Write the loca table in optimum format

Also update the head and maxp tables when subsetting

src/calibre/utils/fonts/sfnt/glyf.py

@@ -85,7 +85,10 @@ class GlyfTable(UnknownTable):
         block = []
         for glyph_id, glyph in iteritems(sorted_glyph_map):
             raw = glyph()
-            ans[glyph_id] = (offset, len(raw))
+            pad = 4 - (len(raw) % 4)
+            if pad < 4:
+                raw += b'\0' * pad
+            ans[glyph_id] = offset, len(raw)
             offset += len(raw)
             block.append(raw)
         self.raw = b''.join(block)

src/calibre/utils/fonts/sfnt/loca.py

@@ -53,8 +53,15 @@ class LocaTable(UnknownTable):
                 self.offset_map[i] = self.offset_map[i-1]
 
         vals = self.offset_map
+        max_offset = max(vals) if vals else 0
+        max_short_offset = 65535 * 2
+        if self.fmt == 'L' and max_offset <= max_short_offset:
+            self.fmt = 'H'
         if self.fmt == 'H':
-            vals = [i//2 for i in self.offset_map]
+            if max_offset > max_short_offset:
+                self.fmt = 'L'
+            else:
+                vals = [i//2 for i in vals]
 
         self.raw = pack(('>%d%s'%(len(vals), self.fmt)).encode('ascii'), *vals)
     subset = update

src/calibre/utils/fonts/sfnt/subset.py

@@ -64,6 +64,9 @@ def subset_truetype(sfnt, character_map, extra_glyphs):
 
     # Update the loca table
     loca.subset(glyph_offset_map)
+    head.index_to_loc_format = 1 if loca.fmt == 'L' else 0
+    head.update()
+    maxp.num_glyphs = len(glyph_offset_map)
 
 # }}}