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* [Bug fortran/105924] New: false floating point exception when evaluating exponential function
@ 2022-06-11 7:20 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
0 siblings, 2 replies; 3+ messages in thread
From: yelinhui at hotmail dot com @ 2022-06-11 7:20 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105924
Bug ID: 105924
Summary: false floating point exception when evaluating
exponential function
Product: gcc
Version: 7.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: yelinhui at hotmail dot com
Target Milestone: ---
$ gfortran --version
GNU Fortran (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
$ cat test.f
program test
implicit none
real*8 :: e
e=-4.d2
print *, e, exp(-e*e)
end program test
$ gfortran -O0 -g -fbacktrace
-ffpe-trap=zero,overflow,underflow,invalid,denormal test.f
$./a.out
Program received signal SIGFPE: Floating-point exception - erroneous arithmetic
operation.
Backtrace for this error:
#0 0x1554d03f82ed in ???
#1 0x1554d03f7503 in ???
#2 0x1554cfc8cf0f in ???
#3 0x1554d00c5ea4 in ???
#4 0x1554d004e1fe in ???
#5 0x55b38e68a9d5 in test
at /tmp/test.f:7
#6 0x55b38e68aa54 in main
at /tmp/test.f:9
Floating point exception (core dumped)
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug fortran/105924] false floating point exception when evaluating exponential function
2022-06-11 7:20 [Bug fortran/105924] New: false floating point exception when evaluating exponential function yelinhui at hotmail dot com
@ 2022-06-11 16:22 ` kargl at gcc dot gnu.org
2022-08-03 8:41 ` yelinhui at hotmail dot com
1 sibling, 0 replies; 3+ messages in thread
From: kargl at gcc dot gnu.org @ 2022-06-11 16:22 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105924
kargl at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
CC| |kargl at gcc dot gnu.org
Resolution|--- |INVALID
--- Comment #1 from kargl at gcc dot gnu.org ---
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).
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug fortran/105924] false floating point exception when evaluating exponential function
2022-06-11 7:20 [Bug fortran/105924] New: false floating point exception when evaluating exponential function 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
1 sibling, 0 replies; 3+ messages in thread
From: yelinhui at hotmail dot com @ 2022-08-03 8:41 UTC (permalink / raw)
To: gcc-bugs
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).
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-08-03 8:41 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2022-06-11 7:20 [Bug fortran/105924] New: false floating point exception when evaluating exponential function 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
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