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 // If the TT move is at least SingleReplyMargin better then the
176 // remaining ones we will extend it.
177 const Value SingleReplyMargin = Value(0x64);
179 // Margins for futility pruning in the quiescence search, and at frontier
180 // and near frontier nodes.
181 const Value FutilityMarginQS = Value(0x80);
183 // Each move futility margin is decreased
184 const Value IncrementalFutilityMargin = Value(0x8);
186 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
187 const Value FutilityMargins[12] = { Value(0x100), Value(0x120), Value(0x200), Value(0x220), Value(0x250), Value(0x270),
188 // 4 ply 4.5 ply 5 ply 5.5 ply 6 ply 6.5 ply
189 Value(0x2A0), Value(0x2C0), Value(0x340), Value(0x360), Value(0x3A0), Value(0x3C0) };
191 const Depth RazorDepth = 4*OnePly;
193 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
194 const Value RazorMargins[6] = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
196 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
197 const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
200 /// Variables initialized by UCI options
202 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
203 int LMRPVMoves, LMRNonPVMoves; // heavy SMP read access for the latter
205 // Depth limit for use of dynamic threat detection
206 Depth ThreatDepth; // heavy SMP read access
208 // Last seconds noise filtering (LSN)
209 const bool UseLSNFiltering = true;
210 const int LSNTime = 4000; // In milliseconds
211 const Value LSNValue = value_from_centipawns(200);
212 bool loseOnTime = false;
214 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
215 // There is heavy SMP read access on these arrays
216 Depth CheckExtension[2], SingleReplyExtension[2], PawnPushTo7thExtension[2];
217 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
219 // Iteration counters
221 BetaCounterType BetaCounter; // has per-thread internal data
223 // Scores and number of times the best move changed for each iteration
224 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
225 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
230 // Time managment variables
232 int MaxNodes, MaxDepth;
233 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
237 bool StopOnPonderhit;
238 bool AbortSearch; // heavy SMP read access
244 // Show current line?
245 bool ShowCurrentLine;
249 std::ofstream LogFile;
251 // MP related variables
252 int ActiveThreads = 1;
253 Depth MinimumSplitDepth;
254 int MaxThreadsPerSplitPoint;
255 Thread Threads[THREAD_MAX];
258 bool AllThreadsShouldExit = false;
259 const int MaxActiveSplitPoints = 8;
260 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
263 #if !defined(_MSC_VER)
264 pthread_cond_t WaitCond;
265 pthread_mutex_t WaitLock;
267 HANDLE SitIdleEvent[THREAD_MAX];
270 // Node counters, used only by thread[0] but try to keep in different
271 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
273 int NodesBetweenPolls = 30000;
281 Value id_loop(const Position& pos, Move searchMoves[]);
282 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
283 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
284 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
285 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
286 void sp_search(SplitPoint* sp, int threadID);
287 void sp_search_pv(SplitPoint* sp, int threadID);
288 void init_node(SearchStack ss[], int ply, int threadID);
289 void update_pv(SearchStack ss[], int ply);
290 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
291 bool connected_moves(const Position& pos, Move m1, Move m2);
292 bool value_is_mate(Value value);
293 bool move_is_killer(Move m, const SearchStack& ss);
294 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
295 bool ok_to_do_nullmove(const Position& pos);
296 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d);
297 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
298 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
299 void update_killers(Move m, SearchStack& ss);
301 bool fail_high_ply_1();
302 int current_search_time();
306 void print_current_line(SearchStack ss[], int ply, int threadID);
307 void wait_for_stop_or_ponderhit();
308 void init_ss_array(SearchStack ss[]);
310 void idle_loop(int threadID, SplitPoint* waitSp);
311 void init_split_point_stack();
312 void destroy_split_point_stack();
313 bool thread_should_stop(int threadID);
314 bool thread_is_available(int slave, int master);
315 bool idle_thread_exists(int master);
316 bool split(const Position& pos, SearchStack* ss, int ply,
317 Value *alpha, Value *beta, Value *bestValue,
318 const Value futilityValue, const Value approximateValue,
319 Depth depth, int *moves,
320 MovePicker *mp, int master, bool pvNode);
321 void wake_sleeping_threads();
323 #if !defined(_MSC_VER)
324 void *init_thread(void *threadID);
326 DWORD WINAPI init_thread(LPVOID threadID);
337 /// perft() is our utility to verify move generation is bug free. All the
338 /// legal moves up to given depth are generated and counted and the sum returned.
340 int perft(Position& pos, Depth depth)
344 MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H);
346 // If we are at the last ply we don't need to do and undo
347 // the moves, just to count them.
348 if (depth <= OnePly) // Replace with '<' to test also qsearch
350 while (mp.get_next_move()) sum++;
354 // Loop through all legal moves
356 while ((move = mp.get_next_move()) != MOVE_NONE)
359 pos.do_move(move, st, ci, pos.move_is_check(move, ci));
360 sum += perft(pos, depth - OnePly);
367 /// think() is the external interface to Stockfish's search, and is called when
368 /// the program receives the UCI 'go' command. It initializes various
369 /// search-related global variables, and calls root_search(). It returns false
370 /// when a quit command is received during the search.
372 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
373 int time[], int increment[], int movesToGo, int maxDepth,
374 int maxNodes, int maxTime, Move searchMoves[]) {
376 // Look for a book move
377 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
380 if (get_option_value_string("Book File") != OpeningBook.file_name())
381 OpeningBook.open("book.bin");
383 bookMove = OpeningBook.get_move(pos);
384 if (bookMove != MOVE_NONE)
386 std::cout << "bestmove " << bookMove << std::endl;
391 // Initialize global search variables
393 SearchStartTime = get_system_time();
394 for (int i = 0; i < THREAD_MAX; i++)
396 Threads[i].nodes = 0ULL;
397 Threads[i].failHighPly1 = false;
400 InfiniteSearch = infinite;
401 PonderSearch = ponder;
402 StopOnPonderhit = false;
408 ExactMaxTime = maxTime;
410 // Read UCI option values
411 TT.set_size(get_option_value_int("Hash"));
412 if (button_was_pressed("Clear Hash"))
415 loseOnTime = false; // reset at the beginning of a new game
418 bool PonderingEnabled = get_option_value_bool("Ponder");
419 MultiPV = get_option_value_int("MultiPV");
421 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
422 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
424 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
425 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
427 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
428 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
430 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
431 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
433 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
434 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
436 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
437 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
439 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
440 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
441 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
443 Chess960 = get_option_value_bool("UCI_Chess960");
444 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
445 UseLogFile = get_option_value_bool("Use Search Log");
447 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
449 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
450 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
452 read_weights(pos.side_to_move());
454 // Set the number of active threads
455 int newActiveThreads = get_option_value_int("Threads");
456 if (newActiveThreads != ActiveThreads)
458 ActiveThreads = newActiveThreads;
459 init_eval(ActiveThreads);
462 // Wake up sleeping threads
463 wake_sleeping_threads();
465 for (int i = 1; i < ActiveThreads; i++)
466 assert(thread_is_available(i, 0));
469 int myTime = time[side_to_move];
470 int myIncrement = increment[side_to_move];
472 if (!movesToGo) // Sudden death time control
476 MaxSearchTime = myTime / 30 + myIncrement;
477 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
478 } else { // Blitz game without increment
479 MaxSearchTime = myTime / 30;
480 AbsoluteMaxSearchTime = myTime / 8;
483 else // (x moves) / (y minutes)
487 MaxSearchTime = myTime / 2;
488 AbsoluteMaxSearchTime =
489 (myTime > 3000)? (myTime - 500) : ((myTime * 3) / 4);
491 MaxSearchTime = myTime / Min(movesToGo, 20);
492 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
496 if (PonderingEnabled)
498 MaxSearchTime += MaxSearchTime / 4;
499 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
502 // Fixed depth or fixed number of nodes?
