Depth depth;
Move EasyMove = MOVE_NONE;
Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
+ int researchCountFL, researchCountFH;
// Moves to search are verified, scored and sorted
RootMoveList rml(pos, searchMoves);
depth = (Iteration - 2) * ONE_PLY + InitialDepth;
- // Search to the current depth, rml is updated and sorted
- value = root_search(pos, ss, alpha, beta, depth, rml);
+ researchCountFL = researchCountFH = 0;
+
+ // We start with small aspiration window and in case of fail high/low, we
+ // research with bigger window until we are not failing high/low anymore.
+ while (true)
+ {
+ // Sort the moves before to (re)search
+ rml.set_non_pv_scores(pos, rml[0].pv[0], ss);
+ rml.sort();
+
+ // Search to the current depth, rml is updated and sorted
+ value = root_search(pos, ss, alpha, beta, depth, rml);
+
+ if (StopRequest)
+ break;
+
+ assert(value >= alpha);
+
+ if (value >= beta)
+ {
+ // Prepare for a research after a fail high, each time with a wider window
+ beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
+ researchCountFH++;
+ }
+ else if (value <= alpha)
+ {
+ AspirationFailLow = true;
+ StopOnPonderhit = false;
+
+ // Prepare for a research after a fail low, each time with a wider window
+ alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
+ researchCountFL++;
+ }
+ else
+ break;
+ }
if (StopRequest)
break; // Value cannot be trusted. Break out immediately!
stopSearch = true;
// Stop search early when the last two iterations returned a mate score
- if ( Iteration >= 6
+ if ( Iteration >= 6
&& abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
&& abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
stopSearch = true;
Value root_search(Position& pos, SearchStack* ss, Value alpha,
Value beta, Depth depth, RootMoveList& rml) {
- StateInfo st;
+
+ assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
+ assert(beta > alpha && beta <= VALUE_INFINITE);
+ assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
+
Move movesSearched[MOVES_MAX];
- CheckInfo ci(pos);
- int64_t nodes;
+ StateInfo st;
+ Key posKey;
Move move;
Depth ext, newDepth;
+ ValueType vt;
Value value, oldAlpha;
- RootMoveList::iterator rm;
bool isCheck, moveIsCheck, captureOrPromotion, dangerous, isPvMove;
- int moveCount, researchCountFH, researchCountFL;
+ int moveCount = 0;
- researchCountFH = researchCountFL = 0;
+ value = -VALUE_INFINITE;
oldAlpha = alpha;
isCheck = pos.is_check();
// Step 2. Check for aborted search (omitted at root)
// Step 3. Mate distance pruning (omitted at root)
// Step 4. Transposition table lookup (omitted at root)
+ posKey = pos.get_key();
// Step 5. Evaluate the position statically
// At root we do this only to get reference value for child nodes
// Step 8. Null move search with verification search (omitted at root)
// Step 9. Internal iterative deepening (omitted at root)
- // Step extra. Fail low loop
- // We start with small aspiration window and in case of fail low, we research
- // with bigger window until we are not failing low anymore.
- while (1)
- {
- // Sort the moves before to (re)search
- rml.set_non_pv_scores(pos, rml[0].pv[0], ss);
- rml.sort();
- moveCount = 0;
+ CheckInfo ci(pos);
+ int64_t nodes;
+ RootMoveList::iterator rm = rml.begin();
- // Step 10. Loop through all moves in the root move list
- for (rm = rml.begin(); rm != rml.end() && !StopRequest; ++rm)
- {
- // This is used by time management
- FirstRootMove = (rm == rml.begin());
+ // Step 10. Loop through moves
+ // Loop through all legal moves until no moves remain or a beta cutoff occurs
+ while ( alpha < beta
+ && rm != rml.end()
+ && !StopRequest)
+ {
+ move = ss->currentMove = rm->pv[0];
+ movesSearched[moveCount++] = move;
+ isPvMove = (moveCount <= MultiPV);
- // Save the current node count before the move is searched
- nodes = pos.nodes_searched();
+ // This is used by time management
+ FirstRootMove = (rm == rml.begin());
- // If it's time to send nodes info, do it here where we have the
- // correct accumulated node counts searched by each thread.
- if (SendSearchedNodes)
- {
- SendSearchedNodes = false;
- cout << "info nodes " << nodes
- << " nps " << nps(pos)
- << " time " << current_search_time() << endl;
- }
+ // Save the current node count before the move is searched
+ nodes = pos.nodes_searched();
- // Pick the next root move, and print the move and the move number to
- // the standard output.
- move = ss->currentMove = rm->pv[0];
- movesSearched[moveCount++] = move;
- isPvMove = (moveCount <= MultiPV);
+ // If it's time to send nodes info, do it here where we have the
+ // correct accumulated node counts searched by each thread.
