[feat] add statistics module

src/common/sequence_number_unwrapper.h

@@ -0,0 +1,70 @@
+/*
+ * @Author: DI JUNKUN
+ * @Date: 2024-08-21
+ * Copyright (c) 2024 by DI JUNKUN, All Rights Reserved.
+ */
+
+#ifndef _SEQUENCE_NUMBER_UNWRAPPER_H_
+#define _SEQUENCE_NUMBER_UNWRAPPER_H_
+
+#include <stdint.h>
+
+#include <limits>
+#include <type_traits>
+
+// A sequence number unwrapper where the first unwrapped value equals the
+// first value being unwrapped.
+template <typename T, T M = 0>
+class SeqNumUnwrapper {
+  static_assert(
+      std::is_unsigned<T>::value &&
+          std::numeric_limits<T>::max() < std::numeric_limits<int64_t>::max(),
+      "Type unwrapped must be an unsigned integer smaller than int64_t.");
+
+ public:
+  // Unwraps `value` and updates the internal state of the unwrapper.
+  int64_t Unwrap(T value) {
+    if (!last_value_) {
+      last_unwrapped_ = {value};
+    } else {
+      last_unwrapped_ += Delta(*last_value_, value);
+    }
+
+    last_value_ = value;
+    return last_unwrapped_;
+  }
+
+  // Returns the `value` without updating the internal state of the unwrapper.
+  int64_t PeekUnwrap(T value) const {
+    if (!last_value_) {
+      return value;
+    }
+    return last_unwrapped_ + Delta(*last_value_, value);
+  }
+
+  // Resets the unwrapper to its initial state. Unwrapped sequence numbers will
+  // being at 0 after resetting.
+  void Reset() {
+    last_unwrapped_ = 0;
+    last_value_.reset();
+  }
+
+ private:
+  static int64_t Delta(T last_value, T new_value) {
+    constexpr int64_t kBackwardAdjustment =
+        M == 0 ? int64_t{std::numeric_limits<T>::max()} + 1 : M;
+    int64_t result = ForwardDiff<T, M>(last_value, new_value);
+    if (!AheadOrAt<T, M>(new_value, last_value)) {
+      result -= kBackwardAdjustment;
+    }
+    return result;
+  }
+
+  int64_t last_unwrapped_ = 0;
+  std::unique_ptr<T> last_value_;
+};
+
+using RtpTimestampUnwrapper = SeqNumUnwrapper<uint32_t>;
+using RtpSeqNumUnwrapper = SeqNumUnwrapper<uint16_t>;
+
+#endif