[A86] Re: TI-86 Menu Routine

To: assembly-86@lists.ticalc.org
Subject: [A86] Re: TI-86 Menu Routine
From: rabidcow@juno.com
Date: Mon, 2 Sep 2002 09:42:49 -0700
Reply-To: assembly-86@lists.ticalc.org

On Mon, 2 Sep 2002 07:08:23 -0500 "David Phillips" <david@acz.org>
writes:
> 
> Michael Williams writes:
> > No, I havent actually done that, but I read about it once.  My 
> other
> > thought would be to do this:
> >
> > ld hl,table
> > call Do_Menu
> 
> Passing arguments in registers will almost always give you better
> performance (space and time) than passing on the stack.  This is 
> especially
> true on the z80 since it doesn't have instructions that optimize 
> stack frame
> creation.

Well, except here the choice is between passing parameters on the stack
or passing them in memory with a pointer, and he's not even using a stack
frame.  This code would not be callable from C, but it reminds me of that
:)

If anyone's wondering, here's how a stack frame generally works on a z80:

; enter stack frame
  push ix
  ld ix,0
  add ix,sp
; here you can allocate space on the stack for local vars
; usually by pushing garbage, but if you need a lot you'd sbc it from sp

; ix-5 = last byte of parameters
; ix+0 = first byte of local vars

; exit stack frame
  ld sp,ix
  pop ix
  ret

Not very efficient at all.

-rabidcow

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