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();
1288 && !value_is_mate(beta)
1289 && ok_to_do_nullmove(pos)
1290 && approximateEval >= beta - NullMoveMargin)
1292 ss[ply].currentMove = MOVE_NULL;
1295 pos.do_null_move(st);
1296 int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
1298 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1300 pos.undo_null_move();
1302 if (nullValue >= beta)
1304 if (depth < 6 * OnePly)
1307 // Do zugzwang verification search
1308 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1312 // The null move failed low, which means that we may be faced with
1313 // some kind of threat. If the previous move was reduced, check if
1314 // the move that refuted the null move was somehow connected to the
1315 // move which was reduced. If a connection is found, return a fail
1316 // low score (which will cause the reduced move to fail high in the
1317 // parent node, which will trigger a re-search with full depth).
1318 if (nullValue == value_mated_in(ply + 2))
1321 ss[ply].threatMove = ss[ply + 1].currentMove;
1322 if ( depth < ThreatDepth
1323 && ss[ply - 1].reduction
1324 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1328 // Null move search not allowed, try razoring
1329 else if ( !value_is_mate(beta)
1330 && depth < RazorDepth
1331 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1332 && ss[ply - 1].currentMove != MOVE_NULL
1333 && ttMove == MOVE_NONE
1334 && !pos.has_pawn_on_7th(pos.side_to_move()))
1336 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1337 if (v < beta - RazorMargins[int(depth) - 2])
1341 // Go with internal iterative deepening if we don't have a TT move
1342 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1343 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1345 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1346 ttMove = ss[ply].pv[ply];
1349 // Initialize a MovePicker object for the current position, and prepare
1350 // to search all moves.
1351 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1353 Move move, movesSearched[256];
1355 Value value, bestValue = -VALUE_INFINITE;
1356 Bitboard dcCandidates = mp.discovered_check_candidates();
1357 Value futilityValue = VALUE_NONE;
1358 bool useFutilityPruning = depth < SelectiveDepth
1361 // Loop through all legal moves until no moves remain or a beta cutoff
1363 while ( bestValue < beta
1364 && (move = mp.get_next_move()) != MOVE_NONE
1365 && !thread_should_stop(threadID))
1367 assert(move_is_ok(move));
1369 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1370 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1371 bool moveIsCapture = pos.move_is_capture(move);
1373 movesSearched[moveCount++] = ss[ply].currentMove = move;
1375 // Decide the new search depth
1377 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1378 Depth newDepth = depth - OnePly + ext;
1381 if ( useFutilityPruning
1384 && !move_is_promotion(move))
1386 // History pruning. See ok_to_prune() definition
1387 if ( moveCount >= 2 + int(depth)
1388 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1391 // Value based pruning
1392 if (approximateEval < beta)
1394 if (futilityValue == VALUE_NONE)
1395 futilityValue = evaluate(pos, ei, threadID)
1396 + FutilityMargins[int(depth) - 2];
1398 if (futilityValue < beta)
1400 if (futilityValue > bestValue)
1401 bestValue = futilityValue;
1407 // Make and search the move
1409 pos.do_move(move, st, dcCandidates);
1411 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1412 // if the move fails high will be re-searched at full depth.
1413 if ( depth >= 3*OnePly
1414 && moveCount >= LMRNonPVMoves
1417 && !move_is_promotion(move)
1418 && !move_is_castle(move)
1419 && !move_is_killer(move, ss[ply]))
1421 ss[ply].reduction = OnePly;
1422 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1425 value = beta; // Just to trigger next condition
1427 if (value >= beta) // Go with full depth non-pv search
1429 ss[ply].reduction = Depth(0);
1430 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1432 pos.undo_move(move);
1434 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1437 if (value > bestValue)
1443 if (value == value_mate_in(ply + 1))
1444 ss[ply].mateKiller = move;
1448 if ( ActiveThreads > 1
1450 && depth >= MinimumSplitDepth
1452 && idle_thread_exists(threadID)
1454 && !thread_should_stop(threadID)
1455 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1456 &mp, dcCandidates, threadID, false))
1460 // All legal moves have been searched. A special case: If there were
1461 // no legal moves, it must be mate or stalemate.
1463 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1465 // If the search is not aborted, update the transposition table,
1466 // history counters, and killer moves.
1467 if (AbortSearch || thread_should_stop(threadID))
1470 if (bestValue < beta)
1471 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1474 BetaCounter.add(pos.side_to_move(), depth, threadID);
1475 Move m = ss[ply].pv[ply];
1476 if (ok_to_history(pos, m)) // Only non capture moves are considered
1478 update_history(pos, m, depth, movesSearched, moveCount);
1479 update_killers(m, ss[ply]);
1481 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1484 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1490 // qsearch() is the quiescence search function, which is called by the main
1491 // search function when the remaining depth is zero (or, to be more precise,
1492 // less than OnePly).
1494 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1495 Depth depth, int ply, int threadID) {
1497 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1498 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1500 assert(ply >= 0 && ply < PLY_MAX);
1501 assert(threadID >= 0 && threadID < ActiveThreads);
1503 // Initialize, and make an early exit in case of an aborted search,
1504 // an instant draw, maximum ply reached, etc.
