Update Harfbuzz to version 2.9.0

[ChangeLog][Text] Updated bundled Harfbuzz to
version 2.9.0.

Pick-to: 6.2
Change-Id: Ib8fed753b99a127d5a4cc793c5c1d55a0090f902
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>

1 files changed, 769 insertions, 0 deletions

diff --git a/src/3rdparty/harfbuzz-ng/src/hb-repacker.hh b/src/3rdparty/harfbuzz-ng/src/hb-repacker.hh
new file mode 100644
index 0000000000..b02128b5c4
--- /dev/null
+++ b/src/3rdparty/harfbuzz-ng/src/hb-repacker.hh
@@ -0,0 +1,769 @@
+/*
+ * Copyright © 2020  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
+ */
+
+#ifndef HB_REPACKER_HH
+#define HB_REPACKER_HH
+
+#include "hb-open-type.hh"
+#include "hb-map.hh"
+#include "hb-priority-queue.hh"
+#include "hb-serialize.hh"
+#include "hb-vector.hh"
+
+
+struct graph_t
+{
+  struct vertex_t
+  {
+    vertex_t () :
+        distance (0),
+        incoming_edges (0),
+        start (0),
+        end (0),
+        priority(0) {}
+
+    void fini () { obj.fini (); }
+
+    hb_serialize_context_t::object_t obj;
+    int64_t distance;
+    unsigned incoming_edges;
+    unsigned start;
+    unsigned end;
+    unsigned priority;
+
+    bool is_shared () const
+    {
+      return incoming_edges > 1;
+    }
+
+    bool is_leaf () const
+    {
+      return !obj.links.length;
+    }
+
+    void raise_priority ()
+    {
+      priority++;
+    }
+
+    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), 0x7FFFFFFFFF);
+      return (modified_distance << 24) | (0x00FFFFFF & order);
+    }
+
+    int64_t distance_modifier () const
+    {
+      if (!priority) return 0;
+      int64_t table_size = obj.tail - obj.head;
+      return -(table_size - table_size / (1 << hb_min(priority, 16u)));
+    }
+  };
+
+  struct overflow_record_t
+  {
+    unsigned parent;
+    const hb_serialize_context_t::object_t::link_t* link;
+  };
+
+  struct clone_buffer_t
+  {
+    clone_buffer_t () : head (nullptr), tail (nullptr) {}
+
+    bool copy (const hb_serialize_context_t::object_t& object)
+    {
+      fini ();
+      unsigned size = object.tail - object.head;
+      head = (char*) hb_malloc (size);
+      if (!head) return false;
+
+      memcpy (head, object.head, size);
+      tail = head + size;
+      return true;
+    }
+
+    char* head;
+    char* tail;
+
+    void fini ()
+    {
+      if (!head) return;
+      hb_free (head);
+      head = nullptr;
+    }
+  };
+
+  /*
+   * 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
+   */
+  graph_t (const hb_vector_t<hb_serialize_context_t::object_t *>& objects)
+      : edge_count_invalid (true),
+        distance_invalid (true),
+        positions_invalid (true),
+        successful (true)
+  {
+    bool removed_nil = false;
+    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;
+      for (unsigned i = 0; i < v->obj.links.length; i++)
+        // Fix indices to account for removed nil object.
+        v->obj.links[i].objidx--;
+    }
+  }
+
+  ~graph_t ()
+  {
+    vertices_.fini_deep ();
+    clone_buffers_.fini_deep ();
+  }
+
+  bool in_error () const
+  {
+    return !successful || vertices_.in_error () || clone_buffers_.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.
+   */
+  void serialize (hb_serialize_context_t* c) const
+  {
+    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) return;
+
+      memcpy (start, vertices_[i].obj.head, size);
+
+      for (const auto& link : vertices_[i].obj.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 ();
+  }
+
+  /*
+   * Generates a new topological sorting of graph using Kahn's
+   * algorithm: https://en.wikipedia.org/wiki/Topological_sorting#Algorithms
+   */
+  void sort_kahn ()
+  {
+    positions_invalid = true;
+
+    if (vertices_.length <= 1) {
+      // Graph of 1 or less doesn't need sorting.
