X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=756b2d5769fb6f44b854cad829f9e1b1242746ef;hp=0619db3a12a2420a2ef85864ab84e709c614a158;hb=ae5d2c38e1b9f6a990c29d31a37d6555d197f939;hpb=12e79be91039796299187ba1b2f1559552642ea4 diff --git a/src/search.cpp b/src/search.cpp index 0619db3a..756b2d57 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -2,7 +2,7 @@ Stockfish, a UCI chess playing engine derived from Glaurung 2.1 Copyright (C) 2004-2008 Tord Romstad (Glaurung author) Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad - Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad + Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad Stockfish is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -66,7 +66,7 @@ namespace { constexpr int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 }; // Razor and futility margins - constexpr int RazorMargin[] = {0, 590, 604}; + constexpr int RazorMargin = 600; Value futility_margin(Depth d, bool improving) { return Value((175 - 50 * improving) * d / ONE_PLY); } @@ -82,7 +82,14 @@ namespace { // History and stats update bonus, based on depth int stat_bonus(Depth depth) { int d = depth / ONE_PLY; - return d > 17 ? 0 : 32 * d * d + 64 * d - 64; + return d > 17 ? 0 : 29 * d * d + 138 * d - 134; + } + + // Add a small random component to draw evaluations to keep search dynamic + // and to avoid 3fold-blindness. + Value value_draw(Depth depth, Thread* thisThread) { + return depth < 4 ? VALUE_DRAW + : VALUE_DRAW + Value(2 * (thisThread->nodes.load(std::memory_order_relaxed) % 2) - 1); } // Skill structure is used to implement strength limit @@ -180,6 +187,7 @@ void Search::clear() { Time.availableNodes = 0; TT.clear(); Threads.clear(); + Tablebases::init(Options["SyzygyPath"]); // Free up mapped files } @@ -246,15 +254,31 @@ void MainThread::search() { && !Skill(Options["Skill Level"]).enabled() && rootMoves[0].pv[0] != MOVE_NONE) { - for (Thread* th : Threads) + std::map votes; + Value minScore = this->rootMoves[0].score; + + // Find out minimum score and reset votes for moves which can be voted + for (Thread* th: Threads) { - Depth depthDiff = th->completedDepth - bestThread->completedDepth; - Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score; + minScore = std::min(minScore, th->rootMoves[0].score); + votes[th->rootMoves[0].pv[0]] = 0; + } - // Select the thread with the best score, always if it is a mate - if ( scoreDiff > 0 - && (depthDiff >= 0 || th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY)) + // Vote according to score and depth + auto square = [](int64_t x) { return x * x; }; + for (Thread* th : Threads) + votes[th->rootMoves[0].pv[0]] += 200 + (square(th->rootMoves[0].score - minScore + 1) + * int64_t(th->completedDepth)); + + // Select best thread + int64_t 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]]; bestThread = th; + } } } @@ -280,6 +304,7 @@ void MainThread::search() { void Thread::search() { Stack stack[MAX_PLY+7], *ss = stack+4; // To reference from (ss-4) to (ss+2) + Move pv[MAX_PLY+1]; Value bestValue, alpha, beta, delta; Move lastBestMove = MOVE_NONE; Depth lastBestMoveDepth = DEPTH_ZERO; @@ -290,7 +315,8 @@ void Thread::search() { std::memset(ss-4, 0, 7 * sizeof(Stack)); for (int i = 4; i > 0; i--) - (ss-i)->continuationHistory = this->continuationHistory[NO_PIECE][0].get(); // Use as sentinel + (ss-i)->continuationHistory = &this->continuationHistory[NO_PIECE][0]; // Use as sentinel + ss->pv = pv; bestValue = delta = alpha = -VALUE_INFINITE; beta = VALUE_INFINITE; @@ -365,7 +391,7 @@ void Thread::search() { if (rootDepth >= 5 * ONE_PLY) { Value previousScore = rootMoves[pvIdx].previousScore; - delta = Value(18); + delta = Value(20); alpha = std::max(previousScore - delta,-VALUE_INFINITE); beta = std::min(previousScore + delta, VALUE_INFINITE); @@ -379,9 +405,11 @@ void Thread::search() { // Start with a small aspiration window and, in the case of a fail // high/low, re-search with a bigger window until we don't fail // high/low anymore. + int failedHighCnt = 0; while (true) { - bestValue = ::search(rootPos, ss, alpha, beta, rootDepth, false); + Depth adjustedDepth = std::max(ONE_PLY, rootDepth - failedHighCnt * ONE_PLY); + bestValue = ::search(rootPos, ss, alpha, beta, adjustedDepth, false); // Bring the best move to the front. It is critical that sorting // is done with a stable algorithm because all the values but the @@ -414,12 +442,17 @@ void Thread::search() { if (mainThread) { + failedHighCnt = 0; failedLow = true; Threads.stopOnPonderhit = false; } } else if (bestValue >= beta) + { beta = std::min(bestValue + delta, VALUE_INFINITE); + if (mainThread) + ++failedHighCnt; + } else break; @@ -462,10 +495,8 @@ void Thread::search() { && !Threads.stop && !Threads.stopOnPonderhit) { - const int F[] = { failedLow, - bestValue - mainThread->previousScore }; - - int improvingFactor = std::max(246, std::min(832, 306 + 119 * F[0] - 6 * F[1])); + double fallingEval = (306 + 119 * failedLow + 6 * (mainThread->previousScore - bestValue)) / 581.0; + fallingEval = std::max(0.5, std::min(1.5, fallingEval)); // If the bestMove is stable over several iterations, reduce time accordingly timeReduction = 1.0; @@ -479,7 +510,7 @@ void Thread::search() { // Stop the search if we have only one legal move, or if available time elapsed if ( rootMoves.size() == 1 - || Time.elapsed() > Time.optimum() * bestMoveInstability * improvingFactor / 581) + || Time.elapsed() > Time.optimum() * bestMoveInstability * fallingEval) { // If we are allowed to ponder do not stop the search now but // keep pondering until the GUI sends "ponderhit" or "stop". @@ -520,7 +551,7 @@ namespace { && !rootNode && pos.has_game_cycle(ss->ply)) { - alpha = VALUE_DRAW; + alpha = value_draw(depth, pos.this_thread()); if (alpha >= beta) return alpha; } @@ -541,7 +572,7 @@ namespace { Key posKey; Move ttMove, move, excludedMove, bestMove; Depth extension, newDepth; - Value bestValue, value, ttValue, eval, maxValue; + Value bestValue, value, ttValue, eval, maxValue, pureStaticEval; bool ttHit, inCheck, givesCheck, improving; bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact; Piece movedPiece; @@ -569,7 +600,8 @@ namespace { if ( Threads.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY) - return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) : VALUE_DRAW; + return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) + : value_draw(depth, pos.this_thread()); // Step 3. Mate distance pruning. Even if we mate at the next move our score // would be at best mate_in(ss->ply+1), but if alpha is already bigger because @@ -587,7 +619,7 @@ namespace { (ss+1)->ply = ss->ply + 1; ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE; - ss->continuationHistory = thisThread->continuationHistory[NO_PIECE][0].get(); + ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0]; (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; Square prevSq = to_sq((ss-1)->currentMove); @@ -624,9 +656,11 @@ namespace { if (!pos.capture_or_promotion(ttMove)) update_quiet_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth)); - // Extra penalty for a quiet TT move in previous ply when it gets refuted - if ((ss-1)->moveCount == 1 && !pos.captured_piece()) - update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY)); + // Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted + if ( (ss-1)->moveCount == 1 + || ((ss-1)->currentMove == (ss-1)->killers[0] && (ss-1)->killers[0])) + if (!pos.captured_piece()) + update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY)); } // Penalty for a quiet ttMove that fails low else if (!pos.capture_or_promotion(ttMove)) @@ -652,6 +686,10 @@ namespace { TB::ProbeState err; TB::WDLScore wdl = Tablebases::probe_wdl(pos, &err); + // Force check of time on the next occasion + if (thisThread == Threads.main()) + static_cast(thisThread)->callsCnt = 0; + if (err != TB::ProbeState::FAIL) { thisThread->tbHits.fetch_add(1, std::memory_order_relaxed); @@ -689,15 +727,16 @@ namespace { // Step 6. Static evaluation of the position if (inCheck) { - ss->staticEval = eval = VALUE_NONE; + ss->staticEval = eval = pureStaticEval = VALUE_NONE; improving = false; goto moves_loop; // Skip early pruning when in check } else if (ttHit) { // Never assume anything on values stored in TT - if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE) - eval = ss->staticEval = evaluate(pos); + ss->staticEval = eval = pureStaticEval = tte->eval(); + if (eval == VALUE_NONE) + ss->staticEval = eval = pureStaticEval = evaluate(pos); // Can ttValue be used as a better position evaluation? if ( ttValue != VALUE_NONE @@ -706,30 +745,32 @@ namespace { } else { - ss->staticEval = eval = - (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) - : -(ss-1)->staticEval + 2 * Eval::Tempo; + if ((ss-1)->currentMove != MOVE_NULL) + { + int p = (ss-1)->statScore; + int bonus = p > 0 ? (-p - 2500) / 512 : + p < 0 ? (-p + 2500) / 512 : 0; - tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, - ss->staticEval); + pureStaticEval = evaluate(pos); + ss->staticEval = eval = pureStaticEval + bonus; + } + else + ss->staticEval = eval = pureStaticEval = -(ss-1)->staticEval + 2 * Eval::Tempo; + + tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, pureStaticEval); } // Step 7. Razoring (~2 Elo) - if ( !PvNode - && depth < 3 * ONE_PLY - && eval <= alpha - RazorMargin[depth / ONE_PLY]) - { - Value ralpha = alpha - (depth >= 2 * ONE_PLY) * RazorMargin[depth / ONE_PLY]; - Value v = qsearch(pos, ss, ralpha, ralpha+1); - if (depth < 2 * ONE_PLY || v <= ralpha) - return v; - } + if ( !rootNode // The required rootNode PV handling is not available in qsearch + && depth < 2 * ONE_PLY + && eval <= alpha - RazorMargin) + return qsearch(pos, ss, alpha, beta); improving = ss->staticEval >= (ss-2)->staticEval || (ss-2)->staticEval == VALUE_NONE; // Step 8. Futility pruning: child node (~30 Elo) - if ( !rootNode + if ( !PvNode && depth < 7 * ONE_PLY && eval - futility_margin(depth, improving) >= beta && eval < VALUE_KNOWN_WIN) // Do not return unproven wins @@ -738,9 +779,9 @@ namespace { // Step 9. Null move search with verification search (~40 Elo) if ( !PvNode && (ss-1)->currentMove != MOVE_NULL - && (ss-1)->statScore < 22500 + && (ss-1)->statScore < 23200 && eval >= beta - && ss->staticEval >= beta - 36 * depth / ONE_PLY + 225 + && pureStaticEval >= beta - 36 * depth / ONE_PLY + 225 && !excludedMove && pos.non_pawn_material(us) && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) @@ -748,10 +789,10 @@ namespace { assert(eval - beta >= 0); // Null move dynamic reduction based on depth and value - Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY; + Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min(int(eval - beta) / 200, 3)) * ONE_PLY; ss->currentMove = MOVE_NULL; - ss->continuationHistory = thisThread->continuationHistory[NO_PIECE][0].get(); + ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0]; pos.do_null_move(st); @@ -791,33 +832,33 @@ namespace { && depth >= 5 * ONE_PLY && abs(beta) < VALUE_MATE_IN_MAX_PLY) { - Value rbeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE); - MovePicker mp(pos, ttMove, rbeta - ss->staticEval, &thisThread->captureHistory); + Value raisedBeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE); + MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &thisThread->captureHistory); int probCutCount = 0; while ( (move = mp.next_move()) != MOVE_NONE && probCutCount < 3) - if (pos.legal(move)) + if (move != excludedMove && pos.legal(move)) { probCutCount++; ss->currentMove = move; - ss->continuationHistory = thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)].get(); + ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)]; assert(depth >= 5 * ONE_PLY); pos.do_move(move, st); // Perform a preliminary qsearch to verify that the move holds - value = -qsearch(pos, ss+1, -rbeta, -rbeta+1); + value = -qsearch(pos, ss+1, -raisedBeta, -raisedBeta+1); // If the qsearch held perform the regular search - if (value >= rbeta) - value = -search(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode); + if (value >= raisedBeta) + value = -search(pos, ss+1, -raisedBeta, -raisedBeta+1, depth - 4 * ONE_PLY, !cutNode); pos.undo_move(move); - if (value >= rbeta) + if (value >= raisedBeta) return value; } } @@ -846,7 +887,7 @@ moves_loop: // When in check, search starts from here value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc skipQuiets = false; - ttCapture = false; + ttCapture = ttMove && pos.capture_or_promotion(ttMove); pvExact = PvNode && ttHit && tte->bound() == BOUND_EXACT; // Step 12. Loop through all pseudo-legal moves until no moves remain @@ -888,30 +929,33 @@ moves_loop: // When in check, search starts from here // Singular extension search (~60 Elo). If all moves but one fail low on a // search of (alpha-s, beta-s), and just one fails high on (alpha, beta), // then that move is singular and should be extended. To verify this we do - // a reduced search on on all the other moves but the ttMove and if the + // a reduced search on all the other moves but the ttMove and if the // result is lower than ttValue minus a margin then we will extend the ttMove. if ( depth >= 8 * ONE_PLY && move == ttMove && !rootNode - && !excludedMove // Recursive singular search is not allowed + && !excludedMove // Avoid recursive singular search && ttValue != VALUE_NONE && (tte->bound() & BOUND_LOWER) && tte->depth() >= depth - 3 * ONE_PLY && pos.legal(move)) { - Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE); + Value reducedBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE); ss->excludedMove = move; - value = search(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode); + value = search(pos, ss, reducedBeta - 1, reducedBeta, depth / 2, cutNode); ss->excludedMove = MOVE_NONE; - if (value < rBeta) + if (value < reducedBeta) extension = ONE_PLY; } else if ( givesCheck // Check extension (~2 Elo) - && !moveCountPruning && pos.see_ge(move)) extension = ONE_PLY; + // Extension if castling + else if (type_of(move) == CASTLING) + extension = ONE_PLY; + // Calculate new depth for this move newDepth = depth - ONE_PLY + extension; @@ -922,7 +966,7 @@ moves_loop: // When in check, search starts