tte = TT.retrieve(posKey);
}
- // Initialize a MovePicker object for the current position, and prepare
- // to search all moves.
+ // 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
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 ( bestValue < beta
&& (move = mp.get_next_move()) != MOVE_NONE
&& !TM.thread_should_stop(threadID))
singleEvasion = (isCheck && mp.number_of_evasions() == 1);
captureOrPromotion = pos.move_is_capture_or_promotion(move);
- // Decide the new search depth
+ // 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
newDepth = depth - OnePly + ext;
- // Update current move
+ // Update current move (this must be done after singular extension search)
movesSearched[moveCount++] = ss[ply].currentMove = move;
- // Futility pruning
+ // Step 12. Futility pruning
if ( !isCheck
&& !dangerous
&& !captureOrPromotion
}
}
- // Make and search the move
+ // Step 13. Make the move
pos.do_move(move, st, ci, moveIsCheck);
- // 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;
}
}
- 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, -(beta-1), newDepth, ply+1, true, 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;
ss[ply].mateKiller = move;
}
- // Split?
+ // Step 18. Check for split
if ( TM.active_threads() > 1
&& bestValue < beta
&& depth >= MinimumSplitDepth
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 one move was excluded return fail low.
if (!moveCount)
return excludedMove ? beta - 1 : (pos.is_check() ? 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))