+      return;
+    }
+
+    hb_vector_t<unsigned> queue;
+    hb_vector_t<vertex_t> sorted_graph;
+    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_incoming_edge_count ();
+
+    queue.push (root_idx ());
+    int new_id = vertices_.length - 1;
+
+    while (!queue.in_error () && queue.length)
+    {
+      unsigned next_id = queue[0];
+      queue.remove (0);
+
+      vertex_t& next = vertices_[next_id];
+      sorted_graph.push (next);
+      id_map[next_id] = new_id--;
+
+      for (const auto& link : next.obj.links) {
+        removed_edges[link.objidx]++;
+        if (!(vertices_[link.objidx].incoming_edges - removed_edges[link.objidx]))
+          queue.push (link.objidx);
+      }
+    }
+
+    check_success (!queue.in_error ());
+    check_success (!sorted_graph.in_error ());
+    if (!check_success (new_id == -1))
+      DEBUG_MSG (SUBSET_REPACK, nullptr, "Graph is not fully connected.");
+
+    remap_obj_indices (id_map, &sorted_graph);
+
+    sorted_graph.as_array ().reverse ();
+
+    vertices_.fini_deep ();
+    vertices_ = sorted_graph;
+    sorted_graph.fini_deep ();
+  }
+
+  /*
+   * 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;
+    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_incoming_edge_count ();
+
+    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;
+
+      vertex_t& next = vertices_[next_id];
+      sorted_graph.push (next);
+      id_map[next_id] = new_id--;
+
+      for (const auto& link : next.obj.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))
+      DEBUG_MSG (SUBSET_REPACK, nullptr, "Graph is not fully connected.");
+
+    remap_obj_indices (id_map, &sorted_graph);
+
+    sorted_graph.as_array ().reverse ();
+
+    vertices_.fini_deep ();
+    vertices_ = sorted_graph;
+    sorted_graph.fini_deep ();
+  }
+
+  /*
+   * 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.
+   */
+  void duplicate (unsigned parent_idx, unsigned child_idx)
+  {
+    DEBUG_MSG (SUBSET_REPACK, nullptr, "  Duplicating %d => %d",
+               parent_idx, child_idx);
+
+    positions_invalid = true;
+
+    auto* clone = vertices_.push ();
+    auto& child = vertices_[child_idx];
+    clone_buffer_t* buffer = clone_buffers_.push ();
+    if (vertices_.in_error ()
+        || clone_buffers_.in_error ()
+        || !check_success (buffer->copy (child.obj))) {
+      return;
+    }
+
+    clone->obj.head = buffer->head;
+    clone->obj.tail = buffer->tail;
+    clone->distance = child.distance;
+
+    for (const auto& l : child.obj.links)
+      clone->obj.links.push (l);
+
+    check_success (!clone->obj.links.in_error ());
+
+    auto& parent = vertices_[parent_idx];
+    unsigned clone_idx = vertices_.length - 2;
+    for (unsigned i = 0; i < parent.obj.links.length; i++)
+    {
+      auto& l = parent.obj.links[i];
+      if (l.objidx == child_idx)
+      {
+        l.objidx = clone_idx;
+        clone->incoming_edges++;
+        child.incoming_edges--;
+      }
+    }
+
+    // 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.
+    vertex_t root = vertices_[vertices_.length - 2];
+    vertices_[vertices_.length - 2] = *clone;
+    vertices_[vertices_.length - 1] = root;
+  }
+
+  /*
+   * Raises the sorting priority of all children.
+   */
+  void 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;
+    for (unsigned i = 0; i < parent.links.length; i++)
+      vertices_[parent.links[i].objidx].raise_priority ();
+  }
+
+  /*
+   * 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--)
+    {
+      for (const auto& link : vertices_[parent_idx].obj.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.link = &link;
+        overflows->push (r);
+      }
+    }
+
+    if (!overflows) return false;
+    return overflows->length;
+  }
+
+  void print_overflows (const hb_vector_t<overflow_record_t>& overflows)
+  {
+    if (!DEBUG_ENABLED(SUBSET_REPACK)) return;
+
+    update_incoming_edge_count ();
+    for (const auto& o : overflows)
+    {
+      const auto& child = vertices_[o.link->objidx];
+      DEBUG_MSG (SUBSET_REPACK, nullptr, "  overflow from %d => %d (%d incoming , %d outgoing)",
+                 o.parent,
+                 o.link->objidx,
+                 child.incoming_edges,
+                 child.obj.links.length);
+    }
+  }
+
+  void err_other_error () { this->successful = false; }
+
+ private:
+
+  bool check_success (bool success)
+  { return this->successful && (success || (err_other_error (), false)); }
+
+  /*
+   * Creates a map from objid to # of incoming edges.
