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"
43 volatile SignalsType Signals;
45 std::vector<Move> SearchMoves;
46 Position RootPosition;
52 using namespace Search;
56 // Set to true to force running with one thread. Used for debugging
57 const bool FakeSplit = false;
59 // Different node types, used as template parameter
60 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
62 // RootMove struct is used for moves at the root of the tree. For each root
63 // move we store a score, a node count, and a PV (really a refutation in the
64 // case of moves which fail low). Score is normally set at -VALUE_INFINITE for
71 score = prevScore = -VALUE_INFINITE;
73 pv.push_back(MOVE_NONE);
76 bool operator<(const RootMove& m) const { return score < m.score; }
77 bool operator==(const Move& m) const { return pv[0] == m; }
79 void extract_pv_from_tt(Position& pos);
80 void insert_pv_in_tt(Position& pos);
91 // Lookup table to check if a Piece is a slider and its access function
92 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
93 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
95 // Maximum depth for razoring
96 const Depth RazorDepth = 4 * ONE_PLY;
98 // Dynamic razoring margin based on depth
99 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
101 // Maximum depth for use of dynamic threat detection when null move fails low
102 const Depth ThreatDepth = 5 * ONE_PLY;
104 // Minimum depth for use of internal iterative deepening
105 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
107 // At Non-PV nodes we do an internal iterative deepening search
108 // when the static evaluation is bigger then beta - IIDMargin.
109 const Value IIDMargin = Value(0x100);
111 // Minimum depth for use of singular extension
112 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
114 // Futility margin for quiescence search
115 const Value FutilityMarginQS = Value(0x80);
117 // Futility lookup tables (initialized at startup) and their access functions
118 Value FutilityMargins[16][64]; // [depth][moveNumber]
119 int FutilityMoveCounts[32]; // [depth]
121 inline Value futility_margin(Depth d, int mn) {
123 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
124 : 2 * VALUE_INFINITE;
127 inline int futility_move_count(Depth d) {
129 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
132 // Reduction lookup tables (initialized at startup) and their access function
133 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
135 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
137 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
140 // Easy move margin. An easy move candidate must be at least this much
141 // better than the second best move.
142 const Value EasyMoveMargin = Value(0x150);
145 /// Namespace variables
147 std::vector<RootMove> RootMoves;
148 size_t MultiPV, UCIMultiPV, MultiPVIdx;
152 bool SkillLevelEnabled;
158 Move id_loop(Position& pos, Move* ponderMove);
160 template <NodeType NT>
161 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
163 template <NodeType NT>
164 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
166 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
167 bool connected_moves(const Position& pos, Move m1, Move m2);
168 Value value_to_tt(Value v, int ply);
169 Value value_from_tt(Value v, int ply);
170 bool can_return_tt(const TTEntry* tte, Depth depth, Value beta, int ply);
171 bool connected_threat(const Position& pos, Move m, Move threat);
172 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
173 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
174 void do_skill_level(Move* best, Move* ponder);
175 int elapsed_time(bool reset = false);
176 string score_to_uci(Value v, Value alpha = -VALUE_INFINITE, Value beta = VALUE_INFINITE);
177 void pv_info_to_log(Position& pos, int depth, Value score, int time, Move pv[]);
178 void pv_info_to_uci(const Position& pos, int depth, Value alpha, Value beta);
180 // MovePickerExt class template extends MovePicker and allows to choose at
181 // compile time the proper moves source according to the type of node. In the
182 // default case we simply create and use a standard MovePicker object.
183 template<bool SpNode> struct MovePickerExt : public MovePicker {
185 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, Stack* ss, Value b)
186 : MovePicker(p, ttm, d, h, ss, b) {}
189 // In case of a SpNode we use split point's shared MovePicker object as moves source
190 template<> struct MovePickerExt<true> : public MovePicker {
192 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, Stack* ss, Value b)
193 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
195 Move get_next_move() { return mp->get_next_move(); }
199 // Overload operator<<() to make it easier to print moves in a coordinate
200 // notation compatible with UCI protocol.
201 std::ostream& operator<<(std::ostream& os, Move m) {
203 bool chess960 = (os.iword(0) != 0); // See set960()
204 return os << move_to_uci(m, chess960);
207 // When formatting a move for std::cout we must know if we are in Chess960 or
208 // not. To keep using the handy operator<<() on the move the trick is to embed
209 // this flag in the stream itself. Function-like named enum set960 is used as
210 // a custom manipulator and the stream internal general-purpose array, accessed
211 // through ios_base::iword(), is used to pass the flag to the move's operator<<
212 // that will read it to properly format castling moves.
215 std::ostream& operator<<(std::ostream& os, const set960& f) {
221 // is_dangerous() checks whether a move belongs to some classes of known
222 // 'dangerous' moves so that we avoid to prune it.
223 FORCE_INLINE bool is_dangerous(const Position& pos, Move m, bool captureOrPromotion) {
225 // Test for a pawn pushed to 7th or a passed pawn move
226 if (type_of(pos.piece_on(move_from(m))) == PAWN)
228 Color c = pos.side_to_move();
229 if ( relative_rank(c, move_to(m)) == RANK_7
230 || pos.pawn_is_passed(c, move_to(m)))
234 // Test for a capture that triggers a pawn endgame
235 if ( captureOrPromotion
236 && type_of(pos.piece_on(move_to(m))) != PAWN
237 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
238 - PieceValueMidgame[pos.piece_on(move_to(m))] == VALUE_ZERO)
248 /// init_search() is called during startup to initialize various lookup tables
250 void Search::init() {
252 int d; // depth (ONE_PLY == 2)
253 int hd; // half depth (ONE_PLY == 1)
256 // Init reductions array
257 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
259 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
260 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
261 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
262 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
265 // Init futility margins array
266 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
267 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
269 // Init futility move count array
270 for (d = 0; d < 32; d++)
271 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
275 /// perft() is our utility to verify move generation. All the leaf nodes up to
276 /// the given depth are generated and counted and the sum returned.
278 int64_t Search::perft(Position& pos, Depth depth) {
283 MoveList<MV_LEGAL> ml(pos);
285 // At the last ply just return the number of moves (leaf nodes)
286 if (depth <= ONE_PLY)
290 for ( ; !ml.end(); ++ml)
292 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
293 sum += perft(pos, depth - ONE_PLY);
294 pos.undo_move(ml.move());
300 /// think() is the external interface to Stockfish's search, and is called by the
301 /// main thread when the program receives the UCI 'go' command. It searches from
302 /// RootPosition and at the end prints the "bestmove" to output.