505 InfiniteSearch = true; // HACK
510 NodesBetweenPolls = Min(MaxNodes, 30000);
511 InfiniteSearch = true; // HACK
513 else if (myTime && myTime < 1000)
514 NodesBetweenPolls = 1000;
515 else if (myTime && myTime < 5000)
516 NodesBetweenPolls = 5000;
518 NodesBetweenPolls = 30000;
520 // Write information to search log file
522 LogFile << "Searching: " << pos.to_fen() << std::endl
523 << "infinite: " << infinite
524 << " ponder: " << ponder
525 << " time: " << myTime
526 << " increment: " << myIncrement
527 << " moves to go: " << movesToGo << std::endl;
530 // We're ready to start thinking. Call the iterative deepening loop function
532 // FIXME we really need to cleanup all this LSN ugliness
535 Value v = id_loop(pos, searchMoves);
536 loseOnTime = ( UseLSNFiltering
543 loseOnTime = false; // reset for next match
544 while (SearchStartTime + myTime + 1000 > get_system_time())
546 id_loop(pos, searchMoves); // to fail gracefully
557 /// init_threads() is called during startup. It launches all helper threads,
558 /// and initializes the split point stack and the global locks and condition
561 void init_threads() {
565 #if !defined(_MSC_VER)
566 pthread_t pthread[1];
569 for (i = 0; i < THREAD_MAX; i++)
570 Threads[i].activeSplitPoints = 0;
572 // Initialize global locks
573 lock_init(&MPLock, NULL);
574 lock_init(&IOLock, NULL);
576 init_split_point_stack();
578 #if !defined(_MSC_VER)
579 pthread_mutex_init(&WaitLock, NULL);
580 pthread_cond_init(&WaitCond, NULL);
582 for (i = 0; i < THREAD_MAX; i++)
583 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
586 // All threads except the main thread should be initialized to idle state
587 for (i = 1; i < THREAD_MAX; i++)
589 Threads[i].stop = false;
590 Threads[i].workIsWaiting = false;
591 Threads[i].idle = true;
592 Threads[i].running = false;
595 // Launch the helper threads
596 for(i = 1; i < THREAD_MAX; i++)
598 #if !defined(_MSC_VER)
599 pthread_create(pthread, NULL, init_thread, (void*)(&i));
602 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
605 // Wait until the thread has finished launching
606 while (!Threads[i].running);
611 /// stop_threads() is called when the program exits. It makes all the
612 /// helper threads exit cleanly.
614 void stop_threads() {
616 ActiveThreads = THREAD_MAX; // HACK
617 Idle = false; // HACK
618 wake_sleeping_threads();
619 AllThreadsShouldExit = true;
620 for (int i = 1; i < THREAD_MAX; i++)
622 Threads[i].stop = true;
623 while(Threads[i].running);
625 destroy_split_point_stack();
629 /// nodes_searched() returns the total number of nodes searched so far in
630 /// the current search.
632 int64_t nodes_searched() {
634 int64_t result = 0ULL;
635 for (int i = 0; i < ActiveThreads; i++)
636 result += Threads[i].nodes;
641 // SearchStack::init() initializes a search stack. Used at the beginning of a
642 // new search from the root.
643 void SearchStack::init(int ply) {
645 pv[ply] = pv[ply + 1] = MOVE_NONE;
646 currentMove = threatMove = MOVE_NONE;
647 reduction = Depth(0);
650 void SearchStack::initKillers() {
652 mateKiller = MOVE_NONE;
653 for (int i = 0; i < KILLER_MAX; i++)
654 killers[i] = MOVE_NONE;
659 // id_loop() is the main iterative deepening loop. It calls root_search
660 // repeatedly with increasing depth until the allocated thinking time has
661 // been consumed, the user stops the search, or the maximum search depth is
664 Value id_loop(const Position& pos, Move searchMoves[]) {
667 SearchStack ss[PLY_MAX_PLUS_2];
669 // searchMoves are verified, copied, scored and sorted
670 RootMoveList rml(p, searchMoves);
672 // Print RootMoveList c'tor startup scoring to the standard output,
673 // so that we print information also for iteration 1.
674 std::cout << "info depth " << 1 << "\ninfo depth " << 1
675 << " score " << value_to_string(rml.get_move_score(0))
676 << " time " << current_search_time()
677 << " nodes " << nodes_searched()
679 << " pv " << rml.get_move(0) << "\n";
685 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
688 Move EasyMove = rml.scan_for_easy_move();
690 // Iterative deepening loop
691 while (Iteration < PLY_MAX)
693 // Initialize iteration
696 BestMoveChangesByIteration[Iteration] = 0;
700 std::cout << "info depth " << Iteration << std::endl;
702 // Calculate dynamic search window based on previous iterations
705 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
707 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
708 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
710 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
712 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
713 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
717 alpha = - VALUE_INFINITE;
718 beta = VALUE_INFINITE;
721 // Search to the current depth
722 Value value = root_search(p, ss, rml, alpha, beta);
724 // Write PV to transposition table, in case the relevant entries have
725 // been overwritten during the search.
726 TT.insert_pv(p, ss[0].pv);
729 break; // Value cannot be trusted. Break out immediately!
731 //Save info about search result
732 Value speculatedValue;
735 Value delta = value - IterationInfo[Iteration - 1].value;
742 speculatedValue = value + delta;
743 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
745 else if (value <= alpha)
747 assert(value == alpha);
751 speculatedValue = value + delta;
752 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
754 speculatedValue = value;
756 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
757 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
759 // Erase the easy move if it differs from the new best move
760 if (ss[0].pv[0] != EasyMove)
761 EasyMove = MOVE_NONE;
768 bool stopSearch = false;
770 // Stop search early if there is only a single legal move
771 if (Iteration >= 6 && rml.move_count() == 1)
774 // Stop search early when the last two iterations returned a mate score
776 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
777 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
780 // Stop search early if one move seems to be much better than the rest
781 int64_t nodes = nodes_searched();
785 && EasyMove == ss[0].pv[0]
786 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
787 && current_search_time() > MaxSearchTime / 16)
788 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
789 && current_search_time() > MaxSearchTime / 32)))
792 // Add some extra time if the best move has changed during the last two iterations
793 if (Iteration > 5 && Iteration <= 50)
794 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
795 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
797 // Stop search if most of MaxSearchTime is consumed at the end of the
798 // iteration. We probably don't have enough time to search the first
799 // move at the next iteration anyway.
800 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
808 StopOnPonderhit = true;
812 if (MaxDepth && Iteration >= MaxDepth)
818 // If we are pondering, we shouldn't print the best move before we
821 wait_for_stop_or_ponderhit();
823 // Print final search statistics
824 std::cout << "info nodes " << nodes_searched()
826 << " time " << current_search_time()
827 << " hashfull " << TT.full() << std::endl;
829 // Print the best move and the ponder move to the standard output
830 if (ss[0].pv[0] == MOVE_NONE)
832 ss[0].pv[0] = rml.get_move(0);
833 ss[0].pv[1] = MOVE_NONE;
835 std::cout << "bestmove " << ss[0].pv[0];
836 if (ss[0].pv[1] != MOVE_NONE)
837 std::cout << " ponder " << ss[0].pv[1];
839 std::cout << std::endl;
844 dbg_print_mean(LogFile);
846 if (dbg_show_hit_rate)
847 dbg_print_hit_rate(LogFile);
850 LogFile << "Nodes: " << nodes_searched() << std::endl
851 << "Nodes/second: " << nps() << std::endl
852 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
854 p.do_move(ss[0].pv[0], st);
855 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
856 << std::endl << std::endl;
858 return rml.get_move_score(0);
862 // root_search() is the function which searches the root node. It is
863 // similar to search_pv except that it uses a different move ordering
864 // scheme (perhaps we should try to use this at internal PV nodes, too?)
865 // and prints some information to the standard output.
867 Value root_search(Position& pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta) {
869 Value oldAlpha = alpha;
873 // Loop through all the moves in the root move list
874 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
878 // We failed high, invalidate and skip next moves, leave node-counters
879 // and beta-counters as they are and quickly return, we will try to do
880 // a research at the next iteration with a bigger aspiration window.
881 rml.set_move_score(i, -VALUE_INFINITE);
889 RootMoveNumber = i + 1;
892 // Remember the node count before the move is searched. The node counts
893 // are used to sort the root moves at the next iteration.
894 nodes = nodes_searched();
896 // Reset beta cut-off counters
899 // Pick the next root move, and print the move and the move number to
900 // the standard output.
901 move = ss[0].currentMove = rml.get_move(i);
902 if (current_search_time() >= 1000)
903 std::cout << "info currmove " << move
904 << " currmovenumber " << i + 1 << std::endl;
906 // Decide search depth for this move
907 bool moveIsCheck = pos.move_is_check(move);
908 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
910 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
911 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
913 // Make the move, and search it
914 pos.do_move(move, st, ci, moveIsCheck);
918 // Aspiration window is disabled in multi-pv case
920 alpha = -VALUE_INFINITE;
922 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
923 // If the value has dropped a lot compared to the last iteration,
924 // set the boolean variable Problem to true. This variable is used
925 // for time managment: When Problem is true, we try to complete the
926 // current iteration before playing a move.
927 Problem = (Iteration >= 2 && value <= IterationInfo[Iteration-1].value - ProblemMargin);
929 if (Problem && StopOnPonderhit)
930 StopOnPonderhit = false;
934 if ( newDepth >= 3*OnePly
935 && i >= MultiPV + LMRPVMoves
937 && !captureOrPromotion
938 && !move_is_castle(move))
940 ss[0].reduction = OnePly;
941 value = -search(pos, ss, -alpha, newDepth-OnePly, 1, true, 0);
943 value = alpha + 1; // Just to trigger next condition
947 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
950 // Fail high! Set the boolean variable FailHigh to true, and
951 // re-search the move with a big window. The variable FailHigh is
952 // used for time managment: We try to avoid aborting the search
953 // prematurely during a fail high research.
