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 BetaCounterType class is used to order moves at ply one.
51 // Apart for the first one that has its score, following moves
52 // normally have score -VALUE_INFINITE, so are ordered according
53 // to the number of beta cutoffs occurred under their subtree during
54 // the last iteration.
56 struct BetaCounterType {
60 void add(Color us, Depth d, int threadID);
61 void read(Color us, int64_t& our, int64_t& their);
63 int64_t hits[THREAD_MAX][2];
67 // The RootMove class is used for moves at the root at the tree. For each
68 // root move, we store a score, a node count, and a PV (really a refutation
69 // in the case of moves which fail low).
74 bool operator<(const RootMove&); // used to sort
78 int64_t nodes, cumulativeNodes;
79 Move pv[PLY_MAX_PLUS_2];
80 int64_t ourBeta, theirBeta;
84 // The RootMoveList class is essentially an array of RootMove objects, with
85 // a handful of methods for accessing the data in the individual moves.
90 RootMoveList(Position &pos, Move searchMoves[]);
91 inline Move get_move(int moveNum) const;
92 inline Value get_move_score(int moveNum) const;
93 inline void set_move_score(int moveNum, Value score);
94 inline void set_move_nodes(int moveNum, int64_t nodes);
95 inline void set_beta_counters(int moveNum, int64_t our, int64_t their);
96 void set_move_pv(int moveNum, const Move pv[]);
97 inline Move get_move_pv(int moveNum, int i) const;
98 inline int64_t get_move_cumulative_nodes(int moveNum) const;
99 inline int move_count() const;
100 Move scan_for_easy_move() const;
102 void sort_multipv(int n);
105 static const int MaxRootMoves = 500;
106 RootMove moves[MaxRootMoves];
111 /// Constants and variables
113 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV
116 int LMRNonPVMoves = 4;
118 // Depth limit for use of dynamic threat detection:
119 Depth ThreatDepth = 5*OnePly;
121 // Depth limit for selective search:
122 Depth SelectiveDepth = 7*OnePly;
124 // Use internal iterative deepening?
125 const bool UseIIDAtPVNodes = true;
126 const bool UseIIDAtNonPVNodes = false;
128 // Internal iterative deepening margin. At Non-PV moves, when
129 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening search
130 // when the static evaluation is at most IIDMargin below beta.
131 const Value IIDMargin = Value(0x100);
133 // Easy move margin. An easy move candidate must be at least this much
134 // better than the second best move.
135 const Value EasyMoveMargin = Value(0x200);
137 // Problem margin. If the score of the first move at iteration N+1 has
138 // dropped by more than this since iteration N, the boolean variable
139 // "Problem" is set to true, which will make the program spend some extra
140 // time looking for a better move.
141 const Value ProblemMargin = Value(0x28);
143 // No problem margin. If the boolean "Problem" is true, and a new move
144 // is found at the root which is less than NoProblemMargin worse than the
145 // best move from the previous iteration, Problem is set back to false.
146 const Value NoProblemMargin = Value(0x14);
148 // Null move margin. A null move search will not be done if the approximate
149 // evaluation of the position is more than NullMoveMargin below beta.
150 const Value NullMoveMargin = Value(0x300);
152 // Pruning criterions. See the code and comments in ok_to_prune() to
153 // understand their precise meaning.
154 const bool PruneEscapeMoves = false;
155 const bool PruneDefendingMoves = false;
156 const bool PruneBlockingMoves = false;
158 // Use futility pruning?
159 bool UseQSearchFutilityPruning = true;
160 bool UseFutilityPruning = true;
162 // Margins for futility pruning in the quiescence search, and at frontier
163 // and near frontier nodes
164 Value FutilityMarginQS = Value(0x80);
165 Value FutilityMargins[6] = { Value(0x100), Value(0x200), Value(0x250),
166 Value(0x2A0), Value(0x340), Value(0x3A0) };
169 const bool RazorAtDepthOne = false;
170 Depth RazorDepth = 4*OnePly;
171 Value RazorMargin = Value(0x300);
173 // Last seconds noise filtering (LSN)
174 bool UseLSNFiltering = false;
175 bool looseOnTime = false;
176 int LSNTime = 4 * 1000; // In milliseconds
177 Value LSNValue = Value(0x200);
179 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
180 Depth CheckExtension[2] = {OnePly, OnePly};
181 Depth SingleReplyExtension[2] = {OnePly / 2, OnePly / 2};
182 Depth PawnPushTo7thExtension[2] = {OnePly / 2, OnePly / 2};
183 Depth PassedPawnExtension[2] = {Depth(0), Depth(0)};
184 Depth PawnEndgameExtension[2] = {OnePly, OnePly};
185 Depth MateThreatExtension[2] = {Depth(0), Depth(0)};
187 // Search depth at iteration 1
188 const Depth InitialDepth = OnePly /*+ OnePly/2*/;
192 int NodesBetweenPolls = 30000;
194 // Iteration counters
196 BetaCounterType BetaCounter;
198 // Scores and number of times the best move changed for each iteration:
199 Value ValueByIteration[PLY_MAX_PLUS_2];
200 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
205 // Time managment variables
207 int MaxNodes, MaxDepth;
208 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
213 bool StopOnPonderhit;
218 bool PonderingEnabled;
221 // Show current line?
222 bool ShowCurrentLine = false;
225 bool UseLogFile = false;
226 std::ofstream LogFile;
228 // MP related variables
229 Depth MinimumSplitDepth = 4*OnePly;
230 int MaxThreadsPerSplitPoint = 4;
231 Thread Threads[THREAD_MAX];
233 bool AllThreadsShouldExit = false;
234 const int MaxActiveSplitPoints = 8;
235 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
238 #if !defined(_MSC_VER)
239 pthread_cond_t WaitCond;
240 pthread_mutex_t WaitLock;
242 HANDLE SitIdleEvent[THREAD_MAX];
248 Value id_loop(const Position &pos, Move searchMoves[]);
249 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml);
250 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
251 Depth depth, int ply, int threadID);
252 Value search(Position &pos, SearchStack ss[], Value beta,
253 Depth depth, int ply, bool allowNullmove, int threadID);
254 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
255 Depth depth, int ply, int threadID);
256 void sp_search(SplitPoint *sp, int threadID);
257 void sp_search_pv(SplitPoint *sp, int threadID);
258 void init_node(const Position &pos, SearchStack ss[], int ply, int threadID);
259 void update_pv(SearchStack ss[], int ply);
260 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
261 bool connected_moves(const Position &pos, Move m1, Move m2);
262 bool value_is_mate(Value value);
263 bool move_is_killer(Move m, const SearchStack& ss);
264 Depth extension(const Position &pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
265 bool ok_to_do_nullmove(const Position &pos);
266 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
267 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
268 bool ok_to_history(const Position &pos, Move m);
269 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
270 void update_killers(Move m, SearchStack& ss);
272 bool fail_high_ply_1();
273 int current_search_time();
277 void print_current_line(SearchStack ss[], int ply, int threadID);
278 void wait_for_stop_or_ponderhit();
280 void idle_loop(int threadID, SplitPoint *waitSp);
281 void init_split_point_stack();
282 void destroy_split_point_stack();
283 bool thread_should_stop(int threadID);
284 bool thread_is_available(int slave, int master);
285 bool idle_thread_exists(int master);
286 bool split(const Position &pos, SearchStack *ss, int ply,
287 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
288 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode);
289 void wake_sleeping_threads();
291 #if !defined(_MSC_VER)
292 void *init_thread(void *threadID);
294 DWORD WINAPI init_thread(LPVOID threadID);
301 //// Global variables
304 // The main transposition table
305 TranspositionTable TT = TranspositionTable(TTDefaultSize);
308 // Number of active threads:
309 int ActiveThreads = 1;
311 // Locks. In principle, there is no need for IOLock to be a global variable,
312 // but it could turn out to be useful for debugging.
315 History H; // Should be made local?
317 // The empty search stack
318 SearchStack EmptySearchStack;
321 // SearchStack::init() initializes a search stack. Used at the beginning of a
322 // new search from the root.
