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[truetype] New function to skip the randomization tag.

* src/truetype/ttobjs.c (tt_skip_pdffont_random_tag):
New function to skip the randomization tag in the names of the
fonts embedded in a PDF.  It is used by tt_check_trickyness_family(),
to keep from mistaking "DLC" in the randomization tag as a
tricky font name. See discussion in:

https://lists.nongnu.org/archive/html/freetype-devel/2021-02/msg00002.html

For technical detail about the randomization tag, please find
PDF Reference 5.5.3 "Font Subsets".  Thanks to Justyna Wawrzynska
for pointing out the issue caused by the randomization tag.

git/fs: mount .git/fs: mount/attach disallowed

--- a/src/truetype/ttobjs.c

+++ b/src/truetype/ttobjs.c

@@ -143,6 +143,30 @@

 #endif /* TT_USE_BYTECODE_INTERPRETER */

+  /* The fonts embedded in PDF changes their family names

+   * by the randomization tag. PDF Reference 5.5.3 "Font

+   * Subsets" defines its format as 6 uppercase letters and

+   * '+' sign.  For safety, we do not skip the tag violating

+   * this rule.

+   */

+

+  static const FT_String*

+  tt_skip_pdffont_random_tag( const FT_String*  name )

+  {

+    unsigned int  i;

+

+

+    if ( name[6] != '+' )

+      return name;

+

+    for ( i = 0; i < 6; i++ )

+      if ( !ft_isupper( name[i] ) )

+        return name;

+

+    FT_TRACE7(( "name without randomization tag: %s\n", name + 7 ));

+    return name + 7;

+  }

+

   /* Compare the face with a list of well-known `tricky' fonts. */

   /* This list shall be expanded as we find more of them.       */

@@ -199,10 +223,12 @@

     };

     int  nn;

+    const FT_String*  name_without_tag;

+    name_without_tag = tt_skip_pdffont_random_tag( name );

     for ( nn = 0; nn < TRICK_NAMES_COUNT; nn++ )

-      if ( ft_strstr( name, trick_names[nn] ) )

+      if ( ft_strstr( name_without_tag, trick_names[nn] ) )

         return TRUE;

     return FALSE;