2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
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/>.
39 #include "ucioption.h"
46 // Set to true to force running with one thread. Used for debugging
47 const bool FakeSplit = false;
49 // Different node types, used as template parameter
50 enum NodeType { NonPV, PV };
52 // RootMove struct is used for moves at the root of the tree. For each root
53 // move, we store two scores, a node count, and a PV (really a refutation
54 // in the case of moves which fail low). Value pv_score is normally set at
55 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
56 // according to the order in which moves are returned by MovePicker.
60 RootMove(const RootMove& rm) { *this = rm; }
61 RootMove& operator=(const RootMove& rm);
63 // RootMove::operator<() is the comparison function used when
64 // sorting the moves. A move m1 is considered to be better
65 // than a move m2 if it has an higher pv_score, or if it has
66 // equal pv_score but m1 has the higher non_pv_score. In this way
67 // we are guaranteed that PV moves are always sorted as first.
68 bool operator<(const RootMove& m) const {
69 return pv_score != m.pv_score ? pv_score < m.pv_score
70 : non_pv_score < m.non_pv_score;
73 void extract_pv_from_tt(Position& pos);
74 void insert_pv_in_tt(Position& pos);
75 std::string pv_info_to_uci(Position& pos, int depth, int selDepth,
76 Value alpha, Value beta, int pvIdx);
80 Move pv[PLY_MAX_PLUS_2];
83 // RootMoveList struct is just a vector of RootMove objects,
84 // with an handful of methods above the standard ones.
85 struct RootMoveList : public std::vector<RootMove> {
87 typedef std::vector<RootMove> Base;
89 void init(Position& pos, Move searchMoves[]);
90 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
91 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
96 // MovePickerExt template class extends MovePicker and allows to choose at compile
97 // time the proper moves source according to the type of node. In the default case
98 // we simply create and use a standard MovePicker object.
99 template<bool SpNode, bool Root> struct MovePickerExt : public MovePicker {
101 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
102 : MovePicker(p, ttm, d, h, ss, b) {}
104 RootMoveList::iterator rm; // Dummy, needed to compile
107 // In case of a SpNode we use split point's shared MovePicker object as moves source
108 template<> struct MovePickerExt<true, false> : public MovePicker {
110 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
111 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
113 Move get_next_move() { return mp->get_next_move(); }
115 RootMoveList::iterator rm; // Dummy, needed to compile
119 // In case of a Root node we use RootMoveList as moves source
120 template<> struct MovePickerExt<false, true> : public MovePicker {
122 MovePickerExt(const Position&, Move, Depth, const History&, SearchStack*, Value);
123 Move get_next_move();
125 RootMoveList::iterator rm;
132 // Lookup table to check if a Piece is a slider and its access function
133 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
134 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
138 // Maximum depth for razoring
139 const Depth RazorDepth = 4 * ONE_PLY;
141 // Dynamic razoring margin based on depth
142 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
144 // Maximum depth for use of dynamic threat detection when null move fails low
145 const Depth ThreatDepth = 5 * ONE_PLY;
147 // Step 9. Internal iterative deepening
149 // Minimum depth for use of internal iterative deepening
150 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
152 // At Non-PV nodes we do an internal iterative deepening search
153 // when the static evaluation is bigger then beta - IIDMargin.
154 const Value IIDMargin = Value(0x100);
156 // Step 11. Decide the new search depth
158 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
159 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
160 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
161 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
162 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
164 // Minimum depth for use of singular extension
165 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
167 // Step 12. Futility pruning
169 // Futility margin for quiescence search
170 const Value FutilityMarginQS = Value(0x80);
172 // Futility lookup tables (initialized at startup) and their access functions
173 Value FutilityMargins[16][64]; // [depth][moveNumber]
174 int FutilityMoveCounts[32]; // [depth]
176 inline Value futility_margin(Depth d, int mn) {
178 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
179 : 2 * VALUE_INFINITE;
182 inline int futility_move_count(Depth d) {
184 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
187 // Step 14. Reduced search
189 // Reduction lookup tables (initialized at startup) and their access function
190 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
192 template <NodeType PV> inline Depth reduction(Depth d, int mn) {
194 return (Depth) Reductions[PV][Min(d / ONE_PLY, 63)][Min(mn, 63)];
197 // Easy move margin. An easy move candidate must be at least this much
198 // better than the second best move.
199 const Value EasyMoveMargin = Value(0x200);
202 /// Namespace variables
211 int MultiPV, UCIMultiPV;
213 // Time management variables
214 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
219 std::ofstream LogFile;
221 // Skill level adjustment
223 bool SkillLevelEnabled;
226 // Node counters, used only by thread[0] but try to keep in different cache
227 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
228 bool SendSearchedNodes;
230 int NodesBetweenPolls = 30000;
238 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
240 template <NodeType PvNode, bool SpNode, bool Root>
241 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
243 template <NodeType PvNode>
244 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
246 template <NodeType PvNode>
247 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
249 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO)
250 : search<PvNode, false, false>(pos, ss, alpha, beta, depth);
253 template <NodeType PvNode>
254 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
256 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
257 bool connected_moves(const Position& pos, Move m1, Move m2);
258 Value value_to_tt(Value v, int ply);
259 Value value_from_tt(Value v, int ply);
260 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
261 bool connected_threat(const Position& pos, Move m, Move threat);
262 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
263 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
264 void update_gains(const Position& pos, Move move, Value before, Value after);
265 void do_skill_level(Move* best, Move* ponder);
267 int current_search_time(int set = 0);
268 std::string value_to_uci(Value v);
269 std::string speed_to_uci(int64_t nodes);
270 void poll(const Position& pos);
271 void wait_for_stop_or_ponderhit();
273 // Overload operator<<() to make it easier to print moves in a coordinate
274 // notation compatible with UCI protocol.
275 std::ostream& operator<<(std::ostream& os, Move m) {
277 bool chess960 = (os.iword(0) != 0); // See set960()
278 return os << move_to_uci(m, chess960);
281 // When formatting a move for std::cout we must know if we are in Chess960
282 // or not. To keep using the handy operator<<() on the move the trick is to
283 // embed this flag in the stream itself. Function-like named enum set960 is
284 // used as a custom manipulator and the stream internal general-purpose array,
285 // accessed through ios_base::iword(), is used to pass the flag to the move's
286 // operator<<() that will read it to properly format castling moves.
