1 | /* $NetBSD: linux_list_sort.c,v 1.2 2014/03/18 18:20:43 riastradh Exp $ */ |
2 | |
3 | /*- |
4 | * Copyright (c) 2013 The NetBSD Foundation, Inc. |
5 | * All rights reserved. |
6 | * |
7 | * This code is derived from software contributed to The NetBSD Foundation |
8 | * by Taylor R. Campbell. |
9 | * |
10 | * Redistribution and use in source and binary forms, with or without |
11 | * modification, are permitted provided that the following conditions |
12 | * are met: |
13 | * 1. Redistributions of source code must retain the above copyright |
14 | * notice, this list of conditions and the following disclaimer. |
15 | * 2. Redistributions in binary form must reproduce the above copyright |
16 | * notice, this list of conditions and the following disclaimer in the |
17 | * documentation and/or other materials provided with the distribution. |
18 | * |
19 | * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS |
20 | * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED |
21 | * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
22 | * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS |
23 | * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
24 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
25 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
26 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
27 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
28 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
29 | * POSSIBILITY OF SUCH DAMAGE. |
30 | */ |
31 | |
32 | #include <sys/cdefs.h> |
33 | __KERNEL_RCSID(0, "$NetBSD: linux_list_sort.c,v 1.2 2014/03/18 18:20:43 riastradh Exp $" ); |
34 | |
35 | #include <sys/systm.h> |
36 | |
37 | #include <machine/limits.h> |
38 | |
39 | #include <linux/list.h> |
40 | #include <linux/list_sort.h> |
41 | |
42 | static struct list_head * |
43 | list_sort_merge(struct list_head *, struct list_head *, |
44 | int (*)(void *, struct list_head *, struct list_head *), |
45 | void *); |
46 | static void list_sort_merge_into(struct list_head *, |
47 | struct list_head *, struct list_head *, |
48 | int (*)(void *, struct list_head *, struct list_head *), |
49 | void *); |
50 | |
51 | void |
52 | list_sort(void *arg, struct list_head *list, |
53 | int (*compare)(void *, struct list_head *, struct list_head *)) |
54 | { |
55 | /* |
56 | * Array of sorted sublists, counting in binary: accumulator[i] |
57 | * is sorted, and either is NULL or has length 2^i. |
58 | */ |
59 | struct list_head *accumulator[64]; |
60 | |
61 | /* Indices into accumulator. */ |
62 | unsigned int logn, max_logn = 0; |
63 | |
64 | /* The sorted list we're currently working on. */ |
65 | struct list_head *sorted; |
66 | |
67 | /* The remainder of the unsorted list. */ |
68 | struct list_head *next; |
69 | |
70 | /* Make sure we can't possibly have more than 2^64-element lists. */ |
71 | __CTASSERT((CHAR_BIT * sizeof(struct list_head *)) <= 64); |
72 | |
73 | for (logn = 0; logn < __arraycount(accumulator); logn++) |
74 | accumulator[logn] = NULL; |
75 | |
76 | list_for_each_safe(sorted, next, list) { |
77 | /* Pick off a single element, always sorted. */ |
78 | sorted->next = NULL; |
79 | |
80 | /* Add one and propagate the carry. */ |
81 | for (logn = 0; accumulator[logn] != NULL; logn++) { |
82 | /* |
83 | * Merge, preferring previously accumulated |
84 | * elements to make the sort stable. |
85 | */ |
86 | sorted = list_sort_merge(accumulator[logn], sorted, |
87 | compare, arg); |
88 | accumulator[logn] = NULL; |
89 | KASSERT((logn + 1) < __arraycount(accumulator)); |
90 | } |
91 | |
92 | /* Remember the highest index seen so far. */ |
93 | if (logn > max_logn) |
94 | max_logn = logn; |
95 | |
96 | /* |
97 | * logn = log_2(length(sorted)), and accumulator[logn] |
98 | * is now empty, so save the sorted sublist there. |
99 | */ |
100 | accumulator[logn] = sorted; |
101 | } |
102 | |
103 | /* |
104 | * Merge ~half of everything we have accumulated. |
105 | */ |
106 | sorted = NULL; |
107 | for (logn = 0; logn < max_logn; logn++) |
108 | sorted = list_sort_merge(accumulator[logn], sorted, compare, |
109 | arg); |
110 | |
111 | /* |
112 | * Merge the last ~halves back into the list, and fix the back |
113 | * pointers. |
114 | */ |
115 | list_sort_merge_into(list, accumulator[max_logn], sorted, compare, |
116 | arg); |
117 | } |
118 | |
119 | /* |
120 | * Merge the NULL-terminated lists starting at nodes `a' and `b', |
121 | * breaking ties by choosing nodes in `a' first, and returning |
122 | * whichever node has the least element. |
123 | */ |
124 | static struct list_head * |
125 | list_sort_merge(struct list_head *a, struct list_head *b, |
126 | int (*compare)(void *, struct list_head *, struct list_head *), void *arg) |
127 | { |
128 | struct list_head head, *tail = &head; |
129 | |
130 | /* |
131 | * Merge while elements in both remain. |
132 | */ |
133 | while ((a != NULL) && (b != NULL)) { |
134 | struct list_head **const first = ((*compare)(arg, a, b) <= 0? |
135 | &a : &b); |
136 | |
137 | tail = tail->next = *first; |
138 | *first = (*first)->next; |
139 | } |
140 | |
141 | /* |
142 | * Attach whatever remains. |
143 | */ |
144 | tail->next = (a != NULL? a : b); |
145 | return head.next; |
146 | } |
147 | |
148 | /* |
149 | * Merge the NULL-terminated lists starting at nodes `a' and `b' into |
150 | * the (uninitialized) list head `list', breaking ties by choosing |
151 | * nodes in `a' first, and setting the `prev' pointers as we go. |
152 | */ |
153 | static void |
154 | list_sort_merge_into(struct list_head *list, |
155 | struct list_head *a, struct list_head *b, |
156 | int (*compare)(void *, struct list_head *, struct list_head *), void *arg) |
157 | { |
158 | struct list_head *prev = list; |
159 | |
160 | /* |
161 | * Merge while elements in both remain. |
162 | */ |
163 | while ((a != NULL) && (b != NULL)) { |
164 | struct list_head **const first = ((*compare)(arg, a, b) <= 0? |
165 | &a : &b); |
166 | |
167 | (*first)->prev = prev; |
168 | prev = prev->next = *first; |
169 | *first = (*first)->next; |
170 | } |
171 | |
172 | /* |
173 | * Attach whichever of a and b remains, and fix up the prev |
174 | * pointers all the way down the rest of the list. |
175 | */ |
176 | struct list_head *tail = (a == NULL? b : a); |
177 | while (tail != NULL) { |
178 | prev->next = tail; |
179 | tail->prev = prev; |
180 | prev = prev->next; |
181 | tail = tail->next; |
182 | } |
183 | |
184 | /* |
185 | * Finally, finish the cycle. |
186 | */ |
187 | prev->next = list; |
188 | list->prev = prev; |
189 | } |
190 | |