From: Davidlohr Bueso <dave@xxxxxxx> We need a list sorting function, just to mention one example user that could benefit is the lib/tt code to sort columns. This patch adds list_sort() which uses the Merge Sort algorithm, behaving nicely in O(nlog(n)), heavily based on the kernel's implementation[1]. The private data (void *priv) passed to the comparison function as been removed to adopt a qsort(3)-like syntax, and IMHO we don't really need it anyways. [1]: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob;f=lib/list_sort.c;h=d7325c6b103f0be078ff3672c35c468ed35738f1;hb=HEAD Signed-off-by: Davidlohr Bueso <dave@xxxxxxx> --- include/c.h | 8 +++ include/list.h | 132 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 140 insertions(+), 0 deletions(-) diff --git a/include/c.h b/include/c.h index c4a95aa..290303e 100644 --- a/include/c.h +++ b/include/c.h @@ -104,6 +104,14 @@ _max1 > _max2 ? _max1 : _max2; }) #endif +#ifndef offsetof +#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER) +#endif + +#define container_of(ptr, type, member) ({ \ + const typeof( ((type *)0)->member ) *__mptr = (ptr); \ + (type *)( (char *)__mptr - offsetof(type,member) );}) + #ifndef HAVE_PROGRAM_INVOCATION_SHORT_NAME # ifdef HAVE___PROGNAME extern char *__progname; diff --git a/include/list.h b/include/list.h index f7b17fe..afcfeeb 100644 --- a/include/list.h +++ b/include/list.h @@ -3,6 +3,7 @@ * Copyright (C) 1999-2008 by Theodore Ts'o * * (based on list.h from e2fsprogs) + * Merge sort based on kernel's implementation. */ #ifndef UTIL_LINUX_LIST_H @@ -192,6 +193,137 @@ _INLINE_ void list_splice(struct list_head *list, struct list_head *head) for (pos = (head)->next, pnext = pos->next; pos != (head); \ pos = pnext, pnext = pos->next) +#define MAX_LIST_LENGTH_BITS 20 + +/* + * 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(int (*cmp)(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)(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(int (*cmp)(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)(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)(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 + * @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. + */ +_INLINE_ void list_sort(struct list_head *head, + int (*cmp)(struct list_head *a, + struct list_head *b)) +{ + struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists + -- last slot is a sentinel */ + 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(cmp, part[lev], cur); + part[lev] = NULL; + } + if (lev > max_lev) { + /* list passed to list_sort() too long for efficiency */ + if (lev >= ARRAY_SIZE(part)-1) + lev--; + max_lev = lev; + } + part[lev] = cur; + } + + for (lev = 0; lev < max_lev; lev++) + if (part[lev]) + list = merge(cmp, part[lev], list); + + merge_and_restore_back_links(cmp, head, part[max_lev], list); +} + #undef _INLINE_ #endif /* UTIL_LINUX_LIST_H */ -- 1.7.4.1 -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
