[PATCH v2 1/2] linux/kernel.h: Introduce IDIV_ROUND_CLOSEST

* [PATCH v2 1/2] linux/kernel.h: Introduce IDIV_ROUND_CLOSEST
@ 2012-08-28 16:30 Guenter Roeck
  2012-08-28 16:30 ` [PATCH 2/2] hwmon: Use IDIV_ROUND_CLOSEST if the dividend can be negative Guenter Roeck
  2012-08-30 23:15 ` [PATCH v2 1/2] linux/kernel.h: Introduce IDIV_ROUND_CLOSEST Andrew Morton
  0 siblings, 2 replies; 4+ messages in thread
From: Guenter Roeck @ 2012-08-28 16:30 UTC (permalink / raw)
  To: linux-kernel
  Cc: Andrew Morton, Pekka Enberg, Ingo Molnar, H. Peter Anvin,
	Jean Delvare, lm-sensors, Guenter Roeck

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, it is sometimes used on integers which can be negative (such as
temperatures). Introduce new macro IDIV_ROUND_CLOSEST which also supports
negative dividends.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
v2: v1 did not work if typeof(divisor) was an unsigned variable type
    (which can obviously not be negative).
    Rework to revert to DIV_ROUND_CLOSEST if the dividend is unsigned,
    or if it is signed but non-negative.

Plan is to merge this patch through my hwmon tree unless there is an objection.

 include/linux/kernel.h |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 6043821..42f1fd6 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -89,6 +89,16 @@
 }							\
 )
 
+#define IDIV_ROUND_CLOSEST(x, divisor)(			\
+{							\
+	typeof(x) __x = x;				\
+	typeof(divisor) __d = divisor;			\
+	(((typeof(x))-1) >= 0 || (__x) >= 0) ?		\
+		DIV_ROUND_CLOSEST((__x), (__d)) :	\
+		(((__x) - ((__d) / 2)) / (__d));	\
+}							\
+)
+
 /*
  * Multiplies an integer by a fraction, while avoiding unnecessary
  * overflow or loss of precision.
-- 
1.7.9.7


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