1#include <stdio.h>
2#include <string.h>
3#include "../flist.h"
4#include "../log.h"
5
6#define MAX_LIST_LENGTH_BITS 20
7
8/*
9 * Returns a list organized in an intermediate format suited
10 * to chaining of merge() calls: null-terminated, no reserved or
11 * sentinel head node, "prev" links not maintained.
12 */
13static struct flist_head *merge(void *priv,
14				int (*cmp)(void *priv, struct flist_head *a,
15					struct flist_head *b),
16				struct flist_head *a, struct flist_head *b)
17{
18	struct flist_head head, *tail = &head;
19
20	while (a && b) {
21		/* if equal, take 'a' -- important for sort stability */
22		if ((*cmp)(priv, a, b) <= 0) {
23			tail->next = a;
24			a = a->next;
25		} else {
26			tail->next = b;
27			b = b->next;
28		}
29		tail = tail->next;
30	}
31	tail->next = a?:b;
32	return head.next;
33}
34
35/*
36 * Combine final list merge with restoration of standard doubly-linked
37 * list structure.  This approach duplicates code from merge(), but
38 * runs faster than the tidier alternatives of either a separate final
39 * prev-link restoration pass, or maintaining the prev links
40 * throughout.
41 */
42static void merge_and_restore_back_links(void *priv,
43				int (*cmp)(void *priv, struct flist_head *a,
44					struct flist_head *b),
45				struct flist_head *head,
46				struct flist_head *a, struct flist_head *b)
47{
48	struct flist_head *tail = head;
49
50	while (a && b) {
51		/* if equal, take 'a' -- important for sort stability */
52		if ((*cmp)(priv, a, b) <= 0) {
53			tail->next = a;
54			a->prev = tail;
55			a = a->next;
56		} else {
57			tail->next = b;
58			b->prev = tail;
59			b = b->next;
60		}
61		tail = tail->next;
62	}
63	tail->next = a ? : b;
64
65	do {
66		/*
67		 * In worst cases this loop may run many iterations.
68		 * Continue callbacks to the client even though no
69		 * element comparison is needed, so the client's cmp()
70		 * routine can invoke cond_resched() periodically.
71		 */
72		(*cmp)(priv, tail->next, tail->next);
73
74		tail->next->prev = tail;
75		tail = tail->next;
76	} while (tail->next);
77
78	tail->next = head;
79	head->prev = tail;
80}
81
82/**
83 * list_sort - sort a list
84 * @priv: private data, opaque to list_sort(), passed to @cmp
85 * @head: the list to sort
86 * @cmp: the elements comparison function
87 *
88 * This function implements "merge sort", which has O(nlog(n))
89 * complexity.
90 *
91 * The comparison function @cmp must return a negative value if @a
92 * should sort before @b, and a positive value if @a should sort after
93 * @b. If @a and @b are equivalent, and their original relative
94 * ordering is to be preserved, @cmp must return 0.
95 */
96void flist_sort(void *priv, struct flist_head *head,
97		int (*cmp)(void *priv, struct flist_head *a,
98			struct flist_head *b))
99{
100	struct flist_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
101						-- last slot is a sentinel */
102	int lev;  /* index into part[] */
103	int max_lev = 0;
104	struct flist_head *list;
105
106	if (flist_empty(head))
107		return;
108
109	memset(part, 0, sizeof(part));
110
111	head->prev->next = NULL;
112	list = head->next;
113
114	while (list) {
115		struct flist_head *cur = list;
116		list = list->next;
117		cur->next = NULL;
118
119		for (lev = 0; part[lev]; lev++) {
120			cur = merge(priv, cmp, part[lev], cur);
121			part[lev] = NULL;
122		}
123		if (lev > max_lev) {
124			if (lev >= MAX_LIST_LENGTH_BITS) {
125				log_err("fio: list passed to"
126					" list_sort() too long for"
127					" efficiency\n");
128				lev--;
129			}
130			max_lev = lev;
131		}
132		part[lev] = cur;
133	}
134
135	for (lev = 0; lev < max_lev; lev++)
136		if (part[lev])
137			list = merge(priv, cmp, part[lev], list);
138
139	merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
140}
141