2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 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/>.
43 #include "ucioption.h"
47 //// Local definitions
54 // IterationInfoType stores search results for each iteration
56 // Because we use relatively small (dynamic) aspiration window,
57 // there happens many fail highs and fail lows in root. And
58 // because we don't do researches in those cases, "value" stored
59 // here is not necessarily exact. Instead in case of fail high/low
60 // we guess what the right value might be and store our guess
61 // as a "speculated value" and then move on. Speculated values are
62 // used just to calculate aspiration window width, so also if are
63 // not exact is not big a problem.
65 struct IterationInfoType {
67 IterationInfoType(Value v = Value(0), Value sv = Value(0))
68 : value(v), speculatedValue(sv) {}
70 Value value, speculatedValue;
74 // The BetaCounterType class is used to order moves at ply one.
75 // Apart for the first one that has its score, following moves
76 // normally have score -VALUE_INFINITE, so are ordered according
77 // to the number of beta cutoffs occurred under their subtree during
78 // the last iteration. The counters are per thread variables to avoid
79 // concurrent accessing under SMP case.
81 struct BetaCounterType {
85 void add(Color us, Depth d, int threadID);
86 void read(Color us, int64_t& our, int64_t& their);
90 // The RootMove class is used for moves at the root at the tree. For each
91 // root move, we store a score, a node count, and a PV (really a refutation
92 // in the case of moves which fail low).
97 bool operator<(const RootMove&); // used to sort
101 int64_t nodes, cumulativeNodes;
102 Move pv[PLY_MAX_PLUS_2];
103 int64_t ourBeta, theirBeta;
107 // The RootMoveList class is essentially an array of RootMove objects, with
108 // a handful of methods for accessing the data in the individual moves.
113 RootMoveList(Position& pos, Move searchMoves[]);
114 inline Move get_move(int moveNum) const;
115 inline Value get_move_score(int moveNum) const;
116 inline void set_move_score(int moveNum, Value score);
117 inline void set_move_nodes(int moveNum, int64_t nodes);
118 inline void set_beta_counters(int moveNum, int64_t our, int64_t their);
119 void set_move_pv(int moveNum, const Move pv[]);
120 inline Move get_move_pv(int moveNum, int i) const;
121 inline int64_t get_move_cumulative_nodes(int moveNum) const;
122 inline int move_count() const;
123 Move scan_for_easy_move() const;
125 void sort_multipv(int n);
128 static const int MaxRootMoves = 500;
129 RootMove moves[MaxRootMoves];
136 // Search depth at iteration 1
137 const Depth InitialDepth = OnePly /*+ OnePly/2*/;
139 // Depth limit for selective search
140 const Depth SelectiveDepth = 7 * OnePly;
142 // Use internal iterative deepening?
143 const bool UseIIDAtPVNodes = true;
144 const bool UseIIDAtNonPVNodes = false;
146 // Internal iterative deepening margin. At Non-PV moves, when
147 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
148 // search when the static evaluation is at most IIDMargin below beta.
149 const Value IIDMargin = Value(0x100);
151 // Easy move margin. An easy move candidate must be at least this much
152 // better than the second best move.
153 const Value EasyMoveMargin = Value(0x200);
155 // Problem margin. If the score of the first move at iteration N+1 has
156 // dropped by more than this since iteration N, the boolean variable
157 // "Problem" is set to true, which will make the program spend some extra
158 // time looking for a better move.
159 const Value ProblemMargin = Value(0x28);
161 // No problem margin. If the boolean "Problem" is true, and a new move
162 // is found at the root which is less than NoProblemMargin worse than the
163 // best move from the previous iteration, Problem is set back to false.
164 const Value NoProblemMargin = Value(0x14);
166 // Null move margin. A null move search will not be done if the approximate
167 // evaluation of the position is more than NullMoveMargin below beta.
168 const Value NullMoveMargin = Value(0x300);
170 // Pruning criterions. See the code and comments in ok_to_prune() to
171 // understand their precise meaning.
172 const bool PruneEscapeMoves = false;
173 const bool PruneDefendingMoves = false;
174 const bool PruneBlockingMoves = false;
176 // Margins for futility pruning in the quiescence search, and at frontier
177 // and near frontier nodes.
178 const Value FutilityMarginQS = Value(0x80);
180 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
181 const Value FutilityMargins[12] = { Value(0x100), Value(0x120), Value(0x200), Value(0x220), Value(0x250), Value(0x270),
182 // 4 ply 4.5 ply 5 ply 5.5 ply 6 ply 6.5 ply
183 Value(0x2A0), Value(0x2C0), Value(0x340), Value(0x360), Value(0x3A0), Value(0x3C0) };
185 const Depth RazorDepth = 4*OnePly;
187 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
188 const Value RazorMargins[6] = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
190 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
191 const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
194 /// Variables initialized by UCI options
196 // Adjustable playing strength
198 const int SlowdownArray[32] = {
199 19, 41, 70, 110, 160, 230, 320, 430, 570, 756, 1000, 1300, 1690, 2197,
200 2834, 3600, 4573, 5809, 7700, 9863, 12633, 16181, 20726, 26584, 34005,
201 43557, 55792, 71463, 91536, 117247, 150180, 192363
204 const int MaxStrength = 25;
206 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
207 int LMRPVMoves, LMRNonPVMoves; // heavy SMP read access for the latter
209 // Depth limit for use of dynamic threat detection
210 Depth ThreatDepth; // heavy SMP read access
212 // Last seconds noise filtering (LSN)
213 const bool UseLSNFiltering = true;
214 const int LSNTime = 4000; // In milliseconds
215 const Value LSNValue = value_from_centipawns(200);
216 bool loseOnTime = false;
218 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
219 // There is heavy SMP read access on these arrays
220 Depth CheckExtension[2], SingleReplyExtension[2], PawnPushTo7thExtension[2];
221 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
223 // Iteration counters
225 BetaCounterType BetaCounter; // has per-thread internal data
227 // Scores and number of times the best move changed for each iteration
228 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
229 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
234 // Time managment variables
236 int MaxNodes, MaxDepth;
237 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
241 bool StopOnPonderhit;
242 bool AbortSearch; // heavy SMP read access
248 // Show current line?
249 bool ShowCurrentLine;
253 std::ofstream LogFile;
255 // MP related variables
256 int ActiveThreads = 1;
257 Depth MinimumSplitDepth;
258 int MaxThreadsPerSplitPoint;
259 Thread Threads[THREAD_MAX];
262 bool AllThreadsShouldExit = false;
263 const int MaxActiveSplitPoints = 8;
264 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
267 #if !defined(_MSC_VER)
268 pthread_cond_t WaitCond;
269 pthread_mutex_t WaitLock;
271 HANDLE SitIdleEvent[THREAD_MAX];
274 // Node counters, used only by thread[0] but try to keep in different
275 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
277 int NodesBetweenPolls = 30000;
285 Value id_loop(const Position& pos, Move searchMoves[]);
286 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
287 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
288 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID);
289 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
290 void sp_search(SplitPoint* sp, int threadID);
291 void sp_search_pv(SplitPoint* sp, int threadID);
292 void init_node(const Position& pos, SearchStack ss[], int ply, int threadID);
293 void update_pv(SearchStack ss[], int ply);
294 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
295 bool connected_moves(const Position& pos, Move m1, Move m2);
296 bool value_is_mate(Value value);
297 bool move_is_killer(Move m, const SearchStack& ss);
298 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
299 bool ok_to_do_nullmove(const Position& pos);
300 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d);
301 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
302 bool ok_to_history(const Position& pos, Move m);
303 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
304 void update_killers(Move m, SearchStack& ss);
305 void slowdown(const Position& pos);
307 bool fail_high_ply_1();
308 int current_search_time();
312 void print_current_line(SearchStack ss[], int ply, int threadID);
313 void wait_for_stop_or_ponderhit();
315 void idle_loop(int threadID, SplitPoint* waitSp);
316 void init_split_point_stack();
317 void destroy_split_point_stack();
318 bool thread_should_stop(int threadID);
319 bool thread_is_available(int slave, int master);
320 bool idle_thread_exists(int master);
321 bool split(const Position& pos, SearchStack* ss, int ply,
322 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
323 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode);
324 void wake_sleeping_threads();
326 #if !defined(_MSC_VER)
327 void *init_thread(void *threadID);
329 DWORD WINAPI init_thread(LPVOID threadID);
339 /// think() is the external interface to Stockfish's search, and is called when
340 /// the program receives the UCI 'go' command. It initializes various
341 /// search-related global variables, and calls root_search(). It returns false
342 /// when a quit command is received during the search.
