xref: /freebsd/contrib/llvm-project/libcxx/include/__chrono/convert_to_tm.h (revision 7ef62cebc2f965b0f640263e179276928885e33d)
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_CONVERT_TO_TM_H
11 #define _LIBCPP___CHRONO_CONVERT_TO_TM_H
12 
13 #include <__chrono/day.h>
14 #include <__chrono/duration.h>
15 #include <__chrono/hh_mm_ss.h>
16 #include <__chrono/month.h>
17 #include <__chrono/month_weekday.h>
18 #include <__chrono/monthday.h>
19 #include <__chrono/statically_widen.h>
20 #include <__chrono/system_clock.h>
21 #include <__chrono/time_point.h>
22 #include <__chrono/weekday.h>
23 #include <__chrono/year.h>
24 #include <__chrono/year_month.h>
25 #include <__chrono/year_month_day.h>
26 #include <__chrono/year_month_weekday.h>
27 #include <__concepts/same_as.h>
28 #include <__config>
29 #include <__memory/addressof.h>
30 #include <cstdint>
31 #include <ctime>
32 
33 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
34 #  pragma GCC system_header
35 #endif
36 
37 _LIBCPP_BEGIN_NAMESPACE_STD
38 
39 #if _LIBCPP_STD_VER > 17
40 
41 // Conerts a chrono date and weekday to a given _Tm type.
42 //
43 // This is an implementation detail for the function
44 //   template <class _Tm, class _ChronoT>
45 //   _Tm __convert_to_tm(const _ChronoT& __value)
46 //
47 // This manually converts the two values to the proper type. It is possible to
48 // convert from sys_days to time_t and then to _Tm. But this leads to the Y2K
49 // bug when time_t is a 32-bit signed integer. Chrono considers years beyond
50 // the year 2038 valid, so instead do the transformation manually.
51 template <class _Tm, class _Date>
52   requires(same_as<_Date, chrono::year_month_day> || same_as<_Date, chrono::year_month_day_last>)
53 _LIBCPP_HIDE_FROM_ABI _Tm __convert_to_tm(const _Date& __date, chrono::weekday __weekday) {
54   _Tm __result = {};
55 #  ifdef __GLIBC__
56   __result.tm_zone = "UTC";
57 #  endif
58   __result.tm_year = static_cast<int>(__date.year()) - 1900;
59   __result.tm_mon  = static_cast<unsigned>(__date.month()) - 1;
60   __result.tm_mday = static_cast<unsigned>(__date.day());
61   __result.tm_wday = static_cast<unsigned>(__weekday.c_encoding());
62   __result.tm_yday =
63       (static_cast<chrono::sys_days>(__date) -
64        static_cast<chrono::sys_days>(chrono::year_month_day{__date.year(), chrono::January, chrono::day{1}}))
65           .count();
66 
67   return __result;
68 }
69 
70 // Convert a chrono (calendar) time point, or dururation to the given _Tm type,
71 // which must have the same properties as std::tm.
72 template <class _Tm, class _ChronoT>
73 _LIBCPP_HIDE_FROM_ABI _Tm __convert_to_tm(const _ChronoT& __value) {
74   _Tm __result = {};
75 #  ifdef __GLIBC__
76   __result.tm_zone = "UTC";
77 #  endif
78 
79   if constexpr (chrono::__is_duration<_ChronoT>::value) {
80     // [time.format]/6
81     //   ...  However, if a flag refers to a "time of day" (e.g. %H, %I, %p,
82     //   etc.), then a specialization of duration is interpreted as the time of
83     //   day elapsed since midnight.
84     uint64_t __sec = chrono::duration_cast<chrono::seconds>(__value).count();
85     __sec %= 24 * 3600;
86     __result.tm_hour = __sec / 3600;
87     __sec %= 3600;
88     __result.tm_min = __sec / 60;
89     __result.tm_sec = __sec % 60;
90   } else if constexpr (same_as<_ChronoT, chrono::day>)
91     __result.tm_mday = static_cast<unsigned>(__value);
92   else if constexpr (same_as<_ChronoT, chrono::month>)
93     __result.tm_mon = static_cast<unsigned>(__value) - 1;
94   else if constexpr (same_as<_ChronoT, chrono::year>)
95     __result.tm_year = static_cast<int>(__value) - 1900;
96   else if constexpr (same_as<_ChronoT, chrono::weekday>)
97     __result.tm_wday = __value.c_encoding();
98   else if constexpr (same_as<_ChronoT, chrono::weekday_indexed> || same_as<_ChronoT, chrono::weekday_last>)
99     __result.tm_wday = __value.weekday().c_encoding();
100   else if constexpr (same_as<_ChronoT, chrono::month_day>) {
101     __result.tm_mday = static_cast<unsigned>(__value.day());
102     __result.tm_mon  = static_cast<unsigned>(__value.month()) - 1;
103   } else if constexpr (same_as<_ChronoT, chrono::month_day_last>) {
104     __result.tm_mon = static_cast<unsigned>(__value.month()) - 1;
105   } else if constexpr (same_as<_ChronoT, chrono::month_weekday> || same_as<_ChronoT, chrono::month_weekday_last>) {
106     __result.tm_wday = __value.weekday_indexed().weekday().c_encoding();
107     __result.tm_mon  = static_cast<unsigned>(__value.month()) - 1;
108   } else if constexpr (same_as<_ChronoT, chrono::year_month>) {
109     __result.tm_year = static_cast<int>(__value.year()) - 1900;
110     __result.tm_mon  = static_cast<unsigned>(__value.month()) - 1;
111   } else if constexpr (same_as<_ChronoT, chrono::year_month_day> || same_as<_ChronoT, chrono::year_month_day_last>) {
112     return std::__convert_to_tm<_Tm>(
113         chrono::year_month_day{__value}, chrono::weekday{static_cast<chrono::sys_days>(__value)});
114   } else if constexpr (same_as<_ChronoT, chrono::year_month_weekday> ||
115                        same_as<_ChronoT, chrono::year_month_weekday_last>) {
116     return std::__convert_to_tm<_Tm>(chrono::year_month_day{static_cast<chrono::sys_days>(__value)}, __value.weekday());
117   } else
118     static_assert(sizeof(_ChronoT) == 0, "Add the missing type specialization");
119 
120   return __result;
121 }
122 
123 #endif //if _LIBCPP_STD_VER > 17
124 
125 _LIBCPP_END_NAMESPACE_STD
126 
127 #endif // _LIBCPP___CHRONO_CONVERT_TO_TM_H
128