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From: "yelinhui at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/105924] false floating point exception when evaluating exponential function
Date: Wed, 03 Aug 2022 08:41:39 +0000	[thread overview]
Message-ID: <bug-105924-4-5AZGezL0Dz@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-105924-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105924

Lin-Hui Ye <yelinhui at hotmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

--- Comment #2 from Lin-Hui Ye <yelinhui at hotmail dot com> ---
Sorry I didn't know this is an underflow. I was expecting exp(-160000) to give
a value close to zero. Thanks for the explanation.

Linhui

(In reply to kargl from comment #1)
> Why do you thing that you should not get an exception?
> 
> e = -400
> e*e = 160000
> -e*e = -160000
> exp(-e*e) = exp(-160000)  <-- This is going to underflow to zero.
> 
> You specifically asked gfortran to signal an exception if
> underflow occurs with the -ffpe-trap=underflow option.  The
> underflow threshold occurs at x = -745 for exp(x).

      parent reply	other threads:[~2022-08-03  8:41 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-11  7:20 [Bug fortran/105924] New: " yelinhui at hotmail dot com
2022-06-11 16:22 ` [Bug fortran/105924] " kargl at gcc dot gnu.org
2022-08-03  8:41 ` yelinhui at hotmail dot com [this message]

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