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 const Value FutilityMarginQS = Value(0x80);
185 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
186 const Value FutilityMargins[12] = { Value(0x100), Value(0x120), Value(0x200), Value(0x220), Value(0x250), Value(0x270),
187 // 4 ply 4.5 ply 5 ply 5.5 ply 6 ply 6.5 ply
188 Value(0x2A0), Value(0x2C0), Value(0x340), Value(0x360), Value(0x3A0), Value(0x3C0) };
190 const Depth RazorDepth = 4*OnePly;
192 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
193 const Value RazorMargins[6] = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
195 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
196 const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
198 // Last seconds noise filtering (LSN)
199 bool UseLSNFiltering;
200 bool looseOnTime = false;
201 int LSNTime; // In milliseconds
204 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
205 Depth CheckExtension[2], SingleReplyExtension[2], PawnPushTo7thExtension[2];
206 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
208 // Search depth at iteration 1
209 const Depth InitialDepth = OnePly /*+ OnePly/2*/;
213 int NodesBetweenPolls = 30000;
215 // Iteration counters
217 BetaCounterType BetaCounter;
219 // Scores and number of times the best move changed for each iteration:
220 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
221 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
226 // Time managment variables
228 int MaxNodes, MaxDepth;
229 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
234 bool StopOnPonderhit;
240 bool PonderingEnabled;
243 // Show current line?
244 bool ShowCurrentLine;
248 std::ofstream LogFile;
250 // MP related variables
251 Depth MinimumSplitDepth;
252 int MaxThreadsPerSplitPoint;
253 Thread Threads[THREAD_MAX];
255 bool AllThreadsShouldExit = false;
256 const int MaxActiveSplitPoints = 8;
257 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
260 #if !defined(_MSC_VER)
261 pthread_cond_t WaitCond;
262 pthread_mutex_t WaitLock;
264 HANDLE SitIdleEvent[THREAD_MAX];
270 Value id_loop(const Position &pos, Move searchMoves[]);
271 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta);
272 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
273 Value search(Position &pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID);
274 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
275 void sp_search(SplitPoint *sp, int threadID);
276 void sp_search_pv(SplitPoint *sp, int threadID);
277 void init_node(SearchStack ss[], int ply, int threadID);
278 void update_pv(SearchStack ss[], int ply);
279 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
280 bool connected_moves(const Position &pos, Move m1, Move m2);
281 bool value_is_mate(Value value);
282 bool move_is_killer(Move m, const SearchStack& ss);
283 Depth extension(const Position &pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
284 bool ok_to_do_nullmove(const Position &pos);
285 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
286 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
287 bool ok_to_history(const Position &pos, Move m);
288 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
289 void update_killers(Move m, SearchStack& ss);
291 bool fail_high_ply_1();
292 int current_search_time();
296 void print_current_line(SearchStack ss[], int ply, int threadID);
297 void wait_for_stop_or_ponderhit();
299 void idle_loop(int threadID, SplitPoint *waitSp);
300 void init_split_point_stack();
301 void destroy_split_point_stack();
302 bool thread_should_stop(int threadID);
303 bool thread_is_available(int slave, int master);
304 bool idle_thread_exists(int master);
305 bool split(const Position &pos, SearchStack *ss, int ply,
306 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
307 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode);
308 void wake_sleeping_threads();
310 #if !defined(_MSC_VER)
311 void *init_thread(void *threadID);
313 DWORD WINAPI init_thread(LPVOID threadID);
320 //// Global variables
323 // The main transposition table
324 TranspositionTable TT;
327 // Number of active threads:
328 int ActiveThreads = 1;
330 // Locks. In principle, there is no need for IOLock to be a global variable,
331 // but it could turn out to be useful for debugging.
334 History H; // Should be made local?
336 // The empty search stack
337 SearchStack EmptySearchStack;
340 // SearchStack::init() initializes a search stack. Used at the beginning of a
341 // new search from the root.
342 void SearchStack::init(int ply) {
344 pv[ply] = pv[ply + 1] = MOVE_NONE;
345 currentMove = threatMove = MOVE_NONE;
346 reduction = Depth(0);
349 void SearchStack::initKillers() {
351 mateKiller = MOVE_NONE;
352 for (int i = 0; i < KILLER_MAX; i++)
353 killers[i] = MOVE_NONE;
361 /// think() is the external interface to Stockfish's search, and is called when
362 /// the program receives the UCI 'go' command. It initializes various
363 /// search-related global variables, and calls root_search()
365 void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
366 int time[], int increment[], int movesToGo, int maxDepth,
367 int maxNodes, int maxTime, Move searchMoves[]) {
369 // Look for a book move
370 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
373 if (get_option_value_string("Book File") != OpeningBook.file_name())
376 OpeningBook.open("book.bin");
378 bookMove = OpeningBook.get_move(pos);
379 if (bookMove != MOVE_NONE)
381 std::cout << "bestmove " << bookMove << std::endl;
386 // Initialize global search variables
388 SearchStartTime = get_system_time();
389 EasyMove = MOVE_NONE;
390 for (int i = 0; i < THREAD_MAX; i++)
392 Threads[i].nodes = 0ULL;
393 Threads[i].failHighPly1 = false;
396 InfiniteSearch = infinite;
397 PonderSearch = ponder;
398 StopOnPonderhit = false;
404 ExactMaxTime = maxTime;
406 // Read UCI option values
407 TT.set_size(get_option_value_int("Hash"));
408 if (button_was_pressed("Clear Hash"))
411 PonderingEnabled = get_option_value_bool("Ponder");
412 MultiPV = get_option_value_int("MultiPV");
414 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
415 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
417 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
418 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
420 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
421 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
423 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
424 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
426 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
427 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
429 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
430 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
432 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
433 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
434 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
436 Chess960 = get_option_value_bool("UCI_Chess960");
437 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
438 UseLogFile = get_option_value_bool("Use Search Log");
440 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
442 UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)");
443 UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)");
445 UseLSNFiltering = get_option_value_bool("LSN filtering");
446 LSNTime = get_option_value_int("LSN Time Margin (sec)") * 1000;
447 LSNValue = value_from_centipawns(get_option_value_int("LSN Value Margin"));
449 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
450 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
452 read_weights(pos.side_to_move());
454 int newActiveThreads = get_option_value_int("Threads");
455 if (newActiveThreads != ActiveThreads)
457 ActiveThreads = newActiveThreads;
458 init_eval(ActiveThreads);
461 // Wake up sleeping threads:
462 wake_sleeping_threads();
464 for (int i = 1; i < ActiveThreads; i++)
465 assert(thread_is_available(i, 0));
467 // Set thinking time:
468 int myTime = time[side_to_move];
469 int myIncrement = increment[side_to_move];
471 if (!movesToGo) // Sudden death time control
475 MaxSearchTime = myTime / 30 + myIncrement;
476 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
477 } else { // Blitz game without increment
478 MaxSearchTime = myTime / 30;
479 AbsoluteMaxSearchTime = myTime / 8;
482 else // (x moves) / (y minutes)
486 MaxSearchTime = myTime / 2;
487 AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
489 MaxSearchTime = myTime / Min(movesToGo, 20);
490 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
494 if (PonderingEnabled)
496 MaxSearchTime += MaxSearchTime / 4;
497 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
500 // Fixed depth or fixed number of nodes?
