int opEquals(Object), and other legacy ints (!)

[Bruno Medeiros]

Bruno Medeiros wrote:
> 
> What does the original Eq1 even do? :
> 
>     sub     ECX,0Ch[EDX]
>     cmp     ECX,1       // Huh?
>     sbb     EAX,EAX
>     neg     EAX
> 
> 

[PS: I've read Frits answer after writing this: ]

Ah I get it now... wasn't understanding what borrow (the mathematical 
notion) was, since I'm not a native english speaker. Nothing a wikipedia 
lookup didn't solve. So, correct me if I'm wrong:

(when I say EDX I mean 0Ch[EDX] or whatever)

// sets the carry flag if zero flag is on,
// that is, if ECX == EDX (from previous instruction)
   cmp   ECX,1

// sets EAX as zero and also subtracts one if carry flag is set
// that is, EAX = -1 if ECX == EDX and EAX = 0 if ECX != EDX
   sbb	EAX,EAX

// two's complement negation of EAX, 0 becomes 0, -1 becomes 1
   neg EAX
// end result: EAX = 1 if ECX == EDX and EAX = 0 if ECX != EDX

So yeah, it seems these 3 instructions do the same as SETE ... ?



-- 
Bruno Medeiros - MSc in CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D