955 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
962 // Finished searching the move. If AbortSearch is true, the search
963 // was aborted because the user interrupted the search or because we
964 // ran out of time. In this case, the return value of the search cannot
965 // be trusted, and we break out of the loop without updating the best
970 // Remember the node count for this move. The node counts are used to
971 // sort the root moves at the next iteration.
972 rml.set_move_nodes(i, nodes_searched() - nodes);
974 // Remember the beta-cutoff statistics
976 BetaCounter.read(pos.side_to_move(), our, their);
977 rml.set_beta_counters(i, our, their);
979 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
981 if (value <= alpha && i >= MultiPV)
982 rml.set_move_score(i, -VALUE_INFINITE);
985 // PV move or new best move!
988 rml.set_move_score(i, value);
990 TT.extract_pv(pos, ss[0].pv, PLY_MAX);
991 rml.set_move_pv(i, ss[0].pv);
995 // We record how often the best move has been changed in each
996 // iteration. This information is used for time managment: When
997 // the best move changes frequently, we allocate some more time.
999 BestMoveChangesByIteration[Iteration]++;
1001 // Print search information to the standard output
1002 std::cout << "info depth " << Iteration
1003 << " score " << value_to_string(value)
1004 << ((value >= beta)?
1005 " lowerbound" : ((value <= alpha)? " upperbound" : ""))
1006 << " time " << current_search_time()
1007 << " nodes " << nodes_searched()
1011 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1012 std::cout << ss[0].pv[j] << " ";
1014 std::cout << std::endl;
1017 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value,
1018 ((value >= beta)? VALUE_TYPE_LOWER
1019 : ((value <= alpha)? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT)),
1026 // Reset the global variable Problem to false if the value isn't too
1027 // far below the final value from the last iteration.
1028 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1033 rml.sort_multipv(i);
1034 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1037 std::cout << "info multipv " << j + 1
1038 << " score " << value_to_string(rml.get_move_score(j))
1039 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1040 << " time " << current_search_time()
1041 << " nodes " << nodes_searched()
1045 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1046 std::cout << rml.get_move_pv(j, k) << " ";
1048 std::cout << std::endl;
1050 alpha = rml.get_move_score(Min(i, MultiPV-1));
1052 } // New best move case
1054 assert(alpha >= oldAlpha);
1056 FailLow = (alpha == oldAlpha);
1062 // search_pv() is the main search function for PV nodes.
1064 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1065 Depth depth, int ply, int threadID) {
1067 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1068 assert(beta > alpha && beta <= VALUE_INFINITE);
1069 assert(ply >= 0 && ply < PLY_MAX);
1070 assert(threadID >= 0 && threadID < ActiveThreads);
1072 Move movesSearched[256];
1077 Depth ext, newDepth;
1078 Value oldAlpha, value;
1079 bool isCheck, mateThreat, singleReply, moveIsCheck, captureOrPromotion, dangerous;
1081 Value bestValue = -VALUE_INFINITE;
1084 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1086 // Initialize, and make an early exit in case of an aborted search,
1087 // an instant draw, maximum ply reached, etc.
1088 init_node(ss, ply, threadID);
1090 // After init_node() that calls poll()
1091 if (AbortSearch || thread_should_stop(threadID))
1097 if (ply >= PLY_MAX - 1)
1098 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1100 // Mate distance pruning
1102 alpha = Max(value_mated_in(ply), alpha);
1103 beta = Min(value_mate_in(ply+1), beta);
1107 // Transposition table lookup. At PV nodes, we don't use the TT for
1108 // pruning, but only for move ordering.
1109 tte = TT.retrieve(pos.get_key());
1110 ttMove = (tte ? tte->move() : MOVE_NONE);
1112 // Go with internal iterative deepening if we don't have a TT move
1113 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
1115 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1116 ttMove = ss[ply].pv[ply];
1119 // Initialize a MovePicker object for the current position, and prepare
1120 // to search all moves
1121 isCheck = pos.is_check();
1122 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1124 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1126 // Loop through all legal moves until no moves remain or a beta cutoff
1128 while ( alpha < beta
1129 && (move = mp.get_next_move()) != MOVE_NONE
1130 && !thread_should_stop(threadID))
1132 assert(move_is_ok(move));
1134 singleReply = (isCheck && mp.number_of_evasions() == 1);
1135 moveIsCheck = pos.move_is_check(move, ci);
1136 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1138 // Decide the new search depth
1139 ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleReply, mateThreat, &dangerous);
1141 // We want to extend the TT move if it is much better then remaining ones.
1142 // To verify this we do a reduced search on all the other moves but the ttMove,
1143 // if result is lower then TT value minus a margin then we assume ttMove is the
1144 // only one playable. It is a kind of relaxed single reply extension.
1145 if ( depth >= 4 * OnePly
1148 && is_lower_bound(tte->type())
1149 && tte->depth() >= depth - 3 * OnePly)
1151 Value ttValue = value_from_tt(tte->value(), ply);
1153 if (abs(ttValue) < VALUE_KNOWN_WIN)
1155 Depth d = Max(Min(depth / 2, depth - 4 * OnePly), OnePly);
1156 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, d, ply, false, threadID, ttMove);
1158 // If search result is well below the foreseen score of the ttMove then we
1159 // assume ttMove is the only one realistically playable and we extend it.
1160 if (excValue < ttValue - SingleReplyMargin)
1165 newDepth = depth - OnePly + ext;
1167 // Update current move
1168 movesSearched[moveCount++] = ss[ply].currentMove = move;
1170 // Make and search the move
1171 pos.do_move(move, st, ci, moveIsCheck);
1173 if (moveCount == 1) // The first move in list is the PV
1174 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1177 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1178 // if the move fails high will be re-searched at full depth.
1179 if ( depth >= 3*OnePly
1180 && moveCount >= LMRPVMoves
1182 && !captureOrPromotion
1183 && !move_is_castle(move)
1184 && !move_is_killer(move, ss[ply]))
1186 ss[ply].reduction = OnePly;
1187 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1190 value = alpha + 1; // Just to trigger next condition
1192 if (value > alpha) // Go with full depth non-pv search
1194 ss[ply].reduction = Depth(0);
1195 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1196 if (value > alpha && value < beta)
1198 // When the search fails high at ply 1 while searching the first
1199 // move at the root, set the flag failHighPly1. This is used for
1200 // time managment: We don't want to stop the search early in
1201 // such cases, because resolving the fail high at ply 1 could
1202 // result in a big drop in score at the root.
1203 if (ply == 1 && RootMoveNumber == 1)
1204 Threads[threadID].failHighPly1 = true;
1206 // A fail high occurred. Re-search at full window (pv search)
1207 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1208 Threads[threadID].failHighPly1 = false;
1212 pos.undo_move(move);
1214 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1217 if (value > bestValue)
1224 if (value == value_mate_in(ply + 1))
1225 ss[ply].mateKiller = move;
1227 // If we are at ply 1, and we are searching the first root move at
1228 // ply 0, set the 'Problem' variable if the score has dropped a lot
1229 // (from the computer's point of view) since the previous iteration.
1232 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1237 if ( ActiveThreads > 1
1239 && depth >= MinimumSplitDepth
1241 && idle_thread_exists(threadID)
1243 && !thread_should_stop(threadID)
1244 && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE, VALUE_NONE,
1245 depth, &moveCount, &mp, threadID, true))
1249 // All legal moves have been searched. A special case: If there were
1250 // no legal moves, it must be mate or stalemate.
1252 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1254 // If the search is not aborted, update the transposition table,
1255 // history counters, and killer moves.
1256 if (AbortSearch || thread_should_stop(threadID))
1259 if (bestValue <= oldAlpha)
1260 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1262 else if (bestValue >= beta)
1264 BetaCounter.add(pos.side_to_move(), depth, threadID);
1265 move = ss[ply].pv[ply];
1266 if (!pos.move_is_capture_or_promotion(move))
1268 update_history(pos, move, depth, movesSearched, moveCount);
1269 update_killers(move, ss[ply]);
1271 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1274 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1280 // search() is the search function for zero-width nodes.
1282 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1283 int ply, bool allowNullmove, int threadID, Move excludedMove) {
1285 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1286 assert(ply >= 0 && ply < PLY_MAX);
1287 assert(threadID >= 0 && threadID < ActiveThreads);
1289 Move movesSearched[256];
1294 Depth ext, newDepth;
1295 Value approximateEval, nullValue, value, futilityValue, futilityValueScaled;
1296 bool isCheck, useFutilityPruning, singleReply, moveIsCheck, captureOrPromotion, dangerous;
1297 bool mateThreat = false;
1299 Value bestValue = -VALUE_INFINITE;
1302 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1304 // Initialize, and make an early exit in case of an aborted search,
1305 // an instant draw, maximum ply reached, etc.