503 InfiniteSearch = true; // HACK
508 NodesBetweenPolls = Min(MaxNodes, 30000);
509 InfiniteSearch = true; // HACK
512 NodesBetweenPolls = 30000;
515 // Write information to search log file:
517 LogFile << "Searching: " << pos.to_fen() << std::endl
518 << "infinite: " << infinite
519 << " ponder: " << ponder
520 << " time: " << myTime
521 << " increment: " << myIncrement
522 << " moves to go: " << movesToGo << std::endl;
525 // We're ready to start thinking. Call the iterative deepening loop
529 Value v = id_loop(pos, searchMoves);
530 looseOnTime = ( UseLSNFiltering
537 looseOnTime = false; // reset for next match
538 while (SearchStartTime + myTime + 1000 > get_system_time())
540 id_loop(pos, searchMoves); // to fail gracefully
557 /// init_threads() is called during startup. It launches all helper threads,
558 /// and initializes the split point stack and the global locks and condition
561 void init_threads() {
565 #if !defined(_MSC_VER)
566 pthread_t pthread[1];
569 for (i = 0; i < THREAD_MAX; i++)
570 Threads[i].activeSplitPoints = 0;
572 // Initialize global locks:
573 lock_init(&MPLock, NULL);
574 lock_init(&IOLock, NULL);
576 init_split_point_stack();
578 #if !defined(_MSC_VER)
579 pthread_mutex_init(&WaitLock, NULL);
580 pthread_cond_init(&WaitCond, NULL);
582 for (i = 0; i < THREAD_MAX; i++)
583 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
586 // All threads except the main thread should be initialized to idle state
587 for (i = 1; i < THREAD_MAX; i++)
589 Threads[i].stop = false;
590 Threads[i].workIsWaiting = false;
591 Threads[i].idle = true;
592 Threads[i].running = false;
595 // Launch the helper threads
596 for(i = 1; i < THREAD_MAX; i++)
598 #if !defined(_MSC_VER)
599 pthread_create(pthread, NULL, init_thread, (void*)(&i));
602 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
605 // Wait until the thread has finished launching:
606 while (!Threads[i].running);
609 // Init also the empty search stack
610 EmptySearchStack.init(0);
611 EmptySearchStack.initKillers();
615 /// stop_threads() is called when the program exits. It makes all the
616 /// helper threads exit cleanly.
618 void stop_threads() {
620 ActiveThreads = THREAD_MAX; // HACK
621 Idle = false; // HACK
622 wake_sleeping_threads();
623 AllThreadsShouldExit = true;
624 for (int i = 1; i < THREAD_MAX; i++)
626 Threads[i].stop = true;
627 while(Threads[i].running);
629 destroy_split_point_stack();
633 /// nodes_searched() returns the total number of nodes searched so far in
634 /// the current search.
636 int64_t nodes_searched() {
638 int64_t result = 0ULL;
639 for (int i = 0; i < ActiveThreads; i++)
640 result += Threads[i].nodes;
647 // id_loop() is the main iterative deepening loop. It calls root_search
648 // repeatedly with increasing depth until the allocated thinking time has
649 // been consumed, the user stops the search, or the maximum search depth is
652 Value id_loop(const Position &pos, Move searchMoves[]) {
655 SearchStack ss[PLY_MAX_PLUS_2];
657 // searchMoves are verified, copied, scored and sorted
658 RootMoveList rml(p, searchMoves);
663 for (int i = 0; i < 3; i++)
668 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
671 EasyMove = rml.scan_for_easy_move();
673 // Iterative deepening loop
674 while (Iteration < PLY_MAX)
676 // Initialize iteration
679 BestMoveChangesByIteration[Iteration] = 0;
683 std::cout << "info depth " << Iteration << std::endl;
685 // Calculate dynamic search window based on previous iterations
688 if (MultiPV == 1 && Iteration >= 6)
690 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
691 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
693 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
695 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
696 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
700 alpha = - VALUE_INFINITE;
701 beta = VALUE_INFINITE;
704 // Search to the current depth
705 Value value = root_search(p, ss, rml, alpha, beta);
707 // Write PV to transposition table, in case the relevant entries have
708 // been overwritten during the search.
709 TT.insert_pv(p, ss[0].pv);
712 break; // Value cannot be trusted. Break out immediately!
714 //Save info about search result
715 Value speculatedValue;
718 Value delta = value - IterationInfo[Iteration - 1].value;
725 speculatedValue = value + delta;
726 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
728 else if (value <= alpha)
730 assert(value == alpha);
734 speculatedValue = value + delta;
735 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
737 speculatedValue = value;
739 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
740 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
742 // Erase the easy move if it differs from the new best move
743 if (ss[0].pv[0] != EasyMove)
744 EasyMove = MOVE_NONE;
751 bool stopSearch = false;
753 // Stop search early if there is only a single legal move:
754 if (Iteration >= 6 && rml.move_count() == 1)
757 // Stop search early when the last two iterations returned a mate score
759 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
760 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
763 // Stop search early if one move seems to be much better than the rest
764 int64_t nodes = nodes_searched();
768 && EasyMove == ss[0].pv[0]
769 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
770 && current_search_time() > MaxSearchTime / 16)
771 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
772 && current_search_time() > MaxSearchTime / 32)))
775 // Add some extra time if the best move has changed during the last two iterations
776 if (Iteration > 5 && Iteration <= 50)
777 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
778 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
780 // Stop search if most of MaxSearchTime is consumed at the end of the
781 // iteration. We probably don't have enough time to search the first
782 // move at the next iteration anyway.
783 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
788 //FIXME: Implement fail-low emergency measures
792 StopOnPonderhit = true;
796 if (MaxDepth && Iteration >= MaxDepth)
802 // If we are pondering, we shouldn't print the best move before we
805 wait_for_stop_or_ponderhit();
807 // Print final search statistics
808 std::cout << "info nodes " << nodes_searched()
810 << " time " << current_search_time()
811 << " hashfull " << TT.full() << std::endl;
813 // Print the best move and the ponder move to the standard output
814 if (ss[0].pv[0] == MOVE_NONE)
816 ss[0].pv[0] = rml.get_move(0);
817 ss[0].pv[1] = MOVE_NONE;
819 std::cout << "bestmove " << ss[0].pv[0];
820 if (ss[0].pv[1] != MOVE_NONE)
821 std::cout << " ponder " << ss[0].pv[1];
823 std::cout << std::endl;
828 dbg_print_mean(LogFile);
830 if (dbg_show_hit_rate)
831 dbg_print_hit_rate(LogFile);
834 LogFile << "Nodes: " << nodes_searched() << std::endl
835 << "Nodes/second: " << nps() << std::endl
836 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
838 p.do_move(ss[0].pv[0], st);
839 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
840 << std::endl << std::endl;
842 return rml.get_move_score(0);
846 // root_search() is the function which searches the root node. It is
847 // similar to search_pv except that it uses a different move ordering
848 // scheme (perhaps we should try to use this at internal PV nodes, too?)
849 // and prints some information to the standard output.
851 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta) {
853 Value oldAlpha = alpha;
855 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
857 // Loop through all the moves in the root move list
858 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
862 // We failed high, invalidate and skip next moves, leave node-counters
863 // and beta-counters as they are and quickly return, we will try to do
864 // a research at the next iteration with a bigger aspiration window.
865 rml.set_move_score(i, -VALUE_INFINITE);
873 RootMoveNumber = i + 1;
876 // Remember the node count before the move is searched. The node counts
877 // are used to sort the root moves at the next iteration.
878 nodes = nodes_searched();
880 // Reset beta cut-off counters
883 // Pick the next root move, and print the move and the move number to
884 // the standard output.
885 move = ss[0].currentMove = rml.get_move(i);
886 if (current_search_time() >= 1000)
887 std::cout << "info currmove " << move
888 << " currmovenumber " << i + 1 << std::endl;
890 // Decide search depth for this move
892 ext = extension(pos, move, true, pos.move_is_capture(move), pos.move_is_check(move), false, false, &dangerous);
893 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
895 // Make the move, and search it
896 pos.do_move(move, st, dcCandidates);
900 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
901 // If the value has dropped a lot compared to the last iteration,
902 // set the boolean variable Problem to true. This variable is used
903 // for time managment: When Problem is true, we try to complete the
904 // current iteration before playing a move.
905 Problem = (Iteration >= 2 && value <= IterationInfo[Iteration-1].value - ProblemMargin);
907 if (Problem && StopOnPonderhit)
908 StopOnPonderhit = false;
912 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
915 // Fail high! Set the boolean variable FailHigh to true, and
916 // re-search the move with a big window. The variable FailHigh is
917 // used for time managment: We try to avoid aborting the search
918 // prematurely during a fail high research.
920 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
926 // Finished searching the move. If AbortSearch is true, the search
927 // was aborted because the user interrupted the search or because we
928 // ran out of time. In this case, the return value of the search cannot
929 // be trusted, and we break out of the loop without updating the best
934 // Remember the node count for this move. The node counts are used to
935 // sort the root moves at the next iteration.
936 rml.set_move_nodes(i, nodes_searched() - nodes);
938 // Remember the beta-cutoff statistics
940 BetaCounter.read(pos.side_to_move(), our, their);
941 rml.set_beta_counters(i, our, their);
943 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
945 if (value <= alpha && i >= MultiPV)
946 rml.set_move_score(i, -VALUE_INFINITE);
949 // PV move or new best move!
952 rml.set_move_score(i, value);
954 rml.set_move_pv(i, ss[0].pv);
958 // We record how often the best move has been changed in each
959 // iteration. This information is used for time managment: When
960 // the best move changes frequently, we allocate some more time.
962 BestMoveChangesByIteration[Iteration]++;
964 // Print search information to the standard output:
965 std::cout << "info depth " << Iteration
966 << " score " << value_to_string(value)
967 << " time " << current_search_time()
968 << " nodes " << nodes_searched()
972 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
973 std::cout << ss[0].pv[j] << " ";
975 std::cout << std::endl;
978 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
984 // Reset the global variable Problem to false if the value isn't too
985 // far below the final value from the last iteration.
986 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
992 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
995 std::cout << "info multipv " << j + 1
996 << " score " << value_to_string(rml.get_move_score(j))
997 << " depth " << ((j <= i)? Iteration : Iteration - 1)
998 << " time " << current_search_time()
999 << " nodes " << nodes_searched()
1003 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1004 std::cout << rml.get_move_pv(j, k) << " ";
1006 std::cout << std::endl;
1008 alpha = rml.get_move_score(Min(i, MultiPV-1));
1010 } // New best move case
1012 assert(alpha >= oldAlpha);
1014 FailLow = (alpha == oldAlpha);
1020 // search_pv() is the main search function for PV nodes.
1022 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
1023 Depth depth, int ply, int threadID) {
1025 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1026 assert(beta > alpha && beta <= VALUE_INFINITE);
1027 assert(ply >= 0 && ply < PLY_MAX);
1028 assert(threadID >= 0 && threadID < ActiveThreads);
1031 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1033 // Initialize, and make an early exit in case of an aborted search,
1034 // an instant draw, maximum ply reached, etc.
1035 init_node(ss, ply, threadID);
1037 // After init_node() that calls poll()
1038 if (AbortSearch || thread_should_stop(threadID))
1046 if (ply >= PLY_MAX - 1)
1047 return evaluate(pos, ei, threadID);
1049 // Mate distance pruning
1050 Value oldAlpha = alpha;
1051 alpha = Max(value_mated_in(ply), alpha);
1052 beta = Min(value_mate_in(ply+1), beta);
1056 // Transposition table lookup. At PV nodes, we don't use the TT for
1057 // pruning, but only for move ordering.
1058 const TTEntry* tte = TT.retrieve(pos.get_key());
1059 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1061 // Go with internal iterative deepening if we don't have a TT move
1062 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
1064 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1065 ttMove = ss[ply].pv[ply];
1068 // Initialize a MovePicker object for the current position, and prepare
1069 // to search all moves
1070 MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
1072 Move move, movesSearched[256];
1074 Value value, bestValue = -VALUE_INFINITE;
1075 Bitboard dcCandidates = mp.discovered_check_candidates();
1076 Color us = pos.side_to_move();
1077 bool isCheck = pos.is_check();
1078 bool mateThreat = pos.has_mate_threat(opposite_color(us));
1080 // Loop through all legal moves until no moves remain or a beta cutoff
1082 while ( alpha < beta
1083 && (move = mp.get_next_move()) != MOVE_NONE
1084 && !thread_should_stop(threadID))
1086 assert(move_is_ok(move));
1088 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1089 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1090 bool moveIsCapture = pos.move_is_capture(move);
1092 movesSearched[moveCount++] = ss[ply].currentMove = move;
1094 // Decide the new search depth
1096 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1097 Depth newDepth = depth - OnePly + ext;
1099 // Make and search the move
1101 pos.do_move(move, st, dcCandidates);
1103 if (moveCount == 1) // The first move in list is the PV
1104 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1107 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1108 // if the move fails high will be re-searched at full depth.
1109 if ( depth >= 2*OnePly
1110 && moveCount >= LMRPVMoves
1113 && !move_promotion(move)
1114 && !move_is_castle(move)
1115 && !move_is_killer(move, ss[ply]))
1117 ss[ply].reduction = OnePly;
1118 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1121 value = alpha + 1; // Just to trigger next condition
1123 if (value > alpha) // Go with full depth non-pv search
1125 ss[ply].reduction = Depth(0);
1126 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1127 if (value > alpha && value < beta)
1129 // When the search fails high at ply 1 while searching the first
1130 // move at the root, set the flag failHighPly1. This is used for
1131 // time managment: We don't want to stop the search early in
1132 // such cases, because resolving the fail high at ply 1 could
1133 // result in a big drop in score at the root.
1134 if (ply == 1 && RootMoveNumber == 1)
1135 Threads[threadID].failHighPly1 = true;
1137 // A fail high occurred. Re-search at full window (pv search)
1138 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1139 Threads[threadID].failHighPly1 = false;
1143 pos.undo_move(move);
1145 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1148 if (value > bestValue)
1155 if (value == value_mate_in(ply + 1))
1156 ss[ply].mateKiller = move;
1158 // If we are at ply 1, and we are searching the first root move at
1159 // ply 0, set the 'Problem' variable if the score has dropped a lot
1160 // (from the computer's point of view) since the previous iteration:
1163 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1168 if ( ActiveThreads > 1
1170 && depth >= MinimumSplitDepth
1172 && idle_thread_exists(threadID)
1174 && !thread_should_stop(threadID)
1175 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1176 &moveCount, &mp, dcCandidates, threadID, true))
1180 // All legal moves have been searched. A special case: If there were
1181 // no legal moves, it must be mate or stalemate:
1183 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1185 // If the search is not aborted, update the transposition table,
1186 // history counters, and killer moves.
1187 if (AbortSearch || thread_should_stop(threadID))
1190 if (bestValue <= oldAlpha)
1191 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1193 else if (bestValue >= beta)
1195 BetaCounter.add(pos.side_to_move(), depth, threadID);
1196 Move m = ss[ply].pv[ply];
1197 if (ok_to_history(pos, m)) // Only non capture moves are considered
1199 update_history(pos, m, depth, movesSearched, moveCount);
1200 update_killers(m, ss[ply]);
1202 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1205 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1211 // search() is the search function for zero-width nodes.
1213 Value search(Position &pos, SearchStack ss[], Value beta, Depth depth,
1214 int ply, bool allowNullmove, int threadID) {
1216 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1217 assert(ply >= 0 && ply < PLY_MAX);
1218 assert(threadID >= 0 && threadID < ActiveThreads);
1221 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1223 // Initialize, and make an early exit in case of an aborted search,
1224 // an instant draw, maximum ply reached, etc.
1225 init_node(ss, ply, threadID);
1227 // After init_node() that calls poll()
1228 if (AbortSearch || thread_should_stop(threadID))
1236 if (ply >= PLY_MAX - 1)
1237 return evaluate(pos, ei, threadID);
1239 // Mate distance pruning
1240 if (value_mated_in(ply) >= beta)
1243 if (value_mate_in(ply + 1) < beta)
1246 // Transposition table lookup
1247 const TTEntry* tte = TT.retrieve(pos.get_key());
1248 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1250 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1252 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1253 return value_from_tt(tte->value(), ply);
1256 Value approximateEval = quick_evaluate(pos);
1257 bool mateThreat = false;
1258 bool isCheck = pos.is_check();
1264 && !value_is_mate(beta)
1265 && ok_to_do_nullmove(pos)
1266 && approximateEval >= beta - NullMoveMargin)
1268 ss[ply].currentMove = MOVE_NULL;
1271 pos.do_null_move(st);
1272 int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
1274 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1276 pos.undo_null_move();
1278 if (value_is_mate(nullValue))
1280 /* Do not return unproven mates */
1282 else if (nullValue >= beta)
1284 if (depth < 6 * OnePly)
1287 // Do zugzwang verification search
1288 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1292 // The null move failed low, which means that we may be faced with
1293 // some kind of threat. If the previous move was reduced, check if
1294 // the move that refuted the null move was somehow connected to the
1295 // move which was reduced. If a connection is found, return a fail
1296 // low score (which will cause the reduced move to fail high in the
1297 // parent node, which will trigger a re-search with full depth).
