2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 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/>.
23 #include <cstring> // For std::memset
36 #include "syzygy/tbprobe.h"
42 StateStackPtr SetupStates;
45 namespace Tablebases {
55 namespace TB = Tablebases;
59 using namespace Search;
63 // Different node types, used as template parameter
64 enum NodeType { Root, PV, NonPV };
66 // Razoring and futility margin based on depth
67 const int razor_margin[4] = { 483, 570, 603, 554 };
68 Value futility_margin(Depth d) { return Value(200 * d); }
70 // Futility and reductions lookup tables, initialized at startup
71 int FutilityMoveCounts[2][16]; // [improving][depth]
72 Depth Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
74 template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
75 return Reductions[PvNode][i][std::min(d, 63 * ONE_PLY)][std::min(mn, 63)];
78 // Skill struct is used to implement strength limiting
80 Skill(int l) : level(l) {}
81 bool enabled() const { return level < 20; }
82 bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
83 Move best_move(size_t multiPV) { return best ? best : pick_best(multiPV); }
84 Move pick_best(size_t multiPV);
87 Move best = MOVE_NONE;
90 // EasyMoveManager struct is used to detect a so called 'easy move'; when PV is
91 // stable across multiple search iterations we can fast return the best move.
92 struct EasyMoveManager {
97 pv[0] = pv[1] = pv[2] = MOVE_NONE;
100 Move get(Key key) const {
101 return expectedPosKey == key ? pv[2] : MOVE_NONE;
104 void update(Position& pos, const std::vector<Move>& newPv) {
106 assert(newPv.size() >= 3);
108 // Keep track of how many times in a row 3rd ply remains stable
109 stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0;
111 if (!std::equal(newPv.begin(), newPv.begin() + 3, pv))
113 std::copy(newPv.begin(), newPv.begin() + 3, pv);
116 pos.do_move(newPv[0], st[0], pos.gives_check(newPv[0], CheckInfo(pos)));
117 pos.do_move(newPv[1], st[1], pos.gives_check(newPv[1], CheckInfo(pos)));
118 expectedPosKey = pos.key();
119 pos.undo_move(newPv[1]);
120 pos.undo_move(newPv[0]);
129 EasyMoveManager EasyMove;
130 bool easyPlayed, failedLow;
131 double BestMoveChanges;
132 Value DrawValue[COLOR_NB];
133 CounterMovesHistoryStats CounterMovesHistory;
135 template <NodeType NT>
136 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
138 template <NodeType NT, bool InCheck>
139 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
141 Value value_to_tt(Value v, int ply);
142 Value value_from_tt(Value v, int ply);
143 void update_pv(Move* pv, Move move, Move* childPv);
144 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
150 /// Search::init() is called during startup to initialize various lookup tables
152 void Search::init() {
154 const double K[][2] = {{ 0.799, 2.281 }, { 0.484, 3.023 }};
156 for (int pv = 0; pv <= 1; ++pv)
157 for (int imp = 0; imp <= 1; ++imp)
158 for (int d = 1; d < 64; ++d)
159 for (int mc = 1; mc < 64; ++mc)
161 double r = K[pv][0] + log(d) * log(mc) / K[pv][1];
164 Reductions[pv][imp][d][mc] = int(r) * ONE_PLY;
166 // Increase reduction when eval is not improving
167 if (!pv && !imp && Reductions[pv][imp][d][mc] >= 2 * ONE_PLY)
168 Reductions[pv][imp][d][mc] += ONE_PLY;
171 for (int d = 0; d < 16; ++d)
173 FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
174 FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
179 /// Search::clear() resets to zero search state, to obtain reproducible results
181 void Search::clear() {
184 CounterMovesHistory.clear();
186 for (Thread* th : Threads)
189 th->counterMoves.clear();
194 /// Search::perft() is our utility to verify move generation. All the leaf nodes
195 /// up to the given depth are generated and counted and the sum returned.
197 uint64_t Search::perft(Position& pos, Depth depth) {
200 uint64_t cnt, nodes = 0;
202 const bool leaf = (depth == 2 * ONE_PLY);
204 for (const auto& m : MoveList<LEGAL>(pos))
206 if (Root && depth <= ONE_PLY)
210 pos.do_move(m, st, pos.gives_check(m, ci));
211 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
216 sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
221 template uint64_t Search::perft<true>(Position&, Depth);
224 /// MainThread::search() is called by the main thread when the program receives
225 /// the UCI 'go' command. It searches from root position and at the end prints
226 /// the "bestmove" to output.
228 void MainThread::search() {
230 Color us = rootPos.side_to_move();
231 Time.init(Limits, us, rootPos.game_ply());
233 int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
234 DrawValue[ us] = VALUE_DRAW - Value(contempt);
235 DrawValue[~us] = VALUE_DRAW + Value(contempt);
238 TB::RootInTB = false;
239 TB::UseRule50 = Options["Syzygy50MoveRule"];
240 TB::ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
241 TB::Cardinality = Options["SyzygyProbeLimit"];
243 // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
244 if (TB::Cardinality > TB::MaxCardinality)
246 TB::Cardinality = TB::MaxCardinality;
247 TB::ProbeDepth = DEPTH_ZERO;
250 if (rootMoves.empty())
252 rootMoves.push_back(RootMove(MOVE_NONE));
253 sync_cout << "info depth 0 score "
254 << UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
259 if (TB::Cardinality >= rootPos.count<ALL_PIECES>(WHITE)
260 + rootPos.count<ALL_PIECES>(BLACK))
262 // If the current root position is in the tablebases then RootMoves
263 // contains only moves that preserve the draw or win.
264 TB::RootInTB = Tablebases::root_probe(rootPos, rootMoves, TB::Score);
267 TB::Cardinality = 0; // Do not probe tablebases during the search
269 else // If DTZ tables are missing, use WDL tables as a fallback
271 // Filter out moves that do not preserve a draw or win
272 TB::RootInTB = Tablebases::root_probe_wdl(rootPos, rootMoves, TB::Score);
274 // Only probe during search if winning
275 if (TB::Score <= VALUE_DRAW)
281 TB::Hits = rootMoves.size();
284 TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
285 : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1
290 for (Thread* th : Threads)
293 th->rootDepth = DEPTH_ZERO;
296 th->rootPos = Position(rootPos, th);
297 th->rootMoves = rootMoves;
298 th->start_searching();
302 Thread::search(); // Let's start searching!
305 // When playing in 'nodes as time' mode, subtract the searched nodes from
306 // the available ones before to exit.
308 Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
310 // When we reach the maximum depth, we can arrive here without a raise of
311 // Signals.stop. However, if we are pondering or in an infinite search,
312 // the UCI protocol states that we shouldn't print the best move before the
313 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
314 // until the GUI sends one of those commands (which also raises Signals.stop).
315 if (!Signals.stop && (Limits.ponder || Limits.infinite))
317 Signals.stopOnPonderhit = true;
321 // Stop the threads if not already stopped
324 // Wait until all threads have finished
325 for (Thread* th : Threads)
327 th->wait_for_search_finished();
329 // Check if there are threads with a better score than main thread.
330 Thread* bestThread = this;
331 if (!easyPlayed && Options["MultiPV"] == 1 && !Skill(Options["Skill Level"]).enabled())
332 for (Thread* th : Threads)
333 if ( th->completedDepth > bestThread->completedDepth
334 && th->rootMoves[0].score > bestThread->rootMoves[0].score)
337 // Send new PV when needed.
338 // FIXME: Breaks multiPV, and skill levels
339 if (bestThread != this)
340 sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
342 sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
344 if (bestThread->rootMoves[0].pv.size() > 1 || bestThread->rootMoves[0].extract_ponder_from_tt(rootPos))
345 std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
347 std::cout << sync_endl;
351 // Thread::search() is the main iterative deepening loop. It calls search()
352 // repeatedly with increasing depth until the allocated thinking time has been
353 // consumed, user stops the search, or the maximum search depth is reached.
355 void Thread::search() {
357 Stack stack[MAX_PLY+4], *ss = stack+2; // To allow referencing (ss-2) and (ss+2)
358 Value bestValue, alpha, beta, delta;
359 Move easyMove = MOVE_NONE;
360 bool isMainThread = (this == Threads.main());
362 std::memset(ss-2, 0, 5 * sizeof(Stack));
364 bestValue = delta = alpha = -VALUE_INFINITE;
365 beta = VALUE_INFINITE;
366 completedDepth = DEPTH_ZERO;
370 easyMove = EasyMove.get(rootPos.key());
377 size_t multiPV = Options["MultiPV"];
378 Skill skill(Options["Skill Level"]);
380 // When playing with strength handicap enable MultiPV search that we will
381 // use behind the scenes to retrieve a set of possible moves.
383 multiPV = std::max(multiPV, (size_t)4);
385 multiPV = std::min(multiPV, rootMoves.size());
387 // Iterative deepening loop until requested to stop or target depth reached
388 while (++rootDepth < DEPTH_MAX && !Signals.stop && (!Limits.depth || rootDepth <= Limits.depth))
390 // Set up the new depth for the helper threads skipping in average each
391 // 2nd ply (using a half density map similar to a Hadamard matrix).
394 int d = rootDepth + rootPos.game_ply();
396 if (idx <= 6 || idx > 24)
398 if (((d + idx) >> (msb(idx + 1) - 1)) % 2)
403 // Table of values of 6 bits with 3 of them set
404 static const int HalfDensityMap[] = {
405 0x07, 0x0b, 0x0d, 0x0e, 0x13, 0x16, 0x19, 0x1a, 0x1c,
406 0x23, 0x25, 0x26, 0x29, 0x2c, 0x31, 0x32, 0x34, 0x38
409 if ((HalfDensityMap[idx - 7] >> (d % 6)) & 1)
414 // Age out PV variability metric
416 BestMoveChanges *= 0.505, failedLow = false;
418 // Save the last iteration's scores before first PV line is searched and
419 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
420 for (RootMove& rm : rootMoves)
421 rm.previousScore = rm.score;
423 // MultiPV loop. We perform a full root search for each PV line
424 for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
426 // Reset aspiration window starting size
427 if (rootDepth >= 5 * ONE_PLY)
430 alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
431 beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
434 // Start with a small aspiration window and, in the case of a fail
435 // high/low, re-search with a bigger window until we're not failing
439 bestValue = ::search<Root>(rootPos, ss, alpha, beta, rootDepth, false);
441 // Bring the best move to the front. It is critical that sorting
442 // is done with a stable algorithm because all the values but the
443 // first and eventually the new best one are set to -VALUE_INFINITE
444 // and we want to keep the same order for all the moves except the
445 // new PV that goes to the front. Note that in case of MultiPV
446 // search the already searched PV lines are preserved.
