average: change to declare precision, not factor

[karo-tx-linux.git] / include / linux / average.h

diff --git a/include/linux/average.h b/include/linux/average.h
index d04aa58280ded5694bbde3638ec602269635a988..7ddaf340d2ac982bf0e7a3a209017c071e2fa42d 100644 (file)
--- a/include/linux/average.h
+++ b/include/linux/average.h
@@ -1,45 +1,66 @@
 #ifndef _LINUX_AVERAGE_H
 #define _LINUX_AVERAGE_H
 
-/* Exponentially weighted moving average (EWMA) */
+/*
+ * Exponentially weighted moving average (EWMA)
+ *
+ * This implements a fixed-precision EWMA algorithm, with both the
+ * precision and fall-off coefficient determined at compile-time
+ * and built into the generated helper funtions.
+ *
+ * The first argument to the macro is the name that will be used
+ * for the struct and helper functions.
+ *
+ * The second argument, the precision, expresses how many bits are
+ * used for the fractional part of the fixed-precision values.
+ *
+ * The third argument, the weight reciprocal, determines how the
+ * new values will be weighed vs. the old state, new values will
+ * get weight 1/weight_rcp and old values 1-1/weight_rcp. Note
+ * that this parameter must be a power of two for efficiency.
+ */
 
-#define DECLARE_EWMA(name, _factor, _weight)                           \
+#define DECLARE_EWMA(name, _precision, _weight_rcp)                    \
        struct ewma_##name {                                            \
                unsigned long internal;                                 \
        };                                                              \
        static inline void ewma_##name##_init(struct ewma_##name *e)    \
        {                                                               \
-               BUILD_BUG_ON(!__builtin_constant_p(_factor));           \
-               BUILD_BUG_ON(!__builtin_constant_p(_weight));           \
-               BUILD_BUG_ON_NOT_POWER_OF_2(_factor);                   \
-               BUILD_BUG_ON_NOT_POWER_OF_2(_weight);                   \
+               BUILD_BUG_ON(!__builtin_constant_p(_precision));        \
+               BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp));       \
+               /*                                                      \
+                * Even if you want to feed it just 0/1 you should have \
+                * some bits for the non-fractional part...             \
+                */                                                     \
+               BUILD_BUG_ON((_precision) > 30);                        \
+               BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp);               \
                e->internal = 0;                                        \
        }                                                               \
        static inline unsigned long                                     \
        ewma_##name##_read(struct ewma_##name *e)                       \
        {                                                               \
-               BUILD_BUG_ON(!__builtin_constant_p(_factor));           \
-               BUILD_BUG_ON(!__builtin_constant_p(_weight));           \
-               BUILD_BUG_ON_NOT_POWER_OF_2(_factor);                   \
-               BUILD_BUG_ON_NOT_POWER_OF_2(_weight);                   \
-               return e->internal >> ilog2(_factor);                   \
+               BUILD_BUG_ON(!__builtin_constant_p(_precision));        \
+               BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp));       \
+               BUILD_BUG_ON((_precision) > 30);                        \
+               BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp);               \
+               return e->internal >> (_precision);                     \
        }                                                               \
        static inline void ewma_##name##_add(struct ewma_##name *e,     \
                                             unsigned long val)         \
        {                                                               \
                unsigned long internal = ACCESS_ONCE(e->internal);      \
-               unsigned long weight = ilog2(_weight);                  \
-               unsigned long factor = ilog2(_factor);                  \
+               unsigned long weight_rcp = ilog2(_weight_rcp);          \
+               unsigned long precision = _precision;                   \
                                                                        \
-               BUILD_BUG_ON(!__builtin_constant_p(_factor));           \
-               BUILD_BUG_ON(!__builtin_constant_p(_weight));           \
-               BUILD_BUG_ON_NOT_POWER_OF_2(_factor);                   \
-               BUILD_BUG_ON_NOT_POWER_OF_2(_weight);                   \
+               BUILD_BUG_ON(!__builtin_constant_p(_precision));        \
+               BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp));       \
+               BUILD_BUG_ON((_precision) > 30);                        \
+               BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp);               \
                                                                        \
                ACCESS_ONCE(e->internal) = internal ?                   \
-                       (((internal << weight) - internal) +            \
-                               (val << factor)) >> weight :            \
-                       (val << factor);                                \
+                       (((internal << weight_rcp) - internal) +        \
+                               (val << precision)) >> weight_rcp :     \
+                       (val << precision);                             \
        }
 
 #endif /* _LINUX_AVERAGE_H */