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 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___FORMAT_PARSER_STD_FORMAT_SPEC_H
 #define _LIBCPP___FORMAT_PARSER_STD_FORMAT_SPEC_H
 
 /// \file Contains the std-format-spec parser.
 ///
 /// Most of the code can be reused in the chrono-format-spec.
 /// This header has some support for the chrono-format-spec since it doesn't
 /// affect the std-format-spec.
 
 #include <__algorithm/copy_n.h>
 #include <__algorithm/min.h>
 #include <__assert>
 #include <__concepts/arithmetic.h>
 #include <__concepts/same_as.h>
 #include <__config>
 #include <__format/format_arg.h>
 #include <__format/format_error.h>
 #include <__format/format_parse_context.h>
 #include <__format/format_string.h>
 #include <__format/unicode.h>
 #include <__format/width_estimation_table.h>
 #include <__iterator/concepts.h>
 #include <__iterator/iterator_traits.h> // iter_value_t
 #include <__memory/addressof.h>
 #include <__type_traits/common_type.h>
 #include <__type_traits/is_constant_evaluated.h>
 #include <__type_traits/is_trivially_copyable.h>
 #include <__variant/monostate.h>
 #include <cstdint>
 #include <string>
 #include <string_view>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER >= 20
 
 namespace __format_spec {
 
 [[noreturn]] _LIBCPP_HIDE_FROM_ABI inline void
 __throw_invalid_option_format_error(const char* __id, const char* __option) {
   std::__throw_format_error(
       (string("The format specifier for ") + __id + " does not allow the " + __option + " option").c_str());
 }
 
 [[noreturn]] _LIBCPP_HIDE_FROM_ABI inline void __throw_invalid_type_format_error(const char* __id) {
   std::__throw_format_error(
       (string("The type option contains an invalid value for ") + __id + " formatting argument").c_str());
 }
 
 template <contiguous_iterator _Iterator, class _ParseContext>
 _LIBCPP_HIDE_FROM_ABI constexpr __format::__parse_number_result<_Iterator>
 __parse_arg_id(_Iterator __begin, _Iterator __end, _ParseContext& __ctx) {
   using _CharT = iter_value_t<_Iterator>;
   // This function is a wrapper to call the real parser. But it does the
   // validation for the pre-conditions and post-conditions.
   if (__begin == __end)
     std::__throw_format_error("End of input while parsing an argument index");
 
   __format::__parse_number_result __r = __format::__parse_arg_id(__begin, __end, __ctx);
 
   if (__r.__last == __end || *__r.__last != _CharT('}'))
     std::__throw_format_error("The argument index is invalid");
 
   ++__r.__last;
   return __r;
 }
 
 template <class _Context>
 _LIBCPP_HIDE_FROM_ABI constexpr uint32_t __substitute_arg_id(basic_format_arg<_Context> __format_arg) {
   // [format.string.std]/8
   //   If the corresponding formatting argument is not of integral type...
   // This wording allows char and bool too. LWG-3720 changes the wording to
   //    If the corresponding formatting argument is not of standard signed or
   //    unsigned integer type,
   // This means the 128-bit will not be valid anymore.
   // TODO FMT Verify this resolution is accepted and add a test to verify
   //          128-bit integrals fail and switch to visit_format_arg.
   return std::__visit_format_arg(
       [](auto __arg) -> uint32_t {
         using _Type = decltype(__arg);
         if constexpr (same_as<_Type, monostate>)
           std::__throw_format_error("The argument index value is too large for the number of arguments supplied");
 
         // [format.string.std]/8
         // If { arg-idopt } is used in a width or precision, the value of the
         // corresponding formatting argument is used in its place. If the
         // corresponding formatting argument is not of standard signed or unsigned
         // integer type, or its value is negative for precision or non-positive for
         // width, an exception of type format_error is thrown.
         //
         // When an integral is used in a format function, it is stored as one of
         // the types checked below. Other integral types are promoted. For example,
         // a signed char is stored as an int.
         if constexpr (same_as<_Type, int> || same_as<_Type, unsigned int> || //
                       same_as<_Type, long long> || same_as<_Type, unsigned long long>) {
           if constexpr (signed_integral<_Type>) {
             if (__arg < 0)
               std::__throw_format_error("An argument index may not have a negative value");
           }
 
           using _CT = common_type_t<_Type, decltype(__format::__number_max)>;
           if (static_cast<_CT>(__arg) > static_cast<_CT>(__format::__number_max))
             std::__throw_format_error("The value of the argument index exceeds its maximum value");
 
           return __arg;
         } else
           std::__throw_format_error("Replacement argument isn't a standard signed or unsigned integer type");
       },
       __format_arg);
 }
 
 /// These fields are a filter for which elements to parse.
 ///
 /// They default to false so when a new field is added it needs to be opted in
 /// explicitly.
 struct _LIBCPP_HIDE_FROM_ABI __fields {
   uint16_t __sign_                 : 1 {false};
   uint16_t __alternate_form_       : 1 {false};
   uint16_t __zero_padding_         : 1 {false};
   uint16_t __precision_            : 1 {false};
   uint16_t __locale_specific_form_ : 1 {false};
   uint16_t __type_                 : 1 {false};
   // Determines the valid values for fill.
   //
   // Originally the fill could be any character except { and }. Range-based
   // formatters use the colon to mark the beginning of the
   // underlying-format-spec. To avoid parsing ambiguities these formatter
   // specializations prohibit the use of the colon as a fill character.
   uint16_t __use_range_fill_ : 1 {false};
   uint16_t __clear_brackets_ : 1 {false};
   uint16_t __consume_all_    : 1 {false};
 };
 
