Hi Guillaume,
The "rep stosb" can't be used unconditionally since it's very slow on some processors.
RĂ©mi sent a similar patch that adds the checks, see: https://source.winehq.org/patches/data/214107 He also improved the C version of the function: https://source.winehq.org/patches/data/214106
Is the "improved C" version good enough for your use case?
Thanks, Piotr