- }
- 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;
- }
- }
-
- // 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, &alpha, beta, &bestValue, VALUE_NONE,
- depth, &moveCount, &mp, threadID, true))
- break;
- }
-
- // 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 (isCheck ? value_mated_in(ply) : VALUE_DRAW);
-
- // 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, staticValue, nullValue, value, futilityValue, futilityValueScaled;
- bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
- bool mateThreat = false;
- int moveCount = 0;
- futilityValue = staticValue = bestValue = value = -VALUE_INFINITE;
-
- if (depth < OnePly)
- return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
-
- // Initialize, and make an early exit in case of an aborted search,
- // an instant draw, maximum ply reached, etc.
- init_node(ss, ply, threadID);
-
- // After init_node() that calls poll()
- if (AbortSearch || TM.thread_should_stop(threadID))
- return Value(0);
-
- if (pos.is_draw() || ply >= PLY_MAX - 1)
- return VALUE_DRAW;
-
- // Mate distance pruning
- if (value_mated_in(ply) >= beta)
- return beta;
-
- 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(posKey);
- ttMove = (tte ? tte->move() : MOVE_NONE);