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c5485a7e BR |
1 | #ifndef _LINUX_AVERAGE_H |
2 | #define _LINUX_AVERAGE_H | |
3 | ||
eb1e011a JB |
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 | */ | |
c5485a7e | 22 | |
eb1e011a | 23 | #define DECLARE_EWMA(name, _precision, _weight_rcp) \ |
2377799c JB |
24 | struct ewma_##name { \ |
25 | unsigned long internal; \ | |
26 | }; \ | |
27 | static inline void ewma_##name##_init(struct ewma_##name *e) \ | |
28 | { \ | |
eb1e011a JB |
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); \ | |
2377799c JB |
37 | e->internal = 0; \ |
38 | } \ | |
39 | static inline unsigned long \ | |
40 | ewma_##name##_read(struct ewma_##name *e) \ | |
41 | { \ | |
eb1e011a JB |
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); \ | |
2377799c JB |
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); \ | |
eb1e011a JB |
52 | unsigned long weight_rcp = ilog2(_weight_rcp); \ |
53 | unsigned long precision = _precision; \ | |
2377799c | 54 | \ |
eb1e011a JB |
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); \ | |
2377799c JB |
59 | \ |
60 | ACCESS_ONCE(e->internal) = internal ? \ | |
eb1e011a JB |
61 | (((internal << weight_rcp) - internal) + \ |
62 | (val << precision)) >> weight_rcp : \ | |
63 | (val << precision); \ | |
2377799c JB |
64 | } |
65 | ||
c5485a7e | 66 | #endif /* _LINUX_AVERAGE_H */ |