_AUDIO COMPRESSION_
by John W. Ratcliff

[LISTING ONE]

;; AC.ASM -> ACOMP assembly language compressor. Written by John W. Ratcliff, 
;; 1991. Uses Turbo Assembler IDEAL mode and makes HEAVE use of macros. This
;; algorithm performs an exhaustive search for the best delta mod for each 
;; section of the waveform. It is very CPU intensive, and the algorithm can
;; be a little difficult to follow in assembly language.

    IDEAL           ; Enter Turbo Assembler's IDEAL mode.
    JUMPS           ; Allow automatic jump sizing.
    INCLUDE "prologue.mac"  ; Include usefull assembly lanugage macro file.

SEGMENT _TEXT   BYTE PUBLIC 'CODE'
    ASSUME  CS:_TEXT
;; This macro computes the amount of error in a frame of data, at this
;; bit resolution and this delta mod location.
Macro   DoError BITS
    LOCAL   @@NO
    mov bx,[COMP]       ; Current delta mod value.
    mov bh,BITS         ; Current bit resolution.
    push    [MINERR]        ; Pass minimum error so far.
    push    [PREV]          ; Pass previous data point.
    call    ComputeError        ; Compute error for frame.
    add sp,4            ; Balance stack.
    cmp dx,[MINERR]     ; Less than previous minimum?
    jge @@NO            ; no, don't update.
    mov [MINERR],dx     ; Save as new miniume
    mov [BESTPREV],ax       ; Best previous location.
    xor ah,ah           ;
    mov al,bl           ; Get best delta modution.
    mov [BEST1],ax      ; save it.
    mov al,bh           ; Get best bits.
    mov [BEST2],ax      ; Save it.
@@NO:
    endm

SQLCH   equ 64      ; Squelch bit.
RESYNC  equ 128     ; Resynchronization bit.

DELTAMOD equ    00110000b   ; Bit mask for delta mod bits.

ONEBIT  equ 00010000b   ; Bit pattern for one bit delta mod.
TWOBIT  equ 00100000b   ; Bit pattern for two bit delta mod.
FOURBIT equ 00110000b   ; Bit pattern for two bit delta mod.

;; This macro echos a message to the text screen, so that we can
;; monitor the progress of the compression algorithm.
Macro   Note    MSG
    push    ax
    lea ax,[MSG]
    push    ax
    call    Notify
    add sp,2
    pop ax
    endm

    public  _CompressAudio
;;This the the ACOMP compression procedure.
;;int far CompressAudio(unsigned char far *shand, 
;;                                           Address of audio data to compress.
;;          unsigned char far *dhand, 
;;                                      Destination address of compressed data.
;;          unsigned int slen, Length of audio data to compress.
;;          int squelch,       Squelch value allowed.
;;          int freq,      Playback frequency of audio data.
;;          int frame,     Frame size.
;;          int maxerr);       Maximum error allowed.
Proc    _CompressAudio  far
        ARG     SHAN:DWORD,DHAN:DWORD,SLEN:WORD,SQUELCH:WORD,FREQ:WORD,
                                                         FRAME:WORD,MAXERR:WORD
    LOCAL   PREV:WORD,COMP:WORD,MINERR:WORD,BEST1:WORD,BEST2:
                                                WORD,BESTPREV:WORD = LocalSpace
    PENTER  LocalSpace
    PushCREGS

    lds si,[SHAN]       ; Get source address.
    les di,[DHAN]       ; Get destination address.
    mov cx,[SLEN]       ; Get length of audio data.

    mov ax,cx       ; Get length of audio sample into AX
    stosw           ; Store it.
    mov ax,[FREQ]   ; Get frequency of recording.
    stosw           ; Store it.
    mov ax,[FRAME]  ; Get the frame size.
    stosb           ; Store it.
    mov ax,[SQUELCH]    ; Get squelch size
    stosb           ; Store it.
    mov ax,[MAXERR] ; Get maximum error allowed.
    stosw           ; Save it.
    xor ax,ax
    lodsb           ; Get first data sample
    mov [PREV],ax
    stosb           ; Store first data sample.
    dec cx      ; Decrement sample size count.
    jz  @@DONE

