Sounds intriguing. If I may ask, why make your own utility? As for your specific question ... dunno. When reverse engineering just get yourself some more data to stare at. As in, get a few more bit+svf files of various content and see if you detect a pattern.
Either that, or just grab the source from other utils (for digilent boards) by other people. Which obviously is option numero uno before starting to stare at bitfiles. So I'll just assume you already did that.