[R] NA in C/C++

[cstrato@EUnet.at]

Dear experts

Thank you all for this interesting information. I have learned a lot and
hopefully can use it in C++.

A personal note: I liked especially the document:
http://www.cs.berkeley.edu/%7Ewkahan/ieee754status/754story.html
since it mentions SANE as one of the few environments supporting
the IEEE standard. The phonebook edition of "Inside Macintosh" was
my only source until now. Luckily I got from you now a lot of  information

on this issue.

Best regards
Christian Stratowa, Vienna


John Chambers wrote:

> A few general comments.
>
> The IEEE 754 floating-point standard is one of the more striking
> successes in getting computer hardware to be more useful for those who
> program.  There are, of course, glitches, both in non-compliance and
> in holes in the standard, but if we can work within the standard as
> far as possible, while complaining about the glitches, we'll be better
> off, and C/C++ software produced will be more likely to port
> gracefully to other environments.
>
> >From that view, using C routines that are part of the standard (while
> perhaps overriding them on machines that don't conform) has advantages
> inside your own C/C++ code, IF that code is not intrinsically R/S
> dependent.  So isnan() would be better in that case, R_IsNaNorNA()
> better for code that is R-dependent.
>
> Where it makes sense, there is also an advantage to doing the relevant
> testing in the S language and passing the result to the C code, either
> directly, say as a logical vector argument, or indirectly by doing the
> selection outside and leaving the C code to just grind away on the
> selected subset of the data.  Within the S language, is.na() is the
> best test, because it deals with either floating point or integer
> data.
>
> Anyone interested in the relevance of the standard, or just a read
> through some insightful if eccentric ranting about numerical
> computation generally should eventually encounter W. Kahan, "the
> father of IEEE 754".
>
> There is a directory on the web at the Berkeley CS department:
>   www.cs.berkeley.edu/%7Ewkahan/ieee754status/
> All the papers in that directory are worth looking at, allowing
> for Kahan's legendary rages at all those who failed his standards.
> Having had the privilege (well, looking back on it anyway) of taking a
> course from Kahan, I can verify that his personality comes across well
> in the papers.
>
> --
> John M. Chambers                  jmc at bell-labs.com
> Bell Labs, Lucent Technologies    office: (908)582-2681
> 700 Mountain Avenue, Room 2C-282  fax:    (908)582-3340
> Murray Hill, NJ  07974            web: http://www.cs.bell-labs.com/~jmc

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