CODEWITHSUNDEEP
cassembly
martin018
martin018

Reputation: 11

How to convert assembly with multiple if statements to c code?

    cmp eax, 1
    je  .L3
    cmp eax, 4
    je  .L4
    jmp .L9
.L3:
    mov DWORD PTR [ebp-16], 1
    jmp .L5
.L4:
    mov DWORD PTR [ebp-16], 2
    jmp .L5

I need some help figuring out how exactly to convert this to C code. I've tried doing a nested if statement but it converts to

    cmp eax, 1
    je  .L3
    cmp eax, 4
    je  .L3

The code I tried was this

if (var1 != 1)
{
   if(var1!=4)
    {
        var2=1;
    }
}

Entire Assembly code for context

    push    ebp
    mov ebp, esp
    sub esp, 16
    mov DWORD PTR [ebp-4], 4
    mov DWORD PTR [ebp-16], 0
    mov DWORD PTR [ebp-8], 0
    mov eax, DWORD PTR [ebp-4]
    cmp eax, 1
    je  .L3
    cmp eax, 4
    je  .L4
    jmp .L9
.L3:
    mov DWORD PTR [ebp-16], 1
    jmp .L5
.L4:
    mov DWORD PTR [ebp-16], 2
    jmp .L5
.L9:
    mov DWORD PTR [ebp-16], 3
.L5:
    mov DWORD PTR [ebp-12], 0
    jmp .L6
.L7:
    mov eax, DWORD PTR [ebp-12]
    add DWORD PTR [ebp-8], eax
    add DWORD PTR [ebp-12], 1
.L6:
    mov eax, DWORD PTR [ebp-12]
    cmp eax, DWORD PTR [ebp-16]
    jl  .L7
    mov eax, 0
    leave
    ret

Upvotes: 1

Views: 102

Answers (1)

Luis Colorado
Luis Colorado

Reputation: 12668

That code should be assimilated to:

if (var1 == 1)
    goto l3; 
else if (var1 == 4) // we use the same value in eax so the same variable is being checked
    goto l4;
else goto l9;
l3: var2 = 1; goto l5;
l4: var2 = 2; goto l5;
l9: var2 = 3;
l5: ...

I should use a switch statement, as all the tests depend on the value of the var1 variable (indeed, the value of var1 is evaluated and stored into eax, and this is the value compared all the time) giving:

    switch (var1) {
    case 1:  var2 = 1; break;
    case 4:  var2 = 2; break;
    default: var2 = 3; break;
    }

Upvotes: 1

Related Questions