R devel - Aug 2009 - readBin() arg check has unnecessary overhead (patch included)

Dear all,

The version of readBin() in R-devel includes a use of match(), through
`%in%`, which can affect its performance significantly. By using
primitives instead of the rather expensive call to match(), I reduce
the time spent inside readBin() by more than 30% in some of my code
(part of the tractor.base package). A simple patch that does this is
given below. This passes "make check-devel" fine, and I don't see
that
it could produce unexpected behaviour -- though I may, of course, be
wrong.

Regards,
Jon

--- R-devel/src/library/base/R/connections.R	2009-08-07 01:52:16.000000000 +0100
+++ R-devel-mod/src/library/base/R/connections.R	2009-08-11
16:22:30.000000000 +0100
@@ -193,6 +193,6 @@
     swap <- endian != .Platform$endian
     if(!is.character(what) || length(what) != 1L
-    	|| !(what %in% c("numeric", "double",
"integer", "int", "logical",
-                         "complex", "character",
"raw")))
+    	|| !any(what == c("numeric", "double",
"integer", "int", "logical",
+                          "complex", "character",
"raw")))
         what <- typeof(what)
     .Internal(readBin(con, what, n, size, signed, swap))


--
Jonathan D. Clayden, Ph.D.
Research Fellow
Radiology and Physics Unit
UCL Institute of Child Health
30 Guilford Street
LONDON  WC1N 1EH
United Kingdom

t | +44 (0)20 7905 2708
f | +44 (0)20 7905 2358
w | www.homepages.ucl.ac.uk/~sejjjd2/
w | www.diffusion-mri.org.uk/people/1

>>>>> Jon Clayden <jon.clayden at gmail.com>
>>>>>     on Tue, 11 Aug 2009 17:51:46 +0100 writes:
    > Dear all,
    > The version of readBin() in R-devel includes a use of match(), through
    > `%in%`, which can affect its performance significantly. By using
    > primitives instead of the rather expensive call to match(), I reduce
    > the time spent inside readBin() by more than 30% in some of my code
    > (part of the tractor.base package). A simple patch that does this is
    > given below. This passes "make check-devel" fine, and I
don't see that
    > it could produce unexpected behaviour -- though I may, of course, be
    > wrong.

actually,  %in%  is liked by programmeRs for its inherent
robustness combined with "expressiveness" (<-> readability)
inspite of its potential efficiency loss wrt to  '=='
... 
and indeed, your patch fails in one case where the original code works:

  readBin(., NA_character_, ...)

However that case can also be checked explicitly,
and I will implement the corresponding patch.

Martin Maechler, ETH Zurich


    > Regards,
    > Jon

    > --- R-devel/src/library/base/R/connections.R	2009-08-07
01:52:16.000000000 +0100
    > +++ R-devel-mod/src/library/base/R/connections.R	2009-08-11
    > 16:22:30.000000000 +0100
    > @@ -193,6 +193,6 @@
    > swap <- endian != .Platform$endian
    > if(!is.character(what) || length(what) != 1L
    > -    	|| !(what %in% c("numeric", "double",
"integer", "int", "logical",
    > -                         "complex", "character",
"raw")))
    > +    	|| !any(what == c("numeric", "double",
"integer", "int", "logical",
    > +                          "complex", "character",
"raw")))
    > what <- typeof(what)
    > .Internal(readBin(con, what, n, size, signed, swap))


    > --
    > Jonathan D. Clayden, Ph.D.
    > Research Fellow
    > Radiology and Physics Unit
    > UCL Institute of Child Health
    > 30 Guilford Street
    > LONDON  WC1N 1EH
    > United Kingdom

    > t | +44 (0)20 7905 2708
    > f | +44 (0)20 7905 2358
    > w | www.homepages.ucl.ac.uk/~sejjjd2/
    > w | www.diffusion-mri.org.uk/people/1

    > ______________________________________________
    > R-devel at r-project.org mailing list
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