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, moveIsCapture, 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 - 2 // Remove -2 and decrease LMRPVMoves instead ?
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);
931 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);
1129 TT.prefetch(pos.get_key());
1131 if (moveCount == 1) // The first move in list is the PV
1132 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1135 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1136 // if the move fails high will be re-searched at full depth.
1137 if ( depth >= 3*OnePly
1138 && moveCount >= LMRPVMoves
1141 && !move_is_promotion(move)
1142 && !move_is_castle(move)
1143 && !move_is_killer(move, ss[ply]))
1145 ss[ply].reduction = OnePly;
1146 value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
1149 value = alpha + 1; // Just to trigger next condition
1151 if (value > alpha) // Go with full depth non-pv search
1153 ss[ply].reduction = Depth(0);
1154 value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
1155 if (value > alpha && value < beta)
1157 // When the search fails high at ply 1 while searching the first
1158 // move at the root, set the flag failHighPly1. This is used for
1159 // time managment: We don't want to stop the search early in
1160 // such cases, because resolving the fail high at ply 1 could
1161 // result in a big drop in score at the root.
1162 if (ply == 1 && RootMoveNumber == 1)
1163 Threads[threadID].failHighPly1 = true;
1165 // A fail high occurred. Re-search at full window (pv search)
1166 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
1167 Threads[threadID].failHighPly1 = false;
1171 pos.undo_move(move);
1173 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1176 if (value > bestValue)
1183 if (value == value_mate_in(ply + 1))
1184 ss[ply].mateKiller = move;
1186 // If we are at ply 1, and we are searching the first root move at
1187 // ply 0, set the 'Problem' variable if the score has dropped a lot
1188 // (from the computer's point of view) since the previous iteration.
1191 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1196 if ( ActiveThreads > 1
1198 && depth >= MinimumSplitDepth
1200 && idle_thread_exists(threadID)
1202 && !thread_should_stop(threadID)
1203 && split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
1204 &moveCount, &mp, dcCandidates, threadID, true))
1208 // All legal moves have been searched. A special case: If there were
1209 // no legal moves, it must be mate or stalemate.
1211 return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
1213 // If the search is not aborted, update the transposition table,
1214 // history counters, and killer moves.
1215 if (AbortSearch || thread_should_stop(threadID))
1218 if (bestValue <= oldAlpha)
1219 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1221 else if (bestValue >= beta)
1223 BetaCounter.add(pos.side_to_move(), depth, threadID);
1224 Move m = ss[ply].pv[ply];
1225 if (ok_to_history(pos, m)) // Only non capture moves are considered
1227 update_history(pos, m, depth, movesSearched, moveCount);
1228 update_killers(m, ss[ply]);
1230 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1233 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
1239 // search() is the search function for zero-width nodes.
1241 Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
1242 int ply, bool allowNullmove, int threadID) {
1244 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1245 assert(ply >= 0 && ply < PLY_MAX);
1246 assert(threadID >= 0 && threadID < ActiveThreads);
1249 return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1251 // Initialize, and make an early exit in case of an aborted search,
1252 // an instant draw, maximum ply reached, etc.
1253 init_node(pos, ss, ply, threadID);
1255 // After init_node() that calls poll()
1256 if (AbortSearch || thread_should_stop(threadID))
1264 if (ply >= PLY_MAX - 1)
1265 return evaluate(pos, ei, threadID);
1267 // Mate distance pruning
1268 if (value_mated_in(ply) >= beta)
1271 if (value_mate_in(ply + 1) < beta)
1274 // Transposition table lookup
1275 const TTEntry* tte = TT.retrieve(pos.get_key());
1276 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1278 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1280 ss[ply].currentMove = ttMove; // can be MOVE_NONE
1281 return value_from_tt(tte->value(), ply);
1284 Value approximateEval = quick_evaluate(pos);
1285 bool mateThreat = false;
1286 bool isCheck = pos.is_check();
1292 && !value_is_mate(beta)
1293 && ok_to_do_nullmove(pos)
1294 && approximateEval >= beta - NullMoveMargin)
1296 ss[ply].currentMove = MOVE_NULL;
1299 pos.do_null_move(st);
1300 TT.prefetch(pos.get_key());
1302 int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
1304 Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
1306 pos.undo_null_move();
1308 if (nullValue >= beta)
1310 if (depth < 6 * OnePly)
1313 // Do zugzwang verification search
1314 Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
1318 // The null move failed low, which means that we may be faced with
1319 // some kind of threat. If the previous move was reduced, check if
1320 // the move that refuted the null move was somehow connected to the
1321 // move which was reduced. If a connection is found, return a fail
1322 // low score (which will cause the reduced move to fail high in the
1323 // parent node, which will trigger a re-search with full depth).
1324 if (nullValue == value_mated_in(ply + 2))
1327 ss[ply].threatMove = ss[ply + 1].currentMove;
1328 if ( depth < ThreatDepth
1329 && ss[ply - 1].reduction
1330 && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
1334 // Null move search not allowed, try razoring
1335 else if ( !value_is_mate(beta)
1336 && depth < RazorDepth
1337 && approximateEval < beta - RazorApprMargins[int(depth) - 2]
1338 && ss[ply - 1].currentMove != MOVE_NULL
1339 && ttMove == MOVE_NONE
1340 && !pos.has_pawn_on_7th(pos.side_to_move()))
1342 Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
1343 if (v < beta - RazorMargins[int(depth) - 2])
1347 // Go with internal iterative deepening if we don't have a TT move
1348 if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
1349 evaluate(pos, ei, threadID) >= beta - IIDMargin)
1351 search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
1352 ttMove = ss[ply].pv[ply];
1355 // Initialize a MovePicker object for the current position, and prepare
1356 // to search all moves.
