HarfBuzz: Update to version 4.4.1

1 files changed, 19 insertions, 1035 deletions

diff --git a/thirdparty/harfbuzz/src/hb-repacker.hh b/thirdparty/harfbuzz/src/hb-repacker.hh
index ce9ff90bb4..683a441ec3 100644
--- a/thirdparty/harfbuzz/src/hb-repacker.hh
+++ b/thirdparty/harfbuzz/src/hb-repacker.hh
@@ -32,1033 +32,18 @@
 #include "hb-priority-queue.hh"
 #include "hb-serialize.hh"
 #include "hb-vector.hh"
+#include "graph/graph.hh"
+#include "graph/serialize.hh"
+
+using graph::graph_t;
 
 /*
  * For a detailed writeup on the overflow resolution algorithm see:
  * docs/repacker.md
  */
-struct graph_t
-{
-  struct vertex_t
-  {
-    hb_serialize_context_t::object_t obj;
-    int64_t distance = 0 ;
-    int64_t space = 0 ;
-    hb_vector_t<unsigned> parents;
-    unsigned start = 0;
-    unsigned end = 0;
-    unsigned priority = 0;
-
-    friend void swap (vertex_t& a, vertex_t& b)
-    {
-      hb_swap (a.obj, b.obj);
-      hb_swap (a.distance, b.distance);
-      hb_swap (a.space, b.space);
-      hb_swap (a.parents, b.parents);
-      hb_swap (a.start, b.start);
-      hb_swap (a.end, b.end);
-      hb_swap (a.priority, b.priority);
-    }
-
-    bool is_shared () const
-    {
-      return parents.length > 1;
-    }
-
-    unsigned incoming_edges () const
-    {
-      return parents.length;
-    }
-
-    void remove_parent (unsigned parent_index)
-    {
-      for (unsigned i = 0; i < parents.length; i++)
-      {
-        if (parents[i] != parent_index) continue;
-        parents.remove (i);
-        break;
-      }
-    }
-
-    void remap_parents (const hb_vector_t<unsigned>& id_map)
-    {
-      for (unsigned i = 0; i < parents.length; i++)
-        parents[i] = id_map[parents[i]];
-    }
-
-    void remap_parent (unsigned old_index, unsigned new_index)
-    {
-      for (unsigned i = 0; i < parents.length; i++)
-      {
-        if (parents[i] == old_index)
-          parents[i] = new_index;
-      }
-    }
-
-    bool is_leaf () const
-    {
-      return !obj.real_links.length && !obj.virtual_links.length;
-    }
-
-    bool raise_priority ()
-    {
-      if (has_max_priority ()) return false;
-      priority++;
-      return true;
-    }
-
-    bool has_max_priority () const {
-      return priority >= 3;
-    }
-
-    int64_t modified_distance (unsigned order) const
-    {
-      // TODO(garretrieger): once priority is high enough, should try
-      // setting distance = 0 which will force to sort immediately after
-      // it's parent where possible.
-
-      int64_t modified_distance =
-          hb_min (hb_max(distance + distance_modifier (), 0), 0x7FFFFFFFFFF);
-      if (has_max_priority ()) {
-        modified_distance = 0;
-      }
-      return (modified_distance << 18) | (0x003FFFF & order);
-    }
-
-    int64_t distance_modifier () const
-    {
-      if (!priority) return 0;
-      int64_t table_size = obj.tail - obj.head;
-
-      if (priority == 1)
-        return -table_size / 2;
-
-      return -table_size;
-    }
-  };
-
-  struct overflow_record_t
-  {
-    unsigned parent;
-    unsigned child;
-  };
-
-  /*
-   * A topological sorting of an object graph. Ordered
-   * in reverse serialization order (first object in the
-   * serialization is at the end of the list). This matches
-   * the 'packed' object stack used internally in the
-   * serializer
-   */
-  template<typename T>
-  graph_t (const T& objects)
-      : parents_invalid (true),
-        distance_invalid (true),
-        positions_invalid (true),
-        successful (true)
-  {
-    num_roots_for_space_.push (1);
-    bool removed_nil = false;
-    vertices_.alloc (objects.length);
-    vertices_scratch_.alloc (objects.length);
-    for (unsigned i = 0; i < objects.length; i++)
-    {
-      // TODO(grieger): check all links point to valid objects.
-
-      // If this graph came from a serialization buffer object 0 is the
-      // nil object. We don't need it for our purposes here so drop it.
-      if (i == 0 && !objects[i])
-      {
-        removed_nil = true;
-        continue;
-      }
-
-      vertex_t* v = vertices_.push ();
-      if (check_success (!vertices_.in_error ()))
-        v->obj = *objects[i];
-      if (!removed_nil) continue;
-      // Fix indices to account for removed nil object.
