Re: [PATCH] add some EFI device smarts

[Matthew Wilcox <willy@debian.org>]

On Wed, Apr 21, 2004 at 06:59:22AM -0600, Bjorn Helgaas wrote:
> > > +		/* Convert Unicode to normal chars */
> > > +		for (i = 0; i < (name_size/sizeof(name_unicode[0])); i++)
> > > +			name_utf8[i] = name_unicode[i] & 0xff;
> > > +		name_utf8[i] = 0;
> > 
> > I've never had a clear understanding of this.  It's not really UTF8
> > (else straight ASCII text could be used), but more like UCS2.
> 
> I don't understand Unicode either.  Maybe the attached is a little
> closer?  The EFI spec (1.10, table 2-2) says strings are stored in
> UTF-16, and I think that UTF-16 is the same as ASCII for
> (0 < c <= 0x7f).

Ah, I know this one ...

UTF-16 is like UCS-2 except that it has escapes to let you use past the
first plane of Unicode.  That is, by and large it's 2-bytes long, but
sometimes it can be 4 or more bytes long.  How to convert?  Let's see ...

	for (i = 0, j = 0; i < (name_size/sizeof(name_unicode[0])); i++) {
		unsigned int rune = name_unicode[i];
		if (0xD7FF < rune && rune < 0xE000) {
			rune = (rune & 0x7ff) << 10;
			rune |= name_unicode[++i] & 0x3ff;
		}
		if (rune < 0x80) {
			name_utf8[j++] = rune;
		} else if (rune < 0x800) {
			name_utf8[j++] = 0xc0 | (rune >> 6);
			name_utf8[j++] = 0x80 | (rune & 0x3f);
		} else if (rune < 0x10000) {
			name_utf8[j++] = 0xe0 | (rune >> 12);
			name_utf8[j++] = 0x80 | ((rune >> 6) & 0x3f);
			name_utf8[j++] = 0x80 | (rune & 0x3f);
		} else {
			name_utf8[j++] = 0xf0 | (rune >> 18);
			name_utf8[j++] = 0x80 | ((rune >> 12) & 0x3f);
			name_utf8[j++] = 0x80 | ((rune >> 6) & 0x3f);
			name_utf8[j++] = 0x80 | (rune & 0x3f);
		}
	}

ftp://ftp.rfc-editor.org/in-notes/rfc2279.txt
ftp://ftp.rfc-editor.org/in-notes/rfc2781.txt

Haven't even tried to compile it ...

-- 
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he enjoys after this process of grotesque self-deception." -- Mark Twain