1357 MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
1359 Move move, movesSearched[256];
1361 Value value, bestValue = -VALUE_INFINITE;
1362 Bitboard dcCandidates = mp.discovered_check_candidates();
1363 Value futilityValue = VALUE_NONE;
1364 bool useFutilityPruning = depth < SelectiveDepth
1367 // Loop through all legal moves until no moves remain or a beta cutoff
1369 while ( bestValue < beta
1370 && (move = mp.get_next_move()) != MOVE_NONE
1371 && !thread_should_stop(threadID))
1373 assert(move_is_ok(move));
1375 bool singleReply = (isCheck && mp.number_of_moves() == 1);
1376 bool moveIsCheck = pos.move_is_check(move, dcCandidates);
1377 bool moveIsCapture = pos.move_is_capture(move);
1379 movesSearched[moveCount++] = ss[ply].currentMove = move;
1381 // Decide the new search depth
1383 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
1384 Depth newDepth = depth - OnePly + ext;
1387 if ( useFutilityPruning
1390 && !move_is_promotion(move))
1392 // History pruning. See ok_to_prune() definition
1393 if ( moveCount >= 2 + int(depth)
1394 && ok_to_prune(pos, move, ss[ply].threatMove, depth))
1397 // Value based pruning
1398 if (approximateEval < beta)
1400 if (futilityValue == VALUE_NONE)
1401 futilityValue = evaluate(pos, ei, threadID)
1402 + FutilityMargins[int(depth) - 2];
1404 if (futilityValue < beta)
1406 if (futilityValue > bestValue)
1407 bestValue = futilityValue;
1413 // Make and search the move
1415 pos.do_move(move, st, dcCandidates);
1416 TT.prefetch(pos.get_key());
1418 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1419 // if the move fails high will be re-searched at full depth.
1420 if ( depth >= 3*OnePly
1421 && moveCount >= LMRNonPVMoves
1424 && !move_is_promotion(move)
1425 && !move_is_castle(move)
1426 && !move_is_killer(move, ss[ply]))
1428 ss[ply].reduction = OnePly;
1429 value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
1432 value = beta; // Just to trigger next condition
1434 if (value >= beta) // Go with full depth non-pv search
1436 ss[ply].reduction = Depth(0);
1437 value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
1439 pos.undo_move(move);
1441 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1444 if (value > bestValue)
1450 if (value == value_mate_in(ply + 1))
1451 ss[ply].mateKiller = move;
1455 if ( ActiveThreads > 1
1457 && depth >= MinimumSplitDepth
1459 && idle_thread_exists(threadID)
1461 && !thread_should_stop(threadID)
1462 && split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
1463 &mp, dcCandidates, threadID, false))
1467 // All legal moves have been searched. A special case: If there were
1468 // no legal moves, it must be mate or stalemate.
1470 return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
1472 // If the search is not aborted, update the transposition table,
1473 // history counters, and killer moves.
1474 if (AbortSearch || thread_should_stop(threadID))
1477 if (bestValue < beta)
1478 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
1481 BetaCounter.add(pos.side_to_move(), depth, threadID);
1482 Move m = ss[ply].pv[ply];
1483 if (ok_to_history(pos, m)) // Only non capture moves are considered
1485 update_history(pos, m, depth, movesSearched, moveCount);
1486 update_killers(m, ss[ply]);
1488 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
1491 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1497 // qsearch() is the quiescence search function, which is called by the main
1498 // search function when the remaining depth is zero (or, to be more precise,
1499 // less than OnePly).
1501 Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
1502 Depth depth, int ply, int threadID) {
1504 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1505 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1507 assert(ply >= 0 && ply < PLY_MAX);
1508 assert(threadID >= 0 && threadID < ActiveThreads);
1510 // Initialize, and make an early exit in case of an aborted search,
1511 // an instant draw, maximum ply reached, etc.
1512 init_node(pos, ss, ply, threadID);
1514 // After init_node() that calls poll()
1515 if (AbortSearch || thread_should_stop(threadID))
1521 // Transposition table lookup, only when not in PV
1522 TTEntry* tte = NULL;
1523 bool pvNode = (beta - alpha != 1);
1526 tte = TT.retrieve(pos.get_key());
1527 if (tte && ok_to_use_TT(tte, depth, beta, ply))
1529 assert(tte->type() != VALUE_TYPE_EVAL);
1531 return value_from_tt(tte->value(), ply);
1534 Move ttMove = (tte ? tte->move() : MOVE_NONE);
1536 // Evaluate the position statically
1539 bool isCheck = pos.is_check();
1540 ei.futilityMargin = Value(0); // Manually initialize futilityMargin
1543 staticValue = -VALUE_INFINITE;
1545 else if (tte && tte->type() == VALUE_TYPE_EVAL)
1547 // Use the cached evaluation score if possible
1548 assert(ei.futilityMargin == Value(0));
1550 staticValue = tte->value();
1553 staticValue = evaluate(pos, ei, threadID);
1555 if (ply == PLY_MAX - 1)
1556 return evaluate(pos, ei, threadID);
1558 // Initialize "stand pat score", and return it immediately if it is
1560 Value bestValue = staticValue;
1562 if (bestValue >= beta)
1564 // Store the score to avoid a future costly evaluation() call
1565 if (!isCheck && !tte && ei.futilityMargin == 0)
1566 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EVAL, Depth(-127*OnePly), MOVE_NONE);
1571 if (bestValue > alpha)
1574 // Initialize a MovePicker object for the current position, and prepare
1575 // to search the moves. Because the depth is <= 0 here, only captures,
1576 // queen promotions and checks (only if depth == 0) will be generated.
1577 MovePicker mp = MovePicker(pos, ttMove, depth, H);
1580 Bitboard dcCandidates = mp.discovered_check_candidates();
1581 Color us = pos.side_to_move();
1582 bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
1584 // Loop through the moves until no moves remain or a beta cutoff
1586 while ( alpha < beta
1587 && (move = mp.get_next_move()) != MOVE_NONE)
1589 assert(move_is_ok(move));
1592 ss[ply].currentMove = move;
1598 && !move_is_promotion(move)
1599 && !pos.move_is_check(move, dcCandidates)
1600 && !pos.move_is_passed_pawn_push(move))
1602 Value futilityValue = staticValue
1603 + Max(pos.midgame_value_of_piece_on(move_to(move)),
1604 pos.endgame_value_of_piece_on(move_to(move)))
1605 + (move_is_ep(move) ? PawnValueEndgame : Value(0))
1607 + ei.futilityMargin;
1609 if (futilityValue < alpha)
1611 if (futilityValue > bestValue)
1612 bestValue = futilityValue;
1617 // Don't search captures and checks with negative SEE values
1619 && !move_is_promotion(move)
1620 && pos.see_sign(move) < 0)
1623 // Make and search the move.
1625 pos.do_move(move, st, dcCandidates);
1626 TT.prefetch(pos.get_key());
1627 Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
1628 pos.undo_move(move);
1630 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1633 if (value > bestValue)
1644 // All legal moves have been searched. A special case: If we're in check
1645 // and no legal moves were found, it is checkmate.
1646 if (pos.is_check() && moveCount == 0) // Mate!
1647 return value_mated_in(ply);
1649 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1651 // Update transposition table
1652 Move m = ss[ply].pv[ply];
1655 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1656 if (bestValue < beta)
1657 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE);
1659 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
1662 // Update killers only for good check moves
1663 if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
1664 update_killers(m, ss[ply]);
1670 // sp_search() is used to search from a split point. This function is called
1671 // by each thread working at the split point. It is similar to the normal
1672 // search() function, but simpler. Because we have already probed the hash
1673 // table, done a null move search, and searched the first move before
1674 // splitting, we don't have to repeat all this work in sp_search(). We
1675 // also don't need to store anything to the hash table here: This is taken
1676 // care of after we return from the split point.
1678 void sp_search(SplitPoint* sp, int threadID) {
1680 assert(threadID >= 0 && threadID < ActiveThreads);
1681 assert(ActiveThreads > 1);
1683 Position pos = Position(sp->pos);
1684 SearchStack* ss = sp->sstack[threadID];
1687 bool isCheck = pos.is_check();
1688 bool useFutilityPruning = sp->depth < SelectiveDepth
1691 while ( sp->bestValue < sp->beta
1692 && !thread_should_stop(threadID)
1693 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1695 assert(move_is_ok(move));
1697 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1698 bool moveIsCapture = pos.move_is_capture(move);
1700 lock_grab(&(sp->lock));
1701 int moveCount = ++sp->moves;
1702 lock_release(&(sp->lock));
1704 ss[sp->ply].currentMove = move;
1706 // Decide the new search depth.
1708 Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
1709 Depth newDepth = sp->depth - OnePly + ext;
1712 if ( useFutilityPruning
1715 && !move_is_promotion(move)
1716 && moveCount >= 2 + int(sp->depth)
1717 && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
1720 // Make and search the move.
1722 pos.do_move(move, st, sp->dcCandidates);
1724 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1725 // if the move fails high will be re-searched at full depth.
1727 && moveCount >= LMRNonPVMoves
1729 && !move_is_promotion(move)
1730 && !move_is_castle(move)
1731 && !move_is_killer(move, ss[sp->ply]))
1733 ss[sp->ply].reduction = OnePly;
1734 value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
1737 value = sp->beta; // Just to trigger next condition
1739 if (value >= sp->beta) // Go with full depth non-pv search
1741 ss[sp->ply].reduction = Depth(0);
1742 value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
1744 pos.undo_move(move);
1746 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1748 if (thread_should_stop(threadID))
1752 lock_grab(&(sp->lock));
1753 if (value > sp->bestValue && !thread_should_stop(threadID))
1755 sp->bestValue = value;
1756 if (sp->bestValue >= sp->beta)
1758 sp_update_pv(sp->parentSstack, ss, sp->ply);
1759 for (int i = 0; i < ActiveThreads; i++)
1760 if (i != threadID && (i == sp->master || sp->slaves[i]))
1761 Threads[i].stop = true;
1763 sp->finished = true;
1766 lock_release(&(sp->lock));
1769 lock_grab(&(sp->lock));
1771 // If this is the master thread and we have been asked to stop because of
1772 // a beta cutoff higher up in the tree, stop all slave threads.
1773 if (sp->master == threadID && thread_should_stop(threadID))
1774 for (int i = 0; i < ActiveThreads; i++)
1776 Threads[i].stop = true;
1779 sp->slaves[threadID] = 0;
1781 lock_release(&(sp->lock));
1785 // sp_search_pv() is used to search from a PV split point. This function
1786 // is called by each thread working at the split point. It is similar to
1787 // the normal search_pv() function, but simpler. Because we have already
1788 // probed the hash table and searched the first move before splitting, we
1789 // don't have to repeat all this work in sp_search_pv(). We also don't
1790 // need to store anything to the hash table here: This is taken care of
1791 // after we return from the split point.
1793 void sp_search_pv(SplitPoint* sp, int threadID) {
1795 assert(threadID >= 0 && threadID < ActiveThreads);
1796 assert(ActiveThreads > 1);
1798 Position pos = Position(sp->pos);
1799 SearchStack* ss = sp->sstack[threadID];
1803 while ( sp->alpha < sp->beta
1804 && !thread_should_stop(threadID)
1805 && (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
1807 bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
1808 bool moveIsCapture = pos.move_is_capture(move);
1810 assert(move_is_ok(move));
1812 lock_grab(&(sp->lock));
1813 int moveCount = ++sp->moves;
1814 lock_release(&(sp->lock));
1816 ss[sp->ply].currentMove = move;
1818 // Decide the new search depth.
