X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=025c1141c97546e6e98693877fad9afff26336d5;hp=8a6105711aae2720c112371c7f6ca3b2cf9a9532;hb=91a76331ca27b40d63f0031fbd7b9e41ead354d4;hpb=d6252ef202f43d42d05b80145f3014da4d22863e diff --git a/src/search.cpp b/src/search.cpp index 8a610571..025c1141 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -107,7 +107,7 @@ namespace { }; template - Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning); + Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode); template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO); @@ -390,7 +390,7 @@ void Thread::search() { // high/low anymore. while (true) { - bestValue = ::search(rootPos, ss, alpha, beta, rootDepth, false, false); + bestValue = ::search(rootPos, ss, alpha, beta, rootDepth, 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 @@ -517,7 +517,7 @@ namespace { // search<>() is the main search function for both PV and non-PV nodes template - Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) { + Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) { // Use quiescence search when needed if (depth < ONE_PLY) @@ -577,6 +577,17 @@ namespace { beta = std::min(mate_in(ss->ply+1), beta); if (alpha >= beta) return alpha; + + // Check if there exists a move which draws by repetition, or an alternative + // earlier move to this position. + if ( pos.rule50_count() >= 3 + && alpha < VALUE_DRAW + && pos.has_game_cycle(ss->ply)) + { + alpha = VALUE_DRAW; + if (alpha >= beta) + return alpha; + } } assert(0 <= ss->ply && ss->ply < MAX_PLY); @@ -682,12 +693,12 @@ namespace { } } - // Step 6. Evaluate the position statically + // Step 6. Static evaluation of the position if (inCheck) { ss->staticEval = eval = VALUE_NONE; improving = false; - goto moves_loop; + goto moves_loop; // Skip early pruning when in check } else if (ttHit) { @@ -710,13 +721,7 @@ namespace { ss->staticEval, TT.generation()); } - improving = ss->staticEval >= (ss-2)->staticEval - ||(ss-2)->staticEval == VALUE_NONE; - - if (skipEarlyPruning || !pos.non_pawn_material(pos.side_to_move())) - goto moves_loop; - - // Step 7. Razoring (skipped when in check, ~2 Elo) + // Step 7. Razoring (~2 Elo) if ( !PvNode && depth < 3 * ONE_PLY && eval <= alpha - RazorMargin[depth / ONE_PLY]) @@ -727,7 +732,10 @@ namespace { return v; } - // Step 8. Futility pruning: child node (skipped when in check, ~30 Elo) + improving = ss->staticEval >= (ss-2)->staticEval + || (ss-2)->staticEval == VALUE_NONE; + + // Step 8. Futility pruning: child node (~30 Elo) if ( !rootNode && depth < 7 * ONE_PLY && eval - futility_margin(depth, improving) >= beta @@ -736,8 +744,12 @@ namespace { // Step 9. Null move search with verification search (~40 Elo) if ( !PvNode + && (ss-1)->currentMove != MOVE_NULL + && (ss-1)->statScore < 22500 && eval >= beta && ss->staticEval >= beta - 36 * depth / ONE_PLY + 225 + && !excludedMove + && pos.non_pawn_material(pos.side_to_move()) && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 != thisThread->nmp_odd)) { assert(eval - beta >= 0); @@ -750,7 +762,7 @@ namespace { pos.do_null_move(st); - Value nullValue = -search(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true); + Value nullValue = -search(pos, ss+1, -beta, -beta+1, depth-R, !cutNode); pos.undo_null_move(); @@ -768,7 +780,7 @@ namespace { thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4; thisThread->nmp_odd = ss->ply % 2; - Value v = search(pos, ss, beta-1, beta, depth-R, false, true); + Value v = search(pos, ss, beta-1, beta, depth-R, false); thisThread->nmp_odd = thisThread->nmp_ply = 0; @@ -777,15 +789,13 @@ namespace { } } - // Step 10. ProbCut (skipped when in check, ~10 Elo) + // Step 10. 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 && depth >= 5 * ONE_PLY && abs(beta) < VALUE_MATE_IN_MAX_PLY) { - assert(is_ok((ss-1)->currentMove)); - Value rbeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE); MovePicker mp(pos, ttMove, rbeta - ss->staticEval, &thisThread->captureHistory); int probCutCount = 0; @@ -808,7 +818,7 @@ namespace { // If the qsearch held perform the regular search if (value >= rbeta) - value = -search(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false); + value = -search(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode); pos.undo_move(move); @@ -817,12 +827,12 @@ namespace { } } - // Step 11. Internal iterative deepening (skipped when in check, ~2 Elo) + // Step 11. Internal iterative deepening (~2 Elo) if ( depth >= 8 * ONE_PLY && !ttMove) { Depth d = 3 * depth / 4 - 2 * ONE_PLY; - search(pos, ss, alpha, beta, d, cutNode, true); + search(pos, ss, alpha, beta, d, cutNode); tte = TT.probe(posKey, ttHit); ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; @@ -897,7 +907,7 @@ moves_loop: // When in check, search starts from here { Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE); ss->excludedMove = move; - value = search(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode, true); + value = search(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode); ss->excludedMove = MOVE_NONE; if (value < rBeta) @@ -1027,7 +1037,7 @@ moves_loop: // When in check, search starts from here Depth d = std::max(newDepth - r, ONE_PLY); - value = -search(pos, ss+1, -(alpha+1), -alpha, d, true, false); + value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); doFullDepthSearch = (value > alpha && d != newDepth); } @@ -1036,7 +1046,7 @@ moves_loop: // When in check, search starts from here // Step 17. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) - value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false); + value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); // 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 @@ -1046,7 +1056,7 @@ moves_loop: // When in check, search starts from here (ss+1)->pv = pv; (ss+1)->pv[0] = MOVE_NONE; - value = -search(pos, ss+1, -beta, -alpha, newDepth, false, false); + value = -search(pos, ss+1, -beta, -alpha, newDepth, false); } // Step 18. Undo move @@ -1154,7 +1164,7 @@ moves_loop: // When in check, search starts from here 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 + else if ( (depth >= 3 * ONE_PLY || PvNode) && !pos.captured_piece() && is_ok((ss-1)->currentMove)) update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));