Re: reducing equality tests in displaying text

[Kenichi Handa]

In article <address@hidden>, YAMAMOTO Mitsuharu <address@hidden> writes:

>>>>>> On Tue, 27 Jan 2009 14:26:42 +0900, Kenichi Handa <address@hidden> said:
>>> 1. Each call of assoc_no_quit (charset,_encoding_charset_alist) in
>>> fontset.c can be replaced with assq_no_quit because
>>> Vfont_encoding_charset_alist is a symbol-keyed alist.

> > Yes, just fixed.

> There's another occurrence in font_for_char.

Oops, just fixed.

> > When font_group is Qnil, in most cases, SUB_CHAR_TABLE_P (table) is
> > zero.  Thus the calculation of FROM and TO must not be that slow.
> > Did you really see the bottle-neck of the performance here?

> Below is a part of the result of an experiment (after your change)
> with Shark.app on Mac OS X 10.5.6. I scrolled up and down the Japanese
> tutorial.  Emacs is compiled with Xft support and the default CFLAGS
> (-g -O2 -Wno-pointer-sign).

>       957.8 ms        emacs   mark_object     
>       194.3 ms        emacs   mark_vectorlike 
>       147.9 ms        emacs   Fgarbage_collect        
>       145.3 ms        libfreetype.6.dylib     tt_cmap4_char_map_binary        
>       108.9 ms        emacs   char_table_ref_and_range        
>       98.8 ms emacs   sub_char_table_ref_and_range    

Are you sure that those calls mostly return nil?  Could you
please check if this patch surely improve the performance?

*** fontset.c.~1.154.~  2009-01-28 15:14:18.000000000 +0900
--- fontset.c   2009-01-28 15:50:37.000000000 +0900
***************
*** 470,476 ****
      return font_group;
    base_fontset = FONTSET_BASE (fontset);
    if (c >= 0)
!     font_group = char_table_ref_and_range (base_fontset, c, &from, &to);
    else
      font_group = FONTSET_FALLBACK (base_fontset);
    if (NILP (font_group))
--- 470,480 ----
      return font_group;
    base_fontset = FONTSET_BASE (fontset);
    if (c >= 0)
!     {
!       font_group = char_table_ref (base_fontset, c);
!       if (! NILP (font_group))
!       font_group = char_table_ref_and_range (base_fontset, c, &from, &to);
!     }
    else
      font_group = FONTSET_FALLBACK (base_fontset);
    if (NILP (font_group))

>>> 3. Despite its argument name, `has_char' functions in font backend
>>> drivers are mostly called for a font object instead of a font
>>> entity.  Some font backend drivers could make use of this fact:
>>> e.g., ftfont_has_char can avoid frequent assoc_no_quit calls if
>>> struct ft_font has a reference to fc_charset in ft_face_cache.

> > I've just fixed ftfont_has_char to use FT_Get_Char_Index directly.

> But FT_Get_Char_Index is much slower than FcCharSetHasChar.
> `tt_cmap4_char_map_binary' in the above table is called from
> FT_Get_Char_Index.

Hmmm.  I've just found that Xft has the function
XftCharExists now.  I remember that it didn't exist in a
rather old vesion.  Does your Xft library have this
function?

---
Kenichi Handa
address@hidden