What is the meaning of XOR in x86 assembly?

Question

I\'m getting into assembly and I keep running into xor, for example:

xor     ax, ax

Does it just clear the register\'s value?

Answer 1

When I started programming a long time ago there was no exclusive or on either the processor or in the compiler. When I got around to it I stuck to the descriptions:

• or: true if a=1 or b=1 or both=1
• xor: true if a=1 or b=1 but not both=1

so:

0 or 0 = 0
0 or 1 = 1
1 or 0 = 1
1 or 1 = 1

and

0 xor 0 = 0
0 xor 1 = 1
1 xor 0 = 1
1 xor 1 = 0