1306 init_node(ss, ply, threadID);
1308 // After init_node() that calls poll()
1309 if (AbortSearch || thread_should_stop(threadID))
1315 if (ply >= PLY_MAX - 1)
1316 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1318 // Mate distance pruning
1319 if (value_mated_in(ply) >= beta)
1322 if (value_mate_in(ply + 1) < beta)
1325 // We don't want the score of a partial search to overwrite a previous full search
1326 // TT value, so we use a different position key in case of an excluded move exsists.
1327 Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1329 // Transposition table lookup
1330 tte = TT.retrieve(posKey);
1331 ttMove = (tte ? tte->move() : MOVE_NONE);
1333 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1335 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1336 return value_from_tt(tte->value(), ply);
1339 approximateEval = quick_evaluate(pos);
1340 isCheck = pos.is_check();
1346 && !value_is_mate(beta)
1347 && ok_to_do_nullmove(pos)
1348 && approximateEval >= beta - NullMoveMargin)
1350 ss[ply].currentMove = MOVE_NULL;
1352 pos.do_null_move(st);
1354 // Null move dynamic reduction based on depth
1355 int R = (depth >= 5 * OnePly ? 4 : 3);
1357 // Null move dynamic reduction based on value
1358 if (approximateEval - beta > PawnValueMidgame)
1361 nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1363 pos.undo_null_move();
1365 if (nullValue >= beta)
1367 if (depth < 6 * OnePly)
1370 // Do zugzwang verification search
1371 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1375 // The null move failed low, which means that we may be faced with
1376 // some kind of threat. If the previous move was reduced, check if
1377 // the move that refuted the null move was somehow connected to the
1378 // move which was reduced. If a connection is found, return a fail
1379 // low score (which will cause the reduced move to fail high in the
1380 // parent node, which will trigger a re-search with full depth).
1381 if (nullValue == value_mated_in(ply + 2))
1384 ss[ply].threatMove = ss[ply + 1].currentMove;
1385 if ( depth < ThreatDepth
1386 && ss[ply - 1].reduction
1387 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1391 // Null move search not allowed, try razoring
1392 else if ( !value_is_mate(beta)
1393 && depth < RazorDepth
1394 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1395 && ss[ply - 1].currentMove != MOVE_NULL
1396 && ttMove == MOVE_NONE
1397 && !pos.has_pawn_on_7th(pos.side_to_move()))
1399 Value rbeta = beta - RazorMargins[int(depth) - 2];
1400 Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
1405 // Go with internal iterative deepening if we don't have a TT move
1406 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1407 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1409 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1410 ttMove = ss[ply].pv[ply];
1413 // Initialize a MovePicker object for the current position, and prepare
1414 // to search all moves.
1415 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1417 futilityValue = VALUE_NONE;
1418 useFutilityPruning = depth < SelectiveDepth && !isCheck;
1420 // Avoid calling evaluate() if we already have the score in TT
1421 if (tte && (tte->type() & VALUE_TYPE_EVAL))
1422 futilityValue = value_from_tt(tte->value(), ply) + FutilityMargins[int(depth) - 2];
1424 // Move count pruning limit
1425 const int MCLimit = 3 + (1 << (3*int(depth)/8));
1427 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1428 while ( bestValue < beta
1429 && (move = mp.get_next_move()) != MOVE_NONE
1430 && !thread_should_stop(threadID))
1432 assert(move_is_ok(move));
1434 if (move == excludedMove)
1437 singleReply = (isCheck && mp.number_of_evasions() == 1);
1438 moveIsCheck = pos.move_is_check(move, ci);
1439 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1441 // Decide the new search depth
1442 ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleReply, mateThreat, &dangerous);
1444 // We want to extend the TT move if it is much better then remaining ones.
1445 // To verify this we do a reduced search on all the other moves but the ttMove,
1446 // if result is lower then TT value minus a margin then we assume ttMove is the
1447 // only one playable. It is a kind of relaxed single reply extension.
1448 if ( depth >= 4 * OnePly
1449 && !excludedMove // do not allow recursive single-reply search
1452 && is_lower_bound(tte->type())
1453 && tte->depth() >= depth - 3 * OnePly)
1455 Value ttValue = value_from_tt(tte->value(), ply);
1457 if (abs(ttValue) < VALUE_KNOWN_WIN)
1459 Depth d = Max(Min(depth / 2, depth - 4 * OnePly), OnePly);
1460 Value excValue = search(pos, ss, ttValue - SingleReplyMargin, d, ply, false, threadID, ttMove);
1462 // If search result is well below the foreseen score of the ttMove then we
1463 // assume ttMove is the only one realistically playable and we extend it.
1464 if (excValue < ttValue - SingleReplyMargin)
1465 ext = (depth >= 8 * OnePly) ? OnePly : ext + OnePly / 2;
1469 newDepth = depth - OnePly + ext;
1471 // Update current move
1472 movesSearched[moveCount++] = ss[ply].currentMove = move;
1475 if ( useFutilityPruning
1477 && !captureOrPromotion
1480 // History pruning. See ok_to_prune() definition
1481 if ( moveCount >= MCLimit
1482 && ok_to_prune(pos, move, ss[ply].threatMove, depth)
1483 && bestValue > value_mated_in(PLY_MAX))
1486 // Value based pruning
1487 if (approximateEval < beta)
1489 if (futilityValue == VALUE_NONE)
1490 futilityValue = evaluate(pos, ei, threadID)
1491 + 64*(2+bitScanReverse32(int(depth) * int(depth)));
1493 futilityValueScaled = futilityValue - moveCount * IncrementalFutilityMargin;
1495 if (futilityValueScaled < beta)
1497 if (futilityValueScaled > bestValue)
1498 bestValue = futilityValueScaled;
1504 // Make and search the move
1505 pos.do_move(move, st, ci, moveIsCheck);
1507 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1508 // if the move fails high will be re-searched at full depth.
1509 if ( depth >= 3*OnePly
1510 && moveCount >= LMRNonPVMoves
1512 && !captureOrPromotion
1513 && !move_is_castle(move)
1514 && !move_is_killer(move, ss[ply]))
1516 ss[ply].reduction = OnePly;
1517 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1520 value = beta; // Just to trigger next condition
1522 if (value >= beta) // Go with full depth non-pv search
1524 ss[ply].reduction = Depth(0);
1525 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1527 pos.undo_move(move);
1529 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1532 if (value > bestValue)
1538 if (value == value_mate_in(ply + 1))
1539 ss[ply].mateKiller = move;
1543 if ( ActiveThreads > 1
1545 && depth >= MinimumSplitDepth
1547 && idle_thread_exists(threadID)
1549 && !thread_should_stop(threadID)
1550 && split(pos, ss, ply, &beta, &beta, &bestValue, futilityValue, approximateEval,
1551 depth, &moveCount, &mp, threadID, false))
1555 // All legal moves have been searched. A special case: If there were
1556 // no legal moves, it must be mate or stalemate.
1558 return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1560 // If the search is not aborted, update the transposition table,
1561 // history counters, and killer moves.
1562 if (AbortSearch || thread_should_stop(threadID))
1565 if (bestValue < beta)
1566 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1569 BetaCounter.add(pos.side_to_move(), depth, threadID);
1570 move = ss[ply].pv[ply];
1571 if (!pos.move_is_capture_or_promotion(move))
1573 update_history(pos, move, depth, movesSearched, moveCount);
1574 update_killers(move, ss[ply]);
1576 TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
1579 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1585 // qsearch() is the quiescence search function, which is called by the main
1586 // search function when the remaining depth is zero (or, to be more precise,
1587 // less than OnePly).
1589 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1590 Depth depth, int ply, int threadID) {
1592 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1593 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1595 assert(ply >= 0 && ply < PLY_MAX);
1596 assert(threadID >= 0 && threadID < ActiveThreads);
1601 Value staticValue, bestValue, value, futilityValue;
1602 bool isCheck, enoughMaterial, moveIsCheck;
1603 const TTEntry* tte = NULL;
1605 bool pvNode = (beta - alpha != 1);
1607 // Initialize, and make an early exit in case of an aborted search,
1608 // an instant draw, maximum ply reached, etc.
1609 init_node(ss, ply, threadID);
1611 // After init_node() that calls poll()
1612 if (AbortSearch || thread_should_stop(threadID))
1618 // Transposition table lookup, only when not in PV
1621 tte = TT.retrieve(pos.get_key());
1622 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1624 assert(tte->type() != VALUE_TYPE_EVAL);
1626 return value_from_tt(tte->value(), ply);
1629 ttMove = (tte ? tte->move() : MOVE_NONE);
1631 // Evaluate the position statically
1632 isCheck = pos.is_check();
1633 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1636 staticValue = -VALUE_INFINITE;
1638 else if (tte && (tte->type() & VALUE_TYPE_EVAL))
1640 // Use the cached evaluation score if possible
1641 assert(ei.futilityMargin == Value(0));
1643 staticValue = tte->value();
1646 staticValue = evaluate(pos, ei, threadID);
1648 if (ply >= PLY_MAX - 1)
1649 return pos.is_check() ? quick_evaluate(pos) : evaluate(pos, ei, threadID);
1651 // Initialize "stand pat score", and return it immediately if it is
1653 bestValue = staticValue;
1655 if (bestValue >= beta)
1657 // Store the score to avoid a future costly evaluation() call
1658 if (!isCheck && !tte && ei.futilityMargin == 0)
1659 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EV_LO, Depth(-127*OnePly), MOVE_NONE);
1664 if (bestValue > alpha)
1667 // Initialize a MovePicker object for the current position, and prepare
1668 // to search the moves. Because the depth is <= 0 here, only captures,
1669 // queen promotions and checks (only if depth == 0) will be generated.
1670 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1672 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1674 // Loop through the moves until no moves remain or a beta cutoff
1676 while ( alpha < beta
1677 && (move = mp.get_next_move()) != MOVE_NONE)
1679 assert(move_is_ok(move));
1682 ss[ply].currentMove = move;
1684 moveIsCheck = pos.move_is_check(move, ci);
1692 && !move_is_promotion(move)
1693 && !pos.move_is_passed_pawn_push(move))
1695 futilityValue = staticValue
1696 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1697 pos.endgame_value_of_piece_on(move_to(move)))
1698 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1700 + ei.futilityMargin;
1702 if (futilityValue < alpha)
1704 if (futilityValue > bestValue)
1705 bestValue = futilityValue;
1710 // Don't search captures and checks with negative SEE values
1713 && !move_is_promotion(move)
1714 && pos.see_sign(move) < 0)
1717 // Make and search the move
1718 pos.do_move(move, st, ci, moveIsCheck);
1719 value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1720 pos.undo_move(move);
1722 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1725 if (value > bestValue)
1736 // All legal moves have been searched. A special case: If we're in check
1737 // and no legal moves were found, it is checkmate.
1738 if (!moveCount && pos.is_check()) // Mate!
1739 return value_mated_in(ply);
1741 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1743 // Update transposition table
1744 move = ss[ply].pv[ply];
1747 // If bestValue isn't changed it means it is still the static evaluation of
1748 // the node, so keep this info to avoid a future costly evaluation() call.
1749 ValueType type = (bestValue == staticValue && !ei.futilityMargin ? VALUE_TYPE_EV_UP : VALUE_TYPE_UPPER);
1750 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1752 if (bestValue < beta)
1753 TT.store(pos.get_key(), value_to_tt(bestValue, ply), type, d, MOVE_NONE);
1755 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, move);
1758 // Update killers only for good check moves
1759 if (alpha >= beta && !pos.move_is_capture_or_promotion(move))
1760 update_killers(move, ss[ply]);
1766 // sp_search() is used to search from a split point. This function is called
1767 // by each thread working at the split point. It is similar to the normal
1768 // search() function, but simpler. Because we have already probed the hash
1769 // table, done a null move search, and searched the first move before
1770 // splitting, we don't have to repeat all this work in sp_search(). We
1771 // also don't need to store anything to the hash table here: This is taken
1772 // care of after we return from the split point.
1774 void sp_search(SplitPoint* sp, int threadID) {
1776 assert(threadID >= 0 && threadID < ActiveThreads);
1777 assert(ActiveThreads > 1);
1779 Position pos = Position(sp->pos);
1781 SearchStack* ss = sp->sstack[threadID];
1784 bool isCheck = pos.is_check();
1785 bool useFutilityPruning = sp->depth < SelectiveDepth
1788 while ( sp->bestValue < sp->beta
1789 && !thread_should_stop(threadID)
1790 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1792 assert(move_is_ok(move));
1794 bool moveIsCheck = pos.move_is_check(move, ci);
1795 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1797 lock_grab(&(sp->lock));
1798 int moveCount = ++sp->moves;
1799 lock_release(&(sp->lock));
1801 ss[sp->ply].currentMove = move;
1803 // Decide the new search depth.
1805 Depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1806 Depth newDepth = sp->depth - OnePly + ext;
1809 if ( useFutilityPruning
1811 && !captureOrPromotion)
1813 // History pruning. See ok_to_prune() definition
1814 if ( moveCount >= 2 + int(sp->depth)
1815 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth)
1816 && sp->bestValue > value_mated_in(PLY_MAX))
1819 // Value based pruning
1820 if (sp->approximateEval < sp->beta)
1822 if (sp->futilityValue == VALUE_NONE)
1825 sp->futilityValue = evaluate(pos, ei, threadID)
1826 + FutilityMargins[int(sp->depth) - 2];
1829 if (sp->futilityValue < sp->beta)
1831 if (sp->futilityValue > sp->bestValue) // Less then 1% of cases
1833 lock_grab(&(sp->lock));
1834 if (sp->futilityValue > sp->bestValue)
1835 sp->bestValue = sp->futilityValue;
1836 lock_release(&(sp->lock));
1843 // Make and search the move.
1845 pos.do_move(move, st, ci, moveIsCheck);
1847 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1848 // if the move fails high will be re-searched at full depth.
1850 && moveCount >= LMRNonPVMoves
1851 && !captureOrPromotion
1852 && !move_is_castle(move)
1853 && !move_is_killer(move, ss[sp->ply]))
1855 ss[sp->ply].reduction = OnePly;
1856 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1859 value = sp->beta; // Just to trigger next condition
1861 if (value >= sp->beta) // Go with full depth non-pv search
1863 ss[sp->ply].reduction = Depth(0);
1864 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1866 pos.undo_move(move);
1868 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1870 if (thread_should_stop(threadID))
1874 if (value > sp->bestValue) // Less then 2% of cases
1876 lock_grab(&(sp->lock));
1877 if (value > sp->bestValue && !thread_should_stop(threadID))
1879 sp->bestValue = value;
1880 if (sp->bestValue >= sp->beta)
1882 sp_update_pv(sp->parentSstack, ss, sp->ply);
1883 for (int i = 0; i < ActiveThreads; i++)
1884 if (i != threadID && (i == sp->master || sp->slaves[i]))
1885 Threads[i].stop = true;
1887 sp->finished = true;
1890 lock_release(&(sp->lock));
1894 lock_grab(&(sp->lock));
1896 // If this is the master thread and we have been asked to stop because of
1897 // a beta cutoff higher up in the tree, stop all slave threads.
1898 if (sp->master == threadID && thread_should_stop(threadID))
1899 for (int i = 0; i < ActiveThreads; i++)
1901 Threads[i].stop = true;
1904 sp->slaves[threadID] = 0;
1906 lock_release(&(sp->lock));
1910 // sp_search_pv() is used to search from a PV split point. This function
1911 // is called by each thread working at the split point. It is similar to
1912 // the normal search_pv() function, but simpler. Because we have already
1913 // probed the hash table and searched the first move before splitting, we
1914 // don't have to repeat all this work in sp_search_pv(). We also don't
1915 // need to store anything to the hash table here: This is taken care of
1916 // after we return from the split point.
1918 void sp_search_pv(SplitPoint* sp, int threadID) {
1920 assert(threadID >= 0 && threadID < ActiveThreads);
1921 assert(ActiveThreads > 1);
1923 Position pos = Position(sp->pos);
1925 SearchStack* ss = sp->sstack[threadID];
1929 while ( sp->alpha < sp->beta
1930 && !thread_should_stop(threadID)
1931 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1933 bool moveIsCheck = pos.move_is_check(move, ci);
1934 bool captureOrPromotion = pos.move_is_capture_or_promotion(move);
1936 assert(move_is_ok(move));
1938 lock_grab(&(sp->lock));
1939 int moveCount = ++sp->moves;
1940 lock_release(&(sp->lock));
1942 ss[sp->ply].currentMove = move;
1944 // Decide the new search depth.
1946 Depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, false, false, &dangerous);
1947 Depth newDepth = sp->depth - OnePly + ext;
1949 // Make and search the move.
1951 pos.do_move(move, st, ci, moveIsCheck);
1953 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1954 // if the move fails high will be re-searched at full depth.
1956 && moveCount >= LMRPVMoves
1957 && !captureOrPromotion
1958 && !move_is_castle(move)
1959 && !move_is_killer(move, ss[sp->ply]))
1961 ss[sp->ply].reduction = OnePly;
1962 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1965 value = sp->alpha + 1; // Just to trigger next condition
1967 if (value > sp->alpha) // Go with full depth non-pv search
1969 ss[sp->ply].reduction = Depth(0);
1970 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1972 if (value > sp->alpha && value < sp->beta)
1974 // When the search fails high at ply 1 while searching the first
1975 // move at the root, set the flag failHighPly1. This is used for
1976 // time managment: We don't want to stop the search early in
1977 // such cases, because resolving the fail high at ply 1 could
1978 // result in a big drop in score at the root.