323 void SearchStack::init(int ply) {
325 pv[ply] = pv[ply + 1] = MOVE_NONE;
326 currentMove = threatMove = MOVE_NONE;
327 reduction = Depth(0);
328 currentMoveCaptureValue = Value(0);
331 void SearchStack::initKillers() {
333 mateKiller = MOVE_NONE;
334 for (int i = 0; i < KILLER_MAX; i++)
335 killers[i] = MOVE_NONE;
343 /// think() is the external interface to Stockfish's search, and is called when
344 /// the program receives the UCI 'go' command. It initializes various
345 /// search-related global variables, and calls root_search()
347 void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
348 int time[], int increment[], int movesToGo, int maxDepth,
349 int maxNodes, int maxTime, Move searchMoves[]) {
351 // Look for a book move
352 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
355 if (get_option_value_string("Book File") != OpeningBook.file_name())
358 OpeningBook.open("book.bin");
360 bookMove = OpeningBook.get_move(pos);
361 if (bookMove != MOVE_NONE)
363 std::cout << "bestmove " << bookMove << std::endl;
368 // Initialize global search variables
370 SearchStartTime = get_system_time();
371 EasyMove = MOVE_NONE;
372 for (int i = 0; i < THREAD_MAX; i++)
374 Threads[i].nodes = 0ULL;
375 Threads[i].failHighPly1 = false;
378 InfiniteSearch = infinite;
379 PonderSearch = ponder;
380 StopOnPonderhit = false;
385 ExactMaxTime = maxTime;
387 // Read UCI option values
388 TT.set_size(get_option_value_int("Hash"));
389 if (button_was_pressed("Clear Hash"))
392 PonderingEnabled = get_option_value_bool("Ponder");
393 MultiPV = get_option_value_int("MultiPV");
395 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
396 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
398 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
399 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
401 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
402 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
404 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
405 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
407 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
408 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
410 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
411 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
413 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
414 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
415 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
416 SelectiveDepth = get_option_value_int("Selective Plies") * OnePly;
418 Chess960 = get_option_value_bool("UCI_Chess960");
419 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
420 UseLogFile = get_option_value_bool("Use Search Log");
422 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
424 UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)");
425 UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)");
427 FutilityMarginQS = value_from_centipawns(get_option_value_int("Futility Margin (Quiescence Search)"));
428 int fmScale = get_option_value_int("Futility Margin Scale Factor (Main Search)");
429 for (int i = 0; i < 6; i++)
430 FutilityMargins[i] = (FutilityMargins[i] * fmScale) / 100;
432 RazorDepth = (get_option_value_int("Maximum Razoring Depth") + 1) * OnePly;
433 RazorMargin = value_from_centipawns(get_option_value_int("Razoring Margin"));
435 UseLSNFiltering = get_option_value_bool("LSN filtering");
436 LSNTime = get_option_value_int("LSN Time Margin (sec)") * 1000;
437 LSNValue = value_from_centipawns(get_option_value_int("LSN Value Margin"));
439 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
440 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
442 read_weights(pos.side_to_move());
444 int newActiveThreads = get_option_value_int("Threads");
445 if (newActiveThreads != ActiveThreads)
447 ActiveThreads = newActiveThreads;
448 init_eval(ActiveThreads);
451 // Wake up sleeping threads:
452 wake_sleeping_threads();
454 for (int i = 1; i < ActiveThreads; i++)
455 assert(thread_is_available(i, 0));
457 // Set thinking time:
458 int myTime = time[side_to_move];
459 int myIncrement = increment[side_to_move];
461 if (!movesToGo) // Sudden death time control
465 MaxSearchTime = myTime / 30 + myIncrement;
466 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
467 } else { // Blitz game without increment
468 MaxSearchTime = myTime / 30;
469 AbsoluteMaxSearchTime = myTime / 8;
472 else // (x moves) / (y minutes)
476 MaxSearchTime = myTime / 2;
477 AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
479 MaxSearchTime = myTime / Min(movesToGo, 20);
480 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
484 if (PonderingEnabled)
486 MaxSearchTime += MaxSearchTime / 4;
487 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
490 // Fixed depth or fixed number of nodes?
493 InfiniteSearch = true; // HACK
498 NodesBetweenPolls = Min(MaxNodes, 30000);
499 InfiniteSearch = true; // HACK
502 NodesBetweenPolls = 30000;
505 // Write information to search log file:
507 LogFile << "Searching: " << pos.to_fen() << std::endl
508 << "infinite: " << infinite
509 << " ponder: " << ponder
510 << " time: " << myTime
511 << " increment: " << myIncrement
512 << " moves to go: " << movesToGo << std::endl;
515 // We're ready to start thinking. Call the iterative deepening loop
519 Value v = id_loop(pos, searchMoves);
520 looseOnTime = ( UseLSNFiltering
527 looseOnTime = false; // reset for next match
528 while (SearchStartTime + myTime + 1000 > get_system_time())
530 id_loop(pos, searchMoves); // to fail gracefully
547 /// init_threads() is called during startup. It launches all helper threads,
548 /// and initializes the split point stack and the global locks and condition
551 void init_threads() {
555 #if !defined(_MSC_VER)
556 pthread_t pthread[1];
559 for (i = 0; i < THREAD_MAX; i++)
560 Threads[i].activeSplitPoints = 0;
562 // Initialize global locks:
563 lock_init(&MPLock, NULL);
564 lock_init(&IOLock, NULL);
566 init_split_point_stack();
568 #if !defined(_MSC_VER)
569 pthread_mutex_init(&WaitLock, NULL);
570 pthread_cond_init(&WaitCond, NULL);
572 for (i = 0; i < THREAD_MAX; i++)
573 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
576 // All threads except the main thread should be initialized to idle state
577 for (i = 1; i < THREAD_MAX; i++)
579 Threads[i].stop = false;
580 Threads[i].workIsWaiting = false;
581 Threads[i].idle = true;
582 Threads[i].running = false;
585 // Launch the helper threads
586 for(i = 1; i < THREAD_MAX; i++)
588 #if !defined(_MSC_VER)
589 pthread_create(pthread, NULL, init_thread, (void*)(&i));
592 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
595 // Wait until the thread has finished launching:
596 while (!Threads[i].running);
599 // Init also the empty search stack
600 EmptySearchStack.init(0);
601 EmptySearchStack.initKillers();
605 /// stop_threads() is called when the program exits. It makes all the
606 /// helper threads exit cleanly.
608 void stop_threads() {
610 ActiveThreads = THREAD_MAX; // HACK
611 Idle = false; // HACK
612 wake_sleeping_threads();
613 AllThreadsShouldExit = true;
614 for (int i = 1; i < THREAD_MAX; i++)
616 Threads[i].stop = true;
617 while(Threads[i].running);
619 destroy_split_point_stack();
623 /// nodes_searched() returns the total number of nodes searched so far in
624 /// the current search.
626 int64_t nodes_searched() {
628 int64_t result = 0ULL;
629 for (int i = 0; i < ActiveThreads; i++)
630 result += Threads[i].nodes;
637 // id_loop() is the main iterative deepening loop. It calls root_search
638 // repeatedly with increasing depth until the allocated thinking time has
639 // been consumed, the user stops the search, or the maximum search depth is
642 Value id_loop(const Position &pos, Move searchMoves[]) {
645 SearchStack ss[PLY_MAX_PLUS_2];
647 // searchMoves are verified, copied, scored and sorted
648 RootMoveList rml(p, searchMoves);
653 for (int i = 0; i < 3; i++)
658 ValueByIteration[0] = Value(0);
659 ValueByIteration[1] = rml.get_move_score(0);
662 EasyMove = rml.scan_for_easy_move();
664 // Iterative deepening loop
665 while (!AbortSearch && Iteration < PLY_MAX)
667 // Initialize iteration
670 BestMoveChangesByIteration[Iteration] = 0;
674 std::cout << "info depth " << Iteration << std::endl;
676 // Search to the current depth
677 ValueByIteration[Iteration] = root_search(p, ss, rml);
679 // Erase the easy move if it differs from the new best move
680 if (ss[0].pv[0] != EasyMove)
681 EasyMove = MOVE_NONE;
688 bool stopSearch = false;
690 // Stop search early if there is only a single legal move:
691 if (Iteration >= 6 && rml.move_count() == 1)
694 // Stop search early when the last two iterations returned a mate score
696 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
697 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
700 // Stop search early if one move seems to be much better than the rest
701 int64_t nodes = nodes_searched();
703 && EasyMove == ss[0].pv[0]
704 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
705 && current_search_time() > MaxSearchTime / 16)
706 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
707 && current_search_time() > MaxSearchTime / 32)))
710 // Add some extra time if the best move has changed during the last two iterations
711 if (Iteration > 5 && Iteration <= 50)
712 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
713 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
715 // Stop search if most of MaxSearchTime is consumed at the end of the
716 // iteration. We probably don't have enough time to search the first
717 // move at the next iteration anyway.
