X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=8e6efb7a1bd9bdc50e041194f9a8c97b35fade5f;hp=7cc307d854705baeff687b39de006f75e379ea17;hb=8ee3124487bdfd871f587bdb46f007ff24fc8303;hpb=a7227ac26ff2be2a0e477b04022a54e56c8bf35f diff --git a/src/search.cpp b/src/search.cpp index 7cc307d8..8e6efb7a 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -106,6 +106,9 @@ namespace { const bool UseIIDAtPVNodes = true; const bool UseIIDAtNonPVNodes = false; + // Use null move driven internal iterative deepening? + bool UseNullDrivenIID = false; + // Internal iterative deepening margin. At Non-PV moves, when // UseIIDAtNonPVNodes is true, we do an internal iterative deepening search // when the static evaluation is at most IIDMargin below beta. @@ -188,7 +191,7 @@ namespace { // Time managment variables int SearchStartTime; int MaxNodes, MaxDepth; - int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, TimeAdvantage; + int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime; Move BestRootMove, PonderMove, EasyMove; int RootMoveNumber; bool InfiniteSearch; @@ -238,19 +241,20 @@ namespace { Depth depth, int ply, int threadID); void sp_search(SplitPoint *sp, int threadID); void sp_search_pv(SplitPoint *sp, int threadID); + void init_search_stack(SearchStack& ss); void init_search_stack(SearchStack ss[]); void init_node(const Position &pos, SearchStack ss[], int ply, int threadID); void update_pv(SearchStack ss[], int ply); void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply); bool connected_moves(const Position &pos, Move m1, Move m2); - Depth extension(const Position &pos, Move m, bool pvNode, bool check, - bool singleReply, bool mateThreat); + bool move_is_killer(Move m, const SearchStack& ss); + Depth extension(const Position &pos, Move m, bool pvNode, bool check, bool singleReply, bool mateThreat, bool* dangerous); bool ok_to_do_nullmove(const Position &pos); bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d); bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply); bool ok_to_history(const Position &pos, Move m); - void update_history(const Position& pos, Move m, Depth depth, - Move movesSearched[], int moveCount); + void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount); + void update_killers(Move m, SearchStack& ss); bool fail_high_ply_1(); int current_search_time(); @@ -298,6 +302,9 @@ Lock IOLock; History H; // Should be made local? +// The empty search stack +SearchStack EmptySearchStack; + //// //// Functions @@ -386,6 +393,7 @@ void think(const Position &pos, bool infinite, bool ponder, int side_to_move, if (UseLogFile) LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app); + UseNullDrivenIID = get_option_value_bool("Null driven IID"); UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)"); UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)"); @@ -423,16 +431,14 @@ void think(const Position &pos, bool infinite, bool ponder, int side_to_move, int myIncrement = increment[side_to_move]; int oppTime = time[1 - side_to_move]; - TimeAdvantage = myTime - oppTime; - if (!movesToGo) // Sudden death time control - { - if (increment) + { + if (myIncrement) { MaxSearchTime = myTime / 30 + myIncrement; AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100); } else { // Blitz game without increment - MaxSearchTime = myTime / 40; + MaxSearchTime = myTime / 30; AbsoluteMaxSearchTime = myTime / 8; } } @@ -562,6 +568,9 @@ void init_threads() { // Wait until the thread has finished launching: while (!Threads[i].running); } + + // Init also the empty search stack + init_search_stack(EmptySearchStack); } @@ -673,10 +682,6 @@ namespace { ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2) + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3); - // If we need some more and we are in time advantage take it - if (ExtraSearchTime > 0 && TimeAdvantage > 2 * MaxSearchTime) - ExtraSearchTime += MaxSearchTime / 2; - // Try to guess if the current iteration is the last one or the last two LastIterations = (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*58) / 128); @@ -771,7 +776,8 @@ namespace { << " currmovenumber " << i + 1 << std::endl; // Decide search depth for this move - ext = extension(pos, move, true, pos.move_is_check(move), false, false); + bool dangerous; + ext = extension(pos, move, true, pos.move_is_check(move), false, false, &dangerous); newDepth = (Iteration - 2) * OnePly + ext + InitialDepth; // Make the move, and search it @@ -788,7 +794,7 @@ namespace { if (Problem && StopOnPonderhit) StopOnPonderhit = false; - } + } else { value = -search(pos, ss, -alpha, newDepth, 1, true, 0); @@ -938,16 +944,14 @@ namespace { // Initialize a MovePicker object for the current position, and prepare // to search all moves - MovePicker mp = MovePicker(pos, true, ttMove, ss[ply].mateKiller, - ss[ply].killer1, ss[ply].killer2, depth); + MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth); Move move, movesSearched[256]; int moveCount = 0; Value value, bestValue = -VALUE_INFINITE; Bitboard dcCandidates = mp.discovered_check_candidates(); bool isCheck = pos.is_check(); - bool mateThreat = MateThreatExtension[1] > Depth(0) - && pos.has_mate_threat(opposite_color(pos.side_to_move())); + bool mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move())); // Loop through all legal moves until no moves remain or a beta cutoff // occurs. @@ -960,7 +964,6 @@ namespace { bool singleReply = (isCheck && mp.number_of_moves() == 1); bool moveIsCheck = pos.move_is_check(move, dcCandidates); bool moveIsCapture = pos.move_is_capture(move); - bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move); movesSearched[moveCount++] = ss[ply].currentMove = move; @@ -972,7 +975,8 @@ namespace { ss[ply].currentMoveCaptureValue = Value(0); // Decide the new search depth - Depth ext = extension(pos, move, true, moveIsCheck, singleReply, mateThreat); + bool dangerous; + Depth ext = extension(pos, move, true, moveIsCheck, singleReply, mateThreat, &dangerous); Depth newDepth = depth - OnePly + ext; // Make and search the move @@ -986,14 +990,12 @@ namespace { // Try to reduce non-pv search depth by one ply if move seems not problematic, // if the move fails high will be re-searched at full depth. if ( depth >= 2*OnePly - && ext == Depth(0) && moveCount >= LMRPVMoves + && !dangerous && !moveIsCapture && !move_promotion(move) - && !moveIsPassedPawnPush && !move_is_castle(move) - && move != ss[ply].killer1 - && move != ss[ply].killer2) + && !move_is_killer(move, ss[ply])) { ss[ply].reduction = OnePly; value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID); @@ -1075,11 +1077,7 @@ namespace { if (ok_to_history(pos, m)) // Only non capture moves are considered { update_history(pos, m, depth, movesSearched, moveCount); - if (m != ss[ply].killer1) - { - ss[ply].killer2 = ss[ply].killer1; - ss[ply].killer1 = m; - } + update_killers(m, ss[ply]); } TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER); } @@ -1130,16 +1128,18 @@ namespace { if (tte && ok_to_use_TT(tte, depth, beta, ply)) { - ss[ply].currentMove = ttMove; // can be MOVE_NONE ? + ss[ply].currentMove = ttMove; // can be MOVE_NONE return value_from_tt(tte->value(), ply); } Value approximateEval = quick_evaluate(pos); bool mateThreat = false; + bool nullDrivenIID = false; bool isCheck = pos.is_check(); // Null move search if ( allowNullmove + && depth > OnePly && !isCheck && ok_to_do_nullmove(pos) && approximateEval >= beta - NullMoveMargin) @@ -1149,7 +1149,21 @@ namespace { UndoInfo u; pos.do_null_move(u); int R = (depth > 7 ? 4 : 3); + Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID); + + // Check for a null capture artifact, if the value without the null capture + // is above beta then there is a good possibility that this is a cut-node. + // We will do an IID later to find a ttMove. + if ( UseNullDrivenIID + && nullValue < beta + && depth > 6 * OnePly + && ttMove == MOVE_NONE + && ss[ply + 1].currentMove != MOVE_NONE + && pos.move_is_capture(ss[ply + 1].currentMove) + && pos.see(ss[ply + 1].currentMove) + nullValue >= beta) + nullDrivenIID = true; + pos.undo_null_move(u); if (nullValue >= beta) @@ -1163,14 +1177,16 @@ namespace { return beta; } else { // The null move failed low, which means that we may be faced with - // some kind of threat. If the previous move was reduced, check if + // some kind of threat. If the previous move was reduced, check if // the move that refuted the null move was somehow connected to the - // move which was reduced. If a connection is found, return a fail + // move which was reduced. If a connection is found, return a fail // low score (which will cause the reduced move to fail high in the // parent node, which will trigger a re-search with full depth). if (nullValue == value_mated_in(ply + 2)) + { mateThreat = true; - + nullDrivenIID = false; + } ss[ply].threatMove = ss[ply + 1].currentMove; if ( depth < ThreatDepth && ss[ply - 1].reduction @@ -1194,11 +1210,24 @@ namespace { search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID); ttMove = ss[ply].pv[ply]; } + else if (nullDrivenIID) + { + // The null move failed low due to a suspicious capture. Perhaps we + // are facing a null capture artifact due to the side to move change + // and this is a cut-node. So it's a good time to search for a ttMove. + Move tm = ss[ply].threatMove; + + assert(tm != MOVE_NONE); + assert(ttMove == MOVE_NONE); + + search(pos, ss, beta, depth/2, ply, false, threadID); + ttMove = ss[ply].pv[ply]; + ss[ply].threatMove = tm; + } // Initialize a MovePicker object for the current position, and prepare // to search all moves: - MovePicker mp = MovePicker(pos, false, ttMove, ss[ply].mateKiller, - ss[ply].killer1, ss[ply].killer2, depth); + MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth); Move move, movesSearched[256]; int moveCount = 0; @@ -1220,19 +1249,18 @@ namespace { bool singleReply = (isCheck && mp.number_of_moves() == 1); bool moveIsCheck = pos.move_is_check(move, dcCandidates); bool moveIsCapture = pos.move_is_capture(move); - bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move); movesSearched[moveCount++] = ss[ply].currentMove = move; // Decide the new search depth - Depth ext = extension(pos, move, false, moveIsCheck, singleReply, mateThreat); + bool dangerous; + Depth ext = extension(pos, move, false, moveIsCheck, singleReply, mateThreat, &dangerous); Depth newDepth = depth - OnePly + ext; // Futility pruning if ( useFutilityPruning - && ext == Depth(0) + && !dangerous && !moveIsCapture - && !moveIsPassedPawnPush && !move_promotion(move)) { if ( moveCount >= 2 + int(depth) @@ -1260,15 +1288,13 @@ namespace { // Try to reduce non-pv search depth by one ply if move seems not problematic, // if the move fails high will be re-searched at full depth. - if ( depth >= 2*OnePly - && ext == Depth(0) - && moveCount >= LMRNonPVMoves + if ( depth >= 2*OnePly + && moveCount >= LMRNonPVMoves + && !dangerous && !moveIsCapture && !move_promotion(move) - && !moveIsPassedPawnPush && !move_is_castle(move) - && move != ss[ply].killer1 - && move != ss[ply].killer2) + && !move_is_killer(move, ss[ply])) { ss[ply].reduction = OnePly; value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID); @@ -1327,11 +1353,7 @@ namespace { if (ok_to_history(pos, m)) // Only non capture moves are considered { update_history(pos, m, depth, movesSearched, moveCount); - if (m != ss[ply].killer1) - { - ss[ply].killer2 = ss[ply].killer1; - ss[ply].killer1 = m; - } + update_killers(m, ss[ply]); } TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER); } @@ -1388,8 +1410,7 @@ namespace { // Initialize a MovePicker object for the current position, and prepare // to search the moves. Because the depth is <= 0 here, only captures, // queen promotions and checks (only if depth == 0) will be generated. - MovePicker mp = MovePicker(pos, false, MOVE_NONE, MOVE_NONE, MOVE_NONE, - MOVE_NONE, depth, &ei); + MovePicker mp = MovePicker(pos, false, MOVE_NONE, EmptySearchStack, depth, &ei); Move move; int moveCount = 0; Bitboard dcCandidates = mp.discovered_check_candidates(); @@ -1404,20 +1425,17 @@ namespace { { assert(move_is_ok(move)); - bool moveIsCheck = pos.move_is_check(move, dcCandidates); - bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move); - moveCount++; ss[ply].currentMove = move; // Futility pruning if ( UseQSearchFutilityPruning + && enoughMaterial && !isCheck - && !moveIsCheck - && !move_promotion(move) - && !moveIsPassedPawnPush && !pvNode - && enoughMaterial) + && !move_promotion(move) + && !pos.move_is_check(move, dcCandidates) + && !pos.move_is_passed_pawn_push(move)) { Value futilityValue = staticValue + Max(pos.midgame_value_of_piece_on(move_to(move)), @@ -1436,7 +1454,6 @@ namespace { // Don't search captures and checks with negative SEE values if ( !isCheck && !move_promotion(move) - && !pvNode && (pos.midgame_value_of_piece_on(move_from(move)) > pos.midgame_value_of_piece_on(move_to(move))) && pos.see(move) < 0) @@ -1477,12 +1494,7 @@ namespace { if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered { // Wrong to update history when depth is <= 0 - - if (m != ss[ply].killer1) - { - ss[ply].killer2 = ss[ply].killer1; - ss[ply].killer1 = m; - } + update_killers(m, ss[ply]); } return bestValue; } @@ -1518,7 +1530,6 @@ namespace { bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates); bool moveIsCapture = pos.move_is_capture(move); - bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move); lock_grab(&(sp->lock)); int moveCount = ++sp->moves; @@ -1527,14 +1538,14 @@ namespace { ss[sp->ply].currentMove = move; // Decide the new search depth. - Depth ext = extension(pos, move, false, moveIsCheck, false, false); + bool dangerous; + Depth ext = extension(pos, move, false, moveIsCheck, false, false, &dangerous); Depth newDepth = sp->depth - OnePly + ext; // Prune? if ( useFutilityPruning - && ext == Depth(0) + && !dangerous && !moveIsCapture - && !moveIsPassedPawnPush && !move_promotion(move) && moveCount >= 2 + int(sp->depth) && ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth)) @@ -1546,14 +1557,12 @@ namespace { // Try to reduce non-pv search depth by one ply if move seems not problematic, // if the move fails high will be re-searched at full depth. - if ( ext == Depth(0) + if ( !dangerous && moveCount >= LMRNonPVMoves && !moveIsCapture - && !moveIsPassedPawnPush && !move_promotion(move) && !move_is_castle(move) - && move != ss[sp->ply].killer1 - && move != ss[sp->ply].killer2) + && !move_is_killer(move, ss[sp->ply])) { ss[sp->ply].reduction = OnePly; value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID); @@ -1631,7 +1640,6 @@ namespace { { bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates); bool moveIsCapture = pos.move_is_capture(move); - bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move); assert(move_is_ok(move)); @@ -1645,7 +1653,8 @@ namespace { ss[sp->ply].currentMove = move; // Decide the new search depth. - Depth ext = extension(pos, move, true, moveIsCheck, false, false); + bool dangerous; + Depth ext = extension(pos, move, true, moveIsCheck, false, false, &dangerous); Depth newDepth = sp->depth - OnePly + ext; // Make and search the move. @@ -1654,14 +1663,12 @@ namespace { // Try to reduce non-pv search depth by one ply if move seems not problematic, // if the move fails high will be re-searched at full depth. - if ( ext == Depth(0) + if ( !dangerous && moveCount >= LMRPVMoves && !moveIsCapture - && !moveIsPassedPawnPush && !move_promotion(move) && !move_is_castle(move) - && move != ss[sp->ply].killer1 - && move != ss[sp->ply].killer2) + && !move_is_killer(move, ss[sp->ply])) { ss[sp->ply].reduction = OnePly; value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID); @@ -1892,17 +1899,28 @@ namespace { // init_search_stack() initializes a search stack at the beginning of a // new search from the root. + void init_search_stack(SearchStack& ss) { + + ss.pv[0] = MOVE_NONE; + ss.pv[1] = MOVE_NONE; + ss.currentMove = MOVE_NONE; + ss.threatMove = MOVE_NONE; + ss.reduction = Depth(0); + for (int j = 0; j < KILLER_MAX; j++) + ss.killers[j] = MOVE_NONE; + } void init_search_stack(SearchStack ss[]) { - for(int i = 0; i < 3; i++) { - ss[i].pv[i] = MOVE_NONE; - ss[i].pv[i+1] = MOVE_NONE; - ss[i].currentMove = MOVE_NONE; - ss[i].mateKiller = MOVE_NONE; - ss[i].killer1 = MOVE_NONE; - ss[i].killer2 = MOVE_NONE; - ss[i].threatMove = MOVE_NONE; - ss[i].reduction = Depth(0); + + for (int i = 0; i < 3; i++) + { + ss[i].pv[i] = MOVE_NONE; + ss[i].pv[i+1] = MOVE_NONE; + ss[i].currentMove = MOVE_NONE; + ss[i].threatMove = MOVE_NONE; + ss[i].reduction = Depth(0); + for (int j = 0; j < KILLER_MAX; j++) + ss[i].killers[j] = MOVE_NONE; } } @@ -1926,13 +1944,13 @@ namespace { NodesSincePoll = 0; } } - ss[ply].pv[ply] = ss[ply].pv[ply+1] = ss[ply].currentMove = MOVE_NONE; ss[ply+2].mateKiller = MOVE_NONE; - ss[ply+2].killer1 = ss[ply+2].killer2 = MOVE_NONE; ss[ply].threatMove = MOVE_NONE; ss[ply].reduction = Depth(0); ss[ply].currentMoveCaptureValue = Value(0); + for (int j = 0; j < KILLER_MAX; j++) + ss[ply+2].killers[j] = MOVE_NONE; if(Threads[threadID].printCurrentLine) print_current_line(ss, ply, threadID); @@ -2035,14 +2053,32 @@ namespace { } + // move_is_killer() checks if the given move is among the + // killer moves of that