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 // Copyright 2023 Matt Borland
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 
 #ifndef BOOST_CHARCONV_DETAIL_PARSER_HPP
 #define BOOST_CHARCONV_DETAIL_PARSER_HPP
 
 #include <boost/charconv/detail/config.hpp>
 #include <boost/charconv/detail/from_chars_result.hpp>
 #include <boost/charconv/detail/from_chars_integer_impl.hpp>
 #include <boost/charconv/detail/integer_search_trees.hpp>
 #include <boost/charconv/limits.hpp>
 #include <boost/charconv/chars_format.hpp>
 #include <system_error>
 #include <type_traits>
 #include <limits>
 #include <cerrno>
 #include <cstdint>
 #include <cstring>
 
 #if defined(__GNUC__) && __GNUC__ < 5 && !defined(__clang__)
 # pragma GCC diagnostic push
 # pragma GCC diagnostic ignored "-Wmissing-field-initializers"
 #endif
 
 namespace boost { namespace charconv { namespace detail {
 
 inline bool is_integer_char(char c) noexcept
 {
     return (c >= '0') && (c <= '9');
 }
 
 inline bool is_hex_char(char c) noexcept
 {
     return is_integer_char(c) || (((c >= 'a') && (c <= 'f')) || ((c >= 'A') && (c <= 'F')));
 }
 
 inline bool is_delimiter(char c, chars_format fmt) noexcept
 {
     if (fmt != chars_format::hex)
     {
         return !is_integer_char(c) && c != 'e' && c != 'E';
     }
 
     return !is_hex_char(c) && c != 'p' && c != 'P';
 }
 
 inline from_chars_result from_chars_dispatch(const char* first, const char* last, std::uint64_t& value, int base) noexcept
 {
     return boost::charconv::detail::from_chars(first, last, value, base);
 }
 
 inline from_chars_result from_chars_dispatch(const char* first, const char* last, uint128& value, int base) noexcept
 {
     return boost::charconv::detail::from_chars128(first, last, value, base);
 }
 
 #ifdef BOOST_CHARCONV_HAS_INT128
 inline from_chars_result from_chars_dispatch(const char* first, const char* last, boost::uint128_type& value, int base) noexcept
 {
     return boost::charconv::detail::from_chars128(first, last, value, base);
 }
 #endif
 
 template <typename Unsigned_Integer, typename Integer>
 inline from_chars_result parser(const char* first, const char* last, bool& sign, Unsigned_Integer& significand, Integer& exponent, chars_format fmt = chars_format::general) noexcept
 {
     if (first > last)
     {
         return {first, std::errc::invalid_argument};
     }
 
     auto next = first;
     bool all_zeros = true;
 
     // First extract the sign
     if (*next == '-')
     {
         sign = true;
         ++next;
     }
     else if (*next == '+')
     {
         return {next, std::errc::invalid_argument};
     }
     else
     {
         sign = false;
     }
 
     // Handle non-finite values
     // Stl allows for string like "iNf" to return inf
     //
     // This is nested ifs rather than a big one-liner to ensure that once we hit an invalid character
     // or an end of buffer we return the correct value of next
     if (next != last && (*next == 'i' || *next == 'I'))
     {
         ++next;
         if (next != last && (*next == 'n' || *next == 'N'))
         {
             ++next;
             if (next != last && (*next == 'f' || *next == 'F'))
             {
                 significand = 0;
                 return {next, std::errc::value_too_large};
             }
         }
 
         return {next, std::errc::invalid_argument};
     }
     else if (next != last && (*next == 'n' || *next == 'N'))
     {
         ++next;
         if (next != last && (*next == 'a' || *next == 'A'))
         {
             ++next;
             if (next != last && (*next == 'n' || *next == 'N'))
             {
                 ++next;
                 if (next != last && (*next == '('))
                 {
                     ++next;
                     if (next != last && (*next == 's' || *next == 'S'))
                     {
                         significand = 1;
                         return {next, std::errc::not_supported};
                     }
                     else if (next != last && (*next == 'i' || *next == 'I'))
                     {
                         significand = 0;
                         return {next, std::errc::not_supported};
                     }
                 }
                 else
                 {
                     significand = 0;
                     return {next, std::errc::not_supported};
                 }
             }
         }
 
         return {next, std::errc::invalid_argument};
     }
 
     // Ignore leading zeros (e.g. 00005 or -002.3e+5)
     while (next != last && *next == '0')
     {
         ++next;
     }
 
     // If the number is 0 we can abort now
     char exp_char;
     char capital_exp_char;
     if (fmt != chars_format::hex)
     {
         exp_char = 'e';
         capital_exp_char = 'E';
     }
     else
     {
         exp_char = 'p';
         capital_exp_char = 'P';
     }
 
     if (next == last || *next == exp_char || *next == -capital_exp_char)
     {
         significand = 0;
         exponent = 0;
         return {next, std::errc()};
     }
 
     // Next we get the significand
     constexpr std::size_t significand_buffer_size = limits<Unsigned_Integer>::max_chars10 - 1; // Base 10 or 16
     char significand_buffer[significand_buffer_size] {};
     std::size_t i = 0;
     std::size_t dot_position = 0;
     Integer extra_zeros = 0;
     Integer leading_zero_powers = 0;
     const auto char_validation_func = (fmt != boost::charconv::chars_format::hex) ? is_integer_char : is_hex_char;
     const int base = (fmt != boost::charconv::chars_format::hex) ? 10 : 16;
 
     while (next != last && char_validation_func(*next) && i < significand_buffer_size)
     {
         all_zeros = false;
         significand_buffer[i] = *next;
         ++next;
         ++i;
     }
 
     bool fractional = false;
     if (next == last)
     {
         // if fmt is chars_format::scientific the e is required
         if (fmt == chars_format::scientific)
         {
             return {first, std::errc::invalid_argument};
         }
         
         exponent = 0;
         std::size_t offset = i;
 
         from_chars_result r = from_chars_dispatch(significand_buffer, significand_buffer + offset, significand, base);
         switch (r.ec)
         {
             case std::errc::invalid_argument:
                 return {first, std::errc::invalid_argument};
             case std::errc::result_out_of_range:
                 return {next, std::errc::result_out_of_range};
             default:
                 return {next, std::errc()};
         }
     }
     else if (*next == '.')
     {
         ++next;
         fractional = true;
         dot_position = i;
 
         // Process the fractional part if we have it
         //
         // if fmt is chars_format::scientific the e is required
         // if fmt is chars_format::fixed and not scientific the e is disallowed
         // if fmt is chars_format::general (which is scientific and fixed) the e is optional
 
         // If we have the value 0.00001 we can continue to chop zeros and adjust the exponent
         // so that we get the useful parts of the fraction
         if (all_zeros)
         {
             while (next != last && *next == '0')
             {
                 ++next;
                 --leading_zero_powers;
             }
 
             if (next == last)
             {
                 return {last, std::errc()};
             }
         }
 
         while (next != last && char_validation_func(*next) && i < significand_buffer_size)
         {
             significand_buffer[i] = *next;
             ++next;
             ++i;
         }
     }
     
     if (i == significand_buffer_size)
     {
         // We can not process any more significant figures into the significand so skip to the end
         // or the exponent part and capture the additional orders of magnitude for the exponent
         bool found_dot = false;
         while (next != last && (char_validation_func(*next) || *next == '.'))
         {
             ++next;
             if (!fractional && !found_dot)
             {
                 ++extra_zeros;
             }
             if (next != last && *next == '.')
             {
                 found_dot = true;
             }
         }
     }
 
     if (next == last || is_delimiter(*next, fmt))
     {
         if (fmt == chars_format::scientific)
         {
             return {first, std::errc::invalid_argument};
         }
         if (dot_position != 0 || fractional)
         {
             exponent = static_cast<Integer>(dot_position) - static_cast<Integer>(i) + extra_zeros + leading_zero_powers;
         }
         else
         {
             exponent = extra_zeros + leading_zero_powers;
         }
         std::size_t offset = i;
         
         from_chars_result r = from_chars_dispatch(significand_buffer, significand_buffer + offset, significand, base);
         switch (r.ec)
         {
             case std::errc::invalid_argument:
                 return {first, std::errc::invalid_argument};
             case std::errc::result_out_of_range:
                 return {next, std::errc::result_out_of_range};
             default:
                 return {next, std::errc()};
         }
     }
     else if (*next == exp_char || *next == capital_exp_char)
     {
         // Would be a number without a significand e.g. e+03
         if (next == first)
         {
             return {next, std::errc::invalid_argument};
         }
 
