Repo created

TMessagesProj/jni/voip/webrtc/net/dcsctp/common/sequence_numbers.h

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+/*
+ *  Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#ifndef NET_DCSCTP_COMMON_SEQUENCE_NUMBERS_H_
+#define NET_DCSCTP_COMMON_SEQUENCE_NUMBERS_H_
+
+#include <cstdint>
+#include <limits>
+#include <utility>
+
+#include "net/dcsctp/common/internal_types.h"
+#include "rtc_base/numerics/sequence_number_unwrapper.h"
+
+namespace dcsctp {
+
+// UnwrappedSequenceNumber handles wrapping sequence numbers and unwraps them to
+// an int64_t value space, to allow wrapped sequence numbers to be easily
+// compared for ordering.
+//
+// Sequence numbers are expected to be monotonically increasing, but they do not
+// need to be unwrapped in order, as long as the difference to the previous one
+// is not larger than half the range of the wrapped sequence number.
+//
+// The WrappedType must be a webrtc::StrongAlias type.
+template <typename WrappedType>
+class UnwrappedSequenceNumber {
+ public:
+  static_assert(
+      !std::numeric_limits<typename WrappedType::UnderlyingType>::is_signed,
+      "The wrapped type must be unsigned");
+  static_assert(
+      std::numeric_limits<typename WrappedType::UnderlyingType>::max() <
+          std::numeric_limits<int64_t>::max(),
+      "The wrapped type must be less than the int64_t value space");
+
+  // The unwrapper is a sort of factory and converts wrapped sequence numbers to
+  // unwrapped ones.
+  class Unwrapper {
+   public:
+    Unwrapper() = default;
+    Unwrapper(const Unwrapper&) = default;
+    Unwrapper& operator=(const Unwrapper&) = default;
+
+    // Given a wrapped `value`, and with knowledge of its current last seen
+    // largest number, will return a value that can be compared using normal
+    // operators, such as less-than, greater-than etc.
+    //
+    // This will also update the Unwrapper's state, to track the last seen
+    // largest value.
+    UnwrappedSequenceNumber<WrappedType> Unwrap(WrappedType value) {
+      return UnwrappedSequenceNumber<WrappedType>(unwrapper_.Unwrap(*value));
+    }
+
+    // Similar to `Unwrap`, but will not update the Unwrappers's internal state.
+    UnwrappedSequenceNumber<WrappedType> PeekUnwrap(WrappedType value) const {
+      return UnwrappedSequenceNumber<WrappedType>(
+          unwrapper_.PeekUnwrap(*value));
+    }
+
+    // Resets the Unwrapper to its pristine state. Used when a sequence number
+    // is to be reset to zero.
+    void Reset() { unwrapper_.Reset(); }
+
+   private:
+    webrtc::SeqNumUnwrapper<typename WrappedType::UnderlyingType> unwrapper_;
+  };
+
+  // Returns the wrapped value this type represents.
+  WrappedType Wrap() const {
+    return static_cast<WrappedType>(value_ % kValueLimit);
+  }
+
+  template <typename H>
+  friend H AbslHashValue(H state,
+                         const UnwrappedSequenceNumber<WrappedType>& hash) {
+    return H::combine(std::move(state), hash.value_);
+  }
+
+  bool operator==(const UnwrappedSequenceNumber<WrappedType>& other) const {
+    return value_ == other.value_;
+  }
+  bool operator!=(const UnwrappedSequenceNumber<WrappedType>& other) const {
+    return value_ != other.value_;
+  }
+  bool operator<(const UnwrappedSequenceNumber<WrappedType>& other) const {
+    return value_ < other.value_;
+  }
+  bool operator>(const UnwrappedSequenceNumber<WrappedType>& other) const {
+    return value_ > other.value_;
+  }
+  bool operator>=(const UnwrappedSequenceNumber<WrappedType>& other) const {
+    return value_ >= other.value_;
+  }
+  bool operator<=(const UnwrappedSequenceNumber<WrappedType>& other) const {
+    return value_ <= other.value_;
+  }
+
+  // Const accessors for underlying value.
+  constexpr const int64_t* operator->() const { return &value_; }
+  constexpr const int64_t& operator*() const& { return value_; }
+  constexpr const int64_t&& operator*() const&& { return std::move(value_); }
+  constexpr const int64_t& value() const& { return value_; }
+  constexpr const int64_t&& value() const&& { return std::move(value_); }
+  constexpr explicit operator const int64_t&() const& { return value_; }
+
+  // Increments the value.
+  void Increment() { ++value_; }
+
+  // Returns the next value relative to this sequence number.
+  UnwrappedSequenceNumber<WrappedType> next_value() const {
+    return UnwrappedSequenceNumber<WrappedType>(value_ + 1);
+  }
+
+  // Returns a new sequence number based on `value`, and adding `delta` (which
+  // may be negative).
+  static UnwrappedSequenceNumber<WrappedType> AddTo(
+      UnwrappedSequenceNumber<WrappedType> value,
+      int delta) {
+    return UnwrappedSequenceNumber<WrappedType>(value.value_ + delta);
+  }
+
+  // Returns the absolute difference between `lhs` and `rhs`.
+  static typename WrappedType::UnderlyingType Difference(
+      UnwrappedSequenceNumber<WrappedType> lhs,
+      UnwrappedSequenceNumber<WrappedType> rhs) {
+    return (lhs.value_ > rhs.value_) ? (lhs.value_ - rhs.value_)
+                                     : (rhs.value_ - lhs.value_);
+  }
+
+ private:
+  explicit UnwrappedSequenceNumber(int64_t value) : value_(value) {}
+  static constexpr int64_t kValueLimit =
+      static_cast<int64_t>(1)
+      << std::numeric_limits<typename WrappedType::UnderlyingType>::digits;
+
+  int64_t value_;
+};
+
+// Unwrapped Transmission Sequence Numbers (TSN)
+using UnwrappedTSN = UnwrappedSequenceNumber<TSN>;
+
+// Unwrapped Stream Sequence Numbers (SSN)
+using UnwrappedSSN = UnwrappedSequenceNumber<SSN>;
+
+// Unwrapped Message Identifier (MID)
+using UnwrappedMID = UnwrappedSequenceNumber<MID>;
+
+}  // namespace dcsctp
+
+#endif  // NET_DCSCTP_COMMON_SEQUENCE_NUMBERS_H_