more assembly questions

Bmxpunk86pl

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Joined

Sep 7, 2001

Location

CT/Poland

• Jun 26, 2002

• #1

hey i got a question, can anyone help?


what is XOR?

EX: XOR ax, bx;

 

XWRed1

Senior Member

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Joined

Oct 31, 2001

• Jun 26, 2002

• #2

I think its an exclusive or, generates a 0 if both of the inputs are 0 or 1, or generates a 1 if one input is 1 and the other 0.

 

Krusty

Insane Overclocking Clown

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Joined

Sep 17, 2001

Location

Orange County

• Jun 26, 2002

• #3

xor is an exclusive or operation. I used it commonly in assembly to zero out a variable by xoring it with itself. x XOR x = 0.

 

Thelemac

Administratively Deficient

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Joined

Mar 15, 2001

• Jun 26, 2002

• #4

That it is.

I prefer ANDing with a zero to zero something out...fewer transistors == more effeciency.

 

OP

Bmxpunk86pl

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Sep 7, 2001

Location

CT/Poland

• Jun 27, 2002

• Thread Starter
• #5

i think i kindof understand it. But I would appreciate it if one of you guys showed a simple piece of code that uses the XOR thing.


thanks,
adam

 

Thelemac

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Mar 15, 2001

• Jun 27, 2002

• #6

I'll make a truth table

bit1 bit0 XOR result

0 | 0 || 0
0 | 1 || 1
1 | 0 || 1
1 | 1 || 0

I think XOR is used a lot in encryption. The logic circuit for it, though, is somewhat large, so I think it's usually somewhat simplified.

 

OP

Bmxpunk86pl

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Joined

Sep 7, 2001

Location

CT/Poland

• Jun 27, 2002

• Thread Starter
• #7

AH there we go. Ok thanks a lot.


one more question:

whats the OR thing?

thanks,
adam

 

Thelemac

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Mar 15, 2001

• Jun 27, 2002

• #8

When either bit one OR bit two is one
Table:

0 | 0 || 0
0 | 1 || 1
1 | 0 || 1
1 | 1 || 1

You might want to find a page on logic gates. I think it'll help you a good deal.

A google search turns up some pretty decent stuff.

 

OP

Bmxpunk86pl

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Sep 7, 2001

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CT/Poland

• Jun 27, 2002

• Thread Starter
• #9

yea ur right, google helps alot. I would have gone there but i did not know what this kinda stuff was called.


thanks,
adam

 

Thelemac

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• Jun 27, 2002

• #10

Bmxpunk86pl said:

yea ur right, google helps alot. I would have gone there but i did not know what this kinda stuff was called.


thanks,
adam

Click to expand...

Not a problem. I kinda figured you weren't really sure on that, since you were asking them one by one.

Much easier to get this off of google than doing it that way, that's for sure (at least, I sure think so)