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 Marco Costalba
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/>.
40 #include "ucioption.h"
44 //// Local definitions
51 // IterationInfoType stores search results for each iteration
53 // Because we use relatively small (dynamic) aspiration window,
54 // there happens many fail highs and fail lows in root. And
55 // because we don't do researches in those cases, "value" stored
56 // here is not necessarily exact. Instead in case of fail high/low
57 // we guess what the right value might be and store our guess
58 // as a "speculated value" and then move on. Speculated values are
59 // used just to calculate aspiration window width, so also if are
60 // not exact is not big a problem.
62 struct IterationInfoType {
64 IterationInfoType(Value v = Value(0), Value sv = Value(0))
65 : value(v), speculatedValue(sv) {}
67 Value value, speculatedValue;
71 // The BetaCounterType class is used to order moves at ply one.
72 // Apart for the first one that has its score, following moves
73 // normally have score -VALUE_INFINITE, so are ordered according
74 // to the number of beta cutoffs occurred under their subtree during
75 // the last iteration.
77 struct BetaCounterType {
81 void add(Color us, Depth d, int threadID);
82 void read(Color us, int64_t& our, int64_t& their);
84 int64_t hits[THREAD_MAX][2];
88 // The RootMove class is used for moves at the root at the tree. For each
89 // root move, we store a score, a node count, and a PV (really a refutation
90 // in the case of moves which fail low).
95 bool operator<(const RootMove&); // used to sort
99 int64_t nodes, cumulativeNodes;
100 Move pv[PLY_MAX_PLUS_2];
101 int64_t ourBeta, theirBeta;
105 // The RootMoveList class is essentially an array of RootMove objects, with
106 // a handful of methods for accessing the data in the individual moves.
111 RootMoveList(Position &pos, Move searchMoves[]);
112 inline Move get_move(int moveNum) const;
113 inline Value get_move_score(int moveNum) const;
114 inline void set_move_score(int moveNum, Value score);
115 inline void set_move_nodes(int moveNum, int64_t nodes);
116 inline void set_beta_counters(int moveNum, int64_t our, int64_t their);
117 void set_move_pv(int moveNum, const Move pv[]);
118 inline Move get_move_pv(int moveNum, int i) const;
119 inline int64_t get_move_cumulative_nodes(int moveNum) const;
120 inline int move_count() const;
121 Move scan_for_easy_move() const;
123 void sort_multipv(int n);
126 static const int MaxRootMoves = 500;
127 RootMove moves[MaxRootMoves];
132 /// Constants and variables initialized from UCI options
134 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV
136 int LMRPVMoves, LMRNonPVMoves;
138 // Depth limit for use of dynamic threat detection
141 // Depth limit for selective search
142 const Depth SelectiveDepth = 7*OnePly;
144 // Use internal iterative deepening?
145 const bool UseIIDAtPVNodes = true;
146 const bool UseIIDAtNonPVNodes = false;
148 // Internal iterative deepening margin. At Non-PV moves, when
149 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening search
150 // when the static evaluation is at most IIDMargin below beta.
151 const Value IIDMargin = Value(0x100);
153 // Easy move margin. An easy move candidate must be at least this much
154 // better than the second best move.
155 const Value EasyMoveMargin = Value(0x200);
157 // Problem margin. If the score of the first move at iteration N+1 has
158 // dropped by more than this since iteration N, the boolean variable
159 // "Problem" is set to true, which will make the program spend some extra
160 // time looking for a better move.
161 const Value ProblemMargin = Value(0x28);
163 // No problem margin. If the boolean "Problem" is true, and a new move
164 // is found at the root which is less than NoProblemMargin worse than the
165 // best move from the previous iteration, Problem is set back to false.
166 const Value NoProblemMargin = Value(0x14);
168 // Null move margin. A null move search will not be done if the approximate
169 // evaluation of the position is more than NullMoveMargin below beta.
170 const Value NullMoveMargin = Value(0x300);
172 // Pruning criterions. See the code and comments in ok_to_prune() to
173 // understand their precise meaning.
174 const bool PruneEscapeMoves = false;
175 const bool PruneDefendingMoves = false;
176 const bool PruneBlockingMoves = false;
178 // Use futility pruning?
179 bool UseQSearchFutilityPruning, UseFutilityPruning;
181 // Margins for futility pruning in the quiescence search, and at frontier
182 // and near frontier nodes
183 Value FutilityMarginQS;
184 Value FutilityMargins[6] = { Value(0x100), Value(0x200), Value(0x250),
185 Value(0x2A0), Value(0x340), Value(0x3A0) };
188 const bool RazorAtDepthOne = false;
192 // Last seconds noise filtering (LSN)
193 bool UseLSNFiltering;
194 bool looseOnTime = false;
195 int LSNTime; // In milliseconds
198 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
199 Depth CheckExtension[2], SingleReplyExtension[2], PawnPushTo7thExtension[2];
200 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
202 // Search depth at iteration 1
203 const Depth InitialDepth = OnePly /*+ OnePly/2*/;
207 int NodesBetweenPolls = 30000;
209 // Iteration counters
211 BetaCounterType BetaCounter;
213 // Scores and number of times the best move changed for each iteration:
214 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
215 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
220 // Time managment variables
222 int MaxNodes, MaxDepth;
223 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
228 bool StopOnPonderhit;
234 bool PonderingEnabled;
237 // Show current line?
238 bool ShowCurrentLine;
242 std::ofstream LogFile;
244 // MP related variables
245 Depth MinimumSplitDepth;
246 int MaxThreadsPerSplitPoint;
247 Thread Threads[THREAD_MAX];
249 bool AllThreadsShouldExit = false;
250 const int MaxActiveSplitPoints = 8;
251 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
254 #if !defined(_MSC_VER)
255 pthread_cond_t WaitCond;
256 pthread_mutex_t WaitLock;
258 HANDLE SitIdleEvent[THREAD_MAX];
264 Value id_loop(const Position &pos, Move searchMoves[]);
265 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta);
266 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
267 Value search(Position &pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID);
268 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
269 void sp_search(SplitPoint *sp, int threadID);
270 void sp_search_pv(SplitPoint *sp, int threadID);
271 void init_node(SearchStack ss[], int ply, int threadID);
272 void update_pv(SearchStack ss[], int ply);
273 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
274 bool connected_moves(const Position &pos, Move m1, Move m2);
275 bool value_is_mate(Value value);
276 bool move_is_killer(Move m, const SearchStack& ss);
277 Depth extension(const Position &pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
278 bool ok_to_do_nullmove(const Position &pos);
279 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
280 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
281 bool ok_to_history(const Position &pos, Move m);
282 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
283 void update_killers(Move m, SearchStack& ss);
285 bool fail_high_ply_1();
286 int current_search_time();
290 void print_current_line(SearchStack ss[], int ply, int threadID);
291 void wait_for_stop_or_ponderhit();
293 void idle_loop(int threadID, SplitPoint *waitSp);
294 void init_split_point_stack();
295 void destroy_split_point_stack();
296 bool thread_should_stop(int threadID);
297 bool thread_is_available(int slave, int master);
298 bool idle_thread_exists(int master);
299 bool split(const Position &pos, SearchStack *ss, int ply,
300 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
301 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode);
302 void wake_sleeping_threads();
304 #if !defined(_MSC_VER)
305 void *init_thread(void *threadID);
307 DWORD WINAPI init_thread(LPVOID threadID);
314 //// Global variables
317 // The main transposition table
318 TranspositionTable TT;
321 // Number of active threads:
322 int ActiveThreads = 1;
324 // Locks. In principle, there is no need for IOLock to be a global variable,
325 // but it could turn out to be useful for debugging.
328 History H; // Should be made local?
330 // The empty search stack
331 SearchStack EmptySearchStack;
334 // SearchStack::init() initializes a search stack. Used at the beginning of a
335 // new search from the root.