@@SQU:  mov ah,0Bh      ; Test keyboard status.
    int 21h
    or  al,al
    jz  @@NOK
    mov ah,08h      ; If a key was pressed get that key
    int 21h     ; value, and see if it was the
    cmp al,27       ; escape key.
    jne @@NOK
    xor ax,ax       ; If escape, return to caller, with abort.
    jmp @@EXIT
@@NOK:
    xor ax,ax
    mov dx,[SQUELCH]    ; Get squelch value.
    push    cx      ; Save remaining data count.
    push    si      ; Save si.
@@CK1:  lodsb           ; Get data byte.
    sub ax,[PREV]   ; Difference from previous data sample?
    jns @@CK2       ; if positive leave it alone.
    neg ax      ; Make it positive.
@@CK2:  cmp ax,dx       ; Is it within the squelch range?
    jg  @@NOS       ; yes, keep checking!
    loop    @@CK1       ; Keep going.
    inc si      ; Plus one, this last one counts.
@@NOS:  pop ax      ; Get back start SI
    mov dx,si       ; DX contains current address.
    sub dx,ax       ; Compute number of squelch bytes encountered.
    dec dx      ; Less, last non squelch byte.
    cmp dx,3        ; At least three?
    jle @@NOSQ      ; no, don't squelch it.
@@SQS:  cmp dx,63       ; Is it under 63?
    jle @@SEND
    mov ax,(63 + SQLCH)  ; Send count.
    sub dx,63       ; Less the 63 count we just sent.
    stosb           ; Write squelch byte out.
    jmp short @@SQS     ; Continue.
@@SEND: mov ax,dx       ; Get remaining count.
    or  ax,SQLCH    ; Or squelch bit on.
    stosb           ; Send squelch count out.
    dec si      ; Back up to last data point.
    pop ax      ; Pull CX off of stack, use current count.
    Note    msg0
    jmp short @@NXT
@@NOSQ: mov si,ax       ; Replace where source was.
    pop cx      ; Get back remaining data count.

@@NXT:  jcxz    @@DONE      ; Exit if done.
    cmp cx,[FRAME]  ; Below current frame size?
    jae @@GO        ; no, go ahead.
@@FIN:  lodsb           ; Get raw sample.
    shr al,1        ; Down to closest aproximated value.
    or  al,RESYNC   ; Add resync bit to it.
    stosb           ; Store out.
    loop    @@FIN       ; Keep sending final bytes.
    jmp @@DONE      ; exit, after sending final bytes.

@@GO:   mov [MINERR],07FFFh
    push    cx
    mov cx,[FRAME]  ; Set CX to frame size.

    mov [COMP],1
@@ALL1: DoError 1       ; Try one bit mode, +/-1.
    inc [COMP]
    cmp [COMP],17   ; Try delta comp values clean up to 16!!
    jne @@ALL1

    mov ax,[MINERR]
    cmp ax,[MAXERR]
    jle @@BCMP      ; Not good enough...
    mov [COMP],1
@@ALL2: DoError 2       ; Try two bit mode, +/-1.
    inc [COMP]
    cmp [COMP],17   ; Try delta comp values clean up to 16!!
    jne @@ALL2

    mov ax,[MINERR]
    cmp ax,[MAXERR]
    jle @@BCMP
    mov [COMP],1
@@ALL4: DoError 8       ; Try four bit mode, +/-1.
    inc [COMP]
    cmp [COMP],17   ; Try delta comp values clean up to 16!!
    jne @@ALL4

    mov ax,[MINERR] ; Get what the minimum error was.
    cmp ax,[MAXERR] ; Minimum error > maximum error?
    jle @@BCMP      ; no, then send frame.
    pop cx      ; Get back CX
    lodsb           ; Get data sample.
    and al,(NOT 1)  ; Strip off bottom bit.
    xor ah,ah
    mov [PREV],ax   ; New previous.
    shr al,1        ; /2
    or  al,RESYNC   ; Or resync bit on.
    stosb           ; Store it out into data stream.
    Note    msg1
    loop    @@SQU       ; Go check squelching.
    jmp @@DONE      ; Done, if this was last data sample.
@@BCMP: mov bx,[BEST1]  ; Get best comp.
    mov ax,[BEST2]  ; Get best bit size.
    mov bh,al       ; Into BH
    mov ax,32000
    push    ax
    push    [PREV]      ; Pass prev.
    call    ComputeError    ; Re-compute error term.
    add sp,4
    mov [PREV],ax   ; New previous.
;; Now time to store results!
    mov bx,[BEST1]  ; Get best comp.
    cmp [BEST2],1   ; 1 bit?
    jne @@NXT1
    call    Fold1Bit    ; Fold 1 bit data.
    Note    msg2
    jmp short @@IN      ; Reenter.
@@NXT1: cmp [BEST2],2   ; 2 bit data?
    jne @@NXT2
    call    Fold2Bit
    Note    msg3
    jmp short @@IN
@@NXT2:
    call    Fold4Bit
    Note    msg4
@@IN:   mov ax,[FRAME]
    pop cx      ; Get back CX
    add si,ax       ; Advance source
    sub cx,ax       ; Decrement data count.
    jnz @@SQU       ; Continue, if not at end.

