sub

8086 and later

Subtract

SUB performs integer subtraction: it subtracts its second operand from its first, and leaves the result in its destination (first) operand. The flags are set according to the result of the operation: in particular, the carry flag is affected and can be used by a subsequent SBB instruction (SBB).

In the forms with an 8-bit immediate second operand and a longer first operand, the second operand is considered to be signed, and is sign-extended to the length of the first operand. In these cases, the BYTE qualifier is necessary to force NASM to generate this form of the instruction.

Forms

Every form of sub the assembler accepts, from NASM's own instruction table. The second column is the processor that introduced the form; a badge marks a form that needs an extension, that is lockable, or that long mode dropped.

Form	Since	Notes
sub r/m8, reg8	8086	lock
sub r/m16, reg16	8086	lock
sub r/m32, reg32	386	lock
sub r/m64, reg64	x86-64	locklong
sub reg8, r/m8	8086
sub reg16, r/m16	8086
sub reg32, r/m32	386
sub reg64, r/m64	x86-64	long
sub r/m16, imm8	8086	lock
sub r/m32, imm8	386	lock
sub r/m64, imm8	x86-64	locklong
sub al, imm8	8086
sub ax, imm16	8086
sub eax, imm32	386
sub rax, imm32	x86-64	long
sub r/m8, imm8	8086	lock
sub r/m16, imm16	8086	lock
sub r/m32, imm32	386	lock
sub r/m64, imm32	x86-64	locklong
sub [reg8], reg8, r/m8	x86-64	apxlong
sub [reg16], reg16, r/m16	x86-64	apxlong
sub [reg32], reg32, r/m32	x86-64	apxlong
sub [reg64], reg64, r/m64	x86-64	apxlong
sub [reg8], r/m8, reg8	x86-64	apxlong
sub [reg16], r/m16, reg16	x86-64	apxlong
sub [reg32], r/m32, reg32	x86-64	apxlong
sub [reg64], r/m64, reg64	x86-64	apxlong
sub [reg16], r/m16, imm8	x86-64	apxlong
sub [reg32], r/m32, imm8	x86-64	apxlong
sub [reg64], r/m64, imm8	x86-64	apxlong
sub [reg8], r/m8, imm8	x86-64	apxlong
sub [reg16], r/m16, imm16	x86-64	apxlong
sub [reg32], r/m32, imm32	x86-64	apxlong
sub [reg64], r/m64, imm32	x86-64	apxlong