# [Rd] Incorrect comment about ISNA(x) in Arith.h (PR#13826)

Tue Jul 14 06:15:17 CEST 2009

```R-2.9.0/include/R_ext/Arith.h has:

int R_IsNA(double);		/* True for R's NA only */
int R_IsNaN(double);		/* True for special NaN, *not* for NA */
int R_finite(double);		/* True if none of NA, NaN, +/-Inf */

#define ISNA(x)	       R_IsNA(x)
/* True for *both* NA and NaN.

The first and last lines are contradictory - if R_IsNA is true only
for NA, not NaN, then ISNA should be the same.

Venables & Ripley S Programming p 137 indicates that
"ISNA does not detect NaN s"

Here's a little .c file and R transcript that shows that V&R are correct,
ISNA(x) is not True for NaN
So the last comment should read
/* True for NA, not NaN

#include "R.h"
void mysum(double *x)
{
double sum = 0.0;
sum = x + x + x;
if (ISNA(sum))
PROBLEM "sum is NA" WARNING(NULL_ENTRY);
if (ISNAN(sum))
PROBLEM "sum is NAN" WARNING(NULL_ENTRY);
if (!(R_FINITE(sum)))
PROBLEM "sum is not finite" WARNING(NULL_ENTRY);
return;
}

> .C("mysum", c(NaN, 0.0, 0.0), NAOK = TRUE, DUP = FALSE)
[]
 NaN   0   0

Warning messages:
1: sum is NAN
2: sum is not finite

--please do not edit the information below--

Version:
platform = x86_64-unknown-linux-gnu
arch = x86_64
os = linux-gnu
system = x86_64, linux-gnu
status =
major = 2
minor = 9.0
year = 2009
month = 04
day = 17
svn rev = 48333
language = R
version.string = R version 2.9.0 (2009-04-17)

Locale: