#ifndef _LINUX_AVERAGE_H
#define _LINUX_AVERAGE_H

/* Exponentially weighted moving average (EWMA) */

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

struct ewma {
	unsigned long internal;
	unsigned long factor;
	unsigned long weight;
};

/*
 * Exponentially weighted moving average (EWMA)
 *
 * This implements a fixed-precision EWMA algorithm, with both the
 * precision and fall-off coefficient determined at compile-time
 * and built into the generated helper funtions.
 *
 * The first argument to the macro is the name that will be used
 * for the struct and helper functions.
 *
 * The second argument, the precision, expresses how many bits are
 * used for the fractional part of the fixed-precision values.
 *
 * The third argument, the weight reciprocal, determines how the
 * new values will be weighed vs. the old state, new values will
 * get weight 1/weight_rcp and old values 1-1/weight_rcp. Note
 * that this parameter must be a power of two for efficiency.
 */

#define DECLARE_EWMA(name, _precision, _weight_rcp)			\
	struct ewma_##name {						\
		unsigned long internal;					\
	};								\
	static inline void ewma_##name##_init(struct ewma_##name *e)	\
	{								\
		e->internal = 0;					\
	}								\
	static inline unsigned long					\
	ewma_##name##_read(struct ewma_##name *e)			\
	{								\
		return e->internal >> (_precision);			\
	}								\
	static inline void ewma_##name##_add(struct ewma_##name *e,	\
					     unsigned long val)		\
	{								\
		unsigned long internal = READ_ONCE(e->internal);	\
		unsigned long weight_rcp = ilog2(_weight_rcp);		\
		unsigned long precision = _precision;			\
		WRITE_ONCE(e->internal, internal ?			\
			(((internal << weight_rcp) - internal) +	\
				(val << precision)) >> weight_rcp :	\
			(val << precision));				\
	}


extern void ewma_init(struct ewma *avg, unsigned long factor,
		      unsigned long weight);

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

/**
 * ewma_read() - Get average value
 * @avg: Average structure
 *
 * Returns the average value held in @avg.
 */
static inline unsigned long ewma_read(const struct ewma *avg)
{
	return avg->internal >> avg->factor;
}

#endif /* _LINUX_AVERAGE_H */