Re: [PATCH v2] clarify usage expectations for cnt32_to_63()

Nicolas Pitre
2008-11-11T00:27:17Z

On Mon, 10 Nov 2008, Andrew Morton wrote:

> On Mon, 10 Nov 2008 18:15:32 -0500 (EST)
> Nicolas Pitre <nico@cam.org> wrote:
>
> > On Mon, 10 Nov 2008, Andrew Morton wrote:
> >
> > > This references its second argument twice, which can cause correctness
> > > or efficiency problems.
> > >
> > > There is no reason that this had to be implemented in cpp.
> > > Implementing it in C will fix the above problem.
> >
> > No, it won't, for correctness and efficiency reasons.
> >
> > And I've explained why already.
>
> I'd be very surprised if you've really found a case where a macro is
> faster than an inlined function. I don't think that has happened
> before.

That hasn't anything to do with "a macro is faster" at all. It's all
about the order used to evaluate provided arguments. And the first one
might be anything like a memory value, an IO operation, an expression,
etc. An inline function would work correctly with pointers only and
therefore totally break apart on x86 for example.

Nicolas