lib/average.c

   1 /*
   2  * lib/average.c
   3  *
   4  * This source code is licensed under the GNU General Public License,
   5  * Version 2.  See the file COPYING for more details.
   6  */
   7
   8 #include <linux/module.h>
   9 #include <linux/average.h>
  10 #include <linux/bug.h>
  11
  12 /**
  13  * DOC: Exponentially Weighted Moving Average (EWMA)
  14  *
  15  * These are generic functions for calculating Exponentially Weighted Moving
  16  * Averages (EWMA). We keep a structure with the EWMA parameters and a scaled
  17  * up internal representation of the average value to prevent rounding errors.
  18  * The factor for scaling up and the exponential weight (or decay rate) have to
  19  * be specified thru the init fuction. The structure should not be accessed
  20  * directly but only thru the helper functions.
  21  */
  22
  23 /**
  24  * ewma_init() - Initialize EWMA parameters
  25  * @avg: Average structure
  26  * @factor: Factor to use for the scaled up internal value. The maximum value
  27  *      of averages can be ULONG_MAX/(factor*weight).
  28  * @weight: Exponential weight, or decay rate. This defines how fast the
  29  *      influence of older values decreases. Has to be bigger than 1.
  30  *
  31  * Initialize the EWMA parameters for a given struct ewma @avg.
  32  */
  33 void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
  34 {
  35         WARN_ON(weight <= 1 || factor == 0);
  36         avg->internal = 0;
  37         avg->weight = weight;
  38         avg->factor = factor;
  39 }
  40 EXPORT_SYMBOL(ewma_init);
  41
  42 /**
  43  * ewma_add() - Exponentially weighted moving average (EWMA)
  44  * @avg: Average structure
  45  * @val: Current value
  46  *
  47  * Add a sample to the average.
  48  */
  49 struct ewma *ewma_add(struct ewma *avg, unsigned long val)
  50 {
  51         avg->internal = avg->internal  ?
  52                 (((avg->internal * (avg->weight - 1)) +
  53                         (val * avg->factor)) / avg->weight) :
  54                 (val * avg->factor);
  55         return avg;
  56 }
  57 EXPORT_SYMBOL(ewma_add);