-      for (auto& l : v->obj.all_links_writer ()) {
-        l.objidx--;
-      }
-    }
-  }
-
-  ~graph_t ()
-  {
-    vertices_.fini ();
-  }
-
-  bool in_error () const
-  {
-    return !successful ||
-        vertices_.in_error () ||
-        num_roots_for_space_.in_error ();
-  }
-
-  const vertex_t& root () const
-  {
-    return vertices_[root_idx ()];
-  }
-
-  unsigned root_idx () const
-  {
-    // Object graphs are in reverse order, the first object is at the end
-    // of the vector. Since the graph is topologically sorted it's safe to
-    // assume the first object has no incoming edges.
-    return vertices_.length - 1;
-  }
-
-  const hb_serialize_context_t::object_t& object(unsigned i) const
-  {
-    return vertices_[i].obj;
-  }
-
-  /*
-   * serialize graph into the provided serialization buffer.
-   */
-  hb_blob_t* serialize () const
-  {
-    hb_vector_t<char> buffer;
-    size_t size = serialized_length ();
-    if (!buffer.alloc (size)) {
-      DEBUG_MSG (SUBSET_REPACK, nullptr, "Unable to allocate output buffer.");
-      return nullptr;
-    }
-    hb_serialize_context_t c((void *) buffer, size);
-
-    c.start_serialize<void> ();
-    for (unsigned i = 0; i < vertices_.length; i++) {
-      c.push ();
-
-      size_t size = vertices_[i].obj.tail - vertices_[i].obj.head;
-      char* start = c.allocate_size <char> (size);
-      if (!start) {
-        DEBUG_MSG (SUBSET_REPACK, nullptr, "Buffer out of space.");
-        return nullptr;
-      }
-
-      memcpy (start, vertices_[i].obj.head, size);
-
-      // Only real links needs to be serialized.
-      for (const auto& link : vertices_[i].obj.real_links)
-        serialize_link (link, start, &c);
-
-      // All duplications are already encoded in the graph, so don't
-      // enable sharing during packing.
-      c.pop_pack (false);
-    }
-    c.end_serialize ();
-
-    if (c.in_error ()) {
-      DEBUG_MSG (SUBSET_REPACK, nullptr, "Error during serialization. Err flag: %d",
-                 c.errors);
-      return nullptr;
-    }
-
-    return c.copy_blob ();
-  }
-
-  /*
-   * Generates a new topological sorting of graph ordered by the shortest
-   * distance to each node.
-   */
-  void sort_shortest_distance ()
-  {
-    positions_invalid = true;
-
-    if (vertices_.length <= 1) {
-      // Graph of 1 or less doesn't need sorting.
-      return;
-    }
-
-    update_distances ();
-
-    hb_priority_queue_t queue;
-    hb_vector_t<vertex_t> &sorted_graph = vertices_scratch_;
-    if (unlikely (!check_success (sorted_graph.resize (vertices_.length)))) return;
-    hb_vector_t<unsigned> id_map;
-    if (unlikely (!check_success (id_map.resize (vertices_.length)))) return;
-
-    hb_vector_t<unsigned> removed_edges;
-    if (unlikely (!check_success (removed_edges.resize (vertices_.length)))) return;
-    update_parents ();
-
-    queue.insert (root ().modified_distance (0), root_idx ());
-    int new_id = root_idx ();
-    unsigned order = 1;
-    while (!queue.in_error () && !queue.is_empty ())
-    {
-      unsigned next_id = queue.pop_minimum().second;
-
-      hb_swap (sorted_graph[new_id], vertices_[next_id]);
-      const vertex_t& next = sorted_graph[new_id];
-
-      id_map[next_id] = new_id--;
-
-      for (const auto& link : next.obj.all_links ()) {
-        removed_edges[link.objidx]++;
-        if (!(vertices_[link.objidx].incoming_edges () - removed_edges[link.objidx]))
-          // Add the order that the links were encountered to the priority.
-          // This ensures that ties between priorities objects are broken in a consistent
-          // way. More specifically this is set up so that if a set of objects have the same
-          // distance they'll be added to the topological order in the order that they are
-          // referenced from the parent object.
-          queue.insert (vertices_[link.objidx].modified_distance (order++),
-                        link.objidx);
-      }
-    }
-
-    check_success (!queue.in_error ());
-    check_success (!sorted_graph.in_error ());
-    if (!check_success (new_id == -1))
-      print_orphaned_nodes ();
-
-    remap_all_obj_indices (id_map, &sorted_graph);
-
-    hb_swap (vertices_, sorted_graph);
-  }
-
-  /*
-   * Assign unique space numbers to each connected subgraph of 32 bit offset(s).