447 std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
449 // Write PV back to transposition table in case the relevant
450 // entries have been overwritten during the search.
451 for (size_t i = 0; i <= PVIdx; ++i)
452 rootMoves[i].insert_pv_in_tt(rootPos);
454 // If search has been stopped break immediately. Sorting and
455 // writing PV back to TT is safe because RootMoves is still
456 // valid, although it refers to previous iteration.
460 // When failing high/low give some update (without cluttering
461 // the UI) before a re-search.
464 && (bestValue <= alpha || bestValue >= beta)
465 && Time.elapsed() > 3000)
466 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
468 // In case of failing low/high increase aspiration window and
469 // re-search, otherwise exit the loop.
470 if (bestValue <= alpha)
472 beta = (alpha + beta) / 2;
473 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
478 Signals.stopOnPonderhit = false;
481 else if (bestValue >= beta)
483 alpha = (alpha + beta) / 2;
484 beta = std::min(bestValue + delta, VALUE_INFINITE);
489 delta += delta / 4 + 5;
491 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
494 // Sort the PV lines searched so far and update the GUI
495 std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
501 sync_cout << "info nodes " << Threads.nodes_searched()
502 << " time " << Time.elapsed() << sync_endl;
504 else if (PVIdx + 1 == multiPV || Time.elapsed() > 3000)
505 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
509 completedDepth = rootDepth;
514 // If skill level is enabled and time is up, pick a sub-optimal best move
515 if (skill.enabled() && skill.time_to_pick(rootDepth))
516 skill.pick_best(multiPV);
518 // Have we found a "mate in x"?
520 && bestValue >= VALUE_MATE_IN_MAX_PLY
521 && VALUE_MATE - bestValue <= 2 * Limits.mate)
524 // Do we have time for the next iteration? Can we stop searching now?
525 if (Limits.use_time_management())
527 if (!Signals.stop && !Signals.stopOnPonderhit)
529 // Take some extra time if the best move has changed
530 if (rootDepth > 4 * ONE_PLY && multiPV == 1)
531 Time.pv_instability(BestMoveChanges);
533 // Stop the search if only one legal move is available or all
534 // of the available time has been used or we matched an easyMove
535 // from the previous search and just did a fast verification.
536 if ( rootMoves.size() == 1
537 || Time.elapsed() > Time.available() * (failedLow? 641 : 315)/640
538 || ( easyPlayed = ( rootMoves[0].pv[0] == easyMove
539 && BestMoveChanges < 0.03
540 && Time.elapsed() > Time.available() / 8)))
542 // If we are allowed to ponder do not stop the search now but
543 // keep pondering until the GUI sends "ponderhit" or "stop".
545 Signals.stopOnPonderhit = true;
551 if (rootMoves[0].pv.size() >= 3)
552 EasyMove.update(rootPos, rootMoves[0].pv);
561 // Clear any candidate easy move that wasn't stable for the last search
562 // iterations; the second condition prevents consecutive fast moves.
563 if (EasyMove.stableCnt < 6 || easyPlayed)
566 // If skill level is enabled, swap best PV line with the sub-optimal one
568 std::swap(rootMoves[0], *std::find(rootMoves.begin(),
569 rootMoves.end(), skill.best_move(multiPV)));
575 // search<>() is the main search function for both PV and non-PV nodes
577 template <NodeType NT>
578 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
580 const bool RootNode = NT == Root;
581 const bool PvNode = NT == PV || NT == Root;
583 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
584 assert(PvNode || (alpha == beta - 1));
585 assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
587 Move pv[MAX_PLY+1], quietsSearched[64];
591 Move ttMove, move, excludedMove, bestMove;
592 Depth extension, newDepth, predictedDepth;
593 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
594 bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
595 bool captureOrPromotion, doFullDepthSearch;
596 int moveCount, quietCount;
598 // Step 1. Initialize node
599 Thread* thisThread = pos.this_thread();
600 inCheck = pos.checkers();
601 moveCount = quietCount = ss->moveCount = 0;
602 bestValue = -VALUE_INFINITE;
603 ss->ply = (ss-1)->ply + 1;
605 // Check for available remaining time
606 if (thisThread->resetCalls.load(std::memory_order_relaxed))
608 thisThread->resetCalls = false;
609 thisThread->callsCnt = 0;
611 if (++thisThread->callsCnt > 4096)
613 for (Thread* th : Threads)
614 th->resetCalls = true;
619 // Used to send selDepth info to GUI
620 if (PvNode && thisThread->maxPly < ss->ply)
621 thisThread->maxPly = ss->ply;
625 // Step 2. Check for aborted search and immediate draw
626 if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw() || ss->ply >= MAX_PLY)
627 return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
628 : DrawValue[pos.side_to_move()];
630 // Step 3. Mate distance pruning. Even if we mate at the next move our score
631 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
632 // a shorter mate was found upward in the tree then there is no need to search
633 // because we will never beat the current alpha. Same logic but with reversed
634 // signs applies also in the opposite condition of being mated instead of giving
635 // mate. In this case return a fail-high score.
