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/>.
39 #include "ucioption.h"
43 //// Local definitions
50 // The RootMove class is used for moves at the root at the tree. For each
51 // root move, we store a score, a node count, and a PV (really a refutation
52 // in the case of moves which fail low).
57 bool operator<(const RootMove&); // used to sort
61 int64_t nodes, cumulativeNodes;
62 Move pv[PLY_MAX_PLUS_2];
66 // The RootMoveList class is essentially an array of RootMove objects, with
67 // a handful of methods for accessing the data in the individual moves.
72 RootMoveList(Position &pos, Move searchMoves[]);
73 inline Move get_move(int moveNum) const;
74 inline Value get_move_score(int moveNum) const;
75 inline void set_move_score(int moveNum, Value score);
76 inline void set_move_nodes(int moveNum, int64_t nodes);
77 void set_move_pv(int moveNum, const Move pv[]);
78 inline Move get_move_pv(int moveNum, int i) const;
79 inline int64_t get_move_cumulative_nodes(int moveNum) const;
80 inline int move_count() const;
81 Move scan_for_easy_move() const;
83 void sort_multipv(int n);
86 static const int MaxRootMoves = 500;
87 RootMove moves[MaxRootMoves];
92 /// Constants and variables
94 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV
97 int LMRNonPVMoves = 4;
99 // Depth limit for use of dynamic threat detection:
100 Depth ThreatDepth = 5*OnePly;
102 // Depth limit for selective search:
103 Depth SelectiveDepth = 7*OnePly;
105 // Use internal iterative deepening?
106 const bool UseIIDAtPVNodes = true;
107 const bool UseIIDAtNonPVNodes = false;
109 // Internal iterative deepening margin. At Non-PV moves, when
110 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening search
111 // when the static evaluation is at most IIDMargin below beta.
112 const Value IIDMargin = Value(0x100);
115 const bool UseEasyMove = true;
117 // Easy move margin. An easy move candidate must be at least this much
118 // better than the second best move.
119 const Value EasyMoveMargin = Value(0x200);
121 // Problem margin. If the score of the first move at iteration N+1 has
122 // dropped by more than this since iteration N, the boolean variable
123 // "Problem" is set to true, which will make the program spend some extra
124 // time looking for a better move.
125 const Value ProblemMargin = Value(0x28);
127 // No problem margin. If the boolean "Problem" is true, and a new move
128 // is found at the root which is less than NoProblemMargin worse than the
129 // best move from the previous iteration, Problem is set back to false.
130 const Value NoProblemMargin = Value(0x14);
132 // Null move margin. A null move search will not be done if the approximate
133 // evaluation of the position is more than NullMoveMargin below beta.
134 const Value NullMoveMargin = Value(0x300);
136 // Pruning criterions. See the code and comments in ok_to_prune() to
137 // understand their precise meaning.
138 const bool PruneEscapeMoves = false;
139 const bool PruneDefendingMoves = false;
140 const bool PruneBlockingMoves = false;
142 // Use futility pruning?
143 bool UseQSearchFutilityPruning = true;
144 bool UseFutilityPruning = true;
146 // Margins for futility pruning in the quiescence search, at frontier
147 // nodes, and at pre-frontier nodes
148 Value FutilityMargin0 = Value(0x80);
149 Value FutilityMargin1 = Value(0x100);
150 Value FutilityMargin2 = Value(0x300);
153 Depth RazorDepth = 4*OnePly;
154 Value RazorMargin = Value(0x300);
156 // Last seconds noise filtering (LSN)
157 bool UseLSNFiltering = false;
158 bool looseOnTime = false;
159 int LSNTime = 4 * 1000; // In milliseconds
160 Value LSNValue = Value(0x200);
162 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
163 Depth CheckExtension[2] = {OnePly, OnePly};
164 Depth SingleReplyExtension[2] = {OnePly / 2, OnePly / 2};
165 Depth PawnPushTo7thExtension[2] = {OnePly / 2, OnePly / 2};
166 Depth PassedPawnExtension[2] = {Depth(0), Depth(0)};
167 Depth PawnEndgameExtension[2] = {OnePly, OnePly};
168 Depth MateThreatExtension[2] = {Depth(0), Depth(0)};
170 // Search depth at iteration 1
171 const Depth InitialDepth = OnePly /*+ OnePly/2*/;
175 int NodesBetweenPolls = 30000;
181 // Scores and number of times the best move changed for each iteration:
182 Value ValueByIteration[PLY_MAX_PLUS_2];
183 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
188 // Time managment variables
190 int MaxNodes, MaxDepth;
191 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
192 Move BestRootMove, PonderMove, EasyMove;
196 bool StopOnPonderhit;
201 bool PonderingEnabled;
204 // Show current line?
205 bool ShowCurrentLine = false;
208 bool UseLogFile = false;
209 std::ofstream LogFile;
211 // MP related variables
212 Depth MinimumSplitDepth = 4*OnePly;
213 int MaxThreadsPerSplitPoint = 4;
214 Thread Threads[THREAD_MAX];
216 bool AllThreadsShouldExit = false;
217 const int MaxActiveSplitPoints = 8;
218 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
221 #if !defined(_MSC_VER)
222 pthread_cond_t WaitCond;
223 pthread_mutex_t WaitLock;
225 HANDLE SitIdleEvent[THREAD_MAX];
231 Value id_loop(const Position &pos, Move searchMoves[]);
232 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml);
233 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
234 Depth depth, int ply, int threadID);
235 Value search(Position &pos, SearchStack ss[], Value beta,
236 Depth depth, int ply, bool allowNullmove, int threadID);
237 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
238 Depth depth, int ply, int threadID);
239 void sp_search(SplitPoint *sp, int threadID);
240 void sp_search_pv(SplitPoint *sp, int threadID);
241 void init_search_stack(SearchStack& ss);
242 void init_search_stack(SearchStack ss[]);
243 void init_node(const Position &pos, SearchStack ss[], int ply, int threadID);
244 void update_pv(SearchStack ss[], int ply);
245 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
246 bool connected_moves(const Position &pos, Move m1, Move m2);
247 bool move_is_killer(Move m, const SearchStack& ss);
248 Depth extension(const Position &pos, Move m, bool pvNode, bool check, bool singleReply, bool mateThreat, bool* dangerous);
249 bool ok_to_do_nullmove(const Position &pos);
250 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
251 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
252 bool ok_to_history(const Position &pos, Move m);
253 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
254 void update_killers(Move m, SearchStack& ss);
256 bool fail_high_ply_1();
257 int current_search_time();
261 void print_current_line(SearchStack ss[], int ply, int threadID);
262 void wait_for_stop_or_ponderhit();
264 void idle_loop(int threadID, SplitPoint *waitSp);
265 void init_split_point_stack();
266 void destroy_split_point_stack();
267 bool thread_should_stop(int threadID);
268 bool thread_is_available(int slave, int master);
269 bool idle_thread_exists(int master);
270 bool split(const Position &pos, SearchStack *ss, int ply,
271 Value *alpha, Value *beta, Value *bestValue, Depth depth,
272 int *moves, MovePicker *mp, Bitboard dcCandidates, int master,
274 void wake_sleeping_threads();
276 #if !defined(_MSC_VER)
277 void *init_thread(void *threadID);
279 DWORD WINAPI init_thread(LPVOID threadID);
286 //// Global variables
289 // The main transposition table
290 TranspositionTable TT = TranspositionTable(TTDefaultSize);
293 // Number of active threads:
294 int ActiveThreads = 1;
296 // Locks. In principle, there is no need for IOLock to be a global variable,
297 // but it could turn out to be useful for debugging.
