[texhax] Crosscompilation of TeX

Uwe Lück uwe.lueck at web.de
Sun Mar 12 17:47:22 CET 2006

At 13:52 11.03.06, Philip TAYLOR wrote:

>Uwe Lück wrote:
> > At 20:37 10.03.06, Karl Berry wrote:
> >
> >>     E.g. the ARM-processor does not contain a floating point unit.
> >>
> >> There is actually a long-standing (as in decades old) patch from Knuth
> >> to make the TeX code use only fixed point arithmetic.  I admit I am not
> >> sure whether it's applied in the current distributions.
> >
> > According to the Wikipedia article on TeX, "fixed point arithmetic only"
> > is an essential feature of TeX.
>Never believe Wikis :-)  Fixed-point arithmetic is an essential
>feature of TeX only where the use of reals could affect DVI output.
>If you look at TeX.web, you will see that there /are/ places where
>"foo: real" is used!
>         @!g:real; {a glue ratio, as a floating point number}
>         @!glue_temp:real; {glue value before rounding}
>         @!cur_glue:real; ...

Nice to learn, thanks, Phil. At a second reading I am glad
to see that not my report was wrong, indeed the article doesn't
mention your qualification. -- It seems that I should read the
responses from the past night before I send a posting
the next morning.

And indeed, here is the discussion on the LaTeX list
that I mentioned:

>Bernd Raichle <raichle at INFORMATIK.UNI-STUTTGART.DE> writes:
> > This was postponed for e-TeX because (a) the implementation will be
> > rather tricky for e.g., special nodes and in some contexts where the
> > result of real arithmetic can be accessed (e.g., \accent
> > constructions) which will lead to implementation dependend
> > behaviour.
>It is my opinion that all of Knuth's attempt to hide the result of
>real arithmetic in TeX are just a source of pain, trouble and
>quirkiness, and should stop being a design criterion.  It also affects
>the output of the trip test, making it system-dependent.
>There are two approaches to get there: either just ignore the system
>dependencies (PostScript more or less does that, I think, and has not
>terribly suffered from it), or replace all occurences of real
>arithmetic by fixed-point arithmetic, and be done.  There are change
>files for that purpose already, if I remember correctly: it was shown
>that this was feasible.
>And indeed, given the rather limited amount of real arithmetic in TeX,
>it should be much easier to make it real-free than its cousin Metafont
>which managed this feat in spite of _much_ more involved calculations.
>The inability to access set glue is a _major_ roadblock for quite a
>few applications.
>David Kastrup, Kriemhildstr. 15, 44793 Bochum

So I had forgotten that Phil's qualification was part of that discussion,
here my report was wrong.

   -- Uwe. 

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