Function update

pub unsafe fn update<F>(f: F)
where
    F: FnOnce(&mut RFlags),

Updates the RFLAGS register, preserves reserved bits.

Safety

Unsafe because undefined becavior can occur if certain flags are modified. For example, the DF flag must be unset in all Rust code. Also, modifying CF, PF, or any other flags also used by Rust/LLVM can result in undefined behavior too.