Meaning of Log f0 delta

Meaning of Log f0 delta

I am just walking through a really long section of code that I need to
rework for a company. I have to re-write it in a different language.
This code deals with calculating "log f0 delta". This has something to do
with audio and a pitch curve.
My question would be: Does anybody know from just hearing this topic what
is done there? The code is REALLY huge, and I would really like to
understand what exactely is calculated there before I re-write it. That
would make it easier for me.
Thank you very much for the help!