linux/lib/average.c
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   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 */
  36void 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}
  44EXPORT_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 */
  53struct 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}
  61EXPORT_SYMBOL(ewma_add);
  62
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