1505 init_node(pos, ss, ply, threadID);
1507 // After init_node() that calls poll()
1508 if (AbortSearch || thread_should_stop(threadID))
1514 // Transposition table lookup, only when not in PV
1515 TTEntry* tte = NULL;
1516 bool pvNode = (beta - alpha != 1);
1519 tte = TT.retrieve(pos.get_key());
1520 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1522 assert(tte->type() != VALUE_TYPE_EVAL);
1524 return value_from_tt(tte->value(), ply);
1527 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1529 // Evaluate the position statically
1532 bool isCheck = pos.is_check();
1533 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1536 staticValue = -VALUE_INFINITE;
1538 else if (tte && tte->type() == VALUE_TYPE_EVAL)
1540 // Use the cached evaluation score if possible
1541 assert(ei.futilityMargin == Value(0));
1543 staticValue = tte->value();
1546 staticValue = evaluate(pos, ei, threadID);
1548 if (ply == PLY_MAX - 1)
1549 return evaluate(pos, ei, threadID);
1551 // Initialize "stand pat score", and return it immediately if it is
1553 Value bestValue = staticValue;
1555 if (bestValue >= beta)
1557 // Store the score to avoid a future costly evaluation() call
1558 if (!isCheck && !tte && ei.futilityMargin == 0)
1559 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EVAL, Depth(-127*OnePly), MOVE_NONE);
1564 if (bestValue > alpha)
1567 // Initialize a MovePicker object for the current position, and prepare
1568 // to search the moves. Because the depth is <= 0 here, only captures,
1569 // queen promotions and checks (only if depth == 0) will be generated.
1570 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1573 Bitboard dcCandidates = mp.discovered_check_candidates();
1574 Color us = pos.side_to_move();
1575 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1577 // Loop through the moves until no moves remain or a beta cutoff
1579 while ( alpha < beta
1580 && (move = mp.get_next_move()) != MOVE_NONE)
1582 assert(move_is_ok(move));
1585 ss[ply].currentMove = move;
1591 && !move_is_promotion(move)
1592 && !pos.move_is_check(move, dcCandidates)
1593 && !pos.move_is_passed_pawn_push(move))
1595 Value futilityValue = staticValue
1596 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1597 pos.endgame_value_of_piece_on(move_to(move)))
1598 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1600 + ei.futilityMargin;
1602 if (futilityValue < alpha)
1604 if (futilityValue > bestValue)
1605 bestValue = futilityValue;
1610 // Don't search captures and checks with negative SEE values
1612 && !move_is_promotion(move)
1613 && pos.see_sign(move) < 0)
1616 // Make and search the move.
1618 pos.do_move(move, st, dcCandidates);
1619 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1620 pos.undo_move(move);
1622 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1625 if (value > bestValue)
1636 // All legal moves have been searched. A special case: If we're in check
1637 // and no legal moves were found, it is checkmate.
1638 if (pos.is_check() && moveCount == 0) // Mate!
1639 return value_mated_in(ply);
1641 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1643 // Update transposition table
1644 Move m = ss[ply].pv[ply];
1647 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1648 if (bestValue < beta)
1649 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE);
1651 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
1654 // Update killers only for good check moves
1655 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1656 update_killers(m, ss[ply]);
1662 // sp_search() is used to search from a split point. This function is called
1663 // by each thread working at the split point. It is similar to the normal
1664 // search() function, but simpler. Because we have already probed the hash
1665 // table, done a null move search, and searched the first move before
1666 // splitting, we don't have to repeat all this work in sp_search(). We
1667 // also don't need to store anything to the hash table here: This is taken
1668 // care of after we return from the split point.
1670 void sp_search(SplitPoint* sp, int threadID) {
1672 assert(threadID >= 0 && threadID < ActiveThreads);
1673 assert(ActiveThreads > 1);
1675 Position pos = Position(sp->pos);
1676 SearchStack* ss = sp->sstack[threadID];
1679 bool isCheck = pos.is_check();
1680 bool useFutilityPruning = sp->depth < SelectiveDepth
1683 while ( sp->bestValue < sp->beta
1684 && !thread_should_stop(threadID)
1685 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1687 assert(move_is_ok(move));
1689 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1690 bool moveIsCapture = pos.move_is_capture(move);
1692 lock_grab(&(sp->lock));
1693 int moveCount = ++sp->moves;
1694 lock_release(&(sp->lock));
1696 ss[sp->ply].currentMove = move;
1698 // Decide the new search depth.
1700 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1701 Depth newDepth = sp->depth - OnePly + ext;
1704 if ( useFutilityPruning
1707 && !move_is_promotion(move)
1708 && moveCount >= 2 + int(sp->depth)
1709 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1712 // Make and search the move.
1714 pos.do_move(move, st, sp->dcCandidates);
1716 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1717 // if the move fails high will be re-searched at full depth.