 // By not placing this constant in the formatter class it's not duplicated for
 // char and wchar_t.
 inline constexpr __fields __fields_bool{.__locale_specific_form_ = true, .__type_ = true, .__consume_all_ = true};
 inline constexpr __fields __fields_integral{
     .__sign_                 = true,
     .__alternate_form_       = true,
     .__zero_padding_         = true,
     .__locale_specific_form_ = true,
     .__type_                 = true,
     .__consume_all_          = true};
 inline constexpr __fields __fields_floating_point{
     .__sign_                 = true,
     .__alternate_form_       = true,
     .__zero_padding_         = true,
     .__precision_            = true,
     .__locale_specific_form_ = true,
     .__type_                 = true,
     .__consume_all_          = true};
 inline constexpr __fields __fields_string{.__precision_ = true, .__type_ = true, .__consume_all_ = true};
 inline constexpr __fields __fields_pointer{.__zero_padding_ = true, .__type_ = true, .__consume_all_ = true};
 
 #  if _LIBCPP_STD_VER >= 23
 inline constexpr __fields __fields_tuple{.__use_range_fill_ = true, .__clear_brackets_ = true};
 inline constexpr __fields __fields_range{.__use_range_fill_ = true, .__clear_brackets_ = true};
 inline constexpr __fields __fields_fill_align_width{};
 #  endif
 
 enum class __alignment : uint8_t {
   /// No alignment is set in the format string.
   __default,
   __left,
   __center,
   __right,
   __zero_padding
 };
 
 enum class __sign : uint8_t {
   /// No sign is set in the format string.
   ///
   /// The sign isn't allowed for certain format-types. By using this value
   /// it's possible to detect whether or not the user explicitly set the sign
   /// flag. For formatting purposes it behaves the same as \ref __minus.
   __default,
   __minus,
   __plus,
   __space
 };
 
 enum class __type : uint8_t {
   __default = 0,
   __string,
   __binary_lower_case,
   __binary_upper_case,
   __octal,
   __decimal,
   __hexadecimal_lower_case,
   __hexadecimal_upper_case,
   __pointer_lower_case,
   __pointer_upper_case,
   __char,
   __hexfloat_lower_case,
   __hexfloat_upper_case,
   __scientific_lower_case,
   __scientific_upper_case,
   __fixed_lower_case,
   __fixed_upper_case,
   __general_lower_case,
   __general_upper_case,
   __debug
 };
 
 _LIBCPP_HIDE_FROM_ABI inline constexpr uint32_t __create_type_mask(__type __t) {
   uint32_t __shift = static_cast<uint32_t>(__t);
   if (__shift == 0)
     return 1;
 
   if (__shift > 31)
     std::__throw_format_error("The type does not fit in the mask");
 
   return 1 << __shift;
 }
 
 inline constexpr uint32_t __type_mask_integer =
     __create_type_mask(__type::__binary_lower_case) |      //
     __create_type_mask(__type::__binary_upper_case) |      //
     __create_type_mask(__type::__decimal) |                //
     __create_type_mask(__type::__octal) |                  //
     __create_type_mask(__type::__hexadecimal_lower_case) | //
     __create_type_mask(__type::__hexadecimal_upper_case);
 
 struct __std {
   __alignment __alignment_     : 3;
   __sign __sign_               : 2;
   bool __alternate_form_       : 1;
   bool __locale_specific_form_ : 1;
   __type __type_;
 };
 
 struct __chrono {
   __alignment __alignment_     : 3;
   bool __locale_specific_form_ : 1;
   bool __hour_                 : 1;
   bool __weekday_name_         : 1;
   bool __weekday_              : 1;
   bool __day_of_year_          : 1;
   bool __week_of_year_         : 1;
   bool __month_name_           : 1;
 };
 
 // The fill UCS scalar value.
 //
 // This is always an array, with 1, 2, or 4 elements.
 // The size of the data structure is always 32-bits.
 template <class _CharT>
 struct __code_point;
 
 template <>
 struct __code_point<char> {
   char __data[4] = {' '};
 };
 
 #  if _LIBCPP_HAS_WIDE_CHARACTERS
 template <>
 struct __code_point<wchar_t> {
   wchar_t __data[4 / sizeof(wchar_t)] = {L' '};
 };
 #  endif
 
 /// Contains the parsed formatting specifications.
 ///
 /// This contains information for both the std-format-spec and the
 /// chrono-format-spec. This results in some unused members for both
 /// specifications. However these unused members don't increase the size
 /// of the structure.
 ///
 /// This struct doesn't cross ABI boundaries so its layout doesn't need to be
 /// kept stable.
 template <class _CharT>
 struct __parsed_specifications {
   union {
     // The field __alignment_ is the first element in __std_ and __chrono_.
     // This allows the code to always inspect this value regards which member
     // of the union is the active member [class.union.general]/2.
     //
     // This is needed since the generic output routines handle the alignment of
     // the output.
     __alignment __alignment_ : 3;
     __std __std_;
     __chrono __chrono_;
   };
 
