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 // Formatting library for C++ - chrono support
 //
 // Copyright (c) 2012 - present, Victor Zverovich
 // All rights reserved.
 //
 // For the license information refer to format.h.
 
 #ifndef FMT_CHRONO_H_
 #define FMT_CHRONO_H_
 
 #include <algorithm>
 #include <chrono>
 #include <cmath>    // std::isfinite
 #include <cstring>  // std::memcpy
 #include <ctime>
 #include <iterator>
 #include <locale>
 #include <ostream>
 #include <type_traits>
 
 #include "ostream.h"  // formatbuf
 
 FMT_BEGIN_NAMESPACE
 
 // Check if std::chrono::local_t is available.
 #ifndef FMT_USE_LOCAL_TIME
 #  ifdef __cpp_lib_chrono
 #    define FMT_USE_LOCAL_TIME (__cpp_lib_chrono >= 201907L)
 #  else
 #    define FMT_USE_LOCAL_TIME 0
 #  endif
 #endif
 
 // Check if std::chrono::utc_timestamp is available.
 #ifndef FMT_USE_UTC_TIME
 #  ifdef __cpp_lib_chrono
 #    define FMT_USE_UTC_TIME (__cpp_lib_chrono >= 201907L)
 #  else
 #    define FMT_USE_UTC_TIME 0
 #  endif
 #endif
 
 // Enable tzset.
 #ifndef FMT_USE_TZSET
 // UWP doesn't provide _tzset.
 #  if FMT_HAS_INCLUDE("winapifamily.h")
 #    include <winapifamily.h>
 #  endif
 #  if defined(_WIN32) && (!defined(WINAPI_FAMILY) || \
                           (WINAPI_FAMILY == WINAPI_FAMILY_DESKTOP_APP))
 #    define FMT_USE_TZSET 1
 #  else
 #    define FMT_USE_TZSET 0
 #  endif
 #endif
 
 // Enable safe chrono durations, unless explicitly disabled.
 #ifndef FMT_SAFE_DURATION_CAST
 #  define FMT_SAFE_DURATION_CAST 1
 #endif
 #if FMT_SAFE_DURATION_CAST
 
 // For conversion between std::chrono::durations without undefined
 // behaviour or erroneous results.
 // This is a stripped down version of duration_cast, for inclusion in fmt.
 // See https://github.com/pauldreik/safe_duration_cast
 //
 // Copyright Paul Dreik 2019
 namespace safe_duration_cast {
 
 template <typename To, typename From,
           FMT_ENABLE_IF(!std::is_same<From, To>::value &&
                         std::numeric_limits<From>::is_signed ==
                             std::numeric_limits<To>::is_signed)>
 FMT_CONSTEXPR auto lossless_integral_conversion(const From from, int& ec)
     -> To {
   ec = 0;
   using F = std::numeric_limits<From>;
   using T = std::numeric_limits<To>;
   static_assert(F::is_integer, "From must be integral");
   static_assert(T::is_integer, "To must be integral");
 
   // A and B are both signed, or both unsigned.
   if (detail::const_check(F::digits <= T::digits)) {
     // From fits in To without any problem.
   } else {
     // From does not always fit in To, resort to a dynamic check.
     if (from < (T::min)() || from > (T::max)()) {
       // outside range.
       ec = 1;
       return {};
     }
   }
   return static_cast<To>(from);
 }
 
 /**
  * converts From to To, without loss. If the dynamic value of from
  * can't be converted to To without loss, ec is set.
  */
 template <typename To, typename From,
           FMT_ENABLE_IF(!std::is_same<From, To>::value &&
                         std::numeric_limits<From>::is_signed !=
                             std::numeric_limits<To>::is_signed)>
 FMT_CONSTEXPR auto lossless_integral_conversion(const From from, int& ec)
     -> To {
   ec = 0;
   using F = std::numeric_limits<From>;
   using T = std::numeric_limits<To>;
   static_assert(F::is_integer, "From must be integral");
   static_assert(T::is_integer, "To must be integral");
 
   if (detail::const_check(F::is_signed && !T::is_signed)) {
     // From may be negative, not allowed!
     if (fmt::detail::is_negative(from)) {
       ec = 1;
       return {};
     }
     // From is positive. Can it always fit in To?
     if (detail::const_check(F::digits > T::digits) &&
         from > static_cast<From>(detail::max_value<To>())) {
       ec = 1;
       return {};
     }
   }
 
   if (detail::const_check(!F::is_signed && T::is_signed &&
                           F::digits >= T::digits) &&
       from > static_cast<From>(detail::max_value<To>())) {
     ec = 1;
     return {};
   }
   return static_cast<To>(from);  // Lossless conversion.
 }
 
 template <typename To, typename From,
           FMT_ENABLE_IF(std::is_same<From, To>::value)>
 FMT_CONSTEXPR auto lossless_integral_conversion(const From from, int& ec)
     -> To {
   ec = 0;
   return from;
 }  // function
 
 // clang-format off
 /**
  * converts From to To if possible, otherwise ec is set.
  *
  * input                            |    output
  * ---------------------------------|---------------
  * NaN                              | NaN
  * Inf                              | Inf
  * normal, fits in output           | converted (possibly lossy)
  * normal, does not fit in output   | ec is set
  * subnormal                        | best effort
  * -Inf                             | -Inf
  */
 // clang-format on
 template <typename To, typename From,
           FMT_ENABLE_IF(!std::is_same<From, To>::value)>
 FMT_CONSTEXPR auto safe_float_conversion(const From from, int& ec) -> To {
   ec = 0;
   using T = std::numeric_limits<To>;
   static_assert(std::is_floating_point<From>::value, "From must be floating");
   static_assert(std::is_floating_point<To>::value, "To must be floating");
 
   // catch the only happy case
   if (std::isfinite(from)) {
     if (from >= T::lowest() && from <= (T::max)()) {
       return static_cast<To>(from);
     }
     // not within range.
     ec = 1;
     return {};
   }
 
   // nan and inf will be preserved
   return static_cast<To>(from);
 }  // function
 
 template <typename To, typename From,
           FMT_ENABLE_IF(std::is_same<From, To>::value)>
 FMT_CONSTEXPR auto safe_float_conversion(const From from, int& ec) -> To {
   ec = 0;
   static_assert(std::is_floating_point<From>::value, "From must be floating");
   return from;
 }
 
 /**
  * safe duration cast between integral durations
  */
 template <typename To, typename FromRep, typename FromPeriod,
           FMT_ENABLE_IF(std::is_integral<FromRep>::value),
           FMT_ENABLE_IF(std::is_integral<typename To::rep>::value)>
 auto safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from,
                         int& ec) -> To {
   using From = std::chrono::duration<FromRep, FromPeriod>;
   ec = 0;
   // the basic idea is that we need to convert from count() in the from type
   // to count() in the To type, by multiplying it with this:
   struct Factor
       : std::ratio_divide<typename From::period, typename To::period> {};
 
   static_assert(Factor::num > 0, "num must be positive");
   static_assert(Factor::den > 0, "den must be positive");
 
   // the conversion is like this: multiply from.count() with Factor::num
   // /Factor::den and convert it to To::rep, all this without
   // overflow/underflow. let's start by finding a suitable type that can hold
   // both To, From and Factor::num
   using IntermediateRep =
       typename std::common_type<typename From::rep, typename To::rep,
                                 decltype(Factor::num)>::type;
 
   // safe conversion to IntermediateRep
   IntermediateRep count =
       lossless_integral_conversion<IntermediateRep>(from.count(), ec);
   if (ec) return {};
   // multiply with Factor::num without overflow or underflow
   if (detail::const_check(Factor::num != 1)) {
     const auto max1 = detail::max_value<IntermediateRep>() / Factor::num;
     if (count > max1) {
       ec = 1;
       return {};
     }
     const auto min1 =
         (std::numeric_limits<IntermediateRep>::min)() / Factor::num;
     if (detail::const_check(!std::is_unsigned<IntermediateRep>::value) &&
         count < min1) {
       ec = 1;
       return {};
     }
     count *= Factor::num;
   }
 
   if (detail::const_check(Factor::den != 1)) count /= Factor::den;
   auto tocount = lossless_integral_conversion<typename To::rep>(count, ec);
   return ec ? To() : To(tocount);
 }
 
 /**
  * safe duration_cast between floating point durations
  */
 template <typename To, typename FromRep, typename FromPeriod,
           FMT_ENABLE_IF(std::is_floating_point<FromRep>::value),
           FMT_ENABLE_IF(std::is_floating_point<typename To::rep>::value)>
 auto safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from,
                         int& ec) -> To {
   using From = std::chrono::duration<FromRep, FromPeriod>;
   ec = 0;
   if (std::isnan(from.count())) {
     // nan in, gives nan out. easy.
     return To{std::numeric_limits<typename To::rep>::quiet_NaN()};
   }
   // maybe we should also check if from is denormal, and decide what to do about
   // it.
 
