lib: Improve EWMA efficiency by using bitshifts

#ifndef _LINUX_AVERAGE_H

#define _LINUX_AVERAGE_H

#include <linux/kernel.h>

/* Exponentially weighted moving average (EWMA) */

/* For more documentation see lib/average.c */

 */

static inline unsigned long ewma_read(const struct ewma *avg)

{

	return DIV_ROUND_CLOSEST(avg->internal, avg->factor);

	return avg->internal >> avg->factor;

}

#endif /* _LINUX_AVERAGE_H */

#include <linux/module.h>

#include <linux/average.h>

#include <linux/bug.h>

#include <linux/log2.h>

/**

 * DOC: Exponentially Weighted Moving Average (EWMA)

 * 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).

 *	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. Has to be bigger than 1.

 *	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(weight <= 1 || factor == 0);

	WARN_ON(!is_power_of_2(weight) || !is_power_of_2(factor));

	avg->weight = ilog2(weight);

	avg->factor = ilog2(factor);

	avg->internal = 0;

	avg->weight = weight;

	avg->factor = factor;

}

EXPORT_SYMBOL(ewma_init);

struct ewma *ewma_add(struct ewma *avg, unsigned long val)

{

	avg->internal = avg->internal  ?

		(((avg->internal * (avg->weight - 1)) +

			(val * avg->factor)) / avg->weight) :

		(val * avg->factor);

		(((avg->internal << avg->weight) - avg->internal) +

			(val << avg->factor)) >> avg->weight :

		(val << avg->factor);

	return avg;

}

EXPORT_SYMBOL(ewma_add);