1298 if (nullValue == value_mated_in(ply + 2))
1301 ss[ply].threatMove = ss[ply + 1].currentMove;
1302 if ( depth < ThreatDepth
1303 && ss[ply - 1].reduction
1304 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1308 // Null move search not allowed, try razoring
1309 else if ( !value_is_mate(beta)
1310 && depth < RazorDepth
1311 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1312 && ss[ply - 1].currentMove != MOVE_NULL
1313 && ttMove == MOVE_NONE
1314 && !pos.has_pawn_on_7th(pos.side_to_move()))
1316 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1317 if (v < beta - RazorMargins[int(depth) - 2])
1321 // Go with internal iterative deepening if we don't have a TT move
1322 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1323 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1325 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1326 ttMove = ss[ply].pv[ply];
1329 // Initialize a MovePicker object for the current position, and prepare
1330 // to search all moves:
1331 MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth);
1333 Move move, movesSearched[256];
1335 Value value, bestValue = -VALUE_INFINITE;
1336 Bitboard dcCandidates = mp.discovered_check_candidates();
1337 Value futilityValue = VALUE_NONE;
1338 bool useFutilityPruning = UseFutilityPruning
1339 && depth < SelectiveDepth
1342 // Loop through all legal moves until no moves remain or a beta cutoff
1344 while ( bestValue < beta
1345 && (move = mp.get_next_move()) != MOVE_NONE
1346 && !thread_should_stop(threadID))
1348 assert(move_is_ok(move));
1350 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1351 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1352 bool moveIsCapture = pos.move_is_capture(move);
1354 movesSearched[moveCount++] = ss[ply].currentMove = move;
1356 // Decide the new search depth
1358 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1359 Depth newDepth = depth - OnePly + ext;
1362 if ( useFutilityPruning
1365 && !move_promotion(move))
1367 // History pruning. See ok_to_prune() definition
1368 if ( moveCount >= 2 + int(depth)
1369 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1372 // Value based pruning
1373 if (approximateEval < beta)
1375 if (futilityValue == VALUE_NONE)
1376 futilityValue = evaluate(pos, ei, threadID)
1377 + FutilityMargins[int(depth) - 2];
1379 if (futilityValue < beta)
1381 if (futilityValue > bestValue)
1382 bestValue = futilityValue;
1388 // Make and search the move
1390 pos.do_move(move, st, dcCandidates);
1392 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1393 // if the move fails high will be re-searched at full depth.
1394 if ( depth >= 2*OnePly
1395 && moveCount >= LMRNonPVMoves
1398 && !move_promotion(move)
1399 && !move_is_castle(move)
1400 && !move_is_killer(move, ss[ply]))
1402 ss[ply].reduction = OnePly;
1403 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1406 value = beta; // Just to trigger next condition
1408 if (value >= beta) // Go with full depth non-pv search
1410 ss[ply].reduction = Depth(0);
1411 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1413 pos.undo_move(move);
1415 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1418 if (value > bestValue)
1424 if (value == value_mate_in(ply + 1))
1425 ss[ply].mateKiller = move;
1429 if ( ActiveThreads > 1
1431 && depth >= MinimumSplitDepth
1433 && idle_thread_exists(threadID)
1435 && !thread_should_stop(threadID)
1436 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1437 &mp, dcCandidates, threadID, false))
1441 // All legal moves have been searched. A special case: If there were
1442 // no legal moves, it must be mate or stalemate.
1444 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1446 // If the search is not aborted, update the transposition table,
1447 // history counters, and killer moves.
1448 if (AbortSearch || thread_should_stop(threadID))
1451 if (bestValue < beta)
1452 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1455 BetaCounter.add(pos.side_to_move(), depth, threadID);
1456 Move m = ss[ply].pv[ply];
1457 if (ok_to_history(pos, m)) // Only non capture moves are considered
1459 update_history(pos, m, depth, movesSearched, moveCount);
1460 update_killers(m, ss[ply]);
1462 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1465 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1471 // qsearch() is the quiescence search function, which is called by the main
1472 // search function when the remaining depth is zero (or, to be more precise,
1473 // less than OnePly).
1475 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
1476 Depth depth, int ply, int threadID) {
1478 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1479 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1481 assert(ply >= 0 && ply < PLY_MAX);
1482 assert(threadID >= 0 && threadID < ActiveThreads);
1484 // Initialize, and make an early exit in case of an aborted search,
1485 // an instant draw, maximum ply reached, etc.
1486 init_node(ss, ply, threadID);
1488 // After init_node() that calls poll()
1489 if (AbortSearch || thread_should_stop(threadID))
1495 // Transposition table lookup, only when not in PV
1496 TTEntry* tte = NULL;
1497 bool pvNode = (beta - alpha != 1);
1500 tte = TT.retrieve(pos.get_key());
1501 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1503 assert(tte->type() != VALUE_TYPE_EVAL);
1505 return value_from_tt(tte->value(), ply);
1508 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1510 // Evaluate the position statically
1513 bool isCheck = pos.is_check();
1514 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1517 staticValue = -VALUE_INFINITE;
1519 else if (tte && tte->type() == VALUE_TYPE_EVAL)
1521 // Use the cached evaluation score if possible
1522 assert(tte->value() == evaluate(pos, ei, threadID));
1523 assert(ei.futilityMargin == Value(0));
1525 staticValue = tte->value();
1528 staticValue = evaluate(pos, ei, threadID);
1530 if (ply == PLY_MAX - 1)
1531 return evaluate(pos, ei, threadID);
1533 // Initialize "stand pat score", and return it immediately if it is
1535 Value bestValue = staticValue;
1537 if (bestValue >= beta)
1539 // Store the score to avoid a future costly evaluation() call
1540 if (!isCheck && !tte && ei.futilityMargin == 0)
1541 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EVAL, Depth(-127*OnePly), MOVE_NONE);
1546 if (bestValue > alpha)
1549 // Initialize a MovePicker object for the current position, and prepare
1550 // to search the moves. Because the depth is <= 0 here, only captures,
1551 // queen promotions and checks (only if depth == 0) will be generated.
1552 MovePicker mp = MovePicker(pos, pvNode, ttMove, EmptySearchStack, depth);
1555 Bitboard dcCandidates = mp.discovered_check_candidates();
1556 Color us = pos.side_to_move();
1557 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1559 // Loop through the moves until no moves remain or a beta cutoff
1561 while ( alpha < beta
1562 && (move = mp.get_next_move()) != MOVE_NONE)
1564 assert(move_is_ok(move));
1567 ss[ply].currentMove = move;
1570 if ( UseQSearchFutilityPruning
1574 && !move_promotion(move)
1575 && !pos.move_is_check(move, dcCandidates)
1576 && !pos.move_is_passed_pawn_push(move))
1578 Value futilityValue = staticValue
1579 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1580 pos.endgame_value_of_piece_on(move_to(move)))
1581 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1583 + ei.futilityMargin;
1585 if (futilityValue < alpha)
1587 if (futilityValue > bestValue)
1588 bestValue = futilityValue;
1593 // Don't search captures and checks with negative SEE values
1595 && !move_promotion(move)
1596 && (pos.midgame_value_of_piece_on(move_from(move)) >
1597 pos.midgame_value_of_piece_on(move_to(move)))
1598 && pos.see(move) < 0)
1601 // Make and search the move.
1603 pos.do_move(move, st, dcCandidates);
1604 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1605 pos.undo_move(move);
1607 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1610 if (value > bestValue)
1621 // All legal moves have been searched. A special case: If we're in check
1622 // and no legal moves were found, it is checkmate:
1623 if (pos.is_check() && moveCount == 0) // Mate!