   // +-inf should be preserved.
   if (std::isinf(from.count())) {
     return To{from.count()};
   }
 
   // the basic idea is that we need to convert from count() in the from type
   // to count() in the To type, by multiplying it with this:
   struct Factor
       : std::ratio_divide<typename From::period, typename To::period> {};
 
   static_assert(Factor::num > 0, "num must be positive");
   static_assert(Factor::den > 0, "den must be positive");
 
   // the conversion is like this: multiply from.count() with Factor::num
   // /Factor::den and convert it to To::rep, all this without
   // overflow/underflow. let's start by finding a suitable type that can hold
   // both To, From and Factor::num
   using IntermediateRep =
       typename std::common_type<typename From::rep, typename To::rep,
                                 decltype(Factor::num)>::type;
 
   // force conversion of From::rep -> IntermediateRep to be safe,
   // even if it will never happen be narrowing in this context.
   IntermediateRep count =
       safe_float_conversion<IntermediateRep>(from.count(), ec);
   if (ec) {
     return {};
   }
 
   // multiply with Factor::num without overflow or underflow
   if (detail::const_check(Factor::num != 1)) {
     constexpr auto max1 = detail::max_value<IntermediateRep>() /
                           static_cast<IntermediateRep>(Factor::num);
     if (count > max1) {
       ec = 1;
       return {};
     }
     constexpr auto min1 = std::numeric_limits<IntermediateRep>::lowest() /
                           static_cast<IntermediateRep>(Factor::num);
     if (count < min1) {
       ec = 1;
       return {};
     }
     count *= static_cast<IntermediateRep>(Factor::num);
   }
 
   // this can't go wrong, right? den>0 is checked earlier.
   if (detail::const_check(Factor::den != 1)) {
     using common_t = typename std::common_type<IntermediateRep, intmax_t>::type;
     count /= static_cast<common_t>(Factor::den);
   }
 
   // convert to the to type, safely
   using ToRep = typename To::rep;
 
   const ToRep tocount = safe_float_conversion<ToRep>(count, ec);
   if (ec) {
     return {};
   }
   return To{tocount};
 }
 }  // namespace safe_duration_cast
 #endif
 
 // Prevents expansion of a preceding token as a function-style macro.
 // Usage: f FMT_NOMACRO()
 #define FMT_NOMACRO
 
 namespace detail {
 template <typename T = void> struct null {};
 inline auto localtime_r FMT_NOMACRO(...) -> null<> { return null<>(); }
 inline auto localtime_s(...) -> null<> { return null<>(); }
 inline auto gmtime_r(...) -> null<> { return null<>(); }
 inline auto gmtime_s(...) -> null<> { return null<>(); }
 
 inline auto get_classic_locale() -> const std::locale& {
   static const auto& locale = std::locale::classic();
   return locale;
 }
 
 template <typename CodeUnit> struct codecvt_result {
   static constexpr const size_t max_size = 32;
   CodeUnit buf[max_size];
   CodeUnit* end;
 };
 
 template <typename CodeUnit>
 void write_codecvt(codecvt_result<CodeUnit>& out, string_view in_buf,
                    const std::locale& loc) {
 #if FMT_CLANG_VERSION
 #  pragma clang diagnostic push
 #  pragma clang diagnostic ignored "-Wdeprecated"
   auto& f = std::use_facet<std::codecvt<CodeUnit, char, std::mbstate_t>>(loc);
 #  pragma clang diagnostic pop
 #else
   auto& f = std::use_facet<std::codecvt<CodeUnit, char, std::mbstate_t>>(loc);
 #endif
   auto mb = std::mbstate_t();
   const char* from_next = nullptr;
   auto result = f.in(mb, in_buf.begin(), in_buf.end(), from_next,
                      std::begin(out.buf), std::end(out.buf), out.end);
   if (result != std::codecvt_base::ok)
     FMT_THROW(format_error("failed to format time"));
 }
 
 template <typename OutputIt>
 auto write_encoded_tm_str(OutputIt out, string_view in, const std::locale& loc)
     -> OutputIt {
   if (detail::is_utf8() && loc != get_classic_locale()) {
     // char16_t and char32_t codecvts are broken in MSVC (linkage errors) and
     // gcc-4.
 #if FMT_MSC_VERSION != 0 || \
     (defined(__GLIBCXX__) && !defined(_GLIBCXX_USE_DUAL_ABI))
     // The _GLIBCXX_USE_DUAL_ABI macro is always defined in libstdc++ from gcc-5
     // and newer.
     using code_unit = wchar_t;
 #else
     using code_unit = char32_t;
 #endif
 
     using unit_t = codecvt_result<code_unit>;
     unit_t unit;
     write_codecvt(unit, in, loc);
     // In UTF-8 is used one to four one-byte code units.
     auto u =
         to_utf8<code_unit, basic_memory_buffer<char, unit_t::max_size * 4>>();
     if (!u.convert({unit.buf, to_unsigned(unit.end - unit.buf)}))
       FMT_THROW(format_error("failed to format time"));
     return copy_str<char>(u.c_str(), u.c_str() + u.size(), out);
   }
   return copy_str<char>(in.data(), in.data() + in.size(), out);
 }
 
 template <typename Char, typename OutputIt,
           FMT_ENABLE_IF(!std::is_same<Char, char>::value)>
 auto write_tm_str(OutputIt out, string_view sv, const std::locale& loc)
     -> OutputIt {
   codecvt_result<Char> unit;
   write_codecvt(unit, sv, loc);
   return copy_str<Char>(unit.buf, unit.end, out);
 }
 
 template <typename Char, typename OutputIt,
           FMT_ENABLE_IF(std::is_same<Char, char>::value)>
 auto write_tm_str(OutputIt out, string_view sv, const std::locale& loc)
     -> OutputIt {
   return write_encoded_tm_str(out, sv, loc);
 }
 
 template <typename Char>
 inline void do_write(buffer<Char>& buf, const std::tm& time,
                      const std::locale& loc, char format, char modifier) {
   auto&& format_buf = formatbuf<std::basic_streambuf<Char>>(buf);
   auto&& os = std::basic_ostream<Char>(&format_buf);
   os.imbue(loc);
   const auto& facet = std::use_facet<std::time_put<Char>>(loc);
   auto end = facet.put(os, os, Char(' '), &time, format, modifier);
   if (end.failed()) FMT_THROW(format_error("failed to format time"));
 }
 
 template <typename Char, typename OutputIt,
           FMT_ENABLE_IF(!std::is_same<Char, char>::value)>
 auto write(OutputIt out, const std::tm& time, const std::locale& loc,
            char format, char modifier = 0) -> OutputIt {
   auto&& buf = get_buffer<Char>(out);
   do_write<Char>(buf, time, loc, format, modifier);
   return get_iterator(buf, out);
 }
 
 template <typename Char, typename OutputIt,
           FMT_ENABLE_IF(std::is_same<Char, char>::value)>
 auto write(OutputIt out, const std::tm& time, const std::locale& loc,
            char format, char modifier = 0) -> OutputIt {
   auto&& buf = basic_memory_buffer<Char>();
   do_write<char>(buf, time, loc, format, modifier);
   return write_encoded_tm_str(out, string_view(buf.data(), buf.size()), loc);
 }
 
 template <typename Rep1, typename Rep2>
 struct is_same_arithmetic_type
     : public std::integral_constant<bool,
                                     (std::is_integral<Rep1>::value &&
                                      std::is_integral<Rep2>::value) ||
                                         (std::is_floating_point<Rep1>::value &&
                                          std::is_floating_point<Rep2>::value)> {
 };
 
 template <
     typename To, typename FromRep, typename FromPeriod,
     FMT_ENABLE_IF(is_same_arithmetic_type<FromRep, typename To::rep>::value)>
 auto fmt_duration_cast(std::chrono::duration<FromRep, FromPeriod> from) -> To {
 #if FMT_SAFE_DURATION_CAST
   // Throwing version of safe_duration_cast is only available for
   // integer to integer or float to float casts.
   int ec;
   To to = safe_duration_cast::safe_duration_cast<To>(from, ec);
   if (ec) FMT_THROW(format_error("cannot format duration"));
   return to;
 #else
   // Standard duration cast, may overflow.
   return std::chrono::duration_cast<To>(from);
 #endif
 }
 
 template <
     typename To, typename FromRep, typename FromPeriod,
     FMT_ENABLE_IF(!is_same_arithmetic_type<FromRep, typename To::rep>::value)>
 auto fmt_duration_cast(std::chrono::duration<FromRep, FromPeriod> from) -> To {
   // Mixed integer <-> float cast is not supported by safe_duration_cast.
   return std::chrono::duration_cast<To>(from);
 }
 
 template <typename Duration>
 auto to_time_t(
     std::chrono::time_point<std::chrono::system_clock, Duration> time_point)
     -> std::time_t {
   // Cannot use std::chrono::system_clock::to_time_t since this would first
   // require a cast to std::chrono::system_clock::time_point, which could
   // overflow.
   return fmt_duration_cast<std::chrono::duration<std::time_t>>(
              time_point.time_since_epoch())
       .count();
 }
 }  // namespace detail
 
 FMT_BEGIN_EXPORT
 
 /**
   Converts given time since epoch as ``std::time_t`` value into calendar time,
   expressed in local time. Unlike ``std::localtime``, this function is
   thread-safe on most platforms.
  */
 inline auto localtime(std::time_t time) -> std::tm {
   struct dispatcher {
     std::time_t time_;
     std::tm tm_;
 
     dispatcher(std::time_t t) : time_(t) {}
 
     auto run() -> bool {
       using namespace fmt::detail;
       return handle(localtime_r(&time_, &tm_));
     }
 
     auto handle(std::tm* tm) -> bool { return tm != nullptr; }
 
     auto handle(detail::null<>) -> bool {
       using namespace fmt::detail;
       return fallback(localtime_s(&tm_, &time_));
     }
 
     auto fallback(int res) -> bool { return res == 0; }
 
 #if !FMT_MSC_VERSION
     auto fallback(detail::null<>) -> bool {
       using namespace fmt::detail;
       std::tm* tm = std::localtime(&time_);
       if (tm) tm_ = *tm;
       return tm != nullptr;
     }
 #endif
   };
   dispatcher lt(time);
   // Too big time values may be unsupported.
   if (!lt.run()) FMT_THROW(format_error("time_t value out of range"));
   return lt.tm_;
 }
 
 #if FMT_USE_LOCAL_TIME
 template <typename Duration>
 inline auto localtime(std::chrono::local_time<Duration> time) -> std::tm {
   return localtime(
       detail::to_time_t(std::chrono::current_zone()->to_sys(time)));
 }
 #endif
 
