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);
1294 ss[ply].currentMove = MOVE_NULL;
1297 pos.do_null_move(st);
1298 int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
1300 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1302 pos.undo_null_move();
1304 if (nullValue >= beta)
1306 if (depth < 6 * OnePly)
1309 // Do zugzwang verification search
1310 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1314 // The null move failed low, which means that we may be faced with
1315 // some kind of threat. If the previous move was reduced, check if
1316 // the move that refuted the null move was somehow connected to the
1317 // move which was reduced. If a connection is found, return a fail
1318 // low score (which will cause the reduced move to fail high in the
1319 // parent node, which will trigger a re-search with full depth).
1320 if (nullValue == value_mated_in(ply + 2))
1323 ss[ply].threatMove = ss[ply + 1].currentMove;
1324 if ( depth < ThreatDepth
1325 && ss[ply - 1].reduction
1326 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1330 // Null move search not allowed, try razoring
1332 && !value_is_mate(beta)
1333 && depth < RazorDepth
1334 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1335 && ss[ply - 1].currentMove != MOVE_NULL
1336 && ttMove == MOVE_NONE
1337 && !pos.has_pawn_on_7th(pos.side_to_move()))
1339 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1340 if (v < beta - RazorMargins[int(depth) - 2])
1344 // Go with internal iterative deepening if we don't have a TT move
1345 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1346 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1348 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1349 ttMove = ss[ply].pv[ply];
1352 // Initialize a MovePicker object for the current position, and prepare
1353 // to search all moves.
1354 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1356 Move move, movesSearched[256];
1358 Value value, bestValue = -VALUE_INFINITE;
1359 Bitboard dcCandidates = mp.discovered_check_candidates();
1360 Value futilityValue = VALUE_NONE;
1361 bool useFutilityPruning = depth < SelectiveDepth
1364 // Loop through all legal moves until no moves remain or a beta cutoff
1366 while ( bestValue < beta
1367 && (move = mp.get_next_move()) != MOVE_NONE
1368 && !thread_should_stop(threadID))
1370 assert(move_is_ok(move));
1372 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1373 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1374 bool moveIsCapture = pos.move_is_capture(move);
1376 movesSearched[moveCount++] = ss[ply].currentMove = move;
1378 // Decide the new search depth
1380 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1381 Depth newDepth = depth - OnePly + ext;
1384 if ( useFutilityPruning
1387 && !move_is_promotion(move))
1389 // History pruning. See ok_to_prune() definition
1390 if ( moveCount >= 2 + int(depth)
1391 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1394 // Value based pruning
1395 if (approximateEval < beta)
1397 if (futilityValue == VALUE_NONE)
1398 futilityValue = evaluate(pos, ei, threadID)
1399 + FutilityMargins[int(depth) - 2];
1401 if (futilityValue < beta)
1403 if (futilityValue > bestValue)
1404 bestValue = futilityValue;
1410 // Make and search the move
1412 pos.do_move(move, st, dcCandidates);
1414 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1415 // if the move fails high will be re-searched at full depth.
1416 if ( depth >= 3*OnePly
1417 && moveCount >= LMRNonPVMoves
1420 && !move_is_promotion(move)
1421 && !move_is_castle(move)
1422 && !move_is_killer(move, ss[ply]))
1424 ss[ply].reduction = OnePly;
1425 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1428 value = beta; // Just to trigger next condition
1430 if (value >= beta) // Go with full depth non-pv search
1432 ss[ply].reduction = Depth(0);
1433 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1435 pos.undo_move(move);
1437 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1440 if (value > bestValue)
1446 if (value == value_mate_in(ply + 1))
1447 ss[ply].mateKiller = move;
1451 if ( ActiveThreads > 1
1453 && depth >= MinimumSplitDepth
1455 && idle_thread_exists(threadID)
1457 && !thread_should_stop(threadID)
1458 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1459 &mp, dcCandidates, threadID, false))
1463 // All legal moves have been searched. A special case: If there were
1464 // no legal moves, it must be mate or stalemate.
1466 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1468 // If the search is not aborted, update the transposition table,
1469 // history counters, and killer moves.
1470 if (AbortSearch || thread_should_stop(threadID))
1473 if (bestValue < beta)
1474 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1477 BetaCounter.add(pos.side_to_move(), depth, threadID);
1478 Move m = ss[ply].pv[ply];
1479 if (ok_to_history(pos, m)) // Only non capture moves are considered
1481 update_history(pos, m, depth, movesSearched, moveCount);
1482 update_killers(m, ss[ply]);
1484 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1487 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1493 // qsearch() is the quiescence search function, which is called by the main
1494 // search function when the remaining depth is zero (or, to be more precise,
1495 // less than OnePly).
1497 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1498 Depth depth, int ply, int threadID) {
1500 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1501 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1503 assert(ply >= 0 && ply < PLY_MAX);
1504 assert(threadID >= 0 && threadID < ActiveThreads);
1506 // Initialize, and make an early exit in case of an aborted search,
1507 // an instant draw, maximum ply reached, etc.
