converting a FASTA file to either a .map , .freq8 or .freq16 files

I am trying to Genmap to compute mapability within a C++ program. Though the code only takes files that are .map, .freq8 or .freq16, I only have a FASTA file. I have researching how to make this conversation, but my I haven't found anything related. I thought to explore what's unique about those file types but I haven't been able to find anything. I hope someone will be able to shed some light on this. Thank you