gfx/harfbuzz/src/hb-priority-queue.hh

   1 /*
   2  * Copyright © 2020  Google, Inc.
   3  *
   4  *  This is part of HarfBuzz, a text shaping library.
   5  *
   6  * Permission is hereby granted, without written agreement and without
   7  * license or royalty fees, to use, copy, modify, and distribute this
   8  * software and its documentation for any purpose, provided that the
   9  * above copyright notice and the following two paragraphs appear in
  10  * all copies of this software.
  11  *
  12  * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
  13  * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
  14  * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
  15  * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
  16  * DAMAGE.
  17  *
  18  * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
  19  * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
  20  * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
  21  * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
  22  * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
  23  *
  24  * Google Author(s): Garret Rieger
  25  */
  26
  27 #ifndef HB_PRIORITY_QUEUE_HH
  28 #define HB_PRIORITY_QUEUE_HH
  29
  30 #include "hb.hh"
  31 #include "hb-vector.hh"
  32
  33 /*
  34  * hb_priority_queue_t
  35  *
  36  * Priority queue implemented as a binary heap. Supports extract minimum
  37  * and insert operations.
  38  *
  39  * The priority queue is implemented as a binary heap, which is a complete
  40  * binary tree. The root of the tree is the minimum element. The heap
  41  * property is that the priority of a node is less than or equal to the
  42  * priority of its children. The heap is stored in an array, with the
  43  * children of node i stored at indices 2i + 1 and 2i + 2.
  44  */
  45 template <typename K>
  46 struct hb_priority_queue_t
  47 {
  48  private:
  49   typedef hb_pair_t<K, unsigned> item_t;
  50   hb_vector_t<item_t> heap;
  51
  52  public:
  53
  54   void reset () { heap.resize (0); }
  55
  56   bool in_error () const { return heap.in_error (); }
  57
  58   bool alloc (unsigned size)
  59   { return heap.alloc (size); }
  60
  61 #ifndef HB_OPTIMIZE_SIZE
  62   HB_ALWAYS_INLINE
  63 #endif
  64   void insert (K priority, unsigned value)
  65   {
  66     heap.push (item_t (priority, value));
  67     if (unlikely (heap.in_error ())) return;
  68     bubble_up (heap.length - 1);
  69   }
  70
  71 #ifndef HB_OPTIMIZE_SIZE
  72   HB_ALWAYS_INLINE
  73 #endif
  74   item_t pop_minimum ()
  75   {
  76     assert (!is_empty ());
  77
  78     item_t result = heap.arrayZ[0];
  79
  80     heap.arrayZ[0] = heap.arrayZ[heap.length - 1];
  81     heap.resize (heap.length - 1);
  82
  83     if (!is_empty ())
  84       bubble_down (0);
  85
  86     return result;
  87   }
  88
  89   const item_t& minimum ()
  90   {
  91     return heap[0];
  92   }
  93
  94   bool is_empty () const { return heap.length == 0; }
  95   explicit operator bool () const { return !is_empty (); }
  96   unsigned int get_population () const { return heap.length; }
  97
  98   /* Sink interface. */
  99   hb_priority_queue_t& operator << (item_t item)
 100   { insert (item.first, item.second); return *this; }
 101
 102  private:
 103
 104   static constexpr unsigned parent (unsigned index)
 105   {
 106     return (index - 1) / 2;
 107   }
 108
 109   static constexpr unsigned left_child (unsigned index)
 110   {
 111     return 2 * index + 1;
 112   }
 113
 114   static constexpr unsigned right_child (unsigned index)
 115   {
 116     return 2 * index + 2;
 117   }
 118
 119   HB_ALWAYS_INLINE
 120   void bubble_down (unsigned index)
 121   {
 122     repeat:
 123     assert (index < heap.length);
 124
 125     unsigned left = left_child (index);
 126     unsigned right = right_child (index);
 127
 128     bool has_left = left < heap.length;
 129     if (!has_left)
 130       // If there's no left, then there's also no right.
 131       return;
 132
 133     bool has_right = right < heap.length;
 134     if (heap.arrayZ[index].first <= heap.arrayZ[left].first
 135         && (!has_right || heap.arrayZ[index].first <= heap.arrayZ[right].first))
 136       return;
 137
 138     unsigned child;
 139     if (!has_right || heap.arrayZ[left].first < heap.arrayZ[right].first)
 140       child = left;
 141     else
 142       child = right;
 143
 144     swap (index, child);
 145     index = child;
 146     goto repeat;
 147   }
 148
 149   HB_ALWAYS_INLINE
 150   void bubble_up (unsigned index)
 151   {
 152     repeat:
 153     assert (index < heap.length);
 154
 155     if (index == 0) return;
 156
 157     unsigned parent_index = parent (index);
 158     if (heap.arrayZ[parent_index].first <= heap.arrayZ[index].first)
 159       return;
 160
 161     swap (index, parent_index);
 162     index = parent_index;
 163     goto repeat;
 164   }
 165
 166   void swap (unsigned a, unsigned b)
 167   {
 168     assert (a < heap.length);
 169     assert (b < heap.length);
 170     hb_swap (heap.arrayZ[a], heap.arrayZ[b]);
 171   }
 172 };
 173
 174 #endif /* HB_PRIORITY_QUEUE_HH */