X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=4f5a3480ef00c68270d38647a14d3f68df511e85;hp=76a88643307aa4138c58415d8955f6bb147aed5d;hb=2b6bc70f7bf266602a3ca59abb606699bdf544c8;hpb=989833205fb63de094c1f28e1c5f803bc8a917e4 diff --git a/src/search.cpp b/src/search.cpp index 76a88643..4f5a3480 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); @@ -1129,12 +1136,38 @@ 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 +1281,7 @@ 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 +1293,7 @@ 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 +1323,12 @@ 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)) @@ -1385,24 +1422,56 @@ 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 @@ -1410,7 +1479,7 @@ 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; @@ -1420,12 +1489,14 @@ 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; } } @@ -1485,7 +1556,7 @@ 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. @@ -1493,7 +1564,7 @@ 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); @@ -1503,7 +1574,7 @@ 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);