1820 Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
1821 Depth newDepth = sp->depth - OnePly + ext;
1823 // Make and search the move.
1825 pos.do_move(move, st, sp->dcCandidates);
1827 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1828 // if the move fails high will be re-searched at full depth.
1830 && moveCount >= LMRPVMoves
1832 && !move_is_promotion(move)
1833 && !move_is_castle(move)
1834 && !move_is_killer(move, ss[sp->ply]))
1836 ss[sp->ply].reduction = OnePly;
1837 value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
1840 value = sp->alpha + 1; // Just to trigger next condition
1842 if (value > sp->alpha) // Go with full depth non-pv search
1844 ss[sp->ply].reduction = Depth(0);
1845 value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
1847 if (value > sp->alpha && value < sp->beta)
1849 // When the search fails high at ply 1 while searching the first
1850 // move at the root, set the flag failHighPly1. This is used for
1851 // time managment: We don't want to stop the search early in
1852 // such cases, because resolving the fail high at ply 1 could
1853 // result in a big drop in score at the root.
1854 if (sp->ply == 1 && RootMoveNumber == 1)
1855 Threads[threadID].failHighPly1 = true;
1857 value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
1858 Threads[threadID].failHighPly1 = false;
1861 pos.undo_move(move);
1863 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1865 if (thread_should_stop(threadID))
1869 lock_grab(&(sp->lock));
1870 if (value > sp->bestValue && !thread_should_stop(threadID))
1872 sp->bestValue = value;
1873 if (value > sp->alpha)
1876 sp_update_pv(sp->parentSstack, ss, sp->ply);
1877 if (value == value_mate_in(sp->ply + 1))
1878 ss[sp->ply].mateKiller = move;
1880 if (value >= sp->beta)
1882 for (int i = 0; i < ActiveThreads; i++)
1883 if (i != threadID && (i == sp->master || sp->slaves[i]))
1884 Threads[i].stop = true;
1886 sp->finished = true;
1889 // If we are at ply 1, and we are searching the first root move at
1890 // ply 0, set the 'Problem' variable if the score has dropped a lot
1891 // (from the computer's point of view) since the previous iteration.
1894 && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
1897 lock_release(&(sp->lock));
1900 lock_grab(&(sp->lock));
1902 // If this is the master thread and we have been asked to stop because of
1903 // a beta cutoff higher up in the tree, stop all slave threads.
1904 if (sp->master == threadID && thread_should_stop(threadID))
1905 for (int i = 0; i < ActiveThreads; i++)
1907 Threads[i].stop = true;
1910 sp->slaves[threadID] = 0;
1912 lock_release(&(sp->lock));
1915 /// The BetaCounterType class
1917 BetaCounterType::BetaCounterType() { clear(); }
1919 void BetaCounterType::clear() {
1921 for (int i = 0; i < THREAD_MAX; i++)
1922 Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
1925 void BetaCounterType::add(Color us, Depth d, int threadID) {
1927 // Weighted count based on depth
1928 Threads[threadID].betaCutOffs[us] += unsigned(d);
1931 void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
1934 for (int i = 0; i < THREAD_MAX; i++)
1936 our += Threads[i].betaCutOffs[us];
1937 their += Threads[i].betaCutOffs[opposite_color(us)];
1942 /// The RootMove class
1946 RootMove::RootMove() {
1947 nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
1950 // RootMove::operator<() is the comparison function used when
1951 // sorting the moves. A move m1 is considered to be better
1952 // than a move m2 if it has a higher score, or if the moves
1953 // have equal score but m1 has the higher node count.
1955 bool RootMove::operator<(const RootMove& m) {
1957 if (score != m.score)
1958 return (score < m.score);
1960 return theirBeta <= m.theirBeta;
1963 /// The RootMoveList class
1967 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
1969 MoveStack mlist[MaxRootMoves];
1970 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
1972 // Generate all legal moves
1973 int lm_count = generate_legal_moves(pos, mlist);
1975 // Add each move to the moves[] array
1976 for (int i = 0; i < lm_count; i++)
1978 bool includeMove = includeAllMoves;
1980 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
1981 includeMove = (searchMoves[k] == mlist[i].move);
1986 // Find a quick score for the move
1988 SearchStack ss[PLY_MAX_PLUS_2];
1990 moves[count].move = mlist[i].move;
1991 pos.do_move(moves[count].move, st);
1992 moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
1993 pos.undo_move(moves[count].move);
1994 moves[count].pv[0] = moves[count].move;
1995 moves[count].pv[1] = MOVE_NONE; // FIXME
2002 // Simple accessor methods for the RootMoveList class
2004 inline Move RootMoveList::get_move(int moveNum) const {
2005 return moves[moveNum].move;
2008 inline Value RootMoveList::get_move_score(int moveNum) const {
2009 return moves[moveNum].score;
2012 inline void RootMoveList::set_move_score(int moveNum, Value score) {
2013 moves[moveNum].score = score;
2016 inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2017 moves[moveNum].nodes = nodes;
2018 moves[moveNum].cumulativeNodes += nodes;
2021 inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2022 moves[moveNum].ourBeta = our;
2023 moves[moveNum].theirBeta = their;
2026 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2028 for(j = 0; pv[j] != MOVE_NONE; j++)
2029 moves[moveNum].pv[j] = pv[j];
2030 moves[moveNum].pv[j] = MOVE_NONE;
2033 inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
2034 return moves[moveNum].pv[i];
2037 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
2038 return moves[moveNum].cumulativeNodes;
2041 inline int RootMoveList::move_count() const {
2046 // RootMoveList::scan_for_easy_move() is called at the end of the first
2047 // iteration, and is used to detect an "easy move", i.e. a move which appears
2048 // to be much bester than all the rest. If an easy move is found, the move
2049 // is returned, otherwise the function returns MOVE_NONE. It is very
2050 // important that this function is called at the right moment: The code
2051 // assumes that the first iteration has been completed and the moves have
2052 // been sorted. This is done in RootMoveList c'tor.
