+#include <stdio.h>
+#include <string.h>
+#include "../flist.h"
+#include "../log.h"
+
+#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 flist_head *merge(void *priv,
+ int (*cmp)(void *priv, struct flist_head *a,
+ struct flist_head *b),
+ struct flist_head *a, struct flist_head *b)
+{
+ struct flist_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 flist_head *a,
+ struct flist_head *b),
+ struct flist_head *head,
+ struct flist_head *a, struct flist_head *b)
+{
+ struct flist_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 flist_sort(void *priv, struct flist_head *head,
+ int (*cmp)(void *priv, struct flist_head *a,
+ struct flist_head *b))
+{
+ struct flist_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 flist_head *list;
+
+ if (flist_empty(head))
+ return;
+
+ memset(part, 0, sizeof(part));
+
+ head->prev->next = NULL;
+ list = head->next;
+
+ while (list) {
+ struct flist_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 (lev >= MAX_LIST_LENGTH_BITS) {
+ log_err("fio: list passed to"
+ " list_sort() too long for"
+ " efficiency\n");
+ 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);
+}
projects / fio.git / commitdiff