304 void Search::think() {
306 static Book book; // Defined static to initialize the PRNG only once
308 Position& pos = RootPosition;
310 TimeMgr.init(Limits, pos.startpos_ply_counter());
312 // Set output stream mode: normal or chess960. Castling notation is different
313 cout << set960(pos.is_chess960());
315 if (Options["OwnBook"].value<bool>())
317 if (Options["Book File"].value<string>() != book.name())
318 book.open(Options["Book File"].value<string>());
320 Move bookMove = book.probe(pos, Options["Best Book Move"].value<bool>());
321 if (bookMove != MOVE_NONE)
323 if (!Signals.stop && (Limits.ponder || Limits.infinite))
324 Threads.wait_for_stop_or_ponderhit();
326 cout << "bestmove " << bookMove << endl;
331 // Read UCI options: GUI could change UCI parameters during the game
332 read_evaluation_uci_options(pos.side_to_move());
333 Threads.read_uci_options();
335 TT.set_size(Options["Hash"].value<int>());
336 if (Options["Clear Hash"].value<bool>())
338 Options["Clear Hash"].set_value("false");
342 UCIMultiPV = Options["MultiPV"].value<size_t>();
343 SkillLevel = Options["Skill Level"].value<int>();
345 // Do we have to play with skill handicap? In this case enable MultiPV that
346 // we will use behind the scenes to retrieve a set of possible moves.
347 SkillLevelEnabled = (SkillLevel < 20);
348 MultiPV = (SkillLevelEnabled ? std::max(UCIMultiPV, (size_t)4) : UCIMultiPV);
350 if (Options["Use Search Log"].value<bool>())
352 Log log(Options["Search Log Filename"].value<string>());
353 log << "\nSearching: " << pos.to_fen()
354 << "\ninfinite: " << Limits.infinite
355 << " ponder: " << Limits.ponder
356 << " time: " << Limits.time
357 << " increment: " << Limits.increment
358 << " moves to go: " << Limits.movesToGo
362 // Wake up needed threads and reset maxPly counter
363 for (int i = 0; i < Threads.size(); i++)
365 Threads[i].maxPly = 0;
366 Threads[i].wake_up();
369 // Set best timer interval to avoid lagging under time pressure. Timer is
370 // used to check for remaining available thinking time.
371 if (TimeMgr.available_time())
372 Threads.set_timer(std::min(100, std::max(TimeMgr.available_time() / 8, 20)));
374 Threads.set_timer(100);
376 // We're ready to start thinking. Call the iterative deepening loop function
377 Move ponderMove = MOVE_NONE;
378 Move bestMove = id_loop(pos, &ponderMove);
380 // Stop timer and send all the slaves to sleep, if not already sleeping
381 Threads.set_timer(0);
384 if (Options["Use Search Log"].value<bool>())
386 int e = elapsed_time();
388 Log log(Options["Search Log Filename"].value<string>());
389 log << "Nodes: " << pos.nodes_searched()
390 << "\nNodes/second: " << (e > 0 ? pos.nodes_searched() * 1000 / e : 0)
391 << "\nBest move: " << move_to_san(pos, bestMove);
394 pos.do_move(bestMove, st);
395 log << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
396 pos.undo_move(bestMove); // Return from think() with unchanged position
399 // When we reach max depth we arrive here even without a StopRequest, but if
400 // we are pondering or in infinite search, we shouldn't print the best move
401 // before we are told to do so.
402 if (!Signals.stop && (Limits.ponder || Limits.infinite))
403 Threads.wait_for_stop_or_ponderhit();
405 // Could be MOVE_NONE when searching on a stalemate position
406 cout << "bestmove " << bestMove;
408 // UCI protol is not clear on allowing sending an empty ponder move, instead
409 // it is clear that ponder move is optional. So skip it if empty.
410 if (ponderMove != MOVE_NONE)
411 cout << " ponder " << ponderMove;
419 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
420 // with increasing depth until the allocated thinking time has been consumed,
421 // user stops the search, or the maximum search depth is reached.
423 Move id_loop(Position& pos, Move* ponderMove) {
425 Stack ss[PLY_MAX_PLUS_2];
426 int bestMoveChanges[PLY_MAX_PLUS_2];
428 Value bestValue, alpha, beta, delta;
429 Move bestMove, skillBest, skillPonder;
430 bool bestMoveNeverChanged = true;
432 memset(ss, 0, 4 * sizeof(Stack));
436 *ponderMove = bestMove = skillBest = skillPonder = MOVE_NONE;
438 bestValue = alpha = -VALUE_INFINITE, beta = delta = VALUE_INFINITE;
439 ss->currentMove = MOVE_NULL; // Hack to skip update gains
441 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
442 if ( SearchMoves.empty()
443 || std::count(SearchMoves.begin(), SearchMoves.end(), ml.move()))
444 RootMoves.push_back(RootMove(ml.move()));
446 // Handle special case of searching on a mate/stalemate position
447 if (RootMoves.empty())
449 cout << "info depth 0"
450 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW, alpha, beta) << endl;
455 // Iterative deepening loop until requested to stop or target depth reached
456 while (!Signals.stop && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
458 // Save now last iteration's scores, before Rml moves are reordered
459 for (size_t i = 0; i < RootMoves.size(); i++)
460 RootMoves[i].prevScore = RootMoves[i].score;
464 // MultiPV loop. We perform a full root search for each PV line
465 for (MultiPVIdx = 0; MultiPVIdx < std::min(MultiPV, RootMoves.size()); MultiPVIdx++)
468 if (depth >= 5 && abs(RootMoves[MultiPVIdx].prevScore) < VALUE_KNOWN_WIN)
471 alpha = RootMoves[MultiPVIdx].prevScore - delta;
472 beta = RootMoves[MultiPVIdx].prevScore + delta;
476 alpha = -VALUE_INFINITE;
477 beta = VALUE_INFINITE;
480 // Start with a small aspiration window and, in case of fail high/low,
481 // research with bigger window until not failing high/low anymore.
483 // Search starts from ss+1 to allow referencing (ss-1). This is
484 // needed by update gains and ss copy when splitting at Root.
485 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
487 // Bring to front the best move. It is critical that sorting is
488 // done with a stable algorithm because all the values but the first
489 // and eventually the new best one are set to -VALUE_INFINITE and
490 // we want to keep the same order for all the moves but the new
491 // PV that goes to the front. Note that in case of MultiPV search
492 // the already searched PV lines are preserved.
493 sort<RootMove>(RootMoves.begin() + MultiPVIdx, RootMoves.end());
495 // In case we have found an exact score and we are going to leave
496 // the fail high/low loop then reorder the PV moves, otherwise
497 // leave the last PV move in its position so to be searched again.
