Question

我正在尝试创建一个x86函数，它接受两个字符串作为参数，并确定哪个更大。参数是通过用户输入获得的，我正在使用NASM。然而，一旦我开始工作，我就会在c程序中调用我的汇编函数，这样可能只会给自己提供比测试所需的更多的工作。我真的很感激任何帮助，找出为什么这个代码错误。

SECTION .data

greet:  db      "Type a word: "
greetL: equ     $-greet
bigprompt:   db "First is bigger"
bigpromptL: equ $-bigprompt
smallprompt:     db "Second is bigger"
smallpromptL:   equ $-smallprompt
sameprompt: db "They same: "
samepromptL:    equ $-sameprompt
LF: equ 10

SECTION .bss

first: resb 30
second: resb 30

SECTION .text

global  _start

_start:
    nop
    mov     eax, 4          ; ask for first word
    mov     ebx, 1          
    mov     ecx, greet      
    mov     edx, greetL     
    int     80H         

    mov     eax, 3          ; get first word
    mov     ebx, 0          
    mov     ecx, first      
    mov     edx, 30 
    int     80H             

    mov     eax, 4                  ; ask for second word
    mov     ebx, 1
    mov     ecx, greet
    mov     edx, greetL
    int         80H

    mov     eax, 3                  ; get second word
    mov     ebx, 0
    mov     ecx, second
    mov     edx, 30
    int 80H


    push first
    push second
    call _Stringgt
    mov esi, eax
    jmp DONE

_Stringgt:  
    push ebp
    mov ebp, esp
    push edx
    mov eax, [ebp+8]
    mov ebx, [ebp+12]
    cld
    xor ecx, ecx
    LOOP:   
            mov al, [eax + ecx]
        cmp [ebx + ecx], al
        jb BIGGER
        ja SMALLER
        cmp al, LF
        je SAME
        inc ecx
        jmp LOOP
    BACK:
        pop ebp
        ret

    BIGGER:
        mov eax, bigprompt
                jmp BACK

    SMALLER:
        mov eax, smallprompt
                jmp BACK
    SAME:
        mov eax, sameprompt
            jmp BACK
DONE:   

    mov eax, 4
    mov ebx, 1
    mov ecx, esi
    mov edx, 30
    int 80H

    mov eax, 1              ; exit
    mov ebx, 0              
    int 80H

Answer 1

这太简单了。您可以使用此函数来获取字符串的长度并确定哪个更大。

;---------------------------------------------------------
;IN: takes zero terminated string address as parameter on stack
;OUT: String length in AX
;---------------------------------------------------------
str_length:

mov bp,sp
mov si, [bp+2]
mov al, [si]
mov bx,0

.loop:

cmp byte [si], 0
je .done
add si,1
add bx,1
jmp .loop


.done:

mov ax,bx
ret
;--------------------------------------------------------------

现在你可以做两次str_length并比较字符串长度，比如

main:
mov ax,string1
push ax              ;give function parameter
call str_length       ;call the function
mov dx,ax             ;store string length in dx

mov ax,string2
push ax
call str_length      ; do this for string2

;now length of string1 is in dx and string2 is in ax we can compare them

cmp ax,dx
je equal
cmp ax,dx
ja greater
cmp ax,dx
jl less

x86汇编中的字符串比较函数 - seg fault

1 个答案: