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) };
193 /// Variables initialized by UCI options
195 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
196 int LMRPVMoves, LMRNonPVMoves; // heavy SMP read access for the latter
198 // Depth limit for use of dynamic threat detection
199 Depth ThreatDepth; // heavy SMP read access
201 // Last seconds noise filtering (LSN)
202 const bool UseLSNFiltering = true;
203 const int LSNTime = 4000; // In milliseconds
204 const Value LSNValue = value_from_centipawns(200);
205 bool loseOnTime = false;
207 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
208 // There is heavy SMP read access on these arrays
209 Depth CheckExtension[2], SingleReplyExtension[2], PawnPushTo7thExtension[2];
210 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
212 // Iteration counters
214 BetaCounterType BetaCounter; // has per-thread internal data
216 // Scores and number of times the best move changed for each iteration
217 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
218 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
223 // Time managment variables
225 int MaxNodes, MaxDepth;
226 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
230 bool StopOnPonderhit;
231 bool AbortSearch; // heavy SMP read access
237 // Show current line?
238 bool ShowCurrentLine;
242 std::ofstream LogFile;
244 // MP related variables
245 int ActiveThreads = 1;
246 Depth MinimumSplitDepth;
247 int MaxThreadsPerSplitPoint;
248 Thread Threads[THREAD_MAX];
251 bool AllThreadsShouldExit = false;
252 const int MaxActiveSplitPoints = 8;
253 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
256 #if !defined(_MSC_VER)
257 pthread_cond_t WaitCond;
258 pthread_mutex_t WaitLock;
260 HANDLE SitIdleEvent[THREAD_MAX];
263 // Node counters, used only by thread[0] but try to keep in different
264 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
266 int NodesBetweenPolls = 30000;
274 Value id_loop(const Position& pos, Move searchMoves[]);
275 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
276 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
277 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID);
278 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
279 void sp_search(SplitPoint* sp, int threadID);
280 void sp_search_pv(SplitPoint* sp, int threadID);
281 void init_node(SearchStack ss[], int ply, int threadID);
282 void update_pv(SearchStack ss[], int ply);
283 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
284 bool connected_moves(const Position& pos, Move m1, Move m2);
285 bool value_is_mate(Value value);
286 bool move_is_killer(Move m, const SearchStack& ss);
287 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
288 bool ok_to_do_nullmove(const Position& pos);
289 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d);
290 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
291 bool ok_to_history(const Position& pos, Move m);
292 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
293 void update_killers(Move m, SearchStack& ss);
295 bool fail_high_ply_1();
296 int current_search_time();
300 void print_current_line(SearchStack ss[], int ply, int threadID);
301 void wait_for_stop_or_ponderhit();
302 void init_ss_array(SearchStack ss[]);
304 void idle_loop(int threadID, SplitPoint* waitSp);
305 void init_split_point_stack();
306 void destroy_split_point_stack();
307 bool thread_should_stop(int threadID);
308 bool thread_is_available(int slave, int master);
309 bool idle_thread_exists(int master);
310 bool split(const Position& pos, SearchStack* ss, int ply,
311 Value *alpha, Value *beta, Value *bestValue,
312 const Value futilityValue, const Value approximateValue,
313 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 // Set the number of active threads
418 int newActiveThreads = get_option_value_int("Threads");
419 if (newActiveThreads != ActiveThreads)
421 ActiveThreads = newActiveThreads;
422 init_eval(ActiveThreads);
425 // Wake up sleeping threads
426 wake_sleeping_threads();
428 for (int i = 1; i < ActiveThreads; i++)
429 assert(thread_is_available(i, 0));
432 int myTime = time[side_to_move];
433 int myIncrement = increment[side_to_move];
435 if (!movesToGo) // Sudden death time control
439 MaxSearchTime = myTime / 30 + myIncrement;
440 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
441 } else { // Blitz game without increment
442 MaxSearchTime = myTime / 30;
443 AbsoluteMaxSearchTime = myTime / 8;
446 else // (x moves) / (y minutes)
450 MaxSearchTime = myTime / 2;
451 AbsoluteMaxSearchTime =
452 (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
454 MaxSearchTime = myTime / Min(movesToGo, 20);
455 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
459 if (PonderingEnabled)
461 MaxSearchTime += MaxSearchTime / 4;
462 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
465 // Fixed depth or fixed number of nodes?
468 InfiniteSearch = true; // HACK
473 NodesBetweenPolls = Min(MaxNodes, 30000);
474 InfiniteSearch = true; // HACK
476 else if (myTime && myTime < 1000)
477 NodesBetweenPolls = 1000;
478 else if (myTime && myTime < 5000)
479 NodesBetweenPolls = 5000;
481 NodesBetweenPolls = 30000;
483 // Write information to search log file
485 LogFile << "Searching: " << pos.to_fen() << std::endl
486 << "infinite: " << infinite
487 << " ponder: " << ponder
488 << " time: " << myTime
489 << " increment: " << myIncrement
490 << " moves to go: " << movesToGo << std::endl;
493 // We're ready to start thinking. Call the iterative deepening loop function
495 // FIXME we really need to cleanup all this LSN ugliness
498 Value v = id_loop(pos, searchMoves);
499 loseOnTime = ( UseLSNFiltering
506 loseOnTime = false; // reset for next match
507 while (SearchStartTime + myTime + 1000 > get_system_time())
509 id_loop(pos, searchMoves); // to fail gracefully
520 /// init_threads() is called during startup. It launches all helper threads,
521 /// and initializes the split point stack and the global locks and condition
524 void init_threads() {
528 #if !defined(_MSC_VER)
529 pthread_t pthread[1];
532 for (i = 0; i < THREAD_MAX; i++)
533 Threads[i].activeSplitPoints = 0;
535 // Initialize global locks
536 lock_init(&MPLock, NULL);
537 lock_init(&IOLock, NULL);
539 init_split_point_stack();
541 #if !defined(_MSC_VER)
542 pthread_mutex_init(&WaitLock, NULL);
543 pthread_cond_init(&WaitCond, NULL);
545 for (i = 0; i < THREAD_MAX; i++)
546 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
549 // All threads except the main thread should be initialized to idle state
550 for (i = 1; i < THREAD_MAX; i++)
552 Threads[i].stop = false;
553 Threads[i].workIsWaiting = false;
554 Threads[i].idle = true;
555 Threads[i].running = false;
558 // Launch the helper threads
559 for(i = 1; i < THREAD_MAX; i++)
561 #if !defined(_MSC_VER)
562 pthread_create(pthread, NULL, init_thread, (void*)(&i));
565 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
568 // Wait until the thread has finished launching
569 while (!Threads[i].running);
574 /// stop_threads() is called when the program exits. It makes all the
575 /// helper threads exit cleanly.
577 void stop_threads() {
579 ActiveThreads = THREAD_MAX; // HACK
580 Idle = false; // HACK
581 wake_sleeping_threads();
582 AllThreadsShouldExit = true;
583 for (int i = 1; i < THREAD_MAX; i++)
585 Threads[i].stop = true;
586 while(Threads[i].running);
588 destroy_split_point_stack();
592 /// nodes_searched() returns the total number of nodes searched so far in
593 /// the current search.
595 int64_t nodes_searched() {
597 int64_t result = 0ULL;
598 for (int i = 0; i < ActiveThreads; i++)
599 result += Threads[i].nodes;
604 // SearchStack::init() initializes a search stack. Used at the beginning of a
605 // new search from the root.
606 void SearchStack::init(int ply) {
608 pv[ply] = pv[ply + 1] = MOVE_NONE;
609 currentMove = threatMove = MOVE_NONE;
610 reduction = Depth(0);
613 void SearchStack::initKillers() {
615 mateKiller = MOVE_NONE;
616 for (int i = 0; i < KILLER_MAX; i++)
617 killers[i] = MOVE_NONE;
622 // id_loop() is the main iterative deepening loop. It calls root_search
623 // repeatedly with increasing depth until the allocated thinking time has
624 // been consumed, the user stops the search, or the maximum search depth is
627 Value id_loop(const Position& pos, Move searchMoves[]) {
630 SearchStack ss[PLY_MAX_PLUS_2];
632 // searchMoves are verified, copied, scored and sorted
633 RootMoveList rml(p, searchMoves);
635 // Print RootMoveList c'tor startup scoring to the standard output,
636 // so that we print information also for iteration 1.
