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

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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>
This commit is contained in:
Niklas Söderlund 2017-02-24 15:01:01 -08:00 committed by Linus Torvalds
parent e4afd2e556
commit 4f5901f5a6
1 changed files with 6 additions and 4 deletions
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10
include/linux/kernel.h
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@ -100,16 +100,18 @@
) )
/* /*
* Divide positive or negative dividend by positive divisor and round * Divide positive or negative dividend by positive or negative divisor
* to closest integer. Result is undefined for negative divisors and * and round to closest integer. Result is undefined for negative
* for negative dividends if the divisor variable type is unsigned. * 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)( \ #define DIV_ROUND_CLOSEST(x, divisor)( \
{ \ { \
typeof(x) __x = x; \ typeof(x) __x = x; \
typeof(divisor) __d = divisor; \ typeof(divisor) __d = divisor; \
(((typeof(x))-1) > 0 || \ (((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)) : \
(((__x) - ((__d) / 2)) / (__d)); \ (((__x) - ((__d) / 2)) / (__d)); \
} \ } \