Is there a way to know if a variable is NaN, +infinity, -infinity?

[zaikunzhang]

The intrinsic module ieee_arithmetic contains procedures to do these jobs.

However, note that they may not always work as expected when the compilers are invoked with some “special” options. For example, see the following discussions.

Is this expected? Fortran standard is not respected by `gfortran --fdefault-integer-8`, `ifort -i8`, or `nagfor -i8`

I would like to draw your attention to a discussion here: fortran - Bug? MATLAB MEX changes the kind of the default logical - Stack Overflow In brief, even though Fortran standard 2018 requires that ieee_is_nan should return a default logical, we will have kind(ieee_is_nan(1.0) /= kind(.false.) with gfortran --fdefault-integer-8, ifort -i8, or nagfor -i8. Assuming that the constant .false. is a default logical, we find that the compilers violate the Fortran standard. A minimal working example …

Checking Inf/NaN when compilers are invoked with aggressive optimization flags

I have posted on GitHub some functions for checking Inf/NaN, which aim to work even when compilers are invoked with aggressive optimization flags, such as gfortran -Ofast. There are many ways to implement functions like is_nan. However, not all of them work with aggressive optimization flags. For example, there are such discussions on StackOverflow. In addition, some compilers are buggy concerning the return type of ieee_is_nan when some special compilation options are imposed, as has been di…