2 * Copyright © 2020 Google, Inc.
4 * This is part of HarfBuzz, a text shaping library.
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.
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
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.
24 * Google Author(s): Garret Rieger
27 #ifndef HB_PRIORITY_QUEUE_HH
28 #define HB_PRIORITY_QUEUE_HH
31 #include "hb-vector.hh"
36 * Priority queue implemented as a binary heap. Supports extract minimum
37 * and insert operations.
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.
46 struct hb_priority_queue_t
49 typedef hb_pair_t<K, unsigned> item_t;
50 hb_vector_t<item_t> heap;
54 void reset () { heap.resize (0); }
56 bool in_error () const { return heap.in_error (); }
58 #ifndef HB_OPTIMIZE_SIZE
61 void insert (K priority, unsigned value)
63 heap.push (item_t (priority, value));
64 if (unlikely (heap.in_error ())) return;
65 bubble_up (heap.length - 1);
68 #ifndef HB_OPTIMIZE_SIZE
73 assert (!is_empty ());
75 item_t result = heap.arrayZ[0];
77 heap.arrayZ[0] = heap.arrayZ[heap.length - 1];
78 heap.resize (heap.length - 1);
86 const item_t& minimum ()
91 bool is_empty () const { return heap.length == 0; }
92 explicit operator bool () const { return !is_empty (); }
93 unsigned int get_population () const { return heap.length; }
96 hb_priority_queue_t& operator << (item_t item)
97 { insert (item.first, item.second); return *this; }
101 static constexpr unsigned parent (unsigned index)
103 return (index - 1) / 2;
106 static constexpr unsigned left_child (unsigned index)
108 return 2 * index + 1;
111 static constexpr unsigned right_child (unsigned index)
113 return 2 * index + 2;
117 void bubble_down (unsigned index)
120 assert (index < heap.length);
122 unsigned left = left_child (index);
123 unsigned right = right_child (index);
125 bool has_left = left < heap.length;
127 // If there's no left, then there's also no right.
130 bool has_right = right < heap.length;
131 if (heap.arrayZ[index].first <= heap.arrayZ[left].first
132 && (!has_right || heap.arrayZ[index].first <= heap.arrayZ[right].first))
136 if (!has_right || heap.arrayZ[left].first < heap.arrayZ[right].first)
147 void bubble_up (unsigned index)
150 assert (index < heap.length);
152 if (index == 0) return;
154 unsigned parent_index = parent (index);
155 if (heap.arrayZ[parent_index].first <= heap.arrayZ[index].first)
158 swap (index, parent_index);
159 index = parent_index;
163 void swap (unsigned a, unsigned b)
165 assert (a < heap.length);
166 assert (b < heap.length);
167 hb_swap (heap.arrayZ[a], heap.arrayZ[b]);
171 #endif /* HB_PRIORITY_QUEUE_HH */