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