+ if (SendSearchedNodes)
+ {
+ SendSearchedNodes = false;
+ cout << "info nodes " << nodes
+ << " nps " << nps(pos)
+ << " time " << current_search_time() << endl;
+ }
- if (current_search_time() >= 1000)
- cout << "info currmove " << move
- << " currmovenumber " << moveCount << endl;
+ if (current_search_time() >= 1000)
+ cout << "info currmove " << move
+ << " currmovenumber " << moveCount << endl;
- moveIsCheck = pos.move_is_check(move);
- captureOrPromotion = pos.move_is_capture_or_promotion(move);
+ moveIsCheck = pos.move_is_check(move);
+ captureOrPromotion = pos.move_is_capture_or_promotion(move);
- // Step 11. Decide the new search depth
-
ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
- newDepth = depth + ext;
+ // Step 11. Decide the new search depth
+ ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
+ newDepth = depth + ext;
- // Step 12. Futility pruning (omitted at root)
+ // Step 12. Futility pruning (omitted at root)
+ // Step 13. Make the move
+ pos.do_move(move, st, ci, moveIsCheck);
- // Step extra. Fail high loop
- // If move fails high, we research with bigger window until we are not failing
- // high anymore.
- value = -VALUE_INFINITE;
+ // Step extra. pv search
+ // We do pv search for PV moves
+ if (isPvMove)
+ {
+ // Aspiration window is disabled in multi-pv case
+ if (MultiPV > 1)
+ alpha = -VALUE_INFINITE;
- while (1)
+ // Full depth PV search, done on first move or after a fail high
+ value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
+ }
+ else
+ {
+ // Step 14. Reduced search
+ // if the move fails high will be re-searched at full depth
+ bool doFullDepthSearch = true;
+
+ if ( depth >= 3 * ONE_PLY
+ && !captureOrPromotion
+ && !dangerous
+ && !move_is_castle(move)
+ && ss->killers[0] != move
+ && ss->killers[1] != move)
{
- // Step 13. Make the move
- pos.do_move(move, st, ci, moveIsCheck);
-
- // Step extra. pv search
- // We do pv search for PV moves and when failing high
- if (isPvMove || value > alpha)
- {
- // Aspiration window is disabled in multi-pv case
- if (MultiPV > 1)
- alpha = -VALUE_INFINITE;
+ ss->reduction = reduction<PV>(depth, moveCount - MultiPV + 1);
- // Full depth PV search, done on first move or after a fail high
- value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
- }
- else
+ if (ss->reduction)
{
- // Step 14. Reduced search
- // if the move fails high will be re-searched at full depth
- bool doFullDepthSearch = true;
-
- if ( depth >= 3 * ONE_PLY
- && !dangerous
- && !captureOrPromotion
- && !move_is_castle(move))
- {
- ss->reduction = reduction<PV>(depth, moveCount - MultiPV + 1);
- if (ss->reduction)
- {
- assert(newDepth-ss->reduction >= ONE_PLY);
-
- // Reduced depth non-pv search using alpha as upperbound
- value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
- doFullDepthSearch = (value > alpha);
- }
- ss->reduction = DEPTH_ZERO; // Restore original reduction
- }
-
- // Step 15. Full depth search
- if (doFullDepthSearch)
- {
- // Full depth non-pv search using alpha as upperbound
- value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
-
- // 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+1, -beta, -alpha, newDepth, 1);
- }
- }
-
- // Step 16. Undo move
- pos.undo_move(move);
-
- // Can we exit fail high loop ?
- if (StopRequest || value < beta)
- break;
-
- // We are failing high and going to do a research. It's important to update
- // the score before research in case we run out of time while researching.
- ss->bestMove = move;
- rm->pv_score = value;
- rm->extract_pv_from_tt(pos);
+ Depth d = newDepth - ss->reduction;
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, 1);
- // Update killers and history only for non capture moves that fails high
- if (!pos.move_is_capture_or_promotion(move))
- {
- update_history(pos, move, depth, movesSearched, moveCount);
- update_killers(move, ss->killers);
+ doFullDepthSearch = (value > alpha);
}
+ ss->reduction = DEPTH_ZERO; // Restore original reduction
+ }
- // Inform GUI that PV has changed
- cout << rm->pv_info_to_uci(pos, alpha, beta) << endl;
-
- // Prepare for a research after a fail high, each time with a wider window
- beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
- researchCountFH++;
+ // Step 15. Full depth search
+ if (doFullDepthSearch)
+ {
+ // Full depth non-pv search using alpha as upperbound
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
- } // End of fail high loop
+ // 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+1, -beta, -alpha, newDepth, 1);
+ }
+ }
- // Finished searching the move. If AbortSearch is true, the search
- // was aborted because the user interrupted the search or because we
- // ran out of time. In this case, the return value of the search cannot
- // be trusted, and we break out of the loop without updating the best
- // move and/or PV.
- if (StopRequest)
- break;
+ // Step 16. Undo move
+ pos.undo_move(move);
- // Remember searched nodes counts for this move
- rm->nodes += pos.nodes_searched() - nodes;
+ assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
- assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
- assert(value < beta);
+ // Finished searching the move. If StopRequest is true, the search
+ // was aborted because the user interrupted the search or because we
+ // ran out of time. In this case, the return value of the search cannot
+ // be trusted, and we break out of the loop without updating the best
+ // move and/or PV.
+ if (StopRequest)
+ break;
- // Step 17. Check for new best move
- if (!isPvMove && value <= alpha)
- rm->pv_score = -VALUE_INFINITE;
- else
- {
- // PV move or new best move!
+ // Remember searched nodes counts for this move
+ rm->nodes += pos.nodes_searched() - nodes;
- // Update PV
- ss->bestMove = move;
- rm->pv_score = value;
- rm->extract_pv_from_tt(pos);
+ // Step 17. Check for new best move
+ if (!isPvMove && value <= alpha)
+ rm->pv_score = -VALUE_INFINITE;
+ else
+ {
+ // PV move or new best move!
- // We record how often the best move has been changed in each
- // iteration. This information is used for time managment: When
- // the best move changes frequently, we allocate some more time.
- if (!isPvMove && MultiPV == 1)
- BestMoveChangesByIteration[Iteration]++;
+ // Update PV
+ ss->bestMove = move;
+ rm->pv_score = value;
+ rm->extract_pv_from_tt(pos);
- // Inform GUI that PV has changed, in case of multi-pv UCI protocol
- // requires we send all the PV lines properly sorted.
- rml.sort_multipv(moveCount);
+ // We record how often the best move has been changed in each
+ // iteration. This information is used for time managment: When
+ // the best move changes frequently, we allocate some more time.
+ if (!isPvMove && MultiPV == 1)
+ BestMoveChangesByIteration[Iteration]++;
- for (int j = 0; j < Min(MultiPV, (int)rml.size()); j++)
- cout << rml[j].pv_info_to_uci(pos, alpha, beta, j) << endl;
+ // Inform GUI that PV has changed, in case of multi-pv UCI protocol
+ // requires we send all the PV lines properly sorted.
+ rml.sort_multipv(moveCount);
- // Update alpha. In multi-pv we don't use aspiration window
- if (MultiPV == 1)
- {
- // Raise alpha to setup proper non-pv search upper bound
- if (value > alpha)
- alpha = value;
- }
- else // Set alpha equal to minimum score among the PV lines
- alpha = rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
+ for (int j = 0; j < Min(MultiPV, (int)rml.size()); j++)
+ cout << rml[j].pv_info_to_uci(pos, alpha, beta, j) << endl;
- } // PV move or new best move
+ // Update alpha. In multi-pv we don't use aspiration window
+ if (MultiPV == 1)
+ {
+ // Raise alpha to setup proper non-pv search upper bound
+ if (value > alpha)
+ alpha = value;
+ }
+ else // Set alpha equal to minimum score among the PV lines
+ alpha = rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
- assert(alpha >= oldAlpha);
+ } // PV move or new best move
- AspirationFailLow = (alpha == oldAlpha);
+ ++rm;
- if (AspirationFailLow && StopOnPonderhit)
- StopOnPonderhit = false;
+ } // Root moves loop
- } // Root moves loop
- // Can we exit fail low loop ?
- if (StopRequest || !AspirationFailLow)
- break;
+ // Step 20. Update tables
+ // If the search is not aborted, update the transposition table,
+ // history counters, and killer moves.
+ if (!StopRequest)
+ {
+ move = alpha <= oldAlpha ? MOVE_NONE : ss->bestMove;
+ vt = alpha <= oldAlpha ? VALUE_TYPE_UPPER
+ : alpha >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
- // Prepare for a research after a fail low, each time with a wider window
- oldAlpha = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
- researchCountFL++;
+ TT.store(posKey, value_to_tt(alpha, 0), vt, depth, move, ss->eval, ss->evalMargin);
- } // Fail low loop
+ // Update killers and history only for non capture moves that fails high
+ if ( alpha >= beta
+ && !pos.move_is_capture_or_promotion(move))
+ {
+ update_history(pos, move, depth, movesSearched, moveCount);
+ update_killers(move, ss->killers);
+ }
+ }
// Sort the moves before to return
rml.sort();
for (int i = 0; i < Min(MultiPV, (int)rml.size()); i++)
rml[i].insert_pv_in_tt(pos);
+ assert(alpha > -VALUE_INFINITE && alpha < VALUE_INFINITE);
+
return alpha;
}
projects / stockfish / commitdiff