libcxx/include/__chrono/convert_to_tm.h

   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/calendar.h>
  14 #include <__chrono/concepts.h>
  15 #include <__chrono/day.h>
  16 #include <__chrono/duration.h>
  17 #include <__chrono/file_clock.h>
  18 #include <__chrono/hh_mm_ss.h>
  19 #include <__chrono/month.h>
  20 #include <__chrono/month_weekday.h>
  21 #include <__chrono/monthday.h>
  22 #include <__chrono/statically_widen.h>
  23 #include <__chrono/system_clock.h>
  24 #include <__chrono/time_point.h>
  25 #include <__chrono/weekday.h>
  26 #include <__chrono/year.h>
  27 #include <__chrono/year_month.h>
  28 #include <__chrono/year_month_day.h>
  29 #include <__chrono/year_month_weekday.h>
  30 #include <__concepts/same_as.h>
  31 #include <__config>
  32 #include <__format/format_error.h>
  33 #include <__memory/addressof.h>
  34 #include <__type_traits/is_convertible.h>
  35 #include <cstdint>
  36 #include <ctime>
  37 #include <limits>
  38
  39 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  40 #  pragma GCC system_header
  41 #endif
  42
  43 _LIBCPP_PUSH_MACROS
  44 #include <__undef_macros>
  45
  46 _LIBCPP_BEGIN_NAMESPACE_STD
  47
  48 #if _LIBCPP_STD_VER >= 20
  49
  50 // Conerts a chrono date and weekday to a given _Tm type.
  51 //
  52 // This is an implementation detail for the function
  53 //   template <class _Tm, class _ChronoT>
  54 //   _Tm __convert_to_tm(const _ChronoT& __value)
  55 //
  56 // This manually converts the two values to the proper type. It is possible to
  57 // convert from sys_days to time_t and then to _Tm. But this leads to the Y2K
  58 // bug when time_t is a 32-bit signed integer. Chrono considers years beyond
  59 // the year 2038 valid, so instead do the transformation manually.
  60 template <class _Tm, class _Date>
  61   requires(same_as<_Date, chrono::year_month_day> || same_as<_Date, chrono::year_month_day_last>)
  62 _LIBCPP_HIDE_FROM_ABI _Tm __convert_to_tm(const _Date& __date, chrono::weekday __weekday) {
  63   _Tm __result = {};
  64 #  ifdef __GLIBC__
  65   __result.tm_zone = "UTC";
  66 #  endif
  67   __result.tm_year = static_cast<int>(__date.year()) - 1900;
  68   __result.tm_mon  = static_cast<unsigned>(__date.month()) - 1;
  69   __result.tm_mday = static_cast<unsigned>(__date.day());
  70   __result.tm_wday = static_cast<unsigned>(__weekday.c_encoding());
  71   __result.tm_yday =
  72       (static_cast<chrono::sys_days>(__date) -
  73        static_cast<chrono::sys_days>(chrono::year_month_day{__date.year(), chrono::January, chrono::day{1}}))
  74           .count();
  75
  76   return __result;
  77 }
  78
  79 template <class _Tm, class _Duration>
  80 _LIBCPP_HIDE_FROM_ABI _Tm __convert_to_tm(const chrono::sys_time<_Duration> __tp) {
  81   chrono::sys_days __days = chrono::floor<chrono::days>(__tp);
  82   chrono::year_month_day __ymd{__days};
  83
  84   _Tm __result = std::__convert_to_tm<_Tm>(chrono::year_month_day{__ymd}, chrono::weekday{__days});
  85
  86   uint64_t __sec =
  87       chrono::duration_cast<chrono::seconds>(__tp - chrono::time_point_cast<chrono::seconds>(__days)).count();
  88   __sec %= 24 * 3600;
  89   __result.tm_hour = __sec / 3600;
  90   __sec %= 3600;
  91   __result.tm_min = __sec / 60;
  92   __result.tm_sec = __sec % 60;
  93
  94   return __result;
  95 }
  96
  97 // Convert a chrono (calendar) time point, or dururation to the given _Tm type,
  98 // which must have the same properties as std::tm.
  99 template <class _Tm, class _ChronoT>
 100 _LIBCPP_HIDE_FROM_ABI _Tm __convert_to_tm(const _ChronoT& __value) {
 101   _Tm __result = {};
 102 #  ifdef __GLIBC__
 103   __result.tm_zone = "UTC";
 104 #  endif
 105
 106   if constexpr (__is_time_point<_ChronoT>) {
 107     if constexpr (same_as<typename _ChronoT::clock, chrono::system_clock>)
 108       return std::__convert_to_tm<_Tm>(__value);
 109     else if constexpr (same_as<typename _ChronoT::clock, chrono::file_clock>)
 110       return std::__convert_to_tm<_Tm>(_ChronoT::clock::to_sys(__value));
 111     else if constexpr (same_as<typename _ChronoT::clock, chrono::local_t>)
 112       return std::__convert_to_tm<_Tm>(chrono::sys_time<typename _ChronoT::duration>{__value.time_since_epoch()});
 113     else
 114       static_assert(sizeof(_ChronoT) == 0, "TODO: Add the missing clock specialization");
 115   } else if constexpr (chrono::__is_duration<_ChronoT>::value) {
 116     // [time.format]/6
 117     //   ...  However, if a flag refers to a "time of day" (e.g. %H, %I, %p,
 118     //   etc.), then a specialization of duration is interpreted as the time of
 119     //   day elapsed since midnight.
