说明：  lzw壓縮encode,字典壓縮部份使用16位元儲存在文字檔中,缺點為壓縮效率太差,一個文字需用四個bit表示
(lzw compression encode, some use 16-bit compression dictionary is stored in text files, the shortcomings of bad for the compression efficiency of a four bit word, said Xu Yong)