344 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
345 int time[], int increment[], int movesToGo, int maxDepth,
346 int maxNodes, int maxTime, Move searchMoves[]) {
348 // Look for a book move
349 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
352 if (get_option_value_string("Book File") != OpeningBook.file_name())
353 OpeningBook.open("book.bin");
355 bookMove = OpeningBook.get_move(pos);
356 if (bookMove != MOVE_NONE)
358 std::cout << "bestmove " << bookMove << std::endl;
363 // Initialize global search variables
365 SearchStartTime = get_system_time();
366 for (int i = 0; i < THREAD_MAX; i++)
368 Threads[i].nodes = 0ULL;
369 Threads[i].failHighPly1 = false;
372 InfiniteSearch = infinite;
373 PonderSearch = ponder;
374 StopOnPonderhit = false;
380 ExactMaxTime = maxTime;
382 // Read UCI option values
383 TT.set_size(get_option_value_int("Hash"));
384 if (button_was_pressed("Clear Hash"))
387 loseOnTime = false; // reset at the beginning of a new game
390 bool PonderingEnabled = get_option_value_bool("Ponder");
391 MultiPV = get_option_value_int("MultiPV");
393 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
394 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
396 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
397 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
399 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
400 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
402 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
403 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
405 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
406 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
408 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
409 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
411 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
412 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
413 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
415 Chess960 = get_option_value_bool("UCI_Chess960");
416 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
417 UseLogFile = get_option_value_bool("Use Search Log");
419 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
421 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
422 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
424 read_weights(pos.side_to_move());
426 // Set the number of active threads. If UCI_LimitStrength is enabled, never
427 // use more than one thread.
428 int newActiveThreads =
429 get_option_value_bool("UCI_LimitStrength")? 1 : get_option_value_int("Threads");
430 if (newActiveThreads != ActiveThreads)
432 ActiveThreads = newActiveThreads;
433 init_eval(ActiveThreads);
436 // Wake up sleeping threads
437 wake_sleeping_threads();
439 for (int i = 1; i < ActiveThreads; i++)
440 assert(thread_is_available(i, 0));
442 // Set playing strength
443 if (get_option_value_bool("UCI_LimitStrength"))
445 Strength = (get_option_value_int("UCI_Elo") - 2100) / 25;
447 (Strength == MaxStrength)? 0 : SlowdownArray[Max(0, 31-Strength)];
451 Strength = MaxStrength;
456 int myTime = time[side_to_move];
457 int myIncrement = increment[side_to_move];
459 if (!movesToGo) // Sudden death time control
463 MaxSearchTime = myTime / 30 + myIncrement;
464 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
465 } else { // Blitz game without increment
466 MaxSearchTime = myTime / 30;
467 AbsoluteMaxSearchTime = myTime / 8;
470 else // (x moves) / (y minutes)
474 MaxSearchTime = myTime / 2;
475 AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
477 MaxSearchTime = myTime / Min(movesToGo, 20);
478 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
482 if (PonderingEnabled)
484 MaxSearchTime += MaxSearchTime / 4;
485 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
488 // Fixed depth or fixed number of nodes?
491 InfiniteSearch = true; // HACK
496 NodesBetweenPolls = Min(MaxNodes, 30000);
497 InfiniteSearch = true; // HACK
500 if (Slowdown > 50000) NodesBetweenPolls = 30;
501 else if (Slowdown > 10000) NodesBetweenPolls = 100;
502 else if (Slowdown > 1000) NodesBetweenPolls = 500;
503 else if (Slowdown > 100) NodesBetweenPolls = 3000;
504 else NodesBetweenPolls = 15000;
507 NodesBetweenPolls = 30000;
509 // Write information to search log file
511 LogFile << "Searching: " << pos.to_fen() << std::endl
512 << "infinite: " << infinite
513 << " ponder: " << ponder
514 << " time: " << myTime
515 << " increment: " << myIncrement
516 << " moves to go: " << movesToGo << std::endl;
519 // We're ready to start thinking. Call the iterative deepening loop function
521 // FIXME we really need to cleanup all this LSN ugliness
524 Value v = id_loop(pos, searchMoves);
525 loseOnTime = ( UseLSNFiltering
532 loseOnTime = false; // reset for next match
533 while (SearchStartTime + myTime + 1000 > get_system_time())
535 id_loop(pos, searchMoves); // to fail gracefully
546 /// init_threads() is called during startup. It launches all helper threads,
547 /// and initializes the split point stack and the global locks and condition
550 void init_threads() {
554 #if !defined(_MSC_VER)
555 pthread_t pthread[1];
558 for (i = 0; i < THREAD_MAX; i++)
559 Threads[i].activeSplitPoints = 0;
561 // Initialize global locks
562 lock_init(&MPLock, NULL);
563 lock_init(&IOLock, NULL);
565 init_split_point_stack();
567 #if !defined(_MSC_VER)
568 pthread_mutex_init(&WaitLock, NULL);
569 pthread_cond_init(&WaitCond, NULL);
571 for (i = 0; i < THREAD_MAX; i++)
572 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
575 // All threads except the main thread should be initialized to idle state
576 for (i = 1; i < THREAD_MAX; i++)
578 Threads[i].stop = false;
579 Threads[i].workIsWaiting = false;
580 Threads[i].idle = true;
581 Threads[i].running = false;
584 // Launch the helper threads
585 for(i = 1; i < THREAD_MAX; i++)
587 #if !defined(_MSC_VER)
588 pthread_create(pthread, NULL, init_thread, (void*)(&i));
591 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
594 // Wait until the thread has finished launching
595 while (!Threads[i].running);
600 /// stop_threads() is called when the program exits. It makes all the
601 /// helper threads exit cleanly.
603 void stop_threads() {
605 ActiveThreads = THREAD_MAX; // HACK
606 Idle = false; // HACK
607 wake_sleeping_threads();
608 AllThreadsShouldExit = true;
609 for (int i = 1; i < THREAD_MAX; i++)
611 Threads[i].stop = true;
612 while(Threads[i].running);
614 destroy_split_point_stack();
618 /// nodes_searched() returns the total number of nodes searched so far in
619 /// the current search.
621 int64_t nodes_searched() {
623 int64_t result = 0ULL;
624 for (int i = 0; i < ActiveThreads; i++)
625 result += Threads[i].nodes;
630 // SearchStack::init() initializes a search stack. Used at the beginning of a
631 // new search from the root.
632 void SearchStack::init(int ply) {
634 pv[ply] = pv[ply + 1] = MOVE_NONE;
635 currentMove = threatMove = MOVE_NONE;
636 reduction = Depth(0);
639 void SearchStack::initKillers() {
641 mateKiller = MOVE_NONE;
642 for (int i = 0; i < KILLER_MAX; i++)
643 killers[i] = MOVE_NONE;
648 // id_loop() is the main iterative deepening loop. It calls root_search
649 // repeatedly with increasing depth until the allocated thinking time has
650 // been consumed, the user stops the search, or the maximum search depth is
653 Value id_loop(const Position& pos, Move searchMoves[]) {
656 SearchStack ss[PLY_MAX_PLUS_2];
658 // searchMoves are verified, copied, scored and sorted
659 RootMoveList rml(p, searchMoves);
664 for (int i = 0; i < 3; i++)
669 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
672 Move EasyMove = rml.scan_for_easy_move();
674 // Iterative deepening loop
675 while (Iteration < PLY_MAX)
677 // Initialize iteration
680 BestMoveChangesByIteration[Iteration] = 0;
684 std::cout << "info depth " << Iteration << std::endl;
686 // Calculate dynamic search window based on previous iterations
689 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
691 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
692 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
694 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
696 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
697 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
701 alpha = - VALUE_INFINITE;
702 beta = VALUE_INFINITE;
705 // Search to the current depth
706 Value value = root_search(p, ss, rml, alpha, beta);
708 // Write PV to transposition table, in case the relevant entries have
709 // been overwritten during the search.
710 TT.insert_pv(p, ss[0].pv);
713 break; // Value cannot be trusted. Break out immediately!
715 //Save info about search result
716 Value speculatedValue;
719 Value delta = value - IterationInfo[Iteration - 1].value;
726 speculatedValue = value + delta;
727 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
729 else if (value <= alpha)
731 assert(value == alpha);
735 speculatedValue = value + delta;
736 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
738 speculatedValue = value;
740 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
741 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
743 // Erase the easy move if it differs from the new best move
744 if (ss[0].pv[0] != EasyMove)
745 EasyMove = MOVE_NONE;
752 bool stopSearch = false;
754 // Stop search early if there is only a single legal move
755 if (Iteration >= 6 && rml.move_count() == 1)
758 // Stop search early when the last two iterations returned a mate score
760 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
761 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
764 // Stop search early if one move seems to be much better than the rest
765 int64_t nodes = nodes_searched();
769 && EasyMove == ss[0].pv[0]
770 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
771 && current_search_time() > MaxSearchTime / 16)
772 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
773 && current_search_time() > MaxSearchTime / 32)))
776 // Add some extra time if the best move has changed during the last two iterations
777 if (Iteration > 5 && Iteration <= 50)
778 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
779 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
781 // Stop search if most of MaxSearchTime is consumed at the end of the
782 // iteration. We probably don't have enough time to search the first
783 // move at the next iteration anyway.