1719 && moveCount >= LMRNonPVMoves
1721 && !move_is_promotion(move)
1722 && !move_is_castle(move)
1723 && !move_is_killer(move, ss[sp->ply]))
1725 ss[sp->ply].reduction = OnePly;
1726 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1729 value = sp->beta; // Just to trigger next condition
1731 if (value >= sp->beta) // Go with full depth non-pv search
1733 ss[sp->ply].reduction = Depth(0);
1734 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1736 pos.undo_move(move);
1738 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1740 if (thread_should_stop(threadID))
1744 lock_grab(&(sp->lock));
1745 if (value > sp->bestValue && !thread_should_stop(threadID))
1747 sp->bestValue = value;
1748 if (sp->bestValue >= sp->beta)
1750 sp_update_pv(sp->parentSstack, ss, sp->ply);
1751 for (int i = 0; i < ActiveThreads; i++)
1752 if (i != threadID && (i == sp->master || sp->slaves[i]))
1753 Threads[i].stop = true;
1755 sp->finished = true;
1758 lock_release(&(sp->lock));
1761 lock_grab(&(sp->lock));
1763 // If this is the master thread and we have been asked to stop because of
1764 // a beta cutoff higher up in the tree, stop all slave threads.
1765 if (sp->master == threadID && thread_should_stop(threadID))
1766 for (int i = 0; i < ActiveThreads; i++)
1768 Threads[i].stop = true;
1771 sp->slaves[threadID] = 0;
1773 lock_release(&(sp->lock));
1777 // sp_search_pv() is used to search from a PV split point. This function
1778 // is called by each thread working at the split point. It is similar to
1779 // the normal search_pv() function, but simpler. Because we have already
1780 // probed the hash table and searched the first move before splitting, we
1781 // don't have to repeat all this work in sp_search_pv(). We also don't
1782 // need to store anything to the hash table here: This is taken care of
1783 // after we return from the split point.
1785 void sp_search_pv(SplitPoint* sp, int threadID) {
1787 assert(threadID >= 0 && threadID < ActiveThreads);
1788 assert(ActiveThreads > 1);
1790 Position pos = Position(sp->pos);
1791 SearchStack* ss = sp->sstack[threadID];
1795 while ( sp->alpha < sp->beta
1796 && !thread_should_stop(threadID)
1797 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1799 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1800 bool moveIsCapture = pos.move_is_capture(move);
1802 assert(move_is_ok(move));
1804 lock_grab(&(sp->lock));
1805 int moveCount = ++sp->moves;
1806 lock_release(&(sp->lock));
1808 ss[sp->ply].currentMove = move;
1810 // Decide the new search depth.
1812 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1813 Depth newDepth = sp->depth - OnePly + ext;
1815 // Make and search the move.
1817 pos.do_move(move, st, sp->dcCandidates);
1819 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1820 // if the move fails high will be re-searched at full depth.
1822 && moveCount >= LMRPVMoves
1824 && !move_is_promotion(move)
1825 && !move_is_castle(move)
1826 && !move_is_killer(move, ss[sp->ply]))
1828 ss[sp->ply].reduction = OnePly;
1829 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1832 value = sp->alpha + 1; // Just to trigger next condition
1834 if (value > sp->alpha) // Go with full depth non-pv search
1836 ss[sp->ply].reduction = Depth(0);
1837 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1839 if (value > sp->alpha && value < sp->beta)
1841 // When the search fails high at ply 1 while searching the first
1842 // move at the root, set the flag failHighPly1. This is used for
1843 // time managment: We don't want to stop the search early in
1844 // such cases, because resolving the fail high at ply 1 could
1845 // result in a big drop in score at the root.
1846 if (sp->ply == 1 && RootMoveNumber == 1)
1847 Threads[threadID].failHighPly1 = true;
1849 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1850 Threads[threadID].failHighPly1 = false;
1853 pos.undo_move(move);
1855 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1857 if (thread_should_stop(threadID))
1861 lock_grab(&(sp->lock));
1862 if (value > sp->bestValue && !thread_should_stop(threadID))
1864 sp->bestValue = value;
1865 if (value > sp->alpha)
1868 sp_update_pv(sp->parentSstack, ss, sp->ply);
1869 if (value == value_mate_in(sp->ply + 1))
1870 ss[sp->ply].mateKiller = move;
1872 if (value >= sp->beta)
1874 for (int i = 0; i < ActiveThreads; i++)
1875 if (i != threadID && (i == sp->master || sp->slaves[i]))
1876 Threads[i].stop = true;
1878 sp->finished = true;
1881 // If we are at ply 1, and we are searching the first root move at
1882 // ply 0, set the 'Problem' variable if the score has dropped a lot
1883 // (from the computer's point of view) since the previous iteration.
1886 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1889 lock_release(&(sp->lock));
1892 lock_grab(&(sp->lock));
1894 // If this is the master thread and we have been asked to stop because of
1895 // a beta cutoff higher up in the tree, stop all slave threads.