636 alpha = std::max(mated_in(ss->ply), alpha);
637 beta = std::min(mate_in(ss->ply+1), beta);
642 assert(0 <= ss->ply && ss->ply < MAX_PLY);
644 ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
645 (ss+1)->skipEarlyPruning = false;
646 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
648 // Step 4. Transposition table lookup. We don't want the score of a partial
649 // search to overwrite a previous full search TT value, so we use a different
650 // position key in case of an excluded move.
651 excludedMove = ss->excludedMove;
652 posKey = excludedMove ? pos.exclusion_key() : pos.key();
653 tte = TT.probe(posKey, ttHit);
654 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
655 ttMove = RootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
656 : ttHit ? tte->move() : MOVE_NONE;
658 // At non-PV nodes we check for an early TT cutoff
661 && tte->depth() >= depth
662 && ttValue != VALUE_NONE // Possible in case of TT access race
663 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
664 : (tte->bound() & BOUND_UPPER)))
666 ss->currentMove = ttMove; // Can be MOVE_NONE
668 // If ttMove is quiet, update killers, history, counter move on TT hit
669 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove))
670 update_stats(pos, ss, ttMove, depth, nullptr, 0);
675 // Step 4a. Tablebase probe
676 if (!RootNode && TB::Cardinality)
678 int piecesCnt = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
680 if ( piecesCnt <= TB::Cardinality
681 && (piecesCnt < TB::Cardinality || depth >= TB::ProbeDepth)
682 && pos.rule50_count() == 0)
684 int found, v = Tablebases::probe_wdl(pos, &found);
690 int drawScore = TB::UseRule50 ? 1 : 0;
692 value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
693 : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
694 : VALUE_DRAW + 2 * v * drawScore;
696 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
697 std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
698 MOVE_NONE, VALUE_NONE, TT.generation());
705 // Step 5. Evaluate the position statically
708 ss->staticEval = eval = VALUE_NONE;
714 // Never assume anything on values stored in TT
715 if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
716 eval = ss->staticEval = evaluate(pos);
718 // Can ttValue be used as a better position evaluation?
719 if (ttValue != VALUE_NONE)
720 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
725 eval = ss->staticEval =
726 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
727 : -(ss-1)->staticEval + 2 * Eval::Tempo;
729 tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
730 ss->staticEval, TT.generation());
733 if (ss->skipEarlyPruning)
736 // Step 6. Razoring (skipped when in check)
738 && depth < 4 * ONE_PLY
739 && eval + razor_margin[depth] <= alpha
740 && ttMove == MOVE_NONE)
742 if ( depth <= ONE_PLY
743 && eval + razor_margin[3 * ONE_PLY] <= alpha)
744 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
746 Value ralpha = alpha - razor_margin[depth];
747 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
752 // Step 7. Futility pruning: child node (skipped when in check)
754 && depth < 7 * ONE_PLY
755 && eval - futility_margin(depth) >= beta
756 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
757 && pos.non_pawn_material(pos.side_to_move()))
758 return eval - futility_margin(depth);
760 // Step 8. Null move search with verification search (is omitted in PV nodes)
762 && depth >= 2 * ONE_PLY
764 && pos.non_pawn_material(pos.side_to_move()))
766 ss->currentMove = MOVE_NULL;
768 assert(eval - beta >= 0);
770 // Null move dynamic reduction based on depth and value
771 Depth R = ((823 + 67 * depth) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
773 pos.do_null_move(st);
774 (ss+1)->skipEarlyPruning = true;
775 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
776 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
777 (ss+1)->skipEarlyPruning = false;
778 pos.undo_null_move();
780 if (nullValue >= beta)
782 // Do not return unproven mate scores
783 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
786 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
789 // Do verification search at high depths
790 ss->skipEarlyPruning = true;
791 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
792 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
793 ss->skipEarlyPruning = false;
800 // Step 9. ProbCut (skipped when in check)
801 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
802 // and a reduced search returns a value much above beta, we can (almost)
803 // safely prune the previous move.
