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+/*
+ * 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>
+
+/**
+ * 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).
+ * @weight: Exponential weight, or decay rate. This defines how fast the
+ * influence of older values decreases. Has to be bigger than 1.
+ *
+ * Initialize the EWMA parameters for a given struct ewma @avg.
+ */
+void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
+{
+ WARN_ON(weight <= 1 || factor == 0);
+ avg->internal = 0;
+ avg->weight = weight;
+ avg->factor = factor;
+}
+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 - 1)) +
+ (val * avg->factor)) / avg->weight) :
+ (val * avg->factor);
+ return avg;
+}
+EXPORT_SYMBOL(ewma_add);
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