[MultipleSubst] Rewrite serialize() in terms of iterators

Unused still, and hence untested

src/OT/Layout/GSUB/MultipleSubst.hh

@@ -35,19 +35,19 @@ struct MultipleSubst
     }
   }
 
-  /* TODO This function is unused and not updated to 24bit GIDs. Should be done by using
-   * iterators. While at it perhaps using iterator of arrays of hb_codepoint_t instead. */
+  template<typename GlyphIterator, typename SequenceIterator,
+           hb_requires (hb_is_sorted_source_of (GlyphIterator, hb_codepoint_t)),
+           hb_requires (hb_is_source_of (typename SequenceIterator::item_t, hb_codepoint_t))>
   bool serialize (hb_serialize_context_t *c,
-                  hb_sorted_array_t<const HBGlyphID16> glyphs,
-                  hb_array_t<const unsigned int> substitute_len_list,
-                  hb_array_t<const HBGlyphID16> substitute_glyphs_list)
+		  GlyphIterator glyphs,
+		  SequenceIterator sequences)
   {
     TRACE_SERIALIZE (this);
     if (unlikely (!c->extend_min (u.format))) return_trace (false);
     unsigned int format = 1;
     u.format = format;
     switch (u.format) {
-    case 1: return_trace (u.format1.serialize (c, glyphs, substitute_len_list, substitute_glyphs_list));
+    case 1: return_trace (u.format1.serialize (c, glyphs, sequences));
     default:return_trace (false);
     }
   }

src/OT/Layout/GSUB/MultipleSubstFormat1.hh

@@ -71,22 +71,24 @@ struct MultipleSubstFormat1_2
     return_trace ((this+sequence[index]).apply (c));
   }
 
+  template<typename GlyphIterator, typename SequenceIterator,
+           hb_requires (hb_is_sorted_source_of (GlyphIterator, hb_codepoint_t)),
+           hb_requires (hb_is_source_of (typename SequenceIterator::item_t, hb_codepoint_t))>
   bool serialize (hb_serialize_context_t *c,
-                  hb_sorted_array_t<const HBGlyphID16> glyphs,
-                  hb_array_t<const unsigned int> substitute_len_list,
-                  hb_array_t<const HBGlyphID16> substitute_glyphs_list)
+		  GlyphIterator glyphs,
+		  SequenceIterator sequences)
   {
     TRACE_SERIALIZE (this);
     if (unlikely (!c->extend_min (this))) return_trace (false);
     if (unlikely (!sequence.serialize (c, glyphs.length))) return_trace (false);
-    for (unsigned int i = 0; i < glyphs.length; i++)
+
+    for (auto& pair : hb_zip (sequences, sequence))
     {
-      unsigned int substitute_len = substitute_len_list[i];
-      if (unlikely (!sequence[i]
-                        .serialize_serialize (c, substitute_glyphs_list.sub_array (0, substitute_len))))
+      if (unlikely (!pair.second
+		    .serialize_serialize (c, pair.first)))
         return_trace (false);
-      substitute_glyphs_list += substitute_len;
     }
+
     return_trace (coverage.serialize_serialize (c, glyphs));
   }
 

src/OT/Layout/GSUB/SubstLookup.hh

@@ -119,19 +119,20 @@ struct SubstLookup : Lookup
     return_trace (false);
   }
 
-  bool serialize_multiple (hb_serialize_context_t *c,
-                           uint32_t lookup_props,
-                           hb_sorted_array_t<const HBGlyphID16> glyphs,
-                           hb_array_t<const unsigned int> substitute_len_list,
-                           hb_array_t<const HBGlyphID16> substitute_glyphs_list)
+  template<typename GlyphIterator, typename SequenceIterator,
+           hb_requires (hb_is_sorted_source_of (GlyphIterator, hb_codepoint_t)),
+           hb_requires (hb_is_source_of (typename SequenceIterator::item_t, hb_codepoint_t))>
+  bool serialize (hb_serialize_context_t *c,
+		  uint32_t lookup_props,
+		  GlyphIterator glyphs,
+		  SequenceIterator sequences)
   {
     TRACE_SERIALIZE (this);
     if (unlikely (!Lookup::serialize (c, SubTable::Multiple, lookup_props, 1))) return_trace (false);
     if (c->push<SubTable> ()->u.multiple.
         serialize (c,
-                   glyphs,
-                   substitute_len_list,
-                   substitute_glyphs_list))
+		   glyphs,
+		   sequences))
     {
       c->add_link (get_subtables<SubTable> ()[0], c->pop_pack ());
       return_trace (true);