.
2664 if (ActiveThreads == 2)
2667 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2668 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2669 // could have been set to 0 by another thread leading to an out of bound access.
2670 if (SplitPointStack[slave][localActiveSplitPoints - 1].slaves[master])
2677 // available_thread_exists() tries to find an idle thread which is available as
2678 // a slave for the thread with threadID "master".
2680 bool ThreadsManager::available_thread_exists(int master) const {
2682 assert(master >= 0 && master < ActiveThreads);
2683 assert(ActiveThreads > 1);
2685 for (int i = 0; i < ActiveThreads; i++)
2686 if (thread_is_available(i, master))
2693 // split() does the actual work of distributing the work at a node between
2694 // several threads at PV nodes. If it does not succeed in splitting the
2695 // node (because no idle threads are available, or because we have no unused
2696 // split point objects), the function immediately returns false. If
2697 // splitting is possible, a SplitPoint object is initialized with all the
2698 // data that must be copied to the helper threads (the current position and
2699 // search stack, alpha, beta, the search depth, etc.), and we tell our
2700 // helper threads that they have been assigned work. This will cause them
2701 // to instantly leave their idle loops and call sp_search_pv(). When all
2702 // threads have returned from sp_search_pv (or, equivalently, when
2703 // splitPoint->cpus becomes 0), split() returns true.
2705 bool ThreadsManager::split(const Position& p, SearchStack* sstck, int ply,
2706 Value* alpha, const Value beta, Value* bestValue,
2707 Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode) {
2710 assert(sstck != NULL);
2711 assert(ply >= 0 && ply < PLY_MAX);
2712 assert(*bestValue >= -VALUE_INFINITE);
2713 assert( ( pvNode && *bestValue <= *alpha)
2714 || (!pvNode && *bestValue < beta ));
2715 assert(!pvNode || *alpha < beta);
2716 assert(beta <= VALUE_INFINITE);
2717 assert(depth > Depth(0));
2718 assert(master >= 0 && master < ActiveThreads);
2719 assert(ActiveThreads > 1);
2721 SplitPoint* splitPoint;
2725 // If no other thread is available to help us, or if we have too many
2726 // active split points, don't split.
2727 if ( !available_thread_exists(master)
2728 || threads[master].activeSplitPoints >= ACTIVE_SPLIT_POINTS_MAX)
2730 lock_release(&MPLock);
2734 // Pick the next available split point object from the split point stack
2735 splitPoint = &SplitPointStack[master][threads[master].activeSplitPoints];
2737 // Initialize the split point object
2738 splitPoint->parent = threads[master].splitPoint;
2739 splitPoint->stopRequest = false;
2740 splitPoint->ply = ply;
2741 splitPoint->depth = depth;
2742 splitPoint->mateThreat = mateThreat;
2743 splitPoint->alpha = *alpha;
2744 splitPoint->beta = beta;
2745 splitPoint->pvNode = pvNode;
2746 splitPoint->bestValue = *bestValue;
2747 splitPoint->master = master;
2748 splitPoint->mp = mp;
2749 splitPoint->moves = *moves;
2750 splitPoint->cpus = 1;
2751 splitPoint->pos = &p;
2752 splitPoint->parentSstack = sstck;
2753 for (int i = 0; i < ActiveThreads; i++)
2754 splitPoint->slaves[i] = 0;
2756 threads[master].splitPoint = splitPoint;
2757 threads[master].activeSplitPoints++;
2759 // If we are here it means we are not available
2760 assert(threads[master].state != THREAD_AVAILABLE);
2762 // Allocate available threads setting state to THREAD_BOOKED
2763 for (int i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint; i++)
2764 if (thread_is_available(i, master))
2766 threads[i].state = THREAD_BOOKED;
2767 threads[i].splitPoint = splitPoint;
2768 splitPoint->slaves[i] = 1;
2772 assert(splitPoint->cpus > 1);
2774 // We can release the lock because slave threads are already booked and master is not available
2775 lock_release(&MPLock);
2777 // Tell the threads that they have work to do. This will make them leave
2778 // their idle loop. But before copy search stack tail for each thread.
