1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_AVERAGE_H
3#define _LINUX_AVERAGE_H
4
5#include <linux/bug.h>
6#include <linux/compiler.h>
7#include <linux/log2.h>
8
9/*
10 * Exponentially weighted moving average (EWMA)
11 *
12 * This implements a fixed-precision EWMA algorithm, with both the
13 * precision and fall-off coefficient determined at compile-time
14 * and built into the generated helper funtions.
15 *
16 * The first argument to the macro is the name that will be used
17 * for the struct and helper functions.
18 *
19 * The second argument, the precision, expresses how many bits are
20 * used for the fractional part of the fixed-precision values.
21 *
22 * The third argument, the weight reciprocal, determines how the
23 * new values will be weighed vs. the old state, new values will
24 * get weight 1/weight_rcp and old values 1-1/weight_rcp. Note
25 * that this parameter must be a power of two for efficiency.
26 */
27
28#define DECLARE_EWMA(name, _precision, _weight_rcp)			\
29	struct ewma_##name {						\
30		unsigned long internal;					\
31	};								\
32	static inline void ewma_##name##_init(struct ewma_##name *e)	\
33	{								\
34		BUILD_BUG_ON(!__builtin_constant_p(_precision));	\
35		BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp));	\
36		/*							\
37		 * Even if you want to feed it just 0/1 you should have	\
38		 * some bits for the non-fractional part...		\
39		 */							\
40		BUILD_BUG_ON((_precision) > 30);			\
41		BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp);		\
42		e->internal = 0;					\
43	}								\
44	static inline unsigned long					\
45	ewma_##name##_read(struct ewma_##name *e)			\
46	{								\
47		BUILD_BUG_ON(!__builtin_constant_p(_precision));	\
48		BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp));	\
49		BUILD_BUG_ON((_precision) > 30);			\
50		BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp);		\
51		return e->internal >> (_precision);			\
52	}								\
53	static inline void ewma_##name##_add(struct ewma_##name *e,	\
54					     unsigned long val)		\
55	{								\
56		unsigned long internal = READ_ONCE(e->internal);	\
57		unsigned long weight_rcp = ilog2(_weight_rcp);		\
58		unsigned long precision = _precision;			\
59									\
60		BUILD_BUG_ON(!__builtin_constant_p(_precision));	\
61		BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp));	\
62		BUILD_BUG_ON((_precision) > 30);			\
63		BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp);		\
64									\
65		WRITE_ONCE(e->internal, internal ?			\
66			(((internal << weight_rcp) - internal) +	\
67				(val << precision)) >> weight_rcp :	\
68			(val << precision));				\
69	}
70
71#endif /* _LINUX_AVERAGE_H */
72