Revert "mbrtowc: fix handling invalid UTF-8 4 byte sequences if wchar_t == UTF-16"

This reverts commit b374973d14ac7969b10ba719feedc709f6971c0d.

Turns out this patch breaks mbrtowc.  Example:

--- SNIP ---

void mb(unsigned char c)
{
  wchar_t wc;
  int ret = mbrtowc(&wc, &c, 1, 0);
  printf("%02X -> %04X : %d\n", c, wc, ret);
}

void main ()
{
  setlocale (LC_CTYPE, "");

  mb(0xF0);
  mb(0x9F);
  mb(0x98);
  mb(0x8E);
}
--- SNAP ---

Output before commit b374973d14ac:

F0 -> 0000 : -2
9F -> 0000 : -2
98 -> D83D : 1
8E -> DE0E : 1

Output after commit b374973d14ac:

F0 -> 0000 : -2
9F -> 0000 : -2
98 -> 0000 : -2
8E -> D83D : 3

By using mbrtowc(), the high surrogate is only emitted after byte 4, and
there's no way to recover the low surrogate.  The byte count is also incorrect.

Conclusion: We have to emit the high surrogate already after byte 3
to be able to emit the low surrogate after byte 4.

Reported-by: Thomas Wolff <towo@towo.net>
Addresses: https://cygwin.com/pipermail/cygwin/2025-July/258513.html
Fixes: b374973d14ac ("mbrtowc: fix handling invalid UTF-8 4 byte sequences if wchar_t == UTF-16")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

0 files changed, 0 insertions, 0 deletions