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