1979 if (sp->ply == 1 && RootMoveNumber == 1)
1980 Threads[threadID].failHighPly1 = true;
1982 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1983 Threads[threadID].failHighPly1 = false;
1986 pos.undo_move(move);
1988 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1990 if (thread_should_stop(threadID))
1994 lock_grab(&(sp->lock));
1995 if (value > sp->bestValue && !thread_should_stop(threadID))
1997 sp->bestValue = value;
1998 if (value > sp->alpha)
2001 sp_update_pv(sp->parentSstack, ss, sp->ply);
2002 if (value == value_mate_in(sp->ply + 1))
2003 ss[sp->ply].mateKiller = move;
2005 if (value >= sp->beta)
2007 for (int i = 0; i < ActiveThreads; i++)
2008 if (i != threadID && (i == sp->master || sp->slaves[i]))
2009 Threads[i].stop = true;
2011 sp->finished = true;
2014 // If we are at ply 1, and we are searching the first root move at
2015 // ply 0, set the 'Problem' variable if the score has dropped a lot
2016 // (from the computer's point of view) since the previous iteration.
2019 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
2022 lock_release(&(sp->lock));
2025 lock_grab(&(sp->lock));
2027 // If this is the master thread and we have been asked to stop because of
2028 // a beta cutoff higher up in the tree, stop all slave threads.
2029 if (sp->master == threadID && thread_should_stop(threadID))
2030 for (int i = 0; i < ActiveThreads; i++)
2032 Threads[i].stop = true;
2035 sp->slaves[threadID] = 0;
2037 lock_release(&(sp->lock));
2040 /// The BetaCounterType class
2042 BetaCounterType::BetaCounterType() { clear(); }
2044 void BetaCounterType::clear() {
2046 for (int i = 0; i < THREAD_MAX; i++)
2047 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
2050 void BetaCounterType::add(Color us, Depth d, int threadID) {
2052 // Weighted count based on depth
2053 Threads[threadID].betaCutOffs[us] += unsigned(d);
2056 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
2059 for (int i = 0; i < THREAD_MAX; i++)
2061 our += Threads[i].betaCutOffs[us];
2062 their += Threads[i].betaCutOffs[opposite_color(us)];
2067 /// The RootMove class
2071 RootMove::RootMove() {
2072 nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
2075 // RootMove::operator<() is the comparison function used when
2076 // sorting the moves. A move m1 is considered to be better
2077 // than a move m2 if it has a higher score, or if the moves
2078 // have equal score but m1 has the higher node count.
2080 bool RootMove::operator<(const RootMove& m) {
2082 if (score != m.score)
2083 return (score < m.score);
2085 return theirBeta <= m.theirBeta;
2088 /// The RootMoveList class
2092 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2094 MoveStack mlist[MaxRootMoves];
2095 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2097 // Generate all legal moves
2098 MoveStack* last = generate_moves(pos, mlist);
2100 // Add each move to the moves[] array
2101 for (MoveStack* cur = mlist; cur != last; cur++)
2103 bool includeMove = includeAllMoves;
2105 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2106 includeMove = (searchMoves[k] == cur->move);
2111 // Find a quick score for the move
2113 SearchStack ss[PLY_MAX_PLUS_2];
2116 moves[count].move = cur->move;
2117 pos.do_move(moves[count].move, st);
2118 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
2119 pos.undo_move(moves[count].move);
2120 moves[count].pv[0] = moves[count].move;
2121 moves[count].pv[1] = MOVE_NONE;
2128 // Simple accessor methods for the RootMoveList class
2130 inline Move RootMoveList::get_move(int moveNum) const {
2131 return moves[moveNum].move;
2134 inline Value RootMoveList::get_move_score(int moveNum) const {
2135 return moves[moveNum].score;
2138 inline void RootMoveList::set_move_score(int moveNum, Value score) {
2139 moves[moveNum].score = score;
2142 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2143 moves[moveNum].nodes = nodes;
2144 moves[moveNum].cumulativeNodes += nodes;
2147 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2148 moves[moveNum].ourBeta = our;
2149 moves[moveNum].theirBeta = their;
2152 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2154 for(j = 0; pv[j] != MOVE_NONE; j++)
2155 moves[moveNum].pv[j] = pv[j];
2156 moves[moveNum].pv[j] = MOVE_NONE;
2159 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2160 return moves[moveNum].pv[i];
2163 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2164 return moves[moveNum].cumulativeNodes;
2167 inline int RootMoveList::move_count() const {
2172 // RootMoveList::scan_for_easy_move() is called at the end of the first
2173 // iteration, and is used to detect an "easy move", i.e. a move which appears
2174 // to be much bester than all the rest. If an easy move is found, the move
2175 // is returned, otherwise the function returns MOVE_NONE. It is very
2176 // important that this function is called at the right moment: The code
2177 // assumes that the first iteration has been completed and the moves have
2178 // been sorted. This is done in RootMoveList c'tor.
2180 Move RootMoveList::scan_for_easy_move() const {
2187 // moves are sorted so just consider the best and the second one
2188 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
2194 // RootMoveList::sort() sorts the root move list at the beginning of a new
2197 inline void RootMoveList::sort() {
2199 sort_multipv(count - 1); // all items
2203 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2204 // list by their scores and depths. It is used to order the different PVs
2205 // correctly in MultiPV mode.
2207 void RootMoveList::sort_multipv(int n) {
2209 for (int i = 1; i <= n; i++)
2211 RootMove rm = moves[i];
2213 for (j = i; j > 0 && moves[j-1] < rm; j--)
2214 moves[j] = moves[j-1];
2220 // init_node() is called at the beginning of all the search functions
2221 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2222 // stack object corresponding to the current node. Once every
2223 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2224 // for user input and checks whether it is time to stop the search.
2226 void init_node(SearchStack ss[], int ply, int threadID) {
2228 assert(ply >= 0 && ply < PLY_MAX);
2229 assert(threadID >= 0 && threadID < ActiveThreads);
2231 Threads[threadID].nodes++;
2236 if (NodesSincePoll >= NodesBetweenPolls)
2243 ss[ply+2].initKillers();
2245 if (Threads[threadID].printCurrentLine)
2246 print_current_line(ss, ply, threadID);
2250 // update_pv() is called whenever a search returns a value > alpha. It
2251 // updates the PV in the SearchStack object corresponding to the current
2254 void update_pv(SearchStack ss[], int ply) {
2255 assert(ply >= 0 && ply < PLY_MAX);
2257 ss[ply].pv[ply] = ss[ply].currentMove;
2259 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2260 ss[ply].pv[p] = ss[ply+1].pv[p];
2261 ss[ply].pv[p] = MOVE_NONE;
2265 // sp_update_pv() is a variant of update_pv for use at split points. The
2266 // difference between the two functions is that sp_update_pv also updates
2267 // the PV at the parent node.
2269 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2270 assert(ply >= 0 && ply < PLY_MAX);
2272 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2274 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2275 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2276 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2280 // connected_moves() tests whether two moves are 'connected' in the sense
2281 // that the first move somehow made the second move possible (for instance
2282 // if the moving piece is the same in both moves). The first move is
2283 // assumed to be the move that was made to reach the current position, while
2284 // the second move is assumed to be a move from the current position.
2286 bool connected_moves(const Position& pos, Move m1, Move m2) {
2288 Square f1, t1, f2, t2;
2291 assert(move_is_ok(m1));
2292 assert(move_is_ok(m2));
2294 if (m2 == MOVE_NONE)
2297 // Case 1: The moving piece is the same in both moves
2303 // Case 2: The destination square for m2 was vacated by m1
2309 // Case 3: Moving through the vacated square
2310 if ( piece_is_slider(pos.piece_on(f2))
2311 && bit_is_set(squares_between(f2, t2), f1))
2314 // Case 4: The destination square for m2 is attacked by the moving piece in m1
2315 p = pos.piece_on(t1);
2316 if (bit_is_set(pos.attacks_from(p, t1), t2))
2319 // Case 5: Discovered check, checking piece is the piece moved in m1
2320 if ( piece_is_slider(p)
2321 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2322 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
2324 Bitboard occ = pos.occupied_squares();
2325 Color us = pos.side_to_move();
2326 Square ksq = pos.king_square(us);
2327 clear_bit(&occ, f2);
2328 if (type_of_piece(p) == BISHOP)
2330 if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2333 else if (type_of_piece(p) == ROOK)
2335 if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
2340 assert(type_of_piece(p) == QUEEN);
2341 if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
2349 // value_is_mate() checks if the given value is a mate one
2350 // eventually compensated for the ply.
2352 bool value_is_mate(Value value) {
2354 assert(abs(value) <= VALUE_INFINITE);
2356 return value <= value_mated_in(PLY_MAX)
2357 || value >= value_mate_in(PLY_MAX);
2361 // move_is_killer() checks if the given move is among the
2362 // killer moves of that ply.
