[Rcpp-devel] Rcpp Timer

[Dirk Eddelbuettel]

On 30 December 2016 at 06:37, Dirk Eddelbuettel wrote:
| 
| On 29 December 2016 at 11:25, Jonathan Christensen wrote:
| | Hi Kaspar and Dirk,
| | 
| | It is indeed cumulative. Previously (presumably when that gallery page was
| | written) it was not cumulative, but Romain Francois changed the behavior of the
| | step() function several years ago, in this commit: https://github.com/RcppCore/
| | Rcpp/commit/e295b2b178de55291e63705966368404bb0ce5e1.
| 
| Nice catch.
|  
| | There is no indication or reasoning about changing the behavior, so it may be
| | that making it cumulative was unintentional.
| 
| Let's presume it was intentional to the author of the change -- but as you
| rightly point out, it did of course change and reverse previous behaviour.
| 
| We could easily add a toggle to the constructor to get an either/or behaviour.

Even easier:
    - Add a step() call immediately after creating timer()
    - This also records the start
    - Results are still cumulative
    - Running diff() over it shows changes:

Demo using minimally modified Rcpp Gallery piece (just added step("start"); )

    R> sourceCpp("/tmp/timer.cpp")

    R> tt <- useTimer()

    R> tt         # cumulative
          start     get/put g/p+rnorm()  empty loop 
       0.000114 1629.043000 3996.890739 3996.893329 

    R> diff(tt)   # incremental
        get/put g/p+rnorm()  empty loop 
     1629.04289  2367.84774     0.00259 
    R>

I will alter the gallery story accordingly. We can always add a 'zero' step
to the constructor to get these two behaviours cheaply.

Dirk

-- 
http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org