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Add TimeMicrosToNtp to calculate current NtpTime without Clock

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Bug: webrtc:6733, webrtc:8239
Change-Id: I8ac4464cd7a7ec2b2dbad44430f1141a80ba39c1
Reviewed-on: https://webrtc-review.googlesource.com/25541
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20904}
This commit is contained in:
Danil Chapovalov
2017-11-28 10:26:54 +01:00
committed by Commit Bot
parent fb09eeb8f1
commit 2492984441
3 changed files with 84 additions and 3 deletions
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41
modules/rtp_rtcp/source/time_util.cc
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@ -12,6 +12,8 @@
#include <algorithm>
#include "rtc_base/timeutils.h"
namespace webrtc {
namespace {
// TODO(danilchap): Make generic, optimize and move to base.
@ -19,20 +21,53 @@ 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 int64_t kMicrosecondsInSecond = 1000000;
constexpr int kCompactNtpInSecond = 0x10000;
if (us <= 0)
return 0;
if (us >= kMaxCompactNtp * kMicrosecondsInSecond / kCompactNtpInSecond)
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, kMicrosecondsInSecond);
return DivideRoundToNearest(us * kCompactNtpInSecond,
rtc::kNumMicrosecsPerSec);
}
int64_t CompactNtpRttToMs(uint32_t compact_ntp_interval) {