498 // Of course this is needed only in MultiPV search.
499 if (MultiPVIdx && bestValue > alpha && bestValue < beta)
500 sort<RootMove>(RootMoves.begin(), RootMoves.begin() + MultiPVIdx);
502 // Write PV back to transposition table in case the relevant entries
503 // have been overwritten during the search.
504 for (size_t i = 0; i <= MultiPVIdx; i++)
505 RootMoves[i].insert_pv_in_tt(pos);
507 // If search has been stopped exit the aspiration window loop,
508 // note that sorting and writing PV back to TT is safe becuase
509 // Rml is still valid, although refers to the previous iteration.
513 // Send full PV info to GUI if we are going to leave the loop or
514 // if we have a fail high/low and we are deep in the search.
515 if ((bestValue > alpha && bestValue < beta) || elapsed_time() > 2000)
516 pv_info_to_uci(pos, depth, alpha, beta);
518 // In case of failing high/low increase aspiration window and
519 // research, otherwise exit the fail high/low loop.
520 if (bestValue >= beta)
525 else if (bestValue <= alpha)
527 Signals.failedLowAtRoot = true;
528 Signals.stopOnPonderhit = false;
536 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
538 } while (abs(bestValue) < VALUE_KNOWN_WIN);
541 bestMove = RootMoves[0].pv[0];
542 *ponderMove = RootMoves[0].pv[1];
543 bestMoveChanges[depth] = BestMoveChanges;
545 // Skills: Do we need to pick now the best and the ponder moves ?
546 if (SkillLevelEnabled && depth == 1 + SkillLevel)
547 do_skill_level(&skillBest, &skillPonder);
549 if (Options["Use Search Log"].value<bool>())
550 pv_info_to_log(pos, depth, bestValue, elapsed_time(), &RootMoves[0].pv[0]);
552 // Filter out startup noise when monitoring best move stability
553 if (depth > 2 && bestMoveChanges[depth])
554 bestMoveNeverChanged = false;
556 // Do we have time for the next iteration? Can we stop searching now?
557 if (!Signals.stop && !Signals.stopOnPonderhit && Limits.useTimeManagement())
559 bool stop = false; // Local variable instead of the volatile Signals.stop
561 // Take in account some extra time if the best move has changed
562 if (depth > 4 && depth < 50)
563 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
565 // Stop search if most of available time is already consumed. We probably don't
566 // have enough time to search the first move at the next iteration anyway.
567 if (elapsed_time() > (TimeMgr.available_time() * 62) / 100)
570 // Stop search early if one move seems to be much better than others
573 && ( bestMoveNeverChanged
574 || elapsed_time() > (TimeMgr.available_time() * 40) / 100))
576 Value rBeta = bestValue - EasyMoveMargin;
577 (ss+1)->excludedMove = bestMove;
578 (ss+1)->skipNullMove = true;
579 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth * ONE_PLY) / 2);
580 (ss+1)->skipNullMove = false;
581 (ss+1)->excludedMove = MOVE_NONE;
589 // If we are allowed to ponder do not stop the search now but
590 // keep pondering until GUI sends "ponderhit" or "stop".
592 Signals.stopOnPonderhit = true;
599 // When using skills overwrite best and ponder moves with the sub-optimal ones
600 if (SkillLevelEnabled)
602 if (skillBest == MOVE_NONE) // Still unassigned ?
603 do_skill_level(&skillBest, &skillPonder);
605 bestMove = skillBest;
606 *ponderMove = skillPonder;
613 // search<>() is the main search function for both PV and non-PV nodes and for
614 // normal and SplitPoint nodes. When called just after a split point the search
615 // is simpler because we have already probed the hash table, done a null move
616 // search, and searched the first move before splitting, we don't have to repeat
617 // all this work again. We also don't need to store anything to the hash table
618 // here: This is taken care of after we return from the split point.
620 template <NodeType NT>
621 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
623 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
624 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
625 const bool RootNode = (NT == Root || NT == SplitPointRoot);
627 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
628 assert(beta > alpha && beta <= VALUE_INFINITE);
629 assert(PvNode || alpha == beta - 1);
630 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
632 Move movesSearched[MAX_MOVES];
637 Move ttMove, move, excludedMove, threatMove;
640 Value bestValue, value, oldAlpha;
641 Value refinedValue, nullValue, futilityBase, futilityValue;
642 bool isPvMove, inCheck, singularExtensionNode, givesCheck;
643 bool captureOrPromotion, dangerous, doFullDepthSearch;
644 int moveCount = 0, playedMoveCount = 0;
645 Thread& thread = Threads[pos.thread()];
646 SplitPoint* sp = NULL;
648 refinedValue = bestValue = value = -VALUE_INFINITE;
650 inCheck = pos.in_check();
651 ss->ply = (ss-1)->ply + 1;
653 // Used to send selDepth info to GUI
654 if (PvNode && thread.maxPly < ss->ply)
655 thread.maxPly = ss->ply;
657 // Step 1. Initialize node
660 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
661 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
662 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
668 ttMove = excludedMove = MOVE_NONE;
669 threatMove = sp->threatMove;
670 goto split_point_start;
673 // Step 2. Check for aborted search and immediate draw
675 || pos.is_draw<false>()
676 || ss->ply > PLY_MAX) && !RootNode)
679 // Step 3. Mate distance pruning
682 alpha = std::max(value_mated_in(ss->ply), alpha);
683 beta = std::min(value_mate_in(ss->ply+1), beta);
688 // Step 4. Transposition table lookup
689 // We don't want the score of a partial search to overwrite a previous full search
690 // TT value, so we use a different position key in case of an excluded move.
691 excludedMove = ss->excludedMove;
692 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
693 tte = TT.probe(posKey);
694 ttMove = RootNode ? RootMoves[MultiPVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
696 // At PV nodes we check for exact scores, while at non-PV nodes we check for
697 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
698 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
699 // we should also update RootMoveList to avoid bogus output.
700 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
701 : can_return_tt(tte, depth, beta, ss->ply)))
704 ss->bestMove = move = ttMove; // Can be MOVE_NONE
705 value = value_from_tt(tte->value(), ss->ply);
709 && !pos.is_capture_or_promotion(move)
710 && move != ss->killers[0])
712 ss->killers[1] = ss->killers[0];
713 ss->killers[0] = move;
718 // Step 5. Evaluate the position statically and update parent's gain statistics
720 ss->eval = ss->evalMargin = VALUE_NONE;
723 assert(tte->static_value() != VALUE_NONE);
725 ss->eval = tte->static_value();
726 ss->evalMargin = tte->static_value_margin();
727 refinedValue = refine_eval(tte, ss->eval, ss->ply);
731 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
732 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
735 // Update gain for the parent non-capture move given the static position
736 // evaluation before and after the move.
