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+/*
+ * Copyright (c) 2009-2015 Richard Braun.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ *
+ * Upstream site with license notes :
+ * http://git.sceen.net/rbraun/librbraun.git/
+ *
+ *
+ * List sorting implementation.
+ *
+ * In addition to most common list operations, this implementation includes
+ * a sort operation. The algorithm used is a variant of the bottom-up
+ * mergesort algorithm. It has the following properties :
+ * - It is iterative (no recursion overhead).
+ * - It is stable (the relative order of equal entries is preserved).
+ * - It only requires constant additional space (as it works on linked lists).
+ * - It performs at O(n log n) for average and worst cases.
+ * - It is adaptive, performing faster on already sorted lists.
+ */
+
+#include "list.h"
+
+/*
+ * Split input_list into two lists.
+ *
+ * The list_size first entries of input_list are moved into left_list while
+ * the "right" list is actually the list_size first entries of input_list
+ * after completion.
+ */
+static void
+_list_divide(struct list *input_list, struct list *left_list,
+ unsigned int list_size)
+{
+ struct list *node;
+ unsigned int i;
+
+ node = input_list->next;
+
+ for (i = 0; (i < list_size) && !list_end(input_list, node); i++) {
+ node = node->next;
+ }
+
+ list_split(left_list, input_list, node);
+}
+
+/*
+ * Merge left_list and right_list at the tail of output_list.
+ */
+static void
+_list_merge(struct list *left_list, struct list *right_list,
+ struct list *output_list, unsigned int right_list_size,
+ list_sort_cmp_fn_t cmp_fn)
+{
+ struct list *left, *right;
+
+ left = left_list->prev;
+ right = right_list->next;
+
+ /*
+ * Try to concatenate lists instead of merging first. This reduces
+ * complexity for already sorted lists.
+ */
+ if (!list_end(left_list, left)
+ && ((right_list_size > 0) && !list_end(right_list, right))
+ && (cmp_fn(left, right) <= 0)) {
+ struct list tmp_list;
+
+ list_concat(output_list, left_list);
+ list_init(left_list);
+
+ while ((right_list_size > 0) && !list_end(right_list, right)) {
+ right = right->next;
+ right_list_size--;
+ }
+
+ list_split(&tmp_list, right_list, right);
+ list_concat(output_list, &tmp_list);
+ return;
+ }
+
+ left = left_list->next;
+
+ while (!list_end(left_list, left)
+ || ((right_list_size > 0) && !list_end(right_list, right)))
+ if (((right_list_size == 0) || list_end(right_list, right))
+ || (!list_end(left_list, left) && (cmp_fn(left, right) <= 0))) {
+ list_remove(left);
+ list_insert_tail(output_list, left);
+ left = left_list->next;
+ } else {
+ list_remove(right);
+ list_insert_tail(output_list, right);
+ right = right_list->next;
+ right_list_size--;
+ }
+}
+
+void
+list_sort(struct list *list, list_sort_cmp_fn_t cmp_fn)
+{
+ struct list left_list, output_list;
+ unsigned int list_size, nr_merges;
+
+ list_init(&left_list);
+ list_init(&output_list);
+
+ for (list_size = 1; /* no condition */; list_size <<= 1) {
+ for (nr_merges = 0; /* no condition */; nr_merges++) {
+ if (list_empty(list)) {
+ break;
+ }
+
+ _list_divide(list, &left_list, list_size);
+ _list_merge(&left_list, list, &output_list, list_size, cmp_fn);
+ }
+
+ list_concat(list, &output_list);
+ list_init(&output_list);
+
+ if (nr_merges <= 1) {
+ return;
+ }
+ }
+}