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, TimeAdvantage;
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);
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);
255 bool fail_high_ply_1();
256 int current_search_time();
260 void print_current_line(SearchStack ss[], int ply, int threadID);
261 void wait_for_stop_or_ponderhit();
263 void idle_loop(int threadID, SplitPoint *waitSp);
264 void init_split_point_stack();
265 void destroy_split_point_stack();
266 bool thread_should_stop(int threadID);
267 bool thread_is_available(int slave, int master);
268 bool idle_thread_exists(int master);
269 bool split(const Position &pos, SearchStack *ss, int ply,
270 Value *alpha, Value *beta, Value *bestValue, Depth depth,
271 int *moves, MovePicker *mp, Bitboard dcCandidates, int master,
273 void wake_sleeping_threads();
275 #if !defined(_MSC_VER)
276 void *init_thread(void *threadID);
278 DWORD WINAPI init_thread(LPVOID threadID);
285 //// Global variables
288 // The main transposition table
289 TranspositionTable TT = TranspositionTable(TTDefaultSize);
292 // Number of active threads:
293 int ActiveThreads = 1;
295 // Locks. In principle, there is no need for IOLock to be a global variable,
296 // but it could turn out to be useful for debugging.
299 History H; // Should be made local?
301 // The empty search stack
302 SearchStack EmptySearchStack;
309 /// think() is the external interface to Stockfish's search, and is called when
310 /// the program receives the UCI 'go' command. It initializes various
311 /// search-related global variables, and calls root_search()
313 void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
314 int time[], int increment[], int movesToGo, int maxDepth,
315 int maxNodes, int maxTime, Move searchMoves[]) {
317 // Look for a book move
318 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
321 if (get_option_value_string("Book File") != OpeningBook.file_name())
324 OpeningBook.open("book.bin");
326 bookMove = OpeningBook.get_move(pos);
327 if (bookMove != MOVE_NONE)
329 std::cout << "bestmove " << bookMove << std::endl;
334 // Initialize global search variables
336 SearchStartTime = get_system_time();
337 BestRootMove = MOVE_NONE;
338 PonderMove = MOVE_NONE;
339 EasyMove = MOVE_NONE;
340 for (int i = 0; i < THREAD_MAX; i++)
342 Threads[i].nodes = 0ULL;
343 Threads[i].failHighPly1 = false;
346 InfiniteSearch = infinite;
347 PonderSearch = ponder;
348 StopOnPonderhit = false;
353 ExactMaxTime = maxTime;
355 // Read UCI option values
356 TT.set_size(get_option_value_int("Hash"));
357 if (button_was_pressed("Clear Hash"))
360 PonderingEnabled = get_option_value_bool("Ponder");
361 MultiPV = get_option_value_int("MultiPV");
363 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
364 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
366 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
367 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
369 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
370 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
372 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
373 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
375 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
376 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
378 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
379 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
381 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
382 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
383 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
384 SelectiveDepth = get_option_value_int("Selective Plies") * OnePly;
386 Chess960 = get_option_value_bool("UCI_Chess960");
387 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
388 UseLogFile = get_option_value_bool("Use Search Log");
390 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
392 UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)");
393 UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)");
395 FutilityMargin0 = value_from_centipawns(get_option_value_int("Futility Margin 0"));
396 FutilityMargin1 = value_from_centipawns(get_option_value_int("Futility Margin 1"));
397 FutilityMargin2 = value_from_centipawns(get_option_value_int("Futility Margin 2"));
399 RazorDepth = (get_option_value_int("Maximum Razoring Depth") + 1) * OnePly;
400 RazorMargin = value_from_centipawns(get_option_value_int("Razoring Margin"));
402 UseLSNFiltering = get_option_value_bool("LSN filtering");
403 LSNTime = get_option_value_int("LSN Time Margin (sec)") * 1000;
404 LSNValue = value_from_centipawns(get_option_value_int("LSN Value Margin"));
406 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
407 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
409 read_weights(pos.side_to_move());
411 int newActiveThreads = get_option_value_int("Threads");
412 if (newActiveThreads != ActiveThreads)
414 ActiveThreads = newActiveThreads;
415 init_eval(ActiveThreads);
418 // Wake up sleeping threads:
419 wake_sleeping_threads();
421 for (int i = 1; i < ActiveThreads; i++)
422 assert(thread_is_available(i, 0));
424 // Set thinking time:
425 int myTime = time[side_to_move];
426 int myIncrement = increment[side_to_move];
427 int oppTime = time[1 - side_to_move];
429 TimeAdvantage = myTime - oppTime;
431 if (!movesToGo) // Sudden death time control
435 MaxSearchTime = myTime / 30 + myIncrement;
436 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
437 } else { // Blitz game without increment
438 MaxSearchTime = myTime / 40;
439 AbsoluteMaxSearchTime = myTime / 8;
442 else // (x moves) / (y minutes)
446 MaxSearchTime = myTime / 2;
447 AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
449 MaxSearchTime = myTime / Min(movesToGo, 20);
450 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
454 if (PonderingEnabled)
456 MaxSearchTime += MaxSearchTime / 4;
457 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
460 // Fixed depth or fixed number of nodes?
463 InfiniteSearch = true; // HACK
468 NodesBetweenPolls = Min(MaxNodes, 30000);
469 InfiniteSearch = true; // HACK
472 NodesBetweenPolls = 30000;
475 // Write information to search log file:
477 LogFile << "Searching: " << pos.to_fen() << std::endl
478 << "infinite: " << infinite
479 << " ponder: " << ponder
480 << " time: " << myTime
481 << " increment: " << myIncrement
482 << " moves to go: " << movesToGo << std::endl;
485 // We're ready to start thinking. Call the iterative deepening loop
489 Value v = id_loop(pos, searchMoves);
490 looseOnTime = ( UseLSNFiltering
497 looseOnTime = false; // reset for next match
498 while (SearchStartTime + myTime + 1000 > get_system_time())
500 id_loop(pos, searchMoves); // to fail gracefully
517 /// init_threads() is called during startup. It launches all helper threads,
518 /// and initializes the split point stack and the global locks and condition
521 void init_threads() {
525 #if !defined(_MSC_VER)
526 pthread_t pthread[1];
529 for (i = 0; i < THREAD_MAX; i++)
530 Threads[i].activeSplitPoints = 0;
532 // Initialize global locks:
533 lock_init(&MPLock, NULL);
534 lock_init(&IOLock, NULL);
536 init_split_point_stack();
538 #if !defined(_MSC_VER)
539 pthread_mutex_init(&WaitLock, NULL);
540 pthread_cond_init(&WaitCond, NULL);
542 for (i = 0; i < THREAD_MAX; i++)
543 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
546 // All threads except the main thread should be initialized to idle state
547 for (i = 1; i < THREAD_MAX; i++)
549 Threads[i].stop = false;
550 Threads[i].workIsWaiting = false;
551 Threads[i].idle = true;
552 Threads[i].running = false;
555 // Launch the helper threads
556 for(i = 1; i < THREAD_MAX; i++)
558 #if !defined(_MSC_VER)
559 pthread_create(pthread, NULL, init_thread, (void*)(&i));
562 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
565 // Wait until the thread has finished launching:
566 while (!Threads[i].running);
569 // Init also the empty search stack
570 init_search_stack(EmptySearchStack);
574 /// stop_threads() is called when the program exits. It makes all the
575 /// helper threads exit cleanly.
577 void stop_threads() {
579 ActiveThreads = THREAD_MAX; // HACK
580 Idle = false; // HACK
581 wake_sleeping_threads();
582 AllThreadsShouldExit = true;
583 for (int i = 1; i < THREAD_MAX; i++)
585 Threads[i].stop = true;
586 while(Threads[i].running);
588 destroy_split_point_stack();
592 /// nodes_searched() returns the total number of nodes searched so far in
593 /// the current search.