 /**
   Converts given time since epoch as ``std::time_t`` value into calendar time,
   expressed in Coordinated Universal Time (UTC). Unlike ``std::gmtime``, this
   function is thread-safe on most platforms.
  */
 inline auto gmtime(std::time_t time) -> std::tm {
   struct dispatcher {
     std::time_t time_;
     std::tm tm_;
 
     dispatcher(std::time_t t) : time_(t) {}
 
     auto run() -> bool {
       using namespace fmt::detail;
       return handle(gmtime_r(&time_, &tm_));
     }
 
     auto handle(std::tm* tm) -> bool { return tm != nullptr; }
 
     auto handle(detail::null<>) -> bool {
       using namespace fmt::detail;
       return fallback(gmtime_s(&tm_, &time_));
     }
 
     auto fallback(int res) -> bool { return res == 0; }
 
 #if !FMT_MSC_VERSION
     auto fallback(detail::null<>) -> bool {
       std::tm* tm = std::gmtime(&time_);
       if (tm) tm_ = *tm;
       return tm != nullptr;
     }
 #endif
   };
   auto gt = dispatcher(time);
   // Too big time values may be unsupported.
   if (!gt.run()) FMT_THROW(format_error("time_t value out of range"));
   return gt.tm_;
 }
 
 template <typename Duration>
 inline auto gmtime(
     std::chrono::time_point<std::chrono::system_clock, Duration> time_point)
     -> std::tm {
   return gmtime(detail::to_time_t(time_point));
 }
 
 namespace detail {
 
 // Writes two-digit numbers a, b and c separated by sep to buf.
 // The method by Pavel Novikov based on
 // https://johnnylee-sde.github.io/Fast-unsigned-integer-to-time-string/.
 inline void write_digit2_separated(char* buf, unsigned a, unsigned b,
                                    unsigned c, char sep) {
   unsigned long long digits =
       a | (b << 24) | (static_cast<unsigned long long>(c) << 48);
   // Convert each value to BCD.
   // We have x = a * 10 + b and we want to convert it to BCD y = a * 16 + b.
   // The difference is
   //   y - x = a * 6
   // a can be found from x:
   //   a = floor(x / 10)
   // then
   //   y = x + a * 6 = x + floor(x / 10) * 6
   // floor(x / 10) is (x * 205) >> 11 (needs 16 bits).
   digits += (((digits * 205) >> 11) & 0x000f00000f00000f) * 6;
   // Put low nibbles to high bytes and high nibbles to low bytes.
   digits = ((digits & 0x00f00000f00000f0) >> 4) |
            ((digits & 0x000f00000f00000f) << 8);
   auto usep = static_cast<unsigned long long>(sep);
   // Add ASCII '0' to each digit byte and insert separators.
   digits |= 0x3030003030003030 | (usep << 16) | (usep << 40);
 
   constexpr const size_t len = 8;
   if (const_check(is_big_endian())) {
     char tmp[len];
     std::memcpy(tmp, &digits, len);
     std::reverse_copy(tmp, tmp + len, buf);
   } else {
     std::memcpy(buf, &digits, len);
   }
 }
 
 template <typename Period>
 FMT_CONSTEXPR inline auto get_units() -> const char* {
   if (std::is_same<Period, std::atto>::value) return "as";
   if (std::is_same<Period, std::femto>::value) return "fs";
   if (std::is_same<Period, std::pico>::value) return "ps";
   if (std::is_same<Period, std::nano>::value) return "ns";
   if (std::is_same<Period, std::micro>::value) return "µs";
   if (std::is_same<Period, std::milli>::value) return "ms";
   if (std::is_same<Period, std::centi>::value) return "cs";
   if (std::is_same<Period, std::deci>::value) return "ds";
   if (std::is_same<Period, std::ratio<1>>::value) return "s";
   if (std::is_same<Period, std::deca>::value) return "das";
   if (std::is_same<Period, std::hecto>::value) return "hs";
   if (std::is_same<Period, std::kilo>::value) return "ks";
   if (std::is_same<Period, std::mega>::value) return "Ms";
   if (std::is_same<Period, std::giga>::value) return "Gs";
   if (std::is_same<Period, std::tera>::value) return "Ts";
   if (std::is_same<Period, std::peta>::value) return "Ps";
   if (std::is_same<Period, std::exa>::value) return "Es";
   if (std::is_same<Period, std::ratio<60>>::value) return "min";
   if (std::is_same<Period, std::ratio<3600>>::value) return "h";
   if (std::is_same<Period, std::ratio<86400>>::value) return "d";
   return nullptr;
 }
 
 enum class numeric_system {
   standard,
   // Alternative numeric system, e.g. 十二 instead of 12 in ja_JP locale.
   alternative
 };
 
 // Glibc extensions for formatting numeric values.
 enum class pad_type {
   unspecified,
   // Do not pad a numeric result string.
   none,
   // Pad a numeric result string with zeros even if the conversion specifier
   // character uses space-padding by default.
   zero,
   // Pad a numeric result string with spaces.
   space,
 };
 
 template <typename OutputIt>
 auto write_padding(OutputIt out, pad_type pad, int width) -> OutputIt {
   if (pad == pad_type::none) return out;
   return std::fill_n(out, width, pad == pad_type::space ? ' ' : '0');
 }
 
 template <typename OutputIt>
 auto write_padding(OutputIt out, pad_type pad) -> OutputIt {
   if (pad != pad_type::none) *out++ = pad == pad_type::space ? ' ' : '0';
   return out;
 }
 
 // Parses a put_time-like format string and invokes handler actions.
 template <typename Char, typename Handler>
 FMT_CONSTEXPR auto parse_chrono_format(const Char* begin, const Char* end,
                                        Handler&& handler) -> const Char* {
   if (begin == end || *begin == '}') return begin;
   if (*begin != '%') FMT_THROW(format_error("invalid format"));
   auto ptr = begin;
   pad_type pad = pad_type::unspecified;
   while (ptr != end) {
     auto c = *ptr;
     if (c == '}') break;
     if (c != '%') {
       ++ptr;
       continue;
     }
     if (begin != ptr) handler.on_text(begin, ptr);
     ++ptr;  // consume '%'
     if (ptr == end) FMT_THROW(format_error("invalid format"));
     c = *ptr;
     switch (c) {
     case '_':
       pad = pad_type::space;
       ++ptr;
       break;
     case '-':
       pad = pad_type::none;
       ++ptr;
       break;
     case '0':
       pad = pad_type::zero;
       ++ptr;
       break;
     }
     if (ptr == end) FMT_THROW(format_error("invalid format"));
     c = *ptr++;
     switch (c) {
     case '%':
       handler.on_text(ptr - 1, ptr);
       break;
     case 'n': {
       const Char newline[] = {'\n'};
       handler.on_text(newline, newline + 1);
       break;
     }
     case 't': {
       const Char tab[] = {'\t'};
       handler.on_text(tab, tab + 1);
       break;
     }
     // Year:
     case 'Y':
       handler.on_year(numeric_system::standard);
       break;
     case 'y':
       handler.on_short_year(numeric_system::standard);
       break;
     case 'C':
       handler.on_century(numeric_system::standard);
       break;
     case 'G':
       handler.on_iso_week_based_year();
       break;
     case 'g':
       handler.on_iso_week_based_short_year();
       break;
     // Day of the week:
     case 'a':
       handler.on_abbr_weekday();
       break;
     case 'A':
       handler.on_full_weekday();
       break;
     case 'w':
       handler.on_dec0_weekday(numeric_system::standard);
       break;
     case 'u':
       handler.on_dec1_weekday(numeric_system::standard);
       break;
     // Month:
     case 'b':
     case 'h':
       handler.on_abbr_month();
       break;
     case 'B':
       handler.on_full_month();
       break;
     case 'm':
       handler.on_dec_month(numeric_system::standard);
       break;
     // Day of the year/month:
     case 'U':
       handler.on_dec0_week_of_year(numeric_system::standard);
       break;
     case 'W':
       handler.on_dec1_week_of_year(numeric_system::standard);
       break;
     case 'V':
       handler.on_iso_week_of_year(numeric_system::standard);
       break;
     case 'j':
       handler.on_day_of_year();
       break;
     case 'd':
       handler.on_day_of_month(numeric_system::standard);
       break;
     case 'e':
       handler.on_day_of_month_space(numeric_system::standard);
       break;
     // Hour, minute, second:
     case 'H':
       handler.on_24_hour(numeric_system::standard, pad);
       break;
     case 'I':
       handler.on_12_hour(numeric_system::standard, pad);
       break;
     case 'M':
       handler.on_minute(numeric_system::standard, pad);
       break;
     case 'S':
       handler.on_second(numeric_system::standard, pad);
       break;
     // Other:
     case 'c':
       handler.on_datetime(numeric_system::standard);
       break;
     case 'x':
       handler.on_loc_date(numeric_system::standard);
       break;
     case 'X':
       handler.on_loc_time(numeric_system::standard);
       break;
     case 'D':
       handler.on_us_date();
       break;
     case 'F':
       handler.on_iso_date();
       break;
     case 'r':
       handler.on_12_hour_time();
       break;
     case 'R':
       handler.on_24_hour_time();
       break;
     case 'T':
       handler.on_iso_time();
       break;
     case 'p':
       handler.on_am_pm();
       break;
     case 'Q':
       handler.on_duration_value();
       break;
     case 'q':
       handler.on_duration_unit();
       break;
     case 'z':
       handler.on_utc_offset(numeric_system::standard);
       break;
     case 'Z':
       handler.on_tz_name();
       break;
     // Alternative representation:
     case 'E': {
       if (ptr == end) FMT_THROW(format_error("invalid format"));
       c = *ptr++;
       switch (c) {
       case 'Y':
         handler.on_year(numeric_system::alternative);
         break;
       case 'y':
         handler.on_offset_year();
         break;
       case 'C':
         handler.on_century(numeric_system::alternative);
         break;
       case 'c':
         handler.on_datetime(numeric_system::alternative);
         break;
       case 'x':
         handler.on_loc_date(numeric_system::alternative);
         break;
       case 'X':
         handler.on_loc_time(numeric_system::alternative);
         break;
       case 'z':
         handler.on_utc_offset(numeric_system::alternative);
         break;
       default:
         FMT_THROW(format_error("invalid format"));
       }
       break;
     }
     case 'O':
       if (ptr == end) FMT_THROW(format_error("invalid format"));
       c = *ptr++;
       switch (c) {
       case 'y':
         handler.on_short_year(numeric_system::alternative);
         break;
       case 'm':
         handler.on_dec_month(numeric_system::alternative);
         break;
       case 'U':
         handler.on_dec0_week_of_year(numeric_system::alternative);
         break;
       case 'W':
         handler.on_dec1_week_of_year(numeric_system::alternative);
         break;
       case 'V':
         handler.on_iso_week_of_year(numeric_system::alternative);
         break;
       case 'd':
         handler.on_day_of_month(numeric_system::alternative);
         break;
       case 'e':
         handler.on_day_of_month_space(numeric_system::alternative);
         break;
       case 'w':
         handler.on_dec0_weekday(numeric_system::alternative);
         break;
       case 'u':
         handler.on_dec1_weekday(numeric_system::alternative);
         break;
       case 'H':
         handler.on_24_hour(numeric_system::alternative, pad);
         break;
       case 'I':
         handler.on_12_hour(numeric_system::alternative, pad);
         break;
       case 'M':
         handler.on_minute(numeric_system::alternative, pad);
         break;
       case 'S':
         handler.on_second(numeric_system::alternative, pad);
         break;
       case 'z':
         handler.on_utc_offset(numeric_system::alternative);
         break;
       default:
         FMT_THROW(format_error("invalid format"));
       }
       break;
     default:
       FMT_THROW(format_error("invalid format"));
     }
     begin = ptr;
   }
   if (begin != ptr) handler.on_text(begin, ptr);
   return ptr;
 }
 
