[PATCH v3] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative operands

[Guenter Roeck]

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@xxxxxxxxxxxx>
---
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

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