[R] build on Irix failed reg-tests

[Liaw, Andy]

> From: Thomas Lumley [mailto:tlumley at u.washington.edu] 
> 
> On Wed, 17 Mar 2004, Liaw, Andy wrote:
> 
> > Sorry for being dense:  So What is the likely source of the 
> problem, then?
> > Is it the compiler, the OS, R itself, or some combination 
> of these?  Any
> > suggestion on how to resolve this?
> 
> In a sense it is R itself, making assumptions that hold on 
> many, but not
> all systems.  There are many different NaN values, all of which are
> guaranteed to give NaN results in arithmetic observations.  On many
> systems, if one operand is NaN and the other is a valid 
> number the result
> is not only NaN, but *the same NaN* as the operand.
> 
> In R we call one particular one of these NaN values "NA".  
> The standards
> guarantee that any operation on NA gives some NaN, but we 
> have assumed it
> gives the right NaN, the NA one.  On Irix this seems not to 
> be the case.
> 
> The solution is to change arithmetic.c not to make this 
> assumption, which
> will be slower. It would be nice to detect at build time whether the
> assumption holds, so as to keep the current behaviour on 
> other systems.
> 
> It should be rare for the error to make any difference, since 
> is.na() is
> still true for NaN.  AFAICT the only problem would be that 
> is.nan(0+NA)
> can be TRUE when it should be FALSE.
> 
> 	-thomas

Thanks very much for the clarification, Thomas.  So would it be fairly safe
for us to edit that part of reg-tests-1.R so it passes this step, so make
check can go on from there?

Best,
Andy


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