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/>.
42 #include "ucioption.h"
46 //// Local definitions
53 // IterationInfoType stores search results for each iteration
55 // Because we use relatively small (dynamic) aspiration window,
56 // there happens many fail highs and fail lows in root. And
57 // because we don't do researches in those cases, "value" stored
58 // here is not necessarily exact. Instead in case of fail high/low
59 // we guess what the right value might be and store our guess
60 // as a "speculated value" and then move on. Speculated values are
61 // used just to calculate aspiration window width, so also if are
62 // not exact is not big a problem.
64 struct IterationInfoType {
66 IterationInfoType(Value v = Value(0), Value sv = Value(0))
67 : value(v), speculatedValue(sv) {}
69 Value value, speculatedValue;
73 // The BetaCounterType class is used to order moves at ply one.
74 // Apart for the first one that has its score, following moves
75 // normally have score -VALUE_INFINITE, so are ordered according
76 // to the number of beta cutoffs occurred under their subtree during
77 // the last iteration. The counters are per thread variables to avoid
78 // concurrent accessing under SMP case.
80 struct BetaCounterType {
84 void add(Color us, Depth d, int threadID);
85 void read(Color us, int64_t& our, int64_t& their);
89 // The RootMove class is used for moves at the root at the tree. For each
90 // root move, we store a score, a node count, and a PV (really a refutation
91 // in the case of moves which fail low).
96 bool operator<(const RootMove&); // used to sort
100 int64_t nodes, cumulativeNodes;
101 Move pv[PLY_MAX_PLUS_2];
102 int64_t ourBeta, theirBeta;
106 // The RootMoveList class is essentially an array of RootMove objects, with
107 // a handful of methods for accessing the data in the individual moves.
112 RootMoveList(Position& pos, Move searchMoves[]);
113 inline Move get_move(int moveNum) const;
114 inline Value get_move_score(int moveNum) const;
115 inline void set_move_score(int moveNum, Value score);
116 inline void set_move_nodes(int moveNum, int64_t nodes);
117 inline void set_beta_counters(int moveNum, int64_t our, int64_t their);
118 void set_move_pv(int moveNum, const Move pv[]);
119 inline Move get_move_pv(int moveNum, int i) const;
120 inline int64_t get_move_cumulative_nodes(int moveNum) const;
121 inline int move_count() const;
122 Move scan_for_easy_move() const;
124 void sort_multipv(int n);
127 static const int MaxRootMoves = 500;
128 RootMove moves[MaxRootMoves];
135 // Search depth at iteration 1
136 const Depth InitialDepth = OnePly /*+ OnePly/2*/;
138 // Depth limit for selective search
139 const Depth SelectiveDepth = 7 * OnePly;
141 // Use internal iterative deepening?
142 const bool UseIIDAtPVNodes = true;
143 const bool UseIIDAtNonPVNodes = false;
145 // Internal iterative deepening margin. At Non-PV moves, when
146 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
147 // search when the static evaluation is at most IIDMargin below beta.
148 const Value IIDMargin = Value(0x100);
150 // Easy move margin. An easy move candidate must be at least this much
151 // better than the second best move.
152 const Value EasyMoveMargin = Value(0x200);
154 // Problem margin. If the score of the first move at iteration N+1 has
155 // dropped by more than this since iteration N, the boolean variable
156 // "Problem" is set to true, which will make the program spend some extra
157 // time looking for a better move.
158 const Value ProblemMargin = Value(0x28);
160 // No problem margin. If the boolean "Problem" is true, and a new move
161 // is found at the root which is less than NoProblemMargin worse than the
162 // best move from the previous iteration, Problem is set back to false.
163 const Value NoProblemMargin = Value(0x14);
165 // Null move margin. A null move search will not be done if the approximate
166 // evaluation of the position is more than NullMoveMargin below beta.
167 const Value NullMoveMargin = Value(0x300);
169 // Pruning criterions. See the code and comments in ok_to_prune() to
170 // understand their precise meaning.
171 const bool PruneEscapeMoves = false;
172 const bool PruneDefendingMoves = false;
173 const bool PruneBlockingMoves = false;
175 // Margins for futility pruning in the quiescence search, and at frontier
176 // and near frontier nodes.
177 const Value FutilityMarginQS = Value(0x80);
179 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
180 const Value FutilityMargins[12] = { Value(0x100), Value(0x120), Value(0x200), Value(0x220), Value(0x250), Value(0x270),
181 // 4 ply 4.5 ply 5 ply 5.5 ply 6 ply 6.5 ply
182 Value(0x2A0), Value(0x2C0), Value(0x340), Value(0x360), Value(0x3A0), Value(0x3C0) };
184 const Depth RazorDepth = 4*OnePly;
186 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
187 const Value RazorMargins[6] = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
189 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
190 const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
192 // The main transposition table
193 TranspositionTable TT;
196 /// Variables initialized by UCI options
198 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
199 int LMRPVMoves, LMRNonPVMoves; // heavy SMP read access for the latter
201 // Depth limit for use of dynamic threat detection
202 Depth ThreatDepth; // heavy SMP read access
204 // Last seconds noise filtering (LSN)
205 const bool UseLSNFiltering = true;
206 const int LSNTime = 4000; // In milliseconds
207 const Value LSNValue = value_from_centipawns(200);
208 bool loseOnTime = false;
210 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
211 // There is heavy SMP read access on these arrays
212 Depth CheckExtension[2], SingleReplyExtension[2], PawnPushTo7thExtension[2];
213 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
215 // Iteration counters
217 BetaCounterType BetaCounter; // has per-thread internal data
219 // Scores and number of times the best move changed for each iteration
220 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
221 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
226 // Time managment variables
228 int MaxNodes, MaxDepth;
229 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
233 bool StopOnPonderhit;
234 bool AbortSearch; // heavy SMP read access
240 // Show current line?
241 bool ShowCurrentLine;
245 std::ofstream LogFile;
247 // MP related variables
248 int ActiveThreads = 1;
249 Depth MinimumSplitDepth;
250 int MaxThreadsPerSplitPoint;
251 Thread Threads[THREAD_MAX];
254 bool AllThreadsShouldExit = false;
255 const int MaxActiveSplitPoints = 8;
256 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
259 #if !defined(_MSC_VER)
260 pthread_cond_t WaitCond;
261 pthread_mutex_t WaitLock;
263 HANDLE SitIdleEvent[THREAD_MAX];
266 // Node counters, used only by thread[0] but try to keep in different
267 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
269 int NodesBetweenPolls = 30000;
277 Value id_loop(const Position& pos, Move searchMoves[]);
278 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
279 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
280 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID);
281 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
282 void sp_search(SplitPoint* sp, int threadID);
283 void sp_search_pv(SplitPoint* sp, int threadID);
284 void init_node(SearchStack ss[], int ply, int threadID);
285 void update_pv(SearchStack ss[], int ply);
286 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
287 bool connected_moves(const Position& pos, Move m1, Move m2);
288 bool value_is_mate(Value value);
289 bool move_is_killer(Move m, const SearchStack& ss);
290 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
291 bool ok_to_do_nullmove(const Position& pos);
292 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d);
293 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
294 bool ok_to_history(const Position& pos, Move m);
295 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
296 void update_killers(Move m, SearchStack& ss);
298 bool fail_high_ply_1();
299 int current_search_time();
303 void print_current_line(SearchStack ss[], int ply, int threadID);
304 void wait_for_stop_or_ponderhit();
306 void idle_loop(int threadID, SplitPoint* waitSp);
307 void init_split_point_stack();
308 void destroy_split_point_stack();
309 bool thread_should_stop(int threadID);
310 bool thread_is_available(int slave, int master);
311 bool idle_thread_exists(int master);
312 bool split(const Position& pos, SearchStack* ss, int ply,
313 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
314 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode);
315 void wake_sleeping_threads();
317 #if !defined(_MSC_VER)
318 void *init_thread(void *threadID);
320 DWORD WINAPI init_thread(LPVOID threadID);
330 /// think() is the external interface to Stockfish's search, and is called when
331 /// the program receives the UCI 'go' command. It initializes various
332 /// search-related global variables, and calls root_search(). It returns false
333 /// when a quit command is received during the search.
