diff --git a/src/search.cpp b/src/search.cpp index 7cc51c60..95aa76c4 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -194,8 +194,7 @@ namespace { Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2]; // Minimum depth for use of singular extension - const Depth SingularExtensionDepthAtPVNodes = 6 * OnePly; - const Depth SingularExtensionDepthAtNonPVNodes = 8 * OnePly; + const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */}; // If the TT move is at least SingularExtensionMargin better then the // remaining ones we will extend it. @@ -280,8 +279,10 @@ namespace { Value id_loop(const Position& pos, Move searchMoves[]); Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr); - 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, Move excludedMove = MOVE_NONE); + + template + Value search(Position& pos, SearchStack ss[], Value alpha, 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); @@ -869,7 +870,7 @@ namespace { alpha = -VALUE_INFINITE; // Full depth PV search, done on first move or after a fail high - value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0); + value = -search(pos, ss, -beta, -alpha, newDepth, 1, false, 0); } else { @@ -886,7 +887,7 @@ namespace { if (ss[0].reduction) { // Reduced depth non-pv search using alpha as upperbound - value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0); + value = -search(pos, ss, -(alpha+1), -alpha, newDepth-ss[0].reduction, 1, true, 0); doFullDepthSearch = (value > alpha); } } @@ -896,12 +897,12 @@ namespace { { // Full depth non-pv search using alpha as upperbound ss[0].reduction = Depth(0); - value = -search(pos, ss, -alpha, newDepth, 1, true, 0); + value = -search(pos, ss, -(alpha+1), -alpha, newDepth, 1, true, 0); // If we are above alpha then research at same depth but as PV // to get a correct score or eventually a fail high above beta. if (value > alpha) - value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0); + value = -search(pos, ss, -beta, -alpha, newDepth, 1, false, 0); } } @@ -1023,8 +1024,10 @@ namespace { // search_pv() is the main search function for PV nodes. - Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, - Depth depth, int ply, int threadID) { + template + Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, + Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove) { + assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE); assert(beta > alpha && beta <= VALUE_INFINITE); @@ -1038,10 +1041,12 @@ namespace { Move ttMove, move; Depth ext, newDepth; Value bestValue, value, oldAlpha; + Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous; bool mateThreat = false; int moveCount = 0; - bestValue = value = -VALUE_INFINITE; + refinedValue = bestValue = value = -VALUE_INFINITE; + oldAlpha = alpha; if (depth < OnePly) return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID); @@ -1058,13 +1063,20 @@ namespace { return VALUE_DRAW; // Step 3. Mate distance pruning - oldAlpha = alpha; alpha = Max(value_mated_in(ply), alpha); beta = Min(value_mate_in(ply+1), beta); if (alpha >= beta) return alpha; // Step 4. Transposition table lookup + + // 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 exists. + Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key(); + + tte = TT.retrieve(posKey); + ttMove = (tte ? tte->move() : MOVE_NONE); + // At PV nodes, we don't use the TT for pruning, but only for move ordering. // This is to avoid problems in the following areas: // @@ -1072,57 +1084,173 @@ namespace { // * Fifty move rule detection // * Searching for a mate // * Printing of full PV line - tte = TT.retrieve(pos.get_key()); - ttMove = (tte ? tte->move() : MOVE_NONE); + + if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply)) + { + // Refresh tte entry to avoid aging + TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove); + + ss[ply].currentMove = ttMove; // Can be MOVE_NONE + return value_from_tt(tte->value(), ply); + } // Step 5. Evaluate the position statically // At PV nodes we do this only to update gain statistics isCheck = pos.is_check(); if (!isCheck) { - ss[ply].eval = evaluate(pos, ei, threadID); + if (!PvNode && tte && (tte->type() & VALUE_TYPE_EVAL)) + ss[ply].eval = value_from_tt(tte->value(), ply); + else + ss[ply].eval = evaluate(pos, ei, threadID); + + refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval); } // Step 