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/*
* Copyright (c) 2017 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 MODULES_INCLUDE_MODULE_COMMON_TYPES_PUBLIC_H_
#define MODULES_INCLUDE_MODULE_COMMON_TYPES_PUBLIC_H_
#include <limits>
#include "absl/types/optional.h"
namespace webrtc {
template <typename U>
inline bool IsNewer(U value, U prev_value) {
static_assert(!std::numeric_limits<U>::is_signed, "U must be unsigned");
// kBreakpoint is the half-way mark for the type U. For instance, for a
// uint16_t it will be 0x8000, and for a uint32_t, it will be 0x8000000.
constexpr U kBreakpoint = (std::numeric_limits<U>::max() >> 1) + 1;
// Distinguish between elements that are exactly kBreakpoint apart.
// If t1>t2 and |t1-t2| = kBreakpoint: IsNewer(t1,t2)=true,
// IsNewer(t2,t1)=false
// rather than having IsNewer(t1,t2) = IsNewer(t2,t1) = false.
if (value - prev_value == kBreakpoint) {
return value > prev_value;
}
return value != prev_value &&
static_cast<U>(value - prev_value) < kBreakpoint;
}
// Utility class to unwrap a number to a larger type. The numbers will never be
// unwrapped to a negative value.
template <typename U>
class Unwrapper {
static_assert(!std::numeric_limits<U>::is_signed, "U must be unsigned");
static_assert(std::numeric_limits<U>::max() <=
std::numeric_limits<uint32_t>::max(),
"U must not be wider than 32 bits");
public:
// Get the unwrapped value, but don't update the internal state.
int64_t UnwrapWithoutUpdate(U value) const {
if (!last_value_)
return value;
constexpr int64_t kMaxPlusOne =
static_cast<int64_t>(std::numeric_limits<U>::max()) + 1;
U cropped_last = static_cast<U>(*last_value_);
int64_t delta = value - cropped_last;
if (IsNewer(value, cropped_last)) {
if (delta < 0)
delta += kMaxPlusOne; // Wrap forwards.
} else if (delta > 0 && (*last_value_ + delta - kMaxPlusOne) >= 0) {
// If value is older but delta is positive, this is a backwards
// wrap-around. However, don't wrap backwards past 0 (unwrapped).
delta -= kMaxPlusOne;
}
return *last_value_ + delta;
}
// Only update the internal state to the specified last (unwrapped) value.
void UpdateLast(int64_t last_value) { last_value_ = last_value; }
// Unwrap the value and update the internal state.
int64_t Unwrap(U value) {
int64_t unwrapped = UnwrapWithoutUpdate(value);
UpdateLast(unwrapped);
return unwrapped;
}
private:
absl::optional<int64_t> last_value_;
};
using SequenceNumberUnwrapper = Unwrapper<uint16_t>;
using TimestampUnwrapper = Unwrapper<uint32_t>;
// NB: Doesn't fulfill strict weak ordering requirements.
// Mustn't be used as std::map Compare function.
inline bool IsNewerSequenceNumber(uint16_t sequence_number,
uint16_t prev_sequence_number) {
return IsNewer(sequence_number, prev_sequence_number);
}
// NB: Doesn't fulfill strict weak ordering requirements.
// Mustn't be used as std::map Compare function.
inline bool IsNewerTimestamp(uint32_t timestamp, uint32_t prev_timestamp) {
return IsNewer(timestamp, prev_timestamp);
}
inline uint16_t LatestSequenceNumber(uint16_t sequence_number1,
uint16_t sequence_number2) {
return IsNewerSequenceNumber(sequence_number1, sequence_number2)
? sequence_number1
: sequence_number2;
}
inline uint32_t LatestTimestamp(uint32_t timestamp1, uint32_t timestamp2) {
return IsNewerTimestamp(timestamp1, timestamp2) ? timestamp1 : timestamp2;
}
} // namespace webrtc
#endif // MODULES_INCLUDE_MODULE_COMMON_TYPES_PUBLIC_H_