汇编在dos下显示字符串的子程序

assume cs:code,ss:stack,ds:data

data segment
    db ‘welcome to masm‘,‘0‘
data ends

stack segment
    dw 8 dup (0)
stack ends

code segment
start:
    mov dh,8
    mov dl,3
    mov cl,2
    mov ax,data
    mov ds,ax
    mov si,0
    mov ss,stack
    call show_str

    mov ax,4c00h
    int 21h

show_str: //显示字符串的子程序
    push ax
    push cx
    push dx
    push ss
    push si//现场的保留

    mov ax,0b800h
    mov es,ax
    mov di,0

    mov al,0a0h
    dec dh
    mul dh
    mov bx,almov al,2
    dec dl
    mul dl
    add bx,al

//计算要显示的位置的偏移地址，且用的是ax寄存器的低八位

    mov al,ch
s:
    mov ch,0
    mov cl,ds:[di]
    jcxz ok//判断读入的字符是不是0
    mov ch,al
    mov es:[bx+si],cx

    inc di
    add si,2

jmp short s

ok:
    pop si
    pop ss
     pop dx
    pop cx
    pop ax
    ret//回复现场

end start
code ends

王爽老师书上的实验10.1。