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 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___CXX03___CHRONO_FORMATTER_H
 #define _LIBCPP___CXX03___CHRONO_FORMATTER_H
 
 #include <__cxx03/__algorithm/ranges_copy.h>
 #include <__cxx03/__chrono/calendar.h>
 #include <__cxx03/__chrono/concepts.h>
 #include <__cxx03/__chrono/convert_to_tm.h>
 #include <__cxx03/__chrono/day.h>
 #include <__cxx03/__chrono/duration.h>
 #include <__cxx03/__chrono/file_clock.h>
 #include <__cxx03/__chrono/hh_mm_ss.h>
 #include <__cxx03/__chrono/local_info.h>
 #include <__cxx03/__chrono/month.h>
 #include <__cxx03/__chrono/month_weekday.h>
 #include <__cxx03/__chrono/monthday.h>
 #include <__cxx03/__chrono/ostream.h>
 #include <__cxx03/__chrono/parser_std_format_spec.h>
 #include <__cxx03/__chrono/statically_widen.h>
 #include <__cxx03/__chrono/sys_info.h>
 #include <__cxx03/__chrono/system_clock.h>
 #include <__cxx03/__chrono/time_point.h>
 #include <__cxx03/__chrono/weekday.h>
 #include <__cxx03/__chrono/year.h>
 #include <__cxx03/__chrono/year_month.h>
 #include <__cxx03/__chrono/year_month_day.h>
 #include <__cxx03/__chrono/year_month_weekday.h>
 #include <__cxx03/__chrono/zoned_time.h>
 #include <__cxx03/__concepts/arithmetic.h>
 #include <__cxx03/__concepts/same_as.h>
 #include <__cxx03/__config>
 #include <__cxx03/__format/concepts.h>
 #include <__cxx03/__format/format_error.h>
 #include <__cxx03/__format/format_functions.h>
 #include <__cxx03/__format/format_parse_context.h>
 #include <__cxx03/__format/formatter.h>
 #include <__cxx03/__format/parser_std_format_spec.h>
 #include <__cxx03/__format/write_escaped.h>
 #include <__cxx03/__memory/addressof.h>
 #include <__cxx03/__type_traits/is_specialization.h>
 #include <__cxx03/cmath>
 #include <__cxx03/ctime>
 #include <__cxx03/limits>
 #include <__cxx03/sstream>
 #include <__cxx03/string_view>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER >= 20
 
 namespace __formatter {
 
 /// Formats a time based on a tm struct.
 ///
 /// This formatter passes the formatting to time_put which uses strftime. When
 /// the value is outside the valid range it's unspecified what strftime will
 /// output. For example weekday 8 can print 1 when the day is processed modulo
 /// 7 since that handles the Sunday for 0-based weekday. It can also print 8 if
 /// 7 is handled as a special case.
 ///
 /// The Standard doesn't specify what to do in this case so the result depends
 /// on the result of the underlying code.
 ///
 /// \pre When the (abbreviated) weekday or month name are used, the caller
 ///      validates whether the value is valid. So the caller handles that
 ///      requirement of Table 97: Meaning of conversion specifiers
 ///      [tab:time.format.spec].
 ///
 /// When no chrono-specs are provided it uses the stream formatter.
 
 // For tiny ratios it's not possible to convert a duration to a hh_mm_ss. This
 // fails compile-time due to the limited precision of the ratio (64-bit is too
 // small). Therefore a duration uses its own conversion.
 template <class _CharT, class _Rep, class _Period>
 _LIBCPP_HIDE_FROM_ABI void
 __format_sub_seconds(basic_stringstream<_CharT>& __sstr, const chrono::duration<_Rep, _Period>& __value) {
   __sstr << std::use_facet<numpunct<_CharT>>(__sstr.getloc()).decimal_point();
 
   using __duration = chrono::duration<_Rep, _Period>;
 
