>>> d) Extend Fceiling, Ffloor, Fround and Ftruncate to support bignums by
>>>    updating rounding_driver.
> 
> I worked on these and installed patches to master that should do (a), (b), and 
> (c). For (d) I wrote the attached patch, and plan to test it a bit more before 
> installing, as it's the hairiest.

It took me longer to write the test cases than the code, but the tests did find 
bugs so it was worth it. I installed the attached.

While we're on the subject I moved the definition of 'bignump' and 'fixnump' 
from C to Lisp, since they are easily implementable in Lisp and don't seem to be 
performance relevant. Hope you don't mind too much that I would rather minimize 
the low-level details that the C code exports.

Both patches attached.