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From: "bugs at dhbailey dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/65757] New: gfortran gives incorrect result for anint with real*16 argument
Date: Mon, 13 Apr 2015 23:33:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65757

            Bug ID: 65757
           Summary: gfortran gives incorrect result for anint with real*16
                    argument
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bugs at dhbailey dot com

gfortran gives an incorrect result for the anint (nearest whole number)
function for certain real*16 arguments.  Here is a simple example:

program anintbug
implicit none
real (kind (0.q0)) q1, q2, q3

q1 = 233181505644407.99996948242187500000q0
q2 = anint (q1)
q3 = 233181505644408.00000000000000000000q0

write (6, '(f50.25)') q1, q2, q3
write (6, '(z35)') q1, q2, q3
stop
end

When compiled with "gfortran anintbug.f90", this program produces the following
output.  The second result should equal the third result, but does not.

         233181505644407.9999694824218750000000000
         233181505644407.9999694824218750000000000
         233181505644408.0000000000000000000000000
   402EA827999FCEEFFFFC000000000000
   402EA827999FCEEFFFFC000000000000
   402EA827999FCEF00000000000000000