Re: new module mbrtoc32-regular

[Bruno Haible]

Paul Eggert wrote:
> > DEFINITION: We call an mbrtoc32 function_regular_  if
> >    - It never returns (size_t)-3.
> >    - When it returns < (size_t)-2, the mbstate_t is in the initial state.
> 
> "the initial state" -> "an initial state". But even with that change 
> isn't the second part of this definition a bit too strict? Even if 
> mbsinit returns nonzero, things are still OK if further scanning behaves 
> as if the mbstate_t were all zero. Although this implementation behavior 
> would be silly, POSIX doesn't prohibit it

Not only this implementation behavior would be "silly". No known implementation
behaves like this: In the extensive tests/test-mbrtoc32.c tests we have
  ASSERT (mbsinit (&state));
after every mbrtoc32 return < (size_t)-2, and none of these assertions fail
on the various platforms. Likewise with mbrtowc and tests/test-mbrtowc.c.

Therefore, we don't need to bother about this situation. And if it ever
occurs, the unit test will tell us.

> > +#  if GNULIB_MBRTOC32_REGULAR
> > +  /* Verify that mbrtoc32 is regular.  */
> > +  if (ret < (size_t) -3 && ! mbsinit (ps))
> > +    /* This occurs on glibc 2.36.  */
> > +    memset (ps, '\0', sizeof (mbstate_t));
> > +  if (ret == (size_t) -3)
> > +    abort ();
> > +#  endif
> 
> Since this is inside mbrtoc32, performance is relevant, so shouldn't 
> this be tested at configure-time instead of at run-time? That is, 
> shouldn't the "#if" test be something more like "#if 
> GNULIB_MBRTOC32_REGULAR && HAVE_MBRTOC32_RETURNS_MINUS_3", where 
> GNULIB_MBRTOC32_RETURNS_MINUS_3 is zero on all known platforms?

Well, since I reported https://sourceware.org/bugzilla/show_bug.cgi?id=30611 ,
I expect to see a change in glibc behaviour in this area. But binaries
compiled with a current glibc should continue to work fine with future
glibc versions. This means, we cannot optimize through a configure test here.

We could at most use a cached runtime test, but that is ugly code...

Bruno