2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
43 #include "ucioption.h"
47 //// Local definitions
54 // IterationInfoType stores search results for each iteration
56 // Because we use relatively small (dynamic) aspiration window,
57 // there happens many fail highs and fail lows in root. And
58 // because we don't do researches in those cases, "value" stored
59 // here is not necessarily exact. Instead in case of fail high/low
60 // we guess what the right value might be and store our guess
61 // as a "speculated value" and then move on. Speculated values are
62 // used just to calculate aspiration window width, so also if are
63 // not exact is not big a problem.
65 struct IterationInfoType {
67 IterationInfoType(Value v = Value(0), Value sv = Value(0))
68 : value(v), speculatedValue(sv) {}
70 Value value, speculatedValue;
74 // The BetaCounterType class is used to order moves at ply one.
75 // Apart for the first one that has its score, following moves
76 // normally have score -VALUE_INFINITE, so are ordered according
77 // to the number of beta cutoffs occurred under their subtree during
78 // the last iteration. The counters are per thread variables to avoid
79 // concurrent accessing under SMP case.
81 struct BetaCounterType {
85 void add(Color us, Depth d, int threadID);
86 void read(Color us, int64_t& our, int64_t& their);
90 // The RootMove class is used for moves at the root at the tree. For each
91 // root move, we store a score, a node count, and a PV (really a refutation
92 // in the case of moves which fail low).
97 bool operator<(const RootMove&); // used to sort
101 int64_t nodes, cumulativeNodes;
102 Move pv[PLY_MAX_PLUS_2];
103 int64_t ourBeta, theirBeta;
107 // The RootMoveList class is essentially an array of RootMove objects, with
108 // a handful of methods for accessing the data in the individual moves.
113 RootMoveList(Position& pos, Move searchMoves[]);
114 inline Move get_move(int moveNum) const;
115 inline Value get_move_score(int moveNum) const;
116 inline void set_move_score(int moveNum, Value score);
117 inline void set_move_nodes(int moveNum, int64_t nodes);
118 inline void set_beta_counters(int moveNum, int64_t our, int64_t their);
119 void set_move_pv(int moveNum, const Move pv[]);
120 inline Move get_move_pv(int moveNum, int i) const;
121 inline int64_t get_move_cumulative_nodes(int moveNum) const;
122 inline int move_count() const;
123 Move scan_for_easy_move() const;
125 void sort_multipv(int n);
128 static const int MaxRootMoves = 500;
129 RootMove moves[MaxRootMoves];
136 // Search depth at iteration 1
137 const Depth InitialDepth = OnePly /*+ OnePly/2*/;
139 // Depth limit for selective search
140 const Depth SelectiveDepth = 7 * OnePly;
142 // Use internal iterative deepening?
143 const bool UseIIDAtPVNodes = true;
144 const bool UseIIDAtNonPVNodes = false;
146 // Internal iterative deepening margin. At Non-PV moves, when
147 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
148 // search when the static evaluation is at most IIDMargin below beta.
149 const Value IIDMargin = Value(0x100);
151 // Easy move margin. An easy move candidate must be at least this much
152 // better than the second best move.
153 const Value EasyMoveMargin = Value(0x200);
155 // Problem margin. If the score of the first move at iteration N+1 has
156 // dropped by more than this since iteration N, the boolean variable
157 // "Problem" is set to true, which will make the program spend some extra
158 // time looking for a better move.
159 const Value ProblemMargin = Value(0x28);
161 // No problem margin. If the boolean "Problem" is true, and a new move
162 // is found at the root which is less than NoProblemMargin worse than the
163 // best move from the previous iteration, Problem is set back to false.
164 const Value NoProblemMargin = Value(0x14);
166 // Null move margin. A null move search will not be done if the approximate
167 // evaluation of the position is more than NullMoveMargin below beta.
168 const Value NullMoveMargin = Value(0x300);
170 // Pruning criterions. See the code and comments in ok_to_prune() to
171 // understand their precise meaning.
172 const bool PruneEscapeMoves = false;
173 const bool PruneDefendingMoves = false;
174 const bool PruneBlockingMoves = false;
176 // Margins for futility pruning in the quiescence search, and at frontier
177 // and near frontier nodes.
178 const Value FutilityMarginQS = Value(0x80);
180 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
181 const Value FutilityMargins[12] = { Value(0x100), Value(0x120), Value(0x200), Value(0x220), Value(0x250), Value(0x270),
182 // 4 ply 4.5 ply 5 ply 5.5 ply 6 ply 6.5 ply
183 Value(0x2A0), Value(0x2C0), Value(0x340), Value(0x360), Value(0x3A0), Value(0x3C0) };
185 const Depth RazorDepth = 4*OnePly;
187 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
188 const Value RazorMargins[6] = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
190 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
191 const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
193 // The main transposition table
194 TranspositionTable TT;
197 /// Variables initialized by UCI options
199 // Adjustable playing strength
201 const int SlowdownArray[32] = {
202 19, 41, 70, 110, 160, 230, 320, 430, 570, 756, 1000, 1300, 1690, 2197,
203 2834, 3600, 4573, 5809, 7700, 9863, 12633, 16181, 20726, 26584, 34005,
204 43557, 55792, 71463, 91536, 117247, 150180, 192363
207 const int MaxStrength = 25;
209 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
210 int LMRPVMoves, LMRNonPVMoves; // heavy SMP read access for the latter
212 // Depth limit for use of dynamic threat detection
213 Depth ThreatDepth; // heavy SMP read access
215 // Last seconds noise filtering (LSN)
216 const bool UseLSNFiltering = true;
217 const int LSNTime = 4000; // In milliseconds
218 const Value LSNValue = value_from_centipawns(200);
219 bool loseOnTime = false;
221 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
222 // There is heavy SMP read access on these arrays
223 Depth CheckExtension[2], SingleReplyExtension[2], PawnPushTo7thExtension[2];
224 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
226 // Iteration counters
228 BetaCounterType BetaCounter; // has per-thread internal data
230 // Scores and number of times the best move changed for each iteration
231 IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
232 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
237 // Time managment variables
239 int MaxNodes, MaxDepth;
240 int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
244 bool StopOnPonderhit;
245 bool AbortSearch; // heavy SMP read access
251 // Show current line?
252 bool ShowCurrentLine;
256 std::ofstream LogFile;
258 // MP related variables
259 int ActiveThreads = 1;
260 Depth MinimumSplitDepth;
261 int MaxThreadsPerSplitPoint;
262 Thread Threads[THREAD_MAX];
265 bool AllThreadsShouldExit = false;
266 const int MaxActiveSplitPoints = 8;
267 SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
270 #if !defined(_MSC_VER)
271 pthread_cond_t WaitCond;
272 pthread_mutex_t WaitLock;
274 HANDLE SitIdleEvent[THREAD_MAX];
277 // Node counters, used only by thread[0] but try to keep in different
278 // cache lines (64 bytes each) from the heavy SMP read accessed variables.
280 int NodesBetweenPolls = 30000;
288 Value id_loop(const Position& pos, Move searchMoves[]);
289 Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
290 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
291 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID);
292 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
293 void sp_search(SplitPoint* sp, int threadID);
294 void sp_search_pv(SplitPoint* sp, int threadID);
295 void init_node(const Position& pos, SearchStack ss[], int ply, int threadID);
296 void update_pv(SearchStack ss[], int ply);
297 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
298 bool connected_moves(const Position& pos, Move m1, Move m2);
299 bool value_is_mate(Value value);
300 bool move_is_killer(Move m, const SearchStack& ss);
301 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
302 bool ok_to_do_nullmove(const Position& pos);
303 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d);
304 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
305 bool ok_to_history(const Position& pos, Move m);
306 void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
307 void update_killers(Move m, SearchStack& ss);
308 void slowdown(const Position& pos);
310 bool fail_high_ply_1();
311 int current_search_time();
315 void print_current_line(SearchStack ss[], int ply, int threadID);
316 void wait_for_stop_or_ponderhit();
318 void idle_loop(int threadID, SplitPoint* waitSp);
319 void init_split_point_stack();
320 void destroy_split_point_stack();
321 bool thread_should_stop(int threadID);
322 bool thread_is_available(int slave, int master);
323 bool idle_thread_exists(int master);
324 bool split(const Position& pos, SearchStack* ss, int ply,
325 Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
326 MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode);
327 void wake_sleeping_threads();
329 #if !defined(_MSC_VER)
330 void *init_thread(void *threadID);
332 DWORD WINAPI init_thread(LPVOID threadID);
342 /// think() is the external interface to Stockfish's search, and is called when
343 /// the program receives the UCI 'go' command. It initializes various
344 /// search-related global variables, and calls root_search(). It returns false
345 /// when a quit command is received during the search.
347 bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
348 int time[], int increment[], int movesToGo, int maxDepth,
349 int maxNodes, int maxTime, Move searchMoves[]) {
351 // Look for a book move
352 if (!infinite && !ponder && get_option_value_bool("OwnBook"))
355 if (get_option_value_string("Book File") != OpeningBook.file_name())
356 OpeningBook.open("book.bin");
358 bookMove = OpeningBook.get_move(pos);
359 if (bookMove != MOVE_NONE)
361 std::cout << "bestmove " << bookMove << std::endl;
366 // Initialize global search variables
368 SearchStartTime = get_system_time();
369 for (int i = 0; i < THREAD_MAX; i++)
371 Threads[i].nodes = 0ULL;
372 Threads[i].failHighPly1 = false;
375 InfiniteSearch = infinite;
376 PonderSearch = ponder;
377 StopOnPonderhit = false;
383 ExactMaxTime = maxTime;
385 // Read UCI option values
386 TT.set_size(get_option_value_int("Hash"));
387 if (button_was_pressed("Clear Hash"))
390 loseOnTime = false; // reset at the beginning of a new game
393 bool PonderingEnabled = get_option_value_bool("Ponder");
394 MultiPV = get_option_value_int("MultiPV");
396 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
397 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
399 SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
400 SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
402 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
403 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
405 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
406 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
408 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
409 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
411 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
412 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
414 LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
415 LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
416 ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
418 Chess960 = get_option_value_bool("UCI_Chess960");
419 ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
420 UseLogFile = get_option_value_bool("Use Search Log");
422 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
424 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
425 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
427 read_weights(pos.side_to_move());
429 // Set the number of active threads. If UCI_LimitStrength is enabled, never
430 // use more than one thread.
431 int newActiveThreads =
432 get_option_value_bool("UCI_LimitStrength")? 1 : get_option_value_int("Threads");
433 if (newActiveThreads != ActiveThreads)
435 ActiveThreads = newActiveThreads;
436 init_eval(ActiveThreads);
439 // Wake up sleeping threads
440 wake_sleeping_threads();
442 for (int i = 1; i < ActiveThreads; i++)
443 assert(thread_is_available(i, 0));
445 // Set playing strength
446 if (get_option_value_bool("UCI_LimitStrength"))
448 Strength = (get_option_value_int("UCI_Elo") - 2100) / 25;
450 (Strength == MaxStrength)? 0 : SlowdownArray[Max(0, 31-Strength)];
454 Strength = MaxStrength;
459 int myTime = time[side_to_move];
460 int myIncrement = increment[side_to_move];
462 if (!movesToGo) // Sudden death time control
466 MaxSearchTime = myTime / 30 + myIncrement;
467 AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
468 } else { // Blitz game without increment
469 MaxSearchTime = myTime / 30;
470 AbsoluteMaxSearchTime = myTime / 8;
473 else // (x moves) / (y minutes)
477 MaxSearchTime = myTime / 2;
478 AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
480 MaxSearchTime = myTime / Min(movesToGo, 20);
481 AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
485 if (PonderingEnabled)
487 MaxSearchTime += MaxSearchTime / 4;
488 MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
491 // Fixed depth or fixed number of nodes?
494 InfiniteSearch = true; // HACK
499 NodesBetweenPolls = Min(MaxNodes, 30000);
500 InfiniteSearch = true; // HACK
503 if (Slowdown > 50000) NodesBetweenPolls = 30;
504 else if (Slowdown > 10000) NodesBetweenPolls = 100;
505 else if (Slowdown > 1000) NodesBetweenPolls = 500;
506 else if (Slowdown > 100) NodesBetweenPolls = 3000;
507 else NodesBetweenPolls = 15000;
510 NodesBetweenPolls = 30000;
512 // Write information to search log file
514 LogFile << "Searching: " << pos.to_fen() << std::endl
515 << "infinite: " << infinite
516 << " ponder: " << ponder
517 << " time: " << myTime
518 << " increment: " << myIncrement
519 << " moves to go: " << movesToGo << std::endl;
522 // We're ready to start thinking. Call the iterative deepening loop function
524 // FIXME we really need to cleanup all this LSN ugliness
527 Value v = id_loop(pos, searchMoves);
528 loseOnTime = ( UseLSNFiltering
535 loseOnTime = false; // reset for next match
536 while (SearchStartTime + myTime + 1000 > get_system_time())
538 id_loop(pos, searchMoves); // to fail gracefully
549 /// init_threads() is called during startup. It launches all helper threads,
550 /// and initializes the split point stack and the global locks and condition
553 void init_threads() {
557 #if !defined(_MSC_VER)
558 pthread_t pthread[1];
561 for (i = 0; i < THREAD_MAX; i++)
562 Threads[i].activeSplitPoints = 0;
564 // Initialize global locks
565 lock_init(&MPLock, NULL);
566 lock_init(&IOLock, NULL);
568 init_split_point_stack();
570 #if !defined(_MSC_VER)
571 pthread_mutex_init(&WaitLock, NULL);
572 pthread_cond_init(&WaitCond, NULL);
574 for (i = 0; i < THREAD_MAX; i++)
575 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
578 // All threads except the main thread should be initialized to idle state
579 for (i = 1; i < THREAD_MAX; i++)
581 Threads[i].stop = false;
582 Threads[i].workIsWaiting = false;
583 Threads[i].idle = true;
584 Threads[i].running = false;
587 // Launch the helper threads
588 for(i = 1; i < THREAD_MAX; i++)
590 #if !defined(_MSC_VER)
591 pthread_create(pthread, NULL, init_thread, (void*)(&i));
594 CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
597 // Wait until the thread has finished launching
598 while (!Threads[i].running);
603 /// stop_threads() is called when the program exits. It makes all the
604 /// helper threads exit cleanly.
606 void stop_threads() {
608 ActiveThreads = THREAD_MAX; // HACK
609 Idle = false; // HACK
610 wake_sleeping_threads();
611 AllThreadsShouldExit = true;
612 for (int i = 1; i < THREAD_MAX; i++)
614 Threads[i].stop = true;
615 while(Threads[i].running);
617 destroy_split_point_stack();
621 /// nodes_searched() returns the total number of nodes searched so far in
622 /// the current search.
624 int64_t nodes_searched() {
626 int64_t result = 0ULL;
627 for (int i = 0; i < ActiveThreads; i++)
628 result += Threads[i].nodes;
633 // SearchStack::init() initializes a search stack. Used at the beginning of a
634 // new search from the root.
635 void SearchStack::init(int ply) {
637 pv[ply] = pv[ply + 1] = MOVE_NONE;
638 currentMove = threatMove = MOVE_NONE;
639 reduction = Depth(0);
642 void SearchStack::initKillers() {
644 mateKiller = MOVE_NONE;
645 for (int i = 0; i < KILLER_MAX; i++)
646 killers[i] = MOVE_NONE;
651 // id_loop() is the main iterative deepening loop. It calls root_search
652 // repeatedly with increasing depth until the allocated thinking time has
653 // been consumed, the user stops the search, or the maximum search depth is
656 Value id_loop(const Position& pos, Move searchMoves[]) {
659 SearchStack ss[PLY_MAX_PLUS_2];
661 // searchMoves are verified, copied, scored and sorted
662 RootMoveList rml(p, searchMoves);
667 for (int i = 0; i < 3; i++)
672 IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
675 Move EasyMove = rml.scan_for_easy_move();
677 // Iterative deepening loop
678 while (Iteration < PLY_MAX)
680 // Initialize iteration
683 BestMoveChangesByIteration[Iteration] = 0;
687 std::cout << "info depth " << Iteration << std::endl;
689 // Calculate dynamic search window based on previous iterations
692 if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
694 int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
695 int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
697 int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
699 alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
700 beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
704 alpha = - VALUE_INFINITE;
705 beta = VALUE_INFINITE;
708 // Search to the current depth
709 Value value = root_search(p, ss, rml, alpha, beta);
711 // Write PV to transposition table, in case the relevant entries have
712 // been overwritten during the search.
713 TT.insert_pv(p, ss[0].pv);
716 break; // Value cannot be trusted. Break out immediately!
718 //Save info about search result
719 Value speculatedValue;
722 Value delta = value - IterationInfo[Iteration - 1].value;
729 speculatedValue = value + delta;
730 BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
732 else if (value <= alpha)
734 assert(value == alpha);
738 speculatedValue = value + delta;
739 BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
741 speculatedValue = value;
743 speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
744 IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
746 // Erase the easy move if it differs from the new best move
747 if (ss[0].pv[0] != EasyMove)
748 EasyMove = MOVE_NONE;
755 bool stopSearch = false;
757 // Stop search early if there is only a single legal move
758 if (Iteration >= 6 && rml.move_count() == 1)
761 // Stop search early when the last two iterations returned a mate score
763 && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
764 && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
767 // Stop search early if one move seems to be much better than the rest
768 int64_t nodes = nodes_searched();
772 && EasyMove == ss[0].pv[0]
773 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
774 && current_search_time() > MaxSearchTime / 16)
775 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
776 && current_search_time() > MaxSearchTime / 32)))
779 // Add some extra time if the best move has changed during the last two iterations
780 if (Iteration > 5 && Iteration <= 50)
781 ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
782 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
784 // Stop search if most of MaxSearchTime is consumed at the end of the
785 // iteration. We probably don't have enough time to search the first
786 // move at the next iteration anyway.
787 if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
792 //FIXME: Implement fail-low emergency measures
796 StopOnPonderhit = true;
800 if (MaxDepth && Iteration >= MaxDepth)
806 // If we are pondering, we shouldn't print the best move before we
809 wait_for_stop_or_ponderhit();
811 // Print final search statistics
812 std::cout << "info nodes " << nodes_searched()
814 << " time " << current_search_time()
815 << " hashfull " << TT.full() << std::endl;
817 // Print the best move and the ponder move to the standard output
818 if (ss[0].pv[0] == MOVE_NONE)
820 ss[0].pv[0] = rml.get_move(0);
821 ss[0].pv[1] = MOVE_NONE;
823 std::cout << "bestmove " << ss[0].pv[0];
824 if (ss[0].pv[1] != MOVE_NONE)
825 std::cout << " ponder " << ss[0].pv[1];
827 std::cout << std::endl;
832 dbg_print_mean(LogFile);
834 if (dbg_show_hit_rate)
835 dbg_print_hit_rate(LogFile);
838 LogFile << "Nodes: " << nodes_searched() << std::endl
839 << "Nodes/second: " << nps() << std::endl
840 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
842 p.do_move(ss[0].pv[0], st);
843 LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
844 << std::endl << std::endl;
846 return rml.get_move_score(0);
850 // root_search() is the function which searches the root node. It is
851 // similar to search_pv except that it uses a different move ordering
852 // scheme (perhaps we should try to use this at internal PV nodes, too?)
853 // and prints some information to the standard output.
855 Value root_search(Position& pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta) {
857 Value oldAlpha = alpha;
859 Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
861 // Loop through all the moves in the root move list
862 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
866 // We failed high, invalidate and skip next moves, leave node-counters
867 // and beta-counters as they are and quickly return, we will try to do
868 // a research at the next iteration with a bigger aspiration window.
869 rml.set_move_score(i, -VALUE_INFINITE);
877 RootMoveNumber = i + 1;
880 // Remember the node count before the move is searched. The node counts
881 // are used to sort the root moves at the next iteration.
882 nodes = nodes_searched();
884 // Reset beta cut-off counters
887 // Pick the next root move, and print the move and the move number to
888 // the standard output.
889 move = ss[0].currentMove = rml.get_move(i);
890 if (current_search_time() >= 1000)
891 std::cout << "info currmove " << move
892 << " currmovenumber " << i + 1 << std::endl;
894 // Decide search depth for this move
895 bool moveIsCapture = pos.move_is_capture(move);
897 ext = extension(pos, move, true, pos.move_is_capture(move), pos.move_is_check(move), false, false, &dangerous);
898 newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
900 // Make the move, and search it
901 pos.do_move(move, st, dcCandidates);
905 // Aspiration window is disabled in multi-pv case
907 alpha = -VALUE_INFINITE;
909 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
910 // If the value has dropped a lot compared to the last iteration,
911 // set the boolean variable Problem to true. This variable is used
912 // for time managment: When Problem is true, we try to complete the
913 // current iteration before playing a move.
914 Problem = (Iteration >= 2 && value <= IterationInfo[Iteration-1].value - ProblemMargin);
916 if (Problem && StopOnPonderhit)
917 StopOnPonderhit = false;
921 if (newDepth >= 3*OnePly
922 && i + MultiPV >= LMRPVMoves
925 && !move_is_promotion(move)
926 && !move_is_castle(move))
928 ss[0].reduction = OnePly;
929 value = -search(pos, ss, -alpha, newDepth-OnePly, 1, true, 0);
932 value = alpha + 1; // Just to trigger next condition
935 value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
938 // Fail high! Set the boolean variable FailHigh to true, and
939 // re-search the move with a big window. The variable FailHigh is
940 // used for time managment: We try to avoid aborting the search
941 // prematurely during a fail high research.
943 value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
950 // Finished searching the move. If AbortSearch is true, the search
951 // was aborted because the user interrupted the search or because we
952 // ran out of time. In this case, the return value of the search cannot
953 // be trusted, and we break out of the loop without updating the best
958 // Remember the node count for this move. The node counts are used to
959 // sort the root moves at the next iteration.
960 rml.set_move_nodes(i, nodes_searched() - nodes);
962 // Remember the beta-cutoff statistics
964 BetaCounter.read(pos.side_to_move(), our, their);
965 rml.set_beta_counters(i, our, their);
967 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
969 if (value <= alpha && i >= MultiPV)
970 rml.set_move_score(i, -VALUE_INFINITE);
973 // PV move or new best move!
976 rml.set_move_score(i, value);
978 TT.extract_pv(pos, ss[0].pv);
979 rml.set_move_pv(i, ss[0].pv);
983 // We record how often the best move has been changed in each
984 // iteration. This information is used for time managment: When
985 // the best move changes frequently, we allocate some more time.
987 BestMoveChangesByIteration[Iteration]++;
989 // Print search information to the standard output
990 std::cout << "info depth " << Iteration
991 << " score " << value_to_string(value)
993 " lowerbound" : ((value <= alpha)? " upperbound" : ""))
994 << " time " << current_search_time()
995 << " nodes " << nodes_searched()
999 for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
1000 std::cout << ss[0].pv[j] << " ";
1002 std::cout << std::endl;
1005 LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
1011 // Reset the global variable Problem to false if the value isn't too
1012 // far below the final value from the last iteration.
1013 if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
1018 rml.sort_multipv(i);
1019 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
1022 std::cout << "info multipv " << j + 1
1023 << " score " << value_to_string(rml.get_move_score(j))
1024 << " depth " << ((j <= i)? Iteration : Iteration - 1)
1025 << " time " << current_search_time()
1026 << " nodes " << nodes_searched()
1030 for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
1031 std::cout << rml.get_move_pv(j, k) << " ";
1033 std::cout << std::endl;
1035 alpha = rml.get_move_score(Min(i, MultiPV-1));
1037 } // New best move case
1039 assert(alpha >= oldAlpha);
1041 FailLow = (alpha == oldAlpha);
1047 // search_pv() is the main search function for PV nodes.
1049 Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
1050 Depth depth, int ply, int threadID) {
1052 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1053 assert(beta > alpha && beta <= VALUE_INFINITE);
1054 assert(ply >= 0 && ply < PLY_MAX);
1055 assert(threadID >= 0 && threadID < ActiveThreads);
1058 return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
1060 // Initialize, and make an early exit in case of an aborted search,
1061 // an instant draw, maximum ply reached, etc.
1062 init_node(pos, ss, ply, threadID);
1064 // After init_node() that calls poll()
1065 if (AbortSearch || thread_should_stop(threadID))
1073 if (ply >= PLY_MAX - 1)
1074 return evaluate(pos, ei, threadID);
1076 // Mate distance pruning
1077 Value oldAlpha = alpha;
1078 alpha = Max(value_mated_in(ply), alpha);
1079 beta = Min(value_mate_in(ply+1), beta);
1083 // Transposition table lookup. At PV nodes, we don't use the TT for
1084 // pruning, but only for move ordering.
1085 const TTEntry* tte = TT.retrieve(pos.get_key());
1086 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1088 // Go with internal iterative deepening if we don't have a TT move
1089 if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
1091 search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
1092 ttMove = ss[ply].pv[ply];
1095 // Initialize a MovePicker object for the current position, and prepare
1096 // to search all moves
1097 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1099 Move move, movesSearched[256];
1101 Value value, bestValue = -VALUE_INFINITE;
1102 Bitboard dcCandidates = mp.discovered_check_candidates();
1103 Color us = pos.side_to_move();
1104 bool isCheck = pos.is_check();
1105 bool mateThreat = pos.has_mate_threat(opposite_color(us));
1107 // Loop through all legal moves until no moves remain or a beta cutoff
1109 while ( alpha < beta
1110 && (move = mp.get_next_move()) != MOVE_NONE
1111 && !thread_should_stop(threadID))
1113 assert(move_is_ok(move));
1115 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1116 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1117 bool moveIsCapture = pos.move_is_capture(move);
1119 movesSearched[moveCount++] = ss[ply].currentMove = move;
1121 // Decide the new search depth
1123 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1124 Depth newDepth = depth - OnePly + ext;
1126 // Make and search the move
1128 pos.do_move(move, st, dcCandidates);
1130 if (moveCount == 1) // The first move in list is the PV
1131 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1134 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1135 // if the move fails high will be re-searched at full depth.
