如何访问一个字符数组，并更改小写字母为大写，反之亦然 [英] How to access a char array and change lower case letters to upper case, and vice versa

问题描述

目前正在使用的x86处理器结构计算机组成一类项目。我正在访问的值是一个1字节字符，但我不知道该怎么把它比作一个大写。他们说，使用十六进制格式的ASCII表，但我不知道怎么甚至比较两个。

currently working on a class project for Structured Computer Organization using an x86 processor. The value that I am accessing is an 1 byte char, but I do not know how to compare it to an uppercase. They said to use an ascii table of the hex format, but I'm not sure how to even compare the two.

void changeCase (char char_array[], int array_size ) {

__asm{
        // BEGIN YOUR CODE HERE

    mov eax, char_array;        //eax is base image
    mov edi, 0;

readArray:
    cmp edi, array_size;
    jge  exit;
    mov ebx, edi;           //using ebx as offset
    shl ebx, 2;
    mov cl, [eax + ebx];    //using ecx to be the storage register

check:
    //working on it
    cmp cl, 0x41;       //check if cl is <= than ASCII value 65 (A)
    jl next_indx;
    cmp cl, 0x7A;       //check if cl is >= than ASCII value 122 (z)
    jg next_indx;
    cmp cl, 'a';
    jl convert_down;
    jge convert_up;


convert_down:
    or cl, 0x20;        //make it lowercase
    jmp write;

convert_up:
    and cl, 0x20;       //make it uppercase
    jmp write;

write:
    mov byte ptr [eax + ebx], cl    //slight funky town issue here,

next_indx:
    inc edi;

exit:
    cmp edi, array_size;
    jl readArray;

mov char_array, eax;
        // END YOUR CODE HERE
}

}

任何有助于在这一点上。预先感谢您的帮助！

Anything helps at this point. Thank you in advance for the help!

感谢所有的建议和清晰的点，编辑我的code，以反映变化。一些问题，现在访问冲突。

Thanks for all the suggestion and points of clarity, edited my code to reflect change. Some problem with access violation now.

谢谢你的帮助的眼睛的人。我仍然得到到现在翻译的所有字母。

Thanks for the helpful eyes people. I'm still getting to translating all letters now.

推荐答案

为了清楚起见，我就用纯汇编，并假设...

For clarity's sake, I'll just use pure assembly and assume that...

• CHAR_ARRAY 以32位指针 [EBP + 8] 。


• ARRAY_SIZE 是一个补32位数字，在 [EBP + 12] 。


• 对于您的平台（这是这种方式对大多数反正），字符的编码是ASCII。

• char_array is a 32-bit pointer at [ebp+8].
• array_size is a two's complement 32-bit number at [ebp+12].
• For your platform (it is this way for most anyway), char's encoding is ASCII.

您应该能够这个自己演绎成内联汇编。现在，如果你看一下表每个人都应该记住，但几乎没有人不中，你会发现一些重要的详细资料...

You should be able to deduce this yourself into inline assembly. Now, if you look at the table everyone is supposed to remember but barely anyone does, you'll notice some important details...

• 大写字母 A 到以Z 映射到codeS ×41 到 5AH即可，分别为。


• 小写字母 A 到以Z 映射到codeS 0x61 到 0x7A ，分别为。


• 一切是不是一个字母，因而不需要大小写转换。


• 如果你看一下大写和小写字母范围的二进制重新presentation，你会发现，他们是完全一样的，与唯一的例外是大写字母有6位清零，小写字母有它集。

• Uppercase letters A through Z map into codes 0x41 through 0x5A, respectively.
• Lowercase letters a through z map into codes 0x61 through 0x7A, respectively.
• Everything else is not a letter, and thus need no case conversion.
• If you look at the binary representation of the upper and lowercase letter ranges, you'll notice that they are exactly the same, with the sole exception that uppercase letters have bit 6 cleared, and lowercase ones have it set.

其结果是，该算法将是...

As a result, the algorithm would be...

while array_size != 0
    byte = *char_array
    if byte >= 0x41 and byte <= 0x5A
        *char_array |= 0x20 // Turn it lowercase
    else if byte >= 0x61 and byte <= 0x7A
        *char_array &= 0xDF // Turn it uppercase
    array_size -= 1
    char_array += 1

现在，让我们转换成组装此...

Now, let's translate this into assembly...

mov eax, [ebp+8]      # char *eax = char_array
mov ecx, [ebp+12]     # int ecx = array_size

.loop:
    or ecx, ecx       # Compare ecx against itself
    jz .end_loop      # If ecx (array_size) is zero, we're done
    mov dl, [eax]     # Otherwise, store the byte at *eax (*char_array) into `char dl`
    cmp dl, 'A'       # Compare dl (*char_array) against 'A' (lower bound of uppercase letters)
    jb .continue      # If dl` (*char_array) is lesser than `A`, continue the loop
    cmp dl, 'Z'       # Compare dl (*char_array) against 'Z' (upper bound of uppercase letters)
    jbe .is_uppercase # If dl (*char_array) is lesser or equal to 'Z', then jump to .is_uppercase
    cmp dl, 'a'       # Compare dl (*char_array) against 'a' (lower bound of lowercase letters)
    jb .continue      # If dl (*char_array) is lesser than 'a', continue the loop
    cmp dl, 'z'       # Compare dl (*char_array) against 'z' (upper bound of lowercase letters)
    jbe .is_lowercase # If dl (*char_array) is lesser or equal to 'z', then jump to .is_lowercase
    jmp .continue     # All tests failed, so continue the loop

    .is_uppercase:
        or dl, 20h    # Set the 6th bit
        mov [eax], dl # Send the byte back to where it came from
        jmp .continue # Continue the loop

    .is_lowercase:
        and dl, DFh   # Clear the 6th bit
        mov [eax], dl # Send the byte back to where it came from
        jmp .continue # Continue the loop

    .continue:
        inc eax       # Increment `eax` (`char_array`), much of like a pointer increment
        dec ecx       # Decrement `ecx` (`array_size`), so as to match the previous pointer increment
        jmp .loop     # Continue

.end_loop:

在code到达 .end_loop ，你就大功告成了。

Once code reaches .end_loop, you're done.

我希望这导致光你！

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