300 History H; // Should be made local?
302 // The empty search stack
303 SearchStack EmptySearchStack;
310 /// think() is the external interface to Stockfish's search, and is called when
311 /// the program receives the UCI 'go' command. It initializes various
312 /// search-related global variables, and calls root_search()
314 void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
315 int time[], int increment[], int movesToGo, int maxDepth,
316 int maxNodes, int maxTime, Move searchMoves[]) {
318 // Look for a book move
319 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
322 if (get_option_value_string("Book File") != OpeningBook.file_name())
325 OpeningBook.open("book.bin");
327 bookMove = OpeningBook.get_move(pos);
328 if (bookMove != MOVE_NONE)
330 std::cout << "bestmove " << bookMove << std::endl;
335 // Initialize global search variables
337 SearchStartTime = get_system_time();
338 BestRootMove = MOVE_NONE;
339 PonderMove = MOVE_NONE;
340 EasyMove = MOVE_NONE;
341 for (int i = 0; i < THREAD_MAX; i++)
343 Threads[i].nodes = 0ULL;
344 Threads[i].failHighPly1 = false;
347 InfiniteSearch = infinite;
348 PonderSearch = ponder;
349 StopOnPonderhit = false;
354 ExactMaxTime = maxTime;
356 // Read UCI option values
357 TT.set_size(get_option_value_int("Hash"));
358 if (button_was_pressed("Clear Hash"))
361 PonderingEnabled = get_option_value_bool("Ponder");
362 MultiPV = get_option_value_int("MultiPV");
364 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
365 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
367 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
368 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
370 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
371 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
373 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
374 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
376 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
377 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
379 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
380 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
382 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
383 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
384 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
385 SelectiveDepth = get_option_value_int("Selective Plies") * OnePly;
387 Chess960 = get_option_value_bool("UCI_Chess960");
388 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
389 UseLogFile = get_option_value_bool("Use Search Log");
391 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
393 UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)");
394 UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)");
396 FutilityMargin0 = value_from_centipawns(get_option_value_int("Futility Margin 0"));
397 FutilityMargin1 = value_from_centipawns(get_option_value_int("Futility Margin 1"));
398 FutilityMargin2 = value_from_centipawns(get_option_value_int("Futility Margin 2"));
400 RazorDepth = (get_option_value_int("Maximum Razoring Depth") + 1) * OnePly;
401 RazorMargin = value_from_centipawns(get_option_value_int("Razoring Margin"));
403 UseLSNFiltering = get_option_value_bool("LSN filtering");
404 LSNTime = get_option_value_int("LSN Time Margin (sec)") * 1000;
405 LSNValue = value_from_centipawns(get_option_value_int("LSN Value Margin"));
407 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
408 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
410 read_weights(pos.side_to_move());
412 int newActiveThreads = get_option_value_int("Threads");
413 if (newActiveThreads != ActiveThreads)
415 ActiveThreads = newActiveThreads;
416 init_eval(ActiveThreads);
419 // Wake up sleeping threads:
420 wake_sleeping_threads();
422 for (int i = 1; i < ActiveThreads; i++)
423 assert(thread_is_available(i, 0));
425 // Set thinking time:
426 int myTime = time[side_to_move];
427 int myIncrement = increment[side_to_move];
428 int oppTime = time[1 - side_to_move];
430 if (!movesToGo) // Sudden death time control
434 MaxSearchTime = myTime / 30 + myIncrement;
435 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
436 } else { // Blitz game without increment
437 MaxSearchTime = myTime / 30;
438 AbsoluteMaxSearchTime = myTime / 8;
441 else // (x moves) / (y minutes)
445 MaxSearchTime = myTime / 2;
446 AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
448 MaxSearchTime = myTime / Min(movesToGo, 20);
449 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
453 if (PonderingEnabled)
455 MaxSearchTime += MaxSearchTime / 4;
456 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
459 // Fixed depth or fixed number of nodes?
462 InfiniteSearch = true; // HACK
467 NodesBetweenPolls = Min(MaxNodes, 30000);
468 InfiniteSearch = true; // HACK
471 NodesBetweenPolls = 30000;
474 // Write information to search log file:
476 LogFile << "Searching: " << pos.to_fen() << std::endl
477 << "infinite: " << infinite
478 << " ponder: " << ponder
479 << " time: " << myTime
480 << " increment: " << myIncrement
481 << " moves to go: " << movesToGo << std::endl;
484 // We're ready to start thinking. Call the iterative deepening loop
488 Value v = id_loop(pos, searchMoves);
489 looseOnTime = ( UseLSNFiltering
496 looseOnTime = false; // reset for next match
497 while (SearchStartTime + myTime + 1000 > get_system_time())
499 id_loop(pos, searchMoves); // to fail gracefully
516 /// init_threads() is called during startup. It launches all helper threads,
517 /// and initializes the split point stack and the global locks and condition
520 void init_threads() {
524 #if !defined(_MSC_VER)
525 pthread_t pthread[1];
528 for (i = 0; i < THREAD_MAX; i++)
529 Threads[i].activeSplitPoints = 0;
531 // Initialize global locks:
532 lock_init(&MPLock, NULL);
533 lock_init(&IOLock, NULL);
535 init_split_point_stack();
537 #if !defined(_MSC_VER)
538 pthread_mutex_init(&WaitLock, NULL);
539 pthread_cond_init(&WaitCond, NULL);
541 for (i = 0; i < THREAD_MAX; i++)
542 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
545 // All threads except the main thread should be initialized to idle state
546 for (i = 1; i < THREAD_MAX; i++)
548 Threads[i].stop = false;
549 Threads[i].workIsWaiting = false;
550 Threads[i].idle = true;
551 Threads[i].running = false;
554 // Launch the helper threads
555 for(i = 1; i < THREAD_MAX; i++)
557 #if !defined(_MSC_VER)
558 pthread_create(pthread, NULL, init_thread, (void*)(&i));
561 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
564 // Wait until the thread has finished launching:
565 while (!Threads[i].running);
568 // Init also the empty search stack
569 init_search_stack(EmptySearchStack);
573 /// stop_threads() is called when the program exits. It makes all the
574 /// helper threads exit cleanly.
576 void stop_threads() {
578 ActiveThreads = THREAD_MAX; // HACK
579 Idle = false; // HACK
580 wake_sleeping_threads();
581 AllThreadsShouldExit = true;
582 for (int i = 1; i < THREAD_MAX; i++)
584 Threads[i].stop = true;
585 while(Threads[i].running);
587 destroy_split_point_stack();
591 /// nodes_searched() returns the total number of nodes searched so far in
592 /// the current search.
594 int64_t nodes_searched() {
596 int64_t result = 0ULL;
597 for (int i = 0; i < ActiveThreads; i++)
598 result += Threads[i].nodes;
605 // id_loop() is the main iterative deepening loop. It calls root_search
606 // repeatedly with increasing depth until the allocated thinking time has
607 // been consumed, the user stops the search, or the maximum search depth is
610 Value id_loop(const Position &pos, Move searchMoves[]) {
613 SearchStack ss[PLY_MAX_PLUS_2];
615 // searchMoves are verified, copied, scored and sorted
616 RootMoveList rml(p, searchMoves);
621 init_search_stack(ss);
623 ValueByIteration[0] = Value(0);
624 ValueByIteration[1] = rml.get_move_score(0);
626 LastIterations = false;
628 EasyMove = rml.scan_for_easy_move();
630 // Iterative deepening loop
631 while (!AbortSearch && Iteration < PLY_MAX)
633 // Initialize iteration
636 BestMoveChangesByIteration[Iteration] = 0;
640 std::cout << "info depth " << Iteration << std::endl;
642 // Search to the current depth
643 ValueByIteration[Iteration] = root_search(p, ss, rml);
645 // Erase the easy move if it differs from the new best move
646 if (ss[0].pv[0] != EasyMove)
647 EasyMove = MOVE_NONE;
654 bool stopSearch = false;
656 // Stop search early if there is only a single legal move:
657 if (Iteration >= 6 && rml.move_count() == 1)
660 // Stop search early when the last two iterations returned a mate score
662 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
663 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
666 // Stop search early if one move seems to be much better than the rest
667 int64_t nodes = nodes_searched();
669 && EasyMove == ss[0].pv[0]
670 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
671 && current_search_time() > MaxSearchTime / 16)
672 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
673 && current_search_time() > MaxSearchTime / 32)))
676 // Add some extra time if the best move has changed during the last two iterations
677 if (Iteration > 5 && Iteration <= 50)
678 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
679 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
681 // Try to guess if the current iteration is the last one or the last two
682 LastIterations = (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*58) / 128);
684 // Stop search if most of MaxSearchTime is consumed at the end of the
685 // iteration. We probably don't have enough time to search the first
686 // move at the next iteration anyway.
687 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
695 StopOnPonderhit = true;
698 // Write PV to transposition table, in case the relevant entries have
699 // been overwritten during the search:
700 TT.insert_pv(p, ss[0].pv);
702 if (MaxDepth && Iteration >= MaxDepth)
708 // If we are pondering, we shouldn't print the best move before we
711 wait_for_stop_or_ponderhit();
713 // Print final search statistics
714 std::cout << "info nodes " << nodes_searched()
716 << " time " << current_search_time()
717 << " hashfull " << TT.full() << std::endl;
719 // Print the best move and the ponder move to the standard output
720 std::cout << "bestmove " << ss[0].pv[0];
721 if (ss[0].pv[1] != MOVE_NONE)
722 std::cout << " ponder " << ss[0].pv[1];
724 std::cout << std::endl;
729 LogFile << "Nodes: " << nodes_searched() << std::endl
730 << "Nodes/second: " << nps() << std::endl
731 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
733 p.do_move(ss[0].pv[0], u);
734 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
735 << std::endl << std::endl;
737 return rml.get_move_score(0);
741 // root_search() is the function which searches the root node. It is
742 // similar to search_pv except that it uses a different move ordering
743 // scheme (perhaps we should try to use this at internal PV nodes, too?)