289 std::ostream& operator<< (std::ostream& os, const set960& f) {
291 os.iword(0) = int(f);
298 /// init_search() is called during startup to initialize various lookup tables
302 int d; // depth (ONE_PLY == 2)
303 int hd; // half depth (ONE_PLY == 1)
306 // Init reductions array
307 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
309 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
310 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
311 Reductions[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
312 Reductions[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
315 // Init futility margins array
316 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
317 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
319 // Init futility move count array
320 for (d = 0; d < 32; d++)
321 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
325 /// perft() is our utility to verify move generation. All the legal moves up to
326 /// given depth are generated and counted and the sum returned.
328 int64_t perft(Position& pos, Depth depth) {
330 MoveStack mlist[MAX_MOVES];
335 // Generate all legal moves
336 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
338 // If we are at the last ply we don't need to do and undo
339 // the moves, just to count them.
340 if (depth <= ONE_PLY)
341 return int(last - mlist);
343 // Loop through all legal moves
345 for (MoveStack* cur = mlist; cur != last; cur++)
348 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
349 sum += perft(pos, depth - ONE_PLY);
356 /// think() is the external interface to Stockfish's search, and is called when
357 /// the program receives the UCI 'go' command. It initializes various global
358 /// variables, and calls id_loop(). It returns false when a "quit" command is
359 /// received during the search.
361 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
363 // Initialize global search-related variables
364 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
366 current_search_time(get_system_time());
368 TimeMgr.init(Limits, pos.startpos_ply_counter());
370 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
372 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
373 else if (Limits.time && Limits.time < 1000)
374 NodesBetweenPolls = 1000;
375 else if (Limits.time && Limits.time < 5000)
376 NodesBetweenPolls = 5000;
378 NodesBetweenPolls = 30000;
380 // Look for a book move
381 if (Options["OwnBook"].value<bool>())
383 if (Options["Book File"].value<std::string>() != OpeningBook.name())
384 OpeningBook.open(Options["Book File"].value<std::string>());
386 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
387 if (bookMove != MOVE_NONE)
390 wait_for_stop_or_ponderhit();
392 cout << "bestmove " << bookMove << endl;
398 UCIMultiPV = Options["MultiPV"].value<int>();
399 SkillLevel = Options["Skill level"].value<int>();
401 read_evaluation_uci_options(pos.side_to_move());
402 Threads.read_uci_options();
404 // If needed allocate pawn and material hash tables and adjust TT size
405 Threads.init_hash_tables();
406 TT.set_size(Options["Hash"].value<int>());
408 if (Options["Clear Hash"].value<bool>())
410 Options["Clear Hash"].set_value("false");
414 // Do we have to play with skill handicap? In this case enable MultiPV that
415 // we will use behind the scenes to retrieve a set of possible moves.
416 SkillLevelEnabled = (SkillLevel < 20);
417 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
419 // Wake up needed threads and reset maxPly counter
420 for (int i = 0; i < Threads.size(); i++)
422 Threads[i].wake_up();
423 Threads[i].maxPly = 0;
426 // Write to log file and keep it open to be accessed during the search
427 if (Options["Use Search Log"].value<bool>())
429 std::string name = Options["Search Log Filename"].value<std::string>();
430 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
432 if (LogFile.is_open())
433 LogFile << "\nSearching: " << pos.to_fen()
434 << "\ninfinite: " << Limits.infinite
435 << " ponder: " << Limits.ponder
436 << " time: " << Limits.time
437 << " increment: " << Limits.increment
438 << " moves to go: " << Limits.movesToGo
442 // We're ready to start thinking. Call the iterative deepening loop function
443 Move ponderMove = MOVE_NONE;
444 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
446 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
448 // Write final search statistics and close log file
449 if (LogFile.is_open())
451 int t = current_search_time();
453 LogFile << "Nodes: " << pos.nodes_searched()
454 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
455 << "\nBest move: " << move_to_san(pos, bestMove);
458 pos.do_move(bestMove, st);
459 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
460 pos.undo_move(bestMove); // Return from think() with unchanged position
464 // This makes all the threads to go to sleep
467 // If we are pondering or in infinite search, we shouldn't print the
468 // best move before we are told to do so.
469 if (!StopRequest && (Limits.ponder || Limits.infinite))
470 wait_for_stop_or_ponderhit();
472 // Could be MOVE_NONE when searching on a stalemate position
473 cout << "bestmove " << bestMove;
475 // UCI protol is not clear on allowing sending an empty ponder move, instead
476 // it is clear that ponder move is optional. So skip it if empty.
477 if (ponderMove != MOVE_NONE)
478 cout << " ponder " << ponderMove;
488 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
489 // with increasing depth until the allocated thinking time has been consumed,
490 // user stops the search, or the maximum search depth is reached.
492 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
494 SearchStack ss[PLY_MAX_PLUS_2];
495 Value bestValues[PLY_MAX_PLUS_2];
496 int bestMoveChanges[PLY_MAX_PLUS_2];
497 int depth, selDepth, aspirationDelta;
498 Value value, alpha, beta;
499 Move bestMove, easyMove, skillBest, skillPonder;
501 // Initialize stuff before a new search
502 memset(ss, 0, 4 * sizeof(SearchStack));
505 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
506 depth = aspirationDelta = 0;
507 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
508 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
510 // Moves to search are verified and copied
511 Rml.init(pos, searchMoves);
513 // Handle special case of searching on a mate/stalemate position
516 cout << "info depth 0 score "
517 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
523 // Iterative deepening loop until requested to stop or target depth reached
524 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
526 Rml.bestMoveChanges = 0;
527 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
529 // Calculate dynamic aspiration window based on previous iterations
530 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
532 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
533 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
535 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
536 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
538 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
539 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
542 // Start with a small aspiration window and, in case of fail high/low,
543 // research with bigger window until not failing high/low anymore.
545 // Search starting from ss+1 to allow calling update_gains()
546 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY);
548 // Write PV back to transposition table in case the relevant entries
549 // have been overwritten during the search.
550 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
551 Rml[i].insert_pv_in_tt(pos);
553 // Value cannot be trusted. Break out immediately!
557 assert(value >= alpha);
559 // In case of failing high/low increase aspiration window and research,
560 // otherwise exit the fail high/low loop.
563 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
564 aspirationDelta += aspirationDelta / 2;
566 else if (value <= alpha)
568 AspirationFailLow = true;
569 StopOnPonderhit = false;
571 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
572 aspirationDelta += aspirationDelta / 2;
577 } while (abs(value) < VALUE_KNOWN_WIN);
579 // Collect info about search result
580 bestMove = Rml[0].pv[0];
581 *ponderMove = Rml[0].pv[1];
582 bestValues[depth] = value;
583 bestMoveChanges[depth] = Rml.bestMoveChanges;
585 // Do we need to pick now the best and the ponder moves ?
