[R] NA in C/C++

[cstrato@EUnet.at]

Dear Dr. Dalgaard

Thank you, too, for your fast response.

I have checked the web-site you mentioned. There is a function:
    int isnan(floating-type x)
for floating point numbers, which I could use.
For integers I will check Arith.h and Arithmetic.c

Best regards
Christian Stratowa


Peter Dalgaard BSA wrote:

> Prof Brian D Ripley <ripley at stats.ox.ac.uk> writes:
>
> > > Although I know that IEEE floating point arithmetics supports NaN and
> > > Inf, I cannot find
> > > any information about this (e.g. in any of my many C++ books)
> ...
> > It's in Writing R Extensions (sections 3.7.3 and 4.4 in the copy I have to
> > hand, but it's in the concept index). You cannot assume in R that NA is
> > represented by an NaN, although on most machines it is.  Conversely, most
> > NaNs are not NA.
>
> Perhaps it is necessary to be a little more specific here: The IEEE
> NaN is not a single value, but a set of values characterized by having
> an all-ones exponent and a non-zero significand (the cases with a zero
> significand are +Inf and -Inf). Have a look at
>
> http://www.linuxsupportline.com/~billm/index.html
>
> for the details.
>
> The double NA in R on IEEE-supporting systems is the NaN with
> significand 1954 (no, I don't know who was born that year...).
>
> However integers have no definition of NaN, so NaInt is INT_MIN and
> for systems that don't support IEEE, we have some special hacks too.
> Have a look in src/include/R_ext/Arith.h and src/main/arithmetic.c.
>
> --
>    O__  ---- Peter Dalgaard             Blegdamsvej 3
>   c/ /'_ --- Dept. of Biostatistics     2200 Cph. N
>  (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
> ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907

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