595 int64_t nodes_searched() {
597 int64_t result = 0ULL;
598 for (int i = 0; i < ActiveThreads; i++)
599 result += Threads[i].nodes;
606 // id_loop() is the main iterative deepening loop. It calls root_search
607 // repeatedly with increasing depth until the allocated thinking time has
608 // been consumed, the user stops the search, or the maximum search depth is
611 Value id_loop(const Position &pos, Move searchMoves[]) {
614 SearchStack ss[PLY_MAX_PLUS_2];
616 // searchMoves are verified, copied, scored and sorted
617 RootMoveList rml(p, searchMoves);
622 init_search_stack(ss);
624 ValueByIteration[0] = Value(0);
625 ValueByIteration[1] = rml.get_move_score(0);
627 LastIterations = false;
629 EasyMove = rml.scan_for_easy_move();
631 // Iterative deepening loop
632 while (!AbortSearch && Iteration < PLY_MAX)
634 // Initialize iteration
637 BestMoveChangesByIteration[Iteration] = 0;
641 std::cout << "info depth " << Iteration << std::endl;
643 // Search to the current depth
644 ValueByIteration[Iteration] = root_search(p, ss, rml);
646 // Erase the easy move if it differs from the new best move
647 if (ss[0].pv[0] != EasyMove)
648 EasyMove = MOVE_NONE;
655 bool stopSearch = false;
657 // Stop search early if there is only a single legal move:
658 if (Iteration >= 6 && rml.move_count() == 1)
661 // Stop search early when the last two iterations returned a mate score
663 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
664 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
667 // Stop search early if one move seems to be much better than the rest
668 int64_t nodes = nodes_searched();
670 && EasyMove == ss[0].pv[0]
671 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
672 && current_search_time() > MaxSearchTime / 16)
673 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
674 && current_search_time() > MaxSearchTime / 32)))
677 // Add some extra time if the best move has changed during the last two iterations
678 if (Iteration > 5 && Iteration <= 50)
679 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
680 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
682 // If we need some more and we are in time advantage take it
683 if (ExtraSearchTime > 0 && TimeAdvantage > 2 * MaxSearchTime)
684 ExtraSearchTime += MaxSearchTime / 2;
686 // Try to guess if the current iteration is the last one or the last two
687 LastIterations = (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*58) / 128);
689 // Stop search if most of MaxSearchTime is consumed at the end of the
690 // iteration. We probably don't have enough time to search the first
691 // move at the next iteration anyway.
692 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
700 StopOnPonderhit = true;
703 // Write PV to transposition table, in case the relevant entries have
704 // been overwritten during the search:
705 TT.insert_pv(p, ss[0].pv);
707 if (MaxDepth && Iteration >= MaxDepth)
713 // If we are pondering, we shouldn't print the best move before we
716 wait_for_stop_or_ponderhit();
718 // Print final search statistics
719 std::cout << "info nodes " << nodes_searched()
721 << " time " << current_search_time()
722 << " hashfull " << TT.full() << std::endl;
724 // Print the best move and the ponder move to the standard output
725 std::cout << "bestmove " << ss[0].pv[0];
726 if (ss[0].pv[1] != MOVE_NONE)
727 std::cout << " ponder " << ss[0].pv[1];
729 std::cout << std::endl;
734 LogFile << "Nodes: " << nodes_searched() << std::endl
735 << "Nodes/second: " << nps() << std::endl
736 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
738 p.do_move(ss[0].pv[0], u);
739 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
740 << std::endl << std::endl;
742 return rml.get_move_score(0);
746 // root_search() is the function which searches the root node. It is
747 // similar to search_pv except that it uses a different move ordering
748 // scheme (perhaps we should try to use this at internal PV nodes, too?)
749 // and prints some information to the standard output.
751 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml) {
753 Value alpha = -VALUE_INFINITE;
754 Value beta = VALUE_INFINITE, value;
755 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
757 // Loop through all the moves in the root move list
758 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
765 RootMoveNumber = i + 1;
768 // Remember the node count before the move is searched. The node counts
769 // are used to sort the root moves at the next iteration.
770 nodes = nodes_searched();
772 // Pick the next root move, and print the move and the move number to
773 // the standard output.
774 move = ss[0].currentMove = rml.get_move(i);
775 if (current_search_time() >= 1000)
776 std::cout << "info currmove " << move
777 << " currmovenumber " << i + 1 << std::endl;
779 // Decide search depth for this move
780 ext = extension(pos, move, true, pos.move_is_check(move), false, false);
781 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
783 // Make the move, and search it
784 pos.do_move(move, u, dcCandidates);
788 value = -search_pv(pos, ss, -beta, VALUE_INFINITE, newDepth, 1, 0);
789 // If the value has dropped a lot compared to the last iteration,
790 // set the boolean variable Problem to true. This variable is used
791 // for time managment: When Problem is true, we try to complete the
792 // current iteration before playing a move.
793 Problem = (Iteration >= 2 && value <= ValueByIteration[Iteration-1] - ProblemMargin);
795 if (Problem && StopOnPonderhit)
796 StopOnPonderhit = false;
800 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
803 // Fail high! Set the boolean variable FailHigh to true, and
804 // re-search the move with a big window. The variable FailHigh is
805 // used for time managment: We try to avoid aborting the search
806 // prematurely during a fail high research.
808 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
812 pos.undo_move(move, u);
814 // Finished searching the move. If AbortSearch is true, the search
815 // was aborted because the user interrupted the search or because we
816 // ran out of time. In this case, the return value of the search cannot
817 // be trusted, and we break out of the loop without updating the best
822 // Remember the node count for this move. The node counts are used to
823 // sort the root moves at the next iteration.
824 rml.set_move_nodes(i, nodes_searched() - nodes);
826 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
828 if (value <= alpha && i >= MultiPV)
829 rml.set_move_score(i, -VALUE_INFINITE);
835 rml.set_move_score(i, value);
837 rml.set_move_pv(i, ss[0].pv);
841 // We record how often the best move has been changed in each
842 // iteration. This information is used for time managment: When
843 // the best move changes frequently, we allocate some more time.
845 BestMoveChangesByIteration[Iteration]++;
847 // Print search information to the standard output:
848 std::cout << "info depth " << Iteration
849 << " score " << value_to_string(value)
850 << " time " << current_search_time()
851 << " nodes " << nodes_searched()
855 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
856 std::cout << ss[0].pv[j] << " ";
858 std::cout << std::endl;
861 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
866 // Reset the global variable Problem to false if the value isn't too
867 // far below the final value from the last iteration.
868 if (value > ValueByIteration[Iteration - 1] - NoProblemMargin)
874 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
877 std::cout << "info multipv " << j + 1
878 << " score " << value_to_string(rml.get_move_score(j))
879 << " depth " << ((j <= i)? Iteration : Iteration - 1)
880 << " time " << current_search_time()
881 << " nodes " << nodes_searched()
885 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
886 std::cout << rml.get_move_pv(j, k) << " ";
888 std::cout << std::endl;
890 alpha = rml.get_move_score(Min(i, MultiPV-1));
898 // search_pv() is the main search function for PV nodes.
900 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
901 Depth depth, int ply, int threadID) {
903 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
904 assert(beta > alpha && beta <= VALUE_INFINITE);
905 assert(ply >= 0 && ply < PLY_MAX);
906 assert(threadID >= 0 && threadID < ActiveThreads);
908 // Initialize, and make an early exit in case of an aborted search,
909 // an instant draw, maximum ply reached, etc.
910 if (AbortSearch || thread_should_stop(threadID))
914 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
916 init_node(pos, ss, ply, threadID);
923 if (ply >= PLY_MAX - 1)
924 return evaluate(pos, ei, threadID);
926 // Mate distance pruning
927 Value oldAlpha = alpha;
928 alpha = Max(value_mated_in(ply), alpha);
929 beta = Min(value_mate_in(ply+1), beta);
933 // Transposition table lookup. At PV nodes, we don't use the TT for
934 // pruning, but only for move ordering.
935 const TTEntry* tte = TT.retrieve(pos);
936 Move ttMove = (tte ? tte->move() : MOVE_NONE);
938 // Go with internal iterative deepening if we don't have a TT move
939 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
941 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
942 ttMove = ss[ply].pv[ply];
945 // Initialize a MovePicker object for the current position, and prepare
946 // to search all moves
947 MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
949 Move move, movesSearched[256];
951 Value value, bestValue = -VALUE_INFINITE;
952 Bitboard dcCandidates = mp.discovered_check_candidates();
953 bool isCheck = pos.is_check();
954 bool mateThreat = MateThreatExtension[1] > Depth(0)
955 && pos.has_mate_threat(opposite_color(pos.side_to_move()));
957 // Loop through all legal moves until no moves remain or a beta cutoff
960 && (move = mp.get_next_move()) != MOVE_NONE
961 && !thread_should_stop(threadID))
963 assert(move_is_ok(move));
965 bool singleReply = (isCheck && mp.number_of_moves() == 1);
966 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
967 bool moveIsCapture = pos.move_is_capture(move);
968 bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
970 movesSearched[moveCount++] = ss[ply].currentMove = move;
973 ss[ply].currentMoveCaptureValue = pos.midgame_value_of_piece_on(move_to(move));
974 else if (move_is_ep(move))
975 ss[ply].currentMoveCaptureValue = PawnValueMidgame;
977 ss[ply].currentMoveCaptureValue = Value(0);
979 // Decide the new search depth
980 Depth ext = extension(pos, move, true, moveIsCheck, singleReply, mateThreat);
981 Depth newDepth = depth - OnePly + ext;
983 // Make and search the move
985 pos.do_move(move, u, dcCandidates);
987 if (moveCount == 1) // The first move in list is the PV
988 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
991 // Try to reduce non-pv search depth by one ply if move seems not problematic,
992 // if the move fails high will be re-searched at full depth.
993 if ( depth >= 2*OnePly
995 && moveCount >= LMRPVMoves
997 && !move_promotion(move)
998 && !moveIsPassedPawnPush
999 && !move_is_castle(move)
1000 && !move_is_killer(move, ss[ply]))
1002 ss[ply].reduction = OnePly;
1003 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1006 value = alpha + 1; // Just to trigger next condition
1008 if (value > alpha) // Go with full depth pv search
1010 ss[ply].reduction = Depth(0);
1011 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1012 if (value > alpha && value < beta)
1014 // When the search fails high at ply 1 while searching the first
1015 // move at the root, set the flag failHighPly1. This is used for
1016 // time managment: We don't want to stop the search early in
1017 // such cases, because resolving the fail high at ply 1 could
1018 // result in a big drop in score at the root.
1019 if (ply == 1 && RootMoveNumber == 1)
1020 Threads[threadID].failHighPly1 = true;
1022 // A fail high occurred. Re-search at full window (pv search)
1023 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1024 Threads[threadID].failHighPly1 = false;
1028 pos.undo_move(move, u);
1030 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1033 if (value > bestValue)
1040 if (value == value_mate_in(ply + 1))
1041 ss[ply].mateKiller = move;
1043 // If we are at ply 1, and we are searching the first root move at
1044 // ply 0, set the 'Problem' variable if the score has dropped a lot
1045 // (from the computer's point of view) since the previous iteration:
1046 if (Iteration >= 2 && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
1051 if ( ActiveThreads > 1
1053 && depth >= MinimumSplitDepth
1055 && idle_thread_exists(threadID)
1057 && !thread_should_stop(threadID)
1058 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1059 &moveCount, &mp, dcCandidates, threadID, true))
1063 // All legal moves have been searched. A special case: If there were
1064 // no legal moves, it must be mate or stalemate:
1066 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1068 // If the search is not aborted, update the transposition table,
1069 // history counters, and killer moves.
1070 if (AbortSearch || thread_should_stop(threadID))
1073 if (bestValue <= oldAlpha)
1074 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1076 else if (bestValue >= beta)
1078 Move m = ss[ply].pv[ply];
1079 if (ok_to_history(pos, m)) // Only non capture moves are considered
1081 update_history(pos, m, depth, movesSearched, moveCount);
1082 if (m != ss[ply].killers[0])
1084 ss[ply].killers[1] = ss[ply].killers[0];
1085 ss[ply].killers[0] = m;
1088 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1091 TT.store(pos, value_to_tt(bestValue, ply), depth, ss[ply].pv[ply], VALUE_TYPE_EXACT);
1097 // search() is the search function for zero-width nodes.
1099 Value search(Position &pos, SearchStack ss[], Value beta, Depth depth,
1100 int ply, bool allowNullmove, int threadID) {
1102 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1103 assert(ply >= 0 && ply < PLY_MAX);
1104 assert(threadID >= 0 && threadID < ActiveThreads);
1108 // Initialize, and make an early exit in case of an aborted search,
1109 // an instant draw, maximum ply reached, etc.
1110 if (AbortSearch || thread_should_stop(threadID))
1114 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1116 init_node(pos, ss, ply, threadID);
1121 if (ply >= PLY_MAX - 1)
1122 return evaluate(pos, ei, threadID);
1124 // Mate distance pruning
1125 if (value_mated_in(ply) >= beta)
1128 if (value_mate_in(ply + 1) < beta)
1131 // Transposition table lookup
1132 const TTEntry* tte = TT.retrieve(pos);
1133 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1135 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1137 ss[ply].currentMove = ttMove; // can be MOVE_NONE ?
1138 return value_from_tt(tte->value(), ply);
1141 Value approximateEval = quick_evaluate(pos);
1142 bool mateThreat = false;
1143 bool isCheck = pos.is_check();
1148 && ok_to_do_nullmove(pos)
1149 && approximateEval >= beta - NullMoveMargin)
1151 ss[ply].currentMove = MOVE_NULL;
1154 pos.do_null_move(u);
1155 int R = (depth > 7 ? 4 : 3);
1156 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1157 pos.undo_null_move(u);
1159 if (nullValue >= beta)
1161 if (depth < 6 * OnePly)
1164 // Do zugzwang verification search
1165 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1169 // The null move failed low, which means that we may be faced with
1170 // some kind of threat. If the previous move was reduced, check if
1171 // the move that refuted the null move was somehow connected to the
1172 // move which was reduced. If a connection is found, return a fail
1173 // low score (which will cause the reduced move to fail high in the
1174 // parent node, which will trigger a re-search with full depth).
1175 if (nullValue == value_mated_in(ply + 2))
1178 ss[ply].threatMove = ss[ply + 1].currentMove;
1179 if ( depth < ThreatDepth
1180 && ss[ply - 1].reduction
1181 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1185 // Null move search not allowed, try razoring
1186 else if ( (approximateEval < beta - RazorMargin && depth < RazorDepth)
1187 ||(approximateEval < beta - PawnValueMidgame && depth <= OnePly))
1189 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1194 // Go with internal iterative deepening if we don't have a TT move
1195 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1196 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1198 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1199 ttMove = ss[ply].pv[ply];
1202 // Initialize a MovePicker object for the current position, and prepare
1203 // to search all moves:
1204 MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth);
1206 Move move, movesSearched[256];
1208 Value value, bestValue = -VALUE_INFINITE;
1209 Bitboard dcCandidates = mp.discovered_check_candidates();
1210 Value futilityValue = VALUE_NONE;
1211 bool useFutilityPruning = UseFutilityPruning
1212 && depth < SelectiveDepth
1215 // Loop through all legal moves until no moves remain or a beta cutoff
1217 while ( bestValue < beta
1218 && (move = mp.get_next_move()) != MOVE_NONE
1219 && !thread_should_stop(threadID))
1221 assert(move_is_ok(move));
1223 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1224 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1225 bool moveIsCapture = pos.move_is_capture(move);
1226 bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
1228 movesSearched[moveCount++] = ss[ply].currentMove = move;
1230 // Decide the new search depth
1231 Depth ext = extension(pos, move, false, moveIsCheck, singleReply, mateThreat);
1232 Depth newDepth = depth - OnePly + ext;
1235 if ( useFutilityPruning
1238 && !moveIsPassedPawnPush
1239 && !move_promotion(move))
1241 if ( moveCount >= 2 + int(depth)
1242 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1245 if (depth < 3 * OnePly && approximateEval < beta)
1247 if (futilityValue == VALUE_NONE)
1248 futilityValue = evaluate(pos, ei, threadID)
1249 + (depth < 2 * OnePly ? FutilityMargin1 : FutilityMargin2);
1251 if (futilityValue < beta)
1253 if (futilityValue > bestValue)
1254 bestValue = futilityValue;
1260 // Make and search the move
1262 pos.do_move(move, u, dcCandidates);
1264 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1265 // if the move fails high will be re-searched at full depth.