586 if (SkillLevelEnabled && depth == 1 + SkillLevel)
587 do_skill_level(&skillBest, &skillPonder);
589 // Retrieve max searched depth among threads
591 for (int i = 0; i < Threads.size(); i++)
592 if (Threads[i].maxPly > selDepth)
593 selDepth = Threads[i].maxPly;
595 // Send PV line to GUI and to log file
596 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
597 cout << Rml[i].pv_info_to_uci(pos, depth, selDepth, alpha, beta, i) << endl;
599 if (LogFile.is_open())
600 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
602 // Init easyMove after first iteration or drop if differs from the best move
603 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
605 else if (bestMove != easyMove)
606 easyMove = MOVE_NONE;
608 // Check for some early stop condition
609 if (!StopRequest && Limits.useTimeManagement())
611 // Stop search early when the last two iterations returned a mate score
613 && abs(bestValues[depth]) >= VALUE_MATE_IN_PLY_MAX
614 && abs(bestValues[depth - 1]) >= VALUE_MATE_IN_PLY_MAX)
617 // Stop search early if one move seems to be much better than the
618 // others or if there is only a single legal move. Also in the latter
619 // case we search up to some depth anyway to get a proper score.
621 && easyMove == bestMove
623 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
624 && current_search_time() > TimeMgr.available_time() / 16)
625 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
626 && current_search_time() > TimeMgr.available_time() / 32)))
629 // Take in account some extra time if the best move has changed
630 if (depth > 4 && depth < 50)
631 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
633 // Stop search if most of available time is already consumed. We probably don't
634 // have enough time to search the first move at the next iteration anyway.
635 if (current_search_time() > (TimeMgr.available_time() * 62) / 100)
638 // If we are allowed to ponder do not stop the search now but keep pondering
639 if (StopRequest && Limits.ponder)
642 StopOnPonderhit = true;
647 // When using skills overwrite best and ponder moves with the sub-optimal ones
648 if (SkillLevelEnabled)
650 if (skillBest == MOVE_NONE) // Still unassigned ?
651 do_skill_level(&skillBest, &skillPonder);
653 bestMove = skillBest;
654 *ponderMove = skillPonder;
661 // search<>() is the main search function for both PV and non-PV nodes and for
662 // normal and SplitPoint nodes. When called just after a split point the search
663 // is simpler because we have already probed the hash table, done a null move
664 // search, and searched the first move before splitting, we don't have to repeat
665 // all this work again. We also don't need to store anything to the hash table
666 // here: This is taken care of after we return from the split point.
668 template <NodeType PvNode, bool SpNode, bool Root>
669 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
671 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
672 assert(beta > alpha && beta <= VALUE_INFINITE);
673 assert(PvNode || alpha == beta - 1);
674 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
676 Move movesSearched[MAX_MOVES];
681 Move ttMove, move, excludedMove, threatMove;
684 Value bestValue, value, oldAlpha;
685 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
686 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous, isBadCap;
687 int moveCount = 0, playedMoveCount = 0;
688 int threadID = pos.thread();
689 SplitPoint* sp = NULL;
691 refinedValue = bestValue = value = -VALUE_INFINITE;
693 isCheck = pos.is_check();
694 ss->ply = (ss-1)->ply + 1;
696 // Used to send selDepth info to GUI
697 if (PvNode && Threads[threadID].maxPly < ss->ply)
698 Threads[threadID].maxPly = ss->ply;
704 ttMove = excludedMove = MOVE_NONE;
705 threatMove = sp->threatMove;
706 goto split_point_start;
711 // Step 1. Initialize node and poll. Polling can abort search
712 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
713 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
714 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
716 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
722 // Step 2. Check for aborted search and immediate draw
724 || Threads[threadID].cutoff_occurred()
726 || ss->ply > PLY_MAX) && !Root)
729 // Step 3. Mate distance pruning
730 alpha = Max(value_mated_in(ss->ply), alpha);
731 beta = Min(value_mate_in(ss->ply+1), beta);
735 // Step 4. Transposition table lookup
736 // We don't want the score of a partial search to overwrite a previous full search
737 // TT value, so we use a different position key in case of an excluded move.
738 excludedMove = ss->excludedMove;
739 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
741 tte = TT.retrieve(posKey);
742 ttMove = tte ? tte->move() : MOVE_NONE;
744 // At PV nodes we check for exact scores, while at non-PV nodes we check for
745 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
746 // smooth experience in analysis mode.
749 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
750 : ok_to_use_TT(tte, depth, beta, ss->ply)))
753 ss->bestMove = ttMove; // Can be MOVE_NONE
754 return value_from_tt(tte->value(), ss->ply);
757 // Step 5. Evaluate the position statically and update parent's gain statistics
759 ss->eval = ss->evalMargin = VALUE_NONE;
762 assert(tte->static_value() != VALUE_NONE);
764 ss->eval = tte->static_value();
765 ss->evalMargin = tte->static_value_margin();
766 refinedValue = refine_eval(tte, ss->eval, ss->ply);
770 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
771 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
774 // Save gain for the parent non-capture move
775 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
777 // Step 6. Razoring (is omitted in PV nodes)
779 && depth < RazorDepth
781 && refinedValue + razor_margin(depth) < beta
782 && ttMove == MOVE_NONE
783 && abs(beta) < VALUE_MATE_IN_PLY_MAX
784 && !pos.has_pawn_on_7th(pos.side_to_move()))
786 Value rbeta = beta - razor_margin(depth);
787 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
789 // Logically we should return (v + razor_margin(depth)), but
790 // surprisingly this did slightly weaker in tests.
794 // Step 7. Static null move pruning (is omitted in PV nodes)
795 // We're betting that the opponent doesn't have a move that will reduce
796 // the score by more than futility_margin(depth) if we do a null move.
