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
next 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
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