如何在程序集(MASM)中的循环内部打印字符串 [英] How to print a string inside of a loop in assembly (MASM)

问题描述

所以我刚接触汇编，而我的教授在实际解释正在发生的事情时远没有帮助.

So I'm new to assembly, and my professor is far from helpful when it comes to actually explaining what's happening.

在课堂上，我们像这样设置循环:

In class, we set up loops like this:

mov si, 0
mov cx, 5 (repeating the loop 5 times)

L1:
   ...
   loop L1

我们打印出这样的字符串:

And we print strings like this:

mov ah, 40h                 ;write to 
mov bx, handle              ;file
mov cx, lmess2              ;number of bytes to write
mov dx, offset mess2        ;
int 21h

所以现在的问题是我需要在循环内打印一个字符串.我看到的问题是在字符串打印和循环中都使用了CX寄存器，因此当我尝试运行它时，它会按预期方式挂起.

So now the issue is that I need to print a string inside the loop. The issue I see with this is that the CX register is used in both the string printing and the loop, so when I try running it, it hangs, as expected.

循环和字符串打印是否可以使用其他寄存器/方法?

Is there a different register/method I can use for the loop and the string printing?

也许我可以将SI寄存器的值与所需的循环次数进行比较，然后使用JE跳转来跳出循环?但是在我看来，这有点奇怪.

Perhaps I can compare the value of the SI register to however many iterations of the loop I want, and then use a JE jump to jump out of the loop? But to me that seems a bit odd.

如果有人可以引导我朝正确的方向前进，我将不胜感激.我敢肯定，有一种我忽略的简单方法.

If anyone could guide me in the right direction, I'd greatly appreciate it. I'm sure there's an easy way to do this that I'm overlooking.

推荐答案

两个解决方案:

解决方案#1

mov si, 0
mov bp, 5  ;DON'T USE CX, USE AN UNUSED REGISTER, LIKE BP.

L1:
   ...
   dec  bp      ;BP - 1. Zero-Flag turns on when BP becomes zero.
   jnz  L1      ;IF BP != 0 JUMP L1. JNZ = jump if last result is not zero.

解决方案2

mov si, 0
mov cx, 5 (repeating the loop 5 times)

L1:
   PUSH CX         ;PRESERVE CX BEFORE IT CHANGES.
   ... ;PRINT HERE.
   POP  CX         ;RESTORE CX FOR PREVIOUS VALUE.
   loop L1

所选择的解决方案取决于情况:使用寄存器是最快的方法，推入弹出的速度较慢(由于堆栈).如果您有未使用的寄存器，请使用它们，这样会更快，如果没有，请使用堆栈.

The chosen solution depends on the situation : using registers is the fastest way, pushing-popping is slower (because of stack). If you have unused registers, use them, it's faster, if you don't, use stack.

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