   /// The requested width.
   ///
   /// When the format-spec used an arg-id for this field it has already been
   /// replaced with the value of that arg-id.
   int32_t __width_;
 
   /// The requested precision.
   ///
   /// When the format-spec used an arg-id for this field it has already been
   /// replaced with the value of that arg-id.
   int32_t __precision_;
 
   __code_point<_CharT> __fill_;
 
   _LIBCPP_HIDE_FROM_ABI constexpr bool __has_width() const { return __width_ > 0; }
 
   _LIBCPP_HIDE_FROM_ABI constexpr bool __has_precision() const { return __precision_ >= 0; }
 };
 
 // Validate the struct is small and cheap to copy since the struct is passed by
 // value in formatting functions.
 static_assert(sizeof(__parsed_specifications<char>) == 16);
 static_assert(is_trivially_copyable_v<__parsed_specifications<char>>);
 #  if _LIBCPP_HAS_WIDE_CHARACTERS
 static_assert(sizeof(__parsed_specifications<wchar_t>) == 16);
 static_assert(is_trivially_copyable_v<__parsed_specifications<wchar_t>>);
 #  endif
 
 /// The parser for the std-format-spec.
 ///
 /// Note this class is a member of std::formatter specializations. It's
 /// expected developers will create their own formatter specializations that
 /// inherit from the std::formatter specializations. This means this class
 /// must be ABI stable. To aid the stability the unused bits in the class are
 /// set to zero. That way they can be repurposed if a future revision of the
 /// Standards adds new fields to std-format-spec.
 template <class _CharT>
 class _LIBCPP_TEMPLATE_VIS __parser {
 public:
   // Parses the format specification.
   //
   // Depending on whether the parsing is done compile-time or run-time
   // the method slightly differs.
   // - Only parses a field when it is in the __fields. Accepting all
   //   fields and then validating the valid ones has a performance impact.
   //   This is faster but gives slighly worse error messages.
   // - At compile-time when a field is not accepted the parser will still
   //   parse it and give an error when it's present. This gives a more
   //   accurate error.
   // The idea is that most times the format instead of the vformat
   // functions are used. In that case the error will be detected during
   // compilation and there is no need to pay for the run-time overhead.
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator __parse(_ParseContext& __ctx, __fields __fields) {
     auto __begin = __ctx.begin();
     auto __end   = __ctx.end();
     if (__begin == __end || *__begin == _CharT('}') || (__fields.__use_range_fill_ && *__begin == _CharT(':')))
       return __begin;
 
     if (__parse_fill_align(__begin, __end) && __begin == __end)
       return __begin;
 
     if (__fields.__sign_) {
       if (__parse_sign(__begin) && __begin == __end)
         return __begin;
     } else if (std::is_constant_evaluated() && __parse_sign(__begin)) {
       std::__throw_format_error("The format specification does not allow the sign option");
     }
 
     if (__fields.__alternate_form_) {
       if (__parse_alternate_form(__begin) && __begin == __end)
         return __begin;
     } else if (std::is_constant_evaluated() && __parse_alternate_form(__begin)) {
       std::__throw_format_error("The format specifier does not allow the alternate form option");
     }
 
     if (__fields.__zero_padding_) {
       if (__parse_zero_padding(__begin) && __begin == __end)
         return __begin;
     } else if (std::is_constant_evaluated() && __parse_zero_padding(__begin)) {
       std::__throw_format_error("The format specifier does not allow the zero-padding option");
     }
 
     if (__parse_width(__begin, __end, __ctx) && __begin == __end)
       return __begin;
 
     if (__fields.__precision_) {
       if (__parse_precision(__begin, __end, __ctx) && __begin == __end)
         return __begin;
     } else if (std::is_constant_evaluated() && __parse_precision(__begin, __end, __ctx)) {
       std::__throw_format_error("The format specifier does not allow the precision option");
     }
 
     if (__fields.__locale_specific_form_) {
       if (__parse_locale_specific_form(__begin) && __begin == __end)
         return __begin;
     } else if (std::is_constant_evaluated() && __parse_locale_specific_form(__begin)) {
       std::__throw_format_error("The format specifier does not allow the locale-specific form option");
     }
 
     if (__fields.__clear_brackets_) {
       if (__parse_clear_brackets(__begin) && __begin == __end)
         return __begin;
     } else if (std::is_constant_evaluated() && __parse_clear_brackets(__begin)) {
       std::__throw_format_error("The format specifier does not allow the n option");
     }
 
     if (__fields.__type_)
       __parse_type(__begin);
 
     if (!__fields.__consume_all_)
       return __begin;
 
     if (__begin != __end && *__begin != _CharT('}'))
       std::__throw_format_error("The format specifier should consume the input or end with a '}'");
 
