https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88342
kargl at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P4
--- Comment #3 from kargl at gcc dot gnu.org ---
(In reply to kargl from comment #2)
> (In reply to kargl from comment #1)
> > (In reply to Matt Thompson from comment #0)
> > > All,
> > >
> > > A colleague of mine encountered an issue with 8.2.0 (but it's also in
> > > 7.3.0
> > > at least). We believe it might be a bug since our reading of the Standard
> > > seems to make it legal.
> > >
> > > Namely if this program:
> > >
> > > PROGRAM test
> > > USE, INTRINSIC :: ieee_arithmetic
> > > IMPLICIT NONE
> > > REAL :: inf
> > > inf = IEEE_VALUE(inf, IEEE_POSITIVE_INF)
> > > END PROGRAM test
> > >
> > > is compiled with -ffpe-trap=overflow the code FPEs:
> >
> > gfortran's IEEE modules and the -ffpe-trap option are independent
> > of each other. As the manual states, -ffpe-trap is a *debugging*
> > option, and will enabling traps on floating point exceptions. You
> > specifically requested an overflow trap. What do you expect to
> > happen?
> >
> > The likely correct solution is to manipulate the halting
> > behavior with a combination of IEEE_GET_HALTING_MODE and
> > IEEE_SET_HALTING_MODE. In fact, F2018, 17.11.6 contains
> > this exact example.
> >
> > Example. To store the halting mode for IEEE_OVERFLOW, do a
> > calculation without halting, and restore the halting mode later:
> >
> > USE, INTRINSIC :: IEEE_ARITHMETIC
> > LOGICAL HALTING
> > ...
> > CALL IEEE_GET_HALTING_MODE (IEEE_OVERFLOW, HALTING) ! Store halting mode
> > CALL IEEE_SET_HALTING_MODE (IEEE_OVERFLOW, .FALSE.) ! No halting
> > ... ! calculation without halting
> > CALL IEEE_SET_HALTING_MODE (IEEE_OVERFLOW, HALTING) ! Restore halting
> > mode
> >
> > whether or not these functions works is something that I
> > haven't investigated.
>
> Just tested.
>
> program test
> use, intrinsic :: ieee_arithmetic
> implicit none
> real :: inf
> logical h
> call ieee_get_halting_mode(ieee_overflow, h) ! store halting mode
> call ieee_set_halting_mode(ieee_overflow, .false.) ! no halting
> inf = ieee_value(inf, ieee_positive_inf)
> print *, inf
> call ieee_set_halting_mode(ieee_overflow, h) ! restore halting mode
> end program test
>
> % gfcx -o z a.f90 && ./z
> Infinity
> % gfcx -o z -ffpe-trap=overflow a.f90 && ./z
> Infinity
>
> This seems to give the desired behavior.
Something like the following is probably want people want.
I don't know how robust this is.
Index: libgfortran/ieee/ieee_arithmetic.F90
===================================================================
--- libgfortran/ieee/ieee_arithmetic.F90 (revision 266766)
+++ libgfortran/ieee/ieee_arithmetic.F90 (working copy)
@@ -861,6 +861,7 @@ contains
real(kind=4), intent(in) :: X
type(IEEE_CLASS_TYPE), intent(in) :: CLASS
+ logical flag
select case (CLASS%hidden)
case (1) ! IEEE_SIGNALING_NAN
@@ -888,8 +889,15 @@ contains
case (9) ! IEEE_POSITIVE_NORMAL
res = 42
case (10) ! IEEE_POSITIVE_INF
+ if (ieee_support_halting(ieee_overflow)) then
+ call ieee_get_halting_mode(ieee_overflow, flag)
+ call ieee_set_halting_mode(ieee_overflow, .false.)
+ end if
res = huge(res)
res = res * res
+ if (ieee_support_halting(ieee_overflow)) then
+ call ieee_set_halting_mode(ieee_overflow, flag)
+ end if
case default ! IEEE_OTHER_VALUE, should not happen
res = 0
end select