744 // and prints some information to the standard output.
746 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml) {
748 Value alpha = -VALUE_INFINITE;
749 Value beta = VALUE_INFINITE, value;
750 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
752 // Loop through all the moves in the root move list
753 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
760 RootMoveNumber = i + 1;
763 // Remember the node count before the move is searched. The node counts
764 // are used to sort the root moves at the next iteration.
765 nodes = nodes_searched();
767 // Pick the next root move, and print the move and the move number to
768 // the standard output.
769 move = ss[0].currentMove = rml.get_move(i);
770 if (current_search_time() >= 1000)
771 std::cout << "info currmove " << move
772 << " currmovenumber " << i + 1 << std::endl;
774 // Decide search depth for this move
776 ext = extension(pos, move, true, pos.move_is_check(move), false, false, &dangerous);
777 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
779 // Make the move, and search it
780 pos.do_move(move, u, dcCandidates);
784 value = -search_pv(pos, ss, -beta, VALUE_INFINITE, newDepth, 1, 0);
785 // If the value has dropped a lot compared to the last iteration,
786 // set the boolean variable Problem to true. This variable is used
787 // for time managment: When Problem is true, we try to complete the
788 // current iteration before playing a move.
789 Problem = (Iteration >= 2 && value <= ValueByIteration[Iteration-1] - ProblemMargin);
791 if (Problem && StopOnPonderhit)
792 StopOnPonderhit = false;
796 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
799 // Fail high! Set the boolean variable FailHigh to true, and
800 // re-search the move with a big window. The variable FailHigh is
801 // used for time managment: We try to avoid aborting the search
802 // prematurely during a fail high research.
804 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
808 pos.undo_move(move, u);
810 // Finished searching the move. If AbortSearch is true, the search
811 // was aborted because the user interrupted the search or because we
812 // ran out of time. In this case, the return value of the search cannot
813 // be trusted, and we break out of the loop without updating the best
818 // Remember the node count for this move. The node counts are used to
819 // sort the root moves at the next iteration.
820 rml.set_move_nodes(i, nodes_searched() - nodes);
822 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
824 if (value <= alpha && i >= MultiPV)
825 rml.set_move_score(i, -VALUE_INFINITE);
831 rml.set_move_score(i, value);
833 rml.set_move_pv(i, ss[0].pv);
837 // We record how often the best move has been changed in each
838 // iteration. This information is used for time managment: When
839 // the best move changes frequently, we allocate some more time.
841 BestMoveChangesByIteration[Iteration]++;
843 // Print search information to the standard output:
844 std::cout << "info depth " << Iteration
845 << " score " << value_to_string(value)
846 << " time " << current_search_time()
847 << " nodes " << nodes_searched()
851 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
852 std::cout << ss[0].pv[j] << " ";
854 std::cout << std::endl;
857 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
862 // Reset the global variable Problem to false if the value isn't too
863 // far below the final value from the last iteration.
864 if (value > ValueByIteration[Iteration - 1] - NoProblemMargin)
870 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
873 std::cout << "info multipv " << j + 1
874 << " score " << value_to_string(rml.get_move_score(j))
875 << " depth " << ((j <= i)? Iteration : Iteration - 1)
876 << " time " << current_search_time()
877 << " nodes " << nodes_searched()
881 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
882 std::cout << rml.get_move_pv(j, k) << " ";
884 std::cout << std::endl;
886 alpha = rml.get_move_score(Min(i, MultiPV-1));
894 // search_pv() is the main search function for PV nodes.
896 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
897 Depth depth, int ply, int threadID) {
899 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
900 assert(beta > alpha && beta <= VALUE_INFINITE);
901 assert(ply >= 0 && ply < PLY_MAX);
902 assert(threadID >= 0 && threadID < ActiveThreads);
904 // Initialize, and make an early exit in case of an aborted search,
905 // an instant draw, maximum ply reached, etc.
906 if (AbortSearch || thread_should_stop(threadID))
910 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
912 init_node(pos, ss, ply, threadID);
919 if (ply >= PLY_MAX - 1)
920 return evaluate(pos, ei, threadID);
922 // Mate distance pruning
923 Value oldAlpha = alpha;
924 alpha = Max(value_mated_in(ply), alpha);
925 beta = Min(value_mate_in(ply+1), beta);
929 // Transposition table lookup. At PV nodes, we don't use the TT for
930 // pruning, but only for move ordering.
931 const TTEntry* tte = TT.retrieve(pos);
932 Move ttMove = (tte ? tte->move() : MOVE_NONE);
934 // Go with internal iterative deepening if we don't have a TT move
935 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
937 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
938 ttMove = ss[ply].pv[ply];
941 // Initialize a MovePicker object for the current position, and prepare
942 // to search all moves
943 MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
945 Move move, movesSearched[256];
947 Value value, bestValue = -VALUE_INFINITE;
948 Bitboard dcCandidates = mp.discovered_check_candidates();
949 bool isCheck = pos.is_check();
950 bool mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
952 // Loop through all legal moves until no moves remain or a beta cutoff
955 && (move = mp.get_next_move()) != MOVE_NONE
956 && !thread_should_stop(threadID))
958 assert(move_is_ok(move));
960 bool singleReply = (isCheck && mp.number_of_moves() == 1);
961 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
962 bool moveIsCapture = pos.move_is_capture(move);
964 movesSearched[moveCount++] = ss[ply].currentMove = move;
967 ss[ply].currentMoveCaptureValue = pos.midgame_value_of_piece_on(move_to(move));
968 else if (move_is_ep(move))
969 ss[ply].currentMoveCaptureValue = PawnValueMidgame;
971 ss[ply].currentMoveCaptureValue = Value(0);
973 // Decide the new search depth
975 Depth ext = extension(pos, move, true, moveIsCheck, singleReply, mateThreat, &dangerous);
976 Depth newDepth = depth - OnePly + ext;
978 // Make and search the move
980 pos.do_move(move, u, dcCandidates);
982 if (moveCount == 1) // The first move in list is the PV
983 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
986 // Try to reduce non-pv search depth by one ply if move seems not problematic,
987 // if the move fails high will be re-searched at full depth.
988 if ( depth >= 2*OnePly
989 && moveCount >= LMRPVMoves
992 && !move_promotion(move)
993 && !move_is_castle(move)
994 && !move_is_killer(move, ss[ply]))
996 ss[ply].reduction = OnePly;
997 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1000 value = alpha + 1; // Just to trigger next condition
1002 if (value > alpha) // Go with full depth pv search
1004 ss[ply].reduction = Depth(0);
1005 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1006 if (value > alpha && value < beta)
1008 // When the search fails high at ply 1 while searching the first
1009 // move at the root, set the flag failHighPly1. This is used for
1010 // time managment: We don't want to stop the search early in
1011 // such cases, because resolving the fail high at ply 1 could
1012 // result in a big drop in score at the root.
1013 if (ply == 1 && RootMoveNumber == 1)
1014 Threads[threadID].failHighPly1 = true;
1016 // A fail high occurred. Re-search at full window (pv search)
1017 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1018 Threads[threadID].failHighPly1 = false;
1022 pos.undo_move(move, u);
1024 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1027 if (value > bestValue)
1034 if (value == value_mate_in(ply + 1))
1035 ss[ply].mateKiller = move;
1037 // If we are at ply 1, and we are searching the first root move at
1038 // ply 0, set the 'Problem' variable if the score has dropped a lot
1039 // (from the computer's point of view) since the previous iteration:
1040 if (Iteration >= 2 && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
1045 if ( ActiveThreads > 1
1047 && depth >= MinimumSplitDepth
1049 && idle_thread_exists(threadID)
1051 && !thread_should_stop(threadID)
1052 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1053 &moveCount, &mp, dcCandidates, threadID, true))
1057 // All legal moves have been searched. A special case: If there were
1058 // no legal moves, it must be mate or stalemate:
1060 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1062 // If the search is not aborted, update the transposition table,
1063 // history counters, and killer moves.
