One thing that I often do when dealing with old code that's performing low-level operations and outputting some binary format is to md5 the output. After that,

One thing that I often do when dealing with old code that's performing low-level operations and outputting some binary format is to md5 the output. After that, I can change the code and I often do this when people ask for less memory usage, better over-all performance, etc. Once the code has been changed, I can prove that it uses less memory/CPU/whatever, and verify the md5sum of my output against the original output so I know the code still outputs as intended.