1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
|
/*
* Copyright (c) 2016 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.
*/
#include "modules/rtp_rtcp/source/time_util.h"
#include <algorithm>
#include "rtc_base/timeutils.h"
namespace webrtc {
namespace {
// TODO(danilchap): Make generic, optimize and move to base.
inline int64_t DivideRoundToNearest(int64_t x, uint32_t y) {
// Callers ensure x is positive and x + y / 2 doesn't overflow.
return (x + y / 2) / y;
}
int64_t NtpOffsetUs() {
constexpr int64_t kNtpJan1970Sec = 2208988800;
int64_t clock_time = rtc::TimeMicros();
int64_t utc_time = rtc::TimeUTCMicros();
return utc_time - clock_time + kNtpJan1970Sec * rtc::kNumMicrosecsPerSec;
}
} // namespace
NtpTime TimeMicrosToNtp(int64_t time_us) {
// Calculate the offset once.
static int64_t ntp_offset_us = NtpOffsetUs();
int64_t time_ntp_us = time_us + ntp_offset_us;
RTC_DCHECK_GE(time_ntp_us, 0); // Time before year 1900 is unsupported.
// TODO(danilchap): Convert both seconds and fraction together using int128
// when that type is easily available.
// Currently conversion is done separetly for seconds and fraction of a second
// to avoid overflow.
// Convert seconds to uint32 through uint64 for well-defined cast.
// Wrap around (will happen in 2036) is expected for ntp time.
uint32_t ntp_seconds =
static_cast<uint64_t>(time_ntp_us / rtc::kNumMicrosecsPerSec);
// Scale fractions of the second to ntp resolution.
constexpr int64_t kNtpInSecond = 1LL << 32;
int64_t us_fractions = time_ntp_us % rtc::kNumMicrosecsPerSec;
uint32_t ntp_fractions =
us_fractions * kNtpInSecond / rtc::kNumMicrosecsPerSec;
return NtpTime(ntp_seconds, ntp_fractions);
}
uint32_t SaturatedUsToCompactNtp(int64_t us) {
constexpr uint32_t kMaxCompactNtp = 0xFFFFFFFF;
constexpr int kCompactNtpInSecond = 0x10000;
if (us <= 0)
return 0;
if (us >= kMaxCompactNtp * rtc::kNumMicrosecsPerSec / kCompactNtpInSecond)
return kMaxCompactNtp;
// To convert to compact ntp need to divide by 1e6 to get seconds,
// then multiply by 0x10000 to get the final result.
// To avoid float operations, multiplication and division swapped.
return DivideRoundToNearest(us * kCompactNtpInSecond,
rtc::kNumMicrosecsPerSec);
}
int64_t CompactNtpRttToMs(uint32_t compact_ntp_interval) {
// Interval to convert expected to be positive, e.g. rtt or delay.
// Because interval can be derived from non-monotonic ntp clock,
// it might become negative that is indistinguishable from very large values.
// Since very large rtt/delay are less likely than non-monotonic ntp clock,
// those values consider to be negative and convert to minimum value of 1ms.
if (compact_ntp_interval > 0x80000000)
return 1;
// Convert to 64bit value to avoid multiplication overflow.
int64_t value = static_cast<int64_t>(compact_ntp_interval);
// To convert to milliseconds need to divide by 2^16 to get seconds,
// then multiply by 1000 to get milliseconds. To avoid float operations,
// multiplication and division swapped.
int64_t ms = DivideRoundToNearest(value * 1000, 1 << 16);
// Rtt value 0 considered too good to be true and increases to 1.
return std::max<int64_t>(ms, 1);
}
} // namespace webrtc
|