   auto __fraction = __value - chrono::duration_cast<chrono::seconds>(__value);
   // Converts a negative fraction to its positive value.
   if (__value < chrono::seconds{0} && __fraction != __duration{0})
     __fraction += chrono::seconds{1};
   if constexpr (chrono::treat_as_floating_point_v<_Rep>)
     // When the floating-point value has digits itself they are ignored based
     // on the wording in [tab:time.format.spec]
     //   If the precision of the input cannot be exactly represented with
     //   seconds, then the format is a decimal floating-point number with a
     //   fixed format and a precision matching that of the precision of the
     //   input (or to a microseconds precision if the conversion to
     //   floating-point decimal seconds cannot be made within 18 fractional
     //   digits).
     //
     // This matches the behaviour of MSVC STL, fmtlib interprets this
     // differently and uses 3 decimals.
     // https://godbolt.org/z/6dsbnW8ba
     std::format_to(std::ostreambuf_iterator<_CharT>{__sstr},
                    _LIBCPP_STATICALLY_WIDEN(_CharT, "{:0{}.0f}"),
                    chrono::duration_cast<typename chrono::hh_mm_ss<__duration>::precision>(__fraction).count(),
                    chrono::hh_mm_ss<__duration>::fractional_width);
   else
     std::format_to(std::ostreambuf_iterator<_CharT>{__sstr},
                    _LIBCPP_STATICALLY_WIDEN(_CharT, "{:0{}}"),
                    chrono::duration_cast<typename chrono::hh_mm_ss<__duration>::precision>(__fraction).count(),
                    chrono::hh_mm_ss<__duration>::fractional_width);
 }
 
 template <class _CharT, __is_time_point _Tp>
 _LIBCPP_HIDE_FROM_ABI void __format_sub_seconds(basic_stringstream<_CharT>& __sstr, const _Tp& __value) {
   __formatter::__format_sub_seconds(__sstr, __value.time_since_epoch());
 }
 
 template <class _CharT, class _Duration>
 _LIBCPP_HIDE_FROM_ABI void
 __format_sub_seconds(basic_stringstream<_CharT>& __sstr, const chrono::hh_mm_ss<_Duration>& __value) {
   __sstr << std::use_facet<numpunct<_CharT>>(__sstr.getloc()).decimal_point();
   if constexpr (chrono::treat_as_floating_point_v<typename _Duration::rep>)
     std::format_to(std::ostreambuf_iterator<_CharT>{__sstr},
                    _LIBCPP_STATICALLY_WIDEN(_CharT, "{:0{}.0f}"),
                    __value.subseconds().count(),
                    __value.fractional_width);
   else
     std::format_to(std::ostreambuf_iterator<_CharT>{__sstr},
                    _LIBCPP_STATICALLY_WIDEN(_CharT, "{:0{}}"),
                    __value.subseconds().count(),
                    __value.fractional_width);
 }
 
 #  if !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB) && !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) &&                     \
       !defined(_LIBCPP_HAS_NO_FILESYSTEM) && !defined(_LIBCPP_HAS_NO_LOCALIZATION)
 template <class _CharT, class _Duration, class _TimeZonePtr>
 _LIBCPP_HIDE_FROM_ABI void
 __format_sub_seconds(basic_stringstream<_CharT>& __sstr, const chrono::zoned_time<_Duration, _TimeZonePtr>& __value) {
   __formatter::__format_sub_seconds(__sstr, __value.get_local_time().time_since_epoch());
 }
 #  endif
 
 template <class _Tp>
 consteval bool __use_fraction() {
   if constexpr (__is_time_point<_Tp>)
     return chrono::hh_mm_ss<typename _Tp::duration>::fractional_width;
 #  if !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB) && !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) &&                     \
       !defined(_LIBCPP_HAS_NO_FILESYSTEM) && !defined(_LIBCPP_HAS_NO_LOCALIZATION)
   else if constexpr (__is_specialization_v<_Tp, chrono::zoned_time>)
     return chrono::hh_mm_ss<typename _Tp::duration>::fractional_width;
 #  endif
   else if constexpr (chrono::__is_duration<_Tp>::value)
     return chrono::hh_mm_ss<_Tp>::fractional_width;
   else if constexpr (__is_hh_mm_ss<_Tp>)
     return _Tp::fractional_width;
   else
     return false;
 }
 
 template <class _CharT>
 _LIBCPP_HIDE_FROM_ABI void __format_year(basic_stringstream<_CharT>& __sstr, int __year) {
   if (__year < 0) {
     __sstr << _CharT('-');
     __year = -__year;
   }
 
