[Rd] speed up R_IsNA, R_IsNaN for vector input

[Jan Gorecki]

Dear Tomas,

I was thinking it is because of taking

    ieee_double y;

out from the loop, and re-using across iterations.
Now I checked that was not the reason of speed up.
So as you wrote, it was only due to inlining.
I am surprised the difference is so significant.
Thank you,
Jan

On Mon, Sep 30, 2019 at 10:31 AM Tomas Kalibera
<tomas.kalibera using gmail.com> wrote:
>
> 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.
>
> Best
> Tomas
>
> > 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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> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
>