Method format_hexfloat

include/fmt/format.h:3072–3149

// Formats a floating-point number using the hexfloat format.
template <typename Float, FMT_ENABLE_IF(!is_double_double<Float>::value)>
FMT_CONSTEXPR20 void format_hexfloat(Float value, format_specs specs,
                                     buffer<char>& buf) {
  // float is passed as double to reduce the number of instantiations and to
  // simplify implementation.
  static_assert(!std::is_same<Float, float>::value, "");

  using info = dragonbox::float_info<Float>;

  // Assume Float is in the format [sign][exponent][significand].
  using carrier_uint = typename info::carrier_uint;

  const auto num_float_significand_bits = detail::num_significand_bits<Float>();

  basic_fp<carrier_uint> f(value);
  f.e += num_float_significand_bits;
  if (!has_implicit_bit<Float>()) --f.e;

  const auto num_fraction_bits =
      num_float_significand_bits + (has_implicit_bit<Float>() ? 1 : 0);
  const auto num_xdigits = (num_fraction_bits + 3) / 4;

  const auto leading_shift = ((num_xdigits - 1) * 4);
  const auto leading_mask = carrier_uint(0xF) << leading_shift;
  const auto leading_xdigit =
      static_cast<uint32_t>((f.f & leading_mask) >> leading_shift);
  if (leading_xdigit > 1) f.e -= (32 - countl_zero(leading_xdigit) - 1);

  int print_xdigits = num_xdigits - 1;
  if (specs.precision >= 0 && print_xdigits > specs.precision) {
    const int shift = ((print_xdigits - specs.precision - 1) * 4);
    const auto mask = carrier_uint(0xF) << shift;
    const auto v = static_cast<uint32_t>((f.f & mask) >> shift);

    if (v >= 8) {
      const auto inc = carrier_uint(1) << (shift + 4);
      f.f += inc;
      f.f &= ~(inc - 1);
    }

    // Check long double overflow
    if (!has_implicit_bit<Float>()) {
      const auto implicit_bit = carrier_uint(1) << num_float_significand_bits;
      if ((f.f & implicit_bit) == implicit_bit) {
        f.f >>= 4;
        f.e += 4;
      }
    }

    print_xdigits = specs.precision;
  }

  char xdigits[num_bits<carrier_uint>() / 4];
  detail::fill_n(xdigits, sizeof(xdigits), '0');
  format_base2e(4, xdigits, f.f, num_xdigits, specs.upper());

  // Remove zero tail
  while (print_xdigits > 0 && xdigits[print_xdigits] == '0') --print_xdigits;