c3xfir.asm

用dsp解压mp3程序的算法

*********************************************************************
*  C3XFIR - C3x assembly routine for FIR filtering
*              L-1
*       y(n) = sum bi * x(n-i)
*              i=0
*     AR0 points to bL-1, AR1 points to x(n-L+1), RC = L-2
*********************************************************************
*
FIR   MPYF3   *AR0++(1)%,*AR1++(1)%,R1
                        ; bL-1 * x(n-L+1) -> R1
      NOP
      LDF     0.0,R2    ; 0.0 -> R2
      RPTS    RC        ; repeat next parallel instructions L-2 times
      MPYF3   *AR0++(1)%,*AR1++(1)%,R1
                        ; bi * x(n-i) -> R1
||    ADDF3   R1,R2,R2  ; R2 + R1 -> R2
      ADDF3   R1,R2,R2  ; add last product, R1 + R2 -> R2 = y(n)
      RETS              ; return to main program