+ // extension() decides whether a move should be searched with normal depth,
+ // or with extended depth. Certain classes of moves (checking moves, in
+ // particular) are searched with bigger depth than ordinary moves and in
+ // any case are marked as 'dangerous'. Note that also if a move is not
+ // extended, as example because the corresponding UCI option is set to zero,
+ // the move is marked as 'dangerous' so, at least, we avoid to prune it.
+ template <bool PvNode>
+ FORCE_INLINE Depth extension(const Position& pos, Move m, bool captureOrPromotion,
+ bool moveIsCheck, bool* dangerous) {
+ assert(m != MOVE_NONE);
+
+ Depth result = DEPTH_ZERO;
+ *dangerous = moveIsCheck;
+
+ if (moveIsCheck && pos.see_sign(m) >= 0)
+ result += CheckExtension[PvNode];
+
+ if (pos.type_of_piece_on(move_from(m)) == PAWN)
+ {
+ Color c = pos.side_to_move();
+ if (relative_rank(c, move_to(m)) == RANK_7)
+ {
+ result += PawnPushTo7thExtension[PvNode];
+ *dangerous = true;
+ }
+ if (pos.pawn_is_passed(c, move_to(m)))
+ {
+ result += PassedPawnExtension[PvNode];
+ *dangerous = true;
+ }
+ }
+
+ if ( captureOrPromotion
+ && pos.type_of_piece_on(move_to(m)) != PAWN
+ && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
+ - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
+ && !move_is_special(m))
+ {
+ result += PawnEndgameExtension[PvNode];
+ *dangerous = true;
+ }
+
+ return Min(result, ONE_PLY);
+ }
+