718 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
726 StopOnPonderhit = true;
729 // Write PV to transposition table, in case the relevant entries have
730 // been overwritten during the search:
731 TT.insert_pv(p, ss[0].pv);
733 if (MaxDepth && Iteration >= MaxDepth)
739 // If we are pondering, we shouldn't print the best move before we
742 wait_for_stop_or_ponderhit();
744 // Print final search statistics
745 std::cout << "info nodes " << nodes_searched()
747 << " time " << current_search_time()
748 << " hashfull " << TT.full() << std::endl;
750 // Print the best move and the ponder move to the standard output
751 if (ss[0].pv[0] == MOVE_NONE)
753 ss[0].pv[0] = rml.get_move(0);
754 ss[0].pv[1] = MOVE_NONE;
756 std::cout << "bestmove " << ss[0].pv[0];
757 if (ss[0].pv[1] != MOVE_NONE)
758 std::cout << " ponder " << ss[0].pv[1];
760 std::cout << std::endl;
765 dbg_print_mean(LogFile);
767 if (dbg_show_hit_rate)
768 dbg_print_hit_rate(LogFile);
771 LogFile << "Nodes: " << nodes_searched() << std::endl
772 << "Nodes/second: " << nps() << std::endl
773 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
775 p.do_move(ss[0].pv[0], st);
776 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
777 << std::endl << std::endl;
779 return rml.get_move_score(0);
783 // root_search() is the function which searches the root node. It is
784 // similar to search_pv except that it uses a different move ordering
785 // scheme (perhaps we should try to use this at internal PV nodes, too?)
786 // and prints some information to the standard output.
788 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml) {
790 Value alpha = -VALUE_INFINITE;
791 Value beta = VALUE_INFINITE, value;
792 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
794 // Loop through all the moves in the root move list
795 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
802 RootMoveNumber = i + 1;
805 // Remember the node count before the move is searched. The node counts
806 // are used to sort the root moves at the next iteration.
807 nodes = nodes_searched();
809 // Reset beta cut-off counters
812 // Pick the next root move, and print the move and the move number to
813 // the standard output.
814 move = ss[0].currentMove = rml.get_move(i);
815 if (current_search_time() >= 1000)
816 std::cout << "info currmove " << move
817 << " currmovenumber " << i + 1 << std::endl;
819 // Decide search depth for this move
821 ext = extension(pos, move, true, pos.move_is_capture(move), pos.move_is_check(move), false, false, &dangerous);
822 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
824 // Make the move, and search it
825 pos.do_move(move, st, dcCandidates);
829 value = -search_pv(pos, ss, -beta, VALUE_INFINITE, newDepth, 1, 0);
830 // If the value has dropped a lot compared to the last iteration,
831 // set the boolean variable Problem to true. This variable is used
832 // for time managment: When Problem is true, we try to complete the
833 // current iteration before playing a move.
834 Problem = (Iteration >= 2 && value <= ValueByIteration[Iteration-1] - ProblemMargin);
836 if (Problem && StopOnPonderhit)
837 StopOnPonderhit = false;
841 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
844 // Fail high! Set the boolean variable FailHigh to true, and
845 // re-search the move with a big window. The variable FailHigh is
846 // used for time managment: We try to avoid aborting the search
847 // prematurely during a fail high research.
849 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
855 // Finished searching the move. If AbortSearch is true, the search
856 // was aborted because the user interrupted the search or because we
857 // ran out of time. In this case, the return value of the search cannot
858 // be trusted, and we break out of the loop without updating the best
863 // Remember the node count for this move. The node counts are used to
864 // sort the root moves at the next iteration.
865 rml.set_move_nodes(i, nodes_searched() - nodes);
867 // Remember the beta-cutoff statistics
869 BetaCounter.read(pos.side_to_move(), our, their);
870 rml.set_beta_counters(i, our, their);
872 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
874 if (value <= alpha && i >= MultiPV)
875 rml.set_move_score(i, -VALUE_INFINITE);
881 rml.set_move_score(i, value);
883 rml.set_move_pv(i, ss[0].pv);
887 // We record how often the best move has been changed in each
888 // iteration. This information is used for time managment: When
889 // the best move changes frequently, we allocate some more time.
891 BestMoveChangesByIteration[Iteration]++;
893 // Print search information to the standard output:
894 std::cout << "info depth " << Iteration
895 << " score " << value_to_string(value)
896 << " time " << current_search_time()
897 << " nodes " << nodes_searched()
901 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
902 std::cout << ss[0].pv[j] << " ";
904 std::cout << std::endl;
907 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
912 // Reset the global variable Problem to false if the value isn't too
913 // far below the final value from the last iteration.
914 if (value > ValueByIteration[Iteration - 1] - NoProblemMargin)
920 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
923 std::cout << "info multipv " << j + 1
924 << " score " << value_to_string(rml.get_move_score(j))
925 << " depth " << ((j <= i)? Iteration : Iteration - 1)
926 << " time " << current_search_time()
927 << " nodes " << nodes_searched()
931 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
932 std::cout << rml.get_move_pv(j, k) << " ";
934 std::cout << std::endl;
936 alpha = rml.get_move_score(Min(i, MultiPV-1));
944 // search_pv() is the main search function for PV nodes.
946 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
947 Depth depth, int ply, int threadID) {
949 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
950 assert(beta > alpha && beta <= VALUE_INFINITE);
951 assert(ply >= 0 && ply < PLY_MAX);
952 assert(threadID >= 0 && threadID < ActiveThreads);
955 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
957 // Initialize, and make an early exit in case of an aborted search,
958 // an instant draw, maximum ply reached, etc.
959 init_node(pos, ss, ply, threadID);
961 // After init_node() that calls poll()
962 if (AbortSearch || thread_should_stop(threadID))
970 if (ply >= PLY_MAX - 1)
971 return evaluate(pos, ei, threadID);
973 // Mate distance pruning
974 Value oldAlpha = alpha;
975 alpha = Max(value_mated_in(ply), alpha);
976 beta = Min(value_mate_in(ply+1), beta);
980 // Transposition table lookup. At PV nodes, we don't use the TT for
981 // pruning, but only for move ordering.
982 const TTEntry* tte = TT.retrieve(pos);
983 Move ttMove = (tte ? tte->move() : MOVE_NONE);
985 // Go with internal iterative deepening if we don't have a TT move
986 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
988 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
989 ttMove = ss[ply].pv[ply];
992 // Initialize a MovePicker object for the current position, and prepare
993 // to search all moves
994 MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
996 Move move, movesSearched[256];
998 Value value, bestValue = -VALUE_INFINITE;
999 Bitboard dcCandidates = mp.discovered_check_candidates();
1000 Color us = pos.side_to_move();
1001 bool isCheck = pos.is_check();
1002 bool mateThreat = pos.has_mate_threat(opposite_color(us));
1004 // Loop through all legal moves until no moves remain or a beta cutoff
1006 while ( alpha < beta
1007 && (move = mp.get_next_move()) != MOVE_NONE
1008 && !thread_should_stop(threadID))
1010 assert(move_is_ok(move));
1012 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1013 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1014 bool moveIsCapture = pos.move_is_capture(move);
1016 movesSearched[moveCount++] = ss[ply].currentMove = move;
1019 ss[ply].currentMoveCaptureValue =
1020 move_is_ep(move)? PawnValueMidgame : pos.midgame_value_of_piece_on(move_to(move));
1022 ss[ply].currentMoveCaptureValue = Value(0);
1024 // Decide the new search depth
1026 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1027 Depth newDepth = depth - OnePly + ext;
1029 // Make and search the move
1031 pos.do_move(move, st, dcCandidates);
1033 if (moveCount == 1) // The first move in list is the PV
1034 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1037 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1038 // if the move fails high will be re-searched at full depth.
1039 if ( depth >= 2*OnePly
1040 && moveCount >= LMRPVMoves
1043 && !move_promotion(move)
1044 && !move_is_castle(move)
1045 && !move_is_killer(move, ss[ply]))
1047 ss[ply].reduction = OnePly;
1048 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1051 value = alpha + 1; // Just to trigger next condition
1053 if (value > alpha) // Go with full depth non-pv search
1055 ss[ply].reduction = Depth(0);
1056 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1057 if (value > alpha && value < beta)
1059 // When the search fails high at ply 1 while searching the first
1060 // move at the root, set the flag failHighPly1. This is used for
1061 // time managment: We don't want to stop the search early in
1062 // such cases, because resolving the fail high at ply 1 could
1063 // result in a big drop in score at the root.
1064 if (ply == 1 && RootMoveNumber == 1)
1065 Threads[threadID].failHighPly1 = true;
1067 // A fail high occurred. Re-search at full window (pv search)
1068 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1069 Threads[threadID].failHighPly1 = false;
1073 pos.undo_move(move);
1075 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1078 if (value > bestValue)
1085 if (value == value_mate_in(ply + 1))
1086 ss[ply].mateKiller = move;
1088 // If we are at ply 1, and we are searching the first root move at
1089 // ply 0, set the 'Problem' variable if the score has dropped a lot
1090 // (from the computer's point of view) since the previous iteration:
1093 && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
1098 if ( ActiveThreads > 1
1100 && depth >= MinimumSplitDepth
1102 && idle_thread_exists(threadID)
1104 && !thread_should_stop(threadID)
1105 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1106 &moveCount, &mp, dcCandidates, threadID, true))
1110 // All legal moves have been searched. A special case: If there were
1111 // no legal moves, it must be mate or stalemate:
1113 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1115 // If the search is not aborted, update the transposition table,
1116 // history counters, and killer moves.
