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diff --git a/src/feature/stats/bw_array_st.h b/src/feature/stats/bw_array_st.h
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+/* Copyright (c) 2001 Matej Pfajfar.
+ * Copyright (c) 2001-2004, Roger Dingledine.
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2020, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * @file bw_array_st.h
+ * @brief Declaration for bw_array_t structure and related constants
+ **/
+
+#ifndef TOR_FEATURE_STATS_BW_ARRAY_ST_H
+#define TOR_FEATURE_STATS_BW_ARRAY_ST_H
+
+/** For how many seconds do we keep track of individual per-second bandwidth
+ * totals? */
+#define NUM_SECS_ROLLING_MEASURE 10
+/** How large are the intervals for which we track and report bandwidth use? */
+#define NUM_SECS_BW_SUM_INTERVAL (24*60*60)
+/** How far in the past do we remember and publish bandwidth use? */
+#define NUM_SECS_BW_SUM_IS_VALID (5*24*60*60)
+/** How many bandwidth usage intervals do we remember? (derived) */
+#define NUM_TOTALS (NUM_SECS_BW_SUM_IS_VALID/NUM_SECS_BW_SUM_INTERVAL)
+
+/** Structure to track bandwidth use, and remember the maxima for a given
+ * time period.
+ */
+struct bw_array_t {
+  /** Observation array: Total number of bytes transferred in each of the last
+   * NUM_SECS_ROLLING_MEASURE seconds. This is used as a circular array. */
+  uint64_t obs[NUM_SECS_ROLLING_MEASURE];
+  int cur_obs_idx; /**< Current position in obs. */
+  time_t cur_obs_time; /**< Time represented in obs[cur_obs_idx] */
+  uint64_t total_obs; /**< Total for all members of obs except
+                       * obs[cur_obs_idx] */
+  uint64_t max_total; /**< Largest value that total_obs has taken on in the
+                       * current period. */
+  uint64_t total_in_period; /**< Total bytes transferred in the current
+                             * period. */
+
+  /** When does the next period begin? */
+  time_t next_period;
+  /** Where in 'maxima' should the maximum bandwidth usage for the current
+   * period be stored? */
+  int next_max_idx;
+  /** How many values in maxima/totals have been set ever? */
+  int num_maxes_set;
+  /** Circular array of the maximum
+   * bandwidth-per-NUM_SECS_ROLLING_MEASURE usage for the last
+   * NUM_TOTALS periods */
+  uint64_t maxima[NUM_TOTALS];
+  /** Circular array of the total bandwidth usage for the last NUM_TOTALS
+   * periods */
+  uint64_t totals[NUM_TOTALS];
+};
+
+#endif /* !defined(TOR_FEATURE_STATS_BW_ARRAY_ST_H) */