X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=4ea010728574e04c80f0112a388c610185845a46;hp=1786a6fdc60ebb235e708a7d7cfedaa63479987e;hb=48246468f2874c9e5e985baf224e202433d53fd3;hpb=5e340346db94446587c78e791507ab9e2cffe3fa diff --git a/src/search.cpp b/src/search.cpp index 1786a6fd..4ea01072 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -172,10 +172,17 @@ namespace { const bool PruneDefendingMoves = false; const bool PruneBlockingMoves = false; + // If the TT move is at least SingleReplyMargin better then the + // remaining ones we will extend it. + const Value SingleReplyMargin = Value(0x64); + // Margins for futility pruning in the quiescence search, and at frontier // and near frontier nodes. const Value FutilityMarginQS = Value(0x80); + // Each move futility margin is decreased + const Value IncrementalFutilityMargin = Value(0x8); + // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply const Value FutilityMargins[12] = { Value(0x100), Value(0x120), Value(0x200), Value(0x220), Value(0x250), Value(0x270), // 4 ply 4.5 ply 5 ply 5.5 ply 6 ply 6.5 ply @@ -274,7 +281,7 @@ namespace { Value id_loop(const Position& pos, Move searchMoves[]); Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta); Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID); - Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID); + Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE); Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID); void sp_search(SplitPoint* sp, int threadID); void sp_search_pv(SplitPoint* sp, int threadID); @@ -333,14 +340,14 @@ namespace { int perft(Position& pos, Depth depth) { Move move; - MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H); int sum = 0; + MovePicker mp = MovePicker(pos, MOVE_NONE, depth, H); // If we are at the last ply we don't need to do and undo // the moves, just to count them. if (depth <= OnePly) // Replace with '<' to test also qsearch { - while ((move = mp.get_next_move()) != MOVE_NONE) sum++; + while (mp.get_next_move()) sum++; return sum; } @@ -348,10 +355,10 @@ int perft(Position& pos, Depth depth) CheckInfo ci(pos); while ((move = mp.get_next_move()) != MOVE_NONE) { - StateInfo st; - pos.do_move(move, st, ci, pos.move_is_check(move, ci)); - sum += perft(pos, depth - OnePly); - pos.undo_move(move); + StateInfo st; + pos.do_move(move, st, ci, pos.move_is_check(move, ci)); + sum += perft(pos, depth - OnePly); + pos.undo_move(move); } return sum; } @@ -795,7 +802,6 @@ namespace { if (stopSearch) { - //FIXME: Implement fail-low emergency measures if (!PonderSearch) break; else @@ -1129,12 +1135,38 @@ namespace { moveIsCheck = pos.move_is_check(move, ci); captureOrPromotion = pos.move_is_capture_or_promotion(move); - movesSearched[moveCount++] = ss[ply].currentMove = move; - // Decide the new search depth ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleReply, mateThreat, &dangerous); + + // We want to extend the TT move if it is much better then remaining ones. + // To verify this we do a reduced search on all the other moves but the ttMove, + // if result is lower then TT value minus a margin then we assume ttMove is the + // only one playable. It is a kind of relaxed single reply extension. + if ( depth >= 4 * OnePly + && move == ttMove + && ext < OnePly + && is_lower_bound(tte->type()) + && tte->depth() >= depth - 3 * OnePly) + { + Value ttValue = value_from_tt(tte->value(), ply); + + if (abs(ttValue) < VALUE_KNOWN_WIN) + { + Depth d = Max(Min(depth / 2, depth - 4 * OnePly), OnePly); + Value excValue = search(pos, ss, ttValue - SingleReplyMargin, d, ply, false, threadID, ttMove); + + // If search result is well below the foreseen score of the ttMove then we + // assume ttMove is the only one realistically playable and we extend it. + if (excValue < ttValue - SingleReplyMargin) + ext = OnePly; + } + } + newDepth = depth - OnePly + ext; + // Update current move + movesSearched[moveCount++] = ss[ply].currentMove = move; + // Make and search the move pos.do_move(move, st, ci, moveIsCheck); @@ -1248,7 +1280,7 @@ namespace { // search() is the search function for zero-width nodes. Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, - int ply, bool allowNullmove, int threadID) { + int ply, bool allowNullmove, int threadID, Move excludedMove) { assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE); assert(ply >= 0 && ply < PLY_MAX); @@ -1260,7 +1292,7 @@ namespace { const TTEntry* tte; Move ttMove, move; Depth ext, newDepth; - Value approximateEval, nullValue, value, futilityValue; + Value approximateEval, nullValue, value, futilityValue, futilityValueScaled; bool isCheck, useFutilityPruning, singleReply, moveIsCheck, captureOrPromotion, dangerous; bool mateThreat = false; int moveCount = 0; @@ -1290,8 +1322,12 @@ namespace { if (value_mate_in(ply + 1) < beta) return beta - 1; + // We don't want the score of a partial search to overwrite a previous full search + // TT value, so we use a different position key in case of an excluded move exsists. + Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key(); + // Transposition table lookup - tte = TT.retrieve(pos.get_key()); + tte = TT.retrieve(posKey); ttMove = (tte ? tte->move() : MOVE_NONE); if (tte && ok_to_use_TT(tte, depth, beta, ply)) @@ -1314,7 +1350,13 @@ namespace { ss[ply].currentMove = MOVE_NULL; pos.do_null_move(st); - int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction + + // Null move dynamic reduction based on depth + int R = (depth >= 5 * OnePly ? 