   // TODO FMT Write an issue
   //   If the result has less than four digits it is zero-padded with 0 to two digits.
   // is less -> has less
   // left-padded -> zero-padded, otherwise the proper value would be 000-0.
 
   // Note according to the wording it should be left padded, which is odd.
   __sstr << std::format(_LIBCPP_STATICALLY_WIDEN(_CharT, "{:04}"), __year);
 }
 
 template <class _CharT>
 _LIBCPP_HIDE_FROM_ABI void __format_century(basic_stringstream<_CharT>& __sstr, int __year) {
   // TODO FMT Write an issue
   // [tab:time.format.spec]
   //   %C The year divided by 100 using floored division. If the result is a
   //   single decimal digit, it is prefixed with 0.
 
   bool __negative = __year < 0;
   int __century   = (__year - (99 * __negative)) / 100; // floored division
   __sstr << std::format(_LIBCPP_STATICALLY_WIDEN(_CharT, "{:02}"), __century);
 }
 
 // Implements the %z format specifier according to [tab:time.format.spec], where
 // '__modifier' signals %Oz or %Ez were used. (Both modifiers behave the same,
 // so there is no need to distinguish between them.)
 template <class _CharT>
 _LIBCPP_HIDE_FROM_ABI void
 __format_zone_offset(basic_stringstream<_CharT>& __sstr, chrono::seconds __offset, bool __modifier) {
   if (__offset < 0s) {
     __sstr << _CharT('-');
     __offset = -__offset;
   } else {
     __sstr << _CharT('+');
   }
 
   chrono::hh_mm_ss __hms{__offset};
   std::ostreambuf_iterator<_CharT> __out_it{__sstr};
   // Note HMS does not allow formatting hours > 23, but the offset is not limited to 24H.
   std::format_to(__out_it, _LIBCPP_STATICALLY_WIDEN(_CharT, "{:02}"), __hms.hours().count());
   if (__modifier)
     __sstr << _CharT(':');
   std::format_to(__out_it, _LIBCPP_STATICALLY_WIDEN(_CharT, "{:02}"), __hms.minutes().count());
 }
 
 // Helper to store the time zone information needed for formatting.
 struct _LIBCPP_HIDE_FROM_ABI __time_zone {
   // Typically these abbreviations are short and fit in the string's internal
   // buffer.
   string __abbrev;
   chrono::seconds __offset;
 };
 
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI __time_zone __convert_to_time_zone([[maybe_unused]] const _Tp& __value) {
 #  if !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
   if constexpr (same_as<_Tp, chrono::sys_info>)
     return {__value.abbrev, __value.offset};
 #    if !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&                          \
         !defined(_LIBCPP_HAS_NO_LOCALIZATION)
   else if constexpr (__is_specialization_v<_Tp, chrono::zoned_time>)
     return __formatter::__convert_to_time_zone(__value.get_info());
 #    endif
   else
 #  endif // !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
     return {"UTC", chrono::seconds{0}};
 }
 
 template <class _CharT, class _Tp>
 _LIBCPP_HIDE_FROM_ABI void __format_chrono_using_chrono_specs(
     basic_stringstream<_CharT>& __sstr, const _Tp& __value, basic_string_view<_CharT> __chrono_specs) {
   tm __t              = std::__convert_to_tm<tm>(__value);
   __time_zone __z     = __formatter::__convert_to_time_zone(__value);
   const auto& __facet = std::use_facet<time_put<_CharT>>(__sstr.getloc());
   for (auto __it = __chrono_specs.begin(); __it != __chrono_specs.end(); ++__it) {
     if (*__it == _CharT('%')) {
       auto __s = __it;
       ++__it;
       // We only handle the types that can't be directly handled by time_put.
       // (as an optimization n, t, and % are also handled directly.)
       switch (*__it) {
       case _CharT('n'):
         __sstr << _CharT('\n');
         break;
       case _CharT('t'):
         __sstr << _CharT('\t');
         break;
       case _CharT('%'):
         __sstr << *__it;
         break;
 
