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Re: XC-WIDTH in the new Forth standard XCHAR section

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Alex <alex@rivadpm.com> writes:
>What is the source of the XC-WIDTH table?
>http://forth-standard.org/standard/xchar/XC-WIDTH
>
>There's a bug in it, which I've not reported on the page, since it seems 
>inappropriate there.
>
>0 1058 1059 wc,     1 0000 1100 wc,     2 1100 115f wc,
>.                     ^^^^
>
>Should be at least 1060, but I'm not sure what value it's meant to be.

Looking at
<http://git.savannah.gnu.org/cgit/gforth.git/tree/engine/wcwidth.c>

I think the "1 0000 1100 wc," part could be removed.  There is no
other entry for width 1 in the table, and width 1 is the result if no
table entry is found.  However, you can also leave it in if you are
using the linear search that's used in XC-WIDTH; it gives the result a
little faster if your input is below $1100 and the width is 1.

I think it would be better to have a binary search, and a table that
stores only the boundary between each region and the next (instead of
the start and the end of the region), plus the result for the region.
A direct table lookup for values below $10000, with a small table for
the rest is harder on the caches, but easier on the branch predictor.

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2016: http://www.euroforth.org/ef16/

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XC-WIDTH in the new Forth standard XCHAR section Alex <alex@rivadpm.com> - 2017-03-07 17:16 +0000
  Re: XC-WIDTH in the new Forth standard XCHAR section anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-03-07 18:16 +0000

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