120 lines
3.8 KiB
C++
120 lines
3.8 KiB
C++
/*
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* Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef RTC_BASE_NUMERICS_SEQUENCE_NUMBER_UTIL_H_
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#define RTC_BASE_NUMERICS_SEQUENCE_NUMBER_UTIL_H_
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#include <stdint.h>
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#include <limits>
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#include <type_traits>
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#include "absl/types/optional.h"
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#include "rtc_base/checks.h"
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#include "rtc_base/numerics/mod_ops.h"
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namespace webrtc {
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// Test if the sequence number |a| is ahead or at sequence number |b|.
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//
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// If |M| is an even number and the two sequence numbers are at max distance
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// from each other, then the sequence number with the highest value is
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// considered to be ahead.
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template <typename T, T M>
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inline typename std::enable_if<(M > 0), bool>::type AheadOrAt(T a, T b) {
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static_assert(std::is_unsigned<T>::value,
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"Type must be an unsigned integer.");
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const T maxDist = M / 2;
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if (!(M & 1) && MinDiff<T, M>(a, b) == maxDist)
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return b < a;
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return ForwardDiff<T, M>(b, a) <= maxDist;
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}
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template <typename T, T M>
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inline typename std::enable_if<(M == 0), bool>::type AheadOrAt(T a, T b) {
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static_assert(std::is_unsigned<T>::value,
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"Type must be an unsigned integer.");
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const T maxDist = std::numeric_limits<T>::max() / 2 + T(1);
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if (a - b == maxDist)
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return b < a;
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return ForwardDiff(b, a) < maxDist;
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}
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template <typename T>
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inline bool AheadOrAt(T a, T b) {
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return AheadOrAt<T, 0>(a, b);
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}
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// Test if the sequence number |a| is ahead of sequence number |b|.
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//
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// If |M| is an even number and the two sequence numbers are at max distance
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// from each other, then the sequence number with the highest value is
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// considered to be ahead.
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template <typename T, T M = 0>
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inline bool AheadOf(T a, T b) {
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static_assert(std::is_unsigned<T>::value,
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"Type must be an unsigned integer.");
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return a != b && AheadOrAt<T, M>(a, b);
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}
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// Comparator used to compare sequence numbers in a continuous fashion.
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//
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// WARNING! If used to sort sequence numbers of length M then the interval
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// covered by the sequence numbers may not be larger than floor(M/2).
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template <typename T, T M = 0>
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struct AscendingSeqNumComp {
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bool operator()(T a, T b) const { return AheadOf<T, M>(a, b); }
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};
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// Comparator used to compare sequence numbers in a continuous fashion.
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//
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// WARNING! If used to sort sequence numbers of length M then the interval
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// covered by the sequence numbers may not be larger than floor(M/2).
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template <typename T, T M = 0>
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struct DescendingSeqNumComp {
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bool operator()(T a, T b) const { return AheadOf<T, M>(b, a); }
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};
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// A sequence number unwrapper where the first unwrapped value equals the
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// first value being unwrapped.
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template <typename T, T M = 0>
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class SeqNumUnwrapper {
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static_assert(
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std::is_unsigned<T>::value &&
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std::numeric_limits<T>::max() < std::numeric_limits<int64_t>::max(),
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"Type unwrapped must be an unsigned integer smaller than int64_t.");
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public:
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int64_t Unwrap(T value) {
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if (!last_value_) {
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last_unwrapped_ = {value};
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} else {
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last_unwrapped_ += ForwardDiff<T, M>(*last_value_, value);
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if (!AheadOrAt<T, M>(value, *last_value_)) {
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constexpr int64_t kBackwardAdjustment =
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M == 0 ? int64_t{std::numeric_limits<T>::max()} + 1 : M;
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last_unwrapped_ -= kBackwardAdjustment;
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}
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}
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last_value_ = value;
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return last_unwrapped_;
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}
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private:
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int64_t last_unwrapped_ = 0;
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absl::optional<T> last_value_;
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};
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} // namespace webrtc
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#endif // RTC_BASE_NUMERICS_SEQUENCE_NUMBER_UTIL_H_
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