lkml.org 
[lkml]   [2012]   [Aug]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends
Date
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


\
 
 \ /
  Last update: 2012-08-31 17:21    [W:0.665 / U:0.404 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site