ply. + + bool move_is_killer(Move m, const SearchStack& ss) { + + const Move* k = ss.killers; + for (int i = 0; i < KILLER_MAX; i++, k++) + if (*k == m) + return true; + + return false; + } + + // extension() decides whether a move should be searched with normal depth, // or with extended depth. Certain classes of moves (checking moves, in - // particular) are searched with bigger depth than ordinary moves. + // particular) are searched with bigger depth than ordinary moves and in + // any case are marked as 'dangerous'. Note that also if a move is not + // extended, as example because the corresponding UCI option is set to zero, + // the move is marked as 'dangerous' so, at least, we avoid to prune it. - Depth extension(const Position &pos, Move m, bool pvNode, - bool check, bool singleReply, bool mateThreat) { + Depth extension(const Position &pos, Move m, bool pvNode, bool check, + bool singleReply, bool mateThreat, bool* dangerous) { Depth result = Depth(0); + *dangerous = check || singleReply || mateThreat; if (check) result += CheckExtension[pvNode]; @@ -2050,26 +2086,37 @@ namespace { if (singleReply) result += SingleReplyExtension[pvNode]; + if (mateThreat) + result += MateThreatExtension[pvNode]; + if (pos.move_is_pawn_push_to_7th(m)) + { result += PawnPushTo7thExtension[pvNode]; - + *dangerous = true; + } if (pos.move_is_passed_pawn_push(m)) + { result += PassedPawnExtension[pvNode]; + *dangerous = true; + } - if (mateThreat) - result += MateThreatExtension[pvNode]; - - if ( pos.midgame_value_of_piece_on(move_to(m)) >= RookValueMidgame - && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) - - pos.midgame_value_of_piece_on(move_to(m)) == Value(0)) + if ( pos.midgame_value_of_piece_on(move_to(m)) >= RookValueMidgame + && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) + - pos.midgame_value_of_piece_on(move_to(m)) == Value(0)) && !move_promotion(m)) + { result += PawnEndgameExtension[pvNode]; - + *dangerous = true; + } + if ( pvNode && pos.move_is_capture(m) && pos.type_of_piece_on(move_to(m)) != PAWN && pos.see(m) >= 0) + { result += OnePly/2; + *dangerous = true; + } return Min(result, OnePly); } @@ -2111,31 +2158,34 @@ namespace { tto = move_to(threat); // Case 1: Castling moves are never pruned. - if(move_is_castle(m)) - return false; + if (move_is_castle(m)) + return false; // Case 2: Don't prune moves which move the threatened piece - if(!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto) - return false; + if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto) + return false; // Case 3: If the threatened piece has value less than or equal to the // value of the threatening piece, don't prune move which defend it. - if(!PruneDefendingMoves && threat != MOVE_NONE - && (piece_value_midgame(pos.piece_on(tfrom)) - >= piece_value_midgame(pos.piece_on(tto))) - && pos.move_attacks_square(m, tto)) + if ( !PruneDefendingMoves + && threat != MOVE_NONE + && pos.type_of_piece_on(tto) != NO_PIECE_TYPE + && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto) + || pos.type_of_piece_on(tfrom) == KING) + && pos.move_attacks_square(m, tto)) return false; // Case 4: Don't prune moves with good history. - if(!H.ok_to_prune(pos.piece_on(move_from(m)), m, d)) - return false; + if (!H.ok_to_prune(pos.piece_on(move_from(m)), m, d)) + return false; // Case 5: If the moving piece in the threatened move is a slider, don't // prune safe moves which block its ray. - if(!PruneBlockingMoves && threat != MOVE_NONE - && piece_is_slider(pos.piece_on(tfrom)) - && bit_is_set(squares_between(tfrom, tto), mto) && pos.see(m) >= 0) - return false; + if ( !PruneBlockingMoves + && threat != MOVE_NONE + && piece_is_slider(pos.piece_on(tfrom)) + && bit_is_set(squares_between(tfrom, tto), mto) && pos.see(m) >= 0) + return false; return true; } @@ -2182,6 +2232,21 @@ namespace { } } + + // update_killers() add a good move that produced a beta-cutoff + // among the killer moves of that ply. + + void update_killers(Move m, SearchStack& ss) { + + if (m == ss.killers[0]) + return; + + for (int i = KILLER_MAX - 1; i > 0; i--) + ss.killers[i] = ss.killers[i - 1]; + + ss.killers[0] = m; + } + // fail_high_ply_1() checks if some thread is currently resolving a fail // high at ply 1 at the node below the first root node. This information // is used for time managment.