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/*
* Copyright (c) 2009, 2010 Richard Braun.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*
* 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;
}
}
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