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);