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Unicode (was RE: JIT-compilation for OCaml?)
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Date: 2001-01-22 (22:05)
From: John Max Skaller <skaller@o...>
Subject: Re: Unicode (was RE: JIT-compilation for OCaml?)
Pierpaolo BERNARDI wrote:

> Let me repeat: ISO has formally agreed to not use code points outside of
> the Unicode possibility.  

	OK, accepted.

> This leaves room for about 2^20 characters.

> > Indeed, some code points from the BMP are reserved
> > so Unicode can use multi-word encodings of the lower 4 planes.
> Unicode can be encoded in several ways, for example, UTF-8, UTF-16,
> UTF-32, UCS2, etc..  This has nothing to do with the number of characters
> that can be encoded.

	This is not quite right. Unicode is 16 bit, it supports
only 2^16 code points: again, unless this has
changed recently. However, some of the code points are reserved
for UCS-16 encoding of a larger space of 2^20 code points (another
four bits -- I was wrong, this is the lower 16 (not 4) planes).

	So it is not quite true that it has 'nothing to do with
the number of characters that can be encoded', since some of
the code points of the BMP are reserved precisely for the purpose
of two word encodings of a larger space. (I think these are
the High and Low Surrogates: U+d8xx, U+dcxx respectively).

	Note that this is only loosely connected with
the encoding of _characters_, since some code points are
not characters (such as 'newline'), and some sequences
of code points represent a single (accented) character :-)

John (Max) Skaller, mailto:skaller@maxtal.com.au
10/1 Toxteth Rd Glebe NSW 2037 Australia voice: 61-2-9660-0850
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