_asm {점프 할때의 플래그들 정리}

점프 할때의 플래그들 정리

비슷한 의미 별로 그룹화 시켜놓은것들, 필요 할 때 참고삼아

Getting the sense for jumps and flags has long been a troublesome area for me, especially since the Intel assembler book shows 32 of these, all with similar-sounding names. Looking more closely I found that many of the instructions were synonyms for each other, and in practice the whole gamut is not needed, and in the process found that my copy of Intel's 80386 Programmer's Reference Manual gave an incorrect description for one of the instructions.

So I have grouped these functionally, with all instruction synonyms in the same row.

Instruction	Description	signed-ness	Flags	short  jump  opcodes	near  jump  opcodes
JO	Jump if overflow		OF = 1	70	0F 80
JNO	Jump if not overflow		OF = 0	71	0F 81
JS	Jump if sign		SF = 1	78	0F 88
JNS	Jump if not sign		SF = 0	79	0F 89
JE  JZ	Jump if equal  Jump if zero		ZF = 1	74	0F 84
JNE  JNZ	Jump if not equal  Jump if not zero		ZF = 0	75	0F 85
JB  JNAE  JC	Jump if below  Jump if not above or equal  Jump if carry	unsigned	CF = 1	72	0F 82
JNB  JAE  JNC	Jump if not below  Jump if above or equal  Jump if not carry	unsigned	CF = 0	73	0F 83
JBE  JNA	Jump if below or equal  Jump if not above	unsigned	CF = 1 or ZF = 1	76	0F 86
JA  JNBE	Jump if above  Jump if not below or equal	unsigned	CF = 0 and ZF = 0	77	0F 87
JL  JNGE	Jump if less  Jump if not greater or equal	signed	SF <> OF	7C	0F 8C
JGE  JNL	Jump if greater or equal  Jump if not less	signed	SF = OF	7D	0F 8D
JLE  JNG	Jump if less or equal  Jump if not greater	signed	ZF = 1 or SF <> OF	7E	0F 8E
JG  JNLE	Jump if greater  Jump if not less or equal	signed	ZF = 0 and SF = OF	7F	0F 8F
JP  JPE	Jump if parity  Jump if parity even		PF = 1	7A	0F 8A
JNP  JPO	Jump if not parity  Jump if parity odd		PF = 0	7B	0F 8B
JCXZ  JECXZ	Jump if %CX register is 0  Jump if %ECX register is 0		%CX = 0  %ECX = 0	E3

Processor Flags

The x86 processors have a large set of flags that represent the state of the processor, and the conditional jump instructions can key off of them in combination.

CF - carry flag(c에서는 CY)

Set on high-order bit carry or borrow; cleared otherwise

PF - parity flag(c에서는 PE)

Set if low-order eight bits of result contain an even number of "1" bits; cleared otherwise

ZF - zero flags(c에서는 ZR)

Set if result is zero; cleared otherwise

SF - sign flag(c에서는 PL이던디)

Set equal to high-order bit of result (0 if positive 1 if negative)

OF - overflow flag(c에서는 OV)

Set if result is too large a positive number or too small a negative number (excluding sign bit) to fit in destination operand; cleared otherwise

http://unixwiz.net/techtips/x86-jumps.html