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    The Intel 8086 / 8088 / 80186 / 80286 / 80386 / 80486 Jump Instructions

    This HTML version of the file intel.doc from the PC Game Programmer's guide was produced by , Fancy HTML modifications are copyright © 2005 by , all rights reserved. This information is provided in the hope that it will be useful, but without any warranty; it is provided AS-IS, without even the implied warranty of fitness for a particular purpose.

    J Instructions

    Jxx - Jump Instructions Table
        Mnemonic              Meaning                    Jump Condition
          JA     Jump if Above                         CF=0 and ZF=0
          JAE    Jump if Above or Equal                CF=0
          JB     Jump if Below                         CF=1
          JBE    Jump if Below or Equal                CF=1 or ZF=1
          JC     Jump if Carry                         CF=1
          JCXZ   Jump if CX Zero                       CX=0
          JE     Jump if Equal                         ZF=1
          JG     Jump if Greater (signed)              ZF=0 and SF=OF
          JGE    Jump if Greater or Equal (signed)     SF=OF
          JL     Jump if Less (signed)                 SF != OF
          JLE    Jump if Less or Equal (signed)        ZF=1 or SF != OF
          JMP    Unconditional Jump                    unconditional
          JNA    Jump if Not Above                     CF=1 or ZF=1
          JNAE   Jump if Not Above or Equal            CF=1
          JNB    Jump if Not Below                     CF=0
          JNBE   Jump if Not Below or Equal            CF=0 and ZF=0
          JNC    Jump if Not Carry                     CF=0
          JNE    Jump if Not Equal                     ZF=0
          JNG    Jump if Not Greater (signed)          ZF=1 or SF != OF
          JNGE   Jump if Not Greater or Equal (signed) SF != OF
          JNL    Jump if Not Less (signed)             SF=OF
          JNLE   Jump if Not Less or Equal (signed)    ZF=0 and SF=OF
          JNO    Jump if Not Overflow (signed)         OF=0
          JNP    Jump if No Parity                     PF=0
          JNS    Jump if Not Signed (signed)           SF=0
          JNZ    Jump if Not Zero                      ZF=0
          JO     Jump if Overflow (signed)             OF=1
          JP     Jump if Parity                        PF=1
          JPE    Jump if Parity Even                   PF=1
          JPO    Jump if Parity Odd                    PF=0
          JS     Jump if Signed (signed)               SF=1
          JZ     Jump if Zero                          ZF=1
    Clocks Size
    Operands 808x 286 386 486 Bytes
    Jx: jump 16 7+m 7+m 3 2
    no jump 4 3 3 1
    Jx: near-label - - 7+m 3 4
    no jump - - 3 1
        - It's a good programming practice to organize code so the
          expected case is executed without a jump since the actual
          jump takes longer to execute than falling through the test.
        - see   JCXZ  and  JMP  for their respective timings

    JCXZ/JECXZ - Jump if Register (E)CX is Zero
        Usage:  JCXZ    label
                JECXZ   label  (386+)
        Modifies flags: None
        Causes execution to branch to "label" if register CX is zero.  Uses
        unsigned comparision.
                                 Clocks                 Size
        Operands         808x  286   386   486          Bytes
        label:  jump      18   8+m   9+m    8             2
                no jump    6    4     5     5

    JMP - Unconditional Jump
        Usage:  JMP     target
        Modifies flags: None
        Unconditionally transfers control to "label".  Jumps by default
        are within -32768 to 32767 bytes from the instruction following
        the jump.  NEAR and SHORT jumps cause the IP to be updated while FAR
        jumps cause CS and IP to be updated.
                   Operands                     808x  286    386   486
        rel8  (relative)                        15    7+m    7+m    3
        rel16 (relative)                        15    7+m    7+m    3
        rel32 (relative)                         -     -     7+m    3
        reg16 (near, register indirect)         11    7+m    7+m    5
        reg32 (near, register indirect)          -     -     7+m    5
        mem16 (near, mem indirect)             18+EA  11+m  10+m    5
        mem32 (near, mem indirect)             24+EA  15+m  10+m    5
        ptr16:16 (far, dword immed)              -     -    12+m    17
        ptr16:16 (far, PM dword immed)           -     -    27+m    19
        ptr16:16 (call gate, same priv.)         -    38+m  45+m    32
        ptr16:16 (via TSS)                       -   175+m   TS   42+TS
        ptr16:16 (via task gate)                 -   180+m   TS   43+TS
        mem16:16 (far, indirect)                 -     -    43+m    13
        mem16:16 (far, PM indirect)              -     -    31+m    18
        mem16:16 (call gate, same priv.)         -    41+m  49+m    31
        mem16:16 (via TSS)                       -   178+m  5+TS  41+TS
        mem16:16 (via task gate)                 -   183+m  5+TS  42+TS
        ptr16:32 (far, 6 byte immed)             -     -    12+m    13
        ptr16:32 (far, PM 6 byte immed)          -     -    27+m    18
        ptr16:32 (call gate, same priv.)         -     -    45+m    31
        ptr16:32 (via TSS)                       -     -     TS   42+TS
        ptr16:32 (via task state)                -     -     TS   43+TS
        m16:32 (far, address at dword)           -     -    43+m    13
        m16:32 (far, address at dword)           -     -    31+m    18
        m16:32 (call gate, same priv.)           -     -    49+m    31
        m16:32 (via TSS)                         -     -    5+TS  41+TS
        m16:32 (via task state)                  -     -    5+TS  42+TS

    © Zack Smith