-   */
-  bool assign_32bit_spaces ()
-  {
-    unsigned root_index = root_idx ();
-    hb_set_t visited;
-    hb_set_t roots;
-    for (unsigned i = 0; i <= root_index; i++)
-    {
-      // Only real links can form 32 bit spaces
-      for (auto& l : vertices_[i].obj.real_links)
-      {
-        if (l.width == 4 && !l.is_signed)
-        {
-          roots.add (l.objidx);
-          find_subgraph (l.objidx, visited);
-        }
-      }
-    }
-
-    // Mark everything not in the subgraphs of 32 bit roots as visited.
-    // This prevents 32 bit subgraphs from being connected via nodes not in the 32 bit subgraphs.
-    visited.invert ();
-
-    if (!roots) return false;
-
-    while (roots)
-    {
-      unsigned next = HB_SET_VALUE_INVALID;
-      if (unlikely (!check_success (!roots.in_error ()))) break;
-      if (!roots.next (&next)) break;
-
-      hb_set_t connected_roots;
-      find_connected_nodes (next, roots, visited, connected_roots);
-      if (unlikely (!check_success (!connected_roots.in_error ()))) break;
-
-      isolate_subgraph (connected_roots);
-      if (unlikely (!check_success (!connected_roots.in_error ()))) break;
-
-      unsigned next_space = this->next_space ();
-      num_roots_for_space_.push (0);
-      for (unsigned root : connected_roots)
-      {
-        DEBUG_MSG (SUBSET_REPACK, nullptr, "Subgraph %u gets space %u", root, next_space);
-        vertices_[root].space = next_space;
-        num_roots_for_space_[next_space] = num_roots_for_space_[next_space] + 1;
-        distance_invalid = true;
-        positions_invalid = true;
-      }
-
-      // TODO(grieger): special case for GSUB/GPOS use extension promotions to move 16 bit space
-      //                into the 32 bit space as needed, instead of using isolation.
-    }
-
-
-
-    return true;
-  }
-
-  /*
-   * Isolates the subgraph of nodes reachable from root. Any links to nodes in the subgraph
-   * that originate from outside of the subgraph will be removed by duplicating the linked to
-   * object.
-   *
-   * Indices stored in roots will be updated if any of the roots are duplicated to new indices.
-   */
-  bool isolate_subgraph (hb_set_t& roots)
-  {
-    update_parents ();
-    hb_hashmap_t<unsigned, unsigned> subgraph;
-
-    // incoming edges to root_idx should be all 32 bit in length so we don't need to de-dup these
-    // set the subgraph incoming edge count to match all of root_idx's incoming edges
-    hb_set_t parents;
-    for (unsigned root_idx : roots)
-    {
-      subgraph.set (root_idx, wide_parents (root_idx, parents));
-      find_subgraph (root_idx, subgraph);
-    }
-
-    unsigned original_root_idx = root_idx ();
-    hb_hashmap_t<unsigned, unsigned> index_map;
-    bool made_changes = false;
-    for (auto entry : subgraph.iter ())
-    {
-      const auto& node = vertices_[entry.first];
-      unsigned subgraph_incoming_edges = entry.second;
-
-      if (subgraph_incoming_edges < node.incoming_edges ())
-      {
-        // Only  de-dup objects with incoming links from outside the subgraph.
-        made_changes = true;
-        duplicate_subgraph (entry.first, index_map);
-      }
-    }
-
-    if (!made_changes)
-      return false;
-
-    if (original_root_idx != root_idx ()
-        && parents.has (original_root_idx))
-    {
-      // If the root idx has changed since parents was determined, update root idx in parents
-      parents.add (root_idx ());
-      parents.del (original_root_idx);
-    }
-
-    auto new_subgraph =
-        + subgraph.keys ()
-        | hb_map([&] (unsigned node_idx) {
-          if (index_map.has (node_idx)) return index_map[node_idx];
-          return node_idx;
-        })
-        ;
-
-    remap_obj_indices (index_map, new_subgraph);
-    remap_obj_indices (index_map, parents.iter (), true);
-
-    // Update roots set with new indices as needed.
