[PATCH] Faster glyph lookup by BMP index

[PATCH] Faster glyph lookup by BMP index

[Vladimir 'φ-coder/phcoder' Serbinenko]

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Hello. Basic Multilingual Plane is range of Unicode characters in
0-65535 and it contains most of the characters needed by most of the
languages of the world. By keeping an array with pointers to such
characters at the cost of 128KiB per font we can almost instantenously
lookup characters which are likely to be used in grub. Available in
experimental

-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko


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=== added file 'ChangeLog.bmpidx'
--- ChangeLog.bmpidx	1970-01-01 00:00:00 +0000
+++ ChangeLog.bmpidx	2009-11-29 14:17:03 +0000
@@ -0,0 +1,9 @@
+2009-11-29  Vladimir Serbinenko  <phcoder@gmail.com>
+
+	Optimise glyph lookup by Basic Multilingual Plane lookup array.
+
+	* font/font.c (struct grub_font): New member 'bmp_idx'.
+	(font_init): Initialise 'bmp_idx'.
+	(load_font_index): Fill 'bmp_idx'.
+	(find_glyph): Make inline. Use bmp_idx for BMP characters.
+

=== modified file 'font/font.c'
--- font/font.c	2009-07-20 17:37:37 +0000
+++ font/font.c	2009-11-29 13:24:58 +0000
@@ -58,6 +58,7 @@ struct grub_font
   short leading;
   grub_uint32_t num_chars;
   struct char_index_entry *char_index;
+  grub_uint16_t *bmp_idx;
 };
 
 /* Definition of font registry.  */
@@ -180,6 +181,7 @@ font_init (grub_font_t font)
   font->descent = 0;
   font->num_chars = 0;
   font->char_index = 0;
+  font->bmp_idx = 0;
 }
 
 /* Open the next section in the file.
@@ -273,6 +275,14 @@ load_font_index (grub_file_t file, grub_
                                   * sizeof (struct char_index_entry));
   if (! font->char_index)
     return 1;
+  font->bmp_idx = grub_malloc (0x10000 * sizeof (grub_uint16_t));
+  if (! font->bmp_idx)
+    {
+      grub_free (font->char_index);
+      return 1;
+    }
+  grub_memset (font->bmp_idx, 0xff, 0x10000 * sizeof (grub_uint16_t));
+
 
 #if FONT_DEBUG >= 2
   grub_printf("num_chars=%d)\n", font->num_chars);
@@ -299,6 +309,9 @@ load_font_index (grub_file_t file, grub_
           return 1;
         }
 
+      if (entry->code < 0x10000)
+	font->bmp_idx[entry->code] = i;
+
       last_code = entry->code;
 
       /* Read storage flags byte.  */
@@ -594,7 +607,7 @@ read_be_int16 (grub_file_t file, grub_in
 
 /* Return a pointer to the character index entry for the glyph corresponding to
    the codepoint CODE in the font FONT.  If not found, return zero.  */
-static struct char_index_entry *
+static inline struct char_index_entry *
 find_glyph (const grub_font_t font, grub_uint32_t code)
 {
   struct char_index_entry *table;
@@ -602,8 +615,17 @@ find_glyph (const grub_font_t font, grub
   grub_size_t hi;
   grub_size_t mid;
 
-  /* Do a binary search in `char_index', which is ordered by code point.  */
   table = font->char_index;
+
+  /* Use BMP index if possible.  */
+  if (code < 0x10000)
+    {
+      if (font->bmp_idx[code] == 0xffff)
+	return 0;
+      return &table[font->bmp_idx[code]];
+    }
+
+  /* Do a binary search in `char_index', which is ordered by code point.  */
   lo = 0;
   hi = font->num_chars - 1;
 


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Re: [PATCH] Faster glyph lookup by BMP index

[richardvoigt]

Is this table stored in the file or built during font load?  128KiB in
memory is no issue at all on modern systems, 128KiB in a file is
somewhat more troublesome since it won't fit in a boot sector, is a
big chunk of a rescue diskette, and the I/O cost is noticeable.  These
glyphs are stored in sorted order in the file, correct?  May I suggest
that only every Nth index be stored in the file header (where N = 16
for example) and the intermediate ones discovered at runtime, in those
subranges containing a character actually used (and the indexes and
character data for those glyphs are then cached in memory)?  This also
means block reads from the file (block length is easily calculated as
the difference of two adjacent indices) instead of extraction of
individual characters, most languages tend to have good locality so
this should also be a win.  Or is the entire font file cached in
memory anyway?

2009/11/29 Vladimir 'φ-coder/phcoder' Serbinenko <phcoder@gmail.com>:
> Hello. Basic Multilingual Plane is range of Unicode characters in
> 0-65535 and it contains most of the characters needed by most of the
> languages of the world. By keeping an array with pointers to such
> characters at the cost of 128KiB per font we can almost instantenously
> lookup characters which are likely to be used in grub. Available in
> experimental
>
> --
> Regards
> Vladimir 'φ-coder/phcoder' Serbinenko
>
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> http://lists.gnu.org/mailman/listinfo/grub-devel
>
>

Re: [PATCH] Faster glyph lookup by BMP index

[Vladimir 'φ-coder/phcoder' Serbinenko]

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richardvoigt@gmail.com wrote:
> Is this table stored in the file or built during font load?  
This table is generated on file load
> 2009/11/29 Vladimir 'φ-coder/phcoder' Serbinenko <phcoder@gmail.com>:
>   
>> Hello. Basic Multilingual Plane is range of Unicode characters in
>> 0-65535 and it contains most of the characters needed by most of the
>> languages of the world. By keeping an array with pointers to such
>> characters at the cost of 128KiB per font we can almost instantenously
>> lookup characters which are likely to be used in grub. Available in
>> experimental
>>
>> --
>> Regards
>> Vladimir 'φ-coder/phcoder' Serbinenko
>>
>>
>> _______________________________________________
>> Grub-devel mailing list
>> Grub-devel@gnu.org
>> http://lists.gnu.org/mailman/listinfo/grub-devel
>>
>>
>>     
>
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> http://lists.gnu.org/mailman/listinfo/grub-devel
>
>   


-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko



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Re: [PATCH] Faster glyph lookup by BMP index

[Robert Millan]

On Sun, Nov 29, 2009 at 03:29:18PM +0100, Vladimir 'φ-coder/phcoder' Serbinenko wrote:
> Hello. Basic Multilingual Plane is range of Unicode characters in
> 0-65535 and it contains most of the characters needed by most of the
> languages of the world. By keeping an array with pointers to such
> characters at the cost of 128KiB per font we can almost instantenously
> lookup characters which are likely to be used in grub. Available in
> experimental

Seems fine (for trunk as well), just one thing:

> +  grub_memset (font->bmp_idx, 0xff, 0x10000 * sizeof (grub_uint16_t));
> [...]
> +      if (entry->code < 0x10000)
> [...]
> +  /* Use BMP index if possible.  */
> +  if (code < 0x10000)
> +    {
> +      if (font->bmp_idx[code] == 0xffff)

Could these be macroified?  Makes it harder to do mistakes in the future.

-- 
Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
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