Opcode Instruction Clocks Description
77 cb JA rel8 7+m,3 Jump short if above (CF=0 and
ZF=0)
73 cb JAE rel8 7+m,3 Jump short if above or equal
(CF=0)
72 cb JB rel8 7+m,3 Jump short if below (CF=1)
76 cb JBE rel8 7+m,3 Jump short if below or equal
(CF=1 or ZF=1)
72 cb JC rel8 7+m,3 Jump short if carry (CF=1)
E3 cb JCXZ rel8 9+m,5 Jump short if CX register is 0
E3 cb JECXZ rel8 9+m,5 Jump short if ECX register is 0
74 cb JE rel8 7+m,3 Jump short if equal (ZF=1)
74 cb JZ rel8 7+m,3 Jump short if 0 (ZF=1)
7F cb JG rel8 7+m,3 Jump short if greater (ZF=0 and
SF=OF)
7D cb JGE rel8 7+m,3 Jump short if greater or equal
(SF=OF)
7C cb JL rel8 7+m,3 Jump short if less (SF<>OF)
7E cb JLE rel8 7+m,3 Jump short if less or equal
(ZF=1 and SF<>OF)
76 cb JNA rel8 7+m,3 Jump short if not above (CF=1 or
ZF=1)
72 cb JNAE rel8 7+m,3 Jump short if not above or equal
(CF=1)
73 cb JNB rel8 7+m,3 Jump short if not below (CF=0)
77 cb JNBE rel8 7+m,3 Jump short if not below or equal
(CF=0 and ZF=0)
73 cb JNC rel8 7+m,3 Jump short if not carry (CF=0)
75 cb JNE rel8 7+m,3 Jump short if not equal (ZF=0)
7E cb JNG rel8 7+m,3 Jump short if not greater (ZF=1
or SF<>OF)
7C cb JNGE rel8 7+m,3 Jump short if not greater or
equal (SF<>OF)
7D cb JNL rel8 7+m,3 Jump short if not less (SF=OF)
7F cb JNLE rel8 7+m,3 Jump short if not less or equal
(ZF=0 and SF=OF)
71 cb JNO rel8 7+m,3 Jump short if not overflow
(OF=0)
7B cb JNP rel8 7+m,3 Jump short if not parity (PF=0)
79 cb JNS rel8 7+m,3 Jump short if not sign (SF=0)
75 cb JNZ rel8 7+m,3 Jump short if not zero (ZF=0)
70 cb JO rel8 7+m,3 Jump short if overflow (OF=1)
7A cb JP rel8 7+m,3 Jump short if parity (PF=1)
7A cb JPE rel8 7+m,3 Jump short if parity even (PF=1)
7B cb JPO rel8 7+m,3 Jump short if parity odd (PF=0)
78 cb JS rel8 7+m,3 Jump short if sign (SF=1)
74 cb JZ rel8 7+m,3 Jump short if zero (ZF = 1)
0F 87 cw/cd JA rel16/32 7+m,3 Jump near if above (CF=0 and
ZF=0)
0F 83 cw/cd JAE rel16/32 7+m,3 Jump near if above or equal
(CF=0)
0F 82 cw/cd JB rel16/32 7+m,3 Jump near if below (CF=1)
0F 86 cw/cd JBE rel16/32 7+m,3 Jump near if below or equal
(CF=1 or ZF=1)
0F 82 cw/cd JC rel16/32 7+m,3 Jump near if carry (CF=1)
0F 84 cw/cd JE rel16/32 7+m,3 Jump near if equal (ZF=1)
0F 84 cw/cd JZ rel16/32 7+m,3 Jump near if 0 (ZF=1)
0F 8F cw/cd JG rel16/32 7+m,3 Jump near if greater (ZF=0 and
SF=OF)
0F 8D cw/cd JGE rel16/32 7+m,3 Jump near if greater or equal
(SF=OF)
0F 8C cw/cd JL rel16/32 7+m,3 Jump near if less (SF<>OF)
0F 8E cw/cd JLE rel16/32 7+m,3 Jump near if less or equal (ZF=1
and SF<>OF)
0F 86 cw/cd JNA rel16/32 7+m,3 Jump near if not above (CF=1 or
ZF=1)
0F 82 cw/cd JNAE rel16/32 7+m,3 Jump near if not above or equal
(CF=1)
0F 83 cw/cd JNB rel16/32 7+m,3 Jump near if not below (CF=0)
0F 87 cw/cd JNBE rel16/32 7+m,3 Jump near if not below or equal
