CALL和RET指令实验

实验10

1.在屏幕8行3列，用绿色显示data段中的字符串

assume cs:code
data segment
    db'Welcome to masm!',0
data ends

code segment
start:
    mov dh,8            ;行
    mov dl,3            ;列
    mov cl,2            ;颜色
    mov ax,data
    mov ds,ax
    mov si,0            ;字符串首地址
    call show_str
    mov ax,4c00h
    int 21h

show_str:
    push ax             ;用到的寄存器入栈
    push bx
    push cx
    push dx
    push es
    push di
    
    mov ax,0B800h       ;定义显示缓冲区的段地址
    mov es,ax
   
;N为行，M为列
;计算写入首地址的偏移地址   公式:1) 0A0H*(N)+M*2 
    mov al,dh
    mov ah,0

   mov bl,0A0h         ;每行偏移A0H
    mul bl
    mov bl,dl
    mov bh,0
    add ax,bx
    add ax,bx
    mov di,ax           ;ax为首地址的偏移地址
    mov dl,cl           ;dl存颜色
    mov ch,0
    
nx:
    mov cl,ds:[si]         ;判断字符是否为00
    jcxz over
    mov bl,cl
    mov bh,dl
    mov es:[di],bx      ;赋值
    add si,1
    add di,2
    jmp short nx
    
over:
   pop di
    pop es
    pop dx
    pop cx
    pop bx
    pop ax
    ret


code ends
end start

2.解决除法溢出

参数：ax=被除数的低16位，dx=被除数的高16位，cx=除数

返回值：dx=结果的高16位，ad=结果的低16位，cx=余数

assume cs:code
code segment
start:
    mov ax,4240h
    mov dx,000fh
    mov cx,0Ah
    call divdw
    mov ax,4c00h
    int 21h
divdw:
        push ax
        mov ax,dx
        mov dx,0
        div cx
        mov bx,ax
        pop ax
        div cx
        mov cx,dx
        mov dx,bx
        ret
code ends
end start

3.数值显示

将data段中的数据以十进制形式显示出来

assume cs:code
data segment
    dw 123,12666,1,8,3,38
    dw 0,0,0,0,0,0,0,0
data ends

code segment
start:
    mov ax,data
    mov ds,ax
    mov ax,20h
    mov ax,0
    mov ax,0B800h
    mov es,ax
    mov si,0            ;si为数据段的偏移
    mov di,0            ;di为显示缓冲区的偏移
    mov cx,6   
    call dioffset         ;计算di值
    
s:push cx
    mov ax,[si]         ;取数据
    mov dx,[0]
    mov bx,0              ;bx为数字的位数
    mov bp,0ch
    call dtoc
    mov cx,bx
    s5:call display
    loop s5
    add si,2
    pop cx
    loop s
    mov ax,4c00h
    int 21h

;把数字转为字符串
dtoc:
    mov cx,10   ;除数10
    call divdw
    jcxz s6
    add cx,30h
    mov ds:[bp],cx     ;数字入栈
    add bp,2
    inc bx      ;数字位数加1
    jmp short dtoc
    s6:ret

;把字符存入显示缓冲区中
display:
    push dx
    mov dx,ds:[bp-2]
    sub bp,2
    mov dh,02
    mov es:[di],dx      ;赋值
    add di,2
    pop dx
    ret
    
;求显示缓冲区偏移地址
dioffset:
    push bx
    push dx
    mov dh,8            ;行
    mov dl,3            ;列
    mov al,dh
    mov ah,0
   mov bl,0A0h         ;每行偏移A0H
    mul bl
    mov bl,dl
    mov bh,0
    add ax,bx
    add ax,bx
    mov di,ax           ;ax为首地址的偏移地址
    pop dx
    pop bx
    ret
;防溢出除法
divdw:
        push bx
        push ax
        mov ax,dx
        mov dx,0
        div cx
        mov bx,ax
        pop ax
        div cx
        mov cx,dx
        mov dx,bx
        pop bx
        ret
        
code ends
end start