I was thinking about the isleadbyte issue and seems that the explicit
cast to unsigned char should be used. Basically every ISO C is* function
from ctype.h has defined same behavior. Function takes argument of signed
int type which should be either EOF or value in range of unsigned char.
Function isleadbyte() is not in ISO C but it makes sense if it follow
above logic. As EOF is defined as -1, it means that sign-extended input
would never work for (char)255. I would suggest to check all usage of
is*() functions in mingw-w64 that there is explicit cast to unsigned char.
On Thursday 04 September 2025 09:50:22 Kirill Makurin wrote:
> Out of curiosity I tried to configure mingw-w64 for crtdll.dll and run the
> tests. Something strange happens in tests for mbrlen, mbrtowc and mbsrtowcs
> functions.
>
> First, it seems that crtdll's setlocale() does not allow string which specify
> ACP/OCP instead of actual code page (it's not a big issue, I'll send a patch
> in coming days). Second, something seems to be wrong with crtdll's
> isleadbyte().
>
> For mbrlen's test, the failing assertion was
>
> ```
> assert (mbrlen ((char *) Multibyte, 1, &state) == (size_t) -2);
> ```
>
> It seems to me that the issue may come from line 78 in mbrtowc.c:
>
> ```
> } else if (mb_cur_max == 2 && isleadbyte (mbs[0])) {
> ```
>
> Here mbs[0] is passed to isleadbyte(). If value of mbs[0] is outside of range
> [0,127] (as all lead bytes are), it will be sign-extended. This seems to be
> the source of the issue. I tried re-run tests after adding a cast to
> `unsigned char` and it seems to fix it.
>
> I tried configuring and running tests with msvcrt20.dll and they pass. I do
> not have msvcrt10.dll to run tests with it. It would be helpful if anyone
> could run tests with crtdll.dll and msvcrt10.dll to see how they behave.
>
> If the issue is sign-extended input to isleadbyte(), it is fixable by a
> simple patch with cast to `unsigned char`. If issue is indeed in crtdll's
> isleadbyte(), I suggest we replace it by emu.
>
> - Kirill Makurin
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