1896 if (sp->master == threadID && thread_should_stop(threadID))
1897 for (int i = 0; i < ActiveThreads; i++)
1899 Threads[i].stop = true;
1902 sp->slaves[threadID] = 0;
1904 lock_release(&(sp->lock));
1907 /// The BetaCounterType class
1909 BetaCounterType::BetaCounterType() { clear(); }
1911 void BetaCounterType::clear() {
1913 for (int i = 0; i < THREAD_MAX; i++)
1914 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
1917 void BetaCounterType::add(Color us, Depth d, int threadID) {
1919 // Weighted count based on depth
1920 Threads[threadID].betaCutOffs[us] += unsigned(d);
1923 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1926 for (int i = 0; i < THREAD_MAX; i++)
1928 our += Threads[i].betaCutOffs[us];
1929 their += Threads[i].betaCutOffs[opposite_color(us)];
1934 /// The RootMove class
1938 RootMove::RootMove() {
1939 nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
1942 // RootMove::operator<() is the comparison function used when
1943 // sorting the moves. A move m1 is considered to be better
1944 // than a move m2 if it has a higher score, or if the moves
1945 // have equal score but m1 has the higher node count.
1947 bool RootMove::operator<(const RootMove& m) {
1949 if (score != m.score)
1950 return (score < m.score);
1952 return theirBeta <= m.theirBeta;
1955 /// The RootMoveList class
1959 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1961 MoveStack mlist[MaxRootMoves];
1962 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1964 // Generate all legal moves
1965 int lm_count = generate_legal_moves(pos, mlist);
1967 // Add each move to the moves[] array
1968 for (int i = 0; i < lm_count; i++)
1970 bool includeMove = includeAllMoves;
1972 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1973 includeMove = (searchMoves[k] == mlist[i].move);
1978 // Find a quick score for the move
1980 SearchStack ss[PLY_MAX_PLUS_2];
1982 moves[count].move = mlist[i].move;
1983 pos.do_move(moves[count].move, st);
1984 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
1985 pos.undo_move(moves[count].move);
1986 moves[count].pv[0] = moves[count].move;
1987 moves[count].pv[1] = MOVE_NONE; // FIXME
1994 // Simple accessor methods for the RootMoveList class
1996 inline Move RootMoveList::get_move(int moveNum) const {
1997 return moves[moveNum].move;
2000 inline Value RootMoveList::get_move_score(int moveNum) const {
2001 return moves[moveNum].score;
2004 inline void RootMoveList::set_move_score(int moveNum, Value score) {
2005 moves[moveNum].score = score;
2008 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2009 moves[moveNum].nodes = nodes;
2010 moves[moveNum].cumulativeNodes += nodes;
2013 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2014 moves[moveNum].ourBeta = our;
2015 moves[moveNum].theirBeta = their;
2018 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2020 for(j = 0; pv[j] != MOVE_NONE; j++)
2021 moves[moveNum].pv[j] = pv[j];
2022 moves[moveNum].pv[j] = MOVE_NONE;
2025 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2026 return moves[moveNum].pv[i];
2029 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2030 return moves[moveNum].cumulativeNodes;
2033 inline int RootMoveList::move_count() const {
2038 // RootMoveList::scan_for_easy_move() is called at the end of the first
2039 // iteration, and is used to detect an "easy move", i.e. a move which appears
2040 // to be much bester than all the rest. If an easy move is found, the move
2041 // is returned, otherwise the function returns MOVE_NONE. It is very
2042 // important that this function is called at the right moment: The code
2043 // assumes that the first iteration has been completed and the moves have
2044 // been sorted. This is done in RootMoveList c'tor.
2046 Move RootMoveList::scan_for_easy_move() const {
2053 // moves are sorted so just consider the best and the second one
2054 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
2060 // RootMoveList::sort() sorts the root move list at the beginning of a new
2063 inline void RootMoveList::sort() {
2065 sort_multipv(count - 1); // all items
2069 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2070 // list by their scores and depths. It is used to order the different PVs
2071 // correctly in MultiPV mode.
2073 void RootMoveList::sort_multipv(int n) {
2075 for (int i = 1; i <= n; i++)
2077 RootMove rm = moves[i];
2079 for (j = i; j > 0 && moves[j-1] < rm; j--)
2080 moves[j] = moves[j-1];
2086 // init_node() is called at the beginning of all the search functions
2087 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2088 // stack object corresponding to the current node. Once every
2089 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2090 // for user input and checks whether it is time to stop the search.
2092 void init_node(const Position& pos, SearchStack ss[], int ply, int threadID) {
2094 assert(ply >= 0 && ply < PLY_MAX);
2095 assert(threadID >= 0 && threadID < ActiveThreads);
2097 if (Slowdown && Iteration >= 3)
2100 Threads[threadID].nodes++;
2105 if (NodesSincePoll >= NodesBetweenPolls)
2112 ss[ply+2].initKillers();
2114 if (Threads[threadID].printCurrentLine)
2115 print_current_line(ss, ply, threadID);
2119 // update_pv() is called whenever a search returns a value > alpha. It
2120 // updates the PV in the SearchStack object corresponding to the current
2123 void update_pv(SearchStack ss[], int ply) {
2124 assert(ply >= 0 && ply < PLY_MAX);
2126 ss[ply].pv[ply] = ss[ply].currentMove;
2128 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2129 ss[ply].pv[p] = ss[ply+1].pv[p];
2130 ss[ply].pv[p] = MOVE_NONE;
2134 // sp_update_pv() is a variant of update_pv for use at split points. The
2135 // difference between the two functions is that sp_update_pv also updates
2136 // the PV at the parent node.