from here { if ( !captureOrPromotion && !givesCheck - && (!pos.advanced_pawn_push(move) || pos.non_pawn_material() >= Value(5000))) + && !pos.advanced_pawn_push(move)) { // Move count based pruning (~30 Elo) if (moveCountPruning) @@ -935,7 +979,7 @@ moves_loop: // When in check, search starts from here int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY; // Countermoves based pruning (~20 Elo) - if ( lmrDepth < 3 + if ( lmrDepth < 3 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1) && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold) continue; @@ -965,12 +1009,9 @@ moves_loop: // When in check, search starts from here continue; } - if (move == ttMove && captureOrPromotion) - ttCapture = true; - // Update the current move (this must be done after singular extension search) ss->currentMove = move; - ss->continuationHistory = thisThread->continuationHistory[movedPiece][to_sq(move)].get(); + ss->continuationHistory = &thisThread->continuationHistory[movedPiece][to_sq(move)]; // Step 15. Make the move pos.do_move(move, st, givesCheck); @@ -983,20 +1024,12 @@ moves_loop: // When in check, search starts from here { Depth r = reduction(improving, depth, moveCount); - if (captureOrPromotion) // (~5 Elo) - { - // Increase reduction by comparing opponent's stat score - if ((ss-1)->statScore >= 0) - r += ONE_PLY; + // Decrease reduction if opponent's move count is high (~10 Elo) + if ((ss-1)->moveCount > 15) + r -= ONE_PLY; - r -= r ? ONE_PLY : DEPTH_ZERO; - } - else + if (!captureOrPromotion) { - // Decrease reduction if opponent's move count is high (~5 Elo) - if ((ss-1)->moveCount > 15) - r -= ONE_PLY; - // Decrease reduction for exact PV nodes (~0 Elo) if (pvExact) r -= ONE_PLY; @@ -1030,10 +1063,10 @@ 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 = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->statScore / 20000) * ONE_PLY); + r -= ss->statScore / 20000 * ONE_PLY; } - Depth d = std::max(newDepth - r, ONE_PLY); + Depth d = std::max(newDepth - std::max(r, DEPTH_ZERO), ONE_PLY); value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); @@ -1158,9 +1191,12 @@ moves_loop: // When in check, search starts from here update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth + ONE_PLY)); - // Extra penalty for a quiet TT move in previous ply when it gets refuted - if ((ss-1)->moveCount == 1 && !pos.captured_piece()) - update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY)); + // Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted + if ( (ss-1)->moveCount == 1 + || ((ss-1)->currentMove == (ss-1)->killers[0] && (ss-1)->killers[0])) + if (!pos.captured_piece()) + update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY)); + } // Bonus for prior countermove that caused the fail low else if ( (depth >= 3 * ONE_PLY || PvNode) @@ -1175,7 +1211,7 @@ moves_loop: // When in check, search starts from here tte->save(posKey, value_to_tt(bestValue, ss->ply), bestValue >= beta ? BOUND_LOWER : PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER, - depth, bestMove, ss->staticEval); + depth, bestMove, pureStaticEval); assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE); @@ -1215,7 +1251,7 @@ moves_loop: // When in check, search starts from here Thread* thisThread = pos.this_thread(); (ss+1)->ply = ss->ply + 1; ss->currentMove = bestMove = MOVE_NONE; - ss->continuationHistory = thisThread->continuationHistory[NO_PIECE][0].get(); + ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0]; inCheck = pos.checkers(); moveCount = 0; @@ -1350,7 +1386,7 @@ moves_loop: // When in check, search starts from here } ss->currentMove = move; - ss->continuationHistory = thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)].get(); + ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)]; // Make and search the move pos.do_move(move, st, givesCheck); @@ -1366,21 +1402,15 @@ moves_loop: // When in check, search starts from here if (value > alpha) { + bestMove = move; + if (PvNode) // Update pv even in fail-high case update_pv(ss->pv, move, (ss+1)->pv); if (PvNode && value < beta) // Update alpha here! - { alpha = value; - bestMove = move; - } - else // Fail high - { - tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER, - ttDepth, move, ss->staticEval); - - return value; - } + else + break; // Fail high } } } @@ -1391,7 +1421,8 @@ moves_loop: // When in check, search starts from here return mated_in(ss->ply); // Plies to mate from the root tte->save(posKey, value_to_tt(bestValue, ss->ply), - PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER, + bestValue >= beta ? BOUND_LOWER : + PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER, ttDepth, bestMove, ss->staticEval); assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);