 template <typename Derived> struct null_chrono_spec_handler {
   FMT_CONSTEXPR void unsupported() {
     static_cast<Derived*>(this)->unsupported();
   }
   FMT_CONSTEXPR void on_year(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_short_year(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_offset_year() { unsupported(); }
   FMT_CONSTEXPR void on_century(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_iso_week_based_year() { unsupported(); }
   FMT_CONSTEXPR void on_iso_week_based_short_year() { unsupported(); }
   FMT_CONSTEXPR void on_abbr_weekday() { unsupported(); }
   FMT_CONSTEXPR void on_full_weekday() { unsupported(); }
   FMT_CONSTEXPR void on_dec0_weekday(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_dec1_weekday(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_abbr_month() { unsupported(); }
   FMT_CONSTEXPR void on_full_month() { unsupported(); }
   FMT_CONSTEXPR void on_dec_month(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_dec0_week_of_year(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_dec1_week_of_year(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_iso_week_of_year(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_day_of_year() { unsupported(); }
   FMT_CONSTEXPR void on_day_of_month(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_day_of_month_space(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_24_hour(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_12_hour(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_minute(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_second(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_datetime(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_loc_date(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_loc_time(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_us_date() { unsupported(); }
   FMT_CONSTEXPR void on_iso_date() { unsupported(); }
   FMT_CONSTEXPR void on_12_hour_time() { unsupported(); }
   FMT_CONSTEXPR void on_24_hour_time() { unsupported(); }
   FMT_CONSTEXPR void on_iso_time() { unsupported(); }
   FMT_CONSTEXPR void on_am_pm() { unsupported(); }
   FMT_CONSTEXPR void on_duration_value() { unsupported(); }
   FMT_CONSTEXPR void on_duration_unit() { unsupported(); }
   FMT_CONSTEXPR void on_utc_offset(numeric_system) { unsupported(); }
   FMT_CONSTEXPR void on_tz_name() { unsupported(); }
 };
 
 struct tm_format_checker : null_chrono_spec_handler<tm_format_checker> {
   FMT_NORETURN void unsupported() { FMT_THROW(format_error("no format")); }
 
   template <typename Char>
   FMT_CONSTEXPR void on_text(const Char*, const Char*) {}
   FMT_CONSTEXPR void on_year(numeric_system) {}
   FMT_CONSTEXPR void on_short_year(numeric_system) {}
   FMT_CONSTEXPR void on_offset_year() {}
   FMT_CONSTEXPR void on_century(numeric_system) {}
   FMT_CONSTEXPR void on_iso_week_based_year() {}
   FMT_CONSTEXPR void on_iso_week_based_short_year() {}
   FMT_CONSTEXPR void on_abbr_weekday() {}
   FMT_CONSTEXPR void on_full_weekday() {}
   FMT_CONSTEXPR void on_dec0_weekday(numeric_system) {}
   FMT_CONSTEXPR void on_dec1_weekday(numeric_system) {}
   FMT_CONSTEXPR void on_abbr_month() {}
   FMT_CONSTEXPR void on_full_month() {}
   FMT_CONSTEXPR void on_dec_month(numeric_system) {}
   FMT_CONSTEXPR void on_dec0_week_of_year(numeric_system) {}
   FMT_CONSTEXPR void on_dec1_week_of_year(numeric_system) {}
   FMT_CONSTEXPR void on_iso_week_of_year(numeric_system) {}
   FMT_CONSTEXPR void on_day_of_year() {}
   FMT_CONSTEXPR void on_day_of_month(numeric_system) {}
   FMT_CONSTEXPR void on_day_of_month_space(numeric_system) {}
   FMT_CONSTEXPR void on_24_hour(numeric_system, pad_type) {}
   FMT_CONSTEXPR void on_12_hour(numeric_system, pad_type) {}
   FMT_CONSTEXPR void on_minute(numeric_system, pad_type) {}
   FMT_CONSTEXPR void on_second(numeric_system, pad_type) {}
   FMT_CONSTEXPR void on_datetime(numeric_system) {}
   FMT_CONSTEXPR void on_loc_date(numeric_system) {}
   FMT_CONSTEXPR void on_loc_time(numeric_system) {}
   FMT_CONSTEXPR void on_us_date() {}
   FMT_CONSTEXPR void on_iso_date() {}
   FMT_CONSTEXPR void on_12_hour_time() {}
   FMT_CONSTEXPR void on_24_hour_time() {}
   FMT_CONSTEXPR void on_iso_time() {}
   FMT_CONSTEXPR void on_am_pm() {}
   FMT_CONSTEXPR void on_utc_offset(numeric_system) {}
   FMT_CONSTEXPR void on_tz_name() {}
 };
 
 inline auto tm_wday_full_name(int wday) -> const char* {
   static constexpr const char* full_name_list[] = {
       "Sunday",   "Monday", "Tuesday", "Wednesday",
       "Thursday", "Friday", "Saturday"};
   return wday >= 0 && wday <= 6 ? full_name_list[wday] : "?";
 }
 inline auto tm_wday_short_name(int wday) -> const char* {
   static constexpr const char* short_name_list[] = {"Sun", "Mon", "Tue", "Wed",
                                                     "Thu", "Fri", "Sat"};
   return wday >= 0 && wday <= 6 ? short_name_list[wday] : "???";
 }
 
 inline auto tm_mon_full_name(int mon) -> const char* {
   static constexpr const char* full_name_list[] = {
       "January", "February", "March",     "April",   "May",      "June",
       "July",    "August",   "September", "October", "November", "December"};
   return mon >= 0 && mon <= 11 ? full_name_list[mon] : "?";
 }
 inline auto tm_mon_short_name(int mon) -> const char* {
   static constexpr const char* short_name_list[] = {
       "Jan", "Feb", "Mar", "Apr", "May", "Jun",
       "Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
   };
   return mon >= 0 && mon <= 11 ? short_name_list[mon] : "???";
 }
 
 template <typename T, typename = void>
 struct has_member_data_tm_gmtoff : std::false_type {};
 template <typename T>
 struct has_member_data_tm_gmtoff<T, void_t<decltype(T::tm_gmtoff)>>
     : std::true_type {};
 
 template <typename T, typename = void>
 struct has_member_data_tm_zone : std::false_type {};
 template <typename T>
 struct has_member_data_tm_zone<T, void_t<decltype(T::tm_zone)>>
     : std::true_type {};
 
 #if FMT_USE_TZSET
 inline void tzset_once() {
   static bool init = []() -> bool {
     _tzset();
     return true;
   }();
   ignore_unused(init);
 }
 #endif
 
 // Converts value to Int and checks that it's in the range [0, upper).
 template <typename T, typename Int, FMT_ENABLE_IF(std::is_integral<T>::value)>
 inline auto to_nonnegative_int(T value, Int upper) -> Int {
   if (!std::is_unsigned<Int>::value &&
       (value < 0 || to_unsigned(value) > to_unsigned(upper))) {
     FMT_THROW(fmt::format_error("chrono value is out of range"));
   }
   return static_cast<Int>(value);
 }
 template <typename T, typename Int, FMT_ENABLE_IF(!std::is_integral<T>::value)>
 inline auto to_nonnegative_int(T value, Int upper) -> Int {
   if (value < 0 || value > static_cast<T>(upper))
     FMT_THROW(format_error("invalid value"));
   return static_cast<Int>(value);
 }
 
 constexpr auto pow10(std::uint32_t n) -> long long {
   return n == 0 ? 1 : 10 * pow10(n - 1);
 }
 
 // Counts the number of fractional digits in the range [0, 18] according to the
 // C++20 spec. If more than 18 fractional digits are required then returns 6 for
 // microseconds precision.
 template <long long Num, long long Den, int N = 0,
           bool Enabled = (N < 19) && (Num <= max_value<long long>() / 10)>
 struct count_fractional_digits {
   static constexpr int value =
       Num % Den == 0 ? N : count_fractional_digits<Num * 10, Den, N + 1>::value;
 };
 
 // Base case that doesn't instantiate any more templates
 // in order to avoid overflow.
 template <long long Num, long long Den, int N>
 struct count_fractional_digits<Num, Den, N, false> {
   static constexpr int value = (Num % Den == 0) ? N : 6;
 };
 
