From: Andrew Morton <akpm@linux-foundation.org>
To: Guenter Roeck <linux@roeck-us.net>
Cc: linux-kernel@vger.kernel.org, Pekka Enberg <penberg@kernel.org>,
Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
Jean Delvare <khali@linux-fr.org>,
lm-sensors@lm-sensors.org
Subject: Re: [PATCH v2 1/2] linux/kernel.h: Introduce IDIV_ROUND_CLOSEST
Date: Thu, 30 Aug 2012 16:15:32 -0700 [thread overview]
Message-ID: <20120830161532.0db909c9.akpm@linux-foundation.org> (raw)
In-Reply-To: <1346171456-29255-1-git-send-email-linux@roeck-us.net>
On Tue, 28 Aug 2012 09:30:55 -0700
Guenter Roeck <linux@roeck-us.net> 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 sometimes used on integers which can be negative (such as
> temperatures). Introduce new macro IDIV_ROUND_CLOSEST which also supports
> negative dividends.
>
Can't we just fix DIV_ROUND_CLOSEST? That will make it a bit slower
but it's not exactly a speed demon right now. And fixing
DIV_ROUND_CLOSEST() might just fix other bugs that we don't know about
yet.
Also, the name IDIV_ROUND_CLOSEST doesn't communicate much at all.
> +#define IDIV_ROUND_CLOSEST(x, divisor)( \
> +{ \
> + typeof(x) __x = x; \
> + typeof(divisor) __d = divisor; \
> + (((typeof(x))-1) >= 0 || (__x) >= 0) ? \
> + DIV_ROUND_CLOSEST((__x), (__d)) : \
> + (((__x) - ((__d) / 2)) / (__d)); \
> +} \
> +)
And it doesn't help that the new "function" is undocumented. Yes, we
screwed up with DIV_ROUND_CLOSEST(), but that doesn't mean we need to
keep screwing up!
next prev parent reply other threads:[~2012-08-30 23:15 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-28 16:30 [PATCH v2 1/2] linux/kernel.h: Introduce IDIV_ROUND_CLOSEST Guenter Roeck
2012-08-28 16:30 ` [PATCH 2/2] hwmon: Use IDIV_ROUND_CLOSEST if the dividend can be negative Guenter Roeck
2012-08-30 23:15 ` Andrew Morton [this message]
2012-08-30 23:50 ` [PATCH v2 1/2] linux/kernel.h: Introduce IDIV_ROUND_CLOSEST Guenter Roeck
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