-    unsigned next = HB_SET_VALUE_INVALID;
-    while (roots.next (&next))
-    {
-      if (index_map.has (next))
-      {
-        roots.del (next);
-        roots.add (index_map[next]);
-      }
-    }
-
-    return true;
-  }
-
-  void find_subgraph (unsigned node_idx, hb_hashmap_t<unsigned, unsigned>& subgraph)
-  {
-    for (const auto& link : vertices_[node_idx].obj.all_links ())
-    {
-      if (subgraph.has (link.objidx))
-      {
-        subgraph.set (link.objidx, subgraph[link.objidx] + 1);
-        continue;
-      }
-      subgraph.set (link.objidx, 1);
-      find_subgraph (link.objidx, subgraph);
-    }
-  }
-
-  void find_subgraph (unsigned node_idx, hb_set_t& subgraph)
-  {
-    if (subgraph.has (node_idx)) return;
-    subgraph.add (node_idx);
-    for (const auto& link : vertices_[node_idx].obj.all_links ())
-      find_subgraph (link.objidx, subgraph);
-  }
-
-  /*
-   * duplicates all nodes in the subgraph reachable from node_idx. Does not re-assign
-   * links. index_map is updated with mappings from old id to new id. If a duplication has already
-   * been performed for a given index, then it will be skipped.
-   */
-  void duplicate_subgraph (unsigned node_idx, hb_hashmap_t<unsigned, unsigned>& index_map)
-  {
-    if (index_map.has (node_idx))
-      return;
-
-    index_map.set (node_idx, duplicate (node_idx));
-    for (const auto& l : object (node_idx).all_links ()) {
-      duplicate_subgraph (l.objidx, index_map);
-    }
-  }
-
-  /*
-   * Creates a copy of node_idx and returns it's new index.
-   */
-  unsigned duplicate (unsigned node_idx)
-  {
-    positions_invalid = true;
-    distance_invalid = true;
-
-    auto* clone = vertices_.push ();
-    auto& child = vertices_[node_idx];
-    if (vertices_.in_error ()) {
-      return -1;
-    }
-
-    clone->obj.head = child.obj.head;
-    clone->obj.tail = child.obj.tail;
-    clone->distance = child.distance;
-    clone->space = child.space;
-    clone->parents.reset ();
-
-    unsigned clone_idx = vertices_.length - 2;
-    for (const auto& l : child.obj.real_links)
-    {
-      clone->obj.real_links.push (l);
-      vertices_[l.objidx].parents.push (clone_idx);
-    }
-    for (const auto& l : child.obj.virtual_links)
-    {
-      clone->obj.virtual_links.push (l);
-      vertices_[l.objidx].parents.push (clone_idx);
-    }
-
-    check_success (!clone->obj.real_links.in_error ());
-    check_success (!clone->obj.virtual_links.in_error ());
-
-    // 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;
-  }
-
-  /*
-   * Creates a copy of child and re-assigns the link from
-   * parent to the clone. The copy is a shallow copy, objects
-   * linked from child are not duplicated.
-   */
-  bool duplicate (unsigned parent_idx, unsigned child_idx)
-  {
-    update_parents ();
-
-    unsigned links_to_child = 0;
-    for (const auto& l : vertices_[parent_idx].obj.all_links ())
-    {
-      if (l.objidx == child_idx) links_to_child++;
-    }
-
-    if (vertices_[child_idx].incoming_edges () <= links_to_child)
-    {
-      // Can't duplicate this node, doing so would orphan the original one as all remaining links
-      // to child are from parent.
-      DEBUG_MSG (SUBSET_REPACK, nullptr, "  Not duplicating %d => %d",
-                 parent_idx, child_idx);
-      return false;
-    }
-
-    DEBUG_MSG (SUBSET_REPACK, nullptr, "  Duplicating %d => %d",
-               parent_idx, child_idx);
-
-    unsigned clone_idx = duplicate (child_idx);
-    if (clone_idx == (unsigned) -1) return false;
-    // duplicate shifts the root node idx, so if parent_idx was root update it.
-    if (parent_idx == clone_idx) parent_idx++;
-
-    auto& parent = vertices_[parent_idx];
-    for (auto& l : parent.obj.all_links_writer ())
-    {
-      if (l.objidx != child_idx)
-        continue;
-
-      reassign_link (l, parent_idx, clone_idx);
-    }
-
-    return true;
-  }
-
-  /*
-   * Raises the sorting priority of all children.
-   */
-  bool raise_childrens_priority (unsigned parent_idx)
-  {
-    DEBUG_MSG (SUBSET_REPACK, nullptr, "  Raising priority of all children of %d",
-               parent_idx);
-    // This operation doesn't change ordering until a sort is run, so no need
-    // to invalidate positions. It does not change graph structure so no need
-    // to update distances or edge counts.
-    auto& parent = vertices_[parent_idx].obj;
-    bool made_change = false;
-    for (auto& l : parent.all_links_writer ())
-      made_change |= vertices_[l.objidx].raise_priority ();
-    return made_change;
-  }
-
-  /*
-   * Will any offsets overflow on graph when it's serialized?
-   */
-  bool will_overflow (hb_vector_t<overflow_record_t>* overflows = nullptr)
-  {
-    if (overflows) overflows->resize (0);
-    update_positions ();
-
-    for (int parent_idx = vertices_.length - 1; parent_idx >= 0; parent_idx--)
-    {
-      // Don't need to check virtual links for overflow
-      for (const auto& link : vertices_[parent_idx].obj.real_links)
-      {
-        int64_t offset = compute_offset (parent_idx, link);
-        if (is_valid_offset (offset, link))
-          continue;
-
-        if (!overflows) return true;
-
-        overflow_record_t r;
-        r.parent = parent_idx;
-        r.child = link.objidx;
-        overflows->push (r);
-      }
-    }
-
-    if (!overflows) return false;
-    return overflows->length;
-  }
-
-  void print_orphaned_nodes ()
-  {
-    if (!DEBUG_ENABLED(SUBSET_REPACK)) return;
-
-    DEBUG_MSG (SUBSET_REPACK, nullptr, "Graph is not fully connected.");
-    parents_invalid = true;
-    update_parents();
-
-    for (unsigned i = 0; i < root_idx (); i++)
-    {
-      const auto& v = vertices_[i];
-      if (!v.parents)
-        DEBUG_MSG (SUBSET_REPACK, nullptr, "Node %u is orphaned.", i);
-    }
-  }
-
-  void print_overflows (const hb_vector_t<overflow_record_t>& overflows)
-  {
-    if (!DEBUG_ENABLED(SUBSET_REPACK)) return;
-
-    update_parents ();
-    int limit = 10;
-    for (const auto& o : overflows)
-    {
-      if (!limit--) break;
-      const auto& parent = vertices_[o.parent];
-      const auto& child = vertices_[o.child];
-      DEBUG_MSG (SUBSET_REPACK, nullptr,
-                 "  overflow from "
-                 "%4d (%4d in, %4d out, space %2d) => "
-                 "%4d (%4d in, %4d out, space %2d)",
-                 o.parent,
-                 parent.incoming_edges (),
-                 parent.obj.real_links.length + parent.obj.virtual_links.length,
-                 space_for (o.parent),
-                 o.child,
-                 child.incoming_edges (),
-                 child.obj.real_links.length + child.obj.virtual_links.length,
-                 space_for (o.child));
-    }
-    if (overflows.length > 10) {
-      DEBUG_MSG (SUBSET_REPACK, nullptr, "  ... plus %d more overflows.", overflows.length - 10);
-    }
-  }
-
-  unsigned num_roots_for_space (unsigned space) const
-  {
-    return num_roots_for_space_[space];
-  }
-
-  unsigned next_space () const
-  {
-    return num_roots_for_space_.length;
-  }
-
-  void move_to_new_space (const hb_set_t& indices)
-  {
-    num_roots_for_space_.push (0);
-    unsigned new_space = num_roots_for_space_.length - 1;
-
-    for (unsigned index : indices) {
-      auto& node = vertices_[index];
-      num_roots_for_space_[node.space] = num_roots_for_space_[node.space] - 1;
-      num_roots_for_space_[new_space] = num_roots_for_space_[new_space] + 1;
-      node.space = new_space;
-      distance_invalid = true;
-      positions_invalid = true;
-    }
-  }
-
-  unsigned space_for (unsigned index, unsigned* root = nullptr) const
-  {
-    const auto& node = vertices_[index];
-    if (node.space)
-    {
-      if (root != nullptr)
-        *root = index;
-      return node.space;
-    }
-
-    if (!node.parents)
-    {
-      if (root)
-        *root = index;
-      return 0;
-    }
-
-    return space_for (node.parents[0], root);
-  }
-
-  void err_other_error () { this->successful = false; }
-
- private:
-
-  size_t serialized_length () const {
-    size_t total_size = 0;
-    for (unsigned i = 0; i < vertices_.length; i++) {
-      size_t size = vertices_[i].obj.tail - vertices_[i].obj.head;
-      total_size += size;
-    }
-    return total_size;
-  }
-
-  /*
-   * Returns the numbers of incoming edges that are 32bits wide.
-   */
-  unsigned wide_parents (unsigned node_idx, hb_set_t& parents) const
-  {
-    unsigned count = 0;
-    hb_set_t visited;
-    for (unsigned p : vertices_[node_idx].parents)
-    {
-      if (visited.has (p)) continue;
-      visited.add (p);
-
-      // Only real links can be wide
-      for (const auto& l : vertices_[p].obj.real_links)
-      {
-        if (l.objidx == node_idx && l.width == 4 && !l.is_signed)
-        {
-          count++;
-          parents.add (p);
-        }
-      }
-    }
-    return count;
-  }
-
-  bool check_success (bool success)
-  { return this->successful && (success || (err_other_error (), false)); }
-
-  /*
-   * Creates a map from objid to # of incoming edges.
