O D I T S Z A P C OF: Overflow flag TF: Trap flag AF: Aux carry F F F F F F F F F DF: Direction flag SF: Sign flag PF: Parity flag * * * * * * IF: Interrupt flag ZF: Zero flag CF: Carry flag
NEG r8 NEG m8 NEG r16 NEG m16 NEG r32 386+ NEG m32 386+
NEG AL NEG DX NEG ECX NEG BYTE [BX] ; Negates BYTE quantity at [BX] NEG WORD [DI] ; Negates WORD quantity at [BX] NEG DWORD [EAX] ; Negates DWORD quantity at [EAX]
This is the assembly language equivalent of multiplying a value by −1. Keep in mind that negation is not the same as simply inverting each bit in the operand. (Another instruction, NOT, does that.) The process is also known as generating the two's complement of a value. The two's complement of a value added to that value yields zero. −1 = $FF; −2 = $FE; −3 = $FD; and so forth.
If the operand is 0, CF is cleared and ZF is set; otherwise, CF is set and ZF is cleared. If the operand contains the maximum negative value (−128 for 8-bit or −32,768 for 16-bit), the operand does not change, but OF and CF are set. SF is set if the result is negative, or else SF is cleared. PF is set if the low-order 8 bits of the result contain an even number of set (1) bits; otherwise, PF is cleared.
| Note |
You must use a size specifier (BYTE, WORD, DWORD) with memory data! |
r8 = AL AH BL BH CL CH DL DH r16 = AX BX CX DX BP SP SI DI sr = CS DS SS ES FS GS r32 = EAX EBX ECX EDX EBP ESP ESI EDI m8 = 8-bit memory data m16 = 16-bit memory data m32 = 32-bit memory data i8 = 8-bit immediate data i16 = 16-bit immediate data i32 = 32-bit immediate data d8 = 8-bit signed displacement d16 = 16-bit signed displacement d32 = 32-bit unsigned displacement