xref: /openbmc/u-boot/lib/list_sort.c (revision 2a046ff5)
1 #ifndef __UBOOT__
2 #include <linux/kernel.h>
3 #include <linux/module.h>
4 #include <linux/slab.h>
5 #else
6 #include <linux/compat.h>
7 #include <common.h>
8 #include <malloc.h>
9 #endif
10 #include <linux/list.h>
11 #include <linux/list_sort.h>
12 
13 #define MAX_LIST_LENGTH_BITS 20
14 
15 /*
16  * Returns a list organized in an intermediate format suited
17  * to chaining of merge() calls: null-terminated, no reserved or
18  * sentinel head node, "prev" links not maintained.
19  */
20 static struct list_head *merge(void *priv,
21 				int (*cmp)(void *priv, struct list_head *a,
22 					struct list_head *b),
23 				struct list_head *a, struct list_head *b)
24 {
25 	struct list_head head, *tail = &head;
26 
27 	while (a && b) {
28 		/* if equal, take 'a' -- important for sort stability */
29 		if ((*cmp)(priv, a, b) <= 0) {
30 			tail->next = a;
31 			a = a->next;
32 		} else {
33 			tail->next = b;
34 			b = b->next;
35 		}
36 		tail = tail->next;
37 	}
38 	tail->next = a?:b;
39 	return head.next;
40 }
41 
42 /*
43  * Combine final list merge with restoration of standard doubly-linked
44  * list structure.  This approach duplicates code from merge(), but
45  * runs faster than the tidier alternatives of either a separate final
46  * prev-link restoration pass, or maintaining the prev links
47  * throughout.
48  */
49 static void merge_and_restore_back_links(void *priv,
50 				int (*cmp)(void *priv, struct list_head *a,
51 					struct list_head *b),
52 				struct list_head *head,
53 				struct list_head *a, struct list_head *b)
54 {
55 	struct list_head *tail = head;
56 
57 	while (a && b) {
58 		/* if equal, take 'a' -- important for sort stability */
59 		if ((*cmp)(priv, a, b) <= 0) {
60 			tail->next = a;
61 			a->prev = tail;
62 			a = a->next;
63 		} else {
64 			tail->next = b;
65 			b->prev = tail;
66 			b = b->next;
67 		}
68 		tail = tail->next;
69 	}
70 	tail->next = a ? : b;
71 
72 	do {
73 		/*
74 		 * In worst cases this loop may run many iterations.
75 		 * Continue callbacks to the client even though no
76 		 * element comparison is needed, so the client's cmp()
77 		 * routine can invoke cond_resched() periodically.
78 		 */
79 		(*cmp)(priv, tail->next, tail->next);
80 
81 		tail->next->prev = tail;
82 		tail = tail->next;
83 	} while (tail->next);
84 
85 	tail->next = head;
86 	head->prev = tail;
87 }
88 
89 /**
90  * list_sort - sort a list
91  * @priv: private data, opaque to list_sort(), passed to @cmp
92  * @head: the list to sort
93  * @cmp: the elements comparison function
94  *
95  * This function implements "merge sort", which has O(nlog(n))
96  * complexity.
97  *
98  * The comparison function @cmp must return a negative value if @a
99  * should sort before @b, and a positive value if @a should sort after
100  * @b. If @a and @b are equivalent, and their original relative
101  * ordering is to be preserved, @cmp must return 0.
102  */
103 void list_sort(void *priv, struct list_head *head,
104 		int (*cmp)(void *priv, struct list_head *a,
105 			struct list_head *b))
106 {
107 	struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
108 						-- last slot is a sentinel */
109 	int lev;  /* index into part[] */
110 	int max_lev = 0;
111 	struct list_head *list;
112 
113 	if (list_empty(head))
114 		return;
115 
116 	memset(part, 0, sizeof(part));
117 
118 	head->prev->next = NULL;
119 	list = head->next;
120 
121 	while (list) {
122 		struct list_head *cur = list;
123 		list = list->next;
124 		cur->next = NULL;
125 
126 		for (lev = 0; part[lev]; lev++) {
127 			cur = merge(priv, cmp, part[lev], cur);
128 			part[lev] = NULL;
129 		}
130 		if (lev > max_lev) {
131 			if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
132 				printk_once(KERN_DEBUG "list passed to"
133 					" list_sort() too long for"
134 					" efficiency\n");
135 				lev--;
136 			}
137 			max_lev = lev;
138 		}
139 		part[lev] = cur;
140 	}
141 
142 	for (lev = 0; lev < max_lev; lev++)
143 		if (part[lev])
144 			list = merge(priv, cmp, part[lev], list);
145 
146 	merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
147 }
148 EXPORT_SYMBOL(list_sort);
149 
150 #ifdef CONFIG_TEST_LIST_SORT
151 
152 #include <linux/random.h>
153 
154 /*
155  * The pattern of set bits in the list length determines which cases
156  * are hit in list_sort().
