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[freetype2] hdmx-advances de70a40: [truetype] Binary search through `hdm
From: |
Werner Lemberg |
Subject: |
[freetype2] hdmx-advances de70a40: [truetype] Binary search through `hdmx` records. |
Date: |
Wed, 1 Dec 2021 10:32:17 -0500 (EST) |
branch: hdmx-advances
commit de70a401aad9bb99a295b2cbfb8f7253a9a8d589
Author: Alexei Podtelezhnikov <apodtele@gmail.com>
Commit: Alexei Podtelezhnikov <apodtele@gmail.com>
[truetype] Binary search through `hdmx` records.
The `hdmx` table is supposed to be sorted by ppem size, which
enables binary search. We also drop the check for the sufficient
length of the record because it is now enforced when the table
is loaded.
* src/truetype/ttpload.c (tt_face_load_hdmx): Prudently sort records.
(tt_face_get_device_metrics): Implement binary search to retrieve
advances.
---
src/truetype/ttpload.c | 37 ++++++++++++++++++++++++++++---------
1 file changed, 28 insertions(+), 9 deletions(-)
diff --git a/src/truetype/ttpload.c b/src/truetype/ttpload.c
index 71db75a..2a2af70 100644
--- a/src/truetype/ttpload.c
+++ b/src/truetype/ttpload.c
@@ -498,6 +498,14 @@
}
+ FT_COMPARE_DEF( int )
+ compare_ppem( const void* a,
+ const void* b )
+ {
+ return *(FT_Byte*)a - *(FT_Byte*)b;
+ }
+
+
/**************************************************************************
*
* @Function:
@@ -577,8 +585,10 @@
if ( FT_QNEW_ARRAY( face->hdmx_record_sizes, num_records ) )
goto Fail;
- /* XXX: We do not check if the records are sorted by ppem */
- /* and cannot use binary search later. */
+ /* The records must be already sorted by ppem but it does not */
+ /* hurt to make sure so that the binary search works later. */
+ ft_qsort( p, num_records, record_size, compare_ppem );
+
for ( nn = 0; nn < num_records; nn++ )
{
if ( p + record_size > limit )
@@ -619,27 +629,36 @@
/**************************************************************************
*
* Return the advance width table for a given pixel size if it is found
- * in the font's `hdmx' table (if any).
+ * in the font's `hdmx' table (if any). The records must be sorted for
+ * the binary search to work properly.
*/
FT_LOCAL_DEF( FT_Byte* )
tt_face_get_device_metrics( TT_Face face,
FT_UInt ppem,
FT_UInt gindex )
{
- FT_UInt nn;
+ FT_UInt min = 0;
+ FT_UInt max = face->hdmx_record_count;
+ FT_UInt mid;
FT_Byte* result = NULL;
FT_ULong record_size = face->hdmx_record_size;
FT_Byte* record = FT_OFFSET( face->hdmx_table, 8 );
- for ( nn = 0; nn < face->hdmx_record_count; nn++ )
- if ( face->hdmx_record_sizes[nn] == ppem )
+ while ( min < max )
+ {
+ mid = ( min + max ) >> 1;
+
+ if ( face->hdmx_record_sizes[mid] > ppem )
+ max = mid;
+ else if ( face->hdmx_record_sizes[mid] < ppem )
+ min = mid + 1;
+ else
{
- gindex += 2;
- if ( gindex < record_size )
- result = record + nn * record_size + gindex;
+ result = record + mid * record_size + gindex + 2;
break;
}
+ }
return result;
}
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