1508 init_node(pos, ss, ply, threadID);
1510 // After init_node() that calls poll()
1511 if (AbortSearch || thread_should_stop(threadID))
1517 // Transposition table lookup, only when not in PV
1518 TTEntry* tte = NULL;
1519 bool pvNode = (beta - alpha != 1);
1522 tte = TT.retrieve(pos.get_key());
1523 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1525 assert(tte->type() != VALUE_TYPE_EVAL);
1527 return value_from_tt(tte->value(), ply);
1530 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1532 // Evaluate the position statically
1535 bool isCheck = pos.is_check();
1536 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1539 staticValue = -VALUE_INFINITE;
1541 else if (tte && tte->type() == VALUE_TYPE_EVAL)
1543 // Use the cached evaluation score if possible
1544 assert(ei.futilityMargin == Value(0));
1546 staticValue = tte->value();
1549 staticValue = evaluate(pos, ei, threadID);
1551 if (ply == PLY_MAX - 1)
1552 return evaluate(pos, ei, threadID);
1554 // Initialize "stand pat score", and return it immediately if it is
1556 Value bestValue = staticValue;
1558 if (bestValue >= beta)
1560 // Store the score to avoid a future costly evaluation() call
1561 if (!isCheck && !tte && ei.futilityMargin == 0)
1562 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EVAL, Depth(-127*OnePly), MOVE_NONE);
1567 if (bestValue > alpha)
1570 // Initialize a MovePicker object for the current position, and prepare
1571 // to search the moves. Because the depth is <= 0 here, only captures,
1572 // queen promotions and checks (only if depth == 0) will be generated.
1573 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1576 Bitboard dcCandidates = mp.discovered_check_candidates();
1577 Color us = pos.side_to_move();
1578 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1580 // Loop through the moves until no moves remain or a beta cutoff
1582 while ( alpha < beta
1583 && (move = mp.get_next_move()) != MOVE_NONE)
1585 assert(move_is_ok(move));
1588 ss[ply].currentMove = move;
1594 && !move_is_promotion(move)
1595 && !pos.move_is_check(move, dcCandidates)
1596 && !pos.move_is_passed_pawn_push(move))
1598 Value futilityValue = staticValue
1599 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1600 pos.endgame_value_of_piece_on(move_to(move)))
1601 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1603 + ei.futilityMargin;
1605 if (futilityValue < alpha)
1607 if (futilityValue > bestValue)
1608 bestValue = futilityValue;
1613 // Don't search captures and checks with negative SEE values
1615 && !move_is_promotion(move)
1616 && pos.see_sign(move) < 0)
1619 // Make and search the move.
1621 pos.do_move(move, st, dcCandidates);
1622 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1623 pos.undo_move(move);
1625 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1628 if (value > bestValue)
1639 // All legal moves have been searched. A special case: If we're in check
1640 // and no legal moves were found, it is checkmate.
1641 if (pos.is_check() && moveCount == 0) // Mate!
1642 return value_mated_in(ply);
1644 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1646 // Update transposition table
1647 Move m = ss[ply].pv[ply];
1650 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1651 if (bestValue < beta)
1652 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE);
1654 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
1657 // Update killers only for good check moves
1658 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1659 update_killers(m, ss[ply]);
1665 // sp_search() is used to search from a split point. This function is called
1666 // by each thread working at the split point. It is similar to the normal
1667 // search() function, but simpler. Because we have already probed the hash
1668 // table, done a null move search, and searched the first move before
1669 // splitting, we don't have to repeat all this work in sp_search(). We
1670 // also don't need to store anything to the hash table here: This is taken
1671 // care of after we return from the split point.
1673 void sp_search(SplitPoint* sp, int threadID) {
1675 assert(threadID >= 0 && threadID < ActiveThreads);
1676 assert(ActiveThreads > 1);
1678 Position pos = Position(sp->pos);
1679 SearchStack* ss = sp->sstack[threadID];
1682 bool isCheck = pos.is_check();
1683 bool useFutilityPruning = sp->depth < SelectiveDepth
1686 while ( sp->bestValue < sp->beta
1687 && !thread_should_stop(threadID)
1688 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1690 assert(move_is_ok(move));
1692 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1693 bool moveIsCapture = pos.move_is_capture(move);
1695 lock_grab(&(sp->lock));
1696 int moveCount = ++sp->moves;
1697 lock_release(&(sp->lock));
1699 ss[sp->ply].currentMove = move;
1701 // Decide the new search depth.
1703 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1704 Depth newDepth = sp->depth - OnePly + ext;
1707 if ( useFutilityPruning
1710 && !move_is_promotion(move)
1711 && moveCount >= 2 + int(sp->depth)
1712 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1715 // Make and search the move.
1717 pos.do_move(move, st, sp->dcCandidates);
1719 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1720 // if the move fails high will be re-searched at full depth.