799 && depth < RazorDepth
801 && refinedValue - futility_margin(depth, 0) >= beta
802 && abs(beta) < VALUE_MATE_IN_PLY_MAX
803 && pos.non_pawn_material(pos.side_to_move()))
804 return refinedValue - futility_margin(depth, 0);
806 // Step 8. Null move search with verification search (is omitted in PV nodes)
811 && refinedValue >= beta
812 && abs(beta) < VALUE_MATE_IN_PLY_MAX
813 && pos.non_pawn_material(pos.side_to_move()))
815 ss->currentMove = MOVE_NULL;
817 // Null move dynamic reduction based on depth
818 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
820 // Null move dynamic reduction based on value
821 if (refinedValue - PawnValueMidgame > beta)
824 pos.do_null_move(st);
825 (ss+1)->skipNullMove = true;
826 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
827 (ss+1)->skipNullMove = false;
828 pos.undo_null_move();
830 if (nullValue >= beta)
832 // Do not return unproven mate scores
833 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
836 if (depth < 6 * ONE_PLY)
839 // Do verification search at high depths
840 ss->skipNullMove = true;
841 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
842 ss->skipNullMove = false;
849 // The null move failed low, which means that we may be faced with
850 // some kind of threat. If the previous move was reduced, check if
851 // the move that refuted the null move was somehow connected to the
852 // move which was reduced. If a connection is found, return a fail
853 // low score (which will cause the reduced move to fail high in the
854 // parent node, which will trigger a re-search with full depth).
855 threatMove = (ss+1)->bestMove;
857 if ( depth < ThreatDepth
859 && threatMove != MOVE_NONE
860 && connected_moves(pos, (ss-1)->currentMove, threatMove))
865 // Step 9. Internal iterative deepening
866 if ( depth >= IIDDepth[PvNode]
867 && ttMove == MOVE_NONE
868 && (PvNode || (!isCheck && ss->eval + IIDMargin >= beta)))
870 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
872 ss->skipNullMove = true;
873 search<PvNode>(pos, ss, alpha, beta, d);
874 ss->skipNullMove = false;
876 ttMove = ss->bestMove;
877 tte = TT.retrieve(posKey);
880 split_point_start: // At split points actual search starts from here
882 // Initialize a MovePicker object for the current position
883 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
885 ss->bestMove = MOVE_NONE;
886 futilityBase = ss->eval + ss->evalMargin;
887 singularExtensionNode = !Root
889 && depth >= SingularExtensionDepth[PvNode]
892 && !excludedMove // Do not allow recursive singular extension search
893 && (tte->type() & VALUE_TYPE_LOWER)
894 && tte->depth() >= depth - 3 * ONE_PLY;
897 lock_grab(&(sp->lock));
898 bestValue = sp->bestValue;
901 // Step 10. Loop through moves
902 // Loop through all legal moves until no moves remain or a beta cutoff occurs
903 while ( bestValue < beta
904 && (move = mp.get_next_move()) != MOVE_NONE
905 && !Threads[threadID].cutoff_occurred())
907 assert(move_is_ok(move));
911 moveCount = ++sp->moveCount;
912 lock_release(&(sp->lock));
914 else if (move == excludedMove)
921 // This is used by time management
922 FirstRootMove = (moveCount == 1);
924 // Save the current node count before the move is searched
925 nodes = pos.nodes_searched();
927 // If it's time to send nodes info, do it here where we have the
928 // correct accumulated node counts searched by each thread.
929 if (SendSearchedNodes)
931 SendSearchedNodes = false;
932 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
935 if (current_search_time() > 2000)
936 cout << "info currmove " << move
937 << " currmovenumber " << moveCount << endl;
940 // At Root and at first iteration do a PV search on all the moves to score root moves
941 isPvMove = (PvNode && moveCount <= (Root ? depth <= ONE_PLY ? 1000 : MultiPV : 1));
942 moveIsCheck = pos.move_is_check(move, ci);
943 captureOrPromotion = pos.move_is_capture_or_promotion(move);
945 // Step 11. Decide the new search depth
946 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, &dangerous);
948 // Singular extension search. If all moves but one fail low on a search of
949 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
950 // is singular and should be extended. To verify this we do a reduced search
951 // on all the other moves but the ttMove, if result is lower than ttValue minus
952 // a margin then we extend ttMove.
953 if ( singularExtensionNode
954 && move == tte->move()
957 Value ttValue = value_from_tt(tte->value(), ss->ply);
959 if (abs(ttValue) < VALUE_KNOWN_WIN)
961 Value rBeta = ttValue - int(depth);
962 ss->excludedMove = move;
963 ss->skipNullMove = true;
964 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
965 ss->skipNullMove = false;
966 ss->excludedMove = MOVE_NONE;
967 ss->bestMove = MOVE_NONE;
973 // Update current move (this must be done after singular extension search)
974 ss->currentMove = move;
975 newDepth = depth - ONE_PLY + ext;
977 // Step 12. Futility pruning (is omitted in PV nodes)
979 && !captureOrPromotion
983 && !move_is_castle(move))
985 // Move count based pruning
986 if ( moveCount >= futility_move_count(depth)
987 && (!threatMove || !connected_threat(pos, move, threatMove))
988 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
991 lock_grab(&(sp->lock));
996 // Value based pruning
997 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
998 // but fixing this made program slightly weaker.
999 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1000 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1001 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1003 if (futilityValueScaled < beta)
1007 lock_grab(&(sp->lock));
1008 if (futilityValueScaled > sp->bestValue)
1009 sp->bestValue = bestValue = futilityValueScaled;
1011 else if (futilityValueScaled > bestValue)
1012 bestValue = futilityValueScaled;
1017 // Prune moves with negative SEE at low depths
1018 if ( predictedDepth < 2 * ONE_PLY
1019 && bestValue > VALUE_MATED_IN_PLY_MAX
1020 && pos.see_sign(move) < 0)
1023 lock_grab(&(sp->lock));
1029 // Bad capture detection. Will be used by prob-cut search
1030 isBadCap = depth >= 3 * ONE_PLY
1031 && depth < 8 * ONE_PLY
1032 && captureOrPromotion
1035 && !move_is_promotion(move)
1036 && abs(alpha) < VALUE_MATE_IN_PLY_MAX
1037 && pos.see_sign(move) < 0;
1039 // Step 13. Make the move
1040 pos.do_move(move, st, ci, moveIsCheck);
1042 if (!SpNode && !captureOrPromotion)
1043 movesSearched[playedMoveCount++] = move;
1045 // Step extra. pv search (only in PV nodes)
1046 // The first move in list is the expected PV
1049 // Aspiration window is disabled in multi-pv case
1050 if (Root && MultiPV > 1)
1051 alpha = -VALUE_INFINITE;
1053 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1057 // Step 14. Reduced depth search
1058 // If the move fails high will be re-searched at full depth.
