XOR register,register (assembler)

Question

From time to time we have to analyze pieces of assembler code (IA32), and more than often i come across an instruction that looks like this:

xor ax, ax
         


        

Answer 1

It's a common assembler idiom to set a register to 0.

xor ax, ax corresponds to ax = ax ^ ax which, as you already notices, is effectively ax = 0.

If I recall correctly the main advantage is that its code-size is smaller than mov ax, 0