--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/common/date/tz.h	Tue Aug 17 11:19:54 2021 +0200
@@ -0,0 +1,2762 @@
+#ifndef TZ_H
+#define TZ_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016, 2017 Howard Hinnant
+// Copyright (c) 2017 Jiangang Zhuang
+// Copyright (c) 2017 Aaron Bishop
+// Copyright (c) 2017 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that would involve another several millennia of evolution).
+// We did not mean to shout.
+
+// Get more recent database at http://www.iana.org/time-zones
+
+// The notion of "current timezone" is something the operating system is expected to "just
+// know". How it knows this is system specific. It's often a value set by the user at OS
+// installation time and recorded by the OS somewhere. On Linux and Mac systems the current
+// timezone name is obtained by looking at the name or contents of a particular file on
+// disk. On Windows the current timezone name comes from the registry. In either method,
+// there is no guarantee that the "native" current timezone name obtained will match any
+// of the "Standard" names in this library's "database". On Linux, the names usually do
+// seem to match so mapping functions to map from native to "Standard" are typically not
+// required. On Windows, the names are never "Standard" so mapping is always required.
+// Technically any OS may use the mapping process but currently only Windows does use it.
+
+#ifndef USE_OS_TZDB
+#  define USE_OS_TZDB 0
+#endif
+
+#ifndef HAS_REMOTE_API
+#  if USE_OS_TZDB == 0
+#    ifdef _WIN32
+#      define HAS_REMOTE_API 0
+#    else
+#      define HAS_REMOTE_API 1
+#    endif
+#  else  // HAS_REMOTE_API makes no since when using the OS timezone database
+#    define HAS_REMOTE_API 0
+#  endif
+#endif
+
+#ifdef __clang__
+# pragma clang diagnostic push
+# pragma clang diagnostic ignored "-Wconstant-logical-operand"
+#endif
+
+static_assert(!(USE_OS_TZDB && HAS_REMOTE_API),
+              "USE_OS_TZDB and HAS_REMOTE_API can not be used together");
+
+#ifdef __clang__
+# pragma clang diagnostic pop
+#endif
+
+#ifndef AUTO_DOWNLOAD
+#  define AUTO_DOWNLOAD HAS_REMOTE_API
+#endif
+
+static_assert(HAS_REMOTE_API == 0 ? AUTO_DOWNLOAD == 0 : true,
+              "AUTO_DOWNLOAD can not be turned on without HAS_REMOTE_API");
+
+#ifndef USE_SHELL_API
+#  define USE_SHELL_API 1
+#endif
+
+#if USE_OS_TZDB
+#  ifdef _WIN32
+#    error "USE_OS_TZDB can not be used on Windows"
+#  endif
+#  ifndef MISSING_LEAP_SECONDS
+#    ifdef __APPLE__
+#      define MISSING_LEAP_SECONDS 1
+#    else
+#      define MISSING_LEAP_SECONDS 0
+#    endif
+#  endif
+#else
+#  define MISSING_LEAP_SECONDS 0
+#endif
+
+#ifndef HAS_DEDUCTION_GUIDES
+#  if __cplusplus >= 201703
+#    define HAS_DEDUCTION_GUIDES 1
+#  else
+#    define HAS_DEDUCTION_GUIDES 0
+#  endif
+#endif  // HAS_DEDUCTION_GUIDES
+
+#include "date.h"
+
+#if defined(_MSC_VER) && (_MSC_VER < 1900)
+#include "tz_private.h"
+#endif
+
+#include <algorithm>
+#include <atomic>
+#include <cassert>
+#include <chrono>
+#include <istream>
+#include <locale>
+#include <memory>
+#include <mutex>
+#include <ostream>
+#include <sstream>
+#include <stdexcept>
+#include <string>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#ifdef _WIN32
+#  ifdef DATE_BUILD_DLL
+#    define DATE_API __declspec(dllexport)
+#  elif defined(DATE_USE_DLL)
+#    define DATE_API __declspec(dllimport)
+#  else
+#    define DATE_API
+#  endif
+#else
+#  ifdef DATE_BUILD_DLL
+#    define DATE_API __attribute__ ((visibility ("default")))
+#  else
+#    define DATE_API
+#  endif
+#endif
+
+namespace date
+{
+
+enum class choose {earliest, latest};
+
+namespace detail
+{
+    struct undocumented;
+
+    template<typename T>
+    struct nodeduct
+    {
+       using type = T;
+    };
+
+    template<typename T>
+    using nodeduct_t = typename nodeduct<T>::type;
+}
+
+struct sys_info
+{
+    sys_seconds          begin;
+    sys_seconds          end;
+    std::chrono::seconds offset;
+    std::chrono::minutes save;
+    std::string          abbrev;
+};
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const sys_info& r)
+{
+    os << r.begin << '\n';
+    os << r.end << '\n';
+    os << make_time(r.offset) << "\n";
+    os << make_time(r.save) << "\n";
+    os << r.abbrev << '\n';
+    return os;
+}
+
+struct local_info
+{
+    enum {unique, nonexistent, ambiguous} result;
+    sys_info first;
+    sys_info second;
+};
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const local_info& r)
+{
+    if (r.result == local_info::nonexistent)
+        os << "nonexistent between\n";
+    else if (r.result == local_info::ambiguous)
+        os << "ambiguous between\n";
+    os << r.first;
+    if (r.result != local_info::unique)
+    {
+        os << "and\n";
+        os << r.second;
+    }
+    return os;
+}
+
+class nonexistent_local_time
+    : public std::runtime_error
+{
+public:
+    template <class Duration>
+        nonexistent_local_time(local_time<Duration> tp, const local_info& i);
+
+private:
+    template <class Duration>
+    static
+    std::string
+    make_msg(local_time<Duration> tp, const local_info& i);
+};
+
+template <class Duration>
+inline
+nonexistent_local_time::nonexistent_local_time(local_time<Duration> tp,
+                                               const local_info& i)
+    : std::runtime_error(make_msg(tp, i))
+{
+}
+
+template <class Duration>
+std::string
+nonexistent_local_time::make_msg(local_time<Duration> tp, const local_info& i)
+{
+    assert(i.result == local_info::nonexistent);
+    std::ostringstream os;
+    os << tp << " is in a gap between\n"
+       << local_seconds{i.first.end.time_since_epoch()} + i.first.offset << ' '
+       << i.first.abbrev << " and\n"
+       << local_seconds{i.second.begin.time_since_epoch()} + i.second.offset << ' '
+       << i.second.abbrev
+       << " which are both equivalent to\n"
+       << i.first.end << " UTC";
+    return os.str();
+}
+
+class ambiguous_local_time
+    : public std::runtime_error
+{
+public:
+    template <class Duration>
+        ambiguous_local_time(local_time<Duration> tp, const local_info& i);
+
+private:
+    template <class Duration>
+    static
+    std::string
+    make_msg(local_time<Duration> tp, const local_info& i);
+};
+
+template <class Duration>
+inline
+ambiguous_local_time::ambiguous_local_time(local_time<Duration> tp, const local_info& i)
+    : std::runtime_error(make_msg(tp, i))
+{
+}
+
+template <class Duration>
+std::string
+ambiguous_local_time::make_msg(local_time<Duration> tp, const local_info& i)
+{
+    assert(i.result == local_info::ambiguous);
+    std::ostringstream os;
+    os << tp << " is ambiguous.  It could be\n"
+       << tp << ' ' << i.first.abbrev << " == "
+       << tp - i.first.offset << " UTC or\n"
+       << tp << ' ' << i.second.abbrev  << " == "
+       << tp - i.second.offset  << " UTC";
+    return os.str();
+}
+
+class time_zone;
+
+#if HAS_STRING_VIEW
+DATE_API const time_zone* locate_zone(std::string_view tz_name);
+#else
+DATE_API const time_zone* locate_zone(const std::string& tz_name);
+#endif
+
+DATE_API const time_zone* current_zone();
+
+template <class T>
+struct zoned_traits
+{
+};
+
+template <>
+struct zoned_traits<const time_zone*>
+{
+    static
+    const time_zone*
+    default_zone()
+    {
+        return date::locate_zone("Etc/UTC");
+    }
+
+#if HAS_STRING_VIEW
+
+    static
+    const time_zone*
+    locate_zone(std::string_view name)
+    {
+        return date::locate_zone(name);
+    }
+
+#else  // !HAS_STRING_VIEW
+
+    static
+    const time_zone*
+    locate_zone(const std::string& name)
+    {
+        return date::locate_zone(name);
+    }
+
+    static
+    const time_zone*
+    locate_zone(const char* name)
+    {
+        return date::locate_zone(name);
+    }
+
+#endif  // !HAS_STRING_VIEW
+};
+
+template <class Duration, class TimeZonePtr>
+class zoned_time;
+
+template <class Duration1, class Duration2, class TimeZonePtr>
+bool
+operator==(const zoned_time<Duration1, TimeZonePtr>& x,
+           const zoned_time<Duration2, TimeZonePtr>& y);
+
+template <class Duration, class TimeZonePtr = const time_zone*>
+class zoned_time
+{
+public:
+    using duration = typename std::common_type<Duration, std::chrono::seconds>::type;
+
+private:
+    TimeZonePtr        zone_;
+    sys_time<duration> tp_;
+
+public:
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class T = TimeZonePtr,
+              class = decltype(zoned_traits<T>::default_zone())>
+#endif
+        zoned_time();
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class T = TimeZonePtr,
+              class = decltype(zoned_traits<T>::default_zone())>
+#endif
+        zoned_time(const sys_time<Duration>& st);
+    explicit zoned_time(TimeZonePtr z);
+
+#if HAS_STRING_VIEW
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string_view()))
+                  >::value
+              >::type>
+        explicit zoned_time(std::string_view name);
+#else
+#  if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string()))
+                  >::value
+              >::type>
+#  endif
+        explicit zoned_time(const std::string& name);
+#endif
+
+    template <class Duration2,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value
