X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=e405a3732d768ea015b11061001d1cd58a102bd4;hp=6e37fba1e524f8725d9737cab9568ea5d7081e4d;hb=b1bb376c3cc9a2e197759b3e6f0d365c8aae7e72;hpb=04a320666efce725ef66d1a84aaef493a880153d diff --git a/src/search.cpp b/src/search.cpp index 6e37fba1..e405a373 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -1,6 +1,6 @@ /* Stockfish, a UCI chess playing engine derived from Glaurung 2.1 - Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file) + Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file) Stockfish is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -62,10 +62,9 @@ namespace { constexpr uint64_t TtHitAverageWindow = 4096; constexpr uint64_t TtHitAverageResolution = 1024; - // Razor and futility margins - constexpr int RazorMargin = 510; + // Futility margin Value futility_margin(Depth d, bool improving) { - return Value(223 * (d - improving)); + return Value(234 * (d - improving)); } // Reductions lookup table, initialized at startup @@ -73,7 +72,7 @@ namespace { Depth reduction(bool i, Depth d, int mn) { int r = Reductions[d] * Reductions[mn]; - return (r + 509) / 1024 + (!i && r > 894); + return (r + 503) / 1024 + (!i && r > 915); } constexpr int futility_move_count(bool improving, Depth depth) { @@ -82,7 +81,7 @@ namespace { // History and stats update bonus, based on depth int stat_bonus(Depth d) { - return d > 13 ? 29 : 17 * d * d + 134 * d - 134; + return d > 14 ? 29 : 8 * d * d + 224 * d - 215; } // Add a small random component to draw evaluations to avoid 3fold-blindness @@ -194,7 +193,7 @@ namespace { void Search::init() { for (int i = 1; i < MAX_MOVES; ++i) - Reductions[i] = int((22.0 + 2 * std::log(Threads.size())) * std::log(i + 0.25 * std::log(i))); + Reductions[i] = int((21.3 + 2 * std::log(Threads.size())) * std::log(i + 0.25 * std::log(i))); } @@ -410,7 +409,7 @@ void Thread::search() { beta = std::min(prev + delta, VALUE_INFINITE); // Adjust contempt based on root move's previousScore (dynamic contempt) - int dct = ct + (105 - ct / 2) * prev / (abs(prev) + 149); + int dct = ct + (113 - ct / 2) * prev / (abs(prev) + 147); contempt = (us == WHITE ? make_score(dct, dct / 2) : -make_score(dct, dct / 2)); @@ -676,6 +675,7 @@ namespace { ss->ttPv = PvNode || (ss->ttHit && tte->is_pv()); formerPv = ss->ttPv && !PvNode; + // Update low ply history for previous move if we are near root and position is or has been in PV if ( ss->ttPv && depth > 12 && ss->ply - 1 < MAX_LPH @@ -700,6 +700,7 @@ namespace { { if (ttValue >= beta) { + // Bonus for a quiet ttMove that fails high if (!pos.capture_or_promotion(ttMove)) update_quiet_stats(pos, ss, ttMove, stat_bonus(depth), depth); @@ -716,6 +717,8 @@ namespace { } } + // Partial workaround for the graph history interaction problem + // For high rule50 counts don't produce transposition table cutoffs. if (pos.rule50_count() < 90) return ttValue; } @@ -789,6 +792,7 @@ namespace { if (eval == VALUE_NONE) ss->staticEval = eval = evaluate(pos); + // Randomize draw evaluation if (eval == VALUE_DRAW) eval = value_draw(thisThread); @@ -799,38 +803,46 @@ namespace { } else { + // In case of null move search use previous static eval with a different sign + // and addition of two tempos if ((ss-1)->currentMove != MOVE_NULL) ss->staticEval = eval = evaluate(pos); else ss->staticEval = eval = -(ss-1)->staticEval + 2 * Tempo; + // Save static evaluation into transposition table tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); } - // Step 7. Razoring (~1 Elo) - if ( !rootNode // The required rootNode PV handling is not available in qsearch - && depth == 1 - && eval <= alpha - RazorMargin) - return qsearch(pos, ss, alpha, beta); + // Use static evaluation difference to improve quiet move ordering + if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture) + { + int bonus = std::clamp(-depth * 4 * int((ss-1)->staticEval + ss->staticEval - 2 * Tempo), -1000, 1000); + thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus; + } + // Set up improving flag that is used in various pruning heuristics + // We define position as improving if static evaluation of position is better + // Than the previous static evaluation at our turn + // In case of us being in check at our previous move we look at move prior to it improving = (ss-2)->staticEval == VALUE_NONE ? ss->staticEval > (ss-4)->staticEval || (ss-4)->staticEval == VALUE_NONE : ss->staticEval > (ss-2)->staticEval; - // Step 8. Futility pruning: child node (~50 Elo) + // Step 7. Futility pruning: child node (~50 Elo) if ( !PvNode - && depth < 8 + && depth < 9 && eval - futility_margin(depth, improving) >= beta && eval < VALUE_KNOWN_WIN) // Do not return unproven wins return eval; - // Step 9. Null move search with verification search (~40 Elo) + // Step 8. Null move search with verification search (~40 Elo) if ( !PvNode && (ss-1)->currentMove != MOVE_NULL && (ss-1)->statScore < 22977 && eval >= beta && eval >= ss->staticEval - && ss->staticEval >= beta - 30 * depth - 28 * improving + 84 * ss->ttPv + 182 + && ss->staticEval >= beta - 30 * depth - 28 * improving + 84 * ss->ttPv + 168 && !excludedMove && pos.non_pawn_material(us) && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) @@ -838,7 +850,7 @@ namespace { assert(eval - beta >= 0); // Null move dynamic reduction based on depth and value - Depth R = (982 + 85 * depth) / 256 + std::min(int(eval - beta) / 192, 3); + Depth R = (1015 + 85 * depth) / 256 + std::min(int(eval - beta) / 191, 3); ss->currentMove = MOVE_NULL; ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0]; @@ -855,7 +867,7 @@ namespace { if (nullValue >= VALUE_TB_WIN_IN_MAX_PLY) nullValue = beta; - if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 13)) + if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 14)) return nullValue; assert(!thisThread->nmpMinPly); // Recursive verification is not allowed @@ -874,9 +886,9 @@ namespace { } } - probCutBeta = beta + 176 - 49 * improving; + probCutBeta = beta + 194 - 49 * improving; - // Step 10. ProbCut (~10 Elo) + // Step 9. ProbCut (~10 Elo) // If we have a good enough capture and a reduced search returns a value // much above beta, we can (almost) safely prune the previous move. if ( !PvNode @@ -949,7 +961,7 @@ namespace { ss->ttPv = ttPv; } - // Step 11. If the position is not in TT, decrease depth by 2 + // Step 10. If the position is not in TT, decrease depth by 2 if ( PvNode && depth >= 6 && !ttMove) @@ -978,7 +990,7 @@ moves_loop: // When in check, search starts from here // Mark this node as being searched ThreadHolding th(thisThread, posKey, ss->ply); - // Step 12. Loop through all pseudo-legal moves until no moves remain + // Step 11. Loop through all pseudo-legal moves until no moves remain // or a beta cutoff occurs. while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE) { @@ -1016,7 +1028,7 @@ moves_loop: // When in check, search starts from here // Calculate new depth for this move newDepth = depth - 1; - // Step 13. Pruning at shallow depth (~200 Elo) + // Step 12. Pruning at shallow depth (~200 Elo) if ( !rootNode && pos.non_pawn_material(us) && bestValue > VALUE_TB_LOSS_IN_MAX_PLY) @@ -1027,8 +1039,20 @@ moves_loop: // When in check, search starts from here // Reduced depth of the next LMR search int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0); - if ( !captureOrPromotion - && !givesCheck) + if ( captureOrPromotion + || givesCheck) + { + // Capture history based pruning when the move doesn't give check + if ( !givesCheck + && lmrDepth < 1 + && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0) + continue; + + // SEE based pruning + if (!pos.see_ge(move, Value(-218) * depth)) // (~25 Elo) + continue; + } + else { // Countermoves based pruning (~20 Elo) if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1) @@ -1039,32 +1063,20 @@ moves_loop: // When in check, search starts from here // Futility pruning: parent node (~5 Elo) if ( lmrDepth < 7 && !ss->inCheck - && ss->staticEval + 283 + 170 * lmrDepth <= alpha + && ss->staticEval + 254 + 159 * lmrDepth <= alpha && (*contHist[0])[movedPiece][to_sq(move)] + (*contHist[1])[movedPiece][to_sq(move)] + (*contHist[3])[movedPiece][to_sq(move)] - + (*contHist[5])[movedPiece][to_sq(move)] / 2 < 27376) + + (*contHist[5])[movedPiece][to_sq(move)] / 2 < 26394) continue; // Prune moves with negative SEE (~20 Elo) - if (!pos.see_ge(move, Value(-(29 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth))) - continue; - } - else - { - // Capture history based pruning when the move doesn't give check - if ( !givesCheck - && lmrDepth < 1 - && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0) - continue; - - // See based pruning - if (!pos.see_ge(move, Value(-221) * depth)) // (~25 Elo) + if (!pos.see_ge(move, Value(-(30 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth))) continue; } } - // Step 14. Extensions (~75 Elo) + // Step 13. Extensions (~75 Elo) // Singular extension search (~70 Elo). If all moves but one fail low on a // search of (alpha-s, beta-s), and just one fails high on (alpha, beta), @@ -1123,12 +1135,6 @@ moves_loop: // When in check, search starts from here && pos.non_pawn_material() <= 2 * RookValueMg) extension = 1; - // Late irreversible move extension - if ( move == ttMove - && pos.rule50_count() > 80 - && (captureOrPromotion || type_of(movedPiece) == PAWN)) - extension = 2; - // Add extension to new depth newDepth += extension; @@ -1142,10 +1148,10 @@ moves_loop: // When in check, search starts from here [movedPiece] [to_sq(move)]; - // Step 15. Make the move + // Step 14. Make the move pos.do_move(move, st, givesCheck); - // Step 16. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be + // Step 15. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be // re-searched at full depth. if ( depth >= 3 && moveCount > 1 + 2 * rootNode @@ -1153,15 +1159,16 @@ moves_loop: // When in check, search starts from here || moveCountPruning || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha || cutNode - || thisThread->ttHitAverage < 427 * TtHitAverageResolution * TtHitAverageWindow / 1024)) + || (!PvNode && !formerPv && captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 4506) + || thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024)) { Depth r = reduction(improving, depth, moveCount); // Decrease reduction if the ttHit running average is large - if (thisThread->ttHitAverage > 509 * TtHitAverageResolution * TtHitAverageWindow / 1024) + if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024) r--; - // Reduction if other threads are searching this position + // Increase reduction if other threads are searching this position if (th.marked()) r++; @@ -1169,6 +1176,11 @@ moves_loop: // When in check, search starts from here if (ss->ttPv) r -= 2; + // Increase reduction at root and non-PV nodes when the best move does not change frequently + if ((rootNode || !PvNode) && thisThread->rootDepth > 10 && thisThread->bestMoveChanges <= 2) + r++; + + // More reductions for late moves if position was not in previous PV if (moveCountPruning && !formerPv) r++; @@ -1180,7 +1192,14 @@ moves_loop: // When in check, search starts from here if (singularQuietLMR) r--; - if (!captureOrPromotion) + if (captureOrPromotion) + { + // Unless giving check, this capture is likely bad + if ( !givesCheck + && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 210 * depth <= alpha) + r++; + } + else { // Increase reduction if ttMove is a capture (~5 Elo) if (ttCapture) @@ -1207,26 +1226,15 @@ moves_loop: // When in check, search starts from here - 5287; // Decrease/increase reduction by comparing opponent's stat score (~10 Elo) - if (ss->statScore >= -106 && (ss-1)->statScore < -104) + if (ss->statScore >= -105 && (ss-1)->statScore < -103) r--; - else if ((ss-1)->statScore >= -119 && ss->statScore < -140) + else if ((ss-1)->statScore >= -122 && ss->statScore < -129) r++; // Decrease/increase reduction for moves with a good/bad history (~30 Elo) r -= ss->statScore / 14884; } - else - { - // Increase reduction for captures/promotions if late move and at low depth - if (depth < 8 && moveCount > 2) - r++; - - // Unless giving check, this capture is likely bad - if ( !givesCheck - && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 213 * depth <= alpha) - r++; - } Depth d = std::clamp(newDepth - r, 1, newDepth); @@ -1243,19 +1251,17 @@ moves_loop: // When in check, search starts from here didLMR = false; } - // Step 17. Full depth search when LMR is skipped or fails high + // Step 16. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) { value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); + // If the move passed LMR update its stats if (didLMR && !captureOrPromotion) { int bonus = value > alpha ? stat_bonus(newDepth) : -stat_bonus(newDepth); - if (move == ss->killers[0]) - bonus += bonus / 4; - update_continuation_histories(ss, movedPiece, to_sq(move), bonus); } } @@ -1272,12 +1278,12 @@ moves_loop: // When in check, search starts from here std::min(maxNextDepth, newDepth), false); } - // Step 18. Undo move + // Step 17. Undo move pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // Step 19. Check for a new best move + // Step 18. Check for a new best move // Finished searching the move. If a stop occurred, the return value of // the search cannot be trusted, and we return immediately without // updating best move, PV and TT. @@ -1302,8 +1308,7 @@ moves_loop: // When in check, search starts from here rm.pv.push_back(*m); // We record how often the best move has been changed in each - // iteration. This information is used for time management: when - // the best move changes frequently, we allocate some more time. + // iteration. This information is used for time management and LMR if (moveCount > 1) ++thisThread->bestMoveChanges; } @@ -1336,6 +1341,7 @@ moves_loop: // When in check, search starts from here } } + // If the move is worse than some previously searched move, remember it to update its stats later if (move != bestMove) { if (captureOrPromotion && captureCount < 32) @@ -1354,7 +1360,7 @@ moves_loop: // When in check, search starts from here return VALUE_DRAW; */ - // Step 20. Check for mate and stalemate + // Step 19. Check for mate and stalemate // All legal moves have been searched and if there are no legal moves, it // must be a mate or a stalemate. If we are in a singular extension search then // return a fail low score. @@ -1365,6 +1371,7 @@ moves_loop: // When in check, search starts from here bestValue = excludedMove ? alpha : ss->inCheck ? mated_in(ss->ply) : VALUE_DRAW; + // If there is a move which produces search value greater than alpha we update stats of searched moves else if (bestMove) update_all_stats(pos, ss, bestMove, bestValue, beta, prevSq, quietsSearched, quietCount, capturesSearched, captureCount, depth); @@ -1386,6 +1393,7 @@ moves_loop: // When in check, search starts from here else if (depth > 3) ss->ttPv = ss->ttPv && (ss+1)->ttPv; + // Write gathered information in transposition table if (!excludedMove && !