1266 if ( depth >= 2*OnePly
1268 && moveCount >= LMRNonPVMoves
1270 && !move_promotion(move)
1271 && !moveIsPassedPawnPush
1272 && !move_is_castle(move)
1273 && !move_is_killer(move, ss[ply]))
1275 ss[ply].reduction = OnePly;
1276 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1279 value = beta; // Just to trigger next condition
1281 if (value >= beta) // Go with full depth non-pv search
1283 ss[ply].reduction = Depth(0);
1284 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1286 pos.undo_move(move, u);
1288 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1291 if (value > bestValue)
1297 if (value == value_mate_in(ply + 1))
1298 ss[ply].mateKiller = move;
1302 if ( ActiveThreads > 1
1304 && depth >= MinimumSplitDepth
1306 && idle_thread_exists(threadID)
1308 && !thread_should_stop(threadID)
1309 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1310 &mp, dcCandidates, threadID, false))
1314 // All legal moves have been searched. A special case: If there were
1315 // no legal moves, it must be mate or stalemate.
1317 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1319 // If the search is not aborted, update the transposition table,
1320 // history counters, and killer moves.
1321 if (AbortSearch || thread_should_stop(threadID))
1324 if (bestValue < beta)
1325 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1328 Move m = ss[ply].pv[ply];
1329 if (ok_to_history(pos, m)) // Only non capture moves are considered
1331 update_history(pos, m, depth, movesSearched, moveCount);
1332 if (m != ss[ply].killers[0])
1334 ss[ply].killers[1] = ss[ply].killers[0];
1335 ss[ply].killers[0] = m;
1338 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1344 // qsearch() is the quiescence search function, which is called by the main
1345 // search function when the remaining depth is zero (or, to be more precise,
1346 // less than OnePly).
1348 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
1349 Depth depth, int ply, int threadID) {
1351 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1352 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1354 assert(ply >= 0 && ply < PLY_MAX);
1355 assert(threadID >= 0 && threadID < ActiveThreads);
1359 // Initialize, and make an early exit in case of an aborted search,
1360 // an instant draw, maximum ply reached, etc.
1361 if (AbortSearch || thread_should_stop(threadID))
1364 init_node(pos, ss, ply, threadID);
1369 // Transposition table lookup
1370 const TTEntry* tte = TT.retrieve(pos);
1371 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1372 return value_from_tt(tte->value(), ply);
1374 // Evaluate the position statically
1375 Value staticValue = evaluate(pos, ei, threadID);
1377 if (ply == PLY_MAX - 1)
1380 // Initialize "stand pat score", and return it immediately if it is
1382 Value bestValue = (pos.is_check() ? -VALUE_INFINITE : staticValue);
1384 if (bestValue >= beta)
1387 if (bestValue > alpha)
1390 // Initialize a MovePicker object for the current position, and prepare
1391 // to search the moves. Because the depth is <= 0 here, only captures,
1392 // queen promotions and checks (only if depth == 0) will be generated.
1393 MovePicker mp = MovePicker(pos, false, MOVE_NONE, EmptySearchStack, depth, &ei);
1396 Bitboard dcCandidates = mp.discovered_check_candidates();
1397 bool isCheck = pos.is_check();
1398 bool pvNode = (beta - alpha != 1);
1399 bool enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1401 // Loop through the moves until no moves remain or a beta cutoff
1403 while ( alpha < beta
1404 && (move = mp.get_next_move()) != MOVE_NONE)
1406 assert(move_is_ok(move));
1408 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1409 bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
1412 ss[ply].currentMove = move;
1415 if ( UseQSearchFutilityPruning
1418 && !move_promotion(move)
1419 && !moveIsPassedPawnPush
1423 Value futilityValue = staticValue
1424 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1425 pos.endgame_value_of_piece_on(move_to(move)))
1427 + ei.futilityMargin;
1429 if (futilityValue < alpha)
1431 if (futilityValue > bestValue)
1432 bestValue = futilityValue;
1437 // Don't search captures and checks with negative SEE values
1439 && !move_promotion(move)
1441 && (pos.midgame_value_of_piece_on(move_from(move)) >
1442 pos.midgame_value_of_piece_on(move_to(move)))
1443 && pos.see(move) < 0)
1446 // Make and search the move.
1448 pos.do_move(move, u, dcCandidates);
1449 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1450 pos.undo_move(move, u);
1452 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1455 if (value > bestValue)
1466 // All legal moves have been searched. A special case: If we're in check
1467 // and no legal moves were found, it is checkmate:
1468 if (pos.is_check() && moveCount == 0) // Mate!
1469 return value_mated_in(ply);
1471 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1473 // Update transposition table
1474 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_EXACT);
1476 // Update killers only for good check moves
1477 Move m = ss[ply].currentMove;
1478 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1480 // Wrong to update history when depth is <= 0
1482 if (m != ss[ply].killers[0])
1484 ss[ply].killers[1] = ss[ply].killers[0];
1485 ss[ply].killers[0] = m;
1492 // sp_search() is used to search from a split point. This function is called
1493 // by each thread working at the split point. It is similar to the normal
1494 // search() function, but simpler. Because we have already probed the hash
1495 // table, done a null move search, and searched the first move before
1496 // splitting, we don't have to repeat all this work in sp_search(). We
1497 // also don't need to store anything to the hash table here: This is taken
1498 // care of after we return from the split point.
1500 void sp_search(SplitPoint *sp, int threadID) {
1502 assert(threadID >= 0 && threadID < ActiveThreads);
1503 assert(ActiveThreads > 1);
1505 Position pos = Position(sp->pos);
1506 SearchStack *ss = sp->sstack[threadID];
1509 bool isCheck = pos.is_check();
1510 bool useFutilityPruning = UseFutilityPruning
1511 && sp->depth < SelectiveDepth
1514 while ( sp->bestValue < sp->beta
1515 && !thread_should_stop(threadID)
1516 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1518 assert(move_is_ok(move));
1520 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1521 bool moveIsCapture = pos.move_is_capture(move);
1522 bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
1524 lock_grab(&(sp->lock));
1525 int moveCount = ++sp->moves;
1526 lock_release(&(sp->lock));
1528 ss[sp->ply].currentMove = move;
1530 // Decide the new search depth.
1531 Depth ext = extension(pos, move, false, moveIsCheck, false, false);
1532 Depth newDepth = sp->depth - OnePly + ext;
1535 if ( useFutilityPruning
1538 && !moveIsPassedPawnPush
1539 && !move_promotion(move)
1540 && moveCount >= 2 + int(sp->depth)
1541 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1544 // Make and search the move.
1546 pos.do_move(move, u, sp->dcCandidates);
1548 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1549 // if the move fails high will be re-searched at full depth.
