Re: [PATCH rdma-next 08/12] overflow.h: Add arithmetic shift helper

[Leon Romanovsky]

On Wed, Jun 27, 2018 at 11:36:03AM +0200, Rasmus Villemoes wrote:
> On 26 June 2018 at 19:54, Jason Gunthorpe <jgg@xxxxxxxxxxxx> wrote:
>
> > On Tue, Jun 26, 2018 at 10:07:07AM +0200, Rasmus Villemoes wrote:
> > >    On 25 June 2018 at 19:11, Jason Gunthorpe <[1]jgg@xxxxxxxxxxxx>
> > wrote:
> > >
> >
> > When thinking about signed cases.. The explicit u64 cast, and
> > implict promotion to typeof(d), produce something counter intuitive,
> > eg:
> >
> >   (u64)(s32)-1 == 0xffffffffffffffff
> >
> > Which would result in a shift oucome that is not what anyone would
> > expect, IMHO... So the first version isn't what I'd expect either..
> >
>
> Wouldn't check_shift_overflow(-1, 4, &someint) just put -16 in someint and
> report no overflow? That's what I'd expect, if negative values are to be
> supported at all.

Most if not all the times we don't do shifts on negative values, so I
don't think that we should support them.

Thanks

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