Static foremost means that the value is preserved from the last function invocation. This is very different behaviour, than an automatically allocated variable. So calling a function with a static variable isn't idempotent, even when all global variables are the same.

> If I ever need multiple calls to it in same thread:

What is this code supposed to do???? It hands out a different pointer, the first 8 times, than starts from the beginning again? I don't see what this is useful for!