805 && depth >= 5 * ONE_PLY
806 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
808 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
809 Depth rdepth = depth - 4 * ONE_PLY;
811 assert(rdepth >= ONE_PLY);
812 assert((ss-1)->currentMove != MOVE_NONE);
813 assert((ss-1)->currentMove != MOVE_NULL);
815 MovePicker mp(pos, ttMove, thisThread->history, PieceValue[MG][pos.captured_piece_type()]);
818 while ((move = mp.next_move()) != MOVE_NONE)
819 if (pos.legal(move, ci.pinned))
821 ss->currentMove = move;
822 pos.do_move(move, st, pos.gives_check(move, ci));
823 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
830 // Step 10. Internal iterative deepening (skipped when in check)
831 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
833 && (PvNode || ss->staticEval + 256 >= beta))
835 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
836 ss->skipEarlyPruning = true;
837 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
838 ss->skipEarlyPruning = false;
840 tte = TT.probe(posKey, ttHit);
841 ttMove = ttHit ? tte->move() : MOVE_NONE;
844 moves_loop: // When in check search starts from here
846 Square prevSq = to_sq((ss-1)->currentMove);
847 Move cm = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
848 const CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
850 MovePicker mp(pos, ttMove, depth, thisThread->history, cmh, cm, ss);
852 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
853 improving = ss->staticEval >= (ss-2)->staticEval
854 || ss->staticEval == VALUE_NONE
855 ||(ss-2)->staticEval == VALUE_NONE;
857 singularExtensionNode = !RootNode
858 && depth >= 8 * ONE_PLY
859 && ttMove != MOVE_NONE
860 /* && ttValue != VALUE_NONE Already implicit in the next condition */
861 && abs(ttValue) < VALUE_KNOWN_WIN
862 && !excludedMove // Recursive singular search is not allowed
863 && (tte->bound() & BOUND_LOWER)
864 && tte->depth() >= depth - 3 * ONE_PLY;
866 // Step 11. Loop through moves
867 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
868 while ((move = mp.next_move()) != MOVE_NONE)
872 if (move == excludedMove)
875 // At root obey the "searchmoves" option and skip moves not listed in Root
876 // Move List. As a consequence any illegal move is also skipped. In MultiPV
877 // mode we also skip PV moves which have been already searched.
878 if (RootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
879 thisThread->rootMoves.end(), move))
882 ss->moveCount = ++moveCount;
884 if (RootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
885 sync_cout << "info depth " << depth / ONE_PLY
886 << " currmove " << UCI::move(move, pos.is_chess960())
887 << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
890 (ss+1)->pv = nullptr;
892 extension = DEPTH_ZERO;
893 captureOrPromotion = pos.capture_or_promotion(move);
895 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
896 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
897 : pos.gives_check(move, ci);
899 // Step 12. Extend checks
900 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
903 // Singular extension search. If all moves but one fail low on a search of
904 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
905 // is singular and should be extended. To verify this we do a reduced search
906 // on all the other moves but the ttMove and if the result is lower than
907 // ttValue minus a margin then we extend the ttMove.
908 if ( singularExtensionNode
911 && pos.legal(move, ci.pinned))
913 Value rBeta = ttValue - 2 * depth / ONE_PLY;
914 ss->excludedMove = move;
915 ss->skipEarlyPruning = true;
916 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
917 ss->skipEarlyPruning = false;
918 ss->excludedMove = MOVE_NONE;
924 // Update the current move (this must be done after singular extension search)
925 newDepth = depth - ONE_PLY + extension;
927 // Step 13. Pruning at shallow depth
929 && !captureOrPromotion
932 && !pos.advanced_pawn_push(move)
933 && bestValue > VALUE_MATED_IN_MAX_PLY)
935 // Move count based pruning
936 if ( depth < 16 * ONE_PLY
937 && moveCount >= FutilityMoveCounts[improving][depth])
940 // History based pruning
941 if ( depth <= 4 * ONE_PLY
942 && move != ss->killers[0]
943 && thisThread->history[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO
944 && cmh[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO)
947 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
949 // Futility pruning: parent node
950 if (predictedDepth < 7 * ONE_PLY)
952 futilityValue = ss->staticEval + futility_margin(predictedDepth) + 256;
954 if (futilityValue <= alpha)
956 bestValue = std::max(bestValue, futilityValue);
961 // Prune moves with negative SEE at low depths
962 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
966 // Speculative prefetch as early as possible
967 prefetch(TT.first_entry(pos.key_after(move)));
969 // Check for legality just before making the move
970 if (!RootNode && !pos.legal(move, ci.pinned))
972 ss->moveCount = --moveCount;
976 ss->currentMove = move;
978 // Step 14. Make the move
979 pos.do_move(move, st, givesCheck);
981 // Step 15. Reduced depth search (LMR). If the move fails high it will be
982 // re-searched at full depth.
983 if ( depth >= 3 * ONE_PLY
985 && !captureOrPromotion)
987 Depth r = reduction<PvNode>(improving, depth, moveCount);
989 // Increase reduction for cut nodes and moves with a bad history
990 if ( (!PvNode && cutNode)
991 || ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] < VALUE_ZERO
992 && cmh[pos.piece_on(to_sq(move))][to_sq(move)] <= VALUE_ZERO))
995 // Decrease reduction for moves with a good history
996 if ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO
997 && cmh[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO)
998 r = std::max(DEPTH_ZERO, r - ONE_PLY);
1000 // Decrease reduction for moves that escape a capture
1002 && type_of(move) == NORMAL
1003 && type_of(pos.piece_on(to_sq(move))) != PAWN
1004 && pos.see(make_move(to_sq(move), from_sq(move))) < VALUE_ZERO)
1005 r = std::max(DEPTH_ZERO, r - ONE_PLY);
1007 Depth d = std::max(newDepth - r, ONE_PLY);
1009 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
1011 doFullDepthSearch = (value > alpha && r != DEPTH_ZERO);
1014 doFullDepthSearch = !PvNode || moveCount > 1;
1016 // Step 16. Full depth search, when LMR is skipped or fails high
1017 if (doFullDepthSearch)
1018 value = newDepth < ONE_PLY ?
1019 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1020 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1021 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
1023 // For PV nodes only, do a full PV search on the first move or after a fail
1024 // high (in the latter case search only if value < beta), otherwise let the
1025 // parent node fail low with value <= alpha and to try another move.
1026 if (PvNode && (moveCount == 1 || (value > alpha && (RootNode || value < beta))))
1029 (ss+1)->pv[0] = MOVE_NONE;
1031 value = newDepth < ONE_PLY ?
1032 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1033 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1034 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
1037 // Step 17. Undo move
1038 pos.undo_move(move);
1040 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1042 // Step 18. Check for new best move
1043 // Finished searching the move. If a stop occurred, the return value of
1044 // the search cannot be trusted, and we return immediately without
1045 // updating best move, PV and TT.
1046 if (Signals.stop.load(std::memory_order_relaxed))
1051 RootMove& rm = *std::find(thisThread->rootMoves.begin(),
1052 thisThread->rootMoves.end(), move);
1054 // PV move or new best move ?
1055 if (moveCount == 1 || value > alpha)
1062 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
1063 rm.pv.push_back(*m);
1065 // We record how often the best move has been changed in each
1066 // iteration. This information is used for time management: When
1067 // the best move changes frequently, we allocate some more time.
1068 if (moveCount > 1 && thisThread == Threads.main())
1072 // All other moves but the PV are set to the lowest value: this is
1073 // not a problem when sorting because the sort is stable and the
1074 // move position in the list is preserved - just the PV is pushed up.
1075 rm.score = -VALUE_INFINITE;
1078 if (value > bestValue)
1084 // If there is an easy move for this position, clear it if unstable
1086 && thisThread == Threads.main()
1087 && EasyMove.get(pos.key())
1088 && (move != EasyMove.get(pos.key()) || moveCount > 1))
1093 if (PvNode && !RootNode) // Update pv even in fail-high case
1094 update_pv(ss->pv, move, (ss+1)->pv);
1096 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1100 assert(value >= beta); // Fail high
1106 if (!captureOrPromotion && move != bestMove && quietCount < 64)
1107 quietsSearched[quietCount++] = move;
1110 // Following condition would detect a stop only after move loop has been
1111 // completed. But in this case bestValue is valid because we have fully
1112 // searched our subtree, and we can anyhow save the result in TT.
1118 // Step 20. Check for mate and stalemate
1119 // All legal moves have been searched and if there are no legal moves, it
1120 // must be mate or stalemate. If we are in a singular extension search then
1121 // return a fail low score.
1123 bestValue = excludedMove ? alpha
1124 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1126 // Quiet best move: update killers, history and countermoves
1127 else if (bestMove && !pos.capture_or_promotion(bestMove))
1128 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount);
1130 // Bonus for prior countermove that caused the fail low
1131 else if ( depth >= 3 * ONE_PLY
1134 && !pos.captured_piece_type()
1135 && is_ok((ss - 1)->currentMove)
1136 && is_ok((ss - 2)->currentMove))
1138 Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
1139 Square prevPrevSq = to_sq((ss - 2)->currentMove);
1140 CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
1141 prevCmh.update(pos.piece_on(prevSq), prevSq, bonus);
1144 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1145 bestValue >= beta ? BOUND_LOWER :
1146 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1147 depth, bestMove, ss->staticEval, TT.generation());
1149 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1155 // qsearch() is the quiescence search function, which is called by the main
1156 // search function when the remaining depth is zero (or, to be more precise,
1157 // less than ONE_PLY).
1159 template <NodeType NT, bool InCheck>
1160 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1162 const bool PvNode = NT == PV;
1164 assert(NT == PV || NT == NonPV);
1165 assert(InCheck == !!pos.checkers());
1166 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1167 assert(PvNode || (alpha == beta - 1));
1168 assert(depth <= DEPTH_ZERO);
1174 Move ttMove, move, bestMove;
1175 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1176 bool ttHit, givesCheck, evasionPrunable;
1181 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1183 ss->pv[0] = MOVE_NONE;
1186 ss->currentMove = bestMove = MOVE_NONE;
1187 ss->ply = (ss-1)->ply + 1;
1189 // Check for an instant draw or if the maximum ply has been reached
1190 if (pos.is_draw() || ss->ply >= MAX_PLY)
1191 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
1192 : DrawValue[pos.side_to_move()];
1194 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1196 // Decide whether or not to include checks: this fixes also the type of
1197 // TT entry depth that we are going to use. Note that in qsearch we use
1198 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1199 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1200 : DEPTH_QS_NO_CHECKS;
1202 // Transposition table lookup
1204 tte = TT.probe(posKey, ttHit);
1205 ttMove = ttHit ? tte->move() : MOVE_NONE;
1206 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
1210 && tte->depth() >= ttDepth
1211 && ttValue != VALUE_NONE // Only in case of TT access race
1212 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1213 : (tte->bound() & BOUND_UPPER)))
1215 ss->currentMove = ttMove; // Can be MOVE_NONE
1219 // Evaluate the position statically
1222 ss->staticEval = VALUE_NONE;
1223 bestValue = futilityBase = -VALUE_INFINITE;
1229 // Never assume anything on values stored in TT
1230 if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
1231 ss->staticEval = bestValue = evaluate(pos);
1233 // Can ttValue be used as a better position evaluation?
1234 if (ttValue != VALUE_NONE)
1235 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1236 bestValue = ttValue;
1239 ss->staticEval = bestValue =
1240 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
1241 : -(ss-1)->staticEval + 2 * Eval::Tempo;
1243 // Stand pat. Return immediately if static value is at least beta
1244 if (bestValue >= beta)
1247 tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1248 DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
1253 if (PvNode && bestValue > alpha)
1256 futilityBase = bestValue + 128;
1259 // Initialize a MovePicker object for the current position, and prepare
1260 // to search the moves. Because the depth is <= 0 here, only captures,
1261 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1263 MovePicker mp(pos, ttMove, depth, pos.this_thread()->history, to_sq((ss-1)->currentMove));
1266 // Loop through the moves until no moves remain or a beta cutoff occurs
1267 while ((move = mp.next_move()) != MOVE_NONE)
1269 assert(is_ok(move));
1271 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1272 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1273 : pos.gives_check(move, ci);
1278 && futilityBase > -VALUE_KNOWN_WIN
1279 && !pos.advanced_pawn_push(move))
1281 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1283 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1285 if (futilityValue <= alpha)
1287 bestValue = std::max(bestValue, futilityValue);
1291 if (futilityBase <= alpha && pos.see(move) <= VALUE_ZERO)
1293 bestValue = std::max(bestValue, futilityBase);
1298 // Detect non-capture evasions that are candidates to be pruned
1299 evasionPrunable = InCheck
1300 && bestValue > VALUE_MATED_IN_MAX_PLY
1301 && !pos.capture(move);
1303 // Don't search moves with negative SEE values
1304 if ( (!InCheck || evasionPrunable)
1305 && type_of(move) != PROMOTION
1306 && pos.see_sign(move) < VALUE_ZERO)
1309 // Speculative prefetch as early as possible
1310 prefetch(TT.first_entry(pos.key_after(move)));
1312 // Check for legality just before making the move
1313 if (!pos.legal(move, ci.pinned))
1316 ss->currentMove = move;
1318 // Make and search the move
1319 pos.do_move(move, st, givesCheck);
1320 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1321 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1322 pos.undo_move(move);
1324 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1326 // Check for new best move
1327 if (value > bestValue)
1333 if (PvNode) // Update pv even in fail-high case
1334 update_pv(ss->pv, move, (ss+1)->pv);
1336 if (PvNode && value < beta) // Update alpha here!
1343 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1344 ttDepth, move, ss->staticEval, TT.generation());
1352 // All legal moves have been searched. A special case: If we're in check
1353 // and no legal moves were found, it is checkmate.
1354 if (InCheck && bestValue == -VALUE_INFINITE)
1355 return mated_in(ss->ply); // Plies to mate from the root
1357 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1358 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1359 ttDepth, bestMove, ss->staticEval, TT.generation());
1361 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1367 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1368 // "plies to mate from the current position". Non-mate scores are unchanged.
1369 // The function is called before storing a value in the transposition table.
1371 Value value_to_tt(Value v, int ply) {
1373 assert(v != VALUE_NONE);
1375 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1376 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1380 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1381 // from the transposition table (which refers to the plies to mate/be mated
1382 // from current position) to "plies to mate/be mated from the root".
1384 Value value_from_tt(Value v, int ply) {
1386 return v == VALUE_NONE ? VALUE_NONE
1387 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1388 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1392 // update_pv() adds current move and appends child pv[]
1394 void update_pv(Move* pv, Move move, Move* childPv) {
1396 for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
1402 // update_stats() updates killers, history, countermove and countermove
1403 // history when a new quiet best move is found.