784 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
789 //FIXME: Implement fail-low emergency measures
793 StopOnPonderhit = true;
797 if (MaxDepth && Iteration >= MaxDepth)
803 // If we are pondering, we shouldn't print the best move before we
806 wait_for_stop_or_ponderhit();
808 // Print final search statistics
809 std::cout << "info nodes " << nodes_searched()
811 << " time " << current_search_time()
812 << " hashfull " << TT.full() << std::endl;
814 // Print the best move and the ponder move to the standard output
815 if (ss[0].pv[0] == MOVE_NONE)
817 ss[0].pv[0] = rml.get_move(0);
818 ss[0].pv[1] = MOVE_NONE;
820 std::cout << "bestmove " << ss[0].pv[0];
821 if (ss[0].pv[1] != MOVE_NONE)
822 std::cout << " ponder " << ss[0].pv[1];
824 std::cout << std::endl;
829 dbg_print_mean(LogFile);
831 if (dbg_show_hit_rate)
832 dbg_print_hit_rate(LogFile);
835 LogFile << "Nodes: " << nodes_searched() << std::endl
836 << "Nodes/second: " << nps() << std::endl
837 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
839 p.do_move(ss[0].pv[0], st);
840 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
841 << std::endl << std::endl;
843 return rml.get_move_score(0);
847 // root_search() is the function which searches the root node. It is
848 // similar to search_pv except that it uses a different move ordering
849 // scheme (perhaps we should try to use this at internal PV nodes, too?)
850 // and prints some information to the standard output.
852 Value root_search(Position& pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta) {
854 Value oldAlpha = alpha;
856 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
858 // Loop through all the moves in the root move list
859 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
863 // We failed high, invalidate and skip next moves, leave node-counters
864 // and beta-counters as they are and quickly return, we will try to do
865 // a research at the next iteration with a bigger aspiration window.
866 rml.set_move_score(i, -VALUE_INFINITE);
874 RootMoveNumber = i + 1;
877 // Remember the node count before the move is searched. The node counts
878 // are used to sort the root moves at the next iteration.
879 nodes = nodes_searched();
881 // Reset beta cut-off counters
884 // Pick the next root move, and print the move and the move number to
885 // the standard output.
886 move = ss[0].currentMove = rml.get_move(i);
887 if (current_search_time() >= 1000)
888 std::cout << "info currmove " << move
889 << " currmovenumber " << i + 1 << std::endl;
891 // Decide search depth for this move
892 bool moveIsCapture = pos.move_is_capture(move);
894 ext = extension(pos, move, true, moveIsCapture, pos.move_is_check(move), false, false, &dangerous);
895 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
897 // Make the move, and search it
898 pos.do_move(move, st, dcCandidates);
902 // Aspiration window is disabled in multi-pv case
904 alpha = -VALUE_INFINITE;
906 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
907 // If the value has dropped a lot compared to the last iteration,
908 // set the boolean variable Problem to true. This variable is used
909 // for time managment: When Problem is true, we try to complete the
910 // current iteration before playing a move.
911 Problem = (Iteration >= 2 && value <= IterationInfo[Iteration-1].value - ProblemMargin);
913 if (Problem && StopOnPonderhit)
914 StopOnPonderhit = false;
918 if ( newDepth >= 3*OnePly
919 && i >= MultiPV + LMRPVMoves - 2 // Remove -2 and decrease LMRPVMoves instead ?
922 && !move_is_promotion(move)
923 && !move_is_castle(move))
925 ss[0].reduction = OnePly;
926 value = -search(pos, ss, -alpha, newDepth-OnePly, 1, true, 0);
928 value = alpha + 1; // Just to trigger next condition
932 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
935 // Fail high! Set the boolean variable FailHigh to true, and
936 // re-search the move with a big window. The variable FailHigh is
937 // used for time managment: We try to avoid aborting the search
938 // prematurely during a fail high research.
940 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
947 // Finished searching the move. If AbortSearch is true, the search
948 // was aborted because the user interrupted the search or because we
949 // ran out of time. In this case, the return value of the search cannot
950 // be trusted, and we break out of the loop without updating the best
955 // Remember the node count for this move. The node counts are used to
956 // sort the root moves at the next iteration.
957 rml.set_move_nodes(i, nodes_searched() - nodes);
959 // Remember the beta-cutoff statistics
961 BetaCounter.read(pos.side_to_move(), our, their);
962 rml.set_beta_counters(i, our, their);
964 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
966 if (value <= alpha && i >= MultiPV)
967 rml.set_move_score(i, -VALUE_INFINITE);
970 // PV move or new best move!
973 rml.set_move_score(i, value);
975 TT.extract_pv(pos, ss[0].pv);
976 rml.set_move_pv(i, ss[0].pv);
980 // We record how often the best move has been changed in each
981 // iteration. This information is used for time managment: When
982 // the best move changes frequently, we allocate some more time.
984 BestMoveChangesByIteration[Iteration]++;
986 // Print search information to the standard output
987 std::cout << "info depth " << Iteration
988 << " score " << value_to_string(value)
990 " lowerbound" : ((value <= alpha)? " upperbound" : ""))
991 << " time " << current_search_time()
992 << " nodes " << nodes_searched()
996 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
997 std::cout << ss[0].pv[j] << " ";
999 std::cout << std::endl;
1002 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
1008 // Reset the global variable Problem to false if the value isn't too
1009 // far below the final value from the last iteration.
1010 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1015 rml.sort_multipv(i);
1016 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1019 std::cout << "info multipv " << j + 1
1020 << " score " << value_to_string(rml.get_move_score(j))
1021 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1022 << " time " << current_search_time()
1023 << " nodes " << nodes_searched()
1027 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1028 std::cout << rml.get_move_pv(j, k) << " ";
1030 std::cout << std::endl;
1032 alpha = rml.get_move_score(Min(i, MultiPV-1));
1034 } // New best move case
1036 assert(alpha >= oldAlpha);
1038 FailLow = (alpha == oldAlpha);
1044 // search_pv() is the main search function for PV nodes.
1046 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1047 Depth depth, int ply, int threadID) {
1049 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1050 assert(beta > alpha && beta <= VALUE_INFINITE);
1051 assert(ply >= 0 && ply < PLY_MAX);
1052 assert(threadID >= 0 && threadID < ActiveThreads);
1055 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1057 // Initialize, and make an early exit in case of an aborted search,
1058 // an instant draw, maximum ply reached, etc.
1059 init_node(pos, ss, ply, threadID);
1061 // After init_node() that calls poll()
1062 if (AbortSearch || thread_should_stop(threadID))
1070 if (ply >= PLY_MAX - 1)
1071 return evaluate(pos, ei, threadID);
1073 // Mate distance pruning
1074 Value oldAlpha = alpha;
1075 alpha = Max(value_mated_in(ply), alpha);
1076 beta = Min(value_mate_in(ply+1), beta);
1080 // Transposition table lookup. At PV nodes, we don't use the TT for
1081 // pruning, but only for move ordering.
1082 const TTEntry* tte = TT.retrieve(pos.get_key());
1083 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1085 // Go with internal iterative deepening if we don't have a TT move
1086 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
1088 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1089 ttMove = ss[ply].pv[ply];
1092 // Initialize a MovePicker object for the current position, and prepare
1093 // to search all moves
1094 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1096 Move move, movesSearched[256];
1098 Value value, bestValue = -VALUE_INFINITE;
1099 Bitboard dcCandidates = mp.discovered_check_candidates();
1100 Color us = pos.side_to_move();
1101 bool isCheck = pos.is_check();
1102 bool mateThreat = pos.has_mate_threat(opposite_color(us));
1104 // Loop through all legal moves until no moves remain or a beta cutoff
1106 while ( alpha < beta
1107 && (move = mp.get_next_move()) != MOVE_NONE
1108 && !thread_should_stop(threadID))
1110 assert(move_is_ok(move));
1112 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1113 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1114 bool moveIsCapture = pos.move_is_capture(move);
1116 movesSearched[moveCount++] = ss[ply].currentMove = move;
1118 // Decide the new search depth
1120 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1121 Depth newDepth = depth - OnePly + ext;
1123 // Make and search the move
1125 pos.do_move(move, st, dcCandidates);
1127 if (moveCount == 1) // The first move in list is the PV
1128 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1131 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1132 // if the move fails high will be re-searched at full depth.
1133 if ( depth >= 3*OnePly
1134 && moveCount >= LMRPVMoves
1137 && !move_is_promotion(move)
1138 && !move_is_castle(move)
1139 && !move_is_killer(move, ss[ply]))
1141 ss[ply].reduction = OnePly;
1142 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1145 value = alpha + 1; // Just to trigger next condition
1147 if (value > alpha) // Go with full depth non-pv search
1149 ss[ply].reduction = Depth(0);
1150 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1151 if (value > alpha && value < beta)
1153 // When the search fails high at ply 1 while searching the first
1154 // move at the root, set the flag failHighPly1. This is used for
1155 // time managment: We don't want to stop the search early in
1156 // such cases, because resolving the fail high at ply 1 could
1157 // result in a big drop in score at the root.
1158 if (ply == 1 && RootMoveNumber == 1)
1159 Threads[threadID].failHighPly1 = true;
1161 // A fail high occurred. Re-search at full window (pv search)
1162 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1163 Threads[threadID].failHighPly1 = false;
1167 pos.undo_move(move);
1169 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1172 if (value > bestValue)
1179 if (value == value_mate_in(ply + 1))
1180 ss[ply].mateKiller = move;
1182 // If we are at ply 1, and we are searching the first root move at
1183 // ply 0, set the 'Problem' variable if the score has dropped a lot
1184 // (from the computer's point of view) since the previous iteration.
1187 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1192 if ( ActiveThreads > 1
1194 && depth >= MinimumSplitDepth
1196 && idle_thread_exists(threadID)
1198 && !thread_should_stop(threadID)
1199 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1200 &moveCount, &mp, dcCandidates, threadID, true))
1204 // All legal moves have been searched. A special case: If there were
1205 // no legal moves, it must be mate or stalemate.
1207 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1209 // If the search is not aborted, update the transposition table,
1210 // history counters, and killer moves.
1211 if (AbortSearch || thread_should_stop(threadID))
1214 if (bestValue <= oldAlpha)
1215 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1217 else if (bestValue >= beta)
1219 BetaCounter.add(pos.side_to_move(), depth, threadID);
1220 Move m = ss[ply].pv[ply];
1221 if (ok_to_history(pos, m)) // Only non capture moves are considered
1223 update_history(pos, m, depth, movesSearched, moveCount);
1224 update_killers(m, ss[ply]);
1226 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1229 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1235 // search() is the search function for zero-width nodes.
1237 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1238 int ply, bool allowNullmove, int threadID) {
1240 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1241 assert(ply >= 0 && ply < PLY_MAX);
1242 assert(threadID >= 0 && threadID < ActiveThreads);
1245 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1247 // Initialize, and make an early exit in case of an aborted search,
1248 // an instant draw, maximum ply reached, etc.
1249 init_node(pos, ss, ply, threadID);
1251 // After init_node() that calls poll()
1252 if (AbortSearch || thread_should_stop(threadID))
1260 if (ply >= PLY_MAX - 1)
1261 return evaluate(pos, ei, threadID);
1263 // Mate distance pruning
1264 if (value_mated_in(ply) >= beta)
1267 if (value_mate_in(ply + 1) < beta)
1270 // Transposition table lookup
1271 const TTEntry* tte = TT.retrieve(pos.get_key());
1272 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1274 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1276 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1277 return value_from_tt(tte->value(), ply);
1280 Value approximateEval = quick_evaluate(pos);
1281 bool mateThreat = false;
1282 bool isCheck = pos.is_check();
1284 bool useNullMove = ( allowNullmove
1287 && !value_is_mate(beta)
1288 && ok_to_do_nullmove(pos)
1289 && approximateEval >= beta - NullMoveMargin);
1291 // Null move search not allowed, try razoring
1293 && !value_is_mate(beta)
1294 && depth < RazorDepth
1295 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1296 && ss[ply - 1].currentMove != MOVE_NULL
1297 && ttMove == MOVE_NONE
1298 && !pos.has_pawn_on_7th(pos.side_to_move()))
1300 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1301 if (v < beta - RazorMargins[int(depth) - 2])
1305 // Go with internal iterative deepening if we don't have a TT move
1306 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1307 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1309 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1310 ttMove = ss[ply].pv[ply];
1313 // Initialize a MovePicker object for the current position, and prepare
1314 // to search all moves.
1315 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], useNullMove);
1317 Move move, movesSearched[256];
1319 Value value, bestValue = -VALUE_INFINITE;
1320 Bitboard dcCandidates = mp.discovered_check_candidates();
1321 Value futilityValue = VALUE_NONE;
1322 bool useFutilityPruning = depth < SelectiveDepth
1325 // Loop through all legal moves until no moves remain or a beta cutoff
1327 while ( bestValue < beta
1328 && (move = mp.get_next_move()) != MOVE_NONE
1329 && !thread_should_stop(threadID))
1333 if (move == MOVE_NULL)
1335 ss[ply].currentMove = MOVE_NULL;
1338 pos.do_null_move(st);
1339 int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
1341 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1343 pos.undo_null_move();
1345 if (nullValue >= beta)
1347 if (depth < 6 * OnePly)
1350 // Do zugzwang verification search
1351 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1355 // The null move failed low, which means that we may be faced with
1356 // some kind of threat. If the previous move was reduced, check if
1357 // the move that refuted the null move was somehow connected to the
1358 // move which was reduced. If a connection is found, return a fail
1359 // low score (which will cause the reduced move to fail high in the
1360 // parent node, which will trigger a re-search with full depth).
1361 if (nullValue == value_mated_in(ply + 2))
1364 ss[ply].threatMove = ss[ply + 1].currentMove;
1365 if ( depth < ThreatDepth
1366 && ss[ply - 1].reduction
1367 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1373 assert(move_is_ok(move));
1375 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1376 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1377 bool moveIsCapture = pos.move_is_capture(move);
1379 movesSearched[moveCount++] = ss[ply].currentMove = move;
1381 // Decide the new search depth
1383 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1384 Depth newDepth = depth - OnePly + ext;
1387 if ( useFutilityPruning
1390 && !move_is_promotion(move))
1392 // History pruning. See ok_to_prune() definition
1393 if ( moveCount >= 2 + int(depth)
1394 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1397 // Value based pruning
1398 if (approximateEval < beta)
1400 if (futilityValue == VALUE_NONE)
1401 futilityValue = evaluate(pos, ei, threadID)
1402 + FutilityMargins[int(depth) - 2];
1404 if (futilityValue < beta)
1406 if (futilityValue > bestValue)
1407 bestValue = futilityValue;
1413 // Make and search the move
1415 pos.do_move(move, st, dcCandidates);
1417 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1418 // if the move fails high will be re-searched at full depth.
1419 if ( depth >= 3*OnePly
1420 && moveCount >= LMRNonPVMoves
1423 && !move_is_promotion(move)
1424 && !move_is_castle(move)
1425 && !move_is_killer(move, ss[ply]))
1427 ss[ply].reduction = OnePly;
1428 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1431 value = beta; // Just to trigger next condition
1433 if (value >= beta) // Go with full depth non-pv search
1435 ss[ply].reduction = Depth(0);
1436 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1438 pos.undo_move(move);
1440 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1443 if (value > bestValue)
1449 if (value == value_mate_in(ply + 1))
1450 ss[ply].mateKiller = move;
1454 if ( ActiveThreads > 1
1456 && depth >= MinimumSplitDepth
1458 && idle_thread_exists(threadID)
1460 && !thread_should_stop(threadID)
1461 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1462 &mp, dcCandidates, threadID, false))
1466 // All legal moves have been searched. A special case: If there were
1467 // no legal moves, it must be mate or stalemate.
1469 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1471 // If the search is not aborted, update the transposition table,
1472 // history counters, and killer moves.
1473 if (AbortSearch || thread_should_stop(threadID))
1476 if (bestValue < beta)
1477 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1480 BetaCounter.add(pos.side_to_move(), depth, threadID);
1481 Move m = ss[ply].pv[ply];
1482 if (ok_to_history(pos, m)) // Only non capture moves are considered
1484 update_history(pos, m, depth, movesSearched, moveCount);
1485 update_killers(m, ss[ply]);
1487 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1490 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1496 // qsearch() is the quiescence search function, which is called by the main
1497 // search function when the remaining depth is zero (or, to be more precise,
1498 // less than OnePly).
1500 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1501 Depth depth, int ply, int threadID) {
1503 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1504 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1506 assert(ply >= 0 && ply < PLY_MAX);
1507 assert(threadID >= 0 && threadID < ActiveThreads);
1509 // Initialize, and make an early exit in case of an aborted search,
1510 // an instant draw, maximum ply reached, etc.