336 void SearchStack::init(int ply) {
338 pv[ply] = pv[ply + 1] = MOVE_NONE;
339 currentMove = threatMove = MOVE_NONE;
340 reduction = Depth(0);
343 void SearchStack::initKillers() {
345 mateKiller = MOVE_NONE;
346 for (int i = 0; i < KILLER_MAX; i++)
347 killers[i] = MOVE_NONE;
355 /// think() is the external interface to Stockfish's search, and is called when
356 /// the program receives the UCI 'go' command. It initializes various
357 /// search-related global variables, and calls root_search()
359 void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
360 int time[], int increment[], int movesToGo, int maxDepth,
361 int maxNodes, int maxTime, Move searchMoves[]) {
363 // Look for a book move
364 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
367 if (get_option_value_string("Book File") != OpeningBook.file_name())
370 OpeningBook.open("book.bin");
372 bookMove = OpeningBook.get_move(pos);
373 if (bookMove != MOVE_NONE)
375 std::cout << "bestmove " << bookMove << std::endl;
380 // Initialize global search variables
382 SearchStartTime = get_system_time();
383 EasyMove = MOVE_NONE;
384 for (int i = 0; i < THREAD_MAX; i++)
386 Threads[i].nodes = 0ULL;
387 Threads[i].failHighPly1 = false;
390 InfiniteSearch = infinite;
391 PonderSearch = ponder;
392 StopOnPonderhit = false;
398 ExactMaxTime = maxTime;
400 // Read UCI option values
401 TT.set_size(get_option_value_int("Hash"));
402 if (button_was_pressed("Clear Hash"))
405 PonderingEnabled = get_option_value_bool("Ponder");
406 MultiPV = get_option_value_int("MultiPV");
408 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
409 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
411 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
412 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply 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)"));
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)"));
420 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
421 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
423 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
424 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
426 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
427 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
428 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
430 Chess960 = get_option_value_bool("UCI_Chess960");
431 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
432 UseLogFile = get_option_value_bool("Use Search Log");
434 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
436 UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)");
437 UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)");
439 FutilityMarginQS = value_from_centipawns(get_option_value_int("Futility Margin (Quiescence Search)"));
440 int fmScale = get_option_value_int("Futility Margin Scale Factor (Main Search)");
441 for (int i = 0; i < 6; i++)
442 FutilityMargins[i] = (FutilityMargins[i] * fmScale) / 100;
444 RazorDepth = (get_option_value_int("Maximum Razoring Depth") + 1) * OnePly;
445 RazorMargin = value_from_centipawns(get_option_value_int("Razoring Margin"));
447 UseLSNFiltering = get_option_value_bool("LSN filtering");
448 LSNTime = get_option_value_int("LSN Time Margin (sec)") * 1000;
449 LSNValue = value_from_centipawns(get_option_value_int("LSN Value Margin"));
451 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
452 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
454 read_weights(pos.side_to_move());
456 int newActiveThreads = get_option_value_int("Threads");
457 if (newActiveThreads != ActiveThreads)
459 ActiveThreads = newActiveThreads;
460 init_eval(ActiveThreads);
463 // Wake up sleeping threads:
464 wake_sleeping_threads();
466 for (int i = 1; i < ActiveThreads; i++)
467 assert(thread_is_available(i, 0));
469 // Set thinking time:
470 int myTime = time[side_to_move];
471 int myIncrement = increment[side_to_move];
473 if (!movesToGo) // Sudden death time control
477 MaxSearchTime = myTime / 30 + myIncrement;
478 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
479 } else { // Blitz game without increment
480 MaxSearchTime = myTime / 30;
481 AbsoluteMaxSearchTime = myTime / 8;
484 else // (x moves) / (y minutes)
488 MaxSearchTime = myTime / 2;
489 AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
491 MaxSearchTime = myTime / Min(movesToGo, 20);
492 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
496 if (PonderingEnabled)
498 MaxSearchTime += MaxSearchTime / 4;
499 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
502 // Fixed depth or fixed number of nodes?
505 InfiniteSearch = true; // HACK
510 NodesBetweenPolls = Min(MaxNodes, 30000);
511 InfiniteSearch = true; // HACK
514 NodesBetweenPolls = 30000;
517 // Write information to search log file:
519 LogFile << "Searching: " << pos.to_fen() << std::endl
520 << "infinite: " << infinite
521 << " ponder: " << ponder
522 << " time: " << myTime
523 << " increment: " << myIncrement
524 << " moves to go: " << movesToGo << std::endl;
527 // We're ready to start thinking. Call the iterative deepening loop
531 Value v = id_loop(pos, searchMoves);
532 looseOnTime = ( UseLSNFiltering
539 looseOnTime = false; // reset for next match
540 while (SearchStartTime + myTime + 1000 > get_system_time())
542 id_loop(pos, searchMoves); // to fail gracefully
559 /// init_threads() is called during startup. It launches all helper threads,
560 /// and initializes the split point stack and the global locks and condition
563 void init_threads() {
567 #if !defined(_MSC_VER)
568 pthread_t pthread[1];
571 for (i = 0; i < THREAD_MAX; i++)
572 Threads[i].activeSplitPoints = 0;
574 // Initialize global locks:
575 lock_init(&MPLock, NULL);
576 lock_init(&IOLock, NULL);
578 init_split_point_stack();
580 #if !defined(_MSC_VER)
581 pthread_mutex_init(&WaitLock, NULL);
582 pthread_cond_init(&WaitCond, NULL);
584 for (i = 0; i < THREAD_MAX; i++)
585 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
588 // All threads except the main thread should be initialized to idle state
589 for (i = 1; i < THREAD_MAX; i++)
591 Threads[i].stop = false;
592 Threads[i].workIsWaiting = false;
593 Threads[i].idle = true;
594 Threads[i].running = false;
597 // Launch the helper threads
598 for(i = 1; i < THREAD_MAX; i++)
600 #if !defined(_MSC_VER)
601 pthread_create(pthread, NULL, init_thread, (void*)(&i));
604 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
607 // Wait until the thread has finished launching:
608 while (!Threads[i].running);
611 // Init also the empty search stack
612 EmptySearchStack.init(0);
613 EmptySearchStack.initKillers();
617 /// stop_threads() is called when the program exits. It makes all the
618 /// helper threads exit cleanly.
620 void stop_threads() {
622 ActiveThreads = THREAD_MAX; // HACK
623 Idle = false; // HACK
624 wake_sleeping_threads();
625 AllThreadsShouldExit = true;
626 for (int i = 1; i < THREAD_MAX; i++)
628 Threads[i].stop = true;
629 while(Threads[i].running);
631 destroy_split_point_stack();
635 /// nodes_searched() returns the total number of nodes searched so far in
636 /// the current search.
638 int64_t nodes_searched() {
640 int64_t result = 0ULL;
641 for (int i = 0; i < ActiveThreads; i++)
642 result += Threads[i].nodes;
649 // id_loop() is the main iterative deepening loop. It calls root_search
650 // repeatedly with increasing depth until the allocated thinking time has
651 // been consumed, the user stops the search, or the maximum search depth is
654 Value id_loop(const Position &pos, Move searchMoves[]) {
657 SearchStack ss[PLY_MAX_PLUS_2];
659 // searchMoves are verified, copied, scored and sorted
660 RootMoveList rml(p, searchMoves);
665 for (int i = 0; i < 3; i++)
670 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
673 EasyMove = rml.scan_for_easy_move();
675 // Iterative deepening loop
676 while (Iteration < PLY_MAX)
678 // Initialize iteration
681 BestMoveChangesByIteration[Iteration] = 0;
685 std::cout << "info depth " << Iteration << std::endl;
687 // Calculate dynamic search window based on previous iterations
690 if (MultiPV == 1 && Iteration >= 6)
692 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
693 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
695 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
697 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
698 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
702 alpha = - VALUE_INFINITE;
703 beta = VALUE_INFINITE;
706 // Search to the current depth
707 Value value = root_search(p, ss, rml, alpha, beta);
709 // Write PV to transposition table, in case the relevant entries have
710 // been overwritten during the search.
711 TT.insert_pv(p, ss[0].pv);
714 break; // Value cannot be trusted. Break out immediately!
716 //Save info about search result
717 Value speculatedValue;
720 Value delta = value - IterationInfo[Iteration - 1].value;
727 speculatedValue = value + delta;
728 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
730 else if (value <= alpha)
732 assert(value == alpha);
736 speculatedValue = value + delta;
737 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
739 speculatedValue = value;
741 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
742 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
744 // Erase the easy move if it differs from the new best move
745 if (ss[0].pv[0] != EasyMove)
746 EasyMove = MOVE_NONE;
753 bool stopSearch = false;
755 // Stop search early if there is only a single legal move:
756 if (Iteration >= 6 && rml.move_count() == 1)
759 // Stop search early when the last two iterations returned a mate score
761 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
762 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
765 // Stop search early if one move seems to be much better than the rest
766 int64_t nodes = nodes_searched();
770 && EasyMove == ss[0].pv[0]
771 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
772 && current_search_time() > MaxSearchTime / 16)
773 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
774 && current_search_time() > MaxSearchTime / 32)))
777 // Add some extra time if the best move has changed during the last two iterations
778 if (Iteration > 5 && Iteration <= 50)
779 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
780 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
782 // Stop search if most of MaxSearchTime is consumed at the end of the
783 // iteration. We probably don't have enough time to search the first
784 // move at the next iteration anyway.
