/*-
* SPDX-License-Identifier: BSD-2-Clause
*
* Copyright (c) 2020-2021 The FreeBSD Foundation
*
* This software was developed by Björn Zeeb under sponsorship from
* the FreeBSD Foundation.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef _LINUXKPI_LINUX_AVERAGE_H
#define _LINUXKPI_LINUX_AVERAGE_H
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/types.h>
#include <linux/log2.h>
/* EWMA stands for Exponentially Weighted Moving Average. */
/*
* Z_t = d X_t + (1 - d) * Z_(t-1); 0 < d <= 1, t >= 1; Roberts (1959).
* t : observation number in time.
* d : weight for current observation.
* Xt : observations over time.
* Zt : EWMA value after observation t.
*
* wmba_*_read seems to return up-to [u]long values; have to deal with 32/64bit.
* According to the ath5k.h change log this seems to be a fix-(_p)recision impl.
* assert 2/4 bits for frac.
* Also all (_d) values seem to be pow2 which simplifies maths (shift by
* d = ilog2(_d) instead of doing division (d = 1/_d)). Keep it this way until
* we hit the CTASSERT.
*/
#define DECLARE_EWMA(_name, _p, _d) \
\
CTASSERT((sizeof(unsigned long) <= 4) ? (_p < 30) : (_p < 60)); \
CTASSERT(_d > 0 && powerof2(_d)); \
\
struct ewma_ ## _name { \
unsigned long zt; \
}; \
\
static __inline void \
ewma_ ## _name ## _init(struct ewma_ ## _name *ewma) \
{ \
/* No target (no historical data). */ \
ewma->zt = 0; \
} \
\
static __inline void \
ewma_ ## _name ## _add(struct ewma_ ## _name *ewma, unsigned long x) \
{ \
unsigned long ztm1 = ewma->zt; /* Z_(t-1). */ \
int d = ilog2(_d); \
\
if (ewma->zt == 0) \
ewma->zt = x << (_p); \
else \
ewma->zt = ((x << (_p)) >> d) + \
(((ztm1 << d) - ztm1) >> d); \
} \
\
static __inline unsigned long \
ewma_ ## _name ## _read(struct ewma_ ## _name *ewma) \
{ \
return (ewma->zt >> (_p)); \
} \
#endif /* _LINUXKPI_LINUX_AVERAGE_H */