1059 bool doFullDepthSearch = true;
1060 alpha = SpNode ? sp->alpha : alpha;
1062 if ( depth >= 3 * ONE_PLY
1063 && !captureOrPromotion
1065 && !move_is_castle(move)
1066 && ss->killers[0] != move
1067 && ss->killers[1] != move)
1069 ss->reduction = reduction<PvNode>(depth, moveCount);
1072 alpha = SpNode ? sp->alpha : alpha;
1073 Depth d = newDepth - ss->reduction;
1074 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1076 doFullDepthSearch = (value > alpha);
1078 ss->reduction = DEPTH_ZERO; // Restore original reduction
1081 // Probcut search for bad captures. If a reduced search returns a value
1082 // very below beta then we can (almost) safely prune the bad capture.
1085 ss->reduction = 3 * ONE_PLY;
1086 Value rAlpha = alpha - 300;
1087 Depth d = newDepth - ss->reduction;
1088 value = -search<NonPV>(pos, ss+1, -(rAlpha+1), -rAlpha, d);
1089 doFullDepthSearch = (value > rAlpha);
1090 ss->reduction = DEPTH_ZERO; // Restore original reduction
1093 // Step 15. Full depth search
1094 if (doFullDepthSearch)
1096 alpha = SpNode ? sp->alpha : alpha;
1097 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1099 // Step extra. pv search (only in PV nodes)
1100 // Search only for possible new PV nodes, if instead value >= beta then
1101 // parent node fails low with value <= alpha and tries another move.
1102 if (PvNode && value > alpha && (Root || value < beta))
1103 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1107 // Step 16. Undo move
1108 pos.undo_move(move);
1110 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1112 // Step 17. Check for new best move
1115 lock_grab(&(sp->lock));
1116 bestValue = sp->bestValue;
1120 if (value > bestValue && !(SpNode && Threads[threadID].cutoff_occurred()))
1125 sp->bestValue = value;
1127 if (!Root && value > alpha)
1129 if (PvNode && value < beta) // We want always alpha < beta
1137 sp->is_betaCutoff = true;
1139 if (value == value_mate_in(ss->ply + 1))
1140 ss->mateKiller = move;
1142 ss->bestMove = move;
1145 sp->ss->bestMove = move;
1151 // Finished searching the move. If StopRequest is true, the search
1152 // was aborted because the user interrupted the search or because we
1153 // ran out of time. In this case, the return value of the search cannot
1154 // be trusted, and we break out of the loop without updating the best
1159 // Remember searched nodes counts for this move
1160 mp.rm->nodes += pos.nodes_searched() - nodes;
1162 // PV move or new best move ?
1163 if (isPvMove || value > alpha)
1166 ss->bestMove = move;
1167 mp.rm->pv_score = value;
1168 mp.rm->extract_pv_from_tt(pos);
1170 // We record how often the best move has been changed in each
1171 // iteration. This information is used for time management: When
1172 // the best move changes frequently, we allocate some more time.
1173 if (!isPvMove && MultiPV == 1)
1174 Rml.bestMoveChanges++;
1176 Rml.sort_multipv(moveCount);
1178 // Update alpha. In multi-pv we don't use aspiration window, so
1179 // set alpha equal to minimum score among the PV lines.
1181 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1182 else if (value > alpha)
1186 mp.rm->pv_score = -VALUE_INFINITE;
1190 // Step 18. Check for split
1193 && depth >= Threads.min_split_depth()
1195 && Threads.available_slave_exists(threadID)
1197 && !Threads[threadID].cutoff_occurred())
1198 Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1199 threatMove, moveCount, &mp, PvNode);
1202 // Step 19. Check for mate and stalemate
1203 // All legal moves have been searched and if there are
1204 // no legal moves, it must be mate or stalemate.
1205 // If one move was excluded return fail low score.
1206 if (!SpNode && !moveCount)
1207 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1209 // Step 20. Update tables
1210 // If the search is not aborted, update the transposition table,
1211 // history counters, and killer moves.
1212 if (!SpNode && !StopRequest && !Threads[threadID].cutoff_occurred())
1214 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1215 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1216 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1218 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1220 // Update killers and history only for non capture moves that fails high
1221 if ( bestValue >= beta
1222 && !pos.move_is_capture_or_promotion(move))
1224 if (move != ss->killers[0])
1226 ss->killers[1] = ss->killers[0];
1227 ss->killers[0] = move;
1229 update_history(pos, move, depth, movesSearched, playedMoveCount);
1235 // Here we have the lock still grabbed
1236 sp->is_slave[threadID] = false;
1237 sp->nodes += pos.nodes_searched();
1238 lock_release(&(sp->lock));
1241 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1246 // qsearch() is the quiescence search function, which is called by the main
1247 // search function when the remaining depth is zero (or, to be more precise,
1248 // less than ONE_PLY).
1250 template <NodeType PvNode>
1251 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1253 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1254 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1255 assert(PvNode || alpha == beta - 1);
1257 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1261 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1262 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1265 Value oldAlpha = alpha;
1267 ss->bestMove = ss->currentMove = MOVE_NONE;
1268 ss->ply = (ss-1)->ply + 1;
1270 // Check for an instant draw or maximum ply reached
1271 if (ss->ply > PLY_MAX || pos.is_draw())
1274 // Decide whether or not to include checks, this fixes also the type of
1275 // TT entry depth that we are going to use. Note that in qsearch we use
1276 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1277 isCheck = pos.is_check();
1278 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1280 // Transposition table lookup. At PV nodes, we don't use the TT for
1281 // pruning, but only for move ordering.
