https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109186
--- Comment #2 from john.harper at vuw dot ac.nz ---
The results I expected were that
nearest(huge(sp1),-sp1) would be near huge(sp1)/(1+epsilon(sp1)),
nearest(huge(dp1),-dp1) would be near huge(dp1)/(1+epsilon(dp1)),
nearest(huge(ep1),-ep1) would be near huge(ep1)/(1+epsilon(ep1)),
nearest(huge(qp1),-qp1) would be near huge(qp1)/(1+epsilon(qp1)).
The results from gfortran were different from those by a factor near 2.
On compiling with ifort I got results close to what I had expected, which
is why I thought the bug was not in my program. The g95 compiler (now
about 10 years old) gave results identical to those of ifort except
for ep = selected_real_kind(18) which ifort treats as if it were
selected_real_kind(33) because ifort has only three real kinds.
By the way I thought I was using gfortran 12.0. Compiling with -v said
GNU Fortran (Ubuntu 12.1.0-2ubuntu1~22.04) version 12.1.0
(x86_64-linux-gnu)
I wish to apologise for that error in my bug report. I got the same output
on another machine with GNU Fortran (GCC) version 12.2.0
(x86_64-pc-linux-gnu)
The factor 2 discrepancies become clearer in this version of my program,
which has 4 more lines printing huge/nearest for the 4 real kinds.
program nearesttest3
implicit none
integer,parameter::sp = kind(1.0), dp=kind(1d0), ncases = 2, &
ep = selected_real_kind(18),qp = selected_real_kind(33)
character(*),parameter:: fmt(4) = &
"(A,ES"//["16.08E2","26.17E3","30.20E4","44.34E4"]//")"
character(24),dimension(2):: splist,dplist,eplist,qplist
integer n
real(sp),parameter::sp1 = 1.0_sp
real(sp):: spx(ncases) = [huge(sp1),nearest(huge(sp1),-sp1)]
data splist/'huge(sp1)','nearest(huge(sp1),-sp1)'/
real(dp),parameter::dp1 = 1.0_dp
real(dp):: dpx(ncases) = [huge(dp1),nearest(huge(dp1),-dp1)]
data dplist/'huge(dp1)','nearest(huge(dp1),-dp1)'/
real(ep),parameter::ep1 = 1.0_ep
real(ep):: epx(ncases) = [huge(ep1),nearest(huge(ep1),-ep1)]
data eplist/'huge(ep1)','nearest(huge(ep1),-ep1)'/
real(qp),parameter::qp1 = 1.0_qp
real(qp):: qpx(ncases) = [huge(qp1),nearest(huge(qp1),-qp1)]
data qplist/'huge(qp1)','nearest(huge(qp1),-qp1)'/
print fmt(1),(splist(n),spx(n),n=1,ncases)
print fmt(1),'huge/nearest = ',huge(sp1)/nearest(huge(sp1),-sp1)
print fmt(2),(dplist(n),dpx(n),n=1,ncases)
print fmt(2),'huge/nearest = ',huge(dp1)/nearest(huge(dp1),-dp1)
print fmt(3),(eplist(n),epx(n),n=1,ncases)
print fmt(3),'huge/nearest = ',huge(ep1)/nearest(huge(ep1),-ep1)
print fmt(4),(qplist(n),qpx(n),n=1,ncases)
print fmt(4),'huge/nearest = ',huge(qp1)/nearest(huge(qp1),-qp1)
end program nearesttest3
Its gfortran output:
huge(sp1) 3.40282347E+38
nearest(huge(sp1),-sp1) 1.70141173E+38
huge/nearest = 2.00000000E+00
huge(dp1) 1.79769313486231571E+308
nearest(huge(dp1),-dp1) 8.98846567431157854E+307
huge/nearest = 2.00000000000000000E+000
huge(ep1) 1.18973149535723176502E+4932
nearest(huge(ep1),-ep1) 5.94865747678615882511E+4931
huge/nearest = 2.00000000000000000000E+0000
huge(qp1) 1.1897314953572317650857593266280070E+4932
nearest(huge(qp1),-qp1) 5.9486574767861588254287966331400351E+4931
huge/nearest = 2.0000000000000000000000000000000000E+0000
Its g95 output:
uge(sp1) 3.40282347E+38
nearest(huge(sp1),-sp1) 3.40282326E+38
huge/nearest = 1.00000012E+00
huge(dp1) 1.79769313486231571E+308
nearest(huge(dp1),-dp1) 1.79769313486231551E+308
huge/nearest = 1.00000000000000022E+000
huge(ep1) 1.18973149535723176502E+4932
nearest(huge(ep1),-ep1) 1.18973149535723176496E+4932
huge/nearest = 1.00000000000000000011E+0000
huge(qp1) 1.1897314953572317650857593266280070E+4932
nearest(huge(qp1),-qp1) 1.1897314953572317650857593266280069E+4932
huge/nearest = 1.0000000000000000000000000000000002E+0000
On Sun, 19 Mar 2023, jvdelisle at gcc dot gnu.org wrote:
> Date: Sun, 19 Mar 2023 05:06:47 +0000
> From: jvdelisle at gcc dot gnu.org <gcc-bugzi...@gcc.gnu.org>
> To: John Harper <john.har...@vuw.ac.nz>
> Subject: [Bug fortran/109186] nearest(huge(x),
> -1.0_kind(x)) half of correct value
> Resent-Date: Sun, 19 Mar 2023 18:06:59 +1300 (NZDT)
> Resent-From: <john.har...@vuw.ac.nz>
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109186
>
> Jerry DeLisle <jvdelisle at gcc dot gnu.org> changed:
>
> What |Removed |Added
> ----------------------------------------------------------------------------
> CC| |jvdelisle at gcc dot gnu.org
>
> --- Comment #1 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
> Can you clarify what you expect the correct results should be that you expect?
>
> --
> You are receiving this mail because:
> You reported the bug.
>
-- John Harper, School of Mathematics and Statistics
Victoria Univ. of Wellington, PO Box 600, Wellington 6140, New Zealand.
e-mail john.har...@vuw.ac.nz phone +64(0) 4 463 5276
