[bdf, pfr, psnames] Accelarate charmap searches.

The binary searches within charmaps can be accelerated because they
often contain dense continuous blocks of character codes. Within such
blocks, you can predict matches based on misses.  This method has been
deployed in `bdf` since 0f122fef34; we only refactor it there.  We now
use it in `pfr` and `psnames`, which speeds up the unicode charmap
access by about 50% in PFR and Type 1 fonts.

* src/bdf/bdfdrivr.c (bdf_cmap_char_{index,next}): Refactor.
* src/pfr/pfrcmap.c (pfr_cmap_char_{index,next}): Predict `mid` based
on the mismatch distance.
* src/psnames/psmodule.c (ps_unicodes_char_{index,next}): Ditto.

1 files changed, 17 insertions, 14 deletions

diff --git a/src/psnames/psmodule.c b/src/psnames/psmodule.c
index e7d51e950..4730d8bf0 100644
--- a/src/psnames/psmodule.c
+++ b/src/psnames/psmodule.c
@@ -412,21 +412,18 @@
   ps_unicodes_char_index( PS_Unicodes  table,
                           FT_UInt32    unicode )
   {
-    PS_UniMap  *min, *max, *mid, *result = NULL;
+    PS_UniMap  *result = NULL;
+    PS_UniMap  *min = table->maps;
+    PS_UniMap  *max = min + table->num_maps;
+    PS_UniMap  *mid = min + ( ( max - min ) >> 1 );
 
 
     /* Perform a binary search on the table. */
-
-    min = table->maps;
-    max = min + table->num_maps - 1;
-
-    while ( min <= max )
+    while ( min < max )
     {
       FT_UInt32  base_glyph;
 
 
-      mid = min + ( ( max - min ) >> 1 );
-
       if ( mid->unicode == unicode )
       {
         result = mid;
@@ -438,13 +435,15 @@
       if ( base_glyph == unicode )
         result = mid; /* remember match but continue search for base glyph */
 
-      if ( min == max )
-        break;
-
       if ( base_glyph < unicode )
         min = mid + 1;
       else
-        max = mid - 1;
+        max = mid;
+
+      /* reasonable prediction in a continuous block */
+      mid += unicode - base_glyph;
+      if ( mid >= max || mid < min )
+        mid = min + ( ( max - min ) >> 1 );
     }
 
     if ( result )
@@ -465,14 +464,13 @@
     {
       FT_UInt     min = 0;
       FT_UInt     max = table->num_maps;
-      FT_UInt     mid;
+      FT_UInt     mid = min + ( ( max - min ) >> 1 );
       PS_UniMap*  map;
       FT_UInt32   base_glyph;
 
 
       while ( min < max )
       {
-        mid = min + ( ( max - min ) >> 1 );
         map = table->maps + mid;
 
         if ( map->unicode == char_code )
@@ -490,6 +488,11 @@
           min = mid + 1;
         else
           max = mid;
+
+        /* reasonable prediction in a continuous block */
+        mid += char_code - base_glyph;
+        if ( mid >= max || mid < min )
+          mid = min + ( max - min ) / 2;
       }
 
       if ( result )