Working with fixed-point calculations in C

Hi!

I need to make some fixed-point calculations inside the C code that I'm
developing as an extension to PostgreSQL. I was reading a bit, and if I
understood the datatype NUMBER correctly, it seems to be just what I'm
looking for, a fixed-point datatype. (I couldn't actually find any
thing in the documentation that specifically mentions that it is a
fixed point datatype. But it seems to work the same. So I might be
wrong here and if so please tell me)

Anyway, I thought that it would be good to store the decimal numbers in
the database as the datatype NUMBER, and then just use the C version of
it when I need to work with it in the code. But when I look at the
documentation for writing C functions, I can't find the C version of
it? Is that something that just hasn't made it to the documentation, or
is there a reason for it not being listed there?

Was hoping that I wouldn't need to reinvent the wheel here or include
another library to handle this, as it increases the risk of creating
bugs. But if I have to I'll do it.

Link to the documentation:
https://www.postgresql.org/docs/current/xfunc-c.html#XFUNC-C-BASETYPE
You have to scroll down a little and you will find a table matching
PostgreSQL:s datatypes with the datatypes in C

Best regards
Oskar