Re: [Xen-devel] libxc: Casting of xen virtual address type xen_vaddr_t to signed int64 type: (int64_t)vaddr

[Viktor Mitin <viktor.mitin.19@xxxxxxxxx>]

> > Mean that result of "(int64_t)vaddr >> 63" can be 0 or 1.
> > So the next code may not work properly in case of another 'implementations'.
> > With another compiler (i.e. clang, etc) this code may introduce bugs
> > which are hard to find.
> >
> > ((int64_t)vaddr >> 47) == ((int64_t)vaddr >> 63)
> >
> > For this reason it is better to avoid implementation-defined code.
>
> Well, ideally we'd like to get away without using implementation
> defined behavior. But I'm afraid we're quite far from that, and
> we'd not always be willing to accept the worse source and/or
> binary code that would be needed to avoid it.

How about using the next one-liner to avoid implementation-defined code :

//Returns true in case when the top left 17 bits are all zero or are all one
return ((!(vaddr >> 47)) || (((vaddr >> 47)&0x1FFFF) == 0x1FFFF))

Agree?

Thanks

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