     return __begin;
   }
 
   // Validates the selected the parsed data.
   //
   // The valid fields in the parser may depend on the display type
   // selected. But the type is the last optional field, so by the time
   // it's known an option can't be used, it already has been parsed.
   // This does the validation again.
   //
   // For example an integral may have a sign, zero-padding, or alternate
   // form when the type option is not 'c'. So the generic approach is:
   //
   // typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_integral);
   // if (__parser.__type_ == __format_spec::__type::__char) {
   //   __parser.__validate((__format_spec::__fields_bool, "an integer");
   //   ... // more char adjustments
   // } else {
   //   ... // validate an integral type.
   // }
   //
   // For some types all valid options need a second validation run, like
   // boolean types.
   //
   // Depending on whether the validation is done at compile-time or
   // run-time the error differs
   // - run-time the exception is thrown and contains the type of field
   //   being validated.
   // - at compile-time the line with `std::__throw_format_error` is shown
   //   in the output. In that case it's important for the error to be on one
   //   line.
   // Note future versions of C++ may allow better compile-time error
   // reporting.
   _LIBCPP_HIDE_FROM_ABI constexpr void
   __validate(__fields __fields, const char* __id, uint32_t __type_mask = -1) const {
     if (!__fields.__sign_ && __sign_ != __sign::__default) {
       if (std::is_constant_evaluated())
         std::__throw_format_error("The format specifier does not allow the sign option");
       else
         __format_spec::__throw_invalid_option_format_error(__id, "sign");
     }
 
     if (!__fields.__alternate_form_ && __alternate_form_) {
       if (std::is_constant_evaluated())
         std::__throw_format_error("The format specifier does not allow the alternate form option");
       else
         __format_spec::__throw_invalid_option_format_error(__id, "alternate form");
     }
 
     if (!__fields.__zero_padding_ && __alignment_ == __alignment::__zero_padding) {
       if (std::is_constant_evaluated())
         std::__throw_format_error("The format specifier does not allow the zero-padding option");
       else
         __format_spec::__throw_invalid_option_format_error(__id, "zero-padding");
     }
 
     if (!__fields.__precision_ && __precision_ != -1) { // Works both when the precision has a value or an arg-id.
       if (std::is_constant_evaluated())
         std::__throw_format_error("The format specifier does not allow the precision option");
       else
         __format_spec::__throw_invalid_option_format_error(__id, "precision");
     }
 
     if (!__fields.__locale_specific_form_ && __locale_specific_form_) {
       if (std::is_constant_evaluated())
         std::__throw_format_error("The format specifier does not allow the locale-specific form option");
       else
         __format_spec::__throw_invalid_option_format_error(__id, "locale-specific form");
     }
 
     if ((__create_type_mask(__type_) & __type_mask) == 0) {
       if (std::is_constant_evaluated())
         std::__throw_format_error("The format specifier uses an invalid value for the type option");
       else
         __format_spec::__throw_invalid_type_format_error(__id);
     }
   }
 
   /// \returns the `__parsed_specifications` with the resolved dynamic sizes..
   _LIBCPP_HIDE_FROM_ABI __parsed_specifications<_CharT> __get_parsed_std_specifications(auto& __ctx) const {
     return __parsed_specifications<_CharT>{
         .__std_ = __std{.__alignment_            = __alignment_,
                         .__sign_                 = __sign_,
                         .__alternate_form_       = __alternate_form_,
                         .__locale_specific_form_ = __locale_specific_form_,
                         .__type_                 = __type_},
         .__width_{__get_width(__ctx)},
         .__precision_{__get_precision(__ctx)},
         .__fill_{__fill_}};
   }
 
   _LIBCPP_HIDE_FROM_ABI __parsed_specifications<_CharT> __get_parsed_chrono_specifications(auto& __ctx) const {
     return __parsed_specifications<_CharT>{
         .__chrono_ =
             __chrono{.__alignment_            = __alignment_,
                      .__locale_specific_form_ = __locale_specific_form_,
                      .__hour_                 = __hour_,
                      .__weekday_name_         = __weekday_name_,
                      .__weekday_              = __weekday_,
                      .__day_of_year_          = __day_of_year_,
                      .__week_of_year_         = __week_of_year_,
                      .__month_name_           = __month_name_},
         .__width_{__get_width(__ctx)},
         .__precision_{__get_precision(__ctx)},
         .__fill_{__fill_}};
   }
 
   __alignment __alignment_     : 3 {__alignment::__default};
   __sign __sign_               : 2 {__sign::__default};
   bool __alternate_form_       : 1 {false};
   bool __locale_specific_form_ : 1 {false};
   bool __clear_brackets_       : 1 {false};
   __type __type_{__type::__default};
 
   // These flags are only used for formatting chrono. Since the struct has
   // padding space left it's added to this structure.
   bool __hour_ : 1 {false};
 
   bool __weekday_name_ : 1 {false};
   bool __weekday_      : 1 {false};
 
   bool __day_of_year_  : 1 {false};
   bool __week_of_year_ : 1 {false};
 
   bool __month_name_ : 1 {false};
 
   uint8_t __reserved_0_ : 2 {0};
   uint8_t __reserved_1_ : 6 {0};
   // These two flags are only used internally and not part of the
   // __parsed_specifications. Therefore put them at the end.
   bool __width_as_arg_     : 1 {false};
   bool __precision_as_arg_ : 1 {false};
 
   /// The requested width, either the value or the arg-id.
   int32_t __width_{0};
 
   /// The requested precision, either the value or the arg-id.
   int32_t __precision_{-1};
 
   __code_point<_CharT> __fill_{};
 
 private:
   _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_alignment(_CharT __c) {
     switch (__c) {
     case _CharT('<'):
       __alignment_ = __alignment::__left;
       return true;
 
     case _CharT('^'):
       __alignment_ = __alignment::__center;
       return true;
 
     case _CharT('>'):
       __alignment_ = __alignment::__right;
       return true;
     }
     return false;
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr void __validate_fill_character(_CharT __fill) {
     // The forbidden fill characters all code points formed from a single code unit, thus the
     // check can be omitted when more code units are used.
     if (__fill == _CharT('{'))
       std::__throw_format_error("The fill option contains an invalid value");
   }
 