6. Razoring (is omitted in PV nodes) - // Step 7. Static null move pruning (is omitted in PV nodes) - // Step 8. Null move search with verification search (is omitted in PV nodes) - - // Step 9. Internal iterative deepening - if ( depth >= IIDDepthAtPVNodes - && ttMove == MOVE_NONE) + if ( !PvNode + && refinedValue < beta - razor_margin(depth) + && ttMove == MOVE_NONE + && ss[ply - 1].currentMove != MOVE_NULL + && depth < RazorDepth + && !isCheck + && !value_is_mate(beta) + && !pos.has_pawn_on_7th(pos.side_to_move())) { - search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID); - ttMove = ss[ply].pv[ply]; - tte = TT.retrieve(pos.get_key()); + Value rbeta = beta - razor_margin(depth); + Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID); + if (v < rbeta) + // Logically we should return (v + razor_margin(depth)), but + // surprisingly this did slightly weaker in tests. + return v; } + // Step 7. Static null move pruning (is omitted in PV nodes) + // We're betting that the opponent doesn't have a move that will reduce + // the score by more than futility_margin(depth) if we do a null move. + if ( !PvNode + && allowNullmove + && depth < RazorDepth + && !isCheck + && !value_is_mate(beta) + && ok_to_do_nullmove(pos) + && refinedValue >= beta + futility_margin(depth, 0)) + return refinedValue - futility_margin(depth, 0); + + // Step 8. Null move search with verification search (is omitted in PV nodes) + // When we jump directly to qsearch() we do a null move only if static value is + // at least beta. Otherwise we do a null move if static value is not more than + // NullMoveMargin under beta. + if ( !PvNode + && allowNullmove + && depth > OnePly + && !isCheck + && !value_is_mate(beta) + && ok_to_do_nullmove(pos) + && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)) + { + ss[ply].currentMove = MOVE_NULL; + + // Null move dynamic reduction based on depth + int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0); + + // Null move dynamic reduction based on value + if (refinedValue - beta > PawnValueMidgame) + R++; + + pos.do_null_move(st); + + nullValue = -search(pos, ss, -beta, -alpha, depth-R*OnePly, ply+1, false, threadID); + + pos.undo_null_move(); + + if (nullValue >= beta) + { + // Do not return unproven mate scores + if (nullValue >= value_mate_in(PLY_MAX)) + nullValue = beta; + + if (depth < 6 * OnePly) + return nullValue; + + // Do zugzwang verification search + Value v = search(pos, ss, alpha, beta, depth-5*OnePly, ply, false, threadID); + if (v >= beta) + return nullValue; + } else { + // The null move failed low, which means that we may be faced with + // some kind of threat. If the previous move was reduced, check if + // the move that refuted the null move was somehow connected to the + // move which was reduced. If a connection is found, return a fail + // low score (which will cause the reduced move to fail high in the + // parent node, which will trigger a re-search with full depth). + if (nullValue == value_mated_in(ply + 2)) + mateThreat = true; + + ss[ply].threatMove = ss[ply + 1].currentMove; + if ( depth < ThreatDepth + && ss[ply - 1].reduction + && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove)) + return beta - 1; + } + } + + // Step 9. Internal iterative deepening + // We have different rules for PV nodes and non-pv nodes + if ( PvNode + && depth >= IIDDepthAtPVNodes + && ttMove == MOVE_NONE) + { + search(pos, ss, alpha, beta, depth-2*OnePly, ply, false, threadID); + ttMove = ss[ply].pv[ply]; + tte = TT.retrieve(posKey); + } + + if ( !PvNode + && depth >= IIDDepthAtNonPVNodes + && ttMove == MOVE_NONE + && !isCheck + && ss[ply].eval >= beta - IIDMargin) + { + search(pos, ss, alpha, beta, depth/2, ply, false, threadID); + ttMove = ss[ply].pv[ply]; + tte = TT.retrieve(posKey); + } + + // Expensive mate threat detection (only for PV nodes) + if (PvNode) + mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move())); + // Initialize a MovePicker object for the current position - mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move())); - MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]); + MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], (PvNode ? -VALUE_INFINITE : beta)); CheckInfo ci(pos); // Step 