ntp_time_util.h (2520B)
1 /* 2 * Copyright (c) 2015 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_RTP_RTCP_SOURCE_NTP_TIME_UTIL_H_ 12 #define MODULES_RTP_RTCP_SOURCE_NTP_TIME_UTIL_H_ 13 14 #include <stdint.h> 15 16 #include "api/units/time_delta.h" 17 #include "rtc_base/numerics/safe_conversions.h" 18 #include "system_wrappers/include/ntp_time.h" 19 20 namespace webrtc { 21 22 // Helper function for compact ntp representation: 23 // RFC 3550, Section 4. Time Format. 24 // Wallclock time is represented using the timestamp format of 25 // the Network Time Protocol (NTP). 26 // ... 27 // In some fields where a more compact representation is 28 // appropriate, only the middle 32 bits are used; that is, the low 16 29 // bits of the integer part and the high 16 bits of the fractional part. 30 inline uint32_t CompactNtp(NtpTime ntp) { 31 return (ntp.seconds() << 16) | (ntp.fractions() >> 16); 32 } 33 34 // Converts interval to compact ntp (1/2^16 seconds) resolution. 35 // Negative values converted to 0, Overlarge values converted to max uint32_t. 36 uint32_t SaturatedToCompactNtp(TimeDelta delta); 37 38 // Convert interval to the NTP time resolution (1/2^32 seconds ~= 0.2 ns). 39 // For deltas with absolute value larger than 35 minutes result is unspecified. 40 inline constexpr int64_t ToNtpUnits(TimeDelta delta) { 41 // For better precision `delta` is taken with best TimeDelta precision (us), 42 // then multiplaction and conversion to seconds are swapped to avoid float 43 // arithmetic. 44 // 2^31 us ~= 35.8 minutes. 45 return (saturated_cast<int32_t>(delta.us()) * (int64_t{1} << 32)) / 1'000'000; 46 } 47 48 // Converts interval from compact ntp (1/2^16 seconds) resolution to TimeDelta. 49 // This interval can be up to ~9.1 hours (2^15 seconds). 50 // Values close to 2^16 seconds are considered negative. 51 TimeDelta CompactNtpIntervalToTimeDelta(uint32_t compact_ntp_interval); 52 53 // Converts interval from compact ntp (1/2^16 seconds) resolution to TimeDelta. 54 // This interval can be up to ~9.1 hours (2^15 seconds). 55 // Values close to 2^16 seconds are considered negative and are converted to 56 // minimum value of 1ms. 57 TimeDelta CompactNtpRttToTimeDelta(uint32_t compact_ntp_interval); 58 59 } // namespace webrtc 60 #endif // MODULES_RTP_RTCP_SOURCE_NTP_TIME_UTIL_H_