[Bug libstdc++/105441] New: The floating point overload of from_chars ignores 'P' for hex format

[Bug libstdc++/105441] New: The floating point overload of from_chars ignores 'P' for hex format

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105441

            Bug ID: 105441
           Summary: The floating point overload of from_chars ignores 'P'
                    for hex format
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

>From StackOverflow
https://stackoverflow.com/questions/72068948/is-stdfrom-chars-supposed-to-handle-uppercase-hexadecimal-exponents/72069971#72069971

testsuite:
https://godbolt.org/z/ad1es7eE6

[Bug libstdc++/105441] The floating point overload of from_chars ignores 'P' for hex format

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105441

--- Comment #1 from 康桓瑋 <hewillk at gmail dot com> ---
floating_from_chars.cc#L667

// Parse the written exponent.
int written_exponent = 0;
if (first != last && *first == 'p')
  {
    // Tentatively consume the 'p' and try to parse a decimal number.
    const char* const fallback_first = first;

it seems like it should be

if (first != last && std::tolower((unsigned char)*first) == 'p')

[Bug libstdc++/105441] The floating point overload of from_chars ignores 'P' for hex format

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105441

--- Comment #2 from 康桓瑋 <hewillk at gmail dot com> ---
floating_from_chars.cc#L667

// Parse the written exponent.
int written_exponent = 0;
if (first != last && *first == 'p')
  {
    // Tentatively consume the 'p' and try to parse a decimal number.
    const char* const fallback_first = first;

it seems like it should be

if (first != last && std::tolower((unsigned char)*first) == 'p')

[Bug libstdc++/105441] [12/13 Regression] The floating point overload of from_chars ignores 'P' for hex format

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105441

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
   Last reconfirmed|                            |2022-04-30
   Target Milestone|---                         |12.0
      Known to fail|                            |12.0, 13.0
            Summary|The floating point overload |[12/13 Regression] The
                   |of from_chars ignores 'P'   |floating point overload of
                   |for hex format              |from_chars ignores 'P' for
                   |                            |hex format

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Thanks for reporting and analyzing this!

(In reply to 康桓瑋 from comment #2)
> floating_from_chars.cc#L667
> 
> // Parse the written exponent.
> int written_exponent = 0;
> if (first != last && *first == 'p')
>   {
>     // Tentatively consume the 'p' and try to parse a decimal number.
>     const char* const fallback_first = first;
> 
> it seems like it should be
> 
> if (first != last && std::tolower((unsigned char)*first) == 'p')

I'm not sure we can use tolower here because it's locale dependent and charconv
isn't.  So we should just test for 'p' and 'P' directly.  And we should
probably replace the existing use of tolower in find_end_of_float.

I wonder why the SO user is seeing this bug with GCC 11.2?  The new hexfloat
parser (r12-6645-gcc3bf3404e4b1c) is GCC 12 only.

[Bug libstdc++/105441] [12/13 Regression] The floating point overload of from_chars ignores 'P' for hex format

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105441

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:576f975cabb0fd9843de152a2d247d486a967b08

commit r13-69-g576f975cabb0fd9843de152a2d247d486a967b08
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon May 2 07:00:48 2022 -0400

    libstdc++: case-sensitivity in hexfloat std::from_chars [PR105441]

    The hexfloat parser for binary32/64 added in r12-6645-gcc3bf3404e4b1c
    overlooked that the exponent part can also begin with an uppercase 'P'.

            PR libstdc++/105441

    libstdc++-v3/ChangeLog:

            * src/c++17/floating_from_chars.cc (__floating_from_chars_hex):
            Also accept 'P' as the start of the exponent.
            * testsuite/20_util/from_chars/7.cc: Add corresponding testcase.

[Bug libstdc++/105441] [12/13 Regression] The floating point overload of from_chars ignores 'P' for hex format

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105441

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:4a6d7da796e456115bbac92e056123f095a3780c

commit r12-8327-g4a6d7da796e456115bbac92e056123f095a3780c
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon May 2 07:00:48 2022 -0400

    libstdc++: case-sensitivity in hexfloat std::from_chars [PR105441]

    The hexfloat parser for binary32/64 added in r12-6645-gcc3bf3404e4b1c
    overlooked that the exponent part can also begin with an uppercase 'P'.

            PR libstdc++/105441

    libstdc++-v3/ChangeLog:

            * src/c++17/floating_from_chars.cc (__floating_from_chars_hex):
            Also accept 'P' as the start of the exponent.
            * testsuite/20_util/from_chars/7.cc: Add corresponding testcase.

    (cherry picked from commit 576f975cabb0fd9843de152a2d247d486a967b08)

[Bug libstdc++/105441] [12/13 Regression] The floating point overload of from_chars ignores 'P' for hex format

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105441

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Should be fixed.

Replacing the use of std::tolower was done in the subsequent commit
r13-70-g86d821ddf5615e.