+                      >::type>
+        zoned_time(const zoned_time<Duration2, TimeZonePtr>& zt) NOEXCEPT;
+
+    zoned_time(TimeZonePtr z, const sys_time<Duration>& st);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_convertible
+                  <
+                      decltype(std::declval<T&>()->to_sys(local_time<Duration>{})),
+                      sys_time<duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(TimeZonePtr z, const local_time<Duration>& tp);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_convertible
+                  <
+                      decltype(std::declval<T&>()->to_sys(local_time<Duration>{},
+                                                          choose::earliest)),
+                      sys_time<duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(TimeZonePtr z, const local_time<Duration>& tp, choose c);
+
+    template <class Duration2, class TimeZonePtr2,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value
+                      >::type>
+        zoned_time(TimeZonePtr z, const zoned_time<Duration2, TimeZonePtr2>& zt);
+
+    template <class Duration2, class TimeZonePtr2,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value
+                      >::type>
+        zoned_time(TimeZonePtr z, const zoned_time<Duration2, TimeZonePtr2>& zt, choose);
+
+#if HAS_STRING_VIEW
+
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string_view())),
+                      sys_time<Duration>
+                  >::value
+              >::type>
+        zoned_time(std::string_view name, detail::nodeduct_t<const sys_time<Duration>&> st);
+
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string_view())),
+                      local_time<Duration>
+                  >::value
+              >::type>
+        zoned_time(std::string_view name, detail::nodeduct_t<const local_time<Duration>&> tp);
+
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string_view())),
+                      local_time<Duration>,
+                      choose
+                  >::value
+              >::type>
+        zoned_time(std::string_view name, detail::nodeduct_t<const local_time<Duration>&> tp, choose c);
+
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string_view())),
+                              zoned_time
+                          >::value
+                      >::type>
+        zoned_time(std::string_view name, const zoned_time<Duration2, TimeZonePtr2>& zt);
+
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string_view())),
+                              zoned_time,
+                              choose
+                          >::value
+                      >::type>
+        zoned_time(std::string_view name, const zoned_time<Duration2, TimeZonePtr2>& zt, choose);
+
+#else  // !HAS_STRING_VIEW
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      sys_time<Duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(const std::string& name, const sys_time<Duration>& st);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      sys_time<Duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(const char* name, const sys_time<Duration>& st);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      local_time<Duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(const std::string& name, const local_time<Duration>& tp);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      local_time<Duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(const char* name, const local_time<Duration>& tp);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      local_time<Duration>,
+                      choose
+                  >::value
+              >::type>
+#endif
+        zoned_time(const std::string& name, const local_time<Duration>& tp, choose c);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      local_time<Duration>,
+                      choose
+                  >::value
+              >::type>
+#endif
+        zoned_time(const char* name, const local_time<Duration>& tp, choose c);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string())),
+                              zoned_time
+                          >::value
+                      >::type>
+#else
+    template <class Duration2, class TimeZonePtr2>
+#endif
+        zoned_time(const std::string& name, const zoned_time<Duration2, TimeZonePtr2>& zt);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string())),
+                              zoned_time
+                          >::value
+                      >::type>
+#else
+    template <class Duration2, class TimeZonePtr2>
+#endif
+        zoned_time(const char* name, const zoned_time<Duration2, TimeZonePtr2>& zt);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string())),
+                              zoned_time,
+                              choose
+                          >::value
+                      >::type>
+#else
+    template <class Duration2, class TimeZonePtr2>
+#endif
+        zoned_time(const std::string& name, const zoned_time<Duration2, TimeZonePtr2>& zt,
+                   choose);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string())),
+                              zoned_time,
+                              choose
+                          >::value
+                      >::type>
+#else
+    template <class Duration2, class TimeZonePtr2>
+#endif
+        zoned_time(const char* name, const zoned_time<Duration2, TimeZonePtr2>& zt,
+                   choose);
+
+#endif  // !HAS_STRING_VIEW
+
+    zoned_time& operator=(const sys_time<Duration>& st);
+    zoned_time& operator=(const local_time<Duration>& ut);
+
+    explicit operator sys_time<duration>() const;
+    explicit operator local_time<duration>() const;
+
+    TimeZonePtr          get_time_zone() const;
+    local_time<duration> get_local_time() const;
+    sys_time<duration>   get_sys_time() const;
+    sys_info             get_info() const;
+
+    template <class Duration1, class Duration2, class TimeZonePtr1>
+    friend
+    bool
+    operator==(const zoned_time<Duration1, TimeZonePtr1>& x,
+               const zoned_time<Duration2, TimeZonePtr1>& y);
+
+    template <class CharT, class Traits, class Duration1, class TimeZonePtr1>
+    friend
+    std::basic_ostream<CharT, Traits>&
+    operator<<(std::basic_ostream<CharT, Traits>& os,
+               const zoned_time<Duration1, TimeZonePtr1>& t);
+
+private:
+    template <class D, class T> friend class zoned_time;
+};
+
+using zoned_seconds = zoned_time<std::chrono::seconds>;
+
+#if HAS_DEDUCTION_GUIDES
+
+namespace detail
+{
+   template<typename TimeZonePtrOrName>
+   using time_zone_representation =
+       std::conditional_t
+       <
+           std::is_convertible<TimeZonePtrOrName, std::string_view>::value,
+           time_zone const*,
+           std::remove_cv_t<std::remove_reference_t<TimeZonePtrOrName>>
+       >;
+}
+
+zoned_time()
+    -> zoned_time<std::chrono::seconds>;
+
+template <class Duration>
+zoned_time(sys_time<Duration>)
+    -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>>;
+
+template <class TimeZonePtrOrName>
+zoned_time(TimeZonePtrOrName&&)
+    -> zoned_time<std::chrono::seconds, detail::time_zone_representation<TimeZonePtrOrName>>;
+
+template <class TimeZonePtrOrName, class Duration>
+zoned_time(TimeZonePtrOrName&&, sys_time<Duration>)
+    -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>, detail::time_zone_representation<TimeZonePtrOrName>>;
+
+template <class TimeZonePtrOrName, class Duration>
+zoned_time(TimeZonePtrOrName&&, local_time<Duration>, choose = choose::earliest)
+    -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>, detail::time_zone_representation<TimeZonePtrOrName>>;
+
+template <class Duration, class TimeZonePtrOrName, class TimeZonePtr2>
+zoned_time(TimeZonePtrOrName&&, zoned_time<Duration, TimeZonePtr2>, choose = choose::earliest)
+    -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>, detail::time_zone_representation<TimeZonePtrOrName>>;
+
+#endif  // HAS_DEDUCTION_GUIDES
+
+template <class Duration1, class Duration2, class TimeZonePtr>
+inline
+bool
+operator==(const zoned_time<Duration1, TimeZonePtr>& x,
+           const zoned_time<Duration2, TimeZonePtr>& y)
+{
+    return x.zone_ == y.zone_ && x.tp_ == y.tp_;
+}
+
+template <class Duration1, class Duration2, class TimeZonePtr>
+inline
+bool
+operator!=(const zoned_time<Duration1, TimeZonePtr>& x,
+           const zoned_time<Duration2, TimeZonePtr>& y)
+{
+    return !(x == y);
+}
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+namespace detail
+{
+#  if USE_OS_TZDB
+    struct transition;
+    struct expanded_ttinfo;
+#  else  // !USE_OS_TZDB
+    struct zonelet;
+    class Rule;
+#  endif  // !USE_OS_TZDB
+}
+
+#endif  // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+class time_zone
+{
+private:
+    std::string                          name_;
+#if USE_OS_TZDB
+    std::vector<detail::transition>      transitions_;
+    std::vector<detail::expanded_ttinfo> ttinfos_;
+#else  // !USE_OS_TZDB
+    std::vector<detail::zonelet>         zonelets_;
+#endif  // !USE_OS_TZDB
+    std::unique_ptr<std::once_flag>      adjusted_;
+
+public:
