TITLE: What functions can computers evaluate directly?
QUESTION [5 upvotes]: From Wikipedia 

computers can directly evaluate polynomials

What precisely does direct evaluation mean? As far as I know, function evaluation can be difficult in complexity theory.
I was wondering if polynomials are the only functions that computers can evaluate directly? Thanks and regards!

REPLY [4 votes]: I can think of many functions that are not polynomials which a computer should be able to evaluate directly by any obvious definition of "evaluate directly", such as:

$y=|x|$
$y=2^x$
$y$ is the smallest prime factor of the integer $x$

I am not sure that they have a precise definition of "evaluate directly", but as a first stab, I would suggest something along the lines of "can calculate (by sensible algorithm) the precise value of the function, given the precise value of the argument".

REPLY [3 votes]: I am guessing that they were referring to such things as Evaluation of Polynomials 
By Computer by Knuth.
If you look at what this means today, you would look to a vast array of functions that can be approximated using various means of computing. 
For example, look at the Mathematica list of functions to be inclusive of what is possible.
Regards