785 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
790 //FIXME: Implement fail-low emergency measures
794 StopOnPonderhit = true;
798 if (MaxDepth && Iteration >= MaxDepth)
804 // If we are pondering, we shouldn't print the best move before we
807 wait_for_stop_or_ponderhit();
809 // Print final search statistics
810 std::cout << "info nodes " << nodes_searched()
812 << " time " << current_search_time()
813 << " hashfull " << TT.full() << std::endl;
815 // Print the best move and the ponder move to the standard output
816 if (ss[0].pv[0] == MOVE_NONE)
818 ss[0].pv[0] = rml.get_move(0);
819 ss[0].pv[1] = MOVE_NONE;
821 std::cout << "bestmove " << ss[0].pv[0];
822 if (ss[0].pv[1] != MOVE_NONE)
823 std::cout << " ponder " << ss[0].pv[1];
825 std::cout << std::endl;
830 dbg_print_mean(LogFile);
832 if (dbg_show_hit_rate)
833 dbg_print_hit_rate(LogFile);
836 LogFile << "Nodes: " << nodes_searched() << std::endl
837 << "Nodes/second: " << nps() << std::endl
838 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
840 p.do_move(ss[0].pv[0], st);
841 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
842 << std::endl << std::endl;
844 return rml.get_move_score(0);
848 // root_search() is the function which searches the root node. It is
849 // similar to search_pv except that it uses a different move ordering
850 // scheme (perhaps we should try to use this at internal PV nodes, too?)
851 // and prints some information to the standard output.
853 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta) {
855 Value oldAlpha = alpha;
857 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
859 // Loop through all the moves in the root move list
860 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
864 // We failed high, invalidate and skip next moves, leave node-counters
865 // and beta-counters as they are and quickly return, we will try to do
866 // a research at the next iteration with a bigger aspiration window.
867 rml.set_move_score(i, -VALUE_INFINITE);
875 RootMoveNumber = i + 1;
878 // Remember the node count before the move is searched. The node counts
879 // are used to sort the root moves at the next iteration.
880 nodes = nodes_searched();
882 // Reset beta cut-off counters
885 // Pick the next root move, and print the move and the move number to
886 // the standard output.
887 move = ss[0].currentMove = rml.get_move(i);
888 if (current_search_time() >= 1000)
889 std::cout << "info currmove " << move
890 << " currmovenumber " << i + 1 << std::endl;
892 // Decide search depth for this move
894 ext = extension(pos, move, true, pos.move_is_capture(move), pos.move_is_check(move), false, false, &dangerous);
895 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
897 // Make the move, and search it
898 pos.do_move(move, st, dcCandidates);
902 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
903 // If the value has dropped a lot compared to the last iteration,
904 // set the boolean variable Problem to true. This variable is used
905 // for time managment: When Problem is true, we try to complete the
906 // current iteration before playing a move.
907 Problem = (Iteration >= 2 && value <= IterationInfo[Iteration-1].value - ProblemMargin);
909 if (Problem && StopOnPonderhit)
910 StopOnPonderhit = false;
914 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
917 // Fail high! Set the boolean variable FailHigh to true, and
918 // re-search the move with a big window. The variable FailHigh is
919 // used for time managment: We try to avoid aborting the search
920 // prematurely during a fail high research.
922 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
928 // Finished searching the move. If AbortSearch is true, the search
929 // was aborted because the user interrupted the search or because we
930 // ran out of time. In this case, the return value of the search cannot
931 // be trusted, and we break out of the loop without updating the best
936 // Remember the node count for this move. The node counts are used to
937 // sort the root moves at the next iteration.
938 rml.set_move_nodes(i, nodes_searched() - nodes);
940 // Remember the beta-cutoff statistics
942 BetaCounter.read(pos.side_to_move(), our, their);
943 rml.set_beta_counters(i, our, their);
945 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
947 if (value <= alpha && i >= MultiPV)
948 rml.set_move_score(i, -VALUE_INFINITE);
951 // PV move or new best move!
954 rml.set_move_score(i, value);
956 rml.set_move_pv(i, ss[0].pv);
960 // We record how often the best move has been changed in each
961 // iteration. This information is used for time managment: When
962 // the best move changes frequently, we allocate some more time.
964 BestMoveChangesByIteration[Iteration]++;
966 // Print search information to the standard output:
967 std::cout << "info depth " << Iteration
968 << " score " << value_to_string(value)
969 << " time " << current_search_time()
970 << " nodes " << nodes_searched()
974 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
975 std::cout << ss[0].pv[j] << " ";
977 std::cout << std::endl;
980 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
986 // Reset the global variable Problem to false if the value isn't too
987 // far below the final value from the last iteration.
988 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
994 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
997 std::cout << "info multipv " << j + 1
998 << " score " << value_to_string(rml.get_move_score(j))
999 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1000 << " time " << current_search_time()
1001 << " nodes " << nodes_searched()
1005 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1006 std::cout << rml.get_move_pv(j, k) << " ";
1008 std::cout << std::endl;
1010 alpha = rml.get_move_score(Min(i, MultiPV-1));
1012 } // New best move case
1014 assert(alpha >= oldAlpha);
1016 FailLow = (alpha == oldAlpha);
1022 // search_pv() is the main search function for PV nodes.
1024 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
1025 Depth depth, int ply, int threadID) {
1027 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1028 assert(beta > alpha && beta <= VALUE_INFINITE);
1029 assert(ply >= 0 && ply < PLY_MAX);
1030 assert(threadID >= 0 && threadID < ActiveThreads);
1033 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1035 // Initialize, and make an early exit in case of an aborted search,
1036 // an instant draw, maximum ply reached, etc.
1037 init_node(ss, ply, threadID);
1039 // After init_node() that calls poll()
1040 if (AbortSearch || thread_should_stop(threadID))
1048 if (ply >= PLY_MAX - 1)
1049 return evaluate(pos, ei, threadID);
1051 // Mate distance pruning
1052 Value oldAlpha = alpha;
1053 alpha = Max(value_mated_in(ply), alpha);
1054 beta = Min(value_mate_in(ply+1), beta);
1058 // Transposition table lookup. At PV nodes, we don't use the TT for
1059 // pruning, but only for move ordering.
1060 const TTEntry* tte = TT.retrieve(pos);
1061 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1063 // Go with internal iterative deepening if we don't have a TT move
1064 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
1066 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1067 ttMove = ss[ply].pv[ply];
1070 // Initialize a MovePicker object for the current position, and prepare
1071 // to search all moves
1072 MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
1074 Move move, movesSearched[256];
1076 Value value, bestValue = -VALUE_INFINITE;
1077 Bitboard dcCandidates = mp.discovered_check_candidates();
1078 Color us = pos.side_to_move();
1079 bool isCheck = pos.is_check();
1080 bool mateThreat = pos.has_mate_threat(opposite_color(us));
1082 // Loop through all legal moves until no moves remain or a beta cutoff
1084 while ( alpha < beta
1085 && (move = mp.get_next_move()) != MOVE_NONE
1086 && !thread_should_stop(threadID))
1088 assert(move_is_ok(move));
1090 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1091 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1092 bool moveIsCapture = pos.move_is_capture(move);
1094 movesSearched[moveCount++] = ss[ply].currentMove = move;
1096 // Decide the new search depth
1098 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1099 Depth newDepth = depth - OnePly + ext;
1101 // Make and search the move
1103 pos.do_move(move, st, dcCandidates);
1105 if (moveCount == 1) // The first move in list is the PV
1106 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1109 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1110 // if the move fails high will be re-searched at full depth.
1111 if ( depth >= 2*OnePly
1112 && moveCount >= LMRPVMoves
1115 && !move_promotion(move)
1116 && !move_is_castle(move)
1117 && !move_is_killer(move, ss[ply]))
1119 ss[ply].reduction = OnePly;
1120 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1123 value = alpha + 1; // Just to trigger next condition
1125 if (value > alpha) // Go with full depth non-pv search
1127 ss[ply].reduction = Depth(0);
1128 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1129 if (value > alpha && value < beta)
1131 // When the search fails high at ply 1 while searching the first
1132 // move at the root, set the flag failHighPly1. This is used for
1133 // time managment: We don't want to stop the search early in
1134 // such cases, because resolving the fail high at ply 1 could
1135 // result in a big drop in score at the root.
