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 v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends
Date: Fri, 31 Aug 2012 08:02:19 -0700 [thread overview]
Message-ID: <1346425339-17138-1-git-send-email-linux@roeck-us.net> (raw)
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, DIV_ROUND_CLOSEST is sometimes used on integers which can be
negative (such as temperatures).
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
v4: Don't address negative divisors to improve chances for compile-time
optimization. Document DIV_ROUND_CLOSEST macro.
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 | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 6043821..594b419 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -82,10 +82,18 @@
__x - (__x % (y)); \
} \
)
+
+/*
+ * Divide positive or negative dividend by positive divisor and round
+ * to closest integer. Result is undefined for negative divisors.
+ */
#define DIV_ROUND_CLOSEST(x, divisor)( \
{ \
- typeof(divisor) __divisor = divisor; \
- (((x) + ((__divisor) / 2)) / (__divisor)); \
+ typeof(x) __x = x; \
+ typeof(divisor) __d = divisor; \
+ (((typeof(x))-1) >= 0 || (__x) >= 0) ? \
+ (((__x) + ((__d) / 2)) / (__d)) : \
+ (((__x) - ((__d) / 2)) / (__d)); \
} \
)
--
1.7.9.7
next reply other threads:[~2012-08-31 15:02 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-31 15:02 Guenter Roeck [this message]
2012-08-31 19:38 ` [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends Andrew Morton
2012-08-31 21:05 ` Guenter Roeck
2012-09-01 17:02 ` Jean Delvare
2012-09-02 2:14 ` Guenter Roeck
2012-09-09 14:57 ` Geert Uytterhoeven
2012-09-09 16:17 ` Guenter Roeck
2012-09-09 20:38 ` Geert Uytterhoeven
2012-09-09 21:30 ` Guenter Roeck
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