    * initialization
    n       equ   20
    start   equ   $40
    wddr    equ   $0
    cddr    equ   $0
    input   equ   $ffe0
    output  equ   $ffe1
    ;
            org   p:start
            move  #wddr,r0  ;r0 ¬ samples
            move  #cddr,r4  ;r1 ¬ coefﬁcients
            move  #n-1,m0   ;set modulo arithmetic
            move  m0,m4     ;for the 2 circular buffers
    ;
            opt   cc
    ;       filter loop :8+(n-1) cycles

            movep y:input,x: (r0)              ;input sample in memory
            clr   a                x:(r0)+,x0  y: (r4)+,y0
            rep   #n-1
            mac   x0,y0,a          x:(r0)+,x0  y:(r4)+,y0
            macr  x0,x0,a          (r0)-

            movep a,y:output                   ;output ﬁltered sample

    fftr2a macro points,data,coef
    fftr2a: ident 1,1

            move #points/2,n0  ;initialize butterﬂies per group
            move #1,n2         ;initialize groups per pass
            move #points/4,n6  ;initialize C pointer offset
            move #-1,m0        ;initialize A and B address modiﬁers
            move m0,m1         ;for linear addressing
            move m0,m4
            move m0,m5
            move #0,m6         ;initialize C address modiﬁer for
                               ;reverse carry (bit-reversed) addressing

            do   #@cvi (@log(points)/@log(2)+0.5),_end_pass
            move #data,r0       ;initialize A input pointer
            move r0,r4          ;initialize A output pointer

    _end_bfy
            move a,x:(r5)+n5 y:(r1)+n1,y1

    end_cell
            rnd a
            movep #0,x:$fffe
            dc @sin(@cvf(count)*freq)
            move #twiddle,r2

            MOVE L:<$1,A
            SUB X,A L:<$3,B

     bad_label
     good_label: