2 * Copyright (C) 1995-2007 University of Karlsruhe. All right reserved.
4 * This file is part of libFirm.
6 * This file may be distributed and/or modified under the terms of the
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8 * Foundation and appearing in the file LICENSE.GPL included in the
9 * packaging of this file.
11 * Licensees holding valid libFirm Professional Edition licenses may use
12 * this file in accordance with the libFirm Commercial License.
13 * Agreement provided with the Software.
15 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
16 * WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * @author Christian Wuerdig, Matthias Braun
23 * @brief Priority Queue implementation based on the heap datastructure
32 * Implementation note: It might seem strange that we start indexing at 0
33 * but use 2*i and 2*i+1 to find the left and right sucessor of an index.
34 * The trick is that for index 0 the left successor is 0 again, and the
35 * right successor is 1 in this scheme. For the right successor 1 everything
36 * works like usual. We simply took care in the algorithms that they still
37 * work with the left child of 0 being 0 again. This was possible without
38 * any extra ifs or arithmetic.
39 * Thus we can save the wastage of 1 array position you can see in other
40 * implementations or the ugly (i+1)*2 - 1 and (i+1)*2 for calculating the
41 * left and right child. (At the expense that stuff easily breaks when you make
42 * changes and don't think that the left child of 0 is 0 :-/)
46 typedef struct _pqueue_el_t {
56 * Enforces the heap characteristics if the queue
57 * starting from element at position @p pos.
59 static void pqueue_heapify(pqueue *q, int pos) {
60 int len = ARR_LEN(q->elems);
62 while (pos * 2 < len) {
66 if (q->elems[exchange].key < q->elems[pos * 2].key) {
70 if ((pos * 2 + 1) < len && q->elems[exchange].key < q->elems[pos * 2 + 1].key) {
71 exchange = pos * 2 + 1;
78 q->elems[pos] = q->elems[exchange];
79 q->elems[exchange] = tmp;
86 * Sifts up a newly inserted element at position @p pos.
88 static void pqueue_sift_up(pqueue *q, int pos) {
89 while(q->elems[pos].key > q->elems[pos / 2].key) {
93 q->elems[pos] = q->elems[pos / 2];
94 q->elems[pos / 2] = tmp;
101 * Creates a new priority queue.
102 * @return A priority queue of initial length 0.
104 pqueue *new_pqueue(void) {
105 pqueue *res = xmalloc(sizeof(*res));
106 res->elems = NEW_ARR_F(pqueue_el_t, 0);
111 * Frees all memory allocated by the priority queue.
112 * @param q The priority queue to destroy.
114 void del_pqueue(pqueue *q) {
120 * Inserts a new element into a priority queue.
121 * @param q The priority queue the element should be inserted to.
122 * @param data The actual data which should be stored in the queue.
123 * @param key The priority for the data.
125 void pqueue_put(pqueue *q, void *data, int key) {
131 ARR_APP1(pqueue_el_t, q->elems, el);
133 pqueue_sift_up(q, ARR_LEN(q->elems) - 1);
137 * Returns and removes the first element, ie. that one with the highest priority, from the queue.
138 * @param q The priority queue.
139 * @return The first element of the queue. Asserts if queue is empty.
141 void *pqueue_get(pqueue *q) {
142 switch(ARR_LEN(q->elems)) {
144 assert(0 && "Attempt to retrieve element from empty priority queue.");
148 ARR_SHRINKLEN(q->elems, 0);
149 return q->elems[0].data;
152 void *data = q->elems[0].data;
153 int len = ARR_LEN(q->elems) - 1;
155 q->elems[0] = q->elems[len];
156 ARR_SHRINKLEN(q->elems, len);
157 pqueue_heapify(q, 0);
165 * Get the length of the priority queue.
166 * @param q The priority queue.
167 * @return The length of the queue.
169 int pqueue_length(pqueue *q) {
170 return ARR_LEN(q->elems);
174 * Returns true if queue is empty.
175 * @param q The priority queue.
176 * @return 1 if the queue is empty, 0 otherwise.
178 int pqueue_empty(pqueue *q) {
179 return ARR_LEN(q->elems) == 0;