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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/108046] The dot in the floating-point alternative
 form has wrong position
Date: Wed, 27 Sep 2023 16:17:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108046

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:da1ba03245c212ef1ba100e7806588802f3ad46f

commit r13-7914-gda1ba03245c212ef1ba100e7806588802f3ad46f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jul 27 14:07:09 2023 +0100

    libstdc++: Fix std::format alternate form for floating-point [PR108046]

    A decimal point was being added to the end of the string for {:#.0}
    because the __expc character was not being set, for the _Pres_none
    presentation type, so __s.find(__expc) didn't the 'e' in "1e+01" and so
    we created "1e+01." by appending the radix char to the end.

    This can be fixed by ensuring that __expc=3D'e' is set for the _Pres_no=
ne
    case. I realized we can also set __expc=3D'P' and __expc=3D'E' when nee=
ded,
    to save a call to std::toupper later.

    For the {:#.0g} format, __expc=3D'e' was being set and so the 'e' was
    found in "1e+10" but then __z =3D __prec - __sigfigs would wraparound to
    SIZE_MAX. That meant we would decide not to add a radix char because the
    number of extra characters to insert would be 1+SIZE_MAX i.e. zero.

    This can be fixed by using __z =3D=3D 0 when __prec =3D=3D 0.

    libstdc++-v3/ChangeLog:

            PR libstdc++/108046
            * include/std/format (__formatter_fp::format): Ensure __expc is
            always set for all presentation types. Set __z correctly for
            zero precision.
            * testsuite/std/format/functions/format.cc: Check problem cases.

    (cherry picked from commit 50bc490c090cc95175e6068ed7438788d7fd7040)=