[repacker] for ext promotion choose lookups from highest subtables per byte to lowest.

Attempts to roughly maximize the number of subtables that are non-ext.

src/Makefile.sources

@@ -348,6 +348,8 @@ HB_SUBSET_sources = \
 	hb-subset.hh \
 	hb-repacker.hh \
 	graph/graph.hh \
+	graph/gsubgpos-graph.hh \
+	graph/gsubgpos-graph.cc \
 	graph/serialize.hh \
 	$(NULL)
 

src/graph/graph.hh

@@ -24,6 +24,10 @@
  * Google Author(s): Garret Rieger
  */
 
+#include "hb-set.hh"
+#include "hb-priority-queue.hh"
+#include "hb-serialize.hh"
+
 #ifndef GRAPH_GRAPH_HH
 #define GRAPH_GRAPH_HH
 
@@ -107,6 +111,10 @@ struct graph_t
       return priority >= 3;
     }
 
+    size_t table_size () const {
+      return obj.tail - obj.head;
+    }
+
     int64_t modified_distance (unsigned order) const
     {
       // TODO(garretrieger): once priority is high enough, should try
@@ -199,7 +207,7 @@ struct graph_t
     return vertices_.length - 1;
   }
 
-  const hb_serialize_context_t::object_t& object(unsigned i) const
+  const hb_serialize_context_t::object_t& object (unsigned i) const
   {
     return vertices_[i].obj;
   }
@@ -310,6 +318,22 @@ struct graph_t
     }
   }
 
+  unsigned index_for_offset(unsigned node_idx, const void* offset) const
+  {
+    const auto& node = object (node_idx);
+    if (offset < node.head || offset >= node.tail) return -1;
+
+    for (const auto& link : node.real_links)
+    {
+      if (offset != node.head + link.position)
+        continue;
+      return link.objidx;
+    }
+
+    return -1;
+  }
+
+
   /*
    * Assign unique space numbers to each connected subgraph of 24 bit and/or 32 bit offset(s).
    * Currently, this is implemented specifically tailored to the structure of a GPOS/GSUB
@@ -317,6 +341,8 @@ struct graph_t
    */
   bool assign_spaces ()
   {
+    update_parents ();
+
     hb_set_t visited;
     hb_set_t roots;
     find_space_roots (visited, roots);
@@ -458,6 +484,21 @@ struct graph_t
       find_subgraph (link.objidx, subgraph);
   }
 
+  size_t find_subgraph_size (unsigned node_idx, hb_set_t& subgraph, unsigned max_depth = -1)
+  {
+    if (subgraph.has (node_idx)) return 0;
+    subgraph.add (node_idx);
+
+    const auto& o = vertices_[node_idx].obj;
+    size_t size = o.tail - o.head;
+    if (max_depth == 0)
+      return size;
+
+    for (const auto& link : o.all_links ())
+      size += find_subgraph_size (link.objidx, subgraph, max_depth - 1);
+    return size;
+  }
+
   /*
    * Finds the topmost children of 32bit offsets in the subgraph starting
    * at node_idx. Found indices are placed into 'found'.
@@ -581,6 +622,39 @@ struct graph_t
     return true;
   }
 
+
+  /*
+   * Adds a new node to the graph, not connected to anything.
+   */
+  unsigned new_node (char* head, char* tail)
+  {
+    positions_invalid = true;
+    distance_invalid = true;
+
+    auto* clone = vertices_.push ();
+    if (vertices_.in_error ()) {
+      return -1;
+    }
+
+    clone->obj.head = head;
+    clone->obj.tail = tail;
+    clone->distance = 0;
+    clone->space = 0;
+
+    unsigned clone_idx = vertices_.length - 2;
+
+    // The last object is the root of the graph, so swap back the root to the end.
+    // The root's obj idx does change, however since it's root nothing else refers to it.
+    // all other obj idx's will be unaffected.
+    hb_swap (vertices_[vertices_.length - 2], *clone);
+
+    // Since the root moved, update the parents arrays of all children on the root.
+    for (const auto& l : root ().obj.all_links ())
+      vertices_[l.objidx].remap_parent (root_idx () - 1, root_idx ());
+
+    return clone_idx;
+  }
+
   /*
    * Raises the sorting priority of all children.
    */

src/graph/gsubgpos-graph.cc

@@ -0,0 +1,60 @@
+/*
+ * Copyright © 2022  Google, Inc.
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ * Google Author(s): Garret Rieger
+ */
+
+#include "gsubgpos-graph.hh"
+
+namespace graph {
+
+make_extension_context_t::make_extension_context_t (hb_tag_t table_tag_,
+                                                    graph_t& graph_,
+                                                    hb_vector_t<char>& buffer_)
+    : table_tag (table_tag_),
+      graph (graph_),
+      buffer (buffer_),
+      lookup_list_index (0),
+      lookups ()
+{
+  GSTAR* gstar = graph::GSTAR::graph_to_gstar (graph_);
+  if (gstar) {
+    gstar->find_lookups (graph, lookups);
+    lookup_list_index = gstar->get_lookup_list_index (graph_);
+  }
+
+  unsigned extension_size = OT::ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>::static_size;
+  buffer.alloc (num_non_ext_subtables () * extension_size);
+}
+
+unsigned make_extension_context_t::num_non_ext_subtables ()  {
+  unsigned count = 0;
+  for (auto l : lookups.values ())
+  {
+    if (l->is_extension (table_tag)) continue;
+    count += l->number_of_subtables ();
+  }
+  return count;
+}
+
+}

src/graph/gsubgpos-graph.hh

@@ -0,0 +1,260 @@
+/*
+ * Copyright © 2022  Google, Inc.
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ * Google Author(s): Garret Rieger
+ */
+
+#include "graph.hh"
+#include "hb-ot-layout-gsubgpos.hh"
+#include "OT/Layout/GSUB/ExtensionSubst.hh"
+
+#ifndef GRAPH_GSUBGPOS_GRAPH_HH
+#define GRAPH_GSUBGPOS_GRAPH_HH
+
+namespace graph {
+
+struct Lookup;
+
+struct make_extension_context_t
+{
+  hb_tag_t table_tag;
+  graph_t& graph;
+  hb_vector_t<char>& buffer;
+  unsigned lookup_list_index;
+  hb_hashmap_t<unsigned, graph::Lookup*> lookups;
+
+  HB_INTERNAL make_extension_context_t (hb_tag_t table_tag_,
+                                        graph_t& graph_,
+                                        hb_vector_t<char>& buffer_);
+
+  bool in_error () const
+  {
+    return buffer.in_error ();
+  }
+
+ private:
+  HB_INTERNAL unsigned num_non_ext_subtables ();
+};
+
+template<typename T>
+struct ExtensionFormat1 : public OT::ExtensionFormat1<T>
+{
+  void reset(unsigned type)
+  {
+    this->format = 1;
+    this->extensionLookupType = type;
+    this->extensionOffset = 0;
+  }
+};
+
+struct Lookup : public OT::Lookup
+{
+  unsigned number_of_subtables () const
+  {
+    return subTable.len;
+  }
+
+  bool sanitize (graph_t::vertex_t& vertex) const
+  {
+    int64_t vertex_len = vertex.obj.tail - vertex.obj.head;
+    if (vertex_len < OT::Lookup::min_size) return false;
+    return vertex_len >= this->get_size ();
+  }
+
+  bool is_extension (hb_tag_t table_tag) const
+  {
+    return lookupType == extension_type (table_tag);
+  }
+
+  bool make_extension (make_extension_context_t& c,
+                       unsigned this_index)
+  {
+    unsigned type = lookupType;
+    unsigned ext_type = extension_type (c.table_tag);
+    if (!ext_type || is_extension (c.table_tag))
+    {
+      // NOOP
+      return true;
+    }
+
+    DEBUG_MSG (SUBSET_REPACK, nullptr,
+               "Promoting lookup type %u (obj %u) to extension.",
+               type,
+               this_index);
+
+    for (unsigned i = 0; i < subTable.len; i++)
+    {
+      unsigned subtable_index = c.graph.index_for_offset (this_index, &subTable[i]);
+      if (!make_subtable_extension (c,
+                                    this_index,
+                                    subtable_index))
+        return false;
+    }
+
+    lookupType = ext_type;
+    return true;
+  }
+
+  bool make_subtable_extension (make_extension_context_t& c,
+                                unsigned lookup_index,
+                                unsigned subtable_index)
+  {
+    unsigned type = lookupType;
+    unsigned extension_size = OT::ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>::static_size;
+    unsigned start = c.buffer.length;
+    unsigned end = start + extension_size;
+    if (!c.buffer.resize (c.buffer.length + extension_size))
+      return false;
+
+    ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>* extension =
+        (ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>*) &c.buffer[start];
+    extension->reset (type);
+
+    unsigned ext_index = c.graph.new_node (&c.buffer.arrayZ[start],
+                                           &c.buffer.arrayZ[end]);
+    if (ext_index == (unsigned) -1) return false;
+
+    auto& lookup_vertex = c.graph.vertices_[lookup_index];
+    for (auto& l : lookup_vertex.obj.real_links.writer ())
+    {
+      if (l.objidx == subtable_index)
+        // Change lookup to point at the extension.
+        l.objidx = ext_index;
+    }
+
+    // Make extension point at the subtable.
+    auto& ext_vertex = c.graph.vertices_[ext_index];
+    auto& subtable_vertex = c.graph.vertices_[subtable_index];
+    auto* l = ext_vertex.obj.real_links.push ();
+
+    l->width = 4;
+    l->objidx = subtable_index;
+    l->is_signed = 0;
+    l->whence = 0;
+    l->position = 4;
+    l->bias = 0;
+
+    ext_vertex.parents.push (lookup_index);
+    subtable_vertex.remap_parent (lookup_index, ext_index);
+
+    return true;
+  }
+
+ private:
+  unsigned extension_type (hb_tag_t table_tag) const
+  {
+    switch (table_tag)
+    {
+    case HB_OT_TAG_GPOS: return 9;
+    case HB_OT_TAG_GSUB: return 7;
+    default: return 0;
+    }
+  }
+};
+
+template <typename T>
+struct LookupList : public OT::LookupList<T>
+{
+  bool sanitize (const graph_t::vertex_t& vertex) const
+  {
+    int64_t vertex_len = vertex.obj.tail - vertex.obj.head;
+    if (vertex_len < OT::LookupList<T>::min_size) return false;
+    return vertex_len >= OT::LookupList<T>::item_size * this->len;
+  }
+};
+
+struct GSTAR : public OT::GSUBGPOS
+{
+  static GSTAR* graph_to_gstar (graph_t& graph)
+  {
+    const auto& r = graph.root ();
+
+    GSTAR* gstar = (GSTAR*) r.obj.head;
+    if (!gstar->sanitize (r))
+      return nullptr;
+
+    return gstar;
+  }
+
+  const void* get_lookup_list_field_offset () const
+  {
+    switch (u.version.major) {
+    case 1: return u.version1.get_lookup_list_offset ();
+#ifndef HB_NO_BORING_EXPANSION
+    case 2: return u.version2.get_lookup_list_offset ();
+#endif
+    default: return 0;
+    }
+  }
+
+  bool sanitize (const graph_t::vertex_t& vertex)
+  {
+    int64_t len = vertex.obj.tail - vertex.obj.head;
+    if (len < OT::GSUBGPOS::min_size) return false;
+    return len >= get_size ();
+  }
+
+  void find_lookups (graph_t& graph,
+                     hb_hashmap_t<unsigned, Lookup*>& lookups /* OUT */)
+  {
+    switch (u.version.major) {
+      case 1: find_lookups<SmallTypes> (graph, lookups); break;
+#ifndef HB_NO_BORING_EXPANSION
+      case 2: find_lookups<MediumTypes> (graph, lookups); break;
+#endif
+    }
+  }
+
+  unsigned get_lookup_list_index (graph_t& graph)
+  {
+    return graph.index_for_offset (graph.root_idx (),
+                                   get_lookup_list_field_offset());
+  }
+
+  template<typename Types>
+  void find_lookups (graph_t& graph,
+                     hb_hashmap_t<unsigned, Lookup*>& lookups /* OUT */)
+  {
+    unsigned lookup_list_idx = get_lookup_list_index (graph);
+
+    const LookupList<Types>* lookupList =
+        (const LookupList<Types>*) graph.object (lookup_list_idx).head;
+    if (!lookupList->sanitize (graph.vertices_[lookup_list_idx]))
+      return;
+
+    for (unsigned i = 0; i < lookupList->len; i++)
+    {
+      unsigned lookup_idx = graph.index_for_offset (lookup_list_idx, &(lookupList->arrayZ[i]));
+      Lookup* lookup = (Lookup*) graph.object (lookup_idx).head;
+      if (!lookup->sanitize (graph.vertices_[lookup_idx])) continue;
+      lookups.set (lookup_idx, lookup);
+    }
+  }
+};
+
+
+
+
+}
+
+#endif  /* GRAPH_GSUBGPOS_GRAPH_HH */

src/hb-ot-layout-common.hh

@@ -1337,7 +1337,7 @@ struct Lookup
     return_trace (true);
   }
 
-  private:
+  protected:
   HBUINT16	lookupType;		/* Different enumerations for GSUB and GPOS */
   HBUINT16	lookupFlag;		/* Lookup qualifiers */
   Array16Of<Offset16>

src/hb-ot-layout-gsubgpos.hh

@@ -4011,6 +4011,11 @@ struct GSUBGPOSVersion1_2
 	   (version.to_int () >= 0x00010001u ? featureVars.static_size : 0);
   }
 
+  const typename Types::template OffsetTo<LookupList<Types>>* get_lookup_list_offset () const
+  {
+    return &lookupList;
+  }
+
   template <typename TLookup>
   bool sanitize (hb_sanitize_context_t *c) const
   {

src/hb-repacker.hh

@@ -29,10 +29,9 @@
 
 #include "hb-open-type.hh"
 #include "hb-map.hh"
-#include "hb-priority-queue.hh"
-#include "hb-serialize.hh"
 #include "hb-vector.hh"
 #include "graph/graph.hh"
+#include "graph/gsubgpos-graph.hh"
 #include "graph/serialize.hh"
 
 using graph::graph_t;
@@ -42,6 +41,124 @@ using graph::graph_t;
  * docs/repacker.md
  */
 