(CF=0 and ZF=0)
0F 83 cw/cd JNC rel16/32 7+m,3 Jump near if not carry (CF=0)
0F 85 cw/cd JNE rel16/32 7+m,3 Jump near if not equal (ZF=0)
0F 8E cw/cd JNG rel16/32 7+m,3 Jump near if not greater (ZF=1
or SF<>OF)
0F 8C cw/cd JNGE rel16/32 7+m,3 Jump near if not greater or
equal (SF<>OF)
0F 8D cw/cd JNL rel16/32 7+m,3 Jump near if not less (SF=OF)
0F 8F cw/cd JNLE rel16/32 7+m,3 Jump near if not less or equal
(ZF=0 and SF=OF)
0F 81 cw/cd JNO rel16/32 7+m,3 Jump near if not overflow (OF=0)
0F 8B cw/cd JNP rel16/32 7+m,3 Jump near if not parity (PF=0)
0F 89 cw/cd JNS rel16/32 7+m,3 Jump near if not sign (SF=0)
0F 85 cw/cd JNZ rel16/32 7+m,3 Jump near if not zero (ZF=0)
0F 80 cw/cd JO rel16/32 7+m,3 Jump near if overflow (OF=1)
0F 8A cw/cd JP rel16/32 7+m,3 Jump near if parity (PF=1)
0F 8A cw/cd JPE rel16/32 7+m,3 Jump near if parity even (PF=1)
0F 8B cw/cd JPO rel16/32 7+m,3 Jump near if parity odd (PF=0)
0F 88 cw/cd JS rel16/32 7+m,3 Jump near if sign (SF=1)
0F 84 cw/cd JZ rel16/32 7+m,3 Jump near if 0 (ZF=1)
IF condition THEN EIP := EIP + SignExtend(rel8/16/32); IF OperandSize = 16 THEN EIP := EIP AND 0000FFFFH; FI; FI;
If the given condition is true, a jump is made to the location provided as the operand. Instruction coding is most efficient when the target for the conditional jump is in the current code segment and within -128 to +127 bytes of the next instruction's first byte. The jump can also target -32768 thru +32767 (segment size attribute 16) or -2^(31) thru +2^(31) -1 (segment size attribute 32) relative to the next instruction's first byte. When the target for the conditional jump is in a different segment, use the opposite case of the jump instruction (i.e., JE and JNE), and then access the target with an unconditional far jump to the other segment. For example, you cannot code--
JZ FARLABEL;You must instead code--
JNZ BEYOND; JMP FARLABEL; BEYOND:Because there can be several ways to interpret a particular state of the flags, ASM386 provides more than one mnemonic for most of the conditional jump opcodes. For example, if you compared two characters in AX and want to jump if they are equal, use JE; or, if you ANDed AX with a bit field mask and only want to jump if the result is 0, use JZ, a synonym for JE.
JCXZ differs from other conditional jumps because it tests the contents of the CX or ECX register for 0, not the flags. JCXZ is useful at the beginning of a conditional loop that terminates with a conditional loop instruction (such as LOOPNE TARGET LABEL). The JCXZ prevents entering the loop with CX or ECX equal to zero, which would cause the loop to execute 64K or 32G times instead of zero times.
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Chapter 17 -- 80386 Instruction Set
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