1511 init_node(pos, ss, ply, threadID);
1513 // After init_node() that calls poll()
1514 if (AbortSearch || thread_should_stop(threadID))
1520 // Transposition table lookup, only when not in PV
1521 TTEntry* tte = NULL;
1522 bool pvNode = (beta - alpha != 1);
1525 tte = TT.retrieve(pos.get_key());
1526 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1528 assert(tte->type() != VALUE_TYPE_EVAL);
1530 return value_from_tt(tte->value(), ply);
1533 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1535 // Evaluate the position statically
1538 bool isCheck = pos.is_check();
1539 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1542 staticValue = -VALUE_INFINITE;
1544 else if (tte && tte->type() == VALUE_TYPE_EVAL)
1546 // Use the cached evaluation score if possible
1547 assert(ei.futilityMargin == Value(0));
1549 staticValue = tte->value();
1552 staticValue = evaluate(pos, ei, threadID);
1554 if (ply == PLY_MAX - 1)
1555 return evaluate(pos, ei, threadID);
1557 // Initialize "stand pat score", and return it immediately if it is
1559 Value bestValue = staticValue;
1561 if (bestValue >= beta)
1563 // Store the score to avoid a future costly evaluation() call
1564 if (!isCheck && !tte && ei.futilityMargin == 0)
1565 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EVAL, Depth(-127*OnePly), MOVE_NONE);
1570 if (bestValue > alpha)
1573 // Initialize a MovePicker object for the current position, and prepare
1574 // to search the moves. Because the depth is <= 0 here, only captures,
1575 // queen promotions and checks (only if depth == 0) will be generated.
1576 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1579 Bitboard dcCandidates = mp.discovered_check_candidates();
1580 Color us = pos.side_to_move();
1581 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1583 // Loop through the moves until no moves remain or a beta cutoff
1585 while ( alpha < beta
1586 && (move = mp.get_next_move()) != MOVE_NONE)
1588 assert(move_is_ok(move));
1591 ss[ply].currentMove = move;
1597 && !move_is_promotion(move)
1598 && !pos.move_is_check(move, dcCandidates)
1599 && !pos.move_is_passed_pawn_push(move))
1601 Value futilityValue = staticValue
1602 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1603 pos.endgame_value_of_piece_on(move_to(move)))
1604 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1606 + ei.futilityMargin;
1608 if (futilityValue < alpha)
1610 if (futilityValue > bestValue)
1611 bestValue = futilityValue;
1616 // Don't search captures and checks with negative SEE values
1618 && !move_is_promotion(move)
1619 && pos.see_sign(move) < 0)
1622 // Make and search the move.
1624 pos.do_move(move, st, dcCandidates);
1625 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1626 pos.undo_move(move);
1628 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1631 if (value > bestValue)
1642 // All legal moves have been searched. A special case: If we're in check
1643 // and no legal moves were found, it is checkmate.
1644 if (pos.is_check() && moveCount == 0) // Mate!
1645 return value_mated_in(ply);
1647 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1649 // Update transposition table
1650 Move m = ss[ply].pv[ply];
1653 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1654 if (bestValue < beta)
1655 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE);
1657 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
1660 // Update killers only for good check moves
1661 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1662 update_killers(m, ss[ply]);
1668 // sp_search() is used to search from a split point. This function is called
1669 // by each thread working at the split point. It is similar to the normal
1670 // search() function, but simpler. Because we have already probed the hash
1671 // table, done a null move search, and searched the first move before
1672 // splitting, we don't have to repeat all this work in sp_search(). We
1673 // also don't need to store anything to the hash table here: This is taken
1674 // care of after we return from the split point.
1676 void sp_search(SplitPoint* sp, int threadID) {
1678 assert(threadID >= 0 && threadID < ActiveThreads);
1679 assert(ActiveThreads > 1);
1681 Position pos = Position(sp->pos);
1682 SearchStack* ss = sp->sstack[threadID];
1685 bool isCheck = pos.is_check();
1686 bool useFutilityPruning = sp->depth < SelectiveDepth
1689 while ( sp->bestValue < sp->beta
1690 && !thread_should_stop(threadID)
1691 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1693 assert(move_is_ok(move));
1695 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1696 bool moveIsCapture = pos.move_is_capture(move);
1698 lock_grab(&(sp->lock));
1699 int moveCount = ++sp->moves;
1700 lock_release(&(sp->lock));
1702 ss[sp->ply].currentMove = move;
1704 // Decide the new search depth.
1706 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1707 Depth newDepth = sp->depth - OnePly + ext;
1710 if ( useFutilityPruning
1713 && !move_is_promotion(move)
1714 && moveCount >= 2 + int(sp->depth)
1715 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1718 // Make and search the move.
1720 pos.do_move(move, st, sp->dcCandidates);
1722 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1723 // if the move fails high will be re-searched at full depth.
1725 && moveCount >= LMRNonPVMoves
1727 && !move_is_promotion(move)
1728 && !move_is_castle(move)
1729 && !move_is_killer(move, ss[sp->ply]))
1731 ss[sp->ply].reduction = OnePly;
1732 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1735 value = sp->beta; // Just to trigger next condition
1737 if (value >= sp->beta) // Go with full depth non-pv search
1739 ss[sp->ply].reduction = Depth(0);
1740 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1742 pos.undo_move(move);
1744 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1746 if (thread_should_stop(threadID))
1750 lock_grab(&(sp->lock));
1751 if (value > sp->bestValue && !thread_should_stop(threadID))
1753 sp->bestValue = value;
1754 if (sp->bestValue >= sp->beta)
1756 sp_update_pv(sp->parentSstack, ss, sp->ply);
1757 for (int i = 0; i < ActiveThreads; i++)
1758 if (i != threadID && (i == sp->master || sp->slaves[i]))
1759 Threads[i].stop = true;
1761 sp->finished = true;
1764 lock_release(&(sp->lock));
1767 lock_grab(&(sp->lock));
1769 // If this is the master thread and we have been asked to stop because of
1770 // a beta cutoff higher up in the tree, stop all slave threads.
1771 if (sp->master == threadID && thread_should_stop(threadID))
1772 for (int i = 0; i < ActiveThreads; i++)
1774 Threads[i].stop = true;
1777 sp->slaves[threadID] = 0;
1779 lock_release(&(sp->lock));
1783 // sp_search_pv() is used to search from a PV split point. This function
1784 // is called by each thread working at the split point. It is similar to
1785 // the normal search_pv() function, but simpler. Because we have already
1786 // probed the hash table and searched the first move before splitting, we
1787 // don't have to repeat all this work in sp_search_pv(). We also don't
1788 // need to store anything to the hash table here: This is taken care of
1789 // after we return from the split point.
1791 void sp_search_pv(SplitPoint* sp, int threadID) {
1793 assert(threadID >= 0 && threadID < ActiveThreads);
1794 assert(ActiveThreads > 1);
1796 Position pos = Position(sp->pos);
1797 SearchStack* ss = sp->sstack[threadID];
1801 while ( sp->alpha < sp->beta
1802 && !thread_should_stop(threadID)
1803 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1805 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1806 bool moveIsCapture = pos.move_is_capture(move);
1808 assert(move_is_ok(move));
1810 lock_grab(&(sp->lock));
1811 int moveCount = ++sp->moves;
1812 lock_release(&(sp->lock));
1814 ss[sp->ply].currentMove = move;
1816 // Decide the new search depth.
1818 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1819 Depth newDepth = sp->depth - OnePly + ext;
1821 // Make and search the move.
1823 pos.do_move(move, st, sp->dcCandidates);
1825 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1826 // if the move fails high will be re-searched at full depth.
1828 && moveCount >= LMRPVMoves
1830 && !move_is_promotion(move)
1831 && !move_is_castle(move)
1832 && !move_is_killer(move, ss[sp->ply]))
1834 ss[sp->ply].reduction = OnePly;
1835 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1838 value = sp->alpha + 1; // Just to trigger next condition
1840 if (value > sp->alpha) // Go with full depth non-pv search
1842 ss[sp->ply].reduction = Depth(0);
1843 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1845 if (value > sp->alpha && value < sp->beta)
1847 // When the search fails high at ply 1 while searching the first
1848 // move at the root, set the flag failHighPly1. This is used for
1849 // time managment: We don't want to stop the search early in
1850 // such cases, because resolving the fail high at ply 1 could
1851 // result in a big drop in score at the root.
1852 if (sp->ply == 1 && RootMoveNumber == 1)
1853 Threads[threadID].failHighPly1 = true;
1855 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1856 Threads[threadID].failHighPly1 = false;
1859 pos.undo_move(move);
1861 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1863 if (thread_should_stop(threadID))
1867 lock_grab(&(sp->lock));
1868 if (value > sp->bestValue && !thread_should_stop(threadID))
1870 sp->bestValue = value;
1871 if (value > sp->alpha)
1874 sp_update_pv(sp->parentSstack, ss, sp->ply);
1875 if (value == value_mate_in(sp->ply + 1))
1876 ss[sp->ply].mateKiller = move;
1878 if (value >= sp->beta)
1880 for (int i = 0; i < ActiveThreads; i++)
1881 if (i != threadID && (i == sp->master || sp->slaves[i]))
1882 Threads[i].stop = true;
1884 sp->finished = true;
1887 // If we are at ply 1, and we are searching the first root move at
1888 // ply 0, set the 'Problem' variable if the score has dropped a lot
1889 // (from the computer's point of view) since the previous iteration.