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+    time_zone(time_zone&&) = default;
+    time_zone& operator=(time_zone&&) = default;
+#else   // defined(_MSC_VER) && (_MSC_VER < 1900)
+    time_zone(time_zone&& src);
+    time_zone& operator=(time_zone&& src);
+#endif  // defined(_MSC_VER) && (_MSC_VER < 1900)
+
+    DATE_API explicit time_zone(const std::string& s, detail::undocumented);
+
+    const std::string& name() const NOEXCEPT;
+
+    template <class Duration> sys_info   get_info(sys_time<Duration> st) const;
+    template <class Duration> local_info get_info(local_time<Duration> tp) const;
+
+    template <class Duration>
+        sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_sys(local_time<Duration> tp) const;
+
+    template <class Duration>
+        sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_sys(local_time<Duration> tp, choose z) const;
+
+    template <class Duration>
+        local_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_local(sys_time<Duration> tp) const;
+
+    friend bool operator==(const time_zone& x, const time_zone& y) NOEXCEPT;
+    friend bool operator< (const time_zone& x, const time_zone& y) NOEXCEPT;
+    friend DATE_API std::ostream& operator<<(std::ostream& os, const time_zone& z);
+
+#if !USE_OS_TZDB
+    DATE_API void add(const std::string& s);
+#endif  // !USE_OS_TZDB
+
+private:
+    DATE_API sys_info   get_info_impl(sys_seconds tp) const;
+    DATE_API local_info get_info_impl(local_seconds tp) const;
+
+    template <class Duration>
+        sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_sys_impl(local_time<Duration> tp, choose z, std::false_type) const;
+    template <class Duration>
+        sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_sys_impl(local_time<Duration> tp, choose, std::true_type) const;
+
+#if USE_OS_TZDB
+    DATE_API void init() const;
+    DATE_API void init_impl();
+    DATE_API sys_info
+        load_sys_info(std::vector<detail::transition>::const_iterator i) const;
+
+    template <class TimeType>
+    DATE_API void
+    load_data(std::istream& inf, std::int32_t tzh_leapcnt, std::int32_t tzh_timecnt,
+                                 std::int32_t tzh_typecnt, std::int32_t tzh_charcnt);
+#else  // !USE_OS_TZDB
+    DATE_API sys_info   get_info_impl(sys_seconds tp, int timezone) const;
+    DATE_API void adjust_infos(const std::vector<detail::Rule>& rules);
+    DATE_API void parse_info(std::istream& in);
+#endif  // !USE_OS_TZDB
+};
+
+#if defined(_MSC_VER) && (_MSC_VER < 1900)
+
+inline
+time_zone::time_zone(time_zone&& src)
+    : name_(std::move(src.name_))
+    , zonelets_(std::move(src.zonelets_))
+    , adjusted_(std::move(src.adjusted_))
+    {}
+
+inline
+time_zone&
+time_zone::operator=(time_zone&& src)
+{
+    name_ = std::move(src.name_);
+    zonelets_ = std::move(src.zonelets_);
+    adjusted_ = std::move(src.adjusted_);
+    return *this;
+}
+
+#endif  // defined(_MSC_VER) && (_MSC_VER < 1900)
+
+inline
+const std::string&
+time_zone::name() const NOEXCEPT
+{
+    return name_;
+}
+
+template <class Duration>
+inline
+sys_info
+time_zone::get_info(sys_time<Duration> st) const
+{
+    return get_info_impl(date::floor<std::chrono::seconds>(st));
+}
+
+template <class Duration>
+inline
+local_info
+time_zone::get_info(local_time<Duration> tp) const
+{
+    return get_info_impl(date::floor<std::chrono::seconds>(tp));
+}
+
+template <class Duration>
+inline
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_sys(local_time<Duration> tp) const
+{
+    return to_sys_impl(tp, choose{}, std::true_type{});
+}
+
+template <class Duration>
+inline
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_sys(local_time<Duration> tp, choose z) const
+{
+    return to_sys_impl(tp, z, std::false_type{});
+}
+
+template <class Duration>
+inline
+local_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_local(sys_time<Duration> tp) const
+{
+    using LT = local_time<typename std::common_type<Duration, std::chrono::seconds>::type>;
+    auto i = get_info(tp);
+    return LT{(tp + i.offset).time_since_epoch()};
+}
+
+inline bool operator==(const time_zone& x, const time_zone& y) NOEXCEPT {return x.name_ == y.name_;}
+inline bool operator< (const time_zone& x, const time_zone& y) NOEXCEPT {return x.name_ < y.name_;}
+
+inline bool operator!=(const time_zone& x, const time_zone& y) NOEXCEPT {return !(x == y);}
+inline bool operator> (const time_zone& x, const time_zone& y) NOEXCEPT {return   y < x;}
+inline bool operator<=(const time_zone& x, const time_zone& y) NOEXCEPT {return !(y < x);}
+inline bool operator>=(const time_zone& x, const time_zone& y) NOEXCEPT {return !(x < y);}
+
+template <class Duration>
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_sys_impl(local_time<Duration> tp, choose z, std::false_type) const
+{
+    auto i = get_info(tp);
+    if (i.result == local_info::nonexistent)
+    {
+        return i.first.end;
+    }
+    else if (i.result == local_info::ambiguous)
+    {
+        if (z == choose::latest)
+            return sys_time<Duration>{tp.time_since_epoch()} - i.second.offset;
+    }
+    return sys_time<Duration>{tp.time_since_epoch()} - i.first.offset;
+}
+
+template <class Duration>
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_sys_impl(local_time<Duration> tp, choose, std::true_type) const
+{
+    auto i = get_info(tp);
+    if (i.result == local_info::nonexistent)
+        throw nonexistent_local_time(tp, i);
+    else if (i.result == local_info::ambiguous)
+        throw ambiguous_local_time(tp, i);
+    return sys_time<Duration>{tp.time_since_epoch()} - i.first.offset;
+}
+
+#if !USE_OS_TZDB
+
+class link
+{
+private:
+    std::string name_;
+    std::string target_;
+public:
+    DATE_API explicit link(const std::string& s);
+
+    const std::string& name() const {return name_;}
+    const std::string& target() const {return target_;}
+
+    friend bool operator==(const link& x, const link& y) {return x.name_ == y.name_;}
+    friend bool operator< (const link& x, const link& y) {return x.name_ < y.name_;}
+
+    friend DATE_API std::ostream& operator<<(std::ostream& os, const link& x);
+};
+
+inline bool operator!=(const link& x, const link& y) {return !(x == y);}
+inline bool operator> (const link& x, const link& y) {return   y < x;}
+inline bool operator<=(const link& x, const link& y) {return !(y < x);}
+inline bool operator>=(const link& x, const link& y) {return !(x < y);}
+
+#endif  // !USE_OS_TZDB
+
+#if !MISSING_LEAP_SECONDS
+
+class leap
+{
+private:
+    sys_seconds date_;
+
+public:
+#if USE_OS_TZDB
+    DATE_API explicit leap(const sys_seconds& s, detail::undocumented);
+#else
+    DATE_API explicit leap(const std::string& s, detail::undocumented);
+#endif
+
+    sys_seconds date() const {return date_;}
+
+    friend bool operator==(const leap& x, const leap& y) {return x.date_ == y.date_;}
+    friend bool operator< (const leap& x, const leap& y) {return x.date_ < y.date_;}
+
+    template <class Duration>
+    friend
+    bool
+    operator==(const leap& x, const sys_time<Duration>& y)
+    {
+        return x.date_ == y;
+    }
+
+    template <class Duration>
+    friend
+    bool
+    operator< (const leap& x, const sys_time<Duration>& y)
+    {
+        return x.date_ < y;
+    }
+
+    template <class Duration>
+    friend
+    bool
+    operator< (const sys_time<Duration>& x, const leap& y)
+    {
+        return x < y.date_;
+    }
+
+    friend DATE_API std::ostream& operator<<(std::ostream& os, const leap& x);
+};
+
+inline bool operator!=(const leap& x, const leap& y) {return !(x == y);}
+inline bool operator> (const leap& x, const leap& y) {return   y < x;}
+inline bool operator<=(const leap& x, const leap& y) {return !(y < x);}
+inline bool operator>=(const leap& x, const leap& y) {return !(x < y);}
+
+template <class Duration>
+inline
+bool
+operator==(const sys_time<Duration>& x, const leap& y)
+{
+    return y == x;
+}
+
+template <class Duration>
+inline
+bool
+operator!=(const leap& x, const sys_time<Duration>& y)
+{
+    return !(x == y);
+}
+
+template <class Duration>
+inline
+bool
+operator!=(const sys_time<Duration>& x, const leap& y)
+{
+    return !(x == y);
+}
+
+template <class Duration>
+inline
+bool
+operator> (const leap& x, const sys_time<Duration>& y)
+{
+    return y < x;
+}
+
+template <class Duration>
+inline
+bool
+operator> (const sys_time<Duration>& x, const leap& y)
+{
+    return y < x;
+}
+
+template <class Duration>
+inline
+bool
+operator<=(const leap& x, const sys_time<Duration>& y)
+{
+    return !(y < x);
+}
+
+template <class Duration>
+inline
+bool
+operator<=(const sys_time<Duration>& x, const leap& y)
+{
+    return !(y < x);
+}
+
+template <class Duration>
+inline
+bool
+operator>=(const leap& x, const sys_time<Duration>& y)
+{
+    return !(x < y);
+}
+
+template <class Duration>
+inline
+bool
+operator>=(const sys_time<Duration>& x, const leap& y)
+{
+    return !(x < y);
+}
+
+#endif  // !MISSING_LEAP_SECONDS
+
+#ifdef _WIN32
+
+namespace detail
+{
+
+// The time zone mapping is modelled after this data file:
+// http://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml
+// and the field names match the element names from the mapZone element
+// of windowsZones.xml.