 #  if _LIBCPP_HAS_UNICODE
   // range-fill and tuple-fill are identical
   template <contiguous_iterator _Iterator>
     requires same_as<_CharT, char>
 #    if _LIBCPP_HAS_WIDE_CHARACTERS
           || (same_as<_CharT, wchar_t> && sizeof(wchar_t) == 2)
 #    endif
   _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_fill_align(_Iterator& __begin, _Iterator __end) {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         __begin != __end,
         "when called with an empty input the function will cause "
         "undefined behavior by evaluating data not in the input");
     __unicode::__code_point_view<_CharT> __view{__begin, __end};
     __unicode::__consume_result __consumed = __view.__consume();
     if (__consumed.__status != __unicode::__consume_result::__ok)
       std::__throw_format_error("The format specifier contains malformed Unicode characters");
 
     if (__view.__position() < __end && __parse_alignment(*__view.__position())) {
       ptrdiff_t __code_units = __view.__position() - __begin;
       if (__code_units == 1)
         // The forbidden fill characters all are code points encoded
         // in one code unit, thus the check can be omitted when more
         // code units are used.
         __validate_fill_character(*__begin);
 
       std::copy_n(__begin, __code_units, std::addressof(__fill_.__data[0]));
       __begin += __code_units + 1;
       return true;
     }
 
     if (!__parse_alignment(*__begin))
       return false;
 
     ++__begin;
     return true;
   }
 
 #    if _LIBCPP_HAS_WIDE_CHARACTERS
   template <contiguous_iterator _Iterator>
     requires(same_as<_CharT, wchar_t> && sizeof(wchar_t) == 4)
   _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_fill_align(_Iterator& __begin, _Iterator __end) {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         __begin != __end,
         "when called with an empty input the function will cause "
         "undefined behavior by evaluating data not in the input");
     if (__begin + 1 != __end && __parse_alignment(*(__begin + 1))) {
       if (!__unicode::__is_scalar_value(*__begin))
         std::__throw_format_error("The fill option contains an invalid value");
 
       __validate_fill_character(*__begin);
 
       __fill_.__data[0] = *__begin;
       __begin += 2;
       return true;
     }
 
     if (!__parse_alignment(*__begin))
       return false;
 
     ++__begin;
     return true;
   }
 
 #    endif // _LIBCPP_HAS_WIDE_CHARACTERS
 
 #  else // _LIBCPP_HAS_UNICODE
   // range-fill and tuple-fill are identical
   template <contiguous_iterator _Iterator>
   _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_fill_align(_Iterator& __begin, _Iterator __end) {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         __begin != __end,
         "when called with an empty input the function will cause "
         "undefined behavior by evaluating data not in the input");
     if (__begin + 1 != __end) {
       if (__parse_alignment(*(__begin + 1))) {
         __validate_fill_character(*__begin);
 
         __fill_.__data[0] = *__begin;
         __begin += 2;
         return true;
       }
     }
 
     if (!__parse_alignment(*__begin))
       return false;
 
     ++__begin;
     return true;
   }
 
 #  endif // _LIBCPP_HAS_UNICODE
 
   template <contiguous_iterator _Iterator>
   _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_sign(_Iterator& __begin) {
     switch (*__begin) {
     case _CharT('-'):
       __sign_ = __sign::__minus;
       break;
     case _CharT('+'):
       __sign_ = __sign::__plus;
       break;
     case _CharT(' '):
       __sign_ = __sign::__space;
       break;
     default:
       return false;
     }
     ++__begin;
     return true;
   }
 
   template <contiguous_iterator _Iterator>
   _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_alternate_form(_Iterator& __begin) {
     if (*__begin != _CharT('#'))
       return false;
 
     __alternate_form_ = true;
     ++__begin;
     return true;
   }
 
   template <contiguous_iterator _Iterator>
   _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_zero_padding(_Iterator& __begin) {
     if (*__begin != _CharT('0'))
       return false;
 
     if (__alignment_ == __alignment::__default)
       __alignment_ = __alignment::__zero_padding;
     ++__begin;
     return true;
   }
 
   template <contiguous_iterator _Iterator>
   _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_width(_Iterator& __begin, _Iterator __end, auto& __ctx) {
     if (*__begin == _CharT('0'))
       std::__throw_format_error("The width option should not have a leading zero");
 
     if (*__begin == _CharT('{')) {
       __format::__parse_number_result __r = __format_spec::__parse_arg_id(++__begin, __end, __ctx);
       __width_as_arg_                     = true;
       __width_                            = __r.__value;
       __begin                             = __r.__last;
       return true;
     }
 
     if (*__begin < _CharT('0') || *__begin > _CharT('9'))
       return false;
 
     __format::__parse_number_result __r = __format::__parse_number(__begin, __end);
     __width_                            = __r.__value;
     _LIBCPP_ASSERT_INTERNAL(__width_ != 0,
                             "A zero value isn't allowed and should be impossible, "
                             "due to validations in this function");
     __begin = __r.__last;
     return true;
   }
 
   template <contiguous_iterator _Iterator>
   _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_precision(_Iterator& __begin, _Iterator __end, auto& __ctx) {
     if (*__begin != _CharT('.'))
       return false;
 