@@DONE:
    mov ax,di       ; Size of compressed file.
    les di,[DHAN]
    sub ax,di       ; Difference.

@@EXIT:
    PopCREGS
    PLEAVE
    ret
    endp

;; Compute error:  Registers on entry are:
;;         DS:SI -> source data.
;;         CX    -> number of bytes to compute error term in.
;;         DX    -> total error incurred.
;;         BL    -> delta comp size.
;;         BH    -> maximum bit size value, positive or negative.
;; Exit: CX,DS:SI stay the same.
;;   DX -> total error term.
;;   AX -> new previous.
Proc    ComputeError    near
    ARG PREV:WORD,MINERR:WORD
    LOCAL   CUR:WORD = LocalSpace
    PENTER  LocalSpace

    push    cx
    push    si
    push    di      ; Save destination address.
    xor dx,dx       ; Initally no error.

@@CERR: lodsb           ; Get a data byte.
    xor ah,ah       ; Zero high byte.
    mov [CUR],ax    ; Save as current sample.
    sub ax,[PREV]
    cmp bl,1
    je  @@ND
    idiv    bl      ; Divided by delta mod size.
@@ND:   or  al,al
    js  @@DON       ; Do negative side.
    jnz @@CNT       ; If not zero then continue.
    inc al      ; Can't represent a zero, make it one.
@@CNT:  cmp al,bh       ; > max representative size?
    jle @@OK        ; no, it fit as is.
    mov al,bh       ; Make it the max representative size.
    jmp short @@OK      ;
@@DON:  neg al      ; Make it positive.
    cmp al,bh       ; > max representative size?
    jbe @@K2        ; no, use it.
    mov al,bh       ; Make it the max representative size.
@@K2:   neg al      ; Make it negative again.
@@OK:
    stosb           ; Store data value out.
    imul    bl      ; Times delta comp value.
    add ax,[PREV]   ; Add to previous data point.
    js  @@CS        ; Do signed case.
    cmp ax,255      ; Did it over flow?
    jle @@K3        ; No, then it fit byte sized.
    mov ax,255      ; Make it byte sized.
    jmp short @@K3      ; Re-enter
@@CS:   xor ax,ax       ; Close as we can get, underflow.
@@K3:   mov [PREV],ax   ; This is our new aproximated value.
    sub ax,[CUR]    ; Less actual value.
    jns @@K4        ; if positive then fine.
    neg ax      ; Take absolute value.
@@K4:   add dx,ax       ; Add into total error.
    cmp dx,[MINERR] ; Greater than minimum error allowed?
    jg  @@OUT
    loop    @@CERR
@@OUT:  mov ax,[PREV]   ; Current previous data point.
    pop di      ; Restore destination address.
    pop si      ; Reset SI back to start.
    pop cx      ; Reset CX back to start.
    PLEAVE
    ret
    endp
Macro   BuildByte
    LOCAL   @@HOP1,@@HOP2
    lodsb
    or  al,al       ; Is it signed?
    jns @@HOP1
    shl ah,1        ; Rotate.
    jmp short @@HOP2
@@HOP1: stc
    rcl ah,1
@@HOP2:
    endm
;; Fold 1 bit data.
;; ES:DI -> points to data ready to fold out.
;; CX-> frame size.
;; BL-> contains delta size.
Proc    Fold1Bit    near
    push    ds
    push    si
    push    di      ; Header byte address.
    push    es
    pop ds      ; DS=ES
    mov si,di       ; Source and dest.
    inc di      ; skip past header byte.
@@FOLD: xor ah,ah       ; Dest byte to be built, zero it.
    BuildByte
    BuildByte
    BuildByte
    BuildByte
    BuildByte
    BuildByte
    BuildByte
    BuildByte
    mov al,ah
    stosb           ; Store it out.
    sub cx,8        ; Less the 8 samples just folded up.
    jnz @@FOLD      ; Continue.

