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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-vector.hh"
#include "graph/graph.hh"
#include "graph/gsubgpos-graph.hh"
#include "graph/serialize.hh"
using graph::graph_t;
/*
* For a detailed writeup on the overflow resolution algorithm see:
* docs/repacker.md
*/
struct lookup_size_t
{
unsigned lookup_index;
size_t size;
unsigned num_subtables;
static int cmp (const void* a, const void* b)
{
return cmp ((const lookup_size_t*) a,
(const lookup_size_t*) b);
}
static int cmp (const lookup_size_t* a, const lookup_size_t* b)
{
double subtables_per_byte_a = (double) a->num_subtables / (double) a->size;
double subtables_per_byte_b = (double) b->num_subtables / (double) b->size;
if (subtables_per_byte_a == subtables_per_byte_b) {
return b->lookup_index - a->lookup_index;
}
double cmp = subtables_per_byte_b - subtables_per_byte_a;
if (cmp < 0) return -1;
if (cmp > 0) return 1;
return 0;
}
};
static inline
bool _presplit_subtables_if_needed (graph::gsubgpos_graph_context_t& ext_context)
{
// For each lookup this will check the size of subtables and split them as needed
// so that no subtable is at risk of overflowing. (where we support splitting for
// that subtable type).
//
// TODO(grieger): de-dup newly added nodes as necessary. Probably just want a full de-dup
// pass after this processing is done. Not super necessary as splits are
// only done where overflow is likely, so de-dup probably will get undone
// later anyways.
// The loop below can modify the contents of ext_context.lookups if new subtables are added
// to a lookup during a split. So save the initial set of lookup indices so the iteration doesn't
// risk access free'd memory if ext_context.lookups gets resized.
hb_set_t lookup_indices(ext_context.lookups.keys ());
for (unsigned lookup_index : lookup_indices)
{
graph::Lookup* lookup = ext_context.lookups.get(lookup_index);
if (!lookup->split_subtables_if_needed (ext_context, lookup_index))
return false;
}
return true;
}
/*
* Analyze the lookups in a GSUB/GPOS table and decide if any should be promoted
* to extension lookups.
*/
static inline
bool _promote_extensions_if_needed (graph::gsubgpos_graph_context_t& ext_context)
{
// Simple Algorithm (v1, current):
// 1. Calculate how many bytes each non-extension lookup consumes.
// 2. Select up to 64k of those to remain as non-extension (greedy, highest subtables per byte first)
// 3. Promote the rest.
//
// Advanced Algorithm (v2, not implemented):
// 1. Perform connected component analysis using lookups as roots.
// 2. Compute size of each connected component.
// 3. Select up to 64k worth of connected components to remain as non-extensions.
// (greedy, highest subtables per byte first)
// 4. Promote the rest.
// TODO(garretrieger): support extension demotion, then consider all lookups. Requires advanced algo.
// TODO(garretrieger): also support extension promotion during iterative resolution phase, then
// we can use a less conservative threshold here.
// TODO(grieger): skip this for the 24 bit case.
if (!ext_context.lookups) return true;
unsigned total_lookup_table_sizes = 0;
hb_vector_t<lookup_size_t> lookup_sizes;
lookup_sizes.alloc (ext_context.lookups.get_population (), true);
for (unsigned lookup_index : ext_context.lookups.keys ())
{
const auto& lookup_v = ext_context.graph.vertices_[lookup_index];
total_lookup_table_sizes += lookup_v.table_size ();
const graph::Lookup* lookup = ext_context.lookups.get(lookup_index);
hb_set_t visited;
lookup_sizes.push (lookup_size_t {
lookup_index,
ext_context.graph.find_subgraph_size (lookup_index, visited),
lookup->number_of_subtables (),
});
}
lookup_sizes.qsort ();
size_t lookup_list_size = ext_context.graph.vertices_[ext_context.lookup_list_index].table_size ();
size_t l2_l3_size = lookup_list_size + total_lookup_table_sizes; // Lookup List + Lookups
size_t l3_l4_size = total_lookup_table_sizes; // Lookups + SubTables
size_t l4_plus_size = 0; // SubTables + their descendants
// Start by assuming all lookups are using extension subtables, this size will be removed later
// if it's decided to not make a lookup extension.
for (auto p : lookup_sizes)
{
// TODO(garretrieger): this overestimates the extension subtables size because some extension subtables may be
// reused. However, we can't correct this until we have connected component analysis in place.