2054 Move RootMoveList::scan_for_easy_move() const {
2061 // moves are sorted so just consider the best and the second one
2062 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
2068 // RootMoveList::sort() sorts the root move list at the beginning of a new
2071 inline void RootMoveList::sort() {
2073 sort_multipv(count - 1); // all items
2077 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2078 // list by their scores and depths. It is used to order the different PVs
2079 // correctly in MultiPV mode.
2081 void RootMoveList::sort_multipv(int n) {
2083 for (int i = 1; i <= n; i++)
2085 RootMove rm = moves[i];
2087 for (j = i; j > 0 && moves[j-1] < rm; j--)
2088 moves[j] = moves[j-1];
2094 // init_node() is called at the beginning of all the search functions
2095 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2096 // stack object corresponding to the current node. Once every
2097 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2098 // for user input and checks whether it is time to stop the search.
2100 void init_node(const Position& pos, SearchStack ss[], int ply, int threadID) {
2102 assert(ply >= 0 && ply < PLY_MAX);
2103 assert(threadID >= 0 && threadID < ActiveThreads);
2105 if (Slowdown && Iteration >= 3)
2108 Threads[threadID].nodes++;
2113 if (NodesSincePoll >= NodesBetweenPolls)
2120 ss[ply+2].initKillers();
2122 if (Threads[threadID].printCurrentLine)
2123 print_current_line(ss, ply, threadID);
2127 // update_pv() is called whenever a search returns a value > alpha. It
2128 // updates the PV in the SearchStack object corresponding to the current
2131 void update_pv(SearchStack ss[], int ply) {
2132 assert(ply >= 0 && ply < PLY_MAX);
2134 ss[ply].pv[ply] = ss[ply].currentMove;
2136 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2137 ss[ply].pv[p] = ss[ply+1].pv[p];
2138 ss[ply].pv[p] = MOVE_NONE;
2142 // sp_update_pv() is a variant of update_pv for use at split points. The
2143 // difference between the two functions is that sp_update_pv also updates
2144 // the PV at the parent node.
2146 void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
2147 assert(ply >= 0 && ply < PLY_MAX);
2149 ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
2151 for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
2152 ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
2153 ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
2157 // connected_moves() tests whether two moves are 'connected' in the sense
2158 // that the first move somehow made the second move possible (for instance
2159 // if the moving piece is the same in both moves). The first move is
2160 // assumed to be the move that was made to reach the current position, while
2161 // the second move is assumed to be a move from the current position.
2163 bool connected_moves(const Position& pos, Move m1, Move m2) {
2164 Square f1, t1, f2, t2;
2166 assert(move_is_ok(m1));
2167 assert(move_is_ok(m2));
2169 if (m2 == MOVE_NONE)
2172 // Case 1: The moving piece is the same in both moves
2178 // Case 2: The destination square for m2 was vacated by m1
2184 // Case 3: Moving through the vacated square
2185 if ( piece_is_slider(pos.piece_on(f2))
2186 && bit_is_set(squares_between(f2, t2), f1))
2189 // Case 4: The destination square for m2 is attacked by the moving piece in m1
2190 if (pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
2193 // Case 5: Discovered check, checking piece is the piece moved in m1
2194 if ( piece_is_slider(pos.piece_on(t1))
2195 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
2196 && !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())), t2))
2198 Bitboard occ = pos.occupied_squares();
2199 Color us = pos.side_to_move();
2200 Square ksq = pos.king_square(us);
2201 clear_bit(&occ, f2);
2202 if (pos.type_of_piece_on(t1) == BISHOP)
2204 if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
2207 else if (pos.type_of_piece_on(t1) == ROOK)
2209 if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
2214 assert(pos.type_of_piece_on(t1) == QUEEN);
2215 if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
2223 // value_is_mate() checks if the given value is a mate one
2224 // eventually compensated for the ply.
2226 bool value_is_mate(Value value) {
2228 assert(abs(value) <= VALUE_INFINITE);
2230 return value <= value_mated_in(PLY_MAX)
2231 || value >= value_mate_in(PLY_MAX);
2235 // move_is_killer() checks if the given move is among the
2236 // killer moves of that ply.
2238 bool move_is_killer(Move m, const SearchStack& ss) {
2240 const Move* k = ss.killers;
2241 for (int i = 0; i < KILLER_MAX; i++, k++)
2249 // extension() decides whether a move should be searched with normal depth,
2250 // or with extended depth. Certain classes of moves (checking moves, in
2251 // particular) are searched with bigger depth than ordinary moves and in
2252 // any case are marked as 'dangerous'. Note that also if a move is not
2253 // extended, as example because the corresponding UCI option is set to zero,
2254 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2256 Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
2257 bool singleReply, bool mateThreat, bool* dangerous) {
2259 assert(m != MOVE_NONE);
2261 Depth result = Depth(0);
2262 *dangerous = check | singleReply | mateThreat;
2267 result += CheckExtension[pvNode];
2270 result += SingleReplyExtension[pvNode];
2273 result += MateThreatExtension[pvNode];
2276 if (pos.type_of_piece_on(move_from(m)) == PAWN)
2278 if (pos.move_is_pawn_push_to_7th(m))
2280 result += PawnPushTo7thExtension[pvNode];
2283 if (pos.move_is_passed_pawn_push(m))
2285 result += PassedPawnExtension[pvNode];
2291 && pos.type_of_piece_on(move_to(m)) != PAWN
2292 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
2293 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
2294 && !move_is_promotion(m)
2297 result += PawnEndgameExtension[pvNode];
2303 && pos.type_of_piece_on(move_to(m)) != PAWN
2304 && pos.see_sign(m) >= 0)
2310 return Min(result, OnePly);
2314 // ok_to_do_nullmove() looks at the current position and decides whether
2315 // doing a 'null move' should be allowed. In order to avoid zugzwang
2316 // problems, null moves are not allowed when the side to move has very
2317 // little material left. Currently, the test is a bit too simple: Null
2318 // moves are avoided only when the side to move has only pawns left. It's
2319 // probably a good idea to avoid null moves in at least some more
2320 // complicated endgames, e.g. KQ vs KR. FIXME
2322 bool ok_to_do_nullmove(const Position& pos) {
2324 return pos.non_pawn_material(pos.side_to_move()) != Value(0);
2328 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2329 // non-tactical moves late in the move list close to the leaves are
2330 // candidates for pruning.
