This function sort the list, taken from linux kernel. Signed-off-by: Liu Yuan <namei.unix at gmail.com> --- include/list.h | 3 ++ lib/util.c | 137 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 140 insertions(+) diff --git a/include/list.h b/include/list.h index 44db5a6..4b9d9a7 100644 --- a/include/list.h +++ b/include/list.h @@ -251,4 +251,7 @@ static inline void hlist_add_after(struct hlist_node *n, ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); \ pos = n) +void list_sort(void *priv, struct list_head *head, + int (*cmp)(void *priv, struct list_head *a, + struct list_head *b)); #endif /* __LIST_H__ */ diff --git a/lib/util.c b/lib/util.c index 198cf0a..9781fd8 100644 --- a/lib/util.c +++ b/lib/util.c @@ -598,3 +598,140 @@ close_fd: end: return ret; } + +/* + * Returns a list organized in an intermediate format suited + * to chaining of merge() calls: null-terminated, no reserved or + * sentinel head node, "prev" links not maintained. + */ +static struct list_head *merge(void *priv, + int (*cmp)(void *priv, struct list_head *a, + struct list_head *b), + struct list_head *a, struct list_head *b) +{ + struct list_head head, *tail = &head; + + while (a && b) { + /* if equal, take 'a' -- important for sort stability */ + if ((*cmp)(priv, a, b) <= 0) { + tail->next = a; + a = a->next; + } else { + tail->next = b; + b = b->next; + } + tail = tail->next; + } + tail->next = a?:b; + return head.next; +} + +/* + * Combine final list merge with restoration of standard doubly-linked + * list structure. This approach duplicates code from merge(), but + * runs faster than the tidier alternatives of either a separate final + * prev-link restoration pass, or maintaining the prev links + * throughout. + */ +static void +merge_and_restore_back_links(void *priv, + int (*cmp)(void *priv, struct list_head *a, + struct list_head *b), + struct list_head *head, + struct list_head *a, struct list_head *b) +{ + struct list_head *tail = head; + + while (a && b) { + /* if equal, take 'a' -- important for sort stability */ + if ((*cmp)(priv, a, b) <= 0) { + tail->next = a; + a->prev = tail; + a = a->next; + } else { + tail->next = b; + b->prev = tail; + b = b->next; + } + tail = tail->next; + } + tail->next = a ? : b; + + do { + /* + * In worst cases this loop may run many iterations. + * Continue callbacks to the client even though no + * element comparison is needed, so the client's cmp() + * routine can invoke cond_resched() periodically. + */ + (*cmp)(priv, tail->next, tail->next); + + tail->next->prev = tail; + tail = tail->next; + } while (tail->next); + + tail->next = head; + head->prev = tail; +} + +/* + * list_sort - sort a list + * @priv: private data, opaque to list_sort(), passed to @cmp + * @head: the list to sort + * @cmp: the elements comparison function + * + * This function implements "merge sort", which has O(nlog(n)) + * complexity. + * + * The comparison function @cmp must return a negative value if @a + * should sort before @b, and a positive value if @a should sort after + * @b. If @a and @b are equivalent, and their original relative + * ordering is to be preserved, @cmp must return 0. + */ +void list_sort(void *priv, struct list_head *head, + int (*cmp)(void *priv, struct list_head *a, + struct list_head *b)) +{ + /* sorted partial lists -- last slot is a sentinel */ +#define MAX_LIST_LENGTH_BITS 20 + struct list_head *part[MAX_LIST_LENGTH_BITS+1]; + int lev; /* index into part[] */ + int max_lev = 0; + struct list_head *list; + + if (list_empty(head)) + return; + + memset(part, 0, sizeof(part)); + + head->prev->next = NULL; + list = head->next; + + while (list) { + struct list_head *cur = list; + list = list->next; + cur->next = NULL; + + for (lev = 0; part[lev]; lev++) { + cur = merge(priv, cmp, part[lev], cur); + part[lev] = NULL; + } + if (lev > max_lev) { + if (unlikely(lev >= ARRAY_SIZE(part)-1)) { + /* + * list passed to list_sort() too long for + * efficiency + */ + lev--; + } + max_lev = lev; + } + part[lev] = cur; + } + + for (lev = 0; lev < max_lev; lev++) + if (part[lev]) + list = merge(priv, cmp, part[lev], list); + + merge_and_restore_back_links(priv, cmp, head, part[max_lev], list); +} -- 1.7.9.5 |