737 if ( (move = (ss-1)->currentMove) != MOVE_NULL
738 && (ss-1)->eval != VALUE_NONE
739 && ss->eval != VALUE_NONE
740 && pos.captured_piece_type() == PIECE_TYPE_NONE
741 && !is_special(move))
743 Square to = move_to(move);
744 H.update_gain(pos.piece_on(to), to, -(ss-1)->eval - ss->eval);
747 // Step 6. Razoring (is omitted in PV nodes)
749 && depth < RazorDepth
751 && refinedValue + razor_margin(depth) < beta
752 && ttMove == MOVE_NONE
753 && abs(beta) < VALUE_MATE_IN_PLY_MAX
754 && !pos.has_pawn_on_7th(pos.side_to_move()))
756 Value rbeta = beta - razor_margin(depth);
757 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
759 // Logically we should return (v + razor_margin(depth)), but
760 // surprisingly this did slightly weaker in tests.
764 // Step 7. Static null move pruning (is omitted in PV nodes)
765 // We're betting that the opponent doesn't have a move that will reduce
766 // the score by more than futility_margin(depth) if we do a null move.
769 && depth < RazorDepth
771 && refinedValue - futility_margin(depth, 0) >= beta
772 && abs(beta) < VALUE_MATE_IN_PLY_MAX
773 && pos.non_pawn_material(pos.side_to_move()))
774 return refinedValue - futility_margin(depth, 0);
776 // Step 8. Null move search with verification search (is omitted in PV nodes)
781 && refinedValue >= beta
782 && abs(beta) < VALUE_MATE_IN_PLY_MAX
783 && pos.non_pawn_material(pos.side_to_move()))
785 ss->currentMove = MOVE_NULL;
787 // Null move dynamic reduction based on depth
788 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
790 // Null move dynamic reduction based on value
791 if (refinedValue - PawnValueMidgame > beta)
794 pos.do_null_move<true>(st);
795 (ss+1)->skipNullMove = true;
796 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
797 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
798 (ss+1)->skipNullMove = false;
799 pos.do_null_move<false>(st);
801 if (nullValue >= beta)
803 // Do not return unproven mate scores
804 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
807 if (depth < 6 * ONE_PLY)
810 // Do verification search at high depths
811 ss->skipNullMove = true;
812 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
813 ss->skipNullMove = false;
820 // The null move failed low, which means that we may be faced with
821 // some kind of threat. If the previous move was reduced, check if
822 // the move that refuted the null move was somehow connected to the
823 // move which was reduced. If a connection is found, return a fail
824 // low score (which will cause the reduced move to fail high in the
825 // parent node, which will trigger a re-search with full depth).
826 threatMove = (ss+1)->bestMove;
828 if ( depth < ThreatDepth
830 && threatMove != MOVE_NONE
831 && connected_moves(pos, (ss-1)->currentMove, threatMove))
836 // Step 9. ProbCut (is omitted in PV nodes)
837 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
838 // and a reduced search returns a value much above beta, we can (almost) safely
839 // prune the previous move.
841 && depth >= RazorDepth + ONE_PLY
844 && excludedMove == MOVE_NONE
845 && abs(beta) < VALUE_MATE_IN_PLY_MAX)
847 Value rbeta = beta + 200;
848 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
850 assert(rdepth >= ONE_PLY);
852 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
855 while ((move = mp.get_next_move()) != MOVE_NONE)
856 if (pos.pl_move_is_legal(move, ci.pinned))
858 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
859 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
866 // Step 10. Internal iterative deepening
867 if ( depth >= IIDDepth[PvNode]
868 && ttMove == MOVE_NONE
869 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
871 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
873 ss->skipNullMove = true;
874 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
875 ss->skipNullMove = false;
877 tte = TT.probe(posKey);
878 ttMove = tte ? tte->move() : MOVE_NONE;
881 split_point_start: // At split points actual search starts from here
883 MovePickerExt<SpNode> mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
885 ss->bestMove = MOVE_NONE;
886 futilityBase = ss->eval + ss->evalMargin;
887 singularExtensionNode = !RootNode
889 && depth >= SingularExtensionDepth[PvNode]
890 && ttMove != MOVE_NONE
891 && !excludedMove // Recursive singular search is not allowed
892 && (tte->type() & VALUE_TYPE_LOWER)
893 && tte->depth() >= depth - 3 * ONE_PLY;
896 lock_grab(&(sp->lock));
897 bestValue = sp->bestValue;
898 moveCount = sp->moveCount;
900 assert(bestValue > -VALUE_INFINITE && moveCount > 0);
903 // Step 11. Loop through moves
904 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
905 while ( bestValue < beta
906 && (move = mp.get_next_move()) != MOVE_NONE
907 && !thread.cutoff_occurred())
911 if (move == excludedMove)
914 // At root obey the "searchmoves" option and skip moves not listed in Root
915 // Move List, as a consequence any illegal move is also skipped. In MultiPV
916 // mode we also skip PV moves which have been already searched.
917 if (RootNode && !std::count(RootMoves.begin() + MultiPVIdx, RootMoves.end(), move))
920 // At PV and SpNode nodes we want all moves to be legal since the beginning
921 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
926 moveCount = ++sp->moveCount;
927 lock_release(&(sp->lock));
934 // This is used by time management
935 Signals.firstRootMove = (moveCount == 1);
937 nodes = pos.nodes_searched();
939 if (pos.thread() == 0 && elapsed_time() > 2000)
940 cout << "info depth " << depth / ONE_PLY
941 << " currmove " << move
942 << " currmovenumber " << moveCount + MultiPVIdx << endl;
945 isPvMove = (PvNode && moveCount <= 1);
946 captureOrPromotion = pos.is_capture_or_promotion(move);
947 givesCheck = pos.move_gives_check(move, ci);
948 dangerous = givesCheck || is_dangerous(pos, move, captureOrPromotion);
951 // Step 12. Extend checks and, in PV nodes, also dangerous moves
952 if (PvNode && dangerous)
955 else if (givesCheck && pos.see_sign(move) >= 0)
956 ext = PvNode ? ONE_PLY : ONE_PLY / 2;
958 // Singular extension search. If all moves but one fail low on a search of
959 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
960 // is singular and should be extended. To verify this we do a reduced search
961 // on all the other moves but the ttMove, if result is lower than ttValue minus
962 // a margin then we extend ttMove.
