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FFTR2CN.ASM
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Assembly Source File
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1990-01-17
|
7KB
|
166 lines
;
; This program originally available on the Motorola DSP bulletin board.
; It is provided under a DISCLAMER OF WARRANTY available from
; Motorola DSP Operation, 6501 Wm. Cannon Drive W., Austin, Tx., 78735.
;
; Radix 2, In-Place, Decimation-In-Time FFT (fast).
;
; Last Update 18 Aug 88 Version 1.0
;
fftr2cn macro points,data,odata,coef
fftr2cn ident 1,0
;
; Radix 2 Decimation in Time In-Place Fast Fourier Transform Routine
;
; Complex input and output data
; Real data in X memory
; Imaginary data in Y memory
; Normally ordered input data
; Normally ordered output data
; Coefficient lookup table
; -Cosine values in X memory
; -Sine values in Y memory
;
; Macro Call - fftr2cn points,data,odata,coef
;
; points number of points (16-32768, power of 2)
; data start of data buffer
; odata start of output data buffer
; coef start of sine/cosine table
;
; Alters Data ALU Registers
; x1 x0 y1 y0
; a2 a1 a0 a
; b2 b1 b0 b
;
; Alters Address Registers
; r0 n0 m0
; r1 n1 m1
; n2
;
; r4 n4 m4
; r5 n5 m5
; r6 n6 m6
;
; Alters Program Control Registers
; pc sr
;
; Uses 6 locations on System Stack
;
; Latest Revision - 18 Aug-88
;
move #data,r0 ;initialize input pointer
move #points/4,n0 ;initialize input and output pointers offset
move n0,n4 ;
move n0,n6 ;initialize coefficient offset
move #points-1,m0 ;initialize address modifiers
move m0,m1 ;for modulo addressing
move m0,m4
move m0,m5
;
; Do first and second Radix 2 FFT passes, combined as 4-point butterflies
;
move x:(r0)+n0,x0
tfr x0,a x:(r0)+n0,y1
do n0,_twopass
tfr y1,b x:(r0)+n0,y0
add y0,a x:(r0),x1 ;ar+cr
add x1,b r0,r4 ;br+dr
add a,b (r0)+n0 ;ar'=(ar+cr)+(br+dr)
subl b,a b,x:(r0)+n0 ;br'=(ar+cr)-(br+dr)
tfr x0,a a,x0 y:(r0),b
sub y0,a y:(r4)+n4,y0 ;ar-cr
sub y0,b x0,x:(r0) ;bi-di
add a,b y:(r0)+n0,x0 ;cr'=(ar-cr)+(bi-di)
subl b,a b,x:(r0) ;dr'=(ar-cr)-(bi-di)
tfr x0,a a,x0 y:(r4),b
add y0,a y:(r0)+n0,y0 ;bi+di
add y0,b x0,x:(r0)+n0 ;ai+ci
add b,a y:(r0)+,x0 ;ai'=(ai+ci)+(bi+di)
subl a,b a,y:(r4)+n4 ;bi'=(ai+ci)-(bi+di)
tfr x0,a b,y:(r4)+n4
sub y0,a x1,b ;ai-ci
sub y1,b x:(r0)+n0,x0 ;dr-br
add a,b x:(r0)+n0,y1 ;ci'=(ai-ci)+(dr-br)
subl b,a b,y:(r4)+n4 ;di'=(ai-ci)-(dr-br)
tfr x0,a a,y:(r4)+
_twopass
;
; Perform all next FFT passes except last pass with triple nested DO loop
;
move #points/8,n1 ;initialize butterflies per group
move #4,n2 ;initialize groups per pass
move #-1,m2 ;linear addressing for r2
move #0,m6 ;initialize C address modifier for
;reverse carry (bit-reversed) addressing
do #@cvi(@log(points)/@log(2)-2.5),_end_pass ;example: 7 passes for 1024 pt. FFT
move #data,r0 ;initialize A input pointer
move r0,r1
move n1,r2
move r0,r4 ;initialize A output pointer
move (r1)+n1 ;initialize B input pointer
move r1,r5 ;initialize B output pointer
move #coef,r6 ;initialize C input pointer
lua (r2)+,n0 ;initialize pointer offsets
move n0,n4
move n0,n5
move (r2)- ;butterfly loop count
move x:(r1),x1 y:(r6),y0 ;lookup -sine and -cosine values
move x:(r6)+n6,x0 y:(r0),b ;update C pointer, preload data
mac x1,y0,b y:(r1)+,y1
macr -x0,y1,b y:(r0),a
do n2,_end_grp
do r2,_end_bfy
subl b,a x:(r0),b b,y:(r4) ;Radix 2 DIT butterfly kernel
mac -x1,x0,b x:(r0)+,a a,y:(r5)
macr -y1,y0,b x:(r1),x1
subl b,a b,x:(r4)+ y:(r0),b
mac x1,y0,b y:(r1)+,y1
macr -x0,y1,b a,x:(r5)+ y:(r0),a
_end_bfy
move (r1)+n1
subl b,a x:(r0),b b,y:(r4)
mac -x1,x0,b x:(r0)+n0,a a,y:(r5)
macr -y1,y0,b x:(r1),x1 y:(r6),y0
subl b,a b,x:(r4)+n4 y:(r0),b
mac x1,y0,b x:(r6)+n6,x0 y:(r1)+,y1
macr -x0,y1,b a,x:(r5)+n5 y:(r0),a
_end_grp
move n1,b1
lsr b n2,a1 ;divide butterflies per group by two
lsl a b1,n1 ;multiply groups per pass by two
move a1,n2
_end_pass
;
; Do last FFT pass
;
move #2,n0 ;initialize pointer offsets
move n0,n1
move #points/4,n4 ;output pointer A offset
move n4,n5 ;output pointer B offset
move #data,r0 ;initialize A input pointer
move #odata,r4 ;initialize A output pointer
move r4,r2 ;save A output pointer
lua (r0)+,r1 ;initialize B input pointer
lua (r2)+n2,r5 ;initialize B output pointer
move #0,m4 ;bit-reversed addressing for output ptr. A
move m4,m5 ;bit-reversed addressing for output ptr. B
move #coef,r6 ;initialize C input pointer
move (r5)-n5 ;predecrement output pointer
move x:(r1),x1 y:(r6),y0
move x:(r5),a y:(r0),b
do n2,_lastpass
mac x1,y0,b x:(r6)+n6,x0 y:(r1)+n1,y1 ;Radix 2 DIT butterfly kernel
macr -x0,y1,b a,x:(r5)+n5 y:(r0),a ;with one butterfly per group
subl b,a x:(r0),b b,y:(r4)
mac -x1,x0,b x:(r0)+n0,a a,y:(r5)
macr -y1,y0,b x:(r1),x1 y:(r6),y0
subl b,a b,x:(r4)+n4 y:(r0),b
_lastpass
move a,x:(r5)+n5
endm
^Z