惠普实验室的经典代码。用于huffman编码的快速实现，具有参考价值-HP Labs classic code. Huffman coding for the rapid realization of value with reference

In signal processing, a finite impulse response (FIR) filter is a filter whose impulse response (or response to any finite length input) is of finite duration, because it settles to zero in finite time. This is in contrast to infinite impulse respons