1064 if (AbortSearch || thread_should_stop(threadID))
1067 if (bestValue <= oldAlpha)
1068 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1070 else if (bestValue >= beta)
1072 Move m = ss[ply].pv[ply];
1073 if (ok_to_history(pos, m)) // Only non capture moves are considered
1075 update_history(pos, m, depth, movesSearched, moveCount);
1076 update_killers(m, ss[ply]);
1078 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1081 TT.store(pos, value_to_tt(bestValue, ply), depth, ss[ply].pv[ply], VALUE_TYPE_EXACT);
1087 // search() is the search function for zero-width nodes.
1089 Value search(Position &pos, SearchStack ss[], Value beta, Depth depth,
1090 int ply, bool allowNullmove, int threadID) {
1092 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1093 assert(ply >= 0 && ply < PLY_MAX);
1094 assert(threadID >= 0 && threadID < ActiveThreads);
1098 // Initialize, and make an early exit in case of an aborted search,
1099 // an instant draw, maximum ply reached, etc.
1100 if (AbortSearch || thread_should_stop(threadID))
1104 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1106 init_node(pos, ss, ply, threadID);
1111 if (ply >= PLY_MAX - 1)
1112 return evaluate(pos, ei, threadID);
1114 // Mate distance pruning
1115 if (value_mated_in(ply) >= beta)
1118 if (value_mate_in(ply + 1) < beta)
1121 // Transposition table lookup
1122 const TTEntry* tte = TT.retrieve(pos);
1123 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1125 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1127 ss[ply].currentMove = ttMove; // can be MOVE_NONE ?
1128 return value_from_tt(tte->value(), ply);
1131 Value approximateEval = quick_evaluate(pos);
1132 bool mateThreat = false;
1133 bool isCheck = pos.is_check();
1138 && ok_to_do_nullmove(pos)
1139 && approximateEval >= beta - NullMoveMargin)
1141 ss[ply].currentMove = MOVE_NULL;
1144 pos.do_null_move(u);
1145 int R = (depth > 7 ? 4 : 3);
1146 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1147 pos.undo_null_move(u);
1149 if (nullValue >= beta)
1151 if (depth < 6 * OnePly)
1154 // Do zugzwang verification search
1155 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1159 // The null move failed low, which means that we may be faced with
1160 // some kind of threat. If the previous move was reduced, check if
1161 // the move that refuted the null move was somehow connected to the
1162 // move which was reduced. If a connection is found, return a fail
1163 // low score (which will cause the reduced move to fail high in the
1164 // parent node, which will trigger a re-search with full depth).
1165 if (nullValue == value_mated_in(ply + 2))
1168 ss[ply].threatMove = ss[ply + 1].currentMove;
1169 if ( depth < ThreatDepth
1170 && ss[ply - 1].reduction
1171 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1175 // Null move search not allowed, try razoring
1176 else if ( (approximateEval < beta - RazorMargin && depth < RazorDepth)
1177 ||(approximateEval < beta - PawnValueMidgame && depth <= OnePly))
1179 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1184 // Go with internal iterative deepening if we don't have a TT move
1185 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1186 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1188 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1189 ttMove = ss[ply].pv[ply];
1192 // Initialize a MovePicker object for the current position, and prepare
1193 // to search all moves:
1194 MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth);
1196 Move move, movesSearched[256];
1198 Value value, bestValue = -VALUE_INFINITE;
1199 Bitboard dcCandidates = mp.discovered_check_candidates();
1200 Value futilityValue = VALUE_NONE;
1201 bool useFutilityPruning = UseFutilityPruning
1202 && depth < SelectiveDepth
1205 // Loop through all legal moves until no moves remain or a beta cutoff
1207 while ( bestValue < beta
1208 && (move = mp.get_next_move()) != MOVE_NONE
1209 && !thread_should_stop(threadID))
1211 assert(move_is_ok(move));
1213 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1214 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1215 bool moveIsCapture = pos.move_is_capture(move);
1217 movesSearched[moveCount++] = ss[ply].currentMove = move;
1219 // Decide the new search depth
1221 Depth ext = extension(pos, move, false, moveIsCheck, singleReply, mateThreat, &dangerous);
1222 Depth newDepth = depth - OnePly + ext;
1225 if ( useFutilityPruning
1228 && !move_promotion(move))
1230 if ( moveCount >= 2 + int(depth)
1231 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1234 if (depth < 3 * OnePly && approximateEval < beta)
1236 if (futilityValue == VALUE_NONE)
1237 futilityValue = evaluate(pos, ei, threadID)
1238 + (depth < 2 * OnePly ? FutilityMargin1 : FutilityMargin2);
1240 if (futilityValue < beta)
1242 if (futilityValue > bestValue)
1243 bestValue = futilityValue;
1249 // Make and search the move
1251 pos.do_move(move, u, dcCandidates);
1253 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1254 // if the move fails high will be re-searched at full depth.
1255 if ( depth >= 2*OnePly
1256 && moveCount >= LMRNonPVMoves
1259 && !move_promotion(move)
1260 && !move_is_castle(move)
1261 && !move_is_killer(move, ss[ply]))
1263 ss[ply].reduction = OnePly;
1264 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1267 value = beta; // Just to trigger next condition
1269 if (value >= beta) // Go with full depth non-pv search
1271 ss[ply].reduction = Depth(0);
1272 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1274 pos.undo_move(move, u);
1276 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1279 if (value > bestValue)
1285 if (value == value_mate_in(ply + 1))
1286 ss[ply].mateKiller = move;
1290 if ( ActiveThreads > 1
1292 && depth >= MinimumSplitDepth
1294 && idle_thread_exists(threadID)
1296 && !thread_should_stop(threadID)
1297 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1298 &mp, dcCandidates, threadID, false))
1302 // All legal moves have been searched. A special case: If there were
1303 // no legal moves, it must be mate or stalemate.
1305 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1307 // If the search is not aborted, update the transposition table,
1308 // history counters, and killer moves.
1309 if (AbortSearch || thread_should_stop(threadID))
1312 if (bestValue < beta)
1313 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1316 Move m = ss[ply].pv[ply];
1317 if (ok_to_history(pos, m)) // Only non capture moves are considered
1319 update_history(pos, m, depth, movesSearched, moveCount);
1320 update_killers(m, ss[ply]);
1322 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1328 // qsearch() is the quiescence search function, which is called by the main
1329 // search function when the remaining depth is zero (or, to be more precise,
1330 // less than OnePly).
1332 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
1333 Depth depth, int ply, int threadID) {
1335 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1336 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1338 assert(ply >= 0 && ply < PLY_MAX);
1339 assert(threadID >= 0 && threadID < ActiveThreads);
1343 // Initialize, and make an early exit in case of an aborted search,
1344 // an instant draw, maximum ply reached, etc.
1345 if (AbortSearch || thread_should_stop(threadID))
1348 init_node(pos, ss, ply, threadID);
1353 // Transposition table lookup
1354 const TTEntry* tte = TT.retrieve(pos);
1355 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1356 return value_from_tt(tte->value(), ply);
1358 // Evaluate the position statically
1359 Value staticValue = evaluate(pos, ei, threadID);
1361 if (ply == PLY_MAX - 1)
1364 // Initialize "stand pat score", and return it immediately if it is
1366 Value bestValue = (pos.is_check() ? -VALUE_INFINITE : staticValue);
1368 if (bestValue >= beta)
1371 if (bestValue > alpha)
1374 // Initialize a MovePicker object for the current position, and prepare
1375 // to search the moves. Because the depth is <= 0 here, only captures,
1376 // queen promotions and checks (only if depth == 0) will be generated.
1377 MovePicker mp = MovePicker(pos, false, MOVE_NONE, EmptySearchStack, depth, &ei);
1380 Bitboard dcCandidates = mp.discovered_check_candidates();
1381 bool isCheck = pos.is_check();
1382 bool pvNode = (beta - alpha != 1);
1383 bool enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1385 // Loop through the moves until no moves remain or a beta cutoff
1387 while ( alpha < beta
1388 && (move = mp.get_next_move()) != MOVE_NONE)
1390 assert(move_is_ok(move));
1393 ss[ply].currentMove = move;
1396 if ( UseQSearchFutilityPruning
1400 && !move_promotion(move)
1401 && !pos.move_is_check(move, dcCandidates)
1402 && !pos.move_is_passed_pawn_push(move))
1404 Value futilityValue = staticValue
1405 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1406 pos.endgame_value_of_piece_on(move_to(move)))
1408 + ei.futilityMargin;
1410 if (futilityValue < alpha)
1412 if (futilityValue > bestValue)
1413 bestValue = futilityValue;
1418 // Don't search captures and checks with negative SEE values
1420 && !move_promotion(move)
1421 && (pos.midgame_value_of_piece_on(move_from(move)) >
1422 pos.midgame_value_of_piece_on(move_to(move)))
1423 && pos.see(move) < 0)
1426 // Make and search the move.