1117 if (AbortSearch || thread_should_stop(threadID))
1120 if (bestValue <= oldAlpha)
1121 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1123 else if (bestValue >= beta)
1125 BetaCounter.add(pos.side_to_move(), depth, threadID);
1126 Move m = ss[ply].pv[ply];
1127 if (ok_to_history(pos, m)) // Only non capture moves are considered
1129 update_history(pos, m, depth, movesSearched, moveCount);
1130 update_killers(m, ss[ply]);
1132 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1135 TT.store(pos, value_to_tt(bestValue, ply), depth, ss[ply].pv[ply], VALUE_TYPE_EXACT);
1141 // search() is the search function for zero-width nodes.
1143 Value search(Position &pos, SearchStack ss[], Value beta, Depth depth,
1144 int ply, bool allowNullmove, int threadID) {
1146 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1147 assert(ply >= 0 && ply < PLY_MAX);
1148 assert(threadID >= 0 && threadID < ActiveThreads);
1151 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1153 // Initialize, and make an early exit in case of an aborted search,
1154 // an instant draw, maximum ply reached, etc.
1155 init_node(pos, ss, ply, threadID);
1157 // After init_node() that calls poll()
1158 if (AbortSearch || thread_should_stop(threadID))
1166 if (ply >= PLY_MAX - 1)
1167 return evaluate(pos, ei, threadID);
1169 // Mate distance pruning
1170 if (value_mated_in(ply) >= beta)
1173 if (value_mate_in(ply + 1) < beta)
1176 // Transposition table lookup
1177 const TTEntry* tte = TT.retrieve(pos);
1178 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1180 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1182 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1183 return value_from_tt(tte->value(), ply);
1186 Value approximateEval = quick_evaluate(pos);
1187 bool mateThreat = false;
1188 bool isCheck = pos.is_check();
1194 && !value_is_mate(beta)
1195 && ok_to_do_nullmove(pos)
1196 && approximateEval >= beta - NullMoveMargin)
1198 ss[ply].currentMove = MOVE_NULL;
1201 pos.do_null_move(st);
1202 int R = (depth >= 4 * OnePly ? 4 : 3); // Null move dynamic reduction
1204 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1206 pos.undo_null_move();
1208 if (value_is_mate(nullValue))
1210 /* Do not return unproven mates */
1212 else if (nullValue >= beta)
1214 if (depth < 6 * OnePly)
1217 // Do zugzwang verification search
1218 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1222 // The null move failed low, which means that we may be faced with
1223 // some kind of threat. If the previous move was reduced, check if
1224 // the move that refuted the null move was somehow connected to the
1225 // move which was reduced. If a connection is found, return a fail
1226 // low score (which will cause the reduced move to fail high in the
1227 // parent node, which will trigger a re-search with full depth).
1228 if (nullValue == value_mated_in(ply + 2))
1231 ss[ply].threatMove = ss[ply + 1].currentMove;
1232 if ( depth < ThreatDepth
1233 && ss[ply - 1].reduction
1234 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1238 // Null move search not allowed, try razoring
1239 else if ( !value_is_mate(beta)
1240 && approximateEval < beta - RazorMargin
1241 && depth < RazorDepth
1242 && (RazorAtDepthOne || depth > OnePly)
1243 && ttMove == MOVE_NONE
1244 && !pos.has_pawn_on_7th(pos.side_to_move()))
1246 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1247 if ( (v < beta - RazorMargin - RazorMargin / 4)
1248 || (depth < 3*OnePly && v < beta - RazorMargin)
1249 || (depth < 2*OnePly && v < beta - RazorMargin / 2))
1253 // Go with internal iterative deepening if we don't have a TT move
1254 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1255 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1257 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1258 ttMove = ss[ply].pv[ply];
1261 // Initialize a MovePicker object for the current position, and prepare
1262 // to search all moves:
1263 MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth);
1265 Move move, movesSearched[256];
1267 Value value, bestValue = -VALUE_INFINITE;
1268 Bitboard dcCandidates = mp.discovered_check_candidates();
1269 Value futilityValue = VALUE_NONE;
1270 bool useFutilityPruning = UseFutilityPruning
1271 && depth < SelectiveDepth
1274 // Loop through all legal moves until no moves remain or a beta cutoff
1276 while ( bestValue < beta
1277 && (move = mp.get_next_move()) != MOVE_NONE
1278 && !thread_should_stop(threadID))
1280 assert(move_is_ok(move));
1282 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1283 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1284 bool moveIsCapture = pos.move_is_capture(move);
1286 movesSearched[moveCount++] = ss[ply].currentMove = move;
1288 // Decide the new search depth
1290 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1291 Depth newDepth = depth - OnePly + ext;
1294 if ( useFutilityPruning
1297 && !move_promotion(move))
1299 // History pruning. See ok_to_prune() definition
1300 if ( moveCount >= 2 + int(depth)
1301 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1304 // Value based pruning
1305 if (depth < 7 * OnePly && approximateEval < beta)
1307 if (futilityValue == VALUE_NONE)
1308 futilityValue = evaluate(pos, ei, threadID)
1309 + FutilityMargins[int(depth)/2 - 1]
1312 if (futilityValue < beta)
1314 if (futilityValue > bestValue)
1315 bestValue = futilityValue;
1321 // Make and search the move
1323 pos.do_move(move, st, dcCandidates);
1325 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1326 // if the move fails high will be re-searched at full depth.
1327 if ( depth >= 2*OnePly
1328 && moveCount >= LMRNonPVMoves
1331 && !move_promotion(move)
1332 && !move_is_castle(move)
1333 && !move_is_killer(move, ss[ply]))
1335 // LMR dynamic reduction
1336 Depth R = (moveCount >= 3 * LMRNonPVMoves && depth >= 7*OnePly ? 2*OnePly : OnePly);
1338 ss[ply].reduction = R;
1339 value = -search(pos, ss, -(beta-1), newDepth-R, ply+1, true, threadID);
1342 value = beta; // Just to trigger next condition
1344 if (value >= beta) // Go with full depth non-pv search
1346 ss[ply].reduction = Depth(0);
1347 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1349 pos.undo_move(move);
1351 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1354 if (value > bestValue)
1360 if (value == value_mate_in(ply + 1))
1361 ss[ply].mateKiller = move;
1365 if ( ActiveThreads > 1
1367 && depth >= MinimumSplitDepth
1369 && idle_thread_exists(threadID)
1371 && !thread_should_stop(threadID)
1372 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1373 &mp, dcCandidates, threadID, false))
1377 // All legal moves have been searched. A special case: If there were
1378 // no legal moves, it must be mate or stalemate.
1380 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1382 // If the search is not aborted, update the transposition table,
1383 // history counters, and killer moves.
1384 if (AbortSearch || thread_should_stop(threadID))
1387 if (bestValue < beta)
1388 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1391 BetaCounter.add(pos.side_to_move(), depth, threadID);
1392 Move m = ss[ply].pv[ply];
1393 if (ok_to_history(pos, m)) // Only non capture moves are considered
1395 update_history(pos, m, depth, movesSearched, moveCount);
1396 update_killers(m, ss[ply]);
1398 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1401 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1407 // qsearch() is the quiescence search function, which is called by the main
1408 // search function when the remaining depth is zero (or, to be more precise,
1409 // less than OnePly).
1411 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
1412 Depth depth, int ply, int threadID) {
1414 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1415 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1417 assert(ply >= 0 && ply < PLY_MAX);
1418 assert(threadID >= 0 && threadID < ActiveThreads);
1420 // Initialize, and make an early exit in case of an aborted search,
1421 // an instant draw, maximum ply reached, etc.
1422 init_node(pos, ss, ply, threadID);
1424 // After init_node() that calls poll()
1425 if (AbortSearch || thread_should_stop(threadID))
1431 // Transposition table lookup, only when not in PV
1432 bool pvNode = (beta - alpha != 1);
1435 const TTEntry* tte = TT.retrieve(pos);
1436 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1437 return value_from_tt(tte->value(), ply);
1440 // Evaluate the position statically
1442 bool isCheck = pos.is_check();
1443 Value staticValue = (isCheck ? -VALUE_INFINITE : evaluate(pos, ei, threadID));
1445 if (ply == PLY_MAX - 1)
1446 return evaluate(pos, ei, threadID);
1448 // Initialize "stand pat score", and return it immediately if it is
1450 Value bestValue = staticValue;
1452 if (bestValue >= beta)
1455 if (bestValue > alpha)
1458 // Initialize a MovePicker object for the current position, and prepare
1459 // to search the moves. Because the depth is <= 0 here, only captures,
1460 // queen promotions and checks (only if depth == 0) will be generated.
