From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id 6472B3858023; Tue, 23 Feb 2021 16:55:42 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 6472B3858023
From: "ppalka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/98384] [11 Regression] new test case
 20_util/to_chars/long_double.cc in r11-6249 fails on powerpc64 BE
Date: Tue, 23 Feb 2021 16:55:42 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 11.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: ppalka at gcc dot gnu.org
X-Bugzilla-Status: ASSIGNED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P1
X-Bugzilla-Assigned-To: ppalka at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 11.0
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-98384-4-d8i8YLbbfy@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-98384-4@http.gcc.gnu.org/bugzilla/>
References: <bug-98384-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Tue, 23 Feb 2021 16:55:42 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98384

--- Comment #11 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #9)
> I think glibc %a printing uses 0x1.xxxx (for normalized values) at least =
for
> float/double and the IEEE quad long doubles, but uses 0xf.xxxx printing e=
tc.
> for the 80-bit long doubles.  My personal preference would be to always u=
se
> 0x1.xxxx for normalized numbers and for denormals 0x0.xxxx, I think it is
> less surprising to users, and transforming one form to another is pretty
> easy.

Yeah, currently to_chars hex output mimics glibc's choice of leading hex di=
git.
 But always using 0/1, even for 80-bit long double sounds good to me too.

FWIW, I think the shortest hex form for some number is at most 3 characters
shorter than any other conforming hex form, e.g. 1.2p+12 vs 9p+9.

> And agree on the tests just trying to parse the returned string back to s=
ee
> if it is the original value.

I posted a patch at
https://gcc.gnu.org/pipermail/gcc-patches/2021-February/565726.html that do=
es
this, but also salvages the verification via printf by first checking if the
leading hex digit of the printf output agrees with that of to_chars.=20
Conveniently, the patch sidesteps the question of choosing a consistent
representation vs shortest representation :)=