lkml.org 
[lkml]   [2012]   [Aug]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] kernel.h: Introduce IDIV_ROUND_CLOSEST
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 <khali@linux-fr.org>

>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> 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


\
 
 \ /
  Last update: 2012-08-28 18:41    [W:0.034 / U:0.884 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site