1136 if (ply == 1 && RootMoveNumber == 1)
1137 Threads[threadID].failHighPly1 = true;
1139 // A fail high occurred. Re-search at full window (pv search)
1140 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1141 Threads[threadID].failHighPly1 = false;
1145 pos.undo_move(move);
1147 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1150 if (value > bestValue)
1157 if (value == value_mate_in(ply + 1))
1158 ss[ply].mateKiller = move;
1160 // If we are at ply 1, and we are searching the first root move at
1161 // ply 0, set the 'Problem' variable if the score has dropped a lot
1162 // (from the computer's point of view) since the previous iteration:
1165 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1170 if ( ActiveThreads > 1
1172 && depth >= MinimumSplitDepth
1174 && idle_thread_exists(threadID)
1176 && !thread_should_stop(threadID)
1177 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1178 &moveCount, &mp, dcCandidates, threadID, true))
1182 // All legal moves have been searched. A special case: If there were
1183 // no legal moves, it must be mate or stalemate:
1185 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1187 // If the search is not aborted, update the transposition table,
1188 // history counters, and killer moves.
1189 if (AbortSearch || thread_should_stop(threadID))
1192 if (bestValue <= oldAlpha)
1193 TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1195 else if (bestValue >= beta)
1197 BetaCounter.add(pos.side_to_move(), depth, threadID);
1198 Move m = ss[ply].pv[ply];
1199 if (ok_to_history(pos, m)) // Only non capture moves are considered
1201 update_history(pos, m, depth, movesSearched, moveCount);
1202 update_killers(m, ss[ply]);
1204 TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1207 TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1213 // search() is the search function for zero-width nodes.
1215 Value search(Position &pos, SearchStack ss[], Value beta, Depth depth,
1216 int ply, bool allowNullmove, int threadID) {
1218 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1219 assert(ply >= 0 && ply < PLY_MAX);
1220 assert(threadID >= 0 && threadID < ActiveThreads);
1223 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1225 // Initialize, and make an early exit in case of an aborted search,
1226 // an instant draw, maximum ply reached, etc.
1227 init_node(ss, ply, threadID);
1229 // After init_node() that calls poll()
1230 if (AbortSearch || thread_should_stop(threadID))
1238 if (ply >= PLY_MAX - 1)
1239 return evaluate(pos, ei, threadID);
1241 // Mate distance pruning
1242 if (value_mated_in(ply) >= beta)
1245 if (value_mate_in(ply + 1) < beta)
1248 // Transposition table lookup
1249 const TTEntry* tte = TT.retrieve(pos);
1250 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1252 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1254 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1255 return value_from_tt(tte->value(), ply);
1258 Value approximateEval = quick_evaluate(pos);
1259 bool mateThreat = false;
1260 bool isCheck = pos.is_check();
1266 && !value_is_mate(beta)
1267 && ok_to_do_nullmove(pos)
1268 && approximateEval >= beta - NullMoveMargin)
1270 ss[ply].currentMove = MOVE_NULL;
1273 pos.do_null_move(st);
1274 int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
1276 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1278 pos.undo_null_move();
1280 if (value_is_mate(nullValue))
1282 /* Do not return unproven mates */
1284 else if (nullValue >= beta)
1286 if (depth < 6 * OnePly)
1289 // Do zugzwang verification search
1290 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1294 // The null move failed low, which means that we may be faced with
1295 // some kind of threat. If the previous move was reduced, check if
1296 // the move that refuted the null move was somehow connected to the
1297 // move which was reduced. If a connection is found, return a fail
1298 // low score (which will cause the reduced move to fail high in the
1299 // parent node, which will trigger a re-search with full depth).
1300 if (nullValue == value_mated_in(ply + 2))
1303 ss[ply].threatMove = ss[ply + 1].currentMove;
1304 if ( depth < ThreatDepth
1305 && ss[ply - 1].reduction
1306 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1310 // Null move search not allowed, try razoring
1311 else if ( !value_is_mate(beta)
1312 && approximateEval < beta - RazorMargin
1313 && depth < RazorDepth
1314 && (RazorAtDepthOne || depth > OnePly)
1315 && ttMove == MOVE_NONE
1316 && !pos.has_pawn_on_7th(pos.side_to_move()))
1318 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1319 if ( (v < beta - RazorMargin - RazorMargin / 4)
1320 || (depth <= 2*OnePly && v < beta - RazorMargin)
1321 || (depth <= OnePly && v < beta - RazorMargin / 2))
1325 // Go with internal iterative deepening if we don't have a TT move
1326 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1327 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1329 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1330 ttMove = ss[ply].pv[ply];
1333 // Initialize a MovePicker object for the current position, and prepare
1334 // to search all moves:
1335 MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth);
1337 Move move, movesSearched[256];
1339 Value value, bestValue = -VALUE_INFINITE;
1340 Bitboard dcCandidates = mp.discovered_check_candidates();
1341 Value futilityValue = VALUE_NONE;
1342 bool useFutilityPruning = UseFutilityPruning
1343 && depth < SelectiveDepth
1346 // Loop through all legal moves until no moves remain or a beta cutoff
1348 while ( bestValue < beta
1349 && (move = mp.get_next_move()) != MOVE_NONE
1350 && !thread_should_stop(threadID))
1352 assert(move_is_ok(move));
1354 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1355 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1356 bool moveIsCapture = pos.move_is_capture(move);
1358 movesSearched[moveCount++] = ss[ply].currentMove = move;
1360 // Decide the new search depth
1362 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1363 Depth newDepth = depth - OnePly + ext;
1366 if ( useFutilityPruning
1369 && !move_promotion(move))
1371 // History pruning. See ok_to_prune() definition
1372 if ( moveCount >= 2 + int(depth)
1373 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1376 // Value based pruning
1377 if (approximateEval < beta)
1379 if (futilityValue == VALUE_NONE)
1380 futilityValue = evaluate(pos, ei, threadID)
1381 + FutilityMargins[int(depth)/2 - 1]
1384 if (futilityValue < beta)
1386 if (futilityValue > bestValue)
1387 bestValue = futilityValue;
1393 // Make and search the move
1395 pos.do_move(move, st, dcCandidates);
1397 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1398 // if the move fails high will be re-searched at full depth.
1399 if ( depth >= 2*OnePly
1400 && moveCount >= LMRNonPVMoves
1403 && !move_promotion(move)
1404 && !move_is_castle(move)
1405 && !move_is_killer(move, ss[ply]))
1407 ss[ply].reduction = OnePly;
1408 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1411 value = beta; // Just to trigger next condition
1413 if (value >= beta) // Go with full depth non-pv search
1415 ss[ply].reduction = Depth(0);
1416 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1418 pos.undo_move(move);
1420 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1423 if (value > bestValue)
1429 if (value == value_mate_in(ply + 1))
1430 ss[ply].mateKiller = move;
1434 if ( ActiveThreads > 1
1436 && depth >= MinimumSplitDepth
1438 && idle_thread_exists(threadID)
1440 && !thread_should_stop(threadID)
1441 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1442 &mp, dcCandidates, threadID, false))
1446 // All legal moves have been searched. A special case: If there were
1447 // no legal moves, it must be mate or stalemate.
1449 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1451 // If the search is not aborted, update the transposition table,
1452 // history counters, and killer moves.
1453 if (AbortSearch || thread_should_stop(threadID))
1456 if (bestValue < beta)
1457 TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1460 BetaCounter.add(pos.side_to_move(), depth, threadID);
1461 Move m = ss[ply].pv[ply];
1462 if (ok_to_history(pos, m)) // Only non capture moves are considered
1464 update_history(pos, m, depth, movesSearched, moveCount);
1465 update_killers(m, ss[ply]);
1467 TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1470 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1476 // qsearch() is the quiescence search function, which is called by the main
1477 // search function when the remaining depth is zero (or, to be more precise,
1478 // less than OnePly).
1480 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
1481 Depth depth, int ply, int threadID) {
1483 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1484 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1486 assert(ply >= 0 && ply < PLY_MAX);
1487 assert(threadID >= 0 && threadID < ActiveThreads);
1489 // Initialize, and make an early exit in case of an aborted search,
1490 // an instant draw, maximum ply reached, etc.
1491 init_node(ss, ply, threadID);
1493 // After init_node() that calls poll()
1494 if (AbortSearch || thread_should_stop(threadID))
1500 // Transposition table lookup, only when not in PV
1501 TTEntry* tte = NULL;
1502 bool pvNode = (beta - alpha != 1);
1505 tte = TT.retrieve(pos);
1506 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1508 assert(tte->type() != VALUE_TYPE_EVAL);
1510 return value_from_tt(tte->value(), ply);
1513 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1515 // Evaluate the position statically
1518 bool isCheck = pos.is_check();
1519 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1522 staticValue = -VALUE_INFINITE;
1524 else if (tte && tte->type() == VALUE_TYPE_EVAL)
1526 // Use the cached evaluation score if possible
1527 assert(tte->value() == evaluate(pos, ei, threadID));
1528 assert(ei.futilityMargin == Value(0));
1530 staticValue = tte->value();
1533 staticValue = evaluate(pos, ei, threadID);
1535 if (ply == PLY_MAX - 1)
1536 return evaluate(pos, ei, threadID);
1538 // Initialize "stand pat score", and return it immediately if it is
1540 Value bestValue = staticValue;
1542 if (bestValue >= beta)
1544 // Store the score to avoid a future costly evaluation() call
1545 if (!isCheck && !tte && ei.futilityMargin == 0)
1546 TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_EVAL, Depth(-127*OnePly), MOVE_NONE);
1551 if (bestValue > alpha)
1554 // Initialize a MovePicker object for the current position, and prepare
1555 // to search the moves. Because the depth is <= 0 here, only captures,
1556 // queen promotions and checks (only if depth == 0) will be generated.