+// The website displays this file here:
+// http://www.unicode.org/cldr/charts/latest/supplemental/zone_tzid.html
+// The html view is sorted before being displayed but is otherwise the same
+// There is a mapping between the os centric view (in this case windows)
+// the html displays uses and the generic view the xml file.
+// That mapping is this:
+// display column "windows" -> xml field "other".
+// display column "region"  -> xml field "territory".
+// display column "tzid"    -> xml field "type".
+// This structure uses the generic terminology because it could be
+// used to to support other os/native name conversions, not just windows,
+// and using the same generic names helps retain the connection to the
+// origin of the data that we are using.
+struct timezone_mapping
+{
+    timezone_mapping(const char* other, const char* territory, const char* type)
+        : other(other), territory(territory), type(type)
+    {
+    }
+    timezone_mapping() = default;
+    std::string other;
+    std::string territory;
+    std::string type;
+};
+
+}  // detail
+
+#endif  // _WIN32
+
+struct tzdb
+{
+    std::string               version = "unknown";
+    std::vector<time_zone>    zones;
+#if !USE_OS_TZDB
+    std::vector<link>         links;
+#endif
+#if !MISSING_LEAP_SECONDS
+    std::vector<leap>         leaps;
+#endif
+#if !USE_OS_TZDB
+    std::vector<detail::Rule> rules;
+#endif
+#ifdef _WIN32
+    std::vector<detail::timezone_mapping> mappings;
+#endif
+    tzdb* next = nullptr;
+
+    tzdb() = default;
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+    tzdb(tzdb&&) = default;
+    tzdb& operator=(tzdb&&) = default;
+#else  // defined(_MSC_VER) && (_MSC_VER < 1900)
+    tzdb(tzdb&& src)
+        : version(std::move(src.version))
+        , zones(std::move(src.zones))
+        , links(std::move(src.links))
+        , leaps(std::move(src.leaps))
+        , rules(std::move(src.rules))
+        , mappings(std::move(src.mappings))
+    {}
+
+    tzdb& operator=(tzdb&& src)
+    {
+        version = std::move(src.version);
+        zones = std::move(src.zones);
+        links = std::move(src.links);
+        leaps = std::move(src.leaps);
+        rules = std::move(src.rules);
+        mappings = std::move(src.mappings);
+        return *this;
+    }
+#endif  // defined(_MSC_VER) && (_MSC_VER < 1900)
+
+#if HAS_STRING_VIEW
+    const time_zone* locate_zone(std::string_view tz_name) const;
+#else
+    const time_zone* locate_zone(const std::string& tz_name) const;
+#endif
+    const time_zone* current_zone() const;
+};
+
+using TZ_DB = tzdb;
+
+DATE_API std::ostream&
+operator<<(std::ostream& os, const tzdb& db);
+
+DATE_API const tzdb& get_tzdb();
+
+class tzdb_list
+{
+    std::atomic<tzdb*> head_{nullptr};
+
+public:
+    ~tzdb_list();
+    tzdb_list() = default;
+    tzdb_list(tzdb_list&& x) noexcept;
+
+    const tzdb& front() const noexcept {return *head_;}
+          tzdb& front()       noexcept {return *head_;}
+
+    class const_iterator;
+
+    const_iterator begin() const noexcept;
+    const_iterator end() const noexcept;
+
+    const_iterator cbegin() const noexcept;
+    const_iterator cend() const noexcept;
+
+    const_iterator erase_after(const_iterator p) noexcept;
+
+    struct undocumented_helper;
+private:
+    void push_front(tzdb* tzdb) noexcept;
+};
+
+class tzdb_list::const_iterator
+{
+    tzdb* p_ = nullptr;
+
+    explicit const_iterator(tzdb* p) noexcept : p_{p} {}
+public:
+    const_iterator() = default;
+
+    using iterator_category = std::forward_iterator_tag;
+    using value_type        = tzdb;
+    using reference         = const value_type&;
+    using pointer           = const value_type*;
+    using difference_type   = std::ptrdiff_t;
+
+    reference operator*() const noexcept {return *p_;}
+    pointer  operator->() const noexcept {return p_;}
+
+    const_iterator& operator++() noexcept {p_ = p_->next; return *this;}
+    const_iterator  operator++(int) noexcept {auto t = *this; ++(*this); return t;}
+
+    friend
+    bool
+    operator==(const const_iterator& x, const const_iterator& y) noexcept
+        {return x.p_ == y.p_;}
+
+    friend
+    bool
+    operator!=(const const_iterator& x, const const_iterator& y) noexcept
+        {return !(x == y);}
+
+    friend class tzdb_list;
+};
+
+inline
+tzdb_list::const_iterator
+tzdb_list::begin() const noexcept
+{
+    return const_iterator{head_};
+}
+
+inline
+tzdb_list::const_iterator
+tzdb_list::end() const noexcept
+{
+    return const_iterator{nullptr};
+}
+
+inline
+tzdb_list::const_iterator
+tzdb_list::cbegin() const noexcept
+{
+    return begin();
+}
+
+inline
+tzdb_list::const_iterator
+tzdb_list::cend() const noexcept
+{
+    return end();
+}
+
+DATE_API tzdb_list& get_tzdb_list();
+
+#if !USE_OS_TZDB
+
+DATE_API const tzdb& reload_tzdb();
+DATE_API void        set_install(const std::string& install);
+
+#endif  // !USE_OS_TZDB
+
+#if HAS_REMOTE_API
+
+DATE_API std::string remote_version();
+DATE_API bool        remote_download(const std::string& version);
+DATE_API bool        remote_install(const std::string& version);
+
+#endif
+
+// zoned_time
+
+namespace detail
+{
+
+template <class T>
+inline
+T*
+to_raw_pointer(T* p) noexcept
+{
+    return p;
+}
+
+template <class Pointer>
+inline
+auto
+to_raw_pointer(Pointer p) noexcept
+    -> decltype(detail::to_raw_pointer(p.operator->()))
+{
+    return detail::to_raw_pointer(p.operator->());
+}
+
+}  // namespace detail
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time()
+    : zone_(zoned_traits<TimeZonePtr>::default_zone())
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const sys_time<Duration>& st)
+    : zone_(zoned_traits<TimeZonePtr>::default_zone())
+    , tp_(st)
+    {}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z)
+    : zone_(std::move(z))
+    {assert(detail::to_raw_pointer(zone_) != nullptr);}
+
+#if HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+template <class T, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name))
+    {}
+
+#else  // !HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name))
+    {}
+
+#endif  // !HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+template <class Duration2, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const zoned_time<Duration2, TimeZonePtr>& zt) NOEXCEPT
+    : zone_(zt.zone_)
+    , tp_(zt.tp_)
+    {}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z, const sys_time<Duration>& st)
+    : zone_(std::move(z))
+    , tp_(st)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z, const local_time<Duration>& t)
+    : zone_(std::move(z))
+    , tp_(zone_->to_sys(t))
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z, const local_time<Duration>& t,
+                                              choose c)
+    : zone_(std::move(z))
+    , tp_(zone_->to_sys(t, c))
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class Duration2, class TimeZonePtr2, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt)
+    : zone_(std::move(z))
+    , tp_(zt.tp_)
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class Duration2, class TimeZonePtr2, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z,
+                                      const zoned_time<Duration2, TimeZonePtr2>& zt, choose)
+    : zoned_time(std::move(z), zt)
+    {}
+
+#if HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+template <class T, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name,
+                                              detail::nodeduct_t<const sys_time<Duration>&> st)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), st)
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class T, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name,
+                                              detail::nodeduct_t<const local_time<Duration>&> t)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t)
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class T, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name,
+                                              detail::nodeduct_t<const local_time<Duration>&> t, choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t, c)
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class Duration2, class TimeZonePtr2, class, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt)
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class Duration2, class TimeZonePtr2, class, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt,
+                                              choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt, c)
+    {}
+
+#else  // !HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name,
+                                              const sys_time<Duration>& st)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), st)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const char* name,
+                                              const sys_time<Duration>& st)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), st)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name,
+                                              const local_time<Duration>& t)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const char* name,
+                                              const local_time<Duration>& t)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name,
+                                              const local_time<Duration>& t, choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t, c)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const char* name,
