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Re: Best tools for writing an assembler?

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Hannah wrote:

> Hi!
>
> glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote:
>
> Actually, our moderator wrote:
>
> >[Variable length instructions aren't that hard.  You start by assuming
> >everything will be the long form, then iterate over the code a few
> >times shrinking what you can.  That isn't always perfectly optimal
> >(which is known to be NP complete), but it's pretty close. -John]
>
> Can't one also go the other way round: Start in the short(est) form and
> lengthen as long as needed?
>
> Hannah.
> [Shrinking long versions has the advantage that the code is always valid,
> even if you miss a few. -John]

One processor that we did a few years ago had three branch types
4 bit signed offset, jump within 256 byte page and unlimited jump.
(National COP8) Coded as 1,2,3 byte instructions. The page jump
caused all kinds of havoc as the code moved around as the branches
were being optimized.

It was the first processor I saw that that starting long and shrinking
the code wouldn't work cleanly.

Walter Banks
[The PDP-8 had short references to the current page or page 0,
and long indirect references.  Back in that era, we juggled code
into pages by hand. -John]

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Best tools for writing an assembler? tpphysik@gmail.com - 2014-02-18 16:04 -0800
  Re: Best tools for writing an assembler? "C. Bergström" <cbergstrom@pathscale.com> - 2014-02-19 11:14 +0700
  Re: Best tools for writing an assembler? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-02-19 04:25 +0000
  Re: Best tools for writing an assembler? Ivan Godard <ivan@ootbcomp.com> - 2014-02-18 23:23 -0800
    Re: Best tools for writing an assembler? Robert A Duff <bobduff@TheWorld.com> - 2014-02-19 18:20 -0500
      Re: Best tools for writing an assembler? Sébastien Fricker <sebastien.fricker@gmail.com> - 2014-02-21 12:00 +0100
      Re: Best tools for writing an assembler? "BartC" <bc@freeuk.com> - 2014-02-22 00:28 +0000
      Re: Best tools for writing an assembler? noitalmost <noitalmost@cox.net> - 2014-02-23 11:22 -0500
        Re: Best tools for writing an assembler? Sébastien Fricker <sebastien.fricker@gmail.com> - 2014-02-24 07:32 +0100
          Re: Best tools for writing an assembler? Louis Krupp <lkrupp@pssw.com> - 2014-02-24 15:39 -0700
          Re: Best tools for writing an assembler? Ivan Godard <ivan@ootbcomp.com> - 2014-02-24 15:04 -0800
            Re: Best tools for writing an assembler? rpw3@rpw3.org (Rob Warnock) - 2014-02-25 13:00 +0000
          Re: Best tools for writing an assembler? Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2014-02-25 04:09 +0100
        Re: Best tools for writing an assembler? "James Harris" <james.harris.1@gmail.com> - 2014-02-24 23:18 +0000
        Re: Best tools for writing an assembler? noitalmost <noitalmost@cox.net> - 2014-02-27 18:11 -0500
          Re: Best tools for writing an assembler? George Neuner <gneuner2@comcast.net> - 2014-03-01 13:09 -0500
            Re: Best tools for writing an assembler? federation2005@netzero.com - 2014-03-26 17:57 -0700
              Re: Best tools for writing an assembler? federation2005@netzero.com - 2014-04-13 12:24 -0700
  Re: Best tools for writing an assembler? Sébastien Fricker <sebastien.fricker@gmail.com> - 2014-02-19 09:59 +0100
    Re: Best tools for writing an assembler? Robert A Duff <bobduff@shell01.TheWorld.com> - 2014-02-19 18:27 -0500
  Re: Best tools for writing an assembler? Patrik Túri <tpphysik@gmail.com> - 2014-02-20 17:15 -0800
    Re: Best tools for writing an assembler? Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2014-02-21 12:09 +0100
      Re: Best tools for writing an assembler? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-02-24 20:42 +0000
        Re: Best tools for writing an assembler? Ivan Godard <ivan@ootbcomp.com> - 2014-02-24 15:13 -0800
        Re: Best tools for writing an assembler? hu47121@usenet.kitty.sub.org (Hannah) - 2014-02-25 00:43 +0000
          Re: Best tools for writing an assembler? Walter Banks <walter@bytecraft.com> - 2014-02-27 14:14 -0500
        Re: Best tools for writing an assembler? Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2014-02-25 04:23 +0100
    Re: Best tools for writing an assembler? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-02-24 20:35 +0000

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