lib/list_sort: test: use generic random32
[linux-3.10.git] / lib / list_sort.c
1 #include <linux/kernel.h>
2 #include <linux/module.h>
3 #include <linux/list_sort.h>
4 #include <linux/slab.h>
5 #include <linux/list.h>
6
7 #define MAX_LIST_LENGTH_BITS 20
8
9 /*
10  * Returns a list organized in an intermediate format suited
11  * to chaining of merge() calls: null-terminated, no reserved or
12  * sentinel head node, "prev" links not maintained.
13  */
14 static struct list_head *merge(void *priv,
15                                 int (*cmp)(void *priv, struct list_head *a,
16                                         struct list_head *b),
17                                 struct list_head *a, struct list_head *b)
18 {
19         struct list_head head, *tail = &head;
20
21         while (a && b) {
22                 /* if equal, take 'a' -- important for sort stability */
23                 if ((*cmp)(priv, a, b) <= 0) {
24                         tail->next = a;
25                         a = a->next;
26                 } else {
27                         tail->next = b;
28                         b = b->next;
29                 }
30                 tail = tail->next;
31         }
32         tail->next = a?:b;
33         return head.next;
34 }
35
36 /*
37  * Combine final list merge with restoration of standard doubly-linked
38  * list structure.  This approach duplicates code from merge(), but
39  * runs faster than the tidier alternatives of either a separate final
40  * prev-link restoration pass, or maintaining the prev links
41  * throughout.
42  */
43 static void merge_and_restore_back_links(void *priv,
44                                 int (*cmp)(void *priv, struct list_head *a,
45                                         struct list_head *b),
46                                 struct list_head *head,
47                                 struct list_head *a, struct list_head *b)
48 {
49         struct list_head *tail = head;
50
51         while (a && b) {
52                 /* if equal, take 'a' -- important for sort stability */
53                 if ((*cmp)(priv, a, b) <= 0) {
54                         tail->next = a;
55                         a->prev = tail;
56                         a = a->next;
57                 } else {
58                         tail->next = b;
59                         b->prev = tail;
60                         b = b->next;
61                 }
62                 tail = tail->next;
63         }
64         tail->next = a ? : b;
65
66         do {
67                 /*
68                  * In worst cases this loop may run many iterations.
69                  * Continue callbacks to the client even though no
70                  * element comparison is needed, so the client's cmp()
71                  * routine can invoke cond_resched() periodically.
72                  */
73                 (*cmp)(priv, tail->next, tail->next);
74
75                 tail->next->prev = tail;
76                 tail = tail->next;
77         } while (tail->next);
78
79         tail->next = head;
80         head->prev = tail;
81 }
82
83 /**
84  * list_sort - sort a list
85  * @priv: private data, opaque to list_sort(), passed to @cmp
86  * @head: the list to sort
87  * @cmp: the elements comparison function
88  *
89  * This function implements "merge sort", which has O(nlog(n))
90  * complexity.
91  *
92  * The comparison function @cmp must return a negative value if @a
93  * should sort before @b, and a positive value if @a should sort after
94  * @b. If @a and @b are equivalent, and their original relative
95  * ordering is to be preserved, @cmp must return 0.
96  */
97 void list_sort(void *priv, struct list_head *head,
98                 int (*cmp)(void *priv, struct list_head *a,
99                         struct list_head *b))
100 {
101         struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
102                                                 -- last slot is a sentinel */
103         int lev;  /* index into part[] */
104         int max_lev = 0;
105         struct list_head *list;
106
107         if (list_empty(head))
108                 return;
109
110         memset(part, 0, sizeof(part));
111
112         head->prev->next = NULL;
113         list = head->next;
114
115         while (list) {
116                 struct list_head *cur = list;
117                 list = list->next;
118                 cur->next = NULL;
119
120                 for (lev = 0; part[lev]; lev++) {
121                         cur = merge(priv, cmp, part[lev], cur);
122                         part[lev] = NULL;
123                 }
124                 if (lev > max_lev) {
125                         if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
126                                 printk_once(KERN_DEBUG "list passed to"
127                                         " list_sort() too long for"
128                                         " efficiency\n");
129                                 lev--;
130                         }
131                         max_lev = lev;
132                 }
133                 part[lev] = cur;
134         }
135
136         for (lev = 0; lev < max_lev; lev++)
137                 if (part[lev])
138                         list = merge(priv, cmp, part[lev], list);
139
140         merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
141 }
142 EXPORT_SYMBOL(list_sort);
143
144 #ifdef CONFIG_TEST_LIST_SORT
145
146 #include <linux/random.h>
147
148 struct debug_el {
149         struct list_head list;
150         int value;
151         unsigned serial;
152 };
153
154 static int cmp(void *priv, struct list_head *a, struct list_head *b)
155 {
156         return container_of(a, struct debug_el, list)->value
157              - container_of(b, struct debug_el, list)->value;
158 }
159
160 /*
161  * The pattern of set bits in the list length determines which cases
162  * are hit in list_sort().
163  */
164 #define TEST_LIST_LEN (512+128+2) /* not including head */
165
166 static int __init list_sort_test(void)
167 {
168         int i, count;
169         struct list_head *head = kmalloc(sizeof(*head), GFP_KERNEL);
170         struct list_head *cur;
171
172         printk(KERN_DEBUG "testing list_sort()\n");
173
174         cur = head;
175         for (i = 0; i < TEST_LIST_LEN; i++) {
176                 struct debug_el *el = kmalloc(sizeof(*el), GFP_KERNEL);
177                 BUG_ON(!el);
178                  /* force some equivalencies */
179                 el->value = random32() % (TEST_LIST_LEN/3);
180                 el->serial = i;
181
182                 el->list.prev = cur;
183                 cur->next = &el->list;
184                 cur = cur->next;
185         }
186         head->prev = cur;
187
188         list_sort(NULL, head, cmp);
189
190         count = 1;
191         for (cur = head->next; cur->next != head; cur = cur->next) {
192                 struct debug_el *el = container_of(cur, struct debug_el, list);
193                 int cmp_result = cmp(NULL, cur, cur->next);
194                 if (cur->next->prev != cur) {
195                         printk(KERN_ERR "list_sort() returned "
196                                         "a corrupted list!\n");
197                         return 1;
198                 } else if (cmp_result > 0) {
199                         printk(KERN_ERR "list_sort() failed to sort!\n");
200                         return 1;
201                 } else if (cmp_result == 0 &&
202                                 el->serial >= container_of(cur->next,
203                                         struct debug_el, list)->serial) {
204                         printk(KERN_ERR "list_sort() failed to preserve order "
205                                         "of equivalent elements!\n");
206                         return 1;
207                 }
208                 kfree(cur->prev);
209                 count++;
210         }
211         kfree(cur);
212         if (count != TEST_LIST_LEN) {
213                 printk(KERN_ERR "list_sort() returned list of "
214                                 "different length!\n");
215                 return 1;
216         }
217         return 0;
218 }
219 module_init(list_sort_test);
220 #endif /* CONFIG_TEST_LIST_SORT */