-   */
-  void update_parents ()
-  {
-    if (!parents_invalid) return;
-
-    for (unsigned i = 0; i < vertices_.length; i++)
-      vertices_[i].parents.reset ();
-
-    for (unsigned p = 0; p < vertices_.length; p++)
-    {
-      for (auto& l : vertices_[p].obj.all_links ())
-      {
-        vertices_[l.objidx].parents.push (p);
-      }
-    }
-
-    parents_invalid = false;
-  }
-
-  /*
-   * compute the serialized start and end positions for each vertex.
-   */
-  void update_positions ()
-  {
-    if (!positions_invalid) return;
-
-    unsigned current_pos = 0;
-    for (int i = root_idx (); i >= 0; i--)
-    {
-      auto& v = vertices_[i];
-      v.start = current_pos;
-      current_pos += v.obj.tail - v.obj.head;
-      v.end = current_pos;
-    }
-
-    positions_invalid = false;
-  }
-
-  /*
-   * Finds the distance to each object in the graph
-   * from the initial node.
-   */
-  void update_distances ()
-  {
-    if (!distance_invalid) return;
-
-    // Uses Dijkstra's algorithm to find all of the shortest distances.
-    // https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
-    //
-    // Implementation Note:
-    // Since our priority queue doesn't support fast priority decreases
-    // we instead just add new entries into the queue when a priority changes.
-    // Redundant ones are filtered out later on by the visited set.
-    // According to https://www3.cs.stonybrook.edu/~rezaul/papers/TR-07-54.pdf
-    // for practical performance this is faster then using a more advanced queue
-    // (such as a fibonacci queue) with a fast decrease priority.
-    for (unsigned i = 0; i < vertices_.length; i++)
-    {
-      if (i == vertices_.length - 1)
-        vertices_[i].distance = 0;
-      else
-        vertices_[i].distance = hb_int_max (int64_t);
-    }
-
-    hb_priority_queue_t queue;
-    queue.insert (0, vertices_.length - 1);
-
-    hb_vector_t<bool> visited;
-    visited.resize (vertices_.length);
-
-    while (!queue.in_error () && !queue.is_empty ())
-    {
-      unsigned next_idx = queue.pop_minimum ().second;
-      if (visited[next_idx]) continue;
-      const auto& next = vertices_[next_idx];
-      int64_t next_distance = vertices_[next_idx].distance;
-      visited[next_idx] = true;
-
-      for (const auto& link : next.obj.all_links ())
-      {
-        if (visited[link.objidx]) continue;
-
-        const auto& child = vertices_[link.objidx].obj;
-        unsigned link_width = link.width ? link.width : 4; // treat virtual offsets as 32 bits wide
-        int64_t child_weight = (child.tail - child.head) +
-                               ((int64_t) 1 << (link_width * 8)) * (vertices_[link.objidx].space + 1);
-        int64_t child_distance = next_distance + child_weight;
-
-        if (child_distance < vertices_[link.objidx].distance)
-        {
-          vertices_[link.objidx].distance = child_distance;
-          queue.insert (child_distance, link.objidx);
-        }
-      }
-    }
-
-    check_success (!queue.in_error ());
-    if (!check_success (queue.is_empty ()))
-    {
-      print_orphaned_nodes ();
-      return;
-    }
-
-    distance_invalid = false;
-  }
-
-  int64_t compute_offset (
-      unsigned parent_idx,
-      const hb_serialize_context_t::object_t::link_t& link) const
-  {
-    const auto& parent = vertices_[parent_idx];
-    const auto& child = vertices_[link.objidx];
-    int64_t offset = 0;
-    switch ((hb_serialize_context_t::whence_t) link.whence) {
-      case hb_serialize_context_t::whence_t::Head:
-        offset = child.start - parent.start; break;
-      case hb_serialize_context_t::whence_t::Tail:
-        offset = child.start - parent.end; break;
-      case hb_serialize_context_t::whence_t::Absolute:
-        offset = child.start; break;
-    }
-
-    assert (offset >= link.bias);
-    offset -= link.bias;
-    return offset;
-  }
-
-  bool is_valid_offset (int64_t offset,
-                        const hb_serialize_context_t::object_t::link_t& link) const
-  {
-    if (unlikely (!link.width))
-      // Virtual links can't overflow.