1722 && moveCount >= LMRNonPVMoves
1724 && !move_is_promotion(move)
1725 && !move_is_castle(move)
1726 && !move_is_killer(move, ss[sp->ply]))
1728 ss[sp->ply].reduction = OnePly;
1729 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1732 value = sp->beta; // Just to trigger next condition
1734 if (value >= sp->beta) // Go with full depth non-pv search
1736 ss[sp->ply].reduction = Depth(0);
1737 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1739 pos.undo_move(move);
1741 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1743 if (thread_should_stop(threadID))
1747 lock_grab(&(sp->lock));
1748 if (value > sp->bestValue && !thread_should_stop(threadID))
1750 sp->bestValue = value;
1751 if (sp->bestValue >= sp->beta)
1753 sp_update_pv(sp->parentSstack, ss, sp->ply);
1754 for (int i = 0; i < ActiveThreads; i++)
1755 if (i != threadID && (i == sp->master || sp->slaves[i]))
1756 Threads[i].stop = true;
1758 sp->finished = true;
1761 lock_release(&(sp->lock));
1764 lock_grab(&(sp->lock));
1766 // If this is the master thread and we have been asked to stop because of
1767 // a beta cutoff higher up in the tree, stop all slave threads.
1768 if (sp->master == threadID && thread_should_stop(threadID))
1769 for (int i = 0; i < ActiveThreads; i++)
1771 Threads[i].stop = true;
1774 sp->slaves[threadID] = 0;
1776 lock_release(&(sp->lock));
1780 // sp_search_pv() is used to search from a PV split point. This function
1781 // is called by each thread working at the split point. It is similar to
1782 // the normal search_pv() function, but simpler. Because we have already
1783 // probed the hash table and searched the first move before splitting, we
1784 // don't have to repeat all this work in sp_search_pv(). We also don't
1785 // need to store anything to the hash table here: This is taken care of
1786 // after we return from the split point.
1788 void sp_search_pv(SplitPoint* sp, int threadID) {
1790 assert(threadID >= 0 && threadID < ActiveThreads);
1791 assert(ActiveThreads > 1);
1793 Position pos = Position(sp->pos);
1794 SearchStack* ss = sp->sstack[threadID];
1798 while ( sp->alpha < sp->beta
1799 && !thread_should_stop(threadID)
1800 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1802 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1803 bool moveIsCapture = pos.move_is_capture(move);
1805 assert(move_is_ok(move));
1807 lock_grab(&(sp->lock));
1808 int moveCount = ++sp->moves;
1809 lock_release(&(sp->lock));
1811 ss[sp->ply].currentMove = move;
1813 // Decide the new search depth.
1815 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1816 Depth newDepth = sp->depth - OnePly + ext;
1818 // Make and search the move.
1820 pos.do_move(move, st, sp->dcCandidates);
1822 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1823 // if the move fails high will be re-searched at full depth.
1825 && moveCount >= LMRPVMoves
1827 && !move_is_promotion(move)
1828 && !move_is_castle(move)
1829 && !move_is_killer(move, ss[sp->ply]))
1831 ss[sp->ply].reduction = OnePly;
1832 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1835 value = sp->alpha + 1; // Just to trigger next condition
1837 if (value > sp->alpha) // Go with full depth non-pv search
1839 ss[sp->ply].reduction = Depth(0);
1840 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1842 if (value > sp->alpha && value < sp->beta)
1844 // When the search fails high at ply 1 while searching the first
1845 // move at the root, set the flag failHighPly1. This is used for
1846 // time managment: We don't want to stop the search early in
1847 // such cases, because resolving the fail high at ply 1 could
1848 // result in a big drop in score at the root.
1849 if (sp->ply == 1 && RootMoveNumber == 1)
1850 Threads[threadID].failHighPly1 = true;
1852 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1853 Threads[threadID].failHighPly1 = false;
1856 pos.undo_move(move);
1858 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1860 if (thread_should_stop(threadID))
1864 lock_grab(&(sp->lock));
1865 if (value > sp->bestValue && !thread_should_stop(threadID))
1867 sp->bestValue = value;
1868 if (value > sp->alpha)
1871 sp_update_pv(sp->parentSstack, ss, sp->ply);
1872 if (value == value_mate_in(sp->ply + 1))
1873 ss[sp->ply].mateKiller = move;
1875 if (value >= sp->beta)
1877 for (int i = 0; i < ActiveThreads; i++)
1878 if (i != threadID && (i == sp->master || sp->slaves[i]))
1879 Threads[i].stop = true;
1881 sp->finished = true;
1884 // If we are at ply 1, and we are searching the first root move at
1885 // ply 0, set the 'Problem' variable if the score has dropped a lot
1886 // (from the computer's point of view) since the previous iteration.
1889 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1892 lock_release(&(sp->lock));
1895 lock_grab(&(sp->lock));
1897 // If this is the master thread and we have been asked to stop because of
1898 // a beta cutoff higher up in the tree, stop all slave threads.
