[mirror_ubuntu-bionic-kernel.git] / lib / average.c

/*
 * 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);
Commit	Line	Data
c5485a7e BR	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>
af556884	11	#include <linux/log2.h>
c5485a7e BR	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
af556884 BR	28	* of averages can be ULONG_MAX/(factor*weight). For performance reasons
af556884 BR	29	* factor has to be a power of 2.
c5485a7e	30	* @weight: Exponential weight, or decay rate. This defines how fast the
af556884 BR	31	* influence of older values decreases. For performance reasons weight has
af556884 BR	32	* to be a power of 2.
c5485a7e BR	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	{
af556884 BR	38	WARN_ON(!is_power_of_2(weight) \|\| !is_power_of_2(factor));
	39
	40	avg->weight = ilog2(weight);
	41	avg->factor = ilog2(factor);
c5485a7e	42	avg->internal = 0;
c5485a7e BR	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 ?
af556884 BR	56	(((avg->internal << avg->weight) - avg->internal) +
	57	(val << avg->factor)) >> avg->weight :
	58	(val << avg->factor);
c5485a7e BR	59	return avg;
	60	}
	61	EXPORT_SYMBOL(ewma_add);