Method parse_float

src/toml.hpp:13920–14073

		TOML_NODISCARD
		TOML_NEVER_INLINE
		double parse_float()
		{
			return_if_error({});
			assert_not_eof();
			TOML_ASSERT_ASSUME(is_match(*cp, U'+', U'-', U'.') || is_decimal_digit(*cp));
			push_parse_scope("floating-point"sv);

			// sign
			const int sign = *cp == U'-' ? -1 : 1;
			if (is_match(*cp, U'+', U'-'))
				advance_and_return_if_error_or_eof({});

			// consume value chars
			char chars[utf8_buffered_reader::max_history_length];
			size_t length			   = {};
			const utf8_codepoint* prev = {};
			bool seen_decimal = false, seen_exponent = false;
			char first_integer_part = '\0';
			while (!is_eof() && !is_value_terminator(*cp))
			{
				if (*cp == U'_')
				{
					if (!prev || !is_decimal_digit(*prev))
						set_error_and_return_default("underscores may only follow digits"sv);

					prev = cp;
					advance_and_return_if_error_or_eof({});
					continue;
				}
				else if TOML_UNLIKELY(prev && *prev == U'_' && !is_decimal_digit(*cp))
					set_error_and_return_default("underscores must be followed by digits"sv);
				else if TOML_UNLIKELY(length == sizeof(chars))
					set_error_and_return_default("exceeds length limit of "sv,
												 sizeof(chars),
												 " digits"sv,
												 (seen_exponent ? ""sv : " (consider using exponent notation)"sv));
				else if (*cp == U'.')
				{
					// .1
					// -.1
					// +.1 (no integer part)
					if (!first_integer_part)
						set_error_and_return_default("expected decimal digit, saw '.'"sv);

					// 1.0e+.10 (exponent cannot have '.')
					else if (seen_exponent)
						set_error_and_return_default("expected exponent decimal digit or sign, saw '.'"sv);

					// 1.0.e+.10
					// 1..0
					// (multiple '.')
					else if (seen_decimal)
						set_error_and_return_default("expected decimal digit or exponent, saw '.'"sv);

					seen_decimal = true;
				}
				else if (is_match(*cp, U'e', U'E'))
				{