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2492984441
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}
90 lines
3.5 KiB
C++
90 lines
3.5 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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#include "modules/rtp_rtcp/source/time_util.h"
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#include <algorithm>
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#include "rtc_base/timeutils.h"
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namespace webrtc {
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namespace {
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// TODO(danilchap): Make generic, optimize and move to base.
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inline int64_t DivideRoundToNearest(int64_t x, uint32_t y) {
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// Callers ensure x is positive and x + y / 2 doesn't overflow.
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return (x + y / 2) / y;
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}
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int64_t NtpOffsetUs() {
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constexpr int64_t kNtpJan1970Sec = 2208988800;
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int64_t clock_time = rtc::TimeMicros();
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int64_t utc_time = rtc::TimeUTCMicros();
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return utc_time - clock_time + kNtpJan1970Sec * rtc::kNumMicrosecsPerSec;
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}
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} // namespace
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NtpTime TimeMicrosToNtp(int64_t time_us) {
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// Calculate the offset once.
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static int64_t ntp_offset_us = NtpOffsetUs();
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int64_t time_ntp_us = time_us + ntp_offset_us;
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RTC_DCHECK_GE(time_ntp_us, 0); // Time before year 1900 is unsupported.
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// TODO(danilchap): Convert both seconds and fraction together using int128
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// when that type is easily available.
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// Currently conversion is done separetly for seconds and fraction of a second
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// to avoid overflow.
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// Convert seconds to uint32 through uint64 for well-defined cast.
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// Wrap around (will happen in 2036) is expected for ntp time.
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uint32_t ntp_seconds =
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static_cast<uint64_t>(time_ntp_us / rtc::kNumMicrosecsPerSec);
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// Scale fractions of the second to ntp resolution.
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constexpr int64_t kNtpInSecond = 1LL << 32;
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int64_t us_fractions = time_ntp_us % rtc::kNumMicrosecsPerSec;
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uint32_t ntp_fractions =
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us_fractions * kNtpInSecond / rtc::kNumMicrosecsPerSec;
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return NtpTime(ntp_seconds, ntp_fractions);
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}
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uint32_t SaturatedUsToCompactNtp(int64_t us) {
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constexpr uint32_t kMaxCompactNtp = 0xFFFFFFFF;
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constexpr int kCompactNtpInSecond = 0x10000;
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if (us <= 0)
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return 0;
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if (us >= kMaxCompactNtp * rtc::kNumMicrosecsPerSec / kCompactNtpInSecond)
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return kMaxCompactNtp;
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// To convert to compact ntp need to divide by 1e6 to get seconds,
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// then multiply by 0x10000 to get the final result.
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// To avoid float operations, multiplication and division swapped.
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return DivideRoundToNearest(us * kCompactNtpInSecond,
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rtc::kNumMicrosecsPerSec);
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}
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int64_t CompactNtpRttToMs(uint32_t compact_ntp_interval) {
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// Interval to convert expected to be positive, e.g. rtt or delay.
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// Because interval can be derived from non-monotonic ntp clock,
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// it might become negative that is indistinguishable from very large values.
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// Since very large rtt/delay are less likely than non-monotonic ntp clock,
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// those values consider to be negative and convert to minimum value of 1ms.
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if (compact_ntp_interval > 0x80000000)
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return 1;
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// Convert to 64bit value to avoid multiplication overflow.
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int64_t value = static_cast<int64_t>(compact_ntp_interval);
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// To convert to milliseconds need to divide by 2^16 to get seconds,
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// then multiply by 1000 to get milliseconds. To avoid float operations,
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// multiplication and division swapped.
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int64_t ms = DivideRoundToNearest(value * 1000, 1 << 16);
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// Rtt value 0 considered too good to be true and increases to 1.
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return std::max<int64_t>(ms, 1);
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}
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} // namespace webrtc
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