GNU bug report logs - #11082
24.0.94; u.glyphless member in struct glyph does not fit in 32 bits

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From: Kenichi Handa <handa <at> m17n.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 11082 <at> debbugs.gnu.org, mituharu <at> math.s.chiba-u.ac.jp
Subject: bug#11082: 24.0.94; u.glyphless member in struct glyph does not fit in 32 bits
Date: Mon, 26 Mar 2012 14:47:16 +0900

In article <83zkb6trdb.fsf <at> gnu.org>, Eli Zaretskii <eliz <at> gnu.org> writes:

> >    447	    /* Sub-stretch for type == GLYPHLESS_GLYPH.  */
> >    448	    struct
> >    449	    {
> >    450	      /* Value is an enum of the type glyphless_display_method.  */
> >    451	      unsigned method : 2;
> >    452	      /* 1 iff this glyph is for a character of no font. */
> >    453	      unsigned for_no_font : 1;
> >    454	      /* Length of acronym or hexadecimal code string (at most 8).  */
> >    455	      unsigned len : 4;
> >    456	      /* Character to display.  Actually we need only 22 bits.  */
> >    457	      unsigned ch : 26;
> >    458	    } glyphless;
[...]
> > According to the comment above, it seems to be OK to shorten the
> > length of `u.glyphless.ch' member from 26 to 25.  Could someone
> > confirm this?

> Confirmed.  From the ELisp manual:
[...]
> I would actually suggest to use 22-bit for this field, to avoid
> confusion in the future.

I agree to change the bit length.  I don't remeber well but I
think the current bit length setting was just my mistake.

In article <jwv4ntch6w6.fsf-monnier+emacs <at> gnu.org>, Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

> >   dispextern.h (struct glyph): Change the bit length of glyphless.ch to 22
> > to make the member glyphless fit in 32 bits.

> I think it's safer to reduce it to 25 bits, otherwise `val' field will
> refer to undefined bits.

Ok.  I've just installed that change.

---
Kenichi Handa
handa <at> m17n.org

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