 120
 121     // Not all values can be converted to hours, it may run into ratio
 122     // conversion errors. In that case the conversion to seconds works.
 123     if constexpr (is_convertible_v<_ChronoT, chrono::hours>) {
 124       auto __hour      = chrono::floor<chrono::hours>(__value);
 125       auto __sec       = chrono::duration_cast<chrono::seconds>(__value - __hour);
 126       __result.tm_hour = __hour.count() % 24;
 127       __result.tm_min  = __sec.count() / 60;
 128       __result.tm_sec  = __sec.count() % 60;
 129     } else {
 130       uint64_t __sec = chrono::duration_cast<chrono::seconds>(__value).count();
 131       __sec %= 24 * 3600;
 132       __result.tm_hour = __sec / 3600;
 133       __sec %= 3600;
 134       __result.tm_min = __sec / 60;
 135       __result.tm_sec = __sec % 60;
 136     }
 137   } else if constexpr (same_as<_ChronoT, chrono::day>)
 138     __result.tm_mday = static_cast<unsigned>(__value);
 139   else if constexpr (same_as<_ChronoT, chrono::month>)
 140     __result.tm_mon = static_cast<unsigned>(__value) - 1;
 141   else if constexpr (same_as<_ChronoT, chrono::year>)
 142     __result.tm_year = static_cast<int>(__value) - 1900;
 143   else if constexpr (same_as<_ChronoT, chrono::weekday>)
 144     __result.tm_wday = __value.c_encoding();
 145   else if constexpr (same_as<_ChronoT, chrono::weekday_indexed> || same_as<_ChronoT, chrono::weekday_last>)
 146     __result.tm_wday = __value.weekday().c_encoding();
 147   else if constexpr (same_as<_ChronoT, chrono::month_day>) {
 148     __result.tm_mday = static_cast<unsigned>(__value.day());
 149     __result.tm_mon  = static_cast<unsigned>(__value.month()) - 1;
 150   } else if constexpr (same_as<_ChronoT, chrono::month_day_last>) {
 151     __result.tm_mon = static_cast<unsigned>(__value.month()) - 1;
 152   } else if constexpr (same_as<_ChronoT, chrono::month_weekday> || same_as<_ChronoT, chrono::month_weekday_last>) {
 153     __result.tm_wday = __value.weekday_indexed().weekday().c_encoding();
 154     __result.tm_mon  = static_cast<unsigned>(__value.month()) - 1;
 155   } else if constexpr (same_as<_ChronoT, chrono::year_month>) {
 156     __result.tm_year = static_cast<int>(__value.year()) - 1900;
 157     __result.tm_mon  = static_cast<unsigned>(__value.month()) - 1;
 158   } else if constexpr (same_as<_ChronoT, chrono::year_month_day> || same_as<_ChronoT, chrono::year_month_day_last>) {
 159     return std::__convert_to_tm<_Tm>(
 160         chrono::year_month_day{__value}, chrono::weekday{static_cast<chrono::sys_days>(__value)});
 161   } else if constexpr (same_as<_ChronoT, chrono::year_month_weekday> ||
 162                        same_as<_ChronoT, chrono::year_month_weekday_last>) {
 163     return std::__convert_to_tm<_Tm>(chrono::year_month_day{static_cast<chrono::sys_days>(__value)}, __value.weekday());
 164   } else if constexpr (__is_hh_mm_ss<_ChronoT>) {
 165     __result.tm_sec = __value.seconds().count();
 166     __result.tm_min = __value.minutes().count();
 167     // In libc++ hours is stored as a long. The type in std::tm is an int. So
 168     // the overflow can only occur when hour uses more bits than an int
 169     // provides.
 170     if constexpr (sizeof(std::chrono::hours::rep) > sizeof(__result.tm_hour))
 171       if (__value.hours().count() > std::numeric_limits<decltype(__result.tm_hour)>::max())
 172         std::__throw_format_error("Formatting hh_mm_ss, encountered an hour overflow");
 173     __result.tm_hour = __value.hours().count();
 174   } else
 175     static_assert(sizeof(_ChronoT) == 0, "Add the missing type specialization");
 176
 177   return __result;
 178 }
 179
 180 #endif // if _LIBCPP_STD_VER >= 20
 181
 182 _LIBCPP_END_NAMESPACE_STD
 183
 184 _LIBCPP_POP_MACROS
 185
 186 #endif // _LIBCPP___CHRONO_CONVERT_TO_TM_H