637 std::cout << "info depth " << 1 << "\ninfo depth " << 1
638 << " score " << value_to_string(rml.get_move_score(0))
639 << " time " << current_search_time()
640 << " nodes " << nodes_searched()
642 << " pv " << rml.get_move(0) << "\n";
648 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
651 Move EasyMove = rml.scan_for_easy_move();
653 // Iterative deepening loop
654 while (Iteration < PLY_MAX)
656 // Initialize iteration
659 BestMoveChangesByIteration[Iteration] = 0;
663 std::cout << "info depth " << Iteration << std::endl;
665 // Calculate dynamic search window based on previous iterations
668 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
670 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
671 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
673 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
675 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
676 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
680 alpha = - VALUE_INFINITE;
681 beta = VALUE_INFINITE;
684 // Search to the current depth
685 Value value = root_search(p, ss, rml, alpha, beta);
687 // Write PV to transposition table, in case the relevant entries have
688 // been overwritten during the search.
689 TT.insert_pv(p, ss[0].pv);
692 break; // Value cannot be trusted. Break out immediately!
694 //Save info about search result
695 Value speculatedValue;
698 Value delta = value - IterationInfo[Iteration - 1].value;
705 speculatedValue = value + delta;
706 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
708 else if (value <= alpha)
710 assert(value == alpha);
714 speculatedValue = value + delta;
715 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
717 speculatedValue = value;
719 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
720 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
722 // Erase the easy move if it differs from the new best move
723 if (ss[0].pv[0] != EasyMove)
724 EasyMove = MOVE_NONE;
731 bool stopSearch = false;
733 // Stop search early if there is only a single legal move
734 if (Iteration >= 6 && rml.move_count() == 1)
737 // Stop search early when the last two iterations returned a mate score
739 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
740 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
743 // Stop search early if one move seems to be much better than the rest
744 int64_t nodes = nodes_searched();
748 && EasyMove == ss[0].pv[0]
749 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
750 && current_search_time() > MaxSearchTime / 16)
751 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
752 && current_search_time() > MaxSearchTime / 32)))
755 // Add some extra time if the best move has changed during the last two iterations
756 if (Iteration > 5 && Iteration <= 50)
757 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
758 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
760 // Stop search if most of MaxSearchTime is consumed at the end of the
761 // iteration. We probably don't have enough time to search the first
762 // move at the next iteration anyway.
763 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
768 //FIXME: Implement fail-low emergency measures
772 StopOnPonderhit = true;
776 if (MaxDepth && Iteration >= MaxDepth)
782 // If we are pondering, we shouldn't print the best move before we
785 wait_for_stop_or_ponderhit();
787 // Print final search statistics
788 std::cout << "info nodes " << nodes_searched()
790 << " time " << current_search_time()
791 << " hashfull " << TT.full() << std::endl;
793 // Print the best move and the ponder move to the standard output
794 if (ss[0].pv[0] == MOVE_NONE)
796 ss[0].pv[0] = rml.get_move(0);
797 ss[0].pv[1] = MOVE_NONE;
799 std::cout << "bestmove " << ss[0].pv[0];
800 if (ss[0].pv[1] != MOVE_NONE)
801 std::cout << " ponder " << ss[0].pv[1];
803 std::cout << std::endl;
808 dbg_print_mean(LogFile);
810 if (dbg_show_hit_rate)
811 dbg_print_hit_rate(LogFile);
814 LogFile << "Nodes: " << nodes_searched() << std::endl
815 << "Nodes/second: " << nps() << std::endl
816 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
818 p.do_move(ss[0].pv[0], st);
819 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
820 << std::endl << std::endl;
822 return rml.get_move_score(0);
826 // root_search() is the function which searches the root node. It is
827 // similar to search_pv except that it uses a different move ordering
828 // scheme (perhaps we should try to use this at internal PV nodes, too?)
829 // and prints some information to the standard output.
831 Value root_search(Position& pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta) {
833 Value oldAlpha = alpha;
835 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
837 // Loop through all the moves in the root move list
838 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
842 // We failed high, invalidate and skip next moves, leave node-counters
843 // and beta-counters as they are and quickly return, we will try to do
844 // a research at the next iteration with a bigger aspiration window.
845 rml.set_move_score(i, -VALUE_INFINITE);
853 RootMoveNumber = i + 1;
856 // Remember the node count before the move is searched. The node counts
857 // are used to sort the root moves at the next iteration.
858 nodes = nodes_searched();
860 // Reset beta cut-off counters
863 // Pick the next root move, and print the move and the move number to
864 // the standard output.
865 move = ss[0].currentMove = rml.get_move(i);
866 if (current_search_time() >= 1000)
867 std::cout << "info currmove " << move
868 << " currmovenumber " << i + 1 << std::endl;
870 // Decide search depth for this move
871 bool moveIsCapture = pos.move_is_capture(move);
873 ext = extension(pos, move, true, moveIsCapture, pos.move_is_check(move), false, false, &dangerous);
874 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
876 // Make the move, and search it
877 pos.do_move(move, st, dcCandidates);
881 // Aspiration window is disabled in multi-pv case
883 alpha = -VALUE_INFINITE;
885 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
886 // If the value has dropped a lot compared to the last iteration,
887 // set the boolean variable Problem to true. This variable is used
888 // for time managment: When Problem is true, we try to complete the
889 // current iteration before playing a move.
890 Problem = (Iteration >= 2 && value <= IterationInfo[Iteration-1].value - ProblemMargin);
892 if (Problem && StopOnPonderhit)
893 StopOnPonderhit = false;
897 if ( newDepth >= 3*OnePly
898 && i >= MultiPV + LMRPVMoves
901 && !move_is_promotion(move)
902 && !move_is_castle(move))
904 ss[0].reduction = OnePly;
905 value = -search(pos, ss, -alpha, newDepth-OnePly, 1, true, 0);
907 value = alpha + 1; // Just to trigger next condition
911 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
914 // Fail high! Set the boolean variable FailHigh to true, and
915 // re-search the move with a big window. The variable FailHigh is
916 // used for time managment: We try to avoid aborting the search
917 // prematurely during a fail high research.
919 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
926 // Finished searching the move. If AbortSearch is true, the search
927 // was aborted because the user interrupted the search or because we
928 // ran out of time. In this case, the return value of the search cannot
929 // be trusted, and we break out of the loop without updating the best
934 // Remember the node count for this move. The node counts are used to
935 // sort the root moves at the next iteration.
936 rml.set_move_nodes(i, nodes_searched() - nodes);
938 // Remember the beta-cutoff statistics
940 BetaCounter.read(pos.side_to_move(), our, their);
941 rml.set_beta_counters(i, our, their);
943 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
945 if (value <= alpha && i >= MultiPV)
946 rml.set_move_score(i, -VALUE_INFINITE);
949 // PV move or new best move!
952 rml.set_move_score(i, value);
954 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
955 rml.set_move_pv(i, ss[0].pv);
959 // We record how often the best move has been changed in each
960 // iteration. This information is used for time managment: When
961 // the best move changes frequently, we allocate some more time.
963 BestMoveChangesByIteration[Iteration]++;
965 // Print search information to the standard output
966 std::cout << "info depth " << Iteration
967 << " score " << value_to_string(value)
969 " lowerbound" : ((value <= alpha)? " upperbound" : ""))
970 << " time " << current_search_time()
971 << " nodes " << nodes_searched()
975 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
976 std::cout << ss[0].pv[j] << " ";
978 std::cout << std::endl;
981 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value,
982 ((value >= beta)? VALUE_TYPE_LOWER
983 : ((value <= alpha)? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT)),
990 // Reset the global variable Problem to false if the value isn't too
991 // far below the final value from the last iteration.