2779 for (int i = 0; i < ActiveThreads; i++)
2780 if (i == master || splitPoint->slaves[i])
2782 memcpy(splitPoint->sstack[i] + ply - 1, sstck + ply - 1, 4 * sizeof(SearchStack));
2784 assert(i == master || threads[i].state == THREAD_BOOKED);
2786 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2789 // Everything is set up. The master thread enters the idle loop, from
2790 // which it will instantly launch a search, because its state is
2791 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2792 // idle loop, which means that the main thread will return from the idle
2793 // loop when all threads have finished their work at this split point
2794 // (i.e. when splitPoint->cpus == 0).
2795 idle_loop(master, splitPoint);
2797 // We have returned from the idle loop, which means that all threads are
2798 // finished. Update alpha and bestValue, and return.
2801 *alpha = splitPoint->alpha;
2802 *bestValue = splitPoint->bestValue;
2803 threads[master].activeSplitPoints--;
2804 threads[master].splitPoint = splitPoint->parent;
2806 lock_release(&MPLock);
2811 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2812 // to start a new search from the root.
2814 void ThreadsManager::wake_sleeping_threads() {
2816 assert(AllThreadsShouldSleep);
2817 assert(ActiveThreads > 0);
2819 AllThreadsShouldSleep = false;
2821 if (ActiveThreads == 1)
2824 #if !defined(_MSC_VER)
2825 pthread_mutex_lock(&WaitLock);
2826 pthread_cond_broadcast(&WaitCond);
2827 pthread_mutex_unlock(&WaitLock);
2829 for (int i = 1; i < MAX_THREADS; i++)
2830 SetEvent(SitIdleEvent[i]);
2836 // put_threads_to_sleep() makes all the threads go to sleep just before
2837 // to leave think(), at the end of the search. Threads should have already
2838 // finished the job and should be idle.
2840 void ThreadsManager::put_threads_to_sleep() {
2842 assert(!AllThreadsShouldSleep);
2844 // This makes the threads to go to sleep
2845 AllThreadsShouldSleep = true;
2848 /// The RootMoveList class
2850 // RootMoveList c'tor
2852 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2854 SearchStack ss[PLY_MAX_PLUS_2];
2855 MoveStack mlist[MaxRootMoves];
2857 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2859 // Generate all legal moves
2860 MoveStack* last = generate_moves(pos, mlist);
2862 // Add each move to the moves[] array
2863 for (MoveStack* cur = mlist; cur != last; cur++)
2865 bool includeMove = includeAllMoves;
2867 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2868 includeMove = (searchMoves[k] == cur->move);
2873 // Find a quick score for the move
2875 pos.do_move(cur->move, st);
2876 moves[count].move = cur->move;
2877 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2878 moves[count].pv[0] = cur->move;
2879 moves[count].pv[1] = MOVE_NONE;
2880 pos.undo_move(cur->move);
2887 // RootMoveList simple methods definitions
2889 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2891 moves[moveNum].nodes = nodes;
2892 moves[moveNum].cumulativeNodes += nodes;
2895 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2897 moves[moveNum].ourBeta = our;
2898 moves[moveNum].theirBeta = their;
2901 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2905 for (j = 0; pv[j] != MOVE_NONE; j++)
2906 moves[moveNum].pv[j] = pv[j];
2908 moves[moveNum].pv[j] = MOVE_NONE;
2912 // RootMoveList::sort() sorts the root move list at the beginning of a new
2915 void RootMoveList::sort() {
2917 sort_multipv(count - 1); // Sort all items
2921 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2922 // list by their scores and depths. It is used to order the different PVs
2923 // correctly in MultiPV mode.
2925 void RootMoveList::sort_multipv(int n) {
2929 for (i = 1; i <= n; i++)
2931 RootMove rm = moves[i];
2932 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2933 moves[j] = moves[j - 1];