1624 return value_mated_in(ply);
1626 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1628 // Update transposition table
1629 Move m = ss[ply].pv[ply];
1632 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1633 if (bestValue < beta)
1634 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE);
1636 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
1639 // Update killers only for good check moves
1640 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1641 update_killers(m, ss[ply]);
1647 // sp_search() is used to search from a split point. This function is called
1648 // by each thread working at the split point. It is similar to the normal
1649 // search() function, but simpler. Because we have already probed the hash
1650 // table, done a null move search, and searched the first move before
1651 // splitting, we don't have to repeat all this work in sp_search(). We
1652 // also don't need to store anything to the hash table here: This is taken
1653 // care of after we return from the split point.
1655 void sp_search(SplitPoint *sp, int threadID) {
1657 assert(threadID >= 0 && threadID < ActiveThreads);
1658 assert(ActiveThreads > 1);
1660 Position pos = Position(sp->pos);
1661 SearchStack *ss = sp->sstack[threadID];
1664 bool isCheck = pos.is_check();
1665 bool useFutilityPruning = UseFutilityPruning
1666 && sp->depth < SelectiveDepth
1669 while ( sp->bestValue < sp->beta
1670 && !thread_should_stop(threadID)
1671 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1673 assert(move_is_ok(move));
1675 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1676 bool moveIsCapture = pos.move_is_capture(move);
1678 lock_grab(&(sp->lock));
1679 int moveCount = ++sp->moves;
1680 lock_release(&(sp->lock));
1682 ss[sp->ply].currentMove = move;
1684 // Decide the new search depth.
1686 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1687 Depth newDepth = sp->depth - OnePly + ext;
1690 if ( useFutilityPruning
1693 && !move_promotion(move)
1694 && moveCount >= 2 + int(sp->depth)
1695 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1698 // Make and search the move.
1700 pos.do_move(move, st, sp->dcCandidates);
1702 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1703 // if the move fails high will be re-searched at full depth.
1705 && moveCount >= LMRNonPVMoves
1707 && !move_promotion(move)
1708 && !move_is_castle(move)
1709 && !move_is_killer(move, ss[sp->ply]))
1711 ss[sp->ply].reduction = OnePly;
1712 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1715 value = sp->beta; // Just to trigger next condition
1717 if (value >= sp->beta) // Go with full depth non-pv search
1719 ss[sp->ply].reduction = Depth(0);
1720 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1722 pos.undo_move(move);
1724 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1726 if (thread_should_stop(threadID))
1730 lock_grab(&(sp->lock));
1731 if (value > sp->bestValue && !thread_should_stop(threadID))
1733 sp->bestValue = value;
1734 if (sp->bestValue >= sp->beta)
1736 sp_update_pv(sp->parentSstack, ss, sp->ply);
1737 for (int i = 0; i < ActiveThreads; i++)
1738 if (i != threadID && (i == sp->master || sp->slaves[i]))
1739 Threads[i].stop = true;
1741 sp->finished = true;
1744 lock_release(&(sp->lock));
1747 lock_grab(&(sp->lock));
1749 // If this is the master thread and we have been asked to stop because of
1750 // a beta cutoff higher up in the tree, stop all slave threads:
1751 if (sp->master == threadID && thread_should_stop(threadID))
1752 for (int i = 0; i < ActiveThreads; i++)
1754 Threads[i].stop = true;
1757 sp->slaves[threadID] = 0;
1759 lock_release(&(sp->lock));
1763 // sp_search_pv() is used to search from a PV split point. This function
1764 // is called by each thread working at the split point. It is similar to
1765 // the normal search_pv() function, but simpler. Because we have already
1766 // probed the hash table and searched the first move before splitting, we
1767 // don't have to repeat all this work in sp_search_pv(). We also don't
1768 // need to store anything to the hash table here: This is taken care of
1769 // after we return from the split point.
1771 void sp_search_pv(SplitPoint *sp, int threadID) {
1773 assert(threadID >= 0 && threadID < ActiveThreads);
1774 assert(ActiveThreads > 1);
1776 Position pos = Position(sp->pos);
1777 SearchStack *ss = sp->sstack[threadID];
1781 while ( sp->alpha < sp->beta
1782 && !thread_should_stop(threadID)
1783 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1785 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1786 bool moveIsCapture = pos.move_is_capture(move);
1788 assert(move_is_ok(move));
1790 lock_grab(&(sp->lock));
1791 int moveCount = ++sp->moves;
1792 lock_release(&(sp->lock));
1794 ss[sp->ply].currentMove = move;
1796 // Decide the new search depth.
1798 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1799 Depth newDepth = sp->depth - OnePly + ext;
1801 // Make and search the move.
1803 pos.do_move(move, st, sp->dcCandidates);
1805 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1806 // if the move fails high will be re-searched at full depth.
1808 && moveCount >= LMRPVMoves
1810 && !move_promotion(move)
1811 && !move_is_castle(move)
1812 && !move_is_killer(move, ss[sp->ply]))
1814 ss[sp->ply].reduction = OnePly;
1815 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1818 value = sp->alpha + 1; // Just to trigger next condition
1820 if (value > sp->alpha) // Go with full depth non-pv search
1822 ss[sp->ply].reduction = Depth(0);
1823 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1825 if (value > sp->alpha && value < sp->beta)
1827 // When the search fails high at ply 1 while searching the first
1828 // move at the root, set the flag failHighPly1. This is used for
1829 // time managment: We don't want to stop the search early in
1830 // such cases, because resolving the fail high at ply 1 could
1831 // result in a big drop in score at the root.
1832 if (sp->ply == 1 && RootMoveNumber == 1)
1833 Threads[threadID].failHighPly1 = true;
1835 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1836 Threads[threadID].failHighPly1 = false;
1839 pos.undo_move(move);
1841 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1843 if (thread_should_stop(threadID))
1847 lock_grab(&(sp->lock));
1848 if (value > sp->bestValue && !thread_should_stop(threadID))
1850 sp->bestValue = value;
1851 if (value > sp->alpha)
1854 sp_update_pv(sp->parentSstack, ss, sp->ply);
1855 if (value == value_mate_in(sp->ply + 1))
1856 ss[sp->ply].mateKiller = move;
1858 if(value >= sp->beta)
1860 for(int i = 0; i < ActiveThreads; i++)
1861 if(i != threadID && (i == sp->master || sp->slaves[i]))
1862 Threads[i].stop = true;
1864 sp->finished = true;
1867 // If we are at ply 1, and we are searching the first root move at
1868 // ply 0, set the 'Problem' variable if the score has dropped a lot
1869 // (from the computer's point of view) since the previous iteration.
1872 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1875 lock_release(&(sp->lock));
1878 lock_grab(&(sp->lock));
1880 // If this is the master thread and we have been asked to stop because of
1881 // a beta cutoff higher up in the tree, stop all slave threads.
1882 if (sp->master == threadID && thread_should_stop(threadID))
1883 for (int i = 0; i < ActiveThreads; i++)
1885 Threads[i].stop = true;
1888 sp->slaves[threadID] = 0;
1890 lock_release(&(sp->lock));
1893 /// The BetaCounterType class
1895 BetaCounterType::BetaCounterType() { clear(); }
1897 void BetaCounterType::clear() {
1899 for (int i = 0; i < THREAD_MAX; i++)
1900 hits[i][WHITE] = hits[i][BLACK] = 0ULL;
1903 void BetaCounterType::add(Color us, Depth d, int threadID) {
1905 // Weighted count based on depth
1906 hits[threadID][us] += int(d);
1909 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1912 for (int i = 0; i < THREAD_MAX; i++)
1915 their += hits[i][opposite_color(us)];
1920 /// The RootMove class
1924 RootMove::RootMove() {
1925 nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
1928 // RootMove::operator<() is the comparison function used when
1929 // sorting the moves. A move m1 is considered to be better
1930 // than a move m2 if it has a higher score, or if the moves
1931 // have equal score but m1 has the higher node count.
