[repacker] add utility that can calculate the size of Coverage+ClassDef via incremental class inclusion.

src/Makefile.am

@@ -371,6 +371,7 @@ COMPILED_TESTS = \
 	test-unicode-ranges \
 	test-vector \
 	test-repacker \
+	test-classdef-graph \
 	$(NULL)
 COMPILED_TESTS_CPPFLAGS = $(HBCFLAGS) -DMAIN -UNDEBUG
 COMPILED_TESTS_LDADD = libharfbuzz.la $(HBLIBS)
@@ -417,6 +418,10 @@ test_repacker_SOURCES = test-repacker.cc hb-static.cc graph/gsubgpos-context.cc
 test_repacker_CPPFLAGS = $(HBCFLAGS)
 test_repacker_LDADD = libharfbuzz.la libharfbuzz-subset.la $(HBLIBS)
 
+test_classdef_graph_SOURCES = graph/test-classdef-graph.cc hb-static.cc graph/gsubgpos-context.cc
+test_classdef_graph_CPPFLAGS = $(HBCFLAGS)
+test_classdef_graph_LDADD = libharfbuzz.la libharfbuzz-subset.la $(HBLIBS)
+
 test_set_SOURCES = test-set.cc hb-static.cc
 test_set_CPPFLAGS = $(COMPILED_TESTS_CPPFLAGS)
 test_set_LDADD = $(COMPILED_TESTS_LDADD)

src/graph/classdef-graph.hh

@@ -123,6 +123,88 @@ struct ClassDef : public OT::ClassDef
 };
 
 
+struct class_def_size_estimator_t
+{
+  template<typename It>
+  class_def_size_estimator_t (It glyph_and_class)
+      : gids_consecutive (true), num_ranges_per_class (), glyphs_per_class ()
+  {
+    unsigned last_gid = (unsigned) -1;
+    for (auto p : + glyph_and_class)
+    {
+      unsigned gid = p.first;
+      unsigned klass = p.second;
+
+      if (last_gid != (unsigned) -1 && gid != last_gid + 1)
+        gids_consecutive = false;
+      last_gid = gid;
+
+      hb_set_t* glyphs;
+      if (glyphs_per_class.has (klass, &glyphs) && glyphs) {
+        glyphs->add (gid);
+        continue;
+      }
+
+      hb_set_t new_glyphs;
+      new_glyphs.add (gid);
+      glyphs_per_class.set (klass, std::move (new_glyphs));
+    }
+
+    if (in_error ()) return;
+
+    for (unsigned klass : glyphs_per_class.keys ())
+    {
+      if (!klass) continue; // class 0 doesn't get encoded.
+
+      const hb_set_t& glyphs = glyphs_per_class.get (klass);
+      hb_codepoint_t start = HB_SET_VALUE_INVALID;
+      hb_codepoint_t end = HB_SET_VALUE_INVALID;
+
+      unsigned count = 0;
+      while (glyphs.next_range (&start, &end))
+        count++;
+
+      num_ranges_per_class.set (klass, count);
+    }
+  }
+
+  // Incremental increase in the Coverage and ClassDef table size
+  // (worst case) if all glyphs associated with 'klass' were added.
+  unsigned incremental_size_for_class (unsigned klass) const
+  {
+    // Coverage takes 2 bytes per glyph worst case,
+    unsigned cov_size = 2 * glyphs_per_class.get (klass).get_population ();
+    // ClassDef takes 6 bytes per range
+    unsigned class_def_2_size = 6 * num_ranges_per_class.get (klass);
+    if (gids_consecutive)
+    {
+      // ClassDef1 takes 2 bytes per glyph, but only can be used
+      // when gids are consecutive.
+      return cov_size + hb_min (cov_size, class_def_2_size);
+    }
+
+    return cov_size + class_def_2_size;
+  }
+
+  bool in_error ()
+  {
+    if (num_ranges_per_class.in_error ()) return true;
+    if (glyphs_per_class.in_error ()) return true;
+
+    for (const hb_set_t& s : glyphs_per_class.values ())
+    {
+      if (s.in_error ()) return true;
+    }
+    return false;
+  }
+
+ private:
+  bool gids_consecutive;
+  hb_hashmap_t<unsigned, unsigned> num_ranges_per_class;
+  hb_hashmap_t<unsigned, hb_set_t> glyphs_per_class;
+};
+
+
 }
 