    pop si      ; Get back header byte address.
    mov al,bl       ; Get delta comp size.
    dec al      ; Less one.
    or  al,ONEBIT   ; Or the One Bit mode flag on.
    mov [ds:si],al  ; Store header byte.

    pop si
    pop ds
    ret
    endp

;; 2 Bit Format:  00 -> -2
;;        01 -> -1
;;        10 -> +1
;;        11 -> +2
Macro   BByte
    LOCAL   @@HOP1,@@HOP2
    lodsb
    or  al,al       ; Is it signed?
    jns @@HOP1
    add al,2        ; Adjust it.
    jmp short @@HOP2
@@HOP1: inc al      ; Plus 1 to fit into format size.
@@HOP2: shl ah,1
    shl ah,1
    or  ah,al       ; Place bits into byte being built.
    endm
;; Fold 2 bit data.
;; ES:DI -> points to data ready to fold out.
;; CX-> frame size.
;; BL-> contains delta size.
Proc    Fold2Bit    near
    push    ds
    push    si
@@F2:
    push    di      ; Header byte address.

    push    es
    pop ds      ; DS=ES
    mov si,di       ; Source and dest.
    inc di      ; skip past header byte.
@@FOLD: xor ah,ah       ; Dest byte to be built, zero it.
    BByte
    BByte
    BByte
    BByte
    mov al,ah
    stosb           ; Store it out.
    sub cx,4        ; Folded up 4 samples.
    jnz @@FOLD      ; Continue.

    pop si      ; Get back header byte address.
    mov al,bl       ; Get delta comp size.
    dec al      ; Less one.
    or  al,TWOBIT   ; Or the One Bit mode flag on.
    mov [ds:si],al  ; Store header byte.

    pop si
    pop ds
    ret
    endp
;; Four bit format:
;; 0 -> -8
;; 1 -> -7
;; 2 -> -6
;; 3 -> -5
;; 4 -> -4
;; 5 -> -3
;; 6 -> -2
;; 7 -> -1
;; 8 -> +1
;; 9 -> +2
;;10 -> +3
;;11 -> +4
;;12 -> +5
;;13 -> +6
;;14 -> +7
;;15 -> +8
Macro   Adjust4bit
    LOCAL   @@HOP1,@@HOP2
    lodsb
    or  al,al
    jns @@HOP1
    add al,8        ; Adjust it.
    jmp short @@HOP2
@@HOP1: add al,7        ; Adjust it.
@@HOP2:
    endm
;; Fold 4 bit data.
;; ES:DI -> points to data ready to fold out.
;; CX-> frame size.
;; BL-> contains delta size.
Proc    Fold4Bit    near
    push    ds
    push    si

    push    di      ; Header byte address.

    push    es
    pop ds      ; DS=ES
    mov si,di       ; Source and dest the same.
    inc di      ; skip past header byte.
@@FOLD: Adjust4bit      ; Get first sample.
    ShiftL  al,4        ; Into high nibble.
    mov ah,al       ; Into AH
    Adjust4bit      ; Get next nibble.
    or  al,ah       ; One whole byte.
    stosb           ; Store it out.
    sub cx,2        ; Folded up 4 samples.
    jnz @@FOLD      ; Continue.

    pop si      ; Get back header byte address.
    mov al,bl       ; Get delta comp size.
    dec al      ; Less one.
    or  al,FOURBIT  ; Or the One Bit mode flag on.
    mov [ds:si],al  ; Store header byte.

    pop si
    pop ds
    ret
    endp
msg0    db  "SQUELCH"
msg1    db  "RESYNC "
msg2    db  "1 BIT  "
msg3    db  "2 BIT  "
msg4    db  "4 BIT  "

Proc    Notify  near
    ARG MSG:WORD
    PENTER  0
    PushAll

    push    cs
    pop ds
    mov ax,0B800h
    mov es,ax
    mov si,[MSG]
    xor di,di
    mov ah,1Fh
    mov cx,7
@@SND:  lodsb
    stosw
    loop    @@SND

    PopAll
    PLEAVE
    ret
    endp

    ENDS
    END



[LISTING TWO]

;; UC.ASM		-> Uncompress ACOMP compressed audio data.
;;			   Written by John W. Ratcliff, 1991.
;;			   Uses Turbo Assembler IDEAL mode.