1550 if ( ext == Depth(0)
1551 && moveCount >= LMRNonPVMoves
1553 && !moveIsPassedPawnPush
1554 && !move_promotion(move)
1555 && !move_is_castle(move)
1556 && !move_is_killer(move, ss[sp->ply]))
1558 ss[sp->ply].reduction = OnePly;
1559 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1562 value = sp->beta; // Just to trigger next condition
1564 if (value >= sp->beta) // Go with full depth non-pv search
1566 ss[sp->ply].reduction = Depth(0);
1567 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1569 pos.undo_move(move, u);
1571 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1573 if (thread_should_stop(threadID))
1577 lock_grab(&(sp->lock));
1578 if (value > sp->bestValue && !thread_should_stop(threadID))
1580 sp->bestValue = value;
1581 if (sp->bestValue >= sp->beta)
1583 sp_update_pv(sp->parentSstack, ss, sp->ply);
1584 for (int i = 0; i < ActiveThreads; i++)
1585 if (i != threadID && (i == sp->master || sp->slaves[i]))
1586 Threads[i].stop = true;
1588 sp->finished = true;
1591 lock_release(&(sp->lock));
1594 lock_grab(&(sp->lock));
1596 // If this is the master thread and we have been asked to stop because of
1597 // a beta cutoff higher up in the tree, stop all slave threads:
1598 if (sp->master == threadID && thread_should_stop(threadID))
1599 for (int i = 0; i < ActiveThreads; i++)
1601 Threads[i].stop = true;
1604 sp->slaves[threadID] = 0;
1606 lock_release(&(sp->lock));
1610 // sp_search_pv() is used to search from a PV split point. This function
1611 // is called by each thread working at the split point. It is similar to
1612 // the normal search_pv() function, but simpler. Because we have already
1613 // probed the hash table and searched the first move before splitting, we
1614 // don't have to repeat all this work in sp_search_pv(). We also don't
1615 // need to store anything to the hash table here: This is taken care of
1616 // after we return from the split point.
1618 void sp_search_pv(SplitPoint *sp, int threadID) {
1620 assert(threadID >= 0 && threadID < ActiveThreads);
1621 assert(ActiveThreads > 1);
1623 Position pos = Position(sp->pos);
1624 SearchStack *ss = sp->sstack[threadID];
1628 while ( sp->alpha < sp->beta
1629 && !thread_should_stop(threadID)
1630 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1632 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1633 bool moveIsCapture = pos.move_is_capture(move);
1634 bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
1636 assert(move_is_ok(move));
1638 ss[sp->ply].currentMoveCaptureValue = move_is_ep(move)?
1639 PawnValueMidgame : pos.midgame_value_of_piece_on(move_to(move));
1641 lock_grab(&(sp->lock));
1642 int moveCount = ++sp->moves;
1643 lock_release(&(sp->lock));
1645 ss[sp->ply].currentMove = move;
1647 // Decide the new search depth.
1648 Depth ext = extension(pos, move, true, moveIsCheck, false, false);
1649 Depth newDepth = sp->depth - OnePly + ext;
1651 // Make and search the move.
1653 pos.do_move(move, u, sp->dcCandidates);
1655 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1656 // if the move fails high will be re-searched at full depth.
1657 if ( ext == Depth(0)
1658 && moveCount >= LMRPVMoves
1660 && !moveIsPassedPawnPush
1661 && !move_promotion(move)
1662 && !move_is_castle(move)
1663 && !move_is_killer(move, ss[sp->ply]))
1665 ss[sp->ply].reduction = OnePly;
1666 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1669 value = sp->alpha + 1; // Just to trigger next condition
1671 if (value > sp->alpha) // Go with full depth non-pv search
1673 ss[sp->ply].reduction = Depth(0);
1674 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1676 if (value > sp->alpha && value < sp->beta)
1678 // When the search fails high at ply 1 while searching the first
1679 // move at the root, set the flag failHighPly1. This is used for
1680 // time managment: We don't want to stop the search early in
1681 // such cases, because resolving the fail high at ply 1 could
1682 // result in a big drop in score at the root.
1683 if (sp->ply == 1 && RootMoveNumber == 1)
1684 Threads[threadID].failHighPly1 = true;
1686 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1687 Threads[threadID].failHighPly1 = false;
1690 pos.undo_move(move, u);
1692 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1694 if (thread_should_stop(threadID))
1698 lock_grab(&(sp->lock));
1699 if (value > sp->bestValue && !thread_should_stop(threadID))
1701 sp->bestValue = value;
1702 if (value > sp->alpha)
1705 sp_update_pv(sp->parentSstack, ss, sp->ply);
1706 if (value == value_mate_in(sp->ply + 1))
1707 ss[sp->ply].mateKiller = move;
1709 if(value >= sp->beta)
1711 for(int i = 0; i < ActiveThreads; i++)
1712 if(i != threadID && (i == sp->master || sp->slaves[i]))
1713 Threads[i].stop = true;
1715 sp->finished = true;
1718 // If we are at ply 1, and we are searching the first root move at
1719 // ply 0, set the 'Problem' variable if the score has dropped a lot
1720 // (from the computer's point of view) since the previous iteration:
1721 if (Iteration >= 2 && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
1724 lock_release(&(sp->lock));
1727 lock_grab(&(sp->lock));
1729 // If this is the master thread and we have been asked to stop because of
1730 // a beta cutoff higher up in the tree, stop all slave threads:
1731 if (sp->master == threadID && thread_should_stop(threadID))
1732 for (int i = 0; i < ActiveThreads; i++)
1734 Threads[i].stop = true;
1737 sp->slaves[threadID] = 0;
1739 lock_release(&(sp->lock));
1743 /// The RootMove class
1747 RootMove::RootMove() {
1748 nodes = cumulativeNodes = 0ULL;
1751 // RootMove::operator<() is the comparison function used when
1752 // sorting the moves. A move m1 is considered to be better
1753 // than a move m2 if it has a higher score, or if the moves
1754 // have equal score but m1 has the higher node count.
1756 bool RootMove::operator<(const RootMove& m) {
1758 if (score != m.score)
1759 return (score < m.score);
1761 return nodes <= m.nodes;
1764 /// The RootMoveList class
1768 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1770 MoveStack mlist[MaxRootMoves];
1771 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1773 // Generate all legal moves
1774 int lm_count = generate_legal_moves(pos, mlist);
1776 // Add each move to the moves[] array
1777 for (int i = 0; i < lm_count; i++)
1779 bool includeMove = includeAllMoves;
1781 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1782 includeMove = (searchMoves[k] == mlist[i].move);
1786 // Find a quick score for the move
1788 SearchStack ss[PLY_MAX_PLUS_2];
1790 moves[count].move = mlist[i].move;
1791 moves[count].nodes = 0ULL;
1792 pos.do_move(moves[count].move, u);
1793 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE,
1795 pos.undo_move(moves[count].move, u);
1796 moves[count].pv[0] = moves[i].move;
1797 moves[count].pv[1] = MOVE_NONE; // FIXME
1805 // Simple accessor methods for the RootMoveList class
1807 inline Move RootMoveList::get_move(int moveNum) const {
1808 return moves[moveNum].move;
1811 inline Value RootMoveList::get_move_score(int moveNum) const {
1812 return moves[moveNum].score;
1815 inline void RootMoveList::set_move_score(int moveNum, Value score) {
1816 moves[moveNum].score = score;
1819 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
1820 moves[moveNum].nodes = nodes;
1821 moves[moveNum].cumulativeNodes += nodes;
1824 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
1826 for(j = 0; pv[j] != MOVE_NONE; j++)
1827 moves[moveNum].pv[j] = pv[j];
1828 moves[moveNum].pv[j] = MOVE_NONE;
1831 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
1832 return moves[moveNum].pv[i];
1835 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
1836 return moves[moveNum].cumulativeNodes;
1839 inline int RootMoveList::move_count() const {
1844 // RootMoveList::scan_for_easy_move() is called at the end of the first
1845 // iteration, and is used to detect an "easy move", i.e. a move which appears
1846 // to be much bester than all the rest. If an easy move is found, the move
1847 // is returned, otherwise the function returns MOVE_NONE. It is very
1848 // important that this function is called at the right moment: The code
1849 // assumes that the first iteration has been completed and the moves have
1850 // been sorted. This is done in RootMoveList c'tor.
