linux/kernel.h: Fix warning seen with W=1 due to change in DIV_ROUND_CLOSEST
Guenter Roeck [Wed, 19 Sep 2012 03:42:31 +0000 (20:42 -0700)]
After commit b6d86d3d (Fix DIV_ROUND_CLOSEST to support negative dividends),
the following warning is seen if the kernel is compiled with W=1 (-Wextra):

warning: comparison of unsigned expression >= 0 is always true

The warning is due to the test '((typeof(x))-1) >= 0', which is used to detect
if the variable type is unsigned. Research on the web suggests that the warning
disappears if '>' instead of '>=' is used for the comparison.

Tests after changing the macro along that line show that the warning is gone,
and that the result is still correct:

i=-4: DIV_ROUND_CLOSEST(i, 2)=-2
i=-3: DIV_ROUND_CLOSEST(i, 2)=-2
i=-2: DIV_ROUND_CLOSEST(i, 2)=-1
i=-1: DIV_ROUND_CLOSEST(i, 2)=-1
i=0: DIV_ROUND_CLOSEST(i, 2)=0
i=1: DIV_ROUND_CLOSEST(i, 2)=1
i=2: DIV_ROUND_CLOSEST(i, 2)=1
i=3: DIV_ROUND_CLOSEST(i, 2)=2
i=4: DIV_ROUND_CLOSEST(i, 2)=2

Code size is the same as before.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Acked-by: Jean Delvare <khali@linux-fr.org>

include/linux/kernel.h

index 594b419..2451f1f 100644 (file)
@@ -91,7 +91,7 @@
 {                                                      \
        typeof(x) __x = x;                              \
        typeof(divisor) __d = divisor;                  \
-       (((typeof(x))-1) >= 0 || (__x) >= 0) ?          \
+       (((typeof(x))-1) > 0 || (__x) > 0) ?            \
                (((__x) + ((__d) / 2)) / (__d)) :       \
                (((__x) - ((__d) / 2)) / (__d));        \
 }                                                      \