Availability of Software Defined Radios (SDRs) capable of operating with the GNSS frequency bands has spurred interest in performing advanced GNSS signal-based research using software radio processing techniques. It is most convenient to perform this research in high-level software algorithm development environments. However, these tools are generally lacking in performance when processing the large data files typically seen in this type of research. This paper describes the development of a low-level software library for accelerating the unpacking and decoding of SDR samples. The performance figures generated for this paper can be used to guide future decisions on the architecture of Satnav SDR receivers.