335 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
336 int time[], int increment[], int movesToGo, int maxDepth,
337 int maxNodes, int maxTime, Move searchMoves[]) {
339 // Look for a book move
340 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
343 if (get_option_value_string("Book File") != OpeningBook.file_name())
344 OpeningBook.open("book.bin");
346 bookMove = OpeningBook.get_move(pos);
347 if (bookMove != MOVE_NONE)
349 std::cout << "bestmove " << bookMove << std::endl;
354 // Initialize global search variables
356 SearchStartTime = get_system_time();
357 for (int i = 0; i < THREAD_MAX; i++)
359 Threads[i].nodes = 0ULL;
360 Threads[i].failHighPly1 = false;
363 InfiniteSearch = infinite;
364 PonderSearch = ponder;
365 StopOnPonderhit = false;
371 ExactMaxTime = maxTime;
373 // Read UCI option values
374 TT.set_size(get_option_value_int("Hash"));
375 if (button_was_pressed("Clear Hash"))
378 loseOnTime = false; // reset at the beginning of a new game
381 bool PonderingEnabled = get_option_value_bool("Ponder");
382 MultiPV = get_option_value_int("MultiPV");
384 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
385 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
387 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
388 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
390 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
391 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
393 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
394 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
396 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
397 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
399 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
400 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
402 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
403 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
404 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
406 Chess960 = get_option_value_bool("UCI_Chess960");
407 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
408 UseLogFile = get_option_value_bool("Use Search Log");
410 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
412 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
413 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
415 read_weights(pos.side_to_move());
417 int newActiveThreads = get_option_value_int("Threads");
418 if (newActiveThreads != ActiveThreads)
420 ActiveThreads = newActiveThreads;
421 init_eval(ActiveThreads);
424 // Wake up sleeping threads
425 wake_sleeping_threads();
427 for (int i = 1; i < ActiveThreads; i++)
428 assert(thread_is_available(i, 0));
431 int myTime = time[side_to_move];
432 int myIncrement = increment[side_to_move];
434 if (!movesToGo) // Sudden death time control
438 MaxSearchTime = myTime / 30 + myIncrement;
439 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
440 } else { // Blitz game without increment
441 MaxSearchTime = myTime / 30;
442 AbsoluteMaxSearchTime = myTime / 8;
445 else // (x moves) / (y minutes)
449 MaxSearchTime = myTime / 2;
450 AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
452 MaxSearchTime = myTime / Min(movesToGo, 20);
453 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
457 if (PonderingEnabled)
459 MaxSearchTime += MaxSearchTime / 4;
460 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
463 // Fixed depth or fixed number of nodes?
466 InfiniteSearch = true; // HACK
471 NodesBetweenPolls = Min(MaxNodes, 30000);
472 InfiniteSearch = true; // HACK
475 NodesBetweenPolls = 30000;
478 // Write information to search log file
480 LogFile << "Searching: " << pos.to_fen() << std::endl
481 << "infinite: " << infinite
482 << " ponder: " << ponder
483 << " time: " << myTime
484 << " increment: " << myIncrement
485 << " moves to go: " << movesToGo << std::endl;
488 // We're ready to start thinking. Call the iterative deepening loop function
490 // FIXME we really need to cleanup all this LSN ugliness
493 Value v = id_loop(pos, searchMoves);
494 loseOnTime = ( UseLSNFiltering
501 loseOnTime = false; // reset for next match
502 while (SearchStartTime + myTime + 1000 > get_system_time())
504 id_loop(pos, searchMoves); // to fail gracefully
515 /// init_threads() is called during startup. It launches all helper threads,
516 /// and initializes the split point stack and the global locks and condition
519 void init_threads() {
523 #if !defined(_MSC_VER)
524 pthread_t pthread[1];
527 for (i = 0; i < THREAD_MAX; i++)
528 Threads[i].activeSplitPoints = 0;
530 // Initialize global locks
531 lock_init(&MPLock, NULL);
532 lock_init(&IOLock, NULL);
534 init_split_point_stack();
536 #if !defined(_MSC_VER)
537 pthread_mutex_init(&WaitLock, NULL);
538 pthread_cond_init(&WaitCond, NULL);
540 for (i = 0; i < THREAD_MAX; i++)
541 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
544 // All threads except the main thread should be initialized to idle state
545 for (i = 1; i < THREAD_MAX; i++)
547 Threads[i].stop = false;
548 Threads[i].workIsWaiting = false;
549 Threads[i].idle = true;
550 Threads[i].running = false;
553 // Launch the helper threads
554 for(i = 1; i < THREAD_MAX; i++)
556 #if !defined(_MSC_VER)
557 pthread_create(pthread, NULL, init_thread, (void*)(&i));
560 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
563 // Wait until the thread has finished launching
564 while (!Threads[i].running);
569 /// stop_threads() is called when the program exits. It makes all the
570 /// helper threads exit cleanly.
572 void stop_threads() {
574 ActiveThreads = THREAD_MAX; // HACK
575 Idle = false; // HACK
576 wake_sleeping_threads();
577 AllThreadsShouldExit = true;
578 for (int i = 1; i < THREAD_MAX; i++)
580 Threads[i].stop = true;
581 while(Threads[i].running);
583 destroy_split_point_stack();
587 /// nodes_searched() returns the total number of nodes searched so far in
588 /// the current search.
590 int64_t nodes_searched() {
592 int64_t result = 0ULL;
593 for (int i = 0; i < ActiveThreads; i++)
594 result += Threads[i].nodes;
599 // SearchStack::init() initializes a search stack. Used at the beginning of a
600 // new search from the root.
601 void SearchStack::init(int ply) {
603 pv[ply] = pv[ply + 1] = MOVE_NONE;
604 currentMove = threatMove = MOVE_NONE;
605 reduction = Depth(0);
608 void SearchStack::initKillers() {
610 mateKiller = MOVE_NONE;
611 for (int i = 0; i < KILLER_MAX; i++)
612 killers[i] = MOVE_NONE;
617 // id_loop() is the main iterative deepening loop. It calls root_search
618 // repeatedly with increasing depth until the allocated thinking time has
619 // been consumed, the user stops the search, or the maximum search depth is
622 Value id_loop(const Position& pos, Move searchMoves[]) {
625 SearchStack ss[PLY_MAX_PLUS_2];
627 // searchMoves are verified, copied, scored and sorted
628 RootMoveList rml(p, searchMoves);
633 for (int i = 0; i < 3; i++)
638 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
641 Move EasyMove = rml.scan_for_easy_move();
643 // Iterative deepening loop
644 while (Iteration < PLY_MAX)
646 // Initialize iteration
649 BestMoveChangesByIteration[Iteration] = 0;
653 std::cout << "info depth " << Iteration << std::endl;
655 // Calculate dynamic search window based on previous iterations
658 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
660 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
661 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
663 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
665 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
666 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
670 alpha = - VALUE_INFINITE;
671 beta = VALUE_INFINITE;
674 // Search to the current depth
675 Value value = root_search(p, ss, rml, alpha, beta);
677 // Write PV to transposition table, in case the relevant entries have
678 // been overwritten during the search.
679 TT.insert_pv(p, ss[0].pv);
682 break; // Value cannot be trusted. Break out immediately!
684 //Save info about search result
685 Value speculatedValue;
688 Value delta = value - IterationInfo[Iteration - 1].value;
695 speculatedValue = value + delta;
696 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
698 else if (value <= alpha)
700 assert(value == alpha);
704 speculatedValue = value + delta;
705 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
707 speculatedValue = value;
709 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
710 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
712 // Erase the easy move if it differs from the new best move
713 if (ss[0].pv[0] != EasyMove)
714 EasyMove = MOVE_NONE;
721 bool stopSearch = false;
723 // Stop search early if there is only a single legal move
724 if (Iteration >= 6 && rml.move_count() == 1)
727 // Stop search early when the last two iterations returned a mate score
729 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
730 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
733 // Stop search early if one move seems to be much better than the rest
734 int64_t nodes = nodes_searched();
738 && EasyMove == ss[0].pv[0]
739 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
740 && current_search_time() > MaxSearchTime / 16)
741 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
742 && current_search_time() > MaxSearchTime / 32)))
745 // Add some extra time if the best move has changed during the last two iterations
746 if (Iteration > 5 && Iteration <= 50)
747 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
748 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
750 // Stop search if most of MaxSearchTime is consumed at the end of the
751 // iteration. We probably don't have enough time to search the first
752 // move at the next iteration anyway.
