Slide 11.7: XOR instruction

XOR Instruction

The XOR instruction performs a boolean (bitwise) exclusive-OR operation between each pair of matching bits in two operands and places the result in the destination operand. The operands can be 8, 16, or 32 bits, and they must be the same size.

`X`	`Y`	`X XOR Y`
0	0	0
0	1	1
1	0	1
1	1	0

XOR — Exclusive OR

Usage: XOR dest, src

Flag	O	D	I	S	Z	A	P	C
Result	*			*	*	?	*	0

Performs a bitwise exclusive OR of the operands and returns the result in the destination.

	Clocks
Operands	286	386	486	Size Bytes
reg, reg	2	2	1	2
mem, reg	7	6	3	2-4
reg, mem	7	7	2	2-4
reg, immed	3	2	1	3-4
mem, immed	7	7	3	3-6
accum, immed	3	2	1	2-3

Any bit exclusive-ORed with 0 retains its value.
Any bit exclusive-ORed with 1 is complemented.
XOR reverses itself when applied twice to the same operand. This makes it an ideal tool for a simple form of data encryption.

`XOR`ed with 0	`XOR`ed with 1	`XOR`ed Twice
.code mov eax, 12345678h xor eax, 00000000h call WriteHex	.code mov eax, 12345678h xor eax, 0FFFFFFFFh call WriteHex	.code mov eax, 0 mov al, 00111010b mov ch, 10100011b xor al, ch xor al, ch call WriteHex
Output	Output	Output