-      return link.is_signed || offset >= 0;
-
-    if (link.is_signed)
-    {
-      if (link.width == 4)
-        return offset >= -((int64_t) 1 << 31) && offset < ((int64_t) 1 << 31);
-      else
-        return offset >= -(1 << 15) && offset < (1 << 15);
-    }
-    else
-    {
-      if (link.width == 4)
-        return offset >= 0 && offset < ((int64_t) 1 << 32);
-      else if (link.width == 3)
-        return offset >= 0 && offset < ((int32_t) 1 << 24);
-      else
-        return offset >= 0 && offset < (1 << 16);
-    }
-  }
-
-  /*
-   * Updates a link in the graph to point to a different object. Corrects the
-   * parents vector on the previous and new child nodes.
-   */
-  void reassign_link (hb_serialize_context_t::object_t::link_t& link,
-                      unsigned parent_idx,
-                      unsigned new_idx)
-  {
-    unsigned old_idx = link.objidx;
-    link.objidx = new_idx;
-    vertices_[old_idx].remove_parent (parent_idx);
-    vertices_[new_idx].parents.push (parent_idx);
-  }
-
-  /*
-   * Updates all objidx's in all links using the provided mapping. Corrects incoming edge counts.
-   */
-  template<typename Iterator, hb_requires (hb_is_iterator (Iterator))>
-  void remap_obj_indices (const hb_hashmap_t<unsigned, unsigned>& id_map,
-                          Iterator subgraph,
-                          bool only_wide = false)
-  {
-    if (!id_map) return;
-    for (unsigned i : subgraph)
-    {
-      for (auto& link : vertices_[i].obj.all_links_writer ())
-      {
-        if (!id_map.has (link.objidx)) continue;
-        if (only_wide && !(link.width == 4 && !link.is_signed)) continue;
-
-        reassign_link (link, i, id_map[link.objidx]);
-      }
-    }
-  }
-
-  /*
-   * Updates all objidx's in all links using the provided mapping.
-   */
-  void remap_all_obj_indices (const hb_vector_t<unsigned>& id_map,
-                              hb_vector_t<vertex_t>* sorted_graph) const
-  {
-    for (unsigned i = 0; i < sorted_graph->length; i++)
-    {
-      (*sorted_graph)[i].remap_parents (id_map);
-      for (auto& link : (*sorted_graph)[i].obj.all_links_writer ())
-      {
-        link.objidx = id_map[link.objidx];
-      }
-    }
-  }
-
-  template <typename O> void
-  serialize_link_of_type (const hb_serialize_context_t::object_t::link_t& link,
-                          char* head,
-                          hb_serialize_context_t* c) const
-  {
-    OT::Offset<O>* offset = reinterpret_cast<OT::Offset<O>*> (head + link.position);
-    *offset = 0;
-    c->add_link (*offset,
-                 // serializer has an extra nil object at the start of the
-                 // object array. So all id's are +1 of what our id's are.
-                 link.objidx + 1,
-                 (hb_serialize_context_t::whence_t) link.whence,
-                 link.bias);
-  }
-
-  void serialize_link (const hb_serialize_context_t::object_t::link_t& link,
-                 char* head,
-                 hb_serialize_context_t* c) const
-  {
-    switch (link.width)
-    {
-    case 0:
-      // Virtual links aren't serialized.
-      return;
-    case 4:
-      if (link.is_signed)
-      {
-        serialize_link_of_type<OT::HBINT32> (link, head, c);
-      } else {
-        serialize_link_of_type<OT::HBUINT32> (link, head, c);
-      }
-      return;
-    case 2:
-      if (link.is_signed)
-      {
-        serialize_link_of_type<OT::HBINT16> (link, head, c);
-      } else {
-        serialize_link_of_type<OT::HBUINT16> (link, head, c);
-      }
-      return;
-    case 3:
-      serialize_link_of_type<OT::HBUINT24> (link, head, c);
-      return;
-    default:
-      // Unexpected link width.
-      assert (0);
-    }
-  }
-
-  /*
-   * Finds all nodes in targets that are reachable from start_idx, nodes in visited will be skipped.
-   * For this search the graph is treated as being undirected.
-   *
-   * Connected targets will be added to connected and removed from targets. All visited nodes
-   * will be added to visited.
-   */
-  void find_connected_nodes (unsigned start_idx,
-                             hb_set_t& targets,
-                             hb_set_t& visited,
-                             hb_set_t& connected)
-  {
-    if (unlikely (!check_success (!visited.in_error ()))) return;
-    if (visited.has (start_idx)) return;
-    visited.add (start_idx);
-
-    if (targets.has (start_idx))
-    {
-      targets.del (start_idx);
-      connected.add (start_idx);
-    }
-
-    const auto& v = vertices_[start_idx];
-
-    // Graph is treated as undirected so search children and parents of start_idx
-    for (const auto& l : v.obj.all_links ())
-      find_connected_nodes (l.objidx, targets, visited, connected);
-
-    for (unsigned p : v.parents)
-      find_connected_nodes (p, targets, visited, connected);
-  }
-
- public:
-  // TODO(garretrieger): make private, will need to move most of offset overflow code into graph.