1899 if (sp->master == threadID && thread_should_stop(threadID))
1900 for (int i = 0; i < ActiveThreads; i++)
1902 Threads[i].stop = true;
1905 sp->slaves[threadID] = 0;
1907 lock_release(&(sp->lock));
1910 /// The BetaCounterType class
1912 BetaCounterType::BetaCounterType() { clear(); }
1914 void BetaCounterType::clear() {
1916 for (int i = 0; i < THREAD_MAX; i++)
1917 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
1920 void BetaCounterType::add(Color us, Depth d, int threadID) {
1922 // Weighted count based on depth
1923 Threads[threadID].betaCutOffs[us] += unsigned(d);
1926 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1929 for (int i = 0; i < THREAD_MAX; i++)
1931 our += Threads[i].betaCutOffs[us];
1932 their += Threads[i].betaCutOffs[opposite_color(us)];
1937 /// The RootMove class
1941 RootMove::RootMove() {
1942 nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
1945 // RootMove::operator<() is the comparison function used when
1946 // sorting the moves. A move m1 is considered to be better
1947 // than a move m2 if it has a higher score, or if the moves
1948 // have equal score but m1 has the higher node count.
1950 bool RootMove::operator<(const RootMove& m) {
1952 if (score != m.score)
1953 return (score < m.score);
1955 return theirBeta <= m.theirBeta;
1958 /// The RootMoveList class
1962 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1964 MoveStack mlist[MaxRootMoves];
1965 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1967 // Generate all legal moves
1968 int lm_count = generate_legal_moves(pos, mlist);
1970 // Add each move to the moves[] array
1971 for (int i = 0; i < lm_count; i++)
1973 bool includeMove = includeAllMoves;
1975 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1976 includeMove = (searchMoves[k] == mlist[i].move);
1981 // Find a quick score for the move
1983 SearchStack ss[PLY_MAX_PLUS_2];
1985 moves[count].move = mlist[i].move;
1986 pos.do_move(moves[count].move, st);
1987 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
1988 pos.undo_move(moves[count].move);
1989 moves[count].pv[0] = moves[count].move;
1990 moves[count].pv[1] = MOVE_NONE; // FIXME
1997 // Simple accessor methods for the RootMoveList class
1999 inline Move RootMoveList::get_move(int moveNum) const {
2000 return moves[moveNum].move;
2003 inline Value RootMoveList::get_move_score(int moveNum) const {
2004 return moves[moveNum].score;
2007 inline void RootMoveList::set_move_score(int moveNum, Value score) {
2008 moves[moveNum].score = score;
2011 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2012 moves[moveNum].nodes = nodes;
2013 moves[moveNum].cumulativeNodes += nodes;
2016 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2017 moves[moveNum].ourBeta = our;
2018 moves[moveNum].theirBeta = their;
2021 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2023 for(j = 0; pv[j] != MOVE_NONE; j++)
2024 moves[moveNum].pv[j] = pv[j];
2025 moves[moveNum].pv[j] = MOVE_NONE;
2028 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2029 return moves[moveNum].pv[i];
2032 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2033 return moves[moveNum].cumulativeNodes;
2036 inline int RootMoveList::move_count() const {
2041 // RootMoveList::scan_for_easy_move() is called at the end of the first
2042 // iteration, and is used to detect an "easy move", i.e. a move which appears
2043 // to be much bester than all the rest. If an easy move is found, the move
2044 // is returned, otherwise the function returns MOVE_NONE. It is very
2045 // important that this function is called at the right moment: The code
2046 // assumes that the first iteration has been completed and the moves have
2047 // been sorted. This is done in RootMoveList c'tor.
2049 Move RootMoveList::scan_for_easy_move() const {
2056 // moves are sorted so just consider the best and the second one
2057 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
2063 // RootMoveList::sort() sorts the root move list at the beginning of a new
2066 inline void RootMoveList::sort() {
2068 sort_multipv(count - 1); // all items
2072 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2073 // list by their scores and depths. It is used to order the different PVs
2074 // correctly in MultiPV mode.
2076 void RootMoveList::sort_multipv(int n) {
2078 for (int i = 1; i <= n; i++)
2080 RootMove rm = moves[i];
2082 for (j = i; j > 0 && moves[j-1] < rm; j--)
2083 moves[j] = moves[j-1];
2089 // init_node() is called at the beginning of all the search functions
2090 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2091 // stack object corresponding to the current node. Once every
2092 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2093 // for user input and checks whether it is time to stop the search.
2095 void init_node(const Position& pos, SearchStack ss[], int ply, int threadID) {
2097 assert(ply >= 0 && ply < PLY_MAX);
2098 assert(threadID >= 0 && threadID < ActiveThreads);
2100 if (Slowdown && Iteration >= 3)
2103 Threads[threadID].nodes++;
2108 if (NodesSincePoll >= NodesBetweenPolls)
2115 ss[ply+2].initKillers();
2117 if (Threads[threadID].printCurrentLine)
2118 print_current_line(ss, ply, threadID);
2122 // update_pv() is called whenever a search returns a value > alpha. It
2123 // updates the PV in the SearchStack object corresponding to the current
2126 void update_pv(SearchStack ss[], int ply) {
2127 assert(ply >= 0 && ply < PLY_MAX);
2129 ss[ply].pv[ply] = ss[ply].currentMove;
2131 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2132 ss[ply].pv[p] = ss[ply+1].pv[p];
2133 ss[ply].pv[p] = MOVE_NONE;
2137 // sp_update_pv() is a variant of update_pv for use at split points. The
2138 // difference between the two functions is that sp_update_pv also updates
2139 // the PV at the parent node.
