Clean up / refactor Swift 4 function reading binary file

I have a function written in Swift 4 for OSX that reads in some data from a binary file. It does work and reads in the data! It is not too long. This function was converted over from some old c / c++ code. I'm looking for the attached file to be cleaned up, refactored, etc. so it is professional modern Swift 4 The function does work so hopefully, this is just some cleanup and possible simplification.