2138 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2139 assert(ply >= 0 && ply < PLY_MAX);
2141 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2143 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2144 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2145 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2149 // connected_moves() tests whether two moves are 'connected' in the sense
2150 // that the first move somehow made the second move possible (for instance
2151 // if the moving piece is the same in both moves). The first move is
2152 // assumed to be the move that was made to reach the current position, while
2153 // the second move is assumed to be a move from the current position.
2155 bool connected_moves(const Position& pos, Move m1, Move m2) {
2156 Square f1, t1, f2, t2;
2158 assert(move_is_ok(m1));
2159 assert(move_is_ok(m2));
2161 if (m2 == MOVE_NONE)
2164 // Case 1: The moving piece is the same in both moves
2170 // Case 2: The destination square for m2 was vacated by m1
2176 // Case 3: Moving through the vacated square
2177 if ( piece_is_slider(pos.piece_on(f2))
2178 && bit_is_set(squares_between(f2, t2), f1))
2181 // Case 4: The destination square for m2 is attacked by the moving piece in m1
2182 if (pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
2185 // Case 5: Discovered check, checking piece is the piece moved in m1
2186 if ( piece_is_slider(pos.piece_on(t1))
2187 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2188 && !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())), t2))
2190 Bitboard occ = pos.occupied_squares();
2191 Color us = pos.side_to_move();
2192 Square ksq = pos.king_square(us);
2193 clear_bit(&occ, f2);
2194 if (pos.type_of_piece_on(t1) == BISHOP)
2196 if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2199 else if (pos.type_of_piece_on(t1) == ROOK)
2201 if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
2206 assert(pos.type_of_piece_on(t1) == QUEEN);
2207 if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
2215 // value_is_mate() checks if the given value is a mate one
2216 // eventually compensated for the ply.
2218 bool value_is_mate(Value value) {
2220 assert(abs(value) <= VALUE_INFINITE);
2222 return value <= value_mated_in(PLY_MAX)
2223 || value >= value_mate_in(PLY_MAX);
2227 // move_is_killer() checks if the given move is among the
2228 // killer moves of that ply.
2230 bool move_is_killer(Move m, const SearchStack& ss) {
2232 const Move* k = ss.killers;
2233 for (int i = 0; i < KILLER_MAX; i++, k++)
2241 // extension() decides whether a move should be searched with normal depth,
2242 // or with extended depth. Certain classes of moves (checking moves, in
2243 // particular) are searched with bigger depth than ordinary moves and in
2244 // any case are marked as 'dangerous'. Note that also if a move is not
2245 // extended, as example because the corresponding UCI option is set to zero,
2246 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2248 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2249 bool singleReply, bool mateThreat, bool* dangerous) {
2251 assert(m != MOVE_NONE);
2253 Depth result = Depth(0);
2254 *dangerous = check | singleReply | mateThreat;
2259 result += CheckExtension[pvNode];
2262 result += SingleReplyExtension[pvNode];
2265 result += MateThreatExtension[pvNode];
2268 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2270 if (pos.move_is_pawn_push_to_7th(m))
2272 result += PawnPushTo7thExtension[pvNode];
2275 if (pos.move_is_passed_pawn_push(m))
2277 result += PassedPawnExtension[pvNode];
2283 && pos.type_of_piece_on(move_to(m)) != PAWN
2284 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2285 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2286 && !move_is_promotion(m)
2289 result += PawnEndgameExtension[pvNode];
2295 && pos.type_of_piece_on(move_to(m)) != PAWN
2296 && pos.see_sign(m) >= 0)
2302 return Min(result, OnePly);
2306 // ok_to_do_nullmove() looks at the current position and decides whether
2307 // doing a 'null move' should be allowed. In order to avoid zugzwang
2308 // problems, null moves are not allowed when the side to move has very
2309 // little material left. Currently, the test is a bit too simple: Null
2310 // moves are avoided only when the side to move has only pawns left. It's
2311 // probably a good idea to avoid null moves in at least some more
2312 // complicated endgames, e.g. KQ vs KR. FIXME
2314 bool ok_to_do_nullmove(const Position& pos) {
2316 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2320 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2321 // non-tactical moves late in the move list close to the leaves are
2322 // candidates for pruning.
2324 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d) {
2326 assert(move_is_ok(m));
2327 assert(threat == MOVE_NONE || move_is_ok(threat));
2328 assert(!move_is_promotion(m));
2329 assert(!pos.move_is_check(m));
2330 assert(!pos.move_is_capture(m));
2331 assert(!pos.move_is_passed_pawn_push(m));
2332 assert(d >= OnePly);
2334 Square mfrom, mto, tfrom, tto;
2336 mfrom = move_from(m);
2338 tfrom = move_from(threat);
2339 tto = move_to(threat);
2341 // Case 1: Castling moves are never pruned
2342 if (move_is_castle(m))
2345 // Case 2: Don't prune moves which move the threatened piece
2346 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2349 // Case 3: If the threatened piece has value less than or equal to the
2350 // value of the threatening piece, don't prune move which defend it.
