X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=fa592a859947e09e1f30fcefb8bd276ccccec16f;hp=3da3d04ea963e579b7d2c6154015eb7cc1a8ee19;hb=f3b296c2e2061951d366edfbd5287f336e865553;hpb=87586b3d0c8961c2fc9330e2f8ac2f8c3fe79018 diff --git a/src/search.cpp b/src/search.cpp index 3da3d04e..fa592a85 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -35,6 +35,8 @@ #include "uci.h" #include "syzygy/tbprobe.h" +namespace Stockfish { + namespace Search { LimitsType Limits; @@ -81,7 +83,7 @@ namespace { // History and stats update bonus, based on depth int stat_bonus(Depth d) { - return d > 14 ? 29 : 8 * d * d + 224 * d - 215; + return d > 14 ? 66 : 6 * d * d + 231 * d - 206; } // Add a small random component to draw evaluations to avoid 3-fold blindness @@ -422,7 +424,7 @@ void Thread::search() { while (true) { Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter); - bestValue = ::search(rootPos, ss, alpha, beta, adjustedDepth, false); + bestValue = Stockfish::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 @@ -616,6 +618,7 @@ namespace { moveCount = captureCount = quietCount = ss->moveCount = 0; bestValue = -VALUE_INFINITE; maxValue = VALUE_INFINITE; + ss->distanceFromPv = (PvNode ? 0 : ss->distanceFromPv); // Check for the available remaining time if (thisThread == Threads.main()) @@ -839,10 +842,10 @@ namespace { // Step 8. Null move search with verification search (~40 Elo) if ( !PvNode && (ss-1)->currentMove != MOVE_NULL - && (ss-1)->statScore < 22977 + && (ss-1)->statScore < 24185 && eval >= beta && eval >= ss->staticEval - && ss->staticEval >= beta - 30 * depth - 28 * improving + 84 * ss->ttPv + 168 + && ss->staticEval >= beta - 24 * depth - 34 * improving + 162 * ss->ttPv + 159 && !excludedMove && pos.non_pawn_material(us) && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) @@ -850,7 +853,7 @@ namespace { assert(eval - beta >= 0); // Null move dynamic reduction based on depth and value - Depth R = (1015 + 85 * depth) / 256 + std::min(int(eval - beta) / 191, 3); + Depth R = (1062 + 68 * depth) / 256 + std::min(int(eval - beta) / 190, 3); ss->currentMove = MOVE_NULL; ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0]; @@ -886,7 +889,7 @@ namespace { } } - probCutBeta = beta + 194 - 49 * improving; + probCutBeta = beta + 209 - 44 * improving; // Step 9. ProbCut (~10 Elo) // If we have a good enough capture and a reduced search returns a value @@ -969,6 +972,23 @@ namespace { moves_loop: // When in check, search starts from here + ttCapture = ttMove && pos.capture_or_promotion(ttMove); + + // Step 11. A small Probcut idea, when we are in check + probCutBeta = beta + 400; + if ( ss->inCheck + && !PvNode + && depth >= 4 + && ttCapture + && (tte->bound() & BOUND_LOWER) + && tte->depth() >= depth - 3 + && ttValue >= probCutBeta + && abs(ttValue) <= VALUE_KNOWN_WIN + && abs(beta) <= VALUE_KNOWN_WIN + ) + return probCutBeta; + + const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr , (ss-4)->continuationHistory, nullptr , (ss-6)->continuationHistory }; @@ -985,12 +1005,11 @@ moves_loop: // When in check, search starts from here value = bestValue; singularQuietLMR = moveCountPruning = false; - ttCapture = ttMove && pos.capture_or_promotion(ttMove); // Mark this node as being searched ThreadHolding th(thisThread, posKey, ss->ply); - // Step 11. Loop through all pseudo-legal moves until no moves remain + // 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) { @@ -1025,10 +1044,18 @@ moves_loop: // When in check, search starts from here movedPiece = pos.moved_piece(move); givesCheck = pos.gives_check(move); + // Indicate PvNodes that will probably fail low if node was searched with non-PV search + // at depth equal or greater to current depth and result of this search was far below alpha + bool likelyFailLow = PvNode + && ttMove + && (tte->bound() & BOUND_UPPER) + && ttValue < alpha + 200 + 100 * depth + && tte->depth() >= depth; + // Calculate new depth for this move newDepth = depth - 1; - // Step 12. Pruning at shallow depth (~200 Elo) + // Step 13. Pruning at shallow depth (~200 Elo) if ( !rootNode && pos.non_pawn_material(us) && bestValue > VALUE_TB_LOSS_IN_MAX_PLY) @@ -1063,11 +1090,11 @@ moves_loop: // When in check, search starts from here // Futility pruning: parent node (~5 Elo) if ( lmrDepth < 7 && !ss->inCheck - && ss->staticEval + 254 + 159 * lmrDepth <= alpha + && ss->staticEval + 174 + 157 * 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 < 26394) + + (*contHist[5])[movedPiece][to_sq(move)] / 3 < 28255) continue; // Prune moves with negative SEE (~20 Elo) @@ -1076,7 +1103,7 @@ moves_loop: // When in check, search starts from here } } - // Step 13. Extensions (~75 Elo) + // Step 14. 