+                                              const local_time<Duration>& t, choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t, c)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class Duration2, class TimeZonePtr2, class, class>
+#else
+template <class Duration2, class TimeZonePtr2>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class Duration2, class TimeZonePtr2, class, class>
+#else
+template <class Duration2, class TimeZonePtr2>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const char* name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class Duration2, class TimeZonePtr2, class, class>
+#else
+template <class Duration2, class TimeZonePtr2>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt,
+                                              choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt, c)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+template <class Duration2, class TimeZonePtr2, class, class>
+#else
+template <class Duration2, class TimeZonePtr2>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const char* name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt,
+                                              choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt, c)
+    {}
+
+#endif  // HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>&
+zoned_time<Duration, TimeZonePtr>::operator=(const sys_time<Duration>& st)
+{
+    tp_ = st;
+    return *this;
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>&
+zoned_time<Duration, TimeZonePtr>::operator=(const local_time<Duration>& ut)
+{
+    tp_ = zone_->to_sys(ut);
+    return *this;
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>::operator local_time<typename zoned_time<Duration, TimeZonePtr>::duration>() const
+{
+    return get_local_time();
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>::operator sys_time<typename zoned_time<Duration, TimeZonePtr>::duration>() const
+{
+    return get_sys_time();
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+TimeZonePtr
+zoned_time<Duration, TimeZonePtr>::get_time_zone() const
+{
+    return zone_;
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+local_time<typename zoned_time<Duration, TimeZonePtr>::duration>
+zoned_time<Duration, TimeZonePtr>::get_local_time() const
+{
+    return zone_->to_local(tp_);
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+sys_time<typename zoned_time<Duration, TimeZonePtr>::duration>
+zoned_time<Duration, TimeZonePtr>::get_sys_time() const
+{
+    return tp_;
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+sys_info
+zoned_time<Duration, TimeZonePtr>::get_info() const
+{
+    return zone_->get_info(tp_);
+}
+
+// make_zoned_time
+
+inline
+zoned_time<std::chrono::seconds>
+make_zoned()
+{
+    return zoned_time<std::chrono::seconds>();
+}
+
+template <class Duration>
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+make_zoned(const sys_time<Duration>& tp)
+{
+    return zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type>(tp);
+}
+
+template <class TimeZonePtr
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+          , class = typename std::enable_if
+          <
+            std::is_class
+            <
+                typename std::decay
+                <
+                    decltype(*detail::to_raw_pointer(std::declval<TimeZonePtr&>()))
+                >::type
+            >{}
+          >::type
+#endif
+         >
+inline
+zoned_time<std::chrono::seconds, TimeZonePtr>
+make_zoned(TimeZonePtr z)
+{
+    return zoned_time<std::chrono::seconds, TimeZonePtr>(std::move(z));
+}
+
+inline
+zoned_seconds
+make_zoned(const std::string& name)
+{
+    return zoned_seconds(name);
+}
+
+template <class Duration, class TimeZonePtr
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+          , class = typename std::enable_if
+          <
+            std::is_class<typename std::decay<decltype(*std::declval<TimeZonePtr&>())>::type>{}
+          >::type
+#endif
+         >
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type, TimeZonePtr>
+make_zoned(TimeZonePtr zone, const local_time<Duration>& tp)
+{
+    return zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type,
+                      TimeZonePtr>(std::move(zone), tp);
+}
+
+template <class Duration, class TimeZonePtr
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+          , class = typename std::enable_if
+          <
+            std::is_class<typename std::decay<decltype(*std::declval<TimeZonePtr&>())>::type>{}
+          >::type
+#endif
+         >
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type, TimeZonePtr>
+make_zoned(TimeZonePtr zone, const local_time<Duration>& tp, choose c)
+{
+    return zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type,
+                      TimeZonePtr>(std::move(zone), tp, c);
+}
+
+template <class Duration>
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+make_zoned(const std::string& name, const local_time<Duration>& tp)
+{
+    return zoned_time<typename std::common_type<Duration,
+                      std::chrono::seconds>::type>(name, tp);
+}
+
+template <class Duration>
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+make_zoned(const std::string& name, const local_time<Duration>& tp, choose c)
+{
+    return zoned_time<typename std::common_type<Duration,
+                      std::chrono::seconds>::type>(name, tp, c);
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>
+make_zoned(TimeZonePtr zone, const zoned_time<Duration, TimeZonePtr>& zt)
+{
+    return zoned_time<Duration, TimeZonePtr>(std::move(zone), zt);
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>
+make_zoned(const std::string& name, const zoned_time<Duration, TimeZonePtr>& zt)
+{
+    return zoned_time<Duration, TimeZonePtr>(name, zt);
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>
+make_zoned(TimeZonePtr zone, const zoned_time<Duration, TimeZonePtr>& zt, choose c)
+{
+    return zoned_time<Duration, TimeZonePtr>(std::move(zone), zt, c);
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>
+make_zoned(const std::string& name, const zoned_time<Duration, TimeZonePtr>& zt, choose c)
+{
+    return zoned_time<Duration, TimeZonePtr>(name, zt, c);
+}
+
+template <class Duration, class TimeZonePtr
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+          , class = typename std::enable_if
+          <
+            std::is_class<typename std::decay<decltype(*std::declval<TimeZonePtr&>())>::type>{}
+          >::type
+#endif
+         >
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type, TimeZonePtr>
+make_zoned(TimeZonePtr zone, const sys_time<Duration>& st)
+{
+    return zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type,
+                      TimeZonePtr>(std::move(zone), st);
+}
+
+template <class Duration>
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+make_zoned(const std::string& name, const sys_time<Duration>& st)
+{
+    return zoned_time<typename std::common_type<Duration,
+                      std::chrono::seconds>::type>(name, st);
+}
+
+template <class CharT, class Traits, class Duration, class TimeZonePtr>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const zoned_time<Duration, TimeZonePtr>& tp)
+{
+    using duration = typename zoned_time<Duration, TimeZonePtr>::duration;
+    using LT = local_time<duration>;
+    auto const st = tp.get_sys_time();
+    auto const info = tp.get_time_zone()->get_info(st);
+    return to_stream(os, fmt, LT{(st+info.offset).time_since_epoch()},
+                     &info.abbrev, &info.offset);
+}
+
+template <class CharT, class Traits, class Duration, class TimeZonePtr>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const zoned_time<Duration, TimeZonePtr>& t)
+{
+    const CharT fmt[] = {'%', 'F', ' ', '%', 'T', ' ', '%', 'Z', CharT{}};
+    return to_stream(os, fmt, t);
+}
+
+#if !MISSING_LEAP_SECONDS
+
+class utc_clock
+{
+public:
+    using duration                  = std::chrono::system_clock::duration;
+    using rep                       = duration::rep;
+    using period                    = duration::period;
+    using time_point                = std::chrono::time_point<utc_clock>;
+    static CONSTDATA bool is_steady = false;
+
+    static time_point now();
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<std::chrono::system_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    to_sys(const std::chrono::time_point<utc_clock, Duration>&);
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<utc_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    from_sys(const std::chrono::time_point<std::chrono::system_clock, Duration>&);
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<local_t, typename std::common_type<Duration, std::chrono::seconds>::type>
+    to_local(const std::chrono::time_point<utc_clock, Duration>&);
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<utc_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    from_local(const std::chrono::time_point<local_t, Duration>&);
+};
+
+template <class Duration>
+    using utc_time = std::chrono::time_point<utc_clock, Duration>;
+
+using utc_seconds = utc_time<std::chrono::seconds>;
+
+template <class Duration>
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+utc_clock::from_sys(const sys_time<Duration>& st)
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    auto const& leaps = get_tzdb().leaps;
+    auto const lt = std::upper_bound(leaps.begin(), leaps.end(), st);
+    return utc_time<CD>{st.time_since_epoch() + seconds{lt-leaps.begin()}};
+}
+
+// Return pair<is_leap_second, seconds{number_of_leap_seconds_since_1970}>
+// first is true if ut is during a leap second insertion, otherwise false.