1282 tte = TT.retrieve(pos.get_key());
1283 ttMove = (tte ? tte->move() : MOVE_NONE);
1285 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1287 ss->bestMove = ttMove; // Can be MOVE_NONE
1288 return value_from_tt(tte->value(), ss->ply);
1291 // Evaluate the position statically
1294 bestValue = futilityBase = -VALUE_INFINITE;
1295 ss->eval = evalMargin = VALUE_NONE;
1296 enoughMaterial = false;
1302 assert(tte->static_value() != VALUE_NONE);
1304 evalMargin = tte->static_value_margin();
1305 ss->eval = bestValue = tte->static_value();
1308 ss->eval = bestValue = evaluate(pos, evalMargin);
1310 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1312 // Stand pat. Return immediately if static value is at least beta
1313 if (bestValue >= beta)
1316 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1321 if (PvNode && bestValue > alpha)
1324 // Futility pruning parameters, not needed when in check
1325 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1326 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1329 // Initialize a MovePicker object for the current position, and prepare
1330 // to search the moves. Because the depth is <= 0 here, only captures,
1331 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1333 MovePicker mp(pos, ttMove, depth, H);
1336 // Loop through the moves until no moves remain or a beta cutoff occurs
1337 while ( alpha < beta
1338 && (move = mp.get_next_move()) != MOVE_NONE)
1340 assert(move_is_ok(move));
1342 moveIsCheck = pos.move_is_check(move, ci);
1350 && !move_is_promotion(move)
1351 && !pos.move_is_passed_pawn_push(move))
1353 futilityValue = futilityBase
1354 + pos.endgame_value_of_piece_on(move_to(move))
1355 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1357 if (futilityValue < alpha)
1359 if (futilityValue > bestValue)
1360 bestValue = futilityValue;
1364 // Prune moves with negative or equal SEE
1365 if ( futilityBase < beta
1366 && depth < DEPTH_ZERO
1367 && pos.see(move) <= 0)
1371 // Detect non-capture evasions that are candidate to be pruned
1372 evasionPrunable = isCheck
1373 && bestValue > VALUE_MATED_IN_PLY_MAX
1374 && !pos.move_is_capture(move)
1375 && !pos.can_castle(pos.side_to_move());
1377 // Don't search moves with negative SEE values
1379 && (!isCheck || evasionPrunable)
1381 && !move_is_promotion(move)
1382 && pos.see_sign(move) < 0)
1385 // Don't search useless checks
1390 && !pos.move_is_capture_or_promotion(move)
1391 && ss->eval + PawnValueMidgame / 4 < beta
1392 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1394 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1395 bestValue = ss->eval + PawnValueMidgame / 4;
1400 // Update current move
1401 ss->currentMove = move;
1403 // Make and search the move
1404 pos.do_move(move, st, ci, moveIsCheck);
1405 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1406 pos.undo_move(move);
1408 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1411 if (value > bestValue)
1417 ss->bestMove = move;
1422 // All legal moves have been searched. A special case: If we're in check
1423 // and no legal moves were found, it is checkmate.
1424 if (isCheck && bestValue == -VALUE_INFINITE)
1425 return value_mated_in(ss->ply);
1427 // Update transposition table
1428 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1429 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1431 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1437 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1438 // bestValue is updated only when returning false because in that case move
1441 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1443 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1444 Square from, to, ksq, victimSq;
1447 Value futilityValue, bv = *bestValue;
1449 from = move_from(move);
1451 them = opposite_color(pos.side_to_move());
1452 ksq = pos.king_square(them);
1453 kingAtt = pos.attacks_from<KING>(ksq);
1454 pc = pos.piece_on(from);
1456 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1457 oldAtt = pos.attacks_from(pc, from, occ);
1458 newAtt = pos.attacks_from(pc, to, occ);
1460 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1461 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1463 if (!(b && (b & (b - 1))))
1466 // Rule 2. Queen contact check is very dangerous
1467 if ( type_of_piece(pc) == QUEEN
1468 && bit_is_set(kingAtt, to))
1471 // Rule 3. Creating new double threats with checks
1472 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1476 victimSq = pop_1st_bit(&b);
1477 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1479 // Note that here we generate illegal "double move"!
1480 if ( futilityValue >= beta
1481 && pos.see_sign(make_move(from, victimSq)) >= 0)
1484 if (futilityValue > bv)
1488 // Update bestValue only if check is not dangerous (because we will prune the move)
1494 // connected_moves() tests whether two moves are 'connected' in the sense
1495 // that the first move somehow made the second move possible (for instance
1496 // if the moving piece is the same in both moves). The first move is assumed
1497 // to be the move that was made to reach the current position, while the
1498 // second move is assumed to be a move from the current position.
1500 bool connected_moves(const Position& pos, Move m1, Move m2) {
1502 Square f1, t1, f2, t2;
1505 assert(m1 && move_is_ok(m1));
1506 assert(m2 && move_is_ok(m2));
1508 // Case 1: The moving piece is the same in both moves
1514 // Case 2: The destination square for m2 was vacated by m1
1520 // Case 3: Moving through the vacated square
1521 if ( piece_is_slider(pos.piece_on(f2))
1522 && bit_is_set(squares_between(f2, t2), f1))
1525 // Case 4: The destination square for m2 is defended by the moving piece in m1
1526 p = pos.piece_on(t1);
1527 if (bit_is_set(pos.attacks_from(p, t1), t2))
1530 // Case 5: Discovered check, checking piece is the piece moved in m1
1531 if ( piece_is_slider(p)
1532 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1533 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1535 // discovered_check_candidates() works also if the Position's side to
1536 // move is the opposite of the checking piece.
1537 Color them = opposite_color(pos.side_to_move());
1538 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1540 if (bit_is_set(dcCandidates, f2))
1547 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1548 // "plies to mate from the current ply". Non-mate scores are unchanged.
1549 // The function is called before storing a value to the transposition table.
1551 Value value_to_tt(Value v, int ply) {
1553 if (v >= VALUE_MATE_IN_PLY_MAX)
1556 if (v <= VALUE_MATED_IN_PLY_MAX)
1563 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1564 // the transposition table to a mate score corrected for the current ply.
1566 Value value_from_tt(Value v, int ply) {
1568 if (v >= VALUE_MATE_IN_PLY_MAX)
1571 if (v <= VALUE_MATED_IN_PLY_MAX)
1578 // extension() decides whether a move should be searched with normal depth,
1579 // or with extended depth. Certain classes of moves (checking moves, in
1580 // particular) are searched with bigger depth than ordinary moves and in
1581 // any case are marked as 'dangerous'. Note that also if a move is not
1582 // extended, as example because the corresponding UCI option is set to zero,
1583 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1584 template <NodeType PvNode>
1585 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1586 bool moveIsCheck, bool* dangerous) {
1588 assert(m != MOVE_NONE);
1590 Depth result = DEPTH_ZERO;
1591 *dangerous = moveIsCheck;
1593 if (moveIsCheck && pos.see_sign(m) >= 0)
1594 result += CheckExtension[PvNode];
1596 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1598 Color c = pos.side_to_move();
1599 if (relative_rank(c, move_to(m)) == RANK_7)
1601 result += PawnPushTo7thExtension[PvNode];
1604 if (pos.pawn_is_passed(c, move_to(m)))
1606 result += PassedPawnExtension[PvNode];
1611 if ( captureOrPromotion
1612 && pos.type_of_piece_on(move_to(m)) != PAWN
1613 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1614 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1615 && !move_is_special(m))
1617 result += PawnEndgameExtension[PvNode];
1621 return Min(result, ONE_PLY);
1625 // connected_threat() tests whether it is safe to forward prune a move or if
1626 // is somehow connected to the threat move returned by null search.
1628 bool connected_threat(const Position& pos, Move m, Move threat) {
1630 assert(move_is_ok(m));
1631 assert(threat && move_is_ok(threat));
1632 assert(!pos.move_is_check(m));
1633 assert(!pos.move_is_capture_or_promotion(m));
1634 assert(!pos.move_is_passed_pawn_push(m));
1636 Square mfrom, mto, tfrom, tto;
1638 mfrom = move_from(m);
1640 tfrom = move_from(threat);
1641 tto = move_to(threat);
1643 // Case 1: Don't prune moves which move the threatened piece
1647 // Case 2: If the threatened piece has value less than or equal to the
1648 // value of the threatening piece, don't prune moves which defend it.
1649 if ( pos.move_is_capture(threat)
1650 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1651 || pos.type_of_piece_on(tfrom) == KING)
1652 && pos.move_attacks_square(m, tto))
1655 // Case 3: If the moving piece in the threatened move is a slider, don't
1656 // prune safe moves which block its ray.
1657 if ( piece_is_slider(pos.piece_on(tfrom))
1658 && bit_is_set(squares_between(tfrom, tto), mto)
1659 && pos.see_sign(m) >= 0)
1666 // ok_to_use_TT() returns true if a transposition table score
1667 // can be used at a given point in search.
1669 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1671 Value v = value_from_tt(tte->value(), ply);
1673 return ( tte->depth() >= depth
1674 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1675 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1677 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1678 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1682 // refine_eval() returns the transposition table score if
1683 // possible otherwise falls back on static position evaluation.
1685 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1689 Value v = value_from_tt(tte->value(), ply);
1691 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1692 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1699 // update_history() registers a good move that produced a beta-cutoff
1700 // in history and marks as failures all the other moves of that ply.
1702 void update_history(const Position& pos, Move move, Depth depth,
1703 Move movesSearched[], int moveCount) {
1705 Value bonus = Value(int(depth) * int(depth));
1707 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1709 for (int i = 0; i < moveCount - 1; i++)
1711 m = movesSearched[i];
1715 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1720 // update_gains() updates the gains table of a non-capture move given
1721 // the static position evaluation before and after the move.
1723 void update_gains(const Position& pos, Move m, Value before, Value after) {
1726 && before != VALUE_NONE
1727 && after != VALUE_NONE
1728 && pos.captured_piece_type() == PIECE_TYPE_NONE
1729 && !move_is_special(m))
1730 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1734 // current_search_time() returns the number of milliseconds which have passed
1735 // since the beginning of the current search.
1737 int current_search_time(int set) {
1739 static int searchStartTime;
1742 searchStartTime = set;
1744 return get_system_time() - searchStartTime;
1748 // value_to_uci() converts a value to a string suitable for use with the UCI
1749 // protocol specifications:
1751 // cp <x> The score from the engine's point of view in centipawns.
1752 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1753 // use negative values for y.
1755 std::string value_to_uci(Value v) {
1757 std::stringstream s;
1759 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1760 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1762 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1768 // speed_to_uci() returns a string with time stats of current search suitable
1769 // to be sent to UCI gui.
1771 std::string speed_to_uci(int64_t nodes) {
1773 std::stringstream s;
1774 int t = current_search_time();
1776 s << " nodes " << nodes
1777 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1784 // poll() performs two different functions: It polls for user input, and it
1785 // looks at the time consumed so far and decides if it's time to abort the
1788 void poll(const Position& pos) {
1790 static int lastInfoTime;
1791 int t = current_search_time();
1794 if (input_available())
1796 // We are line oriented, don't read single chars
1797 std::string command;
1799 if (!std::getline(std::cin, command) || command == "quit")
1801 // Quit the program as soon as possible
1802 Limits.ponder = false;
1803 QuitRequest = StopRequest = true;
1806 else if (command == "stop")
1808 // Stop calculating as soon as possible, but still send the "bestmove"
1809 // and possibly the "ponder" token when finishing the search.
1810 Limits.ponder = false;
1813 else if (command == "ponderhit")
1815 // The opponent has played the expected move. GUI sends "ponderhit" if
1816 // we were told to ponder on the same move the opponent has played. We
1817 // should continue searching but switching from pondering to normal search.
1818 Limits.ponder = false;
1820 if (StopOnPonderhit)
1825 // Print search information
1829 else if (lastInfoTime > t)
1830 // HACK: Must be a new search where we searched less than
1831 // NodesBetweenPolls nodes during the first second of search.
1834 else if (t - lastInfoTime >= 1000)
1839 dbg_print_hit_rate();
1841 // Send info on searched nodes as soon as we return to root
1842 SendSearchedNodes = true;
1845 // Should we stop the search?
1849 bool stillAtFirstMove = FirstRootMove
1850 && !AspirationFailLow
1851 && t > TimeMgr.available_time();
1853 bool noMoreTime = t > TimeMgr.maximum_time()
1854 || stillAtFirstMove;
1856 if ( (Limits.useTimeManagement() && noMoreTime)
1857 || (Limits.maxTime && t >= Limits.maxTime)
1858 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1863 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1864 // while the program is pondering. The point is to work around a wrinkle in
1865 // the UCI protocol: When pondering, the engine is not allowed to give a
1866 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1867 // We simply wait here until one of these commands is sent, and return,
1868 // after which the bestmove and pondermove will be printed.
1870 void wait_for_stop_or_ponderhit() {
1872 std::string command;
1874 // Wait for a command from stdin
1875 while ( std::getline(std::cin, command)
1876 && command != "ponderhit" && command != "stop" && command != "quit") {};
1878 if (command != "ponderhit" && command != "stop")
1879 QuitRequest = true; // Must be "quit" or getline() returned false
1883 // When playing with strength handicap choose best move among the MultiPV set
1884 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1885 void do_skill_level(Move* best, Move* ponder) {
1887 assert(MultiPV > 1);
1889 // Rml list is already sorted by pv_score in descending order
1891 int max_s = -VALUE_INFINITE;
1892 int size = Min(MultiPV, (int)Rml.size());
1893 int max = Rml[0].pv_score;
1894 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
1895 int wk = 120 - 2 * SkillLevel;
1897 // PRNG sequence should be non deterministic
1898 for (int i = abs(get_system_time() % 50); i > 0; i--)
1899 RK.rand<unsigned>();
1901 // Choose best move. For each move's score we add two terms both dependent
1902 // on wk, one deterministic and bigger for weaker moves, and one random,
1903 // then we choose the move with the resulting highest score.