     ++__begin;
     if (__begin == __end)
       std::__throw_format_error("End of input while parsing format specifier precision");
 
     if (*__begin == _CharT('{')) {
       __format::__parse_number_result __arg_id = __format_spec::__parse_arg_id(++__begin, __end, __ctx);
       __precision_as_arg_                      = true;
       __precision_                             = __arg_id.__value;
       __begin                                  = __arg_id.__last;
       return true;
     }
 
     if (*__begin < _CharT('0') || *__begin > _CharT('9'))
       std::__throw_format_error("The precision option does not contain a value or an argument index");
 
     __format::__parse_number_result __r = __format::__parse_number(__begin, __end);
     __precision_                        = __r.__value;
     __precision_as_arg_                 = false;
     __begin                             = __r.__last;
     return true;
   }
 
   template <contiguous_iterator _Iterator>
   _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_locale_specific_form(_Iterator& __begin) {
     if (*__begin != _CharT('L'))
       return false;
 
     __locale_specific_form_ = true;
     ++__begin;
     return true;
   }
 
   template <contiguous_iterator _Iterator>
   _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_clear_brackets(_Iterator& __begin) {
     if (*__begin != _CharT('n'))
       return false;
 
     __clear_brackets_ = true;
     ++__begin;
     return true;
   }
 
   template <contiguous_iterator _Iterator>
   _LIBCPP_HIDE_FROM_ABI constexpr void __parse_type(_Iterator& __begin) {
     // Determines the type. It does not validate whether the selected type is
     // valid. Most formatters have optional fields that are only allowed for
     // certain types. These parsers need to do validation after the type has
     // been parsed. So its easier to implement the validation for all types in
     // the specific parse function.
     switch (*__begin) {
     case 'A':
       __type_ = __type::__hexfloat_upper_case;
       break;
     case 'B':
       __type_ = __type::__binary_upper_case;
       break;
     case 'E':
       __type_ = __type::__scientific_upper_case;
       break;
     case 'F':
       __type_ = __type::__fixed_upper_case;
       break;
     case 'G':
       __type_ = __type::__general_upper_case;
       break;
     case 'X':
       __type_ = __type::__hexadecimal_upper_case;
       break;
     case 'a':
       __type_ = __type::__hexfloat_lower_case;
       break;
     case 'b':
       __type_ = __type::__binary_lower_case;
       break;
     case 'c':
       __type_ = __type::__char;
       break;
     case 'd':
       __type_ = __type::__decimal;
       break;
     case 'e':
       __type_ = __type::__scientific_lower_case;
       break;
     case 'f':
       __type_ = __type::__fixed_lower_case;
       break;
     case 'g':
       __type_ = __type::__general_lower_case;
       break;
     case 'o':
       __type_ = __type::__octal;
       break;
     case 'p':
       __type_ = __type::__pointer_lower_case;
       break;
     case 'P':
       __type_ = __type::__pointer_upper_case;
       break;
     case 's':
       __type_ = __type::__string;
       break;
     case 'x':
       __type_ = __type::__hexadecimal_lower_case;
       break;
 #  if _LIBCPP_STD_VER >= 23
     case '?':
       __type_ = __type::__debug;
       break;
 #  endif
     default:
       return;
     }
     ++__begin;
   }
 
   _LIBCPP_HIDE_FROM_ABI int32_t __get_width(auto& __ctx) const {
     if (!__width_as_arg_)
       return __width_;
 
     return __format_spec::__substitute_arg_id(__ctx.arg(__width_));
   }
 
   _LIBCPP_HIDE_FROM_ABI int32_t __get_precision(auto& __ctx) const {
     if (!__precision_as_arg_)
       return __precision_;
 
     return __format_spec::__substitute_arg_id(__ctx.arg(__precision_));
   }
 };
 
 // Validates whether the reserved bitfields don't change the size.
 static_assert(sizeof(__parser<char>) == 16);
 #  if _LIBCPP_HAS_WIDE_CHARACTERS
 static_assert(sizeof(__parser<wchar_t>) == 16);
 #  endif
 
 _LIBCPP_HIDE_FROM_ABI constexpr void __process_display_type_string(__format_spec::__type __type) {
   switch (__type) {
   case __format_spec::__type::__default:
   case __format_spec::__type::__string:
   case __format_spec::__type::__debug:
     break;
 
   default:
     std::__throw_format_error("The type option contains an invalid value for a string formatting argument");
   }
 }
 
 template <class _CharT>
 _LIBCPP_HIDE_FROM_ABI constexpr void __process_display_type_bool_string(__parser<_CharT>& __parser, const char* __id) {
   __parser.__validate(__format_spec::__fields_bool, __id);
   if (__parser.__alignment_ == __alignment::__default)
     __parser.__alignment_ = __alignment::__left;
 }
 
 template <class _CharT>
 _LIBCPP_HIDE_FROM_ABI constexpr void __process_display_type_char(__parser<_CharT>& __parser, const char* __id) {
   __format_spec::__process_display_type_bool_string(__parser, __id);
 }
 
 template <class _CharT>
 _LIBCPP_HIDE_FROM_ABI constexpr void __process_parsed_bool(__parser<_CharT>& __parser, const char* __id) {
   switch (__parser.__type_) {
   case __format_spec::__type::__default:
   case __format_spec::__type::__string:
     __format_spec::__process_display_type_bool_string(__parser, __id);
     break;
 
