MSAVT.ASM

;MSAVT.ASM: ¥§¨¤¥­â­ë© (¤¥)è¨äà â®à á ¯¥à¥­®á®¬ ª®¤  ¢ PSP
;१¨¤¥­â: 288 ¡ ©â (MSDOS 7.1), 272 ¡ ©â  (TOSHIBA DOS 5.0)
;¡¥§ ¯¥à¥­®á  § ­¨¬ « 416 :)

;‚¥è ¥âáï ­  ¯à¥à뢠­¨¥ 21h
;AX=0DEAFh - ¤¥ª®¤¨à®¢ âì
;AX=0BEEFh - ª®¤¨à®¢ âì
;AX=0FACEh - à®¢¥àª  ­  ãáâ ­®¢ªã. ‚®§¢à é ¥â 2002, ¥á«¨ ãáâ ­®¢«¥­
;ˆá¯®«ì§ã¥âáï ¤®à ¡®â ­­ë©  «£®à¨â¬ è¨ä஢ ­¨ï ‹ìî¨á  Ší஫« , ¯®á«¥ í⮣®
;áç¨â ¥âáï ª®­â஫쭠ï á㬬  ¨ १ã«ìâ â XOR¨âáï ª®­â஫쭮© á㬬®©.
;(„¥)ª®¤¨àã¥â ¡«®ª ¬¨ ¯® CX ¡ ©â.

	.model tiny
	.code
	org	2ch
envseg	dw	?
	org	100h
start:
	jmp	init

new_int21h	proc	far
;ax=0DEAFh - decode
;ax=0BEEFh - encode
;si - @buffer
;dx - @keyword
;di-@2nd buffer;
;bx-length_of_keyword
	pushf
	cmp	ax,0DEAFh
	je	@@decode
	cmp	ax,0BEEFh
	je	@@encode
	cmp	ax,0FACEh
	je	@@ident
	jmp	short @@99

@@decode:
	push	cx
	push	bp
	dec	bx
	push	bx
	mov	bp,sp

	xor	ax,ax
	mov	cx,4

@@d05:	mov	bx,cx
	dec	bx
	add	bx,dx
	add	al,byte ptr [bx]
	loop	@@d05
	push	ax

	xor	bx,bx
	mov	cx,[bp+4]
@@d10:	lodsb
	xor	al,byte ptr [bp-2]
	push	bx
	add	bx,dx
	mov	ah,byte ptr [bx]
	sub	al,ah
	inc	ax
	stosb
	pop	bx
	inc	bx			;<<<
	cmp	bx,word ptr [bp]
	jbe	@@d15
	xor	bx,bx
@@d15:	loop	@@d10

	jmp	short @@98

@@encode:
	push	cx
	push	bp
	dec	bx
	push	bx
	mov	bp,sp

	xor	ax,ax
	mov	cx,4
@@05:	mov	bx,cx
	dec	bx
	add	bx,dx
	add	al,byte ptr [bx]
	loop	@@05
	push	ax

	xor	bx,bx
	mov	cx,[bp+4]
@@10:	lodsb
	push	bx
	add	bx,dx
	mov	ah,byte ptr [bx]
	add	al,ah
	dec	al
	xor	al,byte ptr [bp-2]
	stosb
	pop	bx
	inc	bx			;<<<
	cmp	bx,word ptr [bp]
	jbe	@@15
	xor	bx,bx
@@15:	loop	@@10

@@98:	pop	ax
	pop	bx
	pop	bp
	pop	cx
@@ident:
	popf
	mov	ax,2002h
	iret

@@99:	popf
		db	0EAh	; JMP FAR (­ ç «® ª®¤  ª®¬ ­¤ë ¤ «ì­¥£® ¯¥à¥å®¤ 
old_int21h	dd	0	; á ¯à®æ¥¤ãà  ¨­¨æ¨ «¨§ æ¨¨ § ¯¨è¥â  ¤à¥á
				; ¯à¥¤ë¤ã饣® ®¡à ¡®â稪  INT 21h
new_int21h	endp
;-----------------------------------------------
t_length	=	$-new_int21h
init:
	mov	ax,0FACEh
	int	21h
	cmp	ax,2002h
	je	not_install
	push	es
	mov	ax,3521h
	int	21h
	mov	word ptr old_int21h,bx
	mov	word ptr old_int21h+2,es
	pop	es
	
	cld
	mov	si,offset new_int21h
	mov	di,80h
	mov	cx,t_length
	rep movsb
	
	mov	ax,2521h
	mov	dx,80h
	int	21h

	mov	ah,49h
	mov	es,word ptr envseg
	int	21h

	mov	dx,80h+t_length	; ¥à¢ë© ¡ ©â ¯®á«¥ ª®­æ  १¨¤¥­â 
	int	27h

not_install:
	ret
	db	256 dup ('MSAV')
	end	start