1136 if ( depth >= 3*OnePly
1137 && moveCount >= LMRPVMoves
1140 && !move_is_promotion(move)
1141 && !move_is_castle(move)
1142 && !move_is_killer(move, ss[ply]))
1144 ss[ply].reduction = OnePly;
1145 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1148 value = alpha + 1; // Just to trigger next condition
1150 if (value > alpha) // Go with full depth non-pv search
1152 ss[ply].reduction = Depth(0);
1153 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1154 if (value > alpha && value < beta)
1156 // When the search fails high at ply 1 while searching the first
1157 // move at the root, set the flag failHighPly1. This is used for
1158 // time managment: We don't want to stop the search early in
1159 // such cases, because resolving the fail high at ply 1 could
1160 // result in a big drop in score at the root.
1161 if (ply == 1 && RootMoveNumber == 1)
1162 Threads[threadID].failHighPly1 = true;
1164 // A fail high occurred. Re-search at full window (pv search)
1165 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1166 Threads[threadID].failHighPly1 = false;
1170 pos.undo_move(move);
1172 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1175 if (value > bestValue)
1182 if (value == value_mate_in(ply + 1))
1183 ss[ply].mateKiller = move;
1185 // If we are at ply 1, and we are searching the first root move at
1186 // ply 0, set the 'Problem' variable if the score has dropped a lot
1187 // (from the computer's point of view) since the previous iteration.
1190 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1195 if ( ActiveThreads > 1
1197 && depth >= MinimumSplitDepth
1199 && idle_thread_exists(threadID)
1201 && !thread_should_stop(threadID)
1202 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1203 &moveCount, &mp, dcCandidates, threadID, true))
1207 // All legal moves have been searched. A special case: If there were
1208 // no legal moves, it must be mate or stalemate.
1210 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1212 // If the search is not aborted, update the transposition table,
1213 // history counters, and killer moves.
1214 if (AbortSearch || thread_should_stop(threadID))
1217 if (bestValue <= oldAlpha)
1218 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1220 else if (bestValue >= beta)
1222 BetaCounter.add(pos.side_to_move(), depth, threadID);
1223 Move m = ss[ply].pv[ply];
1224 if (ok_to_history(pos, m)) // Only non capture moves are considered
1226 update_history(pos, m, depth, movesSearched, moveCount);
1227 update_killers(m, ss[ply]);
1229 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1232 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1238 // search() is the search function for zero-width nodes.
1240 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1241 int ply, bool allowNullmove, int threadID) {
1243 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1244 assert(ply >= 0 && ply < PLY_MAX);
1245 assert(threadID >= 0 && threadID < ActiveThreads);
1248 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1250 // Initialize, and make an early exit in case of an aborted search,
1251 // an instant draw, maximum ply reached, etc.
1252 init_node(pos, ss, ply, threadID);
1254 // After init_node() that calls poll()
1255 if (AbortSearch || thread_should_stop(threadID))
1263 if (ply >= PLY_MAX - 1)
1264 return evaluate(pos, ei, threadID);
1266 // Mate distance pruning
1267 if (value_mated_in(ply) >= beta)
1270 if (value_mate_in(ply + 1) < beta)
1273 // Transposition table lookup
1274 const TTEntry* tte = TT.retrieve(pos.get_key());
1275 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1277 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1279 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1280 return value_from_tt(tte->value(), ply);
1283 Value approximateEval = quick_evaluate(pos);
1284 bool mateThreat = false;
1285 bool isCheck = pos.is_check();
1291 && !value_is_mate(beta)
1292 && ok_to_do_nullmove(pos)
1293 && approximateEval >= beta - NullMoveMargin)
1295 ss[ply].currentMove = MOVE_NULL;
1298 pos.do_null_move(st);
1299 int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
1301 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1303 pos.undo_null_move();
1305 if (nullValue >= beta)
1307 if (depth < 6 * OnePly)
1310 // Do zugzwang verification search
1311 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1315 // The null move failed low, which means that we may be faced with
1316 // some kind of threat. If the previous move was reduced, check if
1317 // the move that refuted the null move was somehow connected to the
1318 // move which was reduced. If a connection is found, return a fail
1319 // low score (which will cause the reduced move to fail high in the
1320 // parent node, which will trigger a re-search with full depth).
1321 if (nullValue == value_mated_in(ply + 2))
1324 ss[ply].threatMove = ss[ply + 1].currentMove;
1325 if ( depth < ThreatDepth
1326 && ss[ply - 1].reduction
1327 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1331 // Null move search not allowed, try razoring
1332 else if ( !value_is_mate(beta)
1333 && depth < RazorDepth
1334 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1335 && ss[ply - 1].currentMove != MOVE_NULL
1336 && ttMove == MOVE_NONE
1337 && !pos.has_pawn_on_7th(pos.side_to_move()))
1339 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1340 if (v < beta - RazorMargins[int(depth) - 2])
1344 // Go with internal iterative deepening if we don't have a TT move
1345 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1346 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1348 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1349 ttMove = ss[ply].pv[ply];
1352 // Initialize a MovePicker object for the current position, and prepare
1353 // to search all moves.
1354 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1356 Move move, movesSearched[256];
1358 Value value, bestValue = -VALUE_INFINITE;
1359 Bitboard dcCandidates = mp.discovered_check_candidates();
1360 Value futilityValue = VALUE_NONE;
1361 bool useFutilityPruning = depth < SelectiveDepth
1364 // Loop through all legal moves until no moves remain or a beta cutoff
1366 while ( bestValue < beta
1367 && (move = mp.get_next_move()) != MOVE_NONE
1368 && !thread_should_stop(threadID))
1370 assert(move_is_ok(move));
1372 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1373 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1374 bool moveIsCapture = pos.move_is_capture(move);
1376 movesSearched[moveCount++] = ss[ply].currentMove = move;
1378 // Decide the new search depth
1380 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1381 Depth newDepth = depth - OnePly + ext;
1384 if ( useFutilityPruning
1387 && !move_is_promotion(move))
1389 // History pruning. See ok_to_prune() definition
1390 if ( moveCount >= 2 + int(depth)
1391 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1394 // Value based pruning
1395 if (approximateEval < beta)
1397 if (futilityValue == VALUE_NONE)
1398 futilityValue = evaluate(pos, ei, threadID)
1399 + FutilityMargins[int(depth) - 2];
1401 if (futilityValue < beta)
1403 if (futilityValue > bestValue)
1404 bestValue = futilityValue;
1410 // Make and search the move
1412 pos.do_move(move, st, dcCandidates);
1414 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1415 // if the move fails high will be re-searched at full depth.
1416 if ( depth >= 3*OnePly
1417 && moveCount >= LMRNonPVMoves
1420 && !move_is_promotion(move)
1421 && !move_is_castle(move)
1422 && !move_is_killer(move, ss[ply]))
1424 ss[ply].reduction = OnePly;
1425 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1428 value = beta; // Just to trigger next condition
1430 if (value >= beta) // Go with full depth non-pv search
1432 ss[ply].reduction = Depth(0);
1433 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1435 pos.undo_move(move);
1437 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1440 if (value > bestValue)
1446 if (value == value_mate_in(ply + 1))
1447 ss[ply].mateKiller = move;
1451 if ( ActiveThreads > 1
1453 && depth >= MinimumSplitDepth
1455 && idle_thread_exists(threadID)
1457 && !thread_should_stop(threadID)
1458 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1459 &mp, dcCandidates, threadID, false))
1463 // All legal moves have been searched. A special case: If there were
1464 // no legal moves, it must be mate or stalemate.
1466 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1468 // If the search is not aborted, update the transposition table,
1469 // history counters, and killer moves.
1470 if (AbortSearch || thread_should_stop(threadID))
1473 if (bestValue < beta)
1474 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1477 BetaCounter.add(pos.side_to_move(), depth, threadID);
1478 Move m = ss[ply].pv[ply];
1479 if (ok_to_history(pos, m)) // Only non capture moves are considered
1481 update_history(pos, m, depth, movesSearched, moveCount);
1482 update_killers(m, ss[ply]);
1484 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1487 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1493 // qsearch() is the quiescence search function, which is called by the main
1494 // search function when the remaining depth is zero (or, to be more precise,
1495 // less than OnePly).
1497 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1498 Depth depth, int ply, int threadID) {
1500 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1501 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1503 assert(ply >= 0 && ply < PLY_MAX);
1504 assert(threadID >= 0 && threadID < ActiveThreads);
1506 // Initialize, and make an early exit in case of an aborted search,
1507 // an instant draw, maximum ply reached, etc.
