On Sat, Sep 01, 2012 at 07:02:54PM +0200, Jean Delvare wrote:
> Hi Andrew, Guenter,
>
> On Fri, 31 Aug 2012 12:38:12 -0700, Andrew Morton wrote:
> > On Fri, 31 Aug 2012 08:02:19 -0700
> > Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> >
> > > DIV_ROUND_CLOSEST returns a bad result for negative dividends:
> > > DIV_ROUND_CLOSEST(-2, 2) = 0
> > >
> > > Most of the time this does not matter. However, in the hardware monitoring
> > > subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be
> > > negative (such as temperatures).
> > >
> > > ...
> > >
> > > +
> > > +/*
> > > + * Divide positive or negative dividend by positive divisor and round
> > > + * to closest integer. Result is undefined for negative divisors.
> > > + */
> > > #define DIV_ROUND_CLOSEST(x, divisor)( \
> > > { \
> > > - typeof(divisor) __divisor = divisor; \
> > > - (((x) + ((__divisor) / 2)) / (__divisor)); \
> > > + typeof(x) __x = x; \
> > > + typeof(divisor) __d = divisor; \
> > > + (((typeof(x))-1) >= 0 || (__x) >= 0) ? \
> > > + (((__x) + ((__d) / 2)) / (__d)) : \
> > > + (((__x) - ((__d) / 2)) / (__d)); \
> > > } \
> >
> > Looks good to me.
>
> My testing looks good too.
>
> Acked-by: Jean Delvare <khali@xxxxxxxxxxxx>
>
Thanks a lot!
> > The patch causes no change in text size for
> > kernel/sched/fair.o and drivers/cpuidle/governors/menu.o, so it seems
> > that the cc trickery is working.
>
> Indeed. I looked for test size increase, and for my config, besides
> hwmon, I only spotted the following ones:
>
> drivers/media/rc/mceusb.o
> drivers/gpu/drm/i915/intel_pm.o
> drivers/tty/serial/pch_uart.o
>
> These don't look like hot paths, so I'd say we don't care. Plus the
> intel_pm one can probably be solved by using an unsigned int, I don't
> see why/how ia_freq could be negative (negative frequency anyone?) And
> for mceusb it can be solved easily by changing "1" to "1U".
>
Yes, it helps a lot that the C trickery optimizes the changes away most of the time.
I'll let the patch rest in -next for a few more days before I send it to Linus.
Guenter
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