initial checkin of priority queue implementation

[r12714]

ir/adt/pqueue.c

+#include "array.h"
+#include "pqueue.h"
+
+/**
+ * Implements a heap.
+ *
+ * Implementation note: It might seem strange that we start indexing at 0
+ * but use 2*i and 2*i+1 to find the left and right sucessor of an index.
+ * The trick is that for index 0 the left successor is 0 again, and the
+ * right successor is 1 in this scheme. For the right successor 1 everything
+ * works like usual. We simply took care in the algorithms that they still
+ * work with the left child of 0 being 0 again. This was possible without
+ * any extra ifs or arithmetic.
+ * Thus we can save the wastage of 1 array position you can see in other
+ * implementations or the ugly (i+1)*2 - 1 and (i+1)*2 for calculating the
+ * left and right child. (At the expense that stuff easily breaks when you make
+ * changes and don't think that the left child of 0 is 0 :-/)
+ * @author matze
+ *
+ */
+
+typedef struct _pqueue_el_t {
+	void *data;
+	int  key;
+} pqueue_el_t;
+
+struct _pqueue_t {
+	pqueue_el_t *elems;
+};
+
+/**
+ * Enforces the heap characteristics if the queue
+ * starting from element at position @p pos.
+ */
+static void pqueue_heapify(pqueue *q, int pos) {
+	int len = ARR_LEN(q->elems);
+
+	while (pos * 2 < len) {
+		pqueue_el_t tmp;
+		int         exchange = pos;
+
+		if (q->elems[exchange].key < q->elems[pos * 2].key) {
+			exchange = pos * 2;
+		}
+
+		if ((pos * 2 + 1) < len && q->elems[exchange].key < q->elems[pos * 2 + 1].key) {
+			exchange = pos * 2 + 1;
+		}
+
+		if (exchange == pos)
+			break;
+
+		tmp                = q->elems[pos];
+		q->elems[pos]      = q->elems[exchange];
+		q->elems[exchange] = tmp;
+
+		pos = exchange;
+	}
+}
+
+/**
+ * Sifts up a newly inserted element at position @p pos.
+ */
+static void pqueue_sift_up(pqueue *q, int pos) {
+	while(q->elems[pos].key > q->elems[pos / 2].key) {
+		pqueue_el_t tmp;
+
+		tmp               = q->elems[pos];
+		q->elems[pos]     = q->elems[pos / 2];
+		q->elems[pos / 2] = tmp;
+
+		pos /= 2;
+	}
+}
+
+/**
+ * Creates a new priority queue.
+ * @return A priority queue of initial length 0.
+ */
+pqueue *new_pqueue() {
+	pqueue *res = xmalloc(sizeof(*res));
+	res->elems = NEW_ARR_F(pqueue_el_t, 0);
+	return res;
+}
+
+/**
+ * Frees all memory allocated by the priority queue.
+ * @param q   The priority queue to destroy.
+ */
+void del_pqueue(pqueue *q) {
+	DEL_ARR_F(q->elems);
+	free(q);
+}
+
+/**
+ * Inserts a new element into a priority queue.
+ * @param q      The priority queue the element should be inserted to.
+ * @param data   The actual data which should be stored in the queue.
+ * @param key    The priority for the data.
+ */
+void pqueue_put(pqueue *q, void *data, int key) {
+	pqueue_el_t el;
+
+	el.data = data;
+	el.key  = key;
+
+	ARR_APP1(pqueue_el_t, q->elems, el);
+
+	pqueue_sift_up(q, ARR_LEN(q->elems));
+}
+
+/**
+ * Returns and removes the first element, ie. that one with the highest priority, from the queue.
+ * @param q   The priority queue.
+ * @return The first element of the queue. Asserts if queue is empty.
+ */
+void *pqueue_get(pqueue *q) {
+	switch(ARR_LEN(q->elems)) {
+		case 0:
+			assert(0 && "Attempt to retrieve element from empty priority queue.");
+			return NULL;
+			break;
+		case 1:
+			ARR_SHRINKLEN(q->elems, 0);
+			return q->elems[0].data;
+			break;
+		default: {
+			void *data = q->elems[0].data;
+			int  len   = ARR_LEN(q->elems) - 1;
+
+			q->elems[0] = q->elems[len];
+			ARR_SHRINKLEN(q->elems, len);
+			pqueue_heapify(q, 0);
+
+			return data;
+		}
+	}
+}
+
+/**
+ * Get the length of the priority queue.
+ * @param q   The priority queue.
+ * @return The length of the queue.
+ */
+int pqueue_length(pqueue *q) {
+	return ARR_LEN(q->elems);
+}
+
+/**
+ * Returns true if queue is empty.
+ * @param q   The priority queue.
+ * @return 1 if the queue is empty, 0 otherwise.
+ */
+int pqueue_empty(pqueue *q) {
+	return ARR_LEN(q->elems) == 0;
+}

ir/adt/pqueue.h

+/**
+* @file    pqueue.h
+* @date    18.04.2007
+* @author  Christian Wuerdig
+* @brief   Implementation of a priority queue. This is the ported version of the
+*          original Java implementation by Matthias Braun.
+* @version $Id$
+*/
+
+#ifndef _PQUEUE_H_
+#define _PQUEUE_H_
+
+typedef struct _pqueue_t pqueue;
+
+/**
+ * Creates a new priority queue.
+ * @return A priority queue of initial length 0.
+ */
+pqueue *new_pqueue();
+
+/**
+ * Frees all memory allocated by the priority queue.
+ * @param q   The priority queue to destroy.
+ */
+void del_pqueue(pqueue *q);
+
+/**
+ * Inserts a new element into a priority queue.
+ * @param q      The priority queue the element should be inserted to.
+ * @param data   The actual data which should be stored in the queue.
+ * @param key    The priority for the data.
+ */
+void pqueue_put(pqueue *q, void *data, int key);
+
+/**
+ * Returns and removes the first element, ie. that one with the highest priority, from the queue.
+ * @param q   The priority queue.
+ * @return The first element of the queue. Asserts if queue is empty.
+ */
+void *pqueue_get(pqueue *q);
+
+/**
+ * Get the length of the priority queue.
+ * @param q   The priority queue.
+ * @return The length of the queue.
+ */
+int pqueue_length(pqueue *q);
+
+/**
+ * Returns true if queue is empty.
+ * @param q   The priority queue.
+ * @return 1 if the queue is empty, 0 otherwise.
+ */
+int pqueue_empty(pqueue *q);
+
+#endif /* _PQUEUE_H_ */