and

Logical AND

AND r/m, r

Performs bitwise AND.

Pseudocode Operation

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

Example

AND EAX, 0xFF ; Keep lowest 8 bits
AND ECX, EDX  ; Bitwise AND of ECX and EDX

Encoding

Binary Layout

Format Legacy

Opcode 21

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
24 ib	AND AL, imm8	I	Valid Valid	AL AND imm8.
25 iw	AND AX, imm16	I	Valid Valid	AX AND imm16.
25 id	AND EAX, imm32	I	Valid Valid	EAX AND imm32.
REX.W + 25 id	AND RAX, imm32	I	Valid N.E.	RAX AND imm32 sign-extended to 64-bits.
80 /4 ib	AND r/m8, imm81	MI	Valid Valid	r/m8 AND imm8.
81 /4 iw	AND r/m16, imm16	MI	Valid Valid	r/m16 AND imm16.
81 /4 id	AND r/m32, imm32	MI	Valid Valid	r/m32 AND imm32.
REX.W + 81 /4 id	AND r/m64, imm32	MI	Valid N.E.	r/m64 AND imm32 sign extended to 64-bits.
83 /4 ib	AND r/m16, imm8	MI	Valid Valid	r/m16 AND imm8 (sign-extended).
83 /4 ib	AND r/m32, imm8	MI	Valid Valid	r/m32 AND imm8 (sign-extended).
REX.W + 83 /4 ib	AND r/m64, imm8	MI	Valid N.E.	r/m64 AND imm8 (sign-extended).
20 /r	AND r/m8, r8	MR	Valid Valid	r/m8 AND r8.
21 /r	AND r/m16, r16	MR	Valid Valid	r/m16 AND r16.
21 /r	AND r/m32, r32	MR	Valid Valid	r/m32 AND r32.
REX.W + 21 /r	AND r/m64, r64	MR	Valid N.E.	r/m64 AND r64.
22 /r	AND r8, r/m8	RM	Valid Valid	r8 AND r/m8.
23 /r	AND r16, r/m16	RM	Valid Valid	r16 AND r/m16.
23 /r	AND r32, r/m32	RM	Valid Valid	r32 AND r/m32.
REX.W + 23 /r	AND r64, r/m64	RM	Valid N.E.	r64 AND r/m64.

Description

Performs a bitwise AND 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 set to 1 if both corresponding bits of the first and second operands are 1; otherwise, it is set to 0. This instruction can be used with a LOCK prefix to allow the it to be executed atomically. In 64-bit mode, the instruction’s default operation size is 32 bits. 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 AND 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. AND-Logical AND Vol. 2A 3-61

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