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 #include <linux/log2.h>
  12
  13 /**
  14  * DOC: Exponentially Weighted Moving Average (EWMA)
  15  *
  16  * These are generic functions for calculating Exponentially Weighted Moving
  17  * Averages (EWMA). We keep a structure with the EWMA parameters and a scaled
  18  * up internal representation of the average value to prevent rounding errors.
  19  * The factor for scaling up and the exponential weight (or decay rate) have to
  20  * be specified thru the init fuction. The structure should not be accessed
  21  * directly but only thru the helper functions.
  22  */
  23
  24 /**
  25  * ewma_init() - Initialize EWMA parameters
  26  * @avg: Average structure
  27  * @factor: Factor to use for the scaled up internal value. The maximum value
  28  *      of averages can be ULONG_MAX/(factor*weight). For performance reasons
  29  *      factor has to be a power of 2.
  30  * @weight: Exponential weight, or decay rate. This defines how fast the
  31  *      influence of older values decreases. For performance reasons weight has
  32  *      to be a power of 2.
  33  *
  34  * Initialize the EWMA parameters for a given struct ewma @avg.
  35  */
  36 void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
  37 {
  38         WARN_ON(!is_power_of_2(weight) || !is_power_of_2(factor));
  39
  40         avg->weight = ilog2(weight);
  41         avg->factor = ilog2(factor);
  42         avg->internal = 0;
  43 }
  44 EXPORT_SYMBOL(ewma_init);
  45
  46 /**
  47  * ewma_add() - Exponentially weighted moving average (EWMA)
  48  * @avg: Average structure
  49  * @val: Current value
  50  *
  51  * Add a sample to the average.
  52  */
  53 struct ewma *ewma_add(struct ewma *avg, unsigned long val)
  54 {
  55         avg->internal = avg->internal  ?
  56                 (((avg->internal << avg->weight) - avg->internal) +
  57                         (val << avg->factor)) >> avg->weight :
  58                 (val << avg->factor);
  59         return avg;
  60 }
  61 EXPORT_SYMBOL(ewma_add);