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/*
* 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 */
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