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 //Null move search refutes move when Nullvalue >= Beta - Delta. Index is depth
153 //in full plies. Last index is 9+.
154 const Value NullMoveDeltaMidgame[] =
155 { Value(-8), Value( 6), Value(-15), Value( 9), Value(21),
156 Value(34), Value(54), Value( 59), Value(61), Value(61) };
158 const Value NullMoveDeltaEndgame[] =
159 { Value( 6), Value( 0), Value(-13), Value(-9), Value(-35),
160 Value(12), Value(24), Value( 9), Value( 5), Value( 5) };
162 // Pruning criterions. See the code and comments in ok_to_prune() to
163 // understand their precise meaning.
164 const bool PruneEscapeMoves = false;
165 const bool PruneDefendingMoves = false;
166 const bool PruneBlockingMoves = false;
168 // Use futility pruning?
169 bool UseQSearchFutilityPruning = true;
170 bool UseFutilityPruning = true;
172 // Margins for futility pruning in the quiescence search, and at frontier
173 // and near frontier nodes
174 Value FutilityMarginQS = Value(0x80);
175 Value FutilityMargins[6] = { Value(0x100), Value(0x200), Value(0x250),
176 Value(0x2A0), Value(0x340), Value(0x3A0) };
179 const bool RazorAtDepthOne = false;
180 Depth RazorDepth = 4*OnePly;
181 Value RazorMargin = Value(0x300);
183 // Last seconds noise filtering (LSN)
184 bool UseLSNFiltering = false;
185 bool looseOnTime = false;
186 int LSNTime = 4 * 1000; // In milliseconds
187 Value LSNValue = Value(0x200);
189 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
190 Depth CheckExtension[2] = {OnePly, OnePly};
191 Depth SingleReplyExtension[2] = {OnePly / 2, OnePly / 2};
192 Depth PawnPushTo7thExtension[2] = {OnePly / 2, OnePly / 2};
193 Depth PassedPawnExtension[2] = {Depth(0), Depth(0)};
194 Depth PawnEndgameExtension[2] = {OnePly, OnePly};
195 Depth MateThreatExtension[2] = {Depth(0), Depth(0)};
197 // Search depth at iteration 1
198 const Depth InitialDepth = OnePly /*+ OnePly/2*/;
202 int NodesBetweenPolls = 30000;
204 // Iteration counters
207 BetaCounterType BetaCounter;
209 // Scores and number of times the best move changed for each iteration:
210 Value ValueByIteration[PLY_MAX_PLUS_2];
211 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
216 // Time managment variables
218 int MaxNodes, MaxDepth;
219 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
220 Move BestRootMove, PonderMove, EasyMove;
224 bool StopOnPonderhit;
229 bool PonderingEnabled;
232 // Show current line?
233 bool ShowCurrentLine = false;
236 bool UseLogFile = false;
237 std::ofstream LogFile;
239 // MP related variables
240 Depth MinimumSplitDepth = 4*OnePly;
241 int MaxThreadsPerSplitPoint = 4;
242 Thread Threads[THREAD_MAX];
244 bool AllThreadsShouldExit = false;
245 const int MaxActiveSplitPoints = 8;
246 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
249 #if !defined(_MSC_VER)
250 pthread_cond_t WaitCond;
251 pthread_mutex_t WaitLock;
253 HANDLE SitIdleEvent[THREAD_MAX];
259 Value id_loop(const Position &pos, Move searchMoves[]);
260 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml);
261 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
262 Depth depth, int ply, int threadID);
263 Value search(Position &pos, SearchStack ss[], Value beta,
264 Depth depth, int ply, bool allowNullmove, int threadID);
265 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
266 Depth depth, int ply, int threadID);
267 void sp_search(SplitPoint *sp, int threadID);
268 void sp_search_pv(SplitPoint *sp, int threadID);
269 void init_node(const Position &pos, SearchStack ss[], int ply, int threadID);
270 void update_pv(SearchStack ss[], int ply);
271 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
272 bool connected_moves(const Position &pos, Move m1, Move m2);
273 bool value_is_mate(Value value);
274 bool move_is_killer(Move m, const SearchStack& ss);
275 Depth extension(const Position &pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
276 bool ok_to_do_nullmove(const Position &pos);
277 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
278 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
279 bool ok_to_history(const Position &pos, Move m);
280 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
281 void update_killers(Move m, SearchStack& ss);
283 bool fail_high_ply_1();
284 int current_search_time();
288 void print_current_line(SearchStack ss[], int ply, int threadID);
289 void wait_for_stop_or_ponderhit();
291 void idle_loop(int threadID, SplitPoint *waitSp);
292 void init_split_point_stack();
293 void destroy_split_point_stack();
294 bool thread_should_stop(int threadID);
295 bool thread_is_available(int slave, int master);
296 bool idle_thread_exists(int master);
297 bool split(const Position &pos, SearchStack *ss, int ply,
298 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
299 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode);
300 void wake_sleeping_threads();
302 #if !defined(_MSC_VER)
303 void *init_thread(void *threadID);
305 DWORD WINAPI init_thread(LPVOID threadID);
312 //// Global variables
315 // The main transposition table
316 TranspositionTable TT = TranspositionTable(TTDefaultSize);
319 // Number of active threads:
320 int ActiveThreads = 1;
322 // Locks. In principle, there is no need for IOLock to be a global variable,
323 // but it could turn out to be useful for debugging.
326 History H; // Should be made local?
328 // The empty search stack
329 SearchStack EmptySearchStack;
332 // SearchStack::init() initializes a search stack. Used at the beginning of a
333 // new search from the root.
334 void SearchStack::init(int ply) {
336 pv[ply] = pv[ply + 1] = MOVE_NONE;
337 currentMove = threatMove = MOVE_NONE;
338 reduction = Depth(0);
339 currentMoveCaptureValue = Value(0);
342 void SearchStack::initKillers() {
344 mateKiller = MOVE_NONE;
345 for (int i = 0; i < KILLER_MAX; i++)
346 killers[i] = MOVE_NONE;
354 /// think() is the external interface to Stockfish's search, and is called when
355 /// the program receives the UCI 'go' command. It initializes various
356 /// search-related global variables, and calls root_search()
358 void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
359 int time[], int increment[], int movesToGo, int maxDepth,
360 int maxNodes, int maxTime, Move searchMoves[]) {
362 // Look for a book move
363 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
366 if (get_option_value_string("Book File") != OpeningBook.file_name())
369 OpeningBook.open("book.bin");
371 bookMove = OpeningBook.get_move(pos);
372 if (bookMove != MOVE_NONE)
374 std::cout << "bestmove " << bookMove << std::endl;
379 // Initialize global search variables
381 SearchStartTime = get_system_time();
382 BestRootMove = MOVE_NONE;
383 PonderMove = MOVE_NONE;
384 EasyMove = MOVE_NONE;
385 for (int i = 0; i < THREAD_MAX; i++)
387 Threads[i].nodes = 0ULL;
388 Threads[i].failHighPly1 = false;
391 InfiniteSearch = infinite;
392 PonderSearch = ponder;
393 StopOnPonderhit = false;
398 ExactMaxTime = maxTime;
400 // Read UCI option values
401 TT.set_size(get_option_value_int("Hash"));
402 if (button_was_pressed("Clear Hash"))
405 PonderingEnabled = get_option_value_bool("Ponder");
406 MultiPV = get_option_value_int("MultiPV");
408 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
409 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
411 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
412 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
414 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
415 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
417 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
418 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
420 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
421 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
423 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
424 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
426 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
427 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
428 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
429 SelectiveDepth = get_option_value_int("Selective Plies") * OnePly;
431 Chess960 = get_option_value_bool("UCI_Chess960");
432 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
433 UseLogFile = get_option_value_bool("Use Search Log");
435 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
437 UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)");
438 UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)");
440 FutilityMarginQS = value_from_centipawns(get_option_value_int("Futility Margin (Quiescence Search)"));
441 int fmScale = get_option_value_int("Futility Margin Scale Factor (Main Search)");
442 for (int i = 0; i < 6; i++)
443 FutilityMargins[i] = (FutilityMargins[i] * fmScale) / 100;
445 RazorDepth = (get_option_value_int("Maximum Razoring Depth") + 1) * OnePly;
446 RazorMargin = value_from_centipawns(get_option_value_int("Razoring Margin"));
448 UseLSNFiltering = get_option_value_bool("LSN filtering");
449 LSNTime = get_option_value_int("LSN Time Margin (sec)") * 1000;
450 LSNValue = value_from_centipawns(get_option_value_int("LSN Value Margin"));
452 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
453 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
455 read_weights(pos.side_to_move());
457 int newActiveThreads = get_option_value_int("Threads");
458 if (newActiveThreads != ActiveThreads)
460 ActiveThreads = newActiveThreads;
461 init_eval(ActiveThreads);
464 // Wake up sleeping threads:
465 wake_sleeping_threads();
467 for (int i = 1; i < ActiveThreads; i++)
468 assert(thread_is_available(i, 0));
470 // Set thinking time:
471 int myTime = time[side_to_move];
472 int myIncrement = increment[side_to_move];
474 if (!movesToGo) // Sudden death time control
478 MaxSearchTime = myTime / 30 + myIncrement;
479 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
480 } else { // Blitz game without increment
481 MaxSearchTime = myTime / 30;
482 AbsoluteMaxSearchTime = myTime / 8;
485 else // (x moves) / (y minutes)
489 MaxSearchTime = myTime / 2;
490 AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
492 MaxSearchTime = myTime / Min(movesToGo, 20);
493 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
497 if (PonderingEnabled)
499 MaxSearchTime += MaxSearchTime / 4;
500 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
503 // Fixed depth or fixed number of nodes?
506 InfiniteSearch = true; // HACK
511 NodesBetweenPolls = Min(MaxNodes, 30000);
512 InfiniteSearch = true; // HACK
515 NodesBetweenPolls = 30000;
518 // Write information to search log file:
520 LogFile << "Searching: " << pos.to_fen() << std::endl
521 << "infinite: " << infinite
522 << " ponder: " << ponder
523 << " time: " << myTime
524 << " increment: " << myIncrement
525 << " moves to go: " << movesToGo << std::endl;
528 // We're ready to start thinking. Call the iterative deepening loop
532 Value v = id_loop(pos, searchMoves);
533 looseOnTime = ( UseLSNFiltering
540 looseOnTime = false; // reset for next match
541 while (SearchStartTime + myTime + 1000 > get_system_time())
543 id_loop(pos, searchMoves); // to fail gracefully
560 /// init_threads() is called during startup. It launches all helper threads,
561 /// and initializes the split point stack and the global locks and condition
564 void init_threads() {
568 #if !defined(_MSC_VER)
569 pthread_t pthread[1];
572 for (i = 0; i < THREAD_MAX; i++)
573 Threads[i].activeSplitPoints = 0;
575 // Initialize global locks:
576 lock_init(&MPLock, NULL);
577 lock_init(&IOLock, NULL);
579 init_split_point_stack();
581 #if !defined(_MSC_VER)
582 pthread_mutex_init(&WaitLock, NULL);
583 pthread_cond_init(&WaitCond, NULL);
585 for (i = 0; i < THREAD_MAX; i++)
586 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
589 // All threads except the main thread should be initialized to idle state
590 for (i = 1; i < THREAD_MAX; i++)
592 Threads[i].stop = false;
593 Threads[i].workIsWaiting = false;
594 Threads[i].idle = true;
595 Threads[i].running = false;
598 // Launch the helper threads
599 for(i = 1; i < THREAD_MAX; i++)
601 #if !defined(_MSC_VER)
602 pthread_create(pthread, NULL, init_thread, (void*)(&i));
605 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
608 // Wait until the thread has finished launching:
609 while (!Threads[i].running);
612 // Init also the empty search stack
613 EmptySearchStack.init(0);
614 EmptySearchStack.initKillers();
618 /// stop_threads() is called when the program exits. It makes all the
619 /// helper threads exit cleanly.
621 void stop_threads() {
623 ActiveThreads = THREAD_MAX; // HACK
624 Idle = false; // HACK
625 wake_sleeping_threads();
626 AllThreadsShouldExit = true;
627 for (int i = 1; i < THREAD_MAX; i++)
629 Threads[i].stop = true;
630 while(Threads[i].running);
632 destroy_split_point_stack();
636 /// nodes_searched() returns the total number of nodes searched so far in
637 /// the current search.
639 int64_t nodes_searched() {
641 int64_t result = 0ULL;
642 for (int i = 0; i < ActiveThreads; i++)
643 result += Threads[i].nodes;
650 // id_loop() is the main iterative deepening loop. It calls root_search
651 // repeatedly with increasing depth until the allocated thinking time has
652 // been consumed, the user stops the search, or the maximum search depth is
655 Value id_loop(const Position &pos, Move searchMoves[]) {
658 SearchStack ss[PLY_MAX_PLUS_2];
660 // searchMoves are verified, copied, scored and sorted
661 RootMoveList rml(p, searchMoves);
666 for (int i = 0; i < 3; i++)
671 ValueByIteration[0] = Value(0);
672 ValueByIteration[1] = rml.get_move_score(0);
674 LastIterations = false;
676 EasyMove = rml.scan_for_easy_move();
678 // Iterative deepening loop
679 while (!AbortSearch && Iteration < PLY_MAX)
681 // Initialize iteration
684 BestMoveChangesByIteration[Iteration] = 0;
688 std::cout << "info depth " << Iteration << std::endl;
690 // Search to the current depth
691 ValueByIteration[Iteration] = root_search(p, ss, rml);
693 // Erase the easy move if it differs from the new best move
694 if (ss[0].pv[0] != EasyMove)
695 EasyMove = MOVE_NONE;
702 bool stopSearch = false;
704 // Stop search early if there is only a single legal move:
705 if (Iteration >= 6 && rml.move_count() == 1)
708 // Stop search early when the last two iterations returned a mate score
710 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
711 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
714 // Stop search early if one move seems to be much better than the rest
715 int64_t nodes = nodes_searched();
717 && EasyMove == ss[0].pv[0]
718 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
719 && current_search_time() > MaxSearchTime / 16)
720 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
721 && current_search_time() > MaxSearchTime / 32)))
724 // Add some extra time if the best move has changed during the last two iterations
725 if (Iteration > 5 && Iteration <= 50)
726 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
727 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
729 // Try to guess if the current iteration is the last one or the last two
730 LastIterations = (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*58) / 128);
732 // Stop search if most of MaxSearchTime is consumed at the end of the
733 // iteration. We probably don't have enough time to search the first
734 // move at the next iteration anyway.
735 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
743 StopOnPonderhit = true;
746 // Write PV to transposition table, in case the relevant entries have
747 // been overwritten during the search:
748 TT.insert_pv(p, ss[0].pv);
750 if (MaxDepth && Iteration >= MaxDepth)
756 // If we are pondering, we shouldn't print the best move before we
759 wait_for_stop_or_ponderhit();
761 // Print final search statistics
762 std::cout << "info nodes " << nodes_searched()
764 << " time " << current_search_time()
765 << " hashfull " << TT.full() << std::endl;
767 // Print the best move and the ponder move to the standard output
768 std::cout << "bestmove " << ss[0].pv[0];
769 if (ss[0].pv[1] != MOVE_NONE)
770 std::cout << " ponder " << ss[0].pv[1];
772 std::cout << std::endl;
777 dbg_print_mean(LogFile);
779 if (dbg_show_hit_rate)
780 dbg_print_hit_rate(LogFile);
783 LogFile << "Nodes: " << nodes_searched() << std::endl
784 << "Nodes/second: " << nps() << std::endl
785 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
787 p.do_move(ss[0].pv[0], st);
788 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
789 << std::endl << std::endl;
791 return rml.get_move_score(0);
795 // root_search() is the function which searches the root node. It is
796 // similar to search_pv except that it uses a different move ordering
797 // scheme (perhaps we should try to use this at internal PV nodes, too?)
798 // and prints some information to the standard output.
800 Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml) {
802 Value alpha = -VALUE_INFINITE;
803 Value beta = VALUE_INFINITE, value;
804 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
806 // Loop through all the moves in the root move list
807 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
814 RootMoveNumber = i + 1;
817 // Remember the node count before the move is searched. The node counts
818 // are used to sort the root moves at the next iteration.
819 nodes = nodes_searched();
821 // Reset beta cut-off counters
824 // Pick the next root move, and print the move and the move number to
825 // the standard output.