unsigned subtables_size = p.num_subtables * 8;
l3_l4_size += subtables_size;
l4_plus_size += subtables_size;
}
bool layers_full = false;
for (auto p : lookup_sizes)
{
const graph::Lookup* lookup = ext_context.lookups.get(p.lookup_index);
if (lookup->is_extension (ext_context.table_tag))
// already an extension so size is counted by the loop above.
continue;
if (!layers_full)
{
size_t lookup_size = ext_context.graph.vertices_[p.lookup_index].table_size ();
hb_set_t visited;
size_t subtables_size = ext_context.graph.find_subgraph_size (p.lookup_index, visited, 1) - lookup_size;
size_t remaining_size = p.size - subtables_size - lookup_size;
l3_l4_size += subtables_size;
l3_l4_size -= p.num_subtables * 8;
l4_plus_size += subtables_size + remaining_size;
if (l2_l3_size < (1 << 16)
&& l3_l4_size < (1 << 16)
&& l4_plus_size < (1 << 16)) continue; // this lookup fits within all layers groups
layers_full = true;
}
if (!ext_context.lookups.get(p.lookup_index)->make_extension (ext_context, p.lookup_index))
return false;
}
return true;
}
static inline
bool _try_isolating_subgraphs (const hb_vector_t<graph::overflow_record_t>& overflows,
graph_t& sorted_graph)
{
unsigned space = 0;
hb_set_t roots_to_isolate;
for (int i = overflows.length - 1; i >= 0; i--)
{
const graph::overflow_record_t& r = overflows[i];
unsigned root;
unsigned overflow_space = sorted_graph.space_for (r.parent, &root);
if (!overflow_space) continue;
if (sorted_graph.num_roots_for_space (overflow_space) <= 1) continue;
if (!space) {
space = overflow_space;
}
if (space == overflow_space)
roots_to_isolate.add(root);
}
if (!roots_to_isolate) return false;
unsigned maximum_to_move = hb_max ((sorted_graph.num_roots_for_space (space) / 2u), 1u);
if (roots_to_isolate.get_population () > maximum_to_move) {
// Only move at most half of the roots in a space at a time.
unsigned extra = roots_to_isolate.get_population () - maximum_to_move;
while (extra--) {
uint32_t root = HB_SET_VALUE_INVALID;
roots_to_isolate.previous (&root);
roots_to_isolate.del (root);
}
}
DEBUG_MSG (SUBSET_REPACK, nullptr,
"Overflow in space %u (%u roots). Moving %u roots to space %u.",
space,
sorted_graph.num_roots_for_space (space),
roots_to_isolate.get_population (),
sorted_graph.next_space ());
sorted_graph.isolate_subgraph (roots_to_isolate);
sorted_graph.move_to_new_space (roots_to_isolate);
return true;
}
static inline
bool _resolve_shared_overflow(const hb_vector_t<graph::overflow_record_t>& overflows,
int overflow_index,
graph_t& sorted_graph)
{
const graph::overflow_record_t& r = overflows[overflow_index];
// Find all of the parents in overflowing links that link to this
// same child node. We will then try duplicating the child node and
// re-assigning all of these parents to the duplicate.
hb_set_t parents;
parents.add(r.parent);
for (int i = overflow_index - 1; i >= 0; i--) {
const graph::overflow_record_t& r2 = overflows[i];
if (r2.child == r.child) {
parents.add(r2.parent);
}
}
unsigned result = sorted_graph.duplicate(&parents, r.child);
if (result == (unsigned) -1 && parents.get_population() > 2) {
// All links to the child are overflowing, so we can't include all
// in the duplication. Remove one parent from the duplication.
// Remove the lowest index parent, which will be the closest to the child.
parents.del(parents.get_min());
result = sorted_graph.duplicate(&parents, r.child);
}
if (result == (unsigned) -1) return result;
if (parents.get_population() > 1) {
// If the duplicated node has more than one parent pre-emptively raise it's priority to the maximum.
// This will place it close to the parents. Node's with only one parent, don't need this as normal overflow
// resolution will raise priority if needed.