2141 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2142 assert(ply >= 0 && ply < PLY_MAX);
2144 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2146 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2147 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2148 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2152 // connected_moves() tests whether two moves are 'connected' in the sense
2153 // that the first move somehow made the second move possible (for instance
2154 // if the moving piece is the same in both moves). The first move is
2155 // assumed to be the move that was made to reach the current position, while
2156 // the second move is assumed to be a move from the current position.
2158 bool connected_moves(const Position& pos, Move m1, Move m2) {
2159 Square f1, t1, f2, t2;
2161 assert(move_is_ok(m1));
2162 assert(move_is_ok(m2));
2164 if (m2 == MOVE_NONE)
2167 // Case 1: The moving piece is the same in both moves
2173 // Case 2: The destination square for m2 was vacated by m1
2179 // Case 3: Moving through the vacated square
2180 if ( piece_is_slider(pos.piece_on(f2))
2181 && bit_is_set(squares_between(f2, t2), f1))
2184 // Case 4: The destination square for m2 is attacked by the moving piece in m1
2185 if (pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
2188 // Case 5: Discovered check, checking piece is the piece moved in m1
2189 if ( piece_is_slider(pos.piece_on(t1))
2190 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2191 && !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())), t2))
2193 Bitboard occ = pos.occupied_squares();
2194 Color us = pos.side_to_move();
2195 Square ksq = pos.king_square(us);
2196 clear_bit(&occ, f2);
2197 if (pos.type_of_piece_on(t1) == BISHOP)
2199 if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2202 else if (pos.type_of_piece_on(t1) == ROOK)
2204 if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
2209 assert(pos.type_of_piece_on(t1) == QUEEN);
2210 if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
2218 // value_is_mate() checks if the given value is a mate one
2219 // eventually compensated for the ply.
2221 bool value_is_mate(Value value) {
2223 assert(abs(value) <= VALUE_INFINITE);
2225 return value <= value_mated_in(PLY_MAX)
2226 || value >= value_mate_in(PLY_MAX);
2230 // move_is_killer() checks if the given move is among the
2231 // killer moves of that ply.
2233 bool move_is_killer(Move m, const SearchStack& ss) {
2235 const Move* k = ss.killers;
2236 for (int i = 0; i < KILLER_MAX; i++, k++)
2244 // extension() decides whether a move should be searched with normal depth,
2245 // or with extended depth. Certain classes of moves (checking moves, in
2246 // particular) are searched with bigger depth than ordinary moves and in
2247 // any case are marked as 'dangerous'. Note that also if a move is not
2248 // extended, as example because the corresponding UCI option is set to zero,
2249 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2251 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2252 bool singleReply, bool mateThreat, bool* dangerous) {
2254 assert(m != MOVE_NONE);
2256 Depth result = Depth(0);
2257 *dangerous = check | singleReply | mateThreat;
2262 result += CheckExtension[pvNode];
2265 result += SingleReplyExtension[pvNode];
2268 result += MateThreatExtension[pvNode];
2271 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2273 Color c = pos.side_to_move();
2274 if (relative_rank(c, move_to(m)) == RANK_7)
2276 result += PawnPushTo7thExtension[pvNode];
2279 if (pos.pawn_is_passed(c, move_to(m)))
2281 result += PassedPawnExtension[pvNode];
2287 && pos.type_of_piece_on(move_to(m)) != PAWN
2288 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2289 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2290 && !move_is_promotion(m)
2293 result += PawnEndgameExtension[pvNode];
2299 && pos.type_of_piece_on(move_to(m)) != PAWN
2300 && pos.see_sign(m) >= 0)
2306 return Min(result, OnePly);
2310 // ok_to_do_nullmove() looks at the current position and decides whether
2311 // doing a 'null move' should be allowed. In order to avoid zugzwang
2312 // problems, null moves are not allowed when the side to move has very
2313 // little material left. Currently, the test is a bit too simple: Null
2314 // moves are avoided only when the side to move has only pawns left. It's
2315 // probably a good idea to avoid null moves in at least some more
2316 // complicated endgames, e.g. KQ vs KR. FIXME
2318 bool ok_to_do_nullmove(const Position& pos) {
2320 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2324 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2325 // non-tactical moves late in the move list close to the leaves are
2326 // candidates for pruning.
2328 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d) {
2330 assert(move_is_ok(m));
2331 assert(threat == MOVE_NONE || move_is_ok(threat));
2332 assert(!move_is_promotion(m));
2333 assert(!pos.move_is_check(m));
2334 assert(!pos.move_is_capture(m));
2335 assert(!pos.move_is_passed_pawn_push(m));
2336 assert(d >= OnePly);
2338 Square mfrom, mto, tfrom, tto;
2340 mfrom = move_from(m);
2342 tfrom = move_from(threat);
2343 tto = move_to(threat);
2345 // Case 1: Castling moves are never pruned
2346 if (move_is_castle(m))
2349 // Case 2: Don't prune moves which move the threatened piece
2350 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2353 // Case 3: If the threatened piece has value less than or equal to the
2354 // value of the threatening piece, don't prune move which defend it.