1852 Move RootMoveList::scan_for_easy_move() const {
1859 // moves are sorted so just consider the best and the second one
1860 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
1866 // RootMoveList::sort() sorts the root move list at the beginning of a new
1869 inline void RootMoveList::sort() {
1871 sort_multipv(count - 1); // all items
1875 // RootMoveList::sort_multipv() sorts the first few moves in the root move
1876 // list by their scores and depths. It is used to order the different PVs
1877 // correctly in MultiPV mode.
1879 void RootMoveList::sort_multipv(int n) {
1881 for (int i = 1; i <= n; i++)
1883 RootMove rm = moves[i];
1885 for (j = i; j > 0 && moves[j-1] < rm; j--)
1886 moves[j] = moves[j-1];
1892 // init_search_stack() initializes a search stack at the beginning of a
1893 // new search from the root.
1894 void init_search_stack(SearchStack ss) {
1896 ss.pv[0] = MOVE_NONE;
1897 ss.pv[1] = MOVE_NONE;
1898 ss.currentMove = MOVE_NONE;
1899 ss.threatMove = MOVE_NONE;
1900 ss.reduction = Depth(0);
1901 for (int j = 0; j < KILLER_MAX; j++)
1902 ss.killers[j] = MOVE_NONE;
1905 void init_search_stack(SearchStack ss[]) {
1907 for (int i = 0; i < 3; i++)
1909 ss[i].pv[i] = MOVE_NONE;
1910 ss[i].pv[i+1] = MOVE_NONE;
1911 ss[i].currentMove = MOVE_NONE;
1912 ss[i].threatMove = MOVE_NONE;
1913 ss[i].reduction = Depth(0);
1914 for (int j = 0; j < KILLER_MAX; j++)
1915 ss[i].killers[j] = MOVE_NONE;
1920 // init_node() is called at the beginning of all the search functions
1921 // (search(), search_pv(), qsearch(), and so on) and initializes the search
1922 // stack object corresponding to the current node. Once every
1923 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1924 // for user input and checks whether it is time to stop the search.
1926 void init_node(const Position &pos, SearchStack ss[], int ply, int threadID) {
1927 assert(ply >= 0 && ply < PLY_MAX);
1928 assert(threadID >= 0 && threadID < ActiveThreads);
1930 Threads[threadID].nodes++;
1934 if(NodesSincePoll >= NodesBetweenPolls) {
1940 ss[ply].pv[ply] = ss[ply].pv[ply+1] = ss[ply].currentMove = MOVE_NONE;
1941 ss[ply+2].mateKiller = MOVE_NONE;
1942 ss[ply+2].killers[0] = ss[ply+2].killers[1] = MOVE_NONE;
1943 ss[ply].threatMove = MOVE_NONE;
1944 ss[ply].reduction = Depth(0);
1945 ss[ply].currentMoveCaptureValue = Value(0);
1947 if(Threads[threadID].printCurrentLine)
1948 print_current_line(ss, ply, threadID);
1952 // update_pv() is called whenever a search returns a value > alpha. It
1953 // updates the PV in the SearchStack object corresponding to the current
1956 void update_pv(SearchStack ss[], int ply) {
1957 assert(ply >= 0 && ply < PLY_MAX);
1959 ss[ply].pv[ply] = ss[ply].currentMove;
1961 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
1962 ss[ply].pv[p] = ss[ply+1].pv[p];
1963 ss[ply].pv[p] = MOVE_NONE;
1967 // sp_update_pv() is a variant of update_pv for use at split points. The
1968 // difference between the two functions is that sp_update_pv also updates
1969 // the PV at the parent node.
1971 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply) {
1972 assert(ply >= 0 && ply < PLY_MAX);
1974 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
1976 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
1977 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
1978 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
1982 // connected_moves() tests whether two moves are 'connected' in the sense
1983 // that the first move somehow made the second move possible (for instance
1984 // if the moving piece is the same in both moves). The first move is
1985 // assumed to be the move that was made to reach the current position, while
1986 // the second move is assumed to be a move from the current position.
1988 bool connected_moves(const Position &pos, Move m1, Move m2) {
1989 Square f1, t1, f2, t2;
1991 assert(move_is_ok(m1));
1992 assert(move_is_ok(m2));
1997 // Case 1: The moving piece is the same in both moves.
2003 // Case 2: The destination square for m2 was vacated by m1.
2009 // Case 3: Moving through the vacated square:
2010 if(piece_is_slider(pos.piece_on(f2)) &&
2011 bit_is_set(squares_between(f2, t2), f1))
2014 // Case 4: The destination square for m2 is attacked by the moving piece
2016 if(pos.piece_attacks_square(t1, t2))
2019 // Case 5: Discovered check, checking piece is the piece moved in m1:
2020 if(piece_is_slider(pos.piece_on(t1)) &&
2021 bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())),
2023 !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())),
2025 Bitboard occ = pos.occupied_squares();
2026 Color us = pos.side_to_move();
2027 Square ksq = pos.king_square(us);
2028 clear_bit(&occ, f2);
2029 if(pos.type_of_piece_on(t1) == BISHOP) {
2030 if(bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2033 else if(pos.type_of_piece_on(t1) == ROOK) {
2034 if(bit_is_set(rook_attacks_bb(ksq, occ), t1))
2038 assert(pos.type_of_piece_on(t1) == QUEEN);
2039 if(bit_is_set(queen_attacks_bb(ksq, occ), t1))
2048 // move_is_killer() checks if the given move is among the
2049 // killer moves of that ply.
2051 bool move_is_killer(Move m, const SearchStack& ss) {
2053 const Move* k = ss.killers;
2054 for (int i = 0; i < KILLER_MAX; i++, k++)
2062 // extension() decides whether a move should be searched with normal depth,
2063 // or with extended depth. Certain classes of moves (checking moves, in
2064 // particular) are searched with bigger depth than ordinary moves.
2066 Depth extension(const Position &pos, Move m, bool pvNode,
2067 bool check, bool singleReply, bool mateThreat) {
2069 Depth result = Depth(0);
2072 result += CheckExtension[pvNode];
2075 result += SingleReplyExtension[pvNode];
2077 if (pos.move_is_pawn_push_to_7th(m))
2078 result += PawnPushTo7thExtension[pvNode];
2080 if (pos.move_is_passed_pawn_push(m))
2081 result += PassedPawnExtension[pvNode];
2084 result += MateThreatExtension[pvNode];
2086 if ( pos.midgame_value_of_piece_on(move_to(m)) >= RookValueMidgame
2087 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2088 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2089 && !move_promotion(m))
2090 result += PawnEndgameExtension[pvNode];
2093 && pos.move_is_capture(m)
2094 && pos.type_of_piece_on(move_to(m)) != PAWN
2098 return Min(result, OnePly);
2102 // ok_to_do_nullmove() looks at the current position and decides whether
2103 // doing a 'null move' should be allowed. In order to avoid zugzwang
2104 // problems, null moves are not allowed when the side to move has very
2105 // little material left. Currently, the test is a bit too simple: Null
2106 // moves are avoided only when the side to move has only pawns left. It's
2107 // probably a good idea to avoid null moves in at least some more
2108 // complicated endgames, e.g. KQ vs KR. FIXME
2110 bool ok_to_do_nullmove(const Position &pos) {
2111 if(pos.non_pawn_material(pos.side_to_move()) == Value(0))
2117 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2118 // non-tactical moves late in the move list close to the leaves are
2119 // candidates for pruning.