992 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
998 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1001 std::cout << "info multipv " << j + 1
1002 << " score " << value_to_string(rml.get_move_score(j))
1003 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1004 << " time " << current_search_time()
1005 << " nodes " << nodes_searched()
1009 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1010 std::cout << rml.get_move_pv(j, k) << " ";
1012 std::cout << std::endl;
1014 alpha = rml.get_move_score(Min(i, MultiPV-1));
1016 } // New best move case
1018 assert(alpha >= oldAlpha);
1020 FailLow = (alpha == oldAlpha);
1026 // search_pv() is the main search function for PV nodes.
1028 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1029 Depth depth, int ply, int threadID) {
1031 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1032 assert(beta > alpha && beta <= VALUE_INFINITE);
1033 assert(ply >= 0 && ply < PLY_MAX);
1034 assert(threadID >= 0 && threadID < ActiveThreads);
1037 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1039 // Initialize, and make an early exit in case of an aborted search,
1040 // an instant draw, maximum ply reached, etc.
1041 init_node(ss, ply, threadID);
1043 // After init_node() that calls poll()
1044 if (AbortSearch || thread_should_stop(threadID))
1052 if (ply >= PLY_MAX - 1)
1053 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1055 // Mate distance pruning
1056 Value oldAlpha = alpha;
1057 alpha = Max(value_mated_in(ply), alpha);
1058 beta = Min(value_mate_in(ply+1), beta);
1062 // Transposition table lookup. At PV nodes, we don't use the TT for
1063 // pruning, but only for move ordering.
1064 const TTEntry* tte = TT.retrieve(pos.get_key());
1065 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1067 // Go with internal iterative deepening if we don't have a TT move
1068 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
1070 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1071 ttMove = ss[ply].pv[ply];
1074 // Initialize a MovePicker object for the current position, and prepare
1075 // to search all moves
1076 Move move, movesSearched[256];
1078 Value value, bestValue = -VALUE_INFINITE;
1079 Color us = pos.side_to_move();
1080 bool isCheck = pos.is_check();
1081 bool mateThreat = pos.has_mate_threat(opposite_color(us));
1083 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1084 Bitboard dcCandidates = mp.discovered_check_candidates();
1086 // Loop through all legal moves until no moves remain or a beta cutoff
1088 while ( alpha < beta
1089 && (move = mp.get_next_move()) != MOVE_NONE
1090 && !thread_should_stop(threadID))
1092 assert(move_is_ok(move));
1094 bool singleReply = (isCheck && mp.number_of_evasions() == 1);
1095 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1096 bool moveIsCapture = pos.move_is_capture(move);
1098 movesSearched[moveCount++] = ss[ply].currentMove = move;
1100 // Decide the new search depth
1102 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1103 Depth newDepth = depth - OnePly + ext;
1105 // Make and search the move
1107 pos.do_move(move, st, dcCandidates);
1109 if (moveCount == 1) // The first move in list is the PV
1110 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1113 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1114 // if the move fails high will be re-searched at full depth.
1115 if ( depth >= 3*OnePly
1116 && moveCount >= LMRPVMoves
1119 && !move_is_promotion(move)
1120 && !move_is_castle(move)
1121 && !move_is_killer(move, ss[ply]))
1123 ss[ply].reduction = OnePly;
1124 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1127 value = alpha + 1; // Just to trigger next condition
1129 if (value > alpha) // Go with full depth non-pv search
1131 ss[ply].reduction = Depth(0);
1132 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1133 if (value > alpha && value < beta)
1135 // When the search fails high at ply 1 while searching the first
1136 // move at the root, set the flag failHighPly1. This is used for
1137 // time managment: We don't want to stop the search early in
1138 // such cases, because resolving the fail high at ply 1 could
1139 // result in a big drop in score at the root.
1140 if (ply == 1 && RootMoveNumber == 1)
1141 Threads[threadID].failHighPly1 = true;
1143 // A fail high occurred. Re-search at full window (pv search)
1144 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1145 Threads[threadID].failHighPly1 = false;
1149 pos.undo_move(move);
1151 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1154 if (value > bestValue)
1161 if (value == value_mate_in(ply + 1))
1162 ss[ply].mateKiller = move;
1164 // If we are at ply 1, and we are searching the first root move at
1165 // ply 0, set the 'Problem' variable if the score has dropped a lot
1166 // (from the computer's point of view) since the previous iteration.
1169 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1174 if ( ActiveThreads > 1
1176 && depth >= MinimumSplitDepth
1178 && idle_thread_exists(threadID)
1180 && !thread_should_stop(threadID)
1181 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE, VALUE_NONE, depth,
1182 &moveCount, &mp, dcCandidates, threadID, true))
1186 // All legal moves have been searched. A special case: If there were
1187 // no legal moves, it must be mate or stalemate.
1189 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1191 // If the search is not aborted, update the transposition table,
1192 // history counters, and killer moves.
1193 if (AbortSearch || thread_should_stop(threadID))
1196 if (bestValue <= oldAlpha)
1197 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1199 else if (bestValue >= beta)
1201 BetaCounter.add(pos.side_to_move(), depth, threadID);
1202 Move m = ss[ply].pv[ply];
1203 if (ok_to_history(pos, m)) // Only non capture moves are considered
1205 update_history(pos, m, depth, movesSearched, moveCount);
1206 update_killers(m, ss[ply]);
1208 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1211 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1217 // search() is the search function for zero-width nodes.
1219 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1220 int ply, bool allowNullmove, int threadID) {
1222 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1223 assert(ply >= 0 && ply < PLY_MAX);
1224 assert(threadID >= 0 && threadID < ActiveThreads);
1227 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1229 // Initialize, and make an early exit in case of an aborted search,
1230 // an instant draw, maximum ply reached, etc.
1231 init_node(ss, ply, threadID);
1233 // After init_node() that calls poll()
1234 if (AbortSearch || thread_should_stop(threadID))
1242 if (ply >= PLY_MAX - 1)
1243 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1245 // Mate distance pruning
1246 if (value_mated_in(ply) >= beta)
1249 if (value_mate_in(ply + 1) < beta)
1252 // Transposition table lookup
1253 const TTEntry* tte = TT.retrieve(pos.get_key());
1254 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1256 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1258 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1259 return value_from_tt(tte->value(), ply);
1262 Value approximateEval = quick_evaluate(pos);
1263 bool mateThreat = false;
1264 bool isCheck = pos.is_check();
1270 && !value_is_mate(beta)
1271 && ok_to_do_nullmove(pos)
1272 && approximateEval >= beta - NullMoveMargin)
1274 ss[ply].currentMove = MOVE_NULL;
1277 pos.do_null_move(st);
1278 int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
1280 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1282 pos.undo_null_move();
1284 if (nullValue >= beta)
1286 if (depth < 6 * OnePly)
1289 // Do zugzwang verification search
1290 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1294 // The null move failed low, which means that we may be faced with
1295 // some kind of threat. If the previous move was reduced, check if
1296 // the move that refuted the null move was somehow connected to the
1297 // move which was reduced. If a connection is found, return a fail
1298 // low score (which will cause the reduced move to fail high in the
1299 // parent node, which will trigger a re-search with full depth).
1300 if (nullValue == value_mated_in(ply + 2))
1303 ss[ply].threatMove = ss[ply + 1].currentMove;
1304 if ( depth < ThreatDepth
1305 && ss[ply - 1].reduction
1306 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1310 // Null move search not allowed, try razoring
1311 else if ( !value_is_mate(beta)
1312 && depth < RazorDepth
1313 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1314 && ss[ply - 1].currentMove != MOVE_NULL
1315 && ttMove == MOVE_NONE
1316 && !pos.has_pawn_on_7th(pos.side_to_move()))
1318 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1319 if (v < beta - RazorMargins[int(depth) - 2])
1323 // Go with internal iterative deepening if we don't have a TT move
1324 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1325 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1327 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1328 ttMove = ss[ply].pv[ply];
1331 // Initialize a MovePicker object for the current position, and prepare
1332 // to search all moves.