//
// Reasoning: most of the parents to this child are likely at the same layer in the graph. Duplicating
// the child will theoretically allow it to be placed closer to it's parents. However, due to the shortest
// distance sort by default it's placement will remain in the same layer, thus it will remain in roughly the
// same position (and distance from parents) as the original child node. The overflow resolution will attempt
// to move nodes closer, but only for non-shared nodes. Since this node is shared, it will simply be given
// further duplication which defeats the attempt to duplicate with multiple parents. To fix this we
// pre-emptively raise priority now which allows the duplicated node to pack into the same layer as it's parents.
sorted_graph.vertices_[result].give_max_priority();
}
return result;
}
static inline
bool _process_overflows (const hb_vector_t<graph::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::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 (!_resolve_shared_overflow(overflows, i, sorted_graph)) 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): 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.
if (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;
}
inline bool
hb_resolve_graph_overflows (hb_tag_t table_tag,
unsigned max_rounds ,
bool always_recalculate_extensions,
graph_t& sorted_graph /* IN/OUT */)
{
DEBUG_MSG (SUBSET_REPACK, nullptr, "Repacking %c%c%c%c.", HB_UNTAG(table_tag));
sorted_graph.sort_shortest_distance ();
if (sorted_graph.in_error ())
{
DEBUG_MSG (SUBSET_REPACK, nullptr, "Sorted graph in error state after initial sort.");
return false;
}
bool will_overflow = graph::will_overflow (sorted_graph);
if (!will_overflow)
return true;
bool is_gsub_or_gpos = (table_tag == HB_OT_TAG_GPOS || table_tag == HB_OT_TAG_GSUB);
graph::gsubgpos_graph_context_t ext_context (table_tag, sorted_graph);
if (is_gsub_or_gpos && will_overflow)
{
DEBUG_MSG (SUBSET_REPACK, nullptr, "Applying GSUB/GPOS repacking specializations.");
if (always_recalculate_extensions)
{
DEBUG_MSG (SUBSET_REPACK, nullptr, "Splitting subtables if needed.");
if (!_presplit_subtables_if_needed (ext_context)) {
DEBUG_MSG (SUBSET_REPACK, nullptr, "Subtable splitting failed.");
return false;
}
DEBUG_MSG (SUBSET_REPACK, nullptr, "Promoting lookups to extensions if needed.");
if (!_promote_extensions_if_needed (ext_context)) {
DEBUG_MSG (SUBSET_REPACK, nullptr, "Extensions promotion failed.");
return false;
}
}
DEBUG_MSG (SUBSET_REPACK, nullptr, "Assigning spaces to 32 bit subgraphs.");
if (sorted_graph.assign_spaces ())
sorted_graph.sort_shortest_distance ();
else
sorted_graph.sort_shortest_distance_if_needed ();
}
unsigned round = 0;
hb_vector_t<graph::overflow_record_t> overflows;
// TODO(garretrieger): select a good limit for max rounds.
while (!sorted_graph.in_error ()
&& graph::will_overflow (sorted_graph, &overflows)
&& round < max_rounds) {
DEBUG_MSG (SUBSET_REPACK, nullptr, "=== Overflow resolution round %u ===", round);
print_overflows (sorted_graph, overflows);
hb_set_t priority_bumped_parents;
if (!_try_isolating_subgraphs (overflows, sorted_graph))
{
// Don't count space isolation towards round limit. Only increment
// round counter if space isolation made no changes.
round++;
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 ())
{
DEBUG_MSG (SUBSET_REPACK, nullptr, "Sorted graph in error state.");
return false;
}
if (graph::will_overflow (sorted_graph))
{
if (is_gsub_or_gpos && !always_recalculate_extensions) {
// If this a GSUB/GPOS table and we didn't try to extension promotion and table splitting then
// as a last ditch effort, re-run the repacker with it enabled.
DEBUG_MSG (SUBSET_REPACK, nullptr, "Failed to find a resolution. Re-running with extension promotion and table splitting enabled.");
return hb_resolve_graph_overflows (table_tag, max_rounds, true, sorted_graph);
}
DEBUG_MSG (SUBSET_REPACK, nullptr, "Offset overflow resolution failed.");
return false;
}
return true;
}
/*
* 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
*/
template<typename T>
inline hb_blob_t*
hb_resolve_overflows (const T& packed,
hb_tag_t table_tag,
unsigned max_rounds = 32,
bool recalculate_extensions = false) {
graph_t sorted_graph (packed);
if (sorted_graph.in_error ())
{
// Invalid graph definition.
return nullptr;
}
if (!sorted_graph.is_fully_connected ())
{
sorted_graph.print_orphaned_nodes ();
return nullptr;
}
if (sorted_graph.in_error ())
{
// Allocations failed somewhere
DEBUG_MSG (SUBSET_REPACK, nullptr,
"Graph is in error, likely due to a memory allocation error.");
return nullptr;
}
if (!hb_resolve_graph_overflows (table_tag, max_rounds, recalculate_extensions, sorted_graph))
return nullptr;
return graph::serialize (sorted_graph);
}
#endif /* HB_REPACKER_HH */