X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=2c2321ee9ca0bb5f48bd99b4fc068986a8d2a297;hp=bafc374ba29993ab05b62c8ec95729990a7fbbb8;hb=0dbc72d82e7f5f314499b22a04dcef45edcdba9a;hpb=b6d11028bbb5e428cdbd709ba46d8b14bab17c88 diff --git a/src/search.cpp b/src/search.cpp index bafc374b..2c2321ee 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -70,9 +70,9 @@ namespace { // Reductions lookup table, initialized at startup int Reductions[MAX_MOVES]; // [depth or moveNumber] - template Depth reduction(bool i, Depth d, int mn) { - int r = Reductions[d / ONE_PLY] * Reductions[mn] / 1024; - return ((r + 512) / 1024 + (!i && r > 1024) - PvNode) * ONE_PLY; + Depth reduction(bool i, Depth d, int mn) { + int r = Reductions[d / ONE_PLY] * Reductions[mn]; + return ((r + 512) / 1024 + (!i && r > 1024)) * ONE_PLY; } constexpr int futility_move_count(bool improving, int depth) { @@ -102,6 +102,48 @@ namespace { Move best = MOVE_NONE; }; + // Breadcrumbs are used to mark nodes as being searched by a given thread. + struct Breadcrumb { + std::atomic thread; + std::atomic key; + }; + std::array breadcrumbs; + + // ThreadHolding keeps track of which thread left breadcrumbs at the given node for potential reductions. + // A free node will be marked upon entering the moves loop, and unmarked upon leaving that loop, by the ctor/dtor of this struct. + struct ThreadHolding { + explicit ThreadHolding(Thread* thisThread, Key posKey, int ply) { + location = ply < 8 ? &breadcrumbs[posKey & (breadcrumbs.size() - 1)] : nullptr; + otherThread = false; + owning = false; + if (location) + { + // see if another already marked this location, if not, mark it ourselves. + Thread* tmp = (*location).thread.load(std::memory_order_relaxed); + if (tmp == nullptr) + { + (*location).thread.store(thisThread, std::memory_order_relaxed); + (*location).key.store(posKey, std::memory_order_relaxed); + owning = true; + } + else if ( tmp != thisThread + && (*location).key.load(std::memory_order_relaxed) == posKey) + otherThread = true; + } + } + + ~ThreadHolding() { + if (owning) // free the marked location. + (*location).thread.store(nullptr, std::memory_order_relaxed); + } + + bool marked() { return otherThread; } + + private: + Breadcrumb* location; + bool otherThread, owning; + }; + template Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode); @@ -149,7 +191,7 @@ namespace { void Search::init() { for (int i = 1; i < MAX_MOVES; ++i) - Reductions[i] = int(1024 * std::log(i) / std::sqrt(1.95)); + Reductions[i] = int(22.9 * std::log(i)); } @@ -229,7 +271,7 @@ void MainThread::search() { // Check if there are threads with a better score than main thread if ( Options["MultiPV"] == 1 && !Limits.depth - && !Skill(Options["Skill Level"]).enabled() + && !(Skill(Options["Skill Level"]).enabled() || Options["UCI_LimitStrength"]) && rootMoves[0].pv[0] != MOVE_NONE) { std::map votes; @@ -239,21 +281,15 @@ void MainThread::search() { for (Thread* th: Threads) minScore = std::min(minScore, th->rootMoves[0].score); - // Vote according to score and depth + // Vote according to score and depth, and select the best thread for (Thread* th : Threads) { - int64_t s = th->rootMoves[0].score - minScore + 1; - votes[th->rootMoves[0].pv[0]] += 200 + s * s * int(th->completedDepth); - } + votes[th->rootMoves[0].pv[0]] += + (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth); - // Select best thread - auto bestVote = votes[this->rootMoves[0].pv[0]]; - for (Thread* th : Threads) - if (votes[th->rootMoves[0].pv[0]] > bestVote) - { - bestVote = votes[th->rootMoves[0].pv[0]]; + if (votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]) bestThread = th; - } + } } previousScore = bestThread->rootMoves[0].score; @@ -298,8 +334,20 @@ void Thread::search() { bestValue = delta = alpha = -VALUE_INFINITE; beta = VALUE_INFINITE; - size_t multiPV = Options["MultiPV"]; - Skill skill(Options["Skill Level"]); + multiPV = Options["MultiPV"]; + + // Pick integer skill levels, but non-deterministically round up or down + // such that the average integer skill corresponds to the input floating point one. + // UCI_Elo is converted to a suitable fractional skill level, using anchoring + // to CCRL Elo (goldfish 1.13 = 2000) and a fit through Ordo derived Elo + // for match (TC 60+0.6) results spanning a wide range of k values. + PRNG rng(now()); + double floatLevel = Options["UCI_LimitStrength"] ? + clamp(std::pow((Options["UCI_Elo"] - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0) : + double(Options["Skill Level"]); + int intLevel = int(floatLevel) + + ((floatLevel - int(floatLevel)) * 1024 > rng.rand() % 1024 ? 