1461 MovePicker mp = MovePicker(pos, pvNode, MOVE_NONE, EmptySearchStack, depth, isCheck ? NULL : &ei);
1464 Bitboard dcCandidates = mp.discovered_check_candidates();
1465 Color us = pos.side_to_move();
1466 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1468 // Loop through the moves until no moves remain or a beta cutoff
1470 while ( alpha < beta
1471 && (move = mp.get_next_move()) != MOVE_NONE)
1473 assert(move_is_ok(move));
1476 ss[ply].currentMove = move;
1479 if ( UseQSearchFutilityPruning
1483 && !move_promotion(move)
1484 && !pos.move_is_check(move, dcCandidates)
1485 && !pos.move_is_passed_pawn_push(move))
1487 Value futilityValue = staticValue
1488 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1489 pos.endgame_value_of_piece_on(move_to(move)))
1490 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1492 + ei.futilityMargin;
1494 if (futilityValue < alpha)
1496 if (futilityValue > bestValue)
1497 bestValue = futilityValue;
1502 // Don't search captures and checks with negative SEE values
1504 && !move_promotion(move)
1505 && (pos.midgame_value_of_piece_on(move_from(move)) >
1506 pos.midgame_value_of_piece_on(move_to(move)))
1507 && pos.see(move) < 0)
1510 // Make and search the move.
1512 pos.do_move(move, st, dcCandidates);
1513 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1514 pos.undo_move(move);
1516 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1519 if (value > bestValue)
1530 // All legal moves have been searched. A special case: If we're in check
1531 // and no legal moves were found, it is checkmate:
1532 if (pos.is_check() && moveCount == 0) // Mate!
1533 return value_mated_in(ply);
1535 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1537 // Update transposition table
1538 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_EXACT);
1540 // Update killers only for good check moves
1541 Move m = ss[ply].currentMove;
1542 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1544 // Wrong to update history when depth is <= 0
1545 update_killers(m, ss[ply]);
1551 // sp_search() is used to search from a split point. This function is called
1552 // by each thread working at the split point. It is similar to the normal
1553 // search() function, but simpler. Because we have already probed the hash
1554 // table, done a null move search, and searched the first move before
1555 // splitting, we don't have to repeat all this work in sp_search(). We
1556 // also don't need to store anything to the hash table here: This is taken
1557 // care of after we return from the split point.
1559 void sp_search(SplitPoint *sp, int threadID) {
1561 assert(threadID >= 0 && threadID < ActiveThreads);
1562 assert(ActiveThreads > 1);
1564 Position pos = Position(sp->pos);
1565 SearchStack *ss = sp->sstack[threadID];
1568 bool isCheck = pos.is_check();
1569 bool useFutilityPruning = UseFutilityPruning
1570 && sp->depth < SelectiveDepth
1573 while ( sp->bestValue < sp->beta
1574 && !thread_should_stop(threadID)
1575 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1577 assert(move_is_ok(move));
1579 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1580 bool moveIsCapture = pos.move_is_capture(move);
1582 lock_grab(&(sp->lock));
1583 int moveCount = ++sp->moves;
1584 lock_release(&(sp->lock));
1586 ss[sp->ply].currentMove = move;
1588 // Decide the new search depth.
1590 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1591 Depth newDepth = sp->depth - OnePly + ext;
1594 if ( useFutilityPruning
1597 && !move_promotion(move)
1598 && moveCount >= 2 + int(sp->depth)
1599 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1602 // Make and search the move.
1604 pos.do_move(move, st, sp->dcCandidates);
1606 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1607 // if the move fails high will be re-searched at full depth.
1609 && moveCount >= LMRNonPVMoves
1611 && !move_promotion(move)
1612 && !move_is_castle(move)
1613 && !move_is_killer(move, ss[sp->ply]))
1615 ss[sp->ply].reduction = OnePly;
1616 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1619 value = sp->beta; // Just to trigger next condition
1621 if (value >= sp->beta) // Go with full depth non-pv search
1623 ss[sp->ply].reduction = Depth(0);
1624 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1626 pos.undo_move(move);
1628 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1630 if (thread_should_stop(threadID))
1634 lock_grab(&(sp->lock));
1635 if (value > sp->bestValue && !thread_should_stop(threadID))
1637 sp->bestValue = value;
1638 if (sp->bestValue >= sp->beta)
1640 sp_update_pv(sp->parentSstack, ss, sp->ply);
1641 for (int i = 0; i < ActiveThreads; i++)
1642 if (i != threadID && (i == sp->master || sp->slaves[i]))
1643 Threads[i].stop = true;
1645 sp->finished = true;
1648 lock_release(&(sp->lock));
1651 lock_grab(&(sp->lock));
1653 // If this is the master thread and we have been asked to stop because of
1654 // a beta cutoff higher up in the tree, stop all slave threads:
1655 if (sp->master == threadID && thread_should_stop(threadID))
1656 for (int i = 0; i < ActiveThreads; i++)
1658 Threads[i].stop = true;
1661 sp->slaves[threadID] = 0;
1663 lock_release(&(sp->lock));
1667 // sp_search_pv() is used to search from a PV split point. This function
1668 // is called by each thread working at the split point. It is similar to
1669 // the normal search_pv() function, but simpler. Because we have already
1670 // probed the hash table and searched the first move before splitting, we
1671 // don't have to repeat all this work in sp_search_pv(). We also don't
1672 // need to store anything to the hash table here: This is taken care of
1673 // after we return from the split point.
1675 void sp_search_pv(SplitPoint *sp, int threadID) {
1677 assert(threadID >= 0 && threadID < ActiveThreads);
1678 assert(ActiveThreads > 1);
1680 Position pos = Position(sp->pos);
1681 SearchStack *ss = sp->sstack[threadID];
1685 while ( sp->alpha < sp->beta
1686 && !thread_should_stop(threadID)
1687 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1689 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1690 bool moveIsCapture = pos.move_is_capture(move);
1692 assert(move_is_ok(move));
1695 ss[sp->ply].currentMoveCaptureValue =
1696 move_is_ep(move)? PawnValueMidgame : pos.midgame_value_of_piece_on(move_to(move));
1698 ss[sp->ply].currentMoveCaptureValue = Value(0);
1700 lock_grab(&(sp->lock));
1701 int moveCount = ++sp->moves;
1702 lock_release(&(sp->lock));
1704 ss[sp->ply].currentMove = move;
1706 // Decide the new search depth.
1708 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1709 Depth newDepth = sp->depth - OnePly + ext;
1711 // Make and search the move.
1713 pos.do_move(move, st, sp->dcCandidates);
1715 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1716 // if the move fails high will be re-searched at full depth.
1718 && moveCount >= LMRPVMoves
1720 && !move_promotion(move)
1721 && !move_is_castle(move)
1722 && !move_is_killer(move, ss[sp->ply]))
1724 ss[sp->ply].reduction = OnePly;
1725 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1728 value = sp->alpha + 1; // Just to trigger next condition
1730 if (value > sp->alpha) // Go with full depth non-pv search
1732 ss[sp->ply].reduction = Depth(0);
1733 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1735 if (value > sp->alpha && value < sp->beta)
1737 // When the search fails high at ply 1 while searching the first
1738 // move at the root, set the flag failHighPly1. This is used for
1739 // time managment: We don't want to stop the search early in
1740 // such cases, because resolving the fail high at ply 1 could
1741 // result in a big drop in score at the root.
1742 if (sp->ply == 1 && RootMoveNumber == 1)
1743 Threads[threadID].failHighPly1 = true;
1745 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1746 Threads[threadID].failHighPly1 = false;
1749 pos.undo_move(move);
1751 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1753 if (thread_should_stop(threadID))
1757 lock_grab(&(sp->lock));
1758 if (value > sp->bestValue && !thread_should_stop(threadID))
1760 sp->bestValue = value;
1761 if (value > sp->alpha)
1764 sp_update_pv(sp->parentSstack, ss, sp->ply);
1765 if (value == value_mate_in(sp->ply + 1))
1766 ss[sp->ply].mateKiller = move;
1768 if(value >= sp->beta)
1770 for(int i = 0; i < ActiveThreads; i++)
1771 if(i != threadID && (i == sp->master || sp->slaves[i]))
1772 Threads[i].stop = true;
1774 sp->finished = true;
1777 // If we are at ply 1, and we are searching the first root move at
1778 // ply 0, set the 'Problem' variable if the score has dropped a lot
1779 // (from the computer's point of view) since the previous iteration.
