Method do_write_float

include/fmt/format.h:2588–2624

template <typename Char, typename Grouping, typename OutputIt,
          typename DecimalFP>
FMT_CONSTEXPR20 auto do_write_float(OutputIt out, const DecimalFP& f,
                                    const format_specs& specs, sign s,
                                    int exp_upper, locale_ref loc) -> OutputIt {
  Char point = specs.localized() ? detail::decimal_point<Char>(loc) : Char('.');
  int significand_size = get_significand_size(f);
  int exp = f.exponent + significand_size - 1;
  if (specs.type() == presentation_type::fixed ||
      (specs.type() != presentation_type::exp &&
       use_fixed(exp, specs.precision > 0 ? specs.precision : exp_upper))) {
    return write_fixed<Char, Grouping>(out, f, significand_size, point, specs,
                                       s, loc);
  }

  // Write value in the exponential format.
  int num_zeros = 0;
  long long size = significand_size + (s != sign::none ? 1 : 0);
  if (specs.alt()) {
    num_zeros = max_of(specs.precision - significand_size, 0);
    size += num_zeros;
  } else if (significand_size == 1) {
    point = Char();
  }
  size += (point ? 1 : 0) + compute_exp_size(exp);
  char exp_char = specs.upper() ? 'E' : 'e';
  auto write = [=](reserve_iterator<OutputIt> it) {
    if (s != sign::none) *it++ = detail::getsign<Char>(s);
    // Insert a decimal point after the first digit and add an exponent.
    it = write_significand(it, f.significand, significand_size, 1, point);
    if (num_zeros > 0) it = detail::fill_n(it, num_zeros, Char('0'));
    *it++ = Char(exp_char);
    return write_exponent<Char>(exp, it);
  };
  size_t usize = static_cast<size_t>(size);
  return specs.width > 0
             ? write_padded<Char, align::right>(out, specs, usize, write)
             : base_iterator(out, write(reserve(out, usize)));
}

template <typename Char, typename OutputIt, typename DecimalFP>
FMT_CONSTEXPR20 auto write_float(OutputIt out, const DecimalFP& f,