2364 bool move_is_killer(Move m, const SearchStack& ss) {
2366 const Move* k = ss.killers;
2367 for (int i = 0; i < KILLER_MAX; i++, k++)
2375 // extension() decides whether a move should be searched with normal depth,
2376 // or with extended depth. Certain classes of moves (checking moves, in
2377 // particular) are searched with bigger depth than ordinary moves and in
2378 // any case are marked as 'dangerous'. Note that also if a move is not
2379 // extended, as example because the corresponding UCI option is set to zero,
2380 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2382 Depth extension(const Position& pos, Move m, bool pvNode, bool captureOrPromotion,
2383 bool check, bool singleReply, bool mateThreat, bool* dangerous) {
2385 assert(m != MOVE_NONE);
2387 Depth result = Depth(0);
2388 *dangerous = check | singleReply | mateThreat;
2393 result += CheckExtension[pvNode];
2396 result += SingleReplyExtension[pvNode];
2399 result += MateThreatExtension[pvNode];
2402 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2404 Color c = pos.side_to_move();
2405 if (relative_rank(c, move_to(m)) == RANK_7)
2407 result += PawnPushTo7thExtension[pvNode];
2410 if (pos.pawn_is_passed(c, move_to(m)))
2412 result += PassedPawnExtension[pvNode];
2417 if ( captureOrPromotion
2418 && pos.type_of_piece_on(move_to(m)) != PAWN
2419 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2420 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2421 && !move_is_promotion(m)
2424 result += PawnEndgameExtension[pvNode];
2429 && captureOrPromotion
2430 && pos.type_of_piece_on(move_to(m)) != PAWN
2431 && pos.see_sign(m) >= 0)
2437 return Min(result, OnePly);
2441 // ok_to_do_nullmove() looks at the current position and decides whether
2442 // doing a 'null move' should be allowed. In order to avoid zugzwang
2443 // problems, null moves are not allowed when the side to move has very
2444 // little material left. Currently, the test is a bit too simple: Null
2445 // moves are avoided only when the side to move has only pawns left. It's
2446 // probably a good idea to avoid null moves in at least some more
2447 // complicated endgames, e.g. KQ vs KR. FIXME
2449 bool ok_to_do_nullmove(const Position& pos) {
2451 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2455 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2456 // non-tactical moves late in the move list close to the leaves are
2457 // candidates for pruning.
2459 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d) {
2461 assert(move_is_ok(m));
2462 assert(threat == MOVE_NONE || move_is_ok(threat));
2463 assert(!pos.move_is_check(m));
2464 assert(!pos.move_is_capture_or_promotion(m));
2465 assert(!pos.move_is_passed_pawn_push(m));
2466 assert(d >= OnePly);
2468 Square mfrom, mto, tfrom, tto;
2470 mfrom = move_from(m);
2472 tfrom = move_from(threat);
2473 tto = move_to(threat);
2475 // Case 1: Castling moves are never pruned
2476 if (move_is_castle(m))
2479 // Case 2: Don't prune moves which move the threatened piece
2480 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2483 // Case 3: If the threatened piece has value less than or equal to the
2484 // value of the threatening piece, don't prune move which defend it.
2485 if ( !PruneDefendingMoves
2486 && threat != MOVE_NONE
2487 && pos.move_is_capture(threat)
2488 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2489 || pos.type_of_piece_on(tfrom) == KING)
2490 && pos.move_attacks_square(m, tto))
2493 // Case 4: Don't prune moves with good history
2494 if (!H.ok_to_prune(pos.piece_on(mfrom), mto, d))
2497 // Case 5: If the moving piece in the threatened move is a slider, don't
2498 // prune safe moves which block its ray.
2499 if ( !PruneBlockingMoves
2500 && threat != MOVE_NONE
2501 && piece_is_slider(pos.piece_on(tfrom))
2502 && bit_is_set(squares_between(tfrom, tto), mto)
2503 && pos.see_sign(m) >= 0)
2510 // ok_to_use_TT() returns true if a transposition table score
2511 // can be used at a given point in search.
2513 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2515 Value v = value_from_tt(tte->value(), ply);
2517 return ( tte->depth() >= depth
2518 || v >= Max(value_mate_in(100), beta)
2519 || v < Min(value_mated_in(100), beta))
2521 && ( (is_lower_bound(tte->type()) && v >= beta)
2522 || (is_upper_bound(tte->type()) && v < beta));
2526 // update_history() registers a good move that produced a beta-cutoff
2527 // in history and marks as failures all the other moves of that ply.
2529 void update_history(const Position& pos, Move m, Depth depth,
2530 Move movesSearched[], int moveCount) {
2532 H.success(pos.piece_on(move_from(m)), move_to(m), depth);
2534 for (int i = 0; i < moveCount - 1; i++)
2536 assert(m != movesSearched[i]);
2537 if (!pos.move_is_capture_or_promotion(movesSearched[i]))
2538 H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]));
2543 // update_killers() add a good move that produced a beta-cutoff
2544 // among the killer moves of that ply.
2546 void update_killers(Move m, SearchStack& ss) {
2548 if (m == ss.killers[0])
2551 for (int i = KILLER_MAX - 1; i > 0; i--)
2552 ss.killers[i] = ss.killers[i - 1];
2558 // fail_high_ply_1() checks if some thread is currently resolving a fail
2559 // high at ply 1 at the node below the first root node. This information
2560 // is used for time managment.
2562 bool fail_high_ply_1() {
2564 for(int i = 0; i < ActiveThreads; i++)
2565 if (Threads[i].failHighPly1)
2572 // current_search_time() returns the number of milliseconds which have passed
2573 // since the beginning of the current search.
2575 int current_search_time() {
2576 return get_system_time() - SearchStartTime;
2580 // nps() computes the current nodes/second count.
2583 int t = current_search_time();
2584 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2588 // poll() performs two different functions: It polls for user input, and it
2589 // looks at the time consumed so far and decides if it's time to abort the
2594 static int lastInfoTime;
2595 int t = current_search_time();
2600 // We are line oriented, don't read single chars
2601 std::string command;
2602 if (!std::getline(std::cin, command))
2605 if (command == "quit")
2608 PonderSearch = false;
2612 else if (command == "stop")
2615 PonderSearch = false;
2617 else if (command == "ponderhit")
2620 // Print search information
2624 else if (lastInfoTime > t)
2625 // HACK: Must be a new search where we searched less than
2626 // NodesBetweenPolls nodes during the first second of search.
2629 else if (t - lastInfoTime >= 1000)
2636 if (dbg_show_hit_rate)
2637 dbg_print_hit_rate();
2639 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2640 << " time " << t << " hashfull " << TT.full() << std::endl;
2641 lock_release(&IOLock);
2642 if (ShowCurrentLine)
2643 Threads[0].printCurrentLine = true;
2645 // Should we stop the search?
2649 bool overTime = t > AbsoluteMaxSearchTime
2650 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2651 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2652 && t > 6*(MaxSearchTime + ExtraSearchTime));
2654 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2655 || (ExactMaxTime && t >= ExactMaxTime)
2656 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2661 // ponderhit() is called when the program is pondering (i.e. thinking while
2662 // it's the opponent's turn to move) in order to let the engine know that
2663 // it correctly predicted the opponent's move.
2667 int t = current_search_time();
2668 PonderSearch = false;
2669 if (Iteration >= 3 &&
2670 (!InfiniteSearch && (StopOnPonderhit ||
2671 t > AbsoluteMaxSearchTime ||
2672 (RootMoveNumber == 1 &&
2673 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2674 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2675 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2680 // print_current_line() prints the current line of search for a given
2681 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2683 void print_current_line(SearchStack ss[], int ply, int threadID) {
2685 assert(ply >= 0 && ply < PLY_MAX);
2686 assert(threadID >= 0 && threadID < ActiveThreads);
2688 if (!Threads[threadID].idle)
2691 std::cout << "info currline " << (threadID + 1);
2692 for (int p = 0; p < ply; p++)
2693 std::cout << " " << ss[p].currentMove;
2695 std::cout << std::endl;
2696 lock_release(&IOLock);
2698 Threads[threadID].printCurrentLine = false;
2699 if (threadID + 1 < ActiveThreads)
2700 Threads[threadID + 1].printCurrentLine = true;
2704 // init_ss_array() does a fast reset of the first entries of a SearchStack array
2706 void init_ss_array(SearchStack ss[]) {
2708 for (int i = 0; i < 3; i++)
2711 ss[i].initKillers();
2716 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2717 // while the program is pondering. The point is to work around a wrinkle in
2718 // the UCI protocol: When pondering, the engine is not allowed to give a
2719 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2720 // We simply wait here until one of these commands is sent, and return,
2721 // after which the bestmove and pondermove will be printed (in id_loop()).
2723 void wait_for_stop_or_ponderhit() {
2725 std::string command;
2729 if (!std::getline(std::cin, command))
2732 if (command == "quit")
2737 else if (command == "ponderhit" || command == "stop")
2743 // idle_loop() is where the threads are parked when they have no work to do.
2744 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2745 // object for which the current thread is the master.