1508 init_node(pos, ss, ply, threadID);
1510 // After init_node() that calls poll()
1511 if (AbortSearch || thread_should_stop(threadID))
1517 // Transposition table lookup, only when not in PV
1518 TTEntry* tte = NULL;
1519 bool pvNode = (beta - alpha != 1);
1522 tte = TT.retrieve(pos.get_key());
1523 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1525 assert(tte->type() != VALUE_TYPE_EVAL);
1527 return value_from_tt(tte->value(), ply);
1530 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1532 // Evaluate the position statically
1535 bool isCheck = pos.is_check();
1536 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1539 staticValue = -VALUE_INFINITE;
1541 else if (tte && tte->type() == VALUE_TYPE_EVAL)
1543 // Use the cached evaluation score if possible
1544 assert(ei.futilityMargin == Value(0));
1546 staticValue = tte->value();
1549 staticValue = evaluate(pos, ei, threadID);
1551 if (ply == PLY_MAX - 1)
1552 return evaluate(pos, ei, threadID);
1554 // Initialize "stand pat score", and return it immediately if it is
1556 Value bestValue = staticValue;
1558 if (bestValue >= beta)
1560 // Store the score to avoid a future costly evaluation() call
1561 if (!isCheck && !tte && ei.futilityMargin == 0)
1562 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EVAL, Depth(-127*OnePly), MOVE_NONE);
1567 if (bestValue > alpha)
1570 // Initialize a MovePicker object for the current position, and prepare
1571 // to search the moves. Because the depth is <= 0 here, only captures,
1572 // queen promotions and checks (only if depth == 0) will be generated.
1573 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1576 Bitboard dcCandidates = mp.discovered_check_candidates();
1577 Color us = pos.side_to_move();
1578 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1580 // Loop through the moves until no moves remain or a beta cutoff
1582 while ( alpha < beta
1583 && (move = mp.get_next_move()) != MOVE_NONE)
1585 assert(move_is_ok(move));
1588 ss[ply].currentMove = move;
1594 && !move_is_promotion(move)
1595 && !pos.move_is_check(move, dcCandidates)
1596 && !pos.move_is_passed_pawn_push(move))
1598 Value futilityValue = staticValue
1599 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1600 pos.endgame_value_of_piece_on(move_to(move)))
1601 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1603 + ei.futilityMargin;
1605 if (futilityValue < alpha)
1607 if (futilityValue > bestValue)
1608 bestValue = futilityValue;
1613 // Don't search captures and checks with negative SEE values
1615 && !move_is_promotion(move)
1616 && pos.see_sign(move) < 0)
1619 // Make and search the move.
1621 pos.do_move(move, st, dcCandidates);
1622 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1623 pos.undo_move(move);
1625 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1628 if (value > bestValue)
1639 // All legal moves have been searched. A special case: If we're in check
1640 // and no legal moves were found, it is checkmate.
1641 if (pos.is_check() && moveCount == 0) // Mate!
1642 return value_mated_in(ply);
1644 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1646 // Update transposition table
1647 Move m = ss[ply].pv[ply];
1650 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1651 if (bestValue < beta)
1652 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE);
1654 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
1657 // Update killers only for good check moves
1658 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1659 update_killers(m, ss[ply]);
1665 // sp_search() is used to search from a split point. This function is called
1666 // by each thread working at the split point. It is similar to the normal
1667 // search() function, but simpler. Because we have already probed the hash
1668 // table, done a null move search, and searched the first move before
1669 // splitting, we don't have to repeat all this work in sp_search(). We
1670 // also don't need to store anything to the hash table here: This is taken
1671 // care of after we return from the split point.
1673 void sp_search(SplitPoint* sp, int threadID) {
1675 assert(threadID >= 0 && threadID < ActiveThreads);
1676 assert(ActiveThreads > 1);
1678 Position pos = Position(sp->pos);
1679 SearchStack* ss = sp->sstack[threadID];
1682 bool isCheck = pos.is_check();
1683 bool useFutilityPruning = sp->depth < SelectiveDepth
1686 while ( sp->bestValue < sp->beta
1687 && !thread_should_stop(threadID)
1688 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1690 assert(move_is_ok(move));
1692 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1693 bool moveIsCapture = pos.move_is_capture(move);
1695 lock_grab(&(sp->lock));
1696 int moveCount = ++sp->moves;
1697 lock_release(&(sp->lock));
1699 ss[sp->ply].currentMove = move;
1701 // Decide the new search depth.
1703 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1704 Depth newDepth = sp->depth - OnePly + ext;
1707 if ( useFutilityPruning
1710 && !move_is_promotion(move)
1711 && moveCount >= 2 + int(sp->depth)
1712 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1715 // Make and search the move.
1717 pos.do_move(move, st, sp->dcCandidates);
1719 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1720 // if the move fails high will be re-searched at full depth.
1722 && moveCount >= LMRNonPVMoves
1724 && !move_is_promotion(move)
1725 && !move_is_castle(move)
1726 && !move_is_killer(move, ss[sp->ply]))
1728 ss[sp->ply].reduction = OnePly;
1729 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1732 value = sp->beta; // Just to trigger next condition
1734 if (value >= sp->beta) // Go with full depth non-pv search
1736 ss[sp->ply].reduction = Depth(0);
1737 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1739 pos.undo_move(move);
1741 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1743 if (thread_should_stop(threadID))
1747 lock_grab(&(sp->lock));
1748 if (value > sp->bestValue && !thread_should_stop(threadID))
1750 sp->bestValue = value;
1751 if (sp->bestValue >= sp->beta)
1753 sp_update_pv(sp->parentSstack, ss, sp->ply);
1754 for (int i = 0; i < ActiveThreads; i++)
1755 if (i != threadID && (i == sp->master || sp->slaves[i]))
1756 Threads[i].stop = true;
1758 sp->finished = true;
1761 lock_release(&(sp->lock));
1764 lock_grab(&(sp->lock));
1766 // If this is the master thread and we have been asked to stop because of
1767 // a beta cutoff higher up in the tree, stop all slave threads.
1768 if (sp->master == threadID && thread_should_stop(threadID))
1769 for (int i = 0; i < ActiveThreads; i++)
1771 Threads[i].stop = true;
1774 sp->slaves[threadID] = 0;
1776 lock_release(&(sp->lock));
1780 // sp_search_pv() is used to search from a PV split point. This function
1781 // is called by each thread working at the split point. It is similar to
1782 // the normal search_pv() function, but simpler. Because we have already
1783 // probed the hash table and searched the first move before splitting, we
1784 // don't have to repeat all this work in sp_search_pv(). We also don't
1785 // need to store anything to the hash table here: This is taken care of
1786 // after we return from the split point.
1788 void sp_search_pv(SplitPoint* sp, int threadID) {
1790 assert(threadID >= 0 && threadID < ActiveThreads);
1791 assert(ActiveThreads > 1);
1793 Position pos = Position(sp->pos);
1794 SearchStack* ss = sp->sstack[threadID];
1798 while ( sp->alpha < sp->beta
1799 && !thread_should_stop(threadID)
1800 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1802 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1803 bool moveIsCapture = pos.move_is_capture(move);
1805 assert(move_is_ok(move));
1807 lock_grab(&(sp->lock));
1808 int moveCount = ++sp->moves;
1809 lock_release(&(sp->lock));
1811 ss[sp->ply].currentMove = move;
1813 // Decide the new search depth.
1815 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1816 Depth newDepth = sp->depth - OnePly + ext;
1818 // Make and search the move.
1820 pos.do_move(move, st, sp->dcCandidates);
1822 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1823 // if the move fails high will be re-searched at full depth.
1825 && moveCount >= LMRPVMoves
1827 && !move_is_promotion(move)
1828 && !move_is_castle(move)
1829 && !move_is_killer(move, ss[sp->ply]))
1831 ss[sp->ply].reduction = OnePly;
1832 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1835 value = sp->alpha + 1; // Just to trigger next condition
1837 if (value > sp->alpha) // Go with full depth non-pv search
1839 ss[sp->ply].reduction = Depth(0);
1840 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1842 if (value > sp->alpha && value < sp->beta)
1844 // When the search fails high at ply 1 while searching the first
1845 // move at the root, set the flag failHighPly1. This is used for
1846 // time managment: We don't want to stop the search early in
1847 // such cases, because resolving the fail high at ply 1 could
1848 // result in a big drop in score at the root.
1849 if (sp->ply == 1 && RootMoveNumber == 1)
1850 Threads[threadID].failHighPly1 = true;
1852 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1853 Threads[threadID].failHighPly1 = false;
1856 pos.undo_move(move);
1858 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1860 if (thread_should_stop(threadID))
1864 lock_grab(&(sp->lock));
1865 if (value > sp->bestValue && !thread_should_stop(threadID))
1867 sp->bestValue = value;
1868 if (value > sp->alpha)
1871 sp_update_pv(sp->parentSstack, ss, sp->ply);
1872 if (value == value_mate_in(sp->ply + 1))
1873 ss[sp->ply].mateKiller = move;
1875 if (value >= sp->beta)
1877 for (int i = 0; i < ActiveThreads; i++)
1878 if (i != threadID && (i == sp->master || sp->slaves[i]))
1879 Threads[i].stop = true;
1881 sp->finished = true;
1884 // If we are at ply 1, and we are searching the first root move at
1885 // ply 0, set the 'Problem' variable if the score has dropped a lot
1886 // (from the computer's point of view) since the previous iteration.