1904 for (int i = 0; i < size; i++)
1906 s = Rml[i].pv_score;
1908 // Don't allow crazy blunders even at very low skills
1909 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
1912 // This is our magical formula
1913 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
1918 *best = Rml[i].pv[0];
1919 *ponder = Rml[i].pv[1];
1925 /// RootMove and RootMoveList method's definitions
1927 RootMove::RootMove() {
1930 pv_score = non_pv_score = -VALUE_INFINITE;
1934 RootMove& RootMove::operator=(const RootMove& rm) {
1936 const Move* src = rm.pv;
1939 // Avoid a costly full rm.pv[] copy
1940 do *dst++ = *src; while (*src++ != MOVE_NONE);
1943 pv_score = rm.pv_score;
1944 non_pv_score = rm.non_pv_score;
1948 void RootMoveList::init(Position& pos, Move searchMoves[]) {
1950 MoveStack mlist[MAX_MOVES];
1954 bestMoveChanges = 0;
1956 // Generate all legal moves and add them to RootMoveList
1957 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
1958 for (MoveStack* cur = mlist; cur != last; cur++)
1960 // If we have a searchMoves[] list then verify cur->move
1961 // is in the list before to add it.
1962 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
1964 if (searchMoves[0] && *sm != cur->move)
1968 rm.pv[0] = cur->move;
1969 rm.pv[1] = MOVE_NONE;
1970 rm.pv_score = -VALUE_INFINITE;
1975 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
1976 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
1977 // allow to always have a ponder move even when we fail high at root and also a
1978 // long PV to print that is important for position analysis.
1980 void RootMove::extract_pv_from_tt(Position& pos) {
1982 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1986 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
1988 pos.do_move(pv[0], *st++);
1990 while ( (tte = TT.retrieve(pos.get_key())) != NULL
1991 && tte->move() != MOVE_NONE
1992 && pos.move_is_legal(tte->move())
1994 && (!pos.is_draw() || ply < 2))
1996 pv[ply] = tte->move();
1997 pos.do_move(pv[ply++], *st++);
1999 pv[ply] = MOVE_NONE;
2001 do pos.undo_move(pv[--ply]); while (ply);
2004 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2005 // the PV back into the TT. This makes sure the old PV moves are searched
2006 // first, even if the old TT entries have been overwritten.
2008 void RootMove::insert_pv_in_tt(Position& pos) {
2010 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2013 Value v, m = VALUE_NONE;
2016 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2020 tte = TT.retrieve(k);
2022 // Don't overwrite existing correct entries
2023 if (!tte || tte->move() != pv[ply])
2025 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2026 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2028 pos.do_move(pv[ply], *st++);
2030 } while (pv[++ply] != MOVE_NONE);
2032 do pos.undo_move(pv[--ply]); while (ply);
2035 // pv_info_to_uci() returns a string with information on the current PV line
2036 // formatted according to UCI specification.
2038 std::string RootMove::pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha,
2039 Value beta, int pvIdx) {
2040 std::stringstream s;
2042 s << "info depth " << depth
2043 << " seldepth " << selDepth
2044 << " multipv " << pvIdx + 1
2045 << " score " << value_to_uci(pv_score)
2046 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2047 << speed_to_uci(pos.nodes_searched())
2050 for (Move* m = pv; *m != MOVE_NONE; m++)
2056 // Specializations for MovePickerExt in case of Root node
2057 MovePickerExt<false, true>::MovePickerExt(const Position& p, Move ttm, Depth d,
2058 const History& h, SearchStack* ss, Value b)
2059 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
2061 Value score = VALUE_ZERO;
2063 // Score root moves using standard ordering used in main search, the moves
2064 // are scored according to the order in which they are returned by MovePicker.
2065 // This is the second order score that is used to compare the moves when
2066 // the first orders pv_score of both moves are equal.
2067 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
2068 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
2069 if (rm->pv[0] == move)
2071 rm->non_pv_score = score--;
2079 Move MovePickerExt<false, true>::get_next_move() {
2086 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
2092 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2093 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2094 // object for which the current thread is the master.
2096 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2098 assert(threadID >= 0 && threadID < MAX_THREADS);
2105 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2106 // master should exit as last one.
2107 if (allThreadsShouldExit)
2110 threads[threadID].state = Thread::TERMINATED;
2114 // If we are not thinking, wait for a condition to be signaled
2115 // instead of wasting CPU time polling for work.
2116 while ( threadID >= activeThreads
2117 || threads[threadID].state == Thread::INITIALIZING
2118 || (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
2120 assert(!sp || useSleepingThreads);
2121 assert(threadID != 0 || useSleepingThreads);
2123 if (threads[threadID].state == Thread::INITIALIZING)
2124 threads[threadID].state = Thread::AVAILABLE;
2126 // Grab the lock to avoid races with Thread::wake_up()
2127 lock_grab(&threads[threadID].sleepLock);
2129 // If we are master and all slaves have finished do not go to sleep
2130 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2131 allFinished = (i == activeThreads);
2133 if (allFinished || allThreadsShouldExit)
2135 lock_release(&threads[threadID].sleepLock);
2139 // Do sleep here after retesting sleep conditions
2140 if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
2141 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2143 lock_release(&threads[threadID].sleepLock);
2146 // If this thread has been assigned work, launch a search
2147 if (threads[threadID].state == Thread::WORKISWAITING)
2149 assert(!allThreadsShouldExit);
2151 threads[threadID].state = Thread::SEARCHING;
2153 // Copy split point position and search stack and call search()
2154 // with SplitPoint template parameter set to true.
2155 SearchStack ss[PLY_MAX_PLUS_2];
2156 SplitPoint* tsp = threads[threadID].splitPoint;
2157 Position pos(*tsp->pos, threadID);
2159 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2163 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2165 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2167 assert(threads[threadID].state == Thread::SEARCHING);
2169 threads[threadID].state = Thread::AVAILABLE;
2171 // Wake up master thread so to allow it to return from the idle loop in
2172 // case we are the last slave of the split point.
2173 if ( useSleepingThreads
2174 && threadID != tsp->master
2175 && threads[tsp->master].state == Thread::AVAILABLE)
2176 threads[tsp->master].wake_up();
2179 // If this thread is the master of a split point and all slaves have
2180 // finished their work at this split point, return from the idle loop.
2181 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2182 allFinished = (i == activeThreads);
2186 // Because sp->slaves[] is reset under lock protection,
2187 // be sure sp->lock has been released before to return.
2188 lock_grab(&(sp->lock));
2189 lock_release(&(sp->lock));
2191 // In helpful master concept a master can help only a sub-tree, and
2192 // because here is all finished is not possible master is booked.
2193 assert(threads[threadID].state == Thread::AVAILABLE);
2195 threads[threadID].state = Thread::SEARCHING;