 #endif  // GRAPH_CLASSDEF_GRAPH_HH

src/graph/test-classdef-graph.cc

@@ -0,0 +1,110 @@
+/*
+ * Copyright © 2022  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
+ */
+
+#include "gsubgpos-context.hh"
+#include "classdef-graph.hh"
+
+typedef hb_pair_t<hb_codepoint_t, hb_codepoint_t> gid_and_class_t;
+typedef hb_vector_t<gid_and_class_t> gid_and_class_list_t;
+
+
+static bool incremental_size_is (const gid_and_class_list_t& list, unsigned klass, unsigned expected)
+{
+  graph::class_def_size_estimator_t estimator (list.iter ());
+  unsigned result = estimator.incremental_size_for_class (klass);
+  if (result != expected)
+  {
+    printf ("FAIL: expected size %u but was %u\n", expected, result);
+    return false;
+  }
+
+  return true;
+}
+
+static void test_class_and_coverage_size_estimates ()
+{
+  gid_and_class_list_t empty = {
+  };
+  assert (incremental_size_is (empty, 0, 0));
+  assert (incremental_size_is (empty, 1, 0));
+
+  gid_and_class_list_t class_zero = {
+    {5, 0},
+  };
+  assert (incremental_size_is (class_zero, 0, 2));
+
+  gid_and_class_list_t consecutive = {
+    {4, 0},
+    {5, 0},
+    {6, 1},
+    {7, 1},
+    {8, 2},
+    {9, 2},
+    {10, 2},
+    {11, 2},
+  };
+  assert (incremental_size_is (consecutive, 0, 4));
+  assert (incremental_size_is (consecutive, 1, 4 + 4));
+  assert (incremental_size_is (consecutive, 2, 8 + 6));
+
+  gid_and_class_list_t non_consecutive = {
+    {4, 0},
+    {5, 0},
+
+    {6, 1},
+    {7, 1},
+
+    {9, 2},
+    {10, 2},
+    {11, 2},
+    {12, 2},
+  };
+  assert (incremental_size_is (non_consecutive, 0, 4));
+  assert (incremental_size_is (non_consecutive, 1, 4 + 6));
+  assert (incremental_size_is (non_consecutive, 2, 8 + 6));
+
+  gid_and_class_list_t multiple_ranges = {
+    {4, 0},
+    {5, 0},
+
+    {6, 1},
+    {7, 1},
+
+    {9, 1},
+
+    {11, 1},
+    {12, 1},
+    {13, 1},
+  };
+  assert (incremental_size_is (multiple_ranges, 0, 4));
+  assert (incremental_size_is (multiple_ranges, 1, 2 * 6 + 3 * 6));
+}
+
+int
+main (int argc, char **argv)
+{
+  test_class_and_coverage_size_estimates ();
+}

src/meson.build

@@ -581,6 +581,7 @@ if get_option('tests').enabled()
     'test-ot-tag': ['hb-ot-tag.cc'],
     'test-priority-queue': ['test-priority-queue.cc', 'hb-static.cc'],
     'test-repacker': ['test-repacker.cc', 'hb-static.cc', 'graph/gsubgpos-context.cc'],
+    'test-classdef-graph': ['graph/test-classdef-graph.cc', 'hb-static.cc', 'graph/gsubgpos-context.cc'],
     'test-set': ['test-set.cc', 'hb-static.cc'],
     'test-serialize': ['test-serialize.cc', 'hb-static.cc'],
     'test-unicode-ranges': ['test-unicode-ranges.cc'],