4 : 3); + + // Null move dynamic reduction based on value + if (approximateEval - beta > PawnValueMidgame) + R++; nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID); @@ -1354,8 +1396,9 @@ namespace { && ttMove == MOVE_NONE && !pos.has_pawn_on_7th(pos.side_to_move())) { - Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID); - if (v < beta - RazorMargins[int(depth) - 2]) + Value rbeta = beta - RazorMargins[int(depth) - 2]; + Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID); + if (v < rbeta) return v; } @@ -1378,24 +1421,56 @@ namespace { if (tte && (tte->type() & VALUE_TYPE_EVAL)) futilityValue = value_from_tt(tte->value(), ply) + FutilityMargins[int(depth) - 2]; - // Loop through all legal moves until no moves remain or a beta cutoff - // occurs. + // Move count pruning limit + const int MCLimit = 3 + (1 << (3*int(depth)/8)); + + // Loop through all legal moves until no moves remain or a beta cutoff occurs while ( bestValue < beta && (move = mp.get_next_move()) != MOVE_NONE && !thread_should_stop(threadID)) { assert(move_is_ok(move)); + if (move == excludedMove) + continue; + singleReply = (isCheck && mp.number_of_evasions() == 1); moveIsCheck = pos.move_is_check(move, ci); captureOrPromotion = pos.move_is_capture_or_promotion(move); - movesSearched[moveCount++] = ss[ply].currentMove = move; - // Decide the new search depth ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleReply, mateThreat, &dangerous); + + // We want to extend the TT move if it is much better then remaining ones. + // To verify this we do a reduced search on all the other moves but the ttMove, + // if result is lower then TT value minus a margin then we assume ttMove is the + // only one playable. It is a kind of relaxed single reply extension. + if ( depth >= 4 * OnePly + && !excludedMove // do not allow recursive single-reply search + && move == ttMove + && ext < OnePly + && is_lower_bound(tte->type()) + && tte->depth() >= depth - 3 * OnePly) + { + Value ttValue = value_from_tt(tte->value(), ply); + + if (abs(ttValue) < VALUE_KNOWN_WIN) + { + Depth d = Max(Min(depth / 2, depth - 4 * OnePly), OnePly); + Value excValue = search(pos, ss, ttValue - SingleReplyMargin, d, ply, false, threadID, ttMove); + + // If search result is well below the foreseen score of the ttMove then we + // assume ttMove is the only one realistically playable and we extend it. + if (excValue < ttValue - SingleReplyMargin) + ext = (depth >= 8 * OnePly) ? OnePly : ext + OnePly / 2; + } + } + newDepth = depth - OnePly + ext; + // Update current move + movesSearched[moveCount++] = ss[ply].currentMove = move; + // Futility pruning if ( useFutilityPruning && !dangerous @@ -1403,7 +1478,7 @@ namespace { && move != ttMove) { // History pruning. See ok_to_prune() definition - if ( moveCount >= 2 + int(depth) + if ( moveCount >= MCLimit && ok_to_prune(pos, move, ss[ply].threatMove, depth) && bestValue > value_mated_in(PLY_MAX)) continue; @@ -1413,12 +1488,14 @@ namespace { { if (futilityValue == VALUE_NONE) futilityValue = evaluate(pos, ei, threadID) - + FutilityMargins[int(depth) - 2]; + + 64*(2+bitScanReverse32(int(depth) * int(depth))); + + futilityValueScaled = futilityValue - moveCount * IncrementalFutilityMargin; - if (futilityValue < beta) + if (futilityValueScaled < beta) { - if (futilityValue > bestValue) - bestValue = futilityValue; + if (futilityValueScaled > bestValue) + bestValue = futilityValueScaled; continue; } } @@ -1478,7 +1555,7 @@ namespace { // All legal moves have been searched. A special case: If there were // no legal moves, it must be mate or stalemate. if (moveCount == 0) - return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW); + return excludedMove ? beta - 1 : (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW); // If the search is not aborted, update the transposition table, // history counters, and killer moves. @@ -1486,7 +1563,7 @@ namespace { return bestValue; if (bestValue < beta) - TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE); + TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE); else { BetaCounter.add(pos.side_to_move(), depth, threadID); @@ -1496,7 +1573,7 @@ namespace { update_history(pos, move, depth, movesSearched, moveCount); update_killers(move, ss[ply]); } - TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move); + TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move); } assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE); @@ -2041,7 +2118,7 @@ namespace { moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0); pos.undo_move(moves[count].move); moves[count].pv[0] = moves[count].move; - moves[count].pv[1] = MOVE_NONE; // FIXME + moves[count].pv[1] = MOVE_NONE; count++; } sort();