What functions are you missing? What would be convenient, or possibly faster, with a built in function?
We’ve recently discussed a few that I’ll start with:

hypot(x,y)
sqrt(x*x + y*y)

hypot3(x, y, z)
sqrt(x*x + y*y + z*z)

trunc(n)
 removes fractional components for positive or negative numbers. e.g.trunc(5.5) == 5
,trunc(5.5) == 5
. (Note: I’d usewhole()
but JS and C usetrunc()
) 
frac(n)
 just the fractional component, liken % 1
. e.g.frac(5.5) == .5
frac(5.5) == .5
So thattrunc(n) + frac(n) == n
for positive and negative numbers.
I have a huge list in addition to this but I’m curious what you have in mind!