1428 pos.do_move(move, u, dcCandidates);
1429 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1430 pos.undo_move(move, u);
1432 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1435 if (value > bestValue)
1446 // All legal moves have been searched. A special case: If we're in check
1447 // and no legal moves were found, it is checkmate:
1448 if (pos.is_check() && moveCount == 0) // Mate!
1449 return value_mated_in(ply);
1451 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1453 // Update transposition table
1454 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_EXACT);
1456 // Update killers only for good check moves
1457 Move m = ss[ply].currentMove;
1458 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1460 // Wrong to update history when depth is <= 0
1461 update_killers(m, ss[ply]);
1467 // sp_search() is used to search from a split point. This function is called
1468 // by each thread working at the split point. It is similar to the normal
1469 // search() function, but simpler. Because we have already probed the hash
1470 // table, done a null move search, and searched the first move before
1471 // splitting, we don't have to repeat all this work in sp_search(). We
1472 // also don't need to store anything to the hash table here: This is taken
1473 // care of after we return from the split point.
1475 void sp_search(SplitPoint *sp, int threadID) {
1477 assert(threadID >= 0 && threadID < ActiveThreads);
1478 assert(ActiveThreads > 1);
1480 Position pos = Position(sp->pos);
1481 SearchStack *ss = sp->sstack[threadID];
1484 bool isCheck = pos.is_check();
1485 bool useFutilityPruning = UseFutilityPruning
1486 && sp->depth < SelectiveDepth
1489 while ( sp->bestValue < sp->beta
1490 && !thread_should_stop(threadID)
1491 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1493 assert(move_is_ok(move));
1495 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1496 bool moveIsCapture = pos.move_is_capture(move);
1498 lock_grab(&(sp->lock));
1499 int moveCount = ++sp->moves;
1500 lock_release(&(sp->lock));
1502 ss[sp->ply].currentMove = move;
1504 // Decide the new search depth.
1506 Depth ext = extension(pos, move, false, moveIsCheck, false, false, &dangerous);
1507 Depth newDepth = sp->depth - OnePly + ext;
1510 if ( useFutilityPruning
1513 && !move_promotion(move)
1514 && moveCount >= 2 + int(sp->depth)
1515 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1518 // Make and search the move.
1520 pos.do_move(move, u, sp->dcCandidates);
1522 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1523 // if the move fails high will be re-searched at full depth.
1525 && moveCount >= LMRNonPVMoves
1527 && !move_promotion(move)
1528 && !move_is_castle(move)
1529 && !move_is_killer(move, ss[sp->ply]))
1531 ss[sp->ply].reduction = OnePly;
1532 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1535 value = sp->beta; // Just to trigger next condition
1537 if (value >= sp->beta) // Go with full depth non-pv search
1539 ss[sp->ply].reduction = Depth(0);
1540 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1542 pos.undo_move(move, u);
1544 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1546 if (thread_should_stop(threadID))
1550 lock_grab(&(sp->lock));
1551 if (value > sp->bestValue && !thread_should_stop(threadID))
1553 sp->bestValue = value;
1554 if (sp->bestValue >= sp->beta)
1556 sp_update_pv(sp->parentSstack, ss, sp->ply);
1557 for (int i = 0; i < ActiveThreads; i++)
1558 if (i != threadID && (i == sp->master || sp->slaves[i]))
1559 Threads[i].stop = true;
1561 sp->finished = true;
1564 lock_release(&(sp->lock));
1567 lock_grab(&(sp->lock));
1569 // If this is the master thread and we have been asked to stop because of
1570 // a beta cutoff higher up in the tree, stop all slave threads:
1571 if (sp->master == threadID && thread_should_stop(threadID))
1572 for (int i = 0; i < ActiveThreads; i++)
1574 Threads[i].stop = true;
1577 sp->slaves[threadID] = 0;
1579 lock_release(&(sp->lock));
1583 // sp_search_pv() is used to search from a PV split point. This function
1584 // is called by each thread working at the split point. It is similar to
1585 // the normal search_pv() function, but simpler. Because we have already
1586 // probed the hash table and searched the first move before splitting, we
1587 // don't have to repeat all this work in sp_search_pv(). We also don't
1588 // need to store anything to the hash table here: This is taken care of
1589 // after we return from the split point.
1591 void sp_search_pv(SplitPoint *sp, int threadID) {
1593 assert(threadID >= 0 && threadID < ActiveThreads);
1594 assert(ActiveThreads > 1);
1596 Position pos = Position(sp->pos);
1597 SearchStack *ss = sp->sstack[threadID];
1601 while ( sp->alpha < sp->beta
1602 && !thread_should_stop(threadID)
1603 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1605 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1606 bool moveIsCapture = pos.move_is_capture(move);
1608 assert(move_is_ok(move));
1610 ss[sp->ply].currentMoveCaptureValue = move_is_ep(move)?
1611 PawnValueMidgame : pos.midgame_value_of_piece_on(move_to(move));
1613 lock_grab(&(sp->lock));
1614 int moveCount = ++sp->moves;
1615 lock_release(&(sp->lock));
1617 ss[sp->ply].currentMove = move;
1619 // Decide the new search depth.
1621 Depth ext = extension(pos, move, true, moveIsCheck, false, false, &dangerous);
1622 Depth newDepth = sp->depth - OnePly + ext;
1624 // Make and search the move.
1626 pos.do_move(move, u, sp->dcCandidates);
1628 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1629 // if the move fails high will be re-searched at full depth.
1631 && moveCount >= LMRPVMoves
1633 && !move_promotion(move)
1634 && !move_is_castle(move)
1635 && !move_is_killer(move, ss[sp->ply]))
1637 ss[sp->ply].reduction = OnePly;
1638 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1641 value = sp->alpha + 1; // Just to trigger next condition
1643 if (value > sp->alpha) // Go with full depth non-pv search
1645 ss[sp->ply].reduction = Depth(0);
1646 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1648 if (value > sp->alpha && value < sp->beta)
1650 // When the search fails high at ply 1 while searching the first
1651 // move at the root, set the flag failHighPly1. This is used for
1652 // time managment: We don't want to stop the search early in
1653 // such cases, because resolving the fail high at ply 1 could
1654 // result in a big drop in score at the root.
1655 if (sp->ply == 1 && RootMoveNumber == 1)
1656 Threads[threadID].failHighPly1 = true;
1658 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1659 Threads[threadID].failHighPly1 = false;
1662 pos.undo_move(move, u);
1664 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1666 if (thread_should_stop(threadID))
1670 lock_grab(&(sp->lock));
1671 if (value > sp->bestValue && !thread_should_stop(threadID))
1673 sp->bestValue = value;
1674 if (value > sp->alpha)
1677 sp_update_pv(sp->parentSstack, ss, sp->ply);
1678 if (value == value_mate_in(sp->ply + 1))
1679 ss[sp->ply].mateKiller = move;
1681 if(value >= sp->beta)
1683 for(int i = 0; i < ActiveThreads; i++)
1684 if(i != threadID && (i == sp->master || sp->slaves[i]))
1685 Threads[i].stop = true;
1687 sp->finished = true;
1690 // If we are at ply 1, and we are searching the first root move at
1691 // ply 0, set the 'Problem' variable if the score has dropped a lot
1692 // (from the computer's point of view) since the previous iteration:
1693 if (Iteration >= 2 && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
1696 lock_release(&(sp->lock));
1699 lock_grab(&(sp->lock));
1701 // If this is the master thread and we have been asked to stop because of
1702 // a beta cutoff higher up in the tree, stop all slave threads:
1703 if (sp->master == threadID && thread_should_stop(threadID))
1704 for (int i = 0; i < ActiveThreads; i++)
1706 Threads[i].stop = true;
1709 sp->slaves[threadID] = 0;
1711 lock_release(&(sp->lock));
1715 /// The RootMove class
1719 RootMove::RootMove() {
1720 nodes = cumulativeNodes = 0ULL;
1723 // RootMove::operator<() is the comparison function used when
1724 // sorting the moves. A move m1 is considered to be better
1725 // than a move m2 if it has a higher score, or if the moves
1726 // have equal score but m1 has the higher node count.