753 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
758 //FIXME: Implement fail-low emergency measures
762 StopOnPonderhit = true;
766 if (MaxDepth && Iteration >= MaxDepth)
772 // If we are pondering, we shouldn't print the best move before we
775 wait_for_stop_or_ponderhit();
777 // Print final search statistics
778 std::cout << "info nodes " << nodes_searched()
780 << " time " << current_search_time()
781 << " hashfull " << TT.full() << std::endl;
783 // Print the best move and the ponder move to the standard output
784 if (ss[0].pv[0] == MOVE_NONE)
786 ss[0].pv[0] = rml.get_move(0);
787 ss[0].pv[1] = MOVE_NONE;
789 std::cout << "bestmove " << ss[0].pv[0];
790 if (ss[0].pv[1] != MOVE_NONE)
791 std::cout << " ponder " << ss[0].pv[1];
793 std::cout << std::endl;
798 dbg_print_mean(LogFile);
800 if (dbg_show_hit_rate)
801 dbg_print_hit_rate(LogFile);
804 LogFile << "Nodes: " << nodes_searched() << std::endl
805 << "Nodes/second: " << nps() << std::endl
806 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
808 p.do_move(ss[0].pv[0], st);
809 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
810 << std::endl << std::endl;
812 return rml.get_move_score(0);
816 // root_search() is the function which searches the root node. It is
817 // similar to search_pv except that it uses a different move ordering
818 // scheme (perhaps we should try to use this at internal PV nodes, too?)
819 // and prints some information to the standard output.
821 Value root_search(Position& pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta) {
823 Value oldAlpha = alpha;
825 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
827 // Loop through all the moves in the root move list
828 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
832 // We failed high, invalidate and skip next moves, leave node-counters
833 // and beta-counters as they are and quickly return, we will try to do
834 // a research at the next iteration with a bigger aspiration window.
835 rml.set_move_score(i, -VALUE_INFINITE);
843 RootMoveNumber = i + 1;
846 // Remember the node count before the move is searched. The node counts
847 // are used to sort the root moves at the next iteration.
848 nodes = nodes_searched();
850 // Reset beta cut-off counters
853 // Pick the next root move, and print the move and the move number to
854 // the standard output.
855 move = ss[0].currentMove = rml.get_move(i);
856 if (current_search_time() >= 1000)
857 std::cout << "info currmove " << move
858 << " currmovenumber " << i + 1 << std::endl;
860 // Decide search depth for this move
862 ext = extension(pos, move, true, pos.move_is_capture(move), pos.move_is_check(move), false, false, &dangerous);
863 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
865 // Make the move, and search it
866 pos.do_move(move, st, dcCandidates);
870 // Aspiration window is disabled in multi-pv case
872 alpha = -VALUE_INFINITE;
874 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
875 // If the value has dropped a lot compared to the last iteration,
876 // set the boolean variable Problem to true. This variable is used
877 // for time managment: When Problem is true, we try to complete the
878 // current iteration before playing a move.
879 Problem = (Iteration >= 2 && value <= IterationInfo[Iteration-1].value - ProblemMargin);
881 if (Problem && StopOnPonderhit)
882 StopOnPonderhit = false;
886 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
889 // Fail high! Set the boolean variable FailHigh to true, and
890 // re-search the move with a big window. The variable FailHigh is
891 // used for time managment: We try to avoid aborting the search
892 // prematurely during a fail high research.
894 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
900 // Finished searching the move. If AbortSearch is true, the search
901 // was aborted because the user interrupted the search or because we
902 // ran out of time. In this case, the return value of the search cannot
903 // be trusted, and we break out of the loop without updating the best
908 // Remember the node count for this move. The node counts are used to
909 // sort the root moves at the next iteration.
910 rml.set_move_nodes(i, nodes_searched() - nodes);
912 // Remember the beta-cutoff statistics
914 BetaCounter.read(pos.side_to_move(), our, their);
915 rml.set_beta_counters(i, our, their);
917 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
919 if (value <= alpha && i >= MultiPV)
920 rml.set_move_score(i, -VALUE_INFINITE);
923 // PV move or new best move!
926 rml.set_move_score(i, value);
928 rml.set_move_pv(i, ss[0].pv);
932 // We record how often the best move has been changed in each
933 // iteration. This information is used for time managment: When
934 // the best move changes frequently, we allocate some more time.
936 BestMoveChangesByIteration[Iteration]++;
938 // Print search information to the standard output
939 std::cout << "info depth " << Iteration
940 << " score " << value_to_string(value)
941 << " time " << current_search_time()
942 << " nodes " << nodes_searched()
946 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
947 std::cout << ss[0].pv[j] << " ";
949 std::cout << std::endl;
952 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
958 // Reset the global variable Problem to false if the value isn't too
959 // far below the final value from the last iteration.
960 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
966 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
969 std::cout << "info multipv " << j + 1
970 << " score " << value_to_string(rml.get_move_score(j))
971 << " depth " << ((j <= i)? Iteration : Iteration - 1)
972 << " time " << current_search_time()
973 << " nodes " << nodes_searched()
977 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
978 std::cout << rml.get_move_pv(j, k) << " ";
980 std::cout << std::endl;
982 alpha = rml.get_move_score(Min(i, MultiPV-1));
984 } // New best move case
986 assert(alpha >= oldAlpha);
988 FailLow = (alpha == oldAlpha);
994 // search_pv() is the main search function for PV nodes.
996 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
997 Depth depth, int ply, int threadID) {
999 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1000 assert(beta > alpha && beta <= VALUE_INFINITE);
1001 assert(ply >= 0 && ply < PLY_MAX);
1002 assert(threadID >= 0 && threadID < ActiveThreads);
1005 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1007 // Initialize, and make an early exit in case of an aborted search,
1008 // an instant draw, maximum ply reached, etc.
1009 init_node(ss, ply, threadID);
1011 // After init_node() that calls poll()
1012 if (AbortSearch || thread_should_stop(threadID))
1020 if (ply >= PLY_MAX - 1)
1021 return evaluate(pos, ei, threadID);
1023 // Mate distance pruning
1024 Value oldAlpha = alpha;
1025 alpha = Max(value_mated_in(ply), alpha);
1026 beta = Min(value_mate_in(ply+1), beta);
1030 // Transposition table lookup. At PV nodes, we don't use the TT for
1031 // pruning, but only for move ordering.
1032 const TTEntry* tte = TT.retrieve(pos.get_key());
1033 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1035 // Go with internal iterative deepening if we don't have a TT move
1036 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
1038 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1039 ttMove = ss[ply].pv[ply];
1042 // Initialize a MovePicker object for the current position, and prepare
1043 // to search all moves
1044 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1046 Move move, movesSearched[256];
1048 Value value, bestValue = -VALUE_INFINITE;
1049 Bitboard dcCandidates = mp.discovered_check_candidates();
1050 Color us = pos.side_to_move();
1051 bool isCheck = pos.is_check();
1052 bool mateThreat = pos.has_mate_threat(opposite_color(us));
1054 // Loop through all legal moves until no moves remain or a beta cutoff
1056 while ( alpha < beta
1057 && (move = mp.get_next_move()) != MOVE_NONE
1058 && !thread_should_stop(threadID))
1060 assert(move_is_ok(move));
1062 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1063 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1064 bool moveIsCapture = pos.move_is_capture(move);
1066 movesSearched[moveCount++] = ss[ply].currentMove = move;
1068 // Decide the new search depth
1070 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1071 Depth newDepth = depth - OnePly + ext;
1073 // Make and search the move
1075 pos.do_move(move, st, dcCandidates);
1077 if (moveCount == 1) // The first move in list is the PV
1078 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1081 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1082 // if the move fails high will be re-searched at full depth.
1083 if ( depth >= 3*OnePly
1084 && moveCount >= LMRPVMoves
1087 && !move_is_promotion(move)
1088 && !move_is_castle(move)
1089 && !move_is_killer(move, ss[ply]))
1091 ss[ply].reduction = OnePly;
1092 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1095 value = alpha + 1; // Just to trigger next condition
1097 if (value > alpha) // Go with full depth non-pv search
1099 ss[ply].reduction = Depth(0);
1100 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1101 if (value > alpha && value < beta)
1103 // When the search fails high at ply 1 while searching the first
1104 // move at the root, set the flag failHighPly1. This is used for
1105 // time managment: We don't want to stop the search early in
1106 // such cases, because resolving the fail high at ply 1 could
1107 // result in a big drop in score at the root.
1108 if (ply == 1 && RootMoveNumber == 1)
1109 Threads[threadID].failHighPly1 = true;
1111 // A fail high occurred. Re-search at full window (pv search)
1112 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1113 Threads[threadID].failHighPly1 = false;
1117 pos.undo_move(move);
1119 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1122 if (value > bestValue)
1129 if (value == value_mate_in(ply + 1))
1130 ss[ply].mateKiller = move;
1132 // If we are at ply 1, and we are searching the first root move at
1133 // ply 0, set the 'Problem' variable if the score has dropped a lot
1134 // (from the computer's point of view) since the previous iteration.