2121 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d) {
2122 Square mfrom, mto, tfrom, tto;
2124 assert(move_is_ok(m));
2125 assert(threat == MOVE_NONE || move_is_ok(threat));
2126 assert(!move_promotion(m));
2127 assert(!pos.move_is_check(m));
2128 assert(!pos.move_is_capture(m));
2129 assert(!pos.move_is_passed_pawn_push(m));
2130 assert(d >= OnePly);
2132 mfrom = move_from(m);
2134 tfrom = move_from(threat);
2135 tto = move_to(threat);
2137 // Case 1: Castling moves are never pruned.
2138 if(move_is_castle(m))
2141 // Case 2: Don't prune moves which move the threatened piece
2142 if(!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2145 // Case 3: If the threatened piece has value less than or equal to the
2146 // value of the threatening piece, don't prune move which defend it.
2147 if(!PruneDefendingMoves && threat != MOVE_NONE
2148 && (piece_value_midgame(pos.piece_on(tfrom))
2149 >= piece_value_midgame(pos.piece_on(tto)))
2150 && pos.move_attacks_square(m, tto))
2153 // Case 4: Don't prune moves with good history.
2154 if(!H.ok_to_prune(pos.piece_on(move_from(m)), m, d))
2157 // Case 5: If the moving piece in the threatened move is a slider, don't
2158 // prune safe moves which block its ray.
2159 if(!PruneBlockingMoves && threat != MOVE_NONE
2160 && piece_is_slider(pos.piece_on(tfrom))
2161 && bit_is_set(squares_between(tfrom, tto), mto) && pos.see(m) >= 0)
2168 // ok_to_use_TT() returns true if a transposition table score
2169 // can be used at a given point in search.
2171 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2173 Value v = value_from_tt(tte->value(), ply);
2175 return ( tte->depth() >= depth
2176 || v >= Max(value_mate_in(100), beta)
2177 || v < Min(value_mated_in(100), beta))
2179 && ( (is_lower_bound(tte->type()) && v >= beta)
2180 || (is_upper_bound(tte->type()) && v < beta));
2184 // ok_to_history() returns true if a move m can be stored
2185 // in history. Should be a non capturing move nor a promotion.
2187 bool ok_to_history(const Position& pos, Move m) {
2189 return !pos.move_is_capture(m) && !move_promotion(m);
2193 // update_history() registers a good move that produced a beta-cutoff
2194 // in history and marks as failures all the other moves of that ply.
2196 void update_history(const Position& pos, Move m, Depth depth,
2197 Move movesSearched[], int moveCount) {
2199 H.success(pos.piece_on(move_from(m)), m, depth);
2201 for (int i = 0; i < moveCount - 1; i++)
2203 assert(m != movesSearched[i]);
2204 if (ok_to_history(pos, movesSearched[i]))
2205 H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
2209 // fail_high_ply_1() checks if some thread is currently resolving a fail
2210 // high at ply 1 at the node below the first root node. This information
2211 // is used for time managment.
2213 bool fail_high_ply_1() {
2214 for(int i = 0; i < ActiveThreads; i++)
2215 if(Threads[i].failHighPly1)
2221 // current_search_time() returns the number of milliseconds which have passed
2222 // since the beginning of the current search.
2224 int current_search_time() {
2225 return get_system_time() - SearchStartTime;
2229 // nps() computes the current nodes/second count.
2232 int t = current_search_time();
2233 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2237 // poll() performs two different functions: It polls for user input, and it
2238 // looks at the time consumed so far and decides if it's time to abort the
2243 static int lastInfoTime;
2244 int t = current_search_time();
2249 // We are line oriented, don't read single chars
2250 std::string command;
2251 if (!std::getline(std::cin, command))
2254 if (command == "quit")
2257 PonderSearch = false;
2260 else if(command == "stop")
2263 PonderSearch = false;
2265 else if(command == "ponderhit")
2268 // Print search information
2272 else if (lastInfoTime > t)
2273 // HACK: Must be a new search where we searched less than
2274 // NodesBetweenPolls nodes during the first second of search.
2277 else if (t - lastInfoTime >= 1000)
2284 if (dbg_show_hit_rate)
2285 dbg_print_hit_rate();
2287 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2288 << " time " << t << " hashfull " << TT.full() << std::endl;
2289 lock_release(&IOLock);
2290 if (ShowCurrentLine)
2291 Threads[0].printCurrentLine = true;
2293 // Should we stop the search?
2297 bool overTime = t > AbsoluteMaxSearchTime
2298 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime)
2299 || ( !FailHigh && !fail_high_ply_1() && !Problem
2300 && t > 6*(MaxSearchTime + ExtraSearchTime));
2302 if ( (Iteration >= 2 && (!InfiniteSearch && overTime))
2303 || (ExactMaxTime && t >= ExactMaxTime)
2304 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2309 // ponderhit() is called when the program is pondering (i.e. thinking while
2310 // it's the opponent's turn to move) in order to let the engine know that
2311 // it correctly predicted the opponent's move.
2314 int t = current_search_time();
2315 PonderSearch = false;
2316 if(Iteration >= 2 &&
2317 (!InfiniteSearch && (StopOnPonderhit ||
2318 t > AbsoluteMaxSearchTime ||
2319 (RootMoveNumber == 1 &&
2320 t > MaxSearchTime + ExtraSearchTime) ||
2321 (!FailHigh && !fail_high_ply_1() && !Problem &&
2322 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2327 // print_current_line() prints the current line of search for a given
2328 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2330 void print_current_line(SearchStack ss[], int ply, int threadID) {
2331 assert(ply >= 0 && ply < PLY_MAX);
2332 assert(threadID >= 0 && threadID < ActiveThreads);
2334 if(!Threads[threadID].idle) {
2336 std::cout << "info currline " << (threadID + 1);
2337 for(int p = 0; p < ply; p++)
2338 std::cout << " " << ss[p].currentMove;
2339 std::cout << std::endl;
2340 lock_release(&IOLock);
2342 Threads[threadID].printCurrentLine = false;
2343 if(threadID + 1 < ActiveThreads)
2344 Threads[threadID + 1].printCurrentLine = true;
2348 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2349 // while the program is pondering. The point is to work around a wrinkle in
2350 // the UCI protocol: When pondering, the engine is not allowed to give a
2351 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2352 // We simply wait here until one of these commands is sent, and return,
2353 // after which the bestmove and pondermove will be printed (in id_loop()).
2355 void wait_for_stop_or_ponderhit() {
2356 std::string command;
2359 if(!std::getline(std::cin, command))
2362 if(command == "quit") {
2363 OpeningBook.close();
2368 else if(command == "ponderhit" || command == "stop")
2374 // idle_loop() is where the threads are parked when they have no work to do.
2375 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2376 // object for which the current thread is the master.
2378 void idle_loop(int threadID, SplitPoint *waitSp) {
2379 assert(threadID >= 0 && threadID < THREAD_MAX);
2381 Threads[threadID].running = true;
2384 if(AllThreadsShouldExit && threadID != 0)
2387 // If we are not thinking, wait for a condition to be signaled instead
2388 // of wasting CPU time polling for work:
2389 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2390 #if !defined(_MSC_VER)
2391 pthread_mutex_lock(&WaitLock);
2392 if(Idle || threadID >= ActiveThreads)
2393 pthread_cond_wait(&WaitCond, &WaitLock);
2394 pthread_mutex_unlock(&WaitLock);
2396 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2400 // If this thread has been assigned work, launch a search:
2401 if(Threads[threadID].workIsWaiting) {
2402 Threads[threadID].workIsWaiting = false;
2403 if(Threads[threadID].splitPoint->pvNode)
2404 sp_search_pv(Threads[threadID].splitPoint, threadID);
2406 sp_search(Threads[threadID].splitPoint, threadID);
2407 Threads[threadID].idle = true;
2410 // If this thread is the master of a split point and all threads have
2411 // finished their work at this split point, return from the idle loop:
2412 if(waitSp != NULL && waitSp->cpus == 0)
2416 Threads[threadID].running = false;
2420 // init_split_point_stack() is called during program initialization, and
2421 // initializes all split point objects.