1728 bool RootMove::operator<(const RootMove& m) {
1730 if (score != m.score)
1731 return (score < m.score);
1733 return nodes <= m.nodes;
1736 /// The RootMoveList class
1740 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1742 MoveStack mlist[MaxRootMoves];
1743 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1745 // Generate all legal moves
1746 int lm_count = generate_legal_moves(pos, mlist);
1748 // Add each move to the moves[] array
1749 for (int i = 0; i < lm_count; i++)
1751 bool includeMove = includeAllMoves;
1753 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1754 includeMove = (searchMoves[k] == mlist[i].move);
1758 // Find a quick score for the move
1760 SearchStack ss[PLY_MAX_PLUS_2];
1762 moves[count].move = mlist[i].move;
1763 moves[count].nodes = 0ULL;
1764 pos.do_move(moves[count].move, u);
1765 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE,
1767 pos.undo_move(moves[count].move, u);
1768 moves[count].pv[0] = moves[i].move;
1769 moves[count].pv[1] = MOVE_NONE; // FIXME
1777 // Simple accessor methods for the RootMoveList class
1779 inline Move RootMoveList::get_move(int moveNum) const {
1780 return moves[moveNum].move;
1783 inline Value RootMoveList::get_move_score(int moveNum) const {
1784 return moves[moveNum].score;
1787 inline void RootMoveList::set_move_score(int moveNum, Value score) {
1788 moves[moveNum].score = score;
1791 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
1792 moves[moveNum].nodes = nodes;
1793 moves[moveNum].cumulativeNodes += nodes;
1796 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
1798 for(j = 0; pv[j] != MOVE_NONE; j++)
1799 moves[moveNum].pv[j] = pv[j];
1800 moves[moveNum].pv[j] = MOVE_NONE;
1803 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
1804 return moves[moveNum].pv[i];
1807 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
1808 return moves[moveNum].cumulativeNodes;
1811 inline int RootMoveList::move_count() const {
1816 // RootMoveList::scan_for_easy_move() is called at the end of the first
1817 // iteration, and is used to detect an "easy move", i.e. a move which appears
1818 // to be much bester than all the rest. If an easy move is found, the move
1819 // is returned, otherwise the function returns MOVE_NONE. It is very
1820 // important that this function is called at the right moment: The code
1821 // assumes that the first iteration has been completed and the moves have
1822 // been sorted. This is done in RootMoveList c'tor.
1824 Move RootMoveList::scan_for_easy_move() const {
1831 // moves are sorted so just consider the best and the second one
1832 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
1838 // RootMoveList::sort() sorts the root move list at the beginning of a new
1841 inline void RootMoveList::sort() {
1843 sort_multipv(count - 1); // all items
1847 // RootMoveList::sort_multipv() sorts the first few moves in the root move
1848 // list by their scores and depths. It is used to order the different PVs
1849 // correctly in MultiPV mode.
1851 void RootMoveList::sort_multipv(int n) {
1853 for (int i = 1; i <= n; i++)
1855 RootMove rm = moves[i];
1857 for (j = i; j > 0 && moves[j-1] < rm; j--)
1858 moves[j] = moves[j-1];
1864 // init_search_stack() initializes a search stack at the beginning of a
1865 // new search from the root.
1866 void init_search_stack(SearchStack& ss) {
1868 ss.pv[0] = MOVE_NONE;
1869 ss.pv[1] = MOVE_NONE;
1870 ss.currentMove = MOVE_NONE;
1871 ss.threatMove = MOVE_NONE;
1872 ss.reduction = Depth(0);
1873 for (int j = 0; j < KILLER_MAX; j++)
1874 ss.killers[j] = MOVE_NONE;
1877 void init_search_stack(SearchStack ss[]) {
1879 for (int i = 0; i < 3; i++)
1881 ss[i].pv[i] = MOVE_NONE;
1882 ss[i].pv[i+1] = MOVE_NONE;
1883 ss[i].currentMove = MOVE_NONE;
1884 ss[i].threatMove = MOVE_NONE;
1885 ss[i].reduction = Depth(0);
1886 for (int j = 0; j < KILLER_MAX; j++)
1887 ss[i].killers[j] = MOVE_NONE;
1892 // init_node() is called at the beginning of all the search functions
1893 // (search(), search_pv(), qsearch(), and so on) and initializes the search
1894 // stack object corresponding to the current node. Once every
1895 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1896 // for user input and checks whether it is time to stop the search.
1898 void init_node(const Position &pos, SearchStack ss[], int ply, int threadID) {
1899 assert(ply >= 0 && ply < PLY_MAX);
1900 assert(threadID >= 0 && threadID < ActiveThreads);
1902 Threads[threadID].nodes++;
1906 if(NodesSincePoll >= NodesBetweenPolls) {
1911 ss[ply].pv[ply] = ss[ply].pv[ply+1] = ss[ply].currentMove = MOVE_NONE;
1912 ss[ply+2].mateKiller = MOVE_NONE;
1913 ss[ply].threatMove = MOVE_NONE;
1914 ss[ply].reduction = Depth(0);
1915 ss[ply].currentMoveCaptureValue = Value(0);
1916 for (int j = 0; j < KILLER_MAX; j++)
1917 ss[ply+2].killers[j] = MOVE_NONE;
1919 if(Threads[threadID].printCurrentLine)
1920 print_current_line(ss, ply, threadID);
1924 // update_pv() is called whenever a search returns a value > alpha. It
1925 // updates the PV in the SearchStack object corresponding to the current
1928 void update_pv(SearchStack ss[], int ply) {
1929 assert(ply >= 0 && ply < PLY_MAX);
1931 ss[ply].pv[ply] = ss[ply].currentMove;
1933 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
1934 ss[ply].pv[p] = ss[ply+1].pv[p];
1935 ss[ply].pv[p] = MOVE_NONE;
1939 // sp_update_pv() is a variant of update_pv for use at split points. The
1940 // difference between the two functions is that sp_update_pv also updates
1941 // the PV at the parent node.
1943 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply) {
1944 assert(ply >= 0 && ply < PLY_MAX);
1946 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
1948 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
1949 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
1950 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
1954 // connected_moves() tests whether two moves are 'connected' in the sense
1955 // that the first move somehow made the second move possible (for instance
1956 // if the moving piece is the same in both moves). The first move is
1957 // assumed to be the move that was made to reach the current position, while
1958 // the second move is assumed to be a move from the current position.
1960 bool connected_moves(const Position &pos, Move m1, Move m2) {
1961 Square f1, t1, f2, t2;
1963 assert(move_is_ok(m1));
1964 assert(move_is_ok(m2));
1969 // Case 1: The moving piece is the same in both moves.
1975 // Case 2: The destination square for m2 was vacated by m1.
1981 // Case 3: Moving through the vacated square:
1982 if(piece_is_slider(pos.piece_on(f2)) &&
1983 bit_is_set(squares_between(f2, t2), f1))
1986 // Case 4: The destination square for m2 is attacked by the moving piece
1988 if(pos.piece_attacks_square(t1, t2))
1991 // Case 5: Discovered check, checking piece is the piece moved in m1:
1992 if(piece_is_slider(pos.piece_on(t1)) &&
1993 bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())),
1995 !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())),
1997 Bitboard occ = pos.occupied_squares();
1998 Color us = pos.side_to_move();
1999 Square ksq = pos.king_square(us);
2000 clear_bit(&occ, f2);
2001 if(pos.type_of_piece_on(t1) == BISHOP) {
2002 if(bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2005 else if(pos.type_of_piece_on(t1) == ROOK) {
2006 if(bit_is_set(rook_attacks_bb(ksq, occ), t1))
2010 assert(pos.type_of_piece_on(t1) == QUEEN);
2011 if(bit_is_set(queen_attacks_bb(ksq, occ), t1))
2020 // move_is_killer() checks if the given move is among the
2021 // killer moves of that ply.