1933 bool RootMove::operator<(const RootMove& m) {
1935 if (score != m.score)
1936 return (score < m.score);
1938 return theirBeta <= m.theirBeta;
1941 /// The RootMoveList class
1945 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1947 MoveStack mlist[MaxRootMoves];
1948 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1950 // Generate all legal moves
1951 int lm_count = generate_legal_moves(pos, mlist);
1953 // Add each move to the moves[] array
1954 for (int i = 0; i < lm_count; i++)
1956 bool includeMove = includeAllMoves;
1958 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1959 includeMove = (searchMoves[k] == mlist[i].move);
1964 // Find a quick score for the move
1966 SearchStack ss[PLY_MAX_PLUS_2];
1968 moves[count].move = mlist[i].move;
1969 pos.do_move(moves[count].move, st);
1970 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
1971 pos.undo_move(moves[count].move);
1972 moves[count].pv[0] = moves[count].move;
1973 moves[count].pv[1] = MOVE_NONE; // FIXME
1980 // Simple accessor methods for the RootMoveList class
1982 inline Move RootMoveList::get_move(int moveNum) const {
1983 return moves[moveNum].move;
1986 inline Value RootMoveList::get_move_score(int moveNum) const {
1987 return moves[moveNum].score;
1990 inline void RootMoveList::set_move_score(int moveNum, Value score) {
1991 moves[moveNum].score = score;
1994 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
1995 moves[moveNum].nodes = nodes;
1996 moves[moveNum].cumulativeNodes += nodes;
1999 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2000 moves[moveNum].ourBeta = our;
2001 moves[moveNum].theirBeta = their;
2004 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2006 for(j = 0; pv[j] != MOVE_NONE; j++)
2007 moves[moveNum].pv[j] = pv[j];
2008 moves[moveNum].pv[j] = MOVE_NONE;
2011 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2012 return moves[moveNum].pv[i];
2015 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2016 return moves[moveNum].cumulativeNodes;
2019 inline int RootMoveList::move_count() const {
2024 // RootMoveList::scan_for_easy_move() is called at the end of the first
2025 // iteration, and is used to detect an "easy move", i.e. a move which appears
2026 // to be much bester than all the rest. If an easy move is found, the move
2027 // is returned, otherwise the function returns MOVE_NONE. It is very
2028 // important that this function is called at the right moment: The code
2029 // assumes that the first iteration has been completed and the moves have
2030 // been sorted. This is done in RootMoveList c'tor.
2032 Move RootMoveList::scan_for_easy_move() const {
2039 // moves are sorted so just consider the best and the second one
2040 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
2046 // RootMoveList::sort() sorts the root move list at the beginning of a new
2049 inline void RootMoveList::sort() {
2051 sort_multipv(count - 1); // all items
2055 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2056 // list by their scores and depths. It is used to order the different PVs
2057 // correctly in MultiPV mode.
2059 void RootMoveList::sort_multipv(int n) {
2061 for (int i = 1; i <= n; i++)
2063 RootMove rm = moves[i];
2065 for (j = i; j > 0 && moves[j-1] < rm; j--)
2066 moves[j] = moves[j-1];
2072 // init_node() is called at the beginning of all the search functions
2073 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2074 // stack object corresponding to the current node. Once every
2075 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2076 // for user input and checks whether it is time to stop the search.
2078 void init_node(SearchStack ss[], int ply, int threadID) {
2079 assert(ply >= 0 && ply < PLY_MAX);
2080 assert(threadID >= 0 && threadID < ActiveThreads);
2082 Threads[threadID].nodes++;
2086 if(NodesSincePoll >= NodesBetweenPolls) {
2093 ss[ply+2].initKillers();
2095 if(Threads[threadID].printCurrentLine)
2096 print_current_line(ss, ply, threadID);
2100 // update_pv() is called whenever a search returns a value > alpha. It
2101 // updates the PV in the SearchStack object corresponding to the current
2104 void update_pv(SearchStack ss[], int ply) {
2105 assert(ply >= 0 && ply < PLY_MAX);
2107 ss[ply].pv[ply] = ss[ply].currentMove;
2109 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2110 ss[ply].pv[p] = ss[ply+1].pv[p];
2111 ss[ply].pv[p] = MOVE_NONE;
2115 // sp_update_pv() is a variant of update_pv for use at split points. The
2116 // difference between the two functions is that sp_update_pv also updates
2117 // the PV at the parent node.
2119 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply) {
2120 assert(ply >= 0 && ply < PLY_MAX);
2122 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2124 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2125 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2126 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2130 // connected_moves() tests whether two moves are 'connected' in the sense
2131 // that the first move somehow made the second move possible (for instance
2132 // if the moving piece is the same in both moves). The first move is
2133 // assumed to be the move that was made to reach the current position, while
2134 // the second move is assumed to be a move from the current position.
2136 bool connected_moves(const Position &pos, Move m1, Move m2) {
2137 Square f1, t1, f2, t2;
2139 assert(move_is_ok(m1));
2140 assert(move_is_ok(m2));
2145 // Case 1: The moving piece is the same in both moves.
2151 // Case 2: The destination square for m2 was vacated by m1.
2157 // Case 3: Moving through the vacated square:
2158 if(piece_is_slider(pos.piece_on(f2)) &&
2159 bit_is_set(squares_between(f2, t2), f1))
2162 // Case 4: The destination square for m2 is attacked by the moving piece
2164 if(pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
2167 // Case 5: Discovered check, checking piece is the piece moved in m1:
2168 if(piece_is_slider(pos.piece_on(t1)) &&
2169 bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())),
2171 !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())),
2173 Bitboard occ = pos.occupied_squares();
2174 Color us = pos.side_to_move();
2175 Square ksq = pos.king_square(us);
2176 clear_bit(&occ, f2);
2177 if(pos.type_of_piece_on(t1) == BISHOP) {
2178 if(bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2181 else if(pos.type_of_piece_on(t1) == ROOK) {
2182 if(bit_is_set(rook_attacks_bb(ksq, occ), t1))
2186 assert(pos.type_of_piece_on(t1) == QUEEN);
2187 if(bit_is_set(queen_attacks_bb(ksq, occ), t1))
2196 // value_is_mate() checks if the given value is a mate one
2197 // eventually compensated for the ply.
2199 bool value_is_mate(Value value) {
2201 assert(abs(value) <= VALUE_INFINITE);
2203 return value <= value_mated_in(PLY_MAX)
2204 || value >= value_mate_in(PLY_MAX);
2208 // move_is_killer() checks if the given move is among the
2209 // killer moves of that ply.
2211 bool move_is_killer(Move m, const SearchStack& ss) {
2213 const Move* k = ss.killers;
2214 for (int i = 0; i < KILLER_MAX; i++, k++)
2222 // extension() decides whether a move should be searched with normal depth,
2223 // or with extended depth. Certain classes of moves (checking moves, in
2224 // particular) are searched with bigger depth than ordinary moves and in
2225 // any case are marked as 'dangerous'. Note that also if a move is not
2226 // extended, as example because the corresponding UCI option is set to zero,
2227 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2229 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2230 bool singleReply, bool mateThreat, bool* dangerous) {
2232 assert(m != MOVE_NONE);
2234 Depth result = Depth(0);
2235 *dangerous = check || singleReply || mateThreat;
2238 result += CheckExtension[pvNode];
2241 result += SingleReplyExtension[pvNode];
2244 result += MateThreatExtension[pvNode];
2246 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2248 if (pos.move_is_pawn_push_to_7th(m))
2250 result += PawnPushTo7thExtension[pvNode];
2253 if (pos.move_is_passed_pawn_push(m))
2255 result += PassedPawnExtension[pvNode];
2261 && pos.type_of_piece_on(move_to(m)) != PAWN
2262 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2263 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2264 && !move_promotion(m)
2267 result += PawnEndgameExtension[pvNode];
2273 && pos.type_of_piece_on(move_to(m)) != PAWN
2280 return Min(result, OnePly);
2284 // ok_to_do_nullmove() looks at the current position and decides whether
2285 // doing a 'null move' should be allowed. In order to avoid zugzwang
2286 // problems, null moves are not allowed when the side to move has very
2287 // little material left. Currently, the test is a bit too simple: Null
2288 // moves are avoided only when the side to move has only pawns left. It's
2289 // probably a good idea to avoid null moves in at least some more
2290 // complicated endgames, e.g. KQ vs KR. FIXME
2292 bool ok_to_do_nullmove(const Position &pos) {
2293 if(pos.non_pawn_material(pos.side_to_move()) == Value(0))
2299 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2300 // non-tactical moves late in the move list close to the leaves are
2301 // candidates for pruning.
