| 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 | |