Dual Quadtree Representation for VLSI Designs

The Quad-CIF tree has been proposed as a data structure for hierarchical design of VLSI. Frequently encountered operations in VLSI design require a lot of serach effort on a Quad-CIF tree. Additionally, since the empty spaces are not explicitly stored in the tree, layout compaction is difficult to achieve. To support such operations efficiently, we propose a dual quadtree structure for VLSI design. At the first level we represent a cell in the layout as a "painted quadtree". The painted quadtree stores the entire region spanned by all the rectangles in the cell. Once the cell is designed it is stored in the form of boundary codes. At the second level of the dual structure, these boundary codes are stored in a Quad-CIF tree. Therefore, the dual structure affords us the convenience of using the painted quadtree for interactive design and the excellent features of the Quad-CIF tree for hierarchical design and compact storage representation.