Any cause to do a XOR EAX, EAX? - GSM-Forum

Y.P.Y · 06-29-2012, 07:46

Why does Microsoft Visual C++ in some cases put it in codes?

Is it more efficient that mov eax, 0 ?

012B1002 in al,dx
012B1003 push ecx
int i = 5;
012B1004 mov dword ptr [i],5
return 0;
012B100B xor eax,eax

BR.

Stikmann · 06-29-2012, 13:18

XOR EAX,EAX is only 2 bytes in length, whereas MOV EAX,0 is 3 to 6 bytes. The xor one fits better in cache.

oOXTCOo · 06-30-2012, 23:07

and xor is faster! i had same question to sergey some time back...

06-29-2012, 07:46	#1 (permalink)
Y.P.Y Freak Poster Join Date: Apr 2009 Location: QQ:2557307931 Posts: 132 Member: 1010502 Status: Offline Sonork: whats this?! Thanks Meter: 316	Any cause to do a XOR EAX, EAX? Why does Microsoft Visual C++ in some cases put it in codes? Is it more efficient that mov eax, 0 ? 012B1002 in al,dx 012B1003 push ecx int i = 5; 012B1004 mov dword ptr [i],5 return 0; 012B100B xor eax,eax BR.

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06-29-2012, 13:18	#2 (permalink)
Stikmann Junior Member Join Date: Nov 2011 Location: The cache Posts: 21 Member: 1698024 Status: Offline Thanks Meter: 5	XOR EAX,EAX is only 2 bytes in length, whereas MOV EAX,0 is 3 to 6 bytes. The xor one fits better in cache.

06-30-2012, 23:07	#3 (permalink)
oOXTCOo No Life Poster Join Date: Dec 2000 Location: J.A.U - Just Another Unlocker Age: 43 Posts: 3,498 Member: 2878 Status: Offline Thanks Meter: 9,123	and xor is faster! i had same question to sergey some time back...