X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=7abffb8779dda1df915c660577a6ebd9330eb559;hp=5f545ef62fca42aa1a0f19acadae840006bae291;hb=37c2b5685efa8a0c3de04604c73e19f6e82dd6e8;hpb=c57c71bf5c56665b0339fa983665bdef4bf8a099 diff --git a/src/search.cpp b/src/search.cpp index 5f545ef6..7abffb87 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 @@ -62,8 +62,7 @@ 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(234 * (d - improving)); } @@ -85,7 +84,7 @@ namespace { return d > 14 ? 29 : 8 * d * d + 224 * d - 215; } - // Add a small random component to draw evaluations to avoid 3fold-blindness + // Add a small random component to draw evaluations to avoid 3-fold blindness Value value_draw(Thread* thisThread) { return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1); } @@ -822,12 +821,6 @@ namespace { thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus; } - // 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); - // 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 @@ -836,14 +829,14 @@ namespace { ? 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 < 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 @@ -895,7 +888,7 @@ namespace { 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 @@ -968,7 +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) @@ -997,7 +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) { @@ -1035,7 +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) @@ -1046,8 +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) @@ -1069,21 +1074,9 @@ moves_loop: // When in check, search starts from here if (!pos.see_ge(move, Value(-(30 - 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(-218) * depth)) // (~25 Elo) - 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), @@ -1134,7 +1127,7 @@ moves_loop: // When in check, search starts from here // Check extension (~2 Elo) else if ( givesCheck - && (pos.is_discovery_check_on_king(~us, move) || pos.see_ge(move))) + && (pos.is_discovered_check_on_king(~us, move) || pos.see_ge(move))) extension = 1; // Last captures extension @@ -1142,12 +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; @@ -1161,10 +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 @@ -1172,7 +1159,7 @@ moves_loop: // When in check, search starts from here || moveCountPruning || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha || cutNode - || (!PvNode && !formerPv && thisThread->captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 4506) + || (!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); @@ -1205,7 +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) @@ -1239,14 +1233,13 @@ moves_loop: // When in check, search starts from here r++; // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - r -= ss->statScore / 14884; - } - else - { - // Unless giving check, this capture is likely bad - if ( !givesCheck - && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 210 * depth <= alpha) - r++; + // If we are not in check use statScore, if we are in check + // use sum of main history and first continuation history with an offset + if (ss->inCheck) + r -= (thisThread->mainHistory[us][from_to(move)] + + (*contHist[0])[movedPiece][to_sq(move)] - 4333) / 16384; + else + r -= ss->statScore / 14884; } Depth d = std::clamp(newDepth - r, 1, newDepth); @@ -1264,7 +1257,7 @@ 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); @@ -1291,12 +1284,12 @@ 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. @@ -1373,7 +1366,7 @@ 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. @@ -1554,7 +1547,7 @@ moves_loop: // When in check, search starts from here && futilityBase > -VALUE_KNOWN_WIN && !pos.advanced_pawn_push(move)) { - assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push + assert(type_of(move) != EN_PASSANT); // Due to !pos.advanced_pawn_push // moveCount pruning if (moveCount > 2)