[subset] Add a basic priority queue datastructure (binary heap).

src/Makefile.am

@@ -342,7 +342,7 @@ test_gsub_would_substitute_SOURCES = test-gsub-would-substitute.cc
 test_gsub_would_substitute_CPPFLAGS = $(HBCFLAGS) $(FREETYPE_CFLAGS)
 test_gsub_would_substitute_LDADD = libharfbuzz.la $(HBLIBS) $(FREETYPE_LIBS)
 
-COMPILED_TESTS = test-algs test-array test-iter test-meta test-number test-ot-tag test-unicode-ranges test-bimap test-repacker
+COMPILED_TESTS = test-algs test-array test-iter test-meta test-number test-ot-tag test-priority-queue test-unicode-ranges test-bimap test-repacker
 COMPILED_TESTS_CPPFLAGS = $(HBCFLAGS) -DMAIN -UNDEBUG
 COMPILED_TESTS_LDADD = libharfbuzz.la $(HBLIBS)
 check_PROGRAMS += $(COMPILED_TESTS)
@@ -356,6 +356,10 @@ test_array_SOURCES = test-array.cc
 test_array_CPPFLAGS = $(HBCFLAGS)
 test_array_LDADD = libharfbuzz.la $(HBLIBS)
 
+test_priority_queue_SOURCES = test-priority-queue.cc hb-static.cc
+test_priority_queue_CPPFLAGS = $(HBCFLAGS)
+test_priority_queue_LDADD = libharfbuzz.la $(HBLIBS)
+
 test_repacker_SOURCES = test-repacker.cc hb-static.cc
 test_repacker_CPPFLAGS = $(HBCFLAGS)
 test_repacker_LDADD = libharfbuzz.la libharfbuzz-subset.la $(HBLIBS)

src/Makefile.sources

@@ -167,6 +167,7 @@ HB_BASE_sources = \
 	hb-unicode.hh \
 	hb-utf.hh \
 	hb-vector.hh \
+	hb-priority-queue.hh \
 	hb.hh \
 	$(NULL)
 

src/hb-priority-queue.hh

@@ -0,0 +1,149 @@
+/*
+ * 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_PRIORITY_QUEUE_HH
+#define HB_PRIORITY_QUEUE_HH
+
+#include "hb.hh"
+#include "hb-vector.hh"
+
+/*
+ * hb_priority_queue_t
+ *
+ * Priority queue implemented as a binary heap. Supports extract minimum
+ * and insert operations.
+ */
+struct hb_priority_queue_t
+{
+  HB_DELETE_COPY_ASSIGN (hb_priority_queue_t);
+  hb_priority_queue_t ()  { init (); }
+  ~hb_priority_queue_t () { fini (); }
+
+ private:
+  typedef hb_pair_t<unsigned, unsigned> item_t;
+  hb_vector_t<item_t> heap;
+
+ public:
+  void init () { heap.init (); }
+
+  void fini () { heap.fini (); }
+
+  void reset () { heap.resize (0); }
+
+  bool in_error () const { return heap.in_error (); }
+
+  void insert (unsigned value, unsigned priority)
+  {
+    heap.push (item_t (value, priority));
+    bubble_up (heap.length - 1);
+  }
+
+  item_t extract_minimum ()
+  {
+    item_t result = heap[0];
+
+    heap[0] = heap[heap.length - 1];
+    heap.shrink (heap.length - 1);
+    bubble_down (0);
+
+    return result;
+  }
+
+  const item_t& minimum ()
+  {
+    return heap[0];
+  }
+
+  bool is_empty () const { return heap.length == 0; }
+
+  /* Sink interface. */
+  hb_priority_queue_t& operator << (item_t item)
+  { insert (item.first, item.second); return *this; }
+
+ private:
+
+  unsigned parent (unsigned index)
+  {
+    return (index - 1) / 2;
+  }
+
+  unsigned left_child (unsigned index)
+  {
+    return 2 * index + 1;
+  }
+
+  unsigned right_child (unsigned index)
+  {
+    return 2 * index + 2;
+  }
+
+  void bubble_down (unsigned index)
+  {
+    unsigned left = left_child (index);
+    unsigned right = right_child (index);
+
+    bool has_left = left < heap.length;
+    if (!has_left)
+      // If there's no left, then there's also no right.
+      return;
+
+    bool has_right = right < heap.length;
+    if (heap[index] <= heap[left]
+        && (!has_right || heap[index] <= heap[right]))
+      return;
+
+    if (!has_right || heap[left] < heap[right])
+    {
+      swap (index, left);
+      bubble_down (left);
+      return;
+    }
+
+    swap (index, right);
+    bubble_down (right);
+  }
+
+  void bubble_up (unsigned index)
+  {
+    if (index == 0) return;
+
+    unsigned parent_index = parent (index);
+    if (heap[parent_index].second <= heap[index].second)
+      return;
+
+    swap (index, parent_index);
+    bubble_up (parent_index);
+  }
+
+  void swap (unsigned a, unsigned b)
+  {
+    item_t temp = heap[a];
+    heap[a] = heap[b];
+    heap[b] = temp;
+  }
+};
+
+#endif /* HB_PRIORITY_QUEUE_HH */

src/test-priority-queue.cc

@@ -0,0 +1,89 @@
+/*
+ * 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
+ */
+
+#include "hb.hh"
+#include "hb-priority-queue.hh"
+
+static void
+test_insert ()
+{
+  hb_priority_queue_t queue;
+  assert (queue.is_empty ());
+
+  queue.insert (0, 10);
+  assert (!queue.is_empty ());
+  assert (queue.minimum () == hb_pair (0, 10));
+
+  queue.insert (1, 20);
+  assert (queue.minimum () == hb_pair (0, 10));
+
+  queue.insert (2, 5);
+  assert (queue.minimum () == hb_pair (2, 5));
+
+  queue.insert (3, 15);
+  assert (queue.minimum () == hb_pair (2, 5));
+
+  queue.insert (4, 1);
+  assert (queue.minimum () == hb_pair (4, 1));
+}
+
+static void
+test_extract ()
+{
+  hb_priority_queue_t queue;
+  queue.insert (0, 0);
+  queue.insert (6, 60);
+  queue.insert (3, 30);
+  queue.insert (4, 40);
+  queue.insert (2, 20);
+  queue.insert (5, 50);
+  queue.insert (7, 70);
+  queue.insert (1, 10);
+
+  for (int i = 0; i < 8; i++)
+  {
+    assert (!queue.is_empty ());
+    assert (queue.minimum () == hb_pair (i, i * 10));
+    assert (queue.extract_minimum () == hb_pair (i, i * 10));
+  }
+
+  assert (queue.is_empty ());
+}
+
+static void
+test_extract_empty ()
+{
+  hb_priority_queue_t queue;
+  assert (queue.extract_minimum () == hb_pair (0, 0));
+}
+
+int
+main (int argc, char **argv)
+{
+  test_insert ();
+  test_extract ();
+  test_extract_empty ();
+}