       case _CharT('C'): {
         // strftime's output is only defined in the range [00, 99].
         int __year = __t.tm_year + 1900;
         if (__year < 1000 || __year > 9999)
           __formatter::__format_century(__sstr, __year);
         else
           __facet.put(
               {__sstr}, __sstr, _CharT(' '), std::addressof(__t), std::to_address(__s), std::to_address(__it + 1));
       } break;
 
       case _CharT('j'):
         if constexpr (chrono::__is_duration<_Tp>::value)
           // Converting a duration where the period has a small ratio to days
           // may fail to compile. This due to loss of precision in the
           // conversion. In order to avoid that issue convert to seconds as
           // an intemediate step.
           __sstr << chrono::duration_cast<chrono::days>(chrono::duration_cast<chrono::seconds>(__value)).count();
         else
           __facet.put(
               {__sstr}, __sstr, _CharT(' '), std::addressof(__t), std::to_address(__s), std::to_address(__it + 1));
         break;
 
       case _CharT('q'):
         if constexpr (chrono::__is_duration<_Tp>::value) {
           __sstr << chrono::__units_suffix<_CharT, typename _Tp::period>();
           break;
         }
         __builtin_unreachable();
 
       case _CharT('Q'):
         // TODO FMT Determine the proper ideas
         // - Should it honour the precision?
         // - Shoult it honour the locale setting for the separators?
         // The wording for Q doesn't use the word locale and the effect of
         // precision is unspecified.
         //
         // MSVC STL ignores precision but uses separator
         // FMT honours precision and has a bug for separator
         // https://godbolt.org/z/78b7sMxns
         if constexpr (chrono::__is_duration<_Tp>::value) {
           __sstr << std::format(_LIBCPP_STATICALLY_WIDEN(_CharT, "{}"), __value.count());
           break;
         }
         __builtin_unreachable();
 
       case _CharT('S'):
       case _CharT('T'):
         __facet.put(
             {__sstr}, __sstr, _CharT(' '), std::addressof(__t), std::to_address(__s), std::to_address(__it + 1));
         if constexpr (__use_fraction<_Tp>())
           __formatter::__format_sub_seconds(__sstr, __value);
         break;
 
         // Unlike time_put and strftime the formatting library requires %Y
         //
         // [tab:time.format.spec]
         //   The year as a decimal number. If the result is less than four digits
         //   it is left-padded with 0 to four digits.
         //
         // This means years in the range (-1000, 1000) need manual formatting.
         // It's unclear whether %EY needs the same treatment. For example the
         // Japanese EY contains the era name and year. This is zero-padded to 2
         // digits in time_put (note that older glibc versions didn't do
         // padding.) However most eras won't reach 100 years, let alone 1000.
         // So padding to 4 digits seems unwanted for Japanese.
         //
         // The same applies to %Ex since that too depends on the era.
         //
         // %x the locale's date representation is currently doesn't handle the
         // zero-padding too.
         //
         // The 4 digits can be implemented better at a later time. On POSIX
         // systems the required information can be extracted by nl_langinfo
         // https://man7.org/linux/man-pages/man3/nl_langinfo.3.html
         //
         // Note since year < -1000 is expected to be rare it uses the more
         // expensive year routine.
         //
         // TODO FMT evaluate the comment above.
 
