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                                 *