Re: [Qemu-devel] [PATCH v5 09/36] ppc/xive: notify the CPU when the interrupt priority is more privileged

[Eric Blake]

On 11/27/18 8:41 PM, David Gibson wrote:
> On Wed, Nov 28, 2018 at 01:32:21PM +1100, Benjamin Herrenschmidt wrote:
> > On Wed, 2018-11-28 at 11:13 +1100, David Gibson wrote:
> > > Don't you need a cast to avoid (nsr << 8) being a shift-wider-than-size?
> >
> > Shouldn't be a problem as long as it fits in an int, no ?
>
> I dunno, I can never remember the rules about when C extends and when
> it doesn't.  I'm not sure anybody does, which is kind of the point.

As soon as you perform arithmetic on a type narrower than int, it is 
first promoted to at least int (possibly wider, depending on the type of 
the other operand to the binary operator).  And, since C guarantees that 
int is larger than 8 bits, 'uint8_t << 8' and 'int8_t << 8' are both 
well-defined, without needing a cast of nsr.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org