Re: Usage of standard-display-table in MSDOS

["Ehud Karni" <ehud@unix.mvs.co.il>]

On Sun, 29 Aug 2010 14:49:03 Ehud Karni wrote:
>
> On Sun, 29 Aug 2010 07:21:26 Eli Zaretskii wrote:
> >
> > > From: "Ehud Karni" <ehud@unix.mvs.co.il>
> > >
> > > > ;; For NBSP (U+00A0)
> > > > (aset standard-display-table #xA0
> > > >       (vector (unibyte-char-to-multibyte #xA0)))
> > >
> > > The result in 21.3 is correct:
> > >     Byte: E0 (224),  Char: 0C60 (3168)
> > >
> > > But on 23.1 I get:
> > >     Byte: E0 (224),  Char: 3FFFE0 (4194272)
> > > i.e. "literal" #xE0.
> >
> > The last result is correct 0x3FFFE0 is the internal representation of
> > 0xE0 in Emacs 23.  Emacs 23 and later extends the Unicode code space
> > with these characters (and some others).
> >
> > Why did you think it was incorrect?
>
> Because of my coding system (iso-8859, remember ?) the #xE0 should be
> displayed as Aleph, not some 8 bit byte E0.

From another thread, I found Handa san suggestion to use `decode-char'.

So my my check function looks now like this:

(defun check-multibyte-code (byte)
       (message "Byte: %02X (%d),  M-Char: %04X (%d),  D-Char: %04X (%d)"
                byte byte
                (unibyte-char-to-multibyte byte)
                (unibyte-char-to-multibyte byte)
                (decode-char 'iso-8859-8 byte)
                (decode-char 'iso-8859-8 byte)))

It fails for Emacs-21.3 because `decode-char' returns nil.
For Emacs-23.1 the result is:
    Byte: E0 (224),  M-Char: 3FFFE0 (4194272),  D-Char 05D0 (1488)

So I can use `decode-char' in 23.1 and `unibyte-char-to-multibyte'
in 21.3 for building a display table.

Can you give the reasons to the changes in these functions ?

I think it is a bad practice to keep the function names while
changing how they work. It breaks tested code.

Ehud.


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