1557 MovePicker mp = MovePicker(pos, pvNode, ttMove, EmptySearchStack, depth);
1560 Bitboard dcCandidates = mp.discovered_check_candidates();
1561 Color us = pos.side_to_move();
1562 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1564 // Loop through the moves until no moves remain or a beta cutoff
1566 while ( alpha < beta
1567 && (move = mp.get_next_move()) != MOVE_NONE)
1569 assert(move_is_ok(move));
1572 ss[ply].currentMove = move;
1575 if ( UseQSearchFutilityPruning
1579 && !move_promotion(move)
1580 && !pos.move_is_check(move, dcCandidates)
1581 && !pos.move_is_passed_pawn_push(move))
1583 Value futilityValue = staticValue
1584 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1585 pos.endgame_value_of_piece_on(move_to(move)))
1586 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1588 + ei.futilityMargin;
1590 if (futilityValue < alpha)
1592 if (futilityValue > bestValue)
1593 bestValue = futilityValue;
1598 // Don't search captures and checks with negative SEE values
1600 && !move_promotion(move)
1601 && (pos.midgame_value_of_piece_on(move_from(move)) >
1602 pos.midgame_value_of_piece_on(move_to(move)))
1603 && pos.see(move) < 0)
1606 // Make and search the move.
1608 pos.do_move(move, st, dcCandidates);
1609 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1610 pos.undo_move(move);
1612 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1615 if (value > bestValue)
1626 // All legal moves have been searched. A special case: If we're in check
1627 // and no legal moves were found, it is checkmate:
1628 if (pos.is_check() && moveCount == 0) // Mate!
1629 return value_mated_in(ply);
1631 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1633 // Update transposition table
1634 Move m = ss[ply].pv[ply];
1637 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1638 if (bestValue < beta)
1639 TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE);
1641 TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
1644 // Update killers only for good check moves
1645 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1646 update_killers(m, ss[ply]);
1652 // sp_search() is used to search from a split point. This function is called
1653 // by each thread working at the split point. It is similar to the normal
1654 // search() function, but simpler. Because we have already probed the hash
1655 // table, done a null move search, and searched the first move before
1656 // splitting, we don't have to repeat all this work in sp_search(). We
1657 // also don't need to store anything to the hash table here: This is taken
1658 // care of after we return from the split point.
1660 void sp_search(SplitPoint *sp, int threadID) {
1662 assert(threadID >= 0 && threadID < ActiveThreads);
1663 assert(ActiveThreads > 1);
1665 Position pos = Position(sp->pos);
1666 SearchStack *ss = sp->sstack[threadID];
1669 bool isCheck = pos.is_check();
1670 bool useFutilityPruning = UseFutilityPruning
1671 && sp->depth < SelectiveDepth
1674 while ( sp->bestValue < sp->beta
1675 && !thread_should_stop(threadID)
1676 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1678 assert(move_is_ok(move));
1680 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1681 bool moveIsCapture = pos.move_is_capture(move);
1683 lock_grab(&(sp->lock));
1684 int moveCount = ++sp->moves;
1685 lock_release(&(sp->lock));
1687 ss[sp->ply].currentMove = move;
1689 // Decide the new search depth.
1691 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1692 Depth newDepth = sp->depth - OnePly + ext;
1695 if ( useFutilityPruning
1698 && !move_promotion(move)
1699 && moveCount >= 2 + int(sp->depth)
1700 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1703 // Make and search the move.
1705 pos.do_move(move, st, sp->dcCandidates);
1707 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1708 // if the move fails high will be re-searched at full depth.
1710 && moveCount >= LMRNonPVMoves
1712 && !move_promotion(move)
1713 && !move_is_castle(move)
1714 && !move_is_killer(move, ss[sp->ply]))
1716 ss[sp->ply].reduction = OnePly;
1717 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1720 value = sp->beta; // Just to trigger next condition
1722 if (value >= sp->beta) // Go with full depth non-pv search
1724 ss[sp->ply].reduction = Depth(0);
1725 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1727 pos.undo_move(move);
1729 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1731 if (thread_should_stop(threadID))
1735 lock_grab(&(sp->lock));
1736 if (value > sp->bestValue && !thread_should_stop(threadID))
1738 sp->bestValue = value;
1739 if (sp->bestValue >= sp->beta)
1741 sp_update_pv(sp->parentSstack, ss, sp->ply);
1742 for (int i = 0; i < ActiveThreads; i++)
1743 if (i != threadID && (i == sp->master || sp->slaves[i]))
1744 Threads[i].stop = true;
1746 sp->finished = true;
1749 lock_release(&(sp->lock));
1752 lock_grab(&(sp->lock));
1754 // If this is the master thread and we have been asked to stop because of
1755 // a beta cutoff higher up in the tree, stop all slave threads:
1756 if (sp->master == threadID && thread_should_stop(threadID))
1757 for (int i = 0; i < ActiveThreads; i++)
1759 Threads[i].stop = true;
1762 sp->slaves[threadID] = 0;
1764 lock_release(&(sp->lock));
1768 // sp_search_pv() is used to search from a PV split point. This function
1769 // is called by each thread working at the split point. It is similar to
1770 // the normal search_pv() function, but simpler. Because we have already
1771 // probed the hash table and searched the first move before splitting, we
1772 // don't have to repeat all this work in sp_search_pv(). We also don't
1773 // need to store anything to the hash table here: This is taken care of
1774 // after we return from the split point.
1776 void sp_search_pv(SplitPoint *sp, int threadID) {
1778 assert(threadID >= 0 && threadID < ActiveThreads);
1779 assert(ActiveThreads > 1);
1781 Position pos = Position(sp->pos);
1782 SearchStack *ss = sp->sstack[threadID];
1786 while ( sp->alpha < sp->beta
1787 && !thread_should_stop(threadID)
1788 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1790 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1791 bool moveIsCapture = pos.move_is_capture(move);
1793 assert(move_is_ok(move));
1795 lock_grab(&(sp->lock));
1796 int moveCount = ++sp->moves;
1797 lock_release(&(sp->lock));
1799 ss[sp->ply].currentMove = move;
1801 // Decide the new search depth.
1803 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1804 Depth newDepth = sp->depth - OnePly + ext;
1806 // Make and search the move.
1808 pos.do_move(move, st, sp->dcCandidates);
1810 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1811 // if the move fails high will be re-searched at full depth.
1813 && moveCount >= LMRPVMoves
1815 && !move_promotion(move)
1816 && !move_is_castle(move)
1817 && !move_is_killer(move, ss[sp->ply]))
1819 ss[sp->ply].reduction = OnePly;
1820 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1823 value = sp->alpha + 1; // Just to trigger next condition
1825 if (value > sp->alpha) // Go with full depth non-pv search
1827 ss[sp->ply].reduction = Depth(0);
1828 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1830 if (value > sp->alpha && value < sp->beta)
1832 // When the search fails high at ply 1 while searching the first
1833 // move at the root, set the flag failHighPly1. This is used for
1834 // time managment: We don't want to stop the search early in
1835 // such cases, because resolving the fail high at ply 1 could
1836 // result in a big drop in score at the root.
1837 if (sp->ply == 1 && RootMoveNumber == 1)
1838 Threads[threadID].failHighPly1 = true;
1840 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1841 Threads[threadID].failHighPly1 = false;
1844 pos.undo_move(move);
1846 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1848 if (thread_should_stop(threadID))
1852 lock_grab(&(sp->lock));
1853 if (value > sp->bestValue && !thread_should_stop(threadID))
1855 sp->bestValue = value;
1856 if (value > sp->alpha)
1859 sp_update_pv(sp->parentSstack, ss, sp->ply);
1860 if (value == value_mate_in(sp->ply + 1))
1861 ss[sp->ply].mateKiller = move;
1863 if(value >= sp->beta)
1865 for(int i = 0; i < ActiveThreads; i++)
1866 if(i != threadID && (i == sp->master || sp->slaves[i]))
1867 Threads[i].stop = true;
1869 sp->finished = true;
1872 // If we are at ply 1, and we are searching the first root move at
1873 // ply 0, set the 'Problem' variable if the score has dropped a lot
1874 // (from the computer's point of view) since the previous iteration.
