Why use or al, al instead of cmp al, 0?

[matias_beretta]

I noticed that people use: or al, al instead of cmp al, 0.

Is it the same?

[earlz]

you will get more replies if you name your topic more appropriately...

[matias_beretta]

thanks, this answer helped me a lot!

[OrOS]

I assume that was sarcasm....

[frank]

I noticed that people use: or al, al instead of cmp al, 0.

Is it the same?

It achieves the same result, but maybe or al, al is faster or takes up less space in the binary.

EDIT: Well actually they are the same size. So that rules that out. However or eax, eax is 1 byte shorter than cmp eax, 0.

[earlz]

well, isn't 'cmp al,al' just 'and al,al' without changing the destination?

so, or al,al would not be faster.... I've also never seen this though(I don't look at much asm source though..)

...sorry for useless response...I should've put what I put here, but anyway...

[Craze Frog]

I noticed that people use: or al, al instead of cmp al, 0.

Is it the same?

cmp performs a subtraction and or only a bitwise boolean operation, so it is theorethically slightly faster. But or destroys the value of al.

[kataklinger]

But or destroys the value of al.

or al,al doesn't change value of al!

[Craze Frog]

But or destroys the value of al.

or al,al doesn't change value of al!

You're right. I forgot the source and destination had the same value...