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   Message 237 of 25 for search * help
   
   Re: What's Diabolo? (and who's Po Ching?)
   Author:   John/Lori <henk@spamsuxdoitnow.com>
   Date:   1999/02/23
   Forum:   comp.sys.cbm
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> >What do you mean "the optimizer is rather, er, overzealous."?
>
> ... is the overzealous part. It tries to find complimentary instructions and
> wipe them out. For example:
>
>         sty x0
>         ldy x0
>
> are useless instructions when following each other, so the compiler will writ
e
> neither one. Problematically, if the last two bytes written
> just happened to be the opcode "sty" and the zero page location for "x0",
> even if they were part of a 16-bit quantity, the compiler will nuke them if
> it's about to write "ldy x0". A rarely seen bug -- I've yet to see it in the
> code it generates -- but one that is nonetheless possible.
>
> I don't know if any optimisers do stuff like this. Probably, but I have no
> formal degree in computer science, so this is all stuff I've discovered.
>

That's sort of the basic form of "peep hole" optimization, and maybe the
first, (it's usually the first mentioned)

You also have to be careful you don't mess things up by "nuking"
the target's of GOTO's and such.

> >What sort of multiply and divide algorithms does it impliment?
>
> Internally, 8-bit imult/idiv. 16-bit imult/idiv is done with a small,
> relocatable RTL. All other arithmetic is internal.
>

What I really meant was how does the RTL work?

shift and add, table look ups, Booth's algorithm etc.

Or maybe these are variable? for optimization (which RTL you use depends
on what your doing)

> Gallipoli is not ready for prime time, but I could be prodded to show you
> what I have, provided you haven't eaten anything recently or have no
> easily aggravated chronic infirmities. It's another reason why God doesn't
> want me to be a computer programmer. :-)
>

I'd love to see it.

I'd think, in light of my prior admissions about my own efforts,
you'd realise I have a strong stomach and my chronic infirmities
are already aggravated :)
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