[Mono-list] conversions

[Jonathan Pryor]

A quick perusal through Perl's "Category.pl" shows this:

(1) Numbers are categorized as "Nd"
(2) The only ranges that are "Nd" seem to be:

	0030 - 0039	'0' - '9'
	0660 - 0669	ARABIC-INDIC DIGIT 0 - 9 (same order as ASCII)
	06F0 - 06F9	EXTENDED ARABIC-INDIC DIGIT 0-9 ("")
	0966 - 096F	DEVANAGRAI DIGIT 0-9
	09E6 - 09EF	BENGALI DIGIT 0-9
	0A66 - 0A6F
	0AE6 - 0AEF
	0B66 - 0B6F
	0BE7 - 0BEF
	0C66 - 0C6F
	0CE6 - 0CEF
	0D66 - 0D6F
	0E50 - 0E59
	0ED0 - 0ED9
	0F20 - 0F29
	... Plus 8 more...

I'm too lazy to look at all of these ranges, but the ones I did look at
all had digits in the order 0..9.  The subtraction should be legal for
all of these glyphs.  (Which is probably by design; it would be very odd
-- broken? -- to have so many digits in the "right" order, and then have
a few in a different order...)

Gnome's Character Map program (gucharmap) is very handy for looking up
the Unicode Category a character belongs to.  Too bad the opposite
direction (Unicode Category -> characters) tends to be more difficult
(hence consulting Perl's internal tables).

 - Jon

On Tue, 2004-10-05 at 07:31, Polton, Richard (IT) wrote:
> Thanks for this. Is it fair to say, then, that only Arabic numerals are
> counted as digits?  Even though other numeric characters have integer
> values?
> 
> -----Original Message-----
> From: Jonathan Pryor [mailto:jonpryor@vt.edu] 
> Sent: 05 October 2004 11:32
> To: Polton, Richard (IT)
> Cc: Jambunathan Jambunathan; mono-list@lists.ximian.com
> Subject: RE: [Mono-list] conversions
> 
> On Tue, 2004-10-05 at 04:34, Polton, Richard (IT) wrote:
> >  In fact, habing given it further thought, I have a couple of
> questions:
> > 
> > i) if I sit at a Japanese terminal (for example) and enter '-', i.e.
> > ichi or 'one', is this a valid Unicode character?
> 
> Yes.
> 
> > ii) how wide is the 'char' datatype? I assume it contains Unicode 
> > rather than single-byte ASCII.
> 
> 16-bit unsigned value.  It supports Unicode.
> 
> > iii) if entering 'ichi' is valid, and char contains Unicode, then I 
> > suspect that the below subtration will return a number substantially 
> > greater than one.
> 
> No.  At least, not if it's remotely like CVS HEAD:
> 
> 	public static int Val (char Expression) {
> 		if (char.IsDigit(Expression)) {
> 			return Expression - '0';
> 		}
> 		else {
> 			throw new ArgumentException();
> 		}
> 	}
> 
> Ichi isn't a digit, so it will generate an ArgumentException.
> 
> (Assuming that Ichi is Unicode U+4E00, which certainly looks like '-'. 
> It's in the Unicode category "Letter, Other".)
> 
> The subtraction should be safe, as (1) it's only done on digits, and (2)
> Unicode follows the ASCII character ordering (for glyphs 0-127), which
> permits this subtraction.
> 
>  - Jon 
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