1782 && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
1785 lock_release(&(sp->lock));
1788 lock_grab(&(sp->lock));
1790 // If this is the master thread and we have been asked to stop because of
1791 // a beta cutoff higher up in the tree, stop all slave threads.
1792 if (sp->master == threadID && thread_should_stop(threadID))
1793 for (int i = 0; i < ActiveThreads; i++)
1795 Threads[i].stop = true;
1798 sp->slaves[threadID] = 0;
1800 lock_release(&(sp->lock));
1803 /// The BetaCounterType class
1805 BetaCounterType::BetaCounterType() { clear(); }
1807 void BetaCounterType::clear() {
1809 for (int i = 0; i < THREAD_MAX; i++)
1810 hits[i][WHITE] = hits[i][BLACK] = 0ULL;
1813 void BetaCounterType::add(Color us, Depth d, int threadID) {
1815 // Weighted count based on depth
1816 hits[threadID][us] += int(d);
1819 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1822 for (int i = 0; i < THREAD_MAX; i++)
1825 their += hits[i][opposite_color(us)];
1830 /// The RootMove class
1834 RootMove::RootMove() {
1835 nodes = cumulativeNodes = 0ULL;
1838 // RootMove::operator<() is the comparison function used when
1839 // sorting the moves. A move m1 is considered to be better
1840 // than a move m2 if it has a higher score, or if the moves
1841 // have equal score but m1 has the higher node count.
1843 bool RootMove::operator<(const RootMove& m) {
1845 if (score != m.score)
1846 return (score < m.score);
1848 return theirBeta <= m.theirBeta;
1851 /// The RootMoveList class
1855 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1857 MoveStack mlist[MaxRootMoves];
1858 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1860 // Generate all legal moves
1861 int lm_count = generate_legal_moves(pos, mlist);
1863 // Add each move to the moves[] array
1864 for (int i = 0; i < lm_count; i++)
1866 bool includeMove = includeAllMoves;
1868 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1869 includeMove = (searchMoves[k] == mlist[i].move);
1873 // Find a quick score for the move
1875 SearchStack ss[PLY_MAX_PLUS_2];
1877 moves[count].move = mlist[i].move;
1878 moves[count].nodes = 0ULL;
1879 pos.do_move(moves[count].move, st);
1880 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE,
1882 pos.undo_move(moves[count].move);
1883 moves[count].pv[0] = moves[i].move;
1884 moves[count].pv[1] = MOVE_NONE; // FIXME
1892 // Simple accessor methods for the RootMoveList class
1894 inline Move RootMoveList::get_move(int moveNum) const {
1895 return moves[moveNum].move;
1898 inline Value RootMoveList::get_move_score(int moveNum) const {
1899 return moves[moveNum].score;
1902 inline void RootMoveList::set_move_score(int moveNum, Value score) {
1903 moves[moveNum].score = score;
1906 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
1907 moves[moveNum].nodes = nodes;
1908 moves[moveNum].cumulativeNodes += nodes;
1911 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
1912 moves[moveNum].ourBeta = our;
1913 moves[moveNum].theirBeta = their;
1916 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
1918 for(j = 0; pv[j] != MOVE_NONE; j++)
1919 moves[moveNum].pv[j] = pv[j];
1920 moves[moveNum].pv[j] = MOVE_NONE;
1923 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
1924 return moves[moveNum].pv[i];
1927 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
1928 return moves[moveNum].cumulativeNodes;
1931 inline int RootMoveList::move_count() const {
1936 // RootMoveList::scan_for_easy_move() is called at the end of the first
1937 // iteration, and is used to detect an "easy move", i.e. a move which appears
1938 // to be much bester than all the rest. If an easy move is found, the move
1939 // is returned, otherwise the function returns MOVE_NONE. It is very
1940 // important that this function is called at the right moment: The code
1941 // assumes that the first iteration has been completed and the moves have
1942 // been sorted. This is done in RootMoveList c'tor.
1944 Move RootMoveList::scan_for_easy_move() const {
1951 // moves are sorted so just consider the best and the second one
1952 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
1958 // RootMoveList::sort() sorts the root move list at the beginning of a new
1961 inline void RootMoveList::sort() {
1963 sort_multipv(count - 1); // all items
1967 // RootMoveList::sort_multipv() sorts the first few moves in the root move
1968 // list by their scores and depths. It is used to order the different PVs
1969 // correctly in MultiPV mode.
1971 void RootMoveList::sort_multipv(int n) {
1973 for (int i = 1; i <= n; i++)
1975 RootMove rm = moves[i];
1977 for (j = i; j > 0 && moves[j-1] < rm; j--)
1978 moves[j] = moves[j-1];
1984 // init_node() is called at the beginning of all the search functions
1985 // (search(), search_pv(), qsearch(), and so on) and initializes the search
1986 // stack object corresponding to the current node. Once every
1987 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1988 // for user input and checks whether it is time to stop the search.
1990 void init_node(const Position &pos, SearchStack ss[], int ply, int threadID) {
1991 assert(ply >= 0 && ply < PLY_MAX);
1992 assert(threadID >= 0 && threadID < ActiveThreads);
1994 Threads[threadID].nodes++;
1998 if(NodesSincePoll >= NodesBetweenPolls) {
2005 ss[ply+2].initKillers();
2007 if(Threads[threadID].printCurrentLine)
2008 print_current_line(ss, ply, threadID);
2012 // update_pv() is called whenever a search returns a value > alpha. It
2013 // updates the PV in the SearchStack object corresponding to the current
2016 void update_pv(SearchStack ss[], int ply) {
2017 assert(ply >= 0 && ply < PLY_MAX);
2019 ss[ply].pv[ply] = ss[ply].currentMove;
2021 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2022 ss[ply].pv[p] = ss[ply+1].pv[p];
2023 ss[ply].pv[p] = MOVE_NONE;
2027 // sp_update_pv() is a variant of update_pv for use at split points. The
2028 // difference between the two functions is that sp_update_pv also updates
2029 // the PV at the parent node.
2031 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply) {
2032 assert(ply >= 0 && ply < PLY_MAX);
2034 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2036 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2037 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2038 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2042 // connected_moves() tests whether two moves are 'connected' in the sense
2043 // that the first move somehow made the second move possible (for instance
2044 // if the moving piece is the same in both moves). The first move is
2045 // assumed to be the move that was made to reach the current position, while
2046 // the second move is assumed to be a move from the current position.
2048 bool connected_moves(const Position &pos, Move m1, Move m2) {
2049 Square f1, t1, f2, t2;
2051 assert(move_is_ok(m1));
2052 assert(move_is_ok(m2));
2057 // Case 1: The moving piece is the same in both moves.
2063 // Case 2: The destination square for m2 was vacated by m1.
2069 // Case 3: Moving through the vacated square:
2070 if(piece_is_slider(pos.piece_on(f2)) &&
2071 bit_is_set(squares_between(f2, t2), f1))
2074 // Case 4: The destination square for m2 is attacked by the moving piece
2076 if(pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
2079 // Case 5: Discovered check, checking piece is the piece moved in m1:
2080 if(piece_is_slider(pos.piece_on(t1)) &&
2081 bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())),
2083 !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())),
2085 Bitboard occ = pos.occupied_squares();
2086 Color us = pos.side_to_move();
2087 Square ksq = pos.king_square(us);
2088 clear_bit(&occ, f2);
2089 if(pos.type_of_piece_on(t1) == BISHOP) {
2090 if(bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2093 else if(pos.type_of_piece_on(t1) == ROOK) {
2094 if(bit_is_set(rook_attacks_bb(ksq, occ), t1))
2098 assert(pos.type_of_piece_on(t1) == QUEEN);
2099 if(bit_is_set(queen_attacks_bb(ksq, occ), t1))
2108 // value_is_mate() checks if the given value is a mate one
2109 // eventually compensated for the ply.
2111 bool value_is_mate(Value value) {
2113 assert(abs(value) <= VALUE_INFINITE);
2115 return value <= value_mated_in(PLY_MAX)
2116 || value >= value_mate_in(PLY_MAX);
2120 // move_is_killer() checks if the given move is among the
2121 // killer moves of that ply.