+// If ut is during a leap second insertion, that leap second is included in the count
+template <class Duration>
+std::pair<bool, std::chrono::seconds>
+is_leap_second(date::utc_time<Duration> const& ut)
+{
+    using std::chrono::seconds;
+    using duration = typename std::common_type<Duration, seconds>::type;
+    auto const& leaps = get_tzdb().leaps;
+    auto tp = sys_time<duration>{ut.time_since_epoch()};
+    auto const lt = std::upper_bound(leaps.begin(), leaps.end(), tp);
+    auto ds = seconds{lt-leaps.begin()};
+    tp -= ds;
+    auto ls = false;
+    if (lt > leaps.begin())
+    {
+        if (tp < lt[-1])
+        {
+            if (tp >= lt[-1].date() - seconds{1})
+                ls = true;
+            else
+                --ds;
+        }
+    }
+    return {ls, ds};
+}
+
+struct leap_second_info
+{
+    bool is_leap_second;
+    std::chrono::seconds elapsed;
+};
+
+template <class Duration>
+leap_second_info
+get_leap_second_info(date::utc_time<Duration> const& ut)
+{
+    auto p = is_leap_second(ut);
+    return {p.first, p.second};
+}
+
+template <class Duration>
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+utc_clock::to_sys(const utc_time<Duration>& ut)
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    auto ls = is_leap_second(ut);
+    auto tp = sys_time<CD>{ut.time_since_epoch() - ls.second};
+    if (ls.first)
+        tp = floor<seconds>(tp) + seconds{1} - CD{1};
+    return tp;
+}
+
+inline
+utc_clock::time_point
+utc_clock::now()
+{
+    return from_sys(std::chrono::system_clock::now());
+}
+
+template <class Duration>
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+utc_clock::from_local(const local_time<Duration>& st)
+{
+    return from_sys(sys_time<Duration>{st.time_since_epoch()});
+}
+
+template <class Duration>
+local_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+utc_clock::to_local(const utc_time<Duration>& ut)
+{
+    using CD = typename std::common_type<Duration, std::chrono::seconds>::type;
+    return local_time<CD>{to_sys(ut).time_since_epoch()};
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const utc_time<Duration>& t)
+{
+    using std::chrono::seconds;
+    using CT = typename std::common_type<Duration, seconds>::type;
+    const std::string abbrev("UTC");
+    CONSTDATA seconds offset{0};
+    auto ls = is_leap_second(t);
+    auto tp = sys_time<CT>{t.time_since_epoch() - ls.second};
+    auto const sd = floor<days>(tp);
+    year_month_day ymd = sd;
+    auto time = make_time(tp - sys_seconds{sd});
+    time.seconds(detail::undocumented{}) += seconds{ls.first};
+    fields<CT> fds{ymd, time};
+    return to_stream(os, fmt, fds, &abbrev, &offset);
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const utc_time<Duration>& t)
+{
+    const CharT fmt[] = {'%', 'F', ' ', '%', 'T', CharT{}};
+    return to_stream(os, fmt, t);
+}
+
+template <class Duration, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            utc_time<Duration>& tp, std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using std::chrono::seconds;
+    using std::chrono::minutes;
+    using CT = typename std::common_type<Duration, seconds>::type;
+    minutes offset_local{};
+    auto offptr = offset ? offset : &offset_local;
+    fields<CT> fds{};
+    fds.has_tod = true;
+    from_stream(is, fmt, fds, abbrev, offptr);
+    if (!fds.ymd.ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+    {
+        bool is_60_sec = fds.tod.seconds() == seconds{60};
+        if (is_60_sec)
+            fds.tod.seconds(detail::undocumented{}) -= seconds{1};
+        auto tmp = utc_clock::from_sys(sys_days(fds.ymd) - *offptr + fds.tod.to_duration());
+        if (is_60_sec)
+            tmp += seconds{1};
+        if (is_60_sec != is_leap_second(tmp).first || !fds.tod.in_conventional_range())
+        {
+            is.setstate(std::ios::failbit);
+            return is;
+        }
+        tp = std::chrono::time_point_cast<Duration>(tmp);
+    }
+    return is;
+}
+
+// tai_clock
+
+class tai_clock
+{
+public:
+    using duration                  = std::chrono::system_clock::duration;
+    using rep                       = duration::rep;
+    using period                    = duration::period;
+    using time_point                = std::chrono::time_point<tai_clock>;
+    static const bool is_steady     = false;
+
+    static time_point now();
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<utc_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    to_utc(const std::chrono::time_point<tai_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<tai_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    from_utc(const std::chrono::time_point<utc_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<local_t, typename std::common_type<Duration, date::days>::type>
+    to_local(const std::chrono::time_point<tai_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<tai_clock, typename std::common_type<Duration, date::days>::type>
+    from_local(const std::chrono::time_point<local_t, Duration>&) NOEXCEPT;
+};
+
+template <class Duration>
+    using tai_time = std::chrono::time_point<tai_clock, Duration>;
+
+using tai_seconds = tai_time<std::chrono::seconds>;
+
+template <class Duration>
+inline
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+tai_clock::to_utc(const tai_time<Duration>& t) NOEXCEPT
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    return utc_time<CD>{t.time_since_epoch()} -
+            (sys_days(year{1970}/January/1) - sys_days(year{1958}/January/1) + seconds{10});
+}
+
+template <class Duration>
+inline
+tai_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+tai_clock::from_utc(const utc_time<Duration>& t) NOEXCEPT
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    return tai_time<CD>{t.time_since_epoch()} +
+            (sys_days(year{1970}/January/1) - sys_days(year{1958}/January/1) + seconds{10});
+}
+
+inline
+tai_clock::time_point
+tai_clock::now()
+{
+    return from_utc(utc_clock::now());
+}
+
+template <class Duration>
+inline
+local_time<typename std::common_type<Duration, date::days>::type>
+tai_clock::to_local(const tai_time<Duration>& t) NOEXCEPT
+{
+    using CD = typename std::common_type<Duration, date::days>::type;
+    return local_time<CD>{t.time_since_epoch()} -
+           (local_days(year{1970}/January/1) - local_days(year{1958}/January/1));
+}
+
+template <class Duration>
+inline
+tai_time<typename std::common_type<Duration, date::days>::type>
+tai_clock::from_local(const local_time<Duration>& t) NOEXCEPT
+{
+    using CD = typename std::common_type<Duration, date::days>::type;
+    return tai_time<CD>{t.time_since_epoch()} +
+            (local_days(year{1970}/January/1) - local_days(year{1958}/January/1));
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const tai_time<Duration>& t)
+{
+    const std::string abbrev("TAI");
+    CONSTDATA std::chrono::seconds offset{0};
+    return to_stream(os, fmt, tai_clock::to_local(t), &abbrev, &offset);
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const tai_time<Duration>& t)
+{
+    const CharT fmt[] = {'%', 'F', ' ', '%', 'T', CharT{}};
+    return to_stream(os, fmt, t);
+}
+
+template <class Duration, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            tai_time<Duration>& tp,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    local_time<Duration> lp;
