I've been seeing a lot of code lately that inverts pointers (1's complement).. I was wondering what this tends to be used for? So far, I haven't made sense of it:
void __fastcall(int *arg0):
lea eax, [ecx+4] ; ecx is a parameter; load the address of the second 32-bit value
mov [ecx], 0
mov [eax], eax ; store the address of the parameter in the parameter itself
not eax ; Invert the address of the second parameter
mov [ecx+8], eax ; Store the inverted address in the third 32-bit spot
ret
I just can't figure out why they would invert the pointer and store it. The array ends as:
arg[0]: 0x00000000
arg[1]: &arg[1]
arg[2]: ~&arg[1]
Does anybody know what use a structure like that is?
Thanks
I have seen it used with linked lists. A 1's complement pointer can mean end of list, pointing back to head or something like that.
Why would they invert it for that, though? Wouldn't it make more sense to leave it as-is?
Linked list is making sense, though. It looks like they're setting up some kind of data structure. They call that little function probably 12 or 14 times on different parts of a large array.