2351 if ( !PruneDefendingMoves
2352 && threat != MOVE_NONE
2353 && pos.move_is_capture(threat)
2354 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2355 || pos.type_of_piece_on(tfrom) == KING)
2356 && pos.move_attacks_square(m, tto))
2359 // Case 4: Don't prune moves with good history
2360 if (!H.ok_to_prune(pos.piece_on(mfrom), mto, d))
2363 // Case 5: If the moving piece in the threatened move is a slider, don't
2364 // prune safe moves which block its ray.
2365 if ( !PruneBlockingMoves
2366 && threat != MOVE_NONE
2367 && piece_is_slider(pos.piece_on(tfrom))
2368 && bit_is_set(squares_between(tfrom, tto), mto)
2369 && pos.see_sign(m) >= 0)
2376 // ok_to_use_TT() returns true if a transposition table score
2377 // can be used at a given point in search.
2379 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2381 Value v = value_from_tt(tte->value(), ply);
2383 return ( tte->depth() >= depth
2384 || v >= Max(value_mate_in(100), beta)
2385 || v < Min(value_mated_in(100), beta))
2387 && ( (is_lower_bound(tte->type()) && v >= beta)
2388 || (is_upper_bound(tte->type()) && v < beta));
2392 // ok_to_history() returns true if a move m can be stored
2393 // in history. Should be a non capturing move nor a promotion.
2395 bool ok_to_history(const Position& pos, Move m) {
2397 return !pos.move_is_capture(m) && !move_is_promotion(m);
2401 // update_history() registers a good move that produced a beta-cutoff
2402 // in history and marks as failures all the other moves of that ply.
2404 void update_history(const Position& pos, Move m, Depth depth,
2405 Move movesSearched[], int moveCount) {
2407 H.success(pos.piece_on(move_from(m)), move_to(m), depth);
2409 for (int i = 0; i < moveCount - 1; i++)
2411 assert(m != movesSearched[i]);
2412 if (ok_to_history(pos, movesSearched[i]))
2413 H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]));
2418 // update_killers() add a good move that produced a beta-cutoff
2419 // among the killer moves of that ply.
2421 void update_killers(Move m, SearchStack& ss) {
2423 if (m == ss.killers[0])
2426 for (int i = KILLER_MAX - 1; i > 0; i--)
2427 ss.killers[i] = ss.killers[i - 1];
2433 // slowdown() simply wastes CPU cycles doing nothing useful. It's used
2434 // in strength handicap mode.
2436 void slowdown(const Position &pos) {
2439 for (i = 0; i < n; i++) {
2440 Square s = Square(i&63);
2441 if (count_1s(pos.attacks_to(s)) > 63)
2442 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;
2447 // fail_high_ply_1() checks if some thread is currently resolving a fail
2448 // high at ply 1 at the node below the first root node. This information
2449 // is used for time managment.
2451 bool fail_high_ply_1() {
2453 for(int i = 0; i < ActiveThreads; i++)
2454 if (Threads[i].failHighPly1)
2461 // current_search_time() returns the number of milliseconds which have passed
2462 // since the beginning of the current search.
2464 int current_search_time() {
2465 return get_system_time() - SearchStartTime;
2469 // nps() computes the current nodes/second count.
2472 int t = current_search_time();
2473 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2477 // poll() performs two different functions: It polls for user input, and it
2478 // looks at the time consumed so far and decides if it's time to abort the
2483 static int lastInfoTime;
2484 int t = current_search_time();
2489 // We are line oriented, don't read single chars
2490 std::string command;
2491 if (!std::getline(std::cin, command))
2494 if (command == "quit")
2497 PonderSearch = false;
2501 else if (command == "stop")
2504 PonderSearch = false;
2506 else if (command == "ponderhit")
2509 // Print search information
2513 else if (lastInfoTime > t)
2514 // HACK: Must be a new search where we searched less than
2515 // NodesBetweenPolls nodes during the first second of search.
2518 else if (t - lastInfoTime >= 1000)
2525 if (dbg_show_hit_rate)
2526 dbg_print_hit_rate();
2528 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2529 << " time " << t << " hashfull " << TT.full() << std::endl;
2530 lock_release(&IOLock);
2531 if (ShowCurrentLine)
2532 Threads[0].printCurrentLine = true;
2534 // Should we stop the search?
2538 bool overTime = t > AbsoluteMaxSearchTime
2539 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2540 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2541 && t > 6*(MaxSearchTime + ExtraSearchTime));
2543 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2544 || (ExactMaxTime && t >= ExactMaxTime)
2545 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2550 // ponderhit() is called when the program is pondering (i.e. thinking while
2551 // it's the opponent's turn to move) in order to let the engine know that
2552 // it correctly predicted the opponent's move.