826 move = ss[0].currentMove = rml.get_move(i);
827 if (current_search_time() >= 1000)
828 std::cout << "info currmove " << move
829 << " currmovenumber " << i + 1 << std::endl;
831 // Decide search depth for this move
833 ext = extension(pos, move, true, pos.move_is_capture(move), pos.move_is_check(move), false, false, &dangerous);
834 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
836 // Make the move, and search it
837 pos.do_move(move, st, dcCandidates);
841 value = -search_pv(pos, ss, -beta, VALUE_INFINITE, newDepth, 1, 0);
842 // If the value has dropped a lot compared to the last iteration,
843 // set the boolean variable Problem to true. This variable is used
844 // for time managment: When Problem is true, we try to complete the
845 // current iteration before playing a move.
846 Problem = (Iteration >= 2 && value <= ValueByIteration[Iteration-1] - ProblemMargin);
848 if (Problem && StopOnPonderhit)
849 StopOnPonderhit = false;
853 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
856 // Fail high! Set the boolean variable FailHigh to true, and
857 // re-search the move with a big window. The variable FailHigh is
858 // used for time managment: We try to avoid aborting the search
859 // prematurely during a fail high research.
861 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
867 // Finished searching the move. If AbortSearch is true, the search
868 // was aborted because the user interrupted the search or because we
869 // ran out of time. In this case, the return value of the search cannot
870 // be trusted, and we break out of the loop without updating the best
875 // Remember the node count for this move. The node counts are used to
876 // sort the root moves at the next iteration.
877 rml.set_move_nodes(i, nodes_searched() - nodes);
879 // Remember the beta-cutoff statistics
881 BetaCounter.read(pos.side_to_move(), our, their);
882 rml.set_beta_counters(i, our, their);
884 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
886 if (value <= alpha && i >= MultiPV)
887 rml.set_move_score(i, -VALUE_INFINITE);
893 rml.set_move_score(i, value);
895 rml.set_move_pv(i, ss[0].pv);
899 // We record how often the best move has been changed in each
900 // iteration. This information is used for time managment: When
901 // the best move changes frequently, we allocate some more time.
903 BestMoveChangesByIteration[Iteration]++;
905 // Print search information to the standard output:
906 std::cout << "info depth " << Iteration
907 << " score " << value_to_string(value)
908 << " time " << current_search_time()
909 << " nodes " << nodes_searched()
913 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
914 std::cout << ss[0].pv[j] << " ";
916 std::cout << std::endl;
919 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
924 // Reset the global variable Problem to false if the value isn't too
925 // far below the final value from the last iteration.
926 if (value > ValueByIteration[Iteration - 1] - NoProblemMargin)
932 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
935 std::cout << "info multipv " << j + 1
936 << " score " << value_to_string(rml.get_move_score(j))
937 << " depth " << ((j <= i)? Iteration : Iteration - 1)
938 << " time " << current_search_time()
939 << " nodes " << nodes_searched()
943 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
944 std::cout << rml.get_move_pv(j, k) << " ";
946 std::cout << std::endl;
948 alpha = rml.get_move_score(Min(i, MultiPV-1));
956 // search_pv() is the main search function for PV nodes.
958 Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
959 Depth depth, int ply, int threadID) {
961 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
962 assert(beta > alpha && beta <= VALUE_INFINITE);
963 assert(ply >= 0 && ply < PLY_MAX);
964 assert(threadID >= 0 && threadID < ActiveThreads);
967 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
969 // Initialize, and make an early exit in case of an aborted search,
970 // an instant draw, maximum ply reached, etc.
971 init_node(pos, ss, ply, threadID);
973 // After init_node() that calls poll()
974 if (AbortSearch || thread_should_stop(threadID))
982 if (ply >= PLY_MAX - 1)
983 return evaluate(pos, ei, threadID);
985 // Mate distance pruning
986 Value oldAlpha = alpha;
987 alpha = Max(value_mated_in(ply), alpha);
988 beta = Min(value_mate_in(ply+1), beta);
992 // Transposition table lookup. At PV nodes, we don't use the TT for
993 // pruning, but only for move ordering.
994 const TTEntry* tte = TT.retrieve(pos);
995 Move ttMove = (tte ? tte->move() : MOVE_NONE);
997 // Go with internal iterative deepening if we don't have a TT move
998 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
1000 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1001 ttMove = ss[ply].pv[ply];
1004 // Initialize a MovePicker object for the current position, and prepare
1005 // to search all moves
1006 MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
1008 Move move, movesSearched[256];
1010 Value value, bestValue = -VALUE_INFINITE;
1011 Bitboard dcCandidates = mp.discovered_check_candidates();
1012 Color us = pos.side_to_move();
1013 bool isCheck = pos.is_check();
1014 bool mateThreat = pos.has_mate_threat(opposite_color(us));
1016 // Loop through all legal moves until no moves remain or a beta cutoff
1018 while ( alpha < beta
1019 && (move = mp.get_next_move()) != MOVE_NONE
1020 && !thread_should_stop(threadID))
1022 assert(move_is_ok(move));
1024 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1025 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1026 bool moveIsCapture = pos.move_is_capture(move);
1028 movesSearched[moveCount++] = ss[ply].currentMove = move;
1031 ss[ply].currentMoveCaptureValue =
1032 move_is_ep(move)? PawnValueMidgame : pos.midgame_value_of_piece_on(move_to(move));
1034 ss[ply].currentMoveCaptureValue = Value(0);
1036 // Decide the new search depth
1038 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1039 Depth newDepth = depth - OnePly + ext;
1041 // Make and search the move
1043 pos.do_move(move, st, dcCandidates);
1045 if (moveCount == 1) // The first move in list is the PV
1046 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1049 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1050 // if the move fails high will be re-searched at full depth.
1051 if ( depth >= 2*OnePly
1052 && moveCount >= LMRPVMoves
1055 && !move_promotion(move)
1056 && !move_is_castle(move)
1057 && !move_is_killer(move, ss[ply]))
1059 ss[ply].reduction = OnePly;
1060 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1063 value = alpha + 1; // Just to trigger next condition
1065 if (value > alpha) // Go with full depth non-pv search
1067 ss[ply].reduction = Depth(0);
1068 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1069 if (value > alpha && value < beta)
1071 // When the search fails high at ply 1 while searching the first
1072 // move at the root, set the flag failHighPly1. This is used for
1073 // time managment: We don't want to stop the search early in
1074 // such cases, because resolving the fail high at ply 1 could
1075 // result in a big drop in score at the root.
1076 if (ply == 1 && RootMoveNumber == 1)
1077 Threads[threadID].failHighPly1 = true;
1079 // A fail high occurred. Re-search at full window (pv search)
1080 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1081 Threads[threadID].failHighPly1 = false;
1085 pos.undo_move(move);
1087 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1090 if (value > bestValue)
1097 if (value == value_mate_in(ply + 1))
1098 ss[ply].mateKiller = move;
1100 // If we are at ply 1, and we are searching the first root move at
1101 // ply 0, set the 'Problem' variable if the score has dropped a lot
1102 // (from the computer's point of view) since the previous iteration:
1105 && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
1110 if ( ActiveThreads > 1
1112 && depth >= MinimumSplitDepth
1114 && idle_thread_exists(threadID)
1116 && !thread_should_stop(threadID)
1117 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1118 &moveCount, &mp, dcCandidates, threadID, true))
1122 // All legal moves have been searched. A special case: If there were
1123 // no legal moves, it must be mate or stalemate:
1125 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1127 // If the search is not aborted, update the transposition table,
1128 // history counters, and killer moves.
1129 if (AbortSearch || thread_should_stop(threadID))
1132 if (bestValue <= oldAlpha)
1133 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1135 else if (bestValue >= beta)
1137 BetaCounter.add(pos.side_to_move(), depth, threadID);
1138 Move m = ss[ply].pv[ply];
1139 if (ok_to_history(pos, m)) // Only non capture moves are considered
1141 update_history(pos, m, depth, movesSearched, moveCount);
1142 update_killers(m, ss[ply]);
1144 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1147 TT.store(pos, value_to_tt(bestValue, ply), depth, ss[ply].pv[ply], VALUE_TYPE_EXACT);
1153 // search() is the search function for zero-width nodes.
1155 Value search(Position &pos, SearchStack ss[], Value beta, Depth depth,
1156 int ply, bool allowNullmove, int threadID) {
1158 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1159 assert(ply >= 0 && ply < PLY_MAX);
1160 assert(threadID >= 0 && threadID < ActiveThreads);
1163 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1165 // Initialize, and make an early exit in case of an aborted search,
1166 // an instant draw, maximum ply reached, etc.
