If conditions

Basic If statements may look like this:

• If (X == 50) (assuming 0x0001000 represents the X variable):

mov eax, 50
cmp dword ptr [00010000h],eax

• If (X | 00001000b) (| represents the OR logical gate):

mov eax, 000001000b
test dword ptr [00010000h],eax

In order to understand the branching and flow redirection, let's take a look at the following diagram to see how it's manifested in pseudocode:

Figure 7: Conditional flow redirection

To apply this branching sequence in assembly, the compiler uses a mix of conditional and unconditional jumps, as follows:

• IF.. THEN.. ENDIF:

cmp dword ptr [00010000h],50
 jnz 3rd_Block ; if not true
 …
 Some Code
 …
 3rd_Block:
 Some code

• IF.. THEN.. ELSE.. ENDIF:

cmp dword ptr [00010000h],50
 jnz Else_Block ; if not true
 ...
 Some code
 ...
 jmp 4th_Block ;Jump after Else
 Else_Block:
 ...
 Some code
 ...
 4th_Block:
...
 Some code