2332 bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d) {
2334 assert(move_is_ok(m));
2335 assert(threat == MOVE_NONE || move_is_ok(threat));
2336 assert(!move_is_promotion(m));
2337 assert(!pos.move_is_check(m));
2338 assert(!pos.move_is_capture(m));
2339 assert(!pos.move_is_passed_pawn_push(m));
2340 assert(d >= OnePly);
2342 Square mfrom, mto, tfrom, tto;
2344 mfrom = move_from(m);
2346 tfrom = move_from(threat);
2347 tto = move_to(threat);
2349 // Case 1: Castling moves are never pruned
2350 if (move_is_castle(m))
2353 // Case 2: Don't prune moves which move the threatened piece
2354 if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
2357 // Case 3: If the threatened piece has value less than or equal to the
2358 // value of the threatening piece, don't prune move which defend it.
2359 if ( !PruneDefendingMoves
2360 && threat != MOVE_NONE
2361 && pos.move_is_capture(threat)
2362 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
2363 || pos.type_of_piece_on(tfrom) == KING)
2364 && pos.move_attacks_square(m, tto))
2367 // Case 4: Don't prune moves with good history
2368 if (!H.ok_to_prune(pos.piece_on(mfrom), mto, d))
2371 // Case 5: If the moving piece in the threatened move is a slider, don't
2372 // prune safe moves which block its ray.
2373 if ( !PruneBlockingMoves
2374 && threat != MOVE_NONE
2375 && piece_is_slider(pos.piece_on(tfrom))
2376 && bit_is_set(squares_between(tfrom, tto), mto)
2377 && pos.see_sign(m) >= 0)
2384 // ok_to_use_TT() returns true if a transposition table score
2385 // can be used at a given point in search.
2387 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
2389 Value v = value_from_tt(tte->value(), ply);
2391 return ( tte->depth() >= depth
2392 || v >= Max(value_mate_in(100), beta)
2393 || v < Min(value_mated_in(100), beta))
2395 && ( (is_lower_bound(tte->type()) && v >= beta)
2396 || (is_upper_bound(tte->type()) && v < beta));
2400 // ok_to_history() returns true if a move m can be stored
2401 // in history. Should be a non capturing move nor a promotion.
2403 bool ok_to_history(const Position& pos, Move m) {
2405 return !pos.move_is_capture(m) && !move_is_promotion(m);
2409 // update_history() registers a good move that produced a beta-cutoff
2410 // in history and marks as failures all the other moves of that ply.
2412 void update_history(const Position& pos, Move m, Depth depth,
2413 Move movesSearched[], int moveCount) {
2415 H.success(pos.piece_on(move_from(m)), move_to(m), depth);
2417 for (int i = 0; i < moveCount - 1; i++)
2419 assert(m != movesSearched[i]);
2420 if (ok_to_history(pos, movesSearched[i]))
2421 H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]));
2426 // update_killers() add a good move that produced a beta-cutoff
2427 // among the killer moves of that ply.
2429 void update_killers(Move m, SearchStack& ss) {
2431 if (m == ss.killers[0])
2434 for (int i = KILLER_MAX - 1; i > 0; i--)
2435 ss.killers[i] = ss.killers[i - 1];
2441 // slowdown() simply wastes CPU cycles doing nothing useful. It's used
2442 // in strength handicap mode.
2444 void slowdown(const Position &pos) {
2447 for (i = 0; i < n; i++) {
2448 Square s = Square(i&63);
2449 if (count_1s(pos.attacks_to(s)) > 63)
2450 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;
2455 // fail_high_ply_1() checks if some thread is currently resolving a fail
2456 // high at ply 1 at the node below the first root node. This information
2457 // is used for time managment.
2459 bool fail_high_ply_1() {
2461 for(int i = 0; i < ActiveThreads; i++)
2462 if (Threads[i].failHighPly1)
2469 // current_search_time() returns the number of milliseconds which have passed
2470 // since the beginning of the current search.
2472 int current_search_time() {
2473 return get_system_time() - SearchStartTime;
2477 // nps() computes the current nodes/second count.
2480 int t = current_search_time();
2481 return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
2485 // poll() performs two different functions: It polls for user input, and it
2486 // looks at the time consumed so far and decides if it's time to abort the
2491 static int lastInfoTime;
2492 int t = current_search_time();
2497 // We are line oriented, don't read single chars
2498 std::string command;
2499 if (!std::getline(std::cin, command))
2502 if (command == "quit")
2505 PonderSearch = false;
2509 else if (command == "stop")
2512 PonderSearch = false;
2514 else if (command == "ponderhit")
2517 // Print search information
2521 else if (lastInfoTime > t)
2522 // HACK: Must be a new search where we searched less than
2523 // NodesBetweenPolls nodes during the first second of search.
