Root/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/export.h>
9#include <linux/average.h>
10#include <linux/kernel.h>
11#include <linux/bug.h>
12#include <linux/log2.h>
13
14/**
15 * DOC: Exponentially Weighted Moving Average (EWMA)
16 *
17 * These are generic functions for calculating Exponentially Weighted Moving
18 * Averages (EWMA). We keep a structure with the EWMA parameters and a scaled
19 * up internal representation of the average value to prevent rounding errors.
20 * The factor for scaling up and the exponential weight (or decay rate) have to
21 * be specified thru the init fuction. The structure should not be accessed
22 * directly but only thru the helper functions.
23 */
24
25/**
26 * ewma_init() - Initialize EWMA parameters
27 * @avg: Average structure
28 * @factor: Factor to use for the scaled up internal value. The maximum value
29 * of averages can be ULONG_MAX/(factor*weight). For performance reasons
30 * factor has to be a power of 2.
31 * @weight: Exponential weight, or decay rate. This defines how fast the
32 * influence of older values decreases. For performance reasons weight has
33 * to be a power of 2.
34 *
35 * Initialize the EWMA parameters for a given struct ewma @avg.
36 */
37void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
38{
39    WARN_ON(!is_power_of_2(weight) || !is_power_of_2(factor));
40
41    avg->weight = ilog2(weight);
42    avg->factor = ilog2(factor);
43    avg->internal = 0;
44}
45EXPORT_SYMBOL(ewma_init);
46
47/**
48 * ewma_add() - Exponentially weighted moving average (EWMA)
49 * @avg: Average structure
50 * @val: Current value
51 *
52 * Add a sample to the average.
53 */
54struct ewma *ewma_add(struct ewma *avg, unsigned long val)
55{
56    avg->internal = avg->internal ?
57        (((avg->internal << avg->weight) - avg->internal) +
58            (val << avg->factor)) >> avg->weight :
59        (val << avg->factor);
60    return avg;
61}
62EXPORT_SYMBOL(ewma_add);
63

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