 // Format subseconds which are given as an integer type with an appropriate
 // number of digits.
 template <typename Char, typename OutputIt, typename Duration>
 void write_fractional_seconds(OutputIt& out, Duration d, int precision = -1) {
   constexpr auto num_fractional_digits =
       count_fractional_digits<Duration::period::num,
                               Duration::period::den>::value;
 
   using subsecond_precision = std::chrono::duration<
       typename std::common_type<typename Duration::rep,
                                 std::chrono::seconds::rep>::type,
       std::ratio<1, detail::pow10(num_fractional_digits)>>;
 
   const auto fractional = d - fmt_duration_cast<std::chrono::seconds>(d);
   const auto subseconds =
       std::chrono::treat_as_floating_point<
           typename subsecond_precision::rep>::value
           ? fractional.count()
           : fmt_duration_cast<subsecond_precision>(fractional).count();
   auto n = static_cast<uint32_or_64_or_128_t<long long>>(subseconds);
   const int num_digits = detail::count_digits(n);
 
   int leading_zeroes = (std::max)(0, num_fractional_digits - num_digits);
   if (precision < 0) {
     FMT_ASSERT(!std::is_floating_point<typename Duration::rep>::value, "");
     if (std::ratio_less<typename subsecond_precision::period,
                         std::chrono::seconds::period>::value) {
       *out++ = '.';
       out = std::fill_n(out, leading_zeroes, '0');
       out = format_decimal<Char>(out, n, num_digits).end;
     }
   } else {
     *out++ = '.';
     leading_zeroes = (std::min)(leading_zeroes, precision);
     out = std::fill_n(out, leading_zeroes, '0');
     int remaining = precision - leading_zeroes;
     if (remaining != 0 && remaining < num_digits) {
       n /= to_unsigned(detail::pow10(to_unsigned(num_digits - remaining)));
       out = format_decimal<Char>(out, n, remaining).end;
       return;
     }
     out = format_decimal<Char>(out, n, num_digits).end;
     remaining -= num_digits;
     out = std::fill_n(out, remaining, '0');
   }
 }
 
 // Format subseconds which are given as a floating point type with an
 // appropriate number of digits. We cannot pass the Duration here, as we
 // explicitly need to pass the Rep value in the chrono_formatter.
 template <typename Duration>
 void write_floating_seconds(memory_buffer& buf, Duration duration,
                             int num_fractional_digits = -1) {
   using rep = typename Duration::rep;
   FMT_ASSERT(std::is_floating_point<rep>::value, "");
 
   auto val = duration.count();
 
   if (num_fractional_digits < 0) {
     // For `std::round` with fallback to `round`:
     // On some toolchains `std::round` is not available (e.g. GCC 6).
     using namespace std;
     num_fractional_digits =
         count_fractional_digits<Duration::period::num,
                                 Duration::period::den>::value;
     if (num_fractional_digits < 6 && static_cast<rep>(round(val)) != val)
       num_fractional_digits = 6;
   }
 
   fmt::format_to(std::back_inserter(buf), FMT_STRING("{:.{}f}"),
                  std::fmod(val * static_cast<rep>(Duration::period::num) /
                                static_cast<rep>(Duration::period::den),
                            static_cast<rep>(60)),
                  num_fractional_digits);
 }
 
 template <typename OutputIt, typename Char,
           typename Duration = std::chrono::seconds>
 class tm_writer {
  private:
   static constexpr int days_per_week = 7;
 
   const std::locale& loc_;
   const bool is_classic_;
   OutputIt out_;
   const Duration* subsecs_;
   const std::tm& tm_;
 
   auto tm_sec() const noexcept -> int {
     FMT_ASSERT(tm_.tm_sec >= 0 && tm_.tm_sec <= 61, "");
     return tm_.tm_sec;
   }
   auto tm_min() const noexcept -> int {
     FMT_ASSERT(tm_.tm_min >= 0 && tm_.tm_min <= 59, "");
     return tm_.tm_min;
   }
   auto tm_hour() const noexcept -> int {
     FMT_ASSERT(tm_.tm_hour >= 0 && tm_.tm_hour <= 23, "");
     return tm_.tm_hour;
   }
   auto tm_mday() const noexcept -> int {
     FMT_ASSERT(tm_.tm_mday >= 1 && tm_.tm_mday <= 31, "");
     return tm_.tm_mday;
   }
   auto tm_mon() const noexcept -> int {
     FMT_ASSERT(tm_.tm_mon >= 0 && tm_.tm_mon <= 11, "");
     return tm_.tm_mon;
   }
   auto tm_year() const noexcept -> long long { return 1900ll + tm_.tm_year; }
   auto tm_wday() const noexcept -> int {
     FMT_ASSERT(tm_.tm_wday >= 0 && tm_.tm_wday <= 6, "");
     return tm_.tm_wday;
   }
   auto tm_yday() const noexcept -> int {
     FMT_ASSERT(tm_.tm_yday >= 0 && tm_.tm_yday <= 365, "");
     return tm_.tm_yday;
   }
 
   auto tm_hour12() const noexcept -> int {
     const auto h = tm_hour();
     const auto z = h < 12 ? h : h - 12;
     return z == 0 ? 12 : z;
   }
 
   // POSIX and the C Standard are unclear or inconsistent about what %C and %y
   // do if the year is negative or exceeds 9999. Use the convention that %C
   // concatenated with %y yields the same output as %Y, and that %Y contains at
   // least 4 characters, with more only if necessary.
   auto split_year_lower(long long year) const noexcept -> int {
     auto l = year % 100;
     if (l < 0) l = -l;  // l in [0, 99]
     return static_cast<int>(l);
   }
 
   // Algorithm: https://en.wikipedia.org/wiki/ISO_week_date.
   auto iso_year_weeks(long long curr_year) const noexcept -> int {
     const auto prev_year = curr_year - 1;
     const auto curr_p =
         (curr_year + curr_year / 4 - curr_year / 100 + curr_year / 400) %
         days_per_week;
     const auto prev_p =
         (prev_year + prev_year / 4 - prev_year / 100 + prev_year / 400) %
         days_per_week;
     return 52 + ((curr_p == 4 || prev_p == 3) ? 1 : 0);
   }
   auto iso_week_num(int tm_yday, int tm_wday) const noexcept -> int {
     return (tm_yday + 11 - (tm_wday == 0 ? days_per_week : tm_wday)) /
            days_per_week;
   }
   auto tm_iso_week_year() const noexcept -> long long {
     const auto year = tm_year();
     const auto w = iso_week_num(tm_yday(), tm_wday());
     if (w < 1) return year - 1;
     if (w > iso_year_weeks(year)) return year + 1;
     return year;
   }
   auto tm_iso_week_of_year() const noexcept -> int {
     const auto year = tm_year();
     const auto w = iso_week_num(tm_yday(), tm_wday());
     if (w < 1) return iso_year_weeks(year - 1);
     if (w > iso_year_weeks(year)) return 1;
     return w;
   }
 
   void write1(int value) {
     *out_++ = static_cast<char>('0' + to_unsigned(value) % 10);
   }
   void write2(int value) {
     const char* d = digits2(to_unsigned(value) % 100);
     *out_++ = *d++;
     *out_++ = *d;
   }
   void write2(int value, pad_type pad) {
     unsigned int v = to_unsigned(value) % 100;
     if (v >= 10) {
       const char* d = digits2(v);
       *out_++ = *d++;
       *out_++ = *d;
     } else {
       out_ = detail::write_padding(out_, pad);
       *out_++ = static_cast<char>('0' + v);
     }
   }
 
   void write_year_extended(long long year) {
     // At least 4 characters.
     int width = 4;
     if (year < 0) {
       *out_++ = '-';
       year = 0 - year;
       --width;
     }
     uint32_or_64_or_128_t<long long> n = to_unsigned(year);
     const int num_digits = count_digits(n);
     if (width > num_digits) out_ = std::fill_n(out_, width - num_digits, '0');
     out_ = format_decimal<Char>(out_, n, num_digits).end;
   }
   void write_year(long long year) {
     if (year >= 0 && year < 10000) {
       write2(static_cast<int>(year / 100));
       write2(static_cast<int>(year % 100));
     } else {
       write_year_extended(year);
     }
   }
 
   void write_utc_offset(long offset, numeric_system ns) {
     if (offset < 0) {
       *out_++ = '-';
       offset = -offset;
     } else {
       *out_++ = '+';
     }
     offset /= 60;
     write2(static_cast<int>(offset / 60));
     if (ns != numeric_system::standard) *out_++ = ':';
     write2(static_cast<int>(offset % 60));
   }
   template <typename T, FMT_ENABLE_IF(has_member_data_tm_gmtoff<T>::value)>
   void format_utc_offset_impl(const T& tm, numeric_system ns) {
     write_utc_offset(tm.tm_gmtoff, ns);
   }
   template <typename T, FMT_ENABLE_IF(!has_member_data_tm_gmtoff<T>::value)>
   void format_utc_offset_impl(const T& tm, numeric_system ns) {
 #if defined(_WIN32) && defined(_UCRT)
 #  if FMT_USE_TZSET
     tzset_once();
 #  endif
     long offset = 0;
     _get_timezone(&offset);
     if (tm.tm_isdst) {
       long dstbias = 0;
       _get_dstbias(&dstbias);
       offset += dstbias;
     }
     write_utc_offset(-offset, ns);
 #else
     if (ns == numeric_system::standard) return format_localized('z');
 
