I'm also impressed with the xorlw technique. I just put it in some code
where I had to pretty much do a switch-case situation where there are
only a few choices and they are not close to each other. A table would've
been huge.

Harold


On Thu, 7 Jun 2001 18:18:56 +1000 Roman Black <fastvid@EZY.NET.AU>
writes:
> Bob Ammerman wrote:
> >
> > Yes: xorlw method is a bit smaller.
> >
> > Yes: this method requires at least one word in low half of page.
> >
> > But: this method is significantly faster.
> >
> > So: horses for courses.
>
>
> Yep it's a bit quicker, but a lot messier.
> The XORLW system you posted is as neat as
> a normal table, and can have more units added
> to it at any point or subtracted from it.
>
> Also with a larger table size it would get
> significantly smaller (and be MUCH neater).
>
> All in all I thought your XORLW system was
> totally brilliant, only takes 2 words per
> table byte and is very neat and simple.
> Unless speed is the main issue I think it
> would be horse chosen for my course. ;o)
> -Roman
>
>
> > > > Bob Ammerman wrote:
> > > > >
> > > > > I knew it, I knew it...
> > > > >
> > > > > There _is_ a two instruction per entry technique!
> > > > >
> > > > >     movlw     value1^value2^value3
> > > > >     decfsz    count,F
> > > > >     xorlw       value1
> > > > >     decfsz    count,F
> > > > >     xorlw       value2
> > > > >     decfsz    count,F
> > > > >     xorlw       value3
> > > > >     etc.
> > > > >
> > > > > Notice what happens:
> > > > >
> > > > > If count == 1 on entry then all the xor's except value1
> occur,
> > > > > leaving 'value1' in W.
> > > > >
> > > > > If count == 2 on entry then all the xor's except value2
> occur,
> > > > > leaving 'value2' in W.
> > > > >
> > > > > If count == 3 on entry then all the xor's except value3
> occur,
> > > > > leaving 'value3' in W.
>
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