[Bug fortran/66864] New: floor function error

[Bug fortran/66864] New: floor function error

[dm577216smith at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66864

            Bug ID: 66864
           Summary: floor function error
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dm577216smith at gmail dot com
  Target Milestone: ---

Here is a small program showing an error in the FLOOR function on my machine.
I get similar results with gfortran 5.1 and also an older 4.6 version.

I noticed that each of the incorrect results, 94906264, 777666496, and
2000111104
seem to be the correct value chopped to 24 bits.

Also, if I compile the program with 64-bit integers with -fdefault-integer-8,
all the results are ok.


      PROGRAM T

      DOUBLE PRECISION :: X

      WRITE (*,*) ' '

      X = 2.0D0 ** 26.5D0
      WRITE (*,*) ' X = 2.0D0 ** 26.5D0 = ', X
      WRITE (*,*) ' FLOOR(X) = ', FLOOR(X)
      WRITE (*,*) ' '

      WRITE (*,*) ' But  FLOOR( 2.0D0 ** 26.5D0 ) = ', FLOOR( 2.0D0 ** 26.5D0 )
      WRITE (*,*) ' '
      WRITE (*,*) ' '

      X = 777666555.6D0
      WRITE (*,*) ' X = 777666555.6D0 gives ', X,'  FLOOR(X) = ', FLOOR(X)
      WRITE (*,*) ' '

      WRITE (*,*) ' But  FLOOR(777666555.6D0) = ', FLOOR(777666555.6D0)
      WRITE (*,*) ' '
      WRITE (*,*) ' '

      X = 2000111222.6D0
      WRITE (*,*) ' X = 2000111222.6D0 gives ', X,'  FLOOR(X) = ', FLOOR(X)
      WRITE (*,*) ' '

      WRITE (*,*) ' But  FLOOR(2000111222.6D0) = ', FLOOR(2000111222.6D0)
      WRITE (*,*) ' '
      WRITE (*,*) ' '

      END PROGRAM T


Output from the program:


  X = 2.0D0 ** 26.5D0 =    94906265.624251559     
  FLOOR(X) =     94906265

  But  FLOOR( 2.0D0 ** 26.5D0 ) =     94906264


  X = 777666555.6D0 gives    777666555.60000002        FLOOR(X) =    777666555

  But  FLOOR(777666555.6D0) =    777666496


  X = 2000111222.6D0 gives    2000111222.5999999        FLOOR(X) =   2000111222

  But  FLOOR(2000111222.6D0) =   2000111104

[Bug fortran/66864] floor function error

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66864

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-07-14
                 CC|                            |kargl at gcc dot gnu.org
     Ever confirmed|0                           |1
      Known to fail|                            |4.7.4, 4.8.5, 4.9.3, 5.1.1,
                   |                            |6.0

--- Comment #1 from kargl at gcc dot gnu.org ---
It seems constant folding in simplify.c may be broken.  Here's
a testcase suitable for the testsuite once the bug is fixed.

! { dg-do run }
! PR fortran/66864
!
program t
   implicit none
   real(8) x
   x = 2.0d0**26.5d0
   if (floor(x) /= 94906265) call abort
   if (floor(2.0d0**26.5d0)/= 94906265) call abort
   x = 777666555.6d0
   if (floor(x) /= 777666555) call abort
   if (floor(777666555.6d0) /= 777666555) call abort
   x = 2000111222.6d0
   if (floor(x) /= 2000111222) call abort
   if (floor(2000111222.6d0) /= 2000111222) call abort
end program t

[Bug fortran/66864] floor function error

[sgk at troutmask dot apl.washington.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66864

--- Comment #2 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Tue, Jul 14, 2015 at 05:03:55PM +0000, kargl at gcc dot gnu.org wrote:
> 
> --- Comment #1 from kargl at gcc dot gnu.org ---
> It seems constant folding in simplify.c may be broken.  Here's
> a testcase suitable for the testsuite once the bug is fixed.

I have a patch.

[Bug fortran/66864] floor function error

[sgk at troutmask dot apl.washington.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66864

--- Comment #3 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Tue, Jul 14, 2015 at 07:02:32PM +0000, sgk at troutmask dot
apl.washington.edu wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66864
> 
> --- Comment #2 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
> On Tue, Jul 14, 2015 at 05:03:55PM +0000, kargl at gcc dot gnu.org wrote:
> > 
> > --- Comment #1 from kargl at gcc dot gnu.org ---
> > It seems constant folding in simplify.c may be broken.  Here's
> > a testcase suitable for the testsuite once the bug is fixed.
> 
> I have a patch.
> 

Patch posted.

https://gcc.gnu.org/ml/gcc-patches/2015-07/msg01193.html

[Bug fortran/66864] floor function error

[sgk at troutmask dot apl.washington.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66864

--- Comment #4 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Tue, Jul 14, 2015 at 12:31:11PM -0700, Steve Kargl wrote:
> On Tue, Jul 14, 2015 at 07:02:32PM +0000, sgk at troutmask dot apl.washington.edu wrote:
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66864
> > 
> > --- Comment #2 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
> > On Tue, Jul 14, 2015 at 05:03:55PM +0000, kargl at gcc dot gnu.org wrote:
> > > 
> > > --- Comment #1 from kargl at gcc dot gnu.org ---
> > > It seems constant folding in simplify.c may be broken.  Here's
> > > a testcase suitable for the testsuite once the bug is fixed.
> > 
> > I have a patch.
> > 
> 
> Patch posted.
> 
> https://gcc.gnu.org/ml/gcc-patches/2015-07/msg01193.html
> 

I committed the patch to trunk, but forgot to include
the PR number in the ChangeLog entry.

[Bug fortran/66864] floor function error

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66864

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |5.3

--- Comment #6 from kargl at gcc dot gnu.org ---
Fixed on trunk and 5-branch.  Thanks for the bug report.

[Bug fortran/66864] floor function error

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66864

--- Comment #5 from kargl at gcc dot gnu.org ---
Author: kargl
Date: Thu Jul 16 19:22:38 2015
New Revision: 225903

URL: https://gcc.gnu.org/viewcvs?rev=225903&root=gcc&view=rev
Log:
2015-07-16  Steven G. Kargl  <kargl@gcc.gnu.org>

        PR fortran/66864
        * simplify.c (gfc_simplify_floor): Set precision of temporary to
        that of arg.

2015-07-16  Steven G. Kargl  <kargl@gcc.gnu.org>

        PR fortran/66864
        * gfortran.dg/pr66864.f90: New test.

Added:
    branches/gcc-5-branch/gcc/testsuite/gfortran.dg/pr66864.f90
Modified:
    branches/gcc-5-branch/gcc/fortran/ChangeLog
    branches/gcc-5-branch/gcc/fortran/simplify.c
    branches/gcc-5-branch/gcc/testsuite/ChangeLog