     // Extract timezone offset from timezone conversion functions.
     std::tm gtm = tm;
     std::time_t gt = std::mktime(&gtm);
     std::tm ltm = gmtime(gt);
     std::time_t lt = std::mktime(&ltm);
     long offset = gt - lt;
     write_utc_offset(offset, ns);
 #endif
   }
 
   template <typename T, FMT_ENABLE_IF(has_member_data_tm_zone<T>::value)>
   void format_tz_name_impl(const T& tm) {
     if (is_classic_)
       out_ = write_tm_str<Char>(out_, tm.tm_zone, loc_);
     else
       format_localized('Z');
   }
   template <typename T, FMT_ENABLE_IF(!has_member_data_tm_zone<T>::value)>
   void format_tz_name_impl(const T&) {
     format_localized('Z');
   }
 
   void format_localized(char format, char modifier = 0) {
     out_ = write<Char>(out_, tm_, loc_, format, modifier);
   }
 
  public:
   tm_writer(const std::locale& loc, OutputIt out, const std::tm& tm,
             const Duration* subsecs = nullptr)
       : loc_(loc),
         is_classic_(loc_ == get_classic_locale()),
         out_(out),
         subsecs_(subsecs),
         tm_(tm) {}
 
   auto out() const -> OutputIt { return out_; }
 
   FMT_CONSTEXPR void on_text(const Char* begin, const Char* end) {
     out_ = copy_str<Char>(begin, end, out_);
   }
 
   void on_abbr_weekday() {
     if (is_classic_)
       out_ = write(out_, tm_wday_short_name(tm_wday()));
     else
       format_localized('a');
   }
   void on_full_weekday() {
     if (is_classic_)
       out_ = write(out_, tm_wday_full_name(tm_wday()));
     else
       format_localized('A');
   }
   void on_dec0_weekday(numeric_system ns) {
     if (is_classic_ || ns == numeric_system::standard) return write1(tm_wday());
     format_localized('w', 'O');
   }
   void on_dec1_weekday(numeric_system ns) {
     if (is_classic_ || ns == numeric_system::standard) {
       auto wday = tm_wday();
       write1(wday == 0 ? days_per_week : wday);
     } else {
       format_localized('u', 'O');
     }
   }
 
   void on_abbr_month() {
     if (is_classic_)
       out_ = write(out_, tm_mon_short_name(tm_mon()));
     else
       format_localized('b');
   }
   void on_full_month() {
     if (is_classic_)
       out_ = write(out_, tm_mon_full_name(tm_mon()));
     else
       format_localized('B');
   }
 
   void on_datetime(numeric_system ns) {
     if (is_classic_) {
       on_abbr_weekday();
       *out_++ = ' ';
       on_abbr_month();
       *out_++ = ' ';
       on_day_of_month_space(numeric_system::standard);
       *out_++ = ' ';
       on_iso_time();
       *out_++ = ' ';
       on_year(numeric_system::standard);
     } else {
       format_localized('c', ns == numeric_system::standard ? '\0' : 'E');
     }
   }
   void on_loc_date(numeric_system ns) {
     if (is_classic_)
       on_us_date();
     else
       format_localized('x', ns == numeric_system::standard ? '\0' : 'E');
   }
   void on_loc_time(numeric_system ns) {
     if (is_classic_)
       on_iso_time();
     else
       format_localized('X', ns == numeric_system::standard ? '\0' : 'E');
   }
   void on_us_date() {
     char buf[8];
     write_digit2_separated(buf, to_unsigned(tm_mon() + 1),
                            to_unsigned(tm_mday()),
                            to_unsigned(split_year_lower(tm_year())), '/');
     out_ = copy_str<Char>(std::begin(buf), std::end(buf), out_);
   }
   void on_iso_date() {
     auto year = tm_year();
     char buf[10];
     size_t offset = 0;
     if (year >= 0 && year < 10000) {
       copy2(buf, digits2(static_cast<size_t>(year / 100)));
     } else {
       offset = 4;
       write_year_extended(year);
       year = 0;
     }
     write_digit2_separated(buf + 2, static_cast<unsigned>(year % 100),
                            to_unsigned(tm_mon() + 1), to_unsigned(tm_mday()),
                            '-');
     out_ = copy_str<Char>(std::begin(buf) + offset, std::end(buf), out_);
   }
 
   void on_utc_offset(numeric_system ns) { format_utc_offset_impl(tm_, ns); }
   void on_tz_name() { format_tz_name_impl(tm_); }
 
   void on_year(numeric_system ns) {
     if (is_classic_ || ns == numeric_system::standard)
       return write_year(tm_year());
     format_localized('Y', 'E');
   }
   void on_short_year(numeric_system ns) {
     if (is_classic_ || ns == numeric_system::standard)
       return write2(split_year_lower(tm_year()));
     format_localized('y', 'O');
   }
   void on_offset_year() {
     if (is_classic_) return write2(split_year_lower(tm_year()));
     format_localized('y', 'E');
   }
 
   void on_century(numeric_system ns) {
     if (is_classic_ || ns == numeric_system::standard) {
       auto year = tm_year();
       auto upper = year / 100;
       if (year >= -99 && year < 0) {
         // Zero upper on negative year.
         *out_++ = '-';
         *out_++ = '0';
       } else if (upper >= 0 && upper < 100) {
         write2(static_cast<int>(upper));
       } else {
         out_ = write<Char>(out_, upper);
       }
     } else {
       format_localized('C', 'E');
     }
   }
 
   void on_dec_month(numeric_system ns) {
     if (is_classic_ || ns == numeric_system::standard)
       return write2(tm_mon() + 1);
     format_localized('m', 'O');
   }
 
   void on_dec0_week_of_year(numeric_system ns) {
     if (is_classic_ || ns == numeric_system::standard)
       return write2((tm_yday() + days_per_week - tm_wday()) / days_per_week);
     format_localized('U', 'O');
   }
   void on_dec1_week_of_year(numeric_system ns) {
     if (is_classic_ || ns == numeric_system::standard) {
       auto wday = tm_wday();
       write2((tm_yday() + days_per_week -
               (wday == 0 ? (days_per_week - 1) : (wday - 1))) /
              days_per_week);
     } else {
       format_localized('W', 'O');
     }
   }
   void on_iso_week_of_year(numeric_system ns) {
     if (is_classic_ || ns == numeric_system::standard)
       return write2(tm_iso_week_of_year());
     format_localized('V', 'O');
   }
 
   void on_iso_week_based_year() { write_year(tm_iso_week_year()); }
   void on_iso_week_based_short_year() {
     write2(split_year_lower(tm_iso_week_year()));
   }
 
   void on_day_of_year() {
     auto yday = tm_yday() + 1;
     write1(yday / 100);
     write2(yday % 100);
   }
   void on_day_of_month(numeric_system ns) {
     if (is_classic_ || ns == numeric_system::standard) return write2(tm_mday());
     format_localized('d', 'O');
   }
   void on_day_of_month_space(numeric_system ns) {
     if (is_classic_ || ns == numeric_system::standard) {
       auto mday = to_unsigned(tm_mday()) % 100;
       const char* d2 = digits2(mday);
       *out_++ = mday < 10 ? ' ' : d2[0];
       *out_++ = d2[1];
     } else {
       format_localized('e', 'O');
     }
   }
 
   void on_24_hour(numeric_system ns, pad_type pad) {
     if (is_classic_ || ns == numeric_system::standard)
       return write2(tm_hour(), pad);
     format_localized('H', 'O');
   }
   void on_12_hour(numeric_system ns, pad_type pad) {
     if (is_classic_ || ns == numeric_system::standard)
       return write2(tm_hour12(), pad);
     format_localized('I', 'O');
   }
   void on_minute(numeric_system ns, pad_type pad) {
     if (is_classic_ || ns == numeric_system::standard)
       return write2(tm_min(), pad);
     format_localized('M', 'O');
   }
 
   void on_second(numeric_system ns, pad_type pad) {
     if (is_classic_ || ns == numeric_system::standard) {
       write2(tm_sec(), pad);
       if (subsecs_) {
         if (std::is_floating_point<typename Duration::rep>::value) {
           auto buf = memory_buffer();
           write_floating_seconds(buf, *subsecs_);
           if (buf.size() > 1) {
             // Remove the leading "0", write something like ".123".
             out_ = std::copy(buf.begin() + 1, buf.end(), out_);
           }
         } else {
           write_fractional_seconds<Char>(out_, *subsecs_);
         }
       }
     } else {
       // Currently no formatting of subseconds when a locale is set.
       format_localized('S', 'O');
     }
   }
 
   void on_12_hour_time() {
     if (is_classic_) {
       char buf[8];
       write_digit2_separated(buf, to_unsigned(tm_hour12()),
                              to_unsigned(tm_min()), to_unsigned(tm_sec()), ':');
       out_ = copy_str<Char>(std::begin(buf), std::end(buf), out_);
       *out_++ = ' ';
       on_am_pm();
     } else {
       format_localized('r');
     }
   }
   void on_24_hour_time() {
     write2(tm_hour());
     *out_++ = ':';
     write2(tm_min());
   }
   void on_iso_time() {
     on_24_hour_time();
     *out_++ = ':';
     on_second(numeric_system::standard, pad_type::unspecified);
   }
 
   void on_am_pm() {
     if (is_classic_) {
       *out_++ = tm_hour() < 12 ? 'A' : 'P';
       *out_++ = 'M';
     } else {
       format_localized('p');
     }
   }
 
   // These apply to chrono durations but not tm.
   void on_duration_value() {}
   void on_duration_unit() {}
 };
 
 struct chrono_format_checker : null_chrono_spec_handler<chrono_format_checker> {
   bool has_precision_integral = false;
 
   FMT_NORETURN void unsupported() { FMT_THROW(format_error("no date")); }
 
   template <typename Char>
   FMT_CONSTEXPR void on_text(const Char*, const Char*) {}
   FMT_CONSTEXPR void on_day_of_year() {}
   FMT_CONSTEXPR void on_24_hour(numeric_system, pad_type) {}
   FMT_CONSTEXPR void on_12_hour(numeric_system, pad_type) {}
   FMT_CONSTEXPR void on_minute(numeric_system, pad_type) {}
   FMT_CONSTEXPR void on_second(numeric_system, pad_type) {}
   FMT_CONSTEXPR void on_12_hour_time() {}
   FMT_CONSTEXPR void on_24_hour_time() {}
   FMT_CONSTEXPR void on_iso_time() {}
   FMT_CONSTEXPR void on_am_pm() {}
   FMT_CONSTEXPR void on_duration_value() const {
     if (has_precision_integral) {
       FMT_THROW(format_error("precision not allowed for this argument type"));
     }
   }
   FMT_CONSTEXPR void on_duration_unit() {}
 };
 
 template <typename T,
           FMT_ENABLE_IF(std::is_integral<T>::value&& has_isfinite<T>::value)>
 inline auto isfinite(T) -> bool {
   return true;
 }
 
 template <typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
 inline auto mod(T x, int y) -> T {
   return x % static_cast<T>(y);
 }
 template <typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value)>
 inline auto mod(T x, int y) -> T {
   return std::fmod(x, static_cast<T>(y));
 }
 