1877 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1880 lock_release(&(sp->lock));
1883 lock_grab(&(sp->lock));
1885 // If this is the master thread and we have been asked to stop because of
1886 // a beta cutoff higher up in the tree, stop all slave threads.
1887 if (sp->master == threadID && thread_should_stop(threadID))
1888 for (int i = 0; i < ActiveThreads; i++)
1890 Threads[i].stop = true;
1893 sp->slaves[threadID] = 0;
1895 lock_release(&(sp->lock));
1898 /// The BetaCounterType class
1900 BetaCounterType::BetaCounterType() { clear(); }
1902 void BetaCounterType::clear() {
1904 for (int i = 0; i < THREAD_MAX; i++)
1905 hits[i][WHITE] = hits[i][BLACK] = 0ULL;
1908 void BetaCounterType::add(Color us, Depth d, int threadID) {
1910 // Weighted count based on depth
1911 hits[threadID][us] += int(d);
1914 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1917 for (int i = 0; i < THREAD_MAX; i++)
1920 their += hits[i][opposite_color(us)];
1925 /// The RootMove class
1929 RootMove::RootMove() {
1930 nodes = cumulativeNodes = 0ULL;
1933 // RootMove::operator<() is the comparison function used when
1934 // sorting the moves. A move m1 is considered to be better
1935 // than a move m2 if it has a higher score, or if the moves
1936 // have equal score but m1 has the higher node count.
1938 bool RootMove::operator<(const RootMove& m) {
1940 if (score != m.score)
1941 return (score < m.score);
1943 return theirBeta <= m.theirBeta;
1946 /// The RootMoveList class
1950 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1952 MoveStack mlist[MaxRootMoves];
1953 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1955 // Generate all legal moves
1956 int lm_count = generate_legal_moves(pos, mlist);
1958 // Add each move to the moves[] array
1959 for (int i = 0; i < lm_count; i++)
1961 bool includeMove = includeAllMoves;
1963 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1964 includeMove = (searchMoves[k] == mlist[i].move);
1968 // Find a quick score for the move
1970 SearchStack ss[PLY_MAX_PLUS_2];
1972 moves[count].move = mlist[i].move;
1973 moves[count].nodes = 0ULL;
1974 pos.do_move(moves[count].move, st);
1975 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE,
1977 pos.undo_move(moves[count].move);
1978 moves[count].pv[0] = moves[i].move;
1979 moves[count].pv[1] = MOVE_NONE; // FIXME
1987 // Simple accessor methods for the RootMoveList class
1989 inline Move RootMoveList::get_move(int moveNum) const {
1990 return moves[moveNum].move;
1993 inline Value RootMoveList::get_move_score(int moveNum) const {
1994 return moves[moveNum].score;
1997 inline void RootMoveList::set_move_score(int moveNum, Value score) {
1998 moves[moveNum].score = score;
2001 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2002 moves[moveNum].nodes = nodes;
2003 moves[moveNum].cumulativeNodes += nodes;
2006 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2007 moves[moveNum].ourBeta = our;
2008 moves[moveNum].theirBeta = their;
2011 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2013 for(j = 0; pv[j] != MOVE_NONE; j++)
2014 moves[moveNum].pv[j] = pv[j];
2015 moves[moveNum].pv[j] = MOVE_NONE;
2018 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2019 return moves[moveNum].pv[i];
2022 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2023 return moves[moveNum].cumulativeNodes;
2026 inline int RootMoveList::move_count() const {
2031 // RootMoveList::scan_for_easy_move() is called at the end of the first
2032 // iteration, and is used to detect an "easy move", i.e. a move which appears
2033 // to be much bester than all the rest. If an easy move is found, the move
2034 // is returned, otherwise the function returns MOVE_NONE. It is very
2035 // important that this function is called at the right moment: The code
2036 // assumes that the first iteration has been completed and the moves have
2037 // been sorted. This is done in RootMoveList c'tor.
2039 Move RootMoveList::scan_for_easy_move() const {
2046 // moves are sorted so just consider the best and the second one
2047 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
2053 // RootMoveList::sort() sorts the root move list at the beginning of a new
2056 inline void RootMoveList::sort() {
2058 sort_multipv(count - 1); // all items
2062 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2063 // list by their scores and depths. It is used to order the different PVs
2064 // correctly in MultiPV mode.
2066 void RootMoveList::sort_multipv(int n) {
2068 for (int i = 1; i <= n; i++)
2070 RootMove rm = moves[i];
2072 for (j = i; j > 0 && moves[j-1] < rm; j--)
2073 moves[j] = moves[j-1];
2079 // init_node() is called at the beginning of all the search functions
2080 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2081 // stack object corresponding to the current node. Once every
2082 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2083 // for user input and checks whether it is time to stop the search.
2085 void init_node(SearchStack ss[], int ply, int threadID) {
2086 assert(ply >= 0 && ply < PLY_MAX);
2087 assert(threadID >= 0 && threadID < ActiveThreads);
2089 Threads[threadID].nodes++;
2093 if(NodesSincePoll >= NodesBetweenPolls) {
2100 ss[ply+2].initKillers();
2102 if(Threads[threadID].printCurrentLine)
2103 print_current_line(ss, ply, threadID);
2107 // update_pv() is called whenever a search returns a value > alpha. It
2108 // updates the PV in the SearchStack object corresponding to the current
2111 void update_pv(SearchStack ss[], int ply) {
2112 assert(ply >= 0 && ply < PLY_MAX);
2114 ss[ply].pv[ply] = ss[ply].currentMove;
2116 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2117 ss[ply].pv[p] = ss[ply+1].pv[p];
2118 ss[ply].pv[p] = MOVE_NONE;
2122 // sp_update_pv() is a variant of update_pv for use at split points. The
2123 // difference between the two functions is that sp_update_pv also updates
2124 // the PV at the parent node.
2126 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply) {
2127 assert(ply >= 0 && ply < PLY_MAX);
2129 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2131 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2132 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2133 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2137 // connected_moves() tests whether two moves are 'connected' in the sense
2138 // that the first move somehow made the second move possible (for instance
2139 // if the moving piece is the same in both moves). The first move is
2140 // assumed to be the move that was made to reach the current position, while
2141 // the second move is assumed to be a move from the current position.
2143 bool connected_moves(const Position &pos, Move m1, Move m2) {
2144 Square f1, t1, f2, t2;
2146 assert(move_is_ok(m1));
2147 assert(move_is_ok(m2));
2152 // Case 1: The moving piece is the same in both moves.
2158 // Case 2: The destination square for m2 was vacated by m1.
2164 // Case 3: Moving through the vacated square:
2165 if(piece_is_slider(pos.piece_on(f2)) &&
2166 bit_is_set(squares_between(f2, t2), f1))
2169 // Case 4: The destination square for m2 is attacked by the moving piece
2171 if(pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
2174 // Case 5: Discovered check, checking piece is the piece moved in m1:
2175 if(piece_is_slider(pos.piece_on(t1)) &&
2176 bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())),
2178 !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())),
2180 Bitboard occ = pos.occupied_squares();
2181 Color us = pos.side_to_move();
2182 Square ksq = pos.king_square(us);
2183 clear_bit(&occ, f2);
2184 if(pos.type_of_piece_on(t1) == BISHOP) {
2185 if(bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2188 else if(pos.type_of_piece_on(t1) == ROOK) {
2189 if(bit_is_set(rook_attacks_bb(ksq, occ), t1))
2193 assert(pos.type_of_piece_on(t1) == QUEEN);
2194 if(bit_is_set(queen_attacks_bb(ksq, occ), t1))
2203 // value_is_mate() checks if the given value is a mate one
2204 // eventually compensated for the ply.
2206 bool value_is_mate(Value value) {
2208 assert(abs(value) <= VALUE_INFINITE);
2210 return value <= value_mated_in(PLY_MAX)
2211 || value >= value_mate_in(PLY_MAX);
2215 // move_is_killer() checks if the given move is among the
2216 // killer moves of that ply.
2218 bool move_is_killer(Move m, const SearchStack& ss) {
2220 const Move* k = ss.killers;
2221 for (int i = 0; i < KILLER_MAX; i++, k++)
2229 // extension() decides whether a move should be searched with normal depth,
2230 // or with extended depth. Certain classes of moves (checking moves, in
2231 // particular) are searched with bigger depth than ordinary moves and in
2232 // any case are marked as 'dangerous'. Note that also if a move is not
2233 // extended, as example because the corresponding UCI option is set to zero,
2234 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2236 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2237 bool singleReply, bool mateThreat, bool* dangerous) {
2239 assert(m != MOVE_NONE);
2241 Depth result = Depth(0);
2242 *dangerous = check || singleReply || mateThreat;
2245 result += CheckExtension[pvNode];
2248 result += SingleReplyExtension[pvNode];
2251 result += MateThreatExtension[pvNode];
2253 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2255 if (pos.move_is_pawn_push_to_7th(m))
2257 result += PawnPushTo7thExtension[pvNode];
2260 if (pos.move_is_passed_pawn_push(m))
2262 result += PassedPawnExtension[pvNode];
2268 && pos.type_of_piece_on(move_to(m)) != PAWN
2269 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2270 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2271 && !move_promotion(m)
2274 result += PawnEndgameExtension[pvNode];
2280 && pos.type_of_piece_on(move_to(m)) != PAWN
2287 return Min(result, OnePly);
2291 // ok_to_do_nullmove() looks at the current position and decides whether
2292 // doing a 'null move' should be allowed. In order to avoid zugzwang
2293 // problems, null moves are not allowed when the side to move has very
2294 // little material left. Currently, the test is a bit too simple: Null
2295 // moves are avoided only when the side to move has only pawns left. It's
2296 // probably a good idea to avoid null moves in at least some more
2297 // complicated endgames, e.g. KQ vs KR. FIXME
2299 bool ok_to_do_nullmove(const Position &pos) {
2300 if(pos.non_pawn_material(pos.side_to_move()) == Value(0))
2306 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2307 // non-tactical moves late in the move list close to the leaves are
2308 // candidates for pruning.
2310 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d) {
2311 Square mfrom, mto, tfrom, tto;
2313 assert(move_is_ok(m));
2314 assert(threat == MOVE_NONE || move_is_ok(threat));
2315 assert(!move_promotion(m));
2316 assert(!pos.move_is_check(m));
2317 assert(!pos.move_is_capture(m));
2318 assert(!pos.move_is_passed_pawn_push(m));
2319 assert(d >= OnePly);
2321 mfrom = move_from(m);
2323 tfrom = move_from(threat);
2324 tto = move_to(threat);
2326 // Case 1: Castling moves are never pruned.
2327 if (move_is_castle(m))
2330 // Case 2: Don't prune moves which move the threatened piece
2331 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2334 // Case 3: If the threatened piece has value less than or equal to the
2335 // value of the threatening piece, don't prune move which defend it.
2336 if ( !PruneDefendingMoves
2337 && threat != MOVE_NONE
2338 && pos.move_is_capture(threat)
2339 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2340 || pos.type_of_piece_on(tfrom) == KING)
2341 && pos.move_attacks_square(m, tto))
2344 // Case 4: Don't prune moves with good history.
2345 if (!H.ok_to_prune(pos.piece_on(move_from(m)), m, d))
2348 // Case 5: If the moving piece in the threatened move is a slider, don't
2349 // prune safe moves which block its ray.
2350 if ( !PruneBlockingMoves
2351 && threat != MOVE_NONE
2352 && piece_is_slider(pos.piece_on(tfrom))
2353 && bit_is_set(squares_between(tfrom, tto), mto)
2361 // ok_to_use_TT() returns true if a transposition table score
2362 // can be used at a given point in search.
2364 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2366 Value v = value_from_tt(tte->value(), ply);
2368 return ( tte->depth() >= depth
2369 || v >= Max(value_mate_in(100), beta)
2370 || v < Min(value_mated_in(100), beta))
2372 && ( (is_lower_bound(tte->type()) && v >= beta)
2373 || (is_upper_bound(tte->type()) && v < beta));
2377 // ok_to_history() returns true if a move m can be stored
2378 // in history. Should be a non capturing move nor a promotion.
2380 bool ok_to_history(const Position& pos, Move m) {
2382 return !pos.move_is_capture(m) && !move_promotion(m);
2386 // update_history() registers a good move that produced a beta-cutoff
2387 // in history and marks as failures all the other moves of that ply.
2389 void update_history(const Position& pos, Move m, Depth depth,
2390 Move movesSearched[], int moveCount) {
2392 H.success(pos.piece_on(move_from(m)), m, depth);
2394 for (int i = 0; i < moveCount - 1; i++)
2396 assert(m != movesSearched[i]);
2397 if (ok_to_history(pos, movesSearched[i]))
2398 H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
2403 // update_killers() add a good move that produced a beta-cutoff
2404 // among the killer moves of that ply.
2406 void update_killers(Move m, SearchStack& ss) {
2408 if (m == ss.killers[0])
2411 for (int i = KILLER_MAX - 1; i > 0; i--)
2412 ss.killers[i] = ss.killers[i - 1];
2417 // fail_high_ply_1() checks if some thread is currently resolving a fail
2418 // high at ply 1 at the node below the first root node. This information
2419 // is used for time managment.
2421 bool fail_high_ply_1() {
2422 for(int i = 0; i < ActiveThreads; i++)
2423 if(Threads[i].failHighPly1)
2429 // current_search_time() returns the number of milliseconds which have passed
2430 // since the beginning of the current search.
2432 int current_search_time() {
2433 return get_system_time() - SearchStartTime;
2437 // nps() computes the current nodes/second count.
2440 int t = current_search_time();
2441 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2445 // poll() performs two different functions: It polls for user input, and it
2446 // looks at the time consumed so far and decides if it's time to abort the
2451 static int lastInfoTime;
2452 int t = current_search_time();
2457 // We are line oriented, don't read single chars
2458 std::string command;
2459 if (!std::getline(std::cin, command))
2462 if (command == "quit")
2465 PonderSearch = false;
2468 else if(command == "stop")
2471 PonderSearch = false;
2473 else if(command == "ponderhit")
2476 // Print search information
2480 else if (lastInfoTime > t)
2481 // HACK: Must be a new search where we searched less than
2482 // NodesBetweenPolls nodes during the first second of search.
2485 else if (t - lastInfoTime >= 1000)
2492 if (dbg_show_hit_rate)
2493 dbg_print_hit_rate();
2495 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2496 << " time " << t << " hashfull " << TT.full() << std::endl;
2497 lock_release(&IOLock);
2498 if (ShowCurrentLine)
2499 Threads[0].printCurrentLine = true;
2501 // Should we stop the search?
2505 bool overTime = t > AbsoluteMaxSearchTime
2506 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2507 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2508 && t > 6*(MaxSearchTime + ExtraSearchTime));
2510 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2511 || (ExactMaxTime && t >= ExactMaxTime)
2512 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2517 // ponderhit() is called when the program is pondering (i.e. thinking while
2518 // it's the opponent's turn to move) in order to let the engine know that
2519 // it correctly predicted the opponent's move.
2522 int t = current_search_time();
2523 PonderSearch = false;
2524 if(Iteration >= 3 &&
2525 (!InfiniteSearch && (StopOnPonderhit ||
2526 t > AbsoluteMaxSearchTime ||
2527 (RootMoveNumber == 1 &&
2528 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2529 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2530 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2535 // print_current_line() prints the current line of search for a given
2536 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2538 void print_current_line(SearchStack ss[], int ply, int threadID) {
2539 assert(ply >= 0 && ply < PLY_MAX);
2540 assert(threadID >= 0 && threadID < ActiveThreads);
2542 if(!Threads[threadID].idle) {
2544 std::cout << "info currline " << (threadID + 1);
2545 for(int p = 0; p < ply; p++)
2546 std::cout << " " << ss[p].currentMove;
2547 std::cout << std::endl;
2548 lock_release(&IOLock);
2550 Threads[threadID].printCurrentLine = false;
2551 if(threadID + 1 < ActiveThreads)
2552 Threads[threadID + 1].printCurrentLine = true;
2556 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2557 // while the program is pondering. The point is to work around a wrinkle in
2558 // the UCI protocol: When pondering, the engine is not allowed to give a
2559 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2560 // We simply wait here until one of these commands is sent, and return,
2561 // after which the bestmove and pondermove will be printed (in id_loop()).
2563 void wait_for_stop_or_ponderhit() {
2564 std::string command;
2567 if(!std::getline(std::cin, command))
2570 if(command == "quit") {
2571 OpeningBook.close();
2576 else if(command == "ponderhit" || command == "stop")
2582 // idle_loop() is where the threads are parked when they have no work to do.
2583 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2584 // object for which the current thread is the master.