+    from_stream(is, fmt, lp, abbrev, offset);
+    if (!is.fail())
+        tp = tai_clock::from_local(lp);
+    return is;
+}
+
+// gps_clock
+
+class gps_clock
+{
+public:
+    using duration                  = std::chrono::system_clock::duration;
+    using rep                       = duration::rep;
+    using period                    = duration::period;
+    using time_point                = std::chrono::time_point<gps_clock>;
+    static const bool is_steady     = false;
+
+    static time_point now();
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<utc_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    to_utc(const std::chrono::time_point<gps_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<gps_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    from_utc(const std::chrono::time_point<utc_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<local_t, typename std::common_type<Duration, date::days>::type>
+    to_local(const std::chrono::time_point<gps_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<gps_clock, typename std::common_type<Duration, date::days>::type>
+    from_local(const std::chrono::time_point<local_t, Duration>&) NOEXCEPT;
+};
+
+template <class Duration>
+    using gps_time = std::chrono::time_point<gps_clock, Duration>;
+
+using gps_seconds = gps_time<std::chrono::seconds>;
+
+template <class Duration>
+inline
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+gps_clock::to_utc(const gps_time<Duration>& t) NOEXCEPT
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    return utc_time<CD>{t.time_since_epoch()} +
+            (sys_days(year{1980}/January/Sunday[1]) - sys_days(year{1970}/January/1) +
+             seconds{9});
+}
+
+template <class Duration>
+inline
+gps_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+gps_clock::from_utc(const utc_time<Duration>& t) NOEXCEPT
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    return gps_time<CD>{t.time_since_epoch()} -
+            (sys_days(year{1980}/January/Sunday[1]) - sys_days(year{1970}/January/1) +
+             seconds{9});
+}
+
+inline
+gps_clock::time_point
+gps_clock::now()
+{
+    return from_utc(utc_clock::now());
+}
+
+template <class Duration>
+inline
+local_time<typename std::common_type<Duration, date::days>::type>
+gps_clock::to_local(const gps_time<Duration>& t) NOEXCEPT
+{
+    using CD = typename std::common_type<Duration, date::days>::type;
+    return local_time<CD>{t.time_since_epoch()} +
+            (local_days(year{1980}/January/Sunday[1]) - local_days(year{1970}/January/1));
+}
+
+template <class Duration>
+inline
+gps_time<typename std::common_type<Duration, date::days>::type>
+gps_clock::from_local(const local_time<Duration>& t) NOEXCEPT
+{
+    using CD = typename std::common_type<Duration, date::days>::type;
+    return gps_time<CD>{t.time_since_epoch()} -
+            (local_days(year{1980}/January/Sunday[1]) - local_days(year{1970}/January/1));
+}
+
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const gps_time<Duration>& t)
+{
+    const std::string abbrev("GPS");
+    CONSTDATA std::chrono::seconds offset{0};
+    return to_stream(os, fmt, gps_clock::to_local(t), &abbrev, &offset);
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const gps_time<Duration>& t)
+{
+    const CharT fmt[] = {'%', 'F', ' ', '%', 'T', CharT{}};
+    return to_stream(os, fmt, t);
+}
+
+template <class Duration, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            gps_time<Duration>& tp,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    local_time<Duration> lp;
+    from_stream(is, fmt, lp, abbrev, offset);
+    if (!is.fail())
+        tp = gps_clock::from_local(lp);
+    return is;
+}
+
+// clock_time_conversion
+
+template <class DstClock, class SrcClock>
+struct clock_time_conversion
+{};
+
+template <>
+struct clock_time_conversion<std::chrono::system_clock, std::chrono::system_clock>
+{
+    template <class Duration>
+    sys_time<Duration>
+    operator()(const sys_time<Duration>& st) const
+    {
+        return st;
+    }
+};
+
+template <>
+struct clock_time_conversion<utc_clock, utc_clock>
+{
+    template <class Duration>
+    utc_time<Duration>
+    operator()(const utc_time<Duration>& ut) const
+    {
+        return ut;
+    }
+};
+
+template<>
+struct clock_time_conversion<local_t, local_t>
+{
+    template <class Duration>
+    local_time<Duration>
+    operator()(const local_time<Duration>& lt) const
+    {
+        return lt;
+    }
+};
+
+template <>
+struct clock_time_conversion<utc_clock, std::chrono::system_clock>
+{
+    template <class Duration>
+    utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+    operator()(const sys_time<Duration>& st) const
+    {
+        return utc_clock::from_sys(st);
+    }
+};
+
+template <>
+struct clock_time_conversion<std::chrono::system_clock, utc_clock>
+{
+    template <class Duration>
+    sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+    operator()(const utc_time<Duration>& ut) const
+    {
+        return utc_clock::to_sys(ut);
+    }
+};
+
+template<>
+struct clock_time_conversion<local_t, std::chrono::system_clock>
+{
+    template <class Duration>
+    local_time<Duration>
+    operator()(const sys_time<Duration>& st) const
+    {
+       return local_time<Duration>{st.time_since_epoch()};
+    }
+};
+
+template<>
+struct clock_time_conversion<std::chrono::system_clock, local_t>
+{
+    template <class Duration>
+    sys_time<Duration>
+    operator()(const local_time<Duration>& lt) const
+    {
+        return sys_time<Duration>{lt.time_since_epoch()};
+    }
+};
+
+template<>
+struct clock_time_conversion<utc_clock, local_t>
+{
+    template <class Duration>
+    utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+    operator()(const local_time<Duration>& lt) const
+    {
+       return utc_clock::from_local(lt);
+    }
+};
+
+template<>
+struct clock_time_conversion<local_t, utc_clock>
+{
+    template <class Duration>
+    local_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+    operator()(const utc_time<Duration>& ut) const
+    {
+       return utc_clock::to_local(ut);
+    }
+};
+
+template<typename Clock>
+struct clock_time_conversion<Clock, Clock>
+{
+    template <class Duration>
+    std::chrono::time_point<Clock, Duration>
+    operator()(const std::chrono::time_point<Clock, Duration>& tp) const
+    {
+        return tp;
+    }
+};
+
+namespace ctc_detail
+{
+
+template <class Clock, class Duration>
+    using time_point = std::chrono::time_point<Clock, Duration>;
+
+using std::declval;
+using std::chrono::system_clock;
+
+//Check if TimePoint is time for given clock,
+//if not emits hard error
+template <class Clock, class TimePoint>
+struct return_clock_time
+{
+    using clock_time_point = time_point<Clock, typename TimePoint::duration>;
+    using type             = TimePoint;
+
+    static_assert(std::is_same<TimePoint, clock_time_point>::value,
+                  "time point with appropariate clock shall be returned");
+};
+
+// Check if Clock has to_sys method accepting TimePoint with given duration const& and
+// returning sys_time. If so has nested type member equal to return type to_sys.