(rootNode && thisThread->pvIdx)) tte->save(posKey, value_to_tt(bestValue, ss->ply), ss->ttPv, bestValue >= beta ? BOUND_LOWER : @@ -1481,6 +1489,8 @@ moves_loop: // When in check, search starts from here bestValue = ttValue; } else + // In case of null move search use previous static eval with a different sign + // and addition of two tempos ss->staticEval = bestValue = (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Tempo; @@ -1488,6 +1498,7 @@ moves_loop: // When in check, search starts from here // Stand pat. Return immediately if static value is at least beta if (bestValue >= beta) { + // Save gathered info in transposition table if (!ss->ttHit) tte->save(posKey, value_to_tt(bestValue, ss->ply), false, BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->staticEval); @@ -1498,7 +1509,7 @@ moves_loop: // When in check, search starts from here if (PvNode && bestValue > alpha) alpha = bestValue; - futilityBase = bestValue + 145; + futilityBase = bestValue + 155; } const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, @@ -1525,7 +1536,7 @@ moves_loop: // When in check, search starts from here moveCount++; // Futility pruning - if ( !ss->inCheck + if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY && !givesCheck && futilityBase > -VALUE_KNOWN_WIN && !pos.advanced_pawn_push(move)) @@ -1552,8 +1563,7 @@ moves_loop: // When in check, search starts from here } // Do not search moves with negative SEE values - if ( !ss->inCheck - && !(givesCheck && pos.is_discovery_check_on_king(~pos.side_to_move(), move)) + if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY && !pos.see_ge(move)) continue; @@ -1616,6 +1626,7 @@ moves_loop: // When in check, search starts from here return mated_in(ss->ply); // Plies to mate from the root } + // Save gathered info in transposition table tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit, bestValue >= beta ? BOUND_LOWER : PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER, @@ -1699,9 +1710,10 @@ moves_loop: // When in check, search starts from here if (!pos.capture_or_promotion(bestMove)) { + // Increase stats for the best move in case it was a quiet move update_quiet_stats(pos, ss, bestMove, bonus2, depth); - // Decrease all the non-best quiet moves + // Decrease stats for all non-best quiet moves for (int i = 0; i < quietCount; ++i) { thisThread->mainHistory[us][from_to(quietsSearched[i])] << -bonus2; @@ -1709,14 +1721,16 @@ moves_loop: // When in check, search starts from here } } else + // Increase stats for the best move in case it was a capture move captureHistory[moved_piece][to_sq(bestMove)][captured] << bonus1; - // Extra penalty for a quiet early move that was not a TT move or main killer move in previous ply when it gets refuted + // Extra penalty for a quiet early move that was not a TT move or + // main killer move in previous ply when it gets refuted. if ( ((ss-1)->moveCount == 1 + (ss-1)->ttHit || ((ss-1)->currentMove == (ss-1)->killers[0])) && !pos.captured_piece()) update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -bonus1); - // Decrease all the non-best capture moves + // Decrease stats for all non-best capture moves for (int i = 0; i < captureCount; ++i) { moved_piece = pos.moved_piece(capturesSearched[i]); @@ -1733,6 +1747,7 @@ moves_loop: // When in check, search starts from here for (int i : {1, 2, 4, 6}) { + // Only update first 2 continuation histories if we are in check if (ss->inCheck && i > 2) break; if (is_ok((ss-i)->currentMove)) @@ -1745,6 +1760,7 @@ moves_loop: // When in check, search starts from here void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus, int depth) { + // Update killers if (ss->killers[0] != move) { ss->killers[1] = ss->killers[0]; @@ -1756,15 +1772,18 @@ moves_loop: // When in check, search starts from here thisThread->mainHistory[us][from_to(move)] << bonus; update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus); + // Penalty for reversed move in case of moved piece not being a pawn if (type_of(pos.moved_piece(move)) != PAWN) thisThread->mainHistory[us][from_to(reverse_move(move))] << -bonus; + // Update countermove history if (is_ok((ss-1)->currentMove)) { Square prevSq = to_sq((ss-1)->currentMove); thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] = move; } + // Update low ply history if (depth > 11 && ss->ply < MAX_LPH) thisThread->lowPlyHistory[ss->ply][from_to(move)] << stat_bonus(depth - 7); }