[Bug libstdc++/108046] The dot in the floating-point alternative form has wrong position

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108046

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:50bc490c090cc95175e6068ed7438788d7fd7040

commit r14-2825-g50bc490c090cc95175e6068ed7438788d7fd7040
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='e' is set for the _Pres_none
    case. I realized we can also set __expc='P' and __expc='E' when needed,
    to save a call to std::toupper later.

    For the {:#.0g} format, __expc='e' was being set and so the 'e' was
    found in "1e+10" but then __z = __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 == 0 when __prec == 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.