1889 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1892 lock_release(&(sp->lock));
1895 lock_grab(&(sp->lock));
1897 // If this is the master thread and we have been asked to stop because of
1898 // a beta cutoff higher up in the tree, stop all slave threads.
1899 if (sp->master == threadID && thread_should_stop(threadID))
1900 for (int i = 0; i < ActiveThreads; i++)
1902 Threads[i].stop = true;
1905 sp->slaves[threadID] = 0;
1907 lock_release(&(sp->lock));
1910 /// The BetaCounterType class
1912 BetaCounterType::BetaCounterType() { clear(); }
1914 void BetaCounterType::clear() {
1916 for (int i = 0; i < THREAD_MAX; i++)
1917 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
1920 void BetaCounterType::add(Color us, Depth d, int threadID) {
1922 // Weighted count based on depth
1923 Threads[threadID].betaCutOffs[us] += unsigned(d);
1926 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1929 for (int i = 0; i < THREAD_MAX; i++)
1931 our += Threads[i].betaCutOffs[us];
1932 their += Threads[i].betaCutOffs[opposite_color(us)];
1937 /// The RootMove class
1941 RootMove::RootMove() {
1942 nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
1945 // RootMove::operator<() is the comparison function used when
1946 // sorting the moves. A move m1 is considered to be better
1947 // than a move m2 if it has a higher score, or if the moves
1948 // have equal score but m1 has the higher node count.
1950 bool RootMove::operator<(const RootMove& m) {
1952 if (score != m.score)
1953 return (score < m.score);
1955 return theirBeta <= m.theirBeta;
1958 /// The RootMoveList class
1962 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1964 MoveStack mlist[MaxRootMoves];
1965 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1967 // Generate all legal moves
1968 int lm_count = generate_legal_moves(pos, mlist);
1970 // Add each move to the moves[] array
1971 for (int i = 0; i < lm_count; i++)
1973 bool includeMove = includeAllMoves;
1975 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1976 includeMove = (searchMoves[k] == mlist[i].move);
1981 // Find a quick score for the move
1983 SearchStack ss[PLY_MAX_PLUS_2];
1985 moves[count].move = mlist[i].move;
1986 pos.do_move(moves[count].move, st);
1987 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
1988 pos.undo_move(moves[count].move);
1989 moves[count].pv[0] = moves[count].move;
1990 moves[count].pv[1] = MOVE_NONE; // FIXME
1997 // Simple accessor methods for the RootMoveList class
1999 inline Move RootMoveList::get_move(int moveNum) const {
2000 return moves[moveNum].move;
2003 inline Value RootMoveList::get_move_score(int moveNum) const {
2004 return moves[moveNum].score;
2007 inline void RootMoveList::set_move_score(int moveNum, Value score) {
2008 moves[moveNum].score = score;
2011 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2012 moves[moveNum].nodes = nodes;
2013 moves[moveNum].cumulativeNodes += nodes;
2016 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2017 moves[moveNum].ourBeta = our;
2018 moves[moveNum].theirBeta = their;
2021 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2023 for(j = 0; pv[j] != MOVE_NONE; j++)
2024 moves[moveNum].pv[j] = pv[j];
2025 moves[moveNum].pv[j] = MOVE_NONE;
2028 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2029 return moves[moveNum].pv[i];
2032 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2033 return moves[moveNum].cumulativeNodes;
2036 inline int RootMoveList::move_count() const {
2041 // RootMoveList::scan_for_easy_move() is called at the end of the first
2042 // iteration, and is used to detect an "easy move", i.e. a move which appears
2043 // to be much bester than all the rest. If an easy move is found, the move
2044 // is returned, otherwise the function returns MOVE_NONE. It is very
2045 // important that this function is called at the right moment: The code
2046 // assumes that the first iteration has been completed and the moves have
2047 // been sorted. This is done in RootMoveList c'tor.
2049 Move RootMoveList::scan_for_easy_move() const {
2056 // moves are sorted so just consider the best and the second one
2057 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
2063 // RootMoveList::sort() sorts the root move list at the beginning of a new
2066 inline void RootMoveList::sort() {
2068 sort_multipv(count - 1); // all items
2072 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2073 // list by their scores and depths. It is used to order the different PVs
2074 // correctly in MultiPV mode.
2076 void RootMoveList::sort_multipv(int n) {
2078 for (int i = 1; i <= n; i++)
2080 RootMove rm = moves[i];
2082 for (j = i; j > 0 && moves[j-1] < rm; j--)
2083 moves[j] = moves[j-1];
2089 // init_node() is called at the beginning of all the search functions
2090 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2091 // stack object corresponding to the current node. Once every
2092 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2093 // for user input and checks whether it is time to stop the search.
2095 void init_node(const Position& pos, SearchStack ss[], int ply, int threadID) {
2097 assert(ply >= 0 && ply < PLY_MAX);
2098 assert(threadID >= 0 && threadID < ActiveThreads);
2100 if (Slowdown && Iteration >= 3)
2103 Threads[threadID].nodes++;
2108 if (NodesSincePoll >= NodesBetweenPolls)
2115 ss[ply+2].initKillers();
2117 if (Threads[threadID].printCurrentLine)
2118 print_current_line(ss, ply, threadID);
2122 // update_pv() is called whenever a search returns a value > alpha. It
2123 // updates the PV in the SearchStack object corresponding to the current
2126 void update_pv(SearchStack ss[], int ply) {
2127 assert(ply >= 0 && ply < PLY_MAX);
2129 ss[ply].pv[ply] = ss[ply].currentMove;
2131 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2132 ss[ply].pv[p] = ss[ply+1].pv[p];
2133 ss[ply].pv[p] = MOVE_NONE;
2137 // sp_update_pv() is a variant of update_pv for use at split points. The
2138 // difference between the two functions is that sp_update_pv also updates
2139 // the PV at the parent node.
2141 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2142 assert(ply >= 0 && ply < PLY_MAX);
2144 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2146 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2147 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2148 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2152 // connected_moves() tests whether two moves are 'connected' in the sense
2153 // that the first move somehow made the second move possible (for instance
2154 // if the moving piece is the same in both moves). The first move is
2155 // assumed to be the move that was made to reach the current position, while
2156 // the second move is assumed to be a move from the current position.
2158 bool connected_moves(const Position& pos, Move m1, Move m2) {
2159 Square f1, t1, f2, t2;
2161 assert(move_is_ok(m1));
2162 assert(move_is_ok(m2));
2164 if (m2 == MOVE_NONE)
2167 // Case 1: The moving piece is the same in both moves
2173 // Case 2: The destination square for m2 was vacated by m1
2179 // Case 3: Moving through the vacated square
2180 if ( piece_is_slider(pos.piece_on(f2))
2181 && bit_is_set(squares_between(f2, t2), f1))
2184 // Case 4: The destination square for m2 is attacked by the moving piece in m1
2185 if (pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
2188 // Case 5: Discovered check, checking piece is the piece moved in m1
2189 if ( piece_is_slider(pos.piece_on(t1))
2190 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2191 && !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())), t2))
2193 Bitboard occ = pos.occupied_squares();
2194 Color us = pos.side_to_move();
2195 Square ksq = pos.king_square(us);
2196 clear_bit(&occ, f2);
2197 if (pos.type_of_piece_on(t1) == BISHOP)
2199 if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2202 else if (pos.type_of_piece_on(t1) == ROOK)
2204 if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
2209 assert(pos.type_of_piece_on(t1) == QUEEN);
2210 if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
2218 // value_is_mate() checks if the given value is a mate one
2219 // eventually compensated for the ply.
2221 bool value_is_mate(Value value) {
2223 assert(abs(value) <= VALUE_INFINITE);
2225 return value <= value_mated_in(PLY_MAX)
2226 || value >= value_mate_in(PLY_MAX);
2230 // move_is_killer() checks if the given move is among the
2231 // killer moves of that ply.
