Re: [colorforth] If? and A.

[Robert Patten <pattenre@xxxxxxxxxxx>]

The a  register  is used for scratch and pointer  to memory for fetch and
store operations.

----- Original Message -----
From: "Mark Slicker" <maslicke@xxxxxxxxxxx>
To: <colorforth@xxxxxxxxxxxxxxxxxx>
Sent: Thursday, October 31, 2002 10:08 AM
Subject: Re: [colorforth] If? and A.


> On Thu, 31 Oct 2002, Peter Appelman wrote:
>
> > Not being familiar with c18, I turn to the group for these questions.
> >
> > First:
> >
> > Should 'if' (and -if) be defined as:
> > if c023 2, 74 2, here ;
> > which is: and eax,eax; jz nn
> >
> > I do not know when the flags are set in the c18.
>
> I belive c18 operates on the TOS (top of stack), it doesn't have flags
> like the pentium. The way it is defined on the pentium, you can use the
> side effects of operations to conditionally branch. The virtual machine is
> more complex, but I suppose there is may be improved efficiency.
>
> > Second:
> >
> > Why use edx as A register? Edx is used for mult/div and more. If
> > ebp was used, would that not more acurately reflect what happens on the
> > c18. Once an address is stored it would remain unchanged?
>
> I don't know the details of the c18, but from what I've seen of the
> pentium colorForth the A register is mostly used in the implementation of
> macros. The contents will change in using many of these primitives, such
> as '!' or 'swap'. I don't think it was intended to be used to store
> variables for long periods of execution, someone please correct me if I'm
> wrong.
>
> Mark
>
>
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