2526 else if (t - lastInfoTime >= 1000)
2533 if (dbg_show_hit_rate)
2534 dbg_print_hit_rate();
2536 std::cout << "info nodes " << nodes_searched() << " nps " << nps()
2537 << " time " << t << " hashfull " << TT.full() << std::endl;
2538 lock_release(&IOLock);
2539 if (ShowCurrentLine)
2540 Threads[0].printCurrentLine = true;
2542 // Should we stop the search?
2546 bool overTime = t > AbsoluteMaxSearchTime
2547 || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
2548 || ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
2549 && t > 6*(MaxSearchTime + ExtraSearchTime));
2551 if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
2552 || (ExactMaxTime && t >= ExactMaxTime)
2553 || (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
2558 // ponderhit() is called when the program is pondering (i.e. thinking while
2559 // it's the opponent's turn to move) in order to let the engine know that
2560 // it correctly predicted the opponent's move.
2564 int t = current_search_time();
2565 PonderSearch = false;
2566 if (Iteration >= 3 &&
2567 (!InfiniteSearch && (StopOnPonderhit ||
2568 t > AbsoluteMaxSearchTime ||
2569 (RootMoveNumber == 1 &&
2570 t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
2571 (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
2572 t > 6*(MaxSearchTime + ExtraSearchTime)))))
2577 // print_current_line() prints the current line of search for a given
2578 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2580 void print_current_line(SearchStack ss[], int ply, int threadID) {
2582 assert(ply >= 0 && ply < PLY_MAX);
2583 assert(threadID >= 0 && threadID < ActiveThreads);
2585 if (!Threads[threadID].idle)
2588 std::cout << "info currline " << (threadID + 1);
2589 for (int p = 0; p < ply; p++)
2590 std::cout << " " << ss[p].currentMove;
2592 std::cout << std::endl;
2593 lock_release(&IOLock);
2595 Threads[threadID].printCurrentLine = false;
2596 if (threadID + 1 < ActiveThreads)
2597 Threads[threadID + 1].printCurrentLine = true;
2601 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2602 // while the program is pondering. The point is to work around a wrinkle in
2603 // the UCI protocol: When pondering, the engine is not allowed to give a
2604 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2605 // We simply wait here until one of these commands is sent, and return,
2606 // after which the bestmove and pondermove will be printed (in id_loop()).
2608 void wait_for_stop_or_ponderhit() {
2610 std::string command;
2614 if (!std::getline(std::cin, command))
2617 if (command == "quit")
2622 else if (command == "ponderhit" || command == "stop")
2628 // idle_loop() is where the threads are parked when they have no work to do.
2629 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2630 // object for which the current thread is the master.
2632 void idle_loop(int threadID, SplitPoint* waitSp) {
2633 assert(threadID >= 0 && threadID < THREAD_MAX);
2635 Threads[threadID].running = true;
2638 if(AllThreadsShouldExit && threadID != 0)
2641 // If we are not thinking, wait for a condition to be signaled instead
2642 // of wasting CPU time polling for work:
2643 while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
2644 #if !defined(_MSC_VER)
2645 pthread_mutex_lock(&WaitLock);
2646 if(Idle || threadID >= ActiveThreads)
2647 pthread_cond_wait(&WaitCond, &WaitLock);
2648 pthread_mutex_unlock(&WaitLock);
2650 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2654 // If this thread has been assigned work, launch a search
2655 if(Threads[threadID].workIsWaiting) {
2656 Threads[threadID].workIsWaiting = false;
2657 if(Threads[threadID].splitPoint->pvNode)
2658 sp_search_pv(Threads[threadID].splitPoint, threadID);
2660 sp_search(Threads[threadID].splitPoint, threadID);
2661 Threads[threadID].idle = true;
2664 // If this thread is the master of a split point and all threads have
2665 // finished their work at this split point, return from the idle loop.
2666 if(waitSp != NULL && waitSp->cpus == 0)
2670 Threads[threadID].running = false;
2674 // init_split_point_stack() is called during program initialization, and
2675 // initializes all split point objects.
2677 void init_split_point_stack() {
2678 for(int i = 0; i < THREAD_MAX; i++)
2679 for(int j = 0; j < MaxActiveSplitPoints; j++) {
2680 SplitPointStack[i][j].parent = NULL;
2681 lock_init(&(SplitPointStack[i][j].lock), NULL);
2686 // destroy_split_point_stack() is called when the program exits, and
2687 // destroys all locks in the precomputed split point objects.
2689 void destroy_split_point_stack() {
2690 for(int i = 0; i < THREAD_MAX; i++)
2691 for(int j = 0; j < MaxActiveSplitPoints; j++)
2692 lock_destroy(&(SplitPointStack[i][j].lock));
2696 // thread_should_stop() checks whether the thread with a given threadID has
2697 // been asked to stop, directly or indirectly. This can happen if a beta
2698 // cutoff has occured in thre thread's currently active split point, or in
2699 // some ancestor of the current split point.
2701 bool thread_should_stop(int threadID) {
2702 assert(threadID >= 0 && threadID < ActiveThreads);
2706 if(Threads[threadID].stop)
2708 if(ActiveThreads <= 2)
2710 for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
2712 Threads[threadID].stop = true;
2719 // thread_is_available() checks whether the thread with threadID "slave" is
2720 // available to help the thread with threadID "master" at a split point. An
2721 // obvious requirement is that "slave" must be idle. With more than two
2722 // threads, this is not by itself sufficient: If "slave" is the master of
2723 // some active split point, it is only available as a slave to the other
2724 // threads which are busy searching the split point at the top of "slave"'s
2725 // split point stack (the "helpful master concept" in YBWC terminology).
2727 bool thread_is_available(int slave, int master) {
2728 assert(slave >= 0 && slave < ActiveThreads);
2729 assert(master >= 0 && master < ActiveThreads);
2730 assert(ActiveThreads > 1);
2732 if(!Threads[slave].idle || slave == master)
2735 if(Threads[slave].activeSplitPoints == 0)
2736 // No active split points means that the thread is available as a slave
2737 // for any other thread.
