add

Add

ADD r/m, r

Adds src to dest and stores result in dest.

Pseudocode Operation

result ← dest + src;
OF ← overflow_occurred(dest, src, result);
SF ← (result < 0);
ZF ← (result == 0);
AF ← carry_from_bit(3);
PF ← parity(result);
CF ← carry_out;
dest ← result;

Example

ADD EAX, EBX  ; Add EBX to EAX
ADD [EAX], 5  ; Add 5 to the 32-bit integer at address EAX

Encoding

Binary Layout

Format Legacy

Opcode 01

Extension Base

Operands

dest
Register or memory operand
src
General-purpose register

Across architectures

Integer Addition : how x86, ARM, RISC-V, and PowerISA each do this.

Reference

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

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	Description
04 ib	ADD AL, imm8	I	Valid Valid	Add imm8 to AL.
05 iw	ADD AX, imm16	I	Valid Valid	Add imm16 to AX.
05 id	ADD EAX, imm32	I	Valid Valid	Add imm32 to EAX.
REX.W + 05 id	ADD RAX, imm32	I	Valid N.E.	Add imm32 sign-extended to 64-bits to RAX.
80 /0 ib	ADD r/m8, imm8	MI	Valid Valid	Add imm8 to r/m8.
81 /0 iw	ADD r/m16, imm16	MI	Valid Valid	Add imm16 to r/m16.
81 /0 id	ADD r/m32, imm32	MI	Valid Valid	Add imm32 to r/m32.
REX.W + 81 /0 id	ADD r/m64, imm32	MI	Valid N.E.	Add imm32 sign-extended to 64-bits to r/m64.
83 /0 ib	ADD r/m16, imm8	MI	Valid Valid	Add sign-extended imm8 to r/m16.
83 /0 ib	ADD r/m32, imm8	MI	Valid Valid	Add sign-extended imm8 to r/m32.
REX.W + 83 /0 ib	ADD r/m64, imm8	MI	Valid N.E.	Add sign-extended imm8 to r/m64.
00 /r	ADD r/m8, r8	MR	Valid Valid	Add r8 to r/m8.
01 /r	ADD r/m16, r16	MR	Valid Valid	Add r16 to r/m16.
01 /r	ADD r/m32, r32	MR	Valid Valid	Add r32 to r/m32.
REX.W + 01 /r	ADD r/m64, r64	MR	Valid N.E.	Add r64 to r/m64.
02 /r	ADD r8, r/m8	RM	Valid Valid	Add r/m8 to r8.
03 /r	ADD r16, r/m16	RM	Valid Valid	Add r/m16 to r16.
03 /r	ADD r32, r/m32	RM	Valid Valid	Add r/m32 to r32.
REX.W + 03 /r	ADD r64, r/m64	RM	Valid N.E.	Add r/m64 to r64.

Description

Adds the destination operand (first operand) and the source operand (second operand) and then stores the result in the destination operand. The destination operand can be a register or a memory location; the source operand can be an immediate, a register, or a memory location. (However, two memory operands cannot be used in one instruction.) When an immediate value is used as an operand, it is sign-extended to the length of the destination operand format. The ADD instruction performs integer addition. It evaluates the result for both signed and unsigned integer operands and sets the OF and CF flags to indicate a carry (overflow) in the signed or unsigned result, respectively. The SF flag indicates the sign of the signed result. This instruction can be used with a LOCK prefix to allow the instruction 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 + SRC;

Flags Affected

The OF, SF, ZF, AF, CF, and PF flags are set according to the result.

Exceptions

Protected Mode Exceptions

#GP(0) If the destination is located in 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 is used to access memory and it 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. ADD-Add Vol. 2A 3-15

add

Add