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Re: Best tools for writing an assembler?

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On 2/24/2014 12:42 PM, glen herrmannsfeldt wrote:

<snip>


> -- glen [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]
>

Shrink is not NP, it is exact using a relaxation algorithm: track pairs
of addresses, one the smallest address assuming all unresolved are
resolved short, and one largest assuming all unresolved address are
long. Resolve long all those spreads whose shortest is longer than the
longest short; resolve short all those spreads whose longest is shorter
than than the longest short. Iterate resolution until you do a pass in
which no more were resolved. Set any remaining unresolved to short.

In practice, three iterations are always sufficient, including the final
one that resolves nothing.
[With some assumptions about chaining variable length jumps,
it really is NP-complete.  See this 1978 CACM article
http://dx.doi.org/10.1145/359460.359474 -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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