Commit 4f5901f5 authored Feb 24, 2017 by Niklas Söderlund Committed by Linus Torvalds Feb 24, 2017

linux/kernel.h: fix DIV_ROUND_CLOSEST to support negative divisors

While working on a thermal driver I encounter a scenario where the
divisor could be negative, instead of adding local code to handle this I
though I first try to add support for this in DIV_ROUND_CLOSEST.

Add support to DIV_ROUND_CLOSEST for negative divisors if both dividend
and divisor variable types are signed.  This should not alter current
behavior for users of the macro as previously negative divisors where
not supported.

Before:

DIV_ROUND_CLOSEST(  59,  4) =  15
DIV_ROUND_CLOSEST(  59, -4) = -14
DIV_ROUND_CLOSEST( -59,  4) = -15
DIV_ROUND_CLOSEST( -59, -4) =  14

After:

DIV_ROUND_CLOSEST(  59,  4) =  15
DIV_ROUND_CLOSEST(  59, -4) = -15
DIV_ROUND_CLOSEST( -59,  4) = -15
DIV_ROUND_CLOSEST( -59, -4) =  15

[akpm@linux-foundation.org: fix comment, per Guenter]
Link: http://lkml.kernel.org/r/20161222102217.29011-1-niklas.soderlund+renesas@ragnatech.se


Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent e4afd2e5

include/linux/kernel.h

+6 −4

Original line number	Diff line number	Diff line
		@@ -100,16 +100,18 @@
		)

		/*
		* Divide positive or negative dividend by positive divisor and round
		* to closest integer. Result is undefined for negative divisors and
		* for negative dividends if the divisor variable type is unsigned.
		* Divide positive or negative dividend by positive or negative divisor
		* and round to closest integer. Result is undefined for negative
		* divisors if he dividend variable type is unsigned and for negative
		* dividends if the divisor variable type is unsigned.
		*/
		#define DIV_ROUND_CLOSEST(x, divisor)( \
		{ \
		typeof(x) __x = x; \
		typeof(divisor) __d = divisor; \
		(((typeof(x))-1) > 0 \|\| \
		((typeof(divisor))-1) > 0 \|\| (__x) > 0) ? \
		((typeof(divisor))-1) > 0 \|\| \
		(((__x) > 0) == ((__d) > 0))) ? \
		(((__x) + ((__d) / 2)) / (__d)) : \
		(((__x) - ((__d) / 2)) / (__d)); \
		} \

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