2355 if ( !PruneDefendingMoves
2356 && threat != MOVE_NONE
2357 && pos.move_is_capture(threat)
2358 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2359 || pos.type_of_piece_on(tfrom) == KING)
2360 && pos.move_attacks_square(m, tto))
2363 // Case 4: Don't prune moves with good history
2364 if (!H.ok_to_prune(pos.piece_on(mfrom), mto, d))
2367 // Case 5: If the moving piece in the threatened move is a slider, don't
2368 // prune safe moves which block its ray.
2369 if ( !PruneBlockingMoves
2370 && threat != MOVE_NONE
2371 && piece_is_slider(pos.piece_on(tfrom))
2372 && bit_is_set(squares_between(tfrom, tto), mto)
2373 && pos.see_sign(m) >= 0)
2380 // ok_to_use_TT() returns true if a transposition table score
2381 // can be used at a given point in search.
2383 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2385 Value v = value_from_tt(tte->value(), ply);
2387 return ( tte->depth() >= depth
2388 || v >= Max(value_mate_in(100), beta)
2389 || v < Min(value_mated_in(100), beta))
2391 && ( (is_lower_bound(tte->type()) && v >= beta)
2392 || (is_upper_bound(tte->type()) && v < beta));
2396 // ok_to_history() returns true if a move m can be stored
2397 // in history. Should be a non capturing move nor a promotion.
2399 bool ok_to_history(const Position& pos, Move m) {
2401 return !pos.move_is_capture(m) && !move_is_promotion(m);
2405 // update_history() registers a good move that produced a beta-cutoff
2406 // in history and marks as failures all the other moves of that ply.
2408 void update_history(const Position& pos, Move m, Depth depth,
2409 Move movesSearched[], int moveCount) {
2411 H.success(pos.piece_on(move_from(m)), move_to(m), depth);
2413 for (int i = 0; i < moveCount - 1; i++)
2415 assert(m != movesSearched[i]);
2416 if (ok_to_history(pos, movesSearched[i]))
2417 H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]));
2422 // update_killers() add a good move that produced a beta-cutoff
2423 // among the killer moves of that ply.
2425 void update_killers(Move m, SearchStack& ss) {
2427 if (m == ss.killers[0])
2430 for (int i = KILLER_MAX - 1; i > 0; i--)
2431 ss.killers[i] = ss.killers[i - 1];
2437 // slowdown() simply wastes CPU cycles doing nothing useful. It's used
2438 // in strength handicap mode.
2440 void slowdown(const Position &pos) {
2443 for (i = 0; i < n; i++) {
2444 Square s = Square(i&63);
2445 if (count_1s(pos.attacks_to(s)) > 63)
2446 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;
2451 // fail_high_ply_1() checks if some thread is currently resolving a fail
2452 // high at ply 1 at the node below the first root node. This information
2453 // is used for time managment.
2455 bool fail_high_ply_1() {
2457 for(int i = 0; i < ActiveThreads; i++)
2458 if (Threads[i].failHighPly1)
2465 // current_search_time() returns the number of milliseconds which have passed
2466 // since the beginning of the current search.
2468 int current_search_time() {
2469 return get_system_time() - SearchStartTime;
2473 // nps() computes the current nodes/second count.
2476 int t = current_search_time();
2477 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2481 // poll() performs two different functions: It polls for user input, and it
2482 // looks at the time consumed so far and decides if it's time to abort the
2487 static int lastInfoTime;
2488 int t = current_search_time();
2493 // We are line oriented, don't read single chars
2494 std::string command;
2495 if (!std::getline(std::cin, command))
2498 if (command == "quit")
2501 PonderSearch = false;
2505 else if (command == "stop")
2508 PonderSearch = false;
2510 else if (command == "ponderhit")
2513 // Print search information
2517 else if (lastInfoTime > t)
2518 // HACK: Must be a new search where we searched less than
2519 // NodesBetweenPolls nodes during the first second of search.
2522 else if (t - lastInfoTime >= 1000)
2529 if (dbg_show_hit_rate)
2530 dbg_print_hit_rate();
2532 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2533 << " time " << t << " hashfull " << TT.full() << std::endl;
2534 lock_release(&IOLock);
2535 if (ShowCurrentLine)
2536 Threads[0].printCurrentLine = true;
2538 // Should we stop the search?
2542 bool overTime = t > AbsoluteMaxSearchTime
2543 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2544 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2545 && t > 6*(MaxSearchTime + ExtraSearchTime));
2547 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2548 || (ExactMaxTime && t >= ExactMaxTime)
2549 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2554 // ponderhit() is called when the program is pondering (i.e. thinking while
2555 // it's the opponent's turn to move) in order to let the engine know that
2556 // it correctly predicted the opponent's move.
