1. An apparatus for implementing an application specific processor, the apparatus comprising: an interface configured to receive a plurality of function units corresponding to components for implementing a signal processing core as an application specific processor and configured to receive interconnection information for connecting the plurality of function units, wherein a defined function unit from a library that approximates an undefined function unit is selected when the plurality of function units includes the undefined function unit; and a processor configured to generate a hardware description for instantiating the plurality of function units and connecting the plurality of function units.