Hi Guenter, On Fri, 24 Aug 2012 17:53:17 -0700, Guenter Roeck 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, it is often used on integers which can be negative (such as > temperatures). Introduce new macro IDIV_ROUND_CLOSEST which also supports > negative dividends.
Good catch. It's been broken for years and I never noticed :( Acked-by: Jean Delvare <[email protected]> > > Signed-off-by: Guenter Roeck <[email protected]> > --- > I can take this patch through my hwmon tree, but would like to get an Ack > first. > Alternative would be to put it into include/linux/hwmon.h, but I would prefer > to avoid that. I agree it should sit next to DIV_ROUND_CLOSEST in <linux/kernel.h>. > > Also, if someone has an idea for a simpler implementation, I would really like > to know about it. I can't think of anything better. Note that your implementation only supports negative dividend not divisor. While it won't be a problem for hwmon drivers, and most probably not a problem for other drivers either, it might be worth putting in a comment so as to prevent false expectations from the reader. > > include/linux/kernel.h | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index 6043821..a89483c 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -89,6 +89,15 @@ > } \ > ) > > +#define IDIV_ROUND_CLOSEST(x, divisor)( \ > +{ \ > + typeof(x) __x = x; \ > + typeof(divisor) __d1 = divisor; \ > + typeof(divisor) __d2 = (__x) < 0 ? -(__d1) : (__d1);\ > + (((__x) + ((__d2) / 2)) / (__d1)); \ > +} \ > +) > + > /* > * Multiplies an integer by a fraction, while avoiding unnecessary > * overflow or loss of precision. -- Jean Delvare -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
