A decoder for decoding an input bit stream into a plurality of symbols is provided. The decoder includes an extractor, a length generator, a base selector, and a processing unit. The extractor receives the input bit stream and extracts a code with a predetermined codeword length therefrom. The length generator receives the extracted code and determines a first codeword length corresponding to a symbol according to the extracted code and a base table. The base selector determines a codeword base corresponding to the first codeword length according to the base table. The processing unit generates the symbol corresponding to the extracted code according to the codeword base, an offset table and the first codeword length.