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+/* gheap.c
+ *
+ * Copyright (C) 2014 Christian Hergert <christian@hergert.me>
+ *
+ * This file is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This file is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include <string.h>
+
+#include "gheap.h"
+
+/**
+ * SECTION:gheap
+ * @title: Heaps
+ * @short_description: efficient priority queues using min/max heaps
+ *
+ * Heaps are similar to a partially sorted tree but implemented as an
+ * array. They allow for efficient O(1) lookup of the highest priority
+ * item as it will always be the first item of the array.
+ *
+ * To create a new heap use g_heap_new().
+ *
+ * To add items to the heap, use g_heap_insert_val() or
+ * g_heap_insert_vals() to insert in bulk.
+ *
+ * To access an item in the heap, use g_heap_index().
+ *
+ * To remove an arbitrary item from the heap, use g_heap_extract_index().
+ *
+ * To remove the highest priority item in the heap, use g_heap_extract().
+ *
+ * To free a heap, use g_heap_unref().
+ *
+ * Here is an example that stores integers in a #GHeap:
+ * |[<!-- language="C" -->
+ * static int
+ * cmpint (gconstpointer a,
+ * gconstpointer b)
+ * {
+ * return *(const gint *)a - *(const gint *)b;
+ * }
+ *
+ * int
+ * main (gint argc,
+ * gchar *argv[])
+ * {
+ * GHeap *heap;
+ * gint i;
+ * gint v;
+ *
+ * heap = g_heap_new (sizeof (gint), cmpint);
+ *
+ * for (i = 0; i < 10000; i++)
+ * g_heap_insert_val (heap, i);
+ * for (i = 0; i < 10000; i++)
+ * g_heap_extract (heap, &v);
+ *
+ * g_heap_unref (heap);
+ * }
+ * ]|
+ */
+
+#define MIN_HEAP_SIZE 16
+
+/*
+ * Based upon Mastering Algorithms in C by Kyle Loudon.
+ * Section 10 - Heaps and Priority Queues.
+ */
+
+typedef struct _GHeapReal GHeapReal;
+
+struct _GHeapReal
+{
+ gchar *data;
+ gsize len;
+ volatile gint ref_count;
+ guint element_size;
+ gsize allocated_len;
+ GCompareFunc compare;
+ gchar tmp[0];
+};
+
+#define heap_parent(npos) (((npos)-1)/2)
+#define heap_left(npos) (((npos)*2)+1)
+#define heap_right(npos) (((npos)*2)+2)
+#define heap_index(h,i) ((h)->data + (i * (h)->element_size))
+#define heap_compare(h,a,b) ((h)->compare(heap_index(h,a), heap_index(h,b)))
+#define heap_swap(h,a,b) \
+ G_STMT_START { \
+ memcpy ((h)->tmp, heap_index (h, a), (h)->element_size); \
+ memcpy (heap_index (h, a), heap_index (h, b), (h)->element_size); \
+ memcpy (heap_index (h, b), (h)->tmp, (h)->element_size); \
+ } G_STMT_END
+
+GHeap *
+g_heap_new (guint element_size,
+ GCompareFunc compare_func)
+{
+ GHeapReal *real;
+
+ g_return_val_if_fail (element_size, NULL);
+ g_return_val_if_fail (compare_func, NULL);
+
+ real = g_malloc_n (1, sizeof (GHeapReal) + element_size);
+ real->data = NULL;
+ real->len = 0;
+ real->ref_count = 1;
+ real->element_size = element_size;
+ real->allocated_len = 0;
+ real->compare = compare_func;
+
+ return (GHeap *)real;
+}
+
+GHeap *
+g_heap_ref (GHeap *heap)
+{
+ GHeapReal *real = (GHeapReal *)heap;
+
+ g_return_val_if_fail (heap, NULL);
+ g_return_val_if_fail (real->ref_count, NULL);
+
+ g_atomic_int_inc (&real->ref_count);
+
+ return heap;
+}
+
+static void
+g_heap_real_free (GHeapReal *real)
+{
+ g_assert (real);
+ g_assert_cmpint (real->ref_count, ==, 0);
+
+ g_free (real->data);
+ g_free (real);
+}
+
+void
+g_heap_unref (GHeap *heap)
+{
+ GHeapReal *real = (GHeapReal *)heap;
+
+ g_return_if_fail (heap);
+ g_return_if_fail (real->ref_count);
+
+ if (g_atomic_int_dec_and_test (&real->ref_count)) {
+ g_heap_real_free (real);
+ }
+}
+
+static void
+g_heap_real_grow (GHeapReal *real)
+{
+ g_assert (real);
+ g_assert_cmpint (real->allocated_len, <, G_MAXSIZE / 2);
