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Re: [PATCH] Update newlib so that it passes libc++'s tests

On Dec 18 14:52, Steven Abner wrote:
> On 17 Dec 2013, at 4:58 PM, Corinna Vinschen wrote:
> > On Dec 17 15:53, Craig Howland wrote:
> >> 
> >> On 12/17/2013 04:42 AM, Corinna Vinschen wrote:
> >>> On Dec 16 16:54, JF Bastien wrote:
> >>>> +#ifndef WCHAR_MAX
> >>>> #ifdef __WCHAR_MAX__
> >>>> #define WCHAR_MAX __WCHAR_MAX__
> >>>> +#elif defined(__WCHAR_UNSIGNED__)
> >>>> +#define WCHAR_MAX 0xffffffffu
> >>>> +#else
> >>>> +#define WCHAR_MAX 0x7fffffffu
> >>>> #endif
> >>> and this is not quite ok.  You're assuming that wchar_t is 4 bytes, but it
> >>> isn't on all platforms.  The fallbacks should take that into account,
> >>> along the lines of
> >>> 
> >>>  #define WCHAR_MAX ((wchar_t)-1)
> >>> 
> >>> 
> >>     Unfortunately, this is not OK in general, as *_MAX defines are
> >> required to be able to be used in preprocessor expressions, and
> >> casts are not always allowed in them.
> > 
> > Then it has to be done differently.  The point is, you can't just set
> > WCHAR_MAX to 0xffffffffu or 0x7fffffffu because it's wrong for some
> > platforms.  If the compiler doesn't provide the information, there has
> > to be another way.
> Hi
> I have a question.  The original post was about compiling newlib as the
> C library. I thought newlib supports UTF32 encodings? If so then why
> can't newlib use 0xffffffff? I can see how an embedded system could
> redefine to 0xff if they only use ASCII. So if the original question one
> that the person compiled using LLVM's libc++ without an architecture
> defining wchar_t ?

Not the C lib defines the size of wchar_t, the underlying system and the
compiler does.  On Windows-based systems like Cygwin, for instance,
wchar_t is 2 bytes since that matches the UTF-16 UNICODE representation
of the underlying Windows.  Cygwin's gcc returns:

  #define __WCHAR_MAX__ 65535
  #define __WCHAR_MIN__ 0
  #define __WCHAR_TYPE__ short unsigned int
  #define __SIZEOF_WCHAR_T__ 2

and the system designed of arbitrary embedded targets might do the same.


Corinna Vinschen
Cygwin Maintainer
Red Hat

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