feat: add rolling counter utility

2026-10-18 13:41:22 +08:00 · 2024-02-01 22:22:30 +08:00
parent 50ee1d759f
commit c81d40d351
1 changed files with 106 additions and 0 deletions
@@ -0,0 +1,106 @@
+/**
+ * NEURON IIoT System for Industry 4.0
+ * Copyright (C) 2020-2024 EMQ Technologies Co., Ltd All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ **/
+#ifndef NEURON_UTILS_ROLLING_COUNTER_H
+#define NEURON_UTILS_ROLLING_COUNTER_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+/** Rolling counter.
+ *
+ * This counter is for counting values within some latest time span, like
+ * network bytes sent within the last 5 seconds etc.
+ */
+typedef struct {
+    uint64_t val;      // accumulator
+    uint64_t ts;       // head time stamp in milliseconds
+    uint32_t res : 22; // time resolution in milliseconds
+    uint32_t hd : 5;   // head position
+    uint32_t n : 5;    // number of counters
+    uint32_t counts[]; // bins of counters
+} neu_rolling_counter_t;
+
+/** Create rolling counter.
+ *
+ * @param   span   time span in milliseconds
+ */
+static inline neu_rolling_counter_t *neu_rolling_counter_new(unsigned span)
+{
+    unsigned n = span <= 6000 ? 4 : span <= 32000 ? 8 : span <= 64000 ? 16 : 32;
+    assert(span / n < (1 << 22)); // should not overflow ti
+
+    neu_rolling_counter_t *counter = (neu_rolling_counter_t *) calloc(
+        1, sizeof(*counter) + sizeof(counter->counts[0]) * n);
+    if (counter) {
+        counter->res = span / n;
+        counter->n   = n;
+    }
+    return counter;
+}
+
+/** Destructs the rolling counter.
+ */
+static inline void neu_rolling_counter_free(neu_rolling_counter_t *counter)
+{
+    if (counter) {
+        free(counter);
+    }
+}
+
+/** Increment the rolling counter and return the value;
+ *
+ * @param   ts    time stamp in milliseconds, should be monotonic
+ * @param   dt    delta value to increment by
+ */
+static inline uint64_t neu_rolling_counter_inc(neu_rolling_counter_t *counter,
+                                               uint64_t ts, unsigned dt)
+{
+    uint64_t step = (ts - counter->ts) / counter->res;
+    for (unsigned i = 0; i < step && i < counter->n; ++i) {
+        counter->hd = (counter->hd + 1) & (counter->n - 1);
+        counter->val -= counter->counts[counter->hd];
+        counter->counts[counter->hd] = 0;
+    }
+    counter->val += dt;
+    counter->counts[counter->hd] += dt;
+    counter->ts += step * counter->res;
+    return counter->val;
+}
+
+/** Return the counter value.
+ *
+ * NOTE: may return stale value if the counter is not updated frequent enough.
+ */
+static inline uint64_t neu_rolling_counter_value(neu_rolling_counter_t *counter)
+{
+    return counter->val;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif