代码部分：
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* This function can be called in the c programs and in the *
* assmbly programs. *
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* filename: fir_filter *
* author:skycanny *
* date:2004,11,03 *
* argument1:the program coffcients pointer *
* argument2:the data coffcients pointer *
* argument3:the input pointer *
* argument4:the output pointer *
*
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*c syntax: *
* fir_filter(arg1,arg2,arg3,arg4) *
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*assembly syntax: *
* frame -3 |return address| *
* st arg2,*sp(0) | arg2 |<--sp *
* st arg3,*sp(1) | arg3 | *
* st arg4,*sp(2) | arg4 | *
* calld _fir_filter *
* ld arg1,0,a *
* frame 3 * | 