-  hb_vector_t<vertex_t> vertices_;
-  hb_vector_t<vertex_t> vertices_scratch_;
- private:
-  bool parents_invalid;
-  bool distance_invalid;
-  bool positions_invalid;
-  bool successful;
-  hb_vector_t<unsigned> num_roots_for_space_;
-};
 
 static inline
-bool _try_isolating_subgraphs (const hb_vector_t<graph_t::overflow_record_t>& overflows,
+bool _try_isolating_subgraphs (const hb_vector_t<graph::overflow_record_t>& overflows,
                                graph_t& sorted_graph)
 {
   unsigned space = 0;
@@ -1066,7 +51,7 @@ bool _try_isolating_subgraphs (const hb_vector_t<graph_t::overflow_record_t>& ov
 
   for (int i = overflows.length - 1; i >= 0; i--)
   {
-    const graph_t::overflow_record_t& r = overflows[i];
+    const graph::overflow_record_t& r = overflows[i];
 
     unsigned root;
     unsigned overflow_space = sorted_graph.space_for (r.parent, &root);
@@ -1108,7 +93,7 @@ bool _try_isolating_subgraphs (const hb_vector_t<graph_t::overflow_record_t>& ov
 }
 
 static inline
-bool _process_overflows (const hb_vector_t<graph_t::overflow_record_t>& overflows,
+bool _process_overflows (const hb_vector_t<graph::overflow_record_t>& overflows,
                          hb_set_t& priority_bumped_parents,
                          graph_t& sorted_graph)
 {
@@ -1117,7 +102,7 @@ bool _process_overflows (const hb_vector_t<graph_t::overflow_record_t>& overflow
   // Try resolving the furthest overflows first.
   for (int i = overflows.length - 1; i >= 0; i--)
   {
-    const graph_t::overflow_record_t& r = overflows[i];
+    const graph::overflow_record_t& r = overflows[i];
     const auto& child = sorted_graph.vertices_[r.child];
     if (child.is_shared ())
     {
@@ -1173,19 +158,18 @@ inline hb_blob_t*
 hb_resolve_overflows (const T& packed,
                       hb_tag_t table_tag,
                       unsigned max_rounds = 20) {
-  // Kahn sort is ~twice as fast as shortest distance sort and works for many fonts
-  // so try it first to save time.
   graph_t sorted_graph (packed);
-  if (!sorted_graph.will_overflow ())
+  sorted_graph.sort_shortest_distance ();
+
+  bool will_overflow = graph::will_overflow (sorted_graph);
+  if (!will_overflow)
   {
-    return sorted_graph.serialize ();
+    return graph::serialize (sorted_graph);
   }
 
-  sorted_graph.sort_shortest_distance ();
-
   if ((table_tag == HB_OT_TAG_GPOS
        ||  table_tag == HB_OT_TAG_GSUB)
-      && sorted_graph.will_overflow ())
+      && will_overflow)
   {
     DEBUG_MSG (SUBSET_REPACK, nullptr, "Assigning spaces to 32 bit subgraphs.");
     if (sorted_graph.assign_32bit_spaces ())
@@ -1193,13 +177,13 @@ hb_resolve_overflows (const T& packed,
   }
 
   unsigned round = 0;
-  hb_vector_t<graph_t::overflow_record_t> overflows;
+  hb_vector_t<graph::overflow_record_t> overflows;
   // TODO(garretrieger): select a good limit for max rounds.
   while (!sorted_graph.in_error ()
-         && sorted_graph.will_overflow (&overflows)
+         && graph::will_overflow (sorted_graph, &overflows)
          && round++ < max_rounds) {
     DEBUG_MSG (SUBSET_REPACK, nullptr, "=== Overflow resolution round %d ===", round);
-    sorted_graph.print_overflows (overflows);
+    print_overflows (sorted_graph, overflows);
 
     hb_set_t priority_bumped_parents;
 
@@ -1221,13 +205,13 @@ hb_resolve_overflows (const T& packed,
     return nullptr;
   }
 
-  if (sorted_graph.will_overflow ())
+  if (graph::will_overflow (sorted_graph))
   {
     DEBUG_MSG (SUBSET_REPACK, nullptr, "Offset overflow resolution failed.");
     return nullptr;
   }
 
-  return sorted_graph.serialize ();
+  return graph::serialize (sorted_graph);
 }
 
 #endif /* HB_REPACKER_HH */