2586 void idle_loop(int threadID, SplitPoint *waitSp) {
2587 assert(threadID >= 0 && threadID < THREAD_MAX);
2589 Threads[threadID].running = true;
2592 if(AllThreadsShouldExit && threadID != 0)
2595 // If we are not thinking, wait for a condition to be signaled instead
2596 // of wasting CPU time polling for work:
2597 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2598 #if !defined(_MSC_VER)
2599 pthread_mutex_lock(&WaitLock);
2600 if(Idle || threadID >= ActiveThreads)
2601 pthread_cond_wait(&WaitCond, &WaitLock);
2602 pthread_mutex_unlock(&WaitLock);
2604 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2608 // If this thread has been assigned work, launch a search:
2609 if(Threads[threadID].workIsWaiting) {
2610 Threads[threadID].workIsWaiting = false;
2611 if(Threads[threadID].splitPoint->pvNode)
2612 sp_search_pv(Threads[threadID].splitPoint, threadID);
2614 sp_search(Threads[threadID].splitPoint, threadID);
2615 Threads[threadID].idle = true;
2618 // If this thread is the master of a split point and all threads have
2619 // finished their work at this split point, return from the idle loop:
2620 if(waitSp != NULL && waitSp->cpus == 0)
2624 Threads[threadID].running = false;
2628 // init_split_point_stack() is called during program initialization, and
2629 // initializes all split point objects.
2631 void init_split_point_stack() {
2632 for(int i = 0; i < THREAD_MAX; i++)
2633 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2634 SplitPointStack[i][j].parent = NULL;
2635 lock_init(&(SplitPointStack[i][j].lock), NULL);
2640 // destroy_split_point_stack() is called when the program exits, and
2641 // destroys all locks in the precomputed split point objects.
2643 void destroy_split_point_stack() {
2644 for(int i = 0; i < THREAD_MAX; i++)
2645 for(int j = 0; j < MaxActiveSplitPoints; j++)
2646 lock_destroy(&(SplitPointStack[i][j].lock));
2650 // thread_should_stop() checks whether the thread with a given threadID has
2651 // been asked to stop, directly or indirectly. This can happen if a beta
2652 // cutoff has occured in thre thread's currently active split point, or in
2653 // some ancestor of the current split point.
2655 bool thread_should_stop(int threadID) {
2656 assert(threadID >= 0 && threadID < ActiveThreads);
2660 if(Threads[threadID].stop)
2662 if(ActiveThreads <= 2)
2664 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2666 Threads[threadID].stop = true;
2673 // thread_is_available() checks whether the thread with threadID "slave" is
2674 // available to help the thread with threadID "master" at a split point. An
2675 // obvious requirement is that "slave" must be idle. With more than two
2676 // threads, this is not by itself sufficient: If "slave" is the master of
2677 // some active split point, it is only available as a slave to the other
2678 // threads which are busy searching the split point at the top of "slave"'s
2679 // split point stack (the "helpful master concept" in YBWC terminology).
2681 bool thread_is_available(int slave, int master) {
2682 assert(slave >= 0 && slave < ActiveThreads);
2683 assert(master >= 0 && master < ActiveThreads);
2684 assert(ActiveThreads > 1);
2686 if(!Threads[slave].idle || slave == master)
2689 if(Threads[slave].activeSplitPoints == 0)
2690 // No active split points means that the thread is available as a slave
2691 // for any other thread.
2694 if(ActiveThreads == 2)
2697 // Apply the "helpful master" concept if possible.
2698 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2705 // idle_thread_exists() tries to find an idle thread which is available as
2706 // a slave for the thread with threadID "master".
2708 bool idle_thread_exists(int master) {
2709 assert(master >= 0 && master < ActiveThreads);
2710 assert(ActiveThreads > 1);
2712 for(int i = 0; i < ActiveThreads; i++)
2713 if(thread_is_available(i, master))
2719 // split() does the actual work of distributing the work at a node between
2720 // several threads at PV nodes. If it does not succeed in splitting the
2721 // node (because no idle threads are available, or because we have no unused
2722 // split point objects), the function immediately returns false. If
2723 // splitting is possible, a SplitPoint object is initialized with all the
2724 // data that must be copied to the helper threads (the current position and
2725 // search stack, alpha, beta, the search depth, etc.), and we tell our
2726 // helper threads that they have been assigned work. This will cause them
2727 // to instantly leave their idle loops and call sp_search_pv(). When all
2728 // threads have returned from sp_search_pv (or, equivalently, when
2729 // splitPoint->cpus becomes 0), split() returns true.
2731 bool split(const Position &p, SearchStack *sstck, int ply,
2732 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
2733 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode) {
2736 assert(sstck != NULL);
2737 assert(ply >= 0 && ply < PLY_MAX);
2738 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2739 assert(!pvNode || *alpha < *beta);
2740 assert(*beta <= VALUE_INFINITE);
2741 assert(depth > Depth(0));
2742 assert(master >= 0 && master < ActiveThreads);
2743 assert(ActiveThreads > 1);
2745 SplitPoint *splitPoint;
2750 // If no other thread is available to help us, or if we have too many
2751 // active split points, don't split:
2752 if(!idle_thread_exists(master) ||
2753 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2754 lock_release(&MPLock);
2758 // Pick the next available split point object from the split point stack:
2759 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2760 Threads[master].activeSplitPoints++;
2762 // Initialize the split point object:
2763 splitPoint->parent = Threads[master].splitPoint;
2764 splitPoint->finished = false;
2765 splitPoint->ply = ply;
2766 splitPoint->depth = depth;
2767 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2768 splitPoint->beta = *beta;
2769 splitPoint->pvNode = pvNode;
2770 splitPoint->dcCandidates = dcCandidates;
2771 splitPoint->bestValue = *bestValue;
2772 splitPoint->master = master;
2773 splitPoint->mp = mp;
2774 splitPoint->moves = *moves;
2775 splitPoint->cpus = 1;
2776 splitPoint->pos.copy(p);
2777 splitPoint->parentSstack = sstck;
2778 for(i = 0; i < ActiveThreads; i++)
2779 splitPoint->slaves[i] = 0;
2781 // Copy the current position and the search stack to the master thread:
2782 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2783 Threads[master].splitPoint = splitPoint;
2785 // Make copies of the current position and search stack for each thread:
2786 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2788 if(thread_is_available(i, master)) {
2789 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2790 Threads[i].splitPoint = splitPoint;
2791 splitPoint->slaves[i] = 1;
2795 // Tell the threads that they have work to do. This will make them leave
2797 for(i = 0; i < ActiveThreads; i++)
2798 if(i == master || splitPoint->slaves[i]) {
2799 Threads[i].workIsWaiting = true;
2800 Threads[i].idle = false;
2801 Threads[i].stop = false;
2804 lock_release(&MPLock);
2806 // Everything is set up. The master thread enters the idle loop, from
2807 // which it will instantly launch a search, because its workIsWaiting
2808 // slot is 'true'. We send the split point as a second parameter to the
2809 // idle loop, which means that the main thread will return from the idle
2810 // loop when all threads have finished their work at this split point
2811 // (i.e. when // splitPoint->cpus == 0).
2812 idle_loop(master, splitPoint);
2814 // We have returned from the idle loop, which means that all threads are
2815 // finished. Update alpha, beta and bestvalue, and return:
2817 if(pvNode) *alpha = splitPoint->alpha;
2818 *beta = splitPoint->beta;
2819 *bestValue = splitPoint->bestValue;
2820 Threads[master].stop = false;
2821 Threads[master].idle = false;
2822 Threads[master].activeSplitPoints--;
2823 Threads[master].splitPoint = splitPoint->parent;
2824 lock_release(&MPLock);
2830 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2831 // to start a new search from the root.
2833 void wake_sleeping_threads() {
2834 if(ActiveThreads > 1) {
2835 for(int i = 1; i < ActiveThreads; i++) {
2836 Threads[i].idle = true;
2837 Threads[i].workIsWaiting = false;
2839 #if !defined(_MSC_VER)
2840 pthread_mutex_lock(&WaitLock);
2841 pthread_cond_broadcast(&WaitCond);
2842 pthread_mutex_unlock(&WaitLock);
2844 for(int i = 1; i < THREAD_MAX; i++)
2845 SetEvent(SitIdleEvent[i]);
2851 // init_thread() is the function which is called when a new thread is
2852 // launched. It simply calls the idle_loop() function with the supplied
2853 // threadID. There are two versions of this function; one for POSIX threads
2854 // and one for Windows threads.
2856 #if !defined(_MSC_VER)
2858 void *init_thread(void *threadID) {
2859 idle_loop(*(int *)threadID, NULL);
2865 DWORD WINAPI init_thread(LPVOID threadID) {
2866 idle_loop(*(int *)threadID, NULL);