1 // -*- C++ -*- 2 //===----------------------------------------------------------------------===// 3 // 4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 5 // See https://llvm.org/LICENSE.txt for license information. 6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 7 // 8 //===----------------------------------------------------------------------===// 9 10 #ifndef _LIBCPP___CHRONO_TAI_CLOCK_H 11 #define _LIBCPP___CHRONO_TAI_CLOCK_H 12 13 #include <version> 14 // Enable the contents of the header only when libc++ was built with experimental features enabled. 15 #if _LIBCPP_HAS_EXPERIMENTAL_TZDB 16 17 # include <__assert> 18 # include <__chrono/duration.h> 19 # include <__chrono/time_point.h> 20 # include <__chrono/utc_clock.h> 21 # include <__config> 22 # include <__type_traits/common_type.h> 23 24 # if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 25 # pragma GCC system_header 26 # endif 27 28 _LIBCPP_PUSH_MACROS 29 # include <__undef_macros> 30 31 _LIBCPP_BEGIN_NAMESPACE_STD 32 33 # if _LIBCPP_STD_VER >= 20 && _LIBCPP_HAS_TIME_ZONE_DATABASE && _LIBCPP_HAS_FILESYSTEM && _LIBCPP_HAS_LOCALIZATION 34 35 namespace chrono { 36 37 class tai_clock; 38 39 template <class _Duration> 40 using tai_time = time_point<tai_clock, _Duration>; 41 using tai_seconds = tai_time<seconds>; 42 43 // [time.clock.tai.overview]/1 44 // The clock tai_clock measures seconds since 1958-01-01 00:00:00 and is 45 // offset 10s ahead of UTC at this date. That is, 1958-01-01 00:00:00 TAI is 46 // equivalent to 1957-12-31 23:59:50 UTC. Leap seconds are not inserted into 47 // TAI. Therefore every time a leap second is inserted into UTC, UTC shifts 48 // another second with respect to TAI. For example by 2000-01-01 there had 49 // been 22 positive and 0 negative leap seconds inserted so 2000-01-01 50 // 00:00:00 UTC is equivalent to 2000-01-01 00:00:32 TAI (22s plus the 51 // initial 10s offset). 52 // 53 // Note this does not specify what the UTC offset before 1958-01-01 00:00:00 54 // TAI is, nor does it follow the "real" TAI clock between 1958-01-01 and the 55 // start of the UTC epoch. So while the member functions are fully specified in 56 // the standard, they do not technically follow the "real-world" TAI clock with 57 // 100% accuracy. 58 // 59 // https://koka-lang.github.io/koka/doc/std_time_utc.html contains more 60 // information and references. 61 class tai_clock { 62 public: 63 using rep = utc_clock::rep; 64 using period = utc_clock::period; 65 using duration = chrono::duration<rep, period>; 66 using time_point = chrono::time_point<tai_clock>; 67 static constexpr bool is_steady = false; // The utc_clock is not steady. 68 69 // The static difference between UTC and TAI time. 70 static constexpr chrono::seconds __offset{378691210}; 71 now()72 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI static time_point now() { return from_utc(utc_clock::now()); } 73 74 template <class _Duration> 75 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI static utc_time<common_type_t<_Duration, seconds>> to_utc(const tai_time<_Duration> & __time)76 to_utc(const tai_time<_Duration>& __time) noexcept { 77 using _Rp = common_type_t<_Duration, seconds>; 78 _Duration __time_since_epoch = __time.time_since_epoch(); 79 _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(__time_since_epoch >= utc_time<_Rp>::min().time_since_epoch() + __offset, 80 "the TAI to UTC conversion would underflow"); 81 82 return utc_time<_Rp>{__time_since_epoch - __offset}; 83 } 84 85 template <class _Duration> 86 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI static tai_time<common_type_t<_Duration, seconds>> from_utc(const utc_time<_Duration> & __time)87 from_utc(const utc_time<_Duration>& __time) noexcept { 88 using _Rp = common_type_t<_Duration, seconds>; 89 _Duration __time_since_epoch = __time.time_since_epoch(); 90 _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(__time_since_epoch <= utc_time<_Rp>::max().time_since_epoch() - __offset, 91 "the UTC to TAI conversion would overflow"); 92 93 return tai_time<_Rp>{__time_since_epoch + __offset}; 94 } 95 }; 96 97 } // namespace chrono 98 99 # endif // _LIBCPP_STD_VER >= 20 && _LIBCPP_HAS_TIME_ZONE_DATABASE && _LIBCPP_HAS_FILESYSTEM && 100 // _LIBCPP_HAS_LOCALIZATION 101 102 _LIBCPP_END_NAMESPACE_STD 103 104 _LIBCPP_POP_MACROS 105 106 #endif // _LIBCPP_HAS_EXPERIMENTAL_TZDB 107 108 #endif // _LIBCPP___CHRONO_TAI_CLOCK_H 109