Question

First a little background. The z80 CPU has an instruction called DJNZ which can be used in a similar manner as a for loop. Basically DJNZ decrements the B register and jumps to a label if not zero. For example:

    ld      b,96                    ; erase all of the line
disp_version_erase_loop:
    call    _vputblank              ; erase pixels at cursor (uses b reg)
    djnz    disp_version_erase_loop ; loop 

Of course you can do the same thing using regular comparison and jump instructions, but often it is handy to use the single instruction.

With that out of the way, my question is, do other CPU architectures include a similar control instruction?

Answer 1

That was a fairly common instruction on machines of that era, and occurs in many other places as well.

• Corewar supports it using the DJN instruction with the pre-decrement addressing mode.
• Likewise the m68k supports BNE with a pre-decrement addressing mode.
• The minimalist PDP-8 has a similar instruction
  

  ISZ – increment operand and skip if result is zero.

And so on