3-673
INSTRUCTION SET REFERENCE
SUB—Subtract
Description
This instruction subtracts the second operand (source operand) from the first operand (destina-
tion operand) and 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, register, or memory
location. (However, two memory operands cannot be used in one instruction.) When an imme-
diate value is used as an operand, it is sign-extended to the length of the destination operand
format.
The SUB instruction does not distinguish between signed or unsigned operands. Instead, the
processor evaluates the result for both data types and sets the OF and CF flags to indicate a
borrow in the signed or unsigned result, respectively. The SF flag indicates the sign of the signed
result.
Operation
DEST
<
DEST – SRC;
Flags Affected
The OF, SF, ZF, AF, PF, and CF flags are set according to the result.
Opcode
Instruction
Description
2C ib
SUB AL,imm8
Subtract imm8 from AL
2D iw
SUB AX,imm16
Subtract imm16 from AX
2D id
SUB EAX,imm32
Subtract imm32 from EAX
80 /5 ib
SUB r/m8,imm8
Subtract imm8 from r/m8
81 /5 iw
SUB r/m16,imm16
Subtract imm16 from r/m16
81 /5 id
SUB r/m32,imm32
Subtract imm32 from r/m32
83 /5 ib
SUB r/m16,imm8
Subtract sign-extended imm8 from r/m16
83 /5 ib
SUB r/m32,imm8
Subtract sign-extended imm8 from r/m32
28 /r
SUB r/m8,r8
Subtract r8 from r/m8
29 /r
SUB r/m16,r16
Subtract r16 from r/m16
29 /r
SUB r/m32,r32
Subtract r32 from r/m32
2A /r
SUB r8,r/m8
Subtract r/m8 from r8
2B /r
SUB r16,r/m16
Subtract r/m16 from r16
2B /r
SUB r32,r/m32
Subtract r/m32 from r32