1333 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1335 Move move, movesSearched[256];
1337 Value value, bestValue = -VALUE_INFINITE;
1338 Bitboard dcCandidates = mp.discovered_check_candidates();
1339 Value futilityValue = VALUE_NONE;
1340 bool useFutilityPruning = depth < SelectiveDepth
1343 // Avoid calling evaluate() if we already have the score in TT
1344 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1345 futilityValue = value_from_tt(tte->value(), ply) + FutilityMargins[int(depth) - 2];
1347 // Loop through all legal moves until no moves remain or a beta cutoff
1349 while ( bestValue < beta
1350 && (move = mp.get_next_move()) != MOVE_NONE
1351 && !thread_should_stop(threadID))
1353 assert(move_is_ok(move));
1355 bool singleReply = (isCheck && mp.number_of_evasions() == 1);
1356 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1357 bool moveIsCapture = pos.move_is_capture(move);
1359 movesSearched[moveCount++] = ss[ply].currentMove = move;
1361 // Decide the new search depth
1363 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1364 Depth newDepth = depth - OnePly + ext;
1367 if ( useFutilityPruning
1370 && !move_is_promotion(move))
1372 // History pruning. See ok_to_prune() definition
1373 if ( moveCount >= 2 + int(depth)
1374 && ok_to_prune(pos, move, ss[ply].threatMove, depth)
1375 && bestValue > value_mated_in(PLY_MAX))
1378 // Value based pruning
1379 if (approximateEval < beta)
1381 if (futilityValue == VALUE_NONE)
1382 futilityValue = evaluate(pos, ei, threadID)
1383 + FutilityMargins[int(depth) - 2];
1385 if (futilityValue < beta)
1387 if (futilityValue > bestValue)
1388 bestValue = futilityValue;
1394 // Make and search the move
1396 pos.do_move(move, st, dcCandidates);
1398 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1399 // if the move fails high will be re-searched at full depth.
1400 if ( depth >= 3*OnePly
1401 && moveCount >= LMRNonPVMoves
1404 && !move_is_promotion(move)
1405 && !move_is_castle(move)
1406 && !move_is_killer(move, ss[ply]))
1408 ss[ply].reduction = OnePly;
1409 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1412 value = beta; // Just to trigger next condition
1414 if (value >= beta) // Go with full depth non-pv search
1416 ss[ply].reduction = Depth(0);
1417 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1419 pos.undo_move(move);
1421 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1424 if (value > bestValue)
1430 if (value == value_mate_in(ply + 1))
1431 ss[ply].mateKiller = move;
1435 if ( ActiveThreads > 1
1437 && depth >= MinimumSplitDepth
1439 && idle_thread_exists(threadID)
1441 && !thread_should_stop(threadID)
1442 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue, approximateEval, depth, &moveCount,
1443 &mp, dcCandidates, threadID, false))
1447 // All legal moves have been searched. A special case: If there were
1448 // no legal moves, it must be mate or stalemate.
1450 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1452 // If the search is not aborted, update the transposition table,
1453 // history counters, and killer moves.
1454 if (AbortSearch || thread_should_stop(threadID))
1457 if (bestValue < beta)
1458 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1461 BetaCounter.add(pos.side_to_move(), depth, threadID);
1462 Move m = ss[ply].pv[ply];
1463 if (ok_to_history(pos, m)) // Only non capture moves are considered
1465 update_history(pos, m, depth, movesSearched, moveCount);
1466 update_killers(m, ss[ply]);
1468 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1471 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1477 // qsearch() is the quiescence search function, which is called by the main
1478 // search function when the remaining depth is zero (or, to be more precise,
1479 // less than OnePly).
1481 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1482 Depth depth, int ply, int threadID) {
1484 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1485 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1487 assert(ply >= 0 && ply < PLY_MAX);
1488 assert(threadID >= 0 && threadID < ActiveThreads);
1490 // Initialize, and make an early exit in case of an aborted search,
1491 // an instant draw, maximum ply reached, etc.
1492 init_node(ss, ply, threadID);
1494 // After init_node() that calls poll()
1495 if (AbortSearch || thread_should_stop(threadID))
1501 // Transposition table lookup, only when not in PV
1502 TTEntry* tte = NULL;
1503 bool pvNode = (beta - alpha != 1);
1506 tte = TT.retrieve(pos.get_key());
1507 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1509 assert(tte->type() != VALUE_TYPE_EVAL);
1511 return value_from_tt(tte->value(), ply);
1514 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1516 // Evaluate the position statically
1519 bool isCheck = pos.is_check();
1520 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1523 staticValue = -VALUE_INFINITE;
1525 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1527 // Use the cached evaluation score if possible
1528 assert(ei.futilityMargin == Value(0));
1530 staticValue = tte->value();
1533 staticValue = evaluate(pos, ei, threadID);
1535 if (ply >= PLY_MAX - 1)
1536 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1538 // Initialize "stand pat score", and return it immediately if it is
1540 Value bestValue = staticValue;
1542 if (bestValue >= beta)
1544 // Store the score to avoid a future costly evaluation() call
1545 if (!isCheck && !tte && ei.futilityMargin == 0)
1546 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1551 if (bestValue > alpha)
1554 // Initialize a MovePicker object for the current position, and prepare
1555 // to search the moves. Because the depth is <= 0 here, only captures,
1556 // queen promotions and checks (only if depth == 0) will be generated.
1557 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1560 Bitboard dcCandidates = mp.discovered_check_candidates();
1561 Color us = pos.side_to_move();
1562 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1564 // Loop through the moves until no moves remain or a beta cutoff
1566 while ( alpha < beta
1567 && (move = mp.get_next_move()) != MOVE_NONE)
1569 assert(move_is_ok(move));
1572 ss[ply].currentMove = move;
1578 && !move_is_promotion(move)
1579 && !pos.move_is_check(move, dcCandidates)
1580 && !pos.move_is_passed_pawn_push(move))
1582 Value futilityValue = staticValue
1583 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1584 pos.endgame_value_of_piece_on(move_to(move)))
1585 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1587 + ei.futilityMargin;
1589 if (futilityValue < alpha)
1591 if (futilityValue > bestValue)
1592 bestValue = futilityValue;
1597 // Don't search captures and checks with negative SEE values
1599 && !move_is_promotion(move)
1600 && pos.see_sign(move) < 0)
1603 // Make and search the move.
1605 pos.do_move(move, st, dcCandidates);
1606 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1607 pos.undo_move(move);
1609 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1612 if (value > bestValue)
1623 // All legal moves have been searched. A special case: If we're in check
1624 // and no legal moves were found, it is checkmate.
1625 if (pos.is_check() && moveCount == 0) // Mate!
1626 return value_mated_in(ply);
1628 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1630 // Update transposition table
1631 Move m = ss[ply].pv[ply];
1634 // If bestValue isn't changed it means it is still the static evaluation of
1635 // the node, so keep this info to avoid a future costly evaluation() call.
1636 ValueType type = (bestValue == staticValue && !ei.futilityMargin ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1637 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1639 if (bestValue < beta)
1640 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1642 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
1645 // Update killers only for good check moves
1646 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1647 update_killers(m, ss[ply]);
1653 // sp_search() is used to search from a split point. This function is called
1654 // by each thread working at the split point. It is similar to the normal
1655 // search() function, but simpler. Because we have already probed the hash
1656 // table, done a null move search, and searched the first move before
1657 // splitting, we don't have to repeat all this work in sp_search(). We
1658 // also don't need to store anything to the hash table here: This is taken
1659 // care of after we return from the split point.
1661 void sp_search(SplitPoint* sp, int threadID) {
1663 assert(threadID >= 0 && threadID < ActiveThreads);
1664 assert(ActiveThreads > 1);
1666 Position pos = Position(sp->pos);
1667 SearchStack* ss = sp->sstack[threadID];
1670 bool isCheck = pos.is_check();
1671 bool useFutilityPruning = sp->depth < SelectiveDepth
1674 while ( sp->bestValue < sp->beta
1675 && !thread_should_stop(threadID)
1676 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1678 assert(move_is_ok(move));
1680 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1681 bool moveIsCapture = pos.move_is_capture(move);
1683 lock_grab(&(sp->lock));
1684 int moveCount = ++sp->moves;
1685 lock_release(&(sp->lock));
1687 ss[sp->ply].currentMove = move;
1689 // Decide the new search depth.