1137 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1142 if ( ActiveThreads > 1
1144 && depth >= MinimumSplitDepth
1146 && idle_thread_exists(threadID)
1148 && !thread_should_stop(threadID)
1149 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1150 &moveCount, &mp, dcCandidates, threadID, true))
1154 // All legal moves have been searched. A special case: If there were
1155 // no legal moves, it must be mate or stalemate.
1157 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1159 // If the search is not aborted, update the transposition table,
1160 // history counters, and killer moves.
1161 if (AbortSearch || thread_should_stop(threadID))
1164 if (bestValue <= oldAlpha)
1165 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1167 else if (bestValue >= beta)
1169 BetaCounter.add(pos.side_to_move(), depth, threadID);
1170 Move m = ss[ply].pv[ply];
1171 if (ok_to_history(pos, m)) // Only non capture moves are considered
1173 update_history(pos, m, depth, movesSearched, moveCount);
1174 update_killers(m, ss[ply]);
1176 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1179 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1185 // search() is the search function for zero-width nodes.
1187 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1188 int ply, bool allowNullmove, int threadID) {
1190 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1191 assert(ply >= 0 && ply < PLY_MAX);
1192 assert(threadID >= 0 && threadID < ActiveThreads);
1195 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1197 // Initialize, and make an early exit in case of an aborted search,
1198 // an instant draw, maximum ply reached, etc.
1199 init_node(ss, ply, threadID);
1201 // After init_node() that calls poll()
1202 if (AbortSearch || thread_should_stop(threadID))
1210 if (ply >= PLY_MAX - 1)
1211 return evaluate(pos, ei, threadID);
1213 // Mate distance pruning
1214 if (value_mated_in(ply) >= beta)
1217 if (value_mate_in(ply + 1) < beta)
1220 // Transposition table lookup
1221 const TTEntry* tte = TT.retrieve(pos.get_key());
1222 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1224 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1226 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1227 return value_from_tt(tte->value(), ply);
1230 Value approximateEval = quick_evaluate(pos);
1231 bool mateThreat = false;
1232 bool isCheck = pos.is_check();
1238 && !value_is_mate(beta)
1239 && ok_to_do_nullmove(pos)
1240 && approximateEval >= beta - NullMoveMargin)
1242 ss[ply].currentMove = MOVE_NULL;
1245 pos.do_null_move(st);
1246 int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
1248 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1250 pos.undo_null_move();
1252 if (value_is_mate(nullValue))
1254 if (nullValue == value_mated_in(ply + 2))
1257 /* Do not return unproven mates */
1259 else if (nullValue >= beta)
1261 if (depth < 6 * OnePly)
1264 // Do zugzwang verification search
1265 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1269 // The null move failed low, which means that we may be faced with
1270 // some kind of threat. If the previous move was reduced, check if
1271 // the move that refuted the null move was somehow connected to the
1272 // move which was reduced. If a connection is found, return a fail
1273 // low score (which will cause the reduced move to fail high in the
1274 // parent node, which will trigger a re-search with full depth).
1275 ss[ply].threatMove = ss[ply + 1].currentMove;
1276 if ( depth < ThreatDepth
1277 && ss[ply - 1].reduction
1278 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1282 // Null move search not allowed, try razoring
1283 else if ( !value_is_mate(beta)
1284 && depth < RazorDepth
1285 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1286 && ss[ply - 1].currentMove != MOVE_NULL
1287 && ttMove == MOVE_NONE
1288 && !pos.has_pawn_on_7th(pos.side_to_move()))
1290 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1291 if (v < beta - RazorMargins[int(depth) - 2])
1295 // Go with internal iterative deepening if we don't have a TT move
1296 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1297 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1299 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1300 ttMove = ss[ply].pv[ply];
1303 // Initialize a MovePicker object for the current position, and prepare
1304 // to search all moves.
1305 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1307 Move move, movesSearched[256];
1309 Value value, bestValue = -VALUE_INFINITE;
1310 Bitboard dcCandidates = mp.discovered_check_candidates();
1311 Value futilityValue = VALUE_NONE;
1312 bool useFutilityPruning = depth < SelectiveDepth
1315 // Loop through all legal moves until no moves remain or a beta cutoff
1317 while ( bestValue < beta
1318 && (move = mp.get_next_move()) != MOVE_NONE
1319 && !thread_should_stop(threadID))
1321 assert(move_is_ok(move));
1323 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1324 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1325 bool moveIsCapture = pos.move_is_capture(move);
1327 movesSearched[moveCount++] = ss[ply].currentMove = move;
1329 // Decide the new search depth
1331 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1332 Depth newDepth = depth - OnePly + ext;
1335 if ( useFutilityPruning
1338 && !move_is_promotion(move))
1340 // History pruning. See ok_to_prune() definition
1341 if ( moveCount >= 2 + int(depth)
1342 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1345 // Value based pruning
1346 if (approximateEval < beta)
1348 if (futilityValue == VALUE_NONE)
1349 futilityValue = evaluate(pos, ei, threadID)
1350 + FutilityMargins[int(depth) - 2];
1352 if (futilityValue < beta)
1354 if (futilityValue > bestValue)
1355 bestValue = futilityValue;
1361 // Make and search the move
1363 pos.do_move(move, st, dcCandidates);
1365 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1366 // if the move fails high will be re-searched at full depth.
1367 if ( depth >= 3*OnePly
1368 && moveCount >= LMRNonPVMoves
1371 && !move_is_promotion(move)
1372 && !move_is_castle(move)
1373 && !move_is_killer(move, ss[ply]))
1375 ss[ply].reduction = OnePly;
1376 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1379 value = beta; // Just to trigger next condition
1381 if (value >= beta) // Go with full depth non-pv search
1383 ss[ply].reduction = Depth(0);
1384 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1386 pos.undo_move(move);
1388 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1391 if (value > bestValue)
1397 if (value == value_mate_in(ply + 1))
1398 ss[ply].mateKiller = move;
1402 if ( ActiveThreads > 1
1404 && depth >= MinimumSplitDepth
1406 && idle_thread_exists(threadID)
1408 && !thread_should_stop(threadID)
1409 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1410 &mp, dcCandidates, threadID, false))
1414 // All legal moves have been searched. A special case: If there were
1415 // no legal moves, it must be mate or stalemate.
1417 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1419 // If the search is not aborted, update the transposition table,
1420 // history counters, and killer moves.
1421 if (AbortSearch || thread_should_stop(threadID))
1424 if (bestValue < beta)
1425 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1428 BetaCounter.add(pos.side_to_move(), depth, threadID);
1429 Move m = ss[ply].pv[ply];
1430 if (ok_to_history(pos, m)) // Only non capture moves are considered
1432 update_history(pos, m, depth, movesSearched, moveCount);
1433 update_killers(m, ss[ply]);
1435 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1438 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1444 // qsearch() is the quiescence search function, which is called by the main
1445 // search function when the remaining depth is zero (or, to be more precise,
1446 // less than OnePly).
1448 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1449 Depth depth, int ply, int threadID) {
1451 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1452 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1454 assert(ply >= 0 && ply < PLY_MAX);
1455 assert(threadID >= 0 && threadID < ActiveThreads);
1457 // Initialize, and make an early exit in case of an aborted search,
1458 // an instant draw, maximum ply reached, etc.
1459 init_node(ss, ply, threadID);
1461 // After init_node() that calls poll()
1462 if (AbortSearch || thread_should_stop(threadID))
1468 // Transposition table lookup, only when not in PV
1469 TTEntry* tte = NULL;
1470 bool pvNode = (beta - alpha != 1);
1473 tte = TT.retrieve(pos.get_key());
1474 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1476 assert(tte->type() != VALUE_TYPE_EVAL);
1478 return value_from_tt(tte->value(), ply);
1481 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1483 // Evaluate the position statically
1486 bool isCheck = pos.is_check();
1487 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1490 staticValue = -VALUE_INFINITE;
1492 else if (tte && tte->type() == VALUE_TYPE_EVAL)
1494 // Use the cached evaluation score if possible
1495 assert(ei.futilityMargin == Value(0));
1497 staticValue = tte->value();
1500 staticValue = evaluate(pos, ei, threadID);
1502 if (ply == PLY_MAX - 1)
1503 return evaluate(pos, ei, threadID);
1505 // Initialize "stand pat score", and return it immediately if it is
1507 Value bestValue = staticValue;
1509 if (bestValue >= beta)
1511 // Store the score to avoid a future costly evaluation() call
1512 if (!isCheck && !tte && ei.futilityMargin == 0)
1513 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EVAL, Depth(-127*OnePly), MOVE_NONE);
1518 if (bestValue > alpha)
1521 // Initialize a MovePicker object for the current position, and prepare
1522 // to search the moves. Because the depth is <= 0 here, only captures,
1523 // queen promotions and checks (only if depth == 0) will be generated.
