On Thu, Apr 26, 2012 at 06:13:00PM -0400, Nick Sabalausky wrote:
"H. S. Teoh" <[email protected]> wrote in message
news:[email protected]...
[...]
> And don't forget that some code points (notably from the CJK
> block)
> are specified as "double-width", so if you're trying to do
> text
> layout, you'll want yet a different length (layoutLength?).
>
Correction: the official term for this is "full-width" (as
opposed to
the "half-width" of the typical European scripts).
Interesting. Kinda makes sence that such thing exists, though:
The CJK
characters (even the relatively simple Japanese *kanas) are
detailed
enough that they need to be larger to achieve the same
readability.
And that's the *non*-double-length ones. So I don't doubt
there's ones
that need to be tagged as "Draw Extra Big!!" :)
Have you seen U+9598? It's an insanely convoluted glyph
composed of
*three copies* of an already extremely complex glyph.
http://upload.wikimedia.org/wikipedia/commons/3/3c/U%2B9F98.png
(And yes, that huge thing is supposed to fit inside a SINGLE
character... what *were* those ancient Chinese scribes
thinking?!)
For example, I have my font size in Windows Notepad set to a
comfortable value. But when I want to use hiragana or
katakana, I have
to go into the settings and increase the font size so I can
actually
read it (Well, to what *little* extent I can even read it in
the first
place ;) ). And those kana's tend to be among the simplest CJK
characters.
(Don't worry - I only use Notepad as a quick-n-dirty scrap
space,
never for real coding/writing).
LOL... love the fact that you felt obligated to justify your
use of
notepad. :-P
> So we really need all four lengths. Ain't unicode fun?! :-)
>
No kidding. The *one* thing I really, really hate about
Unicode is the
fact that most (if not all) of its complexity actually *is*
necessary.
We're lucky the more imaginative scribes of the world have
either been
dead for centuries or have restricted themselves to writing
fictional
languages. :-) The inventions of the dead ones have been
codified and
simplified by the unfortunate people who inherited their overly
complex
systems (*cough*CJK glyphs*cough), and the inventions of the
living ones
are largely ignored by the world due to the fact that, well,
their
scripts are only useful for writing fictional languages. :-)
So despite the fact that there are still some crazy convoluted
stuff out
there, such as Arabic or Indic scripts with pair-wise
substitution rules
in Unicode, overall things are relatively tame. At least the
subcomponents of CJK glyphs are no longer productive (actively
being
used to compose new characters by script users) -- can you
imagine the
insanity if Unicode had to support composition by those
radicals and
subparts? Or if Unicode had to support a script like this one:
http://www.arthaey.com/conlang/ashaille/writing/sarapin.html
whose components are graphically composed in, shall we say,
entirely
non-trivial ways (see the composed samples at the bottom of the
page)?
Unicode *itself* is undisputably necessary, but I do sure miss
ASCII.
In an ideal world, where memory is not an issue and bus width is
indefinitely wide, a Unicode string would simply be a sequence
of
integers (of arbitrary size). Things like combining diacritics,
etc.,
would have dedicated bits/digits for representing them, so
there's no
need of the complexity of UTF-8, UTF-16, etc.. Everything fits
into a
single character. Every possible combination of diacritics on
every
possible character has a unique representation as a single
integer.
String length would be equal to glyph count.
In such an ideal world, screens would also be of indefinitely
detailed
resolution, so anything can fit inside a single grid cell, so
there's no
need of half-width/double-width distinctions. You could port
ancient
ASCII-centric C code just by increasing sizeof(char), and
things would
Just Work.
Yeah I know. Totally impossible. But one can dream, right? :-)
[...]
> I've been thinking about unicode processing recently.
> Traditionally,
> we have to decode narrow strings into UTF-32 (aka dchar)
> then do
> table lookups and such. But unicode encoding and properties,
> etc.,
> are static information (at least within a single unicode
> release).
> So why bother with hardcoding tables and stuff at all?
>
> What we *really* should be doing, esp. for commonly-used
> functions
> like computing various lengths, is to automatically process
> said
> tables and encode the computation in finite-state machines
> that can
> then be optimized at the FSM level (there are known algos for
> generating optimal FSMs), codegen'd, and then optimized
> again at the
> assembly level by the compiler. These FSMs will operate at
> the
> native narrow string char type level, so that there will be
> no need
> for explicit decoding.
>
> The generation algo can then be run just once per unicode
> release,
> and everything will Just Work.
>
While I find that very intersting...I'm afraid I don't actually
understand your suggestion :/ (I do understand FSM's and how
they
work, though) Could you give a little example of what you mean?
[...]
Currently, std.uni code (argh the pun!!) is hand-written with
tables of
which character belongs to which class, etc.. These hand-coded
tables
are error-prone and unnecessary. For example, think of
computing the
layout width of a UTF-8 stream. Why waste time decoding into
dchar, and
then doing all sorts of table lookups to compute the width?
Instead,
treat the stream as a byte stream, with certain sequences of
bytes
evaluating to length 2, others to length 1, and yet others to
length 0.
A lexer engine is perfectly suited for recognizing these kinds
of
sequences with optimal speed. The only difference from a real
lexer is
that instead of spitting out tokens, it keeps a running total
(layout)
length, which is output at the end.
So what we should do is to write a tool that processes
Unicode.txt (the
official table of character properties from the Unicode
standard) and
generates lexer engines that compute various Unicode properties
(grapheme count, layout length, etc.) for each of the UTF
encodings.
This way, we get optimal speed for these algorithms, plus we
don't need
to manually maintain tables and stuff, we just run the tool on
Unicode.txt each time there's a new Unicode release, and the
correct
code will be generated automatically.
T