+struct lookup_size_t
+{
+  unsigned lookup_index;
+  size_t size;
+  unsigned num_subtables;
+};
+
+inline int compare_sizes (const void* a, const void* b)
+{
+  lookup_size_t* size_a = (lookup_size_t*) a;
+  lookup_size_t* size_b = (lookup_size_t*) b;
+
+  double subtables_per_byte_a = (double) size_a->num_subtables / (double) size_a->size;
+  double subtables_per_byte_b = (double) size_b->num_subtables / (double) size_b->size;
+
+  if (subtables_per_byte_a == subtables_per_byte_b) {
+    return size_b->lookup_index - size_b->lookup_index;
+
+  }
+  double cmp = subtables_per_byte_b - subtables_per_byte_a;
+  if (cmp < 0) return -1;
+  if (cmp > 0) return 1;
+  return 0;
+}
+
+/*
+ * Analyze the lookups in a GSUB/GPOS table and decide if any should be promoted
+ * to extension lookups.
+ */
+static inline
+bool _promote_extensions_if_needed (graph::make_extension_context_t& ext_context)
+{
+  // Simple Algorithm (v1, current):
+  // 1. Calculate how many bytes each non-extension lookup consumes.
+  // 2. Select up to 64k of those to remain as non-extension (greedy, smallest first).
+  // 3. Promote the rest.
+  //
+  // Advanced Algorithm (v2, not implemented):
+  // 1. Perform connected component analysis using lookups as roots.
+  // 2. Compute size of each connected component.
+  // 3. Select up to 64k worth of connected components to remain as non-extensions.
+  //    (greedy, smallest first)
+  // 4. Promote the rest.
+
+  // TODO(garretrieger): support extension demotion, then consider all lookups. Requires advanced algo.
+  // TODO(garretrieger): also support extension promotion during iterative resolution phase, then
+  //                     we can use a less conservative threshold here.
+  // TODO(grieger): skip this for the 24 bit case.
+  // TODO(grieger): sort by # subtables / size instead (high to low). Goal is to get as many subtables
+  //                as possible into  space 0 to minimize the number of extension subtables added.
+  //                A fully optimal solution will require a backpack problem dynamic programming type
+  //                solution.
+  if (!ext_context.lookups) return true;
+
+  hb_vector_t<lookup_size_t> lookup_sizes;
+  lookup_sizes.alloc (ext_context.lookups.get_population ());
+
+  for (unsigned lookup_index : ext_context.lookups.keys ())
+  {
+    const graph::Lookup* lookup = ext_context.lookups.get(lookup_index);
+    hb_set_t visited;
+    lookup_sizes.push (lookup_size_t {
+        lookup_index,
+        ext_context.graph.find_subgraph_size (lookup_index, visited),
+        lookup->number_of_subtables (),
+      });
+  }
+
+  lookup_sizes.qsort (compare_sizes);
+
+  size_t lookup_list_size = ext_context.graph.vertices_[ext_context.lookup_list_index].table_size ();
+  size_t l2_l3_size = lookup_list_size; // Lookup List + Lookups
+  size_t l3_l4_size = 0; // Lookups + SubTables
+  size_t l4_plus_size = 0; // SubTables + their descendants
+
+  // Start by assuming all lookups are using extension subtables, this size will be removed later
+  // if it's decided to not make a lookup extension.
+  for (auto p : lookup_sizes)
+  {
+    unsigned subtables_size = p.num_subtables * 8;
+    l3_l4_size += subtables_size;
+    l4_plus_size += subtables_size;
+  }
+
+  bool layers_full = false;
+  for (auto p : lookup_sizes)
+  {
+    const graph::Lookup* lookup = ext_context.lookups.get(p.lookup_index);
+    if (lookup->is_extension (ext_context.table_tag))
+      // already an extension so size is counted by the loop above.
+      continue;
+
+    if (!layers_full)
+    {
+      size_t lookup_size = ext_context.graph.vertices_[p.lookup_index].table_size ();
+      hb_set_t visited;
+      size_t subtables_size = ext_context.graph.find_subgraph_size (p.lookup_index, visited, 1) - lookup_size;
+      size_t remaining_size = p.size - subtables_size - lookup_size;
+
+      l2_l3_size   += lookup_size;
+      l3_l4_size   += lookup_size + subtables_size;
+      l3_l4_size   -= p.num_subtables * 8;
+      l4_plus_size += subtables_size + remaining_size;
+
+      if (l2_l3_size < (1 << 16)
+          && l3_l4_size < (1 << 16)
+          && l4_plus_size < (1 << 16)) continue; // this lookup fits within all layers groups
+
+      layers_full = true;
+    }
+
+    if (!ext_context.lookups.get(p.lookup_index)->make_extension (ext_context, p.lookup_index))
+      return false;
+  }
+
+  return true;
+}
+
 static inline
 bool _try_isolating_subgraphs (const hb_vector_t<graph::overflow_record_t>& overflows,
                                graph_t& sorted_graph)
@@ -157,7 +274,8 @@ template<typename T>
 inline hb_blob_t*
 hb_resolve_overflows (const T& packed,
                       hb_tag_t table_tag,
-                      unsigned max_rounds = 20) {
+                      unsigned max_rounds = 20,
+                      bool recalculate_extensions = false) {
   graph_t sorted_graph (packed);
   sorted_graph.sort_shortest_distance ();
 
@@ -167,10 +285,24 @@ hb_resolve_overflows (const T& packed,
     return graph::serialize (sorted_graph);
   }
 
+  hb_vector_t<char> extension_buffer; // Needs to live until serialization is done.
+
   if ((table_tag == HB_OT_TAG_GPOS
        ||  table_tag == HB_OT_TAG_GSUB)
       && will_overflow)
   {
+    if (recalculate_extensions)
+    {
+      graph::make_extension_context_t ext_context (table_tag, sorted_graph, extension_buffer);
+      if (ext_context.in_error ())
+        return nullptr;
+
+      if (!_promote_extensions_if_needed (ext_context)) {
+        DEBUG_MSG (SUBSET_REPACK, nullptr, "Extensions promotion failed.");
+        return nullptr;
+      }
+    }
+
     DEBUG_MSG (SUBSET_REPACK, nullptr, "Assigning spaces to 32 bit subgraphs.");
     if (sorted_graph.assign_spaces ())
       sorted_graph.sort_shortest_distance ();

src/hb-subset-repacker.cc

@@ -44,6 +44,9 @@ hb_blob_t* hb_subset_repack_or_fail (hb_object_t* hb_objects, unsigned num_hb_ob
   for (unsigned i = 0 ; i < num_hb_objs ; i++)
     packed.push (&(hb_objects[i]));
 
