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02b12b7a28
Clarify and correct header comment of list_sort(). Signed-off-by: Don Mullis <don.mullis@gmail.com> Cc: Dave Airlie <airlied@redhat.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Dave Chinner <david@fromorbit.com> Cc: Artem Bityutskiy <dedekind@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
218 lines
5.3 KiB
C
218 lines
5.3 KiB
C
#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/list_sort.h>
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#include <linux/slab.h>
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#include <linux/list.h>
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#define MAX_LIST_LENGTH_BITS 20
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/*
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* Returns a list organized in an intermediate format suited
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* to chaining of merge() calls: null-terminated, no reserved or
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* sentinel head node, "prev" links not maintained.
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*/
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static struct list_head *merge(void *priv,
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int (*cmp)(void *priv, struct list_head *a,
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struct list_head *b),
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struct list_head *a, struct list_head *b)
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{
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struct list_head head, *tail = &head;
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while (a && b) {
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/* if equal, take 'a' -- important for sort stability */
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if ((*cmp)(priv, a, b) <= 0) {
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tail->next = a;
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a = a->next;
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} else {
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tail->next = b;
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b = b->next;
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}
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tail = tail->next;
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}
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tail->next = a?:b;
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return head.next;
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}
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/*
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* Combine final list merge with restoration of standard doubly-linked
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* list structure. This approach duplicates code from merge(), but
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* runs faster than the tidier alternatives of either a separate final
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* prev-link restoration pass, or maintaining the prev links
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* throughout.
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*/
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static void merge_and_restore_back_links(void *priv,
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int (*cmp)(void *priv, struct list_head *a,
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struct list_head *b),
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struct list_head *head,
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struct list_head *a, struct list_head *b)
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{
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struct list_head *tail = head;
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while (a && b) {
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/* if equal, take 'a' -- important for sort stability */
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if ((*cmp)(priv, a, b) <= 0) {
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tail->next = a;
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a->prev = tail;
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a = a->next;
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} else {
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tail->next = b;
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b->prev = tail;
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b = b->next;
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}
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tail = tail->next;
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}
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tail->next = a ? : b;
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do {
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/*
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* In worst cases this loop may run many iterations.
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* Continue callbacks to the client even though no
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* element comparison is needed, so the client's cmp()
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* routine can invoke cond_resched() periodically.
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*/
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(*cmp)(priv, tail, tail);
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tail->next->prev = tail;
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tail = tail->next;
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} while (tail->next);
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tail->next = head;
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head->prev = tail;
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}
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/**
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* list_sort - sort a list
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* @priv: private data, opaque to list_sort(), passed to @cmp
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* @head: the list to sort
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* @cmp: the elements comparison function
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*
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* This function implements "merge sort", which has O(nlog(n))
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* complexity.
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*
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* The comparison function @cmp must return a negative value if @a
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* should sort before @b, and a positive value if @a should sort after
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* @b. If @a and @b are equivalent, and their original relative
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* ordering is to be preserved, @cmp must return 0.
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*/
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void list_sort(void *priv, struct list_head *head,
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int (*cmp)(void *priv, struct list_head *a,
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struct list_head *b))
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{
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struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
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-- last slot is a sentinel */
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int lev; /* index into part[] */
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int max_lev = 0;
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struct list_head *list;
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if (list_empty(head))
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return;
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memset(part, 0, sizeof(part));
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head->prev->next = NULL;
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list = head->next;
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while (list) {
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struct list_head *cur = list;
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list = list->next;
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cur->next = NULL;
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for (lev = 0; part[lev]; lev++) {
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cur = merge(priv, cmp, part[lev], cur);
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part[lev] = NULL;
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}
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if (lev > max_lev) {
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if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
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printk_once(KERN_DEBUG "list passed to"
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" list_sort() too long for"
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" efficiency\n");
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lev--;
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}
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max_lev = lev;
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}
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part[lev] = cur;
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}
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for (lev = 0; lev < max_lev; lev++)
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if (part[lev])
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list = merge(priv, cmp, part[lev], list);
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merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
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}
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EXPORT_SYMBOL(list_sort);
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#ifdef DEBUG_LIST_SORT
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struct debug_el {
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struct list_head l_h;
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int value;
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unsigned serial;
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};
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static int cmp(void *priv, struct list_head *a, struct list_head *b)
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{
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return container_of(a, struct debug_el, l_h)->value
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- container_of(b, struct debug_el, l_h)->value;
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}
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/*
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* The pattern of set bits in the list length determines which cases
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* are hit in list_sort().
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*/
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#define LIST_SORT_TEST_LENGTH (512+128+2) /* not including head */
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static int __init list_sort_test(void)
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{
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int i, r = 1, count;
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struct list_head *head = kmalloc(sizeof(*head), GFP_KERNEL);
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struct list_head *cur;
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printk(KERN_WARNING "testing list_sort()\n");
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cur = head;
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for (i = 0; i < LIST_SORT_TEST_LENGTH; i++) {
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struct debug_el *el = kmalloc(sizeof(*el), GFP_KERNEL);
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BUG_ON(!el);
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/* force some equivalencies */
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el->value = (r = (r * 725861) % 6599) % (LIST_SORT_TEST_LENGTH/3);
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el->serial = i;
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el->l_h.prev = cur;
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cur->next = &el->l_h;
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cur = cur->next;
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}
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head->prev = cur;
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list_sort(NULL, head, cmp);
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count = 1;
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for (cur = head->next; cur->next != head; cur = cur->next) {
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struct debug_el *el = container_of(cur, struct debug_el, l_h);
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int cmp_result = cmp(NULL, cur, cur->next);
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if (cur->next->prev != cur) {
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printk(KERN_EMERG "list_sort() returned "
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"a corrupted list!\n");
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return 1;
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} else if (cmp_result > 0) {
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printk(KERN_EMERG "list_sort() failed to sort!\n");
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return 1;
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} else if (cmp_result == 0 &&
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el->serial >= container_of(cur->next,
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struct debug_el, l_h)->serial) {
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printk(KERN_EMERG "list_sort() failed to preserve order"
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" of equivalent elements!\n");
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return 1;
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}
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kfree(cur->prev);
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count++;
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}
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kfree(cur);
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if (count != LIST_SORT_TEST_LENGTH) {
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printk(KERN_EMERG "list_sort() returned list of"
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"different length!\n");
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return 1;
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}
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return 0;
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}
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module_init(list_sort_test);
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#endif
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