963 if ( singularExtensionNode
966 && pos.pl_move_is_legal(move, ci.pinned))
968 Value ttValue = value_from_tt(tte->value(), ss->ply);
970 if (abs(ttValue) < VALUE_KNOWN_WIN)
972 Value rBeta = ttValue - int(depth);
973 ss->excludedMove = move;
974 ss->skipNullMove = true;
975 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
976 ss->skipNullMove = false;
977 ss->excludedMove = MOVE_NONE;
978 ss->bestMove = MOVE_NONE;
984 // Update current move (this must be done after singular extension search)
985 newDepth = depth - ONE_PLY + ext;
987 // Step 13. Futility pruning (is omitted in PV nodes)
989 && !captureOrPromotion
994 && (bestValue > VALUE_MATED_IN_PLY_MAX || bestValue == -VALUE_INFINITE))
996 // Move count based pruning
997 if ( moveCount >= futility_move_count(depth)
998 && (!threatMove || !connected_threat(pos, move, threatMove)))
1001 lock_grab(&(sp->lock));
1006 // Value based pruning
1007 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1008 // but fixing this made program slightly weaker.
1009 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1010 futilityValue = futilityBase + futility_margin(predictedDepth, moveCount)
1011 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1013 if (futilityValue < beta)
1016 lock_grab(&(sp->lock));
1021 // Prune moves with negative SEE at low depths
1022 if ( predictedDepth < 2 * ONE_PLY
1023 && pos.see_sign(move) < 0)
1026 lock_grab(&(sp->lock));
1032 // Check for legality only before to do the move
1033 if (!pos.pl_move_is_legal(move, ci.pinned))
1039 ss->currentMove = move;
1040 if (!SpNode && !captureOrPromotion)
1041 movesSearched[playedMoveCount++] = move;
1043 // Step 14. Make the move
1044 pos.do_move(move, st, ci, givesCheck);
1046 // Step 15. Reduced depth search (LMR). If the move fails high will be
1047 // re-searched at full depth.
1048 if ( depth > 3 * ONE_PLY
1050 && !captureOrPromotion
1053 && ss->killers[0] != move
1054 && ss->killers[1] != move)
1056 ss->reduction = reduction<PvNode>(depth, moveCount);
1057 Depth d = newDepth - ss->reduction;
1058 alpha = SpNode ? sp->alpha : alpha;
1060 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1061 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1063 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
1064 ss->reduction = DEPTH_ZERO;
1067 doFullDepthSearch = !isPvMove;
1069 // Step 16. Full depth search, when LMR is skipped or fails high
1070 if (doFullDepthSearch)
1072 alpha = SpNode ? sp->alpha : alpha;
1073 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1074 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1077 // Only for PV nodes do a full PV search on the first move or after a fail
1078 // high, in the latter case search only if value < beta, otherwise let the
1079 // parent node to fail low with value <= alpha and to try another move.
1080 if (PvNode && (isPvMove || (value > alpha && (RootNode || value < beta))))
1081 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1082 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1084 // Step 17. Undo move
1085 pos.undo_move(move);
1087 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1089 // Step 18. Check for new best move
1092 lock_grab(&(sp->lock));
1093 bestValue = sp->bestValue;
1097 // Finished searching the move. If StopRequest is true, the search
1098 // was aborted because the user interrupted the search or because we
1099 // ran out of time. In this case, the return value of the search cannot
1100 // be trusted, and we don't update the best move and/or PV.
1101 if (RootNode && !Signals.stop)
1103 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
1104 rm.nodes += pos.nodes_searched() - nodes;
1106 // PV move or new best move ?
1107 if (isPvMove || value > alpha)
1110 rm.extract_pv_from_tt(pos);
1112 // We record how often the best move has been changed in each
1113 // iteration. This information is used for time management: When
1114 // the best move changes frequently, we allocate some more time.
1115 if (!isPvMove && MultiPV == 1)
1119 // All other moves but the PV are set to the lowest value, this
1120 // is not a problem when sorting becuase sort is stable and move
1121 // position in the list is preserved, just the PV is pushed up.
1122 rm.score = -VALUE_INFINITE;
1126 if (value > bestValue)
1129 ss->bestMove = move;
1133 && value < beta) // We want always alpha < beta
1136 if (SpNode && !thread.cutoff_occurred())
1138 sp->bestValue = value;
1139 sp->ss->bestMove = move;
1141 sp->is_betaCutoff = (value >= beta);
1145 // Step 19. Check for split
1147 && depth >= Threads.min_split_depth()
1149 && Threads.available_slave_exists(pos.thread())
1151 && !thread.cutoff_occurred())
1152 bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, depth,
1153 threatMove, moveCount, &mp, NT);
1156 // Step 20. Check for mate and stalemate
1157 // All legal moves have been searched and if there are no legal moves, it
1158 // must be mate or stalemate. Note that we can have a false positive in
1159 // case of StopRequest or thread.cutoff_occurred() are set, but this is
1160 // harmless because return value is discarded anyhow in the parent nodes.
1161 // If we are in a singular extension search then return a fail low score.
1163 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1165 // If we have pruned all the moves without searching return a fail-low score
1166 if (bestValue == -VALUE_INFINITE)
1168 assert(!playedMoveCount);
1173 // Step 21. Update tables
1174 // Update transposition table entry, history and killers
1175 if (!SpNode && !Signals.stop && !thread.cutoff_occurred())
1177 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1178 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1179 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1181 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1183 // Update killers and history only for non capture moves that fails high
1184 if ( bestValue >= beta
1185 && !pos.is_capture_or_promotion(move))
1187 if (move != ss->killers[0])
1189 ss->killers[1] = ss->killers[0];
1190 ss->killers[0] = move;
1192 update_history(pos, move, depth, movesSearched, playedMoveCount);
1198 // Here we have the lock still grabbed
1199 sp->is_slave[pos.thread()] = false;
1200 sp->nodes += pos.nodes_searched();
1201 lock_release(&(sp->lock));
1204 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1210 // qsearch() is the quiescence search function, which is called by the main
1211 // search function when the remaining depth is zero (or, to be more precise,
1212 // less than ONE_PLY).
1214 template <NodeType NT>
1215 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1217 const bool PvNode = (NT == PV);
1219 assert(NT == PV || NT == NonPV);
1220 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1221 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1222 assert(PvNode || alpha == beta - 1);
1224 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1228 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1229 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1233 Value oldAlpha = alpha;
1235 ss->bestMove = ss->currentMove = MOVE_NONE;
1236 ss->ply = (ss-1)->ply + 1;
1238 // Check for an instant draw or maximum ply reached
1239 if (pos.is_draw<true>() || ss->ply > PLY_MAX)
1242 // Decide whether or not to include checks, this fixes also the type of
1243 // TT entry depth that we are going to use. Note that in qsearch we use
1244 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1245 inCheck = pos.in_check();
1246 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1248 // Transposition table lookup. At PV nodes, we don't use the TT for
1249 // pruning, but only for move ordering.
1250 tte = TT.probe(pos.get_key());
1251 ttMove = (tte ? tte->move() : MOVE_NONE);
1253 if (!PvNode && tte && can_return_tt(tte, ttDepth, beta, ss->ply))
1255 ss->bestMove = ttMove; // Can be MOVE_NONE
1256 return value_from_tt(tte->value(), ss->ply);
1259 // Evaluate the position statically
1262 bestValue = futilityBase = -VALUE_INFINITE;
1263 ss->eval = evalMargin = VALUE_NONE;
1264 enoughMaterial = false;
1270 assert(tte->static_value() != VALUE_NONE);
1272 evalMargin = tte->static_value_margin();
1273 ss->eval = bestValue = tte->static_value();
1276 ss->eval = bestValue = evaluate(pos, evalMargin);
1278 // Stand pat. Return immediately if static value is at least beta
1279 if (bestValue >= beta)
1282 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1287 if (PvNode && bestValue > alpha)
1290 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1291 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1294 // Initialize a MovePicker object for the current position, and prepare
1295 // to search the moves. Because the depth is <= 0 here, only captures,
1296 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1298 MovePicker mp(pos, ttMove, depth, H, move_to((ss-1)->currentMove));
1301 // Loop through the moves until no moves remain or a beta cutoff occurs
1302 while ( bestValue < beta
1303 && (move = mp.get_next_move()) != MOVE_NONE)
1305 assert(is_ok(move));
1307 givesCheck = pos.move_gives_check(move, ci);
1315 && !is_promotion(move)
1316 && !pos.is_passed_pawn_push(move))
1318 futilityValue = futilityBase
1319 + PieceValueEndgame[pos.piece_on(move_to(move))]
1320 + (is_enpassant(move) ? PawnValueEndgame : VALUE_ZERO);
1322 if (futilityValue < beta)
1324 if (futilityValue > bestValue)
1325 bestValue = futilityValue;
1330 // Prune moves with negative or equal SEE
1331 if ( futilityBase < beta
1332 && depth < DEPTH_ZERO
1333 && pos.see(move) <= 0)
1337 // Detect non-capture evasions that are candidate to be pruned
1338 evasionPrunable = !PvNode
1340 && bestValue > VALUE_MATED_IN_PLY_MAX
1341 && !pos.is_capture(move)
1342 && !pos.can_castle(pos.side_to_move());
1344 // Don't search moves with negative SEE values
1346 && (!inCheck || evasionPrunable)
1348 && !is_promotion(move)
1349 && pos.see_sign(move) < 0)
1352 // Don't search useless checks
1357 && !pos.is_capture_or_promotion(move)
1358 && ss->eval + PawnValueMidgame / 4 < beta
1359 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1361 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1362 bestValue = ss->eval + PawnValueMidgame / 4;
1367 // Check for legality only before to do the move
1368 if (!pos.pl_move_is_legal(move, ci.pinned))
1371 ss->currentMove = move;
1373 // Make and search the move
1374 pos.do_move(move, st, ci, givesCheck);
1375 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1376 pos.undo_move(move);
1378 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1381 if (value > bestValue)
1384 ss->bestMove = move;
1388 && value < beta) // We want always alpha < beta
1393 // All legal moves have been searched. A special case: If we're in check
1394 // and no legal moves were found, it is checkmate.
1395 if (inCheck && bestValue == -VALUE_INFINITE)
1396 return value_mated_in(ss->ply);
1398 // Update transposition table
1399 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1400 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1401 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1403 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, move, ss->eval, evalMargin);
1405 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1411 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1412 // bestValue is updated only when returning false because in that case move
1415 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1417 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1418 Square from, to, ksq, victimSq;
1421 Value futilityValue, bv = *bestValue;
1423 from = move_from(move);
1425 them = flip(pos.side_to_move());
1426 ksq = pos.king_square(them);
1427 kingAtt = pos.attacks_from<KING>(ksq);
1428 pc = pos.piece_on(from);
1430 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1431 oldAtt = pos.attacks_from(pc, from, occ);
1432 newAtt = pos.attacks_from(pc, to, occ);
1434 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1435 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1437 if (!(b && (b & (b - 1))))
1440 // Rule 2. Queen contact check is very dangerous
1441 if ( type_of(pc) == QUEEN
1442 && bit_is_set(kingAtt, to))
1445 // Rule 3. Creating new double threats with checks
1446 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1450 victimSq = pop_1st_bit(&b);
1451 futilityValue = futilityBase + PieceValueEndgame[pos.piece_on(victimSq)];
1453 // Note that here we generate illegal "double move"!
1454 if ( futilityValue >= beta
1455 && pos.see_sign(make_move(from, victimSq)) >= 0)
1458 if (futilityValue > bv)
1462 // Update bestValue only if check is not dangerous (because we will prune the move)
1468 // connected_moves() tests whether two moves are 'connected' in the sense
1469 // that the first move somehow made the second move possible (for instance
1470 // if the moving piece is the same in both moves). The first move is assumed
1471 // to be the move that was made to reach the current position, while the
1472 // second move is assumed to be a move from the current position.
1474 bool connected_moves(const Position& pos, Move m1, Move m2) {
1476 Square f1, t1, f2, t2;
1483 // Case 1: The moving piece is the same in both moves
1489 // Case 2: The destination square for m2 was vacated by m1
1495 // Case 3: Moving through the vacated square
1496 p2 = pos.piece_on(f2);
1497 if ( piece_is_slider(p2)
1498 && bit_is_set(squares_between(f2, t2), f1))
1501 // Case 4: The destination square for m2 is defended by the moving piece in m1
1502 p1 = pos.piece_on(t1);
1503 if (bit_is_set(pos.attacks_from(p1, t1), t2))
1506 // Case 5: Discovered check, checking piece is the piece moved in m1
1507 ksq = pos.king_square(pos.side_to_move());
1508 if ( piece_is_slider(p1)
1509 && bit_is_set(squares_between(t1, ksq), f2))
1511 Bitboard occ = pos.occupied_squares();
1512 clear_bit(&occ, f2);
1513 if (bit_is_set(pos.attacks_from(p1, t1, occ), ksq))
1520 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1521 // "plies to mate from the current ply". Non-mate scores are unchanged.
1522 // The function is called before storing a value to the transposition table.
