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/*
* lib/average.c
*
* This source code is licensed under the GNU General Public License,
* Version 2. See the file COPYING for more details.
*/

#include <linux/module.h>
#include <linux/average.h>
#include <linux/bug.h>
#include <linux/log2.h>

/**
* DOC: Exponentially Weighted Moving Average (EWMA)
*
* These are generic functions for calculating Exponentially Weighted Moving
* Averages (EWMA). We keep a structure with the EWMA parameters and a scaled
* up internal representation of the average value to prevent rounding errors.
* The factor for scaling up and the exponential weight (or decay rate) have to
* be specified thru the init fuction. The structure should not be accessed
* directly but only thru the helper functions.
*/

/**
* ewma_init() - Initialize EWMA parameters
* @avg: Average structure
* @factor: Factor to use for the scaled up internal value. The maximum value
* of averages can be ULONG_MAX/(factor*weight). For performance reasons
* factor has to be a power of 2.
* @weight: Exponential weight, or decay rate. This defines how fast the
* influence of older values decreases. For performance reasons weight has
* to be a power of 2.
*
* Initialize the EWMA parameters for a given struct ewma @avg.
*/
void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
{
WARN_ON(!is_power_of_2(weight) || !is_power_of_2(factor));

avg->weight = ilog2(weight);
avg->factor = ilog2(factor);
avg->internal = 0;
}
EXPORT_SYMBOL(ewma_init);

/**
* ewma_add() - Exponentially weighted moving average (EWMA)
* @avg: Average structure
* @val: Current value
*
* Add a sample to the average.
*/
struct ewma *ewma_add(struct ewma *avg, unsigned long val)
{
avg->internal = avg->internal ?
(((avg->internal << avg->weight) - avg->internal) +
(val << avg->factor)) >> avg->weight :
(val << avg->factor);
return avg;
}
EXPORT_SYMBOL(ewma_add);
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