2740 if(ActiveThreads == 2)
2743 // Apply the "helpful master" concept if possible.
2744 if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
2751 // idle_thread_exists() tries to find an idle thread which is available as
2752 // a slave for the thread with threadID "master".
2754 bool idle_thread_exists(int master) {
2755 assert(master >= 0 && master < ActiveThreads);
2756 assert(ActiveThreads > 1);
2758 for(int i = 0; i < ActiveThreads; i++)
2759 if(thread_is_available(i, master))
2765 // split() does the actual work of distributing the work at a node between
2766 // several threads at PV nodes. If it does not succeed in splitting the
2767 // node (because no idle threads are available, or because we have no unused
2768 // split point objects), the function immediately returns false. If
2769 // splitting is possible, a SplitPoint object is initialized with all the
2770 // data that must be copied to the helper threads (the current position and
2771 // search stack, alpha, beta, the search depth, etc.), and we tell our
2772 // helper threads that they have been assigned work. This will cause them
2773 // to instantly leave their idle loops and call sp_search_pv(). When all
2774 // threads have returned from sp_search_pv (or, equivalently, when
2775 // splitPoint->cpus becomes 0), split() returns true.
2777 bool split(const Position& p, SearchStack* sstck, int ply,
2778 Value* alpha, Value* beta, Value* bestValue, Depth depth, int* moves,
2779 MovePicker* mp, Bitboard dcCandidates, int master, bool pvNode) {
2782 assert(sstck != NULL);
2783 assert(ply >= 0 && ply < PLY_MAX);
2784 assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
2785 assert(!pvNode || *alpha < *beta);
2786 assert(*beta <= VALUE_INFINITE);
2787 assert(depth > Depth(0));
2788 assert(master >= 0 && master < ActiveThreads);
2789 assert(ActiveThreads > 1);
2791 SplitPoint* splitPoint;
2796 // If no other thread is available to help us, or if we have too many
2797 // active split points, don't split.
2798 if(!idle_thread_exists(master) ||
2799 Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
2800 lock_release(&MPLock);
2804 // Pick the next available split point object from the split point stack
2805 splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
2806 Threads[master].activeSplitPoints++;
2808 // Initialize the split point object
2809 splitPoint->parent = Threads[master].splitPoint;
2810 splitPoint->finished = false;
2811 splitPoint->ply = ply;
2812 splitPoint->depth = depth;
2813 splitPoint->alpha = pvNode? *alpha : (*beta - 1);
2814 splitPoint->beta = *beta;
2815 splitPoint->pvNode = pvNode;
2816 splitPoint->dcCandidates = dcCandidates;
2817 splitPoint->bestValue = *bestValue;
2818 splitPoint->master = master;
2819 splitPoint->mp = mp;
2820 splitPoint->moves = *moves;
2821 splitPoint->cpus = 1;
2822 splitPoint->pos.copy(p);
2823 splitPoint->parentSstack = sstck;
2824 for(i = 0; i < ActiveThreads; i++)
2825 splitPoint->slaves[i] = 0;
2827 // Copy the current position and the search stack to the master thread
2828 memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
2829 Threads[master].splitPoint = splitPoint;
2831 // Make copies of the current position and search stack for each thread
2832 for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
2834 if(thread_is_available(i, master)) {
2835 memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
2836 Threads[i].splitPoint = splitPoint;
2837 splitPoint->slaves[i] = 1;
2841 // Tell the threads that they have work to do. This will make them leave
2843 for(i = 0; i < ActiveThreads; i++)
2844 if(i == master || splitPoint->slaves[i]) {
2845 Threads[i].workIsWaiting = true;
2846 Threads[i].idle = false;
2847 Threads[i].stop = false;
2850 lock_release(&MPLock);
2852 // Everything is set up. The master thread enters the idle loop, from
2853 // which it will instantly launch a search, because its workIsWaiting
2854 // slot is 'true'. We send the split point as a second parameter to the
2855 // idle loop, which means that the main thread will return from the idle
2856 // loop when all threads have finished their work at this split point
2857 // (i.e. when // splitPoint->cpus == 0).
2858 idle_loop(master, splitPoint);
2860 // We have returned from the idle loop, which means that all threads are
2861 // finished. Update alpha, beta and bestvalue, and return.
2863 if(pvNode) *alpha = splitPoint->alpha;
2864 *beta = splitPoint->beta;
2865 *bestValue = splitPoint->bestValue;
2866 Threads[master].stop = false;
2867 Threads[master].idle = false;
2868 Threads[master].activeSplitPoints--;
2869 Threads[master].splitPoint = splitPoint->parent;
2870 lock_release(&MPLock);
2876 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2877 // to start a new search from the root.
2879 void wake_sleeping_threads() {
2880 if(ActiveThreads > 1) {
2881 for(int i = 1; i < ActiveThreads; i++) {
2882 Threads[i].idle = true;
2883 Threads[i].workIsWaiting = false;
2885 #if !defined(_MSC_VER)
2886 pthread_mutex_lock(&WaitLock);
2887 pthread_cond_broadcast(&WaitCond);
2888 pthread_mutex_unlock(&WaitLock);
2890 for(int i = 1; i < THREAD_MAX; i++)
2891 SetEvent(SitIdleEvent[i]);
2897 // init_thread() is the function which is called when a new thread is
2898 // launched. It simply calls the idle_loop() function with the supplied
2899 // threadID. There are two versions of this function; one for POSIX threads
2900 // and one for Windows threads.
2902 #if !defined(_MSC_VER)
2904 void *init_thread(void *threadID) {
2905 idle_loop(*(int *)threadID, NULL);
2911 DWORD WINAPI init_thread(LPVOID threadID) {
2912 idle_loop(*(int *)threadID, NULL);