2233 bool move_is_killer(Move m, const SearchStack& ss) {
2235 const Move* k = ss.killers;
2236 for (int i = 0; i < KILLER_MAX; i++, k++)
2244 // extension() decides whether a move should be searched with normal depth,
2245 // or with extended depth. Certain classes of moves (checking moves, in
2246 // particular) are searched with bigger depth than ordinary moves and in
2247 // any case are marked as 'dangerous'. Note that also if a move is not
2248 // extended, as example because the corresponding UCI option is set to zero,
2249 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2251 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2252 bool singleReply, bool mateThreat, bool* dangerous) {
2254 assert(m != MOVE_NONE);
2256 Depth result = Depth(0);
2257 *dangerous = check | singleReply | mateThreat;
2262 result += CheckExtension[pvNode];
2265 result += SingleReplyExtension[pvNode];
2268 result += MateThreatExtension[pvNode];
2271 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2273 if (pos.move_is_pawn_push_to_7th(m))
2275 result += PawnPushTo7thExtension[pvNode];
2278 if (pos.move_is_passed_pawn_push(m))
2280 result += PassedPawnExtension[pvNode];
2286 && pos.type_of_piece_on(move_to(m)) != PAWN
2287 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2288 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2289 && !move_is_promotion(m)
2292 result += PawnEndgameExtension[pvNode];
2298 && pos.type_of_piece_on(move_to(m)) != PAWN
2299 && pos.see_sign(m) >= 0)
2305 return Min(result, OnePly);
2309 // ok_to_do_nullmove() looks at the current position and decides whether
2310 // doing a 'null move' should be allowed. In order to avoid zugzwang
2311 // problems, null moves are not allowed when the side to move has very
2312 // little material left. Currently, the test is a bit too simple: Null
2313 // moves are avoided only when the side to move has only pawns left. It's
2314 // probably a good idea to avoid null moves in at least some more
2315 // complicated endgames, e.g. KQ vs KR. FIXME
2317 bool ok_to_do_nullmove(const Position& pos) {
2319 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2323 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2324 // non-tactical moves late in the move list close to the leaves are
2325 // candidates for pruning.
2327 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d) {
2329 assert(move_is_ok(m));
2330 assert(threat == MOVE_NONE || move_is_ok(threat));
2331 assert(!move_is_promotion(m));
2332 assert(!pos.move_is_check(m));
2333 assert(!pos.move_is_capture(m));
2334 assert(!pos.move_is_passed_pawn_push(m));
2335 assert(d >= OnePly);
2337 Square mfrom, mto, tfrom, tto;
2339 mfrom = move_from(m);
2341 tfrom = move_from(threat);
2342 tto = move_to(threat);
2344 // Case 1: Castling moves are never pruned
2345 if (move_is_castle(m))
2348 // Case 2: Don't prune moves which move the threatened piece
2349 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2352 // Case 3: If the threatened piece has value less than or equal to the
2353 // value of the threatening piece, don't prune move which defend it.
2354 if ( !PruneDefendingMoves
2355 && threat != MOVE_NONE
2356 && pos.move_is_capture(threat)
2357 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2358 || pos.type_of_piece_on(tfrom) == KING)
2359 && pos.move_attacks_square(m, tto))
2362 // Case 4: Don't prune moves with good history
2363 if (!H.ok_to_prune(pos.piece_on(mfrom), mto, d))
2366 // Case 5: If the moving piece in the threatened move is a slider, don't
2367 // prune safe moves which block its ray.
2368 if ( !PruneBlockingMoves
2369 && threat != MOVE_NONE
2370 && piece_is_slider(pos.piece_on(tfrom))
2371 && bit_is_set(squares_between(tfrom, tto), mto)
2372 && pos.see_sign(m) >= 0)
2379 // ok_to_use_TT() returns true if a transposition table score
2380 // can be used at a given point in search.
2382 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2384 Value v = value_from_tt(tte->value(), ply);
2386 return ( tte->depth() >= depth
2387 || v >= Max(value_mate_in(100), beta)
2388 || v < Min(value_mated_in(100), beta))
2390 && ( (is_lower_bound(tte->type()) && v >= beta)
2391 || (is_upper_bound(tte->type()) && v < beta));
2395 // ok_to_history() returns true if a move m can be stored
2396 // in history. Should be a non capturing move nor a promotion.
2398 bool ok_to_history(const Position& pos, Move m) {
2400 return !pos.move_is_capture(m) && !move_is_promotion(m);
2404 // update_history() registers a good move that produced a beta-cutoff
2405 // in history and marks as failures all the other moves of that ply.
2407 void update_history(const Position& pos, Move m, Depth depth,
2408 Move movesSearched[], int moveCount) {
2410 H.success(pos.piece_on(move_from(m)), move_to(m), depth);
2412 for (int i = 0; i < moveCount - 1; i++)
2414 assert(m != movesSearched[i]);
2415 if (ok_to_history(pos, movesSearched[i]))
2416 H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]));
2421 // update_killers() add a good move that produced a beta-cutoff
2422 // among the killer moves of that ply.
2424 void update_killers(Move m, SearchStack& ss) {
2426 if (m == ss.killers[0])
2429 for (int i = KILLER_MAX - 1; i > 0; i--)
2430 ss.killers[i] = ss.killers[i - 1];
2436 // slowdown() simply wastes CPU cycles doing nothing useful. It's used
2437 // in strength handicap mode.
2439 void slowdown(const Position &pos) {
2442 for (i = 0; i < n; i++) {
2443 Square s = Square(i&63);
2444 if (count_1s(pos.attacks_to(s)) > 63)
2445 std::cout << "This can't happen, but I put this string here anyway, in order to prevent the compiler from optimizing away the useless computation." << std::endl;
2450 // fail_high_ply_1() checks if some thread is currently resolving a fail
2451 // high at ply 1 at the node below the first root node. This information
2452 // is used for time managment.
2454 bool fail_high_ply_1() {
2456 for(int i = 0; i < ActiveThreads; i++)
2457 if (Threads[i].failHighPly1)
2464 // current_search_time() returns the number of milliseconds which have passed
2465 // since the beginning of the current search.
2467 int current_search_time() {
2468 return get_system_time() - SearchStartTime;
2472 // nps() computes the current nodes/second count.
2475 int t = current_search_time();
2476 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2480 // poll() performs two different functions: It polls for user input, and it
2481 // looks at the time consumed so far and decides if it's time to abort the
2486 static int lastInfoTime;
2487 int t = current_search_time();
2492 // We are line oriented, don't read single chars
2493 std::string command;
2494 if (!std::getline(std::cin, command))
2497 if (command == "quit")
2500 PonderSearch = false;
2504 else if (command == "stop")
2507 PonderSearch = false;
2509 else if (command == "ponderhit")
2512 // Print search information
2516 else if (lastInfoTime > t)
2517 // HACK: Must be a new search where we searched less than
2518 // NodesBetweenPolls nodes during the first second of search.
2521 else if (t - lastInfoTime >= 1000)
2528 if (dbg_show_hit_rate)
2529 dbg_print_hit_rate();
2531 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2532 << " time " << t << " hashfull " << TT.full() << std::endl;
2533 lock_release(&IOLock);
2534 if (ShowCurrentLine)
2535 Threads[0].printCurrentLine = true;
2537 // Should we stop the search?
2541 bool overTime = t > AbsoluteMaxSearchTime
2542 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2543 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2544 && t > 6*(MaxSearchTime + ExtraSearchTime));
2546 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2547 || (ExactMaxTime && t >= ExactMaxTime)
2548 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2553 // ponderhit() is called when the program is pondering (i.e. thinking while
2554 // it's the opponent's turn to move) in order to let the engine know that
2555 // it correctly predicted the opponent's move.
2559 int t = current_search_time();
2560 PonderSearch = false;
2561 if (Iteration >= 3 &&
2562 (!InfiniteSearch && (StopOnPonderhit ||
2563 t > AbsoluteMaxSearchTime ||
2564 (RootMoveNumber == 1 &&
2565 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2566 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2567 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2572 // print_current_line() prints the current line of search for a given
2573 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2575 void print_current_line(SearchStack ss[], int ply, int threadID) {
2577 assert(ply >= 0 && ply < PLY_MAX);
2578 assert(threadID >= 0 && threadID < ActiveThreads);
2580 if (!Threads[threadID].idle)
2583 std::cout << "info currline " << (threadID + 1);
2584 for (int p = 0; p < ply; p++)
2585 std::cout << " " << ss[p].currentMove;
2587 std::cout << std::endl;
2588 lock_release(&IOLock);
2590 Threads[threadID].printCurrentLine = false;
2591 if (threadID + 1 < ActiveThreads)
2592 Threads[threadID + 1].printCurrentLine = true;
2596 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2597 // while the program is pondering. The point is to work around a wrinkle in
2598 // the UCI protocol: When pondering, the engine is not allowed to give a
2599 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2600 // We simply wait here until one of these commands is sent, and return,
2601 // after which the bestmove and pondermove will be printed (in id_loop()).
2603 void wait_for_stop_or_ponderhit() {
2605 std::string command;
2609 if (!std::getline(std::cin, command))
2612 if (command == "quit")
2617 else if (command == "ponderhit" || command == "stop")
2623 // idle_loop() is where the threads are parked when they have no work to do.
2624 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2625 // object for which the current thread is the master.