1691 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1692 Depth newDepth = sp->depth - OnePly + ext;
1695 if ( useFutilityPruning
1698 && !move_is_promotion(move))
1700 // History pruning. See ok_to_prune() definition
1701 if ( moveCount >= 2 + int(sp->depth)
1702 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth)
1703 && sp->bestValue > value_mated_in(PLY_MAX))
1706 // Value based pruning
1707 if (sp->approximateEval < sp->beta)
1709 if (sp->futilityValue == VALUE_NONE)
1712 sp->futilityValue = evaluate(pos, ei, threadID)
1713 + FutilityMargins[int(sp->depth) - 2];
1716 if (sp->futilityValue < sp->beta)
1718 if (sp->futilityValue > sp->bestValue) // Less then 1% of cases
1720 lock_grab(&(sp->lock));
1721 if (sp->futilityValue > sp->bestValue)
1722 sp->bestValue = sp->futilityValue;
1723 lock_release(&(sp->lock));
1730 // Make and search the move.
1732 pos.do_move(move, st, sp->dcCandidates);
1734 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1735 // if the move fails high will be re-searched at full depth.
1737 && moveCount >= LMRNonPVMoves
1739 && !move_is_promotion(move)
1740 && !move_is_castle(move)
1741 && !move_is_killer(move, ss[sp->ply]))
1743 ss[sp->ply].reduction = OnePly;
1744 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1747 value = sp->beta; // Just to trigger next condition
1749 if (value >= sp->beta) // Go with full depth non-pv search
1751 ss[sp->ply].reduction = Depth(0);
1752 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1754 pos.undo_move(move);
1756 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1758 if (thread_should_stop(threadID))
1762 lock_grab(&(sp->lock));
1763 if (value > sp->bestValue && !thread_should_stop(threadID))
1765 sp->bestValue = value;
1766 if (sp->bestValue >= sp->beta)
1768 sp_update_pv(sp->parentSstack, ss, sp->ply);
1769 for (int i = 0; i < ActiveThreads; i++)
1770 if (i != threadID && (i == sp->master || sp->slaves[i]))
1771 Threads[i].stop = true;
1773 sp->finished = true;
1776 lock_release(&(sp->lock));
1779 lock_grab(&(sp->lock));
1781 // If this is the master thread and we have been asked to stop because of
1782 // a beta cutoff higher up in the tree, stop all slave threads.
1783 if (sp->master == threadID && thread_should_stop(threadID))
1784 for (int i = 0; i < ActiveThreads; i++)
1786 Threads[i].stop = true;
1789 sp->slaves[threadID] = 0;
1791 lock_release(&(sp->lock));
1795 // sp_search_pv() is used to search from a PV split point. This function
1796 // is called by each thread working at the split point. It is similar to
1797 // the normal search_pv() function, but simpler. Because we have already
1798 // probed the hash table and searched the first move before splitting, we
1799 // don't have to repeat all this work in sp_search_pv(). We also don't
1800 // need to store anything to the hash table here: This is taken care of
1801 // after we return from the split point.
1803 void sp_search_pv(SplitPoint* sp, int threadID) {
1805 assert(threadID >= 0 && threadID < ActiveThreads);
1806 assert(ActiveThreads > 1);
1808 Position pos = Position(sp->pos);
1809 SearchStack* ss = sp->sstack[threadID];
1813 while ( sp->alpha < sp->beta
1814 && !thread_should_stop(threadID)
1815 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1817 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1818 bool moveIsCapture = pos.move_is_capture(move);
1820 assert(move_is_ok(move));
1822 lock_grab(&(sp->lock));
1823 int moveCount = ++sp->moves;
1824 lock_release(&(sp->lock));
1826 ss[sp->ply].currentMove = move;
1828 // Decide the new search depth.
1830 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1831 Depth newDepth = sp->depth - OnePly + ext;
1833 // Make and search the move.
1835 pos.do_move(move, st, sp->dcCandidates);
1837 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1838 // if the move fails high will be re-searched at full depth.
1840 && moveCount >= LMRPVMoves
1842 && !move_is_promotion(move)
1843 && !move_is_castle(move)
1844 && !move_is_killer(move, ss[sp->ply]))
1846 ss[sp->ply].reduction = OnePly;
1847 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1850 value = sp->alpha + 1; // Just to trigger next condition
1852 if (value > sp->alpha) // Go with full depth non-pv search
1854 ss[sp->ply].reduction = Depth(0);
1855 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1857 if (value > sp->alpha && value < sp->beta)
1859 // When the search fails high at ply 1 while searching the first
1860 // move at the root, set the flag failHighPly1. This is used for
1861 // time managment: We don't want to stop the search early in
1862 // such cases, because resolving the fail high at ply 1 could
1863 // result in a big drop in score at the root.
1864 if (sp->ply == 1 && RootMoveNumber == 1)
1865 Threads[threadID].failHighPly1 = true;
1867 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1868 Threads[threadID].failHighPly1 = false;
1871 pos.undo_move(move);
1873 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1875 if (thread_should_stop(threadID))
1879 lock_grab(&(sp->lock));
1880 if (value > sp->bestValue && !thread_should_stop(threadID))
1882 sp->bestValue = value;
1883 if (value > sp->alpha)
1886 sp_update_pv(sp->parentSstack, ss, sp->ply);
1887 if (value == value_mate_in(sp->ply + 1))
1888 ss[sp->ply].mateKiller = move;
1890 if (value >= sp->beta)
1892 for (int i = 0; i < ActiveThreads; i++)
1893 if (i != threadID && (i == sp->master || sp->slaves[i]))
1894 Threads[i].stop = true;
1896 sp->finished = true;
1899 // If we are at ply 1, and we are searching the first root move at
1900 // ply 0, set the 'Problem' variable if the score has dropped a lot
1901 // (from the computer's point of view) since the previous iteration.
1904 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1907 lock_release(&(sp->lock));
1910 lock_grab(&(sp->lock));
1912 // If this is the master thread and we have been asked to stop because of
1913 // a beta cutoff higher up in the tree, stop all slave threads.
1914 if (sp->master == threadID && thread_should_stop(threadID))
1915 for (int i = 0; i < ActiveThreads; i++)
1917 Threads[i].stop = true;
1920 sp->slaves[threadID] = 0;
1922 lock_release(&(sp->lock));
1925 /// The BetaCounterType class
1927 BetaCounterType::BetaCounterType() { clear(); }
1929 void BetaCounterType::clear() {
1931 for (int i = 0; i < THREAD_MAX; i++)
1932 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
1935 void BetaCounterType::add(Color us, Depth d, int threadID) {
1937 // Weighted count based on depth
1938 Threads[threadID].betaCutOffs[us] += unsigned(d);
1941 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1944 for (int i = 0; i < THREAD_MAX; i++)
1946 our += Threads[i].betaCutOffs[us];
1947 their += Threads[i].betaCutOffs[opposite_color(us)];
1952 /// The RootMove class
1956 RootMove::RootMove() {
1957 nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
1960 // RootMove::operator<() is the comparison function used when
1961 // sorting the moves. A move m1 is considered to be better
1962 // than a move m2 if it has a higher score, or if the moves
1963 // have equal score but m1 has the higher node count.
1965 bool RootMove::operator<(const RootMove& m) {
1967 if (score != m.score)
1968 return (score < m.score);
1970 return theirBeta <= m.theirBeta;
1973 /// The RootMoveList class
1977 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1979 MoveStack mlist[MaxRootMoves];
1980 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1982 // Generate all legal moves
1983 MoveStack* last = generate_moves(pos, mlist);
1985 // Add each move to the moves[] array
1986 for (MoveStack* cur = mlist; cur != last; cur++)
1988 bool includeMove = includeAllMoves;
1990 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1991 includeMove = (searchMoves[k] == cur->move);
1996 // Find a quick score for the move
1998 SearchStack ss[PLY_MAX_PLUS_2];
2001 moves[count].move = cur->move;
2002 pos.do_move(moves[count].move, st);
2003 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2004 pos.undo_move(moves[count].move);
2005 moves[count].pv[0] = moves[count].move;
2006 moves[count].pv[1] = MOVE_NONE; // FIXME
2013 // Simple accessor methods for the RootMoveList class
2015 inline Move RootMoveList::get_move(int moveNum) const {
2016 return moves[moveNum].move;
2019 inline Value RootMoveList::get_move_score(int moveNum) const {
2020 return moves[moveNum].score;
2023 inline void RootMoveList::set_move_score(int moveNum, Value score) {
2024 moves[moveNum].score = score;
2027 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2028 moves[moveNum].nodes = nodes;
2029 moves[moveNum].cumulativeNodes += nodes;
2032 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2033 moves[moveNum].ourBeta = our;
2034 moves[moveNum].theirBeta = their;
2037 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2039 for(j = 0; pv[j] != MOVE_NONE; j++)
2040 moves[moveNum].pv[j] = pv[j];
2041 moves[moveNum].pv[j] = MOVE_NONE;
2044 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2045 return moves[moveNum].pv[i];
2048 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2049 return moves[moveNum].cumulativeNodes;
2052 inline int RootMoveList::move_count() const {
2057 // RootMoveList::scan_for_easy_move() is called at the end of the first
2058 // iteration, and is used to detect an "easy move", i.e. a move which appears
2059 // to be much bester than all the rest. If an easy move is found, the move
2060 // is returned, otherwise the function returns MOVE_NONE. It is very
2061 // important that this function is called at the right moment: The code
2062 // assumes that the first iteration has been completed and the moves have
2063 // been sorted. This is done in RootMoveList c'tor.
2065 Move RootMoveList::scan_for_easy_move() const {
2072 // moves are sorted so just consider the best and the second one
2073 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
2079 // RootMoveList::sort() sorts the root move list at the beginning of a new
2082 inline void RootMoveList::sort() {
2084 sort_multipv(count - 1); // all items
2088 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2089 // list by their scores and depths. It is used to order the different PVs
2090 // correctly in MultiPV mode.
2092 void RootMoveList::sort_multipv(int n) {
2094 for (int i = 1; i <= n; i++)
2096 RootMove rm = moves[i];
2098 for (j = i; j > 0 && moves[j-1] < rm; j--)
2099 moves[j] = moves[j-1];
2105 // init_node() is called at the beginning of all the search functions
2106 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2107 // stack object corresponding to the current node. Once every
2108 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2109 // for user input and checks whether it is time to stop the search.
2111 void init_node(SearchStack ss[], int ply, int threadID) {
2113 assert(ply >= 0 && ply < PLY_MAX);
2114 assert(threadID >= 0 && threadID < ActiveThreads);
2116 Threads[threadID].nodes++;
2121 if (NodesSincePoll >= NodesBetweenPolls)
2128 ss[ply+2].initKillers();
2130 if (Threads[threadID].printCurrentLine)
2131 print_current_line(ss, ply, threadID);
2135 // update_pv() is called whenever a search returns a value > alpha. It
2136 // updates the PV in the SearchStack object corresponding to the current
2139 void update_pv(SearchStack ss[], int ply) {
2140 assert(ply >= 0 && ply < PLY_MAX);
2142 ss[ply].pv[ply] = ss[ply].currentMove;
2144 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2145 ss[ply].pv[p] = ss[ply+1].pv[p];
2146 ss[ply].pv[p] = MOVE_NONE;
2150 // sp_update_pv() is a variant of update_pv for use at split points. The
2151 // difference between the two functions is that sp_update_pv also updates
2152 // the PV at the parent node.
2154 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2155 assert(ply >= 0 && ply < PLY_MAX);
2157 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2159 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2160 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2161 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2165 // connected_moves() tests whether two moves are 'connected' in the sense
2166 // that the first move somehow made the second move possible (for instance
2167 // if the moving piece is the same in both moves). The first move is
2168 // assumed to be the move that was made to reach the current position, while
2169 // the second move is assumed to be a move from the current position.
2171 bool connected_moves(const Position& pos, Move m1, Move m2) {
2173 Square f1, t1, f2, t2;
2176 assert(move_is_ok(m1));
2177 assert(move_is_ok(m2));
2179 if (m2 == MOVE_NONE)
2182 // Case 1: The moving piece is the same in both moves
2188 // Case 2: The destination square for m2 was vacated by m1
2194 // Case 3: Moving through the vacated square
2195 if ( piece_is_slider(pos.piece_on(f2))
2196 && bit_is_set(squares_between(f2, t2), f1))
2199 // Case 4: The destination square for m2 is attacked by the moving piece in m1
2200 p = pos.piece_on(t1);
2201 if (bit_is_set(pos.attacks_from(p, t1), t2))
2204 // Case 5: Discovered check, checking piece is the piece moved in m1
2205 if ( piece_is_slider(p)
2206 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2207 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2209 Bitboard occ = pos.occupied_squares();
2210 Color us = pos.side_to_move();
2211 Square ksq = pos.king_square(us);
2212 clear_bit(&occ, f2);
2213 if (type_of_piece(p) == BISHOP)
2215 if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2218 else if (type_of_piece(p) == ROOK)
2220 if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
2225 assert(type_of_piece(p) == QUEEN);
2226 if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
2234 // value_is_mate() checks if the given value is a mate one
2235 // eventually compensated for the ply.
2237 bool value_is_mate(Value value) {
2239 assert(abs(value) <= VALUE_INFINITE);
2241 return value <= value_mated_in(PLY_MAX)
2242 || value >= value_mate_in(PLY_MAX);
2246 // move_is_killer() checks if the given move is among the
2247 // killer moves of that ply.
2249 bool move_is_killer(Move m, const SearchStack& ss) {
2251 const Move* k = ss.killers;
2252 for (int i = 0; i < KILLER_MAX; i++, k++)
2260 // extension() decides whether a move should be searched with normal depth,
2261 // or with extended depth. Certain classes of moves (checking moves, in
2262 // particular) are searched with bigger depth than ordinary moves and in
2263 // any case are marked as 'dangerous'. Note that also if a move is not
2264 // extended, as example because the corresponding UCI option is set to zero,
2265 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2267 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2268 bool singleReply, bool mateThreat, bool* dangerous) {
2270 assert(m != MOVE_NONE);
2272 Depth result = Depth(0);
2273 *dangerous = check | singleReply | mateThreat;
2278 result += CheckExtension[pvNode];
2281 result += SingleReplyExtension[pvNode];
2284 result += MateThreatExtension[pvNode];
2287 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2289 Color c = pos.side_to_move();
2290 if (relative_rank(c, move_to(m)) == RANK_7)
2292 result += PawnPushTo7thExtension[pvNode];
2295 if (pos.pawn_is_passed(c, move_to(m)))
2297 result += PassedPawnExtension[pvNode];
2303 && pos.type_of_piece_on(move_to(m)) != PAWN
2304 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2305 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2306 && !move_is_promotion(m)
2309 result += PawnEndgameExtension[pvNode];
2315 && pos.type_of_piece_on(move_to(m)) != PAWN
2316 && pos.see_sign(m) >= 0)
2322 return Min(result, OnePly);
2326 // ok_to_do_nullmove() looks at the current position and decides whether
2327 // doing a 'null move' should be allowed. In order to avoid zugzwang
2328 // problems, null moves are not allowed when the side to move has very
2329 // little material left. Currently, the test is a bit too simple: Null
2330 // moves are avoided only when the side to move has only pawns left. It's
2331 // probably a good idea to avoid null moves in at least some more
2332 // complicated endgames, e.g. KQ vs KR. FIXME
2334 bool ok_to_do_nullmove(const Position& pos) {
2336 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2340 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2341 // non-tactical moves late in the move list close to the leaves are
2342 // candidates for pruning.