2303 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d) {
2304 Square mfrom, mto, tfrom, tto;
2306 assert(move_is_ok(m));
2307 assert(threat == MOVE_NONE || move_is_ok(threat));
2308 assert(!move_promotion(m));
2309 assert(!pos.move_is_check(m));
2310 assert(!pos.move_is_capture(m));
2311 assert(!pos.move_is_passed_pawn_push(m));
2312 assert(d >= OnePly);
2314 mfrom = move_from(m);
2316 tfrom = move_from(threat);
2317 tto = move_to(threat);
2319 // Case 1: Castling moves are never pruned.
2320 if (move_is_castle(m))
2323 // Case 2: Don't prune moves which move the threatened piece
2324 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2327 // Case 3: If the threatened piece has value less than or equal to the
2328 // value of the threatening piece, don't prune move which defend it.
2329 if ( !PruneDefendingMoves
2330 && threat != MOVE_NONE
2331 && pos.move_is_capture(threat)
2332 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2333 || pos.type_of_piece_on(tfrom) == KING)
2334 && pos.move_attacks_square(m, tto))
2337 // Case 4: Don't prune moves with good history.
2338 if (!H.ok_to_prune(pos.piece_on(move_from(m)), m, d))
2341 // Case 5: If the moving piece in the threatened move is a slider, don't
2342 // prune safe moves which block its ray.
2343 if ( !PruneBlockingMoves
2344 && threat != MOVE_NONE
2345 && piece_is_slider(pos.piece_on(tfrom))
2346 && bit_is_set(squares_between(tfrom, tto), mto)
2354 // ok_to_use_TT() returns true if a transposition table score
2355 // can be used at a given point in search.
2357 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2359 Value v = value_from_tt(tte->value(), ply);
2361 return ( tte->depth() >= depth
2362 || v >= Max(value_mate_in(100), beta)
2363 || v < Min(value_mated_in(100), beta))
2365 && ( (is_lower_bound(tte->type()) && v >= beta)
2366 || (is_upper_bound(tte->type()) && v < beta));
2370 // ok_to_history() returns true if a move m can be stored
2371 // in history. Should be a non capturing move nor a promotion.
2373 bool ok_to_history(const Position& pos, Move m) {
2375 return !pos.move_is_capture(m) && !move_promotion(m);
2379 // update_history() registers a good move that produced a beta-cutoff
2380 // in history and marks as failures all the other moves of that ply.
2382 void update_history(const Position& pos, Move m, Depth depth,
2383 Move movesSearched[], int moveCount) {
2385 H.success(pos.piece_on(move_from(m)), m, depth);
2387 for (int i = 0; i < moveCount - 1; i++)
2389 assert(m != movesSearched[i]);
2390 if (ok_to_history(pos, movesSearched[i]))
2391 H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
2396 // update_killers() add a good move that produced a beta-cutoff
2397 // among the killer moves of that ply.
2399 void update_killers(Move m, SearchStack& ss) {
2401 if (m == ss.killers[0])
2404 for (int i = KILLER_MAX - 1; i > 0; i--)
2405 ss.killers[i] = ss.killers[i - 1];
2410 // fail_high_ply_1() checks if some thread is currently resolving a fail
2411 // high at ply 1 at the node below the first root node. This information
2412 // is used for time managment.
2414 bool fail_high_ply_1() {
2415 for(int i = 0; i < ActiveThreads; i++)
2416 if(Threads[i].failHighPly1)
2422 // current_search_time() returns the number of milliseconds which have passed
2423 // since the beginning of the current search.
2425 int current_search_time() {
2426 return get_system_time() - SearchStartTime;
2430 // nps() computes the current nodes/second count.
2433 int t = current_search_time();
2434 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2438 // poll() performs two different functions: It polls for user input, and it
2439 // looks at the time consumed so far and decides if it's time to abort the
2444 static int lastInfoTime;
2445 int t = current_search_time();
2450 // We are line oriented, don't read single chars
2451 std::string command;
2452 if (!std::getline(std::cin, command))
2455 if (command == "quit")
2458 PonderSearch = false;
2461 else if(command == "stop")
2464 PonderSearch = false;
2466 else if(command == "ponderhit")
2469 // Print search information
2473 else if (lastInfoTime > t)
2474 // HACK: Must be a new search where we searched less than
2475 // NodesBetweenPolls nodes during the first second of search.
2478 else if (t - lastInfoTime >= 1000)
2485 if (dbg_show_hit_rate)
2486 dbg_print_hit_rate();
2488 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2489 << " time " << t << " hashfull " << TT.full() << std::endl;
2490 lock_release(&IOLock);
2491 if (ShowCurrentLine)
2492 Threads[0].printCurrentLine = true;
2494 // Should we stop the search?
2498 bool overTime = t > AbsoluteMaxSearchTime
2499 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2500 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2501 && t > 6*(MaxSearchTime + ExtraSearchTime));
2503 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2504 || (ExactMaxTime && t >= ExactMaxTime)
2505 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2510 // ponderhit() is called when the program is pondering (i.e. thinking while
2511 // it's the opponent's turn to move) in order to let the engine know that
2512 // it correctly predicted the opponent's move.
2515 int t = current_search_time();
2516 PonderSearch = false;
2517 if(Iteration >= 3 &&
2518 (!InfiniteSearch && (StopOnPonderhit ||
2519 t > AbsoluteMaxSearchTime ||
2520 (RootMoveNumber == 1 &&
2521 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2522 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2523 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2528 // print_current_line() prints the current line of search for a given
2529 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2531 void print_current_line(SearchStack ss[], int ply, int threadID) {
2532 assert(ply >= 0 && ply < PLY_MAX);
2533 assert(threadID >= 0 && threadID < ActiveThreads);
2535 if(!Threads[threadID].idle) {
2537 std::cout << "info currline " << (threadID + 1);
2538 for(int p = 0; p < ply; p++)
2539 std::cout << " " << ss[p].currentMove;
2540 std::cout << std::endl;
2541 lock_release(&IOLock);
2543 Threads[threadID].printCurrentLine = false;
2544 if(threadID + 1 < ActiveThreads)
2545 Threads[threadID + 1].printCurrentLine = true;
2549 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2550 // while the program is pondering. The point is to work around a wrinkle in
2551 // the UCI protocol: When pondering, the engine is not allowed to give a
2552 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2553 // We simply wait here until one of these commands is sent, and return,
2554 // after which the bestmove and pondermove will be printed (in id_loop()).
2556 void wait_for_stop_or_ponderhit() {
2557 std::string command;
2560 if(!std::getline(std::cin, command))
2563 if(command == "quit") {
2564 OpeningBook.close();
2569 else if(command == "ponderhit" || command == "stop")
2575 // idle_loop() is where the threads are parked when they have no work to do.
2576 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2577 // object for which the current thread is the master.
2579 void idle_loop(int threadID, SplitPoint *waitSp) {
2580 assert(threadID >= 0 && threadID < THREAD_MAX);
2582 Threads[threadID].running = true;
2585 if(AllThreadsShouldExit && threadID != 0)
2588 // If we are not thinking, wait for a condition to be signaled instead
2589 // of wasting CPU time polling for work:
2590 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2591 #if !defined(_MSC_VER)
2592 pthread_mutex_lock(&WaitLock);
2593 if(Idle || threadID >= ActiveThreads)
2594 pthread_cond_wait(&WaitCond, &WaitLock);
2595 pthread_mutex_unlock(&WaitLock);
2597 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2601 // If this thread has been assigned work, launch a search:
2602 if(Threads[threadID].workIsWaiting) {
2603 Threads[threadID].workIsWaiting = false;
2604 if(Threads[threadID].splitPoint->pvNode)
2605 sp_search_pv(Threads[threadID].splitPoint, threadID);
2607 sp_search(Threads[threadID].splitPoint, threadID);
2608 Threads[threadID].idle = true;
2611 // If this thread is the master of a split point and all threads have
2612 // finished their work at this split point, return from the idle loop:
2613 if(waitSp != NULL && waitSp->cpus == 0)
2617 Threads[threadID].running = false;
2621 // init_split_point_stack() is called during program initialization, and
2622 // initializes all split point objects.
