On Tue, 11 Nov 2008 15:05:02 -0800 (PST)
Trent Piepho <tpiepho at freescale.com> wrote:
> On Mon, 10 Nov 2008, Darrick J. Wong wrote:
> > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > index fba141d..fb02266 100644
> > --- a/include/linux/kernel.h
> > +++ b/include/linux/kernel.h
> > @@ -48,6 +48,12 @@ extern const char linux_proc_banner[];
> > #define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))
> > #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
> > #define roundup(x, y) ((((x) + ((y) - 1)) / (y)) * (y))
> > +#define DIV_ROUND_CLOSEST(x, divisor)( \
> > +{ \
> > + typeof(divisor) __divisor = divisor; \
> > + (((x) + ((__divisor) / 2)) / (__divisor)); \
> > +} \
> > +)
>
> Maybe you can do away with the statement-expression extension? I've seen
> cases where it cases gcc to generate worse code. It seems like it
> shouldn't, but it does. I know DIV_ROUND_CLOSEST (maybe DIV_ROUND_NEAR?)
> uses divisor twice, but all the also divide macros do that too, so why does
> this one need to be different?
The others need fixing too.
> Note that if divisor is a signed variable, divisor/2 generates worse code
> than divisor>>1.
yup. I wonder why the compiler doesn't do that for itself - is there a
case where it will generate a different result?