157  */
158 #define TEST_LIST_LEN (512+128+2) /* not including head */
159 
160 #define TEST_POISON1 0xDEADBEEF
161 #define TEST_POISON2 0xA324354C
162 
163 struct debug_el {
164 	unsigned int poison1;
165 	struct list_head list;
166 	unsigned int poison2;
167 	int value;
168 	unsigned serial;
169 };
170 
171 /* Array, containing pointers to all elements in the test list */
172 static struct debug_el **elts __initdata;
173 
174 static int __init check(struct debug_el *ela, struct debug_el *elb)
175 {
176 	if (ela->serial >= TEST_LIST_LEN) {
177 		printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
178 				ela->serial);
179 		return -EINVAL;
180 	}
181 	if (elb->serial >= TEST_LIST_LEN) {
182 		printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
183 				elb->serial);
184 		return -EINVAL;
185 	}
186 	if (elts[ela->serial] != ela || elts[elb->serial] != elb) {
187 		printk(KERN_ERR "list_sort_test: error: phantom element\n");
188 		return -EINVAL;
189 	}
190 	if (ela->poison1 != TEST_POISON1 || ela->poison2 != TEST_POISON2) {
191 		printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
192 				ela->poison1, ela->poison2);
193 		return -EINVAL;
194 	}
195 	if (elb->poison1 != TEST_POISON1 || elb->poison2 != TEST_POISON2) {
196 		printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
197 				elb->poison1, elb->poison2);
198 		return -EINVAL;
199 	}
200 	return 0;
201 }
202 
203 static int __init cmp(void *priv, struct list_head *a, struct list_head *b)
204 {
205 	struct debug_el *ela, *elb;
206 
207 	ela = container_of(a, struct debug_el, list);
208 	elb = container_of(b, struct debug_el, list);
209 
210 	check(ela, elb);
211 	return ela->value - elb->value;
212 }
213 
214 static int __init list_sort_test(void)
215 {
216 	int i, count = 1, err = -EINVAL;
217 	struct debug_el *el;
218 	struct list_head *cur, *tmp;
219 	LIST_HEAD(head);
220 
221 	printk(KERN_DEBUG "list_sort_test: start testing list_sort()\n");
222 
223 	elts = kmalloc(sizeof(void *) * TEST_LIST_LEN, GFP_KERNEL);
224 	if (!elts) {
225 		printk(KERN_ERR "list_sort_test: error: cannot allocate "
226 				"memory\n");
227 		goto exit;
228 	}
229 
230 	for (i = 0; i < TEST_LIST_LEN; i++) {
231 		el = kmalloc(sizeof(*el), GFP_KERNEL);
232 		if (!el) {
233 			printk(KERN_ERR "list_sort_test: error: cannot "
234 					"allocate memory\n");
235 			goto exit;
236 		}
237 		 /* force some equivalencies */
238 		el->value = prandom_u32() % (TEST_LIST_LEN / 3);
239 		el->serial = i;
240 		el->poison1 = TEST_POISON1;
241 		el->poison2 = TEST_POISON2;
242 		elts[i] = el;
243 		list_add_tail(&el->list, &head);
244 	}
245 
246 	list_sort(NULL, &head, cmp);
247 
248 	for (cur = head.next; cur->next != &head; cur = cur->next) {
249 		struct debug_el *el1;
250 		int cmp_result;
251 
252 		if (cur->next->prev != cur) {
253 			printk(KERN_ERR "list_sort_test: error: list is "
254 					"corrupted\n");
255 			goto exit;
256 		}
257 
258 		cmp_result = cmp(NULL, cur, cur->next);
259 		if (cmp_result > 0) {
260 			printk(KERN_ERR "list_sort_test: error: list is not "
261 					"sorted\n");
262 			goto exit;
263 		}
264 
265 		el = container_of(cur, struct debug_el, list);
266 		el1 = container_of(cur->next, struct debug_el, list);
267 		if (cmp_result == 0 && el->serial >= el1->serial) {
268 			printk(KERN_ERR "list_sort_test: error: order of "
269 					"equivalent elements not preserved\n");
270 			goto exit;
271 		}
272 
273 		if (check(el, el1)) {
274 			printk(KERN_ERR "list_sort_test: error: element check "
275 					"failed\n");
276 			goto exit;
277 		}
278 		count++;
279 	}
280 
281 	if (count != TEST_LIST_LEN) {
282 		printk(KERN_ERR "list_sort_test: error: bad list length %d",
283 				count);
284 		goto exit;
285 	}
286 
287 	err = 0;
288 exit:
289 	kfree(elts);
290 	list_for_each_safe(cur, tmp, &head) {
291 		list_del(cur);
292 		kfree(container_of(cur, struct debug_el, list));
293 	}
294 	return err;
295 }
296 module_init(list_sort_test);
297 #endif /* CONFIG_TEST_LIST_SORT */
298