linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Guenter Roeck <linux@roeck-us.net>
To: linux-kernel@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.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, Guenter Roeck <linux@roeck-us.net>
Subject: [PATCH v3] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative operands
Date: Thu, 30 Aug 2012 17:10:47 -0700	[thread overview]
Message-ID: <1346371847-21384-1-git-send-email-linux@roeck-us.net> (raw)

DIV_ROUND_CLOSEST returns a bad result for dividends with different sign:
	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).

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
v3: Instead of adding a new macro, fix DIV_ROUND_CLOSEST.
    This version works for negative dividend and divisor.

v2: v1 did not work if typeof(divisor) was an unsigned variable type
    (which can obviously not be negative).
    Rework to revert to DIV_ROUND_CLOSEST if the dividend is unsigned,
    or if it is signed but non-negative.

 include/linux/kernel.h |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 6043821..4b180de 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -84,8 +84,11 @@
 )
 #define DIV_ROUND_CLOSEST(x, divisor)(			\
 {							\
-	typeof(divisor) __divisor = divisor;		\
-	(((x) + ((__divisor) / 2)) / (__divisor));	\
+	typeof(x) __x = x;				\
+	typeof(divisor) __d = divisor;			\
+	((__x) < 0) == ((__d) < 0) ?			\
+		(((__x) + ((__d) / 2)) / (__d)) :	\
+		(((__x) - ((__d) / 2)) / (__d));	\
 }							\
 )
 
-- 
1.7.9.7


             reply	other threads:[~2012-08-31  0:10 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-31  0:10 Guenter Roeck [this message]
2012-08-31  0:35 ` [PATCH v3] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative operands Andrew Morton
2012-08-31  1:12   ` Guenter Roeck

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1346371847-21384-1-git-send-email-linux@roeck-us.net \
    --to=linux@roeck-us.net \
    --cc=akpm@linux-foundation.org \
    --cc=hpa@zytor.com \
    --cc=khali@linux-fr.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=lm-sensors@lm-sensors.org \
    --cc=mingo@kernel.org \
    --cc=penberg@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).