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