Function code_point_length

include/fmt/base.h:1286–1290

// Returns the number of code units in a code point or 1 on error.
template <typename Char>
FMT_CONSTEXPR auto code_point_length(const Char* begin) -> int {
  if FMT_CONSTEXPR20 (sizeof(Char) != 1) return 1;
  auto c = static_cast<unsigned char>(*begin);
  return static_cast<int>((0x3a55000000000000ull >> (2 * (c >> 3))) & 3) + 1;
}

// Parses the range [begin, end) as an unsigned integer. This function assumes
// that the range is non-empty and the first character is a digit.