1 : 0); + Skill skill(intLevel); // When playing with strength handicap enable MultiPV search that we will // use behind the scenes to retrieve a set of possible moves. @@ -406,17 +454,14 @@ void Thread::search() { beta = (alpha + beta) / 2; alpha = std::max(bestValue - delta, -VALUE_INFINITE); + failedHighCnt = 0; if (mainThread) - { - failedHighCnt = 0; mainThread->stopOnPonderhit = false; - } } else if (bestValue >= beta) { beta = std::min(bestValue + delta, VALUE_INFINITE); - if (mainThread) - ++failedHighCnt; + ++failedHighCnt; } else break; @@ -465,7 +510,7 @@ void Thread::search() { // If the bestMove is stable over several iterations, reduce time accordingly timeReduction = lastBestMoveDepth + 10 * ONE_PLY < completedDepth ? 1.95 : 1.0; - double reduction = std::pow(mainThread->previousTimeReduction, 0.528) / timeReduction; + double reduction = (1.25 + mainThread->previousTimeReduction) / (2.25 * timeReduction); // Use part of the gained time from a previous stable move for the current move for (Thread* th : Threads) @@ -540,16 +585,16 @@ namespace { Move ttMove, move, excludedMove, bestMove; Depth extension, newDepth; Value bestValue, value, ttValue, eval, maxValue; - bool ttHit, ttPv, inCheck, givesCheck, improving; + bool ttHit, ttPv, inCheck, givesCheck, improving, doLMR; bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture; Piece movedPiece; - int moveCount, captureCount, quietCount; + int moveCount, captureCount, quietCount, singularLMR; // Step 1. Initialize node Thread* thisThread = pos.this_thread(); inCheck = pos.checkers(); Color us = pos.side_to_move(); - moveCount = captureCount = quietCount = ss->moveCount = 0; + moveCount = captureCount = quietCount = singularLMR = ss->moveCount = 0; bestValue = -VALUE_INFINITE; maxValue = VALUE_INFINITE; @@ -594,10 +639,10 @@ namespace { // starts with statScore = 0. Later grandchildren start with the last calculated // statScore of the previous grandchild. This influences the reduction rules in // LMR which are based on the statScore of parent position. - if (rootNode) - (ss + 4)->statScore = 0; - else - (ss + 2)->statScore = 0; + if (rootNode) + (ss + 4)->statScore = 0; + else + (ss + 2)->statScore = 0; // Step 4. Transposition table lookup. We don't want the score of a partial // search to overwrite a previous full search TT value, so we use a different @@ -608,7 +653,7 @@ namespace { ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0] : ttHit ? tte->move() : MOVE_NONE; - ttPv = (ttHit && tte->is_pv()) || (PvNode && depth > 4 * ONE_PLY); + ttPv = PvNode || (ttHit && tte->is_pv()); // At non-PV nodes we check for an early TT cutoff if ( !PvNode @@ -701,7 +746,7 @@ namespace { } else if (ttHit) { - // Never assume anything on values stored in TT + // Never assume anything about values stored in TT ss->staticEval = eval = tte->eval(); if (eval == VALUE_NONE) ss->staticEval = eval = evaluate(pos); @@ -856,6 +901,9 @@ moves_loop: // When in check, search starts from here moveCountPruning = false; ttCapture = ttMove && pos.capture_or_promotion(ttMove); + // Mark this node as being searched. + ThreadHolding th(thisThread, posKey, ss->ply); + // Step 12. Loop through all pseudo-legal moves until no moves remain // or a beta cutoff occurs. while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE) @@ -879,6 +927,12 @@ moves_loop: // When in check, search starts from here sync_cout << "info depth " << depth / ONE_PLY << " currmove " << UCI::move(move, pos.is_chess960()) << " currmovenumber " << moveCount + thisThread->pvIdx << sync_endl; + + // In MultiPV mode also skip moves which will be searched later as PV moves + if (rootNode && std::count(thisThread->rootMoves.begin() + thisThread->pvIdx + 1, + thisThread->rootMoves.begin() + thisThread->multiPV, move)) + continue; + if (PvNode) (ss+1)->pv = nullptr; @@ -911,20 +965,27 @@ moves_loop: // When in check, search starts from here ss->excludedMove = MOVE_NONE; if (value < singularBeta) + { extension = ONE_PLY; + singularLMR++; + + if (value < singularBeta - std::min(3 * depth / ONE_PLY, 39)) + singularLMR++; + } // Multi-cut pruning // Our ttMove is assumed to fail high, and now we failed high also on a reduced // search without the ttMove. So we assume this expected Cut-node is not singular, - // that is multiple moves fail high, and we can prune the whole subtree by returning - // the hard beta bound. - else if (cutNode && singularBeta > beta) - return beta; + // that multiple moves fail high, and we can prune the whole subtree by returning + // a soft bound. + else if ( eval >= beta + && singularBeta >= beta) + return singularBeta; } // Check extension (~2 Elo) else if ( givesCheck - && (pos.blockers_for_king(~us) & from_sq(move) || pos.see_ge(move))) + && (pos.is_discovery_check_on_king(~us, move) || pos.see_ge(move))) extension = ONE_PLY; // Castling extension @@ -935,7 +996,7 @@ moves_loop: // When in check, search starts from here else if ( PvNode && pos.rule50_count() > 18 && depth < 3 * ONE_PLY - && ss->ply < 3 * thisThread->rootDepth / ONE_PLY) // To avoid too deep searches + && ++thisThread->shuffleExts < thisThread->nodes.load(std::memory_order_relaxed) / 4) // To avoid too many extensions extension = ONE_PLY; // Passed pawn extension @@ -957,14 +1018,14 @@ moves_loop: // When in check, search starts from here if ( !captureOrPromotion && !givesCheck - && !pos.advanced_pawn_push(move)) + && (!pos.advanced_pawn_push(move) || pos.non_pawn_material(~us) > BishopValueMg)) { - // Move count based pruning (~30 Elo) + // Move count based pruning if (moveCountPruning) continue; // Reduced depth of the next LMR search - int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO); + int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO); lmrDepth /= ONE_PLY; // Countermoves based pruning (~20 Elo) @@ -983,7 +1044,8 @@ moves_loop: // When in check, search starts from here if (!pos.see_ge(move, Value(-29 * lmrDepth * lmrDepth))) continue; } - else if (!pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) // (~20 Elo) + else if ( (!givesCheck || !extension) + && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) // (~20 Elo) continue; } @@ -1007,21 +1069,28 @@ moves_loop: // When in check, search starts from here // Step 16. Reduced depth search (LMR). If the move fails high it will be // re-searched at full depth. if ( depth >= 3 * ONE_PLY - && moveCount > 1 + && moveCount > 1 + 3 * rootNode && ( !captureOrPromotion || moveCountPruning || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha)) { - Depth r = reduction(improving, depth, moveCount); + Depth r = reduction(improving, depth, moveCount); + + // Reduction if other threads are searching this position. + if (th.marked()) + r += ONE_PLY; // Decrease reduction if position is or has been on the PV if (ttPv) - r -= ONE_PLY; + r -= 2 * ONE_PLY; // Decrease reduction if opponent's move count is high (~10 Elo) if ((ss-1)->moveCount > 15) r -= ONE_PLY; + // Decrease reduction if move has been singularly extended + r -= singularLMR * ONE_PLY; + if (!captureOrPromotion) { // Increase reduction if ttMove is a capture (~0 Elo) @@ -1053,22 +1122,32 @@ moves_loop: // When in check, search starts from here r += ONE_PLY; // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - r -= ss->statScore / 20000 * ONE_PLY; + r -= ss->statScore / 16384 * ONE_PLY; } - Depth d = std::max(newDepth - std::max(r, DEPTH_ZERO), ONE_PLY); + Depth d = clamp(newDepth - r, ONE_PLY, newDepth); value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); - doFullDepthSearch = (value > alpha && d != newDepth); + doFullDepthSearch = (value > alpha && d != newDepth), doLMR = true; } else - doFullDepthSearch = !PvNode || moveCount > 1; + doFullDepthSearch = !PvNode || moveCount > 1, doLMR = false; // Step 17. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) + { value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); + if (doLMR && !captureOrPromotion) + { + int bonus = value > alpha ? stat_bonus(newDepth) + : -stat_bonus(newDepth); + + update_continuation_histories(ss, movedPiece, to_sq(move), bonus); + } + } + // For PV nodes only, do a full PV search on the first move or after a fail // high (in the latter case search only if value < beta), otherwise let the // parent node fail low with value <= alpha and try another move. @@ -1279,7 +1358,7 @@ moves_loop: // When in check, search starts from here { if (ttHit) { - // Never assume anything on values stored in TT + // Never assume anything about values stored in TT if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE) ss->staticEval = bestValue = evaluate(pos); @@ -1362,6 +1441,7 @@ moves_loop: // When in check, search starts from here // Don't search moves with negative SEE values if ( (!inCheck || evasionPrunable) + && (!givesCheck || !(pos.blockers_for_king(~pos.side_to_move()) & from_sq(move))) && !pos.see_ge(move)) continue; @@ -1472,7 +1552,7 @@ moves_loop: // When in check, search starts from here void update_capture_stats(const Position& pos, Move move, Move* captures, int captureCount, int bonus) { - CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory; + CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory; Piece moved_piece = pos.moved_piece(move); PieceType captured = type_of(pos.piece_on(to_sq(move))); @@ -1713,7 +1793,7 @@ void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) { } else { - // Assign the same rank to all moves + // Clean up if root_probe() and root_probe_wdl() have failed for (auto& m : rootMoves) m.tbRank = 0; }