 #  if defined(__GLIBC__) || defined(_AIX) || defined(_WIN32)
       case _CharT('y'):
         // Glibc fails for negative values, AIX for positive values too.
         __sstr << std::format(_LIBCPP_STATICALLY_WIDEN(_CharT, "{:02}"), (std::abs(__t.tm_year + 1900)) % 100);
         break;
 #  endif // defined(__GLIBC__) || defined(_AIX) || defined(_WIN32)
 
       case _CharT('Y'):
         // Depending on the platform's libc the range of supported years is
         // limited. Instead of of testing all conditions use the internal
         // implementation unconditionally.
         __formatter::__format_year(__sstr, __t.tm_year + 1900);
         break;
 
       case _CharT('F'):
         // Depending on the platform's libc the range of supported years is
         // limited. Instead of testing all conditions use the internal
         // implementation unconditionally.
         __formatter::__format_year(__sstr, __t.tm_year + 1900);
         __sstr << std::format(_LIBCPP_STATICALLY_WIDEN(_CharT, "-{:02}-{:02}"), __t.tm_mon + 1, __t.tm_mday);
         break;
 
       case _CharT('z'):
         __formatter::__format_zone_offset(__sstr, __z.__offset, false);
         break;
 
       case _CharT('Z'):
         // __abbrev is always a char so the copy may convert.
         ranges::copy(__z.__abbrev, std::ostreambuf_iterator<_CharT>{__sstr});
         break;
 
       case _CharT('O'):
         if constexpr (__use_fraction<_Tp>()) {
           // Handle OS using the normal representation for the non-fractional
           // part. There seems to be no locale information regarding how the
           // fractional part should be formatted.
           if (*(__it + 1) == 'S') {
             ++__it;
             __facet.put(
                 {__sstr}, __sstr, _CharT(' '), std::addressof(__t), std::to_address(__s), std::to_address(__it + 1));
             __formatter::__format_sub_seconds(__sstr, __value);
             break;
           }
         }
 
         // Oz produces the same output as Ez below.
         [[fallthrough]];
       case _CharT('E'):
         ++__it;
         if (*__it == 'z') {
           __formatter::__format_zone_offset(__sstr, __z.__offset, true);
           break;
         }
         [[fallthrough]];
       default:
         __facet.put(
             {__sstr}, __sstr, _CharT(' '), std::addressof(__t), std::to_address(__s), std::to_address(__it + 1));
         break;
       }
     } else {
       __sstr << *__it;
     }
   }
 }
 
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI constexpr bool __weekday_ok(const _Tp& __value) {
   if constexpr (__is_time_point<_Tp>)
     return true;
   else if constexpr (same_as<_Tp, chrono::day>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::year>)
     return true;
   else if constexpr (same_as<_Tp, chrono::weekday>)
     return true;
   else if constexpr (same_as<_Tp, chrono::weekday_indexed>)
     return true;
   else if constexpr (same_as<_Tp, chrono::weekday_last>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month_day>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month_day_last>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month_weekday>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month_weekday_last>)
     return true;
   else if constexpr (same_as<_Tp, chrono::year_month>)
     return true;
   else if constexpr (same_as<_Tp, chrono::year_month_day>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::year_month_day_last>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::year_month_weekday>)
     return __value.weekday().ok();
   else if constexpr (same_as<_Tp, chrono::year_month_weekday_last>)
     return __value.weekday().ok();
   else if constexpr (__is_hh_mm_ss<_Tp>)
     return true;
 #  if !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
   else if constexpr (same_as<_Tp, chrono::sys_info>)
     return true;
   else if constexpr (same_as<_Tp, chrono::local_info>)
     return true;
 #    if !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&                          \
         !defined(_LIBCPP_HAS_NO_LOCALIZATION)
   else if constexpr (__is_specialization_v<_Tp, chrono::zoned_time>)
     return true;
 #    endif
 #  endif // !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
   else
     static_assert(sizeof(_Tp) == 0, "Add the missing type specialization");
 }
 
