SPUC

From the site:

The objective of SPUC is to provide the Communications Systems Designer or DSP Algorithm designer with simple, efficient and reusable DSP building block objects. Thus allowing a transition from System design to implementation in either programmable DSP chips or hardwired DSP logic. While Matlab is perhaps the most useful available tool for this purpose, it can be quite slow for simulation and it favors a matrix/block based approach rather than the sample by sample simulations that are often most useful for communications systems design. Also Matlab is generally awkward or inefficient when dealing with several interactive feedback loops where C/C++ is perhaps the most useful environment. For bit-accurate simulations (for VLSI design) C/C++ generally outperforms and is easier to manipulate than Matlab or other GUI-based tools.