2556 int t = current_search_time();
2557 PonderSearch = false;
2558 if (Iteration >= 3 &&
2559 (!InfiniteSearch && (StopOnPonderhit ||
2560 t > AbsoluteMaxSearchTime ||
2561 (RootMoveNumber == 1 &&
2562 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2563 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2564 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2569 // print_current_line() prints the current line of search for a given
2570 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2572 void print_current_line(SearchStack ss[], int ply, int threadID) {
2574 assert(ply >= 0 && ply < PLY_MAX);
2575 assert(threadID >= 0 && threadID < ActiveThreads);
2577 if (!Threads[threadID].idle)
2580 std::cout << "info currline " << (threadID + 1);
2581 for (int p = 0; p < ply; p++)
2582 std::cout << " " << ss[p].currentMove;
2584 std::cout << std::endl;
2585 lock_release(&IOLock);
2587 Threads[threadID].printCurrentLine = false;
2588 if (threadID + 1 < ActiveThreads)
2589 Threads[threadID + 1].printCurrentLine = true;
2593 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2594 // while the program is pondering. The point is to work around a wrinkle in
2595 // the UCI protocol: When pondering, the engine is not allowed to give a
2596 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2597 // We simply wait here until one of these commands is sent, and return,
2598 // after which the bestmove and pondermove will be printed (in id_loop()).
2600 void wait_for_stop_or_ponderhit() {
2602 std::string command;
2606 if (!std::getline(std::cin, command))
2609 if (command == "quit")
2614 else if (command == "ponderhit" || command == "stop")
2620 // idle_loop() is where the threads are parked when they have no work to do.
2621 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2622 // object for which the current thread is the master.
2624 void idle_loop(int threadID, SplitPoint* waitSp) {
2625 assert(threadID >= 0 && threadID < THREAD_MAX);
2627 Threads[threadID].running = true;
2630 if(AllThreadsShouldExit && threadID != 0)
2633 // If we are not thinking, wait for a condition to be signaled instead
2634 // of wasting CPU time polling for work:
2635 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2636 #if !defined(_MSC_VER)
2637 pthread_mutex_lock(&WaitLock);
2638 if(Idle || threadID >= ActiveThreads)
2639 pthread_cond_wait(&WaitCond, &WaitLock);
2640 pthread_mutex_unlock(&WaitLock);
2642 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2646 // If this thread has been assigned work, launch a search
2647 if(Threads[threadID].workIsWaiting) {
2648 Threads[threadID].workIsWaiting = false;
2649 if(Threads[threadID].splitPoint->pvNode)
2650 sp_search_pv(Threads[threadID].splitPoint, threadID);
2652 sp_search(Threads[threadID].splitPoint, threadID);
2653 Threads[threadID].idle = true;
2656 // If this thread is the master of a split point and all threads have
2657 // finished their work at this split point, return from the idle loop.
2658 if(waitSp != NULL && waitSp->cpus == 0)
2662 Threads[threadID].running = false;
2666 // init_split_point_stack() is called during program initialization, and
2667 // initializes all split point objects.
2669 void init_split_point_stack() {
2670 for(int i = 0; i < THREAD_MAX; i++)
2671 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2672 SplitPointStack[i][j].parent = NULL;
2673 lock_init(&(SplitPointStack[i][j].lock), NULL);
2678 // destroy_split_point_stack() is called when the program exits, and
2679 // destroys all locks in the precomputed split point objects.
2681 void destroy_split_point_stack() {
2682 for(int i = 0; i < THREAD_MAX; i++)
2683 for(int j = 0; j < MaxActiveSplitPoints; j++)
2684 lock_destroy(&(SplitPointStack[i][j].lock));
2688 // thread_should_stop() checks whether the thread with a given threadID has
2689 // been asked to stop, directly or indirectly. This can happen if a beta
2690 // cutoff has occured in thre thread's currently active split point, or in
2691 // some ancestor of the current split point.
2693 bool thread_should_stop(int threadID) {
2694 assert(threadID >= 0 && threadID < ActiveThreads);
2698 if(Threads[threadID].stop)
2700 if(ActiveThreads <= 2)
2702 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2704 Threads[threadID].stop = true;
2711 // thread_is_available() checks whether the thread with threadID "slave" is
2712 // available to help the thread with threadID "master" at a split point. An
2713 // obvious requirement is that "slave" must be idle. With more than two
2714 // threads, this is not by itself sufficient: If "slave" is the master of
2715 // some active split point, it is only available as a slave to the other
2716 // threads which are busy searching the split point at the top of "slave"'s
2717 // split point stack (the "helpful master concept" in YBWC terminology).
2719 bool thread_is_available(int slave, int master) {
2720 assert(slave >= 0 && slave < ActiveThreads);
2721 assert(master >= 0 && master < ActiveThreads);
2722 assert(ActiveThreads > 1);
2724 if(!Threads[slave].idle || slave == master)
2727 if(Threads[slave].activeSplitPoints == 0)
2728 // No active split points means that the thread is available as a slave
2729 // for any other thread.
2732 if(ActiveThreads == 2)
2735 // Apply the "helpful master" concept if possible.
2736 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2743 // idle_thread_exists() tries to find an idle thread which is available as
2744 // a slave for the thread with threadID "master".
