X86 NASM大会将低级到鞋面和鞋帮​​为小写字符 [英] X86 NASM Assembly converting lower to upper and upper to lowercase characters

问题描述

因为我是pretty新的组装，我在关于如何我应该从小写如果用户在装配一个大写字母，反之亦然转换为大写的几个问题。以下是我迄今为止：

As i am pretty new to assembly, i have a few questions in regards to how i should convert from a lowercase to an uppercase if the user enters an uppercase letter or vice versa in assembly. here is what i have so far:

section .data
Enter db "Enter: "
Enter_Len equ $-Enter

Output db "Output: "
Output_Len equ $-Output

Thanks db "Thanks!"
Thanks_Len equ $-Thanks

Loop_Iter dd 0 ; Loop counter

section .bss
In_Buffer resb 2
In_Buffer_Len equ $-In_Buffer

section .text
global _start

_start:
    ; Print Enter message
    mov eax, 4 ; sys_write
    mov ebx, 1
    mov ecx, Enter
    mov edx, Enter_Len
    int 80h

    ; Read input
    mov eax, 3 ; sys_read
    mov ebx, 0
    mov ecx, In_Buffer
    mov edx, In_Buffer_Len
    int 80h

所以基本上，如果我是正确的，我的EDX包含输入的字符串。现在，来自下到上和上转换为小写的窘境。由于我绝对新来这个，有字面上不知道该怎么做。任何帮助将是非常美联社preciated：）

So basically, if i am correct, my edx contains the string entered. Now comes the dilemma of converting from lower to upper and upper to lowercase. As i am absolutely new to this, have literally no clue what to do. Any help would be much appreciated :)

推荐答案

如果你只支持ASCII，那么你可以使用强制将小写字母或0x20的

If you only support ASCII, then you can force lowercase using an OR 0x20

  or   eax, 0x20

同样，您可以将信件通过清除该位为大写：

Similarly, you can transform a letter to uppercase by clearing that bit:

  and  eax, 0xBF   ; or use ~0x20

和作为nneonneo提到的，字符大小写可以使用 XOR 指令进行交换：

And as nneonneo mentioned, the character case can be swapped using the XOR instruction:

  xor  eax, 0x20

这只是工作，如果 EAX 是'A'到'z'或'A'和'Z'之间，所以你必须进行比较，并确保你的范围是：

That only works if eax is between 'a' and 'z' or 'A' and 'Z', so you'd have to compare and make sure you are in the range:

  cmp  eax, 'a'
  jl   .not-lower
  cmp  eax, 'z'
  jg   .not-lower
  or   eax, 0x20
.not-lower:

我用NASM语法。您可能希望确保 JL 和 JG 是正确的太...

如果您需要转换的任何国际字符，那么这是一个复杂多了，除非你可以调用tolower的一个的libc（）或TOUPPER（）函数接受统一code字符。

If you need to transform any international character, then that's a lot more complicated unless you can call a libc tolower() or toupper() function that accept Unicode characters.

作为一个公平的问题：为什么要工作？ （由kuhaku问）

As a fair question: why would it work? (asked by kuhaku)

ASCII字符（也通过了ISO-8859）拥有的0x41和和5AH即可与0x61之间0x7A小写字符之间定义的基本大写字符。

ASCII characters (also ISO-8859-1) have the basic uppercase characters defined between 0x41 and 0x5A and the lowercase characters between 0x61 and 0x7A.

要强制四成及6成5 7，你强迫第5位（0x20的）进行设置。

To force 4 into 6 and 5 into 7, you force bit 5 (0x20) to be set.

要到大写，你却反其道而行之，删除第5位，使其成为零。

To go to uppercase, you do the opposite, you remove bit 5 so it becomes zero.

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