154 lines
3.7 KiB
C++
154 lines
3.7 KiB
C++
/*
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* Copyright © 2020 Google, Inc.
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*
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* This is part of HarfBuzz, a text shaping library.
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*
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* Permission is hereby granted, without written agreement and without
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* license or royalty fees, to use, copy, modify, and distribute this
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* software and its documentation for any purpose, provided that the
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* above copyright notice and the following two paragraphs appear in
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* all copies of this software.
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*
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* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
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* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
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* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
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* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*
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* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
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* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
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* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
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* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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*
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* Google Author(s): Garret Rieger
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*/
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#ifndef HB_PRIORITY_QUEUE_HH
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#define HB_PRIORITY_QUEUE_HH
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#include "hb.hh"
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#include "hb-vector.hh"
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/*
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* hb_priority_queue_t
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*
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* Priority queue implemented as a binary heap. Supports extract minimum
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* and insert operations.
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*/
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struct hb_priority_queue_t
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{
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private:
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typedef hb_pair_t<int64_t, unsigned> item_t;
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hb_vector_t<item_t> heap;
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public:
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void reset () { heap.resize (0); }
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bool in_error () const { return heap.in_error (); }
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void insert (int64_t priority, unsigned value)
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{
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heap.push (item_t (priority, value));
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if (unlikely (heap.in_error ())) return;
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bubble_up (heap.length - 1);
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}
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item_t pop_minimum ()
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{
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assert (!is_empty ());
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item_t result = heap.arrayZ[0];
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heap.arrayZ[0] = heap.arrayZ[heap.length - 1];
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heap.shrink (heap.length - 1);
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if (!is_empty ())
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bubble_down (0);
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return result;
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}
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const item_t& minimum ()
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{
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return heap[0];
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}
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bool is_empty () const { return heap.length == 0; }
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explicit operator bool () const { return !is_empty (); }
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unsigned int get_population () const { return heap.length; }
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/* Sink interface. */
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hb_priority_queue_t& operator << (item_t item)
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{ insert (item.first, item.second); return *this; }
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private:
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static constexpr unsigned parent (unsigned index)
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{
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return (index - 1) / 2;
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}
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static constexpr unsigned left_child (unsigned index)
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{
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return 2 * index + 1;
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}
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static constexpr unsigned right_child (unsigned index)
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{
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return 2 * index + 2;
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}
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void bubble_down (unsigned index)
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{
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assert (index < heap.length);
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unsigned left = left_child (index);
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unsigned right = right_child (index);
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bool has_left = left < heap.length;
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if (!has_left)
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// If there's no left, then there's also no right.
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return;
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bool has_right = right < heap.length;
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if (heap.arrayZ[index].first <= heap.arrayZ[left].first
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&& (!has_right || heap.arrayZ[index].first <= heap.arrayZ[right].first))
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return;
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if (!has_right || heap.arrayZ[left].first < heap.arrayZ[right].first)
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{
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swap (index, left);
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bubble_down (left);
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return;
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}
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swap (index, right);
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bubble_down (right);
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}
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void bubble_up (unsigned index)
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{
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assert (index < heap.length);
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if (index == 0) return;
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unsigned parent_index = parent (index);
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if (heap.arrayZ[parent_index].first <= heap.arrayZ[index].first)
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return;
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swap (index, parent_index);
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bubble_up (parent_index);
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}
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void swap (unsigned a, unsigned b)
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{
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assert (a < heap.length);
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assert (b < heap.length);
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hb_swap (heap.arrayZ[a], heap.arrayZ[b]);
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}
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};
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#endif /* HB_PRIORITY_QUEUE_HH */
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