linux-kernel - [PATCH] linux/kernel.h: Fix warning seen with W=1 due to change in DIV_ROUND

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Message-Id: <1348027209-29710-1-git-send-email-linux@roeck-us.net>
Date:	Tue, 18 Sep 2012 21:00:09 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	linux-kernel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jean Delvare <khali@...ux-fr.org>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	lm-sensors@...sensors.org, Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH] linux/kernel.h: Fix warning seen with W=1 due to change in DIV_ROUND_CLOSEST

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@...ck-us.net>
---
 include/linux/kernel.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 594b419..2451f1f 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -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));	\
 }							\
-- 
1.7.9.7

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