From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-440114-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 27666 invoked by alias); 12 Jan 2014 01:48:57 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Received: (qmail 25949 invoked by uid 48); 12 Jan 2014 01:48:51 -0000
From: "jvdelisle at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libfortran/59774] [Regression] Inconsistent rounding between -m32 and -m64
Date: Sun, 12 Jan 2014 01:48:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libfortran
X-Bugzilla-Version: 4.9.0
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jvdelisle at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: jvdelisle at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields: short_desc
Message-ID: <bug-59774-4-8iOykjeeas@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-59774-4@http.gcc.gnu.org/bugzilla/>
References: <bug-59774-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2014-01/txt/msg01256.txt.bz2

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59774

Jerry DeLisle <jvdelisle at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Inconsistent rounding       |[Regression] Inconsistent
                   |between -m32 and -m64       |rounding between -m32 and
                   |                            |-m64

--- Comment #2 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
I think this gets back to:

http://gcc.gnu.org/viewcvs/gcc?view=revision&revision=185433

Using:

 print "(ru,g11.2)", 99._8
 print "(ru,g11.2)", 99._4
end


Looking at the buffer in output_float we get:

$ gfc  -m32 pr59771.f90 
$ ./a.out 
buffer=+99900000000000000000000e+01<<<
   0.99E+02
buffer=+99.000000000000<<<
    10.    
$ gfc  -m64 pr59771.f90 
$ ./a.out 
buffer=+99900000000000000000000e+01<<<
   0.99E+02
buffer=+999000000000000e+01<<<
   0.99E+02

Notice the '.' in the buffer for kind=4 vs kind=8

I don't know all the reasons for the changes made, but think "." needs to get
stripped out before we ever get to output_float and the exponent needs to be
there.  I do recall the reason gfortran does its own rounding is because the C
implementations across platforms are not consistent.