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Date: Thu, 28 May 2026 19:45:39 +0200
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Subject: Re: wcwidth broken with gcc 16
To: cygwin AT cygwin DOT com
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From: Thomas Wolff via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Thomas Wolff <towo AT towo DOT net>
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Am 25.05.2026 um 18:53 schrieb Thomas Wolff via Cygwin:
>
> Am 05.05.2026 um 08:37 schrieb Thomas Wolff via Cygwin:
>>
>> Am 04.05.2026 um 23:52 schrieb Jakob Bohm via Cygwin:
>>> On 03/05/2026 18:14, Brian Inglis via Cygwin wrote:
>>>> On 2026-05-03 06:00, Thomas Wolff via Cygwin wrote:
>>>>> Am 03.05.2026 um 12:58 schrieb Dimitry Andric:
>>>>>> On 3 May 2026, at 12:47, Thomas Wolff via Cygwin 
>>>>>> <cygwin AT cygwin DOT com> wrote:
>>>>>>> Am 03.05.2026 um 07:35 schrieb ASSI via Cygwin:
>>>>>>>> Thomas Wolff via Cygwin writes:
>>>>>>>>> Observed with gcc 16:
>>>>>>>>> For a number of character ranges, mainly (but not only) from CJK
>>>>>>>>> ranges, wcwidth incorrectly reports width 1 instead of 2, 0, 
>>>>>>>>> or -1.
>>>>>>>>> Test file attached.
>>>>>>>> Can you report this upstream, please?
>>>>>>> I couldn't yet test it with gcc 16 on Linux as there is no 
>>>>>>> Debian package.
>>>>>>> Did you test it?
>>>>>> It looks like BSD-based libc gives 1 for U+D7C6, U+D7CB and 
>>>>>> U+D7CB, while glibc gives 0.
>>>>> Thanks. Despite some differences, none of them gives the broken 
>>>>> results of gcc-16 on cygwin, so I wonder whether it makes sense to 
>>>>> report upstream at this time.
>>>>
>>>> It appears that libiberty does not contain any mb/wc 
>>>> macros/functions, , and only contains safe-ctype IS... 
>>>> macros/functions with fixed ASCII characters.
>>>>
>>>> Does gcc, like most GNU products, include some release of gnulib?
>>>> Could gnulib or gcc config detect some lack of support and "fix" 
>>>> newlib-cygwin support of Unicode properties declared in 
>>>> wchar.h/wctype.h, or used in i18n, libunistring, and Unicode string 
>>>> functions, especially if doing any kind of cross-bootstrap?
>>>>
>>>> https://www.gnu.org/software/gnulib/MODULES.html
>>>>
>>>> I also note that w32api-headers/runtime are gcc runtime 
>>>> dependencies and hope they are used only in COFF/PE-related 
>>>> generation?
>>>>
>>> Under Cygwin, does wcwidth() use Cygwin-provided table, derived 
>>> either from upstream Unicode data or from Windows OS APIs that use 
>>> OS bundled Unicode data?
>> Cygwin/newlib provides a wcwidth function that uses a table generated 
>> from unicode.org data, but apparently gcc 16 does not (fully?) use 
>> that function.
> Now reported upstream: 125451 – wcwidth broken with gcc 16 on cygwin 
> <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125451>
>
As discussed in the upstream issue, it may because by the include file 
which specifies:
int    wcwidth (const wchar_t);
although the parameter type should be wint_t (as it is in newlib) to 
support full Unicode.
gcc 16 sign-extends the parameter to a signed 16-bit value, while 
earlier gcc zero-extends it to an unsigned.
Why it extends a short value for an assumed short parameter at all, and 
why the signedness of this extension changed in gcc 16, remains obscure 
for now.
(Maybe further discussion in the upstream issue will shed light on this.)
But in any case I guess it would help to fix the include file and make 
it consistent with both newlib and the wcwidth manual page.
Thomas

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