+template <class Clock, class Duration, class = void>
+struct return_to_sys
+{};
+
+template <class Clock, class Duration>
+struct return_to_sys
+       <
+           Clock, Duration,
+           decltype(Clock::to_sys(declval<time_point<Clock, Duration> const&>()), void())
+       >
+    : return_clock_time
+      <
+          system_clock,
+          decltype(Clock::to_sys(declval<time_point<Clock, Duration> const&>()))
+      >
+{};
+
+// Similiar to above
+template <class Clock, class Duration, class = void>
+struct return_from_sys
+{};
+
+template <class Clock, class Duration>
+struct return_from_sys
+       <
+           Clock, Duration,
+           decltype(Clock::from_sys(declval<time_point<system_clock, Duration> const&>()),
+                    void())
+       >
+    : return_clock_time
+      <
+          Clock,
+          decltype(Clock::from_sys(declval<time_point<system_clock, Duration> const&>()))
+      >
+{};
+
+// Similiar to above
+template <class Clock, class Duration, class = void>
+struct return_to_utc
+{};
+
+template <class Clock, class Duration>
+struct return_to_utc
+       <
+           Clock, Duration,
+           decltype(Clock::to_utc(declval<time_point<Clock, Duration> const&>()), void())
+       >
+    : return_clock_time
+      <
+          utc_clock,
+          decltype(Clock::to_utc(declval<time_point<Clock, Duration> const&>()))>
+{};
+
+// Similiar to above
+template <class Clock, class Duration, class = void>
+struct return_from_utc
+{};
+
+template <class Clock, class Duration>
+struct return_from_utc
+       <
+           Clock, Duration,
+           decltype(Clock::from_utc(declval<time_point<utc_clock, Duration> const&>()),
+                    void())
+       >
+    : return_clock_time
+      <
+          Clock,
+          decltype(Clock::from_utc(declval<time_point<utc_clock, Duration> const&>()))
+      >
+{};
+
+// Similiar to above
+template<typename Clock, typename Duration, typename = void>
+struct return_to_local
+{};
+
+template<typename Clock, typename Duration>
+struct return_to_local
+       <
+          Clock, Duration,
+          decltype(Clock::to_local(declval<time_point<Clock, Duration> const&>()),
+                   void())
+       >
+     : return_clock_time
+       <
+           local_t,
+           decltype(Clock::to_local(declval<time_point<Clock, Duration> const&>()))
+       >
+{};
+
+// Similiar to above
+template<typename Clock, typename Duration, typename = void>
+struct return_from_local
+{};
+
+template<typename Clock, typename Duration>
+struct return_from_local
+       <
+           Clock, Duration,
+           decltype(Clock::from_local(declval<time_point<local_t, Duration> const&>()),
+                    void())
+       >
+     : return_clock_time
+       <
+           Clock,
+           decltype(Clock::from_local(declval<time_point<local_t, Duration> const&>()))
+       >
+{};
+
+}  // namespace ctc_detail
+
+template <class SrcClock>
+struct clock_time_conversion<std::chrono::system_clock, SrcClock>
+{
+    template <class Duration>
+    typename ctc_detail::return_to_sys<SrcClock, Duration>::type
+    operator()(const std::chrono::time_point<SrcClock, Duration>& tp) const
+    {
+        return SrcClock::to_sys(tp);
+    }
+};
+
+template <class DstClock>
+struct clock_time_conversion<DstClock, std::chrono::system_clock>
+{
+    template <class Duration>
+    typename ctc_detail::return_from_sys<DstClock, Duration>::type
+    operator()(const sys_time<Duration>& st) const
+    {
+        return DstClock::from_sys(st);
+    }
+};
+
+template <class SrcClock>
+struct clock_time_conversion<utc_clock, SrcClock>
+{
+    template <class Duration>
+    typename ctc_detail::return_to_utc<SrcClock, Duration>::type
+    operator()(const std::chrono::time_point<SrcClock, Duration>& tp) const
+    {
+        return SrcClock::to_utc(tp);
+    }
+};
+
+template <class DstClock>
+struct clock_time_conversion<DstClock, utc_clock>
+{
+    template <class Duration>
+    typename ctc_detail::return_from_utc<DstClock, Duration>::type
+    operator()(const utc_time<Duration>& ut) const
+    {
+        return DstClock::from_utc(ut);
+    }
+};
+
+template<typename SrcClock>
+struct clock_time_conversion<local_t, SrcClock>
+{
+    template <class Duration>
+    typename ctc_detail::return_to_local<SrcClock, Duration>::type
+    operator()(const std::chrono::time_point<SrcClock, Duration>& tp) const
+    {
+        return SrcClock::to_local(tp);
+    }
+};
+
+template<typename DstClock>
+struct clock_time_conversion<DstClock, local_t>
+{
+    template <class Duration>
+    typename ctc_detail::return_from_local<DstClock, Duration>::type
+    operator()(const local_time<Duration>& lt) const
+    {
+        return DstClock::from_local(lt);
+    }
+};
+
+namespace clock_cast_detail
+{
+
+template <class Clock, class Duration>
+    using time_point = std::chrono::time_point<Clock, Duration>;
+using std::chrono::system_clock;
+
+template <class DstClock, class SrcClock, class Duration>
+auto
+conv_clock(const time_point<SrcClock, Duration>& t)
+    -> decltype(std::declval<clock_time_conversion<DstClock, SrcClock>>()(t))
+{
+    return clock_time_conversion<DstClock, SrcClock>{}(t);
+}
+
+//direct trait conversion, 1st candidate
+template <class DstClock, class SrcClock, class Duration>
+auto
+cc_impl(const time_point<SrcClock, Duration>& t, const time_point<SrcClock, Duration>*)
+    -> decltype(conv_clock<DstClock>(t))
+{
+    return conv_clock<DstClock>(t);
+}
+
+//conversion through sys, 2nd candidate
+template <class DstClock, class SrcClock, class Duration>
+auto
+cc_impl(const time_point<SrcClock, Duration>& t, const void*)
+    -> decltype(conv_clock<DstClock>(conv_clock<system_clock>(t)))
+{
+    return conv_clock<DstClock>(conv_clock<system_clock>(t));
+}
+
+//conversion through utc, 2nd candidate
+template <class DstClock, class SrcClock, class Duration>
+auto
+cc_impl(const time_point<SrcClock, Duration>& t, const void*)
+    -> decltype(0,  // MSVC_WORKAROUND
+                conv_clock<DstClock>(conv_clock<utc_clock>(t)))
+{
+    return conv_clock<DstClock>(conv_clock<utc_clock>(t));
+}
+
+//conversion through sys and utc, 3rd candidate
+template <class DstClock, class SrcClock, class Duration>
+auto
+cc_impl(const time_point<SrcClock, Duration>& t, ...)
+    -> decltype(conv_clock<DstClock>(conv_clock<utc_clock>(conv_clock<system_clock>(t))))
+{
+    return conv_clock<DstClock>(conv_clock<utc_clock>(conv_clock<system_clock>(t)));
+}
+
+//conversion through utc and sys, 3rd candidate
+template <class DstClock, class SrcClock, class Duration>
+auto
+cc_impl(const time_point<SrcClock, Duration>& t, ...)
+    -> decltype(0,  // MSVC_WORKAROUND
+                conv_clock<DstClock>(conv_clock<system_clock>(conv_clock<utc_clock>(t))))
+{
+    return conv_clock<DstClock>(conv_clock<system_clock>(conv_clock<utc_clock>(t)));
+}
+
+}  // namespace clock_cast_detail
+
+template <class DstClock, class SrcClock, class Duration>
+auto
+clock_cast(const std::chrono::time_point<SrcClock, Duration>& tp)
+    -> decltype(clock_cast_detail::cc_impl<DstClock>(tp, &tp))
+{
+    return clock_cast_detail::cc_impl<DstClock>(tp, &tp);
+}
+
+// Deprecated API
+
+template <class Duration>
+inline
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_sys_time(const utc_time<Duration>& t)
+{
+    return utc_clock::to_sys(t);
+}
+
+template <class Duration>
+inline
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_sys_time(const tai_time<Duration>& t)
+{
+    return utc_clock::to_sys(tai_clock::to_utc(t));
+}
+
+template <class Duration>
+inline
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_sys_time(const gps_time<Duration>& t)
+{
+    return utc_clock::to_sys(gps_clock::to_utc(t));
+}
+
+
+template <class Duration>
+inline
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_utc_time(const sys_time<Duration>& t)
+{
+    return utc_clock::from_sys(t);
+}
+
+template <class Duration>
+inline
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_utc_time(const tai_time<Duration>& t)
+{
+    return tai_clock::to_utc(t);
+}
+
+template <class Duration>
+inline
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_utc_time(const gps_time<Duration>& t)
+{
+    return gps_clock::to_utc(t);
+}
+
+
+template <class Duration>
+inline
+tai_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_tai_time(const sys_time<Duration>& t)
+{
+    return tai_clock::from_utc(utc_clock::from_sys(t));
+}
+
+template <class Duration>
+inline
+tai_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_tai_time(const utc_time<Duration>& t)
+{
+    return tai_clock::from_utc(t);
+}
+
+template <class Duration>
+inline
+tai_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_tai_time(const gps_time<Duration>& t)
+{
+    return tai_clock::from_utc(gps_clock::to_utc(t));
+}
+
+
+template <class Duration>
+inline
+gps_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_gps_time(const sys_time<Duration>& t)
+{
+    return gps_clock::from_utc(utc_clock::from_sys(t));
+}
+
+template <class Duration>
+inline
+gps_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_gps_time(const utc_time<Duration>& t)
+{
+    return gps_clock::from_utc(t);
+}
+
+template <class Duration>
+inline
+gps_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_gps_time(const tai_time<Duration>& t)
+{
+    return gps_clock::from_utc(tai_clock::to_utc(t));
+}
+
+#endif  // !MISSING_LEAP_SECONDS
+
+}  // namespace date
+
+#endif  // TZ_H