- singleEvasion = (isCheck && mp.number_of_evasions() == 1);
- moveIsCheck = pos.move_is_check(move, ci);
- captureOrPromotion = pos.move_is_capture_or_promotion(move);
-
- // Decide the new search depth
- ext = extension(pos, move, true, 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 >= 6 * OnePly
- && tte
- && move == tte->move()
- && 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 - SingleReplyMargin, depth / 2, ply, false, threadID, move);
-
- 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);
-
- if (moveCount == 1) // The first move in list is the PV
- value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
- else
- {
- // Try to reduce non-pv search depth by one ply if move seems not problematic,
- // if the move fails high will be re-searched at full depth.
- if ( depth >= 3*OnePly
- && !dangerous
- && !captureOrPromotion
- && !move_is_castle(move)
- && !move_is_killer(move, ss[ply]))
- {
- double red = 0.5 + ln(moveCount) * ln(depth / 2) / 6.0;
- if (red >= 1.0)
- {
- ss[ply].reduction = Depth(int(floor(red * int(OnePly))));
- value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
- }
- else
- value = alpha + 1; // Just to trigger next condition
- }
- else
- value = alpha + 1; // Just to trigger next condition
-
- if (value > alpha) // Go with full depth non-pv search
- {
- ss[ply].reduction = Depth(0);
- value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
- if (value > alpha && value < beta)
- {
- // When the search fails high at ply 1 while searching the first
- // move at the root, set the flag failHighPly1. This is used for
- // time managment: We don't want to stop the search early in
- // such cases, because resolving the fail high at ply 1 could
- // result in a big drop in score at the root.
- if (ply == 1 && RootMoveNumber == 1)
- Threads[threadID].failHighPly1 = true;
-
- // A fail high occurred. Re-search at full window (pv search)
- value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
- Threads[threadID].failHighPly1 = false;
- }
- }
- }
- pos.undo_move(move);
-
- assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
-
- // New best move?
- if (value > bestValue)
- {
- bestValue = value;
- if (value > alpha)
- {
- alpha = value;
- update_pv(ss, ply);
- if (value == value_mate_in(ply + 1))
- ss[ply].mateKiller = move;
- }
- // If we are at ply 1, and we are searching the first root move at
- // ply 0, set the 'Problem' variable if the score has dropped a lot
- // (from the computer's point of view) since the previous iteration.
- if ( ply == 1
- && Iteration >= 2
- && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
- Problem = true;
- }
-
- // Split?
- if ( ActiveThreads > 1
- && bestValue < beta
- && depth >= MinimumSplitDepth
- && Iteration <= 99
- && idle_thread_exists(threadID)
- && !AbortSearch
- && !thread_should_stop(threadID)
- && split(pos, ss, ply, &alpha, &beta, &bestValue, VALUE_NONE,
- depth, &moveCount, &mp, threadID, true))
- break;