Merge branch 'master' into tk71

[mv-sheeva.git] / lib / average.c

diff --git a/lib/average.c b/lib/average.c
new file mode 100644 (file)
index 0000000..5576c28
--- /dev/null
+++ b/lib/average.c
@@ -0,0 +1,61 @@
+/*
+ * lib/average.c
+ *
+ * This source code is licensed under the GNU General Public License,
+ * Version 2.  See the file COPYING for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/average.h>
+#include <linux/bug.h>
+#include <linux/log2.h>
+
+/**
+ * DOC: Exponentially Weighted Moving Average (EWMA)
+ *
+ * These are generic functions for calculating Exponentially Weighted Moving
+ * Averages (EWMA). We keep a structure with the EWMA parameters and a scaled
+ * up internal representation of the average value to prevent rounding errors.
+ * The factor for scaling up and the exponential weight (or decay rate) have to
+ * be specified thru the init fuction. The structure should not be accessed
+ * directly but only thru the helper functions.
+ */
+
+/**
+ * ewma_init() - Initialize EWMA parameters
+ * @avg: Average structure
+ * @factor: Factor to use for the scaled up internal value. The maximum value
+ *     of averages can be ULONG_MAX/(factor*weight). For performance reasons
+ *     factor has to be a power of 2.
+ * @weight: Exponential weight, or decay rate. This defines how fast the
+ *     influence of older values decreases. For performance reasons weight has
+ *     to be a power of 2.
+ *
+ * Initialize the EWMA parameters for a given struct ewma @avg.
+ */
+void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
+{
+       WARN_ON(!is_power_of_2(weight) || !is_power_of_2(factor));
+
+       avg->weight = ilog2(weight);
+       avg->factor = ilog2(factor);
+       avg->internal = 0;
+}
+EXPORT_SYMBOL(ewma_init);
+
+/**
+ * ewma_add() - Exponentially weighted moving average (EWMA)
+ * @avg: Average structure
+ * @val: Current value
+ *
+ * Add a sample to the average.
+ */
+struct ewma *ewma_add(struct ewma *avg, unsigned long val)
+{
+       avg->internal = avg->internal  ?
+               (((avg->internal << avg->weight) - avg->internal) +
+                       (val << avg->factor)) >> avg->weight :
+               (val << avg->factor);
+       return avg;
+}
+EXPORT_SYMBOL(ewma_add);