 // If T is an integral type, maps T to its unsigned counterpart, otherwise
 // leaves it unchanged (unlike std::make_unsigned).
 template <typename T, bool INTEGRAL = std::is_integral<T>::value>
 struct make_unsigned_or_unchanged {
   using type = T;
 };
 
 template <typename T> struct make_unsigned_or_unchanged<T, true> {
   using type = typename std::make_unsigned<T>::type;
 };
 
 template <typename Rep, typename Period,
           FMT_ENABLE_IF(std::is_integral<Rep>::value)>
 inline auto get_milliseconds(std::chrono::duration<Rep, Period> d)
     -> std::chrono::duration<Rep, std::milli> {
   // this may overflow and/or the result may not fit in the
   // target type.
 #if FMT_SAFE_DURATION_CAST
   using CommonSecondsType =
       typename std::common_type<decltype(d), std::chrono::seconds>::type;
   const auto d_as_common = fmt_duration_cast<CommonSecondsType>(d);
   const auto d_as_whole_seconds =
       fmt_duration_cast<std::chrono::seconds>(d_as_common);
   // this conversion should be nonproblematic
   const auto diff = d_as_common - d_as_whole_seconds;
   const auto ms =
       fmt_duration_cast<std::chrono::duration<Rep, std::milli>>(diff);
   return ms;
 #else
   auto s = fmt_duration_cast<std::chrono::seconds>(d);
   return fmt_duration_cast<std::chrono::milliseconds>(d - s);
 #endif
 }
 
 template <typename Char, typename Rep, typename OutputIt,
           FMT_ENABLE_IF(std::is_integral<Rep>::value)>
 auto format_duration_value(OutputIt out, Rep val, int) -> OutputIt {
   return write<Char>(out, val);
 }
 
 template <typename Char, typename Rep, typename OutputIt,
           FMT_ENABLE_IF(std::is_floating_point<Rep>::value)>
 auto format_duration_value(OutputIt out, Rep val, int precision) -> OutputIt {
   auto specs = format_specs<Char>();
   specs.precision = precision;
   specs.type = precision >= 0 ? presentation_type::fixed_lower
                               : presentation_type::general_lower;
   return write<Char>(out, val, specs);
 }
 
 template <typename Char, typename OutputIt>
 auto copy_unit(string_view unit, OutputIt out, Char) -> OutputIt {
   return std::copy(unit.begin(), unit.end(), out);
 }
 
 template <typename OutputIt>
 auto copy_unit(string_view unit, OutputIt out, wchar_t) -> OutputIt {
   // This works when wchar_t is UTF-32 because units only contain characters
   // that have the same representation in UTF-16 and UTF-32.
   utf8_to_utf16 u(unit);
   return std::copy(u.c_str(), u.c_str() + u.size(), out);
 }
 
 template <typename Char, typename Period, typename OutputIt>
 auto format_duration_unit(OutputIt out) -> OutputIt {
   if (const char* unit = get_units<Period>())
     return copy_unit(string_view(unit), out, Char());
   *out++ = '[';
   out = write<Char>(out, Period::num);
   if (const_check(Period::den != 1)) {
     *out++ = '/';
     out = write<Char>(out, Period::den);
   }
   *out++ = ']';
   *out++ = 's';
   return out;
 }
 
 class get_locale {
  private:
   union {
     std::locale locale_;
   };
   bool has_locale_ = false;
 
  public:
   get_locale(bool localized, locale_ref loc) : has_locale_(localized) {
     if (localized)
       ::new (&locale_) std::locale(loc.template get<std::locale>());
   }
   ~get_locale() {
     if (has_locale_) locale_.~locale();
   }
   operator const std::locale&() const {
     return has_locale_ ? locale_ : get_classic_locale();
   }
 };
 
 template <typename FormatContext, typename OutputIt, typename Rep,
           typename Period>
 struct chrono_formatter {
   FormatContext& context;
   OutputIt out;
   int precision;
   bool localized = false;
   // rep is unsigned to avoid overflow.
   using rep =
       conditional_t<std::is_integral<Rep>::value && sizeof(Rep) < sizeof(int),
                     unsigned, typename make_unsigned_or_unchanged<Rep>::type>;
   rep val;
   using seconds = std::chrono::duration<rep>;
   seconds s;
   using milliseconds = std::chrono::duration<rep, std::milli>;
   bool negative;
 
   using char_type = typename FormatContext::char_type;
   using tm_writer_type = tm_writer<OutputIt, char_type>;
 
   chrono_formatter(FormatContext& ctx, OutputIt o,
                    std::chrono::duration<Rep, Period> d)
       : context(ctx),
         out(o),
         val(static_cast<rep>(d.count())),
         negative(false) {
     if (d.count() < 0) {
       val = 0 - val;
       negative = true;
     }
 
     // this may overflow and/or the result may not fit in the
     // target type.
     // might need checked conversion (rep!=Rep)
     s = fmt_duration_cast<seconds>(std::chrono::duration<rep, Period>(val));
   }
 
   // returns true if nan or inf, writes to out.
   auto handle_nan_inf() -> bool {
     if (isfinite(val)) {
       return false;
     }
     if (isnan(val)) {
       write_nan();
       return true;
     }
     // must be +-inf
     if (val > 0) {
       write_pinf();
     } else {
       write_ninf();
     }
     return true;
   }
 
   auto days() const -> Rep { return static_cast<Rep>(s.count() / 86400); }
   auto hour() const -> Rep {
     return static_cast<Rep>(mod((s.count() / 3600), 24));
   }
 
   auto hour12() const -> Rep {
     Rep hour = static_cast<Rep>(mod((s.count() / 3600), 12));
     return hour <= 0 ? 12 : hour;
   }
 
   auto minute() const -> Rep {
     return static_cast<Rep>(mod((s.count() / 60), 60));
   }
   auto second() const -> Rep { return static_cast<Rep>(mod(s.count(), 60)); }
 
   auto time() const -> std::tm {
     auto time = std::tm();
     time.tm_hour = to_nonnegative_int(hour(), 24);
     time.tm_min = to_nonnegative_int(minute(), 60);
     time.tm_sec = to_nonnegative_int(second(), 60);
     return time;
   }
 
   void write_sign() {
     if (negative) {
       *out++ = '-';
       negative = false;
     }
   }
 
   void write(Rep value, int width, pad_type pad = pad_type::unspecified) {
     write_sign();
     if (isnan(value)) return write_nan();
     uint32_or_64_or_128_t<int> n =
         to_unsigned(to_nonnegative_int(value, max_value<int>()));
     int num_digits = detail::count_digits(n);
     if (width > num_digits) {
       out = detail::write_padding(out, pad, width - num_digits);
     }
     out = format_decimal<char_type>(out, n, num_digits).end;
   }
 
   void write_nan() { std::copy_n("nan", 3, out); }
   void write_pinf() { std::copy_n("inf", 3, out); }
   void write_ninf() { std::copy_n("-inf", 4, out); }
 
   template <typename Callback, typename... Args>
   void format_tm(const tm& time, Callback cb, Args... args) {
     if (isnan(val)) return write_nan();
     get_locale loc(localized, context.locale());
     auto w = tm_writer_type(loc, out, time);
     (w.*cb)(args...);
     out = w.out();
   }
 
   void on_text(const char_type* begin, const char_type* end) {
     std::copy(begin, end, out);
   }
 
   // These are not implemented because durations don't have date information.
   void on_abbr_weekday() {}
   void on_full_weekday() {}
   void on_dec0_weekday(numeric_system) {}
   void on_dec1_weekday(numeric_system) {}
   void on_abbr_month() {}
   void on_full_month() {}
   void on_datetime(numeric_system) {}
   void on_loc_date(numeric_system) {}
   void on_loc_time(numeric_system) {}
   void on_us_date() {}
   void on_iso_date() {}
   void on_utc_offset(numeric_system) {}
   void on_tz_name() {}
   void on_year(numeric_system) {}
   void on_short_year(numeric_system) {}
   void on_offset_year() {}
   void on_century(numeric_system) {}
   void on_iso_week_based_year() {}
   void on_iso_week_based_short_year() {}
   void on_dec_month(numeric_system) {}
   void on_dec0_week_of_year(numeric_system) {}
   void on_dec1_week_of_year(numeric_system) {}
   void on_iso_week_of_year(numeric_system) {}
   void on_day_of_month(numeric_system) {}
   void on_day_of_month_space(numeric_system) {}
 
   void on_day_of_year() {
     if (handle_nan_inf()) return;
     write(days(), 0);
   }
 
   void on_24_hour(numeric_system ns, pad_type pad) {
     if (handle_nan_inf()) return;
 
     if (ns == numeric_system::standard) return write(hour(), 2, pad);
     auto time = tm();
     time.tm_hour = to_nonnegative_int(hour(), 24);
     format_tm(time, &tm_writer_type::on_24_hour, ns, pad);
   }
 
   void on_12_hour(numeric_system ns, pad_type pad) {
     if (handle_nan_inf()) return;
 
     if (ns == numeric_system::standard) return write(hour12(), 2, pad);
     auto time = tm();
     time.tm_hour = to_nonnegative_int(hour12(), 12);
     format_tm(time, &tm_writer_type::on_12_hour, ns, pad);
   }
 
   void on_minute(numeric_system ns, pad_type pad) {
     if (handle_nan_inf()) return;
 
     if (ns == numeric_system::standard) return write(minute(), 2, pad);
     auto time = tm();
     time.tm_min = to_nonnegative_int(minute(), 60);
     format_tm(time, &tm_writer_type::on_minute, ns, pad);
   }
 
   void on_second(numeric_system ns, pad_type pad) {
     if (handle_nan_inf()) return;
 
     if (ns == numeric_system::standard) {
       if (std::is_floating_point<rep>::value) {
         auto buf = memory_buffer();
         write_floating_seconds(buf, std::chrono::duration<rep, Period>(val),
                                precision);
         if (negative) *out++ = '-';
         if (buf.size() < 2 || buf[1] == '.') {
           out = detail::write_padding(out, pad);
         }
         out = std::copy(buf.begin(), buf.end(), out);
       } else {
         write(second(), 2, pad);
         write_fractional_seconds<char_type>(
             out, std::chrono::duration<rep, Period>(val), precision);
       }
       return;
     }
     auto time = tm();
     time.tm_sec = to_nonnegative_int(second(), 60);
     format_tm(time, &tm_writer_type::on_second, ns, pad);
   }
 
   void on_12_hour_time() {
     if (handle_nan_inf()) return;
     format_tm(time(), &tm_writer_type::on_12_hour_time);
   }
 
   void on_24_hour_time() {
     if (handle_nan_inf()) {
       *out++ = ':';
       handle_nan_inf();
       return;
     }
 
     write(hour(), 2);
     *out++ = ':';
     write(minute(), 2);
   }
 
   void on_iso_time() {
     on_24_hour_time();
     *out++ = ':';
     if (handle_nan_inf()) return;
     on_second(numeric_system::standard, pad_type::unspecified);
   }
 
   void on_am_pm() {
     if (handle_nan_inf()) return;
     format_tm(time(), &tm_writer_type::on_am_pm);
   }
 
   void on_duration_value() {
     if (handle_nan_inf()) return;
     write_sign();
     out = format_duration_value<char_type>(out, val, precision);
   }
 
   void on_duration_unit() {
     out = format_duration_unit<char_type, Period>(out);
   }
 };
 
