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From: Luca Donatini <lucadonatini.k@gmail.com>
Date: Thu, 04 Oct 2018 20:26:00 -0000
Message-ID: <CAC5oXR28H5tLKDV_hxLo0zn-BnEMjt7kVF6ZSA6bajmcN6aVnA@mail.gmail.com>
Subject: Unexpected NaN value
To: fortran@gcc.gnu.org
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Dear all,

I noticed a strange behaviour of the gfortran compiler.

In the source file below, when the real variable b has an "integer-like"
value (e.g. "2", "2.", "2.0" ...) the code correctly writes out a numerical
result. But when a "real-like" value is assigned to b (e.g. "2.1",
"2.0000009", "2.83" ...) , the code writes a NaN value.
This does not occurr when the sample code is compiled with an Intel
compiler (I tested version 2018a).

I have the NaN value problem with both:

   - gfortran 8.2.1 20180831 (Arch Linux package)
   - gfortran 6.3.0 20170516 (Debian Stretch package).


Is this a bug? A known one?

Many thanks in advance for all the clarifications,


Luca Donatini

*** example source file ***

program test
    implicit none

    real :: a = -1.57079637
    real :: b = 2.1

    write(*,*) cos(a)
    write(*,*) cos(a) **(2*b)

end program