Re: Integer & glyph (trunk and emacs_unicode)

[Vinicius Jose Latorre]

Drew Adams wrote:
> > > (defun make-glyph-code (char &optional face)
> > >   "Return a glyph code representing char CHAR with face FACE."
> > >   ;; Due to limitations on Emacs integer values, faces with
> > >   ;; face id greater that 4091 are silently ignored.
> > >   (if (and face (<= (face-id face) #xfff))
> > >       (logior char (lsh (face-id face) 19))
> > >     char))
> > >       
> > > So, it assumes 12 bits for face id and 19 bits for char code,
> > > the result is an integer of 31 bits.
> > >       
> > I suspect that the "19" used to be something else (e.g. 16 when
> > integers were 28bits, so 16+12=28).
> >
> > In any case, the test should be made more robust by not assuming
> > anything about the available range of integers (which has changed over
> > the years and can change depending on your config).
> > How 'bout
> >
> >    (let ((id (and face (face-id face)))
> >      (if (and (numberp id)
> >               ;; Due to limitations on Emacs integer values, only
> >               ;; face ids below a certain limit can be used.
> >               (= id (lsh (lsh id 19) -19)))
> >          (logior char (lsh id 19))
> >        char))
> >     

Yes, this fix the problem.

Also it could be made a constant for the number of bits for char like:

(defconst glyph-char-bits
  (if (<= emacs-major-version 22) 19 22)
  "Specify the number of bits used by a char code in a glyph.")

And the code:

   (let ((id (and face (face-id face))))
     (if (and (numberp id)
              ;; Due to limitations on Emacs integer values, only
              ;; face ids below a certain limit can be used.
              (= id (lsh (lsh id glyph-char-bits) (- glyph-char-bits))))
         (logior char (lsh id glyph-char-bits))
       char))

Is there any problem if I implement this solution in trunk and Emacs 
unicode?

> I'm not really following this, but is this about the change from `19' to
> `22' in this code (this is my own version, to accommodate both the old and
> new)?
>
> (defun make-glyph-code (char &optional face)
>   "Return a glyph code representing char CHAR with face FACE."
>   (if face
>       (logior char (lsh (face-id face)
>                         (if (<= emacs-major-version 22) 19 22)))
>     char))
>
> That is, is this related to thread "bug of display-table & make-glyph-code,
> 2007-09-10?
>   

No, the problem is this test:

   (if (and face (<= (face-id face) #xfff))

Which assumes 12 bits for face (constant #xFFF), it should be 10 bits 
(#x3FF).  This test in Emacs unicode should be with #x3F (7 bits).

But the solution given by Stefan is better as it is only needed to 
specify the number of bits used in a char code.