when 64
              if endianness == :BIG_ENDIAN
                return buffer[lower_bound..upper_bound].unpack(PACK_BIG_ENDIAN_64_BIT_FLOAT)[0]
              else # endianness == :LITTLE_ENDIAN
                return buffer[lower_bound..upper_bound].unpack(PACK_LITTLE_ENDIAN_64_BIT_FLOAT)[0]