2123 bool move_is_killer(Move m, const SearchStack& ss) {
2125 const Move* k = ss.killers;
2126 for (int i = 0; i < KILLER_MAX; i++, k++)
2134 // extension() decides whether a move should be searched with normal depth,
2135 // or with extended depth. Certain classes of moves (checking moves, in
2136 // particular) are searched with bigger depth than ordinary moves and in
2137 // any case are marked as 'dangerous'. Note that also if a move is not
2138 // extended, as example because the corresponding UCI option is set to zero,
2139 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2141 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2142 bool singleReply, bool mateThreat, bool* dangerous) {
2144 assert(m != MOVE_NONE);
2146 Depth result = Depth(0);
2147 *dangerous = check || singleReply || mateThreat;
2150 result += CheckExtension[pvNode];
2153 result += SingleReplyExtension[pvNode];
2156 result += MateThreatExtension[pvNode];
2158 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2160 if (pos.move_is_pawn_push_to_7th(m))
2162 result += PawnPushTo7thExtension[pvNode];
2165 if (pos.move_is_passed_pawn_push(m))
2167 result += PassedPawnExtension[pvNode];
2173 && pos.type_of_piece_on(move_to(m)) != PAWN
2174 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2175 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2176 && !move_promotion(m)
2179 result += PawnEndgameExtension[pvNode];
2185 && pos.type_of_piece_on(move_to(m)) != PAWN
2192 return Min(result, OnePly);
2196 // ok_to_do_nullmove() looks at the current position and decides whether
2197 // doing a 'null move' should be allowed. In order to avoid zugzwang
2198 // problems, null moves are not allowed when the side to move has very
2199 // little material left. Currently, the test is a bit too simple: Null
2200 // moves are avoided only when the side to move has only pawns left. It's
2201 // probably a good idea to avoid null moves in at least some more
2202 // complicated endgames, e.g. KQ vs KR. FIXME
2204 bool ok_to_do_nullmove(const Position &pos) {
2205 if(pos.non_pawn_material(pos.side_to_move()) == Value(0))
2211 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2212 // non-tactical moves late in the move list close to the leaves are
2213 // candidates for pruning.
2215 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d) {
2216 Square mfrom, mto, tfrom, tto;
2218 assert(move_is_ok(m));
2219 assert(threat == MOVE_NONE || move_is_ok(threat));
2220 assert(!move_promotion(m));
2221 assert(!pos.move_is_check(m));
2222 assert(!pos.move_is_capture(m));
2223 assert(!pos.move_is_passed_pawn_push(m));
2224 assert(d >= OnePly);
2226 mfrom = move_from(m);
2228 tfrom = move_from(threat);
2229 tto = move_to(threat);
2231 // Case 1: Castling moves are never pruned.
2232 if (move_is_castle(m))
2235 // Case 2: Don't prune moves which move the threatened piece
2236 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2239 // Case 3: If the threatened piece has value less than or equal to the
2240 // value of the threatening piece, don't prune move which defend it.
2241 if ( !PruneDefendingMoves
2242 && threat != MOVE_NONE
2243 && pos.move_is_capture(threat)
2244 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2245 || pos.type_of_piece_on(tfrom) == KING)
2246 && pos.move_attacks_square(m, tto))
2249 // Case 4: Don't prune moves with good history.
2250 if (!H.ok_to_prune(pos.piece_on(move_from(m)), m, d))
2253 // Case 5: If the moving piece in the threatened move is a slider, don't
2254 // prune safe moves which block its ray.
2255 if ( !PruneBlockingMoves
2256 && threat != MOVE_NONE
2257 && piece_is_slider(pos.piece_on(tfrom))
2258 && bit_is_set(squares_between(tfrom, tto), mto)
2266 // ok_to_use_TT() returns true if a transposition table score
2267 // can be used at a given point in search.
2269 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2271 Value v = value_from_tt(tte->value(), ply);
2273 return ( tte->depth() >= depth
2274 || v >= Max(value_mate_in(100), beta)
2275 || v < Min(value_mated_in(100), beta))
2277 && ( (is_lower_bound(tte->type()) && v >= beta)
2278 || (is_upper_bound(tte->type()) && v < beta));
2282 // ok_to_history() returns true if a move m can be stored
2283 // in history. Should be a non capturing move nor a promotion.
2285 bool ok_to_history(const Position& pos, Move m) {
2287 return !pos.move_is_capture(m) && !move_promotion(m);
2291 // update_history() registers a good move that produced a beta-cutoff
2292 // in history and marks as failures all the other moves of that ply.
2294 void update_history(const Position& pos, Move m, Depth depth,
2295 Move movesSearched[], int moveCount) {
2297 H.success(pos.piece_on(move_from(m)), m, depth);
2299 for (int i = 0; i < moveCount - 1; i++)
2301 assert(m != movesSearched[i]);
2302 if (ok_to_history(pos, movesSearched[i]))
2303 H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
2308 // update_killers() add a good move that produced a beta-cutoff
2309 // among the killer moves of that ply.
2311 void update_killers(Move m, SearchStack& ss) {
2313 if (m == ss.killers[0])
2316 for (int i = KILLER_MAX - 1; i > 0; i--)
2317 ss.killers[i] = ss.killers[i - 1];
2322 // fail_high_ply_1() checks if some thread is currently resolving a fail
2323 // high at ply 1 at the node below the first root node. This information
2324 // is used for time managment.
2326 bool fail_high_ply_1() {
2327 for(int i = 0; i < ActiveThreads; i++)
2328 if(Threads[i].failHighPly1)
2334 // current_search_time() returns the number of milliseconds which have passed
2335 // since the beginning of the current search.
2337 int current_search_time() {
2338 return get_system_time() - SearchStartTime;
2342 // nps() computes the current nodes/second count.
2345 int t = current_search_time();
2346 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2350 // poll() performs two different functions: It polls for user input, and it
2351 // looks at the time consumed so far and decides if it's time to abort the
2356 static int lastInfoTime;
2357 int t = current_search_time();
2362 // We are line oriented, don't read single chars
2363 std::string command;
2364 if (!std::getline(std::cin, command))
2367 if (command == "quit")
2370 PonderSearch = false;
2373 else if(command == "stop")
2376 PonderSearch = false;
2378 else if(command == "ponderhit")
2381 // Print search information
2385 else if (lastInfoTime > t)
2386 // HACK: Must be a new search where we searched less than
2387 // NodesBetweenPolls nodes during the first second of search.
2390 else if (t - lastInfoTime >= 1000)
2397 if (dbg_show_hit_rate)
2398 dbg_print_hit_rate();
2400 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2401 << " time " << t << " hashfull " << TT.full() << std::endl;
2402 lock_release(&IOLock);
2403 if (ShowCurrentLine)
2404 Threads[0].printCurrentLine = true;
2406 // Should we stop the search?
2410 bool overTime = t > AbsoluteMaxSearchTime
2411 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime)
2412 || ( !FailHigh && !fail_high_ply_1() && !Problem
2413 && t > 6*(MaxSearchTime + ExtraSearchTime));
2415 if ( (Iteration >= 2 && (!InfiniteSearch && overTime))
2416 || (ExactMaxTime && t >= ExactMaxTime)
2417 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2422 // ponderhit() is called when the program is pondering (i.e. thinking while
2423 // it's the opponent's turn to move) in order to let the engine know that
2424 // it correctly predicted the opponent's move.
2427 int t = current_search_time();
2428 PonderSearch = false;
2429 if(Iteration >= 2 &&
2430 (!InfiniteSearch && (StopOnPonderhit ||
2431 t > AbsoluteMaxSearchTime ||
2432 (RootMoveNumber == 1 &&
2433 t > MaxSearchTime + ExtraSearchTime) ||
2434 (!FailHigh && !fail_high_ply_1() && !Problem &&
2435 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2440 // print_current_line() prints the current line of search for a given
2441 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2443 void print_current_line(SearchStack ss[], int ply, int threadID) {
2444 assert(ply >= 0 && ply < PLY_MAX);
2445 assert(threadID >= 0 && threadID < ActiveThreads);
2447 if(!Threads[threadID].idle) {
2449 std::cout << "info currline " << (threadID + 1);
2450 for(int p = 0; p < ply; p++)
2451 std::cout << " " << ss[p].currentMove;
2452 std::cout << std::endl;
2453 lock_release(&IOLock);
2455 Threads[threadID].printCurrentLine = false;
2456 if(threadID + 1 < ActiveThreads)
2457 Threads[threadID + 1].printCurrentLine = true;
2461 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2462 // while the program is pondering. The point is to work around a wrinkle in
2463 // the UCI protocol: When pondering, the engine is not allowed to give a
2464 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2465 // We simply wait here until one of these commands is sent, and return,
2466 // after which the bestmove and pondermove will be printed (in id_loop()).
2468 void wait_for_stop_or_ponderhit() {
2469 std::string command;
2472 if(!std::getline(std::cin, command))
2475 if(command == "quit") {
2476 OpeningBook.close();
2481 else if(command == "ponderhit" || command == "stop")
2487 // idle_loop() is where the threads are parked when they have no work to do.
2488 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2489 // object for which the current thread is the master.