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), @@ -1148,18 +1175,22 @@ moves_loop: // When in check, search starts from here [movedPiece] [to_sq(move)]; - // Step 14. Make the move + // Step 15. Make the move pos.do_move(move, st, givesCheck); - // Step 15. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be - // re-searched at full depth. + (ss+1)->distanceFromPv = ss->distanceFromPv + moveCount - 1; + + // Step 16. Late moves reduction / extension (LMR, ~200 Elo) + // We use various heuristics for the sons of a node after the first son has + // been searched. In general we would like to reduce them, but there are many + // cases where we extend a son if it has good chances to be "interesting". if ( depth >= 3 && moveCount > 1 + 2 * rootNode && ( !captureOrPromotion || moveCountPruning || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha || cutNode - || (!PvNode && !formerPv && captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 4506) + || (!PvNode && !formerPv && captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 3678) || thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024)) { Depth r = reduction(improving, depth, moveCount); @@ -1172,8 +1203,9 @@ moves_loop: // When in check, search starts from here if (th.marked()) r++; - // Decrease reduction if position is or has been on the PV (~10 Elo) - if (ss->ttPv) + // Decrease reduction if position is or has been on the PV + // and node is not likely to fail low. (~10 Elo) + if (ss->ttPv && !likelyFailLow) r -= 2; // Increase reduction at root and non-PV nodes when the best move does not change frequently @@ -1223,35 +1255,43 @@ moves_loop: // When in check, search starts from here + (*contHist[0])[movedPiece][to_sq(move)] + (*contHist[1])[movedPiece][to_sq(move)] + (*contHist[3])[movedPiece][to_sq(move)] - - 5287; + - 4741; // Decrease/increase reduction by comparing opponent's stat score (~10 Elo) - if (ss->statScore >= -105 && (ss-1)->statScore < -103) + if (ss->statScore >= -89 && (ss-1)->statScore < -116) r--; - else if ((ss-1)->statScore >= -122 && ss->statScore < -129) + else if ((ss-1)->statScore >= -112 && ss->statScore < -100) r++; // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - r -= ss->statScore / 14884; + // If we are not in check use statScore, but if we are in check we use + // the 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)] - 3833) / 16384; + else + r -= ss->statScore / 14790; } - Depth d = std::clamp(newDepth - r, 1, newDepth); + // In general we want to cap the LMR depth search at newDepth. But for nodes + // close to the principal variation the cap is at (newDepth + 1), which will + // allow these nodes to be searched deeper than the pv (up to 4 plies deeper). + Depth d = std::clamp(newDepth - r, 1, newDepth + ((ss+1)->distanceFromPv <= 4)); value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); - doFullDepthSearch = value > alpha && d != newDepth; - + // If the son is reduced and fails high it will be re-searched at full depth + doFullDepthSearch = value > alpha && d < newDepth; didLMR = true; } else { doFullDepthSearch = !PvNode || moveCount > 1; - didLMR = false; } - // Step 16. Full depth search when LMR is skipped or fails high + // Step 17. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) { value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); @@ -1278,12 +1318,12 @@ moves_loop: // When in check, search starts from here std::min(maxNextDepth, newDepth), false); } - // Step 17. Undo move + // Step 18. Undo move pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // Step 18. Check for a new best move + // Step 19. 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. @@ -1360,7 +1400,7 @@ moves_loop: // When in check, search starts from here return VALUE_DRAW; */ - // Step 19. Check for mate and stalemate + // Step 20. 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. @@ -1535,15 +1575,13 @@ moves_loop: // When in check, search starts from here moveCount++; - // Futility pruning + // Futility pruning and moveCount pruning if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY && !givesCheck && futilityBase > -VALUE_KNOWN_WIN && !pos.advanced_pawn_push(move)) { - assert(type_of(move) != EN_PASSANT); // Due to !pos.advanced_pawn_push - // moveCount pruning if (moveCount > 2) continue; @@ -1705,8 +1743,8 @@ moves_loop: // When in check, search starts from here PieceType captured = type_of(pos.piece_on(to_sq(bestMove))); bonus1 = stat_bonus(depth + 1); - bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus - : stat_bonus(depth); // smaller bonus + bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus + : std::min(bonus1, stat_bonus(depth)); // smaller bonus if (!pos.capture_or_promotion(bestMove)) { @@ -1996,3 +2034,5 @@ void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) { m.tbRank = 0; } } + +} // namespace Stockfish