1 /*
2 * Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
11 #ifndef MODULES_INCLUDE_MODULE_COMMON_TYPES_PUBLIC_H_
12 #define MODULES_INCLUDE_MODULE_COMMON_TYPES_PUBLIC_H_
13
14 #include <limits>
15
16 #include "api/optional.h"
17 #include "typedefs.h" // NOLINT(build/include)
18
19 namespace webrtc {
20
21 template <typename U>
IsNewer(U value,U prev_value)22 inline bool IsNewer(U value, U prev_value) {
23 static_assert(!std::numeric_limits<U>::is_signed, "U must be unsigned");
24 // kBreakpoint is the half-way mark for the type U. For instance, for a
25 // uint16_t it will be 0x8000, and for a uint32_t, it will be 0x8000000.
26 constexpr U kBreakpoint = (std::numeric_limits<U>::max() >> 1) + 1;
27 // Distinguish between elements that are exactly kBreakpoint apart.
28 // If t1>t2 and |t1-t2| = kBreakpoint: IsNewer(t1,t2)=true,
29 // IsNewer(t2,t1)=false
30 // rather than having IsNewer(t1,t2) = IsNewer(t2,t1) = false.
31 if (value - prev_value == kBreakpoint) {
32 return value > prev_value;
33 }
34 return value != prev_value &&
35 static_cast<U>(value - prev_value) < kBreakpoint;
36 }
37
38 // Utility class to unwrap a number to a larger type. The numbers will never be
39 // unwrapped to a negative value.
40 template <typename U>
41 class Unwrapper {
42 static_assert(!std::numeric_limits<U>::is_signed, "U must be unsigned");
43 static_assert(std::numeric_limits<U>::max() <=
44 std::numeric_limits<uint32_t>::max(),
45 "U must not be wider than 32 bits");
46
47 public:
48 // Get the unwrapped value, but don't update the internal state.
UnwrapWithoutUpdate(U value)49 int64_t UnwrapWithoutUpdate(U value) const {
50 if (!last_value_)
51 return value;
52
53 constexpr int64_t kMaxPlusOne =
54 static_cast<int64_t>(std::numeric_limits<U>::max()) + 1;
55
56 U cropped_last = static_cast<U>(*last_value_);
57 int64_t delta = value - cropped_last;
58 if (IsNewer(value, cropped_last)) {
59 if (delta < 0)
60 delta += kMaxPlusOne; // Wrap forwards.
61 } else if (delta > 0 && (*last_value_ + delta - kMaxPlusOne) >= 0) {
62 // If value is older but delta is positive, this is a backwards
63 // wrap-around. However, don't wrap backwards past 0 (unwrapped).
64 delta -= kMaxPlusOne;
65 }
66
67 return *last_value_ + delta;
68 }
69
70 // Only update the internal state to the specified last (unwrapped) value.
UpdateLast(int64_t last_value)71 void UpdateLast(int64_t last_value) {
72 last_value_ = last_value;
73 }
74
75 // Unwrap the value and update the internal state.
Unwrap(U value)76 int64_t Unwrap(U value) {
77 int64_t unwrapped = UnwrapWithoutUpdate(value);
78 UpdateLast(unwrapped);
79 return unwrapped;
80 }
81
82 private:
83 rtc::Optional<int64_t> last_value_;
84 };
85
86 using SequenceNumberUnwrapper = Unwrapper<uint16_t>;
87 using TimestampUnwrapper = Unwrapper<uint32_t>;
88
IsNewerSequenceNumber(uint16_t sequence_number,uint16_t prev_sequence_number)89 inline bool IsNewerSequenceNumber(uint16_t sequence_number,
90 uint16_t prev_sequence_number) {
91 return IsNewer(sequence_number, prev_sequence_number);
92 }
93
IsNewerTimestamp(uint32_t timestamp,uint32_t prev_timestamp)94 inline bool IsNewerTimestamp(uint32_t timestamp, uint32_t prev_timestamp) {
95 return IsNewer(timestamp, prev_timestamp);
96 }
97
LatestSequenceNumber(uint16_t sequence_number1,uint16_t sequence_number2)98 inline uint16_t LatestSequenceNumber(uint16_t sequence_number1,
99 uint16_t sequence_number2) {
100 return IsNewerSequenceNumber(sequence_number1, sequence_number2)
101 ? sequence_number1
102 : sequence_number2;
103 }
104
LatestTimestamp(uint32_t timestamp1,uint32_t timestamp2)105 inline uint32_t LatestTimestamp(uint32_t timestamp1, uint32_t timestamp2) {
106 return IsNewerTimestamp(timestamp1, timestamp2) ? timestamp1 : timestamp2;
107 }
108
109 } // namespace webrtc
110 #endif // MODULES_INCLUDE_MODULE_COMMON_TYPES_PUBLIC_H_
111