A few months ago I adapted a merge sort implementation from
http://www.chiark.greenend.org.uk/~sgtatham/algorithms/listsort.html
to work with Linux's list.h. I figure I should get it into the
archives just in case anyone might want such a thing. So here it is.
void list_sort(struct list_head *head, int (*cmp)(struct list_head *a, struct list_head *b))
{
struct list_head *p, *q, *e, *list, *tail, *oldhead;
int insize, nmerges, psize, qsize, i;
list = head->next;
list_del(head);
insize = 1;
for (;;) {
p = oldhead = list;
list = tail = NULL;
nmerges = 0;
while (p) {
nmerges++;
q = p;
psize = 0;
for (i = 0; i < insize; i++) {
psize++;
q = q->next == oldhead ? NULL : q->next;
if (!q)
break;
}
qsize = insize;
while (psize > 0 || (qsize > 0 && q)) {
if (!psize) {
e = q;
q = q->next;
qsize--;
if (q == oldhead)
q = NULL;
} else if (!qsize || !q) {
e = p;
p = p->next;
psize--;
if (p == oldhead)
p = NULL;
} else if (cmp(p, q) <= 0) {
e = p;
p = p->next;
psize--;
if (p == oldhead)
p = NULL;
} else {
e = q;
q = q->next;
qsize--;
if (q == oldhead)
q = NULL;
}
if (tail)
tail->next = e;
else
list = e;
e->prev = tail;
tail = e;
}
p = q;
}
tail->next = list;
list->prev = tail;
if (nmerges <= 1)
break;
insize *= 2;
}
head->next = list;
head->prev = list->prev;
list->prev->next = head;
list->prev = head;
}