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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-exception7//8//===----------------------------------------------------------------------===//9 10#ifndef _LIBCPP___CHRONO_TAI_CLOCK_H11#define _LIBCPP___CHRONO_TAI_CLOCK_H12 13#include <version>14// Enable the contents of the header only when libc++ was built with experimental features enabled.15#if _LIBCPP_HAS_EXPERIMENTAL_TZDB16 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_header26# endif27 28_LIBCPP_PUSH_MACROS29# include <__undef_macros>30 31_LIBCPP_BEGIN_NAMESPACE_STD32 33# if _LIBCPP_STD_VER >= 20 && _LIBCPP_HAS_TIME_ZONE_DATABASE && _LIBCPP_HAS_FILESYSTEM && _LIBCPP_HAS_LOCALIZATION34 35namespace chrono {36 37class tai_clock;38 39template <class _Duration>40using tai_time = time_point<tai_clock, _Duration>;41using tai_seconds = tai_time<seconds>;42 43// [time.clock.tai.overview]/144// The clock tai_clock measures seconds since 1958-01-01 00:00:00 and is45// offset 10s ahead of UTC at this date. That is, 1958-01-01 00:00:00 TAI is46// equivalent to 1957-12-31 23:59:50 UTC. Leap seconds are not inserted into47// TAI. Therefore every time a leap second is inserted into UTC, UTC shifts48// another second with respect to TAI. For example by 2000-01-01 there had49// been 22 positive and 0 negative leap seconds inserted so 2000-01-0150// 00:00:00 UTC is equivalent to 2000-01-01 00:00:32 TAI (22s plus the51// initial 10s offset).52//53// Note this does not specify what the UTC offset before 1958-01-01 00:00:0054// TAI is, nor does it follow the "real" TAI clock between 1958-01-01 and the55// start of the UTC epoch. So while the member functions are fully specified in56// the standard, they do not technically follow the "real-world" TAI clock with57// 100% accuracy.58//59// https://koka-lang.github.io/koka/doc/std_time_utc.html contains more60// information and references.61class tai_clock {62public: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 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>>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>>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 chrono98 99# endif // _LIBCPP_STD_VER >= 20 && _LIBCPP_HAS_TIME_ZONE_DATABASE && _LIBCPP_HAS_FILESYSTEM &&100 // _LIBCPP_HAS_LOCALIZATION101 102_LIBCPP_END_NAMESPACE_STD103 104_LIBCPP_POP_MACROS105 106#endif // _LIBCPP_HAS_EXPERIMENTAL_TZDB107 108#endif // _LIBCPP___CHRONO_TAI_CLOCK_H109