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Re: cyg1.7 - DOS character remapping: change request.


Corinna Vinschen wrote:
On Nov 23 20:29, Linda Walsh wrote:
Eric Blake wrote:
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According to Linda Walsh on 11/23/2009 4:59 PM:
Instead of using random characters out of the 'random free area' --
which could display as anything if you aren't in cygwin, depending
on what charset you have loaded, why not use 'dedicated' unicode
characters that map to the signs for those characters? They aren't
exactly equivalent, as they include some built-in display spacing,
BUT, they would display a colon as a colon, "*" as a asterisk, etc.
But then, how would you distinguish between the valid UTF-16 replacement
used to represent an invalid character, and a valid UTF-16 character
representing itself? I'm sorry, but the value of a 1-to-1 round trip
mapping outweighs the convenience of displaying a glyph that looks the
same but causes ambiguous round trip conversions.
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You've already broken 1-to-1 round trip compatibility by NOT
using an **INVALID** UTF-16 character. You are using "the 0xf000-0xf0ff

There is no invalid UTF-16. There could be invalid UTF-32, but that's
not used by Windows.
Isolated surrogates are invalid UTF-16. Low surrogates could be used for this purpose, don't know if that was already discussed as an alternative.
range. This range is part of the UNICODE block 95, "Private Use Area".
These are *valid* unicode characters -- they are just NOT reserved for
a particular application. This means they will be displayed randomly
and CAN be used by other applications

Right, and we use them to map characters from the base plane. There's no area in the entire Unicode plane which would not conflict one way or the other. We're using the same mapping as Interix does, so we're at least compatible with one other product.
Which is a convincing argument since this choice is kind of native...

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