Re: Processor specific optimisations

perle@cs.tu-berlin.de (Frank Wilde) wrote in message news:02-01-164...
> Rick Hohensee <rickh@capaccess.org> wrote:
>
> > [...] Speaking of the 6502 and deliberately falling off the edge
> > of the earth as a programming technique, has anyone ever used 6502
> > "pre-indexed indirect" addressing? I didn't find any occurance of it
> > in the C64 ROMs, 8k by Commodore and 8k by Microsoft.
>
> That would be ($nn,X), right? I'd suspect management of the
> connectedness of screen lines to logical lines (present in all CBM
> machines with less than 80 cpl) of having used that mode; why else
> would they reserve (about) 24 precious zero-page variables for just a
> flag per byte?
>
> Ciao,
> Perle


I don't know. I do recall searching the ROMs, BASIC and kernal, for
the bit patterns I thought would show use of pre-indexed indirect, and
got no hits. I definitely did that, but I may not have done it
correctly.


I doubt if linking lines requires P-I-I. I think what P-I-I really
does on 6502 is implement a data structure something like a set of
cylindrical data objects, with diameters of 256 bytes, but this is
VERY vague memory. (I recall thinking it resembled a drumkit.)
Rick Hohensee

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