Assembly to C code

Question

This Assembly code:

cmp [Variable1], 10
jae AlternateBlock
call SomeFunction
jmp AfterIfBlock
cmp [Variable1], 345
jne AfterIfBlock
call SomeOtherFunction

equals to this C code?:

if (variable1 >= 10)
{
    goto AlternateBlock;
    SomeFunction();
    goto AfterIfBlock;
}
else if (Variable1 != 345)
{
    goto AfterIfBlock;
    SomeOtherFunction();
}

Mike Kwan · Accepted Answer · 2011-06-22 14:41:02Z

5

More succinctly:

if( variable1 < 10 ) {
  SomeFunction();
} else if( variable1 == 345 ) {
  SomeOtherFunction()
}

Explanation:

cmp [Variable1], 10
jae AlternateBlock     ; if variable1 is >= 10 then go to alternate block
call SomeFunction      ; else fall through and call SomeFunction(). ie. when variable1 < 10
jmp AfterIfBlock       ; prevent falling through to next conditional
cmp [Variable1], 345
jne AfterIfBlock       ; if variable1 is not equal to 345 then jump to afterifblock
call SomeOtherFunction ; else fall through to call SomeOtherFunction

If you take some time to understand it you should see it's semantically equivalent to the C code. Perhaps this helps.

cmp [Variable1], 10
jb @f
call SomeFunction
jmp end
  @@:
cmp [Variable1], 345
jnz end
call SomeOtherFunction
  end:

edited Jun 22, 2011 at 14:41

answered Jun 22, 2011 at 14:34

Mike Kwan

24.5k12 gold badges65 silver badges98 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

David Heffernan · Accepted Answer · 2011-06-22 14:37:02Z

4

No, it's probably more like this:

if (variable1 < 10)
    SomeFunction();
else if (Variable1 == 345)
    SomeOtherFunction();

But you've not included the labels in your assembler so I can't be sure. I've assumed the labels are like this:

    cmp [Variable1], 10
    jae AlternateBlock
    call SomeFunction
    jmp AfterIfBlock
@@AlternateBlock:
    cmp [Variable1], 345
    jne AfterIfBlock
    call SomeOtherFunction
@@AfterIfBlock:

edited Jun 22, 2011 at 14:37

answered Jun 22, 2011 at 14:32

David Heffernan

616k46 gold badges1.1k silver badges1.5k bronze badges

1 Comment

David Heffernan Over a year ago

@Mike Yes I've just spotted that when checking through again. Thanks.

Armen Tsirunyan · Accepted Answer · 2011-06-22 14:32:48Z

0

No, it's not. If variable1 is less than 10, the assembly code will call SomeFunction, and the C code will not, it will jump to AlternateBlock

answered Jun 22, 2011 at 14:32

Armen Tsirunyan

134k61 gold badges336 silver badges442 bronze badges

6 Comments

Thanos Papas Over a year ago

But why is it; if variable1 < 10, jae isn't jump if above or equal?

Armen Tsirunyan Over a year ago

@Thanos: Yes, so bacause variable is less than 10, it will NOT jump anywhere and will go to the next statement, which is call someFunction

Thanos Papas Over a year ago

I mean that JAE isn't if (>=)?

David Heffernan Over a year ago

@Thanos JAE is indeed jump if greater than or equals. Think about it!

Thanos Papas Over a year ago

Oh yes, now I understood, I have been stuck for a moment, thank you.

|

Collectives™ on Stack Overflow

Assembly to C code

3 Answers 3

Comments

1 Comment

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related