1167 init_node(pos, ss, ply, threadID);
1169 // After init_node() that calls poll()
1170 if (AbortSearch || thread_should_stop(threadID))
1178 if (ply >= PLY_MAX - 1)
1179 return evaluate(pos, ei, threadID);
1181 // Mate distance pruning
1182 if (value_mated_in(ply) >= beta)
1185 if (value_mate_in(ply + 1) < beta)
1188 // Transposition table lookup
1189 const TTEntry* tte = TT.retrieve(pos);
1190 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1192 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1194 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1195 return value_from_tt(tte->value(), ply);
1198 Value approximateEval = quick_evaluate(pos);
1199 bool mateThreat = false;
1200 bool isCheck = pos.is_check();
1206 && !value_is_mate(beta)
1207 && ok_to_do_nullmove(pos)
1208 && approximateEval >= beta - NullMoveMargin)
1210 //Calculate correct delta. Idea and tuning from Joona Kiiski.
1211 ScaleFactor factor[2] = { SCALE_FACTOR_NORMAL, SCALE_FACTOR_NORMAL };
1212 Phase phase = pos.game_phase();
1213 int i = Min(depth / OnePly, 9);
1214 Value delta = scale_by_game_phase(NullMoveDeltaMidgame[i], NullMoveDeltaEndgame[i], phase, factor);
1216 ss[ply].currentMove = MOVE_NULL;
1219 pos.do_null_move(st);
1220 int R = (depth >= 4 * OnePly ? 4 : 3); // Null move dynamic reduction
1222 Value nullValue = -search(pos, ss, -(beta-delta-1), depth-R*OnePly, ply+1, false, threadID);
1224 pos.undo_null_move();
1226 if (value_is_mate(nullValue))
1228 /* Do not return unproven mates */
1230 else if (nullValue >= beta - delta)
1232 if (depth < 6 * OnePly)
1235 // Do zugzwang verification search
1236 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1240 // The null move failed low, which means that we may be faced with
1241 // some kind of threat. If the previous move was reduced, check if
1242 // the move that refuted the null move was somehow connected to the
1243 // move which was reduced. If a connection is found, return a fail
1244 // low score (which will cause the reduced move to fail high in the
1245 // parent node, which will trigger a re-search with full depth).
1246 if (nullValue == value_mated_in(ply + 2))
1249 ss[ply].threatMove = ss[ply + 1].currentMove;
1250 if ( depth < ThreatDepth
1251 && ss[ply - 1].reduction
1252 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1256 // Null move search not allowed, try razoring
1257 else if ( !value_is_mate(beta)
1258 && approximateEval < beta - RazorMargin
1259 && depth < RazorDepth
1260 && (RazorAtDepthOne || depth > OnePly)
1261 && ttMove == MOVE_NONE
1262 && !pos.has_pawn_on_7th(pos.side_to_move()))
1264 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1265 if ( (v < beta - RazorMargin - RazorMargin / 4)
1266 || (depth < 3*OnePly && v < beta - RazorMargin)
1267 || (depth < 2*OnePly && v < beta - RazorMargin / 2))
1271 // Go with internal iterative deepening if we don't have a TT move
1272 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1273 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1275 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1276 ttMove = ss[ply].pv[ply];
1279 // Initialize a MovePicker object for the current position, and prepare
1280 // to search all moves:
1281 MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth);
1283 Move move, movesSearched[256];
1285 Value value, bestValue = -VALUE_INFINITE;
1286 Bitboard dcCandidates = mp.discovered_check_candidates();
1287 Value futilityValue = VALUE_NONE;
1288 bool useFutilityPruning = UseFutilityPruning
1289 && depth < SelectiveDepth
1292 // Loop through all legal moves until no moves remain or a beta cutoff
1294 while ( bestValue < beta
1295 && (move = mp.get_next_move()) != MOVE_NONE
1296 && !thread_should_stop(threadID))
1298 assert(move_is_ok(move));
1300 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1301 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1302 bool moveIsCapture = pos.move_is_capture(move);
1304 movesSearched[moveCount++] = ss[ply].currentMove = move;
1306 // Decide the new search depth
1308 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1309 Depth newDepth = depth - OnePly + ext;
1312 if ( useFutilityPruning
1315 && !move_promotion(move))
1317 // History pruning. See ok_to_prune() definition
1318 if ( moveCount >= 2 + int(depth)
1319 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1322 // Value based pruning
1323 if (depth < 7 * OnePly && approximateEval < beta)
1325 if (futilityValue == VALUE_NONE)
1326 futilityValue = evaluate(pos, ei, threadID)
1327 + FutilityMargins[int(depth)/2 - 1]
1330 if (futilityValue < beta)
1332 if (futilityValue > bestValue)
1333 bestValue = futilityValue;
1339 // Make and search the move
1341 pos.do_move(move, st, dcCandidates);
1343 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1344 // if the move fails high will be re-searched at full depth.
1345 if ( depth >= 2*OnePly
1346 && moveCount >= LMRNonPVMoves
1349 && !move_promotion(move)
1350 && !move_is_castle(move)
1351 && !move_is_killer(move, ss[ply]))
1353 ss[ply].reduction = OnePly;
1354 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1357 value = beta; // Just to trigger next condition
1359 if (value >= beta) // Go with full depth non-pv search
1361 ss[ply].reduction = Depth(0);
1362 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1364 pos.undo_move(move);
1366 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1369 if (value > bestValue)
1375 if (value == value_mate_in(ply + 1))
1376 ss[ply].mateKiller = move;
1380 if ( ActiveThreads > 1
1382 && depth >= MinimumSplitDepth
1384 && idle_thread_exists(threadID)
1386 && !thread_should_stop(threadID)
1387 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1388 &mp, dcCandidates, threadID, false))
1392 // All legal moves have been searched. A special case: If there were
1393 // no legal moves, it must be mate or stalemate.
1395 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1397 // If the search is not aborted, update the transposition table,
1398 // history counters, and killer moves.
1399 if (AbortSearch || thread_should_stop(threadID))
1402 if (bestValue < beta)
1403 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
1406 BetaCounter.add(pos.side_to_move(), depth, threadID);
1407 Move m = ss[ply].pv[ply];
1408 if (ok_to_history(pos, m)) // Only non capture moves are considered
1410 update_history(pos, m, depth, movesSearched, moveCount);
1411 update_killers(m, ss[ply]);
1413 TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
1419 // qsearch() is the quiescence search function, which is called by the main
1420 // search function when the remaining depth is zero (or, to be more precise,
1421 // less than OnePly).
1423 Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
1424 Depth depth, int ply, int threadID) {
1426 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1427 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1429 assert(ply >= 0 && ply < PLY_MAX);
1430 assert(threadID >= 0 && threadID < ActiveThreads);
1432 // Initialize, and make an early exit in case of an aborted search,
1433 // an instant draw, maximum ply reached, etc.
1434 init_node(pos, ss, ply, threadID);
1436 // After init_node() that calls poll()
1437 if (AbortSearch || thread_should_stop(threadID))
1443 // Transposition table lookup
1444 const TTEntry* tte = TT.retrieve(pos);
1445 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1446 return value_from_tt(tte->value(), ply);
1448 // Evaluate the position statically
1450 bool isCheck = pos.is_check();
1451 Value staticValue = (isCheck ? -VALUE_INFINITE : evaluate(pos, ei, threadID));
1453 if (ply == PLY_MAX - 1)
1454 return evaluate(pos, ei, threadID);
1456 // Initialize "stand pat score", and return it immediately if it is
1458 Value bestValue = staticValue;
1460 if (bestValue >= beta)
1463 if (bestValue > alpha)
1466 // Initialize a MovePicker object for the current position, and prepare
1467 // to search the moves. Because the depth is <= 0 here, only captures,
1468 // queen promotions and checks (only if depth == 0) will be generated.
1469 bool pvNode = (beta - alpha != 1);
1470 MovePicker mp = MovePicker(pos, pvNode, MOVE_NONE, EmptySearchStack, depth, isCheck ? NULL : &ei);
1473 Bitboard dcCandidates = mp.discovered_check_candidates();
1474 Color us = pos.side_to_move();
1475 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1477 // Loop through the moves until no moves remain or a beta cutoff
1479 while ( alpha < beta
1480 && (move = mp.get_next_move()) != MOVE_NONE)
1482 assert(move_is_ok(move));
1485 ss[ply].currentMove = move;
1488 if ( UseQSearchFutilityPruning
1492 && !move_promotion(move)
1493 && !pos.move_is_check(move, dcCandidates)
1494 && !pos.move_is_passed_pawn_push(move))
1496 Value futilityValue = staticValue
1497 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1498 pos.endgame_value_of_piece_on(move_to(move)))
1499 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1501 + ei.futilityMargin;
1503 if (futilityValue < alpha)
1505 if (futilityValue > bestValue)
1506 bestValue = futilityValue;
1511 // Don't search captures and checks with negative SEE values
1513 && !move_promotion(move)
1514 && (pos.midgame_value_of_piece_on(move_from(move)) >
1515 pos.midgame_value_of_piece_on(move_to(move)))
1516 && pos.see(move) < 0)
1519 // Make and search the move.
1521 pos.do_move(move, st, dcCandidates);
1522 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1523 pos.undo_move(move);
1525 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1528 if (value > bestValue)
1539 // All legal moves have been searched. A special case: If we're in check
1540 // and no legal moves were found, it is checkmate:
1541 if (pos.is_check() && moveCount == 0) // Mate!
1542 return value_mated_in(ply);
1544 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1546 // Update transposition table
1547 TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_EXACT);
1549 // Update killers only for good check moves
1550 Move m = ss[ply].currentMove;
1551 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1553 // Wrong to update history when depth is <= 0
1554 update_killers(m, ss[ply]);
1560 // sp_search() is used to search from a split point. This function is called
1561 // by each thread working at the split point. It is similar to the normal
1562 // search() function, but simpler. Because we have already probed the hash
1563 // table, done a null move search, and searched the first move before
1564 // splitting, we don't have to repeat all this work in sp_search(). We
1565 // also don't need to store anything to the hash table here: This is taken
1566 // care of after we return from the split point.
1568 void sp_search(SplitPoint *sp, int threadID) {
1570 assert(threadID >= 0 && threadID < ActiveThreads);
1571 assert(ActiveThreads > 1);
1573 Position pos = Position(sp->pos);
1574 SearchStack *ss = sp->sstack[threadID];
1577 bool isCheck = pos.is_check();
1578 bool useFutilityPruning = UseFutilityPruning
1579 && sp->depth < SelectiveDepth
1582 while ( sp->bestValue < sp->beta
1583 && !thread_should_stop(threadID)
1584 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1586 assert(move_is_ok(move));
1588 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1589 bool moveIsCapture = pos.move_is_capture(move);
1591 lock_grab(&(sp->lock));
1592 int moveCount = ++sp->moves;
1593 lock_release(&(sp->lock));
1595 ss[sp->ply].currentMove = move;
1597 // Decide the new search depth.
1599 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1600 Depth newDepth = sp->depth - OnePly + ext;
1603 if ( useFutilityPruning
1606 && !move_promotion(move)
1607 && moveCount >= 2 + int(sp->depth)
1608 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1611 // Make and search the move.
1613 pos.do_move(move, st, sp->dcCandidates);
1615 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1616 // if the move fails high will be re-searched at full depth.
1618 && moveCount >= LMRNonPVMoves
1620 && !move_promotion(move)
1621 && !move_is_castle(move)
1622 && !move_is_killer(move, ss[sp->ply]))
1624 ss[sp->ply].reduction = OnePly;
1625 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1628 value = sp->beta; // Just to trigger next condition
1630 if (value >= sp->beta) // Go with full depth non-pv search
1632 ss[sp->ply].reduction = Depth(0);
1633 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1635 pos.undo_move(move);
1637 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1639 if (thread_should_stop(threadID))
1643 lock_grab(&(sp->lock));
1644 if (value > sp->bestValue && !thread_should_stop(threadID))
1646 sp->bestValue = value;
1647 if (sp->bestValue >= sp->beta)
1649 sp_update_pv(sp->parentSstack, ss, sp->ply);
1650 for (int i = 0; i < ActiveThreads; i++)
1651 if (i != threadID && (i == sp->master || sp->slaves[i]))
1652 Threads[i].stop = true;
1654 sp->finished = true;
1657 lock_release(&(sp->lock));
1660 lock_grab(&(sp->lock));
1662 // If this is the master thread and we have been asked to stop because of
1663 // a beta cutoff higher up in the tree, stop all slave threads:
1664 if (sp->master == threadID && thread_should_stop(threadID))
1665 for (int i = 0; i < ActiveThreads; i++)
1667 Threads[i].stop = true;
1670 sp->slaves[threadID] = 0;
1672 lock_release(&(sp->lock));
1676 // sp_search_pv() is used to search from a PV split point. This function
1677 // is called by each thread working at the split point. It is similar to
1678 // the normal search_pv() function, but simpler. Because we have already
1679 // probed the hash table and searched the first move before splitting, we
1680 // don't have to repeat all this work in sp_search_pv(). We also don't
1681 // need to store anything to the hash table here: This is taken care of
1682 // after we return from the split point.
1684 void sp_search_pv(SplitPoint *sp, int threadID) {
1686 assert(threadID >= 0 && threadID < ActiveThreads);
1687 assert(ActiveThreads > 1);
1689 Position pos = Position(sp->pos);
1690 SearchStack *ss = sp->sstack[threadID];
1694 while ( sp->alpha < sp->beta
1695 && !thread_should_stop(threadID)
1696 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1698 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1699 bool moveIsCapture = pos.move_is_capture(move);
1701 assert(move_is_ok(move));
1704 ss[sp->ply].currentMoveCaptureValue =
1705 move_is_ep(move)? PawnValueMidgame : pos.midgame_value_of_piece_on(move_to(move));
1707 ss[sp->ply].currentMoveCaptureValue = Value(0);
1709 lock_grab(&(sp->lock));
1710 int moveCount = ++sp->moves;
1711 lock_release(&(sp->lock));
1713 ss[sp->ply].currentMove = move;
1715 // Decide the new search depth.
1717 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1718 Depth newDepth = sp->depth - OnePly + ext;
1720 // Make and search the move.
1722 pos.do_move(move, st, sp->dcCandidates);
1724 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1725 // if the move fails high will be re-searched at full depth.
1727 && moveCount >= LMRPVMoves
1729 && !move_promotion(move)
1730 && !move_is_castle(move)
1731 && !move_is_killer(move, ss[sp->ply]))
1733 ss[sp->ply].reduction = OnePly;
1734 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1737 value = sp->alpha + 1; // Just to trigger next condition
1739 if (value > sp->alpha) // Go with full depth non-pv search
1741 ss[sp->ply].reduction = Depth(0);
1742 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1744 if (value > sp->alpha && value < sp->beta)
1746 // When the search fails high at ply 1 while searching the first
1747 // move at the root, set the flag failHighPly1. This is used for
1748 // time managment: We don't want to stop the search early in
1749 // such cases, because resolving the fail high at ply 1 could
1750 // result in a big drop in score at the root.
1751 if (sp->ply == 1 && RootMoveNumber == 1)
1752 Threads[threadID].failHighPly1 = true;
1754 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1755 Threads[threadID].failHighPly1 = false;
1758 pos.undo_move(move);
1760 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1762 if (thread_should_stop(threadID))
1766 lock_grab(&(sp->lock));
1767 if (value > sp->bestValue && !thread_should_stop(threadID))
1769 sp->bestValue = value;
1770 if (value > sp->alpha)
1773 sp_update_pv(sp->parentSstack, ss, sp->ply);
1774 if (value == value_mate_in(sp->ply + 1))
1775 ss[sp->ply].mateKiller = move;
1777 if(value >= sp->beta)
1779 for(int i = 0; i < ActiveThreads; i++)
1780 if(i != threadID && (i == sp->master || sp->slaves[i]))
1781 Threads[i].stop = true;
1783 sp->finished = true;
1786 // If we are at ply 1, and we are searching the first root move at
1787 // ply 0, set the 'Problem' variable if the score has dropped a lot
1788 // (from the computer's point of view) since the previous iteration.
1791 && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
1794 lock_release(&(sp->lock));
1797 lock_grab(&(sp->lock));
1799 // If this is the master thread and we have been asked to stop because of
1800 // a beta cutoff higher up in the tree, stop all slave threads.
1801 if (sp->master == threadID && thread_should_stop(threadID))
1802 for (int i = 0; i < ActiveThreads; i++)
1804 Threads[i].stop = true;
1807 sp->slaves[threadID] = 0;
1809 lock_release(&(sp->lock));
1812 /// The BetaCounterType class
1814 BetaCounterType::BetaCounterType() { clear(); }
1816 void BetaCounterType::clear() {
1818 for (int i = 0; i < THREAD_MAX; i++)
1819 hits[i][WHITE] = hits[i][BLACK] = 0ULL;
1822 void BetaCounterType::add(Color us, Depth d, int threadID) {
1824 // Weighted count based on depth
1825 hits[threadID][us] += int(d);
1828 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1831 for (int i = 0; i < THREAD_MAX; i++)
1834 their += hits[i][opposite_color(us)];
1839 /// The RootMove class
1843 RootMove::RootMove() {
1844 nodes = cumulativeNodes = 0ULL;
1847 // RootMove::operator<() is the comparison function used when
1848 // sorting the moves. A move m1 is considered to be better
1849 // than a move m2 if it has a higher score, or if the moves
1850 // have equal score but m1 has the higher node count.
1852 bool RootMove::operator<(const RootMove& m) {
1854 if (score != m.score)
1855 return (score < m.score);
1857 return theirBeta <= m.theirBeta;
1860 /// The RootMoveList class
1864 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1866 MoveStack mlist[MaxRootMoves];
1867 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1869 // Generate all legal moves
1870 int lm_count = generate_legal_moves(pos, mlist);
1872 // Add each move to the moves[] array
1873 for (int i = 0; i < lm_count; i++)
1875 bool includeMove = includeAllMoves;
1877 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1878 includeMove = (searchMoves[k] == mlist[i].move);
1882 // Find a quick score for the move
1884 SearchStack ss[PLY_MAX_PLUS_2];
1886 moves[count].move = mlist[i].move;
1887 moves[count].nodes = 0ULL;
1888 pos.do_move(moves[count].move, st);
1889 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE,
1891 pos.undo_move(moves[count].move);
1892 moves[count].pv[0] = moves[i].move;
1893 moves[count].pv[1] = MOVE_NONE; // FIXME
1901 // Simple accessor methods for the RootMoveList class
1903 inline Move RootMoveList::get_move(int moveNum) const {
1904 return moves[moveNum].move;
1907 inline Value RootMoveList::get_move_score(int moveNum) const {
1908 return moves[moveNum].score;
1911 inline void RootMoveList::set_move_score(int moveNum, Value score) {
1912 moves[moveNum].score = score;
1915 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
1916 moves[moveNum].nodes = nodes;
1917 moves[moveNum].cumulativeNodes += nodes;
1920 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
1921 moves[moveNum].ourBeta = our;
1922 moves[moveNum].theirBeta = their;
1925 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
1927 for(j = 0; pv[j] != MOVE_NONE; j++)
1928 moves[moveNum].pv[j] = pv[j];
1929 moves[moveNum].pv[j] = MOVE_NONE;
1932 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
1933 return moves[moveNum].pv[i];
1936 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
1937 return moves[moveNum].cumulativeNodes;
1940 inline int RootMoveList::move_count() const {
1945 // RootMoveList::scan_for_easy_move() is called at the end of the first
1946 // iteration, and is used to detect an "easy move", i.e. a move which appears
1947 // to be much bester than all the rest. If an easy move is found, the move
1948 // is returned, otherwise the function returns MOVE_NONE. It is very
1949 // important that this function is called at the right moment: The code
1950 // assumes that the first iteration has been completed and the moves have
1951 // been sorted. This is done in RootMoveList c'tor.
1953 Move RootMoveList::scan_for_easy_move() const {
1960 // moves are sorted so just consider the best and the second one
1961 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
1967 // RootMoveList::sort() sorts the root move list at the beginning of a new
1970 inline void RootMoveList::sort() {
1972 sort_multipv(count - 1); // all items
1976 // RootMoveList::sort_multipv() sorts the first few moves in the root move
1977 // list by their scores and depths. It is used to order the different PVs
1978 // correctly in MultiPV mode.
1980 void RootMoveList::sort_multipv(int n) {
1982 for (int i = 1; i <= n; i++)
1984 RootMove rm = moves[i];
1986 for (j = i; j > 0 && moves[j-1] < rm; j--)
1987 moves[j] = moves[j-1];
1993 // init_node() is called at the beginning of all the search functions
1994 // (search(), search_pv(), qsearch(), and so on) and initializes the search
1995 // stack object corresponding to the current node. Once every
1996 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
1997 // for user input and checks whether it is time to stop the search.
1999 void init_node(const Position &pos, SearchStack ss[], int ply, int threadID) {
2000 assert(ply >= 0 && ply < PLY_MAX);
2001 assert(threadID >= 0 && threadID < ActiveThreads);
2003 Threads[threadID].nodes++;
2007 if(NodesSincePoll >= NodesBetweenPolls) {
2014 ss[ply+2].initKillers();
2016 if(Threads[threadID].printCurrentLine)
2017 print_current_line(ss, ply, threadID);
2021 // update_pv() is called whenever a search returns a value > alpha. It
2022 // updates the PV in the SearchStack object corresponding to the current
2025 void update_pv(SearchStack ss[], int ply) {
2026 assert(ply >= 0 && ply < PLY_MAX);
2028 ss[ply].pv[ply] = ss[ply].currentMove;
2030 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2031 ss[ply].pv[p] = ss[ply+1].pv[p];
2032 ss[ply].pv[p] = MOVE_NONE;
2036 // sp_update_pv() is a variant of update_pv for use at split points. The
2037 // difference between the two functions is that sp_update_pv also updates
2038 // the PV at the parent node.
2040 void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply) {
2041 assert(ply >= 0 && ply < PLY_MAX);
2043 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2045 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2046 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2047 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2051 // connected_moves() tests whether two moves are 'connected' in the sense
2052 // that the first move somehow made the second move possible (for instance
2053 // if the moving piece is the same in both moves). The first move is
2054 // assumed to be the move that was made to reach the current position, while
2055 // the second move is assumed to be a move from the current position.
2057 bool connected_moves(const Position &pos, Move m1, Move m2) {
2058 Square f1, t1, f2, t2;
2060 assert(move_is_ok(m1));
2061 assert(move_is_ok(m2));
2066 // Case 1: The moving piece is the same in both moves.
2072 // Case 2: The destination square for m2 was vacated by m1.
2078 // Case 3: Moving through the vacated square:
2079 if(piece_is_slider(pos.piece_on(f2)) &&
2080 bit_is_set(squares_between(f2, t2), f1))
2083 // Case 4: The destination square for m2 is attacked by the moving piece
2085 if(pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
2088 // Case 5: Discovered check, checking piece is the piece moved in m1:
2089 if(piece_is_slider(pos.piece_on(t1)) &&
2090 bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())),
2092 !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())),
2094 Bitboard occ = pos.occupied_squares();
2095 Color us = pos.side_to_move();
2096 Square ksq = pos.king_square(us);
2097 clear_bit(&occ, f2);
2098 if(pos.type_of_piece_on(t1) == BISHOP) {
2099 if(bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2102 else if(pos.type_of_piece_on(t1) == ROOK) {
2103 if(bit_is_set(rook_attacks_bb(ksq, occ), t1))
2107 assert(pos.type_of_piece_on(t1) == QUEEN);
2108 if(bit_is_set(queen_attacks_bb(ksq, occ), t1))
2117 // value_is_mate() checks if the given value is a mate one
2118 // eventually compensated for the ply.
2120 bool value_is_mate(Value value) {
2122 assert(abs(value) <= VALUE_INFINITE);
2124 return value <= value_mated_in(PLY_MAX)
2125 || value >= value_mate_in(PLY_MAX);
2129 // move_is_killer() checks if the given move is among the
2130 // killer moves of that ply.