2023 bool move_is_killer(Move m, const SearchStack& ss) {
2025 const Move* k = ss.killers;
2026 for (int i = 0; i < KILLER_MAX; i++, k++)
2034 // extension() decides whether a move should be searched with normal depth,
2035 // or with extended depth. Certain classes of moves (checking moves, in
2036 // particular) are searched with bigger depth than ordinary moves and in
2037 // any case are marked as 'dangerous'. Note that also if a move is not
2038 // extended, as example because the corresponding UCI option is set to zero,
2039 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2041 Depth extension(const Position &pos, Move m, bool pvNode, bool check,
2042 bool singleReply, bool mateThreat, bool* dangerous) {
2044 Depth result = Depth(0);
2045 *dangerous = check || singleReply || mateThreat;
2048 result += CheckExtension[pvNode];
2051 result += SingleReplyExtension[pvNode];
2054 result += MateThreatExtension[pvNode];
2056 if (pos.move_is_pawn_push_to_7th(m))
2058 result += PawnPushTo7thExtension[pvNode];
2061 if (pos.move_is_passed_pawn_push(m))
2063 result += PassedPawnExtension[pvNode];
2067 if ( pos.midgame_value_of_piece_on(move_to(m)) >= RookValueMidgame
2068 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2069 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2070 && !move_promotion(m))
2072 result += PawnEndgameExtension[pvNode];
2077 && pos.move_is_capture(m)
2078 && pos.type_of_piece_on(move_to(m)) != PAWN
2085 return Min(result, OnePly);
2089 // ok_to_do_nullmove() looks at the current position and decides whether
2090 // doing a 'null move' should be allowed. In order to avoid zugzwang
2091 // problems, null moves are not allowed when the side to move has very
2092 // little material left. Currently, the test is a bit too simple: Null
2093 // moves are avoided only when the side to move has only pawns left. It's
2094 // probably a good idea to avoid null moves in at least some more
2095 // complicated endgames, e.g. KQ vs KR. FIXME
2097 bool ok_to_do_nullmove(const Position &pos) {
2098 if(pos.non_pawn_material(pos.side_to_move()) == Value(0))
2104 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2105 // non-tactical moves late in the move list close to the leaves are
2106 // candidates for pruning.
2108 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d) {
2109 Square mfrom, mto, tfrom, tto;
2111 assert(move_is_ok(m));
2112 assert(threat == MOVE_NONE || move_is_ok(threat));
2113 assert(!move_promotion(m));
2114 assert(!pos.move_is_check(m));
2115 assert(!pos.move_is_capture(m));
2116 assert(!pos.move_is_passed_pawn_push(m));
2117 assert(d >= OnePly);
2119 mfrom = move_from(m);
2121 tfrom = move_from(threat);
2122 tto = move_to(threat);
2124 // Case 1: Castling moves are never pruned.
2125 if(move_is_castle(m))
2128 // Case 2: Don't prune moves which move the threatened piece
2129 if(!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2132 // Case 3: If the threatened piece has value less than or equal to the
2133 // value of the threatening piece, don't prune move which defend it.
2134 if(!PruneDefendingMoves && threat != MOVE_NONE
2135 && (piece_value_midgame(pos.piece_on(tfrom))
2136 >= piece_value_midgame(pos.piece_on(tto)))
2137 && pos.move_attacks_square(m, tto))
2140 // Case 4: Don't prune moves with good history.
2141 if(!H.ok_to_prune(pos.piece_on(move_from(m)), m, d))
2144 // Case 5: If the moving piece in the threatened move is a slider, don't
2145 // prune safe moves which block its ray.
2146 if(!PruneBlockingMoves && threat != MOVE_NONE
2147 && piece_is_slider(pos.piece_on(tfrom))
2148 && bit_is_set(squares_between(tfrom, tto), mto) && pos.see(m) >= 0)
2155 // ok_to_use_TT() returns true if a transposition table score
2156 // can be used at a given point in search.
2158 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2160 Value v = value_from_tt(tte->value(), ply);
2162 return ( tte->depth() >= depth
2163 || v >= Max(value_mate_in(100), beta)
2164 || v < Min(value_mated_in(100), beta))
2166 && ( (is_lower_bound(tte->type()) && v >= beta)
2167 || (is_upper_bound(tte->type()) && v < beta));
2171 // ok_to_history() returns true if a move m can be stored
2172 // in history. Should be a non capturing move nor a promotion.
2174 bool ok_to_history(const Position& pos, Move m) {
2176 return !pos.move_is_capture(m) && !move_promotion(m);
2180 // update_history() registers a good move that produced a beta-cutoff
2181 // in history and marks as failures all the other moves of that ply.
2183 void update_history(const Position& pos, Move m, Depth depth,
2184 Move movesSearched[], int moveCount) {
2186 H.success(pos.piece_on(move_from(m)), m, depth);
2188 for (int i = 0; i < moveCount - 1; i++)
2190 assert(m != movesSearched[i]);
2191 if (ok_to_history(pos, movesSearched[i]))
2192 H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
2197 // update_killers() add a good move that produced a beta-cutoff
2198 // among the killer moves of that ply.
2200 void update_killers(Move m, SearchStack& ss) {
2202 if (m == ss.killers[0])
2205 for (int i = KILLER_MAX - 1; i > 0; i--)
2206 ss.killers[i] = ss.killers[i - 1];
2211 // fail_high_ply_1() checks if some thread is currently resolving a fail
2212 // high at ply 1 at the node below the first root node. This information
2213 // is used for time managment.
2215 bool fail_high_ply_1() {
2216 for(int i = 0; i < ActiveThreads; i++)
2217 if(Threads[i].failHighPly1)
2223 // current_search_time() returns the number of milliseconds which have passed
2224 // since the beginning of the current search.
2226 int current_search_time() {
2227 return get_system_time() - SearchStartTime;
2231 // nps() computes the current nodes/second count.
2234 int t = current_search_time();
2235 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2239 // poll() performs two different functions: It polls for user input, and it
2240 // looks at the time consumed so far and decides if it's time to abort the
2245 static int lastInfoTime;
2246 int t = current_search_time();
2251 // We are line oriented, don't read single chars
2252 std::string command;
2253 if (!std::getline(std::cin, command))
2256 if (command == "quit")
2259 PonderSearch = false;
2262 else if(command == "stop")
2265 PonderSearch = false;
2267 else if(command == "ponderhit")
2270 // Print search information
2274 else if (lastInfoTime > t)
2275 // HACK: Must be a new search where we searched less than
2276 // NodesBetweenPolls nodes during the first second of search.
2279 else if (t - lastInfoTime >= 1000)
2286 if (dbg_show_hit_rate)
2287 dbg_print_hit_rate();
2289 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2290 << " time " << t << " hashfull " << TT.full() << std::endl;
2291 lock_release(&IOLock);
2292 if (ShowCurrentLine)
2293 Threads[0].printCurrentLine = true;
2295 // Should we stop the search?
2299 bool overTime = t > AbsoluteMaxSearchTime
2300 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime)
2301 || ( !FailHigh && !fail_high_ply_1() && !Problem
2302 && t > 6*(MaxSearchTime + ExtraSearchTime));
2304 if ( (Iteration >= 2 && (!InfiniteSearch && overTime))
2305 || (ExactMaxTime && t >= ExactMaxTime)
2306 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2311 // ponderhit() is called when the program is pondering (i.e. thinking while
2312 // it's the opponent's turn to move) in order to let the engine know that
2313 // it correctly predicted the opponent's move.
2316 int t = current_search_time();
2317 PonderSearch = false;
2318 if(Iteration >= 2 &&
2319 (!InfiniteSearch && (StopOnPonderhit ||
2320 t > AbsoluteMaxSearchTime ||
2321 (RootMoveNumber == 1 &&
2322 t > MaxSearchTime + ExtraSearchTime) ||
2323 (!FailHigh && !fail_high_ply_1() && !Problem &&
2324 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2329 // print_current_line() prints the current line of search for a given
2330 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2332 void print_current_line(SearchStack ss[], int ply, int threadID) {
2333 assert(ply >= 0 && ply < PLY_MAX);
2334 assert(threadID >= 0 && threadID < ActiveThreads);
2336 if(!Threads[threadID].idle) {
2338 std::cout << "info currline " << (threadID + 1);
2339 for(int p = 0; p < ply; p++)
2340 std::cout << " " << ss[p].currentMove;
2341 std::cout << std::endl;
2342 lock_release(&IOLock);
2344 Threads[threadID].printCurrentLine = false;
2345 if(threadID + 1 < ActiveThreads)
2346 Threads[threadID + 1].printCurrentLine = true;
2350 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2351 // while the program is pondering. The point is to work around a wrinkle in
2352 // the UCI protocol: When pondering, the engine is not allowed to give a
2353 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2354 // We simply wait here until one of these commands is sent, and return,
2355 // after which the bestmove and pondermove will be printed (in id_loop()).
2357 void wait_for_stop_or_ponderhit() {
2358 std::string command;
2361 if(!std::getline(std::cin, command))
2364 if(command == "quit") {
2365 OpeningBook.close();
2370 else if(command == "ponderhit" || command == "stop")
2376 // idle_loop() is where the threads are parked when they have no work to do.
2377 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2378 // object for which the current thread is the master.