+   */
+  void update_incoming_edge_count ()
+  {
+    if (!edge_count_invalid) return;
+
+    for (unsigned i = 0; i < vertices_.length; i++)
+      vertices_[i].incoming_edges = 0;
+
+    for (const vertex_t& v : vertices_)
+    {
+      for (auto& l : v.obj.links)
+      {
+        vertices_[l.objidx].incoming_edges++;
+      }
+    }
+
+    edge_count_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 fibonaacci 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_set_t visited;
+
+    while (!queue.in_error () && !queue.is_empty ())
+    {
+      unsigned next_idx = queue.pop_minimum ().second;
+      if (visited.has (next_idx)) continue;
+      const auto& next = vertices_[next_idx];
+      int64_t next_distance = vertices_[next_idx].distance;
+      visited.add (next_idx);
+
+      for (const auto& link : next.obj.links)
+      {
+        if (visited.has (link.objidx)) continue;
+
+        const auto& child = vertices_[link.objidx].obj;
+        int64_t child_weight = child.tail - child.head +
+                               ((int64_t) 1 << (link.width * 8));
+        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 ()))
+    {
+      DEBUG_MSG (SUBSET_REPACK, nullptr, "Graph is not fully connected.");
+      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 (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 all objidx's in all links using the provided mapping.
+   */
+  void remap_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++)
+    {
+      for (unsigned j = 0; j < (*sorted_graph)[i].obj.links.length; j++)
+      {
+        auto& link = (*sorted_graph)[i].obj.links[j];
+        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 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);
+    }
+  }
+
+ public:
+  // TODO(garretrieger): make private, will need to move most of offset overflow code into graph.
+  hb_vector_t<vertex_t> vertices_;
+ private:
+  hb_vector_t<clone_buffer_t> clone_buffers_;
+  bool edge_count_invalid;
+  bool distance_invalid;
+  bool positions_invalid;
+  bool successful;
+};
+
+
+/*
+ * Attempts to modify the topological sorting of the provided object graph to
+ * eliminate offset overflows in the links between objects of the graph. If a
+ * non-overflowing ordering is found the updated graph is serialized it into the
+ * provided serialization context.
+ *
+ * If necessary the structure of the graph may be modified in ways that do not
+ * affect the functionality of the graph. For example shared objects may be
+ * duplicated.
+ */
+inline void
+hb_resolve_overflows (const hb_vector_t<hb_serialize_context_t::object_t *>& packed,
+                      hb_serialize_context_t* c) {
+  // 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);
+  sorted_graph.sort_kahn ();
+  if (!sorted_graph.will_overflow ())
+  {
+    sorted_graph.serialize (c);
+    return;
+  }
+
+  sorted_graph.sort_shortest_distance ();
+
+  unsigned round = 0;
+  hb_vector_t<graph_t::overflow_record_t> overflows;
+  // TODO(garretrieger): select a good limit for max rounds.
+  while (!sorted_graph.in_error ()
+         && sorted_graph.will_overflow (&overflows)
+         && round++ < 10) {
+    DEBUG_MSG (SUBSET_REPACK, nullptr, "=== Over flow resolution round %d ===", round);
+    sorted_graph.print_overflows (overflows);
+
+    bool resolution_attempted = false;
+    hb_set_t priority_bumped_parents;
+    // 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 auto& child = sorted_graph.vertices_[r.link->objidx];
+      if (child.is_shared ())
+      {
+        // The child object is shared, we may be able to eliminate the overflow
+        // by duplicating it.
+        sorted_graph.duplicate (r.parent, r.link->objidx);
+        resolution_attempted = true;
+
+        // Stop processing overflows for this round so that object order can be
+        // updated to account for the newly added object.
+        break;
+      }
+
+      if (child.is_leaf () && !priority_bumped_parents.has (r.parent))
+      {
+        // This object is too far from it's parent, attempt to move it closer.
+        //
+        // TODO(garretrieger): initially limiting this to leaf's since they can be
+        //                     moved closer with fewer consequences. However, this can
+        //                     likely can be used for non-leafs as well.
+        // TODO(garretrieger): add a maximum priority, don't try to raise past this.
+        // TODO(garretrieger): also try lowering priority of the parent. Make it
+        //                     get placed further up in the ordering, closer to it's children.
+        //                     this is probably preferable if the total size of the parent object
+        //                     is < then the total size of the children (and the parent can be moved).
+        //                     Since in that case moving the parent will cause a smaller increase in
+        //                     the length of other offsets.
+        sorted_graph.raise_childrens_priority (r.parent);
+        priority_bumped_parents.add (r.parent);
+        resolution_attempted = true;
+        continue;
+      }
+
+      // TODO(garretrieger): add additional offset resolution strategies
+      // - Promotion to extension lookups.
+      // - Table splitting.
+    }
+
+    if (resolution_attempted)
+    {
+      sorted_graph.sort_shortest_distance ();
+      continue;
+    }
+
+    DEBUG_MSG (SUBSET_REPACK, nullptr, "No resolution available :(");
+    c->err (HB_SERIALIZE_ERROR_OFFSET_OVERFLOW);
+    return;
+  }
+
+  if (sorted_graph.in_error ())
+  {
+    c->err (HB_SERIALIZE_ERROR_OTHER);
+    return;
+  }
+  sorted_graph.serialize (c);
+}
+
+
+#endif /* HB_REPACKER_HH */