	IDEAL		; Enter Turbo Assembler IDEAL mode.
	JUMPS		; Allow automatic jump sizing.

	INCLUDE "prologue.mac"  ; Include common useful assembly macros.

SMALL_MODEL	equ	0   ;: true only if trying to generate near calls

	SETUPSEGMENT			; Setup _TEXT segment.

Macro	CPROC	name
	public	_&name
IF	SMALL_MODEL
Proc	_&name	near
ELSE
Proc	_&name	far
ENDIF
	endm

SQLCH	equ	64		; Squelch byte flag
RESYNC	equ	128		; Resync byte flag.

DELTAMOD equ	00110000b	; Bit mask for delta mod bits.

ONEBIT	equ	00010000b	; Bit pattern for one bit delta mod.
TWOBIT	equ	00100000b	; Bit pattern for two bit delta mod.
FOURBIT equ	00110000b	; Bit pattern for two bit delta mod.


base	dw	?		; Base address inside translate table.


TRANS	db	-8,-7,-6,-5,-4,-3,-2,-1,1,2,3,4,5,6,7,8
	db	-16,-14,-12,-10,-8,-6,-4,-2,2,4,6,8,10,12,14,16
	db	-24,-21,-18,-15,-12,-9,-6,-3,3,6,9,12,15,18,21,24
	db	-32,-28,-24,-20,-16,-12,-8,-4,4,8,12,16,20,24,28,32
	db	-40,-35,-30,-25,-20,-15,-10,-5,5,10,15,20,25,30,35,40
	db	-48,-42,-36,-30,-24,-18,-12,-6,6,12,18,24,30,36,42,48
	db	-56,-49,-42,-35,-28,-21,-14,-7,7,14,21,28,35,42,49,56
	db	-64,-56,-48,-40,-32,-24,-16,-8,8,16,24,32,40,48,56,64
	db	-72,-63,-54,-45,-36,-27,-18,-9,9,18,27,36,45,54,63,72
	db	-80,-70,-60,-50,-40,-30,-20,-10,10,20,30,40,50,60,70,80
	db	-88,-77,-66,-55,-44,-33,-22,-11,11,22,33,44,55,66,77,88
	db	-96,-84,-72,-60,-48,-36,-24,-12,12,24,36,48,60,72,84,96
	db	-104,-91,-78,-65,-52,-39,-26,-13,13,26,39,52,65,78,91,104
	db	-112,-98,-84,-70,-56,-42,-28,-14,14,28,42,56,70,84,98,112
	db	-120,-105,-90,-75,-60,-45,-30,-15,15,30,45,60,75,90,105,120
	db	-128,-112,-96,-80,-64,-48,-32,-16,16,32,48,64,80,96,112,127

CPROC	GetFreq 		; Report playback frequency for an ACOMP file.
	ARG	SOURCE:DWORD
	PENTER	0
	push	es
	les	bx,[SOURCE]
	mov	ax,[es:bx+2]
	pop	es
	PLEAVE
	ret
	endp

;; DX contains PREVIOUS.
;; AH contains bit mask being rotated out.
;; BX up/down 1 bit value.
Macro	Delta1
	LOCAL	@@UP,@@STORE
	shl	ah,1	; Rotate bit mask out.
	jc	@@UP
	sub	dx,bx
	jns	@@STORE
	xor	dx,dx	; Zero it out.
	jmp short @@STORE
@@UP:	add	dx,bx
	or	dh,dh
	jz	@@STORE
	mov	dx,255
@@STORE:mov	al,dl		; Store result.
	stosb
	endm

;; BX-> base address of translate table.
;; DX-> previous.
;; AL-> index.
Macro	DeModulate
	LOCAL	@@HIGH,@@OK
	xlat	[cs:bx] ; Translate into lookup table.
	cbw		; Make it a signed word.
	add	dx,ax	; Do word sized add, into previous.
	jns	@@HIGH
	xor	dx,dx	; Underflowed.
@@HIGH: or	dh,dh	; Did it overflow?
	jz	@@OK
	mov	dx,255	; Maxed out.
@@OK:	mov	al,dl
	stosb
	endm