1524 Value value_to_tt(Value v, int ply) {
1526 if (v >= VALUE_MATE_IN_PLY_MAX)
1529 if (v <= VALUE_MATED_IN_PLY_MAX)
1536 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1537 // the transposition table to a mate score corrected for the current ply.
1539 Value value_from_tt(Value v, int ply) {
1541 if (v >= VALUE_MATE_IN_PLY_MAX)
1544 if (v <= VALUE_MATED_IN_PLY_MAX)
1551 // connected_threat() tests whether it is safe to forward prune a move or if
1552 // is somehow connected to the threat move returned by null search.
1554 bool connected_threat(const Position& pos, Move m, Move threat) {
1557 assert(is_ok(threat));
1558 assert(!pos.is_capture_or_promotion(m));
1559 assert(!pos.is_passed_pawn_push(m));
1561 Square mfrom, mto, tfrom, tto;
1563 mfrom = move_from(m);
1565 tfrom = move_from(threat);
1566 tto = move_to(threat);
1568 // Case 1: Don't prune moves which move the threatened piece
1572 // Case 2: If the threatened piece has value less than or equal to the
1573 // value of the threatening piece, don't prune moves which defend it.
1574 if ( pos.is_capture(threat)
1575 && ( PieceValueMidgame[pos.piece_on(tfrom)] >= PieceValueMidgame[pos.piece_on(tto)]
1576 || type_of(pos.piece_on(tfrom)) == KING)
1577 && pos.move_attacks_square(m, tto))
1580 // Case 3: If the moving piece in the threatened move is a slider, don't
1581 // prune safe moves which block its ray.
1582 if ( piece_is_slider(pos.piece_on(tfrom))
1583 && bit_is_set(squares_between(tfrom, tto), mto)
1584 && pos.see_sign(m) >= 0)
1591 // can_return_tt() returns true if a transposition table score can be used to
1592 // cut-off at a given point in search.
1594 bool can_return_tt(const TTEntry* tte, Depth depth, Value beta, int ply) {
1596 Value v = value_from_tt(tte->value(), ply);
1598 return ( tte->depth() >= depth
1599 || v >= std::max(VALUE_MATE_IN_PLY_MAX, beta)
1600 || v < std::min(VALUE_MATED_IN_PLY_MAX, beta))
1602 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1603 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1607 // refine_eval() returns the transposition table score if possible, otherwise
1608 // falls back on static position evaluation.
1610 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1614 Value v = value_from_tt(tte->value(), ply);
1616 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1617 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1624 // update_history() registers a good move that produced a beta-cutoff in
1625 // history and marks as failures all the other moves of that ply.
1627 void update_history(const Position& pos, Move move, Depth depth,
1628 Move movesSearched[], int moveCount) {
1630 Value bonus = Value(int(depth) * int(depth));
1632 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1634 for (int i = 0; i < moveCount - 1; i++)
1636 m = movesSearched[i];
1640 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1645 // current_search_time() returns the number of milliseconds which have passed
1646 // since the beginning of the current search.
1648 int elapsed_time(bool reset) {
1650 static int searchStartTime;
1653 searchStartTime = get_system_time();
1655 return get_system_time() - searchStartTime;
1659 // score_to_uci() converts a value to a string suitable for use with the UCI
1660 // protocol specifications:
1662 // cp <x> The score from the engine's point of view in centipawns.
1663 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1664 // use negative values for y.
1666 string score_to_uci(Value v, Value alpha, Value beta) {
1668 std::stringstream s;
1670 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1671 s << " score cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1673 s << " score mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1675 s << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1681 // pv_info_to_uci() sends search info to GUI. UCI protocol requires to send all
1682 // the PV lines also if are still to be searched and so refer to the previous
1685 void pv_info_to_uci(const Position& pos, int depth, Value alpha, Value beta) {
1687 int t = elapsed_time();
1690 for (int i = 0; i < Threads.size(); i++)
1691 if (Threads[i].maxPly > selDepth)
1692 selDepth = Threads[i].maxPly;
1694 for (size_t i = 0; i < std::min(UCIMultiPV, RootMoves.size()); i++)
1696 bool updated = (i <= MultiPVIdx);
1698 if (depth == 1 && !updated)
1701 int d = (updated ? depth : depth - 1);
1702 Value s = (updated ? RootMoves[i].score : RootMoves[i].prevScore);
1706 << " seldepth " << selDepth
1707 << (i == MultiPVIdx ? score_to_uci(s, alpha, beta) : score_to_uci(s))
1708 << " nodes " << pos.nodes_searched()
1709 << " nps " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
1711 << " multipv " << i + 1 << " pv";
1713 for (int j = 0; RootMoves[i].pv[j] != MOVE_NONE; j++)
1714 cout << " " << RootMoves[i].pv[j];
1721 // pv_info_to_log() writes human-readable search information to the log file
1722 // (which is created when the UCI parameter "Use Search Log" is "true"). It
1723 // uses the two below helpers to pretty format time and score respectively.
1725 string time_to_string(int millisecs) {
1727 const int MSecMinute = 1000 * 60;
1728 const int MSecHour = 1000 * 60 * 60;
1730 int hours = millisecs / MSecHour;
1731 int minutes = (millisecs % MSecHour) / MSecMinute;
1732 int seconds = ((millisecs % MSecHour) % MSecMinute) / 1000;
1734 std::stringstream s;
1739 s << std::setfill('0') << std::setw(2) << minutes << ':'
1740 << std::setw(2) << seconds;
1744 string score_to_string(Value v) {
1746 std::stringstream s;
1748 if (v >= VALUE_MATE_IN_PLY_MAX)
1749 s << "#" << (VALUE_MATE - v + 1) / 2;
1750 else if (v <= VALUE_MATED_IN_PLY_MAX)
1751 s << "-#" << (VALUE_MATE + v) / 2;
1753 s << std::setprecision(2) << std::fixed << std::showpos
1754 << float(v) / PawnValueMidgame;
1759 void pv_info_to_log(Position& pos, int depth, Value value, int time, Move pv[]) {
1761 const int64_t K = 1000;
1762 const int64_t M = 1000000;
1764 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1766 string san, padding;
1768 std::stringstream s;
1770 s << set960(pos.is_chess960())
1771 << std::setw(2) << depth
1772 << std::setw(8) << score_to_string(value)
1773 << std::setw(8) << time_to_string(time);
1775 if (pos.nodes_searched() < M)
1776 s << std::setw(8) << pos.nodes_searched() / 1 << " ";
1778 else if (pos.nodes_searched() < K * M)
1779 s << std::setw(7) << pos.nodes_searched() / K << "K ";
1782 s << std::setw(7) << pos.nodes_searched() / M << "M ";
1784 padding = string(s.str().length(), ' ');
1785 length = padding.length();
1787 while (*m != MOVE_NONE)
1789 san = move_to_san(pos, *m);
1791 if (length + san.length() > 80)
1793 s << "\n" + padding;
1794 length = padding.length();
1798 length += san.length() + 1;
1800 pos.do_move(*m++, *st++);
1804 pos.undo_move(*--m);
1806 Log l(Options["Search Log Filename"].value<string>());
1807 l << s.str() << endl;
1811 // When playing with strength handicap choose best move among the MultiPV set
1812 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1814 void do_skill_level(Move* best, Move* ponder) {
1816 assert(MultiPV > 1);
1820 // PRNG sequence should be not deterministic
1821 for (int i = abs(get_system_time() % 50); i > 0; i--)
1822 rk.rand<unsigned>();
1824 // Rml list is already sorted by score in descending order
1825 size_t size = std::min(MultiPV, RootMoves.size());
1826 int variance = std::min(RootMoves[0].score - RootMoves[size - 1].score, PawnValueMidgame);
1827 int weakness = 120 - 2 * SkillLevel;
1828 int max_s = -VALUE_INFINITE;
1830 // Choose best move. For each move score we add two terms both dependent on
1831 // weakness, one deterministic and bigger for weaker moves, and one random,
1832 // then we choose the move with the resulting highest score.