1524 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1527 Bitboard dcCandidates = mp.discovered_check_candidates();
1528 Color us = pos.side_to_move();
1529 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1531 // Loop through the moves until no moves remain or a beta cutoff
1533 while ( alpha < beta
1534 && (move = mp.get_next_move()) != MOVE_NONE)
1536 assert(move_is_ok(move));
1539 ss[ply].currentMove = move;
1545 && !move_is_promotion(move)
1546 && !pos.move_is_check(move, dcCandidates)
1547 && !pos.move_is_passed_pawn_push(move))
1549 Value futilityValue = staticValue
1550 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1551 pos.endgame_value_of_piece_on(move_to(move)))
1552 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1554 + ei.futilityMargin;
1556 if (futilityValue < alpha)
1558 if (futilityValue > bestValue)
1559 bestValue = futilityValue;
1564 // Don't search captures and checks with negative SEE values
1566 && !move_is_promotion(move)
1567 && pos.see_sign(move) < 0)
1570 // Make and search the move.
1572 pos.do_move(move, st, dcCandidates);
1573 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1574 pos.undo_move(move);
1576 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1579 if (value > bestValue)
1590 // All legal moves have been searched. A special case: If we're in check
1591 // and no legal moves were found, it is checkmate.
1592 if (pos.is_check() && moveCount == 0) // Mate!
1593 return value_mated_in(ply);
1595 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1597 // Update transposition table
1598 Move m = ss[ply].pv[ply];
1601 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1602 if (bestValue < beta)
1603 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE);
1605 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
1608 // Update killers only for good check moves
1609 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1610 update_killers(m, ss[ply]);
1616 // sp_search() is used to search from a split point. This function is called
1617 // by each thread working at the split point. It is similar to the normal
1618 // search() function, but simpler. Because we have already probed the hash
1619 // table, done a null move search, and searched the first move before
1620 // splitting, we don't have to repeat all this work in sp_search(). We
1621 // also don't need to store anything to the hash table here: This is taken
1622 // care of after we return from the split point.
1624 void sp_search(SplitPoint* sp, int threadID) {
1626 assert(threadID >= 0 && threadID < ActiveThreads);
1627 assert(ActiveThreads > 1);
1629 Position pos = Position(sp->pos);
1630 SearchStack* ss = sp->sstack[threadID];
1633 bool isCheck = pos.is_check();
1634 bool useFutilityPruning = sp->depth < SelectiveDepth
1637 while ( sp->bestValue < sp->beta
1638 && !thread_should_stop(threadID)
1639 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1641 assert(move_is_ok(move));
1643 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1644 bool moveIsCapture = pos.move_is_capture(move);
1646 lock_grab(&(sp->lock));
1647 int moveCount = ++sp->moves;
1648 lock_release(&(sp->lock));
1650 ss[sp->ply].currentMove = move;
1652 // Decide the new search depth.
1654 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1655 Depth newDepth = sp->depth - OnePly + ext;
1658 if ( useFutilityPruning
1661 && !move_is_promotion(move)
1662 && moveCount >= 2 + int(sp->depth)
1663 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1666 // Make and search the move.
1668 pos.do_move(move, st, sp->dcCandidates);
1670 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1671 // if the move fails high will be re-searched at full depth.
1673 && moveCount >= LMRNonPVMoves
1675 && !move_is_promotion(move)
1676 && !move_is_castle(move)
1677 && !move_is_killer(move, ss[sp->ply]))
1679 ss[sp->ply].reduction = OnePly;
1680 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1683 value = sp->beta; // Just to trigger next condition
1685 if (value >= sp->beta) // Go with full depth non-pv search
1687 ss[sp->ply].reduction = Depth(0);
1688 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1690 pos.undo_move(move);
1692 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1694 if (thread_should_stop(threadID))
1698 lock_grab(&(sp->lock));
1699 if (value > sp->bestValue && !thread_should_stop(threadID))
1701 sp->bestValue = value;
1702 if (sp->bestValue >= sp->beta)
1704 sp_update_pv(sp->parentSstack, ss, sp->ply);
1705 for (int i = 0; i < ActiveThreads; i++)
1706 if (i != threadID && (i == sp->master || sp->slaves[i]))
1707 Threads[i].stop = true;
1709 sp->finished = true;
1712 lock_release(&(sp->lock));
1715 lock_grab(&(sp->lock));
1717 // If this is the master thread and we have been asked to stop because of
1718 // a beta cutoff higher up in the tree, stop all slave threads.
1719 if (sp->master == threadID && thread_should_stop(threadID))
1720 for (int i = 0; i < ActiveThreads; i++)
1722 Threads[i].stop = true;
1725 sp->slaves[threadID] = 0;
1727 lock_release(&(sp->lock));
1731 // sp_search_pv() is used to search from a PV split point. This function
1732 // is called by each thread working at the split point. It is similar to
1733 // the normal search_pv() function, but simpler. Because we have already
1734 // probed the hash table and searched the first move before splitting, we
1735 // don't have to repeat all this work in sp_search_pv(). We also don't
1736 // need to store anything to the hash table here: This is taken care of
1737 // after we return from the split point.
1739 void sp_search_pv(SplitPoint* sp, int threadID) {
1741 assert(threadID >= 0 && threadID < ActiveThreads);
1742 assert(ActiveThreads > 1);
1744 Position pos = Position(sp->pos);
1745 SearchStack* ss = sp->sstack[threadID];
1749 while ( sp->alpha < sp->beta
1750 && !thread_should_stop(threadID)
1751 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1753 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1754 bool moveIsCapture = pos.move_is_capture(move);
1756 assert(move_is_ok(move));
1758 lock_grab(&(sp->lock));
1759 int moveCount = ++sp->moves;
1760 lock_release(&(sp->lock));
1762 ss[sp->ply].currentMove = move;
1764 // Decide the new search depth.
1766 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1767 Depth newDepth = sp->depth - OnePly + ext;
1769 // Make and search the move.
1771 pos.do_move(move, st, sp->dcCandidates);
1773 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1774 // if the move fails high will be re-searched at full depth.
1776 && moveCount >= LMRPVMoves
1778 && !move_is_promotion(move)
1779 && !move_is_castle(move)
1780 && !move_is_killer(move, ss[sp->ply]))
1782 ss[sp->ply].reduction = OnePly;
1783 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1786 value = sp->alpha + 1; // Just to trigger next condition
1788 if (value > sp->alpha) // Go with full depth non-pv search
1790 ss[sp->ply].reduction = Depth(0);
1791 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1793 if (value > sp->alpha && value < sp->beta)
1795 // When the search fails high at ply 1 while searching the first
1796 // move at the root, set the flag failHighPly1. This is used for
1797 // time managment: We don't want to stop the search early in
1798 // such cases, because resolving the fail high at ply 1 could
1799 // result in a big drop in score at the root.
1800 if (sp->ply == 1 && RootMoveNumber == 1)
1801 Threads[threadID].failHighPly1 = true;
1803 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1804 Threads[threadID].failHighPly1 = false;
1807 pos.undo_move(move);
1809 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1811 if (thread_should_stop(threadID))
1815 lock_grab(&(sp->lock));
1816 if (value > sp->bestValue && !thread_should_stop(threadID))
1818 sp->bestValue = value;
1819 if (value > sp->alpha)
1822 sp_update_pv(sp->parentSstack, ss, sp->ply);
1823 if (value == value_mate_in(sp->ply + 1))
1824 ss[sp->ply].mateKiller = move;
1826 if (value >= sp->beta)
1828 for (int i = 0; i < ActiveThreads; i++)
1829 if (i != threadID && (i == sp->master || sp->slaves[i]))
1830 Threads[i].stop = true;
1832 sp->finished = true;
1835 // If we are at ply 1, and we are searching the first root move at
1836 // ply 0, set the 'Problem' variable if the score has dropped a lot
1837 // (from the computer's point of view) since the previous iteration.
