王爽 汇编 实验16 编写包含多个功能子程序的中断例程

assume cs:code

code segment
start:
	mov ax,cs
	mov ds,ax
	mov si,offset setscreen
	mov ax,0
	mov es,ax
	mov di,0200h
	mov cx,offset endsetscreen-offset setscreen
	rep movsb

	mov ax,0
	mov es,ax
	mov word ptr es:[7ch*4],0200h
	mov word ptr es:[7ch*4+2],0000h

	mov ax,4c00h
	int 21h

setscreen:

	jmp short set
	table dw clear-setscreen+200h,foreground-setscreen+200h,background-setscreen+200h,rollup-setscreen+200h;
	set:
	push bx
	cmp ah,0
	jb sret
	cmp ah,3
	ja sret
	mov bl,ah
	mov bh,0
	add bx,bx
	call word ptr cs:[table+bx-setscreen+200h]

	sret:
	pop bx
	iret


clear:
	push bx
	push cx
	push es
	push si

	mov bx,0b800h
	mov es,bx
	mov si,0
	mov cx,2000

	loopclear:
	mov byte ptr es:[si],' '
	add si,2
	loop loopclear
	
	pop si
	pop es
	pop cx
	pop bx
	ret

foreground:
	push bx
	push cx
	push es
	push si

	mov bx,0b800h
	mov es,bx
	mov si,1
	mov cx,2000

	loopforeground:
	and byte ptr es:[si],11111000b
	or es:[si],al
	add si,2
	loop loopforeground

	pop si
	pop es
	pop cx
	pop bx
	ret

background:
	push bx
	push cx
	push es
	push si

	mov bx,0b800h
	mov es,bx
	mov si,1
	mov cx,2000
	shl al,1
	shl al,1
	shl al,1
	shl al,1

	loopbackground:
	and byte ptr es:[si],10001111b
	or es:[si],al
	add si,2
	loop loopbackground

	pop si
	pop es
	pop cx
	pop bx
	ret

rollup:
	push bx
	push cx
	push ds
	push es
	push si
	push di

	mov bx,0b800h
	mov ds,bx
	mov es,bx
	mov cx,24
	mov si,160
	mov di,0
	cld
	looprollup:
	push cx
	mov cx,160
	rep movsb
	pop cx
	loop looprollup

	mov cx,80
	mov si,0
	clearlast:
	mov byte ptr es:[160*24+si],' '
	add si,2
	loop clearlast

	pop di
	pop si
	pop es
	pop ds
	pop cx
	pop bx
	ret

	endsetscreen:
	nop



code ends
end start