2132 bool move_is_killer(Move m, const SearchStack& ss) {
2134 const Move* k = ss.killers;
2135 for (int i = 0; i < KILLER_MAX; i++, k++)
2143 // extension() decides whether a move should be searched with normal depth,
2144 // or with extended depth. Certain classes of moves (checking moves, in
2145 // particular) are searched with bigger depth than ordinary moves and in
2146 // any case are marked as 'dangerous'. Note that also if a move is not
2147 // extended, as example because the corresponding UCI option is set to zero,
2148 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2150 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2151 bool singleReply, bool mateThreat, bool* dangerous) {
2153 assert(m != MOVE_NONE);
2155 Depth result = Depth(0);
2156 *dangerous = check || singleReply || mateThreat;
2159 result += CheckExtension[pvNode];
2162 result += SingleReplyExtension[pvNode];
2165 result += MateThreatExtension[pvNode];
2167 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2169 if (pos.move_is_pawn_push_to_7th(m))
2171 result += PawnPushTo7thExtension[pvNode];
2174 if (pos.move_is_passed_pawn_push(m))
2176 result += PassedPawnExtension[pvNode];
2182 && pos.type_of_piece_on(move_to(m)) != PAWN
2183 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2184 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2185 && !move_promotion(m)
2188 result += PawnEndgameExtension[pvNode];
2194 && pos.type_of_piece_on(move_to(m)) != PAWN
2201 return Min(result, OnePly);
2205 // ok_to_do_nullmove() looks at the current position and decides whether
2206 // doing a 'null move' should be allowed. In order to avoid zugzwang
2207 // problems, null moves are not allowed when the side to move has very
2208 // little material left. Currently, the test is a bit too simple: Null
2209 // moves are avoided only when the side to move has only pawns left. It's
2210 // probably a good idea to avoid null moves in at least some more
2211 // complicated endgames, e.g. KQ vs KR. FIXME
2213 bool ok_to_do_nullmove(const Position &pos) {
2214 if(pos.non_pawn_material(pos.side_to_move()) == Value(0))
2220 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2221 // non-tactical moves late in the move list close to the leaves are
2222 // candidates for pruning.
2224 bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d) {
2225 Square mfrom, mto, tfrom, tto;
2227 assert(move_is_ok(m));
2228 assert(threat == MOVE_NONE || move_is_ok(threat));
2229 assert(!move_promotion(m));
2230 assert(!pos.move_is_check(m));
2231 assert(!pos.move_is_capture(m));
2232 assert(!pos.move_is_passed_pawn_push(m));
2233 assert(d >= OnePly);
2235 mfrom = move_from(m);
2237 tfrom = move_from(threat);
2238 tto = move_to(threat);
2240 // Case 1: Castling moves are never pruned.
2241 if (move_is_castle(m))
2244 // Case 2: Don't prune moves which move the threatened piece
2245 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2248 // Case 3: If the threatened piece has value less than or equal to the
2249 // value of the threatening piece, don't prune move which defend it.
2250 if ( !PruneDefendingMoves
2251 && threat != MOVE_NONE
2252 && pos.move_is_capture(threat)
2253 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2254 || pos.type_of_piece_on(tfrom) == KING)
2255 && pos.move_attacks_square(m, tto))
2258 // Case 4: Don't prune moves with good history.
2259 if (!H.ok_to_prune(pos.piece_on(move_from(m)), m, d))
2262 // Case 5: If the moving piece in the threatened move is a slider, don't
2263 // prune safe moves which block its ray.
2264 if ( !PruneBlockingMoves
2265 && threat != MOVE_NONE
2266 && piece_is_slider(pos.piece_on(tfrom))
2267 && bit_is_set(squares_between(tfrom, tto), mto)
2275 // ok_to_use_TT() returns true if a transposition table score
2276 // can be used at a given point in search.
2278 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2280 Value v = value_from_tt(tte->value(), ply);
2282 return ( tte->depth() >= depth
2283 || v >= Max(value_mate_in(100), beta)
2284 || v < Min(value_mated_in(100), beta))
2286 && ( (is_lower_bound(tte->type()) && v >= beta)
2287 || (is_upper_bound(tte->type()) && v < beta));
2291 // ok_to_history() returns true if a move m can be stored
2292 // in history. Should be a non capturing move nor a promotion.
2294 bool ok_to_history(const Position& pos, Move m) {
2296 return !pos.move_is_capture(m) && !move_promotion(m);
2300 // update_history() registers a good move that produced a beta-cutoff
2301 // in history and marks as failures all the other moves of that ply.
2303 void update_history(const Position& pos, Move m, Depth depth,
2304 Move movesSearched[], int moveCount) {
2306 H.success(pos.piece_on(move_from(m)), m, depth);
2308 for (int i = 0; i < moveCount - 1; i++)
2310 assert(m != movesSearched[i]);
2311 if (ok_to_history(pos, movesSearched[i]))
2312 H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
2317 // update_killers() add a good move that produced a beta-cutoff
2318 // among the killer moves of that ply.
2320 void update_killers(Move m, SearchStack& ss) {
2322 if (m == ss.killers[0])
2325 for (int i = KILLER_MAX - 1; i > 0; i--)
2326 ss.killers[i] = ss.killers[i - 1];
2331 // fail_high_ply_1() checks if some thread is currently resolving a fail
2332 // high at ply 1 at the node below the first root node. This information
2333 // is used for time managment.
2335 bool fail_high_ply_1() {
2336 for(int i = 0; i < ActiveThreads; i++)
2337 if(Threads[i].failHighPly1)
2343 // current_search_time() returns the number of milliseconds which have passed
2344 // since the beginning of the current search.
2346 int current_search_time() {
2347 return get_system_time() - SearchStartTime;
2351 // nps() computes the current nodes/second count.
2354 int t = current_search_time();
2355 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2359 // poll() performs two different functions: It polls for user input, and it
2360 // looks at the time consumed so far and decides if it's time to abort the
2365 static int lastInfoTime;
2366 int t = current_search_time();
2371 // We are line oriented, don't read single chars
2372 std::string command;
2373 if (!std::getline(std::cin, command))
2376 if (command == "quit")
2379 PonderSearch = false;
2382 else if(command == "stop")
2385 PonderSearch = false;
2387 else if(command == "ponderhit")
2390 // Print search information
2394 else if (lastInfoTime > t)
2395 // HACK: Must be a new search where we searched less than
2396 // NodesBetweenPolls nodes during the first second of search.
2399 else if (t - lastInfoTime >= 1000)
2406 if (dbg_show_hit_rate)
2407 dbg_print_hit_rate();
2409 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2410 << " time " << t << " hashfull " << TT.full() << std::endl;
2411 lock_release(&IOLock);
2412 if (ShowCurrentLine)
2413 Threads[0].printCurrentLine = true;
2415 // Should we stop the search?
2419 bool overTime = t > AbsoluteMaxSearchTime
2420 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime)
2421 || ( !FailHigh && !fail_high_ply_1() && !Problem
2422 && t > 6*(MaxSearchTime + ExtraSearchTime));
2424 if ( (Iteration >= 2 && (!InfiniteSearch && overTime))
2425 || (ExactMaxTime && t >= ExactMaxTime)
2426 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2431 // ponderhit() is called when the program is pondering (i.e. thinking while
2432 // it's the opponent's turn to move) in order to let the engine know that
2433 // it correctly predicted the opponent's move.
2436 int t = current_search_time();
2437 PonderSearch = false;
2438 if(Iteration >= 2 &&
2439 (!InfiniteSearch && (StopOnPonderhit ||
2440 t > AbsoluteMaxSearchTime ||
2441 (RootMoveNumber == 1 &&
2442 t > MaxSearchTime + ExtraSearchTime) ||
2443 (!FailHigh && !fail_high_ply_1() && !Problem &&
2444 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2449 // print_current_line() prints the current line of search for a given
2450 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2452 void print_current_line(SearchStack ss[], int ply, int threadID) {
2453 assert(ply >= 0 && ply < PLY_MAX);
2454 assert(threadID >= 0 && threadID < ActiveThreads);
2456 if(!Threads[threadID].idle) {
2458 std::cout << "info currline " << (threadID + 1);
2459 for(int p = 0; p < ply; p++)
2460 std::cout << " " << ss[p].currentMove;
2461 std::cout << std::endl;
2462 lock_release(&IOLock);
2464 Threads[threadID].printCurrentLine = false;
2465 if(threadID + 1 < ActiveThreads)
2466 Threads[threadID + 1].printCurrentLine = true;
2470 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2471 // while the program is pondering. The point is to work around a wrinkle in
2472 // the UCI protocol: When pondering, the engine is not allowed to give a
2473 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2474 // We simply wait here until one of these commands is sent, and return,
2475 // after which the bestmove and pondermove will be printed (in id_loop()).
2477 void wait_for_stop_or_ponderhit() {
2478 std::string command;
2481 if(!std::getline(std::cin, command))
2484 if(command == "quit") {
2485 OpeningBook.close();
2490 else if(command == "ponderhit" || command == "stop")
2496 // idle_loop() is where the threads are parked when they have no work to do.
2497 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2498 // object for which the current thread is the master.
