linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends

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>
Acked-by: Jean Delvare <khali@linux-fr.org>

1 files changed, 10 insertions, 2 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 604382143bc..594b419b7d2 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));        \
 }                                                       \
 )