2747 void idle_loop(int threadID, SplitPoint* waitSp) {
2748 assert(threadID >= 0 && threadID < THREAD_MAX);
2750 Threads[threadID].running = true;
2753 if(AllThreadsShouldExit && threadID != 0)
2756 // If we are not thinking, wait for a condition to be signaled instead
2757 // of wasting CPU time polling for work:
2758 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2759 #if !defined(_MSC_VER)
2760 pthread_mutex_lock(&WaitLock);
2761 if(Idle || threadID >= ActiveThreads)
2762 pthread_cond_wait(&WaitCond, &WaitLock);
2763 pthread_mutex_unlock(&WaitLock);
2765 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2769 // If this thread has been assigned work, launch a search
2770 if(Threads[threadID].workIsWaiting) {
2771 Threads[threadID].workIsWaiting = false;
2772 if(Threads[threadID].splitPoint->pvNode)
2773 sp_search_pv(Threads[threadID].splitPoint, threadID);
2775 sp_search(Threads[threadID].splitPoint, threadID);
2776 Threads[threadID].idle = true;
2779 // If this thread is the master of a split point and all threads have
2780 // finished their work at this split point, return from the idle loop.
2781 if(waitSp != NULL && waitSp->cpus == 0)
2785 Threads[threadID].running = false;
2789 // init_split_point_stack() is called during program initialization, and
2790 // initializes all split point objects.
2792 void init_split_point_stack() {
2793 for(int i = 0; i < THREAD_MAX; i++)
2794 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2795 SplitPointStack[i][j].parent = NULL;
2796 lock_init(&(SplitPointStack[i][j].lock), NULL);
2801 // destroy_split_point_stack() is called when the program exits, and
2802 // destroys all locks in the precomputed split point objects.
2804 void destroy_split_point_stack() {
2805 for(int i = 0; i < THREAD_MAX; i++)
2806 for(int j = 0; j < MaxActiveSplitPoints; j++)
2807 lock_destroy(&(SplitPointStack[i][j].lock));
2811 // thread_should_stop() checks whether the thread with a given threadID has
2812 // been asked to stop, directly or indirectly. This can happen if a beta
2813 // cutoff has occured in thre thread's currently active split point, or in
2814 // some ancestor of the current split point.
2816 bool thread_should_stop(int threadID) {
2817 assert(threadID >= 0 && threadID < ActiveThreads);
2821 if(Threads[threadID].stop)
2823 if(ActiveThreads <= 2)
2825 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2827 Threads[threadID].stop = true;
2834 // thread_is_available() checks whether the thread with threadID "slave" is
2835 // available to help the thread with threadID "master" at a split point. An
2836 // obvious requirement is that "slave" must be idle. With more than two
2837 // threads, this is not by itself sufficient: If "slave" is the master of
2838 // some active split point, it is only available as a slave to the other
2839 // threads which are busy searching the split point at the top of "slave"'s
2840 // split point stack (the "helpful master concept" in YBWC terminology).
2842 bool thread_is_available(int slave, int master) {
2843 assert(slave >= 0 && slave < ActiveThreads);
2844 assert(master >= 0 && master < ActiveThreads);
2845 assert(ActiveThreads > 1);
2847 if(!Threads[slave].idle || slave == master)
2850 if(Threads[slave].activeSplitPoints == 0)
2851 // No active split points means that the thread is available as a slave
2852 // for any other thread.
2855 if(ActiveThreads == 2)
2858 // Apply the "helpful master" concept if possible.
2859 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2866 // idle_thread_exists() tries to find an idle thread which is available as
2867 // a slave for the thread with threadID "master".
2869 bool idle_thread_exists(int master) {
2870 assert(master >= 0 && master < ActiveThreads);
2871 assert(ActiveThreads > 1);
2873 for(int i = 0; i < ActiveThreads; i++)
2874 if(thread_is_available(i, master))
2880 // split() does the actual work of distributing the work at a node between
2881 // several threads at PV nodes. If it does not succeed in splitting the
2882 // node (because no idle threads are available, or because we have no unused
2883 // split point objects), the function immediately returns false. If
2884 // splitting is possible, a SplitPoint object is initialized with all the
2885 // data that must be copied to the helper threads (the current position and
2886 // search stack, alpha, beta, the search depth, etc.), and we tell our
2887 // helper threads that they have been assigned work. This will cause them
2888 // to instantly leave their idle loops and call sp_search_pv(). When all
2889 // threads have returned from sp_search_pv (or, equivalently, when
2890 // splitPoint->cpus becomes 0), split() returns true.
2892 bool split(const Position& p, SearchStack* sstck, int ply,
2893 Value* alpha, Value* beta, Value* bestValue, const Value futilityValue,
2894 const Value approximateEval, Depth depth, int* moves,
2895 MovePicker* mp, int master, bool pvNode) {
2898 assert(sstck != NULL);
2899 assert(ply >= 0 && ply < PLY_MAX);
2900 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2901 assert(!pvNode || *alpha < *beta);
2902 assert(*beta <= VALUE_INFINITE);
2903 assert(depth > Depth(0));
2904 assert(master >= 0 && master < ActiveThreads);
2905 assert(ActiveThreads > 1);
2907 SplitPoint* splitPoint;
2912 // If no other thread is available to help us, or if we have too many
2913 // active split points, don't split.
2914 if(!idle_thread_exists(master) ||
2915 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2916 lock_release(&MPLock);
2920 // Pick the next available split point object from the split point stack
2921 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2922 Threads[master].activeSplitPoints++;
2924 // Initialize the split point object
2925 splitPoint->parent = Threads[master].splitPoint;
2926 splitPoint->finished = false;
2927 splitPoint->ply = ply;
2928 splitPoint->depth = depth;
2929 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2930 splitPoint->beta = *beta;
2931 splitPoint->pvNode = pvNode;
2932 splitPoint->bestValue = *bestValue;
2933 splitPoint->futilityValue = futilityValue;
2934 splitPoint->approximateEval = approximateEval;
2935 splitPoint->master = master;
2936 splitPoint->mp = mp;
2937 splitPoint->moves = *moves;
2938 splitPoint->cpus = 1;
2939 splitPoint->pos.copy(p);
2940 splitPoint->parentSstack = sstck;
2941 for(i = 0; i < ActiveThreads; i++)
2942 splitPoint->slaves[i] = 0;
2944 // Copy the current position and the search stack to the master thread
2945 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2946 Threads[master].splitPoint = splitPoint;
2948 // Make copies of the current position and search stack for each thread
2949 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2951 if(thread_is_available(i, master)) {
2952 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2953 Threads[i].splitPoint = splitPoint;
2954 splitPoint->slaves[i] = 1;
2958 // Tell the threads that they have work to do. This will make them leave
2960 for(i = 0; i < ActiveThreads; i++)
2961 if(i == master || splitPoint->slaves[i]) {
2962 Threads[i].workIsWaiting = true;
2963 Threads[i].idle = false;
2964 Threads[i].stop = false;
2967 lock_release(&MPLock);
2969 // Everything is set up. The master thread enters the idle loop, from
2970 // which it will instantly launch a search, because its workIsWaiting
2971 // slot is 'true'. We send the split point as a second parameter to the
2972 // idle loop, which means that the main thread will return from the idle
2973 // loop when all threads have finished their work at this split point
2974 // (i.e. when // splitPoint->cpus == 0).
2975 idle_loop(master, splitPoint);
2977 // We have returned from the idle loop, which means that all threads are
2978 // finished. Update alpha, beta and bestvalue, and return.
2980 if(pvNode) *alpha = splitPoint->alpha;
2981 *beta = splitPoint->beta;
2982 *bestValue = splitPoint->bestValue;
2983 Threads[master].stop = false;
2984 Threads[master].idle = false;
2985 Threads[master].activeSplitPoints--;
2986 Threads[master].splitPoint = splitPoint->parent;
2987 lock_release(&MPLock);
2993 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2994 // to start a new search from the root.
2996 void wake_sleeping_threads() {
2997 if(ActiveThreads > 1) {
2998 for(int i = 1; i < ActiveThreads; i++) {
2999 Threads[i].idle = true;
3000 Threads[i].workIsWaiting = false;
3002 #if !defined(_MSC_VER)
3003 pthread_mutex_lock(&WaitLock);
3004 pthread_cond_broadcast(&WaitCond);
3005 pthread_mutex_unlock(&WaitLock);
3007 for(int i = 1; i < THREAD_MAX; i++)
3008 SetEvent(SitIdleEvent[i]);
3014 // init_thread() is the function which is called when a new thread is
3015 // launched. It simply calls the idle_loop() function with the supplied
3016 // threadID. There are two versions of this function; one for POSIX threads
3017 // and one for Windows threads.
3019 #if !defined(_MSC_VER)
3021 void *init_thread(void *threadID) {
3022 idle_loop(*(int *)threadID, NULL);
3028 DWORD WINAPI init_thread(LPVOID threadID) {
3029 idle_loop(*(int *)threadID, NULL);