11. Conditional Jump Limitation and Workaround

• Conditional jumps on the 80386 and 80486 processors cannot reference a label more than 32 kbytes away.

          ; Jump to target less than 128 bytes away
          jz      target          ; If previous operation resulted
                                  ; in zero, jump to target
  

• However, if target is too distant, the following sequence is necessary to enable a longer jump. Note this sequence is logically equivalent to the preceding example:

          ; Jumps to distant targets previously required two steps
          jnz     skip            ; If previous operation result is
                                  ;   NOT zero, jump to "skip"
          jmp     target          ;   Otherwise, jump to target
      skip:
  

• By default MASM enables automatic jump expansion facility:

• Jump expansion is based on simple workaround:

           jne $ + 2 + (length in bytes of the next instruction)
           jmp NEAR PTR target
  

• See jump_expansion.asm sample program for a complete example.