2491 void idle_loop(int threadID, SplitPoint *waitSp) {
2492 assert(threadID >= 0 && threadID < THREAD_MAX);
2494 Threads[threadID].running = true;
2497 if(AllThreadsShouldExit && threadID != 0)
2500 // If we are not thinking, wait for a condition to be signaled instead
2501 // of wasting CPU time polling for work:
2502 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2503 #if !defined(_MSC_VER)
2504 pthread_mutex_lock(&WaitLock);
2505 if(Idle || threadID >= ActiveThreads)
2506 pthread_cond_wait(&WaitCond, &WaitLock);
2507 pthread_mutex_unlock(&WaitLock);
2509 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2513 // If this thread has been assigned work, launch a search:
2514 if(Threads[threadID].workIsWaiting) {
2515 Threads[threadID].workIsWaiting = false;
2516 if(Threads[threadID].splitPoint->pvNode)
2517 sp_search_pv(Threads[threadID].splitPoint, threadID);
2519 sp_search(Threads[threadID].splitPoint, threadID);
2520 Threads[threadID].idle = true;
2523 // If this thread is the master of a split point and all threads have
2524 // finished their work at this split point, return from the idle loop:
2525 if(waitSp != NULL && waitSp->cpus == 0)
2529 Threads[threadID].running = false;
2533 // init_split_point_stack() is called during program initialization, and
2534 // initializes all split point objects.
2536 void init_split_point_stack() {
2537 for(int i = 0; i < THREAD_MAX; i++)
2538 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2539 SplitPointStack[i][j].parent = NULL;
2540 lock_init(&(SplitPointStack[i][j].lock), NULL);
2545 // destroy_split_point_stack() is called when the program exits, and
2546 // destroys all locks in the precomputed split point objects.
2548 void destroy_split_point_stack() {
2549 for(int i = 0; i < THREAD_MAX; i++)
2550 for(int j = 0; j < MaxActiveSplitPoints; j++)
2551 lock_destroy(&(SplitPointStack[i][j].lock));
2555 // thread_should_stop() checks whether the thread with a given threadID has
2556 // been asked to stop, directly or indirectly. This can happen if a beta
2557 // cutoff has occured in thre thread's currently active split point, or in
2558 // some ancestor of the current split point.
2560 bool thread_should_stop(int threadID) {
2561 assert(threadID >= 0 && threadID < ActiveThreads);
2565 if(Threads[threadID].stop)
2567 if(ActiveThreads <= 2)
2569 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2571 Threads[threadID].stop = true;
2578 // thread_is_available() checks whether the thread with threadID "slave" is
2579 // available to help the thread with threadID "master" at a split point. An
2580 // obvious requirement is that "slave" must be idle. With more than two
2581 // threads, this is not by itself sufficient: If "slave" is the master of
2582 // some active split point, it is only available as a slave to the other
2583 // threads which are busy searching the split point at the top of "slave"'s
2584 // split point stack (the "helpful master concept" in YBWC terminology).
2586 bool thread_is_available(int slave, int master) {
2587 assert(slave >= 0 && slave < ActiveThreads);
2588 assert(master >= 0 && master < ActiveThreads);
2589 assert(ActiveThreads > 1);
2591 if(!Threads[slave].idle || slave == master)
2594 if(Threads[slave].activeSplitPoints == 0)
2595 // No active split points means that the thread is available as a slave
2596 // for any other thread.
2599 if(ActiveThreads == 2)
2602 // Apply the "helpful master" concept if possible.
2603 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2610 // idle_thread_exists() tries to find an idle thread which is available as
2611 // a slave for the thread with threadID "master".
2613 bool idle_thread_exists(int master) {
2614 assert(master >= 0 && master < ActiveThreads);
2615 assert(ActiveThreads > 1);
2617 for(int i = 0; i < ActiveThreads; i++)
2618 if(thread_is_available(i, master))
2624 // split() does the actual work of distributing the work at a node between
2625 // several threads at PV nodes. If it does not succeed in splitting the
2626 // node (because no idle threads are available, or because we have no unused
2627 // split point objects), the function immediately returns false. If
2628 // splitting is possible, a SplitPoint object is initialized with all the
2629 // data that must be copied to the helper threads (the current position and
2630 // search stack, alpha, beta, the search depth, etc.), and we tell our
2631 // helper threads that they have been assigned work. This will cause them
2632 // to instantly leave their idle loops and call sp_search_pv(). When all
2633 // threads have returned from sp_search_pv (or, equivalently, when
2634 // splitPoint->cpus becomes 0), split() returns true.
2636 bool split(const Position &p, SearchStack *sstck, int ply,
2637 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
2638 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode) {
2641 assert(sstck != NULL);
2642 assert(ply >= 0 && ply < PLY_MAX);
2643 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2644 assert(!pvNode || *alpha < *beta);
2645 assert(*beta <= VALUE_INFINITE);
2646 assert(depth > Depth(0));
2647 assert(master >= 0 && master < ActiveThreads);
2648 assert(ActiveThreads > 1);
2650 SplitPoint *splitPoint;
2655 // If no other thread is available to help us, or if we have too many
2656 // active split points, don't split:
2657 if(!idle_thread_exists(master) ||
2658 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2659 lock_release(&MPLock);
2663 // Pick the next available split point object from the split point stack:
2664 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2665 Threads[master].activeSplitPoints++;
2667 // Initialize the split point object:
2668 splitPoint->parent = Threads[master].splitPoint;
2669 splitPoint->finished = false;
2670 splitPoint->ply = ply;
2671 splitPoint->depth = depth;
2672 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2673 splitPoint->beta = *beta;
2674 splitPoint->pvNode = pvNode;
2675 splitPoint->dcCandidates = dcCandidates;
2676 splitPoint->bestValue = *bestValue;
2677 splitPoint->master = master;
2678 splitPoint->mp = mp;
2679 splitPoint->moves = *moves;
2680 splitPoint->cpus = 1;
2681 splitPoint->pos.copy(p);
2682 splitPoint->parentSstack = sstck;
2683 for(i = 0; i < ActiveThreads; i++)
2684 splitPoint->slaves[i] = 0;
2686 // Copy the current position and the search stack to the master thread:
2687 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2688 Threads[master].splitPoint = splitPoint;
2690 // Make copies of the current position and search stack for each thread:
2691 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2693 if(thread_is_available(i, master)) {
2694 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2695 Threads[i].splitPoint = splitPoint;
2696 splitPoint->slaves[i] = 1;
2700 // Tell the threads that they have work to do. This will make them leave
2702 for(i = 0; i < ActiveThreads; i++)
2703 if(i == master || splitPoint->slaves[i]) {
2704 Threads[i].workIsWaiting = true;
2705 Threads[i].idle = false;
2706 Threads[i].stop = false;
2709 lock_release(&MPLock);
2711 // Everything is set up. The master thread enters the idle loop, from
2712 // which it will instantly launch a search, because its workIsWaiting
2713 // slot is 'true'. We send the split point as a second parameter to the
2714 // idle loop, which means that the main thread will return from the idle
2715 // loop when all threads have finished their work at this split point
2716 // (i.e. when // splitPoint->cpus == 0).
2717 idle_loop(master, splitPoint);
2719 // We have returned from the idle loop, which means that all threads are
2720 // finished. Update alpha, beta and bestvalue, and return:
2722 if(pvNode) *alpha = splitPoint->alpha;
2723 *beta = splitPoint->beta;
2724 *bestValue = splitPoint->bestValue;
2725 Threads[master].stop = false;
2726 Threads[master].idle = false;
2727 Threads[master].activeSplitPoints--;
2728 Threads[master].splitPoint = splitPoint->parent;
2729 lock_release(&MPLock);
2735 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2736 // to start a new search from the root.
2738 void wake_sleeping_threads() {
2739 if(ActiveThreads > 1) {
2740 for(int i = 1; i < ActiveThreads; i++) {
2741 Threads[i].idle = true;
2742 Threads[i].workIsWaiting = false;
2744 #if !defined(_MSC_VER)
2745 pthread_mutex_lock(&WaitLock);
2746 pthread_cond_broadcast(&WaitCond);
2747 pthread_mutex_unlock(&WaitLock);
2749 for(int i = 1; i < THREAD_MAX; i++)
2750 SetEvent(SitIdleEvent[i]);
2756 // init_thread() is the function which is called when a new thread is
2757 // launched. It simply calls the idle_loop() function with the supplied
2758 // threadID. There are two versions of this function; one for POSIX threads
2759 // and one for Windows threads.
2761 #if !defined(_MSC_VER)
2763 void *init_thread(void *threadID) {
2764 idle_loop(*(int *)threadID, NULL);
2770 DWORD WINAPI init_thread(LPVOID threadID) {
2771 idle_loop(*(int *)threadID, NULL);