-  return hb_resolve_overflows (packed, HB_OT_TAG_GSUB);
+  return hb_resolve_overflows (packed,
+                               HB_OT_TAG_GSUB,
+                               20,
+                               true);
 }
 #endif

src/meson.build

@@ -345,6 +345,7 @@ hb_subset_sources = files(
   'hb-subset-plan.cc',
   'hb-subset-plan.hh',
   'hb-subset-repacker.cc',
+  'graph/gsubgpos-graph.cc',
   'hb-subset.cc',
   'hb-subset.hh',
 )
@@ -565,7 +566,7 @@ if get_option('tests').enabled()
     'test-number': ['test-number.cc', 'hb-number.cc'],
     'test-ot-tag': ['hb-ot-tag.cc'],
     'test-priority-queue': ['test-priority-queue.cc', 'hb-static.cc'],
-    'test-repacker': ['test-repacker.cc', 'hb-static.cc'],
+    'test-repacker': ['test-repacker.cc', 'hb-static.cc', 'graph/gsubgpos-graph.cc'],
     'test-set': ['test-set.cc', 'hb-static.cc'],
     'test-serialize': ['test-serialize.cc', 'hb-static.cc'],
     'test-unicode-ranges': ['test-unicode-ranges.cc'],

src/test-repacker.cc

@@ -30,16 +30,22 @@
 #include "hb-open-type.hh"
 #include "graph/serialize.hh"
 
+static void extend (const char* value,
+                    unsigned len,
+                    hb_serialize_context_t* c)
+{
+  char* obj = c->allocate_size<char> (len);
+  memcpy (obj, value, len);
+}
+
 static void start_object(const char* tag,
                          unsigned len,
                          hb_serialize_context_t* c)
 {
   c->push ();
-  char* obj = c->allocate_size<char> (len);
-  strncpy (obj, tag, len);
+  extend (tag, len, c);
 }
 
-
 static unsigned add_object(const char* tag,
                            unsigned len,
                            hb_serialize_context_t* c)
@@ -76,7 +82,8 @@ static void add_wide_offset (unsigned id,
 static void run_resolve_overflow_test (const char* name,
                                        hb_serialize_context_t& overflowing,
                                        hb_serialize_context_t& expected,
-                                       unsigned num_iterations = 0)
+                                       unsigned num_iterations = 0,
+                                       bool recalculate_extensions = false)
 {
   printf (">>> Testing overflowing resolution for %s\n",
           name);
@@ -86,7 +93,9 @@ static void run_resolve_overflow_test (const char* name,
 
   assert (overflowing.offset_overflow ());
   hb_blob_t* out = hb_resolve_overflows (overflowing.object_graph (),
-                                         HB_TAG ('G', 'S', 'U', 'B'), num_iterations);
+                                         HB_TAG ('G', 'S', 'U', 'B'),
+                                         num_iterations,
+                                         recalculate_extensions);
   assert (out);
 
   hb_bytes_t result = out->as_bytes ();
@@ -95,11 +104,21 @@ static void run_resolve_overflow_test (const char* name,
   hb_bytes_t expected_result = expected.copy_bytes ();
 
   assert (result.length == expected_result.length);
+
+  bool equal = true;
   for (unsigned i = 0; i < expected_result.length; i++)
   {
-    assert (result[i] == expected_result[i]);
+    if (result[i] != expected_result[i])
+    {
+      equal = false;
+      uint8_t a = result[i];
+      uint8_t b = expected_result[i];
+      printf("%08u: %x != %x\n", i, a, b);
+    }
   }
 
+  assert (equal);
+
   expected_result.fini ();
   hb_blob_destroy (out);
 }
@@ -865,6 +884,89 @@ populate_serializer_with_24_and_32_bit_offsets (hb_serialize_context_t* c)
   c->end_serialize();
 }
 