2344 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d) {
2346 assert(move_is_ok(m));
2347 assert(threat == MOVE_NONE || move_is_ok(threat));
2348 assert(!move_is_promotion(m));
2349 assert(!pos.move_is_check(m));
2350 assert(!pos.move_is_capture(m));
2351 assert(!pos.move_is_passed_pawn_push(m));
2352 assert(d >= OnePly);
2354 Square mfrom, mto, tfrom, tto;
2356 mfrom = move_from(m);
2358 tfrom = move_from(threat);
2359 tto = move_to(threat);
2361 // Case 1: Castling moves are never pruned
2362 if (move_is_castle(m))
2365 // Case 2: Don't prune moves which move the threatened piece
2366 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2369 // Case 3: If the threatened piece has value less than or equal to the
2370 // value of the threatening piece, don't prune move which defend it.
2371 if ( !PruneDefendingMoves
2372 && threat != MOVE_NONE
2373 && pos.move_is_capture(threat)
2374 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2375 || pos.type_of_piece_on(tfrom) == KING)
2376 && pos.move_attacks_square(m, tto))
2379 // Case 4: Don't prune moves with good history
2380 if (!H.ok_to_prune(pos.piece_on(mfrom), mto, d))
2383 // Case 5: If the moving piece in the threatened move is a slider, don't
2384 // prune safe moves which block its ray.
2385 if ( !PruneBlockingMoves
2386 && threat != MOVE_NONE
2387 && piece_is_slider(pos.piece_on(tfrom))
2388 && bit_is_set(squares_between(tfrom, tto), mto)
2389 && pos.see_sign(m) >= 0)
2396 // ok_to_use_TT() returns true if a transposition table score
2397 // can be used at a given point in search.
2399 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2401 Value v = value_from_tt(tte->value(), ply);
2403 return ( tte->depth() >= depth
2404 || v >= Max(value_mate_in(100), beta)
2405 || v < Min(value_mated_in(100), beta))
2407 && ( (is_lower_bound(tte->type()) && v >= beta)
2408 || (is_upper_bound(tte->type()) && v < beta));
2412 // ok_to_history() returns true if a move m can be stored
2413 // in history. Should be a non capturing move nor a promotion.
2415 bool ok_to_history(const Position& pos, Move m) {
2417 return !pos.move_is_capture(m) && !move_is_promotion(m);
2421 // update_history() registers a good move that produced a beta-cutoff
2422 // in history and marks as failures all the other moves of that ply.
2424 void update_history(const Position& pos, Move m, Depth depth,
2425 Move movesSearched[], int moveCount) {
2427 H.success(pos.piece_on(move_from(m)), move_to(m), depth);
2429 for (int i = 0; i < moveCount - 1; i++)
2431 assert(m != movesSearched[i]);
2432 if (ok_to_history(pos, movesSearched[i]))
2433 H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]));
2438 // update_killers() add a good move that produced a beta-cutoff
2439 // among the killer moves of that ply.
2441 void update_killers(Move m, SearchStack& ss) {
2443 if (m == ss.killers[0])
2446 for (int i = KILLER_MAX - 1; i > 0; i--)
2447 ss.killers[i] = ss.killers[i - 1];
2453 // fail_high_ply_1() checks if some thread is currently resolving a fail
2454 // high at ply 1 at the node below the first root node. This information
2455 // is used for time managment.
2457 bool fail_high_ply_1() {
2459 for(int i = 0; i < ActiveThreads; i++)
2460 if (Threads[i].failHighPly1)
2467 // current_search_time() returns the number of milliseconds which have passed
2468 // since the beginning of the current search.
2470 int current_search_time() {
2471 return get_system_time() - SearchStartTime;
2475 // nps() computes the current nodes/second count.
2478 int t = current_search_time();
2479 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2483 // poll() performs two different functions: It polls for user input, and it
2484 // looks at the time consumed so far and decides if it's time to abort the
2489 static int lastInfoTime;
2490 int t = current_search_time();
2495 // We are line oriented, don't read single chars
2496 std::string command;
2497 if (!std::getline(std::cin, command))
2500 if (command == "quit")
2503 PonderSearch = false;
2507 else if (command == "stop")
2510 PonderSearch = false;
2512 else if (command == "ponderhit")
2515 // Print search information
2519 else if (lastInfoTime > t)
2520 // HACK: Must be a new search where we searched less than
2521 // NodesBetweenPolls nodes during the first second of search.
2524 else if (t - lastInfoTime >= 1000)
2531 if (dbg_show_hit_rate)
2532 dbg_print_hit_rate();
2534 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2535 << " time " << t << " hashfull " << TT.full() << std::endl;
2536 lock_release(&IOLock);
2537 if (ShowCurrentLine)
2538 Threads[0].printCurrentLine = true;
2540 // Should we stop the search?
2544 bool overTime = t > AbsoluteMaxSearchTime
2545 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2546 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2547 && t > 6*(MaxSearchTime + ExtraSearchTime));
2549 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2550 || (ExactMaxTime && t >= ExactMaxTime)
2551 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2556 // ponderhit() is called when the program is pondering (i.e. thinking while
2557 // it's the opponent's turn to move) in order to let the engine know that
2558 // it correctly predicted the opponent's move.
2562 int t = current_search_time();
2563 PonderSearch = false;
2564 if (Iteration >= 3 &&
2565 (!InfiniteSearch && (StopOnPonderhit ||
2566 t > AbsoluteMaxSearchTime ||
2567 (RootMoveNumber == 1 &&
2568 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2569 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2570 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2575 // print_current_line() prints the current line of search for a given
2576 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2578 void print_current_line(SearchStack ss[], int ply, int threadID) {
2580 assert(ply >= 0 && ply < PLY_MAX);
2581 assert(threadID >= 0 && threadID < ActiveThreads);
2583 if (!Threads[threadID].idle)
2586 std::cout << "info currline " << (threadID + 1);
2587 for (int p = 0; p < ply; p++)
2588 std::cout << " " << ss[p].currentMove;
2590 std::cout << std::endl;
2591 lock_release(&IOLock);
2593 Threads[threadID].printCurrentLine = false;
2594 if (threadID + 1 < ActiveThreads)
2595 Threads[threadID + 1].printCurrentLine = true;
2599 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2601 void init_ss_array(SearchStack ss[]) {
2603 for (int i = 0; i < 3; i++)
2606 ss[i].initKillers();
2611 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2612 // while the program is pondering. The point is to work around a wrinkle in
2613 // the UCI protocol: When pondering, the engine is not allowed to give a
2614 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2615 // We simply wait here until one of these commands is sent, and return,
2616 // after which the bestmove and pondermove will be printed (in id_loop()).
2618 void wait_for_stop_or_ponderhit() {
2620 std::string command;
2624 if (!std::getline(std::cin, command))
2627 if (command == "quit")
2632 else if (command == "ponderhit" || command == "stop")
2638 // idle_loop() is where the threads are parked when they have no work to do.
2639 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2640 // object for which the current thread is the master.
2642 void idle_loop(int threadID, SplitPoint* waitSp) {
2643 assert(threadID >= 0 && threadID < THREAD_MAX);
2645 Threads[threadID].running = true;
2648 if(AllThreadsShouldExit && threadID != 0)
2651 // If we are not thinking, wait for a condition to be signaled instead
2652 // of wasting CPU time polling for work:
2653 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2654 #if !defined(_MSC_VER)
2655 pthread_mutex_lock(&WaitLock);
2656 if(Idle || threadID >= ActiveThreads)
2657 pthread_cond_wait(&WaitCond, &WaitLock);
2658 pthread_mutex_unlock(&WaitLock);
2660 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2664 // If this thread has been assigned work, launch a search
2665 if(Threads[threadID].workIsWaiting) {
2666 Threads[threadID].workIsWaiting = false;
2667 if(Threads[threadID].splitPoint->pvNode)
2668 sp_search_pv(Threads[threadID].splitPoint, threadID);
2670 sp_search(Threads[threadID].splitPoint, threadID);
2671 Threads[threadID].idle = true;
2674 // If this thread is the master of a split point and all threads have
2675 // finished their work at this split point, return from the idle loop.