2624 void init_split_point_stack() {
2625 for(int i = 0; i < THREAD_MAX; i++)
2626 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2627 SplitPointStack[i][j].parent = NULL;
2628 lock_init(&(SplitPointStack[i][j].lock), NULL);
2633 // destroy_split_point_stack() is called when the program exits, and
2634 // destroys all locks in the precomputed split point objects.
2636 void destroy_split_point_stack() {
2637 for(int i = 0; i < THREAD_MAX; i++)
2638 for(int j = 0; j < MaxActiveSplitPoints; j++)
2639 lock_destroy(&(SplitPointStack[i][j].lock));
2643 // thread_should_stop() checks whether the thread with a given threadID has
2644 // been asked to stop, directly or indirectly. This can happen if a beta
2645 // cutoff has occured in thre thread's currently active split point, or in
2646 // some ancestor of the current split point.
2648 bool thread_should_stop(int threadID) {
2649 assert(threadID >= 0 && threadID < ActiveThreads);
2653 if(Threads[threadID].stop)
2655 if(ActiveThreads <= 2)
2657 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2659 Threads[threadID].stop = true;
2666 // thread_is_available() checks whether the thread with threadID "slave" is
2667 // available to help the thread with threadID "master" at a split point. An
2668 // obvious requirement is that "slave" must be idle. With more than two
2669 // threads, this is not by itself sufficient: If "slave" is the master of
2670 // some active split point, it is only available as a slave to the other
2671 // threads which are busy searching the split point at the top of "slave"'s
2672 // split point stack (the "helpful master concept" in YBWC terminology).
2674 bool thread_is_available(int slave, int master) {
2675 assert(slave >= 0 && slave < ActiveThreads);
2676 assert(master >= 0 && master < ActiveThreads);
2677 assert(ActiveThreads > 1);
2679 if(!Threads[slave].idle || slave == master)
2682 if(Threads[slave].activeSplitPoints == 0)
2683 // No active split points means that the thread is available as a slave
2684 // for any other thread.
2687 if(ActiveThreads == 2)
2690 // Apply the "helpful master" concept if possible.
2691 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2698 // idle_thread_exists() tries to find an idle thread which is available as
2699 // a slave for the thread with threadID "master".
2701 bool idle_thread_exists(int master) {
2702 assert(master >= 0 && master < ActiveThreads);
2703 assert(ActiveThreads > 1);
2705 for(int i = 0; i < ActiveThreads; i++)
2706 if(thread_is_available(i, master))
2712 // split() does the actual work of distributing the work at a node between
2713 // several threads at PV nodes. If it does not succeed in splitting the
2714 // node (because no idle threads are available, or because we have no unused
2715 // split point objects), the function immediately returns false. If
2716 // splitting is possible, a SplitPoint object is initialized with all the
2717 // data that must be copied to the helper threads (the current position and
2718 // search stack, alpha, beta, the search depth, etc.), and we tell our
2719 // helper threads that they have been assigned work. This will cause them
2720 // to instantly leave their idle loops and call sp_search_pv(). When all
2721 // threads have returned from sp_search_pv (or, equivalently, when
2722 // splitPoint->cpus becomes 0), split() returns true.
2724 bool split(const Position &p, SearchStack *sstck, int ply,
2725 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
2726 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode) {
2729 assert(sstck != NULL);
2730 assert(ply >= 0 && ply < PLY_MAX);
2731 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2732 assert(!pvNode || *alpha < *beta);
2733 assert(*beta <= VALUE_INFINITE);
2734 assert(depth > Depth(0));
2735 assert(master >= 0 && master < ActiveThreads);
2736 assert(ActiveThreads > 1);
2738 SplitPoint *splitPoint;
2743 // If no other thread is available to help us, or if we have too many
2744 // active split points, don't split:
2745 if(!idle_thread_exists(master) ||
2746 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2747 lock_release(&MPLock);
2751 // Pick the next available split point object from the split point stack:
2752 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2753 Threads[master].activeSplitPoints++;
2755 // Initialize the split point object:
2756 splitPoint->parent = Threads[master].splitPoint;
2757 splitPoint->finished = false;
2758 splitPoint->ply = ply;
2759 splitPoint->depth = depth;
2760 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2761 splitPoint->beta = *beta;
2762 splitPoint->pvNode = pvNode;
2763 splitPoint->dcCandidates = dcCandidates;
2764 splitPoint->bestValue = *bestValue;
2765 splitPoint->master = master;
2766 splitPoint->mp = mp;
2767 splitPoint->moves = *moves;
2768 splitPoint->cpus = 1;
2769 splitPoint->pos.copy(p);
2770 splitPoint->parentSstack = sstck;
2771 for(i = 0; i < ActiveThreads; i++)
2772 splitPoint->slaves[i] = 0;
2774 // Copy the current position and the search stack to the master thread:
2775 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2776 Threads[master].splitPoint = splitPoint;
2778 // Make copies of the current position and search stack for each thread:
2779 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2781 if(thread_is_available(i, master)) {
2782 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2783 Threads[i].splitPoint = splitPoint;
2784 splitPoint->slaves[i] = 1;
2788 // Tell the threads that they have work to do. This will make them leave
2790 for(i = 0; i < ActiveThreads; i++)
2791 if(i == master || splitPoint->slaves[i]) {
2792 Threads[i].workIsWaiting = true;
2793 Threads[i].idle = false;
2794 Threads[i].stop = false;
2797 lock_release(&MPLock);
2799 // Everything is set up. The master thread enters the idle loop, from
2800 // which it will instantly launch a search, because its workIsWaiting
2801 // slot is 'true'. We send the split point as a second parameter to the
2802 // idle loop, which means that the main thread will return from the idle
2803 // loop when all threads have finished their work at this split point
2804 // (i.e. when // splitPoint->cpus == 0).
2805 idle_loop(master, splitPoint);
2807 // We have returned from the idle loop, which means that all threads are
2808 // finished. Update alpha, beta and bestvalue, and return:
2810 if(pvNode) *alpha = splitPoint->alpha;
2811 *beta = splitPoint->beta;
2812 *bestValue = splitPoint->bestValue;
2813 Threads[master].stop = false;
2814 Threads[master].idle = false;
2815 Threads[master].activeSplitPoints--;
2816 Threads[master].splitPoint = splitPoint->parent;
2817 lock_release(&MPLock);
2823 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2824 // to start a new search from the root.
2826 void wake_sleeping_threads() {
2827 if(ActiveThreads > 1) {
2828 for(int i = 1; i < ActiveThreads; i++) {
2829 Threads[i].idle = true;
2830 Threads[i].workIsWaiting = false;
2832 #if !defined(_MSC_VER)
2833 pthread_mutex_lock(&WaitLock);
2834 pthread_cond_broadcast(&WaitCond);
2835 pthread_mutex_unlock(&WaitLock);
2837 for(int i = 1; i < THREAD_MAX; i++)
2838 SetEvent(SitIdleEvent[i]);
2844 // init_thread() is the function which is called when a new thread is
2845 // launched. It simply calls the idle_loop() function with the supplied
2846 // threadID. There are two versions of this function; one for POSIX threads
2847 // and one for Windows threads.
2849 #if !defined(_MSC_VER)
2851 void *init_thread(void *threadID) {
2852 idle_loop(*(int *)threadID, NULL);
2858 DWORD WINAPI init_thread(LPVOID threadID) {
2859 idle_loop(*(int *)threadID, NULL);