10. Loop through moves // Loop through all legal moves until no moves remain or a beta cutoff occurs - while ( alpha < beta + while ( bestValue < beta && (move = mp.get_next_move()) != MOVE_NONE && !TM.thread_should_stop(threadID)) { assert(move_is_ok(move)); + if (move == excludedMove) + continue; + singleEvasion = (isCheck && mp.number_of_evasions() == 1); moveIsCheck = pos.move_is_check(move, ci); captureOrPromotion = pos.move_is_capture_or_promotion(move); // Step 11. Decide the new search depth - ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous); + ext = extension(pos, move, PvNode, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous); // Singular extension search. We extend the TT move if its value is much better than // its siblings. To verify this we do a reduced search on all the other moves but the // ttMove, if result is lower then ttValue minus a margin then we extend ttMove. - if ( depth >= SingularExtensionDepthAtPVNodes + if ( depth >= SingularExtensionDepth[PvNode] && tte && move == tte->move() + && !excludedMove // Do not allow recursive singular extension search && ext < OnePly && is_lower_bound(tte->type()) && tte->depth() >= depth - 3 * OnePly) @@ -1131,7 +1259,7 @@ namespace { if (abs(ttValue) < VALUE_KNOWN_WIN) { - Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move); + Value excValue = search(pos, ss, ttValue - SingularExtensionMargin - 1, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move); if (excValue < ttValue - SingularExtensionMargin) ext = OnePly; @@ -1144,14 +1272,39 @@ namespace { movesSearched[moveCount++] = ss[ply].currentMove = move; // Step 12. Futility pruning (is omitted in PV nodes) + if ( !PvNode + && !isCheck + && !dangerous + && !captureOrPromotion + && !move_is_castle(move) + && move != ttMove) + { + // Move count based pruning + if ( moveCount >= futility_move_count(depth) + && ok_to_prune(pos, move, ss[ply].threatMove) + && bestValue > value_mated_in(PLY_MAX)) + continue; + + // Value based pruning + Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly + futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount) + + H.gain(pos.piece_on(move_from(move)), move_to(move)); + + if (futilityValueScaled < beta) + { + if (futilityValueScaled > bestValue) + bestValue = futilityValueScaled; + continue; + } + } // Step 13. Make the move pos.do_move(move, st, ci, moveIsCheck); // Step extra. pv search (only in PV nodes) // The first move in list is the expected PV - if (moveCount == 1) - value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID); + if (PvNode && moveCount == 1) + value = -search(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID); else { // Step 14. Reduced search @@ -1164,10 +1317,10 @@ namespace { && !move_is_castle(move) && !move_is_killer(move, ss[ply])) { - ss[ply].reduction = pv_reduction(depth, moveCount); + ss[ply].reduction = (PvNode ? pv_reduction(depth, moveCount) : nonpv_reduction(depth, moveCount)); if (ss[ply].reduction) { - value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID); + value = -search(pos, ss, -(alpha+1), -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID); doFullDepthSearch = (value > alpha); } } @@ -1176,11 +1329,11 @@ namespace { if (doFullDepthSearch) { ss[ply].reduction = Depth(0); - value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID); + value = -search(pos, ss, -(alpha+1), -alpha, newDepth, ply+1, true, threadID); // Step extra. pv search (only in PV nodes) - if (value > alpha && value < beta) - value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID); + if (PvNode && value > alpha && value < beta) + value = -search(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID); } } @@ -1211,342 +1364,7 @@ namespace { && !AbortSearch && !TM.thread_should_stop(threadID) && TM.split(pos, ss, ply, &alpha, beta, &bestValue, - depth, mateThreat, &moveCount, &mp, threadID, true)) - break; - } - - // Step 19. Check for mate and stalemate - // All legal moves have been searched and if there were - // no legal moves, it must be mate or stalemate. - if (moveCount == 0) - return (isCheck ? value_mated_in(ply) : VALUE_DRAW); - - // Step 20. Update tables - // If the search is not aborted, update the transposition table, - // history counters, and killer moves. - if (AbortSearch || TM.thread_should_stop(threadID)) - return bestValue; - - if (bestValue <= oldAlpha) - TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE); - - else if (bestValue >= beta) - { - TM.incrementBetaCounter(pos.side_to_move(), depth, threadID); - move = ss[ply].pv[ply]; - if (!pos.move_is_capture_or_promotion(move)) - { - 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); - } - else - TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]); - - return bestValue; - } - - - // 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, Move excludedMove) { - - assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE); - assert(ply >= 0 && ply < PLY_MAX); - assert(threadID >= 0 && threadID < TM.active_threads()); - - Move movesSearched[256]; - EvalInfo ei; - StateInfo st; - const TTEntry* tte; - Move ttMove, move; - Depth ext, newDepth; - Value bestValue, refinedValue, nullValue, value, futilityValueScaled; - bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous; - bool mateThreat = false; - int moveCount = 0; - refinedValue = bestValue = value = -VALUE_INFINITE; - - if (depth < OnePly) - return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID); - - // Step 1. Initialize node and poll - // Polling can abort search. - init_node(ss, ply, threadID); - - // Step 2. Check for aborted search and immediate draw - if (AbortSearch || TM.thread_should_stop(threadID)) - return Value(0); - - if (pos.is_draw() || ply >= PLY_MAX - 1) - return VALUE_DRAW; - - // Step 3. Mate distance pruning - if (value_mated_in(ply) >= beta) - return beta; - - if (value_mate_in(ply + 1) < beta) - return beta - 1; - - // Step 4. Transposition table lookup - - // 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 exists. - Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key(); - - tte = TT.retrieve(posKey); - ttMove = (tte ? tte->move() : MOVE_NONE); - - if (tte && ok_to_use_TT(tte, depth, beta, ply)) - { - // Refresh tte entry to avoid aging - TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove); - - ss[ply].currentMove = ttMove; // Can be MOVE_NONE - return value_from_tt(tte->value(), ply); - } - - // Step 5. Evaluate the position statically - isCheck = pos.is_check(); - - if (!isCheck) - { - if (tte && (tte->type() & VALUE_TYPE_EVAL)) - ss[ply].eval = value_from_tt(tte->value(), ply); - else - ss[ply].eval = evaluate(pos, ei, threadID); - - refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible - update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval); - } - - // Step 6. Razoring - if ( refinedValue < beta - razor_margin(depth) - && ttMove == MOVE_NONE - && ss[ply - 1].currentMove != MOVE_NULL - && depth < RazorDepth - && !isCheck - && !value_is_mate(beta) - && !pos.has_pawn_on_7th(pos.side_to_move())) - { - Value rbeta = beta - razor_margin(depth); - Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID); - if (v < rbeta) - // Logically we should return (v + razor_margin(depth)), but - // surprisingly this did slightly weaker in tests. - return v; - } - - // Step 7. Static null move pruning - // We're betting that the opponent doesn't have a move that will reduce - // the score by more than futility_margin(depth) if we do a null move. - if ( allowNullmove - && depth < RazorDepth - && !isCheck - && !value_is_mate(beta) - && ok_to_do_nullmove(pos) - && refinedValue >= beta + futility_margin(depth, 0)) - return refinedValue - futility_margin(depth, 0); - - // Step 8. Null move search with verification search - // When we jump directly to qsearch() we do a null move only if static value is - // at least beta. Otherwise we do a null move if static value is not more than - // NullMoveMargin under beta. - if ( allowNullmove - && depth > OnePly - && !isCheck - && !value_is_mate(beta) - && ok_to_do_nullmove(pos) - && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)) - { - ss[ply].currentMove = MOVE_NULL; - - // Null move dynamic reduction based on depth - int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0); - - // Null move dynamic reduction based on value - if (refinedValue - beta > PawnValueMidgame) - R++; - - pos.do_null_move(st); - - nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID); - - pos.undo_null_move(); - - if (nullValue >= beta) - { - // Do not return unproven mate scores - if (nullValue >= value_mate_in(PLY_MAX)) - nullValue = beta; - - if (depth < 6 * OnePly) - return nullValue; - - // Do zugzwang verification search - Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID); - if (v >= beta) - return nullValue; - } else { - // The null move failed low, which means that we may be faced with - // some kind of threat. If the previous move was reduced, check if - // the move that refuted the null move was somehow connected to the - // move which was reduced. If a connection is found, return a fail - // low score (which will cause the reduced move to fail high in the - // parent node, which will trigger a re-search with full depth). - if (nullValue == value_mated_in(ply + 2)) - mateThreat = true; - - ss[ply].threatMove = ss[ply + 1].currentMove; - if ( depth < ThreatDepth - && ss[ply - 1].reduction - && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove)) - return beta - 1; - } - } - - // Step 9. Internal iterative deepening - if ( depth >= IIDDepthAtNonPVNodes - && ttMove == MOVE_NONE - && !isCheck - && ss[ply].eval >= beta - IIDMargin) - { - search(pos, ss, beta, depth/2, ply, false, threadID); - ttMove = ss[ply].pv[ply]; - tte = TT.retrieve(posKey); - } - - // Initialize a MovePicker object for the current position - MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta); - CheckInfo ci(pos); - - // Step 10. Loop through moves - // Loop through all legal moves until no moves remain or a beta cutoff occurs - while ( bestValue < beta - && (move = mp.get_next_move()) != MOVE_NONE - && !TM.thread_should_stop(threadID)) - { - assert(move_is_ok(move)); - - if (move == excludedMove) - continue; - - moveIsCheck = pos.move_is_check(move, ci); - singleEvasion = (isCheck && mp.number_of_evasions() == 1); - captureOrPromotion = pos.move_is_capture_or_promotion(move); - - // Step 11. Decide the new search depth - ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous); - - // Singular extension search. We extend the TT move if its value is much better than - // its siblings. To verify this we do a reduced search on all the other moves but the - // ttMove, if result is lower then ttValue minus a margin then we extend ttMove. - if ( depth >= SingularExtensionDepthAtNonPVNodes - && tte - && move == tte->move() - && !excludedMove // Do not allow recursive singular extension search - && 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) - { - Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move); - - if (excValue < ttValue - SingularExtensionMargin) - ext = OnePly; - } - } - - newDepth = depth - OnePly + ext; - - // Update current move (this must be done after singular extension search) - movesSearched[moveCount++] = ss[ply].currentMove = move; - - // Step 12. Futility pruning - if ( !isCheck - && !dangerous - && !captureOrPromotion - && !move_is_castle(move) - && move != ttMove) - { - // Move count based pruning - if ( moveCount >= futility_move_count(depth) - && ok_to_prune(pos, move, ss[ply].threatMove) - && bestValue > value_mated_in(PLY_MAX)) - continue; - - // Value based pruning - Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly - futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount) - + H.gain(pos.piece_on(move_from(move)), move_to(move)); - - if (futilityValueScaled < beta) - { - if (futilityValueScaled > bestValue) - bestValue = futilityValueScaled; - continue; - } - } - - // Step 13. Make the move - pos.do_move(move, st, ci, moveIsCheck); - - // Step 14. Reduced search, if the move fails high - // will be re-searched at full depth. - bool doFullDepthSearch = true; - - if ( depth >= 3*OnePly - && !dangerous - && !captureOrPromotion - && !move_is_castle(move) - && !move_is_killer(move, ss[ply])) - { - ss[ply].reduction = nonpv_reduction(depth, moveCount); - if (ss[ply].reduction) - { - value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID); - doFullDepthSearch = (value >= beta); - } - } - - // Step 15. Full depth search - if (doFullDepthSearch) - { - ss[ply].reduction = Depth(0); - value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID); - } - - // Step 16. Undo move - pos.undo_move(move); - - assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - - // Step 17. Check for new best move - if (value > bestValue) - { - bestValue = value; - if (value >= beta) - update_pv(ss, ply); - - if (value == value_mate_in(ply + 1)) - ss[ply].mateKiller = move; - } - - // Step 18. Check for split - if ( TM.active_threads() > 1 - && bestValue < beta - && depth >= MinimumSplitDepth - && Iteration <= 99 - && TM.available_thread_exists(threadID) - && !AbortSearch - && !TM.thread_should_stop(threadID) - && TM.split(pos, ss, ply, NULL, beta, &bestValue, - depth, mateThreat, &moveCount, &mp, threadID, false)) + depth, mateThreat, &moveCount, &mp, threadID, PvNode)) break; } @@ -1555,7 +1373,7 @@ namespace { // no legal moves, it must be mate or stalemate. // If one move was excluded return fail low score. if (!moveCount) - return excludedMove ? beta - 1 : (isCheck ? value_mated_in(ply) : VALUE_DRAW); + return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW); // Step 20. Update tables // If the search is not aborted, update the transposition table, @@ -1563,9 +1381,10 @@ namespace { if (AbortSearch || TM.thread_should_stop(threadID)) return bestValue; - if (bestValue < beta) + if (bestValue <= oldAlpha) TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE); - else + + else if (bestValue >= beta) { TM.incrementBetaCounter(pos.side_to_move(), depth, threadID); move = ss[ply].pv[ply]; @@ -1575,8 +1394,9 @@ namespace { update_history(pos, move, depth, movesSearched, moveCount); update_killers(move, ss[ply]); } - } + else + TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]); assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE); @@ -1868,7 +1688,7 @@ namespace { ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount); if (ss[sp->ply].reduction) { - value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID); + value = -search(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID); doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID)); } } @@ -1877,7 +1697,7 @@ namespace { if (doFullDepthSearch) { ss[sp->ply].reduction = Depth(0); - value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID); + value = -search(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth, sp->ply+1, true, threadID); } // Step 16. Undo move @@ -1974,7 +1794,7 @@ namespace { if (ss[sp->ply].reduction) { Value localAlpha = sp->alpha; - value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID); + value = -search(pos, ss, -(localAlpha+1), -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID); doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID)); } } @@ -1984,7 +1804,7 @@ namespace { { Value localAlpha = sp->alpha; ss[sp->ply].reduction = Depth(0); - value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID); + value = -search(pos, ss, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1, true, threadID); if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID)) { @@ -1992,7 +1812,7 @@ namespace { // to be higher or equal then beta, if so, avoid to start a PV search. localAlpha = sp->alpha; if (localAlpha < sp->beta) - value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID); + value = -search(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, false, threadID); } } @@ -2032,7 +1852,7 @@ namespace { // init_node() is called at the beginning of all the search functions - // (search(), search_pv(), qsearch(), and so on) and initializes the + // (search() qsearch(), and so on) and initializes the // search stack object corresponding to the current node. Once every // NodesBetweenPolls nodes, init_node() also calls poll(), which polls // for user input and checks whether it is time to stop the search. @@ -2922,7 +2742,7 @@ namespace { splitPoint->ply = ply; splitPoint->depth = depth; splitPoint->mateThreat = mateThreat; - splitPoint->alpha = pvNode ? *alpha : beta - 1; + splitPoint->alpha = *alpha; splitPoint->beta = beta; splitPoint->pvNode = pvNode; splitPoint->bestValue = *bestValue; @@ -2977,12 +2797,10 @@ namespace { idle_loop(master, splitPoint); // We have returned from the idle loop, which means that all threads are - // finished. Update alpha, beta and bestValue, and return. + // finished. Update alpha and bestValue, and return. lock_grab(&MPLock); - if (pvNode) - *alpha = splitPoint->alpha; - + *alpha = splitPoint->alpha; *bestValue = splitPoint->bestValue; threads[master].activeSplitPoints--; threads[master].splitPoint = splitPoint->parent;