1833 for (size_t i = 0; i < size; i++)
1835 int s = RootMoves[i].score;
1837 // Don't allow crazy blunders even at very low skills
1838 if (i > 0 && RootMoves[i-1].score > s + EasyMoveMargin)
1841 // This is our magic formula
1842 s += ( weakness * int(RootMoves[0].score - s)
1843 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1848 *best = RootMoves[i].pv[0];
1849 *ponder = RootMoves[i].pv[1];
1855 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
1856 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
1857 // allow to always have a ponder move even when we fail high at root and also a
1858 // long PV to print that is important for position analysis.
1860 void RootMove::extract_pv_from_tt(Position& pos) {
1862 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1867 assert(m != MOVE_NONE && pos.is_pseudo_legal(m));
1871 pos.do_move(m, *st++);
1873 while ( (tte = TT.probe(pos.get_key())) != NULL
1874 && tte->move() != MOVE_NONE
1875 && pos.is_pseudo_legal(tte->move())
1876 && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces())
1878 && (!pos.is_draw<false>() || ply < 2))
1880 pv.push_back(tte->move());
1881 pos.do_move(tte->move(), *st++);
1884 pv.push_back(MOVE_NONE);
1886 do pos.undo_move(pv[--ply]); while (ply);
1890 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
1891 // the PV back into the TT. This makes sure the old PV moves are searched
1892 // first, even if the old TT entries have been overwritten.
1894 void RootMove::insert_pv_in_tt(Position& pos) {
1896 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1899 Value v, m = VALUE_NONE;
1902 assert(pv[ply] != MOVE_NONE && pos.is_pseudo_legal(pv[ply]));
1908 // Don't overwrite existing correct entries
1909 if (!tte || tte->move() != pv[ply])
1911 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
1912 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
1914 pos.do_move(pv[ply], *st++);
1916 } while (pv[++ply] != MOVE_NONE);
1918 do pos.undo_move(pv[--ply]); while (ply);
1924 /// Thread::idle_loop() is where the thread is parked when it has no work to do.
1925 /// The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint object
1926 /// for which the thread is the master.
1928 void Thread::idle_loop(SplitPoint* sp) {
1932 // If we are not searching, wait for a condition to be signaled
1933 // instead of wasting CPU time polling for work.
1936 || (Threads.use_sleeping_threads() && !is_searching))
1938 assert((!sp && threadID) || Threads.use_sleeping_threads());
1946 // Grab the lock to avoid races with Thread::wake_up()
1947 lock_grab(&sleepLock);
1949 // If we are master and all slaves have finished don't go to sleep
1950 if (sp && Threads.split_point_finished(sp))
1952 lock_release(&sleepLock);
1956 // Do sleep after retesting sleep conditions under lock protection, in
1957 // particular we need to avoid a deadlock in case a master thread has,
1958 // in the meanwhile, allocated us and sent the wake_up() call before we
1959 // had the chance to grab the lock.
1960 if (do_sleep || !is_searching)
1961 cond_wait(&sleepCond, &sleepLock);
1963 lock_release(&sleepLock);
1966 // If this thread has been assigned work, launch a search
1969 assert(!do_terminate);
1971 // Copy split point position and search stack and call search()
1972 Stack ss[PLY_MAX_PLUS_2];
1973 SplitPoint* tsp = splitPoint;
1974 Position pos(*tsp->pos, threadID);
1976 memcpy(ss, tsp->ss - 1, 4 * sizeof(Stack));
1979 if (tsp->nodeType == Root)
1980 search<SplitPointRoot>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
1981 else if (tsp->nodeType == PV)
1982 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
1983 else if (tsp->nodeType == NonPV)
1984 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
1988 assert(is_searching);
1990 is_searching = false;
1992 // Wake up master thread so to allow it to return from the idle loop in
1993 // case we are the last slave of the split point.
1994 if ( Threads.use_sleeping_threads()
1995 && threadID != tsp->master
1996 && !Threads[tsp->master].is_searching)
1997 Threads[tsp->master].wake_up();
2000 // If this thread is the master of a split point and all slaves have
2001 // finished their work at this split point, return from the idle loop.
2002 if (sp && Threads.split_point_finished(sp))
2004 // Because sp->is_slave[] is reset under lock protection,
2005 // be sure sp->lock has been released before to return.
2006 lock_grab(&(sp->lock));
2007 lock_release(&(sp->lock));
2014 /// do_timer_event() is called by the timer thread when the timer triggers. It
2015 /// is used to print debug info and, more important, to detect when we are out of
2016 /// available time and so stop the search.
2018 void do_timer_event() {
2020 static int lastInfoTime;
2021 int e = elapsed_time();
2023 if (get_system_time() - lastInfoTime >= 1000 || !lastInfoTime)
2025 lastInfoTime = get_system_time();
2028 dbg_print_hit_rate();
2034 bool stillAtFirstMove = Signals.firstRootMove
2035 && !Signals.failedLowAtRoot
2036 && e > TimeMgr.available_time();
2038 bool noMoreTime = e > TimeMgr.maximum_time()
2039 || stillAtFirstMove;
2041 if ( (Limits.useTimeManagement() && noMoreTime)
2042 || (Limits.maxTime && e >= Limits.maxTime)
2043 /* missing nodes limit */ ) // FIXME
2044 Signals.stop = true;