1892 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1895 lock_release(&(sp->lock));
1898 lock_grab(&(sp->lock));
1900 // If this is the master thread and we have been asked to stop because of
1901 // a beta cutoff higher up in the tree, stop all slave threads.
1902 if (sp->master == threadID && thread_should_stop(threadID))
1903 for (int i = 0; i < ActiveThreads; i++)
1905 Threads[i].stop = true;
1908 sp->slaves[threadID] = 0;
1910 lock_release(&(sp->lock));
1913 /// The BetaCounterType class
1915 BetaCounterType::BetaCounterType() { clear(); }
1917 void BetaCounterType::clear() {
1919 for (int i = 0; i < THREAD_MAX; i++)
1920 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
1923 void BetaCounterType::add(Color us, Depth d, int threadID) {
1925 // Weighted count based on depth
1926 Threads[threadID].betaCutOffs[us] += unsigned(d);
1929 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1932 for (int i = 0; i < THREAD_MAX; i++)
1934 our += Threads[i].betaCutOffs[us];
1935 their += Threads[i].betaCutOffs[opposite_color(us)];
1940 /// The RootMove class
1944 RootMove::RootMove() {
1945 nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
1948 // RootMove::operator<() is the comparison function used when
1949 // sorting the moves. A move m1 is considered to be better
1950 // than a move m2 if it has a higher score, or if the moves
1951 // have equal score but m1 has the higher node count.
1953 bool RootMove::operator<(const RootMove& m) {
1955 if (score != m.score)
1956 return (score < m.score);
1958 return theirBeta <= m.theirBeta;
1961 /// The RootMoveList class
1965 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1967 MoveStack mlist[MaxRootMoves];
1968 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1970 // Generate all legal moves
1971 MoveStack* last = generate_legal_moves(pos, mlist);
1973 // Add each move to the moves[] array
1974 for (MoveStack* cur = mlist; cur != last; cur++)
1976 bool includeMove = includeAllMoves;
1978 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1979 includeMove = (searchMoves[k] == cur->move);
1984 // Find a quick score for the move
1986 SearchStack ss[PLY_MAX_PLUS_2];
1988 moves[count].move = cur->move;
1989 pos.do_move(moves[count].move, st);
1990 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
1991 pos.undo_move(moves[count].move);
1992 moves[count].pv[0] = moves[count].move;
1993 moves[count].pv[1] = MOVE_NONE; // FIXME
2000 // Simple accessor methods for the RootMoveList class
2002 inline Move RootMoveList::get_move(int moveNum) const {
2003 return moves[moveNum].move;
2006 inline Value RootMoveList::get_move_score(int moveNum) const {
2007 return moves[moveNum].score;
2010 inline void RootMoveList::set_move_score(int moveNum, Value score) {
2011 moves[moveNum].score = score;
2014 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2015 moves[moveNum].nodes = nodes;
2016 moves[moveNum].cumulativeNodes += nodes;
2019 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2020 moves[moveNum].ourBeta = our;
2021 moves[moveNum].theirBeta = their;
2024 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2026 for(j = 0; pv[j] != MOVE_NONE; j++)
2027 moves[moveNum].pv[j] = pv[j];
2028 moves[moveNum].pv[j] = MOVE_NONE;
2031 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2032 return moves[moveNum].pv[i];
2035 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2036 return moves[moveNum].cumulativeNodes;
2039 inline int RootMoveList::move_count() const {
2044 // RootMoveList::scan_for_easy_move() is called at the end of the first
2045 // iteration, and is used to detect an "easy move", i.e. a move which appears
2046 // to be much bester than all the rest. If an easy move is found, the move
2047 // is returned, otherwise the function returns MOVE_NONE. It is very
2048 // important that this function is called at the right moment: The code
2049 // assumes that the first iteration has been completed and the moves have
2050 // been sorted. This is done in RootMoveList c'tor.
2052 Move RootMoveList::scan_for_easy_move() const {
2059 // moves are sorted so just consider the best and the second one
2060 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
2066 // RootMoveList::sort() sorts the root move list at the beginning of a new
2069 inline void RootMoveList::sort() {
2071 sort_multipv(count - 1); // all items
2075 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2076 // list by their scores and depths. It is used to order the different PVs
2077 // correctly in MultiPV mode.
2079 void RootMoveList::sort_multipv(int n) {
2081 for (int i = 1; i <= n; i++)
2083 RootMove rm = moves[i];
2085 for (j = i; j > 0 && moves[j-1] < rm; j--)
2086 moves[j] = moves[j-1];
2092 // init_node() is called at the beginning of all the search functions
2093 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2094 // stack object corresponding to the current node. Once every
2095 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2096 // for user input and checks whether it is time to stop the search.
2098 void init_node(const Position& pos, SearchStack ss[], int ply, int threadID) {
2100 assert(ply >= 0 && ply < PLY_MAX);
2101 assert(threadID >= 0 && threadID < ActiveThreads);
2103 if (Slowdown && Iteration >= 3)
2106 Threads[threadID].nodes++;
2111 if (NodesSincePoll >= NodesBetweenPolls)
2118 ss[ply+2].initKillers();
2120 if (Threads[threadID].printCurrentLine)
2121 print_current_line(ss, ply, threadID);
2125 // update_pv() is called whenever a search returns a value > alpha. It
2126 // updates the PV in the SearchStack object corresponding to the current
2129 void update_pv(SearchStack ss[], int ply) {
2130 assert(ply >= 0 && ply < PLY_MAX);
2132 ss[ply].pv[ply] = ss[ply].currentMove;
2134 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2135 ss[ply].pv[p] = ss[ply+1].pv[p];
2136 ss[ply].pv[p] = MOVE_NONE;
2140 // sp_update_pv() is a variant of update_pv for use at split points. The
2141 // difference between the two functions is that sp_update_pv also updates
2142 // the PV at the parent node.
2144 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2145 assert(ply >= 0 && ply < PLY_MAX);
2147 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2149 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2150 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2151 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2155 // connected_moves() tests whether two moves are 'connected' in the sense
2156 // that the first move somehow made the second move possible (for instance
2157 // if the moving piece is the same in both moves). The first move is
2158 // assumed to be the move that was made to reach the current position, while
2159 // the second move is assumed to be a move from the current position.
2161 bool connected_moves(const Position& pos, Move m1, Move m2) {
2162 Square f1, t1, f2, t2;
2164 assert(move_is_ok(m1));
2165 assert(move_is_ok(m2));
2167 if (m2 == MOVE_NONE)
2170 // Case 1: The moving piece is the same in both moves
2176 // Case 2: The destination square for m2 was vacated by m1
2182 // Case 3: Moving through the vacated square
2183 if ( piece_is_slider(pos.piece_on(f2))
2184 && bit_is_set(squares_between(f2, t2), f1))
2187 // Case 4: The destination square for m2 is attacked by the moving piece in m1
2188 if (pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
2191 // Case 5: Discovered check, checking piece is the piece moved in m1
2192 if ( piece_is_slider(pos.piece_on(t1))
2193 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2194 && !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())), t2))
2196 Bitboard occ = pos.occupied_squares();
2197 Color us = pos.side_to_move();
2198 Square ksq = pos.king_square(us);
2199 clear_bit(&occ, f2);
2200 if (pos.type_of_piece_on(t1) == BISHOP)
2202 if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2205 else if (pos.type_of_piece_on(t1) == ROOK)
2207 if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
2212 assert(pos.type_of_piece_on(t1) == QUEEN);
2213 if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
2221 // value_is_mate() checks if the given value is a mate one
2222 // eventually compensated for the ply.
2224 bool value_is_mate(Value value) {
2226 assert(abs(value) <= VALUE_INFINITE);
2228 return value <= value_mated_in(PLY_MAX)
2229 || value >= value_mate_in(PLY_MAX);
2233 // move_is_killer() checks if the given move is among the
2234 // killer moves of that ply.
