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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-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 | + |
| 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 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 |
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