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI constexpr bool __weekday_name_ok(const _Tp& __value) {
   if constexpr (__is_time_point<_Tp>)
     return true;
   else if constexpr (same_as<_Tp, chrono::day>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::year>)
     return true;
   else if constexpr (same_as<_Tp, chrono::weekday>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::weekday_indexed>)
     return __value.weekday().ok();
   else if constexpr (same_as<_Tp, chrono::weekday_last>)
     return __value.weekday().ok();
   else if constexpr (same_as<_Tp, chrono::month_day>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month_day_last>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month_weekday>)
     return __value.weekday_indexed().ok();
   else if constexpr (same_as<_Tp, chrono::month_weekday_last>)
     return __value.weekday_indexed().ok();
   else if constexpr (same_as<_Tp, chrono::year_month>)
     return true;
   else if constexpr (same_as<_Tp, chrono::year_month_day>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::year_month_day_last>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::year_month_weekday>)
     return __value.weekday().ok();
   else if constexpr (same_as<_Tp, chrono::year_month_weekday_last>)
     return __value.weekday().ok();
   else if constexpr (__is_hh_mm_ss<_Tp>)
     return true;
 #  if !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
   else if constexpr (same_as<_Tp, chrono::sys_info>)
     return true;
   else if constexpr (same_as<_Tp, chrono::local_info>)
     return true;
 #    if !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&                          \
         !defined(_LIBCPP_HAS_NO_LOCALIZATION)
   else if constexpr (__is_specialization_v<_Tp, chrono::zoned_time>)
     return true;
 #    endif
 #  endif // !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
   else
     static_assert(sizeof(_Tp) == 0, "Add the missing type specialization");
 }
 
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI constexpr bool __date_ok(const _Tp& __value) {
   if constexpr (__is_time_point<_Tp>)
     return true;
   else if constexpr (same_as<_Tp, chrono::day>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::year>)
     return true;
   else if constexpr (same_as<_Tp, chrono::weekday>)
     return true;
   else if constexpr (same_as<_Tp, chrono::weekday_indexed>)
     return true;
   else if constexpr (same_as<_Tp, chrono::weekday_last>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month_day>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month_day_last>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month_weekday>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month_weekday_last>)
     return true;
   else if constexpr (same_as<_Tp, chrono::year_month>)
     return true;
   else if constexpr (same_as<_Tp, chrono::year_month_day>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::year_month_day_last>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::year_month_weekday>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::year_month_weekday_last>)
     return __value.ok();
   else if constexpr (__is_hh_mm_ss<_Tp>)
     return true;
 #  if !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
   else if constexpr (same_as<_Tp, chrono::sys_info>)
     return true;
   else if constexpr (same_as<_Tp, chrono::local_info>)
     return true;
 #    if !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&                          \
         !defined(_LIBCPP_HAS_NO_LOCALIZATION)
   else if constexpr (__is_specialization_v<_Tp, chrono::zoned_time>)
     return true;
 #    endif
 #  endif // !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
   else
     static_assert(sizeof(_Tp) == 0, "Add the missing type specialization");
 }
 
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI constexpr bool __month_name_ok(const _Tp& __value) {
   if constexpr (__is_time_point<_Tp>)
     return true;
   else if constexpr (same_as<_Tp, chrono::day>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month>)
     return __value.ok();
   else if constexpr (same_as<_Tp, chrono::year>)
     return true;
   else if constexpr (same_as<_Tp, chrono::weekday>)
     return true;
   else if constexpr (same_as<_Tp, chrono::weekday_indexed>)
     return true;
   else if constexpr (same_as<_Tp, chrono::weekday_last>)
     return true;
   else if constexpr (same_as<_Tp, chrono::month_day>)
     return __value.month().ok();
   else if constexpr (same_as<_Tp, chrono::month_day_last>)
     return __value.month().ok();
   else if constexpr (same_as<_Tp, chrono::month_weekday>)
     return __value.month().ok();
   else if constexpr (same_as<_Tp, chrono::month_weekday_last>)
     return __value.month().ok();
   else if constexpr (same_as<_Tp, chrono::year_month>)
     return __value.month().ok();
   else if constexpr (same_as<_Tp, chrono::year_month_day>)
     return __value.month().ok();
   else if constexpr (same_as<_Tp, chrono::year_month_day_last>)
     return __value.month().ok();
   else if constexpr (same_as<_Tp, chrono::year_month_weekday>)
     return __value.month().ok();
   else if constexpr (same_as<_Tp, chrono::year_month_weekday_last>)
     return __value.month().ok();
   else if constexpr (__is_hh_mm_ss<_Tp>)
     return true;
 #  if !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
   else if constexpr (same_as<_Tp, chrono::sys_info>)
     return true;
   else if constexpr (same_as<_Tp, chrono::local_info>)
     return true;
 #    if !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&                          \
         !defined(_LIBCPP_HAS_NO_LOCALIZATION)
   else if constexpr (__is_specialization_v<_Tp, chrono::zoned_time>)
     return true;
 #    endif
 #  endif // !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
   else
     static_assert(sizeof(_Tp) == 0, "Add the missing type specialization");
 }
 
