学 Win32 汇编[15]: LOOP 与标号

Loop 是反复执行;
从哪反复? 这要用到 "标号";
反复几次? 把反复的次数告诉 ECX 寄存器即可.

---

笨办法计算 3 * 8 = 24

---

; Test15_1.asm

.386

.model flat, stdcall



include    windows.inc

include    kernel32.inc

include    masm32.inc

include    debug.inc

includelib kernel32.lib

includelib masm32.lib

includelib debug.lib



.data

    val dd 3

.code

main proc

    xor eax, eax

    add eax, val

    add eax, val

    add eax, val

    add eax, val

    add eax, val

    add eax, val

    add eax, val

    add eax, val

    PrintDec eax  ;24

    ret

main endp

end main


 
   

使用 LOOP 和标号:

---

; Test15_2.asm

.386

.model flat, stdcall



include    windows.inc

include    kernel32.inc

include    masm32.inc

include    debug.inc

includelib kernel32.lib

includelib masm32.lib

includelib debug.lib



.data

    val dd 3

.code

main proc

    xor eax, eax

    mov ecx, 8

L1:               ;命名为 "L1" 的标号

    add eax, val

    loop L1       ;反复到指定标号; 每次反复 ecx 会减 1, 直到 ecx 为 0 才向下执行



    PrintDec eax  ;24

    ret

main endp

end main


 
   

数组求和的例子:

---

; Test15_3.asm

.386

.model flat,  stdcall



include    windows.inc

include    kernel32.inc

include    masm32.inc

include    debug.inc

includelib kernel32.lib

includelib masm32.lib

includelib debug.lib

    

.data

    dwArr dd 1,2,3,4,5

.code

main proc

    lea edi, dwArr           ;把数组起始地址给一个寄存器

    mov ecx, lengthof dwArr  ;把数组元素数(将要反复的次数)给 ECX

    xor eax, eax

L1:

    add  eax, [edi]          ;edi 中的地址将不断变化, 通过 [edi] 获取元素值

    add  edi, type dwArr     ;获取下一个元素的地址

    loop L1

    

    PrintDec eax  ;15

    ret

main endp

end main


 
   

复制字符串的例子:

---

; Test15_4.asm

.386

.model flat, stdcall



include    windows.inc

include    kernel32.inc

include    masm32.inc

include    debug.inc

includelib kernel32.lib

includelib masm32.lib

includelib debug.lib

    

.data

    szSource db 'Hello World!', 0       ;定义源字符串

    szDest   db sizeof szSource dup(0)  ;定义相同大小的目的字符串

.code

main proc

    mov  esi, 0                ;这里选择使用 esi 做数组索引

    mov  ecx, sizeof szSource  ;这是要循环的次数

L1:

    mov  al, szSource[esi]     ;mov 的操作数不允许两个都是变量, 用 al 中转一下

    mov  szDest[esi], al       ;

    inc  esi                   ;调整索引

    loop L1

    

    PrintString szDest         ;Hello World!

    ret

main endp

end main


 
   

如果仅仅是复制字符串, 可以使用声明在 masm32.inc 中的 szCopy 函数:

---

; Test15_5.asm

.386

.model flat, stdcall



include    windows.inc

include    kernel32.inc

include    masm32.inc

include    debug.inc

includelib kernel32.lib

includelib masm32.lib

includelib debug.lib

    

.data

    szSource db 'Hello World!', 0

    szDest   db sizeof szSource dup(0)

.code

main proc

    invoke szCopy, addr szSource, addr szDest

    PrintString szDest  ;Hello World!

    ret

main endp

end main


 
   

关于 @@、@B、@F:

---

; 如果懒得给标号取名, 可以使用 @@ 做标号;

; @B 表示前面最近的一个标号、@F 表示后面最近的一个标号;

; 使用 @@ 可以把前面 3*8=24 的例子修改如下:



; Test15_6.asm

.386

.model flat, stdcall



include    windows.inc

include    kernel32.inc

include    masm32.inc

include    debug.inc

includelib kernel32.lib

includelib masm32.lib

includelib debug.lib



.data

    val dd 3

.code

main proc

    xor eax, eax

    mov ecx, 8

@@:

    add eax, val

    loop @B

    PrintDec eax  ;24

    ret

main endp

end main


 
   

关于全局标号:

---

; 上面例子中的标号都是局部标号;

; 如果一个标号定义在子过程之外, 那它就是全局标号了.

; 能不能在子过程中定义全局标号呢? 后面加两个 : 就是了.



; Test15_7.asm

.386

.model flat, stdcall



include    windows.inc

include    kernel32.inc

include    masm32.inc

include    debug.inc

includelib kernel32.lib

includelib masm32.lib

includelib debug.lib



.data

    val dd 3

.code



MyProc proc

Label1::               ;是 Label1:: 而不是 Label1:

    PrintText 'MyProc'

    ret

MyProc endp



main proc

    PrintText 'main'

    jmp Label1  ;jmp 是无条件跳转指令

    ret

main endp

end main