It's hard to give an answer without knowing more about your input data and what you intend to do with the output. On general principle, "math plus syntax" seem

It's hard to give an answer without knowing more about your input data and what you intend to do with the output. On general principle, "math plus syntax" seems like a highly error-prone approach, especially if you need to process anything that's not a standard English name, or if you have lots of users named Pat. E.g. diminutives of Russian masculine names often end in "a". I'm sure there's names which are masculine in some countries and feminine in others. Etc.