1840 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1843 lock_release(&(sp->lock));
1846 lock_grab(&(sp->lock));
1848 // If this is the master thread and we have been asked to stop because of
1849 // a beta cutoff higher up in the tree, stop all slave threads.
1850 if (sp->master == threadID && thread_should_stop(threadID))
1851 for (int i = 0; i < ActiveThreads; i++)
1853 Threads[i].stop = true;
1856 sp->slaves[threadID] = 0;
1858 lock_release(&(sp->lock));
1861 /// The BetaCounterType class
1863 BetaCounterType::BetaCounterType() { clear(); }
1865 void BetaCounterType::clear() {
1867 for (int i = 0; i < THREAD_MAX; i++)
1868 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
1871 void BetaCounterType::add(Color us, Depth d, int threadID) {
1873 // Weighted count based on depth
1874 Threads[threadID].betaCutOffs[us] += unsigned(d);
1877 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1880 for (int i = 0; i < THREAD_MAX; i++)
1882 our += Threads[i].betaCutOffs[us];
1883 their += Threads[i].betaCutOffs[opposite_color(us)];
1888 /// The RootMove class
1892 RootMove::RootMove() {
1893 nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
1896 // RootMove::operator<() is the comparison function used when
1897 // sorting the moves. A move m1 is considered to be better
1898 // than a move m2 if it has a higher score, or if the moves
1899 // have equal score but m1 has the higher node count.
1901 bool RootMove::operator<(const RootMove& m) {
1903 if (score != m.score)
1904 return (score < m.score);
1906 return theirBeta <= m.theirBeta;
1909 /// The RootMoveList class
1913 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1915 MoveStack mlist[MaxRootMoves];
1916 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1918 // Generate all legal moves
1919 int lm_count = generate_legal_moves(pos, mlist);
1921 // Add each move to the moves[] array
1922 for (int i = 0; i < lm_count; i++)
1924 bool includeMove = includeAllMoves;
1926 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1927 includeMove = (searchMoves[k] == mlist[i].move);
1932 // Find a quick score for the move
1934 SearchStack ss[PLY_MAX_PLUS_2];
1936 moves[count].move = mlist[i].move;
1937 pos.do_move(moves[count].move, st);
1938 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
1939 pos.undo_move(moves[count].move);
1940 moves[count].pv[0] = moves[count].move;
1941 moves[count].pv[1] = MOVE_NONE; // FIXME
1948 // Simple accessor methods for the RootMoveList class
1950 inline Move RootMoveList::get_move(int moveNum) const {
1951 return moves[moveNum].move;
1954 inline Value RootMoveList::get_move_score(int moveNum) const {
1955 return moves[moveNum].score;
1958 inline void RootMoveList::set_move_score(int moveNum, Value score) {
1959 moves[moveNum].score = score;
1962 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
1963 moves[moveNum].nodes = nodes;
1964 moves[moveNum].cumulativeNodes += nodes;
1967 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
1968 moves[moveNum].ourBeta = our;
1969 moves[moveNum].theirBeta = their;
1972 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
1974 for(j = 0; pv[j] != MOVE_NONE; j++)
1975 moves[moveNum].pv[j] = pv[j];
1976 moves[moveNum].pv[j] = MOVE_NONE;
1979 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
1980 return moves[moveNum].pv[i];
1983 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
1984 return moves[moveNum].cumulativeNodes;
1987 inline int RootMoveList::move_count() const {
1992 // RootMoveList::scan_for_easy_move() is called at the end of the first
1993 // iteration, and is used to detect an "easy move", i.e. a move which appears
1994 // to be much bester than all the rest. If an easy move is found, the move
1995 // is returned, otherwise the function returns MOVE_NONE. It is very
1996 // important that this function is called at the right moment: The code
1997 // assumes that the first iteration has been completed and the moves have
1998 // been sorted. This is done in RootMoveList c'tor.
2000 Move RootMoveList::scan_for_easy_move() const {
2007 // moves are sorted so just consider the best and the second one
2008 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
2014 // RootMoveList::sort() sorts the root move list at the beginning of a new
2017 inline void RootMoveList::sort() {
2019 sort_multipv(count - 1); // all items
2023 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2024 // list by their scores and depths. It is used to order the different PVs
2025 // correctly in MultiPV mode.
2027 void RootMoveList::sort_multipv(int n) {
2029 for (int i = 1; i <= n; i++)
2031 RootMove rm = moves[i];
2033 for (j = i; j > 0 && moves[j-1] < rm; j--)
2034 moves[j] = moves[j-1];
2040 // init_node() is called at the beginning of all the search functions
2041 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2042 // stack object corresponding to the current node. Once every
2043 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2044 // for user input and checks whether it is time to stop the search.
2046 void init_node(SearchStack ss[], int ply, int threadID) {
2048 assert(ply >= 0 && ply < PLY_MAX);
2049 assert(threadID >= 0 && threadID < ActiveThreads);
2051 Threads[threadID].nodes++;
2056 if (NodesSincePoll >= NodesBetweenPolls)
2063 ss[ply+2].initKillers();
2065 if (Threads[threadID].printCurrentLine)
2066 print_current_line(ss, ply, threadID);
2070 // update_pv() is called whenever a search returns a value > alpha. It
2071 // updates the PV in the SearchStack object corresponding to the current
2074 void update_pv(SearchStack ss[], int ply) {
2075 assert(ply >= 0 && ply < PLY_MAX);
2077 ss[ply].pv[ply] = ss[ply].currentMove;
2079 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2080 ss[ply].pv[p] = ss[ply+1].pv[p];
2081 ss[ply].pv[p] = MOVE_NONE;
2085 // sp_update_pv() is a variant of update_pv for use at split points. The
2086 // difference between the two functions is that sp_update_pv also updates
2087 // the PV at the parent node.
2089 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2090 assert(ply >= 0 && ply < PLY_MAX);
2092 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2094 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2095 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2096 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2100 // connected_moves() tests whether two moves are 'connected' in the sense
2101 // that the first move somehow made the second move possible (for instance
2102 // if the moving piece is the same in both moves). The first move is
2103 // assumed to be the move that was made to reach the current position, while
2104 // the second move is assumed to be a move from the current position.
2106 bool connected_moves(const Position& pos, Move m1, Move m2) {
2107 Square f1, t1, f2, t2;
2109 assert(move_is_ok(m1));
2110 assert(move_is_ok(m2));
2112 if (m2 == MOVE_NONE)
2115 // Case 1: The moving piece is the same in both moves
2121 // Case 2: The destination square for m2 was vacated by m1
2127 // Case 3: Moving through the vacated square
2128 if ( piece_is_slider(pos.piece_on(f2))
2129 && bit_is_set(squares_between(f2, t2), f1))
2132 // Case 4: The destination square for m2 is attacked by the moving piece in m1
2133 if (pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
2136 // Case 5: Discovered check, checking piece is the piece moved in m1
2137 if ( piece_is_slider(pos.piece_on(t1))
2138 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2139 && !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())), t2))
2141 Bitboard occ = pos.occupied_squares();
2142 Color us = pos.side_to_move();
2143 Square ksq = pos.king_square(us);
2144 clear_bit(&occ, f2);
2145 if (pos.type_of_piece_on(t1) == BISHOP)
2147 if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2150 else if (pos.type_of_piece_on(t1) == ROOK)
2152 if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
2157 assert(pos.type_of_piece_on(t1) == QUEEN);
2158 if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
2166 // value_is_mate() checks if the given value is a mate one
2167 // eventually compensated for the ply.
2169 bool value_is_mate(Value value) {
2171 assert(abs(value) <= VALUE_INFINITE);
2173 return value <= value_mated_in(PLY_MAX)
2174 || value >= value_mate_in(PLY_MAX);
2178 // move_is_killer() checks if the given move is among the
2179 // killer moves of that ply.
