[Rd] speed up R_IsNA, R_IsNaN for vector input

Tomas Kalibera tom@@@k@||ber@ @end|ng |rom gm@||@com
Mon Sep 30 10:31:13 CEST 2019

On 9/29/19 1:09 PM, Jan Gorecki wrote:
> Dear R developers,
> I spotted that R_isNA and R_IsNaN could be improved when applied on a
> vector where we could take out small part of their logic, run it once,
> and then reuse inside the loop.

Dear Jan,

Looking at your examples, I just see you have hand-inlined 
R_IsNA/R_IsNaN, or is there anything more? In principle we could put 
R_IsNA, R_IsNAN into Rinlinedfuns to allow inlining across compilation 
modules, but we can't put all functions there - so there would have to 
be a clear case for a performance problem in some specific function in a 
different module.

If you were curious there are optimized checks for non-finite values in 
vectors in array.c, which are used for matrix multiplication before 
calling to BLAS. These have to be fast and the optimization is biased 
towards the case that such values are rare and that it is ok to 
sometimes say "there may be non-finite values" even when in fact they 
are not.


> I setup tiny plain-C experiment. Taking R_IsNA, R_IsNaN from R's
> arithmetic.c, and building R_vIsNA and R_vIsNaN accordingly.
> For double input of size 1e9 (having some NA and NaN) I observed
> following timings:
> R_IsNA    6.729s
> R_vIsNA   4.386s
> R_IsNaN   6.874s
> R_vIsNaN  4.479s
> ISNAN     4.392s
> It looks like R_vIsN(A|aN) are close to ISNAN (which just wraps to
> math.h::isnan).
> Should I follow up with a patch?
> The experiment is a single nan.c file of 127 lines (includes R C
> funs). Large enough to not paste in the email. Here is the link:
> https://gist.github.com/jangorecki/c140fed3a3672620c1e2af90a768d785
> Run it as:
> gcc nan.c -lm
> ./a.out R_vIsNA 8
> ./a.out R_IsNA 8
> ./a.out R_vIsNaN 8
> ./a.out R_IsNaN 8
> ./a.out ISNAN 8
> Best regards,
> Jan Gorecki
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