2560 int t = current_search_time();
2561 PonderSearch = false;
2562 if (Iteration >= 3 &&
2563 (!InfiniteSearch && (StopOnPonderhit ||
2564 t > AbsoluteMaxSearchTime ||
2565 (RootMoveNumber == 1 &&
2566 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2567 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2568 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2573 // print_current_line() prints the current line of search for a given
2574 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2576 void print_current_line(SearchStack ss[], int ply, int threadID) {
2578 assert(ply >= 0 && ply < PLY_MAX);
2579 assert(threadID >= 0 && threadID < ActiveThreads);
2581 if (!Threads[threadID].idle)
2584 std::cout << "info currline " << (threadID + 1);
2585 for (int p = 0; p < ply; p++)
2586 std::cout << " " << ss[p].currentMove;
2588 std::cout << std::endl;
2589 lock_release(&IOLock);
2591 Threads[threadID].printCurrentLine = false;
2592 if (threadID + 1 < ActiveThreads)
2593 Threads[threadID + 1].printCurrentLine = true;
2597 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2598 // while the program is pondering. The point is to work around a wrinkle in
2599 // the UCI protocol: When pondering, the engine is not allowed to give a
2600 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2601 // We simply wait here until one of these commands is sent, and return,
2602 // after which the bestmove and pondermove will be printed (in id_loop()).
2604 void wait_for_stop_or_ponderhit() {
2606 std::string command;
2610 if (!std::getline(std::cin, command))
2613 if (command == "quit")
2618 else if (command == "ponderhit" || command == "stop")
2624 // idle_loop() is where the threads are parked when they have no work to do.
2625 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2626 // object for which the current thread is the master.
2628 void idle_loop(int threadID, SplitPoint* waitSp) {
2629 assert(threadID >= 0 && threadID < THREAD_MAX);
2631 Threads[threadID].running = true;
2634 if(AllThreadsShouldExit && threadID != 0)
2637 // If we are not thinking, wait for a condition to be signaled instead
2638 // of wasting CPU time polling for work:
2639 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2640 #if !defined(_MSC_VER)
2641 pthread_mutex_lock(&WaitLock);
2642 if(Idle || threadID >= ActiveThreads)
2643 pthread_cond_wait(&WaitCond, &WaitLock);
2644 pthread_mutex_unlock(&WaitLock);
2646 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2650 // If this thread has been assigned work, launch a search
2651 if(Threads[threadID].workIsWaiting) {
2652 Threads[threadID].workIsWaiting = false;
2653 if(Threads[threadID].splitPoint->pvNode)
2654 sp_search_pv(Threads[threadID].splitPoint, threadID);
2656 sp_search(Threads[threadID].splitPoint, threadID);
2657 Threads[threadID].idle = true;
2660 // If this thread is the master of a split point and all threads have
2661 // finished their work at this split point, return from the idle loop.
2662 if(waitSp != NULL && waitSp->cpus == 0)
2666 Threads[threadID].running = false;
2670 // init_split_point_stack() is called during program initialization, and
2671 // initializes all split point objects.
2673 void init_split_point_stack() {
2674 for(int i = 0; i < THREAD_MAX; i++)
2675 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2676 SplitPointStack[i][j].parent = NULL;
2677 lock_init(&(SplitPointStack[i][j].lock), NULL);
2682 // destroy_split_point_stack() is called when the program exits, and
2683 // destroys all locks in the precomputed split point objects.
2685 void destroy_split_point_stack() {
2686 for(int i = 0; i < THREAD_MAX; i++)
2687 for(int j = 0; j < MaxActiveSplitPoints; j++)
2688 lock_destroy(&(SplitPointStack[i][j].lock));
2692 // thread_should_stop() checks whether the thread with a given threadID has
2693 // been asked to stop, directly or indirectly. This can happen if a beta
2694 // cutoff has occured in thre thread's currently active split point, or in
2695 // some ancestor of the current split point.
2697 bool thread_should_stop(int threadID) {
2698 assert(threadID >= 0 && threadID < ActiveThreads);
2702 if(Threads[threadID].stop)
2704 if(ActiveThreads <= 2)
2706 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2708 Threads[threadID].stop = true;
2715 // thread_is_available() checks whether the thread with threadID "slave" is
2716 // available to help the thread with threadID "master" at a split point. An
2717 // obvious requirement is that "slave" must be idle. With more than two
2718 // threads, this is not by itself sufficient: If "slave" is the master of
2719 // some active split point, it is only available as a slave to the other
2720 // threads which are busy searching the split point at the top of "slave"'s
2721 // split point stack (the "helpful master concept" in YBWC terminology).
2723 bool thread_is_available(int slave, int master) {
2724 assert(slave >= 0 && slave < ActiveThreads);
2725 assert(master >= 0 && master < ActiveThreads);
2726 assert(ActiveThreads > 1);
2728 if(!Threads[slave].idle || slave == master)
2731 if(Threads[slave].activeSplitPoints == 0)
2732 // No active split points means that the thread is available as a slave
2733 // for any other thread.
2736 if(ActiveThreads == 2)
2739 // Apply the "helpful master" concept if possible.
2740 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2747 // idle_thread_exists() tries to find an idle thread which is available as
2748 // a slave for the thread with threadID "master".