2181 bool move_is_killer(Move m, const SearchStack& ss) {
2183 const Move* k = ss.killers;
2184 for (int i = 0; i < KILLER_MAX; i++, k++)
2192 // extension() decides whether a move should be searched with normal depth,
2193 // or with extended depth. Certain classes of moves (checking moves, in
2194 // particular) are searched with bigger depth than ordinary moves and in
2195 // any case are marked as 'dangerous'. Note that also if a move is not
2196 // extended, as example because the corresponding UCI option is set to zero,
2197 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2199 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2200 bool singleReply, bool mateThreat, bool* dangerous) {
2202 assert(m != MOVE_NONE);
2204 Depth result = Depth(0);
2205 *dangerous = check || singleReply || mateThreat;
2208 result += CheckExtension[pvNode];
2211 result += SingleReplyExtension[pvNode];
2214 result += MateThreatExtension[pvNode];
2216 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2218 if (pos.move_is_pawn_push_to_7th(m))
2220 result += PawnPushTo7thExtension[pvNode];
2223 if (pos.move_is_passed_pawn_push(m))
2225 result += PassedPawnExtension[pvNode];
2231 && pos.type_of_piece_on(move_to(m)) != PAWN
2232 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2233 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2234 && !move_is_promotion(m)
2237 result += PawnEndgameExtension[pvNode];
2243 && pos.type_of_piece_on(move_to(m)) != PAWN
2244 && pos.see_sign(m) >= 0)
2250 return Min(result, OnePly);
2254 // ok_to_do_nullmove() looks at the current position and decides whether
2255 // doing a 'null move' should be allowed. In order to avoid zugzwang
2256 // problems, null moves are not allowed when the side to move has very
2257 // little material left. Currently, the test is a bit too simple: Null
2258 // moves are avoided only when the side to move has only pawns left. It's
2259 // probably a good idea to avoid null moves in at least some more
2260 // complicated endgames, e.g. KQ vs KR. FIXME
2262 bool ok_to_do_nullmove(const Position& pos) {
2264 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2268 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2269 // non-tactical moves late in the move list close to the leaves are
2270 // candidates for pruning.
2272 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d) {
2274 assert(move_is_ok(m));
2275 assert(threat == MOVE_NONE || move_is_ok(threat));
2276 assert(!move_is_promotion(m));
2277 assert(!pos.move_is_check(m));
2278 assert(!pos.move_is_capture(m));
2279 assert(!pos.move_is_passed_pawn_push(m));
2280 assert(d >= OnePly);
2282 Square mfrom, mto, tfrom, tto;
2284 mfrom = move_from(m);
2286 tfrom = move_from(threat);
2287 tto = move_to(threat);
2289 // Case 1: Castling moves are never pruned
2290 if (move_is_castle(m))
2293 // Case 2: Don't prune moves which move the threatened piece
2294 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2297 // Case 3: If the threatened piece has value less than or equal to the
2298 // value of the threatening piece, don't prune move which defend it.
2299 if ( !PruneDefendingMoves
2300 && threat != MOVE_NONE
2301 && pos.move_is_capture(threat)
2302 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2303 || pos.type_of_piece_on(tfrom) == KING)
2304 && pos.move_attacks_square(m, tto))
2307 // Case 4: Don't prune moves with good history
2308 if (!H.ok_to_prune(pos.piece_on(mfrom), mto, d))
2311 // Case 5: If the moving piece in the threatened move is a slider, don't
2312 // prune safe moves which block its ray.
2313 if ( !PruneBlockingMoves
2314 && threat != MOVE_NONE
2315 && piece_is_slider(pos.piece_on(tfrom))
2316 && bit_is_set(squares_between(tfrom, tto), mto)
2317 && pos.see_sign(m) >= 0)
2324 // ok_to_use_TT() returns true if a transposition table score
2325 // can be used at a given point in search.
2327 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2329 Value v = value_from_tt(tte->value(), ply);
2331 return ( tte->depth() >= depth
2332 || v >= Max(value_mate_in(100), beta)
2333 || v < Min(value_mated_in(100), beta))
2335 && ( (is_lower_bound(tte->type()) && v >= beta)
2336 || (is_upper_bound(tte->type()) && v < beta));
2340 // ok_to_history() returns true if a move m can be stored
2341 // in history. Should be a non capturing move nor a promotion.
2343 bool ok_to_history(const Position& pos, Move m) {
2345 return !pos.move_is_capture(m) && !move_is_promotion(m);
2349 // update_history() registers a good move that produced a beta-cutoff
2350 // in history and marks as failures all the other moves of that ply.
2352 void update_history(const Position& pos, Move m, Depth depth,
2353 Move movesSearched[], int moveCount) {
2355 H.success(pos.piece_on(move_from(m)), move_to(m), depth);
2357 for (int i = 0; i < moveCount - 1; i++)
2359 assert(m != movesSearched[i]);
2360 if (ok_to_history(pos, movesSearched[i]))
2361 H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]));
2366 // update_killers() add a good move that produced a beta-cutoff
2367 // among the killer moves of that ply.
2369 void update_killers(Move m, SearchStack& ss) {
2371 if (m == ss.killers[0])
2374 for (int i = KILLER_MAX - 1; i > 0; i--)
2375 ss.killers[i] = ss.killers[i - 1];
2380 // fail_high_ply_1() checks if some thread is currently resolving a fail
2381 // high at ply 1 at the node below the first root node. This information
2382 // is used for time managment.
2384 bool fail_high_ply_1() {
2386 for(int i = 0; i < ActiveThreads; i++)
2387 if (Threads[i].failHighPly1)
2394 // current_search_time() returns the number of milliseconds which have passed
2395 // since the beginning of the current search.
2397 int current_search_time() {
2398 return get_system_time() - SearchStartTime;
2402 // nps() computes the current nodes/second count.
2405 int t = current_search_time();
2406 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2410 // poll() performs two different functions: It polls for user input, and it
2411 // looks at the time consumed so far and decides if it's time to abort the
2416 static int lastInfoTime;
2417 int t = current_search_time();
2422 // We are line oriented, don't read single chars
2423 std::string command;
2424 if (!std::getline(std::cin, command))
2427 if (command == "quit")
2430 PonderSearch = false;
2434 else if (command == "stop")
2437 PonderSearch = false;
2439 else if (command == "ponderhit")
2442 // Print search information
2446 else if (lastInfoTime > t)
2447 // HACK: Must be a new search where we searched less than
2448 // NodesBetweenPolls nodes during the first second of search.
2451 else if (t - lastInfoTime >= 1000)
2458 if (dbg_show_hit_rate)
2459 dbg_print_hit_rate();
2461 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2462 << " time " << t << " hashfull " << TT.full() << std::endl;
2463 lock_release(&IOLock);
2464 if (ShowCurrentLine)
2465 Threads[0].printCurrentLine = true;
2467 // Should we stop the search?
2471 bool overTime = t > AbsoluteMaxSearchTime
2472 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2473 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2474 && t > 6*(MaxSearchTime + ExtraSearchTime));
2476 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2477 || (ExactMaxTime && t >= ExactMaxTime)
2478 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2483 // ponderhit() is called when the program is pondering (i.e. thinking while
2484 // it's the opponent's turn to move) in order to let the engine know that
2485 // it correctly predicted the opponent's move.
2489 int t = current_search_time();
2490 PonderSearch = false;
2491 if (Iteration >= 3 &&
2492 (!InfiniteSearch && (StopOnPonderhit ||
2493 t > AbsoluteMaxSearchTime ||
2494 (RootMoveNumber == 1 &&
2495 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2496 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2497 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2502 // print_current_line() prints the current line of search for a given
2503 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2505 void print_current_line(SearchStack ss[], int ply, int threadID) {
2507 assert(ply >= 0 && ply < PLY_MAX);
2508 assert(threadID >= 0 && threadID < ActiveThreads);
2510 if (!Threads[threadID].idle)
2513 std::cout << "info currline " << (threadID + 1);
2514 for (int p = 0; p < ply; p++)
2515 std::cout << " " << ss[p].currentMove;
2517 std::cout << std::endl;
2518 lock_release(&IOLock);
2520 Threads[threadID].printCurrentLine = false;
2521 if (threadID + 1 < ActiveThreads)
2522 Threads[threadID + 1].printCurrentLine = true;
2526 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2527 // while the program is pondering. The point is to work around a wrinkle in
2528 // the UCI protocol: When pondering, the engine is not allowed to give a
2529 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2530 // We simply wait here until one of these commands is sent, and return,
2531 // after which the bestmove and pondermove will be printed (in id_loop()).
2533 void wait_for_stop_or_ponderhit() {
2535 std::string command;
2539 if (!std::getline(std::cin, command))
2542 if (command == "quit")
2547 else if (command == "ponderhit" || command == "stop")
2553 // idle_loop() is where the threads are parked when they have no work to do.
2554 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2555 // object for which the current thread is the master.
