嵌套循环产生错误Assembly / x86 / MASM

Question

I made a nested loop to try to find the composite numbers from 1...400 and save them to an array. Its not working out so great, unfortunately. Can anybody help me out?

UPPER_LIMIT equ 400
    .data
    CoArray DWORD 500 DUP(?)

Push the offset of array in main before making the function call:

main PROC
   push OFFSET CoArray
   call calc
main ENDP

And this is the procedure itself:

calc PROC
    push    ebp                     ; Save base pointer
    mov     ebp, esp                ; Base of stack frame
    mov     esi,[ebp + 8]           ; offset of the array

    ; esi now holds offset of the array

    mov     ecx, 4
L1:
    cmp     ecx, UPPER_LIMIT
    jnle    done

    mov     ebx, 2
L2: 
    mov     edx, ecx
    sub     edx, 1
    cmp     ebx, edx
    jge     loopOne
    mov     eax, ecx
    cdq
    div     ebx
    cmp     edx, 0
    je      composite
resume:
    inc     ebx
    jmp     L2
loopOne:
    inc     ecx
    jmp     L1

done:
    pop     ebp
    ret     4

composite:
    mov     [esi], ecx                                      ; Add the number to the array and increment esi
    add     esi, TYPE DWORD
    jmp     resume
calc ENDP

I should mention that it asks for the user to enter a integer in a range (1 to 400) and stores it in a variable. However, when I enter 10 the program terminates immediately. However, if I enter 20 or higher it hangs up. Very odd.

Answer 1

There's one big problem with your code, but it's not dependent on any sort of user input so it's not causing the problem you described at the end of your question. I'm going to assume that paragraph is irrelevant and describes a different version of your code that you haven't posted.

The problem is that once your code finds a composite number it's not moving on to next possible composite number. After placing the composite number in the array your code continues to look for more divisors of the number it's already determined to be composite. This means composite numbers will get placed in the array multiple times, once for each divisor other than 1 and itself. To solve this problem simply have the jmp resume statement at the end of your procedure jump to loopOne instead.