2746 bool idle_thread_exists(int master) {
2747 assert(master >= 0 && master < ActiveThreads);
2748 assert(ActiveThreads > 1);
2750 for(int i = 0; i < ActiveThreads; i++)
2751 if(thread_is_available(i, master))
2757 // split() does the actual work of distributing the work at a node between
2758 // several threads at PV nodes. If it does not succeed in splitting the
2759 // node (because no idle threads are available, or because we have no unused
2760 // split point objects), the function immediately returns false. If
2761 // splitting is possible, a SplitPoint object is initialized with all the
2762 // data that must be copied to the helper threads (the current position and
2763 // search stack, alpha, beta, the search depth, etc.), and we tell our
2764 // helper threads that they have been assigned work. This will cause them
2765 // to instantly leave their idle loops and call sp_search_pv(). When all
2766 // threads have returned from sp_search_pv (or, equivalently, when
2767 // splitPoint->cpus becomes 0), split() returns true.
2769 bool split(const Position& p, SearchStack* sstck, int ply,
2770 Value* alpha, Value* beta, Value* bestValue, Depth depth, int* moves,
2771 MovePicker* mp, Bitboard dcCandidates, int master, bool pvNode) {
2774 assert(sstck != NULL);
2775 assert(ply >= 0 && ply < PLY_MAX);
2776 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2777 assert(!pvNode || *alpha < *beta);
2778 assert(*beta <= VALUE_INFINITE);
2779 assert(depth > Depth(0));
2780 assert(master >= 0 && master < ActiveThreads);
2781 assert(ActiveThreads > 1);
2783 SplitPoint* splitPoint;
2788 // If no other thread is available to help us, or if we have too many
2789 // active split points, don't split.
2790 if(!idle_thread_exists(master) ||
2791 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2792 lock_release(&MPLock);
2796 // Pick the next available split point object from the split point stack
2797 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2798 Threads[master].activeSplitPoints++;
2800 // Initialize the split point object
2801 splitPoint->parent = Threads[master].splitPoint;
2802 splitPoint->finished = false;
2803 splitPoint->ply = ply;
2804 splitPoint->depth = depth;
2805 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2806 splitPoint->beta = *beta;
2807 splitPoint->pvNode = pvNode;
2808 splitPoint->dcCandidates = dcCandidates;
2809 splitPoint->bestValue = *bestValue;
2810 splitPoint->master = master;
2811 splitPoint->mp = mp;
2812 splitPoint->moves = *moves;
2813 splitPoint->cpus = 1;
2814 splitPoint->pos.copy(p);
2815 splitPoint->parentSstack = sstck;
2816 for(i = 0; i < ActiveThreads; i++)
2817 splitPoint->slaves[i] = 0;
2819 // Copy the current position and the search stack to the master thread
2820 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2821 Threads[master].splitPoint = splitPoint;
2823 // Make copies of the current position and search stack for each thread
2824 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2826 if(thread_is_available(i, master)) {
2827 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2828 Threads[i].splitPoint = splitPoint;
2829 splitPoint->slaves[i] = 1;
2833 // Tell the threads that they have work to do. This will make them leave
2835 for(i = 0; i < ActiveThreads; i++)
2836 if(i == master || splitPoint->slaves[i]) {
2837 Threads[i].workIsWaiting = true;
2838 Threads[i].idle = false;
2839 Threads[i].stop = false;
2842 lock_release(&MPLock);
2844 // Everything is set up. The master thread enters the idle loop, from
2845 // which it will instantly launch a search, because its workIsWaiting
2846 // slot is 'true'. We send the split point as a second parameter to the
2847 // idle loop, which means that the main thread will return from the idle
2848 // loop when all threads have finished their work at this split point
2849 // (i.e. when // splitPoint->cpus == 0).
2850 idle_loop(master, splitPoint);
2852 // We have returned from the idle loop, which means that all threads are
2853 // finished. Update alpha, beta and bestvalue, and return.
2855 if(pvNode) *alpha = splitPoint->alpha;
2856 *beta = splitPoint->beta;
2857 *bestValue = splitPoint->bestValue;
2858 Threads[master].stop = false;
2859 Threads[master].idle = false;
2860 Threads[master].activeSplitPoints--;
2861 Threads[master].splitPoint = splitPoint->parent;
2862 lock_release(&MPLock);
2868 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2869 // to start a new search from the root.
2871 void wake_sleeping_threads() {
2872 if(ActiveThreads > 1) {
2873 for(int i = 1; i < ActiveThreads; i++) {
2874 Threads[i].idle = true;
2875 Threads[i].workIsWaiting = false;
2877 #if !defined(_MSC_VER)
2878 pthread_mutex_lock(&WaitLock);
2879 pthread_cond_broadcast(&WaitCond);
2880 pthread_mutex_unlock(&WaitLock);
2882 for(int i = 1; i < THREAD_MAX; i++)
2883 SetEvent(SitIdleEvent[i]);
2889 // init_thread() is the function which is called when a new thread is
2890 // launched. It simply calls the idle_loop() function with the supplied
2891 // threadID. There are two versions of this function; one for POSIX threads
2892 // and one for Windows threads.
2894 #if !defined(_MSC_VER)
2896 void *init_thread(void *threadID) {
2897 idle_loop(*(int *)threadID, NULL);
2903 DWORD WINAPI init_thread(LPVOID threadID) {
2904 idle_loop(*(int *)threadID, NULL);