xor

Logical Exclusive OR

XOR r/m, r

Performs bitwise XOR.

Pseudocode Operation

dest ← dest ^ src; ZF ← (result == 0); SF ← (result < 0); PF ← parity(result); CF ← 0; OF ← 0; AF ← undefined;

Example

XOR EAX, EAX  ; Clear EAX (set to 0)
XOR EAX, 5    ; Toggle bits 0 and 2

Encoding

Binary Layout

Format Legacy

Opcode 31

Extension Base

Operands

dest
Register/Memory
src
Register

Reference

View in Intel® 64 and IA-32 Architectures SDM ↗ Intel® SDM

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	Description
34 ib	XOR AL, imm8	I	Valid Valid	AL XOR imm8.
35 iw	XOR AX, imm16	I	Valid Valid	AX XOR imm16.
35 id	XOR EAX, imm32	I	Valid Valid	EAX XOR imm32.
REX.W + 35 id	XOR RAX, imm32	I	Valid N.E.	RAX XOR imm32 (sign-extended).
80 /6 ib	XOR r/m8, imm8	MI	Valid Valid	r/m8 XOR imm8.
81 /6 iw	XOR r/m16, imm16	MI	Valid Valid	r/m16 XOR imm16.
81 /6 id	XOR r/m32, imm32	MI	Valid Valid	r/m32 XOR imm32.
REX.W + 81 /6 id	XOR r/m64, imm32	MI	Valid N.E.	r/m64 XOR imm32 (sign-extended).
83 /6 ib	XOR r/m16, imm8	MI	Valid Valid	r/m16 XOR imm8 (sign-extended).
83 /6 ib	XOR r/m32, imm8	MI	Valid Valid	r/m32 XOR imm8 (sign-extended).
REX.W + 83 /6 ib	XOR r/m64, imm8	MI	Valid N.E.	r/m64 XOR imm8 (sign-extended).
30 /r	XOR r/m8, r8	MR	Valid Valid	r/m8 XOR r8.
31 /r	XOR r/m16, r16	MR	Valid Valid	r/m16 XOR r16.
31 /r	XOR r/m32, r32	MR	Valid Valid	r/m32 XOR r32.
REX.W + 31 /r	XOR r/m64, r64	MR	Valid N.E.	r/m64 XOR r64.
32 /r	XOR r8,1 r/m8	RM	Valid Valid	r8 XOR r/m8.
33 /r	XOR r16, r/m16	RM	Valid Valid	r16 XOR r/m16.
33 /r	XOR r32, r/m32	RM	Valid Valid	r32 XOR r/m32.
REX.W + 33 /r	XOR r64, r/m64	RM	Valid N.E.	r64 XOR r/m64.

Description

Performs a bitwise exclusive OR (XOR) operation on the destination (first) and source (second) operands and stores the result in the destination operand location. The source operand can be an immediate, a register, or a memory location; the destination operand can be a register or a memory location. (However, two memory operands cannot be used in one instruction.) Each bit of the result is 1 if the corresponding bits of the operands are different; each bit is 0 if the corresponding bits are the same. This instruction can be used with a LOCK prefix to allow the instruction to be executed atomically. In 64-bit mode, using a REX prefix in the form of REX.R permits access to additional registers (R8-R15). Using a REX prefix in the form of REX.W promotes operation to 64 bits. See the summary chart at the beginning of this section for encoding data and limits.

Operation

DEST := DEST XOR SRC;

Flags Affected

The OF and CF flags are cleared; the SF, ZF, and PF flags are set according to the result. The state of the AF flag is undefined.

Exceptions

Protected Mode Exceptions

#GP(0) If the destination operand points to a non-writable segment. If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit. If the DS, ES, FS, or GS register contains a NULL segment selector. #SS(0) If a memory operand effective address is outside the SS segment limit. #PF(fault-code) If a page fault occurs. #AC(0) If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3. #UD If the LOCK prefix is used but the destination is not a memory operand.

Real-Address Mode Exceptions

#GP If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit. #SS If a memory operand effective address is outside the SS segment limit. #UD If the LOCK prefix is used but the destination is not a memory operand.

Virtual-8086 Mode Exceptions

#GP(0) If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit. #SS(0) If a memory operand effective address is outside the SS segment limit. #PF(fault-code) If a page fault occurs. #AC(0) If alignment checking is enabled and an unaligned memory reference is made. #UD If the LOCK prefix is used but the destination is not a memory operand.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

#SS(0) If a memory address referencing the SS segment is in a non-canonical form. #GP(0) If the memory address is in a non-canonical form. #PF(fault-code) If a page fault occurs. #AC(0) If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3. #UD If the LOCK prefix is used but the destination is not a memory operand. XOR-Logical Exclusive OR Vol. 2D 6-40

xor