[Bug libstdc++/104870] New: fast_float doesn't work for 16-bit size_t, but is used anyway by floating_from_chars.cc

[dv at vollmann dot ch via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104870

            Bug ID: 104870
           Summary: fast_float doesn't work for 16-bit size_t, but is used
                    anyway by floating_from_chars.cc
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dv at vollmann dot ch
                CC: dv at vollmann dot ch
  Target Milestone: ---
              Host: x86_64-linux-gnu
            Target: avr
             Build: x86_64-linux-gnu

Created attachment 52602
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52602&action=edit
Patch to not use fast_float on unsupported platform

libstdc++-v3/src/c++17/fast_float/fast_float.h doesn't support 16-bit
platforms:

#error Unknown platform (16-bit, unsupported)

But libstdc++-v3/src/c++17/floating_from_chars.cc includes it anyway for
specific float/double sizes:

#if _GLIBCXX_FLOAT_IS_IEEE_BINARY32 && _GLIBCXX_DOUBLE_IS_IEEE_BINARY64
# define USE_LIB_FAST_FLOAT 1