   case __format_spec::__type::__binary_lower_case:
   case __format_spec::__type::__binary_upper_case:
   case __format_spec::__type::__octal:
   case __format_spec::__type::__decimal:
   case __format_spec::__type::__hexadecimal_lower_case:
   case __format_spec::__type::__hexadecimal_upper_case:
     break;
 
   default:
     __format_spec::__throw_invalid_type_format_error(__id);
   }
 }
 
 template <class _CharT>
 _LIBCPP_HIDE_FROM_ABI constexpr void __process_parsed_char(__parser<_CharT>& __parser, const char* __id) {
   switch (__parser.__type_) {
   case __format_spec::__type::__default:
   case __format_spec::__type::__char:
   case __format_spec::__type::__debug:
     __format_spec::__process_display_type_char(__parser, __id);
     break;
 
   case __format_spec::__type::__binary_lower_case:
   case __format_spec::__type::__binary_upper_case:
   case __format_spec::__type::__octal:
   case __format_spec::__type::__decimal:
   case __format_spec::__type::__hexadecimal_lower_case:
   case __format_spec::__type::__hexadecimal_upper_case:
     break;
 
   default:
     __format_spec::__throw_invalid_type_format_error(__id);
   }
 }
 
 template <class _CharT>
 _LIBCPP_HIDE_FROM_ABI constexpr void __process_parsed_integer(__parser<_CharT>& __parser, const char* __id) {
   switch (__parser.__type_) {
   case __format_spec::__type::__default:
   case __format_spec::__type::__binary_lower_case:
   case __format_spec::__type::__binary_upper_case:
   case __format_spec::__type::__octal:
   case __format_spec::__type::__decimal:
   case __format_spec::__type::__hexadecimal_lower_case:
   case __format_spec::__type::__hexadecimal_upper_case:
     break;
 
   case __format_spec::__type::__char:
     __format_spec::__process_display_type_char(__parser, __id);
     break;
 
   default:
     __format_spec::__throw_invalid_type_format_error(__id);
   }
 }
 
 template <class _CharT>
 _LIBCPP_HIDE_FROM_ABI constexpr void __process_parsed_floating_point(__parser<_CharT>& __parser, const char* __id) {
   switch (__parser.__type_) {
   case __format_spec::__type::__default:
   case __format_spec::__type::__hexfloat_lower_case:
   case __format_spec::__type::__hexfloat_upper_case:
     // Precision specific behavior will be handled later.
     break;
   case __format_spec::__type::__scientific_lower_case:
   case __format_spec::__type::__scientific_upper_case:
   case __format_spec::__type::__fixed_lower_case:
   case __format_spec::__type::__fixed_upper_case:
   case __format_spec::__type::__general_lower_case:
   case __format_spec::__type::__general_upper_case:
     if (!__parser.__precision_as_arg_ && __parser.__precision_ == -1)
       // Set the default precision for the call to to_chars.
       __parser.__precision_ = 6;
     break;
 
   default:
     __format_spec::__throw_invalid_type_format_error(__id);
   }
 }
 
 _LIBCPP_HIDE_FROM_ABI constexpr void __process_display_type_pointer(__format_spec::__type __type, const char* __id) {
   switch (__type) {
   case __format_spec::__type::__default:
   case __format_spec::__type::__pointer_lower_case:
   case __format_spec::__type::__pointer_upper_case:
     break;
 
   default:
     __format_spec::__throw_invalid_type_format_error(__id);
   }
 }
 
 template <contiguous_iterator _Iterator>
 struct __column_width_result {
   /// The number of output columns.
   size_t __width_;
   /// One beyond the last code unit used in the estimation.
   ///
   /// This limits the original output to fit in the wanted number of columns.
   _Iterator __last_;
 };
 
 template <contiguous_iterator _Iterator>
 __column_width_result(size_t, _Iterator) -> __column_width_result<_Iterator>;
 
 /// Since a column width can be two it's possible that the requested column
 /// width can't be achieved. Depending on the intended usage the policy can be
 /// selected.
 /// - When used as precision the maximum width may not be exceeded and the
 ///   result should be "rounded down" to the previous boundary.
 /// - When used as a width we're done once the minimum is reached, but
 ///   exceeding is not an issue. Rounding down is an issue since that will
 ///   result in writing fill characters. Therefore the result needs to be
 ///   "rounded up".
 enum class __column_width_rounding { __down, __up };
 
 #  if _LIBCPP_HAS_UNICODE
 
 namespace __detail {
 template <contiguous_iterator _Iterator>
 _LIBCPP_HIDE_FROM_ABI constexpr __column_width_result<_Iterator> __estimate_column_width_grapheme_clustering(
     _Iterator __first, _Iterator __last, size_t __maximum, __column_width_rounding __rounding) noexcept {
   using _CharT = iter_value_t<_Iterator>;
   __unicode::__extended_grapheme_cluster_view<_CharT> __view{__first, __last};
 
   __column_width_result<_Iterator> __result{0, __first};
   while (__result.__last_ != __last && __result.__width_ <= __maximum) {
     typename __unicode::__extended_grapheme_cluster_view<_CharT>::__cluster __cluster = __view.__consume();
     int __width = __width_estimation_table::__estimated_width(__cluster.__code_point_);
 
     // When the next entry would exceed the maximum width the previous width
     // might be returned. For example when a width of 100 is requested the
     // returned width might be 99, since the next code point has an estimated
     // column width of 2. This depends on the rounding flag.
     // When the maximum is exceeded the loop will abort the next iteration.
     if (__rounding == __column_width_rounding::__down && __result.__width_ + __width > __maximum)
       return __result;
 
     __result.__width_ += __width;
     __result.__last_ = __cluster.__last_;
   }
 
   return __result;
 }
 
 } // namespace __detail
 
 // Unicode can be stored in several formats: UTF-8, UTF-16, and UTF-32.
 // Depending on format the relation between the number of code units stored and
 // the number of output columns differs. The first relation is the number of
 // code units forming a code point. (The text assumes the code units are
 // unsigned.)
 // - UTF-8 The number of code units is between one and four. The first 127
 //   Unicode code points match the ASCII character set. When the highest bit is
 //   set it means the code point has more than one code unit.
 // - UTF-16: The number of code units is between 1 and 2. When the first
 //   code unit is in the range [0xd800,0xdfff) it means the code point uses two
 //   code units.
 // - UTF-32: The number of code units is always one.
 //
 // The code point to the number of columns is specified in
 // [format.string.std]/11. This list might change in the future.
 //
 // Another thing to be taken into account is Grapheme clustering. This means
 // that in some cases multiple code points are combined one element in the
 // output. For example:
 // - an ASCII character with a combined diacritical mark
 // - an emoji with a skin tone modifier
 // - a group of combined people emoji to create a family
 // - a combination of flag emoji
 //
 // See also:
 // - [format.string.general]/11
 // - https://en.wikipedia.org/wiki/UTF-8#Encoding
 // - https://en.wikipedia.org/wiki/UTF-16#U+D800_to_U+DFFF
 
 _LIBCPP_HIDE_FROM_ABI constexpr bool __is_ascii(char32_t __c) { return __c < 0x80; }
 
 /// Determines the number of output columns needed to render the input.
 ///
 /// \note When the scanner encounters malformed Unicode it acts as-if every
 /// code unit is a one column code point. Typically a terminal uses the same
 /// strategy and replaces every malformed code unit with a one column
 /// replacement character.
 ///
 /// \param __first    Points to the first element of the input range.
 /// \param __last     Points beyond the last element of the input range.
 /// \param __maximum  The maximum number of output columns. The returned number
 ///                   of estimated output columns will not exceed this value.
 /// \param __rounding Selects the rounding method.
 ///                   \c __down result.__width_ <= __maximum
 ///                   \c __up result.__width_ <= __maximum + 1
 template <class _CharT, class _Iterator = typename basic_string_view<_CharT>::const_iterator>
 _LIBCPP_HIDE_FROM_ABI constexpr __column_width_result<_Iterator> __estimate_column_width(
     basic_string_view<_CharT> __str, size_t __maximum, __column_width_rounding __rounding) noexcept {
   // The width estimation is done in two steps:
   // - Quickly process for the ASCII part. ASCII has the following properties
   //   - One code unit is one code point
   //   - Every code point has an estimated width of one
   // - When needed it will a Unicode Grapheme clustering algorithm to find
   //   the proper place for truncation.
 
   if (__str.empty() || __maximum == 0)
     return {0, __str.begin()};
 
   // ASCII has one caveat; when an ASCII character is followed by a non-ASCII
   // character they might be part of an extended grapheme cluster. For example:
   //   an ASCII letter and a COMBINING ACUTE ACCENT
   // The truncate should happen after the COMBINING ACUTE ACCENT. Therefore we
   // need to scan one code unit beyond the requested precision. When this code
   // unit is non-ASCII we omit the current code unit and let the Grapheme
   // clustering algorithm do its work.
   auto __it = __str.begin();
   if (__format_spec::__is_ascii(*__it)) {
     do {
       --__maximum;
       ++__it;
       if (__it == __str.end())
         return {__str.size(), __str.end()};
 
       if (__maximum == 0) {
         if (__format_spec::__is_ascii(*__it))
           return {static_cast<size_t>(__it - __str.begin()), __it};
 
         break;
       }
     } while (__format_spec::__is_ascii(*__it));
     --__it;
     ++__maximum;
   }
 
   ptrdiff_t __ascii_size = __it - __str.begin();
   __column_width_result __result =
       __detail::__estimate_column_width_grapheme_clustering(__it, __str.end(), __maximum, __rounding);
 
   __result.__width_ += __ascii_size;
   return __result;
 }
 #  else // _LIBCPP_HAS_UNICODE
 template <class _CharT>
 _LIBCPP_HIDE_FROM_ABI constexpr __column_width_result<typename basic_string_view<_CharT>::const_iterator>
 __estimate_column_width(basic_string_view<_CharT> __str, size_t __maximum, __column_width_rounding) noexcept {
   // When Unicode isn't supported assume ASCII and every code unit is one code
   // point. In ASCII the estimated column width is always one. Thus there's no
   // need for rounding.
   size_t __width = std::min(__str.size(), __maximum);
   return {__width, __str.begin() + __width};
 }
 
 #  endif // _LIBCPP_HAS_UNICODE
 
 } // namespace __format_spec
 
 #endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP___FORMAT_PARSER_STD_FORMAT_SPEC_H

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