[Dev-luatex] A design philosophy question...

David Kastrup dak at gnu.org
Mon Apr 2 23:47:12 CEST 2007


I have this year reported something as a bug to Barbara Beeton (the
bug collector for TeX) which I find disturbing: TeX's arithmetic on
units truncates and thus is biased.

This has the annoying effect that "1in", supposedly representing one
inch which is _exactly_ 72.27 points, will in TeX stand for the value
"72.26999pt" and be actually smaller than the value "72.27pt".

Of course, fixing this might change existing documents.  Also we have:

**\dimen0=1in
entering extended mode

*\showthe\dimen0
> 72.26999pt.

*\showthe\dimexpr100\dimen0\relax
> 7226.9989pt.

*\dimen0=72.27pt

*\showthe\dimen0
> 72.27pt.

*\showthe\dimexpr100\dimen0\relax
> 7227.00043pt.


So while "72.27pt" is _quite_ closer to one inch than "1in" is, it is
larger.

Anyway, is something like that an area that LuaTeX would actually ever
consider touching?  After all, it would break document compatibility.
Which might be, I believe, less of a holy grail for ConTeXt than for
LaTeX.

Opinions?

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum


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