Question

我在NASM中遇到阵列问题。我正在尝试实现此伪代码，但结果不正确。

例如，当我发送＆＃39; abcdefgh＆＃39; as byte_arr我应该得到8 7 6 5 4 3 2 1.然而，我实际收到：5 4 3 2 1 1 1 1.这里是代码：

maxLyn(Z[0 . . n − 1], n, k) : returns integer 

if k = n − 1 

   return 1

p ← 1 

for i ← k+1 to n − 1 
{

    if Z[i−p] = Z[i] 

        if Z[i−p] > Z[i] 

            return p 
        else 

            p ← i+1−k 
}

return p.

我希望将它存储为全局变量，而不是返回p，我可以在其他子例程中访问它。以下是我编写代码的尝试：

enter 0, 0           ; creates stack
pusha                ; pushes current register values onto stack

mov eax, [ebp+16]    ; kth index
mov ebx, [ebp+12]    ; length   
mov edi, [ebp+8]     ; byte_arr

mov [len], ebx      ; len = length    
sub [len], dword 1  ; len = len - 1   
mov ebx, [len]      ; ebx contains len - 1   

mov [k], eax        ; k = epb+16   
mov [p], dword 1    ; p = 1   
mov [i], eax        ; i = k   
inc dword [i]       ; i = k+1    
mov ecx, [i]        ; ecx = i  

cmp [k], ebx        ; checks if kth index is last element
  je ENDFOR

  FOR: cmp dword [i], ebx  ; goes from ith index to len     
    ja ENDFOR
    mov esi, [edi + ecx*1] ; esi = array[i]  
    mov [i_temp], esi      ; store array[i] in variable     
    sub ecx, [p]           ; ecx = i-p
    mov edx, [edi + ecx*1] ; edx = array [i-p]

    cmp edx, [i_temp]      
   je REPEAT               ; array[i-p] = array[i]
   ja ENDFOR               ; array[i-p] > array[i]     
   mov eax, dword [i]      
   mov [p], eax            ;p = i
   inc dword [p]           ;p = i + 1       
   mov eax, dword [p]     
   sub eax, [k]            ;eax = p - k     
   mov [p], eax            ;p = i+1-k  

   REPEAT:     
     inc dword [i]         ; i = i + 1
     mov ecx, [i]          ; ecx = i + 1
     jmp FOR   

   ENDFOR:  
     popa                  ; saves register values and pops them off
     leave                 ; cleans up
     ret                   ; returns to caller

Answer 1

mov esi, [edi + ecx*1] ; esi = array[i]  
mov [i_temp], esi      ; store array[i] in variable     
sub ecx, [p]           ; ecx = i-p
mov edx, [edi + ecx*1] ; edx = array [i-p]

cmp edx, [i_temp]      
je REPEAT               ; array[i-p] = array[i]
ja ENDFOR               ; array[i-p] > array[i]

在这些行中，您将数组元素读为 dwords ，但实际上您使用的是字节数组！这就是比较失败的原因。将此cmp更改为：

cmp dl, byte ptr [i_temp]

或者重新编写代码，以便在适当的地方使用字节大小的变量/寄存器。

在Assembly中索引数组元素

1 个答案: