Method write_int

include/fmt/format.h:2086–2147

template <typename Char, typename OutputIt, typename T>
FMT_CONSTEXPR FMT_INLINE auto write_int(OutputIt out, write_int_arg<T> arg,
                                        const format_specs& specs) -> OutputIt {
  static_assert(std::is_same<T, uint32_or_64_or_128_t<T>>::value, "");

  constexpr size_t buffer_size = num_bits<T>();
  char buffer[buffer_size];
  if (is_constant_evaluated()) fill_n(buffer, buffer_size, '\0');
  const char* begin = nullptr;
  const char* end = buffer + buffer_size;

  auto abs_value = arg.abs_value;
  auto prefix = arg.prefix;
  switch (specs.type()) {
  default: FMT_ASSERT(false, ""); FMT_FALLTHROUGH;
  case presentation_type::none:
  case presentation_type::dec:
    begin = do_format_decimal(buffer, abs_value, buffer_size);
    break;
  case presentation_type::hex:
    begin = do_format_base2e(4, buffer, abs_value, buffer_size, specs.upper());
    if (specs.alt())
      prefix_append(prefix, unsigned(specs.upper() ? 'X' : 'x') << 8 | '0');
    break;
  case presentation_type::oct: {
    begin = do_format_base2e(3, buffer, abs_value, buffer_size);
    // Octal prefix '0' is counted as a digit, so only add it if precision
    // is not greater than the number of digits.
    auto num_digits = end - begin;
    if (specs.alt() && specs.precision <= num_digits && abs_value != 0)
      prefix_append(prefix, '0');
    break;
  }
  case presentation_type::bin:
    begin = do_format_base2e(1, buffer, abs_value, buffer_size);
    if (specs.alt())
      prefix_append(prefix, unsigned(specs.upper() ? 'B' : 'b') << 8 | '0');
    break;
  case presentation_type::chr:
    return write_char<Char>(out, static_cast<Char>(abs_value), specs);
  }

  // Write an integer in the format
  //   <left-padding><prefix><numeric-padding><digits><right-padding>
  // prefix contains chars in three lower bytes and the size in the fourth byte.
  int num_digits = static_cast<int>(end - begin);
  // Slightly faster check for specs.width == 0 && specs.precision == -1.
  if ((specs.width | (specs.precision + 1)) == 0) {
    auto it = reserve(out, to_unsigned(num_digits) + (prefix >> 24));
    for (unsigned p = prefix & 0xffffff; p != 0; p >>= 8)
      *it++ = static_cast<Char>(p & 0xff);
    return base_iterator(out, copy<Char>(begin, end, it));
  }
  auto sp = size_padding(num_digits, prefix, specs);
  unsigned padding = sp.padding;
  return write_padded<Char, align::right>(
      out, specs, sp.size, [=](reserve_iterator<OutputIt> it) {
        for (unsigned p = prefix & 0xffffff; p != 0; p >>= 8)
          *it++ = static_cast<Char>(p & 0xff);