X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=a052ea18f8828d3c56c8dc8cee94c0cde34bcbcc;hb=3c31776a20370cad008e1d4b0203c7b02b1b8ec6;hp=5426ce489ab851ade016e01d648a98f100de67f9;hpb=9eedc0a46346bddb8b29c47a84fe6fe8f80d14af;p=stockfish diff --git a/src/search.cpp b/src/search.cpp index 5426ce48..a052ea18 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -1052,37 +1052,50 @@ namespace { if (depth < OnePly) return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID); - // Initialize, and make an early exit in case of an aborted search, - // an instant draw, maximum ply reached, etc. + // Step 1. Initialize node and poll + // Polling can abort search. init_node(ss, ply, threadID); - // After init_node() that calls poll() + // 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; - // Mate distance pruning + // 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; - // Transposition table lookup. 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: + // Step 4. Transposition table lookup + // 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: // // * Repetition draw detection // * 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); - // Go with internal iterative deepening if we don't have a TT move + // Step 5. Evaluate the position statically + // At PV nodes we do this only to update gain statistics + isCheck = pos.is_check(); + if (!isCheck) + { + EvalInfo ei; + ss[ply].eval = evaluate(pos, ei, threadID); + 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 ( UseIIDAtPVNodes && depth >= 5*OnePly && ttMove == MOVE_NONE) @@ -1092,24 +1105,14 @@ namespace { tte = TT.retrieve(pos.get_key()); } - isCheck = pos.is_check(); - if (!isCheck) - { - // Update gain statistics of the previous move that lead - // us in this position. - EvalInfo ei; - ss[ply].eval = evaluate(pos, ei, threadID); - update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval); - } + // Step 10. Loop through moves + // Loop through all legal moves until no moves remain or a beta cutoff occurs - // Initialize a MovePicker object for the current position, and prepare - // to search all moves + // Initialize a MovePicker object for the current position mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move())); - CheckInfo ci(pos); MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]); + CheckInfo ci(pos); - // Loop through all legal moves until no moves remain or a beta cutoff - // occurs. while ( alpha < beta && (move = mp.get_next_move()) != MOVE_NONE && !TM.thread_should_stop(threadID)) @@ -1120,7 +1123,7 @@ namespace { moveIsCheck = pos.move_is_check(move, ci); captureOrPromotion = pos.move_is_capture_or_promotion(move); - // Decide the new search depth + // Step 11. 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 @@ -1146,17 +1149,21 @@ namespace { newDepth = depth - OnePly + ext; - // Update current move + // Update current move (this must be done after singular extension search) movesSearched[moveCount++] = ss[ply].currentMove = move; - // Make and search the move + // Step 12. Futility pruning (is omitted in PV nodes) + + // Step 13. Make the move pos.do_move(move, st, ci, moveIsCheck); - if (moveCount == 1) // The first move in list is the PV + // 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); else { - // Try to reduce non-pv search depth by one ply if move seems not problematic, + // Step 14. Reduced search // if the move fails high will be re-searched at full depth. bool doFullDepthSearch = true; @@ -1174,19 +1181,24 @@ namespace { } } - if (doFullDepthSearch) // Go with full depth non-pv search + // Step 15. Full depth search + if (doFullDepthSearch) { ss[ply].reduction = Depth(0); value = -search(pos, ss, -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); } } + + // Step 16. Undo move pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // New best move? + // Step 17. Check for new best move if (value > bestValue) { bestValue = value; @@ -1199,7 +1211,7 @@ namespace { } } - // Split? + // Step 18. Check for split if ( TM.active_threads() > 1 && bestValue < beta && depth >= MinimumSplitDepth @@ -1212,11 +1224,13 @@ namespace { break; } - // All legal moves have been searched. A special case: If there were + // 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))