2676 if(waitSp != NULL && waitSp->cpus == 0)
2680 Threads[threadID].running = false;
2684 // init_split_point_stack() is called during program initialization, and
2685 // initializes all split point objects.
2687 void init_split_point_stack() {
2688 for(int i = 0; i < THREAD_MAX; i++)
2689 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2690 SplitPointStack[i][j].parent = NULL;
2691 lock_init(&(SplitPointStack[i][j].lock), NULL);
2696 // destroy_split_point_stack() is called when the program exits, and
2697 // destroys all locks in the precomputed split point objects.
2699 void destroy_split_point_stack() {
2700 for(int i = 0; i < THREAD_MAX; i++)
2701 for(int j = 0; j < MaxActiveSplitPoints; j++)
2702 lock_destroy(&(SplitPointStack[i][j].lock));
2706 // thread_should_stop() checks whether the thread with a given threadID has
2707 // been asked to stop, directly or indirectly. This can happen if a beta
2708 // cutoff has occured in thre thread's currently active split point, or in
2709 // some ancestor of the current split point.
2711 bool thread_should_stop(int threadID) {
2712 assert(threadID >= 0 && threadID < ActiveThreads);
2716 if(Threads[threadID].stop)
2718 if(ActiveThreads <= 2)
2720 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2722 Threads[threadID].stop = true;
2729 // thread_is_available() checks whether the thread with threadID "slave" is
2730 // available to help the thread with threadID "master" at a split point. An
2731 // obvious requirement is that "slave" must be idle. With more than two
2732 // threads, this is not by itself sufficient: If "slave" is the master of
2733 // some active split point, it is only available as a slave to the other
2734 // threads which are busy searching the split point at the top of "slave"'s
2735 // split point stack (the "helpful master concept" in YBWC terminology).
2737 bool thread_is_available(int slave, int master) {
2738 assert(slave >= 0 && slave < ActiveThreads);
2739 assert(master >= 0 && master < ActiveThreads);
2740 assert(ActiveThreads > 1);
2742 if(!Threads[slave].idle || slave == master)
2745 if(Threads[slave].activeSplitPoints == 0)
2746 // No active split points means that the thread is available as a slave
2747 // for any other thread.
2750 if(ActiveThreads == 2)
2753 // Apply the "helpful master" concept if possible.
2754 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2761 // idle_thread_exists() tries to find an idle thread which is available as
2762 // a slave for the thread with threadID "master".
2764 bool idle_thread_exists(int master) {
2765 assert(master >= 0 && master < ActiveThreads);
2766 assert(ActiveThreads > 1);
2768 for(int i = 0; i < ActiveThreads; i++)
2769 if(thread_is_available(i, master))
2775 // split() does the actual work of distributing the work at a node between
2776 // several threads at PV nodes. If it does not succeed in splitting the
2777 // node (because no idle threads are available, or because we have no unused
2778 // split point objects), the function immediately returns false. If
2779 // splitting is possible, a SplitPoint object is initialized with all the
2780 // data that must be copied to the helper threads (the current position and
2781 // search stack, alpha, beta, the search depth, etc.), and we tell our
2782 // helper threads that they have been assigned work. This will cause them
2783 // to instantly leave their idle loops and call sp_search_pv(). When all
2784 // threads have returned from sp_search_pv (or, equivalently, when
2785 // splitPoint->cpus becomes 0), split() returns true.
2787 bool split(const Position& p, SearchStack* sstck, int ply,
2788 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2789 const Value approximateEval, Depth depth, int* moves,
2790 MovePicker* mp, Bitboard dcCandidates, int master, bool pvNode) {
2793 assert(sstck != NULL);
2794 assert(ply >= 0 && ply < PLY_MAX);
2795 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2796 assert(!pvNode || *alpha < *beta);
2797 assert(*beta <= VALUE_INFINITE);
2798 assert(depth > Depth(0));
2799 assert(master >= 0 && master < ActiveThreads);
2800 assert(ActiveThreads > 1);
2802 SplitPoint* splitPoint;
2807 // If no other thread is available to help us, or if we have too many
2808 // active split points, don't split.
2809 if(!idle_thread_exists(master) ||
2810 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2811 lock_release(&MPLock);
2815 // Pick the next available split point object from the split point stack
2816 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2817 Threads[master].activeSplitPoints++;
2819 // Initialize the split point object
2820 splitPoint->parent = Threads[master].splitPoint;
2821 splitPoint->finished = false;
2822 splitPoint->ply = ply;
2823 splitPoint->depth = depth;
2824 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2825 splitPoint->beta = *beta;
2826 splitPoint->pvNode = pvNode;
2827 splitPoint->dcCandidates = dcCandidates;
2828 splitPoint->bestValue = *bestValue;
2829 splitPoint->futilityValue = futilityValue;
2830 splitPoint->approximateEval = approximateEval;
2831 splitPoint->master = master;
2832 splitPoint->mp = mp;
2833 splitPoint->moves = *moves;
2834 splitPoint->cpus = 1;
2835 splitPoint->pos.copy(p);
2836 splitPoint->parentSstack = sstck;
2837 for(i = 0; i < ActiveThreads; i++)
2838 splitPoint->slaves[i] = 0;
2840 // Copy the current position and the search stack to the master thread
2841 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2842 Threads[master].splitPoint = splitPoint;
2844 // Make copies of the current position and search stack for each thread
2845 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2847 if(thread_is_available(i, master)) {
2848 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2849 Threads[i].splitPoint = splitPoint;
2850 splitPoint->slaves[i] = 1;
2854 // Tell the threads that they have work to do. This will make them leave
2856 for(i = 0; i < ActiveThreads; i++)
2857 if(i == master || splitPoint->slaves[i]) {
2858 Threads[i].workIsWaiting = true;
2859 Threads[i].idle = false;
2860 Threads[i].stop = false;
2863 lock_release(&MPLock);
2865 // Everything is set up. The master thread enters the idle loop, from
2866 // which it will instantly launch a search, because its workIsWaiting
2867 // slot is 'true'. We send the split point as a second parameter to the
2868 // idle loop, which means that the main thread will return from the idle
2869 // loop when all threads have finished their work at this split point
2870 // (i.e. when // splitPoint->cpus == 0).
2871 idle_loop(master, splitPoint);
2873 // We have returned from the idle loop, which means that all threads are
2874 // finished. Update alpha, beta and bestvalue, and return.
2876 if(pvNode) *alpha = splitPoint->alpha;
2877 *beta = splitPoint->beta;
2878 *bestValue = splitPoint->bestValue;
2879 Threads[master].stop = false;
2880 Threads[master].idle = false;
2881 Threads[master].activeSplitPoints--;
2882 Threads[master].splitPoint = splitPoint->parent;
2883 lock_release(&MPLock);
2889 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2890 // to start a new search from the root.
2892 void wake_sleeping_threads() {
2893 if(ActiveThreads > 1) {
2894 for(int i = 1; i < ActiveThreads; i++) {
2895 Threads[i].idle = true;
2896 Threads[i].workIsWaiting = false;
2898 #if !defined(_MSC_VER)
2899 pthread_mutex_lock(&WaitLock);
2900 pthread_cond_broadcast(&WaitCond);
2901 pthread_mutex_unlock(&WaitLock);
2903 for(int i = 1; i < THREAD_MAX; i++)
2904 SetEvent(SitIdleEvent[i]);
2910 // init_thread() is the function which is called when a new thread is
2911 // launched. It simply calls the idle_loop() function with the supplied
2912 // threadID. There are two versions of this function; one for POSIX threads
2913 // and one for Windows threads.
2915 #if !defined(_MSC_VER)
2917 void *init_thread(void *threadID) {
2918 idle_loop(*(int *)threadID, NULL);
2924 DWORD WINAPI init_thread(LPVOID threadID) {
2925 idle_loop(*(int *)threadID, NULL);