2 * Copyright (C) 1995-2008 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
7 * GNU General Public License version 2 as published by the Free Software
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
36 * Implementation note: It might seem strange that we start indexing at 0
37 * but use 2*i and 2*i+1 to find the left and right sucessor of an index.
38 * The trick is that for index 0 the left successor is 0 again, and the
39 * right successor is 1 in this scheme. For the right successor 1 everything
40 * works like usual. We simply took care in the algorithms that they still
41 * work with the left child of 0 being 0 again. This was possible without
42 * any extra ifs or arithmetic.
43 * Thus we can save the wastage of 1 array position you can see in other
44 * implementations or the ugly (i+1)*2 - 1 and (i+1)*2 for calculating the
45 * left and right child. (At the expense that stuff easily breaks when you make
46 * changes and don't think that the left child of 0 is 0 :-/)
50 typedef struct _pqueue_el_t {
60 * Enforces the heap characteristics if the queue
61 * starting from element at position @p pos.
63 static void pqueue_heapify(pqueue_t *q, unsigned pos) {
64 unsigned len = ARR_LEN(q->elems);
66 while (pos * 2 < len) {
68 unsigned exchange = pos;
70 if (q->elems[exchange].priority < q->elems[pos * 2].priority) {
74 if ((pos * 2 + 1) < len
75 && q->elems[exchange].priority < q->elems[pos * 2 + 1].priority) {
76 exchange = pos * 2 + 1;
83 q->elems[pos] = q->elems[exchange];
84 q->elems[exchange] = tmp;
91 * Sifts up a newly inserted element at position @p pos.
93 static void pqueue_sift_up(pqueue_t *q, unsigned pos) {
94 while(q->elems[pos].priority > q->elems[pos / 2].priority) {
98 q->elems[pos] = q->elems[pos / 2];
99 q->elems[pos / 2] = tmp;
105 pqueue_t *new_pqueue(void) {
106 pqueue_t *res = XMALLOC(pqueue_t);
107 res->elems = NEW_ARR_F(pqueue_el_t, 0);
111 void del_pqueue(pqueue_t *q) {
116 void pqueue_put(pqueue_t *q, void *data, int priority) {
120 el.priority = priority;
122 ARR_APP1(pqueue_el_t, q->elems, el);
124 pqueue_sift_up(q, ARR_LEN(q->elems) - 1);
127 void *pqueue_pop_front(pqueue_t *q) {
128 switch(ARR_LEN(q->elems)) {
130 assert(0 && "Attempt to retrieve element from empty priority queue.");
134 ARR_SHRINKLEN(q->elems, 0);
135 return q->elems[0].data;
138 void *data = q->elems[0].data;
139 int len = ARR_LEN(q->elems) - 1;
141 q->elems[0] = q->elems[len];
142 ARR_SHRINKLEN(q->elems, len);
143 pqueue_heapify(q, 0);
150 int pqueue_length(const pqueue_t *q) {
151 return ARR_LEN(q->elems);
154 int pqueue_empty(const pqueue_t *q) {
155 return ARR_LEN(q->elems) == 0;