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Diffstat (limited to 'thirdparty/harfbuzz/src/hb-repacker.hh')
| -rw-r--r-- | thirdparty/harfbuzz/src/hb-repacker.hh | 1194 |
1 files changed, 1194 insertions, 0 deletions
diff --git a/thirdparty/harfbuzz/src/hb-repacker.hh b/thirdparty/harfbuzz/src/hb-repacker.hh new file mode 100644 index 0000000000..26faa56ea8 --- /dev/null +++ b/thirdparty/harfbuzz/src/hb-repacker.hh @@ -0,0 +1,1194 @@ +/* + * 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" + +/* + * For a detailed writeup on the overflow resolution algorithm see: + * docs/repacker.md + */ + +struct graph_t +{ + struct vertex_t + { + vertex_t () : + distance (0), + space (0), + parents (), + start (0), + end (0), + priority(0) {} + + void fini () { + obj.fini (); + parents.fini (); + } + + hb_serialize_context_t::object_t obj; + int64_t distance; + int64_t space; + hb_vector_t<unsigned> parents; + unsigned start; + unsigned end; + unsigned 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.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 << 22) | (0x003FFFFF & 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; + 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 + */ + graph_t (const hb_vector_t<hb_serialize_context_t::object_t *>& objects) + : parents_invalid (true), + distance_invalid (true), + positions_invalid (true), + successful (true) + { + num_roots_for_space_.push (1); + 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 (); + } + + 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. + */ + 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; + 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.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[new_id] = 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)) + print_orphaned_nodes (); + + remap_all_obj_indices (id_map, &sorted_graph); + + hb_swap (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; + 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; + + vertex_t& next = vertices_[next_id]; + sorted_graph[new_id] = 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)) + print_orphaned_nodes (); + + remap_all_obj_indices (id_map, &sorted_graph); + + hb_swap (vertices_, sorted_graph); + sorted_graph.fini_deep (); + } + + /* + * 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++) + { + for (auto& l : vertices_[i].obj.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 (!roots.next (&next)) break; + + hb_set_t connected_roots; + find_connected_nodes (next, roots, visited, connected_roots); + isolate_subgraph (connected_roots); + + 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.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.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).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.links) + { + clone->obj.links.push (l); + vertices_[l.objidx].parents.push (clone_idx); + } + + check_success (!clone->obj.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. + vertex_t root = vertices_[vertices_.length - 2]; + vertices_[clone_idx] = *clone; + vertices_[vertices_.length - 1] = root; + + // Since the root moved, update the parents arrays of all children on the root. + for (const auto& l : root.obj.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.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 (unsigned i = 0; i < parent.obj.links.length; i++) + { + auto& l = parent.obj.links[i]; + if (l.objidx != child_idx) + continue; + + reassign_link (l, parent_idx, clone_idx); + } + + return true; + } + + /* + * 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.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 (); + for (const auto& o : overflows) + { + 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.links.length, + space_for (o.parent), + o.child, + child.incoming_edges (), + child.obj.links.length, + space_for (o.child)); + } + } + + 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 (unsigned index) + { + auto& node = vertices_[index]; + num_roots_for_space_.push (1); + num_roots_for_space_[node.space] = num_roots_for_space_[node.space] - 1; + node.space = num_roots_for_space_.length - 1; + } + + 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: + + /* + * 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); + + for (const auto& l : vertices_[p].obj.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.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 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_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.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 (unsigned j = 0; j < vertices_[i].obj.links.length; j++) + { + auto& link = vertices_[i].obj.links[j]; + 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 (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 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 (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.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_; + private: + bool parents_invalid; + bool distance_invalid; + bool positions_invalid; + bool successful; + hb_vector_t<unsigned> num_roots_for_space_; +}; + +static bool _try_isolating_subgraphs (const hb_vector_t<graph_t::overflow_record_t>& overflows, + graph_t& sorted_graph) +{ + for (int i = overflows.length - 1; i >= 0; i--) + { + const graph_t::overflow_record_t& r = overflows[i]; + unsigned root = 0; + unsigned space = sorted_graph.space_for (r.parent, &root); + if (!space) continue; + if (sorted_graph.num_roots_for_space (space) <= 1) continue; + + DEBUG_MSG (SUBSET_REPACK, nullptr, "Overflow in space %d moving subgraph %d to space %d.", + space, + root, + sorted_graph.next_space ()); + + hb_set_t roots; + roots.add (root); + sorted_graph.isolate_subgraph (roots); + for (unsigned new_root : roots) + sorted_graph.move_to_new_space (new_root); + return true; + } + return false; +} + +static bool _process_overflows (const hb_vector_t<graph_t::overflow_record_t>& overflows, + hb_set_t& priority_bumped_parents, + graph_t& sorted_graph) +{ + bool resolution_attempted = false; + + // 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.child]; + if (child.is_shared ()) + { + // The child object is shared, we may be able to eliminate the overflow + // by duplicating it. + if (!sorted_graph.duplicate (r.parent, r.child)) continue; + return true; + } + + 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. + } + + return resolution_attempted; +} + +/* + * 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. + * + * For a detailed writeup describing how the algorithm operates see: + * docs/repacker.md + */ +inline void +hb_resolve_overflows (const hb_vector_t<hb_serialize_context_t::object_t *>& packed, + hb_tag_t table_tag, + hb_serialize_context_t* c, + unsigned max_rounds = 10) { + // 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 (); + + if ((table_tag == HB_OT_TAG_GPOS + || table_tag == HB_OT_TAG_GSUB) + && sorted_graph.will_overflow ()) + { + DEBUG_MSG (SUBSET_REPACK, nullptr, "Assigning spaces to 32 bit subgraphs."); + if (sorted_graph.assign_32bit_spaces ()) + 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++ < max_rounds) { + DEBUG_MSG (SUBSET_REPACK, nullptr, "=== Overflow resolution round %d ===", round); + sorted_graph.print_overflows (overflows); + + hb_set_t priority_bumped_parents; + + if (!_try_isolating_subgraphs (overflows, sorted_graph)) + { + if (!_process_overflows (overflows, priority_bumped_parents, sorted_graph)) + { + DEBUG_MSG (SUBSET_REPACK, nullptr, "No resolution available :("); + break; + } + } + + sorted_graph.sort_shortest_distance (); + } + + if (sorted_graph.in_error ()) + { + c->err (HB_SERIALIZE_ERROR_OTHER); + return; + } + + if (sorted_graph.will_overflow ()) + { + c->err (HB_SERIALIZE_ERROR_OFFSET_OVERFLOW); + DEBUG_MSG (SUBSET_REPACK, nullptr, "Offset overflow resolution failed."); + return; + } + sorted_graph.serialize (c); +} + +#endif /* HB_REPACKER_HH */ |