+
+ real->allocated_len = MAX (MIN_HEAP_SIZE, (real->allocated_len * 2));
+ real->data = g_realloc_n (real->data,
+ real->allocated_len,
+ real->element_size);
+}
+
+static void
+g_heap_real_shrink (GHeapReal *real)
+{
+ g_assert (real);
+ g_assert ((real->allocated_len / 2) >= real->len);
+
+ real->allocated_len = MAX (MIN_HEAP_SIZE, real->allocated_len / 2);
+ real->data = g_realloc_n (real->data,
+ real->allocated_len,
+ real->element_size);
+}
+
+static void
+g_heap_real_insert_val (GHeapReal *real,
+ gconstpointer data)
+{
+ gint ipos;
+ gint ppos;
+
+ g_assert (real);
+ g_assert (data);
+
+ if (G_UNLIKELY (real->len == real->allocated_len)) {
+ g_heap_real_grow (real);
+ }
+
+ memcpy (real->data + (real->element_size * real->len), data,
+ real->element_size);
+
+ ipos = real->len;
+ ppos = heap_parent (ipos);
+
+ while ((ipos > 0) && (heap_compare (real, ppos, ipos) < 0)) {
+ heap_swap (real, ppos, ipos);
+ ipos = ppos;
+ ppos = heap_parent (ipos);
+ }
+
+ real->len++;
+}
+
+void
+g_heap_insert_vals (GHeap *heap,
+ gconstpointer data,
+ guint len)
+{
+ GHeapReal *real = (GHeapReal *)heap;
+ const gchar *ptr = data;
+ guint i;
+
+ g_return_if_fail (heap);
+ g_return_if_fail (data);
+ g_return_if_fail (len);
+
+ for (i = 0; i < len; i++, ptr += real->element_size) {
+ g_heap_real_insert_val (real, ptr);
+ }
+}
+
+gboolean
+g_heap_extract (GHeap *heap,
+ gpointer result)
+{
+ GHeapReal *real = (GHeapReal *)heap;
+ gboolean ret;
+ gint ipos;
+ gint lpos;
+ gint rpos;
+ gint mpos;
+
+ g_return_val_if_fail (heap, FALSE);
+
+ ret = (real->len > 0);
+
+ if (ret) {
+ if (result) {
+ memcpy (result, heap_index (real, 0), real->element_size);
+ }
+
+ if (real->len && --real->len) {
+ memmove (real->data, heap_index (real, real->len), real->element_size);
+
+ ipos = 0;
+
+ for (;;) {
+ lpos = heap_left (ipos);
+ rpos = heap_right (ipos);
+
+ if ((lpos < real->len) && (heap_compare (real, lpos, ipos) > 0)) {
+ mpos = lpos;
+ } else {
+ mpos = ipos;
+ }
+
+ if ((rpos < real->len) && (heap_compare (real, rpos, mpos) > 0)) {
+ mpos = rpos;
+ }
+
+ if (mpos == ipos) {
+ break;
+ }
+
+ heap_swap (real, mpos, ipos);
+
+ ipos = mpos;
+ }
+ }
+ }
+
+ if ((real->len >= MIN_HEAP_SIZE) &&
+ (real->allocated_len / 2) >= real->len) {
+ g_heap_real_shrink (real);
+ }
+
+ return ret;
+}
+
+gboolean
+g_heap_extract_index (GHeap *heap,
+ guint index_,
+ gpointer result)
+{
+ GHeapReal *real = (GHeapReal *)heap;
+ gboolean ret;
+ gint ipos;
+ gint lpos;
+ gint mpos;
+ gint ppos;
+ gint rpos;
+
+ g_return_val_if_fail (heap, FALSE);
+
+ ret = (real->len > 0);
+
+ if (real->len) {
+ if (result) {
+ memcpy (result, heap_index (real, 0), real->element_size);
+ }
+
+ real->len--;
+
+ if (real->len && index_ != real->len) {
+ memcpy (heap_index (real, index_),
+ heap_index (real, real->len),
+ real->element_size);
+
+ ipos = index_;
+ ppos = heap_parent (ipos);
+
+ while (heap_compare (real, ipos, ppos) > 0) {
+ heap_swap (real, ipos, ppos);
+ ipos = ppos;
+ ppos = heap_parent (ppos);
+ }
+
+ if (ipos == index_) {
+ for (;;) {
+ lpos = heap_left (ipos);
+ rpos = heap_right (ipos);
+
+ if ((lpos < real->len) && (heap_compare (real, lpos, ipos) > 0)) {
+ mpos = lpos;
+ } else {
+ mpos = ipos;
+ }
+
+ if ((rpos < real->len) && (heap_compare (real, rpos, mpos) > 0)) {
+ mpos = rpos;
+ }
+
+ if (mpos == ipos) {
+ break;
+ }
+
+ heap_swap (real, mpos, ipos);
+
+ ipos = mpos;
+ }
+ }
+ }
+ }
+
+ if ((real->len >= MIN_HEAP_SIZE) &&
+ (real->allocated_len / 2) >= real->len) {
+ g_heap_real_shrink (real);
+ }
+
+ return ret;
+}
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