2236 bool move_is_killer(Move m, const SearchStack& ss) {
2238 const Move* k = ss.killers;
2239 for (int i = 0; i < KILLER_MAX; i++, k++)
2247 // extension() decides whether a move should be searched with normal depth,
2248 // or with extended depth. Certain classes of moves (checking moves, in
2249 // particular) are searched with bigger depth than ordinary moves and in
2250 // any case are marked as 'dangerous'. Note that also if a move is not
2251 // extended, as example because the corresponding UCI option is set to zero,
2252 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2254 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2255 bool singleReply, bool mateThreat, bool* dangerous) {
2257 assert(m != MOVE_NONE);
2259 Depth result = Depth(0);
2260 *dangerous = check | singleReply | mateThreat;
2265 result += CheckExtension[pvNode];
2268 result += SingleReplyExtension[pvNode];
2271 result += MateThreatExtension[pvNode];
2274 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2276 Color c = pos.side_to_move();
2277 if (relative_rank(c, move_to(m)) == RANK_7)
2279 result += PawnPushTo7thExtension[pvNode];
2282 if (pos.pawn_is_passed(c, move_to(m)))
2284 result += PassedPawnExtension[pvNode];
2290 && pos.type_of_piece_on(move_to(m)) != PAWN
2291 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2292 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2293 && !move_is_promotion(m)
2296 result += PawnEndgameExtension[pvNode];
2302 && pos.type_of_piece_on(move_to(m)) != PAWN
2303 && pos.see_sign(m) >= 0)
2309 return Min(result, OnePly);
2313 // ok_to_do_nullmove() looks at the current position and decides whether
2314 // doing a 'null move' should be allowed. In order to avoid zugzwang
2315 // problems, null moves are not allowed when the side to move has very
2316 // little material left. Currently, the test is a bit too simple: Null
2317 // moves are avoided only when the side to move has only pawns left. It's
2318 // probably a good idea to avoid null moves in at least some more
2319 // complicated endgames, e.g. KQ vs KR. FIXME
2321 bool ok_to_do_nullmove(const Position& pos) {
2323 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2327 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2328 // non-tactical moves late in the move list close to the leaves are
2329 // candidates for pruning.
2331 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d) {
2333 assert(move_is_ok(m));
2334 assert(threat == MOVE_NONE || move_is_ok(threat));
2335 assert(!move_is_promotion(m));
2336 assert(!pos.move_is_check(m));
2337 assert(!pos.move_is_capture(m));
2338 assert(!pos.move_is_passed_pawn_push(m));
2339 assert(d >= OnePly);
2341 Square mfrom, mto, tfrom, tto;
2343 mfrom = move_from(m);
2345 tfrom = move_from(threat);
2346 tto = move_to(threat);
2348 // Case 1: Castling moves are never pruned
2349 if (move_is_castle(m))
2352 // Case 2: Don't prune moves which move the threatened piece
2353 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2356 // Case 3: If the threatened piece has value less than or equal to the
2357 // value of the threatening piece, don't prune move which defend it.
2358 if ( !PruneDefendingMoves
2359 && threat != MOVE_NONE
2360 && pos.move_is_capture(threat)
2361 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2362 || pos.type_of_piece_on(tfrom) == KING)
2363 && pos.move_attacks_square(m, tto))
2366 // Case 4: Don't prune moves with good history
2367 if (!H.ok_to_prune(pos.piece_on(mfrom), mto, d))
2370 // Case 5: If the moving piece in the threatened move is a slider, don't
2371 // prune safe moves which block its ray.
2372 if ( !PruneBlockingMoves
2373 && threat != MOVE_NONE
2374 && piece_is_slider(pos.piece_on(tfrom))
2375 && bit_is_set(squares_between(tfrom, tto), mto)
2376 && pos.see_sign(m) >= 0)
2383 // ok_to_use_TT() returns true if a transposition table score
2384 // can be used at a given point in search.
2386 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2388 Value v = value_from_tt(tte->value(), ply);
2390 return ( tte->depth() >= depth
2391 || v >= Max(value_mate_in(100), beta)
2392 || v < Min(value_mated_in(100), beta))
2394 && ( (is_lower_bound(tte->type()) && v >= beta)
2395 || (is_upper_bound(tte->type()) && v < beta));
2399 // ok_to_history() returns true if a move m can be stored
2400 // in history. Should be a non capturing move nor a promotion.
2402 bool ok_to_history(const Position& pos, Move m) {
2404 return !pos.move_is_capture(m) && !move_is_promotion(m);
2408 // update_history() registers a good move that produced a beta-cutoff
2409 // in history and marks as failures all the other moves of that ply.
2411 void update_history(const Position& pos, Move m, Depth depth,
2412 Move movesSearched[], int moveCount) {
2414 H.success(pos.piece_on(move_from(m)), move_to(m), depth);
2416 for (int i = 0; i < moveCount - 1; i++)
2418 assert(m != movesSearched[i]);
2419 if (ok_to_history(pos, movesSearched[i]))
2420 H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]));
2425 // update_killers() add a good move that produced a beta-cutoff
2426 // among the killer moves of that ply.
2428 void update_killers(Move m, SearchStack& ss) {
2430 if (m == ss.killers[0])
2433 for (int i = KILLER_MAX - 1; i > 0; i--)
2434 ss.killers[i] = ss.killers[i - 1];
2440 // slowdown() simply wastes CPU cycles doing nothing useful. It's used
2441 // in strength handicap mode.
2443 void slowdown(const Position &pos) {
2446 for (i = 0; i < n; i++) {
2447 Square s = Square(i&63);
2448 if (count_1s(pos.attacks_to(s)) > 63)
2449 std::cout << "This can't happen, but I put this string here anyway, in order to prevent the compiler from optimizing away the useless computation." << std::endl;
2454 // fail_high_ply_1() checks if some thread is currently resolving a fail
2455 // high at ply 1 at the node below the first root node. This information
2456 // is used for time managment.
2458 bool fail_high_ply_1() {
2460 for(int i = 0; i < ActiveThreads; i++)
2461 if (Threads[i].failHighPly1)
2468 // current_search_time() returns the number of milliseconds which have passed
2469 // since the beginning of the current search.
2471 int current_search_time() {
2472 return get_system_time() - SearchStartTime;
2476 // nps() computes the current nodes/second count.
2479 int t = current_search_time();
2480 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2484 // poll() performs two different functions: It polls for user input, and it
2485 // looks at the time consumed so far and decides if it's time to abort the
2490 static int lastInfoTime;
2491 int t = current_search_time();
2496 // We are line oriented, don't read single chars
2497 std::string command;
2498 if (!std::getline(std::cin, command))
2501 if (command == "quit")
2504 PonderSearch = false;
2508 else if (command == "stop")
2511 PonderSearch = false;
2513 else if (command == "ponderhit")
2516 // Print search information
2520 else if (lastInfoTime > t)
2521 // HACK: Must be a new search where we searched less than
2522 // NodesBetweenPolls nodes during the first second of search.
2525 else if (t - lastInfoTime >= 1000)
2532 if (dbg_show_hit_rate)
2533 dbg_print_hit_rate();
2535 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2536 << " time " << t << " hashfull " << TT.full() << std::endl;
2537 lock_release(&IOLock);
2538 if (ShowCurrentLine)
2539 Threads[0].printCurrentLine = true;
2541 // Should we stop the search?
2545 bool overTime = t > AbsoluteMaxSearchTime
2546 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2547 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2548 && t > 6*(MaxSearchTime + ExtraSearchTime));
2550 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2551 || (ExactMaxTime && t >= ExactMaxTime)
2552 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2557 // ponderhit() is called when the program is pondering (i.e. thinking while
2558 // it's the opponent's turn to move) in order to let the engine know that
2559 // it correctly predicted the opponent's move.
2563 int t = current_search_time();
2564 PonderSearch = false;
2565 if (Iteration >= 3 &&
2566 (!InfiniteSearch && (StopOnPonderhit ||
2567 t > AbsoluteMaxSearchTime ||
2568 (RootMoveNumber == 1 &&
2569 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2570 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2571 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2576 // print_current_line() prints the current line of search for a given
2577 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2579 void print_current_line(SearchStack ss[], int ply, int threadID) {
2581 assert(ply >= 0 && ply < PLY_MAX);
2582 assert(threadID >= 0 && threadID < ActiveThreads);
2584 if (!Threads[threadID].idle)
2587 std::cout << "info currline " << (threadID + 1);
2588 for (int p = 0; p < ply; p++)
2589 std::cout << " " << ss[p].currentMove;
2591 std::cout << std::endl;
2592 lock_release(&IOLock);
2594 Threads[threadID].printCurrentLine = false;
2595 if (threadID + 1 < ActiveThreads)
2596 Threads[threadID + 1].printCurrentLine = true;
2600 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2601 // while the program is pondering. The point is to work around a wrinkle in
2602 // the UCI protocol: When pondering, the engine is not allowed to give a
2603 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2604 // We simply wait here until one of these commands is sent, and return,
2605 // after which the bestmove and pondermove will be printed (in id_loop()).
2607 void wait_for_stop_or_ponderhit() {
2609 std::string command;
2613 if (!std::getline(std::cin, command))
2616 if (command == "quit")
2621 else if (command == "ponderhit" || command == "stop")
2627 // idle_loop() is where the threads are parked when they have no work to do.
2628 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2629 // object for which the current thread is the master.
2631 void idle_loop(int threadID, SplitPoint* waitSp) {
2632 assert(threadID >= 0 && threadID < THREAD_MAX);
2634 Threads[threadID].running = true;
2637 if(AllThreadsShouldExit && threadID != 0)
2640 // If we are not thinking, wait for a condition to be signaled instead
2641 // of wasting CPU time polling for work:
2642 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2643 #if !defined(_MSC_VER)
2644 pthread_mutex_lock(&WaitLock);
2645 if(Idle || threadID >= ActiveThreads)
2646 pthread_cond_wait(&WaitCond, &WaitLock);
2647 pthread_mutex_unlock(&WaitLock);
2649 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2653 // If this thread has been assigned work, launch a search
2654 if(Threads[threadID].workIsWaiting) {
2655 Threads[threadID].workIsWaiting = false;
2656 if(Threads[threadID].splitPoint->pvNode)
2657 sp_search_pv(Threads[threadID].splitPoint, threadID);
2659 sp_search(Threads[threadID].splitPoint, threadID);
2660 Threads[threadID].idle = true;
2663 // If this thread is the master of a split point and all threads have
2664 // finished their work at this split point, return from the idle loop.
2665 if(waitSp != NULL && waitSp->cpus == 0)
2669 Threads[threadID].running = false;
2673 // init_split_point_stack() is called during program initialization, and
2674 // initializes all split point objects.
2676 void init_split_point_stack() {
2677 for(int i = 0; i < THREAD_MAX; i++)
2678 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2679 SplitPointStack[i][j].parent = NULL;
2680 lock_init(&(SplitPointStack[i][j].lock), NULL);
2685 // destroy_split_point_stack() is called when the program exits, and
2686 // destroys all locks in the precomputed split point objects.
2688 void destroy_split_point_stack() {
2689 for(int i = 0; i < THREAD_MAX; i++)
2690 for(int j = 0; j < MaxActiveSplitPoints; j++)
2691 lock_destroy(&(SplitPointStack[i][j].lock));
2695 // thread_should_stop() checks whether the thread with a given threadID has
2696 // been asked to stop, directly or indirectly. This can happen if a beta
2697 // cutoff has occured in thre thread's currently active split point, or in
2698 // some ancestor of the current split point.
2700 bool thread_should_stop(int threadID) {
2701 assert(threadID >= 0 && threadID < ActiveThreads);
2705 if(Threads[threadID].stop)
2707 if(ActiveThreads <= 2)
2709 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2711 Threads[threadID].stop = true;
2718 // thread_is_available() checks whether the thread with threadID "slave" is
2719 // available to help the thread with threadID "master" at a split point. An
2720 // obvious requirement is that "slave" must be idle. With more than two
2721 // threads, this is not by itself sufficient: If "slave" is the master of
2722 // some active split point, it is only available as a slave to the other
2723 // threads which are busy searching the split point at the top of "slave"'s
2724 // split point stack (the "helpful master concept" in YBWC terminology).
2726 bool thread_is_available(int slave, int master) {
2727 assert(slave >= 0 && slave < ActiveThreads);
2728 assert(master >= 0 && master < ActiveThreads);
2729 assert(ActiveThreads > 1);
2731 if(!Threads[slave].idle || slave == master)
2734 if(Threads[slave].activeSplitPoints == 0)
2735 // No active split points means that the thread is available as a slave
2736 // for any other thread.
2739 if(ActiveThreads == 2)
2742 // Apply the "helpful master" concept if possible.
2743 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2750 // idle_thread_exists() tries to find an idle thread which is available as
2751 // a slave for the thread with threadID "master".
2753 bool idle_thread_exists(int master) {
2754 assert(master >= 0 && master < ActiveThreads);
2755 assert(ActiveThreads > 1);
2757 for(int i = 0; i < ActiveThreads; i++)
2758 if(thread_is_available(i, master))
2764 // split() does the actual work of distributing the work at a node between
2765 // several threads at PV nodes. If it does not succeed in splitting the
2766 // node (because no idle threads are available, or because we have no unused
2767 // split point objects), the function immediately returns false. If
2768 // splitting is possible, a SplitPoint object is initialized with all the
2769 // data that must be copied to the helper threads (the current position and
2770 // search stack, alpha, beta, the search depth, etc.), and we tell our
2771 // helper threads that they have been assigned work. This will cause them
2772 // to instantly leave their idle loops and call sp_search_pv(). When all
2773 // threads have returned from sp_search_pv (or, equivalently, when
2774 // splitPoint->cpus becomes 0), split() returns true.
2776 bool split(const Position& p, SearchStack* sstck, int ply,
2777 Value* alpha, Value* beta, Value* bestValue, Depth depth, int* moves,
2778 MovePicker* mp, Bitboard dcCandidates, int master, bool pvNode) {
2781 assert(sstck != NULL);
2782 assert(ply >= 0 && ply < PLY_MAX);
2783 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2784 assert(!pvNode || *alpha < *beta);
2785 assert(*beta <= VALUE_INFINITE);
2786 assert(depth > Depth(0));
2787 assert(master >= 0 && master < ActiveThreads);
2788 assert(ActiveThreads > 1);
2790 SplitPoint* splitPoint;
2795 // If no other thread is available to help us, or if we have too many
2796 // active split points, don't split.
2797 if(!idle_thread_exists(master) ||
2798 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2799 lock_release(&MPLock);
2803 // Pick the next available split point object from the split point stack
2804 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2805 Threads[master].activeSplitPoints++;
2807 // Initialize the split point object
2808 splitPoint->parent = Threads[master].splitPoint;
2809 splitPoint->finished = false;
2810 splitPoint->ply = ply;
2811 splitPoint->depth = depth;
2812 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2813 splitPoint->beta = *beta;
2814 splitPoint->pvNode = pvNode;
2815 splitPoint->dcCandidates = dcCandidates;
2816 splitPoint->bestValue = *bestValue;
2817 splitPoint->master = master;
2818 splitPoint->mp = mp;
2819 splitPoint->moves = *moves;
2820 splitPoint->cpus = 1;
2821 splitPoint->pos.copy(p);
2822 splitPoint->parentSstack = sstck;
2823 for(i = 0; i < ActiveThreads; i++)
2824 splitPoint->slaves[i] = 0;
2826 // Copy the current position and the search stack to the master thread
2827 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2828 Threads[master].splitPoint = splitPoint;
2830 // Make copies of the current position and search stack for each thread
2831 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2833 if(thread_is_available(i, master)) {
2834 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2835 Threads[i].splitPoint = splitPoint;
2836 splitPoint->slaves[i] = 1;
2840 // Tell the threads that they have work to do. This will make them leave
2842 for(i = 0; i < ActiveThreads; i++)
2843 if(i == master || splitPoint->slaves[i]) {
2844 Threads[i].workIsWaiting = true;
2845 Threads[i].idle = false;
2846 Threads[i].stop = false;
2849 lock_release(&MPLock);
2851 // Everything is set up. The master thread enters the idle loop, from
2852 // which it will instantly launch a search, because its workIsWaiting
2853 // slot is 'true'. We send the split point as a second parameter to the
2854 // idle loop, which means that the main thread will return from the idle
2855 // loop when all threads have finished their work at this split point
2856 // (i.e. when // splitPoint->cpus == 0).
2857 idle_loop(master, splitPoint);
2859 // We have returned from the idle loop, which means that all threads are
2860 // finished. Update alpha, beta and bestvalue, and return.
2862 if(pvNode) *alpha = splitPoint->alpha;
2863 *beta = splitPoint->beta;
2864 *bestValue = splitPoint->bestValue;
2865 Threads[master].stop = false;
2866 Threads[master].idle = false;
2867 Threads[master].activeSplitPoints--;
2868 Threads[master].splitPoint = splitPoint->parent;
2869 lock_release(&MPLock);
2875 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2876 // to start a new search from the root.
2878 void wake_sleeping_threads() {
2879 if(ActiveThreads > 1) {
2880 for(int i = 1; i < ActiveThreads; i++) {
2881 Threads[i].idle = true;
2882 Threads[i].workIsWaiting = false;
2884 #if !defined(_MSC_VER)
2885 pthread_mutex_lock(&WaitLock);
2886 pthread_cond_broadcast(&WaitCond);
2887 pthread_mutex_unlock(&WaitLock);
2889 for(int i = 1; i < THREAD_MAX; i++)
2890 SetEvent(SitIdleEvent[i]);
2896 // init_thread() is the function which is called when a new thread is
2897 // launched. It simply calls the idle_loop() function with the supplied
2898 // threadID. There are two versions of this function; one for POSIX threads
2899 // and one for Windows threads.
2901 #if !defined(_MSC_VER)
2903 void *init_thread(void *threadID) {
2904 idle_loop(*(int *)threadID, NULL);
2910 DWORD WINAPI init_thread(LPVOID threadID) {
2911 idle_loop(*(int *)threadID, NULL);