Merge branch 'hwmon-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/groec...

[pandora-kernel.git] / lib / average.c

diff --git a/lib/average.c b/lib/average.c
index f1d1b46..5576c28 100644 (file)
--- a/lib/average.c
+++ b/lib/average.c
@@ -8,6 +8,7 @@
 #include <linux/module.h>
 #include <linux/average.h>
 #include <linux/bug.h>
+#include <linux/log2.h>
 
 /**
  * DOC: Exponentially Weighted Moving Average (EWMA)
@@ -24,18 +25,21 @@
  * ewma_init() - Initialize EWMA parameters
  * @avg: Average structure
  * @factor: Factor to use for the scaled up internal value. The maximum value
- *     of averages can be ULONG_MAX/(factor*weight).
+ *     of averages can be ULONG_MAX/(factor*weight). For performance reasons
+ *     factor has to be a power of 2.
  * @weight: Exponential weight, or decay rate. This defines how fast the
- *     influence of older values decreases. Has to be bigger than 1.
+ *     influence of older values decreases. For performance reasons weight has
+ *     to be a power of 2.
  *
  * Initialize the EWMA parameters for a given struct ewma @avg.
  */
 void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
 {
-       WARN_ON(weight <= 1 || factor == 0);
+       WARN_ON(!is_power_of_2(weight) || !is_power_of_2(factor));
+
+       avg->weight = ilog2(weight);
+       avg->factor = ilog2(factor);
        avg->internal = 0;
-       avg->weight = weight;
-       avg->factor = factor;
 }
 EXPORT_SYMBOL(ewma_init);
 
@@ -49,9 +53,9 @@ EXPORT_SYMBOL(ewma_init);
 struct ewma *ewma_add(struct ewma *avg, unsigned long val)
 {
        avg->internal = avg->internal  ?
-               (((avg->internal * (avg->weight - 1)) +
-                       (val * avg->factor)) / avg->weight) :
-               (val * avg->factor);
+               (((avg->internal << avg->weight) - avg->internal) +
+                       (val << avg->factor)) >> avg->weight :
+               (val << avg->factor);
        return avg;
 }
 EXPORT_SYMBOL(ewma_add);