gnulib/doc/posix-functions/isnan.texi

@node isnan
@section @code{isnan}
@findex isnan

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9699919799/functions/isnan.html}

Gnulib module: isnan

Portability problems fixed by Gnulib:
@itemize
@item
This macro is missing on some platforms:
MSVC 9.
@item
@code{isnan} was introduced with C99 and is thus commonly not present
on pre-C99 systems.
@item
@code{isnan} is not a macro on some platforms:
IRIX 6.5, Solaris 11.4.
@item
This macro does not work on some platforms:
MSVC 14.
@item
On IRIX 6.5 with @code{cc}, @code{isnan} does not recognize some NaNs.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
This macro returns an unspecified result when given noncanonical values
such as unnormalized numbers, pseudo-denormals, pseudo-NaNs,
pseudo-Infinities, and pseudo-zeroes.
@end itemize