Why isn't there more if(__ctfe) in std.math ?

[Juraj Mojzis]

Hi,
browsing trough phobos bugzilla I found a couple of open issues 
regarding CTFE and basic math functions ( Issue 4177, 5227).
It looks to me that at least floor/ceil could by fixed by a 
simple:
if (__ctfe) return simple_floor_impl(x);

But that looks too easy and would surely be implemented already. 
So I would like to ask what the real problems are.

Thanks,
Juraj