2750 bool idle_thread_exists(int master) {
2751 assert(master >= 0 && master < ActiveThreads);
2752 assert(ActiveThreads > 1);
2754 for(int i = 0; i < ActiveThreads; i++)
2755 if(thread_is_available(i, master))
2761 // split() does the actual work of distributing the work at a node between
2762 // several threads at PV nodes. If it does not succeed in splitting the
2763 // node (because no idle threads are available, or because we have no unused
2764 // split point objects), the function immediately returns false. If
2765 // splitting is possible, a SplitPoint object is initialized with all the
2766 // data that must be copied to the helper threads (the current position and
2767 // search stack, alpha, beta, the search depth, etc.), and we tell our
2768 // helper threads that they have been assigned work. This will cause them
2769 // to instantly leave their idle loops and call sp_search_pv(). When all
2770 // threads have returned from sp_search_pv (or, equivalently, when
2771 // splitPoint->cpus becomes 0), split() returns true.
2773 bool split(const Position& p, SearchStack* sstck, int ply,
2774 Value* alpha, Value* beta, Value* bestValue, Depth depth, int* moves,
2775 MovePicker* mp, Bitboard dcCandidates, int master, bool pvNode) {
2778 assert(sstck != NULL);
2779 assert(ply >= 0 && ply < PLY_MAX);
2780 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2781 assert(!pvNode || *alpha < *beta);
2782 assert(*beta <= VALUE_INFINITE);
2783 assert(depth > Depth(0));
2784 assert(master >= 0 && master < ActiveThreads);
2785 assert(ActiveThreads > 1);
2787 SplitPoint* splitPoint;
2792 // If no other thread is available to help us, or if we have too many
2793 // active split points, don't split.
2794 if(!idle_thread_exists(master) ||
2795 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2796 lock_release(&MPLock);
2800 // Pick the next available split point object from the split point stack
2801 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2802 Threads[master].activeSplitPoints++;
2804 // Initialize the split point object
2805 splitPoint->parent = Threads[master].splitPoint;
2806 splitPoint->finished = false;
2807 splitPoint->ply = ply;
2808 splitPoint->depth = depth;
2809 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2810 splitPoint->beta = *beta;
2811 splitPoint->pvNode = pvNode;
2812 splitPoint->dcCandidates = dcCandidates;
2813 splitPoint->bestValue = *bestValue;
2814 splitPoint->master = master;
2815 splitPoint->mp = mp;
2816 splitPoint->moves = *moves;
2817 splitPoint->cpus = 1;
2818 splitPoint->pos.copy(p);
2819 splitPoint->parentSstack = sstck;
2820 for(i = 0; i < ActiveThreads; i++)
2821 splitPoint->slaves[i] = 0;
2823 // Copy the current position and the search stack to the master thread
2824 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2825 Threads[master].splitPoint = splitPoint;
2827 // Make copies of the current position and search stack for each thread
2828 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2830 if(thread_is_available(i, master)) {
2831 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2832 Threads[i].splitPoint = splitPoint;
2833 splitPoint->slaves[i] = 1;
2837 // Tell the threads that they have work to do. This will make them leave
2839 for(i = 0; i < ActiveThreads; i++)
2840 if(i == master || splitPoint->slaves[i]) {
2841 Threads[i].workIsWaiting = true;
2842 Threads[i].idle = false;
2843 Threads[i].stop = false;
2846 lock_release(&MPLock);
2848 // Everything is set up. The master thread enters the idle loop, from
2849 // which it will instantly launch a search, because its workIsWaiting
2850 // slot is 'true'. We send the split point as a second parameter to the
2851 // idle loop, which means that the main thread will return from the idle
2852 // loop when all threads have finished their work at this split point
2853 // (i.e. when // splitPoint->cpus == 0).
2854 idle_loop(master, splitPoint);
2856 // We have returned from the idle loop, which means that all threads are
2857 // finished. Update alpha, beta and bestvalue, and return.
2859 if(pvNode) *alpha = splitPoint->alpha;
2860 *beta = splitPoint->beta;
2861 *bestValue = splitPoint->bestValue;
2862 Threads[master].stop = false;
2863 Threads[master].idle = false;
2864 Threads[master].activeSplitPoints--;
2865 Threads[master].splitPoint = splitPoint->parent;
2866 lock_release(&MPLock);
2872 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2873 // to start a new search from the root.
2875 void wake_sleeping_threads() {
2876 if(ActiveThreads > 1) {
2877 for(int i = 1; i < ActiveThreads; i++) {
2878 Threads[i].idle = true;
2879 Threads[i].workIsWaiting = false;
2881 #if !defined(_MSC_VER)
2882 pthread_mutex_lock(&WaitLock);
2883 pthread_cond_broadcast(&WaitCond);
2884 pthread_mutex_unlock(&WaitLock);
2886 for(int i = 1; i < THREAD_MAX; i++)
2887 SetEvent(SitIdleEvent[i]);
2893 // init_thread() is the function which is called when a new thread is
2894 // launched. It simply calls the idle_loop() function with the supplied
2895 // threadID. There are two versions of this function; one for POSIX threads
2896 // and one for Windows threads.
2898 #if !defined(_MSC_VER)
2900 void *init_thread(void *threadID) {
2901 idle_loop(*(int *)threadID, NULL);
2907 DWORD WINAPI init_thread(LPVOID threadID) {
2908 idle_loop(*(int *)threadID, NULL);