;;unsigned int	  far UnCompressAudio(unsigned char far *source,unsigned char far *dest);
;; UnCompressAudio will decompress data which was compressed using ACOMP
;; into the destination address provided.  UnCompressAudio returns the
;; total size, in bytes, of the uncompressed audio data.
CPROC	UnCompressAudio
	ARG	SHAN:DWORD,DHAN:DWORD
	LOCAL	SLEN:WORD,FREQ:WORD,FRAME:WORD,BITS:WORD = LocalSpace
	PENTER	LocalSpace
	PushCREGS

	lds	si,[SHAN]		; Get source segment
	les	di,[DHAN]		; Get destination segment

	lodsw				; Get length.
	mov	[SLEN],ax		; Save length.
	mov	cx,ax			; Into CX
	lodsw				; Frequency.
	mov	[FREQ],ax		; Save frequency
	lodsb				; Get frame size.
	xor	ah,ah			; Zero high byte
	mov	[FRAME],ax		; Save it.
	lodsb				; Get squelch, and skip it.
	lodsw				; Get maximum error, and skip it.
	lodsb				; Get initial previous data point.
	stosb				; Store it.
	xor	ah,ah			; zero high byte.
	mov	dx,ax		; Save into previous word.
	dec	cx		; Decrement total by one.
	jz	@@DONE		; Exit
	mov	ah,al		; AH, always the previous.
@@DCMP: lodsb			; Get sample.
	test	al,RESYNC	; Resync byte?
	jz	@@NOTR		; no, skip.
	shl	al,1		; Times two.
	mov	dl,al		; Into previous.
	xor	dh,dh		; Zero high word.
	stosb			; Store it.
	loop	@@DCMP		; Next one.
	jmp	@@DONE

@@NOTR: test	al,SQLCH	; Squelch byte?
	jz	@@FRAM		; no, then it is a frame.
	and	al,00111111b	; Leave just the count.
	push	cx		; Save current countdown counter.
	mov	cl,al		; get repeat count
	xor	ch,ch		; zero high byte of CX
	mov	bx,cx		; Repeat count in DX
	mov	al,dl		; Repeat of previous.
	rep	stosb		; Repeat it.
	pop	cx		; Get back remaining count.
	sub	cx,bx		; Less.
	jnz	@@DCMP		; Keep going.
	jmp	@@DONE

@@FRAM:
	mov	bx,ax		; command byte into BX
	and	bx,0Fh		; Multiplier being used.
	ShiftL	bx,4		; Times 16.
	add	bx,offset TRANS ; Plus address of translate table.
	and	al,DELTAMOD	; Leave just delta mod.
	push	cx
	mov	cx,[FRAME]	; Get frame size.
	cmp	al,ONEBIT	; In one bit delta mod?
	jne	@@NEXT1 	; no, try other.
	ShiftR	cx,3		; /8
	mov	bl,[cs:bx+8]	; Get up amount
	xor	bh,bh		; Zero high byte.
@@GO:	lodsb
	xchg	al,ah		; Place prev in AL, Bit mask in AH
	Delta1
	Delta1
	Delta1
	Delta1
	Delta1
	Delta1
	Delta1
	Delta1
	mov	ah,al
	loop	@@GO
	jmp	@@RENTER

@@NEXT1:cmp	al,TWOBIT	; In two bit delta mod mode?
	jne	@@NEXT2
	add	bx,6		; Point at +- 2 bit's in table.
	shr	cx,1
	shr	cx,1		; 4 samples per byte.
@@GOGO: lodsb
	ShiftR	al,6
	DeModulate
	mov	al,[ds:si-1]
	ShiftR	al,4
	and	al,3
	DeModulate
	mov	al,[ds:si-1]
	ShiftR	al,2
	and	al,3
	DeModulate
	mov	al,[ds:si-1]
	and	al,3
	DeModulate
	loop	@@GOGO
	jmp short @@RENTER
@@NEXT2:shr	cx,1		; Two samples per byte.
@@GO2:	lodsb			; Get sample.
	ShiftR	al,4
	DeModulate
	mov	al,[ds:si-1]
	and	al,0Fh
	DeModulate
	loop	@@GO2

@@RENTER:
	pop	cx
	sub	cx,[FRAME]
	jnz	@@DCMP		; Continue decompress

@@DONE:
	mov	ax,[SLEN]	; Uncompressed length.

	PopCREGS
	PLEAVE
	ret
	endp


	ENDS
	END