2500 void idle_loop(int threadID, SplitPoint *waitSp) {
2501 assert(threadID >= 0 && threadID < THREAD_MAX);
2503 Threads[threadID].running = true;
2506 if(AllThreadsShouldExit && threadID != 0)
2509 // If we are not thinking, wait for a condition to be signaled instead
2510 // of wasting CPU time polling for work:
2511 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2512 #if !defined(_MSC_VER)
2513 pthread_mutex_lock(&WaitLock);
2514 if(Idle || threadID >= ActiveThreads)
2515 pthread_cond_wait(&WaitCond, &WaitLock);
2516 pthread_mutex_unlock(&WaitLock);
2518 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2522 // If this thread has been assigned work, launch a search:
2523 if(Threads[threadID].workIsWaiting) {
2524 Threads[threadID].workIsWaiting = false;
2525 if(Threads[threadID].splitPoint->pvNode)
2526 sp_search_pv(Threads[threadID].splitPoint, threadID);
2528 sp_search(Threads[threadID].splitPoint, threadID);
2529 Threads[threadID].idle = true;
2532 // If this thread is the master of a split point and all threads have
2533 // finished their work at this split point, return from the idle loop:
2534 if(waitSp != NULL && waitSp->cpus == 0)
2538 Threads[threadID].running = false;
2542 // init_split_point_stack() is called during program initialization, and
2543 // initializes all split point objects.
2545 void init_split_point_stack() {
2546 for(int i = 0; i < THREAD_MAX; i++)
2547 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2548 SplitPointStack[i][j].parent = NULL;
2549 lock_init(&(SplitPointStack[i][j].lock), NULL);
2554 // destroy_split_point_stack() is called when the program exits, and
2555 // destroys all locks in the precomputed split point objects.
2557 void destroy_split_point_stack() {
2558 for(int i = 0; i < THREAD_MAX; i++)
2559 for(int j = 0; j < MaxActiveSplitPoints; j++)
2560 lock_destroy(&(SplitPointStack[i][j].lock));
2564 // thread_should_stop() checks whether the thread with a given threadID has
2565 // been asked to stop, directly or indirectly. This can happen if a beta
2566 // cutoff has occured in thre thread's currently active split point, or in
2567 // some ancestor of the current split point.
2569 bool thread_should_stop(int threadID) {
2570 assert(threadID >= 0 && threadID < ActiveThreads);
2574 if(Threads[threadID].stop)
2576 if(ActiveThreads <= 2)
2578 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2580 Threads[threadID].stop = true;
2587 // thread_is_available() checks whether the thread with threadID "slave" is
2588 // available to help the thread with threadID "master" at a split point. An
2589 // obvious requirement is that "slave" must be idle. With more than two
2590 // threads, this is not by itself sufficient: If "slave" is the master of
2591 // some active split point, it is only available as a slave to the other
2592 // threads which are busy searching the split point at the top of "slave"'s
2593 // split point stack (the "helpful master concept" in YBWC terminology).
2595 bool thread_is_available(int slave, int master) {
2596 assert(slave >= 0 && slave < ActiveThreads);
2597 assert(master >= 0 && master < ActiveThreads);
2598 assert(ActiveThreads > 1);
2600 if(!Threads[slave].idle || slave == master)
2603 if(Threads[slave].activeSplitPoints == 0)
2604 // No active split points means that the thread is available as a slave
2605 // for any other thread.
2608 if(ActiveThreads == 2)
2611 // Apply the "helpful master" concept if possible.
2612 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2619 // idle_thread_exists() tries to find an idle thread which is available as
2620 // a slave for the thread with threadID "master".
2622 bool idle_thread_exists(int master) {
2623 assert(master >= 0 && master < ActiveThreads);
2624 assert(ActiveThreads > 1);
2626 for(int i = 0; i < ActiveThreads; i++)
2627 if(thread_is_available(i, master))
2633 // split() does the actual work of distributing the work at a node between
2634 // several threads at PV nodes. If it does not succeed in splitting the
2635 // node (because no idle threads are available, or because we have no unused
2636 // split point objects), the function immediately returns false. If
2637 // splitting is possible, a SplitPoint object is initialized with all the
2638 // data that must be copied to the helper threads (the current position and
2639 // search stack, alpha, beta, the search depth, etc.), and we tell our
2640 // helper threads that they have been assigned work. This will cause them
2641 // to instantly leave their idle loops and call sp_search_pv(). When all
2642 // threads have returned from sp_search_pv (or, equivalently, when
2643 // splitPoint->cpus becomes 0), split() returns true.
2645 bool split(const Position &p, SearchStack *sstck, int ply,
2646 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
2647 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode) {
2650 assert(sstck != NULL);
2651 assert(ply >= 0 && ply < PLY_MAX);
2652 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2653 assert(!pvNode || *alpha < *beta);
2654 assert(*beta <= VALUE_INFINITE);
2655 assert(depth > Depth(0));
2656 assert(master >= 0 && master < ActiveThreads);
2657 assert(ActiveThreads > 1);
2659 SplitPoint *splitPoint;
2664 // If no other thread is available to help us, or if we have too many
2665 // active split points, don't split:
2666 if(!idle_thread_exists(master) ||
2667 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2668 lock_release(&MPLock);
2672 // Pick the next available split point object from the split point stack:
2673 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2674 Threads[master].activeSplitPoints++;
2676 // Initialize the split point object:
2677 splitPoint->parent = Threads[master].splitPoint;
2678 splitPoint->finished = false;
2679 splitPoint->ply = ply;
2680 splitPoint->depth = depth;
2681 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2682 splitPoint->beta = *beta;
2683 splitPoint->pvNode = pvNode;
2684 splitPoint->dcCandidates = dcCandidates;
2685 splitPoint->bestValue = *bestValue;
2686 splitPoint->master = master;
2687 splitPoint->mp = mp;
2688 splitPoint->moves = *moves;
2689 splitPoint->cpus = 1;
2690 splitPoint->pos.copy(p);
2691 splitPoint->parentSstack = sstck;
2692 for(i = 0; i < ActiveThreads; i++)
2693 splitPoint->slaves[i] = 0;
2695 // Copy the current position and the search stack to the master thread:
2696 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2697 Threads[master].splitPoint = splitPoint;
2699 // Make copies of the current position and search stack for each thread:
2700 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2702 if(thread_is_available(i, master)) {
2703 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2704 Threads[i].splitPoint = splitPoint;
2705 splitPoint->slaves[i] = 1;
2709 // Tell the threads that they have work to do. This will make them leave
2711 for(i = 0; i < ActiveThreads; i++)
2712 if(i == master || splitPoint->slaves[i]) {
2713 Threads[i].workIsWaiting = true;
2714 Threads[i].idle = false;
2715 Threads[i].stop = false;
2718 lock_release(&MPLock);
2720 // Everything is set up. The master thread enters the idle loop, from
2721 // which it will instantly launch a search, because its workIsWaiting
2722 // slot is 'true'. We send the split point as a second parameter to the
2723 // idle loop, which means that the main thread will return from the idle
2724 // loop when all threads have finished their work at this split point
2725 // (i.e. when // splitPoint->cpus == 0).
2726 idle_loop(master, splitPoint);
2728 // We have returned from the idle loop, which means that all threads are
2729 // finished. Update alpha, beta and bestvalue, and return:
2731 if(pvNode) *alpha = splitPoint->alpha;
2732 *beta = splitPoint->beta;
2733 *bestValue = splitPoint->bestValue;
2734 Threads[master].stop = false;
2735 Threads[master].idle = false;
2736 Threads[master].activeSplitPoints--;
2737 Threads[master].splitPoint = splitPoint->parent;
2738 lock_release(&MPLock);
2744 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2745 // to start a new search from the root.
2747 void wake_sleeping_threads() {
2748 if(ActiveThreads > 1) {
2749 for(int i = 1; i < ActiveThreads; i++) {
2750 Threads[i].idle = true;
2751 Threads[i].workIsWaiting = false;
2753 #if !defined(_MSC_VER)
2754 pthread_mutex_lock(&WaitLock);
2755 pthread_cond_broadcast(&WaitCond);
2756 pthread_mutex_unlock(&WaitLock);
2758 for(int i = 1; i < THREAD_MAX; i++)
2759 SetEvent(SitIdleEvent[i]);
2765 // init_thread() is the function which is called when a new thread is
2766 // launched. It simply calls the idle_loop() function with the supplied
2767 // threadID. There are two versions of this function; one for POSIX threads
2768 // and one for Windows threads.
2770 #if !defined(_MSC_VER)
2772 void *init_thread(void *threadID) {
2773 idle_loop(*(int *)threadID, NULL);
2779 DWORD WINAPI init_thread(LPVOID threadID) {
2780 idle_loop(*(int *)threadID, NULL);