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/*
* Copyright (c) 2022 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 RTC_BASE_NUMERICS_SEQUENCE_NUMBER_UNWRAPPER_H_
#define RTC_BASE_NUMERICS_SEQUENCE_NUMBER_UNWRAPPER_H_
#include <stdint.h>
#include <limits>
#include "absl/types/optional.h"
#include "rtc_base/numerics/sequence_number_util.h"
namespace webrtc {
// 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;
absl::optional<T> last_value_;
};
using RtpTimestampUnwrapper = SeqNumUnwrapper<uint32_t>;
using RtpSequenceNumberUnwrapper = SeqNumUnwrapper<uint16_t>;
} // namespace webrtc
#endif // RTC_BASE_NUMERICS_SEQUENCE_NUMBER_UNWRAPPER_H_
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