1405 void update_stats(const Position& pos, Stack* ss, Move move,
1406 Depth depth, Move* quiets, int quietsCnt) {
1408 if (ss->killers[0] != move)
1410 ss->killers[1] = ss->killers[0];
1411 ss->killers[0] = move;
1414 Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
1416 Square prevSq = to_sq((ss-1)->currentMove);
1417 CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
1418 Thread* thisThread = pos.this_thread();
1420 thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus);
1422 if (is_ok((ss-1)->currentMove))
1424 thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
1425 cmh.update(pos.moved_piece(move), to_sq(move), bonus);
1428 // Decrease all the other played quiet moves
1429 for (int i = 0; i < quietsCnt; ++i)
1431 thisThread->history.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1433 if (is_ok((ss-1)->currentMove))
1434 cmh.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1437 // Extra penalty for a quiet TT move in previous ply when it gets refuted
1438 if ( (ss-1)->moveCount == 1
1439 && !pos.captured_piece_type()
1440 && is_ok((ss-2)->currentMove))
1442 Square prevPrevSq = to_sq((ss-2)->currentMove);
1443 CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
1444 prevCmh.update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY);
1449 // When playing with strength handicap, choose best move among a set of RootMoves
1450 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1452 Move Skill::pick_best(size_t multiPV) {
1454 const Search::RootMoveVector& rootMoves = Threads.main()->rootMoves;
1455 static PRNG rng(now()); // PRNG sequence should be non-deterministic
1457 // RootMoves are already sorted by score in descending order
1458 Value topScore = rootMoves[0].score;
1459 int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
1460 int weakness = 120 - 2 * level;
1461 int maxScore = -VALUE_INFINITE;
1463 // Choose best move. For each move score we add two terms, both dependent on
1464 // weakness. One deterministic and bigger for weaker levels, and one random,
1465 // then we choose the move with the resulting highest score.
1466 for (size_t i = 0; i < multiPV; ++i)
1468 // This is our magic formula
1469 int push = ( weakness * int(topScore - rootMoves[i].score)
1470 + delta * (rng.rand<unsigned>() % weakness)) / 128;
1472 if (rootMoves[i].score + push > maxScore)
1474 maxScore = rootMoves[i].score + push;
1475 best = rootMoves[i].pv[0];
1483 // check_time() is used to print debug info and, more importantly, to detect
1484 // when we are out of available time and thus stop the search.
1488 static TimePoint lastInfoTime = now();
1490 int elapsed = Time.elapsed();
1491 TimePoint tick = Limits.startTime + elapsed;
1493 if (tick - lastInfoTime >= 1000)
1495 lastInfoTime = tick;
1499 // An engine may not stop pondering until told so by the GUI
1503 if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
1504 || (Limits.movetime && elapsed >= Limits.movetime)
1505 || (Limits.nodes && Threads.nodes_searched() >= Limits.nodes))
1506 Signals.stop = true;
1512 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
1513 /// that all (if any) unsearched PV lines are sent using a previous search score.
1515 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1517 std::stringstream ss;
1518 int elapsed = Time.elapsed() + 1;
1519 const Search::RootMoveVector& rootMoves = pos.this_thread()->rootMoves;
1520 size_t PVIdx = pos.this_thread()->PVIdx;
1521 size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
1522 uint64_t nodes_searched = Threads.nodes_searched();
1524 for (size_t i = 0; i < multiPV; ++i)
1526 bool updated = (i <= PVIdx);
1528 if (depth == ONE_PLY && !updated)
1531 Depth d = updated ? depth : depth - ONE_PLY;
1532 Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
1534 bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
1535 v = tb ? TB::Score : v;
1537 if (ss.rdbuf()->in_avail()) // Not at first line
1541 << " depth " << d / ONE_PLY
1542 << " seldepth " << pos.this_thread()->maxPly
1543 << " multipv " << i + 1
1544 << " score " << UCI::value(v);
1546 if (!tb && i == PVIdx)
1547 ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1549 ss << " nodes " << nodes_searched
1550 << " nps " << nodes_searched * 1000 / elapsed;
1552 if (elapsed > 1000) // Earlier makes little sense
1553 ss << " hashfull " << TT.hashfull();
1555 ss << " tbhits " << TB::Hits
1556 << " time " << elapsed
1559 for (Move m : rootMoves[i].pv)
1560 ss << " " << UCI::move(m, pos.is_chess960());
1567 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1568 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1569 /// first, even if the old TT entries have been overwritten.
1571 void RootMove::insert_pv_in_tt(Position& pos) {
1573 StateInfo state[MAX_PLY], *st = state;
1578 assert(MoveList<LEGAL>(pos).contains(m));
1580 TTEntry* tte = TT.probe(pos.key(), ttHit);
1582 if (!ttHit || tte->move() != m) // Don't overwrite correct entries
1583 tte->save(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE,
1584 m, VALUE_NONE, TT.generation());
1586 pos.do_move(m, *st++, pos.gives_check(m, CheckInfo(pos)));
1589 for (size_t i = pv.size(); i > 0; )
1590 pos.undo_move(pv[--i]);
1594 /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
1595 /// before exiting the search, for instance in case we stop the search during a
1596 /// fail high at root. We try hard to have a ponder move to return to the GUI,
1597 /// otherwise in case of 'ponder on' we have nothing to think on.
1599 bool RootMove::extract_ponder_from_tt(Position& pos)
1604 assert(pv.size() == 1);
1606 pos.do_move(pv[0], st, pos.gives_check(pv[0], CheckInfo(pos)));
1607 TTEntry* tte = TT.probe(pos.key(), ttHit);
1608 pos.undo_move(pv[0]);
1612 Move m = tte->move(); // Local copy to be SMP safe
1613 if (MoveList<LEGAL>(pos).contains(m))
1614 return pv.push_back(m), true;