2380 void idle_loop(int threadID, SplitPoint *waitSp) {
2381 assert(threadID >= 0 && threadID < THREAD_MAX);
2383 Threads[threadID].running = true;
2386 if(AllThreadsShouldExit && threadID != 0)
2389 // If we are not thinking, wait for a condition to be signaled instead
2390 // of wasting CPU time polling for work:
2391 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2392 #if !defined(_MSC_VER)
2393 pthread_mutex_lock(&WaitLock);
2394 if(Idle || threadID >= ActiveThreads)
2395 pthread_cond_wait(&WaitCond, &WaitLock);
2396 pthread_mutex_unlock(&WaitLock);
2398 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2402 // If this thread has been assigned work, launch a search:
2403 if(Threads[threadID].workIsWaiting) {
2404 Threads[threadID].workIsWaiting = false;
2405 if(Threads[threadID].splitPoint->pvNode)
2406 sp_search_pv(Threads[threadID].splitPoint, threadID);
2408 sp_search(Threads[threadID].splitPoint, threadID);
2409 Threads[threadID].idle = true;
2412 // If this thread is the master of a split point and all threads have
2413 // finished their work at this split point, return from the idle loop:
2414 if(waitSp != NULL && waitSp->cpus == 0)
2418 Threads[threadID].running = false;
2422 // init_split_point_stack() is called during program initialization, and
2423 // initializes all split point objects.
2425 void init_split_point_stack() {
2426 for(int i = 0; i < THREAD_MAX; i++)
2427 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2428 SplitPointStack[i][j].parent = NULL;
2429 lock_init(&(SplitPointStack[i][j].lock), NULL);
2434 // destroy_split_point_stack() is called when the program exits, and
2435 // destroys all locks in the precomputed split point objects.
2437 void destroy_split_point_stack() {
2438 for(int i = 0; i < THREAD_MAX; i++)
2439 for(int j = 0; j < MaxActiveSplitPoints; j++)
2440 lock_destroy(&(SplitPointStack[i][j].lock));
2444 // thread_should_stop() checks whether the thread with a given threadID has
2445 // been asked to stop, directly or indirectly. This can happen if a beta
2446 // cutoff has occured in thre thread's currently active split point, or in
2447 // some ancestor of the current split point.
2449 bool thread_should_stop(int threadID) {
2450 assert(threadID >= 0 && threadID < ActiveThreads);
2454 if(Threads[threadID].stop)
2456 if(ActiveThreads <= 2)
2458 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2460 Threads[threadID].stop = true;
2467 // thread_is_available() checks whether the thread with threadID "slave" is
2468 // available to help the thread with threadID "master" at a split point. An
2469 // obvious requirement is that "slave" must be idle. With more than two
2470 // threads, this is not by itself sufficient: If "slave" is the master of
2471 // some active split point, it is only available as a slave to the other
2472 // threads which are busy searching the split point at the top of "slave"'s
2473 // split point stack (the "helpful master concept" in YBWC terminology).
2475 bool thread_is_available(int slave, int master) {
2476 assert(slave >= 0 && slave < ActiveThreads);
2477 assert(master >= 0 && master < ActiveThreads);
2478 assert(ActiveThreads > 1);
2480 if(!Threads[slave].idle || slave == master)
2483 if(Threads[slave].activeSplitPoints == 0)
2484 // No active split points means that the thread is available as a slave
2485 // for any other thread.
2488 if(ActiveThreads == 2)
2491 // Apply the "helpful master" concept if possible.
2492 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2499 // idle_thread_exists() tries to find an idle thread which is available as
2500 // a slave for the thread with threadID "master".
2502 bool idle_thread_exists(int master) {
2503 assert(master >= 0 && master < ActiveThreads);
2504 assert(ActiveThreads > 1);
2506 for(int i = 0; i < ActiveThreads; i++)
2507 if(thread_is_available(i, master))
2513 // split() does the actual work of distributing the work at a node between
2514 // several threads at PV nodes. If it does not succeed in splitting the
2515 // node (because no idle threads are available, or because we have no unused
2516 // split point objects), the function immediately returns false. If
2517 // splitting is possible, a SplitPoint object is initialized with all the
2518 // data that must be copied to the helper threads (the current position and
2519 // search stack, alpha, beta, the search depth, etc.), and we tell our
2520 // helper threads that they have been assigned work. This will cause them
2521 // to instantly leave their idle loops and call sp_search_pv(). When all
2522 // threads have returned from sp_search_pv (or, equivalently, when
2523 // splitPoint->cpus becomes 0), split() returns true.
2525 bool split(const Position &p, SearchStack *sstck, int ply,
2526 Value *alpha, Value *beta, Value *bestValue,
2527 Depth depth, int *moves,
2528 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode) {
2530 assert(sstck != NULL);
2531 assert(ply >= 0 && ply < PLY_MAX);
2532 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2533 assert(!pvNode || *alpha < *beta);
2534 assert(*beta <= VALUE_INFINITE);
2535 assert(depth > Depth(0));
2536 assert(master >= 0 && master < ActiveThreads);
2537 assert(ActiveThreads > 1);
2539 SplitPoint *splitPoint;
2544 // If no other thread is available to help us, or if we have too many
2545 // active split points, don't split:
2546 if(!idle_thread_exists(master) ||
2547 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2548 lock_release(&MPLock);
2552 // Pick the next available split point object from the split point stack:
2553 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2554 Threads[master].activeSplitPoints++;
2556 // Initialize the split point object:
2557 splitPoint->parent = Threads[master].splitPoint;
2558 splitPoint->finished = false;
2559 splitPoint->ply = ply;
2560 splitPoint->depth = depth;
2561 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2562 splitPoint->beta = *beta;
2563 splitPoint->pvNode = pvNode;
2564 splitPoint->dcCandidates = dcCandidates;
2565 splitPoint->bestValue = *bestValue;
2566 splitPoint->master = master;
2567 splitPoint->mp = mp;
2568 splitPoint->moves = *moves;
2569 splitPoint->cpus = 1;
2570 splitPoint->pos.copy(p);
2571 splitPoint->parentSstack = sstck;
2572 for(i = 0; i < ActiveThreads; i++)
2573 splitPoint->slaves[i] = 0;
2575 // Copy the current position and the search stack to the master thread:
2576 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2577 Threads[master].splitPoint = splitPoint;
2579 // Make copies of the current position and search stack for each thread:
2580 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2582 if(thread_is_available(i, master)) {
2583 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2584 Threads[i].splitPoint = splitPoint;
2585 splitPoint->slaves[i] = 1;
2589 // Tell the threads that they have work to do. This will make them leave
2591 for(i = 0; i < ActiveThreads; i++)
2592 if(i == master || splitPoint->slaves[i]) {
2593 Threads[i].workIsWaiting = true;
2594 Threads[i].idle = false;
2595 Threads[i].stop = false;
2598 lock_release(&MPLock);
2600 // Everything is set up. The master thread enters the idle loop, from
2601 // which it will instantly launch a search, because its workIsWaiting
2602 // slot is 'true'. We send the split point as a second parameter to the
2603 // idle loop, which means that the main thread will return from the idle
2604 // loop when all threads have finished their work at this split point
2605 // (i.e. when // splitPoint->cpus == 0).
2606 idle_loop(master, splitPoint);
2608 // We have returned from the idle loop, which means that all threads are
2609 // finished. Update alpha, beta and bestvalue, and return:
2611 if(pvNode) *alpha = splitPoint->alpha;
2612 *beta = splitPoint->beta;
2613 *bestValue = splitPoint->bestValue;
2614 Threads[master].stop = false;
2615 Threads[master].idle = false;
2616 Threads[master].activeSplitPoints--;
2617 Threads[master].splitPoint = splitPoint->parent;
2618 lock_release(&MPLock);
2624 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2625 // to start a new search from the root.
2627 void wake_sleeping_threads() {
2628 if(ActiveThreads > 1) {
2629 for(int i = 1; i < ActiveThreads; i++) {
2630 Threads[i].idle = true;
2631 Threads[i].workIsWaiting = false;
2633 #if !defined(_MSC_VER)
2634 pthread_mutex_lock(&WaitLock);
2635 pthread_cond_broadcast(&WaitCond);
2636 pthread_mutex_unlock(&WaitLock);
2638 for(int i = 1; i < THREAD_MAX; i++)
2639 SetEvent(SitIdleEvent[i]);
2645 // init_thread() is the function which is called when a new thread is
2646 // launched. It simply calls the idle_loop() function with the supplied
2647 // threadID. There are two versions of this function; one for POSIX threads
2648 // and one for Windows threads.
2650 #if !defined(_MSC_VER)
2652 void *init_thread(void *threadID) {
2653 idle_loop(*(int *)threadID, NULL);
2659 DWORD WINAPI init_thread(LPVOID threadID) {
2660 idle_loop(*(int *)threadID, NULL);