[subset/loca] Reduce a vector allocation

src/OT/glyf/glyf-helpers.hh

@@ -16,20 +16,30 @@ template<typename IteratorIn, typename IteratorOut,
 	 hb_requires (hb_is_source_of (IteratorIn, unsigned int)),
 	 hb_requires (hb_is_sink_of (IteratorOut, unsigned))>
 static void
-_write_loca (IteratorIn&& it, bool short_offsets, IteratorOut&& dest)
+_write_loca (IteratorIn&& it,
+	     const hb_sorted_vector_t<hb_pair_t<hb_codepoint_t, hb_codepoint_t>> new_to_old_gid_list,
+	     bool short_offsets,
+	     IteratorOut&& dest)
 {
+  unsigned num_glyphs = hb_len (dest) - 1;
   unsigned right_shift = short_offsets ? 1 : 0;
-  unsigned int offset = 0;
-  dest << 0;
-  + it
-  | hb_map ([=, &offset] (unsigned int padded_size)
-	    {
-	      offset += padded_size;
-	      DEBUG_MSG (SUBSET, nullptr, "loca entry offset %u", offset);
-	      return offset >> right_shift;
-	    })
-  | hb_sink (dest)
-  ;
+  unsigned offset = 0;
+  *dest++ = 0;
+  for (hb_codepoint_t i = 0, j = 0; i < num_glyphs; i++)
+  {
+    if (i != new_to_old_gid_list[j].first)
+    {
+      DEBUG_MSG (SUBSET, nullptr, "loca entry empty offset %u", offset);
+      *dest++ = offset >> right_shift;
+      continue;
+    }
+
+    j++;
+    unsigned padded_size = *it++;
+    offset += padded_size;
+    DEBUG_MSG (SUBSET, nullptr, "loca entry offset %u padded-size %u", offset, padded_size);
+    *dest++ = offset >> right_shift;
+  }
 }
 
 static bool
@@ -67,9 +77,13 @@ _add_head_and_set_loca_version (hb_subset_plan_t *plan, bool use_short_loca)
 template<typename Iterator,
 	 hb_requires (hb_is_source_of (Iterator, unsigned int))>
 static bool
-_add_loca_and_head (hb_subset_plan_t * plan, Iterator padded_offsets, bool use_short_loca)
+_add_loca_and_head (hb_subset_plan_t * plan,
+		    Iterator padded_offsets,
+		    const hb_sorted_vector_t<hb_pair_t<hb_codepoint_t, hb_codepoint_t>> new_to_old_gid_list,
+		    unsigned num_glyphs,
+		    bool use_short_loca)
 {
-  unsigned num_offsets = padded_offsets.len () + 1;
+  unsigned num_offsets = num_glyphs + 1;
   unsigned entry_size = use_short_loca ? 2 : 4;
   char *loca_prime_data = (char *) hb_malloc (entry_size * num_offsets);
 
@@ -79,9 +93,9 @@ _add_loca_and_head (hb_subset_plan_t * plan, Iterator padded_offsets, bool use_s
 	     entry_size, num_offsets, entry_size * num_offsets);
 
   if (use_short_loca)
-    _write_loca (padded_offsets, true, hb_array ((HBUINT16 *) loca_prime_data, num_offsets));
+    _write_loca (padded_offsets, new_to_old_gid_list, true, hb_array ((HBUINT16 *) loca_prime_data, num_offsets));
   else
-    _write_loca (padded_offsets, false, hb_array ((HBUINT32 *) loca_prime_data, num_offsets));
+    _write_loca (padded_offsets, new_to_old_gid_list, false, hb_array ((HBUINT32 *) loca_prime_data, num_offsets));
 
   hb_blob_t *loca_blob = hb_blob_create (loca_prime_data,
 					 entry_size * num_offsets,

src/OT/glyf/glyf.hh

@@ -95,14 +95,6 @@ struct glyf
       if (unlikely (!font)) return false;
     }
 
-    hb_vector_t<unsigned> padded_offsets;
-    unsigned num_glyphs = c->plan->num_output_glyphs ();
-    if (unlikely (!padded_offsets.resize (num_glyphs, false, true)))
-    {
-      hb_font_destroy (font);
-      return false;
-    }
-
     hb_vector_t<glyf_impl::SubsetGlyph> glyphs;
     if (!_populate_subset_glyphs (c->plan, font, glyphs))
     {
@@ -113,16 +105,18 @@ struct glyf
     if (font)
       hb_font_destroy (font);
 
-    auto new_to_old_gid_list = c->plan->new_to_old_gid_list;
+    // Calculate glyph sizes for `loca` table
+
+    hb_vector_t<unsigned> padded_offsets;
+    if (unlikely (!padded_offsets.alloc (glyphs.length, true)))
+      return false;
 
     unsigned max_offset = 0;
-    for (unsigned i = 0, j = 0; i < num_glyphs; i++)
+    for (auto &g : glyphs)
     {
-      if (i == new_to_old_gid_list[j].first)
-	padded_offsets.arrayZ[i] = glyphs[j++].padded_size ();
-      else
-	padded_offsets.arrayZ[i] = 0;
-      max_offset += padded_offsets[i];
+      unsigned size = g.padded_size ();
+      padded_offsets.push (size);
+      max_offset += size;
     }
 
     bool use_short_loca = false;
@@ -131,11 +125,9 @@ struct glyf
 
     if (!use_short_loca)
     {
-      for (unsigned i = 0, j = 0; i < num_glyphs; i++)
-	if (i == new_to_old_gid_list[j].first)
-	  padded_offsets.arrayZ[i] = glyphs[j++].length ();
-	else
-	  padded_offsets.arrayZ[i] = 0;
+      padded_offsets.resize (0);
+      for (auto &g : glyphs)
+	padded_offsets.push (g.length ());
     }
 
     bool result = glyf_prime->serialize (c->serializer, glyphs, use_short_loca, c->plan);
@@ -148,6 +140,8 @@ struct glyf
 
     return_trace (c->serializer->check_success (glyf_impl::_add_loca_and_head (c->plan,
 									       padded_offsets.iter (),
+									       c->plan->new_to_old_gid_list,
+									       c->plan->num_output_glyphs (),
 									       use_short_loca)));
   }