 template <class _CharT, class _Tp, class _FormatContext>
 _LIBCPP_HIDE_FROM_ABI auto
 __format_chrono(const _Tp& __value,
                 _FormatContext& __ctx,
                 __format_spec::__parsed_specifications<_CharT> __specs,
                 basic_string_view<_CharT> __chrono_specs) {
   basic_stringstream<_CharT> __sstr;
   // [time.format]/2
   // 2.1 - the "C" locale if the L option is not present in chrono-format-spec, otherwise
   // 2.2 - the locale passed to the formatting function if any, otherwise
   // 2.3 - the global locale.
   // Note that the __ctx's locale() call does 2.2 and 2.3.
   if (__specs.__chrono_.__locale_specific_form_)
     __sstr.imbue(__ctx.locale());
   else
     __sstr.imbue(locale::classic());
 
   if (__chrono_specs.empty())
     __sstr << __value;
   else {
     if constexpr (chrono::__is_duration<_Tp>::value) {
       // A duration can be a user defined arithmetic type. Users may specialize
       // numeric_limits, but they may not specialize is_signed.
       if constexpr (numeric_limits<typename _Tp::rep>::is_signed) {
         if (__value < __value.zero()) {
           __sstr << _CharT('-');
           __formatter::__format_chrono_using_chrono_specs(__sstr, -__value, __chrono_specs);
         } else
           __formatter::__format_chrono_using_chrono_specs(__sstr, __value, __chrono_specs);
       } else
         __formatter::__format_chrono_using_chrono_specs(__sstr, __value, __chrono_specs);
       // TODO FMT When keeping the precision it will truncate the string.
       // Note that the behaviour what the precision does isn't specified.
       __specs.__precision_ = -1;
     } else {
       // Test __weekday_name_ before __weekday_ to give a better error.
       if (__specs.__chrono_.__weekday_name_ && !__formatter::__weekday_name_ok(__value))
         std::__throw_format_error("Formatting a weekday name needs a valid weekday");
 
       if (__specs.__chrono_.__weekday_ && !__formatter::__weekday_ok(__value))
         std::__throw_format_error("Formatting a weekday needs a valid weekday");
 
       if (__specs.__chrono_.__day_of_year_ && !__formatter::__date_ok(__value))
         std::__throw_format_error("Formatting a day of year needs a valid date");
 
       if (__specs.__chrono_.__week_of_year_ && !__formatter::__date_ok(__value))
         std::__throw_format_error("Formatting a week of year needs a valid date");
 
       if (__specs.__chrono_.__month_name_ && !__formatter::__month_name_ok(__value))
         std::__throw_format_error("Formatting a month name from an invalid month number");
 
       if constexpr (__is_hh_mm_ss<_Tp>) {
         // Note this is a pedantic intepretation of the Standard. A hh_mm_ss
         // is no longer a time_of_day and can store an arbitrary number of
         // hours. A number of hours in a 12 or 24 hour clock can't represent
         // 24 hours or more. The functions std::chrono::make12 and
         // std::chrono::make24 reaffirm this view point.
         //
         // Interestingly this will be the only output stream function that
         // throws.
         //
         // TODO FMT The wording probably needs to be adapted to
         // - The displayed hours is hh_mm_ss.hours() % 24
         // - It should probably allow %j in the same fashion as duration.
         // - The stream formatter should change its output when hours >= 24
         //   - Write it as not valid,
         //   - or write the number of days.
         if (__specs.__chrono_.__hour_ && __value.hours().count() > 23)
           std::__throw_format_error("Formatting a hour needs a valid value");
 
