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speed up R_IsNA, R_IsNaN for vector input

3 messages · Jan Gorecki, Tomas Kalibera

Original
Jan Gorecki
# 
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.
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
Tomas Kalibera
#
On 9/29/19 1:09 PM, Jan Gorecki wrote:
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
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 at gmail.com> wrote: