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/* $NetBSD: linux_list_sort.c,v 1.2 2014/03/18 18:20:43 riastradh Exp $ */
/*-
* Copyright (c) 2013 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Taylor R. Campbell.
*
* 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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``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 FOUNDATION OR CONTRIBUTORS
* 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.
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <machine/limits.h>
#include <linux/list.h>
static struct list_head *
list_sort_merge(struct list_head *, struct list_head *,
int (*)(void *, struct list_head *,
struct list_head *), void *);
static void
list_sort_merge_into(struct list_head *,
struct list_head *, struct list_head *,
int (*)(void *, struct list_head *,
struct list_head *), void *);
void
list_sort(void *arg, struct list_head *list,
int (*compare)(void *, struct list_head *, struct list_head *))
{
/*
* Array of sorted sublists, counting in binary: accum[i]
* is sorted, and either is NULL or has length 2^i.
*/
struct list_head *accum[64];
/* Indices into accum. */
unsigned int logn, max_logn = 0;
/* The sorted list we're currently working on. */
struct list_head *sorted;
/* The remainder of the unsorted list. */
struct list_head *next;
/* Make sure we can't possibly have more than 2^64-element lists. */
CTASSERT((CHAR_BIT * sizeof(struct list_head *)) <= 64);
for (logn = 0; logn < nitems(accum); logn++)
accum[logn] = NULL;
list_for_each_safe(sorted, next, list) {
/* Pick off a single element, always sorted. */
sorted->next = NULL;
/* Add one and propagate the carry. */
for (logn = 0; accum[logn] != NULL; logn++) {
/*
* Merge, preferring previously accumulated
* elements to make the sort stable.
*/
sorted = list_sort_merge(accum[logn], sorted, compare, arg);
accum[logn] = NULL;
KASSERT((logn + 1) < nitems(accum));
}
/* Remember the highest index seen so far. */
if (logn > max_logn)
max_logn = logn;
/*
* logn = log_2(length(sorted)), and accum[logn]
* is now empty, so save the sorted sublist there.
*/
accum[logn] = sorted;
}
/*
* Merge ~half of everything we have accumulated.
*/
sorted = NULL;
for (logn = 0; logn < max_logn; logn++)
sorted = list_sort_merge(accum[logn], sorted, compare, arg);
/*
* Merge the last ~halves back into the list, and fix the back
* pointers.
*/
list_sort_merge_into(list, accum[max_logn], sorted, compare, arg);
}
/*
* Merge the NULL-terminated lists starting at nodes `a' and `b',
* breaking ties by choosing nodes in `a' first, and returning
* whichever node has the least element.
*/
static struct list_head *
list_sort_merge(struct list_head *a, struct list_head *b,
int (*compare)(void *, struct list_head *,
struct list_head *), void *arg)
{
struct list_head head, *tail = &head;
/*
* Merge while elements in both remain.
*/
while ((a != NULL) && (b != NULL)) {
struct list_head **const first = ((*compare)(arg, a, b) <= 0?
&a : &b);
tail = tail->next = *first;
*first = (*first)->next;
}
/*
* Attach whatever remains.
*/
tail->next = (a != NULL? a : b);
return head.next;
}
/*
* Merge the NULL-terminated lists starting at nodes `a' and `b' into
* the (uninitialized) list head `list', breaking ties by choosing
* nodes in `a' first, and setting the `prev' pointers as we go.
*/
static void
list_sort_merge_into(struct list_head *list,
struct list_head *a, struct list_head *b,
int (*compare)(void *, struct list_head *,
struct list_head *), void *arg)
{
struct list_head *prev = list;
/*
* Merge while elements in both remain.
*/
while ((a != NULL) && (b != NULL)) {
struct list_head **const first = (
(*compare)(arg, a, b) <= 0 ? &a : &b);
(*first)->prev = prev;
prev = prev->next = *first;
*first = (*first)->next;
}
/*
* Attach whichever of a and b remains, and fix up the prev
* pointers all the way down the rest of the list.
*/
struct list_head *tail = (a == NULL? b : a);
while (tail != NULL) {
prev->next = tail;
tail->prev = prev;
prev = prev->next;
tail = tail->next;
}
/*
* Finally, finish the cycle.
*/
prev->next = list;
list->prev = prev;
}
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