         if (__value.is_negative())
           __sstr << _CharT('-');
       }
 
       __formatter::__format_chrono_using_chrono_specs(__sstr, __value, __chrono_specs);
     }
   }
 
   return __formatter::__write_string(__sstr.view(), __ctx.out(), __specs);
 }
 
 } // namespace __formatter
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS __formatter_chrono {
 public:
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator
   __parse(_ParseContext& __ctx, __format_spec::__fields __fields, __format_spec::__flags __flags) {
     return __parser_.__parse(__ctx, __fields, __flags);
   }
 
   template <class _Tp, class _FormatContext>
   _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(const _Tp& __value, _FormatContext& __ctx) const {
     return __formatter::__format_chrono(
         __value, __ctx, __parser_.__parser_.__get_parsed_chrono_specifications(__ctx), __parser_.__chrono_specs_);
   }
 
   __format_spec::__parser_chrono<_CharT> __parser_;
 };
 
 template <class _Duration, __fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::sys_time<_Duration>, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__clock);
   }
 };
 
 template <class _Duration, __fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::file_time<_Duration>, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__clock);
   }
 };
 
 template <class _Duration, __fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::local_time<_Duration>, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     // The flags are not __clock since there is no associated time-zone.
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date_time);
   }
 };
 
 template <class _Rep, class _Period, __fmt_char_type _CharT>
 struct formatter<chrono::duration<_Rep, _Period>, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     // [time.format]/1
     // Giving a precision specification in the chrono-format-spec is valid only
     // for std::chrono::duration types where the representation type Rep is a
     // floating-point type. For all other Rep types, an exception of type
     // format_error is thrown if the chrono-format-spec contains a precision
     // specification.
     //
     // Note this doesn't refer to chrono::treat_as_floating_point_v<_Rep>.
     if constexpr (std::floating_point<_Rep>)
       return _Base::__parse(__ctx, __format_spec::__fields_chrono_fractional, __format_spec::__flags::__duration);
     else
       return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__duration);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::day, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__day);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::month, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::year, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__year);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::weekday, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__weekday);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::weekday_indexed, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__weekday);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::weekday_last, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__weekday);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::month_day, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month_day);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::month_day_last, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::month_weekday, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month_weekday);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::month_weekday_last, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month_weekday);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::year_month, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__year_month);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::year_month_day, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::year_month_day_last, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::year_month_weekday, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<chrono::year_month_weekday_last, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
   }
 };
 
 template <class _Duration, __fmt_char_type _CharT>
 struct formatter<chrono::hh_mm_ss<_Duration>, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__time);
   }
 };
 
 #  if !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
 template <__fmt_char_type _CharT>
 struct formatter<chrono::sys_info, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__time_zone);
   }
 };
 
 template <__fmt_char_type _CharT>
 struct formatter<chrono::local_info, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags{});
   }
 };
 #    if !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&                          \
         !defined(_LIBCPP_HAS_NO_LOCALIZATION)
 // Note due to how libc++'s formatters are implemented there is no need to add
 // the exposition only local-time-format-t abstraction.
 template <class _Duration, class _TimeZonePtr, __fmt_char_type _CharT>
 struct formatter<chrono::zoned_time<_Duration, _TimeZonePtr>, _CharT> : public __formatter_chrono<_CharT> {
 public:
   using _Base = __formatter_chrono<_CharT>;
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__clock);
   }
 };
 #    endif // !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&
            // !defined(_LIBCPP_HAS_NO_LOCALIZATION)
 #  endif   // !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB)
 
 #endif // if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif //  _LIBCPP___CXX03___CHRONO_FORMATTER_H

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