2557 void idle_loop(int threadID, SplitPoint* waitSp) {
2558 assert(threadID >= 0 && threadID < THREAD_MAX);
2560 Threads[threadID].running = true;
2563 if(AllThreadsShouldExit && threadID != 0)
2566 // If we are not thinking, wait for a condition to be signaled instead
2567 // of wasting CPU time polling for work:
2568 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2569 #if !defined(_MSC_VER)
2570 pthread_mutex_lock(&WaitLock);
2571 if(Idle || threadID >= ActiveThreads)
2572 pthread_cond_wait(&WaitCond, &WaitLock);
2573 pthread_mutex_unlock(&WaitLock);
2575 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2579 // If this thread has been assigned work, launch a search
2580 if(Threads[threadID].workIsWaiting) {
2581 Threads[threadID].workIsWaiting = false;
2582 if(Threads[threadID].splitPoint->pvNode)
2583 sp_search_pv(Threads[threadID].splitPoint, threadID);
2585 sp_search(Threads[threadID].splitPoint, threadID);
2586 Threads[threadID].idle = true;
2589 // If this thread is the master of a split point and all threads have
2590 // finished their work at this split point, return from the idle loop.
2591 if(waitSp != NULL && waitSp->cpus == 0)
2595 Threads[threadID].running = false;
2599 // init_split_point_stack() is called during program initialization, and
2600 // initializes all split point objects.
2602 void init_split_point_stack() {
2603 for(int i = 0; i < THREAD_MAX; i++)
2604 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2605 SplitPointStack[i][j].parent = NULL;
2606 lock_init(&(SplitPointStack[i][j].lock), NULL);
2611 // destroy_split_point_stack() is called when the program exits, and
2612 // destroys all locks in the precomputed split point objects.
2614 void destroy_split_point_stack() {
2615 for(int i = 0; i < THREAD_MAX; i++)
2616 for(int j = 0; j < MaxActiveSplitPoints; j++)
2617 lock_destroy(&(SplitPointStack[i][j].lock));
2621 // thread_should_stop() checks whether the thread with a given threadID has
2622 // been asked to stop, directly or indirectly. This can happen if a beta
2623 // cutoff has occured in thre thread's currently active split point, or in
2624 // some ancestor of the current split point.
2626 bool thread_should_stop(int threadID) {
2627 assert(threadID >= 0 && threadID < ActiveThreads);
2631 if(Threads[threadID].stop)
2633 if(ActiveThreads <= 2)
2635 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2637 Threads[threadID].stop = true;
2644 // thread_is_available() checks whether the thread with threadID "slave" is
2645 // available to help the thread with threadID "master" at a split point. An
2646 // obvious requirement is that "slave" must be idle. With more than two
2647 // threads, this is not by itself sufficient: If "slave" is the master of
2648 // some active split point, it is only available as a slave to the other
2649 // threads which are busy searching the split point at the top of "slave"'s
2650 // split point stack (the "helpful master concept" in YBWC terminology).
2652 bool thread_is_available(int slave, int master) {
2653 assert(slave >= 0 && slave < ActiveThreads);
2654 assert(master >= 0 && master < ActiveThreads);
2655 assert(ActiveThreads > 1);
2657 if(!Threads[slave].idle || slave == master)
2660 if(Threads[slave].activeSplitPoints == 0)
2661 // No active split points means that the thread is available as a slave
2662 // for any other thread.
2665 if(ActiveThreads == 2)
2668 // Apply the "helpful master" concept if possible.
2669 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2676 // idle_thread_exists() tries to find an idle thread which is available as
2677 // a slave for the thread with threadID "master".
2679 bool idle_thread_exists(int master) {
2680 assert(master >= 0 && master < ActiveThreads);
2681 assert(ActiveThreads > 1);
2683 for(int i = 0; i < ActiveThreads; i++)
2684 if(thread_is_available(i, master))
2690 // split() does the actual work of distributing the work at a node between
2691 // several threads at PV nodes. If it does not succeed in splitting the
2692 // node (because no idle threads are available, or because we have no unused
2693 // split point objects), the function immediately returns false. If
2694 // splitting is possible, a SplitPoint object is initialized with all the
2695 // data that must be copied to the helper threads (the current position and
2696 // search stack, alpha, beta, the search depth, etc.), and we tell our
2697 // helper threads that they have been assigned work. This will cause them
2698 // to instantly leave their idle loops and call sp_search_pv(). When all
2699 // threads have returned from sp_search_pv (or, equivalently, when
2700 // splitPoint->cpus becomes 0), split() returns true.
2702 bool split(const Position& p, SearchStack* sstck, int ply,
2703 Value* alpha, Value* beta, Value* bestValue, Depth depth, int* moves,
2704 MovePicker* mp, Bitboard dcCandidates, int master, bool pvNode) {
2707 assert(sstck != NULL);
2708 assert(ply >= 0 && ply < PLY_MAX);
2709 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2710 assert(!pvNode || *alpha < *beta);
2711 assert(*beta <= VALUE_INFINITE);
2712 assert(depth > Depth(0));
2713 assert(master >= 0 && master < ActiveThreads);
2714 assert(ActiveThreads > 1);
2716 SplitPoint* splitPoint;
2721 // If no other thread is available to help us, or if we have too many
2722 // active split points, don't split.
2723 if(!idle_thread_exists(master) ||
2724 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2725 lock_release(&MPLock);
2729 // Pick the next available split point object from the split point stack
2730 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2731 Threads[master].activeSplitPoints++;
2733 // Initialize the split point object
2734 splitPoint->parent = Threads[master].splitPoint;
2735 splitPoint->finished = false;
2736 splitPoint->ply = ply;
2737 splitPoint->depth = depth;
2738 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2739 splitPoint->beta = *beta;
2740 splitPoint->pvNode = pvNode;
2741 splitPoint->dcCandidates = dcCandidates;
2742 splitPoint->bestValue = *bestValue;
2743 splitPoint->master = master;
2744 splitPoint->mp = mp;
2745 splitPoint->moves = *moves;
2746 splitPoint->cpus = 1;
2747 splitPoint->pos.copy(p);
2748 splitPoint->parentSstack = sstck;
2749 for(i = 0; i < ActiveThreads; i++)
2750 splitPoint->slaves[i] = 0;
2752 // Copy the current position and the search stack to the master thread
2753 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2754 Threads[master].splitPoint = splitPoint;
2756 // Make copies of the current position and search stack for each thread
2757 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2759 if(thread_is_available(i, master)) {
2760 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2761 Threads[i].splitPoint = splitPoint;
2762 splitPoint->slaves[i] = 1;
2766 // Tell the threads that they have work to do. This will make them leave
2768 for(i = 0; i < ActiveThreads; i++)
2769 if(i == master || splitPoint->slaves[i]) {
2770 Threads[i].workIsWaiting = true;
2771 Threads[i].idle = false;
2772 Threads[i].stop = false;
2775 lock_release(&MPLock);
2777 // Everything is set up. The master thread enters the idle loop, from
2778 // which it will instantly launch a search, because its workIsWaiting
2779 // slot is 'true'. We send the split point as a second parameter to the
2780 // idle loop, which means that the main thread will return from the idle
2781 // loop when all threads have finished their work at this split point
2782 // (i.e. when // splitPoint->cpus == 0).
2783 idle_loop(master, splitPoint);
2785 // We have returned from the idle loop, which means that all threads are
2786 // finished. Update alpha, beta and bestvalue, and return.
2788 if(pvNode) *alpha = splitPoint->alpha;
2789 *beta = splitPoint->beta;
2790 *bestValue = splitPoint->bestValue;
2791 Threads[master].stop = false;
2792 Threads[master].idle = false;
2793 Threads[master].activeSplitPoints--;
2794 Threads[master].splitPoint = splitPoint->parent;
2795 lock_release(&MPLock);
2801 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2802 // to start a new search from the root.
2804 void wake_sleeping_threads() {
2805 if(ActiveThreads > 1) {
2806 for(int i = 1; i < ActiveThreads; i++) {
2807 Threads[i].idle = true;
2808 Threads[i].workIsWaiting = false;
2810 #if !defined(_MSC_VER)
2811 pthread_mutex_lock(&WaitLock);
2812 pthread_cond_broadcast(&WaitCond);
2813 pthread_mutex_unlock(&WaitLock);
2815 for(int i = 1; i < THREAD_MAX; i++)
2816 SetEvent(SitIdleEvent[i]);
2822 // init_thread() is the function which is called when a new thread is
2823 // launched. It simply calls the idle_loop() function with the supplied
2824 // threadID. There are two versions of this function; one for POSIX threads
2825 // and one for Windows threads.
2827 #if !defined(_MSC_VER)
2829 void *init_thread(void *threadID) {
2830 idle_loop(*(int *)threadID, NULL);
2836 DWORD WINAPI init_thread(LPVOID threadID) {
2837 idle_loop(*(int *)threadID, NULL);