 }  // namespace detail
 
 #if defined(__cpp_lib_chrono) && __cpp_lib_chrono >= 201907
 using weekday = std::chrono::weekday;
 #else
 // A fallback version of weekday.
 class weekday {
  private:
   unsigned char value;
 
  public:
   weekday() = default;
   explicit constexpr weekday(unsigned wd) noexcept
       : value(static_cast<unsigned char>(wd != 7 ? wd : 0)) {}
   constexpr auto c_encoding() const noexcept -> unsigned { return value; }
 };
 
 class year_month_day {};
 #endif
 
 // A rudimentary weekday formatter.
 template <typename Char> struct formatter<weekday, Char> {
  private:
   bool localized = false;
 
  public:
   FMT_CONSTEXPR auto parse(basic_format_parse_context<Char>& ctx)
       -> decltype(ctx.begin()) {
     auto begin = ctx.begin(), end = ctx.end();
     if (begin != end && *begin == 'L') {
       ++begin;
       localized = true;
     }
     return begin;
   }
 
   template <typename FormatContext>
   auto format(weekday wd, FormatContext& ctx) const -> decltype(ctx.out()) {
     auto time = std::tm();
     time.tm_wday = static_cast<int>(wd.c_encoding());
     detail::get_locale loc(localized, ctx.locale());
     auto w = detail::tm_writer<decltype(ctx.out()), Char>(loc, ctx.out(), time);
     w.on_abbr_weekday();
     return w.out();
   }
 };
 
 template <typename Rep, typename Period, typename Char>
 struct formatter<std::chrono::duration<Rep, Period>, Char> {
  private:
   format_specs<Char> specs_;
   detail::arg_ref<Char> width_ref_;
   detail::arg_ref<Char> precision_ref_;
   bool localized_ = false;
   basic_string_view<Char> format_str_;
 
  public:
   FMT_CONSTEXPR auto parse(basic_format_parse_context<Char>& ctx)
       -> decltype(ctx.begin()) {
     auto it = ctx.begin(), end = ctx.end();
     if (it == end || *it == '}') return it;
 
     it = detail::parse_align(it, end, specs_);
     if (it == end) return it;
 
     it = detail::parse_dynamic_spec(it, end, specs_.width, width_ref_, ctx);
     if (it == end) return it;
 
     auto checker = detail::chrono_format_checker();
     if (*it == '.') {
       checker.has_precision_integral = !std::is_floating_point<Rep>::value;
       it = detail::parse_precision(it, end, specs_.precision, precision_ref_,
                                    ctx);
     }
     if (it != end && *it == 'L') {
       localized_ = true;
       ++it;
     }
     end = detail::parse_chrono_format(it, end, checker);
     format_str_ = {it, detail::to_unsigned(end - it)};
     return end;
   }
 
   template <typename FormatContext>
   auto format(std::chrono::duration<Rep, Period> d, FormatContext& ctx) const
       -> decltype(ctx.out()) {
     auto specs = specs_;
     auto precision = specs.precision;
     specs.precision = -1;
     auto begin = format_str_.begin(), end = format_str_.end();
     // As a possible future optimization, we could avoid extra copying if width
     // is not specified.
     auto buf = basic_memory_buffer<Char>();
     auto out = std::back_inserter(buf);
     detail::handle_dynamic_spec<detail::width_checker>(specs.width, width_ref_,
                                                        ctx);
     detail::handle_dynamic_spec<detail::precision_checker>(precision,
                                                            precision_ref_, ctx);
     if (begin == end || *begin == '}') {
       out = detail::format_duration_value<Char>(out, d.count(), precision);
       detail::format_duration_unit<Char, Period>(out);
     } else {
       using chrono_formatter =
           detail::chrono_formatter<FormatContext, decltype(out), Rep, Period>;
       auto f = chrono_formatter(ctx, out, d);
       f.precision = precision;
       f.localized = localized_;
       detail::parse_chrono_format(begin, end, f);
     }
     return detail::write(
         ctx.out(), basic_string_view<Char>(buf.data(), buf.size()), specs);
   }
 };
 
 template <typename Char, typename Duration>
 struct formatter<std::chrono::time_point<std::chrono::system_clock, Duration>,
                  Char> : formatter<std::tm, Char> {
   FMT_CONSTEXPR formatter() {
     this->format_str_ = detail::string_literal<Char, '%', 'F', ' ', '%', 'T'>{};
   }
 
   template <typename FormatContext>
   auto format(std::chrono::time_point<std::chrono::system_clock, Duration> val,
               FormatContext& ctx) const -> decltype(ctx.out()) {
     using period = typename Duration::period;
     if (detail::const_check(
             period::num != 1 || period::den != 1 ||
             std::is_floating_point<typename Duration::rep>::value)) {
       const auto epoch = val.time_since_epoch();
       auto subsecs = detail::fmt_duration_cast<Duration>(
           epoch - detail::fmt_duration_cast<std::chrono::seconds>(epoch));
 
       if (subsecs.count() < 0) {
         auto second =
             detail::fmt_duration_cast<Duration>(std::chrono::seconds(1));
         if (epoch.count() < ((Duration::min)() + second).count())
           FMT_THROW(format_error("duration is too small"));
         subsecs += second;
         val -= second;
       }
 
       return formatter<std::tm, Char>::do_format(gmtime(val), ctx, &subsecs);
     }
 
     return formatter<std::tm, Char>::format(gmtime(val), ctx);
   }
 };
 
 #if FMT_USE_LOCAL_TIME
 template <typename Char, typename Duration>
 struct formatter<std::chrono::local_time<Duration>, Char>
     : formatter<std::tm, Char> {
   FMT_CONSTEXPR formatter() {
     this->format_str_ = detail::string_literal<Char, '%', 'F', ' ', '%', 'T'>{};
   }
 
   template <typename FormatContext>
   auto format(std::chrono::local_time<Duration> val, FormatContext& ctx) const
       -> decltype(ctx.out()) {
     using period = typename Duration::period;
     if (period::num != 1 || period::den != 1 ||
         std::is_floating_point<typename Duration::rep>::value) {
       const auto epoch = val.time_since_epoch();
       const auto subsecs = detail::fmt_duration_cast<Duration>(
           epoch - detail::fmt_duration_cast<std::chrono::seconds>(epoch));
 
       return formatter<std::tm, Char>::do_format(localtime(val), ctx, &subsecs);
     }
 
     return formatter<std::tm, Char>::format(localtime(val), ctx);
   }
 };
 #endif
 
 #if FMT_USE_UTC_TIME
 template <typename Char, typename Duration>
 struct formatter<std::chrono::time_point<std::chrono::utc_clock, Duration>,
                  Char>
     : formatter<std::chrono::time_point<std::chrono::system_clock, Duration>,
                 Char> {
   template <typename FormatContext>
   auto format(std::chrono::time_point<std::chrono::utc_clock, Duration> val,
               FormatContext& ctx) const -> decltype(ctx.out()) {
     return formatter<
         std::chrono::time_point<std::chrono::system_clock, Duration>,
         Char>::format(std::chrono::utc_clock::to_sys(val), ctx);
   }
 };
 #endif
 
 template <typename Char> struct formatter<std::tm, Char> {
  private:
   format_specs<Char> specs_;
   detail::arg_ref<Char> width_ref_;
 
  protected:
   basic_string_view<Char> format_str_;
 
   template <typename FormatContext, typename Duration>
   auto do_format(const std::tm& tm, FormatContext& ctx,
                  const Duration* subsecs) const -> decltype(ctx.out()) {
     auto specs = specs_;
     auto buf = basic_memory_buffer<Char>();
     auto out = std::back_inserter(buf);
     detail::handle_dynamic_spec<detail::width_checker>(specs.width, width_ref_,
                                                        ctx);
 
     auto loc_ref = ctx.locale();
     detail::get_locale loc(static_cast<bool>(loc_ref), loc_ref);
     auto w =
         detail::tm_writer<decltype(out), Char, Duration>(loc, out, tm, subsecs);
     detail::parse_chrono_format(format_str_.begin(), format_str_.end(), w);
     return detail::write(
         ctx.out(), basic_string_view<Char>(buf.data(), buf.size()), specs);
   }
 
  public:
   FMT_CONSTEXPR auto parse(basic_format_parse_context<Char>& ctx)
       -> decltype(ctx.begin()) {
     auto it = ctx.begin(), end = ctx.end();
     if (it == end || *it == '}') return it;
 
     it = detail::parse_align(it, end, specs_);
     if (it == end) return it;
 
     it = detail::parse_dynamic_spec(it, end, specs_.width, width_ref_, ctx);
     if (it == end) return it;
 
     end = detail::parse_chrono_format(it, end, detail::tm_format_checker());
     // Replace the default format_str only if the new spec is not empty.
     if (end != it) format_str_ = {it, detail::to_unsigned(end - it)};
     return end;
   }
 
   template <typename FormatContext>
   auto format(const std::tm& tm, FormatContext& ctx) const
       -> decltype(ctx.out()) {
     return do_format<FormatContext, std::chrono::seconds>(tm, ctx, nullptr);
   }
 };
 
 FMT_END_EXPORT
 FMT_END_NAMESPACE
 
 #endif  // FMT_CHRONO_H_