+
+static void
+populate_serializer_with_extension_promotion (hb_serialize_context_t* c,
+                                              int num_extensions = 0)
+{
+  constexpr int num_lookups = 5;
+  constexpr int num_subtables = num_lookups * 2;
+  unsigned int lookups[num_lookups];
+  unsigned int subtables[num_subtables];
+  unsigned int extensions[num_subtables];
+
+  std::string large_string(60000, 'a');
+  c->start_serialize<char> ();
+
+
+  for (int i = num_subtables - 1; i >= 0; i--)
+    subtables[i] = add_object(large_string.c_str (), 15000, c);
+
+  for (int i = num_subtables - 1;
+       i >= (num_lookups - num_extensions) * 2;
+       i--)
+  {
+    char ext[] = {
+      0, 1,
+      0, 5
+    };
+
+    unsigned ext_index = i - (num_lookups - num_extensions) * 2; // 5
+    unsigned subtable_index = num_subtables - ext_index - 1; // 10 - 5 - 1 = 4
+
+    start_object (ext, 4, c);
+    add_wide_offset (subtables[subtable_index], c);
+
+    extensions[i] = c->pop_pack (false);
+  }
+
+  for (int i = num_lookups - 1; i >= 0; i--)
+  {
+    bool is_ext = (i >= (num_lookups - num_extensions));
+
+    char lookup[] = {
+      0, is_ext ? (char) 7 : (char) 5, // type
+      0, 0, // flag
+      0, 2, // num subtables
+    };
+
+    start_object (lookup, 6, c);
+    if (is_ext) {
+      add_offset (extensions[i * 2], c);
+      add_offset (extensions[i * 2 + 1], c);
+    } else {
+      add_offset (subtables[i * 2], c);
+      add_offset (subtables[i * 2 + 1], c);
+    }
+
+    char filter[] = {0, 0};
+    extend (filter, 2, c);
+
+    lookups[i] = c->pop_pack (false);
+  }
+
+  char lookup_count[] = {0, num_lookups};
+  start_object  ((char *) &lookup_count, 2, c);
+
+  for (int i = 0; i < num_lookups; i++)
+    add_offset (lookups[i], c);
+
+  unsigned lookup_list = c->pop_pack (false);
+
+  char gsub_header[] = {
+    0, 1, // major
+    0, 0, // minor
+    0, 0, // script list
+    0, 0, // feature list
+  };
+
+  start_object (gsub_header, 8, c);
+  add_offset (lookup_list, c);
+  c->pop_pack (false);
+
+  c->end_serialize();
+}
+
 static void test_sort_shortest ()
 {
   size_t buffer_size = 100;
@@ -1212,6 +1314,28 @@ static void test_resolve_mixed_overflows_via_isolation_spaces ()
   hb_blob_destroy (out);
 }
 
+static void test_resolve_with_extension_promotion ()
+{
+  size_t buffer_size = 200000;
+  void* buffer = malloc (buffer_size);
+  assert (buffer);
+  hb_serialize_context_t c (buffer, buffer_size);
+  populate_serializer_with_extension_promotion (&c);
+
+  void* expected_buffer = malloc (buffer_size);
+  assert (expected_buffer);
+  hb_serialize_context_t e (expected_buffer, buffer_size);
+  populate_serializer_with_extension_promotion (&e, 3);
+
+  run_resolve_overflow_test ("test_resolve_with_extension_promotion",
+                             c,
+                             e,
+                             20,
+                             true);
+  free (buffer);
+  free (expected_buffer);
+}
+
 static void test_resolve_overflows_via_splitting_spaces ()
 {
   size_t buffer_size = 160000;
@@ -1358,4 +1482,8 @@ main (int argc, char **argv)
   test_duplicate_interior ();
   test_virtual_link ();
   test_shared_node_with_virtual_links ();
+  test_resolve_with_extension_promotion ();
+  // TODO(grieger): test with extensions already mixed in as well.
+  // TODO(grieger): test two layer ext promotion setup.
+  // TODO(grieger): test sorting by subtables per byte in ext. promotion.
 }