2627 void idle_loop(int threadID, SplitPoint* waitSp) {
2628 assert(threadID >= 0 && threadID < THREAD_MAX);
2630 Threads[threadID].running = true;
2633 if(AllThreadsShouldExit && threadID != 0)
2636 // If we are not thinking, wait for a condition to be signaled instead
2637 // of wasting CPU time polling for work:
2638 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2639 #if !defined(_MSC_VER)
2640 pthread_mutex_lock(&WaitLock);
2641 if(Idle || threadID >= ActiveThreads)
2642 pthread_cond_wait(&WaitCond, &WaitLock);
2643 pthread_mutex_unlock(&WaitLock);
2645 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2649 // If this thread has been assigned work, launch a search
2650 if(Threads[threadID].workIsWaiting) {
2651 Threads[threadID].workIsWaiting = false;
2652 if(Threads[threadID].splitPoint->pvNode)
2653 sp_search_pv(Threads[threadID].splitPoint, threadID);
2655 sp_search(Threads[threadID].splitPoint, threadID);
2656 Threads[threadID].idle = true;
2659 // If this thread is the master of a split point and all threads have
2660 // finished their work at this split point, return from the idle loop.
2661 if(waitSp != NULL && waitSp->cpus == 0)
2665 Threads[threadID].running = false;
2669 // init_split_point_stack() is called during program initialization, and
2670 // initializes all split point objects.
2672 void init_split_point_stack() {
2673 for(int i = 0; i < THREAD_MAX; i++)
2674 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2675 SplitPointStack[i][j].parent = NULL;
2676 lock_init(&(SplitPointStack[i][j].lock), NULL);
2681 // destroy_split_point_stack() is called when the program exits, and
2682 // destroys all locks in the precomputed split point objects.
2684 void destroy_split_point_stack() {
2685 for(int i = 0; i < THREAD_MAX; i++)
2686 for(int j = 0; j < MaxActiveSplitPoints; j++)
2687 lock_destroy(&(SplitPointStack[i][j].lock));
2691 // thread_should_stop() checks whether the thread with a given threadID has
2692 // been asked to stop, directly or indirectly. This can happen if a beta
2693 // cutoff has occured in thre thread's currently active split point, or in
2694 // some ancestor of the current split point.
2696 bool thread_should_stop(int threadID) {
2697 assert(threadID >= 0 && threadID < ActiveThreads);
2701 if(Threads[threadID].stop)
2703 if(ActiveThreads <= 2)
2705 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2707 Threads[threadID].stop = true;
2714 // thread_is_available() checks whether the thread with threadID "slave" is
2715 // available to help the thread with threadID "master" at a split point. An
2716 // obvious requirement is that "slave" must be idle. With more than two
2717 // threads, this is not by itself sufficient: If "slave" is the master of
2718 // some active split point, it is only available as a slave to the other
2719 // threads which are busy searching the split point at the top of "slave"'s
2720 // split point stack (the "helpful master concept" in YBWC terminology).
2722 bool thread_is_available(int slave, int master) {
2723 assert(slave >= 0 && slave < ActiveThreads);
2724 assert(master >= 0 && master < ActiveThreads);
2725 assert(ActiveThreads > 1);
2727 if(!Threads[slave].idle || slave == master)
2730 if(Threads[slave].activeSplitPoints == 0)
2731 // No active split points means that the thread is available as a slave
2732 // for any other thread.
2735 if(ActiveThreads == 2)
2738 // Apply the "helpful master" concept if possible.
2739 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2746 // idle_thread_exists() tries to find an idle thread which is available as
2747 // a slave for the thread with threadID "master".
2749 bool idle_thread_exists(int master) {
2750 assert(master >= 0 && master < ActiveThreads);
2751 assert(ActiveThreads > 1);
2753 for(int i = 0; i < ActiveThreads; i++)
2754 if(thread_is_available(i, master))
2760 // split() does the actual work of distributing the work at a node between
2761 // several threads at PV nodes. If it does not succeed in splitting the
2762 // node (because no idle threads are available, or because we have no unused
2763 // split point objects), the function immediately returns false. If
2764 // splitting is possible, a SplitPoint object is initialized with all the
2765 // data that must be copied to the helper threads (the current position and
2766 // search stack, alpha, beta, the search depth, etc.), and we tell our
2767 // helper threads that they have been assigned work. This will cause them
2768 // to instantly leave their idle loops and call sp_search_pv(). When all
2769 // threads have returned from sp_search_pv (or, equivalently, when
2770 // splitPoint->cpus becomes 0), split() returns true.
2772 bool split(const Position& p, SearchStack* sstck, int ply,
2773 Value* alpha, Value* beta, Value* bestValue, Depth depth, int* moves,
2774 MovePicker* mp, Bitboard dcCandidates, int master, bool pvNode) {
2777 assert(sstck != NULL);
2778 assert(ply >= 0 && ply < PLY_MAX);
2779 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2780 assert(!pvNode || *alpha < *beta);
2781 assert(*beta <= VALUE_INFINITE);
2782 assert(depth > Depth(0));
2783 assert(master >= 0 && master < ActiveThreads);
2784 assert(ActiveThreads > 1);
2786 SplitPoint* splitPoint;
2791 // If no other thread is available to help us, or if we have too many
2792 // active split points, don't split.
2793 if(!idle_thread_exists(master) ||
2794 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2795 lock_release(&MPLock);
2799 // Pick the next available split point object from the split point stack
2800 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2801 Threads[master].activeSplitPoints++;
2803 // Initialize the split point object
2804 splitPoint->parent = Threads[master].splitPoint;
2805 splitPoint->finished = false;
2806 splitPoint->ply = ply;
2807 splitPoint->depth = depth;
2808 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2809 splitPoint->beta = *beta;
2810 splitPoint->pvNode = pvNode;
2811 splitPoint->dcCandidates = dcCandidates;
2812 splitPoint->bestValue = *bestValue;
2813 splitPoint->master = master;
2814 splitPoint->mp = mp;
2815 splitPoint->moves = *moves;
2816 splitPoint->cpus = 1;
2817 splitPoint->pos.copy(p);
2818 splitPoint->parentSstack = sstck;
2819 for(i = 0; i < ActiveThreads; i++)
2820 splitPoint->slaves[i] = 0;
2822 // Copy the current position and the search stack to the master thread
2823 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2824 Threads[master].splitPoint = splitPoint;
2826 // Make copies of the current position and search stack for each thread
2827 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2829 if(thread_is_available(i, master)) {
2830 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2831 Threads[i].splitPoint = splitPoint;
2832 splitPoint->slaves[i] = 1;
2836 // Tell the threads that they have work to do. This will make them leave
2838 for(i = 0; i < ActiveThreads; i++)
2839 if(i == master || splitPoint->slaves[i]) {
2840 Threads[i].workIsWaiting = true;
2841 Threads[i].idle = false;
2842 Threads[i].stop = false;
2845 lock_release(&MPLock);
2847 // Everything is set up. The master thread enters the idle loop, from
2848 // which it will instantly launch a search, because its workIsWaiting
2849 // slot is 'true'. We send the split point as a second parameter to the
2850 // idle loop, which means that the main thread will return from the idle
2851 // loop when all threads have finished their work at this split point
2852 // (i.e. when // splitPoint->cpus == 0).
2853 idle_loop(master, splitPoint);
2855 // We have returned from the idle loop, which means that all threads are
2856 // finished. Update alpha, beta and bestvalue, and return.
2858 if(pvNode) *alpha = splitPoint->alpha;
2859 *beta = splitPoint->beta;
2860 *bestValue = splitPoint->bestValue;
2861 Threads[master].stop = false;
2862 Threads[master].idle = false;
2863 Threads[master].activeSplitPoints--;
2864 Threads[master].splitPoint = splitPoint->parent;
2865 lock_release(&MPLock);
2871 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2872 // to start a new search from the root.
2874 void wake_sleeping_threads() {
2875 if(ActiveThreads > 1) {
2876 for(int i = 1; i < ActiveThreads; i++) {
2877 Threads[i].idle = true;
2878 Threads[i].workIsWaiting = false;
2880 #if !defined(_MSC_VER)
2881 pthread_mutex_lock(&WaitLock);
2882 pthread_cond_broadcast(&WaitCond);
2883 pthread_mutex_unlock(&WaitLock);
2885 for(int i = 1; i < THREAD_MAX; i++)
2886 SetEvent(SitIdleEvent[i]);
2892 // init_thread() is the function which is called when a new thread is
2893 // launched. It simply calls the idle_loop() function with the supplied
2894 // threadID. There are two versions of this function; one for POSIX threads
2895 // and one for Windows threads.
2897 #if !defined(_MSC_VER)
2899 void *init_thread(void *threadID) {
2900 idle_loop(*(int *)threadID, NULL);
2906 DWORD WINAPI init_thread(LPVOID threadID) {
2907 idle_loop(*(int *)threadID, NULL);