         ++next;
         if (fmt == chars_format::fixed)
         {
             return {first, std::errc::invalid_argument};
         }
 
         exponent = static_cast<Integer>(i - 1);
         std::size_t offset = i;
         bool round = false;
         // If more digits are present than representable in the significand of the target type
         // we set the maximum
         if (offset > significand_buffer_size)
         {
             offset = significand_buffer_size - 1;
             i = significand_buffer_size;
             if (significand_buffer[offset] == '5' ||
                 significand_buffer[offset] == '6' ||
                 significand_buffer[offset] == '7' ||
                 significand_buffer[offset] == '8' ||
                 significand_buffer[offset] == '9')
             {
                 round = true;
             }
         }
         
         // If the significand is 0 from chars will return std::errc::invalid_argument because there is nothing in the buffer,
         // but it is a valid value. We need to continue parsing to get the correct value of ptr even
         // though we know we could bail now.
         //
         // See GitHub issue #29: https://github.com/cppalliance/charconv/issues/29
         if (offset != 0)
         {
             from_chars_result r = from_chars_dispatch(significand_buffer, significand_buffer + offset, significand, base);
             switch (r.ec)
             {
                 case std::errc::invalid_argument:
                     return {first, std::errc::invalid_argument};
                 case std::errc::result_out_of_range:
                     return {next, std::errc::result_out_of_range};
                 default:
                     break;
             }
 
             if (round)
             {
                 significand += 1;
             }
         }
     }
     else
     {
         return {first, std::errc::invalid_argument};
     }
 
     // Finally we get the exponent
     constexpr std::size_t exponent_buffer_size = 6; // Float128 min exp is −16382
     char exponent_buffer[exponent_buffer_size] {};
     const auto significand_digits = i;
     i = 0;
 
     // Get the sign first
     if (next != last && *next == '-')
     {
         exponent_buffer[i] = *next;
         ++next;
         ++i;
     }
     else if (next != last && *next == '+')
     {
         ++next;
     }
 
     // Next strip any leading zeros
     while (next != last && *next == '0')
     {
         ++next;
     }
 
     // Process the significant values
     while (next != last && is_integer_char(*next) && i < exponent_buffer_size)
     {
         exponent_buffer[i] = *next;
         ++next;
         ++i;
     }
 
     // If the exponent can't fit in the buffer the number is not representable
     if (next != last && i == exponent_buffer_size)
     {
         return {next, std::errc::result_out_of_range};
     }
 
     // If the exponent was e+00 or e-00
     if (i == 0 || (i == 1 && exponent_buffer[0] == '-'))
     {
         if (fractional)
         {
             exponent = static_cast<Integer>(dot_position - significand_digits);
         }
         else
         {
             exponent = extra_zeros;
         }
 
         return {next, std::errc()};
     }
 
     const auto r = from_chars(exponent_buffer, exponent_buffer + i, exponent);
 
     exponent += leading_zero_powers;
 
     switch (r.ec)
     {
         case std::errc::invalid_argument:
             return {first, std::errc::invalid_argument};
         case std::errc::result_out_of_range:
             return {next, std::errc::result_out_of_range};
         default:
             if (fractional)
             {
                 // Need to take the offset from 1.xxx because compute_floatXXX assumes the significand is an integer
                 // so the exponent is off by the number of digits in the significand - 1
                 if (fmt == chars_format::hex)
                 {
                     // In hex the number of digits parsed is possibly less than the number of digits in base10
                     exponent -= num_digits(significand) - static_cast<Integer>(dot_position);
                 }
                 else
                 {
                     exponent -= static_cast<Integer>(significand_digits - dot_position);
                 }
             }
             else
             {
                 exponent += extra_zeros;
             }
 
             return {next, std::errc()};
     }
 }
 
 }}} // Namespaces
 
 #if defined(__GNUC__) && __GNUC__ < 5 && !defined(__clang__)
 # pragma GCC diagnostic pop
 #endif
 
 #endif // BOOST_CHARCONV_DETAIL_PARSER_HPP

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