2423 void init_split_point_stack() {
2424 for(int i = 0; i < THREAD_MAX; i++)
2425 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2426 SplitPointStack[i][j].parent = NULL;
2427 lock_init(&(SplitPointStack[i][j].lock), NULL);
2432 // destroy_split_point_stack() is called when the program exits, and
2433 // destroys all locks in the precomputed split point objects.
2435 void destroy_split_point_stack() {
2436 for(int i = 0; i < THREAD_MAX; i++)
2437 for(int j = 0; j < MaxActiveSplitPoints; j++)
2438 lock_destroy(&(SplitPointStack[i][j].lock));
2442 // thread_should_stop() checks whether the thread with a given threadID has
2443 // been asked to stop, directly or indirectly. This can happen if a beta
2444 // cutoff has occured in thre thread's currently active split point, or in
2445 // some ancestor of the current split point.
2447 bool thread_should_stop(int threadID) {
2448 assert(threadID >= 0 && threadID < ActiveThreads);
2452 if(Threads[threadID].stop)
2454 if(ActiveThreads <= 2)
2456 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2458 Threads[threadID].stop = true;
2465 // thread_is_available() checks whether the thread with threadID "slave" is
2466 // available to help the thread with threadID "master" at a split point. An
2467 // obvious requirement is that "slave" must be idle. With more than two
2468 // threads, this is not by itself sufficient: If "slave" is the master of
2469 // some active split point, it is only available as a slave to the other
2470 // threads which are busy searching the split point at the top of "slave"'s
2471 // split point stack (the "helpful master concept" in YBWC terminology).
2473 bool thread_is_available(int slave, int master) {
2474 assert(slave >= 0 && slave < ActiveThreads);
2475 assert(master >= 0 && master < ActiveThreads);
2476 assert(ActiveThreads > 1);
2478 if(!Threads[slave].idle || slave == master)
2481 if(Threads[slave].activeSplitPoints == 0)
2482 // No active split points means that the thread is available as a slave
2483 // for any other thread.
2486 if(ActiveThreads == 2)
2489 // Apply the "helpful master" concept if possible.
2490 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2497 // idle_thread_exists() tries to find an idle thread which is available as
2498 // a slave for the thread with threadID "master".
2500 bool idle_thread_exists(int master) {
2501 assert(master >= 0 && master < ActiveThreads);
2502 assert(ActiveThreads > 1);
2504 for(int i = 0; i < ActiveThreads; i++)
2505 if(thread_is_available(i, master))
2511 // split() does the actual work of distributing the work at a node between
2512 // several threads at PV nodes. If it does not succeed in splitting the
2513 // node (because no idle threads are available, or because we have no unused
2514 // split point objects), the function immediately returns false. If
2515 // splitting is possible, a SplitPoint object is initialized with all the
2516 // data that must be copied to the helper threads (the current position and
2517 // search stack, alpha, beta, the search depth, etc.), and we tell our
2518 // helper threads that they have been assigned work. This will cause them
2519 // to instantly leave their idle loops and call sp_search_pv(). When all
2520 // threads have returned from sp_search_pv (or, equivalently, when
2521 // splitPoint->cpus becomes 0), split() returns true.
2523 bool split(const Position &p, SearchStack *sstck, int ply,
2524 Value *alpha, Value *beta, Value *bestValue,
2525 Depth depth, int *moves,
2526 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode) {
2528 assert(sstck != NULL);
2529 assert(ply >= 0 && ply < PLY_MAX);
2530 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2531 assert(!pvNode || *alpha < *beta);
2532 assert(*beta <= VALUE_INFINITE);
2533 assert(depth > Depth(0));
2534 assert(master >= 0 && master < ActiveThreads);
2535 assert(ActiveThreads > 1);
2537 SplitPoint *splitPoint;
2542 // If no other thread is available to help us, or if we have too many
2543 // active split points, don't split:
2544 if(!idle_thread_exists(master) ||
2545 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2546 lock_release(&MPLock);
2550 // Pick the next available split point object from the split point stack:
2551 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2552 Threads[master].activeSplitPoints++;
2554 // Initialize the split point object:
2555 splitPoint->parent = Threads[master].splitPoint;
2556 splitPoint->finished = false;
2557 splitPoint->ply = ply;
2558 splitPoint->depth = depth;
2559 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2560 splitPoint->beta = *beta;
2561 splitPoint->pvNode = pvNode;
2562 splitPoint->dcCandidates = dcCandidates;
2563 splitPoint->bestValue = *bestValue;
2564 splitPoint->master = master;
2565 splitPoint->mp = mp;
2566 splitPoint->moves = *moves;
2567 splitPoint->cpus = 1;
2568 splitPoint->pos.copy(p);
2569 splitPoint->parentSstack = sstck;
2570 for(i = 0; i < ActiveThreads; i++)
2571 splitPoint->slaves[i] = 0;
2573 // Copy the current position and the search stack to the master thread:
2574 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2575 Threads[master].splitPoint = splitPoint;
2577 // Make copies of the current position and search stack for each thread:
2578 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2580 if(thread_is_available(i, master)) {
2581 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2582 Threads[i].splitPoint = splitPoint;
2583 splitPoint->slaves[i] = 1;
2587 // Tell the threads that they have work to do. This will make them leave
2589 for(i = 0; i < ActiveThreads; i++)
2590 if(i == master || splitPoint->slaves[i]) {
2591 Threads[i].workIsWaiting = true;
2592 Threads[i].idle = false;
2593 Threads[i].stop = false;
2596 lock_release(&MPLock);
2598 // Everything is set up. The master thread enters the idle loop, from
2599 // which it will instantly launch a search, because its workIsWaiting
2600 // slot is 'true'. We send the split point as a second parameter to the
2601 // idle loop, which means that the main thread will return from the idle
2602 // loop when all threads have finished their work at this split point
2603 // (i.e. when // splitPoint->cpus == 0).
2604 idle_loop(master, splitPoint);
2606 // We have returned from the idle loop, which means that all threads are
2607 // finished. Update alpha, beta and bestvalue, and return:
2609 if(pvNode) *alpha = splitPoint->alpha;
2610 *beta = splitPoint->beta;
2611 *bestValue = splitPoint->bestValue;
2612 Threads[master].stop = false;
2613 Threads[master].idle = false;
2614 Threads[master].activeSplitPoints--;
2615 Threads[master].splitPoint = splitPoint->parent;
2616 lock_release(&MPLock);
2622 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2623 // to start a new search from the root.
2625 void wake_sleeping_threads() {
2626 if(ActiveThreads > 1) {
2627 for(int i = 1; i < ActiveThreads; i++) {
2628 Threads[i].idle = true;
2629 Threads[i].workIsWaiting = false;
2631 #if !defined(_MSC_VER)
2632 pthread_mutex_lock(&WaitLock);
2633 pthread_cond_broadcast(&WaitCond);
2634 pthread_mutex_unlock(&WaitLock);
2636 for(int i = 1; i < THREAD_MAX; i++)
2637 SetEvent(SitIdleEvent[i]);
2643 // init_thread() is the function which is called when a new thread is
2644 // launched. It simply calls the idle_loop() function with the supplied
2645 // threadID. There are two versions of this function; one for POSIX threads
2646 // and one for Windows threads.
2648 #if !defined(_MSC_VER)
2650 void *init_thread(void *threadID) {
2651 idle_loop(*(int *)threadID, NULL);
2657 DWORD WINAPI init_thread(LPVOID threadID) {
2658 idle_loop(*(int *)threadID, NULL);